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Sample records for metal mechanic sector

  1. Do Innovation and Cooperation Influence SMEs’ Competitiveness? Evidence From the Andalusian Metal-Mechanic Sector

    Directory of Open Access Journals (Sweden)

    Juan A. Tamayo

    2015-01-01

    Full Text Available This study’s main objective is to determine the influence of innovation and cooperation on the competitiveness of SMEs in the metal-mechanic sector of Andalusia (Spain. Using information obtained by interviewing managers of a sample of 80 firms, we proposed a model of structural equations based on the Partial Least Squares (PLS technique. This model, which explained 37% of the variability of competitiveness, also allowed us to test hypotheses about the positive influence of quality management, knowledge, financial resources and cooperation on innovative outcomes. Along with the contrasted hypotheses, the most noteworthy finding was that cooperation does not significantly influence the innovative outcomes of firms in this sector.

  2. Sectoral Market Mechanisms

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    2009-07-01

    This paper first reviews proposals for the design of sectoral and related market mechanisms currently debated, both in the UNFCCC negotiations, and in different domestic legislative contexts. Secondly, it addresses the possible principles and technical requirements that Parties may wish to consider as the foundations for further elaboration of the mechanisms. The third issue explored herein is domestic implementation of sectoral market mechanisms by host countries, incentives to move to new market mechanisms, as well as how the transition between current and future mechanisms could be managed.

  3. Rearrangement of the layout of the welding equipment of a company in the metal mechanical sector using the Systematic Layout Planning method (SLP

    Directory of Open Access Journals (Sweden)

    Silvio Alexsandro Turati

    2016-06-01

    Full Text Available The correct physical layout is relevant to the operational efficiency of the company. This study proposes rearranging the layout of the welding equipment of a company in the metal mechanical sector, which is located in Araras/SP, aiming to improve the production workflow. The Systematic Layout Planning method (SLP was used, with the field research divided into steps: obtaining detailed information about the process and the product; meetings with stakeholders; determining inter-related activities; analyzing space requirements; developing a new layout. The new layout has space allocated for the purchasing of new machinery, the existing machinery has been redistributed by specialty, and the unloading of raw materials has been transferred to the shed, maximizing the use of overhead cranes and keeping the stock close to the warehouse. In addition, forklift traffic flow has decreased; new movement corridors were demarcated; and painting areas were isolated. In conclusion, the SLP method proved efficient in creating a layout.

  4. Proposal for evaluation of the level of implementation of typical practices of lean production in company a sector of the metal-mechanic

    Directory of Open Access Journals (Sweden)

    Maria da Graça Saraiva Nogueira

    2008-07-01

    Full Text Available Aiming at the advantages obtained when performing lean production, different sectors of the production of goods and services have adopted its principles and practices. Due to its degree of abstraction, it is difficult to establish a level of incorporation of such concepts. On the other hand, because of the operational features of its practices, such assessment becomes possible through the quantification of the elements involved (time, cost, raw material. The use of lean production practices does not guarantee its implementation and sustainability. However, the assessment of such practices might, in an indirect way, provide hints on how widespread its principles are and to what extent they are being adopted. The present assessment took place at an metal-mechanic company which has been implementing lean production as a philosophy of production at corporate levels since 2002. The operational manager and managers responsible for quality, production, sales, purchase, maintenance, and PCP also took part in this research. Each manager answered to an interview and filled a checklist and a ranking in order to evaluate performance and importance, respectively. Just-in-time, leveling production (heijunka, and integration practices with the supply chain yielded the most unfavorable results, whereas group technology, continuous improvement, and visual management yielded the best results. With regard to the importance criterion, the practices of standardized operations, just-in-time, and quick changeover were considered the most important, whereas workforce flexibility, group technology, and development of lean product were the least important. Key-words: Lean Production; Measurement of Performance and Importance, Sector of the metal-mechanic

  5. Public Sector Salariats' Poverty-Coping Mechanisms:A Comparative ...

    African Journals Online (AJOL)

    This paper attempts to develop a modality through which anti-poverty effects of adjustment mechanisms can be quantified. It compares the salariats in Khartoum with those in El-Obeid, the capital of North Kordofan State, in Western Sudan, so as to provide a profile of the living conditions of the salariats in the public sector.

  6. Sectoral crediting mechanism: How far China has to go

    International Nuclear Information System (INIS)

    Cai Wenjia; Wang Can; Chen Jining; Wang Siqiang

    2012-01-01

    Based on the review of the basic design of the sectoral crediting mechanism (SCM) – a promising option for developing countries’ emission reduction commitments – this paper analyzes five important practical issues for China to solve before participating in SCM, which include (1) difficulties in determining a crediting baseline (2) the unsolved over-supply problem in the carbon market (3) the very likely “carbon credits falling short of mitigation costs” problem (4) the immature market-oriented price system jeopardizing the success of motivation incentives and (5) inadequate capacity building. Corresponding suggestions or compromise solutions are given after a discussion of each issue. It is also recommended that in order to witness SCM come into being, researchers and negotiators should endeavor to solve the practical issues that SCM meets now, bearing in mind the balance of interests of both developing and developed countries. Finally we believe that SCM’s political barriers can be overcome when technical, economic institutional and capacity problems are solved. - Highlights: ► Latest developments in Sectoral Crediting Mechanism design have been reviewed. ► Ten years would be an ideal duration to adjust sectoral crediting baseline in China. ► Specific sectors could be selected to solve the carbon credits over-supply problem. ► SCM credits may come short of the mitigation costs, claiming a rising carbon price. ► Pricing system in China’s electricity sector makes it not a good candidate for SCM.

  7. Mechanisms of metal dusting corrosion

    DEFF Research Database (Denmark)

    Hummelshøj, Thomas Strabo

    In this thesis the early stages of metal dusting corrosion is addressed; the development of carbon expanded austenite, C, and the decomposition hereof into carbides. Later stages of metal dusting corrosion are explored by a systematic study of stainless steel foils exposed to metal dusting...... the supersaturated alloy, into a diverse carbide network. Finally, the foils turn into metal dust accompanied by a thinning and disappearance of the foils. Investigations of TEM samples, prepared by means of FIB, on the carbide network revealed a lamellar structure with carbides and austenite. Finally, the mutual...... influence of oxygen and carbon on the metal dusting corrosion is explored. The results indicate that exposure to metal dusting conditions have a detrimental effect on the resistance against oxidation and, conversely, that exposure to oxidation has a detrimental effect on the resistance towards metal dusting...

  8. Mechanical and metal trades handbook

    CERN Document Server

    2012-01-01

    Englische Ausgabe des vielfach bewährten Tabellenbuchs Metall, 45. Auflage. Translation of the 45th edition of the well-known "Tabellenbuch Metall". It is well suited for shop reference, tooling, machine building, maintenance and as a general book of knowledge. It is also useful for educational purposes, especially in practical work or curricula, continuing education programs. The contents of this book include tables and formulae in eight chapters. The tables contain the most important guidelines, designs, types, dimensions and standard values for their subject areas.

  9. Mechanisms of bacterial metals removal from solids

    International Nuclear Information System (INIS)

    Torma, A.E.; Pryfogle, P.A.

    1990-01-01

    The Great Lakes area sediments are contaminated with varying amounts of heavy metals and polychlorinated organic matter. With respect to the bioremediation of metallic contents of these sediments, it was shown that a number of microorganisms exist which can effectively solubilize heavy metals. The basic reaction mechanisms of bioleaching processes were discussed and the effects of semiconductor character of the sulfide substrate explained. A special emphasis was made to comment on INEL's bioremediation capability. 37 refs

  10. Metals bioaccumulation mechanism in neem bark

    Science.gov (United States)

    The aim of this work was to define the bioaccumulation mechanism of metals onto the non-living biomaterial prepared from an extensively available plant bark biomass of neem (Azadirachta indica). Based on maximum ultimate fixation capacities (mmol/g) of the product, metals ions could be arranged as H...

  11. Mechanical Performance of Amorphous Metallic Cellular Structures

    Science.gov (United States)

    Schramm, Joseph P.

    Metallic glass and metallic glass matrix composites are excellent candidates for application in cellular structures because of their outstanding plastic yield strengths and their ability to deform plastically prior to fracture. The mechanical performance of metallic-glass and metallic-glass-matrix-composite honeycomb structures are discussed, and their strength and energy absorption capabilities examined in quasi-static compression tests for both in-plane and out-of-plane loading. These structures exhibit strengths and energy absorption that well exceed the performance of similar structures made from crystalline metals. The strength and energy absorption capabilities of amorphous metal foams produced by a powder metallurgy process are also examined, showing that foams produced by this method can be highly porous and are able to inherit the strength of the parent metallic glass and absorb large amounts of energy. The mechanical properties of a highly stochastic set of foams are examined at low and high strain rates. It is observed that upon a drastic increase in strain rate, the dominant mechanism of yielding for these foams undergoes a change from elastic buckling to plastic yielding. This mechanism change is thought to be the result of the rate of the mechanical test approaching or even eclipsing the speed of elastic waves in the material.

  12. Mechanical pumps for liquid metals

    International Nuclear Information System (INIS)

    Baumier, J.; Gollion, H.J.

    1964-01-01

    The pumping of liquid metals by centrifugal pumps poses two principal problems. These are hermetic sealing of the rotating shaft and, its guidance where immersed in liquid metal. The solutions to the problems used on 13 experimental pumps are given here. The resolution of the guidance problem consists in the majority of cases in the utilisation of hydrostatic bearings. Accordingly, a theoretical study was instituted for the first time to calculate the bearings of the earlier pumps. After this, an experimental study was carried out, to check the theory by water tests. A relation for bearing calculation of pumps with diffusers is proposed. Finally the influence of the bearing elasticity on the shafts critical speed is studied. (authors) [fr

  13. Reducing barriers to energy efficiency in the German mechanical engineering sector. Final report

    Energy Technology Data Exchange (ETDEWEB)

    Schleich, J.; Boede, U.

    2000-12-01

    This report describes the empirical research into barriers to energy efficiency in the German mechanical engineering (ME) sector. It is one of nine such reports in the BARRIERS project. The report contains description and analysis of four case studies of energy management in German companies in the ME sector. The results are analysed using the theoretical framework developed for the BARRIERS project. The report also provides brief recommendations on how these barriers to the rational use of energy (RUE) may be overcome and how energy efficiency within the ME sector may be improved. The results of the study for the ME sector in Germany are summarised in this executive summary under the following headings: - Characterising the mechanical engineering sector; - Case studies of energy management in the German mechanical engineering sector; - Evidence of barriers in the German mechanical engineering sector; - The role of energy service companies in the mechanical engineering sector; - Policy implications. (orig.)

  14. Reducing barriers to energy efficiency in the German mechanical engineering sector. Executive summary

    Energy Technology Data Exchange (ETDEWEB)

    Schleich, J.; Boede, U.

    2000-12-01

    This report describes the empirical research into barriers to energy efficiency in the German mechanical engineering (ME) sector. It is one of nine such reports in the BARRIERS project. The report contains description and analysis of four case studies of energy management in German companies in the ME sector. The results are analysed using the theoretical framework developed for the BARRIERS project. The report also provides brief recommendations on how these barriers to the rational use of energy (RUE) may be overcome and how energy efficiency within the ME sector may be improved. The results of the study for the ME sector in Germany are summarised in this executive summary under the following headings: - Characterising the mechanical engineering sector; - Case studies of energy management in the German mechanical engineering sector; - Evidence of barriers in the German mechanical engineering sector; - The role of energy service companies in the mechanical engineering sector; - Policy implications. (orig.)

  15. Mechanism of metal cationization in organic SIMS

    International Nuclear Information System (INIS)

    Wojciechowski, I.; Delcorte, A.; Gonze, X.; Bertrand, P.

    2003-01-01

    A scenario of metal cationization in which the organic molecule combines with a neutral excited metal atom is proposed. Ionization of the nascent complex occurs via ejection of an electron during the association process. Electron structure calculations for the model systems C 6 H 6 +Me (Me=Ag, Cu, Au) using the density functional theory give a strong argument in favor of the proposed mechanism

  16. Mechanical Alloying of Metal-Organic Frameworks.

    Science.gov (United States)

    Panda, Tamas; Horike, Satoshi; Hagi, Keisuke; Ogiwara, Naoki; Kadota, Kentaro; Itakura, Tomoya; Tsujimoto, Masahiko; Kitagawa, Susumu

    2017-02-20

    The solvent-free mechanical milling process for two distinct metal-organic framework (MOF) crystals induced the formation of a solid solution, which is not feasible by conventional solution-based syntheses. X-ray and STEM-EDX studies revealed that performing mechanical milling under an Ar atmosphere promotes the high diffusivity of each metal ion in an amorphous solid matrix; the amorphous state turns into the porous crystalline structure by vapor exposure treatment to form a new phase of a MOF solid solution. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  17. LMET Mechanical testing in liquid metals

    International Nuclear Information System (INIS)

    Jong, Monica

    2013-01-01

    LMET is successfully developed to perform mechanical tests in heavy liquid metals up to 400 ° C. Fracture toughness tests and fatigue crack propagation tests are successfully performed. Tensile tests and fatigue tests applicability looks promising. With performing the precrack and the fracture toughness test in one sequence, wetting of the crack surface is assured. Data retrieved with LMET is reliable

  18. Mechanisms of lichen resistance to metallic pollution

    Energy Technology Data Exchange (ETDEWEB)

    Sarret, C.; Manceau, A.; Eybert-Berard, L. [Univ. of Grenoble and CNRS (France). Environmental Geochemistry Group; Cuny, D.; Haluwyn, C. van [Lab. de Botanique et de Cryptogamie, Lille (France); Deruelle, S. [Institut d`Ecologie, Paris (France); Hazemann, J.L.; Menthonnex, J.J. [Univ. of Grenoble and CNRS (France). Environmental Geochemistry Group]|[CNRS, Grenoble (France). Lab. de Cristallographie; Soldo, Y. [CNRS, Grenoble (France). Lab. de Cristallographie

    1998-11-01

    Some lichens have a unique ability to grow in heavily contaminated areas due to the development of adaptative mechanisms allowing a high tolerance to metals. Here the authors report on the chemical forms of Pb and Zn in the metal hyperaccumulator Diploschistes muscorum and of Pb in the metal tolerant lichen Xanthoria parietina. The speciation of Zn and Pb has been investigated by powder X-ray diffraction (XRD) and extended X-ray absorption fine structure (EXAFS) spectroscopy using the advanced third-generation synchrotron radiation source of the European synchrotron radiation facility (ESRF in Grenoble). This study reveals that in both lichens cells are protected from toxicity by complexation of heavy metals, but the strategies differ: in D. muscorum, Pb and Zn are accumulated through an enhanced synthesis of oxalate, which precipitates toxic elements as insoluble salts, whereas in X. parietina, Pb is complexed to carboxylic groups of the fungal cell walls. The authors conclude that hyperaccumulation of metals results from a reactive mechanism of organic acid production, whereas metallo-tolerance is achieved by a passive complexation to existing functional groups.

  19. Multidimensional supersymmetric quantum mechanics: spurious states for the tensor sector two Hamiltonian.

    Science.gov (United States)

    Chou, Chia-Chun; Kouri, Donald J

    2013-04-25

    We show that there exist spurious states for the sector two tensor Hamiltonian in multidimensional supersymmetric quantum mechanics. For one-dimensional supersymmetric quantum mechanics on an infinite domain, the sector one and two Hamiltonians have identical spectra with the exception of the ground state of the sector one. For tensorial multidimensional supersymmetric quantum mechanics, there exist normalizable spurious states for the sector two Hamiltonian with energy equal to the ground state energy of the sector one. These spurious states are annihilated by the adjoint charge operator, and hence, they do not correspond to physical states for the original Hamiltonian. The Hermitian property of the sector two Hamiltonian implies the orthogonality between spurious and physical states. In addition, we develop a method for construction of a specific form of the spurious states for any quantum system and also generate several spurious states for a two-dimensional anharmonic oscillator system and for the hydrogen atom.

  20. Magneto-mechanical impedance of metallic structures.

    Science.gov (United States)

    Zagrai, Andrei N

    2009-01-01

    Impedance measurements with a magneto-elastic active sensor are explored for inferring the magneto-mechanical impedance (MMI) of a metallic structure. It is shown that the MMI contains electrical response of the sensor and both electrical and mechanical structural responses. An analytical model is suggested that accounts for electrical characteristics of the sensor, sensor/structure electromagnetic interaction, and multimodal structural dynamic behavior. The model is validated with a set of MMI experiments demonstrating feasibility of deducing structural natural frequencies and structural vibration modes.

  1. Modelling of atmospheric transport of heavy metals emitted from Polish power sector

    International Nuclear Information System (INIS)

    Zysk, Janusz

    2016-01-01

    Modelling of atmospheric transport of heavy metals emitted from Polish power sector. Many studies have been conducted to investigate the atmospheric heavy metals contamination and its deposition to ecosystems. The increasing attention to mercury pollution has been mainly driven by the growing evidence of its negative impacts on wildlife, ecosystems and particularly human health. Lead and cadmium are also toxics which are being emitted into the atmosphere by anthropogenic as well as natural sources. The harmful influence of these three heavy metals was underlined in the Aarhus Protocol on Heavy Metals of 1998. The Parties of this protocol (including Poland) are obligated to reduce emissions, observe the transport and the amounts of lead, mercury and cadmium in the environment. Poland is one of the biggest emitter of mercury, lead and cadmium in Europe mainly due to emission from coal combustion processes. Therefore in Poland, research efforts to study the heavy metals emission, atmospheric transport, concentration and deposition are extremely important. The objectives of this work were twofold: - The practical objective was to develop and run a model to represent the atmospheric dispersion of mercury and to implement it in the air quality modelling platform Polyphemus.- The scientific objective was to perform heavy metals dispersion studies over Europe and detailed studies of the impact of the polish power sector on the air quality regarding mercury, cadmium and lead. To meet the declared aim, a new mercury chemical model was implemented into the Polyphemus air quality system. The scientific literature was reviewed regarding mercury chemistry and mercury chemical models. It can be concluded that the chemistry of mercury is still not well known. The models also differ in the way of calculating the dry and wet deposition of mercury. The elemental gaseous mercury ambient concentrations are evenly distributed, on the contrary, high variations in the spatial gradients of

  2. Investigation of tribological and mechanical properties of metal ...

    Indian Academy of Sciences (India)

    Administrator

    2009-09-02

    -ferrous metals; bearings; tribology; mechanical properties. 1. Introduction. In the past few years, wood, iron and skin have been used as journal bearing materials. Later, brass, bronze and white metal have also found some ...

  3. Potential for recycling of slightly radioactive metals arising from decommissioning within nuclear sector in Slovakia.

    Science.gov (United States)

    Hrncir, Tomas; Strazovec, Roman; Zachar, Matej

    2017-09-07

    The decommissioning of nuclear installations represents a complex process resulting in the generation of large amounts of waste materials containing various concentrations of radionuclides. Selection of an appropriate strategy of management of the mentioned materials strongly influences the effectiveness of decommissioning process keeping in mind safety, financial and other relevant aspects. In line with international incentives for optimization of radioactive material management, concepts of recycling and reuse of materials are widely discussed and applications of these concepts are analysed. Recycling of some portion of these materials within nuclear sector (e.g. scrap metals or concrete rubble) seems to be highly desirable from economical point of view and may lead to conserve some disposal capacity. However, detailed safety assessment along with cost/benefit calculations and feasibility study should be developed in order to prove the safety, practicality and cost effectiveness of possible recycling scenarios. Paper discussed the potential for recycling of slightly radioactive metals arising from decommissioning of NPPs within nuclear sector in Slovakia. Various available recycling scenarios are introduced and method for overall assessment of various recycling scenarios is outlined including the preliminary assessment of safety and financial aspects. Copyright © 2017 Elsevier Ltd. All rights reserved.

  4. Amorphous Metals for Opto-Mechanical Fixtures and Mechanisms Project

    Data.gov (United States)

    National Aeronautics and Space Administration — The new JPL Metallurgy Facility is a small-scale foundry-type laboratory with capabilities for fabricating new metal alloys and metal-matrix-composites, casting...

  5. Mechanisms of Metal Resistance and Homeostasis in Haloarchaea

    Science.gov (United States)

    Srivastava, Pallavee; Kowshik, Meenal

    2013-01-01

    Haloarchaea are the predominant microflora of hypersaline econiches such as solar salterns, soda lakes, and estuaries where the salinity ranges from 35 to 400 ppt. Econiches like estuaries and solar crystallizer ponds may contain high concentrations of metals since they serve as ecological sinks for metal pollution and also as effective traps for river borne metals. The availability of metals in these econiches is determined by the type of metal complexes formed and the solubility of the metal species at such high salinity. Haloarchaea have developed specialized mechanisms for the uptake of metals required for various key physiological processes and are not readily available at high salinity, beside evolving resistance mechanisms for metals with high solubility. The present paper seeks to give an overview of the main molecular mechanisms involved in metal tolerance in haloarchaea and focuses on factors such as salinity and metal speciation that affect the bioavailability of metals to haloarchaea. Global transcriptomic analysis during metal stress in these organisms will help in determining the various factors differentially regulated and essential for metal physiology. PMID:23533331

  6. Mechanisms of metal resistance and homeostasis in haloarchaea.

    Science.gov (United States)

    Srivastava, Pallavee; Kowshik, Meenal

    2013-01-01

    Haloarchaea are the predominant microflora of hypersaline econiches such as solar salterns, soda lakes, and estuaries where the salinity ranges from 35 to 400 ppt. Econiches like estuaries and solar crystallizer ponds may contain high concentrations of metals since they serve as ecological sinks for metal pollution and also as effective traps for river borne metals. The availability of metals in these econiches is determined by the type of metal complexes formed and the solubility of the metal species at such high salinity. Haloarchaea have developed specialized mechanisms for the uptake of metals required for various key physiological processes and are not readily available at high salinity, beside evolving resistance mechanisms for metals with high solubility. The present paper seeks to give an overview of the main molecular mechanisms involved in metal tolerance in haloarchaea and focuses on factors such as salinity and metal speciation that affect the bioavailability of metals to haloarchaea. Global transcriptomic analysis during metal stress in these organisms will help in determining the various factors differentially regulated and essential for metal physiology.

  7. Mechanisms of Metal Resistance and Homeostasis in Haloarchaea

    Directory of Open Access Journals (Sweden)

    Pallavee Srivastava

    2013-01-01

    Full Text Available Haloarchaea are the predominant microflora of hypersaline econiches such as solar salterns, soda lakes, and estuaries where the salinity ranges from 35 to 400 ppt. Econiches like estuaries and solar crystallizer ponds may contain high concentrations of metals since they serve as ecological sinks for metal pollution and also as effective traps for river borne metals. The availability of metals in these econiches is determined by the type of metal complexes formed and the solubility of the metal species at such high salinity. Haloarchaea have developed specialized mechanisms for the uptake of metals required for various key physiological processes and are not readily available at high salinity, beside evolving resistance mechanisms for metals with high solubility. The present paper seeks to give an overview of the main molecular mechanisms involved in metal tolerance in haloarchaea and focuses on factors such as salinity and metal speciation that affect the bioavailability of metals to haloarchaea. Global transcriptomic analysis during metal stress in these organisms will help in determining the various factors differentially regulated and essential for metal physiology.

  8. FINANCING MECHANISMS FOR INVESTMENT PROJECTS IN THE AGRICULTURAL SECTOR OF UKRAINE'S ECONOMY INVOLVING ANGEL INVESTORS

    Directory of Open Access Journals (Sweden)

    T. Nagachevska

    2014-06-01

    Full Text Available The challenges connected with attracting foreign investments into the agricultural sector of the Ukrainian economy as well as diversification of forms of international investments are actual due to the immediate needs of realization of innovative development, technological upgrading and strengthening of agricultural sector attractiveness on the world market. Current situation and problems connected with attracting foreign investments into the agricultural sector of the Ukrainian economy are revealed. It is detected that level of attracting foreign investments into the agricultural sector of Ukraine and into AIC together don't meet the needs of its innovative potential. The following factors of agricultural sector attractiveness have been considered: high soil fertility and favorable weather conditions for growing crops; export capacity; high yield of the Ukrainian farming companies; undervalued assets and low level of capitalization of agricultural companies; attractive tax regime for agricultural producers. It is recommended that agricultural producers should indicate these factors in investment proposals and projects that they present to potential international investors. State investment policy in the agricultural sector is viewed to consolidate the resource base and the sources of investment have been determined. Suggestions to expand the financing mechanisms for investment projects in the agricultural sector involving angel investors have been justified. Economic feasibility of attracting foreign investments for financing of innovation activity of farming companies has been revealed. The key requirements and main stages of investments of angel investment association have been described.

  9. IT Governance Mechanisms and Administration/IT Alignment in the Public Sector

    DEFF Research Database (Denmark)

    Winkler, Till

    2013-01-01

    The mechanisms of information technology (IT) governance have been widely recognized as practices to sustain alignment of business and IT units. However, the IT governance literature so far has drawn little attention to the possible idiosyncrasies of governance arrangements in the public sector....... In this paper we propose a conceptual model to investigate the relationship between IT governance mechanisms and according performance outcomes specifically for public sector organizations. A survey instrument is developed and validated based on in-depth interviews with IT representatives from three different...

  10. [INVOLVEMENT OF PLANT CYTOSKELETON INTO CELLULAR MECHANISMS OF METALS TOXICITY].

    Science.gov (United States)

    Horiunova, L; Krasylenko, Yu A; Yemets, A I; Blume, Ya B

    2016-01-01

    This review summarizes published date and the results of the author's own researches cantering the participation of plant cells cytoskeleton. It is considered cytotoxic impact of metals on the cytoskeleton's components, including microtubules and actin filaments. Particular attention is paid to the cellular and molecular mechanisms of influence of metals on cytoskeleton. We discussed the most probable binding sites of heavy metals and alternative mechanisms of their impact on the cytoskeleton.

  11. IT Governance Mechanisms and Administration/IT Alignment in the Public Sector

    DEFF Research Database (Denmark)

    Winkler, Till

    2013-01-01

    . In this paper we propose a conceptual model to investigate the relationship between IT governance mechanisms and according performance outcomes specifically for public sector organizations. A survey instrument is developed and validated based on in-depth interviews with IT representatives from three different...

  12. PUBLIC-PRIVATE PARTNERSHIPS AS MECHANISMS FOR RISK MANAGEMENT IN THE WATER SECTOR

    Directory of Open Access Journals (Sweden)

    Simona FRONE

    2013-08-01

    Full Text Available Some forms of Public Private Partnership (PPP have been long since used in the procurement and operation of water infrastructure, as shown in the first part of the paper. The main object of the paper is to highlight the mechanisms of PPP in the water sector and to suggest that in times of economic and financial distress, when both the public sector and the private sector face additional risks and challenges, various models of PPP may be used to manage and mitigate the risks and to improve performance in providing the public services of Water Supply and Sanitation (WSS. The economic and financial risks of the WSS sector are commonly classified in two broad categories but within these broad categories there are many more specific risks. Therefore, we shall analyse some of these main risks and their potential interrelations, by employing several methodologies: literature review, case studies, performance indicators, risk matrix, analysis and synthesis. The mechanisms, features and experiences of PPP in this branch of the water sector are summarized and comparatively analysed, from the viewpoint of risk sharing, leading to some conclusions and recommendations on the opportunity and effectiveness of implementing such arrangements especially in Romania.

  13. Metal accumulation and detoxification mechanisms in mycorrhizal Betula pubescens.

    Science.gov (United States)

    Fernández-Fuego, D; Bertrand, A; González, A

    2017-12-01

    Metal detoxification in plants is a complex process that involves different mechanisms, such as the retention of metals to the cell wall and their chelation and subsequent compartmentalization in plant vacuoles. In order to identify the mechanisms involved in metal accumulation and tolerance in Betula pubescens, as well as the role of mycorrhization in these processes, mycorrhizal and non-mycorrhizal plants were grown in two industrial soils with contrasting concentrations of heavy metals. Mycorrhization increased metal uptake at low metal concentrations in the soil and reduced it at high metal concentrations, which led to an enhanced growth and biomass production of the host when growing in the most polluted soil. Our results suggest that the sequestration on the cell wall is the main detoxification mechanism in white birch exposed to acute chronic metal-stress, while phytochelatins play a role mitigating metal toxicity inside the cells. Given its high Mn and Zn root-to-shoot translocation rate, Betula pubescens is a very promising species for the phytoremediation of soils polluted with these metals. Copyright © 2017 Elsevier Ltd. All rights reserved.

  14. Identification and assessment of the need to improve the operation of production systems in the metal sector enterprises

    Directory of Open Access Journals (Sweden)

    M. Górska

    2017-01-01

    Full Text Available In this paper an attempt was made to identify the areas of metal products manufacturing processes that require improvement. Determination of such areas may become a source of a lot of valuable information for the enterprise, enabling the development of its improvement directions. The results of survey allowed also to define a model of implementation importance for tasks contributing to the metal sector enterprises improvement.

  15. Mechanical behaviour of dissimilar metal welds

    International Nuclear Information System (INIS)

    Escaravage, C.

    1990-01-01

    This report addresses the problems of dissimilar metal welds connecting an austenitic stainless steel component to a ferritic steel component. In LMFBRs such welds appear at the junction of the austenitic stainless steel vessel with the ferritic steel roof and in sodium and water or steam pipes. The latter are exposed to high temperatures in the creep range. A wide range of austenitic stainless steels and ferritic steels (carbon steels, low allow steels and alloy steels) are covered; the study encompasses more than 20 different weld metals (austenitic stainless steels and nickel base alloys). The report begins with a presentation of the materials, geometries and welding procedures treated in the study, followed by a review of service experience from examinations of dissimilar metal welds after elevated temperature service, in particular failed welds. Results of laboratory tests performed for reproducing service failures are then discussed. A further section is devoted to a review of test results on fatigue behaviour and impact toughness for dissimilar metal welded joints when creep is not significant. Finally, the problem of residual life assessment is addressed. A set of recommendations concludes the report. They concern the material selection, welding procedure, life prediction and testing of dissimilar metal welds. 84 refs

  16. Mechanical Properties and Deformation Behavior of Bulk Metallic Glasses

    Directory of Open Access Journals (Sweden)

    Alexander Yu. Churyumov

    2012-12-01

    Full Text Available Metallic glasses demonstrate unique properties, including large elastic limit and high strength, which make them attractive for practical applications. Unlike crystalline alloys, metallic glasses, in general, do not exhibit a strain hardening effect, while plastic deformation at room temperature is localized in narrow shear bands. Room-temperature mechanical properties and deformation behavior of bulk metallic glassy samples and the crystal-glassy composites are reviewed in the present paper.

  17. Bioaccumulation of heavy metals in marine organisms from the Romanian sector of the Black Sea.

    Science.gov (United States)

    Jitar, Oana; Teodosiu, Carmen; Oros, Andra; Plavan, Gabriel; Nicoara, Mircea

    2015-05-25

    The aim of this research was to study the accumulation of heavy metals (cadmium - Cd, lead - Pb, chromium - Cr, nickel - Ni, and copper - Cu) from water and sediments into living tissues of relevant marine species from different trophic levels of a food web, representative for shallow waters of the Romanian Black Sea Coast where the main anthropogenic impacts exist. The heavy metals concentrations were analysed by using an Atomic Absorption Spectrometer with graphite furnace, the results being further used to calculate the bioconcentration factors for a few key taxa like green and red algae, molluscs and fishes. Seven sampling sites influenced by anthropogenic pollution sources (municipal wastewater treatment plants and diffuse sources) were considered and a total of 300 samples were analysed for the period 2011-2012, this being the first unitary study for the Romanian Black Sea marine ecosystem. In 2011 and 2012 there were no significant differences between the sampling areas considering the heavy metals concentrations in water. For the sediments significant differences were observed between sampling sites for some heavy metals, namely Pb in 2011 and Pb, Cu and Cd in 2012, the highest concentrations being registered in the southern sector of the Romanian Black Sea shore, where the anthropogenic pollution sources are represented by the harbour and wastewater treatment plants. The values of the bioaccumulation factors (BCFsed) shows that algae are good accumulators for Cu>Pb>Ni>Cr>Cd, in comparison with BCFwater where the order of heavy metal accumulation was different: Cr>Ni>Pb>Cd>Cu. Molluscs have higher bioconcentration factors for Cu and Cd for sediments and for Cu and Ni for water. Rapana venosa accumulated more Cd and Cu. For fishes, Pb, Cu and Ni had the highest values in the tissues of benthonic species Mullus barbatus. In bivalve molluscs and fishes, in the majority of cases, there were not recorded exceeding mean concentrations as compared to the maximum

  18. effects of metal inert gas welding parameters on some mechanical ...

    African Journals Online (AJOL)

    EFFECTS OF METAL INERT GAS WELDING PARAMETERS ON SOME MECHANICAL PROPERTIES OF AUSTENITIC STAINLESS STEEL IN ACIDIC ... Design Expert Software, Scanning Electron Microscopy (SEM), Rockwell Hardness Test, Monsanto Tensometer and Izod Impact Test were used to determine the ...

  19. [Mechanisms of articulation between the informal and the formal urban sectors].

    Science.gov (United States)

    Lomnitz, L

    1978-01-01

    This article utilizes field data from Mexico City squatter settlements and personal interviews with employers to analyze some aspects of social relations between the informal sector and the formal urban sector, and compares the results with findings of other anthropologists in Mexico and elsewhere to derive a series of theoretical generalizations concerning mechanisms of articulation between the marginal sector and the formal economic and political institutions of the society. The formal sector is postulated to consist of the 3 subsectors of power, capital, and labor, which are in permanent conflict among themselves but all of which enjoy labor security and an assured minimal level of income. The marginal or informal sector lacks employment security, a minimal income level, and bargaining power. It is characterized by a small scale economy utilizing intensive familial labor. The informal sector is marginal to the dominant industrial system of production and the state apparatus, although it fulfills functions in terms of the national economy. 2 types of relationships may be distinguished in the social organization of the marginal sector: reciprocal relations between equals which form a network for the exchange of goods and services, or patron/client relations which are used, for example, in the case of petty entrepreneurs utilizing their relatives and acquaintances to create units of production. The functions of reciprocal relations are affected by social, physical, economic, and psychosocial distance or proximity and may result in exchanges of information, labor assistance, loans, services, or moral support. Patron/client relations may be direct, or the "patron" may be an intermediary. Some reciprocal networks display a pattern of incipient asymmetry leading to formation of true patron/client ties and some petty entrepreneurs or intermediaries manage to develop true patron/client networks; case histories are used to illustrate both phenomena. Intermediaries

  20. 40 CFR Appendix A to Part 438 - Typical Products in Metal Products and Machinery Sectors

    Science.gov (United States)

    2010-07-01

    ... Machine Tool Accessories & Measuring Devices Machine Tools, Metal Cutting Types Machine Tools, Metal... Prefabricated Metal Buildings & Components Screw Machine Products Sheet Metal Work Special Dies & Tools, Die... Diag. & Insp. Cntrs.) Automotive Equipment Automotive Glass Replacement Shops Automotive Repairs Shops...

  1. Manipulation of dermis based collagen networks with engineered mechanical behaviour for applications in the tanning sector

    OpenAIRE

    Autiello, Maria Assunta

    2015-01-01

    In this thesis, technologies and processes of the biomaterial field, were implemented in the tanning sector, in order to obtain leather prototypes having engineered mechanical properties such as tear resistance and elastic recovery. The work is basically divided in two parts. First, the characterization of conventional leather material is reported and it is aimed at defining the benchmarks to which the chemical physical parameters of the engineered products need to be compared. The obtained r...

  2. Creep mechanisms and constitutive relations in pure metals

    International Nuclear Information System (INIS)

    Nix, W.D.

    1979-01-01

    The mechanisms of creep of pure metals is briefly reviewed and divided into two parts: steady state flow mechanisms, and non-steady state flow mechanisms and constitutive relations. Creep by diffusional flow is now reasonably well understood, with theory and experiment in good agreement. The closely related phenomenon of Harper--Dorn creep can also be understood in terms of diffusion between dislocations. Power law creep involves the climb of edge disloctions controlled by lattice self diffusion. Theoretical treatments of this process invariably give a power law exponent of 3. This natural creep law is compared with the data for FCC and BCC metals. It is suggested that diffusion controlled climb is the controlling process in BCC metals at very high temperatures. Stacking fault energy effects may preclude the possibility that creep is controlled entirely by lattice self diffusion in some FCC metals. The subject of power law breakdown is presented as a natural consequence of the transition to low temperature flow phenomena. The role of core diffusion in this transition is briefly discussed. The mechanisms are presented by which pure metals creep at elevated temperatures. While most of this review deals with the mechanisms of steady state flow, some discussion is devoted to creep flow under non-steady state conditions. This topic is discussed in connection with the development of constitutive equations for describing plastic flow in metals

  3. Mechanics of Metals with Phase Changes

    Energy Technology Data Exchange (ETDEWEB)

    Lashley, Jason C. [Brigham Young Univ., Provo, UT (United States)

    2001-01-01

    New experimental data is presented on some exotic metals that exhibit phase changes at cryogenic temperatures. The types of phase changes that were detected in the specific heat data range from martensitic (diffusion less) transitions to superconducting transitions. In addition, the charge density wave (CDW) state in uranium metal was detected in the specific heat. Specific-heat measurements were made in zero-magnetic field using an apparatus capable of obtaining temperatures as low as 0.4 K. Calibration performed on this apparatus, using a single-crystal copper sample, show its accuracy to be 0.50%, while the resolution was better than 0.1%. Our measurements demonstrate that similar high precision and accurate specific-heat measurements can be obtained on milligram-scale samples. In Chapters 2 and 3, specific-heat measurements are presented for the B2 (CsCl structure) alloy AuZn and for α-uranium (orthorhombic symmetry). The AuZn alloy exhibits a continuous transition at 64.75 K and an entropy of transition of (ΔStr) 2.02 J K-1 mol-1. Calculation of the Debye temperature, by extrapolating of the high temperature phase elastic constants to T = 0 K yields a value of 207 K (±2 K), in favorable agreement with the calorimetric value of 219 K (±0.50 K), despite the intervening martensitic transition. Reported results for single-crystal α-U show a low-temperature limiting θD of 256 K (±0.50 K) and four low-temperature anomalies: a superconducting transition below 1 K, an electronic transition at 22 K, and two anomalies at 38 K and at 42 K indicative of the CDW state. In order to continue the study of the actinide series of elements, a program was initiated to first purify and then grow single crystals of plutonium. Accordingly, the focus of Chapters 4 through 6 will be a description of plutonium sample preparation. In this program plutonium metal was purified via zone refining, using a levitated molten zone to minimize

  4. Metal uptake and acute toxicity in zebrafish: Common mechanisms across multiple metals

    Energy Technology Data Exchange (ETDEWEB)

    Alsop, Derek, E-mail: alsopde@mcmaster.ca [Department of Biology, McMaster University, 1280 Main St. W., Hamilton, ON L8S 4K1 (Canada); Wood, Chris M. [Department of Biology, McMaster University, 1280 Main St. W., Hamilton, ON L8S 4K1 (Canada)

    2011-10-15

    All metals tested reduced calcium uptake in zebrafish larvae. However, it was whole body sodium loss that was functionally related to toxicity. The zebrafish larvae acute toxicity assay save time, space and resources. - Abstract: Zebrafish larvae (Danio rerio) were used to examine the mechanisms of action and acute toxicities of metals. Larvae had similar physiological responses and sensitivities to waterborne metals as adults. While cadmium and zinc have previously been shown to reduce Ca{sup 2+} uptake, copper and nickel also decreased Ca{sup 2+} uptake, suggesting that the epithelial transport of all these metals is through Ca{sup 2+} pathways. However, exposure to cadmium, copper or nickel for up to 48 h had little or no effect on total whole body Ca{sup 2+} levels, indicating that the reduction of Ca{sup 2+} uptake is not the acute toxic mechanism of these metals. Instead, mortalities were effectively related to whole body Na{sup +}, which decreased up to 39% after 48 h exposures to different metals around their respective 96 h LC50s. Decreases in whole body K{sup +} were also observed, although they were not as pronounced or frequent as Na{sup +} losses. None of the metals tested inhibited Na{sup +} uptake in zebrafish (Na{sup +} uptake was in fact increased with exposure) and the observed losses of Na{sup +}, K{sup +}, Ca{sup 2+} and Mg{sup 2+} were proportional to the ionic gradients between the plasma and water, indicating diffusive ion loss with metal exposure. This study has shown that there is a common pathway for metal uptake and a common mechanism of acute toxicity across groups of metals in zebrafish. The disruption of ion uptake accompanying metal exposure does not appear to be responsible for the acute toxicity of metals, as has been previously suggested, but rather the toxicity is instead due to total ion loss (predominantly Na{sup +}).

  5. Latin America: market mechanisms and supply adequacy in power sector reforms

    Energy Technology Data Exchange (ETDEWEB)

    Hammons, T.J. [University of Glasgow, Glasgow (United Kingdom); Barroso, L.A. [PSR, Rio de Janeiro (Brazil); Rudnick, H. [Pontificia Universidad Catolica de Chile, Santiago (Chile)

    2011-03-15

    The process of transformation in government and operations in the power sector leads to interaction between increasing integrated markets and public agencies in charge of policy making, regulation and control. This is examined for Latin America where state and marketing power sector planning, contract auctions to assure supply adequacy in an uncertain market environment, cross-border contracts, financing challenges for generation investments, and auctions of contracts to secure supply adequacy in the second stage of power sector reform are discussed. First, the state and market in power sector planning reform and state policies in Latin America are considered. Here, present concerns; the state-market relationship (the position of regulation, globalisation, internationalisation), and state market in the energy sector (correction and adjustments) are reviewed. Case studies for Argentina and Brazil are briefly outlined. The paper then examines contract auctions to assure supply adequacy in an uncertain energy environment that are being explored to face supply problems over recent years in the Chilean electricity market, taking into account the unexpected restrictions in natural gas transfers from Argentina. Also discussed are supply adequacy mechanisms and cross-border contracts in the Central American regional electricity market including firm transmission rights and financing challenges for generation investments. The final part of the paper discusses auctions of contracts and energy call options to ensure supply adequacy in the Brazilian power sector reform. Here, first stage of power sector reform, what went wrong, the second stage of reform and the move towards energy supply auctions, energy supply auctions so far and what's next in the challenges of environmental constraints and electricity-gas integration are reviewed. The reform being proposed to the electric regulatory framework for wholesale transactions in Peru is also reviewed. Considered are bids for

  6. Mechanisms of metal sorption by biochars: Biochar characteristics and modifications.

    Science.gov (United States)

    Li, Hongbo; Dong, Xiaoling; da Silva, Evandro B; de Oliveira, Letuzia M; Chen, Yanshan; Ma, Lena Q

    2017-07-01

    Biochar produced by thermal decomposition of biomass under oxygen-limited conditions has received increasing attention as a cost-effective sorbent to treat metal-contaminated waters. However, there is a lack of information on the roles of different sorption mechanisms for different metals and recent development of biochar modification to enhance metal sorption capacity, which is critical for biochar field application. This review summarizes the characteristics of biochar (e.g., surface area, porosity, pH, surface charge, functional groups, and mineral components) and main mechanisms governing sorption of As, Cr, Cd, Pb, and Hg by biochar. Biochar properties vary considerably with feedstock material and pyrolysis temperature, with high temperature producing biochars with higher surface area, porosity, pH, and mineral contents, but less functional groups. Different mechanisms dominate sorption of As (complexation and electrostatic interactions), Cr (electrostatic interactions, reduction, and complexation), Cd and Pb (complexation, cation exchange, and precipitation), and Hg (complexation and reduction). Besides sorption mechanisms, recent advance in modifying biochar by loading with minerals, reductants, organic functional groups, and nanoparticles, and activation with alkali solution to enhance metal sorption capacity is discussed. Future research needs for field application of biochar include competitive sorption mechanisms of co-existing metals, biochar reuse, and cost reduction of biochar production. Published by Elsevier Ltd.

  7. Inter-provincial clean development mechanism in China: A case study of the solar PV sector

    International Nuclear Information System (INIS)

    Jacques, David A.; Guan, Dabo; Geng, Yong; Xue, Bing; Wang, Xiaoguang

    2013-01-01

    With ever growing urgency, climate change mitigation is fast becoming a priority for China. A successful policy of implementing and expanding sustainable development and the use of renewable energy is therefore vital. As well as long-term and near-term targets for installed capacity of renewable energy, in its 12th five-year plan, China has created strict and ambitious carbon intensity targets for each province. This study proposes an inter-provincial clean development mechanism to assist in meeting these targets. This mechanism will create potential co-benefits of assisting in sustainable development in lesser developed provinces, increasing local air quality and supporting the growth of China's renewable energy sector. This paper also highlights the potential that this inter-provincial clean development mechanism has in accelerating the growth of the domestic solar photovoltaics (PV) sector, for which the market in China is still in its infancy. - Highlights: ► We recognise the necessity for each province in China to reduce its GHG emissions. ► We assess the potential of a national scale a CDM style mechanism for China. ► We consider the effect that the national CDM could have on solar PV in China

  8. Mechanisms of diffusional phase transformations in metals and alloys

    CERN Document Server

    Aaronson, Hubert I; Lee, Jong K

    2010-01-01

    Developed by the late metallurgy professor and master experimentalist Hubert I. Aaronson, this collection of lecture notes details the fundamental principles of phase transformations in metals and alloys upon which steel and other metals industries are based. Mechanisms of Diffusional Phase Transformations in Metals and Alloys is devoted to solid-solid phase transformations in which elementary atomic processes are diffusional jumps, and these processes occur in a series of so-called nucleation and growth through interface migration. Instead of relying strictly on a pedagogical approach, it doc

  9. Metal uptake and acute toxicity in zebrafish: common mechanisms across multiple metals.

    Science.gov (United States)

    Alsop, Derek; Wood, Chris M

    2011-10-01

    Zebrafish larvae (Danio rerio) were used to examine the mechanisms of action and acute toxicities of metals. Larvae had similar physiological responses and sensitivities to waterborne metals as adults. While cadmium and zinc have previously been shown to reduce Ca(2+) uptake, copper and nickel also decreased Ca(2+) uptake, suggesting that the epithelial transport of all these metals is through Ca(2+) pathways. However, exposure to cadmium, copper or nickel for up to 48 h had little or no effect on total whole body Ca(2+) levels, indicating that the reduction of Ca(2+) uptake is not the acute toxic mechanism of these metals. Instead, mortalities were effectively related to whole body Na(+), which decreased up to 39% after 48 h exposures to different metals around their respective 96 h LC50s. Decreases in whole body K(+) were also observed, although they were not as pronounced or frequent as Na(+) losses. None of the metals tested inhibited Na(+) uptake in zebrafish (Na(+) uptake was in fact increased with exposure) and the observed losses of Na(+), K(+), Ca(2+) and Mg(2+) were proportional to the ionic gradients between the plasma and water, indicating diffusive ion loss with metal exposure. This study has shown that there is a common pathway for metal uptake and a common mechanism of acute toxicity across groups of metals in zebrafish. The disruption of ion uptake accompanying metal exposure does not appear to be responsible for the acute toxicity of metals, as has been previously suggested, but rather the toxicity is instead due to total ion loss (predominantly Na(+)). Copyright © 2011 Elsevier B.V. All rights reserved.

  10. Mechanical failure and glass transition in metallic glasses

    International Nuclear Information System (INIS)

    Egami, T.

    2011-01-01

    Research highlights: → We review the recent results of molecular dynamics simulations on metallic glasses. → They show the equivalence of mechanical failure and glass transition. → We discuss the microscopic mechanism behind this equivalence. → We show that the density of defects in metallic glasses is as high as a quarter. → Our concepts about the defect state in glasses need to be changed. - Abstract: The current majority view on the phenomenon of mechanical failure in metallic glasses appears to be that it is caused by the activity of some structural defects, such as free-volumes or shear transformation zones, and the concentration of such defects is small, only of the order of 1%. However, the recent results compel us to revise this view. Through molecular dynamics simulation it has been shown that mechanical failure is the stress-induced glass transition. According to our theory the concentration of the liquid-like sites (defects) is well over 20% at the glass transition. We suggest that the defect concentration in metallic glasses is actually very high, and percolation of such defects causes atomic avalanche and mechanical failure. In this article we discuss the glass transition, mechanical failure and viscosity from such a point of view.

  11. Accidents of Electrical and Mechanical Works for Public Sector Projects in Hong Kong.

    Science.gov (United States)

    Wong, Francis K W; Chan, Albert P C; Wong, Andy K D; Hon, Carol K H; Choi, Tracy N Y

    2018-03-10

    A study on electrical and mechanical (E&M) works-related accidents for public sector projects provided the opportunity to gain a better understanding of the causes of accidents by analyzing the circumstances of all E&M works accidents. The research aims to examine accidents of E&M works which happened in public sector projects. A total of 421 E&M works-related accidents in the "Public Works Programme Construction Site Safety and Environmental Statistics" (PCSES) system were extracted for analysis. Two-step cluster analysis was conducted to classify the E&M accidents into different groups. The results identified three E&M accidents groups: (1) electricians with over 15 years of experience were prone to 'fall of person from height'; (2) electricians with zero to five years of experience were prone to 'slip, trip or fall on same level'; (3) air-conditioning workers with zero to five years of experience were prone to multiple types of accidents. Practical measures were recommended for each specific cluster group to avoid recurrence of similar accidents. The accident analysis would be vital for industry practitioners to enhance the safety performance of public sector projects. This study contributes to filling the knowledge gap of how and why E&M accidents occur and promulgating preventive measures for E&M accidents which have been under researched.

  12. Metal resistance or tolerance? Acidophiles confront high metal loads via both abiotic and biotic mechanisms

    Directory of Open Access Journals (Sweden)

    Mark eDopson

    2014-04-01

    Full Text Available All metals are toxic at high concentrations and consequently their intracellular concentrations must be regulated. Acidophilic microorganisms have an optimum growth pH < 3 and proliferate in natural and anthropogenic low pH environments. Some acidophiles are involved in the catalysis of sulfide mineral dissolution, resulting in high concentrations of metals in solution. Acidophiles are often described as highly metal resistant via mechanisms such as multiple and/or more efficient active resistance systems than are present in neutrophiles. However, this is not the case for all acidophiles and we contend that their growth in high metal concentrations is partially due to an intrinsic tolerance as a consequence of the environment in which they live. In this perspective, we highlight metal tolerance via complexation of free metals by sulfate ions and passive tolerance to metal influx via an internal positive cytoplasmic transmembrane potential. These tolerance mechanisms have been largely ignored in past studies of acidophile growth in the presence of metals and should be taken into account.

  13. Mechanisms of chelation of heavy metals by chitosan

    International Nuclear Information System (INIS)

    Averbach, B.L.

    1980-01-01

    The concentration profiles of several heavy metal ions and anions have been measured in chitosan membranes immersed in dilute aqueous solutions. The shapes of the concentration curves for the metal ions is characteristic of a diffusion process in which the diffusion coefficient is a function of the concentration. The anion penetrates much more rapidly than the cation, however, and the concentration appears to be dependent on the reaction kinetics. We propose a mechanism whereby the metal ion bonds with the nitrogen in the functional amino group, with the bridging oxygen and with two hydroxyl groups in a neighboring glucose ring. The anion, on the other hand, bonds ionically to the metal-amino complex in order to neutralize the charge and to the protonated amino sites which have not reacted with the metal ion. In the case of uranium in sea water, it is probable that the uranium is present as a uranyl complex and that bonding with chitosan will occur by ionic bonding, that is, salt formation, rather than by covalent bonding to the amino groups. Uranyl complexes in dilute concentration will thus compete with chloride and the relative concentrations will be determined by the equilibrium constants. Work on the reaction between chitosan and dilute solutions of copper sulfate is reported. A mechanism for these reactions is postulated, and it is suggested that the same mechanism carries over to uranium in sea water. This suggests certain limitations on the process which should be explored if chitosan is to be used for this purpose

  14. Heavy Metal Stress and Some Mechanisms of Plant Defense Response

    Directory of Open Access Journals (Sweden)

    Abolghassem Emamverdian

    2015-01-01

    Full Text Available Unprecedented bioaccumulation and biomagnification of heavy metals (HMs in the environment have become a dilemma for all living organisms including plants. HMs at toxic levels have the capability to interact with several vital cellular biomolecules such as nuclear proteins and DNA, leading to excessive augmentation of reactive oxygen species (ROS. This would inflict serious morphological, metabolic, and physiological anomalies in plants ranging from chlorosis of shoot to lipid peroxidation and protein degradation. In response, plants are equipped with a repertoire of mechanisms to counteract heavy metal (HM toxicity. The key elements of these are chelating metals by forming phytochelatins (PCs or metallothioneins (MTs metal complex at the intra- and intercellular level, which is followed by the removal of HM ions from sensitive sites or vacuolar sequestration of ligand-metal complex. Nonenzymatically synthesized compounds such as proline (Pro are able to strengthen metal-detoxification capacity of intracellular antioxidant enzymes. Another important additive component of plant defense system is symbiotic association with arbuscular mycorrhizal (AM fungi. AM can effectively immobilize HMs and reduce their uptake by host plants via binding metal ions to hyphal cell wall and excreting several extracellular biomolecules. Additionally, AM fungi can enhance activities of antioxidant defense machinery of plants.

  15. Heavy Metal Stress and Some Mechanisms of Plant Defense Response

    Science.gov (United States)

    Emamverdian, Abolghassem; Ding, Yulong; Mokhberdoran, Farzad; Xie, Yinfeng

    2015-01-01

    Unprecedented bioaccumulation and biomagnification of heavy metals (HMs) in the environment have become a dilemma for all living organisms including plants. HMs at toxic levels have the capability to interact with several vital cellular biomolecules such as nuclear proteins and DNA, leading to excessive augmentation of reactive oxygen species (ROS). This would inflict serious morphological, metabolic, and physiological anomalies in plants ranging from chlorosis of shoot to lipid peroxidation and protein degradation. In response, plants are equipped with a repertoire of mechanisms to counteract heavy metal (HM) toxicity. The key elements of these are chelating metals by forming phytochelatins (PCs) or metallothioneins (MTs) metal complex at the intra- and intercellular level, which is followed by the removal of HM ions from sensitive sites or vacuolar sequestration of ligand-metal complex. Nonenzymatically synthesized compounds such as proline (Pro) are able to strengthen metal-detoxification capacity of intracellular antioxidant enzymes. Another important additive component of plant defense system is symbiotic association with arbuscular mycorrhizal (AM) fungi. AM can effectively immobilize HMs and reduce their uptake by host plants via binding metal ions to hyphal cell wall and excreting several extracellular biomolecules. Additionally, AM fungi can enhance activities of antioxidant defense machinery of plants. PMID:25688377

  16. Toxicity, mechanism and health effects of some heavy metals

    Directory of Open Access Journals (Sweden)

    Jaishankar Monisha

    2014-06-01

    Full Text Available Heavy metal toxicity has proven to be a major threat and there are several health risks associated with it. The toxic effects of these metals, even though they do not have any biological role, remain present in some or the other form harmful for the human body and its proper functioning. They sometimes act as a pseudo element of the body while at certain times they may even interfere with metabolic processes. Few metals, such as aluminium, can be removed through elimination activities, while some metals get accumulated in the body and food chain, exhibiting a chronic nature. Various public health measures have been undertaken to control, prevent and treat metal toxicity occurring at various levels, such as occupational exposure, accidents and environmental factors. Metal toxicity depends upon the absorbed dose, the route of exposure and duration of exposure, i.e. acute or chronic. This can lead to various disorders and can also result in excessive damage due to oxidative stress induced by free radical formation. This review gives details about some heavy metals and their toxicity mechanisms, along with their health effects

  17. Soft Ferromagnetic Bulk Metallic Glasses with Enhanced Mechanical Properties

    OpenAIRE

    Ramasamy, Parthiban

    2018-01-01

    Fe-based bulk metallic glasses (BMGs) have gained considerable interest due to their excellent soft magnetic properties with high saturation magnetization, high electrical resistivity, very good corrosion resistance, low materials cost, extremely high mechanical strength and hardness. In spite of having excellent strength, Fe-based BMGs are not used as structural materials in service, so far. The major obstacle is their inherent brittleness under mechanical loading, once a crack is developed ...

  18. effects of metal inert gas welding parameters on some mechanical

    African Journals Online (AJOL)

    HOD

    Surface corrosion deposit composition was analyzed with the SEM paired with energy dispersive spectrometer (EDS) to ascertain microstructural behavior of the material. Keywords- MIG, Mechanical Destructive tests, Current, Speed, ASS, SEM, HCl. 1. INTRODUCTION. Metal Inert Gas (MIG) welding is a process that has ...

  19. Heavy Metals in Soils of auto- mechanic shops and refuse ...

    African Journals Online (AJOL)

    Dumpsites soil samples in Apir and North Bank Auto- mechanic workshop locations in Makurdi, the Benue State capital located on latitude 70 44'N and longitude 80 32'E of the Equator situated in a valley in north central Nigeria, 100m above sea level, were collected and analyzed for content of selected heavy metals.

  20. A deformation mechanism of hard metal surrounded by soft metal during roll forming

    Science.gov (United States)

    Yu, Hailiang; Tieu, A. Kiet; Lu, Cheng; Liu, Xiong; Godbole, Ajit; Li, Huijun; Kong, Charlie; Qin, Qinghua

    2014-05-01

    It is interesting to imagine what would happen when a mixture of soft-boiled eggs and stones is deformed together. A foil made of pure Ti is stronger than that made of Cu. When a composite Cu/Ti foil deforms, the harder Ti will penetrate into the softer Cu in the convex shapes according to previously reported results. In this paper, we describe the fabrication of multilayer Cu/Ti foils by the roll bonding technique and report our observations. The experimental results lead us to propose a new deformation mechanism for a hard metal surrounded by a soft metal during rolling of a laminated foil, particularly when the thickness of hard metal foil (Ti, 25 μm) is much less than that of the soft metal foil (Cu, 300 μm). Transmission Electron Microscope (TEM) imaging results show that the hard metal penetrates into the soft metal in the form of concave protrusions. Finite element simulations of the rolling process of a Cu/Ti/Cu composite foil are described. Finally, we focus on an analysis of the deformation mechanism of Ti foils and its effects on grain refinement, and propose a grain refinement mechanism from the inside to the outside of the laminates during rolling.

  1. Mechanics of metal-catecholate complexes: The roles of coordination state and metal types

    Science.gov (United States)

    Xu, Zhiping

    2013-01-01

    There have been growing evidences for the critical roles of metal-coordination complexes in defining structural and mechanical properties of unmineralized biological materials, including hardness, toughness, and abrasion resistance. Their dynamic (e.g. pH-responsive, self-healable, reversible) properties inspire promising applications of synthetic materials following this concept. However, mechanics of these coordination crosslinks, which lays the ground for predictive and rational material design, has not yet been well addressed. Here we present a first-principles study of representative coordination complexes between metals and catechols. The results show that these crosslinks offer stiffness and strength near a covalent bond, which strongly depend on the coordination state and type of metals. This dependence is discussed by analyzing the nature of bonding between metals and catechols. The responsive mechanics of metal-coordination is further mapped from the single-molecule level to a networked material. The results presented here provide fundamental understanding and principles for material selection in metal-coordination-based applications. PMID:24107799

  2. Energy consumption analysis of Spanish food and drink, textile, chemical and non-metallic mineral products sectors

    International Nuclear Information System (INIS)

    Aranda-Usón, Alfonso; Ferreira, Germán; Mainar-Toledo, M.D.; Scarpellini, Sabina; Llera Sastresa, Eva

    2012-01-01

    This paper provides quantitative information for energy consumption from four different industry sectors based on an energy analysis obtained by means of in-situ energy audits and complementary information. The latter information was taken from Saving Strategy and Energy Efficiency in Spain (Estrategia de Ahorro y Eficiencia Energética en España 2004–2010, E4) documents and the 2009 Industrial Survey of Spain from the National Statistics Institute (Instituto Nacional de Estadística, INE). The results show an estimate of energy consumption for each sector, namely Spanish food, drink and tobacco (9.6%), textile (4.5%), chemical (14.7%), and non-metallic mineral products (24.3%), as well as the degree of inefficiency for each, obtained by means of a stochastic frontier production function model. These results are combined with the energy consumption analysis to identify potential energy saving opportunities around 20.0% of the total energy consumption for all studied sectors. These energy saving opportunities are classified according to thermal or electrical energy consumption and percentage savings of the total energy consumption. -- Highlights: ► This study presents the analysis of four Spanish energy-consuming industrial sectors. ► The four selected sectors account for 33.0% of the total industrial SMEs. ► An audit was carried out in several factories from each analysed industrial sector. ► Stochastic Cobb-Douglas frontiers were used to estimate production frontiers. ► Potential energy saving opportunities around 20.0% of the total energy consumption.

  3. Enhanced metal extractive behavior using dual mechanism bifunctional polymer: an effective metal chelatogen.

    Science.gov (United States)

    Prabhakaran, D; Subramanian, M S

    2003-11-12

    A new class of chelating polymers using Amberlite XAD-16 (AXAD-16) modified with (N-(3,4-dihydroxy)benzyl)-4-amino,3-hydroxynapthalene-1-sulphonic acid has been developed based on dual mechanism bifunctional polymers, for the extraction of transition and post-transition metal ions. The optimum pH conditions for the quantitative sorption of metal ions were studied. The developed method showed superior extraction qualities with high metal loading capacities of 71, 85, 182, 130 and 46 mg g(-1) for Ni(II), Cd(II), Pb(II), Cu(II) and Co(II), respectively. The rate of metal ion uptake i.e. kinetics studies performed under optimum levels showed a time duration of metal ion saturation. Desorption of metal ions were effective with 15 ml of 2 M HCl/HNO(3) prior to detection using flame atomic absorption spectrophotometer. The chelating polymer was highly ion-selective in nature even in the presence of large concentrations of alkali and alkaline earth metal ions, with a high preconcentrating ability for the metal ions of interest. The developed chelating matrix was tested on its utility with synthetic and real samples like river/sea/tap/well water samples and also with multivitamin/mineral tablets, showed R.S.D. values of <2.5% reflecting on the accuracy and reproducibility of data using the newly developed resin matrix.

  4. Evaporation as the transport mechanism of metals in arid regions

    KAUST Repository

    Lima, Ana T.

    2014-09-01

    Soils of arid regions are exposed to drought and drastic temperature oscillations throughout the year. Transport mechanisms in these soils are therefore very different from the ones in temperate regions, where rain dictates the fate of most elements in soils. Due to the low rainfall and high evaporation rates in arid regions, groundwater quality is not threatened and all soil contamination issues tend to be overlooked. But if soil contamination happens, where do contaminants go? This study tests the hypothesis of upward metal movement in soils when evaporation is the main transport mechanism. Laboratory evaporation tests were carried out with heavy metal spiked Saudi soil, using circulation of air as the driving force (Fig. 1). Main results show that loamy soil retains heavy metals quite well while evaporation drives heavy metals to the surface of a sandy soil. Evaporation transports heavy metals upward in sandy soils of arid regions, making them accumulate at the soil surface. Sand being the dominating type of soil in arid regions, soils can then be a potential source of contaminated aerosols and atmospheric pollution - a transboundary problem. Some other repercussions for this problem are foreseen, such as the public ingestion or inhalation of dust. © 2014 Elsevier Ltd.

  5. Operationalizing clean development mechanism baselines: A case study of China's electrical sector

    Science.gov (United States)

    Steenhof, Paul A.

    The global carbon market is rapidly developing as the first commitment period of the Kyoto Protocol draws closer and Parties to the Protocol with greenhouse gas (GHG) emission reduction targets seek alternative ways to reduce their emissions. The Protocol includes the Clean Development Mechanism (CDM), a tool that encourages project-based investments to be made in developing nations that will lead to an additional reduction in emissions. Due to China's economic size and rate of growth, technological characteristics, and its reliance on coal, it contains a large proportion of the global CDM potential. As China's economy modernizes, more technologies and processes are requiring electricity and demand for this energy source is accelerating rapidly. Relatively inefficient technology to generate electricity in China thereby results in the electrical sector having substantial GHG emission reduction opportunities as related to the CDM. In order to ensure the credibility of the CDM in leading to a reduction in GHG emissions, it is important that the baseline method used in the CDM approval process is scientifically sound and accessible for both others to use and for evaluation purposes. Three different methods for assessing CDM baselines and environmental additionality are investigated in the context of China's electrical sector: a method based on a historical perspective of the electrical sector (factor decomposition), a method structured upon a current perspective (operating and build margins), and a simulation of the future (dispatch analysis). Assessing future emission levels for China's electrical sector is a very challenging task given the complexity of the system, its dynamics, and that it is heavily influenced by internal and external forces, but of the different baseline methods investigated, dispatch modelling is best suited for the Chinese context as it is able to consider the important regional and temporal dimensions of its economy and its future development

  6. Analyzing the effects of applying IoT to a metal-mechanical company

    Directory of Open Access Journals (Sweden)

    Eduardo Cañizares

    2018-04-01

    Full Text Available Purpose: The purpose of this paper is to show the improvements obtained through the application of IoT in a company of the metal-mechanical sector. Design/methodology/approach: The methodology used has been the collection of data before and after the application of the IoT in the process to manufacture tool-machines. Findings: Improvements obtained in some aspects of the process are very high (above 30%, making it a process that is more efficient allowing reduce costs. Research limitations/implications: Some aspects or details are difficult to quantify because there are no measurable parameters. Practical implications: Technological advances and new technologies applied to the industry, allows significant improvements in production. Social implications: Improvements obtained in the process can improve the conditions of workers. Originality/value: Originality of the paper is very high, because there are no publications of study or practical cases in the sector, due to the confidentiality and competitiveness of the sector.

  7. Regulatory mechanisms for absenteeism in the health sector: a systematic review of strategies and their implementation

    Science.gov (United States)

    Kisakye, Angela N; Tweheyo, Raymond; Ssengooba, Freddie; Pariyo, George W; Rutebemberwa, Elizeus; Kiwanuka, Suzanne N

    2016-01-01

    Background A systematic review was undertaken to identify regulatory mechanisms aimed at mitigating health care worker absenteeism, to describe where and how they have been implemented as well as their possible effects. The goal was to propose potential policy options for managing the problem of absenteeism among human resources for health in low- and middle-income countries. Mechanisms described in this review are at the local workplace and broader national policy level. Methods A comprehensive online search was conducted on EMBASE, CINAHL, PubMed, Google Scholar, Google, and Social Science Citation Index using MEDLINE search terms. Retrieved studies were uploaded onto reference manager and screened by two independent reviewers. Only publications in English were included. Data were extracted and synthesized according to the objectives of the review. Results Twenty six of the 4,975 published articles retrieved were included. All were from high-income countries and covered all cadres of health workers. The regulatory mechanisms and possible effects include 1) organizational-level mechanisms being reported as effective in curbing absenteeism in low- and middle-income countries (LMICs); 2) prohibition of private sector activities in LMICs offering benefits but presenting a challenge for the government to monitor the health workforce; 3) contractual changes from temporary to fixed posts having been associated with no reduction in absenteeism and not being appropriate for LMICs; 4) multifaceted work interventions being implemented in most settings; 5) the possibility of using financial and incentive regulatory mechanisms in LMICs; 6) health intervention mechanisms reducing absenteeism when integrated with exercise programs; and 7) attendance by legislation during emergencies being criticized for violating human rights in the United States and not being effective in curbing absenteeism. Conclusion Most countries have applied multiple strategies to mitigate health care

  8. Regulatory mechanisms for absenteeism in the health sector: a systematic review of strategies and their implementation.

    Science.gov (United States)

    Kisakye, Angela N; Tweheyo, Raymond; Ssengooba, Freddie; Pariyo, George W; Rutebemberwa, Elizeus; Kiwanuka, Suzanne N

    2016-01-01

    A systematic review was undertaken to identify regulatory mechanisms aimed at mitigating health care worker absenteeism, to describe where and how they have been implemented as well as their possible effects. The goal was to propose potential policy options for managing the problem of absenteeism among human resources for health in low- and middle-income countries. Mechanisms described in this review are at the local workplace and broader national policy level. A comprehensive online search was conducted on EMBASE, CINAHL, PubMed, Google Scholar, Google, and Social Science Citation Index using MEDLINE search terms. Retrieved studies were uploaded onto reference manager and screened by two independent reviewers. Only publications in English were included. Data were extracted and synthesized according to the objectives of the review. Twenty six of the 4,975 published articles retrieved were included. All were from high-income countries and covered all cadres of health workers. The regulatory mechanisms and possible effects include 1) organizational-level mechanisms being reported as effective in curbing absenteeism in low- and middle-income countries (LMICs); 2) prohibition of private sector activities in LMICs offering benefits but presenting a challenge for the government to monitor the health workforce; 3) contractual changes from temporary to fixed posts having been associated with no reduction in absenteeism and not being appropriate for LMICs; 4) multifaceted work interventions being implemented in most settings; 5) the possibility of using financial and incentive regulatory mechanisms in LMICs; 6) health intervention mechanisms reducing absenteeism when integrated with exercise programs; and 7) attendance by legislation during emergencies being criticized for violating human rights in the United States and not being effective in curbing absenteeism. Most countries have applied multiple strategies to mitigate health care worker absenteeism. The success of these

  9. To implicate the private sector in funding: The Kyoto mechanisms and SUMO policies

    International Nuclear Information System (INIS)

    Leguet, Benoit; Morel, Romain

    2015-01-01

    Internationally set objectives in the fight against climate change cannot be reached without funding from the private sector. Public money, a scarce resource, must be used as best possible, in particular when it has a leverage effect on private funding. In this respect, feedback from the Kyoto Protocol's clean development mechanism is of interest. On the eve of the 2015 Paris Climate Conference, we must ramp up the mobilization of private resources. Smart unconventional monetary (SUMO) policies could help us toward this goal. Several countries have adopted such policies to cope with macro-economic circumstances or systemic risks. Is the destabilization of the climate not a risk of this sort?

  10. Consideraciones actuales en la utilización de coronas unitarias libres de metal en el sector posterior

    OpenAIRE

    Castro-Aguilar, Enrique Gabriel; Matta-Morales, Carlos Octavio; Orellana-Valdivieso, Oscar

    2014-01-01

    Actualmente se están desarrollando sistemas libres de metal para la confección de restauraciones protésicas que cumplan con altas expectativas funcionales, biocompatibilidad y estética. Sin embargo, a pesar de la introducción de nuevos materiales y avances tecnológicos en el proceso de elaboración, se ha cuestionado el comportamiento mecánico de las coronas unitarias en el sector posterior relacionado con fracturas de la cerámica feldespática de recubrimiento, para mejorar estas deficiencias,...

