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Sample records for additional virulence mechanism

  1. Mechanisms of disease: Helicobacter pylori virulence factors.

    Science.gov (United States)

    Yamaoka, Yoshio

    2010-11-01

    Helicobacter pylori plays an essential role in the development of various gastroduodenal diseases; however, only a small proportion of people infected with H. pylori develop these diseases. Some populations that have a high prevalence of H. pylori infection also have a high incidence of gastric cancer (for example, in East Asia), whereas others do not (for example, in Africa and South Asia). Even within East Asia, the incidence of gastric cancer varies (decreasing in the south). H. pylori is a highly heterogeneous bacterium and its virulence varies geographically. Geographic differences in the incidence of gastric cancer can be explained, at least in part, by the presence of different types of H. pylori virulence factor, especially CagA, VacA and OipA. However, it is still unclear why the pathogenicity of H. pylori increased as it migrated from Africa to East Asia during the course of evolution. H. pylori infection is also thought to be involved in the development of duodenal ulcer, which is at the opposite end of the disease spectrum to gastric cancer. This discrepancy can be explained in part by the presence of H. pylori virulence factor DupA. Despite advances in our understanding of the development of H. pylori-related diseases, further work is required to clarify the roles of H. pylori virulence factors.

  2. Investigating the ?Trojan Horse? Mechanism of Yersinia pestis Virulence

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    McCutchen-Maloney, S L; Fitch, J P

    2005-02-08

    Yersinia pestis, the etiological agent of plague, is a Gram-negative, highly communicable, enteric bacterium that has been responsible for three historic plague pandemics. Currently, several thousand cases of plague are reported worldwide annually, and Y. pestis remains a considerable threat from a biodefense perspective. Y. pestis infection can manifest in three forms: bubonic, septicemic, and pneumonic plague. Of these three forms, pneumonic plague has the highest fatality rate ({approx}100% if left untreated), the shortest intervention time ({approx}24 hours), and is highly contagious. Currently, there are no rapid, widely available vaccines for plague and though plague may be treated with antibiotics, the emergence of both naturally occurring and potentially engineered antibiotic resistant strains makes the search for more effective therapies and vaccines for plague of pressing concern. The virulence mechanism of this deadly bacterium involves induction of a Type III secretion system, a syringe-like apparatus that facilitates the injection of virulence factors, termed Yersinia outer membrane proteins (Yops), into the host cell. These virulence factors inhibit phagocytosis and cytokine secretion, and trigger apoptosis of the host cell. Y. pestis virulence factors and the Type III secretion system are induced thermally, when the bacterium enters the mammalian host from the flea vector, and through host cell contact (or conditions of low Ca{sup 2+} in vitro). Apart from the temperature increase from 26 C to 37 C and host cell contact (or low Ca{sup 2+} conditions), other molecular mechanisms that influence virulence induction in Y. pestis are largely uncharacterized. This project focused on characterizing two novel mechanisms that regulate virulence factor induction in Y. pestis, immunoglobulin G (IgG) binding and quorum sensing, using a real-time reporter system to monitor induction of virulence. Incorporating a better understanding of the mechanisms of virulence

  3. Network analysis of S. aureus response to ramoplanin reveals modules for virulence factors and resistance mechanisms and characteristic novel genes.

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    Subramanian, Devika; Natarajan, Jeyakumar

    2015-12-10

    Staphylococcus aureus is a major human pathogen and ramoplanin is an antimicrobial attributed for effective treatment. The goal of this study was to examine the transcriptomic profiles of ramoplanin sensitive and resistant S. aureus to identify putative modules responsible for virulence and resistance-mechanisms and its characteristic novel genes. The dysregulated genes were used to reconstruct protein functional association networks for virulence-factors and resistance-mechanisms individually. Strong link between metabolic-pathways and development of virulence/resistance is suggested. We identified 15 putative modules of virulence factors. Six hypothetical genes were annotated with novel virulence activity among which SACOL0281 was discovered to be an essential virulence factor EsaD. The roles of MazEF toxin-antitoxin system, SACOL0202/SACOL0201 two-component system and that of amino-sugar and nucleotide-sugar metabolism in virulence are also suggested. In addition, 14 putative modules of resistance mechanisms including modules of ribosomal protein-coding genes and metabolic pathways such as biotin-synthesis, TCA-cycle, riboflavin-biosynthesis, peptidoglycan-biosynthesis etc. are also indicated. Copyright © 2015 Elsevier B.V. All rights reserved.

  4. Mechanics of additively manufactured biomaterials.

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    Zadpoor, Amir A

    2017-06-01

    Additive manufacturing (3D printing) has found many applications in healthcare including fabrication of biomaterials as well as bioprinting of tissues and organs. Additively manufactured (AM) biomaterials may possess arbitrarily complex micro-architectures that give rise to novel mechanical, physical, and biological properties. The mechanical behavior of such porous biomaterials including their quasi-static mechanical properties and fatigue resistance is not yet well understood. It is particularly important to understand the relationship between the designed micro-architecture (topology) and the resulting mechanical properties. The current special issue is dedicated to understanding the mechanical behavior of AM biomaterials. Although various types of AM biomaterials are represented in the special issue, the primary focus is on AM porous metallic biomaterials. As a prelude to this special issue, this editorial reviews some of the latest findings in the mechanical behavior of AM porous metallic biomaterials so as to describe the current state-of-the-art and set the stage for the other studies appearing in the issue. Some areas that are important for future research are also briefly mentioned. Copyright © 2017 Elsevier Ltd. All rights reserved.

  5. Caenorhabditis elegans reveals novel Pseudomonas aeruginosa virulence mechanism

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    Utari, Putri Dwi; Quax, Wim J.

    The susceptibility of Caenorhabditis elegans to different virulent phenotypes of Pseudomonas aeruginosa makes the worms an excellent model for studying host-pathogen interactions. Including the recently described liquid killing, five different killing assays are now available offering superb

  6. Talaromyces marneffei Genomic, Transcriptomic, Proteomic and Metabolomic Studies Reveal Mechanisms for Environmental Adaptations and Virulence

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    Susanna K. P. Lau

    2017-06-01

    Full Text Available Talaromyces marneffei is a thermally dimorphic fungus causing systemic infections in patients positive for HIV or other immunocompromised statuses. Analysis of its ~28.9 Mb draft genome and additional transcriptomic, proteomic and metabolomic studies revealed mechanisms for environmental adaptations and virulence. Meiotic genes and genes for pheromone receptors, enzymes which process pheromones, and proteins involved in pheromone response pathway are present, indicating its possibility as a heterothallic fungus. Among the 14 Mp1p homologs, only Mp1p is a virulence factor binding a variety of host proteins, fatty acids and lipids. There are 23 polyketide synthase genes, one for melanin and two for mitorubrinic acid/mitorubrinol biosynthesis, which are virulence factors. Another polyketide synthase is for biogenesis of the diffusible red pigment, which consists of amino acid conjugates of monascorubin and rubropunctatin. Novel microRNA-like RNAs (milRNAs and processing proteins are present. The dicer protein, dcl-2, is required for biogenesis of two milRNAs, PM-milR-M1 and PM-milR-M2, which are more highly expressed in hyphal cells. Comparative transcriptomics showed that tandem repeat-containing genes were overexpressed in yeast phase, generating protein polymorphism among cells, evading host’s immunity. Comparative proteomics between yeast and hyphal cells revealed that glyceraldehyde-3-phosphate dehydrogenase, up-regulated in hyphal cells, is an adhesion factor for conidial attachment.

  7. effects of sulphur addition on addition on and mechanical properties

    African Journals Online (AJOL)

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    234-8034714355. 8034714355. 1. EFFECTS OF SULPHUR ADDITION ON. ADDITION ON. 2. AND MECHANICAL PROPERTIES O. 3. 4. C. W. Onyia. 5. 1DEPT. OF METALLURGICAL AND MATERIALS. 6. 2, 4DEPT. OF METALLURGICAL ...

  8. Mechanisms relevant to the enhanced virulence of a dihydroxynaphthalene-melanin metabolically engineered entomopathogen.

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    Min-Nan Tseng

    Full Text Available The entomopathogenic fungus Metarhizium anisopliae MA05-169 is a transformant strain that has been metabolically engineered to express dihydroxynaphthalene-melanin biosynthesis genes. In contrast to the wild type strain, the transformant displays a greater resistance to environmental stress and a higher virulence toward target insect host. However, the underlying mechanisms for these characteristics remain unclear; hence experiments were initiated to explore the possible mechanism(s through physiological and molecular approaches. Although both transformant and wild type strains could infect and share the same insect host range, the former germinated faster and produced more appressoria than the latter, both in vivo and in vitro. The transformant showed a significantly shorter median lethal time (LT50 when infecting the diamondback moth (Plutella xylostella and the striped flea beetle (Phyllotreta striolata, than the wild type. Additionally, the transformant was more tolerant to reactive oxygen species (ROS, produced 40-fold more orthosporin and notably overexpressed the transcripts of the pathogenicity-relevant hydrolytic enzymes (chitinase, protease, and phospholipase genes in vivo. In contrast, appressorium turgor pressure and destruxin A content were slightly decreased compared to the wild type. The transformant's high anti-stress tolerance, its high virulence against five important insect pests (cowpea aphid Aphis craccivora, diamondback moth Pl. xylostella, striped flea beetle Ph. striolata, and silverleaf whitefly Bemisia argentifolii and its capacity to colonize the root system are key properties for its potential bio-control field application.

  9. Dynamic protein S-palmitoylation mediates parasite life cycle progression and diverse mechanisms of virulence.

    Science.gov (United States)

    Brown, Robert W B; Sharma, Aabha I; Engman, David M

    2017-04-01

    Eukaryotic parasites possess complex life cycles and utilize an assortment of molecular mechanisms to overcome physical barriers, suppress and/or bypass the host immune response, including invading host cells where they can replicate in a protected intracellular niche. Protein S-palmitoylation is a dynamic post-translational modification in which the fatty acid palmitate is covalently linked to cysteine residues on proteins by the enzyme palmitoyl acyltransferase (PAT) and can be removed by lysosomal palmitoyl-protein thioesterase (PPT) or cytosolic acyl-protein thioesterase (APT). In addition to anchoring proteins to intracellular membranes, functions of dynamic palmitoylation include - targeting proteins to specific intracellular compartments via trafficking pathways, regulating the cycling of proteins between membranes, modulating protein function and regulating protein stability. Recent studies in the eukaryotic parasites - Plasmodium falciparum, Toxoplasma gondii, Trypanosoma brucei, Cryptococcus neoformans and Giardia lamblia - have identified large families of PATs and palmitoylated proteins. Many palmitoylated proteins are important for diverse aspects of pathogenesis, including differentiation into infective life cycle stages, biogenesis and tethering of secretory organelles, assembling the machinery powering motility and targeting virulence factors to the plasma membrane. This review aims to summarize our current knowledge of palmitoylation in eukaryotic parasites, highlighting five exemplary mechanisms of parasite virulence dependent on palmitoylation.

  10. The Mechanisms of Virulence Regulation by Small Noncoding RNAs in Low GC Gram-Positive Pathogens

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    Stephanie Pitman

    2015-12-01

    Full Text Available The discovery of small noncoding regulatory RNAs (sRNAs in bacteria has grown tremendously recently, giving new insights into gene regulation. The implementation of computational analysis and RNA sequencing has provided new tools to discover and analyze potential sRNAs. Small regulatory RNAs that act by base-pairing to target mRNAs have been found to be ubiquitous and are the most abundant class of post-transcriptional regulators in bacteria. The majority of sRNA studies has been limited to E. coli and other gram-negative bacteria. However, examples of sRNAs in gram-positive bacteria are still plentiful although the detailed gene regulation mechanisms behind them are not as well understood. Strict virulence control is critical for a pathogen’s survival and many sRNAs have been found to be involved in that process. This review outlines the targets and currently known mechanisms of trans-acting sRNAs involved in virulence regulation in various gram-positive pathogens. In addition, their shared characteristics such as CU interaction motifs, the role of Hfq, and involvement in two-component regulators, riboswitches, quorum sensing, or toxin/antitoxin systems are described.

  11. Additive Effects of Quorum Sensing Anti-Activators on Pseudomonas aeruginosa Virulence Traits and Transcriptome

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    Kyle L. Asfahl

    2018-01-01

    Full Text Available In the opportunistic pathogen Pseudomonas aeruginosa, quorum sensing (QS via acyl-homoserine lactone (AHL signals coordinates virulence gene expression. AHL signals must reach a critical threshold before enough is bound by cognate regulators LasR and RhlR to drive transcription of target genes. In addition, three anti-activator proteins, QteE, QscR, and QslA, sequester QS regulators to increase the threshold for induction and delay expression of QS target genes. It remains unclear how multiple anti-activators work together to achieve the quorum threshold. Here, we employed a combination of mutational, kinetic, phenotypic, and transcriptomic analysis to examine regulatory effects and interactions of the three distinct anti-activators. We observed combinatorial, additive effects on QS gene expression. As measured by reporter gene fusion, individual deletion of each anti-activator gene increased lasB expression and QS-controlled virulence factor production. Deletion of qslA in combination with the deletion of any other anti-activator gene resulted in the greatest increase and earliest activation of lasB gene expression. Western analysis revealed that relative increases in soluble LasR in anti-activator mutants correlate with increased lasB expression and QS-controlled virulence factor production. RNA-seq of the previously uncharacterized QslA and QteE regulons revealed overlapping, yet distinct groups of differentially expressed genes. Simultaneous inactivation of qteE and qslA had the largest effect on gene expression with 999 genes induced and 798 genes repressed in the double mutant vs. wild-type. We found that LasR and RhlR-activated QS genes formed a subset of the genes induced in the qteE, qslA, and double mutant. The activation of almost all of these QS genes was advanced from stationary phase to log phase in the qteE qslA double mutant. Taken together, our results identify additive effects of anti-activation on QS gene expression, likely

  12. effects of sulphur addition on addition on and mechanical properties

    African Journals Online (AJOL)

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    on the microstructure and mechanical properties of sand cast been investigated ... owed that the addition of sulphur to Al-12wt%Si alloy. 12wt%Si alloy .... 28 materials. 29. Element. Aluminum. Silicon. Al. Si. Ca. Fe. Cu. Zn. Mn. Mg. Cr. B. 99.71.

  13. Insights on the virulence mechanisms of European Edwardsiella tarda strains isolated from turbot

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    Nuria Castro Iglesias

    2014-06-01

    Full Text Available Edwardsiella tarda is a common inhabitant of diverse ecological niches as well as a common guest of a high variety of animals including fish, reptiles, amphibians, chickens and other warm-blooded animals as humans. With regard to the aquatic environments, E. tarda has been described as the causative agent of infections in more than 20 fish species including some important fish species in aquaculture industry. Several potential pathogenic properties have been suggested to contribute to the infection process of E. tarda, which include adhesins, Type III and Type VI secretion system, and ability to survive and replicate in phagocytes, among others. Identification of these virulence-related genes is essential for understanding the pathogenesis of the species. Since E. tarda causes great losses in the Chinese aquaculture, great efforts have been recently devoted to study the pathogenicity mechanism of E. tarda in Asian countries. However, all these studies were conducted employing Asian isolates. Being E. tarda a pathogen of great economical concern in European turbot aquaculture and since the high intraspecific variability of E. tarda is well known, it becomes evident that additional pathogenicity studies conducted with non-Asiatic strains are needed. Enzymes such as chondroitinase are believed to play an important role in the pathogenicity of bacteria that cause infections (Tam et al., 1982. Chondroitinase activity was proposed to be one virulence contributor in Edwardsiella spp. and mediates the cartilage degradation in the chronic “hole-in-the-head” lesion. In Gram-negative bacteria, the most intensively studied quorum sensing systems rely on the use of N-acylhomoserine lactones (AHLs, which production is common among marine and fish pathogenic Proteobacteria, controlling the expression of key virulence factors. In the case of E. tarda, strain NUF251 from diseased flounder had the ability to produce two kinds of AHL molecules. It is likely

  14. New insights into virulence mechanisms of rice pathogen Acidovorax avenae subsp. avenae strain RS-1 following exposure to ß-lactam antibiotics.

    Science.gov (United States)

    Li, Bin; Ge, Mengyu; Zhang, Yang; Wang, Li; Ibrahim, Muhammad; Wang, Yanli; Sun, Guochang; Chen, Gongyou

    2016-02-26

    Recent research has shown that pathogen virulence can be altered by exposure to antibiotics, even when the growth rate is unaffected. Investigating this phenomenon provides new insights into understanding the virulence mechanisms of bacterial pathogens. This study investigates the phenotypic and transcriptomic responses of the rice pathogenic bacterium Acidovorax avenae subsp. avenae (Aaa) strain RS-1 to ß-lactam antibiotics especially Ampicillin (Amp). Our results indicate that exposure to Amp does not influence bacterial growth and biofilm formation, but alters the virulence, colonization capacity, composition of extracellular polymeric substances and secretion of Type VI secretion system (T6SS) effector Hcp. This attenuation in virulence is linked to unique or differential expression of known virulence-associated genes based on genome-wide transcriptomic analysis. The reliability of expression data generated by RNA-Seq was verified with quantitative real-time PCR of 21 selected T6SS genes, where significant down-regulation in expression of hcp gene, corresponding to the reduction in secretion of Hcp, was observed under exposure to Amp. Hcp is highlighted as a potential target for Amp, with similar changes observed in virulence-associated phenotypes between exposure to Amp and mutation of hcp gene. In addition, Hcp secretion is reduced in knockout mutants of 4 differentially expressed T6SS genes.

  15. Mechanical Properties of Additively Manufactured Thick Honeycombs

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    Reza Hedayati

    2016-07-01

    Full Text Available Honeycombs resemble the structure of a number of natural and biological materials such as cancellous bone, wood, and cork. Thick honeycomb could be also used for energy absorption applications. Moreover, studying the mechanical behavior of honeycombs under in-plane loading could help understanding the mechanical behavior of more complex 3D tessellated structures such as porous biomaterials. In this paper, we study the mechanical behavior of thick honeycombs made using additive manufacturing techniques that allow for fabrication of honeycombs with arbitrary and precisely controlled thickness. Thick honeycombs with different wall thicknesses were produced from polylactic acid (PLA using fused deposition modelling, i.e., an additive manufacturing technique. The samples were mechanically tested in-plane under compression to determine their mechanical properties. We also obtained exact analytical solutions for the stiffness matrix of thick hexagonal honeycombs using both Euler-Bernoulli and Timoshenko beam theories. The stiffness matrix was then used to derive analytical relationships that describe the elastic modulus, yield stress, and Poisson’s ratio of thick honeycombs. Finite element models were also built for computational analysis of the mechanical behavior of thick honeycombs under compression. The mechanical properties obtained using our analytical relationships were compared with experimental observations and computational results as well as with analytical solutions available in the literature. It was found that the analytical solutions presented here are in good agreement with experimental and computational results even for very thick honeycombs, whereas the analytical solutions available in the literature show a large deviation from experimental observation, computational results, and our analytical solutions.

  16. Mechanical properties of additively manufactured octagonal honeycombs

    Energy Technology Data Exchange (ETDEWEB)

    Hedayati, R., E-mail: rezahedayati@gmail.com [Department of Mechanical Engineering, Amirkabir University of Technology (Tehran Polytechnic), Hafez Ave, Tehran (Iran, Islamic Republic of); Department of Biomechanical Engineering, Faculty of Mechanical, Maritime, and Materials Engineering, Delft University of Technology (TU Delft), Mekelweg 2, 2628 CD Delft (Netherlands); Sadighi, M.; Mohammadi-Aghdam, M. [Department of Mechanical Engineering, Amirkabir University of Technology (Tehran Polytechnic), Hafez Ave, Tehran (Iran, Islamic Republic of); Zadpoor, A.A. [Department of Biomechanical Engineering, Faculty of Mechanical, Maritime, and Materials Engineering, Delft University of Technology (TU Delft), Mekelweg 2, 2628 CD Delft (Netherlands)

    2016-12-01

    Honeycomb structures have found numerous applications as structural and biomedical materials due to their favourable properties such as low weight, high stiffness, and porosity. Application of additive manufacturing and 3D printing techniques allows for manufacturing of honeycombs with arbitrary shape and wall thickness, opening the way for optimizing the mechanical and physical properties for specific applications. In this study, the mechanical properties of honeycomb structures with a new geometry, called octagonal honeycomb, were investigated using analytical, numerical, and experimental approaches. An additive manufacturing technique, namely fused deposition modelling, was used to fabricate the honeycomb from polylactic acid (PLA). The honeycombs structures were then mechanically tested under compression and the mechanical properties of the structures were determined. In addition, the Euler-Bernoulli and Timoshenko beam theories were used for deriving analytical relationships for elastic modulus, yield stress, Poisson's ratio, and buckling stress of this new design of honeycomb structures. Finite element models were also created to analyse the mechanical behaviour of the honeycombs computationally. The analytical solutions obtained using Timoshenko beam theory were close to computational results in terms of elastic modulus, Poisson's ratio and yield stress, especially for relative densities smaller than 25%. The analytical solutions based on the Timoshenko analytical solution and the computational results were in good agreement with experimental observations. Finally, the elastic properties of the proposed honeycomb structure were compared to those of other honeycomb structures such as square, triangular, hexagonal, mixed, diamond, and Kagome. The octagonal honeycomb showed yield stress and elastic modulus values very close to those of regular hexagonal honeycombs and lower than the other considered honeycombs. - Highlights: • The octagonal

  17. New insights into virulence mechanisms of rice pathogen Acidovorax avenae subsp. avenae strain RS-1 following exposure to ?-lactam antibiotics

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    Li, Bin; Ge, Mengyu; Zhang, Yang; Wang, Li; Ibrahim, Muhammad; Wang, Yanli; Sun, Guochang; Chen, Gongyou

    2016-01-01

    Recent research has shown that pathogen virulence can be altered by exposure to antibiotics, even when the growth rate is unaffected. Investigating this phenomenon provides new insights into understanding the virulence mechanisms of bacterial pathogens. This study investigates the phenotypic and transcriptomic responses of the rice pathogenic bacterium Acidovorax avenae subsp. avenae (Aaa) strain RS-1 to ?-lactam antibiotics especially Ampicillin (Amp). Our results indicate that exposure to A...

  18. Carbon storage regulator A contributes to the virulence of Haemophilus ducreyi in humans by multiple mechanisms.

    Science.gov (United States)

    Gangaiah, Dharanesh; Li, Wei; Fortney, Kate R; Janowicz, Diane M; Ellinger, Sheila; Zwickl, Beth; Katz, Barry P; Spinola, Stanley M

    2013-02-01

    The carbon storage regulator A (CsrA) controls a wide variety of bacterial processes, including metabolism, adherence, stress responses, and virulence. Haemophilus ducreyi, the causative agent of chancroid, harbors a homolog of csrA. Here, we generated an unmarked, in-frame deletion mutant of csrA to assess its contribution to H. ducreyi pathogenesis. In human inoculation experiments, the csrA mutant was partially attenuated for pustule formation compared to its parent. Deletion of csrA resulted in decreased adherence of H. ducreyi to human foreskin fibroblasts (HFF); Flp1 and Flp2, the determinants of H. ducreyi adherence to HFF cells, were downregulated in the csrA mutant. Compared to its parent, the csrA mutant had a significantly reduced ability to tolerate oxidative stress and heat shock. The enhanced sensitivity of the mutant to oxidative stress was more pronounced in bacteria grown to stationary phase compared to that in bacteria grown to mid-log phase. The csrA mutant also had a significant survival defect within human macrophages when the bacteria were grown to stationary phase but not to mid-log phase. Complementation in trans partially or fully restored the mutant phenotypes. These data suggest that CsrA contributes to virulence by multiple mechanisms and that these contributions may be more profound in bacterial cell populations that are not rapidly dividing in the human host.

  19. Mechanical properties of additively manufactured thick honeycombs

    NARCIS (Netherlands)

    Hedayati, R.; Sadighi, M.; Mohammadi-Aghdam, M; Zadpoor, A.A.

    2016-01-01

    Honeycombs resemble the structure of a number of natural and biological materials such as cancellous bone, wood, and cork. Thick honeycomb could be also used for energy absorption applications. Moreover, studying the mechanical behavior of honeycombs under in-plane loading could help understanding

  20. Neuraminidase stalk length and additional glycosylation of the hemagglutinin influence the virulence of influenza H5N1 viruses for mice.

    Science.gov (United States)

    Matsuoka, Yumiko; Swayne, David E; Thomas, Colleen; Rameix-Welti, Marie-Anne; Naffakh, Nadia; Warnes, Christine; Altholtz, Melanie; Donis, Ruben; Subbarao, Kanta

    2009-05-01

    Following circulation of avian influenza H5 and H7 viruses in poultry, the hemagglutinin (HA) can acquire additional glycosylation sites, and the neuraminidase (NA) stalk becomes shorter. We investigated whether these features play a role in the pathogenesis of infection in mammalian hosts. From 1996 to 2007, H5N1 viruses with a short NA stalk have become widespread in several avian species. Compared to viruses with a long-stalk NA, viruses with a short-stalk NA showed a decreased capacity to elute from red blood cells and an increased virulence in mice, but not in chickens. The presence of additional HA glycosylation sites had less of an effect on virulence than did NA stalk length. The short-stalk NA of H5N1 viruses circulating in Asia may contribute to virulence in humans.

  1. Neuraminidase Stalk Length and Additional Glycosylation of the Hemagglutinin Influence the Virulence of Influenza H5N1 Viruses for Mice▿

    Science.gov (United States)

    Matsuoka, Yumiko; Swayne, David E.; Thomas, Colleen; Rameix-Welti, Marie-Anne; Naffakh, Nadia; Warnes, Christine; Altholtz, Melanie; Donis, Ruben; Subbarao, Kanta

    2009-01-01

    Following circulation of avian influenza H5 and H7 viruses in poultry, the hemagglutinin (HA) can acquire additional glycosylation sites, and the neuraminidase (NA) stalk becomes shorter. We investigated whether these features play a role in the pathogenesis of infection in mammalian hosts. From 1996 to 2007, H5N1 viruses with a short NA stalk have become widespread in several avian species. Compared to viruses with a long-stalk NA, viruses with a short-stalk NA showed a decreased capacity to elute from red blood cells and an increased virulence in mice, but not in chickens. The presence of additional HA glycosylation sites had less of an effect on virulence than did NA stalk length. The short-stalk NA of H5N1 viruses circulating in Asia may contribute to virulence in humans. PMID:19225004

  2. Mechanism and kinetics of addition polymerizations

    CERN Document Server

    Kucera, M

    1991-01-01

    This volume presents an up-to-date survey of knowledge concerning addition type polymerizations. It contains nine chapters, each of which covers a particular basic term. Whenever necessary, the phenomena are discussed from the viewpoint of both stationary and non-stationary state of radical, ionic (i.e. anionic and cationic) and coordination polymerization. Special attention has been paid to the propagation process. It provides not only a general overview but also information on important special cases (theoretical conditions of propagation, influence of external factors, controlled propagatio

  3. Virulence factors and mechanisms of antimicrobial resistance in Shigella strains from periurban areas of Lima (Peru).

    Science.gov (United States)

    Lluque, Angela; Mosquito, Susan; Gomes, Cláudia; Riveros, Maribel; Durand, David; Tilley, Drake H; Bernal, María; Prada, Ana; Ochoa, Theresa J; Ruiz, Joaquim

    2015-01-01

    The study was aimed to describe the serotype, mechanisms of antimicrobial resistance, and virulence determinants in Shigella spp. isolated from Peruvian children. Eighty three Shigella spp. were serogrouped and serotyped being established the antibiotic susceptibility. The presence of 12 virulence factors (VF) and integrase 1 and 2, along with commonly found antibiotic resistance genes was established by PCR. S. flexneri was the most relevant serogroup (55 isolates, 66%), with serotype 2a most frequently detected (27 of 55, 49%), followed by S. boydii and S. sonnei at 12 isolates each (14%) and S. dysenteriae (four isolates, 5%). Fifty isolates (60%) were multi-drug resistant (MDR) including 100% of S. sonnei and 64% of S. flexneri. Resistance levels were high to trimethoprim-sulfamethoxazole (86%), tetracycline (74%), ampicillin (67%), and chloramphenicol (65%). Six isolates showed decreased azithromycin susceptibility. No isolate was resistant to nalidixic acid, ciprofloxacin, nitrofurantoin, or ceftriaxone. The most frequent resistance genes were sul2 (95%), tet(B) (92%), cat (80%), dfrA1 (47%), blaOXA-1like (40%), with intl1 and intl2 detected in 51 and 52% of the isolates, respectively. Thirty-one different VF profiles were observed, being the ipaH (100%), sen (77%), virA and icsA (75%) genes the most frequently found. Differences in the prevalence of VF were observed between species with S. flexneri isolates, particularly serotype 2a, possessing high numbers of VF. In conclusion, this study highlights the high heterogeneity of Shigella VF and resistance genes, and prevalence of MDR organisms within this geographic region. Copyright © 2015 Elsevier GmbH. All rights reserved.

  4. Single Nucleotide Polymorphisms in Regulator-Encoding Genes Have an Additive Effect on Virulence Gene Expression in a Vibrio cholerae Clinical Isolate.

    Science.gov (United States)

    Carignan, Bailey M; Brumfield, Kyle D; Son, Mike S

    2016-01-01

    patients suffering from increasingly severe symptoms and of disease progression at a much higher rate than previously observed has emerged. As recent cholera outbreaks caused by increasingly virulent strains have resulted in higher mortality rates, the need to investigate the mechanism(s) allowing this observed increased virulence is apparent. The significance of our research is in identifying the mechanism for increased virulence capabilities, which will allow the development of a model that will greatly enhance our understanding of cholera disease and V. cholerae pathogenesis, leading to broader biomedical impacts, as cholera serves as a model for other enteric diarrheal diseases.

  5. How to kill the honey bee larva: genomic potential and virulence mechanisms of Paenibacillus larvae.

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    Marvin Djukic

    Full Text Available Paenibacillus larvae, a Gram positive bacterial pathogen, causes American Foulbrood (AFB, which is the most serious infectious disease of honey bees. In order to investigate the genomic potential of P. larvae, two strains belonging to two different genotypes were sequenced and used for comparative genome analysis. The complete genome sequence of P. larvae strain DSM 25430 (genotype ERIC II consisted of 4,056,006 bp and harbored 3,928 predicted protein-encoding genes. The draft genome sequence of P. larvae strain DSM 25719 (genotype ERIC I comprised 4,579,589 bp and contained 4,868 protein-encoding genes. Both strains harbored a 9.7 kb plasmid and encoded a large number of virulence-associated proteins such as toxins and collagenases. In addition, genes encoding large multimodular enzymes producing nonribosomally peptides or polyketides were identified. In the genome of strain DSM 25719 seven toxin associated loci were identified and analyzed. Five of them encoded putatively functional toxins. The genome of strain DSM 25430 harbored several toxin loci that showed similarity to corresponding loci in the genome of strain DSM 25719, but were non-functional due to point mutations or disruption by transposases. Although both strains cause AFB, significant differences between the genomes were observed including genome size, number and composition of transposases, insertion elements, predicted phage regions, and strain-specific island-like regions. Transposases, integrases and recombinases are important drivers for genome plasticity. A total of 390 and 273 mobile elements were found in strain DSM 25430 and strain DSM 25719, respectively. Comparative genomics of both strains revealed acquisition of virulence factors by horizontal gene transfer and provided insights into evolution and pathogenicity.

  6. How to kill the honey bee larva: genomic potential and virulence mechanisms of Paenibacillus larvae.

    Science.gov (United States)

    Djukic, Marvin; Brzuszkiewicz, Elzbieta; Fünfhaus, Anne; Voss, Jörn; Gollnow, Kathleen; Poppinga, Lena; Liesegang, Heiko; Garcia-Gonzalez, Eva; Genersch, Elke; Daniel, Rolf

    2014-01-01

    Paenibacillus larvae, a Gram positive bacterial pathogen, causes American Foulbrood (AFB), which is the most serious infectious disease of honey bees. In order to investigate the genomic potential of P. larvae, two strains belonging to two different genotypes were sequenced and used for comparative genome analysis. The complete genome sequence of P. larvae strain DSM 25430 (genotype ERIC II) consisted of 4,056,006 bp and harbored 3,928 predicted protein-encoding genes. The draft genome sequence of P. larvae strain DSM 25719 (genotype ERIC I) comprised 4,579,589 bp and contained 4,868 protein-encoding genes. Both strains harbored a 9.7 kb plasmid and encoded a large number of virulence-associated proteins such as toxins and collagenases. In addition, genes encoding large multimodular enzymes producing nonribosomally peptides or polyketides were identified. In the genome of strain DSM 25719 seven toxin associated loci were identified and analyzed. Five of them encoded putatively functional toxins. The genome of strain DSM 25430 harbored several toxin loci that showed similarity to corresponding loci in the genome of strain DSM 25719, but were non-functional due to point mutations or disruption by transposases. Although both strains cause AFB, significant differences between the genomes were observed including genome size, number and composition of transposases, insertion elements, predicted phage regions, and strain-specific island-like regions. Transposases, integrases and recombinases are important drivers for genome plasticity. A total of 390 and 273 mobile elements were found in strain DSM 25430 and strain DSM 25719, respectively. Comparative genomics of both strains revealed acquisition of virulence factors by horizontal gene transfer and provided insights into evolution and pathogenicity.

  7. Iron Acquisition Mechanisms and Their Role in the Virulence of Burkholderia Species

    Science.gov (United States)

    Butt, Aaron T.; Thomas, Mark S.

    2017-01-01

    Burkholderia is a genus within the β-Proteobacteriaceae that contains at least 90 validly named species which can be found in a diverse range of environments. A number of pathogenic species occur within the genus. These include Burkholderia cenocepacia and Burkholderia multivorans, opportunistic pathogens that can infect the lungs of patients with cystic fibrosis, and are members of the Burkholderia cepacia complex (Bcc). Burkholderia pseudomallei is also an opportunistic pathogen, but in contrast to Bcc species it causes the tropical human disease melioidosis, while its close relative Burkholderia mallei is the causative agent of glanders in horses. For these pathogens to survive within a host and cause disease they must be able to acquire iron. This chemical element is essential for nearly all living organisms due to its important role in many enzymes and metabolic processes. In the mammalian host, the amount of accessible free iron is negligible due to the low solubility of the metal ion in its higher oxidation state and the tight binding of this element by host proteins such as ferritin and lactoferrin. As with other pathogenic bacteria, Burkholderia species have evolved an array of iron acquisition mechanisms with which to capture iron from the host environment. These mechanisms include the production and utilization of siderophores and the possession of a haem uptake system. Here, we summarize the known mechanisms of iron acquisition in pathogenic Burkholderia species and discuss the evidence for their importance in the context of virulence and the establishment of infection in the host. We have also carried out an extensive bioinformatic analysis to identify which siderophores are produced by each Burkholderia species that is pathogenic to humans. PMID:29164069

  8. Effective but costly, evolved mechanisms of defense against a virulent opportunistic pathogen in Drosophila melanogaster.

    Directory of Open Access Journals (Sweden)

    Yixin H Ye

    2009-04-01

    Full Text Available Drosophila harbor substantial genetic variation for antibacterial defense, and investment in immunity is thought to involve a costly trade-off with life history traits, including development, life span, and reproduction. To understand the way in which insects invest in fighting bacterial infection, we selected for survival following systemic infection with the opportunistic pathogen Pseudomonas aeruginosa in wild-caught Drosophila melanogaster over 10 generations. We then examined genome-wide changes in expression in the selected flies relative to unselected controls, both of which had been infected with the pathogen. This powerful combination of techniques allowed us to specifically identify the genetic basis of the evolved immune response. In response to selection, population-level survivorship to infection increased from 15% to 70%. The evolved capacity for defense was costly, however, as evidenced by reduced longevity and larval viability and a rapid loss of the trait once selection pressure was removed. Counter to expectation, we observed more rapid developmental rates in the selected flies. Selection-associated changes in expression of genes with dual involvement in developmental and immune pathways suggest pleiotropy as a possible mechanism for the positive correlation. We also found that both the Toll and the Imd pathways work synergistically to limit infectivity and that cellular immunity plays a more critical role in overcoming P. aeruginosa infection than previously reported. This work reveals novel pathways by which Drosophila can survive infection with a virulent pathogen that may be rare in wild populations, however, due to their cost.

  9. B cell activation by outer membrane vesicles--a novel virulence mechanism.

    Directory of Open Access Journals (Sweden)

    Maria Laura A Perez Vidakovics

    2010-01-01

    Full Text Available Secretion of outer membrane vesicles (OMV is an intriguing phenomenon of Gram-negative bacteria and has been suggested to play a role as virulence factors. The respiratory pathogens Moraxella catarrhalis reside in tonsils adjacent to B cells, and we have previously shown that M. catarrhalis induce a T cell independent B cell response by the immunoglobulin (Ig D-binding superantigen MID. Here we demonstrate that Moraxella are endocytosed and killed by human tonsillar B cells, whereas OMV have the potential to interact and activate B cells leading to bacterial rescue. The B cell response induced by OMV begins with IgD B cell receptor (BCR clustering and Ca(2+ mobilization followed by BCR internalization. In addition to IgD BCR, TLR9 and TLR2 were found to colocalize in lipid raft motifs after exposure to OMV. Two components of the OMV, i.e., MID and unmethylated CpG-DNA motifs, were found to be critical for B cell activation. OMV containing MID bound to and activated tonsillar CD19(+ IgD(+ lymphocytes resulting in IL-6 and IgM production in addition to increased surface marker density (HLA-DR, CD45, CD64, and CD86, whereas MID-deficient OMV failed to induce B cell activation. DNA associated with OMV induced full B cell activation by signaling through TLR9. Importantly, this concept was verified in vivo, as OMV equipped with MID and DNA were found in a 9-year old patient suffering from Moraxella sinusitis. In conclusion, Moraxella avoid direct interaction with host B cells by redirecting the adaptive humoral immune response using its superantigen-bearing OMV as decoys.

  10. Evolutionary mechanisms involved in the virulence of infectious salmon anaemia virus (ISAV), a piscine orthomyxovirus

    International Nuclear Information System (INIS)

    Markussen, Turhan; Jonassen, Christine Monceyron; Numanovic, Sanela; Braaen, Stine; Hjortaas, Monika; Nilsen, Hanne; Mjaaland, Siri

    2008-01-01

    Infectious salmon anaemia virus (ISAV) is an orthomyxovirus causing a multisystemic, emerging disease in Atlantic salmon. Here we present, for the first time, detailed sequence analyses of the full-genome sequence of a presumed avirulent isolate displaying a full-length hemagglutinin-esterase (HE) gene (HPR0), and compare this with full-genome sequences of 11 Norwegian ISAV isolates from clinically diseased fish. These analyses revealed the presence of a virulence marker right upstream of the putative cleavage site R 267 in the fusion (F) protein, suggesting a Q 266 → L 266 substitution to be a prerequisite for virulence. To gain virulence in isolates lacking this substitution, a sequence insertion near the cleavage site seems to be required. This strongly suggests the involvement of a protease recognition pattern at the cleavage site of the fusion protein as a determinant of virulence, as seen in highly pathogenic influenza A virus H5 or H7 and the paramyxovirus Newcastle disease virus

  11. Genome-Wide Transposon Mutagenesis Indicates that Mycobacterium marinum Customizes Its Virulence Mechanisms for Survival and Replication in Different Hosts

    KAUST Repository

    Weerdenburg, Eveline M.

    2015-02-17

    The interaction of environmental bacteria with unicellular eukaryotes is generally considered a major driving force for the evolution of intracellular pathogens, allowing them to survive and replicate in phagocytic cells of vertebrate hosts. To test this hypothesis on a genome-wide level, we determined for the intracellular pathogen Mycobacterium marinum whether it uses conserved strategies to exploit host cells from both protozoan and vertebrate origin. Using transposon-directed insertion site sequencing (TraDIS), we determined differences in genetic requirements for survival and replication in phagocytic cells of organisms from different kingdoms. In line with the general hypothesis, we identified a number of general virulence mechanisms, including the type VII protein secretion system ESX-1, biosynthesis of polyketide lipids, and utilization of sterols. However, we were also able to show that M. marinum contains an even larger set of host-specific virulence determinants, including proteins involved in the modification of surface glycolipids and, surprisingly, the auxiliary proteins of the ESX-1 system. Several of these factors were in fact counterproductive in other hosts. Therefore, M. marinum contains different sets of virulence factors that are tailored for specific hosts. Our data imply that although amoebae could function as a training ground for intracellular pathogens, they do not fully prepare pathogens for crossing species barriers.

  12. The Complete Genome Sequence of the Fish Pathogen Tenacibaculum maritimum Provides Insights into Virulence Mechanisms

    Directory of Open Access Journals (Sweden)

    David Pérez-Pascual

    2017-08-01

    Full Text Available Tenacibaculum maritimum is a devastating bacterial pathogen of wild and farmed marine fish with a broad host range and a worldwide distribution. We report here the complete genome sequence of the T. maritimum type strain NCIMB 2154T. The genome consists of a 3,435,971-base pair circular chromosome with 2,866 predicted protein-coding genes. Genes encoding the biosynthesis of exopolysaccharides, the type IX secretion system, iron uptake systems, adhesins, hemolysins, proteases, and glycoside hydrolases were identified. They are likely involved in the virulence process including immune escape, invasion, colonization, destruction of host tissues, and nutrient scavenging. Among the predicted virulence factors, type IX secretion-mediated and cell-surface exposed proteins were identified including an atypical sialidase, a sphingomyelinase and a chondroitin AC lyase which activities were demonstrated in vitro.

  13. Additively homomorphic encryption with a double decryption mechanism, revisited

    NARCIS (Netherlands)

    Peter, Andreas; Kronberg, M.; Trei, W.; Katzenbeisser, S.

    We revisit the notion of additively homomorphic encryption with a double decryption mechanism (DD-PKE), which allows for additions in the encrypted domain while having a master decryption procedure that can decrypt all properly formed ciphertexts by using a special master secret. This type of

  14. Chlamydia trachomatis In Vivo to In Vitro Transition Reveals Mechanisms of Phase Variation and Down-Regulation of Virulence Factors.

    Directory of Open Access Journals (Sweden)

    Vítor Borges

    Full Text Available Research on the obligate intracellular bacterium Chlamydia trachomatis demands culture in cell-lines, but the adaptive process behind the in vivo to in vitro transition is not understood. We assessed the genomic and transcriptomic dynamics underlying C. trachomatis in vitro adaptation of strains representing the three disease groups (ocular, epithelial-genital and lymphogranuloma venereum propagated in epithelial cells over multiple passages. We found genetic features potentially underlying phase variation mechanisms mediating the regulation of a lipid A biosynthesis enzyme (CT533/LpxC, and the functionality of the cytotoxin (CT166 through an ON/OFF mechanism. We detected inactivating mutations in CT713/porB, a scenario suggesting metabolic adaptation to the available carbon source. CT135 was inactivated in a tropism-specific manner, with CT135-negative clones emerging for all epithelial-genital populations (but not for LGV and ocular populations and rapidly increasing in frequency (~23% mutants per 10 passages. RNA-sequencing analyses revealed that a deletion event involving CT135 impacted the expression of multiple virulence factors, namely effectors known to play a role in the C. trachomatis host-cell invasion or subversion (e.g., CT456/Tarp, CT694, CT875/TepP and CT868/ChlaDub1. This reflects a scenario of attenuation of C. trachomatis virulence in vitro, which may take place independently or in a cumulative fashion with the also observed down-regulation of plasmid-related virulence factors. This issue may be relevant on behalf of the recent advances in Chlamydia mutagenesis and transformation where culture propagation for selecting mutants/transformants is mandatory. Finally, there was an increase in the growth rate for all strains, reflecting gradual fitness enhancement over time. In general, these data shed light on the adaptive process underlying the C. trachomatis in vivo to in vitro transition, and indicates that it would be prudent to

  15. Mechanical Properties of Austenitic Stainless Steel Made by Additive Manufacturing.

    Science.gov (United States)

    Luecke, William E; Slotwinski, John A

    2014-01-01

    Using uniaxial tensile and hardness testing, we evaluated the variability and anisotropy of the mechanical properties of an austenitic stainless steel, UNS S17400, manufactured by an additive process, selective laser melting. Like wrought materials, the mechanical properties depend on the orientation introduced by the processing. The recommended stress-relief heat treatment increases the tensile strength, reduces the yield strength, and decreases the extent of the discontinuous yielding. The mechanical properties, assessed by hardness, are very uniform across the build plate, but the stress-relief heat treatment introduced a small non-uniformity that had no correlation to position on the build plate. Analysis of the mechanical property behavior resulted in four conclusions. (1) The within-build and build-to-build tensile properties of the UNS S17400 stainless steel are less repeatable than mature engineering structural alloys, but similar to other structural alloys made by additive manufacturing. (2) The anisotropy of the mechanical properties of the UNS S17400 material of this study is larger than that of mature structural alloys, but is similar to other structural alloys made by additive manufacturing. (3) The tensile mechanical properties of the UNS S17400 material fabricated by selective laser melting are very different from those of wrought, heat-treated 17-4PH stainless steel. (4) The large discontinuous yielding strain in all tests resulted from the formation and propagation of Lüders bands.

  16. Metal Additive Manufacturing: A Review of Mechanical Properties

    Science.gov (United States)

    Lewandowski, John J.; Seifi, Mohsen

    2016-07-01

    This article reviews published data on the mechanical properties of additively manufactured metallic materials. The additive manufacturing techniques utilized to generate samples covered in this review include powder bed fusion (e.g., EBM, SLM, DMLS) and directed energy deposition (e.g., LENS, EBF3). Although only a limited number of metallic alloy systems are currently available for additive manufacturing (e.g., Ti-6Al-4V, TiAl, stainless steel, Inconel 625/718, and Al-Si-10Mg), the bulk of the published mechanical properties information has been generated on Ti-6Al-4V. However, summary tables for published mechanical properties and/or key figures are included for each of the alloys listed above, grouped by the additive technique used to generate the data. Published values for mechanical properties obtained from hardness, tension/compression, fracture toughness, fatigue crack growth, and high cycle fatigue are included for as-built, heat-treated, and/or HIP conditions, when available. The effects of test orientation/build direction on properties, when available, are also provided, along with discussion of the potential source(s) (e.g., texture, microstructure changes, defects) of anisotropy in properties. Recommendations for additional work are also provided.

  17. Build platform that provides mechanical engagement with additive manufacturing prints

    Science.gov (United States)

    Elliott, Amelia M.

    2018-03-06

    A build platform and methods of fabricating an article with such a platform in an extrusion-type additive manufacturing machine are provided. A platform body 202 includes features 204 that extend outward from the body 202. The features 204 define protrusive areas 206 and recessive areas 208 that cooperate to mechanically engage the extruded material that forms the initial layers 220 of an article when the article is being fabricated by a nozzle 12 of the additive manufacturing machine 10.

  18. Crystal Structure of the LasA Virulence Factor from Pseudomonas aeruginosa: Substrate Specificity and Mechanism of M23 Metallopeptidases

    Energy Technology Data Exchange (ETDEWEB)

    Spencer, James; Murphy, Loretta M.; Conners, Rebecca; Sessions, Richard B.; Gamblin, Steven J. (Wales); (Bristol Med Sci); (NIMR)

    2010-09-21

    Pseudomonas aeruginosa is an opportunist Gram-negative bacterial pathogen responsible for a wide range of infections in immunocompromized individuals and is a leading cause of mortality in cystic fibrosis patients. A number of secreted virulence factors, including various proteolytic enzymes, contribute to the establishment and maintenance of Pseudomonas infection. One such is LasA, an M23 metallopeptidase related to autolytic glycylglycine endopeptidases such as Staphylococcus aureus lysostaphin and LytM, and to DD-endopeptidases involved in entry of bacteriophage to host bacteria. LasA is implicated in a range of processes related to Pseudomonas virulence, including stimulating ectodomain shedding of the cell surface heparan sulphate proteoglycan syndecan-1 and elastin degradation in connective tissue. Here we present crystal structures of active LasA as a complex with tartrate and in the uncomplexed form. While the overall fold resembles that of the other M23 family members, the LasA active site is less constricted and utilizes a different set of metal ligands. The active site of uncomplexed LasA contains a five-coordinate zinc ion with trigonal bipyramidal geometry and two metal-bound water molecules. Using these structures as a starting point, we propose a model for substrate binding by LasA that explains its activity against a wider range of substrates than those used by related lytic enzymes, and offer a catalytic mechanism for M23 metallopeptidases consistent with available structural and mutagenesis data. Our results highlight how LasA is a structurally distinct member of this endopeptidase family, consistent with its activity against a wider range of substrates and with its multiple roles in Pseudomonas virulence.

  19. Ammonium nitrate: combustion mechanism and the role of additives

    Energy Technology Data Exchange (ETDEWEB)

    Sinditskii, Valery P.; Egorshev, Viacheslav Yu.; Levshenkov, Anton I.; Serushkin, Valery V. [Department of Chemical Engineering, Mendeleev University of Chemical Technology, 9 Miusskaya Sq., 125047, Moscow (Russian Federation)

    2005-09-01

    This paper presents an analysis of the observed combustion behavior of AN mixtures with different additives, fuels, and energetic materials. It has been determined on the basis of flame structure investigation by fine tungsten-rhenium thermocouples that the surface temperature of AN is controlled by the dissociation reaction of the salt occurring at the surface. Results obtained have indicated that the leading reaction of combustion of AN doped with additives proceeds in the condensed phase up to pressures of 20-30 MPa. A reason for the inability of pure AN to burn is suggested and the role of additives in the combustion mechanism is discussed. (Abstract Copyright [2005], Wiley Periodicals, Inc.)

  20. Microstructure and mechanical properties of molybdenum silicides with Al additions

    International Nuclear Information System (INIS)

    Rosales, I.; Bahena, D.; Colin, J.

    2007-01-01

    Several molybdenum silicides alloys with different aluminum additions were produced by the arc-cast method. Microstructure observed in the alloys presented a variation of the precipitated second phase respect to the aluminum content. Evaluation of the compressive behavior at high temperature of the alloys shows an important improvement in its ductility, approximately of 20%. Fracture toughness was increased proportionally with Al content. In addition at room temperature the alloys show a better mechanical behavior in comparison with the sample unalloyed. In general, Al additions result to be a good alternative to improve the resistance of these intermetallic alloys. The results are interpreted on the base of the analysis of second phase strengthening

  1. Effects of sulphur addition on modification and mechanical ...

    African Journals Online (AJOL)

    CW Onyia, BA Okorie, NI Amalu, SI Neife ... The results showed that the addition of sulphur to Al-12wt%Si alloy modified the Al-Si eutectic ... of the eutectic silicon structure with significant decrease in mechanical properties of the alloy and this ...

  2. Damage evolution and failure mechanisms in additively manufactured stainless steel

    Energy Technology Data Exchange (ETDEWEB)

    Carlton, Holly D., E-mail: carlton4@llnl.gov [Materials Engineering Division, Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94550 (United States); Haboub, Abdel [Lincoln University, Life and Physical Sciences Department, 820 Chestnut St, Jefferson City, MO 65101 (United States); Gallegos, Gilbert F. [Materials Engineering Division, Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94550 (United States); Parkinson, Dilworth Y.; MacDowell, Alastair A. [Advanced Light Source, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720 (United States)

    2016-01-10

    In situ tensile tests were performed on additively manufactured austenitic stainless steel to track damage evolution within the material. For these experiments Synchrotron Radiation micro-Tomography was used to measure three-dimensional pore volume, distribution, and morphology in stainless steel at the micrometer length-scale while tensile loading was applied. The results showed that porosity distribution played a larger role in affecting the fracture mechanisms than measured bulk density. Specifically, additively manufactured stainless steel specimens with large inhomogeneous void distributions displayed a flaw-dominated failure where cracks were shown to initiate at pre-existing voids, while annealed additively manufactured stainless steel specimens, which contained low porosity and randomly distributed pores, displayed fracture mechanisms that closely resembled wrought metal.

  3. Mechanical and Fatigue Properties of Additively Manufactured Metallic Materials

    Science.gov (United States)

    Yadollahi, Aref

    This study aims to investigate the mechanical and fatigue behavior of additively manufactured metallic materials. Several challenges associated with different metal additive manufacturing (AM) techniques (i.e. laser-powder bed fusion and direct laser deposition) have been addressed experimentally and numerically. Experiments have been carried out to study the effects of process inter-layer time interval--i.e. either building the samples one-at-a-time or multi-at-a-time (in-parallel)--on the microstructural features and mechanical properties of 316L stainless steel samples, fabricated via a direct laser deposition (DLD). Next, the effect of building orientation--i.e. the orientation in which AM parts are built--on microstructure, tensile, and fatigue behaviors of 17-4 PH stainless steel, fabricated via a laser-powder bed fusion (L-PBF) method was investigated. Afterwards, the effect of surface finishing--here, as-built versus machined--on uniaxial fatigue behavior and failure mechanisms of Inconel 718 fabricated via a laser-powder bed fusion technique was sought. The numerical studies, as part of this dissertation, aimed to model the mechanical behavior of AM materials, under monotonic and cyclic loading, based on the observations and findings from the experiments. Despite significant research efforts for optimizing process parameters, achieving a homogenous, defect-free AM product--immediately after fabrication--has not yet been fully demonstrated. Thus, one solution for ensuring the adoption of AM materials for application should center on predicting the variations in mechanical behavior of AM parts based on their resultant microstructure. In this regard, an internal state variable (ISV) plasticity-damage model was employed to quantify the damage evolution in DLD 316L SS, under tensile loading, using the microstructural features associated with the manufacturing process. Finally, fatigue behavior of AM parts has been modeled based on the crack-growth concept

  4. The Effects of Low-Shear Mechanical Stress on Yersinia pestis Virulence

    Science.gov (United States)

    Lawal, Abidat; Jejelowo, Olufisayo A.; Rosenzweig, Jason A.

    2010-11-01

    Manned space exploration has created a need to evaluate the effects of spacelike stress on pathogenic and opportunistic microbes astronauts could carry with them to the International Space Station and beyond. Yersinia pestis (YP) causes bubonic, septicemic, and pneumonic plague and is capable of killing infected patients within 3-7 days. In this study, low-shear modeled microgravity (LSMMG), a spacelike stress, was used to physically stress YP; and its effects on proliferation, cold growth, and type III secretion system (T3SS) function were evaluated. YP was grown to saturation in either LSMMG or normal gravity (NG) conditions prior to being used for RAW 246.7 cell infections, HeLa cell infections, and Yop secretion assays. A mutant strain of YP (ΔyopB) that lacks the ability to inject Yersinia outer membrane proteins (Yops) into the host cell was used as a negative control in cell infection experiments. Our experimental results indicate that YP cultivated under LSMMG resulted in reduced YopM production and secretion compared to its NG-grown counterpart. Similarly, NG-grown YP induced more cell rounding in HeLa cells than did the LSMMG-grown YP, which suggests that LSMMG somehow impairs T3SS optimum function. Also, LSMMG-grown YP used to infect cultured RAW 246.7 cells showed a similar pattern of dysfunction in that it proliferated less than did its NG-grown counterpart during an 8-hour infection period. This study suggests that LSMMG can attenuate bacterial virulence contrary to previously published data that have demonstrated LSMMG-induced hypervirulence of other Gram-negative enterics.

  5. A Novel Insight into Dehydroleucodine Mediated Attenuation of Pseudomonas aeruginosa Virulence Mechanism

    Directory of Open Access Journals (Sweden)

    S. Mustafi

    2015-01-01

    Full Text Available Increasing resistance of Pseudomonas aeruginosa (P. aeruginosa to conventional treatments demands the search for novel therapeutic strategies. In this study, the antimicrobial activity of dehydroleucodine (DhL, a sesquiterpene lactone obtained from Artemisia (A. douglasiana, was screened against several pathogenic virulence effectors of P. aeruginosa. In vitro, minimum inhibitory concentration of DhL was determined against P. aeruginosa strains PAO1, PA103, PA14, and multidrug resistant clinical strain, CDN118. Results showed that DhL was active against each strain where PAO1 and PA103 showed higher susceptibility (MIC 0.48 mg/mL as compared to PA14 (MIC 0.96 mg/mL and CDN118 (MIC 0.98 mg/mL. Also, when PAO1 strain was grown in the presence of DhL (MIC50, 0.12 mg/mL, a delay in the generation time was noticed along with significant inhibition of secretory protease and elastase activities, interruption in biofilm attachment phase in a stationary culture, and a significant decline in Type III effector ExoS. At MIC50, DhL treatment increased the sensitivity of P. aeruginosa towards potent antibiotics. Furthermore, treatment of P. aeruginosa with DhL prevented toxin-induced apoptosis in macrophages. These observations suggest that DhL activity was at the bacterial transcriptional level. Hence, antimicrobial activity of DhL may serve as leads in the development of new anti-Pseudomonas pharmaceuticals.

  6. Structural and Molecular Mechanism of CdpR Involved in Quorum-Sensing and Bacterial Virulence in Pseudomonas aeruginosa.

    Directory of Open Access Journals (Sweden)

    Jingru Zhao

    2016-04-01

    Full Text Available Although quorum-sensing (QS systems are important regulators of virulence gene expression in the opportunistic human pathogen Pseudomonas aeruginosa, their detailed regulatory mechanisms have not been fully characterized. Here, we show that deletion of PA2588 resulted in increased production of pyocyanin and biofilm, as well as enhanced pathogenicity in a mouse model. To gain insights into the function of PA2588, we performed a ChIP-seq assay and identified 28 targets of PA2588, including the intergenic region between PA2588 and pqsH, which encodes the key synthase of Pseudomonas quinolone signal (PQS. Though the C-terminal domain was similar to DNA-binding regions of other AraC family members, structural studies revealed that PA2588 has a novel fold at the N-terminal region (NTR, and its C-terminal HTH (helix-turn-helix domain is also unique in DNA recognition. We also demonstrated that the adaptor protein ClpS, an essential regulator of ATP-dependent protease ClpAP, directly interacted with PA2588 before delivering CdpR to ClpAP for degradation. We named PA2588 as CdpR (ClpAP-degradation and pathogenicity Regulator. Moreover, deletion of clpP or clpS/clpA promotes bacterial survival in a mouse model of acute pneumonia infection. Taken together, this study uncovered that CdpR is an important QS regulator, which can interact with the ClpAS-P system to regulate the expression of virulence factors and pathogenicity.

  7. Transient virulence of emerging pathogens.

    Science.gov (United States)

    Bolker, Benjamin M; Nanda, Arjun; Shah, Dharmini

    2010-05-06

    Should emerging pathogens be unusually virulent? If so, why? Existing theories of virulence evolution based on a tradeoff between high transmission rates and long infectious periods imply that epidemic growth conditions will select for higher virulence, possibly leading to a transient peak in virulence near the beginning of an epidemic. This transient selection could lead to high virulence in emerging pathogens. Using a simple model of the epidemiological and evolutionary dynamics of emerging pathogens, along with rough estimates of parameters for pathogens such as severe acute respiratory syndrome, West Nile virus and myxomatosis, we estimated the potential magnitude and timing of such transient virulence peaks. Pathogens that are moderately evolvable, highly transmissible, and highly virulent at equilibrium could briefly double their virulence during an epidemic; thus, epidemic-phase selection could contribute significantly to the virulence of emerging pathogens. In order to further assess the potential significance of this mechanism, we bring together data from the literature for the shapes of tradeoff curves for several pathogens (myxomatosis, HIV, and a parasite of Daphnia) and the level of genetic variation for virulence for one (myxomatosis). We discuss the need for better data on tradeoff curves and genetic variance in order to evaluate the plausibility of various scenarios of virulence evolution.

  8. Rice-Infecting Pseudomonas Genomes Are Highly Accessorized and Harbor Multiple Putative Virulence Mechanisms to Cause Sheath Brown Rot

    Science.gov (United States)

    Quibod, Ian Lorenzo; Grande, Genelou; Oreiro, Eula Gems; Borja, Frances Nikki; Dossa, Gerbert Sylvestre; Mauleon, Ramil; Cruz, Casiana Vera; Oliva, Ricardo

    2015-01-01

    Sheath rot complex and seed discoloration in rice involve a number of pathogenic bacteria that cannot be associated with distinctive symptoms. These pathogens can easily travel on asymptomatic seeds and therefore represent a threat to rice cropping systems. Among the rice-infecting Pseudomonas, P. fuscovaginae has been associated with sheath brown rot disease in several rice growing areas around the world. The appearance of a similar Pseudomonas population, which here we named P. fuscovaginae-like, represents a perfect opportunity to understand common genomic features that can explain the infection mechanism in rice. We showed that the novel population is indeed closely related to P. fuscovaginae. A comparative genomics approach on eight rice-infecting Pseudomonas revealed heterogeneous genomes and a high number of strain-specific genes. The genomes of P. fuscovaginae-like harbor four secretion systems (Type I, II, III, and VI) and other important pathogenicity machinery that could probably facilitate rice colonization. We identified 123 core secreted proteins, most of which have strong signatures of positive selection suggesting functional adaptation. Transcript accumulation of putative pathogenicity-related genes during rice colonization revealed a concerted virulence mechanism. The study suggests that rice-infecting Pseudomonas causing sheath brown rot are intrinsically diverse and maintain a variable set of metabolic capabilities as a potential strategy to occupy a range of environments. PMID:26422147

  9. Additional mechanisms conferring genetic susceptibility to Alzheimer's disease

    Directory of Open Access Journals (Sweden)

    Miguel eCalero

    2015-04-01

    Full Text Available Familial Alzheimer's disease (AD, mostly associated with early onset, is caused by mutations in three genes (APP, PSEN1 and PSEN2 involved in the production of the amyloid  peptide. In contrast, the molecular mechanisms that trigger the most common late onset sporadic AD remain largely unknown. With the implementation of an increasing number of case-control studies and the upcoming of large-scale genome-wide association studies (GWAS there is a mounting list of genetic risk factors associated to common genetic variants that have been associated to sporadic AD. Besides APOE, that presents a strong association with the disease (OR~4, the rest of these genes have moderate or low degrees of association, with OR ranging from 0.88 to 1.23. Taking together, these genes may account only for a fraction of the attributable AD risk and therefore, rare variants and epistastic gene interactions should be taken into account in order to get the full picture of the genetic risks associated to AD. Here, we review recent whole-exome studies looking for rare variants, somatic brain mutations with a strong association to the disease, and several studies dealing with epistasis as additional mechanisms conferring genetic susceptibility to AD. Altogether, recent evidence underlines the importance of defining molecular and genetic pathways and networks rather than the contribution of specific genes.

  10. Bioinspired Cellular Structures: Additive Manufacturing and Mechanical Properties

    Science.gov (United States)

    Stampfl, J.; Pettermann, H. E.; Liska, R.

    Biological materials (e.g., wood, trabecular bone, marine skeletons) rely heavily on the use of cellular architecture, which provides several advantages. (1) The resulting structures can bear the variety of "real life" load spectra using a minimum of a given bulk material, featuring engineering lightweight design principles. (2) The inside of the structures is accessible to body fluids which deliver the required nutrients. (3) Furthermore, cellular architectures can grow organically by adding or removing individual struts or by changing the shape of the constituting elements. All these facts make the use of cellular architectures a reasonable choice for nature. Using additive manufacturing technologies (AMT), it is now possible to fabricate such structures for applications in engineering and biomedicine. In this chapter, we present methods that allow the 3D computational analysis of the mechanical properties of cellular structures with open porosity. Various different cellular architectures including disorder are studied. In order to quantify the influence of architecture, the apparent density is always kept constant. Furthermore, it is shown that how new advanced photopolymers can be used to tailor the mechanical and functional properties of the fabricated structures.

  11. Genome-Wide Transposon Mutagenesis Indicates that Mycobacterium marinum Customizes Its Virulence Mechanisms for Survival and Replication in Different Hosts

    KAUST Repository

    Weerdenburg, Eveline M.; Abdallah, Abdallah; Rangkuti, Farania; Abd El Ghany, Moataz; Otto, Thomas D.; Adroub, Sabir; Molenaar, Douwe; Ummels, Roy; ter Veen, Kars; van Stempvoort, Gunny; van der Sar, Astrid M.; Ali, Shahjahan; Langridge, Gemma C.; Thomson, Nicholas R.; Pain, Arnab; Bitter, Wilbert

    2015-01-01

    the type VII protein secretion system ESX-1, biosynthesis of polyketide lipids, and utilization of sterols. However, we were also able to show that M. marinum contains an even larger set of host-specific virulence determinants, including proteins involved

  12. Toxin-independent virulence of Bacillus anthracis in rabbits.

    Directory of Open Access Journals (Sweden)

    Haim Levy

    Full Text Available The accepted paradigm states that anthrax is both an invasive and toxinogenic disease and that the toxins play a major role in pathogenicity. In the guinea pig (GP model we have previously shown that deletion of all three toxin components results in a relatively moderate attenuation in virulence, indicating that B. anthracis possesses an additional toxin-independent virulence mechanism. To characterize this toxin-independent mechanism in anthrax disease, we developed a new rabbit model by intravenous injection (IV of B. anthracis encapsulated vegetative cells, artificially creating bacteremia. Using this model we were able to demonstrate that also in rabbits, B. anthracis mutants lacking the toxins are capable of killing the host within 24 hours. This virulent trait depends on the activity of AtxA in the presence of pXO2, as, in the absence of the toxin genes, deletion of either component abolishes virulence. Furthermore, this IV virulence depends mainly on AtxA rather than the whole pXO1. A similar pattern was shown in the GP model using subcutaneous (SC administration of spores of the mutant strains, demonstrating the generality of the phenomenon. The virulent strains showed higher bacteremia levels and more efficient tissue dissemination; however our interpretation is that tissue dissemination per se is not the main determinant of virulence whose exact nature requires further elucidation.

  13. Effects of organic additives on microstructure and mechanical ...

    Indian Academy of Sciences (India)

    Administrator

    State Key Laboratory for Mechanical Behaviour of Materials, Xi'an Jiaotong University, Xi'an 710049, P.R. China ... porosity are of interest for engineering applications, as gas filters ... Flow diagram for fabricating porous silicon nitride samples.

  14. Mechanical Behavior of Additively Manufactured Uranium-6 wt. pct. Niobium

    Energy Technology Data Exchange (ETDEWEB)

    Wu, A. S. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Wraith, M. W. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Burke, S. C. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Hamza, A. V. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Brown, D. W. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Clausen, B. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Hsiung, L. L. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); McKeown, J. T. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Lindvall, R. E. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Sedillo, E. M. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Teslich, N. E. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Torres, S. G. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Urabe, D. S. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Freeman, D. C. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Alexander, P. A. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Iniguez, M. R. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Ryerson, F. J. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Ancheta, D. S. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Lotscher, J. P. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Young, E. W. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Evans, C. L. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Florando, J. N. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Gallegos, G. F. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Margraff, M. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Hrousis, C. A. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Campbell, G. H. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

    2017-09-15

    This report describes an effort to process uranium-6 weight% niobium using laser powder bed fusion. The chemistry, crystallography, microstructure and mechanical response resulting from this process are discussed with particular emphasis on the effect of the laser powder bed fusion process on impurities. In an effort to achieve homogenization and uniform mechanical behavior from different builds, as well as to induce a more conventional loading response, we explore post-processing heat treatments on this complex alloy. Elevated temperature heat treatment for recrystallization is evaluated and the effect of recrystallization on mechanical behavior in laser powder bed fusion processed U-6Nb is discussed. Wrought-like mechanical behavior and grain sizes are achieved through post-processing and are reported herein.

  15. Identification of Brucella melitensis Rev.1 vaccine-strain genetic markers: Towards understanding the molecular mechanism behind virulence attenuation.

    Science.gov (United States)

    Issa, Mohammad Nouh; Ashhab, Yaqoub

    2016-09-22

    Brucella melitensis Rev.1 is an avirulent strain that is widely used as a live vaccine to control brucellosis in small ruminants. Although an assembled draft version of Rev.1 genome has been available since 2009, this genome has not been investigated to characterize this important vaccine. In the present work, we used the draft genome of Rev.1 to perform a thorough genomic comparison and sequence analysis to identify and characterize the panel of its unique genetic markers. The draft genome of Rev.1 was compared with genome sequences of 36 different Brucella melitensis strains from the Brucella project of the Broad Institute of MIT and Harvard. The comparative analyses revealed 32 genetic alterations (30 SNPs, 1 single-bp insertion and 1 single-bp deletion) that are exclusively present in the Rev.1 genome. In silico analyses showed that 9 out of the 17 non-synonymous mutations are deleterious. Three ABC transporters are among the disrupted genes that can be linked to virulence attenuation. Out of the 32 mutations, 11 Rev.1 specific markers were selected to test their potential to discriminate Rev.1 using a bi-directional allele-specific PCR assay. Six markers were able to distinguish between Rev.1 and a set of control strains. We succeeded in identifying a panel of 32 genome-specific markers of the B. melitensis Rev.1 vaccine strain. Extensive in silico analysis showed that a considerable number of these mutations could severely affect the function of the associated genes. In addition, some of the discovered markers were able to discriminate Rev.1 strain from a group of control strains using practical PCR tests that can be applied in resource-limited settings. Copyright © 2016 Elsevier Ltd. All rights reserved.

  16. Plasma membrane lipids and their role in fungal virulence.

    Science.gov (United States)

    Rella, Antonella; Farnoud, Amir M; Del Poeta, Maurizio

    2016-01-01

    There has been considerable evidence in recent years suggesting that plasma membrane lipids are important regulators of fungal pathogenicity. Various glycolipids have been shown to impart virulent properties in several fungal species, while others have been shown to play a role in host defense. In addition to their role as virulence factors, lipids also contribute to other virulence mechanisms such as drug resistance, biofilm formation, and release of extracellular vesicles. In addition, lipids also affect the mechanical properties of the plasma membrane through the formation of packed microdomains composed mainly of sphingolipids and sterols. Changes in the composition of lipid microdomains have been shown to disrupt the localization of virulence factors and affect fungal pathogenicity. This review gathers evidence on the various roles of plasma membrane lipids in fungal virulence and how lipids might contribute to the different processes that occur during infection and treatment. Insight into the role of lipids in fungal virulence can lead to an improved understanding of the process of fungal pathogenesis and the development of new lipid-mediated therapeutic strategies. Published by Elsevier Ltd.

  17. When green and red mycology meet: Impressions from an interdisciplinary forum on virulence mechanisms of phyto- and human-pathogenic fungi.

    Science.gov (United States)

    Yu, Yidong; Hube, Bernhard; Kämper, Jörg; Meyer, Vera; Krappmann, Sven

    2017-10-03

    Fungal infections pose a constant threat to plants and humans, but detailed knowledge about pathogenesis, immunity, or virulence is rather scarce. Due to the fact that a certain overlap in the armoury of infection exists between plant- and human-pathogenic fungi, an interdisciplinary forum was held in October 2016 at the Institute for Clinical Microbiology, Immunology and Hygiene in Erlangen under the organisational umbrella from two special interest groups of German microbial societies. Scientific exchange and intense discussion of this timely topic was fostered by bringing together renowned experts in their respective fields to present their thoughts and recent findings in the course of a plenary lecture and six themed sessions, accompanied by oral and poster contributions of young researchers. By targeting the topic of fungal virulence mechanisms from various angles and in the context of plant and human hosts, some common grounds and exciting perspectives could be deduced during this vibrant scientific event.

  18. Effect of carbon nanofibre addition on the mechanical properties of ...

    Indian Academy of Sciences (India)

    Owing to the good mechanical properties of the carbon nanofibres (CNFs), they ... 8H Satin, T-300 carbon fabric (C-fabric) was used as rein- forcement. ... below. Absolute strength (S) in MPa at a given Vf: S = a + bVf + cV 2 f , where 'a' is the ...

  19. Influence of silicon addition on the mechanical properties and ...

    Indian Academy of Sciences (India)

    The addition of silicon to low-alloy steel allows to modify the materials' microstructure and thus to improve their ... Graphite supplied by TIMCAL) was added to the mixture powders ... cut into halves using a diamond disk in the Accutom-2 cut-.

  20. Fluid Mechanics Of Molten Metal Droplets In Additive Manufacturing

    Czech Academy of Sciences Publication Activity Database

    Tesař, Václav; Šonský, Jiří

    2016-01-01

    Roč. 4, č. 4 (2016), s. 403-412 ISSN 2046-0546 R&D Projects: GA ČR GA13-23046S Institutional support: RVO:61388998 Keywords : additive manufacturing * droplets * molten metal Subject RIV: BK - Fluid Dynamics http://www.witpress.com/elibrary/cmem-volumes/4/4/1545

  1. Metal Additive Manufacturing: A Review of Mechanical Properties (Postprint)

    Science.gov (United States)

    2016-04-21

    treated 1,257 1,436 Laser IN718 As built NA NA 590 845 11 NA 188 Heat treated 1,133 1,240 9 EBF3 IN718 As built XY 159 580 910 22 NA 189 EBF3 IN718 As... Raman S, Christensen A. 2010. Mechanical evaluation of porous titanium (Ti6Al4V) structures with electron beam melting (EBM). J. Mech. Behav. Biomed...335 Raman Studies of Carbon Nanostructures Ado Jorio and Antonio G. Souza Filho

  2. Additive contributions of two manganese-cored superoxide dismutases (MnSODs to antioxidation, UV tolerance and virulence of Beauveria bassiana.

    Directory of Open Access Journals (Sweden)

    Xue-Qin Xie

    Full Text Available The biocontrol potential of entomopathogenic fungi against arthropod pests depends on not only their virulence to target pests but tolerance to outdoor high temperature and solar UV irradiation. Two Beauveria bassiana superoxide dismutases (SODs, BbSod2 and BbSod3, were characterized as cytosolic and mitochondrial manganese-cored isoenzymes (MnSODs dominating the total SOD activity of the fungal entomopathogen under normal growth conditions. To probe their effects on the biocontrol potential of B. bassiana, ΔBbSod2, ΔBbSod3, and three hairpin RNA-interfered (RNAi mutants with the transcripts of both BbSod2 and BbSod3 being suppressed by 91-97% were constructed and assayed for various phenotypic parameters in conjunction with ΔBbSod2/BbSod2, ΔBbSod3/BbSod3 and wild-type (control strains. In normal cultures, the knockout and RNAi mutants showed significant phenotypic alterations, including delayed sporulation, reduced conidial yields, and impaired conidial quality, but little change in colony morphology. Their mycelia or conidia became much more sensitive to menadione or H(2O(2-induced oxidative stress but had little change in sensitivity to the hyperosmolarity of NaCl and the high temperature of 45°C. Accompanied with the decreased antioxidative capability, conidial tolerances to UV-A and UV-B irradiations were reduced by 16.8% and 45.4% for ΔBbSod2, 18.7% and 44.7% for ΔBbSod3, and ∼33.7% and ∼63.8% for the RNAi mutants, respectively. Their median lethal times (LT(50s against Myzus persicae apterae, which were topically inoculated under a standardized spray, were delayed by 18.8%, 14.5% and 37.1%, respectively. Remarkably, the effects of cytosolic BbSod2 and mitochondrial BbSod3 on the phenotypic parameters important for the fungal bioncontrol potential were additive, well in accordance with the decreased SOD activities and the increased superoxide levels in the knockout and RNAi mutants. Our findings highlight for the first time that

  3. Recent additions to fundament aspects of quantum mechanics

    International Nuclear Information System (INIS)

    Flamm, D.

    1991-01-01

    Problems like those of Schroedinger's can comprise quantum systems as classical systems, the measurement process and reality. After a reviewing the history of interpretation of quantum mechanics it is shown how a generalized algebraic quantum theory (e.g. G.G. Emch 1986) can tackle these problems and paradoxes. This theory treats systems with infinite degrees of freedom and open systems. It is applicable both to quantum as to classical systems and thus to the measurement process with its irreversibility. The usual linear Schroedinger equation is replaced by a non-linear one where the nonlinear terms reflect the interaction of the system with its environment or with the measuring apparatus. (Quittner) To appear also in 'Naturwissenschaft und Weltbild', 1992

  4. Structure of Vibrio cholerae ToxT reveals a mechanism for fatty acid regulation of virulence genes

    Energy Technology Data Exchange (ETDEWEB)

    Lowden, Michael J.; Skorupski, Karen; Pellegrini, Maria; Chiorazzo, Michael G.; Taylor, Ronald K.; Kull, F. Jon (Dartmouth)

    2010-03-04

    Cholera is an acute intestinal infection caused by the bacterium Vibrio cholerae. In order for V. cholerae to cause disease, it must produce two virulence factors, the toxin-coregulated pilus (TCP) and cholera toxin (CT), whose expression is controlled by a transcriptional cascade culminating with the expression of the AraC-family regulator, ToxT. We have solved the 1.9 {angstrom} resolution crystal structure of ToxT, which reveals folds in the N- and C-terminal domains that share a number of features in common with AraC, MarA, and Rob as well as the unexpected presence of a buried 16-carbon fatty acid, cis-palmitoleate. The finding that cis-palmitoleic acid reduces TCP and CT expression in V. cholerae and prevents ToxT from binding to DNA in vitro provides a direct link between the host environment of V. cholerae and regulation of virulence gene expression.

  5. Effect of addition of organo clay on mechanical properties and dynamic-mechanical based TPV

    International Nuclear Information System (INIS)

    Honorato, Luciana R.; Silva, Adriana A.; Soares, Bluma G.; Soares, Ketly P.

