The stability of gabion walls for earth retaining structures

Directory of Open Access Journals (Sweden)

Mahyuddin Ramli

2013-12-01

Full Text Available The stability of earth retaining structures in flood prone areas has become a serious problem in many countries. The two most basic causes of failure arising from flooding are scouring and erosion of the foundation of the superstructure. Hence, a number of structures like bridges employ scour-arresting devices, e.g., gabions to acting on the piers and abutments during flooding. Research was therefore undertaken to improve gabion resistance against lateral movement by means of an interlocking configuration instead of the conventional stack-and-pair system. This involved simulating lateral thrusts against two dimensionally identical retaining wall systems configured according to the rectangular and hexagonal gabion type. The evolution of deformation observed suggested that the interlocking design exhibits better structural integrity than the conventional box gabion-based wall in resisting lateral movement and therefore warrants consideration for use as an appropriate scour-arresting device for earth retaining structures.

Stability Analysis Of Earth Dam Slopes Subjected To Earthquake Using ERT Results Interpretation

Directory of Open Access Journals (Sweden)

Eko Andi Suryo

2018-01-01

Full Text Available Earth Dam stability can be affected significantly by the existence of excessive leakage. This is due to decreasing of shear strength of the dam material and additional overturning moment. In such scenario, the non-destructive soil investigation method is needed to analyze the stability of earth dam in current condition. This paper examines the use of Electrical Resistivity Tomography (ERT to investigate soil layers and to measure parameters of soil shear strength indirectly. First survey was carried out at dam crest and downstream using Wenner Configuration along profile lines at electrode spacing of 5 m. There were 5 profile lines of 180m long each and 10m distance of spacing. Furthermore, two profiles lines at weak cross-section based on its resistivity soil values were undertaken. Laboratory tests were conducted to determine relationship between resistivity value, moisture content, cohesion and angle of friction for each type of dam materials. From the ERT results and lab testing, a model dam can be obtained using current material parameters to perform stability analysis of dam subjected to earthquake. The lowest FOS was found at the upstream side about 1.15 and at the downstream side about 1.14 after applying seismic load of 100 years return period. Keywords: Stability Analysis, ERT,resistivity, leakage, dam

Effect of the addition of Na2O on the thermal stability of alumino silicated glasses rich in rare earths

International Nuclear Information System (INIS)

Lassalle-Herraud, Olivier; Matecki, Marc; Glorieux, Benoit; Sadiki, Najim; Montoullout, Valerie; Dussossoy, Jean-Luc

2006-01-01

Alumino silicated glasses rich in rare earths have been prepared by concentrated solar way. Their recrystallization, the structural and microstructural properties as well as the mechanical and thermal properties of these glasses have been studied. The results show the effect of sodium addition on the thermal stability of the materials, the vitreous transition temperature and the recrystallization temperature. A heat treatment has allowed to reveal the formation of sodium apatite micro-crystallites and of lanthanum silicate in the glasses. (O.M.)

Assessment on the mechanical stability of underground excavations

International Nuclear Information System (INIS)

Kuroki, Shigemori; Taniguchi, Wataru; Sugino, Hiroyuki; Koo, Shigeru; Hasegawa, Hiroshi; Kubota, Shigeru; Dewa, Katsuyuki

1999-11-01

It is planned to construct the tunnels and emplace waste packages at several hundred meters to 1,000 meters under the ground for the repository of high-level radioactive waste based on a policy to assure the safe life environment. It is required to be mechanically stable for the tunnels to assure the work safety throughout the construction, operation and closure phase. In this report, the mechanical stability of tunnels, that is a factor of design requisites, was evaluated by the analyses to present an outline of the technical reliability of geological disposal. To put it concretely, the tunnel sections were determined to have the required areas and shapes, and the analyses on the mechanical stability at tunnel excavations and earthquake, at tunnel intersections were conducted by the theoretical analysis and finite element method. The results obtained by these investigations are shown below: It will be able to construct the tunnels with present techniques. The mechanical stability of tunnels will be assured if proper supports are given, and adequate tunnel spacing and disposal-pit pitches are set. The mechanical stability will be assured at the tunnel intersections if proper reinforcement measures are taken. The reinforcement will be required for the intersection areas over the distance of 1D (D: diameter of tunnels) on the obtuse angle side, and 4D on the acute angle side, when intersection angle is set at 30 degrees. The investigations were conducted on the assumption that the experienced big earthquake occurred. The results show that the effect of earthquake on the mechanical stability of tunnels is small, and tunnels are stable at the earthquake when the mechanical stability at tunnel excavations is assured. (author)

On the mechanical vibrator-earth contact geometry and its dynamics

NARCIS (Netherlands)

Noorlandt, R.P.; Drijkoningen, G.G.

2016-01-01

The geometry of the contact between a vibrator and the earth underneath influences the dynamics of the vibrator. Although a vibrator might appear to be well-coupled with the earth on a macroscale, perfect coupling certainly does not occur on the microscale. With the aid of contact mechanical

The dynamic stability of OPEC's oil price mechanism

International Nuclear Information System (INIS)

Hammoudeh, S.; Madan, V.

1992-01-01

This paper examines OPEC's long-lived mechanism which targets the oil price and adjusts the quality ceiling to meet the target. The stability of this controversial mechanism is compared to that of two alternatives: one requires quantity control without any price targeting and the other is a synthesis of quantity control and the OPEC mechanisms. All three mechanisms passed the stability test and the two alternatives give rise to some interesting policy implications. Practicality considerations which involve the availability of specific information make OPEC's mechanism the most appropriate in terms of achieved targeted revenues. The paper also offers a convergence strategy that speeds up the achievement of targeted revenues under OPEC's current mechanism. (author)

Thermal Stability and Proton Conductivity of Rare Earth Orthophosphate Hydrates

DEFF Research Database (Denmark)

Anfimova, Tatiana; Li, Qingfeng; Jensen, Jens Oluf

2014-01-01

as the rhabdophane structure is preserved. The bound hydrate water is accommodated in the rhabdophane structure and is stable at temperatures of up to 650 oC. The thermal stability of the hydrate water and the phosphate structure are of significance for the proton conductivity. The LaPO4·0.6H2O and NdPO4•0.5H2O......Hydrated orthophosphate powders of three rare earth metals, lanthanum, neodymium and gadolinium, were prepared and studied as potential proton conducting materials for intermediate temperature electrochemical applications. The phosphates undergo a transformation from the rhabdophane structure...... to the monazite structure upon dehydration. The thermal stability of the hydrate is studied and found to contain water of two types, physically adsorbed and structurally bound hydrate water. The adsorbed water is correlated to the specific surface area and can be reversibly recovered when dehydrated as long...

On a stabilization mechanism for low-velocity detonations

KAUST Repository

Sow, Aliou; Semenko, Roman E.; Kasimov, Aslan R.

2017-01-01

We use numerical simulations of the reactive Lula equations to analyse the nonlinear stability of steady-state one-dimensional solutions for gaseous detonations in the presence of both momentum and heat losses. Our results point to a possible stabilization mechanism for the low-velocity detonations in such systems. The mechanism stems from the existence of a one-parameter family of solutions found in Semenko el al.

On a stabilization mechanism for low-velocity detonations

KAUST Repository

Sow, Aliou

2017-03-08

We use numerical simulations of the reactive Lula equations to analyse the nonlinear stability of steady-state one-dimensional solutions for gaseous detonations in the presence of both momentum and heat losses. Our results point to a possible stabilization mechanism for the low-velocity detonations in such systems. The mechanism stems from the existence of a one-parameter family of solutions found in Semenko el al.

Solar radiation pressure application for orbital motion stabilization near the Sun-Earth collinear libration point

Science.gov (United States)

Polyakhova, Elena; Shmyrov, Alexander; Shmyrov, Vasily

2018-05-01

Orbital maneuvering in a neighborhood of the collinear libration point L1 of Sun-Earth system has specific properties, primarily associated with the instability L1. For a long stay in this area of space the stabilization problem of orbital motion requires a solution. Numerical experiments have shown that for stabilization of motion it is requires very small control influence in comparison with the gravitational forces. On the other hand, the stabilization time is quite long - months, and possibly years. This makes it highly desirable to use solar pressure forces. In this paper we illustrate the solar sail possibilities for solving of stabilization problem in a neighborhood L1 with use of the model example.

Stability and equilibrium in quantum statistical mechanics

International Nuclear Information System (INIS)

Kastler, Daniel.

1975-01-01

A derivation of the Gibbs Ansatz, base of the equilibrium statistical mechanics is provided from a stability requirements, in technical connection with the harmonic analysis of non-commutative dynamical systems. By the same token a relation is established between stability and the positivity of Hamiltonian in the zero temperature case [fr

Structures, stabilities, and electronic properties for rare-earth lanthanum doped gold clusters

International Nuclear Information System (INIS)

Zhao, Ya-Ru

2015-01-01

The structures, stabilities, and electronic properties of rare-earth lanthanum doped gold La 2 Au n (n = 1-9) and pure gold Au n (n ≤ 11) clusters have been investigated by using density functional theory. The optimized geometries show that the lowest energy structures of La 2 Au n clusters favour the 3D structure at n ≥ 3. The lanthanum atoms can strongly enhance the stabilities of gold clusters and tend to occupy the most highly coordinated position. By analysing the gap, vertical ionization potential, and chemical hardness, it is found that the La 2 Au 6 isomer possesses higher stability for small-sized La 2 Au n clusters (n = 1-9). The charges in the La 2 Au n clusters transfer from La atoms to the Au n host. In addition, Wiberg bond indices analysis reveals that the intensity of different bonds of La 2 Au n clusters exhibits a sequence of La-La bond > La-Au bond > Au-Au bond.

C-5 Propynyl Modifications Enhance the Mechanical Stability of DNA.

Science.gov (United States)

Aschenbrenner, Daniela; Baumann, Fabian; Milles, Lukas F; Pippig, Diana A; Gaub, Hermann E

2015-07-20

Increased thermal or mechanical stability of DNA duplexes is desired for many applications in nanotechnology or -medicine where DNA is used as a programmable building block. Modifications of pyrimidine bases are known to enhance thermal stability and have the advantage of standard base-pairing and easy integration during chemical DNA synthesis. Through single-molecule force spectroscopy experiments with atomic force microscopy and the molecular force assay we investigated the effect of pyrimidines harboring C-5 propynyl modifications on the mechanical stability of double-stranded DNA. Utilizing these complementary techniques, we show that propynyl bases significantly increase the mechanical stability if the DNA is annealed at high temperature. In contrast, modified DNA complexes formed at room temperature and short incubation times display the same stability as non-modified DNA duplexes. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Stabilization and Degradation Mechanisms of Cytoplasmic Ataxin-1

Directory of Open Access Journals (Sweden)

Mayumi F. Kohiyama

2015-01-01

Full Text Available Aggregation-prone proteins in neurodegenerative disease disrupt cellular protein stabilization and degradation pathways. The neurodegenerative disease spinocerebellar ataxia type 1 (SCA1 is caused by a coding polyglutamine expansion in the Ataxin-1 gene ( ATXN1 , which gives rise to the aggregation-prone mutant form of ATXN1 protein. Cerebellar Purkinje neurons, preferentially vulnerable in SCA1, produce ATXN1 protein in both cytoplasmic and nuclear compartments. Cytoplasmic stabilization of ATXN1 by phosphorylation and 14-3-3-mediated mechanisms ultimately drive translocation of the protein to the nucleus where aggregation may occur. However, experimental inhibition of phosphorylation and 14-3-3 binding results in rapid degradation of ATXN1, thus preventing nuclear translocation and cellular toxicity. The exact mechanism of cytoplasmic ATXN1 degradation is currently unknown; further investigation of degradation may provide future therapeutic targets. This review examines the present understanding of cytoplasmic ATXN1 stabilization and potential degradation mechanisms during normal and pathogenic states.

Stability and degradation mechanisms in organic solar cells

Energy Technology Data Exchange (ETDEWEB)

Ecker, Bernhard

2012-04-26

This thesis deals with stability improvements and the investigation of degradation mechanisms in organic solar cells. Organic solar cells have been in the focus of extensive academic research for over almost two decades and are currently entering the market in small scale applications. For successful large scale applications, next to the improvement of the power conversion efficiency, the stability of organic solar cells has to be increased. This thesis is dedicated to the investigation of novel materials and architectures to study stability-related issues and degradation mechanisms in order to contribute to the basic understanding of the working principles of organic solar cells. Here, impedance spectroscopy, a frequency domain technique, is used to gain information about stability and degradation mechanisms in organic solar cells. In combination with systematic variations in the preparation of solar cells, impedance spectroscopy gives the possibility to differentiate between interface and bulk dominated effects. Additionally, impedance spectroscopy gives access to the dielectric properties of the device, such as capacitance. This offers among other things the opportunity to probe the charge carrier concentration and the density of states. Another powerful way of evaluation is the combination of experimentally obtained impedance spectra with equivalent circuit modelling. The thesis presents results on novel materials and solar cell architectures for efficient hole and electron extraction. This indicates the importance of knowledge over interlayers and interfaces for improving both the efficiency and stability of organic solar cells.

Improving the mechanical stability of a standard capacitor

CSIR Research Space (South Africa)

Moodley, SS

2003-04-01

Full Text Available temperature coefficients of capacitance, they were susceptible to mechanical shock. During 1999, a project was initiated to improve the mechanical stability of the capacitors after two capacitors were damaged during transit, while being transported as separate...

Science 101: What Are the Earth's Heating and Cooling Mechanisms?

Science.gov (United States)

Robertson, Bill

2015-01-01

In this article, author Bill Robertson attempts to help readers understand some of the Earth's heating and cooling mechanisms and how they relate to global warming. Figures are provided to help facilitate learning.

The rock mechanical stability of the VLJ repository

International Nuclear Information System (INIS)

Kuula, H.; Johansson, E.

1991-03-01

The aim of the study was to determine the rock mechanical stability around the VLJ repository based on the rock mechanical monitoring and rock mechanical modeling. Rock mechanical calculations were made in order to calculate the rock mass displacements and to analyze the stability around the VLJ repository The calculations were performed with three diiferent methods: continuum finite difference code FLAC, distinct element code UDEC and three dimensional distinct element code 3DEC. The first analyses were based on preliminary site investigations. The final modeling was based on investigations and rock mechanical monitoring done during the excavation. Some sensitive analyses were also performed. The modelled rock mass behaviour and the measured behaviour are generally close to each other. Both results show that the VLJ repository is rock mechanically stable. The modelled displacements and stresses were small enough to cause no instability around the rock caverns. The measured values do not indicate any discontinuous deformations like block movements or joint slip. The measured displacements in the extensometers during excavation indicates that the rock mass is even stiffer than anticipated

Mechanical behavior of embankments overlying on loose subgrade stabilized by deep mixed columns

Directory of Open Access Journals (Sweden)

Morteza Esmaeili

2016-10-01

Full Text Available Deep mixed column (DMC is known as one of the effective methods for stabilizing the natural earth beneath road or railway embankments to control stability and settlements under traffic loads. The load distribution mechanism of embankment overlying on loose subgrades stabilized with DMCs considerably depends on the columns' mechanical and geometrical specifications. The present study uses the laboratory investigation to understand the behavior of embankments lying on loose sandy subgrade in three different conditions: (1 subgrade without reinforcement, (2 subgrade reinforced with DMCs in a triangular pattern and horizontal plan, and (3 subgrade reinforced with DMCs in a square pattern and horizontal plan. For this purpose, by adopting the scale factor of 1:10, a reference embankment with 20 cm height, 250 cm length, and 93% maximum dry density achieved in standard Proctor compaction test was constructed over a 70 cm thick loose sandy bed with the relative density of 50% in a loading chamber, and its load-displacement behavior was evaluated until the failure occurred. In the next two tests, DMCs (with 10 cm diameter, 40 cm length, and 25 cm center-to-center spacing were placed in groups in two different patterns (square and triangular in the same sandy bed beneath the embankment and, consequently, the embankments were constructed over the reinforced subgrades and gradually loaded until the failure happened. In all the three tests, the load-displacement behaviors of the embankment and the selected DMCs were instrumented for monitoring purpose. The obtained results implied 64% increase in failure load and 40% decrease in embankment crest settlement when using the square pattern of DMCs compared with those of the reference embankment, while these values were 63% and 12%, respectively, for DMCs in triangular pattern. This confirmed generally better performance of DMCs with a triangular pattern.

Corrosion-electrochemical and mechanical properties of aluminium-berylium alloys alloyed by rare-earth metals

International Nuclear Information System (INIS)

Safarov, A.M.; Odinaev, Kh.E.; Shukroev, M.Sh.; Saidov, R.Kh.

1997-01-01

In order to study influence of rare earth metals on corrosion-electrochemical and mechanical properties of aluminium-berylium alloys the alloys contain 1 mass % beryllium and different amount of rare earth metals were obtained.-electrochemical and mechanical properties of aluminium-berylium alloys. The electrochemical characteristics of obtained alloys, including stationary potential, potentials of passivation beginning and full passivation, potentials of pitting formation and re passivation were defined.

Mechanical properties of silicate glasses exposed to a low-Earth orbit

Science.gov (United States)

Wiedlocher, David E.; Tucker, Dennis S.; Nichols, Ron; Kinser, Donald L.

1992-01-01

The effects of a 5.8 year exposure to low earth orbit environment upon the mechanical properties of commercial optical fused silica, low iron soda-lime-silica, Pyrex 7740, Vycor 7913, BK-7, and the glass ceramic Zerodur were examined. Mechanical testing employed the ASTM-F-394 piston on 3-ball method in a liquid nitrogen environment. Samples were exposed on the Long Duration Exposure Facility (LDEF) in two locations. Impacts were observed on all specimens except Vycor. Weibull analysis as well as a standard statistical evaluation were conducted. The Weibull analysis revealed no differences between control samples and the two exposed samples. We thus concluded that radiation components of the Earth orbital environment did not degrade the mechanical strength of the samples examined within the limits of experimental error. The upper bound of strength degradation for meteorite impacted samples based upon statistical analysis and observation was 50 percent.

COMPREHENSIVE ANALYSIS ON SEEPAGE AND STRUCTURAL STABILITY OF EARTH-ROCK DAM: A CASE STUDY OF XIQUANYAN DAM IN CHINA

Directory of Open Access Journals (Sweden)

Qingqing GUO

2016-07-01

Full Text Available Earth-rock dam is commonly used in the high-dam engineering around the world. It has been widely accepted that the analysis on structural and seepage stability plays a very important role, and it is necessary to take into account while designing the earth-rock dam. In performing the analysis of structural and seepage stability, many remarkable methods are available at current stage. However, there are still some important issues remaining unsolved, including: (1 Finite element methods (FEMs is a means of solutions to analysis seepage process, but it is often a difficult task to determine the so-called seepage coefficient, because the common-used water injection test is limited in the practical work due to the high cost and complex procedure. (2 It has long been discussed that the key parameters for structural stability analysis show a significant spatial and temporal variations. It may be partly explained by the inhomogeneous dam-filling during construction work and the developing seepage process. The consequence is that one constant value of the parameter cannot represent the above variations. In this context, we solve the above issues and introduce the solution with a practical earth-rock dam project. For determining the seepage coefficient, the data from the piezo metric tube is used to calculate the potential value, based on which the seepage coefficient can be back-analysed. Then the seepage field, as well as the seepage stability are numerically analysed using the FEM-based SEEP/W program. As to the structural safety, we take into account the spatial and temporal variations of the key parameters, and incorporate the Monte-Carlo simulation method into the commonly used M-P method to calculate the frequency distribution of the obtained structural safety factor. In this way, the structural and seepage safety can be well analysed. This study is also beneficial to provide a mature method and a theoretical insight into the earth-rock dam design

Mechanism of structural type formation of rare earth polychalcogenides

International Nuclear Information System (INIS)

Kuz'micheva, G.M.; Eliseev, A.A.; Khalina, S.Yu.

1981-01-01

It proved to be possible to obtain the structural motives not only of all the known polychalcogenides of rare earth elements but to forecast compounds not yet existing on the basis of two initial structural motives. All the structural motives can be divided into superstructures and polytypes as to the mechanism of their formation [ru

Innovative Application of Mechanical Activation for Rare Earth Elements Recovering: Process Optimization and Mechanism Exploration

OpenAIRE

Quanyin Tan; Chao Deng; Jinhui Li

2016-01-01

With the rapidly expanding use of fluorescent lamps (FLs) and increasing interest in conservation and sustainable utilization of critical metals such as rare earth elements (REEs), the recovering of REEs from phosphors in waste FLs is becoming a critical environmental and economic issue. To effectively recycle REEs with metallurgical methods, mechanical activation by ball milling was introduced to pretreat the waste phosphors. This current study put the emphasis on the mechanical activation a...

Characterizing material properties of cement-stabilized rammed earth to construct sustainable insulated walls

Directory of Open Access Journals (Sweden)

Rishi Gupta

2014-01-01

Full Text Available Use of local materials can reduce the hauling of construction materials over long distances, thus reducing the greenhouse gas emissions associated with transporting such materials. Use of locally available soils (earth for construction of walls has been used in many parts of the world. Owing to the thermal mass of these walls and the potential to have insulation embedded in the wall section has brought this construction material/technology at the forefront in recent years. However, the mechanical properties of the rammed earth and the parameters required for design of steel reinforced walls are not fully understood. In this paper, the author presents a case study where full-scale walls were constructed using rammed earth to understand the effect of two different types of shear detailing on the structural performance of the walls. The mechanical properties of the material essential for design such as compressive strength of the material including effect of coring on the strength, pull out strength of different rebar diameters, flexural performance and out-of-plane bending on walls was studied. These results are presented in this case study.

Chemical Mechanisms and Their Applications in the Goddard Earth Observing System (GEOS) Earth System Model.

Science.gov (United States)

Nielsen, J Eric; Pawson, Steven; Molod, Andrea; Auer, Benjamin; da Silva, Arlindo M; Douglass, Anne R; Duncan, Bryan; Liang, Qing; Manyin, Michael; Oman, Luke D; Putman, William; Strahan, Susan E; Wargan, Krzysztof

2017-12-01

NASA's Goddard Earth Observing System (GEOS) Earth System Model (ESM) is a modular, general circulation model (GCM), and data assimilation system (DAS) that is used to simulate and study the coupled dynamics, physics, chemistry, and biology of our planet. GEOS is developed by the Global Modeling and Assimilation Office (GMAO) at NASA Goddard Space Flight Center. It generates near-real-time analyzed data products, reanalyses, and weather and seasonal forecasts to support research targeted to understanding interactions among Earth System processes. For chemistry, our efforts are focused on ozone and its influence on the state of the atmosphere and oceans, and on trace gas data assimilation and global forecasting at mesoscale discretization. Several chemistry and aerosol modules are coupled to the GCM, which enables GEOS to address topics pertinent to NASA's Earth Science Mission. This paper describes the atmospheric chemistry components of GEOS and provides an overview of its Earth System Modeling Framework (ESMF)-based software infrastructure, which promotes a rich spectrum of feedbacks that influence circulation and climate, and impact human and ecosystem health. We detail how GEOS allows model users to select chemical mechanisms and emission scenarios at run time, establish the extent to which the aerosol and chemical components communicate, and decide whether either or both influence the radiative transfer calculations. A variety of resolutions facilitates research on spatial and temporal scales relevant to problems ranging from hourly changes in air quality to trace gas trends in a changing climate. Samples of recent GEOS chemistry applications are provided.

Multi-Mission Earth Vehicle Subsonic Dynamic Stability Testing and Analyses

Science.gov (United States)

Glaab, Louis J.; Fremaux, C. Michael

2013-01-01

Multi-Mission Earth Entry Vehicles (MMEEVs) are blunt-body vehicles designed with the purpose of transporting payloads from outer space to the surface of the Earth. To achieve high-reliability and minimum weight, MMEEVs avoid use of limited-reliability systems, such as parachutes, retro-rockets, and reaction control systems and rely on the natural aerodynamic stability of the vehicle throughout the Entry, Descent, and Landing (EDL) phase of flight. The Multi-Mission Systems Analysis for Planetary Entry (M-SAPE) parametric design tool is used to facilitate the design of MMEEVs for an array of missions and develop and visualize the trade space. Testing in NASA Langley?s Vertical Spin Tunnel (VST) was conducted to significantly improve M-SAPE?s subsonic aerodynamic models. Vehicle size and shape can be driven by entry flight path angle and speed, thermal protection system performance, terminal velocity limitations, payload mass and density, among other design parameters. The objectives of the VST testing were to define usable subsonic center of gravity limits, and aerodynamic parameters for 6-degree-of-freedom (6-DOF) simulations, for a range of MMEEV designs. The range of MMEEVs tested was from 1.8m down to 1.2m diameter. A backshell extender provided the ability to test a design with a much larger payload for the 1.2m MMEEV.

Stability of vertical posture explored with unexpected mechanical perturbations: synergy indices and motor equivalence.

Science.gov (United States)

Yamagata, Momoko; Falaki, Ali; Latash, Mark L

2018-03-21

We explored the relations between indices of mechanical stability of vertical posture and synergy indices under unexpected perturbations. The main hypotheses predicted higher posture-stabilizing synergy indices and higher mechanical indices of center of pressure stability during perturbations perceived by subjects as less challenging. Healthy subjects stood on a force platform and held in fully extended arms a bar attached to two loads acting downward and upward. One of the loads was unexpectedly released by the experimenter causing a postural perturbations. In different series, subjects either knew or did not know which of the two loads would be released. Forward perturbations were perceived as more challenging and accompanied by co-activation patterns among the main agonist-antagonist pairs. Backward perturbation led to reciprocal muscle activation patterns and was accompanied by indices of mechanical stability and of posture-stabilizing synergy which indicated higher stability. Changes in synergy indices were observed as early as 50-100 ms following the perturbation reflecting involuntary mechanisms. In contrast, predictability of perturbation direction had weak or no effect on mechanical and synergy indices of stability. These observations are interpreted within a hierarchical scheme of synergic control of motor tasks and a hypothesis on the control of movements with shifts of referent coordinates. The findings show direct correspondence between stability indices based on mechanics and on the analysis of multi-muscle synergies. They suggest that involuntary posture-stabilizing mechanisms show synergic organization. They also show that predictability of perturbation direction has strong effects on anticipatory postural adjustment but not corrective adjustments. We offer an interpretation of co-activation patterns that questions their contribution to postural stability.

The formation of the economic mechanism of stabilization of enterprise’s activity

Directory of Open Access Journals (Sweden)

L. A. Zaporozhtseva

2018-01-01

Full Text Available The authors bring the research of regularities of enterprise’s economic development; bring the research of change sequence of life cycle stages in the article. There is established that a stage of maturity not always gives way to decline stage and in the next to crisis stage. Life processes of "ageing" of the enterprise can be successfully resisted. It is proved that the stage of maturity of the enterprise is associated with a "crisis of stability". Getting into the stages of recession, growth or maintaining stability becomes the way out of the crisis. The authors prove that there are such zones of staying on the life cycle’s curve in the practice of commercial organizations functioning when it is necessary to use the mechanism of stabilization (at detection of "crisis of stability", at transfer from the stage of maturity to the stage of recession and at diagnostics of hit to the stage of recession. In this regard the authors elaborate an economic mechanism for stabilization of the enterprise’s activity as a system of measures aimed at maintaining the achieved financial balance of the enterprise in a long period, which includes the following blocks: information support of the assessment of financial condition; assessment of the level of payment, business and capital stability of the enterprise; determination of the stage of the enterprise’s life cycle; characteristics of the applicable strategy; the need to use the tools for adjust the strategy to stabilize the enterprise’s activity and evaluate the results. At the same time, it is important to focus on maintaining achievable growth rates through the using of special management decisions, along with monitoring the life cycle and controlling the financial condition of the enterprise. The introduction of the economic stabilization mechanism in the enterprise’s activity jointly with the existing organizational and economic mechanism will correct the elements of the basic mechanism and

The stability mechanism of MJ0305

Science.gov (United States)

Song, Hyundeok; Beck, Thomas

2010-10-01

Methanococcus jannaschii (MJ) is a methane-producing thermophile, which was discovered in a 2600m-deep Pacific Ocean vent in 1983. It has the ability to thrive at high temperatures and high pressures, which are unfavorable for most life forms. There have been some experiments to study its stability under extreme conditions, but still the origin of the stability of MJ is not exactly known. MJ0305 is MJ's chloride channel protein. We have investigated the stability mechanism of MJ0305 by computer simulation. The structure of MJ0305 was built by homology modeling. We compared the stability of MJ0305 with mesophilic Ecoli at 300K, 330K, 360K, and 1atm, 130atm, 260atm by computer simulation to test the effects of both temperature and pressure. Our results show that high temperatures and high pressures significantly affect the salt bridges and hydrogen bonds. High temperatures decreased the average number of hydrogen bonds for Ecoli and MJ0305. However, high pressures at 360K increased the number of salt bridges for Ecoli and MJ0305. The radius of gyration of MJ0305 was decreased at high temperatures. Increased compactness at high temperatures, and Increased salt bridges at high pressures make MJ0305 more stable. This research may have impacts on renewable energy and chemical sensors.

Mechanical stability of titanium and plasma polymer nanoclusters in nanocomposite coatings

Energy Technology Data Exchange (ETDEWEB)

Palesch, E. [Institute of Materials Chemistry, Brno University of Technology, Brno (Czech Republic); Marek, A. [HVM Plasma, spol. s r.o., Prague (Czech Republic); Solar, P.; Kylian, O. [Faculty of Mathematics and Physics, Charles University, Prague (Czech Republic); Vyskocil, J. [HVM Plasma, spol. s r.o., Prague (Czech Republic); Biederman, H. [Faculty of Mathematics and Physics, Charles University, Prague (Czech Republic); Cech, V., E-mail: cech@fch.vutbr.cz [Institute of Materials Chemistry, Brno University of Technology, Brno (Czech Republic)

2013-10-01

The mechanical stability of nanoclusters embedded in nanocomposite coatings was investigated by scratch and wear tests supported by atomic force microscopy using surface topography mode. Titanium and plasma polymer nanoclusters were deposited on planar substrates (glass, titanium) using a magnetron-based gas aggregation cluster source. The deposited clusters were overcoated with a thin titanium film of different thicknesses to stabilize the position of the clusters in the nanocomposite coating. Nanotribological measurements were carried out to optimize the thickness of the overcoating film for sufficient interfacial adhesion of the cluster/film system. - Highlights: ► Titanium and plasma polymer nanoclusters were overcoated with thin titanium film. ► The mechanical stability of nanoclusters was characterized by nanotribological tests. ► The film thickness was optimized to stabilize the position of the clusters in coating.

Rare earth sulfates

International Nuclear Information System (INIS)

Komissarova, L.N.; Shatskij, V.M.; Pokrovskij, A.N.; Chizhov, S.M.; Bal'kina, T.I.; Suponitskij, Yu.L.

1986-01-01

Results of experimental works on the study of synthesis conditions, structure and physico-chemical properties of rare earth, scandium and yttrium sulfates, have been generalized. Phase diagrams of solubility and fusibility, thermodynamic and crystallochemical characteristics, thermal stability of hydrates and anhydrous sulfates of rare earths, including normal, double (with cations of alkali and alkaline-earth metals), ternary and anion-mixed sulfates of rare earths, as well as their adducts, are considered. The state of ions of rare earths, scandium and yttrium in aqueous sulfuric acid solutions is discussed. Data on the use of rare earth sulfates are given

Dynamics and stability of a tethered centrifuge in low earth orbit

Science.gov (United States)

Quadrelli, B. M.; Lorenzini, E. C.

1992-01-01

The three-dimensional attitude dynamics of a spaceborne tethered centrifuge for artificial gravity experiments in low earth orbit is analyzed using two different methods. First, the tethered centrifuge is modeled as a dumbbell with a straight viscoelastic tether, point tip-masses, and sophisticated environmental models such as nonspherical gravity, thermal perturbations, and a dynamic atmospheric model. The motion of the centrifuge during spin-up, de-spin, and steady-rotation is then simulated. Second, a continuum model of the tether is developed for analyzing the stability of lateral tether oscillations. Results indicate that the maximum fluctuation about the 1-g radial acceleration level is less than 0.001 g; the time required for spin-up and de-spin is less than one orbit; and lateral oscillations are stable for any practical values of the system parameters.

THEORETICAL CONSIDERATIONS REGARDING THE AUTOMATIC FISCAL STABILIZERS OPERATING MECHANISM

Directory of Open Access Journals (Sweden)

Gondor Mihaela

2012-07-01

Full Text Available This paper examines the role of Automatic Fiscal Stabilizers (AFS for stabilizing the cyclical fluctuations of macroeconomic output as an alternative to discretionary fiscal policy, admitting its huge potential of being an anti crisis solution. The objectives of the study are the identification of the general features of the concept of automatic fiscal stabilizers and the logical assessment of them from economic perspectives. Based on the literature in the field, this paper points out the disadvantages of fiscal discretionary policy and argue the need of using Automatic Fiscal Stabilizers in order to provide a faster decision making process, shielded from political interference, and reduced uncertainty for households and business environment. The paper conclude about the need of using fiscal policy for smoothing the economic cycle, but in a way which includes among its features transparency, responsibility and clear operating mechanisms. Based on the research results the present paper assumes that pro-cyclicality reduces de effectiveness of the Automatic Fiscal Stabilizer and as a result concludes that it is very important to avoid the pro-cyclicality in fiscal rule design. Moreover, by committing in advance to specific fiscal policy action contingent on economic developments, uncertainty about the fiscal policy framework during a recession should be reduced. Being based on logical analysis and not focused on empirical, contextualized one, the paper presents some features of AFS operating mechanism and also identifies and systematizes the factors which provide its importance and national individuality. Reaching common understanding on the Automatic Fiscal Stabilizer concept as a institutional device for smoothing the gap of the economic cycles across different countries, particularly for the European Union Member States, will facilitate efforts to coordinate fiscal policy responses during a crisis, especially in the context of the fiscal

Carbon substituting for oxygen in silicates: A novel mechanism for carbon incorporation in the deep Earth

Science.gov (United States)

Armentrout, M. M.; Tavakoli, A.; Ionescu, E.; Mera, G.; Riedel, R.; Navrotsky, A.

2013-12-01

Traditionally, carbon in the deep Earth has been thought of in terms of either carbonate at high oxygen fugacities or graphite or diamond under more reducing conditions. However, material science studies of amorphous Si-O-C polymer derived ceramics have demonstrated that carbon can be accommodated as an anion substituting for oxygen in mixed silica tetrahedra. Furthermore these structures are energetically favorable relative to a mixture of crystalline silica, silicon carbide, and graphite by ten or more kJ/g.atom. Thermodynamic stability suggests that these nano-structured composites are a potentially important storage mechanism for carbon under moderately reducing conditions. Here we expand the scope of the previous work by examining the compositional effect of geologically relevant cations (calcium and magnesium) on the thermodynamic stability, nanostructure, and ability to accommodate carbon of these composites. Silicon oxy-carbides doped with magnesium, magnesium and calcium or undoped resisted crystallization at 1100 C under inert atmosphere. 29Si NMR of the samples shows a similar distribution of silicon between end-member and mixed sites (Table 1). Results are presented from studies utilizing NMR, high temperature solution calorimetry, and microprobe. Table 1. Percentages of Si species in each material as determined by 29Si NMR.

Methods of stability analysis in nonlinear mechanics

International Nuclear Information System (INIS)

Warnock, R.L.; Ruth, R.D.; Gabella, W.; Ecklund, K.

1989-01-01

We review our recent work on methods to study stability in nonlinear mechanics, especially for the problems of particle accelerators, and compare our ideals to those of other authors. We emphasize methods that (1) show promise as practical design tools, (2) are effective when the nonlinearity is large, and (3) have a strong theoretical basis. 24 refs., 2 figs., 2 tabs

Possible mechanism of the interplanetary medium effect on the diurnal rotation rate of the Earth

International Nuclear Information System (INIS)

Krymskij, P.F.

1993-01-01

Mechanism is proposed for effect of the solar wind and interplanetary magnetic field on the Earth rotation. In the mechanism base is Hall current generation in the plasma layer of the magnetosphere tail

Gravitational mechanism of active life of the Earth, planets and satellites

Science.gov (United States)

Barkin, Yury

2010-05-01

From positions of geodynamic model of the forced gravitational swing, wobble and displacements of shells of a planet are studied and fundamental problems of geodynamics, geology, geophysics, planetary sciences are solved etc.: 1) The mechanism of cyclic variations of activity of natural processes in various time scales. 2) The power of endogenous activity of planetary natural processes on planets and satellites. 3) The phenomenon of polar inversion of natural processes on planets and satellites. 4) Spasmodic and catastrophic changes of activity of natural processes. 5) The phenomenon of twisting of hemispheres (latitude zones or belts) of celestial bodies. 6) Formation of the pear-shaped form of celestial bodies and the mechanism of its change. 7) The ordered planetary structures of geological formations. 8) The phenomena of bipolarity of celestial bodies and antipodality of geology formations. Mechanism. The fundamental feature of a structure of celestial bodies is their shell structure. The most investigated is the internal structure of the Earth. For the Moon and wide set of other bodies of solar system models of an internal structure have been constructed on the basis of the data of observations obtained at studying of their gravitational fields as a result of realization of the appropriate space missions. The basic components for the majority of celestial bodies are the core, the mantle and the crust. To other shells we concern atmospheres (for example, at Venus, Mars, the Titan etc.) and oceanic shells (the Titan, the Earth, Enceladus etc.). Shells are the complex (composite) formations. Planets and satellites are not spherical celestial bodies. The centers of mass of shells of the given planet (or the satellite) and their appropriate principal axes of inertia do not coincide. Accordingly, all their shells are characterized by the certain dynamic oblatenesses. Differences of dynamical oblatenesses results in various forced influences of external celestial

Dispersive heterodyne probing method for laser frequency stabilization based on spectral hole burning in rare-earth doped crystals

DEFF Research Database (Denmark)

Gobron, Olivier; Jung, K.; Galland, N.

2017-01-01

Frequency-locking a laser to a spectral hole in rare-earth doped crystals at cryogenic temperature has been shown to be a promising alternative to the use of high finesse Fabry-Perot cavities when seeking a very high short term stability laser (M. J. Thorpe et al., Nature Photonics 5, 688 (2011......)). We demonstrate here a novel technique for achieving such stabilization, based on generating a heterodyne beat-note between a master laser and a slave laser whose dephasing caused by propagation near a spectral hole generate the error signal of the frequency lock. The master laser is far detuned from...

Finite element analysis of mechanical stability of coarsened nanoporous gold

International Nuclear Information System (INIS)

Cho, Hoon-Hwe; Chen-Wiegart, Yu-chen Karen; Dunand, David C.

2016-01-01

The mechanical stability of nanoporous gold (np-Au) at various stages of thermal coarsening is studied via finite element analysis under volumetric compression using np-Au architectures imaged via X-ray nano-tomography. As the np-Au is coarsened thermally over ligament sizes ranging from 185 to 465 nm, the pore volume fraction is determinant for the mechanical stability of the coarsened np-Au, unlike the curvature and surface orientation of the ligaments. The computed Young's modulus and yield strength of the structures are compared with the Gibson–Ashby model. The geometry of the structures determines the locations where stress concentrations occur at the onset of yielding.

[Stabilization of Cadmium Contaminated Soils by Ferric Ion Modified Attapulgite (Fe/ATP)--Characterizations and Stabilization Mechanism].

Science.gov (United States)

Rong, Yang; Li, Rong-bo; Zhou, Yong-li; Chen, Jing; Wang, Lin-ling; Lu, Xiao-hua

2015-08-01

Ferric ion modified attapulgite (Fe/ATP) was prepared by impregnation and its structure and morphology were characterized. The toxicity characteristic leaching procedure (TCLP) was used to evaluate the effect of Cadmium( Cd) stabilization in soil with the addition of attapulgite (ATP) and Fe/ATP. The stabilization mechanism of Cd was further elucidated by comparing the morphologies and structure of ATP and Fe/ATP before and after Cd adsorption. Fe/ATP exhibited much better adsorption capacity than ATP, suggesting different adsorption mechanisms occurred between ATP and Fe/ATP. The leaching concentrations of Cd in soil decreased by 45% and 91% respectively, with the addition of wt. 20% ATP and Fe/ATP. The former was attributed to the interaction between Cd2 and --OH groups by chemical binding to form inner-sphere complexes in ATP and the attachment between Cd2+ and the defect sites in ATP framework. Whereas Cd stabilization with Fe/ATP was resulted from the fact that the active centers (--OH bonds or O- sites) on ATP could react with Fe3+ giving Fe--O--Cd-- bridges, which helped stabilize Cd in surface soil. What'more, the ferric oxides and metal hydroxides on the surface of ATP could interact with Cd, probably by the formation of cadmium ferrite. In conclusion, Fe/ATP, which can be easily prepared, holds promise as a potential low-cost and environmental friendly stabilizing agent for remediation of soil contaminated with heavy metals.

Vibration Stabilization of a Mechanical Model of a X-Band Linear Collider Final Focus Magnet

CERN Document Server

Frisch, J; Decker, V; Hendrickson, L; Markiewicz, T W; Partridge, R; Seryi, Andrei

2004-01-01

The small beam sizes at the interaction point of a X-band linear collider require mechanical stabilization of the final focus magnets at the nanometer level. While passive systems provide adequate performance at many potential sites, active mechanical stabilization is useful if the natural or cultural ground vibration is higher than expected. A mechanical model of a room temperature linear collider final focus magnet has been constructed and actively stabilized with an accelerometer based system.

Vibration Stabilization of a Mechanical Model of a X-Band Linear Collider Final Focus Magnet

International Nuclear Information System (INIS)

Frisch, Josef; Chang, Allison; Decker, Valentin; Doyle, Eric; Eriksson, Leif; Hendrickson, Linda; Himel, Thomas; Markiewicz, Thomas; Partridge, Richard; Seryi, Andrei; SLAC

2006-01-01

The small beam sizes at the interaction point of a X-band linear collider require mechanical stabilization of the final focus magnets at the nanometer level. While passive systems provide adequate performance at many potential sites, active mechanical stabilization is useful if the natural or cultural ground vibration is higher than expected. A mechanical model of a room temperature linear collider final focus magnet has been constructed and actively stabilized with an accelerometer based system

Many-body forces and stability of the alkaline-earth tetramers

International Nuclear Information System (INIS)

Diaz-Torrejon, C.C.; Kaplan, Ilya G.

2011-01-01

Graphical abstract: Many-body forces effect. In a three-particle system, the two-body interaction energies depend upon coordinates of all three particles. The comparative study of the interaction energy and its many-body decomposition for alkaline-earths tetramers Be 4 , Mg 4 , and Ca 4 at the all-electron CCSD(T)/aug-cc-pVQZ level is performed. For study of dependence of the binding energy and the orbital population on the cluster size the corresponding dimers and trimers were also calculated at the same level of theory. In comparison with weakly bound dimers, the binding energy in trimers and, especially, in tetramers drastically increases; e.g., E b /N in Be 3 is 7 times larger and in Be 4 is 18.4 times larger than in Be 2 . This sharp increase is explained as a manifestation of many-body forces. The trimers and tetramers are stabilized by the three-body forces, whereas the two- and four-body forces are repulsive. The attractive contribution to the three-body forces has a three-atom electron exchange origin. The natural bond orbital (NBO) population analysis reveals a relatively large np-population in trimers and tetramers. The population of the valence np-orbitals leads to the sp-hybridization providing the covalent bonding. Research highlights: → The alkaline-earths trimers and tetramers are stabilized by the three-body forces. → Two- and four-body forces are repulsive for trimers and tetramers. → The attractive contribution to the three-body forces has a three-atom electron exchange origin. → The population of the np-orbitals leads to the sp-hybridization providing the covalent bonding. - Abstract: The comparative study of the interaction energy and its many-body decomposition for Be 4 , Mg 4 , and Ca 4 at the all-electron CCSD(T)/aug-cc-pVQZ level is performed. For study of dependence of the binding energy and the orbital population on the cluster size the corresponding dimers and trimers were also calculated at the same level of theory. In

Geared Topological Metamaterials with Tunable Mechanical Stability

Directory of Open Access Journals (Sweden)

Anne S. Meeussen

2016-11-01

Full Text Available The classification of materials into insulators and conductors has been shaken up by the discovery of topological insulators that conduct robustly at the edge but not in the bulk. In mechanics, designating a material as insulating or conducting amounts to asking if it is rigid or floppy. Although mechanical structures that display topological floppy modes have been proposed, they are all vulnerable to global collapse. Here, we design and build mechanical metamaterials that are stable and yet capable of harboring protected edge and bulk modes, analogous to those in electronic topological insulators and Weyl semimetals. To do so, we exploit gear assemblies that, unlike point masses connected by springs, incorporate both translational and rotational degrees of freedom. Global structural stability is achieved by eliminating geometrical frustration of collective gear rotations extending through the assembly. The topological robustness of the mechanical modes makes them appealing across scales from engineered macrostructures to networks of toothed microrotors of potential use in micromachines.

Structure and Mechanical Properties of Al-Cu-Fe-X Alloys with Excellent Thermal Stability.

Science.gov (United States)

Školáková, Andrea; Novák, Pavel; Mejzlíková, Lucie; Průša, Filip; Salvetr, Pavel; Vojtěch, Dalibor

2017-11-05

In this work, the structure and mechanical properties of innovative Al-Cu-Fe based alloys were studied. We focused on preparation and characterization of rapidly solidified and hot extruded Al-Cu-Fe, Al-Cu-Fe-Ni and Al-Cu-Fe-Cr alloys. The content of transition metals affects mechanical properties and structure. For this reason, microstructure, phase composition, hardness and thermal stability have been investigated in this study. The results showed exceptional thermal stability of these alloys and very good values of mechanical properties. Alloying by chromium ensured the highest thermal stability, while nickel addition refined the structure of the consolidated alloy. High thermal stability of all tested alloys was described in context with the transformation of the quasicrystalline phases to other types of intermetallics.

Influence of slope and gradation on rip rap stability and degradation mechanisms

International Nuclear Information System (INIS)

Lefebvre, G.; Rohan, K.; Belfahdel, M. B.

1997-01-01

A major investigation was undertaken at the La Grande hydroelectric complex with some 220 dikes and dams to study rip rap stability and repair. Degradation mechanisms were also studied under laboratory conditions to verify the main field study conclusions and to test different repair techniques. The result of both laboratory and field observation was that rip rap gradation has only marginal effect on slope stability and degradation mechanisms. On the other hand, the inclusion of even a small fraction of fine blocks (as little as 10 per cent) into the rip rap was shown to be very detrimental to the stability of steep rip rap but only marginally effective on flat slopes. 15 refs., 8 figs

Structure and Mechanical Properties of Al-Cu-Fe-X Alloys with Excellent Thermal Stability

Directory of Open Access Journals (Sweden)

Andrea Školáková

2017-11-01

Full Text Available In this work, the structure and mechanical properties of innovative Al-Cu-Fe based alloys were studied. We focused on preparation and characterization of rapidly solidified and hot extruded Al-Cu-Fe, Al-Cu-Fe-Ni and Al-Cu-Fe-Cr alloys. The content of transition metals affects mechanical properties and structure. For this reason, microstructure, phase composition, hardness and thermal stability have been investigated in this study. The results showed exceptional thermal stability of these alloys and very good values of mechanical properties. Alloying by chromium ensured the highest thermal stability, while nickel addition refined the structure of the consolidated alloy. High thermal stability of all tested alloys was described in context with the transformation of the quasicrystalline phases to other types of intermetallics.

Stability and anisotropy of (FexNi1-x)2O under high pressure and implications in Earth's and super-Earths' core.

Science.gov (United States)

Huang, Shengxuan; Wu, Xiang; Qin, Shan

2018-01-10

Oxygen is thought to be an important light element in Earth's core but the amount of oxygen in Earth's core remains elusive. In addition, iron-rich iron oxides are of great interest and significance in the field of geoscience and condensed matter physics. Here, static calculations based on density functional theory demonstrate that I4/mmm-Fe 2 O is dynamically and mechanically stable and becomes energetically favorable with respect to the assemblage of hcp-Fe and [Formula: see text]-FeO above 270 GPa, which indicates that I4/mmm-Fe 2 O can be a strong candidate phase for stable iron-rich iron oxides at high pressure, perhaps even at high temperature. The elasticity and anisotropy of I4/mmm-(Fe x Ni 1-x ) 2 O at high pressures are also determined. Based on these results, we have derived the upper limit of oxygen to be 4.3 wt% in Earth's lower outer core. On the other hand, I4/mmm-(Fe x Ni 1-x ) 2 O with high AV S is likely to exist in a super-Earth's or an ocean planet's solid core causing the locally seismic heterogeneity. Our results not only give some clues to explore and synthesize novel iron-rich iron oxides but also shed light on the fundamental information of oxygen in the planetary core.

Effect of Earth's rotation on the quantum mechanical phase of the neutron

International Nuclear Information System (INIS)

Werner, S.A.; Staudenmann, J.; Colella, R.

1979-01-01

Using a neutron interferometer of the type first developed by Bonse and Hart for x rays, we have observed the effect of Earth's rotation on the phase of the neutron wave function. This experiment is the quantum mechanical analog of the optical interferometry observations of Michelson, Gale, and Pearson

Facile fabrication of a superhydrophobic fabric with mechanical stability and easy-repairability.

Science.gov (United States)

Zhu, Xiaotao; Zhang, Zhaozhu; Yang, Jin; Xu, Xianghui; Men, Xuehu; Zhou, Xiaoyan

2012-08-15

The poor mechanical stability of superhydrophobic fabrics severely hindered their use in practical applications. Herein, to address this problem, we fabricated a superhydrophobic fabric with both mechanical stability and easy-repairability by a simple method. The mechanical durability of the obtained superhydrophobic fabric was evaluated by finger touching and abrasion with sandpaper. The results show that rough surface textures of the fabric were retained, and the fabric surface still exhibited superhydrophobicity after tests. More importantly, when the fabric lost its superhydrophobicity after a long-time abrasion, it can be easily rendered with superhydrophobicity once more by a regeneration process. Copyright © 2012 Elsevier Inc. All rights reserved.

Solid state mechanics

International Nuclear Information System (INIS)

Habib, P.

1988-01-01

The 1988 progress report of the Solid State Mechanics laboratory (Polytechnic School, France) is presented. The research program domains are the following: investigations concerning the stability and bifurcation of the reversible or irreversible mechanical systems, the problems related to the theoretical and experimental determination of the materials rheological properties, the fatigue crack formation and propagation in multiple-axial stress conditions, the expert systems, and the software applied in the reinforced earth structures dimensioning. Moreover, the published papers, the books, the congress communications, the thesis, and the patents are listed [fr

Mechanical stability of heat-treated nanoporous anodic alumina subjected to repetitive mechanical deformation

Science.gov (United States)

Bankova, A.; Videkov, V.; Tzaneva, B.; Mitov, M.

2018-03-01

We report studies on the mechanical response and deformation behavior of heat-treated nanoporous anodic alumina using a micro-balance test and experimental test equipment especially designed for this purpose. AAO samples were characterized mechanically by a three-point bending test using a micro-analytical balance. The deformation behavior was studied by repetitive mechanical bending of the AAO membranes using an electronically controlled system. The nanoporous AAO structures were prepared electrochemically from Al sheet substrates using a two-step anodizing technique in oxalic acid followed by heat treatment at 700 °C in air. The morphological study of the aluminum oxide layer after the mechanical tests and mechanical deformation was conducted using scanning electron and optical microscopy, respectively. The experimental results showed that the techniques proposed are simple and accurate; they could, therefore, be combined to constitute a method for mechanical stability assessment of nanostructured AAO films, which are important structural components in the design of MEMS devices and sensors.

Earth mortars and earth-lime renders

Directory of Open Access Journals (Sweden)

Maria Fernandes

2008-01-01

Full Text Available Earth surface coatings play a decorative architectural role, apart from their function as wall protection. In Portuguese vernacular architecture, earth mortars were usually applied on stone masonry, while earth renders and plasters were used on indoors surface coatings. Limestone exists only in certain areas of the country and consequently lime was not easily available everywhere, especially on granite and schist regions where stone masonry was a current building technique. In the central west coast of Portugal, the lime slaking procedure entailed slaking the quicklime mixed with earth (sandy soil, in a pit; the resulting mixture would then be combined in a mortar or plaster. This was also the procedure for manufactured adobes stabilized with lime. Adobe buildings with earth-lime renderings and plasters were also traditional in the same region, using lime putty and lime wash for final coat and decoration. Classic decoration on earth architecture from the 18th-19th century was in many countries a consequence of the François Cointeraux (1740-1830 manuals - Les Cahiers d'Architecture Rurale" (1793 - a French guide for earth architecture and building construction. This manual arrived to Portugal in the beginning of XIX century, but was never translated to Portuguese. References about decoration for earth houses were explained on this manual, as well as procedures about earth-lime renders and ornamentation of earth walls; in fact, these procedures are exactly the same as the ones used in adobe buildings in this Portuguese region. The specific purpose of the present paper is to show some cases of earth mortars, renders and plasters on stone buildings in Portugal and to explain the methods of producing earth-lime renders, and also to show some examples of rendering and coating with earth-lime in Portuguese adobe vernacular architecture.

Method and Mechanisms of Soil Stabilization Using Electric Arc Furnace Dust

Science.gov (United States)

Al-Amoudi, Omar S. Baghabra; Al-Homidy, Abdullah A.; Maslehuddin, Mohammed; Saleh, Tawfik A.

2017-04-01

This paper reports the method and mechanism for improving the strength of marl and desert sand utilizing electric arc furnace dust (EAFD), an industrial by-product, in lieu of cement or lime. EAFD was used in conjunction with a small quantity (2%) of cement. The mechanical properties and durability characteristics of marl and sand mixed with 2% cement plus 5-, 10-, 20- or 30%-EAFD, by weight of the soil, were evaluated. The soil-cement-EAFD mixtures were used to determine their unconfined compressive strength (UCS), soaked California Bearing Ratio (CBR) and durability. The risk of leaching of toxic heavy metals, such as lead and cadmium, from the stabilized soils to the groundwater was also investigated. The mechanisms of stabilization of the selected soils due to the use of EAFD along with a small quantity of cement are also elucidated. The usage of 20 to 30% EAFD with 2% cement was noted to considerably improve the mechanical properties and durability of both marl and sand.

Rare earth effect on microstructure, mechanical and tribological properties of CoCrW coatings

International Nuclear Information System (INIS)

Zhang Zhenyu; Lu Xinchun; Han Baolei; Luo Jianbin

2007-01-01

Eight different CoCrW coatings doped with rare earth oxide were deposited by supersonic plasma spraying (SPS). Environmental scanning electron microscopy, microhardness tester, X-ray diffractometer, and self-developed tribometer for high temperature were employed to investigate the properties of sprayed coatings. The results show that rare earth can refine the microstructure effectively, and make the element distribution uniform, which leads to the increase of average microhardness and the corresponding decrease of fluctuation range of sectioned surface of SPS coatings. Furthermore, the rare earth can reduce the friction coefficient between the SPS coating and glass during the sliding process at about 973 K largely, and the mechanism of anti-friction is also discussed

Magnetically levitated space elevator to low-earth orbit

International Nuclear Information System (INIS)

Hull, J. R.; Mulcahy, T. M.

2001-01-01

The properties of currently available NbTi superconductor and carbon-fiber structural materials enable the possibility of constructing a magnetically levitated space elevator from the earth's surface up to an altitude of(approx) 200 km. The magnetic part of the elevator consists of a long loop of current-carrying NbTi, composed of one length that is attached to the earth's surface in an east-west direction and a levitated-arch portion. The critical current density of NbTi is sufficiently high that these conductors will stably levitate in the earth's magnetic field. The magnetic self-field from the loop increases the levitational force and for some geometries assists levitational stability. The 200-km maximum height of the levitated arch is limited by the allowable stresses of the structural material. The loop is cryogenically cooled with helium, and the system utilizes intermediate pumping and cooling stations along both the ground and the levitated portion of the loop, similar to other large terrestrial cryogenic systems. Mechanically suspended from the basic loop is an elevator structure, upon which mass can be moved between the earth's surface and the top of the loop by a linear electric motor or other mechanical or electrical means. At the top of the loop, vehicles may be accelerated to orbital velocity or higher by rocket motors, electromagnetic propulsion, or hybrid methods

Influence of mechanical and thermal treatments on microstructure and mechanical properties of titanium stabilized austenitic stainless steels

International Nuclear Information System (INIS)

Sidhom, H.