  11. CDM (Clean Development Mechanism) opportunities for the oil and gas sector

    Energy Technology Data Exchange (ETDEWEB)

    Franco, Joana Chiavari [FEEM - Fondazione Eni Enrico Mattei, Milan (Italy). Eni/Agip Group

    2004-07-01

    Due to the broad impact of legislation limiting greenhouse gas emissions and the increasing public awareness concerning the environment, the oil industry has been currently incorporating climate change considerations in its corporate strategy. However, compliance in the carbon constrained economy does not merely represent a cost issue; it also represents an opportunity. Projects developed under the Clean Development Mechanism (CDM) in particular represent an incentive both for companies and governments to invest in emission reduction projects in developing countries and earn carbon credits, while promoting sustainable development. The oil industry is characterized by a high emission reduction potential and is able to deliver to the market an amount of credits which is by far higher than the amount that most projects developers are able to offer. However some critical issues, such as the current interpretation of the additionally concept, may represent a barrier for the full utilization of such mechanism, particularly regarding petroleum-sector projects, thus reducing the benefits the CDM can actually produce. Considering that a very large number of CDM projects may be needed for the implementation of a successful climate policy, the engagement of the oil industry on the Kyoto mechanisms is very important and auspicial. (author)

  12. Phytoremediation of radionuclides - heavy metals in mycorrhizosphere soil and enzymatic mechanism

    International Nuclear Information System (INIS)

    Fulekar, M.H.; Bhawana, P.; Anamika, S.A.

    2012-01-01

    Nuclear industry plays a vital role in the economic growth and development of manufacturing sector of a developing country. The nuclear industry is a fastest growing industry in India which contributes 2% production of renewable energy. The nuclear industry involves the handling and uses of radioactive materials. Nuclear wastes generated through chemical processing and/or nuclear weapons program have also enhanced the level of hazardous environmental contaminants. In low level nuclear wastes, concentration involved are low and volumes are large. Hence, physical and chemical methods may not be effective practice to decontaminate the low level nuclear waste. The organic as well as inorganic chemicals present in the nuclear wastes find their way in soil and water causing environmental pollution. In present research study, the mycorrhiza soil has been developed using pot culture technique in green house. The mycorrhiza soil characterization was done for physico-chemical and microbial parameters. The heavy metals such as Cu, Pb and Zn toxicity in mycorrhiza soil at a concentration viz. 0, 5, 10, 20, 50, 75 and 100 ppm was assessed using the green plants such as Medicago sativa, Brassica juncea and Alfalfa. These green plants have been used for phytoremediation of heavy metals at a varying concentration of 0, 5, 10, 20 and 50 ppm using the pot culture technique. The chlorophyll content and caretenoid as an indicator of plant growth and the enzymatic activities have been assessed as a defence mechanism during phytoremediation of heavy metals by these green plants. The mycorrhiza soil has been found as an effective and efficient natural fertilizer to remediate heavy metals by green plants. Phytoremediation of heavy metals in mycorrhizosphere has proved that it is an effective, efficient, ecofriendly, low cost, sustainable green technology for restoration of ecosystem in radionuclides - heavy metal polluted environment. (author)

  13. Metallic-glass-matrix composite structures with benchmark mechanical performance

    Science.gov (United States)

    Schramm, Joseph P.; Hofmann, Douglas C.; Demetriou, Marios D.; Johnson, William L.

    2010-12-01

    Metallic-glass-matrix composites demonstrating unusual combination of high strength, high toughness, and excellent processability are utilized to fabricate cellular structures of egg-box topology. Under compressive loading, the egg-box panels are capable of undergoing extensive plastic collapse at very high plateau stresses enabling absorption of large amounts of mechanical energy. In terms of specific mechanical energy absorbed, the present panels far outperform panels of similar topology made of aluminum or fiber-reinforced polymer composites, and even surpass steel structures of highly buckling-resistant topologies, thus emerging among the highest performance structures of any kind.

  14. Regulatory mechanisms for absenteeism in the health sector: a systematic review of strategies and their implementation

    Directory of Open Access Journals (Sweden)

    Kisakye AN

    2016-11-01

    Full Text Available Angela N Kisakye,1 Raymond Tweheyo,1 Freddie Ssengooba,1 George W Pariyo,2 Elizeus Rutebemberwa,1 Suzanne N Kiwanuka1 1Department of Health Policy Planning and Management, Makerere University School of Public Health, Kampala, Uganda; 2Department of International Health, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD, USA Background: A systematic review was undertaken to identify regulatory mechanisms aimed at mitigating health care worker absenteeism, to describe where and how they have been implemented as well as their possible effects. The goal was to propose potential policy options for managing the problem of absenteeism among human resources for health in low- and middle-income countries. Mechanisms described in this review are at the local workplace and broader national policy level. Methods: A comprehensive online search was conducted on EMBASE, CINAHL, PubMed, Google Scholar, Google, and Social Science Citation Index using MEDLINE search terms. Retrieved studies were uploaded onto reference manager and screened by two independent reviewers. Only publications in English were included. Data were extracted and synthesized according to the objectives of the review. Results: Twenty six of the 4,975 published articles retrieved were included. All were from high-income countries and covered all cadres of health workers. The regulatory mechanisms and possible effects include 1 organizational-level mechanisms being reported as effective in curbing absenteeism in low- and middle-income countries (LMICs; 2 prohibition of private sector activities in LMICs offering benefits but presenting a challenge for the government to monitor the health workforce; 3 contractual changes from temporary to fixed posts having been associated with no reduction in absenteeism and not being appropriate for LMICs; 4 multifaceted work interventions being implemented in most settings; 5 the possibility of using financial and incentive regulatory mechanisms

  15. Analysis of the technological capacity of pymes in the metal sector- an evaluation methodology

    Directory of Open Access Journals (Sweden)

    José Divitt Velosa García

    2012-08-01

    Full Text Available Rev.esc.adm.neg Las pymes del sector metalmecánico, requieren mejorar su desempeño empresarial de tal forma que esto permita el desarrollo de ventajas competitivas frente a mercados globales. Estas ventajas se pueden lograr de muchas formas, pero una de las fuentes que en los últimos años ha tomado gran importancia es a través del sistema de producción (Hill, 2000. En este trabajo se presenta una metodología para medir la capacidad tecnológica de producción en las pymes del sector metalmecánico colombiano, con el objetivo de evaluar la gestión frente a dos aspectos específicos diseño y manufactura, y de acuerdo con los resultados proponer estrategias para que estas empresas puedan mejorar su capacidad tecnológica.

  16. Evaluation of the information quality in a company of metal-mechanical industry

    Directory of Open Access Journals (Sweden)

    Guilherme Augusto Spiegel Gualazzi

    2012-11-01

    Full Text Available This paper presents the application of an instrument for assessing the quality of information based on attributes such as accuracy, reliability, performance, among others. This instrument was applied in order to evaluate and identify ineffective information in a specific scenario of an engineering company in the metal-mechanic sector from the point of view of users of technical information. The case study aimed to demonstrate the applicability and functionality of the assessment instrument, the interest of people in evaluating their information and, finally, evaluate the scope of their results. The result of this evaluation allowed the company researched a plan of action to correct problems in its processes and identified inaccuracies in the information, indicating that the problem was solved by the method of problem solving.

  17. Corrosion fatigue of biomedical metallic alloys: mechanisms and mitigation.

    Science.gov (United States)

    Antunes, Renato Altobelli; de Oliveira, Mara Cristina Lopes

    2012-03-01

    Cyclic stresses are often related to the premature mechanical failure of metallic biomaterials. The complex interaction between fatigue and corrosion in the physiological environment has been subject of many investigations. In this context, microstructure, heat treatments, plastic deformation, surface finishing and coatings have decisive influence on the mechanisms of fatigue crack nucleation and growth. Furthermore, wear is frequently present and contributes to the process. However, despite all the effort at elucidating the mechanisms that govern corrosion fatigue of biomedical alloys, failures continue to occur. This work reviews the literature on corrosion-fatigue-related phenomena of Ti alloys, surgical stainless steels, Co-Cr-Mo and Mg alloys. The aim was to discuss the correlation between structural and surface aspects of these materials and the onset of fatigue in the highly saline environment of the human body. By understanding such correlation, mitigation of corrosion fatigue failure may be achieved in a reliable scientific-based manner. Different mitigation methods are also reviewed and discussed throughout the text. It is intended that the information condensed in this article should be a valuable tool in the development of increasingly successful designs against the corrosion fatigue of metallic implants. Copyright © 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

  18. Small specimen technique for assessing mechanical properties of metallic components

    Energy Technology Data Exchange (ETDEWEB)

    Lobo, Raquel M.; Andrade, Arnaldo H.P.; Morcelli, Aparecido E., E-mail: rmlobo@ipen.br, E-mail: morcelliae@gmail.com [Instituto de Pesquisas Energeticas e Nucleares (IPEN/CNEN-SP), Sao Paulo, SP (Brazil)

    2017-11-01

    Small Punch Test (SPT) is one of the most promising techniques of small specimen test, which was originally applied in testing of irradiated materials in nuclear engineering. Then it was introduced to other fields as an almost nondestructive method to measure the local mechanical properties that are difficult to be obtained using conventional mechanical tests. Most studies to date are focused on metallic materials, although SPT applications are recently spreading to other materials. The small punch test (SPT) employs small-sized specimens (for example, samples measuring 8 mm in diameter and 0.5 mm thick). The specimen is firmly clamped between two circular dies and is bi-axially strained until failure into a circular hole using a hemispherical punch. The 'load-punch displacement' record can be used to estimate the yield strength, the ultimate tensile strength, the tensile elongation, and the temperature of the ductile-to-brittle transition. Recently, some researchers are working on the use of miniature notched or pre-cracked specimens (denoted as p-SPT) to validate its geometry and dimensions for obtaining the fracture properties of metallic materials. In a first approach, the technique makes it possible to convert primary experimental data into conventional mechanical properties of a massive specimen. In this paper a comprehensive review of the different STP applications is presented with the aim of clarifying its usefulness. (author)

  19. Small specimen technique for assessing mechanical properties of metallic components

    International Nuclear Information System (INIS)

    Lobo, Raquel M.; Andrade, Arnaldo H.P.; Morcelli, Aparecido E.

    2017-01-01

    Small Punch Test (SPT) is one of the most promising techniques of small specimen test, which was originally applied in testing of irradiated materials in nuclear engineering. Then it was introduced to other fields as an almost nondestructive method to measure the local mechanical properties that are difficult to be obtained using conventional mechanical tests. Most studies to date are focused on metallic materials, although SPT applications are recently spreading to other materials. The small punch test (SPT) employs small-sized specimens (for example, samples measuring 8 mm in diameter and 0.5 mm thick). The specimen is firmly clamped between two circular dies and is bi-axially strained until failure into a circular hole using a hemispherical punch. The 'load-punch displacement' record can be used to estimate the yield strength, the ultimate tensile strength, the tensile elongation, and the temperature of the ductile-to-brittle transition. Recently, some researchers are working on the use of miniature notched or pre-cracked specimens (denoted as p-SPT) to validate its geometry and dimensions for obtaining the fracture properties of metallic materials. In a first approach, the technique makes it possible to convert primary experimental data into conventional mechanical properties of a massive specimen. In this paper a comprehensive review of the different STP applications is presented with the aim of clarifying its usefulness. (author)

  20. A conjoint analysis of corporate preferences for the sectoral crediting mechanism: a case study of Shanxi Province in China

    NARCIS (Netherlands)

    Gao, S.; Smits, M.; Wang, C.

    2016-01-01

    It is crucial to understand corporate preferences in designing and planning new market-based instruments. Using the method of conjoint analysis, this paper evaluates corporate preferences for policy alternatives of the sectoral crediting mechanism aiming at supporting its discussions and

  1. Dynamics of technology shifts in the household sector-implications for clean development mechanism

    International Nuclear Information System (INIS)

    Reddy, B. Sudhakara; Balachandra, P.

    2006-01-01

    The present paper attempts to analyse the dynamics of energy end-use technology shifts in the household sector in India. The technology shifts can be categorized as naturally occurring shifts (with increasing household incomes and availability of energy carriers) and policy-induced shifts (by creating a favourable environment). Initially, the households energy usage patterns, types of energy carriers and the technologies in use are analysed using the data from the National Sample Survey (1999-2000). The energy consumption is disaggregated according to end-use activity and by income groups for rural as well as urban households. It is observed that large variations in energy use exist across different sections of households-urban/rural, low/high-income groups, etc. Further, the paper provides a methodological framework for the diffusion of energy-efficient technologies, and the implications of such diffusions for the Clean Development Mechanism (CDM). It analyses the reasons for the gap between possible and practical implementation of energy-efficient measures, study the reasons for households not using the cost-effective technologies available to them, the benefits of innovation of energy efficiency, and the required policies and specific proposals for government intervention to achieve the potential for the CDM

  2. How to use the clean development mechanism in the residential sector? The case of Brazilian refrigerators

    International Nuclear Information System (INIS)

    Khalil, Helioui; Cohen, Claude; Salem Szklo, Alexandre

    2006-01-01

    The definition of simple and reliable emission baselines is crucial to foster clean development mechanism (CDM) projects. This paper assesses a project methodology that could boost large-scale energy-efficiency projects in the sector of domestic appliances. The baseline appliance is defined a priori in a 'conservative' manner as the design option minimizing life-cycle social costs. The project methodology consists in a program which rebates new appliances according to their emission savings compared to the baseline. Is the proposed baseline acceptable? What could be the impact of such project on emissions? To address these questions, we look for insights from a hypothetical case on Brazilian refrigerators. A rational choice model is developed which assumes that households select design options minimizing life-cycle private costs. Results suggest that electricity tariff distortions and financial constraints might hamper project performances and allow significant free-riding. Low income households remain trapped into low-efficiency choices and high income households adopt outperforming appliances, whether rebated or not. However, simple solutions likely to improve the project methodology do exist

  3. Atomistic simulations of Mg-Cu metallic glasses: Mechanical properties

    DEFF Research Database (Denmark)

    Bailey, Nicholas; Schiøtz, Jakob; Jacobsen, Karsten Wedel

    2004-01-01

    The atomistic mechanisms of plastic deformation in amorphous metals are far from being understood. We have derived potential parameters for molecular dynamics simulations of Mg-Cu amorphous alloys using the Effective Medium Theory. We have simulated the formation of alloys by cooling from the melt......, and have used these glassy configurations to carry out simulations of plastic deformation. These involved different compositions, temperatures (including zero), and types of deformation (uniaxial strain/pure shear), and yielded stress-strain curves and values of flow stress. Separate simulations were...

  4. Mechanism of the superior mechanical strength of nanometer-sized metal single crystals revealed

    KAUST Repository

    Afify, N. D.

    2013-10-01

    Clear understanding of the superior mechanical strength of nanometer-sized metal single crystals is required to derive advanced mechanical components retaining such superiority. Although high quality studies have been reported on nano-crystalline metals, the superiority of small single crystals has neither been fundamentally explained nor quantified to this date. Here we present a molecular dynamics study of aluminum single crystals in the size range from 4.1 nm to 40.5 nm. We show that the ultimate mechanical strength deteriorates exponentially as the single crystal size increases. The small crystals superiority is explained by their ability to continuously form vacancies and to recover them. © 2013 Published by Elsevier B.V.

  5. Enterprise systems in financial sector - an application in precious metal trading forecasting

    Science.gov (United States)

    Chen, Xiaozhu; Fang, Yiwei

    2013-11-01

    The use of enterprise systems has become increasingly popular in the financial service industry. This paper discusses the applications of enterprise systems in the financial sectors and presents an application in gold price forecasting. We carefully examine the impacts of a few most widely assumed factors that have significant impact on the long-term gold price using statistical regression techniques. The analysis on our proposed linear regression mode indicates that the United States ultra scale of M2 money supply has been the most important catalyst for the rising price of gold, and the CRB index upward trend has also been the weighty factor for pushing up the gold price. In addition, the gold price has a low negative correlation with the Dow Jones Industrial Average, and low positive correlations with the US dollar index and the gold ETFs holdings.

  6. Typology of Clean Development Mechanism project in the nuclear power generation sector; Tipologia de projeto de CDM (Clean Development Mechanism) no setor nucleoeletrico

    Energy Technology Data Exchange (ETDEWEB)

    Carvalho, Everton de Almeida [Industrias Nucleares Brasileiras (INB), Rio de Janeiro, RJ (Brazil)

    2002-07-01

    This work, facing the Brazilian energetic conditions under the government directives, and the electric sector, suggests a typology of nuclear Clean Development Mechanism, of international cooperation, in the frame of the efforts susceptible to be developed reaching the reduction of the gaseous emissions responsible for the global heating. Other aspects related to technical, legal and market aspects are analysed and proposed.

  7. Evolution of metal-metal wear mechanisms in martensitic steel deposits for recharging

    International Nuclear Information System (INIS)

    Gualco, Agustin; Svoboda, Hernan G; Surian, Estela S; De Vedia, Luis A

    2008-01-01

    This work studied metal recharged by welding with a martensitic steel (Cr, Mn, Mo, V and W alloy), deposited with a metal filled tubular wire on a low carbon steel, using semi-automatic welding with a contributing heat of 2 kJ/mm and under a gaseous protection of Ar-2%CO 2 . Transverse cuts were extracted from the welded sample for microstructural characterization, hardness measurement, determination of chemical composition and wear tests. The microstructural characterization was performed using light microscopy (LM) and scanning electron microscopy (SEM), X-Ray diffraction (XRD) and energy dispersive spectroscopy (EDS). The wear tests (metal-metal) were carried out on an Amsler machine in natural flow condition, with 500, 1250 and 2000 N of applied charge. The reference material was SAE 1020 steel. The weight loss curves were determined as a function of the distance run up to 5000 meters for all conditions. Then the test's wear surfaces and debris were analyzed. The microstructure consisted mostly of martensite and a fraction of retained austenite. A pattern of dendritic segregation was observed. The hardness on the wear surface averaged 670 HV 1 . The wear behavior showed a lineal variation between the loss of weight and the distance run, for the different loads applied. The rates of wear for each condition were obtained. The observed wear mechanisms were abrasion and adhesion, with plastic deformation. At low charges, the predominant mechanism was mild oxidative wear and at bigger loads heavy oxidative wear with the presence of zones with adhesion. The oxides formed on the surface of the eroded plate were identified

  8. The influence of metal nanoparticles on the mechanical properties of composite materials

    Directory of Open Access Journals (Sweden)

    KARIMOV Eduard Khasanovich

    2017-08-01

    Full Text Available The article presents the results of studies on changes in mechanical and physical properties of polymeric construction materials after the introduction of metal nanoparticles. As an example of metal nanoparticles the influence of nanoparticles of copper has been considered. The ways of formation of copper with dimensions of nanometers, a brief methodology and structure of the obtained filler are shown. Copper nanoparticles have unique anti-bacterial, thermal and conductive properties. These properties substantially remain in the polymer material. The resulting composite material has technological properties of polymers and unique physical properties of the filler. Polymer material was selected among the products of large-tonnage production: polyvinyl chloride, elastomers, polyethylene, polypropylene, polystyrene.The selection of copper ions from the nanoparticles depends on the type of stabilizing agent and on the chemical nature of the environment. The performance of antimicrobial properties in polymer materials is achieved by the dosage of copper in the amount of 1–2% by weight. To give a material the conductive properties of copper nanoparticles a higher concentration of metal is required. To use only plastic PVC as the carrier will limit the effectiveness of nanocrystals of copper and affect the mechanical parameters of the material. Therefore it is considered a more complex type of polymer material. Thermoplastic elastomers obtained from blends of rubber and plastic (or plastics, became of great interest in the industrial sector. The wax embedded in a polymeric matrix of polyethylene is used for heat storage of solar energy; thermal protection of electronic devices, nutritional products and medical products; a reduction in installed capacity and thermal comfort in vehicles. To improve the thermal conductivity copper nanoparticles are introduced in the mixture of polyethylene and wax. To obtain the polypropylene with copper nanoparticles

  9. Study of the static airtightness mechanisms of metal seals

    International Nuclear Information System (INIS)

    Tlili, A.

    2013-01-01

    The thesis aims to better understand the sealing mechanisms in contact at the interface between a metal gasket and clamps. The proposed approach is based on the development of a numerical model of the clamping seal by incorporating the laws' behavior of materials that will be determined by micro instrumented indentation testing. This model is particularly interested in identifying ways of providing the fluid leak to be sealed and to determine leakage rates resulting from the identified paths, as well as the evolution of the conductance of the interface over time. Particular attention will be paid to the roughness of the surfaces, changing leak paths at different levels depending on the tightening of the seal and gas flow rates in the different types of defects. The study was conducted in Pierrelatte's Sealing laboratory that develops metal seals for the aerospace, nuclear and scientific research. The thesis focuses on real surfaces and was supplemented by measurements of helium leaks using a press which applies different loads at different gas pressures and different roughness. (author) [fr

  10. The mechanism of anomalous hardening in transition-metal monoborides.

    Science.gov (United States)

    Liang, Yongcheng; Gao, Zhenbang; Qin, Ping; Gao, Li; Tang, Chun

    2017-07-06

    The quest for novel nanomaterials with unusual functionalities continues to be a central challenge to modern nanoscience. Here we report a surprisingly anomalous hardening behavior exhibited by a class of transition-metal monoborides (TMB). Most remarkable is the occurrence of the intrinsic hardness maximum at the valence-electron concentration (VEC) of about 8 electrons per formula unit (e per f.u.); both lower and higher VECs lead to the decrease of hardness, contrasting with the expected positive correlation between hardness and VEC. Such an unexpected phenomenon originates from the presence of two sorts of bands near the Fermi level that respond oppositely to the movement of dislocations within the metal bilayer. Furthermore, we demonstrate that the hardness is closely related to the formation energy for TMB, which justifies the importance of the thermodynamic stability in designing superhard materials. Our findings not only elucidate the unique mechanism responsible for unusual atom-scale hardening but also open a new avenue towards designing novel multifunctional nanomaterials with the coexistence of high hardness and excellent electrical conductivity.

  11. Mechanical and Structural Investigation of Porous Bulk Metallic Glasses

    Directory of Open Access Journals (Sweden)

    Baran Sarac

    2015-06-01

    Full Text Available The intrinsic properties of advanced alloy systems can be altered by changing their microstructural features. Here, we present a highly efficient method to produce and characterize structures with systematically-designed pores embedded inside. The fabrication stage involves a combination of photolithography and deep reactive ion etching of a Si template replicated using the concept of thermoplastic forming. Pt- and Zr-based bulk metallic glasses (BMGs were evaluated through uniaxial tensile test, followed by scanning electron microscope (SEM fractographic and shear band analysis. Compositional investigation of the fracture surface performed via energy dispersive X-ray spectroscopy (EDX, as well as Auger spectroscopy (AES shows a moderate amount of interdiffusion (5 at.% maximum of the constituent elements between the deformed and undeformed regions. Furthermore, length-scale effects on the mechanical behavior of porous BMGs were explored through molecular dynamics (MD simulations, where shear band formation is observed for a material width of 18 nm.

  12. Investigating Deformation and Failure Mechanisms in Nanoscale Multilayer Metallic Composites

    Energy Technology Data Exchange (ETDEWEB)

    Zbib, Hussein M. [Washington State Univ., Pullman, WA (United States); Bahr, David F. [Purdue Univ., West Lafayette, IN (United States)

    2014-10-22

    Over the history of materials science there are many examples of materials discoveries that have made superlative materials; the strongest, lightest, or toughest material is almost always a goal when we invent new materials. However, often these have been a result of enormous trial and error approaches. A new methodology, one in which researchers design, from the atoms up, new ultra-strong materials for use in energy applications, is taking hold within the science and engineering community. This project focused on one particular new classification of materials; nanolaminate metallic composites. These materials, where two metallic materials are intimately bonded and layered over and over to form sheets or coatings, have been shown over the past decade to reach strengths over 10 times that of their constituents. However, they are not yet widely used in part because while extremely strong (they don’t permanently bend), they are also not particularly tough (they break relatively easily when notched). Our program took a coupled approach to investigating new materials systems within the laminate field. We used computational materials science to explore ways to institute new deformation mechanisms that occurred when a tri-layer, rather than the more common bi-layer system was created. Our predictions suggested that copper-nickel or copper-niobium composites (two very common bi-layer systems) with layer thicknesses on the order of 20 nm and then layered 100’s of times, would be less tough than a copper-nickel-niobium metallic composite of similar thicknesses. In particular, a particular mode of permanent deformation, cross-slip, could be activated only in the tri-layer system; the crystal structure of the other bi-layers would prohibit this particular mode of deformation. We then experimentally validated this predication using a wide range of tools. We utilized a DOE user facility, the Center for Integrated Nanotechnology (CINT), to fabricate, for the first time, these

  13. Stress relaxation insensitive designs for metal compliant mechanism threshold accelerometers

    Directory of Open Access Journals (Sweden)

    Carlos Vilorio

    2015-12-01

    Full Text Available We present two designs for metal compliant mechanisms for use as threshold accelerometers which require zero external power. Both designs rely on long, thin flexures positioned orthogonally to a flat body. The first design involves cutting or stamping a thin spring-steel sheet and then bending elements to form the necessary thin flexors. The second design uses precut spring-steel flexure elements mounted into a mold which is then filled with molten tin to form a bimetallic device. Accelerations necessary to switch the devices between bistable states were measured using a centrifuge. Both designs showed very little variation in threshold acceleration due to stress relaxation over a period of several weeks. Relatively large variations in threshold acceleration were observed for devices of the same design, most likely due to variations in the angle of the flexor elements relative to the main body of the devices.

  14. Bulk Mechanical Properties Testing of Metallic Marginal Glass Formers

    Directory of Open Access Journals (Sweden)

    Thien Q. Phan

    2016-01-01

    Full Text Available We developed a unique three-point bend testing apparatus to measure bulk mechanical properties of a model metallic glass alloy (SAM2X5 with nominal composition Fe49.7Cr17.1Mn1.9Mo7.4W1.6B15.2C3.8Si2.4 prepared by spark plasma sintering. The relatively large sample sizes in the present work allowed for the preparation of test specimens with a macroscale cross section (in the millimeter range with well-controlled sample dimensions closer to standardized tests. Wire saw cutting allowed for a relatively sharp notch radius (3x smaller than previous studies and minimal sample damage. We determined that Young’s modulus and notch fracture toughness measured by our three-point bending apparatus are 230 GPa and 4.9 MPa·m1/2. Also, Vickers indentation and flexure testing provided consistent results for Young’s modulus. Indentation fracture toughness measured by Vickers indentation produced values at least 50% lower than by flexure. The microscale mechanical properties testing technique presented in this work and subsequent analyses are applicable to specimens of other compositions or ones prepared by other methods.

  15. Autocatalytic effects in the mechanically induced hydriding of refractory metals

    International Nuclear Information System (INIS)

    Bab, M.A.; Baum, L.A.; Mendoza-Zelis, L.

    2007-01-01

    Mechanical milling of powders in a gaseous ambient is an efficient tool to induce gas-solid reactions and several nanocrystalline metallic oxides, nitrides and hydrides may be obtained at room temperature and moderated pressures by this route. We present here a study of the mechanically induced hydriding of Ti, Zr and Hf elemental powders, ground in an oscillatory mill under hydrogen gas at constant volume. The final formation of nanocrystalline cubic δ-MH 2 , together with a varying fraction of tetragonal ε-MH 2 , was verified by X-ray diffraction. From the measured pressure drop during the milling process the hydriding kinetics was determined and two distinct regimes were observed. For Ti and-at low milling frequencies-for Zr and Hf, a normal regime, characterized by a sigmoidal trend and a linear dependence of the rate constant on the milling intensity, was found. Otherwise, a sudden increase in the reacted fraction was observed in the absorption curve, typical of a self-sustained regime. The magnitude of the observed jump increases with the milling intensity and afterwards the reaction proceeds normally until it is completed. This critical behavior is discussed in terms of the reaction rate, the degree of transformation and the ε-phase content

  16. Dual Mechanism Nonlinear Response of Selected Metal Organic Chromophores

    National Research Council Canada - National Science Library

    Peak, John D

    2007-01-01

    13 The goal for the research described herein is the development of a series of transition metal based metal organic chromophores that display both two-photon and excited state absorption (TPA/ESA) character...

  17. Understanding cellular responses to toxic agents: a model for mechanism-choice in bacterial metal resistance.

    Science.gov (United States)

    Rouch, D A; Lee, B T; Morby, A P

    1995-02-01

    Bacterial resistances to metals are heterogeneous in both their genetic and biochemical bases. Metal resistance may be chromosomally-, plasmid- or transposon-encoded, and one or more genes may be involved: at the biochemical level at least six different mechanisms are responsible for resistance. Various types of resistance mechanisms can occur singly or in combination and for a particular metal different mechanisms of resistance can occur in the same species. To understand better the diverse responses of bacteria to metal ion challenge we have constructed a qualitative model for the selection of metal resistance in bacteria. How a bacterium becomes resistant to a particular metal depends on the number and location of cellular components sensitive to the specific metal ion. Other important selective factors include the nature of the uptake systems for the metal, the role and interactions of the metal in the normal metabolism of the cell and the availability of plasmid (or transposon) encoded resistance mechanisms. The selection model presented is based on the interaction of these factors and allows predictions to be made about the evolution of metal resistance in bacterial populations. It also allows prediction of the genetic basis and of mechanisms of resistance which are in substantial agreement with those in well-documented populations. The interaction of, and selection for resistance to, toxic substances in addition to metals, such as antibiotics and toxic analogues, involve similar principles to those concerning metals. Potentially, models for selection of resistance to any substance can be derived using this approach.

  18. On Thermocapillary Mechanism of Spatial Separation of Metal Melts

    Science.gov (United States)

    Demin, V. A.; Mizev, A. I.; Petukhov, M. I.

    2018-02-01

    Theoretical research has been devoted to the study of binary metal melts behavior in a thin capillary. Earlier it has been found experimentally that unusually significant and quick redistribution of melts components takes place along capillary after the cooling. Numerical simulation of concentration-induced convection has been carried out to explain these experimental data. Two-component melt of both liquid metals filling vertical thin capillary with non-uniform temperature distribution on the boundaries is considered. It is assumed that the condition of absolute non-wetting is valid on the sidewalls. Because of this effect there is a free surface on vertical boundaries, where thermocapillary force is appeared due to the external longitudinal temperature gradient. It makes to move liquid elements at a big distance, compared with axial size of capillary. Effects of adsorption-desorption on the surface, thermal and concentration-capillary forces, convective motion in a volume and diffusion generate the large-scale circulation. This process includes the admixture carrying-out on the surface in the more hot higher part of the channel, its following transfer down along the boundary due to the thermocapillary force and its return in the volume over the desorption in the lower part of capillary. Intensity of motion and processes of adsorption-desorption on the free boundary have the decisive influence upon the formation of concentration fields and speed of components redistribution. Thus, one of the possible mechanisms of longitudinal division on components of liquid binary mixtures in thin channels has been demonstrated.

  19. Tree Leaves as Bioindicator of Heavy Metal Pollution in Mechanic ...

    African Journals Online (AJOL)

    Metal contamination issues are becoming increasingly common in automobile workshop and elsewhere, Heavy metals, such as cadmium, copper, lead, are major environmental pollutants. Heavy metal accumulation in soils is of concern in agricultural production due to the adverse effects on food safety and marketability, ...

  20. STATISTICAL MECHANICS MODELING OF MESOSCALE DEFORMATION IN METALS

    Energy Technology Data Exchange (ETDEWEB)

    Anter El-Azab

    2013-04-08

    The research under this project focused on a theoretical and computational modeling of dislocation dynamics of mesoscale deformation of metal single crystals. Specifically, the work aimed to implement a continuum statistical theory of dislocations to understand strain hardening and cell structure formation under monotonic loading. These aspects of crystal deformation are manifestations of the evolution of the underlying dislocation system under mechanical loading. The project had three research tasks: 1) Investigating the statistical characteristics of dislocation systems in deformed crystals. 2) Formulating kinetic equations of dislocations and coupling these kinetics equations and crystal mechanics. 3) Computational solution of coupled crystal mechanics and dislocation kinetics. Comparison of dislocation dynamics predictions with experimental results in the area of statistical properties of dislocations and their field was also a part of the proposed effort. In the first research task, the dislocation dynamics simulation method was used to investigate the spatial, orientation, velocity, and temporal statistics of dynamical dislocation systems, and on the use of the results from this investigation to complete the kinetic description of dislocations. The second task focused on completing the formulation of a kinetic theory of dislocations that respects the discrete nature of crystallographic slip and the physics of dislocation motion and dislocation interaction in the crystal. Part of this effort also targeted the theoretical basis for establishing the connection between discrete and continuum representation of dislocations and the analysis of discrete dislocation simulation results within the continuum framework. This part of the research enables the enrichment of the kinetic description with information representing the discrete dislocation systems behavior. The third task focused on the development of physics-inspired numerical methods of solution of the coupled

  1. Bacterial mediated alleviation of heavy metal stress and decreased accumulation of metals in plant tissues: Mechanisms and future prospects.

    Science.gov (United States)

    Etesami, Hassan

    2018-01-01

    Heavy metal pollution of agricultural soils is one of main concerns causing some of the different ecological and environmental problems. Excess accumulation of these metals in soil has changed microbial community (e.g., structure, function, and diversity), deteriorated soil, decreased the growth and yield of plant, and entered into the food chain. Plants' tolerance to heavy metal stress needs to be improved in order to allow growth of crops with minimum or no accumulation of heavy metals in edible parts of plant that satisfy safe food demands for the world's rapidly increasing population. It is well known that PGPRs (plant growth-promoting rhizobacteria) enhance crop productivity and plant resistance to heavy metal stress. Many recent reports describe the application of heavy metal resistant-PGPRs to enhance agricultural yields without accumulation of metal in plant tissues. This review provides information about the mechanisms possessed by heavy metal resistant-PGPRs that ameliorate heavy metal stress to plants and decrease the accumulation of these metals in plant, and finally gives some perspectives for research on these bacteria in agriculture in the future. Copyright © 2017 Elsevier Inc. All rights reserved.

  2. Study of inelastic deformation mechanisms in metal glass volume

    International Nuclear Information System (INIS)

    Bakaj, S.A.; Neklyudov, I.M.; Savchenko, V.I.; Ehkert, Yu.

    2001-01-01

    The results of investigations of the mechanical properties and internal friction of the bulk amorphous alloy Zr 53.5 Ti 5 Cu 17.5 Ni 14.6 Al 10.4 within the temperature range from the room temperature up to glass-transition temperature are reported. The yield stress and transition from homogeneous to inhomogeneous plastic deformation are investigated. The temperature dependence of low-frequency internal friction, Q -1 (T), in the amplitude-independent limit of oscillations is obtained. The temperature range within which the homogeneous plastic deformation is observed under compression stress is determined. The superplasticity of the amorphous alloy is revealed at the temperature which is 100K lower than the glass-transition temperature. The lowest temperature, at which the superplasticity is revealed, turns to be an edge of the temperature range where Q -1 (T) increases fast. The microscopic nature of the observed phenomena are interpreted on the base of the polycluster model of the metallic glasses

  3. Mechanical deformation of atomic-scale metallic contacts: Structure and mechanisms

    DEFF Research Database (Denmark)

    Sørensen, Mads Reinholdt; Brandbyge, Mads; Jacobsen, Karsten Wedel

    1998-01-01

    electronic conductance. Various defects such as intersecting stacking faults, local disorder, and vacancies are created during the deformation. Disordered regions act as weak spots that reduce the strength of the contacts. The disorder tends to anneal out again during the subsequent atomic rearrangements......We have simulated the mechanical deformation of atomic-scale metallic contacts under tensile strain using molecular dynamics and effective medium theory potentials. The evolution of the structure of the contacts and the underlying deformation mechanisms are described along with the calculated...... that the results measured in a nanocontact experiment depend significantly on the elastic stiffness of the experimental apparatus. For a soft setup, some of the atomic rearrangements might not be detected, whereas others are amplified....

  4. Model systems to unravel the molecular mechanisms of heavy metal tolerance in the ericoid mycorrhizal symbiosis.

    Science.gov (United States)

    Daghino, Stefania; Martino, Elena; Perotto, Silvia

    2016-05-01

    Ericoid mycorrhizal plants dominate in harsh environments where nutrient-poor, acidic soil conditions result in a higher availability of potentially toxic metals. Although metal-tolerant plant species and ecotypes are known in the Ericaceae, metal tolerance in these plants has been mainly attributed to their association with ericoid mycorrhizal fungi. The mechanisms underlying plant protection by the fungal symbiont are poorly understood, whereas some insights have been achieved regarding the molecular mechanisms of heavy metal tolerance in the fungal symbiont. This review will briefly introduce the general features of heavy metal tolerance in mycorrhizal fungi and will then focus on the use of "omics" approaches and heterologous expression in model organisms to reveal the molecular bases of fungal response to heavy metals. Functional complementation in Saccharomyces cerevisiae has allowed the identification of several ericoid mycorrhizal fungi genes (i.e., antioxidant enzymes, metal transporters, and DNA damage repair proteins) that may contribute to metal tolerance in a metal-tolerant ericoid Oidiodendron maius isolate. Although a powerful system, the use of the yeast complementation assay to study metal tolerance in mycorrhizal symbioses has limitations. Thus, O. maius has been developed as a model system to study heavy metal tolerance mechanisms in mycorrhizal fungi, thanks to its high metal tolerance, easy handling and in vitro mycorrhization, stable genetic transformation, genomics, transcriptomic and proteomic resources.

  5. Synthesis of borohydrides of rare earth metals by mechanic-chemical methods

    International Nuclear Information System (INIS)

    Gafurov, B.A.; Nasrulloeva, D.Kh.; Khakyorov, I.Z.; Saidov, V.Ya.

    2010-01-01

    Present article is devoted to synthesis of borohydrides of rare earth metals by mechanic-chemical methods. The borohydrides of rare earth metals were obtained by means of mechanic-chemical methods. Physicochemical properties of obtained lanthanoid borohydrides were studied by means of X-ray phase analysis.

  6. PNGMDR 2013-2015. ANDRA's opinion on the development of sector of recycling of VLA ferrous metallic waste

    International Nuclear Information System (INIS)

    2014-01-01

    The scope of this report is to state the ANDRA's opinion on the recycling of very-low-level metallic wastes, and mainly ferrous metallic wastes which are the main stream of them. After having evoked a study jointly performed by EDF, AREVA, the CEA and the ANDRA to assess the technical and economic feasibility of a valorisation of very-low-level metallic wastes in the nuclear sector, this study proposes an assessment of ferrous metals which might be recycled over about thirty years. After having outlined the strong motivation of the ANDRA for such a recycling, the report proposes an overview of the heterogeneous stream of metallic wastes, by distinguishing scrap materials from very heterogeneous origins like those brought to the Cires storage centre, and those with more homogeneous origins (for example, from dismantling activities). The next part proposes an overview of various non coordinated initiatives, notably by the ANDRA, on different storage sites. The report identifies the keys for a successful recycling of contaminated metals in Europe, and the main challenges for the recycling of very-low-level ferrous metal in France (in competition with direct storage, and with the application of the risk-related regulation for some metallic wastes). Some proposals made by the ANDRA are then stated: a reference industrial scheme, and a coordination of actors under the auspices of the State

  7. Characterizing time-dependent mechanics in metallic MEMS

    Directory of Open Access Journals (Sweden)

    Geers M.G.D.

    2010-06-01

    Full Text Available Experiments for characterization of time-dependent material properties in free-standing metallic microelectromechanical system (MEMS pose challenges: e.g. fabrication and handling (sub-μm sized specimens, control and measurement of sub-μN loads and sub-μm displacements over long periods and various temperatures [1]. A variety of experimental setups have been reported each having their pros and cons. One example is a micro-tensile tester with an ingenious electro-static specimen gripping system [2] aiding simple specimen design giving good results at μN and sub-μm levels, but without in-situ full-field observations. Other progressive examples assimilate the specimen, MEMS actuators and load cells on a single chip [3,4] yielding significant results at nN and nm levels with in-situ TEM/SEM observability, though not without complications: complex load actuator/sensor calibration per chip, measures to reduce fabrication failure and unfeasible cofabrication on wafers with commercial metallic MEMS. This work aims to overcome these drawbacks by developing experimental methods with high sensitivity, precision and in-situ full-field observation capabilities. Moreover, these should be applicable to simple free-standing metallic MEMS that can be co-fabricated with commercial devices. These methods will then serve in systematic studies into size-effects in time-dependent material properties. First a numeric-experimental method is developed. It characterizes bending deformation of onwafer μm-sized aluminum cantilevers. A specially designed micro-clamp is used to mechanically apply a constant precise deflection of the beam (zres <50 nm for a prolonged period, see fig. 1. After this period, the deflection by the micro-clamp is removed. Full-field height maps with the ensuing deformation are measured over time with confocal optical profilometry (COP. This yields the tip deflection as function of time with ~3 nm precision, see fig.2. To extract material

  8. Fundamental mechanical and microstructural observations in metallic glass coating production

    NARCIS (Netherlands)

    Matthews, D.T.A.; Ocelik, V.; de Hosson, J.T.M.; DeHosson, JTM; Brebbia, CA; Nishida, SI

    2005-01-01

    The production of a wide range of metallic Glass Forming Alloys (GFA) has been investigated by several processing routes including simple arc-casting and melt-spinning to form Bulk Metallic Glasses (BMG). The concepts surrounding such alloys have been directed towards the production of thick (> 300

  9. ICT Infrastructure in the Metal Mechanical SMEs of Quito and its Relationship with Business Management

    Directory of Open Access Journals (Sweden)

    Juan Ibujés Villacís

    2017-04-01

    Full Text Available The central argument which supports this research is that Information and Communication Technologies (ICT are not only a key element for economic and social development of towns, but also introduce new variables to the analysis of the effects of the exchange of information in the markets, such as those related to productivity and competitiveness. In addition, from a business perspective, small and medium-sized enterprises (SMEs play a very important role in the development of any economy, mainly because of its impact on the generation of jobs and promoting economic growth. In this study of SMEs in the metal mechanical sector of Quito, capital of Ecuador, it determines the importance that this business group gives to ICT from three different areas but they are related. The first of these is focused on determining the importance that this type of SMES gives to investments in ICT in the annual budget for management, the second relates to know what type of ICT infrastructure invests this type of SMEs in and in which productive activities they use them. Finally, the study analyzes how ICT can help this business group to face the challenges of increasing productivity and competitiveness in the domestic and international markets. By grouping these three components of the research, it will determine if there is evidence of the positive impact of ICT on the productivity of the companies.

  10. Levels of metals, arsenic and phosphorus in sediments from two sectors of a Brazilian Marine Protected Area (Tupinambás Ecological Station).

    Science.gov (United States)

    Hoff, Natasha T; Figueira, Rubens C L; Abessa, Denis M S

    2015-02-28

    The Tupinambás Ecological Station (TES) is a Marine Protected Area consisting of two sectors: the Archipelago of Alcatrazes and the Cabras and Palmas islets. This investigation aimed to provide a first diagnosis of the concentrations of metals (Al,Cr,Cu,Fe,Hg,Ni,Pb,Zn), As and P in sediments from the TES. 24 sediment samples were collected in both sectors using a Van Veen grab sampler. Sediment textures and levels of Organic Matter (OM) and CaCO3 were determined, as well as the concentrations of the above-mentioned elements after partial acid digestion. Sediments were predominantly sandy. Higher levels of CaCO3 occurred in the Alcatrazes sector, whereas the OM contents were higher in the islets sector. Metals concentrations were low and associated with fines, while P and As presented a different behavior. The observed concentrations to all studies elements in sediments from the TES were considered as background values. Copyright © 2014 Elsevier Ltd. All rights reserved.

  11. Mechanisms of silicon-mediated alleviation of heavy metal toxicity in plants: A review.

    Science.gov (United States)

    Adrees, Muhammad; Ali, Shafaqat; Rizwan, Muhammad; Zia-Ur-Rehman, Muhammad; Ibrahim, Muhammad; Abbas, Farhat; Farid, Mujahid; Qayyum, Muhammad Farooq; Irshad, Muhammad Kashif

    2015-09-01

    In present era, heavy metal pollution is rapidly increasing which present many environmental problems. These heavy metals are mainly accumulated in soil and are transferred to food chain through plants grown on these soils. Silicon (Si) is the second most abundant element in the soil. It has been widely reported that Si can stimulate plant growth and alleviate various biotic and abiotic stresses, including heavy metal stress. Research to date has explored a number of mechanisms through which Si can alleviate heavy metal toxicity in plants at both plant and soil levels. Here we reviewed the mechanisms through which Si can alleviate heavy metal toxicity in plants. The key mechanisms evoked include reducing active heavy metal ions in growth media, reduced metal uptake and root-to-shoot translocation, chelation and stimulation of antioxidant systems in plants, complexation and co-precipitation of toxic metals with Si in different plant parts, compartmentation and structural alterations in plants and regulation of the expression of metal transport genes. However, these mechanisms might be associated with plant species, genotypes, metal elements, growth conditions, duration of the stress imposed and so on. Further research orientation is also discussed. Copyright © 2015 Elsevier Inc. All rights reserved.

  12. Review of thermodinamic and mechanical properties of hydrogen-transition metal systems

    International Nuclear Information System (INIS)

    Mathias, H.; Katz, Y.

    1978-04-01

    A large body of fundamental and empirical knowledge has been acquired during many years of research concerning the interactions between hydrogen and metals, the location of hydrogen in metal structures, its mobility in metals and its influence on mechanical properties of metals. Much progress has been made in the understanding of related phenomena, and various theories have been proposed, but considerable disagreement still exist about basic mechanisms involved. The growing interest in these subjects and their important role in science and technology are well documented by many reviews and symposia. A general survey of these topics with reference to experimental results and theories related to thermodynamic and mechanical properties of hydrogen-transition metal systems, such as H-Pd, H-Ti, H-Fe etc. is given in the present review. Special emphasis is given to hydrogen embrittlement of metals

  13. Mechanisms in the shaping of organic food as strategy in the Danish food sector

    DEFF Research Database (Denmark)

    Jørgensen, Michael Søgaard

    Whether one is pessimist or optimist one can either phrase the development of organic agriculture and organic food in Denmark either as ‘only 7% of the agricultural area has been converted’ or ‘even 7% of the agricultural area has been converted’. The point of this paper is that one has to use both...... views in an analysis of the development of organic agriculture and organic food in Denmark. On the one hand a new product niche and maybe even a new development path has developed and on the other hand the conventional agriculture is still dominating with more than 90% of the agricultural area....... The paper analyses some of the changes that have taken place in the Danish food sector during the last 10-15 years with respect to organic food. The paper looks for how changes in the systems of production, consumption, knowledge and regulation have interacted and what kind of coherence and dissonance among...

  14. Accelerator and Technical Sector Seminar: Mechanical stabilization and positioning of CLIC quadrupoles with sub-nanometre resolution

    CERN Multimedia

    2011-01-01

    Thursday 24 November 2010 Accelerator and Technical Sector Seminar at 14:15  -  BE Auditorium, bldg. 6 (Meyrin) – please note unusual place Mechanical stabilization and positioning of CLIC quadrupoles with sub-nanometre resolution Stef Janssens /EN-MME Abstract: To reach the required luminosity at the CLIC interaction point, about 4000 quadrupoles are needed to obtain a vertical beam size of 1 nm at the interaction point. The mechanical jitter of the quadrupole magnets will result in an emittance growth. An active vibration isolation system is required to reduce vibrations from the ground and from external forces to about 1.5 nm integrated root mean square (r.m.s.) vertical displacement at 1 Hz. A short overview of vibration damping and isolation strategies will be presented as well as a comparison of existing systems. The unprecedented resolution requirements and the instruments enabling these measurements will be discussed. The vibration sources from which the magnets need to...

  15. Ecological Risk Assessment of Metal Pollution along Greater Cairo Sector of the River Nile, Egypt, Using Nile Tilapia, Oreochromis niloticus, as Bioindicator

    Directory of Open Access Journals (Sweden)

    Wael A. Omar

    2015-01-01

    Full Text Available The present work aims to evaluate seasonal metal pollution along Greater Cairo sector of the River Nile, Egypt, using wild Nile tilapia, Oreochromis niloticus, as bioindicator and to conduct a risk assessment for human consumers. Greater Cairo is the largest populated area along the whole course of River Nile with a wide range of anthropogenic activities. Effects of metal pollution on fish body indices were studied using condition factor (CF and scaled mass index (SMI. Metal pollution index (MPI showed that the total metal load in fish organs followed the follwoing order: kidney > liver > gill > muscle which gives a better idea about the target organs for metal accumulation. Metal concentrations in fish muscle (edible tissue showed the following arrangement: Fe > Zn > Cu > Mn > Pb > Cd. Metal’s bioaccumulation factor (BAF in fish muscle showed the following arrangement: Zn > Cu > Fe > Mn > Cd and Pb. The hazard index (HI as an indicator of human health risks associated with fish consumption showed that adverse health effects are not expected to occur in most cases. However, the metals’ cumulative risk effects gave an alarming sign specifically at high fish consumption rates.

  16. Liquid metal embrittlement of T91 and 316L steels by heavy liquid metals: A fracture mechanics assessment

    Science.gov (United States)

    Auger, T.; Hamouche, Z.; Medina-Almazàn, L.; Gorse, D.

    2008-06-01

    LME of the martensitic T91 and the austenitic 316L steels have been investigated in the CCT geometry in the plane-stress condition. Using such a geometry, premature cracking induced by a liquid metal (PbBi and Hg) can be studied using a fracture mechanics approach based on CTOD, J-Δ a and fracture assessment diagram. One is able to measure a reduction of the crack tip blunting and a reduction of the energy required for crack propagation induced by the liquid metal. In spite of some limitations, this qualitative evaluation shows that liquid metals do not induce strong embrittlement on steels in plane-stress condition. Rather, the effect of the liquid metal seems to promote a fracture mode by plastic collapse linked with strain localization. It indicates that the materials, in spite of a potential embrittlement, should still be acceptable in terms of safety criteria.

  17. Mechanisms of metallization degradation in high power diodes

    DEFF Research Database (Denmark)

    Brincker, Mads; Kristensen, Peter Kjær; Pedersen, Kristian Bonderup

    2016-01-01

    electron microscopy (SEM) and X-ray diffraction (XRD). To study the evolution of the chemical composition of the metallization, energy dispersive X-ray spectroscopy (EDX) is also applied. Since the degradation depends on the initial microstructure of the metallization, the film texture and grain size...... distribution is determined using electron backscatter diffraction (EBSD). The obtained data show that the type of atmosphere plays a minor role in the degradation process, with a slight tendency that cycling in dry nitrogen atmosphere accelerates the degradation compared to the experiments in ambient...

  18. Revelations from the Nematode Caenorhabditis elegans on the Complex Interplay of Metal Toxicological Mechanisms

    Directory of Open Access Journals (Sweden)

    Ebany J. Martinez-Finley

    2011-01-01

    Full Text Available Metals have been definitively linked to a number of disease states. Due to the widespread existence of metals in our environment from both natural and anthropogenic sources, understanding the mechanisms of their cellular detoxification is of upmost importance. Organisms have evolved cellular detoxification systems including glutathione, metallothioneins, pumps and transporters, and heat shock proteins to regulate intracellular metal levels. The model organism, Caenorhabditis elegans (C. elegans, contains these systems and provides several advantages for deciphering the mechanisms of metal detoxification. This review provides a brief summary of contemporary literature on the various mechanisms involved in the cellular detoxification of metals, specifically, antimony, arsenic, cadmium, copper, manganese, mercury, and depleted uranium using the C. elegans model system for investigation and analysis.

  19. Metal resistance mechanisms in Gram-negative bacteria and their potential to remove Hg in the presence of other metals.

    Science.gov (United States)

    Giovanella, Patricia; Cabral, Lucélia; Costa, Alexandre Pereira; de Oliveira Camargo, Flávio Anastácio; Gianello, Clesio; Bento, Fátima Menezes

    2017-06-01

    Contamination of the environment by heavy metals has been increasing in recent years due to industrial activities. Thus research involving microorganisms capable of surviving in multi-contaminated environments is extremely important. The objectives of the present study were to evaluate the removal of mercury alone and in the presence of cadmium, nickel and lead by four mercury-resistant microorganisms; estimate the removal of Cd, Ni and Pb; understand the mechanisms involved (reduction, siderophores, biofilms, biosorption and bioaccumulation) in the metal resistance of the isolate Pseudomonas sp. B50D; and determine the capacity of Pseudomonas sp. B50D in removing Hg, Cd, Ni and Pb from an industrial effluent. It was shown that the four isolates evaluated were capable of removing from 62% to 95% of mercury from a culture medium with no addition of other metals. The isolate Pseudomonas sp. B50D showed the best performance in the removal of mercury when evaluated concomitantly with other metals. This isolate was capable of removing 75% of Hg in the presence of Cd and 91% in the presence of Ni and Pb. With respect to the other metals it removed 60%, 15% and 85% of Cd, Ni and Pb, respectively. In tests with effluent, the isolate Pseudomonas sp. B50D removed 85% of Hg but did not remove the other metals. This isolate presented reduction, biosorption, biofilm production and siderophore production as its metal resistance mechanisms. Pseudomonas sp. B50D was thus a candidate with potential for application in the bioremediation of effluents with complex metal contaminations. Copyright © 2017 Elsevier Inc. All rights reserved.

  20. La cadena de suministro del sector metalúrgico: un análisis de sus principales eslabones (The Supply Chain in the metallurgical sector: an analysis of the main links

    Directory of Open Access Journals (Sweden)

    Patricia Carbajo-de-Lera

    2011-12-01

    Full Text Available Los directivos actuales conciben que la competencia ya no es empresa frente a empresa, sino que desborda este plano generándose una competencia cadena de suministro frente a cadena de suministro. Por ello, la gestión de la cadena de suministro se convierte en un elemento clave para la supervivencia empresarial y la obtención de ventajas competitivas. El diseño de la cadena de suministro viene definido, en buena parte, por las características del sector al que pertenece. En consecuencia, es de interés realizar análisis sectoriales. El presente trabajo tiene como objetivo analizar la cadena de suministro en un sector de gran importancia en la economía española, como es el metalúrgico. En concreto, buscamos determinar su cadena de suministro, definiendo los principales eslabones que la configuran y las relaciones entre ellos.Abstract: In the current business context, competition is no longer firm against firm, but has moved on to a higher plane, with the generation of supply chain against supply chain competition.  Therefore, Supply Chain Management (SCM has strategic relevance as a source of competitive advantage. The design of the supply chain is defined largely by the characteristics of the sector. Consequently, sectorial analysis is required. The aim of this paper is to analyze the supply chain of the metallurgical sector. Specifically, it will be focused on determining its supply chain and defining its main links and relationships.

  1. Mechanisms of change of a novel weight loss programme provided by a third sector organisation: a qualitative interview study.

    Science.gov (United States)

    McMahon, Naoimh E; Visram, Shelina; Connell, Louise A

    2016-05-10

    There is a need for theory-driven studies that explore the underlying mechanisms of change of complex weight loss programmes. Such studies will contribute to the existing evidence-base on how these programmes work and thus inform the future development and evaluation of tailored, effective interventions to tackle overweight and obesity. This study explored the mechanisms by which a novel weight loss programme triggered change amongst participants. The programme, delivered by a third sector organisation, addressed both diet and physical activity. Over a 26 week period participants engaged in three weekly sessions (education and exercise in a large group, exercise in a small group and a one-to-one education and exercise session). Novel aspects included the intensity and duration of the programme, a competitive selection process, milestone physical challenges (e.g. working up to a 5 K and 10 K walk/run during the programme), alumni support (face-to-face and online) and family attendance at exercise sessions. Data were collected through interviews with programme providers (n = 2) and focus groups with participants (n = 12). Discussions were audio-recorded, transcribed and analysed using NVivo10. Published behaviour change frameworks and behaviour change technique taxonomies were used to guide the coding process. Clients' interactions with components of the weight loss programme brought about a change in their commitment, knowledge, beliefs about capabilities and social and environmental contexts. Intervention components that generated these changes included the competitive selection process, group and online support, family involvement and overcoming milestone challenges over the 26 week programme. The mechanisms by which these components triggered change differed between participants. There is an urgent need to establish robust interventions that can support people who are overweight and obese to achieve a healthy weight and maintain this change. Third

  2. Mechanisms of change of a novel weight loss programme provided by a third sector organisation: a qualitative interview study

    Directory of Open Access Journals (Sweden)

    Naoimh E. McMahon

    2016-05-01

    Full Text Available Abstract Background There is a need for theory-driven studies that explore the underlying mechanisms of change of complex weight loss programmes. Such studies will contribute to the existing evidence-base on how these programmes work and thus inform the future development and evaluation of tailored, effective interventions to tackle overweight and obesity. This study explored the mechanisms by which a novel weight loss programme triggered change amongst participants. The programme, delivered by a third sector organisation, addressed both diet and physical activity. Over a 26 week period participants engaged in three weekly sessions (education and exercise in a large group, exercise in a small group and a one-to-one education and exercise session. Novel aspects included the intensity and duration of the programme, a competitive selection process, milestone physical challenges (e.g. working up to a 5 K and 10 K walk/run during the programme, alumni support (face-to-face and online and family attendance at exercise sessions. Methods Data were collected through interviews with programme providers (n = 2 and focus groups with participants (n = 12. Discussions were audio-recorded, transcribed and analysed using NVivo10. Published behaviour change frameworks and behaviour change technique taxonomies were used to guide the coding process. Results Clients’ interactions with components of the weight loss programme brought about a change in their commitment, knowledge, beliefs about capabilities and social and environmental contexts. Intervention components that generated these changes included the competitive selection process, group and online support, family involvement and overcoming milestone challenges over the 26 week programme. The mechanisms by which these components triggered change differed between participants. Conclusions There is an urgent need to establish robust interventions that can support people who are overweight and

  3. Comparative study of Heavy Metals Distribution in a Mechanic ...

    African Journals Online (AJOL)

    A comparative study of heavy metals; Lead, Chromium, Arsenic, Nickel, Cadmium and Mercury distribution was carried out in Oluku and Otofure both in Metropolitan Benin City, Edo State Nigeria with the view to determine the level of concentration and contribution of each site investigated. Thirty eight (38) soil samples were ...

  4. Investigation of tribological and mechanical properties of metal ...

    Indian Academy of Sciences (India)

    Administrator

    2009-09-02

    Lepper et al 1997). Until the early. 1940s, white metal was used and then Al alloys were used as bearing materials (Niinomi et al 1997). Al alloys can be used in applications where corrosion is a problem. Wear resistance of Si added ...

  5. 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

  6. Use of absorption mechanisms to decrease heavy metal mobility.

    Science.gov (United States)

    2014-02-01

    The objective of this project is to reduce the toxic heavy metal leaching from coal fly ash so that the fly ash may be used for road : surface or related applications. Trona (trisodium hydrogendicarbonate dihydrate, Na3HCO3CO32H2O) is injected into...

  7. Lattice mechanical properties of some fcc f-shell metals

    Indian Academy of Sciences (India)

    noble metals it is highly desirable to have simple method of general applicability which ... Hence, effect called. 'hybridization' would require a repulsive term in the model potential. Hence, in r-space, inside the core radius the model potential is a combination of repulsive and attractive .... achievement of the present model.

  8. Experimental Investigation on Corrosion Effect on Mechanical Properties of Buried Metal Pipes

    Directory of Open Access Journals (Sweden)

    Yingbo Hou

    2016-01-01

    Full Text Available Corrosion has been found to be the most predominant cause for failures of buried metal pipes. A review of published literature on pipe corrosion reveals that little research has been undertaken on the effect of corrosion on mechanical properties of pipe materials and almost no research has been conducted on corrosion effect on fracture toughness. The intention of this paper is to present a comprehensive test program designed to investigate the effect of corrosion on mechanical properties of metals in soil. Two types of metals, namely, cast iron and steel, are tested under corrosion in three different environments. A relationship between corrosion and deterioration of mechanical property of metals is developed. It is found in the paper that the more acidic the environment is, the more corrosion the metal undergoes and that the corrosion reduces both the tensile strength and fracture toughness of the metal. The results presented in the paper can contribute to the body of knowledge of corrosion behavior and its effect on mechanical properties of metals in soil environment, which in turn enable more accurate prediction of failures of buried metal pipes.

  9. Mechanical properties of vapor-deposited thin metallic films: a status report

    International Nuclear Information System (INIS)

    Adler, P.H.

    1982-01-01

    The mechanical properties of vapor-deposited thin metallic films are being studied in conjunction with the target fabrication group associated with the laser-fusion energy program. The purpose of the work is to gain an understanding as to which metals are structurally best suited to contain a glass microsphere filled with deuterium-tritium (D-T) gas at large internal pressures

  10. Thermo-mechanically induced texture evolution and micro-structural change of aluminum metallization

    DEFF Research Database (Denmark)

    Brincker, Mads; Walter, Thomas; Kristensen, Peter Kjær

    2018-01-01

    During operation of high power electronic chips the topside metallization is subjected to cyclic compressive and tensile stresses leading to unwanted thermo-mechanical fatigue of the metallization layer. The stress is caused by the difference in the thermal expansion coefficients of the metalliza...

  11. The mechanisms of heavy metal immobilization by cementitious material treatments and thermal treatments: A review.

    Science.gov (United States)

    Guo, Bin; Liu, Bo; Yang, Jian; Zhang, Shengen

    2017-05-15

    Safe disposal of solid wastes containing heavy metals is a significant task for environment protection. Immobilization treatment is an effective technology to achieve this task. Cementitious material treatments and thermal treatments are two types of attractive immobilization treatments due to that the heavy metals could be encapsulated in their dense and durable wasteforms. This paper discusses the heavy metal immobilization mechanisms of these methods in detail. Physical encapsulation and chemical stabilization are two fundamental mechanisms that occur simultaneously during the immobilization processes. After immobilization treatments, the wasteforms build up a low permeable barrier for the contaminations. This reduces the exposed surface of wastes. Chemical stabilization occurs when the heavy metals transform into more stable and less soluble metal bearing phases. The heavy metal bearing phases in the wasteforms are also reviewed in this paper. If the heavy metals are incorporated into more stable and less soluble metal bearing phases, the potential hazards of heavy metals will be lower. Thus, converting heavy metals into more stable phases during immobilization processes should be a common way to enhance the immobilization effect of these immobilization methods. Copyright © 2017 Elsevier Ltd. All rights reserved.

  12. Energy Impacts of Envelope Tightening and Mechanical Ventilation for the U.S. Residential Sector

    Energy Technology Data Exchange (ETDEWEB)

    Logue, J. M. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Sherman, M. H. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Walker, I. S. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Singer, B. C. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)

    2013-01-01

    Effective residential envelope air sealing reduces infiltration and associated energy costs for thermal conditioning, yet often creates a need for mechanical ventilation to protect indoor air quality. This study estimated the potential energy savings of implementing airtightness improvements or absolute standards along with mechanical ventilation throughout the U.S. housing stock. We used a physics-based modeling framework to simulate the impact of envelope tightening, providing mechanical ventilation as needed. There are 113 million homes in the US. We calculated the change in energy demand for each home in a nationally representative sample of 50,000 virtual homes developed from the 2009 Residential Energy Consumption Survey. Ventilation was provided as required by 2010 and proposed 2013 versions of ASHRAE Standard 62.2. Ensuring that all current homes comply with 62.2-2010 would increase residential site energy demand by 0.07 quads (0.07 exajoules (EJ)) annually. Improving airtightness of all homes at current average retrofit performance levels would decrease demand by 0.7 quads (0.74 EJ) annually and upgrading all homes to be as airtight as the top 10% of similar homes would double the savings, leading to roughly $22 billion in annual savings in energy bills. We also analyzed the potential benefits of bringing the entire stock to airtightness specifications of IECC 2012, Canada's R2000, and Passive House standards.

  13. Adhesive and abrasive wear mechanisms in ion implanted metals

    International Nuclear Information System (INIS)

    Dearnaley, G.

    1985-01-01

    The distinction between adhesive and abrasive wear processes was introduced originally by Burwell during the nineteen-fifties, though some authors prefer to classify wear according to whether it is mild or severe. It is argued here that, on the basis of the performance of a variety of ion implanted metal surfaces, exposed to different modes of wear, the Burwell distinction is a valid one which, moreover, enables us to predict under which circumstances a given treatment will perform well. It is shown that, because wear rates under abrasive conditions are very sensitive to the ratio of the hardness of the surface to that of the abrasive particles, large increases in working life are attainable as a result of ion implantation. Under adhesive wear conditions, the wear rate appears to fall inversely as the hardness increases, and it is advantageous to implant species which will create and retain a hard surface oxide or other continuous film in order to reduce metal-metal contact. By the appropriate combination of physico-chemical changes in an implanted layer it has been possible to reduce wear rates by up to three orders of magnitude. Such rates compensate for the shallow depths achievable by ion implantation. (orig.)

  14. Restructuring of the corporate sector of national economy: content and mechanism of realization

    Directory of Open Access Journals (Sweden)

    S. I. Gusakov

    2016-08-01

    It has been suggested to distinguish three directions of the restructuring: inner corporate restructuring; restructuring of relations; economics conditions restructuring. Inner corporate restructuring includes property forms changes, entity structure changes, capital structure changes, form of incorporation changes, management bodies changes, management changes, staff politics changes, reorganization, liquidation, privatization, corporatization. Restructuring of relations includes sales market changes, conversion of enterprises, diversification, contractor’s changes, property assignation, lease, concession, franchising, debt’s restructuring, changes of credit politics, technical supplement, using alternative power sources, standardization etc. Economics conditions restructuring includes regulation and legislation changes, tax regulation changes, currency market changes, changes in credit policies, changers in stock market. Accordingly, every restructuring direction includes many mechanisms of its possible fulfillment. The author has distinguished twenty six mechanisms all the restructuring and they are presented in the table form.The corporate management models’ use in correlation to corporate restructuring models has been described in the article. The author has come to the conclusion that pragmatic model of the corporate restructuring is more preferable in comparison with world recognized valuable model because of the peculiarities of the post-social economy in Ukraine.

  15. Residual thermal stress control in composite reinforced metal structures. [by mechanical loading of metal component prior to bonding

    Science.gov (United States)

    Kelly, J. B.; June, R. R.

    1972-01-01

    Advanced composite materials, composed of boron or graphite fibers and a supporting matrix, make significant structural efficiency improvements available to aircraft and aerospace designers. Residual stress induced during bonding of composite reinforcement to metal structural elements can be reduced or eliminated through suitable modification to the manufacturing processes. The most successful method employed during this program used a steel tool capable of mechanically loading the metal component in compression prior to the adhesive bonding cycle. Compression loading combined with heating to 350 F during the bond cycle can result in creep deformation in aluminum components. The magnitude of the deformation increases with increasing stress level during exposure to 350 F.

  16. Microalloying of transition metal silicides by mechanical activation and field-activated reaction

    Energy Technology Data Exchange (ETDEWEB)

    Munir, Zuhair A [Davis, CA; Woolman, Joseph N [Davis, CA; Petrovic, John J [Los Alamos, NM

    2003-09-02

    Alloys of transition metal suicides that contain one or more alloying elements are fabricated by a two-stage process involving mechanical activation as the first stage and densification and field-activated reaction as the second stage. Mechanical activation, preferably performed by high-energy planetary milling, results in the incorporation of atoms of the alloying element(s) into the crystal lattice of the transition metal, while the densification and field-activated reaction, preferably performed by spark plasma sintering, result in the formation of the alloyed transition metal silicide. Among the many advantages of the process are its ability to accommodate materials that are incompatible in other alloying methods.

  17. Metal Oxide Nanomaterial QNAR Models: Available Structural Descriptors and Understanding of Toxicity Mechanisms

    Directory of Open Access Journals (Sweden)

    Jiali Ying

    2015-10-01

    Full Text Available Metal oxide nanomaterials are widely used in various areas; however, the divergent published toxicology data makes it difficult to determine whether there is a risk associated with exposure to metal oxide nanomaterials. The application of quantitative structure activity relationship (QSAR modeling in metal oxide nanomaterials toxicity studies can reduce the need for time-consuming and resource-intensive nanotoxicity tests. The nanostructure and inorganic composition of metal oxide nanomaterials makes this approach different from classical QSAR study; this review lists and classifies some structural descriptors, such as size, cation charge, and band gap energy, in recent metal oxide nanomaterials quantitative nanostructure activity relationship (QNAR studies and discusses the mechanism of metal oxide nanomaterials toxicity based on these descriptors and traditional nanotoxicity tests.

  18. Study of the Fracture Mechanisms of Electroplated Metallization Systems Using In Situ Microtension Test

    Science.gov (United States)

    Msolli, Sabeur; Kim, Heung Soo

    2018-03-01

    This framework assesses the mechanical behavior of some potential thin/thick metallization systems in use as either ohmic contacts for diamond semi-conductors or for metallization on copper double bounded ceramic substrates present in the next-generation power electronics packaging. The interesting and unique characteristic of this packaging is the use of diamond as a semi-conductor material instead of silicon to increase the lifetime of embedded power converters for use in aeronautical applications. Theoretically, such packaging is able to withstand temperatures of up to 300 °C without breaking the semi-conductor, provided that the constitutive materials of the packaging are compatible. Metallization is very important to protect the chips and substrates. Therefore, we address this issue in the present work. The tested metallization systems are Ni/Au, Ni/Cr/Au and Ni/Cr. These specific systems were studied since they can be used in conjunction with existing bonding technologies, including AuGe soldering, Ag-In Transient liquid Phase Bonding and silver nanoparticle sintering. The metallization is achieved via electrodeposition, and a mechanical test, consisting of a microtension technique, is carried out at room temperature inside a scanning electron microscopy chamber. The technique permits observations the cracks initiation and growth in the metallization to locate the deformation zones and identify the fracture mechanisms. Different failure mechanisms were shown to occur depending on the metallic layers deposited on top of the copper substrate. The density of these cracks depends on the imposed load and the involved metallization. These observations will help choose the metallization that is compatible with the particular bonding material, and manage mechanical stress due to thermal cycling so that they can be used as a constitutive component for high-temperature power electronics packaging.

  19. The mechanism of electroforming of metal oxide memristive switches

    Science.gov (United States)

    Joshua Yang, J.; Miao, Feng; Pickett, Matthew D.; Ohlberg, Douglas A. A.; Stewart, Duncan R.; Lau, Chun Ning; Williams, R. Stanley

    2009-05-01

    Metal and semiconductor oxides are ubiquitous electronic materials. Normally insulating, oxides can change behavior under high electric fields—through 'electroforming' or 'breakdown'—critically affecting CMOS (complementary metal-oxide-semiconductor) logic, DRAM (dynamic random access memory) and flash memory, and tunnel barrier oxides. An initial irreversible electroforming process has been invariably required for obtaining metal oxide resistance switches, which may open urgently needed new avenues for advanced computer memory and logic circuits including ultra-dense non-volatile random access memory (NVRAM) and adaptive neuromorphic logic circuits. This electrical switching arises from the coupled motion of electrons and ions within the oxide material, as one of the first recognized examples of a memristor (memory-resistor) device, the fourth fundamental passive circuit element originally predicted in 1971 by Chua. A lack of device repeatability has limited technological implementation of oxide switches, however. Here we explain the nature of the oxide electroforming as an electro-reduction and vacancy creation process caused by high electric fields and enhanced by electrical Joule heating with direct experimental evidence. Oxygen vacancies are created and drift towards the cathode, forming localized conducting channels in the oxide. Simultaneously, O2- ions drift towards the anode where they evolve O2 gas, causing physical deformation of the junction. The problematic gas eruption and physical deformation are mitigated by shrinking to the nanoscale and controlling the electroforming voltage polarity. Better yet, electroforming problems can be largely eliminated by engineering the device structure to remove 'bulk' oxide effects in favor of interface-controlled electronic switching.