    2011-01-01

    The effect of organophilic clay on the mechanical and dynamical-mechanical properties of thermoplastic elastomers based on polypropylene (PP) and nitrile rubber (NBR) was investigated. The addition of clay was performed from a master batch prepared by a solution intercalation of NBR inside the clay galleries. Since the PP/NBR blend is highly incompatible, PP functionalized with maleic anhydride (PP-g-MA) and carboxylated NBR (XNBR) were employed as compatibilizing system together with triethylene-tetramine (TETA) used as coupling agent. The addition of Clay inside the elastomeric phase of the TPV resulted in a significant decrease of the elongation at break without changes on the tensile strength. The presence of clay also promoted a slight increase of the storage modulus and the glass transition temperature. The small angle X ray scattering confirmed the high dispersion of clay inside the TPV. Analysis of light scattering small angle (SAXS) confirmed the high dispersion of clay in the matrix of the TPV. (author)

  6. Differential virulence mechanisms of infectious hematopoietic necrosis virus in rainbow trout (Oncorhynchus mykiss) include host entry and virus replication kinetics

    Science.gov (United States)

    Penaranda, M.M.D.; Purcell, M.K.; Kurath, G.

    2009-01-01

    Host specificity is a phenomenon exhibited by all viruses. For the fish rhabdovirus infectious hematopoietic necrosis virus (IHNV), differential specificity of virus strains from the U and M genogroups has been established both in the field and in experimental challenges. In rainbow trout (Oncorhynchus mykiss), M IHNV strains are consistently more prevalent and more virulent than U IHNV. The basis of the differential ability of these two IHNV genogroups to cause disease in rainbow trout was investigated in live infection challenges with representative U and M IHNV strains. When IHNV was delivered by intraperitoneal injection, the mortality caused by U IHNV increased, indicating that the low virulence of U IHNV is partly due to inefficiency in entering the trout host. Analyses of in vivo replication showed that U IHNV consistently had lower prevalence and lower viral load than M IHNV during the course of infection. In analyses of the host immune response, M IHNV-infected fish consistently had higher and longer expression of innate immune-related genes such as Mx-1. This suggests that the higher virulence of M IHNV is not due to suppression of the immune response in rainbow trout. Taken together, the results support a kinetics hypothesis wherein faster replication enables M IHNV to rapidly achieve a threshold level of virus necessary to override the strong host innate immune response. ?? 2009 SGM.

  7. Changing the game: using integrative genomics to probe virulence mechanisms of the stem rust pathogen Puccinia graminis f. sp. tritici

    Directory of Open Access Journals (Sweden)

    Melania eFigueroa

    2016-02-01

    Full Text Available The recent resurgence of wheat stem rust caused by new virulent races of Puccinia graminis f. sp. tritici (Pgt poses a threat to food security. These concerns have catalyzed an extensive global effort towards controlling this disease. Substantial research and breeding programs target the identification and introduction of new stem rust resistance (Sr genes in cultivars for genetic protection against the disease. Such resistance genes typically encode immune receptor proteins that recognize specific components of the pathogen, known as avirulence (Avr proteins. A significant drawback to deploying cultivars with single Sr genes is that they are often overcome by evolution of the pathogen to escape recognition through alterations in Avr genes. Thus, a key element in achieving durable rust control is the deployment of multiple effective Sr genes in combination, either through conventional breeding or transgenic approaches, to minimize the risk of resistance breakdown. In this situation, evolution of pathogen virulence would require simultaneous changes in multiple Avr genes in order to bypass recognition. However, choosing the optimal Sr gene combinations to deploy is a challenge that requires detailed knowledge of the pathogen Avr genes with which they interact and the virulence phenotypes of Pgt existing in nature. Identifying specific Avr genes from Pgt will provide screening tools to enhance pathogen virulence monitoring, assess heterozygosity and propensity for mutation in pathogen populations, and confirm individual Sr gene functions in crop varieties carrying multiple effective resistance genes. Towards this goal, much progress has been made in assembling a high quality reference genome sequence for Pgt, as well as a Pan-genome encompassing variation between multiple field isolates with diverse virulence spectra. In turn this has allowed prediction of Pgt effector gene candidates based on known features of Avr genes in other plant pathogens

  8. Changing the Game: Using Integrative Genomics to Probe Virulence Mechanisms of the Stem Rust Pathogen Puccinia graminis f. sp. tritici.

    Science.gov (United States)

    Figueroa, Melania; Upadhyaya, Narayana M; Sperschneider, Jana; Park, Robert F; Szabo, Les J; Steffenson, Brian; Ellis, Jeff G; Dodds, Peter N

    2016-01-01

    The recent resurgence of wheat stem rust caused by new virulent races of Puccinia graminis f. sp. tritici (Pgt) poses a threat to food security. These concerns have catalyzed an extensive global effort toward controlling this disease. Substantial research and breeding programs target the identification and introduction of new stem rust resistance (Sr) genes in cultivars for genetic protection against the disease. Such resistance genes typically encode immune receptor proteins that recognize specific components of the pathogen, known as avirulence (Avr) proteins. A significant drawback to deploying cultivars with single Sr genes is that they are often overcome by evolution of the pathogen to escape recognition through alterations in Avr genes. Thus, a key element in achieving durable rust control is the deployment of multiple effective Sr genes in combination, either through conventional breeding or transgenic approaches, to minimize the risk of resistance breakdown. In this situation, evolution of pathogen virulence would require changes in multiple Avr genes in order to bypass recognition. However, choosing the optimal Sr gene combinations to deploy is a challenge that requires detailed knowledge of the pathogen Avr genes with which they interact and the virulence phenotypes of Pgt existing in nature. Identifying specific Avr genes from Pgt will provide screening tools to enhance pathogen virulence monitoring, assess heterozygosity and propensity for mutation in pathogen populations, and confirm individual Sr gene functions in crop varieties carrying multiple effective resistance genes. Toward this goal, much progress has been made in assembling a high quality reference genome sequence for Pgt, as well as a Pan-genome encompassing variation between multiple field isolates with diverse virulence spectra. In turn this has allowed prediction of Pgt effector gene candidates based on known features of Avr genes in other plant pathogens, including the related flax rust

  9. Host cell interactions of outer membrane vesicle-associated virulence factors of enterohemorrhagic Escherichia coli O157: Intracellular delivery, trafficking and mechanisms of cell injury

    Science.gov (United States)

    Greune, Lilo; Jarosch, Kevin-André; Steil, Daniel; Zhang, Wenlan; He, Xiaohua; Lloubes, Roland; Fruth, Angelika; Kim, Kwang Sik; Schmidt, M. Alexander; Dobrindt, Ulrich; Mellmann, Alexander; Karch, Helge

    2017-01-01

    Outer membrane vesicles (OMVs) are important tools in bacterial virulence but their role in the pathogenesis of infections caused by enterohemorrhagic Escherichia coli (EHEC) O157, the leading cause of life-threatening hemolytic uremic syndrome, is poorly understood. Using proteomics, electron and confocal laser scanning microscopy, immunoblotting, and bioassays, we investigated OMVs secreted by EHEC O157 clinical isolates for virulence factors cargoes, interactions with pathogenetically relevant human cells, and mechanisms of cell injury. We demonstrate that O157 OMVs carry a cocktail of key virulence factors of EHEC O157 including Shiga toxin 2a (Stx2a), cytolethal distending toxin V (CdtV), EHEC hemolysin, and flagellin. The toxins are internalized by cells via dynamin-dependent endocytosis of OMVs and differentially separate from vesicles during intracellular trafficking. Stx2a and CdtV-B, the DNase-like CdtV subunit, separate from OMVs in early endosomes. Stx2a is trafficked, in association with its receptor globotriaosylceramide within detergent-resistant membranes, to the Golgi complex and the endoplasmic reticulum from where the catalytic Stx2a A1 fragment is translocated to the cytosol. CdtV-B is, after its retrograde transport to the endoplasmic reticulum, translocated to the nucleus to reach DNA. CdtV-A and CdtV-C subunits remain OMV-associated and are sorted with OMVs to lysosomes. EHEC hemolysin separates from OMVs in lysosomes and targets mitochondria. The OMV-delivered CdtV-B causes cellular DNA damage, which activates DNA damage responses leading to G2 cell cycle arrest. The arrested cells ultimately die of apoptosis induced by Stx2a and CdtV via caspase-9 activation. By demonstrating that naturally secreted EHEC O157 OMVs carry and deliver into cells a cocktail of biologically active virulence factors, thereby causing cell death, and by performing first comprehensive analysis of intracellular trafficking of OMVs and OMV-delivered virulence factors

  10. Amoebapore is an important virulence factor of Entamoeba histolytica

    Indian Academy of Sciences (India)

    ... ap-a genes. The silenced transfectant was not virulent at all. These results demonstrate that important factors need to be expressed at the correct cellular location and that the parasite has additional internal control mechanisms such as transcriptional gene silencing which can prevent excess amounts of gene expression.

  11. Bacterial size matters: Multiple mechanisms controlling septum cleavage and diplococcus formation are critical for the virulence of the opportunistic pathogen Enterococcus faecalis

    Science.gov (United States)

    Salamaga, Bartłomiej; Prajsnar, Tomasz K.; Willemse, Joost; Bewley, Martin A.; Chau, Françoise

    2017-01-01

    Enterococcus faecalis is an opportunistic pathogen frequently isolated in clinical settings. This organism is intrinsically resistant to several clinically relevant antibiotics and can transfer resistance to other pathogens. Although E. faecalis has emerged as a major nosocomial pathogen, the mechanisms underlying the virulence of this organism remain elusive. We studied the regulation of daughter cell separation during growth and explored the impact of this process on pathogenesis. We demonstrate that the activity of the AtlA peptidoglycan hydrolase, an enzyme dedicated to septum cleavage, is controlled by several mechanisms, including glycosylation and recognition of the peptidoglycan substrate. We show that the long cell chains of E. faecalis mutants are more susceptible to phagocytosis and are no longer able to cause lethality in the zebrafish model of infection. Altogether, this work indicates that control of cell separation during division underpins the pathogenesis of E. faecalis infections and represents a novel enterococcal virulence factor. We propose that inhibition of septum cleavage during division represents an attractive therapeutic strategy to control infections. PMID:28742152

  12. Bacterial size matters: Multiple mechanisms controlling septum cleavage and diplococcus formation are critical for the virulence of the opportunistic pathogen Enterococcus faecalis.

    Directory of Open Access Journals (Sweden)

    Bartłomiej Salamaga

    2017-07-01

    Full Text Available Enterococcus faecalis is an opportunistic pathogen frequently isolated in clinical settings. This organism is intrinsically resistant to several clinically relevant antibiotics and can transfer resistance to other pathogens. Although E. faecalis has emerged as a major nosocomial pathogen, the mechanisms underlying the virulence of this organism remain elusive. We studied the regulation of daughter cell separation during growth and explored the impact of this process on pathogenesis. We demonstrate that the activity of the AtlA peptidoglycan hydrolase, an enzyme dedicated to septum cleavage, is controlled by several mechanisms, including glycosylation and recognition of the peptidoglycan substrate. We show that the long cell chains of E. faecalis mutants are more susceptible to phagocytosis and are no longer able to cause lethality in the zebrafish model of infection. Altogether, this work indicates that control of cell separation during division underpins the pathogenesis of E. faecalis infections and represents a novel enterococcal virulence factor. We propose that inhibition of septum cleavage during division represents an attractive therapeutic strategy to control infections.

  13. Influence of boron addition on the grain refinement and mechanical properties of AZ91 Mg alloy

    International Nuclear Information System (INIS)

    Suresh, M.; Srinivasan, A.; Ravi, K.R.; Pillai, U.T.S.; Pai, B.C.

    2009-01-01

    This article reports the effect of boron addition on the grain refinement efficiency and mechanical properties of AZ91 magnesium alloy. The results show that the addition of boron in the form of Al-4B master alloy, significantly refines the grain size of AZ91 alloy. This refinement is due to the presence of AlB 2 particles, which act as potential nucleants for Mg grains. Improved mechanical properties are obtained with the addition of boron due to the finer grains.

  14. Mechanical Properties Analysis Of Composite Magnetic Base On hexa ferrite And Polyester Or Epoxy Matrix With Silane Additive Addition

    International Nuclear Information System (INIS)

    Sudirman; Ridwan; Mujamilah; K K, Aloma; Rembulan, Marisa; Fitriyanti

    2003-01-01

    Application of composite magnetic especially hexa ferrite magnet for industry and home industry in Indonesia has been used. Research purposes were making composite magnetic by mixing hexa ferrite powder with polyester or epoxy and studying the effect of coupling agent 3-aminopropyltriethoxysilane (3-APE) addition on mechanical properties of composite magnetic. The coupling agent may increase bonding properties between magnetic powder and matrix polymer, so that tensile strength of magnetic composite will increase without decreasing the magnetic properties. Magnetic powder (SrM or BaM) wich be coated by coupling agent were added to matrix polyester and mekpo or epoxy and versamid, mixed until homogen then pressing into to the dumbbell form molding. For epoxy matrix, pressing was done in hot press at 70 deg. C and 150 kg/cm 2 following by cooling in cold press, while for polyester matrix pressing was done in hydraulic press and following by curing at 70 deg. C in an oven for 1 hour. The composition of magnetic powder were varied to 30, 40 and 50% volume fraction and coupling agent were varied to 5, 10 and 15 ml for every volume fraction. The result showed that 10 ml added of coupling agent was give best mechanical properties both polyester and epoxy matrix. However generally, increasing of magnetic powder content decreased the tensile strength of magnetic composite. The properties of magnetic composite SrM was better than BaM either in polyester or epoxy matrix

  15. Mucoid conversion of Pseudomonas aeruginosa by hydrogen peroxide: a mechanism for virulence activation in the cystic fibrosis lung

    DEFF Research Database (Denmark)

    Mathee, Kalai; Ciofu, Oana; Sternberg, Claus

    1999-01-01

    leukocytes (PMNs), which release free oxygen radicals such as H(2)O(2) The mucoid phenotype among the strains infecting CF patients indicates overproduction of a linear polysaccharide called alginate. To mimic the inflammatory environment of the CF lung, P. aeruginosa PAO1, a typical non-mucoid strain....... These findings indicate that gene activation in bacteria by toxic oxygen radicals, similar to that found in plants and mammalian cells, may serve as a defence mechanism for the bacteria. This suggests that mucoid conversion is a response to oxygen radical exposure and that this response is a mechanism of defence...... by the bacteria. This is the first report to show that PMNs and their oxygen radicals can cause this phenotypic and genotypic change which is so typical of the intractable form of P. aeruginosa in the CF lung. These findings may provide a basis for the development of anti-oxidant and anti-inflammatory therapy...

  16. Influence of niobium addition on the high temperature mechanical properties of a centrifugally cast HP alloy

    International Nuclear Information System (INIS)

    Andrade, A.R.; Bolfarini, C.; Ferreira, L.A.M.; Vilar, A.A.A.; Souza Filho, C.D.; Bonazzi, L.H.C.

    2015-01-01

    The influence of niobium addition on the mechanical properties at high temperature of HP alloy has been investigated. Two HP alloys were centrifugally cast with a similar chemical composition differing only in the niobium content. Low strain rate high temperature tensile tests and creep-rupture tests were performed in the range of 900–1100 °C, and the results compared between the alloys. According to the results, the high temperature mechanical behavior of both alloys is controlled by several factors like solid solution, network of eutectic carbides, intradendritic precipitation and dendrite spacing. A significant increase in the mechanical properties for the HP alloy with niobium addition was found within the temperature range of 900–1050 °C. Beyond this temperature the mechanical behavior of both alloys is basically the same

  17. Convergent and divergent pathways decoding hierarchical additive mechanisms in treating cerebral ischemia-reperfusion injury.

    Science.gov (United States)

    Zhang, Ying-Ying; Li, Hai-Xia; Chen, Yin-Ying; Fang, Hong; Yu, Ya-Nan; Liu, Jun; Jing, Zhi-Wei; Wang, Zhong; Wang, Yong-Yan

    2014-03-01

    Cerebral ischemia is considered to be a highly complex disease resulting from the complicated interplay of multiple pathways. Disappointedly, most of the previous studies were limited to a single gene or a single pathway. The extent to which all involved pathways are translated into fusing mechanisms of a combination therapy is of fundamental importance. We report an integrative strategy to reveal the additive mechanism that a combination (BJ) of compound baicalin (BA) and jasminoidin (JA) fights against cerebral ischemia based on variation of pathways and functional communities. We identified six pathways of BJ group that shared diverse additive index from 0.09 to 1, which assembled broad cross talks from seven pathways of BA and 16 pathways of JA both at horizontal and vertical levels. Besides a total of 60 overlapping functions as a robust integration background among the three groups based on significantly differential subnetworks, additive mechanism with strong confidence by networks altered functions. These results provide strong evidence that the additive mechanism is more complex than previously appreciated, and an integrative analysis of pathways may suggest an important paradigm for revealing pharmacological mechanisms underlying drug combinations. © 2013 John Wiley & Sons Ltd.

  18. Effect of Zn addition on microstructure and mechanical properties of an Al–Mg–Si alloy

    Directory of Open Access Journals (Sweden)

    Lizhen Yan

    2014-04-01

    Full Text Available In the present work, an Al–0.66Mg–0.85Si–0.2Cu alloy with Zn addition was investigated by electron back scattering diffraction (EBSD, high resolution electron microscopy (HREM, tensile and Erichsen tests. The mechanical properties of the alloy after pre-aging met the standards of sheet forming. After paint baking, the yield strength of the alloy was improved apparently. GP(II zones and ηʹ phases were formed during aging process due to Zn addition. With the precipitation of GP zones, β″ phases, GP(II zones and ηʹ phases, the alloys displayed excellent mechanical properties.

  19. Effect of Trace Be and Sc Additions on the Mechanical Properties of A357 Alloys

    Directory of Open Access Journals (Sweden)

    Yu-Chih Tzeng

    2018-03-01

    Full Text Available The effect of the addition of Be and Sc on the microstructure and mechanical properties of A357 alloy were systematically investigated. The results show that the addition of small amounts of Be and Sc could change the acicular structure of iron-bearing intermetallic compounds to harmless compact Al-Fe-Si and Sc-Fe iron-bearing intermetallic compounds. Compact iron-bearing intermetallic compounds could improve fluidity, causing a reduction in interdendritic shrinkage during solidification. The addition of 0.05 wt % Be enhanced the quality index of the A357 alloy by 11% and increased the notch-yield ratio of fracture toughness by 4.5%. In contrast, the addition of 0.05 wt % Sc increased the quality index and the notch to yield ratio of fracture toughness up to 17% and 9%, respectively. Therefore, the microstructure and mechanical properties of the A357 alloy could be improved by substituting Be with Sc.

  20. Antifungal activity of phlorotannins against dermatophytes and yeasts: approaches to the mechanism of action and influence on Candida albicans virulence factor.

    Directory of Open Access Journals (Sweden)

    Graciliana Lopes

    Full Text Available In the last few decades, fungal infections, particularly nosocomial, increased all around the world. This increment stimulated the search for new antifungal agents, especially those derived from nature. Among natural products, those from marine sources have gained prominence in the last years. Purified phlorotannins extracts from three brown seaweeds (Cystoseira nodicaulis (Withering M. Roberts, Cystoseira usneoides (Linnaeus M. Roberts and Fucus spiralis Linnaeus were screened for their antifungal activity against human pathogenic yeast and filamentous fungi. The purified phlorotannins extracts from the studied seaweeds displayed fungistatic and fungicidal activity against yeast and dermatophytes, respectively, pointing to their interest as anti-dermatophyte agent. C. albicans ATCC 10231 was the most susceptible among yeast, while Epidermophyton floccosum and Trichophyton rubrum were the most susceptible among dermatophytes. Since the antifungal mechanism constitutes an important strategy for limiting the emergence of resistance to the commercially available agents, the mechanism of action of purified phlorotannins extracts was approached. C. nodicaulis and C. usneoides seem to act by affecting the ergosterol composition of the cell membrane of yeast and dermatophyte, respectively. F. spiralis influenced the dermatophyte cell wall composition by reducing the levels of chitin. Phlorotannins also seem to affect the respiratory chain function, as all of the studied species significantly increased the activity of mitochondrial dehydrogenases and increased the incorporation of rhodamine 123 by yeast cells. Phlorotannins from F. spiralis inhibited the dimorphic transition of Candida albicans, leading to the formation of pseudohyphae with diminished capacity to adhere to epithelial cells. This finding is associated with a decrease of C. albicans virulence and capacity to invade host cells and can be potentially interesting for combined antifungal

  1. How does tissue regeneration influence the mechanical behavior of additively manufactured porous biomaterials?

    Science.gov (United States)

    Hedayati, R; Janbaz, S; Sadighi, M; Mohammadi-Aghdam, M; Zadpoor, A A

    2017-01-01

    Although the initial mechanical properties of additively manufactured porous biomaterials are intensively studied during the last few years, almost no information is available regarding the evolution of the mechanical properties of implant-bone complex as the tissue regeneration progresses. In this paper, we studied the effects of tissue regeneration on the static and fatigue behavior of selective laser melted porous titanium structures with three different porosities (i.e. 77, 81, and 85%). The porous structures were filled with four different polymeric materials with mechanical properties in the range of those observed for de novo bone (0.7GPamanufactured and filled porous structures were then determined. The static mechanical properties and fatigue life (including endurance limit) of the porous structures were found to increase by factors 2-7, even when they were filled with polymeric materials with relatively low mechanical properties. The relative increase in the mechanical properties was much higher for the porous structures with lower porosities. Moreover, the increase in the fatigue life was more notable as compared to the increase in the static mechanical properties. Such large values of increase in the mechanical properties with the progress of bone tissue regeneration have implications in terms of mechanical stimulus for bone tissue regeneration. Copyright © 2016 Elsevier Ltd. All rights reserved.

  2. Effects of Bi Addition on the Microstructure and Mechanical Properties of Nanocrystalline Ag Coatings

    Directory of Open Access Journals (Sweden)

    Yuxin Wang

    2017-08-01

    Full Text Available In this study we investigated the effects of Bi addition on the microstructure and mechanical properties of an electrodeposited nanocrystalline Ag coating. Microstructural features were investigated with transmission electron microscopy (TEM. The results indicate that the addition of Bi introduced nanometer-scale Ag-Bi solid solution particles and more internal defects to the initial Ag microstructures. The anisotropic elastic-plastic properties of the Ag nanocrystalline coating with and without Bi addition were examined with nanoindentation experiments in conjunction with the recently-developed inverse method. The results indicate that the as-deposited nanocrystalline Ag coating contained high mechanical anisotropy. With the addition of 1 atomic percent (at% Bi, the anisotropy within Ag-Bi coating was very small, and yield strength of the nanocrystalline Ag-Bi alloy in both longitudinal and transverse directions were improved by over 100% compared to that of Ag. On the other hand, the strain-hardening exponent of Ag-Bi was reduced to 0.055 from the original 0.16 of the Ag coating. Furthermore, the addition of Bi only slightly increased the electrical resistivity of the Ag-Bi coating in comparison to Ag. Results of our study indicate that Bi addition is a promising method for improving the mechanical and physical performances of Ag coating for electrical contacts.

  3. Improving Student Understanding of Addition of Angular Momentum in Quantum Mechanics

    Science.gov (United States)

    Zhu, Guangtian; Singh, Chandralekha

    2013-01-01

    We describe the difficulties advanced undergraduate and graduate students have with concepts related to addition of angular momentum in quantum mechanics. We also describe the development and implementation of a research-based learning tool, Quantum Interactive Learning Tutorial (QuILT), to reduce these difficulties. The preliminary evaluation…

  4. Mechanical behavior of polymer-matrix biocomposites modified by nano/micro additives

    Czech Academy of Sciences Publication Activity Database

    Suchý, Tomáš; Balík, Karel; Sucharda, Zbyněk; Černý, Martin; Sochor, M.

    -, 77-78 (2008), s. 8-10 ISSN 1429-7248. [Conference Biomaterials in Medicine and Veterinary Medicine /18./. Rytro, 13.11.2008-16.11.2008] R&D Projects: GA ČR(CZ) GA106/06/1576 Institutional research plan: CEZ:AV0Z30460519 Keywords : additives * calcium phosphates * mechanical properties Subject RIV: JI - Composite Materials

  5. Analytical relationships for prediction of the mechanical properties of additively manufactured porous biomaterials

    NARCIS (Netherlands)

    Zadpoor, A.A.; Hedayati, R.

    2016-01-01

    Recent developments in additive manufacturing techniques have motivated an increasing number of researchers to study regular porous biomaterials that are based on repeating unit cells. The physical and mechanical properties of such porous biomaterials have therefore received increasing attention

  6. On the lubrication mechanism of detonation-synthesis nanodiamond additives in lubricant composites

    Science.gov (United States)

    Shepelevskii, A. A.; Esina, A. V.; Voznyakovskii, A. P.; Fadin, Yu. A.

    2017-09-01

    The lubrication of detonation-synthesis diamond additives in lubricant composites has been discussed. The mechanism of interaction between nanodiamonds and friction surface has been shown to depend on the applied load. Two models of the lubrication of nanodiamonds and the conditions for their validity have also been proposed.

  7. A study on the mechanical properties of additive manufactured polymer materials

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Dong Bum; Lee, In Hwan; Cho, Hae Yong [Dept. of Mechanical Engineering, Chungbuk National University, Cheongju (Korea, Republic of)

    2015-08-15

    Traditionally, additive manufacturing (AM) technology has been used to fabricate prototypes in the early development phase of a product. This technology is being applied to release manufacturing of a product because of its low cost and fast fabrication. AM technology is a process of joining materials to fabricate a product from the 3D CAD data in a layer-by-layer manner. The orientation of a layer during manufacturing can affect the mechanical properties of the product because of its anisotropy. In this paper, tensile testing of polymer-based specimens were built with a typical AM process (FDM, PolyJet and SLA) to study the mechanical properties of the AM materials. The ASTM D 638 tensile testing standard was followed for building the specimens. The mechanical properties of the specimens were determined on the basis of stress-strain curves formed by tensile tests. In addition, the fracture surfaces of the specimens were observed by SEM to analyze the results.

  8. Insight into bacterial virulence mechanisms against host immune response via the Yersinia pestis-human protein-protein interaction network.

    Science.gov (United States)

    Yang, Huiying; Ke, Yuehua; Wang, Jian; Tan, Yafang; Myeni, Sebenzile K; Li, Dong; Shi, Qinghai; Yan, Yanfeng; Chen, Hui; Guo, Zhaobiao; Yuan, Yanzhi; Yang, Xiaoming; Yang, Ruifu; Du, Zongmin

    2011-11-01

    A Yersinia pestis-human protein interaction network is reported here to improve our understanding of its pathogenesis. Up to 204 interactions between 66 Y. pestis bait proteins and 109 human proteins were identified by yeast two-hybrid assay and then combined with 23 previously published interactions to construct a protein-protein interaction network. Topological analysis of the interaction network revealed that human proteins targeted by Y. pestis were significantly enriched in the proteins that are central in the human protein-protein interaction network. Analysis of this network showed that signaling pathways important for host immune responses were preferentially targeted by Y. pestis, including the pathways involved in focal adhesion, regulation of cytoskeleton, leukocyte transendoepithelial migration, and Toll-like receptor (TLR) and mitogen-activated protein kinase (MAPK) signaling. Cellular pathways targeted by Y. pestis are highly relevant to its pathogenesis. Interactions with host proteins involved in focal adhesion and cytoskeketon regulation pathways could account for resistance of Y. pestis to phagocytosis. Interference with TLR and MAPK signaling pathways by Y. pestis reflects common characteristics of pathogen-host interaction that bacterial pathogens have evolved to evade host innate immune response by interacting with proteins in those signaling pathways. Interestingly, a large portion of human proteins interacting with Y. pestis (16/109) also interacted with viral proteins (Epstein-Barr virus [EBV] and hepatitis C virus [HCV]), suggesting that viral and bacterial pathogens attack common cellular functions to facilitate infections. In addition, we identified vasodilator-stimulated phosphoprotein (VASP) as a novel interaction partner of YpkA and showed that YpkA could inhibit in vitro actin assembly mediated by VASP.

  9. PAH growth initiated by propargyl addition: Mechanism development and computational kinetics

    KAUST Repository

    Raj, Abhijeet Dhayal

    2014-04-24

    Polycyclic aromatic hydrocarbon (PAH) growth is known to be the principal pathway to soot formation during fuel combustion, as such, a physical understanding of the PAH growth mechanism is needed to effectively assess, predict, and control soot formation in flames. Although the hydrogen abstraction C2H2 addition (HACA) mechanism is believed to be the main contributor to PAH growth, it has been shown to under-predict some of the experimental data on PAHs and soot concentrations in flames. This article presents a submechanism of PAH growth that is initiated by propargyl (C 3H3) addition onto naphthalene (A2) and the naphthyl radical. C3H3 has been chosen since it is known to be a precursor of benzene in combustion and has appreciable concentrations in flames. This mechanism has been developed up to the formation of pyrene (A4), and the temperature-dependent kinetics of each elementary reaction has been determined using density functional theory (DFT) computations at the B3LYP/6-311++G(d,p) level of theory and transition state theory (TST). H-abstraction, H-addition, H-migration, β-scission, and intramolecular addition reactions have been taken into account. The energy barriers of the two main pathways (H-abstraction and H-addition) were found to be relatively small if not negative, whereas the energy barriers of the other pathways were in the range of (6-89 kcal·mol-1). The rates reported in this study may be extrapolated to larger PAH molecules that have a zigzag site similar to that in naphthalene, and the mechanism presented herein may be used as a complement to the HACA mechanism to improve prediction of PAH and soot formation. © 2014 American Chemical Society.

  10. Effect of V or Zr addition on the mechanical properties of the mechanically alloyed Al-8wt%Ti alloys

    International Nuclear Information System (INIS)

    Moon, I.H.; Lee, J.H.; Lee, K.M.; Kim, Y.D.

    1995-01-01

    Mechanical alloying (MA) of Al-Ti alloy, being a solid state process, offers the unique advantage of producing homogeneous and fine dispersions of thermally stable Al 3 Ti phase, where the formation of the fine Al 3 Ti phase by the other method is restricted from the thermodynamic viewpoint. The MA Al-Ti alloys show substantially higher strength than the conventional Al alloys at the elevated temperature due to the presence of Al 3 Ti as well as Al 4 C 3 and Al 2 O 3 , of which the last two phases were introduced during MA process. The addition of V or Zr to Al-Ti alloy was known to decrease the lattice mismatch between the intermetallic compound and the aluminum matrix, and such decrease in lattice mismatching can influence positively the high temperature mechanical strength of the MA Al-Ti by increasing the resistance to dispersoid coarsening at the elevated temperature. In the present study, therefore, the mechanical behavior of the MA Al-Ti-V and Al-Ti-Zr alloys were investigated in order to evaluate the effect of V or Zr addition on the mechanical properties of the MA Al-8Ti alloy at high temperature

  11. Pathogenic Leptospira: Advances in understanding the molecular pathogenesis and virulence

    Science.gov (United States)

    Ghazaei, Ciamak

    2018-01-01

    Leptospirosis is a common zoonotic disease has emerged as a major public health problem, with developing countries bearing disproportionate burdens. Although the diverse range of clinical manifestations of the leptospirosis in humans is widely documented, the mechanisms through which the pathogen causes disease remain undetermined. In addition, leptospirosis is a much-neglected life-threatening disease although it is one of the most important zoonoses occurring in a diverse range of epidemiological distribution. Recent advances in molecular profiling of pathogenic species of the genus Leptospira have improved our understanding of the evolutionary factors that determine virulence and mechanisms that the bacteria employ to survive. However, a major impediment to the formulation of intervention strategies has been the limited understanding of the disease determinants. Consequently, the association of the biological mechanisms to the pathogenesis of Leptospira, as well as the functions of numerous essential virulence factors still remain implicit. This review examines recent advances in genetic screening technologies, the underlying microbiological processes, the virulence factors and associated molecular mechanisms driving pathogenesis of Leptospira species. PMID:29445617

  12. Effect of the addition of mixture of plant components on the mechanical properties of wheat bread

    Science.gov (United States)

    Wójcik, Monika; Dziki, Dariusz; Biernacka, Beata; Różyło, Renata; Miś, Antoni; Hassoon, Waleed H.

    2017-10-01

    Instrumental methods of measuring the mechanical properties of bread can be used to determine changes in the properties of it during storage, as well as to determine the effect of various additives on the bread texture. The aim of this study was to investigate the effect of the mixture of plant components on the physical properties of wheat bread. In particular, the mechanical properties of the crumb and crust were studied. A sensory evaluation of the end product was also performed. The mixture of plant components included: carob fiber, milled grain red quinoa and black oat (1:2:2) - added at 0, 5, 10, 15, 20, 25 % - into wheat flour. The results showed that the increase of the addition of the proposed additive significantly increased the water absorption of flour mixtures. Moreover, the use of the mixture of plant components above 5% resulted in the increase of bread volume and decrease of crumb density. Furthermore, the addition of the mixture of plant components significantly affected the mechanical properties of bread crumb. The hardness of crumb also decreased as a result of the mixture of plant components addition. The highest cohesiveness was obtained for bread with 10% of additive and the lowest for bread with 25% of mixture of plant components. Most importantly, the enrichment of wheat flour with the mixture of plant components significantly reduced the crust failure force and crust failure work. The results of sensory evaluation showed that the addition of the mixture of plant components of up to 10% had little effect on bread quality.

  13. Virulence Factors IN Fungi OF Systemic Mycoses

    Directory of Open Access Journals (Sweden)

    KUROKAWA Cilmery Suemi

    1998-01-01

    Full Text Available Pathogenic fungi that cause systemic mycoses retain several factors which allow their growth in adverse conditions provided by the host, leading to the establishment of the parasitic relationship and contributing to disease development. These factors are known as virulence factors which favor the infection process and the pathogenesis of the mycoses. The present study evaluates the virulence factors of pathogenic fungi such as Blastomyces dermatitidis, Coccidioides immitis, Cryptococcus neoformans, Histoplasma capsulatum and Paracoccidioides brasiliensis in terms of thermotolerance, dimorphism, capsule or cell wall components as well as enzyme production. Virulence factors favor fungal adhesion, colonization, dissemination and the ability to survive in hostile environments and elude the immune response mechanisms of the host. Both the virulence factors presented by different fungi and the defense mechanisms provided by the host require action and interaction of complex processes whose knowledge allows a better understanding of the pathogenesis of systemic mycoses.

  14. Jasmonate-dependent modifications of the pectin matrix during potato development function as a defense mechanism targeted by Dickeya dadantii virulence factors.

    Science.gov (United States)

    Taurino, Marco; Abelenda, Jose A; Río-Alvarez, Isabel; Navarro, Cristina; Vicedo, Begonya; Farmaki, Theodora; Jiménez, Pedro; García-Agustín, Pilar; López-Solanilla, Emilia; Prat, Salomé; Rojo, Enrique; Sánchez-Serrano, José J; Sanmartín, Maite

    2014-02-01

    The plant cell wall constitutes an essential protection barrier against pathogen attack. In addition, cell-wall disruption leads to accumulation of jasmonates (JAs), which are key signaling molecules for activation of plant inducible defense responses. However, whether JAs in return modulate the cell-wall composition to reinforce this defensive barrier remains unknown. The enzyme 13-allene oxide synthase (13-AOS) catalyzes the first committed step towards biosynthesis of JAs. In potato (Solanum tuberosum), there are two putative St13-AOS genes, which we show here to be differentially induced upon wounding. We also determine that both genes complement an Arabidopsis aos null mutant, indicating that they encode functional 13-AOS enzymes. Indeed, transgenic potato plants lacking both St13-AOS genes (CoAOS1/2 lines) exhibited a significant reduction of JAs, a concomitant decrease in wound-responsive gene activation, and an increased severity of soft rot disease symptoms caused by Dickeya dadantii. Intriguingly, a hypovirulent D. dadantii pel strain lacking the five major pectate lyases, which causes limited tissue maceration on wild-type plants, regained infectivity in CoAOS1/2 plants. In line with this, we found differences in pectin methyl esterase activity and cell-wall pectin composition between wild-type and CoAOS1/2 plants. Importantly, wild-type plants had pectins with a lower degree of methyl esterification, which are the substrates of the pectate lyases mutated in the pel strain. These results suggest that, during development of potato plants, JAs mediate modification of the pectin matrix to form a defensive barrier that is counteracted by pectinolytic virulence factors from D. dadantii. © 2013 The Authors The Plant Journal © 2013 John Wiley & Sons Ltd.

  15. Mechanical properties of sheet metal components with local reinforcement produced by additive manufacturing

    Science.gov (United States)

    Ünsal, Ismail; Hama-Saleh, R.; Sviridov, Alexander; Bambach, Markus; Weisheit, A.; Schleifenbaum, J. H.

    2018-05-01

    New technological challenges like electro-mobility pose an increasing demand for cost-efficient processes for the production of product variants. This demand opens the possibility to combine established die-based manufacturing methods and innovative, dieless technologies like additive manufacturing [1, 2]. In this context, additive manufacturing technologies allow for the weight-efficient local reinforcement of parts before and after forming, enabling manufacturers to produce product variants from series parts [3]. Previous work by the authors shows that the optimal shape of the reinforcing structure can be determined using sizing optimization. Sheet metal parts can then be reinforced using laser metal deposition. The material used is a pearlite-reduced, micro-alloyed steel (ZE 630). The aim of this paper is to determine the effect of the additive manufacturing process on the material behavior and the mechanical properties of the base material and the resulting composite material. The parameters of the AM process are optimized to reach similar material properties in the base material and the build-up volume. A metallographic analysis of the parts is presented, where the additive layers, the base material and also the bonding between the additive layers and the base material are analyzed. The paper shows the feasibility of the approach and details the resulting mechanical properties and performance.

  16. The role of additives in the recombination luminescence mechanism of irradiated 2-methyltetrahydrofuran glasses

    International Nuclear Information System (INIS)

    Krauss, K.H.; Boes, J.

    1981-01-01

    The radiothermoluminescence (RTL) of γ-irradiated pure glassy 2-methyltetrahydrofuran (2-MTHF) and of 2-MTHF glasses containing additives was measured. For pure 2-MTHF a very weak luminescence peak at 93 K (heating rate 0,05 K/s) was found which in the presence of certain additives was enhanced by several orders of magnitude. Using data of radiothermoluminescence, absorption and phosphorescence measurements and bleaching experiments an attempt was made to derive a reaction mechanism. It was found to exist different possibilities for activation the ionic species to give recombination luminescence. (author)

  17. THE INFLUENCE OF NANO-ADDITIVES ON THE PHYSICO-MECHANICAL PROPERTIES FIBER REINFORCED CONCRETE

    Directory of Open Access Journals (Sweden)

    Евгений Петрович Матус

    2018-02-01

    Full Text Available The paper discusses the current state of research of the effect of nanodispersed additives on the properties of fiber reinforced portland cement composites. The results of tests on the strength and viscosity of solutions and samples of fine-grained concrete based on cement binder and cement steel and basalt fiber, carbon nanotubes, silicates, nanosized powder of CaО and degidrol. The effect of methods of introduction of the mixture of nano-additives on the clutch fibers with the matrix. Analysis of experimental data showed the absence of a systematic positive effect of increasing the mechanical strength of the composites due to the introduction of carbon nanotubes.

  18. Structure and mechanical properties of TiZr binary alloy after Al addition

    International Nuclear Information System (INIS)

    Jiang, X.J.; Jing, R.; Liu, C.Y.; Ma, M.Z.; Liu, R.P.

    2013-01-01

    Microstructure and mechanical properties of hot-rolled TiZrAl alloys were studied. The results showed that the microstructure of all alloys mainly consisted of lamellar α phase. The thickness of the lamellar α phase gradually increased with increasing aluminum content. Moreover, large numbers of stacking faults was observed in Ti–25Zr–15Al (at%) alloy. The aluminum addition strongly affected the mechanical properties of the TiZrAl alloys. With increased aluminum contents, the strength increased evidently, whereas, the elongation decreased. Ti–25Zr–15Al (at%) with the highest aluminum contents in all alloys, possessed the highest tensile strength (σ b =1319 MPa), i.e. strengthened by 41% compared with Ti–25Zr (at%) alloy, and still retained the elongation of 5.5%. According to the classical size and/or modulus misfits model, the effect of aluminum addition was significant in TiZr alloys because of the considerable misfits between aluminum and zirconium

  19. Mechanical Behavior of Additive Manufactured Layered Materials, Part 2: Stainless Steels

    Science.gov (United States)

    2015-04-30

    materials. Elsevier, Oxford; 2007: 416 -420. [19] Deng, D., Chen, R., Sun, Q. and Li, X. Microstructural study of 17-4PH stainless steel after plasma...1 Mechanical Behavior of Additive Manufactured Layered Materials, Part 2: Stainless Steels * Todd M. Mower † and Michael J. Long M.I.T. Lincoln... stainless steel alloys produced with Direct Metal Laser Sintering (DMLS) was measured and is compared to that of similar conventional materials

  20. MECHANICAL PROPERTIES OF PARTS OF MEDICAL PRODUCTS PRODUCED USING ADDITIVE MANUFACTURING TECHNOLOGIES

    Directory of Open Access Journals (Sweden)

    Filip Górski

    2017-06-01

    Full Text Available The paper presents results of tests conducted on the elements of medical devices - slings used with medical lifts - manufactured using additive technologies. Project assumptions were: to produce 100 samples of clips with varying design, material and orientation parameter. Samples were manufactured using FDM and SLA processes and then tested for mechanical strength, load transmission and functionality, using certified equipment. Paper shows full methodology and obtained test results.

  1. Structural and mechanical characterization of custom design cranial implant created using additive manufacturing

    OpenAIRE

    Khaja Moiduddin; Saied Darwish; Abdulrahman Al-Ahmari; Sherif ElWatidy; Ashfaq Mohammad; Wadea Ameen

    2017-01-01

    Background: Reconstruction of customized cranial implants with a mesh structure using computer-assisted design and additive manufacturing improves the implant design, surgical planning, defect evaluation, implant-tissue interaction and surgeon's accuracy. The objective of this study is to design, develop and fabricate cranial implant with mechanical properties closer to that of bone and drastically decreases the implant failure and to improve the esthetic outcome in cranial surgery with preci...

  2. Microstructure and mechanical properties of 304L steel fabricated by arc additive manufacturing

    Directory of Open Access Journals (Sweden)

    Ji Lei

    2017-01-01

    Full Text Available For 304L large structural parts used in nuclear power, it is hard and costly to fabricate and machine traditionally. Wire arc additive manufacturing (WAAM has low cost and high material utilization, which provides an efficient way to fabricate the large structural parts. So in this study, WAAM is used to fabricate the parts of 304L stainless steel. Through the tensile test and metallographic analysis, the mechanical properties and microstructure of the 304L stainless steel fabricated by WAAM were explored. The results indicate that with the layers depositing, the cooling rate becomes slower, the dendrites become thicker and the morphology becomes more stable. Due to the existence of dendrites, the grain boundary strengthening effect is different between the transverse direction and longitudinal direction, and resulting in anisotropy of mechanical properties. However, the mechanical properties of the parts correspond to the forged piece, which lays the foundation for future applications.

  3. Mechanical and wear properties of pre-alloyed molybdenum P/M steels with nickel addition

    Directory of Open Access Journals (Sweden)

    Yamanoglu R.

    2012-01-01

    Full Text Available The aim of this study is to understand the effect of nickel addition on mechanical and wear properties of molybdenum and copper alloyed P/M steel. Specimens with three different nickel contents were pressed under 400 MPa and sintered at 1120ºC for 30 minutes then rapidly cooled. Microstructures and mechanical properties (bending strength, hardness and wear properties of the sintered specimens were investigated in detail. Metallographical investigations showed that the microstructures of consolidated specimens consist of tempered martensite, bainite, retained austenite and pores. It is also reported that the amount of pores varies depending on the nickel concentration of the alloys. Hardness of the alloys increases with increasing nickel content. Specimens containing 2% nickel showed minimum pore quantity and maximum wear resistance. The wear mechanism changed from abrasive wear at low nickel content to adhesive wear at higher nickel content.

  4. Effect of the Addition of Carbon Nanomaterials on Electrical and Mechanical Properties of Wood Plastic Composites

    Directory of Open Access Journals (Sweden)

    Xingli Zhang

    2017-11-01

    Full Text Available Wood Plastic Composites (WPCs are a new generation of green composites that could optimize the use of harvested trees and increase the entire value chain. In this study, the electrical and mechanical properties of WPCs containing carbon blacks (CB, flake graphite (FG and carbon nanotubes (CNTs have been investigated. The electrical property of WPCs is improved significantly owing to the introduction of these carbon nanomaterial fillers. The volume and surface resistivity values of the investigated composites all obviously decreased with the increase in filler content, especially CNTs, which displayed the most satisfactory results. Based on a series of laboratory experiments carried out to investigate the mechanical performance, it can be concluded that the addition of the carbon nanomaterial fillers decreases the mechanical properties of WPCs slightly with the increase in filler content because of the weak interfacial interactions between the fillers and polymer matrix.

  5. Virulence-associated genome mutations of murine rotavirus identified by alternating serial passages in mice and cell cultures.

    Science.gov (United States)

    Tsugawa, Takeshi; Tatsumi, Masatoshi; Tsutsumi, Hiroyuki

    2014-05-01

    Although significant clinical efficacy and safety of rotavirus vaccines were recently revealed in many countries, the mechanism of their attenuation is not well understood. We passaged serially a cell culture-adapted murine rotavirus EB strain in mouse pups or in cell cultures alternately and repeatedly and fully sequenced all 11 genes of 21 virus samples passaged in mice or in cell cultures. Sequence analysis revealed that mouse-passaged viruses that regained virulence almost consistently acquired four kinds of amino acid (aa) substitutions in VP4 and substitution in aa 37 (Val to Ala) in NSP4. In addition, they gained and invariably conserved the 3' consensus sequence in NSP1. The molecular changes occurred along with the acquisition of virulence during passages in mice and then disappeared following passages in cell cultures. Intraperitoneal injection of recombinant NSP4 proteins confirmed the aa 37 site as important for its diarrheagenic activity in mice. These genome changes are likely to be correlated with rotavirus virulence. Serial passage of a virulent wild-type virus in vitro often results in loss of virulence of the virus in an original animal host, while serial passage of a cell culture-adapted avirulent virus in vivo often gains virulence in an animal host. Actually, live attenuated virus vaccines were originally produced by serial passage in cell cultures. Although clinical efficacy and safety of rotavirus vaccines were recently revealed, the mechanism of their attenuation is not well understood. We passaged serially a murine rotavirus by alternating switch of host (mice or cell cultures) repeatedly and sequenced the eleven genes of the passaged viruses to identify mutations associated with the emergence or disappearance of virulence. Sequence analysis revealed that changes in three genes (VP4, NSP1, and NSP4) were associated with virulence in mice. Intraperitoneal injection of recombinant NSP4 proteins confirmed its diarrheagenic activity in mice

  6. Virulence-Associated Genome Mutations of Murine Rotavirus Identified by Alternating Serial Passages in Mice and Cell Cultures

    Science.gov (United States)

    Tatsumi, Masatoshi; Tsutsumi, Hiroyuki

    2014-01-01

    ABSTRACT Although significant clinical efficacy and safety of rotavirus vaccines were recently revealed in many countries, the mechanism of their attenuation is not well understood. We passaged serially a cell culture-adapted murine rotavirus EB strain in mouse pups or in cell cultures alternately and repeatedly and fully sequenced all 11 genes of 21 virus samples passaged in mice or in cell cultures. Sequence analysis revealed that mouse-passaged viruses that regained virulence almost consistently acquired four kinds of amino acid (aa) substitutions in VP4 and substitution in aa 37 (Val to Ala) in NSP4. In addition, they gained and invariably conserved the 3′ consensus sequence in NSP1. The molecular changes occurred along with the acquisition of virulence during passages in mice and then disappeared following passages in cell cultures. Intraperitoneal injection of recombinant NSP4 proteins confirmed the aa 37 site as important for its diarrheagenic activity in mice. These genome changes are likely to be correlated with rotavirus virulence. IMPORTANCE Serial passage of a virulent wild-type virus in vitro often results in loss of virulence of the virus in an original animal host, while serial passage of a cell culture-adapted avirulent virus in vivo often gains virulence in an animal host. Actually, live attenuated virus vaccines were originally produced by serial passage in cell cultures. Although clinical efficacy and safety of rotavirus vaccines were recently revealed, the mechanism of their attenuation is not well understood. We passaged serially a murine rotavirus by alternating switch of host (mice or cell cultures) repeatedly and sequenced the eleven genes of the passaged viruses to identify mutations associated with the emergence or disappearance of virulence. Sequence analysis revealed that changes in three genes (VP4, NSP1, and NSP4) were associated with virulence in mice. Intraperitoneal injection of recombinant NSP4 proteins confirmed its

  7. Effect of reinforcement nanoparticles addition on mechanical properties of SBS/curaua fiber composites

    Energy Technology Data Exchange (ETDEWEB)

    Borba, Patricia M. [Servico Nacional de Aprendizagem Industrial (CETEPO/SENAI/RS), Sao Leopoldo, RS (Brazil). Centro Tecnologico de Polimeros; Tedesco, Adriana [Braskem S. A., III Polo Petroquimico, Triunfo, RS (Brazil); Lenz, Denise M., E-mail: denise.lenz@gmail.com [Universidade Luterana do Brasil (ULBRA), Canoas, RS (Brazil). Programa de Pos-graduacao em Engenharia de Materiais e Processos Sustentaveis

    2014-03-15

    Composites of styrene-butadiene-styrene triblock copolymer (SBS) matrix with curauá fiber and/or a nanoparticulated mineral (montmorillonite clay - MMT) used as reinforcing agents were prepared by melt-mixing. The influence of clay addition on properties like tensile and tear strength, rebound resilience, flex fatigue life, abrasion loss, hardness and water absorption of composites with 5, 10 and 20 wt% of curauá fiber was evaluated in presence of maleic anhydride grafted styrene-(ethylene-co-butylene)-styrene triblock copolymer (MA-g-SEBS) coupling agent. Furthermore, the effect of mineral plasticizer loading on tensile strength of selected composites was investigated. The hybrid SBS composite that showed the best overall mechanical performance was composed by 2 wt% of MMT and 5 wt% of curauá fiber. Increasing fiber content up to 20 wt% resulted in a general decrease in all mechanical properties as well as incorporation of 5 wt% MMT caused a decrease in the tensile strength in all fiber contents. The hybrid composites showed clay agglomerates (tactoids) poorly dispersed that could explain the poor mechanical performance of composites at higher concentrations of curauá fiber and MMT nanoparticles. The addition of plasticizer further decreased the tensile strength while the addition of MMT nanoparticles decreased water absorption for all SBS composites. (author)

  8. Microstructural evolution of 316L stainless steels with yttrium addition after mechanical milling and heat treatment

    Energy Technology Data Exchange (ETDEWEB)

    Kotan, Hasan, E-mail: hasankotan@gmail.com

    2015-10-28

    Nanocrystalline 316L stainless steels with yttrium addition were prepared by mechanical milling at cryogenic temperature and subjected to annealing treatments at various temperatures up to 1200 °C. The dependence of hardness on the microstructure was utilized to study the mechanical changes in the steels occurring during annealing. The microstructural evolution of the as-milled and annealed steels was characterized by means of X-ray diffraction (XRD), focused ion beam microscopy (FIB) and transmission electron microscopy (TEM) techniques. The results have revealed that austenite in as-received powder partially transformed to martensite phase during mechanical milling whereas the annealing induced reverse transformation of martensite-to-austenite. Furthermore, while the austenite-to-martensite phase ratio increased with increasing annealing temperature, the equilibrium structure was not achieved after three hours heat treatments up to 1200 °C resulting in a dual-phased steels with around 10% martensite. The grain size of 316L steel was 19 nm after mechanical milling and remained around 116 nm at 1100 °C with yttrium addition as opposed to micron size grains of plain 316L steel at the same annealing temperature. Such microstructural features facilitate the use of these materials at elevated temperatures, as well as the development of scalable processing routes into a dense nanocrystalline compact.

  9. Bistable expression of virulence genes in salmonella leads to the formation of an antibiotic-tolerant subpopulation.

    Directory of Open Access Journals (Sweden)

    Markus Arnoldini

    2014-08-01

    Full Text Available Phenotypic heterogeneity can confer clonal groups of organisms with new functionality. A paradigmatic example is the bistable expression of virulence genes in Salmonella typhimurium, which leads to phenotypically virulent and phenotypically avirulent subpopulations. The two subpopulations have been shown to divide labor during S. typhimurium infections. Here, we show that heterogeneous virulence gene expression in this organism also promotes survival against exposure to antibiotics through a bet-hedging mechanism. Using microfluidic devices in combination with fluorescence time-lapse microscopy and quantitative image analysis, we analyzed the expression of virulence genes at the single cell level and related it to survival when exposed to antibiotics. We found that, across different types of antibiotics and under concentrations that are clinically relevant, the subpopulation of bacterial cells that express virulence genes shows increased survival after exposure to antibiotics. Intriguingly, there is an interplay between the two consequences of phenotypic heterogeneity. The bet-hedging effect that arises through heterogeneity in virulence gene expression can protect clonal populations against avirulent mutants that exploit and subvert the division of labor within these populations. We conclude that bet-hedging and the division of labor can arise through variation in a single trait and interact with each other. This reveals a new degree of functional complexity of phenotypic heterogeneity. In addition, our results suggest a general principle of how pathogens can evade antibiotics: Expression of virulence factors often entails metabolic costs and the resulting growth retardation could generally increase tolerance against antibiotics and thus compromise treatment.

  10. Differential protein accumulations in isolates of the strawberry wilt pathogen Fusarium oxysporum f. sp. fragariae differing in virulence.

    Science.gov (United States)

    Fang, Xiangling; Barbetti, Martin J

    2014-08-28

    This study was conducted to define differences in Fusarium oxysporum f. sp. fragariae (Fof) isolates with different virulence efficiency to strawberry at the proteome level, in combination with their differences in mycelial growth, conidial production and germination. Comparative proteome analyses revealed substantial differences in mycelial proteomes between Fof isolates, where the 54 differentially accumulated protein spots were consistently over-accumulated or exclusively in the highly virulent isolate. These protein spots were identified through MALDI-TOF/TOF mass spectrometry analyses, and the identified proteins were mainly related to primary and protein metabolism, antioxidation, electron transport, cell cycle and transcription based on their putative functions. Proteins of great potential as Fof virulence factors were those involved in ubiquitin/proteasome-mediated protein degradation and reactive oxygen species detoxification; the hydrolysis-related protein haloacid dehalogenase superfamily hydrolase; 3,4-dihydroxy-2-butanone 4-phosphate synthase associated with riboflavin biosynthesis; and those exclusive to the highly virulent isolate. In addition, post-translational modifications may also make an important contribution to Fof virulence. F. oxysporum f. sp. fragariae (Fof), the causal agent of Fusarium wilt in strawberry, is a serious threat to commercial strawberry production worldwide. However, factors and mechanisms contributing to Fof virulence remained unknown. This study provides knowledge of the molecular basis for the differential expression of virulence in Fof, allowing new possibilities towards developing alternative and more effective strategies to manage Fusarium wilt. Copyright © 2014 Elsevier B.V. All rights reserved.

  11. Microstructures and mechanical behavior of Inconel 625 fabricated by solid-state additive manufacturing

    Energy Technology Data Exchange (ETDEWEB)

    Rivera, O.G. [Department of Mechanical Engineering, The University of Alabama, Tuscaloosa, AL (United States); Allison, P.G., E-mail: pallison@eng.ua.edu [Department of Mechanical Engineering, The University of Alabama, Tuscaloosa, AL (United States); Jordon, J.B.; Rodriguez, O.L. [Department of Mechanical Engineering, The University of Alabama, Tuscaloosa, AL (United States); Brewer, L.N. [Department of Metallurgical Engineering, The University of Alabama, Tuscaloosa, AL (United States); McClelland, Z. [US Army Corps of Engineers, Engineer Research and Development Center, Vicksburg, MS (United States); Whittington, W.R.; Francis, D. [Center of Advanced Vehicular Systems, Mississippi State University, Starkville, MS (United States); Su, J. [Aeroprobe Corporation, Christiansburg, VA (United States); Martens, R.L. [Central Analytical Facility, The University of Alabama, Tuscaloosa, AL (United States); Hardwick, N. [Aeroprobe Corporation, Christiansburg, VA (United States)

    2017-05-10

    Here we introduce a novel thermo-mechanical Solid State Additive Manufacturing (SSAM) process referred to as Additive Friction Stir (AFS) manufacturing that provides a new and alternative path to fusion-based additive manufacturing processes for developing fully-dense, near-net shape components with a refined-equiaxed grain morphology. This study is the first to investigate the beneficial grain refinement and densification produced by AFS in IN625 that results in advantageous mechanical properties (YS, UTS, εf) at both quasi-static and high strain rate. Electron Backscatter Diffraction (EBSD) observed grain refinement during the layer deposition in the AFS specimens, where the results identified fine equiaxed grain structures with even finer grain structures forming at the layer interfaces. The EBSD quantified grains as fine as 0.27 µm in these interface regions while the average grain size was approximately 1 µm. Additionally, this is the first study to report on the strain rate dependence of AFS IN625 through quasi-static (QS) (0.001/s) and high strain rate (HR) (1500/s) tensile experiments using a servo hydraulic frame and a direct tension-Kolsky bar, respectively, which captured both yield and ultimate tensile strengths increasing as strain rate increased. The HS results exhibited an approximately 200 MPa increase in engineering strength over the QS results, with the fracture surfaces at both strain rates aligned with the maximum shear plane and exhibiting localized microvoids.

  12. Microstructures and mechanical behavior of Inconel 625 fabricated by solid-state additive manufacturing

    International Nuclear Information System (INIS)

    Rivera, O.G.; Allison, P.G.; Jordon, J.B.; Rodriguez, O.L.; Brewer, L.N.; McClelland, Z.; Whittington, W.R.; Francis, D.; Su, J.; Martens, R.L.; Hardwick, N.

    2017-01-01

    Here we introduce a novel thermo-mechanical Solid State Additive Manufacturing (SSAM) process referred to as Additive Friction Stir (AFS) manufacturing that provides a new and alternative path to fusion-based additive manufacturing processes for developing fully-dense, near-net shape components with a refined-equiaxed grain morphology. This study is the first to investigate the beneficial grain refinement and densification produced by AFS in IN625 that results in advantageous mechanical properties (YS, UTS, εf) at both quasi-static and high strain rate. Electron Backscatter Diffraction (EBSD) observed grain refinement during the layer deposition in the AFS specimens, where the results identified fine equiaxed grain structures with even finer grain structures forming at the layer interfaces. The EBSD quantified grains as fine as 0.27 µm in these interface regions while the average grain size was approximately 1 µm. Additionally, this is the first study to report on the strain rate dependence of AFS IN625 through quasi-static (QS) (0.001/s) and high strain rate (HR) (1500/s) tensile experiments using a servo hydraulic frame and a direct tension-Kolsky bar, respectively, which captured both yield and ultimate tensile strengths increasing as strain rate increased. The HS results exhibited an approximately 200 MPa increase in engineering strength over the QS results, with the fracture surfaces at both strain rates aligned with the maximum shear plane and exhibiting localized microvoids.

  13. Influence of Zr addition on the microstructures and mechanical properties of 14Cr ODS steels

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Liye [State Key Lab of Hydraulic Engineering Simulation and Safety, Tianjin key Lab of Composite and Functional Materials, Tianjin University, Tianjin 300072 (China); Yu, Liming, E-mail: lmyu@tju.edu.cn [State Key Lab of Hydraulic Engineering Simulation and Safety, Tianjin key Lab of Composite and Functional Materials, Tianjin University, Tianjin 300072 (China); Liu, Yongchang; Liu, Chenxi; Li, Huijun [State Key Lab of Hydraulic Engineering Simulation and Safety, Tianjin key Lab of Composite and Functional Materials, Tianjin University, Tianjin 300072 (China); Wu, Jiefeng [Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031 (China)

    2017-05-17

    Oxide dispersion strengthened (ODS) steel is one of the most promising candidate structural materials for the high-temperature nuclear reactor application. In this study, two compositions of ODS steels (14Cr-ODS and 14Cr-Zr-ODS) were prepared to investigate the influence of Zr addition on the microstructures and mechanical properties of ODS steels. The microstructures, including dispersion morphology and crystal structures of oxide particles, particle-matrix interface coherency and particle-dislocation interactions, were characterized using TEM, HRTEM, and SEM, and the mechanical properties at room and high temperatures were measured using uniaxial tensile tests. Results show that Zr addition leads to the formation of finer precipitated particles, which was identified as rhombohedral Y{sub 4}Zr{sub 3}O{sub 12}, with denser dispersion in the matrix. The calculation results reveal that the lattice misfit, δ, at the interface between particle and matrix increases as the particle size increases. In addition, the strength and elongation of ODS steels are improved with Zr addition due to the stronger interface bonding force between fine particles and matrix as well as the larger pinning effect of small particles to dislocation movements.

  14. Corroborating tomographic defect metrics with mechanical response in an additively manufactured precipitation-hardened stainless steel

    Science.gov (United States)

    Madison, Jonathan D.; Underwood, Olivia D.; Swiler, Laura P.; Boyce, Brad L.; Jared, Bradley H.; Rodelas, Jeff M.; Salzbrenner, Bradley C.

    2018-04-01

    The intrinsic relation between structure and performance is a foundational tenant of most all materials science investigations. While the specific form of this relation is dictated by material system, processing route and performance metric of interest, it is widely agreed that appropriate characterization of a material allows for greater accuracy in understanding and/or predicting material response. However, in the context of additive manufacturing, prior models and expectations of material performance must be revisited as performance often diverges from traditional values, even among well explored material systems. This work utilizes micro-computed tomography to quantify porosity and lack of fusion defects in an additively manufactured stainless steel and relates these metrics to performance across a statistically significant population using high-throughput mechanical testing. The degree to which performance in additively manufactured stainless steel can and cannot be correlated to detectable porosity will be presented and suggestions for performing similar experiments will be provided.

  15. Effect of Graphene Addition on Mechanical Properties of TiN

    International Nuclear Information System (INIS)

    Shon, In-Jin; Yoon, Jin-Kook; Hong, Kyung-Tae

    2017-01-01

    Despite of many attractive properties of TiN, the current concern about the TiN focuses on its low fracture toughness below the ductile-brittle transition temperature. To improve its mechanical properties, the approach generally utilized has been the addition of a second phase to form composites and to make nanostructured materials. In this respect, highly dense nanostructured TiN and TiN-graphene composites were obtained within two min at 1250 ℃. The grain size of TiN was reduced remarkably by the addition of graphene. The addition of graphene to TiN simultaneously improved the fracture toughness and hardness of TiN-graphene composite due to refinement of TiN and deterring crack propagation by graphene. This study demonstrates that the graphene can be an effective reinforcing agent for improved hardness and fracture toughness of TiN composites.

  16. Effect of Graphene Addition on Mechanical Properties of TiN

    Energy Technology Data Exchange (ETDEWEB)

    Shon, In-Jin [Chonbuk National University, Jeonju (Korea, Republic of); Yoon, Jin-Kook; Hong, Kyung-Tae [Korea Institute of Science and Technology, Seoul (Korea, Republic of)

    2017-03-15

    Despite of many attractive properties of TiN, the current concern about the TiN focuses on its low fracture toughness below the ductile-brittle transition temperature. To improve its mechanical properties, the approach generally utilized has been the addition of a second phase to form composites and to make nanostructured materials. In this respect, highly dense nanostructured TiN and TiN-graphene composites were obtained within two min at 1250 ℃. The grain size of TiN was reduced remarkably by the addition of graphene. The addition of graphene to TiN simultaneously improved the fracture toughness and hardness of TiN-graphene composite due to refinement of TiN and deterring crack propagation by graphene. This study demonstrates that the graphene can be an effective reinforcing agent for improved hardness and fracture toughness of TiN composites.

  17. Synthesis of Porous and Mechanically Compliant Carbon Aerogels Using Conductive and Structural Additives

    Directory of Open Access Journals (Sweden)

    Carlos Macias

    2016-01-01

    Full Text Available We report the synthesis of conductive and mechanically compliant monolithic carbon aerogels prepared by sol-gel polycondensation of melamine-resorcinol-formaldehyde (MRF mixtures by incorporating diatomite and carbon black additives. The resulting aerogels composites displayed a well-developed porous structure, confirming that the polymerization of the precursors is not impeded in the presence of either additive. The aerogels retained the porous structure after etching off the siliceous additive, indicating adequate cross-linking of the MRF reactants. However, the presence of diatomite caused a significant fall in the pore volumes, accompanied by coarsening of the average pore size (predominance of large mesopores and macropores. The diatomite also prevented structural shrinkage and deformation of the as-prepared monoliths upon densification by carbonization, even after removal of the siliceous framework. The rigid pristine aerogels became more flexible upon incorporation of the diatomite, favoring implementation of binderless monolithic aerogel electrodes.

  18. Mechanical properties of Fe3Al-based alloys with addition of carbon, niobium and titanium

    International Nuclear Information System (INIS)

    Zhang Zhengrong; Liu Wenxi

    2006-01-01

    Several Fe 3 Al-based iron aluminides with the addition of alloying elements carbon, niobium and titanium were produced by vacuum induction melting (VIM) and hot spinning forging. Analytic techniques including transmission electron microscopy (TEM), scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used in studying the microstructure and fracture manner of these alloys. The results show that due to the addition of alloying elements, the superlattice dislocations tend towards multiple slipping, leaving behind on their slip plane ribbons of square-shaped slip-induced antiphase boundaries. The elongation of Fe 3 Al in tension at room temperature increased to about 10% by the addition of suitable alloying elements, the usage of thermo-mechanical processing that has the function of refining grains and substructures, and subsequent annealing

  19. Effect of revert addition on microstructure and mechanical properties of M951 Ni-base superalloy

    International Nuclear Information System (INIS)

    Yang, Y.H.; Yu, J.J.; Sun, X.F.; Jin, T.; Guan, H.R.; Hu, Z.Q.

    2012-01-01

    Highlights: ► The microstructure is not influenced by the additions of recycled alloy. ► The stress rupture life significantly decreases with addition of recycled alloy. ► The stress rupture life is remarkably dependent on various revert additions. ► The stress rupture life has been significantly improved after filtration. ► The melt filtered through 20 ppi shows the lowest stress rupture life. - Abstract: The effect of recycled alloy proportion on the composition, microstructure and mechanical properties of M951 alloy has been investigated. With the addition of the recycled alloy proportion, the concentrations of boron and carbon obviously decrease. The microstructure is not influenced by the additions of recycled alloy. The stress rupture life significantly decreases with the addition of recycled alloy proportion. Because of the removal of oxide inclusions by filtration, the stress rupture life has been significantly improved, and it also shows a clear dependence upon passage size of the filter. The melt filtered through passage size of 20 ppi shows the lowest stress rupture life.

  20. Clean development mechanism and off-grid small-scale hydropower projects: Evaluation of additionality

    International Nuclear Information System (INIS)

    Tanwar, Nitin

    2007-01-01

    The global climate change mitigation policies and their stress on sustainable development have made electrification of rural mountainous villages, using small hydro, an attractive destination for potential clean development mechanism (CDM) projects. This invariably involves judging the additionality of such projects. The paper suggests a new approach to judge the additionality of such stand-alone small hydropower projects. This has been done by breaking up additionality into two components: external and local. The external additionality is project developer dependent. For determining the local additionality, the paper takes into account the probability of a village getting electrified over a period of time, which is kept equal to the possible crediting period. This is done by defining an electrification factor (EF) whose value depends on the degree of isolation, financial constraints and institutional constraints encountered while electrifying a mountainous village. Using this EF, the additionality of a CDM project can be judged in a much easier and accurate way. The paper is based on the data and inputs gathered during site visits to many isolated villages located in the eastern Indian Himalayas

  1. Mechanical properties of open-cell metallic biomaterials manufactured using additive manufacturing

    International Nuclear Information System (INIS)

    Campoli, G.; Borleffs, M.S.; Amin Yavari, S.; Wauthle, R.; Weinans, H.; Zadpoor, A.A.

    2013-01-01

    Highlights: ► Finite element (FE) models were used to predict the mechanical properties of porous biomaterials. ► Porous materials were produced using additive manufacturing techniques. ► Manufacturing irregularities need to be implemented in FE models. ► FE models are more accurate than analytical models in predicting mechanical properties. - Abstract: An important practical problem in application of open-cell porous biomaterials is the prediction of the mechanical properties of the material given its micro-architecture and the properties of its matrix material. Although analytical methods can be used for this purpose, these models are often based on several simplifying assumptions with respect to the complex architecture and cannot provide accurate prediction results. The aim of the current study is to present finite element (FE) models that can predict the mechanical properties of porous titanium produced using selective laser melting or selective electron beam melting. The irregularities caused by the manufacturing process including structural variations of the architecture are implemented in the FE models using statistical models. The predictions of FE models are compared with those of analytical models and are tested against experimental data. It is shown that, as opposed to analytical models, the predictions of FE models are in agreement with experimental observations. It is concluded that manufacturing irregularities significantly affect the mechanical properties of porous biomaterials

  2. Physico-mechanical and dissolution behaviours of ibuprofen crystals crystallized in the presence of various additives

    Directory of Open Access Journals (Sweden)

    A Nokhodchi

    2010-06-01

    Full Text Available "n  "n Background and the purpose of the study: The success of any direct-tableting procedure is strongly affected by the quality of the crystals used in the process. Ibuprofen is a poorly compactible drug with a high tendency for capping. In order to use ibuprofen in direct compression formulations, physico-mechanical properties of ibuprofen should be improved considerably. The aim of the present investigation was to employ crystallization techniques in order to improve the physico-mechanical properties of ibuprofen for direct compression. "nMethods:The experimental methods involved the preparation of ibuprofen crystals by solvent change technique. Ibuprofen was dissolved in ethanol and crystallized out with water in the absence or presence of various hydrophilic additives (PEG 6000, 8000, Brij 98P and polyvinyl alcohol 22000, PVA 22000 with different concentrations. The physico-mechanical properties of the ibuprofen crystals were studied in terms of flow, density, tensile strength and dissolution behaviour. Morphology of ibuprofen crystals was studied by scanning electron microscopic (SEM. Solid state of the recrystallized particles was also investigated using differential scanning calorimeter (DSC and FT-IR. "nResults:Ibuprofen samples crystallized in the presence of PEG 6000 and 8000 and PVA showed remarkable increase in the tensile strengths of the directly compressed tablets, while some other additives, i.e. Brij 98P did not produce improved ibuprofen crystals. Ibuprofen powders made from particles obtained in the presence of PVA and Brij 98P showed similar dissolution profiles to the commercial ibuprofen particles. DSC and FT-IR results ruled out any significant interaction between ibuprofen and additives except for the samples crystallized in the presence of PEG 8000. Conclusion:The crystal habit of ibuprofen can be altered successfully by the crystallization technique which was developed in this study. The crystals developed in the

  3. Mechanical Properties of a Newly Additive Manufactured Implant Material Based on Ti-42Nb.

    Science.gov (United States)

    Schulze, Christian; Weinmann, Markus; Schweigel, Christoph; Keßler, Olaf; Bader, Rainer

    2018-01-13

    The application of Ti-6Al-4V alloy or commercially pure titanium for additive manufacturing enables the fabrication of complex structural implants and patient-specific implant geometries. However, the difference in Young's modulus of α + β-phase Ti alloys compared to the human bone promotes stress-shielding effects in the implant-bone interphase. The aim of the present study is the mechanical characterization of a new pre-alloyed β-phase Ti-42Nb alloy for application in additive manufacturing. The present investigation focuses on the mechanical properties of SLM-printed Ti-42Nb alloy in tensile and compression tests. In addition, the raw Ti-42Nb powder, the microstructure of the specimens prior to and after compression tests, as well as the fracture occurring in tensile tests are characterized by means of the SEM/EDX analysis. The Ti-42Nb raw powder exhibits a dendrite-like Ti-structure, which is melted layer-by-layer into a microstructure with a very homogeneous distribution of Nb and Ti during the SLM process. Tensile tests display Young's modulus of 60.51 ± 3.92 GPa and an ultimate tensile strength of 683.17 ± 16.67 MPa, whereas, under a compressive load, a compressive strength of 1330.74 ± 53.45 MPa is observed. The combination of high mechanical strength and low elastic modulus makes Ti-42Nb an interesting material for orthopedic and dental implants. The spherical shape of the pre-alloyed material additionally allows for application in metal 3D printing, enabling the fabrication of patient-specific structural implants.

  4. Mechanical Properties of a Newly Additive Manufactured Implant Material Based on Ti-42Nb

    Directory of Open Access Journals (Sweden)

    Christian Schulze

    2018-01-01

    Full Text Available The application of Ti-6Al-4V alloy or commercially pure titanium for additive manufacturing enables the fabrication of complex structural implants and patient-specific implant geometries. However, the difference in Young’s modulus of α + β-phase Ti alloys compared to the human bone promotes stress-shielding effects in the implant–bone interphase. The aim of the present study is the mechanical characterization of a new pre-alloyed β-phase Ti-42Nb alloy for application in additive manufacturing. The present investigation focuses on the mechanical properties of SLM-printed Ti-42Nb alloy in tensile and compression tests. In addition, the raw Ti-42Nb powder, the microstructure of the specimens prior to and after compression tests, as well as the fracture occurring in tensile tests are characterized by means of the SEM/EDX analysis. The Ti-42Nb raw powder exhibits a dendrite-like Ti-structure, which is melted layer-by-layer into a microstructure with a very homogeneous distribution of Nb and Ti during the SLM process. Tensile tests display Young’s modulus of 60.51 ± 3.92 GPa and an ultimate tensile strength of 683.17 ± 16.67 MPa, whereas, under a compressive load, a compressive strength of 1330.74 ± 53.45 MPa is observed. The combination of high mechanical strength and low elastic modulus makes Ti-42Nb an interesting material for orthopedic and dental implants. The spherical shape of the pre-alloyed material additionally allows for application in metal 3D printing, enabling the fabrication of patient-specific structural implants.

  5. Effect of Cu addition on the microstructure and mechanical properties of Al–30 wt% Zn alloy

    International Nuclear Information System (INIS)

    Abd El-Rehim, A.F.; Sakr, M.S.; El-Sayed, M.M.; Abd El-Hafez, M.

    2014-01-01

    Highlights: • This paper describes a novel work on the effect of Cu addition on the Al–30 wt% Zn alloy. • The 1 wt% Cu alloy revealed the best hardness of the alloys. • The results indicated two deformation temperature regions (below and above 548 K). - Abstract: The effect of 0.5, 1, 1.5 and 2 wt% Cu addition on the microstructure and mechanical properties of Al–30 wt% Zn alloy has been investigated by stress–strain tests carried out in the temperature range from 508 to 608 K. The work-hardening parameters of the test alloys decreased with increasing the deformation temperature and exhibited discontinuity at 548 K, resulting two deformation temperature regions, the low-temperature region (below 548 K) and high-temperature region (above 548 K). The activation energy of fracture mechanisms has been calculated and found to be 19.6 and 33.2 kJ/mol at the low and high temperature regions respectively. The operating mechanisms of work-hardening of the test alloys were confirmed by the analysis of X-ray diffraction patterns

  6. Additive Manufacturing and Casting Technology Comparison: Mechanical Properties, Productivity and Cost Benchmark

    Science.gov (United States)

    Vevers, A.; Kromanis, A.; Gerins, E.; Ozolins, J.

    2018-04-01

    The casting technology is one of the oldest production technologies in the world but in the recent years metal additive manufacturing also known as metal 3D printing has been evolving with huge steps. Both technologies have capabilities to produce parts with internal holes and at first glance surface roughness is similar for both technologies, which means that for precise dimensions parts have to be machined in places where precise fit is necessary. Benchmark tests have been made to find out if parts which are produced with metal additive manufacturing can be used to replace parts which are produced with casting technology. Most of the comparative tests have been made with GJS-400-15 grade which is one of the most popular cast iron grades. To compare mechanical properties samples have been produced using additive manufacturing and tested for tensile strength, hardness, surface roughness and microstructure and then the results have been compared with the samples produced with casting technology. In addition, both technologies have been compared in terms of the production time and production costs to see if additive manufacturing is competitive with the casting technology. The original paper has been written in the Latvian language as part of the Master Thesis within the framework of the production technology study programme at Riga Technical University.

  7. SLM processing-microstructure-mechanical property correlation in an aluminum alloy produced by additive manufacturing

    Science.gov (United States)

    Alejos, Martin Fernando

    Additive manufacturing has become a highly researched topic in recent years all over the world. The current research evaluates the merits of additive manufacturing based on the mechanical, microstructural, and fracture properties of additive manufactured AlSi10Mg test specimens. The additive manufactured build plates consisted of tensile and fatigue test specimens. They were printed in the 0°, 30°, 60°, and 90° orientations relative to the build platform. Tensile and dynamic fatigue tests were conducted followed by microstructural characterization and fracture analysis. A wrought 6061 T6 aluminum alloy was also tested for comparison. Tensile tests revealed similar ultimate tensile strengths for all aluminum tensile specimens (350-380 MPa). Fatigue strength was greatest for wrought 6061 T6 aluminum (175 MPa). The fatigue behavior was a strong function of build orientation for the additive manufactured specimens. The 0°, 30°, and 60° orientations had fatigue strengths close to 104 MPa while the 90° orientation had a fatigue strength of 125 MPa. All test specimens failed primarily in a ductile manner. The effect of laser power, hatch spacing, and scan speed were also studied using microstructural analysis. Increasing laser power decreased grain size and void size. Increasing scan speed led to the formation of columnar grains. Increasing hatch spacing decreased grain size and the amount of voids present in the microstructure.