1983-12-01

Thermal and mechanical treatments for microstructure optimization in titanium stabilized austenitic stainless steels used in nuclear industry are examined. The steels studied Z10CNDT15-15B and Z6CNDT17-13 are of the type 15-15 Ti and 316 Ti. These treatments allow the elimination of casting heterogeneity produced by dendritic solidification, improve mechanical properties particularly creep and the best compromise between grain size solid solution of metal additions is obtained. Secondary precipitation of (TiMo)C on dislocations is improved by a previous strain hardening. The precipitation reinforce the good effect of strain hardening by stabilization of the microstructure producing a better resistance to recrystallization [fr

Seismic rehabilitation and analysis of Chaohe earth dam

Science.gov (United States)

Fu, Lei; Zeng, Xiangwu

2005-12-01

Stability of earth dams during earthquakes has been a major concern for geotechnical engineers in seismic active regions. Liquefaction induced slope failure occurred at the upstream slope of a major earth dam in the suburb of Beijing, China, during the 1976 Tangshan Earthquake. The gravelly soil with loose initial condition liquefied under relatively small ground vibration. In recent years, a major seismic rehabilitation project was carried out on a similar earth dam nearby using dumped quarry stone. Seismic stability analysis was carried out using model test, finite element simulation, and pseudo-static slope stability program after taking into account the influence of excess pore pressure.

Cu-based shape memory alloys with enhanced thermal stability and mechanical properties

International Nuclear Information System (INIS)

Chung, C.Y.; Lam, C.W.H.

1999-01-01

Cu-based shape memory alloys were developed in the 1960s. They show excellent thermoelastic martensitic transformation. However the problems in mechanical properties and thermal instability have inhibited them from becoming promising engineering alloys. A new Cu-Zn-Al-Mn-Zr Cu-based shape memory alloy has been developed. With the addition of Mn and Zr, the martensitic transformation behaviour and the grain size ca be better controlled. The new alloys demonstrates good mechanical properties with ultimate tensile strenght and ductility, being 460 MPa and 9%, respectively. Experimental results revealed that the alloy has better thermal stability, i.e. martensite stabilisation is less serious. In ordinary Cu-Zn-Al alloys, martensite stabilisation usually occurs at room temperature. The new alloy shows better thermal stability even at elevated temperature (∝150 C, >A f =80 C). A limited small amount of martensite stabilisation was observed upon ageing of the direct quenched samples as well as the step quenched samples. This implies that the thermal stability of the new alloy is less dependent on the quenching procedure. Furthermore, such minor martensite stabilisation can be removed by subsequent suitable parent phase ageing. The new alloy is ideal for engineering applications because of its better thermal stability and better mechanical properties. (orig.)

Stability characteristics of compressible boundary layers over thermo-mechanically compliant walls

Science.gov (United States)

Dettenrieder, Fabian; Bodony, Daniel

2017-11-01

Transition prediction at hypersonic flight conditions continues to be a challenge and results in conservative safety factors that increase vehicle weight. The weight and thus cost reduction of the outer skin panels promises significant impact; however, fluid-structure interaction due to unsteady perturbations in the laminar boundary layer regime has not been systematically studied at conditions relevant for reusable, hypersonic flight. In this talk, we develop and apply convective and global stability analyses for compressible boundary layers over thermo-mechanically compliant panels. This compliance is shown to change the convective stability of the boundary layer modes, with both stabilization and destabilization observed. Finite panel lengths are shown to affect the global stability properties of the boundary layer.

Thermal and mechanical stability of zeolitic imidazolate frameworks polymorphs

Directory of Open Access Journals (Sweden)

Lila Bouëssel du Bourg

2014-12-01

Full Text Available Theoretical studies on the experimental feasibility of hypothetical Zeolitic Imidazolate Frameworks (ZIFs have focused so far on relative energy of various polymorphs by energy minimization at the quantum chemical level. We present here a systematic study of stability of 18 ZIFs as a function of temperature and pressure by molecular dynamics simulations. This approach allows us to better understand the limited stability of some experimental structures upon solvent or guest removal. We also find that many of the hypothetical ZIFs proposed in the literature are not stable at room temperature. Mechanical and thermal stability criteria thus need to be considered for the prediction of new MOF structures. Finally, we predict a variety of thermal expansion behavior for ZIFs as a function of framework topology, with some materials showing large negative volume thermal expansion.

A physical mechanism producing suprathermal populations and initiating substorms in the Earth's magnetotail

Directory of Open Access Journals (Sweden)

D. V. Sarafopoulos

2008-06-01

Full Text Available We suggest a candidate physical mechanism, combining there dimensional structure and temporal development, which is potentially able to produce suprathermal populations and cross-tail current disruptions in the Earth's plasma sheet. At the core of the proposed process is the "akis" structure; in a thin current sheet (TCS the stretched (tail-like magnetic field lines locally terminate into a sharp tip around the tail midplane. At this sharp tip of the TCS, ions become non-adiabatic, while a percentage of electrons are accumulated and trapped: The strong and transient electrostatic electric fields established along the magnetic field lines produce suprathermal populations. In parallel, the tip structure is associated with field aligned and mutually attracted parallel filamentary currents which progressively become more intense and inevitably the structure collapses, and so does the local TCS. The mechanism is observationally based on elementary, almost autonomous and spatiotemporal entities that correspond each to a local thinning/dipolarization pair having duration of ~1 min. Energetic proton and electron populations do not occur simultaneously, and we infer that they are separately accelerated at local thinnings and dipolarizations, respectively. In one example energetic particles are accelerated without any dB/dt variation and before the substorm expansion phase onset. A particular effort is undertaken demonstrating that the proposed acceleration mechanism may explain the plasma sheet ratio Ti/Te≈7. All our inferences are checked by the highest resolution datasets obtained by the Geotail Energetic Particles and Ion Composition (EPIC instrument. The energetic particles are used as the best diagnostics for the accelerating source. Near Earth (X≈10 RE selected events support our basic concept. The proposed mechanism seems to reveal a fundamental building block of the substorm phenomenon and may be the basic process/structure, which is now

Thermal stability and temperature coefficients of four rare-earth-cobalt matrix magnets heated in dry air

Science.gov (United States)

Strnat, R. M. W.; Liu, S.; Strnat, K. J.

1982-03-01

Flux-loss characteristics during long-term air aging of four rare-earth-cobalt matrix magnet types were measured. Irreversible losses and reversible temperature coefficients on heating above room temperature are reported. Purely magnetic and permanent microstructure-related changes during aging were differentiated by measuring hysteresis curves before and after long-term exposure. Three commercial polymer-bonded magnets using different rare-earth-cobalt-transition metal alloys and a solder-matrix magnet with Sm(Co, Cu, Fe, Zr)7.4 were studied. They were cycled between 25 °C and maximum temperatures to 150 °C (25 ° intervals) as applicable. Aging data at 50 and 125 °C for an exposure time of 3300 h are reported. The 2-17 samples have a stability far superior to bonded 1-5. The soft metal binder imparts significantly better aging behavior on precipitation-hardened 2-17 magnet alloys above 100 °C than an epoxy resin matrix.

THE EUROPEAN MECHANISM FOR FINANCIAL STABILITY AND THE EURO-PLUS PACT

Directory of Open Access Journals (Sweden)

AUGUSTIN FUEREA

2012-05-01

Full Text Available The economic crisis that has affected countries from all continents has generated, among others, also a strong financial crisis, which in turn, has caused serious imbalances in the economic and financial environment of EU Member States.Under these circumstances, the Council, being in an exceptional situation, “outside the control of Member States”, as it itself states in the Preamble to Regulation No. 407/2010, considered necessary, “the immediate establishment of a stabilization mechanism at EU level in order to maintain the financial stability in the European Union”, mechanism that “would enable the Union to respond in a coordinated, rapid and effective way to the serious difficulties undergone by a certain Member State”

Relationship between mechanical characteristics and thermal shock stability of refractories

International Nuclear Information System (INIS)

Volkov-Husovic, T.; Raic, K.

2003-01-01

Thermal stability of the refractory material with the content of 60 % Al 2 O 3 was investigated. Water quench test (JUS.B.D8.319) was applied as experimental method for thermal stability testing. Damage of porous materials is commonly related to a modification of strength that is mostly a reduction. This is linked with characteristics related to pore space. Mechanical characteristics are considered such as compressive strength, dynamic modulus of elasticity and resistance parameters resulting from resonance frequency measurements, as well as ultrasonic velocity. (Original)

Mechanisms for the Dissipation of Alfven Waves in Near-Earth Space Plasma

Science.gov (United States)

Singh, Nagendra; Khazanov, George; Krivorutsky, E. N.; Davis, John M. (Technical Monitor)

2002-01-01

Alfven waves are a major mechanism for the transport of electromagnetic energy from the distant part of the magnetosphere to the near-Earth space. This is especially true for the auroral and polar regions of the Earth. However, the mechanisms for their dissipation have remained illusive. One of the mechanisms is the formation of double layers when the current associated with Alfven waves in the inertial regime interact with density cavities, which either are generated nonlinearly by the waves themselves or are a part of the ambient plasma turbulence. Depending on the strength of the cavities, weak and strong double layers could form. Such double layers are transient; their lifetimes depend on that of the cavities. Thus they impulsively accelerate ions and electrons. Another mechanism is the resonant absorption of broadband Alfven- wave noise by the ions at the ion cyclotron frequencies. But this resonant absorption may not be possible for the very low frequency waves, and it may be more suited for electromagnetic ion cyclotron waves. A third mechanism is the excitation of secondary waves by the drifts of electrons and ions in the Alfven wave fields. It is found that under suitable conditions, the relative drifts between different ion species and/or between electrons and ions are large enough to drive lower hybrid waves, which could cause transverse accelerations of ions and parallel accelerations of electrons. This mechanism is being further studied by means of kinetic simulations using 2.5- and 3-D particle-in-cell codes. The ongoing modeling efforts on space weather require quantitative estimates of energy inputs of various kinds, including the electromagnetic energy. Our studies described here contribute to the methods of determining the estimates of the input from ubiquitous Alfven waves.

Atomistic mechanisms governing structural stability change of zinc antimony thermoelectrics

Energy Technology Data Exchange (ETDEWEB)

Yang, Xiaolong [Frontier Institute of Science and Technology, Xi' an Jiaotong University, Xi' an 710054 (China); Lin, Jianping, E-mail: jaredlin@163.com [School of Materials Science and Engineering, Xiamen University of Technology, Xiamen 361024 (China); Qiao, Guanjun [State Key Laboratory for Mechanical Behavior of Materials, Xi' an Jiaotong University, Xi' an 710049 (China); Wang, Zhao, E-mail: zwangzhao@gmail.com [Frontier Institute of Science and Technology, Xi' an Jiaotong University, Xi' an 710054 (China); State Key Laboratory for Mechanical Behavior of Materials, Xi' an Jiaotong University, Xi' an 710049 (China)

2015-01-05

The structural stability of thermoelectric materials is a subject of growing importance for their energy harvesting applications. Here, we study the microscopic mechanisms governing the structural stability change of zinc antimony at its working temperature, using molecular dynamics combined with experimental measurements of the electrical and thermal conductivity. Our results show that the temperature-dependence of the thermal and electrical transport coefficients is strongly correlated with a structural transition. This is found to be associated with a relaxation process, in which a group of Zn atoms migrates between interstitial sites. This atom migration gradually leads to a stabilizing structural transition of the entire crystal framework, and then results in a more stable crystal structure of β–Zn{sub 4}Sb{sub 3} at high temperature.

Mechanisms of Earth activity forsed by external celestial bodies:energy budjet and nature of cyclicity

Science.gov (United States)

Barkin, Yu. V.; Ferrandiz, J. M.

2003-04-01

In given report we discuss tidal and non-tidal mechanisms of forced tectonic (endogenous) activity of the Earth caused by gravitational attraction of the Moon, Sun and the planets. On the base of the classical solution of the problem of elasticity for model of the Earth with concentric mass distribution the evaluations of the tidal energy and power of Earth lunar-solar deformations, including their joint effect, were obtained. Important role of the joint energetic effect of rotational deformation of the Earth with lunar and solar tides was illustrated. Gravitational interaction of the Moon and Sun with non-spherical, non-homogeneous shells of the Earth generates big additional mechanical forces and moments of the interaction of the neighboring shells (rigid core, liquid core, mantle, lithosphere and separate plates). Acting of these forces and moments in the different time scales on the corresponding sells generates cyclic perturbations of the tensional state of the shells, their deformations, small relative translational displacements and small relative rotational oscillations of the shells. In geological period of time it leads to a fundamental tectonic reconstruction of the Earth. These additional forces and moments of the cyclic celestial-mechanical nature produce cyclic deformations of the all layers of the body and organize and control practically all natural processes. The additional force between mantle and core is cyclic and characterized by the wide basis of frequencies typical for orbital motions (of the Sun, Moon and planets), for rotational motion of the Earth, Moon and Sun and for many from observed natural processes. The problem about small relative translatory-rotary motion of the two shells separated by the thin viscous-elastic layer is studied. The differential equations of motion were obtained and have been studied in particular cases (plane motion of system; case of two axisymmetrical interacting shells and oth.) by approximate methods of small

Features and Mechanisms for Ensuring Social and Political Stability in Contemporary Chinese Society

Directory of Open Access Journals (Sweden)

Максим Алексеевич Сущенко

2017-12-01

Full Text Available This article discusses the features and mechanisms of ensuring and maintaining social and political stability in China. Analyzes the scientific theoretical foundation in the study of this phenomenon, developed by Russian and Chinese scientists. Political stability in contemporary China is understood as a precondition for effective social and economic development. The paper studied the treatment of leadership in China from different generations to tools approval of social and political stability as a way of implementing the modernization program of the political course. It has been found that maintaining the political stability of the society in modern China made possible by the harmonization of public relations, flexible national policy, economic growth, trends in socio-economic development and the use of ideological tools. The author studied the basic mechanisms of the stability of the political system of China at the present stage. It is concluded that a stable political development in contemporary China strengthens the regime and the preservation of the monopoly of the CCP to political power.

Rotation of a Moonless Earth

Science.gov (United States)

Lissauer, Jack J.; Barnes, Jason W.; Chambers, John E.

2013-01-01

We numerically explore the obliquity (axial tilt) variations of a hypothetical moonless Earth. Previous work has shown that the Earth's Moon stabilizes Earth's obliquity such that it remains within a narrow range, between 22.1 deg and 24.5 deg. Without lunar influence, a frequency-map analysis by Laskar et al. showed that the obliquity could vary between 0 deg. and 85 deg. This has left an impression in the astrobiology community that a large moon is necessary to maintain a habitable climate on an Earth-like planet. Using a modified version of the orbital integrator mercury, we calculate the obliquity evolution for moonless Earths with various initial conditions for up to 4 Gyr. We find that while obliquity varies significantly more than that of the actual Earth over 100,000 year timescales, the obliquity remains within a constrained range, typically 20-25 deg. in extent, for timescales of hundreds of millions of years. None of our Solar System integrations in which planetary orbits behave in a typical manner show obliquity accessing more than 65% of the full range allowed by frequency-map analysis. The obliquities of moonless Earths that rotate in the retrograde direction are more stable than those of pro-grade rotators. The total obliquity range explored for moonless Earths with rotation periods shorter than 12 h is much less than that for slower-rotating moonless Earths. A large moon thus does not seem to be needed to stabilize the obliquity of an Earth-like planet on timescales relevant to the development of advanced life.

Predictibility of the stability constant of a radium-cryptate by means of in vivo data from radioactive alkaline earthes.

Science.gov (United States)

Müller, W H

1977-08-01

By means of a formula, developed by J. Schubert[9] and A. Catsch, H.J. Heller[3] as well as a relation postulated by A. Catsch[1] the "thermodynamic" stability constant of the Radium (222)-cryptate (KRaRa(222) was calculated from measurements of the total body retention of the total body retention of the radioactive alkaline earthes 85SR, 140Ba and 224Ra and its (222)-cryptates in rats [5-7]. From the same in vivo data a direct lineary relationship between the log of the effectiveness quotient, log EQM(222), and the log of the "thermodynamic" stability log KMM(222) was found graphically. The values from the graph correspond with those of the calculation.

Rotation stability of high speed neutron time-of-flight mechanical chopper

International Nuclear Information System (INIS)

Habib, N.; Adib, M.

1998-01-01

A modified rotation stabilization system has been designed to maintain the stability of a neutron time-of-flight (TOF) mechanical chopper rates from 460 rpm to 16000 rpm. The main principle of the system is based on comparing the chopper's rotation period with the preselected one from a quartz timer. The result of comparison is used to control the current driver of the chopper's motor. A 600 Hz three phase generator controlled by a magnetic amplifier was used as a current driver. The stability of the chopper's rotation rate at 16000 rpm was 0.02%. An improved method precise time scale calibration of the TOF spectrometer is applied

Improving the Mechanical Performance and Thermal Stability of a PVA-Clay Nanocomposite by Electron Beam Irradiation

Science.gov (United States)

Shokuhi Rad, A.; Ebrahimi, D.

2017-07-01

The effects of electron beam irradiation and presence of clay on the mechanical properties and thermal stability of montmorillonite clay-modified polyvinyl alcohol nanocomposites were studied. By using the X-ray diffraction (XRD) and transmission electron microscopy (TEM), the microstructure of the nanocomposites was investigated. The results obtained from TEM and XRD tests showed that montmorillonite clay nanoparticles were located in the polyvinyl alcohol phase. The XRD analysis confirmed the formation of an exfoliated structure in nanocomposites samples. Increasing the amount of clay to 20 wt.% increased the tensile strength and modulus of the nanocomposite. Irradiation up to an absorbed dose of 100 kGy increased its mechanical properties and thermal stability, but at higher irradiation levels, the mechanical strength and thermal stability declined. The sample with 20 wt.% of the nanofiller, exposed to 100 kGy, showed the highest mechanical strength and thermal stability.

Magnetically levitated space elevator to low-earth orbit.

Energy Technology Data Exchange (ETDEWEB)

Hull, J. R.; Mulcahy, T. M.

2001-07-02

The properties of currently available NbTi superconductor and carbon-fiber structural materials enable the possibility of constructing a magnetically levitated space elevator from the earth's surface up to an altitude of {approx} 200 km. The magnetic part of the elevator consists of a long loop of current-carrying NbTi, composed of one length that is attached to the earth's surface in an east-west direction and a levitated-arch portion. The critical current density of NbTi is sufficiently high that these conductors will stably levitate in the earth's magnetic field. The magnetic self-field from the loop increases the levitational force and for some geometries assists levitational stability. The 200-km maximum height of the levitated arch is limited by the allowable stresses of the structural material. The loop is cryogenically cooled with helium, and the system utilizes intermediate pumping and cooling stations along both the ground and the levitated portion of the loop, similar to other large terrestrial cryogenic systems. Mechanically suspended from the basic loop is an elevator structure, upon which mass can be moved between the earth's surface and the top of the loop by a linear electric motor or other mechanical or electrical means. At the top of the loop, vehicles may be accelerated to orbital velocity or higher by rocket motors, electromagnetic propulsion, or hybrid methods.

Atomic scale study of vacancies in Earth's inner core: effect of pressure and chemistry

Science.gov (United States)

Ritterbex, S.; Tsuchiya, T.

2017-12-01

Seismic observations of the Earth's inner core [1] remain ambiguously related to mineral physics studies of the inner core stable crystalline iron phase [2,3,4,5]. This makes it difficult to clarify the role of plastic deformation as one of the primary candidates responsible for the observed seismic anisotropy of Earth's inner core. Nonetheless, atomic self-diffusion mechanisms provide a direct link between plastic deformation and the mechanical properties of Earth's inner core stable iron phase(s). Using first-principles density functional based calculation techniques, we have studied the conjugate effect of pressure and chemistry on vacancy diffusion in HCP-, BCC- and FCC-iron by taking into account potential light alloying elements as hydrogen, silicon and sulfur. Our results show that inner core pressure highly inhibits the rate of intrinsic self-diffusion by suppressing defect concentration rather than by effecting the mobility of the defects. Moreover, we found light elements to be able to affect metallic bonding which allows for extrinsic diffusion mechanisms in iron under inner core conditions. The latter clearly enables to enhance defect concentration and hence to enhance the rate of plastic deformation. This suggests that inner core chemistry affects the rheological properties (e.g.viscosity) of iron alloys which finally should match with seismic observations. references: [1] Deuss, A., 2014. Heterogeneity and Anisotropy of Earth's inner core. An. Rev. Earth Planet. Sci. 42, 103-126. [2] Anzellini, S., Dewaele, A., Mezouar, M., Loubeyre, P., Morard, G., 2013. Melting of iron at Earth's inner core boundary based on fast X-ray diffraction. Science 340, 464-466. [3] Godwal, B.K., Gonzales-Cataldo, F., Verma, A.K., Stixrude, L., Jeanloz, R., 2015. Stability of iron crystal structures at 0.3-1.5 TPa. [4] Vocadlo, L., 2007. Ab initio calculations of the elasticity of iron and iron alloys at inner core conditions: evidence for a partially molten inner core

Mechanical stability assessment of novel orthodontic mini-implant designs: Part 2.

Science.gov (United States)

Hong, Christine; Truong, Peter; Song, Ha Na; Wu, Benjamin M; Moon, Won

2011-11-01

To assess the mechanical stability of a newly revised orthodontic mini-implant design (N2) compared with a design introduced in Part 1 of the study (N1) and the most widely-used commercially-available design (CA). To evaluate the mean buccal bone thickness of maxillary and mandibular posterior teeth using cone-beam computed tomography (CBCT). From the CBCT scans of 20 patients, six tomographic cross-sections were generated for each tooth. Buccal bone thickness was measured from the most convex point on the bone to the root surface. CA (1.5 mm in diameter and 6 mm in length), N1, and N2 (shorter and narrower than N1) were inserted in simulated bone with cortical and trabecular bone layers. Mechanical stability was compared in vitro through torque and lateral displacement tests. The bone thickness ranged from 2.26 to 3.88 mm. Maximum insertion torque was decreased significantly in N2 compared to N1. However, force levels for all displacement distances and torque ratio were the highest in N2, followed by N1 and CA (α = .05). Both torque and lateral displacement tests highlighted the enhanced stability of N2 compared with CA. Design revisions to N1 effectively mitigated N1's high insertion torque and thus potentially reduced microdamage to the surrounding bone. The N2 design is promising as evidenced by enhanced stability and high mechanical efficiency. Moreover, N2 is not limited to placement in interradicular spaces and has the capacity to be placed in the buccal bone superficial to the root surface with diminished risk of endangering nearby anatomic structures during placement and treatment.

Effects of mechanical feedback on the stability of cardiac scroll waves: A bidomain electro-mechanical simulation study.

Science.gov (United States)

Colli Franzone, P; Pavarino, L F; Scacchi, S

2017-09-01

In this work, we investigate the influence of cardiac tissue deformation on re-entrant wave dynamics. We have developed a 3D strongly coupled electro-mechanical Bidomain model posed on an ideal monoventricular geometry, including fiber direction anisotropy and stretch-activated currents (SACs). The cardiac mechanical deformation influences the bioelectrical activity with two main mechanical feedback: (a) the geometric feedback (GEF) due to the presence of the deformation gradient in the diffusion coefficients and in a convective term depending on the deformation rate and (b) the mechano-electric feedback (MEF) due to SACs. Here, we investigate the relative contribution of these two factors with respect to scroll wave stability. We extend the previous works [Keldermann et al., Am. J. Physiol. Heart Circ. Physiol. 299, H134-H143 (2010) and Hu et al., PLoS One 8(4), e60287 (2013)] that were based on the Monodomain model and a simple non-selective linear SAC, while here we consider the full Bidomain model and both selective and non-selective components of SACs. Our simulation results show that the stability of cardiac scroll waves is influenced by MEF, which in case of low reversal potential of non-selective SACs might be responsible for the onset of ventricular fibrillation; GEF increases the scroll wave meandering but does not determine the scroll wave stability.

Transport and deposition of carbon at catchment scale: stabilization mechanisms approach

Science.gov (United States)

Martínez-Mena, María; Almagro, María; Díaz-Pereira, Elvira; García-Franco, Noelia; Boix-Fayos, Carolina

2016-04-01

Terrestrial sedimentation buries large amounts of organic carbon (OC) annually, contributing to the terrestrial carbon sink. The temporal significance of this sink will strongly depend on the attributes of the depositional environment, but also on the characteristics of the OC reaching these sites and its stability upon deposition. The fate of the redistributed OC will ultimately depend on the mechanisms of its physical and chemical protection against decomposition, its turnover rates and the conditions under which the OC is stored in sedimentary settings. This framework is more complex in Mediterranean river basins where sediments are often redistributed under a range of environmental conditions in ephemeral, intermittent and perennial fluvial courses, sometimes within the same catchment. The OC stabilization mechanisms and their relations with aggregation at different transport and sedimentary deposits is under those conditions highly uncertain. The main objective of this work was to characterize the stabilization and mineralization of OC in sediments in transit (suspended load), at a range of depositional settings (alluvial bars, reservoir sediments) and soils from the source areas in a sub-catchment (111 km2) at the headwaters of the Segura catchment in South East Spain. In order to obtain a deeper knowledge on the predominant stabilization mechanism corresponding to each erosional phase, the following organic carbon fractionation method was carried out: Four aggregate size classes were distinguished by sieving (large and small macroaggregates, free microaggregates, and free silt plus clay fraction), and the microaggregates occluded within macroaggregates (SMm) were isolated. As a further step, an oxidation of the OC occluded in silt plus clay fraction and that of the free silt plus clay fraction was performed to estimate the oxidant resistant OC pool. Measured OC in these fractions can be related to three functional pools: active (free particulate organic

Influence of stability of polymer surfactant on oil displacement mechanism

Science.gov (United States)

Liu, Li; Li, Chengliang; Pi, Yanming; Wu, Di; He, Ying; Geng, Liang

2018-02-01

At present, most of the oilfields of China have entered the late stage of high water-cut development, and three oil recovery technique has become the leading technology for improving oil recovery. With the improvement of three oil recovery techniques, the polymer surfactant flooding technology has been widely promoted in oil fields in recent years. But in the actual field experiment, it has been found that the polymer surfactant has chromatographic separation at the extraction end, which indicates that the property of the polymer surfactant has changed during the displacement process. At present, there was few literature about how the stability of polymer surfactant affects the oil displacement mechanism. This paper used HuaDing-I polymer surfactant to conduct a micro photolithography glass flooding experiment, and then compared the oil displacement law of polymer surfactant before and after static setting. Finally, the influence law of stability of polymer surfactant on the oil displacement mechanism is obtained by comprehensive analysis.

[Stabilization Treatment of Pb and Zn in Contaminated Soils and Mechanism Studies].

Science.gov (United States)

Xie, Wei-qiang; Li, Xiao-mingi; Chen, Can; Chen, Xun-feng; Zhong, Yu; Zhong, Zhen-yu; Wan, Yong; Wang, Yan

2015-12-01

In the present work, the combined application of potassium dihydrogen phosphate, quick lime and potassium chloride was used to immobilize the Pb and Zn in contaminated soils. The efficiency of the process was evaluated through leaching tests and Tessier sequential extraction procedure. The mechanism of stabilization was analyzed by X-ray diffraction (XRD) and scanning electron microscope (SEM) to reveal the mechanism of stabilization. The results showed that the stabilizing efficiency of Pb contaminated soils was above 80% and the leaching concentrations of Pb, Zn were far below the threshold when the ratio of exogenous P and soil (mol · mol⁻¹) was 2:1-4: 1, the dosing ratio of CaO was 0.1%-0.5% ( mass fraction) and the dosage of potassium chloride was 0.02-0. 04 mol. Meanwhile, Pb and Zn in soil were transformed from the exchangeable fraction into residual fraction, which implied that the migration of Pb, Zn in soil could be confined by the stabilization treatment. XRD and SEM analysis revealed that Ca-P-Pb precipitation, lead orthophosphate [PbHP0₄, Pb₃ (PO₄)₂], pyromorphite (Pb-PO₄-Cl/OH) and mixed heavy metal deposits (Fe-PO₄- Ca-Pb-Zn-OH) could be formed after solidification/stabilization in which Pb and Zn could be wrapped up to form a solidified composition and to prevent leaching.

Contracts, Vouchers, and Child Care Subsidy Stability: A Preliminary Look at Associations between Subsidy Payment Mechanism and Stability of Subsidy Receipt

Science.gov (United States)

Holod, Aleksandra; Johnson, Anna D.; Martin, Anne; Gardner, Margo; Brooks-Gunn, Jeanne

2012-01-01

Background: The federal child care subsidy program, funded through the Child Care and Development Fund (CCDF), is the nation's largest public investment in early child care. However, little is known about whether and how subsidy payment mechanisms relate to the stability of subsidy receipt or the stability of children's care arrangements.…

Acceleration mechanisms for energetic particles in the earth's magnetosphere

International Nuclear Information System (INIS)

Schiferl, S.; Fan, C.Y.; Hsieh, K.C.; Erickson, K.N.; Gloeckler, G.; Hovestadt, D.

1982-01-01

By analyzing data on energetic particle fluxes measured simultaneously with detector systems on several earth satellites, we searched for signatures of different acceleration mechanisms for these particles. One of the samples is an event observed on ATS-6 and IMP-7. IMP-7 was in the dusk quarter at 38 Rsub(E) while ATS-6 was located at local midnight at a distance of 6.6 Rsub(E). Although the flux variations as observed on the two spacecraft both showed 1.5 min. periodicity, there was a 40-second time lag with IMP-7 behind. The results indicate that the particles are accelerated by magnetic field line annihilation, with the ''x-point'' located at approximately 10 Rsub(E)

Structure and Mechanical Properties of Al-Cu-Fe-X Alloys with Excellent Thermal Stability

OpenAIRE

Školáková, Andrea; Novák, Pavel; Mejzlíková, Lucie; Průša, Filip; Salvetr, Pavel; Vojtěch, Dalibor

2017-01-01

In this work, the structure and mechanical properties of innovative Al-Cu-Fe based alloys were studied. We focused on preparation and characterization of rapidly solidified and hot extruded Al-Cu-Fe, Al-Cu-Fe-Ni and Al-Cu-Fe-Cr alloys. The content of transition metals affects mechanical properties and structure. For this reason, microstructure, phase composition, hardness and thermal stability have been investigated in this study. The results showed exceptional thermal stability of these allo...

Influence of mechanical scratch on the recorded magnetization stability of perpendicular recording media

International Nuclear Information System (INIS)

Nagano, Katsumasa; Sasaki, Syota; Futamoto, Masaaki

2010-01-01

Stability of recorded magnetization of hard disk drives (HDDs) is influenced by external environments, such as temperature, magnetic field, etc. Small scratches are frequently formed on HDD medium surface upon contacts with the magnetic head. Influence of temperature and mechanical scratch on the magnetization structure stability of perpendicular recording media was investigated by using a magnetic force microscope. The magnetic bit shape started to change at around 300 0 C for an area with no scratches, whereas for the area near a shallow mechanical scratch it started to change at a lower temperature around 250 0 C. An analysis of magnetization structure under an influence of temperature and mechanical scratch is carried out for the magnetization structure variation and recorded magnetization strength.

Innovative Application of Mechanical Activation for Rare Earth Elements Recovering: Process Optimization and Mechanism Exploration

Science.gov (United States)

Tan, Quanyin; Deng, Chao; Li, Jinhui

2016-01-01

With the rapidly expanding use of fluorescent lamps (FLs) and increasing interest in conservation and sustainable utilization of critical metals such as rare earth elements (REEs), the recovering of REEs from phosphors in waste FLs is becoming a critical environmental and economic issue. To effectively recycle REEs with metallurgical methods, mechanical activation by ball milling was introduced to pretreat the waste phosphors. This current study put the emphasis on the mechanical activation and leaching processes for REEs, and explored the feasibility of the method from both theoretical and practical standpoints. Results showed physicochemical changes of structural destruction and particle size reduction after mechanical activation, leading to the easy dissolution of REEs in the activated samples. Under optimal conditions, dissolution yields of 89.4%, 93.1% and 94.6% for Tb, Eu and Y, respectively, were achieved from activated waste phosphors using hydrochloric acid as the dissolution agent. The shrinking core model proved to be the most applicable for the leaching procedure, with an apparent activation energy of 10.96 ± 2.79 kJ/mol. This novel process indicates that mechanical activation is an efficient method for recovering REEs from waste phosphors, and it has promising potential for REE recovery with low cost and high efficiency.

Sequential bottom-up assembly of mechanically stabilized synthetic cells by microfluidics

Science.gov (United States)

Weiss, Marian; Frohnmayer, Johannes Patrick; Benk, Lucia Theresa; Haller, Barbara; Janiesch, Jan-Willi; Heitkamp, Thomas; Börsch, Michael; Lira, Rafael B.; Dimova, Rumiana; Lipowsky, Reinhard; Bodenschatz, Eberhard; Baret, Jean-Christophe; Vidakovic-Koch, Tanja; Sundmacher, Kai; Platzman, Ilia; Spatz, Joachim P.

2018-01-01

Compartments for the spatially and temporally controlled assembly of biological processes are essential towards cellular life. Synthetic mimics of cellular compartments based on lipid-based protocells lack the mechanical and chemical stability to allow their manipulation into a complex and fully functional synthetic cell. Here, we present a high-throughput microfluidic method to generate stable, defined sized liposomes termed `droplet-stabilized giant unilamellar vesicles (dsGUVs)’. The enhanced stability of dsGUVs enables the sequential loading of these compartments with biomolecules, namely purified transmembrane and cytoskeleton proteins by microfluidic pico-injection technology. This constitutes an experimental demonstration of a successful bottom-up assembly of a compartment with contents that would not self-assemble to full functionality when simply mixed together. Following assembly, the stabilizing oil phase and droplet shells are removed to release functional self-supporting protocells to an aqueous phase, enabling them to interact with physiologically relevant matrices.

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

Science.gov (United States)

Imandoust, Aidin

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

The opto-mechanical design of the GMT-consortium large earth finder (G-CLEF)

Science.gov (United States)

Mueller, Mark; Baldwin, Daniel; Bean, Jacob; Bergner, Henry; Bigelow, Bruce; Chun, Moo-Young; Crane, Jeffrey; Foster, Jeff; Fżrész, Gabor; Gauron, Thomas; Guzman, Dani; Hertz, Edward; Jordán, Andrés.; Kim, Kang-Min; McCracken, Kenneth; Norton, Timothy; Ordway, Mark; Park, Chan; Park, Sang; Podgorski, William A.; Szentgyorgyi, Andrew; Uomoto, Alan; Yuk, In-Soo

2014-08-01

The GMT-Consortium Large Earth Finder (G-CLEF) is a fiber fed, optical echelle spectrograph that has been selected as a first light instrument for the Giant Magellan Telescope (GMT) currently under construction at the Las Campanas Observatory in Chile's Atacama desert region. We designed G-CLEF as a general-purpose echelle spectrograph with precision radial velocity (PRV) capability used for exoplanet detection. The radial velocity (RV) precision goal of GCLEF is 10 cm/sec, necessary for detection of Earth-sized planets orbiting stars like our Sun in the habitable zone. This goal imposes challenging stability requirements on the optical mounts and the overall spectrograph support structures. Stability in instruments of this type is typically affected by changes in temperature, orientation, and air pressure as well as vibrations caused by telescope tracking. For these reasons, we have chosen to enclose G-CLEF's spectrograph in a thermally insulated, vibration isolated vacuum chamber and place it at a gravity invariant location on GMT's azimuth platform. Additional design constraints posed by the GMT telescope include: a limited space envelope, a thermal emission ceiling, and a maximum weight allowance. Other factors, such as manufacturability, serviceability, available technology and budget are also significant design drivers. All of the previously listed considerations must be managed while ensuring that performance requirements are achieved. In this paper, we discuss the design of G-CLEF's optical mounts and support structures including technical choices made to minimize the system's sensitivity to thermal gradients. A more general treatment of the properties of G-CLEF can be found elsewhere in these proceedings1. We discuss the design of the vacuum chamber which houses the irregularly shaped optical bench and optics while conforming to a challenging space envelope on GMT's azimuth platform. We also discuss the design of G-CLEF's insulated enclosure and thermal

Kinetics and mechanical stability of the fibril state control fibril formation time of polypeptide chains: A computational study

Science.gov (United States)

Kouza, Maksim; Co, Nguyen Truong; Li, Mai Suan; Kmiecik, Sebastian; Kolinski, Andrzej; Kloczkowski, Andrzej; Buhimschi, Irina Alexandra

2018-06-01

Fibril formation resulting from protein misfolding and aggregation is a hallmark of several neurodegenerative diseases such as Alzheimer's and Parkinson's diseases. Despite much progress in the understanding of the protein aggregation process, the factors governing fibril formation rates and fibril stability have not been fully understood. Using lattice models, we have shown that the fibril formation time is controlled by the kinetic stability of the fibril state but not by its energy. Having performed all-atom explicit solvent molecular dynamics simulations with the GROMOS43a1 force field for full-length amyloid beta peptides Aβ40 and Aβ42 and truncated peptides, we demonstrated that kinetic stability can be accessed via mechanical stability in such a way that the higher the mechanical stability or the kinetic stability, the faster the fibril formation. This result opens up a new way for predicting fibril formation rates based on mechanical stability that may be easily estimated by steered molecular dynamics.

Impact of lysozyme on stability mechanism of nanozirconia aqueous suspension

Energy Technology Data Exchange (ETDEWEB)

Szewczuk-Karpisz, Katarzyna, E-mail: k.szewczuk-karpisz@wp.pl; Wiśniewska, Małgorzata

2016-08-30

Highlights: • Adsorption and stabilization-destabilization properties of lysozyme (LSZ) in the nanozirconia-biopolymer solution system were determined. • The stability measurements were performed using turbidimetric method. • Lysozyme macromolecules undergo adsorption on the ZrO{sub 2} surface under electrostatic adsorbent-adsorbate attraction, i.e. at pH 6 and 9. • The biopolymer adsorption impact on the zirconia stability varies at different pH values. - Abstract: The effect of lysozyme (LSZ) presence on the zirconium(IV) oxide (ZrO{sub 2}) aqueous suspension stability was examined. The applied zirconia contains mesopores (with a diameter about 30 nm) and its mean particle size is about 100 nm. To determine the stability mechanism of ZrO{sub 2} suspension in the biopolymer presence, the adsorption and electrokinetic (surface charge density and zeta potential) measurements were performed in the pH range 3–10. The lysozyme adsorption on the nanozirconia surface proceeds mainly through electrostatic forces. Under solid-polymer repulsion conditions, there is no adsorption of lysozyme (pH < 6, C{sub NaCl} 0.01 mol/dm{sup 3}). The increase of solution ionic strength to 0.2 mol/dm{sup 3} causes screening of unfavourable forces and biopolymer adsorption becomes possible. The LSZ addition to the ZrO{sub 2} suspension influences its stability. At pH 3, 4.6 and 7.6, slight improvement of the system stability was obtained. In turn, at pH 9 considerable destabilization of nanozirconia particles covered by polymeric layers occurs.

Mechanical and thermal stability of graphene and graphene-based materials

Science.gov (United States)

Galashev, A. E.; Rakhmanova, O. R.

2014-10-01

Graphene has rapidly become one of the most popular materials for technological applications and a test material for new condensed matter ideas. This paper reviews the mechanical properties of graphene and effects related to them that have recently been discovered experimentally or predicted theoretically or by simulation. The topics discussed are of key importance for graphene's use in integrated electronics, thermal materials, and electromechanical devices and include the following: graphene transformation into other sp^2 hybridization forms; stability to stretching and compression; ion-beam-induced structural modifications; how defects and graphene edges affect the electronic properties and thermal stability of graphene and related composites.

Earth rotation excitation mechanisms derived from geodetic space observations

Science.gov (United States)

Göttl, F.; Schmidt, M.

2009-04-01

Earth rotation variations are caused by mass displacements and motions in the subsystems of the Earth. Via the satellite Gravity and Climate Experiment (GRACE) gravity field variations can be identified which are caused by mass redistribution in the Earth system. Therefore time variable gravity field models (GFZ RL04, CSR RL04, JPL RL04, ITG-Grace03, GRGS, ...) can be used to derive different impacts on Earth rotation. Furthermore satellite altimetry provides accurate information on sea level anomalies (AVISO, DGFI) which are caused by mass and volume changes of seawater. Since Earth rotation is solely affected by mass variations and motions the volume (steric) effect has to be reduced from the altimetric observations in order to infer oceanic contributions to Earth rotation variations. Therefore the steric effect is estimated from physical ocean parameters such as temperature and salinity changes in the oceans (WOA05, Ishii). In this study specific individual geophysical contributions to Earth rotation variations are identified by means of a multitude of accurate geodetic space observations in combination with a realistic error propagation. It will be shown that due to adjustment of altimetric and/or gravimetric solutions the results for polar motion excitations can be improved.

A hybrid online scheduling mechanism with revision and progressive techniques for autonomous Earth observation satellite

Science.gov (United States)

Li, Guoliang; Xing, Lining; Chen, Yingwu

2017-11-01

The autonomicity of self-scheduling on Earth observation satellite and the increasing scale of satellite network attract much attention from researchers in the last decades. In reality, the limited onboard computational resource presents challenge for the online scheduling algorithm. This study considered online scheduling problem for a single autonomous Earth observation satellite within satellite network environment. It especially addressed that the urgent tasks arrive stochastically during the scheduling horizon. We described the problem and proposed a hybrid online scheduling mechanism with revision and progressive techniques to solve this problem. The mechanism includes two decision policies, a when-to-schedule policy combining periodic scheduling and critical cumulative number-based event-driven rescheduling, and a how-to-schedule policy combining progressive and revision approaches to accommodate two categories of task: normal tasks and urgent tasks. Thus, we developed two heuristic (re)scheduling algorithms and compared them with other generally used techniques. Computational experiments indicated that the into-scheduling percentage of urgent tasks in the proposed mechanism is much higher than that in periodic scheduling mechanism, and the specific performance is highly dependent on some mechanism-relevant and task-relevant factors. For the online scheduling, the modified weighted shortest imaging time first and dynamic profit system benefit heuristics outperformed the others on total profit and the percentage of successfully scheduled urgent tasks.

Degradation mechanism and thermal stability of urea nitrate below the melting point

International Nuclear Information System (INIS)

Desilets, Sylvain; Brousseau, Patrick; Chamberland, Daniel; Singh, Shanti; Feng, Hongtu; Turcotte, Richard; Anderson, John

2011-01-01

Highlights: → Decomposition mechanism of urea nitrate. → Spectral characterization of the decomposition mechanism. → Thermal stability of urea nitrate at 50, 70 and 100 o C. → Chemical balance of decomposed products released. - Abstract: Aging and degradation of urea nitrate below the melting point, at 100 o C, was studied by using thermal analysis and spectroscopic methods including IR, Raman, 1 H and 13 C NMR techniques. It was found that urea nitrate was completely degraded after 72 h at 100 o C into a mixture of solids (69%) and released gaseous species (31%). The degradation mechanism below the melting point was clearly identified. The remaining solid mixture was composed of ammonium nitrate, urea and biuret while unreacted residual nitric and isocyanic acids as well as traces of ammonia were released as gaseous species at 100 o C. The thermal stability of urea nitrate, under extreme storage conditions (50 o C), was also examined by isothermal nano-calorimetry.

Improving the Bearing Strength of Sandy Loam Soil Compressed Earth Block Bricks Using Sugercane Bagasse Ash

Directory of Open Access Journals (Sweden)

Ramadhan W. Salim

2014-06-01

Full Text Available The need for affordable and sustainable alternative construction materials to cement in developing countries cannot be underemphasized. Compressed Earth Bricks have gained acceptability as an affordable and sustainable construction material. There is however a need to boost its bearing capacity. Previous research show that Sugarcane Bagasse Ash as a soil stabilizer has yielded positive results. However, there is limited research on its effect on the mechanical property of Compressed Earth Brick. This current research investigated the effect of adding 3%, 5%, 8% and 10% Sugarcane Bagasse Ash on the compressive strength of compressed earth brick. The result showed improvement in its compressive strength by 65% with the addition of 10% Sugarcane Bagasse Ash.

The Development of HfO2-Rare Earth Based Oxide Materials and Barrier Coatings for Thermal Protection Systems

Science.gov (United States)

Zhu, Dongming; Harder, Bryan James

2014-01-01

Advanced hafnia-rare earth oxides, rare earth aluminates and silicates have been developed for thermal environmental barrier systems for aerospace propulsion engine and thermal protection applications. The high temperature stability, low thermal conductivity, excellent oxidation resistance and mechanical properties of these oxide material systems make them attractive and potentially viable for thermal protection systems. This paper will focus on the development of the high performance and high temperature capable ZrO2HfO2-rare earth based alloy and compound oxide materials, processed as protective coating systems using state-or-the-art processing techniques. The emphasis has been in particular placed on assessing their temperature capability, stability and suitability for advanced space vehicle entry thermal protection systems. Fundamental thermophysical and thermomechanical properties of the material systems have been investigated at high temperatures. Laser high-heat-flux testing has also been developed to validate the material systems, and demonstrating durability under space entry high heat flux conditions.

Mechanical and Thermophysical Properties of Cement and/or Paper (Cellulose Stabilized Compressed Clay Bricks

Directory of Open Access Journals (Sweden)

Emmanuel OUEDRAOGO

2015-05-01

Full Text Available This article presents an experimental study of the characterization of clay blocks stabilized with cement and/or recycled papers as construction materials. When they are utilized as finish for building envelops, they must have appropriate mechanical strength and water stability. The measurements of the mechanical and thermophysical properties show differences between the properties of four investigated specimens. Mechanical properties such as compression and tensile tresses of clay-cement and clay-cement-paper mixtures are found to be quite similar but are two to three times greater respectively for clay-paper and purely clay blocks. The values of the thermophysical properties of blocks incorporating paper show improvement of their thermo insulation performances.

Effect of Lumbar Stabilization Exercises Versus Kinesiotaping on Chronic Mechanical Low Back Pain

International Nuclear Information System (INIS)

Abdellatif, M.M.; Kamel, M.R.; Ahmed, H.H.; Diab, H.R.

2016-01-01

Background: Low back pain (LBP) is one of the most common musculoskeletal problems in modern society. Approximately two third of the adults are affected by mechanical low back pain. Lumbar stabilization exercise is a therapeutic technique that uses a progressive sequence of training in coordination, balance, endurance and strengthening. It helps increasing the range of joint motion and reducing associated pain. Kinesiotape is an adhesive tape which has approximately the same elasticity as skin. The flexibility of the tape will lift the skin to create space between the skin and the muscle, prompting improvement of blood circulation and lymphatic fluids drainage in the taped area, and this will decrease pain, increase Range Of Motion (ROM) and improve Activities of Daily Level (ADL). Purpose: This study was conducted to compare the effect of lumbar stabilization exercises and Kinesiotape in patients with Chronic Mechanical Low Back Pain. Design of the study: Thirty patients were divided randomly into two equal groups. Group A was received lumber stabilization exercises and Infrared Radiation and Group B was received kinesiotape and Infrared Radiation. Method: Visual Analogue Scale (VAS) was used to measure the pain intensity level and Dual Inclinometer was used to measure ROM of the lumbar spine. Results: There was a high significant decrease in pain level in both groups Group A (p < 0.0001) and Group B (p < 0.0001). There was a high significant improvement in Lumbar ROM in both groups A and B where Group A: Flexion (p < 0.0001), extension (p < 0.0001), lateral flexion (p < 0.0001) and rotation (p < 0.0001), Group B: Flexion (p < 0.0001), extension (p < 0.0001), later al flexion (p < 0.0001) and rotation (p < 0.0001). Conclusion: There was no significant difference between the Lumbar Stabilization Exercise and kinesiotaping for the patients with chronic mechanical low back pain in increasing lumbar ROM and pain relief after treatment and during the follow up after

Preparation of Rare Earth Doped Alumina-Siloxane Gel and Its ER Effect

Institute of Scientific and Technical Information of China (English)

李幼荣; 张明; 周兰香; 邱关明; 井上真一; 冈本宏

2002-01-01

Poly(methyl methacrylate) (PMMA) was used to wrap alumina-siloxane sol through emulsion polymerization. A kind of suspensions with notable ER effect was produced by fully mixing the prepared microcapsule with silicon oil. Meanwhile a series of PMMA wrapped alumina-siloxane gel doped with rare earths was obtained and its ER effect was tested, like viscosity of different rare earth ion doped samples in different powder concentrations and at different temperatures, at the same time, leak current density and dielectric constant were measured. Results show that the ER effect of this suspension is remarkable, and its stability is much better. The condition of emulsion polymerization and the mechanism of effect are discussed.

Mechanisms of stability of armored bubbles: FY 1995 progress report

International Nuclear Information System (INIS)

Rossen, W.R.; Das, S.K.

1996-04-01

Experimental and theoretical studies of stabilization of liquid films between bubbles were undertaken as part of an effort to model gas release in waste tanks at the Hanford nuclear reservation. Synthetic Hanford waste created here showed solids accumulation at bubble surfaces and some stabilization of bubbles in a froth upon sparging with nitrogen. Dilational interfacial rheological measurements indicate increasing hydrophobicity with increasing EDTA concentration in the wastes. There is greater dilational elasticity of the interface with solid particles present on the interface. Theoretical modeling of a 2D liquid film between bubbles containing one row of solid particles suggests that in 3D such a film would be unstable unless the solids all touch. This hints at a possible mechanism for bubble stabilization, if it can be argued that slowly evolving interfaces, as bubbles grow toward each other in the sludge, have solids closely packed, but that rapid expansion of gas during a rollover event forces the films to expand without additional solids

PARAMETRIC ANALYSIS OF LONGITUDINAL STABILITY UNMANNED AERIAL VEHICLE

Directory of Open Access Journals (Sweden)

Ievgen Udartsev

2013-10-01

Full Text Available 1024x768 We consider the aerodynamic characteristics of unmanned aircraft container type, which were obtained in a wind tunnel and refined amended by soot blowing elements propeller system and the influence of the earth's surface. The estimation of longitudinal static stability and its dependence on altitude, damping, coordinates of center of gravity, shoulder horizontal tail, wings rejection of mechanization. The variation of these parameters enables to optimize balancing system with minimal losses. Normal 0 false false false

The ZX-calculus is complete for stabilizer quantum mechanics

International Nuclear Information System (INIS)

Backens, Miriam

2014-01-01

The ZX-calculus is a graphical calculus for reasoning about quantum systems and processes. It is known to be universal for pure state qubit quantum mechanics (QM), meaning any pure state, unitary operation and post-selected pure projective measurement can be expressed in the ZX-calculus. The calculus is also sound, i.e. any equality that can be derived graphically can also be derived using matrix mechanics. Here, we show that the ZX-calculus is complete for pure qubit stabilizer QM, meaning any equality that can be derived using matrices can also be derived pictorially. The proof relies on bringing diagrams into a normal form based on graph states and local Clifford operations. (paper)

Instability and breakdown of the coral-algae symbiosis upon exceedence of the interglacial pCO2 threshold (>260 ppmv): the "missing" Earth-System feedback mechanism

Science.gov (United States)

Wooldridge, Scott A.

2017-12-01

Changes in the atmospheric partial pressure of CO2 ( pCO2) leads to predictable impacts on the surface ocean carbonate system. Here, the importance of atmospheric pCO2 <260 ppmv is established for the optimum performance (and stability) of the algal endosymbiosis employed by a key suite of tropical reef-building coral species. Violation of this symbiotic threshold is revealed as a prerequisite for major historical reef extinction events, glacial-interglacial feedback climate cycles, and the modern decline of coral reef ecosystems. Indeed, it is concluded that this symbiotic threshold enacts a fundamental feedback mechanism needed to explain the characteristic dynamics (and drivers) of the coupled land-ocean-atmosphere carbon cycle of the Earth System since the mid-Miocene, some 25 million yr ago.

Inspector's manual for mechanically stabilized earth walls.

Science.gov (United States)

2010-06-01

The scope of the project is to develop a condition rating system, creation of an inspector's manual to reference during : inspection or address any training for inspectors at the district level. The research project will develop a MSE wall : conditio...

Stabilization mechanisms for information stored in magnetic nanowire arrays

Energy Technology Data Exchange (ETDEWEB)

Cisternas, Eduardo, E-mail: eduardo.cisternas@gmail.com [Departamento de Ciencias Físicas, Universidad de La Frontera, Casilla 54-D, Temuco (Chile); Faúndez, Julián [Departamento de Ciencias Físicas, Universidad de La Frontera, Casilla 54-D, Temuco (Chile); Vogel, Eugenio E. [Departamento de Ciencias Físicas, Universidad de La Frontera, Casilla 54-D, Temuco (Chile); Center for the Development of Nanoscience and Nanotechnology (CEDENNA), 9170124 Santiago (Chile)

2017-03-15

The durability of the stored information in magnetic systems is one important feature in firmware applications such as security codes, magnetic keys and other similar products. In the present paper we discuss two different ways of preserving patterns in the set of magnetic wires trapped in the porous membranes used to produce them. One of the techniques is the inscription of an opposite magnetic band of about 1/3 the width of the stored pattern which minimizes the repulsive energy among the ferromagnetic cylinders still leaving a potent magnetic signal to be read. The other technique makes use of segmented nanowires which present a competition of repulsive energy of segments within the same layer while the interaction is attractive with the closer segments of the other layer; such a competition can lead to stabilization if the geometrical parameters are properly controlled. The first technique is cheaper and faster to implement, while the second technique needs a more complete fabrication process but can lead to more durable stored information. - Highlights: • Stability of ferromagnetic patterns inscribed on magnetic nanowires arrays. • Information prevalence and stabilization mechanisms. • Applicability to fimware, security codes and magnetic keys.

Carbon stabilization mechanisms in soils in the Andes

Science.gov (United States)

Jansen, Boris; Cammeraat, Erik

2015-04-01

The volcanic ash soils of the Andes contain very large stocks of soil organic matter (SOM) per unit area. Consequently, they constitute significant potential sources or sinks of the greenhouse gas CO2. Climate and/or land use change potentially have a strong effect on these large SOM stocks. To clarify the role of chemical and physical stabilisation mechanisms in volcanic ash soils in the montane tropics, we investigated carbon stocks and stabilization mechanisms in the top- and subsoil along an altitudinal transect in the Ecuadorian Andes. The transect encompassed a sequence of paleosols under forest and grassland (páramo), including a site where vegetation cover changed in the last century. We applied selective extraction techniques, performed X-ray diffraction analyses of the clay fraction and estimated pore size distributions at various depths in the top- and subsoil along the transect. In addition, from several soils the molecular composition of SOM was further characterized with depth in the current soil as well as the entire first and the top of the second paleosol using GC/MS analyses of extractable lipids and Pyrolysis-GC/MS analyses of bulk organic matter. Our results show that organic carbon stocks in the mineral soil under forest a páramo vegetation were roughly twice as large as global averages for volcanic ash soils, regardless of whether the first 30cm, 100cm or 200cm were considered. We found the carbon stabilization mechanisms involved to be: i) direct stabilization of SOM in organo-metallic (Al-OM) complexes; ii) indirect protection of SOM through low soil pH and toxic levels of Al; and iii) physical protection of SOM due to a very high microporosity of the soil (Tonneijck et al., 2010; Jansen et al. 2011). When examining the organic carbon at a molecular level, interestingly we found extensive degradation of lignin in the topsoil while extractable lipids were preferentially preserved in the subsoil (Nierop and Jansen, 2009). Both vegetation

Direct-current cathodic vacuum arc system with magnetic-field mechanism for plasma stabilization.

Science.gov (United States)

Zhang, H-S; Komvopoulos, K

2008-07-01

Filtered cathodic vacuum arc (FCVA) deposition is characterized by plasma beam directionality, plasma energy adjustment via substrate biasing, macroparticle filtering, and independent substrate temperature control. Between the two modes of FCVA deposition, namely, direct current (dc) and pulsed arc, the dc mode yields higher deposition rates than the pulsed mode. However, maintaining the dc arc discharge is challenging because of its inherent plasma instabilities. A system generating a special configuration of magnetic field that stabilizes the dc arc discharge during film deposition is presented. This magnetic field is also part of the out-of-plane magnetic filter used to focus the plasma beam and prevent macroparticle film contamination. The efficiency of the plasma-stabilizing magnetic-field mechanism is demonstrated by the deposition of amorphous carbon (a-C) films exhibiting significantly high hardness and tetrahedral carbon hybridization (sp3) contents higher than 70%. Such high-quality films cannot be produced by dc arc deposition without the plasma-stabilizing mechanism presented in this study.

Direct-current cathodic vacuum arc system with magnetic-field mechanism for plasma stabilization

International Nuclear Information System (INIS)

Zhang, H.-S.; Komvopoulos, K.