  20. A novel mechanism for the extraction of metals from water to ionic liquids.

    Science.gov (United States)

    Janssen, Camiel H C; Sánchez, Antonio; Witkamp, Geert-Jan; Kobrak, Mark N

    2013-11-11

    We present a novel mechanism for the extraction of metals from aqueous phases to room-temperature ionic liquids (ILs) by use of a high-temperature salt as an extraction agent. The mechanism capitalizes on the fact that charged metal complexes are soluble in ILs; this allows for extraction of charged complexes rather than the neutral species, which are formed by conventional approaches. The use of a well-chosen extraction agent also suppresses the competing ion-exchange mechanism, thus preventing degradation of the ionic liquid. The approach permits the use of excess extractant to drive the recovery of metals in high yield. This work presents both a thermodynamic framework for understanding the approach and experimental verification of the process in a range of different ILs. The method has great potential value in the recovery of metals, water purification and nuclear materials processing. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  1. A Sustainable Closed-Loop Supply Chain Decision Mechanism in the Electronic Sector

    Directory of Open Access Journals (Sweden)

    Jiafu Su

    2018-04-01

    Full Text Available In a closed-loop supply chain for electronic products, the manufacturer’s priority is to enhance the residual value of the collected end-of-use product and decide whether to outsource this business to a retailer, a third-party service, or retain it exclusively. In this paper, we constructed three models to study the decision mechanism in a closed-loop supply chain, with different players selected to collect the used product. By comparing the three models, we characterized the conditions under which the manufacturer will benefit most, and we then aimed to determine the best choice for the manufacturer. Our findings show that, when the retailer and the third-party service provider provide equal performance in collecting the used product, the manufacturer will give priority to the third-party service provider if they choose to outsource this business. If the reverse flows managed by the retailer result in a higher payoff for the manufacturer, then the manufacturer will choose to outsource this business to the retailer who will also benefit.

  2. The effects of reimbursement mechanisms on medical technology diffusion in the hospital sector in the Italian NHS.

    Science.gov (United States)

    Finocchiaro Castro, Massimo; Guccio, Calogero; Pignataro, Giacomo; Rizzo, Ilde

    2014-04-01

    The aim of this study was to investigate how the differences across the regional reimbursement mechanisms and in particular the use of the DRGs impact on the level in the high technology equipment diffusion. Based on hospital sector data at a regional level we build up indicators to measure the regional diffusion of high technological medical equipment in the period 1997-2007. These indicators are regressed on regional healthcare characteristics to investigate the relationship between the different reimbursement systems offered by Italian regions and the level of high technological medical equipment. Our results suggest that the per-case payment system is generally associated with a lower level of regional technology endowment per million of inhabitants, especially for the complex and expensive medical equipment. Our findings cast some doubts that an effective regulation of reimbursement mechanisms cannot limit the excessive diffusion of medical equipment that is a relevant driver of the increase in expenditure. Copyright © 2013 Elsevier Ireland Ltd. All rights reserved.

  3. Contact mechanics and elastohydrodynamic lubrication in a novel metal-on-metal hip implant with an aspherical bearing surface.

    Science.gov (United States)

    Meng, Qingen; Gao, Leiming; Liu, Feng; Yang, Peiran; Fisher, John; Jin, Zhongmin

    2010-03-22

    Diameter and diametral clearance of the bearing surfaces of metal-on-metal hip implants and structural supports have been recognised as key factors to reduce the dry contact and hydrodynamic pressures and improve lubrication performance. On the other hand, application of aspherical bearing surfaces can also significantly affect the contact mechanics and lubrication performance by changing the radius of the curvature of a bearing surface and consequently improving the conformity between the head and the cup. In this study, a novel metal-on-metal hip implant employing a specific aspherical bearing surface, Alpharabola, as the acetabular surface was investigated for both contact mechanics and elastohydrodynamic lubrication under steady-state conditions. When compared with conventional spherical bearing surfaces, a more uniform pressure distribution and a thicker lubricant film thickness within the loaded conjunction were predicted for this novel Alpharabola hip implant. The effects of the geometric parameters of this novel acetabular surface on the pressure distribution and lubricant thickness were investigated. A significant increase in the predicted lubricant film thickness and a significant decrease in the dry contact and hydrodynamic pressures were found with appropriate combinations of these geometric parameters, compared with the spherical bearing surface. Copyright (c) 2009 Elsevier Ltd. All rights reserved.

  4. Capability and Mechanisms of Macrofungi in Heavy Metal Accumulation:A Review

    Directory of Open Access Journals (Sweden)

    CHEN Miao-miao

    2017-10-01

    Full Text Available Some macrofungi have the ability to accumulate heavy metals, which is comparable to hyper-accumulator plants. Cordyceps militaris can accumulate Zn up to 20 000 mg·kg-1. Therefore, macrofungi have the potential to be used as an important bioremediation tool for heavy metals. In this review, we summarized the heavy metal resistant capacity of typical macrofungi and known relevant mechanisms. Generally, straw-decay fungi presented better capability for Cu, Ag and Cd enrichment than wood-decay fungi, while wood-decay fungi could accumulate Cr, Mg, Se and Pb. Different macrofungi species, different growth periods(mycelium and fruiting body and different parts of fruiting body showed different capability for heavy metals accumulation. General mechanisms for heavy metals accumulation in macrofungi included extracellular precipitation in the forms of polymeric substances, cell wall adsorption and intracellular absorption. Macrofungi could also detoxify by chelating metal ions by metallothionein(MT, secreting antioxidant enzymes(SOD, CAT, POD and degradating the misfolded proteins by ubiquitin-proteasome system(UPS. We also explored the potential of macrofungi in heavy metal remediation and pollution diagnostics as a biological indicator. Some macrofungi had been applied in the remediation of heavy metal contaminated soils and water. Finally, some future research areas including strain breeding and genetic engineering were discussed, which might provide references for the future studies.

  5. A review of toxicity and mechanisms of individual and mixtures of heavy metals in the environment.

    Science.gov (United States)

    Wu, Xiangyang; Cobbina, Samuel J; Mao, Guanghua; Xu, Hai; Zhang, Zhen; Yang, Liuqing

    2016-05-01

    The rational for the study was to review the literature on the toxicity and corresponding mechanisms associated with lead (Pb), mercury (Hg), cadmium (Cd), and arsenic (As), individually and as mixtures, in the environment. Heavy metals are ubiquitous and generally persist in the environment, enabling them to biomagnify in the food chain. Living systems most often interact with a cocktail of heavy metals in the environment. Heavy metal exposure to biological systems may lead to oxidation stress which may induce DNA damage, protein modification, lipid peroxidation, and others. In this review, the major mechanism associated with toxicities of individual metals was the generation of reactive oxygen species (ROS). Additionally, toxicities were expressed through depletion of glutathione and bonding to sulfhydryl groups of proteins. Interestingly, a metal like Pb becomes toxic to organisms through the depletion of antioxidants while Cd indirectly generates ROS by its ability to replace iron and copper. ROS generated through exposure to arsenic were associated with many modes of action, and heavy metal mixtures were found to have varied effects on organisms. Many models based on concentration addition (CA) and independent action (IA) have been introduced to help predict toxicities and mechanisms associated with metal mixtures. An integrated model which combines CA and IA was further proposed for evaluating toxicities of non-interactive mixtures. In cases where there are molecular interactions, the toxicogenomic approach was used to predict toxicities. The high-throughput toxicogenomics combines studies in genetics, genome-scale expression, cell and tissue expression, metabolite profiling, and bioinformatics.

  6. Exploiting large-pore metal-organic frameworks for separations through entropic molecular mechanisms

    NARCIS (Netherlands)

    Torres-Knoop, A.; Dubbeldam, D.

    2015-01-01

    We review the molecular mechanisms behind adsorption and the separations of mixtures in metal-organic frameworks and zeolites. Separation mechanisms can be based on differences in the affinity of the adsorbate with the framework and on entropic effects. To develop next-generation adsorbents, the

  7. Lattice mechanical properties of some fcc f-shell metals

    International Nuclear Information System (INIS)

    Baria, J.K.; Jani, A.R.

    2003-01-01

    A pseudopotential depending on an effective core radius is proposed to study the binding energy, equation of state, ion-ion interaction, phonon dispersion curves (q-space and r-space analysis), mode Grueneisen parameters and dynamical elastic constants of some fcc f-shell metals La, Yb, Ce and Th. The contribution of the s-like electrons is calculated in the second-order perturbation theory for the potential while d- and f-like electron is taken into account by introducing repulsive short-range Born-Mayer term. The parameter of the potential is evaluated by zero pressure condition. An excellent agreement between theoretical investigations and experimental findings is achieved which confirms the present formalism. (author)

  8. Mechanism of Transition-Metal Nanoparticle Catalytic Graphene Cutting.

    Science.gov (United States)

    Ma, Liang; Wang, Jinlan; Yip, Joanne; Ding, Feng

    2014-04-03

    Catalytic cutting by transition-metal (TM) particles is a promising method for the synthesizing of high-quality graphene quantum dots and nanoribbons with smooth edges. Experimentally, it is observed that the cutting always results in channels with zigzag (ZZ) or armchair (AC) edges. However, the driving force that is responsible for such a cutting behavior remains a puzzle. Here, by calculating the interfacial formation energies of the TM-graphene edges with ab initio method, we show that the surface of a catalyst particle tends to be aligned along either AC or ZZ direction of the graphene lattice, and thus the cutting of graphene is guided as such. The different cutting behaviors of various catalysts are well-explained based on the competition between TM-passivated graphene edges and the etching-agent-terminated ones. Furthermore, the kinetics of graphene catalytic cutting along ZZ and AC directions, respectively, are explored at the atomic level.

  9. Leveraging metal matrix composites to reduce costs in space mechanisms

    Science.gov (United States)

    Nye, Ted; Claridge, Rex; Walker, Jim

    1994-01-01

    Advanced metal matrix composites may be one of the most promising technologies for reducing cost in structural components without compromise to strength or stiffness. A microlight 12.50 N (2.81 lb), two-axis, solar array drive assembly (SADA) was made for the Advanced Materials Applications to Space Structures (AMASS) Program flight experiment. The SADA had both its inner and outer axis housings fabricated from silicon carbide particulate reinforced alumimun. Two versions of the housings were made. The first was machined from a solid billet of material. The second was plaster cast to a near net shape that required minimal finish machining. Both manufacturing methods were compared upon completion. Results showed a cost savings with the cast housing was possible for quantities greater than one and probable for quantities greater than two. For quantities approaching ten, casting resulted in a reduction factor of almost three in the cost per part.

  10. Transport mechanisms in the laser alloying of metals

    Science.gov (United States)

    Pawlak, Ryszard; Tomczyk, Mariusz; Walczak, Maria

    2003-10-01

    This article presents some investigations of a laser alloyed surface layer of nickel doped with gold and of copper doped with aluminum. The velocity of the convectino flow in the laser pool predicted by computation implies that there may exist good miscibility for the range of components different from those obtained by the conventional method. This indicates a predominant role of the Marangoni convection for mixing elements. Some metallurgical cross-sections of Ni-Au; Mo-Au; Cu-Al; Cu-Au layers, alloyed by an Nd-YAG laser, for different contents of doping elements are presented. They may be interesting information about miscibility of these metals during laser pulse τ1=4ms.

  11. The effect of carbon content on mechanical properties, failure and corrosion resistance of deposited chromium metal

    Directory of Open Access Journals (Sweden)

    Леонід Кімович Лещинськiй

    2017-06-01

    Full Text Available It has been shown that if choosing a metal composition for surfacing rolls and rollers of continuous casting machines, both the carbon impact on the mechanical and functional properties and the critical values of the chromium concentration, which determine the corrosion resistance of the metal with regard to electrochemical corrosion theory, should be considered as well. The paper studied the effect of chromium and carbon steel the X5-X12 type on the structure, technological strength, mechanical properties, fracturing resistance and corrosion resistance of the weld metal. The composition of chromium tool steels (deposited metal (X5-used for the rolls of hot rolling mills and (X12-used for continuous casting machines rollers correspond to these values. The impact of carbon on the properties of the deposited metal containing chromium was considered by comparing the data for both types of the deposited metal. It was found that for both types of the deposited metal (X5 and X12, the limiting value of the carbon content, providing an optimal combination of strength, ductility, failure resistance is the same. If the carbon content is more than the limiting value – (0,25% the technological strength and failure resistance of the deposited metal significantly reduce. With increasing carbon content from 0,18 to 0,25% the martensite structure has a mixed morphology – lath and plate. The strength and toughness of the deposited metal grow. Of particular interest is simultaneous increase in the specific work of failure resulted from crack inhibition at the boundary with far less solid and more ductile ferrite. As for the 5% chromium metal, the X12 type composition with 0,25% C, is borderline. With a further increase in the carbon content of the metal both ductility and failure resistance sharply decrease and with 0,40% C the growth rate of fatigue crack increases by almost 1,5 times

  12. Shaping mechanisms of metal specificity in a family of metazoan metallothioneins: evolutionary differentiation of mollusc metallothioneins

    Directory of Open Access Journals (Sweden)

    Atrian Sílvia

    2011-01-01

    Full Text Available Abstract Background The degree of metal binding specificity in metalloproteins such as metallothioneins (MTs can be crucial for their functional accuracy. Unlike most other animal species, pulmonate molluscs possess homometallic MT isoforms loaded with Cu+ or Cd2+. They have, so far, been obtained as native metal-MT complexes from snail tissues, where they are involved in the metabolism of the metal ion species bound to the respective isoform. However, it has not as yet been discerned if their specific metal occupation is the result of a rigid control of metal availability, or isoform expression programming in the hosting tissues or of structural differences of the respective peptides determining the coordinative options for the different metal ions. In this study, the Roman snail (Helix pomatia Cu-loaded and Cd-loaded isoforms (HpCuMT and HpCdMT were used as model molecules in order to elucidate the biochemical and evolutionary mechanisms permitting pulmonate MTs to achieve specificity for their cognate metal ion. Results HpCuMT and HpCdMT were recombinantly synthesized in the presence of Cd2+, Zn2+ or Cu2+ and corresponding metal complexes analysed by electrospray mass spectrometry and circular dichroism (CD and ultra violet-visible (UV-Vis spectrophotometry. Both MT isoforms were only able to form unique, homometallic and stable complexes (Cd6-HpCdMT and Cu12-HpCuMT with their cognate metal ions. Yeast complementation assays demonstrated that the two isoforms assumed metal-specific functions, in agreement with their binding preferences, in heterologous eukaryotic environments. In the snail organism, the functional metal specificity of HpCdMT and HpCuMT was contributed by metal-specific transcription programming and cell-specific expression. Sequence elucidation and phylogenetic analysis of MT isoforms from a number of snail species revealed that they possess an unspecific and two metal-specific MT isoforms, whose metal specificity was

  13. The mechanism of strength and deformation in Gum Metal

    International Nuclear Information System (INIS)

    Furuta, T.; Kuramoto, S.; Morris, J.W.; Nagasako, N.; Withey, E.; Chrzan, D.C.

    2013-01-01

    “Gum Metal” refers to β-Ti alloys that achieve exceptional elastic elongation and, with a specific alloy composition, appear to deform via a dislocation-free mechanism involving elastic instability at the limit of strength. This paper describes the current status of research on its strength, deformation mechanism and the possible role of stress-induced martensite. The theoretical basis for deformation at ideal strength is presented. The relevant experimental data is then discussed, including ex situ nanoindentation behavior and in situ pillar compression observed by transmission electron microscopy

  14. Evaluation of the interaction mechanisms between red muds and heavy metals.

    Science.gov (United States)

    Santona, Laura; Castaldi, Paola; Melis, Pietro

    2006-08-21

    This paper investigated the heavy metal adsorption of non-treated (RM(nt)) and acid-treated red muds (RM(a)), bauxite ore processing waste, in order to evaluate how efficient they are in reducing metal solubility and bioavaliability in polluted soils. Red mud samples were artificially polluted with solutions containing increasing concentrations of Pb, Cd and Zn. Cancrinite and hematite were the main phases of the red muds, and were also the components which adsorbed most heavy metals. The results showed that the RM(nt) adsorption capacity for the three heavy metals was Zn> or =Pb>Cd. Acid treatment with HCl decreased the red mud's capacity to adsorb the heavy metals by 30%. In order to study the different heavy metal-RM interaction mechanisms, all samples after artificial contamination were treated with solutions with gradually increasing extraction capacity. H(2)O and Ca(NO(3))(2) treatments only extracted very low concentrations of Pb, Cd and Zn, while EDTA treatment extracted the most adsorbed heavy metals from the sorbent particles. In particular the water-soluble and exchangeable metal fractions were higher in the RM(a) than they were in the RM(nt), while the concentrations of Pb, Cd and Zn extracted with EDTA were lower. The results showed that red muds can be used successfully to reduce the solubility and bioavailability of heavy metals in polluted soils.

  15. Metals in cyanobacteria: analysis of the copper, nickel, cobalt and arsenic homeostasis mechanisms.

    Science.gov (United States)

    Huertas, María José; López-Maury, Luis; Giner-Lamia, Joaquín; Sánchez-Riego, Ana María; Florencio, Francisco Javier

    2014-12-09

    Traces of metal are required for fundamental biochemical processes, such as photosynthesis and respiration. Cyanobacteria metal homeostasis acquires an important role because the photosynthetic machinery imposes a high demand for metals, making them a limiting factor for cyanobacteria, especially in the open oceans. On the other hand, in the last two centuries, the metal concentrations in marine environments and lake sediments have increased as a result of several industrial activities. In all cases, cells have to tightly regulate uptake to maintain their intracellular concentrations below toxic levels. Mechanisms to obtain metal under limiting conditions and to protect cells from an excess of metals are present in cyanobacteria. Understanding metal homeostasis in cyanobacteria and the proteins involved will help to evaluate the use of these microorganisms in metal bioremediation. Furthermore, it will also help to understand how metal availability impacts primary production in the oceans. In this review, we will focus on copper, nickel, cobalt and arsenic (a toxic metalloid) metabolism, which has been mainly analyzed in model cyanobacterium Synechocystis sp. PCC 6803.

  16. Evaporation as the transport mechanism of metals in arid regions

    NARCIS (Netherlands)

    Lima, A.T.; Safar, Z.; Loch, J.P.G.

    Soils of arid regions are exposed to drought and drastic temperature oscillations throughout the year. Transport mechanisms in these soils are therefore very different from the ones in temperate regions, where rain dictates the fate of most elements in soils. Due to the low rainfall and high

  17. Computer simulations of the mechanical properties of metals

    DEFF Research Database (Denmark)

    Schiøtz, Jakob; Vegge, Tejs

    1999-01-01

    Atomic-scale computer simulations can be used to gain a better understanding of the mechanical properties of materials. In this paper we demonstrate how this can be done in the case of nanocrystalline copper, and give a brief overview of how simulations may be extended to larger length scales...

  18. Heavy metal contamination of soil in mechanic workshops | Ameh ...

    African Journals Online (AJOL)

    Latitude: 11° 4' 0 N, Longitude: 7° 42' 0 E) was studied. The types of mechanic workshops considered were motorcycle, motorcar, truck/lorries and generator set. The soils were sampled in August 2010. The results indicated that there was an ...

  19. A study of mechanisms of liquid lubrication in metal forming

    DEFF Research Database (Denmark)

    Bech, Jakob Ilsted; Bay, Niels; Eriksen, Morten

    1998-01-01

    Plasto HydroStatic Lubrication (MPHSL) is observed and quantified experimentally with varying lubricant viscosity, drawing speed, reduction, die angle, back tension, workpiece material and friction conditions. All these parameters are shown to influence the mechanisms of lubricant escape in an explicable...

  20. Mechanism of yttrium atom formation in electrothermal atomization from metallic and metal-carbide surfaces of a heated graphite atomizer in atomic absorption spectrometry

    International Nuclear Information System (INIS)

    Wahab, H.S.; Chakrabarti, C.L.

    1981-01-01

    Mechanism of Y atom formation from pyrocoated graphite, tantalum and tungsten metal surfaces of a graphite tube atomizer has been studied and a mechanism for the formation for Y atoms is proposed for the first time. (author)

  1. Kinetics and mechanism of the hydridation of uranium and rare-earth metals

    International Nuclear Information System (INIS)

    Bloch, J.

    1989-07-01

    The purpose of this work was to study the rate and the mechanism of the hydridation reaction of uranium and the lanthanide metals. Surface sensitive analysis was used to study the reaction of the metal surface with residual gases of the high vacuum atmosphere. The initial stages of the uranium-hydrogen reaction, taking place on a polished metal surface, were investigated utilizing a hot-stage microscope equipped with TV camera and a video-recorder. The characteristics of formation and advance mechanism of hydride phase in bulk uranium and lanthanide metals were studied utilizing metallographic examination of partially hydrided thin foil samples at different stages of the reaction. The interface velocity of the hydride in uranium was measured as a function of pressure and temprature in a constant volume system. A probabilistic kinetic model for a gas-solid interaction, controlled by a phase transformation step, was developed and applied to the hydridation of uranium and gadolinium

  2. Microstructure and mechanical properties of direct metal laser sintered TI-6AL-4V

    Directory of Open Access Journals (Sweden)

    Becker, Thorsten Hermann

    2015-05-01

    Full Text Available Direct metal laser sintering (DMLS is a selective laser melting (SLM manufacturing process that can produce near net shape parts from metallic powders. A range of materials are suitable for SLM; they include various metals such as titanium, steel, aluminium, and cobalt-chrome alloys. This paper forms part of a research drive that aims to evaluate the material performance of the SLM-manufactured metals. It presents DMLS-produced Ti-6Al-4V, a titanium alloy often used in biomedical and aerospace applications. This paper also studies the effect of several heat treatments on the microstructure and mechanical properties of Ti-6Al-4V processed by SLM. It reports the achievable mechanical properties of the alloy, including quasi-static, crack growth behaviour, density and porosity distribution, and post-processing using various heat-treatment conditions.

  3. Microbial Biofilms as a Mechanism for Metal Sorption on Plastic Debris

    Science.gov (United States)

    Richard, H.; Rochman, C. M.; Komada, T.; Carpenter, E. J.

    2016-02-01

    Heavy metals from the water column accumulate onto weathered plastic debris to a greater extent than onto virgin plastic. Hypothesized mechanisms that drive this process include oxidation by ultraviolet light, precipitation of metal ions onto the surface of the plastic, and biofilm growth. We provide the first example of research quantifying how biofilms influence metal sorption onto plastic debris. We conducted laboratory experiments to find out whether or not the presence of biofilms increases the sorption capacity of plastic debris, and also performed in situ experiments in the San Francisco Bay to compare low-density polyethylene, polylactic acid, and glass as substrates for fouling and metal sorption. This research reveals the potential for plastic debris to act as a vector bringing heavy metals into aquatic food webs relative to other debris materials.

  4. Scattering mechanical performances for brittle bulk metallic glasses

    Directory of Open Access Journals (Sweden)

    J. W. Qiao

    2014-11-01

    Full Text Available Scattering mechanical performances of brittle La- and Mg-based BMGs are found in the present study. Upon dynamic loading, there exist largely scattered fracture strengths even if the strain rates are under the same order, and the BMG systems are the same. The negative strain rate dependence for La- and Mg-based BMGs is obtained, i.e., a decreased fracture strength is dominating from quasi-static to dynamic compression. At cryogenic temperatures, distinguishingly low fracture strengths are available for these two brittle BMGs, and decreased tolerance to accommodate strains makes BMGs more and more brittle. It is concluded that the scattering mechanical performances of brittle BMGs should be carefully evaluated before actual applications.

  5. Mechanical anomaly impact on metal-oxide-semiconductor capacitors on flexible silicon fabric

    KAUST Repository

    Ghoneim, Mohamed T.

    2014-06-09

    We report the impact of mechanical anomaly on high-κ/metal-oxide-semiconductor capacitors built on flexible silicon (100) fabric. The mechanical tests include studying the effect of bending radius up to 5 mm minimum bending radius with respect to breakdown voltage and leakage current of the devices. We also report the effect of continuous mechanical stress on the breakdown voltage over extended periods of times.

  6. Controlled Mechanical Cracking of Metal Films Deposited on Polydimethylsiloxane (PDMS

    Directory of Open Access Journals (Sweden)

    Andreas Polywka

    2016-09-01

    Full Text Available Stretchable large area electronics conform to arbitrarily-shaped 3D surfaces and enables comfortable contact to the human skin and other biological tissue. There are approaches allowing for large area thin films to be stretched by tens of percent without cracking. The approach presented here does not prevent cracking, rather it aims to precisely control the crack positions and their orientation. For this purpose, the polydimethylsiloxane (PDMS is hardened by exposure to ultraviolet radiation (172 nm through an exposure mask. Only well-defined patterns are kept untreated. With these soft islands cracks at the hardened surface can be controlled in terms of starting position, direction and end position. This approach is first investigated at the hardened PDMS surface itself. It is then applied to conductive silver films deposited from the liquid phase. It is found that statistical (uncontrolled cracking of the silver films can be avoided at strain below 35%. This enables metal interconnects to be integrated into stretchable networks. The combination of controlled cracks with wrinkling enables interconnects that are stretchable in arbitrary and changing directions. The deposition and patterning does not involve vacuum processing, photolithography, or solvents.

  7. Microscopic mechanisms of graphene electrolytic delamination from metal substrates

    International Nuclear Information System (INIS)

    Fisichella, G.; Di Franco, S.; Roccaforte, F.; Giannazzo, F.; Ravesi, S.

    2014-01-01

    In this paper, hydrogen bubbling delamination of graphene (Gr) from copper using a strong electrolyte (KOH) water solution was performed, focusing on the effect of the KOH concentration (C KOH ) on the Gr delamination rate. A factor of ∼10 decrease in the time required for the complete Gr delamination from Cu cathodes with the same geometry was found increasing C KOH from ∼0.05 M to ∼0.60 M. After transfer of the separated Gr membranes to SiO 2 substrates by a highly reproducible thermo-compression printing method, an accurate atomic force microscopy investigation of the changes in Gr morphology as a function of C KOH was performed. Supported by these analyses, a microscopic model of the delamination process has been proposed, where a key role is played by graphene wrinkles acting as nucleation sites for H 2 bubbles at the cathode perimeter. With this approach, the H 2 supersaturation generated at the electrode for different electrolyte concentrations was estimated and the inverse dependence of t d on C KOH was quantitatively explained. Although developed in the case of Cu, this analysis is generally valid and can be applied to describe the electrolytic delamination of graphene from several metal substrates.

  8. Label-free histamine detection with nanofluidic diodes through metal ion displacement mechanism

    OpenAIRE

    Ali, Mubarak; Ramirez Hoyos, Patricio; Duznovic, Ivana; Nasir, Saima; Mafe, Salvador; Ensinger, Wolfgang

    2017-01-01

    [EN] We design and characterize a nanofluidic device for the label-free specific detection of histamine neurotransmitter based on a metal ion displacement mechanism. The sensor consists of an asymmetric polymer nanopore fabricated via ion track-etching technique. The nanopore sensor surface having metal-nitrilotriacetic (NTA-Ni2+) chelates is obtained by covalent coupling of native carboxylic acid groups with N-alpha,N-alpha-bis(carboxymethyl)-L-lysine (BCML), followed by exposure to Ni2+ ion...

  9. Mechanisms of stress avoidance and tolerance by plants used in phytoremediation of heavy metals

    OpenAIRE

    Jutsz Anna Małachowska; Gnida Anna

    2015-01-01

    Heavy metal pollution of soil is a significant environmental problem and has a negative impact on human health and agriculture. Phytoremediation can be an alternative environmental treatment technology, using the natural ability of plants to take up and accumulate pollutants or transform them. Proper development of plants in contaminated areas (e.g. heavy metals) requires them to generate the appropriate protective mechanisms against the toxic effects of these pollutants. This paper presents ...

  10. Rupture mechanics of metallic alloys for hydrogen transport

    International Nuclear Information System (INIS)

    Moro, I.; Briottet, L.; Lemoine, P.; Andrieu, E.; Blanc, C.

    2007-01-01

    With the aim to establish a cheap hydrogen distribution system, the transport by pipelines is a solution particularly interesting. Among the high limit of elasticity steels, the X80 has been chosen for hydrogen transport. Its chemical composition and microstructure are given. Important microstructural changes have been revealed in the sheet thickness: the microstructure is thinner and richer in perlite in surface than in bulk. In parallel to this microstructural evolution, a microhardness gradient has been observed: the material microhardness is stronger in surface than in bulk of the sheet. The use of this material for hydrogen transport requires to study its resistance to hydrogen embrittlement. The main aim of this work is to develop an easy rupture mechanics test allowing to qualify the studied material in a gaseous hydrogen environment, to determine the sensitivity of the studied material to the hydrogen embrittlement and to better understand the mechanisms of the hydrogen embrittlement for ferritic materials. Two experimental tests have been used for: the first one is a traction machine coupled to an autoclave; the second one allows to carry out disk rupture tests. The toughness of the material in a gaseous hydrogen environment has thus been determined. The resistance of the material to hydrogen embrittlement has been characterized and by simulation, it has been possible to identify the areas with a strong concentration in hydrogen. The second aim of this work is to study the influence of the steel microstructure on the hydrogen position in the material and on the resistance of the material to the hydrogen embrittlement. The preferential trapping sites on the material not mechanically loaded have at first been identified, as well as the hydrogen position on the different phases and at the ferrite/cementite interface. The interaction between the mechanical loads, the position and the trapping of the hydrogen have been studied then. At last, has been

  11. Mechanism of decomposition of transition metal organometallic compounds and role of intermediate particles in catalysis

    International Nuclear Information System (INIS)

    Dolgoplosk, B.A.

    1984-01-01

    In the review, containing 105 bibliographic references, ways of decomposition of transition metal organic compounds in the moment of their formation are considered. For methyl, benzyl, trimethylsililmethyl and neophilic derivatives of transition metals (Mo, W, Re, Nb, Ta, Nd, Y) α-decay, which is accompanied by the formation of carbene and carbyne particles, is the determining one. Mechanism of the chain processes of metathesis of olefines and cycloolephines under the effect of carbene complexes of transition metals is discussed. Suppositions are made on chemical nature of elementary acts in the reactions of hydrogenolisis, isomerization of carbon carcass; dehydration and hydration of hydrocarbons

  12. Evaluation of mechanical properties in metal wire mesh supported selective catalytic reduction (SCR) catalyst structures

    Science.gov (United States)

    Rajath, S.; Siddaraju, C.; Nandakishora, Y.; Roy, Sukumar

    2018-04-01

    The objective of this research is to evaluate certain specific mechanical properties of certain stainless steel wire mesh supported Selective catalytic reduction catalysts structures wherein the physical properties of the metal wire mesh and also its surface treatments played vital role thereby influencing the mechanical properties. As the adhesion between the stainless steel wire mesh and the catalyst material determines the bond strength and the erosion resistance of catalyst structures, surface modifications of the metal- wire mesh structure in order to facilitate the interface bonding is therefore very important to realize enhanced level of mechanical properties. One way to enhance such adhesion properties, the stainless steel wire mesh is treated with the various acids, i.e., chromic acid, phosphoric acid including certain mineral acids and combination of all those in various molar ratios that could generate surface active groups on metal surface that promotes good interface structure between the metal- wire mesh and metal oxide-based catalyst material and then the stainless steel wire mesh is dipped in the glass powder slurry containing some amount of organic binder. As a result of which the said catalyst material adheres to the metal-wire mesh surface more effectively that improves the erosion profile of supported catalysts structure including bond strength.

  13. Microstructure, Texture, and Mechanical Property Analysis of Gas Metal Arc Welded AISI 304 Austenitic Stainless Steel

    Science.gov (United States)

    Saha, Saptarshi; Mukherjee, Manidipto; Pal, Tapan Kumar

    2015-03-01

    The present study elaborately explains the effect of welding parameters on the microstructure, texture, and mechanical properties of gas metal arc welded AISI 304 austenitic stainless steel sheet (as received) of 4 mm thickness. The welded joints were prepared by varying welding speed (WS) and current simultaneously at a fixed heat input level using a 1.2-mm-diameter austenitic filler metal (AISI 316L). The overall purpose of this study is to investigate the effect of the variation of welding conditions on: (i) Microstructural constituents using optical microscope and transmission electron microscope; (ii) Micro-texture evolution, misorientation distributions, and grain boundaries at welded regions by measuring the orientation data from electron back scattered diffraction; and (iii) Mechanical properties such as hardness and tensile strength, and their correlation with the microstructure and texture. It has been observed that the higher WS along with the higher welding current (weld metal W1) can enhance weld metal mechanical properties through alternation in microstructure and texture of the weld metal. Higher δ-ferrite formation and high-angle boundaries along with the + grain growth direction of the weld metal W1 were responsible for dislocation pile-ups, SFs, deformation twinning, and the induced martensite with consequent strain hardening during tensile deformation. Also, fusion boundary being the weakest link in the welded structure, failure took place mainly at this region.

  14. Mechanical improvement of metal reinforcement rings for a finite ring-shaped superconducting bulk

    Science.gov (United States)

    Huang, Chen-Guang; Zhou, You-He

    2018-03-01

    As a key technique, reinforcement of type-II superconducting bulks with metal rings can efficiently improve their mechanical properties to enhance the maximum trapped field. In this paper, we study the magnetostrictive and fracture behaviors of a finite superconducting ring bulk reinforced by three typical reinforcing structures composed of metal rings during the magnetizing process by means of the minimization of magnetic energy and the finite element method. After a field-dependent critical current density is adopted, the magnetostriction, pinning-induced stress, and crack tip stress intensity factor are calculated considering the demagnetization effects. The results show that the mechanical properties of the ring bulk are strongly dependent on the reinforcing structure and the material and geometrical parameters of the metal rings. Introducing the metal ring can significantly reduce the hoop stress, and the reduction effect by internal reinforcement is much improved relative to external reinforcement. By comparison, bilateral reinforcement seems to be the best candidate structure. Only when the metal rings have particular Young's modulus and radial thickness will they contribute to improve the mechanical properties the most. In addition, if an edge crack is pre-existing in the ring bulk, the presence of metal rings can effectively avoid crack propagation since it reduces the crack tip stress intensity factor by nearly one order of magnitude.

  15. Mechanical improvement of metal reinforcement rings for a finite ring-shaped superconducting bulk

    Directory of Open Access Journals (Sweden)

    Chen-Guang Huang

    2018-03-01

    Full Text Available As a key technique, reinforcement of type-II superconducting bulks with metal rings can efficiently improve their mechanical properties to enhance the maximum trapped field. In this paper, we study the magnetostrictive and fracture behaviors of a finite superconducting ring bulk reinforced by three typical reinforcing structures composed of metal rings during the magnetizing process by means of the minimization of magnetic energy and the finite element method. After a field-dependent critical current density is adopted, the magnetostriction, pinning-induced stress, and crack tip stress intensity factor are calculated considering the demagnetization effects. The results show that the mechanical properties of the ring bulk are strongly dependent on the reinforcing structure and the material and geometrical parameters of the metal rings. Introducing the metal ring can significantly reduce the hoop stress, and the reduction effect by internal reinforcement is much improved relative to external reinforcement. By comparison, bilateral reinforcement seems to be the best candidate structure. Only when the metal rings have particular Young’s modulus and radial thickness will they contribute to improve the mechanical properties the most. In addition, if an edge crack is pre-existing in the ring bulk, the presence of metal rings can effectively avoid crack propagation since it reduces the crack tip stress intensity factor by nearly one order of magnitude.

  16. Reaction mechanisms and microstructures of ceramic-metal composites made by reactive metal penetration

    Energy Technology Data Exchange (ETDEWEB)

    Fahrenholtz, W.F. [Univ. of New Mexico, Albuquerque, NM (United States). Advanced Materials Lab.; Ewsuk, K.G.; Loehman, R.E. [Sandia National Labs., NM (United States)] [and others

    1996-12-31

    Ceramic-metal composites can be made by reactive penetration of molten metals into dense ceramic performs. The metal penetration is driven by a large negative Gibbs energy for reaction, which is different from the more common physical infiltration of porous media. Reactions involving Al can be written generally as (x+2)Al + (3/y)MO{sub y} {yields} Al{sub 2}O{sub 3} + M{sub 3/y}Al{sub x}, where MO{sub y} is an oxide that is wet by molten Al. In low Po{sub 2} atmospheres and at temperature above about 900{degrees}c, molten Al reduces mullite to produce Al{sub 2}O{sub 3} + M{sub 3/y}Al{sub x}, where MO is an oxide that is wet by molten Al. In low Po{sub 2} atmospheres and at temperatures above about 900{degrees}C, molten al reduces mullite to produce Al{sub 2}O{sub 3} and Si. The Al/mullite reaction has a {Delta}G{sub r}{degrees} (1200K) of -1014 kJ/mol and, if the mullite is fully dense, the theoretical volume change on reaction is less than 1%. A microstructure of mutually-interpenetrating metal and ceramic phases generally is obtained. Penetration rate increases with increasing reaction temperature from 900 to 1150{degrees}C, and the reaction layer thickness increases linearly with time. Reaction rate is a maximum at 1150{degrees}C; above that temperature the reaction slows and stops after a relatively short period of linear growth. At 1300{degrees}C and above, no reaction layer is detected by optical microscopy. Observations of the reaction front by TEM show only al and Al{sub 2}O{sub 3} after reaction at 900{degrees}C, but Si is present in increasing amounts as the reaction temperature increases to 1100{degrees}C and above. The kinetic and microstructural data suggest that the deviation from linear growth kinetics at higher reaction temperatures and longer times is due to Si build-up and saturation at the reaction front. The activation energy for short reaction times at 900 to 1150{degrees}C varies from {approximately}90 to {approximately}200 kJ/mole.

  17. Mechanically and electrically robust metal-mask design for organic CMOS circuits

    Science.gov (United States)

    Shintani, Michihiro; Qin, Zhaoxing; Kuribara, Kazunori; Ogasahara, Yasuhiro; Hiromoto, Masayuki; Sato, Takashi

    2018-04-01

    The design of metal masks for fabricating organic CMOS circuits requires the consideration of not only the electrical property of the circuits, but also the mechanical strength of the masks. In this paper, we propose a new design flow for metal masks that realizes coanalysis of the mechanical and electrical properties and enables design exploration considering the trade-off between the two properties. As a case study, we apply a “stitching technique” to the mask design of a ring oscillator and explore the best design. With this technique, mask patterns are divided into separate parts using multiple mask layers to improve the mechanical strength at the cost of high resistance of the vias. By a numerical experiment, the design trade-off of the stitching technique is quantitatively analyzed, and it is demonstrated that the proposed flow is useful for the exploration of the designs of metal masks.

  18. Contribution to diffusion mechanism study in amorphous metallic alloys

    International Nuclear Information System (INIS)

    Delaye, Jean-Marc

    1993-01-01

    This work is dedicated to the study of the vacancy diffusion mechanism in mono-elementary and binary amorphous Lennard-Jones systems, by a molecular dynamics method. The first chapter is a review of the preceding works performed before the beginning of this thesis, the method of simulation is described in the second chapter. We showed in the following chapters that the vacancies, introduced by the removal of one atom, remain stable on a large percentage of sites, especially in the binary system. By calculating some thermodynamical values, formation and migration enthalpies and entropies, we showed that the vacancy mechanism is magnified in a disordered system, as compared to a crystal of the same composition, and therefore can explain the magnitudes of the experimental diffusion coefficients. In parallel, to measure diffusion coefficients, we have settled an experimental method based on the evolution of the resistivity of a multilayer sample during interdiffusion, a gold-silver multilayer in our case (chapter six). By measurements under pressure, the activation volume is determined and our results agree well with the preceding ones. (author) [fr

  19. Nanometric mechanical cutting of metallic glass investigated using atomistic simulation

    International Nuclear Information System (INIS)

    Wu, Cheng-Da; Fang, Te-Hua; Su, Jih-Kai

    2017-01-01

    Highlights: • A nanoscale chip with a shear plane of 135° is extruded by the tool. • Tangential force and normal force increase with increasing tool nose radius. • Resistance factor increases with increasing cutting depth and temperature. - Abstract: The effects of cutting depth, tool nose radius, and temperature on the cutting mechanism and mechanics of amorphous NiAl workpieces are studied using molecular dynamics simulations based on the second-moment approximation of the many-body tight-binding potential. These effects are investigated in terms of atomic trajectories and flow field, shear strain, cutting force, resistance factor, cutting ratio, and pile-up characteristics. The simulation results show that a nanoscale chip with a shear plane of 135° is extruded by the tool from a workpiece surface during the cutting process. The workpiece atoms underneath the tool flow upward due to the adhesion force and elastic recovery. The required tangential force and normal force increase with increasing cutting depth and tool nose radius; both forces also increase with decreasing temperature. The resistance factor increases with increasing cutting depth and temperature, and decreases with increasing tool nose radius.

  20. Occupational exposure to heavy metals in a metal-mechanical auto part manufacturing plant in Puebla, Mexico

    Directory of Open Access Journals (Sweden)

    Maria F Romero-Zarazua

    2015-01-01

    Full Text Available Aims: The concentration of Cd, Cr, Al and Pb present in inhalable air and deposited dust in a metal-mechanical parts manufacturing plant in Puebla, México were determined in order to assess the occupational exposure of workers in this plant. Materials and Methods: Fourteen air samples, six from the metal welding (MW and eight from the metal forming (MF areas, as well as metal dust accumulated on the floor of an auto part manufacturing plant, were collected. Sampling and analysis followed the National Institute for Occupational Safety and Health (NIOSH recommended methods for metals in inhalable air. Results: The average concentration of Al and Cd determined in a volume of inhalable air were adequate under NIOSH maximal exposure concentration limits in both sampled sites. Average concentrations of 0.001 (MF sampling site and 0.105 μg/L (MW sampling site for Al; 0.003 (MF and 0.0005 (MW μg/L for Cd, with respect to the NIOHS limits, 10 and 0.005 μg/L, for Al and Cd, respectively. However, Cr and Pb concentrations exceeded or were close to the limits recommended by NIOHS in both places (0.5 and 0.05 μg/L for Cr and Pb, respectively. Average concentrations of 0.345 (MF and 0.77 (MW μg/L for Cr and 0.153 (MF and 0.649 (MW μg/L for Pb, were determined. Levels of metal content (Cd, Cr and Pb in powder samples collected in both sampling sites were also higher than the suggested limits. Conclusion: The average concentration of Cr and Pb exceeded the limits recommended by the Occupational Safety and Health Administration and NIOSH for inhalable air in the workplace. Workers may be on risk of heavy metal occupational exposure. It is endorsed to implement safety measurements to avoid the breathing of contaminated air and also industrial level systems for dust and aerosol particle filtering or precipitation, altogether with stricter policies to regulate heavy metal exposure at these industries.

  1. Possible electronic entropy-driven mechanism for non-thermal ablation of metals

    Science.gov (United States)

    Tanaka, Yuta; Tsuneyuki, Shinji

    2018-04-01

    The physical mechanism of metal ablation induced by femtosecond laser irradiation was investigated in this study. Calculations based on finite-temperature density functional theory indicate that condensed copper becomes unstable at high electron temperatures due to an electronic entropy effect. Based on these results, an electronic entropy-driven mechanism is proposed to explain the metal ablation. Furthermore, a mathematical model is developed to simulate the ablation depth, where the effect of the electronic entropy is included. This mathematical model can quantitatively describe the experimental data in the low-laser-fluence region, where the electronic entropy effect is determined to be especially important.

  2. The chemical and mechanical behaviors of polymer / reactive metal systems under high strain rates

    Science.gov (United States)

    Shen, Yubin

    As one category of energetic materials, impact-initiated reactive materials are able to release a high amount of stored chemical energy under high strain rate impact loading, and are used extensively in civil and military applications. In general, polymers are introduced as binder materials to trap the reactive metal powders inside, and also act as an oxidizing agent for the metal ingredient. Since critical attention has been paid on the metal / metal reaction, only a few types of polymer / reactive metal interactions have been studied in the literature. With the higher requirement of materials resistant to different thermal and mechanical environments, the understanding and characterization of polymer / reactive metal interactions are in great demand. In this study, PTFE (Polytetrafluoroethylene) 7A / Ti (Titanium) composites were studied under high strain rates by utilizing the Taylor impact and SHPB tests. Taylor impact tests with different impact velocities, sample dimensions and sample configurations were conducted on the composite, equipped with a high-speed camera for tracking transient images during the sudden process. SHPB and Instron tests were carried out to obtain the stress vs. strain curves of the composite under a wide range of strain rates, the result of which were also utilized for fitting the constitutive relations of the composite based on the modified Johnson-Cook strength model. Thermal analyses by DTA tests under different flow rates accompanied with XRD identification were conducted to study the reaction mechanism between PTFE 7A and Ti when only heat was provided. Numerical simulations on Taylor impact tests and microstructural deformations were also performed to validate the constitutive model built for the composite system, and to investigate the possible reaction mechanism between two components. The results obtained from the high strain rate tests, thermal analyses and numerical simulations were combined to provide a systematic study on

  3. La compañía Finlandesa Outokumpu desarrollo y prensencia editorial en el sector minero-metalúrgico mexicano

    Directory of Open Access Journals (Sweden)

    Álvaro Sánchez Crispín

    1995-06-01

    Full Text Available This paper examines the territorial impact of the presence of the Finnish mining company, Outokumpu Oy. in the mining sector of Mexico. The papers describes the expansion of the company, beyond the limits of Finland, the development of mining technology achieved by Outokumpu Oy and how this derives into the selling of specific mining techniques and machinery to different countries, Mexico included. The final part of the paper deals with the issue of the territorial presence of Outokumpu Oy in the Mexican mines.

  4. ELECTROCHEMICAL STUDIES OF URANIUM METAL CORROSION MECHANISM AND KINETICS IN WATER

    International Nuclear Information System (INIS)

    Boudanova, Natalya; Maslennikov, Alexander; Peretroukhine, Vladimir F.; Delegard, Calvin H.

    2006-01-01

    During long-term underwater storage of low burn-up uranium metal fuel, a corrosion product sludge forms containing uranium metal grains, uranium dioxide, uranates and, in some cases, uranium peroxide. Literature data on the corrosion of non-irradiated uranium metal and its alloys do not allow unequivocal prediction of the paragenesis of irradiated uranium in water. The goal of the present work conducted under the program 'CORROSION OF IRRADIATED URANIUM ALLOYS FUEL IN WATER' is to study the corrosion of uranium and uranium alloys and the paragenesis of the corrosion products during long-term underwater storage of uranium alloy fuel irradiated at the Hanford Site. The elucidation of the physico-chemical nature of the corrosion of irradiated uranium alloys in comparison with non-irradiated uranium metal and its alloys is one of the most important aspects of this work. Electrochemical methods are being used to study uranium metal corrosion mechanism and kinetics. The present part of work aims to examine and revise, where appropriate, the understanding of uranium metal corrosion mechanism and kinetics in water

  5. Prediction of contact mechanics in metal-on-metal Total Hip Replacement for parametrically comprehensive designs and loads.

    Science.gov (United States)

    Donaldson, Finn E; Nyman, Edward; Coburn, James C

    2015-07-16

    Manufacturers and investigators of Total Hip Replacement (THR) bearings require tools to predict the contact mechanics resulting from diverse design and loading parameters. This study provides contact mechanics solutions for metal-on-metal (MoM) bearings that encompass the current design space and could aid pre-clinical design optimization and evaluation. Stochastic finite element (FE) simulation was used to calculate the head-on-cup contact mechanics for five thousand combinations of design and loading parameters. FE results were used to train a Random Forest (RF) surrogate model to rapidly predict the contact patch dimensions, contact area, pressures and plastic deformations for arbitrary designs and loading. In addition to widely observed polar and edge contact, FE results included ring-polar, asymmetric-polar, and transitional categories which have previously received limited attention. Combinations of design and load parameters associated with each contact category were identified. Polar contact pressures were predicted in the range of 0-200 MPa with no permanent deformation. Edge loading (with subluxation) was associated with pressures greater than 500 MPa and induced permanent deformation in 83% of cases. Transitional-edge contact (with little subluxation) was associated with intermediate pressures and permanent deformation in most cases, indicating that, even with ideal anatomical alignment, bearings may face extreme wear challenges. Surrogate models were able to accurately predict contact mechanics 18,000 times faster than FE analyses. The developed surrogate models enable rapid prediction of MoM bearing contact mechanics across the most comprehensive range of loading and designs to date, and may be useful to those performing bearing design optimization or evaluation. Published by Elsevier Ltd.

  6. Injection-Molded Soft Magnets Prepared from Fe-Based Metallic Glass: Mechanical and Magnetic Properties

    Science.gov (United States)

    Zhong, Tian; Huang, Ran; Huang, Jia; Ouyang, Wei

    2015-10-01

    The injection-molded metallic glass soft magnet is prepared from the powder of melt-spun ribbon of Fe36Co36B20Si4Nb4 glassy alloy and Nylon 6,6 of wt.% from 5 to 20 via the polymer injection molding technology. The product is characterized by the SEM, mechanical, and magnetic test. The results indicate that this type of materials has comparable mechanical properties and morphological feature with the conventional injection-molded NdFeB magnet and exhibits excellent soft magnetic behaviors. The magnetic properties of the injected magnets are compared with the raw metallic glass, solvent-casted resin bonding magnets, and thermal-treated magnets to confirm that the processing temperature of Nylon injection does not affect the magnetism. The injection technology is a practical processing method to be applied on the metallic glass for potential usage.

  7. Experimental Investigation on Corrosion Effect on Mechanical Properties of Buried Metal Pipes

    OpenAIRE

    Hou, Yingbo; Lei, Deqing; Li, Shujin; Yang, Wei; Li, Chun-Qing

    2016-01-01

    Corrosion has been found to be the most predominant cause for failures of buried metal pipes. A review of published literature on pipe corrosion reveals that little research has been undertaken on the effect of corrosion on mechanical properties of pipe materials and almost no research has been conducted on corrosion effect on fracture toughness. The intention of this paper is to present a comprehensive test program designed to investigate the effect of corrosion on mechanical properties of m...

  8. Transition absorption as a mechanism of surface photoelectron emission from metals

    DEFF Research Database (Denmark)

    Zhukovsky, Sergei; Protsenko, Igor E.; Ikhsanov, Renat Sh

    2015-01-01

    Transition absorption of a photon by an electron passingthrough a boundary between two media with different permit-tivities is described both classically and quantum mechani-cally. Transition absorption is shown to make a substantialcontribution to photoelectron emission at a metal....../semicon-ductor interface in nanoplasmonic systems, and is put forth asa possible microscopic mechanism of the surface photoelec-tric effect in photodetectors and solar cells containing plas-monic nanoparticles....

  9. Effect of metallic dopants on the microstructure and mechanical properties of TiB2

    Czech Academy of Sciences Publication Activity Database

    Chlup, Zdeněk; Bača, L.; Halasová, Martina; Neubauer, E.; Hadraba, Hynek; Stelzer, N.; Roupcová, Pavla

    2015-01-01

    Roč. 35, č. 10 (2015), s. 2745-2754 ISSN 0955-2219 R&D Projects: GA ČR(CZ) GAP108/11/1644; GA MŠk(CZ) ED1.1.00/02.0068 Grant - others:The Austrian Research Promotion Agency (FFG)(AT) 834287 Institutional support: RVO:68081723 Keywords : Titanium diboride * Metallic dopants * Microstructure * Mechanical properties * Fracture behaviour1 Subject RIV: JL - Materials Fatigue, Friction Mechanics Impact factor: 2.933, year: 2015

  10. Mechanical properties of permeable materials with an organized structure on the base of continuous metal fibers

    International Nuclear Information System (INIS)

    Karpinos, D.M.; Rutkovskij, A.E.; Zorin, V.A.; Ivanchuk, A.A.

    1979-01-01

    The mechanical properties were studied for permeable fibrous materials with an organized structure on the base of continuous metal fibers (from Kh18N9T steel) subjected to preliminary reprocessing volumetric net half-finished products. The effect of geometrical parameters of the net half-finished products and of their orientation in packing are shown to affect the mechanical properties within a wide range of porosities

  11. Thermal crackling: study of the mechanical effects of quick temperature fluctuations on metallic surfaces

    International Nuclear Information System (INIS)

    Pradel, P.

    1984-05-01

    After a brief overview of the thermohydraulical conditions of liquid sodium leading to important temperature fluctuations near the metallic surfaces, the author examines the transfer modes of these fluctuations in the structure thickness and the long term mechanical effects. Dimensioning models based on thermal and metallurgical properties are under study for structures subject to such sodium loads [fr

  12. The mechanical properties of thin alumina film deposited by metal-organic chemical vapour deposition

    NARCIS (Netherlands)

    Haanappel, V.A.C.; Haanappel, V.A.C.; Gellings, P.J.; van de Vendel, D.; Metselaar, H.S.C.; van Corbach, H.D.; Fransen, T.

    1995-01-01

    Amorphous alumina films were deposited by metal-organic chemical vapour deposition (MOCVD) on stainless steel, type AISI 304. The MOCVD experiments were performed in nitrogen at low and atmospheric pressures. The effects of deposition temperature, growth rate and film thickness on the mechanical

  13. Mechanisms of energetic efficiency in the transportation sector: environmental impacts and reflections in final energy consumption: PNE 2030; Mecanismos de eficiencia energetica no setor de transportes: impactos ambientais e os reflexos no consumo final de energia: PNE 2030

    Energy Technology Data Exchange (ETDEWEB)

    Berni, Mauro Donizeti [Universidade Estadual de Campinas (NIPE/UNICAMP), SP (Brazil). Nucleo Interdisciplinar de Planejamento Energetico], email: mauro_berni@nipeunicamp.org.br; Dorileo, Ivo Leandro [Universidade Federal do Mato Grosso (NIEPE/UFMT), Cuiaba, MT (Brazil). Nucleo Interdisciplinar de Estudos em Planejamento Energetico; Perez, Andrea Juliana Ortiz [Universidade Estadual de Campinas (DE/FEM/UNICAMP), SP (Brazil). Dept. de Energia. Fac. de Engenharia Mecanica; Paccola, Jose Angelo; Silva Junior, Herculano Xavier da; Bernardes, Cyro Barbosa [MCPAR Engenharia, Campinas, SP (Brazil)

    2010-07-01

    This work presents an energy efficiency mechanisms analysis in the Brazilian transport sector. Significant energy savings can be made in this sector and rely on urgent widespread implementation of mechanisms. The experience of the developed countries serves as base for the critical evaluation of the Brazilian situation, considering the current technological period, the investments and initiatives to reduce CO{sub 2} emissions. (author)

  14. Mechanism of the inhibition of milk xanthine oxidase activity by metal ions: a transient kinetic study.

    Science.gov (United States)

    Mondal, M S; Sau, A K; Mitra, S

    2000-07-14

    The nature and mechanism of the inhibition of the oxidoreductase activity of milk xanthine oxidase (XO) by Cu(2+), Hg(2+) and Ag(+) ions has been studied by steady state and stopped flow transient kinetic measurements. The results show that the nature of the inhibition is noncompetitive. The inhibition constants for Cu(2+) and Hg(2+) are in the micromolar and that for Ag(+) is in the nanomolar range. This suggests that the metal ions have strong affinity towards XO. pH dependence studies of the inhibition indicate that at least two ionisable groups of XO are involved in the binding of these metal ions. The effect of the interaction of the metal ions on the reductive and oxidative half reactions of XO has been investigated, and it is observed that the kinetic parameters of the reductive half reaction are not affected by these metal ions. However, the interaction of these metal ions with XO significantly affects the kinetic parameters of the oxidative half reaction. It is suggested that this may be the main cause for the inhibition of XO activity by the metal ions.

  15. Research into mechanical properties and structure of metals as part of restored construction facilities

    Directory of Open Access Journals (Sweden)

    Gustov Yuriy Ivanovich

    2014-12-01

    Full Text Available The article represents a summarized methodology of the research into small-size pilot metal samples of restored construction facilities. In the article, the co-authors demonstrate an option that provides for the analytical identification of standard characteristic values of mechanical properties, based on initial hardness HRB and conversion of hardness values using the Brinell test. Towards this end, analytical dependence of HB hardness on HRB and HRC is proposed. The numerical identification of the temporary resistance to tensile stress σ в required the pre-setting of the value of the average coefficient of relative elongation. This average coefficient was employed to identify the values of relative elongation and contraction, as well as the yield value of the metal. Standard plasticity and strength values were employed to compile an equation for complex criterion C. This criterion was employed to identify the value of relative uniform elongation and transverse contraction, and both were employed to assess the resistance to tensile stress and fatigue. The optical microscopy method was used to identify the pilot sample of the metal as structural carbon steel having grade C15. Its strength analysis based on the properties of its structural components has proven the identity between the sample metal and the aforementioned steel grade. The method proposed by the co-authors helps to identify the metals of restructured construction facilities on the basis of small-size samples to avoid the collapse of metal structures.

  16. Mechanisms of metal tolerance in marine macroalgae, with emphasis on copper tolerance in Chlorophyta and Rhodophyta.

    Science.gov (United States)

    Moenne, Alejandra; González, Alberto; Sáez, Claudio A

    2016-07-01

    Green and red macroalgae are closely related organisms, and with terrestrial plants, and constitute the base of marine food webs in coastal ecosystems. Green and red seaweeds, as all living organisms, require essential metals, such as copper, iron, zinc, which can act as co-factors for several proteins and enzymes; however, these metals in excess can induce stress and impair cell viability. Most important negative effects of metal excess are related to the induction of an oxidative stress condition, characterized by the over-accumulation of Reactive Oxygen Species (ROS). In this respect, copper, abundant in wastewaters disposed to coastal environments from domestic and industrial activities, has been one of the most studied metals. Different investigations have provided evidence that green and red macroalgae display several defenses against copper excess to prevent, or at least reduce, stress and damage, among which are cellular exclusion mechanisms, synthesis of metal-chelating compounds, and the activation of the antioxidant system. Most important defense mechanisms identified in green and red seaweed involve: metal-binding to cell wall and epibionts; syntheses of metallothioneins and phytochelatins that accumulate in the cytoplasm; and the increase in the activity of antioxidant enzymes such as superoxide dismutase, ascorbate peroxidase, glutathione peroxidase and catalase, and greater production of antioxidant metabolites as glutathione and ascorbate in organelles and the cytoplasm. In this review, we go through historical records, latest advances, and pending tasks aiming to expand our current knowledge on defense mechanisms to copper excess in green and red macroalgae, with emphasis on biochemical and molecular aspects. Copyright © 2016 Elsevier B.V. All rights reserved.

  17. A constitutive model of nanocrystalline metals based on competing grain boundary and grain interior deformation mechanisms

    KAUST Repository

    Gurses, Ercan

    2011-12-01

    In this work, a viscoplastic constitutive model for nanocrystalline metals is presented. The model is based on competing grain boundary and grain interior deformation mechanisms. In particular, inelastic deformations caused by grain boundary diffusion, grain boundary sliding and dislocation activities are considered. Effects of pressure on the grain boundary diffusion and sliding mechanisms are taken into account. Furthermore, the influence of grain size distribution on macroscopic response is studied. The model is shown to capture the fundamental mechanical characteristics of nanocrystalline metals. These include grain size dependence of the strength, i.e., both the traditional and the inverse Hall-Petch effects, the tension-compression asymmetry and the enhanced rate sensitivity. © 2011 Elsevier B.V. All rights reserved.

  18. Evaluation of mechanical properties of aluminium alloy–alumina–boron carbide metal matrix composites

    International Nuclear Information System (INIS)

    Vijaya Ramnath, B.; Elanchezhian, C.; Jaivignesh, M.; Rajesh, S.; Parswajinan, C.; Siddique Ahmed Ghias, A.

    2014-01-01

    Highlights: • Fabrication of MMC with aluminium alloy–alumina–boron carbide is done. • Different proportions of reinforcements are added. • The effects of varying proportions are studied. • Investigation on mechanical properties above composites is performed. • Failure morphology analysis is done using SEM. - Abstract: This paper deals with the fabrication and mechanical investigation of aluminium alloy, alumina (Al 2 O 3 ) and boron carbide metal matrix composites. Aluminium is the matrix metal having properties like light weight, high strength and ease of machinability. Alumina which has better wear resistance, high strength, hardness and boron carbide which has excellent hardness and fracture toughness are added as reinforcements. Here, the fabrication is done by stir casting which involves mixing the required quantities of additives into stirred molten aluminium. After solidification, the samples are prepared and tested to find the various mechanical properties like tensile, flexural, impact and hardness. The internal structure of the composite is observed using Scanning Electron Microscope (SEM)

  19. Environmental reactions and their effects on mechanical behavior of metallic materials. Technical progress report, February 1, 1977--January 31, 1978

    International Nuclear Information System (INIS)

    Gibala, R.; Sethi, V.K.; Fournier, R.

    1977-01-01

    New results obtained in surface oxide softening of the Group VB refractory metals and mechanical behavior of Nb-H and Nb-D alloys are presented. The results include: (a) experimental verification of a model of surface oxide softening of body-centered cubic metals; (b) determination of a stress-differential effect in surface oxide softening; and (c) characterization of hydrogen and deuterium strengthening in Nb and Nb-O alloys. The second section reviews major contributions in topics on: interstitials in metals, mechanical behavior of body-centered cubic metals, solute-defect interactions and internal friction mechanisms in solids

  20. Metallic particles into mechanical and hydraulic systems in agricultural and construction machines

    Energy Technology Data Exchange (ETDEWEB)

    Silva, Jair Rosas da; Silva, Deise Paula da [Instituto Agronomico de Campinas (IAC), Campinas, SP (Brazil). Centro de Engenharia Agricola; Bormio, Marcos Roberto [Universidade Estadual Paulista (UNESP), Bauru, SP (Brazil). Fac. de Engenharia

    2008-07-01

    The lubricant oil analysis are an indicator of the conditions how the lubricant is, may to allow the prevision of damages that occurred into machine due to the internal abrasion of hydraulic and mechanical components of the machines. The present study had the objective to determine the kind and quantity of the metallic particles that occurred into the lubricant oil of the mechanical and hydraulic compartments of the energy transmission systems of three kinds of machines: a tracked-tractor, a sugarcane harvester and a group of power-shovels. The metallic particles presents into these compartments were determined under laboratory tests and concerning to the following elements: iron, copper, chromium, lead, nickel, aluminum, silex, tin and molybdenum. About to the tracked-tractor, the metallic contaminators into to the oil charges surpasses the tolerate levels, considering the technical standards adopted in this evaluation. In the sugarcane harvester only a metallic element in excess was identified and, in a power-shovel group it was showed the need to correct air false entrances in the hydraulic or mechanical systems due the high presence of silex element. (author)

  1. Synthesis and mechanical properties of Fe–Nb–B thin-film metallic glasses

    International Nuclear Information System (INIS)

    Yao, J.H.; Hostert, C.; Music, D.; Frisk, A.; Björck, M.; Schneider, J.M.

    2012-01-01

    Fe–Nb–B thin-film metallic glasses (TFMGs) were synthesized via a combinatorial sputtering approach to probe the property–composition correlation. The boron content was found to dominate the mechanical properties of the TFMGs. The ∼10% smaller strength of Fe–Nb–B TFMGs compared to existing bulk metallic glass with similar composition may be attributed to the absence of a network-like structure based on (Fe,M) 23 B 6 phase due to the extreme quenching conditions employed.

  2. Microstructure and mechanical properties of metallic high-temperature materials. Research report

    International Nuclear Information System (INIS)

    Mughrabi, H.; Gottstein, G.; Mecking, H.; Riedel, H.; Toboloski, J.

    1999-01-01

    This volume contains 38 lectures of research studies performed in the course of the Priority Programme 'Microstructure and Mechanical Properties of Metallic High-Temperature Materials' supported by the Deutsche Forschungsgemeinschaft (DFG) over a period of six years from 1991 to 1997. The four materials selected were: 1. light metal PM-aluminium and titanium base alloys; 2. ferritic chromium and austenitic alloy 800 steels; 3. (monocrystalline) nickel-base superalloys; and 4. nickel- and iron-base oxide-dispersion-strengthened superalloys. All papers have been abstracted separately for the ENERGY database

  3. 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.

  4. The State Investment and Innovation Policy for Development of Forest Sector: the Ecological-Economic Aspects and Mechanisms for Implementation

    Directory of Open Access Journals (Sweden)

    Dzyubenko Oleksandr M.

    2017-09-01

    Full Text Available he need for formation of the State investment and innovation policy for development of forest sector has been substantiated as an important prerequisite for overcoming investment deficits in both the public and the corporate sectors of forest and wood processing production. The main tendencies in the implementation of capital investments by the entities of forestry entrepreneurship, dynamics of involvement of credit resources by forestry enterprises, and shifts in the structure of capital investments in 2016 were analyzed as compared to 2013. It has been found that an important part of the State investment and innovation policy for development of forest sector should be incentives to accelerate the modernization and upgrading of the material-technical base of lumbering and wood processing. The need to form an institutional framework for partnership between the State and business entities in the part of financing the projects of modernization of lumbering and wood processing equipment has been substantiated.

  5. An instrument to measure mechanical up-conversion phenomena in metals in the elastic regime.

    Science.gov (United States)

    Vajente, G; Quintero, E A; Ni, X; Arai, K; Gustafson, E K; Robertson, N A; Sanchez, E J; Greer, J R; Adhikari, R X

    2016-06-01

    Crystalline materials, such as metals, are known to exhibit deviation from a simple linear relation between strain and stress when the latter exceeds the yield stress. In addition, it has been shown that metals respond to varying external stress in a discontinuous way in this regime, exhibiting discrete releases of energy. This crackling noise has been extensively studied both experimentally and theoretically when the metals are operating in the plastic regime. In our study, we focus on the behavior of metals in the elastic regime, where the stresses are well below the yield stress. We describe an instrument that aims to characterize non-linear mechanical noise in metals when stressed in the elastic regime. In macroscopic systems, this phenomenon is expected to manifest as a non-stationary noise modulated by external disturbances applied to the material, a form of mechanical up-conversion of noise. The main motivation for this work is for the case of maraging steel components (cantilevers and wires) in the suspension systems of terrestrial gravitational wave detectors. Such instruments are planned to reach very ambitious displacement sensitivities, and therefore mechanical noise in the cantilevers could prove to be a limiting factor for the detectors' final sensitivities, mainly due to non-linear up-conversion of low frequency residual seismic motion to the frequencies of interest for the gravitational wave observations. We describe here the experimental setup, with a target sensitivity of 10(-15) m/Hz in the frequency range of 10-1000 Hz, a simple phenomenological model of the non-linear mechanical noise, and the analysis method that is inspired by this model.

  6. An instrument to measure mechanical up-conversion phenomena in metals in the elastic regime

    Science.gov (United States)

    Vajente, G.; Quintero, E. A.; Ni, X.; Arai, K.; Gustafson, E. K.; Robertson, N. A.; Sanchez, E. J.; Greer, J. R.; Adhikari, R. X.

    2016-06-01

    Crystalline materials, such as metals, are known to exhibit deviation from a simple linear relation between strain and stress when the latter exceeds the yield stress. In addition, it has been shown that metals respond to varying external stress in a discontinuous way in this regime, exhibiting discrete releases of energy. This crackling noise has been extensively studied both experimentally and theoretically when the metals are operating in the plastic regime. In our study, we focus on the behavior of metals in the elastic regime, where the stresses are well below the yield stress. We describe an instrument that aims to characterize non-linear mechanical noise in metals when stressed in the elastic regime. In macroscopic systems, this phenomenon is expected to manifest as a non-stationary noise modulated by external disturbances applied to the material, a form of mechanical up-conversion of noise. The main motivation for this work is for the case of maraging steel components (cantilevers and wires) in the suspension systems of terrestrial gravitational wave detectors. Such instruments are planned to reach very ambitious displacement sensitivities, and therefore mechanical noise in the cantilevers could prove to be a limiting factor for the detectors' final sensitivities, mainly due to non-linear up-conversion of low frequency residual seismic motion to the frequencies of interest for the gravitational wave observations. We describe here the experimental setup, with a target sensitivity of 10-15 m/ √{ Hz } in the frequency range of 10-1000 Hz, a simple phenomenological model of the non-linear mechanical noise, and the analysis method that is inspired by this model.

  7. Modernization perspectives of the Sao Paulo State sugarcane sector through the clean development mechanism and potential carbon credits generation

    Energy Technology Data Exchange (ETDEWEB)

    Coelho, Suani Teixeira; Lora, Beatriz Acquaro [Brazilian Reference Center on Biomass (CENBIO/USP), SP (Brazil)], Emails: suani@iee.usp.br, blora@iee.usp.br

    2009-07-01

    The world-wide necessity of greenhouse gases mitigation and the intergovernmental mobilization to reach the objectives established by the United Nations Framework on Climate Change (UNFCCC) has opened space for the renewable energy increase in the world's energy matrix. In Brazil, the solid sugarcane industry currently develops business in the scope of the clean development mechanism (CDM) under the Kyoto's Protocol, by means of 18 biomass-based projects, with renewable energy generation through bagasse cogeneration at 20 Sao Paulo State's sugarcane production units. The projects activity's consists of increasing the efficiency in the bagasse cogeneration facilities, qualifying the units to sell surplus electricity to the national grid, avoiding the dispatch of the same amount of energy produced by fossil-fuelled thermal plants to that grid. The reduced emissions are measured in carbon equivalent and can be converted into negotiable credits. The objective of this study was to build a 'state of art' scenario, calculating the potential emissions reduction through CDM projects for the sugarcane sector of Sao Paulo State, in which we consider the adherence of all the production units of the State to the CDM projects. The technological parameters used to elaborate the scenario were provided by the Sao Paulo State Government Bioenergy Special Commission and the baseline factor used of 0,268 tCO{sub 2}e/MWh was the adopted by the CDM projects in operation in the State. The sugarcane database for the calculations was the production ranking provided by UNICA for the 2006/2007 season. In the most conservative scenario (40 bar bagasse) 131 units could generate 607 MWm of surplus power avoiding the emission of 1.404.593 tCO{sub 2}e/year. For the 92 bar (bagasse and straw) scenario, the units could generate 3.055 MWm of surplus power avoiding 12.199.443 tCO{sub 2}e/year. (author)

  8. A new type of sandwich panel with periodic cellular metal cores and its mechanical performances

    International Nuclear Information System (INIS)

    Lim, Chae-Hong; Jeon, Insu; Kang, Ki-Ju

    2009-01-01

    Many studies have been performed on the mechanical properties and optimization of truss PCMs (periodic cellular metals), but those on the fabrication process, which is one of key factors determining the survivability of PCMs in the market, have been relatively limited. This study introduces a new idea on the fabrication of quasi Kagome truss cored sandwich panels, which is based on the expanded-metal process. And the mechanical behavior of the sandwich panels is to be evaluated. The mechanical strengths and failure mechanisms under compression and bending load are estimated based on elementary mechanics of materials, and the optimal design is derived. Its validity is proved by comparison with the results of experiments. The results showed that the new idea is promising with respect to all three requirements, i.e., the morphology, fabrication cost, and raw materials. The simple mechanical analysis was sufficiently effective and accurate for estimating the performance and failure mode of the sandwich panels. In the experiments, sandwich panel specimens of three different designs were compared in their bending behaviors to demonstrate sensitivity of geometric parameters. Namely, although all the designs had little difference in their load capacity-per-weight, the failure mechanisms and the behaviors after a peak load were totally different.

  9. Effects of holding pressure and process temperatures on the mechanical properties of moulded metallic parts

    DEFF Research Database (Denmark)

    Islam, Aminul; Hansen, Hans Nørgaard; Esteves, N.M.