  8. Mechanical properties of potato starch modified by moisture content and addition of lubricant

    Science.gov (United States)

    Stasiak, Mateusz; Molenda, Marek; Horabik, Józef; Mueller, Peter; Opaliński, Ireneusz

    2014-10-01

    Laboratory testing was conducted to deliver a set of characteristics of structure and mechanical properties of pure starch and starch with an addition of a lubricant - magnesium stearate. Considerable influence of moisture content of potato starch was found in the case of density, parameters of internal friction, coefficients of wall friction and flowability. Elasticity was found to be strongly influenced by water content of the material. Addition of magnesium stearate affected density and parameters of flowability, internal friction and elasticity. Bulk density increased from 604 to 774 kg m-3 with decrease in moisture content of potato starch from 17 to for 6%. Addition of magnesium stearate resulted in approximately 10% decrease in bulk density. Angle of internal friction obtained for 10 kPa of consolidation stress decreased from 33 to 24º with increase in moisture content, and to approximately 22º with addition of the lubricant. With an increase of moisture content from 6 to 18% and with addition of the lubricant, the modulus of elasticity during loading decreased from approximately 1.0 to 0.1 MPa. Modulus of elasticity during unloading was found in the range from 19 to 42 MPa and increased with increase of moisture content and amount of lubricant.

  9. EFFECTS OF MO ADDITION ON THE MICROSTRUCTURE AND MECHANICAL PROPERTIES OF CAST MICROALLOYED STEEL

    Directory of Open Access Journals (Sweden)

    H. Torkamani

    2017-09-01

    Full Text Available In industry, the cost of production is an important factor and it is preferred to use conventional and low cost procedures for producing the parts. Heat treatment cycles and alloying additions are the key factors affecting the microstructure and mechanical properties of the cast steels. In this study an attempt was made to evaluate the influence of minor Mo addition on the microstructure and mechanical properties of conventionally heat treated cast micro-alloyed steels. The results of Jominy and dilatometry tests and also microstructural examinations revealed that Mo could effectively increase the hardenability of the investigated steel and change the microstructure features of the air-cooled samples. Acicular microstructure was the consequence of increasing the hardenability in Mo-added steel. Besides, it was found that Mo could greatly affect the isothermal bainitic transformation and higher fraction of martensite after cooling (from isothermal temperature was due to the Mo addition. The results of impact test indicated that the microstructure obtained in air-cooled Mo-added steel led to better impact toughness (28J in comparison with the base steel (23J. Moreover, Mo-added steel possessed higher hardness (291HV, yield (524MPa and tensile (1108MPa strengths compared to the base one.

  10. Effect of carbon nanofiber addition in the mechanical properties and durability of cementitious materials

    Directory of Open Access Journals (Sweden)

    Galao, O.

    2012-09-01

    Full Text Available This paper reports on recent work that is directed at studying the changes in the mechanical properties of Portland cement based mortars due to the addition of carbon nanofiber (CNF. Both flexural and compression strength has been determined and related to the CNF addition to the mix, to the curing time and to the porosity and density of the matrix. Also, corrosion of embedded steel rebars in CNF cement pastes exposed to carbonation and chloride attacks has been investigated. The increase in CNF addition implies higher corrosion intensity and higher levels of mechanical properties.En este artículo se han estudiado los cambios en las propiedades mecánicas de los morteros de cemento Portland debido a la adición de nanofibras de carbono (NFC. Se han determinado las resistencias a flexotracción y a compresión de los morteros en relación a la cantidad de NFC añadidas a la mezcla, al tiempo de curado y a la porosidad y densidad de los mismos. Además se han investigado los niveles de corrosión de barras de acero embebidas en pastas de cemento con NFC expuestos al ataque por carbonatación y por ingreso de cloruros. El aumento en el porcentaje de NFC añadido se traduce en un aumento la intensidad de corrosión registrada y una mejora de las propiedades mecánicas.

  11. Effect of Pr addition on microstructure and mechanical properties of AZ61 magnesium alloy

    Directory of Open Access Journals (Sweden)

    You Zhiyong

    2014-03-01

    Full Text Available To improve the strength, hardness and heat resistance of Mg-6Al-1Zn (AZ61 alloy, the effects of Pr addition on the as-cast microstructure and mechanical properties of AZ61 alloy were investigated at room and elevated temperatures by means of Brinell hardness measurement, optical microscope (OM, scanning electron microscope (SEM, energy dispersive spectroscopy (EDS, X-ray diffractometer (XRD and DNS100 electronic universal testing machine. The results show that the microstructures of Pr-containing AZ61 alloys were refined, with primary β-Mg17Al12 phase distributed homogeneously. When the addition of Pr is up to 1.2wt.%, the β phase becomes finer, and new needle-like or short-rod shaped Al11Pr3 phase and blocky AlPr phase appear. As a result, optimal tensile properties are obtained. However, greater than 1.2wt.% Pr addition leads to poorer mechanical properties due to the aggregation of the needle-like phase and large size of grains. The present research findings provide a new way for strengthening of magnesium alloys at room and elevated temperatures, and a method of producing thermally-stable AZ61 magnesium alloy.

  12. Effects of Zr Addition on Strengthening Mechanisms of Al-Alloyed High-Cr ODS Steels.

    Science.gov (United States)

    Ren, Jian; Yu, Liming; Liu, Yongchang; Liu, Chenxi; Li, Huijun; Wu, Jiefeng

    2018-01-12

    Oxide dispersion strengthened (ODS) steels with different contents of zirconium (denoted as 16Cr ODS, 16Cr-0.3Zr ODS and 16Cr-0.6Zr ODS) were fabricated to investigate the effects of Zr on strengthening mechanism of Al-alloyed 16Cr ODS steel. Electron backscatter diffraction (EBSD) results show that the mean grain size of ODS steels could be decreased by Zr addition. Transmission electron microscope (TEM) results indicate that Zr addition could increase the number density but decrease the mean diameter and inter-particle spacing of oxide particles. Furthermore, it is also found that in addition to Y-Al-O nanoparticles, Y-Zr-O oxides with finer size were observed in 16Cr-0.3Zr ODS and 16Cr-0.6Zr ODS steels. These changes in microstructure significantly increase the yield strength (YS) and ultimate tensile strength (UTS) of ODS steels through mechanisms of grain boundary strengthening and dispersion strengthening.

  13. Performance and mechanism of sludge dewaterability enhanced by potassium ferrate pretreatment and calcium chloride addition

    Directory of Open Access Journals (Sweden)

    Yali Liu

    2017-06-01

    Full Text Available The potential benefits and mechanisms of potassium ferrate pretreatment and calcium chloride addition on sludge dewaterability were investigated in this study. The capillary suction time (CST was used to evaluate sludge dewaterability. Results indicated that potassium ferrate of 0.1 g/g total solids (TS and calcium chloride of 0.4 g/g TS were optimal parameters, and corresponding CST reached 43.7 s. Soluble organics in extracellular polymeric substances (EPS were determined by three-dimensional excitation-emission matrix fluorescence spectroscopy, which was used to explain the mechanism of sludge dewaterability. The fluorescence intensities of protein-like and humic-like substances in EPS had a negative relationship with the CST. Scanning electron microscopy images indicated that calcium chloride neutralized the surface charge of particles, making the soluble protein-like substances agglomerate and form bigger flocs, consequently enhancing sludge dewaterability.

  14. Effects of Sm addition on microstructure and mechanical properties of a Mg-10Y alloy

    Directory of Open Access Journals (Sweden)

    Li Quanan

    2014-01-01

    Full Text Available To further increase the mechanical properties, 0.5wt.% Sm was introduced to a Mg-10Y alloy in this study. The effects of Sm addition on the microstructures and mechanical properties of the Mg-10Y alloy, especially the aged Mg-10Y alloy, were investigated. The microstructure observation and tensile tests were performed by using an optical microscopy, a scanning electron microscopy and a universal material testing machine, respectively. The phase analysis was performed using X-ray diffractometer. The results show that the 0.5wt.% Sm addition can not only promote the formation of fine and dispersed Mg24Y5 phases, but also improve their morphology and distribution; it also increases the thermal stability of Mg24Y5 phases. Sm addition is seen to increase the ultimate tensile strength of Mg-10Y alloy at elevated temperatures (200, 250, 300 and 350 ℃, while decrease the elongation. But the elongation is still up to 7.5% even at 350 ℃. In the range of 250 ℃ to 300℃, the ultimate tensile strength of the alloy reaches its maximum (with a range average of 235 MPa and is not sensitive to the temperature change, which is very useful to the application of heat-resistant magnesium alloys. Even at 350 ℃, the ultimate tensile strength of Mg-10Y-0.5Sm is still up to 155 MPa. Considering both of the ultimate tensile strength and elongation, the maximum application temperature of the Mg-10Y-0.5Sm alloy can be up to 300 ℃. The strengthening mechanisms of Mg-10Y-0.5Sm alloy are mainly attributed to dispersion strengthening of Mg24Y5 phase particles with a certain solubility of Sm and grain refinement strengthening of α-Mg matrix.

  15. Liraglutide, leptin and their combined effects on feeding: additive intake reduction through common intracellular signalling mechanisms.

    Science.gov (United States)

    Kanoski, S E; Ong, Z Y; Fortin, S M; Schlessinger, E S; Grill, H J

    2015-03-01

    To investigate the behavioural and intracellular mechanisms by which the glucagon like peptide-1 (GLP-1) receptor agonist, liraglutide, and leptin in combination enhance the food intake inhibitory and weight loss effects of either treatment alone. We examined the effects of liraglutide (a long-acting GLP-1 analogue) and leptin co-treatment, delivered in low or moderate doses subcutaneously (s.c.) or to the third ventricle, respectively, on cumulative intake, meal patterns and hypothalamic expression of intracellular signalling proteins [phosphorylated signal transducer and activator of transcription-3 (pSTAT3) and protein tyrosine phosphatase-1B (PTP1B)] in lean rats. A low-dose combination of liraglutide (25 µg/kg) and leptin (0.75 µg) additively reduced cumulative food intake and body weight, a result mediated predominantly through a significant reduction in meal frequency that was not present with either drug alone. Liraglutide treatment alone also reduced meal size; an effect not enhanced with leptin co-administration. Moderate doses of liraglutide (75 µg/kg) and leptin (4 µg), examined separately, each reduced meal frequency, cumulative food intake and body weight; only liraglutide reduced meal size. In combination these doses did not further enhance the anorexigenic effects of either treatment alone. Ex vivo immunoblot analysis showed elevated pSTAT3 in the hypothalamic tissue after liraglutide-leptin co-treatment, an effect which was greater than that of leptin treatment alone. In addition, s.c. liraglutide reduced the expression of PTP1B (a negative regulator of leptin receptor signalling), revealing a potential mechanism for the enhanced pSTAT3 response after liraglutide-leptin co-administration. Collectively, these results show novel behavioural and molecular mechanisms underlying the additive reduction in food intake and body weight after liraglutide-leptin combination treatment. © 2014 John Wiley & Sons Ltd.

  16. Failure mechanisms of additively manufactured porous biomaterials: Effects of porosity and type of unit cell.

    Science.gov (United States)

    Kadkhodapour, J; Montazerian, H; Darabi, A Ch; Anaraki, A P; Ahmadi, S M; Zadpoor, A A; Schmauder, S

    2015-10-01

    Since the advent of additive manufacturing techniques, regular porous biomaterials have emerged as promising candidates for tissue engineering scaffolds owing to their controllable pore architecture and feasibility in producing scaffolds from a variety of biomaterials. The architecture of scaffolds could be designed to achieve similar mechanical properties as in the host bone tissue, thereby avoiding issues such as stress shielding in bone replacement procedure. In this paper, the deformation and failure mechanisms of porous titanium (Ti6Al4V) biomaterials manufactured by selective laser melting from two different types of repeating unit cells, namely cubic and diamond lattice structures, with four different porosities are studied. The mechanical behavior of the above-mentioned porous biomaterials was studied using finite element models. The computational results were compared with the experimental findings from a previous study of ours. The Johnson-Cook plasticity and damage model was implemented in the finite element models to simulate the failure of the additively manufactured scaffolds under compression. The computationally predicted stress-strain curves were compared with the experimental ones. The computational models incorporating the Johnson-Cook damage model could predict the plateau stress and maximum stress at the first peak with less than 18% error. Moreover, the computationally predicted deformation modes were in good agreement with the results of scaling law analysis. A layer-by-layer failure mechanism was found for the stretch-dominated structures, i.e. structures made from the cubic unit cell, while the failure of the bending-dominated structures, i.e. structures made from the diamond unit cells, was accompanied by the shearing bands of 45°. Copyright © 2015 Elsevier Ltd. All rights reserved.

  17. Effects of plasma electrolytic oxidation process on the mechanical properties of additively manufactured porous biomaterials.

    Science.gov (United States)

    Gorgin Karaji, Zahra; Hedayati, Reza; Pouran, Behdad; Apachitei, Iulian; Zadpoor, Amir A

    2017-07-01

    Metallic porous biomaterials are recently attracting more attention thanks to the additive manufacturing techniques which help produce more complex structures as compared to conventional techniques. On the other hand, bio-functional surfaces on metallic biomaterials such as titanium and its alloys are necessary to enhance the biological interactions with the host tissue. This study discusses the effect of plasma electrolytic oxidation (PEO), as a surface modification technique to produce bio-functional layers, on the mechanical properties of additively manufactured Ti6Al4V scaffolds based on the cubic unit cell. For this purpose, the PEO process with two different oxidation times was applied on scaffolds with four different values of relative density. The effects of the PEO process were studied by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), optical microscopy as well as static and dynamic (fatigue) mechanical testing under compression. SEM results indicated pore formation on the surface of the scaffolds after oxidation with a thickness of 4.85±0.36μm of the oxide layer after 2min and 9.04±2.27μm after 5min oxidation (based on optical images). The static test results showed the high effect of relative density of porous structure on its mechanical properties. However, oxidation did not influence most of the mechanical properties such as maximum stress, yield stress, plateau stress, and energy absorption, although its effect on the elastic modulus was considerable. Under fatigue loading, none of the scaffolds failed even after 10 6 loading cycles at 70% of their yield stress. Copyright © 2017 Elsevier B.V. All rights reserved.

  18. Fluid mechanics of additive manufacturing of metal objects by accretion of droplets – a survey

    Directory of Open Access Journals (Sweden)

    Tesař Václav

    2016-01-01

    Full Text Available Paper presents a survey of principles of additive manufacturing of metal objects by accretion of molten metal droplets, focusing on fluid-mechanical problems that deserve being investigated. The main problem is slowness of manufacturing due to necessarily small size of added droplets. Increase of droplet repetition rate calls for basic research of the phenomena that take place inside and around the droplets: ballistics of their flight, internal flowfield with heat and mass transfer, oscillation of surfaces, and the ways to elimination of satellite droplets.

  19. Effect of scandium additions on microstructure and mechanical properties of Al-Zn-Mg alloy welds

    International Nuclear Information System (INIS)

    Dev, Selvi; Stuart, A. Archibald; Kumaar, R.C. Ravi Dev; Murty, B.S.; Rao, K. Prasad

    2007-01-01

    The microstructure and mechanical properties of fusion zones of medium strength Al-Zn-Mg alloy (RDE-40) welds obtained by using different fillers containing various amount of scandium was investigated. It was observed that addition of scandium led to very significant grain refinement in the fusion zone especially for scandium levels greater than the eutectic composition (0.55 wt%). The grain refinement led to the reduction in solidification cracking and improved the tensile properties of fusion zone compared to the ones obtained by the commercial AA5556 filler

  20. Fluid mechanics of additive manufacturing of metal objects by accretion of droplets - a survey

    Science.gov (United States)

    Tesař, Václav

    2016-03-01

    Paper presents a survey of principles of additive manufacturing of metal objects by accretion of molten metal droplets, focusing on fluid-mechanical problems that deserve being investigated. The main problem is slowness of manufacturing due to necessarily small size of added droplets. Increase of droplet repetition rate calls for basic research of the phenomena that take place inside and around the droplets: ballistics of their flight, internal flowfield with heat and mass transfer, oscillation of surfaces, and the ways to elimination of satellite droplets.

  1. Effect of glass microfibre addition on the mechanical performances of fly ash-based geopolymer composites

    Directory of Open Access Journals (Sweden)

    Thamer Alomayri

    2017-09-01

    Full Text Available In the present study, various amounts of glass microfibres were introduced into a geopolymer for reinforcement purposes. The influence of these microfibres on the performance of the geopolymer composites was investigated. Results show that the appropriate addition of glass microfibres can improve the mechanical properties of geopolymer composites. In particular, the flexural strength, flexural modulus and impact strength increase at an optimum fibre content of 2 wt%. Further, adding glass microfibres to a plain geopolymer matrix has a significant effect on the pre-cracking behaviour. It substantially enhances the post-cracking response.

  2. Investigation of mechanical properties of masterbatches and composites with small additions of CNTs

    International Nuclear Information System (INIS)

    Burmistrov, I N; Yudintseva, T I; Ilinykh, I A; Khaydarov, B B; Mazov, I N; Anshin, S M; Kuznetsov, D V

    2016-01-01

    The present paper investigated physical and mechanical properties of the nanotube masterbatches and the polymer composites with low contents of carbon nanotubes (CNTs), which were obtained by diluting masterbatches. Ethylene-octene copolymer was used as the binder for the masterbatches, which provides the elasticity of the material at a content 20 wt% of CNT. Masterbatches were obtained with a 2-roller mixer, and their additive to polypropylene was carried out on a single screw injection molding machine. Strength properties of ethylene-octene copolymer increased when additing CNTs in an amount of 5-20 wt%. When the concentration of CNT in masterbatches is reduced to 0.01-0.1 wt% its strength characteristics increased up to 4-18%. The most effective strengthening of polypropylene was observed with the content of CNTs 0.1 wt%. (paper)

  3. Influence of WC addition on the microstructure and mechanical properties of NbC-Co cermets

    International Nuclear Information System (INIS)

    Huang, S.G.; Li, L.; Van der Biest, O.; Vleugels, J.

    2007-01-01

    NbC-24.5 wt.% Co cermets with up to 30 wt.% WC were obtained by solid state hot pressing at 1300 o C under a pressure of 45 MPa for 10 min and pressureless liquid phase sintering at 1360 o C for 60 min. The effect of WC addition on the microstructure and mechanical properties of NbC-Co based cermets was investigated. The hot pressed cermets exhibited interconnected and irregular niobium carbide (NbC) or (Nb,W)C grains, whereas the shape of the NbC grains changed from faceted with rounded corners to spherical, as the WC content increased in the pressureless sintered cermets. The undissolved WC increased with increasing WC addition. A clear core/rim structure was observed in the hot pressed cermets with 10-30 wt.% WC additions, whereas this structure was gradually eliminated when pressureless sintering. The hardness remains nearly constant whereas the fracture toughness slightly increases with increasing WC addition. The dissolution of WC in the Co binder and NbC grains, as well as the formation of a solid solution (Nb,W)C phase were supported by thermodynamic calculations

  4. Influence of the addition of gadolinium on the microstructure and mechanical properties of duplex stainless steel

    International Nuclear Information System (INIS)

    Ahn, Ji-Ho; Jung, Hyun-Do; Im, Jae-Han; Jung, Ki Ho; Moon, Byung-Moon

    2016-01-01

    The aim of this study is to investigate the effects of gadolinium addition on the microstructure and mechanical properties of duplex stainless steel (DSS) fabricated using a normal casting method. The oxygen content in the cast DSS alloy with gadolinium decreased because of the high reactivity of gadolinium with oxygen. The area fraction and size of non-intermetallic inclusions in the alloy decreased from 0.80±0.12% to 0.58±0.04% and from 6.9±0.7 to 5.8±0.4 μm upon gadolinium addition, respectively. Notably, the ultimate tensile strength and strain at break of the cast alloy significantly increased with the addition of gadolinium from 919±25 to 969±8 MPa and from 24.8±1.9% to 28.4±1.1%, respectively. The hardness of the cast alloy with gadolinium increased from 23.6±1.3 to 25.0±1.2 HRC. A significant increase in the impact energy of the cast alloy was observed and the brittle-to-ductile transition temperature slightly decreased by approximately 10 °C with the addition of gadolinium.

  5. INFLUENCE OF COCONUT SHELL ADDITION ON PHYSICO-MECHANICAL PROPERTIES OF WOOD PLASTIC COMPOSITES1

    Directory of Open Access Journals (Sweden)

    Éverton Hillig

    2018-04-01

    Full Text Available ABSTRACT In this study, composites with three types of thermoplastic matrix and cellulosic material in a proportion of 40% were produced. The three thermoplastic matrices were high density polyethylene (HDPE, polypropylene (PP and low density polyethylene (LDPE, and the cellulosic materials were pure wood flour (Pinus taeda L or a mixture of wood flour and coconut shell flour (Cocus nucifera L in equal ratios. The objective was to evaluate the influence of addition of coconut shell on the physico-mechanical properties (density, strength and rigidity and the distribution of the cellulosic material in the thermoplastic matrix of the manufactured composites. It was found that the composites had a satisfactory distribution of wood flour in thermoplastic matrices, but the addition of coconut shell promoted bubble formation in the resulting pieces and, thus, interfered with the material properties. The use of a coupling agent promoted interfacial adhesion (cellulose - thermoplastic matrix, which was better in high density polyethylene composites, followed by polypropylene and low density polyethylene. In general, the coconut shell addition caused a decrease of all properties compared to composites made with Loblolly Pine. In addition, the interactions between thermoplastic type and cellulosic matrix type have been statistically confirmed, which caused variations in the studied properties

  6. Exploring the mechanical strength of additively manufactured metal structures with embedded electrical materials

    Energy Technology Data Exchange (ETDEWEB)

    Li, J., E-mail: J.Li5@lboro.ac.uk; Monaghan, T.; Masurtschak, S.; Bournias-Varotsis, A.; Friel, R.J.; Harris, R.A.

    2015-07-15

    Ultrasonic Additive Manufacturing (UAM) enables the integration of a wide variety of components into solid metal matrices due to the process induced high degree of metal matrix plastic flow at low bulk temperatures. Exploitation of this phenomenon allows the fabrication of previously unobtainable novel engineered metal matrix components. The feasibility of directly embedding electrical materials within UAM metal matrices was investigated in this work. Three different dielectric materials were embedded into UAM fabricated aluminium metal-matrices with, research derived, optimal processing parameters. The effect of the dielectric material hardness on the final metal matrix mechanical strength after UAM processing was investigated systematically via mechanical peel testing and microscopy. It was found that when the Knoop hardness of the dielectric film was increased from 12.1 HK/0.01 kg to 27.3 HK/0.01 kg, the mechanical peel testing and linear weld density of the bond interface were enhanced by 15% and 16%, respectively, at UAM parameters of 1600 N weld force, 25 µm sonotrode amplitude, and 20 mm/s welding speed. This work uniquely identified that the mechanical strength of dielectric containing UAM metal matrices improved with increasing dielectric material hardness. It was therefore concluded that any UAM metal matrix mechanical strength degradation due to dielectric embedding could be restricted by employing a dielectric material with a suitable hardness (larger than 20 HK/0.01 kg). This result is of great interest and a vital step for realising electronic containing multifunctional smart metal composites for future industrial applications.

  7. Effect of Silicon Addition on Microstructure and Mechanical Properties of Chromium and Titanium Based Coatings

    Directory of Open Access Journals (Sweden)

    Luis Carlos Ardila-Téllez

    2014-07-01

    Full Text Available The changes in the microstructure, mechanical properties and residual stresses of AlTiN, AlTiSiN, AlCrN and AlCrSiN coatings, has been studied before and after annealing at 900 ºC and 1100 ºC, using scanning and transmission electron microscopy, along with nano-indentation and X-ray diffraction techniques. The As-deposited coatings show a columnar structure, with a crystallite size between 18 nm and 28 nm. Despite the silicon addition, no effect on the crystallite size refinement was observed.However, the addition of silicon increases hardness, elastic modulus and compressive residual stresses. After annealing at 900 ºC, the crystallite size growth and the residual stress relaxes; therefore, the coating hardness decreases. At 1100 ºC, the oxide layers formed in AlTiN and AlTiSiN, which act as protective layers enhancing oxidation resistance; meanwhile, a complete oxidation of AlCrN and AlCrSiN coatings take place. The Titanium based coatings present some superior mechanical properties and oxidation resistance than the chromium based coatings at 900 ºC and 1100 ºC.

  8. The effects of tantalum addition on the microtexture and mechanical behaviour of tungsten for ITER applications

    Energy Technology Data Exchange (ETDEWEB)

    Tejado, E., E-mail: elena.tejado@mater.upm.es [Departamento de Ciencia de Materiales-CIME, ETSI Caminos, Canales y Puertos, Universidad Politécnica de Madrid, Madrid (Spain); Centro Nacional de Investigaciones Metalúrgicas (CSIC), Madrid (Spain); Carvalho, P.A. [Associação Euratom/IST, Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade Técnica de Lisboa, Av. Rovisco Pais, 1049-001 Lisboa (Portugal); ICEMS, Departamento de Bioengenharia, Instituto Superior Técnico, Av. Rovisco Pais, 1049-001 Lisboa (Portugal); Munoz, A. [Departamento de Física, Universidad Carlos III, Leganés (Spain); Dias, M. [Associação Euratom/IST, Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade Técnica de Lisboa, Av. Rovisco Pais, 1049-001 Lisboa (Portugal); Correia, J.B. [Associação Euratom/IST, Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade Técnica de Lisboa, Av. Rovisco Pais, 1049-001 Lisboa (Portugal); LNEG, Laboratório Nacional de Energia e Geologia, Estrada do Paço do Lumiar, 1649-038 Lisboa (Portugal); and others

    2015-12-15

    Tungsten (W) and its alloys are very promising materials for producing plasma-facing components (PFCs) in the fusion power reactors of the near future, even as a structural part in them. However, whereas the properties of pure tungsten are suitable for a PFC, its structural applications are still limited due to its low toughness, ductile to brittle transition temperature and recrystallization behaviour. Therefore, many efforts have been made to improve its performance by alloying tungsten with other elements. Hence, in this investigation, the thermo-mechanical performance of two new tungsten-tantalum materials has been evaluated. Materials with W–5wt.%Ta and W–15wt.%Ta were processed by mechanical alloying (MA) and later consolidation by hot isostatic pressing (HIP), with distinct settings for each composition. Thus, it was possible to determine the relationship between the microstructure and the addition of Ta with the macroscopic mechanical properties. These were measured by means of hardness, flexural strength and fracture toughness, in the temperature range of 300–1473 K. The microstructure and the fracture surfaces features of the tested materials were analysed by Field Emission Scanning Electron Microscopy (FESEM).

  9. The effects of tantalum addition on the microtexture and mechanical behaviour of tungsten for ITER applications

    International Nuclear Information System (INIS)

    Tejado, E.; Carvalho, P.A.; Munoz, A.; Dias, M.; Correia, J.B.

    2015-01-01

    Tungsten (W) and its alloys are very promising materials for producing plasma-facing components (PFCs) in the fusion power reactors of the near future, even as a structural part in them. However, whereas the properties of pure tungsten are suitable for a PFC, its structural applications are still limited due to its low toughness, ductile to brittle transition temperature and recrystallization behaviour. Therefore, many efforts have been made to improve its performance by alloying tungsten with other elements. Hence, in this investigation, the thermo-mechanical performance of two new tungsten-tantalum materials has been evaluated. Materials with W–5wt.%Ta and W–15wt.%Ta were processed by mechanical alloying (MA) and later consolidation by hot isostatic pressing (HIP), with distinct settings for each composition. Thus, it was possible to determine the relationship between the microstructure and the addition of Ta with the macroscopic mechanical properties. These were measured by means of hardness, flexural strength and fracture toughness, in the temperature range of 300–1473 K. The microstructure and the fracture surfaces features of the tested materials were analysed by Field Emission Scanning Electron Microscopy (FESEM).

  10. Additively Manufactured Scaffolds for Bone Tissue Engineering and the Prediction of their Mechanical Behavior: A Review.

    Science.gov (United States)

    Zhang, Xiang-Yu; Fang, Gang; Zhou, Jie

    2017-01-10

    Additive manufacturing (AM), nowadays commonly known as 3D printing, is a revolutionary materials processing technology, particularly suitable for the production of low-volume parts with high shape complexities and often with multiple functions. As such, it holds great promise for the fabrication of patient-specific implants. In recent years, remarkable progress has been made in implementing AM in the bio-fabrication field. This paper presents an overview on the state-of-the-art AM technology for bone tissue engineering (BTE) scaffolds, with a particular focus on the AM scaffolds made of metallic biomaterials. It starts with a brief description of architecture design strategies to meet the biological and mechanical property requirements of scaffolds. Then, it summarizes the working principles, advantages and limitations of each of AM methods suitable for creating porous structures and manufacturing scaffolds from powdered materials. It elaborates on the finite-element (FE) analysis applied to predict the mechanical behavior of AM scaffolds, as well as the effect of the architectural design of porous structure on its mechanical properties. The review ends up with the authors' view on the current challenges and further research directions.

  11. Design of a mechanical system in gait rehabilitation with progressive addition of weight

    Science.gov (United States)

    Braidot, Ariel A. A.; Aleman, Guillermo L.

    2011-12-01

    In this paper we designed and developed a mechanical device for gait rehabilitation based on the application of "partial body weight reduction therapy". An evaluation of the characteristics of devices based on this therapy currently available on the market was carried out obtaining information of the different mechanisms used in it. The device was designed to adapt to different height and weight of patients and to be used with additional equipment in gait rehabilitation, for example, treadmills, elliptical trainers and vertical scalers. It was envisaged to be used by patients with asymmetry in the lower extremities capabilities. We developed a stable structure in steel ASTM A36 which does not depend on the building conditions of the installation site. RamAdvanse software was used to calculate structural stability. A winch with automatic brake mechanism was used to raise/lower the patient, who was tied to a comfortable harness which provided safety to the patient and therapist. It was possible to quantify precisely, using counterweights, the weight borne by the patient during therapy. We obtained a small-sized and ergonomic low-cost prototype, with similar features to those currently considered cutting-edge devices.

  12. Effect of additives for higher removal rate in lithium niobate chemical mechanical planarization

    International Nuclear Information System (INIS)

    Jeong, Sukhoon; Lee, Hyunseop; Cho, Hanchul; Lee, Sangjik; Kim, Hyoungjae; Kim, Sungryul; Park, Jaehong; Jeong, Haedo

    2010-01-01

    High roughness and a greater number of defects were created by lithium niobate (LN; LiNbO 3 ) processes such as traditional grinding and mechanical polishing (MP), should be decreased for manufacturing LN device. Therefore, an alternative process for gaining defect-free and smooth surface is needed. Chemical mechanical planarization (CMP) is suitable method in the LN process because it uses a combination approach consisting of chemical and mechanical effects. First of all, we investigated the LN CMP process using commercial slurry by changing various process conditions such as down pressure and relative velocity. However, the LN CMP process time using commercial slurry was long to gain a smooth surface because of lower material removal rate (MRR). So, to improve the material removal rate (MRR), the effects of additives such as oxidizer (hydrogen peroxide; H 2 O 2 ) and complexing agent (citric acid; C 6 H 8 O 7 ) in a potassium hydroxide (KOH) based slurry, were investigated. The manufactured slurry consisting of H 2 O 2 -citric acid in the KOH based slurry shows that the MRR of the H 2 O 2 at 2 wt% and the citric acid at 0.06 M was higher than the MRR for other conditions.

  13. Design of a mechanical system in gait rehabilitation with progressive addition of weight

    International Nuclear Information System (INIS)

    Braidot, Ariel A A; Aleman, Guillermo L

    2011-01-01

    In this paper we designed and developed a mechanical device for gait rehabilitation based on the application of p artial body weight reduction therapy . An evaluation of the characteristics of devices based on this therapy currently available on the market was carried out obtaining information of the different mechanisms used in it. The device was designed to adapt to different height and weight of patients and to be used with additional equipment in gait rehabilitation, for example, treadmills, elliptical trainers and vertical scalers. It was envisaged to be used by patients with asymmetry in the lower extremities capabilities. We developed a stable structure in steel ASTM A36 which does not depend on the building conditions of the installation site. RamAdvanse software was used to calculate structural stability. A winch with automatic brake mechanism was used to raise/lower the patient, who was tied to a comfortable harness which provided safety to the patient and therapist. It was possible to quantify precisely, using counterweights, the weight borne by the patient during therapy. We obtained a small-sized and ergonomic low-cost prototype, with similar features to those currently considered cutting-edge devices.

  14. Modeling and additive manufacturing of bio-inspired composites with tunable fracture mechanical properties.

    Science.gov (United States)

    Dimas, Leon S; Buehler, Markus J

    2014-07-07

    Flaws, imperfections and cracks are ubiquitous in material systems and are commonly the catalysts of catastrophic material failure. As stresses and strains tend to concentrate around cracks and imperfections, structures tend to fail far before large regions of material have ever been subjected to significant loading. Therefore, a major challenge in material design is to engineer systems that perform on par with pristine structures despite the presence of imperfections. In this work we integrate knowledge of biological systems with computational modeling and state of the art additive manufacturing to synthesize advanced composites with tunable fracture mechanical properties. Supported by extensive mesoscale computer simulations, we demonstrate the design and manufacturing of composites that exhibit deformation mechanisms characteristic of pristine systems, featuring flaw-tolerant properties. We analyze the results by directly comparing strain fields for the synthesized composites, obtained through digital image correlation (DIC), and the computationally tested composites. Moreover, we plot Ashby diagrams for the range of simulated and experimental composites. Our findings show good agreement between simulation and experiment, confirming that the proposed mechanisms have a significant potential for vastly improving the fracture response of composite materials. We elucidate the role of stiffness ratio variations of composite constituents as an important feature in determining the composite properties. Moreover, our work validates the predictive ability of our models, presenting them as useful tools for guiding further material design. This work enables the tailored design and manufacturing of composites assembled from inferior building blocks, that obtain optimal combinations of stiffness and toughness.

  15. Mechanism of wear and tribofilm formation with ionic liquids and ashless antiwear additives

    Science.gov (United States)

    Sharma, Vibhu

    Increasingly stringent government regulation on emissions (EPA Emissions Standard Reference Guide and latest CAFE standards requiring an average fuel economy of 54.5 mpg (combined cars and trucks) by 2025) impose significant challenges to the automotive and lubricant industries calling for the development and implementation of lower viscosity ILSAC GF-5&6 and API-CJ4&5 oils which further limit the amount of SAPS and deposits in engines. Development of additives that result in lower ash content, volatility and anti-wear property plays a crucial role in being able to reach these standards. The current industrial additive technology i.e. zinc dialkyldithiophosphate (ZDDP) forms harmful deposits on catalytic convertor due to the volatility of Zn, S and P which, impairs its functionality and consequently results in higher emission from vehicles. In this research work, ionic liquids (IL's) that are non-volatile have been studied as new generation environment friendly antiwear additives along with other ashless anti-wear additives including boron based additives to overcome the current challenges of improving the fuel efficiency and reducing the amount of hazardous emissions. The goal of this thesis work is to study the tribological performance of selected IL's and develop a comprehensive understating of IL's chemistry and its consequences to their friction and wear outcomes. As first approach, various P, S and F based ionic liquids are studied for their tribological properties by analyzing the friction and wear results generated using standard tribological experiments. Following this, advanced surface characterization techniques such as X-ray absorption near edge structure (XANES) spectroscopy, SEM, Nano-indentation, SPM techniques are used to investigate the chemical-mechanical properties of the antiwear films. Results indicate that the tribological properties of ionic liquids depend on their solubility in base oil (BO) as well as their chemical interaction with the

  16. Repaglinide-gemfibrozil drug interaction: inhibition of repaglinide glucuronidation as a potential additional contributing mechanism.

    Science.gov (United States)

    Gan, Jinping; Chen, Weiqi; Shen, Hong; Gao, Ling; Hong, Yang; Tian, Yuan; Li, Wenying; Zhang, Yueping; Tang, Yuwei; Zhang, Hongjian; Humphreys, William Griffith; Rodrigues, A David

    2010-12-01

    To further explore the mechanism underlying the interaction between repaglinide and gemfibrozil, alone or in combination with itraconazole. Repaglinide metabolism was assessed in vitro (human liver subcellular fractions, fresh human hepatocytes, and recombinant enzymes) and the resulting incubates were analyzed, by liquid chromatography-mass spectrometry (LC-MS) and radioactivity counting, to identify and quantify the different metabolites therein. Chemical inhibitors, in addition to a trapping agent, were also employed to elucidate the importance of each metabolic pathway. Finally, a panel of human liver microsomes (genotyped for UGT1A1*28 allele status) was used to determine the importance of UGT1A1 in the direct glucuronidation of repaglinide. The results of the present study demonstrate that repaglinide can undergo direct glucuronidation, a pathway that can possibly contribute to the interaction with gemfibrozil. For example, [³H]-repaglinide formed glucuronide and oxidative metabolites (M2 and M4) when incubated with primary human hepatocytes. Gemfibrozil effectively inhibited (∼78%) both glucuronide and M4 formation, but had a minor effect on M2 formation. Concomitantly, the overall turnover of repaglinide was also inhibited (∼80%), and was completely abolished when gemfibrozil was co-incubated with itraconazole. These observations are in qualitative agreement with the in vivo findings. UGT1A1 plays a significant role in the glucuronidation of repaglinide. In addition, gemfibrozil and its glucuronide inhibit repaglinide glucuronidation and the inhibition by gemfibrozil glucuronide is time-dependent. Inhibition of UGT enzymes, especially UGT1A1, by gemfibrozil and its glucuronide is an additional mechanism to consider when rationalizing the interaction between repaglinide and gemfibrozil. © 2010 The Authors. British Journal of Clinical Pharmacology © 2010 The British Pharmacological Society.

  17. Salmonella-secreted Virulence Factors

    Energy Technology Data Exchange (ETDEWEB)

    Heffron, Fred; Niemann, George; Yoon, Hyunjin; Kidwai, Afshan S.; Brown, Roslyn N.; McDermott, Jason E.; Smith, Richard D.; Adkins, Joshua N.

    2011-05-01

    In this short review we discuss secreted virulence factors of Salmonella, which directly affect Salmonella interaction with its host. Salmonella secretes protein to subvert host defenses but also, as discussed, to reduce virulence thereby permitting the bacteria to persist longer and more successfully disperse. The type III secretion system (TTSS) is the best known and well studied of the mechanisms that enable secretion from the bacterial cytoplasm to the host cell cytoplasm. Other secretion systems include outer membrane vesicles, which are present in all Gram-negative bacteria examined to date, two-partner secretion, and type VI secretion will also be addressed. Excellent reviews of Salmonella secreted effectors have focused on themes such as actin rearrangements, vesicular trafficking, ubiquitination, and the activities of the virulence factors themselves. This short review is based on S. Typhimurium infection of mice because it is a model of typhoid like disease in humans. We have organized effectors in terms of events that happen during the infection cycle and how secreted effectors may be involved.

  18. Effect of La addition on the microstructure and mechanical properties of Mg–6 wt% Zn alloys

    Energy Technology Data Exchange (ETDEWEB)

    Du, Yuzhou, E-mail: duyuzhou@xaut.edu.cn [School of Materials Science and Engineering, Xi' an University of Technology, Xi' an 710048 (China); School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001 (China); Zheng, Mingyi, E-mail: zhenghe@hit.edu.cn [School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001 (China); Qiao, Xiaoguang [School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001 (China); Peng, Wenqiang [Institute of Chemical Materials, China Academy of Engineering Physics, Mianyang 621999 (China); Jiang, Bailing [School of Materials Science and Engineering, Xi' an University of Technology, Xi' an 710048 (China)

    2016-09-15

    The Mg–6 wt% Zn alloys microalloyed with different amounts of La were cast and extruded. The second phase in the as-cast Mg–Zn alloy is Mg{sub 4}Zn{sub 7}, which was replaced by Mg–Zn–La intermetallics with orthorhombic structure after La addition. Microalloying with La refined the grain size of dynamic recrystallization slightly, which was due to La solute atom in α-Mg alloy. Addition of La weakened the texture and gave rise to the formation of non-basal texture component, attributing to the existence of La in the form of solute atoms in matrix. The ductility was enhanced significantly by adding La to Mg–6 wt% Zn alloy, while the strength was reduced. Such phenomenon was related to the weakening texture of the La containing alloys. The Mg–6Zn–0.2La (wt%) alloy exhibited a superior ductility with the elongation-to-fracture up to 35%. However, with further increasing of La content to 1 wt%, the strength of the as-extruded Mg–Zn–La alloys was not improved but the ductility was reduced, suggesting that small addition of La is preferred for the improvement of mechanical properties.

  19. Study of the reduction mechanism of ironsands with addition of blast furnace bag dust

    Science.gov (United States)

    Xing, Xiangdong; Chen, Yunfei; Liu, Yiran

    2018-02-01

    To improve the reduction properties of ironsands carbon-containing briquettes, the behavior of ironsand during reduction by the addition of blast furnace bag dust (BFBD) is studied using a high temperature resistance furnace, X-ray diffraction (XRD) analysis and scanning electron microscopy. Additionally, the reduction mechanism is discussed in this study. The results showed that the reduction level and compressive strength of ironsand carbon-containing briquettes could be promoted by increasing the proportion of BFBD. When the addition rate of BFBD was 31.25%, the metallization rate and compressive strength increased from 82.1% and 21.5 N/a to 91.4% and 172.5 N/a, respectively. Metallic iron reduced from BFBD particles favored the carbon gasification reaction, which enhanced the internal CO concentration, and then promoted the FeTiO3 reduction to Fe in ironsand. Meanwhile, a large amount of the liquid phase generated during the reduction process also favored Fe2+ diffusion, spread of iron joined crystals and the growth of crystals, which resulted in the improvement of the compressive strength of the ironsand carbon-containing briquettes.

  20. Effect of Meltable Triazine-DOPO Additive on Rheological, Mechanical, and Flammability Properties of PA6

    Directory of Open Access Journals (Sweden)

    Irina Butnaru

    2015-08-01

    Full Text Available Through a straightforward approach, a new meltable, halogen-free, nitrogen-phosphorus-based flame retardant (FR, 6-(2-(4,6-diamino-1,3,5-triazin-2-ylethyl dibenzo[c,e][1,2]oxaphosphinine 6-oxide (DTE-DOPO was synthesized and incorporated in polyamide 6 (PA6. It was proved that a very low phosphorus content of 1.46 wt% for DTE-DOPO additive improved the flame retardancy of PA6, leading to a non-flammable material. The performance of the new additive was compared to that of the commercially-available Exolit® OP 1230. The PA6 formulations were evaluated by measuring the rheological, mechanical, and flammability behavior. Using compounding by melt extrusion, 17 wt% additives was introduced into PA6 matrix and the corresponding formulations were characterized. The results evidenced a higher homogeneity of DTE-DOPO with PA6, a high thermal stability with a catalyzing decomposition effect on PA6 caused by the presence of the new developed FR, enhanced elasticity for the PA6/DTE-DOPO formulation and a V0 rating for both formulations. Thermal and fire analysis indicated a primary gas-phase activity, combined with a complete suppression of the self-sustained burning for the PA6/DTE-DOPO formulation.

  1. Microstructure refinement and strengthening mechanisms of a 9Cr oxide dispersion strengthened steel by zirconium addition

    International Nuclear Information System (INIS)

    Xu, Hai Jian; Lu, Zheng; Wang, Dong Mei; Liu, Chunming

    2017-01-01

    To study the effects of zirconium (Zr) addition on the microstructure, hardness and the tensile properties of oxide dispersion strengthened (ODS) ferritic-martensitic steels, two kinds of 9Cr-ODS ferritic-martensitic steels with nominal compositions (wt.%) of Fe-9Cr-2W-0.3Y_2O-3 and Fe-9Cr-2W-0.3Zr-0.3Y_2O_3 were fabricated by the mechanical alloying (MA) of premixed powders and then consolidated by hot isostatic pressing (HIP) techniques. The experimental results showed that the average grain size decreases with Zr addition. The trigonal δ-phase Y_4Zr_3O_1_2 oxides and body-centered cubic Y_2O_3 oxides are formed in the 9Cr-Zr-ODS steel and 9Cr non-Zr ODS steel, respectively, and the average size of Y_4Zr_3O_1_2 particles is much smaller than that of Y_2O_3. The dispersion morphology of the oxide particles in 9Cr-Zr-ODS steel is significantly improved and the number density is 1.1 x 10"2"3/m"3 with Zr addition. The 9Cr-Zr-ODS steel shows much higher tensile ductility, ultimate tensile strength and Vickers hardness at the same time

  2. Microstructure refinement and strengthening mechanisms of a 9Cr oxide dispersion strengthened steel by zirconium addition

    Energy Technology Data Exchange (ETDEWEB)

    Xu, Hai Jian; Lu, Zheng; Wang, Dong Mei; Liu, Chunming [Key Laboratory for Anisotropy and Texture of Materials (Ministry of Education), School of Materials Science and Engineering, Northeastern University, Shenyang (China)

    2017-02-15

    To study the effects of zirconium (Zr) addition on the microstructure, hardness and the tensile properties of oxide dispersion strengthened (ODS) ferritic-martensitic steels, two kinds of 9Cr-ODS ferritic-martensitic steels with nominal compositions (wt.%) of Fe-9Cr-2W-0.3Y{sub 2}O-3 and Fe-9Cr-2W-0.3Zr-0.3Y{sub 2}O{sub 3} were fabricated by the mechanical alloying (MA) of premixed powders and then consolidated by hot isostatic pressing (HIP) techniques. The experimental results showed that the average grain size decreases with Zr addition. The trigonal δ-phase Y{sub 4}Zr{sub 3}O{sub 12} oxides and body-centered cubic Y{sub 2}O{sub 3} oxides are formed in the 9Cr-Zr-ODS steel and 9Cr non-Zr ODS steel, respectively, and the average size of Y{sub 4}Zr{sub 3}O{sub 12} particles is much smaller than that of Y{sub 2}O{sub 3}. The dispersion morphology of the oxide particles in 9Cr-Zr-ODS steel is significantly improved and the number density is 1.1 x 10{sup 23}/m{sup 3} with Zr addition. The 9Cr-Zr-ODS steel shows much higher tensile ductility, ultimate tensile strength and Vickers hardness at the same time.

  3. Additional Stress And Fracture Mechanics Analyses Of Pressurized Water Reactor Pressure Vessel Nozzles

    International Nuclear Information System (INIS)

    Walter, Matthew; Yin, Shengjun; Stevens, Gary; Sommerville, Daniel; Palm, Nathan; Heinecke, Carol

    2012-01-01

    In past years, the authors have undertaken various studies of nozzles in both boiling water reactors (BWRs) and pressurized water reactors (PWRs) located in the reactor pressure vessel (RPV) adjacent to the core beltline region. Those studies described stress and fracture mechanics analyses performed to assess various RPV nozzle geometries, which were selected based on their proximity to the core beltline region, i.e., those nozzle configurations that are located close enough to the core region such that they may receive sufficient fluence prior to end-of-life (EOL) to require evaluation of embrittlement as part of the RPV analyses associated with pressure-temperature (P-T) limits. In this paper, additional stress and fracture analyses are summarized that were performed for additional PWR nozzles with the following objectives: To expand the population of PWR nozzle configurations evaluated, which was limited in the previous work to just two nozzles (one inlet and one outlet nozzle). To model and understand differences in stress results obtained for an internal pressure load case using a two-dimensional (2-D) axi-symmetric finite element model (FEM) vs. a three-dimensional (3-D) FEM for these PWR nozzles. In particular, the ovalization (stress concentration) effect of two intersecting cylinders, which is typical of RPV nozzle configurations, was investigated. To investigate the applicability of previously recommended linear elastic fracture mechanics (LEFM) hand solutions for calculating the Mode I stress intensity factor for a postulated nozzle corner crack for pressure loading for these PWR nozzles. These analyses were performed to further expand earlier work completed to support potential revision and refinement of Title 10 to the U.S. Code of Federal Regulations (CFR), Part 50, Appendix G, Fracture Toughness Requirements, and are intended to supplement similar evaluation of nozzles presented at the 2008, 2009, and 2011 Pressure Vessels and Piping (PVP

  4. Effect of yttrium addition on the microstructure and mechanical properties of ODS RAF steels

    International Nuclear Information System (INIS)

    Auger, M.A.; Castro, V. de; Leguey, T.; Tarcísio-Costa, J.; Monge, M.A.; Muñoz, A.; Pareja, R.

    2014-01-01

    An oxide dispersion strengthened (ODS) alloy with nominal composition Fe–14Cr–2W–0.3Ti–0.24Y (wt.%) was produced by mechanical alloying using elemental powders, and subsequent hot isostatic pressing. The microstructure of the material and characteristics of the oxide particle dispersion were investigated by electron microscopy. The effect of heat treatments on the microhardness and tensile properties at room temperature was also studied. The results show that a fine dispersion of Y–O-rich nanoparticles is achieved, together with larger (Cr, Ti)-rich precipitates. The absence of Ti is apparent in the majority of these nanoparticles, in contrast with reported results for ODS Ti-modified steels processed with Y 2 O 3 addition

  5. Effect of yttrium addition on the microstructure and mechanical properties of ODS RAF steels

    Energy Technology Data Exchange (ETDEWEB)

    Auger, M.A., E-mail: maria.auger@materials.ox.ac.uk [Departamento de Física, Universidad Carlos III de Madrid, Av Universidad 30, 28911 Leganés (Spain); Department of Materials, University of Oxford, Parks Road, OX1 3PH Oxford (United Kingdom); Castro, V. de; Leguey, T.; Tarcísio-Costa, J.; Monge, M.A.; Muñoz, A.; Pareja, R. [Departamento de Física, Universidad Carlos III de Madrid, Av Universidad 30, 28911 Leganés (Spain)

    2014-12-15

    An oxide dispersion strengthened (ODS) alloy with nominal composition Fe–14Cr–2W–0.3Ti–0.24Y (wt.%) was produced by mechanical alloying using elemental powders, and subsequent hot isostatic pressing. The microstructure of the material and characteristics of the oxide particle dispersion were investigated by electron microscopy. The effect of heat treatments on the microhardness and tensile properties at room temperature was also studied. The results show that a fine dispersion of Y–O-rich nanoparticles is achieved, together with larger (Cr, Ti)-rich precipitates. The absence of Ti is apparent in the majority of these nanoparticles, in contrast with reported results for ODS Ti-modified steels processed with Y{sub 2}O{sub 3} addition.

  6. Effect of Sc addition on microstructure and mechanical properties of 1460 alloy

    Directory of Open Access Journals (Sweden)

    Juan Ma

    2014-02-01

    Full Text Available The effect of minor addition of Sc on microstructure, age hardening behavior, tensile properties and fracture morphology of 1460 alloy have been studied. It is found that Sc content increase from 0.11 wt% to 0.22 wt% is favorable for grain refinement in as-cast alloy but results in a coarsening of Cu-rich particles. The alloy with 0.11 wt% Sc exhibits enhanced mechanical properties and age hardening effect. Transmission electron microscopy (TEM investigations on the alloy with 0.11 wt% Sc have suggested that a large amount of Al3(Sc, Zr particles precipitated at the earlier aging may inhibit recrystallization effectively.

  7. Mutations induced by ultraviolet radiation affecting virulence in Puccinia striiformis

    International Nuclear Information System (INIS)

    Shang Hongsheng; Jing Jinxue; Li Zhenqi

    1994-01-01

    Uredospores of parent culture, cy 29-1, were treated by ultraviolet radiation and mutations to virulent were tested on resistant wheat cultivars inoculated with treated spores. 7 mutant cultures virulent to the test cultivars were developed with estimated mutation rate 10~6~10~4. The virulence of mutant cultures was different from the all known races of stripe rust. Resistance segregation to mutant cultures was detected in two test cultivars. The results suggested that mutation was important mechanism of virulence variation operative in asexual population of rust fungi

  8. The Effect of Structural Design on Mechanical Properties and Cellular Response of Additive Manufactured Titanium Scaffolds

    Directory of Open Access Journals (Sweden)

    Jan Wieding

    2012-08-01

    Full Text Available Restoration of segmental defects in long bones remains a challenging task in orthopedic surgery. Although autologous bone is still the ‘Gold Standard’ because of its high biocompatibility, it has nevertheless been associated with several disadvantages. Consequently, artificial materials, such as calcium phosphate and titanium, have been considered for the treatment of bone defects. In the present study, the mechanical properties of three different scaffold designs were investigated. The scaffolds were made of titanium alloy (Ti6Al4V, fabricated by means of an additive manufacturing process with defined pore geometry and porosities of approximately 70%. Two scaffolds exhibited rectangular struts, orientated in the direction of loading. The struts for the third scaffold were orientated diagonal to the load direction, and featured a circular cross-section. Material properties were calculated from stress-strain relationships under axial compression testing. In vitro cell testing was undertaken with human osteoblasts on scaffolds fabricated using the same manufacturing process. Although the scaffolds exhibited different strut geometry, the mechanical properties of ultimate compressive strength were similar (145–164 MPa and in the range of human cortical bone. Test results for elastic modulus revealed values between 3.7 and 6.7 GPa. In vitro testing demonstrated proliferation and spreading of bone cells on the scaffold surface.

  9. Effect of addition of semi refined carrageenan on mechanical characteristics of gum arabic edible film

    Science.gov (United States)

    Setyorini, D.; Nurcahyani, P. R.

    2016-04-01

    Currently the seaweed is processed flour and Semi Refined Carraagenan (SRC). However, total production is small, but both of these products have a high value and are used in a wide variety of products such as cosmetics, processed foods, medicines, and edible film. The aim of this study were (1) to determine the effect of SRC on mechanical characteristics of edible film, (2) to determine the best edible film which added by SRC with different concentration. The edible film added by SRC flour which divided into three concentrations of SRC. There are 1.5%; 3%; and 4.5% of SRC, then added 3% glycerol and 0.6% arabic gum. The mechanical properties of the film measured by a universal testing machine Orientec Co. Ltd., while the water vapor permeability measured by the gravimetric method dessicant modified. The experimental design used was completely randomized design with a further test of Duncan. The result show SRC concentration differences affect the elongation breaking point and tensile strength. But not significant effect on the thickness, yield strength and the modulus of elasticity. The best edible film is edible film with the addition of SRC 4.5%.

  10. A Multiscale Understanding of the Thermodynamic and Kinetic Mechanisms of Laser Additive Manufacturing

    Directory of Open Access Journals (Sweden)

    Dongdong Gu

    2017-10-01

    Full Text Available Selective laser melting (SLM additive manufacturing (AM technology has become an important option for the precise manufacturing of complex-shaped metallic parts with high performance. The SLM AM process involves complicated physicochemical phenomena, thermodynamic behavior, and phase transformation as a high-energy laser beam melts loose powder particles. This paper provides multiscale modeling and coordinated control for the SLM of metallic materials including an aluminum (Al-based alloy (AlSi10Mg, a nickel (Ni-based super-alloy (Inconel 718, and ceramic particle-reinforced Al-based and Ni-based composites. The migration and distribution mechanisms of aluminium nitride (AlN particles in SLM-processed Al-based nanocomposites and the in situ formation of a gradient interface between the reinforcement and the matrix in SLM-processed tungsten carbide (WC/Inconel 718 composites were studied in the microscale. The laser absorption and melting/densification behaviors of AlSi10Mg and Inconel 718 alloy powder were disclosed in the mesoscale. Finally, the stress development during line-by-line localized laser scanning and the parameter-dependent control methods for the deformation of SLM-processed composites were proposed in the macroscale. Multiscale numerical simulation and experimental verification methods are beneficial in monitoring the complicated powder-laser interaction, heat and mass transfer behavior, and microstructural and mechanical properties development during the SLM AM process.

  11. Novel Additive Manufacturing Pneumatic Actuators and Mechanisms for Food Handling Grippers

    Directory of Open Access Journals (Sweden)

    Carlos Blanes

    2014-07-01

    Full Text Available Conventional pneumatic grippers are widely used in industrial pick and place robot processes for rigid objects. They are simple, robust and fast, but their design, motion and features are limited, and they do not fulfil the final purpose. Food products have a wide variety of shapes and textures and are susceptible to damaged. Robot grippers for food handling should adapt to this wide range of dimensions and must be fast, cheap, reasonably reliable, and with cheap and reasonable maintenance costs. They should not damage the product and must meet hygienic conditions. The additive manufacturing (AM process is able to manufacture parts without significant restrictions, and is Polyamide approved as food contact material by FDA. This paper presents that, taking the best of plastic flexibility, AM allows the implementation of novel actuators, original compliant mechanisms and practical grippers that are cheap, light, fast, small and easily adaptable to specific food products. However, if they are not carefully designed, the results can present problems, such as permanent deformations, low deformation limits, and low operation speed. We present possible solutions for the use of AM to design proper robot grippers for food handling. Some successful results, such as AM actuators based on deformable air chambers, AM compliant mechanisms, and grippers developed in a single part will be introduced and discussed.

  12. Effect of zirconium addition on the microstructure and mechanical properties of ODS ferritic steels containing aluminum

    International Nuclear Information System (INIS)

    Gao, R.; Zhang, T.; Wang, X.P.; Fang, Q.F.; Liu, C.S.

    2014-01-01

    The oxide dispersion strengthened (ODS) ferritic steels with nominal composition of Fe–16Cr–2W–0.5Ti–0.4Y 2 O 3 –4Al–1Zr (16Cr–4Al–Zr–ODS) were fabricated by a sol–gel method combining with mechanical alloying and spark plasma sintering (SPS) technique, and the 16Cr–ODS and 16Cr–4Al–ODS steels were prepared for comparison in the same way. Microstructure characterization reveals that in the 16Cr–4Al–ODS steel coarse Y–Al–O particles were formed while in the 16Cr–4Al–Zr–ODS steel finer Y–Zr–O particles were formed. The mean size and number density of the nano-oxide particles in the 16Cr–4Al–Zr–ODS steel are about 25 nm and 2.6 × 10 21 /m 3 , respectively. The ultimate tensile strength (UTS) of the 16Cr–ODS steel is about 1045 MPa, but UTS of the 16Cr–4Al–ODS steel decreases to 974 MPa. However, UTS of the 16Cr–4Al–Zr–ODS steel increases to 1180 MPa while keeping a large uniform elongation up to 23%, indicating the enhancement of mechanical properties by Zr addition

  13. Mechanical and radiation shielding properties of mortars with additive fine aggregate mine waste

    International Nuclear Information System (INIS)

    Gallala, Wissem; Hayouni, Yousra; Gaied, Mohamed Essghaier; Fusco, Michael; Alsaied, Jasmin; Bailey, Kathryn; Bourham, Mohamed

    2017-01-01

    Highlights: • Effectiveness of mine waste as additive fine aggregate has been investigated. • Experimental results are verified by computationally from composition of synthesized samples. • Work focuses on shielding materials for nuclear systems including spent fuel storage and drycasks. - Abstract: Incorporation of barite-fluorspar mine waste (BFMW) as a fine aggregate additive has been investigated for its effect on the mechanical and shielding properties of cement mortar. Several mortar mixtures were prepared with different proportions of BFMW ranging from 0% to 30% as fine aggregate replacement. Cement mortar mixtures were evaluated for density, compressive and tensile strengths, and gamma ray radiation shielding. The results revealed that the mortar mixes containing 25% BFMW reaches the highest compressive strength values, which exceeded 50 MPa. Evaluation of gamma-ray attenuation was both measured by experimental tests and computationally calculated using MicroShield software package, and results have shown that using BFMW aggregates increases attenuation coefficient by about 20%. These findings have demonstrated that the mine waste can be suitably used as partial replacement aggregate to improve radiation shielding as well as to reduce the mortar and concrete costs.

  14. Thermal degradation mechanism of addition-cure liquid silicone rubber with urea-containing silane

    International Nuclear Information System (INIS)

    Fang, Weizhen; Zeng, Xingrong; Lai, Xuejun; Li, Hongqiang; Chen, Wanjuan; Zhang, Yajun

    2015-01-01

    Highlights: • The urea-containing silane was incorporated into addition-cure liquid silicone rubber (ALSR) via hydrosilylation reaction. • The thermal stability of the ALSR was improved by DEUPAS both in nitrogen and air • The TG–FTIR of evolved gases during degradation was performed. • The possible degradation mechanism of the ALSR samples was proposed. - Abstract: The reactive urea-containing silane, (γ-diethylureidopropyl) allyloxyethoxysilane (DEUPAS), was synthesized by the trans-etherification reaction. The chemical structure was characterized by Fourier transform infrared spectrometry (FTIR) and 1 H nuclear magnetic resonance spectrometry ( 1 H NMR). Subsequently, DEUPAS was incorporated into addition-cure liquid silicone rubber (ALSR) via hydrosilylation reaction. The thermal stability of the ALSR samples was investigated by thermogravimetry (TG) and thermogravimetry–Fourier transform infrared spectrometry (TG–FTIR). When DEUPAS was incorporated, the temperature of 10% weight loss and 20% weight loss under air atmosphere were respectively increased by 31 °C and 60 °C compared with those of the ALSR without DEUPAS. Meanwhile, the residual weight at 800 °C increased from 33.5% to 58.7%. It was found that the striking enhancement in thermal stability of the ALSR samples was likely attributed to the decomposition of the urea groups to isocyanic acid, which reacted with hydroxyl groups to inhibit the unzipping depolymerization

  15. Thermal degradation mechanism of addition-cure liquid silicone rubber with urea-containing silane

    Energy Technology Data Exchange (ETDEWEB)

    Fang, Weizhen; Zeng, Xingrong, E-mail: psxrzeng@gmail.com; Lai, Xuejun; Li, Hongqiang; Chen, Wanjuan; Zhang, Yajun

    2015-04-10

    Highlights: • The urea-containing silane was incorporated into addition-cure liquid silicone rubber (ALSR) via hydrosilylation reaction. • The thermal stability of the ALSR was improved by DEUPAS both in nitrogen and air • The TG–FTIR of evolved gases during degradation was performed. • The possible degradation mechanism of the ALSR samples was proposed. - Abstract: The reactive urea-containing silane, (γ-diethylureidopropyl) allyloxyethoxysilane (DEUPAS), was synthesized by the trans-etherification reaction. The chemical structure was characterized by Fourier transform infrared spectrometry (FTIR) and {sup 1}H nuclear magnetic resonance spectrometry ({sup 1}H NMR). Subsequently, DEUPAS was incorporated into addition-cure liquid silicone rubber (ALSR) via hydrosilylation reaction. The thermal stability of the ALSR samples was investigated by thermogravimetry (TG) and thermogravimetry–Fourier transform infrared spectrometry (TG–FTIR). When DEUPAS was incorporated, the temperature of 10% weight loss and 20% weight loss under air atmosphere were respectively increased by 31 °C and 60 °C compared with those of the ALSR without DEUPAS. Meanwhile, the residual weight at 800 °C increased from 33.5% to 58.7%. It was found that the striking enhancement in thermal stability of the ALSR samples was likely attributed to the decomposition of the urea groups to isocyanic acid, which reacted with hydroxyl groups to inhibit the unzipping depolymerization.

  16. Mechanical properties of tungsten alloys with Y2O3 and titanium additions

    International Nuclear Information System (INIS)

    Aguirre, M.V.; Martin, A.; Pastor, J.Y.; LLorca, J.; Monge, M.A.; Pareja, R.

    2011-01-01

    In this research the mechanical behaviour of pure tungsten (W) and its alloys (2 wt.% Ti-0.47 wt.% Y 2 O 3 and 4 wt.% Ti-0.5 wt.% Y 2 O 3 ) is compared. These tungsten alloys, have been obtained by powder metallurgy. The yield strength, fracture toughness and elastic modulus have been studied in the temperature interval of 25 deg. C to 1000 deg. C. The results have shown that the addition of Ti substantially improves the bending strength and toughness of W, but it also dramatically increases the DBTT. On the other hand, the addition of 0.5% Y 2 O 3 , is enough to improve noticeably the oxidation behaviour at the higher temperatures. The grain size, fractography and microstructure are studied in these materials. Titanium is a good grain growth inhibitor and effective precursor of liquid phase in HIP. The simultaneous presence of Y 2 O 3 and Ti permits to obtain materials with low pores presence.

  17. Transparent Ethenylene-Bridged Polymethylsiloxane Aerogels: Mechanical Flexibility and Strength and Availability for Addition Reaction.

    Science.gov (United States)

    Shimizu, Taiyo; Kanamori, Kazuyoshi; Maeno, Ayaka; Kaji, Hironori; Doherty, Cara M; Nakanishi, Kazuki

    2017-05-09

    Transparent, low-density ethenylene-bridged polymethylsiloxane [Ethe-BPMS, O 2/2 (CH 3 )Si-CH═CH-Si(CH 3 )O 2/2 ] aerogels from 1,2-bis(methyldiethoxysilyl)ethene have successfully been synthesized via a sol-gel process. A two-step sol-gel process composed of hydrolysis under acidic conditions and polycondensation under basic conditions in a liquid surfactant produces a homogeneous pore structure based on cross-linked nanosized colloidal particles. Visible-light transmittance of the aerogels varies with the concentration of the base catalyst and reaches as high as 87% (at a wavelength of 550 nm for a 10 mm thick sample). Gelation and aging temperature strongly affect the deformation behavior of the resultant aerogels against uniaxial compression, and the obtained aerogels prepared at 80 °C show high elasticity after being unloaded. This highly resilient behavior is primarily derived from the rigidity of ethenylene groups, which is confirmed by a comparison with other aerogels with similar molecular structures, ethylene-bridged polymethylsiloxane and polymethylsilsesquioxane. Applicability of the addition reaction using a Diels-Alder reaction of benzocyclobutene has also been investigated, revealing that a successful addition takes place on the ethenylene linkings, which is verified using Raman and solid-state NMR spectroscopies. Insights into the effect of molecular structure on mechanical properties and the availability of surface functionalization provided in this study are important for realizing transparent aerogels with the desired functionality.

  18. Integrative genomic analysis identifies isoleucine and CodY as regulators of Listeria monocytogenes virulence.

    Directory of Open Access Journals (Sweden)

    Lior Lobel

    2012-09-01

    Full Text Available Intracellular bacterial pathogens are metabolically adapted to grow within mammalian cells. While these adaptations are fundamental to the ability to cause disease, we know little about the relationship between the pathogen's metabolism and virulence. Here we used an integrative Metabolic Analysis Tool that combines transcriptome data with genome-scale metabolic models to define the metabolic requirements of Listeria monocytogenes during infection. Twelve metabolic pathways were identified as differentially active during L. monocytogenes growth in macrophage cells. Intracellular replication requires de novo synthesis of histidine, arginine, purine, and branch chain amino acids (BCAAs, as well as catabolism of L-rhamnose and glycerol. The importance of each metabolic pathway during infection was confirmed by generation of gene knockout mutants in the respective pathways. Next, we investigated the association of these metabolic requirements in the regulation of L. monocytogenes virulence. Here we show that limiting BCAA concentrations, primarily isoleucine, results in robust induction of the master virulence activator gene, prfA, and the PrfA-regulated genes. This response was specific and required the nutrient responsive regulator CodY, which is known to bind isoleucine. Further analysis demonstrated that CodY is involved in prfA regulation, playing a role in prfA activation under limiting conditions of BCAAs. This study evidences an additional regulatory mechanism underlying L. monocytogenes virulence, placing CodY at the crossroads of metabolism and virulence.

  19. The Streptococcus sanguinis competence regulon is not required for infective endocarditis virulence in a rabbit model.

    Directory of Open Access Journals (Sweden)

    Jill E Callahan

    Full Text Available Streptococcus sanguinis is an important component of dental plaque and a leading cause of infective endocarditis. Genetic competence in S. sanguinis requires a quorum sensing system encoded by the early comCDE genes, as well as late genes controlled by the alternative sigma factor, ComX. Previous studies of Streptococcus pneumoniae and Streptococcus mutans have identified functions for the >100-gene com regulon in addition to DNA uptake, including virulence. We investigated this possibility in S. sanguinis. Strains deleted for the comCDE or comX master regulatory genes were created. Using a rabbit endocarditis model in conjunction with a variety of virulence assays, we determined that both mutants possessed infectivity equivalent to that of a virulent control strain, and that measures of disease were similar in rabbits infected with each strain. These results suggest that the com regulon is not required for S. sanguinis infective endocarditis virulence in this model. We propose that the different roles of the S. sanguinis, S. pneumoniae, and S. mutans com regulons in virulence can be understood in relation to the pathogenic mechanisms employed by each species.

  20. The Streptococcus sanguinis competence regulon is not required for infective endocarditis virulence in a rabbit model.

    Science.gov (United States)

    Callahan, Jill E; Munro, Cindy L; Kitten, Todd

    2011-01-01

    Streptococcus sanguinis is an important component of dental plaque and a leading cause of infective endocarditis. Genetic competence in S. sanguinis requires a quorum sensing system encoded by the early comCDE genes, as well as late genes controlled by the alternative sigma factor, ComX. Previous studies of Streptococcus pneumoniae and Streptococcus mutans have identified functions for the >100-gene com regulon in addition to DNA uptake, including virulence. We investigated this possibility in S. sanguinis. Strains deleted for the comCDE or comX master regulatory genes were created. Using a rabbit endocarditis model in conjunction with a variety of virulence assays, we determined that both mutants possessed infectivity equivalent to that of a virulent control strain, and that measures of disease were similar in rabbits infected with each strain. These results suggest that the com regulon is not required for S. sanguinis infective endocarditis virulence in this model. We propose that the different roles of the S. sanguinis, S. pneumoniae, and S. mutans com regulons in virulence can be understood in relation to the pathogenic mechanisms employed by each species.

  1. Mechanism for suppression of radiation-induced segregation by oversized solute addition in austenitic stainless steel

    Science.gov (United States)

    Hackett, Micah Jeremiah

    The objective of this thesis is to quantify the effect of oversized solutes on radiation-induced segregation in austenitic stainless steels and to determine the mechanism of this effect. Zr or Hf additions to austenitic stainless steels demonstrated a reduction in radiation-induced segregation of Cr and Ni at the grain boundary after proton irradiation at 400°C and 500°C to low doses, but the solute effect disappeared at higher doses. Rate theory modeling of RIS was extended to incorporate a solute-vacancy trapping mechanism to predict the effect of solutes on RIS. The model showed that RIS is most sensitive to the solute-vacancy binding energy. First principles calculations were used to determine a binding energy of 1.08 eV for Zr and 0.71 eV for Hf. Model and experiment agreed in showing suppression of Cr depletion at doses of 3 dpa at 400°C and 1 dpa at 500°C, and experimental results were consistent with the model in showing greater effectiveness of Zr relative to Hf due to a larger binding energy. The dislocation loop microstructure was measured at 400°C, 3 and 7 dpa, and a significant decrease in loop density and total loop line length in the oversized solute alloys relative to the reference alloys. The loop microstructure results were consistent with RIS results by confirming enhanced recombination of point defects by solute-vacancy trapping. Increases in RIS with dose indicated a loss of solute effectiveness, which was consistent with an observed increase in loop line length from 3 to 7 dpa. The loss of solute effectiveness at high dose is attributed to a loss of oversized solute from the matrix due to coarsening of carbide precipitates. X-ray diffraction identified a microstructure with ZrC or HfC precipitates prior to irradiation. Precipitate coarsening was identified as the most likely mechanism for the loss of solute effectiveness on RIS by the following: (1) diffusion analysis suggested significant solute diffusion by the vacancy flux to

  2. Unraveling Recrystallization Mechanisms Governing Texture Development from Rare Earth Element Additions to Magnesium

    Science.gov (United States)

    Imandoust, Aidin

    The origin of texture components associated with rare-earth (RE) element additions in wrought magnesium (Mg) alloys is a long-standing problem in magnesium technology. The objective of this research is to identify the mechanisms accountable for rare-earth texture during dynamic recrystallization (DRX). Towards this end, we designed binary Mg-Cerium and Mg-Gadolinium alloys along with complex alloy compositions containing zinc, yttrium and Mischmetal. Binary alloys along with pure Mg were designed to individually investigate their effects on texture evolutions, while complex compositions are designed to develop randomized texture, and be used in automotive and aerospace applications. We selected indirect extrusion to thermo-mechanically process our materials. Different extrusion ratios and speeds were designed to produce partially and fully recrystallized microstructures, allowing us to analyze DRX from its early stages to completion. X-ray diffraction, electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM) were used to conduct microstructure and texture analyses. Our analyses revealed that rare-earth elements in zinc-containing magnesium alloys promote discontinuous dynamic recrystallization at the grain boundaries. During nucleation, the effect of rare earth elements on orientation selection was explained by the concomitant actions of multiple Taylor axes in the same grain. Isotropic grain growth was observed due to rare earth elements segregating to grain boundaries, which lead to texture randomization. The nucleation in binary Mg-RE alloys took place by continuous formation of necklace structures. Stochastic relaxation of basal and non-basal dislocations into low-angle grain boundaries produced chains of embryos with nearly random orientations. Schmid factor analysis showed a lower net activation of dislocations in RE textured grains compared to ones on the other side of the stereographic triangle. Lower dislocation densities within

  3. Additional funding mechanisms for Public Hospitals in Greece: the case of Chania Mental Health Hospital.

    Science.gov (United States)

    Rentoumis, Anastasios; Mantzoufas, Nikolaos; Kouris, Gavriil; Golna, Christina; Souliotis, Kyriakos

    2010-11-10

    To investigate whether the long term lease of public hospital owned land could be an additional financing mechanism for Greek public (mental) health hospitals. We performed a financial analysis of the official 2008 data of a case - study hospital (Mental Health Hospital of Chania). We used a capital budgeting approach to investigate whether value is created for the public hospital by engaging its assets in a project for the development of a private renal dialysis Unit. The development of the private unit in hospital owned land is a good investment decision, as it generates high project Net Present Value and Internal Rate of Return. When the project commences generating operating cash flows, nearly €400.000 will be paid annually to the Mental Health Hospital of Chania as rent, thereby gradually decreasing the annual deficit of the hospital. Revenue generated from the long term lease of public hospital land is crucial to gradually eliminate hospital deficit. The Ministry of Health should encourage similar forms of Public Private Partnerships in order to ensure the sustainability of public (mental) hospitals.

  4. Mechanical strength of welding zones produced by material extrusion additive manufacturing.

    Science.gov (United States)

    Davis, Chelsea S; Hillgartner, Kaitlyn E; Han, Seung Hoon; Seppala, Jonathan E

    2017-08-01

    As more manufacturing processes and research institutions adopt customized manufacturing as a key element in their design strategies and finished products, the resulting mechanical properties of parts produced through additive manufacturing (AM) must be characterized and understood. In material extrusion (MatEx), the most recently extruded polymer filament must bond to the previously extruded filament via polymer diffusion to form a "weld". The strength of the weld limits the performance of the manufactured part and is controlled through processing conditions. Under-standing the role of processing conditions, specifically extruder velocity and extruder temperature, on the overall strength of the weld will allow optimization of MatEx-AM parts. Here, the fracture toughness of a single weld is determined through a facile "trouser tear" Mode III fracture experiment. The actual weld thickness is observed directly by optical microscopy characterization of cross sections of MatEx-AM samples. Representative data of weld strength as a function of printing parameters on a commercial 3D printer demonstrates the robustness of the method.

  5. Additional funding mechanisms for Public Hospitals in Greece: the case of Chania Mental Health Hospital

    Directory of Open Access Journals (Sweden)

    Golna Christina

    2010-11-01

    Full Text Available Abstract Objectives To investigate whether the long term lease of public hospital owned land could be an additional financing mechanism for Greek public (mental health hospitals. Methods We performed a financial analysis of the official 2008 data of a case - study hospital (Mental Health Hospital of Chania. We used a capital budgeting approach to investigate whether value is created for the public hospital by engaging its assets in a project for the development of a private renal dialysis Unit. Results The development of the private unit in hospital owned land is a good investment decision, as it generates high project Net Present Value and Internal Rate of Return. When the project commences generating operating cash flows, nearly €400.000 will be paid annually to the Mental Health Hospital of Chania as rent, thereby gradually decreasing the annual deficit of the hospital. Conclusions Revenue generated from the long term lease of public hospital land is crucial to gradually eliminate hospital deficit. The Ministry of Health should encourage similar forms of Public Private Partnerships in order to ensure the sustainability of public (mental hospitals.

  6. Ti-6Al-4V Additively Manufactured by Selective Laser Melting with Superior Mechanical Properties

    Science.gov (United States)

    Xu, W.; Sun, S.; Elambasseril, J.; Liu, Q.; Brandt, M.; Qian, M.

    2015-03-01

    The Achilles' heel of additively manufactured Ti-6Al-4V by selective laser melting (SLM) is its inferior mechanical properties compared with its wrought (forged) counterparts. Acicular α' martensite resulted from rapid cooling by SLM is primarily responsible for high strength but inadequate tensile ductility achieved in the as-fabricated state. This study presents a solution to eliminating the adverse effect of the nonequilibrium α' martensite. This is achieved by enabling in situ martensite decomposition into a novel ultrafine (200-300 nm) lamellar ( α + β) microstructure via the selection of an array of processing variables including the layer thickness, energy density, and focal offset distance. The resulting tensile elongation reached 11.4% while the yield strength was kept above 1100 MPa. These properties compare favorably with those of mill-annealed Ti-6Al-4V consisting of globular α and β. The fatigue life of SLM-fabricated Ti-6Al-4V with an ultrafine lamellar ( α + β) structure has approached that of the mill-annealed counterparts and is much superior to that of SLM-fabricated Ti-6Al-4V with α' martensite.

  7. Phosphotyrosine-Mediated Regulation of Enterohemorrhagic Escherichia coli Virulence

    Science.gov (United States)

    Robertson, Colin D.; Hazen, Tracy H.; Kaper, James B.