2008-01-01

Filtered cathodic vacuum arc (FCVA) deposition is characterized by plasma beam directionality, plasma energy adjustment via substrate biasing, macroparticle filtering, and independent substrate temperature control. Between the two modes of FCVA deposition, namely, direct current (dc) and pulsed arc, the dc mode yields higher deposition rates than the pulsed mode. However, maintaining the dc arc discharge is challenging because of its inherent plasma instabilities. A system generating a special configuration of magnetic field that stabilizes the dc arc discharge during film deposition is presented. This magnetic field is also part of the out-of-plane magnetic filter used to focus the plasma beam and prevent macroparticle film contamination. The efficiency of the plasma-stabilizing magnetic-field mechanism is demonstrated by the deposition of amorphous carbon (a-C) films exhibiting significantly high hardness and tetrahedral carbon hybridization (sp 3 ) contents higher than 70%. Such high-quality films cannot be produced by dc arc deposition without the plasma-stabilizing mechanism presented in this study

Trajectory Generation and Stability Analysis for Reconfigurable Klann Mechanism Based Walking Robot

Directory of Open Access Journals (Sweden)

Jaichandar Kulandaidaasan Sheba

2016-06-01

Full Text Available Reconfigurable legged robots based on one degree of freedom are highly desired because they are effective on rough and irregular terrains and they provide mobility in such terrain with simple control schemes. It is necessary that reconfigurable legged robots should maintain stability during rest and motion, with a minimum number of legs while maintaining their full range of walking patterns resulting from different gait configuration. In this paper we present a method to generate input trajectory for reconfigurable quadruped robots based on Klann mechanism to properly synchronize movement. Six useful gait cycles based on this reconfigurable Klann mechanism for quadruped robots has been clearly shown here. The platform stability for these six useful gait cycles are validated through simulated results which clearly shows the capabilities of reconfigurable design.

Two drastically different climate states on an Earth-like land planet with overland water recycling

Science.gov (United States)

Kalidindi, S.; Reick, C. H.; Raddatz, T.; Claussen, M.

2017-12-01

edge, the resupply of water at lower latitudes stabilizes the greenhouse effect and keeps the planet in the HD state and may prevent water from getting trapped at higher latitudes in frozen form. Overall, the existence of bi-stability in the presence of an overland recycling mechanism hints at the possibility of a wider habitable zone for Earth-like land planets at lower obliquities.

Dissipation Mechanisms and Particle Acceleration at the Earth's Bow Shock

Science.gov (United States)

Desai, M. I.; Burch, J. L.; Broll, J. M.; Genestreti, K.; Torbert, R. B.; Ergun, R.; Wei, H.; Giles, B. L.; Russell, C. T.; Phan, T.; Chen, L. J.; Lai, H.; Wang, S.; Schwartz, S. J.; Allen, R. C.; Mauk, B.; Gingell, I.

2017-12-01

NASA's Magnetospheric Multiscale (MMS) mission has four spacecraft equipped with identical state-of-the-art instruments that acquire magnetic and electric field, plasma wave, and particle data at unprecedented temporal resolution to study the fundamental physics of magnetic reconnection in the Earth's magnetosphere. During Phase 1a, MMS also encountered and crossed the Earth's bow shock more than 300 times. We use burst data during 2 bow shock crossings to shed new light on key open questions regarding the formation, evolution, and dissipation mechanisms at collisionless shocks. Specifically, we focus on two events that exhibit clear differences in the ion and electron properties, the associated wave activity, and, therefore in the nature of the dissipation. In the case of a quasi-perpendicular, low beta shock crossing, we find that the dissipation processes are most likely associated with field-aligned electron beams that are coincident with high frequency electrostatic waves. On the other hand, the dissipation processes at an oblique, high beta shock crossing are largely governed by the quasi-static electric field and generation of magnetosonic whistler waves that result in perpendicular temperature anisotropy for the electrons. We also discuss the implications of these results for ion heating, reflection, and particle acceleration.

Alkaline earth metals

International Nuclear Information System (INIS)

Brown, Paul L.; Ekberg, Christian

2016-01-01

The beryllium ion has a relatively small ionic radius. As a consequence of this small size, its hydrolysis reactions begin to occur at a relatively low pH. To determine the stability and solubility constants, however, the Gibbs energy of the beryllium ion is required. In aqueous solution calcium, like the other alkaline earth metals, only exists as a divalent cation. The size of the alkaline earth cations increases with increasing atomic number, and the calcium ion is bigger than the magnesium ion. The hydrolysis of barium(II) is weaker than that of strontium(II) and also occurs in quite alkaline pH solutions, and similarly, only the species barium hydroxide has been detected. There is only a single experimental study on the hydrolysis of radium. As with the stability constant trend, it would be expected that the enthalpy of radium would be lower than that of barium due to the larger ionic radius.

Reliably Modeling the Mechanical Stability of Rigid and Flexible Metal-Organic Frameworks.

Science.gov (United States)

Rogge, Sven M J; Waroquier, Michel; Van Speybroeck, Veronique

2018-01-16

Over the past two decades, metal-organic frameworks (MOFs) have matured from interesting academic peculiarities toward a continuously expanding class of hybrid, nanoporous materials tuned for targeted technological applications such as gas storage and heterogeneous catalysis. These oft-times crystalline materials, composed of inorganic moieties interconnected by organic ligands, can be endowed with desired structural and chemical features by judiciously functionalizing or substituting these building blocks. As a result of this reticular synthesis, MOF research is situated at the intriguing intersection between chemistry and physics, and the building block approach could pave the way toward the construction of an almost infinite number of possible crystalline structures, provided that they exhibit stability under the desired operational conditions. However, this enormous potential is largely untapped to date, as MOFs have not yet found a major breakthrough in technological applications. One of the remaining challenges for this scale-up is the densification of MOF powders, which is generally achieved by subjecting the material to a pressurization step. However, application of an external pressure may substantially alter the chemical and physical properties of the material. A reliable theoretical guidance that can presynthetically identify the most stable materials could help overcome this technological challenge. In this Account, we describe the recent research the progress on computational characterization of the mechanical stability of MOFs. So far, three complementary approaches have been proposed, focusing on different aspects of mechanical stability: (i) the Born stability criteria, (ii) the anisotropy in mechanical moduli such as the Young and shear moduli, and (iii) the pressure-versus-volume equations of state. As these three methods are grounded in distinct computational approaches, it is expected that their accuracy and efficiency will vary. To date

Effects of Freezing and Thawing Cycle on Mechanical Properties and Stability of Soft Rock Slope

Directory of Open Access Journals (Sweden)

Yanlong Chen

2017-01-01

Full Text Available To explore the variation laws of mechanical parameters of soft rock and the formed slope stability, an experiment was carried out with collected soft rock material specimens and freezing and thawing cycle was designed. Meanwhile, a computational simulation analysis of the freezing-thawing slope stability was implemented. Key factors that influence the strength of frozen rock specimens were analyzed. Results showed that moisture content and the number of freezing-thawing cycles influenced mechanical parameters of soft rock significantly. With the increase of moisture content, cohesion of frozen soft rock specimens presents a quadratic function decrease and the internal friction angle shows a negative exponential decrease. The stability coefficient of soft rock material slope in seasonal freeze soil area declines continuously. With the increase of freezing and thawing cycle, both cohesion and internal friction angle of soft rock decrease exponentially. The higher the moisture content, the quicker the reduction. Such stability coefficient presents a negative exponential reduction. After three freezing and thawing cycles, the slope stability coefficient only changes slightly. Findings were finally verified by the filed database.

Evaluation of seismic stability of near field

International Nuclear Information System (INIS)

Taniguchi, Wataru; Takaji, Kazuhiko; Sugino, Hiroyuki; Mori, Koji

1999-11-01

For the buffer material of geological disposal of high-level radioactive waste (HLW) in Japan, it is considered to use a compacted bentonite or a compacted sand-mixture bentonite that is one kind of clay. The buffer material is expected to maintain long-term mechanical stability, to hold the waste in designated place, and to avoid the effects on the radionuclides migration. It is considered that the cyclic load due to seismic activities affects long-term mechanical stability in Japan, where many earthquakes have been occurring. In this report, aseismic mechanical stability of engineered barrier of HLW is studied by dynamic analysis based on equation of vibration, mainly in the view point of mechanical stability of the buffer. The analytical computer code that has been developed by JNC in cooperative project with National Research Institute for Earth Science and Disaster Prevention Science and Technology Agency is used in this study. Seismic wave at the disposal depth in the assumed geological environment is established by multiple reflection theory analysis, and then seismic wave at the disposal depth is used for the aseismic mechanical stability analysis. For the aseismic mechanical stability, total stress analyses (single-phase system) with the target field of near field are conducted to evaluate the shear failure of the buffer, the displacement of overpack, and vibrational behavior of the engineered barrier, and then effective stress analyses (two-phase system) with the target field of the engineered barrier are conducted to evaluate excursion in the pore water pressure within the buffer (i. e. liquefaction), concerning the non-linear dynamic properties of the buffer material. From the results, the following conclusions are obtained. (1) From the results of the total stress analyses, it is confirmed that the buffer must not reach a shear failure condition from the stresses caused by an earthquake and the overpack must not move significantly due to the inertial

Mechanical stability of roll-to-roll printed solar cells under cyclic bending and torsion

DEFF Research Database (Denmark)

Finn, Mickey; Martens, Christian James; Zaretski, Aliaksandr V.

2018-01-01

The ability of printed organic solar cells (OSCs) to survive repeated mechanical deformation is critical to large-scale implementation. This paper reports an investigation into the mechanical stability of OSCs through bending and torsion testing of whole printed modules. Two types of modules...

Rare earth metals for automotive exhaust catalysts

International Nuclear Information System (INIS)

Shinjoh, Hirohumi

2006-01-01

The usage of rare earth metals for automotive exhaust catalysts is demonstrated in this paper. Rare earth metals have been widely used in automotive catalysts. In particular, three-way catalysts require the use of ceria compounds as oxygen storage materials, and lanthana as both a stabilizer of alumina and a promoter. The application for diesel catalysts is also illustrated. Effects of inclusion of rare earth metals in automotive catalysts are discussed

Production of rare earth polishing powders in Russia

International Nuclear Information System (INIS)

Kosynkin, V.D.; Ivanov, E.N.; Kotrekhov, V.A.; Shtutza, M.G.; Grabko, A.I.

1998-01-01

Full text: Russia is a potent producer of polishing powders made of rare earth material presented as an extensive and well developed base. Considering the reserves, the facilities predisposition and the polishing agent (cerium dioxide) content the chief mineral source is loparite, apatite and monazite. The production of rare earth polishing powders is based on specially developed continuous technological processes, corrosion-proof equipment, ensuring a high and stable production quality. A special attention is paid to the radiation safety of the powders. The initial material for the rare earth polishing powders based on loparite is the fusion cake of rare earth chlorides obtained at that mineral chlorination. The technology of the polishing powder production from the REE fusion cake includes the following stages: dissolution of the REE fusion cake chlorides; - thorough cleaning of the REE fusion cake chlorides from radioactive and non-rare-earth impurities; chemical precipitation of REE carbonates, obtaining middlings with proper material and granulometric composition, thermal treatment of precipitated carbonates followed with the operations of drying and roasting; classification of roasted oxides, obtaining end products - polishing powders. The production of fluorine-containing powders includes the stage of their fluorination after the stage of carbonate precipitation. The stabilizing doping can be introduced both into the middlings during one of the technological process of powders manufacturing and into the end product. Rare earth polishing powders are manufactured in Russia by the Share Holding Company 'Chepetz Mechanical Plant' (ChMP Co.), the city of Glasov. The plant produces a number of polishing materials, such as; polishing powder Optinol, containing at least 50% by mass of cerium dioxide, used in the mass production of optical and other articles; polishing powder Optinol-10 with doping to improve the sedimentary and aggregate stability of the solid phase

Progress in Understanding Degradation Mechanisms and Improving Stability in Organic Photovoltaics

KAUST Repository

Mateker, William R.

2016-12-23

Understanding the degradation mechanisms of organic photovoltaics is particularly important, as they tend to degrade faster than their inorganic counterparts, such as silicon and cadmium telluride. An overview is provided here of the main degradation mechanisms that researchers have identified so far that cause extrinsic degradation from oxygen and water, intrinsic degradation in the dark, and photo-induced burn-in. In addition, it provides methods for researchers to identify these mechanisms in new materials and device structures to screen them more quickly for promising long-term performance. These general strategies will likely be helpful in other photovoltaic technologies that suffer from insufficient stability, such as perovskite solar cells. Finally, the most promising lifetime results are highlighted and recommendations to improve long-term performance are made. To prevent degradation from oxygen and water for sufficiently long time periods, OPVs will likely need to be encapsulated by barrier materials with lower permeation rates of oxygen and water than typical flexible substrate materials. To improve stability at operating temperatures, materials will likely require glass transition temperatures above 100 °C. Methods to prevent photo-induced burn-in are least understood, but recent research indicates that using pure materials with dense and ordered film morphologies can reduce the burn-in effect.

Progress in Understanding Degradation Mechanisms and Improving Stability in Organic Photovoltaics

KAUST Repository

Mateker, William R.; McGehee, Michael D.

2016-01-01

Understanding the degradation mechanisms of organic photovoltaics is particularly important, as they tend to degrade faster than their inorganic counterparts, such as silicon and cadmium telluride. An overview is provided here of the main degradation mechanisms that researchers have identified so far that cause extrinsic degradation from oxygen and water, intrinsic degradation in the dark, and photo-induced burn-in. In addition, it provides methods for researchers to identify these mechanisms in new materials and device structures to screen them more quickly for promising long-term performance. These general strategies will likely be helpful in other photovoltaic technologies that suffer from insufficient stability, such as perovskite solar cells. Finally, the most promising lifetime results are highlighted and recommendations to improve long-term performance are made. To prevent degradation from oxygen and water for sufficiently long time periods, OPVs will likely need to be encapsulated by barrier materials with lower permeation rates of oxygen and water than typical flexible substrate materials. To improve stability at operating temperatures, materials will likely require glass transition temperatures above 100 °C. Methods to prevent photo-induced burn-in are least understood, but recent research indicates that using pure materials with dense and ordered film morphologies can reduce the burn-in effect.

Modulation of erythrocyte membrane mechanical stability by 2,3-diphosphoglycerate in the neonatal poikilocytosis/elliptocytosis syndrome.

OpenAIRE

Mentzer, W C; Iarocci, T A; Mohandas, N; Lane, P A; Smith, B; Lazerson, J; Hays, T

1987-01-01

To explain the transient anemia and poikilocytosis seen during infancy in hereditary elliptocytosis (HE), we resealed erythrocyte (RBC) ghosts from affected children or their elliptocytic parents with 2,3-diphosphoglycerate (DPG) (0-8 mM), a compound that dissociates membrane skeletons, then measured ghost mechanical stability in the ektacytometer. Without added 2,3-DPG, ghost mechanical stability was subnormal in infantile poikilocytosis (IP) and HE but was even more abnormal in hereditary p...

Evaluation of the effect of heavy rare earth elements on the microstructure and mechanical and electrical properties of zirconia - Yttria ceramics

International Nuclear Information System (INIS)

Lazar, Dolores Ribeiro Ricci

2002-01-01

The use of Yttria concentrates for synthesis and processing of zirconia based ceramics, applied as structural and solid electrolyte materials, was investigated in this work. Terbium, dysprosium, holmium, erbium and ytterbium are chemical elements, classified as heavy rare earths, that can be found in those concentrates due to their association with yttrium ores. The ceramic characteristics were compared to zirconia - Yttria and zirconia - Yttria - rare earth oxide systems. The dopant content was 3 and 9 mol%. The raw materials were prepared by the coprecipitation route using solutions from the chemical processing of zircon and monazite ores and obtained by dissolution of high purity rare earth oxides. In the first part of this work, calcination, milling and ceramic processing were studied to produce ceramics with densities up to 95% TD. Samples were prepared in optimized conditions for the evaluation of the effect of each heavy rare earth element. Powders were characterized by chemical analysis. X-ray diffraction, scanning and transmission electron microscopy, gas adsorption (BET) and laser diffraction for the determination of the agglomerate size distributions. Green pellets were characterized by mercury porosimetry and the sintering kinetic was studied by dilatometry. The characterization of the as-sintered pellets was performed by the apparent density measurement (Archimedes method). X-ray diffraction, microstructure analysis by scanning and transmission electron microscopy, Vickers indentation tests for hardness and fracture toughness determination, dynamic mechanical analysis for the elastic modulus measurement, and impedance spectroscopy for electrical resistivity measurement. It was observed that the presence of heavy rare earths in a concentrate containing 85 wt% of Yttria has no significant influence on the properties of zirconia based ceramics. TZP ceramics, containing 3 mol% of dopants, have grain size smaller than 0.4μm, and Vickers hardness and

A steep road to climate stabilization

Energy Technology Data Exchange (ETDEWEB)

Friedlingstein, P [CEA Saclay, Inst Pierre Simon Laplace, Lab Climate and Environm Sci, F-91191 Gif Sur Yvette, (France)

2008-07-01

The only way to stabilize Earth's climate is to stabilize the concentration of greenhouse gases in the atmosphere, but future changes in the carbon cycle might make this more difficult than has been thought. (author)

A steep road to climate stabilization

International Nuclear Information System (INIS)

Friedlingstein, P.

2008-01-01

The only way to stabilize Earth's climate is to stabilize the concentration of greenhouse gases in the atmosphere, but future changes in the carbon cycle might make this more difficult than has been thought. (author)

Binding energy and mechanical stability of single- and multi-walled carbon nanotube serpentines

International Nuclear Information System (INIS)

Zhao, Junhua; Lu, Lixin; Rabczuk, Timon

2014-01-01

Recently, Geblinger et al. [Nat. Nanotechnol. 3, 195 (2008)] and Machado et al. [Phys. Rev. Lett. 110, 105502 (2013)] reported the experimental and molecular dynamics realization of S-like shaped single-walled carbon nanotubes (CNTs), the so-called CNT serpentines. We reported here results from continuum modeling of the binding energy γ between different single- and multi-walled CNT serpentines and substrates as well as the mechanical stability of the CNT serpentine formation. The critical length for the mechanical stability and adhesion of different CNT serpentines are determined in dependence of E i I i , d, and γ, where E i I i and d are the CNT bending stiffness and distance of the CNT translation period. Our continuum model is validated by comparing its solution to full-atom molecular dynamics calculations. The derived analytical solutions are of great importance for understanding the interaction mechanism between different single- and multi-walled CNT serpentines and substrates

Effects of rare-earth substitution on the stability and electronic structure of REZnOSb (RE = La-Nd, Sm-Gd) investigated via first-principles calculations

International Nuclear Information System (INIS)

Guo Kai; Man Zhenyong; Cao Qigao; Chen Haohong; Guo Xiangxin; Zhao Jingtai

2011-01-01

Graphical abstract: The structure stability of REZnOSb decreases with varying rare-earth from La to Gd because of the increased binding energy. Research highlights: → As increasing the atomic number of the RE, the structural stability of REZnOSb decreases. → Varying the rare-earth elements from La to Gd, the covalent interactions between [ZnSb] and [LaO] layer are enhanced by 4f-electrons. → The electrical transport properties of REZnOSb could be improved using the large atomic number of the RE. - Abstract: The structural stability, chemical bonding, Mulliken populations, and charge-density distribution of REZnOSb (RE = La-Nd, Sm-Gd) were investigated by first-principles calculations. Unit cell parameters calculated by the generalized gradient approximation (GGA) are in better agreement with experimental results than those derived from the local density approximation (LDA). Binding energy comparisons indicate that the structural stability of REZnOSb decreases with the increment of the atomic number of the RE, as confirmed by X-ray diffraction (XRD) results. Semimetal or narrow band-gap semiconductor behaviors are found for selected REZnOSb. Moreover, chemical bonding analysis shows that there exist considerable polar covalent interactions between the participating atoms. It also reveals that the [ZnSb] layers receive some electrons from the [LaO] layers (donor) as an electrons acceptor and holes transport tunnel. The covalent interactions between the [ZnSb] and [LaO] layers, which are enhanced by 4f-electrons of the RE, are supposed to improve the electrical transport properties.

NASA Earth Exchange (NEX)

Data.gov (United States)

National Aeronautics and Space Administration — The NASA Earth Exchange (NEX) represents a new platform for the Earth science community that provides a mechanism for scientific collaboration and knowledge sharing....

WHERE TO FIND HABITABLE ''EARTHS'' IN CIRCUMBINARY SYSTEMS

International Nuclear Information System (INIS)

Liu Huigen; Zhang Hui; Zhou Jilin

2013-01-01

Six P-type planets have been found thus far around five binary systems, i.e., Kepler-16b, 34b, 35b, 38b, and 47b and c, which are all Neptune- or Jupiter-like planets. The stability of planets and the habitable zones are influenced by the gravitational and radiative perturbations of binary companions. In this Letter, we check the stability of an additional habitable Earth-mass planet in each system. Based on our simulations in 10 Myr, a habitable ''Earth'' is hardly stable in Kepler-16, while a stable ''Earth'' in Kepler-47 close to the boundaries of the habitable zone is possible. In contrast, Kepler-34, 35, and 38 seem to have high probabilities of being able to tolerante a stable ''Earth'' in their habitable zones. The affects of transit time variations are quite small due to the small mass of an undetected ''Earth,'' except that of Kepler-16b. With a time precision of 10 –3 day (∼88 s), an ''Earth'' in the corotational resonance with Kepler-16b can be detected in three years, while habitable ''Earths'' in the Kepler-34 and 38 systems can be detected in 10 yr. Habitable ''Earths'' in Kepler-35 and 47 are not likely to be detected in 10 yr under this precision.

Effect of stiffness modulation on mechanical stability of stretchable a-IGZO TFTs

Science.gov (United States)

Park, Hyungjin; Cho, Kyoungah; Oh, Hyungon; Kim, Sangsig

2018-05-01

In this study, we fabricate the amorphous indium gallium zinc oxide (a-IGZO) thin-film transistors (TFTs) on a stretchable substrate with a buffer stage and investigate the mechanical stability and electrical characteristics when the length of the substrate is stretched by 1.7 times. The buffer stage is responsible for the stiffness modulation of the stretchable substrate. The mobility, the threshold voltage and the on/off ratio of the stretchable a-IGZO TFT are measured to be 18.1 cm2/V·s, 1 V, and 3 × 107, respectively. Our simulation conducted by a three dimensional finite elements method reveals that the stiffness modulation reduces the stress experienced by the substrate in the stretched state by about one-tenth. In addition, the mechanical stability and electrical characteristics of the a-IGZO TFT are maintained even when the substrate is stretched by 1.7 times.

Effect Mechanism of Penstock on Stability and Regulation Quality of Turbine Regulating System

Directory of Open Access Journals (Sweden)

Wencheng Guo

2014-01-01

Full Text Available This paper studies the effect mechanism of water inertia and head loss of penstock on stability and regulation quality of turbine regulating system with surge tank or not and proposes the construction method of equivalent model of regulating system. Firstly, the complete linear mathematical model of regulating system is established. Then, the free oscillation equation and time response of the frequency that describe stability and regulation quality, respectively, are obtained. Finally, the effects of penstock are analysed by using stability region and response curves. The results indicate that the stability and regulation quality of system without surge tank are determined by time response of frequency which only depends on water hammer wave in penstock, while, for system with surge tank, the time response of frequency depending on water hammer wave in penstock and water-level fluctuation in surge tank jointly determines the stability and regulation quality. Water inertia of penstock mainly affects the stability and time response of frequency of system without surge tank as well as the stability and head wave of time response of frequency with surge tank. Head loss of penstock mainly affects the stability and tail wave of time response of frequency with surge tank.

Cable Stability

Energy Technology Data Exchange (ETDEWEB)

Bottura, L [European Organization for Nuclear Research, Geneva (Switzerland)

2014-07-01

Superconductor stability is at the core of the design of any successful cable and magnet application. This chapter reviews the initial understanding of the stability mechanism, and reviews matters of importance for stability such as the nature and magnitude of the perturbation spectrum and the cooling mechanisms. Various stability strategies are studied, providing criteria that depend on the desired design and operating conditions.

Durability of the earth mortar: Physico-chemical and mineralogical characterization for the reduction of the capillary rise

Directory of Open Access Journals (Sweden)

Ammari A.

2018-01-01

the standards in force, allows strong results of strength and durability. The chemical and mineralogical elements play an important role, in the presence of an 'optimum' cement dosage, to strengthen the ties between the clays and the grains of the earth.. This approach targets the search for better performances in the use of natural materials resource in an eco-responsible habitat. This study presents the experimental results of the four techniques of mineralogical and chemical analysis on mortar specimens obtained from earth of the city of Fez. The results of the uni-axial compressive tests of the cylindrical specimens for this earth, associated by various percentages 0%, 4%, 7% and 10% by weight of cement, make it possible to analyze the effect of the mineralogical and chemical elements on the mechanical properties, namely Young's modulus, compressive strength and limiting deformation. However, we determine the water absorption coefficient of the mortar for different cement dosages in order to optimize the durability of the mortar against bad weather, rain and / or very wet climates. In the earth mortar of Fez, the strong presence of calcite (CaCO3, quartz SiO2 and dolomite CaMg (CO32 amplifies the improvement of the behavior of the material by the addition of cement. In fact, this strong presence of calcite stabilized the clay by cementing quartz and the cement matrix to strengthen the ties between the grains of the earth. In addition, with respect to the capillary rise, the water absorption decreases with the addition of cement. We also note that the evolution of the mechanical properties is of no importance except in the interval [4 to 7%] which represents the zone of effect for cement stabilization and which houses the optimum technicoeconomic cement dosing.

Charge regulation as a stabilization mechanism for shell-like assemblies of polyoxometalates

NARCIS (Netherlands)

Verhoeff, A.A.; Kistler, M.L.; Bhatt, A.; Pigga, J.; Groenewold, J.; Klokkenburg, M.; Veen, S.J.; Roy, S.; Liu, T.; Kegel, W.K.

2007-01-01

We show that the equilibrium size of single-layer shells composed of polyoxometalate macroions is inversely proportional to the dielectric constant of the medium in which they are dispersed. This behavior is consistent with a stabilization mechanism based on Coulomb repulsion combined with charge

Investigating the Thermal and Phase Stability of Nanocrystalline Ni-W Produced by Electrodeposition, Sputtering, and Mechanical Alloying

Science.gov (United States)

Marvel, Christopher Jonathan

The development of nanocrystalline materials has been increasingly pursued over the last few decades. They have been shown to exhibit superior properties compared to their coarse-grain counterparts, and thus present a tremendous opportunity to revolutionize the performance of nanoscale devices or bulk structural materials. However, nanocrystalline materials are highly prone to grain growth, and if the nanocrystalline grains coarsen, the beneficial properties are lost. There is a strong effort to determine the most effective thermal stability mechanisms to avoid grain growth, but the physical nature of nanocrystalline grain growth is still unclear due to a lack of detailed understanding of nanocrystalline microstructures. Furthermore, the influence of contamination has scarcely been explored with advanced transmission electron microscopy techniques, nor has there been a direct comparison of alloys fabricated with different bulk processes. Therefore, this research has applied aberration-corrected scanning transmission electron microscopy to characterize nanocrystalline Ni-W on the atomic scale and elucidate the physical grain growth behavior. Three primary objectives were pursued: (1) explore the thermal stability mechanisms of nanocrystalline Ni-W, (2) evaluate the phase stability of Ni-W and link any findings to grain growth behavior, and (3) compare the influences of bulk fabrication processing, including electrodeposition, DC magnetron sputtering, and mechanical alloying, on the thermal stability and phase stability of Ni-W. Several thermal stability mechanisms were identified throughout the course of this research. First and foremost, W-segregation was scarcely observed to grain boundaries, and it is unclear if W-segregation improves thermal stability contrary to most reports in the 2 literature. Long-range Ni4W chemical ordering was observed in alloys with more than 20 at.% W, and it is likely Ni4W domains reduce grain boundary mobility. In addition, lattice

Rare earth phosphors and phosphor screens

International Nuclear Information System (INIS)

Buchanan, R.A.; Maple, T.G.; Sklensky, A.F.

1981-01-01

Advances in the use of stabilized rare earth phosphors and of conversion screens using these materials are examined. In particular the new phosphors discussed in this invention consist of oxybromides of yttrium, lanthanum and gadolinium with a luminescent activator ion stabilized by an oxychloride or oxyfluoride surface layer and the conversion screens include trivalent cerium as the activator ion. (U.K.)

Natural Stabilized Earth Panels versus Conventional Façade Systems. Economic and Environmental Impact Assessment

Directory of Open Access Journals (Sweden)

Carmen Galán-Marín

2018-03-01

Full Text Available More effective construction technologies are needed nowadays in order to reduce construction energy consumption during the life-cycle of buildings. Besides which, it is necessary to consider the economic feasibility and associated costs within the framework of these alternative technologies so as to favouring their practical implementation in the construction sector. In this sense, this paper presents an economic and environmental comparison of a new non-bearing façade construction solution based on the extruded unfired stabilized clay panels as opposed to three traditional solutions with similar physical, thermal, and aesthetic characteristics in terms of the exterior cladding. The proposed panels are a sandwich type configuration with an intermediate insulating material and two exterior pieces manufactured by extrusion with raw earth stabilized with alginate and animal wool fibers. In this paper, details of the constructive technology of the system are provided. From the results obtained, it is possible to conclude that the solution is a valid alternative from the environmental point of view, considerably reducing the Global Warming Potential and the Cumulative Energy Demand. And although the environmental improvement of the system can be considered the primary objective of this investigation, on the other hand, once executed, it will also be a competitive constructive technology from the perspective of the system’s final costs.

Global insights into acetic acid resistance mechanisms and genetic stability of Acetobacter pasteurianus strains by comparative genomics

Science.gov (United States)

Wang, Bin; Shao, Yanchun; Chen, Tao; Chen, Wanping; Chen, Fusheng

2015-12-01

Acetobacter pasteurianus (Ap) CICC 20001 and CGMCC 1.41 are two acetic acid bacteria strains that, because of their strong abilities to produce and tolerate high concentrations of acetic acid, have been widely used to brew vinegar in China. To globally understand the fermentation characteristics, acid-tolerant mechanisms and genetic stabilities, their genomes were sequenced. Genomic comparisons with 9 other sequenced Ap strains revealed that their chromosomes were evolutionarily conserved, whereas the plasmids were unique compared with other Ap strains. Analysis of the acid-tolerant metabolic pathway at the genomic level indicated that the metabolism of some amino acids and the known mechanisms of acetic acid tolerance, might collaboratively contribute to acetic acid resistance in Ap strains. The balance of instability factors and stability factors in the genomes of Ap CICC 20001 and CGMCC 1.41 strains might be the basis for their genetic stability, consistent with their stable industrial performances. These observations provide important insights into the acid resistance mechanism and the genetic stability of Ap strains and lay a foundation for future genetic manipulation and engineering of these two strains.

Adaptive and freeze-tolerant heteronetwork organohydrogels with enhanced mechanical stability over a wide temperature range

Science.gov (United States)

Gao, Hainan; Zhao, Ziguang; Cai, Yudong; Zhou, Jiajia; Hua, Wenda; Chen, Lie; Wang, Li; Zhang, Jianqi; Han, Dong; Liu, Mingjie; Jiang, Lei

2017-06-01

Many biological organisms with exceptional freezing tolerance can resist the damages to cells from extra-/intracellular ice crystals and thus maintain their mechanical stability at subzero temperatures. Inspired by the freezing tolerance mechanisms found in nature, here we report a strategy of combining hydrophilic/oleophilic heteronetworks to produce self-adaptive, freeze-tolerant and mechanically stable organohydrogels. The organohydrogels can simultaneously use water and oil as a dispersion medium, and quickly switch between hydrogel- and organogel-like behaviours in response to the nature of the surrounding phase. Accordingly, their surfaces display unusual adaptive dual superlyophobic in oil/water system (that is, they are superhydrophobic under oil and superoleophobic under water). Moreover, the organogel component can inhibit the ice crystallization of the hydrogel component, thus enhancing the mechanical stability of organohydrogel over a wide temperature range (-78 to 80 °C). The organohydrogels may have promising applications in complex and harsh environments.

About the mechanical stability of MnFe(P,Si,B) giant-magnetocaloric materials

Energy Technology Data Exchange (ETDEWEB)

Guillou, F., E-mail: f.guillou@tudelft.nl [FAME, Faculty of Applied Sciences, TU Delft, Mekelweg 15, 2629 JB Delft (Netherlands); Yibole, H.; Dijk, N.H. van [FAME, Faculty of Applied Sciences, TU Delft, Mekelweg 15, 2629 JB Delft (Netherlands); Zhang, L. [BASF Netherlands B.V., Strijkviertel 67, 3454 PK De Meern (Netherlands); Hardy, V. [CRISMAT, Ensicaen, UMR 6508 CNRS, 6 B" d Maréchal Juin, 14050 Caen Cedex (France); Brück, E. [FAME, Faculty of Applied Sciences, TU Delft, Mekelweg 15, 2629 JB Delft (Netherlands)

2014-12-25

Highlights: • Electrical resistivity and hardness show an evolution at T{sub C} with thermal cycling. • Degradation depends on the (c/a) lattice discontinuity at the transition. • Boron substituted materials present an improved mechanical stability. - Abstract: Due to its ability to control the latent heat and the hysteresis (thermal or magnetic) at the first-order transition (FOT) without deteriorating the saturation magnetisation, boron substitution in MnFe(P,Si) materials has recently been reported to be an ideal parameter to reach promising magnetocaloric performances: ΔS ≈ 10 Jkg{sup −1} K{sup −1} and cyclic ΔT of 2.6 K (and more) at a moderate magnetic field of ΔB = 1 T. Additionally, an interesting aspect for applications is the improvement of the mechanical stability in B doped materials compared to the pristine MnFe(P,Si) compounds. These improved mechanical properties were initially supported by naked-eye inspection and the observation of a constant ΔT during a few thousands of magnetic cycles. (Guillou et al., 2014) Here, the evolution upon cycling of MnFe(P,Si,B) materials is studied in a more quantitative and systematic manner. For that purpose transformation temperatures, electrical resistivity, micro-hardness and the microstructure are tracked as a function of the thermal cycling across the FOT for three prototypical compositions in the MnFe(P,Si,B) system. It turns out this set of data confirms the initial finding that B substitution has a positive effect on the mechanical stability. The origin of this improvement is discussed, in particular in respect to the lattice parameter discontinuities at the phase transition.

The Chinese Society of Rare Earth is Studying The Feasibility of Marketing Rare Earth Futures

Institute of Scientific and Technical Information of China (English)

2015-01-01

Lin Donglu,secretary-general of the Chinese Society of Rare Earth recently said,the Chinese Society of Rare Earth undertook the research on subject of the National Social Science Fund Foundation on the reform of Chinese rare earth trading pricing mechanism on promoting RMB globalization,and is focusing on studying the feasibility of marketing rare earth futures variety.

Preparation and properties of mesoporous silica/bismaleimide/diallylbisphenol composites with improved thermal stability, mechanical and dielectric properties

Directory of Open Access Journals (Sweden)

2011-06-01

Full Text Available New composites with improved thermal stability, mechanical and dielectric properties were developed, which consist of 2,2'-diallylbisphenol A (DBA/4,4'-bismaleimidodiphenylmethane (BDM resin and a new kind of organic/inorganic mesoporous silica (MPSA. Typical properties (curing behavior and mechanism, thermal stability, mechanical and dielectric properties of the composites were systematically investigated, and their origins were discussed. Results show that MPSA/DBA/BDM composites have similar curing temperature as DBA/BDM resin does; however, they have different curing mechanisms, and thus different crosslinked networks. The content of MPSA has close relation with the integrated performance of cured composites. Compared with cured DBA/BDM resin, composites with suitable content of MPSA show obviously improved flexural strength and modulus as well as impact strength; in addition, all composites not only have lower dielectric constant and similar frequency dependence, more interestingly, they also exhibit better stability of frequency on dielectric loss. For thermal stability, the addition of MPSA to DBA/BDM resin significantly decreases the coefficient of thermal expansion, and improves the char yield at high temperature with a slightly reduced glass transition temperature. All these differences in macro-properties are attributed to the different crosslinked networks between MPSA/DBA/BDM composites and DBA/BDM resin.

Estimation of stability of polynuclear rare earth complexes with EDTA in the presence of stable monocomplexonates

International Nuclear Information System (INIS)

Le Ba Tkhun; Kupriyanova, G.N.; Smirnova, N.S.; Martynenko, L.I.; Evseeva, A.M.

1987-01-01

Complexing in rare-earth-EDTA system at the mole ratio making up (M 3+ ):(H 2 A 2- )=1:1, 2:1, 5:1, (M=Nd, Yb), C H 2 A 2- =0.010, 0.015 mol/l, μ=0.5 (KCl) is studied in pH 1.6-3.0 interval by pH-metric titration technique using mathematical modelling method. A model containing MA - , MHA, M 2 A 2+ complexes for which stability constants, equalling respectively (lgK) to 15.66, 2.11, 1.06 (for neodymium complexes) and 18.70, 1.78, 0.45 (for ytterbium complexes) are determined by non-linear LSF, appears to be adequate. It is shown that binuclear complex concentration in solution with M 3+ excess is comparable to stable monocomplexonate concentration

Study on Roll Instability Mechanism and Stability Index of Articulated Steering Vehicles

Directory of Open Access Journals (Sweden)

Xuefei Li

2016-01-01

Full Text Available This study examines the roll instability mechanism and stability index of articulated steering vehicles (ASVs by taking wheel loaders as the research object. A seven-degree-of-freedom nonlinear dynamics model of the ASVs is built on the basis of multibody dynamics. A physical prototype model of an ASV is designed and manufactured to validate the dynamic model. Test results reasonably agree with the simulation results, which indicates that the established dynamic model can reasonably describe ASV movements. Detailed analysis of the rollover stability of the wheel loader is performed with the use of the established dynamic model. Analysis results show that rollover will occur when the roll angular velocity exceeds a critical threshold, which is affected by lateral acceleration and slope angle. On this basis, a dynamic stability index applicable to the ASVs is presented.

Space sickness on earth

Science.gov (United States)

Nooij, S. A. E.; Bos, J. E.; Groen, E. L.; Bles, W.; Ockels, W. J.

2007-09-01

During the first days in space, i.e., after a transition from 1G to 0G, more than 50% of the astro- (and cosmonauts) suffer from the Space Adaptation Syndrome (SAS).The symptoms of SAS, like nausea and dizziness, are especially provoked by head movements. Astronauts have mentioned close similarities between the symptoms of SAS and the symptoms they experienced after a 1 hour centrifuge run on Earth, i.e., after a transition from 3G to 1G (denoted by Sickness Induced by Centrifugation, SIC). During several space missions, we related susceptibility to SAS and to SIC in 11 astronauts and found 4 of them being susceptible to both SIC and SAS, and 7 being not susceptible to SIC nor to SAS. This correspondence in susceptibility suggests that SIC and SAS share the same underlying mechanism. To further study this mechanism, several vestibular parameters have been investigated (e.g. postural stability, vestibularly driven eye movements, subjective vertical). We found some striking changes in individual cases that are possibly due to the centrifuge run. However, the variability between subjects generally is very large, making physiological links to SIC and SAS still hard to find.

Thermal stability of nafion membranes under mechanical stress

Energy Technology Data Exchange (ETDEWEB)

Quintilii, M; Struis, R [Paul Scherrer Inst. (PSI), Villigen (Switzerland)

1997-06-01

The feasibility of adequately modified fluoro-ionomer membranes (NAFION{sup R}) is demonstrated for the selective separation of methanol synthesis products from the raw reactor gas at temperatures around 200{sup o}C. For an economically relevant application of this concept on a technical scale the Nafion membranes should be thin ({approx_equal}10 {mu}m) and thermally stable over a long period of time (1-2 years). In cooperation with industry (Methanol Casale SA, Lugano (CH)), we test the thermal stability of Nafion hollow fibers and supported Nafion thin sheet membranes at temperatures between 160 and 200{sup o}C under mechanical stress by applying a gas pressure difference over the membrane surface ({Delta}P{<=} 40 bar). Tests with the hollow fibers revealed that Nafion has visco-elastic properties. Tests with 50 {mu}m thin Nafion sheets supported by a porous metal carrier at 200{sup o}C and {Delta}P=39 bar showed no mechanical defects over a period of 92 days. (author) 5 figs., 4 refs.

Methods for improving mechanical properties of partially stabilized zirconia and the resulting product

International Nuclear Information System (INIS)

Aronov, V.A.

1987-01-01

A method for improving mechanical surface properties of a rigid body comprising partially stabilized zirconia as a constituent is described comprising the following steps: (i) providing a rigid body having an exposed surface and an interior volume; (ii) subjecting the exposed surface region of partially stabilized zirconia to external heating to heat the exposed surface region to 1100 0 C-1600 0 C without heating the interior volume above 500 0 C-800 0 C; and (iii) cooling the rigid body to a temperature of less than 500 0 C to cause a portion of the exposed surface region to transform from the tetragonal lattice modification to the monoclinic lattice modification, thereby creating a compressive stress field in the exposed surface region and improving the mechanical surface properties of the exposed surface region. In a ceramic body comprising a first exposed region of a partially stabilized zirconia, and a second region of a partially stabilized zirconia at an interior portion of the ceramic body, the improvement is described comprising the ceramic body having in the first, exposed region a greater percentage of the monoclinic lattice modification than in the second region; having in the first, exposed region 5 percent to 100 percent in the monoclinic lattice modification; and having a molded surface finish in the first, exposed region; the first, exposed region being subjected to a compressive field resulting from the greater percentage of the monoclinic lattice modification

Molecular Mechanism of AHSP-Mediated Stabilization of Alpha-Hemoglobin

Energy Technology Data Exchange (ETDEWEB)

Feng,L.; Gell, D.; Zhou, S.; Gu, L.; Kong, Y.; Li, J.; Hu, M.; Yan, N.; Lee, C.; et al.

2005-01-01

Hemoglobin A (HbA), the oxygen delivery system in humans, comprises two alpha and two beta subunits. Free alpha-hemoglobin (alphaHb) is unstable, and its precipitation contributes to the pathophysiology of beta thalassemia. In erythrocytes, the alpha-hemoglobin stabilizing protein (AHSP) binds alphaHb and inhibits its precipitation. The crystal structure of AHSP bound to Fe(II)-alphaHb reveals that AHSP specifically recognizes the G and H helices of alphaHb through a hydrophobic interface that largely recapitulates the alpha1-beta1 interface of hemoglobin. The AHSP-alphaHb interactions are extensive but suboptimal, explaining why beta-hemoglobin can competitively displace AHSP to form HbA. Remarkably, the Fe(II)-heme group in AHSP bound alphaHb is coordinated by the distal but not the proximal histidine. Importantly, binding to AHSP facilitates the conversion of oxy-alphaHb to a deoxygenated, oxidized [Fe(III)], nonreactive form in which all six coordinate positions are occupied. These observations reveal the molecular mechanisms by which AHSP stabilizes free alphaHb.

Experimental evidence of the impact of rare-earth elements on particle growth and mechanical behaviour of silicon nitride

International Nuclear Information System (INIS)

Satet, Raphaelle L.; Hoffmann, Michael J.; Cannon, Rowland M.

2006-01-01

The impact of various rare-earth and related doping elements (R = Lu, Sc, Yb, Y, Sm, La) on the grain growth anisotropy and the mechanical properties of polycrystalline β-silicon nitride ceramics has been studied. Model experiments, in which Si 3 N 4 particles can grow freely in an R-Si-Mg-oxynitride glass matrix, show that, with increasing ionic radius of the additive, grain anisotropy increases due to non-linear growth kinetics. Toughness and strength are affected by the rare-earth element. Samples of equivalent grain sizes and morphologies yield an increasing toughness with increasing ion size of the R 3+ , reflecting an increasingly intergranular crack path. These samples are also strong and flaw tolerant, but the trends of strength and toughness do not exactly match. The choice of the rare-earth is essential to tailor microstructure, interfacial strength and mechanical properties. However, somewhat different trends for properties from IIIb and lanthanide additives indicate that more than the R 3+ size (i.e., purely ionic bond strength between R 3+ and its neighbours) is important. The electronic structure of the R-element is responsible for the type of dopant adsorption and the properties of the interface

Improvement of the thermal and thermo-oxidative stability of high-density polyethylene by free radical trapping of rare earth compound

Energy Technology Data Exchange (ETDEWEB)

Ran, Shiya; Zhao, Li; Han, Ligang [Laboratory of Polymer Materials and Engineering, Ningbo Institute of Technology, ZhejiangUniversity, Ningbo, 315100 (China); MOE Key Laboratory of Macromolecular Synthesis and Functionalization, Institute of Polymer Composites, Zhejiang University, Hangzhou, 310027 (China); Guo, Zhenghong, E-mail: guozhenghong@nit.zju.edu.cn [Laboratory of Polymer Materials and Engineering, Ningbo Institute of Technology, ZhejiangUniversity, Ningbo, 315100 (China); Fang, Zhengping [Laboratory of Polymer Materials and Engineering, Ningbo Institute of Technology, ZhejiangUniversity, Ningbo, 315100 (China); MOE Key Laboratory of Macromolecular Synthesis and Functionalization, Institute of Polymer Composites, Zhejiang University, Hangzhou, 310027 (China)

2015-07-20

Highlights: • Polyethylene filled with ytterbium trifluoromethanesulfonate was prepared. • A low Yb loading improved thermal stability of PE obviously by radical trapping. • Yb(OTf){sub 3} is expected to be an efficient thermal stabilizer for the polymer. - Abstract: A kind of rare earth compound, ytterbium trifluoromethanesulfonate (Yb(OTf){sub 3}), was introduced into high-density polyethylene (HDPE) by melt compounding to investigate the effect of Yb(OTf){sub 3} on the thermal and thermo-oxidative stability of HDPE. The results of thermogravimetric (TG) and differential scanning calorimetry (DSC) showed that the addition of Yb(OTf){sub 3} made the thermal degradation temperatures dramatically increased, the oxidative induction time (OIT) extended, and the enthalpy (ΔH{sub d}) reduced. Very low Yb(OTf){sub 3} loading (0.5 wt%) in HDPE could increase the onset degradation temperature in air from 334 to 407 °C, delay the OIT from 11.0 to 24.3 min, and decrease the ΔH{sub d} from 61.0 to 13.0 J/g remarkably. Electron spin resonance spectra (ESR), thermogravimetric analysis coupled to Fourier transform infrared spectroscopy (TGA-FTIR), rheological investigation and pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) indicated that the free radicals-trapping ability of Yb(OTf){sub 3} was responsible for the improved thermal and thermo-oxidative stability.

Effect of Nb2O5 doping on improving the thermo-mechanical stability of sealing interfaces for solid oxide fuel cells.

Science.gov (United States)

Zhang, Qi; Du, Xinhang; Tan, Shengwei; Tang, Dian; Chen, Kongfa; Zhang, Teng

2017-07-13

Nb 2 O 5 is added to a borosilicate sealing system to improve the thermo-mechanical stability of the sealing interface between the glass and Fe-Cr metallic interconnect (Crofer 22APU) in solid oxide fuel cells (SOFCs). The thermo-mechanical stability of the glass/metal interface is evaluated experimentally as well as by using a finite element analysis (FEA) method. The sealing glass doped with 4 mol.% Nb 2 O 5 shows the best thermo-mechanical stability, and the sealing couple of Crofer 22APU/glass/GDC (Gd 0.2 Ce 0.8 O 1.9 ) remains intact after 50 thermal cycles. In addition, all sealing couples show good joining after being held at 750 °C for 1000 h. Moreover, the possible mechanism on the thermo-mechanical stability of sealing interface is investigated in terms of stress-based and energy-based perspectives.

Mechanical synthesis of copper-carbon nanocomposites: Structural changes, strengthening and thermal stabilization

International Nuclear Information System (INIS)

Nunes, D.; Livramento, V.; Mateus, R.; Correia, J.B.; Alves, L.C.; Vilarigues, M.; Carvalho, P.A.

2011-01-01

Highlights: → The study characterized Cu-nanodiamond (Cu-nD) and Cu-graphite (Cu-G) composites. → Preservation of nD crystalline structure during high-energy milling was demonstrated. → Higher refinement of matrix in Cu-nD comparing to Cu-G is due to a milling mechanism. → Remarkable thermal stability and microhardness have been achieved in Cu-nD and Cu-G. → Strengthening resulted mainly from grain refinement and second-phase reinforcement. - Abstract: Processing of copper-carbon nanocomposites by mechanical synthesis poses specific challenges as carbon phases are prone to amorphization and exhibit an intrinsically difficult bonding with copper. The present work investigates Cu-nanodiamond (Cu-nD) and Cu-graphite (Cu-G) composites produced by mechanical synthesis and subsequent heat treatments. Transmission electron microscopy observations showed homogeneous particle distributions and intimate bonding between the metallic matrix and the carbon phases. Ring diffraction patterns of chemically extracted carbon phases demonstrated that milled nanodiamond preserved crystallinity, while an essentially amorphous nature could be inferred for milled graphite. Raman spectra confirmed that nanodiamond particles remained essentially unaffected by the mechanical synthesis, whereas the bands of milled graphite were significantly changed into the typical amorphous carbon fingerprint. Particle-induced X-ray emission spectroscopy showed that the total contamination originating from the milling media remained below 0.7 wt.%. The Cu-nanodiamond composite exhibited remarkable microhardness and microstructural thermal stability when compared with pure nanostructured copper.

Mechanical synthesis of copper-carbon nanocomposites: Structural changes, strengthening and thermal stabilization

Energy Technology Data Exchange (ETDEWEB)

Nunes, D., E-mail: daniela.nunes@ist.utl.pt [Associacao Euratom/IST, Instituto de Plasmas e Fusao Nuclear - Laboratorio Associado, Instituto Superior Tecnico, Av. Rovisco Pais, 1049-001 Lisboa (Portugal); LNEG, Estrada do Paco do Lumiar, 1649-038 Lisboa (Portugal); ICEMS, Instituto Superior Tecnico, Av. Rovisco Pais, 1049-001 Lisboa (Portugal); Livramento, V. [Associacao Euratom/IST, Instituto de Plasmas e Fusao Nuclear - Laboratorio Associado, Instituto Superior Tecnico, Av. Rovisco Pais, 1049-001 Lisboa (Portugal); LNEG, Estrada do Paco do Lumiar, 1649-038 Lisboa (Portugal); Mateus, R. [Associacao Euratom/IST, Instituto de Plasmas e Fusao Nuclear - Laboratorio Associado, Instituto Superior Tecnico, Av. Rovisco Pais, 1049-001 Lisboa (Portugal); Correia, J.B. [LNEG, Estrada do Paco do Lumiar, 1649-038 Lisboa (Portugal); Alves, L.C. [ITN, Instituto Tecnologico e Nuclear, Estrada Nacional 10, 2686-953 Sacavem (Portugal); Vilarigues, M. [Departamento de Conservacao e Restauro e R and D Unit Vidro e da Ceramica Para as Artes, FCT-UNL, Quinta da Torre, 2829-516 Caparica (Portugal); Carvalho, P.A. [ICEMS, Instituto Superior Tecnico, Av. Rovisco Pais, 1049-001 Lisboa (Portugal); Departamento de Bioengenharia, Instituto Superior Tecnico, Av. Rovisco Pais, 1049-001 Lisboa (Portugal)

2011-11-15

Highlights: {yields} The study characterized Cu-nanodiamond (Cu-nD) and Cu-graphite (Cu-G) composites. {yields} Preservation of nD crystalline structure during high-energy milling was demonstrated. {yields} Higher refinement of matrix in Cu-nD comparing to Cu-G is due to a milling mechanism. {yields} Remarkable thermal stability and microhardness have been achieved in Cu-nD and Cu-G. {yields} Strengthening resulted mainly from grain refinement and second-phase reinforcement. - Abstract: Processing of copper-carbon nanocomposites by mechanical synthesis poses specific challenges as carbon phases are prone to amorphization and exhibit an intrinsically difficult bonding with copper. The present work investigates Cu-nanodiamond (Cu-nD) and Cu-graphite (Cu-G) composites produced by mechanical synthesis and subsequent heat treatments. Transmission electron microscopy observations showed homogeneous particle distributions and intimate bonding between the metallic matrix and the carbon phases. Ring diffraction patterns of chemically extracted carbon phases demonstrated that milled nanodiamond preserved crystallinity, while an essentially amorphous nature could be inferred for milled graphite. Raman spectra confirmed that nanodiamond particles remained essentially unaffected by the mechanical synthesis, whereas the bands of milled graphite were significantly changed into the typical amorphous carbon fingerprint. Particle-induced X-ray emission spectroscopy showed that the total contamination originating from the milling media remained below 0.7 wt.%. The Cu-nanodiamond composite exhibited remarkable microhardness and microstructural thermal stability when compared with pure nanostructured copper.

On anodic stability and decomposition mechanism of sulfolane in high-voltage lithium ion battery

International Nuclear Information System (INIS)

Xing, Lidan; Tu, Wenqiang; Vatamanu, Jenel; Liu, Qifeng; Huang, Wenna; Wang, Yating; Zhou, Hebing; Zeng, Ronghua; Li, Weishan

2014-01-01

Graphical abstract: - Highlights: • Influence of lithium salts on the anodic stability of sulfolane has been investigated. • Oxidation decomposition mechanisms of LiPF 6 /Sulfolane electrolyte have been well understood by theoretical and experimental methods. • Decomposition products of the electrolyte can be found on the electrode surface and in the interfacial electrolyte. - Abstract: In this work, we investigated the anodic stability and decomposition mechanism of sulfolane (SL). The anodic stability of SL-based electrolyte with different lithium salts on Pt and LiNi 0.5 Mn 1.5 O 4 electrodes was found to decrease as follows: LiPF 6 /SL > LiBF 4 /SL > LiClO 4 /SL. The oxidation potential of 1M LiPF 6 /SL electrolyte on both Pt and electrodes is about 5.0V vs Li/Li + . The presence of PF 6 - and another SL solvent dramatically alters the decomposition mechanism of SL. Oxidation decomposition of SL-SL cluster is the most favorable reaction in LiPF 6 /SL electrolyte. The dimer products with S-O-R group were detected by IR spectra on the charged LiNi 0.5 Mn 1.5 O 4 electrode surface and in the electrolyte near the electrode surface, and were found to increase the interfacial reaction resistance of the LiNi 0.5 Mn 1.5 O 4 electrode

Influence of different curing systems on the physico-mechanical properties and stability of SBR and NR rubbers

Energy Technology Data Exchange (ETDEWEB)

Basfar, A.A. E-mail: abasfar@kacst.edu.sa; Abdel-Aziz, M.M.; Mofti, S

2002-01-01

The physical properties of radiation, sulfur and peroxide-cured styrene-butadiene rubber (SBR) and natural rubber (NR) were compared. The dependence of the mechanical properties of the radiation-vulcanized SBR and NR on the coagent concentration and radiation dose was studied. The effect of thermal aging on the mechanical properties of the different rubber formulations was discussed. The radiation-cured formulations of SBR have superior mechanical properties and thermal stability compared with those of the chemically vulcanized compounds. Whereas, the radiation-cured formulations of NR have similar mechanical properties but superior thermal stability (based on the % change in E after thermal aging), when compared with those of the sulfur-vulcanized compounds and slightly better than those of the peroxide-vulcanized compounds.

Gaze stabilization in chronic vestibular-loss and in cerebellar ataxia: interactions of feedforward and sensory feedback mechanisms.

Science.gov (United States)

Sağlam, M; Lehnen, N

2014-01-01

During gaze shifts, humans can use visual, vestibular, and proprioceptive feedback, as well as feedforward mechanisms, for stabilization against active and passive head movements. The contributions of feedforward and sensory feedback control, and the role of the cerebellum, are still under debate. To quantify these contributions, we increased the head moment of inertia in three groups (ten healthy, five chronic vestibular-loss and nine cerebellar-ataxia patients) while they performed large gaze shifts to flashed targets in darkness. This induces undesired head oscillations. Consequently, both active (desired) and passive (undesired) head movements had to be compensated for to stabilize gaze. All groups compensated for active and passive head movements, vestibular-loss patients less than the other groups (P feedforward mechanisms substantially contribute to gaze stabilization. Proprioception alone is not sufficient (gain 0.2). Stabilization against active and passive head movements was not impaired in our cerebellar ataxia patients.