    2013-01-01

    Metal injection moulding is gaining more and more importance over the time and needs more research to be done to understand the sensitivity of process to different process parameters. The current paper makes an attempt to better understand the effects of holding pressure and process temperatures...... on the moulded metallic parts. Stainless steel 316L is used in the investigation to produce the specimen by metal injection moulding (MIM) and multiple analyses were carried out on samples produced with different combinations of holding pressure, mould temperature and melt temperature. Finally, the parts were...... characterized to investigate mechanical properties like density, ultimate tensile strength, shrinkage etc. The results are discussed in the paper. The main conclusion from this study is unlike plastic moulding, the tensile properties of MIM parts doesn’t vary based on the flow direction of the melt, and tensile...

  10. Microscopic mechanism and numerical calculation of electroplastic effect on metal's flow stress

    International Nuclear Information System (INIS)

    Li, Dalong; Yu, Enlin; Liu, Zhoutong

    2013-01-01

    Based on the quantum theory and dislocation thermally activated plastic flow concept, the mechanism of electroplastic effect will be studied at a microscopic level. From the perspective of energy exchange between free electrons and metallic ions, the change in free energy of dislocation can be calculated using the quantum theory. According to the thermally activated strain rate equations, the relationship between electric current and strain rate could then be obtained. Eventually a new analytical formulation for the determination of flow stress in the electroplastic forming process will be derived to address the effect of electric current on the plastic deformation of metals. The results of this paper will help establish solid theoretical foundation for the accurate prediction of electroplastic forming process of metals

  11. Impact of silver metallization and electron irradiation on the mechanical deformation of polyimide films

    Science.gov (United States)

    Muradov, A. D.; Mukashev, K. M.; Yar-Mukhamedova, G. Sh.; Korobova, N. E.

    2017-11-01

    The impact of silver metallization and electron irradiation on the physical and mechanical properties of polyimide films has been studied. The metal that impregnated the structure of the polyimide substrate was 1-5 μm. The surface coatings contained 80-97% of the relative silver mirror in the visible and infrared regions. Irradiation was performed at the ELU-6 linear accelerator with an average beam electron energy of 2 MeV, an integral current of up to 1000 μA, a pulse repetition rate of 200 Hz, and a pulse duration of 5 μs. The absorbed dose in the samples was 10, 20, 30, and 40 MGy. The samples were deformed at room temperature under uniaxial tension on an Instron 5982 universal testing system. The structural changes in the composite materials that result from the impact of the physical factors were studied using an X-ray diffractometer DRON-2M in air at 293 K using Cu K α radiation (λαCu = 1.5418 Å). A substantial growth of mechanical characteristics resulting from the film metallization, as compared to the pure film, was observed. The growth of the ultimate strength by Δσ = 105 MPa and the plasticity by Δɛ = 75% is connected with the characteristics of the change of structure of the metallized films and the chemical etching conditions. The electron irradiation of the metallized polyimide film worsens its elastic and strength characteristics due to the formation of new phases in the form of silver oxide in the coating. The concentration of these phases increased with increasing dose, which was also the result of the violation of the ordered material structure, namely, the rupture of polyimide macromolecule bonds and the formation of new phases of silver in the coating. A mathematical model was obtained that predicts the elastic properties of silver metallized polyimide films. This model agrees with the experimental data.

  12. Label-free histamine detection with nanofluidic diodes through metal ion displacement mechanism.

    Science.gov (United States)

    Ali, Mubarak; Ramirez, Patricio; Duznovic, Ivana; Nasir, Saima; Mafe, Salvador; Ensinger, Wolfgang

    2017-02-01

    We design and characterize a nanofluidic device for the label-free specific detection of histamine neurotransmitter based on a metal ion displacement mechanism. The sensor consists of an asymmetric polymer nanopore fabricated via ion track-etching technique. The nanopore sensor surface having metal-nitrilotriacetic (NTA-Ni 2+ ) chelates is obtained by covalent coupling of native carboxylic acid groups with N α ,N α -bis(carboxymethyl)-l-lysine (BCML), followed by exposure to Ni 2+ ion solution. The BCML immobilization and subsequent Ni 2+ ion complexation with NTA moieties change the surface charge concentration, which has a significant impact on the current-voltage (I-V) curve after chemical modification of the nanopore. The sensing mechanism is based on the displacement of the metal ion from the NTA-Ni 2+ chelates. When the modified pore is exposed to histamine solution, the Ni 2+ ion in NTA-Ni 2+ chelate recognizes histamine through a metal ion coordination displacement process and formation of stable Ni-histamine complexes, leading to the regeneration of metal-free NTA groups on the pore surface, as shown in the current-voltage characteristics. Nanomolar concentrations of the histamine in the working electrolyte can be detected. On the contrary, other neurotransmitters such as glycine, serotonin, gamma-aminobutyric acid, and dopamine do not provoke significant changes in the nanopore electronic signal due to their inability to displace the metal ion and form a stable complex with Ni 2+ ion. The nanofluidic sensor exhibits high sensitivity, specificity and reusability towards histamine detection and can then be used to monitor the concentration of biological important neurotransmitters. Copyright © 2016 Elsevier B.V. All rights reserved.

  13. Mechanical and metallurgical properties of dissimilar metal joints using novel joining techniques

    Science.gov (United States)

    Ashcroft, Emma Jane

    In recent years there have been significant new developments in welding processes for joining stainless steel and dissimilar metals. This is associated with the rise in interest of using stainless steel in the automotive industry from both car manufacturers and stainless steel producers. The main reason for using stainless steel within the automotive industry is the combination of formability and high strength but also the improved corrosion resistance when compared to zinc coated mild steel. This research explores the mechanical and metallurgical properties of dissimilar metal joining and determines a relationship between the fatigue properties and weld geometry. The research focuses on the relatively unexplored joining techniques of Laser Hybrid Welding and Cold Metal Transfer applied to joining stainless steel grades Hy-Tens 1000 and LDX 2101 to Dogal 260RP-X mild steel. The joints are assessed in terms of tensile, fatigue and metallurgical properties. Experimental results and analysis show that the fatigue properties of both laser hybrid welding and cold metal transfer joints are a linear relationship with a negative gradient to value of the root angle on the mild steel side of the joints, as the angle at the root decreases the fatigue life increases.It was found that when joining the material combinations outlined in this research with Laser Hybrid Welding the resulting solidified weld pool was chemically inhomogeneous. However, welds produced using Cold Metal Transfer resulted in a chemically homogenous weld pool and consistent microhardness. Comparisons with laser welding show that laser hybrid welding and cold metal transfer can produce joints with mechanical properties comparable to welding methods currently being used in the automotive industry, for example, laser welding.

  14. Bioremediation mechanisms of combined pollution of PAHs and heavy metals by bacteria and fungi: A mini review.

    Science.gov (United States)

    Liu, Shao-Heng; Zeng, Guang-Ming; Niu, Qiu-Ya; Liu, Yang; Zhou, Lu; Jiang, Lu-Hua; Tan, Xiao-Fei; Xu, Piao; Zhang, Chen; Cheng, Min

    2017-01-01

    In recent years, knowledge in regard to bioremediation of combined pollution of polycyclic aromatic hydrocarbons (PAHs) and heavy metals by bacteria and fungi has been widely developed. This paper reviews the species of bacteria and fungi which can tackle with various types of PAHs and heavy metals entering into environment simultaneously or successively. Microbial activity, pollutants bioavailability and environmental factors (e.g. pH, temperature, low molecular weight organic acids and humic acids) can all affect the bioremediation of PAHs and heavy metals. Moreover, this paper summarizes the remediation mechanisms of PAHs and heavy metals by microbes via elucidating the interaction mechanisms of heavy metals with heavy metals, PAHs/PAHs metabolites with PAHs and PAHs with heavy metals. Based on the above reviews, this paper also discusses the potential research needs for this field. Copyright © 2016 Elsevier Ltd. All rights reserved.

  15. Oxidation and metal-insertion in molybdenite surfaces: evaluation of charge-transfer mechanisms and dynamics

    Directory of Open Access Journals (Sweden)

    Shutthanandan V

    2008-06-01

    Full Text Available Abstract Molybdenum disulfide (MoS2, a layered transition-metal dichalcogenide, has been of special importance to the research community of geochemistry, materials and environmental chemistry, and geotechnical engineering. Understanding the oxidation behavior and charge-transfer mechanisms in MoS2 is important to gain better insight into the degradation of this mineral in the environment. In addition, understanding the insertion of metals into molybdenite and evaluation of charge-transfer mechanism and dynamics is important to utilize these minerals in technological applications. Furthermore, a detailed investigation of thermal oxidation behavior and metal-insertion will provide a basis to further explore and model the mechanism of adsorption of metal ions onto geomedia. The present work was performed to understand thermal oxidation and metal-insertion processes of molybdenite surfaces. The analysis was performed using atomic force microscopy (AFM, scanning electron microscopy (SEM, transmission electron microscopy (TEM, Rutherford backscattering spectrometry (RBS, and nuclear reaction analysis (NRA. Structural studies using SEM and TEM indicate the local-disordering of the structure as a result of charge-transfer process between the inserted lithium and the molybdenite layer. Selected area electron diffraction measurements indicate the large variations in the diffusivity of lithium confirming that the charge-transfer is different along and perpendicular to the layers in molybdenite. Thermal heating of molybenite surface in air at 400°C induces surface oxidation, which is slow during the first hour of heating and then increases significantly. The SEM results indicate that the crystals formed on the molybdenite surface as a result of thermal oxidation exhibit regular thin-elongated shape. The average size and density of the crystals on the surface is dependent on the time of annealing; smaller size and high density during the first one-hour and

  16. Decomposition Mechanism and Decomposition Promoting Factors of Waste Hard Metal for Zinc Decomposition Process (ZDP)

    Energy Technology Data Exchange (ETDEWEB)

    Pee, J H; Kim, Y J; Kim, J Y; Cho, W S; Kim, K J [Whiteware Ceramic Center, KICET (Korea, Republic of); Seong, N E, E-mail: pee@kicet.re.kr [Recytech Korea Co., Ltd. (Korea, Republic of)

    2011-10-29

    Decomposition promoting factors and decomposition mechanism in the zinc decomposition process of waste hard metals which are composed mostly of tungsten carbide and cobalt were evaluated. Zinc volatility amount was suppressed and zinc steam pressure was produced in the reaction graphite crucible inside an electric furnace for ZDP. Reaction was done for 2 hrs at 650 deg. C, which 100% decomposed the waste hard metals that were over 30 mm thick. As for the separation-decomposition of waste hard metals, zinc melted alloy formed a liquid composed of a mixture of {gamma}-{beta}1 phase from the cobalt binder layer (reaction interface). The volume of reacted zone was expanded and the waste hard metal layer was decomposed-separated horizontally from the hard metal. Zinc used in the ZDP process was almost completely removed-collected by decantation and volatilization-collection process at 1000 deg. C. The small amount of zinc remaining in the tungsten carbide-cobalt powder which was completely decomposed was fully removed by using phosphate solution which had a slow cobalt dissolution speed.

  17. Human topoisomerase IIα uses a two-metal-ion mechanism for DNA cleavage

    Science.gov (United States)

    Deweese, Joseph E.; Burgin, Alex B.; Osheroff, Neil

    2008-01-01

    The DNA cleavage reaction of human topoisomerase IIα is critical to all of the physiological and pharmacological functions of the protein. While it has long been known that the type II enzyme requires a divalent metal ion in order to cleave DNA, the role of the cation in this process is not known. To resolve this fundamental issue, the present study utilized a series of divalent metal ions with varying thiophilicities in conjunction with DNA cleavage substrates that replaced the 3′-bridging oxygen of the scissile bond with a sulfur atom (i.e. 3′-bridging phosphorothiolates). Rates and levels of DNA scission were greatly enhanced when thiophilic metal ions were included in reactions that utilized sulfur-containing substrates. Based on these results and those of reactions that employed divalent cation mixtures, we propose that topoisomerase IIα mediates DNA cleavage via a two-metal-ion mechanism. In this model, one of the metal ions makes a critical interaction with the 3′-bridging atom of the scissile phosphate. This interaction greatly accelerates rates of enzyme-mediated DNA cleavage, and most likely is needed to stabilize the leaving 3′-oxygen. PMID:18653531

  18. Low-temperature embrittlement and fracture of metals with different crystal lattices – Dislocation mechanisms

    Directory of Open Access Journals (Sweden)

    V.M. Chernov

    2016-12-01

    Full Text Available The state of a low-temperature embrittlement (cold brittleness and dislocation mechanisms for formation of the temperature of a ductile-brittle transition and brittle fracture of metals (mono- and polycrystals with various crystal lattices (BCC, FCC, HCP are considered. The conditions for their formation connected with a stress-deformed state and strength (low temperature yield strength as well as the fracture breaking stress and mobility of dislocations in the top of a crack of the fractured metal are determined. These conditions can be met for BCC and some HCP metals in the initial state (without irradiation and after a low-temperature damaging (neutron irradiation. These conditions are not met for FCC and many HCP metals. In the process of the damaging (neutron irradiation such conditions are not met also and the state of low-temperature embrittlement of metals is absent (suppressed due to arising various radiation dynamic processes, which increase the mobility of dislocations and worsen the strength characteristics.

  19. Atomic mechanism of shear localization during indentation of a nanostructured metal

    International Nuclear Information System (INIS)

    Sansoz, F.; Dupont, V.

    2007-01-01

    Shear localization is an important mode of deformation in nanocrystalline metals. However, it is very difficult to verify the existence of local shear planes in nanocrystalline metals experimentally. Sharp indentation techniques may provide novel opportunities to investigate the effect of shear localization at different length scales, but the relationship between indentation response and atomic-level shear band formation has not been fully addressed. This paper describes an effort to provide direct insight on the mechanism of shear localization during indentation of nanocrystalline metals from atomistic simulations. Molecular statics is performed with the quasi-continuum method to simulate the indentation of single crystal and nanocrystalline Al with a sharp cylindrical probe. In the nanocrystalline regime, two grain sizes are investigated, 5 nm and 10 nm. We find that the indentation of nanocrystalline metals is characterized by serrated plastic flow. This effect seems to be independent of the grain size. Serration in nanocrystalline metals is found to be associated with the formation of shear bands by sliding of aligned interfaces and intragranular slip, which results in deformation twinning

  20. Mechanism of Metal Ion Activation of the Diphtheria Toxin Repressor DtxR

    Energy Technology Data Exchange (ETDEWEB)

    D' Aquino,J.; Tetenbaum-Novatt, J.; White, A.; Berkovitch, F.; Ringe, D.

    2005-01-01

    The diphtheria toxin repressor (DtxR) is a metal ion-activated transcriptional regulator that has been linked to the virulence of Corynebacterium diphtheriae. Structure determination has shown that there are two metal ion binding sites per repressor monomer, and site-directed mutagenesis has demonstrated that binding site 2 (primary) is essential for recognition of the target DNA repressor, leaving the role of binding site 1 (ancillary) unclear. Calorimetric techniques have demonstrated that although binding site 1 (ancillary) has high affinity for metal ion with a binding constant of 2 x 10{sup -7}, binding site 2 (primary) is a low-affinity binding site with a binding constant of 6.3 x 10{sup -4}. These two binding sites act in an independent fashion, and their contribution can be easily dissected by traditional mutational analysis. Our results clearly demonstrate that binding site 1 (ancillary) is the first one to be occupied during metal ion activation, playing a critical role in stabilization of the repressor. In addition, structural data obtained for the mutants Ni-DtxR(H79A, C102D), reported here, and the previously reported DtxR(H79A) have allowed us to propose a mechanism of metal activation for DtxR.

  1. Heavy metal toxicity as a kill mechanism in impact caused mass extinctions

    Science.gov (United States)

    Wdowiak, T. J.; Davenport, S. A.; Jones, D. D.; Wdowiak, P.

    1988-01-01

    Heavy metals that are known to be toxic exist in carbonaceous chrondrites at abundances considerably in excess to that of the terrestrial crust. An impactor of relatively undifferentiated cosmic matter would inject into the terrestrial environment large quantities of toxic elements. The abundances of toxic metals found in the Allende CV carbonaceous chondrite and the ratio of meteoritic abundance to crustal abundance are: Cr, 3630 PPM, 30X; Co, 662 PPM, 23X; ni, 13300 PPm, 134X; se, 8.2 PPM, 164X; Os, 0.828 PPM, 166X. The resulting areal density for global dispersal of impactor derived heavy metals and their dilution with terrestrial ejecta are important factors in the determination of the significance of impactor heavy metal toxicity as a kill mechanism in impact caused mass extinctions. A 10 km-diameter asteroid having a density of 3 gram per cu cm would yield a global areal density of impact dispersed chondritic material of 3 kg per square meter. The present areal density of living matter on the terrestrial land surface is 1 kg per square meter. Dilution of impactor material with terrestrial ejecta is determined by energetics, with the mass of ejecta estimated to be in the range of 10 to 100 times that of the mass of the impactor. Because a pelagic impact would be the most likely case, the result would be a heavy metal rainout.

  2. Influence of deformation mechanisms on the mechanical behavior of metals and alloys: Experiments, constitutive modeling, and validation

    International Nuclear Information System (INIS)

    Gray, G.T. III; Cerreta, E.; Chen, S.R.; Maudlin, P.J.

    2004-01-01

    Jim Williams has made seminal contributions to the field of structure / property relations and its controlling effects on the mechanical behavior of metals and alloys. This talk will discuss experimental results illustrating the role of interstitial content, grain size, texture, temperature, and strain rate on the operative deformation mechanisms, mechanical behavior, and substructure evolution in titanium, zirconium, hafnium, and rhenium. Increasing grain size is shown to significantly decrease the dynamic flow strength of Ti and Zr while increasing work-hardening rates due to an increased incidence of deformation twinning. Increasing oxygen interstitial content is shown to significantly alter both the constitutive response and α-ω shock-induced phase transition in Zr. The influence of crystallographic texture on the mechanical behavior in Ti, Zr, and Hf is discussed in terms of slip system and deformation twinning activity. An example of the utility of incorporation of operative deformation mechanisms into a polycrystalline plasticity constitutive model and validation using Taylor cylinder impact testing is presented

  3. Mechanical properties of metals for biomedical applications using powder metallurgy process: A review

    Science.gov (United States)

    Dewidar, Montasser Marasy; Yoon, Ho-Chel; Lim, Jae Kyoo

    2006-06-01

    The uses of biomaterials have been revolutionizing the biomedical field in deployment as implants for humans. During the past five decades, many implant materials made of metals have been put into practical use. Powder metallurgy techniques have been used to produce controlled porous structures, such as porous coatings applied for dental and orthopedic surgical implants, which allow bony tissue ingrowth within the implant surface, thereby improving fixation. This paper examines various important metals using powder metallurgy technology to produce elements of a total hip replacement. These alloys are 316L stainless steel alloy, Co-Cr-Mo alloy, and Ti-6Al-4V alloy. Also, this paper examines current information on the mechanical properties. Mechanical properties are discussed as a function of type of materials and process of fabrication. This article addresses the engineering aspects concerning the advantages and disadvantages of each type of material.

  4. Agriculture Sectors

    Science.gov (United States)

    The Agriculture sectors comprise establishments primarily engaged in growing crops, raising animals, and harvesting fish and other animals. Find information on compliance, enforcement and guidance on EPA laws and regulations on the NAICS 111 & 112 sectors.

  5. STATISTICAL DISTRIBUTION PATTERNS IN MECHANICAL AND FATIGUE PROPERTIES OF METALLIC MATERIALS

    OpenAIRE

    Tatsuo, SAKAI; Masaki, NAKAJIMA; Keiro, TOKAJI; Norihiko, HASEGAWA; Department of Mechanical Engineering, Ritsumeikan University; Department of Mechanical Engineering, Toyota College of Technology; Department of Mechanical Engineering, Gifu University; Department of Mechanical Engineering, Gifu University

    1997-01-01

    Many papers on the statistical aspect of materials strength have been collected and reviewed by The Research Group for Statistical Aspects of Materials Strength.A book of "Statistical Aspects of Materials Strength" was written by this group, and published in 1992.Based on the experimental data compiled in this book, distribution patterns of mechanical properties are systematically surveyed paying an attention to metallic materials.Thus one can obtain the fundamental knowledge for a reliabilit...

  6. Mechanical behavior of polymer-based vs. metallic-based bioresorbable stents

    OpenAIRE

    Ang, Hui Ying; Huang, Ying Ying; Lim, Soo Teik; Wong, Philip; Joner, Michael; Foin, Nicolas

    2017-01-01

    Bioresorbable scaffolds (BRS) were developed to overcome the drawbacks of current metallic drug-eluting stents (DES), such as late in-stent restenosis and caging of the vessel permanently. The concept of the BRS is to provide transient support to the vessel during healing before being degraded and resorbed by the body, freeing the vessel and restoring vasomotion. The mechanical properties of the BRS are influenced by the choice of the material and processing methods. Due to insufficient radia...

  7. Hybrid Quantum Mechanics/Molecular Mechanics Solvation Scheme for Computing Free Energies of Reactions at Metal-Water Interfaces.

    Science.gov (United States)

    Faheem, Muhammad; Heyden, Andreas

    2014-08-12

    We report the development of a quantum mechanics/molecular mechanics free energy perturbation (QM/MM-FEP) method for modeling chemical reactions at metal-water interfaces. This novel solvation scheme combines planewave density function theory (DFT), periodic electrostatic embedded cluster method (PEECM) calculations using Gaussian-type orbitals, and classical molecular dynamics (MD) simulations to obtain a free energy description of a complex metal-water system. We derive a potential of mean force (PMF) of the reaction system within the QM/MM framework. A fixed-size, finite ensemble of MM conformations is used to permit precise evaluation of the PMF of QM coordinates and its gradient defined within this ensemble. Local conformations of adsorbed reaction moieties are optimized using sequential MD-sampling and QM-optimization steps. An approximate reaction coordinate is constructed using a number of interpolated states and the free energy difference between adjacent states is calculated using the QM/MM-FEP method. By avoiding on-the-fly QM calculations and by circumventing the challenges associated with statistical averaging during MD sampling, a computational speedup of multiple orders of magnitude is realized. The method is systematically validated against the results of ab initio QM calculations and demonstrated for C-C cleavage in double-dehydrogenated ethylene glycol on a Pt (111) model surface.

  8. A general mechanism for intracellular toxicity of metal-containing nanoparticles

    KAUST Repository

    Sabella, Stefania

    2014-04-09

    The assessment of the risks exerted by nanoparticles is a key challenge for academic, industrial, and regulatory communities worldwide. Experimental evidence points towards significant toxicity for a range of nanoparticles both in vitro and in vivo. Worldwide efforts aim at uncovering the underlying mechanisms for this toxicity. Here, we show that the intracellular ion release elicited by the acidic conditions of the lysosomal cellular compartment-where particles are abundantly internalized-is responsible for the cascading events associated with nanoparticles-induced intracellular toxicity. We call this mechanism a "lysosome-enhanced Trojan horse effect" since, in the case of nanoparticles, the protective cellular machinery designed to degrade foreign objects is actually responsible for their toxicity. To test our hypothesis, we compare the toxicity of similar gold particles whose main difference is in the internalization pathways. We show that particles known to pass directly through cell membranes become more toxic when modified so as to be mostly internalized by endocytosis. Furthermore, using experiments with chelating and lysosomotropic agents, we found that the toxicity mechanism for different metal containing NPs (such as metallic, metal oxide, and semiconductor NPs) is mainly associated with the release of the corresponding toxic ions. Finally, we show that particles unable to release toxic ions (such as stably coated NPs, or diamond and silica NPs) are not harmful to intracellular environments. The Royal Society of Chemistry 2014.

  9. Studies on microstructure, mechanical and corrosion properties of high nitrogen stainless steel shielded metal arc welds

    Science.gov (United States)

    Mohammed, Raffi; Madhusudhan Reddy, G.; Srinivasa Rao, K.

    2018-03-01

    The present work is aimed at studying the microstructure, mechanical and corrosion properties of high nitrogen stainless steel shielded metal arc (SMA) welds made with Cromang-N electrode. Basis for selecting this electrode is to increase the solubility of nitrogen in weld metal due to high chromium and manganese content. Microstructures of the welds were characterized using optical microscopy (OM), field emission scanning electron microscopy (FESEM) and electron back scattered diffraction (EBSD) mainly to determine the morphology, phase analysis, grain size and orientation image mapping. Hardness, tensile and ductility bend tests were carried out to determine mechanical properties. Potentio-dynamic polarization testing was carried out to study the pitting corrosion resistance using a GillAC basic electrochemical system. Constant load type testing was carried out to study stress corrosion cracking (SCC) behaviour of welds. The investigation results shown that the selected Cr–Mn–N type electrode resulted in favourable microstructure and completely solidified as single phase coarse austenite. Mechanical properties of SMA welds are found to be inferior when compared to that of base metal and is due to coarse and dendritic structure.

  10. A possibility of using mechanical alloying for developing metal matrix composites with light-weight reinforcements

    International Nuclear Information System (INIS)

    Popov, Vladimir A.; Zhizhin, Konstantin Yu.; Malinina, Elena A.; Ketsko, Valery A.; Kuznetsov, Nikolay T.

    2007-01-01

    A new type of metal matrix composite (MMC) with light-weight reinforcements from 10 types of boron-hydrogen compounds was prepared using the method of mechanical alloying. The boron-hydrogen compounds had a decomposition temperature higher than 500 o C and a density of 1.3-2.5 g/cm 3 . The initial size of particles was 50-500 μm. Aluminum and copper were used as the matrix materials. The reinforcements were 20-40 vol. % of the MMC. Mechanical alloying followed by compaction can yield a good-quality bulk material of reduced density

  11. A Study On The Metal Carbide Composite Diffusion Bonding For Mechanical Seal

    Directory of Open Access Journals (Sweden)

    Kim D.-K.

    2015-06-01

    Full Text Available Mechanical Seal use highly efficient alternative water having a great quantity of an aqueous solution and has an advantage no corrosion brine. Metal Carbide composites have been investigated as potential materials for high temperature structural applications and for application in the processing industry. The existing Mechanical seal material is a highly expensive carbide alloy, and it is difficult to take a price advantage. Therefore the study of replacing body area with inexpensive steel material excluding O-ring and contact area which demands high characteristics is needed.

  12. Stacking faults and mechanisms strain-induced transformations of hcp metals (Ti, Mg) during mechanical activation in liquid hydrocarbons

    Science.gov (United States)

    Lubnin, A. N.; Dorofeev, G. A.; Nikonova, R. M.; Mukhgalin, V. V.; Lad'yanov, V. I.

    2017-11-01

    The evolution of the structure and substructure of metals Ti and Mg with hexagonal close-packed (hcp) lattice is studied during their mechanical activation in a planetary ball mill in liquid hydrocarbons (toluene, n-heptane) and with additions of carbon materials (graphite, fullerite, nanotubes) by X-ray diffraction, scanning electron microscopy, and chemical analysis. The temperature behavior and hydrogen-accumulating properties of mechanocomposites are studied. During mechanical activation of Ti and Mg, liquid hydrocarbons decay, metastable nanocrystalline titanium carbohydride Ti(C,H) x and magnesium hydride β-MgH2 are formed, respectively. The Ti(C,H) x and MgH2 formation mechanisms during mechanical activation are deformation ones and are associated with stacking faults accumulation, and the formation of face-centered cubic (fcc) packing of atoms. Metastable Ti(C,H)x decays at a temperature of 550°C, the partial reverse transformation fcc → hcp occurs. The crystalline defect accumulation (nanograin boundaries, stacking faults), hydrocarbon destruction, and mechanocomposite formation leads to the enhancement of subsequent magnesium hydrogenation in the Sieverts reactor.

  13. Effects of different production technologies on mechanical and metallurgical properties of precious metal denture alloys

    Science.gov (United States)

    Ferro, Paolo; Battaglia, Eleonora; Capuzzi, Stefano; Berto, Filippo

    2017-12-01

    Precious metal alloys can be supplied in traditional plate form or innovative drop form with high degree of purity. The aim of the present work is to evaluate the influence of precious metal alloy form on metallurgical and mechanical properties of the final dental products with particular reference to metal-ceramic bond strength and casting defects. A widely used alloy for denture was selected; its nominal composition was close to 55 wt% Pd - 34 wt% Ag - 6 wt% In - 3 wt% Sn. Specimens were produced starting from the alloy in both plate and drop forms. A specific test method was developed to obtain results that could be representative of the real conditions of use. In order to achieve further information about the adhesion behaviour and resistance, the fracture surfaces of the samples were observed using `Scanning Electron Microscopy (SEM)'. Moreover, material defects caused by the moulding process were studied. The form of the alloy before casting does not significantly influence the shear bond strength between the metal and the ceramic material (p-value=0,976); however, according to SEM images, products from drop form alloy show less solidification defects compared to products obtained with plate form alloy. This was attributed to the absence of polluting additives used in the production of drop form alloy. This study shows that the use of precious metal denture alloys supplied in drop form does not affect the metal-ceramic bond strength compared to alloys supplied in the traditional plate form. However, compared to the plate form, the drop form is found free of solidification defects, less expensive to produce and characterized by minor environmental impacts.

  14. Mechanisms of trace metal sorption in Pseudomonas putida-birnessite assemblages

    Science.gov (United States)

    Peña, J.; Kwon, K. D.; Bargar, J. R.; Sposito, G.

    2012-04-01

    Biogenic manganese oxides (MnO2) are ubiquitous nanoparticulate minerals that contribute strongly to the adsorption of nutrient and toxicant metals in aquatic and terrestrial environments. The formation of these minerals is catalyzed by a diverse and widely-distributed group of bacteria and fungi, often through the enzymatic oxidation of aqueous Mn(II) to Mn(IV). The biogenic Mn(IV) oxide found in field settings, as well as that produced by model bacteria in laboratory culture, is typically layer-type hexagonal birnessite containing abundant cation vacancy sites and enmeshed in an organic matrix of bacterial cells and extracellular polymeric substances. In this talk I summarize the results from laboratory-scale research designed to investigate the mechanisms of metal sorption by the bacterial biomass-birnessite assemblages formed by Pseudomonas putida GB-1 when grown in the presence of 1 mM Mn(II) at circumneutral pH values. The goals of this research were first, to identify the structure of the surface complexes formed by trace metals (e.g., Ni, Cu and Zn) on biogenic birnessite and second, to determine the conditions under which the bacterial cell surfaces and extracellular polymeric substances contribute to metal sorption. Macroscopic and spectroscopic experiments were performed at varying pH values (6 - 8) and over a wide-range of metal concentrations. Extended X-ray absorption fine structure (EXAFS) spectroscopy and first-principles calculations based on density functional theory showed that cation vacancy sites in birnessite drive mineral reactivity, but that surface speciation varies from metal to metal. For, Ni we identified two species, Ni bonded to three surface oxygen atoms vacancy sites as a triple-corner-sharing (TCS) complex and Ni incorporated at vacancy sites, with surface speciation varying with pH and surface loading. Zinc formed TCS complexes at vacancy sites, with the proportion of Zn in tetrahedral or octahedral coordination geometry influenced

  15. Combined toxicity and underlying mechanisms of a mixture of eight heavy metals.

    Science.gov (United States)

    Zhou, Qi; Gu, Yuanliang; Yue, Xia; Mao, Guochuan; Wang, Yafei; Su, Hong; Xu, Jin; Shi, Hongbo; Zou, Baobo; Zhao, Jinshun; Wang, Renyuan

    2017-02-01

    With the rapid development of modernization and industrialization in China, a large quantity of heavy metals, including zinc, copper, lead, cadmium and mercury, have been entering the atmosphere, soil and water, the latter being the primary route of pollution. In the present study, in vitro experiments were performed to examine the joint toxicity and the underlying mechanisms of the eight most common heavy metals contaminating offshore waters on the eastern coast of Ningbo region. Using a cell cycle assay, cell apoptosis and reactive oxygen species (ROS) detection methods, the present study demonstrated that the heavy metal mixture arrested JB6 cells at the S phase, induced the generation of ROS and cell apoptosis. A luciferase assay indicated that the levels of activator protein‑1 and nuclear factor‑κB transcription factors were upregulated. Upregulation of the protein levels of C‑jun and p65 were detected in the JB6 cells by western blot analysis; these two genes have important roles in cell carcinogenesis. These results provide a useful reference for further investigations on the combined toxicity of the exposure to multiple heavy metals.

  16. Bacterial Exopolysaccharide mediated heavy metal removal: A Review on biosynthesis, mechanism and remediation strategies.

    Science.gov (United States)

    Gupta, Pratima; Diwan, Batul

    2017-03-01

    Heavy metal contamination has been recognized as a major public health risk, particularly in developing countries and their toxicological manifestations are well known. Conventional remediation strategies are either expensive or they generate toxic by-products, which adversely affect the environment. Therefore, necessity for an environmentally safe strategy motivates interest towards biological techniques. One of such most profoundly driven approach in recent times is biosorption through microbial biomass and their products. Extracellular polymeric substances are such complex blend of high molecular weight microbial (prokaryotic and eukaryotic) biopolymers. They are mainly composed of proteins, polysaccharides, uronic acids, humic substances, lipids etc. One of its essential constituent is the exopolysaccharide (EPS) released out of self defense against harsh conditions of starvation, pH and temperature, hence it displays exemplary physiological, rheological and physio-chemical properties. Its net anionic makeup allows the biopolymer to effectively sequester positively charged heavy metal ions. The polysaccharide has been expounded deeply in this article with reference to its biosynthesis and emphasizes heavy metal sorption abilities of polymer in terms of mechanism of action and remediation. It reports current investigation and strategic advancements in dealing bacterial cells and their EPS in diverse forms - mixed culture EPS, single cell EPS, live, dead or immobilized EPS. A significant scrutiny is also involved highlighting the existing challenges that still lie in the path of commercialization. The article enlightens the potential of EPS to bring about bio-detoxification of heavy metal contaminated terrestrial and aquatic systems in highly sustainable, economic and eco-friendly manner.

  17. Interface structure and mechanics between graphene and metal substrates: a first-principles study

    International Nuclear Information System (INIS)

    Xu Zhiping; Buehler, Markus J

    2010-01-01

    Graphene is a fascinating material not only for technological applications, but also as a test bed for fundamental insights into condensed matter physics due to its unique two-dimensional structure. One of the most intriguing issues is the understanding of the properties of graphene and various substrate materials. In particular, the interfaces between graphene and metal substrates are of critical importance in applications of graphene in integrated electronics, as thermal materials, and in electromechanical devices. Here we investigate the structure and mechanical interactions at a graphene-metal interface through density functional theory (DFT)-based calculations. We focus on copper (111) and nickel (111) surfaces adhered to a monolayer of graphene, and find that their cohesive energy, strength and electronic structure correlate directly with their atomic geometry. Due to the strong coupling between open d-orbitals, the nickel-graphene interface has a much stronger cohesive energy with graphene than copper. We also find that the interface cohesive energy profile features a well-and-shoulder shape that cannot be captured by simple pair-wise models such as the Lennard-Jones potential. Our results provide a detailed understanding of the interfacial properties of graphene-metal systems, and help to predict the performance of graphene-based nanoelectronics and nanocomposites. The availability of structural and energetic data of graphene-metal interfaces could also be useful for the development of empirical force fields for molecular dynamics simulations.

  18. A spin transition mechanism for cooperative adsorption in metal-organic frameworks

    Science.gov (United States)

    Reed, Douglas A.; Keitz, Benjamin K.; Oktawiec, Julia; Mason, Jarad A.; Runčevski, Tomče; Xiao, Dianne J.; Darago, Lucy E.; Crocellà, Valentina; Bordiga, Silvia; Long, Jeffrey R.

    2017-10-01

    Cooperative binding, whereby an initial binding event facilitates the uptake of additional substrate molecules, is common in biological systems such as haemoglobin. It was recently shown that porous solids that exhibit cooperative binding have substantial energetic benefits over traditional adsorbents, but few guidelines currently exist for the design of such materials. In principle, metal-organic frameworks that contain coordinatively unsaturated metal centres could act as both selective and cooperative adsorbents if guest binding at one site were to trigger an electronic transformation that subsequently altered the binding properties at neighbouring metal sites. Here we illustrate this concept through the selective adsorption of carbon monoxide (CO) in a series of metal-organic frameworks featuring coordinatively unsaturated iron(II) sites. Functioning via a mechanism by which neighbouring iron(II) sites undergo a spin-state transition above a threshold CO pressure, these materials exhibit large CO separation capacities with only small changes in temperature. The very low regeneration energies that result may enable more efficient Fischer-Tropsch conversions and extraction of CO from industrial waste feeds, which currently underutilize this versatile carbon synthon. The electronic basis for the cooperative adsorption demonstrated here could provide a general strategy for designing efficient and selective adsorbents suitable for various separations.

  19. Mechanical and Acoustic Characteristics of the Weld and the Base Metal Machine Part of Career Transport

    Science.gov (United States)

    Smirnov, Alexander N.; Knjaz'kov, Victor L.; Levashova, Elena E.; Ababkov, Nikolay V.; Pimonov, Maksim V.

    2018-01-01

    Currently, many industries use foreign-made machinery. There is no opportunity to purchase quality original spare parts for which machinery. Therefore, enterprises operating this equipment are looking for producers of analogues of various parts and assemblies. Quite often, the metal of such analog components turns out to be substandard, which leads to their breakdown at a much earlier date and the enterprises incur material losses. Due to the fact that the complex of performance characteristics and the resource of products are laid at the stage of their production, it is extremely important to control the quality of the raw materials. The structure, mechanical, acoustic and magnetic characteristics of metal samples of such destroyed details of quarry transport as hydraulic cylinders and detail “axis” of an excavator are investigated. A significant spread of data on the chemical composition of metal, hardness and characteristics of non-destructive testing is established, which gives grounds to recommend to manufacturers and suppliers of parts is more responsible to approach the incoming quality control. The results of the investigation of metal samples by destructive and non-destructive methods of control are compared, which showed that the spectral-acoustic method of nondestructive testing can be used to control the quality of the responsible machine parts under conditions of import substitution.

  20. Mechanical Fracturing of Core-Shell Undercooled Metal Particles for Heat-Free Soldering

    Science.gov (United States)

    Çınar, Simge; Tevis, Ian D.; Chen, Jiahao; Thuo, Martin

    2016-02-01

    Phase-change materials, such as meta-stable undercooled (supercooled) liquids, have been widely recognized as a suitable route for complex fabrication and engineering. Despite comprehensive studies on the undercooling phenomenon, little progress has been made in the use of undercooled metals, primarily due to low yields and poor stability. This paper reports the use of an extension of droplet emulsion technique (SLICE) to produce undercooled core-shell particles of structure; metal/oxide shell-acetate (‘/’ = physisorbed, ‘-’ = chemisorbed), from molten Field’s metal (Bi-In-Sn) and Bi-Sn alloys. These particles exhibit stability against solidification at ambient conditions. Besides synthesis, we report the use of these undercooled metal, liquid core-shell, particles for heat free joining and manufacturing at ambient conditions. Our approach incorporates gentle etching and/or fracturing of outer oxide-acetate layers through mechanical stressing or shearing, thus initiating a cascade entailing fluid flow with concomitant deformation, combination/alloying, shaping, and solidification. This simple and low cost technique for soldering and fabrication enables formation of complex shapes and joining at the meso- and micro-scale at ambient conditions without heat or electricity.

  1. Mechanical Fracturing of Core-Shell Undercooled Metal Particles for Heat-Free Soldering.

    Science.gov (United States)

    Çınar, Simge; Tevis, Ian D; Chen, Jiahao; Thuo, Martin

    2016-02-23

    Phase-change materials, such as meta-stable undercooled (supercooled) liquids, have been widely recognized as a suitable route for complex fabrication and engineering. Despite comprehensive studies on the undercooling phenomenon, little progress has been made in the use of undercooled metals, primarily due to low yields and poor stability. This paper reports the use of an extension of droplet emulsion technique (SLICE) to produce undercooled core-shell particles of structure; metal/oxide shell-acetate ('/' = physisorbed, '-' = chemisorbed), from molten Field's metal (Bi-In-Sn) and Bi-Sn alloys. These particles exhibit stability against solidification at ambient conditions. Besides synthesis, we report the use of these undercooled metal, liquid core-shell, particles for heat free joining and manufacturing at ambient conditions. Our approach incorporates gentle etching and/or fracturing of outer oxide-acetate layers through mechanical stressing or shearing, thus initiating a cascade entailing fluid flow with concomitant deformation, combination/alloying, shaping, and solidification. This simple and low cost technique for soldering and fabrication enables formation of complex shapes and joining at the meso- and micro-scale at ambient conditions without heat or electricity.

  2. Wear Behavior of Mechanically Alloyed Ti-Based Bulk Metallic Glass Composites Containing Carbon Nanotubes

    Directory of Open Access Journals (Sweden)

    Yung-Sheng Lin

    2016-11-01

    Full Text Available The present paper reports the preparation and wear behavior of mechanically alloyed Ti-based bulk metallic glass composites containing carbon nanotube (CNT particles. The differential scanning calorimeter results show that the thermal stability of the amorphous matrix is affected by the presence of CNT particles. Changes in glass transition temperature (Tg and crystallization temperature (Tx suggest that deviations in the chemical composition of the amorphous matrix occurred because of a partial dissolution of the CNT species into the amorphous phase. Although the hardness of CNT/Ti50Cu28Ni15Sn7 bulk metallic glass composites is increased with the addition of CNT particles, the wear resistance of such composites is not directly proportional to their hardness, and does not follow the standard wear law. A worn surface under a high applied load shows that the 12 vol. % CNT/Ti50Cu28Ni15Sn7 bulk metallic glass composite suffers severe wear compared with monolithic Ti50Cu28Ni15Sn7 bulk metallic glass.

  3. The mechanism of formate oxidation by metal-dependent formate dehydrogenases.

    Science.gov (United States)

    Mota, Cristiano S; Rivas, Maria G; Brondino, Carlos D; Moura, Isabel; Moura, José J G; González, Pablo J; Cerqueira, Nuno M F S A

    2011-12-01

    Metal-dependent formate dehydrogenases (Fdh) from prokaryotic organisms are members of the dimethyl sulfoxide reductase family of mononuclear molybdenum-containing and tungsten-containing enzymes. Fdhs catalyze the oxidation of the formate anion to carbon dioxide in a redox reaction that involves the transfer of two electrons from the substrate to the active site. The active site in the oxidized state comprises a hexacoordinated molybdenum or tungsten ion in a distorted trigonal prismatic geometry. Using this structural model, we calculated the catalytic mechanism of Fdh through density functional theory tools. The simulated mechanism was correlated with the experimental kinetic properties of three different Fdhs isolated from three different Desulfovibrio species. Our studies indicate that the C-H bond break is an event involved in the rate-limiting step of the catalytic cycle. The role in catalysis of conserved amino acid residues involved in metal coordination and near the metal active site is discussed on the basis of experimental and theoretical results.

  4. Increasing Mechanical Strength of Gelatin Hydrogels by Divalent Metal Ion Removal

    Science.gov (United States)

    Xing, Qi; Yates, Keegan; Vogt, Caleb; Qian, Zichen; Frost, Megan C.; Zhao, Feng

    2014-04-01

    The usage of gelatin hydrogel is limited due to its instability and poor mechanical properties, especially under physiological conditions. Divalent metal ions present in gelatin such as Ca2+ and Fe2+ play important roles in the gelatin molecule interactions. The objective of this study was to determine the impact of divalent ion removal on the stability and mechanical properties of gelatin gels with and without chemical crosslinking. The gelatin solution was purified by Chelex resin to replace divalent metal ions with sodium ions. The gel was then chemically crosslinked by 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC). Results showed that the removal of divalent metal ions significantly impacted the formation of the gelatin network. The purified gelatin hydrogels had less interactions between gelatin molecules and form larger-pore network which enabled EDC to penetrate and crosslink the gel more efficiently. The crosslinked purified gels showed small swelling ratio, higher crosslinking density and dramatically increased storage and loss moduli. The removal of divalent ions is a simple yet effective method that can significantly improve the stability and strength of gelatin hydrogels. The in vitro cell culture demonstrated that the purified gelatin maintained its ability to support cell attachment and spreading.

  5. Structure and nano-mechanical characteristics of surface oxide layers on a metallic glass.

    Science.gov (United States)

    Caron, A; Qin, C L; Gu, L; González, S; Shluger, A; Fecht, H-J; Louzguine-Luzgin, D V; Inoue, A

    2011-03-04

    Owing to their low elastic moduli, high specific strength and excellent processing characteristics in the undercooled liquid state, metallic glasses are promising materials for applications in micromechanical systems. With miniaturization of metallic mechanical components down to the micrometer scale, the importance of a native oxide layer on a glass surface is increasing. In this work we use TEM and XPS to characterize the structure and properties of the native oxide layer grown on Ni(62)Nb(38) metallic glass and their evolution after annealing in air. The thickness of the oxide layer almost doubled after annealing. In both cases the oxide layer is amorphous and consists predominantly of Nb oxide. We investigate the friction behavior at low loads and in ambient conditions (i.e. at T = 295 K and 60% air humidity) of both as-cast and annealed samples by friction force microscopy. After annealing the friction coefficient is found to have significantly increased. We attribute this effect to the increase of the mechanical stability of the oxide layer upon annealing.

  6. Mechanical and half-metallic properties of half-Heusler CoCrSn

    Science.gov (United States)

    Huang, Hai-Ming; He, Ze-Dong; Zhang, Chuan-Kun; Luo, Shi-Jun

    2018-01-01

    Electronic and elastic properties of the half-Heusler CoCrSn are calculated using first-principles method. The results show that CoCrSn is a half-metallic ferrimagnetism with the total magnetic moment of 1.00 μB per formula unit at equilibrium lattice constant. The results agree well with the Slatere-Pauling rule based on the relationship of valence electrons and total magnetic moment. The half-Heusler CoCrSn maintains the half-metallic stability within the lattice constants ranging from 5.17 Å to 5.91 Å in GGA, from 5.24 Å to 5.89 Å in GGA+SOC, and from the 4.63 Å to 6.18 Å in GGA+U, respectively. The mechanical parameters of CoCrSn, such as elastic constants, bulk modulus, shear modulus, Pough’s ratio, Frantesvich ratio, Young’s modulus, Poisson’s ratio, Kleinman parameter and Debye temperature are calculated for the first time, and the results show that it is mechanically stable and is a ductile material. The studies show that the half-Heusler CoCrSn is a promising half-metal in spintronics.

  7. Texture evolution and mechanical behaviour of irradiated face-centred cubic metals.

    Science.gov (United States)

    Chen, L R; Xiao, X Z; Yu, L; Chu, H J; Duan, H L

    2018-02-01

    A physically based theoretical model is proposed to investigate the mechanical behaviour and crystallographic texture evolution of irradiated face-centred cubic metals. This model is capable of capturing the main features of irradiated polycrystalline materials including irradiation hardening, post-yield softening and plasticity localization. Numerical results show a good agreement with experimental data for both unirradiated and irradiated stress-strain relationships. The study of crystallographic texture reveals that the initial randomly distributed texture of unirradiated metals under tensile loading can evolve into a mixture of [111] and [100] textures. Regarding the irradiated case, crystallographic texture develops in a different way, and an extra part of [110] texture evolves into [100] and [111] textures. Thus, [100] and [111] textures become dominant more quickly compared with those of the unirradiated case for the reason that [100] and [111]-oriented crystals have higher strength, and their plastic deformation behaviours are more active than other oriented crystals. It can be concluded that irradiation-induced defects can affect both the mechanical behaviour and texture evolution of metals, both of which are closely related to irradiation hardening.

  8. Mechanisms governing the interaction of metallic particles with nanosecond laser pulses.

    Science.gov (United States)

    Demos, Stavros G; Negres, Raluca A; Raman, Rajesh N; Shen, Nan; Rubenchik, Alexander M; Matthews, Manyalibo J

    2016-04-04

    The interaction of nanosecond laser pulses at 1064- and 355-nm with micro-scale, nominally spherical metallic particles is investigated in order to elucidate the governing interaction mechanisms as a function of material and laser parameters. The experimental model used involves the irradiation of metal particles located on the surface of transparent plates combined with time-resolved imaging capable of capturing the dynamics of particle ejection, plume formation and expansion along with the kinetics of the dispersed material from the liquefied layer of the particle. The mechanisms investigated in this work are informative and relevant across a multitude of materials and irradiation geometries suitable for the description of a wide range of specific applications. The experimental results were interpreted using physical models incorporating specific processes to assess their contribution to the overall observed behaviors. Analysis of the experimental results suggests that the induced kinetic properties of the particle can be adequately described using the concept of momentum coupling introduced to explain the interaction of plane metal targets to large-aperture laser beams. The results also suggest that laser energy deposition on the formed plasma affects the energy partitioning and the material modifications to the substrate.

  9. Extraction of metals from spent hydrotreating catalysts: physico-mechanical pre-treatments and leaching stage.

    Science.gov (United States)

    Ferella, Francesco; Ognyanova, Albena; De Michelis, Ida; Taglieri, Giuliana; Vegliò, Francesco

    2011-08-15

    The present paper is focused on physico-mechanical pre-treatments of spent hydrotreating catalysts aimed at concentration of at least one of the valuable metals contained in such secondary raw material. In particular, dry Ni-Mo and Co-Mo as well as wet Ni-Mo catalysts were used. Flotation, grain size separation and attrition processes were tested. After that, a rods vibrating mill and a ball mill were used to ground the catalysts in order to understand the best mechanical pre-treatment before leaching extraction. The results showed that flotation is not able to concentrate any metals due to the presence of coke or other depressant compounds. The particle size separation produces two fractions enriched in Mo and Co when dry Co-Mo catalyst is used, whereas attrition is not suitable as metals are uniformely distributed in rings' volume. Roasting at 550°C and vibrating grinding are the most suitable pre-treatments able to produce fractions easily leached by NaOH and H(2)SO(4) after grain size separation. Copyright © 2011 Elsevier B.V. All rights reserved.

  10. Increasing Mechanical Strength of Gelatin Hydrogels by Divalent Metal Ion Removal

    Science.gov (United States)

    Xing, Qi; Yates, Keegan; Vogt, Caleb; Qian, Zichen; Frost, Megan C.; Zhao, Feng

    2014-01-01

    The usage of gelatin hydrogel is limited due to its instability and poor mechanical properties, especially under physiological conditions. Divalent metal ions present in gelatin such as Ca2+ and Fe2+ play important roles in the gelatin molecule interactions. The objective of this study was to determine the impact of divalent ion removal on the stability and mechanical properties of gelatin gels with and without chemical crosslinking. The gelatin solution was purified by Chelex resin to replace divalent metal ions with sodium ions. The gel was then chemically crosslinked by 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC). Results showed that the removal of divalent metal ions significantly impacted the formation of the gelatin network. The purified gelatin hydrogels had less interactions between gelatin molecules and form larger-pore network which enabled EDC to penetrate and crosslink the gel more efficiently. The crosslinked purified gels showed small swelling ratio, higher crosslinking density and dramatically increased storage and loss moduli. The removal of divalent ions is a simple yet effective method that can significantly improve the stability and strength of gelatin hydrogels. The in vitro cell culture demonstrated that the purified gelatin maintained its ability to support cell attachment and spreading. PMID:24736500

  11. Bio-recovery of non-essential heavy metals by intra- and extracellular mechanisms in free-living microorganisms.

    Science.gov (United States)

    García-García, Jorge D; Sánchez-Thomas, Rosina; Moreno-Sánchez, Rafael

    2016-01-01

    Free-living microorganisms may become suitable models for recovery of non-essential and essential heavy metals from wastewater bodies and soils by using and enhancing their accumulating and/or leaching abilities. This review analyzes the variety of different mechanisms developed mainly in bacteria, protists and microalgae to accumulate heavy metals, being the most relevant those involving phytochelatin and metallothionein biosyntheses; phosphate/polyphosphate metabolism; compartmentalization of heavy metal-complexes into vacuoles, chloroplasts and mitochondria; and secretion of malate and other organic acids. Cyanide biosynthesis for extra-cellular heavy metal bioleaching is also examined. These metabolic/cellular processes are herein analyzed at the transcriptional, kinetic and metabolic levels to provide mechanistic basis for developing genetically engineered microorganisms with greater capacities and efficiencies for heavy metal recovery, recycling of heavy metals, biosensing of metal ions, and engineering of metalloenzymes. Copyright © 2016 Elsevier Inc. All rights reserved.

  12. Influence of non-metal inclusions on mechanical properties of Clam steel

    International Nuclear Information System (INIS)

    Liu, S.; Huang, Q.; Li, C.

    2007-01-01

    Full text of publication follows: With good irradiation swelling resistance, thermo-physical and thermo-mechanical properties, the RAFMs (Reduced Activation Ferritic / Martensitic steels) have been considered as the primary candidate structural materials for application in fusion systems in the near future. The China Low Activation Martensitic steel (CLAM) based on the nominal compositions of 9Cr1.5WVTa is being developed in Institute of Plasma Physics, Chinese Academy of Sciences (ASIPP) under wide collaboration with many other institutes and universities in domestic and overseas. The heat treatment of CLAM is quenching at 980 deg. C for 30 minutes and then cooled by air or water and tempering at 760 deg. C for 90 minutes and then cooled by air. Mechanical properties of CLAM were strongly affected by the size and distribution of non-metal inclusions as most steels, and its effects on mechanical properties of CLAM steel has been investigated. The evaluation of the non-metallic inclusions in CLAM has been done by optical microscopy observation, electron microscopy observation and Energy Dispersive X-ray Spectroscopy (EDS) analysis. The results showed that most of the non-metal inclusions in CLAM were brittle alumina phase with large size and non-uniform distribution and those were no good to the mechanical properties of CLAM. So electroslag remelting process was chosen to remelt the ingot which was smelted previously by vacuum induction furnace. Inclusion detection by optical microscopy showed that both of the dimensions and quantity of the inclusions decreased and their distributions became more uniform compared with the case before. And the tensile tests and Charpy V-notch impact tests indicated that electroslag remelting improved the tensile properties and impact toughness of CLAM steel. (authors)

  13. Manipulating Conduction in Metal Oxide Semiconductors: Mechanism Investigation and Conductance Tuning in Doped Fe2O3 Hematite and Metal/Ga2O3/Metal Heterostructure

    Science.gov (United States)

    Zhao, Bo

    This study aims at understanding the fundamental mechanisms of conduction in several metal oxide semiconductors, namely alpha-Fe2O 3 and beta-Ga2O3, and how it could be tuned to desired values/states to enable a wide range of application. In the first effort, by adding Ti dopant, we successfully turned Fe2O3 from insulating to conductive by fabricated compositionally and structurally well-defined epitaxial alpha-(TixFe1-x)2 O3(0001) films for x ≤ 0.09. All films were grown by oxygen plasma assisted molecular beam epitaxy on Al2O3(0001) sapphire substrate with a buffer layer of Cr2O3 to relax the strain from lattice mismatch. Van der Pauw resistivity and Hall effect measurements reveal carrier concentrations between 1019 and 1020 cm-3 at room temperature and mobilities in the range of 0.1 to 0.6 cm2/V˙s. Such low mobility, unlike conventional band-conduction semiconductor, was attributed to hopping mechanism due to strong electron-phonon interaction in the lattice. More interestingly, conduction mechanism transitions from small-polaron hopping at higher temperatures to variable range hopping at lower temperatures with a transition temperature between 180 to 140 K. Consequently, by adding Ti dopant, conductive Fe 2O3 hematite thin films were achieved with a well-understood conducting mechanism that could guide further device application such as spin transistor and water splitting. In the case of Ga2O3, while having a band gap as high as 5 eV, they are usually conductive for commercially available samples due to unintentional Si doping. However, we discovered the conductance could be repeatedly switched between high resistance state and low resistance state when made into metal/Ga2O3 /metal heterostructure. However, to obtain well controlled switching process with consistent switching voltages and resistances, understanding switching mechanism is the key. In this study, we fabricated resistive switching devices utilizing a Ni/Ga2O3/Ir heterostructure. Bipolar

  14. Jacking mechanism for upper internals structure of a liquid metal nuclear reactor

    International Nuclear Information System (INIS)

    Gillett, J.E.; Wineman, A.L.

    1983-01-01

    A jacking mechanism for raising the upper internals structure of a liquid metal nuclear reactor which jacking mechanism uses a system of gears and drive shafts to transmit force from a single motor to four mechanically synchronized ball jacks to raise and lower support columns which support the upper internals structure. The support columns each have a pin which rides in a slot in a housing fixed to the reactor head. The pin has two locking plates which can be rotated around the pin to bring the locking plates into engagement with the housing in a raised or a lowered position of the support column such that the support column is then supported by the locking plate and not by the ball screw jacks. (author)

  15. Nanotribological behavior analysis of graphene/metal nanocomposites via MD simulations: New concepts and underlying mechanisms

    Science.gov (United States)

    Montazeri, A.; Mobarghei, A.

    2018-04-01

    In this article, we report a series of MD-based nanoindentation tests aimed to examine the nanotribological characteristics of metal-based nanocomposites in the presence of graphene sheets. To evaluate the effects of graphene/matrix interactions on the results, nickel and copper are selected as metals having strong and weak interactions with graphene, respectively. Consequently, the influence of graphene layers sliding and their distance from the sample surface on the nanoindentation outputs is thoroughly examined. Additionally, the temperature dependence of the results is deeply investigated with emphasis on the underlying mechanisms. To verify the accuracy of nanoindentation outputs, results of this method are compared with the data obtained via the tensile test. It is concluded that the nanoindentation results are closer to the values obtained by means of experimental setups. Employing these numerical-based experiments enables us to perform parametric studies to find out the dominant factors affecting the nanotribological behavior of these nanocomposites at the atomic-scale.

  16. Mechanical and magnetic properties of semi-Heusler/light-metal composites consolidated by spark plasma sintering

    Czech Academy of Sciences Publication Activity Database

    Koller, M.; Chráska, Tomáš; Cinert, Jakub; Heczko, Oleg; Kopeček, Jaromír; Landa, Michal; Mušálek, Radek; Rameš, Michal; Seiner, Hanuš; Stráský, J.; Janeček, M.

    2017-01-01

    Roč. 126, July (2017), s. 351-357 ISSN 0264-1275 R&D Projects: GA ČR GB14-36566G Institutional support: RVO:61389021 ; RVO:68378271 ; RVO:61388998 Keywords : Metal–metal composites * Spark plasma sintering * Light metals * Ferromagnetic alloys * Mechanical properties Subject RIV: JI - Composite Materials; JI - Composite Materials (FZU-D); JI - Composite Materials (UT-L) OBOR OECD: Composites (including laminates, reinforced plastics, cermets, combined natural and synthetic fibre fabrics; Composites (including laminates, reinforced plastics, cermets, combined natural and synthetic fibre fabrics (FZU-D); Composites (including laminates, reinforced plastics, cermets, combined natural and synthetic fibre fabrics (UT-L) Impact factor: 4.364, year: 2016 https://www.sciencedirect.com/science/article/pii/S0264127517303842?via%3Dih

  17. Mechanism of optical unidirectional transmission in subwavelength dual-metal gratings

    Science.gov (United States)

    Gao, H.; Zheng, Z. Y.; Hao, H. Y.; Dong, A. G.; Fan, Z. J.; Liu, D. H.

    2014-03-01

    The mechanism of optical unidirectional (OUD) transmission in parallel subwavelength dual-metal gratings was investigated. It was found that this kind of OUD phenomenon originates from the coupling of the surface plasmon polaritons (SPPs) between the front grating and a layer of metal film which replaces the rear grating. The higher the intensity of the coupled SPPs at the entrances of the rear grating, the higher the transmittance can be achieved. Basing on this property, an effective OUD example was achieved by exploring the intensity difference at the entrances of the rear gratings between the two incidences of opposite directions. In this kind of OUD, the positive transmittance can exceed 80 % and the difference between the transmittances of the two opposite directions can be as large as 63 %. The detailed design process was also presented.

  18. Catalytic growth of metallic tungsten whiskers based on the vapor-solid-solid mechanism

    International Nuclear Information System (INIS)

    Wang, S L; He, Y H; Huang, B Y; Zou, J; Wang, Y; Huang, H; Liu, C T; Liaw, P K

    2008-01-01

    Metallic W whiskers with tip diameters of 50-250 nm and lengths of 2-4 μm have been successfully synthesized in large quantities using Co-Ni alloyed catalysts. The relatively low growth temperature of 850 deg. C and the large catalyst size (over 100 nm) suggest that the growth of the W whiskers must be governed by the vapor-solid-solid mechanism. Our results show that the vapor-solid-solid model is suitable not only for the growth of nano-scaled whiskers with diameters below 100 nm, but also for submicro-scaled whiskers with diameters well above 100 nm. This technique has great potential to synthesize well controlled metallic whiskers

  19. Heavy metals (Pb, Cd, As and MeHg) as risk factors for cognitive dysfunction: A general review of metal mixture mechanism in brain.

    Science.gov (United States)

    Karri, Venkatanaidu; Schuhmacher, Marta; Kumar, Vikas

    2016-12-01

    Human exposure to toxic heavy metals is a global challenge. Concurrent exposure of heavy metals, such as lead (Pb), cadmium (Cd), arsenic (As) and methylmercury (MeHg) are particularly important due to their long lasting effects on the brain. The exact toxicological mechanisms invoked by exposure to mixtures of the metals Pb, Cd, As and MeHg are still unclear, however they share many common pathways for causing cognitive dysfunction. The combination of metals may produce additive/synergetic effects due to their common binding affinity with NMDA receptor (Pb, As, MeHg), Na + - K + ATP-ase pump (Cd, MeHg), biological Ca +2 (Pb, Cd, MeHg), Glu neurotransmitter (Pb, MeHg), which can lead to imbalance between the pro-oxidant elements (ROS) and the antioxidants (reducing elements). In this process, ROS dominates the antioxidants factors such as GPx, GS, GSH, MT-III, Catalase, SOD, BDNF, and CERB, and finally leads to cognitive dysfunction. The present review illustrates an account of the current knowledge about the individual metal induced cognitive dysfunction mechanisms and analyse common Mode of Actions (MOAs) of quaternary metal mixture (Pb, Cd, As, MeHg). This review aims to help advancement in mixture toxicology and development of next generation predictive model (such as PBPK/PD) combining both kinetic and dynamic interactions of metals. Copyright © 2016 Elsevier B.V. All rights reserved.

  20. Understanding the molecular mechanism of pulse current charging for stable lithium-metal batteries.

    Science.gov (United States)

    Li, Qi; Tan, Shen; Li, Linlin; Lu, Yingying; He, Yi

    2017-07-01

    High energy and safe electrochemical storage are critical components in multiple emerging fields of technologies. Rechargeable lithium-metal batteries are considered to be promising alternatives for current lithium-ion batteries, leading to as much as a 10-fold improvement in anode storage capacity (from 372 to 3860 mAh g -1 ). One of the major challenges for commercializing lithium-metal batteries is the reliability and safety issue, which is often associated with uneven lithium electrodeposition (lithium dendrites) during the charging stage of the battery cycling process. We report that stable lithium-metal batteries can be achieved by simply charging cells with square-wave pulse current. We investigated the effects of charging period and frequency as well as the mechanisms that govern this process at the molecular level. Molecular simulations were performed to study the diffusion and the solvation structure of lithium cations (Li + ) in bulk electrolyte. The model predicts that loose association between cations and anions can enhance the transport of Li + and eventually stabilize the lithium electrodeposition. We also performed galvanostatic measurements to evaluate the cycling behavior and cell lifetime under pulsed electric field and found that the cell lifetime can be more than doubled using certain pulse current waveforms. Both experimental and simulation results demonstrate that the effectiveness of pulse current charging on dendrite suppression can be optimized by choosing proper time- and frequency-dependent pulses. This work provides a molecular basis for understanding the mechanisms of pulse current charging to mitigating lithium dendrites and designing pulse current waveforms for stable lithium-metal batteries.

  1. High temperature oxidation of metals: vacancy injection and consequences on the mechanical properties

    International Nuclear Information System (INIS)

    Perusin, S.

    2004-11-01

    The aim of this work is to account for the effects of the high temperature oxidation of metals on their microstructure and their mechanical properties. 'Model' materials like pure nickel, pure iron and the Ni-20Cr alloy are studied. Nickel foils have been oxidised at 1000 C on one side only in laboratory air, the other side being protected from oxidation by a reducing atmosphere. After the oxidation treatment, the unoxidized face was carefully examined by using an Atomic Force Microscope (AFM). Grain boundaries grooves were characterised and their depth were compared to the ones obtained on the same sample heat treated in the reducing atmosphere during the same time. They are found to be much deeper in the case of the single side oxidised samples. It is shown that this additional grooving is directly linked to the growth of the oxide scale on the opposite side and that it can be explained by the diffusion of the vacancies produced at the oxide scale - metal interface, across the entire sample through grain boundaries. Moreover, the comparison between single side oxidised samples and samples oxidised on both sides points out that voids in grain boundaries are only observed in this latter case proving the vacancies condensation in the metal when the two faces are oxidised. The role of the carbon content and the sample's geometry on this phenomenon is examined in detail. The diffusion of vacancies is coupled with the transport of oxygen so that a mechanism of oxygen transport by vacancies is suggested. The tensile tests realised at room temperature on nickel foils (bamboo microstructure) show that the oxide scale can constitute a barrier to the emergence of dislocations at the metal surface. Finally, the Ni-20Cr alloy is tested in tensile and creep tests between 25 and 825 C in oxidising or reducing atmospheres. (author)

  2. Determination of Informal Sector as Urban Pollution Source : Fume Characterization of Small-scale Manual Metal Arc Welding using Factor Analysis in Bandung City

    International Nuclear Information System (INIS)

    Nastiti, A.; Pramudyastuti, D.Y.; Oginawati, K.; Santoso, M.

    2012-01-01

    In developing countries, the informal sector, particularly small-scale welding activities, are considered to be an important contributor to urban air pollution although studies in this sector are limited. This study aims to identify the composition of small-scale welding fume in order to further investigate the effects and set control strategies and urban pollution abatement policies. Breathing zone air samples were collected from 30 mild steel manual metal arc welders and 17 non-welders in Bandung City, West Java, Indonesia. The respirable particulates in air samples were analyzed using gravimetric method, and Instrumental Neutron Activation Analysis (INAA) was employed to identify characteristic of welding fume. It was found that respirable particulates concentration in welders (range : 315.6 and 3,735.93 µgm -3 ; average 1,545.436 µgm -3 ) were significantly higher than in non-welders (range : 41.84 and 1,688.03 µgm -3 ; average : 375.783 µgm -3 ). Welders' breathing zones contain Fe>Na>K>Mn>Al >Cr>Ti>Cl>Br>I>Zn>Sb>V>Co>Sc; while non-welders' breathing zones contain Cr>F>Al>Ti>Na>Br>I>Mn>Cl>Co>Zn>Sc. Inter-species correlation analysis conducted using Statgraphic Ver. 4.0 shows that Fe (range : n.d. - 775.19 µgm -3 ; average: 0.1674µgm -3 ), Co (range : n.d. - 0.51 µgm -3 ; average: 0.000082 µgm -3 ), Mn (range : 0.39 - 148.37 µgm -3 ; average: 0.0374 µgm -3 ), Na (range: 0.17 and 623.85 µgm -3 ; average: 0.0973 µgm -3 ) and K (range : n.d. - 301.15 µgm -3 ; average: 0.0535 µgm -3 ) were emitted from welding activity, and thus are considered as components of welding fume which contribute to urban air pollution. Although welding fume and the identified species in welding fume were still below permissible limit, small-scale welding activities have great potential in emitting higher fume concentration due to due to high variability of welding activities, such as welding frequency, materials being welded, and varied environmental conditions. (author)

  3. Determination of Informal Sector as Urban Pollution Source : Fume Characterization of Small-scale Manual Metal Arc Welding using Factor Analysis in Bandung City

    Directory of Open Access Journals (Sweden)

    A. Nastiti

    2012-04-01

    Full Text Available In developing countries, the informal sector, particularly small-scale welding activities, are considered to be an important contributor to urban air pollution although studies in this sector are limited. This study aims to identify the composition of small-scale welding fume in order to further investigate the effects and set control strategies and urban pollution abatement policies. Breathing zone air samples were collected from 30 mild steel manual metal arc welders and 17 non-welders in Bandung City, West Java, Indonesia. The respirable particulates in air samples were analyzed using gravimetric method, and Instrumental Neutron Activation Analysis (INAA was employed to identify characteristic of welding fume. It was found that respirable particulates concentration in welders (range : 315.6 and 3,735.93 µgm-3; average 1,545.436 µgm-3 were significantly higher than in non-welders (range : 41.84 and 1,688.03 µgm-3; average : 375.783 µgm-3. Welders’ breathing zones contain Fe>Na>K>Mn>Al >Cr>Ti>Cl>Br>I>Zn>Sb>V>Co>Sc; while non-welders’ breathing zones contain Cr>F>Al>Ti>Na>Br>I>Mn>Cl>Co>Zn>Sc. Inter-species correlation analysis conducted using Statgraphic Ver. 4.0 shows that Fe (range : n.d. – 775.19 µgm-3; average: 0.1674 µgm-3, Co (range : n.d. – 0.51 µgm-3; average: 0.000082 µgm-3, Mn (range : 0.39 – 148.37 µgm-3; average: 0.0374 µgm-3, Na (range: 0.17 and 623.85 µgm-3; average: 0.0973 µgm-3 and K (range : n.d. – 301.15 µgm-3; average: 0.0535 µgm-3 were emitted from welding activity, and thus are considered as components of welding fume which contribute to urban air pollution. Although welding fume and the identified species in welding fume were still below permissible limit, small-scale welding activities have great potential in emitting higher fume concentration due to due to high variability of welding activities, such as welding frequency, materials being welded, and varied environmental conditions

  4. Mechanically durable underwater superoleophobic surfaces based on hydrophilic bulk metals for oil/water separation

    Science.gov (United States)

    Yu, Huadong; Lian, Zhongxu; Xu, Jinkai; Wan, Yanling; Wang, Zuobin; Li, Yiquan; Yu, Zhanjiang; Weng, Zhankun

    2018-04-01

    Despite the success of previous methods for fabricating underwater superoleophobic surfaces, most of the surfaces based on soft materials are prone to collapse and deformation due to their mechanically fragile nature, and they fail to perform their designed functions after the surface materials are damaged in water. In this work, the nanosecond laser-induced oxide coatings on hydrophilic bulk metals are reported which overcomes the limitation and shows the robust underwater superoleophobicity to a mechanical challenge encountered by surfaces deployed in water environment. The results show that the surface materials have the advantage that the underwater superoleophobicity is still preserved after the surfaces are scratched by knife or sandpaper and even completely destroyed because of the hydrophilic property of damaged materials in water. It is important that the results provide a guide for the design of durable underwater superoleophobic surfaces, and the development of superoleophobic materials in many potential applications such as the oil-repellent and the oil/water separation. Additionally, the nanosecond laser technology is simple, cost-effective and suitable for the large-area and mass fabrication of mechanically durable underwater superoleophobic metal materials.