    2018-01-01

    ABSTRACT Enteric pathogens with low infectious doses rely on the ability to orchestrate the expression of virulence and metabolism-associated genes in response to environmental cues for successful infection. Accordingly, the human pathogen enterohemorrhagic Escherichia coli (EHEC) employs a complex multifaceted regulatory network to link the expression of type III secretion system (T3SS) components to nutrient availability. While phosphorylation of histidine and aspartate residues on two-component system response regulators is recognized as an integral part of bacterial signaling, the involvement of phosphotyrosine-mediated control is minimally explored in Gram-negative pathogens. Our recent phosphotyrosine profiling study of E. coli identified 342 phosphorylated proteins, indicating that phosphotyrosine modifications in bacteria are more prevalent than previously anticipated. The present study demonstrates that tyrosine phosphorylation of a metabolite-responsive LacI/GalR family regulator, Cra, negatively affects T3SS expression under glycolytic conditions that are typical for the colonic lumen environment where production of the T3SS is unnecessary. Our data suggest that Cra phosphorylation affects T3SS expression by modulating the expression of ler, which encodes the major activator of EHEC virulence gene expression. Phosphorylation of the Cra Y47 residue diminishes DNA binding to fine-tune the expression of virulence-associated genes, including those of the locus of enterocyte effacement pathogenicity island that encode the T3SS, and thereby negatively affects the formation of attaching and effacing lesions. Our data indicate that tyrosine phosphorylation provides an additional mechanism to control the DNA binding of Cra and other LacI/GalR family regulators, including LacI and PurR. This study describes an initial effort to unravel the role of global phosphotyrosine signaling in the control of EHEC virulence potential. PMID:29487233

  8. Phosphotyrosine-Mediated Regulation of Enterohemorrhagic Escherichia coli Virulence

    Directory of Open Access Journals (Sweden)

    Colin D. Robertson

    2018-02-01

    Full Text Available Enteric pathogens with low infectious doses rely on the ability to orchestrate the expression of virulence and metabolism-associated genes in response to environmental cues for successful infection. Accordingly, the human pathogen enterohemorrhagic Escherichia coli (EHEC employs a complex multifaceted regulatory network to link the expression of type III secretion system (T3SS components to nutrient availability. While phosphorylation of histidine and aspartate residues on two-component system response regulators is recognized as an integral part of bacterial signaling, the involvement of phosphotyrosine-mediated control is minimally explored in Gram-negative pathogens. Our recent phosphotyrosine profiling study of E. coli identified 342 phosphorylated proteins, indicating that phosphotyrosine modifications in bacteria are more prevalent than previously anticipated. The present study demonstrates that tyrosine phosphorylation of a metabolite-responsive LacI/GalR family regulator, Cra, negatively affects T3SS expression under glycolytic conditions that are typical for the colonic lumen environment where production of the T3SS is unnecessary. Our data suggest that Cra phosphorylation affects T3SS expression by modulating the expression of ler, which encodes the major activator of EHEC virulence gene expression. Phosphorylation of the Cra Y47 residue diminishes DNA binding to fine-tune the expression of virulence-associated genes, including those of the locus of enterocyte effacement pathogenicity island that encode the T3SS, and thereby negatively affects the formation of attaching and effacing lesions. Our data indicate that tyrosine phosphorylation provides an additional mechanism to control the DNA binding of Cra and other LacI/GalR family regulators, including LacI and PurR. This study describes an initial effort to unravel the role of global phosphotyrosine signaling in the control of EHEC virulence potential.

  9. Microbial virulence and interactions with metals

    DEFF Research Database (Denmark)

    German, N.; Lüthje, Freja Lea; Hao, X.

    2016-01-01

    Transition metals, such as iron, copper, zinc, and manganese play an important role in many bacterial biological processes that add to an overall evolutional fitness of bacteria. They are often involved in regulation of bacterial virulence as a mechanism of host invasion. However, the same transi...

  10. Expression of virulence factors by Staphylococcus aureus grown in serum.

    Science.gov (United States)

    Oogai, Yuichi; Matsuo, Miki; Hashimoto, Masahito; Kato, Fuminori; Sugai, Motoyuki; Komatsuzawa, Hitoshi

    2011-11-01

    Staphylococcus aureus produces many virulence factors, including toxins, immune-modulatory factors, and exoenzymes. Previous studies involving the analysis of virulence expression were mainly performed by in vitro experiments using bacterial medium. However, when S. aureus infects a host, the bacterial growth conditions are quite different from those in a medium, which may be related to the different expression of virulence factors in the host. In this study, we investigated the expression of virulence factors in S. aureus grown in calf serum. The expression of many virulence factors, including hemolysins, enterotoxins, proteases, and iron acquisition factors, was significantly increased compared with that in bacterial medium. In addition, the expression of RNA III, a global regulon for virulence expression, was significantly increased. This effect was partially restored by the addition of 300 μM FeCl₃ into serum, suggesting that iron depletion is associated with the increased expression of virulence factors in serum. In chemically defined medium without iron, a similar effect was observed. In a mutant with agr inactivated grown in serum, the expression of RNA III, psm, and sec4 was not increased, while other factors were still induced in the mutant, suggesting that another regulatory factor(s) is involved. In addition, we found that serum albumin is a major factor for the capture of free iron to prevent the supply of iron to bacteria grown in serum. These results indicate that S. aureus expresses virulence factors in adaptation to the host environment.

  11. Natural time analysis and Tsallis non-additive entropy statistical mechanics.

    Science.gov (United States)

    Sarlis, N. V.; Skordas, E. S.; Varotsos, P.

    2016-12-01

    Upon analyzing the seismic data in natural time and employing a sliding natural time window comprising a number of events that would occur in a few months, it has been recently uncovered[1] that a precursory Seismic Electric Signals activity[2] initiates almost simultaneously with the appearance of a minimum in the fluctuations of the order parameter of seismicity [3]. Such minima have been ascertained [4] during periods of the magnitude time series exhibiting long range correlations [5] a few months before all earthquakes of magnitude 7.6 or larger that occurred in the entire Japanese area from 1 January 1984 to 11 March 2011 (the day of the M9 Tohoku-Oki earthquake). Before and after these minima, characteristic changes of the temporal correlations between earthquake magnitudes are observed which cannot be captured by Tsallis non-additive entropy statistical mechanics in the frame of which it has been suggested that kappa distributions arise [6]. Here, we extend the study concerning the existence of such minima in a large area that includes Aegean Sea and its surrounding area which exhibits in general seismo-tectonics [7] different than that of the entire Japanese area. References P. A. Varotsos et al., Tectonophysics, 589 (2013) 116. P. Varotsos and M. Lazaridou, Tectonophysics 188 (1991) 321. P.A. Varotsos et al., Phys Rev E 72 (2005) 041103. N. V. Sarlis et al., Proc Natl Acad Sci USA 110 (2013) 13734. P. A. Varotsos, N. V. Sarlis, and E. S. Skordas, J Geophys Res Space Physics 119 (2014), 9192, doi: 10.1002/2014JA0205800. G. Livadiotis, and D. J. McComas, J Geophys Res 114 (2009) A11105, doi:10.1029/2009JA014352. S. Uyeda et al., Tectonophysics, 304 (1999) 41.

  12. Structural, Thermal, Physical, Mechanical, and Barrier Properties of Chitosan Films with the Addition of Xanthan Gum.

    Science.gov (United States)

    de Morais Lima, Maria; Carneiro, Lucia Cesar; Bianchini, Daniela; Dias, Alvaro Renato Guerra; Zavareze, Elessandra da Rosa; Prentice, Carlos; Moreira, Angelita da Silveira

    2017-03-01

    Films based on chitosan and xanthan gum were prepared using casting technique aiming to investigate the potential of these polymers as packaging materials. Six formulations of films were studied varying the proportion of chitosan and xanthan gum: 100:0 (chitosan:xanthan gum, w/w, C100XG0 film); 90:10 (chitosan:xanthan gum, w/w, C90XG10 film); 80:20 (chitosan:xanthan gum, w/w, C80XG20 film); 70:30 (chitosan:xanthan gum, w/w, C70XG30 film); 60:40 (chitosan:xanthan gum, w/w, C60XG40 film); and 50:50 (chitosan:xanthan gum, w/w, C50XG50 film). The total quantity of solids (chitosan and xanthan gum) in the filmogenic solution was 1.5 g per 100 mL of aqueous solution for all treatments, according to the proportion of each polymer. The films were evaluated by their functional groups, structural, thermal, morphological, physical, mechanical, and barrier properties. All films have presented endothermic peaks in the range of 122 to 175 °C and broad exothermic peaks above 200 °C, which were assigned to the melting temperature and thermal decomposition, respectively. These results demonstrated that films with xanthan gum have the highest T m and Δ m H. The films containing higher content of xanthan gum show also the highest tensile strength and the lowest elongation. Xanthan gum addition did not affect the water vapor permeability, solubility, and moisture of films. This set of data suggests the formation of chitosan-xanthan complexes in the films. © 2017 Institute of Food Technologists®.

  13. Effect of CeLa addition on the microstructures and mechanical properties of Al-Cu-Mn-Mg-Fe alloy

    International Nuclear Information System (INIS)

    Du, Jiandi; Ding, Dongyan; Xu, Zhou; Zhang, Junchao; Zhang, Wenlong; Gao, Yongjin; Chen, Guozhen; Chen, Weigao; You, Xiaohua; Chen, Renzong; Huang, Yuanwei; Tang, Jinsong

    2017-01-01

    Development of high strength lithium battery shell alloy is highly desired for new energy automobile industry. The microstructures and mechanical properties of Al-Cu-Mn-Mg-Fe alloy with different CeLa additions were investigated through optical microscopy (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Rietveld refinement and tensile testing. Experimental results indicate that Al 8 Cu 4 Ce and Al 6 Cu 6 La phases formed due to CeLa addition. Addition of 0.25 wt.% CeLa could promote the formation of denser precipitation of Al 20 Cu 2 Mn 3 and Al 6 (Mn, Fe) phases, which improved the mechanical properties of the alloy at room temperature. However, up to 0.50 wt.% CeLa addition could promote the formation of coarse Al 8 Cu 4 Ce phase, Al 6 Cu 6 La phase and Al 6 (Mn, Fe) phase, which resulted in weakened mechanical properties. - Highlights: •Al-Cu-Mn-Mg-Fe alloys with different CeLa addition were fabricated through casting and rolling. •Al 8 Cu 4 Ce and Al 6 Cu 6 La phases formed after CeLa addition. •Addition of 0.25 wt.% CeLa promoted formation of denser precipitates of Al 20 Cu 2 Mn 3 and Al 6 (Mn, Fe). •Mechanical properties of the alloy was improved after 0.25 wt.% CeLa addition.

  14. PAH growth initiated by propargyl addition: Mechanism development and computational kinetics

    KAUST Repository

    Raj, Abhijeet Dhayal; Rachidi, Mariam El; Chung, Suk-Ho; Sarathy, Mani

    2014-01-01

    Polycyclic aromatic hydrocarbon (PAH) growth is known to be the principal pathway to soot formation during fuel combustion, as such, a physical understanding of the PAH growth mechanism is needed to effectively assess, predict, and control soot

  15. Structural and mechanical characterization of custom design cranial implant created using additive manufacturing

    Directory of Open Access Journals (Sweden)

    Khaja Moiduddin

    2017-09-01

    Conclusions: The study reveals that the use of mesh implants in cranial reconstruction satisfies the need of lighter implants with an adequate mechanical strength, thus restoring better functionality and esthetic outcomes for the patients.

  16. Effect of Flyash Addition on Mechanical and Gamma Radiation Shielding Properties of Concrete

    Directory of Open Access Journals (Sweden)

    Kanwaldeep Singh

    2014-01-01

    Full Text Available Six concrete mixtures were prepared with 0%, 20%, 30%, 40%, 50%, and 60% of flyash replacing the cement content and having constant water to cement ratio. The testing specimens were casted and their mechanical parameters were tested experimentally in accordance with the Indian standards. Results of mechanical parameters show their improvement with age of the specimens and results of radiation parameters show no significant effect of flyash substitution on mass attenuation coefficient.

  17. The mechanical problems on additive manufacturing of viscoelastic solids with integral conditions on a surface increasing in the growth process

    Science.gov (United States)

    Parshin, D. A.; Manzhirov, A. V.

    2018-04-01

    Quasistatic mechanical problems on additive manufacturing aging viscoelastic solids are investigated. The processes of piecewise-continuous accretion of such solids are considered. The consideration is carried out in the framework of linear mechanics of growing solids. A theorem about commutativity of the integration over an arbitrary surface increasing in the solid growing process and the time-derived integral operator of viscoelasticity with a limit depending on the solid point is proved. This theorem provides an efficient way to construct on the basis of Saint-Venant principle solutions of nonclassical boundary-value problems for describing the mechanical behaviour of additively formed solids with integral satisfaction of boundary conditions on the surfaces expanding due to the additional material influx to the formed solid. The constructed solutions will retrace the evolution of the stress-strain state of the solids under consideration during and after the processes of their additive formation. An example of applying the proved theorem is given.

  18. Thermo-mechanical properties of poly ε-caprolactone/poly L-lactic acid blends: addition of nalidixic acid and polyethylene glycol additives.

    Science.gov (United States)

    Douglas, P; Albadarin, Ahmad B; Al-Muhtaseb, Ala'a H; Mangwandi, Chirangano; Walker, G M

    2015-05-01

    The search for ideal biomaterials is still on-going for tissue regeneration. In this study, blends of poly ε-caprolactone (PCL) with poly l-lactic acid (PLLA), nalidixic acid (NA) and polyethylene glycol (PEG) were prepared. Mechanical and thermal properties of the blends were investigated by tensile and flexural analysis, DSC, TGA, WXRD, MFI, BET, SEM and hot stage optical microscopy. Results showed that the loading of PLLA caused a significant decrease in tensile strength and almost total eradication of the elongation at break of PCL matrix, especially after PEG and NA addition. Increased stiffness was also noted with additional NA, PEG and PLLA, resulting in an increase in the flexural modulus of the blends. Isothermal degradation indicated that bulk PCL, PLLA and the blends were thermally stable at 200°C for the duration of 2h making extrusion of the blends at this temperature viable. Morphological study showed that increasing the PLLA content and addition of the very low viscosity PEG and powder NA decreased the Melt Flow Indexer and increased the viscosity. At the higher temperature, the PLLA begins to soften and eventually melts allowing for increased flow and, coupling this with, the natural increase in MFI caused by temperature is enhanced further. The PEG and NA addition increased dramatically the pore volume which is important for cell growth and flow transport of nutrients and metabolic waste. Copyright © 2015 Elsevier Ltd. All rights reserved.

  19. Effect of Hypoeutectic Boron Additions on the Grain Size and Mechanical Properties of Ti-6Al-4V Manufactured with Powder Bed Electron Beam Additive Manufacturing

    Science.gov (United States)

    Mahbooba, Zaynab; West, Harvey; Harrysson, Ola; Wojcieszynski, Andrzej; Dehoff, Ryan; Nandwana, Peeyush; Horn, Timothy

    2017-03-01

    In additive manufacturing, microstructural control is feasible via processing parameter alteration. However, the window for parameter variation for certain materials, such as Ti-6Al-4V, is limited, and alternative methods must be employed to customize microstructures. Grain refinement and homogenization in cast titanium alloys has been demonstrated through the addition of hypoeutectic concentrations of boron. This work explores the influence of 0.00 wt.%, 0.25 wt.%, 0.50 wt.%, and 1.0 wt.% boron additions on the microstructure and bulk mechanical properties of Ti-6Al-4V samples fabricated in an Arcam A2 electron beam melting (EBM) system with commercial processing parameters for Ti-6Al-4V. Analyses of EBM fabricated Ti-6Al-4V + B indicate that the addition of 0.25-1.0 wt.% boron progressively refines the grain structure, and it improves hardness and elastic modulus. Despite a reduction in size, the β grain structure remained columnar as a result of directional heat transfer during EBM fabrication.

  20. Glucose starvation boosts Entamoeba histolytica virulence.

    Directory of Open Access Journals (Sweden)

    Ayala Tovy

    2011-08-01

    Full Text Available The unicellular parasite, Entamoeba histolytica, is exposed to numerous adverse conditions, such as nutrient deprivation, during its life cycle stages in the human host. In the present study, we examined whether the parasite virulence could be influenced by glucose starvation (GS. The migratory behaviour of the parasite and its capability to kill mammalian cells and to lyse erythrocytes is strongly enhanced following GS. In order to gain insights into the mechanism underlying the GS boosting effects on virulence, we analyzed differences in protein expression levels in control and glucose-starved trophozoites, by quantitative proteomic analysis. We observed that upstream regulatory element 3-binding protein (URE3-BP, a transcription factor that modulates E.histolytica virulence, and the lysine-rich protein 1 (KRiP1 which is induced during liver abscess development, are upregulated by GS. We also analyzed E. histolytica membrane fractions and noticed that the Gal/GalNAc lectin light subunit LgL1 is up-regulated by GS. Surprisingly, amoebapore A (Ap-A and cysteine proteinase A5 (CP-A5, two important E. histolytica virulence factors, were strongly down-regulated by GS. While the boosting effect of GS on E. histolytica virulence was conserved in strains silenced for Ap-A and CP-A5, it was lost in LgL1 and in KRiP1 down-regulated strains. These data emphasize the unexpected role of GS in the modulation of E.histolytica virulence and the involvement of KRiP1 and Lgl1 in this phenomenon.

  1. The Central Metabolism Regulator EIIAGlc Switches Salmonella from Growth Arrest to Acute Virulence through Activation of Virulence Factor Secretion

    Directory of Open Access Journals (Sweden)

    Alain Mazé

    2014-06-01

    Full Text Available The ability of Salmonella to cause disease depends on metabolic activities and virulence factors. Here, we show that a key metabolic protein, EIIAGlc, is absolutely essential for acute infection, but not for Salmonella survival, in a mouse typhoid fever model. Surprisingly, phosphorylation-dependent EIIAGlc functions, including carbohydrate transport and activation of adenylate cyclase for global regulation, do not explain this virulence phenotype. Instead, biochemical studies, in vitro secretion and translocation assays, and in vivo genetic epistasis experiments suggest that EIIAGlc binds to the type three secretion system 2 (TTSS-2 involved in systemic virulence, stabilizes its cytoplasmic part including the crucial TTSS-2 ATPase, and activates virulence factor secretion. This unexpected role of EIIAGlc reveals a striking direct link between central Salmonella metabolism and a crucial virulence mechanism.

  2. Exploring the Possible Role of Lysine Acetylation on Entamoeba histolytica Virulence: A Focus on the Dynamics of the Actin Cytoskeleton

    Directory of Open Access Journals (Sweden)

    L. López-Contreras

    2013-01-01

    Full Text Available Cytoskeleton remodeling can be regulated, among other mechanisms, by lysine acetylation. The role of acetylation on cytoskeletal and other proteins of Entamoeba histolytica has been poorly studied. Dynamic rearrangements of the actin cytoskeleton are crucial for amebic motility and capping formation, processes that may be effective means of evading the host immune response. Here we report the possible effect of acetylation on the actin cytoskeleton dynamics and in vivo virulence of E. histolytica. Using western blot, immunoprecipitation, microscopy assays, and in silico analysis, we show results that strongly suggest that the increase in Aspirin-induced cytoplasm proteins acetylation reduced cell movement and capping formation, likely as a consequence of alterations in the structuration of the actin cytoskeleton. Additionally, intrahepatic inoculation of Aspirin-treated trophozoites in hamsters resulted in severe impairment of the amebic virulence. Taken together, these results suggest an important role for lysine acetylation in amebic invasiveness and virulence.

  3. Upgrading offshore pipelines concrete coated by silica fume additive against aggressive mechanical laying

    OpenAIRE

    M.I. Abdou; Hesham Abuseda

    2016-01-01

    Studies have been carried out to investigate the possibility of utilizing a broad range of micro-silica partial additions with cement in the production of concrete coating. This study investigated the strength properties and permeability of micro-silica concrete to achieve resistance toward concrete cracking and damage during laying. The chemical composition of micro-silica (silica fume) was determined, and has been conducted on concrete mixes with additions of 3 up to 25% by weight of cement...

  4. Effect of Cu addition on microstructure and mechanical properties of 15%Cr super martensitic stainless steel

    International Nuclear Information System (INIS)

    Ye, Dong; Li, Jun; Jiang, Wen; Su, Jie; Zhao, Kunyu

    2012-01-01

    Highlights: ► Cu contributes to refine the grains. ► Cu solutes in matrix under quenching and precipitates as ε-Cu during tempering. ► Cu promotes the kinetics of reversed austenite formation. ► Mechanical properties are significantly influenced by austenite amount. ► Cu alloyed super martensitic stainless steel exhibits greatly improved mechanical properties. -- Abstract: The effect of adding different content of Cu (0 wt.%, 1.5 wt.% and 3 wt.%) to the 15%Cr super martensitic stainless steel (SMSS) was investigated using optical microscope, scanning electron microscope (SEM), transmission electron microscope (TEM) and X-ray diffraction (XRD). Its consequence on mechanical properties was examined to clarify the role of Cu in the tested steels. The experimental results indicate that the microstructures of three tested steels are tempered martensite, retained austenite and reversed austenite; two kinds of austenites are dispersedly distributed among martensite matrix. Cu can solute in matrix under quenching condition and can precipitate as Cu-rich nanometer phase (ε-Cu) during tempering. Cu is helpful for the grain refinement and to promote the formation of reversed austenite during tempering. The maximum volume fraction of austenite is 55.9% in the steel with 3 wt.% Cu, which is responsible for the improvement of ductility. The results of the mechanical properties tests reveal that the mechanical properties are significantly influenced by the volume fraction of austenite. Cu can cause solid solution strengthening, precipitation strengthening and grain refinement strengthening in SMSS. Cu alloyed super martensitic stainless steel exhibits greatly improved mechanical properties.

  5. Effect of Ce addition on the mechanical and electrochemical properties of a lithium battery shell alloy

    International Nuclear Information System (INIS)

    Zhang, Junchao; Ding, Dongyan; Xu, Xinglong; Gao, Yongjin; Chen, Guozhen; Chen, Weigao; You, Xiaohua; Huang, Yuanwei; Tang, Jinsong

    2014-01-01

    Highlights: • Fabrication of Ce-free and Ce-containing Al–Cu–Mn–Fe–Mg alloy. • TEM, tensile and electrochemical characterization of the alloys. • Ce element greatly affects the precipitation of the alloy. • Ce element had great impact on the tensile strength and corrosion potential of the alloys. - Abstract: Due to severe application environment lithium battery shell of new-energy automotives requires increasing demands for using high performance aluminum alloys. In the present work, effect of Ce addition on the microstructure, tensile and electrochemical properties of an Al–Cu–Mn–Mg–Fe alloy were investigated through using X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), tensile tests and electrochemical tests. The experimental results indicated that the addition of Ce element could promote the precipitation of second phases. With addition of 0.36% Ce, high melting point Al 8 Cu 4 Ce phase and many Al 20 Cu 2 Mn 3 particles could be found. In addition, the precipitation of conventionally dominant phase of Al 2 Cu could be suppressed in alloy. The Ce addition was found to result in enhanced tensile strength and improved corrosion resistance

  6. Effect of Ce addition on the mechanical and electrochemical properties of a lithium battery shell alloy

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Junchao [School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240 (China); Ding, Dongyan, E-mail: dyding@sjtu.edu.cn [School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240 (China); Xu, Xinglong [School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240 (China); Gao, Yongjin; Chen, Guozhen; Chen, Weigao; You, Xiaohua [Huafon NLM Al Co., Ltd, Shanghai 201506 (China); Huang, Yuanwei; Tang, Jinsong [Shanghai Huafon Materials Technology Institute, Shanghai 201203 (China)

    2014-12-25

    Highlights: • Fabrication of Ce-free and Ce-containing Al–Cu–Mn–Fe–Mg alloy. • TEM, tensile and electrochemical characterization of the alloys. • Ce element greatly affects the precipitation of the alloy. • Ce element had great impact on the tensile strength and corrosion potential of the alloys. - Abstract: Due to severe application environment lithium battery shell of new-energy automotives requires increasing demands for using high performance aluminum alloys. In the present work, effect of Ce addition on the microstructure, tensile and electrochemical properties of an Al–Cu–Mn–Mg–Fe alloy were investigated through using X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), tensile tests and electrochemical tests. The experimental results indicated that the addition of Ce element could promote the precipitation of second phases. With addition of 0.36% Ce, high melting point Al{sub 8}Cu{sub 4}Ce phase and many Al{sub 20}Cu{sub 2}Mn{sub 3} particles could be found. In addition, the precipitation of conventionally dominant phase of Al{sub 2}Cu could be suppressed in alloy. The Ce addition was found to result in enhanced tensile strength and improved corrosion resistance.

  7. Flat magnetic exchange springs as mechanism for additional magnetoresistance in magnetic nanoisland arrays

    Energy Technology Data Exchange (ETDEWEB)

    Boltaev, A.P.; Pudonin, F.A. [P. N. Lebedev Physical Institute of the Russian Academy of Sciences, Leninskiy Prospekt 53, 119991 Moscow (Russian Federation); Sherstnev, I.A., E-mail: sherstnev@lebedev.ru [P. N. Lebedev Physical Institute of the Russian Academy of Sciences, Leninskiy Prospekt 53, 119991 Moscow (Russian Federation); Egorov, D.A. [National Research Nuclear University MEPhI, Kashirskoe shosse 31, 115409 Moscow (Russian Federation); Kozmin, A.M. [National Research University of Electronic Technology, Shokin Square, 1, Zelenograd, 124482 Moscow (Russian Federation)

    2017-04-15

    Process of magnetization and magnetoresistance have been studied in nanoisland bilayer systems of FeNi-Co. Hysteresis loops show characteristic features (steps) most clearly observed in certain orientations of the sample in a magnetic field. To explain these features the concept of flat magnetic exchange spring has been introduced for nanoisland bilayers. It has been proposed that additional magnetoresistance can be the result of spin-dependent scattering of electrons in the area of flat magnetic exchange spring. Magnetoresistance studies of bilayer systems has shown that additional magnetoresistance occurs at the same magnetic fields as steps on hysteresis loops. - Highlights: • Metallic FeNi-Co bilayers are studied. • FeNi and Co layers magnetize independently. • Concept of flat spin spring is proposed. • Additional magnetoresistance occurs in intermediate magnetic fields.

  8. Upgrading offshore pipelines concrete coated by silica fume additive against aggressive mechanical laying

    Directory of Open Access Journals (Sweden)

    M.I. Abdou

    2016-06-01

    Full Text Available Studies have been carried out to investigate the possibility of utilizing a broad range of micro-silica partial additions with cement in the production of concrete coating. This study investigated the strength properties and permeability of micro-silica concrete to achieve resistance toward concrete cracking and damage during laying. The chemical composition of micro-silica (silica fume was determined, and has been conducted on concrete mixes with additions of 3 up to 25% by weight of cement in concrete. Properties of hardened concrete such as compressive strength, flexural strength, and permeability have been assessed and analyzed. Cubic specimens and beams were produced and cured in a curing tank for 7 and 28 days. Testing results have shown that additions of silica fume to cement between 5% and 7%, which acts as a filler and cementations material, developed high flexural and compressive strength with reduction of permeability.

  9. Flat magnetic exchange springs as mechanism for additional magnetoresistance in magnetic nanoisland arrays

    International Nuclear Information System (INIS)

    Boltaev, A.P.; Pudonin, F.A.; Sherstnev, I.A.; Egorov, D.A.; Kozmin, A.M.

    2017-01-01

    Process of magnetization and magnetoresistance have been studied in nanoisland bilayer systems of FeNi-Co. Hysteresis loops show characteristic features (steps) most clearly observed in certain orientations of the sample in a magnetic field. To explain these features the concept of flat magnetic exchange spring has been introduced for nanoisland bilayers. It has been proposed that additional magnetoresistance can be the result of spin-dependent scattering of electrons in the area of flat magnetic exchange spring. Magnetoresistance studies of bilayer systems has shown that additional magnetoresistance occurs at the same magnetic fields as steps on hysteresis loops. - Highlights: • Metallic FeNi-Co bilayers are studied. • FeNi and Co layers magnetize independently. • Concept of flat spin spring is proposed. • Additional magnetoresistance occurs in intermediate magnetic fields.

  10. Genome-wide mapping of virulence in brown planthopper identifies loci that break down host plant resistance.

    Science.gov (United States)

    Jing, Shengli; Zhang, Lei; Ma, Yinhua; Liu, Bingfang; Zhao, Yan; Yu, Hangjin; Zhou, Xi; Qin, Rui; Zhu, Lili; He, Guangcun

    2014-01-01

    Insects and plants have coexisted for over 350 million years and their interactions have affected ecosystems and agricultural practices worldwide. Variation in herbivorous insects' virulence to circumvent host resistance has been extensively documented. However, despite decades of investigation, the genetic foundations of virulence are currently unknown. The brown planthopper (Nilaparvata lugens) is the most destructive rice (Oryza sativa) pest in the world. The identification of the resistance gene Bph1 and its introduction in commercial rice varieties prompted the emergence of a new virulent brown planthopper biotype that was able to break the resistance conferred by Bph1. In this study, we aimed to construct a high density linkage map for the brown planthopper and identify the loci responsible for its virulence in order to determine their genetic architecture. Based on genotyping data for hundreds of molecular markers in three mapping populations, we constructed the most comprehensive linkage map available for this species, covering 96.6% of its genome. Fifteen chromosomes were anchored with 124 gene-specific markers. Using genome-wide scanning and interval mapping, the Qhp7 locus that governs preference for Bph1 plants was mapped to a 0.1 cM region of chromosome 7. In addition, two major QTLs that govern the rate of insect growth on resistant rice plants were identified on chromosomes 5 (Qgr5) and 14 (Qgr14). This is the first study to successfully locate virulence in the genome of this important agricultural insect by marker-based genetic mapping. Our results show that the virulence which overcomes the resistance conferred by Bph1 is controlled by a few major genes and that the components of virulence originate from independent genetic characters. The isolation of these loci will enable the elucidation of the molecular mechanisms underpinning the rice-brown planthopper interaction and facilitate the development of durable approaches for controlling this most

  11. Genome-wide mapping of virulence in brown planthopper identifies loci that break down host plant resistance.

    Directory of Open Access Journals (Sweden)

    Shengli Jing

    Full Text Available Insects and plants have coexisted for over 350 million years and their interactions have affected ecosystems and agricultural practices worldwide. Variation in herbivorous insects' virulence to circumvent host resistance has been extensively documented. However, despite decades of investigation, the genetic foundations of virulence are currently unknown. The brown planthopper (Nilaparvata lugens is the most destructive rice (Oryza sativa pest in the world. The identification of the resistance gene Bph1 and its introduction in commercial rice varieties prompted the emergence of a new virulent brown planthopper biotype that was able to break the resistance conferred by Bph1. In this study, we aimed to construct a high density linkage map for the brown planthopper and identify the loci responsible for its virulence in order to determine their genetic architecture. Based on genotyping data for hundreds of molecular markers in three mapping populations, we constructed the most comprehensive linkage map available for this species, covering 96.6% of its genome. Fifteen chromosomes were anchored with 124 gene-specific markers. Using genome-wide scanning and interval mapping, the Qhp7 locus that governs preference for Bph1 plants was mapped to a 0.1 cM region of chromosome 7. In addition, two major QTLs that govern the rate of insect growth on resistant rice plants were identified on chromosomes 5 (Qgr5 and 14 (Qgr14. This is the first study to successfully locate virulence in the genome of this important agricultural insect by marker-based genetic mapping. Our results show that the virulence which overcomes the resistance conferred by Bph1 is controlled by a few major genes and that the components of virulence originate from independent genetic characters. The isolation of these loci will enable the elucidation of the molecular mechanisms underpinning the rice-brown planthopper interaction and facilitate the development of durable approaches for

  12. Asymmetric organocatalytic Michael addition of Meldrum's acid to nitroalkenes: probing the mechanism of bifunctional thiourea organocatalysts

    OpenAIRE

    Kataja, Antti O.; Koskinen, Ari M.P.

    2010-01-01

    The asymmetric Michael addition of Meldrum’s acid to nitroalkenes was studied using a novel type of Cinchona alkaloid-based bifunctional thiourea organocatalyst. The functionality of the thiourea catalysts was also probed by preparing and testing thiourea-N-methylated analogues of the well-known bis-(3,5-trifluoromethyl)phenyl-substituted catalyst. Peer reviewed

  13. Effect of pMDI isocyanate additive on mechanical and thermal ...

    Indian Academy of Sciences (India)

    Incompatibility of natural fibres and polymers is one of the main barriers facing this industry. Researchers have tried to overcome this problem by many ways such as pre-treating fibres, using additives, coupling agents and binders. Various fibre pre-treatments and coupling agents have been used to enhance the fibre matrix ...

  14. Extreme Pressure Synergistic Mechanism of Bismuth Naphthenate and Sulfurized Isobutene Additives

    Science.gov (United States)

    Xu, Xin; Hu, Jianqiang; Yang, Shizhao; Xie, Feng; Guo, Li

    A four-ball tester was used to evaluate the tribological performances of bismuth naphthenate (BiNap), sulfurized isobutene (VSB), and their combinations. The results show that the antiwear properties of BiNap and VSB are not very visible, but they possess good extreme pressure (EP) properties, particularly sulfur containing bismuth additives. Synergistic EP properties of BiNap with various sulfur-containing additives were investigated. The results indicate that BiNap exhibits good EP synergism with sulfur-containing additives. The surface analytical tools, such as X-ray photoelectron spectrometer (XPS) scanning electron microscope (SEM) and energy dispersive X-ray (EDX), were used to investigate the topography, composition contents, and depth profile of some typical elements on the rubbing surface. Smooth topography of wear scar further confirms that the additive showed good EP capacities, and XPS and EDX analyzes indicate that tribochemical mixed protective films composed of bismuth, bismuth oxides, sulfides, and sulfates are formed on the rubbing surface, which improves the tribological properties of lubricants. In particular, a large number of bismuth atoms and bismuth sulfides play an important role in improving the EP properties of oils.

  15. Influence of small additions of Sc and Zr on structure and mechanical properties of Al-Zn-Mg-Cu alloy

    International Nuclear Information System (INIS)

    Kajgorodova, L.I.; Sel'nikhina, E.I.; Tkachenko, E.A.; Senatorova, O.G.

    1996-01-01

    A study was made into Sc and Zr addition effects on grain structure formation, supersaturated solid solution decomposition and mechanical properties of Al-7%Zn-2%Mg-1.2%Cu alloy. It is shown that grain structure is determined by volume fraction and distribution character of disperse particles of Al 3 Sc and Al 3 (Sc 1-x Zr x ). The reason for additives influence on decomposition kinetics during natural and artificial ageing are revealed. The structural factors responsible for the enhancement of mechanical properties on alloying are discussed. 17 refs.; 5 figs.; 2 tabs

  16. Effect of Rapid Solidification and Addition of Cu3P on the Mechanical Properties of Hypereutectic Al-Si Alloys

    OpenAIRE

    Suárez-Rosales,Miguel Ángel; Pinto-Segura,Raúl; Palacios-Beas,Elia Guadalupe; Hernández-Herrera,Alfredo; Chávez-Alcalá,José Federico

    2016-01-01

    The combined processes; rapid solidification, addition of Cu3P compound and heat treatments to improve the mechanical properties of the hypereutectic Al-13Si, Al-20Si and Al-20Si-1.5Fe-0.7Mn alloys (in wt. %) was studied. Optical microscopy and scanning electron microscopy were used to characterize the microstructures. The mechanical properties were evaluated by tensile tests. It was found that the cooling rate (20-50°C/s) used to solidify the alloys plus the addition of Cu3P compound favored...

  17. Mechanical characterization of the 3Y-TZP co-doped with yttria and niobia Equimolar addition

    International Nuclear Information System (INIS)

    Assis, Joao Marcos Kruszynski de; Nono, Maria do Carmo de Andrade; Dorat, Daniele Ramos; Fonseca, Flavia Baccaro; Reis, Danieli Aparecida

    2010-01-01

    The main goal of this work is to study the effect of the yttria and niobia equimolar addition in the 3Y-TZP on the mechanical properties (hardness, fracture toughness and four point bending strength) aiming to get a stable tetragonal phase (t´) under applied stress, to use as TBC´s. Four compositions with equimolar addition of yttria and niobia in the 3Y-TZP were produced, 13%, 14.5%, 16% and 17.5%. The mixtures were prepared in high energy ball milling for 10 minutes and the samples prepared on uniaxial and isostatic pressing. The selected temperature sintering was 1.550 deg C for 1 hour. Analyses of X-Ray Diffraction, hardness, fracture toughness and four point bending strength were performed. An increase on the mechanical properties analyzed was expected with yttria and niobia addition in comparison to 3Y-TZP, but instead a decrease was observed after these additions. (author)

  18. Effects of coal and wheat husk additives on the physical, thermal and mechanical properties of clay bricks

    Energy Technology Data Exchange (ETDEWEB)

    Ahmad, S.; Iqbal, Y.; Muhammad, R.

    2017-07-01

    The use of by-products as additives in brick industry is gaining increased research attention due to their effective role in decreasing the total energy needs of industrial furnaces. In addition, these additives leave pores upon burning, causing a decrease in thermal conductivity and affect the mechanical properties of bricks as well. In the present study, various proportions of coal and wheat husk were used as additives in the initial ingredients of clay bricks. Microstructure, thermal conductivity, coefficient of thermal diffusivity, water absorption, shrinkage, compressive strength and bulk density of fired clay bricks with and without additives were investigated. Clay bricks containing 5–15wt.% additives were found to be within the permissible limits for most of the recommended standard specifications. (Author)

  19. Effect of CeLa addition on the microstructures and mechanical properties of Al-Cu-Mn-Mg-Fe alloy

    Energy Technology Data Exchange (ETDEWEB)

    Du, Jiandi [School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240 (China); Ding, Dongyan, E-mail: dyding@sjtu.edu.cn [School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240 (China); Xu, Zhou; Zhang, Junchao; Zhang, Wenlong [School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240 (China); Gao, Yongjin; Chen, Guozhen; Chen, Weigao; You, Xiaohua [Huafon NLM Al Co., Ltd, Shanghai 201506 (China); Chen, Renzong; Huang, Yuanwei; Tang, Jinsong [Shanghai Huafon Materials Technology Institute, Shanghai 201203 (China)

    2017-01-15

    Development of high strength lithium battery shell alloy is highly desired for new energy automobile industry. The microstructures and mechanical properties of Al-Cu-Mn-Mg-Fe alloy with different CeLa additions were investigated through optical microscopy (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Rietveld refinement and tensile testing. Experimental results indicate that Al{sub 8}Cu{sub 4}Ce and Al{sub 6}Cu{sub 6}La phases formed due to CeLa addition. Addition of 0.25 wt.% CeLa could promote the formation of denser precipitation of Al{sub 20}Cu{sub 2}Mn{sub 3} and Al{sub 6}(Mn, Fe) phases, which improved the mechanical properties of the alloy at room temperature. However, up to 0.50 wt.% CeLa addition could promote the formation of coarse Al{sub 8}Cu{sub 4}Ce phase, Al{sub 6}Cu{sub 6}La phase and Al{sub 6}(Mn, Fe) phase, which resulted in weakened mechanical properties. - Highlights: •Al-Cu-Mn-Mg-Fe alloys with different CeLa addition were fabricated through casting and rolling. •Al{sub 8}Cu{sub 4}Ce and Al{sub 6}Cu{sub 6}La phases formed after CeLa addition. •Addition of 0.25 wt.% CeLa promoted formation of denser precipitates of Al{sub 20}Cu{sub 2}Mn{sub 3} and Al{sub 6}(Mn, Fe). •Mechanical properties of the alloy was improved after 0.25 wt.% CeLa addition.

  20. The relationship of the lipoprotein SsaB, manganese and superoxide dismutase in Streptococcus sanguinis virulence for endocarditis.

    Science.gov (United States)

    Crump, Katie E; Bainbridge, Brian; Brusko, Sarah; Turner, Lauren S; Ge, Xiuchun; Stone, Victoria; Xu, Ping; Kitten, Todd

    2014-06-01

    Streptococcus sanguinis colonizes teeth and is an important cause of infective endocarditis. Our prior work showed that the lipoprotein SsaB is critical for S. sanguinis virulence for endocarditis and belongs to the LraI family of conserved metal transporters. In this study, we demonstrated that an ssaB mutant accumulates less manganese and iron than its parent. A mutant lacking the manganese-dependent superoxide dismutase, SodA, was significantly less virulent than wild-type in a rabbit model of endocarditis, but significantly more virulent than the ssaB mutant. Neither the ssaB nor the sodA mutation affected sensitivity to phagocytic killing or efficiency of heart valve colonization. Animal virulence results for all strains could be reproduced by growing bacteria in serum under physiological levels of O(2). SodA activity was reduced, but not eliminated in the ssaB mutant in serum and in rabbits. Growth of the ssaB mutant in serum was restored upon addition of Mn(2+) or removal of O(2). Antioxidant supplementation experiments suggested that superoxide and hydroxyl radicals were together responsible for the ssaB mutant's growth defect. We conclude that manganese accumulation mediated by the SsaB transport system imparts virulence by enabling cell growth in oxygen through SodA-dependent and independent mechanisms. © 2014 John Wiley & Sons Ltd.

  1. Improvements in mechanical properties in SiC by the addition of TiC particles

    International Nuclear Information System (INIS)

    Wei, G.C.; Becher, P.F.

    1984-01-01

    Silicon carbide ceramics containing up to 24.6 vol% dispersed TiC particles yielded fully dense composites by hot-pressing at 2000 0 C with 1 wt% Al and 1 wt% C added. The microstructure consists of fine TiC particles in a fine-grained SiC matrix. Addition of TiC particles increases the critical fracture toughness of SiC (to approx. =6 MPa /SUP ./ m /SUP 1/2/ at 24.6 vol% TiC) and yields high flexure strength (greater than or equal to 680 MPa), with both properties increasing with increasing volume fraction of TiC. The strengths at high temperatures are also improved by the TiC additions. Observations of the fracture path indicate that the improved toughness and strength are a result of crack deflection by the TiC particles

  2. Electrodeposition mechanism of quaternary compounds Cu2ZnSnS4: Effect of the additives

    Science.gov (United States)

    Tang, Aiyue; Li, Zhilin; Wang, Feng; Dou, Meiling; Liu, Jingjun; Ji, Jing; Song, Ye

    2018-01-01

    The electrodeposition mechanism of pure phase Cu2ZnSnS4 (CZTS) thin film with subsequent annealing was investigated in detail. An electrolyte design principle of quaternary compounds was proposed. The complex ions of Cu(H2C6H5O7)+, Cu2(C6H5O7)+, Zn(C4H5O6)+, Sn(H2C6H5O7)+ and Sn2(C6H5O7)+, which influenced the reduction process and played important roles in co-deposition, were identified by UV spectra. Electrochemical studies indicated that trisodium citrate and tartaric acid could narrow the co-deposition potential range of the four elements to -0.8 V to -1.2 V (vs. SCE). The cause was the synergetic effect that trisodium citrate inhibited the reduction of Cu2+ and Sn2+ and tartaric acid promoted the reduction of Zn2+. The reduction of S2O32- was mainly attributed to the induction effect of the metallic ions, and the H+ dissociated from tartaric acid could also promote the cathode process of S2O32-. The reaction mechanism could be summarized as the following steps: (I) Cu(H2C6H5O7)+, Cu2(C6H5O7)+ → Cu, Sn(H2C6H5O7)+, Sn2(C6H5O7)+ → Sn, Zn(C4H5O6)+ → Zn; (II) the desorption of (H2C6H5O7)- and (C6H5O7)-, and the reduction of S2O32- induced by metallic ions and H+. The mechanism studies provided a path of electrolyte design for multicomponent compounds.

  3. PVC mixtures’ mechanical properties with the addition of modified calcite as filler

    Directory of Open Access Journals (Sweden)

    Vučinić Dušica R.

    2012-01-01

    Full Text Available In this study mechanical properties of PVC mixtures (PVC, stabilizer, lubricant, filler such as tensile strength, tensile elongation, breaking strength, and breaking elongation were investigated. Unmodified calcite, as well as calcite modified by stearic acid, were used as fillers in wet and dry processes. The PVC mixtures containing the calcite modified by wet procedure have better mechanical properties compared to those with the calcite modified by the dry process. Tensile and breaking strength of the PVC mixture containing the calcite modified with 1.5% stearic acid using wet process, are higher for 2.8% and 5.2%, respectively, compared to the PVC mixture containing the calcite modified with the same amount of acid used in the dry process. The tensile strength difference between the mixtures increases with the increase of the concentration of used stearic acid up to 3%. The strength of PVC mixture with the calcite modified by wet process is 3.1% higher compared to the mixture containing calcite modified by dry process. The results showed that the bonding strength between calcite and the adsorbed organic component affected tensile strength, tensile elongation and breaking strength of the PVC mixtures. The best filler was obtained by wet modification using 1.5% stearic acid solution that provided the formation of a stearate monolayer chemisorbed on calcite. The PVC mixtures containing the calcite modified by wet process using 1.5% stearic acid solution exhibited the best mechanical properties. This calcite was completely hydrophobic with dominant chemically adsorbed surfactant, which means that stearate chemisorbed on calcite provided stronger interaction in the calcite-stearic acid-PVC system.

  4. Valence electron structure analysis of refining mecha-nism of Sc and Ti additions on aluminum

    Institute of Scientific and Technical Information of China (English)

    LI PieJie; YE YiCong; HE LiangJu

    2009-01-01

    The mechanism of the difference of refining effect between Sc and Ti adding to aluminum can not be explained substantially with traditional theory. Valence electron structures of AI-Ti and Al-Sc alloys have been studied by using the empirical electron theory of solids and molecules (EET). The covalent bond electron numbers and interfacial electron density differences are calculated. The conclusion is that, in the two alloys, different covalent bond electron numbers of nucleation particles, and different electron densities on the interface between the second phase particles and the matrix, fundamentally lead to the difference of refining effect between Sc and Ti adding to aluminum.

  5. Improving Mechanical Properties of Thermoset Biocomposites by Fiber Coating or Organic Oil Addition

    Directory of Open Access Journals (Sweden)

    Truc T. Ngo

    2015-01-01

    Full Text Available Two different thermoset biocomposite systems are experimented in this study with the hope to improve their mechanical properties. Fiberglass and hemp, in form of fabrics, are used to reinforce the thermoset polymer matrix, which includes a traditional epoxy resin and a linseed oil-based bioresin (UVL. The fiber/polymer matrix interface is modified using two different approaches: adding a plant-based oil (pine or linseed to the polymer matrix or coating the fibers with 3-(aminopropyltriethoxysilane (APTES prior to integrating them into the polymer matrix. Epoxy resin is cured using an amine-based initiator, whereas UVL resin is cured under ultraviolet light. Results show that hemp fibers with APTES prime coat used in either epoxy or UVL matrix exhibit some potential improvements in the composite’s mechanical properties including tensile strength, modulus of elasticity, and ductility. It is also found that adding oil to the epoxy matrix reinforced with fiberglass mostly improves the material’s modulus of elasticity while maintaining its tensile strength and ductility. However, adding oil to the epoxy matrix reinforced with hemp doubles the material’s ductility while slightly reducing its tensile strength and modulus of elasticity.

  6. Constitution, microstructure, mechanical properties, and performance of magnetron-sputtered carbon films with additions of silicon

    Energy Technology Data Exchange (ETDEWEB)

    Bauer, C. [Forschungszentrum Karlsruhe GmbH, Institut fuer Materialforschung I, Postfach 3640, 76021 Karlsruhe (Germany); Leiste, H.; Stueber, M.; Ulrich, S.; Holleck, H.

    2003-11-01

    Amorphous carbon films with additions of silicon were deposited by non-reactive magnetron sputtering on WC-Co hard metal and on silicon substrates. The targets were hot-pressed, homogenous mixtures of graphite and silicon carbide powder. Additional argon ion bombardment of the growing film was applied by a substrate bias varied between 0V and -800 V. The deposited amorphous carbon films with two different silicon contents (5 at.% and 23 at.% respectively) were characterised with respect to their microstructure, density, thickness, residual stress, Vickers hardness, Young's modulus, critical load of failure, friction coefficient, and wear behaviour. The residual stress of the carbon films could be remarkably lowered by silicon additions (23 at.%). The hardness reached high values (2200 HV0.05) and the friction coefficient for unlubricated sliding friction against a steel (1.3505) counterpart was as low as 0.06. (Abstract Copyright [2003], Wiley Periodicals, Inc.) [German] Amorphe Kohlenstoffschichten mit Zusaetzen von Silizium wurden nichtreaktiv durch Magnetronzerstaeubung auf Substraten aus WC-Co Hartmetall und Silizium abgeschieden. Die neuartigen Targets wurden durch Heisspressen einer homogenen Mischung aus Graphit- und Siliziumcarbidpulver hergestellt. Durch Anlegen einer elektrischen Substratvorspannung von 0 V bis -800 V wurden die aufwachsenden Schichten zusaetzlich mit Argonionen unterschiedlicher Energie beschossen. Die abgeschiedenen amorphen Kohlenstoffschichten mit Zusaetzen von Silizium (5 at% bzw. 23 at%) wurden hinsichtlich Struktur, Dichte, Dicke, Eigenspannungen, Vickershaerte, reduziertem Elastizitaetsmodul, kritischer Last des Versagens im Ritztest, Reibwert und Verschleissverhalten untersucht. Fuer Schichten mit hohem Siliziumgehalt (23 at%) erfolgte eine erhebliche Reduzierung der Eigenspannung, die Haerte wurde bei sehr hohen Werten stabilisiert (2200 HV0,05) und der Reibungskoeffizient fuer ungeschmierte Gleitreibung gegen Stahl (1

  7. Effect of boron and carbon addition on microstructure and mechanical properties of Ti-15-3 alloy

    International Nuclear Information System (INIS)

    Sarkar, R.; Ghosal, P.; Muraleedharan, K.; Nandy, T.K.; Ray, K.K.

    2011-01-01

    Highlights: → Development of β Ti alloys with B and C addition for improved mechanical properties. → Detailed characterization of microstructural constituents using electron microscopy. → Microstructure-mechanical property correlation in this new class of alloys. → Strengthening mechanism in β Ti alloy in the presence of hard and non-deformable phases. - Abstract: A detailed microstructure-mechanical property correlation was carried out in beta titanium alloys (Ti-15V-3Al-3Sn-3Cr) with boron and carbon additions. The alloys were prepared by non-consumable vacuum arc melting followed by hot rolling. Microstructural characterization was carried out using an optical microscope, a scanning electron microscope (SEM), a transmission electron microscope (TEM) and a high resolution TEM (HRTEM). Addition of boron and carbon resulted in the precipitation of TiB and TiC, respectively, and these phases acted as reinforcements. Evaluation of mechanical properties in solution treated and solution treated plus aged condition showed strengthening in the boron and carbon containing alloy with respect to the base. Strengthening in solution treated condition was attributed to a synergistic effect of grain refinement and load transfer in the presence of non-deformable phases. On the other hand, higher strength in boron and carbon containing alloys on aging was ascribed to the presence of finer aged microstructures.

  8. Influence of additives on microstructures, mechanical properties and shock-induced reaction characteristics of Al/Ni composites

    Energy Technology Data Exchange (ETDEWEB)

    Xiong, Wei; Zhang, Xianfeng, E-mail: lynx@mail.njust.edu.cn; Wu, Yang; He, Yong; Wang, Chuanting; Guo, Lei

    2015-11-05

    Granular composites containing aluminum (Al) and nickel (Ni) are typical structural energetic materials, which possess ideal combination of both mechanical properties and energy release capability. The influence of two additives, namely Teflon (PTFE) and copper (Cu), on mechanical properties and shock-induced chemical reaction (SICR) characteristics of Al/Ni material system has been investigated. Three composites, namely Al/Ni, Al/Ni/PTFE and Al/Ni/Cu with same volumetric ratio of Al powder to Ni powder, were processed by means of static pressing. Scanning electron microscopy was used to study the microstructure of the mentioned three composites. Quasi static compression tests were also conducted to determine the mechanical properties and fracture behavior of the mentioned three composites. It was shown that the additives affected both compressive strength and fracture mode of the three composites. Impact initiation experiments on the mentioned three composites were performed to determine their shock-induced chemical reaction characteristics by considering pressure histories measured in the test chamber. The experimental results showed that the additives had significant effects on critical initiation velocity, reaction rate, reaction efficiency and post-reaction behavior. - Highlights: • .Al/Ni, Al/Ni/PTFE and Al/Ni/Cu were processed by means of static pressing. • .Microstructures, mechanical properties and shock-induced reactions were studied. • .Microstructures affect both compressive strength and fracture mode. • .Impact velocity is an important factor in shock-induced chemical characteristics. • .Each additive has significant effects on energy release behavior.

  9. Influence of additives on microstructures, mechanical properties and shock-induced reaction characteristics of Al/Ni composites

    International Nuclear Information System (INIS)

    Xiong, Wei; Zhang, Xianfeng; Wu, Yang; He, Yong; Wang, Chuanting; Guo, Lei

    2015-01-01

    Granular composites containing aluminum (Al) and nickel (Ni) are typical structural energetic materials, which possess ideal combination of both mechanical properties and energy release capability. The influence of two additives, namely Teflon (PTFE) and copper (Cu), on mechanical properties and shock-induced chemical reaction (SICR) characteristics of Al/Ni material system has been investigated. Three composites, namely Al/Ni, Al/Ni/PTFE and Al/Ni/Cu with same volumetric ratio of Al powder to Ni powder, were processed by means of static pressing. Scanning electron microscopy was used to study the microstructure of the mentioned three composites. Quasi static compression tests were also conducted to determine the mechanical properties and fracture behavior of the mentioned three composites. It was shown that the additives affected both compressive strength and fracture mode of the three composites. Impact initiation experiments on the mentioned three composites were performed to determine their shock-induced chemical reaction characteristics by considering pressure histories measured in the test chamber. The experimental results showed that the additives had significant effects on critical initiation velocity, reaction rate, reaction efficiency and post-reaction behavior. - Highlights: • .Al/Ni, Al/Ni/PTFE and Al/Ni/Cu were processed by means of static pressing. • .Microstructures, mechanical properties and shock-induced reactions were studied. • .Microstructures affect both compressive strength and fracture mode. • .Impact velocity is an important factor in shock-induced chemical characteristics. • .Each additive has significant effects on energy release behavior

  10. Additively manufactured metallic porous biomaterials based on minimal surfaces : A unique combination of topological, mechanical, and mass transport properties

    NARCIS (Netherlands)

    Bobbert, F S L; Lietaert, K; Eftekhari, A A; Pouran, B; Ahmadi, S M; Weinans, H; Zadpoor, A A

    2017-01-01

    Porous biomaterials that simultaneously mimic the topological, mechanical, and mass transport properties of bone are in great demand but are rarely found in the literature. In this study, we rationally designed and additively manufactured (AM) porous metallic biomaterials based on four different

  11. Effect of nickel addition on mechanical properties of powder forged Fe-Cu-C

    Science.gov (United States)

    Archana Barla, Nikki

    2018-03-01

    Fe-Cu-C system is very popular in P/M industry for its good compressibility and dimensional stability with high strength. Fe-Cu-C is a structural material and is used where high strength with high hardness is required. The composition of powder metallurgy steel plays a vital role in the microstructure and physical properties of the sintered component. Fe-2Cu-0.7C-Ni alloy with varying nickel composition (0%, 0.5%, 1.0%, 1.5%, 2.0%, and 3.0%) wt. % was prepared by powder metallurgy (P/M) sinter forging process. The present work discuss the effect of varying nickel content on microstructure and mechanical properties.

  12. Anti-biofilm, anti-hemolysis, and anti-virulence activities of black pepper, cananga, myrrh oils, and nerolidol against Staphylococcus aureus.

    Science.gov (United States)

    Lee, Kayeon; Lee, Jin-Hyung; Kim, Soon-Il; Cho, Moo Hwan; Lee, Jintae

    2014-11-01

    The long-term usage of antibiotics has resulted in the evolution of multidrug-resistant bacteria. Unlike antibiotics, anti-virulence approaches target bacterial virulence without affecting cell viability, which may be less prone to develop drug resistance. Staphylococcus aureus is a major human pathogen that produces diverse virulence factors, such as α-toxin, which is hemolytic. Also, biofilm formation of S. aureus is one of the mechanisms of its drug resistance. In this study, anti-biofilm screening of 83 essential oils showed that black pepper, cananga, and myrrh oils and their common constituent cis-nerolidol at 0.01 % markedly inhibited S. aureus biofilm formation. Furthermore, the three essential oils and cis-nerolidol at below 0.005 % almost abolished the hemolytic activity of S. aureus. Transcriptional analyses showed that black pepper oil down-regulated the expressions of the α-toxin gene (hla), the nuclease genes, and the regulatory genes. In addition, black pepper, cananga, and myrrh oils and cis-nerolidol attenuated S. aureus virulence in the nematode Caenorhabditis elegans. This study is one of the most extensive on anti-virulence screening using diverse essential oils and provides comprehensive data on the subject. This finding implies other beneficial effects of essential oils and suggests that black pepper, cananga, and myrrh oils have potential use as anti-virulence strategies against persistent S. aureus infections.

  13. Mechanical Performance of Cold-Sprayed A357 Aluminum Alloy Coatings for Repair and Additive Manufacturing

    Science.gov (United States)

    Petráčková, K.; Kondás, J.; Guagliano, M.

    2017-12-01

    Cold-sprayed coatings made of A357 aluminum alloy, a casting alloy widely used in aerospace, underwent set of standard tests as well as newly developed fatigue test to gain an information about potential of cold spray for repair and additive manufacturing of loaded parts. With optimal spray parameters, coating deposition on substrate with smooth surface resulted in relatively good bonding, which can be further improved by application of grit blasting on substrate's surface. However, no enhancement of adhesion was obtained for shot-peened surface. Process temperature, which was set either to 450 or 550 °C, was shown to have an effect on adhesion and cohesion strength, but it does not influence residual stress in the coating. To assess cold spray perspectives for additive manufacturing, flat tensile specimens were machined from coating and tested in as-sprayed and heat-treated (solution treatment and aging) condition. Tensile properties of the coating after the treatment correspond to properties of the cast A357-T61 aluminum alloy. Finally, fatigue specimen was proposed to test overall performance of the coating and coating's fatigue limit is compared to the results obtained on cast A357-T61 aluminum alloy.

  14. Influence of Microencapsulated Phase Change Material (PCM) Addition on (Micro) Mechanical Properties of Cement Paste

    Science.gov (United States)

    Schlangen, Erik

    2017-01-01

    Excessive cracking can be a serious durability problem for reinforced concrete structures. In recent years, addition of microencapsulated phase change materials (PCMs) to concrete has been proposed as a possible solution to crack formation related to temperature gradients. However, the addition of PCM microcapsules to cementitious materials can have some drawbacks, mainly related to strength reduction. In this work, a range of experimental techniques has been used to characterize the microcapsules and their effect on properties of composite cement pastes. On the capsule level, it was shown that they are spherical, enabling good distribution in the material during the mixing process. Force needed to break the microcapsules was shown to depend on the capsule diameter and the temperature, i.e., whether it is below or above the phase change temperature. On the cement paste level, a marked drop of compressive strength with increasing PCM inclusion level was observed. The indentation modulus has also shown to decrease, probably due to the capsules themselves, and to a lesser extent due to changes in porosity caused by their inclusion. Finally, a novel micro-cube splitting technique was used to characterize the tensile strength of the material on the micro-meter length scale. It was shown that the strength decreases with increasing PCM inclusion percentage, but this is accompanied by a decrease in measurement variability. This study will contribute to future developments of cementitious composites incorporating phase change materials for a variety of applications. PMID:28773225

  15. Investigation of variation of additional enthalpy of proteins with respect to pH by statistical mechanical methods

    International Nuclear Information System (INIS)

    Oylumoglu, G.

    2005-01-01

    In this study variation of additional enthalpy with respect to pH has been investigated by the statistical mechanical methods.. To bring up the additional effect, the partition function of the proteins are calculated by single protein molecule approximation. From the partition function, free energies of the proteins are obtained and by this way additional free energy has been used in the calculation of the terms in the thermodynamical quantity. Additional enthalpy H D has been obtained by taking effective electric field E and constant dipole moment M as thermodynamical variables and using Maxwell Equations. In the presented semi phenomenological theory, necessary data are taken from the experimental study of P.L. Privalov. The variation in the additional enthalpy H D has been investigated in the pH interval of 1-5 and the results of the calculations are discussed for Lysozyme

  16. Controlling photo-oxidation processes of a polyfluorene derivative: The effect of additives and mechanism

    Energy Technology Data Exchange (ETDEWEB)

    Ferreira, G.R. [Laboratory of Polymers and Electronic Properties of Materials – UFOP, Ouro Preto, MG (Brazil); Nowacki, B. [Paulo Scarpa Polymer Laboratory – UFPR, Curitiba, PR (Brazil); Magalhães, A. [Instituto de Química, Universidade Estadual de Campinas – UNICAMP, Campinas, SP (Brazil); Azevedo, E.R. de [Instituto de Física de São Carlos, Universidade de São Paulo – USP, São Carlos, SP (Brazil); Sá, E.L. de [Chemistry Department, Federal University of Parana, Curitiba, PR (Brazil); Akcelrud, L.C. [Paulo Scarpa Polymer Laboratory – UFPR, Curitiba, PR (Brazil); Bianchi, R.F., E-mail: bianchi@iceb.ufop.br [Laboratory of Polymers and Electronic Properties of Materials – UFOP, Ouro Preto, MG (Brazil)

    2014-08-01

    The control of the photo degradation of a fluorene–vinylene–phenylene based-polymer, poly(9,9-di-hexylfluorenediylvinylene-alt-1,4-phenylenevinylene) (LaPPS16) was achieved by addition of a radical scavenger (RS) (enhancing photo resistance) or a radical initiator (RI) (reducing photo resistance). Photoluminescence, UV–Vis absorption, {sup 1}H NMR spectroscopies and gel permeation chromatography (GPC) revealed that the incorporating small amounts of RS or RI is an efficient way to control the rates of the photo-oxidation reactions, and thus to obtain the conjugated polymer with foreseeable degradation rates for applications in blue-light sensitive detectors for neonatal phototherapy. - Highlights: • Photo degradation control of a fluorene–vinylene–phenylene based polymer was achieved. • A radical scavenger enhanced photo resistance and radical initiator decreased it. • Color change rate with irradiation dose provided a basis for dosimeter construction.

  17. Metal and pharmaceutical mixtures: Is ion loss the mechanism underlying acute toxicity and widespread additive toxicity in zebrafish?

    International Nuclear Information System (INIS)

    Alsop, Derek; Wood, Chris M.

    2013-01-01

    Highlights: •Zebrafish larvae were used to test the acute toxicity of contaminant mixtures. •Interactions were observed between metals, ammonia and pharmaceuticals. •Larval Na + loss was observed with exposure to all acutely toxic contaminants tested. •Water quality criteria should recognize the toxic interactions between contaminants. -- Abstract: The acute toxicities and mechanisms of action of a variety of environmental contaminants were examined using zebrafish larvae (Danio rerio; 4–8 days post fertilization). Toxic interactions were observed between metals. For example, the addition of a sublethal level of nickel (15% of the LC 50 , one third of the LC 01 ) to all copper treatments decreased the copper 96 h LC 50 by 58%, while sublethal copper exposure (6% of the copper LC 50 , 13% of the LC 01 ) decreased the cadmium 96 h LC 50 by 47%. Two predictive models were assessed, the concentration addition (CA) model, which assumes similar mechanisms of action, and the independent action (IA) model, which assumes different mechanisms of action. Quantitative comparisons indicated the CA model performed better than the IA model; the latter tended to underestimate combined toxicity to a greater extent. The effects of mixtures with nickel or ammonia were typically additive, while mixtures with copper or cadmium were typically greater than additive. Larvae exposed to cadmium, copper or nickel experienced whole body ion loss. Decreases were greatest for Na + followed by K + (as high as 19% and 9%, respectively, in 24 h). Additive toxicity between copper and other pharmaceutical compounds such as fluoxetine (Prozac™), β-naphthoflavone, estrogen and 17α-ethinylestradiol were also observed. Similar to metals, acutely toxic concentrations of fluoxetine, β-naphthoflavone and ammonia all decreased whole body Na + and K + . Overall, whole body Na + loss showed the greatest correlation with mortality across a variety of toxicants. We theorize that a disruption of

  18. Addition of silica nanoparticles to tailor the mechanical properties of nanofibrillated cellulose thin films.

    Science.gov (United States)

    Eita, Mohamed; Arwin, Hans; Granberg, Hjalmar; Wågberg, Lars

    2011-11-15

    Over the last decade, the use of nanocellulose in advanced technological applications has been promoted both due the excellent properties of this material in combination with its renewability. In this study, multilayered thin films composed of nanofibrillated cellulose (NFC), polyvinyl amine (PVAm) and silica nanoparticles were fabricated on polydimethylsiloxane (PDMS) using a layer-by-layer adsorption technique. The multilayer build-up was followed in situ by quartz crystal microbalance with dissipation, which indicated that the PVAm-SiO(2)-PVAm-NFC system adsorbs twice as much wet mass material compared to the PVAm-NFC system for the same number of bilayers. This is accompanied with a higher viscoelasticity for the PVAm-SiO(2)-PVAm-NFC system. Ellipsometry indicated a dry-state thickness of 2.2 and 3.4 nm per bilayer for the PVAm-NFC system and the PVAm-SiO(2)-PVAm-NFC system, respectively. Atomic force microscopy height images indicate that in both systems, a porous network structure is achieved. Young's modulus of these thin films was determined by the Strain-Induced Elastic Buckling Instability for Mechanical Measurements (SIEBIMM) technique. The Young's modulus of the PVAm/NFC films was doubled, from 1 to 2 GPa, upon incorporation of silica nanoparticles in the films. The introduction of the silica nanoparticles lowered the refractive index of the films, most probably due to an increased porosity of the films. Copyright © 2011 Elsevier Inc. All rights reserved.

  19. Effect of nano-additives on microstructure, mechanical properties and wear behaviour of Fe–Cr–B hardfacing alloy

    International Nuclear Information System (INIS)

    Gou, Junfeng; Lu, Pengpeng; Wang, You; Liu, Saiyue; Zou, Zhiwei

    2016-01-01

    Graphical abstract: Wear rate of the hardfacing layers with different nano-additives content and the counterpart GCr15 steel balls under conditions: normal load = 15 N, rotating speed = 400 rpm, total sliding time = 20 min. - Highlights: • Nano-additives remarkably improved the microstructure of hardfacing layers. • The hardness of hardfacing layers increased linearly with the increase of nano-additives. • The wear rate of the hardfacing layer with 0.65 wt.% nano-additives decreased about 88% than that of the hardfacing layer without nano-additives. • According to observation of wear tracks of hardfacing layers, the main wear mechanism was adhesion wear. - Abstract: Fe–Cr–B hardfacing alloys with different nano-additives content were investigated. The effects of nano-additives on the microstructures of hardfacing alloy were studied by using optical microscope, scanning electron microscope, X-ray diffractometer. The hardness and the fracture toughness of hardfacing alloys were measured, respectively. The sliding wear tests were carried out using a ball-on-disc tribometer. The experimental results showed that primary carbide of hardfacing alloys was refined and its distribution became uniform with content of nano-additives increased. The hardfacing alloys are composed of Cr_7C_3, Fe_7C_3, α-Fe and Fe_2B according to the results of X-ray diffraction. The hardness of hardfacing alloys increased linearly with the increase of nano-additives. The hardness of the hardfacing alloy with 1.5 wt.% nano-additives increased 54.8% than that of the hardfacing alloy without nano-additives and reached to 1011HV. The K_I_C of the hardfacing alloy with 0.65 wt.% nano-additives was 15.4 MPam"1"/"2, which reached a maximum. The value increased 57.1% than that of the hardfacing alloy without nano-additives. The wear rates of the hardfacing layer with 0.65 wt.% and 1.0 wt.% nano-additives decreased about 88% than that of the hardfacing layer without nano-additives. The main

  20. In situ polymerized wood polymer composite: effect of additives and nanoclay on the thermal, mechanical properties

    Energy Technology Data Exchange (ETDEWEB)

    Devi, Rashmi R; Maji, Tarun K., E-mail: tkm@tezu.ernet.in [Department of Chemical Sciences, Tezpur University, Assam, (India)

    2013-11-01

    This study concerns the preparation and characterization of wood polymer nanocomposites based on impregnation of styrene acrylonitrile co-polymer-nanoclay intercalating system in presence of glycidyl methacrylate (GMA), a cross linking agent, and vinyl trichloro silane (VTCS) as additives into Simul (Bombex ceiba, L.), a soft wood. The effect of nanoclay and VTCS on the properties of the resultant wood polymer nanocomposites (WPNC) has been evaluated. FTIR spectroscopy shows the interaction among wood, polymers, GMA, nanoclay and VTCS. The penetration of polymer and nanoclay into the wood cell wall is supported by SEM study. The distribution of nanoclay in the SAN polymer matrix present within the wood cell wall has been evidenced by TEM study. TGA results show an improvement in the thermostability of the resultant composites. The inclusion of VTCS enhances the self extinguishing behaviour of the WPNC as revealed by limiting oxygen index (LOI) test. Due to treatment, the resultant WPNC exhibits an improvement in all the properties like water repellency, dimensional stability, hardness, flexural, tensile and thermal stability compared to untreated wood. (author)

  1. In situ polymerized wood polymer composite: effect of additives and nanoclay on the thermal, mechanical properties

    International Nuclear Information System (INIS)

    Devi, Rashmi R; Maji, Tarun K.

    2013-01-01

    This study concerns the preparation and characterization of wood polymer nanocomposites based on impregnation of styrene acrylonitrile co-polymer–nanoclay intercalating system in presence of glycidyl methacrylate (GMA), a cross linking agent, and vinyl trichloro silane (VTCS) as additives into Simul (Bombex ceiba, L.), a soft wood. The effect of nanoclay and VTCS on the properties of the resultant wood polymer nanocomposites (WPNC) has been evaluated. FTIR spectroscopy shows the interaction among wood, polymers, GMA, nanoclay and VTCS. The penetration of polymer and nanoclay into the wood cell wall is supported by SEM study. The distribution of nanoclay in the SAN polymer matrix present within the wood cell wall has been evidenced by TEM study. TGA results show an improvement in the thermostability of the resultant composites. The inclusion of VTCS enhances the self extinguishing behaviour of the WPNC as revealed by limiting oxygen index (LOI) test. Due to treatment, the resultant WPNC exhibits an improvement in all the properties like water repellency, dimensional stability, hardness, flexural, tensile and thermal stability compared to untreated wood. (author)

  2. Constituent phases and mechanical properties of iron oxide-additioned phosphoaluminate cement

    Directory of Open Access Journals (Sweden)

    Yang, Shuai

    2015-06-01

    Full Text Available Iron oxide was added to phosphoaluminate clinker and its effects on cement constituents were determined using XRD, DSC, SEM-EDS and conduction calorimetry analysis. The variations in compressive strength were also studied. The results showed that in moderate amounts, iron oxide acts as a mineraliser during clinker sintering, furthering the conversion of CA1-Y(PY to LHss at a lower temperature than normally required for that reaction. The main constituents of iron oxide-rich phosphoaluminate clinker included LHss, CA1-Y(PY, CP1-Z(AZ and ferrite. The EDS findings showed that the composition of the ferrite phase was nonuniform. The conclusion drawn was that by modifying the dose of Fe2O3 , the composition of phosphoaluminate cement can be controlled to produce clinker and cement compliant with different mechanical strength requirements. The conduction calorimetry findings were consistent with those results.Este trabajo estudia, mediante DRX DSC, SEM-EDS y calorimetría de conducción, el efecto de la adición de óxido de hierro a un clinker de fosfoaluminato, así como las variaciones sufridas en su resistencia a compresión. Los resultados mostraron que en cantidades moderadas, el óxido de hierro actúa como mineralizador durante la sinterización del clinker, promoviendo la conversión de CA1-Y(PY a LHss a una temperatura más baja de la normalmente requerida. Los componentes principales del clínker de fosfoaluminato con óxido de hierrop son LHss, CA1-Y(PY, CP1-Z(AZ y fase ferritica. Los resultados de EDS mostraron que la composición de esta fase ferrítica no era uniforme. DE este estudio se ha podido concluir que variando la dosificación del Fe2O3 , se puede controlar la composición del fosfoaluminato para producir clinker y cemento compatibles con diferentes requisitos de resistencia mecánica. Los resultados de calorimetría de conducción fueron consistentes con los resultados.

  3. The effect of silver (Ag) addition to mechanical and electrical properties of copper alloy (Cu) casting product

    Science.gov (United States)

    Felicia, Dian M.; Rochiem, R.; Laia, Standley M.

    2018-04-01

    Copper have good mechanical properties and good electrical conductivities. Therefore, copper usually used as electrical components. Silver have better electrical conductivities than copper. Female contact resistor is one of the electrical component used in circuit breaker. This study aims to analyze the effect of silver addition to hardness, strength, and electric conductivity properties of copper alloy. This study uses variation of 0; 0.035; 0.07; 0.1 wt. % Ag (silver) addition to determine the effect on mechanical properties and electrical properties of copper alloy through sand casting process. Modelling of thermal analysis and structural analysis was calculated to find the best design for the sand casting experiments. The result of Cu-Ag alloy as cast will be characterized by OES test, metallography test, Brinell hardness test, tensile test, and LCR meter test. The result of this study showed that the addition of silver increase mechanical properties of Cu-Ag. The maximum hardness value of this alloy is 83.1 HRB which is Cu-0.01 Ag and the lowest is 52.26 HRB which is pure Cu. The maximum strength value is 153.2 MPa which is Cu-0.07 Ag and the lowest is 94.6 MPa which is pure Cu. Silver addition decrease electrical properties of this alloy. The highest electric conductivity is 438.98 S/m which is pure Cu and the lowest is 52.61 S.m which is Cu-0.1 Ag.

  4. Influence of compatibilizer and/or montmorillonite addition on the mechanical properties and morphology of PP/recycled PET blends

    International Nuclear Information System (INIS)

    Silva, Murilo S.; Souza, Adriana M.C.

    2011-01-01

    In this work, the mechanical properties and morphology PP/recycled PET blends with addition of P(E-co-MA-co-GMA) copolymer and/or montmorillonite clay (MMT) was investigated. The blends were obtained by extrusion and their morphology was observed by scanning electron microscopy. The mechanical properties were evaluated by tensile and impact tests. Thin films of nanocomposites were characterized by x-ray diffraction (XRD). The addition of P (E-co-MA-co-GMA) or MMT clay separately promoted a decrease of the dispersed phase size. XRD analysis indicated that there was incorporation of polymer in clay galleries. The addition of clay in PP / PET blend resulted in an increase of apparent elastic modulus, impact resistance and HDT and a decrease of tensile strength and elongation at break. The addition of P (E-co-MA-co-GMA) resulted in an increased impact strength and reduction of other properties. There were no significant changes on mechanical properties when the clay and P (E-co-MA-co-GMA) are added simultaneously. (author)

  5. The Influence of Cu Addition on Dispersoid Formation and Mechanical Properties of Al-Mn-Mg 3004 Alloy

    Directory of Open Access Journals (Sweden)

    Zhen Li

    2018-03-01

    Full Text Available The effect of Cu addition on dispersoid precipitation, mechanical properties and creep resistance was investigated in an Al-Mn-Mg 3004 alloy. The addition of Cu promoted dispersoid precipitation by increasing the number density and decreasing the size of dispersoids. Metastable β′-Mg2Si and Q-AlCuMgSi precipitates were observed during the heating process and both could provide favorable nucleation sites for dispersoid precipitation. The addition of Cu improved the thermal stability of dispersoids during a long-term thermal holding at 350 °C for 500 h. Results of mechanical testing show that the addition of Cu remarkably improved the hardness at room temperature, as well as the yield strength and creep resistance at 300 °C, which was mainly attributed to dispersoid strengthening and Cu solid solution strengthening. The yield strength contribution at 300 °C was quantitatively evaluated based on the dispersoid, solid solution and matrix contributions. It was confirmed that dispersoid strengthening is the main strengthening mechanism in the experimental alloys.

  6. Brucella, nitrogen and virulence.

    Science.gov (United States)

    Ronneau, Severin; Moussa, Simon; Barbier, Thibault; Conde-Álvarez, Raquel; Zuniga-Ripa, Amaia; Moriyon, Ignacio; Letesson, Jean-Jacques

    2016-08-01

    The brucellae are α-Proteobacteria causing brucellosis, an important zoonosis. Although multiplying in endoplasmic reticulum-derived vacuoles, they cause no cell death, suggesting subtle but efficient use of host resources. Brucellae are amino-acid prototrophs able to grow with ammonium or use glutamate as the sole carbon-nitrogen source in vitro. They contain more than twice amino acid/peptide/polyamine uptake genes than the amino-acid auxotroph Legionella pneumophila, which multiplies in a similar vacuole, suggesting a different nutritional strategy. During these two last decades, many mutants of key actors in nitrogen metabolism (transporters, enzymes, regulators, etc.) have been described to be essential for full virulence of brucellae. Here, we review the genomic and experimental data on Brucella nitrogen metabolism and its connection with virulence. An analysis of various aspects of this metabolism (transport, assimilation, biosynthesis, catabolism, respiration and regulation) has highlighted differences and similarities in nitrogen metabolism with other α-Proteobacteria. Together, these data suggest that, during their intracellular life cycle, the brucellae use various nitrogen sources for biosynthesis, catabolism and respiration following a strategy that requires prototrophy and a tight regulation of nitrogen use.