The opto-mechanical design of the GMT-Consortium Large Earth Finder (G-CLEF)

Science.gov (United States)

Mueller, Mark; Szentgyorgyi, Andrew; Baldwin, Daniel; Bean, Jacob; Ben-Ami, Sagi; Brennan, Patricia; Budynkiewicz, J.; Chun, Moo-Yung; Crane, Jeffrey D.; Epps, Harland; Evans, Ian; Evans, Janet; Foster, Jeff; Frebel, Anna; Gauron, Thomas; Glenday, Alex; Hare, Tyson; Jang, Bi-Ho; Jang, Jeong-Gyun; Jordan, Andreas; Kim, Jihun; Kim, Kang-Min; Mendes de Oliveira, Claudia; Lopez-Morales, Mercedes; McCracken, Kenneth; McMuldroch, Stuart; Miller, Joseph; Oh, Jae Sok; Onyuksel, Cem; Ordway, Mark; Park, Chan; Park, Sung-Joon; Paxson, Charles; Phillips, David; Plummer, David; Podgorski, William; Seifahrt, Andreas; Steiner, Joao; Uomoto, Alan; Walsworth, Ronald; Yu, Young-Sam

2016-08-01

The GMT-Consortium Large Earth Finder (G-CLEF) is a fiber-fed, optical echelle spectrograph selected as the first light instrument for the Giant Magellan Telescope (GMT) now under construction at the Las Campanas Observatory in Chile. G-CLEF has been designed to be a general-purpose echelle spectrograph with precision radial velocity (PRV) capability for exoplanet detection. The radial velocity (RV) precision goal of G-CLEF is 10 cm/sec, necessary for detection of Earth-sized exoplanets. This goal imposes challenging stability requirements on the optical mounts and the overall spectrograph support structures especially when considering the instrument's operational environment. The accuracy of G-CLEF's PRV measurements will be influenced by minute changes in temperature and ambient air pressure as well as vibrations and micro gravity-vector variations caused by normal telescope slewing. For these reasons we have chosen to enclose G-CLEF's spectrograph in a well-insulated, vibration isolated vacuum chamber in a gravity invariant location on GMT's azimuth platform. Additional design constraints posed by the GMT telescope include: a limited space envelope, a thermal emission ceiling, and a maximum weight allowance. Other factors, such as manufacturability, serviceability, available technology and budget are also significant design drivers. All of the above considerations must be managed while ensuring performance requirements are achieved. In this paper, we discuss the design of G-CLEF's optical mounts and support structures including the choice of a low coefficient of thermal expansion (CTE) carbon-fiber optical bench to minimize the system's sensitivity to thermal soaks and gradients. We discuss design choices made to the vacuum chamber geared towards minimize the influence of daily ambient pressure variations on image motion during observation. We discuss the design of G-CLEF's insulated enclosure and thermal control systems which will maintain the spectrograph at

The Effects of Grain Refinement and Rare Earth Intermetallics on Mechanical Properties of As-Cast and Wrought Magnesium Alloys

Science.gov (United States)

Pourbahari, Bita; Mirzadeh, Hamed; Emamy, Massoud

2018-03-01

The effects of rare earth intermetallics and grain refinement by alloying and hot extrusion on the mechanical properties of Mg-Gd-Al-Zn alloys have been studied to elucidate some useful ways to enhance the mechanical properties of magnesium alloys. It was revealed that aluminum as an alloying element is a much better grain refining agent compared with gadolinium, but the simultaneous presence of Al and Gd can refine the as-cast grain size more efficiently. The presence of fine and widely dispersed rare earth intermetallics was found to be favorable to achieve finer recrystallized grains during hot deformation by extrusion. The presence of coarse dendritic structure in the GZ61 alloy, grain boundary eutectic containing Mg17Al12 phase in the AZ61 alloy, and rare earth intermetallics with unfavorable morphology in the Mg-4Gd-2Al-1Zn alloy was found to be detrimental to mechanical properties of the alloy in the as-cast condition. As a result, the microstructural refinement induced by hot extrusion process resulted in a significant enhancement in strength and ductility of the alloys. The presence of intermetallic compounds in the extruded Mg-4Gd-2Al-1Zn and Mg-2Gd-4Al-1Zn alloys deteriorated tensile properties, which was related to the fact that such intermetallic compounds act as stress risers and microvoid initiation sites.

Stability of Pharmaceuticals in Space

Science.gov (United States)

Nguyen, Y-Uyen

2009-01-01

Stability testing is a tool used to access shelf life and effects of storage conditions for pharmaceutical formulations. Early research from the International Space Station (ISS) revealed that some medications may have degraded while in space. This potential loss of medication efficacy would be very dangerous to Crew health. The aim of this research project, Stability of Pharmacotherapeutic Compounds, is to study how the stability of pharmaceutical compounds is affected by environmental conditions in space. Four identical pharmaceutical payload kits containing medications in different dosage forms (liquid for injection, tablet, capsule, ointment and suppository) were transported to the ISS aboard a Space Shuttle. One of the four kits was stored on that Shuttle and the other three were stored on the ISS for return to Earth at various time intervals aboard a pre-designated Shuttle flight. The Pharmacotherapeutics laboratory used stability test as defined by the United States Pharmacopeia (USP), to access the degree of degradation to the Payload kit medications that may have occurred during space flight. Once these medications returned, the results of stability test performed on them were compared to those from the matching ground controls stored on Earth. Analyses of the results obtained from physical and chemical stability assessments on these payload medications will provide researchers additional tools to promote safe and efficacious medications for space exploration.

On the persistence of unstable bump-on-tail electron velocity distributions in the earth's foreshock

Science.gov (United States)

Klimas, Alexander J.; Fitzenreiter, Richard J.

1988-01-01

This paper presents further evidence for the persistence of bump-on-tail unstable reduced velocity distributions in the earth's electron foreshock, which contradicts the understanding of quasi-linear saturation of the bump-on-tail instability. A modified theory for the saturation of the bump-on-tail instability in the earth's foreshock is proposed to explain the mechanism of this persistence, and the predictions are compared to the results of a numerical simulation of the electron plasma in the foreshock. The results support the thesis that quasi-linear saturation of the bump-on-tail instability is modified in the foreshock, due to the driven nature of the region, so that at saturation the stabilized velocity distribution still appears bump-on-tail unstable to linear plasma analysis.

Environmental and resources geochemistry of earth system mass transfer mechanism, geochemical cycle and the influence of human activity

CERN Document Server

Shikazono, Naotatsu

2015-01-01

The Earth system consists of subsystems that include the atmosphere, hydrosphere (water), geosphere (rocks, minerals), biosphere, and humans. In order to understand these subsystems and their interactions, it is essential to clarify the mass transfer mechanism, geochemical cycle, and influence of human activity on the natural environment. This book presents fundamental theories (thermodynamics, kinetics, mass balance model, coupling models such as the kinetics-fluid flow model, the box model, and others) concerning mechanisms in weathering, formation of hydrothermal ore deposits, hydrothermal alteration, formation of groundwater quality, and the seawater system. The interaction between fluids (atmosphere, water) and solid phases (rocks, minerals) occurs both in low-temperature and also in high-temperature systems. This book considers the complex low-temperature cycle with the high-temperature cycle, a combination that has not been dealt with in previous books concerning Earth systems. Humanity is a small part...

Thermal and mechanical stability of retained austenite in aluminum-containing multiphase TRIP steels

CERN Document Server

Zwaag, S; Kruijver, S O; Sietsma, J

2002-01-01

Stability of retained austenite is the key issue to understand transformation-induced plasticity (TRIP) effect. In this work, both thermal stability and mechanical stability are investigated by thermo-magnetic as well as in situ conventional X-ray diffraction and micro synchrotron radiation diffraction measurements. The thermal stability in a 0.20C-1.52Mn-0.25Si-0.96Al (wt%) TRIP steel is studied in the temperature range between 5 and 300 K under a constant magnetic field of 5T. It is found that almost all austenite transforms thermally to martensite upon cooling to 5K and M sub s and M sub f temperatures are analyzed to be 355 and 115 K. Transformation kinetics on the fraction versus temperature relation are well described by a model based on thermodynamics. From the in situ conventional X-ray and synchrotron diffraction measurements in a 0.17C-1.46Mn-0.26Si-1.81Al (wt%) steel, the volume fraction of retained austenite is found to decrease as the strain increases according to Ludwigson and Berger relation. T...

Non-uniform velocity profile mechanism for flame stabilization in a porous radiant burner

Energy Technology Data Exchange (ETDEWEB)

Catapan, R.C.; Costa, M. [Mechanical Engineering Department, Instituto Superior Tecnico, Technical University of Lisbon, Avenida Rovisco Pais, 1049-001 Lisbon (Portugal); Oliveira, A.A.M. [Mechanical Engineering Department, Federal University of Santa Catarina, Campus Universitario Professor Joao David Ferreira Lima, 88040-900 Florianopolis, SC (Brazil)

2011-01-15

Industrial processes where the heating of large surfaces is required lead to the possibility of using large surface porous radiant burners. This causes additional temperature uniformity problems, since it is increasingly difficult to evenly distribute the reactant mixture over a large burner surface while retaining its stability and keeping low pollutant emissions. In order to allow for larger surface area burners, a non-uniform velocity profile mechanism for flame stabilization in a porous radiant burner using a single large injection hole is proposed and analyzed for a double-layered burner operating in open and closed hot (laboratory-scale furnace, with temperature-controlled, isothermal walls) environments. In both environments, local mean temperatures within the porous medium have been measured. For lower reactant flow rate and ambient temperature the flame shape is conical and anchored at the rim of the injection hole. As the volumetric flow rate or furnace temperature is raised, the flame undergoes a transition to a plane flame stabilized near the external burner surface. However, the stability range envelope remains the same in both regimes. (author)

Effects of Freezing and Thawing Cycle on Mechanical Properties and Stability of Soft Rock Slope

OpenAIRE

Chen, Yanlong; Wu, Peng; Yu, Qing; Xu, Guang

2017-01-01

To explore the variation laws of mechanical parameters of soft rock and the formed slope stability, an experiment was carried out with collected soft rock material specimens and freezing and thawing cycle was designed. Meanwhile, a computational simulation analysis of the freezing-thawing slope stability was implemented. Key factors that influence the strength of frozen rock specimens were analyzed. Results showed that moisture content and the number of freezing-thawing cycles influenced mech...

Stability of source mechanisms inverted from P-wave amplitude microseismic monitoring data acquired at the surface

Czech Academy of Sciences Publication Activity Database

Staněk, František; Eisner, Leo; Moser, T.J.

2014-01-01

Roč. 62, č. 3 (2014), s. 475-490 ISSN 0016-8025 R&D Projects: GA ČR GAP210/12/2451 Institutional support: RVO:67985891 Keywords : microseismic monitoring * inversion * ray modelling * source mechanism Subject RIV: DC - Siesmology, Volcanology, Earth Structure Impact factor: 1.506, year: 2013

Prediction of geological and mechanical processes while disposing of high-level waste (HLW) into the earth crust

International Nuclear Information System (INIS)

Kedrovsky, O.L.; Morozov, V.N.

1992-01-01

Prediction of geological and mechanical processes while disposing of high-level waste of atomic industry into the earth crust is the fundamental base for ecological risk assessment (possible consequences) while developing repository designs. The subject of this paper is the analytical estimate of possibilities of rock fracturing mechanisms to predict isolation properties loss by massif beginning from crystal lattice of minerals up to large fracture disturbances under conditions of long-term influence of pressure, temperature, and radiation. To solve the problem possibilities of kinetic

Thermal Degradation Mechanism of a Thermostable Polyester Stabilized with an Open-Cage Oligomeric Silsesquioxane

Directory of Open Access Journals (Sweden)

Yolanda Bautista

2017-12-01

Full Text Available A polyester composite was prepared through the polymerization of an unsaturated ester resin with styrene and an open-cage oligomeric silsesquioxane with methacrylate groups. The effect of the open-cage oligomeric silsesquioxane on the thermal stability of the thermostable polyester was studied using both thermogravimetric analysis and differential thermal analysis. The results showed that the methacryl oligomeric silsesquioxane improved the thermal stability of the polyester. The decomposition mechanism of the polyester/oligomer silsesquioxane composite was proposed by Fourier transform infrared spectroscopy (FTIR analysis of the volatiles.

Stability of rare earth complexes with 2-(o-hydroxyphenyl)benzimidazole in aqueous-dioxane medium. Ustojchivost' kompleksnykh soedinenij RZEh s 2-(o-oksifenil)benzimidazolom v vodno-dioksanovoj srede

Energy Technology Data Exchange (ETDEWEB)

Akhrimenko, Z M; Panyushkin, V T; Fedorova, M V [Kubanskij Gosudarstvennyj Univ., Krasnodar (USSR)

1990-01-01

Method of potentiometric titration was used to determine protonation constants of 2-(-hydroxyphenyl)benzimidazole (pK{sub 1}=4.5; pK{sub 2}=11.30) and stability constants of Pr,Nd,Sm,Eu,Tb,Dy complexes with this ligand. Nonmonotonous change of lgK{sub 1} with increase of ordinal number of rare earth element was revealed.

Elucidating the mechanical effects of pore water pressure increase on the stability of unsaturated soil slopes

Science.gov (United States)

Buscarnera, G.

2012-12-01

The increase of the pore water pressure due to rain infiltration can be a dominant component in the activation of slope failures. This paper shows an application of the theory of material stability to the triggering analysis of this important class of natural hazards. The goal is to identify the mechanisms through which the process of suction removal promotes the initiation of mechanical instabilities. The interplay between increase in pore water pressure, and failure mechanisms is investigated at material point level. In order to account for multiple failure mechanisms, the second-order work criterion is used and different stability indices are devised. The paper shows that the theory of material stability can assess the risk of shear failure and static liquefaction in both saturated and unsaturated contexts. It is shown that the combined use of an enhanced definition of second-order work for unsaturated porous media and a hydro-mechanical constitutive framework enables to retrieve bifurcation conditions for water-infiltration processes in unsaturated deposits. This finding discloses the importance of the coupling terms that incorporate the interaction between the solid skeleton and the pore fluids. As a consequence, these theoretical results suggest that some material properties that are not directly associated with the shearing resistance (e.g., the potential for wetting compaction) can play an important role in the initiation of slope failures. According to the proposed interpretation, the process of pore pressure increase can be understood as a trigger of uncontrolled strains, which at material point level are reflected by the onset of bifurcation conditions.

Green synthesis of Au nanoparticles using potato extract: stability and growth mechanism

Science.gov (United States)

Castillo-López, D. N.; Pal, U.

2014-08-01

We report on the synthesis of spherical, well-dispersed colloidal gold nanoparticles of 17.5-23.5 nm average sizes in water using potato extract (PE) both as reducing and stabilizing agent. The effects of PE content and the pH value of the reaction mixture have been studied. Formation and growth dynamics of the Au nanoparticles in the colloids were studied using transmission electron microscopy and UV-Vis optical absorption spectroscopy techniques. While the reductor content and, hence, the nucleation and growth rates of the nanoparticles could be controlled by controlling the PE content in the reaction solution, the stability of the nanoparticles depended strongly on the pH of the reaction mixture. The mechanisms of Au ion reduction and stabilization of Au nanoparticles by potato starch have been discussed. The use of common natural solvent like water and biological reductor like PE in our synthesis process opens up the possibility of synthesizing Au nanoparticles in fully green (environmental friendly) way, and the Au nanoparticles produced in such way should have good biocompatibility.

Trimethylamine N-oxide stabilizes proteins via a distinct mechanism compared with betaine and glycine

Science.gov (United States)

Liao, Yi-Ting; Manson, Anthony C.; DeLyser, Michael R.; Noid, William G.; Cremer, Paul S.

2017-01-01

We report experimental and computational studies investigating the effects of three osmolytes, trimethylamine N-oxide (TMAO), betaine, and glycine, on the hydrophobic collapse of an elastin-like polypeptide (ELP). All three osmolytes stabilize collapsed conformations of the ELP and reduce the lower critical solution temperature (LSCT) linearly with osmolyte concentration. As expected from conventional preferential solvation arguments, betaine and glycine both increase the surface tension at the air–water interface. TMAO, however, reduces the surface tension. Atomically detailed molecular dynamics (MD) simulations suggest that TMAO also slightly accumulates at the polymer–water interface, whereas glycine and betaine are strongly depleted. To investigate alternative mechanisms for osmolyte effects, we performed FTIR experiments that characterized the impact of each cosolvent on the bulk water structure. These experiments showed that TMAO red-shifts the OH stretch of the IR spectrum via a mechanism that was very sensitive to the protonation state of the NO moiety. Glycine also caused a red shift in the OH stretch region, whereas betaine minimally impacted this region. Thus, the effects of osmolytes on the OH spectrum appear uncorrelated with their effects upon hydrophobic collapse. Similarly, MD simulations suggested that TMAO disrupts the water structure to the least extent, whereas glycine exerts the greatest influence on the water structure. These results suggest that TMAO stabilizes collapsed conformations via a mechanism that is distinct from glycine and betaine. In particular, we propose that TMAO stabilizes proteins by acting as a surfactant for the heterogeneous surfaces of folded proteins. PMID:28228526

Statistical mechanics provides novel insights into microtubule stability and mechanism of shrinkage.

Directory of Open Access Journals (Sweden)

Ishutesh Jain

2015-02-01

Full Text Available Microtubules are nano-machines that grow and shrink stochastically, making use of the coupling between chemical kinetics and mechanics of its constituent protofilaments (PFs. We investigate the stability and shrinkage of microtubules taking into account inter-protofilament interactions and bending interactions of intrinsically curved PFs. Computing the free energy as a function of PF tip position, we show that the competition between curvature energy, inter-PF interaction energy and entropy leads to a rich landscape with a series of minima that repeat over a length-scale determined by the intrinsic curvature. Computing Langevin dynamics of the tip through the landscape and accounting for depolymerization, we calculate the average unzippering and shrinkage velocities of GDP protofilaments and compare them with the experimentally known results. Our analysis predicts that the strength of the inter-PF interaction (E(s(m has to be comparable to the strength of the curvature energy (E(b(m such that E(s(m - E(b(m ≈ 1kBT, and questions the prevalent notion that unzippering results from the domination of bending energy of curved GDP PFs. Our work demonstrates how the shape of the free energy landscape is crucial in explaining the mechanism of MT shrinkage where the unzippered PFs will fluctuate in a set of partially peeled off states and subunit dissociation will reduce the length.

Swelling, Mechanics, and Thermal/Chemical Stability of Hydrogels Containing Phenylboronic Acid Side Chains

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Arum Kim

2017-12-01

Full Text Available We report here studies of swelling, mechanics, and thermal stability of hydrogels consisting of 20 mol % methacrylamidophenylboronic acid (MPBA and 80 mol % acrylamide (AAm, lightly crosslinked with methylenebisacrylamide (Bis. Swelling was measured in solutions of fixed ionic strength, but with varying pH values and fructose concentrations. Mechanics was studied by compression and hold. In the absence of sugar or in the presence of fructose, the modulus was mostly maintained during the hold period, while a significant stress relaxation was seen in the presence of glucose, consistent with reversible, dynamic crosslinks provided by glucose, but not fructose. Thermal stability was determined by incubating hydrogels at pH 7.4 at room temperature, and 37, 50, and 65 °C, and monitoring swelling. In PBS (phosphate buffered saline solutions containing 9 mM fructose, swelling remained essentially complete for 50 days at room temperature, but decreased substantially with time at the higher temperatures, with accelerated reduction of swelling with increasing temperature. Controls indicated that over long time periods, both the MPBA and AAm units were experiencing conversion to different species.

Enhanced mechanical behavior of a nanocrystallised stainless steel and its thermal stability

International Nuclear Information System (INIS)

Roland, T.; Retraint, D.; Lu, K.; Lu, J.

2007-01-01

This paper discusses the mechanical properties of a nanocrystallised stainless steel obtained using surface mechanical attrition treatment (SMAT) and the underlying grain refinement mechanism using transmission electron microscopy (TEM). It was shown that grain refinement down to the nanometer range has the potential to significantly improve the mechanical properties of a 316L stainless steel which becomes comparable in strength to titanium alloys. Hence, promising structural applications could be considered for such a material. At the same time, the thermal stability of this nanocrystallised material was studied in the temperature range from 100 to 800 deg. C. The results show that the nanometer scaled microstructure is retained up to 600 deg. C and that a controlled annealing treatment could even lead to enhancement of both strength and ductility of this material. All these results are explained in terms of microstructural investigations, X-ray diffraction measurements, tensile and bending tests as well as microhardness measurements

Enhanced mechanical behavior of a nanocrystallised stainless steel and its thermal stability

Energy Technology Data Exchange (ETDEWEB)

Roland, T. [ICD, LASMIS, University of Technology of Troyes, 10010 Troyes (France); Retraint, D. [ICD, LASMIS, University of Technology of Troyes, 10010 Troyes (France)]. E-mail: delphine.retraint@utt.fr; Lu, K. [Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110015 (China); Lu, J. [Department of Mechanical Engineering, Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong (China)

2007-02-15

This paper discusses the mechanical properties of a nanocrystallised stainless steel obtained using surface mechanical attrition treatment (SMAT) and the underlying grain refinement mechanism using transmission electron microscopy (TEM). It was shown that grain refinement down to the nanometer range has the potential to significantly improve the mechanical properties of a 316L stainless steel which becomes comparable in strength to titanium alloys. Hence, promising structural applications could be considered for such a material. At the same time, the thermal stability of this nanocrystallised material was studied in the temperature range from 100 to 800 deg. C. The results show that the nanometer scaled microstructure is retained up to 600 deg. C and that a controlled annealing treatment could even lead to enhancement of both strength and ductility of this material. All these results are explained in terms of microstructural investigations, X-ray diffraction measurements, tensile and bending tests as well as microhardness measurements.

Unified mechanism of alkali and alkaline earth catalyzed gasification reactions of carbon by CO2 and H2O

Science.gov (United States)

Chen, S.G.; Yang, R.T.

1997-01-01

From molecular orbital calculations, a unified mechanism is proposed for the gasification reactions of graphite by CO2 and H2O, both uncatalyzed and catalyzed by alkali and alkaline earth catalysts. In this mechanism, there are two types of oxygen intermediates that are bonded to the active edge carbon atoms: an in-plane semiquinone type, Cf(O), and an off-plane oxygen bonded to two saturated carbon atoms that are adjacent to the semiquinone species, C(O)Cf(O). The rate-limiting step is the decomposition of these intermediates by breaking the C-C bonds that are connected to Cf(O). A new rate equation is derived for the uncatalyzed reactions, and that for the catalyzed reactions is readily available from the proposed mechanism. The proposed mechanism can account for several unresolved experimental observations: TPD and TK (transient kinetics) desorption results of the catalyzed systems, the similar activation energies for the uncatalyzed and catalyzed reactions, and the relative activities of the alkali and alkaline earth elements. The net charge of the edge carbon active site is substantially changed by gaining electron density from the alkali or alkaline earth element (by forming C-O-M, where M stands for metal). The relative catalytic activities of these elements can be correlated with their abilities of donating electrons and changing the net charge of the edge carbon atom. As shown previously (Chen, S. G.; Yang, R. T. J. Catal. 1993, 141, 102), only clusters of the alkali compounds are active. This derives from the ability of the clusters to dissociate CO2 and H2O to form O atoms and the mobility of the dissociated O atoms facilitated by the clusters.

Mechanical stability of the cell nucleus: roles played by the cytoskeleton in nuclear deformation and strain recovery.

Science.gov (United States)

Wang, Xian; Liu, Haijiao; Zhu, Min; Cao, Changhong; Xu, Zhensong; Tsatskis, Yonit; Lau, Kimberly; Kuok, Chikin; Filleter, Tobin; McNeill, Helen; Simmons, Craig A; Hopyan, Sevan; Sun, Yu

2018-05-18

Extracellular forces transmitted through the cytoskeleton can deform the cell nucleus. Large nuclear deformation increases the risk of disrupting the nuclear envelope's integrity and causing DNA damage. Mechanical stability of the nucleus defines its capability of maintaining nuclear shape by minimizing nuclear deformation and recovering strain when deformed. Understanding the deformation and recovery behavior of the nucleus requires characterization of nuclear viscoelastic properties. Here, we quantified the decoupled viscoelastic parameters of the cell membrane, cytoskeleton, and the nucleus. The results indicate that the cytoskeleton enhances nuclear mechanical stability by lowering the effective deformability of the nucleus while maintaining nuclear sensitivity to mechanical stimuli. Additionally, the cytoskeleton decreases the strain energy release rate of the nucleus and might thus prevent shape change-induced structural damage to chromatin. © 2018. Published by The Company of Biologists Ltd.

Integrating plant-microbe interactions to understand soil C stabilization with the MIcrobial-MIneral Carbon Stabilization model (MIMICS)

Science.gov (United States)

Grandy, Stuart; Wieder, Will; Kallenbach, Cynthia; Tiemann, Lisa

2014-05-01

If soil organic matter is predominantly microbial biomass, plant inputs that build biomass should also increase SOM. This seems obvious, but the implications fundamentally change how we think about the relationships between plants, microbes and SOM. Plant residues that build microbial biomass are typically characterized by low C/N ratios and high lignin contents. However, plants with high lignin contents and high C/N ratios are believed to increase SOM, an entrenched idea that still strongly motivates agricultural soil management practices. Here we use a combination of meta-analysis with a new microbial-explicit soil biogeochemistry model to explore the relationships between plant litter chemistry, microbial communities, and SOM stabilization in different soil types. We use the MIcrobial-MIneral Carbon Stabilization (MIMICS) model, newly built upon the Community Land Model (CLM) platform, to enhance our understanding of biology in earth system processes. The turnover of litter and SOM in MIMICS are governed by the activity of r- and k-selected microbial groups and temperature sensitive Michaelis-Menten kinetics. Plant and microbial residues are stabilized short-term by chemical recalcitrance or long-term by physical protection. Fast-turnover litter inputs increase SOM by >10% depending on temperature in clay soils, and it's only in sandy soils devoid of physical protection mechanisms that recalcitrant inputs build SOM. These results challenge centuries of lay knowledge as well as conventional ideas of SOM formation, but are they realistic? To test this, we conducted a meta-analysis of the relationships between the chemistry of plant liter inputs and SOM concentrations. We find globally that the highest SOM concentrations are associated with plant inputs containing low C/N ratios. These results are confirmed by individual tracer studies pointing to greater stabilization of low C/N ratio inputs, particularly in clay soils. Our model and meta-analysis results suggest

Slope Stability. CEGS Programs Publication Number 15.

Science.gov (United States)

Pestrong, Raymond

Slope Stability is one in a series of single-topic problem modules intended for use in undergraduate and earth science courses. The module, also appropriate for use in undergraduate civil engineering and engineering geology courses, is a self-standing introduction to studies of slope stability. It has been designed to supplement standard…

Unique Non-Keplerian Orbit Vantage Locations for Sun-Earth Connection and Earth Science Vision Roadmaps

Science.gov (United States)

Folta, David; Young, Corissa; Ross, Adam

2001-01-01

The purpose of this investigation is to determine the feasibility of attaining and maintaining unique non-Keplerian orbit vantage locations in the Earth/Moon environment in order to obtain continuous scientific measurements. The principal difficulty associated with obtaining continuous measurements is the temporal nature of astrodynamics, i.e., classical orbits. This investigation demonstrates advanced trajectory designs to meet demanding science requirements which cannot be met following traditional orbital mechanic logic. Examples of continuous observer missions addressed include Earth pole-sitters and unique vertical libration orbits that address Sun-Earth Connection and Earth Science Vision roadmaps.

Effect of rare-earth dopants on the growth and structural, optical, electrical and mechanical properties of L-arginine phosphate single crystals

International Nuclear Information System (INIS)

Arjunan, S.; Bhaskaran, A.; Kumar, R. Mohan; Mohan, R.; Jayavel, R.

2010-01-01

Research highlights: → Thorium, Lanthanum and Cerium rare-earth ions were doped with L-arginine phosphate material and the crystals were grown by slow evaporation technique. → The transparency of the rare-earth doped LAP crystals has enhanced compared to pure LAP. → The powder SHG measurements revealed that the SHG output of rare-earth doped LAP crystals increases considerably compared to that of LAP. → Vicker's hardness number of as-grown crystal of LAP is higher than that of rare-earth doped LAP crystals. - Abstract: Effect of Thorium, Lanthanum and Cerium rare-earth ions on the growth and properties of L-arginine phosphate single crystals has been reported. The incorporation of rare-earth dopants into the L-arginine phosphate crystals is confirmed by Inductively Coupled Plasma-Mass Spectroscopy analysis. The unit cell parameters for pure and rare-earth doped L-arginine phosphate crystals have been estimated by powder X-ray diffraction studies. UV-visible studies revealed the transmittance percentage and cut-off wavelengths of the grown crystals. Powder second harmonic generation measurement has been carried out for pure and doped L-arginine phosphate crystals. The dielectric behavior of the grown crystals was analyzed for different frequencies at room temperature. The mechanical properties have been determined for pure and the doped L-arginine phosphate crystals.

Molecular mechanisms underlying the pilsicainide-induced stabilization of hERG proteins in transfected mammalian cells

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Takeshi Onohara, MD

2017-06-01

Conclusions: Pilsicainide penetrates the plasma membrane, stabilizes WT-hERG proteins by acting as a chemical chaperone, and enhances WT-hERG channel currents. This mechanism could also be applicable to modulations of certain mutant-hERG proteins.

Prebiotic Chemistry and Atmospheric Warming of Early Earth by an Active Young Sun

Science.gov (United States)

Airapetian, V. S.; Glocer, A.; Gronoff, G.; Hebrard, E.; Danchi, W.

2016-01-01

Nitrogen is a critical ingredient of complex biological molecules. Molecular nitrogen, however, which was outgassed Into the Earth's early atmosphere, is relatively chemically inert and nitrogen fixation into more chemically reactive compounds requires high temperatures. Possible mechanisms of nitrogen fixation include lightning, atmospheric shock heating by meteorites, and solar ultraviolet radiation. Here we show that nitrogen fixation in the early terrestrial atmosphere can be explained by frequent and powerful coronal mass ejection events from the young Sun -- so-called superflares. Using magnetohydrodynamic simulations constrained by Kepler Space Telescope observations, we find that successive superflare ejections produce shocks that accelerate energetic particles, which would have compressed the early Earth's magnetosphere. The resulting extended polar cap openings provide pathways for energetic particles to penetrate into the atmosphere and, according to our atmospheric chemistry simulations, initiate reactions converting molecular nitrogen, carbon dioxide and methane to the potent greenhouse gas nitrous oxide as well as hydrogen cyanide, an essential compound for life. Furthermore, the destruction of N2, C02 and CH, suggests that these greenhouse gases cannot explain the stability of liquid water on the early Earth. Instead, we propose that the efficient formation of nitrous oxide could explain a warm early Earth.

Mechanical stability and adhesion of ceramic coatings deposited on steels

International Nuclear Information System (INIS)

Ignat, M.; Armann, A.; Moberg, L.; Sibieude, F.

1991-01-01

This paper presents the results of two sorts of deformation experiment performed on coating/substrate systems. The coating/substrate systems were constituted by coatings of titanium nitride and chromium carbide, deposited in both cases on steel substrates. The formation experiments were cyclic bending tests on macroscopic samples with chromium carbide coatings, and straining experiments performed in a scanning electron microscope on samples with titanium nitride coatings. By the analysis of our experimental results we develop an attempt to correlate the mechanical stability of the systems with the interfacial adhesion, by taking into account the internal residual stresses as an adhesion parameter. For the samples with chromium carbide coatings, the evolution of internal stresses is detected from X-ray diffractometry and discussed in terms of the observed induced damaging mechanisms, in the cyclic tests. For the samples with titanium nitride coatings, we discussed the adhesion from the microstructural observations and from the critical parameters determined during the in-situ straining experiments. (orig.)

Rare earths in iron and steelmaking and gaseous desulphurisation

International Nuclear Information System (INIS)

Kay, D.A.R.; Subramanian, S.V.; Meng, V.; Kumar, R.V.

1985-01-01

Rare earth (RE) additions, either as mischmetal or rare earth silicide, are used in many ladle treatment processes in modern ferrous metallurgy. In ironmaking they provide the basis for the control of graphite morphology in cast irons and in steelmaking additions are made to aluminum-killed steels for desulphurisation and the control of inclusion composition and morphology. Rare earth oxides may also be used in the desulphurisation of medium calorific value gaseous fuels and stack gases. In this paper, Ce-S-O and La-S-O phase stability diagrams are used to determine the role of the rare earths in the external processing of iron and steel, and gaseous desulphurisation

Early Earth(s) Across Time and Space

Science.gov (United States)

Mojzsis, S.

2014-04-01

The geochemical and cosmochemical record of our solar system is the baseline for exploring the question: "when could life appear on a world similar to our own?" Data arising from direct analysis of the oldest terrestrial rocks and minerals from the first 500 Myr of Earth history - termed the Hadean Eon - inform us about the timing for the establishment of a habitable silicate world. Liquid water is the key medium for life. The origin of water, and its interaction with the crust as revealed in the geologic record, guides our exploration for a cosmochemically Earth-like planets. From the time of primary planetary accretion to the start of the continuous rock record on Earth at ca. 3850 million years ago, our planet experienced a waning bolide flux that partially or entirely wiped out surface rocks, vaporized oceans, and created transient serpentinizing atmospheres. Arguably, "Early Earths" across the galaxy may start off as ice planets due to feeble insolation from their young stars, occasionally punctuated by steam atmospheres generated by cataclysmic impacts. Alternatively, early global environments conducive to life spanned from a benign surface zone to deep into crustal rocks and sediments. In some scenarios, nascent biospheres benefit from the exogenous delivery of essential bio-elements via leftovers of accretion, and the subsequent establishment of planetary-scale hydrothermal systems. If what is now known about the early dynamical regime of the Earth serves as any measure of the potential habitability of worlds across space and time, several key boundary conditions emerge. These are: (i) availability and long-term stability of liquid water; (ii) presence of energy resources; (iii) accessibility of organic raw materials; (iv) adequate inventory of radioisotopes to drive internal heating; (v) gross compositional parameters such as mantle/core mass ratio, and (vi) P-T conditions at or near the surface suitable for sustaining biological activity. Life could

Fabrication of polylactic acid/hydroxyapatite/graphene oxide composite and their thermal stability, hydrophobic and mechanical properties

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Ming Gong

2017-06-01

Full Text Available A series of polylactic acid/hydroxyapatite/graphene oxide composite (PLA/HA/GO were fabricated via solution blending and casting method using N,N-dimethyl-formamide (DMF and CH2Cl2 as mutual solvents. The physicochemical properties of the resulting composites were characterized by means of FT-IR, SEM, TEM, Raman spectra, XRD and N2-physisorption. Particularly, the thermal stabilities, hydrophobic and mechanical properties of PLA/HA/GO composites were systematically investigated. The influences of GO content on thermal stabilities, hydrophobic and mechanical properties of the composites were also evaluated. The results showed that the addition of GO and HA not only improved the thermal stability of PLA, but also improved the hydrophobic property of PLA-based composites. By compared with the PLA/HA/GO composite, the tensile strength of pristine PLA is slight high. The tensile strength and hardness of PLA/HA/GO composites increased with the increase of GO content. The obtained PLA/HA/GO composite may be a promising material for load-bearing orthopedic implants.

Phase stability, mechanical properties, hardness, and possible reactive routing of chromium triboride from first-principle investigations

International Nuclear Information System (INIS)

Zhong, Ming-Min; Kuang, Xiao-Yu; Wang, Zhen-Hua; Shao, Peng; Ding, Li-Ping; Huang, Xiao-Fen

2013-01-01

The first-principles calculations are employed to provide a fundamental understanding of the structural features and relative stability, mechanical and electronic properties, and possible reactive route for chromium triboride. The predicted new phase of CrB 3 belongs to the rhombohedral phase with R-3m symmetry and it transforms into a hexagonal phase with P-6m2 symmetry at 64 GPa. The mechanical and thermodynamic stabilities of CrB 3 are verified by the calculated elastic constants and formation enthalpies. Also, the full phonon dispersion calculations confirm the dynamic stability of predicted CrB 3 . Considering the role of metallic contributions, the calculated hardness values from our semiempirical method for rhombohedral and hexagonal phases are 23.8 GPa and 22.1 GPa, respectively. In addition, the large shear moduli, Young's moduli, low Poisson's ratios, and small B/G ratios indicate that they are potential hard materials. Relative enthalpy calculations with respect to possible constituents are also investigated to assess the prospects for phase formation and an attempt at high-pressure synthesis is suggested to obtain chromium triboride

Modulation of erythrocyte membrane mechanical stability by 2,3-diphosphoglycerate in the neonatal poikilocytosis/elliptocytosis syndrome.

Science.gov (United States)

Mentzer, W C; Iarocci, T A; Mohandas, N; Lane, P A; Smith, B; Lazerson, J; Hays, T

1987-01-01

To explain the transient anemia and poikilocytosis seen during infancy in hereditary elliptocytosis (HE), we resealed erythrocyte (RBC) ghosts from affected children or their elliptocytic parents with 2,3-diphosphoglycerate (DPG) (0-8 mM), a compound that dissociates membrane skeletons, then measured ghost mechanical stability in the ektacytometer. Without added 2,3-DPG, ghost mechanical stability was subnormal in infantile poikilocytosis (IP) and HE but was even more abnormal in hereditary pyropoikilocytosis (HPP). Addition of 2,3-DPG (2.55 mM) to IP or HE ghosts, decreased their stability to that of HPP ghosts (without 2,3-DPG). Nonphysiological 2,3-DPG levels (6-8 mM) were required to elicit a similar effect in normal ghosts. The data suggest that free 2,3-DPG, present in neonatal RBC as a consequence of diminished binding to HbF, may render HE susceptible to in vivo fragmentation. The developmental switch from fetal to adult hemoglobin, by diminishing available free 2,3-DPG, may explain the abatement of poikilocytosis and hemolytic anemia that accompanies maturation. Images PMID:3818955

Preliminary Slope Stability Study Using Slope/ W

International Nuclear Information System (INIS)

Nazran Harun; Mohd Abd Wahab Yusof; Kamarudin Samuding; Mohd Muzamil Mohd Hashim; Nurul Fairuz Diyana Bahrudin

2014-01-01

Analyzing the stability of earth structures is the oldest type of numerical analysis in geotechnical engineering. Limit equilibrium types of analyses for assessing the stability of earth slopes have been in use in geotechnical engineering for many decades. Modern limit equilibrium software is making it possible to handle ever-increasing complexity within an analysis. It is being considered as the potential method in dealing with complex stratigraphy, highly irregular pore-water pressure conditions, various linear and nonlinear shear strength models and almost any kind of slip surface shape. It allows rapid decision making by providing an early indication of the potential suitability of sites based on slope stability analysis. Hence, a preliminary slope stability study has been developed to improve the capacity of Malaysian Nuclear Agency (Nuclear Malaysia) in assessing potential sites for Borehole Disposal for Disused Sealed Radioactive Sources. The results showed that geometry of cross section A-A ' , B-B ' , C-C ' and D-D ' achieved the factor of safety not less than 1.4 and these are deemed acceptable. (author)

Strength Analysis of Coconut Fiber Stabilized Earth for Farm Structures

Science.gov (United States)

Enokela, O. S.; P. O, Alada

2012-07-01

Investigation of the strength characteristic of soil from alluvial deposit of River Benue in makurdi stabilized with coconut fiber as a stabilizer was carried as local building material for farm structure. Processed coconut fibers were mixed with the soil at four different mix ratios of 1% fiber, 2% fiber, 3% fiber and 4% fiber by percentage weight with 0% fiber as control. Compaction test and compressive strength were carried out on the various stabilizing ratio. From the compaction test, the correlation between the maximum dry density and optimum moisture content is a second order polynomial with a coefficient of 63% obtained at1.91kg/m3and 20.0% respectively while the compressive strength test shows an optimum failure load of 8.62N/mm2 at 2%fibre:100% soil mix ratio at 2.16 maximum dry density.

Impact of OH Radical-Initiated H2CO3 Degradation in the Earth's Atmosphere via Proton-Coupled Electron Transfer Mechanism.

Science.gov (United States)

Ghoshal, Sourav; Hazra, Montu K

2016-02-04

The decomposition of isolated carbonic acid (H2CO3) molecule into CO2 and H2O (H2CO3 → CO2 + H2O) is prevented by a large activation barrier (>35 kcal/mol). Nevertheless, it is surprising that the detection of the H2CO3 molecule has not been possible yet, and the hunt for the free H2CO3 molecule has become challenging not only in the Earth's atmosphere but also on Mars. In view of this fact, we report here the high levels of quantum chemistry calculations investigating both the energetics and kinetics of the OH radical-initiated H2CO3 degradation reaction to interpret the loss of the H2CO3 molecule in the Earth's atmosphere. It is seen from our study that proton-coupled electron transfer (PCET) and hydrogen atom transfer (HAT) are the two mechanisms by which the OH radical initiates the degradation of the H2CO3 molecule. Moreover, the PCET mechanism is potentially the important one, as the effective barrier, defined as the difference between the zero point vibrational energy (ZPE) corrected energy of the transition state and the total energy of the isolated starting reactants in terms of bimolecular encounters, for the PCET mechanism at the CCSD(T)/6-311++G(3df,3pd) level of theory is ∼3 to 4 kcal/mol lower than the effective barrier height associated with the HAT mechanism. The CCSD(T)/6-311++G(3df,3pd) level predicted effective barrier heights for the degradations of the two most stable conformers of H2CO3 molecule via the PCET mechanism are only ∼2.7 and 4.3 kcal/mol. A comparative reaction rate analysis at the CCSD(T)/6-311++G(3df,3pd) level of theory has also been carried out to explore the potential impact of the OH radical-initiated H2CO3 degradation relative to that from water (H2O), formic acid (FA), acetic acid (AA) and sulfuric acid (SA) assisted H2CO3 → CO2 + H2O decomposition reactions in both the Earth's troposphere and stratosphere. The comparison of the reaction rates reveals that, although the atmospheric concentration of the OH radical is

Earth Rotation

Science.gov (United States)

Dickey, Jean O.

1995-01-01

The study of the Earth's rotation in space (encompassing Universal Time (UT1), length of day, polar motion, and the phenomena of precession and nutation) addresses the complex nature of Earth orientation changes, the mechanisms of excitation of these changes and their geophysical implications in a broad variety of areas. In the absence of internal sources of energy or interactions with astronomical objects, the Earth would move as a rigid body with its various parts (the crust, mantle, inner and outer cores, atmosphere and oceans) rotating together at a constant fixed rate. In reality, the world is considerably more complicated, as is schematically illustrated. The rotation rate of the Earth's crust is not constant, but exhibits complicated fluctuations in speed amounting to several parts in 10(exp 8) [corresponding to a variation of several milliseconds (ms) in the Length Of the Day (LOD) and about one part in 10(exp 6) in the orientation of the rotation axis relative to the solid Earth's axis of figure (polar motion). These changes occur over a broad spectrum of time scales, ranging from hours to centuries and longer, reflecting the fact that they are produced by a wide variety of geophysical and astronomical processes. Geodetic observations of Earth rotation changes thus provide insights into the geophysical processes illustrated, which are often difficult to obtain by other means. In addition, these measurements are required for engineering purposes. Theoretical studies of Earth rotation variations are based on the application of Euler's dynamical equations to the problem of finding the response of slightly deformable solid Earth to variety of surface and internal stresses.

Correlation between mechanical behavior of protein films at the air/water interface and intrinsic stability of protein molecules

NARCIS (Netherlands)

Martin, A.H.; Cohen Stuart, M.A.; Bos, M.A.; Vliet, T. van

2005-01-01

The relation between mechanical film properties of various adsorbed protein layers at the air/water interface and intrinsic stability of the corresponding proteins is discussed. Mechanical film properties were determined by surface deformation in shear and dilation. In shear, fracture stress, σf,

Rock mechanics stability at Olkiluoto, Haestholmen, Kivetty and Romuvaara

International Nuclear Information System (INIS)

Johansson, E.; Rautakorpi, J.

2000-02-01

Posiva Oy is studying the suitability of the Finnish bedrock for the geological disposal of spent nuclear fuel at four sites, Olkiluoto in Eurajoki, Haestholmen in Loviisa, Kivetty in Aeaenekoski and Romuvaara in Kuhmo. To enable the rock properties to be specified in great detail, the site-selection research programme has included rock mechanics investigations such as the measurement of in-situ rock stress and laboratory tests on rock samples. This report presents the results of the rock mechanics analyses performed on the main rock types at the Olkiluoto, Romuvaara, Kivetty and Haestholmen sites. The objective of this study was to assess the near-field stability of the final disposal tunnels and deposition holes at each of the investigation sites. Two empirical methods and a numerical method based on three-dimensional element code (3DEC) were used the analysis tools. A statistical approach was used to select the necessary input data and to specify the cases being analysed. The stability of the KBS-3 and MLH (Medium Long Hole) repository concepts during the pre-closure and post-closure phases was analysed. The repository depths investigated lay between 300 m and 700 m. The empirical methods are based on the study of the ratios between rock strength and the in-situ stress which could result in possible fracturing of the rock mass. Interpretation of the numerical analyses is based on the assumption of an elastic distribution of stress around the disposal tunnel and the deposition hole and the brittle rock strength criterion. The results obtained in this study indicate that in general, the rock mechanics conditions during the pre-closure and post-closure phases at each of the investigated sites remain good and stable between the studied depth levels, especially when the deposition rooms are oriented in a direction parallel to the major in-situ stress. If the disposal tunnels are orientated in a direction perpendicular to the major in-situ stress, the resultant

EFFECTS OF CORE STABILIZATION PROGRAM AND CONVENTIONAL EXERCISES IN THE MANAGEMENT OF PATIENTS WITH CHRONIC MECHANICAL LOW BACK PAIN

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Suresh Babu Reddy .A

2015-04-01

Full Text Available Background: Conventional back care exercises are advocated to treat the pain and to strengthen the involved muscles. There will be possibility of the pain getting recurred due to disproportionate balance and stability in the muscles. The core stabilization is major trend in rehabilitation, it aims at improving stability during functional activities, balance, flexibility, strength training and effectively manage the pain as well. Objective: To find the efficacy of the concept of core stabilization when compared to conventional back care exercises in patients with chronic mechanical low back pain. Methods: Forty patients with chronic Mechanical Low back pain were selected through purposive sampling and were randomly assigned into control group who received conventional back exercises and SWD (n=20, experimental group who received core stabilization and SWD (n=20. Both the groups received SWD, along with conventional back exercises for one group and core stabilization for the other group three days a week for 6 weeks. The treatment outcome was assessed using visual analogue scale, Rolland Morris Disability Questionnaire and Lumbar range of motion using goniometer. Results: After a 6 weeks training period the core stabilization group scored significantly higher than the conventional group for VAS (p=0.05 RMDQ (p=0.05 whereas ROM improved higher in conventional group (p=0.05. Conclusion: After the treatment sessions Core stabilization group registered a significant improvement when compared to conventional back care exercises in improving function and in relieving pain.

Synthesis and thermic behaviour (stability and sintering) of rare earth ortho-phosphates

International Nuclear Information System (INIS)

Lucas, S.

2003-04-01

Rare earth ortho-phosphates, LnPO 4 ,nH 2 O (Ln = La, Ce or Y), were synthesized by precipitation in aqueous media. The effect of pH, temperature, reagents stoichiometry and ripening time on the chemical composition and the morphology of the precipitates have been precised. The study of the thermal behaviour showed the presence of meta-phosphates as a secondary phase in the temperature range 1000 C - 1400 C that was very detrimental to the sintering. It is removed by calcining the powders at 1400 C. Thermogravimetry proved to be the best technique in order to insure the purity of the precipitates since it allows the detection of this phase down to a lower threshold than that associated with the other investigated characterization methods (IR or Raman spectrometry, chemical analysis, XRD, DTA). The monazites (La or Ce)PO 4 densify at 1400 C by natural sintering whereas the xenotime YPO 4 is not yet densified at 1500 C. Hot pressing at that temperature is required to its densification. The mechanical properties of the monazites remain low (sf about 120 MPa, K IC about 1.2 MPa.m 1/2 ). The xenotime ceramic is much more mechanically resistant (sf about 320 MPa, K IC about 1.5 MPa.m 1/2 ). An important acicular growth of the grains during the sintering of the xenotime (that occurs also during the synthesis process) is considered to be responsible for the behaviour and properties differences between this material and monazites. (author)

Structural and Mechanical Characterization of Sustainable Composites Based on Recycled and Stabilized Fly Ash

Directory of Open Access Journals (Sweden)

Stefano Besco

2014-08-01

Full Text Available This paper reports the results on the use of an innovative inert, based on stabilized fly ash from municipal solid waste incineration as a filler for polypropylene. The starting material, which contains large quantities of leachable Pb and Zn, was stabilized by means of an innovative process using rice husk ash as a waste silica source, together with other fly ashes, such as coal fly ash and flue gas desulfurization residues. The use of all waste materials to obtain a new filler makes the proposed technology extremely sustainable and competitive. The new composites, obtained by using the stabilized material as a filler for polypropylene, were characterized and their mechanical properties were also investigated. A comparison with a traditional polypropylene and calcium carbonate based compound was also done. This research activity was realized in the frame of the COSMOS-RICE project, financed by the EU Commission.

Demonstrating the Effect of Precipitation on the Mechanical Stability of Fine-Grained Austenite in Reversion-Treated 301LN Stainless Steel

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Antti Järvenpää

2017-09-01

Full Text Available According to recent investigations, a huge difference exists in the mechanical stability of austenite between the grain-refined structure states obtained in reversion annealing at 800–700 °C or at 900 °C, in a 301LN type austenitic stainless steel. Precipitation of chromium nitride occurring at these lower temperatures has been argued to be the factor reducing the stability. To prove this argument, a fine-grained, very stable austenitic structure was created at 900 °C in 1 s, and subsequently annealed at lower temperatures between 850 and 750 °C, up to 1000 s. It was found that the subsequent annealing at 750 and 800 °C resulted in prominent gradual decrease of the mechanical stability under tensile straining, detectable after 10 s annealing duration and continued until 1000 s. Only minimal grain growth occurred, which decreased the stability very marginally. The degree of the stability drop followed the predicted kinetics of the Cr2N precipitation with regards as its dependence on annealing duration and temperature. Further, the tensile yield strength of the fine-grained structure increased slightly due to the annealing. The presence of nano-sized Cr2N particles was verified after 1000 s holding at 750 °C. These observations and predictions yield firm evidence for the imperative contribution of precipitation to the highly reduced mechanical stability of grain-refined austenite in this steel.

Impact of modified graphene and microwave irradiation on thermal stability and degradation mechanism of poly (styrene-co-methyl meth acrylate)

Energy Technology Data Exchange (ETDEWEB)

Zubair, Mukarram [Department of Environmental Engineering, University of Dammam, 31982 Dammam (Saudi Arabia); Shehzad, Farrukh [Department of Chemical Engineering, King Fahd University of Petroleum & Minerals, 31261 Dhahran, Saudi Arabia, (Saudi Arabia); Al-Harthi, Mamdouh A., E-mail: mamdouh@kfupm.edu.sa [Department of Chemical Engineering, King Fahd University of Petroleum & Minerals, 31261 Dhahran, Saudi Arabia, (Saudi Arabia); Center of Research Excellence in Nanotechnology, King Fahd University of Petroleum & Minerals, 31261 Dhahran (Saudi Arabia)

2016-06-10

Highlights: • Modified graphene imparts thermal stability to Poly (styrene-co-methyl methacrylate) [P(st-mma)]. • The thermal stability of P(st-mma) decreased with microwave irradiation. • The thermal stability of P(st-mma)/MG nanocomposites increased with irradiation time up to 10 min and decreased subsequently. • The degradation of P(st-mma) and P(st-mma)/MG is governed by random scission model. - Abstract: Poly (styrene-co-methyl methacrylate) [P(st-mma)] composite containing 0.1 wt% modified graphene (MG) was prepared via melt blending. MG was prepared by oxidation method using nitric acid. The P(st-mma) and P(st-mma)MG composite were irradiated using microwave radiation. The degradation mechanism and thermal stability of the irradiated and un-irradiated samples was analyzed by TGA. P(st-mma)MG showed high thermal stability. The average activation energy of thermal degradation was found to be 200 kJ/mol for P(st-mma), 214 kJ/mol for P(st-mma)MG. The activation energy was highest for 10 min irradiated nanocomposites indicating an improvement in stability. The degradation mechanism was investigated by comparing the master plots constructed using the experimental data with theoretical master plots of various kinetic models. The thermal degradation of P(st-mma) and P(st-mma)MG composite before and after irradiation governs the random scission mechanism. SEM and TEM micrographs showed improved interactions and degradation of composites after 10 min and 20 min irradiation respectively.

Effect of rare-earth dopants on the growth and structural, optical, electrical and mechanical properties of L-arginine phosphate single crystals

Energy Technology Data Exchange (ETDEWEB)

Arjunan, S., E-mail: arjunan_hce@yahoo.co.i [Department of Physics, Sri Ramachandra University, Porur, Chennai (India); Bhaskaran, A. [Department of Physics, Dr. Ambedkar Government College, Chennai (India); Kumar, R. Mohan; Mohan, R. [Department of Physics, Presidency College, Chennai (India); Jayavel, R. [Crystal Growth Centre, Anna University, Chennai (India)

2010-09-17

Research highlights: {yields} Thorium, Lanthanum and Cerium rare-earth ions were doped with L-arginine phosphate material and the crystals were grown by slow evaporation technique. {yields} The transparency of the rare-earth doped LAP crystals has enhanced compared to pure LAP. {yields} The powder SHG measurements revealed that the SHG output of rare-earth doped LAP crystals increases considerably compared to that of LAP. {yields} Vicker's hardness number of as-grown crystal of LAP is higher than that of rare-earth doped LAP crystals. - Abstract: Effect of Thorium, Lanthanum and Cerium rare-earth ions on the growth and properties of L-arginine phosphate single crystals has been reported. The incorporation of rare-earth dopants into the L-arginine phosphate crystals is confirmed by Inductively Coupled Plasma-Mass Spectroscopy analysis. The unit cell parameters for pure and rare-earth doped L-arginine phosphate crystals have been estimated by powder X-ray diffraction studies. UV-visible studies revealed the transmittance percentage and cut-off wavelengths of the grown crystals. Powder second harmonic generation measurement has been carried out for pure and doped L-arginine phosphate crystals. The dielectric behavior of the grown crystals was analyzed for different frequencies at room temperature. The mechanical properties have been determined for pure and the doped L-arginine phosphate crystals.

The formation mechanism of 4179 Toutatis' elongated bi-lobed structure in a close Earth encounter scenario

Science.gov (United States)

Hu, Shoucun; Ji, Jianghui; Richardson, Derek C.; Zhao, Yuhui; Zhang, Yun

2018-04-01

The optical images of near-Earth asteroid 4179 Toutatis acquired by Chang'e-2 spacecraft show that Toutatis has an elongated contact binary configuration, with the contact point located along the long axis. We speculate that such configuration may have resulted from a low-speed impact between two components. In this work, we performed a series of numerical simulations and compared the results with the optical images, to examine the mechanism and better understand the formation of Toutatis. Herein we propose an scenario that an assumed separated binary precursor could undergo a close encounter with Earth, leading to an impact between the primary and secondary, and the elongation is caused by Earth's tide. The precursor is assumed to be a doubly synchronous binary with a semi-major axis of 4 Rp (radius of primary) and the two components are represented as spherical cohesionless self-gravitating granular aggregates. The mutual orbits are simulated in a Monte Carlo routine to provide appropriate parameters for our N-body simulations of impact and tidal distortion. We employ the pkdgrav package with a soft-sphere discrete element method (SSDEM) to explore the entire scenarios. The results show that contact binary configurations are natural outcomes under this scenario, whereas the shape of the primary is almost not affected by the impact of the secondary. However, our simulations further provide an elongated contact binary configuration best-matching to the shape of Toutatis at an approaching distance rp = 1.4 ˜ 1.5 Re (Earth radius), indicative of a likely formation scenario for configurations of Toutatis-like elongated contact binaries.

Mechanism of central ion exchange in the neodymium (3) ethylenediamine-tetraacetate-copper (2) and erbium (3) ethylenediaminetetraacetate-copper (2) systems in ageous solution

International Nuclear Information System (INIS)

Nikitenko, S.I.; Martynenko, L.I.; Pechurova, N.I.; Spitsyn, V.I.

1984-01-01

The spectrophotometry method in the stationary regime and the ''Stopped Flow'' method in the prestationary regime are used to study kinetics and exchange mechanism in NdA - -Cu 2+ and ErA - -Cu 2+ (A=EDTA) systems at pH 4.0-6.0 and initial Cu 2+ concentrations (0.5-6.0)x10 -2 M, Nd 3+ , Er 3 2H+ (0-1.0)x10 -2 M. On the basis of considering the dependence of kinetic exchange characteristics on the value of initial Ln 3+ and Cu 2+ concentrations it is shown that stability constant of appearing intermediate binuclear complex [NdACu 2+ ] correlates with stability constant of copper acetate, i. e. incoming Cu 2+ cation coordinates by EDTA acetogroup at the first stage of reaction. Stability constant of [ErACu + ) correlates with outer spheric association constant, i. e. at the earlier exchange stage in the associative mechanism in the ErA - -Cu 2+ system, formation of outer spheric associate takes place. Considerable difference in exchange mechanisms for light and heavy rare earths is explained by lesser strength in metal-oxygen bond in initial NdA - as compared with ErA - . Bond strengthening in the initial rare earth complexonate prevents the formation of stable intermediate binuclear complexes which causes decrease in the exchange rate according to the associative mechanism in LuAsup(-)-Mnsup(n+) systems

On the persistence of unstable bump-on-tail electron velocity distributions in the earth's foreshock

International Nuclear Information System (INIS)

Klimas, A.J.; Fitzenreiter, R.J.