  5. Research Update: Mechanical properties of metal-organic frameworks – Influence of structure and chemical bonding

    Directory of Open Access Journals (Sweden)

    Wei Li

    2014-12-01

    Full Text Available Metal-organic frameworks (MOFs, a young family of functional materials, have been attracting considerable attention from the chemistry, materials science, and physics communities. In the light of their potential applications in industry and technology, the fundamental mechanical properties of MOFs, which are of critical importance for manufacturing, processing, and performance, need to be addressed and understood. It has been widely accepted that the framework topology, which describes the overall connectivity pattern of the MOF building units, is of vital importance for the mechanical properties. However, recent advances in the area of MOF mechanics reveal that chemistry plays a major role as well. From the viewpoint of materials science, a deep understanding of the influence of chemical effects on MOF mechanics is not only highly desirable for the development of novel functional materials with targeted mechanical response, but also for a better understanding of important properties such as structural flexibility and framework breathing. The present work discusses the intrinsic connection between chemical effects and the mechanical behavior of MOFs through a number of prototypical examples.

  6. Effect of Thermal Treatments on the Mechanical Properties Enhancement of High Reliability Metallic Materials by Laser Shock Processing

    OpenAIRE

    Ocaña Moreno, José Luis; Díaz, M.; Porro González, Juan Antonio; Ruiz de Lara de Luis, Leonardo; Correa, C.

    2014-01-01

    Laser shock processing (LSP) is increasingly applied as an effective technology for the improvement of metallic materials mechanical properties in different types of components as a means of enhancement of their fatigue life behavior. As reported in previous contributions by the authors, a main effect resulting from the application of the LSP technique consists on the generation of relatively deep compression residual stresses fields into metallic components allowing an improved mechanical...

  7. Application of High-Density Electropulsing to Improve the Performance of Metallic Materials: Mechanisms, Microstructure and Properties

    Directory of Open Access Journals (Sweden)

    Yinying Sheng

    2018-01-01

    Full Text Available The technology of high-density electropulsing has been applied to increase the performance of metallic materials since the 1990s and has shown significant advantages over traditional heat treatment in many aspects. However, the microstructure changes in electropulsing treatment (EPT metals and alloys have not been fully explored, and the effects vary significantly on different material. When high-density electrical pulses are applied to metals and alloys, the input of electric energy and thermal energy generally leads to structural rearrangements, such as dynamic recrystallization, dislocation movements and grain refinement. The enhanced mechanical properties of the metals and alloys after high-density electropulsing treatment are reflected by the significant improvement of elongation. As a result, this technology holds great promise in improving the deformation limit and repairing cracks and defects in the plastic processing of metals. This review summarizes the effect of high-density electropulsing treatment on microstructural properties and, thus, the enhancement in mechanical strength, hardness and corrosion performance of metallic materials. It is noteworthy that the change of some properties can be related to the structure state before EPT (quenched, annealed, deformed or others. The mechanisms for the microstructural evolution, grain refinement and formation of oriented microstructures of different metals and alloys are presented. Future research trends of high-density electrical pulse technology for specific metals and alloys are highlighted.

  8. Application of High-Density Electropulsing to Improve the Performance of Metallic Materials: Mechanisms, Microstructure and Properties.

    Science.gov (United States)

    Sheng, Yinying; Hua, Youlu; Wang, Xiaojian; Zhao, Xueyang; Chen, Lianxi; Zhou, Hanyu; Wang, James; Berndt, Christopher C; Li, Wei

    2018-01-24

    The technology of high-density electropulsing has been applied to increase the performance of metallic materials since the 1990s and has shown significant advantages over traditional heat treatment in many aspects. However, the microstructure changes in electropulsing treatment (EPT) metals and alloys have not been fully explored, and the effects vary significantly on different material. When high-density electrical pulses are applied to metals and alloys, the input of electric energy and thermal energy generally leads to structural rearrangements, such as dynamic recrystallization, dislocation movements and grain refinement. The enhanced mechanical properties of the metals and alloys after high-density electropulsing treatment are reflected by the significant improvement of elongation. As a result, this technology holds great promise in improving the deformation limit and repairing cracks and defects in the plastic processing of metals. This review summarizes the effect of high-density electropulsing treatment on microstructural properties and, thus, the enhancement in mechanical strength, hardness and corrosion performance of metallic materials. It is noteworthy that the change of some properties can be related to the structure state before EPT (quenched, annealed, deformed or others). The mechanisms for the microstructural evolution, grain refinement and formation of oriented microstructures of different metals and alloys are presented. Future research trends of high-density electrical pulse technology for specific metals and alloys are highlighted.

  9. Application of High-Density Electropulsing to Improve the Performance of Metallic Materials: Mechanisms, Microstructure and Properties

    Science.gov (United States)

    Sheng, Yinying; Hua, Youlu; Zhao, Xueyang; Chen, Lianxi; Zhou, Hanyu; Wang, James; Berndt, Christopher C.; Li, Wei

    2018-01-01

    The technology of high-density electropulsing has been applied to increase the performance of metallic materials since the 1990s and has shown significant advantages over traditional heat treatment in many aspects. However, the microstructure changes in electropulsing treatment (EPT) metals and alloys have not been fully explored, and the effects vary significantly on different material. When high-density electrical pulses are applied to metals and alloys, the input of electric energy and thermal energy generally leads to structural rearrangements, such as dynamic recrystallization, dislocation movements and grain refinement. The enhanced mechanical properties of the metals and alloys after high-density electropulsing treatment are reflected by the significant improvement of elongation. As a result, this technology holds great promise in improving the deformation limit and repairing cracks and defects in the plastic processing of metals. This review summarizes the effect of high-density electropulsing treatment on microstructural properties and, thus, the enhancement in mechanical strength, hardness and corrosion performance of metallic materials. It is noteworthy that the change of some properties can be related to the structure state before EPT (quenched, annealed, deformed or others). The mechanisms for the microstructural evolution, grain refinement and formation of oriented microstructures of different metals and alloys are presented. Future research trends of high-density electrical pulse technology for specific metals and alloys are highlighted. PMID:29364844

  10. Interaction of NO2 with model NSR catalysts: metal-oxide interaction controls initial NOx storage mechanism.

    Science.gov (United States)

    Desikusumastuti, Aine; Staudt, Thorsten; Qin, Zhihui; Happel, Markus; Laurin, Mathias; Lykhach, Yaroslava; Shaikhutdinov, Shamil; Rohr, Friedemann; Libuda, Jörg

    2008-10-24

    Using scanning tunneling microscopy (STM), molecular-beam (MB) methods and time-resolved infrared reflection absorption spectroscopy (TR-IRAS), we investigate the mechanism of initial NO(x) uptake on a model nitrogen storage and reduction (NSR) catalyst. The model system is prepared by co-deposition of Pd metal particles and Ba-containing oxide particles onto an ordered alumina film on NiAl(110). We show that the metal-oxide interaction between the active noble metal particles and the NO(x) storage compound in NSR model catalysts plays an important role in the reaction mechanism. We suggest that strong interaction facilitates reverse spillover of activated oxygen species from the NO(x) storage compound to the metal. This process leads to partial oxidation of the metal nanoparticles and simultaneous stabilization of the surface nitrite intermediate.

  11. Hybrid metal-coordinate transient networks: using bio-inspired building blocks to engineer the mechanical properties of physical hydrogels

    Science.gov (United States)

    Grindy, Scott; Barrett, Devin; Messersmith, Phillip; Holten-Andersen, Niels

    2014-03-01

    Recently, metal-coordinate complex crosslinks have been suggested to contribute to the self-healing properties of mussel byssi. Two specific amino acid derivatives - 3,4 dihydroxy-L-phenylalanine (dopa) and histidine (his) - are known to form coordinate complexes with trivalent and divalent ions (respectively) in aqueous solutions. We show here that, by functionalizing poly(ethylene glycol) polymers with dopa and his we are (1) able to characterize the fundamental kinetics and energetics of each specific metal-ligand pair using small amplitude oscillatory shear rheology and (2) create hybrid networks using various mixtures of metals and ligands. From this information, we can design gels with specific target mechanical properties by tailoring the amounts and types of metal-ligand crosslinks present in the gel network, resulting in the ability to engineer the mechanical relaxation spectrum. This work provides basic understanding necessary to intelligently design materials which incorporate metal-ligand crosslinks in more complex architectures.

  12. Metal and engineering industry in the Finnish economy

    International Nuclear Information System (INIS)

    Maeenpaeae, I.; Viitanen, M.; Juutinen, A.

    1996-01-01

    The study analyses quantitatively the position, internal structures and environmental aspects of the metal sector (basic metal industry, mechanical engineering, electronics and electrotechnics) in the recent past of the Finnish economy. The changes in the sector by the year 2005 are assessed by means of a macroeconomic simulation model as well. The future development of the metal sector by the year 2005 was assessed by the FMS model system, for which a detailed metal sector sub-model was constructed. The scenario of the general development of the Finnish economy was tuned so that it corresponds as closely as possible to the recent basic projections of the economy made by the government authorities. Three scenarios for the metal sector were constructed: base scenario, rapid and slow growth scenarios. In the base scenario the production volume of the metal sector grows by 6 per cent annually between 1994-2005 while the annual growth rate of the whole industry is 4 per cent and that of the GDP 3 per cent. In the rapid growth scenario, the growth rate of the metal sector goes up to 10 per cent and in the slow growth scenario down to 3 per cent. In the assessment of environmental effects of the metal sector are included energy consumption, emissions into the air, use on natural resources, waste formation and recycling of metals. Although the production volume of the metal sector almost doubles between 1990 - 2000, the consumption of primary energy grows only about one fourth and that of the electricity by 50 per cent

  13. Mechanical tunability via hydrogen bonding in metal-organic frameworks with the perovskite architecture.

    Science.gov (United States)

    Li, Wei; Thirumurugan, A; Barton, Phillip T; Lin, Zheshuai; Henke, Sebastian; Yeung, Hamish H-M; Wharmby, Michael T; Bithell, Erica G; Howard, Christopher J; Cheetham, Anthony K

    2014-06-04

    Two analogous metal-organic frameworks (MOFs) with the perovskite architecture, [C(NH2)3][Mn(HCOO)3] (1) and [(CH2)3NH2][Mn(HCOO)3] (2), exhibit significantly different mechanical properties. The marked difference is attributed to their distinct modes of hydrogen bonding between the A-site amine cation and the anionic framework. The stronger cross-linking hydrogen bonding in 1 gives rise to Young's moduli and hardnesses that are up to twice those in 2, while the thermal expansion is substantially smaller. This study presents clear evidence that the mechanical properties of MOF materials can be substantially tuned via hydrogen-bonding interactions.

  14. Mechanical and corrosion behaviors of developed copper-based metal matrix composites

    Science.gov (United States)

    Singh, Manvandra Kumar; Gautam, Rakesh Kumar; Prakash, Rajiv; Ji, Gopal

    2018-03-01

    This work investigates mechanical properties and corrosion resistances of cast copper-tungsten carbide (WC) metal matrix composites (MMCs). Copper matrix composites have been developed by stir casting technique. Different sizes of micro and nano particles of WC particles are utilized as reinforcement to prepare two copper-based composites, however, nano size of WC particles are prepared by high-energy ball milling. XRD (X-rays diffraction) characterize the materials for involvement of different phases. The mechanical behavior of composites has been studied by Vickers hardness test and compression test; while the corrosion behavior of developed composites is investigated by electrochemical impedance spectroscopy in 0.5 M H2SO4 solutions. The results show that hardness, compressive strength and corrosion resistance of copper matrix composites are very high in comparison to that of copper matrix, which attributed to the microstructural changes occurred during composite formation. SEM (Scanning electron microscopy) reveals the morphology of the corroded surfaces.

  15. Effect of continuum damage mechanics on spring back prediction in metal forming processes

    International Nuclear Information System (INIS)

    Nayebi, Ali; Shahabi, Mehdi

    2017-01-01

    The influence of considering the variations in material properties was investigated through continuum damage mechanics according to the Lemaitre isotropic unified damage law to predict the bending force and spring back in V-bending sheet metal forming processes, with emphasis on Finite element (FE) simulation considerations. The material constants of the damage model were calibrated through a uniaxial tensile test with an appropriate and convenient repeating strategy. Holloman’s isotropic and Ziegler’s linear kinematic hardening laws were employed to describe the behavior of a hardening material. To specify the ideal FE conditions for simulating spring back, the effect of the various numerical considerations during FE simulation was investigated and compared with the experimental outcome. Results indicate that considering continuum damage mechanics decreased the predicted bending force and improved the accuracy of spring back prediction.

  16. Bacterial Exopolysaccharide mediated heavy metal removal: A Review on biosynthesis, mechanism and remediation strategies

    Directory of Open Access Journals (Sweden)

    Pratima Gupta

    2017-03-01

    Full Text Available Heavy metal contamination has been recognized as a major public health risk, particularly in developing countries and their toxicological manifestations are well known. Conventional remediation strategies are either expensive or they generate toxic by-products, which adversely affect the environment. Therefore, necessity for an environmentally safe strategy motivates interest towards biological techniques. One of such most profoundly driven approach in recent times is biosorption through microbial biomass and their products. Extracellular polymeric substances are such complex blend of high molecular weight microbial (prokaryotic and eukaryotic biopolymers. They are mainly composed of proteins, polysaccharides, uronic acids, humic substances, lipids etc. One of its essential constituent is the exopolysaccharide (EPS released out of self defense against harsh conditions of starvation, pH and temperature, hence it displays exemplary physiological, rheological and physio-chemical properties. Its net anionic makeup allows the biopolymer to effectively sequester positively charged heavy metal ions. The polysaccharide has been expounded deeply in this article with reference to its biosynthesis and emphasizes heavy metal sorption abilities of polymer in terms of mechanism of action and remediation. It reports current investigation and strategic advancements in dealing bacterial cells and their EPS in diverse forms – mixed culture EPS, single cell EPS, live, dead or immobilized EPS. A significant scrutiny is also involved highlighting the existing challenges that still lie in the path of commercialization. The article enlightens the potential of EPS to bring about bio-detoxification of heavy metal contaminated terrestrial and aquatic systems in highly sustainable, economic and eco-friendly manner.

  17. Oxidation of β-blockers by birnessite: Kinetics, mechanism and effect of metal ions.

    Science.gov (United States)

    Chen, Yong; Lu, Xiye; Liu, Lu; Wan, Dong; Chen, Huabin; Zhou, Danna; Sharma, Virender K

    2018-03-01

    Manganese dioxides are ubiquitous in natural waters, soils, and sediments and play an important role in oxidative transformation of organic pollutants. This work presents the kinetics of the oxidation of selected β-blockers, betaxolol, metoprolol, and atenolol by birnessite (δ-MnO 2 ) as a function of concentration of the β-blocker, dosage of δ-MnO 2 , and solution pH. The values of pseudo-first-order rate constants (k obs ) of β-blockers decreased in the order betaxolol > atenolol > metoprolol, which was positively correlated with their acid dissociation constants (K a ). Effect of series of metal ions (Fe 3+ , Cr 3+ , Al 3+ , Pb 2+ , Cu 2+ , Zn 2+ , Ni 2+ , Cd 2+ , Mg 2+ , and Ca 2+ ) on the degradation of β-blockers by δ-MnO 2 was systematically examined. All of these metal ions inhibited the oxidation reaction under the same constant ionic strength. The inhibition efficiency was positively correlated with the logarithm of stability constant of metal ions in aqueous solution (logK MeOH ). By LC-ESI-MS/MS analyses, the oxidation of β-blockers primarily involved hydroxylation and cleavage of the parent molecules to the short branched chain compounds. An electron transfer mechanism for the oxidation of β-blockers by δ-MnO 2 was proposed. The oxidation was initiated by the electron transfer from the nonbonding electrons on nitrogen (N-electrons) of β-blockers to δ-MnO 2 , followed by transformation of radical intermediates. These findings will help to understand the oxidation processes of β-blockers and predict the effect of metal ions on the removal of pollutants by δ-MnO 2 in the environment. Copyright © 2017 Elsevier Ltd. All rights reserved.

  18. Metal-organic and supramolecular architectures based on mechanically interlocked molecules

    Science.gov (United States)

    Fernando, Isurika Rosini

    The focus of this work is on mechanically interlocked molecules (MIMs), which have unusual physicochemical and mechanical properties with potential applications in nano-scale/molecular devices and high strength materials. Rotaxanes, for example, consist of an axle-like molecule threaded through a wheel-like molecule, with bulky groups at the two ends of the axle preventing the wheel from dissociating. The position of the wheel along the axle can be switched in a controllable and reversible manner by applying external stimuli, a feature that might lead to the next generation of computers. Molecularly woven materials (MWMs), another example of molecules with mechanically interlocked features, are predicted to be unprecedentedly strong while being lightweight and flexible. With the ultimate goal of achieving control over the functioning of molecular devices in the solid state, a variety of pseudorotaxane building blocks were prepared and characterized, including a novel, rare blue-colored motif. The temperature-dependent assembly/disassembly of pseudorotaxanes was exploited for the construction of single-wavelength colorimetric temperature sensors over a 100 °C window. Pseudorotaxanes based on aromatic crown ether wheels and disubstituted 4,4'-bipyridinium axles were converted into rotaxanes upon binding to metal complexes (zinc, cadmium, mercury, copper, cobalt), and the formation of ordered crystalline arrays was studied in the solid state. The columnar organization of pseudorotaxanes by Hg2X6 2-- complexes (X = Cl, Br, I), leading to unprecedented dichroic (blue/red) rotaxane crystals, was demonstrated for the first time. From the crystal structures studied it became apparent that negatively charged metal complexes are needed for successful assembly with the positively charged pseudorotaxane units. To be able to use the more common, positively charged metal ions for rotaxane framework construction, neutral and negatively charged pseudorotaxanes were synthesized

  19. Mechanism of dihydrogen cleavage by high-valent metal oxo compounds: experimental and computational studies.

    Science.gov (United States)

    Collman, J P; Slaughter, L M; Eberspacher, T A; Strassner, T; Brauman, J I

    2001-11-19

    The oxidation of dihydrogen by metal tetraoxo compounds was investigated. Kinetic measurements of the oxidations of H(2) by MnO(4)(-) and RuO(4), performed by UV-vis spectroscopy, showed these reactions to be quite rapid at 25 degrees C (k(1) approximately (3-6) x 10(-2) M(-1) s(-1)). Rates measured for H(2) oxidation by MnO(4)(-) in aqueous solution (using KMnO(4)) and in chlorobenzene (using (n)Bu(4)NMnO(4)) revealed only a minor solvent effect on the reaction rate. Substantial kinetic isotope effects [(k(H)2/k(D)2 = 3.8(2) (MnO(4)(-), aq), 4.5(5) (MnO(4)(-), C(6)H(5)Cl soln), and 1.8(6) (RuO(4), CCl(4) soln)] indicated that H-H bond cleavage is rate determining and that the mechanism of dihydrogen cleavage is likely similar in aqueous and organic solutions. Third-row transition-metal oxo compounds, such as OsO(4), ReO(4)(-), and MeReO(3), were found to be completely unreactive toward H(2). Experiments were performed to probe for a catalytic hydrogen/deuterium exchange between D(2) and H(2)O as possible evidence of dihydrogen sigma-complex intermediates, but no H/D exchange was observed in the presence of various metal oxo compounds at various pH values. In addition, no inhibition of RuO(4)-catalyzed hydrocarbon oxidation by H(2) was observed. On the basis of the available evidence, a concerted mechanism for the cleavage of H(2) by metal tetraoxo compounds is proposed. Theoretical models were developed for pertinent MnO(4)(-) + H(2) transition states using density functional theory in order to differentiate between concerted [2 + 2] and [3 + 2] scissions of H(2). The density functional theory calculations strongly favor the [3 + 2] mechanism and show that the H(2) cleavage shares some mechanistic features with related hydrocarbon oxidation reactions. The calculated activation energy for the [3 + 2] pathway (DeltaH(++) = 15.4 kcal mol(-1)) is within 2 kcal mol(-1) of the experimental value.

  20. Gallium-Based Liquid Metal Amalgams: Transitional-State Metallic Mixtures (TransM2ixes) with Enhanced and Tunable Electrical, Thermal, and Mechanical Properties.

    Science.gov (United States)

    Tang, Jianbo; Zhao, Xi; Li, Jing; Guo, Rui; Zhou, Yuan; Liu, Jing

    2017-10-18

    Metals are excellent choices for electrical- and thermal-current conducting. However, either the stiffness of solid metals or the fluidity of liquid metals could be troublesome when flexibility and formability are both desired. To address this problem, a reliable two-stage route to improve the functionalities of gallium-based liquid metals is proposed. A series of stable semiliquid/semisolid gallium-based liquid metal amalgams with well-controlled particle packing ratios, which we call TransM 2 ixes, are prepared and characterized. Through effectively packing the liquid metal with copper particles (which are found to turn into intermetallic compound, CuGa 2 , after dispersing), remarkable enhancements in electrical conductivity (6 × 10 6 S m -1 , ∼80% increase) and thermal conductivity (50 W m -1 K -1 , ∼100% increase) are obtained, making the TransM 2 ixes stand out from current conductive soft materials. The TransM 2 ixes also exhibit appealing semiliquid/semisolid mechanical behaviors such as excellent adhesion, tunable formability, and self-healing ability. As a class of highly conductive yet editable metallic mixtures, the TransM 2 ixes demonstrate potential applications in fields like printed and/or flexible electronics and thermal interface materials, as well as other circumstances where the flexibility and conductivity of interfaces and connections are crucial.

  1. Mechanical behavior of polymer-basedvs. metallic-based bioresorbable stents.

    Science.gov (United States)

    Ang, Hui Ying; Huang, Ying Ying; Lim, Soo Teik; Wong, Philip; Joner, Michael; Foin, Nicolas

    2017-08-01

    Bioresorbable scaffolds (BRS) were developed to overcome the drawbacks of current metallic drug-eluting stents (DES), such as late in-stent restenosis and caging of the vessel permanently. The concept of the BRS is to provide transient support to the vessel during healing before being degraded and resorbed by the body, freeing the vessel and restoring vasomotion. The mechanical properties of the BRS are influenced by the choice of the material and processing methods. Due to insufficient radial strength of the bioresorbable material, BRS often required large strut profile as compared to conventional metallic DES. Having thick struts will in turn affect the deliverability of the device and may cause flow disturbance, thereby increasing the incidence of acute thrombotic events. Currently, the bioresorbable poly-l-lactic acid (PLLA) polymer and magnesium (Mg) alloys are being investigated as materials in BRS technologies. The bioresorption process, mechanical properties, in vitro observations and clinical outcomes of PLLA-based and Mg-based BRS will be examined in this review.

  2. Mechanical properties of ultra thin metallic films revealed by synchrotron techniques

    Energy Technology Data Exchange (ETDEWEB)

    Gruber, Patric Alfons

    2007-07-20

    A prerequisite for the study of the scaling behavior of mechanical properties of ultra thin films is a suitable testing technique. Therefore synchrotron-based in situ testing techniques were developed and optimized in order to characterize the stress evolution in ultra thin metallic films on compliant polymer substrates during isothermal tensile tests. Experimental procedures for polycrystalline as well as single crystalline films were established. These techniques were used to systematically investigate the influence of microstructure, film thickness (20 to 1000 nm) and temperature (-150 to 200 C) on the mechanical properties. Passivated and unpassivated Au and Cu films as well as single crystalline Au films on polyimide substrates were tested. Special care was also dedicated to the microstructural characterization of the samples which was very important for the correct interpretation of the results of the mechanical tests. Down to a film thickness of about 100 to 200 nm the yield strength increased for all film systems (passivated and unpassivated) and microstructures (polycrystalline and singlecrystalline). The influence of different interfaces was smaller than expected. This could be explained by a dislocation source model based on the nucleation of perfect dislocations. For polycrystalline films the film thickness as well as the grain size distribution had to be considered. For smaller film thicknesses the increase in flow stress was weaker and the deformation behavior changed because the nucleation of perfect dislocations became unfavorable. Instead, the film materials used alternative mechanisms to relieve the high stresses. For regular and homogeneous deformation the total strain was accommodated by the nucleation and motion of partial dislocations. If the deformation was localized due to initial cracks in a brittle interlayer or local delamination, dislocation plasticity was not effective enough to relieve the stress concentration and the films showed

  3. Statistical mechanics of binary mixture adsorption in metal-organic frameworks in the osmotic ensemble

    Science.gov (United States)

    Dunne, Lawrence J.; Manos, George

    2018-03-01

    Although crucial for designing separation processes little is known experimentally about multi-component adsorption isotherms in comparison with pure single components. Very few binary mixture adsorption isotherms are to be found in the literature and information about isotherms over a wide range of gas-phase composition and mechanical pressures and temperature is lacking. Here, we present a quasi-one-dimensional statistical mechanical model of binary mixture adsorption in metal-organic frameworks (MOFs) treated exactly by a transfer matrix method in the osmotic ensemble. The experimental parameter space may be very complex and investigations into multi-component mixture adsorption may be guided by theoretical insights. The approach successfully models breathing structural transitions induced by adsorption giving a good account of the shape of adsorption isotherms of CO2 and CH4 adsorption in MIL-53(Al). Binary mixture isotherms and co-adsorption-phase diagrams are also calculated and found to give a good description of the experimental trends in these properties and because of the wide model parameter range which reproduces this behaviour suggests that this is generic to MOFs. Finally, a study is made of the influence of mechanical pressure on the shape of CO2 and CH4 adsorption isotherms in MIL-53(Al). Quite modest mechanical pressures can induce significant changes to isotherm shapes in MOFs with implications for binary mixture separation processes. This article is part of the theme issue `Modern theoretical chemistry'.

  4. Post-crisis Zimbabwe's innovative financing mechanisms in the social sectors: a practical approach to implementing the new deal for engagement in fragile states.

    Science.gov (United States)

    Salama, Peter; Ha, Wei; Negin, Joel; Muradzikwa, Samson

    2014-12-14

    Donor engagement in transitional settings, complex emergencies and fragile states is increasing. Neither short-term humanitarian aid nor traditional development financing are well adapted for such environments. Multi-donor trust funds, in their current form, can be unwieldy and subject to long delays in initiation and work best when national governments are already strong. We reviewed the aid modalities used in Zimbabwe through the period of crisis, 2008-2012 and their results and implications. Literature review and case experience was utilised. By focusing on working with line ministries in non-contested sectors to determine local priorities rather than following global prescriptions, pooling funds to achieve scale rather than delivering through fragmented projects, and building on national systems and capacities rather than setting up parallel mechanisms, the Transition Fund Model employed in Zimbabwe by UNICEF and partners in partnership with the Inclusive Government was able to achieve important results in health, education, social support and water services in a challenging setting. In addition, forums for collaboration were developed that provided a platform for further action. The initial emphasis on service delivery diffused much of the political delicateness that impeded progress in other sectors. The Zimbabwean experience may provide a model of innovative financing for countries facing similar circumstances. Such models may represent a new practical application of the Paris Principles, consistent with the major tenets of the 2011 New Deal for Engagement in Fragile States agreed in Busan. As we approach the Millennium Development Goal deadline, an over-arching, mutli-sectoral and independent evaluation of this approach is recommended in order to validate findings and assess broader replicability of this approach.

  5. Sector Switching

    DEFF Research Database (Denmark)

    Newman, Carol; Rand, John; Tarp, Finn

    Much of the literature on industry evolution has found firm dynamics to be an important source of sector-level productivity growth. In this paper, we ask whether the delineation of entry and exit firms matters in assessing the impact of firm turnover. Using detailed firm level data from Vietnam......, it emerges that efficiency differences between sector switchers and exit/entry firms exist. Distinguishing between switchers and firm entry/exit is crucial for understanding the contribution of firm turnover to overall productivity growth. Moreover, we uncover distinct and illuminating firm and sector...

  6. Cure and mechanical properties of carboxylated nitrile rubber (XNBR) vulcanized by alkaline earth metal compounds

    Science.gov (United States)

    Tulyapitak, Tulyapong

    Compounds of carboxylated nitrile rubber (XNBR) with alkaline metal oxides and hydroxide were prepared, and their cure and mechanical properties were investigated. Magnesium oxide (MgO) with different specific surface areas (45, 65, and 140 m2/g) was used. Increased specific surface area and concentration of MgO resulted in higher cure rate. Optimum stiffness, tensile strength, and ultimate strain required an equimolar amount of acidity and MgO. The effect of specific surface area on tensile properties was not significant. Crosslink density of XNBR-MgO vulcanizates increased with increased amounts of MgO. ATR-IR spectroscopy showed that neutralization occurs in two steps: (1) During mixing and storage, MgO reacts with carboxyl groups (RCOOH) to give RCOOMgOH. (2) Upon curing, these react bimolecularly to form RCOOMgOOCR and Mg(OH)2. Dynamic mechanical thermal analysis revealed an ionic transition at higher temperature, in addition to the glass transition. The ionic transition shifts to higher temperature with increasing MgO concentration. Like MgO-XNBR systems, cure rates of XNBR-calcium hydroxide (Ca(OH)2) and XNBR-barium oxide (BaO) compounds increased with increased content of curing agents. Curing by these two agents resulted in ionic crosslinks. To ensure optimum tensile properties, equimolar amounts of carboxyl groups and curing agents were required. Dynamic mechanical analysis revealed the ionic transition in these two systems. It shifted to higher temperature with increased amounts of curing agents. In contrast to MgO, Ca(OH)2, and BaO, calcium oxide (CaO) gave results similar to those for thermally cured samples. No ionic transition was observed in XNBR-CaO systems. Tensile strength of XNBR depended on the strength of ionic crosslinks, which was dependent on the size of the alkaline metal ions.

  7. Investigation of Reactivity Feedback Mechanism of Axial and Radial Expansion Effect of Metal-Fueled Sodium-Cooled Fast Reactor

    International Nuclear Information System (INIS)

    Seong, Seung-Hwan; Choi, Chi-Woong; Jeong, Tae-Kyung; Ha, Gi-Seok

    2015-01-01

    The major inherent reactivity feedback models for a ceramic fuel used in a conventional light water reactor are Doppler feedback and moderator feedback. The metal fuel has these two reactivity feedback mechanisms previously mentioned. In addition, the metal fuel has two more reactivity feedback models related to the thermal expansion phenomena of the metal fuel. Since the metal fuel has a good capability to expand according to the temperature changes of the core, two more feedback mechanisms exist. These additional two feedback mechanism are important to the inherent safety of metal fuel and can make metal-fueled SFR safer than oxide-fueled SFR. These phenomena have already been applied to safety analysis on design extended condition. In this study, the effect of these characteristics on power control capability was examined through a simple load change operation. The axial expansion mechanism is induced from the change of the fuel temperature according to the change of the power level of PGSFR. When the power increases, the fuel temperatures in the metal fuel will increase and then the reactivity will decrease due to the axial elongation of the metal fuel. To evaluate the expansion effect, 2 cases were simulated with the same scenario by using MMS-LMR code developed at KAERI. The first simulation was to analyze the change of the reactor power according to the change of BOP power without the reactivity feedback model of the axial and radial expansion of the core during the power transient event. That is to say, the core had only two reactivity feedback mechanism of Doppler and coolant temperature

  8. Investigating the Mechanical Behavior and Deformation Mechanisms of Ultrafinegrained Metal Films Using Ex-situ and In-situ TEM Techniques

    Science.gov (United States)

    Izadi, Ehsan

    Nanocrystalline (NC) and Ultrafine-grained (UFG) metal films exhibit a wide range of enhanced mechanical properties compared to their coarse-grained counterparts. These properties, such as very high strength, primarily arise from the change in the underlying deformation mechanisms. Experimental and simulation studies have shown that because of the small grain size, conventional dislocation plasticity is curtailed in these materials and grain boundary mediated mechanisms become more important. Although the deformation behavior and the underlying mechanisms in these materials have been investigated in depth, relatively little attention has been focused on the inhomogeneous nature of their microstructure (particularly originating from the texture of the film) and its influence on their macroscopic response. Furthermore, the rate dependency of mechanical response in NC/UFG metal films with different textures has not been systematically investigated. The objectives of this dissertation are two-fold. The first objective is to carry out a systematic investigation of the mechanical behavior of NC/UFG thin films with different textures under different loading rates. This includes a novel approach to study the effect of texture-induced plastic anisotropy on mechanical behavior of the films. Efforts are made to correlate the behavior of UFG metal films and the underlying deformation mechanisms. The second objective is to understand the deformation mechanisms of UFG aluminum films using in-situ transmission electron microscopy (TEM) experiments with Automated Crystal Orientation Mapping. This technique enables us to investigate grain rotations in UFG Al films and to monitor the microstructural changes in these films during deformation, thereby revealing detailed information about the deformation mechanisms prevalent in UFG metal films.

  9. A review of functionalized carbon nanotubes and graphene for heavy metal adsorption from water: Preparation, application, and mechanism.

    Science.gov (United States)

    Xu, Jiang; Cao, Zhen; Zhang, Yilin; Yuan, Zilin; Lou, Zimo; Xu, Xinhua; Wang, Xiangke

    2018-03-01

    Carbon-based nanomaterials, especially carbon nanotubes and graphene, have drawn wide attention in recent years as novel materials for environmental applications. Notably, the functionalized derivatives of carbon nanotubes and graphene with high surface area and adsorption sites are proposed to remove heavy metals via adsorption, addressing the pressing pollution of heavy metal. This critical revies assesses the recent development of various functionalized carbon nanotubes and graphene that are used to remove heavy metals from contaminated water, including the preparation and characterization methods of functionalized carbon nanotubes and graphene, their applications for heavy metal adsorption, effects of water chemistry on the adsorption capacity, and decontamination mechanism. Future research directions have also been proposed with the goal of further improving their adsorption performance, the feasibility of industrial applications, and better simulating adsorption mechanisms. Copyright © 2017 Elsevier Ltd. All rights reserved.

  10. Assessment of trace metals using lichen transplant from automobile mechanic workshop in Ile-Ife metropolis, Nigeria.

    Science.gov (United States)

    Odiwe, Anthony I; Adesanwo, Adeyemi T J; Olowoyo, Joshua O; Raimi, Idris O

    2014-04-01

    The level of air pollution around the automobile mechanic workshops has been generally overlooked. This study, examined the level of trace metals in automobile mechanic workshops and the suitability of using transplanted lichen thalli of Lepraria incana for measuring air pollution in such areas. Samples of the lichen thalli were transplanted into seven different sites and were attached to the bark of trees at each site. The samples were harvested from the sites after 3-month exposure. Concentrations of Pb, Cu, Cd, Fe, Zn, and S content were determined using an atomic absorption spectrophotometer. Results showed that there was a significant difference in the trace metals concentrations across the sites (p trend in the concentration of these heavy metals suggests that activities in these workshops might become a major source of certain heavy metals in the environment and if the pollution activities persist, it might become worrisome over time.

  11. Microstructure and mechanical behavior of direct metal laser sintered Inconel alloy 718

    Energy Technology Data Exchange (ETDEWEB)

    Smith, Derek H. [Department of Mechanical Engineering, University of New Hampshire, Durham, NH 03824 (United States); Bicknell, Jonathan; Jorgensen, Luke [Turbocam Energy Solutions, Turbocam International, Dover, NH 03820 (United States); Patterson, Brian M.; Cordes, Nikolaus L. [Materials Science Division, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States); Tsukrov, Igor [Department of Mechanical Engineering, University of New Hampshire, Durham, NH 03824 (United States); Knezevic, Marko, E-mail: marko.knezevic@unh.edu [Department of Mechanical Engineering, University of New Hampshire, Durham, NH 03824 (United States)

    2016-03-15

    In this paper, we investigate microstructure and quasi-static mechanical behavior of the direct metal laser sintered Inconel 718 superalloy as a function of build direction (BD). The printed material was further processed by annealing and double-aging, hot isostatic pressing (HIP), and machining. We characterize porosity fraction and distribution using micro X-ray computed tomography (μXCT), grain structure and crystallographic texture using electron backscattered diffraction (EBSD), and mechanical response in quasi-static tension and compression using standard mechanical testing at room temperature. Analysis of the μXCT imaging shows that majority of porosity develops in the outer layer of the printed material. However, porosity inside the material is also present. The EBSD measurements reveal formation of columnar grains, which favor < 001 > fiber texture components along the BD. These measurements also show evidence of coarse-grained microstructure present in the samples treated by HIP. Finally, analysis of grain boundaries reveal that HIP results in a large number of annealing twins compared to that in samples that underwent annealing and double-aging. The yield strength varies with the testing direction by approximately 7%, which is governed by a combination of grain morphology and crystallographic texture. In particular, we determine tension–compression asymmetry in the yield stress as well as anisotropy of the material flow during compression. We find that HIP lowers yield stress but improves ductility relative to the annealed and aged material. These results are discussed and critically compared with the data reported for wrought material in the same condition. - Highlights: • Microstructure and mechanical properties of DMLS Inconel 718 are studied in function of build direction. • Inhomogeneity of microstructure in the material in several conditions is quantified by μXCT and EBSD. • Anisotropy and asymmetry in the mechanical response are

  12. Fabrication process optimization for improved mechanical properties of Al 7075/SiCp metal matrix composites

    Directory of Open Access Journals (Sweden)

    Dipti Kanta Das

    2016-04-01

    Full Text Available Two sets of nine different silicon carbide particulate (SiCp reinforced Al 7075 Metal Matrix Composites (MMCs were fabricated using liquid metallurgy stir casting process. Mean particle size and weight percentage of the reinforcement were varied according to Taguchi L9 Design of Experiments (DOE. One set of the cast composites were then heat treated to T6 condition. Optical micrographs of the MMCs reveal consistent dispersion of reinforcements in the matrix phase. Mechanical properties were determined for both as-cast and heat treated MMCs for comparison of the experimental results. Linear regression models were developed for mechanical properties of the heat treated MMCs using list square method of regression analysis. The fabrication process parameters were then optimized using Taguchi based grey relational analysis for the multiple mechanical properties of the heat treated MMCs. The largest value of mean grey relational grade was obtained for the composite with mean particle size 6.18 µm and 25 weight % of reinforcement. The optimal combination of process parameters were then verified through confirmation experiments, which resulted 42% of improvement in the grey relational grade. Finally, the percentage of contribution of each process parameter on the multiple performance characteristics was calculated through Analysis of Variance (ANOVA.

  13. Jacking mechanism for upper internals structure of a liquid metal nuclear reactor

    International Nuclear Information System (INIS)

    Gillett, J.E.; Wineman, A.L.

    1984-01-01

    A jacking mechanism is described for raising the upper internals structure of a liquid metal nuclear reactor which jacking mechanism uses a system of gears and drive shafts to transmit force from a single motor to four mechanically synchronized ball jacks to raise and lower support columns which support the upper internals structure. The support columns have a pin structure which rides up and down in a slot in a housing fixed to the reactor head. The pin has two locking plates which can be rotated around the pin to bring bolt holes through the locking plates into alignment with a set of bolt holes in the housing, there being a set of such housing bolt holes corresponding to both a raised and a lowered position of the support column. When the locking plate is so aligned, a surface of the locking plate mates with a surface in the housing such that the support column is then supported by the locking plate and not by the ball jacks. Since the locking plates are to be installed and bolted to the housing during periods of reactor operation, the ball jacks need not be sized to react the large forces which occur or potentially could occur on the upper internals structure of the reactor during operation. The locking plates react these loads. The ball jacks, used only during refueling, can be smaller, which enable conventionally available equipment to fulfill the precision requirements for the task within available space

  14. The design Life calculation of non-metallic parts in mechanical components using Canadian analysis practice

    International Nuclear Information System (INIS)

    Park, Kyung Heum; Jeong, Sun Chul; Jang, Kyung Nam

    2009-01-01

    Canadian EQ(Environmental Qualification) standard is CSA N290.13-05 mentioned about qualification by analysis is possible only there exists mathematical modelling and comparison with established engineering information and manufacturers' data. So in Canada, EQ qualification by analysis alone are used very often whereas American's. American EQ qualification by analysis are usually used with another qualification method like type testing or operation experience. The typical Canadian qualification method by analysis is using System 1000 program. Most of Cadadian nuclear power utilities like NB Power(owns PointLepreau NPP), Hydro Quebec(owns Gentilly-2 NPP) and OPG(owns Pickering and Darlington NPPs) use the System 1000 program to evaluate the design life for their EQ components. This is the difference with American EQ. Type testing method is preferred than qualification by analysis in America. System 1000 program made by RCM Technologies, Inc. is Material Aging and Radiation Effects Library (they call MAREL). This program provides thermal information calculations, and radiation effects data for organic materials used in various environments. The EQ component selection method is also different American with Canadian. Americans select only electrical components as EQ component, Canadians select both electrical and mechanical component as EQ components. So I use the System 1000 program only for the mechanical components. In this paper, I'd like to practice the Canadian analysis method, using System 1000 program for the design life calculation only for the non-metallic parts in mechanical components

  15. Kinetics and Mechanism of Metal Retention/Release in Geochemical Processes in Soil - Final Report

    Energy Technology Data Exchange (ETDEWEB)

    Taylor, Robert W.

    2000-12-29

    Effective, remediation of soils contaminated with heavy metals requires a better understanding of the mechanisms by which the metals are retained/released in soils over a long period of time. Studies on reaction of Cr(VI) with iron-rich clays indicated that structural iron (II) in these surfaces is capable of reducing chromate to chromium (III). We found that iron (II) either found naturally or produced by treatment of clay with sodium dithionite, effectively reduced Cr (VI) to Cr (III). Thus, in situ remediation of chromium combines reduction of Cr (VI) to Cr (III) and immobilization of chromium on mineral surfaces. During this study, lead sorption on a kaolin surface was found to be a rapid and a pH dependant process in which lead sorption significantly increased with the amount of phosphate on the clay surface. This study verifies that methylmercury cation remains intact when it binds to humic acids, forming a monodentate complex with some sub-population of humic thiol ligands .

  16. The Hydrolytic Stability and Degradation Mechanism of a Hierarchically Porous Metal Alkylphosphonate Framework

    Directory of Open Access Journals (Sweden)

    Kai Lv

    2018-03-01

    Full Text Available To aid the design of a hierarchically porous unconventional metal-phosphonate framework (HP-UMPF for practical radioanalytical separation, a systematic investigation of the hydrolytic stability of bulk phase against acidic corrosion has been carried out for an archetypical HP-UMPF. Bulk dissolution results suggest that aqueous acidity has a more paramount effect on incongruent leaching than the temperature, and the kinetic stability reaches equilibrium by way of an accumulation of a partial leached species on the corrosion conduits. A variation of particle morphology, hierarchical porosity and backbone composition upon corrosion reveals that they are hydrolytically resilient without suffering any great degradation of porous texture, although large aggregates crack into sporadic fractures while the nucleophilic attack of inorganic layers cause the leaching of tin and phosphorus. The remaining selectivity of these HP-UMPFs is dictated by a balance between the elimination of free phosphonate and the exposure of confined phosphonates, thus allowing a real-time tailor of radionuclide sequestration. Moreover, a plausible degradation mechanism has been proposed for the triple progressive dissolution of three-level hierarchical porous structures to elucidate resultant reactivity. These HP-UMPFs are compared with benchmark metal-organic frameworks (MOFs to obtain a rough grading of hydrolytic stability and two feasible approaches are suggested for enhancing their hydrolytic stability that are intended for real-life separation protocols.

  17. Influence of implantation of three metallic ions on the mechanical properties of two polymers

    Energy Technology Data Exchange (ETDEWEB)

    Swain, M.V. [Commonwealth Scientific and Industrial Research Organisation (CSIRO), Lindfield, NSW (Australia). Div. of Applied Physics; Perry, A.J. [Australian National Univ., Canberra, ACT (Australia); Treglio, J.R.

    1996-12-31

    Ion implantation of poly ethylene terephthalate (PET) and polystyrene (PS) with various high energy metallic ions at 70 kV to dose of 3 x 10{sup 16} ions/cm 2 have been made. Measurements of the mechanical properties of the polymers before and after implantation have been made with an ultra microindentation system using both pointed and a small (2 nm) radiused spherical tipped indenter. Significant differences have been observed between the Ti-B dual implanted surfaces and those of the Au and W implanted surfaces. For both the PET and PS the resistance to indenter penetration at very low loads was much greater for the Ti-B dual implanted surfaces. The estimated hardness and modulus versus depth of penetration for both indenters shows that the spherical indenter produces more consistent and less controversial values that are somewhat lower than the optimistic estimates from pointed indenters. 8 refs., 2 fig.

  18. Effect of Sphere Properties on Microstructure and Mechanical Performance of Cast Composite Metal Foams

    Directory of Open Access Journals (Sweden)

    Matias Garcia-Avila

    2015-05-01

    Full Text Available Aluminum-steel composite metal foams (Al-S CMF are manufactured using steel hollow spheres, with a variety of sphere carbon content, surface roughness, and wall porosity, embedded in an Aluminum matrix through gravity casting technique. The microstructural and mechanical properties of the material were studied using scanning electron microscopy, energy dispersive spectroscopy, and quasi-static compressive testing. Higher carbon content and surface roughness in the sphere wall were responsible for an increase in formation of intermetallic phases which had a strengthening effect at lower strain levels, increasing the yield strength of the material by a factor of 2, while higher sphere wall porosity resulted in a decrease on the density of the material and improving its cushioning and ductility maintaining its energy absorption capabilities.

  19. Microstructural and mechanical properties on friction welding of dissimilar metals used in motor vehicles

    Science.gov (United States)

    Jesudoss Hynes, N. Rajesh; Shenbaga Velu, P.

    2018-02-01

    In the last two decades, major car manufacturing companies are exploring the possibilities of joining magnesium with aluminium, via friction welding technique for many crucial automotive applications. Our primary objective, is to carry out an experimental investigation in order to study the behaviour of dissimilar joints. The microscopic structure at the welded joint interface was analysed using an optical microscopy and scanning electron microscope. It was found that, by increasing the value of friction time, the value of the tensile strength increases and the result of tensile strength is found to be 120 MPa at a friction time of 10 s. Micro hardness was found to be higher at the interface of the weldment due to the development of a brittle intermetallic compound. Micro structural studies using SEM reveals, distinct zones such as an unaffected parent metal zone, the heat affected zone, a thermo-mechanically affected zone and a fully deformed plasticised zone.

  20. Achieving optimum mechanical performance in metallic nanolayered Cu/X (X = Zr, Cr) micropillars

    Science.gov (United States)

    Zhang, J. Y.; Li, J.; Liang, X. Q.; Liu, G.; Sun, J.

    2014-03-01

    The selection and design of modern high-performance structural engineering materials such as nanostructured metallic multilayers (NMMs) is driven by optimizing combinations of mechanical properties and requirements for predictable and noncatastrophic failure in service. Here, the Cu/X (X = Zr, Cr) nanolayered micropillars with equal layer thickness (h) spanning from 5-125 nm are uniaxially compressed and it is found that these NMMs exhibit a maximum strain hardening capability and simultaneously display a transition from bulk-like to small-volume materials behavior associated with the strength at a critical intrinsic size h ~ 20 nm. We develop a deformation mode-map to bridge the gap between the interface characteristics of NMMs and their failure phenomena, which, as shrinking the intrinsic size, transit from localized interface debonding/extrusion to interface shearing. Our findings demonstrate that the optimum robust performance can be achieved in NMMs and provide guidance for their microstructure sensitive design for performance optimization.

  1. Mechanical and diffusion properties of refractory me--tal and alloy monocrystals

    International Nuclear Information System (INIS)

    Shinyaev, A.Ya.; Kopalejshvili, N.I.

    1977-01-01

    The temperature dependence of mechanical properties of single crystals Mo, W, Ta, Nb and of alloys Mo-Ta and Nb-Ta has been investigated from the point of view of diffusion processes. The curve of the dependence of the ultimate strength upon the temperature has shown four discontinuities corresponding to various stages of development of intercrystalline and volume diffusions. It is shown that for close-to-ideal solid solutions of Nb-Ta alloys the temperature dependence of the strength properties is the same as for pure metals. In case of appreciable deviations from ideal properties (system Mo-Ta), the drops in strength, due to volume diffusion, shift toward higher temperatures

  2. Light Hydrocarbons Adsorption Mechanisms in Two Calcium-based Microporous Metal Organic Frameworks

    KAUST Repository

    Plonka, Anna M.

    2016-01-25

    The adsorption mechanism of ethane, ethylene and acetylene (C2Hn; n=2, 4, 6) on two microporous metal organic frameworks (MOFs) is described here that is consistent with observations from single crystal and powder X-ray diffraction, calorimetric measurments and gas adsorption isotherm measurements. Two calcium-based MOFs, designated as SBMOF-1 and SBMOF-2 (SB: Stony Brook), form three-dimensional frameworks with one-dimensional open channels. As determined form single crystal diffraction experiments channel geometries of both SBMOF-1 and SBMOF-2 provide multiple adsorption sites for hydrocarbon molecules trough C-H…π and C-H…O interactions, similarly to interactions in the molecular and protein crystals. Both materials selectively adsorb C2 hydrocarbon gases over methane as determined with IAST and breakthrough calculations, with C2H6/CH4 selectivity as high as 74 in SBMOF-1.

  3. Microstructure and mechanical properties of a novel β titanium metallic composite by selective laser melting

    International Nuclear Information System (INIS)

    Vrancken, B.; Thijs, L.; Kruth, J.-P.; Van Humbeeck, J.

    2014-01-01

    Selective laser melting (SLM) is an additive manufacturing process in which functional, complex parts are produced by selectively melting consecutive layers of powder with a laser beam. This flexibility enables the exploration of a wide spectrum of possibilities in creating novel alloys or even metal–metal composites with unique microstructures. In this research, Ti6Al4V-ELI powder was mixed with 10 wt.% Mo powder. In contrast to the fully α′ microstructure of Ti6Al4V after SLM, the novel microstructure consists of a β titanium matrix with randomly dispersed pure Mo particles, as observed by light optical microscopy, scanning electron microscopy and X-ray diffraction. Most importantly, the solidification mechanism changes from planar to cellular mode. Microstructures after heat treatment indicate that the β phase is metastable and locate the β transus at ∼900 °C, and tensile properties are equal to or better than conventional β titanium alloys

  4. Mechanical-optical-electro modulation by stretching a polymer-metal nanocomposite

    Science.gov (United States)

    Minnai, Chloé; Di Vece, Marcel; Milani, Paolo

    2017-09-01

    We report the simultaneous investigation of both the plasmonic resonance and electrical conductance evolution in stretchable metal-polymer nanocomposite films. The films are produced by the implantation of neutral gold nanoparticles in a polydimethylsiloxane substrate by aerodynamic acceleration in a supersonic expansion. A redshift of the gold nanoparticle plasmon peak is found upon stretching as well as a strong correlation between the plasmonic peak wavelength and the nanocomposite electrical resistance. Optical simulations attribute the optical response to the compression of the polymer perpendicular to the stretching direction, which brings the gold particles closer to each other, increasing the plasmonic coupling. Mechanical stretching can induce a simultaneous modulation of the optical and electrical properties of the nanocomposite.

  5. Mechanical Properties of the 2D Re-entrant Honeycomb Made via Direct Metal Printing

    Science.gov (United States)

    Alomarah, Amer; Zhang, Jianjun; Ruan, Dong; Masood, Syed; Lu, Guoxing

    2017-09-01

    Auxetic structural materials show distinctive properties by exhibiting a negative Poisson’s ratio (NPR). When these structures are subjected to uniaxial loading, they expand in tension and contract in compression in both loading and lateral directions. In this paper, two AlSi12 re-entrant honeycomb samples were manufactured using direct metal printing (DMP). Quasi-static uniaxial tension was executed in both X and Y direction. A Digital VIC-2D Image Correlation System was used to record the deformation history. Force and displacement were measured by ZWICK machine. The results show that loading direction has a significant effect on the mechanical properties and auxeticity of the tested structure. Re-entrant honeycomb under X-loading withstand lower force and has smaller magnitude of Poisson’s ratio compared with that under Y-loading.

  6. The Process of Nanostructuring of Metal (Iron Matrix in Composite Materials for Directional Control of the Mechanical Properties

    Directory of Open Access Journals (Sweden)

    Elena Zemtsova

    2014-01-01

    Full Text Available We justified theoretical and experimental bases of synthesis of new class of highly nanostructured composite nanomaterials based on metal matrix with titanium carbide nanowires as dispersed phase. A new combined method for obtaining of metal iron-based composite materials comprising the powder metallurgy processes and the surface design of the dispersed phase is considered. The following stages of material synthesis are investigated: (1 preparation of porous metal matrix; (2 surface structuring of the porous metal matrix by TiC nanowires; (3 pressing and sintering to give solid metal composite nanostructured materials based on iron with TiC nanostructures with size 1–50 nm. This material can be represented as the material type “frame in the frame” that represents iron metal frame reinforcing the frame of different chemical compositions based on TiC. Study of material functional properties showed that the mechanical properties of composite materials based on iron with TiC dispersed phase despite the presence of residual porosity are comparable to the properties of the best grades of steel containing expensive dopants and obtained by molding. This will solve the problem of developing a new generation of nanostructured metal (iron-based materials with improved mechanical properties for the different areas of technology.

  7. Effect of Intraoral Mechanical Cleaning Techniques on Bond Strength of Cast Crowns to Metal Cores.

    Science.gov (United States)

    AlZain, Sahar; Kattadiyil, Mathew T; AlHelal, Abdulaziz; Alqahtani, Ali

    2017-11-30

    To evaluate the effect of cleaning of metal cores from provisional cement, using an intraoral airborne-particle abrasion method, on the bond strength of permanent resin cement with cast crowns to cores. Thirty stainless steel models of a standard complete crown tooth preparation were fabricated. Thirty Type III gold crowns were fabricated. Each cast crown corresponded to one stainless steel crown preparation model. All crowns were cemented with noneugenol zinc oxide cement and stored for 7 days at 37°C. All crowns were debonded, and the cement was cleaned with airborne-particle abrasion using 50 μm aluminum oxide at 4.1 bar (0.41 MPa) followed by ultrasonic cleaning. Based on the mechanical cleaning technique of the remaining provisional cement on surfaces of cast cores, specimens were equally divided into 3 groups: hand cleaning (HC) with a dental excavator, hand cleaning followed by polishing using a brush and pumice (BP), and hand cleaning followed by intraoral airborne-particle abrasion (APA). All crowns were then cemented to their corresponding cores using universal resin cement. All crowns were stored for 7 days at 37°C. An Instron universal testing machine was used to record the bond strength of crowns. Airborne-particle abrasion method for intraoral mechanical cleaning revealed a statistically significantly higher bond strength compared to the other two methods. When comparing the three methods of provisional cement cleaning from metal cores, airborne-particle abrasion resulted in the highest bond strength for cast crowns. © 2017 by the American College of Prosthodontists.

  8. Effect of thermal and mechanical parameter’s damage numerical simulation cycling effects on defects in hot metal forming processes

    Science.gov (United States)

    El Amri, Abdelouahid; el yakhloufi Haddou, Mounir; Khamlichi, Abdellatif

    2017-10-01

    Damage mechanisms in hot metal forming processes are accelerated by mechanical stresses arising during Thermal and mechanical properties variations, because it consists of the materials with different thermal and mechanical loadings and swelling coefficients. In this work, 3D finite element models (FEM) are developed to simulate the effect of Temperature and the stresses on the model development, using a general purpose FE software ABAQUS. Explicit dynamic analysis with coupled Temperature displacement procedure is used for a model. The purpose of this research was to study the thermomechanical damage mechanics in hot forming processes. The important process variables and the main characteristics of various hot forming processes will also be discussed.

  9. The effect of governance mechanisms on food safety in the supply chain: Evidence from the Lebanese dairy sector.

    Science.gov (United States)

    Abebe, Gumataw K; Chalak, Ali; Abiad, Mohamad G

    2017-07-01

    Food safety is a key public health issue worldwide. This study aims to characterise existing governance mechanisms - governance structures (GSs) and food safety management systems (FSMSs) - and analyse the alignment thereof in detecting food safety hazards, based on empirical evidence from Lebanon. Firm-to-firm and public baseline are the dominant FSMSs applied in a large-scale, while chain-wide FSMSs are observed only in a small-scale. Most transactions involving farmers are relational and market-based in contrast to (large-scale) processors, which opt for hierarchical GSs. Large-scale processors use a combination of FSMSs and GSs to minimise food safety hazards albeit potential increase in coordination costs; this is an important feature of modern food supply chains. The econometric analysis reveals contract period, on-farm inspection and experience having significant effects in minimising food safety hazards. However, the potential to implement farm-level FSMS is influenced by formality of the contract, herd size, trading partner choice, and experience. Public baseline FSMSs appear effective in controlling food safety hazards; however, this may not be viable due to the scarcity of public resources. We suggest public policies to focus on long-lasting governance mechanisms by introducing incentive schemes and farm-level FSMSs by providing loans and education to farmers. © 2016 Society of Chemical Industry. © 2016 Society of Chemical Industry.

  10. Fundamental mechanisms of oxidation of alkaline earth-bearing metal precursors: yttrium-barium-copper-silver-palladium and silver bariate

    Science.gov (United States)

    Sitaraman, Vilayannur R.

    Noble-metal-bearing metallic precursors can be selectively oxidized to yield oxide/noble metal composites. This processing method is investigated for producing 123/Ag-Pd laminates from a solid metallic Y-Ba-Cu-Ag-Pd precursor. A unique feature heretofore unnoticed is the external oxidation mechanism of Ba. The extent of external oxidation at 840C in a 3%H2-Ar atmosphere (PO2 ˜ 10-19 atm.) as measured by a segregation factor, is higher for Ba than for Y. Combined with the fact that Ba does not have significant solid solubility in Ag, Cu or Pd, this means that a short circuit transport path is possible for transport of Ba through such metals as described in chapter 1. Since diffusion through grain boundaries, is fast, the effective permeability of Ba can be relatively high even though its solubility is low. This proposed mechanism is proven using a model system, the Ag5Ba intermetallic compound. Both internal and external oxidation has been demonstrated in this material. Grain boundary diffusion is demonstrated using Ag clad Ag 5Ba. Due to a change in the mechanism from external to internal oxidation of Y in Y-Ba-Cu-Ag-Pd alloys, the imbalance in the surface stoichiometry caused by Ba segregation is not easily removed. A mechanism proposed by Meijering for copper oxide dissolution, Cu migration and Cu reoxidation at the outer surface is also consistent with the microstructural observations in oxidized Y-Ba-Cu-Ag-Pd specimens.

  11. Devitrification kinetics and phase selection mechanisms in Cu-Zr metallic glasses

    Energy Technology Data Exchange (ETDEWEB)

    Kalay, Ilkay [Iowa State Univ., Ames, IA (United States)

    2010-01-01

    Metallic glasses have been a promising class of materials since their discovery in the 1960s. Indeed, remarkable chemical, mechanical and physical properties have attracted considerable attention, and several excellent reviews are available. Moreover, the special group of glass forming alloys known as the bulk metallic glasses (BMG) become amorphous solids even at relatively low cooling rates, allowing them to be cast in large cross sections, opening the scope of potential applications to include bulk forms and net shape structural applications. Recent studies have been reported for new bulk metallic glasses produced with lower cooling rates, from 0.1 to several hundred K/s. Some of the application products of BMGs include sporting goods, high performance springs and medical devices. Several rapid solidification techniques, including melt-spinning, atomization and surface melting have been developed to produce amorphous alloys. The aim of all these methods is to solidify the liquid phase rapidly enough to suppress the nucleation and growth of crystalline phases. Furthermore, the production of amorphous/crystalline composite (ACC) materials by partial crystallization of amorphous precursor has recently given rise to materials that provide better mechanical and magnetic properties than the monolithic amorphous or crystalline alloys. In addition, these advances illustrate the broad untapped potential of using the glassy state as an intermediate stage in the processing of new materials and nanostructures. These advances underlie the necessity of investigations on prediction and control of phase stability and microstructural dynamics during both solidification and devitrification processes. This research presented in this dissertation is mainly focused on Cu-Zr and Cu-Zr-Al alloy systems. The Cu-Zr binary system has high glass forming ability in a wide compositional range (35-70 at.% Cu). Thereby, Cu-Zr based alloys have attracted much attention according to fundamental

  12. Estimation and diminution of CO2 emissions by clean development mechanism option at power sector in Oman

    Energy Technology Data Exchange (ETDEWEB)

    Singh Solanki, Parmal; Sarma Mallela, Venkateswara [Caledonian (University) College of Engineering, Muscat (Oman); Zhou, Chengke [Glasgow Caledonian University, Glasgow, Scotland (United Kingdom)

    2013-07-01

    Carbon dioxide (CO2) is one of the major pollutants among greenhouse gases emitted by fossil fuel based power plants and responsible for environmental tribulations. Therefore diminution of carbon dioxide level by Clean Development Mechanism (CDM) is now serious concern worldwide. This paper evaluates the emission factors of national electric grid in Oman and proposes a wind energy based CDM project to diminish the CO2 emissions. Estimations show that operating margin emission factors of national grid during five years lies in the range of 0.74 to 0.69 kg CO2/kWh. Further, proposed CDM project revealed the annual baseline emissions reduction of 45552 ton CO2 and able to earn the revenue of US$ 61.49 million by certify emission reductions in the first crediting period of project. Paper also critically analyse the opportunities for CDM project, its lucrative aspect, barrier and challenges.

  13. Computer-aided study of key factors determining high mechanical properties of nanostructured surface layers in metal-ceramic composites

    Science.gov (United States)

    Konovalenko, Igor S.; Shilko, Evgeny V.; Ovcharenko, Vladimir E.; Psakhie, Sergey G.

    2017-12-01

    The paper presents the movable cellular automaton method. It is based on numerical models of surface layers of the metal-ceramic composite NiCr-TiC modified under electron beam irradiation in inert gas plasmas. The models take into account different geometric, concentration and mechanical parameters of ceramic and metallic components. The authors study the contributions of key structural factors in mechanical properties of surface layers and determine the ranges of their variations by providing the optimum balance of strength, strain hardening and fracture toughness.

  14. Efficient modeling of metallic interconnects for thermo-mechanical simulation of SOFC stacks: homogenized behaviors and effect of contact

    DEFF Research Database (Denmark)

    Tadesse Molla, Tesfaye; Kwok, Kawai; Frandsen, Henrik Lund

    2016-01-01

    Currently thermo-mechanical analysis of the entire solid oxide fuel cell (SOFC) stack at operational conditions is computationally challenging if the geometry of metallic interconnects is considered explicitly. This is particularly the case when creep deformations in the interconnect are considered...... interconnect. Finally, the developed constitutive law is verified by comparing its predictions for creep strain with results from the original 2D finite element model for different loading conditions. The constitutive law is found to satisfactorily describe the mechanical behavior of corrugated metallic...

  15. Regional transport sector mitigation options

    Energy Technology Data Exchange (ETDEWEB)

    Zhou, Peter [EECG Consultants, Gaborone (Botswana)

    1998-10-01

    The rationale for conducting climate change mitigation studies in the transport sector is on the premise that: The transport sector is the second largest consumer of fossil fuels in the region; The regional transport sector is an area with high opportunity for infrastructural development under UNFCCC financial mechanism; The regional transport sector is crucial in the SADC region for trade and coupled with the Trade Protocol will play a major role in development hence the need to make it efficient in terms of energy demand and provision of services; The sector offers many mitigation options but with a challenge to evaluate their energy saving and GHG saving potential and yet there is need to quantify possible emission reduction for possible future emission trading. This is also a sector with potential to qualify for financing through Clean Development Mechanism (CDM) recently stipulated in the Kyoto Protocol. (au)

  16. Regional transport sector mitigation options

    International Nuclear Information System (INIS)

    Zhou, Peter

    1998-01-01

    The rationale for conducting climate change mitigation studies in the transport sector is on the premise that: The transport sector is the second largest consumer of fossil fuels in the region; The regional transport sector is an area with high opportunity for infrastructural development under UNFCCC financial mechanism; The regional transport sector is crucial in the SADC region for trade and coupled with the Trade Protocol will play a major role in development hence the need to make it efficient in terms of energy demand and provision of services; The sector offers many mitigation options but with a challenge to evaluate their energy saving and GHG saving potential and yet there is need to quantify possible emission reduction for possible future emission trading. This is also a sector with potential to qualify for financing through Clean Development Mechanism (CDM) recently stipulated in the Kyoto Protocol. (au)

  17. Photoemission mechanism of water-soluble silver nanoclusters: ligand-to-metal-metal charge transfer vs strong coupling between surface plasmon and emitters.

    Science.gov (United States)

    Chen, Yuting; Yang, Taiqun; Pan, Haifeng; Yuan, Yufeng; Chen, Li; Liu, Mengwei; Zhang, Kun; Zhang, Sanjun; Wu, Peng; Xu, Jianhua

    2014-02-05

    Using carboxylate-protected silver nanoclusters (Ag-carboxylate NCs) as a model, we separately investigated the contribution of the ligand shell and the metal core to understand the nature of photoluminescence of Ag NCs. A new Ag(0)NCs@Ag(I)-carboxylate complex core-shell structural model has been proposed. The emission from the Ag-carboxylate NCs could be attributed to ligand-to-metal-metal charge transfer from Ag(I)-carboxylate complexes (the oxygen atom in the carboxylate ligands to the Ag(I) ions) to the Ag atoms and subsequent radiative relaxation. Additionally, we found that the emission wavelength of the Ag NCs depends on the excitation wavelength implying a strong coupling between surface plasmon and emitter in Ag NCs. The strong coupling between the surface plasmon and the emitter determines the quantum yield and lifetime. The emission mechanism of Ag NCs and its relation to the organic templates and metal cores were clearly clarified. The results should stimulate additional experimental and theoretical research on the molecular-level design of luminescent metal probes for optoelectronics and other applications.

  18. Macro-mechanical material model for fiber reinforced metal matrix composites

    CERN Document Server

    Banks-Sills, L

    1999-01-01

    The stress-strain behavior of a metal matrix composite reinforced with unidirectional, continuous and periodic fibers is investigated. Three-dimensional micro-mechanical analyses of a unit cell by means of the finite element method $9 and homogenization-localization are carried out. These calculations allow the determination of material behavior of the in-plane, as well as the fiber directions. The fibers are assumed to be elastic and the matrix elasto-plastic. $9 The matrix material is governed by a von Mises yield surface, isotropic hardening and an associated flow rule. With the aid of these analyses, the foundation to a macro-mechanical material model is presented which is employed to $9 consider an elementary problem. The model includes an anisotropic yield surface with isotropic hardening and an associated flow rule. A beam in bending containing square fibers under plane strain conditions is analyzed by means of $9 the model. Two cases are considered: one in which the fibers are symmetric with respect t...

  19. Microstructural damage and residual mechanical properties in helium-bearing gas metal Arc weldments

    Science.gov (United States)

    Goods, S. H.; Yang, N. Y. C.

    1992-03-01

    The influence of entrapped helium on microstructural damage and residual mechanical properties subsequent to applying low-penetration gas metal arc (GMA) weld overlays was examined for an AISI Type 304 stainless steel. Two helium levels were examined: 22.5 and 85.0 atomic parts per million (appm) He. Detailed scanning electron microscopy (SEM) revealed the presence of intergranular cracks in the weld heat-affected zone (HAZ). The crack surfaces exhibited a dimple structure that was characteristic of a gas bubble embrittled material. Transmission electron microscopy (TEM) revealed that the size and spacing of the grain boundary helium gas bubbles remained virtually unchanged (relative to that established by the charging and aging procedure) at distances greater than 1 mm from the fusion line. Within this first millimeter, the diameter of the bubbles increased rapidly, and the bubble spacing increased to the characteristic spacing of the dimples that decorated weld-induced cracks. Mechanical testing revealed a loss in strain-to-fracture and ultimate tensile strength (UTS) at the higher helium level. While the majority of the fracture occurred in a transgranular, ductile manner, some deformation-induced intergranular cracking was observed. This cracking occurred over a very narrow region localized to the HAZ of the weldment. At the lower helium level, ductility and strength were unaffected compared to helium-free specimens.

  20. Mechanical modeling of creep, swelling and damage under irradiation for polycrystalline metals

    International Nuclear Information System (INIS)

    Murakami, S.; Mizuno, M.; Okamoto, T.

    1991-01-01

    A constitutive equation of creep, swelling and damage under irradiation for polycrystalline metals applicable to structural analyses in multiaxial state of stress is developed. After reviewing microscopic mechanisms of irradiation creep and swelling, the relevant theories proposed so far from the view point of metallurgical physics and their applicability are discussed first. Then a constitutive model is developed by assuming that creep under irradiation can be decomposed into irradiation-affected thermal creep and irradiation-induced creep. By taking account of the Stress-Induced Preferential Absorption (SIPA) mechanism, the irradiation-induced creep is represented by an isotropic tensor function of order one and zero with respect to stress, which is, at the same time, the function of neutron flux and neutron fluence. The volumetric part of the irradiation-induced creep is identified with swelling. The irradiation-affected thermal creep is described by modifying Kachanov-Rabotnov theory for stress-controlled creep and creep damage by incorporating the effect of irradiation. Finally irradiation creep and swelling of 20% cold-worked type 316 stainless steel at elevated temperature are predicted by the proposed constitutive equations, and the numerical results are compared with the corresponding experimental results. (orig.)

  1. Alkali Metal Cation versus Proton and Methyl Cation Affinities: Structure and Bonding Mechanism.

    Science.gov (United States)

    Boughlala, Zakaria; Fonseca Guerra, Célia; Bickelhaupt, F Matthias

    2016-06-01

    We have analyzed the structure and bonding of gas-phase Cl-X and [HCl-X](+) complexes for X(+)= H(+), CH3 (+), Li(+), and Na(+), using relativistic density functional theory (DFT). We wish to establish a quantitative trend in affinities of the anionic and neutral Lewis bases Cl(-) and HCl for the various cations. The Cl-X bond becomes longer and weaker along X(+) = H(+), CH3 (+), Li(+), and Na(+). Our main purpose is to understand the heterolytic bonding mechanism behind the intrinsic (i.e., in the absence of solvent) alkali metal cation affinities (AMCA) and how this compares with and differs from those of the proton affinity (PA) and methyl cation affinity (MCA). Our analyses are based on Kohn-Sham molecular orbital (KS-MO) theory in combination with a quantitative energy decomposition analysis (EDA) that pinpoints the importance of the different features in the bonding mechanism. Orbital overlap appears to play an important role in determining the trend in cation affinities.

  2. Industrial sector

    International Nuclear Information System (INIS)

    Ainul Hayati Daud; Hazmimi Kasim

    2010-01-01

    The industrial sector is categorized as related to among others, the provision of technical and engineering services, supply of products, testing and troubleshooting of parts, systems and industrial plants, quality control and assurance as well as manufacturing and processing. A total of 161 entities comprising 47 public agencies and 114 private companies were selected for the study in this sector. The majority of the public agencies, 87 %, operate in Peninsular Malaysia. The remainders were located in Sabah and Sarawak. The findings of the study on both public agencies and private companies are presented in subsequent sections of this chapter. (author)

  3. Agricultural sector

    International Nuclear Information System (INIS)

    Ainul Hayati Daud; Hazmimi Kasim

    2010-01-01

    The applications of nuclear technology in agriculture sector cover the use of the technology at every aspects of agricultural activity, starting from the seed to harvesting as well as the management of plantations itself. In this sector, a total of 55 entities comprising 17 public agencies and 38 private companies were selected for the study. Almost all, 91 % of them are located in Peninsular Malaysia; the rest operates in Sabah and Sarawak. The findings of the study in the public agencies and private companies are presented in the next sections. (author)

  4. Metallurgy and mechanical properties variation with heat input,during dissimilar metal welding between stainless and carbon steel

    Science.gov (United States)

    Ramdan, RD; Koswara, AL; Surasno; Wirawan, R.; Faturohman, F.; Widyanto, B.; Suratman, R.