  7. Effect of TaC addition on the microstructures and mechanical properties of Ti(C, N)-based cermets

    International Nuclear Information System (INIS)

    Wu, Peng; Zheng, Yong; Zhao, Yongle; Yu, Haizhou

    2010-01-01

    The microstructures of the prepared Ti(C, N)-based cermets with various TaC additions were studied using X-ray diffractometry (XRD) and scanning electron microscopy (SEM). Mechanical properties such as transverse rupture strength (TRS), fracture toughness (K 1C ) and hardness (HRA) were also measured. The results showed that the grain size of the cermets decreased with increasing TaC addition, but too high TaC addition resulted in agglomeration of the grains. An increasing TaC addition increased the dissolution of tungsten, titanium, molybdenum and tantalum in the binder phase. The hardness of the cermets decreased slightly with increasing TaC addition. The transverse rupture strength was the highest for the cermets with 5 wt.% TaC addition, which was characterized by fine grains, homogeneous microstructure and the moderate thickness of rim phase in the binder. The fracture toughness of the cermets with TaC addition from 0 to 5 wt.% decreased obviously, which resulting from decreased grain size. The further decreasing of fracture toughness for the cermets with 7 wt.% TaC addition was due to increased porosity and interfacial tensile stress.

  8. Virulence evolution at the front line of spreading epidemics.

    Science.gov (United States)

    Griette, Quentin; Raoul, Gaël; Gandon, Sylvain

    2015-11-01

    Understanding and predicting the spatial spread of emerging pathogens is a major challenge for the public health management of infectious diseases. Theoretical epidemiology shows that the speed of an epidemic is governed by the life-history characteristics of the pathogen and its ability to disperse. Rapid evolution of these traits during the invasion may thus affect the speed of epidemics. Here we study the influence of virulence evolution on the spatial spread of an epidemic. At the edge of the invasion front, we show that more virulent and transmissible genotypes are expected to win the competition with other pathogens. Behind the front line, however, more prudent exploitation strategies outcompete virulent pathogens. Crucially, even when the presence of the virulent mutant is limited to the edge of the front, the invasion speed can be dramatically altered by pathogen evolution. We support our analysis with individual-based simulations and we discuss the additional effects of demographic stochasticity taking place at the front line on virulence evolution. We confirm that an increase of virulence can occur at the front, but only if the carrying capacity of the invading pathogen is large enough. These results are discussed in the light of recent empirical studies examining virulence evolution at the edge of spreading epidemics. © 2015 The Author(s). Evolution © 2015 The Society for the Study of Evolution.

  9. Review on effect of chemical, thermal, additive treatment on mechanical properties of basalt fiber and their composites

    Science.gov (United States)

    Jain, Naman; Singh, Vinay Kumar; Chauhan, Sakshi

    2017-12-01

    Basalt fiber is emerging out the new reinforcing material for composites. To overcome some of the disadvantages of fibers such as poor bonding to polymers, low thermal stability and high moisture absorption fiber characteristics are modified with chemical, thermal and additive treatments. Chemical treatment corrosive resistance to alkali and acid were investigated which were used to clean and modify the surface of fiber for higher bonding with resins. To improve the thermal stability and reduce moisture uptake thermal treatment such as plasma and non thermal plasma were used which increased the surface roughness and change the chemical composition of surface of basalt fiber. Additive treatment is used to improve the mechanical properties of fibers, in basalt fiber additive treatment was done with SiO2 additive because of its chemical composition which contains major content of SiO2. In present investigation review on the effect of different treatment such as chemical, thermal and additive were studied. Effect of these treatment on chemical composition of the surface of basalt fiber and corrosion to acidic and alkali solution were studied with their effect on mechanical properties of basalt fiber and their composite.

  10. Comparative Genomics of Mycoplasma bovis Strains Reveals That Decreased Virulence with Increasing Passages Might Correlate with Potential Virulence-Related Factors

    Directory of Open Access Journals (Sweden)

    Muhammad A. Rasheed

    2017-05-01

    Full Text Available Mycoplasma bovis is an important cause of bovine respiratory disease worldwide. To understand its virulence mechanisms, we sequenced three attenuated M. bovis strains, P115, P150, and P180, which were passaged in vitro 115, 150, and 180 times, respectively, and exhibited progressively decreasing virulence. Comparative genomics was performed among the wild-type M. bovis HB0801 (P1 strain and the P115, P150, and P180 strains, and one 14.2-kb deleted region covering 14 genes was detected in the passaged strains. Additionally, 46 non-sense single-nucleotide polymorphisms and indels were detected, which confirmed that more passages result in more mutations. A subsequent collective bioinformatics analysis of paralogs, metabolic pathways, protein-protein interactions, secretory proteins, functionally conserved domains, and virulence-related factors identified 11 genes that likely contributed to the increased attenuation in the passaged strains. These genes encode ascorbate-specific phosphotransferase system enzyme IIB and IIA components, enolase, L-lactate dehydrogenase, pyruvate kinase, glycerol, and multiple sugar ATP-binding cassette transporters, ATP binding proteins, NADH dehydrogenase, phosphate acetyltransferase, transketolase, and a variable surface protein. Fifteen genes were shown to be enriched in 15 metabolic pathways, and they included the aforementioned genes encoding pyruvate kinase, transketolase, enolase, and L-lactate dehydrogenase. Hydrogen peroxide (H2O2 production in M. bovis strains representing seven passages from P1 to P180 decreased progressively with increasing numbers of passages and increased attenuation. However, eight mutants specific to eight individual genes within the 14.2-kb deleted region did not exhibit altered H2O2 production. These results enrich the M. bovis genomics database, and they increase our understanding of the mechanisms underlying M. bovis virulence.

  11. Isolated and modulated effects of topology and material type on the mechanical properties of additively manufactured porous biomaterials.

    Science.gov (United States)

    Hedayati, R; Ahmadi, S M; Lietaert, K; Pouran, B; Li, Y; Weinans, H; Rans, C D; Zadpoor, A A

    2018-03-01

    In this study, we tried to quantify the isolated and modulated effects of topological design and material type on the mechanical properties of AM porous biomaterials. Towards this aim, we assembled a large dataset comprising the mechanical properties of AM porous biomaterials with different topological designs (i.e. different unit cell types and relative densities) and material types. Porous structures were additively manufactured from Co-Cr using a selective laser melting (SLM) machine and tested under quasi-static compression. The normalized mechanical properties obtained from those structures were compared with mechanical properties available from our previous studies for porous structures made from Ti-6Al-4V and pure titanium as well as with analytical solutions. The normalized values of elastic modulus and yield stress were found to be relatively close to each other as well as in agreement with analytical solutions regardless of material type. However, the material type was found to systematically affect the mechanical properties of AM porous biomaterials in general and the post-elastic/post-yield range (plateau stress and energy absorption capacity) in particular. To put this in perspective, topological design could cause up to 10-fold difference in the mechanical properties of AM porous biomaterials while up to 2-fold difference was observed as a consequence of changing the material type. Copyright © 2017 Elsevier Ltd. All rights reserved.

  12. Natural variation in virulence of the entomopathogenic fungus Beauveria bassiana against malaria mosquitoes.

    Science.gov (United States)

    Valero-Jiménez, Claudio A; Debets, Alfons J M; van Kan, Jan A L; Schoustra, Sijmen E; Takken, Willem; Zwaan, Bas J; Koenraadt, Constantianus J M

    2014-12-06

    Insecticide resistance is greatly hampering current efforts to control malaria and therefore alternative methods are needed. Entomopathogenic fungi have been proposed as an alternative with a special focus on the cosmopolitan species Beauveria bassiana. However, few studies have analysed the effects of natural variation within fungal isolates on mosquito survival, and the implications and possible exploitation for malaria control. Laboratory bioassays were performed on adult female mosquitoes (Anopheles coluzzii) with spores from 29 isolates of B. bassiana, originating from different parts of the world. In addition, phenotypic characteristics of the fungal isolates such as sporulation, spore size and growth rate were studied to explore their relationship with virulence. All tested isolates of B. bassiana killed An. coluzzii mosquitoes, and the rate at which this happened differed significantly among the isolates. The risk of mosquitoes dying was around ten times higher when they were exposed to the most virulent as compared to the least virulent isolate. There was significant variation among isolates in spore size, growth rate and sporulation, but none of these morphological characteristics were correlated, and thus predictive, for the ability of the fungal isolate to kill malaria mosquitoes. This study shows that there is a wide natural variation in virulence of isolates of B. bassiana, and that selecting an appropriate fungal isolate is highly relevant in killing and thus controlling malaria mosquitoes, particularly if used as part of an integrated vector management strategy. Also, the wide variation observed in virulence offers the opportunity to better understand the molecular and genetic mechanisms that drive this variation and thus to address the potential development of resistance against entomopathogenic fungi.

  13. The effect of boron addition on microstructure and mechanical properties of biomedical Ti35Nb6Ta alloy

    Energy Technology Data Exchange (ETDEWEB)

    Málek, Jaroslav, E-mail: malek@ujp.cz [UJP PRAHA a.s., Nad Kamínkou 1345, 156 10 Prague, Zbraslav (Czech Republic); CTU in Prague, Faculty of Mechanical Engineering, Department of Materials Engineering, Karlovo Namesti 13, 121 35 Praha 2 (Czech Republic); Hnilica, František, E-mail: hnilica@ujp.cz [UJP PRAHA a.s., Nad Kamínkou 1345, 156 10 Prague, Zbraslav (Czech Republic); Veselý, Jaroslav, E-mail: vesely@ujp.cz [UJP PRAHA a.s., Nad Kamínkou 1345, 156 10 Prague, Zbraslav (Czech Republic); Smola, Bohumil, E-mail: smola@met.mff.cuni.cz [Charles University, Faculty of Mathematics and Physics, Ke Karlovu 5, 121 16 Prague 2 (Czech Republic); Březina, Vítězslav, E-mail: brezinavita@gmail.com [Masaryk University, Faculty of Medicine, Department of Stomathology, Komenského Náměstí 220/2, 662 43 Brno (Czech Republic); Kolařík, Kamil, E-mail: kamil.kolarik@email.cz [Faculty of Mechanical Engineering, University of West Bohemia, Univerzitní 22, 306 14 Plzeň (Czech Republic)

    2014-10-15

    The beta-titanium alloys are promising materials for bioapplications but their processing via melting is difficult. Coarse grains have been observed in as-cast specimens. Subsequent thermo-mechanical processing seems to be necessary in order to obtain fine-grained microstructure with better mechanical properties. The grain size can be decreased significantly by addition of small boron amount. In this work Ti–35Nb–6Ta alloy with various B additions (0, 0.05, 0.1, 0.3 and 0.5 wt.%) has been studied. Even the smallest amount of B leads to significant grain refinement in Ti–35Nb–6Ta alloy (from 1300 to about 350 μm). Slight grain refinement has been observed also after hot forging and solution treatment. TiB particles emerged in specimens due to B addition. These particles contribute to changes in mechanical properties not only in hot forged and solution treated specimens (hardness increase from 140 to 180 HV10), but also in cold swaged specimens (hardness from 230 to 250 HV10, tensile strength from 800 to 920 MPa). The hardness values can be increased up to 370 HV10 during aging at 400 °C (specimen with 0.5 wt.% B). It has been observed that specimens with low boron addition 0.05 wt.% possess no cytotoxicity. On the other hand in specimens with 0.1 wt.% B or more slight adverse effect on cytotoxicity has been observed. - Highlights: • The influence of boron on microstructure and mechanical properties has been studied. • Beta-transus temperature has been determined. • Cytotoxicity depending on boron content has been evaluated. • Possibility of final heat treatment has been determined.

  14. Effect of Sr addition on microstructure and elevated temperature mechanical properties of Mg–3Zn–1Y alloy

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Junwei [College of Materials Science and Engineering, Chongqing University, Chongqing 400044 (China); Peng, Xiaodong, E-mail: pxd@cqu.edu.cn [College of Materials Science and Engineering, Chongqing University, Chongqing 400044 (China); National Engineering Research Center for Magnesium Alloys, Chongqing 400044 (China); Li, Mengluan; Wei, Guobing [College of Materials Science and Engineering, Chongqing University, Chongqing 400044 (China); Xie, Weidong [College of Materials Science and Engineering, Chongqing University, Chongqing 400044 (China); National Engineering Research Center for Magnesium Alloys, Chongqing 400044 (China); Yang, Yan [College of Materials Science and Engineering, Chongqing University, Chongqing 400044 (China)

    2016-02-08

    The effects of Sr addition on the microstructure and elevated temperature mechanical behavior of Mg–3Zn–1Y alloys have been investigated in this research. The results show that α-Mg, W-phase and S-phase are found in the Sr-containing alloys. The S-phase has a higher thermal stability than W-phase, which significantly improves the elevated temperature mechanical properties of the alloy. To further confirm the crystal structure of the S-phase, high resolution transmission electron microscopy analysis was performed and the phase was confirmed to be Mg{sub 6}Zn{sub 2}Sr{sub 1}. With increasing content of Sr, the elevated temperature mechanical properties of the Mg–3Zn–1Y are improved. When the Sr content reached to 0.9 wt%, the alloy shows a much higher ultimate tensile strength of 204 MPa and yield strength of 171 MPa at 250 °C.

  15. Room Temperature Mechanical Properties of A356 Alloy with Ni Additions from 0.5 Wt to 2 Wt %

    Directory of Open Access Journals (Sweden)

    Lucia Lattanzi

    2018-03-01

    Full Text Available In recent years, the influence of Ni on high-temperature mechanical properties of casting Al alloys has been extensively examined in the literature. In the present study, room temperature mechanical properties of an A356 alloy with Ni additions from 0.5 to 2 wt % were investigated. The role of Ni-based compounds and eutectic Si particles in reinforcing the Al matrix was studied with image analysis and was then related to tensile properties and microhardness. In the as-cast condition, the formation of the 3D network is not sufficient to determine an increase of mechanical properties of the alloys since fracture propagates by cleavage through eutectic Si particles and Ni aluminides or by the debonding of brittle phases from the aluminum matrix. After T6 heat treatment the increasing amount of Ni aluminides, due to further addition of Ni to the alloy, together with their brittle behavior, leads to a decrease of yield strength, ultimate tensile strength, and Vickers microhardness. Despite the fact that Ni addition up to 2 wt % hinders spheroidization of eutectic Si particles during T6 heat treatment, it also promotes the formation of a higher number of brittle Ni-based compounds that easily promote fracture propagation.

  16. Influence of additional coupling agent on the mechanical properties of polyester–agave cantala roxb based composites

    Energy Technology Data Exchange (ETDEWEB)

    Ubaidillah, E-mail: ubaidillah@uns.ac.id [Mechanical Engineering Department, Faculty of Engineering, Sebelas Maret University, Jl. Ir. Sutami 36A, Kentingan, Surakarta, 57126 (Indonesia); Malaysia-Japan International Institute of Technology, Universiti Teknologi Malaysia, Jalan Sultan Yahya Petra, Kuala Lumpur (Malaysia); Raharjo, Wijang W.; Wibowo, A. [Mechanical Engineering Department, Faculty of Engineering, Sebelas Maret University, Jl. Ir. Sutami 36A, Kentingan, Surakarta, 57126 (Indonesia); Harjana [Iwany Acoustic Research Group, Sebelas Maret University, Jl. Ir. Sutami 36A, Kentingan, Surakarta, 57126 (Indonesia); Mazlan, S. A., E-mail: amri.kl@utm.my [Malaysia-Japan International Institute of Technology, Universiti Teknologi Malaysia, Jalan Sultan Yahya Petra, Kuala Lumpur (Malaysia)

    2016-03-29

    The mechanical and morphological properties of the unsaturated polyester resins (UPRs)-agave cantala roxb based composite are investigated in this paper. The cantala fiber woven in 3D angle interlock was utilized as the composite reinforcement. Surface grafting of the cantala fiber through chemical treatment was performed by introducing silane coupling agent to improving the compatibility with the polymer matrix. The fabrication of the composite specimens was conducted using vacuum bagging technique. The effect of additional coupling agent to the morphological appearance of surface fracture was observed using scanning electron microscopy. Meanwhile, the influence of additional silane to the mechanical properties was examined using tensile, bending and impact test. The photograph of surface fracture on the treated specimens showed the residual matrix left on the fibers in which the phenomenon was not found in the untreated specimens. Based on mechanical tests, the treated specimens were successfully increased their mechanical properties by 55%, 9.67%, and 92.4% for tensile strength, flexural strength, and impact strength, respectively, at 1.5% silane coupling agent.

  17. Effect of copper addition on mechanical properties, corrosion resistance and antibacterial property of 316L stainless steel

    Energy Technology Data Exchange (ETDEWEB)

    Xi, Tong [School of Materials Science and Engineering, Dalian University of Technology, Dalian 116024 (China); Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016 (China); Shahzad, M. Babar [Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016 (China); Xu, Dake [School of Materials Science and Engineering, Dalian University of Technology, Dalian 116024 (China); Sun, Ziqing; Zhao, Jinlong [Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016 (China); Yang, Chunguang, E-mail: cgyang@imr.ac.cn [Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016 (China); Qi, Min [School of Materials Science and Engineering, Dalian University of Technology, Dalian 116024 (China); Yang, Ke, E-mail: kyang@imr.ac.cn [Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016 (China)

    2017-02-01

    The effects of addition of different Cu content (0, 2.5 and 3.5 wt%) on mechanical properties, corrosion resistance and antibacterial performance of 316L austenitic stainless steel (SS) after solution and aging treatment were investigated by mechanical test, transmission electron microscope (TEM), X-ray diffraction (XRD), electrochemical corrosion, X-ray photoelectron spectroscopy (XPS) and antibacterial test. The results showed that the Cu addition and heat treatment had no obvious influence on the microstructure with complete austenite features. The yield strength (YS) after solution treatment was almost similar, whereas the aging treatment obviously increased the YS due to formation of tiny Cu-rich precipitates. The pitting and protective potential of the solution treated Cu-bearing 316L SS in 0.9 wt% NaCl solution increased with increasing Cu content, while gradually declined after aging, owing to the high density Cu-rich precipitation. The antibacterial test proved that higher Cu content and aging were two compulsory processes to exert good antibacterial performance. The XPS results further indicated that aging enhanced the Cu enrichment in passive film, which could effectively stimulate the Cu ions release from the surface of passive film. - Highlights: • Higher Cu addition and aging guaranteed an excellent antibacterial property. • The Cu addition and heat treatment had no obvious influence on the microstructure. • The lower corrosion resistance for aging was attributed to Cu-rich precipitates.

  18. Effect of Zirconium Addition on Microstructure and Mechanical Property of TiC/Ti6A14V Composites

    Science.gov (United States)

    Ma, Xuliang; Wang, Xiang; Li, Li; Gai, Pengtao; Zhu, Chengwu

    TiC/Ti6A14V composites with different Zr additions were prepared successfully in a consumable vacuum arc furnace equipped with a water-cooled copper crucible and the effect of the Zr content on the microstructure and mechanical property of 15 vol.%TiC/Ti6A14V composites was investigated by XRD, SEM and hardness testing. The results show that when the level of Zr addition is less than 4 wt.%, the morphology of the primary TiC in the composites is dendrite, and the petal-shape, piece-shape or palpus-shape eutectic TiC separates out around the primary TiC. The average size of the primary TiC decreases and the amount of eutectic TiC increases gradually with increasing Zr content. The effects of Zr on morphology of the primary TiC weaken with further addition of Zr. And the hardness (HRC) of composites was obviously increased in the whole range of Zr addition. The refinement mechanism of Zr was attributed to the combined effects of increase in nucleation rate at the constitutionally supercooled zone ahead of the solidification front and reduction in growth rate.

  19. PARAMETER DETERMINATION FOR ADDITIONAL OPERATING FORCE MECHANISM IN DEVICE FOR PNEUMO-CENTRIFUGAL MACHINING OF BALL-SHAPED WORKPIECES

    Directory of Open Access Journals (Sweden)

    A. A. Sukhotsky

    2014-01-01

    Full Text Available The paper describes development of the methodology for optimization of parameters for an additional operating force mechanism in a device for pneumo-centrifugal machining of glass balls. Specific feature in manufacturing glass balls for micro-optics in accordance with technological process for obtaining ball-shaped workpieces is grinding and polishing of spherical surface in a free state. In this case component billets of future balls are made in the form of cubes and the billets are given preliminary a form of ball with the help of rough grinding. An advanced method for obtaining ball-shaped work-pieces from brittle materials is a pneumocentrifugal machining. This method presupposes an application of two conic rings with abrasive working surfaces which are set coaxially with large diameters to each other and the billets are rolled along these rings. Rotation of the billets is conveyed by means of pressure medium.The present devices for pneumo-centrifugal machining are suitable for obtaining balls up to 6 mm. Machining of the work-pieces with full spherical surfaces and large diameter is non-productive due to impossibility to ensure a sufficient force on the billet in the working zone. For this reason the paper proposes a modified device where an additional force on the machined billet is created by upper working disc that is making a reciprocating motion along an axis of abrasive conic rings. The motion is realized with the help of a cylindrical camshaft mechanism in the form of a ring with a profile working end face and the purpose of present paper is to optimize parameters of the proposed device.The paper presents expressions for calculation of constitutive parameters of the additional operating force mechanism including parameters of loading element motion, main dimensions of the additional operating force mechanism and parameters of a profile element in the additional operating force mechanism.Investigation method is a mathematical

  20. Effect of addition of tantalum and zirconium on the mechanical behavior of aluminum grain refined by Ti+ B

    International Nuclear Information System (INIS)

    Zaid, A.I.O.

    2003-01-01

    Aluminum and its alloys normally solidify in a columnar structure with coarse grains. Therefore, they are normally grain refined by adding either titanium or titanium + boron to their melts to obtain finer grain size and better surface quality. Other elements may be added beside the grain refiners to enhance their grain refinement efficiency and improve the mechanical behavior. Some elements were found to improve the grain refining efficiency of the master alloys e.g., vanadium, molybdenum, while others were found to deteriorate the grain refining efficiency e.g., zirconium and tantalum. The literature reveals that in general, only one element is added in the presence of the binary AI-Ti or the ternary AI-Ti-B grain refining master alloy. It is, therefore, anticipated that the addition of Ta and Zr may have different effect when added together from that if each element is added alone. This formed the main objective of this paper. In this paper, the effect of addition of either Zr, Ta or both of them together, with a percentage of 0.1 %wt each, on the grain size, hardness and mechanical behavior of AI and AI grain refined by Ti+B is investigated. It was found that adding Zr or Ta to commercially pure aluminum resulted in grain refinement of its structure and resulted in slight improvement of its hardness. However, a pronounced improvement was obtained in its mechanical strength and formability. On the other hand, addition of either Zr or Ta to Al grain refined by Ti+B resulted in poisoning effect i.e. reducing the grain refining efficiency of the AI- Ti-B master alloy. Practically, addition of either Zr or Ta has no effect on its hardness but resulted in a pronounced improvement of its mechanical strength. Finally, the addition of Zr + Ta to commercially pure aluminum or to aluminum grain refined by Ti+B resulted in reduction of grain size, little improvement in hardness and pronounced improvement in mechanical strength than when each element was added alone

  1. Role of quaternary additions on dislocated martensite, retain austenite and mechanical properties of Fe/Cr/C structural steels

    International Nuclear Information System (INIS)

    Rao, B.V.N.

    1978-02-01

    The influence of quaternary alloy additions of Mn and Ni to Fe/Cr/C steels which have been designed to provide superior mechanical properties has been investigated. Transmission electron microscopy and x-ray analysis revealed increasing amounts of retained austenite with Mn up to 2 w/o and with 5 w/o Ni additions after quenching from 1100 0 C. This is accompanied by a corresponding improvement in toughness properties of the quaternary alloys. In addition, the generally attractive combinations of strength and toughness in these quaternary alloys is attributed to the production of dislocated lath martensite from a homogeneous austenite phase free from undissolved alloy carbides. Grain-refining resulted in a further increase in the amount of retained austenite

  2. Hardening mechanisms of spray formed Al-Zn-Mg-Cu alloys with scandium and other elemental additions

    International Nuclear Information System (INIS)

    Sharma, M.M.; Amateau, M.F.; Eden, T.J.

    2006-01-01

    The hardening mechanisms in spray formed Al-Zn-Mg-Cu alloys with additions of chromium, zinc and scandium were studied. The microstructure of the spray formed alloys was analyzed by transmission electron microscopy. A range of tensile strengths were achieved, and varied based on elemental additions, and second phase particle strengthening. To explain the significantly higher strength in one alloy with scandium, theoretical results due to the yield stress of Al-Zn-Mg-Cu alloys as a function of volume fraction and precipitate particle size, were compared to experimental data. Both the possibilities of coherency and order strengthening are examined. The significant additional hardening achieved in the alloy with scandium is attributed to small ordered particles of Al 3 Sc, which precipitated during aging

  3. Effects of the addition of mechanically deboned poultry meat and collagen fibers on quality characteristics of frankfurter-type sausages.

    Science.gov (United States)

    Pereira, Anirene Galvão Tavares; Ramos, Eduardo Mendes; Teixeira, Jacyara Thaís; Cardoso, Giselle Pereira; Ramos, Alcinéia de Lemos Souza; Fontes, Paulo Rogério

    2011-12-01

    The effects of mechanically deboned poultry meat (MDPM) and levels of collagen fibers on comminuted, cooked sausage quality characteristics were investigated using the central composite rotatable design of response surface methodology (RSM). Use of collagen fiber as an additive affected the sausage characteristics, but the effect depended on the amount of the MDPM used. While MDPM additions resulted in higher cooking loss and darker and redder frankfurters, the addition of collagen fibers improved cooking yields and contributed to the lightness of the final product. Higher collagen fiber content was also accompanied by a significant increase in frankfurter hardness regardless of the MDPM content. Use of collagen fibers countered the negative effects of MDPM on sausage quality attributes, especially on cooking yields and final product color. Copyright © 2011 Elsevier Ltd. All rights reserved.

  4. Influence of cooling rate and antimony addition content on graphite morphology and mechanical properties of a ductile iron

    Directory of Open Access Journals (Sweden)

    Liu Zhe

    2012-05-01

    Full Text Available Cooling rate and inoculation practice can greatly affect the graphite morphology of ductile irons. In the present research, the effects of the cooling rate and antimony addition on the graphite morphology and mechanical properties of ductile irons have been studied. Three ductile iron castings were prepared through solidification under cooling conditions S (slow, M (medium and F (fast. The cooling rates around the equilibrium eutectic temperature (1,150 ℃ for these cooling conditions (S, M and F were set at 0.21 ℃·min-1, 0.32 ℃·min-1 and 0.37 ℃·min-1, respectively. In addition, four ductile iron castings were prepared by adding 0.01%, 0.02%, 0.03% and 0.04% (by weight antimony, respectively under the slow cooling condition. The results show that the nodularity index, tensile strength and hardness of the ductile iron castings without antimony addition are all improved with the increase of cooling rate, while the ductile iron casting solidified under the medium cooling rate possesses the largest number of graphite nodules. Furthermore, for the four antimony containing castings, the graphite morphology and tensile strength are also improved by the antimony additions, and the effect of antimony addition is intensified when the addition increases from 0.01% to 0.03%. Moreover, the rare earth elements (REE/antimony ratio of 2 appears to be the most effective for fine nodular graphite formation in ductile iron.

  5. The synergistic effect of Li addition on microstructure, texture and mechanical properties of extruded Al–Mg–Si alloys

    Energy Technology Data Exchange (ETDEWEB)

    Ud Din, Shamas; Kamran, J. [Department of Metallurgy and Materials Engineering, Pakistan Institute of Engineering and Applied Sciences (PIEAS), Nilore, Islamabad, 45650 (Pakistan); Tariq, N.H., E-mail: naeem421@hotmail.com [Department of Metallurgy and Materials Engineering, Pakistan Institute of Engineering and Applied Sciences (PIEAS), Nilore, Islamabad, 45650 (Pakistan); Hasan, B.A. [Department of Metallurgy and Materials Engineering, Pakistan Institute of Engineering and Applied Sciences (PIEAS), Nilore, Islamabad, 45650 (Pakistan); Petrov, R.H.; Bliznuk, V. [Ghent University, Department of Materials Science and Engineering, Technologiepark 903, Gent (Belgium); Uz Zuha, Shamas [Department of Metallurgy and Materials Engineering, Pakistan Institute of Engineering and Applied Sciences (PIEAS), Nilore, Islamabad, 45650 (Pakistan)

    2016-05-01

    In the present work, 0, 1, 2 and 3 wt.% Li was added to conventional Al-0.9Mg-0.5Si alloy. The samples were extruded and aged to investigate the effect of Li addition on microstructure, texture and mechanical properties. The density of conventional alloy was reduced up to 7.8% while the ultimate tensile strength (UTS) increased by 62% with 3% Li addition. Electron backscatter diffraction (EBSD) revealed that Li addition effectively refined the grain size of the modified alloys. TEM/EDX and XRD analysis revealed the synergistic effect of Li addition which promoted the formation of nano-sized δ′(Al{sub 3}Li) precipitates when Li content is higher then 1%. The ageing trend first decreased for 1 wt.% Li addition and then increased with increasing Li content from 2 to 3 wt.% at the expense of ductility. The intensity of texture increased with the gradual increase in Li content from alloy-1 to 4. - Highlights: • Study of 0, 1, 2 and 3 wt.% Li on Al–Mg–Si alloys in extruded and T6 condition. • Density reduced to 7.8% with UTS increased by 62% for 3% Li addition. • Texture intensity increased with increase in Li content from alloy-1 to 4. • Property enhancement attributed to a refinement of δ′ (Al{sub 3}Li) precipitates.

  6. Metal and pharmaceutical mixtures: Is ion loss the mechanism underlying acute toxicity and widespread additive toxicity in zebrafish?

    Energy Technology Data Exchange (ETDEWEB)

    Alsop, Derek, E-mail: alsopde@mcmaster.ca; Wood, Chris M.

    2013-09-15

    Highlights: •Zebrafish larvae were used to test the acute toxicity of contaminant mixtures. •Interactions were observed between metals, ammonia and pharmaceuticals. •Larval Na{sup +} loss was observed with exposure to all acutely toxic contaminants tested. •Water quality criteria should recognize the toxic interactions between contaminants. -- Abstract: The acute toxicities and mechanisms of action of a variety of environmental contaminants were examined using zebrafish larvae (Danio rerio; 4–8 days post fertilization). Toxic interactions were observed between metals. For example, the addition of a sublethal level of nickel (15% of the LC{sub 50}, one third of the LC{sub 01}) to all copper treatments decreased the copper 96 h LC{sub 50} by 58%, while sublethal copper exposure (6% of the copper LC{sub 50}, 13% of the LC{sub 01}) decreased the cadmium 96 h LC{sub 50} by 47%. Two predictive models were assessed, the concentration addition (CA) model, which assumes similar mechanisms of action, and the independent action (IA) model, which assumes different mechanisms of action. Quantitative comparisons indicated the CA model performed better than the IA model; the latter tended to underestimate combined toxicity to a greater extent. The effects of mixtures with nickel or ammonia were typically additive, while mixtures with copper or cadmium were typically greater than additive. Larvae exposed to cadmium, copper or nickel experienced whole body ion loss. Decreases were greatest for Na{sup +} followed by K{sup +} (as high as 19% and 9%, respectively, in 24 h). Additive toxicity between copper and other pharmaceutical compounds such as fluoxetine (Prozac™), β-naphthoflavone, estrogen and 17α-ethinylestradiol were also observed. Similar to metals, acutely toxic concentrations of fluoxetine, β-naphthoflavone and ammonia all decreased whole body Na{sup +} and K{sup +}. Overall, whole body Na{sup +} loss showed the greatest correlation with mortality across a

  7. Effects of Mn addition on microstructures and mechanical properties of 10Cr ODS ferritic/martensitic steels

    International Nuclear Information System (INIS)

    Jin, Hyun Ju; Kim, Tae Kyu

    2014-01-01

    Ferritic/martensitic (FM) steels are very attractive for the structural materials of fast fission reactors such as a sodium cooled fast reactor (SFR) owing to their excellent irradiation resistance to a void swelling, but are known to reveal an abrupt loss of their creep and tensile strengths at temperatures above 600 .deg. C. Accordingly, high temperature strength should be considerably improved for an application of the FM steel to the structural materials of SFR. Oxide dispersion strengthened (ODS) FM steels are considered to be promising candidate materials for high- temperature components operating in severe environments such as nuclear fusion and fission systems due to their excellent high temperature strength and radiation resistance stemming from the addition of extremely thermally stable oxide particles dispersed in the ferritic/martensitic matrix.. To develop an advanced ODS steel for core structural materials for next generation nuclear reactor system applications, it is important to optimize its compositions to improve the high temperature strength and radiation resistance. This study investigates effects of Mn addition on microstructures and mechanical properties of 10Cr ODS FM steel. For this, two 10 Cr ODS FM steels were prepared by mechanical alloying (MA), hot isostatic pressing (HIP), and hot rolling process. Tensile tests were carried out at room temperature and 700 .deg. C to evaluate the influences of the Mn element on the mechanical properties. The microstructures were observed using SEM, electron back-scatter diffraction (EBSD) and transmission electron microscopy (TEM) with energy dispersive spectroscopy (EDS). In the present study, the effects of Mn addition on the microstructure and mechanical properties of ODS FM steels were investigated. The ODS FM steels were manufactured by the MA, HIP and hot-rolling processes

  8. The effect of CHA-doped Sr addition to the mechanical strength of metakaolin dental implant geopolymer composite

    Science.gov (United States)

    Sunendar, Bambang; Fathina, Afiya; Harmaji, Andrie; Mardhian, Deby Fajar; Asri, Lia; Widodo, Haris Budi

    2017-09-01

    The prospective material for implant plate required sufficient mechanical properties to maintain fracture fixation and resist physiological stress until bone healing process finished. Various problem implant plate based on metal and polymer materials when used as fixation for bone defect case induced developmental of bioceramic for implant plate materials. Materials that now has been attract a lot of attention is carbonate apatite and strontium as doping which known to have good biocompability along with biointegrity and mechanical charateristics. Other materials that have been known to have good mechanical properties are metakaolin and use of chitosan as coupling agent. Metakaolin and carbonate apatite can be produced by sol-gel methode which simpler, economical and energy-saving procedure furthermore use of chitosan which is widely found in the nature of Indonesia can be used to encourage the utilization of natural resources. The aim fo this paper is to investigated effect of CHA-doped Sr 5 (%) mol addition to the mechanical strength of metakaolin dental implant geoploymer composite. In this paper metakaolin is used as geopolymerization precursors. The test results have shown that addition of filler of apatite carbonate doped 5% mol strontium can be said to increase the value of mechnical properties but high concentration of calcium in the nanocomposite also can complicate the equilibrium of the geopolymerization process and induce alkali aggregate reactivity (AAR). The sample group of nanocomposite of metakaolin and carbonate apatite-doped 5% mol strontium (2: 1% wt) with 2% chitosan as a coupling agent based on geopolymerization for implant plate application has the best mechanical properties among all sample groups but does not qualify as an implant plate on cortical bone but can be used for the application of the implant plate on the trabecular bone specifically and potentially as a bone initiator.

  9. Theoretical study of the oxidation mechanisms of naphthalene initiated by hydroxyl radicals: the O2 addition reaction pathways.

    Science.gov (United States)

    Shiroudi, A; Deleuze, M S; Canneaux, S

    2015-05-28

    Atmospheric oxidation of the naphthalene-OH adduct [C10H8OH]˙ (R1) by molecular oxygen in its triplet electronic ground state has been studied using density functional theory along with the B3LYP, ωB97XD, UM05-2x and UM06-2x exchange-correlation functionals. From a thermodynamic viewpoint, the most favourable process is O2 addition at the C2 position in syn mode, followed by O2 addition at the C2 position in anti mode, O2 addition at the C4 position in syn mode, and O2 addition at the C4 position in anti mode, as the second, third and fourth most favourable processes. The syn modes of addition at these positions are thermodynamically favoured over the anti ones by the formation of an intramolecular hydrogen bond between the hydroxyl and peroxy substituents. Analysis of the computed structures, bond orders and free energy profiles demonstrate that the reaction steps involved in the oxidation of the naphthalene-OH adduct by O2 satisfy Hammond's principle. Kinetic rate constants and branching ratios under atmospheric pressure and in the fall-off regime have been supplied, using transition state and RRKM theories. By comparison with experiment, these data confirm the relevance of a two-step reaction mechanism. Whatever the addition mode, O2 addition in C4 position is kinetically favoured over O2 addition in C2 position, in contrast with the expectations drawn from thermodynamics and reaction energies. Under a kinetic control of the reaction, and in line with the computed reaction energy barriers, the most efficient process is O2 addition at the C4 position in syn mode, followed by O2 addition at the C2 position in syn mode, O2 addition at the C4 position in anti mode, and O2 addition at the C2 position in anti mode as the second, third and fourth most rapid processes. The computed branching ratios also indicate that the regioselectivity of the reaction decreases with increasing temperatures and decreasing pressures.

  10. Effect of silver addition on the mechanical and field trapping properties of Gd-Ba-Cu-O bulk superconductors

    CERN Document Server

    Nariki, S; Matsui, M; Murakami, M

    2002-01-01

    The effect of Ag addition on the microstructure and the mechanical and field trapping properties of Gd-Ba-Cu-O bulk superconductor has been investigated. The single grain Gd-Ba-Cu-O bulk superconductors 32 mm in diameter were fabricated with 0-30 mass%Ag/sub 2/O additions by the melt growth method under controlled oxygen partial pressure of 1.0%. From microscopic observations, it was found that the macro- cracks in the a-b plane decreased with Ag addition. The three-point bending test showed that the average strength of Ag-free bulk was 69 MPa at room temperature, while the strength was dramatically improved to 110-115 MPa with 10-30 mass%Ag/sub 2/O additions. The trapped magnetic field of Ag-free bulk sample was 1.3 T at 77 K. The trapped field of bulk Gd-Ba-Cu-O samples with 10-20 mass%Ag/sub 2/O exhibited high values of 1.8-2.0 T at 77 K. However, the trapped field of the sample with 30 mass%Ag/sub 2/O addition was lowered to 1.1 T with decreasing the critical current density. The trapped field of Ag- adde...

  11. In situ morphology studies of the mechanism for solution additive effects on the formation of bulk heterojunction films

    KAUST Repository

    Richter, Lee J.

    2014-09-29

    The most successful active film morphology in organic photovoltaics is the bulk heterojunction (BHJ). The performance of a BHJ arises from a complex interplay of the spatial organization of the segregated donor and acceptor phases and the local order/quality of the respective phases. These critical morphological features develop dynamically during film formation, and it has become common practice to control them by the introduction of processing additives. Here, in situ grazing incidence X-ray diffraction (GIXD) and grazing incidence small angle X-ray scattering (GISAXS) studies of the development of order in BHJ films formed from the donor polymer poly(3-hexylthiophene) and acceptor phenyl-C61-butyric acid methyl ester under the influence of two common additives, 1,8-octanedithiol and 1-chloronaphthalene, are reported. By comparing optical aggregation to crystallization and using GISAXS to determine the number and nature of phases present during drying, two common mechanisms by which the additives increase P3HT crystallinity are identified. Additives accelerate the appearance of pre-crystalline nuclei by controlling solvent quality and allow for extended crystal growth by delaying the onset of PCBM-induced vitrification. The glass transition effects vary system-to-system and may be correlated to the number and composition of phases present during drying. Synchrotron X-ray scattering measurements of nanoscale structure evolution during the drying of polymer-fullerene photovoltaic films are described. Changes in the number and nature of phases, as well as the order within them, reveals the mechanisms by which formulation additives promote structural characteristics leading to higher power conversion efficiencies.

  12. In situ morphology studies of the mechanism for solution additive effects on the formation of bulk heterojunction films

    KAUST Repository

    Richter, Lee J.; DeLongchamp., Dean M.; Bokel, Felicia A.; Engmann, Sebastian; Chou, Kang Wei; Amassian, Aram; Schaible, Eric G.; Hexemer, Alexander

    2014-01-01

    The most successful active film morphology in organic photovoltaics is the bulk heterojunction (BHJ). The performance of a BHJ arises from a complex interplay of the spatial organization of the segregated donor and acceptor phases and the local order/quality of the respective phases. These critical morphological features develop dynamically during film formation, and it has become common practice to control them by the introduction of processing additives. Here, in situ grazing incidence X-ray diffraction (GIXD) and grazing incidence small angle X-ray scattering (GISAXS) studies of the development of order in BHJ films formed from the donor polymer poly(3-hexylthiophene) and acceptor phenyl-C61-butyric acid methyl ester under the influence of two common additives, 1,8-octanedithiol and 1-chloronaphthalene, are reported. By comparing optical aggregation to crystallization and using GISAXS to determine the number and nature of phases present during drying, two common mechanisms by which the additives increase P3HT crystallinity are identified. Additives accelerate the appearance of pre-crystalline nuclei by controlling solvent quality and allow for extended crystal growth by delaying the onset of PCBM-induced vitrification. The glass transition effects vary system-to-system and may be correlated to the number and composition of phases present during drying. Synchrotron X-ray scattering measurements of nanoscale structure evolution during the drying of polymer-fullerene photovoltaic films are described. Changes in the number and nature of phases, as well as the order within them, reveals the mechanisms by which formulation additives promote structural characteristics leading to higher power conversion efficiencies.

  13. Effect of samarium (Sm) addition on the microstructures and mechanical properties of Al–7Si–0.7Mg alloys

    International Nuclear Information System (INIS)

    Qiu, Hongxu; Yan, Hong; Hu, Zhi

    2013-01-01

    Highlights: •Sm affected the secondary dendrite arm spacing of Al–7Si–0.7Mg alloy. •The coarse plate-like eutectic silicon was fully modified into a fine branched and particle structure when 0.6 wt.% Sm added. •The tensile properties were enhanced by the addition of Sm. •Sm has marked effects on eutectic temperature and the latent heat ΔH R on remelting behavior. •The morphology and chemical composition of Sm-rich intermetallics were studied. -- Abstract: The effects of samarium (Sm) additions (0–0.9 wt.%) on the microstructures and mechanical properties of Al–7Si–0.7Mg alloys have been studied in this article. The microstructures of the as-cast samples were examined by optical microscopy (OM) and scanning electron microscopy (SEM). The experimental results indicated that the rare earth Sm affected the secondary dendrite arm spacing (SDAS) of Al–7Si–0.7Mg alloy. And it was found that Sm had great modification effects on the microstructures of eutectic silicon. When 0.6 wt.% Sm was added to the alloy, the coarse plate-like eutectic silicon was fully modified into a fine fibrous structure; the dendrites of Al–7Si–0.7Mg alloy was best refined. The mechanical properties were investigated by tensile test. The findings indicate that the tensile properties and elongation were improved by the addition of Sm. And a good combination of ultimate tensile strength (215 MPa) and elongation (3.3%) was obtained when the Sm addition was up to 0.6 wt.%. Furthermore the results of thermal analysis reveal that Sm addition had marked effects on eutectic temperature and the latent heat ΔH R on remelting behavior

  14. Release mechanism of doxazosin from carrageenan matrix tablets: Effect of ionic strength and addition of sodium dodecyl sulphate.

    Science.gov (United States)

    Kos, Petra; Pavli, Matej; Baumgartner, Saša; Kogej, Ksenija

    2017-08-30

    The polyelectrolyte matrix tablets loaded with an oppositely charged drug exhibit complex drug-release mechanisms. In this study, the release mechanism of a cationic drug doxazosin mesylate (DM) from matrix tablets based on an anionic polyelectrolyte λ-carrageenan (λ-CARR) is investigated. The drug release rates from λ-CARR matrices are correlated with binding results based on potentiometric measurements using the DM ion-sensitive membrane electrode and with molecular characteristics of the DM-λ-CARR-complex particles through hydrodynamic size measurements. Experiments are performed in solutions with different ionic strength and with the addition of an anionic surfactant sodium dodecyl sulphate (SDS). It is demonstrated that in addition to swelling and erosion of tablets, the release rates depend strongly on cooperative interactions between DM and λ-CARR. Addition of SDS at concentrations below its critical micelle concentration (CMC) slows down the DM release through hydrophobic binding of SDS to the DM-λ-CARR complex. On the contrary, at concentrations above the CMC SDS pulls DM from the complex by forming mixed micelles with it and thus accelerates the release. Results involving SDS show that the concentration of surfactants that are naturally present in gastrointestinal environment may have a great impact on the drug release process. Copyright © 2017 Elsevier B.V. All rights reserved.

  15. Effect of molybdenum and chromium additions on the mechanical properties of Fe3Al-based alloys

    International Nuclear Information System (INIS)

    Sun Yangshan; Xue Feng; Mei Jianping; Yu Xingquan; Zhang Lining

    1995-01-01

    Iron aluminides based on Fe 3 Al offer excellent oxidation and sulfidation resistance, with lower material cost and density than stainless steels. However, their potential use as structural material has been hindered by limited ductility and a sharp drop in strength above 600 C. Recent development efforts have indicated that adequate engineering ductility of 10--20% and tensile yield strength of as high as 500 MPa can be achieved through control of composition and microstructure. These improved tensile properties make Fe 3 Al-based alloys more competitive against conventional austenic and ferritic steels. The improvement of high temperature mechanical properties has been achieved mainly by alloying processes. Molybdenum has been found to be one of the most important alloying elements for strengthening Fe 3 Al-based alloys at high temperatures. However, the RT(room temperature) ductility decreases with the increase of a molybdenum addition. On the other hand, a chromium addition to Fe 3 Al-based alloys is very efficient for improving RT ductility but not beneficial to yield strength at temperatures to 800 C. The purpose of the present paper is to report the effects of combined additions of molybdenum and chromium on mechanical properties at ambient temperature and high temperature of 600 C

  16. Effect of Ti additive on (Cr, Fe)7C3 carbide in arc surfacing layer and its refined mechanism

    International Nuclear Information System (INIS)

    Zhou Yefei; Yang Yulin; Yang Jian; Hao Feifei; Li Da; Ren Xuejun; Yang Qingxiang

    2012-01-01

    Arc surfacing layer of hypoeutectic high chromium cast iron (HCCI) expects refiner carbides in the microstructure to improve its mechanical properties. In this paper, Ti additive as a strong carbide forming element was added in the hypoeutectic HCCI arc surfacing layer. Microstructure of titaniferous hypoeutectic HCCI was studied by optical microscopy, X-ray diffraction and field emission scanning electronic microscopy with energy dispersive spectrometer. Furthermore, the M(M = Cr, Fe) 7 C 3 carbide refinement mechanism was explained by the phase diagram calculation and lattice misfit theory. The results show that, the M 7 C 3 carbide in arc surfacing microstructure of hypoeutectic HCCI has been refined with 2 wt.% Ti additive, and TiC carbide can be observed in/around the M 7 C 3 carbide. With Ti addictive increasing, the micro-hardness along the depth in profile section of layer becomes more uniform, and the wear resistance has been improved. According to the phase diagram calculation, MC carbide precipitates prior to M 7 C 3 carbide in Fe-Cr-C-Ti alloy. In addition, the lattice misfit between (1 1 0) TiC and (010) Cr 7 C 3 is 9.257%, which indicates that the TiC as heterogeneous nuclei of the M 7 C 3 is medium effective. Therefore, the M 7 C 3 carbide can be refined.

  17. Effects of heat treatment on microstructure and mechanical behaviour of additive manufactured porous Ti6Al4V

    Science.gov (United States)

    Ahmadi, S. M.; Jain, R. K. Ashok Kumar; Zadpoor, A. A.; Ayas, C.; Popovich, V. A.

    2017-12-01

    Titanium and its alloys such as Ti6Al4V play a major role in the medical industry as bone implants. Nowadays, by the aid of additive manufacturing (AM), it is possible to manufacture porous complex structures which mimic human bone. However, AM parts are near net shape and post processing may be needed to improve their mechanical properties. For instance, AM Ti6Al4V samples may be brittle and incapable of withstanding dynamic mechanical loads due to their martensitic microstructure. The aim of this study was to apply two different heat treatment regimes (below and above β-transus) to investigate their effects on the microstructure and mechanical properties of porous Ti6Al4V specimens. After heat treatment, fine acicular α‧ martensitic microstructure was transformed to a mixture of α and β phases. The ductility of the heat-treated specimens, as well as some mechanical properties such as hardness, plateau stress, and first maximum stress changed while the density and elastic gradient of the porous structure remained unchanged.

  18. Effect of Heat Treatment on Microstructure and Mechanical Properties of Laser Additively Manufactured AISI H13 Tool Steel

    Science.gov (United States)

    Chen, ChangJun; Yan, Kai; Qin, Lanlan; Zhang, Min; Wang, Xiaonan; Zou, Tao; Hu, Zengrong

    2017-11-01

    The effect of heat treatment on microstructure and mechanical properties (microhardness, wear resistance and impact toughness) of laser additively manufactured AISI H13 tool steel was systemically investigated. To understand the variation of microstructure and mechanical properties under different heat treatments, the as-deposited samples were treated at 350, 450, 550, 600 and 650 °C/2 h, respectively. Microstructure and phase transformation were investigated through optical microscopy, scanning electron microscope and transmission electron microscope. The mechanical properties were characterized by nanoindentation tests, Charpy tests and high-temperature wear tests. The microstructure of as-deposited samples consisted of martensite, ultrafine carbides and retained austenite. After the tempering treatment, the martensite was converted into tempered martensite and some fine alloy carbides which precipitated in the matrix. When treated at 550 °C, the greatest hardness and nanohardness were 600 HV0.3 and 6119.4 MPa due to many needle-like carbides precipitation. The value of hardness increased firstly and then decreased when increasing the temperature. When tempered temperatures exceeded 550 °C, the carbides became coarse, and martensitic matrix recrystallized at the temperature of 650 °C. The least impact energy was 6.0 J at a temperature of 550 °C. Samples tempered at 550 °C had larger wear volume loss than that of others. Wear resistances of all samples under atmospheric condition at 400 °C showed an oxidation mechanism.

  19. New Mechanism on Synergistic Effect of Nitrite and Triethanolamine Addition on the Corrosion of Ductile Cast Iron

    Directory of Open Access Journals (Sweden)

    K. T. Kim

    2016-01-01

    Full Text Available In general, we compared the different inhibition mechanisms of organic inhibitor with that of anodic inhibitor. When triethanolamine or nitrite was added separately to tap water for inhibiting the corrosion of ductile cast iron, large amounts of inhibitor were needed. This is because the corrosion inhibitors had to overcome the galvanic corrosion that occurs between graphite and matrix. In this work, we investigated the corrosion of ductile cast iron in tap water with/without inhibitors. The corrosion rate was measured using chemical immersion test and electrochemical methods, including anodic polarization test. The inhibited surface was analyzed using EPMA and XPS. Test solutions were analyzed by performing FT-IR measurement. When triethanolamine and nitrite coexisted in tap water, synergistic effect built up, and the inhibition effect was ca. 30 times more effective than witnessed with single addition. This work focused on the synergistic effect brought about by nitrite and triethanolamine and its novel mechanism was also proposed.

  20. Effects of Ce Addition and Isothermal Aging on the Elevated Temperature Tensile Properties of Mechanically Alloyed Al-Ti Alloys

    Energy Technology Data Exchange (ETDEWEB)

    Kim, JunKi; Oh, YoungMin; Kim, YongDeog; Kim, SeonJin [Hanyang Univ., Seoul (Korea, Republic of); Kim, ByungChul [KOREA ATOMIC RESEARCH INSTITUTE, TAEJON (Korea, Republic of)

    1997-05-01

    The room and elevated temperature tensile strength of mechanically alloyed Al-8wt%. Ti alloy increased by substituting Ce for Ti up to 25at.%. However, further substitution of Ce for Ti decreased the tensile strength. It was considered to be due to the decrease of volume fraction of Ce contained dispersoid. In the meantime, the decrease of tensile strength due to the isothermal aging was effectively reduced by the addition of Ce at 400 deg. C but not 510 deg. C. The activation energies for the deformation of Al-80wt.%(Ti+Ce)alloys measured at the temperature between 300 deg. C{approx}510 deg. C were about 1.3{approx}1.9 times higher than that for pure Al self-diffusion(142 kJ/mole). Thus, it was considered that the elevated temperature deformation of Al-8wt.%(Ti+Ce)alloys was governed by Orowan mechanism (author). 9 refs. 6 figs.

  1. Effect of Si addition on glass-forming ability and mechanical properties of Cu-Zr-Al bulk metallic glass

    International Nuclear Information System (INIS)

    Malekan, M.; Shabestari, S.G.; Zhang, W.; Seyedein, S.H.; Gholamipour, R.; Makino, A.; Inoue, A.

    2010-01-01

    Research highlights: The Cu 50 Zr 43 Al 7 alloy has a surprising GFA, and the glassy rods with diameter of 10 mm have been produced in this research. It has not been reported that the Cu-based glassy rods (Cu ≥ 50 at.%) to be produced with the critical diameter greater than 10 mm. The novelty of this research is that the glass formation has been improved and the critical diameter increased to 12 mm for the alloy having x = 1 with the addition of Si. Different criteria are used to evaluate the influence of Si content on the GFA, and the possible mechanisms involved in the achievement of this GFA are also discussed. - Abstract: The effect of Si addition on the glass-forming ability (GFA) and mechanical properties of (Cu 50 Zr 43 Al 7 ) 100-x Si x (x = 0, 0.5, 1, 1.5 and 2 at.%) alloys were investigated. The GFA of Cu 50 Zr 43 Al 7 alloy is improved by addition of a small amount of Si, and the critical diameter for glass formation increases from 10 mm for the alloy with x = 0-12 mm for the alloy with x = 1 when prepared using copper mold casting. Different criteria are used to evaluate the influence of Si content on the GFA, and the possible mechanisms involved in the achievement of this GFA are also discussed. In the uniaxial compression, the bulk glassy alloys exhibit a limited plastic strain of less than 1%, but the compressive fracture strength and Young's modulus were obtained in high values of 1969-2129 MPa and 101-144 GPa, respectively. Fracture surface and shear bands of samples were studied by using scanning electron microscopy (SEM).

  2. Porous calcium polyphosphate bone substitutes: additive manufacturing versus conventional gravity sinter processing-effect on structure and mechanical properties.

    Science.gov (United States)

    Hu, Youxin; Shanjani, Yaser; Toyserkani, Ehsan; Grynpas, Marc; Wang, Rizhi; Pilliar, Robert

    2014-02-01

    Porous calcium polyphosphate (CPP) structures proposed as bone-substitute implants and made by sintering CPP powders to form bending test samples of approximately 35 vol % porosity were machined from preformed blocks made either by additive manufacturing (AM) or conventional gravity sintering (CS) methods and the structure and mechanical characteristics of samples so made were compared. AM-made samples displayed higher bending strengths (≈1.2-1.4 times greater than CS-made samples), whereas elastic constant (i.e., effective elastic modulus of the porous structures) that is determined by material elastic modulus and structural geometry of the samples was ≈1.9-2.3 times greater for AM-made samples. X-ray diffraction analysis showed that samples made by either method displayed the same crystal structure forming β-CPP after sinter annealing. The material elastic modulus, E, determined using nanoindentation tests also showed the same value for both sample types (i.e., E ≈ 64 GPa). Examination of the porous structures indicated that significantly larger sinter necks resulted in the AM-made samples which presumably resulted in the higher mechanical properties. The development of mechanical properties was attributed to the different sinter anneal procedures required to make 35 vol % porous samples by the two methods. A primary objective of the present study, in addition to reporting on bending strength and sample stiffness (elastic constant) characteristics, was to determine why the two processes resulted in the observed mechanical property differences for samples of equivalent volume percentage of porosity. An understanding of the fundamental reason(s) for the observed effect is considered important for developing improved processes for preparation of porous CPP implants as bone substitutes for use in high load-bearing skeletal sites. Copyright © 2013 Wiley Periodicals, Inc.

  3. Mechanical Deformation Behavior of Sn-Ag-Cu Solders with Minor Addition of 0.05 wt.% Ni

    Science.gov (United States)

    Hammad, A. E.; El-Taher, A. M.

    2014-11-01

    The aim of the present work is to develop a comparative evaluation of the microstructural and mechanical deformation behavior of Sn-Ag-Cu (SAC) solders with the minor addition of 0.05 wt.% Ni. Test results showed that, by adding 0.05Ni element into SAC solders, generated mainly small rod-shaped (Cu,Ni)6Sn5 intermetallic compounds (IMCs) inside the β-Sn phase. Moreover, increasing the Ag content and adding Ni could result in the change of the shape and size of the IMC precipitate. Hence, a significant improvement is observed in the mechanical properties of SAC solders with increasing Ag content and Ni addition. On the other hand, the tensile results of Ni-doped SAC solders showed that both the yield stress and ultimate tensile strengths decrease with increasing temperature and with decreasing strain rate. This behavior was attributed to the competing effects of work hardening and dynamic recovery processes. The Sn-2.0Ag-0.5Cu-0.05Ni solder displayed the highest mechanical properties due to the formation of hard (Cu,Ni)6Sn5 IMCs. Based on the obtained stress exponents and activation energies, it is suggested that the dominant deformation mechanism in SAC (205)-, SAC (0505)- and SAC (0505)-0.05Ni solders is pipe diffusion, and lattice self-diffusion in SAC (205)-0.05Ni solder. In view of these results, the Sn-2.0Ag-0.5Cu-0.05Ni alloy is a more reliable solder alloy with improved properties compared with other solder alloys tested in the present work.

  4. Are Dispersal Mechanisms Changing the Host-Parasite Relationship and Increasing the Virulence of Varroa destructor (Mesostigmata: Varroidae) in Managed Honey Bee (Hymenoptera: Apidae) Colonies?

    Science.gov (United States)

    DeGrandi-Hoffman, Gloria; Ahumada, Fabiana; Graham, Henry

    2017-08-01

    Varroa (Varroa destructor Anderson and Trueman) are a serious pest of European honey bees (Apis mellifera L.), and difficult to control in managed colonies. In our 11-mo longitudinal study, we applied multiple miticide treatments, yet mite numbers remained high and colony losses exceeded 55%. High mortality from varroa in managed apiaries is a departure from the effects of the mite in feral colonies where bees and varroa can coexist. Differences in mite survival strategies and dispersal mechanisms may be contributing factors. In feral colonies, mites can disperse through swarming. In managed apiaries, where swarming is reduced, mites disperse on foragers robbing or drifting from infested hives. Using a honey bee-varroa population model, we show that yearly swarming curtails varroa population growth, enabling colony survival for >5 yr. Without swarming, colonies collapsed by the third year. To disperse, varroa must attach to foragers that then enter other hives. We hypothesize that stress from parasitism and virus infection combined with effects that viruses have on cognitive function may contribute to forager drift and mite and virus dispersal. We also hypothesize that drifting foragers with mites can measurably increase mite populations. Simulations initialized with field data indicate that low levels of drifting foragers with mites can create sharp increases in mite populations in the fall and heavily infested colonies in the spring. We suggest new research directions to investigate factors leading to mite dispersal on foragers, and mite management strategies with consideration of varroa as a migratory pest. Published by Oxford University Press on behalf of Entomological Society of America 2017. This work is written by US Government employees and is in the public domain in the US.

  5. Crystallization, microstructure and mechanical properties of silumins with micro-additions of Cr, Mo, W and V

    Directory of Open Access Journals (Sweden)

    S. Pietrowski

    2010-01-01

    Full Text Available In this paper results of the crystallization, microstructure and mechanical properties studies of hypo-, hyper- and eutectic silumins with addition of: Cr, Mo, W and V in amount of about 0,05% are presented. The influence of Sb, Sr and P together with Ti + B on the silumins crystallization process has been given. Results of: the microstructure, Rm, Rp0,2, A5 and HB testing of silumins after precipitation hardening and heat treatment in temperature of 560°C/3min and water chilling are presented.

  6. Etching characteristic and mechanism of BST thin films using inductively coupled Cl2/Ar plasma with additive CF4 gas

    International Nuclear Information System (INIS)

    Kim, Gwan-Ha; Kim, Kyoung-Tae; Kim, Dong-Pyo; Kim, Chang-Il

    2004-01-01

    BST thin films were etched with inductively coupled CF 4 /(Cl 2 +Ar) plasmas. The maximum etch rate of the BST thin films was 53.6 nm/min for a 10% CF 4 to the Cl 2 /Ar gas mixture at RF power of 700 W, DC bias of -150 V, and chamber pressure of 2 Pa. Small addition of CF 4 to the Cl 2 /Ar mixture increased chemical effect. Consequently, the increased chemical effect caused the increase in the etch rate of the BST thin films. To clarify the etching mechanism, the surface reaction of the BST thin films was investigated by X-ray photoelectron spectroscopy

  7. Virulence Factors of Helicobacter pylori

    Directory of Open Access Journals (Sweden)

    Paul Sinclair

    1991-01-01

    environment with respect to pH. The spiral shape of the cells and their flagellar motility allow them to wind themselves into the mucous layer of the stomach. Some evidence exists for the production of strong proteolytic activity, hence degrading the mucous barrier and increasing permeability for the organism. Cyroroxin excreted by the bacteria may have some effect on the surrounding cells, with the possible lysis and release of bacterial growth factors. There is evidence that a chemotactic response is present due to these growth factors and their higher concentration in the intracellular spaces. The presence of specific and nonspecific adhesion has also been demonstrated, thus allowing the bacterium, once at the epithelial cell surface, to attach and avoid being washed off by movement within the stomach. Although treatment with antimicrobials eradicates the organism and improves symptoms of peptic ulcer patients, there is no indication that the same occurs in nonulcer dyspepsia patients. Further work is essential to describe the virulence mechanisms of H pylori and the possible pathogenic role of the organism.

  8. Theoretical study on the reaction mechanisms of Michael chirality addition between propionaldehyde and nitroalkene catalyzed by an enantioselective catalyst.

    Science.gov (United States)

    Zhou, Xinming; Li, Ling; Sun, Xuejun; Wang, Yajun; Du, Dongmei; Fu, Hui

    2018-06-01

    The asymmetric Michael addition between propionaldehyde and nitroalkene catalyzed by 8-(ethoxycarbonyl)-1,2,3,3a,8,8a-hexahydropyrrolo[2,3-b]indole-2-carboxylic acid has obtained relatively high yields and excellent enantioselectivities at room temperature. In this study, the molecular structures and optical activity of the most stable conformation I are optimized at B3LYP/6-311++ G(d,p) level. We find that levorotatory conformation I catalyzing the same Michael addition can produce laevo-product A and dextrorotatory conformation I' can obtain the dextral-product A'. These results have guiding significance for further studying on the new chemzymes and the mechanism of the obtained different chiral products. © 2018 Wiley Periodicals, Inc.

  9. Effect of Ge addition on mechanical properties and fracture behavior of Cu-Zr-Al bulk metallic glass

    International Nuclear Information System (INIS)

    Malekan, M.; Shabestari, S.G.; Gholamipour, R.; Seyedein, S.H.

    2009-01-01

    Effect of the addition of a small amount of Ge on mechanical properties and fracture behavior of Cu 50 Zr 43 Al 7 (at.%) bulk metallic glass were studied. The Cu 50 Zr 43 Al 7 alloy has a surprising glass-forming ability (GFA), and the glassy rods up to 4 mm in diameter can be formed. Partial addition of Ge causes the crystalline phases precipitate in the glassy matrix of (Cu 50 Zr 43 Al 7 ) 100-x Ge x (x = 0, 1, 2) rods with a diameter of 4 mm. In uniaxial compression, Cu 50 Zr 43 Al 7 bulk metallic glass exhibit high strength of 1692 MPa and very limited plasticity of 0.05%. When Ge increases from 0 to 2 at.%, the strength decreases, but plastic strain increases about 2.5%. Fracture surface and shear bands of samples were investigated by scanning electron microscopy (SEM).

  10. Quantum mechanics/molecular mechanics modeling of covalent addition between EGFR-cysteine 797 and N-(4-anilinoquinazolin-6-yl) acrylamide.

    Science.gov (United States)

    Capoferri, Luigi; Lodola, Alessio; Rivara, Silvia; Mor, Marco

    2015-03-23

    Irreversible epidermal growth factor receptor (EGFR) inhibitors can circumvent resistance to first-generation ATP-competitive inhibitors in the treatment of nonsmall-cell lung cancer. They covalently bind a noncatalytic cysteine (Cys797) at the surface of EGFR active site by an acrylamide warhead. Herein, we used a hybrid quantum mechanics/molecular mechanics (QM/MM) potential in combination with umbrella sampling in the path-collective variable space to investigate the mechanism of alkylation of Cys797 by the prototypical covalent inhibitor N-(4-anilinoquinazolin-6-yl) acrylamide. Calculations show that Cys797 reacts with the acrylamide group of the inhibitor through a direct addition mechanism, with Asp800 acting as a general base/general acid in distinct steps of the reaction. The obtained reaction free energy is negative (ΔA = -12 kcal/mol) consistent with the spontaneous and irreversible alkylation of Cys797 by N-(4-anilinoquinazolin-6-yl) acrylamide. Our calculations identify desolvation of Cys797 thiolate anion as a key step of the alkylation process, indicating that changes in the intrinsic reactivity of the acrylamide would have only a minor impact on the inhibitor potency.

  11. Additively manufactured metallic porous biomaterials based on minimal surfaces: A unique combination of topological, mechanical, and mass transport properties.

    Science.gov (United States)

    Bobbert, F S L; Lietaert, K; Eftekhari, A A; Pouran, B; Ahmadi, S M; Weinans, H; Zadpoor, A A

    2017-04-15

    Porous biomaterials that simultaneously mimic the topological, mechanical, and mass transport properties of bone are in great demand but are rarely found in the literature. In this study, we rationally designed and additively manufactured (AM) porous metallic biomaterials based on four different types of triply periodic minimal surfaces (TPMS) that mimic the properties of bone to an unprecedented level of multi-physics detail. Sixteen different types of porous biomaterials were rationally designed and fabricated using selective laser melting (SLM) from a titanium alloy (Ti-6Al-4V). The topology, quasi-static mechanical properties, fatigue resistance, and permeability of the developed biomaterials were then characterized. In terms of topology, the biomaterials resembled the morphological properties of trabecular bone including mean surface curvatures close to zero. The biomaterials showed a favorable but rare combination of relatively low elastic properties in the range of those observed for trabecular bone and high yield strengths exceeding those reported for cortical bone. This combination allows for simultaneously avoiding stress shielding, while providing ample mechanical support for bone tissue regeneration and osseointegration. Furthermore, as opposed to other AM porous biomaterials developed to date for which the fatigue endurance limit has been found to be ≈20% of their yield (or plateau) stress, some of the biomaterials developed in the current study show extremely high fatigue resistance with endurance limits up to 60% of their yield stress. It was also found that the permeability values measured for the developed biomaterials were in the range of values reported for trabecular bone. In summary, the developed porous metallic biomaterials based on TPMS mimic the topological, mechanical, and physical properties of trabecular bone to a great degree. These properties make them potential candidates to be applied as parts of orthopedic implants and/or as bone

  12. Theoretical study of the oxidation mechanisms of naphthalene initiated by hydroxyl radicals: the OH-addition pathway.

    Science.gov (United States)

    Shiroudi, Abolfazl; Deleuze, Michael S; Canneaux, Sébastien

    2014-07-03

    The oxidation mechanisms of naphthalene by OH radicals under inert (He) conditions have been studied using density functional theory along with various exchange-correlation functionals. Comparison has been made with benchmark CBS-QB3 theoretical results. Kinetic rate constants were correspondingly estimated by means of transition state theory and statistical Rice-Ramsperger-Kassel-Marcus (RRKM) theory. Comparison with experiment confirms that, on the OH-addition reaction pathway leading to 1-naphthol, the first bimolecular reaction step has an effective negative activation energy around -1.5 kcal mol(-1), whereas this step is characterized by an activation energy around 1 kcal mol(-1) on the OH-addition reaction pathway leading to 2-naphthol. Effective rate constants have been calculated according to a steady state analysis upon a two-step model reaction mechanism. In line with experiment, the correspondingly obtained branching ratios indicate that, at temperatures lower than 410 K, the most abundant product resulting from the oxidation of naphthalene by OH radicals must be 1-naphthol. The regioselectivity of the OH(•)-addition onto naphthalene decreases with increasing temperatures and decreasing pressures. Because of slightly positive or even negative activation energies, the RRKM calculations demonstrate that the transition state approximation breaks down at ambient pressure (1 bar) for the first bimolecular reaction steps. Overwhelmingly high pressures, larger than 10(5) bar, would be required for restoring to some extent (within ∼5% accuracy) the validity of this approximation for all the reaction channels that are involved in the OH-addition pathway. Analysis of the computed structures, bond orders, and free energy profiles demonstrate that all reaction steps involved in the oxidation of naphthalene by OH radicals satisfy Leffler-Hammond's principle. Nucleus independent chemical shift indices and natural bond orbital analysis also show that the computed

  13. Effects of sintering additives on the microstructural and mechanical properties of the ion-irradiated SiCf/SiC

    Science.gov (United States)

    Fitriani, Pipit; Sharma, Amit Siddharth; Yoon, Dang-Hyok

    2018-05-01

    SiCf/SiC composites containing three different types of sintering additives viz. Sc-nitrate, Al2O3-Sc2O3, and Al2O3-Y2O3, were subjected to ion irradiation using 0.2 MeV H+ ions with a fluence of 3 × 1020 ions/m2 at room temperature. Although all composites showed volumetric swelling upon ion irradiation, SiCf/SiC with Sc-nitrate showed the smallest change followed by those with the Al2O3-Sc2O3 and Al2O3-Y2O3 additives. In particular, SiCf/SiC containing the conventional Al2O3-Y2O3 additive revealed significant microstructural changes, such as surface roughening and the formation of cracks and voids, resulting in reduced fiber pullout upon irradiation. On the other hand, the SiCf/SiC with Sc-nitrate showed the highest resistance against ion irradiation without showing any macroscopic changes in surface morphology and mechanical strength, indicating the importance of the sintering additive in NITE-based SiCf/SiC for nuclear structural applications.

  14. Research on Mechanisms and Controlling Methods of Macro Defects in TC4 Alloy Fabricated by Wire Additive Manufacturing.

    Science.gov (United States)

    Ji, Lei; Lu, Jiping; Tang, Shuiyuan; Wu, Qianru; Wang, Jiachen; Ma, Shuyuan; Fan, Hongli; Liu, Changmeng

    2018-06-28

    Wire feeding additive manufacturing (WFAM) has broad application prospects because of its advantages of low cost and high efficiency. However, with the mode of lateral wire feeding, including wire and laser additive manufacturing, gas tungsten arc additive manufacturing etc., it is easy to generate macro defects on the surface of the components because of the anisotropy of melted wire, which limits the promotion and application of WFAM. In this work, gas tungsten arc additive manufacturing with lateral wire feeding is proposed to investigate the mechanisms of macro defects. The results illustrate that the defect forms mainly include side spatters, collapse, poor flatness, and unmelted wire. It was found that the heat input, layer thickness, tool path, and wire curvature can have an impact on the macro defects. Side spatters are the most serious defects, mainly because the droplets cannot be transferred to the center of the molten pool in the lateral wire feeding mode. This research indicates that the macro defects can be controlled by optimizing the process parameters. Finally, block parts without macro defects were fabricated, which is meaningful for the further application of WFAM.

  15. Influence of the Mo and W additions on the microstructure evolution and mechanical properties in Si-Cr spring steels

    International Nuclear Information System (INIS)

    Ban, Deok Young; Lee, Sang Lae; Nam, Won Jong

    1998-01-01

    Effects of the Mo and W additions to Si-Cr spring steels on the microstructural evolution and mechanical properties in spring steels were investigated. It was found that the Mo and/or W addition does not change the behavior of tempered carbide at low temperatures, such as the precipitation of ε-carbide and the conversion of ε-carbide to cementite, via dilatometry tests and the observation of microstructure using TEM. However, it would reduce the coarsening rate of cementite at high temperature above 450 .deg. C, resulting in the smaller size of cementite particles due to the lower diffusion rate. Since the sag resistance depends on the distribution and the size of precipitates, steel C(0.2% W) showed the strongest sag resistance whereas steel A showed the weakest sag resistance, when tempered at 450 .deg. C. Also, an abundance of precipitates at 350 deg. C tempering exhibits the maximum loop area, i.e., the sag resistance for all the tested steels. The Mo and W additions to Si-Cr spring steels raised the ratio of loop area/tensile strength. Therefore, the Mo and W additions would be effective method to increase the sag resistance as well as strength in Si-Cr spring steels

  16. Virulence Factors of Streptococcus mutans.

    Science.gov (United States)

    1986-08-01

    763512/715242 Final Report U VIRULENCE FACTORS OF STREPTOCOCCUS MUTANS U Samuel Rosen Department of Oral Biology For the Period April 1, 1983 - June 30...00 FINAL REPORT VIRULENCE FACTORS OF STREPTOCOCCUS MUTANS Sam Rosen, Irving Shklair, E. X. Beck and F. M. Beck Ohio State University Columbus,Oh and...206-212. Johnson CP, Gorss S, Hillman JD (1978). Cariogenic properties of LDH deficient mutants of streptococcus mutans . J Dent Res 57, Special Issue

  17. The Structure and Mechanical Properties of Ni-Mo PM Steels with Addition of Mn And Cu

    Science.gov (United States)

    Lichańska, E.; Kulecki, P.; Pańcikiewicz, K.

    2017-12-01

    The aim of the study was to evaluate the effect of chemical composition on the structure and mechanical properties of Mn-Ni-Mo and Ni-Mo-Cu PM steels. Pre-alloyed powder Astaloy 85Mo, diffusion alloyed powders Distaloy AQ and Distaloy AB produced by Höganäs, low carbon ferromanganese, carbonyl nickel powder T255 with three-dimensional filamentary structure and graphite CU-F have been used as the basic powders. Three mixtures with compositions of Fe-1%Mn-(0.5/1.75)%Ni-(0.5/0.85)%Mo-0.8%C and Fe-1.75%Ni-0.5%Mo-1.5%Cu-0.8%C were prepared in a Turbula mixer. Green compacts were single pressed in a steel die at 660 MPa according to PN-EN ISO 2740 standard. Sinterhardening was carried out at 1250°C in a mixture of 95% N2+5% H2 for 60 minutes. Mechanical tests (tensile, bend, hardness) and microstructural investigations were performed. Additionally, XRD and EDS analysis, fractographic investigations were carried out. The microstructures of steels investigated were mainly bainitic or bainitic-martensitic. Addition 1% Mn to Distaloy AQ based steel caused increase of tensile properties (YS from 422 to 489 MPa, UTS from 522 to 638 MPa, TRS from 901 to 1096 MPa) and decrease of plasticity (elongation from 3.65 to 2.84%).

  18. The Influence of Nickel and Tin Additives on the Microstructural and Mechanical Properties of Al-Zn-Mg-Cu Alloys

    Directory of Open Access Journals (Sweden)

    Haider T. Naeem

    2014-01-01

    Full Text Available The effects of nickel and nickel combined tin additions on mechanical properties and microstructural evolutions of aluminum-zinc-magnesium-copper alloys were investigated. Aluminum alloys containing Ni and Sn additives were homogenized at different temperatures conditions and then aged at 120°C for 24 h (T6 and retrogressed at 180°C for 30 min and then reaged at 120°C for 24 h (RRA. Comparison of the ultimate tensile strength (UTS of as-quenched Al-Zn-Mg-Cu-Ni and Al-Zn-Mg-Cu-Ni-Sn alloys with that of similar alloys which underwent aging treatment at T6 temper showed that gains in tensile strengths by 385 MPa and 370 MPa were attained, respectively. These improvements are attributed to the precipitation hardening effects of the alloying element within the base alloy and the formation of nickel/tin-rich dispersoid compounds. These intermetallic compounds retard the grain growth, lead to grain refinement, and result in further strengthening effects. The outcomes of the retrogression and reaging processes which were carried on aluminum alloys indicate that the mechanical strength and Vickers hardness have been enhanced much better than under the aging at T6 temper.

  19. Electron beam processing of rubber wood fibers - polypropylene composites. Effects of reactive additives on the physical and mechanical properties

    International Nuclear Information System (INIS)

    Nor Yuziah Mohd Yunus; Jalaluddin Harun; Khairul Zaman

    2000-01-01

    The purpose of this study is to determine the suitability of producing agro-fiber reinforced plastic composite (agro-FRPC) from rubber wood fiber blended in polypropylene matrix. The effects of varying fiber dimension and fiber content on the physical and mechanical properties of the composite were evaluated to provide an insight into the fiber matrix adhesion. The effects of reactive additives on the physical and mechanical properties of the composite were evaluated which provides the insight on the reinforcement of the composite. Rubber wood fiber used in this study is currently being used in the manufacturing of medium density fiber (MDF) board. Two sizes of rubber wood fiber were used i.e. 0.5-1.0 mm and 1.0-2.0 mm. Homopolymer polypropylene of MFI 14.0 was used as a matrix. The irradiation work was carried out using electron beam accelerator, 3.0 MeV, 3.0 mA. Various types of reactive additives (RA) with mono-functional, di-functional, tri-functional and oligomer were applied in the blend. For comparison, a conventional chemical cross-linking using two types of maleated polypropylene, MPA (Mw=9,000) and PMAP (Mw=220,000) were also performed. (author)

  20. Electron beam processing of rubber wood fibers - polypropylene composites. Effects of reactive additives on the physical and mechanical properties

    Energy Technology Data Exchange (ETDEWEB)

    Nor Yuziah Mohd Yunus; Jalaluddin Harun [Universiti Putra Malaysia, Selangor Darul Ehsan (Malaysia); Khairul Zaman [Malaysian Institute for Nuclear Technology Research (MINT), Selangor Darul Ehsan (Malaysia)

    2000-07-01

    The purpose of this study is to determine the suitability of producing agro-fiber reinforced plastic composite (agro-FRPC) from rubber wood fiber blended in polypropylene matrix. The effects of varying fiber dimension and fiber content on the physical and mechanical properties of the composite were evaluated to provide an insight into the fiber matrix adhesion. The effects of reactive additives on the physical and mechanical properties of the composite were evaluated which provides the insight on the reinforcement of the composite. Rubber wood fiber used in this study is currently being used in the manufacturing of medium density fiber (MDF) board. Two sizes of rubber wood fiber were used i.e. 0.5-1.0 mm and 1.0-2.0 mm. Homopolymer polypropylene of MFI 14.0 was used as a matrix. The irradiation work was carried out using electron beam accelerator, 3.0 MeV, 3.0 mA. Various types of reactive additives (RA) with mono-functional, di-functional, tri-functional and oligomer were applied in the blend. For comparison, a conventional chemical cross-linking using two types of maleated polypropylene, MPA (Mw=9,000) and PMAP (Mw=220,000) were also performed. (author)

  1. The Effect of Small Additions of Carbon Nanotubes on the Mechanical Properties of Epoxy Polymers under Static and Dynamic Loads

    Science.gov (United States)

    Tarasov, A. E.; Badamshina, E. R.; Anokhin, D. V.; Razorenov, S. V.; Vakorina, G. S.