1988-01-01

Further evidence for the persistence of bump-on-tail unstable reduced velocity distribution in the Earth's electron foreshock is presented. This persistence contradicts our understanding of quasi-linear saturation of the bump-on-tail instability; the distributions should be stabilized through velocity space diffusion too quickly to allow an observation of their unstable form. A modified theory for the saturation of the bump-on-tail instability in the Earth's foreshock is proposed and examined using numerical simulation and quasi-linear theoretical techniques. It is argued the mechanism due to Filbert and Kellogg and to Cairns which is responsible for the creation of the bump-on-tail velocity distribution in the foreshock is still operative during the evolution of the bump-on-tail instability. The saturated state of the plasma must represent a balance between this creation mechanism and velocity space diffusion; the saturated state is not determined by velocity space diffusion alone. Thus the velocity distribution of the saturated stat may still appear bump-on-tail unstable to standard linear analysis which does not take the creation mechanism into account. The bump-on-tail velocity distributions in the foreshock would then represent the state of the plasma after saturation of the bump-on-tail instability, not before

Spacecraft Line-of-Sight Stabilization Using LWIR Earth Signature

Science.gov (United States)

Quadrelli, Marco B.; Piazzolla, Sabino

2012-01-01

The objective of this study is to investigate the potential of using the bright and near-uniform Earth infrared (or wavelength infrared, LWIR) signature as a stable reference for accurate (micro-rad or less) inertial pointing and tracking on-board an space vehicle, including the determination of the fundamental limits of applicability of the proposed method for space missions. We demonstrate sub-micro radian level pointing accuracy under a representative set of disturbances experienced by the spacecraft in orbit.

Thermal stability of rare earth oxychlorides

International Nuclear Information System (INIS)

Bunda, V.V.; Shtilikha, M.V.; Golovej, V.M.

1984-01-01

The thermal stability of oxichlorides of the lanthanum series is investigated to determine the possibility of preparing them in the form of crystals by the method of l chemical gas-transport reactions (CTR). The lanthanide oxichlorides were subjected to thermogravimetric studies in the 20-1500 deg C temperature range under normal conditions. The temperatures of initiation of incongruent decomposition reactions are found. It is found that the process of LnOCl decomposition is preceeded by the exothermal effect connected with the Ln 2 OCl 4 recrsytallization to LnOCl. The thermodynamic and kinetic parameters of decomposition reactions are determined, such as reaction heats ΔH, decomposition rate constants K, dissociation energies E, reaction orders n. The LnOCl specific heats (Csub(P))sub(T) are estimated. It is shown that the LnOCl compounds can be prepared in the form of monocrystals by the CTR method

Mass Extinctions and Biosphere-Geosphere Stability

Science.gov (United States)

Rothman, Daniel; Bowring, Samuel

2015-04-01

Five times in the past 500 million years, mass extinctions have resulted in the loss of greater than three-fourths of living species. Each of these events is associated with significant environmental change recorded in the carbon-isotopic composition of sedimentary rocks. There are also many such environmental events in the geologic record that are not associated with mass extinctions. What makes them different? Two factors appear important: the size of the environmental perturbation, and the time scale over which it occurs. We show that the natural perturbations of Earth's carbon cycle during the past 500 million years exhibit a characteristic rate of change over two orders of magnitude in time scale. This characteristic rate is consistent with the maximum rate that limits quasistatic (i.e., near steady-state) evolution of the carbon cycle. We identify this rate with marginal stability, and show that mass extinctions occur on the fast, unstable side of the stability boundary. These results suggest that the great extinction events of the geologic past, and potentially a "sixth extinction" associated with modern environmental change, are characterized by common mechanisms of instability.

Non-isothermal Crystallization, Thermal Stability, and Mechanical Performance of Poly(L-lactic acid/Barium Phenylphosphonate Systems

Directory of Open Access Journals (Sweden)

Cai Yan-Hua

2017-11-01

Full Text Available The introduction of a nucleating agent in semi-crystalline polymers is a frequently utilized way to improve the crystallization performance, and the use of a nucleating agent has a very great effect on the performance of the polymer in other areas including thermal stability and mechanical properties. In this investigation, barium phenylphosphonate (BaP was prepared as a crystallization accelerator for Poly(L-lactic acid (PLLA, and the non-isothermal crystallization behavior, thermal stability, and mechanical properties of PLLA modified by BaP were investigated using differential scanning calorimetry (DSC, X-ray diffraction (XRD, thermogravimetric analysis (TGA, and electronic tensile testing. Non-isothermal crystallization analysis showed that the BaP could significantly accelerate the crystallization of PLLA, and the non-isothermal crystallization peak shifted to a higher temperature with increasing concentration of BaP, however, the corresponding crystallization peak became wider. XRD results after non-isothermal crystallization confirmed the non-isothermal crystallization DSC results. Additionally, the addition of BaP did not change the crystal form of PLLA. A comparative study on thermal stability indicated that BaP decreased the onset decomposition temperature of PLLA, resulting from the formation of more tiny and imperfect crystals. Whereas the influence of BaP on the thermal decomposition profile of PLLA was negligible. In terms of mechanical properties, the tensile strength and elastic modulus of PLLA/BaP increased compared to the virgin PLLA, unfortunately, the elongation at break decreased.

Mechanisms of stabilization and blowoff of a premixed flame downstream of a heat-conducting perforated plate

KAUST Repository

Kedia, Kushal S.; Ghoniem, Ahmed F.

2012-01-01

The objective of this work is to investigate the flame stabilization mechanism and the conditions leading to the blowoff of a laminar premixed flame anchored downstream of a heat-conducting perforated-plate/multi-hole burner, with overall nearly

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.

Maintaining stability of standalone Micro-Grid by employing electrical and mechanical fault ride through techniques upon fixed speed wind generation systems

International Nuclear Information System (INIS)

Kamel, Rashad M.

2013-01-01

Highlights: • This paper presented two fault ride through techniques for fixed speed wind systems. • The first technique is implemented by inserting a series resistance with the terminals of wind generator. • Second technique is performed by adapting the gear ratio to spill some mechanical power. - Abstract: This study presents two different Fault Ride Through (FRT) techniques to keep and restore stability of Fixed Speed Wind Generation system (FSWGs) installed in standalone Micro-Grid (MG). The first technique is an electrical FRT and is implemented by inserting a series resistance with the terminals of FSWGs during fault to maintain reasonable value of terminal voltage and consequently help stability restoration. The second controller is a mechanical FRT controller and is performed by change the gear ratio of wind generation systems to spill part of extracted mechanical power and consequently improving stability issue. Obtained results proved that each controller able to maintain the stability of FSWGs under the most severe disturbance conditions (400 ms three phase fault at FSWGs terminals). The first controller is faster than the second controller in restoring FSWGs stability. Superior results and performances are obtained when the two FRT techniques are employed simultaneously. Without employing any one of the two FRT techniques, FSWGs is not able to maintain or restore its stability after fault clearing. Consequently, MG will lose one of its micro-sources and cannot keep its stability during the standalone mode, unless load shedding strategy is activated. The two proposed controllers are simple, effective, and economical attractive

Influence of Temperature and Mechanical Scratch on the Recorded Magnetization Stability of Longitudinal and Perpendicular Recording Media

International Nuclear Information System (INIS)

Nagano, Katsumasa; Tobari, Kousuke; Futamoto, Masaaki

2011-01-01

Stability of recorded magnetization of hard disk drive (HDD) is influenced by external environments, such as temperature and magnetic field. Small scratches are frequently formed on HDD medium surface upon contacts with the magnetic head. The influences of temperature and mechanical scratch on the magnetization structure stability are investigated for longitudinal and perpendicular recording media by using a magnetic force microscope. PMR media remained almost unchanged up to about 300 deg. C for the area with no scratches, whereas the areas near and under mechanical scratches started to change around 250 deg. C. The magnetization structure of LMR media started to change at about 100 degrees lower temperature under mechanical scratches when compared with no scratch areas. A quantitative analysis of magnetization structure variation is carried out by measuring the recorded magnetization strength difference estimated from the MFM images observed for a same sample area before and after exposing the sample to different temperatures.

Rare earths: preparation of spectro chemically pure standards, study of their carbonates and synthesis of a new compound series - the peroxy carbonates

International Nuclear Information System (INIS)

Queiroz, Carlos Alberto da Silva

1996-05-01

In this work the following studies are concerned: I) preparation of lanthanum, cerium, praseodymium, neodymium and samarium oxides for use as spectro chemically pure standards; II) behavior of the rare earth (La, Ce, Pr, Nd, Sm) carbonates soluble in ammonium carbonate and mixture of ammonium carbonate/ammonium hydroxide, and III) synthesis and characterization of rare earth peroxy carbonates - a new series of compounds. Data for the synthesis and characterization of the rare earths peroxy carbonates described for the first time in this work are presented and discussed. With the aid of thermal analysis (TG-DTG) the thermal stability and the stoichiometric composition for new compounds were established and a mechanism of thermal decomposition was proposed. The peroxy carbonate was prepared by the addition of hydrogen peroxyde to the complexed soluble rare earths carbonates. These studies included also the determinations of active oxygen, the total rare earth oxide by gravimetry and complexometry and the C, H and N contents by microanalysis. The new compounds were also investigated by infrared spectroscopy. (author)

Porous Lactose-Modified Chitosan Scaffold for Liver Tissue Engineering: Influence of Galactose Moieties on Cell Attachment and Mechanical Stability

Directory of Open Access Journals (Sweden)

Birong Wang

2016-01-01

Full Text Available Galactosylated chitosan (CTS has been widely applied in liver tissue engineering as scaffold. However, the influence of degree of substitution (DS of galactose moieties on cell attachment and mechanical stability is not clear. In this study, we synthesized the lactose-modified chitosan (Lact-CTS with various DS of galactose moieties by Schiff base reaction and reducing action of NaBH4, characterized by FTIR. The DS of Lact-CTS-1, Lact-CTS-2, and Lact-CTS-3 was 19.66%, 48.62%, and 66.21% through the method of potentiometric titration. The cell attachment of hepatocytes on the CTS and Lact-CTS films was enhanced accompanied with the increase of galactose moieties on CTS chain because of the galactose ligand-receptor recognition; however, the mechanical stability of Lact-CTS-3 was reduced contributing to the extravagant hydrophilicity, which was proved using the sessile drop method. Then, the three-dimensional Lact-CTS scaffolds were fabricated by freezing-drying technique. The SEM images revealed the homogeneous pore bearing the favorable connectivity and the pore sizes of scaffolds with majority of 100 μm; however, the extract solution of Lact-CTS-3 scaffold significantly damaged red blood cells by hemolysis assay, indicating that exorbitant DS of Lact-CTS-3 decreased the mechanical stability and increased the toxicity. To sum up, the Lact-CTS-2 with 48.62% of galactose moieties could facilitate the cell attachment and possess great biocompatibility and mechanical stability, indicating that Lact-CTS-2 was a promising material for liver tissue engineering.

Solutions Stability of Initial Boundary Problem, Modeling of Dynamics of Some Discrete Continuum Mechanical System

Directory of Open Access Journals (Sweden)

D. A. Eliseev

2015-01-01

Full Text Available The solution stability of an initial boundary problem for a linear hybrid system of differential equations, which models the rotation of a rigid body with two elastic rods located in the same plane is studied in the paper. To an axis passing through the mass center of the rigid body perpendicularly to the rods location plane is applied the stabilizing moment proportional to the angle of the system rotation, derivative of the angle, integral of the angle. The external moment provides a feedback. A method of studying the behavior of solutions of the initial boundary problem is proposed. This method allows to exclude from the hybrid system of differential equations partial differential equations, which describe the dynamics of distributed elements of a mechanical system. It allows us to build one equation for an angle of the system rotation. Its characteristic equation defines the stability of solutions of all the system. In the space of feedback-coefficients the areas that provide the asymptotic stability of solutions of the initial boundary problem are built up.

On the asymptotic stability of nonlinear mechanical switched systems

Science.gov (United States)

Platonov, A. V.

2018-05-01

Some classes of switched mechanical systems with dissipative and potential forces are considered. The case, where either dissipative or potential forces are essentially nonlinear, is studied. It is assumed that the zero equilibrium position of the system is asymptotically stable at least for one operating mode. We will look for sufficient conditions which guarantee the preservation of asymptotic stability of the equilibrium position under the switching of modes. The Lyapunov direct method is used. A Lyapunov function for considered system is constructed, which satisfies the differential inequality of special form for every operating mode. This inequality is nonlinear for the chosen mode with asymptotically stable equilibrium position, and it is linear for the rest modes. The correlations between the intervals of activity of the pointed mode and the intervals of activity of the rest modes are obtained which guarantee the required properties.

Rapid Ice-Sheet Changes and Mechanical Coupling to Solid-Earth/Sea-Level and Space Geodetic Observation

Science.gov (United States)

Adhikari, S.; Ivins, E. R.; Larour, E. Y.

2015-12-01

Perturbations in gravitational and rotational potentials caused by climate driven mass redistribution on the earth's surface, such as ice sheet melting and terrestrial water storage, affect the spatiotemporal variability in global and regional sea level. Here we present a numerically accurate, computationally efficient, high-resolution model for sea level. Unlike contemporary models that are based on spherical-harmonic formulation, the model can operate efficiently in a flexible embedded finite-element mesh system, thus capturing the physics operating at km-scale yet capable of simulating geophysical quantities that are inherently of global scale with minimal computational cost. One obvious application is to compute evolution of sea level fingerprints and associated geodetic and astronomical observables (e.g., geoid height, gravity anomaly, solid-earth deformation, polar motion, and geocentric motion) as a companion to a numerical 3-D thermo-mechanical ice sheet simulation, thus capturing global signatures of climate driven mass redistribution. We evaluate some important time-varying signatures of GRACE inferred ice sheet mass balance and continental hydrological budget; for example, we identify dominant sources of ongoing sea-level change at the selected tide gauge stations, and explain the relative contribution of different sources to the observed polar drift. We also report our progress on ice-sheet/solid-earth/sea-level model coupling efforts toward realistic simulation of Pine Island Glacier over the past several hundred years.

New enhancement mechanism of the transitions in the Earth of the solar and atmospheric neutrinos crossing the Earth core

International Nuclear Information System (INIS)

Petcov, S.T.

1999-01-01

It is shown that the ν 2 → ν e and ν μ → ν e (ν e → ν μ(τ) ) transitions respectively of the solar and atmospheric neutrinos in the Earth in the case of ν e - ν μ(τ) mixing in vacuum, are strongly enhanced by a new type of resonance when the neutrinos cross the Earth core. The resonance is operative at small mixing angles but differs from the MSW one. It is in many respects similar to the electron paramagnetic resonance taking place in a specific configuration of two magnetic fields. The conditions for existence of the new resonance include, in particular, specific constraints on the neutrino oscillation lengths in the Earth mantle and in the Earth core, thus the resonance is a 'neutrino oscillation length resonance'. It leads also to enhancement of the ν 2 → ν e and ν e → ν s transitions in the case of ν e - ν s mixing and of the ν-bar s (or ν μ → ν s ) transitions at small mixing angles. The presence of the neutrino oscillation length resonance in the transitions of solar and atmospheric neutrinos traversing the Earth core has important implications for current and future solar and atmospheric neutrino experiments, and more specifically, for the interpretation of the results of the Super-Kamiokande experiment

Rare earth oxide reinforced Al{sub 2}O{sub 3}-TiO{sub 2} ceramics for inert coating of metallic parts for petroleum extraction

Energy Technology Data Exchange (ETDEWEB)

Yadava, Yoggendra Prasad; Rego, Sheila Alves Bezerra da Costa; Ferreira, Ricardo Artur Sanguinetti [Universidade Federal de Pernambuco (UFPE), Recife (Brazil)

2012-07-01

Recent findings of largest known pre-salt petroleum reservoir in Brazil have created an intense demand for new materials capable of withstanding direct contact with the crude petroleum as it is a highly corrosive and chemically reactive fluid. Petroleum drilling equipment, storage tanks and transportation systems suffer from constant physical stress caused by chemical attack of crude petroleum on its structure. Ceramics are materials with high chemical stability in hostile environment and therefore can be used as an inert coating material to resolve such problems. To date, ceramics based on alumina are most widely used in practice where there is demand for high mechanical strength and high fracture toughness. However intrinsic fragility of ceramics is still a fatal factor for their use in mechanical structures. To improve these characteristics, usually ceramics are reinforced with one or more ceramic additives. Mechanical properties of alumina based ceramics improve considerably with the addition of TiO{sub 2}, TiN, ZrO{sub 2} etc. ceramic additives. Nucleation and propagation of cracks is a major problem for ceramic coating applications. Initial studies show that addition of small percentages of rare earth oxides can increase the toughness of the alumina based ceramics. In the present work, we have produced rare-earth oxide (CeO{sub 2}) reinforced Al{sub 2}O{sub 3}-TiO{sub 2} ceramics in proportions of 5-20 wt% TiO{sub 2} and 2%wt% CeO{sub 2} through thermomechanical processing and sintering techniques and studied there microstructural characteristics and mechanical properties. To evaluate the potential of these ceramics as inert coatings for crude petroleum extraction, storage and transportation systems, we have studied the physic-chemical and mechanical stability of these ceramics in crude petroleum environment. Our studies presented satisfactory results in terms of physic-chemical and mechanical stability of these materials for the use of 2wt% of CeO{sub 2

Phase stability in yttria-stabilized zirconia from first principles

Energy Technology Data Exchange (ETDEWEB)

Carbogno, Christian; Scheffler, Matthias [Materials Department, University of California, Santa Barbara, CA (United States); Fritz-Haber-Institut der Max-Planck-Gesellschaft, Berlin (Germany); Levi, Carlos G.; Van de Walle, Chris G. [Materials Department, University of California, Santa Barbara, CA (United States)

2012-07-01

Zirconia based ceramics are of pivotal importance for a variety of industrial technologies, e.g., for thermal barrier coatings in gas and airplane turbines. Naturally, the stability of such coatings at elevated temperatures plays a critical role in these applications. It is well known that an aliovalent doping of tetragonal ZrO{sub 2} with yttria, which induces oxygen vacancies due to charge conservation, increases its thermodynamic stability. However, the atomistic mechanisms that determine the phase stability of such yttria-stabilized Zirconia (YSZ) coatings are not yet fully understood. In this work, we use density functional theory calculations to assess the electronic structure of the different YSZ polymorphs at various levels of doping. With the help of population analysis schemes, we are able to unravel the intrinsic mechanisms that govern the interaction in YSZ and that can so explain the relative stabilities of the various polymorphs. We critically compare our results to experimental measurements and discuss the implications of our findings with respect to other oxides.

Molecular Dynamics Simulation Study on the Binding and Stabilization Mechanism of Antiprion Compounds to the "Hot Spot" Region of PrPC.

Science.gov (United States)

Zhou, Shuangyan; Liu, Xuewei; An, Xiaoli; Yao, Xiaojun; Liu, Huanxiang

2017-11-15

Structural transitions in the prion protein from the cellular form, PrP C , into the pathological isoform, PrP Sc , are regarded as the main cause of the transmissible spongiform encephalopathies, also known as prion diseases. Hence, discovering and designing effective antiprion drugs that can inhibit PrP C to PrP Sc conversion is regarded as a promising way to cure prion disease. Among several strategies to inhibit PrP C to PrP Sc conversion, stabilizing the native PrP C via specific binding is believed to be one of the valuable approaches and many antiprion compounds have been reported based on this strategy. However, the detailed mechanism to stabilize the native PrP C is still unknown. As such, to unravel the stabilizing mechanism of these compounds to PrP C is valuable for the further design and discovery of antiprion compounds. In this study, by molecular dynamics simulation method, we investigated the stabilizing mechanism of several antiprion compounds on PrP C that were previously reported to have specific binding to the "hot spot" region of PrP C . Our simulation results reveal that the stabilization mechanism of specific binding compounds can be summarized as (I) to stabilize both the flexible C-terminal of α2 and the hydrophobic core, such as BMD42-29 and GN8; (II) to stabilize the hydrophobic core, such as J1 and GJP49; (III) to stabilize the overall structure of PrP C by high binding affinity, as NPR-056. In addition, as indicated by the H-bond analysis and decomposition analysis of binding free energy, the residues N159 and Q160 play an important role in the specific binding of the studied compounds and all these compounds interact with PrP C in a similar way with the key interacting residues L130 in the β1 strand, P158, N159, Q160, etc. in the α1-β2 loop, and H187, T190, T191, etc. in the α2 C-terminus although the compounds have large structural difference. As a whole, our obtained results can provide some insights into the specific binding

Analysis of Äspö Pillar Stability Experiment: Continuous thermo-mechanical model development and calibration

Czech Academy of Sciences Publication Activity Database

Blaheta, Radim; Byczanski, Petr; Čermák, M.; Hrtus, Rostislav; Kohut, Roman; Kolcun, Alexej; Malík, Josef; Sysala, Stanislav

2013-01-01

Roč. 5, č. 2 (2013), s. 124-135 ISSN 1674-7755 Institutional support: RVO:68145535 Keywords : in situ pillar stability experiment * model calibration by back analysis * continuous mechanics * damage of granite rocks * Finite element method (FEM) Subject RIV: BA - General Mathematics http://www.sciencedirect.com/science/article/pii/S1674775513000103

Complexing in aqueous solutions of rare earth n-aminobenzoates

International Nuclear Information System (INIS)

Efremova, G.I.; Buchkova, R.T.; Lapitskaya, A.V.; Pirkes, S.B.

1977-01-01

Complexing in the system ''ion of a rare-earth metal - n-aminobenzoic acid'' has been investigated by the pH-metric method in the pH range of 3.5-5.5. In the La-Eu series, the stability of n-aminobenzoate complexes increases and attains the maximum value in the complex Eu (lg Ksub(st)=2.66). In the Gd-Lu series the stability of the complex particles decreases monotonically

Leaching behaviour and mechanical properties of copper flotation waste in stabilized/solidified products.

Science.gov (United States)

Mesci, Başak; Coruh, Semra; Ergun, Osman Nuri

2009-02-01

This research describes the investigation of a cement-based solidification/stabilization process for the safe disposal of copper flotation waste and the effect on cement properties of the addition of copper flotation waste (CW) and clinoptilolite (C). In addition to the reference mixture, 17 different mixtures were prepared using different proportions of CW and C. Physical properties such as setting time, specific surface area and compressive strength were determined and compared to a reference mixture and Turkish standards (TS). Different mixtures with the copper flotation waste portion ranging from 2.5 to 12.5% by weight of the mixture were tested for copper leachability. The results show that as cement replacement materials especially clinoptilolite had clear effects on the mechanical properties. Substitution of 5% copper flotation waste for Portland cement gave a similar strength performance to the reference mixture. Higher copper flotation waste addition such as 12.5% replacement yielded lower strength values. As a result, copper flotation waste and clinoptilolite can be used as cementitious materials, and copper flotation waste also can be safely stabilized/solidified in a cement-based solidification/stabilization system.

Aespoe Pillar Stability Experiment. Final coupled 3D thermo-mechanical modeling. Preliminary particle mechanical modeling

International Nuclear Information System (INIS)

Wanne, Toivo; Johansson, Erik; Potyondy, David

2004-02-01

SKB is planning to perform a large-scale pillar stability experiment called APSE (Aespoe Pillar Stability Experiment) at Aespoe HRL. The study is focused on understanding and control of progressive rock failure in hard crystalline rock and damage caused by high stresses. The elastic thermo-mechanical modeling was carried out in three dimensions because of the complex test geometry and in-situ stress tensor by using a finite-difference modeling software FLAC3D. Cracking and damage formation were modeled in the area of interest (pillar between two large scale holes) in two dimensions by using the Particle Flow Code (PFC), which is based on particle mechanics. FLAC and PFC were coupled to minimize the computer resources and the computing time. According to the modeling the initial temperature rises from 15 deg C to about 65 deg C in the pillar area during the heating period of 120 days. The rising temperature due to thermal expansion induces stresses in the pillar area and after 120 days heating the stresses have increased about 33% from the excavation induced maximum stress of 150 MPa to 200 MPa in the end of the heating period. The results from FLAC3D model showed that only regions where the crack initiation stress has exceeded were identified and they extended to about two meters down the hole wall. These could be considered the areas where damage may occur during the in-situ test. When the other hole is pressurized with a 0.8 MPa confining pressure it yields that 5 MPa more stress is needed to damage the rock than without confining pressure. This makes the damaged area in some degree smaller. High compressive stresses in addition to some tensile stresses might induce some AE (acoustic emission) activity in the upper part of the hole from the very beginning of the test and are thus potential areas where AE activities may be detected. Monitoring like acoustic emissions will be measured during the test execution. The 2D coupled PFC-FLAC modeling indicated that

Aespoe Pillar Stability Experiment. Final coupled 3D thermo-mechanical modeling. Preliminary particle mechanical modeling

Energy Technology Data Exchange (ETDEWEB)

Wanne, Toivo; Johansson, Erik; Potyondy, David [Saanio and Riekkola Oy, Helsinki (Finland)

2004-02-01

SKB is planning to perform a large-scale pillar stability experiment called APSE (Aespoe Pillar Stability Experiment) at Aespoe HRL. The study is focused on understanding and control of progressive rock failure in hard crystalline rock and damage caused by high stresses. The elastic thermo-mechanical modeling was carried out in three dimensions because of the complex test geometry and in-situ stress tensor by using a finite-difference modeling software FLAC3D. Cracking and damage formation were modeled in the area of interest (pillar between two large scale holes) in two dimensions by using the Particle Flow Code (PFC), which is based on particle mechanics. FLAC and PFC were coupled to minimize the computer resources and the computing time. According to the modeling the initial temperature rises from 15 deg C to about 65 deg C in the pillar area during the heating period of 120 days. The rising temperature due to thermal expansion induces stresses in the pillar area and after 120 days heating the stresses have increased about 33% from the excavation induced maximum stress of 150 MPa to 200 MPa in the end of the heating period. The results from FLAC3D model showed that only regions where the crack initiation stress has exceeded were identified and they extended to about two meters down the hole wall. These could be considered the areas where damage may occur during the in-situ test. When the other hole is pressurized with a 0.8 MPa confining pressure it yields that 5 MPa more stress is needed to damage the rock than without confining pressure. This makes the damaged area in some degree smaller. High compressive stresses in addition to some tensile stresses might induce some AE (acoustic emission) activity in the upper part of the hole from the very beginning of the test and are thus potential areas where AE activities may be detected. Monitoring like acoustic emissions will be measured during the test execution. The 2D coupled PFC-FLAC modeling indicated that

Thermo-Mechanical Methodology for Stabilizing Shape Memory Alloy Response

Science.gov (United States)

Padula, Santo

2013-01-01

This innovation is capable of significantly reducing the amount of time required to stabilize the strain-temperature response of a shape memory alloy (SMA). Unlike traditional stabilization processes that take days to weeks to achieve stabilized response, this innovation accomplishes stabilization in a matter of minutes, thus making it highly useful for the successful and practical implementation of SMA-based technologies in real-world applications. The innovation can also be applied to complex geometry components, not just simple geometries like wires or rods.

Fluid-injection and the mechanics of frictional stability of shale-bearing faults

Science.gov (United States)

Scuderi, Marco Maria; Collettini, Cristiano; Marone, Chris

2017-04-01

Fluid overpressure is one of the primary mechanisms for triggering tectonic fault slip and human-induced seismicity. This mechanism is appealing because fluids lubricate the fault and reduce the effective normal stress that holds the fault in place. However, current models of earthquake nucleation, based on rate- and state- friction, imply that stable sliding is favored by the increase of pore fluid pressure. Despite this apparent dilemma, there are a few studies on the role of fluid pressure in frictional stability under controlled, laboratory conditions. Here, we describe laboratory experiments on shale fault gouge, conducted in the double direct shear configuration in a true-triaxial machine. To characterize frictional stability and hydrological properties we performed three types of experiments: 1) stable sliding shear experiment to determine the material failure envelope resulting in fault strength of µ=0.28 and fault zone permeability (k 10-19m2); 2) velocity step experiments to determine the rate- and state- frictional properties, characterized by a velocity strengthening behavior with a negative rate parameter b, indicative of stable aseismic creep; 3) creep experiment to study fault slip evolution with increasing pore-fluid pressure. In these creep experiments fault slip history can be divided in three main stages: a) for low fluid pressure the fault is locked and undergoes compaction; b) with increasing fluid pressurization, we observe aseismic creep (i.e. v=0.0001 µm/s) associated with fault dilation, with maintained low permeability; c) As fluid pressure is further increased and we approach the failure criteria fault begins to accelerate, the dilation rate increases causing an increase in permeability. Following the first acceleration we document complex fault slip behavior characterized by periodic accelerations and decelerations with slip velocity that remains slow (i.e. v 200 µm/s), never approaching dynamic slip rates. Surprisingly, this complex

Non-rocket Earth-Moon transport system

Science.gov (United States)

Bolonkin, Alexander

2003-06-01

This paper proposes a new transportation system for travel between Earth and Moon. This transportation system uses mechanical energy transfer and requires only minimal energy, using an engine located on Earth. A cable directly connects a pole of the Earth through a drive station to the lunar surface_ The equation for an optimal equal stress cable for complex gravitational field of Earth-Moon has been derived that allows significantly lower cable masses. The required strength could be provided by cables constructed of carbon nanotubes or carbon whiskers. Some of the constraints on such a system are discussed.

Slope Stability Analysis Based on Type, Physical And Mechanical Properties Rock in Teluk Pandan District, East Kutai Regency, East Kalimantan

Directory of Open Access Journals (Sweden)

Sujiman Kusnadi

2017-12-01

Full Text Available Research was located In Teluk Pandan District, East Kutai Regency, East Kalimantan Province.  It’s aimed to determine the lithology in the  research area and to find out how the amount of slope that will be a landslide at that location. The research conducted with the analysis of coring drilling results and then analyzed in the laboratory of rock mechanics to get the characteristic of physical and mechanical properties of the rocks. The data analysis using Hoek and Bray Method. The results showed that in the area study has a sedimentary rock lithology fine to medium detritus, such as claystone, siltstone and sandstone, as well as inserts are coal and shale. Based on the results of laboratory analysis of rock mechanics obtained density between 2,648 to 2,770. While the test results obtained value triaxial cohesion between (6.66 - 9:05 Kg / cm2, friction angle in between (37.19 - 44.08o, cohesion residual (2.72 - 3.10 Kg / cm2, residual friction angle (27.22 - 32.44o. While the direct shear test the cohesion of the summit between (6.66 - 9:05 Kg / cm2, friction angle in the cohesion peak (36.15 - 43.00o, cohesion residual (2:22 to 3:10 Kg / cm2, friction angle in the cohesion residual (37.22 - 33.85o. The simulation results stability of the slope stability Hoek and Bray using rockslide software, the result is that if the slope with a single slope stability, the stability of the slope is 60o, and if the slope with the stability of the slope overall stability of the slope is 48o.

Factors influencing the mechanical stability of alginate beads applicable for immunoisolation of mammalian cells.

Science.gov (United States)

Bhujbal, Swapnil V; Paredes-Juarez, Genaro A; Niclou, Simone P; de Vos, Paul

2014-09-01

Transplantation of microencapsulated cells has been proposed as a cure for many types of endocrine disorders. Alginate-based microcapsules have been used in many of the feasibility studied addressing cure of the endocrine disorders, and different cancer types. Despite years of intensive research it is still not completely understood which factors have to be controlled and documented for achieving adequate mechanical stability. Here we studied the strength and elasticity of microcapsules of different composition with and without cell load. We compared strength (force) versus elasticity (time) required to compress individual microcapsule to 60% deformation. It is demonstrated that the alginate viscosity, the size of the beads, the alginate type, the gelling time, the storage solution and the cell load are dominant factors in determining the final strength of alginate-based microcapsules while the type of gelling ion, the polyamino acid incubation time, the type of polyamino acid and the culturing time determines the elasticity of the alginate-based microcapsules. Our data underpin the essence of documenting the above mentioned factors in studies on encapsulated cells as mechanical stability is an essential factor in the success and failure of encapsulated grafts. Copyright © 2014 Elsevier Ltd. All rights reserved.

Synergistic effect and mechanism of platinum catalyst and nitrogen-containing silane on the thermal stability of silicone rubber

International Nuclear Information System (INIS)

Chen, Wanjuan; Zeng, Xingrong; Lai, Xuejun; Li, Hongqiang; Fang, Weizhen; Liu, Tian

2016-01-01

Highlights: • Platinum (Pt) and nitrogen-containing silane (NS) were introduced into silicone rubber. • The thermal stability was improved by Pt/NS both under nitrogen and air atmosphere. • The TG-FTIR of evolved gases during degradation was performed. • The synergistic effect and mechanism of Pt and NS were proposed. - Abstract: Platinum (Pt) catalyst and nitrogen-containing silane (NS) were introduced to improve the thermal stability of silicone rubber. The effects of Pt and NS on thermal stability and degradation mechanism of silicone rubber were investigated by thermogravimetry (TG), thermogravimetry-Fourier transform infrared spectrometry (TG-FTIR), scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDXS) and Fourier transform infrared spectrometry (FTIR). A significant synergism was found between Pt and NS for improving the thermal stability of silicone rubber. When 6.67 ppm of Pt and 1.4 phr of NS were introduced, the temperature of 10% and 20% weight loss under nitrogen atmosphere were respectively increased by 36 °C and 119 °C. Meanwhile, the residue weight at 900 °C was doubled to 68% in the presence of Pt/NS. The synergistic mechanism might be that the nitrogen atom coordinated with Pt and improved the catalytic efficiency of Pt. Additionally, NS preserved the catalytic activity of Pt under air atmosphere. Hence, Pt/NS efficiently catalyzed thermal crosslinking and suppressed degradation of silicone chains. Moreover, it revealed that the presence of Pt/NS protected silicone chains from oxidation. Thus, the unzipping depolymerization by silanol groups was reduced significantly.

Synergistic effect and mechanism of platinum catalyst and nitrogen-containing silane on the thermal stability of silicone rubber

Energy Technology Data Exchange (ETDEWEB)

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

2016-05-20

Highlights: • Platinum (Pt) and nitrogen-containing silane (NS) were introduced into silicone rubber. • The thermal stability was improved by Pt/NS both under nitrogen and air atmosphere. • The TG-FTIR of evolved gases during degradation was performed. • The synergistic effect and mechanism of Pt and NS were proposed. - Abstract: Platinum (Pt) catalyst and nitrogen-containing silane (NS) were introduced to improve the thermal stability of silicone rubber. The effects of Pt and NS on thermal stability and degradation mechanism of silicone rubber were investigated by thermogravimetry (TG), thermogravimetry-Fourier transform infrared spectrometry (TG-FTIR), scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDXS) and Fourier transform infrared spectrometry (FTIR). A significant synergism was found between Pt and NS for improving the thermal stability of silicone rubber. When 6.67 ppm of Pt and 1.4 phr of NS were introduced, the temperature of 10% and 20% weight loss under nitrogen atmosphere were respectively increased by 36 °C and 119 °C. Meanwhile, the residue weight at 900 °C was doubled to 68% in the presence of Pt/NS. The synergistic mechanism might be that the nitrogen atom coordinated with Pt and improved the catalytic efficiency of Pt. Additionally, NS preserved the catalytic activity of Pt under air atmosphere. Hence, Pt/NS efficiently catalyzed thermal crosslinking and suppressed degradation of silicone chains. Moreover, it revealed that the presence of Pt/NS protected silicone chains from oxidation. Thus, the unzipping depolymerization by silanol groups was reduced significantly.

Physical Analysis Work for Slope Stability at Shah Alam, Selangor

Science.gov (United States)

Ishak, M. F.; Zaini, M. S. I.

2018-04-01

Slope stability analysis is performed to assess the equilibrium conditions and the safe design of a human-made or natural slope to find the endangered areas. Investigation of potential failure and determination of the slope sensitivity with regard to safety, reliability and economics were parts of this study. Ground anchor is designed to support a structure in this study. Ground anchor were implemented at the Mechanically Stabilized Earth (MSE) wall along Anak Persiaran Jubli Perak to overcome the further cracking of pavement parking, concrete deck and building of the Apartments. A result from the laboratory testing of soil sample such as index test and shear strength test were applied to the Slope/W software with regard to the ground anchors that were implemented. The ground anchors were implemented to increase the value of the factor of safety (FOS) of the MSE Wall. The value of the factor of safety (FOS) before implementing the ground anchor was 0.800 and after the ground anchor was implemented the value increase to 1.555. The increase percentage of factor of safety by implementing on stability of slope was 94.38%.

Rare earth metal alloy magnets

International Nuclear Information System (INIS)

Harris, I.R.; Evans, J.M.; Nyholm, P.S.

1979-01-01

This invention relates to rare earth metal alloy magnets and to methods for their production. The technique is based on the fact that rare earth metal alloys (for e.g. cerium or yttrium) which have been crumbled to form a powder by hydride formation and decomposition can be used for the fabrication of magnets without the disadvantages inherent in alloy particle size reduction by mechanical milling. (UK)

Structural stability, electronic structure and mechanical properties of actinide carbides AnC (An = U, Np)

International Nuclear Information System (INIS)

Manikandan, M.; Santhosh, M.; Rajeswarapalanichamy, R.

2016-01-01

Ab initio calculations are performed to investigate the structural stability, electronic structure and mechanical properties of actinide carbides AnC (An=U, Np) for three different crystal structures, namely NaCl, CsCl and ZnS. Among the considered structures, NaCl structure is found to be the most stable structure for these carbides at normal pressure. A pressure induced structural phase transition from NaCl to ZnS is observed. The electronic structure reveals that these carbides are metals. The calculated elastic constants indicate that these carbides are mechanically stable at normal pressure.

Electrical properties and mechanical stability of anchoring groups for single-molecule electronics

Directory of Open Access Journals (Sweden)

Riccardo Frisenda

2015-07-01

Full Text Available We report on an experimental investigation of transport through single molecules, trapped between two gold nano-electrodes fabricated with the mechanically controlled break junction (MCBJ technique. The four molecules studied share the same core structure, namely oligo(phenylene ethynylene (OPE3, while having different aurophilic anchoring groups: thiol (SAc, methyl sulfide (SMe, pyridyl (Py and amine (NH2. The focus of this paper is on the combined characterization of the electrical and mechanical properties determined by the anchoring groups. From conductance histograms we find that thiol anchored molecules provide the highest conductance; a single-level model fit to current–voltage characteristics suggests that SAc groups exhibit a higher electronic coupling to the electrodes, together with better level alignment than the other three groups. An analysis of the mechanical stability, recording the lifetime in a self-breaking method, shows that Py and SAc yield the most stable junctions while SMe form short-lived junctions. Density functional theory combined with non-equlibrium Green’s function calculations help in elucidating the experimental findings.

Study on Preparation and Property of Poly-Aminosilicone-Rare Earth Composite

Institute of Scientific and Technical Information of China (English)

Zhang Ming(张明); Qiu Guanming(邱关明); Chen Haiyan(陈海燕); Zhou Lanxiang(周兰香); Inoue Shinich; Okamoto Hiroshi

2003-01-01

The poly-aminosilicone-rare earth composite was prepared by poly-aminosilicone cross-linked with rare earth and active silanol. The thermal stability of the composites was studied by thermogravimetric analysis (TG). Force condition of the composites in electric field was analyzed and relative polarizability was derived. It is found that the composites containing different rare earth ions have different relative polarizability. The experiment results reveal that organosilicon materials with different electrical performance can be obtained by this way. Meanwhile, the absorption and flourescene spectrum of composites were also investigated. Compared to rare earth chloride, the spectrum properties of the composite are changed obviously. The possible reasons for these phenomena were discussed.

Effect of suction on the mechanical characteristics of uniformly compacted rammed earth

Science.gov (United States)

El Hajjar, A.; Chauhan, P.; Prime, N.; Plé, O.

2018-04-01

Rammed earth, in the current environmental situation, is an alternative construction technique which can help in reducing energy and raw material consumption owing to its “sustainable” characteristics. To fully understand its behavior and properties, recent scientific investigations consider it as a compacted unsaturated material with suction as its one of the main sources of strength. Eathern constructions face, over their lifetime, variations in the suction state which have a significant impact on their mechanical characteristics. In the present contribution, unconfined compression tests are performed, with and without unload-reload cycles, on homogeneously compacted samples subjected to various suction conditions. This study shows that both the unconfined compressive strength and Young modulus reduce with the reduction of suction states. Suction also seems to influence the amount of plastic strains and damage phenomenon. Indeed, the soils analyzed are slightly active and shows both plasticity behavior and damage phenomenon.

The earths innermost core

International Nuclear Information System (INIS)

Nanda, J.N.

1989-01-01

A new earth model is advanced with a solid innermost core at the centre of the Earth where elements heavier than iron, over and above what can be retained in solution in the iron core, are collected. The innermost core is separated from the solid iron-nickel core by a shell of liquid copper. The innermost core has a natural vibration measured on the earth's surface as the long period 26 seconds microseisms. The earth was formed initially as a liquid sphere with a relatively thin solid crust above the Byerly discontinuity. The trace elements that entered the innermost core amounted to only 0.925 ppm of the molten mass. Gravitational differentiation must have led to the separation of an explosive thickness of pure 235 U causing a fission explosion that could expel beyond the Roche limit a crustal scab which would form the centre piece of the moon. A reservoir of helium floats on the liquid copper. A small proportion of helium-3, a relic of the ancient fission explosion present there will spell the exciting magnetic field. The field is stable for thousands of years because of the presence of large quantity of helium-4 which accounts for most of the gaseous collisions that will not disturb the atomic spin of helium-3 atoms. This field is prone to sudden reversals after long periods of stability. (author). 14 refs

New dynamic system suggested for earth expansion

Energy Technology Data Exchange (ETDEWEB)

Fitzpatrick, J [Asuncion Nacional Univ. (Paraguay). Inst. de Ciencias

1972-01-01

It is here suggested that there may have been much more radioactive materials in the deep interior of the earth than bitherto supposed. Trapped heat being generated in the interior would provide a mechanism for earth expansion. An assumption of heat generation in the deep interior of the earth of the order of 0,5 X 10-13 calories per second, per cubic centimeter, would provide sufficient thermal expansion to account for approximately 0.1 mm. change in the radius of the earth per year.

The Effect of Thermal Cycling Treatments on the Thermal Stability and Mechanical Properties of a Ti-Based Bulk Metallic Glass Composite

Directory of Open Access Journals (Sweden)

Fan Bu

2016-11-01

Full Text Available The effect of thermal cycling treatments on the thermal stability and mechanical properties of a Ti48Zr20Nb12Cu5Be15 bulk metallic glass composite (BMGC has been investigated. Results show that moderate thermal cycles in a temperature range of −196 °C (cryogenic temperature, CT to 25 °C (room temperature, RT or annealing time at CT has not induced obvious changes of thermal stability and then it decreases slightly over critical thermal parameters. In addition, the dendritic second phases with a bcc structure are homogeneously embedded in the amorphous matrix; no visible changes are detected, which shows structural stability. Excellent mechanical properties as high as 1599 MPa yield strength and 34% plastic strain are obtained, and the yield strength and elastic modulus also increase gradually. The effect on the stability is analyzed quantitatively by crystallization kinetics and plastic-flow models, and indicates that the reduction of structural relaxation enthalpy, which is related to the degradation of spatial heterogeneity, reduces thermal stability but does not imperatively deteriorate the plasticity.

Structural evolution of Cu{sub (1−X)}Y{sub X} alloys prepared by mechanical alloying: Their thermal stability and mechanical properties

Energy Technology Data Exchange (ETDEWEB)

Mula, Suhrit, E-mail: smulafmt@iitr.ernet.in [Department of Metallurgical and Materials Engineering, Indian Institute of Technology Roorkee, Roorkee 247667 (India); Setman, Daria [Physics of Nanostructured Materials, University of Vienna, Boltzmanngasse 5, A-1090 Wien (Austria); Youssef, Khaled [Department of Materials Science and Technology, Qatar University, P.O. Box 2713, Doha (Qatar); Scattergood, R.O.; Koch, Carl C [Department of Materials Science and Engineering, NC State University, Raleigh, NC 27695 (United States)

2015-04-05

Highlights: • Metastable solid solutions were prepared from Cu–Y nonequilibrium compositions by mechanical alloying. • Gibbs free energy change as per Miedema’s model confirms the formation of metastable alloys. • High Y content alloys showed high thermal stability during extensive annealing at high temperatures. • Stabilized alloys showed very high hardness and improved yield strength. • Mechanisms of high thermal stability and improved mechanical properties were discussed. - Abstract: In the present study, an attempt has been made to synthesize copper based disordered solid solutions by mechanical alloying (MA) of non-equilibrium compositions. The blended compositions of Cu–1% Y, Cu–3% Y, Cu–5% Y and Cu–7.5% Y (at.%) (all the compositions will be addressed as % only hereafter until unless it is mentioned) were ball-milled for 8 h, and then annealed at different temperatures (200–800 °C) for different length of duration (1–5 h) under high purity argon + 2 vol.% H{sub 2} atmosphere. X-ray diffraction (XRD) analysis and Gibbs free energy change calculation confirm the formation of disordered solid solution (up to 7.5%) of Y in Cu after milling at a room temperature for 8 h. The XRD grain size was calculated to be as low as 7 nm for 7.5% Y and 22 nm for 1% Y alloy. The grain size was retained within 35 nm even after annealing for 1 h at 800 °C. Transmission electron microscopy (TEM) analysis substantiates the formation of ultra-fine grained nanostructures after milling. Microhardness value of the as-milled samples was quite high (3.0–4.75 GPa) compared to that of pure Cu. The hardness value increased with increasing annealing temperatures up to 400 °C for the alloys containing 3–7.5% Y, and thereafter it showed a decreasing trend. The increase in the hardness after annealing is attributed to the formation of uniformly distributed ultrafine intermetallic phases in the nanocrystalline grains. The stabilization effect is achieved due to

Addressing Rare-Earth Element Criticality: An Example from the Aviation Industry

Science.gov (United States)

Ku, Anthony Y.; Dosch, Christopher; Grossman, Theodore R.; Herzog, Joseph L.; Maricocchi, Antonio F.; Polli, Drew; Lipkin, Don M.

2014-11-01

Rare-earth (RE) elements are enablers for a wide range of technologies, including high-strength permanent magnets, energy-efficient lighting, high-temperature thermal barrier coatings, and catalysts. While direct material substitution is difficult in many of these applications because of the specific electronic, optical, or electrochemical properties imparted by the individual rare-earth elements, we describe an example from the aviation industry where supply chain optimization may be an option. Ceramic matrix composite engine components require environmental barrier coatings (EBCs) to protect them from extreme temperatures and adverse reactions with water vapor in the hot gas path. EBC systems based on rare-earth silicates offer a unique combination of environmental resistance, thermal expansion matching, thermal conductivity, and thermal stability across the service temperature window. Several pure rare-earth silicates and solid solutions have been demonstrated in EBC applications. However, all rely on heavy rare-earth elements (HREEs) for phase stability. This article considers the possibility of using separation tailings containing a mixture of HREEs as a source material in lieu of using the high-purity HREE oxides. This option arises because the desired properties of RE-silicate EBCs derive from the average cation size rather than the electronic properties of the individual rare-earth cations. Because separation tailings have not incurred the costs associated with the final stages of separation, they offer an economical alternative to high-purity oxides for this emerging application.

Quantum mechanics and molecular dynamics simulations of complexation of alkaline-earth and lanthanide cations by poly-amino-carboxylate ligands

International Nuclear Information System (INIS)

Durand, S.

1999-01-01

Molecular dynamics (MD) simulations on lanthanide(III) and alkaline-earth(II) complexes with poly-amino-carboxylates (ethylene-diamino-tetra-acetate EDTA 4- , ethylene-diamino-tri-acetate-acetic acid EDTA(H) 3- , tetra-aza-cyclo-dodecane-tetra-acetate DOTA 4- , methylene-imidine-acetate MIDA 2- ) are reported. First, a consistent set of Lennard-Jones parameters for La 3+ , Eu 3+ and Lu 3+ cations has been derived from free energy calculations in aqueous solution. Observed differences in hydration free energies, coordination distances and hydration numbers are reproduced. Then, the solution structures of 1:1 complexes of alkaline-earth and/or lanthanide cations with EDTA 4- , EDTA(H) 3- , DOTA 4- and 1:2 complexes of lanthanide cations with MIDA 2- were studied by MD in water. In addition, free energy calculations were performed to study, for each ligand, the relative thermodynamic stabilities of complexes with Ca 2+ vs Sr 2+ and vs Ba 2+ on the one hand, and with La 3+ vs Eu 3+ and vs Lu 3+ on the other hand. Model does not take into account explicitly polarization and charge transfer. However, the results qualitatively agree with experimental complexation data (structure and selectivities). (author)

Evaluation of long-term mechanical stability of near field

International Nuclear Information System (INIS)

Takaji, Kazuhiko; Sugino, Hiroyuki; Okutsu, Kazuo; Miura, Kazuhiko; Tabei, Kazuto; Noda, Masaru; Takahashi, Shinichi; Sugie, Shigehiko

1999-11-01

In the near field, as tunnels and pits are excavated, a redistribution of stresses in the surrounding rock will occur. For a long period of time after the emplacement of waste packages various events will take place, such as the swelling of the buffer, sinking of the overpack under its own weight, deformation arising from expansion of overpack corrosion products and the creep deformation of the rock mass. The evaluation of what effects these changes in the stress-state will have on the buffer and rock mass is a major issue from the viewpoint of safety assessment. Therefore, rock creep analysis, overpack corrosion expansion analysis and overpack sinking analysis have been made in order to examine the long-term mechanical stability of the near field and the interaction of various events that may affect the stability of the near field over a long period of time. As the results, rock creep behavior, the variations of the stress-state and the range of the influence zone differ from the rock strength, strength of buffer in the tunnel and side pressure coefficient etc. about the hard rock system and soft rock system established as basic cases. And the magnitude of the stress variations for buffer by the overpack sinking and rock creep deformation is negligible compared with it by the overpack corrosion expansion. Furthermore, though very limited zone of buffer around the overpack is close to the critical state by the overpack corrosion expansion, the engineered barrier system attains a comparatively stable state for a long period of time. (author)

Earth Sciences report, 1989--1990

International Nuclear Information System (INIS)

Younker, L.W.; Peterson, S.J.; Price, M.E.

1991-03-01

The Earth Sciences Department at Lawrence Livermore National Laboratory (LLNL) conducts work in support of the Laboratory's energy, defense, environmental, and basic research programs. The Department comprises more than 100 professional scientific personnel spanning a variety of subdisciplines: geology, seismology, physics, geophysics, geochemistry, geohydrology, chemical engineering, and mechanical engineering. Resident technical support groups add significant additional technical expertise, including Containment Engineering, Computations, Electronic Engineering, Mechanical Engineering, Chemistry and Materials Science, and Technical Information. In total, approximately 180 professional scientists and engineers are housed in the Earth Sciences Department, making it one of the largest geo-science research groups in the nation. Previous Earth Sciences reports have presented an outline of the technical capabilities and accomplishments of the groups within the Department. In this FY 89/90 Report, we have chosen instead to present twelve of our projects in full-length technical articles. This Overview introduces those articles and highlights other significant research performed during this period

Earth Sciences report, 1989--1990

Energy Technology Data Exchange (ETDEWEB)

Younker, L.W.; Peterson, S.J.; Price, M.E. (eds.)

1991-03-01

The Earth Sciences Department at Lawrence Livermore National Laboratory (LLNL) conducts work in support of the Laboratory's energy, defense, environmental, and basic research programs. The Department comprises more than 100 professional scientific personnel spanning a variety of subdisciplines: geology, seismology, physics, geophysics, geochemistry, geohydrology, chemical engineering, and mechanical engineering. Resident technical support groups add significant additional technical expertise, including Containment Engineering, Computations, Electronic Engineering, Mechanical Engineering, Chemistry and Materials Science, and Technical Information. In total, approximately 180 professional scientists and engineers are housed in the Earth Sciences Department, making it one of the largest geo-science research groups in the nation. Previous Earth Sciences reports have presented an outline of the technical capabilities and accomplishments of the groups within the Department. In this FY 89/90 Report, we have chosen instead to present twelve of our projects in full-length technical articles. This Overview introduces those articles and highlights other significant research performed during this period.

The Stability of Hydrogen-Rich Atmospheres of Earth-Like Planets

Science.gov (United States)

Zahnle, Kevin

2016-01-01

Understanding hydrogen escape is essential to understanding the limits to habitability, both for liquid water where the Sun is bright, but also to assess the true potential of H2 as a greenhouse gas where the Sun is faint. Hydrogen-rich primary atmospheres of Earth-like planets can result either from gravitational capture of solar nebular gases (with helium), or from impact shock processing of a wide variety of volatile-rich planetesimals (typically accompanied by H2O, CO2, and under the right circumstances, CH4). Most studies of hydrogen escape from planets focus on determining how fast the hydrogen escapes. In general this requires solving hydro- dynamic equations that take into account the acceleration of hydrogen through a critical transonic point and an energy budget that should include radiative heating and cooling, thermal conduction, the work done in lifting the hydrogen against gravity, and the residual heat carried by the hydrogen as it leaves. But for planets from which hydrogen escape is modest or insignificant, the atmosphere can be approximated as hydrostatic, which is much simpler, and for which a relatively full-featured treatment of radiative cooling by embedded molecules, atoms, and ions such as CO2 and H3+ is straightforward. Previous work has overlooked the fact that the H2 molecule is extremely efficient at exciting non-LTE CO2 15 micron emission, and thus that radiative cooling can be markedly more efficient when H2 is abundant. We map out the region of phase space in which terrestrial planets keep hydrogen-rich atmospheres, which is what we actually want to know for habitability. We will use this framework to reassess Tian et al's hypothesis that H2-rich atmospheres may have been rather long-lived on Earth itself. Finally, we will address the empirical observation that rocky planets with thin or negligible atmospheres are rarely or never bigger than 1.6 Earth radii.

Enhancement the Thermal Stability and the Mechanical Properties of Acrylonitrile-Butadiene Copolymer by Grafting Antioxidant

Directory of Open Access Journals (Sweden)

Abdulaziz Ibrahim Al-Ghonamy

2010-01-01

Full Text Available Monomeric antioxidants are widely used as effective antioxidants to protect polymers against thermal oxidation. Low molecular weight antioxidants are easily lost from polymer through migration, evaporation, and extraction. Physical loss of antioxidants is considered to be major concern in the environmental issues and safety regulation as well as long life time of polymers. The grafting copolymerization of natural rubber and o-aminophenol was carried out by using two-roll mill machine. The prepared natural rubber-graft-o-Aminophenol, NR-graft-o-AP, was analysed by using Infrared and 1H-NMR Spectroscopy techniques. The thermal stability, mechanical properties, and ultrasonic attenuation coefficient were evaluated for NBR vulcanizates containing the commercial antioxidant, N-phenyl--naphthylamine (PBN, the prepared grafted antioxidant, NR-graft-o-AP, and the control vulcanizate. Results of the thermal stability showed that the prepared NR-graft-o-AP can protect NBR vulcanizate against thermal treatment much better than the commercial antioxidant, PBN, and control mix, respectively. The prepared grafted antioxidant improves the mechanical properties of NBR vulcanizate.

Enhancement the Thermal Stability and the Mechanical Properties of Acrylonitrile-Butadiene Copolymer by Grafting Antioxidant

International Nuclear Information System (INIS)

Al-Ghonamy, A.I.; El-Wakil, A.A.; Ramadan, M.; El-Wakil, A.A.; Ramadan, M.

2010-01-01

Monomeric antioxidants are widely used as effective antioxidants to protect polymers against thermal oxidation. Low molecular weight antioxidants are easily lost from polymer through migration, evaporation, and extraction. Physical loss of antioxidants is considered to be major concern in the environmental issues and safety regulation as well as long life time of polymers. The grafting copolymerization of natural rubber and o-aminophenol was carried out by using two-roll mill machine. The prepared natural rubber-graft-o-Aminophenol, NR-graft-o-AP, was analysed by using Infrared and 1H-NMR Spectroscopy techniques. The thermal stability, mechanical properties, and ultrasonic attenuation coefficient were evaluated for NBR vulcanizations containing the commercial antioxidant, N-phenyl-β-naphthylamine (PBN), the prepared grafted antioxidant, NR-graft-o-AP, and the control vulcanization. Results of the thermal stability showed that the prepared NR-graft-o-AP can protect NBR vulcanization against thermal treatment much better than the commercial antioxidant, PBN, and control mix, respectively. The prepared grafted antioxidant improves the mechanical properties of NBR vulcanization.