    2018-02-01

    The present research focus on the metallurgy and mechanical aspect of dissimilar metal welding.One of the common parameters that significantly contribute to the metallurgical aspect on the metal during welding is heat input. Regarding this point, in the present research, voltage, current and the welding speed has been varied in order to observe the effect of heat input on the metallurgical and mechanical aspect of both welded metals. Welding was conducted by Gas Metal Arc Welding (GMAW) on stainless and carbon steel with filler metal of ER 309. After welding, hardness test (micro-Vickers), tensile test, macro and micro-structure characterization and Energy Dispersive Spectroscopy (EDS) characterization were performed. It was observed no brittle martensite observed at HAZ of carbon steel, whereas sensitization was observed at the HAZ of stainless steel for all heat input variation at the present research. Generally, both HAZ at carbon steel and stainless steel did not affect tensile test result, however the formation of chromium carbide at the grain boundary of HAZ structure (sensitization) of stainless steel, indicate that better process and control of welding is required for dissimilar metal welding, especially to overcome this issue.

  5. Forests and global warming mitigation in Brazil: opportunities in the Brazilian forest sector for responses to global warming under the 'clean development mechanism''

    International Nuclear Information System (INIS)

    Fearnside, P.M.

    1999-01-01

    The Kyoto Protocol created global warming response opportunities through the clean development mechanism that allow countries like Brazil to receive investments from companies and governments wishing to offset their emissions of greenhouse gases. Brazil has a special place in strategies for combating global warming because its vast areas of tropical forest represent a potentially large source of emissions if deforested. A number of issues need to be settled to properly assign credit for carbon in the types of options presented by the Brazilian forest sector. These include definition of the units of carbon (permanent sequestration versus carbon-ton-years, the latter being most appropriate for forest options), the means of crediting forest reserve establishment, adoption of discounting or other time-preference weighting for carbon, definition of the accounting method (avoided emissions versus stock maintenance), and mechanism to allow program contributions to be counted, rather than restricting consideration to free-standing projects. Silvicultural plantations offer opportunities for carbon benefits, but have high social impacts in the Brazilian context. Plantations also inherently compete with deforestation reduction options for funds. Forest management has been proposed as a global warming response option, but the assignment of any value to time makes this unattractive in terms of carbon benefits. However, reduced-impact logging can substantially reduce emissions over those from traditional logging practices. Slowing deforestation is the major opportunity offered by Brazil. Slowing deforestation will require understanding its causes and creating functional models capable of generating land-use change scenarios with and without different policy changes and other activities. Brazil already has a number of programs designed to slow deforestation, but the continued rapid loss of forest highlights the vast gulf that exists between the magnitude of the problem and the

  6. Lessons Learned from the Private Sector

    Energy Technology Data Exchange (ETDEWEB)

    Robichaud, Robert J [National Renewable Energy Laboratory (NREL), Golden, CO (United States)

    2017-09-07

    This session is focused on lessons learned from private sector energy projects that could be applied to the federal sector. This presentation tees up the subsequent presentations by outlining the differences between private and federal sectors in objectives, metrics for determining success, funding resources/mechanisms, payback and ROI evaluation, risk tolerance/aversion, new technology adoption perspectives, and contracting mechanisms.

  7. Molecular water oxidation mechanisms followed by transition metals: state of the art.

    Science.gov (United States)

    Sala, Xavier; Maji, Somnath; Bofill, Roger; García-Antón, Jordi; Escriche, Lluís; Llobet, Antoni

    2014-02-18

    One clean alternative to fossil fuels would be to split water using sunlight. However, to achieve this goal, researchers still need to fully understand and control several key chemical reactions. One of them is the catalytic oxidation of water to molecular oxygen, which also occurs at the oxygen evolving center of photosystem II in green plants and algae. Despite its importance for biology and renewable energy, the mechanism of this reaction is not fully understood. Transition metal water oxidation catalysts in homogeneous media offer a superb platform for researchers to investigate and extract the crucial information to describe the different steps involved in this complex reaction accurately. The mechanistic information extracted at a molecular level allows researchers to understand both the factors that govern this reaction and the ones that derail the system to cause decomposition. As a result, rugged and efficient water oxidation catalysts with potential technological applications can be developed. In this Account, we discuss the current mechanistic understanding of the water oxidation reaction catalyzed by transition metals in the homogeneous phase, based on work developed in our laboratories and complemented by research from other groups. Rather than reviewing all of the catalysts described to date, we focus systematically on the several key elements and their rationale from molecules studied in homogeneous media. We organize these catalysts based on how the crucial oxygen-oxygen bond step takes place, whether via a water nucleophilic attack or via the interaction of two M-O units, rather than based on the nuclearity of the water oxidation catalysts. Furthermore we have used DFT methodology to characterize key intermediates and transition states. The combination of both theory and experiments has allowed us to get a complete view of the water oxidation cycle for the different catalysts studied. Finally, we also describe the various deactivation pathways for

  8. Further insight into the mechanism of heavy metals partitioning in stormwater runoff.

    Science.gov (United States)

    Djukić, Aleksandar; Lekić, Branislava; Rajaković-Ognjanović, Vladana; Veljović, Djordje; Vulić, Tatjana; Djolić, Maja; Naunovic, Zorana; Despotović, Jovan; Prodanović, Dušan

    2016-03-01

    Various particles and materials, including pollutants, deposited on urban surfaces are washed off by stormwater runoff during rain events. The interactions between the solid and dissolved compounds in stormwater runoff are phenomena of importance for the selection and improvement of optimal stormwater management practices aimed at minimizing pollutant input to receiving waters. The objective of this research was to further investigate the mechanisms responsible for the partitioning of heavy metals (HM) between the solid and liquid phases in urban stormwater runoff. The research involved the collection of samples from urban asphalt surfaces, chemical characterization of the bulk liquid samples, solids separation, particle size distribution fractionation and chemical and physico-chemical characterization of the solid phase particles. The results revealed that a negligible fraction of HM was present in the liquid phase (less than 3% by weight), while there was a strong correlation between the total content of heavy metals and total suspended solids. Examinations of surface morphology and mineralogy revealed that the solid phase particles consist predominantly of natural macroporous materials: alpha quartz (80%), magnetite (11.4%) and silicon diphosphate (8.9%). These materials have a low surface area and do not have significant adsorptive capacity. These materials have a low surface area and do not have significant adsorptive capacity. The presence of HM on the surface of solid particles was not confirmed by scanning electron microscopy and energy dispersive X-ray microanalyses. These findings, along with the results of the liquid phase sample characterization, indicate that the partitioning of HM between the liquid and solid phases in the analyzed samples may be attributed to precipitation processes. Copyright © 2015 Elsevier Ltd. All rights reserved.

  9. An Assessment of Mechanical and Tribological Property of Hybrid Aluminium Metal Matrix Composite

    Directory of Open Access Journals (Sweden)

    R. Santosh Kumar

    2017-04-01

    Full Text Available Composite materials has huge requirement in the area of automobile, aerospace, and wear resistant applications. This study presents the synthesis of composite reinforced with SiC and Al2O3 using gravity stir casting. Stir casting is the manufacturing process that is incorporated to produce the composite material because of its extreme bonding capacity with base material. The composition of reinforcement with 6061 aluminium matrix is SiC-7.5% and Al2O3 -2.5% respectively. The average size of reinforcement particle is 30-40 microns. The synthesised composite casting is machined using EDM to prepare specimens for various tests. Microstructure study was carried and the microstructure images prove the existence and dispersion of reinforcement particles in the metal matrix. There is no visible porosity is observed. The hardness of the specimen is tested using Vickers hardness tester and found considerable increase when compare with parent alloy Al 6061. Also mechanical and tribological properties of hybrid Aluminium metal matrix composite were employed. The fortifying material, Silicon Carbide is composed of tetrahedral of carbon and silicon atoms with strong bonds in crystal lattice along with its excellent wear resistance property and alumina have high strength and wear resistance. To avoid enormous material wastage and to achieve absolute accuracy, wire-cut EDM process is capitalised to engrave the specimen as per required dimensions. Three Tensile test specimens were prepared, in order to achieve reliability in results as per ASTM- E8 standard, and the values were tabulated. Impact test was carried out and the readings were tabulated. Wear test was carried out using pin on disc wear test apparatus and the results show considerable increase in wear resistant property when compare with parent alloy Al6061.The above work proves the successful fabrication of composite and evaluation of properties.

  10. The rate-limiting mechanism of transition metal gettering in multicrystalline silicon

    International Nuclear Information System (INIS)

    McHugo, S.A.; Thompson, A.C.; Imaizumi, M.

    1997-01-01

    Multicrystalline silicon is a very interesting material for terrestrial solar cells. Its low cost and respectable energy conversion efficiency (12-15%) makes it arguably the most cost competitive material for large-volume solar power generation. However, the solar cell efficiency of this material is severely degraded by regions of high minority carrier recombination which have been shown to possess both dislocations and microdefects. These structural defects are known to increase in recombination activity with transition metal decoration. Therefore, gettering of metal impurities from the material would be expected to greatly enhance solar cell performance. Contrary to this rationale, experiments using frontside phosphorus and/or backside aluminum treatments have been found to improve regions with low recombination activity while having little or no effect on the high recombination regions and in turn only slightly improving the overall cell performance. The goal of this research is to determine the mechanism by which gettering is ineffectual on these high recombination regions. The authors have performed studies on integrated circuit (IC) quality single crystal and multicrystalline solar cell silicon (mc-silicon) in the as-grown state and after a variety of processing/gettering steps. With Surface Photovoltage measurements of the minority carrier diffusion length which is inversely proportional to carrier recombination, they have seen that aluminum gettering is effective for improving IC quality material but ineffective for improving the regions of initially low diffusion lengths (high recombination rates) in mc-silicon. Of particular interest is the great increase in diffusion length for IC material as compared to the mc-silicon. Clearly the IC material has benefited to a greater extent from the gettering procedure than the mc-silicon

  11. Microstructure and mechanical behavior of metal injection molded Ti-Nb binary alloys as biomedical material.

    Science.gov (United States)

    Zhao, Dapeng; Chang, Keke; Ebel, Thomas; Qian, Ma; Willumeit, Regine; Yan, Ming; Pyczak, Florian

    2013-12-01

    The application of titanium (Ti) based biomedical materials which are widely used at present, such as commercially pure titanium (CP-Ti) and Ti-6Al-4V, are limited by the mismatch of Young's modulus between the implant and the bones, the high costs of products, and the difficulty of producing complex shapes of materials by conventional methods. Niobium (Nb) is a non-toxic element with strong β stabilizing effect in Ti alloys, which makes Ti-Nb based alloys attractive for implant application. Metal injection molding (MIM) is a cost-efficient near-net shape process. Thus, it attracts growing interest for the processing of Ti and Ti alloys as biomaterial. In this investigation, metal injection molding was applied to the fabrication of a series of Ti-Nb binary alloys with niobium content ranging from 10wt% to 22wt%, and CP-Ti for comparison. Specimens were characterized by melt extraction, optical microscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and transmission electron microscopy (TEM). Titanium carbide formation was observed in all the as-sintered Ti-Nb binary alloys but not in the as-sintered CP-Ti. Selected area electron diffraction (SAED) patterns revealed that the carbides are Ti2C. It was found that with increasing niobium content from 0% to 22%, the porosity increased from about 1.6% to 5.8%, and the carbide area fraction increased from 0% to about 1.8% in the as-sintered samples. The effects of niobium content, porosity and titanium carbides on mechanical properties have been discussed. The as-sintered Ti-Nb specimens exhibited an excellent combination of high tensile strength and low Young's modulus, but relatively low ductility. © 2013 Elsevier Ltd. All rights reserved.

  12. Bureaucratic reform, informal sector and welfare

    OpenAIRE

    Chaudhuri, Sarbajit; Mandal, Biswajit

    2012-01-01

    In this paper we formulate a three-sector general equilibrium model where one sector produces a service or good used as an intermediate input in two other sectors. Intermediate input here resembles bureaucratic (in)efficiency/control, red-tapism etc. in light of these concerns we introduce informal sector where wage is determined through competitive mechanism. We show that informal wage must go up if bureaucratic efficiency increases in general or if informal sector becomes less prone to bure...

  13. TIG AISI-316 welds using an inert gas welding chamber and different filler metals: Changes in mechanical properties and microstructure

    Energy Technology Data Exchange (ETDEWEB)

    Pascual, M.; Salas, F.; Carcel, F.J.; Perales, M.; Sanchez, A.

    2010-07-01

    This report analyses the influence of the use of an inert gas welding chamber with a totally inert atmosphere on the microstructure and mechanical properties of austenitic AISI 316L stainless steel TIG welds, using AISI ER316L, AISI 308L and Inconel 625 as filler metals. When compared with the typical TIG process, the use of the inert gas chamber induced changes in the microstructure, mainly an increase in the presence of vermicular ferrite and ferrite stringers, what resulted in higher yield strengths and lower values of hardness. Its effect on other characteristics of the joins, such as tensile strength, depended on the filler metal. The best combination of mechanical characteristics was obtained when welding in the inert gas chamber using Inconel 625 as filler metal. (Author). 12 refs.

  14. Influence of temper condition on microstructure and mechanical properties of semisolid metal processed Al–Si–Mg alloy A356

    CSIR Research Space (South Africa)

    Moller, H

    2009-01-01

    Full Text Available The microstructures and mechanical properties of strontium modified semisolid metal high pressure die cast A356 alloy are presented. The alloy A356-F (as cast) has a globular primary grain structure containing a fine eutectic. Solution treatment...

  15. 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

  16. Transverse crack initiation under combined thermal and mechanical loading of Fibre Metal Laminates and Glass Fibre Reinforced Polymers

    NARCIS (Netherlands)

    Van De Camp, W.; Dhallé, M. M.J.; Warnet, L.; Wessel, W. A.J.; Vos, G. S.; Akkerman, R.; Ter Brake, H. J.M.

    2017-01-01

    The paper describes a temperature-dependent extension of the classical laminate theory (CLT) that may be used to predict the mechanical behaviour of Fibre Metal Laminates (FML) at cryogenic conditions, including crack initiation. FML are considered as a possible alternative class of structural

  17. Effect of Moisture Cycling on Mechanical Response of Metal-Plate Connector Joints With and Without an Adhesive Interface

    Science.gov (United States)

    Leslie H. Groom

    1995-01-01

    Wood trusses are frequently located in light-frame structures where they are subjected to significant shifts in moisture conditions. However, little is known about the effects of moisture cycling of the wood members on the mechanical behavior of metal-plate connector (MPC) joints. Thus, the primary objective of this study was to quantify the effect of wood moisture...

  18. The Microstructural Evolution and Mechanical Properties of Zr-Based Metallic Glass under Different Strain Rate Compressions.

    Science.gov (United States)

    Chen, Tao-Hsing; Tsai, Chih-Kai

    2015-04-16

    In this study, the high strain rate deformation behavior and the microstructure evolution of Zr-Cu-Al-Ni metallic glasses under various strain rates were investigated. The influence of strain and strain rate on the mechanical properties and fracture behavior, as well as microstructural properties was also investigated. Before mechanical testing, the structure and thermal stability of the Zr-Cu-Al-Ni metallic glasses were studied with X-ray diffraction (XRD) and differential scanning calorimeter. The mechanical property experiments and microstructural observations of Zr-Cu-Al-Ni metallic glasses under different strain rates ranging from 10 -3 to 5.1 × 10³ s -1 and at temperatures of 25 °C were investigated using compressive split-Hopkinson bar (SHPB) and an MTS tester. An in situ transmission electron microscope (TEM) nanoindenter was used to carry out compression tests and investigate the deformation behavior arising at nanopillars of the Zr-based metallic glass. The formation and interaction of shear band during the plastic deformation were investigated. Moreover, it was clearly apparent that the mechanical strength and ductility could be enhanced by impeding the penetration of shear bands with reinforced particles.

  19. The Microstructural Evolution and Mechanical Properties of Zr-Based Metallic Glass under Different Strain Rate Compressions

    Directory of Open Access Journals (Sweden)

    Tao-Hsing Chen

    2015-04-01

    Full Text Available In this study, the high strain rate deformation behavior and the microstructure evolution of Zr-Cu-Al-Ni metallic glasses under various strain rates were investigated. The influence of strain and strain rate on the mechanical properties and fracture behavior, as well as microstructural properties was also investigated. Before mechanical testing, the structure and thermal stability of the Zr-Cu-Al-Ni metallic glasses were studied with X-ray diffraction (XRD and differential scanning calorimeter. The mechanical property experiments and microstructural observations of Zr-Cu-Al-Ni metallic glasses under different strain rates ranging from 10−3 to 5.1 × 103 s−1 and at temperatures of 25 °C were investigated using compressive split-Hopkinson bar (SHPB and an MTS tester. An in situ transmission electron microscope (TEM nanoindenter was used to carry out compression tests and investigate the deformation behavior arising at nanopillars of the Zr-based metallic glass. The formation and interaction of shear band during the plastic deformation were investigated. Moreover, it was clearly apparent that the mechanical strength and ductility could be enhanced by impeding the penetration of shear bands with reinforced particles.

  20. A realist evaluation of social prescribing: an exploration into the context and mechanisms underpinning a pathway linking primary care with the voluntary sector.

    Science.gov (United States)

    Bertotti, Marcello; Frostick, Caroline; Hutt, Patrick; Sohanpal, Ratna; Carnes, Dawn

    2018-05-01

    This article adopts a realist approach to evaluate a social prescribing pilot in the areas of Hackney and City in London (United Kingdom). It unpacks the contextual factors and mechanisms that influenced the development of this pilot for the benefits of GPs, commissioners and practitioners, and reflects on the realist approach to evaluation as a tool for the evaluation of health interventions. Primary care faces considerable challenges including the increase in long-term conditions, GP consultation rates, and widening health inequalities. With its emphasis on linking primary care to non-clinical community services via a social prescribing coordinator (SPC), some models of social prescribing could contribute to reduce the burden on primary care, tackle health inequalities and encourage people to make greater use of non-clinical forms of support. This realist analysis was based on qualitative interviews with users, commissioners, a GP survey, focus groups and learning events to explore stakeholders' experience. To enable a detailed analysis, we adapted the realist approach by subdividing the social prescribing pathway into stages, each with contextual factors, mechanisms and outcomes. SPCs were pivotal to the effective functioning of the social prescribing service and responsible for the activation and initial beneficial impact on users. Although social prescribing shows significant potential for the benefit of patients and primary care, several challenges need to be considered and overcome, including 'buy in' from some GPs, branding, and funding for the third sector in a context where social care cuts are severely affecting the delivery of health care. With its emphasis on context and mechanisms, the realist evaluation approach is useful in understanding how to identify and improve health interventions, and analyse in greater detail the contribution of different stakeholders. As the SPC is central to social prescribing, more needs to be done to understand their role

  1. Residual Stress Induced Mechanical Property Enhancement in Steel Encapsulated Light Metal Matrix Composites

    Science.gov (United States)

    Fudger, Sean James

    Macro hybridized systems consisting of steel encapsulated light metal matrix composites (MMCs) were produced with the goal of creating a low cost/light weight composite system with enhanced mechanical properties. MMCs are frequently incorporated into advanced material systems due to their tailorable material properties. However, they often have insufficient ductility for many structural applications. The macro hybridized systems take advantage of the high strength, modulus, and damage tolerance of steels and high specific stiffness and low density of MMCs while mitigating the high density of steels and the poor ductility of MMCs. Furthermore, a coefficient of thermal expansion (CTE) mismatch induced residual compressive stress method is utilized as a means of improving the ductility of the MMCs and overall efficiency of the macro hybridized systems. Systems consisting of an A36, 304 stainless steel, or NitronicRTM 50 stainless steel shell filled with an Al-SiC, Al-Al2O3, or Mg-B4C MMC are evaluated in this work. Upon cooling from processing temperatures, residual strains are generated due to a CTE mismatch between each of the phases. The resulting systems offer higher specific properties and a more structurally efficient system can be attained. Mechanical testing was performed and improvements in yield stress, ultimate tensile stress, and ductility were observed. However, the combination of these dissimilar materials often results in the formation of intermetallic compounds. In certain loading situations, these typically brittle intermetallic layers can result in degraded performance. X-ray Diffraction (XRD), X-ray Energy Dispersive Spectroscopy (EDS), and Electron Backscatter Diffraction (EBSD) are utilized to characterize the intermetallic layer formation at the interface between the steel and MMC. As the residual stress condition in each phase has a large impact on the mechanical property improvement, accurate quantification of these strains/stresses is

  2. Microstructure, mechanical performance and corrosion properties of base metal solder joints

    Directory of Open Access Journals (Sweden)

    Sujesh Machha

    2011-01-01

    Full Text Available Context: Alloys have been considered to be of paramount importance in the field of prosthodontics. Long span prosthesis may often require joining of one or more individual castings to obtain better fit, occlusal harmony and esthetics in comparison to one-piece casting. Aim: This study was undertaken to evaluate the mechanical properties of base metal alloys joined by two different techniques, namely, gas oxygen torch soldering and laser fusion, compared to a one-piece casting. Mechanical properties evaluated were tensile strength, percentage of elongation and hardness of the solder joint. In addition, corrosion properties and scanning electron microscopic appearance of the joints were also evaluated. Materials and Methods: The samples were prepared according to American Society for Testing Materials specifications (ASTM, E8. Specimens were made with self-cure acrylic and then invested in phosphate-bonded investment material. Casting was done in induction casting machine. Thirty specimens were thus prepared for each group and compared with 30 specimens of the one-piece casting group. Statistical Analysis Used: SPSS software (version 10.0, Chicago, IL, USA was used for statistical analysis. ANOVA and Benferroni post hoc tests were done for multiple comparisons between the groups and within the groups for mean difference and standard error. Results: Results showed that tensile strength of the one-piece casting was higher than laser fused and gas oxygen torch soldered joints. Laser fused joints exhibited higher hardness values compared to that of gas oxygen torch soldered joints. Scanning electron microscopic examination revealed greater porosity in the gas oxygen torch soldered joints. This contributed to the reduction in the strength of the joint. Gas oxygen torch soldered joints showed less corrosion resistance when compared to laser fused joints and one-piece casting. Conclusion: Laser fusion, which is a recent introduction to the field of

  3. Intrinsic air stability mechanisms of two-dimensional transition metal dichalcogenide surfaces: basal versus edge oxidation

    Science.gov (United States)

    Longo, Roberto C.; Addou, Rafik; KC, Santosh; Noh, Ji-Young; Smyth, Christopher M.; Barrera, Diego; Zhang, Chenxi; Hsu, Julia W. P.; Wallace, Robert M.; Cho, Kyeongjae

    2017-06-01

    Layered transition metal dichalcogenides (TMDs) are being considered as a promising alternative channel material in ultra-thin and low power nanoelectronics, due to the significant tunability of their electronic properties via mechanisms such as mechanical strain, control of the material thickness, application of an external field, impurities, doping, alloying, or altering the substrate nature. Initially, monolayer TMDs as counterparts to graphene captured the attention of the scientific community owing to their semiconductor nature with sizable band gaps. However, certain physical and chemical properties of TMDs, such as their oxygen reactivity and stability in air need to be more completely understood in order to crystallize the promising superior performance of TMD-based electronic devices. Here, a comparative analysis of the stability of various TMDs (MX2: \\text{M}=\\text{Mo} , W; \\text{X}=\\text{S} , Se) in air is performed using density-functional theory (DFT) as well as x-ray photoelectron spectroscopy (XPS). We find that the surface chemistry of the basal plane of sulfides and selenides is relatively stable in air although for completely different reasons, which can be explained by investigating oxygen dissociative adsorption kinetics and thermodynamics. On the contrary, the edge of MX2 nanoribbons shows strong driving forces towards O2 dissociation and chemisorption. Our combined theoretical and experimental investigation reveals that the air stability of TMDs should not be placed in the same footing that other 2D materials, like graphene. Thus, this work highlights the importance of having controlled oxygen environment during crystal exfoliation/growth and defect passivation in order to provide high quality uniform materials for TMD-based device fabrication.

  4. Epitaxial Growth of Two-Dimensional Layered Transition-Metal Dichalcogenides: Growth Mechanism, Controllability, and Scalability

    KAUST Repository

    Li, Henan

    2017-07-06

    Recently there have been many research breakthroughs in two-dimensional (2D) materials including graphene, boron nitride (h-BN), black phosphors (BPs), and transition-metal dichalcogenides (TMDCs). The unique electrical, optical, and thermal properties in 2D materials are associated with their strictly defined low dimensionalities. These materials provide a wide range of basic building blocks for next-generation electronics. The chemical vapor deposition (CVD) technique has shown great promise to generate high-quality TMDC layers with scalable size, controllable thickness, and excellent electronic properties suitable for both technological applications and fundamental sciences. The capability to precisely engineer 2D materials by chemical approaches has also given rise to fascinating new physics, which could lead to exciting new applications. In this Review, we introduce the latest development of TMDC synthesis by CVD approaches and provide further insight for the controllable and reliable synthesis of atomically thin TMDCs. Understanding of the vapor-phase growth mechanism of 2D TMDCs could benefit the formation of complicated heterostructures and novel artificial 2D lattices.

  5. Significant enhancement of metal heat dissipation from mechanically exfoliated graphene nanosheets through thermal radiation effect

    Directory of Open Access Journals (Sweden)

    Junxiong Hu

    2017-05-01

    Full Text Available We demonstrate a facile approach to significantly enhance the heat dissipation potential of conventional aluminum (Al heat sinks by mechanically coating graphene nanosheets. For Al and graphene-coated Al heat sinks, the change in temperature with change in coating coverage, coating thickness and heat flux are studied. It is found that with the increase in coating coverage from 0 to 100%, the steady-state temperature is decreased by 5 °C at a heat flux of 1.8 W cm-1. By increasing the average thickness of graphene coating from 480 nm to 1900 nm, a remarkable temperature reduction up to 7 °C can be observed. Moreover, with the increase in heat flux from 1.2 W cm-1 to 2.4 W cm-1, the temperature difference between uncoated and graphene-coated samples increases from 1 °C to 6 °C. The thermal analysis and finite element simulation reveal that the thermal radiation plays a key role in enhancing the heat dissipation performance. The effect of heat convection remains weak owing to the low air velocity at surface-air boundary. This work provides a technological innovation in improving metal heat dissipation using graphene nanosheets.

  6. Mechanism study of selective heavy metal ion removal with polypyrrole-functionalized polyacrylonitrile nanofiber mats

    International Nuclear Information System (INIS)

    Wang, Jianqiang; Luo, Chao; Qi, Genggeng; Pan, Kai; Cao, Bing

    2014-01-01

    Graphical abstract: - Highlights: • PAN/PPy core/shell nanofiber used for Cr(VI) removal. • Adsorption mechanisms were investigated. • Selective adsorption performances were investigated. - Abstract: Polyacrylonitrile/polypyrrole (PAN/PPy) core/shell nanofiber mat was prepared through electrospinning followed by a simple chemical oxidation method. The polypyrrole-functionalized nanofiber mats showed selective adsorption performance for anions. The interaction between heavy metal anions and polypyrrole (especially the interaction between Cr 2 O 7 2− and polypyrrole) during the adsorption process was studied. The results showed that the adsorption process included two steps: one was the anion exchange process between the Cl − and Cr(VI), and the other was the redox process for the Cr(VI) ions. The adsorption amount was related to the protonation time of the PAN/PPy nanofiber mat and increased as protonation time increased. Meanwhile, the Cr(VI) ions were reduced to Cr(III) through the reaction with amino groups of polypyrrole (from secondary amines to tertiary amines). PAN/PPy nanofiber mat showed high selectivity for Cr(VI), and the adsorption performance was nearly unaffected by other co-existing anions (Cl − , NO 3 − , and SO 4 2− ) except for PO 4 3− for the pH change

  7. Mechanism study of selective heavy metal ion removal with polypyrrole-functionalized polyacrylonitrile nanofiber mats

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Jianqiang; Luo, Chao [Key Laboratory of Carbon Fiber and Functional Polymers, Ministry of Education, Beijing University of Chemical Technology, Beijing 100029 (China); Qi, Genggeng [Department of Materials Science and Engineering, Cornell University, Ithaca, NY (United States); Pan, Kai, E-mail: pankai@mail.buct.edu.cn [Key Laboratory of Carbon Fiber and Functional Polymers, Ministry of Education, Beijing University of Chemical Technology, Beijing 100029 (China); Department of Materials Science and Engineering, Cornell University, Ithaca, NY (United States); Cao, Bing, E-mail: bcao@mail.buct.edu.cn [Key Laboratory of Carbon Fiber and Functional Polymers, Ministry of Education, Beijing University of Chemical Technology, Beijing 100029 (China)

    2014-10-15

    Graphical abstract: - Highlights: • PAN/PPy core/shell nanofiber used for Cr(VI) removal. • Adsorption mechanisms were investigated. • Selective adsorption performances were investigated. - Abstract: Polyacrylonitrile/polypyrrole (PAN/PPy) core/shell nanofiber mat was prepared through electrospinning followed by a simple chemical oxidation method. The polypyrrole-functionalized nanofiber mats showed selective adsorption performance for anions. The interaction between heavy metal anions and polypyrrole (especially the interaction between Cr{sub 2}O{sub 7}{sup 2−} and polypyrrole) during the adsorption process was studied. The results showed that the adsorption process included two steps: one was the anion exchange process between the Cl{sup −} and Cr(VI), and the other was the redox process for the Cr(VI) ions. The adsorption amount was related to the protonation time of the PAN/PPy nanofiber mat and increased as protonation time increased. Meanwhile, the Cr(VI) ions were reduced to Cr(III) through the reaction with amino groups of polypyrrole (from secondary amines to tertiary amines). PAN/PPy nanofiber mat showed high selectivity for Cr(VI), and the adsorption performance was nearly unaffected by other co-existing anions (Cl{sup −}, NO{sub 3}{sup −}, and SO{sub 4}{sup 2−}) except for PO{sub 4}{sup 3−} for the pH change.

  8. Repair of 8-oxoG:A mismatches by the MUTYH glycosylase: Mechanism, metals and medicine.

    Science.gov (United States)

    Banda, Douglas M; Nuñez, Nicole N; Burnside, Michael A; Bradshaw, Katie M; David, Sheila S

    2017-06-01

    Reactive oxygen and nitrogen species (RONS) may infringe on the passing of pristine genetic information by inducing DNA inter- and intra-strand crosslinks, protein-DNA crosslinks, and chemical alterations to the sugar or base moieties of DNA. 8-Oxo-7,8-dihydroguanine (8-oxoG) is one of the most prevalent DNA lesions formed by RONS and is repaired through the base excision repair (BER) pathway involving the DNA repair glycosylases OGG1 and MUTYH in eukaryotes. MUTYH removes adenine (A) from 8-oxoG:A mispairs, thus mitigating the potential of G:C to T:A transversion mutations from occurring in the genome. The paramount role of MUTYH in guarding the genome is well established in the etiology of a colorectal cancer predisposition syndrome involving variants of MUTYH, referred to as MUTYH-associated polyposis (MAP). In this review, we highlight recent advances in understanding how MUTYH structure and related function participate in the manifestation of human disease such as MAP. Here we focus on the importance of MUTYH's metal cofactor sites, including a recently discovered "Zinc linchpin" motif, as well as updates to the catalytic mechanism. Finally, we touch on the insight gleaned from studies with MAP-associated MUTYH variants and recent advances in understanding the multifaceted roles of MUTYH in the cell, both in the prevention of mutagenesis and tumorigenesis. Copyright © 2017 Elsevier Inc. All rights reserved.

  9. Mechanical properties testing of several 800 MeV proton irradiated BCC metals and alloys

    International Nuclear Information System (INIS)

    Brown, R.D.; Wechsler, M.S.; Tschalaer, C.

    1986-01-01

    A spallation neutron source for the 600-MeV proton accelerator facility at the Swiss Institute for Nuclear Research (SIN) consists of a vertical cylinder filled with molten Pb-Bi. The proton beam enters the cylinder, passing upward through a window in contact with the Pb-Bi eutectic liquid. Investigations are underway at the 800-MeV proton accelerator at LAMPF to test the performance of candidate SIN window materials. Based on considerations of chemical compatibility with molten Pb-Bi, as well as radiation damage mechanisms, Fe, Ta, Fe-2.25Cr-1Mo, and Fe-12Cr-1Mo (Ht-9) were chosen as candidate materials. Sheet tensile samples were sealed inside capsules containing Pb-Bi and were proton-irradiated at LAMPF to two fluences, 4.8 and 54 x 10 23 p/m 2 . The beam current was approximately equal to the 1 mA anticipated for the upgraded SIN accelerator. Yield and ultimate strengths increased upon irradiation in all materials, while the ductility decreased. The pure metals, Ta and Fe, exhibited the greatest radiation hardening and embrittlement. The HT-9 alloy showed the smallest changes in strength and ductility

  10. TPM and autonomous maintenance: case study in a metal mechanic company

    Directory of Open Access Journals (Sweden)

    Norberto Carvalho Biehl

    2015-12-01

    Full Text Available The purpose of this article was to describe a case of autonomous maintenance implementation in a pilot area of a metal mechanical industry company. The TPM – Total Productive Maintenance is a managerial technology that can help companies to reduce failures and breakages of machines. One of the most important issues of TPM is autonomous maintenance. The method of research was the case study. A program of twelve points was structured and adopted as stand-alone maintenance deployment guide. The program began in a pilot area, including three machining centers. The main results of the pilot program were: increasing by more than 700% the Mean Time between Failure, reducing by more than 40% in the Mean Time to Repair, as well as the consequent increase of more than five percentage points on the availability of the three machines and almost 60% reduction in the cost of maintenance materials. The main conclusion was that the TPM, and in particular the autonomous maintenance, can increase the efficiency of maintenance as strategic factor, which enhances the competitiveness of manufacturing in industrial companies.

  11. Intrinsic homogeneous linewidth and broadening mechanisms of excitons in monolayer transition metal dichalcogenides

    KAUST Repository

    Moody, Galan

    2015-09-18

    The band-edge optical response of transition metal dichalcogenides, an emerging class of atomically thin semiconductors, is dominated by tightly bound excitons localized at the corners of the Brillouin zone (valley excitons). A fundamental yet unknown property of valley excitons in these materials is the intrinsic homogeneous linewidth, which reflects irreversible quantum dissipation arising from system (exciton) and bath (vacuum and other quasiparticles) interactions and determines the timescale during which excitons can be coherently manipulated. Here we use optical two-dimensional Fourier transform spectroscopy to measure the exciton homogeneous linewidth in monolayer tungsten diselenide (WSe2). The homogeneous linewidth is found to be nearly two orders of magnitude narrower than the inhomogeneous width at low temperatures. We evaluate quantitatively the role of exciton–exciton and exciton–phonon interactions and population relaxation as linewidth broadening mechanisms. The key insights reported here—strong many-body effects and intrinsically rapid radiative recombination—are expected to be ubiquitous in atomically thin semiconductors.

  12. Micro-strain Evolution and Toughening Mechanisms in a Trimodal Al-Based Metal Matrix Composite

    Science.gov (United States)

    Zhang, Yuzheng; Topping, Troy D.; Yang, Hanry; Lavernia, Enrique J.; Schoenung, Julie M.; Nutt, Steven R.

    2015-03-01

    A trimodal metal matrix composite (MMC) based on AA (Al alloy) 5083 (Al-4.4Mg-0.7Mn-0.15Cr wt pct) was synthesized by cryomilling powders followed by compaction of blended powders and ceramic particles using two successive dual mode dynamic forgings. The microstructure consisted of 66.5 vol pct ultrafine grain (UFG) region, 30 vol pct coarse grain (CG) region and 3.5 vol pct reinforcing boron carbide particles. The microstructure imparted high-tensile yield strength (581 MPa) compared to a conventional AA 5083 (242 MPa) and enhanced ductility compared to 100 pct UFG Al MMC. The deformation behavior of the heterogeneous structure and the effects of CG regions on crack propagation were investigated using in situ scanning electron microscopy micro-tensile tests. The micro-strain evolution measured using digital image correlation showed early plastic strain localization in CG regions. Micro-voids due to the strain mismatch at CG/UFG interfaces were responsible for crack initiation. CG region toughening was realized by plasticity-induced crack closure and zone shielding of disconnected micro-cracks. However, these toughening mechanisms did not effectively suppress its brittle behavior. Further optimization of the CG distribution (spacing and morphology) is required to achieve toughness levels required for structural applications.

  13. Artificial neural network modeling of mechanical alloying process for synthesizing of metal matrix nanocomposite powders

    International Nuclear Information System (INIS)

    Dashtbayazi, M.R.; Shokuhfar, A.; Simchi, A.

    2007-01-01

    An artificial neural network model was developed for modeling of the effects of mechanical alloying parameters including milling time, milling speed and ball to powder weight ratio on the characteristics of Al-8 vol%SiC nanocomposite powders. The crystallite size and lattice strain of the aluminum matrix were considered for modeling. This nanostructured nanocomposite powder was synthesized by utilizing planetary high energy ball mill and the required data for training were collected from the experimental results. The characteristics of the particles were determined by X-ray diffraction, scanning and transmission electron microscopy. Two types of neural network architecture, i.e. multi-layer perceptron (MLP) and radial basis function (RBF), were used. The steepest descent along with variable learning rate back-propagation algorithm known as a heuristic technique was utilized for training the MLP network. It was found that MLP network yields better results compared to RBF network, giving an acceptable mapping between the network responses and the target data with a high correlation coefficients. The response surfaces between the response variables, i.e. crystallite size, lattice strain of the aluminum matrix and the processing parameters are presented. The procedure modeling can be used for optimization of the MA process for synthesizing of nanostructured metal matrix nanocomposites

  14. Nonlinear continuum mechanical model for investigating plasmonic oscillations phenomena in nanostructured metals

    Science.gov (United States)

    Serebrennikov, Aleksey M.

    2014-09-01

    Here, we introduce a nonlinear continuum mechanical theoretical model of dissipative plasmonic oscillations relying on the principle of least action. The proposed theory has allowed obtaining the expression of a stress tensor for an “electron gas-ionic frame” system. In parallel, an initial boundary value problem for nonlinear integrodifferential equations constituting the model has been formulated. On the basis of a finite-difference approach the iterative solution method, algorithm and solver have been worked out. Thereby we have investigated the phenomena of harmonic multiples generation by a cluster of metal nanoparticles. Also by using these tools the estimate of the density function parameter satisfying the requirement of regular oscillations has been obtained numerically. On the ground of extensive numerical runs it was found that for a given set of parameters the system response turned out to be mainly linear, however the contributions of the closest odd harmonic multiples (third and fifth) were well resolved under quantitative analysis. This result allows the nonlinearity governable by the principal equation of motion to be associated with Kerr's type nonlinearity.

  15. Improved Mechanical and Tribological Properties of Metal-Matrix Composites Dispersion-Strengthened by Nanoparticles

    Directory of Open Access Journals (Sweden)

    Evgenii Levashov

    2009-12-01

    Full Text Available Co- and Fe-based alloys produced by powder technology are being widely used as a matrix for diamond-containing composites in cutting, drilling, grinding pplications, etc. The severe service conditions demand that the mechanical and tribological properties of these alloys be improved. Development of metal-matrix composites (MMCs and alloys reinforced with nanoparticles is a promising way to resolve this problem. In this work, we have investigated the effect of nano-sized WC, ZrO2, Al2O3, and Si3N4 additives on the properties of sintered dispersion-strengthened Co- and Fe-based MMCs. The results show an increase in the hardness (up to 10 HRB, bending strength (up to 50%, wear resistance (by a factor of 2–10 and a decrease in the friction coefficient (up to 4-fold of the dispersion-strengthened materials. The use of designed alloys as a binder of cutting diamond tools gave a 4-fold increment in the service life, without reduction in their cutting speed.

  16. Femtosecond-laser-induced damage initiation mechanism on metal multilayer dielectric gratings for pulse compression

    Science.gov (United States)

    Huang, Haopeng; Kong, Fanyu; Xia, Zhilin; Jin, Yunxia; Li, Linxin; Wang, Leilei; Chen, Junming; Cui, Yun; Shao, Jianda

    2018-01-01

    The femtosecond-laser-induced damage behaviors of metal multilayer dielectric gratings (MMDG) for pulse compression are explored. The grating ridge of this type of MMDG consists of a layer of HfO2 sandwiched between two SiO2 layers. The initial damage position is on the HfO2 layer of the ridge which opposite to the laser beam direction. A theoretical model is constructed to explain the femtosecond-laser-induced damage initiation mechanism on the MMDG, and the model can simulate the evolution of the electron density in the conduction band and the change of the dielectric constants of HfO2 and SiO2 in the sandwiched grating structure. The dramatic increase in the imaginary part of the dielectric constant of the middle HfO2 layer indicates that it strongly absorbs laser energy, resulting in damage to the MMDG. The experimental results and theoretical calculation agree very well with each other.

  17. Viral genome packaging terminase cleaves DNA using the canonical RuvC-like two-metal catalysis mechanism.

    Science.gov (United States)

    Xu, Rui-Gang; Jenkins, Huw T; Chechik, Maria; Blagova, Elena V; Lopatina, Anna; Klimuk, Evgeny; Minakhin, Leonid; Severinov, Konstantin; Greive, Sandra J; Antson, Alfred A

    2017-04-07

    Bacteriophages and large dsDNA viruses encode sophisticated machinery to translocate their DNA into a preformed empty capsid. An essential part of this machine, the large terminase protein, processes viral DNA into constituent units utilizing its nuclease activity. Crystal structures of the large terminase nuclease from the thermophilic bacteriophage G20c show that it is most similar to the RuvC family of the RNase H-like endonucleases. Like RuvC proteins, the nuclease requires either Mn2+, Mg2+ or Co2+ ions for activity, but is inactive with Zn2+ and Ca2+. High resolution crystal structures of complexes with different metals reveal that in the absence of DNA, only one catalytic metal ion is accommodated in the active site. Binding of the second metal ion may be facilitated by conformational variability, which enables the two catalytic aspartic acids to be brought closer to each other. Structural comparison indicates that in common with the RuvC family, the location of the two catalytic metals differs from other members of the RNase H family. In contrast to a recently proposed mechanism, the available data do not support binding of the two metals at an ultra-short interatomic distance. Thus we postulate that viral terminases cleave DNA by the canonical RuvC-like mechanism. © The Author(s) 2017. Published by Oxford University Press on behalf of Nucleic Acids Research.

  18. Impact of the structural state on the mechanical properties in a Zr–Co–Al bulk metallic glass

    International Nuclear Information System (INIS)

    Qiao, J.C.; Pelletier, J.M.; Esnouf, C.; Liu, Y.; Kato, H.

    2014-01-01

    Highlights: • Atomic mobility in metallic glass was studied by DMA, HRTEM and nanoindentation. • Physical ageing and crystallization reduce the atomic mobility. • Plastic deformation, i.e. cold-rolling enhances the atomic mobility. • Atomic mobility in glassy materials can be described by quasi-point defects model. - Abstract: This paper reports on the use of differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and nanoindentation technique to investigate atomic mobility in Zr 56 Co 28 Al 16 bulk metallic glass in the as-cast state, after thermal annealing and after cold rolling. From the DMA results together with nanoindentation data point of view, the atomic mobility is significantly modified by the thermo-mechanical history. On the one hand, atomic mobility in bulk metallic glass is reduced after physical aging or crystallization. On the other hand, the atomic mobility in metallic glass is enhanced by cold rolling. To analyze the atomic mobility in amorphous materials, a physical theory is introduced. This model invoked the concept of quasi-point defects, which correspond to the density fluctuations in the glassy materials. Correlated movements of atoms are assisted by these quasi-point defects and the correlation factor χ is connected to the concentration of these “defects” in metallic glasses: (i) physical aging and crystallization decreases the parameter χ and (ii) the concentration of defects augments via plastic deformation (i.e. cold-rolling), suggesting that the correlation factor χ reflects the atomic mobility for glassy materials in a quantitative manner. This correlation bridges the gap between the mechanical properties on macroscopic scale and atomic mobility in microstructural regions in metallic glasses

  19. The mechanism of metal nanoparticle formation in plants: limits on accumulation

    International Nuclear Information System (INIS)

    Haverkamp, R. G.; Marshall, A. T.

    2009-01-01

    Metal nanoparticles have many potential technological applications. Biological routes to the synthesis of these particles have been proposed including production by vascular plants, known as phytoextraction. While many studies have looked at metal uptake by plants, particularly with regard to phytoremediation and hyperaccumulation, few have distinguished between metal deposition and metal salt accumulation. This work describes the uptake of AgNO 3 , Na 3 Ag(S 2 O 3 ) 2 , and Ag(NH 3 ) 2 NO 3 solutions by hydroponically grown Brassica juncea and the quantitative measurement of the conversion of these salts to silver metal nanoparticles. Using X-ray absorption near edge spectroscopy (XANES) to determine the metal speciation within the plants, combined with atomic absorption spectroscopy (AAS) for total Ag, the quantity of reduction of Ag I to Ag 0 is reported. Transmission electron microscopy (TEM) showed Ag particles of 2-35 nm. The factors controlling the amount of silver accumulated are revealed. It is found that there is a limit on the amount of metal nanoparticles that may be deposited, of about 0.35 wt.% Ag on a dry plant basis, and that higher levels of silver are obtained only by the concentration of metal salts within the plant, not by deposition of metal. The limit on metal nanoparticle accumulation, across a range of metals, is proposed to be controlled by the total reducing capacity of the plant for the reduction potential of the metal species and limited to reactions occurring at an electrochemical potential greater than 0 V (verses the standard hydrogen electrode).

  20. What happened to anti-malarial markets after the Affordable Medicines Facility-malaria pilot? Trends in ACT availability, price and market share from five African countries under continuation of the private sector co-payment mechanism.

    Science.gov (United States)

    Tougher, Sarah; Hanson, Kara; Goodman, Catherine

    2017-04-25

    The private sector supplies anti-malarial treatment for large proportions of patients in sub-Saharan Africa. Following the large-scale piloting of the Affordable Medicines Facility-malaria (AMFm) from 2010 to 2011, a private sector co-payment mechanism (CPM) provided continuation of private sector subsidies for quality-assured artemisinin combination therapies (QAACT). This article analyses for the first time the extent to which improvements in private sector QAACT supply and distribution observed during the AMFm were maintained or intensified during continuation of the CPM through 2015 in Kenya, Madagascar, Nigeria, Tanzania and Uganda using repeat cross-sectional outlet survey data. QAACT market share in all five countries increased during the AMFm period (p co-payment mechanism for QAACT implemented at national scale for 5 years was associated with positive and sustained improvements in QAACT availability, price and market share in Nigeria, Tanzania and Uganda, with more mixed results in Kenya, and few improvements in Madagascar. The subsidy mechanism as implemented over time across countries was not sufficient on its own to achieve optimal QAACT uptake. Supporting interventions to address continued availability and distribution of non-artemisinin therapies, and to create demand for QAACT among providers and consumers need to be effectively implemented to realize the full potential of this subsidy mechanism. Furthermore, there is need for comprehensive market assessments to identify contemporary market barriers to high coverage with both confirmatory testing and appropriate treatment.

  1. Observation of TEC perturbation associated with medium-scale traveling ionospheric disturbance and possible seeding mechanism of atmospheric gravity wave at a Brazilian sector

    Science.gov (United States)

    Jonah, O. F.; Kherani, E. A.; De Paula, E. R.

    2016-03-01

    In the present study, we document daytime total electron content (TEC) disturbances associated with medium-scale traveling ionospheric disturbances (MSTIDs), on few chosen geomagnetically quiet days over Southern Hemisphere of Brazilian longitude sector. These disturbances are derived from TEC data obtained using Global Navigation Satellite System (GNSS) receiver networks. From the keograms and cross-correlation maps, the TEC disturbances are identified as the MSTIDs that are propagating equatorward-eastward, having most of their average wavelengths longer in latitude than in longitude direction. These are the important outcomes of the present study which suggest that the daytime MSTIDs over Southern Hemisphere are similar to their counterparts in the Northern Hemisphere. Another important outcome is that the occurrence characteristics of these MSTIDs and that of atmospheric gravity wave (AGW) activities in the thermosphere are found to be similar on day-to-day basis. This suggests a possible connection between them, confirming the widely accepted AGW forcing mechanism for the generation of these daytime MSTIDs. The source of this AGW is investigated using the Geostationary Operational Environmental Satellite system (GOES) and Constellation Observing System for Meteorology, Ionosphere, and Climate satellite data. Finally, we provided evidences that AGWs are generated by convection activities from the tropospheric region.

  2. MECHANISM(S) OF UPTAKE AND SEQUESTRATION OF LEAD AND OTHER HEAVY METALS BY PSEUDOMONAS AERUGINOSA CHL-004

    Science.gov (United States)

    Heavy metals in soils and sediments of anthropogenic origin are a major environmental concern, due to the significant health risks they pose and due to the difficulties encountered with their remediation. Diverse industries involved in energy production, pigment synthesis and the...

  3. Enrichment of the metallic components from waste printed circuit boards by a mechanical separation process using a stamp mill

    International Nuclear Information System (INIS)

    Yoo, Jae-Min; Jeong, Jinki; Yoo, Kyoungkeun; Lee, Jae-chun; Kim, Wonbaek

    2009-01-01

    Printed circuit boards incorporated in most electrical and electronic equipment contain valuable metals such as Cu, Ni, Au, Ag, Pd, Fe, Sn, and Pb. In order to employ a hydrometallurgical route for the recycling of valuable metals from printed circuit boards, a mechanical pre-treatment step is needed. In this study, the metallic components from waste printed circuit boards have been enriched using a mechanical separation process. Waste printed circuit boards shredded to 5.0 mm. The fractions of milled printed circuit boards of size 5.0 mm fraction and the heavy fraction were subjected to two-step magnetic separation. Through the first magnetic separation at 700 Gauss, 83% of the nickel and iron, based on the whole printed circuit boards, was recovered in the magnetic fraction, and 92% of the copper was recovered in the non-magnetic fraction. The cumulative recovery of nickel-iron concentrate was increased by a second magnetic separation at 3000 Gauss, but the grade of the concentrate decreased remarkably from 76% to 56%. The cumulative recovery of copper concentrate decreased, but the grade increased slightly from 71.6% to 75.4%. This study has demonstrated the feasibility of the mechanical separation process consisting of milling/size classification/gravity separation/two-step magnetic separation for enriching metallic components such as Cu, Ni, Al, and Fe from waste printed circuit boards

  4. Evaluation of the onset of failure under mechanical and thermal stresses on luting agent for metal-ceramic and metal crowns by finite element analysis

    Directory of Open Access Journals (Sweden)

    Hema Agnihotri

    2010-01-01

    Full Text Available Long-term clinical failures of cemented prosthesis depend, to a large extent, on the integrity of the luting agent. The causative factors that lead to microfracture and, hence, failure of the luting agents are the stresses acting inside the oral cavity. Therefore, the present study was designed to develop an understanding of the relationship between stresses in the tooth and the failure potential of the luting agent. Two-dimensional finite element stress analysis was performed on the mandibular second premolar. The behavior of zinc-phosphate and glass-ionomer were studied under different crowns (metal-ceramic and metal crown and loading conditions (mechanical force of 450 N acting vertically over the occlusal surface, thermal loads of 60° and 0°C. It was observed from the study that failure threshold of the luting agent was influenced both by the elastic modulus of the luting agent and by the type of the crown.

  5. Preparation and formation mechanisms of metallic particles with controlled size, shape, structure and surface functionality

    Science.gov (United States)

    Lu, Lu

    Due to their excellent conductivity and chemical stability, particles of silver (Ag), gold (Au), copper (Cu) and their alloys are widely used in the electronic industry. Other unique properties extend their uses to the biomedical, optical and catalysis fields. All of these applications rely on particles with well controlled size, morphology, structure, and surface properties. Chemical precipitation from homogeneous solutions was selected as the synthetic route for the investigations described in this work. Based on the evaluation of key process parameters (temperature, reactant concentrations, reactant addition rate, mixing, etc.) the general formation mechanisms of metallic particles in various selected precipitation systems were investigated and elucidated. Five different systems for preparing particles with controlled size, morphology, structure and surface functionality are discussed. The first system involves the precipitation of Ag nanoparticles with spherical and anisotropic (platy or fiber-like) morphology. It will be shown that the formation of a stable Ag/Daxad complex has a significant impact on the reaction kinetics, and that the chromonic properties of Daxad molecules are responsible for the particle anisotropy. In the second system, Au-Ag core-shell nanoparticles were prepared in aqueous solution by a two-step precipitation process. The optical properties of these particles can be tailored by varying the thickness of the Ag shell. It was also determined that the stability of the bimetallic metallic sols depends on the Cl-ion concentration in solution. The third system discussed deals with preparation by the polyol process of well dispersed Cu nanospheres with high crystallinity and excellent oxidation resistance. We show that the heterogeneous nucleation (seeding) approach has significant merit in controlling particle size and uniformity. The functionalization of Au nanoparticle surfaces with glutathione molecules is discussed in the next section. The

  6. Physical and Mechanical Properties of W-Ni-Fe-Co Metal Foam Modified by Titanium Tungsten Carbide Alloying

    Science.gov (United States)

    Ishchenko, A. N.; Tabachenko, A. N.; Afanas'eva, S. A.; Belov, N. N.; Biryukov, Yu. A.; Burkin, V. V.; D'yachkovskii, A. S.; Rogaev, K. S.; Skosyrskii, A. B.; Yugov, N. T.

    2018-02-01

    The paper studies physical and mechanical properties of tungsten-nickel-iron-cobalt metal foam alloyed with titanium tungsten carbide. Test specimens are obtained by the liquid phase sintering of powder materials, including those containing tungsten nanopowders. High porosity metal foams are prepared through varying the porosity of powder specimens and the content of filling material. The penetration capability of cylinder projectiles made of new alloys is explored in this paper. It is shown that their penetration depth exceeds that of the prototype with relevant weight and size, made of tungsten-nickel-iron alloy, other factors being equal.

  7. The role of mechanical properties in cavitation erosion resistance. [parameters affecting metal fatigue under cavitation flow conditions

    Science.gov (United States)

    Gould, G. C.

    1974-01-01

    Methods for determining the correlations of erosion resistance and mechanical properties of materials are discussed. The most common method of testing cavitation erosion resistance of materials is the vibratory cavitation probe. The instrument and its operation are described. The use of the whirling arm device is considered as a second method. Metallographic investigations of the earliest stages of cavitation erosion damage of metallic materials was conducted. The materials show plastic deformation occurring during the incubation period and increasing until cracks form and metal fragments are lost. The parameters of the work done to cause material fractures are identified. The reactions obtained with specific materials are reported.

  8. Microstructure and bonding mechanism of Al/Ti bonded joint using Al-10Si-1Mg filler metal

    International Nuclear Information System (INIS)

    Sohn, Woong H.; Bong, Ha H.; Hong, Soon H.

    2003-01-01

    The microstructures and liquid state diffusion bonding mechanism of cp-Ti to 1050 Al using an Al-10.0wt.%Si-1.0wt.%Mg filler metal with 100 μm in thickness have been investigated at 620 deg. C under 1x10 -4 Torr. The effects of bonding process parameters on microstructure of bonded joint have been analyzed by using an optical microscope, AES, scanning electron microscopy and EDS. The interfacial bond strength of Al/Ti bonded joints was measured by the single lap shear test. The results show that the bonding at the interface between Al and filler metal proceeds by wetting the Al with molten filler metal, and followed by removal of oxide layer on surface of Al. The interface between Al and filler metal moved during the isothermal solidification of filler metal by the diffusion of Si from filler metal into Al layer. The interface between Al and filler metal became curved in shape with increasing bonding time due to capillary force at grain boundaries. The bonding at the interface between Ti and filler metal proceeds by the formation of two different intermetallic compound layers, identified as Al 5 Si 12 Ti 7 and Al 12 Si 3 Ti 5 , followed by the growth of the intermetallic compound layers. The interfacial bond strength at Al/Ti joint increased with increasing bonding time up to 25 min at 620 deg. C. However, the interfacial bond strength of Al/Ti joint decreased after bonding time of 25 min at 620 deg. C due to formation of cavities in Al near Al/intermetallic interfaces

  9. The mechanism of exchange of cyclopentane with deuterium on metal catalysts: determination of initial product distributions by a Monte Carlo method

    International Nuclear Information System (INIS)

    Faro, A.C. Jr.; Kemball, C.

    1984-01-01

    Monte Carlo methods have been used to calculate the initial distributions of products from the exchange of cyclopentane with deuterium based on different mechanisms for the reaction. Comparisons of the distributions, so obtained, were made with the experimental results on a series of metal catalysts in order to determine which mechanisms appeared to be operating on each metal. (author)

  10. Estimation of heavy metal-contaminated soils' mechanical characteristics using electrical resistivity.

    Science.gov (United States)

    Chu, Ya; Liu, Songyu; Wang, Fei; Cai, Guojun; Bian, Hanliang

    2017-05-01

    Under the process of urbanization in China, more and more attention has been paid to the reuse of heavy metal-contaminated sites. The shear characteristics of heavy metal-contaminated soils are investigated by electrical detection in this paper. Three metal ions (Zn 2+ , Cd 2+ , and Pb 2+ ) were used, the metal concentrations of which are 50, 166.67, 500, 1666.67, and 5000 mg/kg, respectively. Direct shear tests were used to investigate the influence of heavy metal ions on the shear characters of soil samples. It is found that with the addition of heavy metal ions, the shear strength, cohesion, and friction angle of contaminated soils are higher than the control samples. The higher concentration of heavy metal ions penetrated in soils, the higher these engineering characteristics of contaminated soils observed. In addition, an electrical resistivity detection machine is used to evaluate the shear characteristics of contaminated soils. The electrical resistivity test results show that there is a decreasing tendency of resistivity with the increase of heavy metal ion concentrations in soils. Compared with the electrical resistivity and the shear characteristics of metal-contaminated soils, it is found that, under fixed compactness and saturation, shear strength of metal-contaminated soils decreased with the increase of resistivity. A basic linear relationship between C/log(N + 10) and resistivity can be observed, and there is a basic linear relationship between φ/log(N + 10) and resistivity. Besides, a comparison of the measured and predicted shear characteristics shows a high accuracy, indicating that the resistivity can be used to evaluate the shear characteristics of heavy metal contaminated soils.

  11. Sectoral Innovation Watch Space and Aeronautics Sectors. Final sector report

    NARCIS (Netherlands)

    Giessen, A.M. van der

    2011-01-01

    The space and aeronautics sectors are high-technology sectors and belong to the most innovative sectors in Europe1. Analysis of CIS4 data shows that the space and aeronautics sectors continue to be very innovative. 85% of the firms is engaged in intramural R&D. Total R&D expenditures are between 21%

  12. Mechanism of metal nanostructure self-ordering during oblique deposition on pre-patterned surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Numazawa, Satoshi; Heinig, Karl-Heinz [Forschungszentrum Dresden-Rossendorf, Dresden (Germany)

    2010-07-01

    During oblique metal vapor deposition perpendicular to ripples of pre-patterned surfaces, a chain-like formation of metal nanoclusters along the ripples has been observed. The metal nanoclusters are located on the slopes which point towards the evaporation source. The self-ordering of metal nanoclusters has not been observed for normal deposition and for low-angle deposition parallel to the ripple direction. The features of the metal nanostructure depend strongly on the evaporation angle. Here, by means of 3D lattice kinetic Monte Carlo simulations, we studied the process of silver deposition on pre-patterned, oxidized Si surfaces. The experimentally observed Ag nanostructures could be reproduced. It was shown that the extremely low sticking probability of deposited Ag together with a slope-dependent deposition rate leads to a strongly selective Ag nanocluster nucleation on the surface because the nucleation rate depends on the square of the adatom concentration.

  13. Fluorescence quenching dynamics and mechanism of cry1ab toxin from bacillus thuringiensis by different metal ions

    International Nuclear Information System (INIS)

    Zhou, X.; Zhang, J.

    2016-01-01

    The reaction dynamics of Cry1Ab toxin from Bacillus thuringiensis with sodium, calcium and lead ions was studied by fluorescence quenching technique. Gradual quenching was observed by titration of Cry1Ab toxin with metal ions (Na+, Ca/sup 2+/ or Pb/sup 2+/). The quenched strength of these ions in the descending order was: lead ion > calcium ion > sodium ion. The quenching equilibrium of Cry1Ab toxin by metal ions reached within 60 min, and the quenching dynamics of Cry1Ab toxin could be expressed by the Elovich model. The toxin concentration, pH and temperature had influence on the quenching dynamics. The interaction between Cry1Ab toxin and metal ions is based on static quenching mechanism. (author)

  14. Microstructure, mechanical property and metal release of As-SLM CoCrW alloy under different solution treatment conditions.

    Science.gov (United States)

    Lu, Yanjin; Wu, Songquan; Gan, Yiliang; Zhang, Shuyuan; Guo, Sai; Lin, Junjie; Lin, Jinxin

    2015-03-01

    In the study, the microstructure, mechanical property and metal release behavior of selective laser melted CoCrW alloys under different solution treatment conditions were systemically investigated to assess their potential use in orthopedic implants. The effects of the solution treatment on the microstructure, mechanical properties and metal release were systematically studied by OM, SEM, XRD, tensile test, and ICP-AES, respectively. The XRD indicated that during the solution treatment the alloy underwent the transformation of γ-fcc to ε-hcp phase; the ε-hcp phase nearly dominated in the alloy when treated at 1200°C following the water quenching; the results from OM, SEM showed that the microstructural change was occurred under different solution treatments; solution at 1150°C with furnace cooling contributed to the formation of larger precipitates at the grain boundary regions, while the size and number of the precipitates was decreased as heated above 1100°C with the water quenching; moreover, the diamond-like structure was invisible at higher solution temperature over 1150°C following water quenching; compared with the furnace cooling, the alloy quenched by water showed excellent mechanical properties and low amount of metal release; as the alloy heated at 1200°C, the mechanical properties of the alloy reached their optimum combination at UTS=1113.6MPa, 0.2%YS=639.5MPa, and E%=20.1%, whilst showed the lower total quantity of metal release. It is suggested that a proper solution treatment is an efficient strategy for improving the mechanical properties and corrosion resistance of As-SLM CoCrW alloy that show acceptable tensile ductility. Copyright © 2015 Elsevier Ltd. All rights reserved.

  15. Study of the mechanisms involved in the laser superficial hardening process of metallic alloys

    International Nuclear Information System (INIS)

    Silva, Edmara Marques Rodrigues da

    2001-01-01

    The laser superficial hardening process of a ferrous alloy (gray cast iron) and of an aluminum-silicon alloy was investigated in this work. These metallic alloys are used in the automobile industry for manufacturing cylinders and pistons, respectively. By application of individual pulses and single tracks, the involved mechanisms during the processing were studied. Variables such as energy density, power density, temporal width, beam diameter on the sample surface, atmosphere of the processing region, overlapping and scanning velocity. The hardened surface was characterized by optical and scanning electronic microscopy, dispersive energy microanalysis, X-ray mapping, X-ray diffraction, and measurements of roughness and Vickers microhardness. Depending on the processing parameters, it is possible to obtain different microstructures. The affected area of gray cast iron, can be hardened by remelting or transformation hardening (total or partial) if the reached temperature is higher or not that of melting temperature. Laser treatment originated new structures such as retained austenite, martensite and, occasionally, eutectic of cellular dendritic structure. Aluminum-silicon alloy does not have phase transformation in solid state, it can be hardened only by remelting. The increase of hardness is a function of the precipitation hardening process, which makes the silicon particles smaller and more disperse in the matrix. Maximal values of microhardness (700-1000 HV) were reached with the laser treatment in gray cast iron samples. The initial microhardness is of 242 HV. For aluminum-silicon alloy, the laser remelting increases the initial microhardness of 128 HV to the range of 160-320 HV. The found results give a new perspective for using the CLA/IPEN's laser in the heat treatment area. Besides providing a higher absorptivity to the materials, compared with the CO 2 laser, and optical fiber access, the superficial hardening with Nd:YAG laser, depending on the level of

  16. Metal and metalloid foliar uptake by various plant species exposed to atmospheric industrial fallout: Mechanisms involved for lead

    Energy Technology Data Exchange (ETDEWEB)

    Schreck, E., E-mail: eva.schreck@ensat.fr [Universite de Toulouse (France); INP, UPS (France); EcoLab (Laboratoire Ecologie Fonctionnelle et Environnement) (France); ENSAT, Avenue de l' Agrobiopole, 31326 Castanet Tolosan (France); CNRS (France); EcoLab, 31326 Castanet Tolosan (France); Foucault, Y. [Universite de Toulouse (France); INP, UPS (France); EcoLab (Laboratoire Ecologie Fonctionnelle et Environnement) (France); ENSAT, Avenue de l' Agrobiopole, 31326 Castanet Tolosan (France); CNRS (France); EcoLab, 31326 Castanet Tolosan (France); STCM, Societe de Traitements Chimiques des Metaux, 30 Avenue de Fondeyre 31200 Toulouse (France); Sarret, G. [ISTerre (UMR 5275), Universite J. Fourier and CNRS, BP 53, 38041 Grenoble cedex 9 (France); Sobanska, S. [LASIR (UMR CNRS 8516), Universite de Lille 1, Bat. C5, 59655 Villeneuve d' Ascq cedex (France); Cecillon, L. [ISTerre (UMR 5275), Universite J. Fourier and CNRS, BP 53, 38041 Grenoble cedex 9 (France); Castrec-Rouelle, M. [Universite Pierre and Marie Curie (UPMC-Paris 6), Bioemco (Biogeochimie et Ecologie des Milieux Continentaux), Site Jussieu, Tour 56, 4 Place Jussieu, 75252 Paris cedex 05 (France); Uzu, G. [Laboratoire d' Aerologie (UMR 5560), OMP, UPS 14, Avenue Edouard Belin, 31400 Toulouse (France); GET (UMR 5563), IRD, 14, Avenue Edouard Belin, 31400 Toulouse (France); Dumat, C. [Universite de Toulouse (France); INP, UPS (France); EcoLab (Laboratoire Ecologie Fonctionnelle et Environnement) (France); ENSAT, Avenue de l' Agrobiopole, 31326 Castanet Tolosan (France); CNRS (France); EcoLab, 31326 Castanet Tolosan (France)

    2012-06-15

    Fine and ultrafine metallic particulate matters (PMs) are emitted from metallurgic activities in peri-urban zones into the atmosphere and can be deposited in terrestrial ecosystems. The foliar transfer of metals and metalloids and their fate in plant leaves remain unclear, although this way of penetration may be a major contributor to the transfer of metals into plants. This study focused on the foliar uptake of various metals and metalloids from enriched PM (Cu, Zn, Cd, Sn, Sb, As, and especially lead (Pb)) resulting from the emissions of a battery-recycling factory. Metal and metalloid foliar uptake by various vegetable species, exhibiting different morphologies, use (food or fodder) and life-cycle (lettuce, parsley and rye-grass) were studied. The mechanisms involved in foliar metal transfer from atmospheric particulate matter fallout, using lead (Pb) as a model element was also investigated. Several complementary techniques (micro-X-ray fluorescence, scanning electron microscopy coupled with energy dispersive X-ray microanalysis and time-of-flight secondary ion mass spectrometry) were used to investigate the localization and the speciation of lead in their edible parts, i.e. leaves. The results showed lead-enriched PM on the surface of plant leaves. Biogeochemical transformations occurred on the leaf surfaces with the formation of lead secondary species (PbCO{sub 3} and organic Pb). Some compounds were internalized in their primary form (PbSO{sub 4}) underneath an organic layer. Internalization through the cuticle or penetration through stomata openings are proposed as two major mechanisms involved in foliar uptake of particulate matter. - Graphical abstract: Overall picture of performed observations and mechanisms potentially involved in lead foliar uptake. Highlights: Black-Right-Pointing-Pointer Foliar uptake of metallic particulate matter (PM) is of environmental and health concerns. Black-Right-Pointing-Pointer The leaf morphology influences the adsorption

  17. A new lumbar posterior fixation system, the memory metal spinal system: an in-vitro mechanical evaluation.

    Science.gov (United States)

    Kok, Dennis; Firkins, Paul John; Wapstra, Frits H; Veldhuizen, Albert G

    2013-09-18

    Spinal systems that are currently available for correction of spinal deformities or degeneration such as lumbar spondylolisthesis or degenerative disc disease use components manufactured from stainless steel or titanium and typically comprise two spinal rods with associated connection devices (for example: DePuy Spines Titanium Moss Miami Spinal System). The Memory Metal Spinal System of this study consists of a single square spinal rod made of a nickel titanium alloy (Nitinol) used in conjunction with connecting transverse bridges and pedicle screws made of Ti-alloy. Nitinol is best known for its shape memory effect, but is also characterized by its higher flexibility when compared to either stainless steel or titanium. A higher fusion rate with less degeneration of adjacent segments may result because of the elastic properties of the memory metal. In addition, the use of a single, unilateral rod may be of great value for a TLIF procedure. Our objective is to evaluate the mechanical properties of the new Memory Metal Spinal System compared to the Titanium Moss Miami Spinal System. An in-vitro mechanical evaluation of the lumbar Memory Metal Spinal System was conducted. The test protocol followed ASTM Standard F1717-96, "Standard Test Methods for Static and Fatigue for Spinal Implant Constructs in a Corpectomy Model." 1. Static axial testing in a load to failure mode in compression bending, 2. Static testing in a load to failure mode in torsion, 3. Cyclical testing to estimate the maximum run out load value at 5.0 x 10^6 cycles. In the biomechanical testing for static axial compression bending there was no statistical difference between the 2% yield strength and the stiffness of the two types of spinal constructs. In axial compression bending fatigue testing, the Memory Metal Spinal System construct showed a 50% increase in fatigue life compared to the Titanium Moss Miami Spinal System. In static torsional testing the Memory Metal Spinal System constructs showed an

  18. Rapid magnetic removal of aqueous heavy metals and their relevant mechanisms using nanoscale zero valent iron (nZVI) particles.