    2018-01-01

    The results of measurements of the mechanical characteristics of cured epoxy composites containing small and ultrasmall additions of single-walled carbon nanotubes in the concentration range from 0 to 0.133 wt % under static and dynamic loads are presented. Static measurements of strength characteristics have been carried out under standard test conditions. Measurements of the Hugoniot elastic limit and spall strength were performed under a shock wave loading of the samples at a deformation rate of (0.8-1.5) ß 105 s-1 before the fracture using explosive devices by recording and subsequent analyzing the evolution of the full wave profiles. It has been shown that agglomerates of nanotubes present in the structure of the composites after curing cause a significant scatter of the measured strength parameters, both in the static and in the dynamic test modes. However, the effects of carbon nanotube additions in the studied concentration interval on the physical and mechanical characteristics of the parameters were not revealed for both types of loading.

  2. CRISPR interference can prevent natural transformation and virulence acquisition during in vivo bacterial infection.

    Science.gov (United States)

    Bikard, David; Hatoum-Aslan, Asma; Mucida, Daniel; Marraffini, Luciano A

    2012-08-16

    Pathogenic bacterial strains emerge largely due to transfer of virulence and antimicrobial resistance genes between bacteria, a process known as horizontal gene transfer (HGT). Clustered, regularly interspaced, short palindromic repeat (CRISPR) loci of bacteria and archaea encode a sequence-specific defense mechanism against bacteriophages and constitute a programmable barrier to HGT. However, the impact of CRISPRs on the emergence of virulence is unknown. We programmed the human pathogen Streptococcus pneumoniae with CRISPR sequences that target capsule genes, an essential pneumococcal virulence factor, and show that CRISPR interference can prevent transformation of nonencapsulated, avirulent pneumococci into capsulated, virulent strains during infection in mice. Further, at low frequencies bacteria can lose CRISPR function, acquire capsule genes, and mount a successful infection. These results demonstrate that CRISPR interference can prevent the emergence of virulence in vivo and that strong selective pressure for virulence or antibiotic resistance can lead to CRISPR loss in bacterial pathogens. Copyright © 2012 Elsevier Inc. All rights reserved.

  3. Meta-analysis of high-latitude nitrogen-addition and warming studies implies ecological mechanisms overlooked by land models

    Science.gov (United States)

    Bouskill, N. J.; Riley, W. J.; Tang, J. Y.

    2014-12-01

    Accurate representation of ecosystem processes in land models is crucial for reducing predictive uncertainty in energy and greenhouse gas feedbacks with the climate. Here we describe an observational and modeling meta-analysis approach to benchmark land models, and apply the method to the land model CLM4.5 with two versions of belowground biogeochemistry. We focused our analysis on the aboveground and belowground responses to warming and nitrogen addition in high-latitude ecosystems, and identified absent or poorly parameterized mechanisms in CLM4.5. While the two model versions predicted similar soil carbon stock trajectories following both warming and nitrogen addition, other predicted variables (e.g., belowground respiration) differed from observations in both magnitude and direction, indicating that CLM4.5 has inadequate underlying mechanisms for representing high-latitude ecosystems. On the basis of observational synthesis, we attribute the model-observation differences to missing representations of microbial dynamics, aboveground and belowground coupling, and nutrient cycling, and we use the observational meta-analysis to discuss potential approaches to improving the current models. However, we also urge caution concerning the selection of data sets and experiments for meta-analysis. For example, the concentrations of nitrogen applied in the synthesized field experiments (average = 72 kg ha-1 yr-1) are many times higher than projected soil nitrogen concentrations (from nitrogen deposition and release during mineralization), which precludes a rigorous evaluation of the model responses to likely nitrogen perturbations. Overall, we demonstrate that elucidating ecological mechanisms via meta-analysis can identify deficiencies in ecosystem models and empirical experiments.

  4. The influence of mineral additives on the mechanical performances of the conditioning matrix of radioactive waste by cementation

    International Nuclear Information System (INIS)

    Dragolici, F.; Rotarescu, G.; Turcanu, C.N.

    1997-01-01

    To improve the quality of the conditioning matrix of radioactive waste by the cementation technology, mineral additives which are diminishing the leaching rate of the radionuclides in the disposal environment are used. The studies performed until now have as an objective the obtaining of the most propitious mixture of cement and bentonite or cement and volcanic tuff, which have the mechanical properties similar to the cement paste used for the conditioning of the radioactive waste. This mixture, cement - mineral binder, in the future is required to be used at the Radioactive Waste Treatment Plant - IPNE - HH Bucharest- Magurele for the conditioning of the radioactive wastes, taking in consideration the properties of these mineral binders: very good plasticity and capacity of adsorption, which lead at the decrease of porosity. Bentonite is a clay already used in the technology of disposal as a filling material to diminish the radioactive spreading because of degradation in time of the metallic package or the intrusion of casual water. The composition of the cement - bentonite - water system is checked by the cement to water and cement to bentonite ratio, by strength and by the separated water volume. The studies show that the best mechanical performance was obtained for a cement to water ratio 10. Taking in consideration the property of bentonite to fill compactly the free spaces in the presence of water, what entails the occurrence of internal tensions in the matrix structure, which leads, in turn, to appearance of microfissures, the mixtures examined by mechanical tests had in their composition less than 10 % bentonite. For volcanic tuff, similar results were obtained using almost the same ratios. In these conditions, the results obtained allow to draw the conclusion that the adequate usage of the mineral additives do not change the resistance of the cement paste used in the conditioning of the radioactive waste. (authors)

  5. Effect of Sc addition and T6 aging treatment on the microstructure modification and mechanical properties of A356 alloy

    Energy Technology Data Exchange (ETDEWEB)

    Pramod, S.L. [Department of Metallurgical and Materials Engineering, Indian Institute of Technology Madras, Chennai 600036 (India); Ravikirana [Department of Metallurgical and Materials Engineering, Indian Institute of Technology Madras, Chennai 600036 (India); Department of Physics and Nanotechnology, SRM University, Chennai 603203 (India); Rao, A.K. Prasada [College of Engineering and Design, Alliance University, Bengaluru 562106 (India); Murty, B.S., E-mail: murty@iitm.ac.in [Department of Metallurgical and Materials Engineering, Indian Institute of Technology Madras, Chennai 600036 (India); Bakshi, Srinivasa R., E-mail: sbakshi@iitm.ac.in [Department of Metallurgical and Materials Engineering, Indian Institute of Technology Madras, Chennai 600036 (India)

    2016-09-30

    Effect of Sc addition and T6 aging treatment on the secondary dendritic arm spacing (SDAS), modification of eutectic Si morphology, β-Al{sub 5}FeSiand π-Al{sub 8}Mg{sub 3}Si{sub 6}Fe{sub 1} phases and its effect on mechanical properties in A356 alloy has been investigated. Addition of 0.4 wt%Sc in A356 alloy resulted in a 50%reduction in the secondary dendritic arm spacing (SDAS). Sc addition changed the morphology of eutectic Si from plate like to fibrous and globular. The needle like morphology of β-Al{sub 5}FeSi phase in A356 alloy changed to Al{sub 5}Fe(Si,Sc) phase having smaller size and irregular morphology. Transmission electron microscopy (TEM) diffraction pattern and Energy dispersive spectroscopy (EDS) analysis revealed the presence of β-Al{sub 5}FeSiand π-Al{sub 8}Mg{sub 3}Si{sub 6}Fe{sub 1} phases in A356 alloy which changed to β-Al{sub 5}Fe(Si,Sc), π-Al{sub 8}Mg{sub 3}(Si,Sc){sub 6}Fe{sub 1} and additional V-AlSi{sub 2}Sc{sub 2}phase was observed in Sc containing alloys. Addition of 0.4 wt%Sc to A356 alloy improved its Vickers hardness, Ultimate tensile strength (UTS), Yield strength (YS) and ductility by 20%, 25%, 20% and 30% respectively. Artificial aging treatment resulted in significant improvement in the tensile properties for both A356 and Sc added A356 alloys.

  6. Somatic recombination in wheat stem rust leads to virulence for Ug99-effective SR50 resistance

    Science.gov (United States)

    Race-specific resistance genes protect much of the global wheat crop from stem rust disease caused by Puccinia graminis f. sp. tritici (Pgt), but often break down due to evolution of new virulent pathogen races. To understand the molecular mechanisms of virulence evolution in Pgt we identified the p...

  7. Mechanisms of Bunyavirus Virulence: A Genetic Approach.

    Science.gov (United States)

    1984-12-01

    of canine parvovirus Type-2, feline panleukopenia virus and mink enteritis virus. Virology 129,401-414. Partner A., Webster, R. G., and Bean W. J...CM, and Webster RG. Procedures for the characterization of the genetic material of candidate vaccine strains. Develop Biol Standard 39:15-24, 1977

  8. Helicobacter pylori infection: An overview of bacterial virulence factors and pathogenesis

    Directory of Open Access Journals (Sweden)

    Cheng-Yen Kao

    2016-02-01

    Full Text Available Helicobacter pylori pathogenesis and disease outcomes are mediated by a complex interplay between bacterial virulence factors, host, and environmental factors. After H. pylori enters the host stomach, four steps are critical for bacteria to establish successful colonization, persistent infection, and disease pathogenesis: (1 Survival in the acidic stomach; (2 movement toward epithelium cells by flagella-mediated motility; (3 attachment to host cells by adhesins/receptors interaction; (4 causing tissue damage by toxin release. Over the past 20 years, the understanding of H. pylori pathogenesis has been improved by studies focusing on the host and bacterial factors through epidemiology researches and molecular mechanism investigations. These include studies identifying the roles of novel virulence factors and their association with different disease outcomes, especially the bacterial adhesins, cag pathogenicity island, and vacuolating cytotoxin. Recently, the development of large-scale screening methods, including proteomic, and transcriptomic tools, has been used to determine the complex gene regulatory networks in H. pylori. In addition, a more available complete genomic database of H. pylori strains isolated from patients with different gastrointestinal diseases worldwide is helpful to characterize this bacterium. This review highlights the key findings of H. pylori virulence factors reported over the past 20 years.

  9. Microstructural evolution and tensile mechanical properties of thixoformed AZ91D magnesium alloy with the addition of yttrium

    International Nuclear Information System (INIS)

    Zhao Zude; Chen Qiang; Kang Feng; Shu Dayu

    2009-01-01

    The microstructure evolution of AZ91D magnesium alloy in the semi-solid state has been proposed or reported in previous literature. However, no detailed investigation has been conducted regarding the relationship between the microstructure and tensile mechanical properties of the thixoformed AZ91D magnesium alloy. In this paper, the microstructure of AZ91D alloy with the addition of yttrium was produced by the semi-solid thermal transformation (SSTT) route and the strain-induced melt activation (SIMA) route, respectively. Isothermal holding experiments investigated grain coarsening and the degree of spheroidization as a function of holding time in the semi-solid state. The SSTT route and the SIMA route were used to obtain the semi-solid feedstock for thixoforming. The results show that solid particles of the SSTT alloy are spheroidized to some extent but the previous irregular shape is still obvious in some of them. While the SIMA alloy exhibits ideal, fine microstructure, in which completely spheroidized solid particles contain little entrapped liquid. The microstructure of the SSTT alloy is less spheroidized compared with the SIMA alloy under the similar isothermal holding condition. As the holding time increases, the mean solid particle size of the SSTT alloy decreases initially, then increases, while the mean solid particle size of the SIMA alloy increases monotonously at 560 deg. C. Compared with the SSTT alloy, the SIMA alloy obtains finer grains under the similar isothermal holding condition. The mechanical properties of the thixoformed AZ91D alloy with the addition of yttrium produced by the SIMA route are better than those of the thixoformed alloy produced by the SSTT route. The ultimate tensile strength, yield strength and elongation for the thixoformed alloy produced by the SIMA route are 303.1 MPa, 147.6 MPa and 13.27%, respectively. The tensile properties for the AZ91D alloy with the addition of yttrium thixoformed from starting material produced by

  10. The Effect of the Kind of Sands and Additions on the Mechanical Behaviour of S.C.C

    Science.gov (United States)

    Zeghichi, L.; Benghazi, Z.; Baali, L.

    The sand is an inert element essential in the composition of concrete; its use ensures granular continuity between the cement and gravel for better cohesion of concrete. This paper presents the results of a study that investigated the influence of sand quality on the properties of fresh and hardened self-compacting concrete (SCC). The dune sands are very fine materials characterized by a high intergranular porosity, high surface area and low fineness modulus; on the other hand crushed (manufactured) sand has a high rate into thin and irregular shapes which are influencing the workability of concrete. The amount of dune sand varies from (0% 50%, to 100%) by weight of fine aggregates. The effect of additions is also treated (blast furnace slag and lime stone) The results show that the rheological properties favour the use of dune sands; however the mechanical properties support the use of crushed sand.

  11. Effect of addition of Ag nano powder on mechanical properties of epoxy/polyaminoamide adduct coatings filled with conducting polymer

    Energy Technology Data Exchange (ETDEWEB)

    Samad, Ubair Abdus [Department of Chemical Engineering, College of Engineering, King Saud University, P. O. Box 800, Riyadh 11421 (Saudi Arabia); Center of excellence for research in engineering materials (CEREM), Advance Manufacturing Institute, King Saud University, P. O. Box 800, Riyadh 11421 (Saudi Arabia); Khan, Rawaiz [Department of Chemical Engineering, College of Engineering, King Saud University, P. O. Box 800, Riyadh 11421 (Saudi Arabia); Alam, Mohammad Asif [Center of excellence for research in engineering materials (CEREM), Advance Manufacturing Institute, King Saud University, P. O. Box 800, Riyadh 11421 (Saudi Arabia); Al-Othman, Othman Y. [Department of Chemical Engineering, College of Engineering, King Saud University, P. O. Box 800, Riyadh 11421 (Saudi Arabia); Deanship of Graduate Studies, The Saudi Electric University, P. O. Box 93499, Riyadh 11673 (Saudi Arabia); Al-Zahrani, Saeed M. [Center of excellence for research in engineering materials (CEREM), Advance Manufacturing Institute, King Saud University, P. O. Box 800, Riyadh 11421 (Saudi Arabia); SABIC Polymer Research Center (SPRC) and department of chemical engineering, college of engineering, King Saud University, P. O. Box 800, Riyadh 11421 (Saudi Arabia)

    2015-05-22

    In this study the effect of Ag Nano powder on mechanical properties of epoxy coatings filled with optimized ratio of conducting polymers (Polyaniline and Polyppyrole) was evaluated. Bisphenol A diglycidyl ether epoxy resin (DGEBA) along with polyaminoamide adduct (ARADUR 3282-1 BD) is used as curing agent under optimized stoichiometry values. Curing is performed at room temperature with different percentages of Nano filler. Glass and steel panels were used as coating substrate. Bird applicator was used to coat the samples in order to obtain thin film with wet film thickness (WFT) of about 70-90 µm. The samples were kept in dust free environment for about 7 days at room temperature for complete curing. The coated steel panels were used to evaluate the mechanical properties of coating such as hardness, scratch and impact tests whereas coated glass panels were used for measuring pendulum hardness of the coatings. To check the dispersion and morphology of Nano filler in epoxy matrix scanning electron microscopy (SEM) was used in addition Nano indentation was also performed to observe the effect of Nano filler on modulus of elasticity and hardness at Nano scale.

  12. Novel support effects on the mechanism of propene-deuterium: Addition and exchange reactions over dispersed ZrO2

    International Nuclear Information System (INIS)

    Naito, Shuichi; Tanimoto, Mitsutoshi

    1995-01-01

    The effect on the rate and mechanisms of propene-deuterium reactions of dispersing ZrO 2 on various supports such as silica, alumina, and titanium dioxide has been studied by microwave spectroscopic analysis of monodeuteropropene as well as by kinetic investigation. By dispersal of ZrO 2 on these supports, the rate of the C 3 H 6 -D 2 reactions is increased considerbly compared to that over unsupported ZrO 2 , with the decrease of activation energy. Hydrogen exchange in propene proceeds simultaneously with addition via the associative mechanism through n-propyl and s-propyl intermediates. Through XPS analysis of ZrO 2 /SiO 2 , it was found that a monolayer of ZrO 2 is formed over the silica support. The monolayer catalyst exhibits catalytic behavior quite different from that of unsupported ZrO 2 . On the other hand, alumina surfaces modified by ZrO 2 layers may be the main active sites in the case of ZrO 2 /Al 2 O 3 . The marked enhancement of the reaction rate in the lower loading region of ZrO 2 /TiO 2 may be explained by the strong interaction of atomically dispersed zirconium ions with active centers on TiO 2 . 28 refs., 10 figs., 1 tab

  13. Mechanical behaviour of austenitic stainless steels in inert environment and in hot chloride environment: influence of molybdenum addition

    International Nuclear Information System (INIS)

    Daret, Jacques

    1978-01-01

    This research thesis reports the study of the influence of molybdenum addition. It is based on an experimental method which brings to the fore correlations between mechanical and electrochemical parameters of the phenomenon of stress corrosion cracking of austenitic stainless steels. After having recalled some characteristics of dry corrosion and electrochemical corrosion, presented austenitic stainless steels (mechanical properties such as elastic modulus, yield strength, tensile strength, ultimate elongation, creep behaviour, inter-crystalline and pitting corrosion, stress corrosion cracking behaviour), the author addresses the stress corrosion cracking behaviour of these steels in chloride environment (general characteristics, parameters, proposes theories to explain stress corrosion cracking), reports the study of the influence of molybdenum in these steels, notably on corrosion resistance and on stress corrosion cracking. Experimental method and results are described and discussed: tensile tests and creep tests in inert environment, stress corrosion cracking test in chloride environment with analysis based either on corrosion potential evolution or on sample elongation evolution. Results are notably discussed in terms of crack situation within metal lattice, crack growth rate, and scanning electronic microscopy observations [fr

  14. Microstructure Evolution and Mechanical Behavior of 2219 Aluminum Alloys Additively Fabricated by the Cold Metal Transfer Process

    Directory of Open Access Journals (Sweden)

    Xuewei Fang

    2018-05-01

    Full Text Available In this research, four different welding arc modes including conventional cold metal transfer (CMT, CMT-Pulse (CMT-P, CMT-Advanced (CMT-ADV, and CMT pulse advanced (CMT-PADV were used to deposit 2219-Al wire. The effects of different arc modes on porosity, pore size distribution, microstructure evolution, and mechanical properties were thoroughly investigated. The statistical analysis of the porosity and its size distribution indicated that the CMT-PADV process gave the smallest pore area percentage and pore aspect ratio, and had almost no larger pores. The results from optical microscopy, scanning electron microscopy, and fractographic morphology proved that uniform and fine equiaxed grains, evenly distributed Al2Cu second phase particles were formed during the CMT-PADV process. Furthermore, the X-ray diffraction test ascertained that the CMT-PADV sample had the smallest lattice parameter and the highest solute Cu content. Besides, the tensile strength could reach 283 MPa, the data scattering was the smallest, and the strength scattering of the sample in the horizontal direction was the shortest. In addition, the strength properties were nearly isotropic, with only 5 MPa difference in the vertical and horizontal directions. The above mentioned results indicated that the mechanical properties of 2219 aluminum alloy was improved using the CMT-PADV arc mode.

  15. Effect of addition of Ag nano powder on mechanical properties of epoxy/polyaminoamide adduct coatings filled with conducting polymer

    International Nuclear Information System (INIS)

    Samad, Ubair Abdus; Khan, Rawaiz; Alam, Mohammad Asif; Al-Othman, Othman Y.; Al-Zahrani, Saeed M.

    2015-01-01

    In this study the effect of Ag Nano powder on mechanical properties of epoxy coatings filled with optimized ratio of conducting polymers (Polyaniline and Polyppyrole) was evaluated. Bisphenol A diglycidyl ether epoxy resin (DGEBA) along with polyaminoamide adduct (ARADUR 3282-1 BD) is used as curing agent under optimized stoichiometry values. Curing is performed at room temperature with different percentages of Nano filler. Glass and steel panels were used as coating substrate. Bird applicator was used to coat the samples in order to obtain thin film with wet film thickness (WFT) of about 70-90 µm. The samples were kept in dust free environment for about 7 days at room temperature for complete curing. The coated steel panels were used to evaluate the mechanical properties of coating such as hardness, scratch and impact tests whereas coated glass panels were used for measuring pendulum hardness of the coatings. To check the dispersion and morphology of Nano filler in epoxy matrix scanning electron microscopy (SEM) was used in addition Nano indentation was also performed to observe the effect of Nano filler on modulus of elasticity and hardness at Nano scale

  16. Effect of addition of Ag nano powder on mechanical properties of epoxy/polyaminoamide adduct coatings filled with conducting polymer

    Science.gov (United States)

    Samad, Ubair Abdus; Khan, Rawaiz; Alam, Mohammad Asif; Al-Othman, Othman Y.; Al-Zahrani, Saeed M.

    2015-05-01

    In this study the effect of Ag Nano powder on mechanical properties of epoxy coatings filled with optimized ratio of conducting polymers (Polyaniline and Polyppyrole) was evaluated. Bisphenol A diglycidyl ether epoxy resin (DGEBA) along with polyaminoamide adduct (ARADUR 3282-1 BD) is used as curing agent under optimized stoichiometry values. Curing is performed at room temperature with different percentages of Nano filler. Glass and steel panels were used as coating substrate. Bird applicator was used to coat the samples in order to obtain thin film with wet film thickness (WFT) of about 70-90 µm. The samples were kept in dust free environment for about 7 days at room temperature for complete curing. The coated steel panels were used to evaluate the mechanical properties of coating such as hardness, scratch and impact tests whereas coated glass panels were used for measuring pendulum hardness of the coatings. To check the dispersion and morphology of Nano filler in epoxy matrix scanning electron microscopy (SEM) was used in addition Nano indentation was also performed to observe the effect of Nano filler on modulus of elasticity and hardness at Nano scale.

  17. Microstructure Evolution and Mechanical Behavior of 2219 Aluminum Alloys Additively Fabricated by the Cold Metal Transfer Process.

    Science.gov (United States)

    Fang, Xuewei; Zhang, Lijuan; Li, Hui; Li, Chaolong; Huang, Ke; Lu, Bingheng

    2018-05-16

    In this research, four different welding arc modes including conventional cold metal transfer (CMT), CMT-Pulse (CMT-P), CMT-Advanced (CMT-ADV), and CMT pulse advanced (CMT-PADV) were used to deposit 2219-Al wire. The effects of different arc modes on porosity, pore size distribution, microstructure evolution, and mechanical properties were thoroughly investigated. The statistical analysis of the porosity and its size distribution indicated that the CMT-PADV process gave the smallest pore area percentage and pore aspect ratio, and had almost no larger pores. The results from optical microscopy, scanning electron microscopy, and fractographic morphology proved that uniform and fine equiaxed grains, evenly distributed Al₂Cu second phase particles were formed during the CMT-PADV process. Furthermore, the X-ray diffraction test ascertained that the CMT-PADV sample had the smallest lattice parameter and the highest solute Cu content. Besides, the tensile strength could reach 283 MPa, the data scattering was the smallest, and the strength scattering of the sample in the horizontal direction was the shortest. In addition, the strength properties were nearly isotropic, with only 5 MPa difference in the vertical and horizontal directions. The above mentioned results indicated that the mechanical properties of 2219 aluminum alloy was improved using the CMT-PADV arc mode.

  18. Microstructure Evolution and Mechanical Behavior of 2219 Aluminum Alloys Additively Fabricated by the Cold Metal Transfer Process

    Science.gov (United States)

    Fang, Xuewei; Li, Hui; Li, Chaolong; Lu, Bingheng

    2018-01-01

    In this research, four different welding arc modes including conventional cold metal transfer (CMT), CMT-Pulse (CMT-P), CMT-Advanced (CMT-ADV), and CMT pulse advanced (CMT-PADV) were used to deposit 2219-Al wire. The effects of different arc modes on porosity, pore size distribution, microstructure evolution, and mechanical properties were thoroughly investigated. The statistical analysis of the porosity and its size distribution indicated that the CMT-PADV process gave the smallest pore area percentage and pore aspect ratio, and had almost no larger pores. The results from optical microscopy, scanning electron microscopy, and fractographic morphology proved that uniform and fine equiaxed grains, evenly distributed Al2Cu second phase particles were formed during the CMT-PADV process. Furthermore, the X-ray diffraction test ascertained that the CMT-PADV sample had the smallest lattice parameter and the highest solute Cu content. Besides, the tensile strength could reach 283 MPa, the data scattering was the smallest, and the strength scattering of the sample in the horizontal direction was the shortest. In addition, the strength properties were nearly isotropic, with only 5 MPa difference in the vertical and horizontal directions. The above mentioned results indicated that the mechanical properties of 2219 aluminum alloy was improved using the CMT-PADV arc mode. PMID:29772708

  19. Graded microstructure and mechanical properties of additive manufactured Ti–6Al–4V via electron beam melting

    International Nuclear Information System (INIS)

    Tan, Xipeng; Kok, Yihong; Tan, Yu Jun; Descoins, Marion; Mangelinck, Dominique; Tor, Shu Beng; Leong, Kah Fai; Chua, Chee Kai

    2015-01-01

    Electron beam melting (EBM®)-built Ti–6Al–4V has increasingly shown great potential for orthopedic implant and aerospace applications in recent years. The microstructure and mechanical properties of EBM-built Ti–6Al–4V have been systematically investigated in this work. Its microstructure consists of columnar prior β grains delineated by wavy grain boundary α and transformed α/β structures with both cellular colony and basket-weave morphology as well as numerous singular α bulges within the prior β grains. The β phase is found to form as discrete flat rods embedded in continuous α phase and its volume fraction is determined to be ∼3.6%. Moreover, α′ martensite was not observed as it has decomposed into α and β phases. In particular, the α/β interface was studied in detail combined transmission electron microscopy with atom probe tomography. Of note is that graded Ti–6Al–4V microstructure i.e. both prior β grain width and β phase interspacing continuously increase with the build height, was observed, which mainly arises from the decreasing cooling rate. Furthermore, an increasingly pronounced strain hardening effect was also observed as the previously built layers undergo a longer annealing compared to the subsequent layers. As a result, graded mechanical properties of Ti–6Al–4V with degraded microhardness and tensile properties were found. A good agreement with the Hall–Petch relation indicates that the graded property takes place mainly due to the graded microstructure. In addition, this graded microstructure and mechanical properties were discussed based on a quantitative characterization

  20. Modelling the role of intrinsic electric fields in microtubules as an additional control mechanism of bi-directional intracellular transport.

    Science.gov (United States)

    Sataric, M V; Budinski-Petkovic, L; Loncarevic, I; Tuszynski, J A

    2008-01-01

    Active transport is essential for cellular function, while impaired transport has been linked to diseases such as neuronal degeneration. Much long distance transport in cells uses opposite polarity molecular motors of the kinesin and dynein families to move cargos along microtubules. It is clear that many types of cargo are moved by both sets of motors, and frequently in a reverse direction. The general question of how the direction of transport is regulated is still open. The mechanism of the cell's differential control of diverse cargos within the same cytoplasmic background is still unclear as is the answer to the question how endosomes and mitochondria move to different locations within the same cell. To answer these questions we postulate the existence of a local signaling mechanism used by the cell to specifically control different cargos. In particular, we propose an additional physical mechanism that works through the use of constant and alternating intrinsic (endogenous) electric fields as a means of controlling the speed and direction of microtubule-based transport. A specific model is proposed and analyzed in this paper. The model involves the rotational degrees of freedom of the C-termini of tubulin, their interactions and the coupling between elastic and dielectric degrees of freedom. Viscosity of the solution is also included and the resultant equation of motion is found as a nonlinear elliptic equation with dissipation. A particular analytical solution of this equation is obtained in the form of a kink whose properties are analyzed. It is concluded that this solution can be modulated by the presence of electric fields and hence may correspond to the observed behavior of motor protein transport along microtubules.

  1. Meta-analysis of high-latitude nitrogen-addition and warming studies imply ecological mechanisms overlooked by land models

    Science.gov (United States)

    Bouskill, N. J.; Riley, W. J.; Tang, J.

    2014-08-01

    Accurate representation of ecosystem processes in land models is crucial for reducing predictive uncertainty in energy and greenhouse gas feedbacks with the atmosphere. Here we describe an observational and modeling meta-analysis approach to benchmark land models, and apply the method to the land model CLM4.5 with two versions of belowground biogeochemistry. We focused our analysis on the above and belowground high-latitude ecosystem responses to warming and nitrogen addition, and identified mechanisms absent, or poorly parameterized in CLM4.5. While the two model versions predicted similar trajectories for soil carbon stocks following both types of perturbation, other variables (e.g., belowground respiration) differed from the observations in both magnitude and direction, indicating the underlying mechanisms are inadequate for representing high-latitude ecosystems. The observational synthesis attribute these differences to missing representations of microbial dynamics, characterization of above and belowground functional processes, and nutrient competition. We use the observational meta-analyses to discuss potential approaches to improving the current models (e.g., the inclusion of dynamic vegetation or different microbial functional guilds), however, we also raise a cautionary note on the selection of data sets and experiments to be included in a meta-analysis. For example, the concentrations of nitrogen applied in the synthesized field experiments (average =72 kg ha-1 yr-1) are many times higher than projected soil nitrogen concentrations (from nitrogen deposition and release during mineralization), which preclude a rigorous evaluation of the model responses to nitrogen perturbation. Overall, we demonstrate here that elucidating ecological mechanisms via meta-analysis can identify deficiencies in both ecosystem models and empirical experiments.

  2. A bistable switch and anatomical site control Vibrio cholerae virulence gene expression in the intestine.

    Directory of Open Access Journals (Sweden)

    Alex T Nielsen

    2010-09-01

    Full Text Available A fundamental, but unanswered question in host-pathogen interactions is the timing, localization and population distribution of virulence gene expression during infection. Here, microarray and in situ single cell expression methods were used to study Vibrio cholerae growth and virulence gene expression during infection of the rabbit ligated ileal loop model of cholera. Genes encoding the toxin-coregulated pilus (TCP and cholera toxin (CT were powerfully expressed early in the infectious process in bacteria adjacent to epithelial surfaces. Increased growth was found to co-localize with virulence gene expression. Significant heterogeneity in the expression of tcpA, the repeating subunit of TCP, was observed late in the infectious process. The expression of tcpA, studied in single cells in a homogeneous medium, demonstrated unimodal induction of tcpA after addition of bicarbonate, a chemical inducer of virulence gene expression. Striking bifurcation of the population occurred during entry into stationary phase: one subpopulation continued to express tcpA, whereas the expression declined in the other subpopulation. ctxA, encoding the A subunit of CT, and toxT, encoding the proximal master regulator of virulence gene expression also exhibited the bifurcation phenotype. The bifurcation phenotype was found to be reversible, epigenetic and to persist after removal of bicarbonate, features consistent with bistable switches. The bistable switch requires the positive-feedback circuit controlling ToxT expression and formation of the CRP-cAMP complex during entry into stationary phase. Key features of this bistable switch also were demonstrated in vivo, where striking heterogeneity in tcpA expression was observed in luminal fluid in later stages of the infection. When this fluid was diluted into artificial seawater, bacterial aggregates continued to express tcpA for prolonged periods of time. The bistable control of virulence gene expression points to a

  3. Effects of microstructure and CaO addition on the magnetic and mechanical properties of NiCuZn ferrites

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Sea-Fue, E-mail: sfwang@ntut.edu.tw; Hsu, Yung-Fu; Liu, Yi-Xin; Hsieh, Chung-Kai

    2015-11-15

    In this study, the effects of grain size and the addition of CaCO{sub 3} on the magnetic and mechanical properties of Ni{sub 0.5}Cu{sub 0.3}Zn{sub 0.2}Fe{sub 2}O{sub 4} ceramics were investigated. The bending strength of the ferrites increased from 66 to 84 MPa as the grain size of the sintered ceramics decreased from 10.25 μm to 7.53 μm, while the change in hardness was insignificant. The addition of various amounts of CaCO{sub 3} densified the Ni{sub 0.5}Cu{sub 0.3}Zn{sub 0.2}Fe{sub 2}O{sub 4} ceramics at 1075 °C. In the pure Ni{sub 0.5}Cu{sub 0.3}Zn{sub 0.2}Fe{sub 2}O{sub 4} ceramic, second phase CuO was segregated at the grain boundaries. With the CaCO{sub 3} content ≥1.5 wt%, a small amount of discrete plate-like second phase Fe{sub 2}CaO{sub 4} was observed, together with the disappearance of the second phase CuO. The grain size of the Ni{sub 0.5}Cu{sub 0.3}Zn{sub 0.2}Fe{sub 2}O{sub 4} ceramic dropped from 7.80 μm to 4.68 μm, and the grain size distribution widened as the CaCO{sub 3} content increased from 0 to 5 wt%. Initially rising to 807 after CaCO{sub 3} addition up to 2.0 wt%, due to a reduced grain size, the Vickers hardness began to drop as the CaCO{sub 3} content increased. The bending strength grew linearly with the CaCO{sub 3} content and reached twice the value for the Ni{sub 0.5}Cu{sub 0.3}Zn{sub 0.2}Fe{sub 2}O{sub 4} ceramic with an addition of 5.0 wt% CaCO{sub 3}. The initial permeability of the Ni{sub 0.5}Cu{sub 0.3}Zn{sub 0.2}Fe{sub 2}O{sub 4} ceramic decreased substantially from 402 to 103 as the addition of CaCO{sub 3} in ferrite increased from 0 to 5 wt%, and the quality factor of the Ni{sub 0.5}Cu{sub 0.3}Zn{sub 0.2}Fe{sub 2}O{sub 4} ceramic was maximized at 95 for 1.0 wt% CaCO{sub 3} addition. - Highlights: • Effects of grain size and CaCO{sub 3} on the properties of NiCuZn ferrite were studied. • Bending strength increased with grain size of the ferrite but not in the hardness. • Bending strength reached a twice value for

  4. Effects of Cu and B addition on microstructure and mechanical properties of high-strength bainitic steels

    International Nuclear Information System (INIS)

    Shin, Sang Yong; Han, Seung Youb; Hwang, Byoungchul; Lee, Chang Gil; Lee, Sunghak

    2009-01-01

    Effects of Cu and B addition on microstructure and mechanical properties of high-strength bainitic steels were investigated in this study. Six kinds of steels were fabricated by controlling the amount of Cu and B addition, and their microstructures and tensile and Charpy impact properties were investigated. Their effective grain sizes were also characterized by the electron back-scatter diffraction analysis. The tensile test results indicated that the B- or Cu-containing steels had the higher yield and tensile strengths than the B- or Cu-free steels because their volume fractions of acicular ferrite and martensite were quite high. The B- or Cu-free steels had the higher upper shelf energy than the B- or Cu-containing steels because of their lower volume fraction of martensite. In the steel containing 10 ppm B without Cu, the best combination of high strengths, high upper shelf energy, and low energy transition temperature could be obtained by the decrease in effective grain size due to the presence of acicular ferrite having fine effective grain size.

  5. Irradiated recycled plastic as a concrete additive for improved chemo-mechanical properties and lower carbon footprint.

    Science.gov (United States)

    Schaefer, Carolyn E; Kupwade-Patil, Kunal; Ortega, Michael; Soriano, Carmen; Büyüköztürk, Oral; White, Anne E; Short, Michael P

    2018-01-01

    Concrete production contributes heavily to greenhouse gas emissions, thus a need exists for the development of durable and sustainable concrete with a lower carbon footprint. This can be achieved when cement is partially replaced with another material, such as waste plastic, though normally with a tradeoff in compressive strength. This study discusses progress toward a high/medium strength concrete with a dense, cementitious matrix that contains an irradiated plastic additive, recovering the compressive strength while displacing concrete with waste materials to reduce greenhouse gas generation. Compressive strength tests showed that the addition of high dose (100kGy) irradiated plastic in multiple concretes resulted in increased compressive strength as compared to samples containing regular, non-irradiated plastic. This suggests that irradiating plastic at a high dose is a viable potential solution for regaining some of the strength that is lost when plastic is added to cement paste. X-ray Diffraction (XRD), Backscattered Electron Microscopy (BSE), and X-ray microtomography explain the mechanisms for strength retention when using irradiated plastic as a filler for cement paste. By partially replacing Portland cement with a recycled waste plastic, this design may have a potential to contribute to reduced carbon emissions when scaled to the level of mass concrete production. Copyright © 2017 Elsevier Ltd. All rights reserved.

  6. Mechanical properties of tungsten alloys with Y{sub 2}O{sub 3} and titanium additions

    Energy Technology Data Exchange (ETDEWEB)

    Aguirre, M.V., E-mail: mariavega.aguirre@upm.es [Departamento de Tecnologias Especiales Aplicadas a la Aeronautica, Universidad Politecnica de Madrid, E.U.I.T. Aeronautica, 28040 Madrid (Spain); Martin, A.; Pastor, J.Y. [Departamento de Ciencia de Materiales-CISDEM, Universidad Politecnica de Madrid.E.T.S. Ingenieros de Caminos, 28040 Madrid (Spain); LLorca, J. [Departamento de Ciencia de Materiales-CISDEM, Universidad Politecnica de Madrid.E.T.S. Ingenieros de Caminos, 28040 Madrid (Spain); Instituto Madrileno de Estudios Avanzados en Materiales (Instituto IMDEA-Materiales), Ingenieros de Caminos, 28040 Madrid (Spain); Monge, M.A.; Pareja, R. [Departamento de Fisica, Universidad Carlos III de Madrid, 28911 Leganes (Spain)

    2011-10-01

    In this research the mechanical behaviour of pure tungsten (W) and its alloys (2 wt.% Ti-0.47 wt.% Y{sub 2}O{sub 3} and 4 wt.% Ti-0.5 wt.% Y{sub 2}O{sub 3}) is compared. These tungsten alloys, have been obtained by powder metallurgy. The yield strength, fracture toughness and elastic modulus have been studied in the temperature interval of 25 deg. C to 1000 deg. C. The results have shown that the addition of Ti substantially improves the bending strength and toughness of W, but it also dramatically increases the DBTT. On the other hand, the addition of 0.5% Y{sub 2}O{sub 3}, is enough to improve noticeably the oxidation behaviour at the higher temperatures. The grain size, fractography and microstructure are studied in these materials. Titanium is a good grain growth inhibitor and effective precursor of liquid phase in HIP. The simultaneous presence of Y{sub 2}O{sub 3} and Ti permits to obtain materials with low pores presence.

  7. Additive Effects of Mechanical Marrow Ablation and PTH Treatment on de Novo Bone Formation in Mature Adult Rats

    Directory of Open Access Journals (Sweden)

    Jodi A. Carlson Scholz

    2012-12-01

    Full Text Available Mechanical ablation of bone marrow in young rats induces rapid but transient bone growth, which can be enhanced and maintained for three weeks by the administration of parathyroid hormone (PTH. Additionally, marrow ablation, followed by PTH treatment for three months leads to increased cortical thickness. In this study, we sought to determine whether PTH enhances bone formation after marrow ablation in aged rats. Aged rats underwent unilateral femoral marrow ablation and treatment with PTH or vehicle for four weeks. Both femurs from each rat were analyzed by X-ray and pQCT, then analyzed either by microCT, histology or biomechanical testing. Marrow ablation alone induced transient bone formation of low abundance that persisted over four weeks, while marrow ablation followed by PTH induced bone formation of high abundance that also persisted over four weeks. Our data confirms that the osteo-inducive effect of marrow ablation and the additive effect of marrow ablation, followed by PTH, occurs in aged rats. Our observations open new avenues of investigations in the field of tissue regeneration. Local marrow ablation, in conjunction with an anabolic agent, might provide a new platform for rapid site-directed bone growth in areas of high bone loss, such as in the hip and wrist, which are subject to fracture.

  8. Host specific glycans are correlated with susceptibility to infection by lagoviruses, but not with their virulence.

    Science.gov (United States)

    Lopes, Ana M; Breiman, Adrien; Lora, Mónica; Le Moullac-Vaidye, Béatrice; Galanina, Oxana; Nyström, Kristina; Marchandeau, Stephane; Le Gall-Reculé, Ghislaine; Strive, Tanja; Neimanis, Aleksija; Bovin, Nicolai V; Ruvoën-Clouet, Nathalie; Esteves, Pedro J; Abrantes, Joana; Le Pendu, Jacques

    2017-11-29

    The rabbit hemorrhagic disease virus (RHDV) and the European brown hare syndrome virus (EBHSV) are two lagoviruses from the family Caliciviridae that cause fatal diseases in two leporid genera, Oryctolagus and Lepus , respectively. In the last few years, several examples of host jumps of lagoviruses among leporids were recorded. In addition, a new pathogenic genotype of RHDV emerged and many non-pathogenic strains of lagoviruses have been described. The molecular mechanisms behind host shifts and the emergence of virulence are unknown. Since RHDV uses glycans of the histo-blood group antigen type as attachment factors to initiate infection, we studied if glycan specificities of the new pathogenic RHDV genotype, non-pathogenic lagoviruses and EBHSV potentially play a role in determining host range and virulence of lagoviruses. We observed binding to A, B or H antigens of the histo-blood group family for all strains known to primarily infect European rabbits ( Oryctolagus cuniculus ), that have recently been classified as GI strains. Yet, we could not explain the emergence of virulence since similar glycan specificities were found between several pathogenic and non-pathogenic strains. By contrast, EBHSV, recently classified as GII.1, bound to terminal β-linked N-acetylglucosamine residues of O-glycans. Expression of these attachment factors in the upper respiratory and digestive tracts in three lagomorph species ( Oryctolagus cuniculus, Lepus europaeus and Sylvilagus floridanus ) showed species-specific patterns regarding the susceptibility to infection by these viruses, indicating that species-specific glycan expression is likely a major contributor to lagoviruses host specificity and range. IMPORTANCE Lagoviruses constitute a genus of the Caliciviridae family, comprising highly pathogenic viruses, RHDV and EBHSV, which infect rabbits and hares, respectively. Recently, non-pathogenic strains were discovered and new pathogenic strains have emerged. In addition, host

  9. Open-source micro-tensile testers via additive manufacturing for the mechanical characterization of thin films and papers.

    Science.gov (United States)

    Nandy, Krishanu; Collinson, David W; Scheftic, Charlie M; Brinson, L Catherine

    2018-01-01

    The cost of specialized scientific equipment can be high and with limited funding resources, researchers and students are often unable to access or purchase the ideal equipment for their projects. In the fields of materials science and mechanical engineering, fundamental equipment such as tensile testing devices can cost tens to hundreds of thousands of dollars. While a research lab often has access to a large-scale testing machine suitable for conventional samples, loading devices for meso- and micro-scale samples for in-situ testing with the myriad of microscopy tools are often hard to source and cost prohibitive. Open-source software has allowed for great strides in the reduction of costs associated with software development and open-source hardware and additive manufacturing have the potential to similarly reduce the costs of scientific equipment and increase the accessibility of scientific research. To investigate the feasibility of open-source hardware, a micro-tensile tester was designed with a freely accessible computer-aided design package and manufactured with a desktop 3D-printer and off-the-shelf components. To our knowledge this is one of the first demonstrations of a tensile tester with additively manufactured components for scientific research. The capabilities of the tensile tester were demonstrated by investigating the mechanical properties of Graphene Oxide (GO) paper and thin films. A 3D printed tensile tester was successfully used in conjunction with an atomic force microscope to provide one of the first quantitative measurements of GO thin film buckling under compression. The tensile tester was also used in conjunction with an atomic force microscope to observe the change in surface topology of a GO paper in response to increasing tensile strain. No significant change in surface topology was observed in contrast to prior hypotheses from the literature. Based on this result obtained with the new open source tensile stage we propose an

  10. Open-source micro-tensile testers via additive manufacturing for the mechanical characterization of thin films and papers.

    Directory of Open Access Journals (Sweden)

    Krishanu Nandy

    Full Text Available The cost of specialized scientific equipment can be high and with limited funding resources, researchers and students are often unable to access or purchase the ideal equipment for their projects. In the fields of materials science and mechanical engineering, fundamental equipment such as tensile testing devices can cost tens to hundreds of thousands of dollars. While a research lab often has access to a large-scale testing machine suitable for conventional samples, loading devices for meso- and micro-scale samples for in-situ testing with the myriad of microscopy tools are often hard to source and cost prohibitive. Open-source software has allowed for great strides in the reduction of costs associated with software development and open-source hardware and additive manufacturing have the potential to similarly reduce the costs of scientific equipment and increase the accessibility of scientific research. To investigate the feasibility of open-source hardware, a micro-tensile tester was designed with a freely accessible computer-aided design package and manufactured with a desktop 3D-printer and off-the-shelf components. To our knowledge this is one of the first demonstrations of a tensile tester with additively manufactured components for scientific research. The capabilities of the tensile tester were demonstrated by investigating the mechanical properties of Graphene Oxide (GO paper and thin films. A 3D printed tensile tester was successfully used in conjunction with an atomic force microscope to provide one of the first quantitative measurements of GO thin film buckling under compression. The tensile tester was also used in conjunction with an atomic force microscope to observe the change in surface topology of a GO paper in response to increasing tensile strain. No significant change in surface topology was observed in contrast to prior hypotheses from the literature. Based on this result obtained with the new open source tensile stage we

  11. Systems analysis of multiple regulator perturbations allows discovery of virulence factors in Salmonella

    Energy Technology Data Exchange (ETDEWEB)

    Yoon, Hyunjin; Ansong, Charles; McDermott, Jason E.; Gritsenko, Marina A.; Smith, Richard D.; Heffron, Fred; Adkins, Joshua N.

    2011-06-28

    Background: Systemic bacterial infections are highly regulated and complex processes that are orchestrated by numerous virulence factors. Genes that are coordinately controlled by the set of regulators required for systemic infection are potentially required for pathogenicity. Results: In this study we present a systems biology approach in which sample-matched multi-omic measurements of fourteen virulence-essential regulator mutants were coupled with computational network analysis to efficiently identify Salmonella virulence factors. Immunoblot experiments verified network-predicted virulence factors and a subset was determined to be secreted into the host cytoplasm, suggesting that they are virulence factors directly interacting with host cellular components. Two of these, SrfN and PagK2, were required for full mouse virulence and were shown to be translocated independent of either of the type III secretion systems in Salmonella or the type III injectisome-related flagellar mechanism. Conclusions: Integrating multi-omic datasets from Salmonella mutants lacking virulence regulators not only identified novel virulence factors but also defined a new class of translocated effectors involved in pathogenesis. The success of this strategy at discovery of known and novel virulence factors suggests that the approach may have applicability for other bacterial pathogens.

  12. Starch-Glycerol Based Edible Film and Effect of Rosella (Hibiscus Sabdariffa Linn Extract and Surimi Dumbo Catfish (Clarias gariepinus Addition on Its Mechanical Properties

    Directory of Open Access Journals (Sweden)

    Endaruji Sedyadi

    2016-10-01

    Full Text Available Effect of Rosella (Hibiscus Sabdariffa Linn Extract and Surimi Dumbo catfish (Clarias gariepinus addition on Starch-Based Edible Film-Glycerol Mechanical Properties has been done. The purpose of this study is to create an active environment-friendly packaging material. Surimi additions are intended to improve the mechanical properties of bioplastics and additions of Rosella extract intended as a bio-indicator of acidity. The method used was Solvent Casting. An amount of surimi and rosella extract varied to obtain the best mechanical properties. The results shows that the addition of surimi and rosella flower extract significantly effect the elongation of Edible films produced up to 27%.

  13. Delayed onset of tricuspid valve flow in repaired tetralogy of Fallot: an additional mechanism of diastolic dysfunction and interventricular dyssynchrony

    Directory of Open Access Journals (Sweden)

    Benson Lee N

    2011-08-01

    Full Text Available Abstract Background Diastolic dysfunction of the right ventricle (RV is common after repair of tetralogy of Fallot. While restrictive physiology in late diastole has been well known, dysfunction in early diastole has not been described. The present study sought to assess the prevalence and mechanism of early diastolic dysfunction of the RV defined as delayed onset of the tricuspid valve (TV flow after TOF repair. Methods The study population consisted of 31 children with repaired TOF (mean age ± SD, 12.3 ± 4.1 years who underwent postoperative cardiovascular magnetic resonance (CMR. The CMR protocol included simultaneous phase-contrast velocity mapping of the atrioventricular valves, which enabled direct comparison of the timing and patterns of tricuspid (TV and mitral (MV valve flow. The TV flow was defined to have delayed onset when its onset was > 20 ms later than the onset of the MV flow. The TV and MV flow from 14 normal children was used for comparison. The CMR results were correlated with the findings on echocardiography and electrocardiography. Result Delayed onset of the TV flow was observed in 16/31 patients and in none of the controls. The mean delay time was 64.81 ± 27.07 ms (8.7 ± 3.2% of R-R interval. The delay time correlated with the differences in duration of the TV and MV flow (55.94 ± 32.88 ms (r = 0.90, p Conclusions Early diastolic dysfunction with delayed onset of TV flow is common after TOF repair, and is associated with reduced RV ejection fraction. It is a further manifestation of interventricular dyssynchrony and represent an additional mechanism of ventricular diastolic dysfunction.

  14. Influence of Si addition on the microstructure and mechanical properties of Ti-35Nb alloy for applications in orthopedic implants.

    Science.gov (United States)

    Tavares, A M G; Ramos, W S; de Blas, J C G; Lopes, E S N; Caram, R; Batista, W W; Souza, S A

    2015-11-01

    In the development of new materials for orthopedic implants, special attention has been given to Ti alloys that show biocompatible alloy elements and that are capable of reducing the elastic modulus. Accordingly, Ti-Nb-Si alloys show great potential for application. Thus, this is a study on the microstructures and properties of Ti-35Nb-xSi alloys (x=0, 0.15, 0.35 and 0.55) (wt%) which were thermally treated and cooled under the following conditions: furnace cooling (FC), air cooling (AC), and water quenching (WQ). The results showed that Si addition is effective to reduce the density of omega precipitates making beta more stable, and to produce grain refinement. Silicides, referred as (Ti,Nb)3Si, were formed for alloys containing 0.55% Si, and its formation presumably occurred during the heating at 1000°C. In all cooling conditions, the hardness values increased with the increasing of Si content, as a result from the strong Si solid solution strengthening effect, while the elastic modulus underwent a continuous reduction due to the reduction of omega precipitates in beta matrix. Lower elastic moduli were observed in water-quenched alloys, which concentration of 0.15% Si was more effective in their reduction, with value around 65 GPa. Regarding Ti-35Nb-xSi alloys (x=0, 0.15 and 0.35), the "double yield point" phenomenon, which is typical of alloys with shape memory effect, was observed. The increase in Si concentration also produced an increase from 382 MPa to 540 MPa in the alloys' mechanical strength. Ti-35Nb-0.55Si alloy, however, showed brittle mechanical behavior which was related to the presence of silicides at the grain boundary. Copyright © 2015 Elsevier Ltd. All rights reserved.

  15. The effect of Sn addition on aging behavior and mechanical properties of wrought AZ80 magnesium alloy

    International Nuclear Information System (INIS)

    Jiang, Luyao; Zhang, Dingfei; Fan, Xiaowei; Guo, Fei; Hu, Guangshan; Xue, Hansong; Pan, Fusheng

    2015-01-01

    Highlights: • Thermodynamic and precipitation kinetics calculation was used to analyze aging hardening after addition of Sn. • Precipitation sequences were determined by the content of Sn element. • The microstructure of Mg 17 Al 12 discontinuous precipitates were influenced by Mg 2 Sn precipitates. - Abstract: The microstructure and mechanical properties of AZ80 wrought magnesium alloys with varying Sn contents (0, 1, 2 and 4 wt.%) have been studied by thermodynamic and precipitation kinetics calculation and examined using scanning electron microscopy (SEM), transmission electron microscopy (TEM), hardness test and uniaxial tensile test at room temperature in this paper. The results of thermodynamic and precipitation kinetics calculation showed that the precipitation sequences were determined by the content of Sn element. It was found that in the aging treatment of this work, Mg 17 Al 12 phase precipitated sooner than Mg 2 Sn phase in the alloys with less than 1.72 wt.% Sn and there was a contrary precipitation sequence of these two phases in the alloys with more than 1.72 wt.% Sn. Experimental results were in agreement with those of calculation. According to SEM and TEM observation, Sn promoted precipitation of Mg 17 Al 12 on aging temperature, however the preferential Mg 2 Sn phase suppressed discontinuous Mg 17 Al 12 precipitates by hindering the growth of these in their growth direction. AZ80 with 1–2 wt.% Sn as-aged alloys exhibited outstanding mechanical property that UTS, YS and EL were ∼420 MPa, ∼290 MPa and ∼5%, respectively

  16. [Analysis of virulence factors of Porphyromonas endodontalis based on comparative proteomics technique].

    Science.gov (United States)

    Li, H; Ji, H; Wu, S S; Hou, B X

    2016-12-09

    Objective: To analyze the protein expression profile and the potential virulence factors of Porphyromonas endodontalis (Pe) via comparison with that of two strains of Porphyromonas gingivalis (Pg) with high and low virulences, respectively. Methods: Whole cell comparative proteomics of Pe ATCC35406 was examined and compared with that of high virulent strain Pg W83 andlow virulent strain Pg ATCC33277, respectively. Isobaric tags for relative and absolute quantitation (iTRAQ) combined with nano liquid chromatography-tandem mass spectrometry (Nano-LC-MS/MS) were adopted to identify and quantitate the proteins of Pe and two strains of Pg with various virulences by using the methods of isotopically labeled peptides, mass spectrometric detection and bioinformatics analysis. The biological functions of similar proteins expressed by Pe ATCC35406 and two strains of Pg were quantified and analyzed. Results: Totally 1 210 proteins were identified while Pe compared with Pg W83. There were 130 proteins (10.74% of the total proteins) expressed similarly, including 89 known functional proteins and 41 proteins of unknown functions. Totally 1 223 proteins were identified when Pe compared with Pg ATCC33277. There were 110 proteins (8.99% of the total proteins) expressed similarly, including 72 known functional proteins and 38 proteins of unknown functions. The similarly expressed proteins in Pe and Pg strains with various virulences mainly focused on catalytic activity and binding function, including recombination activation gene (RagA), lipoprotein, chaperonin Dnak, Clp family proteins (ClpC and ClpX) and various iron-binding proteins. They were involved in metabolism and cellular processes. In addition, the type and number of similar virulence proteins between Pe and high virulence Pg were higher than those between Pe and low virulence Pg. Conclusions: Lipoprotein, oxygen resistance protein, iron binding protein were probably the potential virulence factors of Pe ATCC35406. It was

  17. Nanometer, submicron and micron sized aluminum powder prepared by semi-solid mechanical stirring method with addition of ceramic particles

    International Nuclear Information System (INIS)

    Qin, X.H.; Jiang, D.L.; Dong, S.M.

    2004-01-01

    Composite powder, which is a mixture of Al/Al 2 O 3 composite particles and nanometer, submicron and micron sized aluminum powder, was prepared by semi-solid mechanical stirring method with addition of Al 2 O 3 ceramic particles. The ceramic particles have an average diameter of 80 μm and a volume fraction of 15% in the slurry. The methods used to measure the size distribution of particles greater than 50 μm and less than 50 μm were sieve analysis and photosedimentation, respectively. The surface morphology and transverse sections of the composite powder of different sizes were examined by scanning electron microscope (SEM), optical microscope and auger electron spectroscopy (AES). The results indicate that the composite powder prepared in present work have a wide size distribution ranging from less than 50-900 μm, and the aluminum particles and Al/Al 2 O 3 composite particles are separated and isolated. The particles greater than 200 μm and less than 50 μm are almost pure aluminum powder. The rate of conversion of ingot aluminum into particles less than 1 μm containing nanometer and submicron sizes is 1.777 wt.% in this work. The aluminum powder of different sizes has different shape and surface morphology, quasi-spherical in shape with rough surface for aluminum particles of micron scale, irregular in shape for aluminum particles of submicron scale, and quite close to a globular or an excellent globular in shape for aluminum particles of nanometer size. On the other hand, the surface of ceramic particle was coated by aluminum particles with maximum thickness less than 10 μm containing nanometer and submicron sizes as a single layer. It is suggested that the surface of ceramic particles can provide more nucleation sites for solidification of liquid aluminum and the nucleation of liquid aluminum can take place readily, grow and adhere on the surface of ceramic particles, although it is poorly wetted by the liquid aluminum and the semi-solid slurry can

  18. Bacterial Prostatitis: Bacterial Virulence, Clinical Outcomes, and New Directions.

    Science.gov (United States)

    Krieger, John N; Thumbikat, Praveen

    2016-02-01

    Four prostatitis syndromes are recognized clinically: acute bacterial prostatitis, chronic bacterial prostatitis, chronic prostatitis/chronic pelvic pain syndrome, and asymptomatic prostatitis. Because Escherichia coli represents the most common cause of bacterial prostatitis, we investigated the importance of bacterial virulence factors and antimicrobial resistance in E. coli strains causing prostatitis and the potential association of these characteristics with clinical outcomes. A structured literature review revealed that we have limited understanding of the virulence-associated characteristics of E. coli causing acute prostatitis. Therefore, we completed a comprehensive microbiological and molecular investigation of a unique strain collection isolated from healthy young men. We also considered new data from an animal model system suggesting certain E. coli might prove important in the etiology of chronic prostatitis/chronic pelvic pain syndrome. Our human data suggest that E. coli needs multiple pathogenicity-associated traits to overcome anatomic and immune responses in healthy young men without urological risk factors. The phylogenetic background and accumulation of an exceptional repertoire of extraintestinal pathogenic virulence-associated genes indicate that these E. coli strains belong to a highly virulent subset of uropathogenic variants. In contrast, antibiotic resistance confers little added advantage to E. coli strains in these healthy outpatients. Our animal model data also suggest that certain pathogenic E. coli may be important in the etiology of chronic prostatitis/chronic pelvic pain syndrome through mechanisms that are dependent on the host genetic background and the virulence of the bacterial strain.

  19. Genetic Regulation of Virulence and Antibiotic Resistance in Acinetobacter baumannii

    Science.gov (United States)

    Kröger, Carsten; Kary, Stefani C.; Schauer, Kristina; Cameron, Andrew D. S.

    2016-01-01

    Multidrug resistant microorganisms are forecast to become the single biggest challenge to medical care in the 21st century. Over the last decades, members of the genus Acinetobacter have emerged as bacterial opportunistic pathogens, in particular as challenging nosocomial pathogens because of the rapid evolution of antimicrobial resistances. Although we lack fundamental biological insight into virulence mechanisms, an increasing number of researchers are working to identify virulence factors and to study antibiotic resistance. Here, we review current knowledge regarding the regulation of virulence genes and antibiotic resistance in Acinetobacter baumannii. A survey of the two-component systems AdeRS, BaeSR, GacSA and PmrAB explains how each contributes to antibiotic resistance and virulence gene expression, while BfmRS regulates cell envelope structures important for pathogen persistence. A. baumannii uses the transcription factors Fur and Zur to sense iron or zinc depletion and upregulate genes for metal scavenging as a critical survival tool in an animal host. Quorum sensing, nucleoid-associated proteins, and non-classical transcription factors such as AtfA and small regulatory RNAs are discussed in the context of virulence and antibiotic resistance. PMID:28036056

  20. The link between morphotype transition and virulence in Cryptococcus neoformans.

    Directory of Open Access Journals (Sweden)

    Linqi Wang

    Full Text Available Cryptococcus neoformans is a ubiquitous human fungal pathogen. This pathogen can undergo morphotype transition between the yeast and the filamentous form and such morphological transition has been implicated in virulence for decades. Morphotype transition is typically observed during mating, which is governed by pheromone signaling. Paradoxically, components specific to the pheromone signaling pathways play no or minimal direct roles in virulence. Thus, the link between morphotype transition and virulence and the underlying molecular mechanism remain elusive. Here, we demonstrate that filamentation can occur independent of pheromone signaling and mating, and both mating-dependent and mating-independent morphotype transition require the transcription factor Znf2. High expression of Znf2 is necessary and sufficient to initiate and maintain sex-independent filamentous growth under host-relevant conditions in vitro and during infection. Importantly, ZNF2 overexpression abolishes fungal virulence in murine models of cryptococcosis. Thus, Znf2 bridges the sex-independent morphotype transition and fungal pathogenicity. The impacts of Znf2 on morphological switch and pathogenicity are at least partly mediated through its effects on cell adhesion property. Cfl1, a Znf2 downstream factor, regulates morphogenesis, cell adhesion, biofilm formation, and virulence. Cfl1 is the first adhesin discovered in the phylum Basidiomycota of the Kingdom Fungi. Together with previous findings in other eukaryotic pathogens, our findings support a convergent evolution of plasticity in morphology and its impact on cell adhesion as a critical adaptive trait for pathogenesis.

  1. The Role of Antibiotics in Modulating Virulence in Staphylococcus aureus.

    Science.gov (United States)

    Hodille, Elisabeth; Rose, Warren; Diep, Binh An; Goutelle, Sylvain; Lina, Gerard; Dumitrescu, Oana

    2017-10-01

    Staphylococcus aureus is often involved in severe infections, in which the effects of bacterial virulence factors have great importance. Antistaphylococcal regimens should take into account the different effects of antibacterial agents on the expression of virulence factors and on the host's immune response. A PubMed literature search was performed to select relevant articles on the effects of antibiotics on staphylococcal toxin production and on the host immune response. Information was sorted according to the methods used for data acquisition (bacterial strains, growth models, and antibiotic concentrations) and the assays used for readout generation. The reported mechanisms underlying S. aureus virulence modulation by antibiotics were reviewed. The relevance of in vitro observations is discussed in relation to animal model data and to clinical evidence extracted from case reports and recommendations on the management of toxin-related staphylococcal diseases. Most in vitro data point to a decreased level of virulence expression upon treatment with ribosomally active antibiotics (linezolid and clindamycin), while cell wall-active antibiotics (beta-lactams) mainly increase exotoxin production. In vivo studies confirmed the suppressive effect of clindamycin and linezolid on virulence expression, supporting their utilization as a valuable management strategy to improve patient outcomes in cases of toxin-associated staphylococcal disease. Copyright © 2017 American Society for Microbiology.

  2. Casein Films: The Effects of Formulation, Environmental Conditions and the Addition of Citric Pectin on the Structure and Mechanical Properties

    Directory of Open Access Journals (Sweden)

    Laetitia M. Bonnaillie

    2014-07-01

    Full Text Available Thin casein films for food packaging applications reportedly possess good strength and low oxygen permeability, but low elasticity and high sensitivity to moisture. Modifying the films to target specific behaviors depending on environmental conditions can enable a variety of commercial applications for casein-based films. The mechanical properties of solvent-cast (15% solids calcium-caseinate/glycerol films (CaCas:Gly ratio of 3:1 were characterized as a function of processing and environmental conditions, including film thickness, solution formulation and ambient humidity (from 22% to 70% relative humidity (RH at ~20 °C. At constant RH, the elongation at break (EAB had a strong positive dependence on the film thickness. When RH increased, the tensile strength (TS and modulus (E decreased approximately linearly, while EAB increased. From 0.05% to 1% (w/w of citric pectin (CP was then incorporated into CaCas/Gly films following seven different formulations (mixing sequences, to alter the protein network and to evaluate the effects of CP on the tensile properties of CaCas/Gly/CP films. At constant film thickness and ~60% RH, the addition of 0.1% or 1.0% CP to the films considerably increased or decreased EAB, TS and E in different directions and to different extents, depending on the formulation, while optical micrographs also showed vastly differing network configurations, suggesting complex formulation- and stoichiometry-dependent casein-pectin interactions within the dried films. Depending on the desired film properties and utilization conditions, pectin may be a useful addition to casein film formulations for food packaging applications.

  3. Blue light treatment of Pseudomonas aeruginosa: Strong bactericidal activity, synergism with antibiotics and inactivation of virulence factors.

    Science.gov (United States)

    Fila, Grzegorz; Kawiak, Anna; Grinholc, Mariusz Stanislaw

    2017-08-18

    Pseudomonas aeruginosa is among the most common pathogens responsible for both acute and chronic infections of high incidence and severity. Additionally, P. aeruginosa resistance to conventional antimicrobials has increased rapidly over the past decade. Therefore, it is crucial to explore new therapeutic options, particularly options that specifically target the pathogenic mechanisms of this microbe. The ability of a pathogenic bacterium to cause disease is dependent upon the production of agents termed 'virulence factors', and approaches to mitigate these agents have gained increasing attention as new antibacterial strategies. Although blue light irradiation is a promising alternative approach, only limited and preliminary studies have described its effect on virulence factors. The current study aimed to investigate the effects of lethal and sub-lethal doses of blue light treatment (BLT) on P. aeruginosa virulence factors. We analyzed the inhibitory effects of blue light irradiation on the production/activity of several virulence factors. Lethal BLT inhibited the activity of pyocyanin, staphylolysin, pseudolysin and other proteases, but sub-lethal BLT did not affect the production/expression of proteases, phospholipases, and flagella- or type IV pili-associated motility. Moreover, a eukaryotic cytotoxicity test confirmed the decreased toxicity of blue light-treated extracellular P. aeruginosa fractions. Finally, the increased antimicrobial susceptibility of P. aeruginosa treated with sequential doses of sub-lethal BLT was demonstrated with a checkerboard test. Thus, this work provides evidence-based proof of the susceptibility of drug-resistant P. aeruginosa to BLT-mediated killing, accompanied by virulence factor reduction, and describes the synergy between antibiotics and sub-lethal BLT.

  4. Effect of location on microstructure and mechanical properties of additive layer manufactured Inconel 625 using gas tungsten arc welding

    Energy Technology Data Exchange (ETDEWEB)

    Wang, J.F. [State Key Laboratory of Advanced Welding and Joining, Harbin Institute of Technology, Harbin 150001 (China); Shandong Provincial Key Laboratory of Special Welding Technology, Harbin Institute of Technology at Weihai, Weihai 264209 (China); Sun, Q.J., E-mail: qjsun@hit.edu.cn [State Key Laboratory of Advanced Welding and Joining, Harbin Institute of Technology, Harbin 150001 (China); Shandong Provincial Key Laboratory of Special Welding Technology, Harbin Institute of Technology at Weihai, Weihai 264209 (China); Wang, H. [State Key Laboratory of Advanced Welding and Joining, Harbin Institute of Technology, Harbin 150001 (China); Liu, J.P. [Shandong Provincial Key Laboratory of Special Welding Technology, Harbin Institute of Technology at Weihai, Weihai 264209 (China); China Nuclear Industry 23 Construction Co., Ltd., Beijing 101300 (China); Feng, J.C. [State Key Laboratory of Advanced Welding and Joining, Harbin Institute of Technology, Harbin 150001 (China); Shandong Provincial Key Laboratory of Special Welding Technology, Harbin Institute of Technology at Weihai, Weihai 264209 (China)

    2016-10-31

    Additive layer manufacturing (ALM), using gas tungsten arc welding (GTAW) as heat source, is a promising technology in producing Inconel 625 components due to significant cost savings, high deposition rate and convenience of processing. With the purpose of revealing how microstructure and mechanical properties are affected by the location within the manufactured wall component, the present study has been carried out. The manufactured Inconel 625 consists of cellular grains without secondary dendrites in the near-substrate region, columnar dendrites structure oriented upwards in the layer bands, followed by the transition from directional dendrites to equiaxed grain in the top region. With the increase in deposited height, segregation behavior of alloying elements Nb and Mo constantly strengthens with maximal evolution in the top region. The primary dendrite arm spacing has a well coherence with the content of Laves phase. The microhardness and tensile strength show obvious variation in different regions. The microhardness and tensile strength of near-substrate region are superior to that of layer bands and top region. The results are further explained in detail through the weld pool behavior and temperature field measurement.

  5. Investigation of thermal, mechanical and magnetic behaviors of the Cu-11%Al alloy with Ag and Mn additions

    International Nuclear Information System (INIS)

    Silva, R.A.G.; Paganotti, A.; Gama, S.; Adorno, A.T.; Carvalho, T.M.; Santos, C.M.A.

    2013-01-01

    The investigation of thermal, mechanical and magnetic behaviors of the Cu-11%Al, Cu-11%Al-3%Ag, Cu-11%Al-10%Mn and Cu-11%Al-10%Mn-3%Ag alloys was made using microhardness measurements, differential scanning calorimetry, X-ray diffractometry, scanning electron microscopy, energy dispersion X-ray spectroscopy and magnetic moment change with applied field measurement. The results indicated that the Mn addition changes the phase stability range, the microhardness values and makes undetectable the eutectoid reaction in annealed Cu-11%Al and Cu-11%Al-3%Ag alloys while the presence of Ag does not modify the phase transformation sequence neither microhardness values of the annealed Cu-11%Al and Cu-11%Al-10%Mn alloys, but it increases the magnetic moment of this latter at about 2.7 times and decreases the rates of eutectoid and peritectoid reactions of the former. - Highlights: ► The microstructure of Cu-Al alloy is modified in the Ag presence. ► (α + γ) phase is stabilized down to room temperature when Ag is added to Cu-Al alloy. ► Ag-rich phase modifies the magnetic characteristics of Cu–Al–Mn alloy.

  6. Effect of location on microstructure and mechanical properties of additive layer manufactured Inconel 625 using gas tungsten arc welding

    International Nuclear Information System (INIS)

    Wang, J.F.; Sun, Q.J.; Wang, H.; Liu, J.P.; Feng, J.C.

    2016-01-01

    Additive layer manufacturing (ALM), using gas tungsten arc welding (GTAW) as heat source, is a promising technology in producing Inconel 625 components due to significant cost savings, high deposition rate and convenience of processing. With the purpose of revealing how microstructure and mechanical properties are affected by the location within the manufactured wall component, the present study has been carried out. The manufactured Inconel 625 consists of cellular grains without secondary dendrites in the near-substrate region, columnar dendrites structure oriented upwards in the layer bands, followed by the transition from directional dendrites to equiaxed grain in the top region. With the increase in deposited height, segregation behavior of alloying elements Nb and Mo constantly strengthens with maximal evolution in the top region. The primary dendrite arm spacing has a well coherence with the content of Laves phase. The microhardness and tensile strength show obvious variation in different regions. The microhardness and tensile strength of near-substrate region are superior to that of layer bands and top region. The results are further explained in detail through the weld pool behavior and temperature field measurement.

  7. Microstructure characterization and mechanical behavior of laser additive manufactured ultrahigh-strength AerMet100 steel

    International Nuclear Information System (INIS)

    Ran, Xianzhe; Liu, Dong; Li, An; Wang, Huaming; Tang, Haibo; Cheng, Xu

    2016-01-01

    Ultrahigh-strength AerMet100 steel thick plate was fabricated by laser additive manufacturing process. The as-deposited microstructures of the test steel were characterized using optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The mechanical properties were then examined using vickers-hardness test and tensile test. Results indicate that the as-deposited microstructures of the steel mainly consist of grain boundary allotriomorphic ferrite (GBA), grain interior irregular proeutectoid ferrite, plate-like upper bainite, needle-like lower bainite and retained austenite, which result in a good strength and some ductility anisotropy. The low deformation compatibility of specimen at the transverse direction (perpendicular to the deposition direction) mainly ascribes to the poor cracking resistance of the prior-austenite columnar grain boundary with coarse GBA phases. Compared to the almost intergranular cracking taken place in the transverse tensile specimen, the fracture mode of the longitudinal tensile specimen is a mixed mode of the predominant transgranular cracking and minor intergranular cracking.

  8. Microstructure-mechanical property relationships for Al-Cu-Li-Zr alloys with minor additions of cadmium, indium or tin

    Science.gov (United States)

    Blackburn, L. B.; Starke, E. A., Jr.

    1989-01-01

    Minor amounts of cadmium, indium or tin were added to a baseline alloy with the nominal composition of Al-2.4Cu-2.4Li-0.15Zr. These elements were added in an attempt to increase the age-hardening response of the material such that high strengths could be achieved through heat-treatment alone, without the need for intermediate mechanical working. The alloy variant containing indium achieved a higher peak hardness in comparison to the other alloy variations, including the baseline material, when aged at temperatures ranging from 160 C to 190 C. Tensile tests on specimens peak-aged at 160 indicated the yield strength of the indium-bearing alloy increased by approximately 15 percent compared to that of the peak-aged baseline alloy. In addition, the yield strength obtained in the indium-bearing alloy was comparable to that reported for similar baseline material subjected to a 6 percent stretch prior to peak-aging at 190 C. The higher strength levels obtaied for the indium-bearing alloy are attributed to increased number densities and homogeneity of both the T1 and theta-prime phases, as determined by TEM studies.

  9. Microstructure characterization and mechanical behavior of laser additive manufactured ultrahigh-strength AerMet100 steel

    Energy Technology Data Exchange (ETDEWEB)

    Ran, Xianzhe [National Engineering Laboratory of Additive Manufacturing for Large Metallic Components, 37 Xueyuan Road, Beijing 100191 (China); School of Materials Science and Engineering, Beihang University, 37 Xueyuan Road, Beijing 100191 (China); Liu, Dong [National Engineering Laboratory of Additive Manufacturing for Large Metallic Components, 37 Xueyuan Road, Beijing 100191 (China); Engineering Research Center of Ministry of Education on Laser Direct Manufacturing for Large Metallic Component, 37 Xueyuan Road, Beijing 100191 (China); School of Materials Science and Engineering, Beihang University, 37 Xueyuan Road, Beijing 100191 (China); Li, An, E-mail: li_an@buaa.edu.cn [National Engineering Laboratory of Additive Manufacturing for Large Metallic Components, 37 Xueyuan Road, Beijing 100191 (China); Engineering Research Center of Ministry of Education on Laser Direct Manufacturing for Large Metallic Component, 37 Xueyuan Road, Beijing 100191 (China); School of Materials Science and Engineering, Beihang University, 37 Xueyuan Road, Beijing 100191 (China); Wang, Huaming; Tang, Haibo [National Engineering Laboratory of Additive Manufacturing for Large Metallic Components, 37 Xueyuan Road, Beijing 100191 (China); Engineering Research Center of Ministry of Education on Laser Direct Manufacturing for Large Metallic Component, 37 Xueyuan Road, Beijing 100191 (China); School of Materials Science and Engineering, Beihang University, 37 Xueyuan Road, Beijing 100191 (China); Cheng, Xu [School of Materials Science and Engineering, Beihang University, 37 Xueyuan Road, Beijing 100191 (China)

    2016-04-29

    Ultrahigh-strength AerMet100 steel thick plate was fabricated by laser additive manufacturing process. The as-deposited microstructures of the test steel were characterized using optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The mechanical properties were then examined using vickers-hardness test and tensile test. Results indicate that the as-deposited microstructures of the steel mainly consist of grain boundary allotriomorphic ferrite (GBA), grain interior irregular proeutectoid ferrite, plate-like upper bainite, needle-like lower bainite and retained austenite, which result in a good strength and some ductility anisotropy. The low deformation compatibility of specimen at the transverse direction (perpendicular to the deposition direction) mainly ascribes to the poor cracking resistance of the prior-austenite columnar grain boundary with coarse GBA phases. Compared to the almost intergranular cracking taken place in the transverse tensile specimen, the fracture mode of the longitudinal tensile specimen is a mixed mode of the predominant transgranular cracking and minor intergranular cracking.

  10. Influence of MWCNTs addition on mechanical and thermal behaviour of epoxy/kenaf multi-scale nanocomposite

    Science.gov (United States)

    Noor, N. A. M.; Razak, J. A.; Ismail, S.; Mohamad, N.; Yaakob, M. Y.; Theng, T. H.

    2017-06-01

    This research was conducted to develop kenaf reinforced epoxy/MWCNTs multi-scale composite using kenaf fibre and MWCNTs as the reinforcement in epoxy as the hosted matrix. The composites were produced by using a combination of hand lay-up and vacuum bagging process. The selection of optimum composition of epoxy-MWCNTs is based on the MWCNTs loading and the resulted mixture viscosity. Lower resin viscosity is required to allow good wetting and interaction between matrix and filler, which will yielded superior final performance of the fabricated composites. Therefore, different loading of MWCNTs (0.0 wt. %, 0.5 wt. %, 1.0 wt. %, 3.0 wt. %, 5.0 wt. %, 7.0 wt. %) were used to investigate the mechanical and thermal properties of the composites. As a result, the epoxy/kenaf/MWCNTs multi-scale composite at 1.0 wt. % of MWCNTs addition had yielded substantial improvement by 15.54 % in tensile strength and 90.54 % in fracture toughness. Besides, the fracture surface morphology of the selected samples were analysed via scanning electron microscopy (SEM) observation to further support the reinforcement characteristic of epoxy/kenaf/MWCNTs multi-scale composite.