Two drastically different climate states on an Earth-like terra-planet

Directory of Open Access Journals (Sweden)

S. Kalidindi

2018-06-01

Full Text Available We study an Earth-like terra-planet (water-limited terrestrial planet with an overland recycling mechanism bringing fresh water back from the high latitudes to the low latitudes. By performing model simulations for such a planet we find two drastically different climate states for the same set of boundary conditions and parameter values: a cold and wet (CW state with dominant low-latitude precipitation and a hot and dry (HD state with only high-latitude precipitation. We notice that for perpetual equinox conditions, both climate states are stable below a certain threshold value of background soil albedo while above the threshold only the CW state is stable. Starting from the HD state and increasing background soil albedo above the threshold causes an abrupt shift from the HD state to the CW state resulting in a sudden cooling of about 35 °C globally, which is of the order of the temperature difference between present day and the Snowball Earth state. When albedo starting from the CW state is reduced down to zero the terra-planet does not shift back to the HD state (no closed hysteresis. This is due to the high cloud cover in the CW state hiding the surface from solar irradiation so that surface albedo has only a minor effect on the top of the atmosphere radiation balance. Additional simulations with present-day Earth's obliquity all lead to the CW state, suggesting a similar abrupt transition from the HD state to the CW state when increasing obliquity from zero. Our study also has implications for the habitability of Earth-like terra-planets. At the inner edge of the habitable zone, the higher cloud cover in the CW state cools the planet and may prevent the onset of a runaway greenhouse state. At the outer edge, the resupply of water at low latitudes stabilizes the greenhouse effect and keeps the planet in the HD state and may prevent water from getting trapped at high latitudes in frozen form. Overall, the existence of bistability in the

Earth science big data at users' fingertips: the EarthServer Science Gateway Mobile

Science.gov (United States)

Barbera, Roberto; Bruno, Riccardo; Calanducci, Antonio; Fargetta, Marco; Pappalardo, Marco; Rundo, Francesco

2014-05-01

The EarthServer project (www.earthserver.eu), funded by the European Commission under its Seventh Framework Program, aims at establishing open access and ad-hoc analytics on extreme-size Earth Science data, based on and extending leading-edge Array Database technology. The core idea is to use database query languages as client/server interface to achieve barrier-free "mix & match" access to multi-source, any-size, multi-dimensional space-time data -- in short: "Big Earth Data Analytics" - based on the open standards of the Open Geospatial Consortium Web Coverage Processing Service (OGC WCPS) and the W3C XQuery. EarthServer combines both, thereby achieving a tight data/metadata integration. Further, the rasdaman Array Database System (www.rasdaman.com) is extended with further space-time coverage data types. On server side, highly effective optimizations - such as parallel and distributed query processing - ensure scalability to Exabyte volumes. In this contribution we will report on the EarthServer Science Gateway Mobile, an app for both iOS and Android-based devices that allows users to seamlessly access some of the EarthServer applications using SAML-based federated authentication and fine-grained authorisation mechanisms.

Microscopic mechanism of stability in yttria-doped zirconia

CERN Document Server

Ostanin, S A

2001-01-01

The relaxed configurations of yttria-stabilized zirconia (YSZ) between 3 and 10 mol. % Y sub 2 O sub 3 were modeled within the pseudopotential technique. The vibration mode corresponding to the soft phonon in pure c-ZrO sub 2 has been calculated for each Y sub 2 O sub 3 composition. These anharmonic vibrations, associated with stabilization of YSZ, have been investigated within the self-consistent phonon approximation that makes obtainable the fine structure in spectral density. In studying the phonon dynamics, it is proposed to use the displacement probability density which can quantify very accurately the transition temperature needed to stabilize the YSZ cubic phase

Emergence of silicic continents as the lower crust peels off on a hot plate-tectonic Earth

Science.gov (United States)

Chowdhury, Priyadarshi; Gerya, Taras; Chakraborty, Sumit

2017-09-01

The rock record and geochemical evidence indicate that continental recycling has been occurring since the early history of the Earth. The stabilization of felsic continents in place of Earth's early mafic crust about 3.0 to 2.0 billion years ago, perhaps due to the initiation of plate tectonics, implies widespread destruction of mafic crust during this time interval. However, the physical mechanisms of such intense recycling on a hotter, (late) Archaean and presumably plate-tectonic Earth remain largely unknown. Here we use thermomechanical modelling to show that extensive recycling via lower crustal peeling-off (delamination but not eclogitic dripping) during continent-continent convergence was near ubiquitous during the late Archaean to early Proterozoic. We propose that such destruction of the early mafic crust, together with felsic magmatism, may have caused both the emergence of silicic continents and their subsequent isostatic rise, possibly above the sea level. Such changes in the continental character have been proposed to influence the Great Oxidation Event and, therefore, peeling-off plate tectonics could be the geodynamic trigger for this event. A transition to the slab break-off controlled syn-orogenic recycling occurred as the Earth aged and cooled, leading to reduced recycling and enhanced preservation of the continental crust of present-day composition.

Thermal Stability, Combustion Behavior, and Mechanical Property in a Flame-Retardant Polypropylene System

Directory of Open Access Journals (Sweden)

Lili Wang

2017-01-01

Full Text Available In order to comprehensively improve the strength, toughness, flame retardancy, smoke suppression, and thermal stability of polypropylene (PP, layered double hydroxide (LDH Ni0.2Mg2.8Al–LDH was synthesized by a coprecipitation method coupled with the microwave-hydrothermal treatment. The X-ray diffraction (XRD, morphology, mechanical, thermal, and fire properties for PP composites containing 1 wt %–20 wt % Ni0.2Mg2.8Al–LDH were investigated. The cone calorimeter tests confirm that the peak heat release rate (pk–HRR of PP–20%LDH was decreased to 500 kW/m2 from the 1057 kW/m2 of PP. The pk–HRR, average mass loss rate (AMLR and effective heat of combustion (EHC analysis indicates that the condensed phase fire retardant mechanism of Ni0.2Mg2.8Al–LDH in the composites. The production rate and mean release yield of CO for composites gradually decrease as Ni0.2Mg2.8Al–LDH increases in the PP matrix. Thermal analysis indicates that the decomposition temperature for PP–5%LDH and PP–10%LDH is 34 °C higher than that of the pure PP. The mechanical tests reveal that the tensile strength of PP–1%LDH is 7.9 MPa higher than that of the pure PP. Furthermore, the elongation at break of PP–10%LDH is 361% higher than PP. In this work, the synthetic LDH Ni0.2Mg2.8Al–LDH can be used as a flame retardant, smoke suppressant, thermal stabilizer, reinforcing, and toughening agent of PP products.

Effect of EVA on thermal stability, flammability, mechanical properties of HDPE/EVA/Mg(OH)2 composites

Science.gov (United States)

Cao, R.; Deng, Z. L.; Ma, Y. H.; Chen, X. L.

2017-06-01

In this work, ethylene vinyl acetate (EVA) is introduced to improve the properties of high-density polyethylene (HDPE)/magnesium hydroxide (MH) composites. The thermal stability, flame retardancy and mechanical properties of HDPE/EVA/MH composites are investigated and discussed. With increasing content of EVA, the limiting oxygen index (LOI) of the composites increases. The thermal stability analysis shows that the initial decomposition temperature begins at a low temperature; however, the residues of the composites at 600°C increase when HDPE is replaced by small amounts of EVA. The early degradation absorbs heat, dilute oxygen and residue. During this process, it protects the matrix inside. Compared with the HDPE/MH and EVA/MH composites, the ternary HDPE/EVA/MH composites exhibit better flame retardancy by increasing the LOI values, and reducing the heat release rate (HRR) and total heat release (THR). With increasing content of EVA, the mechanical properties can also be improved, which is attributed to the good affinity between EVA and MH particles.

Preparation of polyvinyl alcohol graphene oxide phosphonate film and research of thermal stability and mechanical properties.

Science.gov (United States)

Li, Jihui; Song, Yunna; Ma, Zheng; Li, Ning; Niu, Shuai; Li, Yongshen

2018-05-01

In this article, flake graphite, nitric acid, peroxyacetic acid and phosphoric acid are used to prepare graphene oxide phosphonic and phosphinic acids (GOPAs), and GOPAs and polyvinyl alcohol (PVA) are used to synthesize polyvinyl alcohol graphene oxide phosphonate and phosphinate (PVAGOPs) in the case of faint acidity and ultrasound irradiation, and PVAGOPs are used to fabricate PVAGOPs film, and the structure and morphology of GOPAs, PVAGOPs and PVAGOPs film are characterized, and the thermal stability and mechanical properties of PVAGOPs film are investigated. Based on these, it has been proved that GOPAs consist of graphene oxide phosphonic acid and graphene oxide phosphinic acid, and there are CP covalent bonds between them, and PVAGOPs are composed of GOPAs and PVA, and there are six-member lactone rings between GOPAs and PVA, and the thermal stability and mechanical properties of PVAGOPs film are improved effectively. Copyright © 2018 Elsevier B.V. All rights reserved.

Monitoring of Earth Rotation by VLBI

Science.gov (United States)

Ma., Chopo; Macmillan, D. S.

2000-01-01

Monitoring Earth rotation with Very Long Baseline Interferometry (VLBI) has unique potential because of direct access to the Celestial Reference System (CRF and Terrestrial Reference System (TRF) and the feasibility of re-analyzing the entire data set. While formal precision of better than 0.045 mas for pole and 0.002 ms for UT 1 has been seen in the best 24-hr data, the accuracy of the Earth Orientation Parameter (EOP) time series as a whole is subject to logistical, operational, analytical and conceptual constraints. The current issues related to the VLBI data set and the CORE program for greater time resolution such as analysis consistency, network jitter and reference frame stability will be discussed.

Binding of rare earths to serum proteins and DNA

International Nuclear Information System (INIS)

Rosoff, B.; Spencer, H.

1979-01-01

In order to investigate further the physiological behavior of rare earths and rare earth chelates, studies of the binding of 46 Sc, 91 Y, and 140 La to serum proteins and to nucleic acids were performed using the methods of equilibrium dialysis and ultrafiltration. The binding of lanthanum and yttrium as the chlorides to α-globulin increased as the free rare earth concentration increased. When scandium and lanthanum were chelated in nitrilotriacetate (NTA) the binding to α-globulin was considerably less and there was no binding to albumin. The binding of 46 Sc chelated to ethylenediamine di(O-hydroxyphenylacetate) (EDDHA) was five times greater than of 46 Sc chloride. When the free scandium concentration was increased, the moles bound per mole of protein increased proportionally and the binding was reversible. Scandium was 100% filterable from a mixture of human serum and from the scandium chelates with high stability constants scandium diethylenetriaminepentaacetate (ScDTPA), scandium ethylenediaminetetraacetate (ScEDTA) and scandium cyclohexane trans-1,2-diaminetetraacetate (ScCDTA) respectively. In contrast, only 2% of the scandium was filterable when scandium nitrilotriacetate, a scandium chelate of low stability constant, was used. (Auth.)

Studying the effect of a variation in the main parameters on stability of homogeneous earth dams using design experiment

Directory of Open Access Journals (Sweden)

Lakehal Rida

2017-09-01

Full Text Available Deterministic approaches such as the limit equilibrium method (LEM especially Bishop modified method has been traditionally used to evaluate the stability of embankment dams. However, the uncertainty associated with the material properties necessitates the use of the probabilistic method to account the sensitivity of this uncertainty on the response of the deterministic approaches. In this study, the authors propose the application of design experiment, especially central composite design (CCD to determine the effects of independent uncertain parameters on the response of stability. A second-order polynomial model with cross terms is used to create an approximating function referred to as response surface for the implicit limit state surface, for which the input data were provided by stability analyses of different heights of homogeneous earth dams (10 m, 20 m, and 30 m with a depth ratio of DH = 1.5 and a circular slip surface using the Bishop modified limit equilibrium method. The proposed models obtained from this application represent higher prediction accuracy. The study of the effect of geotechnical parameters (material properties of embankment on safety factor show the importance of individual factors in level of linear effect with a positive effect of c’ or φ’ and a negative effect of H, γd, γsat and significant influence of two-factors interaction, the effect of c’ highly dependent on H, β, γd and φ’. Moreover, the effect of φ’ is dependent on the values of H and β. Lastly, the optimization of safety factor with respect to the range of values of material properties was made, and two failures modes are discussed which are (φ’, c’ reduction and γd increase.

A high-response transparent heater based on a CuS nanosheet film with superior mechanical flexibility and chemical stability.

Science.gov (United States)

Xie, Shuyao; Li, Teng; Xu, Zijie; Wang, Yanan; Liu, Xiangyang; Guo, Wenxi

2018-04-05

Transparent heaters are widely used in technologies such as window defrosting/defogging, displays, gas sensing, and medical equipment. Apart from mechanical robustness and electrical and optical reliabilities, outstanding chemical stability is also critical to the application of transparent heaters. In this regard, we first present a highly flexible and large-area CuS transparent heater fabricated by a colloidal crackle pattern method with an optimized sheet resistance (Rs) as low as 21.5 Ω sq-1 at a ∼80% transmittance. The CuS transparent heater exhibits remarkable mechanical robustness during bending tests as well as high chemical stability against acid and alkali environments. In the application as a transparent heater, the CuS heater demonstrates a high thermal resistance of 197 °C W-1 cm2 with a fast switching time (solar panels. These CuS network TCEs with high flexibility, transparency, conductivity, and chemical stability could be widely used in wearable electronic products.

Clouds and the earth's radiation balance

Energy Technology Data Exchange (ETDEWEB)

Schmetz, J; Raschke, E

1986-01-01

Cloud formation mechanisms and cloud effects must be known for all regions of the earth for two important purposes of weather and climate research: First, the circulation characteristics of the atmosphere can be defined and understood only if the energy transfer between the atmosphere and the earth's surface is known; secondly, the energy transfer calculations should be as realistic as possible. The article discusses the influence of clouds on the radiation balance of the earth/atmosphere radiation balance, and the effects on weather and climate.

Elevated-temperature mechanical stability and transformation behavior of retained austenite in a quenching and partitioning steel

Energy Technology Data Exchange (ETDEWEB)

Min, Junying, E-mail: junying.min@gmail.com [Chair of Production Systems, Ruhr-University Bochum, Bochum 44780 (Germany); Hector, Louis G. [General Motors Research & Development, Warren, MI 48095-9055 (United States); Zhang, Ling; Lin, Jianping [School of Mechanical Engineering, Tongji University, Shanghai 201804 (China); Carsley, John E. [General Motors Research & Development, Warren, MI 48095-9055 (United States); Sun, Li [General Motors China Science Lab, Shanghai 201206 (China)

2016-09-15

The mechanical stability and transformation behavior of both film and blocky retained austenite (RA) in a quenching and partitioning steel are investigated at 293 K, 423 K and 573 K with X-ray diffraction measurements and transmission electron microscopy. Blocky RA both completely and incompletely transforms to twinned martensite during deformation at 293 K and 423 K, respectively, and completely transforms to lath martensite during deformation at 573 K. At 293 K and 423 K, only the film RA with widths larger than ~70 nm transforms to twinned martensite. However, film RA incompletely transforms to lath martensite at 573 K. Hence, RA transformation is non-monotonic with temperature. Significant carbide formation at 573 K, and therefore less carbon to stabilize RA, overcomes the increase in austenite stability due to the decrease in the temperature-dependent chemical driving force for the martensite transformation.

Stress evolution and fault stability at Olkiluoto during the Weichselian glaciation

International Nuclear Information System (INIS)

Lund, B.; Schmidt, P.

2011-06-01

In this study we investigate how a model of the Weichselian glacial cycle affects the state of stress in the Earth, and how those changes in stress influence the stability of faults. The main objectives for this study are the evolution of the glacially induced stresses at repository depth in Olkiluoto, Finland, and the stability field at seismogenic depths below the proposed repository. The analysis presented here is similar to the study by Lund et al. (2009) for the proposed Swedish nuclear waste repository sites of Forsmark and Oskarshamn. Along the lines of Lund et al. (2009), this study is a modeling study, where we use three-dimensional ice and earth models to calculate the glacial isostatic adjustment (GIA), i.e. the response of the Earth to an ice load, examining both displacements and stresses

Rare earth ion controlled crystallization of mica glass-ceramics

International Nuclear Information System (INIS)

Garai, Mrinmoy; Karmakar, Basudeb

2016-01-01

In understanding the effects of rare earth ions to control the crystallization and microstructure of alkaline boroaluminosilicate system, the CeO_2, Nd_2O_3, Sm_2O_3 and Gd_2O_3 doped K_2O−MgO−B_2O_3−Al_2O_3−SiO_2−F glasses were synthesized by melt-quenching at 1550 °C. Higher density (2.82–3.06 g cm"−"3) and thermal stability (glass phase) is experiential on addition of rare earth content, which also affects in increasing the glass transition temperature (T_g) and crystallization temperature (T_c). Decrease of thermal expansion in glasses with rare earth ion content is maintained by the stabilization of glass matrix owing to their large cationic field strength. A significant change in the non-isothermal DSC thermogram observed at 750–1050 °C is attributed to fluorophlogopite crystallization. Opaque glass-ceramics were prepared from such glasses by single step heat-treatment at 1050 °C; and the predominant crystalline phases are identified as fluorophlogopite mica, KMg_3(AlSi_3O_1_0)F_2 by XRD and EDX analysis. The compact glass-ceramic microstructure by the agglomeration of fluorophlogopite mica crystallites (crystal size ∼ 100–500 nm, FESEM) is achieved in attendance of rare earth ion; and such microstructure controlled the variation of density, thermal expansion and microhardness value. Higher thermal expansion (11.11–14.08 × 10"−"6/K at 50–800 °C and 50–900 °C) of such glass-ceramics approve that these rare earth containing glasses can be useful for high temperature vacuum sealing application with metal or solid electrolyte. The increase of Vickers microhardness (5.27–5.61 GPa) in attendance of rare earth ions is attributed to the compact crystallinity of fluorophlogopite mica glass-ceramic microstructure. - Highlights: • Synthesis of rare earth oxide doped alkaline boroaluminosilicate glasses. • Development of opaque fluorophlogopite mica glass-ceramics by single-step heat treatment. • Nanocrystalline glass

Evaluating the Effect of Rainfall Infiltration on the Slope Stability of T16 tower of Taipei Mao-kong Gondola by Numerical Methods

Science.gov (United States)

RUNG, J.

2013-12-01

In this study, a series of rainfall-stability analyses were performed to simulate the failure mechanism and the function of remediation works of the down slope of T-16 tower pier, Mao-Kong gondola (or T-16 Slope) at the hillside of Taipei City using two-dimensional finite element method. The failure mechanism of T-16 Slope was simulated using the rainfall hyetograph of Jang-Mi typhoon in 2008 based on the field investigation data, monitoring data, soil/rock mechanical testing data and detail design plots of remediation works. Eventually, the numerical procedures and various input parameters in the analysis were verified by comparing the numerical results with the field observations. In addition, 48 hrs design rainfalls corresponding to 5, 10, 25 and 50 years return periods were prepared using the 20 years rainfall data of Mu-Zha rainfall observation station, Central Weather Bureau for the rainfall-stability analyses of T-16 Slope to inspect the effect of the compound stabilization works on the overall stability of the slope. At T-16 Slope, without considering the longitudinal and transverse drainages on the ground surface, there totally 4 types of stabilization works were installed to stabilize the slope. From the slope top to the slope toe, the stabilization works of T-16 Slope consists of RC-retaining wall with micro-pile foundation at the up-segment, earth anchor at the up-middle-segment, soil nailing at the middle-segment and retaining pile at the down-segment of the slope. The effect of each individual stabilization work on the slope stability under rainfall condition was examined and evaluated by raising field groundwater level.

In vitro and in vivo mechanical stability of orthodontic mini-implants.

Science.gov (United States)

Cho, Il-Sik; Kim, Sung-Kyun; Chang, Young-Il; Baek, Seung-Hak

2012-07-01

To compare in vivo and in vitro mechanical stability of orthodontic mini-implants (OMIs) treated with a sandblasted, large-grit, and anodic-oxidation (SLAO) method vs those treated with a sandblasted, large-grit, and acid-etching (SLA) method. Fifty-four titanium OMIs (cylindrical shape, drill-free type; diameter  =  1.45 mm, length  =  8 mm, Biomaterials Korea Inc, Seoul, Korea) were allocated into control, SLA, and SLAO groups (N  =  12 for in vivo and N  =  6 for in vitro studies per group). In vitro study was carried out on a polyurethane foam bone block (Sawbones, Pacific Research Laboratories Inc, Vashon, Wash). In vivo study was performed in the tibias of Beagles (6 males, age  =  1 year, weight  =  10 to 13 kg; OMIs were removed at 8 weeks after installation). For insertion and removal of OMIs, the speed and maximum torque of the surgical engine were set to 30 rpm and 40 Ncm, respectively. Maximum torque (MT), total energy (TE), and near peak energy (NPE) during the insertion and removal procedures were statistically analyzed. In the in vitro study, although the control group had a higher insertion MT value than the SLA and SLAO groups (P < .01), no differences in insertion TE and NPE or in any of the removal variables were noted among the three groups. In the in vivo study, the control group exhibited higher values for all insertion variables compared with the SLA and SLAO groups (MT, P < .001; TE, P < .01; NPE, P < .001). Although no difference in removal TE and removal NPE was noted among the three groups, the SLAO group presented with a higher removal MT than the SLA and control groups (P < .001). SLAO treatment may be an effective tool in reducing insertion damage to surrounding tissue and improving the mechanical stability of OMIs.

The influences of rare earth content on the microstructure and mechanical properties of Mg-7Zn-5Al alloy

International Nuclear Information System (INIS)

Xiao, Wenlong; Shen, Yusen; Wang, Lidong; Wu, Yaoming; Cao, Zhanyi; Jia, Shusheng; Wang, Limin

2010-01-01

The influences of rare earth (RE) on the microstructure and mechanical properties of Mg-7Zn-5Al alloy were studied. The results indicate that both the dendrite and grain size of the alloy can be refined by low RE addition. The Al 2 REZn 2 phase will be formed with increasing the RE content, however the high RE addition results in the grain coarsening in the alloy due to the decrease of the contribution of Al and Zn solutes on the grain refinement. The strengthening and weakening mechanisms caused by RE addition only lead to the obviously improve on the room temperature ultimate tensile strength. The mechanical properties of the studied alloys can be improved by aging treatment, and the aged Mg-7Zn-5Al-2RE alloy exhibits optimal mechanical properties at room temperature.

Flooding Effect on Earth Walls

Directory of Open Access Journals (Sweden)

Meysam Banimahd

2010-12-01

Full Text Available Earth building is a sustainable, environmentally friendly and economical method of construction that has been used worldwide for many centuries. For the past three decades, earth has seen a revival as a building material for a modern construction method due to its benefits in terms of low carbon content, low cost and energy involved during construction, as well as the fact that it is a sustainable technology of building. Climate change is influencing precipitation levels and patterns around the world, and as a consequence, flood risk is increasing rapidly. When flooding occurs, earth buildings are exposed to water by submersion, causing an increase in the degree of saturation of the earth structures and therefore a decrease of the suction between particles. This study investigated the effect of cycles of flooding (consecutive events of flooding followed by dry periods on earth walls. A series of characterization tests were carried out to obtain the physical and mechanical properties of the studied earth material. In a second stage, Flooding Simulation Tests (FST were performed to explore the earth walls’ response to repeated flooding events. The results obtained for the tested earth wall/samples with reinforced material (straw reveal hydraulic hysteresis when wall/samples are subject to cycles of wetting and drying.

Study of the mechanical stability of the ATLAS Insertable B-Layer

CERN Document Server

The ATLAS collaboration

2015-01-01

During the commissioning and alignment of the ATLAS Insertable B-Layer (IBL) using cosmic-ray data, a mechanical distortion of the IBL was observed. This distortion is caused by a difference in the coefficients of thermal expansion of the IBL stave components. The results of a preliminary study of the mechanical stability of the IBL are presented in this note. The qualitative properties of the distortion are confirmed using a 3D finite element analysis. Using cosmic-ray data collected in March 2015, the magnitude of the distortion is found to depend linearly on the operating temperature of the IBL, with a gradient of $\\sim10~{\\rm \\mu m/K}$. The peak-to-peak temperature variation of the IBL staves is measured to be less than 0.2 K during the same cosmic-ray run. The expected bias to the transverse impact parameter $(d_{0})$ of charged tracks under a temperature variation of 0.2 K is evaluated to be $\\sim 1~{\\rm \\mu m}$ using $Z\\rightarrow{\\mu^+\\mu^-}$ events from a Mote Carlo simulation of proton-proton collis...

Neural robust stabilization via event-triggering mechanism and adaptive learning technique.

Science.gov (United States)

Wang, Ding; Liu, Derong

2018-06-01

The robust control synthesis of continuous-time nonlinear systems with uncertain term is investigated via event-triggering mechanism and adaptive critic learning technique. We mainly focus on combining the event-triggering mechanism with adaptive critic designs, so as to solve the nonlinear robust control problem. This can not only make better use of computation and communication resources, but also conduct controller design from the view of intelligent optimization. Through theoretical analysis, the nonlinear robust stabilization can be achieved by obtaining an event-triggered optimal control law of the nominal system with a newly defined cost function and a certain triggering condition. The adaptive critic technique is employed to facilitate the event-triggered control design, where a neural network is introduced as an approximator of the learning phase. The performance of the event-triggered robust control scheme is validated via simulation studies and comparisons. The present method extends the application domain of both event-triggered control and adaptive critic control to nonlinear systems possessing dynamical uncertainties. Copyright © 2018 Elsevier Ltd. All rights reserved.

The corrosion behaviour of rare-earth containing magnesium alloys in borate buffer solution

Energy Technology Data Exchange (ETDEWEB)

Pinto, R. [ICEMS, Instituto Superior Tecnico, Technical University of Lisbon (Portugal); Ferreira, M.G.S. [ICEMS, Instituto Superior Tecnico, Technical University of Lisbon (Portugal); CICECO, Universidade de Aveiro (Portugal); Carmezim, M.J. [ICEMS, Instituto Superior Tecnico, Technical University of Lisbon (Portugal); Instituto Politecnico de Setubal, ESTSetubal, DEM (Portugal); Montemor, M.F., E-mail: mfmontemor@ist.utl.p [ICEMS, Instituto Superior Tecnico, Technical University of Lisbon (Portugal)

2011-01-01

In this work, the corrosion behaviour of magnesium alloys ZK31, EZ33 and WE54 was studied in sodium borate buffer solution at pH 9.2. The electrochemical processes were studied by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The composition and morphology of the alloys and corrosion products formed were studied by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The experimental findings highlighted the differences in the corrosion mechanisms of the different alloys tested. The results showed that the presence of rare-earth elements (RE) only increases the corrosion resistance when present in solid solution, as is the case of the WE54 alloy. At pH 9.2, an amorphous yttrium oxide/hydroxide thick film was formed, which possesses greater stability when compared to magnesium oxide/hydroxide. The role of RE in the corrosion mechanism was discussed.

Multilayer Thermal Barrier Coating (TBC) Architectures Utilizing Rare Earth Doped YSZ and Rare Earth Pyrochlores

Science.gov (United States)

Schmitt, Michael P.; Rai, Amarendra K.; Bhattacharya, Rabi; Zhu, Dongming; Wolfe, Douglas E.

2014-01-01

To allow for increased gas turbine efficiencies, new insulating thermal barrier coatings (TBCs) must be developed to protect the underlying metallic components from higher operating temperatures. This work focused on using rare earth doped (Yb and Gd) yttria stabilized zirconia (t' Low-k) and Gd2Zr2O7 pyrochlores (GZO) combined with novel nanolayered and thick layered microstructures to enable operation beyond the 1200 C stability limit of current 7 wt% yttria stabilized zirconia (7YSZ) coatings. It was observed that the layered system can reduce the thermal conductivity by approximately 45 percent with respect to YSZ after 20 hr of testing at 1316 C. The erosion rate of GZO is shown to be an order to magnitude higher than YSZ and t' Low-k, but this can be reduced by almost 57 percent when utilizing a nanolayered structure. Lastly, the thermal instability of the layered system is investigated and thought is given to optimization of layer thickness.

The mechanical stability of retained austenite in low-alloyed TRIP steel under shear loading

Energy Technology Data Exchange (ETDEWEB)

Blondé, R., E-mail: r.j.p.blonde@tudelft.nl [Fundamental Aspects of Materials and Energy, Faculty of Applied Sciences, Delft University of Technology, Mekelweg 15, 2629 JB Delft (Netherlands); Materials Innovation Institute, Mekelweg 2, 2628 CD Delft (Netherlands); Jimenez-Melero, E., E-mail: enrique.jimenez-melero@manchester.ac.uk [Dalton Cumbrian Facility, The University of Manchester, Westlakes Science and Technology Park, Moor Row, Cumbria CA24 3HA (United Kingdom); Zhao, L., E-mail: lie.zhao@tudelft.nl [Materials Innovation Institute, Mekelweg 2, 2628 CD Delft (Netherlands); Department of Materials Science and Engineering, Delft University of Technology, Mekelweg 2, 2628 CD Delft (Netherlands); Schell, N., E-mail: norbert.schell@hzg.de [Institute of Materials Research, Helmholtz-Zentrum Geesthacht, Max Planck Strasse 1, 21502 Geesthacht (Germany); Brück, E., E-mail: e.h.bruck@tudelft.nl [Fundamental Aspects of Materials and Energy, Faculty of Applied Sciences, Delft University of Technology, Mekelweg 15, 2629 JB Delft (Netherlands); Zwaag, S. van der, E-mail: s.vanderzwaag@tudelft.nl [Novel Aerospace Materials Group, Faculty of Aerospace Engineering, Delft University of Technology, Kluyverweg 1, 2629 HS Delft (Netherlands); Dijk, N.H. van, E-mail: n.h.vandijk@tudelft.nl [Fundamental Aspects of Materials and Energy, Faculty of Applied Sciences, Delft University of Technology, Mekelweg 15, 2629 JB Delft (Netherlands)

2014-01-31

The microstructure evolution during shear loading of a low-alloyed TRIP steel with different amounts of the metastable austenite phase and its equivalent DP grade has been studied by in-situ high-energy X-ray diffraction. A detailed powder diffraction analysis has been performed to probe the austenite-to-martensite transformation by characterizing simultaneously the evolution of the austenite phase fraction and its carbon concentration, the load partitioning between the austenite and the ferritic matrix and the texture evolution of the constituent phases. Our results show that for shear deformation the TRIP effect extends over a significantly wider deformation range than for simple uniaxial loading. A clear increase in average carbon content during the mechanically-induced transformation indicates that austenite grains with a low carbon concentration are least stable during shear loading. The observed texture evolution indicates that under shear loading the orientation dependence of the austenite stability is relatively weak, while it has previously been found that under tensile load the {110}〈001〉 component transforms preferentially. The mechanical stability of retained austenite in TRIP steel is found to be a complex interplay between the interstitial carbon concentration in the austenite, the grain orientation and the load partitioning.

Rare Earth Oxide Fluoride Nanoparticles And Hydrothermal Method For Forming Nanoparticles

Science.gov (United States)

Fulton, John L.; Hoffmann, Markus M.

2003-12-23

A hydrothermal method for forming nanoparticles of a rare earth element, oxygen and fluorine has been discovered. Nanoparticles comprising a rare earth element, oxygen and fluorine are also described. These nanoparticles can exhibit excellent refractory properties as well as remarkable stability in hydrothermal conditions. The nanoparticles can exhibit excellent properties for numerous applications including fiber reinforcement of ceramic composites, catalyst supports, and corrosion resistant coatings for high-temperature aqueous solutions.

NEW HYPOTHESIS AND ELECTROPHYSICS NATURE OF ADDITIONAL MECHANISMS OF ORIGIN, ACCUMULATION AND DIVISION OF ELECTRIC CHARGES IN THE ATMOSPHERIC CLOUDS OF EARTH

Directory of Open Access Journals (Sweden)

M. I. Baranov

2018-02-01

Full Text Available Purpose. Development of new hypothesis about the possible additional mechanisms of origin, accumulation and division of electric charges in atmospheric clouds, containing shallow dispersible drops of water, shallow particulate dielectric matters and crystals of ice. Methodology. Electrophysics bases of technique of high voltage, theoretical bases of the electrical engineering, theoretical electrophysics, theory of the electromagnetic field, technique of the high electric and magnetic fields. Results. Pulled out and grounded new scientific supposition, related to possible existence in earthly troposphere of additional mechanisms of origin, accumulation and division of electric charges in the atmospheric clouds of Earth, being based on electrization in the warm ascending currents of air of shallow round particulate dielectric matters, getting in an air atmosphere from a terrene and from the smoke extras of industrial enterprises. By a calculation a way it is shown that the offered additional electrophysics mechanisms are able to provide achievement in the atmospheric clouds of such values of volume closeness of charges, total electric charge and tension of the electrostatic field stocked in them inwardly and on the external border of storm clouds which correspond modern experimental information from an area atmospheric electricity. The calculation estimations of levels of electric potential and stocked electric energy executed on the basis of the offered hypothesis in storm clouds specify on possibility of receipt in them of ever higher electric potentials and large supplies of electric energy. The obtained results are supplemented by the known approaches of forming and development in earthly troposphere of the electric charged atmospheric clouds, being based on electrization in the warm ascending streams of air the masses of shallow round aquatic drops. Originality. First on the basis of the well-known theses of technique and electrophysics of

Climate in Earth history

Science.gov (United States)

Berger, W. H.; Crowell, J. C.

1982-01-01

Complex atmosphere-ocean-land interactions govern the climate system and its variations. During the course of Earth history, nature has performed a large number of experiments involving climatic change; the geologic record contains much information regarding these experiments. This information should result in an increased understanding of the climate system, including climatic stability and factors that perturb climate. In addition, the paleoclimatic record has been demonstrated to be useful in interpreting the origin of important resources-petroleum, natural gas, coal, phosphate deposits, and many others.

Mechanisms of impact of greenhouse gases on the Earth's ozone layer in the Polar Regions

Science.gov (United States)

Zadorozhny, Alexander; Dyominov, Igor

A numerical 2-D zonally averaged interactive dynamical radiative-photochemical model of the atmosphere including aerosol physics is used to examine the impact of the greenhouse gases CO2, CH4, and N2O on the future long-term changes of the Earth's ozone layer, in particular on its expected recovery after reduction of anthropogenic discharges of chlorine and bromine compounds into the atmosphere. The model allows calculating self-consistently diabatic circu-lation, temperature, gaseous composition of the troposphere and stratosphere at latitudes from the North to South Poles, as well as distribution of sulphate aerosol particles and polar strato-spheric clouds (PSCs) of types I and II. The scenarios of expected changes of the anthropogenic pollutants for the period from 1980 through 2050 are taken from Climate Change 2001. The processes, which determine the influence of anthropogenic growth of atmospheric abun-dance of the greenhouse gases on the long-term changes of the Earth's ozone layer in the Polar Regions, have been studied in details. Expected cooling of the stratosphere caused by increases of greenhouse gases, most importantly CO2, essentially influences the ozone layer by two ways: through temperature dependencies of the gas phase reaction rates and through enhancement of polar ozone depletion via increased PSC formation. The model calculations show that a weak-ness in efficiencies of all gas phase catalytic cycles of the ozone destruction due to cooling of the stratosphere is a dominant mechanism of the impact of the greenhouse gases on the ozone layer in Antarctic as well as at the lower latitudes. This mechanism leads to a significant acceleration of the ozone layer recovery here because of the greenhouse gases growth. On the contrary, the mechanism of the impact of the greenhouse gases on the ozone through PSC modification be-gins to be more effective in Arctic in comparison with the gas phase mechanism in springs after about 2020, which leads to retard

Optical MEMS for earth observation payloads

Science.gov (United States)

Rodrigues, B.; Lobb, D. R.; Freire, M.

2017-11-01

An ESA study has been taken by Lusospace Ltd and Surrey Satellite Techonoly Ltd (SSTL) into the use of optical Micro Eletro-Mechanical Systems (MEMS) for earth Observation. A review and analysis was undertaken of the Micro-Optical Electro-Mechanical Systems (MOEMS) available in the market with potential application in systems for Earth Observation. A summary of this review will be presented. Following the review two space-instrument design concepts were selected for more detailed analysis. The first was the use of a MEMS device to remove cloud from Earth images. The concept is potentially of interest for any mission using imaging spectrometers. A spectrometer concept was selected and detailed design aspects and benefits evaluated. The second concept developed uses MEMS devices to control the width of entrance slits of spectrometers, to provide variable spectral resolution. This paper will present a summary of the results of the study.

DFT investigations on mechanical stability, electronic structure and magnetism in Co2TaZ (Z = Al, Ga, In) heusler alloys

Science.gov (United States)

Khandy, Shakeel Ahmad; Gupta, Dinesh C.

2017-12-01

Ferromagnetic Heusler compounds have vast and imminent applications for novel devices, smart materials thanks to density functional theory (DFT) based simulations, which have scored out a new approach to study these materials. We forecast the structural stability of Co2TaZ alloys on the basis of total energy calculations and mechanical stability criteria. The elastic constants, robust spin-polarized ferromagnetism and electron densities in these half-metallic alloys are also discussed. The observed structural aspects calculated to predict the stability and equilibrium lattice parameters agree well with the experimental results. The elastic parameters like elastic constants, bulk, Young’s and shear moduli, poison’s and Pugh ratios, melting temperatures, etc have been put together to establish their mechanical properties. The elaborated electronic band structures along with indirect band gaps and spin polarization favour the application of these materials in spintronics and memory device technology.

Thermal Oxidation Resistance of Rare Earth-Containing Composite Elastomer

Institute of Scientific and Technical Information of China (English)

邱关明; 张明; 周兰香; 中北里志; 井上真一; 冈本弘

2001-01-01

The rare earth-containing composite elastomer was obtained by the reaction of vinyl pyridine-SBR (PSBR) latex with rare earth alkoxides, and its thermal oxidation resistance was studied. After aging test, it is found that its retention rate of mechanical properties is far higher than that of the control sample. The results of thermogravimetric analysis show that its thermal-decomposing temperature rises largely. The analysis of oxidation mechanisms indicates that the main reasons for thermal oxidation resistance are that rare earth elements are of the utility to discontinue autoxidation chain reaction and that the formed complex structure has steric hindrance effect on oxidation.

A dynamical stabilizer in the climate system: a mechanism suggested by a simple model

Science.gov (United States)

Bates, J. R.

1999-05-01

involve inter-zone coupling and have coefficients dependent on the values of the equilibrium fluxes and the sensitivity of the angular momentum transport. Analytical solutions for the perturbations are obtained. These provide criteria for the stability of the equilibrium climate. If the evaporative feedback on SST perturbations is omitted, the equilibrium climate is unstable due to the influence of the water vapour/infrared radiative feedback, which dominates over the effects of the sensible heat and ocean heat transport feedbacks. The inclusion of evaporation gives a negative feedback which is of sufficient strength to stabilize the system. The stabilizing mechanism involves wind and humidity factors in the evaporative fluxes that are of comparable magnitude. Both factors involve the angular momentum transport. In including angular momentum and calculating the surface fluxes explicitly, the model presented here differs from the many simple climate models based on the Budyko Sellers formulation. In that formulation, an atmospheric energy balance equation is used to eliminate surface fluxes in favour of top-of-the-atmosphere radiative fluxes and meridional atmospheric energy transports. In the resulting models, infrared radiation appears as a stabilizing influence on SST perturbations and the dynamical stabilizing mechanism found here cannot be identified.

Enzymatic determination of rare earth elements using pyrophosphatases

International Nuclear Information System (INIS)

Shekhovtsova, T.N.; Pirogova, S.V.; Fedorova, O.M.; Dolmanova, I.F.; Bajkov, A.A.

1993-01-01

A highly sensitive(determination limit 8x10 -6 -4x10 -4 μ g/m) and selective enzymatic method for determination of rare earth elements has been developed. The method is based on inhibition action of rare earths on the catalytic activity of pyrophosphates isolated from bakery geast and E.Coli. The mechanism of the rare earth element action, corresponding to competitive inhibition, has been established

A possible mechanism to detect super-earth formation in protoplanetary disks

Science.gov (United States)

Dong, Ruobing; Chiang, Eugene; Li, Hui; Li, Shengtai

2017-06-01

Using combined gas+dust global hydrodynamics and radiative transfer simulations, we calculate the distribution of gas and sub-mm-sized dust in protoplanetary disks with a super-Earth at tens of AU, and examine observational signatures of such systems in resolved observations. We confirm previous results that in a typical disk with a low viscosity ($\\alpha\\lesssim10^{-4}$), a super-Earth is able to open two gaps at $\\sim$scale-height away around its orbit in $\\sim$mm-sized dust (St$\\sim$0.01), due to differential dust drift in a perturbed gas background. Additional rings and gaps may also be produced under certain conditions. These features, particularly a signature ``double-gap'' feature, can be detected in a Taurus target by ALMA in dust continuum under an angular resolution of $\\sim0\\arcsec.025$ with two hours of integration. The features are robust --- it can survive in a variety of background disk profiles, withstand modest planetary radial migration ($|r/\\dot{r}|\\sim$ a few Myr), and last for thousands of orbits. Multiple ring/gap systems observed by ALMA were typically modeled using multiple (Saturn-to-Jupiter sized) planets. Here, we argue that a single super-Earth in a low viscosity disk could produce multiple rings and gaps as well. By examining the prevalence of such features in nearby disks, upcoming high angular resolution ALMA surveys may infer how common super-Earth formation events are at tens of au.

A new dynamic system suggested for earth expansion

International Nuclear Information System (INIS)

Fitzpatrick, J.

1972-01-01

It is here suggested that there may have been much more radioactive materials in the deep interior of the earth than bitherto supposed. Trapped heat being generated in the interior would provide a mechanism for earth expansion. An assumption of heat generation in the deep interior of the earth of the order of 0,5 X 10-13 calories per second, per cubic centimeter, would provide sufficient thermal expansion to account for approximately 0.1 mm. change in the radius of the earth per year

Mechanism of central ion exchange in the neodymium (3) ethylenediamine-tetraacetate-copper (2) and erbium (3) ethylenediaminetetraacetate-copper (2) systems in aqueous solution

Energy Technology Data Exchange (ETDEWEB)

Nikitenko, S.I.; Martynenko, L.I.; Pechurova, N.I.; Spitsyn, V.I. (Moskovskij Gosudarstvennyj Univ. (USSR))

1984-01-01

The spectrophotometry method in the stationary regime and the ''Stopped Flow'' method in the prestationary regime are used to study kinetics and exchange mechanism in NdA/sup -/-Cu/sup 2 +/ and ErA/sup -/-Cu/sup 2 +/ (A=EDTA) systems at pH 4.0-6.0 and initial Cu/sup 2 +/ concentrations (0.5-6.0) x 10/sup -2/ M, Nd/sup 3 +/, Er/sup 3/2H+ (0-1.0) x 10/sup -2/ M. On the basis of considering the dependence of kinetic exchange characteristics on the value of initial Ln/sup 3 +/ and Cu/sup 2 +/ concentrations it is shown that stability constant of appearing intermediate binuclear complex (NdACu/sup 2 +/) correlates with stability constant of copper acetate, i.e. incoming Cu/sup 2 +/ cation coordinates by EDTA acetogroup at the first stage of reaction. Stability constant of (ErACu/sup +/) correlates with outer spheric association constant, i.e. at the earlier exchange stage in the associative mechanism in the ErA/sup -/-Cu/sup 2 +/ system, formation of outer spheric associate takes place. Considerable difference in exchange mechanisms for light and heavy rare earths is explained by lesser strength in metal-oxygen bond in initial NdA/sup -/ as compared with ErA/sup -/. Bond strengthening in the initial rare earth complexonate prevents the formation of stable intermediate binuclear complexes which causes decrease in the exchange rate according to the associative mechanism in LuAsup(-)-Mnsup(n+) systems.

Demonstration of mechanical connections between integrins, cytoskeletal filaments, and nucleoplasm that stabilize nuclear structure

Science.gov (United States)

Maniotis, A. J.; Chen, C. S.; Ingber, D. E.

1997-01-01

We report here that living cells and nuclei are hard-wired such that a mechanical tug on cell surface receptors can immediately change the organization of molecular assemblies in the cytoplasm and nucleus. When integrins were pulled by micromanipulating bound microbeads or micropipettes, cytoskeletal filaments reoriented, nuclei distorted, and nucleoli redistributed along the axis of the applied tension field. These effects were specific for integrins, independent of cortical membrane distortion, and were mediated by direct linkages between the cytoskeleton and nucleus. Actin microfilaments mediated force transfer to the nucleus at low strain; however, tearing of the actin gel resulted with greater distortion. In contrast, intermediate filaments effectively mediated force transfer to the nucleus under both conditions. These filament systems also acted as molecular guy wires to mechanically stiffen the nucleus and anchor it in place, whereas microtubules acted to hold open the intermediate filament lattice and to stabilize the nucleus against lateral compression. Molecular connections between integrins, cytoskeletal filaments, and nuclear scaffolds may therefore provide a discrete path for mechanical signal transfer through cells as well as a mechanism for producing integrated changes in cell and nuclear structure in response to changes in extracellular matrix adhesivity or mechanics.

Rare earths production and marketing opportunities

International Nuclear Information System (INIS)

Falconnet, P.G.

1988-01-01

The rare earths (RE) market is relatively small. The total production during 1968 was only 10000 tons (REO) which rose to 27000 tons (REO) during 1985. The three major areas of application, which are volume market for ceric rare earths are catalysts, glass ceramics and metallurgy. Among the other uses of rare earths, the permanent magnets, lamp phosphors and fine ceramics have registered significant growth in RE consumption. Monazite and bastnasite are the main natural source for rare earths and processing of these for one of the rare earths in high demand leads to over production of some others not in demand, thus creating a balance problem. The growth in RE market has always been influenced by the technology shifts and product substitution. For example, the RE consumption during 1974/76 for desulfurization of steel had substantially decreased due to the usage of calcium. Similarly, 1985 had witnessed a drastic cut in the use of REs in fluid cracking due to the introduction of stabilized zeolites which contain less REO. Thus, the overall compound growth rate of demand was only 3.9 % per year during the period 1970-1985. At present, 37 % of the rare earths production goes to the glass/ceramics industry, 33 % for catalyst and 25 % to metallurgy. The price of REs constantly shows a downward trend. This trend coupled with the rapid changes taking place in the various technological fields, demands greater flexibility and high marketing skills from the RE producers. The key factor for future expansion of RE market will be the development of 'high volume' application of ceric rare earths. (author) 2 figs., 8 tabs

Influence of various amount of diatomaceous earth used as cement substitute on mechanical properties of cement paste

Science.gov (United States)

Pokorný, Jaroslav; Pavlíková, Milena; Medved, Igor; Pavlík, Zbyšek; Zahálková, Jana; Rovnaníková, Pavla; Černý, Robert

2016-06-01

Active silica containing materials in the sub-micrometer size range are commonly used for modification of strength parameters and durability of cement based composites. In addition, these materials also assist to accelerate cement hydration. In this paper, two types of diatomaceous earths are used as partial cement replacement in composition of cement paste mixtures. For raw binders, basic physical and chemical properties are studied. The chemical composition of tested materials is determined using classical chemical analysis combined with XRD method that allowed assessment of SiO2 amorphous phase content. For all tested mixtures, initial and final setting times are measured. Basic physical and mechanical properties are measured on hardened paste samples cured 28 days in water. Here, bulk density, matrix density, total open porosity, compressive and flexural strength, are measured. Relationship between compressive strength and total open porosity is studied using several empirical models. The obtained results give evidence of high pozzolanic activity of tested diatomite earths. Their application leads to the increase of both initial and final setting times, decrease of compressive strength, and increase of flexural strength.

The mechanism of translational displacements of the core of the Earth at inversion molten and solidification of substance at core-mantle boundary in opposite hemispheres

Science.gov (United States)

Barkin, Yu. V.

2009-04-01

Shell dynamics. "The Earth represents system of non-spherical eccentric shells (the core, the mantle, a rigid core etc.) which have various structure and distribution of density. Their moments of inertia and dynamic oblatenesses are various. From the point of view of the mechanics it means, that external celestial bodies (the Moon and the Sun) on miscellaneous (differentially) gravitationally act on the separate shells. They try to cause various accelerations to the centers of masses of shells and various angular accelerations to their rotary motions. It the most external celestial bodies put shells of forced body in difficult state, forcing them to push each other to prevent each other and to struggle with each other. That is between shells there are powerful force interactions: additional forces, and more significant on value, than tidal forces, and the huge moments of forces which all time aspire to turn one of shells relatively to another. The external influence is stronger, the shells are pressed more strongly or taken away. If external action weakens, also shells mutually exist more quietly. External influence depends on position of perturbing celestial bodies. But the last vary cyclically in various time scales. It means, that interactions of shells with each other also are cyclic with the set of frequencies being a derivative from basic frequencies of orbital motions of celestial bodies (coincide with basic frequencies or are their various combinations). Clearly, that the specified mechanical interactions are as though primary which generate then a sequence of every possible interactions of all layers of shells, geodynamic and geophysical processes (which are naturally also cyclic). Elastic layers will test deformations, thus absorbing, and then returning a mechanical energy of translatory - rotary motion of shells and their relative swing. Plastic properties of layers of shells will result in absorption of mechanical energy and to its transformation to

On the capacity to the complexing of alkaline earth metal and magnesium chromates

International Nuclear Information System (INIS)

Orekhov, O.L.

1978-01-01

Considered is the capacity to the complexing of magnesium chromates and alkaline earth metal chromates with ammonium chromates in aqueous solutions. It has been established that the complexing of alkaline earth metal and magnesium chromates is effected by a nature of initial salts as well as their solubilities and the presence of crystallization water. Capacity of magnesium ions and alkaline rare earth metals to the complexing decreases in a series of Mg-Ca-Sr-Ba. Ca complexes exceed magnesium derivatives in respect of stability

Effect of molarity in geo polymer earth brick reinforced with fibrous coir wastes using sandy soil and quarry dust as fine aggregate. (Case study

Directory of Open Access Journals (Sweden)

P. Palanisamy

2018-06-01

Full Text Available The studies are mainly carried out on strength development for various grades of geo-polymer mortar with varying molarity (M for producing geo-polymer earth brick (GPEB. The studies are focused on use of more sandy soil sieved from the raw earth available at site and quarry dust on replaced with river sand for making the un-burnt brick. The brick is reinforced with fibrous coir waste to increase shear strength and further pressed by hand compaction. Geo-polymer mortar is based on an inorganic alumina silicate binder system and it has more advantages of quick strength gain, negligence of water curing, best mechanical properties, eco-friendly, sustainable and alternate to ordinary Portland cement (OPC based mortar. Fly Ash (FA, Ground Granulated Blast-furnace Slag (GGBS, sandy soil sieved from earth and Quarry Dust (QD are mixed with alkaline solution in different molarities 6 M, 8 M and 10 M to prepare specimens. Specimens are tested against workability, compressive strength, and water absorption test, rate of water absorption, abraded test and also fiber content of the brick. The research found that the brick is made by FA & GGBS as binders and soil & quarry dust as fine aggregate in ratio of 0.5:0.5:1.75:0.25 with fibrous coir waste 1% and alkaline solution 10 M for preparing mortar to produce, excellent compressive strength, low water absorption, low rate of absorption, good abrasive resistance etc., The new brick is placed an alternate to compressed stabilized earth block, cement block and traditional burnt brick. Keywords: Fiber reinforced geo-polymer earth brick, Geo-polymer mortar using sandy soil and quarry dust as fine-aggregate, Nature fibrous coir wastes, Un-burnt brick, Alternate to compressed stabilized earth block

Origin of the Earth's Electromagnetic Field Based on the Pulsating Mantle Hypothesis (PMH)

Science.gov (United States)

Gholibeigian, Hassan

2017-11-01

In PMH, the Earth's Inner Core's Dislocation (ICD) and Outer Core's Bulge (OCB) phenomena are generated by unbalanced gravitational fields of the Sun and Moon on the Earth. Distance between the Earth's center and inner core's center varies permanently in magnitude and direction inside two hemispheres. Geometrical loci of the inner core's center has the shape of back and force spiral cone in each hemisphere. In other words, the inner core is rotating fast in the outer core inverse of the Earth's rotation a round per day. This mechanism speed up the processes inside the core and generates a Large Scale Forced Convection System (LSFCS) inverse of the Earth's rotation in the core. The LSFCS is the origin of the Earth's electromagnetic field. The LSFCS generates huge mass transfer and momentum of inertia inside the Earth too. The inner core's axis which is the Earth's electromagnetic axis doesn't cross the Earth's geophysical axis and rotates around it per day. The mechanism of this LSFCS has diurnal, monthly and yearly cycles. These cycles are sources of the Earth's electromagnetic field variability. Direction of the variable Earth's magnetic field lines from the South Pole (hemisphere) to the sky and 146 seconds/years apparent solar day length variations can be two observable factors for this mechanism. This dynamic system may occurred inside the other planets like the Sun and the Jupiter.

A review of the chemical and physical mechanisms of the storage stability of fast pyrolysis bio-oils

Energy Technology Data Exchange (ETDEWEB)

Diebold, J.P.

1999-01-27

Understanding the fundamental chemical and physical aging mechanisms is necessary to learn how to produce a bio-oil that is more stable during shipping and storage. This review provides a basis for this understanding and identifies possible future research paths to produce bio-oils with better storage stability.

Rare earth ion controlled crystallization of mica glass-ceramics

Energy Technology Data Exchange (ETDEWEB)

Garai, Mrinmoy; Karmakar, Basudeb, E-mail: basudebk@cgcri.res.in

2016-09-05

In understanding the effects of rare earth ions to control the crystallization and microstructure of alkaline boroaluminosilicate system, the CeO{sub 2}, Nd{sub 2}O{sub 3}, Sm{sub 2}O{sub 3} and Gd{sub 2}O{sub 3} doped K{sub 2}O−MgO−B{sub 2}O{sub 3}−Al{sub 2}O{sub 3}−SiO{sub 2}−F glasses were synthesized by melt-quenching at 1550 °C. Higher density (2.82–3.06 g cm{sup −3}) and thermal stability (glass phase) is experiential on addition of rare earth content, which also affects in increasing the glass transition temperature (T{sub g}) and crystallization temperature (T{sub c}). Decrease of thermal expansion in glasses with rare earth ion content is maintained by the stabilization of glass matrix owing to their large cationic field strength. A significant change in the non-isothermal DSC thermogram observed at 750–1050 °C is attributed to fluorophlogopite crystallization. Opaque glass-ceramics were prepared from such glasses by single step heat-treatment at 1050 °C; and the predominant crystalline phases are identified as fluorophlogopite mica, KMg{sub 3}(AlSi{sub 3}O{sub 10})F{sub 2} by XRD and EDX analysis. The compact glass-ceramic microstructure by the agglomeration of fluorophlogopite mica crystallites (crystal size ∼ 100–500 nm, FESEM) is achieved in attendance of rare earth ion; and such microstructure controlled the variation of density, thermal expansion and microhardness value. Higher thermal expansion (11.11–14.08 × 10{sup −6}/K at 50–800 °C and 50–900 °C) of such glass-ceramics approve that these rare earth containing glasses can be useful for high temperature vacuum sealing application with metal or solid electrolyte. The increase of Vickers microhardness (5.27–5.61 GPa) in attendance of rare earth ions is attributed to the compact crystallinity of fluorophlogopite mica glass-ceramic microstructure. - Highlights: • Synthesis of rare earth oxide doped alkaline boroaluminosilicate glasses. • Development of opaque

Stability mechanisms of a thermophilic laccase probed by molecular dynamics.

Directory of Open Access Journals (Sweden)

Niels J Christensen

Full Text Available Laccases are highly stable, industrially important enzymes capable of oxidizing a large range of substrates. Causes for their stability are, as for other proteins, poorly understood. In this work, multiple-seed molecular dynamics (MD was applied to a Trametes versicolor laccase in response to variable ionic strengths, temperatures, and glycosylation status. Near-physiological conditions provided excellent agreement with the crystal structure (average RMSD ∼0.92 Å and residual agreement with experimental B-factors. The persistence of backbone hydrogen bonds was identified as a key descriptor of structural response to environment, whereas solvent-accessibility, radius of gyration, and fluctuations were only locally relevant. Backbone hydrogen bonds decreased systematically with temperature in all simulations (∼9 per 50 K, probing structural changes associated with enthalpy-entropy compensation. Approaching T opt (∼350 K from 300 K, this change correlated with a beginning "unzipping" of critical β-sheets. 0 M ionic strength triggered partial denucleation of the C-terminal (known experimentally to be sensitive at 400 K, suggesting a general salt stabilization effect. In contrast, F(- (but not Cl(- specifically impaired secondary structure by formation of strong hydrogen bonds with backbone NH, providing a mechanism for experimentally observed small anion destabilization, potentially remedied by site-directed mutagenesis at critical intrusion sites. N-glycosylation was found to support structural integrity by increasing persistent backbone hydrogen bonds by ∼4 across simulations, mainly via prevention of F(- intrusion. Hydrogen-bond loss in distinct loop regions and ends of critical β-sheets suggest potential strategies for laboratory optimization of these industrially important enzymes.