    Science.gov (United States)

    Huang, Pengpeng; Ye, Zhengfang; Xie, Wuming; Chen, Qi; Li, Jing; Xu, Zhencheng; Yao, Maosheng

    2013-08-01

    Much work is devoted to heavy metal sorption, reduction and relevant mechanisms by nanoscale zero valent iron (nZVI) particle, but fewer studies utilize its magnetic properties in aqueous metal removals. Here, we have investigated the use of nZVI particles both electrosprayed (E-nZVI) and non-electrosprayed (NE-nZVI) with different concentration levels (0.186-1.86 mg/mL) in removing aqueous Cd(II), Cr(IV), and Pb(II) through the magnetic separation means. The effects of the reaction time (5-20 min) and magnetic treatment time (1-30 min) on relevant magnetic removal efficiencies were studied. Metal ion concentration was analyzed using inductively coupled plasma (ICP), and the magnetically obtained metal-nZVI mixtures were further analyzed using X-ray photoelectron spectroscopy (XPS). Results showed that the magnetic removal efficiencies of heavy metals varied with the metal species, nZVI loading, reaction and magnetic separation time. In most cases, use of 1.5 mg/mL E-nZVI or NE-nZVI resulted in removal efficiencies of more than 80% for Pb(II), Cd(II), and Cr(IV). Increasing the magnetic treatment time from 1 to 20 min was shown to lead to ≈ 20% increase in Pb(II) removal efficiency, but no improvements for Cd(II) and Cr(IV). In contrast, increasing the reaction time decreased the Pb(II) removal efficiency, yet no effects observed for Cd(II) and Cr(IV). In general, 1 min reaction and 5 min magnetic treatment were found sufficient to achieve considerable heavy metal removals. For comparable efficiencies, use of magnetic method could significantly reduce nZVI loading. XPS analysis results indicated that atomic percentages of O 1s, Fe 2p, Cd 3d, Pb 4f and Cr 2p varied with metal exposures. Different from Cd(II) and Cr(IV), aqueous iron ions might be possibly present when treating Pb(II). This study demonstrated a rapid heavy metal removal method using the magnetic property of nZVI particles, while contributing to understanding of the relevant removal mechanisms

  19. Mechanism on heavy metals vaporization from municipal solid waste fly ash by MgCl₂⋅6H₂O.

    Science.gov (United States)

    Yu, Jie; Sun, Lushi; Ma, Chuan; Qiao, Yu; Xiang, Jun; Hu, Song; Yao, Hong

    2016-03-01

    This work aims to study the mechanism of heavy metals vaporization by MgCl2⋅6H2O. Firstly, the decomposition mechanism of MgCl2⋅6H2O was investigated by thermodynamic equilibrium calculations, XRD and TG. Upon heating, MgCl2⋅6H2O went through the processes of dehydration and hydrolysis simultaneously accompanied by the release of HCl between 150 and 500°C. At temperature higher than 500°C, Mg(OH)Cl gradually release part of HCl. MgCl2⋅6H2O followed the similar processes of decomposition at both oxidative and reductive atmospheres. In oxidative atmosphere, vaporization of Zn and Cu was significantly accelerated by MgCl2⋅6H2O. However, in inert atmosphere, vaporization of Cu was not promoted since copper chloride was only stable in oxidative atmosphere. Under slow heating condition, vaporization of heavy metals were close to that under fast heating condition. This may be partially attributed to that most heavy metals already reacted with HCl forming metal chlorides below 500°C, which can be vaporized at higher temperature. Moreover, the Mg(OH)Cl contributed to release HCl up to 800°C. At such high temperature, the metal chlorides continue to be formed and then vaporized. After treatment, the leaching concentration of heavy metals from treated fly ashes were much lower than that from raw fly ash and met the regulatory limit of leachate. Since a large amount of MgSiO3 were formed during thermal treatment, the fly ash treated with MgCl2⋅6H2O can be used as raw materials for glass-ceramics production. Copyright © 2015 Elsevier Ltd. All rights reserved.

  20. Abnormal devitrification behavior and mechanical response of cold-rolled Mg-rich Mg-Cu-Gd metallic glasses

    International Nuclear Information System (INIS)

    Lee, J.I.; Kim, J.W.; Oh, H.S.; Park, J.S.; Park, E.S.

    2016-01-01

    Abnormal devitrification behavior and mechanical response of Mg 75 Cu 15 Gd 10 (relatively strong glass former with higher structural stability) and Mg 85 Cu 5 Gd 10 (relatively fragile glass former with lower structural stability) metallic glasses, fabricated by repeated forced cold rolling, have been investigated. When metallic glasses were cold-rolled up to a thickness reduction ratio of ∼33%, the heat of relaxation (ΔH relax. ) below T g of the cold-rolled specimens was reduced, which indicates the formation of local structural ordering via cold rolling due to stress-induced relaxation. The local structural ordering results in abnormal devitrification behavior, such as higher resistance of glass-to-supercooled liquid transition and delayed growth, in the following heat treatment due to increased nuclei density and pinning site. In particular, the fragility index, m, could assist in understanding structural stability and local structural variation by mechanical processing as well as compositional tuning. Indeed, we examine the shear avalanche size to rationalize the variation of the deformation unit size depending on the structural instability before and after cold rolling. The deformation mode in Mg 85 Cu 5 Gd 10 metallic glass might change from self-organized critical state to chaotic state by cold rolling, which results in unique hardening behavior under the condition for coexisting well distributed local structural ordering and numerous thinner shear deformed areas. These results would give us a guideline for atomic scale structural manipulation of metallic glasses, and help develop novel metallic glass matrix composites with optimal properties through effective mechanical processing as well as heat treatment.

  1. Characterization of Printed Circuit Boards for Metal and Energy Recovery after Milling and Mechanical Separation

    Directory of Open Access Journals (Sweden)

    Waldir A. Bizzo

    2014-06-01

    Full Text Available The proper disposal of electrical and electronic waste is currently a concern of researchers and environmental managers not only because of the large volume of such waste generated, but also because of the heavy metals and toxic substances it contains. This study analyzed printed circuit boards (PCBs from discarded computers to determine their metal content and characterized them as solid waste and fuel. The analysis showed that PCBs consist of approximately 26% metal, made up mainly of copper, lead, aluminum, iron and tin, as well as other heavy metals such as cadmium and nickel. Comparison with the results of other studies indicated that the concentration of precious metals (gold and silver has declined over time. Analysis of the leachate revealed high concentrations of cadmium and lead, giving the residue the characteristics of hazardous waste. After milling the PCBs, we found that larger amounts of metal were concentrated in smaller fractions, while the lightest fraction, obtained by density separation, had a gross calorific value of approximately 11 MJ/kg, although with a high ash content. Milling followed by density separation proved potentially useful for recovery of metals and energy-rich fractions.

  2. Cadmium and zinc activate adaptive mechanisms in Nicotiana tabacum similar to those observed in metal tolerant plants.

    Science.gov (United States)

    Vera-Estrella, Rosario; Gómez-Méndez, María F; Amezcua-Romero, Julio C; Barkla, Bronwyn J; Rosas-Santiago, Paul; Pantoja, Omar

    2017-09-01

    Tobacco germinated and grew in the presence of high concentrations of cadmium and zinc without toxic symptoms. Evidence suggests that these ions are sequestered into the vacuole by heavy metal/H + exchanger mechanisms. Heavy metal hyperaccumulation and hypertolerance are traits shared by a small set of plants which show specialized physiological and molecular adaptations allowing them to accumulate and sequester toxic metal ions. Nicotiana tabacum was used to test its potential as a metal-accumulator in a glass house experiment. Seed germination was not affected in the presence of increasing concentrations of zinc and cadmium. Juvenile and adult plants could concentrate CdCl 2 and ZnSO 4 to levels exceeding those in the hydroponic growth medium and maintained or increased their leaf dry weight when treated with 0.5- or 1-mM CdCl 2 or 1-mM ZnSO 4 for 5 days. Accumulation of heavy metals did not affect the chlorophyll and carotenoid levels, while variable effects were observed in cell sap osmolarity. Heavy metal-dependent H + transport across the vacuole membrane was monitored using quinacrine fluorescence quenching. Cadmium- or zinc-dependent fluorescence recovery revealed that increasing concentrations of heavy metals stimulated the activities of the tonoplast Cd 2+ or Zn 2+ /H + exchangers. Immunodetection of the V-ATPase subunits showed that the increased proton transport by zinc was not due to changes in protein amount. MTP1 and MTP4 immunodetection and semiquantitative RT-PCR of NtMTP1, NtNRAMP1, and NtZIP1 helped to identify the genes that are likely involved in sequestration of cadmium and zinc in the leaf and root tissue. Finally, we demonstrated that cadmium and zinc treatments induced an accumulation of zinc in leaf tissues. This study shows that N. tabacum possesses a hyperaccumulation response, and thus could be used for phytoremediation purposes.

  3. Mechanism on the sorption of heavy metals from binary-solution by a low cost montmorillonite and its desorption potential

    Directory of Open Access Journals (Sweden)

    Kovo G. Akpomie

    2015-09-01

    Full Text Available The potential of a low-cost Nigerian montmorillonite for the adsorption of Ni(II and Mn(II ions from aqueous solution was investigated by batch mode. XRD, SEM and BET analysis were used to characterize the adsorbent. The experiments were performed as a function of pH, particle size, adsorbent dose, initial metal ion concentration, contact time, ligands and temperature. The process was found to be dependent on all the parameters investigated, with a pH of 6.0 obtained for optimum removal of both metal ions. The Langmuir monolayer adsorption capacity of 166.67 and 142.86 mg/g was obtained for Ni(II and Mn(II ions respectively. The Freundlich isotherm gave the best fit to the experimental data than the Langmuir, Temkin and Dubinin–Radushkevich isotherms. The scatchard plot analysis indicated the existence of more than one type of active site on the montmorillonite which corroborates the good fit of the Freundlich model. The pseudo-first order, pseudo-second order and intraparticle diffusion models were applied to the kinetic data. The best fit was achieved with the pseudo-first order model and the existence of intraparticle diffusion mechanism was indicated. Thermodynamic studies showed an endothermic, dissociative, spontaneous and a physical adsorption process between the metal ions and the montmorillonite. Desorption studies revealed over 90% desorption of both metal ions from the metal loaded adsorbent.

  4. Mechanical tests imaging on metallic matrix composites. Experimental contribution to homogenization methods validation and identification of phase-related mechanical properties

    International Nuclear Information System (INIS)

    Quoc-Thang Vo

    2013-01-01

    This work is focused on a matrix/inclusion metal composite. A simple method is proposed to evaluate the elastic properties of one phase while the properties of the other phase are assumed to be known. The method is based on both an inverse homogenization scheme and mechanical field's measurements by 2D digital image correlation. The originality of the approach rests on the scale studied, i.e. the microstructure scale of material: the characteristic size of the inclusions is about few tens of microns. The evaluation is performed on standard uniaxial tensile tests associated with a long-distance microscope. It allows observation of the surface of a specimen on the microstructure scale during the mechanical stress. First, the accuracy of the method is estimated on 'perfect' mechanical fields coming from numerical simulations for four microstructures: elastic or porous single inclusions having either spherical or cylindrical shape. Second, this accuracy is estimated on real mechanical field for two simple microstructures: an elasto-plastic metallic matrix containing a single cylindrical micro void or four cylindrical micro voids arranged in a square pattern. Third, the method is used to evaluate elastic properties of αZr inclusions with arbitrary shape in an oxidized Zircaloy-4 sample of the fuel cladding of a pressurized water reactor after an accident loss of coolant accident (LOCA). In all this study, the phases are assumed to have isotropic properties. (author) [fr

  5. Research on Formation Mechanism of Dynamic Response and Residual Stress of Sheet Metal Induced by Laser Shock Wave

    Science.gov (United States)

    Feng, Aixin; Cao, Yupeng; Wang, Heng; Zhang, Zhengang

    2018-01-01

    In order to reveal the quantitative control of the residual stress on the surface of metal materials, the relevant theoretical and experimental studies were carried out to investigate the dynamic response of metal thin plates and the formation mechanism of residual stress induced by laser shock wave. In this paper, the latest research trends on the surface residual stress of laser shock processing technology were elaborated. The main progress of laser shock wave propagation mechanism and dynamic response, laser shock, and surface residual stress were discussed. It is pointed out that the multi-scale characterization of laser and material, surface residual stress and microstructure change is a new hotspot in laser shock strengthening technology.

  6. Photochemistry and electron-transfer mechanism of transition metal oxalato complexes excited in the charge transfer band.

    Science.gov (United States)

    Chen, Jie; Zhang, Hua; Tomov, Ivan V; Ding, Xunliang; Rentzepis, Peter M

    2008-10-07

    The photoredox reaction of trisoxalato cobaltate (III) has been studied by means of ultrafast extended x-ray absorption fine structure and optical transient spectroscopy after excitation in the charge-transfer band with 267-nm femtosecond pulses. The Co-O transient bond length changes and the optical spectra and kinetics have been measured and compared with those of ferrioxalate. Data presented here strongly suggest that both of these metal oxalato complexes operate under similar photoredox reaction mechanisms where the primary reaction involves the dissociation of a metal-oxygen bond. These results also indicate that excitation in the charge-transfer band is not a sufficient condition for the intramolecular electron transfer to be the dominant photochemistry reaction mechanism.

  7. ICARUS-4 : a database of energy reduction options for the Netherlands, 1995-2020 : Sector study for the Metals Products and Electrotechnical Industry

    NARCIS (Netherlands)

    Alsema, E.A.

    2000-01-01

    In this report we describe the energy consumption in 1995 and the energy saving options that exist within the metal products and electrotechnical industry (SBI/NACE 28-32, 34-35) in the Netherlands. The data will be included in the ICARUS-4 database which gives an inventory of the technological

  8. ICARUS-4 : a database of energy reduction options for the Netherlands, 1995-2020 : sector study for the non-ferrous metals industry

    NARCIS (Netherlands)

    Alsema, E.A.

    2000-01-01

    In this report we describe the energy consumption in 1995 and the energy saving options that exist within the non-ferro base metal industry (SBI/NACE 27.4-5) in the Netherlands. The data will be included in the ICARUS-4 database which gives an inventory of the technological options for energy

  9. FINAL TAILINGS OF METAL-WORKING PRODUCTION. Part 3. PHYSICO-MECHANICAL CHARACTERISTICS

    Directory of Open Access Journals (Sweden)

    O. M. Djakonov

    2011-01-01

    Full Text Available The indices of adhesion and friability of metal-containing tailings, their water absorbency and wettability and also abrasive characteristics of tailings with the purpose of prevention of contacting surfaces wear are studied.

  10. Understanding the molecular mechanism of pulse current charging for stable lithium-metal batteries

    OpenAIRE

    Li, Qi; Tan, Shen; Li, Linlin; Lu, Yingying; He, Yi

    2017-01-01

    High energy and safe electrochemical storage are critical components in multiple emerging fields of technologies. Rechargeable lithium-metal batteries are considered to be promising alternatives for current lithium-ion batteries, leading to as much as a 10-fold improvement in anode storage capacity (from 372 to 3860 mAh g?1). One of the major challenges for commercializing lithium-metal batteries is the reliability and safety issue, which is often associated with uneven lithium electrodeposit...

  11. Mechanisms of Heavy Metal Sequestration in Soils: Plant-Microbe Interactions and Organic Matter Aging

    Energy Technology Data Exchange (ETDEWEB)

    Teresa W.-M. Fan; Richard M. Higashi; David Crowley; Andrew N. Lane: Teresa A. Cassel; Peter G. Green

    2004-12-31

    For stabilization of heavy metals at contaminated sites, the three way interaction among soil organic matter (OM)-microbes-plants, and their effect on heavy metal binding is critically important for long-term sustainability, a factor that is poorly understood at the molecular level. Using a soil aging system, the humification of plant matter such as wheat straw was probed along with the effect on microbial community on soil from the former McClellan Air Force Base.

  12. Plasmon mechanism of light transmission through a metal film or a plasma layer

    OpenAIRE

    Bliokh, Yu. P.

    2005-01-01

    It is shown that a smooth metal film (or a plasma layer) can be made transparent for an electromagnetic wave when two identical subwavelength diffraction gratings are placed on both sides of the film. The electromagnetic wave transmission through the metal film is caused by excitation of evanescent surface waves (plasmons) and their transformation into propagating waves at the gratings. A model which is developed analytically shows that the problem of the wave transmission is physically equiv...

  13. Mechanical properties of metal-ceramic systems from nickel-chromium and cobalt-chromium alloys

    Directory of Open Access Journals (Sweden)

    Mirković Nemanja

    2007-01-01

    Full Text Available Background/Aim. Metal-ceramic bond strength and alloys' elastic modulus clearly determine the potential of alloy application, because the ceramic integrity during mastication depends on these two characteristics. The aim of this study was to evaluate metal-ceramic bond strength and elastic modulus of cobalt-chromium alloys in making porcelainfused- to-metal restorations, regarding the application of the most frequent nickel-chromium alloy. Methods. The research was performed as an experimental study. Six metalceramic samples were made from nickel-chromium alloy (Wiron 99 and cobalt-chromium alloy (Wirobond C, according to the manufactures manuals and instructions from ISO 9693: 1996. Three-point bending test was performed up to the ceramic fracture. The fracture load was measured on an universal testing machine (Zwick, type 1464, with cross-head speed of 0,05mm/min. Results. The results of this study confirmed the significant differences between the metal-ceramic bond strength (p < 0.01 and elastic modulus (p < 0.001 of nickel-chromium and cobalt-chromium alloys, where cobalt-chromium alloys showed higher values for both tested parameters. Conclusion. Cobalt-chromium metal-ceramic alloys can successfully replace nickel-chromium alloys, especially for fabrication of long-span metal-ceramic bridges due to the great flexural strength.

  14. Solid state reactions in mechanically alloyed Al-Y alloy with addition of metal oxides; Al-Y gokin to kinzoku sankabutsu tono mechanical alloying to koso hanno

    Energy Technology Data Exchange (ETDEWEB)

    Okubo, M. [Nihon University, Tokyo (Japan); Kaneko, J.; Sugamata, M. [Nihon University, Tokyo (Japan). College of Industrial Technology

    1999-12-15

    With a purpose of attesting preferential oxidation of an alloying element which has low solid solubility in aluminum, an Al-5at%Y alloy was mechanically alloyed with or without addition of metal oxides. Y was chosen as an alloying element since it has higher oxidation tendency than Al and a low maximum solid solubility of 0.17mass% in Al. Mechanically alloyed powders were consolidated by hot-extrusion to the P/M materials of which constituent phases, microstructures and mechanical properties were examined. The added oxygen, either from the process control agent or from oxide powders, acted as oxygen sources for internal oxidation, and Y in Al was shown to be preferentially oxidized to Y{sub 2}O{sub 3} and Al{sub 5}Y{sub 3}O{sub 12}. The P/M materials with addition of oxide powders showed high tensile strength of about 600MPa at room temperature. (author)

  15. Sectoral assessments

    Energy Technology Data Exchange (ETDEWEB)

    Callaway, J.M.; Fenhann, J.; Gorham, R.; Makundi, W.; Sathaye, J.

    1999-09-01

    This publication contains five papers that were written as a part of the GEF project, The Economics of Greenhouse Gas Limitations. The main goal of the project was to assess the greenhouse gas reductions and incremental costs of mitigation option sin Ecuador, Argentina, Senegal, Mauritius, Vietnam, Indonesia, Estonia and Hungary. In addition, regional studies were conducted for the Andean Pact nations and Southern Africa to assess various aspects of regional co-operation in reducing greenhouse gas emissions. The GEF study also involved the development of a methodological framework for climate change assessment, with a special emphasis on developing countries. These guidelines have been published in a separate document, Economics of Greenhouse Gas Limitations: Methodological Guidelines. The papers in this publication focus on various methodological and policy aspects of greenhouse gas mitigation at the sectoral level, and are outgrowth of work performed on other parts of the GEF project. (au)

  16. Microstructure and mechanical properties of aluminum 5083 weldments by gas tungsten arc and gas metal arc welding

    International Nuclear Information System (INIS)

    Liu Yao; Wang Wenjing; Xie Jijia; Sun Shouguang; Wang Liang; Qian Ye; Meng Yuan; Wei Yujie

    2012-01-01

    Highlights: ► Welding zones by GTAW and GMAW are softer than the parent material Al5083. ► GTAW for Al5083 are mechanically more reliable than that welded by GMAW. ► GTAW welds fail by shear, but GMAW welds show mixed shear and normal failure. - Abstract: The mechanical properties and microstructural features of aluminum 5083 (Al5083) weldments processed by gas tungsten arc welding (GTAW) and gas metal arc welding (GMAW) are investigated. Weldments processed by both methods are mechanically softer than the parent material Al5083, and could be potential sites for plastic localization. It is revealed that Al5083 weldments processed by GTAW are mechanical more reliable than those by GMAW. The former bears higher strength, more ductility, and no apparent microstructure defects. Perceivable porosity in weldments by GMAW is found, which could account for the distinct mechanical properties between weldments processed by GTAW and GMAW. It is suggested that caution should be exercised when using GMAW for Al5083 in the high-speed-train industry where such light weight metal is broadly used.

  17. Investigating the gas sorption mechanism in an rht -metal-organic framework through computational studies

    KAUST Repository

    Pham, Tony T.

    2014-01-09

    Grand canonical Monte Carlo (GCMC) simulations were performed to investigate CO2 and H2 sorption in an rht-metal-organic framework (MOF) that was synthesized with a ligand having a nitrogen-rich trigonal core through trisubstituted triazine groups and amine functional groups. This MOF was synthesized by two different groups, each reporting their own distinct gas sorption measurements and crystal structure. Electronic structure calculations demonstrated that the small differences in the atomic positions between each group\\'s crystal structure resulted in different electrostatic parameters about the Cu2+ ions for the respective unit cells. Simulations of CO2 sorption were performed with and without many-body polarization effects and using our recently developed CO2 potentials, in addition to a well-known bulk CO2 model, in both crystallographic unit cells. Simulated CO2 sorption isotherms and calculated isosteric heats of adsorption, Qst, values were in excellent agreement with the results reported previously by Eddaoudi et al. for both structures using the polarizable CO2 potential. For both crystal structures, the initial site for CO2 sorption were the Cu 2+ ions that had the higher positive charge in the unit cell, although the identity of this electropositive Cu2+ ion was different in each case. Simulations of H2 sorption were performed with three different hydrogen potentials of increasing anisotropy in both crystal structures and the results, especially with the highest fidelity model, agreed well with Eddaoudi et al.\\'s experimental data. The preferred site of H 2 sorption at low loading was between two Cu2+ ions of neighboring paddlewheels. The calculation of the normalized hydrogen dipole distribution for the polarizable model in both crystal structures aided in the identification of four distinct sorption sites in the MOF, which is consistent to what was observed in the experimental inelastic neutron scattering (INS) spectra. Lastly, while the

  18. Decomposition mechanism of methylene blue caused by metallic iron-maghemite mixture

    International Nuclear Information System (INIS)

    Kubuki, Shiro; Shibano, Koya; Akiyama, Kazuhiko; Homonnay, Zoltán; Kuzmann, Ernő; Ristić, Mira; Nishida, Tetsuaki

    2013-01-01

    Decomposition mechanism of methylene blue (MB) caused by a mixture of metallic iron-maghemite (Fe 0 -γFe 2 O 3 ) was investigated by means of 57 Fe-Mössbauer spectroscopy, X-ray diffractometry (XRD), Ultraviolet-Visible Absorption Spectroscopy (UV-vis) and electrospray-ionization mass spectroscopy (ESI-MS). Ten day-leaching test of 10 μmol L  − 1 MB aqueous solution and Fe 0 -γFe 2 O 3 mixture (mass ratio 3:7) showed a decrease in the concentration from 10.5 to 4.45 μmol L  − 1 with first-order rate constant (k) of 1.57 x 10 - 1 day - 1. An ESI-MS study of Fe 0 -γFe 2 O 3 mixture (3:7) after the leaching test revealed new peaks at m/z of 100, 110 and 137 due to fragmentation of MB, in addition to those observed at m/z of 284, 270 and 256 which were ascribed to MB, Azure B and Azure A, respectively. 57 Fe-Mössbauer spectra of Fe 0 -γFe 2 O 3 mixture (3:7) resulted in a decrease in absorption area (A) for Fe 0 (δ = 0.00 ±0.01 mm s  − 1 , H int  = 33.0 ±0.1 T) from 37.5 to 21.3, 9.7, 7.9, 7.0 and 4.5 ±0.5 %, together with an increase in A from 0.0 to 5.0, 13.8, 17.2, 21.0 and 22.4 ±0.5 % for octahedral (O h ) iron (Fe II  + Fe III ) of Fe 3 O 4 . XRD study of these samples indicated that the peak intensity at 2Θ of 44.7° being ascribed to Fe 0 was decreased, while that of 35.6° due to Fe 3 O 4 was almost constant; relative peak ratio of Fe 0 /Fe 3 O 4 was decreased from 26.3 to 2.76 after the leaching, indicating that Fe 0 in the Fe 0 -γFe 2 O 3 mixture was oxidized to Fe 3 O 4 . These experimental results suggest that Fe 0 -γFe 2 O 3 mixture could be utilized for the cleaning or decomposition of toxic organic compounds like trichloroethylene.

  19. Hard magnetic properties and coercivity mechanism of melt-spun Misch Metal-Fe-B alloy

    Energy Technology Data Exchange (ETDEWEB)

    Quan, Ningtao; Luo, Yang, E-mail: eluoyang@foxmail.com; Yan, Wenlong; Yuan, Chao; Yu, Dunbo; Sun, Liang; Lu, Shuo; Li, Hongwei; Zhang, Hongbin

    2017-09-01

    Highlights: • Melt-spun MM{sub 13}Fe{sub 81}B{sub 6} alloy shows that the distributions of the La, Ce, Pr, Nd, Fe and B elements is uniformly distributed, and the grain size is in the range of 30–40 nm, it can be seen that Pr-rich and La-rich phases concentrated on grain boundaries, which resulted in the coercivity augment with the increase of MMFe{sub 2} content, and the grain size is around 40–50 nm in MM{sub 16}Fe{sub 78}B{sub 6}. • There is a significant formation of MMFe{sub 2} with abundant Pr and La, and a small amount of Ce and Nd enriched at the interfacial region in MM{sub 16}Fe{sub 78}B{sub 6}, thus an inhomogeneous region was formed. It is considered that the inhomogeneous region is effective in increasing the coercivity. • The optimum-quenched MM{sub 13}Fe{sub 81}B{sub 6} alloy have been shown to exhibit a coercive force of 6.9 kOe and an energy product of 8.5 MGOe, which is superior to anisotropic ferrite magnets of 4.5 MGOe. - Abstract: Magnetic and structural properties of Misch Metal (MM)-Fe-B alloys, were examined in the melt-spun ribbons. Melt-spun MM-Fe-B samples were prepared at the surface velocities of 18–30 m/s. Crystalline structure and their room-temperature magnetization characteristics were analyzed, and the optimum surface velocity of 20 m/s and nominal composition of MM{sub 13}Fe{sub 81}B{sub 6} were obtained. Microstructural analyses indicate that the grain size is approximately 30–50 nm in the alloys with the optimum characteristics. In the MM{sub 16}Fe{sub 78}B{sub 6} alloys, Pr-rich and La-rich phases concentrated on grain boundaries, which resulted in the coercivity augment with the increase of MMFe{sub 2} content. Dependence of coercivity on applied magnetic field suggested that the mechanism of coercivity in moderate MM-content samples was inhomogeneous domain wall pinning type. The melt-spun ribbons in the optimum condition exhibit a coercive force of 6.9 kOe and an energy product of 8.5 MGOe, which can be used as

  20. Physiological and molecular responses to heavy metal stresses suggest different detoxification mechanism of Populus deltoides and P. x canadensis.

    Science.gov (United States)

    Benyó, Dániel; Horváth, Edit; Németh, Edit; Leviczky, Tünde; Takács, Kinga; Lehotai, Nóra; Feigl, Gábor; Kolbert, Zsuzsanna; Ördög, Attila; Gallé, Róbert; Csiszár, Jolán; Szabados, László; Erdei, László; Gallé, Ágnes

    2016-08-20

    Plants have divergent defense mechanisms against the harmful effects of heavy metals present in excess in soils and groundwaters. Poplars (Populus spp.) are widely cultivated because of their rapid growth and high biomass production, and members of the genus are increasingly used as experimental model organisms of trees and for phytoremediation purposes. Our aim was to investigate the copper and zinc stress responses of three outstanding biomass producer bred poplar lines to identify such transcripts of genes involved in the detoxification mechanisms, which can play an important role in the protection against heavy metals. Poplar cuttings were grown hydroponically and subjected to short-term (one week) mild and sublethal copper and zinc stresses. We evaluated the effects of the applied heavy metals and the responses of plants by detecting the changes of multiple physiological and biochemical parameters. The most severe cellular oxidative damage was caused by 30μM copper treatment, while zinc was less harmful. Analysis of stress-related transcripts revealed genotype-specific differences that are likely related to alterations in heavy metal tolerance. P. deltoides clones B-229 and PE 19/66 clones were clearly more effective at inducing the expression of various genes implicated in the detoxification process, such as the glutathione transferases, metallothioneins, ABC transporters, (namely PtGSTU51, PxMT1, PdABCC2,3), while the P. canadensis line M-1 accumulated more metal, resulting in greater cellular oxidative damage. Our results show that all three poplar clones are efficient in stress acclimatization, but with different molecular bases. Copyright © 2016 Elsevier GmbH. All rights reserved.

  1. Selective heavy metals removal from waters by amorphous zirconium phosphate: behavior and mechanism.

    Science.gov (United States)

    Pan, Bingcai; Zhang, Qingrui; Du, Wei; Zhang, Weiming; Pan, Bingjun; Zhang, Qingjian; Xu, Zhengwen; Zhang, Quanxing

    2007-07-01

    Selective removal of heavy metals from water has been of considerable concern for several decades. In the present study, the amorphous zirconium phosphate (ZrP) was synthesized and characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron micrography (SEM), thermogravimetric analysis (TGA) as well as pH-titration experiments. Uptake of heavy metals including lead, cadmium, and zinc onto ZrP was studied by using a polystyrene sulfonic-acid exchanger D-001 as a reference sorbent and Ca(2+) as a competing cation due to its ubiquity in natural or industrial waters. The results indicated that the uptake of heavy metals onto ZrP is essentially an ion-exchange process and dependent upon solution pH. In comparison with D-001, ZrP exhibited more favorable sorption of heavy metals particularly in terms of high selectivity, as indicated by the distribution coefficients of ZrP even several orders higher than D-001 towards heavy metals when calcium ion coexisted at a high level in solution. The Fourier transform-infrared (FT-IR) spectroscopic investigation indicated that the uptake of calcium, cadmium, and zinc ions onto ZrP is only driven by the electrostatic interaction, while that of lead ion is possibly dependent upon the inner-sphere complex formation with ZrP. XPS results further elucidated that ZrP displays different sorption affinity towards heavy metals in the same order as selectivity sequence of Pb(2+)>Zn(2+) approximately Cd(2+)>Ca(2+), which can be explained by hard and soft acids and bases (HASB) theory. Moreover, uptake of heavy metals onto ZrP approached to equilibrium quickly and the used ZrP could be readily regenerated for reuse by the dilute HCl solution. Thus, all the results suggest that amorphous ZrP has excellent potential as a sorption material for water treatment.

  2. Las pequeñas y medianas empresas del sector metalúrgico en la zona sur de la Comunidad de Madrid: Gestión medioambiental y necesidades de formación

    Directory of Open Access Journals (Sweden)

    Ureña, A.

    2004-06-01

    Full Text Available In this study, the environmental management and needs of the small and medium-sized businesses of the metallurgical industry in the south region of Madrid were analysed. Information was obtained through a telephone questionnaire distributed to more than 170 companies. Although most of the respondent employees do not consider environmental training one of their priorities, they expressed their interest in implementing Environmental Management Systems, waste minimization and a higher knowledge of the specific legal aspects.

    En este trabajo se presentan los resultados de un análisis específico de la gestión medioambiental y las necesidades de formación de las pequeñas y medianas empresas (PYMES del sector metalúrgico de la zona sur de la Comunidad de Madrid. Los datos más significativos se han obtenido a través de una encuesta telefónica realizada a más de 170 empresas de la zona. La mayoría de los empleados de las empresas encuestadas no consideran necesaria una formación específica sobre impacto medioambiental. No obstante, el estudio indica el interés, entre otros temas, por el control de vertidos y residuos, la implantación de sistemas de gestión medioambiental y un mayor conocimiento de la legislación y normativa aplicable al sector.

  3. Elucidation of Mechanisms and Selectivities of Metal-Catalyzed Reactions using Quantum Chemical Methodology.

    Science.gov (United States)

    Santoro, Stefano; Kalek, Marcin; Huang, Genping; Himo, Fahmi

    2016-05-17

    Quantum chemical techniques today are indispensable for the detailed mechanistic understanding of catalytic reactions. The development of modern density functional theory approaches combined with the enormous growth in computer power have made it possible to treat quite large systems at a reasonable level of accuracy. Accordingly, quantum chemistry has been applied extensively to a wide variety of catalytic systems. A huge number of problems have been solved successfully, and vast amounts of chemical insights have been gained. In this Account, we summarize some of our recent work in this field. A number of examples concerned with transition metal-catalyzed reactions are selected, with emphasis on reactions with various kinds of selectivities. The discussed cases are (1) copper-catalyzed C-H bond amidation of indoles, (2) iridium-catalyzed C(sp(3))-H borylation of chlorosilanes, (3) vanadium-catalyzed Meyer-Schuster rearrangement and its combination with aldol- and Mannich-type additions, (4) palladium-catalyzed propargylic substitution with phosphorus nucleophiles, (5) rhodium-catalyzed 1:2 coupling of aldehydes and allenes, and finally (6) copper-catalyzed coupling of nitrones and alkynes to produce β-lactams (Kinugasa reaction). First, the methodology adopted in these studies is presented briefly. The electronic structure method in the great majority of these kinds of mechanistic investigations has for the last two decades been based on density functional theory. In the cases discussed here, mainly the B3LYP functional has been employed in conjunction with Grimme's empirical dispersion correction, which has been shown to improve the calculated energies significantly. The effect of the surrounding solvent is described by implicit solvation techniques, and the thermochemical corrections are included using the rigid-rotor harmonic oscillator approximation. The reviewed examples are chosen to illustrate the usefulness and versatility of the adopted methodology in

  4. Heterogeneities in metallic glasses. Atomistic computer simulations on the structure and mechanical properties of copper-zirconium alloys and composites

    International Nuclear Information System (INIS)

    Brink, Tobias

    2017-01-01

    The present thesis deals with molecular dynamics computer simulations of heterogeneities in copper-zirconium metallic glasses, ranging from intrinsic structural fluctuations to crystalline secondary phases. These heterogeneities define, on a microscopic scale, the properties of the glass, and an understanding of their nature and behaviour is required for deriving the proper structure-property relations. In terms of composite systems, we start with the amorphisation of copper nanolayers embedded in a metallic glass matrix. While copper is an fcc metal with a high propensity for crystallisation, amorphisation can in fact occur in such systems for thermodynamic reasons. This is due to interface effects, which are also known from heterogeneous interfaces in crystals or from grain boundary complexions, although in absence of lattice mismatch. In single-phase glasses, intrinsic heterogeneities are often discussed in terms of soft spots or geometrically unfavourable motifs (GUMs), which can be considered to be mechanically weaker, defective regions of the glass. We investigate the relation between these motifs and the boson peak, an anomaly in the vibrational spectrum of all glasses. We demonstrate a relation between the boson peak and soft spots by analysing various amorphous and partially amorphous samples as well as highentropy alloys. Finally, we treat the plastic deformation of glasses, with and without crystalline secondary phases. We propose an explanation for the experimentally observed variations of propagation direction, composition, and density along a shear band. These variations of propagation direction are small in the case of single-phase glasses. A considerably greater influence on shear band propagation can be exerted by precipitates. We systematically investigate composites ranging from low crystalline volume fraction up to systems which resemble a nanocrystalline metal. In this context, we derive a mechanism map for composite systems and observe the

  5. Heterogeneities in metallic glasses. Atomistic computer simulations on the structure and mechanical properties of copper-zirconium alloys and composites

    Energy Technology Data Exchange (ETDEWEB)

    Brink, Tobias

    2017-07-01

    The present thesis deals with molecular dynamics computer simulations of heterogeneities in copper-zirconium metallic glasses, ranging from intrinsic structural fluctuations to crystalline secondary phases. These heterogeneities define, on a microscopic scale, the properties of the glass, and an understanding of their nature and behaviour is required for deriving the proper structure-property relations. In terms of composite systems, we start with the amorphisation of copper nanolayers embedded in a metallic glass matrix. While copper is an fcc metal with a high propensity for crystallisation, amorphisation can in fact occur in such systems for thermodynamic reasons. This is due to interface effects, which are also known from heterogeneous interfaces in crystals or from grain boundary complexions, although in absence of lattice mismatch. In single-phase glasses, intrinsic heterogeneities are often discussed in terms of soft spots or geometrically unfavourable motifs (GUMs), which can be considered to be mechanically weaker, defective regions of the glass. We investigate the relation between these motifs and the boson peak, an anomaly in the vibrational spectrum of all glasses. We demonstrate a relation between the boson peak and soft spots by analysing various amorphous and partially amorphous samples as well as highentropy alloys. Finally, we treat the plastic deformation of glasses, with and without crystalline secondary phases. We propose an explanation for the experimentally observed variations of propagation direction, composition, and density along a shear band. These variations of propagation direction are small in the case of single-phase glasses. A considerably greater influence on shear band propagation can be exerted by precipitates. We systematically investigate composites ranging from low crystalline volume fraction up to systems which resemble a nanocrystalline metal. In this context, we derive a mechanism map for composite systems and observe the

  6. Origins of the different metal preferences of Escherichia coli peptide deformylase and Bacillus thermoproteolyticus thermolysin: a comparative quantum mechanical/molecular mechanical study.

    Science.gov (United States)

    Dong, Minghui; Liu, Haiyan

    2008-08-21

    The Escherichia coli peptide deformylase (PDF) and Bacillus thermoproteolyticus thermolysin (TLN) are two representative metal-requiring peptidases having remarkably similar active centers but distinctively different metal preferences. Zinc is a competent catalytic cofactor for TLN but not for PDF. Reaction pathways and the associated energetics for both enzymes were determined using combined semiempirical and ab initio quantum mechanical/molecular mechanical modeling, without presuming reaction coordinates. The results confirmed that both enzymes catalyze via the same chemical steps, and reproduced their different preferences for zinc or iron as competent cofactors. Further analyses indicated that different feasibility of the nucleophilic attack step leads to different metal preferences of the two enzymes. In TLN, the substrate is strongly activated and can serve as the fifth coordination ligand of zinc prior to the chemical steps. In PDF, the substrate carbonyl is activated by the chemical step itself, and becomes the fifth coordination partner of zinc only in a later stage of the nucleophilic attack. These leads to a much more difficult nucleophilic attack in PDF than in TLN. Different from some earlier suggestions, zinc has no difficulty in accepting an activated substrate as the fifth ligand to switch from tetra- to penta-coordination in either PDF or TLN. When iron replaces zinc, its stronger interaction with the hydroxide ligand may lead to higher activation barrier in TLN. In PDF, the stronger interactions of iron with ligands allow iron-substrate coordination to take place either before or at a very early stage of the chemical step, leading to effective catalysis. Our calculations also show combined semiempirical and ab initio quantum mechanical modeling can be efficient approaches to explore complicated reaction pathways in enzyme systems.

  7. Water Oxidation Mechanisms of Metal Oxide Catalysts by Vibrational Spectroscopy of Transient Intermediates

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Miao [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Chemical Sciences Division; Univ. of California, Berkeley, CA (United States); Frei, Heinz [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Molecular Biophysics and Integrated Bioimaging Division; Univ. of California, Berkeley, CA (United States)

    2017-02-22

    Water oxidation is an essential reaction of an artificial photosystem for solar fuel generation because it provides electrons needed to reduce carbon dioxide or protons to a fuel. Earth-abundant metal oxides are among the most attractive catalytic materials for this reaction because of their robustness and scalability, but their efficiency poses a challenge. Knowledge of catalytic surface intermediates gained by vibrational spectroscopy under reaction conditions plays a key role in uncovering kinetic bottlenecks and provides a basis for catalyst design improvements. Recent dynamic infrared and Raman studies reveal the molecular identity of transient surface intermediates of water oxidation on metal oxides. In conclusion, combined with ultrafast infrared observations of how charges are delivered to active sites of the metal oxide catalyst and drive the multielectron reaction, spectroscopic advances are poised to play a key role in accelerating progress toward improved catalysts for artificial photosynthesis.

  8. Quantum mechanical ab initio simulation of the electron screening effect in metal deuteride crystals

    Energy Technology Data Exchange (ETDEWEB)

    Huke, A.; Chun, S.M.; Biller, A.; Heide, P. [Technische Universitaet Berlin, Institut fuer Optik und Atomare Physik, Berlin (Germany); Czerski, K. [Technische Universitaet Berlin, Institut fuer Optik und Atomare Physik, Berlin (Germany); University of Szczecin, Institute of Physics, Szczecin (Poland)

    2008-02-15

    In antecedent experiments the electron screening energies of the d+d reactions in metallic environments have been determined to be enhanced by an order of magnitude in comparison to the case of gaseous deuterium targets. The analytical models describing averaged material properties have not been able to explain the experimental results so far. Therefore, a first effort has been undertaken to simulate the dynamics of reacting deuterons in a metallic lattice by means of an ab initio Hartree-Fock calculation of the total electrostatic force between the lattice and the successively approaching deuterons via path integration. The calculations have been performed for Li and Ta, clearly showing a migration of electrons from host metallic to the deuterium atoms. However, in order to avoid more of the necessary simplifications in the model the utilization of a massive parallel supercomputer would be required. (orig.) 3.

  9. Metal ion coordination in the E. coli Nudix hydrolase dihydroneopterin triphosphate pyrophosphatase: New clues into catalytic mechanism.

    Directory of Open Access Journals (Sweden)

    Shannon E Hill

    Full Text Available Dihydroneopterin triphosphate pyrophosphatase (DHNTPase, a member of the Mg2+ dependent Nudix hydrolase superfamily, is the recently-discovered enzyme that functions in the second step of the pterin branch of the folate biosynthetic pathway in E. coli. DHNTPase is of interest because inhibition of enzymes in bacterial folate biosynthetic pathways is a strategy for antibiotic development. We determined crystal structures of DHNTPase with and without activating, Mg2+-mimicking metals Co2+ and Ni2+. Four metal ions, identified by anomalous scattering, and stoichiometrically confirmed in solution by isothermal titration calorimetry, are held in place by Glu56 and Glu60 within the Nudix sequence motif, Glu117, waters, and a sulfate ion, of which the latter is further stabilized by a salt bridge with Lys7. In silico docking of the DHNTP substrate reveals a binding mode in which the pterin ring moiety is nestled in a largely hydrophobic pocket, the β-phosphate activated for nucleophilic attack overlays with the crystallographic sulfate and is in line with an activated water molecule, and remaining phosphate groups are stabilized by all four identified metal ions. The structures and binding data provide new details regarding DHNTPase metal requirements, mechanism, and suggest a strategy for efficient inhibition.

  10. Effects of post weld heat treatment and weld overlay on the residual stress and mechanical properties in dissimilar metal weld

    International Nuclear Information System (INIS)

    Campos, Wagner R.C.; Ribeiro, Vladimir S.; Vilela, Alisson H.F.; Almeida, Camila R.O.; Rabello, Emerson G.

    2017-01-01

    The object of this work is a dissimilar metal weld (DMW) pipe joint between carbon steel (A-106 Gr B) and stainless steel (A-312 TP316L) pipes and filler metals of Nickel alloy (82/182), which find wide application in the field of chemical, oil, petroleum industries, fossil fuel and nuclear power plant. A lot of the failures that have occurred in dissimilar metal welded are affected greatly by residual stresses. Residual stress is often a cause of premature failure of critical components under normal operation of welded components. Several methods have been tested and developed for removing the tensile residual stresses. The aim of the methods is to reduce the tensile stress state or to create compressive stresses at a predefined area, such as the inner surface of a welded pipe joint. Post weld heat treatment (PWHT) and weld overlay (WOL) are two of the residual stress mitigation methods which reduce the tensile residual stress, create compressive stresses and arrest crack initiation and crack growth. The technique used to substantially minimized or eliminated this failure development in the root weld is the post weld heat treatments (stress relief heat treatment) or the weld overlay. In this work was studied the effectiveness in reducing internal residual stress in dissimilar metal welded pipe joints subjected to post weld heat treatment and weld overlay, measurement by hole-drilling strain-gage method of stress relaxation. Also held was mechanical characterization of the welded pipe joint itself. (author)

  11. Metal ion coordination in the E. coli Nudix hydrolase dihydroneopterin triphosphate pyrophosphatase: New clues into catalytic mechanism

    Energy Technology Data Exchange (ETDEWEB)

    Hill, Shannon E.; Nguyen, Elaine; Ukachukwu, Chiamaka U.; Freeman, Dana M.; Quirk, Stephen; Lieberman, Raquel L.; Boggon, Titus J.

    2017-07-25

    Dihydroneopterin triphosphate pyrophosphatase (DHNTPase), a member of the Mg2+ dependent Nudix hydrolase superfamily, is the recently-discovered enzyme that functions in the second step of the pterin branch of the folate biosynthetic pathway in E. coli. DHNTPase is of interest because inhibition of enzymes in bacterial folate biosynthetic pathways is a strategy for antibiotic development. We determined crystal structures of DHNTPase with and without activating, Mg2+-mimicking metals Co2+ and Ni2+. Four metal ions, identified by anomalous scattering, and stoichiometrically confirmed in solution by isothermal titration calorimetry, are held in place by Glu56 and Glu60 within the Nudix sequence motif, Glu117, waters, and a sulfate ion, of which the latter is further stabilized by a salt bridge with Lys7. In silico docking of the DHNTP substrate reveals a binding mode in which the pterin ring moiety is nestled in a largely hydrophobic pocket, the β-phosphate activated for nucleophilic attack overlays with the crystallographic sulfate and is in line with an activated water molecule, and remaining phosphate groups are stabilized by all four identified metal ions. The structures and binding data provide new details regarding DHNTPase metal requirements, mechanism, and suggest a strategy for efficient inhibition.

  12. Effects of post weld heat treatment and weld overlay on the residual stress and mechanical properties in dissimilar metal weld

    Energy Technology Data Exchange (ETDEWEB)

    Campos, Wagner R.C.; Ribeiro, Vladimir S.; Vilela, Alisson H.F.; Almeida, Camila R.O.; Rabello, Emerson G., E-mail: wrcc@cdtn.br, E-mail: camilarezende.cr@gmail.com, E-mail: egr@cdtn.br, E-mail: vladimirsoler@hotmail.com, E-mail: ahfv02@outlook.com [Centro de Desenvolvimento da Tecnologia Nuclear (CDTN/CNEN-MG), Belo Horizonte, MG (Brazil)

    2017-07-01

    The object of this work is a dissimilar metal weld (DMW) pipe joint between carbon steel (A-106 Gr B) and stainless steel (A-312 TP316L) pipes and filler metals of Nickel alloy (82/182), which find wide application in the field of chemical, oil, petroleum industries, fossil fuel and nuclear power plant. A lot of the failures that have occurred in dissimilar metal welded are affected greatly by residual stresses. Residual stress is often a cause of premature failure of critical components under normal operation of welded components. Several methods have been tested and developed for removing the tensile residual stresses. The aim of the methods is to reduce the tensile stress state or to create compressive stresses at a predefined area, such as the inner surface of a welded pipe joint. Post weld heat treatment (PWHT) and weld overlay (WOL) are two of the residual stress mitigation methods which reduce the tensile residual stress, create compressive stresses and arrest crack initiation and crack growth. The technique used to substantially minimized or eliminated this failure development in the root weld is the post weld heat treatments (stress relief heat treatment) or the weld overlay. In this work was studied the effectiveness in reducing internal residual stress in dissimilar metal welded pipe joints subjected to post weld heat treatment and weld overlay, measurement by hole-drilling strain-gage method of stress relaxation. Also held was mechanical characterization of the welded pipe joint itself. (author)

  13. The atomic-scale nucleation mechanism of NiTi metallic glasses upon isothermal annealing studied via molecular dynamics simulations.

    Science.gov (United States)

    Li, Yang; Li, JiaHao; Liu, BaiXin

    2015-10-28

    Nucleation is one of the most essential transformation paths in phase transition and exerts a significant influence on the crystallization process. Molecular dynamics simulations were performed to investigate the atomic-scale nucleation mechanisms of NiTi metallic glasses upon devitrification at various temperatures (700 K, 750 K, 800 K, and 850 K). Our simulations reveal that at 700 K and 750 K, nucleation is polynuclear with high nucleation density, while at 800 K it is mononuclear. The underlying nucleation mechanisms have been clarified, manifesting that nucleation can be induced either by the initial ordered clusters (IOCs) or by the other precursors of nuclei evolved directly from the supercooled liquid. IOCs and other precursors stem from the thermal fluctuations of bond orientational order in supercooled liquids during the quenching process and during the annealing process, respectively. The simulation results not only elucidate the underlying nucleation mechanisms varied with temperature, but also unveil the origin of nucleation. These discoveries offer new insights into the devitrification mechanism of metallic glasses.

  14. Mechanisms of Radionuclide-Hyroxycarboxylic Acid Interactions for Decontamination of Metallic Surfaces

    Energy Technology Data Exchange (ETDEWEB)

    A.J. Francis; C.J. Dodge; J.B. Gillow; G.P. Halada; C.R. Clayton

    2002-04-24

    Is this EMSP program we investigated the key fundamental issues involved in the use of simple and safe methods for the removal of radioactive contamination from equipment and facilities using hydroxycarboxylic acids. Specifically, we investigate (i) the association of uranium with various iron oxides commonly formed on corroding plain carbon steel surfaces, (ii) the association of uranium with corroding metal coupons under a variety of conditions, and (iii) the decontamination of the uranium contaminated metal coupons by citric acid or citric acid formulations containing oxalic acid and hydrogen peroxide.

  15. Investigation of the role of grain boundary on the mechanical properties of metals

    International Nuclear Information System (INIS)

    Kheradmand, Nousha; Barnoush, Afrooz; Vehoff, Horst

    2010-01-01

    Compression testing of micropillars was used to investigate the gain boundary effect on the strength of metals which is especially interesting in ultra fine grained and nanocrystalline metals. Single and bicrystal micropillars of different sizes and crystallographic orientations were fabricated using a focused ion beam system and the compression test was performed with a nanoindenter. A reduction of the pillar size as well as the introduction of a grain boundary results in an increase in the yield strength. The results show that the size and the orientation of different adjoining crystals in bicrystalline pillars have an obvious effect on dislocation nucleation and multiplication.

  16. Atomic-scale simulations of the mechanical deformation of nanocrystalline metals

    DEFF Research Database (Denmark)

    Schiøtz, Jakob; Vegge, Tejs; Di Tolla, Francesco

    1999-01-01

    that the main deformation mode is sliding in the grain boundaries through a large number of uncorrelated events, where a few atoms (or a few tens of atoms) slide with respect to each other. Little dislocation activity is seen in the grain interiors. The localization of the deformation to the grain boundaries......Nanocrystalline metals, i.e., metals in which the grain size is in the nanometer range, have a range of technologically interesting properties including increased hardness and yield strength. We present atomic-scale simulations of the plastic behavior of nanocrystalline copper. The simulations show...

  17. Characterization of Mechanical, Thermal and Wear Properties of Titanium Rich Metallic Glasses.

    Science.gov (United States)

    1982-12-20

    Glassy Alloys: To obtain a comprehensive characterization of the composition dependence of the inter-related ( colligative ) thermal-elastic-plastic...indeed colligative , i.e. of similar origin, and depend on the electronic structure of the M metal; however, the proper correlation is still under

  18. Roles of dioxins and heavy metals in cancer and neurological diseases using ROS-mediated mechanisms.

    Science.gov (United States)

    Matés, José M; Segura, Juan A; Alonso, Francisco J; Márquez, Javier

    2010-11-15

    Oxidants have critical functions inside healthy and unhealthy cells. Deregulated cell cycle and apoptosis, both regulated by oxidative stress, have been described as hallmarks of mitotic (cancer) and postmitotic (neuronal) cells. This review provides an updated revision of the oxidant effects of some environmental contaminants such as dioxins and the heavy metals cadmium, cobalt, and copper. Dioxins exert their toxic actions by acting on phase I and phase II enzymes, such as cytochromes P450, superoxide dismutase, and glutathione peroxidase, promoting cell proliferation, growth arrest, and apoptosis, affecting cancer homeostasis and neuronal function. Heavy metals manifest cytotoxic effects in various cells and tissues, and tight regulation of metals is essential to the health of organisms. Cadmium modulates gene expression and signal transduction and reduces activities of proteins involved in antioxidant defense, interfering with DNA repair and modifying cancer development and brain function. Cobalt provokes generation of reactive oxygen species and DNA damage in cancer cells and brain tissues, altering proliferation and differentiation and causing apoptosis. Copper is a key metal in cell division processes in both normal and tumor cells. Copper also has been shown to have an important role in neurodegenerative diseases such as Alzheimer disease, Parkinson disease, and amyotrophic lateral sclerosis. Copyright © 2010 Elsevier Inc. All rights reserved.

  19. MECHANISMS OF HEAVY METAL REMOVAL FROM ACID MINE DRAINAGE USING CHITIN

    Science.gov (United States)

    Acid Mine Drainage (AMD) emanating from inactive or active mine sites contains elevated levels of toxic heavy metals, which can have an adverse impact to the surrounding environment. The major pathway involved in generation of AMD is weathering of pyritic mineral ores, where in s...

  20. Mechanism of radiation and thermal decomposition of sulphide non-ferrous metals

    International Nuclear Information System (INIS)

    Mazhrenova, N.P.

    1998-01-01

    This paper deals with the non-ferrous metals sulfides in term of their radiative sensitivity, directed chances of their physical-chemical, and hence technological properties by radiation influence both on sulfide materials and on the processes with their participation. (author)

  1. Formation of Fe-Nb-X (X=Zr, Ti) amorphous alloys from pure metal elements by mechanical alloying

    Energy Technology Data Exchange (ETDEWEB)

    Xiao Zhiyu [National Engineering Research Center of Near-net-shape Forming for Metallic Materials, South China University of Technology, Guangzhou 510640 (China); Tang Cuiyong, E-mail: hnrtcy@163.com [National Engineering Research Center of Near-net-shape Forming for Metallic Materials, South China University of Technology, Guangzhou 510640 (China); Ngai, Tungwai Leo; Yang Chao; Li Yuanyuan [National Engineering Research Center of Near-net-shape Forming for Metallic Materials, South China University of Technology, Guangzhou 510640 (China)

    2012-01-15

    Fe-based amorphous powders of Fe{sub 56}Nb{sub 6}Zr{sub 38} and Fe{sub 60}Nb{sub 6}Ti{sub 34} based on binary eutectic were prepared by mechanical alloying starting from mixtures of pure metal powders. The amorphization behavior and thermal stability were examined by x-ray diffraction, scanning electron microscopy, transmission electron microscopy and differential scanning calorimetry. Results show that Fe{sub 56}Nb{sub 6}Zr{sub 38} alloy has a better glass forming ability and a relatively lower thermal stability comparing with Fe{sub 60}Nb{sub 6}Ti{sub 34} alloy. The prepared amorphous powders have homogeneous element distribution and no obvious contaminants coming from mechanical alloying. The synthesized amorphous powders offer the potential for consolidation to full density with desirable mechanical properties through the powder metallurgy methods.

  2. Mechanical properties and the electronic structure of transition of metal alloys

    Science.gov (United States)

    Arsenault, R. J.; Drew, H. D.

    1977-01-01

    This interdiscipline research program was undertaken in an effort to investigate the relationship between the mechanical strength of Mo based alloys with their electronic structure. Electronic properties of these alloys were examined through optical studies, and the classical solid solution strengthening mechanisms were considered, based on size and molecular differences to determine if these mechanisms could explain the hardness data.

  3. Decomposition mechanism of methylene blue caused by metallic iron-maghemite mixture

    Energy Technology Data Exchange (ETDEWEB)

    Kubuki, Shiro, E-mail: kubuki@tmu.ac.jp; Shibano, Koya; Akiyama, Kazuhiko [Tokyo Metropolitan University, Department of Chemistry, Graduate School of Science and Engineering (Japan); Homonnay, Zoltan; Kuzmann, Erno [Eoetvoes Lorand University, Laboratory of Nuclear Chemistry, Institute of Chemistry (Hungary); Ristic, Mira [Ruder Boskovic Institute, Division of Materials Chemistry (Croatia); Nishida, Tetsuaki [Kinki University, Department of Biological and Environmental Chemistry, Faculty of Humanity-Oriented Science and Engineering (Japan)

    2013-04-15

    Decomposition mechanism of methylene blue (MB) caused by a mixture of metallic iron-maghemite (Fe{sup 0}-{gamma}Fe{sub 2}O{sub 3}) was investigated by means of {sup 57}Fe-Moessbauer spectroscopy, X-ray diffractometry (XRD), Ultraviolet-Visible Absorption Spectroscopy (UV-vis) and electrospray-ionization mass spectroscopy (ESI-MS). Ten day-leaching test of 10 {mu}mol L{sup - 1} MB aqueous solution and Fe{sup 0}-{gamma}Fe{sub 2}O{sub 3} mixture (mass ratio 3:7) showed a decrease in the concentration from 10.5 to 4.45 {mu}mol L{sup - 1} with first-order rate constant (k) of 1.57 x 10 - 1 day - 1. An ESI-MS study of Fe{sup 0}-{gamma}Fe{sub 2}O{sub 3} mixture (3:7) after the leaching test revealed new peaks at m/z of 100, 110 and 137 due to fragmentation of MB, in addition to those observed at m/z of 284, 270 and 256 which were ascribed to MB, Azure B and Azure A, respectively. {sup 57}Fe-Moessbauer spectra of Fe{sup 0}-{gamma}Fe{sub 2}O{sub 3} mixture (3:7) resulted in a decrease in absorption area (A) for Fe{sup 0} ({delta} = 0.00{sub {+-}0.01} mm s{sup - 1}, H{sub int} = 33.0{sub {+-}0.1} T) from 37.5 to 21.3, 9.7, 7.9, 7.0 and 4.5{sub {+-}0.5} %, together with an increase in A from 0.0 to 5.0, 13.8, 17.2, 21.0 and 22.4{sub {+-}0.5} % for octahedral (O{sub h}) iron (Fe{sup II} + Fe{sup III}) of Fe{sub 3}O{sub 4}. XRD study of these samples indicated that the peak intensity at 2{Theta} of 44.7 Degree-Sign being ascribed to Fe{sup 0} was decreased, while that of 35.6 Degree-Sign due to Fe{sub 3}O{sub 4} was almost constant; relative peak ratio of Fe {sup 0}/Fe{sub 3} O{sub 4} was decreased from 26.3 to 2.76 after the leaching, indicating that Fe{sup 0} in the Fe{sup 0}-{gamma}Fe{sub 2}O{sub 3} mixture was oxidized to Fe{sub 3}O{sub 4}. These experimental results suggest that Fe{sup 0}-{gamma}Fe{sub 2}O{sub 3} mixture could be utilized for the cleaning or decomposition of toxic organic compounds like trichloroethylene.

  4. Heavy metal removal mechanisms of sorptive filter materials for road runoff treatment and remobilization under de-icing salt applications.

    Science.gov (United States)

    Huber, Maximilian; Hilbig, Harald; Badenberg, Sophia C; Fassnacht, Julius; Drewes, Jörg E; Helmreich, Brigitte

    2016-10-01

    The objective of this research study was to elucidate the removal and remobilization behaviors of five heavy metals (i.e., Cd, Cu, Ni, Pb, and Zn) that had been fixed onto sorptive filter materials used in decentralized stormwater treatment systems receiving traffic area runoff. Six filter materials (i.e., granular activated carbon, a mixture of granular activated alumina and porous concrete, granular activated lignite, half-burnt dolomite, and two granular ferric hydroxides) were evaluated in column experiments. First, a simultaneous preloading with the heavy metals was performed for each filter material. Subsequently, the remobilization effect was tested by three de-icing salt experiments in duplicate using pure NaCl, a mixture of NaCl and CaCl2, and a mixture of NaCl and MgCl2. Three layers of each column were separated to specify the attenuation of heavy metals as a function of depth. Cu and Pb were retained best by most of the selected filter materials, and Cu was often released the least of all metals by the three de-icing salts. The mixture of NaCl and CaCl2 resulted in a stronger effect upon remobilization than the other two de-icing salts. For the material with the highest retention, the effect of the preloading level upon remobilization was measured. The removal mechanisms of all filter materials were determined by advanced laboratory methods. For example, the different intrusions of heavy metals into the particles were determined. Findings of this study can result in improved filter materials used in decentralized stormwater treatment systems. Copyright © 2016 Elsevier Ltd. All rights reserved.

  5. Mechanism of removal and retention of heavy metals from the acid mine drainage to coastal wetland in the Patagonian marsh.

    Science.gov (United States)

    Idaszkin, Yanina L; Carol, Eleonora; María Del Pilar, Alvarez

    2017-09-01

    The attenuation of the acid mine drainage is one of the most important environmental challenges facing the mining industry worldwide. Mining waste deposits from an ancient metallurgical extraction of heavy metals were found near to the San Antonio marsh in Patagonia. The aim of this work was to determinate which mechanisms regulate the mobilization and retention of metals by acid drainage. A geological and geomorphological survey was carried out and samples from the mining waste deposits and the marsh were collected to determine soil texture, Eh pH, organic matter, Cu, Pb, Zn and Fe content, and soil mineralogical composition. Metals in marsh plants were determined in above- and below-ground structures. In the mining waste deposits polymetallic sulphides were recognized where the oxidation and formation of oxy-hydroxides and sulphates of Fe, Cu, Pb and Zn occurs. Then, by the alteration of those minerals, the metals enter in solution and are mobilized with the surface drainage towards the marsh where adsorption in the soils fine fraction and organic matter and/or by plants occurs. Locally, in the mining waste deposits, the precipitation/dissolution of Cu, Pb, and Zn sulphates take place in small centripetal drainage basins. In topographically lower portions of the marsh desorption and removal of metals by tidal flow could also be happen. The results allow to concluding that the marsh adjacent to the mining waste deposits is a geochemically active environment that naturally mitigates the contamination caused by acid drainage. Copyright © 2017 Elsevier Ltd. All rights reserved.

  6. The influence of reinforcement size on the microstructure and mechanical behavior of a nanostructured aluminum-based metal matrix composite

    Science.gov (United States)

    Behm, Nathan Adam

    With increased availability and growing commercial applications, aluminum-based metal matrix composites show promise as high specific strength structural materials. Before they can be implemented however, they require thorough characterization and testing. A novel nanostructured aluminum-based metal matrix composite (MMC) was characterized through a combination of microstructural analysis and mechanical testing. Two composites were studied, an aluminum MMC reinforced with 50 nm boron carbide, (B4C) and an aluminum MMC reinforced with 500 nm boron carbide. Transmission electron microscopy (TEM) analysis revealed an ultra-fine grained matrix with grains on the order of 100--300 nm. The quasi-static and dynamic response of the composites was compared with the behavior of the unreinforced aluminum alloy, and it was found that the reinforcement resulted in a 30% improvement in strength. The decrease in the reinforcement size from 500 to 50 nm activated an additional strengthening mechanism, which further improved the strength of the MMC reinforced with the 50 nm B4C. Dynamic compression tests were performed at elevated temperatures up 400°C on the composites, and it was found that they exhibited impressive strengths considering the thermal softening prevalent in aluminum. The reinforcement size was found to play an important role in the strain softening exhibited at elevated temperature, fracture mechanism, and composite strength. Models to describe the composite behavior are presented.

  7. Mechanical stimulated reaction of metal/polymer mixed powders; Kinzoku/kobunshi kongo funmatsu no kikaiteki reiki hanno

    Energy Technology Data Exchange (ETDEWEB)

    Tobita, M.; Sakakibara, A.; Takemoto, Y. [Okayama University, Okayama (Japan). Faculty of Engineering; Iwabu, H. [Kurare Co. Ltd., Osaka (Japan)

    1999-12-15

    Mechanical grinding (MG) with mechanically stimulated reaction was performed on metal/polymer mixed powders. The starting materials used in this study were the metals of Mg, Ti and Mg{sub 2}Ni powders, arid polymer of PTFE, PVC and PE powders. The MG process was investigated using XRD, IR, SEM and TEM. According to XRD results, magnesium fluoride (MgF{sub 2}, TiF{sub 2}) and chloride (MgCl{sub 2}) were detected from MG products of the Mg/PTFE, Ti/PTFE and Mg/PVC blending systems, respectively. Explosive reaction was found during MG of both Mg/PTFE and Ti/PTFE. It was also confirmed by XRD results that the production of MgF{sub 2} had already been formed just before the explosive reaction in Mg/PTFE system. It was found from IR analysis that C-C single bond in the polymers, not only both in PTFE and PVC but also in PE, changed to double bond C=C. Hydrogen produced due to decomposition of PE on blending Mg{sub 2}Ni/PE was absorbed into C-Mg{sub 2}Ni-H as amorphous solutes. These mechanically stimulated reaction was powerful method for decomposition of engineering plastics. (author)

  8. Effect of Ti/TiN multilayer protective nanocoatings on Zr-based metallic glasses mechanical performance

    International Nuclear Information System (INIS)

    Tekaya, A.; Benameur, T.; Labdi, S.; Aubert, P.

    2013-01-01

    Ti/TiN multilayer and monolithic TiN nanocoatings have been deposited on Zr-based metallic glass substrates by means of RF sputtering technique at room temperature. Nanoindentation and nanoscratch tests are used to characterise the mechanical and tribological properties of coated samples. In addition, a Vickers indentation tests and scanning electron microscopy observation have been carried out to explore the deformation mechanism. When coated with the TiN and Ti/TiN multilayers, Zr 60 Ni 10 Cu 20 Al 10 bulk metallic glass shows a significant enhancement of both apparent hardness and elastic modulus with a decrease of the friction coefficient. The Vickers indentation shows a fragile behaviour of TiN coatings compared to the Ti/TiN multilayer one. Based on Bhowmick model description, experimental nanoindentation approach is taken to determine the variation of shear stress as function of the penetration depth. It is found that the shear stress developed in the TiN coatings is higher than that observed in the Ti/TiN multilayer. A correlation between finite-element analysis results and experimental data has been proposed. The monolithic or multilayer type of coatings is found to have an influence on the stress and plastic deformation distributions. - Highlights: • Nanocoating enhances the apparent mechanical performance of bulk metallic glass. • Fragile deformation of TiN coatings comparing with Ti/TiN multilayer coatings • Accommodation of the stress is between the layers and at the film/substrate interface. • Shear stress is higher in TiN coating comparing with Ti/TiN multilayer coatings. • Multilayer coatings exhibit an important influence on the stress distribution

  9. Mechanism of high-temperature background of internal friction in metals

    International Nuclear Information System (INIS)

    Shapoval, B.I.; Arzhavitin, V.M.

    1988-01-01

    Data of theoretical and experimental studies on energy dissipation in vibrating metal at small amplitudes and elevated temperatures (high temperature background of internal friction) are generalized and systematized. Evolution of knowledge of the background as a phenomenon influenced mainly by crystal structure defects - their form, quantity, mobility and interaction is followed. Considered is a wide range of investigated metal states and measurement conditions, and interrelations with other characteristics, for instance, strength ones. On the basis of the data obtained by authors and other investigations a concept of an additional third stage of the background increase with the temperature - the stage of deviation from exponential dependence at premelting point, is introduced. 107 refs.; 32 figs.; 3 tabs

  10. Improvement of the mechanical and thermal properties of the metallized polycarbonate capacitor

    Science.gov (United States)

    Kellerman, H. J.

    1977-01-01

    Changes were studied which enable polycarbonate metallized film capacitors to withstand 500 thermal shock cycles while maintaining electrical characteristic integrity without becoming intermittent, and without losing hermeticity. The task was for metallized polycarbonate film capacitors designed to meet MIL-C-39022/9 and MIL-C-83421/1. The capacitor design improvements implemented were the insertion of a rubber washer between spray cap and end seal and the utilization of a flexible lead assembly. One hundred fifty capacitors incorporating the design improvements were manufactured and subsequently underwent 500 thermal shock cycles. One hundred forty nine capacitors survived the test. Failure analysis revealed that the lone failure was due to a poor solder joint, initially detected in pre-screening tests as having poor dissipation factor and equivalent series resistance measurement readings.

  11. Liquid nanodroplet formation through phase explosion mechanism in laser-irradiated metal targets.

    Science.gov (United States)

    Mazzi, Alberto; Gorrini, Federico; Miotello, Antonio

    2015-09-01

    Some quantitative aspects of laser-irradiated pure metals, while approaching phase explosion, are still not completely understood. Here, we develop a model that describes the main quantities regulating the liquid-vapor explosive phase transition and the expulsion of liquid nanodroplets that, by solidifying, give rise to nanoparticle formation. The model combines both a thermodynamics description of the explosive phase change and a Monte Carlo simulation of the randomly generated critical vapor bubbles. The calculation is performed on a set of seven metals (Al, Fe, Co, Ni, Cu, Ag, and Au) which are frequently used in pulsed laser ablation experiments. Our final predictions about the size distribution of the liquid nanodroplets and the number ratio of liquid/vapor ejected atoms are compared, whenever possible, with available molecular dynamics simulations and experimental data.

  12. Failure Mechanisms of the Coating/Metal Interface in Waterborne Coatings: The Effect of Bonding

    Science.gov (United States)

    Wan, Hongxia; Song, Dongdong; Li, Xiaogang; Zhang, Dawei; Gao, Jin; Du, Cuiwei

    2017-01-01

    Waterborne coating is the most popular type of coating, and improving its performance is a key point of research. Cathodic delamination is one of the major modes of failure for organic coatings. It refers to the weakening or loss of adhesion between the coating and substrate. Physical and chemical characteristics of coatings have been studied via scanning electron microscopy (SEM), atomic force microscopy (AFM), contact angle measurements, Fourier transform infrared spectroscopy (FTIR), and secondary ion mass spectrometry (SIMS). Early heterogeneous swelling at the metal-coating interface in non-defective coated metals was elucidated using frequency-dependent alternating-current scanning electrochemical microscopy. Two types of coatings (styrene-acrylic coating and terpolymer coating) were compared. The effects of thickness, surface roughness, and chemical bonding on cathodic delamination were investigated. PMID:28772757

  13. Failure Mechanisms of the Coating/Metal Interface in Waterborne Coatings: The Effect of Bonding

    Directory of Open Access Journals (Sweden)

    Hongxia Wan

    2017-04-01

    Full Text Available Waterborne coating is the most popular type of coating, and improving its performance is a key point of research. Cathodic delamination is one of the major modes of failure for organic coatings. It refers to the weakening or loss of adhesion between the coating and substrate. Physical and chemical characteristics of coatings have been studied via scanning electron microscopy (SEM, atomic force microscopy (AFM, contact angle measurements, Fourier transform infrared spectroscopy (FTIR, and secondary ion mass spectrometry (SIMS. Early heterogeneous swelling at the metal-coating interface in non-defective coated metals was elucidated using frequency-dependent alternating-current scanning electrochemical microscopy. Two types of coatings (styrene-acrylic coating and terpolymer coating were compared. The effects of thickness, surface roughness, and chemical bonding on cathodic delamination were investigated.

  14. The design and testing of a memory metal actuated boom release mechanism

    Science.gov (United States)

    Powley, D. G.; Brook, G. B.

    1979-01-01

    A boom latch and release mechanism was designed, manufactured and tested, based on a specification for the ISEE-B satellite mechanism. From experimental results obtained, it is possible to calculate the energy available and the operating torques which can be achieved from a torsional shape memory element in terms of the reversible strain induced by prior working. Some guidelines to be followed when designing mechanisms actuated by shape memory elements are included.

  15. Ultrasonic and mechanical soil washing processes for the remediation of heavy-metal-contaminated soil

    Science.gov (United States)

    Kim, Seulgi; Lee, Wontae; Son, Younggyu

    2016-07-01

    Ultrasonic/mechanical soil washing process was investigated and compared with ultrasonic process and mechanical process using a relatively large lab-scale sonoreactor. It was found that higher removal efficiencies were observed in the combined processes for 0.1 and 0.3 M HCl washing liquids. It was due to the combination effects of macroscale removal for the overall range of slurry by mechanical mixing and microscale removal for the limited zone of slurry by cavitational actions.