  11. Influence of Li₂Sb Additions on Microstructure and Mechanical Properties of Al-20Mg₂Si Alloy.

    Science.gov (United States)

    Yu, Hong-Chen; Wang, Hui-Yuan; Chen, Lei; Zha, Min; Wang, Cheng; Li, Chao; Jiang, Qi-Chuan

    2016-03-29

    It is found that Li₂Sb compound can act as the nucleus of primary Mg₂Si during solidification, by which the particle size of primary Mg₂Si decreased from ~300 to ~15-25 μm. Owing to the synergistic effect of the Li₂Sb nucleus and adsorption-poisoning of Li atoms, the effect of complex modification of Li-Sb on primary Mg₂Si was better than that of single modification of Li or Sb. When Li-Sb content increased from 0 to 0.2 and further to 0.5 wt.%, coarse dendrite changed to defective truncated octahedron and finally to perfect truncated octahedral shape. With the addition of Li and Sb, ultimate compression strength (UCS) of Al-20Mg₂Si alloys increased from ~283 to ~341 MPa and the yield strength (YS) at 0.2% offset increased from ~112 to ~179 MPa while almost no change was seen in the uniform elongation. Our study offers a simple method to control the morphology and size of primary Mg₂Si, which will inspire developing new Al-Mg-Si alloys with improved mechanical properties.

  12. A novel plasmid-encoded serotype conversion mechanism through addition of phosphoethanolamine to the O-antigen of Shigella flexneri.

    Directory of Open Access Journals (Sweden)

    Qiangzheng Sun

    Full Text Available Shigella flexneri is the major pathogen causing bacillary dysentery in developing countries. S. flexneri is divided into at least 16 serotypes based on the combination of antigenic determinants present in the O-antigen. All the serotypes (except for serotype 6 share a basic O-unit containing one N-acetyl-d-glucosamine and three l-rhamnose residues, whereas differences between the serotypes are conferred by phage-encoded glucosylation and/or O-acetylation. Serotype Xv is a newly emerged and the most prevalent serotype in China, which can agglutinate with both MASF IV-1 and 7,8 monoclonal antibodies. The factor responsible for the presence of MASF IV-1 (E1037 epitope has not yet been identified. In this study, we analyzed the LPS structure of serotype Xv strains and found that the MASF IV-1 positive phenotype depends on an O-antigen modification with a phosphoethanolamine (PEtN group attached at position 3 of one of the rhamnose residues. A plasmid carried gene, lpt-O (LPS phosphoethanolamine transferase for O-antigen, mediates the addition of PEtN for serotype Xv and other MASF IV-1 positive strains. These findings reveal a novel serotype conversion mechanism in S. flexneri and show the necessity of further extension of the serotype classification scheme recognizing the MASF IV-1 positive strains as distinctive subtypes.

  13. Lead extraction from Cathode Ray Tube (CRT) funnel glass: Reaction mechanisms in thermal reduction with addition of carbon (C).

    Science.gov (United States)

    Lu, Xingwen; Ning, Xun-An; Chen, Da; Chuang, Kui-Hao; Shih, Kaimin; Wang, Fei

    2018-06-01

    This study quantitatively determined the extraction of lead from CRT funnel glass and examined the mechanisms of thermally reducing lead in the products of sintering Pb-glass with carbon in the pre-heated furnace. The experimentally derived results indicate that a 90.3 wt% lead extraction efficiency can be achieved with 20 wt% of C addition at 950 °C for 3 min under air. The formation of viscous semi-liquid glass blocked the oxygen supply between the interaction of C and Pb-glass, and was highly effective for the extraction of metallic Pb. A maximum of 87.3% lead recover was obtained with a C to Na 2 CO 3 ratio of 1/3 at 1200 °C. The decrease of C/Na 2 CO 3 ratio enhanced the metallic lead recovery by increasing the glass viscosity for effective sedimentation of metallic lead in the bottom. However, with the further increase of temperature and treatment time, re-vitrification of lead back to silicate-glass matrix was detected in both Pb-glass/C and Pb-glass/C/Na 2 CO 3 systems. The findings indicated that with proper controls, using C as an inexpensive reagent can effectively reduce treatment time and energy, which is crucial to a waste-to-resource technology for economically recovering lead from the waste CRT glass. Copyright © 2018 Elsevier Ltd. All rights reserved.

  14. Circumventing Y. pestis Virulence by Early Recruitment of Neutrophils to the Lungs during Pneumonic Plague.

    Directory of Open Access Journals (Sweden)

    Yaron Vagima

    2015-05-01

    Full Text Available Pneumonic plague is a fatal disease caused by Yersinia pestis that is associated with a delayed immune response in the lungs. Because neutrophils are the first immune cells recruited to sites of infection, we investigated the mechanisms responsible for their delayed homing to the lung. During the first 24 hr after pulmonary infection with a fully virulent Y. pestis strain, no significant changes were observed in the lungs in the levels of neutrophils infiltrate, expression of adhesion molecules, or the expression of the major neutrophil chemoattractants keratinocyte cell-derived chemokine (KC, macrophage inflammatory protein 2 (MIP-2 and granulocyte colony stimulating factor (G-CSF. In contrast, early induction of chemokines, rapid neutrophil infiltration and a reduced bacterial burden were observed in the lungs of mice infected with an avirulent Y. pestis strain. In vitro infection of lung-derived cell-lines with a YopJ mutant revealed the involvement of YopJ in the inhibition of chemoattractants expression. However, the recruitment of neutrophils to the lungs of mice infected with the mutant was still delayed and associated with rapid bacterial propagation and mortality. Interestingly, whereas KC, MIP-2 and G-CSF mRNA levels in the lungs were up-regulated early after infection with the mutant, their protein levels remained constant, suggesting that Y. pestis may employ additional mechanisms to suppress early chemoattractants induction in the lung. It therefore seems that prevention of the early influx of neutrophils to the lungs is of major importance for Y. pestis virulence. Indeed, pulmonary instillation of KC and MIP-2 to G-CSF-treated mice infected with Y. pestis led to rapid homing of neutrophils to the lung followed by a reduction in bacterial counts at 24 hr post-infection and improved survival rates. These observations shed new light on the virulence mechanisms of Y. pestis during pneumonic plague, and have implications for the

  15. Effect of temperature and aluminium additions on the mechanical properties of the 13% chromium ferrite stainless steels

    International Nuclear Information System (INIS)

    Martins, S.

    1975-01-01

    The potential interest of the ferritic stainless steels as component materials for nuclear power reactors led to investigate how aluminium influences the mechanical properties of 13% chromium ferritic stainless steels between room temperature and about 700 0 C. Nominal 13% chromium and 0.04 to 0.08% carbon ferritic stainless steels containing 0, 0.13, 2.19 and 4.15% aluminium, respectively, were obtained by vacuum remelting of a commercial martensitic-ferritic stainless steel and suitable additions of aluminium. After successive rolling operations and recrystallizations performed in order to obtain final 0.5 mm thick sheets with similar average grain sizes the specimens of the above mentioned steels were tested in a tensile test Instron machine, with a constant strain rate (approximately equal to 1.6 x 10 -3 min -1 ), at room temperature, 140, 265, 415, 565 and 715 0 C. The results obtained show that strengthening by aluminium is strongly temperature dependent. At 265 0 C all the steels presentes serrated plastic deformation (Portevin-Le Chatelier effect), which is attributed to interactions of the interstitial and substitutional solute atoms with dislocations in the body centered cubic structure. Flow stress drops were still observed at 465 0 C, although the tests performed at 565 and 715 0 C showed work-softening of the materials and total absence of serrations. Stress relaxation tests at room temperature yielded values of the apparent activation volumes, which are scattered between about 100 and 130 b 3 (b-Burgers vector), being almost constant with stress, strain and aluminium content. Therefore, although aluminium appreciably strengthens the 13% chromium steel, the behaviour summarized suggests that the mechanism controlling plastic deformation at room temperature is the same for all the tested steels, the values of the apparent activitation volumes being probably determined by the interstitial content. Stress relaxation tests at 20, 75, 140 and 265 0 C for

  16. Effect of Different Chromium Additions on the Microstructure and Mechanical Properties of Multipass Weld Joint of Duplex Stainless Steel

    Science.gov (United States)

    Kang, Dong Hoon; Lee, Hae Woo

    2012-12-01

    The correlation between the mechanical properties and ferrite volume fraction (approximately 40, 50, and 60 Ferrite Number [FN]) in duplex stainless steel weld metals were investigated by changing the Cr content in filler wires with a flux-cored arc-welding (FCAW) process. The interpass temperature was thoroughly maintained under a maximum of 423 K (150 °C), and the heat input was also sustained at a level under 15 KJ/cm in order to minimize defects. The microstructure examination demonstrated that the δ-ferrite volume fraction in the deposited metals increased as the Cr/Ni equivalent ratio increased, and consequently, chromium nitride (Cr2N) precipitation was prone to occur in the ferrite domains due to low solubility of nitrogen in this phase. Thus, more dislocations are pinned by the precipitates, thereby lowering the mobility of the dislocations. Not only can this lead to the strength improvement, but also it can accentuate embrittlement of the weld metal at subzero temperature. Additionally, the solid-solution strengthening by an increase of Cr and Mo content in austenite phase depending on the reduction of austenite proportion also made an impact on the increase of the tensile and yield strength. On the other hand, the impact test (at 293 K, 223 K, and 173 K [20 °C, -50 °C, and -100 °C]) showed that the specimen containing about 40 to 50 FN had the best result. The absorbed energy of about 40 to 50 J sufficiently satisfied the requirements for industrial applications at 223 K (-50 °C), while the ductile-to-brittle transition behavior exhibited in weldment containing 60 FN. As the test temperature decreased under 223 K (-50 °C), a narrow and deep dimple was transformed into a wide and shallow dimple, and a significant portion of the fracture surface was occupied by a flat cleavage facet with river patterns.

  17. Effect of Nb additions on the microstructure, thermal stability and mechanical behavior of high pressure Zr phases under ambient conditions

    International Nuclear Information System (INIS)

    Zhilyaev, A.P.; Sabirov, I.; Gonzalez-Doncel, G.; Molina-Aldareguia, J.; Srinivasarao, B.; Perez-Prado, M.T.

    2011-01-01

    Research highlights: → We analyze the influence of Nb additions on the shear-induced α → ω → β phase transformations in pure Zr by high pressure torsion (HPT). → Nb reduces the transition pressures and increases the transformation kinetics. → High pressure phases are retained under ambient conditions due to the presence of an internal stress. → Post-HPT annealing allows to fabricate bimodal/biphase nanostructures with enhanced mechanical behavior. - Abstract: This paper analyzes the influence of Nb on the shear-induced α → ω → β transformation taking place when processing Zr by high pressure torsion (HPT) under suitable conditions of pressure and shear. With that purpose, pure Zr and Zr-2.5%Nb were processed by HPT at room temperature and at pressures ranging from 0.25 to 6 GPa using 5 anvil turns. Nb causes a further reduction of the transition pressures, which are already lower when applying shear besides pressure. Thus, the transition pressure to the β phase is reduced at least 100 times in the Zr-Nb alloy. Alloying with Nb decreases the grain size of the transformed phases, significantly enhances their thermal stability and increases their UTS and elongation to failure. Selected post-HPT annealing treatments lead to the development of very tough, multiphase Zr and Zr-Nb with bimodal grain size distributions. The retention of the high pressure phases under ambient conditions is explained by the development of a high internal stress during processing. This stress is measured by synchrotron radiation diffraction at HZB-BESSY II. It is proposed that the presence of Nb reduces the internal stress level required for the retention of the high pressure phases.

  18. Genes involved in virulence of the entomopathogenic fungus Beauveria bassiana.

    Science.gov (United States)

    Valero-Jiménez, Claudio A; Wiegers, Harm; Zwaan, Bas J; Koenraadt, Constantianus J M; van Kan, Jan A L

    2016-01-01

    Pest insects cause severe damage to global crop production and pose a threat to human health by transmitting diseases. Traditionally, chemical pesticides (insecticides) have been used to control such pests and have proven to be effective only for a limited amount of time because of the rapid spread of genetic insecticide resistance. The basis of this resistance is mostly caused by (co)dominant mutations in single genes, which explains why insecticide use alone is an unsustainable solution. Therefore, robust solutions for insect pest control need to be sought in alternative methods such as biological control agents for which single-gene resistance is less likely to evolve. The entomopathogenic fungus Beauveria bassiana has shown potential as a biological control agent of insects, and insight into the mechanisms of virulence is essential to show the robustness of its use. With the recent availability of the whole genome sequence of B. bassiana, progress in understanding the genetics that constitute virulence toward insects can be made more quickly. In this review we divide the infection process into distinct steps and provide an overview of what is currently known about genes and mechanisms influencing virulence in B. bassiana. We also discuss the need for novel strategies and experimental methods to better understand the infection mechanisms deployed by entomopathogenic fungi. Such knowledge can help improve biocontrol agents, not only by selecting the most virulent genotypes, but also by selecting the genotypes that use combinations of virulence mechanisms for which resistance in the insect host is least likely to develop. Copyright © 2015 Elsevier Inc. All rights reserved.

  19. Basis of Virulence in Enterotoxin-Mediated Staphylococcal Food Poisoning

    Directory of Open Access Journals (Sweden)

    Emilie L. Fisher

    2018-03-01

    Full Text Available The Staphylococcus aureus enterotoxins are a superfamily of secreted virulence factors that share structural and functional similarities and possess potent superantigenic activity causing disruptions in adaptive immunity. The enterotoxins can be separated into two groups; the classical (SEA-SEE and the newer (SEG-SElY and counting enterotoxin groups. Many members from both these groups contribute to the pathogenesis of several serious human diseases, including toxic shock syndrome, pneumonia, and sepsis-related infections. Additionally, many members demonstrate emetic activity and are frequently responsible for food poisoning outbreaks. Due to their robust tolerance to denaturing, the enterotoxins retain activity in food contaminated previously with S. aureus. The genes encoding the enterotoxins are found mostly on a variety of different mobile genetic elements. Therefore, the presence of enterotoxins can vary widely among different S. aureus isolates. Additionally, the enterotoxins are regulated by multiple, and often overlapping, regulatory pathways, which are influenced by environmental factors. In this review, we also will focus on the newer enterotoxins (SEG-SElY, which matter for the role of S. aureus as an enteropathogen, and summarize our current knowledge on their prevalence in recent food poisoning outbreaks. Finally, we will review the current literature regarding the key elements that govern the complex regulation of enterotoxins, the molecular mechanisms underlying their enterotoxigenic, superantigenic, and immunomodulatory functions, and discuss how these activities may collectively contribute to the overall manifestation of staphylococcal food poisoning.

  20. Life history trade-offs and relaxed selection can decrease bacterial virulence in environmental reservoirs.

    Directory of Open Access Journals (Sweden)

    Lauri Mikonranta

    Full Text Available Pathogen virulence is usually thought to evolve in reciprocal selection with the host. While this might be true for obligate pathogens, the life histories of opportunistic pathogens typically alternate between within-host and outside-host environments during the infection-transmission cycle. As a result, opportunistic pathogens are likely to experience conflicting selection pressures across different environments, and this could affect their virulence through life-history trait correlations. We studied these correlations experimentally by exposing an opportunistic bacterial pathogen Serratia marcescens to its natural protist predator Tetrahymena thermophila for 13 weeks, after which we measured changes in bacterial traits related to both anti-predator defence and virulence. We found that anti-predator adaptation (producing predator-resistant biofilm caused a correlative attenuation in virulence. Even though the direct mechanism was not found, reduction in virulence was most clearly connected to a predator-driven loss of a red bacterial pigment, prodigiosin. Moreover, life-history trait evolution was more divergent among replicate populations in the absence of predation, leading also to lowered virulence in some of the 'predator absent' selection lines. Together these findings suggest that the virulence of non-obligatory, opportunistic bacterial pathogens can decrease in environmental reservoirs through life history trade-offs, or random accumulation of mutations that impair virulence traits under relaxed selection.

  1. Nitrogen Metabolite Repression of Metabolism and Virulence in the Human Fungal Pathogen Cryptococcus neoformans

    Science.gov (United States)

    Lee, I. Russel; Chow, Eve W. L.; Morrow, Carl A.; Djordjevic, Julianne T.; Fraser, James A.

    2011-01-01

    Proper regulation of metabolism is essential to maximizing fitness of organisms in their chosen environmental niche. Nitrogen metabolite repression is an example of a regulatory mechanism in fungi that enables preferential utilization of easily assimilated nitrogen sources, such as ammonium, to conserve resources. Here we provide genetic, transcriptional, and phenotypic evidence of nitrogen metabolite repression in the human pathogen Cryptococcus neoformans. In addition to loss of transcriptional activation of catabolic enzyme-encoding genes of the uric acid and proline assimilation pathways in the presence of ammonium, nitrogen metabolite repression also regulates the production of the virulence determinants capsule and melanin. Since GATA transcription factors are known to play a key role in nitrogen metabolite repression, bioinformatic analyses of the C. neoformans genome were undertaken and seven predicted GATA-type genes were identified. A screen of these deletion mutants revealed GAT1, encoding the only global transcription factor essential for utilization of a wide range of nitrogen sources, including uric acid, urea, and creatinine—three predominant nitrogen constituents found in the C. neoformans ecological niche. In addition to its evolutionarily conserved role in mediating nitrogen metabolite repression and controlling the expression of catabolic enzyme and permease-encoding genes, Gat1 also negatively regulates virulence traits, including infectious basidiospore production, melanin formation, and growth at high body temperature (39°–40°). Conversely, Gat1 positively regulates capsule production. A murine inhalation model of cryptococcosis revealed that the gat1Δ mutant is slightly more virulent than wild type, indicating that Gat1 plays a complex regulatory role during infection. PMID:21441208

  2. Sortase A: an ideal target for anti-virulence drug development.

    Science.gov (United States)

    Cascioferro, Stella; Totsika, Makrina; Schillaci, Domenico

    2014-12-01

    Sortase A is a membrane enzyme responsible for the anchoring of surface-exposed proteins to the cell wall envelope of Gram-positive bacteria. As a well-studied member of the sortase subfamily catalysing the cell wall anchoring of important virulence factors to the surface of staphylococci, enterococci and streptococci, sortase A plays a critical role in Gram-positive bacterial pathogenesis. It is thus considered a promising target for the development of new anti-infective drugs that aim to interfere with important Gram-positive virulence mechanisms, such as adhesion to host tissues, evasion of host defences, and biofilm formation. The additional properties of sortase A as an enzyme that is not required for Gram-positive bacterial growth or viability and is conveniently located on the cell membrane making it more accessible to inhibitor targeting, constitute additional reasons reinforcing the view that sortase A is an ideal target for anti-virulence drug development. Many inhibitors of sortase A have been identified to date using high-throughput or in silico screening of compound libraries (synthetic or natural), and while many have proved useful tools for probing the action model of the enzyme, several are also promising candidates for the development into potent inhibitors. This review is focused on the most promising sortase A inhibitor compounds that are currently in development as leads towards a new class of anti-infective drugs that are urgently needed to help combat the alarming increase in antimicrobial resistance. Copyright © 2014 Elsevier Ltd. All rights reserved.

  3. Genomes and virulence difference between two physiological races of Phytophthora nicotianae.

    Science.gov (United States)

    Liu, Hui; Ma, Xiao; Yu, Haiqin; Fang, Dunhuang; Li, Yongping; Wang, Xiao; Wang, Wen; Dong, Yang; Xiao, Bingguang

    2016-01-01

    Black shank is a severe plant disease caused by the soil-borne pathogen Phytophthora nicotianae. Two physiological races of P. nicotianae, races 0 and 1, are predominantly observed in cultivated tobacco fields around the world. Race 0 has been reported to be more aggressive, having a shorter incubation period, and causing worse root rot symptoms, while race 1 causes more severe necrosis. The molecular mechanisms underlying the difference in virulence between race 0 and 1 remain elusive. We assembled and annotated the genomes of P. nicotianae races 0 and 1, which were obtained by a combination of PacBio single-molecular real-time sequencing and second-generation sequencing (both HiSeq and MiSeq platforms). Gene family analysis revealed a highly expanded ATP-binding cassette transporter gene family in P. nicotianae. Specifically, more RxLR effector genes were found in the genome of race 0 than in that of race 1. In addition, RxLR effector genes were found to be mainly distributed in gene-sparse, repeat-rich regions of the P. nicotianae genome. These results provide not only high quality reference genomes of P. nicotianae, but also insights into the infection mechanisms of P. nicotianae and its co-evolution with the host plant. They also reveal insights into the difference in virulence between the two physiological races.

  4. How Listeria monocytogenes organizes its surface for virulence

    Science.gov (United States)

    Carvalho, Filipe; Sousa, Sandra; Cabanes, Didier

    2014-01-01

    Listeria monocytogenes is a Gram-positive pathogen responsible for the manifestation of human listeriosis, an opportunistic foodborne disease with an associated high mortality rate. The key to the pathogenesis of listeriosis is the capacity of this bacterium to trigger its internalization by non-phagocytic cells and to survive and even replicate within phagocytes. The arsenal of virulence proteins deployed by L. monocytogenes to successfully promote the invasion and infection of host cells has been progressively unveiled over the past decades. A large majority of them is located at the cell envelope, which provides an interface for the establishment of close interactions between these bacterial factors and their host targets. Along the multistep pathways carrying these virulence proteins from the inner side of the cytoplasmic membrane to their cell envelope destination, a multiplicity of auxiliary proteins must act on the immature polypeptides to ensure that they not only maturate into fully functional effectors but also are placed or guided to their correct position in the bacterial surface. As the major scaffold for surface proteins, the cell wall and its metabolism are critical elements in listerial virulence. Conversely, the crucial physical support and protection provided by this structure make it an ideal target for the host immune system. Therefore, mechanisms involving fine modifications of cell envelope components are activated by L. monocytogenes to render it less recognizable by the innate immunity sensors or more resistant to the activity of antimicrobial effectors. This review provides a state-of-the-art compilation of the mechanisms used by L. monocytogenes to organize its surface for virulence, with special focus on those proteins that work “behind the frontline”, either supporting virulence effectors or ensuring the survival of the bacterium within its host. PMID:24809022

  5. Helicobacter pylori virulence and cancer pathogenesis.

    Science.gov (United States)

    Yamaoka, Yoshio; Graham, David Y

    2014-06-01

    Helicobacter pylori is human gastric pathogen that causes chronic and progressive gastric mucosal inflammation and is responsible for the gastric inflammation-associated diseases, gastric cancer and peptic ulcer disease. Specific outcomes reflect the interplay between host-, environmental- and bacterial-specific factors. Progress in understanding putative virulence factors in disease pathogenesis has been limited and many false leads have consumed scarce resources. Few in vitro-in vivo correlations or translational applications have proved clinically relevant. Reported virulence factor-related outcomes reflect differences in relative risk of disease rather than specificity for any specific outcome. Studies of individual virulence factor associations have provided conflicting results. Since virulence factors are linked, studies of groups of putative virulence factors are needed to provide clinically useful information. Here, the authors discuss the progress made in understanding the role of H. pylori virulence factors CagA, vacuolating cytotoxin, OipA and DupA in disease pathogenesis and provide suggestions for future studies.

  6. Effects of nano TiN addition on the microstructure and mechanical properties of TiC based steel bonded carbides

    Institute of Scientific and Technical Information of China (English)

    WANG Zhi'an; DAI Haiyang; ZOU Yu

    2008-01-01

    TiC based steel bonded carbides with the addition of nano TiN were prepared by vicuum sintering techniques.The microstructure was investigated using scanning electron microscopy(SEM)and transmission electron microscopy (TEM),and the mechanical properties,such as bending strength,impact toughness,hardness,and density,were measured.The results indicate that the grain size becomes small and there is uniformity in the steel bonded carbide with nano addition;several smaller carbide particles are also found to be inlaid in the rim of the larger carbide grains and prevent the coalescence of TiC grains.The smaller and larger carbide grains joint firmly,and then the reduction of the average size of the grains leads to the increase in the mechanical properties of the steel bonded carbides with nano addition.But the mechanical properties do not increase monotonously with an increase in nano addition.When the nano TiN addition accounts for 6-8 wt.% of the amount of steel bonded carbides.the mechanical properties reach the maximum values and then decrease with further increase in nano TiN addition.

  7. Comprehensive study on mechanical properties of lime-based pastes with additions of metakaolin and brick dust

    Czech Academy of Sciences Publication Activity Database

    Nežerka, V.; Slížková, Zuzana; Tesárek, P.; Plachý, T.; Frankeová, Dita; Petráňová, Veronika

    2014-01-01

    Roč. 64, October (2014), s. 17-29 ISSN 0008-8846 R&D Projects: GA MK(CZ) DF11P01OVV008 Keywords : microstructure * mechanical properties * CaO * metakaolin * brick dust Subject RIV: AL - Art, Architecture, Cultural Heritage Impact factor: 2.864, year: 2014 http://www.sciencedirect.com/science/article/pii/S0008884614001239

  8. Molecular dynamics simulations for the examination of mechanical properties of hydroxyapatite/ poly α-n-butyl cyanoacrylate under additive manufacturing.

    Science.gov (United States)

    Wang, Yanen; Wei, Qinghua; Pan, Feilong; Yang, Mingming; Wei, Shengmin

    2014-01-01

    Molecular dynamics (MD) simulations emerged to be a helpful tool in the field of material science. In rapid prototyping artificial bone scaffolds process, the binder spraying volume and mechanism are very important for bone scaffolds mechanical properties. In this study, we applied MD simulations to investigating the binding energy of α-n-butyl cyanoacrylate (NBCA) on Hydroxyapatite (HA) crystallographic planes (001, 100 and 110), and to calculating and analyzing the mechanical properties and radial distribution function of the HA(110)/NBCA mixed system. The simulation results suggested that HA (110) has the highest binding energy with NBCA owing to the high planar atom density, and the mechanical properties of HA(110)/NBCA mixed system is stronger than pure HA system. Therefore, the multi-grade strength bone scaffold could be fabricated through spraying various volume NBCA binders during 3D printing process. By calculating the radial distribution function of HA(110)/NBCA, the essence of the interface interaction were successfully elucidated. The forming situation parameters can be referred to calculation results. There exists a strong interaction between HA crystallographic plane (110) and NBCA, it is mainly derived from the hydrogen bonds between O atoms which connect with C atoms of NBCA and H atoms in HA crystal. Furthermore, a strong adsorption effect can be demonstrated between HA and NBCA.

  9. Structure and mechanical properties of composites of poly(6-hexanelactam) combining solid tribological additives and reinforcing components

    Czech Academy of Sciences Publication Activity Database

    Horský, J.; Kolařík, Jan; Fambri, L.

    2004-01-01

    Roč. 289, č. 4 (2004), s. 5249-5260 ISSN 1438-7492 R&D Projects: GA ČR GA104/01/0004 Institutional research plan: CEZ:AV0Z4050913 Keywords : anionic poly merization * composites * mechanical properties Subject RIV: CD - Macromolecular Chemistry Impact factor: 1.452, year: 2004

  10. Casein films: effects of formulation, environmental conditions, and addition of citric pectin on the structure and mechanical properties

    Science.gov (United States)

    Thin casein films for food packaging applications reportedly possess good strength and low oxygen permeability, but low water-resistance and elasticity. Modifying and customizing the mechanical properties of the films to target specific behaviors depending on environmental conditions would enable a...

  11. Diastereoselective Addition of α-Metalated Sulfoxides to Imines Revisited: Mechanism, Computational Studies, and the Effect of External Chiral Ligands

    DEFF Research Database (Denmark)

    Pedersen, Brian; Rein, Tobias; Søtofte, Inger

    2003-01-01

    six-membered "flat chair") was probed by quantum mechanical calculations, which underpinned the idea of using external chiral ligands to enhance the diastereoselectivity of otherwise moderately selective reactions. In this way, the diastereomeric ratio of the product 3a could be raised from (84 : 16...

  12. The effect of hydroxyapatite addition on the mechanical properties of polyvinyl alcohol/chitosan biomaterials for bone scaffolds application

    Science.gov (United States)

    Ramahdita, Ghiska; Puspita, Debie Maya; Albab, Muh Fadhil; Alfata, Rowi; Sofyan, Nofrijon; Yuwono, Akhmad Herman

    2018-02-01

    The increasing number of bone fracture incident in Indonesia from year to year needs an urgent problem solving of the limited bone substitute which can meet the necessary criteria for that purpose. Motivated by this, therefore, the current study is focusing on the optimization of material properties used as bone scaffold. A biomaterial of polyvinyl alcohol (PVA)/chitosan-hydroxyapatite (HA) composite was successfully made by wet chemistry method, followed by freeze thawing and freeze drying. For comparison purposes, the percentage of HA has been varied from 0, 25 and 40 % (wt/v). The resulting composites were characterized by Fourier transform infrared (FTIR) spectroscopy, scanning electron microscope (SEM), compressive test, and swelling behavior. The results showed that the addition of HA up to 40% (wt/v) has yielded a porous structure with an average pore size of 42.39 µm. In addition, the compressive modulus was enhanced from 14 MPa for 0% HA to 143, and 191 MPa for composites with the addition of HA from 25 to 40% (wt/v). The addition of HA has also reduced the swelling ratio from 296% for the sample without HA to 85 and 78 % for sample with addition of HA from 25 to 40 (wt/v), respectively. The obtained results show that PVA/chitosan-HA in this study is potential to be used as scaffold in bone tissue engineering.

  13. Bicarbonate-mediated transcriptional activation of divergent operons by the virulence regulatory protein, RegA, from Citrobacter rodentium.

    Science.gov (United States)

    Yang, Ji; Hart, Emily; Tauschek, Marija; Price, G Dean; Hartland, Elizabeth L; Strugnell, Richard A; Robins-Browne, Roy M

    2008-04-01

    Regulation of virulence gene expression plays a central role in the pathogenesis of enteric bacteria as they encounter diverse environmental conditions in the gastrointestinal tract of their hosts. In this study, we investigated environmental regulation of two putative virulence determinants adcA and kfc by RegA, an AraC/XylS-like regulator, from Citrobacter rodentium, and identified bicarbonate as the environmental signal which induced transcription of adcA and kfc through RegA. Primer extension experiments showed that adcA and kfc were divergently transcribed from sigma(70) promoters. In vivo and in vitro experiments demonstrated that bicarbonate facilitated and stabilized the binding of RegA to an operator located between the two promoters. The interaction of RegA with its DNA target resulted in the formation of a nucleosome-like structure, which evidently displaced the histone-like proteins, H-NS and StpA, from the adcA and kfc promoter regions, leading to transcriptional derepression. In addition, our results indicated that RegA also behaved as a Class I activator by directly stimulating transcription initiation by RNA polymerase. This is the first report to describe the molecular mechanism by which an environmental chemical stimulates transcription of virulence-associated genes of an enteric pathogen through an AraC/XlyS-like activator.

  14. Effect of copper addition and section thickness on the mechanical and physical properties of grey cast iron

    International Nuclear Information System (INIS)

    Malik, F.A.; Zahid, M.; Hassan, M.A.; Sheikh, M.A.; Alam, S.; Qazi, M.A.

    1995-01-01

    Copper is a graphitizer at the stage of solidification and it acts as antiferritizer during transformation cooling range. Due to this, copper additions to grey cast iron prevent at formation of free ferrite in heavy sections. It also reduces the chilling in thin sections, therefore uniform structure is imparted to grey iron by the copper addition. This gives the appropriate strength and hardness properties to grey iron. Thus copper addition gives certain advantages in relation to the machinability and wear resistance which are important for many engineering properties requires by high duty cast iron. The application of copper as allying element is acceptable due to its price and availability as compared to other alloying elements. (author)

  15. Effect of SiC whisker addition on the microstructures and mechanical properties of Ti(C, N)-based cermets

    International Nuclear Information System (INIS)

    Wu, Peng; Zheng, Yong; Zhao, Yongle; Yu, Haizhou

    2011-01-01

    Ti(C, N)-based cermets with addition of SiC whisker (SiC w ) were prepared by vacuum sintering. The microstructures of the prepared cermets were investigated by using X-ray diffractometry (XRD) and scanning electron microscopy (SEM). Mechanical properties such as transverse rupture strength (TRS), fracture toughness (K IC ) and hardness (HRA) were also measured. It was found that the grain size of the cermets was affected by the SiC whisker addition. The cermets with 1.0 wt.% SiC whisker addition exhibited the smallest grain size. The porosities of the cermets increased with increasing SiC whisker additions. The addition of the SiC whisker had no influence on the phase constituents of the cermets. Compared with the cermets with no whisker addition, the highest TRS and fracture toughness for cermets with 1.0 wt.% SiC whisker addition increased by about 24% and 29%, respectively. The strengthening mechanisms were attributed to finer grain size, homogeneous microstructure and moderate thickness of rim phase. The toughening mechanisms were characterized by crack deflection, whisker bridging and whisker pulling-out.

  16. Survival and Virulence of Campylobacter spp. in the Environment

    DEFF Research Database (Denmark)

    Bui, Thanh Xuan

    of environmental stress factors, namely heat shock, starvation, osmosis, and oxidation, on the expression of three virulence genes (ciaB, dnaJ, and htrA) of C. jejuni and its uptake by and intracellular survival within A. castellanii. I also investigated the mechanism(s) involved in phagocytosis and killing of C....... jejuni by A. castellanii. I observed that heat and osmotic stresses reduced the survival of C. jejuni significantly, whereas oxidative stress had no effect. The results of qRT-PCR experiments showed that the transcription of virulence genes of C. jejuni was slightly up-regulated under heat and oxidative...... soil flagellates may play a role for the survival of these food-borne pathogens on plant surfaces and in soil. It would be very interesting to further investigate the impacts of this soil flagellate on the survival of different food-borne pathogens in soil and in plant surface that may explain...

  17. Molecular Characterization of Putative Virulence Determinants in Burkholderia pseudomallei

    Directory of Open Access Journals (Sweden)

    Suat Moi Puah

    2014-01-01

    Full Text Available The Gram-negative saprophyte Burkholderia pseudomallei is the causative agent of melioidosis, an infectious disease which is endemic in Southeast Asia and northern Australia. This bacterium possesses many virulence factors which are thought to contribute to its survival and pathogenicity. Using a virulent clinical isolate of B. pseudomallei and an attenuated strain of the same B. pseudomallei isolate, 6 genes BPSL2033, BP1026B_I2784, BP1026B_I2780, BURPS1106A_A0094, BURPS1106A_1131, and BURPS1710A_1419 were identified earlier by PCR-based subtractive hybridization. These genes were extensively characterized at the molecular level, together with an additional gene BPSL3147 that had been identified by other investigators. Through a reverse genetic approach, single-gene knockout mutants were successfully constructed by using site-specific insertion mutagenesis and were confirmed by PCR. BPSL2033::Km and BURPS1710A_1419::Km mutants showed reduced rates of survival inside macrophage RAW 264.7 cells and also low levels of virulence in the nematode infection model. BPSL2033::Km demonstrated weak statistical significance (P=0.049 at 8 hours after infection in macrophage infection study but this was not seen in BURPS1710A_1419::Km. Nevertheless, complemented strains of both genes were able to partially restore the gene defects in both in vitro and in vivo studies, thus suggesting that they individually play a minor role in the virulence of B. pseudomallei.

  18. Influence of silver additions to type 316 stainless steels on bacterial inhibition, mechanical properties, and corrosion resistance

    DEFF Research Database (Denmark)

    Chiang, Wen-Chi; Tseng, I-Sheng; Møller, Per

    2010-01-01

    Bacterial contamination is a major concern in many areas. In this study, silver was added to type 316 stainless steels in order to obtain an expected bacteria inhibiting property to reduce the occurrence of bacterial contamination. Silver-bearing 316 stainless steels were prepared by vacuum melting...... in areas where hygiene is a major requirement. The possible mechanisms of silver dissolution from the surfaces of silver-bearing 316 stainless steels were also discussed in this report....

  19. Comparative study of mechanical activation of molybdenite (MoS2) with and without magnesium (Mg) addition

    OpenAIRE

    J. Temuujin; N. Setoudeh; N.J. Welham

    2016-01-01

    Molybdenite concentrate was mechanically activated in the presence of magnesium metal using a planetary mill in order to try to form elemental molybdenum. A sample milled for 90 min in planetary mill showed almost the same structural distortion as after 50 h in a tumbling mill, neither showed the presence of molybdenum metal. However, molybdenite milled together with magnesium showed more amorphization than separately milled molybdenite. Despite the apparent lack of reaction, molybdenite show...

  20. The mechanism of deceleration of nucleation and crystal growth by the small addition of transition metals to lithium disilicate glasses

    Science.gov (United States)

    Thieme, Katrin; Avramov, Isak; Rüssel, Christian

    2016-01-01

    The addition of small amounts of niobium or tantalum oxide to lithium disilicate glass provokes a drastic decrease of the steady-state nucleation rates and the crystal growth velocities. The viscosity of the residual glassy matrix is considered as a function of the crystallization degree in the course of a non-isothermal crystallization. For simplification, a homogeneous distribution of the added oxides in the glass matrix is assumed. While the viscosity initially decreases, it significantly increases again for higher crystallization degrees hindering crystal growth. However, it was shown that the additives are enriched at the crystal interface. Several possible reasons for the inhibition of nucleation and growth kinetics such as viscosity, interfacial energy crystal/glassy phase, thermodynamic driving force or impingement rate are discussed. Since the crystallization front is blocked by the additives the impingement rate is decreased with increasing additive concentration. Since small concentrations of Nb2O5 and Ta2O5 have a drastic effect on the nucleation, these components should be enriched at the interface crystal/glass. This will only take place, if it leads to a decrease in the interfacial energy. Since this effect alone should result in an increase of the nucleation rate, it must be overcompensated by kinetic effects. PMID:27150844

  1. Effect of niobium addition on the microstructure and in the mechanical properties in steel with medium and high carbon content

    International Nuclear Information System (INIS)

    Mei, P.R.; Bresciani Filho, E.

    1984-01-01

    The effect of 0.03%Nb addition on the microstructure, hardness, tensile strength and austenite grain diameter, in steel with 0.2 - 0.8wt%C, thermal treated at different conditions was investigated. It is shown that niobium dissolved in the austenite can increases the tensile strength up to 130 MPa, without affecting seriously the ductility. (Author) [pt

  2. Effects of heat treatment on microstructure and mechanical behaviour of additive manufactured porous Ti6Al4V

    NARCIS (Netherlands)

    Ahmadi, S.M.; Ashok Kumar Jain, R. K.; Zadpoor, A.A.; Ayas, C.; Popovich, V.

    2018-01-01

    Titanium and its alloys such as Ti6Al4V play a major role in the medical industry as bone implants. Nowadays, by the aid of additive manufacturing (AM), it is possible to manufacture porous complex structures which mimic human bone. However, AM parts are near net shape and post processing may be

  3. Solvent-free, catalyst-free aza-Michael addition of cyclohexylamine to diethyl maleate: reaction mechanism and kinetics

    Czech Academy of Sciences Publication Activity Database

    Bláha, Michal; Trhlíková, Olga; Podešva, Jiří; Abbrent, Sabina; Steinhart, Miloš; Dybal, Jiří; Dušková-Smrčková, Miroslava

    2018-01-01

    Roč. 74, č. 1 (2018), s. 58-67 ISSN 0040-4020 Institutional support: RVO:61389013 Keywords : Aza-Michael addition * solvent-free * catalyst-free Subject RIV: CD - Macromolecular Chemistry OBOR OECD: Polymer science Impact factor: 2.651, year: 2016

  4. Processing, Mechanical and Optical Properties of Additive-Free ZrC Ceramics Prepared by Spark Plasma Sintering

    Directory of Open Access Journals (Sweden)

    Clara Musa

    2016-06-01

    Full Text Available In the present study, nearly fully dense monolithic ZrC samples are produced and broadly characterized from microstructural, mechanical and optical points of view. Specifically, 98% dense products are obtained by Spark Plasma Sintering (SPS after 20 min dwell time at 1850 °C starting from powders preliminarily prepared by Self-propagating High-temperature Synthesis (SHS followed by 20 min ball milling. A prolonged mechanical treatment up to 2 h of SHS powders does not lead to appreciable benefits. Vickers hardness of the resulting samples (17.5 ± 0.4 GPa is reasonably good for monolithic ceramics, but the mechanical strength (about 250 MPa up to 1000 °C could be further improved by suitable optimization of the starting powder characteristics. The very smoothly polished ZrC specimen subjected to optical measurements displays high absorption in the visible-near infrared region and low thermal emittance at longer wavelengths. Moreover, the sample exhibits goodspectral selectivity (2.1–2.4 in the 1000–1400 K temperature range. These preliminary results suggest that ZrC ceramics produced through the two-step SHS/SPS processing route can be considered as attractive reference materials for the development of innovative solar energy absorbers.

  5. Effect of Dy addition on mechanical and magnetic properties of Mn-rich Ni–Mn–Ga ferromagnetic shape memory alloys

    International Nuclear Information System (INIS)

    Gao, L.; Dong, G.F.; Gao, Z.Y.; Cai, W.

    2012-01-01

    Highlights: ► The Dy addition significantly improves the compressive properties of Ni–Mn–Ga alloy. ► The mechanism of the improved mechanical properties by adding Dy is discussed. ► Dy doping results in a change of the fracture type of Ni–Mn–Ga alloy. ► Curie temperature almost remained unchanged at low Dy content and then decreases. - Abstract: The effects of partial substitution of rare earth Dy for Ga on the mechanical and magnetic properties of Mn-rich Ni 50 Mn 29 Ga 21−x Dy x (0 ≤ x ≤ 5) ferromagnetic shape memory alloys were investigated in detail. The results show that an appropriate amount of Dy addition significantly improves the mechanical properties of Ni–Mn–Ga alloy. With an increase in Dy content, the compressive strength enhances rapidly at first and then becomes stable when the Dy content is more than 1 at.%. However, the compressive strain increases dramatically and reaches a maximum value with 1 at.% Dy addition. Further increase in Dy content makes the compressive strain of the alloys decrease gradually. The mechanism of the improved mechanical properties is also discussed. Moreover, Dy doping changes the fracture type from intergranular fracture of Ni–Mn–Ga alloy to transgranular cleavage fracture of Ni–Mn–Ga–Dy alloys. The Curie temperature remains almost unchanged at low Dy content and subsequently decreases.

  6. Additive manufacturing of Ti-6Al-4V components by shaped metal deposition: Microstructure and mechanical properties

    International Nuclear Information System (INIS)

    Baufeld, Bernd; Biest, Omer Van der; Gault, Rosemary

    2010-01-01

    Shaped metal deposition (SMD) is a relatively new technology of additive manufacturing, which creates near-net shaped components by additive manufacture utilizing tungsten inert gas welding. Especially for Ti alloys, which are difficult to shape by traditional methods and for which the loss of material during machining is also very costly, SMD has great advantages. In the case of Ti-6Al-4V the dense SMD components exhibit large, columnar prior β grains, with a Widmanstaetten α/β microstructure. These prior β grains are slightly tilted in a direction following the temperature field resulting from the moving welding torch. The ultimate tensile strength is between 929 and 1014 MPa, depending on orientation and location of the tensile specimens. Tensile testing vertically to the deposition layers exhibits a strain at failure of 16 ± 3%, while testing parallel to the layers gives a lower value of about 9%.

  7. Ostwald ripening of Pb nanocrystalline phase in mechanically milled Al-Pb alloys and the influence of Cu additive

    International Nuclear Information System (INIS)

    Wu, Z.F.; Zeng, M.Q.; Ouyang, L.Z.; Zhang, X.P.; Zhu, M.

    2005-01-01

    The coarsening behavior of nanosized Pb phase in both Al-10%Pb and Al-10%Pb-4.5%Cu alloys has been studied by X-ray diffraction and transmission electron microscopy analysis. The coarsening of Pb nanophase in Al-Pb alloys still follows the classical ripening theory (the LSW theory) and the addition of Cu decreases the coarsening rate of Pb nanophase

  8. Grain refining mechanism of Al-containing Mg alloys with the addition of Mn-Al alloys

    International Nuclear Information System (INIS)

    Qin, Gaowu W.; Ren Yuping; Huang Wei; Li Song; Pei Wenli

    2010-01-01

    Graphical abstract: Display Omitted Research highlights: The ε-AlMn phase acts as the heterogeneous nucleus of α-Mg phase during the solidification of the AZ31 Mg alloy, not the γ-Al 8 Mn 5 phase. The grain refinement effect is very clear with the addition of only 0.5 wt% Mn-28Al alloy (pure ε-AlMn). The grain refinement does not deteriorate up to the holding time of 60 min at 740 o C. - Abstract: The effect of manganese on grain refinement of Al-containing AZ31 Mg alloy has been investigated by designing a series of Mn-Al alloys composed of either pure ε-AlMn, γ 2 -Al 8 Mn 5 or both of them using optical microscopy and X-ray diffraction. It is experimentally clarified that the grain refinement of the AZ31 Mg alloy is due to the existence of the ε-AlMn phase in the Mn-Al alloys, not the γ 2 -Al 8 Mn 5 phase. The grain size of AZ31 Mg alloy is about 91 μm without any addition of Mn-Al alloys, but remarkably decreases to ∼55 μm with the addition of either Mn-34 wt% Al or Mn-28 wt% Al. With a minor addition of 0.5 wt% Mn-28Al alloy, the grain size of AZ31 alloy decreases to ∼53 μm, and the Mn-28Al alloy can be active as grain refiner for holding time up to 60 min for the melt AZ31 alloy at 750 o C.

  9. Grain refining mechanism of Al-containing Mg alloys with the addition of Mn-Al alloys

    Energy Technology Data Exchange (ETDEWEB)

    Qin, Gaowu W., E-mail: qingw@smm.neu.edu.c [Key Laboratory for Anisotropy and Texture of Materials (Ministry of Education), Northeastern University, Wenhu Road 3-11, Heping District, Shenyang 110004, Liaoning Province (China); Ren Yuping; Huang Wei; Li Song; Pei Wenli [Key Laboratory for Anisotropy and Texture of Materials (Ministry of Education), Northeastern University, Wenhu Road 3-11, Heping District, Shenyang 110004, Liaoning Province (China)

    2010-10-08

    Graphical abstract: Display Omitted Research highlights: The {epsilon}-AlMn phase acts as the heterogeneous nucleus of {alpha}-Mg phase during the solidification of the AZ31 Mg alloy, not the {gamma}-Al{sub 8}Mn{sub 5} phase. The grain refinement effect is very clear with the addition of only 0.5 wt% Mn-28Al alloy (pure {epsilon}-AlMn). The grain refinement does not deteriorate up to the holding time of 60 min at 740 {sup o}C. - Abstract: The effect of manganese on grain refinement of Al-containing AZ31 Mg alloy has been investigated by designing a series of Mn-Al alloys composed of either pure {epsilon}-AlMn, {gamma}{sub 2}-Al{sub 8}Mn{sub 5} or both of them using optical microscopy and X-ray diffraction. It is experimentally clarified that the grain refinement of the AZ31 Mg alloy is due to the existence of the {epsilon}-AlMn phase in the Mn-Al alloys, not the {gamma}{sub 2}-Al{sub 8}Mn{sub 5} phase. The grain size of AZ31 Mg alloy is about 91 {mu}m without any addition of Mn-Al alloys, but remarkably decreases to {approx}55 {mu}m with the addition of either Mn-34 wt% Al or Mn-28 wt% Al. With a minor addition of 0.5 wt% Mn-28Al alloy, the grain size of AZ31 alloy decreases to {approx}53 {mu}m, and the Mn-28Al alloy can be active as grain refiner for holding time up to 60 min for the melt AZ31 alloy at 750 {sup o}C.

  10. Virulence Factors of Aeromonas hydrophila: in the Wake of Reclassification

    Directory of Open Access Journals (Sweden)

    Cody R Rasmussen-Ivey

    2016-08-01

    Full Text Available The ubiquitous jack-of-all-trades, Aeromonas hydrophila, is a freshwater, Gram-negative bacterial pathogen under revision in regard to its phylogenetic and functional affiliation with other aeromonads. While virulence factors are expectedly diverse across A. hydrophila strains and closely related species, our mechanistic knowledge of the vast majority of these factors is based on the molecular characterization of the strains A. hydrophila AH-3 and SSU, which were reclassified as A. piscicola AH-3 in 2009 and A. dhakensis SSU in 2013. Individually, these reclassifications raise important questions involving the applicability of previous research on A. hydrophila virulence mechanisms; however, this issue is exacerbated by a lack of genomic data on other research strains. Collectively, these changes represent a fundamental gap in the literature on A. hydrophila and confirm the necessity of biochemical, molecular, and morphological techniques in the classification of research strains that are used as a foundation for future research. This review revisits what is known about virulence in A. hydrophila and the feasibility of using comparative genomics in light of this phylogenetic revision. Conflicting data between virulence factors, secretion systems, quorum sensing, and their effect on A. hydrophila pathogenicity appears to be an artifact of inappropriate taxonomic comparisons and/or be due to the fact that these properties are strain-specific. This review audits emerging data on dominant virulence factors that are present in both A. dhakensis and A. hydrophila in order to synthesize existing data with the aim of locating where future research is needed.

  11. SigB is a dominant regulator of virulence in Staphylococcus aureus small-colony variants.

    Science.gov (United States)

    Mitchell, Gabriel; Fugère, Alexandre; Pépin Gaudreau, Karine; Brouillette, Eric; Frost, Eric H; Cantin, André M; Malouin, François

    2013-01-01

    Staphylococcus aureus small-colony variants (SCVs) are persistent pathogenic bacteria characterized by slow growth and, for many of these strains, an increased ability to form biofilms and to persist within host cells. The virulence-associated gene expression profile of SCVs clearly differs from that of prototypical strains and is often influenced by SigB rather than by the agr system. One objective of this work was to confirm the role of SigB in the control of the expression of virulence factors involved in biofilm formation and intracellular persistence of SCVs. This study shows that extracellular proteins are involved in the formation of biofilm by three SCV strains, which, additionally, have a low biofilm-dispersing activity. It was determined that SigB activity modulates biofilm formation by strain SCV CF07-S and is dominant over that of the agr system without being solely responsible for the repression of proteolytic activity. On the other hand, the expression of fnbA and the control of nuclease activity contributed to the SigB-dependent formation of biofilm of this SCV strain. SigB was also required for the replication of CF07-S within epithelial cells and may be involved in the colonization of lungs by SCVs in a mouse infection model. This study methodically investigated SigB activity and associated mechanisms in the various aspects of SCV pathogenesis. Results confirm that SigB activity importantly influences the production of virulence factors, biofilm formation and intracellular persistence for some clinical SCV strains.

  12. Structure of Rot, a global regulator of virulence genes in Staphylococcus aureus.

    Science.gov (United States)

    Zhu, Yuwei; Fan, Xiaojiao; Zhang, Xu; Jiang, Xuguang; Niu, Liwen; Teng, Maikun; Li, Xu

    2014-09-01

    Staphylococcus aureus is a highly versatile pathogen that can infect human tissue by producing a large arsenal of virulence factors that are tightly regulated by a complex regulatory network. Rot, which shares sequence similarity with SarA homologues, is a global regulator that regulates numerous virulence genes. However, the recognition model of Rot for the promoter region of target genes and the putative regulation mechanism remain elusive. In this study, the 1.77 Å resolution X-ray crystal structure of Rot is reported. The structure reveals that two Rot molecules form a compact homodimer, each of which contains a typical helix-turn-helix module and a β-hairpin motif connected by a flexible loop. Fluorescence polarization results indicate that Rot preferentially recognizes AT-rich dsDNA with ~30-base-pair nucleotides and that the conserved positively charged residues on the winged-helix motif are vital for binding to the AT-rich dsDNA. It is proposed that the DNA-recognition model of Rot may be similar to that of SarA, SarR and SarS, in which the helix-turn-helix motifs of each monomer interact with the major grooves of target dsDNA and the winged motifs contact the minor grooves. Interestingly, the structure shows that Rot adopts a novel dimerization model that differs from that of other SarA homologues. As expected, perturbation of the dimer interface abolishes the dsDNA-binding ability of Rot, suggesting that Rot functions as a dimer. In addition, the results have been further confirmed in vivo by measuring the transcriptional regulation of α-toxin, a major virulence factor produced by most S. aureus strains.

  13. Sugar Allocation to Metabolic Pathways is Tightly Regulated and Affects the Virulence of Streptococcus mutans

    Directory of Open Access Journals (Sweden)

    Miki Kawada-Matsuo

    2016-12-01

    Full Text Available Bacteria take up and metabolize sugar as a carbohydrate source for survival. Most bacteria can utilize many sugars, including glucose, sucrose, and galactose, as well as amino sugars, such as glucosamine and N-acetylglucosamine. After entering the cytoplasm, the sugars are mainly allocated to the glycolysis pathway (energy production and to various bacterial component biosynthesis pathways, including the cell wall, nucleic acids and amino acids. Sugars are also utilized to produce several virulence factors, such as capsule and lipoteichoic acid. Glutamine-fructose-6-phosphate aminotransferase (GlmS and glucosamine-6-phosphate deaminase (NagB have crucial roles in sugar distribution to the glycolysis pathway and to cell wall biosynthesis. In Streptococcus mutans, a cariogenic pathogen, the expression levels of glmS and nagB are coordinately regulated in response to the presence or absence of amino sugars. In addition, the disruption of this regulation affects the virulence of S. mutans. The expression of nagB and glmS is regulated by NagR in S. mutans, but the precise mechanism underlying glmS regulation is not clear. In Staphylococcus aureus and Bacillus subtilis, the mRNA of glmS has ribozyme activity and undergoes self-degradation at the mRNA level. However, there is no ribozyme activity region on glmS mRNA in S. mutans. In this review article, we summarize the sugar distribution, particularly the coordinated regulation of GlmS and NagB expression, and its relationship with the virulence of S. mutans.

  14. Assessment of Physical and Mechanical Properties of Cement Panel Influenced by Treated and Untreated Coconut Fiber Addition

    Science.gov (United States)

    Abdullah, Alida; Jamaludin, Shamsul Baharin; Anwar, Mohamed Iylia; Noor, Mazlee Mohd; Hussin, Kamarudin

    This project was conducted to produce a cement panel with the addition of treated and untreated coconut fiber in cement panel. Coconut fiber was added to replace coarse aggregate (sand) in this cement panel. In this project, the ratios used to design the mixture were 1:1:0, 1:0.97:0.03, 1:0.94:0.06, 1:0.91:0.09 (cement: sand: coconut fiber). The water cement ratio was constant at 0.55. The sizes of sample tested were, 160 mm x 40 mm x 40 mm for compression test, and 100 mm x 100 mm x 40 mm for density, moisture content and water absorption tests. After curing samples for 28 days, it was found that the addition of coconut fiber, further increase in compressive strength of cement panel with untreated coconut fiber. Moisture content of cement panel with treated coconut fiber increased with increasing content of coconut fiber whereas water absorption of cement panel with untreated coconut fiber increased with increasing content of coconut fiber. The density of cement panel decreased with the addition of untreated and treated coconut fiber.

  15. Thermo-mechanic and sensory properties of wheat and rye breads produced with varying concentration of the additive

    Directory of Open Access Journals (Sweden)

    Demin Mirjana A.

    2013-01-01

    Full Text Available The effects of different concentrations of the complex additive containing emulsifiers, oxido-reductive substances and enzymes, on the rheological conditions of dough, and on the sensory properties of three groups of bread were investigated. The best initial quality and the lowest degree of protein network weakening had the dough obtained from mixed wheat and rye flours. The best expected baking properties were shown by the white wheat flour due to the least damage of its starch. The use of the additive has an effect on the absorption of water and on the majority of C-values of all sorts of flour. The amount of additive had a significant effect on the sensory properties of wheat bread crumb texture. Also, storage duration significantly affected (p <0.01 the sensory properties of integral wheat bread aroma-taste and the weighted mean score. The interaction of these two factors had no significant effect on any of sensory properties of the investigated groups of bread.

  16. Soldering Characteristics and Mechanical Properties of Sn-1.0Ag-0.5Cu Solder with Minor Aluminum Addition

    Directory of Open Access Journals (Sweden)

    Yee Mei Leong

    2016-06-01

    Full Text Available Driven by the trends towards miniaturization in lead free electronic products, researchers are putting immense efforts to improve the properties and reliabilities of Sn based solders. Recently, much interest has been shown on low silver (Ag content solder SAC105 (Sn-1.0Ag-0.5Cu because of economic reasons and improvement of impact resistance as compared to SAC305 (Sn-3.0Ag-0.5Cu. The present work investigates the effect of minor aluminum (Al addition (0.1–0.5 wt.% to SAC105 on the interfacial structure between solder and copper substrate during reflow. The addition of minor Al promoted formation of small, equiaxed Cu-Al particle, which are identified as Cu3Al2. Cu3Al2 resided at the near surface/edges of the solder and exhibited higher hardness and modulus. Results show that the minor addition of Al does not alter the morphology of the interfacial intermetallic compounds, but they substantially suppress the growth of the interfacial Cu6Sn5 intermetallic compound (IMC after reflow. During isothermal aging, minor alloying Al has reduced the thickness of interfacial Cu6Sn5 IMC but has no significant effect on the thickness of Cu3Sn. It is suggested that of atoms of Al exert their influence by hindering the flow of reacting species at the interface.

  17. Soldering Characteristics and Mechanical Properties of Sn-1.0Ag-0.5Cu Solder with Minor Aluminum Addition

    Science.gov (United States)

    Leong, Yee Mei; Haseeb, A.S.M.A.

    2016-01-01

    Driven by the trends towards miniaturization in lead free electronic products, researchers are putting immense efforts to improve the properties and reliabilities of Sn based solders. Recently, much interest has been shown on low silver (Ag) content solder SAC105 (Sn-1.0Ag-0.5Cu) because of economic reasons and improvement of impact resistance as compared to SAC305 (Sn-3.0Ag-0.5Cu. The present work investigates the effect of minor aluminum (Al) addition (0.1–0.5 wt.%) to SAC105 on the interfacial structure between solder and copper substrate during reflow. The addition of minor Al promoted formation of small, equiaxed Cu-Al particle, which are identified as Cu3Al2. Cu3Al2 resided at the near surface/edges of the solder and exhibited higher hardness and modulus. Results show that the minor addition of Al does not alter the morphology of the interfacial intermetallic compounds, but they substantially suppress the growth of the interfacial Cu6Sn5 intermetallic compound (IMC) after reflow. During isothermal aging, minor alloying Al has reduced the thickness of interfacial Cu6Sn5 IMC but has no significant effect on the thickness of Cu3Sn. It is suggested that of atoms of Al exert their influence by hindering the flow of reacting species at the interface. PMID:28773645

  18. Comparative study of mechanical activation of molybdenite (MoS2 with and without magnesium (Mg addition

    Directory of Open Access Journals (Sweden)

    J. Temuujin

    2016-03-01

    Full Text Available Molybdenite concentrate was mechanically activated in the presence of magnesium metal using a planetary mill in order to try to form elemental molybdenum. A sample milled for 90 min in planetary mill showed almost the same structural distortion as after 50 h in a tumbling mill, neither showed the presence of molybdenum metal. However, molybdenite milled together with magnesium showed more amorphization than separately milled molybdenite. Despite the apparent lack of reaction, molybdenite showed higher solubility in dilute HCl after milling with magnesium than without.Mongolian Journal of Chemistry 16 (42, 2015, 30-33

  19. Inhibitors of Mycobacterium marinum virulence identified in a Dictyostelium discoideum host model.

    Directory of Open Access Journals (Sweden)

    Hajer Ouertatani-Sakouhi

    Full Text Available Tuberculosis remains one of the major threats to public health worldwide. Given the prevalence of multi drug resistance (MDR in Mycobacterium tuberculosis strains, there is a strong need to develop new anti-mycobacterial drugs with modes of action distinct from classical antibiotics. Inhibitors of mycobacterial virulence might target new molecular processes and may represent a potential new therapeutic alternative. In this study, we used a Dictyostelium discoideum host model to assess virulence of Mycobacterium marinum and to identify compounds inhibiting mycobacterial virulence. Among 9995 chemical compounds, we selected 12 inhibitors of mycobacterial virulence that do not inhibit mycobacterial growth in synthetic medium. Further analyses revealed that 8 of them perturbed functions requiring an intact mycobacterial cell wall such as sliding motility, bacterial aggregation or cell wall permeability. Chemical analogs of two compounds were analyzed. Chemical modifications altered concomitantly their effect on sliding motility and on mycobacterial virulence, suggesting that the alteration of the mycobacterial cell wall caused the loss of virulence. We characterized further one of the selected compounds and found that it inhibited the ability of mycobacteria to replicate in infected cells. Together these results identify new antimycobacterial compounds that represent new tools to unravel the molecular mechanisms controlling mycobacterial pathogenicity. The isolation of compounds with anti-virulence activity is the first step towards developing new antibacterial treatments.

  20. Inorganic Polyphosphate Is Essential for Salmonella Typhimurium Virulence and Survival in Dictyostelium discoideum

    Directory of Open Access Journals (Sweden)

    Macarena A. Varas

    2018-01-01

    Full Text Available Inorganic polyphosphate (polyP deficiency in enteric bacterial pathogens reduces their ability to invade and establish systemic infections in different hosts. For instance, inactivation of the polyP kinase gene (ppk encoding the enzyme responsible for polyP biosynthesis reduces invasiveness and intracellular survival of Salmonella enterica serovar Typhimurium (S. Typhimurium in epithelial cells and macrophages in vitro. In addition, the virulence in vivo of a S. Typhimurium Δppk mutant is significantly reduced in a murine infection model. In spite of these observations, the role played by polyP during the Salmonella-host interaction is not well understood. The social amoeba Dictyostelium discoideum has proven to be a useful model for studying relevant aspects of the host-pathogen interaction. In fact, many intracellular pathogens can survive within D. discoideum cells using molecular mechanisms also required to survive within macrophages. Recently, we established that S. Typhimurium is able to survive intracellularly in D. discoideum and identified relevant genes linked to virulence that are crucial for this process. The aim of this study was to determine the effect of a polyP deficiency in S. Typhimurium during its interaction with D. discoideum. To do this, we evaluated the intracellular survival of wild-type and Δppk strains of S. Typhimurium in D. discoideum and the ability of these strains to delay the social development of the amoeba. In contrast to the wild-type strain, the Δppk mutant was unable to survive intracellularly in D. discoideum and enabled the social development of the amoeba. Both phenotypes were complemented using a plasmid carrying a copy of the ppk gene. Next, we simultaneously evaluated the proteomic response of both S. Typhimurium and D. discoideum during host-pathogen interaction via global proteomic profiling. The analysis of our results allowed the identification of novel molecular signatures that give insight into

  1. Thermo-mechanical treatment of the Cr-Mo constructional steel plates with Nb, Ti and B additions

    International Nuclear Information System (INIS)

    Adamczyk, J.; Opiela, M.

    2002-01-01

    Results of investigations of the influence of parameters of thermomechanical treatment, carried out by rolling with controlled recrystallization, on the microstructure and mechanical properties of Cr-Mo constructional steel with Nb, Ti and B microadditions, destined for the manufacturing of weldable heavy plates, are presented. These plates show a yield point of over 960 MPa after heat treatment. Two variants of thermomechanical treatment were worked out, based on the obtained results of investigations, when rolling a plate 40 mm thick in several passes to a plate 15 mm thick in a temperature range from 1100 to 900 o C. It was found that the lack of complete recrystallization of the austenite in the first rolling variant, leads to localization of plastic deformation in form of shear bands. There exists a segregation of MC-type carbides and alloying elements in these bands, causing a distinctive reduction of the crack resistance of the steel, as also a disadvantageous anisotropy of plastic properties of plate after tempering. For plates rolled under the same conditions, using a retention shield, a nearly three times higher impact energy in - 40 o C was obtained, as also only a slight anisotropy of plastic properties, saving the required mechanical properties. (author)

  2. Influence of groove size and reinforcements addition on mechanical properties and microstructure of friction stir welded joints

    Science.gov (United States)

    Reddy Baridula, Ravinder; Ibrahim, Abdullah Bin; Yahya, Che Ku Mohammad Faizal Bin Che Ku; Kulkarni, Ratnakar; Varma Ramaraju, Ramgopal

    2018-03-01

    The butt joints fabricated by friction stir welding were found to have more strength than the joints obtained by conventional joining process. The important outcome of this process is the successful fabrication of surface composites with improved properties. Thus in order to further enhance the strength of the dissimilar alloy joints the reinforcements can be deposited in to the aluminium matrix during the process of friction stir welding. In the present study the multi-walled carbon nanotubes were embedded in to the groove by varying the width during joining of dissimilar alloys AA2024 and AA7075. Four widths were selected with constant depth and optimum process parameters were selected to fabricate the sound welded joints. The results show that the mechanical properties of the fabricated butt joints were influenced by the size of the groove, due to variation in the deposition of reinforcement in the stir zone. The microstructural study and identification of the elements of the welded joints show that the reinforcements deposition is influenced by the size of the groove. It has also been observed that the groove with minimum width is more effective than higher width. The mechanical properties are found to be improved due to the pinning of grain boundaries.

  3. The metabolic regulator CodY links L. monocytogenes metabolism to virulence by directly activating the virulence regulatory gene, prfA

    Science.gov (United States)

    Lobel, Lior; Sigal, Nadejda; Borovok, Ilya; Belitsky, Boris R.; Sonenshein, Abraham L.; Herskovits, Anat A.

    2015-01-01

    Summary Metabolic adaptations are critical to the ability of bacterial pathogens to grow within host cells and are normally preceded by sensing of host-specific metabolic signals, which in turn can influence the pathogen's virulence state. Previously, we reported that the intracellular bacterial pathogen Listeria monocytogenes responds to low availability of branched-chain amino acids (BCAA) within mammalian cells by up-regulating both BCAA biosynthesis and virulence genes. The induction of virulence genes required the BCAA-responsive transcription regulator, CodY, but the molecular mechanism governing this mode of regulation was unclear. In this report, we demonstrate that CodY directly binds the coding sequence of the L. monocytogenes master virulence activator gene, prfA, 15 nt downstream of its start codon, and that this binding results in up-regulation of prfA transcription specifically under low concentrations of BCAA. Mutating this site abolished CodY binding and reduced prfA transcription in macrophages, and attenuated bacterial virulence in mice. Notably, the mutated binding site did not alter prfA transcription or PrfA activity under other conditions that are known to activate PrfA, such as during growth in the presence of glucose-1-phosphate. This study highlights the tight crosstalk between L. monocytogenes metabolism and virulence' while revealing novel features of CodY-mediated regulation. PMID:25430920

  4. Effects of Cu and Ni additions on the heat affected zone (HAZ) microstructure and mechanical properties of a C-Mn niobium microalloyed steel

    International Nuclear Information System (INIS)

    Ale, Ricardo Miranda; Rebello, Joao Marques A.; Charlier, Jacques

    1996-01-01

    The influence of small additions of Cu and Ni on the heat affected zone microstructure and mechanical properties, particularly toughness, of C-Mn microalloyed steel has been evaluated. Cu and Ni additions improved the toughness of both coarse grained region and coarse grained region reheated intercritically due to the formation of lower bainite and avoiding Nb precipitation hardening, respectively. With Cu and Ni additions the embrittlement of the coarse grained region reheated intercritically, due to MA constituent, is counterbalanced by the formation of fine ferrite recrystallized grains near the prior austenite grain boundaries and the stabilisation of austenite between ferrite laths. (author)

  5. The effect of some organic and non-organic additions on the shielding and mechanical properties of radiation shielding concrete

    International Nuclear Information System (INIS)

    Kharita, M. H.; Yousef, S.; Al-Nassar, M.

    2011-04-01

    Few studies on the effect of some additives on the shielding properties of concrete have been carried out in this research. These studies included the effect of carbon powder, boron compounds, and waste polyethylene. The effect of water to cement ratio has been studied too. The research results showed that carbon powder and some boron compounds could be used to improve shielding concrete properties, and the possibility to add waste polyethylene in shielding concrete without effects on shielding properties. No significant effect for water to cement ratio on shielding properties of concrete. (author)

  6. Effects of LaB{sub 6} additions on the microstructure and mechanical properties of a sintered and hot worked P/M Ti alloy

    Energy Technology Data Exchange (ETDEWEB)

    Lou, Jia; Gabbitas, Brian, E-mail: briang@waikato.ac.nz; Yang, Fei; Raynova, Stella; Lu, Huiyang

    2016-07-25

    A trace amount of LaB{sub 6} powder was added to P/M Ti and Ti–6Al–4V alloy to improve mechanical properties and refine the microstructure. After sintering, TiB whiskers and La{sub 2}O{sub 3} dispersoids had formed in the microstructure. In a CP Ti alloy, the generation of secondary phases leads to a much refined microstructure, but the alignment of TiB whiskers led to a variation in mechanical properties. Open die forging (ODF) or powder compact extrusion (PCE) was carried out on sintered Ti–6Al–4V alloy to further improve the mechanical properties. This caused severe deformation and re-alignment of the TiB whiskers. Comparing the properties of hot worked Ti–6Al–4V alloy and Ti–6Al–4V alloy with boron additions, an addition of LaB{sub 6} leads to slightly lower strength but gives significant better ductility. - Highlights: • LaB{sub 6} powder was added to sintered and hot worked Ti and Ti–6Al–4V alloy. • TiB whiskers and La{sub 2}O{sub 3} dispersoids formed in the microstructure. • Different alignments of TiB{sub w} led to a variation in mechanical properties. • Hot working caused severe deformation and re-alignment of TiB{sub w}. • An addition of LaB{sub 6} is better than pure boron additions.

  7. Modeling the mechanical and aging properties of silicone rubber and foam - stockpile-historical & additively manufactured materials

    Energy Technology Data Exchange (ETDEWEB)

    Maiti, A; Weisgraber, T H; Gee, R H

    2014-09-30

    M97* and M9763 belong to the M97xx series of cellular silicone materials that have been deployed as stress cushions in some of the LLNL systems. Their purpose of these support foams is to distribute the stress between adjacent components, maintain relative positioning of various components, and mitigate the effects of component size variation due to manufacturing and temperature changes. In service these materials are subjected to a continuous compressive strain over long periods of time. In order to ensure their effectiveness, it is important to understand how their mechanical properties change over time. The properties we are primarily concerned about are: compression set, load retention, and stress-strain response (modulus).

  8. Effects of Ti addition and heat treatments on mechanical and electrical properties of Cu-Ni-Si alloys

    Science.gov (United States)

    Kim, Hyung Giun; Lee, Taeg Woo; Kim, Sang Min; Han, Seung Zeon; Euh, Kwangjun; Kim, Won Yong; Lim, Sung Hwan

    2013-01-01

    The mechanical and electrical properties of Cu-5.98Ni-1.43Si and Cu-5.98Ni-1.29Si-0.24Ti alloys under heat treatment at 400 and 500 °C after hot- and cold-rolling were investigated, and a microstructural analysis using transmission electron microscopy was performed. Cu-5.98Ni-1.29Si-0.24Ti alloy displayed the combined Vickers hardness/electrical conductivity value of 315.9 Hv/57.1%IACS. This was attributed to a decrease of the solution solubility of Ni and Si in the Cu matrix by the formation of smaller and denser δ-Ni2Si precipitates. Meanwhile, the alloyed Ti was detected in the coarse Ni-Si-Ti phase particles, along with other large Ni-Si phase particles, in Cu-5.98Ni-1.29Si-0.24Ti.

  9. Tensile Fracture Behavior and Failure Mechanism of Additively-Manufactured AISI 4140 Low Alloy Steel by Laser Engineered Net Shaping

    Directory of Open Access Journals (Sweden)

    Hoyeol Kim

    2017-11-01

    Full Text Available AISI 4140 powder was directly deposited on AISI 4140 wrought substrate using laser engineered net shaping (LENS to investigate the compatibility of a LENS-deposited part with the substrate. Tensile testing at room temperature was performed to evaluate the interface bond performance and fracture behavior of the test specimens. All the samples failed within the as-deposited zone, indicating that the interfacial bond is stronger than the interlayer bond inside the deposit. The fracture surfaces were analyzed using scanning electron microscopy (SEM and energy disperse X-ray spectrometry (EDS. Results show that the tensile fracture failure of the as-deposited part is primarily affected by lack-of-fusion defects, carbide precipitation, and oxide particles inclusions, which causes premature failure of the deposit by deteriorating the mechanical properties and structural integrity.

  10. Do pathogens become more virulent as they spread? Evidence from the amphibian declines in Central America.

    Science.gov (United States)

    Phillips, Ben L; Puschendorf, Robert

    2013-09-07

    The virulence of a pathogen can vary strongly through time. While cyclical variation in virulence is regularly observed, directional shifts in virulence are less commonly observed and are typically associated with decreasing virulence of biological control agents through coevolution. It is increasingly appreciated, however, that spatial effects can lead to evolutionary trajectories that differ from standard expectations. One such possibility is that, as a pathogen spreads through a naive host population, its virulence increases on the invasion front. In Central America, there is compelling evidence for the recent spread of pathogenic Batrachochytrium dendrobatidis (Bd) and for its strong impact on amphibian populations. Here, we re-examine data on Bd prevalence and amphibian population decline across 13 sites from southern Mexico through Central America, and show that, in the initial phases of the Bd invasion, amphibian population decline lagged approximately 9 years behind the arrival of the pathogen, but that this lag diminished markedly over time. In total, our analysis suggests an increase in Bd virulence as it spread southwards, a pattern consistent with rapid evolution of increased virulence on Bd's invading front. The impact of Bd on amphibians might therefore be driven by rapid evolution in addition to more proximate environmental drivers.

  11. Effect of Yttrium Addition on the Microstructure and Mechanical Properties of Cu-Rich Nano-phase Strengthened Ferritic Steel

    Science.gov (United States)

    Liu, Hongyu; He, Jibai; Luan, Guoqing; Ke, Mingpeng; Fang, Haoyan; Lu, Jianduo

    2018-03-01

    Due to the brittle problem of Cu-rich nano-phase strengthened ferritic steel (CNSFS) after air aging, the effect of Y addition in CNSFS was systemically investigated in the present work. The microstructure, tensile fracture morphology and oxide layer of the steels were surveyed by optical microscope and scanning electron microscope. Transmission electron microscope with the combination of energy-dispersive x-ray spectroscopy and selected area electron diffraction was used to analyze the morphology, size, number density, chemical compositions and crystal structure for nano-crystalline precipitates. Microstructural examinations of the nano-crystalline precipitates show that Cu-rich precipitates and Y compounds in the range of 2-10 and 50-100 nm, respectively, form in the Y-containing steel; meanwhile, the average size of nano-crystalline precipitates in Y-containing steel is larger, but the number density is lower, and the ferritic grains are refined. Furthermore, the tensile strength and ductility of Y-containing steel after air aging are improved, whereas the tensile strength is enhanced and the ductility decreased after vacuum aging. The drag effect of Y makes the oxide layer thinner and be compacted. Tensile properties of CNSFS after air aging are improved due to the refined grains, antioxidation and purification by the addition of Y.

  12. Enhancement of mechanical strength in hot-pressed TiB2 composites by the addition of Fe and Ni

    International Nuclear Information System (INIS)

    Yen, C.F.; Yust, C.S.; Clark, G.W.

    1978-01-01

    Improvement in the fracture strength of TiB 2 composites through the addition of Fe and Ni is reported. Beam specimens containing up to 20 wt % of the metal component were fabricated by hot pressing above the eutectic temperature. Four point bending results indicated that the observed enhancement in strength was proportional to the vol % of the metal present. The results also revealed that TiB 2 --Ni composites have slightly better strength than TiB 2 --Fe samples at elevated temperatures, and that their strengths were consistently about twice that of pure TiB 2 . They also did not exhibit any serious degradation in strength up to 700 0 C. The fracture behavior was characterized using optical and scanning electron microscopy. The strengthening appears to be related to the presence of a metallic grain boundary phase between TiB 2 particles. The results further suggested that the formation of a special eutectic-like grain microstructure could render additional strengthening

  13. Reactions of N+ ions with ethylene: a theoretical study on the addition mechanism into the olefin double bond

    International Nuclear Information System (INIS)

    Di Stefano, Marco; Rosi, Marzio; Sgamellotti, Antonio

    2004-01-01

    The potential energy surface of the reaction between ethylene molecules and N + ions is investigated by using the DFT hybrid functional B3LYP with the 6-31G* basis set. The addition channel leading to the intermediate C 2 NH 4 + is considered. We study eighteen structures of the triplet C 2 NH 4 + cations and the transition states for their isomerizations. Then, we consider the release of a H atom to form the doublet C 2 NH 3 + cations. To obtain more accurate values of reaction energetics and barrier heights, coupled cluster CCSD(T) calculations with the 6-311G** basis set are performed on the B3LYP/6-31G* optimized geometries. The addition of N + into C 2 H 4 is computed as a barrierless process leading to the triplet 1-aziridynil cation which, by ring opening, can easily evolve into the 2-azaallyl isomer. This species can then release a hydrogen atom to form the 2-azaallene cation, process that is computed to be the most likely channel

  14. Quorum-sensing regulators control virulence gene expression in Vibrio cholerae

    OpenAIRE

    Zhu, Jun; Miller, Melissa B.; Vance, Russell E.; Dziejman, Michelle; Bassler, Bonnie L.; Mekalanos, John J.

    2002-01-01

    The production of virulence factors including cholera toxin and the toxin-coregulated pilus in the human pathogen Vibrio cholerae is strongly influenced by environmental conditions. The well-characterized ToxR signal transduction cascade is responsible for sensing and integrating the environmental information and controlling the virulence regulon. We show here that, in addition to the known components of the ToxR signaling circuit, quorum-sensing regulators are involved in regulation of V. ch...