A comparative study of thermal and mechanical stabilities of gamma irradiated ethylene-ethyl acrylate and ethylene-vinyl acetate copolymers

International Nuclear Information System (INIS)

Sen, M.; Gueven, O.

1995-01-01

Ethylene-ethyl acrylate and Ethylene-vinyl acetate copolymers were irradiated in ambient conditions with γ-rays. The influence of the chain scission, crosslinking and relative changes in crystallinity on the thermal and mechanical properties were investigated and a correlation has been tried to find between the thermal and mechanical stabilities of copolymers. For the two copolymers, among various mechanical properties evaluated, the best correlation was found between the toughness (energy to break point) and the time required for 10% weight loss. (Author)

Design of a Single Motor Based Leg Structure with the Consideration of Inherent Mechanical Stability

Science.gov (United States)

Taha Manzoor, Muhammad; Sohail, Umer; Noor-e-Mustafa; Nizami, Muhammad Hamza Asif; Ayaz, Yasar

2017-07-01

The fundamental aspect of designing a legged robot is constructing a leg design that is robust and presents a simple control problem. In this paper, we have successfully designed a robotic leg based on a unique four bar mechanism with only one motor per leg. The leg design parameters used in our platform are extracted from design principles used in biological systems, multiple iterations and previous research findings. These principles guide a robotic leg to have minimal mechanical passive impedance, low leg mass and inertia, a suitable foot trajectory utilizing a practical balance between leg kinematics and robot usage, and the resultant inherent mechanical stability. The designed platform also exhibits the key feature of self-locking. Theoretical tools and software iterations were used to derive these practical features and yield an intuitive sense of the required leg design parameters.

Our sustainable Earth

International Nuclear Information System (INIS)

Orbach, Raymond L

2011-01-01

Recent evidence demonstrates that the Earth has been warming monotonically since 1980. Transient to equilibrium temperature changes take centuries to develop, as oceans are slow to respond to atmospheric temperature changes. Atmospheric CO 2 concentrations, from ice core and observatory measurements, display consistent increases from historical averages, beginning in about 1880, and can be associated with the industrial revolution. The climactic consequences of this human dominated increase in atmospheric CO 2 define a geologic epoch that has been termed the 'Anthropocene.' The issue is whether this is a short term, relatively minor change in global climate, or an extreme deviation that lasts for thousands of years. Eight 'myths' that posit the former are examined in light of known data. The analysis strongly suggests the latter. In order to stabilize global temperatures, sharp reductions in CO 2 emissions are required: an 80% reduction beginning in 2050. Two examples of economically sustainable CO 2 emission reduction demonstrate that technological innovation has the potential to maintain our standard of living while stabilizing global temperatures.

Effect of Ce-rich rare earth on microstructure and mechanical properties of Mg-10Zn-5Al-0.1Sb magnesium alloy

Directory of Open Access Journals (Sweden)

You Zhiyong

2012-05-01

Full Text Available To improve the comprehensive mechanical properties of Mg-10Zn-5Al-0.1Sb magnesium alloy, different amount of Ce-rich rare earth (RE was added to the alloy, and the effect of RE addition on the microstructure and mechanical properties of Mg-10Zn-5Al-0.1Sb alloy was investigated by means of Brinell hardness measurement, scanning electron microscopy (SEM, energy dispersive spectroscope (EDS and X-ray diffraction (XRD. The results show that an appropriate amount of Ce-rich rare earth addition can make the Al4Ce phase particles and CeSb phase disperse more evenly in the alloy. These phases refine the alloy抯 matrix and make the secondary phases [t-Mg32(Al,Zn49 phase and f-Al2Mg5Zn2 phase] finer and more dispersive, therefore significantly improve the mechanical properties of the Mg-10Zn-5Al-0.1Sb alloy. When the RE addition is 1.0 wt.%, the tensile strengths of the alloy both at room temperature and 150 篊 reach the maximum values while the impact toughness is slightly lower than that of the matrix alloy. The hardness increases with the increase of RE addition.

A COMPARATIVE STUDY TO FIND OUT THE EFFECTIVENESS BETWEEN CORE STABILIZATION VS MCKENZIE EXERCISES IN THE TREATMENT OF PATIENTS WITH MECHANICAL LOW BACK PAIN

Directory of Open Access Journals (Sweden)

Abhijit Dutta

2015-10-01

Full Text Available Background: Mechanical Low back pain is a leading cause of disability. It occurs in similar proportions in all cultures, interferes with quality of life and work performance. Both male and female populations are affected; however, there is a tendency towards a higher incidence in male patients. Mechanical low back pain is associated with pain and clinical instability in lumbar motion segments. Exercises play an important part in the rehabilitation of low back pain. The aim of this study was to compare the effectiveness between Core stabilization vs McKenzie exercises in the treatment of patients with mechanical low back pain. Methods: 30 patients were selected between the age groups of 20 yrs to 50 yrs and having a past history of low back pain for one month. 15 patients were allotted to each group of experiment. Group I was given Core stabilization exercises and Group II with McKenzie exercises. Interferential therapy was a common treatment for both the groups. Evaluations of the subjects were done using the Revised Oswestry Disability Index and Dynamic Endurance tests. Results: Data analysis revealed statistically significant difference between both the groups (p<0.05 and proved that Core stabilization exercises is more effective than McKenzie exercises in mechanical low back pain. Conclusion: This study shows that core stabilization exercises possess a greater potential over McKenzie exercises in treating Mechanical Low back pain patients.

Mechanical properties and thermal stability of Al–Fe–Ni alloys prepared by centrifugal atomisation and hot extrusion

Energy Technology Data Exchange (ETDEWEB)

Průša, F., E-mail: Filip.Prusa@vscht.cz; Vojtěch, D.; Michalcová, A.; Marek, I.

2014-05-01

In this work, Al–12Fe and Al–7Fe–5Ni (wt%) alloys prepared by a novel technique including centrifugal atomisation and hot extrusion were studied. The microstructures were investigated using light microscopy, electron scanning microscopy, transmission electron microscopy and X-ray diffraction. The mechanical properties were determined by Vickers hardness measurements and compressive stress–strain tests. To study the thermal stability, the mechanical properties were also measured after 100 h of annealing at 300 °C and 400 °C. In addition, creep tests at a stress of 120 MPa and a temperature of 300 °C were performed. The investigated materials were composed of fine-grained α-Al and intermetallic phases identified as Al{sub 13}Fe{sub 4} and Al{sub 9}FeNi. The Vickers hardness and compressive yield strength were 68 HV5 and 183 MPa, respectively, for the Al–12Fe alloy and 73 HV5 and 226 MPa, respectively, for the Al–7Fe–5Ni alloy. After long-term annealing, the change in the mechanical properties was negligible, indicating the excellent thermal stability of both materials. The creep tests confirmed the highest thermal stability of the Al–7Fe–5Ni alloy with a total compressive creep strain of 15%. The “thermally stable” casting Al–12Si–1Cu–1Mg–1Ni alloy treated by the T6 regime was used as a reference material. The casting alloy exhibited sufficient mechanical properties (hardness and compressive yield strength) at room temperature. However, annealing remarkably softened and reduced its compressive yield strength to almost 50% of the initial values. Additionally, the total creep strain of the casting reference material was almost three times higher than that of the Al–7Fe–5Ni alloy. It has been proven that centrifugally atomised materials quickly compacted via hot extrusion can compete or even exceed the properties of common casting aluminium alloys that are used in automotive industry.

Mechanical properties and thermal stability of Al–Fe–Ni alloys prepared by centrifugal atomisation and hot extrusion

International Nuclear Information System (INIS)

Průša, F.; Vojtěch, D.; Michalcová, A.; Marek, I.

2014-01-01

In this work, Al–12Fe and Al–7Fe–5Ni (wt%) alloys prepared by a novel technique including centrifugal atomisation and hot extrusion were studied. The microstructures were investigated using light microscopy, electron scanning microscopy, transmission electron microscopy and X-ray diffraction. The mechanical properties were determined by Vickers hardness measurements and compressive stress–strain tests. To study the thermal stability, the mechanical properties were also measured after 100 h of annealing at 300 °C and 400 °C. In addition, creep tests at a stress of 120 MPa and a temperature of 300 °C were performed. The investigated materials were composed of fine-grained α-Al and intermetallic phases identified as Al 13 Fe 4 and Al 9 FeNi. The Vickers hardness and compressive yield strength were 68 HV5 and 183 MPa, respectively, for the Al–12Fe alloy and 73 HV5 and 226 MPa, respectively, for the Al–7Fe–5Ni alloy. After long-term annealing, the change in the mechanical properties was negligible, indicating the excellent thermal stability of both materials. The creep tests confirmed the highest thermal stability of the Al–7Fe–5Ni alloy with a total compressive creep strain of 15%. The “thermally stable” casting Al–12Si–1Cu–1Mg–1Ni alloy treated by the T6 regime was used as a reference material. The casting alloy exhibited sufficient mechanical properties (hardness and compressive yield strength) at room temperature. However, annealing remarkably softened and reduced its compressive yield strength to almost 50% of the initial values. Additionally, the total creep strain of the casting reference material was almost three times higher than that of the Al–7Fe–5Ni alloy. It has been proven that centrifugally atomised materials quickly compacted via hot extrusion can compete or even exceed the properties of common casting aluminium alloys that are used in automotive industry

The Geostationary Earth Radiation Budget Project.

Science.gov (United States)

Harries, J. E.; Russell, J. E.; Hanafin, J. A.; Brindley, H.; Futyan, J.; Rufus, J.; Kellock, S.; Matthews, G.; Wrigley, R.; Last, A.; Mueller, J.; Mossavati, R.; Ashmall, J.; Sawyer, E.; Parker, D.; Caldwell, M.; Allan, P. M.; Smith, A.; Bates, M. J.; Coan, B.; Stewart, B. C.; Lepine, D. R.; Cornwall, L. A.; Corney, D. R.; Ricketts, M. J.; Drummond, D.; Smart, D.; Cutler, R.; Dewitte, S.; Clerbaux, N.; Gonzalez, L.; Ipe, A.; Bertrand, C.; Joukoff, A.; Crommelynck, D.; Nelms, N.; Llewellyn-Jones, D. T.; Butcher, G.; Smith, G. L.; Szewczyk, Z. P.; Mlynczak, P. E.; Slingo, A.; Allan, R. P.; Ringer, M. A.

2005-07-01

This paper reports on a new satellite sensor, the Geostationary Earth Radiation Budget (GERB) experiment. GERB is designed to make the first measurements of the Earth's radiation budget from geostationary orbit. Measurements at high absolute accuracy of the reflected sunlight from the Earth, and the thermal radiation emitted by the Earth are made every 15 min, with a spatial resolution at the subsatellite point of 44.6 km (north south) by 39.3 km (east west). With knowledge of the incoming solar constant, this gives the primary forcing and response components of the top-of-atmosphere radiation. The first GERB instrument is an instrument of opportunity on Meteosat-8, a new spin-stabilized spacecraft platform also carrying the Spinning Enhanced Visible and Infrared (SEVIRI) sensor, which is currently positioned over the equator at 3.5°W. This overview of the project includes a description of the instrument design and its preflight and in-flight calibration. An evaluation of the instrument performance after its first year in orbit, including comparisons with data from the Clouds and the Earth's Radiant Energy System (CERES) satellite sensors and with output from numerical models, are also presented. After a brief summary of the data processing system and data products, some of the scientific studies that are being undertaken using these early data are described. This marks the beginning of a decade or more of observations from GERB, as subsequent models will fly on each of the four Meteosat Second Generation satellites.

The Relationship Between Postural and Movement Stability.

Science.gov (United States)

Feldman, Anatol G

2016-01-01

Postural stabilization is provided by stretch reflexes, intermuscular reflexes, and intrinsic muscle properties. Taken together, these posture-stabilizing mechanisms resist deflections from the posture at which balance of muscle and external forces is maintained. Empirical findings suggest that for each muscle, these mechanisms become functional at a specific, spatial threshold-the muscle length or respective joint angle at which motor units begin to be recruited. Empirical data suggest that spinal and supraspinal centers can shift the spatial thresholds for a group of muscles that stabilized the initial posture. As a consequence, the same stabilizing mechanisms, instead of resisting motion from the initial posture, drive the body to another stable posture. In other words by shifting spatial thresholds, the nervous system converts movement resisting to movement-producing mechanisms. It is illustrated that, contrary to conventional view, this control strategy allows the system to transfer body balance to produce locomotion and other actions without loosing stability at any point of them. It also helps orient posture and movement with the direction of gravity. It is concluded that postural and movement stability is provided by a common mechanism.

SmartScan: a robust pushbroom imaging concept for moderate spacecraft attitude stability

Science.gov (United States)

Janschek, K.; Tchernykh, V.; Dyblenko, S.; Harnisch, B.

2017-11-01

Pushbroom scan cameras with linear image sensors, commonly used for Earth observation from satellites, require high attitude stability during the image acquisition. Especially noticeable are the effects of high frequency attitude variations originating from micro shocks and vibrations, produced by momentum and reaction wheels, mechanically activated coolers, steering and deployment mechanics and other reasons. The SMARTSCAN imaging concept offers high quality imaging even with moderate satellite attitude stability on a sole opto-electronic basis without any moving parts. It uses real-time recording of the actual image motion in the focal plane of the remote sensing camera during the frame acquisition and a posteriori correction of the obtained image distortions on base of the image motion record. Exceptional real-time performances with subpixel accuracy image motion measurement are provided by an innovative high-speed onboard optoelectronic correlation processor. SMARTSCAN allows therefore using smart pushbroom cameras for hyper-spectral imagers on satellites and platforms which are not specially intended for imaging missions, e.g. micro satellites. The paper gives an overview on the system concept and main technologies used (advanced optical correlator for ultra high-speed image motion tracking), it discusses the conceptual design for a smart compact space camera and it reports on airborne test results of a functional breadboard model.

Glow phenomenon surrounding the vertical stabilizer and OMS pods

Science.gov (United States)

1994-01-01

This 35mm frame, photographed as the Space Shuttle Columbia was orbiting Earth during a 'night' pass, documents the glow phenomenon surrounding the vertical stabilizer and the Orbital Maneuvering System (OMS) pods of the spacecraft.

Rankine earth pressure theory considering microstructure of porous materials

Science.gov (United States)

Li, Junhu; Xue, Wei; Zhang, Chao; Zhang, Wenchao; Xu, Riqing

2017-11-01

Soil as an engineering material has very complex properties, such as non-continuous, non-uniformity and nonlinear mechanical. In a certain extent, macroscopic properties of soil are affected by the changes of the microstructure. And microscopic porosity of soft clay and its influencing factors, the relationship between macro and micro porosity, the average contact area rate and its influencing factors are studied. Some mechanics problems were analyzed by using the relationship between macro-porosity and the average contact area rate. Combining soil lateral stress transfer principle, a calculation theory of earth pressure considering soil contact area was got. The possible reason of the differences between earth pressure and the actual monitoring earth pressure was analyzed by the case.

Indefinite damping in mechanical systems and gyroscopic stabilization

DEFF Research Database (Denmark)

Kliem, Wolfhard; Pommer, Christian

2009-01-01

This paper deals with gyroscopic stabilization of the unstable system Mx + D(x) over dot + K-x = 0, with positive definite mass and stiffness matrices M and K, respectively, and an indefinite damping matrix D. The main question if for which skew-symmetric matrices G the system Mx (D+ G)(x) over dot...... + K-x = 0 can become stable? After investigating special cases we find an appropriat solution of the Lyapunov matrix equation for the general case. Examples show the deviation of the stability limit found by the Lyapunov method from the exact value....

Mechanical and Hydrologic Effects of Riparian Vegetation on Critical Conditions for Streambank Stability: Upper Truckee River, California

Science.gov (United States)

Simon, A.; Pollen, N. L.; Langendoen, E. J.

2005-05-01

The Upper Truckee River is the single largest contributor of sediment to Lake Tahoe with a large proportion of the suspended-sediment load coming from eroding streambanks. Recent advances in quantifying streambank processes highlight the combined effects of hydraulic erosion at the bank toe with geotechnical stability of the upper part of the bank and resulted in the development of a deterministic model of bank-toe erosion and streambank stability (Simon et al., 1999). The use of riparian vegetation in schemes of bank stabilization and stream restoration have become popular but are often implemented on a trial and error basis because of a lack of quantifiable information on the mechanical and hydrologic effects of vegetation on bank stability. This study, conducted along an unstable reach of the Upper Truckee River, combines field data with numerical modeling to quantify (1) hydraulic and geotechnical driving and resisting forces that control bank failures, (2) the mechanical and hydrologic effects of vegetation on shear strength, and (3) the critical conditions for bank stability with and without indigenous riparian species. Tests were conducted using three top-bank treatments: bare (control), Lemmon's willow, and young Lodgepole pine. The susceptibility of the bank toe to erosion by hydraulic forces was quantified by conducting submerged jet tests of in situ material to determine the erodibility coefficient (k) and the critical shear stress of the material. Drained, shear-strength parameters (cohesion and friction angle) of the banks were determined from borehole shear tests at various depths. Pore-water pressure and matric suction were monitored at three depths (30, 100, and 150 cm) with digital tensiometers to calculate changes in apparent cohesion for the period (September 2003 - May 2004) and to differentiate between the hydrologic effects of the two species. Root reinforcement of the two species was quantified by determining the relation between root

Quantum Mechanical Earth: Where Orbitals Become Orbits

Science.gov (United States)

Keeports, David

2012-01-01

Macroscopic objects, although quantum mechanical by nature, conform to Newtonian mechanics under normal observation. According to the quantum mechanical correspondence principle, quantum behavior is indistinguishable from classical behavior in the limit of very large quantum numbers. The purpose of this paper is to provide an example of the…

Solvent dielectric effect and side chain mutation on the structural stability of Burkholderia cepacia lipase active site: a quantum mechanical/molecular mechanics study.

Science.gov (United States)

Tahan, A; Monajjemi, M

2011-12-01

Quantum mechanical and molecular dynamics methods were used to analyze the structure and stability of neutral and zwitterionic configurations of the extracted active site sequence from a Burkholderia cepacia lipase, histidyl-seryl-glutamin (His86-Ser87-Gln88) and its mutated form, histidyl-cysteyl-glutamin (His86-Cys87-Gln88) in vacuum and different solvents. The effects of solvent dielectric constant, explicit and implicit water molecules and side chain mutation on the structure and stability of this sequence in both neutral and zwitterionic forms are represented. The quantum mechanics computations represent that the relative stability of zwitterionic and neutral configurations depends on the solvent structure and its dielectric constant. Therefore, in vacuum and the considered non-polar solvents, the neutral form of the interested sequences is more stable than the zwitterionic form, while their zwitterionic form is more stable than the neutral form in the aqueous solution and the investigated polar solvents in most cases. However, on the potential energy surfaces calculated, there is a barrier to proton transfer from the positively charged ammonium group to the negatively charged carboxylat group or from the ammonium group to the adjacent carbonyl oxygen and or from side chain oxygen and sulfur to negatively charged carboxylat group. Molecular dynamics simulations (MD) were also performed by using periodic boundary conditions for the zwitterionic configuration of the hydrated molecules in a box of water molecules. The obtained results demonstrated that the presence of explicit water molecules provides the more compact structures of the studied molecules. These simulations also indicated that side chain mutation and replacement of sulfur with oxygen leads to reduction of molecular flexibility and packing.

Synthesis and characterization of anionic rare-earth metal amides stabilized by phenoxy-amido ligands and their catalytic behavior for the polymerization of lactide.

Science.gov (United States)

Lu, Min; Yao, Yingming; Zhang, Yong; Shen, Qi

2010-10-28

A dianionic phenoxyamido ligand was the first to be used to stabilize organo-rare-earth metal amido complexes. Amine elimination reaction of Nd[N(TMS)(2)](3)(μ-Cl)Li(THF)(3) (TMS = SiMe(3)) with aminophenol [HNOH] {[HNOH] = N-p-methylphenyl(2-hydroxy-3,5-di-tert-butyl)benzylamine} in a 1 : 1 molar-ratio gave the anionic phenoxyamido neodymium amide [NO](2)Nd[N(TMS)(2)][Li(THF)](2) (2) in a low isolated yield. A further study revealed that the stoichiometric reactions of Ln[N(TMS)(2)](3)(μ-Cl)Li(THF)(3) with the lithium aminophenoxy [HNOLi(THF)](2) (1) in tetrahydrofuran (THF) gave the anionic rare-earth metal amido complexes [NO](2)Ln[N(TMS)(2)][Li(THF)](2) [Ln = Nd (2), Sm (3), Yb (4), Y (5)] in high isolated yields. All of these complexes are fully characterized. X-Ray structure determination revealed that complex 1 has a solvated dimeric structure, and complexes 2-5 are isostructural, and have solvated monomeric structures. Each of the rare-earth metal ions is coordinated by two oxygen atoms and two nitrogen atoms from two phenoxyamido ligands and one nitrogen atom from the N(TMS)(2) group to form a distorted trigonal bipyramidal geometry. Each of the lithium atoms in complexes 2-5 is coordinated with one oxygen atom and one nitrogen atom from two different phenoxyamido groups, and one oxygen atom from one THF molecule to form a trigonal planar geometry. Furthermore, the catalytic behavior of complexes 2-5 for the ring-opening polymerization of l-lactide was explored.

Lead telluride with increased mechanical stability for cylindrical thermoelectric generators

International Nuclear Information System (INIS)

Schmitz, Andreas

2013-01-01

The aim of this work is to improve the mechanical stability of lead telluride (PbTe), trying to vary its mechanical properties independently from its thermoelectric properties. Thus the influence of material preparation as well as different dopants on the mechanical and thermoelectric properties of lead telluride is being analysed. When using appropriately set process parameters, milling and sintering of lead telluride increases the material's hardness. With sintering temperatures exceeding 300 C stable material of high relative density can be achieved. Milling lead telluride generates lattice defects leading to a reduction of the material's charge carrier density. These defects can be reduced by increased sintering temperatures. Contamination of the powder due to the milling process leads to bloating during thermal cycling and thus reduced density of the sintered material. In addition to that, evaporation of tellurium at elevated temperatures causes instability of the material's thermoelectric properties. Based on the experimental results obtained in this work, the best thermoelectric and mechanical properties can be obtained by sintering coarse powders at around 400 C. Within this work a concept was developed to vary the mechanical properties of lead telluride via synthesis of PbTe with electrically nondoping elements, which thus may keep the thermoelectric properties unchanged. Therefore, the mechanical and thermoelectric properties of Pb 1-x Ca x Te were investigated. Doping pure PbTe with calcium causes a significant increase of the material's hardness while only slightly decreasing the charge carrier density and thus keeping the thermoelectric properties apart from a slight reduction of the electrical conductivity nearly unchanged. The abovementioned concept is proven using sodium doped lead telluride, as it is used for thermoelectric generators: The additional doping with calcium again increases the material's hardness while its thermoelectric properties

The Influence of Irganox 245 on Crystallinity and Mechanics Stability of Polypropylene-Natural Rubber Poly blends

International Nuclear Information System (INIS)

Mashuri; Kristiawan Setia; Darminto; Aloma KK; Sudirman

2008-01-01

The influence of irganox 245 on crystallinity and mechanics stability of polyethylene (PP)- Natural Rubber (NR) poly blends exposure by sunlight for 12 weeks has been studied. For optimalization of antioxidant function to reduce oxidation in PP-NR (4:1) poly blends irganox 245 with variation concentration of 4 %, 6 %, 8 % and 10 % vol were added. Poly blends was made by blending method at 170 o C for 10 minutes with form an 30 rpm. The result showed that irganox 245 could not increasing adhesion at the interface between PP-NR, so PP-NR still immiscible blends. The optimal concentrations of irganox 245 as antioxidant on PP-NR poly blends is 8 % vol. PP-NR-irganox 245 8 % vol have decreasing tensile strength up to 6 % and increasing elongation at break up to 50 % in exposure by sunlight at long time 8 weeks but for 12 weeks tensile strength and elongation at break very weaks. Crystallinity and mechanics stability of PP-NR-irganox 245 8 % vol better than PP-NR poly blends, it is showed by slowly defects and decreasing crystallinity up to 9 % for exposure 12 weeks. (author)

Space exercise and Earth benefits.

Science.gov (United States)

Macias, Brandon R; Groppo, Eli R; Eastlack, Robert K; Watenpaugh, Donald E; Lee, Stuart M C; Schneider, Suzanne M; Boda, Wanda L; Smith, Scott M; Cutuk, Adnan; Pedowitz, Robert A; Meyer, R Scott; Hargens, Alan R

2005-08-01

The detrimental impact of long duration space flight on physiological systems necessitates the development of exercise countermeasures to protect work capabilities in gravity fields of Earth, Moon and Mars. The respective rates of physiological deconditioning for different organ systems during space flight has been described as a result of data collected during and after missions on the Space Shuttle, International Space Station, Mir, and bed rest studies on Earth. An integrated countermeasure that simulates the body's hydrostatic pressure gradient, provides mechanical stress to the bones and muscles, and stimulates the neurovestibular system may be critical for maintaining health and well being of crew during long-duration space travel, such as a mission to Mars. Here we review the results of our studies to date of an integrated exercise countermeasure for space flight, lower body negative pressure (LBNP) treadmill exercise, and potential benefits of its application to athletic training on Earth. Additionally, we review the benefits of Lower Body Positive Pressure (LBPP) exercise for rehabilitation of postoperative patients. Presented first are preliminary data from a 30-day bed rest study evaluating the efficacy of LBNP exercise as an integrated exercise countermeasure for the deconditioning effects of microgravity. Next, we review upright LBNP exercise as a training modality for athletes by evaluating effects on the cardiovascular system and gait mechanics. Finally, LBPP exercise as a rehabilitation device is examined with reference to gait mechanics and safety in two groups of postoperative patients.

The Influence Of Loam Type And Cement Content On The Compressive Strength Of Rammed Earth

Directory of Open Access Journals (Sweden)

Narloch P. L.

2015-03-01

Full Text Available Currently, a worldwide dynamic rise of interest in using soil as a construction material can be observed. This trend is evident in the rapid rise of the amount of standards that deal with soil techniques. In 2012 the number of standards was larger by one third than five years prior. To create a full standardization of the rammed earth technique it is necessary to take into account the diversity of used soil and stabilizing additives. The proportion of the components, the process of element production and the research methods must also be made uniform. The article describes the results of research on the compressive strength of rammed earth samples that differed from each other with regards to the type of loam used for the mixture and the amount of the stabilizer. The stabilizer used was Portland cement CEM I 42.5R. The research and the analysis of the results were based on foreign publications, the New Zealand standard NZS 4298:1998, the American Standard NMAC14.7.4 and archival Polish Standards from the 1960’s that dealt with earth material.

Influence of Zr and nano-Y{sub 2}O{sub 3} additions on thermal stability and improved hardness in mechanically alloyed Fe base ferritic alloys

Energy Technology Data Exchange (ETDEWEB)

Kotan, Hasan, E-mail: hkotan@konya.edu.tr [Department of Metallurgical Engineering and Materials Science, Necmettin Erbakan University, Dere Aşıklar Mah. Demet Sokak, Meram, Konya 42140 (Turkey); Darling, Kris A. [U.S. Army Research Laboratory, Weapons and Materials Research Directorate, RDRL-WMM-F, Aberdeen Proving Ground, MD 21005-5069 (United States); Scattergood, Ronald O.; Koch, Carl C. [Department of Materials Science and Engineering, NC State University, 911 Partners Way, Room 3078, Raleigh, NC 27695-7907 (United States)

2014-12-05

The motivation of this work was driven to improve the thermal stability in systems where polymorphic transformations can result in an additional driving force, upsetting the expected thermodynamic stability. In this study, Fe{sub 92}Ni{sub 8} alloys with Zr and nano-Y{sub 2}O{sub 3} additions were produced by ball milling and then annealed at high temperatures. Emphasis was placed on understanding the effects of dispersed nano-Y{sub 2}O{sub 3} particle additions and their effect on microstructural stability at and above the bcc-to-fcc transformation occurring at 700 °C in Fe–Ni systems. Results reveal that microstructural stability and hardness can be promoted by a combination of Zr and Y{sub 2}O{sub 3} additions, that being mostly effective for stability before and after phase transition, respectively. The mechanical strength of these alloys is achieved by a unique microstructure comprised a ultra-fine grain Fe base matrix, which contains dispersions of both nano-scale in-situ formed Zr base intermetallics and ex-situ added Y{sub 2}O{sub 3} secondary oxide phases. Both of these were found to be essential for a combination of high thermal stability and high mechanical strength properties. - Highlights: • Polymorphic transformations can limit the processing of nanostructured powders. • It causes a rapid grain growth and impairs the improved mechanical properties. • We aim to improve the hardness and thermal stability above the phase transformation. • Thermal stability is achieved by a combination of Zr and Y{sub 2}O{sub 3} additions. • Hardness is promoted by in-situ formed and ex-situ added secondary nano phases.

Time domain optical memories using rare earth ions

International Nuclear Information System (INIS)

Sellars, M.J.; Dyke, T.; Pryde, G.J.; Manson, N.B.

1998-01-01

Full text: Rare earth doped crystals are the chosen materials for the next generation of optical memories where the process of spectral holeburning can be employed to provide an extra dimension of frequency or time to spatial dimensions and with certain rare earth ions increases of the order of 10 7 in storage capacity can be achieved over conventional optical memories. Time domain techniques are preferred over frequency domain techniques and are now well developed. In these techniques arbitrary pulse sequences are stored in the material and read out at some later time with a single read pulse using a stimulated photon echo process. Long pulse sequences will enable more data to be stored but necessitates the use of materials with long dephasing times (corresponding to narrow spectral lines) and it is this characteristic of rare earth systems that makes them the preferred material for the new time domain optical memories. The storage time can range from hours to days but in a practical device will require refreshing or re-enforcing and this puts special requirements on the stability of the laser used for storing the information. The storage process itself can also be weak and more reliable storage can be achieved by recording the data several times with the same pulse sequence. For this to be successful the laser must be at held at a constant frequency and be stable in phase over the entire duration of the pulse sequence. The procedure of reinforcing the data sequence has been proposed before and attempted without attention to the laser frequency stability. However, if the laser is not stable although some data bits will be reinforced or increased in size others will be decreased or even erased. Indeed the reliability of the memory is degraded by the introducing the rewrite process. For our work we have developed a laser with the excellent stability and able to demonstrate reproducible reinforcement of the data sequence. Thus with the rewrite sequence we are able to

Rare-earth transition-metal intermetallics: Structure-bonding-property relationships

Energy Technology Data Exchange (ETDEWEB)

Han, M. K. [Iowa State Univ., Ames, IA (United States)

2006-01-01

The explorations of rare-earth, transition metal intermetallics have resulted in the synthesis and characterization, and electronic structure investigation, as well as understanding the structure-bonding property relationships. The work has presented the following results: (1) Understanding the relationship between compositions and properties in LaFe_13-xSi_x system: A detailed structural and theoretical investigation provided the understanding of the role of a third element on stabilizing the structure and controlling the transformation of cubic NaZn{sub 13}-type structures to the tetragonal derivative, as well as the relationship between the structures and properties. (2) Synthesis of new ternary rare-earth iron silicides Re_2-xFe₄Si_14-y and proposed superstructure: This compound offers complex structural challenges such as fractional occupancies and their ordering in superstructure. (3) Electronic structure calculation of FeSi₂: This shows that the metal-semiconductor phase transition depends on the structure. The mechanism of band gap opening is described in terms of bonding and structural distortion. This result shows that the electronic structure calculations are an essential tool for understanding the relationship between structure and chemical bonding in these compounds. (4) Synthesis of new ternary rare-earth Zinc aluminides Tb₃Zn_3.6Al_7.4: Partially ordered structure of Tb₃Zn_3.6Al_7.4 compound provides new insights into the formation, composition and structure of rare-earth transition-metal intermetallics. Electronic structure calculations attribute the observed composition to optimizing metal-metal bonding in the electronegative (Zn, Al) framework, while the specific ordering is strongly influenced by specific orbital interactions. (5) Synthesis of new structure type of Zn₃₉(Cr_xAl_1-x)₈₁

Rare-Earth Transition-Metal Intermetallics: Structure-bonding-Property Relationships

Energy Technology Data Exchange (ETDEWEB)

Han, Mi-Kyung [Iowa State Univ., Ames, IA (United States)

2006-01-01

Our explorations of rare-earth, transition metal intermetallics have resulted in the synthesis and characterization, and electronic structure investigation, as well as understanding the structure-bonding-property relationships. Our work has presented the following results: (1) Understanding the relationship between compositions and properties in LaFe_13-xSi_x system: A detailed structural and theoretical investigation provided the understanding of the role of a third element on stabilizing the structure and controlling the transformation of cubic NaZn₁₃-type structures to the tetragonal derivative, as well as the relationship between the structures and properties. (2) Synthesis of new ternary rare-earth iron silicides RE_2-xFe₄Si_14-y and proposed superstructure: This compound offers complex structural challenges such as fractional occupancies and their ordering in superstructure. (3) Electronic structure calculation of FeSi₂: This shows that the metal-semiconductor phase transition depends on the structure. The mechanism of band gap opening is described in terms of bonding and structural distortion. This result shows that the electronic structure calculations are an essential tool for understanding the relationship between structure and chemical bonding in these compounds. (4) Synthesis of new ternary rare-earth Zinc aluminides Tb₃Zn_3.6Al_7.4: Partially ordered structure of Tb_3.6Zn_13-xAl_7.4 compound provides new insights into the formation, composition and structure of rare-earth transition-metal intermetallics. Electronic structure calculations attribute the observed composition to optimizing metal-metal bonding in the electronegative (Zn, Al) framework, while the specific ordering is strongly influenced by specific orbital interactions. (5) Synthesis of new structure type of Zn₃₉(Cr_xAl_1-x

The effect of relativity on stability of Copernicium phases, their electronic structure and mechanical properties

Science.gov (United States)

Čenčariková, Hana; Legut, Dominik

2018-05-01

The phase stability of the various crystalline structures of the super-heavy element Copernicium was determined based on the first-principles calculations with different levels of the relativistic effects. We utilized the Darwin term, mass-velocity, and spin-orbit interaction with the single electron framework of the density functional theory while treating the exchange and correlation effects using local density approximations. It is found that the spin-orbit coupling is the key component to stabilize the body-centered cubic (bcc) structure over the hexagonal closed packed (hcp) structure, which is in accord with Sol. Stat. Comm. 152 (2012) 530, but in contrast to Atta-Fynn and Ray (2015) [11], Gaston et al. (2007) [10], Papaconstantopoulos (2015) [9]. It seems that the main role here is the correct description of the semi-core relativistic 6p1/2 orbitals. The all other investigated structures, i.e. face-centered cubic (fcc) , simple cubic (sc) as well as rhombohedral (rh) structures are higher in energy. The criteria of mechanical stability were investigated based on the calculated elastic constants, identifying the phase instability of fcc and rh structures, but surprisingly confirm the stability of the energetically higher sc structure. In addition, the pressure-induced structural transition between two stable sc and bcc phases has been detected. The ground-state bcc structure exhibits the highest elastic anisotropy from single elements of the Periodic table. At last, we support the experimental findings that Copernicium is a metal.

Analysis of mechanical behavior of soft rocks and stability control in deep tunnels

Directory of Open Access Journals (Sweden)

Hui Zhou

2014-06-01

Full Text Available Due to the weakness in mechanical properties of chlorite schist and the high in situ stress in Jinping II hydropower station, the rock mass surrounding the diversion tunnels located in chlorite schist was observed with extremely large deformations. This may significantly increase the risk of tunnel instability during excavation. In order to assess the stability of the diversion tunnels laboratory tests were carried out in association with the petrophysical properties, mechanical behaviors and water-weakening properties of chlorite schist. The continuous deformation of surrounding rock mass, the destruction of the support structure and a large-scale collapse induced by the weak chlorite schist and high in situ stress were analyzed. The distributions of compressive deformation in the excavation zone with large deformations were also studied. In this regard, two reinforcement schemes for the excavation of diversion tunnel bottom section were proposed accordingly. This study could offer theoretical basis for deep tunnel construction in similar geological conditions.

Polyacrylonitrile nanofibers with added zeolitic imidazolate frameworks (ZIF-7) to enhance mechanical and thermal stability

Energy Technology Data Exchange (ETDEWEB)

Lee, Min Wook [Department of Mechanical and Industrial Engineering, University of Illinois at Chicago, 842 W. Taylor St., Chicago, Illinois 60607-7022 (United States); An, Seongpil; Song, Kyo Yong; Joshi, Bhavana N.; Jo, Hong Seok; Yoon, Sam S., E-mail: skyoon@korea.ac.kr, E-mail: ayarin@uic.edu [School of Mechanical Engineering, Korea University, Seoul 136-713 (Korea, Republic of); Al-Deyab, Salem S. [Department of Chemistry, King Saud University, Riyadh 11451 (Saudi Arabia); Yarin, Alexander L., E-mail: skyoon@korea.ac.kr, E-mail: ayarin@uic.edu [Department of Mechanical and Industrial Engineering, University of Illinois at Chicago, 842 W. Taylor St., Chicago, Illinois 60607-7022 (United States); School of Mechanical Engineering, Korea University, Seoul 136-713 (Korea, Republic of)

2015-12-28

Zeolitic imidazolate framework 7/polyacrylonitrile (ZIF-7/PAN) nanofiber mat of high porosity and surface area can be used as a flexible fibrous filtration membrane that is subjected to various modes of mechanical loading resulting in stresses and strains. Therefore, the stress-strain relation of ZIF-7/PAN nanofiber mats in the elastic and plastic regimes of deformation is of significant importance for numerous practical applications, including hydrogen storage, carbon dioxide capture, and molecular sensing. Here, we demonstrated the fabrication of ZIF-7/PAN nanofiber mats via electrospinning and report their mechanical properties measured in tensile tests covering the elastic and plastic domains. The effect of the mat fabrication temperature on the mechanical properties is elucidated. We showed the superior mechanical strength and thermal stability of the compound ZIF-7/PAN nanofiber mats in comparison with that of pure PAN nanofiber mats. Material characterization including scanning electron microscope, energy-dispersive X-ray spectroscopy, tensile tests, differential scanning calorimetry, and Fourier transform infrared spectroscopy revealed the enhanced chemical bonds of the ZIF-7/PAN complex.

Microstructure and mechanical properties of multi-components rare earth oxide-doped molybdenum alloys

International Nuclear Information System (INIS)

Zhang Guojun; Sun Yuanjun; Zuo Chao; Wei Jianfeng; Sun Jun

2008-01-01

Pure molybdenum and molybdenum alloys doped with two- or three-components rare earth oxide particles were prepared by powder metallurgy. Both the tensile property and fracture toughness of the pure molybdenum and multi-components rare earth oxide-doped molybdenum alloys were determined at room temperature. The multi-components rare earth oxide-doped molybdenum alloys are fine grained and contain a homogeneous distribution of fine particles in the submicron and nanometer size ranges, which is why the molybdenum alloys have higher strength and fracture toughness than pure molybdenum. Quantitative analysis is used to explain the increase in yield strength with respect to grain size and second phase strengthening. Furthermore, the relationship between the tensile properties and microstructural parameters is quantitatively established

A Remark on Dilaton Stabilization

CERN Document Server

Dvali, Gia; Dvali, Gia; Kakushadze, Zurab

1998-01-01

Dilaton stabilization may occur in a theory based on a single asymptotically free gauge group with matter due to an interplay between quantum modification of the moduli space and tree-level superpotential. We present a toy model where such a mechanism is realized. Dilaton stabilization in this mechanism tends to occur at strong coupling values unless some unnatural adjustment of parameters is involved.

[Study on mechanism of SOM stabilization of paddy soils under long-term fertilizations].

Science.gov (United States)

Luo, Lu; Zhou, Ping; Tong, Cheng-Li; Shi, Hui; Wu, Jin-Shui; Huang, Tie-Ping

2013-02-01

Fourier transform infrared spectroscopy (FTIR) was applied to study the structure of soil organic matter (SOM) of paddy soils under long-term different fertilization treatments. The aim was to clarify the different distribution of SOM between different fertilization methods and between topsoil and subsoil, and to explore the stability mechanism of SOM under different fertilization treatments. The results showed that the content of topsoil organic carbon (SOC) was the highest under organic-inorganic fertilizations, with the increment of SOC by 18.5%, 12.9% and 18.4% under high organic manure (HOM), low organic manure (LOM) and straw returning (STW) respectively compared with no fertilization treatment (CK). The long-term fertilizations also changed the chemical structure of SOM. As compared with CK, different fertilization treatments increased the functional group absorbing intensity of chemical resistance compounds (aliphatic, aromaticity), carbohydrate and organo-silicon compounds, which was the most distinctive under treatments of HOM, LOM and STW. For example, the absorbing intensity of alkyl was 0.30, 0.25 and 0.29 under HOM, LOM and STW, respectively. These values were increased by 87% , 56% and 81% as compared with that under CK treatment. The functional group absorbing intensity of SOM in the topsoil was stronger than that in the subsoil, with the most distinctive difference under HOM, LOM and STW treatments. The present research indicated that the enhanced chemical resistance of functional group of SOM may contribute to the high contents of SOC in the paddy soils under long-term organic-inorganic fertilizations, which also suggested a chemical stabilization mechanism of SOM in the paddy soils.

On the spacecraft attitude stabilization in the orbital frame

Directory of Open Access Journals (Sweden)

Antipov Kirill A.

2012-01-01

Full Text Available The paper deals with spacecraft in the circular near-Earth orbit. The spacecraft interacts with geomagnetic field by the moments of Lorentz and magnetic forces. The octupole approximation of the Earth’s magnetic field is accepted. The spacecraft electromagnetic parameters, namely the electrostatic charge moment of the first order and the eigen magnetic moment are the controlled quasiperiodic functions. The control algorithms for the spacecraft electromagnetic parameters, which allows to stabilize the spacecraft attitude position in the orbital frame are obtained. The stability of the spacecraft stabilized orientation is proved both analytically and by PC computations.

Stability of the high pressure phase Fe3S2 up to Earth's core pressures in the Fe-S-O and the Fe-S-Si systems

Science.gov (United States)

Zurkowski, C. C.; Chidester, B.; Davis, A.; Brauser, N.; Greenberg, E.; Prakapenka, V. B.; Campbell, A.

2017-12-01

Earth's core is comprised of an iron-nickel alloy that contains 5-15% of a light element component. The abundance and alloying capability of sulfur, silicon and oxygen in the bulk Earth make them important core alloy candidates; therefore, the high-pressure phase equilibria of the Fe-S-O and Fe-S-Si systems are relevant for understanding the possible chemistry of Earth's core. Previously, a Fe3S2 phase was recognized as a low-pressure intermediate phase in the Fe-FeS system that is stable from 14-21 GPa, but the structure of this phase has not been resolved. We report in-situ XRD and chemical analysis of recovered samples to further examine the stability and structure of Fe3S2 as it coexists with other phases in the Fe-S-O and Fe-S-Si systems. In situ high P-T synchrotron XRD experiments were conducted in the laser-heated diamond anvil cell to determine the equilibrium phases in Fe75S7O18 and Fe80S5Si15 compositions between 30 and 174 GPa and up to 3000 K. In the S,O-rich samples, an orthorhombic Fe3S2 phase coexists with hcp-Fe, Fe3S and FeO and undergoes two monoclinic distortions between 60 and 174 GPa. In the S,Si-rich samples, the orthorhombic Fe3S2 phase was observed up to 115 GPa. With increasing pressure, the Fe3S2 phase becomes stable to higher temperatures in both compositions, suggesting possible Fe3(S,O)2 or Fe3(S,Si)2 solid solutions. SEM analysis of a laser heated Fe75S7O18 sample recovered from 40 GPa and 1450 K confirms a Fe3(S,O)2 phase with O dissolved into the structure. Based on the current melting data in the Fe-S-O and Fe-S-Si systems, the Fe3(S,O)2 stability field intersects the solidus in the outer core and could be a possible liquidus phase in Fe,S,O-rich planetary cores, whereas Fe3S is the stable sulfide at outer core pressures in Fe,S,Si-rich systems.

Electronic transport on the Shastry-Sutherland lattice in Ising-type rare-earth tetraborides

Science.gov (United States)

Ye, Linda; Suzuki, Takehito; Checkelsky, Joseph G.

2017-05-01

In the presence of a magnetic field frustrated spin systems may exhibit plateaus at fractional values of saturation magnetization. Such plateau states are stabilized by classical and quantum mechanisms including order by disorder, triplon crystallization, and various competing order effects. In the case of electrically conducting systems, free electrons represent an incisive probe for the plateau states. Here we study the electrical transport of Ising-type rare-earth tetraborides R B4 (R =Er , Tm), a metallic Shastry-Sutherland lattice showing magnetization plateaus. We find that the longitudinal and transverse resistivities reflect scattering with both the static and the dynamic plateau structure. We model these results consistently with the expected strong uniaxial anisotropy on a quantitative level, providing a framework for the study of plateau states in metallic frustrated systems.

Linear stability analysis of a levitated nanomagnet in a static magnetic field: Quantum spin stabilized magnetic levitation

Science.gov (United States)

Rusconi, C. C.; Pöchhacker, V.; Cirac, J. I.; Romero-Isart, O.

2017-10-01

We theoretically study the levitation of a single magnetic domain nanosphere in an external static magnetic field. We show that, apart from the stability provided by the mechanical rotation of the nanomagnet (as in the classical Levitron), the quantum spin origin of its magnetization provides two additional mechanisms to stably levitate the system. Despite the Earnshaw theorem, such stable phases are present even in the absence of mechanical rotation. For large magnetic fields, the Larmor precession of the quantum magnetic moment stabilizes the system in full analogy with magnetic trapping of a neutral atom. For low magnetic fields, the magnetic anisotropy stabilizes the system via the Einstein-de Haas effect. These results are obtained with a linear stability analysis of a single magnetic domain rigid nanosphere with uniaxial anisotropy in a Ioffe-Pritchard magnetic field.

Stabilization of organic matter and nitrogen immobilization during mechanical-biological treatment and landfilling of residual municipal solid waste

International Nuclear Information System (INIS)

Heiss-Ziegler, C.

2000-04-01

Synthesis of humic substances and nitrogen immobilization during mechanical-biological treatment of waste and the behavior of biologically stabilized waste under anaerobic landfill conditions were investigated. Samples were taken from a large-scale treatment plant. Anaerobic conditions were simulated in lab scale test cells. Humic substances were analyzed photometrically and gravimetrically. The nitrogen immobilization was investigated by sequential leaching tests and by analyzing the non acid hydrolyzable nitrogen. Humic acids were mainly synthesized during the beginning of the intensive rotting phase. Later on in the process no significant changes occurred. The humic acid content rose up to 6,8 % DS org. It correlated well with the stability parameters respiration activity and accumulated gas production. In the coarse of the treatment the nitrogen load emitted during the consecutive leaching tests dropped from 50 % down to less than 20 % total nitrogen. The non acid hydrolyzable nitrogen rose from 17 up to 42 % Kjeldahl nitrogen content. Nevertheless the mechanical-biological treatment is not significantly shortening the aftercare period of a landfill concerning liquid nitrogen emissions. The reduced nitrogen emission potential is released more slowly. When reactive waste material was exposed to anaerobic conditions, humic and fulvic acids were synthesized up to the point when intensive gas production started and then were remineralized. Stabilized waste materials after treatment of various intensity behaved differently under anaerobic conditions. Steady and decreasing humic acid contents were observed. (author)

Uncovering stability mechanisms in microbial ecosystems - combining microcosm experiments, computational modelling and ecological theory in a multidisciplinary approach

Science.gov (United States)

Worrich, Anja; König, Sara; Banitz, Thomas; Centler, Florian; Frank, Karin; Kästner, Matthias; Miltner, Anja; Thullner, Martin; Wick, Lukas

2015-04-01

Although bacterial degraders in soil are commonly exposed to fluctuating environmental conditions, the functional performance of the biodegradation processes can often be maintained by resistance and resilience mechanisms. However, there is still a gap in the mechanistic understanding of key factors contributing to the stability of such an ecosystem service. Therefore we developed an integrated approach combining microcosm experiments, simulation models and ecological theory to directly make use of the strengths of these disciplines. In a continuous interplay process, data, hypotheses, and central questions are exchanged between disciplines to initiate new experiments and models to ultimately identify buffer mechanisms and factors providing functional stability. We focus on drying and rewetting-cycles in soil ecosystems, which are a major abiotic driver for bacterial activity. Functional recovery of the system was found to depend on different spatial processes in the computational model. In particular, bacterial motility is a prerequisite for biodegradation if either bacteria or substrate are heterogeneously distributed. Hence, laboratory experiments focussing on bacterial dispersal processes were conducted and confirmed this finding also for functional resistance. Obtained results will be incorporated into the model in the next step. Overall, the combination of computational modelling and laboratory experiments identified spatial processes as the main driving force for functional stability in the considered system, and has proved a powerful methodological approach.

Rare earth permanent magnet with easy magnetization

International Nuclear Information System (INIS)

Kim, A.S.; Camp, F.E.

1998-01-01

Rare earth permanent magnets have high energy products and coercivities, and thus the volume miniaturization of magnetic devices has been possible with improved magnetic performance. Although the high energy products of these rare earth permanent magnets provide substantial advantages for magnetic design and application, the strong magnetic force of the magnetized magnets makes assembly difficult. Therefore, a special device is needed to assemble the magnetized magnets. On the other hand, unmagnetized magnets are assembled and then they are magnetized. The assembled magnets are generally more difficult to magnetize than unassembled magnets because a much less effective magnetic field may be applied to them. This is particularly true for the rare earth permanent magnets because they usually need a much higher magnetic field to be fully magnetized than alnico or ferrite magnets. To obtain optimum magnetic properties, the required minimum magnetizing fields for SmCo 5 , Sm 2 TM 17 and Nd 2 Fe 14 B magnets were reported as 25-30 kOe, 45-60 kOe and 25-30 kOe, respectively. If the required magnetizing field for full saturation could be lowered, the effective utilization of magnetic properties would be maximized and the magnetic design option could be expanded with reduced restrictions. To meet this demand, we have sought to lower the field required for full magnetic saturation, and found that an increase in Dy content in R-(Fe,Co,Cu)-B type magnets lowers the field required for full saturation as well as improves the temperature stability. By increasing the H ci with Dy addition from 14 kOe to 24 and 34 kOe, the field required for full magnetic saturation decreases from about 20 to 15 and 10 kOe, respectively. This dual benefit will open up new application areas with more freedom for magnet design options. The mechanism for the lower magnetizing fields will be discussed. (orig.)

Journal of Earth System Science | Indian Academy of Sciences

Indian Academy of Sciences (India)

Home; Journals; Journal of Earth System Science. Abdul Matin. Articles written in Journal of Earth System Science. Volume 118 Issue 4 August 2009 pp 379-390. Deformation mechanisms in the frontal Lesser Himalayan Duplex in Sikkim Himalaya, India · Abdul Matin Sweety Mazumdar · More Details Abstract Fulltext PDF.

Quantum mechanical study of molecular collisions at ultra-low energy: applications to alkali and alkaline-earth systems

International Nuclear Information System (INIS)

Quemener, G.

2006-10-01

In order to investigate the collisional processes which occur during the formation of molecular Bose-Einstein condensates, a time-independent quantum mechanical formalism, based on hyperspherical coordinates, has been applied to the study of atom-diatom dynamics at ultra-low energies. We present theoretical results for three alkali systems, each composed of lithium, sodium or potassium atoms, and for an alkaline-earth system composed of calcium atoms. We also study dynamics at large and positive atom-atom scattering length. Evidence for the suppression of inelastic processes in a fermionic system is given, as well as a linear relation between the atom-diatom scattering length and the atom-atom scattering length. (author)

The Hydromechanics of Vegetation for Slope Stabilization

Science.gov (United States)

Mulyono, A.; Subardja, A.; Ekasari, I.; Lailati, M.; Sudirja, R.; Ningrum, W.

2018-02-01

Vegetation is one of the alternative technologies in the prevention of shallow landslide prevention that occurs mostly during the rainy season. The application of plant for slope stabilization is known as bioengineering. Knowledge of the vegetative contribution that can be considered in bioengineering was the hydrological and mechanical aspects (hydromechanical). Hydrological effect of the plant on slope stability is to reduce soil water content through transpiration, interception, and evapotranspiration. The mechanical impact of vegetation on slope stability is to stabilize the slope with mechanical reinforcement of soils through roots. Vegetation water consumption varies depending on the age and density, rainfall factors and soil types. Vegetation with high ability to absorb water from the soil and release into the atmosphere through a transpiration process will reduce the pore water stress and increase slope stability, and vegetation with deep root anchoring and strong root binding was potentially more significant to maintain the stability of the slope.

Stability of parallel flows

CERN Document Server

Betchov, R

2012-01-01

Stability of Parallel Flows provides information pertinent to hydrodynamical stability. This book explores the stability problems that occur in various fields, including electronics, mechanics, oceanography, administration, economics, as well as naval and aeronautical engineering. Organized into two parts encompassing 10 chapters, this book starts with an overview of the general equations of a two-dimensional incompressible flow. This text then explores the stability of a laminar boundary layer and presents the equation of the inviscid approximation. Other chapters present the general equation

Thermal structure of the accreting earth

International Nuclear Information System (INIS)

Turcotte, D.L.; Pflugrath, J.C.

1985-01-01

The energy associated with the accretion of the earth and the segregation of the core is more than sufficient to melt the entire earth. In order to understand the thermal evolution of the early earth it is necessary to study the relevant heat transfer mechanisms. In this paper we postulate the existence of a global magma ocean and carry out calculations of the heat flux through it in order to determine its depth. In the solid mantle heat is transferred by the upward migration of magma. This magma supplies the magma ocean. The increase in the mantle liquidus with depth (pressure) is the dominant effect influencing heat transfer through the magma ocean. We find that a magma ocean with a depth of the order of 20 km would have existed as the earth accreted. We conclude that the core segregated and an atmosphere was formed during accretion

Enzymatic determination of rare earth elements by use of pyrophosphotases

International Nuclear Information System (INIS)

Shekhovtseva, T.N.; Pirogova, S.V.; Fedorova, O.M.; Dolmanova, I.F.; Bajkov, A.A.

1993-01-01

A highly sensitive (determination limit 8 x 10 -6 - 4 x 10 -4 μg/ml) and selective enzymatic method for determination of rare earth elements has been developed. The method is based on inhibition action of rare earths on the catalytic activity of pyrophosphates isolated from bakery geast and E. Coli. The mechanism of the rare earth element action, corresponding to competitive inhibition, has been established

Comparative study on sorption/desorption of radioeuropium on alumina, bentonite and red earth: effects of pH, ionic strength, fulvic acid, and iron oxides in red earth

International Nuclear Information System (INIS)

Dong Wenming; Wang Xiangke; Bian Xiaoyan; Wang Aixia; Du Jingzhou; Tao, Z.Y.