  16. Effect of Destined High-Pressure Torsion on the Structure and Mechanical Properties of Rare Earth-Based Metallic Glasses

    Science.gov (United States)

    Zhao, W.; Cheng, H.; Jiang, X.; Wu, M. L.; Li, G.

    2018-03-01

    Changes in the atomic structure and mechanical properties of rare earth-based metallic glasses caused by destined high-pressure torsion (HPT) were studied by X-ray diffraction synchrotron radiation and nanoindentation. Results showed that destined HPT improved nanohardness and wear resistance, which indicated the significant contributions of this technique. The diffraction patterns showed that the contents of pairs between solvent and solute atoms with a large negative mixing enthalpy increased, whereas those of pairs between solvent atoms and between solute atoms decreased after destined HPT. Thus, the process was improved by increasing the proportion of high-intensity pairs between solvent and solute atoms.

  17. PHYSICAL-MATEMATICALSCIENCE MECHANICS SIMULATION CHALLENGES IN OPTIMISING THEORETICAL METAL CUTTING TASKS

    Directory of Open Access Journals (Sweden)

    Rasul V. Guseynov

    2017-01-01

    Full Text Available Abstract. Objectives In the article, problems in the optimising of machining operations, which provide end-unit production of the required quality with a minimum processing cost, are addressed. Methods Increasing the effectiveness of experimental research was achieved through the use of mathematical methods for planning experiments for optimising metal cutting tasks. The minimal processing cost model, in which the objective function is polynomial, is adopted as a criterion for the selection of optimal parameters. Results Polynomial models of the influence of angles φ, α, γ on the torque applied when cutting threads in various steels are constructed. Optimum values of the geometrical tool parameters were obtained using the criterion of minimum cutting forces during processing. The high stability of tools having optimal geometric parameters is determined. It is shown that the use of experimental planning methods allows the optimisation of cutting parameters. In optimising solutions to metal cutting problems, it is found to be expedient to use multifactor experimental planning methods and to select the cutting force as the optimisation parameter when determining tool geometry. Conclusion The joint use of geometric programming and experiment planning methods in order to optimise the parameters of cutting significantly increases the efficiency of technological metal processing approaches. 

  18. Depressing Iron Mineral by Metallic-Starch Complex (MSC in Reverse Flotation and Its Mechanism

    Directory of Open Access Journals (Sweden)

    Tao Yue

    2018-02-01

    Full Text Available A series of metallic-starch complex (MSC solutions, synthesized by mixing relevant metallic ionic solutions with the caustic starch solution, were used as the flotation depressants to investigate their depressing effects on hematite ore. The MSC is a nano-sized colloidal complex which is configured by hydrophilic metallic hydroxide as the colloidal nucleus on which starch and hydroxyl complex are adsorbed, resulting in a larger molecule than starch itself. The flotation tests showed that the depressing abilities of various MSC (Fe3+, Zn2+, Pb2+ and Mg2+ on the iron minerals were higher than the caustic starch, and the order of depression ability was: Zn2+-starch > Pb2+-starch > Fe3+-starch > Mg2+-starch > caustic starch. Based on the adsorption analysis, the high depressing ability of the MSC arose from increasing the adsorption density of starch on iron minerals and slightly reducing the absorption of the collector dodecylamine. Adsorption behaviour also indicated that the adsorption of the MSC on mineral surfaces was thicker than the caustic starch, and among various MSC the adsorption of Fe3+-starch exhibited the thickest adsorption layer while that of Mg2+-starch the thinnest. Zeta potential indicated that with a weaker electronegativity than the caustic starch, MSC adsorbed onto iron minerals more easily, and the strong electrostatic adsorption with the aid of the hydrogen bonding and chemisorption agreed well with the high depressing ability of the MSC.

  19. Structural mechanisms of heavy-metal extrusion by the Cus efflux system.

    Science.gov (United States)

    Delmar, Jared A; Su, Chih-Chia; Yu, Edward W

    2013-08-01

    Resistance-nodulation-cell division (RND) superfamily efflux systems are responsible for the active transport of toxic compounds from the Gram-negative bacterial cell. These pumps typically assemble as tripartite complexes, spanning the inner and outer membranes of the cell envelope. In Escherichia coli, the CusC(F)BA complex, which exports copper(I) and silver(I) and mediates resistance to these two metal ions, is the only known RND transporter with a specificity for heavy metals. We have determined the crystal structures of both the inner membrane pump CusA and membrane fusion protein CusB, as well as the adaptor-transporter CusBA complex formed by these two efflux proteins. In addition, the crystal structures of the outer membrane channel CusC and the periplasmic metallochaperone CusF have been resolved. Based on these structures, the entire assembled model of the tripartite efflux system has been developed, and this efflux complex should be in the form of CusC3-CusB6-CusA3. It has been shown that CusA utilizes methionine clusters to bind and export Cu(I) and Ag(I). This pump is likely to undergo a conformational change, and utilize a relay network of methionine clusters as well as conserved charged residues to extrude the metal ions from the bacterial cell.

  20. Kinetic model for mechanical twinning and its application for intensive loading of metals

    Directory of Open Access Journals (Sweden)

    Mayer Alexander

    2015-01-01

    Full Text Available In this report, we present our twinning model intended for simulation of the dynamic deformation of metals with low values of the stacking fault energy, as well as the results of application of the model to numerical simulation of intensive loading of metals. Generation of a twin is described as an appearance of a stacking fault with size more than some critical value, while growth of a twin is considered as a cooperative movement of partial dislocation along the stacking fault. The twin nucleation rate is expressed through the energy released due to annihilation of dislocations. Movement of partial dislocations in the course of twin growth passes under the action of elastic stress field and phonon drag. The surface energy of the growing twin continuously increases which leads to the appearance of an additional force. Application of this model allows us to investigate plastic response of metals at various dynamic loading conditions and initial defect structures. Influence of twinning at Taylor rod compaction experiments is analyzed including formation of the shape of the lateral surface.

  1. Informal sector labour demand: Evidence from Zimbabwe's urban ...

    African Journals Online (AJOL)

    This paper investigates the major determinants of labour demand in Zimbabwe's urban informal metal sector. Furthermore, the study looks at employment trends in the urban informal metal sector. The paper employs the ordinary least squares (OLS) technique and three stage least squares (3SLS) to take care of the ...

  2. Transcriptional analysis and molecular dynamics simulations reveal the mechanism of toxic metals removal and efflux pumps in Lysinibacillus sphaericus OT4b.31

    KAUST Repository

    Shaw, Dario Rangel

    2017-11-23

    Lysinibacillus sphaericus strain OT4b.31 is a bacterium widely applied in bioremediation processes of hydrocarbon and metal polluted environments. In this study, we identified the molecular mechanism underlying the Pb2+ and Cr6+ resistance. Metal uptake and temporal transcription patterns of metal resistance operons were evaluated using reverse-transcribed quantitative PCR amplification. The function of the resistance determinants was studied applying docking and in silico mutagenesis methods. The results revealed that the adaptation of Lysinibacillus sphaericus OT4b.31 to elevated levels of lead and chromium involves the pbr and chr operons which comprise a transcriptional regulatory component (pbrR and chrB) and efflux ATPases (pbrA and chrA) to expel ions from the cytoplasm. Expression of metal resistance genes was constitutive and specifically inducible to the exposure of Pb2+ and Cr6+. The simultaneous presence of cations didn\\'t affect the bioaccumulation of metals, evidencing the multimetal resistance of L. sphaericus. Docking analysis revealed the key metal-protein interactions and the conformational changes after metal or ATP binding. Results showed that residues with aromatic rings or imidazole in the catalytic domain are crucial for metal binding and achievement of the function. To our knowledge, this is the first report of a specific mechanism for lead and chromium resistance in Lysinibacillus genus. From the findings of this study, it is possible to suggest the bacterium as a suitable candidate for rapid toxic metals bioremediation processes.

  3. Mechanism of ROS scavenging and antioxidant signalling by redox metallic and fullerene nanomaterials: Potential implications in ROS associated degenerative disorders.

    Science.gov (United States)

    Akhtar, Mohd Javed; Ahamed, Maqusood; Alhadlaq, Hisham A; Alshamsan, Aws

    2017-04-01

    The balance between oxidation and anti-oxidation is believed to be critical in maintaining healthy biological systems. However, our endogenous antioxidant defense systems are incomplete without exogenous antioxidants and, therefore, there is a continuous demand for exogenous antioxidants to prevent stress and ageing associated disorders. Nanotechnology has yielded enormous variety of nanomaterials (NMs) of which metallic and carbonic (mainly fullerenes) NMs, with redox property, have been found to be strong scavengers of ROS and antioxidants in preclinical in vitro and in vivo models. Redox activity of metal based NMs and membrane translocation time of fullerene NMs seem to be the major determinants in ROS scavenging potential exhibited by these NMs. A comprehensive knowledge about the effects of ROS scavenging NMs in cellular antioxidant signalling is largely lacking. This review compiles the mechanisms of ROS scavenging as well as antioxidant signalling of the aforementioned metallic and fullerene NMs. Direct interaction between NMs and proteins does greatly affect the corona/adsorption formation dynamics but such interaction does not provide the explanation behind diverse biological outcomes induced by NMs. Indirect interaction, however, that could occur via NMs uptake and dissolution, NMs ROS induction and ROS scavenging property, and NMs membrane translocation time seem to work as a central mode of interaction. The usage of potential antioxidant NMs in biological systems would greatly impact the field of nanomedicine. ROS scavenging NMs hold great promise in the future treatment of ROS related degenerative disorders. Copyright © 2017 Elsevier B.V. All rights reserved.

  4. Influence of Lubricant Pocket Geometry upon Lubrication Mechanisms on Tool-Workpiece Interfaces in Metal Forming

    DEFF Research Database (Denmark)

    Shimizu, I; Martins, P.A.F.; Bay, Niels

    2004-01-01

    mechanisms, during upsetting and strip drawing, by means of a rigid viscoplastic finite element formulation. Special emphasis is placed on the effect of pocket geometry on the build up of hydrostatic pressure, which is responsible for the onset of micro lubrication mechanisms. A good agreement is found...... between the numerically predicted and the experimentally measured distributions of hydrostatic stress....

  5. Pengaruh Milling Time Terhadap Pembentukan Intermetalik ɣ-TiAl Sebagai Reinforced Dalam Metal Matrix Composite (MMCs Hasil Mechanical Alloying

    Directory of Open Access Journals (Sweden)

    Mohammad Badrus Soleh

    2013-03-01

    Full Text Available Paduan TiAl mempunyai berbagai keunggulan dalam sifat mekanik serta sifat termal. Senyawa intermetalik γ-TiAl mempunyai sifat mekanik dan sifat termal yang sangat baik sehingga sesuai apabila diaplikasikan sebagai penguat pada metal matrix composite (MMCs. Penelitian ini bertujuan untuk mensintesis paduan TiAl sehingga terbentuk  fasa intermetalik γ-TiAl yang homogen. Sintesa dilakukan dengan metode mechanical alloying menggunakan modification horizontal ball mill dengan komposisi paduan Ti-36%wt Al dan variasi milling time 0,10,20 jam dengan kecepatan tetap 350rpm. Hasil milling dikompaksi dan di-annealing pada temperatur 9000C selama 30menit.  Fasa intermetalik γ-TiAl terbentuk setelah proses mechanical alloying 20 jam. Hasil pengujian difraksi sinar X menunjukkan ukuran kristal sebesar 198.92Å pada fasa γ-TiAl, memiliki kekerasan 678,1HV.

  6. Freedom or Free-For-All in Irish Healthcare? Establishing Improved Consumer Protection Mechanisms in the Irish Complementary and Alternative Medicine Sector

    OpenAIRE

    O LEARY, CLAIRE LOUISE

    2017-01-01

    APPROVED Despite political rhetoric, the establishment of working groups, and the publication of commissioned reports in the early and mid-2000s recommending improvements in the regulation of the Irish complementary and alternative medicine (CAM) sector, little of significance has changed. Controversies undermining public confidence in authority, global digital dissemination of information, and higher levels of education and wealth have, among other factors, contributed to the increas...

  7. Genotoxicity of metal oxide nanomaterials: review of recent data and discussion of possible mechanisms

    Science.gov (United States)

    Golbamaki, Nazanin; Rasulev, Bakhtiyor; Cassano, Antonio; Marchese Robinson, Richard L.; Benfenati, Emilio; Leszczynski, Jerzy; Cronin, Mark T. D.

    2015-01-01

    Nanotechnology has rapidly entered into human society, revolutionized many areas, including technology, medicine and cosmetics. This progress is due to the many valuable and unique properties that nanomaterials possess. In turn, these properties might become an issue of concern when considering potentially uncontrolled release to the environment. The rapid development of new nanomaterials thus raises questions about their impact on the environment and human health. This review focuses on the potential of nanomaterials to cause genotoxicity and summarizes recent genotoxicity studies on metal oxide/silica nanomaterials. Though the number of genotoxicity studies on metal oxide/silica nanomaterials is still limited, this endpoint has recently received more attention for nanomaterials, and the number of related publications has increased. An analysis of these peer reviewed publications over nearly two decades shows that the test most employed to evaluate the genotoxicity of these nanomaterials is the comet assay, followed by micronucleus, Ames and chromosome aberration tests. Based on the data studied, we concluded that in the majority of the publications analysed in this review, the metal oxide (or silica) nanoparticles of the same core chemical composition did not show different genotoxicity study calls (i.e. positive or negative) in the same test, although some results are inconsistent and need to be confirmed by additional experiments. Where the results are conflicting, it may be due to the following reasons: (1) variation in size of the nanoparticles; (2) variations in size distribution; (3) various purities of nanomaterials; (4) variation in surface areas for nanomaterials with the same average size; (5) differences in coatings; (6) differences in crystal structures of the same types of nanomaterials; (7) differences in size of aggregates in solution/media; (8) differences in assays; (9) different concentrations of nanomaterials in assay tests. Indeed, due to the

  8. Adsorptive kinetic mechanism of heavy metal cations on the surface of graphite oxide and its SiO2 composite

    Science.gov (United States)

    Sheet, Imtithal; Kabbani, Ahmad; Holail, Hanafy

    2017-02-01

    Nanomaterials have gained great attention because of their novel size- and shape-dependent properties, large specific surface area and high reaction activity. Moreover, nanomaterials have a wide range of applications, as in the technological and environmental challenges in the areas of solar energy conversion, catalysis, medicine, and water treatments. In the present study, nanostructured graphite oxide, silica/graphite oxide composites and silica nanoparticles were used for the removal of the heavy metal ions from aqueous solutions by a batch adsorption method and the adsorptive kinetic mechanism of heavy metal cations on the surface of graphite oxide and its SiO2 composite was evaluated. The experimental results revealed a strong adsorption of the metal cations on the surface of graphite oxide, this is reflected in the shifts in wave numbers after adsorption with nanostructured graphite oxide and the big shift in wave numbers (Δv¯) for nickel ions reflects chemosorption type of adsorption. This is confirmed by the coherence between Δv¯, removal percentage and crystal field stabilization energy (CFSE). Silica/ GO (2:3) composite showed the greatest removal percentage at different concentrations compared to pure graphite oxide and silica nanoparticles. The higher removal percentage of nickel ions by silica /GO composite (2:3) was observed at 180 min contact time and basic pH. The kinetic studies showed that silica/ GO (2:3) composite had rapid adsorption rate and efficiency and it was found to follow first order rate expression or an exponential decay of the metal cations from water study.

  9. Structures of intermediates along the catalytic cycle of terminal deoxynucleotidyltransferase: dynamical aspects of the two-metal ion mechanism.

    Science.gov (United States)

    Gouge, Jérôme; Rosario, Sandrine; Romain, Félix; Beguin, Pierre; Delarue, Marc

    2013-11-15

    Terminal deoxynucleotidyltransferase (Tdt) is a non-templated eukaryotic DNA polymerase of the polX family that is responsible for the random addition of nucleotides at the V(D)J junctions of immunoglobulins and T-cell receptors. Here we describe a series of high-resolution X-ray structures that mimic the pre-catalytic state, the post-catalytic state and a competent state that can be transformed into the two other ones in crystallo via the addition of dAMPcPP and Zn(2+), respectively. We examined the effect of Mn(2+), Co(2+) and Zn(2+) because they all have a marked influence on the kinetics of the reaction. We demonstrate a dynamic role of divalent transition metal ions bound to site A: (i) Zn(2+) (or Co(2+)) in Metal A site changes coordination from octahedral to tetrahedral after the chemical step, which explains the known higher affinity of Tdt for the primer strand when these ions are present, and (ii) metal A has to leave to allow the translocation of the primer strand and to clear the active site, a typical feature for a ratchet-like mechanism. Except for Zn(2+), the sugar puckering of the primer strand 3' terminus changes from C2'-endo to C3'-endo during catalysis. In addition, our data are compatible with a scheme where metal A is the last component that binds to the active site to complete its productive assembly, as already inferred in human pol beta. The new structures have potential implications for modeling pol mu, a closely related polX implicated in the repair of DNA double-strand breaks, in a complex with a DNA synapsis. © 2013.

  10. Sorption of chlorophenols on microporous minerals: mechanism and influence of metal cations, solution pH, and humic acid.

    Science.gov (United States)

    Yang, Hui; Hu, Yuanan; Cheng, Hefa

    2016-10-01

    Sorption of 2-chlorophenol (2-CP), 2,4-dichlorophenol (2,4-DCP), and 2,4,6-trichlorophenol (2,4,6-TCP) on a range of dealuminated zeolites were investigated to understand the mechanism of their sorption on microporous minerals, while the influence of common metal cations, solution pH, and humic acid was also studied. Sorption of chlorophenols was found to increase with the hydrophobicity of the sorbates and that of the microporous minerals, indicating the important role of hydrophobic interactions, while sorption was also stronger in the micropores of narrower sizes because of greater enhancement of the dispersion interactions. The presence of metal cations could enhance chlorophenol sorption due to the additional electrostatic attraction between metal cations exchanged into the mineral micropores and the chlorophenolates, and this effect was apparent on the mineral sorbent with a high density of surface cations (2.62 sites/nm(2)) in its micropores. Under circum-neutral or acidic conditions, neutral chlorophenol molecules adsorbed into the hydrophobic micropores through displacing the "loosely bound" water molecules, while their sorption was negligible under moderately alkaline conditions due to electrostatic repulsion between the negatively charged zeolite framework and anionic chlorophenolates. The influence of humic acid on sorption of chlorophenols on dealuminated Y zeolites suggests that its molecules did not block the micropores but created a secondary sorption sites by forming a "coating layer" on the external surface of the zeolites. These mechanistic insights could help better understand the interactions of ionizable chlorophenols and metal cations in mineral micropores and guide the selection and design of reusable microporous mineral sorbents for sorptive removal of chlorophenols from aqueous stream.

  11. The effects of ion implantation upon the mechanical properties of metals and cemented carbides

    International Nuclear Information System (INIS)

    Dearnaley, G.

    1982-01-01

    Ion implantation has been successful in producing significant improvements in the wear resistance and fatigue endurance of metals such as steel, titanium, copper and electrodeposited chromium. Models to explain this behaviour in terms of the pinning of mobile dislocations are presented. Friction coefficients are also modified by ion implantation, and in the composite material cobalt-cemented tungsten carbide this effect is very strong, and is accompanied by a reduction in wear. Examples of the range of tools which have been improved by nitrogen ion implantation are given, and the review concludes with a description of the equipment developed for the industrial application of this process. (author)

  12. ULTRASONIC STUDIES OF THE FUNDAMENTAL MECHANISMS OF RECRYSTALLIZATION AND SINTERING OF METALS

    Energy Technology Data Exchange (ETDEWEB)

    TURNER, JOSEPH A.

    2005-11-30

    The purpose of this project was to develop a fundamental understanding of the interaction of an ultrasonic wave with complex media, with specific emphases on recrystallization and sintering of metals. A combined analytical, numerical, and experimental research program was implemented. Theoretical models of elastic wave propagation through these complex materials were developed using stochastic wave field techniques. The numerical simulations focused on finite element wave propagation solutions through complex media. The experimental efforts were focused on corroboration of the models developed and on the development of new experimental techniques. The analytical and numerical research allows the experimental results to be interpreted quantitatively.

  13. Formation and Mechanical Properties of Pd-Si Binary Bulk Metallic Glasses

    Directory of Open Access Journals (Sweden)

    Na Chen

    2014-01-01

    Full Text Available Glassy spherical samples in the diameters up to 10 mm were produced in a binary Pd-Si alloy system. These Pd-Si bulk metallic glasses (BMGs combine high strength of about 1600 MPa and superplasticity of over 70% together. In addition to abundant micrometer-scale shear bands, 10–20 nanometer-sized shear bands were also observed on the side surface of the deformed sample. The excellent ductility shown by the Pd-Si BMGs is suggested to arise from the nanoscale structural inhomogeneity.

  14. Ballistic-Failure Mechanisms in Gas Metal Arc Welds of Mil A46100 Armor-Grade Steel: A Computational Investigation

    Science.gov (United States)

    Grujicic, M.; Snipes, J. S.; Galgalikar, R.; Ramaswami, S.; Yavari, R.; Yen, C.-F.; Cheeseman, B. A.

    2014-09-01

    In our recent work, a multi-physics computational model for the conventional gas metal arc welding (GMAW) joining process was introduced. The model is of a modular type and comprises five modules, each designed to handle a specific aspect of the GMAW process, i.e.: (i) electro-dynamics of the welding-gun; (ii) radiation-/convection-controlled heat transfer from the electric-arc to the workpiece and mass transfer from the filler-metal consumable electrode to the weld; (iii) prediction of the temporal evolution and the spatial distribution of thermal and mechanical fields within the weld region during the GMAW joining process; (iv) the resulting temporal evolution and spatial distribution of the material microstructure throughout the weld region; and (v) spatial distribution of the as-welded material mechanical properties. In the present work, the GMAW process model has been upgraded with respect to its predictive capabilities regarding the spatial distribution of the mechanical properties controlling the ballistic-limit (i.e., penetration-resistance) of the weld. The model is upgraded through the introduction of the sixth module in the present work in recognition of the fact that in thick steel GMAW weldments, the overall ballistic performance of the armor may become controlled by the (often inferior) ballistic limits of its weld (fusion and heat-affected) zones. To demonstrate the utility of the upgraded GMAW process model, it is next applied to the case of butt-welding of a prototypical high-hardness armor-grade martensitic steel, MIL A46100. The model predictions concerning the spatial distribution of the material microstructure and ballistic-limit-controlling mechanical properties within the MIL A46100 butt-weld are found to be consistent with prior observations and general expectations.

  15. Relationship between organizational life cycle and budgeting process in mechanical metal company of high and middle Valley Itajaí

    Directory of Open Access Journals (Sweden)

    Leandro Marques

    2014-09-01

    Full Text Available The objective of this study was investigate the relationship of the different stages of organizational life cycle of companies in the field of mechanical metal in Alto and Médio Vale do Itajaí, with the profile of the budgeting process. The methodology used was characterized as descriptive performed by means of a survey, with a quantitative approach. We used a questionnaire with 54 questions divided into four blocks, adapted from Frezatti et al. (2010. The life cycle model in the implement of research is to Miller and Friesen (1984. Questionnaires were sent to 193 companies in the metal mechanic industry of the Alto and Médio Vale do Itajaí. We obtained 31 answers who were treated statistically by means of descriptive statistics, discriminant analysis and correlation analysis. The results show that most companies are in stages of birth and rejuvenation. It was also found that the budgeting process most commonly used by companies is budgetary control. It was identified that there is a relationship between budgeting process artifacts and the stage of life cycle that the company is, but this use occurs differently in each stage. Thus it is concluded that, as the company becomes more complex and advanced stages of the life cycle, the greater is the use of budgeting process, with significant drop in the use of these artifacts when the company is at the stage of decline.

  16. Low temperature motion of hydrogen on metal surfaces signals breakdown of quantum mechanics in 3+1 dimensions

    Science.gov (United States)

    Drakova, D.; Doyen, G.

    2013-06-01

    The low temperature motion of hydrogen on solid metal surfaces displays some unexplained experimental features: in the quantum diffusion regime more than nine orders of magnitude difference between the diffusion rates on different metal surfaces have been measured, the lowest diffusion rates being established in the low temperature scanning tunnelling microscope. Furthermore telegraph-signal-like adsorption site change, rather than Rabi oscillations predicted by Schrödinger equation in 3+1 dimensions, is observed, signaling the breakdown of quantum mechanics in 3+1 dimensions. A theory is presented to resolve these problems, involving the entanglement of the adsorbate motion to gravitons in high-dimensional spacetime. Soft local massive gravonons, induced in the presence of the adsorbate, determine the time scale for surface diffusion. The γη-model is used for the evaluation of the soft gravonon modes. Weak and local entanglement of the adsorbate motion with a nearly degenerate graviton continuum of high density of states are the conditions for the telegraph-signal-like time development of adsorption site change. In contrast to the Copenhagen interpretation of quantum mechanics, this apparent "classical" behaviour of the adsorbate in 3+1 dimensional spacetime is the result of the solution of Schrödinger's time dependent equation in high-dimensional spacetime.

  17. Effect of composition and technique of production, on the mechanical behaviour of based-zirconium metallic glasses

    International Nuclear Information System (INIS)

    Nowak, Sophie

    2009-01-01

    The metallic glasses are relatively new materials (50 years), produced by quenching a molten alloy. The amorphous structure of these materials gives them unique properties: very high strength (fracture stress is about 1.7 GPa for Zr based alloys), an elastic deformation reaching 2%, but little or no ductility. The compositions, which could produce both amorphous and bulk samples, are limited. The work, detailed in this manuscript, shows the possibility of sintering using SPS (Spark Plasma Sintering) amorphous powders obtained by atomization (Φaverage = 70 microns). The result is a fully densified and near fully amorphous sample. The optimization of this technique, with the composition Zr 57 Cu 20 Al 10 Ni 8 Ti 5 , gave samples for which mechanical behaviour is close to the bulk metallic glass behaviour. However, partial crystallization of the material occurs, localized at the contact points of particles, but could be reduced by deepening the sintering model outlined in this manuscript. In view of these results, new compositions are designed, and the production of ribbons was conducted. The characterization by nano-indentation estimates reliably the mechanical properties of these alloys. Finally, a new method, evaluating the activation volume, which is the elementary volume initiating plastic deformation, is presented. This technique is a statistical analysis of pseudo-creep tests performed by nano-indentation, at room temperature. In conclusion, this work opens new perspectives to develop bulk samples in broad range of compositions. (author)

  18. Explicit relationship between electrical and topological degradation of polymer-supported metal films subjected to mechanical loading

    Science.gov (United States)

    Glushko, O.; Kraker, P.; Cordill, M. J.

    2017-05-01

    For a comprehensive characterization of mechanical reliability of metallization layers on polymer substrates, both electrical and mechanical degradation should be taken into account. Although it is evident that cracking of a conductive film should lead to electrical degradation, the quantitative relationship between the growth of electric resistance and parameters of the induced crack pattern has remained thus far unexplored. With the help of finite element modelling, we were able to find an explicit and concise expression which shows that electrical resistance grows with the fourth order of the crack length and second order of the areal crack density. The discovered relationship was verified by comparison with the experimental results of tensile testing of polymer-supported thin metal films. The presented model is independent of the length scale and can be applied to films with different thicknesses as long as Ohm's law is valid. It is demonstrated that the linear crack density is an ambiguous parameter, which does not properly capture the development of a crack pattern. For the unambiguous characterization of the intensity of a crack pattern, a universal dimensionless factor is proposed. The presented results show that there is a wide range of possible crack patterns which do not lead to electrical failure of a conductive film that can be used for the failure-free design of flexible electronic devices.

  19. Evaluation of the molecular mechanisms associated with cytotoxicity and inflammation after pulmonary exposure to different metal-rich welding particles.

    Science.gov (United States)

    Shoeb, Mohammad; Kodali, Vamsi; Farris, Breanne; Bishop, Lindsey M; Meighan, Terence; Salmen, Rebecca; Eye, Tracy; Roberts, Jenny R; Zeidler-Erdely, Patti; Erdely, Aaron; Antonini, James M

    2017-08-01

    Welding generates a complex aerosol of incidental nanoparticles and cytotoxic metals, such as chromium (Cr), manganese (Mn), nickel (Ni), and iron (Fe). The goal was to use both in vivo and in vitro methodologies to determine the mechanisms by which different welding fumes may damage the lungs. Sprague-Dawley rats were treated by intratracheal instillation (ITI) with 2.0 mg of gas metal arc-mild steel (GMA-MS) or manual metal arc-stainless steel (MMA-SS) fumes or saline (vehicle control). At 1, 3, and 10 days, bronchoalveolar lavage (BAL) was performed to measure lung toxicity. To assess molecular mechanisms of cytotoxicity, RAW264.7 cells were exposed to both welding fumes for 24 h (0-100 μg/ml). Fume composition was different: MMA-SS (41% Fe, 29% Cr, 17% Mn, 3% Ni) versus GMA-MS (85% Fe, 14% Mn). BAL indicators of lung injury and inflammation were increased by MMA-SS at all time points and by GMA-MS at 3 and 10 days after exposure. RAW264.7 cells exposed to MMA-SS had elevated generation of reactive oxygen species (ROS), protein-HNE (P-HNE) adduct formation, activation of ERK1/2, and expression of cyclooxygenase-2 (COX-2) compared to GMA-MS and control. Increased generation of ROS due to MMA-SS exposure was confirmed by increased expression of Nrf2 and heme oxygenase-1 (HO-1). Results of in vitro studies provide evidence that stainless steel welding fume mediate inflammatory responses via activation of ROS/P-HNE/ERK1/2/Nrf2 signaling pathways. These findings were corroborated by elevated expression of COX-2, Nrf2, and HO-1 in homogenized lung tissue collected 1 day after in vivo exposure.

  20. TIG AISI-316 welds using an inert gas welding chamber and different filler metals: Changes in mechanical properties and microstructure

    Directory of Open Access Journals (Sweden)

    Sánchez, A.

    2010-12-01

    Full Text Available This report analyses the influence of the use of an inert gas welding chamber with a totally inert atmosphere on the microstructure and mechanical properties of austenitic AISI 316L stainless steel TIG welds, using AISI ER316L, AISI 308L and Inconel 625 as filler metals. When compared with the typical TIG process, the use of the inert gas chamber induced changes in the microstructure, mainly an increase in the presence of vermicular ferrite and ferrite stringers, what resulted in higher yield strengths and lower values of hardness. Its effect on other characteristics of the joins, such as tensile strength, depended on the filler metal. The best combination of mechanical characteristics was obtained when welding in the inert gas chamber using Inconel 625 as filler metal.

    En este estudio se analiza la influencia que el uso de una cámara de soldadura de gas inerte tiene sobre la microestructura y las propiedades mecánicas de las soldaduras TIG en el acero inoxidable austenítico AISI-316L cuando se emplean AISI ER316L, AISI 308L e Inconel 625 como materiales de aporte. Cuando se compara con el típico proceso de TIG, el uso de una cámara de gas inerte induce cambios en la microestructura, incrementando la presencia de ferrita vermicular y de laminillas de ferrita, resultando en un aumento del límite elástico y una pérdida de dureza. Su influencia sobre otras características de las soldaduras como la carga de rotura depende de la composición del material de aporte. La mejor combinación de propiedades mecánicas se obtuvo usando el Inconel 625 como material de aporte y soldando en la cámara de gas inerte.

  1. Preparation and mechanical properties of ultra-high-strength nanocrystalline metals

    Czech Academy of Sciences Publication Activity Database

    Marek, I.; Vojtěch, D.; Michalcová, A.; Kubatík, Tomáš František

    2015-01-01

    Roč. 15, č. 4 (2015), s. 596-600 ISSN 1213-2489 Institutional support: RVO:61389021 Keywords : Mechanical properties * Nanocrystalline materials * Selective leaching * Silver * Spark plasma sintering Subject RIV: JG - Metallurgy

  2. Photoexcitation Mechanism of Metallic Sr1-xNbO3 for Watersplitting Photocatalyst

    Science.gov (United States)

    Kaneko, Masanori; Giorgi, Giacomo; Yamashita, Koichi

    The absence of a bandgap makes metallic materials not suitable as water-splitting photocatalysts. In 2012, Xu et al. have reported results about Sr-vacancy SrNbO3 as a water-splitting photocatalyst. Surprisingly, this species is metallic (implying high carrier mobility) with an optical gap of about 1.9 eV and absorb most of the visible light. Authors, by means of DFT based calculations, have predicted its band structure and showed that three bands are separated by a gap: occupied band (B-1), partially empty band (CB), and unoccupied band (B1). More recently several studies have focused on the energy gap of this class of materials. Nevertheless, the results of the photoexcitation of SrNbO3 obtained so far are controversial. Accordingly, we focused my attention on the optical absorption and the position of the bands by means of a DFT analysis. We revealed that photoexcitation around optical gap 1.9 eV is constituted by the CB ->B1 transitions on some k-point along the Γ - X direction and the most contributed k-point isn't placed in the band-diagram. In addition, we investigated the effect of Sr vacancies and substitutionals on the bandstructure and light absorption.

  3. Oxidation feature and diffusion mechanism of Zr-based metallic glasses near the glass transition point

    Science.gov (United States)

    Hu, Zheng; Lei, Xianqi; Wang, Yang; Zhang, Kun

    2018-03-01

    The oxidation behaviors of as-cast, pre-deformed, and crystallized Zr47.9Ti0.3Ni3.1Cu39.3Al9.4 metallic glasses (MGs) were studied near the glass transition point. The oxidation kinetics of the crystallized MGs followed a parabolic-rate law, and the as-cast and pre-deformed MGs exerted a typical two-stage behavior above the glass transition temperature (T g). Most interesting, pre-deformed treatment can significantly improve the oxidation rate of MGs, as the initial oxidation appeared earlier than for the as-cast MGs, and was accompanied by much thicker oxide scale. The EDS and XPS results showed that the metal Al acted as the preferred scavenger that absorbed intrinsic oxygen in the near-surface region of as-cast MGs. However, a homogeneous mixed layer without Al was observed in the pre-deformed MGs. We speculated the accelerated diffusion of other elements in the MGs was due to the local increase in the free volume and significant shear-induced dilation of the local structure. The results from this study demonstrate that MGs exhibit controllable atomic diffusion during the oxidation process, which can facilitate use in super-cooled liquid region applications.

  4. Plastic deformation and failure mechanisms in nano-scale notched metallic glass specimens under tensile loading

    Science.gov (United States)

    Dutta, Tanmay; Chauniyal, Ashish; Singh, I.; Narasimhan, R.; Thamburaja, P.; Ramamurty, U.

    2018-02-01

    In this work, numerical simulations using molecular dynamics and non-local plasticity based finite element analysis are carried out on tensile loading of nano-scale double edge notched metallic glass specimens. The effect of acuteness of notches as well as the metallic glass chemical composition or internal material length scale on the plastic deformation response of the specimens are studied. Both MD and FE simulations, in spite of the fundamental differences in their nature, indicate near-identical deformation features. Results show two distinct transitions in the notch tip deformation behavior as the acuity is increased, first from single shear band dominant plastic flow localization to ligament necking, and then to double shear banding in notches that are very sharp. Specimens with moderately blunt notches and composition showing wider shear bands or higher material length scale characterizing the interaction stress associated with flow defects display profuse plastic deformation and failure by ligament necking. These results are rationalized from the role of the interaction stress and development of the notch root plastic zones.

  5. PROCESS PERFORMANCE LASER CUTTING THROUGH PRACTICE DRY BRANCH IN METAL-MECHANIC

    Directory of Open Access Journals (Sweden)

    Deivis Zismann

    2015-12-01

    Full Text Available The quest for optimization and quality of products has caused many organizations to eliminate the inefficiencies of their production processes, to reduce costs and increase profitability so that they can ensure their survival in the current economic scenario. Thus, it is necessary to use methods and techniques that help in getting better results. Minimize waste and promote overall product quality has become one of the main goals of the organizations. This study is Bibliographically the concept of Lean Manufacturing (Lean Manufacturing, which focused on eliminating waste, served as the basis for this study, which through an action - research aimed to applying lean practices for performance improvement the laser cutting process for an industry of the metalmechanic sector. The results show that the identification of the main sources of waste and the constant search for its elimination brought productivity advantages for the company, by reducing the processes of machines and minimize production costs time. With this, the company started to produce more, and improve their processes in the proper use of available resources.

  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. Experimental and numerical study of the mechanical behaviour modelling of a metal-ceramic composite: MoTiC30%

    International Nuclear Information System (INIS)

    Cedat, D.

    2008-11-01

    In the scope of refractory materials development for structural applications in the core of the future nuclear reactors, several studies have been developed. The aim of this work is to increase the knowledge of the mechanical behaviour and the damage of the ceramic-metal composite Mo(TiC)x% under the temperature range [25-700 C]. The identification of the third phase, formed by diffusion during the sintering step was identified by microstructural characterization. Experimental study also revealed the percolation of the ceramic particles through the structure. Mechanical tests highlight the main characteristics of the material: the macroscopic behaviour depends on the strain rate on the first hand and the temperature on the other hand. These mechanisms are attributed to the thermally activated behaviour of molybdenum. Simulations have been made on several microstructures considering elastic-brittle inclusion in a viscoelastic matrix. A polycrystalline model was used to simulate the evolution of the mechanical behaviour of the composite. The numerical aggregate, used for the simulation, was built from a 3D reconstruction technique thanks to acquisition of FIB/EBSD/SEM data. (author)

  8. A study of long-term static load on degradation and mechanical integrity of Mg alloys-based biodegradable metals

    International Nuclear Information System (INIS)

    Koo, Youngmi; Jang, Yongseok; Yun, Yeoheung

    2017-01-01

    Highlights: • Long-term stress corrosion cracking (SCC) test of Mg alloys was performed. • AZ31B-H24 shows transgranular stress corrosion cracking (TGSCC) and ZE41A-T5 intergranular stress corrosion cracking (IGSCC). • Long-term static loading accelerated crack propagation, leading to the loss of mechanical strength. - Abstract: Predicting degradation behavior of biodegradable metals in vivo is crucial for the clinical success of medical devices. This paper reports on the effect of long-term static stress on degradation of magnesium alloys and further changes in mechanical integrity. AZ31B (H24) and ZE41A (T5) alloys were tested to evaluate stress corrosion cracking (SCC) in a physiological solution for 30 days and 90 days (ASTM G39 testing standard). Scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDX) and micro-computed tomography (micro-CT) were used to characterize surface morphology and micro-structure of degraded alloys. The results show the different mechanisms of stress corrosion cracking for AZ31B (transgranular stress corrosion cracking, TGSCC) and ZE41A (intergranular stress corrosion cracking, IGSCC). AZ31B was more susceptible to stress corrosion cracking under a long term static load than ZE41A. In conclusion, we observed that long-term static loading accelerated crack propagation, leading to the loss of mechanical integrity.

  9. A study of long-term static load on degradation and mechanical integrity of Mg alloys-based biodegradable metals

    Energy Technology Data Exchange (ETDEWEB)

    Koo, Youngmi; Jang, Yongseok; Yun, Yeoheung, E-mail: yyun@ncat.edu

    2017-05-15

    Highlights: • Long-term stress corrosion cracking (SCC) test of Mg alloys was performed. • AZ31B-H24 shows transgranular stress corrosion cracking (TGSCC) and ZE41A-T5 intergranular stress corrosion cracking (IGSCC). • Long-term static loading accelerated crack propagation, leading to the loss of mechanical strength. - Abstract: Predicting degradation behavior of biodegradable metals in vivo is crucial for the clinical success of medical devices. This paper reports on the effect of long-term static stress on degradation of magnesium alloys and further changes in mechanical integrity. AZ31B (H24) and ZE41A (T5) alloys were tested to evaluate stress corrosion cracking (SCC) in a physiological solution for 30 days and 90 days (ASTM G39 testing standard). Scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDX) and micro-computed tomography (micro-CT) were used to characterize surface morphology and micro-structure of degraded alloys. The results show the different mechanisms of stress corrosion cracking for AZ31B (transgranular stress corrosion cracking, TGSCC) and ZE41A (intergranular stress corrosion cracking, IGSCC). AZ31B was more susceptible to stress corrosion cracking under a long term static load than ZE41A. In conclusion, we observed that long-term static loading accelerated crack propagation, leading to the loss of mechanical integrity.

  10. 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

  11. Degradation of Highly Alloyed Metal Halide Perovskite Precursor Inks: Mechanism and Storage Solutions

    Energy Technology Data Exchange (ETDEWEB)

    Dou, Benjia [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Wheeler, Lance M [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Christians, Jeffrey A [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Moore, David [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Harvey, Steven P [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Berry, Joseph J [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Van Hest, Marinus F [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Barnes, Frank S. [University of Colorado; Shaheen, Sean E. [University of Colorado

    2018-03-02

    Whereas the promise of metal halide perovskite (MHP) photovoltaics (PV) is that they can combine high efficiency with solution-processability, the chemistry occurring in precursor inks is largely unexplored. Herein, we investigate the degradation of MHP solutions based on the most widely used solvents, dimethylformamide (DMF) and dimethyl sulfoxide (DMSO). For the MHP inks studied, which contain formamidinium (FA+), methylammonium (MA+), cesium (Cs+), lead (Pb2+), bromide (Br-), and iodide (I-), dramatic compositional changes are observed following storage of the inks in nitrogen in the dark. We show that hydrolysis of DMF in the precursor solution forms dimethylammonium formate, which subsequently incorporates into the MHP film to compromise the ability of Cs+ and MA+ to stabilize FA+-based MHP. The changes in solution chemistry lead to a modification of the perovskite film stoichiometry, band gap, and structure. The solid precursor salts are stable when ball-milled into a powder, allowing for the storage of large quantities of stoichiometric precursor materials.

  12. Crystal Plasticity Modeling of Microstructure Evolution and Mechanical Fields During Processing of Metals Using Spectral Databases

    Science.gov (United States)

    Knezevic, Marko; Kalidindi, Surya R.

    2017-05-01

    This article reviews the advances made in the development and implementation of a novel approach to speeding up crystal plasticity simulations of metal processing by one to three orders of magnitude when compared with the conventional approaches, depending on the specific details of implementation. This is mainly accomplished through the use of spectral crystal plasticity (SCP) databases grounded in the compact representation of the functions central to crystal plasticity computations. A key benefit of the databases is that they allow for a noniterative retrieval of constitutive solutions for any arbitrary plastic stretching tensor (i.e., deformation mode) imposed on a crystal of arbitrary orientation. The article emphasizes the latest developments in terms of embedding SCP databases within implicit finite elements. To illustrate the potential of these novel implementations, the results from several process modeling applications including equichannel angular extrusion and rolling are presented and compared with experimental measurements and predictions from other models.

  13. Solidification mechanism of highly undercooled metal alloys. [tin-lead and nickel-tin alloys

    Science.gov (United States)

    Shiohara, Y.; Chu, M. G.; Macisaac, D. G.; Flemings, M. C.

    1982-01-01

    Experiments were conducted on metal droplet undercooling, using Sn-25wt%Pb and Ni-34wt%Sn alloys. To achieve the high degree of undercooling, emulsification treatments were employed. Results show the fraction of supersaturated primary phase is a function of the amount of undercooling, as is the fineness of the structures. The solidification behavior of the tin-lead droplets during recalescence was analyzed using three different hypotheses; (1) solid forming throughout recalescence is of the maximum thermodynamically stable composition; (2) partitionless solidification below the T sub o temperature, and solid forming thereafter is of the maximum thermodynamically stable composition; and (3) partitionless solidification below the T sub o temperature with solid forming thereafter that is of the maximum thermodynamically metastable composition that is possible. The T sub o temperature is calculated from the equal molar free energies of the liquid solid using the regular solution approximation.

  14. Evaluation of mechanical properties of recasted dental base metal alloys for considering their reusability in dentistry and engineering field

    Directory of Open Access Journals (Sweden)

    Nandish Bantarahalli Thopegowda

    2014-01-01

    Full Text Available Background: Base metal casting alloys are extensively used in dentistry to fabricate many oral appliances and a huge amount is wasted in the form of sprues and buttons during the casting procedure. Recycling and reusing these alloys by clean technologies may save our natural resources from being depleted and as well reduce the cost of the treatment of the patients. Objectives: To study the mechanical properties of recasted dental base metal alloys, and explore possible ways to recycle and reuse in dentistry and other fields of science and technology. Materials and Methods: Two beryllium-free Cobalt-Chromium (Co-Cr dental casting alloys, Wironit and Wirobond-C, were used for this study. Six groups of specimen (melted once, twice, five, ten, fifteen and twenty times per each alloy were casted. The tensile strength and hardness of these samples were measured by using universal testing machine and Vickers hardness number (VHN tester. Results: Tensile strength decreased from 850 MPa to 777 MPa after 5 th recasting and to 674 MPa at the end of 20 th recasting procedure for the Wironit samples. For Wirobond-C samples, tensile strength decreased from 720 MPa to 678 MPa after 5 th recasting and further reduced to 534 MPa at the end of 20 th recasting procedure. Hardness decreased from 380VHN to 335VHN at the end of 20 th recasting for Wironit samples and 328VHN to 247VHN for Wirobond-C samples after 20 th recasting procedure. The slight decrease in their mechanical properties will not have any impact on the clinical performance for dental applications. Conclusion: There is no major degradation in the mechanical properties after recycling, and hence, the left over alloys after casting procedures can be reused in dentistry with a condition to satisfy cytotoxicity tests.

  15. Interface traps contribution on transport mechanisms under illumination in metal-oxide-semiconductor structures based on silicon nanocrystals

    Science.gov (United States)

    Chatbouri, S.; Troudi, M.; Kalboussi, A.; Souifi, A.

    2018-02-01

    The transport phenomena in metal-oxide-semiconductor (MOS) structures having silicon nanocrystals (Si-NCs) inside the dielectric layer have been investigated, in dark condition and under visible illumination. At first, using deep-level transient spectroscopy (DLTS), we find the presence of series electron traps having very close energy levels (comprised between 0.28 and 0.45 eV) for ours devices (with/without Si-NCs). And a single peak appears at low temperature only for MOS with Si-NCs related to Si-NCs DLTS response. In dark condition, the conduction mechanism is dominated by the thermionic fast emission/capture of charge carriers from the highly doped polysilicon layer to Si-substrate through interface trap states for MOS without Si-NCs. The tunneling of charge carriers from highly poly-Si to Si substrate trough the trapping/detrapping mechanism in the Si-NCs, at low temperature, contributed to the conduction mechanism for MOS with Si-NCs. The light effect on transport mechanisms has been investigated using current-voltage ( I- V), and high frequency capacitance-voltage ( C- V) methods. We have been marked the photoactive trap effect in inversion zone at room temperature in I- V characteristics, which confirm the contribution of photo-generated charge on the transport mechanisms from highly poly-Si to Si substrate trough the photo-trapping/detrapping mechanism in the Si-NCs and interfaces traps levels. These results have been confirmed by an increasing about 10 pF in capacity's values for the C- V characteristics of MOS with Si-NCs, in the inversion region for inverse high voltage applied under photoexcitation at low temperature. These results are helpful to understand the principle of charge transport in dark condition and under illumination, of MOS structures having Si-NCs in the SiO x = 1.5 oxide matrix.

  16. Experimental characterization of the dominant multiple nodes charge collection mechanism in metal oxide-semiconductor transistors

    Science.gov (United States)

    Song, Ruiqiang; Chen, Shuming; Chi, Yaqing; Wu, Zhenyu; Liang, Bin; Chen, Jianjun; Xu, Jingyan; Hao, Peipei; Yu, Junting

    2017-06-01

    We propose an experimental method to investigate the dominant multiple node charge collection mechanism. A transistor array-based test structure is used to distinguish charge collection owing to the drift-diffusion and parasitic bipolar amplification effect. Heavy ion experimental results confirm that drift-diffusion dominates multiple node charge collection at low linear energy transfer (LET). However, the parasitic bipolar amplification effect dominates it at high LET. We also propose simple equations to determine the critical LET which may change the dominant multiple node charge collection mechanism. The calculated LET value is consistent with the heavy ion experimental results.

  17. Experimental study on mechanical behavior of fiber/matrix interface in metal matrix composite

    International Nuclear Information System (INIS)

    Wang, Q.; Chiang, F.P.

    1994-01-01

    The technique SIEM(Speckle Interferometry with Electron Microscopy) was employed to quantitatively measure the deformation on the fiber/matrix interface in SCS-6/Ti-6-4 composite at a microscale level. The displacement field within the fiber/matrix interphase zone was determined by in-situ observation with sensitivity of 0.003(microm). The macro-mechanical properties were compared with micro-mechanical behavior. It is shown that the strength in the interphase zone is weaker than the matrix tensile strength. The deformation process can be characterized by the uniform deformation, interface strain concentration and debond, and matrix plastic deformation

  18. Microstructure and High Temperature Mechanical Property of Fe-Cr-B Based Metal/Ceramic Composite Manufactured by Metal Injection Molding Process

    Science.gov (United States)

    Lee, Kee-Ahn; Gwon, Jin-Han; Yoon, Tae-Sik

    2018-02-01

    This study investigated the microstructure and the room and high temperature mechanical properties of Fe-Cr-B alloy manufactured by metal injection molding. In addition, hot isostatic pressing was performed to increase the density of the material, and a comparison of properties was made. Microstructural observation confirmed a bi-continuous structure composed of a three-dimensional network of α-Fe phase and (Cr,Fe)2B phase. The HIPed specimen featured a well-formed adhesion between the α-Fe phase and boride, and the number of fine pores was significantly reduced. The tensile results confirmed that the HIPed specimen (RT to 900 °C) had higher strengths compared to the as-sintered specimen, and the change of elongation starting from 700 °C was significantly greater in the HIPed specimen. Fractography suggested that cracks propagated mostly along the interface between the α-Fe matrix and boride in the as-sintered specimen, while direct fracture of boride was observed in addition to interface separation in the HIPed specimen.

  19. Microstructure and High Temperature Mechanical Property of Fe-Cr-B Based Metal/Ceramic Composite Manufactured by Metal Injection Molding Process

    Science.gov (United States)

    Lee, Kee-Ahn; Gwon, Jin-Han; Yoon, Tae-Sik

    2018-03-01

    This study investigated the microstructure and the room and high temperature mechanical properties of Fe-Cr-B alloy manufactured by metal injection molding. In addition, hot isostatic pressing was performed to increase the density of the material, and a comparison of properties was made. Microstructural observation confirmed a bi-continuous structure composed of a three-dimensional network of α-Fe phase and (Cr,Fe)2B phase. The HIPed specimen featured a well-formed adhesion between the α-Fe phase and boride, and the number of fine pores was significantly reduced. The tensile results confirmed that the HIPed specimen (RT to 900 °C) had higher strengths compared to the as-sintered specimen, and the change of elongation starting from 700 °C was significantly greater in the HIPed specimen. Fractography suggested that cracks propagated mostly along the interface between the α-Fe matrix and boride in the as-sintered specimen, while direct fracture of boride was observed in addition to interface separation in the HIPed specimen.

  20. Effect of central metal ions of analogous metal-organic frameworks on adsorption of organoarsenic compounds from water: plausible mechanism of adsorption and water purification.

    Science.gov (United States)

    Jun, Jong Won; Tong, Minman; Jung, Beom K; Hasan, Zubair; Zhong, Chongli; Jhung, Sung Hwa

    2015-01-02

    The adsorptive removal of organoarsenic compounds such as p-arsanilic acid (ASA) and roxarsone (ROX) from water using metal-organic frameworks (MOFs) has been investigated for the first time. A MOF, iron benzenetricarboxylate (also called MIL-100-Fe) exhibits a much higher adsorption capacity for ASA and ROX than activated carbon, zeolite (HY), goethite, and other MOFs. The adsorption of ASA and ROX over MIL-100-Fe is also much more rapid than that over activated carbon. Moreover, the used MIL-100-Fe can be recycled by simply washing with acidic ethanol. Therefore, it is determined that a MOF such as MIL-100-Fe can be used to remove organoarsenic compounds from contaminated water because of its high adsorption capacity, rapid adsorption, and ready regeneration. Moreover, only one of three analogous MIL-100 species (MIL-100-Fe, rather than MIL-100-Al or MIL-100-Cr) can effectively remove the organoarsenic compounds. This selective and high adsorption over MIL-100-Fe, different from other analogous MIL-100 species, can be explained (through calculations) by the facile desorption of water from MIL-100-Fe as well as the large (absolute value) replacement energy (difference between the adsorption energies of the organoarsenic compounds and water) exhibited by MIL-100-Fe. A plausible adsorption/desorption mechanism is proposed based on the surface charge of the MOFs, FTIR results, calculations, and the reactivation results with respect to the solvents used in the experiments. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  1. Observation of a New Mechanism Balancing Hardening and Softening in Metals

    DEFF Research Database (Denmark)

    Yu, Tianbo; Hansen, Niels; Huang, Xiaoxu

    2014-01-01

    connected by triple junctions. Here, we report that mechanically assisted triple junction motion is an important contributor to dynamic recovery, leading to an almost steady state. Triple junction motion replaces two boundaries by one, while maintaining the structural morphology. The observation...

  2. MECHANICAL PERFORMANCE OF METAL-CERAMIC INTERFACES PRODUCED BY LASER PROCESSING

    NARCIS (Netherlands)

    van den Burg, M.; de Hosson, J.T.M.

    1995-01-01

    This paper concentrates on the mechanical performance of various ceramic coatings of Cr2O3 on Steel (SAF2205), as produced by CO2 laser processing. The thickness of the coating that can be applied by laser coating is limited to about 200 mu m setting a limit to the maximum strain energy release rate

  3. Mechanical Properties and Microstructural Characterization of Aged Nickel-based Alloy 625 Weld Metal

    Science.gov (United States)

    Silva, Cleiton Carvalho; de Albuquerque, Victor Hugo C.; Miná, Emerson Mendonça; Moura, Elineudo P.; Tavares, João Manuel R. S.

    2018-03-01

    The aim of this work was to evaluate the different phases formed during solidification and after thermal aging of the as-welded 625 nickel-based alloy, as well as the influence of microstructural changes on the mechanical properties. The experiments addressed aging temperatures of 650 and 950 °C for 10, 100, and 200 hours. The samples were analyzed by electron microscopy, microanalysis, and X-ray diffraction in order to identify the secondary phases. Mechanical tests such as hardness, microhardness, and Charpy-V impact test were performed. Nondestructive ultrasonic inspection was also conducted to correlate the acquired signals with mechanical and microstructural properties. The results show that the alloy under study experienced microstructural changes when aged at 650 °C. The aging was responsible by the dissolution of the Laves phase formed during the solidification and the appearance of γ″ phase within interdendritic region and fine carbides along the solidification grain boundaries. However, when it was aged at 950 °C, the Laves phase was continuously dissolved and the excess Nb caused the precipitation of the δ-phase (Ni3Nb), which was intensified at 10 hours of aging, with subsequent dissolution for longer periods such as 200 hours. Even when subjected to significant microstructural changes, the mechanical properties, especially toughness, were not sensitive to the dissolution and/or precipitation of the secondary phases.

  4. Public Sector and Europeanization Challenges

    Directory of Open Access Journals (Sweden)

    Lucica Matei

    2006-04-01

    Full Text Available The paper emphasises the role of the market-type mechanisms within the activity of the organisations from the public sector. The end of the 20th century was defined by the effects of the public sector reform. The public sector is placed within the cultural and political environment of each country and the reforms have aimed to redefine the structures of the state organisations in the economy and the relationships such as market-government, government-bureaucracy, government- citizens, bureaucracy-citizens, civil servants-politicians-citizens. The public sector reform, achieved at the managerial systems, organisational structures and regulations levels is accompanied by specific and structural reforms. Accepting the market-type mechanisms instead of bureaucratic mechanisms, meaning not the simple provision of public services but the creation of some governmental “actors”, functioning completely on commercial bases, supporting the development of the partnerships between the public and private sector, introducing privatisation is achieved in view of creating “the facilitating state”. We discuss about “facilities” such as citizens and society involvement in public businesses, making public administration more citizen-friendly and the state closer to the public need. The citizens’ involvement, as customers in the flow of the public service contributes to creating an organic ensemble characterised by two fundamental dimensions: level and type of influence of the customers and the private-public dichotomy. Synthesising, the relationships and market mechanisms enable to the public sector to get closer to the public needs and to create a modern administration based on efficiency, effectiveness and openness towards change.

  5. Large scale simulations of the mechanical properties of layered transition metal ternary compounds for fossil energy power system applications

    Energy Technology Data Exchange (ETDEWEB)

    Ching, Wai-Yim [Univ. of Missouri, Kansas City, MO (United States)

    2014-12-31

    Advanced materials with applications in extreme conditions such as high temperature, high pressure, and corrosive environments play a critical role in the development of new technologies to significantly improve the performance of different types of power plants. Materials that are currently employed in fossil energy conversion systems are typically the Ni-based alloys and stainless steels that have already reached their ultimate performance limits. Incremental improvements are unlikely to meet the more stringent requirements aimed at increased efficiency and reduce risks while addressing environmental concerns and keeping costs low. Computational studies can lead the way in the search for novel materials or for significant improvements in existing materials that can meet such requirements. Detailed computational studies with sufficient predictive power can provide an atomistic level understanding of the key characteristics that lead to desirable properties. This project focuses on the comprehensive study of a new class of materials called MAX phases, or Mn+1AXn (M = a transition metal, A = Al or other group III, IV, and V elements, X = C or N). The MAX phases are layered transition metal carbides or nitrides with a rare combination of metallic and ceramic properties. Due to their unique structural arrangements and special types of bonding, these thermodynamically stable alloys possess some of the most outstanding properties. We used a genomic approach in screening a large number of potential MAX phases and established a database for 665 viable MAX compounds on the structure, mechanical and electronic properties and investigated the correlations between them. This database if then used as a tool for materials informatics for further exploration of this class of intermetallic compounds.

  6. Fracture-mechanical analysis of metal/ceramic composites for applications in high-temperature fuel cells (SOFC); Bruchmechanische Untersuchung von Metall/Keramik-Verbunsystemen fuer die Anwendung in der Hochtemperaturbrennstoffzelle (SOFC)

    Energy Technology Data Exchange (ETDEWEB)

    Kuhn, Bernd Josef

    2008-08-25

    The author investigated the deformation and damage behaviour of soldered ceramic/metal joints in SOFC stacks, using thermochemical methods. Methods for analyzing sandwich systems and for mechanical characterization of joints were adapted and modified in order to provide fundamental understanding of the mechanical properties of soldered joints. [German] In dieser Arbeit wurde das Verformungs- und Schaedigungsverhalten von Keramik/ Metall-Loetverbindungen fuer SOFC-Stacks thermomechanisch untersucht. Verfahren zur Analyse von Schichtsystemen und fuer die mechanische Charakterisierung von Fuegeverbindungen wurden adaptiert und weiterentwickelt, um zu einem grundlegenden Verstaendnis der mechanischen Eigenschaften von Loetverbindungen zu gelangen.

  7. End Uses Mechanical Properties Settled By The Modified Sintering Conditions Of The Metal Injection Molding Process

    International Nuclear Information System (INIS)

    Marray, Tarek; Jaccquet, Philippe; Moinard-Checot, Delphine; Fabre, Agnes; Barrallier, Laurent

    2011-01-01

    Most common mechanical applications require parts with specific properties as hard faced features. It is well known that treating parts under suitable atmospheres may improve hardness and strength yield of steels. Heat treatment process and more particularly thermo-chemical diffusion processes (such as carburizing or its variation: carbonitriding) can be performed to reach the industrial hardness profile requirements. In this work, a low-alloyed steel feedstock based on water soluble binder system is submitted to the MIM process steps (including injection molding, debinding and sintering). As-sintered parts are then treated under a low pressure carbonitriding treatment. This contribution focuses on preliminary results such as microstructural analyses and mechanical properties which are established at each stage of the process to determine and monitor changes.

  8. Characterization of a metallic mechanical standard junction for a specific nuclear application

    International Nuclear Information System (INIS)

    Villanueva, Jose; Miller, Marcelo E.; Vazquez, Luis; Halpert, Silvia

    2007-01-01

    A testing procedure, targeted to promote that an industrial standard component can be used in a nuclear particular application, is designed and applied. Namely, a mechanical standard junction component, that is widely recognized for its industrial reliability, is commonly used to fit two stainless steel tubes, is intended to be used in a particular nuclear application fitting a stainless steel tube to a Zircaloy-4 tube counterpart. The junction will be subjected to pressure and temperature typical of primary circuit coolant in a nuclear power plant. The results found once the test was applied (catastrophic fault and significant water leakage absence) allow to advice using this mechanical junction device as a valid nuclear design option fitting the proposed tubes. (author) [es

  9. Work hardening and mechanical equation of state in some metals in monotonic loading

    International Nuclear Information System (INIS)

    Wire, G.L.; Ellis, F.V.; Li, C.Y.

    The work hardening coefficients of Type 316 stainless steel, niobium, and 1100 aluminum alloy are measured in tensile tests. It is demonstrated experimentally that in the measured stress, plastic strain rate, and temperature range the work hardening coefficient depends only on stress and plastic strain rate. The significance of the experimental results is discussed in terms of the concept of the mechanical equation of state for plastic deformation. 13 figures

  10. Shock loads induced on metal structures by LHC proton beams: modelling of thermo-mechanical effects

    CERN Document Server

    Peroni, L; Dallocchio, A; Bertarelli, A

    2011-01-01

    In this work, the numerical simulations of the LHC high energy particle beam impact against a metal structure are performed using the commercial FEM code LS-DYNA. The evaluation of thermal loads on the hit material is performed using a statistical code, called FLUKA, based on the Monte-Carlo method, which returns an energy map on a particular geometry (taking into account all the particles in the cascade generated by the interaction between the proton beam and the target). The FLUKA results are then used as input for thermo-structural studies. The first step of this work is the validation of the numerical procedure on a simple geometry for two different materials (copper and tungsten) and constitutive material models. In particular, the high energy particle impact is examined on a facially irradiated cylindrical bar: the beam hits the component directly on the centre of the basis. Then the final step is the study of the impact on a real structure with an energy beam of 5 TeV (the next target in the energy val...

  11. Local structural mechanism for frozen-in dynamics in metallic glasses

    Science.gov (United States)

    Liu, X. J.; Wang, S. D.; Wang, H.; Wu, Y.; Liu, C. T.; Li, M.; Lu, Z. P.

    2018-04-01

    The nature of the glass transition is a fundamental and long-standing intriguing issue in the condensed-matter physics and materials science community. In particular, the structural response by which a liquid is arrested dynamically to form a glass or amorphous solid upon approaching its freezing temperature [the glass transition temperature (Tg)] remains unclear. Various structural scenarios in terms of the percolation theory have been proposed recently to understand such a phenomenon; however, there is still no consensus on what the general percolation entity is and how the entity responds to the sudden slowdown dynamics during the glass transition. In this paper, we demonstrate that one-dimensional local linear ordering (LLO) is a universal structural motif associated with the glass transition for various metallic glasses. The quantitative evolution of LLO with temperature indicates that a percolating LLO network forms to serve as the backbone of the rigid glass solid when the temperature approaches the freezing point, resulting in the frozen-in dynamics accompanying the glass transition. The percolation transition occurs by pinning different LLO networks together, which only needs the introduction of a small number of "joint" atoms between them, and therefore the energy expenditure is very low.

  12. Atomistic simulation study of the shear-band deformation mechanism in Mg-Cu metallic glasses

    DEFF Research Database (Denmark)

    Bailey, Nicholas; Schiøtz, Jakob; Jacobsen, Karsten Wedel

    2006-01-01

    We have simulated plastic deformation of a model Mg-Cu metallic glass in order to study shear banding. In uniaxial tension, we find a necking instability occurs rather than shear banding. We can force the latter to occur by deforming in plane strain, forbidding the change of length in one...... of the transverse directions. Furthermore, in most of the simulations a notch is used to initiate shear bands, which lie at a 45 degrees angle to the tensile loading direction. The shear bands are characterized by the Falk and Langer local measure of plastic deformation D-min(2), averaged here over volumes...... containing many atoms. The D-min(2) profile has a peak whose width is around 10 nm; this width is largely independent of the strain rate. Most of the simulations were, at least nominally, at 100 K, about T-g/3 for this system. The development of the shear bands takes a few tens of ps, once plastic flow has...

  13. Elucidating the mechanism responsible for anomalous thermal expansion in a metal-organic framework.

    Science.gov (United States)

    van Heerden, Dewald P; Esterhuysen, Catharine; Barbour, Leonard J

    2016-03-14

    The previously reported anisotropic thermal expansion of a three-dimensional metal-organic framework (MOF) is examined by means of theoretical calculations. Inspection of the 100, 190, 280 and 370 K single crystal X-ray diffraction (SCD) structures indicated a concerted change in the coordination sphere of the zinc centre leading to elongation of the coordination helix in the crystallographic c direction (the Zn-O(H)-Zn angle expands), while the largely unaltered ligands (the ZnLZn distance remains constant) are pulled closer together in the ab plane. This study develops and evaluates a mechanistic model at the DFT level of theory that reproduces the convergent expansion of the coordination helix of the material. The linear increase in energy calculated for extension of a model consisting of six zinc centres and truncated ligands compares favourably with results obtained from a periodic DFT evaluation of the SCD structures. It was also found that the anisotropic thermal expansion trend could be reproduced qualitatively by Molecular Dynamics (MD) simulations in the NPT ensemble.

  14. Microstructure and Mechanical Properties of Accumulative Roll-Bonded AA1050A/AA5005 Laminated Metal Composites

    Directory of Open Access Journals (Sweden)

    Frank Kümmel

    2016-03-01

    Full Text Available Laminated metal composites (LMCs with alternating layers of commercial pure aluminum AA1050A and aluminum alloy AA5005 were produced by accumulative roll-bonding (ARB. In order to vary the layer thickness and the number of layer interfaces, different numbers of ARB cycles (4, 8, 10, 12, 14 and 16 were performed. The microstructure and mechanical properties were characterized in detail. Up to 8 ARB cycles, the ultrafine-grained (UFG microstructure of the layers in the LMC evolves almost equally to those in AA1050A and AA5005 mono-material sheets. However, the grain size in the composites tends to have smaller values. Nevertheless, the local mechanical properties of the individual layers in the LMCs are very similar to those of the mono-material sheets, and the macroscopic static mechanical properties of the LMCs can be calculated as the mean value of the mono-material sheets applying a linear rule of mixture. In contrast, for more than 12 ARB cycles, a homogenous microstructure was obtained where the individual layers within the composite cannot be visually separated any longer; thus, the hardness is at one constant and a high level across the whole sheet thickness. This results also in a significant higher strength in tensile testing. It was revealed that, with decreasing layer thickness, the layer interfaces become more and more dominating.

  15. Removal of hazardous organics from water using metal-organic frameworks (MOFs): plausible mechanisms for selective adsorptions.

    Science.gov (United States)

    Hasan, Zubair; Jhung, Sung Hwa

    2015-01-01

    Provision of clean water is one of the most important issues worldwide because of continuing economic development and the steady increase in the global population. However, clean water resources are decreasing everyday, because of contamination with various pollutants including organic chemicals. Pharmaceutical and personal care products, herbicides/pesticides, dyes, phenolics, and aromatics (from sources such as spilled oil) are typical organics that should be removed from water. Because of their huge porosities, designable pore structures, and facile modification, metal-organic frameworks (MOFs) are used in various adsorption, separation, storage, and delivery applications. In this review, the adsorptive purifications of contaminated water with MOFs are discussed, in order to understand possible applications of MOFs in clean water provision. More importantly, plausible adsorption or interaction mechanisms and selective adsorptions are summarized. The mechanisms of interactions such as electrostatic interaction, acid-base interaction, hydrogen bonding, π-π stacking/interaction, and hydrophobic interaction are discussed for the selective adsorption of organics over MOFs. The adsorption mechanisms will be very helpful not only for understanding adsorptions but also for applications of adsorptions in selective removal, storage, delivery and so on. Copyright © 2014 Elsevier B.V. All rights reserved.

  16. A study of long-term static load on degradation and mechanical integrity of Mg alloys-based biodegradable metals.

    Science.gov (United States)

    Koo, Youngmi; Jang, Yongseok; Yun, Yeoheung

    2017-05-01

    Predicting degradation behavior of biodegradable metals in vivo is crucial for the clinical success of medical devices. This paper reports on the effect of long-term static stress on degradation of magnesium alloys and further changes in mechanical integrity. AZ31B (H24) and ZE41A (T5) alloys were tested to evaluate stress corrosion cracking (SCC) in a physiological solution for 30 days and 90 days (ASTM G39 testing standard). Scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDX) and micro-computed tomography (micro-CT) were used to characterize surface morphology and micro-structure of degraded alloys. The results show the different mechanisms of stress corrosion cracking for AZ31B (transgranular stress corrosion cracking, TGSCC) and ZE41A (intergranular stress corrosion cracking, IGSCC). AZ31B was more susceptible to stress corrosion cracking under a long term static load than ZE41A. In conclusion, we observed that long-term static loading accelerated crack propagation, leading to the loss of mechanical integrity.

  17. Prehistory effects on the VHCF behaviour of engineering metallic materials with different strengthening mechanisms

    Energy Technology Data Exchange (ETDEWEB)

    Zimmermann, M; Stoecker, C; Mueller-Bollenhagen, C; Christ, H-J, E-mail: martina.zimmermann@uni-siegen.d [Institut fuer Werkstofftechnik, Universitaet Siegen, D-57068 Siegen (Germany)

    2010-07-01

    Engineering materials often undergo a plastic deformation during manufacturing, hence the effect of a predeformation on the subsequent fatigue behaviour has to be considered. The effect of a prestrain on the microstructure is strongly influenced by the strengthening mechanism. Different mechanisms are relevant in the materials applied in this study: a solid-solution hardened and a precipitation-hardened nickel-base alloy and a martensite-forming metastable austenitic steel. Prehistory effects become very important, when fatigue failure at very high number of cycles (N > 10{sup 7}) is considered, since damage mechanisms occur different to those observed in the range of conventional fatigue limit. With the global strain amplitude being well below the static elastic limit, only inhomogeneously distributed local plastic deformation takes place in the very high cycle fatigue (VHCF) region. The dislocation motion during cyclic loading thus depends on the effective flow stress, which is defined by the global cyclic stress-strain relation and the local stress distribution as a consequence of the interaction between dislocations and precipitates, grain boundaries, martensite phases and micro-notches. As a consequence, no significant prehistory effect was observed for the VHCF behaviour of the solid-solution hardening alloy, while the precipitation-hardening alloy shows a perceptible prehistory dependence. In the case of the austenitic steel, strain-hardening and the volume fraction of the deformation-induced martensite dominate the fatigue behaviour.

  18. High-throughput exploration of thermoelectric and mechanical properties of amorphous NbO2 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.

  19. High-throughput exploration of thermoelectric and mechanical properties of amorphous NbO2 with transition metal additions

    Science.gov (United States)

    Music, Denis; Geyer, Richard W.; Hans, Marcus

    2016-07-01

    To increase the thermoelectric efficiency and reduce the thermal fatigue upon cyclic heat loading, alloying of amorphous NbO2 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.