  15. Can Clays in Livestock Feed Promote Antibiotic Resistance and Virulence in Pathogenic Bacteria?

    OpenAIRE

    Rodr?guez-Rojas, Alexandro; Rodr?guez-Beltr?n, Jer?nimo; Valverde, Jos? Ram?n; Bl?zquez, Jes?s

    2015-01-01

    The use of antibiotics in animal husbandry has long been associated with the appearance of antibiotic resistance and virulence factor determinants. Nonetheless, the number of cases of human infection involving resistant or virulent microorganisms that originate in farms is increasing. While many antibiotics have been banned as dietary supplements in some countries, other additives thought to be innocuous in terms of the development and spread of antibiotic resistance are used as growth promot...

  16. Anaerobiosis induced virulence of Salmonella typhi

    DEFF Research Database (Denmark)

    Kapoor, Sarika; Singh, R D; Sharma, P C

    2002-01-01

    , we examined the effect of anaerobiosis on the virulence of Salmonella Typhi, a Gram negative bacteria which invades through the gut mucosa and is responsible for typhoid fever. METHODS: Salmonella Typhi (ty2) was cultured in aerobic and anaerobic conditions to compare its virulence by rabbit ileal...

  17. Evolution of viral virulence: empirical studies

    Science.gov (United States)

    Kurath, Gael; Wargo, Andrew R.

    2016-01-01

    The concept of virulence as a pathogen trait that can evolve in response to selection has led to a large body of virulence evolution theory developed in the 1980-1990s. Various aspects of this theory predict increased or decreased virulence in response to a complex array of selection pressures including mode of transmission, changes in host, mixed infection, vector-borne transmission, environmental changes, host vaccination, host resistance, and co-evolution of virus and host. A fundamental concept is prediction of trade-offs between the costs and benefits associated with higher virulence, leading to selection of optimal virulence levels. Through a combination of observational and experimental studies, including experimental evolution of viruses during serial passage, many of these predictions have now been explored in systems ranging from bacteriophage to viruses of plants, invertebrates, and vertebrate hosts. This chapter summarizes empirical studies of viral virulence evolution in numerous diverse systems, including the classic models myxomavirus in rabbits, Marek's disease virus in chickens, and HIV in humans. Collectively these studies support some aspects of virulence evolution theory, suggest modifications for other aspects, and show that predictions may apply in some virus:host interactions but not in others. Finally, we consider how virulence evolution theory applies to disease management in the field.

  18. Virulence, serotype and phylogenetic groups of diarrhoeagenic ...

    African Journals Online (AJOL)

    Dr DADIE Thomas

    2014-02-17

    Feb 17, 2014 ... The virulence, serotype and phylogenetic traits of diarrhoeagenic Escherichia coli were detected in 502 strains isolated during digestive infections. Molecular detection of the target virulence genes, rfb gene of operon O and phylogenetic grouping genes Chua, yjaA and TSPE4.C2 was performed.

  19. The Composition and Spatial Patterns of Bacterial Virulence Factors and Antibiotic Resistance Genes in 19 Wastewater Treatment Plants.

    Directory of Open Access Journals (Sweden)

    Bing Zhang

    Full Text Available Bacterial pathogenicity and antibiotic resistance are of concern for environmental safety and public health. Accumulating evidence suggests that wastewater treatment plants (WWTPs are as an important sink and source of pathogens and antibiotic resistance genes (ARGs. Virulence genes (encoding virulence factors are good indicators for bacterial pathogenic potentials. To achieve a comprehensive understanding of bacterial pathogenic potentials and antibiotic resistance in WWTPs, bacterial virulence genes and ARGs in 19 WWTPs covering a majority of latitudinal zones of China were surveyed by using GeoChip 4.2. A total of 1610 genes covering 13 virulence factors and 1903 genes belonging to 11 ARG families were detected respectively. The bacterial virulence genes exhibited significant spatial distribution patterns of a latitudinal biodiversity gradient and a distance-decay relationship across China. Moreover, virulence genes tended to coexist with ARGs as shown by their strongly positive associations. In addition, key environmental factors shaping the overall virulence gene structure were identified. This study profiles the occurrence, composition and distribution of virulence genes and ARGs in current WWTPs in China, and uncovers spatial patterns and important environmental variables shaping their structure, which may provide the basis for further studies of bacterial virulence factors and antibiotic resistance in WWTPs.

  20. CoCr F75 scaffolds produced by additive manufacturing: Influence of chemical etching on powder removal and mechanical performance.

    Science.gov (United States)

    Hooreweder, Brecht Van; Lietaert, Karel; Neirinck, Bram; Lippiatt, Nicholas; Wevers, Martine

    2017-06-01

    Additive manufacturing techniques such as Selective Laser Melting (SLM) allow carefully controlled production of complex porous structures such as scaffolds. These advanced structures can offer many interesting advantages over conventionally produced products in terms of biological response and patient specific design. The surface finish of AM parts is often poor because of the layer wise nature of the process and adhering particles. Loosening of these particles after implantation should be avoided, as this could put the patient's health at risk. In this study the use of hydrochloric acid and hydrogen peroxide mixtures for surface treatment of cobalt-chromium F75 scaffolds produced by SLM is investigated. A 27% HCl and 8% H 2 O 2 etchant proved effective in removing adhering particles while retaining the quasi-static and fatigue performance of the scaffolds. Copyright © 2017 Elsevier Ltd. All rights reserved.

  1. Evolution of plastic deformation and its effect on mechanical properties of laser additive repaired Ti64ELI titanium alloy

    Science.gov (United States)

    Zhao, Zhuang; Chen, Jing; Tan, Hua; Lin, Xin; Huang, Weidong

    2017-07-01

    In this paper, laser additive manufacturing (LAM) technology with powder feeding has been employed to fabricate 50%LAMed specimens (i.e. the volume fraction of the laser deposited zone was set to 50%). With aid of the 3D-DIC technique, the tensile deformation behavior of 50%LAMed Ti64ELI titanium alloy was investigated. The 50%LAMed specimen exhibits a significant characteristic of strength mismatch due to the heterogeneous microstructure. The tensile fracture of 50%LAMed specimen occurs in WSZ (wrought substrate zone), but the tensile strength is slightly higher and the plastic elongation is significantly lower than that of the wrought specimen. The 3D-DIC results shows that the 50%LAMed specimen exhibits a characteristic of dramatic plastic strain heterogeneity and the maximal strain is invariably concentrated in WSZ. The ABAQUS simulation indicates that, the LDZ (laser deposited zone) can constrain the plastic deformation of the WSZ and biaxial stresses develop at the interface after yielding.

  2. Virulence Gene Pool Detected in Bovine Group C Streptococcus dysgalactiae subsp. dysgalactiae Isolates by Use of a Group A S. pyogenes Virulence Microarray ▿

    Science.gov (United States)

    Rato, Márcia G.; Nerlich, Andreas; Bergmann, René; Bexiga, Ricardo; Nunes, Sandro F.; Vilela, Cristina L.; Santos-Sanches, Ilda; Chhatwal, Gursharan S.

    2011-01-01

    A custom-designed microarray containing 220 virulence genes of Streptococcus pyogenes (group A Streptococcus [GAS]) was used to test group C Streptococcus dysgalactiae subsp. dysgalactiae (GCS) field strains causing bovine mastitis and group C or group G Streptococcus dysgalactiae subsp. equisimilis (GCS/GGS) isolates from human infections, with the latter being used for comparative purposes, for the presence of virulence genes. All bovine and all human isolates carried a fraction of the 220 genes (23% and 39%, respectively). The virulence genes encoding streptolysin S, glyceraldehyde-3-phosphate dehydrogenase, the plasminogen-binding M-like protein PAM, and the collagen-like protein SclB were detected in the majority of both bovine and human isolates (94 to 100%). Virulence factors, usually carried by human beta-hemolytic streptococcal pathogens, such as streptokinase, laminin-binding protein, and the C5a peptidase precursor, were detected in all human isolates but not in bovine isolates. Additionally, GAS bacteriophage-associated virulence genes encoding superantigens, DNase, and/or streptodornase were detected in bovine isolates (72%) but not in the human isolates. Determinants located in non-bacteriophage-related mobile elements, such as the gene encoding R28, were detected in all bovine and human isolates. Several virulence genes, including genes of bacteriophage origin, were shown to be expressed by reverse transcriptase PCR (RT-PCR). Phylogenetic analysis of superantigen gene sequences revealed a high level (>98%) of identity among genes of bovine GCS, of the horse pathogen Streptococcus equi subsp. equi, and of the human pathogen GAS. Our findings indicate that alpha-hemolytic bovine GCS, an important mastitis pathogen and considered to be a nonhuman pathogen, carries important virulence factors responsible for virulence and pathogenesis in humans. PMID:21525223

  3. Differential expression pattern of Vago in bumblebee (Bombus terrestris), induced by virulent and avirulent virus infections.

    Science.gov (United States)

    Niu, Jinzhi; Meeus, Ivan; Smagghe, Guy

    2016-09-29

    Viruses are one of the main drivers of the decline of domesticated and wild bees but the mechanisms of antiviral immunity in pollinators are poorly understood. Recent work has suggested that next to the small interfering RNA (siRNA) pathway other immune-related pathways play a role in the defense of the bee hosts against viral infection. In addition, Vago plays a role in the cross-talk between the innate immune pathways in Culex mosquito cells. Here we describe the Vago orthologue in bumblebees of Bombus terrestris, and investigated its role upon the infection of two different bee viruses, the virulent Israeli acute paralysis virus (IAPV) and the avirulent slow bee paralysis virus (SBPV). Our results showed that BtVago was downregulated upon the infection of IAPV that killed all bumblebees, but not with SBPV where the workers survived the virus infection. Thus, for the first time, Vago/Vago-like expression appears to be associated with the virulence of virus and may act as a modulator of antiviral immunity.

  4. Unravelling the differences: comparative proteomic analysis of a clonal virulent and an attenuated Histomonas meleagridis strain.

    Science.gov (United States)

    Monoyios, Andreas; Patzl, Martina; Schlosser, Sarah; Hess, Michael; Bilic, Ivana

    2018-02-01

    The current study focused on Histomonas meleagridis, a unicellular protozoan, responsible for histomonosis in poultry. Recently, the occurrence of the disease increased due to the ban of effective chemotherapeutic drugs. Basic questions regarding the molecular biology, virulence mechanisms or even life cycle of the flagellate are still puzzling. In order to address some of these issues, we conducted a comparative proteomic analysis of a virulent and an attenuated H. meleagridis strain traced back to a single cell and propagated in vitro as monoxenic mono-eukaryotic cultures. Using two-dimensional electrophoresis (2-DE) for proteome visualization with computational 2-DE gel image and statistical analysis, upregulated proteins in either of the two H. meleagridis strains were detected. Statistical analysis fulfilling two criteria (≥threefold upregulation and P singled out 32 spots as specific for the flagellate. These spots were shown to correspond to 24 different proteins that reflect the increased metabolism, in vitro adaptation of the parasite, and amoeboid morphology. In addition to H. meleagridis proteins, the analysis identified differential expression of Escherichia coli DH5α proteins that could have been influenced by the co-cultivated H. meleagridis strain, indicating a reciprocal interaction of these two organisms during monoxenic cultivation. Copyright © 2017 The Author(s). Published by Elsevier Ltd.. All rights reserved.

  5. Production Of Some Virulence Factors Under Different Growth ...

    African Journals Online (AJOL)

    Production Of Some Virulence Factors Under Different Growth Conditions And Antibiotic Susceptibility Pattern Of ... Animal Research International ... Keywords: Virulence, Haemolytic activity, Susceptibility, Antibiotics, Aeromonas hydrophila

  6. Influence of Cr and Y Addition on Microstructure, Mechanical Properties, and Corrosion Resistance of SPSed Fe-Based Alloys

    Science.gov (United States)

    Muthaiah, V. M. Suntharavel; Mula, Suhrit

    2018-03-01

    Present work investigates the microstructural stability during spark plasma sintering (SPS) of Fe-Cr-Y alloys, its mechanical properties and corrosion behavior for its possible applications in nuclear power plant and petrochemical industries. The SPS was carried out for the Fe-7Cr-1Y and Fe-15Cr-1Y alloys at 800 °C, 900 °C, and 1000 °C due to their superior thermal stability as reported in Muthaiah et al. [Mater Charact 114:43-53, 2016]. Microstructural analysis through TEM and electron back scattered diffraction confirmed that the grain sizes of the sintered samples depicted a dual size grain distribution with >50 pct grains within a range of 200 nm and remaining grains in the range 200 nm to 2 µm. The best combination of hardness, wear resistance, and corrosion behavior was achieved for the samples sintered at 1000 °C. The high hardness (9.6 GPa), minimum coefficient of friction (0.25), and extremely low wear volume (0.00277 × 10-2 mm3) and low corrosion rate (3.43 mpy) are discussed in the light of solid solution strengthening, grain size strengthening, grain boundary segregation, excellent densification due to diffusion bonding, and precipitation hardening due to uniformly distributed nanosize Fe17Y2 phase in the alloy matrix. The SEM analysis of the worn surface and corroded features corroborated well with the wear resistance and corrosion behavior of the corresponding samples.

  7. Reconstituted injectable hyaluronic acid: expanded applications in facial aesthetics and additional thoughts on the mechanism of action in cosmetic medicine.

    Science.gov (United States)

    Fagien, Steven; Cassuto, Daniel

    2012-07-01

    As we currently have a better understanding of the components of facial aging, injectable filling agents have a larger role in nonsurgical facial rejuvenation. Many products are now available worldwide as options for treating the spectrum of indications that include particular agents used for the treatment of various facial rhytides and in larger quantities for regional or panfacial volumization. The latter indication has been most popularly treated with a host of agents classified as hyaluronans or injectable hyaluronic acid gels. The former had been traditionally and more successfully treated with injectable collagen or dermal matrix agents. Attempts to confuse these generalized approaches have often led to unsatisfactory results. With the precipitous disappearance of the availability of most injectable collagen substances, other methods of treating finer facial rhytides have been explored. Of the many options available for the treatment of facial fine lines, the authors describe a novel technique of formulating reduced concentrations of existing hyaluronic acid gels by variable dilution/reconstitution. Over 350 of the authors' collective patients have been treated with this approach. The results have been highly satisfactory, with greater persistence, and have challenged traditional concepts of mechanism of action and biodegradation and suggest alternative options in formulations of currently available products. Reconstituted injectable hyaluronic acid is a highly effective and viable alternative for the aesthetic treatment of facial fine lines and other components of aging. Observations, treatment guidelines, and a rationale for this novel use and concepts to explain these finding are contained in this article.

  8. Effect of Graphene Nanoplatelets addition on mechanical properties of pure aluminum using a semi-powder method

    Directory of Open Access Journals (Sweden)

    Muhammad Rashad

    2014-04-01

    Full Text Available In recent years, graphene has attracted considerable research interest in all fields of science due to its unique properties. Its excellent mechanical properties lead it to be used in nano-composites for strength enhancement. This paper reports an Aluminum–Graphene Nanoplatelets (Al/GNPs composite using a semi-powder method followed by hot extrusion. The effect of GNP nano-particle integration on tensile, compressive and hardness response of Al is investigated in this paper. It is demonstrated that 0.3 wt% Graphene Nanoplatelets distributed homogeneously in the matrix aluminum act as an effective reinforcing filler to prevent deformation. Compared to monolithic aluminum (in tension, Al–0.3 wt% GNPs composite exhibited higher 0.2% yield strength (+14.7%, ultimate tensile strength (+11.1% and lower failure strain (−40.6%. Surprisingly, compared to monolithic Al (in compression, Al–0.3 wt% GNPs composite exhibited same 0.2% compressive yield strength and lower ultimate compression strength (−7.8%, and lower failure strain (−20.2%. The Al–0.3 wt% GNPs composite exhibited higher Vickers hardness compared to monolithic aluminum (+11.8%. Scanning electron microscopy (SEM, Energy-Dispersive X-ray Spectroscopy (EDS and X-ray diffraction (XRD were used to investigate the surface morphology, elemental percentage composition, and phase analysis, respectively.

  9. High-throughput exploration of thermoelectric and mechanical properties of amorphous NbO{sub 2} with transition metal additions

    Energy Technology Data Exchange (ETDEWEB)

    Music, Denis, E-mail: music@mch.rwth-aachen.de; Geyer, Richard W.; Hans, Marcus [Materials Chemistry, RWTH Aachen University, Kopernikusstr. 10, 52074 Aachen (Germany)

    2016-07-28

    To increase the thermoelectric efficiency and reduce the thermal fatigue upon cyclic heat loading, alloying of amorphous NbO{sub 2} with all 3d and 5d transition metals has systematically been investigated using density functional theory. It was found that Ta fulfills the key design criteria, namely, enhancement of the Seebeck coefficient and positive Cauchy pressure (ductility gauge). These quantum mechanical predictions were validated by assessing the thermoelectric and elastic properties on combinatorial thin films, which is a high-throughput approach. The maximum power factor is 2813 μW m{sup −1} K{sup −2} for the Ta/Nb ratio of 0.25, which is a hundredfold increment compared to pure NbO{sub 2} and exceeds many oxide thermoelectrics. Based on the elasticity measurements, the consistency between theory and experiment for the Cauchy pressure was attained within 2%. On the basis of the electronic structure analysis, these configurations can be perceived as metallic, which is consistent with low electrical resistivity and ductile behavior. Furthermore, a pronounced quantum confinement effect occurs, which is identified as the physical origin for the Seebeck coefficient enhancement.

  10. High-throughput exploration of thermoelectric and mechanical properties of amorphous NbO_2 with transition metal additions

    International Nuclear Information System (INIS)

    Music, Denis; Geyer, Richard W.; Hans, Marcus

    2016-01-01

    To increase the thermoelectric efficiency and reduce the thermal fatigue upon cyclic heat loading, alloying of amorphous NbO_2 with all 3d and 5d transition metals has systematically been investigated using density functional theory. It was found that Ta fulfills the key design criteria, namely, enhancement of the Seebeck coefficient and positive Cauchy pressure (ductility gauge). These quantum mechanical predictions were validated by assessing the thermoelectric and elastic properties on combinatorial thin films, which is a high-throughput approach. The maximum power factor is 2813 μW m"−"1 K"−"2 for the Ta/Nb ratio of 0.25, which is a hundredfold increment compared to pure NbO_2 and exceeds many oxide thermoelectrics. Based on the elasticity measurements, the consistency between theory and experiment for the Cauchy pressure was attained within 2%. On the basis of the electronic structure analysis, these configurations can be perceived as metallic, which is consistent with low electrical resistivity and ductile behavior. Furthermore, a pronounced quantum confinement effect occurs, which is identified as the physical origin for the Seebeck coefficient enhancement.

  11. Main functions and taxonomic distribution of virulence genes in Brucella melitensis 16 M.

    Directory of Open Access Journals (Sweden)

    Aniel Jessica Leticia Brambila-Tapia

    Full Text Available Many virulence genes have been detected in attenuated mutants of Brucella melitensis 16 M; nevertheless, a complete report of these genes, including the main Cluster of Orthologous Groups (COG represented as well as the taxonomical distribution among all complete bacterial and archaeal genomes, has not been analyzed. In this work a total of 160 virulence genes that have been reported in attenuated mutants in B. melitensis were included and analyzed. Additionally, we obtained 250 B. melitensis randomly selected genes as a reference group for the taxonomical comparisons. The COGs and the taxonomical distribution profile for 789 nonredundant bacterial and archaeal genomes were obtained and compared with the whole-genome COG distribution and with the 250 randomly selected genes, respectively. The main COGs associated with virulence genes corresponded to the following: intracellular trafficking, secretion and vesicular transport (U; cell motility (N; nucleotide transport and metabolism (F; transcription (K; and cell wall/membrane/envelope biogenesis (M. In addition, we found that virulence genes presented a higher proportion of orthologs in the Euryarchaeota and Proteobacteria phyla, with a significant decrease in Chlamydiae, Bacteroidetes, Tenericutes, Firmicutes and Thermotogae. In conclusion, we found that genes related to specific functions are more relevant to B. melitensis virulence, with the COG U the most significant. Additionally, the taxonomical distribution of virulence genes highlights the importance of these genes in the related Proteobacteria, being less relevant in distant groups of organisms with the exception of Euryarchaeota.

  12. Mechanical characterization of structurally porous biomaterials built via additive manufacturing: experiments, predictive models, and design maps for load-bearing bone replacement implants.

    Science.gov (United States)

    Melancon, D; Bagheri, Z S; Johnston, R B; Liu, L; Tanzer, M; Pasini, D

    2017-11-01

    Porous biomaterials can be additively manufactured with micro-architecture tailored to satisfy the stringent mechano-biological requirements imposed by bone replacement implants. In a previous investigation, we introduced structurally porous biomaterials, featuring strength five times stronger than commercially available porous materials, and confirmed their bone ingrowth capability in an in vivo canine model. While encouraging, the manufactured biomaterials showed geometric mismatches between their internal porous architecture and that of its as-designed counterpart, as well as discrepancies between predicted and tested mechanical properties, issues not fully elucidated. In this work, we propose a systematic approach integrating computed tomography, mechanical testing, and statistical analysis of geometric imperfections to generate statistical based numerical models of high-strength additively manufactured porous biomaterials. The method is used to develop morphology and mechanical maps that illustrate the role played by pore size, porosity, strut thickness, and topology on the relations governing their elastic modulus and compressive yield strength. Overall, there are mismatches between the mechanical properties of ideal-geometry models and as-manufactured porous biomaterials with average errors of 49% and 41% respectively for compressive elastic modulus and yield strength. The proposed methodology gives more accurate predictions for the compressive stiffness and the compressive strength properties with a reduction of the average error to 11% and 7.6%. The implications of the results and the methodology here introduced are discussed in the relevant biomechanical and clinical context, with insight that highlights promises and limitations of additively manufactured porous biomaterials for load-bearing bone replacement implants. In this work, we perform mechanical characterization of load-bearing porous biomaterials for bone replacement over their entire design

  13. The effect of the addition of ground olive stones on the physical and mechanical properties of clay bricks

    Directory of Open Access Journals (Sweden)

    Arezki, S.

    2016-06-01

    Full Text Available This study deals with the effect of ground olive stones (GOS on the performance of fired clay bricks. Seven different clay-GOS mixes with 0, 1, 2, 3, 4, 5 and 10 wt % of GOS respectively were used for making fired brick samples. All samples were fired at 900 °C. The technological properties of the resultant material were then determined, including shrinkage, apparent density, pore size distribution, thermal conductivity, water absorption, and compressive and flexural strength. The addition of GOS to the mixture reduced the compressive strength of fired clay bricks. All clay brick pieces exhibited low firing shrinkage. It was apparent that as the percentage of GOS increased in the body, there was a noticeable increase in porosity. The water absorption coefficient decreased with increasing additions. The results indicated that thermal conductivity decreases with decrease in density and increase in porosity in fired clay bricks.En este trabajo se ha estudiado el efecto de la incorporación de huesos de aceituna triturados en las prestaciones de ladrillos de arcilla cocida. Se utilizaron siete proporciones de huesos de aceituna 0 %, 1 %, 2 %, 3 %, 4 %, 5 % y 10 % en peso. Todas las muestras se calcinaron a 900 °C y posteriormente se determinaron las propiedades resultantes, incluyendo la densidad aparente, retracción, distribución de tamaños de poro, conductividad térmica, absorción de agua y resistencias mecánicas. La adición de huesos de aceituna molidos a la mezcla redujo la resistencia a la compresión de los ladrillos de arcilla cocida. Además se observó que todas las piezas de ladrillo mostraron baja retracción tras exposición a altas temperaturas. Como era de esperar a medida que el porcentaje de huesos de aceituna molidos aumentó, la porosidad se incrementó de manera evidente. El coeficiente de absorción de agua disminuyó con el aumento del porcentaje de sustitución. Los resultados indicaron que la conductividad t

  14. Improvement of nitrogen utilization and soil properties by addition of a mineral soil conditioner: mechanism and performance.

    Science.gov (United States)

    Yan, Xiaodan; Shi, Lin; Cai, Rumeng

    2018-01-01

    A mineral soil conditioner (MSC) composed of activated potash feldspar, gypsum, and calcium carbonate and containing an amount of available mineral nutrients, is shown to be effective for plant growth and acidic soil amelioration. In this study, a field test was conducted over four rice seasons by examining treatment with control check (CK), MSC, biological active carbon, and lime to investigate the nitrogen-use efficiency and mechanism of soil characteristic variations due to the desilicification and allitization of soil as well as the unrestrained use of nitrogen (N) fertilizer in recent years. Influences of MSC on the xylem sap intensity and mean rice yields were evaluated, and the soil type was also analyzed using the FactSage 6.1 Reaction, phase diagram, and Equilib modules. The results of the field trial showed that MSC application increased the xylem sap intensity and nitrogen export intensity by 37.33-39.85% and 31.40-51.20%, respectively. A significant increase (5.63-15.48%) in mean grain yields was achieved with MSC application over that with biological active carbon and lime application. The effects of MSC had a tendency to increase with time in the field experiment results, and grain yields increased after the initial application. The new formation of clay minerals exhibits a significant influence on [Formula: see text] fixation, especially for 2:1 phyllosilicates with illite, owing to the interlayers of the clay minerals. Our preliminary results showed that kaolinite, the main 1:1 phyllosilicate clay mineral in ferralsol, transformed to illite at room temperature as a consequence of the presence of H 4 SiO 4 and available K + supplied by MSC. This indicated that improving the soil quality combined with reducing N losses from soils is an efficient way to control non-point source pollution from agriculture without the risk of decreased in grain yield.

  15. Statistical mechanics of addition polymerisation. Calculations of the expectation and variance of the average atmosphere in growing self avoiding walks

    Science.gov (United States)

    Taniya, Abraham; Deepthi, Murali; Padmanabhan, Alapat

    2018-06-01

    Recent calculations on the change in radial dimensions of reacting (growing) polyethylene in the gas phase experiencing Lennard Jones and Kihara type potentials revealed that a single reacting polyethylene molecule does not experience polymer collapse. This implies that a transition that is the converse of what happens when molten polyethylene crystallizes, i.e. it transforms from random coil like structure to folded rigid rod type structure, occurs. The predicted behaviour of growing polyethylene was explained by treating the head of the growing polymer chain as myopic whereas as the whole chain (i.e. when under equilibrium conditions) being treated as having normal vision, i.e. the growing chain does not see the attractive part of the LJ or Kihara Potentials. In this paper we provide further proof for this argument in two ways. Firstly we carry forward the exact enumeration calculations on growing self avoiding walks reported in that paper to larger values of number of steps by using Monte Carlo type calculations. We thereby assign physical significance to the connective constant of self avoiding walks, which until now was treated as a purely abstract mathematical entity. Secondly since a reacting polymer molecule that grows by addition polymerisation sees only one step ahead at a time, we extend this calculation by estimating the average atmosphere for molecules, with repulsive potential only (growing self avoiding walks in two dimensions), that look at two, three, four, five ...steps ahead. Our calculation shows that the arguments used in the previous work are correct.

  16. Effect of organic additives on mechanical properties of SiC ceramics prepared by a modified gelcasting method

    Directory of Open Access Journals (Sweden)

    Feng Wang

    2016-12-01

    Full Text Available A novel and simple gel system of isobutylene and maleic anhydride (PIBM was used to prepare SiC ceramics. The rheological behaviour of the SiC slurries was investigated as function of organic additives. The SiC slurries with 0.2 wt.% PIBM and 0.2 wt.% tetramethylammonium hydroxide (TMAH showed low viscosity, which was favourable for casting SiC green bodies. In order to obtain homogeneous green bodies, polyvinyl alcohol (PVA was used to assist the dispersion of carbon black in the slurries, and polyethylene glycol (PEG was added to inhibit the surface exfoliation of green bodies. The content of PVA was controlled carefully to avoid the warpage of green bodies during the drying process. Finally, homogeneous defect-free SiC green bodies were successfully fabricated via aqueous gelcasting. The SiC ceramics sintered at 2100 °C (prepared from slurries with solid content of 60 wt.% showed an average flexural strength of 305.7 MPa with porosity of 19.92%.

  17. The OmpA-like protein Loa22 is essential for leptospiral virulence.

    Directory of Open Access Journals (Sweden)

    Paula Ristow

    2007-07-01

    Full Text Available Pathogenic mechanisms of Leptospira interrogans, the causal agent of leptospirosis, remain largely unknown. This is mainly due to the lack of tools for genetic manipulations of pathogenic species. In this study, we characterized a mutant obtained by insertion of the transposon Himar1 into a gene encoding a putative lipoprotein, Loa22, which has a predicted OmpA domain based on sequence identity. The resulting mutant did not express Loa22 and was attenuated in virulence in the guinea pig and hamster models of leptospirosis, whereas the genetically complemented strain was restored in Loa22 expression and virulence. Our results show that Loa22 was expressed during host infection and exposed on the cell surface. Loa22 is therefore necessary for virulence of L. interrogans in the animal model and represents, to our knowledge, the first genetically defined virulence factor in Leptospira species.

  18. Association between virulence and triazole tolerance in the phytopathogenic fungus Mycosphaerella graminicola.

    Directory of Open Access Journals (Sweden)

    Lina Yang

    Full Text Available Host resistance and synthetic antimicrobials such as fungicides are two of the main approaches used to control plant diseases in conventional agriculture. Although pathogens often evolve to overcome host resistance and antimicrobials, the majority of reports have involved qualitative host - pathogen interactions or antimicrobials targeting a single pathogen protein or metabolic pathway. Studies that consider jointly the evolution of virulence, defined as the degree of damage caused to a host by parasite infection, and antimicrobial resistance are rare. Here we compared virulence and fungicide tolerance in the fungal pathogen Mycosphaerella graminicola sampled from wheat fields across three continents and found a positive correlation between virulence and tolerance to a triazole fungicide. We also found that quantitative host resistance selected for higher pathogen virulence. The possible mechanisms responsible for these observations and their consequences for sustainable disease management are discussed.

  19. The effect of scandium addition on microstructure and mechanical properties of Al–Si–Mg alloy: A multi-refinement modifier

    Energy Technology Data Exchange (ETDEWEB)

    Xu, Cong, E-mail: xucong55555@gmail.com [Key Laboratory of Aerospace Advanced Materials and Performance of Ministry of Education, School of Material Science and Engineering, Beihang University, Beijing 100191 (China); Xiao, Wenlong, E-mail: wlxiao@buaa.edu.cn [Key Laboratory of Aerospace Advanced Materials and Performance of Ministry of Education, School of Material Science and Engineering, Beihang University, Beijing 100191 (China); Hanada, Shuji [Institute for Materials Research, Tohoku University, Sendai 980-8577 (Japan); Yamagata, Hiroshi [Center for Advanced Die Engineering and Technology, Gifu University, 1-1 Yanagido, Gifu City, Gifu 501-1193 (Japan); Ma, Chaoli [Key Laboratory of Aerospace Advanced Materials and Performance of Ministry of Education, School of Material Science and Engineering, Beihang University, Beijing 100191 (China)

    2015-12-15

    Effect of scandium (Sc) additions on the microstructure, mechanical properties and fracture behavior of Al–Si–Mg casting alloy (F357) were systematically investigated. It was found that Sc addition caused a multi-refining efficiency on the microstructure of as-cast F357 alloy, including refinement of grains and secondary dendrite arm spacing (SDAS), modification of eutectic Si and harmless disposal of β-Al{sub 5}FeSi phase. Subsequent T6 heat treatment had further induced the complete spheroidization of eutectic Si and precipitation of fine secondary Al{sub 3}Sc dispersoids in the Sc modified alloys. Thus the mechanical properties, especially the ductility, were significantly enhanced by the addition of Sc combined with the heat treatment. The highest ultimate tensile strength, yield strength and elongation were achieved in 0.8 wt.% Sc modified F357 alloy combined with T6 heat treatment. Furthermore, fractographic examinations indicated that the ductile fracture mechanism served as a dominate role in the modified alloys due to the formation of fine, deep and uniformly distributed dimples. - Highlights: • Detailed characterization of the multi-refining microstructure of Sc modified F357 alloy was performed. • The multi-refinement was proposed to refine grain and SDAS, modify eutectic Si and β-phase. • Sc modifier combined with T6 treatment is effective in improving tensile properties. • Modification of eutectic Si in F357 alloy with Sc is consistent with the IIT mechanism.

  20. Hydrogen Abstraction Acetylene Addition and Diels-Alder Mechanisms of PAH Formation:  A Detailed Study Using First Principles Calculations.

    Science.gov (United States)

    Kislov, V V; Islamova, N I; Kolker, A M; Lin, S H; Mebel, A M

    2005-09-01

    Extensive ab initio Gaussian-3-type calculations of potential energy surfaces (PES), which are expected to be accurate within 1-2 kcal/mol, combined with statistical theory calculations of reaction rate constants have been applied to study various possible pathways in the hydrogen abstraction acetylene addition (HACA) mechanism of naphthalene and acenaphthalene formation as well as Diels-Alder pathways to acenaphthalene, phenanthrene, and pyrene. The barrier heights; reaction energies; and molecular parameters of the reactants, products, intermediates, and transition states have been generated for all types of reactions involved in the HACA and Diels-Alder mechanisms, including H abstraction from various aromatic intermediates, acetylene addition to radical sites, ring closures leading to the formation of additional aromatic rings, elimination of hydrogen atoms, H disproportionation, C2H2 cycloaddition, and H2 loss. The reactions participating in various HACA sequences (e.g., Frenklach's, alternative Frenklach's, and Bittner and Howard's routes) are demonstrated to have relatively low barriers and high rate constants under combustion conditions. A comparison of the significance of different HACA mechanisms in PAH growth can be made in the future using PES and molecular parameters obtained in the present work. The results show that the Diels-Alder mechanism cannot compete with the HACA pathways even at high combustion temperatures, because of high barriers and consequently low reaction rate constants. The calculated energetic parameters and rate constants have been compared with experimental and theoretical data available in the literature.

  1. Effects of the addition of casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) on mechanical properties of luting and lining glass ionomer cement

    Science.gov (United States)

    Heravi, Farzin; Bagheri, Hossein; Rangrazi, Abdolrasoul; Mojtaba Zebarjad, Seyed

    2016-07-01

    Recently, the addition of casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) into glass ionomer cements (GICs) has attracted interest due to its remineralization of teeth and its antibacterial effects. However, it should be investigated to ensure that the incorporation of CPP-ACP does not have significant adverse effects on its mechanical properties. The purpose of this study was to evaluate the effects of the addition of CPP-ACP on the mechanical properties of luting and lining GIC. The first step was to synthesize the CPP-ACP. Then the CPP-ACP at concentrations of 1%, 1.56% and 2% of CPP-ACP was added into a luting and lining GIC. GIC without CPP-ACP was used as a control group. The results revealed that the incorporation of CPP-ACP up to 1.56%(w/w) increased the flexural strength (29%), diametral tensile strength (36%) and microhardness (18%), followed by a reduction in these mechanical properties at 2%(w/w) CPP-ACP. The wear rate was significantly decreased (23%) in 1.56%(w/w) concentration of CPP-ACP and it was increased in 2%(w/w). Accordingly, the addition of 1.56%(w/w) CPP-ACP into luting and lining GIC had no adverse effect on the mechanical properties of luting and lining GIC and could be used in clinical practice.

  2. Effect of cerium addition on microstructure and mechanical properties of high-strength Fe85Cr4Mo8V2C1 cast steel

    Energy Technology Data Exchange (ETDEWEB)

    Hufenbach, J., E-mail: j.k.hufenbach@ifw-dresden.de [IFW Dresden, Institute for Complex Materials, P.O. Box 270116, D-01171 Dresden (Germany); Helth, A. [IFW Dresden, Institute for Complex Materials, P.O. Box 270116, D-01171 Dresden (Germany); Lee, M.-H. [Korea Institute of Industrial Technology, Gaetbeol-ro 156, Yeonsu-gu, Incheon 406-840 (Korea, Republic of); Wendrock, H.; Giebeler, L. [IFW Dresden, Institute for Complex Materials, P.O. Box 270116, D-01171 Dresden (Germany); Choe, C.-Y.; Kim, K.-H. [Korea Institute of Industrial Technology, Gaetbeol-ro 156, Yeonsu-gu, Incheon 406-840 (Korea, Republic of); Kühn, U. [IFW Dresden, Institute for Complex Materials, P.O. Box 270116, D-01171 Dresden (Germany); Kim, T.-S. [Korea Institute of Industrial Technology, Gaetbeol-ro 156, Yeonsu-gu, Incheon 406-840 (Korea, Republic of); Eckert, J. [IFW Dresden, Institute for Complex Materials, P.O. Box 270116, D-01171 Dresden (Germany); TU Dresden, Institute of Materials Science, D-01062 Dresden (Germany)

    2016-09-30

    This work presents an investigation on the influence of rare earth additions (Ce) on the microstructure and mechanical properties of a cast Fe85Cr4Mo8V2C1 (element contents in wt%) tool steel. The applied relatively high solidification rate during the casting process promotes the formation of non-equilibrium phases such as martensite, retained austenite as well as a fine network-like structure of complex carbides. This combination of phases and their morphology results in excellent mechanical properties already in the as-cast state. Cerium additions induce a change in phase formation and resulting mechanical properties. Besides morphological and quantitative changes of the main constituent phases, novel carbo-oxide and carbide phases are formed. To investigate this microstructural phenomenon, X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM) combined with energy dispersive X-ray spectroscopy (EDX) were applied. Altogether, the addition of small amounts of the rare earth element cerium together with a tailored casting process results in enhanced mechanical properties compared to the Fe85Cr4Mo8V2C1 alloy and offers new possibilities to obtain high-strength and simultaneously adequate ductile cast steels for advanced tool design.

  3. Grain Refinement and Mechanical Properties of Cu-Cr-Zr Alloys with Different Nano-Sized TiCp Addition.

    Science.gov (United States)

    Zhang, Dongdong; Bai, Fang; Wang, Yong; Wang, Jinguo; Wang, Wenquan

    2017-08-08

    The TiC p /Cu master alloy was prepared via thermal explosion reaction. Afterwards, the nano-sized TiC p /Cu master alloy was dispersed by electromagnetic stirring casting into the melting Cu-Cr-Zr alloys to fabricate the nano-sized TiC p -reinforced Cu-Cr-Zr composites. Results show that nano-sized TiC p can effectively refine the grain size of Cu-Cr-Zr alloys. The morphologies of grain in Cu-Cr-Zr composites changed from dendritic grain to equiaxed crystal because of the addition and dispersion of nano-sized TiC p . The grain size decreased from 82 to 28 μm with the nano-sized TiC p content. Compared with Cu-Cr-Zr alloys, the ultimate compressive strength (σ UCS ) and yield strength (σ 0.2 ) of 4 wt% TiC p -reinforced Cu-Cr-Zr composites increased by 6.7% and 9.4%, respectively. The wear resistance of the nano-sized TiCp-reinforced Cu-Cr-Zr composites increased with the increasing nano-sized TiCp content. The wear loss of the nano-sized TiC p -reinforced Cu-Cr-Zr composites decreased with the increasing TiC p content under abrasive particles. The eletrical conductivity of Cu-Cr-Zr alloys, 2% and 4% nano-sized TiCp-reinforced Cu-Cr-Zr composites are 64.71% IACS, 56.77% IACS and 52.93% IACS, respectively.

  4. Effect of micron size Ni particle addition in Sn–8Zn–3Bi lead-free solder alloy on the microstructure, thermal and mechanical properties

    Energy Technology Data Exchange (ETDEWEB)

    Billah, Md. Muktadir; Shorowordi, Kazi Mohammad; Sharif, Ahmed, E-mail: asharif@mme.buet.ac.bd

    2014-02-05

    Highlights: • Ni-added Sn-Zn-Bi were characterized metallographically, thermally and mechanically. • The volume fraction of α-Zn phase increased with both Bi and Ni in Sn-Zn-Bi alloys. • Micron-sized Ni particles reacted with neither Sn nor Zn to form intermetallics. • Better combination of thermal and mechanical properties can be achieved with Ni. -- Abstract: Micron-sized Ni particle-reinforced Sn–8Zn–3Bi composite solders were prepared by mechanically dispersing Ni particles into Sn–8Zn–3Bi alloy and the bulk properties of the composite solder alloy were characterized metallographically, thermally and mechanically. Different percentage of Ni particle viz. 0.25, 0.5 and 1 wt.% were added in the liquid Sn–8Zn–3Bi alloy and then cast into the metal molds. Melting behavior was studied by differential thermal analyzer (DTA). Microstructural investigation was carried out by both optical and scanning electron microscope. Tensile properties were determined using an Instron Universal Testing Machine at a strain rate 3.00 mm/min. The results indicated that the Ni addition increased the melting temperature of Sn–8Zn–3Bi alloy. The addition of Ni was also found to increase the solidification range. In the Sn–8Zn–3Bi alloy, needle-shaped α-Zn phase was found to be uniformly distributed in the β-Sn matrix. However, it was found that the small amount of Ni addition in Sn–8Zn–3Bi alloy refined the Zn needles throughout the matrix. Also an enhanced precipitation of Zn in the structure was observed with the addition of Ni. All these structural changes improved the mechanical properties like tensile strength and hardness of the newly developed quaternary alloy.

  5. The effects of Mg addition on the microstructure and mechanical properties of thixoformed Al–5%Si–Cu alloys

    International Nuclear Information System (INIS)

    Salleh, M.S.; Omar, M.Z.; Syarif, J.

    2015-01-01

    Highlights: • The average globule size of α-Al decreased when Mg amount is increased. • T6 heat treatment has increased the strength of the thixoformed alloys. • The elongation after T6 heat treatment is even significantly improved. • Thixoformed alloy with high Mg content shows a brittle type fracture. • Thixoformed alloy in T6 condition shows a ductile type fracture. - Abstract: In this study, the effects of different amounts of magnesium (Mg) on the microstructures and tensile properties of thixoformed Al–5%Si–Cu alloys were investigated. Three different alloys containing various amounts of Mg (0.5, 0.8 and 1.2 wt%) were prepared through the cooling slope casting technique, before they were thixoformed using a compression press. Several of the thixoformed samples were then treated with a T6 heat treatment, that is, solution treatment at 525 °C for 8 h, quenching in warm water at 60 °C, followed by aging at 155 °C for 4 h. All of the samples were then characterised by optical microscopy (OM), scanning electron microscopy (SEM) energy dispersive X-ray (EDX) spectroscopy and X-ray diffraction (XRD) analysis as well as by tensile tests. The results revealed that magnesium was able to refine the size of α-Al globules and the eutectic silicon in the samples. It was also observed that a compact π-Al 9 FeMg 3 Si 5 phase was formed when the magnesium content was 0.8 wt% and 1.2 wt%. The mechanical properties of the thixoformed alloys improved significantly after the T6 heat treatment. The highest attainment was recorded by the latter alloy (i.e. with 1.2 wt%Mg) with its ultimate tensile strength (UTS) as high as 306 MPa, yield strength (YS), 264 MPa, and elongation to fracture of 1.8%. The fracture of thixoformed alloy with a low Mg content (0.5 wt%) showed a combination of dimple and cleavage fracture, whereas in the alloy that contained the highest Mg content (1.2 wt%), cleavage fracture was observed

  6. The effects of Mg addition on the microstructure and mechanical properties of thixoformed Al–5%Si–Cu alloys

    Energy Technology Data Exchange (ETDEWEB)

    Salleh, M.S., E-mail: shukor@utem.edu.my [Department of Mechanical and Materials Engineering, Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia, 43600 Selangor (Malaysia); Department of Manufacturing Process, Faculty of Manufacturing Engineering, Universiti Teknikal Malaysia Melaka, Hang Tuah Jaya, 76100 Durian Tunggal, Melaka (Malaysia); Omar, M.Z., E-mail: zaidi@eng.ukm.my [Department of Mechanical and Materials Engineering, Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia, 43600 Selangor (Malaysia); Syarif, J., E-mail: syarif@eng.ukm.my [Department of Mechanical and Materials Engineering, Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia, 43600 Selangor (Malaysia)

    2015-02-05

    Highlights: • The average globule size of α-Al decreased when Mg amount is increased. • T6 heat treatment has increased the strength of the thixoformed alloys. • The elongation after T6 heat treatment is even significantly improved. • Thixoformed alloy with high Mg content shows a brittle type fracture. • Thixoformed alloy in T6 condition shows a ductile type fracture. - Abstract: In this study, the effects of different amounts of magnesium (Mg) on the microstructures and tensile properties of thixoformed Al–5%Si–Cu alloys were investigated. Three different alloys containing various amounts of Mg (0.5, 0.8 and 1.2 wt%) were prepared through the cooling slope casting technique, before they were thixoformed using a compression press. Several of the thixoformed samples were then treated with a T6 heat treatment, that is, solution treatment at 525 °C for 8 h, quenching in warm water at 60 °C, followed by aging at 155 °C for 4 h. All of the samples were then characterised by optical microscopy (OM), scanning electron microscopy (SEM) energy dispersive X-ray (EDX) spectroscopy and X-ray diffraction (XRD) analysis as well as by tensile tests. The results revealed that magnesium was able to refine the size of α-Al globules and the eutectic silicon in the samples. It was also observed that a compact π-Al{sub 9}FeMg{sub 3}Si{sub 5} phase was formed when the magnesium content was 0.8 wt% and 1.2 wt%. The mechanical properties of the thixoformed alloys improved significantly after the T6 heat treatment. The highest attainment was recorded by the latter alloy (i.e. with 1.2 wt%Mg) with its ultimate tensile strength (UTS) as high as 306 MPa, yield strength (YS), 264 MPa, and elongation to fracture of 1.8%. The fracture of thixoformed alloy with a low Mg content (0.5 wt%) showed a combination of dimple and cleavage fracture, whereas in the alloy that contained the highest Mg content (1.2 wt%), cleavage fracture was observed.

  7. Enhancement of the Mechanical Properties of Basalt Fiber-Wood-Plastic Composites via Maleic Anhydride Grafted High-Density Polyethylene (MAPE Addition

    Directory of Open Access Journals (Sweden)

    Yun Lu

    2013-06-01

    Full Text Available This study investigated the mechanisms, using microscopy and strength testing approaches, by which the addition of maleic anhydride grafted high-density polyethylene (MAPE enhances the mechanical properties of basalt fiber-wood-plastic composites (BF-WPCs. The maximum values of the specific tensile and flexural strengths are achieved at a MAPE content of 5%–8%. The elongation increases rapidly at first and then continues slowly. The nearly complete integration of the wood fiber with the high-density polyethylene upon MAPE addition to WPC is examined, and two models of interfacial behavior are proposed. We examined the physical significance of both interfacial models and their ability to accurately describe the effects of MAPE addition. The mechanism of formation of the Model I interface and the integrated matrix is outlined based on the chemical reactions that may occur between the various components as a result of hydrogen bond formation or based on the principle of compatibility, resulting from similar polarity. The Model I fracture occurred on the outer surface of the interfacial layer, visually demonstrating the compatibilization effect of MAPE addition.

  8. Enhancement of the Mechanical Properties of Basalt Fiber-Wood-Plastic Composites via Maleic Anhydride Grafted High-Density Polyethylene (MAPE) Addition.

    Science.gov (United States)

    Chen, Jinxiang; Wang, Yong; Gu, Chenglong; Liu, Jianxun; Liu, Yufu; Li, Min; Lu, Yun

    2013-06-18

    This study investigated the mechanisms, using microscopy and strength testing approaches, by which the addition of maleic anhydride grafted high-density polyethylene (MAPE) enhances the mechanical properties of basalt fiber-wood-plastic composites (BF-WPCs). The maximum values of the specific tensile and flexural strengths are achieved at a MAPE content of 5%-8%. The elongation increases rapidly at first and then continues slowly. The nearly complete integration of the wood fiber with the high-density polyethylene upon MAPE addition to WPC is examined, and two models of interfacial behavior are proposed. We examined the physical significance of both interfacial models and their ability to accurately describe the effects of MAPE addition. The mechanism of formation of the Model I interface and the integrated matrix is outlined based on the chemical reactions that may occur between the various components as a result of hydrogen bond formation or based on the principle of compatibility, resulting from similar polarity. The Model I fracture occurred on the outer surface of the interfacial layer, visually demonstrating the compatibilization effect of MAPE addition.

  9. Influence of silver addition on the microstructure and mechanical properties of squeeze cast Mg-6Al-1Sn-0.3Mn-0.3Ti

    International Nuclear Information System (INIS)

    Acikgoez, Sehzat; Sevik, Hueseyin; Kurnaz, S.Can

    2011-01-01

    Graphical abstract: Highlights: → X-ray diffractometry reveals that the main phases are α-Mg, α-Ti, β-Mg 17 Al 12 and Al 8 Mn 5 in the base alloy. → With addition of silver, Al 81 Mn 19 phase was found. → The mechanical properties of the base alloy are improved with addition of silver. → The fracture surface of base alloy shows relatively deeper and more amount of dimples than that of alloys containing silver. - Abstract: In this study, the effect of silver (0, 0.2, 0.5, and 1 wt.%) on the microstructure and mechanical properties of a magnesium-based alloy (Mg-Al 6 wt.%-Sn 1 wt.%-Mn 0.3 wt.%-Ti 0.3 wt.%) were investigated. The alloys were produced under a controlled atmosphere by a squeeze-casting process. X-ray diffractometry revealed that the main phases are α-Mg, α-Ti, β-Mg 17 Al 12 and Al 8 Mn 5 in the all of alloys. In addition to, Al 81 Mn 19 phase was found with Ag additive. Besides, the amount of β-Mg 17 Al 12 phase was decreased with increasing the amount of Ag. The strength of the base alloy was increased by solid solution mechanism and decreasing the amount of β-Mg 17 Al 12 phase with addition of Ag. Furthermore, existence of Al 81 Mn 19 phase can be acted an important role in the increase on the mechanical properties of the alloys.

  10. Pleiotropic Regulation of Virulence Genes in Streptococcus mutans by the Conserved Small Protein SprV.

    Science.gov (United States)

    Shankar, Manoharan; Hossain, Mohammad S; Biswas, Indranil

    2017-04-15

    Streptococcus mutans , an oral pathogen associated with dental caries, colonizes tooth surfaces as polymicrobial biofilms known as dental plaque. S. mutans expresses several virulence factors that allow the organism to tolerate environmental fluctuations and compete with other microorganisms. We recently identified a small hypothetical protein (90 amino acids) essential for the normal growth of the bacterium. Inactivation of the gene, SMU.2137, encoding this protein caused a significant growth defect and loss of various virulence-associated functions. An S. mutans strain lacking this gene was more sensitive to acid, temperature, osmotic, oxidative, and DNA damage-inducing stresses. In addition, we observed an altered protein profile and defects in biofilm formation, bacteriocin production, and natural competence development, possibly due to the fitness defect associated with SMU.2137 deletion. Transcriptome sequencing revealed that nearly 20% of the S. mutans genes were differentially expressed upon SMU.2137 deletion, thereby suggesting a pleiotropic effect. Therefore, we have renamed this hitherto uncharacterized gene as sprV ( s treptococcal p leiotropic r egulator of v irulence). The transcript levels of several relevant genes in the sprV mutant corroborated the phenotypes observed upon sprV deletion. Owing to its highly conserved nature, inactivation of the sprV ortholog in Streptococcus gordonii also resulted in poor growth and defective UV tolerance and competence development as in the case of S. mutans Our experiments suggest that SprV is functionally distinct from its homologs identified by structure and sequence homology. Nonetheless, our current work is aimed at understanding the importance of SprV in the S. mutans biology. IMPORTANCE Streptococcus mutans employs several virulence factors and stress resistance mechanisms to colonize tooth surfaces and cause dental caries. Bacterial pathogenesis is generally controlled by regulators of fitness that are

  11. Effect of addition of butyl benzyl phthalate plasticizer and zinc oxide nanoparticles on mechanical properties of cellulose acetate butyrate/organoclay biocomposite

    Science.gov (United States)

    Putra, B. A. P.; Juwono, A. L.; Rochman, N. T.

    2017-07-01

    Plastics as packaging materials and coatings undergo increasing demands globally each year. This pose a serious problem to the environment due to its difficulty to degrade. One solution to addressing the problem of plastic wastes is the use of bioplastics. According to the European Organization Bioplastic, one of the biodegradable plastics is derivative of cellulose. To improve mechanical properties of bioplastic, biocomposites are made with the addition of certain additives and fillers. The aim of this study is to investigate the effect of butyl benzyl phthalate plasticizer (BBP) and ZnO nanoparticles addition on mechanical properties of cellulose acetate butyrate (CAB) / organoclay biocomposite. ZnO nanoparticles synthesized from commercial ZnO precursor by using sol-gel size reduction method. ZnO was dissolved in a solution of citric acid in the ratio 1:1 to 1:5 to form zinc citrate. Zinc citrate then decomposed by calcination at temperature of 600oC. ZnO nanoparticles with an average size of 44.4 nm is obtained at a ratio of 1: 2. The addition of ZnO nanoparticles and BBP plasticizer was varied to determine the effect on the mechanical properties of biocomposite. The addition of 10 - 15 %wt ZnO nanoparticles and 30 - 40 %wt BBP plasticizer was studied to determine the effect on the tensile strength, elongation, and modulus elasticity of the biocomposites. Biocomposite films were made by using solution casting method with acetone as solvent. The addition of plasticizer BBP and ZnO nanoparticles by 30% and 10% made biocomposite has a tensile strength of 2.223 MPa.

  12. Assessing the Capacity of the US Health Care System to Use Additional Mechanical Ventilators During a Large-Scale Public Health Emergency.

    Science.gov (United States)

    Ajao, Adebola; Nystrom, Scott V; Koonin, Lisa M; Patel, Anita; Howell, David R; Baccam, Prasith; Lant, Tim; Malatino, Eileen; Chamberlin, Margaret; Meltzer, Martin I

    2015-12-01

    A large-scale public health emergency, such as a severe influenza pandemic, can generate large numbers of critically ill patients in a short time. We modeled the number of mechanical ventilators that could be used in addition to the number of hospital-based ventilators currently in use. We identified key components of the health care system needed to deliver ventilation therapy, quantified the maximum number of additional ventilators that each key component could support at various capacity levels (ie, conventional, contingency, and crisis), and determined the constraining key component at each capacity level. Our study results showed that US hospitals could absorb between 26,200 and 56,300 additional ventilators at the peak of a national influenza pandemic outbreak with robust pre-pandemic planning. The current US health care system may have limited capacity to use additional mechanical ventilators during a large-scale public health emergency. Emergency planners need to understand their health care systems' capability to absorb additional resources and expand care. This methodology could be adapted by emergency planners to determine stockpiling goals for critical resources or to identify alternatives to manage overwhelming critical care need.

  13. Control device for a nuclear reactor with a multitude of control rods, extending into the reactor core from above, with linear drive mechanisms and additional gripper devices

    International Nuclear Information System (INIS)

    Bevilacqua, F.

    1979-01-01

    The components of the additional gripper devices with magnetically operated finger-shaped latches are separated from the also magnetically operated latches of the linear drive mechanisms in order to avoid common-mode failures when fast shutdown is required. Only part of the safety rods are held by the additional gripping devices in the withdrawn position. There is provided for recording elements indicating positively which one of the safety locks is gearing with the control rods. At the upper end of each control rod there is a coupling head held by electromagnetically operated locking devices in the withdrawn position, if control power is available. (DG) [de

  14. Influence of DAD-TA temperature-reducing additive on physical and mechanical properties of bitumen and compaction of asphalt concrete.

    Science.gov (United States)

    Yadykina, V. V.; Akimov, A. E.; Trautvain, A. I.; Kholopov, V. S.

    2018-03-01

    The paper is devoted to the use of DAD-TA temperature-reducing additive for the preparation and pouring of asphalt concrete mixes at reduced temperatures. It also shows positive influence of the modified bitumen on the efficiency of organo-mineral composite compaction at reduced temperatures. Physical and mechanical properties of asphalt concrete with the use of bitumen modified by DAD-TA additive including indicators characterizing road surfacing life are presented. Arguments to use this material from the point of view of its production technology and environmental impact are given.

  15. Evidence for acquisition of virulence effectors in pathogenic chytrids

    Directory of Open Access Journals (Sweden)

    Summers Kyle

    2011-07-01

    Full Text Available Abstract Background The decline in amphibian populations across the world is frequently linked to the infection of the chytrid fungus Batrachochytrium dendrobatidis (Bd. This is particularly perplexing because Bd was only recently discovered in 1999 and no chytrid fungus had previously been identified as a vertebrate pathogen. Results In this study, we show that two large families of known virulence effector genes, crinkler (CRN proteins and serine peptidases, were acquired by Bd from oomycete pathogens and bacteria, respectively. These two families have been duplicated after their acquisition by Bd. Additional selection analyses indicate that both families evolved under strong positive selection, suggesting that they are involved in the adaptation of Bd to its hosts. Conclusions We propose that the acquisition of virulence effectors, in combination with habitat disruption and climate change, may have driven the Bd epidemics and the decline in amphibian populations. This finding provides a starting point for biochemical investigations of chytridiomycosis.

  16. Exploring virulence and immunogenicity in the emerging pathogen Sporothrix brasiliensis.

    Science.gov (United States)

    Della Terra, Paula Portella; Rodrigues, Anderson Messias; Fernandes, Geisa Ferreira; Nishikaku, Angela Satie; Burger, Eva; de Camargo, Zoilo Pires

    2017-08-01

    between S. brasiliensis and S. schenckii proteomes. Despite great diversity in the immunoblot profiles, antibodies were mainly derived against 3-carboxymuconate cyclase, a glycoprotein oscillating between 60 and 70 kDa (gp60-gp70) and a 100-kDa molecule in nearly 100% of the assays. Thus, our data broaden the current view of virulence and immunogenicity in the Sporothrix-sporotrichosis system, substantially expanding the possibilities for comparative genomic with isolates bearing divergent virulence traits and helping uncover the molecular mechanisms and evolutionary pressures underpinning the emergence of Sporothrix virulence.

  17. Influence of addition elements on the stacking-fault energy and mechanical properties of an austenitic Fe-Mn-C steel

    International Nuclear Information System (INIS)

    Dumay, A.; Chateau, J.-P.; Allain, S.; Migot, S.; Bouaziz, O.

    2008-01-01

    We present a thermochemical model of the stacking-fault energy (SFE) in the Fe-Mn-C system with few percent of Cu, Cr, Al and Si in addition. Aluminium strongly increases the SFE, contrary to chromium, while the effect of silicon is more complex. Copper also increases the SFE, but strongly decreases the Neel temperature. The SFE is the relevant parameter that controls mechanical twinning, which is known to be at the origin of the excellent mechanical properties of these steels. Using this model, copper containing Fe-Mn-C grades were elaborated with SFE below 18 mJ/m 2 , in the range where ε-martensite platelets form instead of microtwins during plastic deformation. This substitution of deformation modes, confirmed by X-ray diffraction, does not significantly damage the mechanical properties, as long as the SFE is greater than 12 mJ/m 2 , which avoids the formation of α'-martensite

  18. Preparation and characterization of new dental porcelains, using K-feldspar and quartz raw materials. Effect of B2O3 additions on sintering and mechanical properties.

    Science.gov (United States)

    Harabi, Abdelhamid; Guerfa, Fatiha; Harabi, Esma; Benhassine, Mohamed-Tayeb; Foughali, Lazhar; Zaiou, Soumia

    2016-08-01

    The aim of this work was to determine the effect of temperature and boric oxide (B2O3) addition on sintering and mechanical properties of a newly developed dental porcelain (DP) prepared from local Algerian raw materials. Based on a preliminary work, the new selected composition was 75wt.% feldspar, 20wt.% quartz and 5wt.% kaolin. It was prepared by sintering the mixture at different temperatures (1100-1250°C). The optimum sintering conditions gave a relatively higher density (2.47g/cm(3)) and excellent mechanical properties. The three point flexural strength (3PFS) and Martens micro-hardness of dental porcelains were 149MPa and 2600MPa, respectively. This obtained 3PFS value is more than four times greater than that of hydroxyapatite (HA) value (about 37MPa) sintered under the same conditions. However, the sintering temperature was lowered by about 25 and 50°C for 3 and 5wt.% B2O3 additions, respectively. But, it did not improve furthermore the samples density and their mechanical properties. It has also been found that B2O3 additions provoke a glass matrix composition variation which delays the leucite formation during sintering. Copyright © 2016 Elsevier B.V. All rights reserved.

  19. Effect of the Addition of Nickel Powder and Post Weld Heat Treatment on the Metallurgical and Mechanical Properties of the Welded UNS S32304 Duplex Stainless Steel

    Directory of Open Access Journals (Sweden)

    Ali Tahaei

    Full Text Available Abstract In this research, the effect of the addition of nickel powder and the application of a post weld heat treatment (PWHT on the welding properties of the UNS S32304 lean duplex stainless steel were investigated in order to improve the microstructure and mechanical properties. Nickel powder was directly poured inside the joint gap and mixed with the filler metal during the Gas Tungsten Arc Welding (GTAW process; moreover, the solution heat treatment was performed at 1100 °C for 10 min. The joints were characterized by optical microscopy (OM and the evolution of the phase percentages in the different zones was studied by means of the image analysis technique. Tensile and hardness tests were carried out on the joints in order to evaluate the improvement of the mechanical properties. The results showed that both the addition of nickel powder during the welding process and the post weld heat treatment made it possible to improve the mechanical properties of the weld joints. PWHT had the best effect in restoring the equal percentage of ferrite and austenite compared to the addition of nickel powder.

  20. Effect of zirconium addition on the microstructure and mechanical properties of 15Cr-ODS ferritic Steels consolidated by hot isostatic pressing

    Energy Technology Data Exchange (ETDEWEB)

    Xu, Haijian, E-mail: haijianxu@eis.hokudai.ac.jp [Key Laboratory for Anisotropy and Texture of Materials, Ministry of Education, Northeastern University, Shenyang 110819 (China); Material Science and Engineering, Faculty of Engineering, Hokkaido University, Sapporo 060-8628 (Japan); Lu, Zheng; Wang, Dongmei; Liu, Chunming [Key Laboratory for Anisotropy and Texture of Materials, Ministry of Education, Northeastern University, Shenyang 110819 (China)

    2017-01-15

    The influence of Zr addition on the microstructure and mechanical properties of mechanically alloyed (MA) ODS ferritic steels were studied in this work. The microstructure characteristics included the grain size, oxide particles number densities, size distributions, crystal structures and compositions. TEM foils measurements were complemented by studies of alloys on carbon extraction replica and focus ion beam (FIB) foils. The tensile properties were carried out at different temperatures. The microstructure and mechanical properties were analyzed and compared with nominal compositions (wt.%): Fe-15Cr-2W-0.3Y{sub 2}O{sub 3} and Fe-15Cr −2W-0.3Zr-0.3Y{sub 2}O{sub 3}. The experimental revealed that the addition of Zr increased the volume fraction of the smallest and equiaxed ferritic grains, number density of nano-oxide particles and decreased the average size of oxide particles within the ferritic matrix, promoting the formation of fine trigonal δ-phase Y{sub 4}Zr{sub 3}O{sub 12} nano-oxides and leading to the enhancement of the mechanical properties of the ODS steels.

  1. Influence of Zr and nano-Y{sub 2}O{sub 3} additions on thermal stability and improved hardness in mechanically alloyed Fe base ferritic alloys

    Energy Technology Data Exchange (ETDEWEB)

    Kotan, Hasan, E-mail: hkotan@konya.edu.tr [Department of Metallurgical Engineering and Materials Science, Necmettin Erbakan University, Dere Aşıklar Mah. Demet Sokak, Meram, Konya 42140 (Turkey); Darling, Kris A. [U.S. Army Research Laboratory, Weapons and Materials Research Directorate, RDRL-WMM-F, Aberdeen Proving Ground, MD 21005-5069 (United States); Scattergood, Ronald O.; Koch, Carl C. [Department of Materials Science and Engineering, NC State University, 911 Partners Way, Room 3078, Raleigh, NC 27695-7907 (United States)

    2014-12-05

    The motivation of this work was driven to improve the thermal stability in systems where polymorphic transformations can result in an additional driving force, upsetting the expected thermodynamic stability. In this study, Fe{sub 92}Ni{sub 8} alloys with Zr and nano-Y{sub 2}O{sub 3} additions were produced by ball milling and then annealed at high temperatures. Emphasis was placed on understanding the effects of dispersed nano-Y{sub 2}O{sub 3} particle additions and their effect on microstructural stability at and above the bcc-to-fcc transformation occurring at 700 °C in Fe–Ni systems. Results reveal that microstructural stability and hardness can be promoted by a combination of Zr and Y{sub 2}O{sub 3} additions, that being mostly effective for stability before and after phase transition, respectively. The mechanical strength of these alloys is achieved by a unique microstructure comprised a ultra-fine grain Fe base matrix, which contains dispersions of both nano-scale in-situ formed Zr base intermetallics and ex-situ added Y{sub 2}O{sub 3} secondary oxide phases. Both of these were found to be essential for a combination of high thermal stability and high mechanical strength properties. - Highlights: • Polymorphic transformations can limit the processing of nanostructured powders. • It causes a rapid grain growth and impairs the improved mechanical properties. • We aim to improve the hardness and thermal stability above the phase transformation. • Thermal stability is achieved by a combination of Zr and Y{sub 2}O{sub 3} additions. • Hardness is promoted by in-situ formed and ex-situ added secondary nano phases.

  2. Virulence regulation in Staphylococcus aureus: the need for in vivo analysis of virulence factor regulation.

    Science.gov (United States)

    Pragman, Alexa A; Schlievert, Patrick M

    2004-10-01

    Staphylococcus aureus is a pathogenic microorganism that is responsible for a wide variety of clinical infections. These infections can be relatively mild, but serious, life-threatening infections may result from the expression of staphylococcal virulence factors that are coordinated by virulence regulators. Much work has been done to characterize the actions of staphylococcal virulence regulators in broth culture. Recently, several laboratories showed that transcriptional analyses of virulence regulators in in vivo animal models or in human infection did not correlate with transcriptional analyses accomplished in vitro. In describing the differences between in vitro and in vivo transcription of staphylococcal virulence regulators, we hope to encourage investigators to study virulence regulators using infection models whenever possible.

  3. Effects of Rare Earth Metals addition and aging treatment on the corrosion resistance and mechanical properties of super duplex stainless steels

    Science.gov (United States)

    Park, Yong-Soo; Kim, Soon-Tae; Lee, In-Sung; Song, Chi-Bok

    2002-05-01

    Effects of rare earth metals addition and aging treatment on corrosion resistance and mechanical properties of super duplex stainless steels were investigated using optical/SEM/TEM metallographic examination, an X-ray diffraction test, a potentiodynamic anodic polarization test and a tensile test. The performance of the experimental alloy with 0.32% REM addition was compared with commercial super duplex stainless steel such as SAF 2507 when they were exposed to solution annealing heat treatment and aging treatment. The corrosion resistance in Cl- environments and mechanical properties of the experimental alloy were found superior to those of the commercial duplex stainless steel. The REM with larger atomic radii than those of Cr, Mo and W may fill vacancies inside the matrix and around the grain boundaries, retarding formation of harmful intermetallic σ and η phases. In addition, fine REM oxides/oxy-sulfides (1-3 μm) seemed to enhance the retardation effects. With REM additions, strength and ductility increased due to the phase and grain refinement caused by fine REM oxides and oxy-sulfides.

  4. Effects of the sp element additions on the microstructure and mechanical properties of NiCoFeCr based high entropy alloys

    International Nuclear Information System (INIS)

    Vida, Adam; Varga, Lajos K.; Chinh, Nguyen Quang; Molnar, David; Huang, Shuo; Vitos, Levente

    2016-01-01

    The effects of the sp (Al, Ga, Ge, Sn) element additions on the microstructure and mechanical properties of equimolar NiCoFeCr High Entropy Alloys (HEAs) are investigated. The results of X-ray diffraction measurements combined with scanning electron microscopy SEM investigations, as well as the results of nanoindentation test revealed that while the structure of the basic alloy is full FCC, the addition of sp elements has changed it to a multiphase containing both FCC and BCC components, but in different scales. Accordingly, the addition of sp elements strongly increases the strength of the basic state, especially in the case of alloys where the BCC phase is dominant in the microstructure. The physical properties as the Young’s- and shear moduli of the investigated HEAs were also determined using ultrasound methods. The correlation between these two moduli suggests a general relationship for metallic alloys.

  5. Assessing the capacity of the healthcare system to use additional mechanical ventilators during a large-scale public health emergency (PHE)

    Science.gov (United States)

    Ajao, Adebola; Nystrom, Scott V.; Koonin, Lisa M.; Patel, Anita; Howell, David R.; Baccam, Prasith; Lant, Tim; Malatino, Eileen; Chamberlin, Margaret; Meltzer, Martin I.

    2015-01-01

    A large-scale Public Health Emergency (PHE), like a severe influenza pandemic can generate large numbers of critically ill patients in a short time. We modeled the number of mechanical ventilators that could be used in addition to the number of hospital-based ventilators currently in use. We identified key components of the healthcare system needed to deliver ventilation therapy, quantified the maximum number of additional ventilators that each key component could support at various capacity levels (i.e. conventional, contingency and crisis) and determined the constraining key component at each capacity level. Our study results showed that U.S. hospitals could absorb between 26,200 and 56,300 additional ventilators at the peak of a national influenza pandemic outbreak with robust pre-pandemic planning. This methodology could be adapted by emergency planners to determine stockpiling goals for critical resources or identify alternatives to manage overwhelming critical care need. PMID:26450633

  6. Mechanical and functional properties of two-phase Ni53Mn22Co6Ga19 high-temperature shape memory alloy with the addition of Dy

    International Nuclear Information System (INIS)

    Yang, S Y; Wang, C P; Liu, X J

    2013-01-01

    The effects of Dy addition on microstructure, martensitic transformation, mechanical and shape memory properties of the two-phase Ni 53 Mn 22 Co 6 Ga 19 high-temperature shape memory alloy were investigated. It is found that a small Dy addition results in the refinement of grain size, which can effectively improve the tensile ductility and strength of the two-phase Ni 53 Mn 22 Co 6 Ga 19 alloy. However, a Dy(Ni,Mn) 4 Ga precipitate forms in the alloys with the Dy addition, and its amount increases with an increase in the Dy addition. This change causes the ductility of the alloys to decrease when the Dy addition is further increased to 0.3 at.%. The results further show that the changes in the martensitic transformation temperature of the studied alloys can be attributed to the combined effects of the tetragonality (c/a) and electron concentration (e/a) of martensite. Additionally, the shape memory effects of the alloys are closely related to the refinement of grain size and the alloy strength. In this study, the (Ni 53 Mn 22 Co 6 Ga 19 ) 99.8 Dy 0.2 alloy exhibits a variety of good properties, including a high martensitic transformation starting temperature of 385.7 °C, a tensile ductility of 10.3% and a shape memory effect of 2.8%. (paper)

  7. A functional gene array for detection of bacterial virulence elements

    Energy Technology Data Exchange (ETDEWEB)

    Jaing, C

    2007-11-01

    We report our development of the first of a series of microarrays designed to detect pathogens with known mechanisms of virulence and antibiotic resistance. By targeting virulence gene families as well as genes unique to specific biothreat agents, these arrays will provide important data about the pathogenic potential and drug resistance profiles of unknown organisms in environmental samples. To validate our approach, we developed a first generation array targeting genes from Escherichia coli strains K12 and CFT073, Enterococcus faecalis and Staphylococcus aureus. We determined optimal probe design parameters for microorganism detection and discrimination, measured the required target concentration, and assessed tolerance for mismatches between probe and target sequences. Mismatch tolerance is a priority for this application, due to DNA sequence variability among members of gene families. Arrays were created using the NimbleGen Maskless Array Synthesizer at Lawrence Livermore National Laboratory. Purified genomic DNA from combinations of one or more of the four target organisms, pure cultures of four related organisms, and environmental aerosol samples with spiked-in genomic DNA were hybridized to the arrays. Based on the success of this prototype, we plan to design further arrays in this series, with the goal of detecting all known virulence and antibiotic resistance gene families in a greatly expanded set of organisms.

  8. Virulence and genomic feature of multidrug resistant Campylobacter jejuni isolated from broiler chicken

    Directory of Open Access Journals (Sweden)

    Haihong Hao

    2016-10-01

    Full Text Available The aim of this study was to reveal the molecular mechanism involved in multidrug resistance and virulence of Campylobacter jejuni isolated from broiler chickens. The virulence of six multidrug resistant C. jejuni was determined by in vitro and in vivo methods. The de novo whole genome sequencing technology and molecular biology methods were used to analyze the genomic features associated with the multidrug resistance and virulence of a selected isolate (C. jejuni 1655. The comparative genomic analyses revealed a large number of single nucleotide polymorphisms, deletions, rearrangements, and inversions in C. jejuni 1655 compared to reference C. jejuni genomes. The co-emergence of Thr-86-Ile mutation in gyrA gene, A2075G mutation in 23S rRNA gene, tetO, aphA and aadE genes and pTet plasmid in C. jejuni 1655 contributed its multidrug resistance to fluoroquinolones, macrolides, tetracycline and aminoglycosides. The combination of multiple virulence genes may work together to confer the relative higher virulence in C. jejuni 1655. The co-existence of mobile gene elements (e.g. pTet and CRISPR-Cas system in C. jejuni 1655 may play an important role in the gene transfer and immune defense. The present study provides basic information of phenotypic and genomic features of C. jejuni 1655, a strain recently isolated from a chicken displaying multidrug resistance and relatively high level of virulence.

  9. Long-distance delivery of bacterial virulence factors by Pseudomonas aeruginosa outer membrane vesicles.

    Directory of Open Access Journals (Sweden)

    Jennifer M Bomberger

    2009-04-01

    Full Text Available Bacteria use a variety of secreted virulence factors to manipulate host cells, thereby causing significant morbidity and mortality. We report a mechanism for the long-distance delivery of multiple bacterial virulence factors, simultaneously and directly into the host cell cytoplasm, thus obviating the need for direct interaction of the pathogen with the host cell to cause cytotoxicity. We show that outer membrane-derived vesicles (OMV secreted by the opportunistic human pathogen Pseudomonas aeruginosa deliver multiple virulence factors, including beta-lactamase, alkaline phosphatase, hemolytic phospholipase C, and Cif, directly into the host cytoplasm via fusion of OMV with lipid rafts in the host plasma membrane. These virulence factors enter the cytoplasm of the host cell via N-WASP-mediated actin trafficking, where they rapidly distribute to specific subcellular locations to affect host cell biology. We propose that secreted virulence factors are not released individually as naked proteins into the surrounding milieu where they may randomly contact the surface of the host cell, but instead bacterial derived OMV deliver multiple virulence factors simultaneously and directly into the host cell cytoplasm in a coordinated manner.

  10. Use of Metarhizium anisopliae Chitinase Genes for Genotyping and Virulence Characterization

    Directory of Open Access Journals (Sweden)

    Saliou Niassy

    2013-01-01

    Full Text Available Virulence is the primary factor used for selection of entomopathogenic fungi (EPF for development as biopesticides. To understand the genetic mechanisms underlying differences in virulence of fungal isolates on various arthropod pests, we compared the chitinase genes, chi2 and chi4, of 8 isolates of Metarhizium anisopliae. The clustering of the isolates showed various groups depending on their virulence. However, the analysis of their chitinase DNA sequences chi2 and chi4 did not reveal major divergences. Although their protein translates have been implicated in fungal virulence, the predicted protein structure of chi2 was identical for all isolates. Despite the critical role of chitin digestion in fungal infection, we conclude that chi2 and chi4 genes cannot serve as molecular markers to characterize observed variations in virulence among M. anisopliae isolates as previously suggested. Nevertheless, processes controlling the efficient upregulation of chitinase expression might be responsible for different virulence characteristics. Further studies using comparative “in vitro” chitin digestion techniques would be more appropriate to compare the quality and the quantity of chitinase production between fungal isolates.

  11. Nucleophilic addition to olefins. 7. Kinetic deuterium isotope effects as criterion for an enforced preassociation mechanism in the hydrolysis of substituted benzylidene Meldrum's acids

    International Nuclear Information System (INIS)

    Bernasconi, C.F.; Leonarduzzi, G.D.

    1982-01-01

    The hydrolysis of the title compounds occurs in four steps: (1) nucleophilic attack by water or hydroxide ion to form the addition complex T/sub OH/ - ; (2) carbon protonation of T/sub OH/ - to form T/sub OH/ 0 ; (3) oxygen deprotonation of T/sub OH/ 0 to form T/sub OH/ 0 - ; (4) collapse of the tetrahedral intermediate T/sub OH/ - into the respective benzaldehyde and Meldrum's acid anion. There is also a water-catalyzed collapse of T/sub OH/ 0 which becomes dominant in strongly acidic solution. In basic solution carbon protonation of T/sub OH/ - (step 2) is rate limiting; in strongly acidic media the water-catalyzed collapse of T/sub OH/ 0 is rate limiting for all substrates. In moderatly acidic solution two types of behavior were observed. With the p-nitro derivative step 4 is rate limiting at high, step 3 at low buffer concentrations. The latter situation is equivalent to a diffusion-controlled trapping mechanism in the reverse direction. With the parent and the p-methoxy derivative, collapse of T/sub OH/ 0 - occurs before the protonated base catalyst generated in step 3 can diffuse away; this is equivalent to an enforced preassociation mechanism in the reverse direction and is analogous to the reaction of thiol anions with acetaldehyde studied by Gilbert and Jencks. Our interpretation is strongly supported by (1) α secondary kinetic deuterium isotope effects which are large for the preassociation mechanism but essentially nil for the trapping mechanism and (2) by Bronsted #betta# values around 0.8 in the case of the preassociation mechanism and 1.0 for the trapping mechanism. The mechanism for the water-catalyzed collapse of T/sub OH/ 0 - is proba