2001-01-01

The sorption and desorption of Eu(III) as a representative of trivalent lanthanides and actinides on bentonite, alumina, red earth and red earth treated to remove free iron oxides were comparatively investigated by using batch technique and radiotracer 152+154 Eu. The effects of pH, ionic strength, fulvic acid, iron oxides in red earth and the sorption mechanism were also discussed. As compared to alumina and red earth, Eu(III) presents a considerable distribution coefficient (K d ) onto bentonite. It was found that the pH and the presence of clay minerals are the main factors dominating the sorption/desorption characteristic of Eu 3+ in the soil, and that a sorption-desorption hysteresis on bentonite and red earth actually occurs. Furthermore, the main sorption mechanism of lanthanides onto bentonite, alumina and red earth is the formation of bridged hydroxo complexes with the surface, and there are negative effects of fulvic acid and free iron oxides in red earth on the sorption of Eu(III). The results of this paper indicate that the additivity rule on the sorption characteristic of a soil from the individual component's characteristics is not general

GIANT IMPACT: AN EFFICIENT MECHANISM FOR THE DEVOLATILIZATION OF SUPER-EARTHS

Energy Technology Data Exchange (ETDEWEB)

Liu, Shang-Fei [Department of Earth and Planetary Sciences, University of California, Santa Cruz, CA 95064 (United States); Hori, Yasunori; Lin, D. N. C. [Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064 (United States); Asphaug, Erik, E-mail: sliu26@ucsc.edu, E-mail: yahori@ucsc.edu, E-mail: lin@ucolick.org, E-mail: easphaug@asu.edu [School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287 (United States)

2015-10-20

Mini-Neptunes and volatile-poor super-Earths coexist on adjacent orbits in proximity to host stars such as Kepler-36 and Kepler-11. Several post-formation processes have been proposed for explaining the origin of the compositional diversity between neighboring planets: mass loss via stellar XUV irradiation, degassing of accreted material, and in situ accumulation of the disk gas. Close-in planets are also likely to experience giant impacts during the advanced stage of planet formation. This study examines the possibility of transforming volatile-rich super-Earths/mini-Neptunes into volatile-depleted super-Earths through giant impacts. We present the results of three-dimensional hydrodynamic simulations of giant impacts in the accretionary and disruptive regimes. Target planets are modeled with a three-layered structure composed of an iron core, silicate mantle, and hydrogen/helium envelope. In the disruptive case, the giant impact can remove most of the H/He atmosphere immediately and homogenize the refractory material in the planetary interior. In the accretionary case, the planet is able to retain more than half of the original gaseous envelope, while a compositional gradient suppresses efficient heat transfer as the planetary interior undergoes double-diffusive convection. After the giant impact, a hot and inflated planet cools and contracts slowly. The extended atmosphere enhances the mass loss via both a Parker wind induced by thermal pressure and hydrodynamic escape driven by the stellar XUV irradiation. As a result, the entire gaseous envelope is expected to be lost due to the combination of those processes in both cases. Based on our results, we propose that Kepler-36b may have been significantly devolatilized by giant impacts, while a substantial fraction of Kepler-36c’s atmosphere may remain intact. Furthermore, the stochastic nature of giant impacts may account for the observed large dispersion in the mass–radius relationship of close-in super-Earths

Physical and mechanical properties of sand stabilized by cement and natural zeolite

Science.gov (United States)

Salamatpoor, Sina; Jafarian, Yaser; Hajiannia, Alborz

2018-05-01

Loose sands are prone to lose their shear strength when being subjected to static or cyclic loads. To this end, there exist several methods to improve the mechanical properties of sands, but the most crucial and viable approach is the one with the lowest harmful environmental impact both in production and recycling processes. In this regard, zeolite as a natural pozzolanic additive offers an eco-friendly improvement in strength parameters of cemented sandy soils. Thereby, in this study, a series of unconfined compressive strength (UCS) tests are conducted to evaluate the mechanical parameters of the zeolite-cemented sand. The results demonstrate a meaningful increase in the UCS of the treated sand samples for replacement of cement by zeolite at an optimum proportion of 40% in specimens with 14 and 28 days curing time. The effectiveness of the improvement process is demonstrated by the strength improvement ratio which was up to be 128% to 209% for the samples with 14 and 28 days curing time, respectively. With regard to the above results, zeolite can be introduced as a promising cement substitute in stabilization of sandy ground including backfills, roadbed, embankments, and other structural filling systems.

Alkaline earth metal doped tin oxide as a novel oxygen storage material

Energy Technology Data Exchange (ETDEWEB)

Dong, Qiang, E-mail: dong@tagen.tohoku.ac.jp [Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1 Katahira, Aoba-ku Sendai 980-8577 (Japan); Yin, Shu; Yoshida, Mizuki; Wu, Xiaoyong; Liu, Bin [Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1 Katahira, Aoba-ku Sendai 980-8577 (Japan); Miura, Akira; Takei, Takahiro; Kumada, Nobuhiro [Department of Research Interdisciplinary Graduate School of Medicine and Engineering, University of Yamanashi, Miyamae cho-7, Kofu 400-8511 (Japan); Sato, Tsugio [Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1 Katahira, Aoba-ku Sendai 980-8577 (Japan)

2015-09-15

Alkaline earth metal doped tin oxide (SnO{sub 2}) hollow nanospheres with a diameter of 50 nm have been synthesized successfully via a facial solvothermal route in a very simple system composed of only ethanol, acetic acid, SnCl{sub 4}·5H{sub 2}O and A(NO{sub 3}){sub 2}·xH{sub 2}O (A = Mg, Ca, Sr, Ba). The synthesized undoped SnO{sub 2} and A-doped SnO{sub 2} hollow nanospheres were characterized by the oxygen storage capacity (OSC), X-ray diffraction, transmission electron microscopy and the Brunauer–Emmet–Teller (BET) technique. The OSC values of all samples were measured using thermogravimetric-differential thermal analysis. The incorporation of alkaline earth metal ion into tin oxide greatly enhanced the thermal stability and OSC. Especially, Ba-doped SnO{sub 2} hollow nanospheres calcined at 1000 °C for 20 h with a BET surface area of 61 m{sup 2} g{sup −1} exhibited the considerably high OSC of 457 μmol-O g{sup −1} and good thermal stability. Alkaline earth metal doped tin oxide has the potential to be a novel oxygen storage material.

Mechanical coupling between transsynaptic N-cadherin adhesions and actin flow stabilizes dendritic spines

Science.gov (United States)

Chazeau, Anaël; Garcia, Mikael; Czöndör, Katalin; Perrais, David; Tessier, Béatrice; Giannone, Grégory; Thoumine, Olivier

2015-01-01

The morphology of neuronal dendritic spines is a critical indicator of synaptic function. It is regulated by several factors, including the intracellular actin/myosin cytoskeleton and transcellular N-cadherin adhesions. To examine the mechanical relationship between these molecular components, we performed quantitative live-imaging experiments in primary hippocampal neurons. We found that actin turnover and structural motility were lower in dendritic spines than in immature filopodia and increased upon expression of a nonadhesive N-cadherin mutant, resulting in an inverse relationship between spine motility and actin enrichment. Furthermore, the pharmacological stimulation of myosin II induced the rearward motion of actin structures in spines, showing that myosin II exerts tension on the actin network. Strikingly, the formation of stable, spine-like structures enriched in actin was induced at contacts between dendritic filopodia and N-cadherin–coated beads or micropatterns. Finally, computer simulations of actin dynamics mimicked various experimental conditions, pointing to the actin flow rate as an important parameter controlling actin enrichment in dendritic spines. Together these data demonstrate that a clutch-like mechanism between N-cadherin adhesions and the actin flow underlies the stabilization of dendritic filopodia into mature spines, a mechanism that may have important implications in synapse initiation, maturation, and plasticity in the developing brain. PMID:25568337

Structural stability, electronic, mechanical and superconducting properties of CrC and MoC

Energy Technology Data Exchange (ETDEWEB)

Kavitha, M.; Sudha Priyanga, G. [Department of Physics, N.M.S.S.V.N College, Madurai 625019, Tamilnadu (India); Rajeswarapalanichamy, R., E-mail: rrpalanichamy@gmail.com [Department of Physics, N.M.S.S.V.N College, Madurai 625019, Tamilnadu (India); Iyakutti, K. [Department of Physics and Nanotechnology, SRM University, Chennai 603203, Tamilnadu (India)

2016-02-01

The structural, electronic, mechanical and superconducting properties of chromium carbide (CrC) and molybdenum carbide (MoC) are investigated using first principles calculations based on density functional theory (DFT). The computed ground state properties like equilibrium lattice constants and cell volume are in good agreement with available theoretical and experimental data. A pressure induced structural phase transition from tungsten carbide phase (WC) to zinc blende phase (ZB) and then zinc blende phase (ZB) to nickel arsenide phase (NiAs) are observed in both chromium and molybdenum carbides. Electronic structure reveals that these carbides are metallic at ambient condition. All the calculated elastic constants obey the Born–Huang stability criteria, suggesting that they are mechanically stable at normal and high pressure. The super conducting transition temperatures for CrC and MoC in WC phase are found to be 31.12 K and 17.14 K respectively at normal pressure. - Highlights: • Electronic and mechanical properties of CrC and MoC are investigated. • Pressure induced structural phase transition is predicted at high pressure. • Electronic structure reveals that these materials exhibit metallic behaviour. • Debye temperature values are computed for CrC and MoC. • Superconducting transition temperature values are computed.

Synthesis, microstructural, optical and mechanical properties of yttria stabilized zirconia thin films

International Nuclear Information System (INIS)

Amézaga-Madrid, P.; Hurtado-Macías, A.; Antúnez-Flores, W.; Estrada-Ortiz, F.; Pizá-Ruiz, P.; Miki-Yoshida, M.

2012-01-01

Highlights: ► Thin films of YSZ obtained by AACVD have high quality. ► They are uniform, very transparent, and have high hardness. ► Optical characterization were performed in detail, optical constants and band gap energy were determined as a function of dopant content. - Abstract: Thin films of yttria-stabilized zirconia (YSZ) exhibit exceptional properties, such as high thermal, chemical and mechanical stability. Here, we report the synthesis of YSZ thin films by aerosol assisted chemical vapour deposition onto borosilicate glass and fused silica substrates. Optimum deposition temperature was 673 ± 5 K. In addition, different Y content was tried to analyse its influence in the microstructure and properties of the films. The films were uniform, transparent and non-light scattering. Surface morphology and cross sectional microstructure were studied by field emission scanning electron microscopy. The microstructure of the films was characterized by grazing incidence X-ray diffraction. Crystallite size and lattice parameter were obtained. Optical properties were analysed from reflectance and transmittance spectra; from these measurements, optical constants and band gap were obtained. Quantum confinement effect, due to the small grain size of the films, was evident in the high band gap energy obtained. Nanoindentation tests were realized at room temperature employing the continuous stiffness measurement method, to determine the hardness and elastic modulus as a function of Y content.

The electronic structure of rare-earth luminescent centre in alkaline-earth sulphides

International Nuclear Information System (INIS)

Zheng Qingqi; Pan Wei; Huang Maichun; He Xiaoguang

1988-09-01

The cluster method is used to investigate the electronic structure of rare-earth Eu 2+ and Ce 3+ doped SrS and CaS alkaline-earth sulphides in the local density theory regime. The ground state is obtained self-consistently by the DV-X α method, while the transition state theory is used to calculate the excited states. The energy difference between ground state and excited state is 2.95 eV (420 nm) for CaS:Eu is in good agreement with the experimental data of 430 nm for the absorption peak in SrS:Cu. The composition of ground state and excited state is also calculated which can give information about the EL excitation mechanism. (author). 7 refs, 4 figs, 3 tabs

Ab-initio study of pressure evolution of structural, mechanical and magnetic properties of cementite (Fe3C) phase

Science.gov (United States)

Gorai, S.; Ghosh, P. S.; Bhattacharya, C.; Arya, A.

2018-04-01

The pressure evolution of phase stability, structural and mechanical properties of Fe3C in ferro-magnetic (FM) and high pressure non magnetic (NM) phase is investigated from first principle calculations. The 2nd order FM to NM phase transition of Fe3C is identified around 60 GPa. Pressure (or density) variation of sound velocities from our ab-initio calculated single crystal elastic constants are determined to predict these parameters at Earth's outer core pressure.

Earth Observing System (EOS) Aqua Launch and Early Mission Attitude Support Experiences

Science.gov (United States)

Tracewell, D.; Glickman, J.; Hashmall, J.; Natanson, G.; Sedlak, J.

2003-01-01

The Earth Observing System (EOS) Aqua satellite was successfully launched on May 4,2002. Aqua is the second in the series of EOS satellites. EOS is part of NASA s Earth Science Enterprise Program, whose goals are to advance the scientific understanding of the Earth system. Aqua is a three-axis stabilized, Earth-pointing spacecraft in a nearly circular, sun-synchronous orbit at an altitude of 705 km. The Goddard Space Flight Center (GSFC) Flight Dynamics attitude team supported all phases of the launch and early mission. This paper presents the main results and lessons learned during this period, including: real-time attitude mode transition support, sensor calibration, onboard computer attitude validation, response to spacecraft emergencies, postlaunch attitude analyses, and anomaly resolution. In particular, Flight Dynamics support proved to be invaluable for successful Earth acquisition, fine-point mode transition, and recognition and correction of several anomalies, including support for the resolution of problems observed with the MODIS instrument.

Triphenylamine - a 'new' stabilizer for nitrocellulose based propellants. Pt. 1: chemical stability studies

Energy Technology Data Exchange (ETDEWEB)

Wilker, Stephan; Heeb, Gerhard [WIWEB ASt Heimerzheim, Grosses Cent, 53913 Swisttal (Germany); Vogelsanger, Beat [Nitrochemie Wimmis AG, Niesenstr. 44, 3752 Wimmis (Switzerland); Petrzilek, Jan; Skladal, Jan [Explosia a.s. - Research Institute of Industrial Chemistry (VUPCH), 532 17 Pardubice (Czech Republic)

2007-04-15

Triphenylamine (TPA) was used for the first time in France in 1937 as a stabilizer for propellants. The stability of those samples was described as 'good'. Around 1950 an American group produced TPA stabilized propellants and investigated the decomposition mechanism. Apart from one single experiment in the 1970s no further attempts were made to take TPA as a stabilizer for propellants. With the background of an increasingly critical discussion about nitrosamines in propellants and their declaration of being carcinogenic, TPA revealed a renaissance since the year 2000. To achieve the goal of nitrosamine free propellants several TPA stabilized propellants were produced. Their processability, stability and ballistic properties were investigated. This publication summarizes the most important results of stability tests on more than 30 different TPA stabilized propellants including the decomposition mechanism, the synthesis of the consecutive products and their stabilizing properties. In addition, the internal compatibility of TPA with the most important propellant ingredients is discussed and its relative decomposition rate is compared with that of other stabilizers. In summary TPA is a suitable stabilizer for propellants. It has nevertheless two disadvantages. It is relatively rapidly consumed in double base formulations (which makes it difficult to pass the criteria of AOP-48, Ed. 2) and the stabilizing activity of the two major consecutive products 4-NO{sub 2}-TPA and especially 4,4{sup '}-di-NO{sub 2}-TPA is low. (Abstract Copyright [2007], Wiley Periodicals, Inc.)

Earth's radiation belts

International Nuclear Information System (INIS)

Moslehi Fard, M.

1984-01-01

The theory of trapped particles in a magnetic field of approximated dipole is described completely in the first part. Second part contains experimental results. The mechanism of radiation belt source ''albedo neutrons'' and also types of dissipation mechanism about radiation belt is explained. The trapped protons and electrons by radiation belt is discussed and the life-time of trapped particles are presented. Finally the magnetic fields of Moon, Venus, Mars, and Saturn, measured by passengers Mariner 4,10 and pioneer 10,11 are indicated. The experimental and theoretical results for the explanation of trapped plasma around the earth which is looked like two internal and external belt have almost good correspondence

Inclusion Mechanism and Heat Stability of the Complex of 4 ...

African Journals Online (AJOL)

The physicochemical properties of the complex were evaluated by Fourier transform infrared spectroscopy (FT-IR) and x-ray diffractometry (XRD) while the heat stability of the complex was measured by thermogravimetric/differential scanning calorimetry (TG/DSC). Results: The stability constants of the complexes were ...

Rare Earth Elements: A Tool for Understanding the Behaviour of Trivalent Actinides in the Geosphere

International Nuclear Information System (INIS)

Buil, Belen; Gomez, Paloma; Garralon, Antonio; Turrero, M. Jesus

2007-01-01

Rare earth element (REE) concentrations have been determined in groundwaters, granite and fracture fillings in a restored uranium mine. The granitoids normalized REE patterns of groundwaters show heavy rare earth elements (HREE)-enrichment and positive Eu anomalies. This suggests that the REE are fractionated during leaching from the source rocks by groundwaters. Preferential leaching of HREE would be consistent with the greater stability of their aqueous complexes compared to those of the light rare earth elements (LREE), together with the dissolution of certain fracture filling minerals, dissolution/alteration of phyllosilicates and colloidal transport. (authors)

Zwitterionization of glycine in water environment: Stabilization mechanism and NMR spectral signatures

Science.gov (United States)

Valverde, Danillo; da Costa Ludwig, Zélia Maria; da Costa, Célia Regina; Ludwig, Valdemir; Georg, Herbert C.

2018-01-01

At physiological conditions, myriads of biomolecules (e.g., amino acids, peptides, and proteins) exist predominantly in the zwitterionic structural form and their biological functions will result in these conditions. However these geometrical structures are inaccessible energetically in the gas phase, and at this point, stabilization of amino-acids in physiological conditions is still under debate. In this paper, the electronic properties of a glycine molecule in the liquid environment were studied by performing a relaxation of the glycine geometry in liquid water using the free energy gradient method combined with a sequential quantum mechanics/molecular mechanics approach. A series of Monte Carlo Metropolis simulations of the glycine molecule embedded in liquid water, followed by only a quantum mechanical calculation in each of them were carried out. Both the local and global liquid environments were emphasized to obtain nuclear magnetic resonance (NMR) parameters for the glycine molecule in liquid water. The results of the equilibrium structure in solution and the systematic study of the hydrogen bonds were used to discard the direct proton transfer from the carboxyl group to the ammonium group of the glycine molecule in water solution. The calculations of the Density Functional Theory (DFT) were performed to study the polarization of the solvent in the parameters of nuclear magnetic resonance of the glycine molecule in liquid water. DFT calculations predicted isotropic chemical changes on the H, C, N, and O atoms of glycine in liquid water solution which agree with the available experimental data.

Environmental effects of large impacts on the earth; relation to extinction mechanisms

Science.gov (United States)

Okeefe, John D.; Ahrens, Thomas J.; Koschny, Detlef

1988-01-01

Since Alvarez et al., discovered a worldwide approx. cm-thick layer of fine sediments laden with platinum group elements in approximately chondritic proportions exactly at the Cretaceous-Tertiary (C-T) boundary, and proposed bolide-impact as triggering mass extinctions, many have studied this hypothesis and the layer itself with its associated spherules and shocked quartz. At issue is whether the mass extinctions, and this horizon has an impact versus volcanic origin. A critical feature of the Alvarez hypothesis is the suggestion that the bolide or possibly a shower of objects delivered to the earth approx. 0.6 x 10 to the 18th power g of material which resulted in aerosol-sized ejecta such that global insolation was drastically reduced for significant periods. Such an event would lower temperatures on continents and halt photosynthesis in the upper 200 m of th eocean. The latter would strangle the marine food chain and thus produce the major marine faunal extinctions which mark the C-T boundary. Crucial issues examined include: What are the dynamics of atmospheric flow occurring upon impact of a large bolide with the earth; What is the size distributions of the very fine impact ejecta and how do these compare to the models of ejecta which are used to model the earth's radiative thermal balance. The flow field due to passage of a 10 km diameter bolide through an exponential atmosphere and the interaction of the gas flow and bolide with the solid ear was calculated. The CO2 released upon impact onto shallow marine carbonate sections was modeled and found that the mass of CO2 released exceeds the present 10 to the 18th power g CO2 budget of the earth's atmosphere by several times. Using the calculations of Kasting and Toon it was found that to compute the temperature rise of the earth's surface as a function of CO2 content, it was found that sudden and prolonged global increases are induced from impact of 20 to 50 km radius projectiles and propose that sudden

Magnetohydrodynamics and the earth's core selected works by Paul Roberts

CERN Document Server

Soward, Andrew M

2003-01-01

Paul Roberts'' research contributions are remarkable in their diversity, depth and international appeal. Papers from the Paul Roberts'' Anniversary meeting at the University of Exeter are presented in this volume. Topics include geomagnetism and dynamos, fluid mechanics and MHD, superfluidity, mixed phase regions, mean field electrodynamics and the Earth''s inner core. An incisive commentary of the papers puts the work of Paul Roberts into historical context. Magnetohydrodynamics and the Earth''s Core provides a valuable source of reference for graduates and researchers working in this area of geoscience.

Analysis of “Favorable Growth Element” Based on Rare Earth-aluminum Composite Mechanism of Compound Process

Science.gov (United States)

Hao, Baohong; Zeng, Qihui; Zhao, Jin

2018-01-01

Under the background that failure resulted in by high temperature once only aluminum oxide is used as the gasoline additive. This paper, with the purpose to solve this problem, is to synthesize AcAl oxide for gasoline additive. In order to get the rare-earth-aluminum oxide, first, a complex model of rare earth oxide based on theories about ion coordination is established. Then, by the complex model, the type of “compound growth unit” when rare earth elements join the hydrothermal conditions and the inclination that “diversification” might probably happen are deduced. Depending on the results got by complex model, this paper introduces the type of compound and its existence conditions of “Compound growth unit” owned by stable rare-earth-aluminum oxide. By adjusting the compositions of modifier, compound materials of rare earth-aluminum oxide used for gasoline additive is made. By XRD test, aperture test, adsorption test and desorption test, the theoretical deduction is proved to be right. From the experiment, it is concluded that: a dense environment is the pre-condition to form rare-earth-aluminum polymer, which is also an essential condition for the polymer to update to a favorable growth unit and produce mesoporous rare-earth-aluminum oxide with high activity.

Argonne program to assess superconducting stability

International Nuclear Information System (INIS)

Wang, S.T.; Turner, L.R.; Huang, Y.C.; Dawson, J.W.; Harrang, J.; Hilal, M.A.; Lieberg, M.; Gonczy, J.D.; Kim, S.H.

1978-01-01

To assess superconductor stability, a complete program is developed to obtain basic information on the effects of local mechanical perturbations on the cryostatic stability. An analytical model for computing the transient recovery following the mechanical perturbation is developed. A test program is undertaken to develop data needed to verify the conclusions reached through the analytical studies

Boundary layer stability and Arctic climate change: a feedback study using EC-Earth

Energy Technology Data Exchange (ETDEWEB)

Bintanja, R.; Linden, E.C. van der; Hazeleger, W. [Royal Netherlands Meteorological Institute (KNMI), De Bilt (Netherlands)

2012-12-15

Amplified Arctic warming is one of the key features of climate change. It is evident in observations as well as in climate model simulations. Usually referred to as Arctic amplification, it is generally recognized that the surface albedo feedback governs the response. However, a number of feedback mechanisms play a role in AA, of which those related to the prevalent near-surface inversion have received relatively little attention. Here we investigate the role of the near-surface thermal inversion, which is caused by radiative surface cooling in autumn and winter, on Arctic warming. We employ idealized climate change experiments using the climate model EC-Earth together with ERA-Interim reanalysis data to show that boundary-layer mixing governs the efficiency by which the surface warming signal is 'diluted' to higher levels. Reduced vertical mixing, as in the stably stratified inversion layer in Arctic winter, thus amplifies surface warming. Modelling results suggest that both shortwave - through the (seasonal) interaction with the sea ice feedback - and longwave feedbacks are affected by boundary-layer mixing, both in the Arctic and globally, with the effect on the shortwave feedback dominating. The amplifying effect will decrease, however, with climate warming because the surface inversion becomes progressively weaker. We estimate that the reduced Arctic inversion has slowed down global warming by about 5% over the past 2 decades, and we anticipate that it will continue to do so with ongoing Arctic warming. (orig.)

Analysis of the parameters involved in the design of slope stabilizing dowels

International Nuclear Information System (INIS)

Lopez Dominguez, J. J.; Estaire Gepp, J.

2014-01-01

The use of dowels to stabilize landslides is a common practice nowadays. There are many theories, even contradictory, to design such dowels. This paper describes the methods proposed by Estaire and Sopena (2001), based on the fact that the earth pressures on the dowels, produced by the movement of the sliding ground, are equivalent to the stabilizing forces exerted by such dowels to improve the safety level of the slope. The method consists on the following steps: definition of the hydrogeological model, quantification of the initial safety level, determination of stabilization force, position of dowels in the slope, calculation of the dowel embedment and the acting load laws, election of the dowel separation and typology, and the structural design. The paper performs a critical review of some of the main design parameters: influence of the position of the dowels in the slope, the distribution of the earth pressure on the dowels and the restrains in the head of the dowels. (Author)

Numerical modelling of levee stability based on coupled mechanical, thermal and hydrogeological processes

Directory of Open Access Journals (Sweden)

Dwornik Maciej

2016-01-01

Full Text Available The numerical modelling of coupled mechanical, thermal and hydrogeological processes for a soil levee is presented in the paper. The modelling was performed for a real levee that was built in Poland as a part of the ISMOP project. Only four parameters were changed to build different flood waves: the water level, period of water increase, period of water decrease, and period of low water level after the experiment. Results of numerical modelling shows that it is possible and advisable to calculate simultaneously changes of thermal and hydro-mechanical fields. The presented results show that it is also possible to use thermal sensors in place of more expensive pore pressure sensors, with some limitations. The results of stability analysis show that the levee is less stable when the water level decreases, after which factor of safety decreases significantly. For all flooding wave parameters described in the paper, the levee is very stable and factor of safety variations for any particular stage were not very large.

Sparse Reconstruction of Regional Gravity Signal Based on Stabilized Orthogonal Matching Pursuit (SOMP)

Science.gov (United States)

Saadat, S. A.; Safari, A.; Needell, D.

2016-06-01

The main role of gravity field recovery is the study of dynamic processes in the interior of the Earth especially in exploration geophysics. In this paper, the Stabilized Orthogonal Matching Pursuit (SOMP) algorithm is introduced for sparse reconstruction of regional gravity signals of the Earth. In practical applications, ill-posed problems may be encountered regarding unknown parameters that are sensitive to the data perturbations. Therefore, an appropriate regularization method needs to be applied to find a stabilized solution. The SOMP algorithm aims to regularize the norm of the solution vector, while also minimizing the norm of the corresponding residual vector. In this procedure, a convergence point of the algorithm that specifies optimal sparsity-level of the problem is determined. The results show that the SOMP algorithm finds the stabilized solution for the ill-posed problem at the optimal sparsity-level, improving upon existing sparsity based approaches.

Influence of oxazolidines and zirconium oxalate crosslinkers on the hydrothermal, enzymatic, and thermo mechanical stability of type 1 collagen fiber

International Nuclear Information System (INIS)

Haroun, Mahdi A.; Khirstova, Palmina K.; Gasmelseed, Gurashi A.; Covington, Antony D.

2009-01-01

Stabilization of type I rat tail tendon (RTT) collagen by crosslink agent oxazolidine and zirconium oxalate was studied to understand the effect on the thermal, enzymatic and mechanical stability of collagen. The results show that both oxazolidine and zirconium oxalate imparts thermal stability to collagen, and oxazolidine exhibits a marked increase in the peak temperature and enthalpy changes when compared to both native and zirconium oxalate tanned RTT. There is a decrease in the peak temperature and the enthalpy changes of oxazolidine tanned RTT fibers after treatment with urea, suggesting the possibility of alterations in the secondary structure of collagen after tanning. Oxazolidine, which forms carbocationic intermediates species in solution, have better crosslinking with collagen as seen from viscometry studies and hence provides better enzymatic stability to collagen than zirconium, which largely forms monomeric species in solution. Zirconium does not seem to change the tensile strength of RTT fibers significantly in wet condition as well as oxazolidine

Influence of oxazolidines and zirconium oxalate crosslinkers on the hydrothermal, enzymatic, and thermo mechanical stability of type 1 collagen fiber

Energy Technology Data Exchange (ETDEWEB)

Haroun, Mahdi A. [Department of Chemical and Environmental Engineering, Faculty of Engineering, Universiti Putra Malaysia, 43400 UPM, Serdang (Malaysia)], E-mail: Mahdiupm@hotmail.com; Khirstova, Palmina K. [People' s Hall 11113, P.O. Box 6272, Khartoum (Sudan); Gasmelseed, Gurashi A. [Juba University, Leather Dept. P.O. Box 12327 Khartoum (Sudan); Covington, Antony D. [Leather Centre, University College Northampton, Northampton (United Kingdom)

2009-02-20

Stabilization of type I rat tail tendon (RTT) collagen by crosslink agent oxazolidine and zirconium oxalate was studied to understand the effect on the thermal, enzymatic and mechanical stability of collagen. The results show that both oxazolidine and zirconium oxalate imparts thermal stability to collagen, and oxazolidine exhibits a marked increase in the peak temperature and enthalpy changes when compared to both native and zirconium oxalate tanned RTT. There is a decrease in the peak temperature and the enthalpy changes of oxazolidine tanned RTT fibers after treatment with urea, suggesting the possibility of alterations in the secondary structure of collagen after tanning. Oxazolidine, which forms carbocationic intermediates species in solution, have better crosslinking with collagen as seen from viscometry studies and hence provides better enzymatic stability to collagen than zirconium, which largely forms monomeric species in solution. Zirconium does not seem to change the tensile strength of RTT fibers significantly in wet condition as well as oxazolidine.

Adducts of rare earth tris-acetylacetonates with dimethyl sulfoxide

International Nuclear Information System (INIS)

Dzyubenko, N.G.; Kalenichenko, Yu.V.; Martynenko, L.I.

1988-01-01

Adducts of rare earth and yttrium (r.e.e., M) acetylacetonates with dimethyl sulfoxide (DMSO), MA 3 xnDMSO are synthesized. The acetylacetonates of light r.e.e. (M=La-Tb) are shown by different physico-chemical methods to form diadducts of the MA 3 x2DMSOxH 2 O composition, where A - -acetylacetonate-ion, and the acetyl-acetonates of heavy r.e.e. (M=Dy-Lu, Y)-monoadducts MA 3 xDMSO. The estimation of adduct thermal stability is carried out using the values of seeming activation energy of their thermal degradation. Monoadducts are shown to give volatile forms of rare earth acetylacetonates during heating in vacuum, and diadducts do not form volatile forms of acetylacetonates

Microstructural stability of heat-resistant high-pressure die-cast Mg-4Al-4Ce alloy

Energy Technology Data Exchange (ETDEWEB)

Wang, Wei; Zhang, Jinghuai; Li, Guoqiang; Feng, Yan; Su, Minliang; Wu, Ruizhi; Zhang, Zhongwu [Harbin Engineering Univ. (China). Key Laboratory of Superlight Material and Surface Technology; Jiao, Yufeng [Jiamusi Univ. (China). College of Materials Science and Engineering

2017-05-15

The thermal stability of Al-RE (rare earth) intermetallic phases with individual RE for heat-resistant high-pressure die-casting Mg-Al-RE alloys is investigated. The results of this study show that the main strengthening phase of Mg-4Al-4Ce alloy is Al{sub 11}Ce{sub 3}, whose content is about 5 wt.% according to quantitative X-ray diffraction phase analysis. The Al{sub 11}Ce{sub 3} phase appears to have high thermal stability at 200 C and 300 C, while phase morphology change with no phase structure transition could occur for Al{sub 11}Ce{sub 3} when the temperature reaches 400 C. Furthermore, besides the kinds of rare earths and temperature, stress is also an influencing factor in the microstructural stability of Mg-4Al-4Ce alloy.

Mechanical core coupling and reactors stability

International Nuclear Information System (INIS)

Suarez Antola, R.

2006-01-01

Structural parts of nuclear reactors are complex mechanical systems, able to vibrate with a set of proper frequencies when suitably excited. Cyclical variations in the strain state of the materials, including density perturbations, are produced. This periodic changes may affect reactor reactivity. But a variation in reactivity affects reactor thermal power, thus modifying the temperature field of the abovementiones materials. If the variation in temperature fields is fast enough, thermal-mechanical coupling may produce fast variations in strain states, and this, at its turn, modifies the reactivity, and so on. This coupling between mechanical vibrations of the structure and the materials of the core, with power oscillations of the reactor, not only may not be excluded a priori, but it seems that it has been present in some stage of the incidents or accidents that happened during the development of nuclear reactor technology. The purpose of the present communication is: (a) To review and generalize some mathematical models that were proposed in order to describe thermal-mechanical coupling in nuclear reactors. (b) To discuss some conditions in which significant instabilities could arise, including large amplitude power oscillations coupled with mechanical vibrations whose amplitudes are too small to be excluded by conventional criteria of mechanical design. Enough Certain aspects of thr physical safety of nuclear power reactors, that are objected by people that opposes to the renaissance of nucleoelectric generation, are discussed in the framework of the mathematical model proposed in this paper [es

Exceptional increase in the creep life of magnesium rare-earth alloys due to localized bond stiffening.

Science.gov (United States)

Choudhuri, Deep; Srinivasan, Srivilliputhur G; Gibson, Mark A; Zheng, Yufeng; Jaeger, David L; Fraser, Hamish L; Banerjee, Rajarshi

2017-12-08

Several recent papers report spectacular, and unexpected, order of magnitude improvement in creep life of alloys upon adding small amounts of elements like zinc. This microalloying effect raises fundamental questions regarding creep deformation mechanisms. Here, using atomic-scale characterization and first principles calculations, we attribute the 600% increase in creep life in a prototypical Mg-rare earth (RE)-Zn alloy to multiple mechanisms caused by RE-Zn bonding-stabilization of a large volume fraction of strengthening precipitates on slip planes, increase in vacancy diffusion barrier, reduction in activated cross-slip, and enhancement of covalent character and bond strength around Zn solutes along the c-axis of Mg. We report that increased vacancy diffusion barrier, which correlates with the observed 25% increase in interplanar bond stiffness, primarily enhances the high-temperature creep life. Thus, we demonstrate that an approach of local, randomized tailoring of bond stiffness via microalloying enhances creep performance of alloys.

Effect of meniscus replacement fixation technique on restoration of knee contact mechanics and stability.

Science.gov (United States)

D'Lima, D D; Chen, P C; Kessler, O; Hoenecke, H R; Colwell, C W

2011-06-01

success of meniscal replacement. While contact conditions are mainly sensitive to meniscus horn fixation, the stability of the knee under anteroposterior shear loads appeared to be more sensitive to meniscal rim fixation. This model may also be useful in predicting the effect of biomaterial mechanical properties and meniscal replacement shape on knee contact conditions.

Boiling Heat Transfer Mechanisms in Earth and Low Gravity: Boundary Condition and Heater Aspect Ratio Effects

Science.gov (United States)

Kim, Jungho

2004-01-01

Boiling is a complex phenomenon where hydrodynamics, heat transfer, mass transfer, and interfacial phenomena are tightly interwoven. An understanding of boiling and critical heat flux in microgravity environments is of importance to space based hardware and processes such as heat exchange, cryogenic fuel storage and transportation, electronic cooling, and material processing due to the large amounts of heat that can be removed with relatively little increase in temperature. Although research in this area has been performed in the past four decades, the mechanisms by which heat is removed from surfaces in microgravity are still unclear. Recently, time and space resolved heat transfer data were obtained in both earth and low gravity environments using an array of microheaters varying in size between 100 microns to 700 microns. These heaters were operated in both constant temperature as well as constant heat flux mode. Heat transfer under nucleating bubbles in earth gravity were directly measured using a microheater array with 100 m resolution operated in constant temperature mode with low and high subcooled bulk liquid along with images from below and from the side. The individual bubble departure diameter and energy transfer were larger with low subcooling but the departure frequency increased at high subcooling, resulting in higher overall heat transfer. The bubble growth for both subcoolings was primarily due to energy transfer from the superheated liquid layer relatively little was due to wall heat transfer during the bubble growth process. Oscillating bubbles and sliding bubbles were also observed in highly subcooled boiling. Transient conduction and/or microconvection was the dominant heat transfer mechanism in the above cases. A transient conduction model was developed and compared with the experimental data with good agreement. Data was also obtained with the heater array operated in a constant heat flux mode and measuring the temperature distribution across

Two main and a new type rare earth elements in Mg alloys: A review

Science.gov (United States)

Kong, Linghang

2017-09-01

Magnesium (Mg) alloys stand for the lightest structure engineering materials. Moreover, the strengthening of Mg alloys in ductility, toughness and corrosion predominates their wide applications. With adding rare earth elements in Mg, the mechanical properties will be improved remarkably, especially their plasticity and strength. A brief overview of the addition of rare earth elements for Mg alloys is shown. The basic mechanisms of strengthening Mg alloys with rare earth elements are reviewed, including the solid solution strengthening, grain refinement and long period stacking ordered (LPSO) phase. Furthermore, the available rare earth elements are summarized by type, chemical or physical effects and other unique properties. Finally, some challenge problems that the research is facing and future expectations of ra-re-earth Mg alloys are stated and discussed.

Physico-mechanical properties and thermal stability of thermoset nanocomposites based on styrene-butadiene rubber/phenolic resin blend

Energy Technology Data Exchange (ETDEWEB)

Shojaei, Akbar, E-mail: akbar.shojaei@sharif.edu [Department of Chemical and Petroleum Engineering, Sharif University of Technology, P.O. Box 11155-9465, Tehran (Iran, Islamic Republic of); Faghihi, Morteza [Department of Chemical and Petroleum Engineering, Sharif University of Technology, P.O. Box 11155-9465, Tehran (Iran, Islamic Republic of)

2010-02-15

Effect of organoclay (OC) on the performance of styrene-butadiene rubber (SBR)/phenolic resin (PH) blend prepared by two-roll mill was investigated. The influence of OC content ranging between 2.5 and 30 phr on the performance of SBR/PH was investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), interfacial energy analysis, tensile, dynamic mechanical, swelling, cure rheometry and thermogravimetric analysis (TGA). It was found that the OC is mainly localized in the SBR phase of SBR/PH blend through the kinetically favored mechanism relevant to rubber chains. The results also demonstrated the positive role of PH on the dispersion of OC. Both PH and OC showed accelerating role on the cure rate of SBR and increased the crosslinking density of the rubber phase. Additionally, the mechanical and dynamic mechanical properties of SBR were influenced by incorporation of both PH and OC. TGA showed that the OC improves thermal stability of SBR vulcanizate, while it exhibits a catalytic role in presence of PH.

Physico-mechanical properties and thermal stability of thermoset nanocomposites based on styrene-butadiene rubber/phenolic resin blend

International Nuclear Information System (INIS)

Shojaei, Akbar; Faghihi, Morteza

2010-01-01

Effect of organoclay (OC) on the performance of styrene-butadiene rubber (SBR)/phenolic resin (PH) blend prepared by two-roll mill was investigated. The influence of OC content ranging between 2.5 and 30 phr on the performance of SBR/PH was investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), interfacial energy analysis, tensile, dynamic mechanical, swelling, cure rheometry and thermogravimetric analysis (TGA). It was found that the OC is mainly localized in the SBR phase of SBR/PH blend through the kinetically favored mechanism relevant to rubber chains. The results also demonstrated the positive role of PH on the dispersion of OC. Both PH and OC showed accelerating role on the cure rate of SBR and increased the crosslinking density of the rubber phase. Additionally, the mechanical and dynamic mechanical properties of SBR were influenced by incorporation of both PH and OC. TGA showed that the OC improves thermal stability of SBR vulcanizate, while it exhibits a catalytic role in presence of PH.

New image-stabilizing system

Science.gov (United States)

Zhao, Yuejin

1996-06-01

In this paper, a new method for image stabilization with a three-axis image- stabilizing reflecting prism assembly is presented, and the principle of image stabilization in this prism assembly, formulae for image stabilization and working formulae with an approximation up to the third power are given in detail. In this image-stabilizing system, a single chip microcomputer is used to calculate value of compensating angles and thus to control the prism assembly. Two gyroscopes act as sensors from which information of angular perturbation is obtained, three stepping motors drive the prism assembly to compensate for the movement of image produced by angular perturbation. The image-stabilizing device so established is a multifold system which involves optics, mechanics, electronics and computer.

Recent advances in rare earth doped alkali-alkaline earth borates for solid state lighting applications

Science.gov (United States)

Verma, Shefali; Verma, Kartikey; Kumar, Deepak; Chaudhary, Babulal; Som, Sudipta; Sharma, Vishal; Kumar, Vijay; Swart, Hendrik C.

2018-04-01

As a novel class of inorganic phosphor, the alkali-alkaline earth borate phosphors have gained huge attention due to their charming applications in solid-state lighting (SSL) and display devices. The current research drive shows that phosphors based on the alkali-alkaline earth borates have transformed the science and technology due to their high transparency over a broad spectral range, their flexibility in structure and durability for mechanical and high-laser applications. Recent advances in various aspects of rare-earth (RE) doped borate based phosphors and their utilizations in SSL and light emitting diodes are summarized in this review article. Moreover, the present status and upcoming scenario of RE-doped borate phosphors were reviewed in general along with the proper credential from the existing literature. It is believed that this review is a sole compilation of crucial information about the RE-doped borate phosphors in a single platform.

Sensitivity analysis on mechanical stability of the underground excavations for an high-level radioactive waste repository

International Nuclear Information System (INIS)

Park, Jeong Hwa; Kwon, Sang Ki; Choi, Jong Won; Kang, Chul Hyung

2001-01-01

For the safe design of an underground nuclear waste repository, it is necessary to investigate the influence of the major parameters on the tunnel stability. In this study, sensitivity analysis was carried out to find the major parameters on the mechanical stability point of view. Fourteen parameters consisted of 10 site parameters and 4 design parameters were included in the FLAC3D. From the numerical analyses employing single parameter variation, it was possible to determine important parameters. In order to investigate the interaction between the parameters, fractional factorial design for the parameters, such as in situ stress ratio, depth, tunnel dimensions, joint spacing, joint stiffness, friction angle, and rock strength, was carried out. And in order to investigate the interaction between design parameters, fractional factorial design for parameters, such as in situ stress, depth, tunnel size, tunnel spacing and borehole spacing, was carried out

Effect of Electrodynamic Forces on the Attitude Stabilization of a Satellite in Ecliptic orbits

Science.gov (United States)

Abdel-Aziz, Yehia

This work is based on the previous paper of the author [1]. The present paper is devoted to the investigation of the attitude dynamics of an ecliptic satellite moving in the magnetic field of the Earth. Eelectrodynamic forces result from the motion of a charged satelite relative to the magnetic field of the Earth. The torque due to electrodynamic effect of the Lorentz forces on the attitude stabilization of the satellite is studied with the detailed model of the Earth's magnetic field. A method for estimating the stable and unstable regions of the equilibrium positions based on Euler's equation is also discussed. The results show that Lorentz forces can affect the stablization of the satellite, in particular for highly eccentric orbits and also for large satellte. [1] Abdel-Aziz, Y. A. Attitude Stabilization of a Rigid Spacecraft in the Geomagnetic Field. AdSpR 40, 18-24, 2007.

Angle Stability Analysis for Voltage-Controlled Converters

DEFF Research Database (Denmark)

Lin, Hengwei; Jia, Chenxi; Guerrero, Josep M.

2017-01-01

a criterion to analyze the quasi-steady angle stability and the direct current (DC) side stability for VSCs. The operating limit and the angle instability mechanism are revealed, which is generally applicable to the voltage-controlled converters. During the analysis, the influence of the parameters on angle...... stability is studied. Further, the difference on instability mechanism between power electronic converters and synchronous generators are explained in detail. Finally, experiment results with corrective actions verify the analysis....

Biomechanical stability of novel mechanically adapted open-porous titanium scaffolds in metatarsal bone defects of sheep.

Science.gov (United States)

Wieding, Jan; Lindner, Tobias; Bergschmidt, Philipp; Bader, Rainer

2015-04-01

Open-porous titanium scaffolds for large segmental bone defects offer advantages like early weight-bearing and limited risk of implant failure. The objective of this experimental study was to determine the biomechanical behavior of novel open-porous titanium scaffolds with mechanical-adapted properties in vivo. Two types of the custom-made, open-porous scaffolds made of Ti6Al4V (Young's modulus: 6-8 GPa and different pore sizes) were implanted into a 20 mm segmental defect in the mid-diaphysis of the metatarsus of sheep, and were stabilized with an osteosynthesis plate. After 12 and 24 weeks postoperatively, torsional testing was performed on the implanted bone and compared to the contralateral non-treated side. Maximum torque, maximum angle, torsional stiffness, fracture energy, shear modulus and shear stress were investigated. Furthermore, bone mineral density (BMD) of the newly formed bone was determined. Mechanical loading capabilities for both scaffolds were similar and about 50% after 12 weeks (e.g., max. torque of approximately 20 Nm). A further increase after 24 weeks was found for most of the investigated parameters. Results for torsional stiffness and shear modulus as well as bone formation depended on the type of scaffold. Increased BMD after 24 weeks was found for one scaffold type but remained constant for the other one. The present data showed the capability of mechanically adapted open-porous titanium scaffolds to function as bone scaffolds for large segmental defects and the influence of the scaffold's stiffness. A further increase in the biomechanical stability can be assumed for longer observation periods of greater than six months. Copyright © 2014 Elsevier Ltd. All rights reserved.

The Acinar Cage: Basement Membranes Determine Molecule Exchange and Mechanical Stability of Human Breast Cell Acini.

Directory of Open Access Journals (Sweden)

Aljona Gaiko-Shcherbak

Full Text Available The biophysical properties of the basement membrane that surrounds human breast glands are poorly understood, but are thought to be decisive for normal organ function and malignancy. Here, we characterize the breast gland basement membrane with a focus on molecule permeation and mechanical stability, both crucial for organ function. We used well-established and nature-mimicking MCF10A acini as 3D cell model for human breast glands, with ether low- or highly-developed basement membrane scaffolds. Semi-quantitative dextran tracer (3 to 40 kDa experiments allowed us to investigate the basement membrane scaffold as a molecule diffusion barrier in human breast acini in vitro. We demonstrated that molecule permeation correlated positively with macromolecule size and intriguingly also with basement membrane development state, revealing a pore size of at least 9 nm. Notably, an intact collagen IV mesh proved to be essential for this permeation function. Furthermore, we performed ultra-sensitive atomic force microscopy to quantify the response of native breast acini and of decellularized basement membrane shells against mechanical indentation. We found a clear correlation between increasing acinar force resistance and basement membrane formation stage. Most important native acini with highly-developed basement membranes as well as cell-free basement membrane shells could both withstand physiologically relevant loads (≤ 20 nN without loss of structural integrity. In contrast, low-developed basement membranes were significantly softer and more fragile. In conclusion, our study emphasizes the key role of the basement membrane as conductor of acinar molecule influx and mechanical stability of human breast glands, which are fundamental for normal organ function.

On the spin-axis dynamics of a Moonless Earth

Energy Technology Data Exchange (ETDEWEB)

Li, Gongjie; Batygin, Konstantin, E-mail: gli@cfa.harvard.edu [Harvard-Smithsonian Center for Astrophysics, The Institute for Theory and Computation, 60 Garden Street, Cambridge, MA 02138 (United States)

2014-07-20

The variation of a planet's obliquity is influenced by the existence of satellites with a high mass ratio. For instance, Earth's obliquity is stabilized by the Moon and would undergo chaotic variations in the Moon's absence. In turn, such variations can lead to large-scale changes in the atmospheric circulation, rendering spin-axis dynamics a central issue for understanding climate. The relevant quantity for dynamically forced climate change is the rate of chaotic diffusion. Accordingly, here we re-examine the spin-axis evolution of a Moonless Earth within the context of a simplified perturbative framework. We present analytical estimates of the characteristic Lyapunov coefficient as well as the chaotic diffusion rate and demonstrate that even in absence of the Moon, the stochastic change in Earth's obliquity is sufficiently slow to not preclude long-term habitability. Our calculations are consistent with published numerical experiments and illustrate the putative system's underlying dynamical structure in a simple and intuitive manner.

Prebiotic chemistry and atmospheric warming of early Earth by an active young Sun

Science.gov (United States)

Airapetian, V. S.; Glocer, A.; Gronoff, G.; Hébrard, E.; Danchi, W.

2016-06-01

Nitrogen is a critical ingredient of complex biological molecules. Molecular nitrogen, however, which was outgassed into the Earth’s early atmosphere, is relatively chemically inert and nitrogen fixation into more chemically reactive compounds requires high temperatures. Possible mechanisms of nitrogen fixation include lightning, atmospheric shock heating by meteorites, and solar ultraviolet radiation. Here we show that nitrogen fixation in the early terrestrial atmosphere can be explained by frequent and powerful coronal mass ejection events from the young Sun--so-called superflares. Using magnetohydrodynamic simulations constrained by Kepler Space Telescope observations, we find that successive superflare ejections produce shocks that accelerate energetic particles, which would have compressed the early Earth’s magnetosphere. The resulting extended polar cap openings provide pathways for energetic particles to penetrate into the atmosphere and, according to our atmospheric chemistry simulations, initiate reactions converting molecular nitrogen, carbon dioxide and methane to the potent greenhouse gas nitrous oxide as well as hydrogen cyanide, an essential compound for life. Furthermore, the destruction of N2, CO2 and CH4 suggests that these greenhouse gases cannot explain the stability of liquid water on the early Earth. Instead, we propose that the efficient formation of nitrous oxide could explain a warm early Earth.

Samarium-cobalt type rare earth permanent magnets

International Nuclear Information System (INIS)

Kamat, S.V.

2014-01-01

Permanent magnets are one of the oldest and largest applications of magnetic materials and form an integral part of our modern industrial society. They belong to a special class of functional materials and are characterized for remanence (flux output from the magnet), coercivity (resistance to demagnetization) and energy product (material energy density) from the second quadrant of the magnetic hysteresis loop. The reliability, stability, size, weight, cost and performance of many electro-technical devices depend mainly on the properties of permanent magnets used in them. There are three important families of permanent magnets viz., Ferrites, Alnicos and Rare Earth Permanent Magnets (REPMs) with energy product values ranging from 3 to 50 MGOe and among the front ranking high performance REPMs, SmCo 5 , Sm 2 Co 17 type and NdFeB alloys are technologically the most important materials. They are used in a wide range of applications ranging from consumer products to very specialized areas of tele-communications, microelectronics, defence, space, avionics etc. While NdFeB has the highest energy product, Sm-Co based magnets are preferred for most critical applications where temperature stability of magnetic properties is essential because of their significantly higher Curie temperatures. In this presentation some of the key challenges associated with these Sm-Co based rare earth permanent magnets will be highlighted. (author)

Aespoe Pillar Stability Experiment. Final 2D coupled thermo-mechanical modelling

Energy Technology Data Exchange (ETDEWEB)

Fredriksson, Anders; Staub, Isabelle; Outters, Nils [Golder Associates AB, Uppsala (Sweden)

2004-02-01

A site scale Pillar Stability Experiment is planned in the Aespoe Hard Rock Laboratory. One of the experiment's aims is to demonstrate the possibilities of predicting spalling in the fractured rock mass. In order to investigate the probability and conditions for spalling in the pillar 'prior to experiment' numerical simulations have been undertaken. This report presents the results obtained from 2D coupled thermo-mechanical numerical simulations that have been done with the Finite Element based programme JobFem. The 2D numerical simulations were conducted at two different depth levels, 0.5 and 1.5 m below tunnel floor. The in situ stresses have been confirmed with convergence measurements during the excavation of the tunnel. After updating the mechanical and thermal properties of the rock mass the final simulations have been undertaken. According to the modelling results the temperature in the pillar will increase from the initial 15.2 deg up to 58 deg after 120 days of heating. Based on these numerical simulations and on the thermal induced stresses the total stresses are expected to exceed 210 MPa at the border of the pillar for the level at 0.5 m below tunnel floor and might reach 180-182 MPa for the level at 1.5 m below tunnel floor. The stresses are slightly higher at the border of the confined hole. Upon these results and according to the rock mechanical properties the Crack Initiation Stress is exceeded at the border of the pillar already after the excavation phase. These results also illustrate that the Crack Damage Stress is exceeded only for the level at 0.5 m below tunnel floor and after at least 80 days of heating. The interpretation of the results shows that the required level of stress for spalling can be reached in the pillar.

Differential compaction mechanism for earth fissures near Casa Grande, Arizona.

Science.gov (United States)

Jachens, R.C.; Holzer, T.L.

1982-01-01

Precise gravity measurements indicate that earth fissures or tension cracks caused by ground-water withdrawal within a 10km2 area SE of Casa Grande are associated with relief on the buried interface between the alluvial aquifer and underlying bedrock. These relations suggest that the fissures are forming in response to localized differential compaction caused by localized variations of aquifer-system thickness. -from Authors

Long-term stability of the near-field about high-level radioactive waste repository in thermo-hydro-mechanical coupling action condition

International Nuclear Information System (INIS)

Liu Yuemiao; Wang Ju; Ke Dan; Cai Meifeng

2008-01-01

It is a long-term process for the high-level radioactive waste repository, from opening, construction to end of its service. The long-term stability of the near-field is the key issue for the design of HLW repository because the opening and heat generated from the HLW. Through a nationwide investigation, Beishan area, a Gobi desert in Gansu province, is considered as a suitable candidate and GMZ bentonite deposit which located in Xinghe County, Inner Mongolia has been proposed for the supplier of buffer/backfill material for HLW geological repository in China. According to the R and D guide of high-level radioactive waste disposal in China, the 3D model of HLW repository with high-level radioactive waste, canister and buffer/backfill material is established using FLAC3D. To take into account in situ stress, geothermal gradient, groundwater, thermal relief of HLW and swelling pressure of buffer/backfill material, the evolution of temperature, stress and displacement of HLW repository under thermo-mechanical coupling, hydro-mechanical coupling and thermo-hydro-mechanical coupling conditions was analyzed respectively. The long-term stability of HLW repository in Beishan area was studied. (authors)

Rare-Earth Tantalates and Niobates Single Crystals: Promising Scintillators and Laser Materials

Directory of Open Access Journals (Sweden)

Renqin Dou

2018-01-01

Full Text Available Rare-earth tantalates, with high density and monoclinic structure, and niobates with monoclinic structure have been paid great attention as potential optical materials. In the last decade, we focused on the crystal growth technology of rare-earth tantalates and niobates and studied their luminescence and physical properties. A series of rare-earth tantalates and niobates crystals have been grown by the Czochralski method successfully. In this work, we summarize the research results on the crystal growth, scintillation, and laser properties of them, including the absorption and emission spectra, spectral parameters, energy levels structure, and so on. Most of the tantalates and niobates exhibit excellent luminescent properties, rich physical properties, and good chemical stability, indicating that they are potential outstanding scintillators and laser materials.

Synthesis, structuring and characterization of rare earth oxide thin films: Modeling of the effects of stress and defects on the phase stability

International Nuclear Information System (INIS)

Gaboriaud, R.J.; Paumier, F.; Lacroix, B.

2014-01-01

This work studies the effects of the deposition parameters on the microstructure and the related residual stress in a rare earth oxide thin film. This study is focused on the yttrium sesquioxide (Y 2 O 3 ) thin films deposited on Si (100) substrates using the ion beam sputtering technique. This technique allows the control of the microstructure and the related residual stress in the thin films by monitoring the energy of the argon beam used in the deposition process. Measurements of the stresses within the oxide layer were performed by the X-ray diffraction-sin 2 Ψ method. The results show that the classic model of a pure biaxial in-plane model of stress, generally proposed in thin films, is not satisfying. A model that includes a hydrostatic stress due to the crystalline defects generated during the deposition process and a biaxial stress called a fixation stress, gives a good agreement with the experimental results. This modeling of the residual stress, based on nanometer-scale inclusions (point, extended defects) inducing a hydrostatic stress field, leads to a quantitative analysis of the nature and the concentration of the defects. This work shows results that establish a relationship between residual stress, defects and non-equilibrium phase stabilization during growth. - Highlights: • Microstructure of Y 2 O 3 thin films • Measurements of residual stresses in the thin films • Modeling of a triaxial residual stress state • Stress-induced stabilization of non-equilibrium phase

Optimization of the geometrical stability in square ring laser gyroscopes

International Nuclear Information System (INIS)

Santagata, R; Beghi, A; Cuccato, D; Belfi, J; Beverini, N; Virgilio, A Di; Ortolan, A; Porzio, A; Solimeno, S

2015-01-01

Ultra-sensitive ring laser gyroscopes are regarded as potential detectors of the general relativistic frame-dragging effect due to the rotation of the Earth. Our project for this goal is called GINGER (gyroscopes in general relativity), and consists of a ground-based triaxial array of ring lasers aimed at measuring the rotation rate of the Earth with an accuracy of 10 −14 rad s −1 . Such an ambitious goal is now within reach, as large-area ring lasers are very close to the required sensitivity and stability. However, demanding constraints on the geometrical stability of the optical path of the laser inside the ring cavity are required. Thus, we have begun a detailed study of the geometry of an optical cavity in order to find a control strategy for its geometry that could meet the specifications of the GINGER project. As the cavity perimeter has a stationary point for the square configuration, we identify a set of transformations on the mirror positions that allows us to adjust the laser beam steering to the shape of a square. We show that the geometrical stability of a square cavity strongly increases by implementing a suitable system to measure the mirror distances, and that the geometry stabilization can be achieved by measuring the absolute lengths of the two diagonals and the perimeter of the ring. (paper)

Synthesis, microstructure and mechanical properties of ceria stabilized tetragonal zirconia prepared by spray drying technique

International Nuclear Information System (INIS)

Sharma, S.C.; Gokhale, N.M.; Dayal, Rajiv; Lazl, Ramji

2002-01-01

Ceria stabilized zirconia powders with ceria concentration varying from 6 to 16 mol% were synthesized using spray drying technique. Powders were characterized for their particle size distribution and specific surface area. The dense sintered ceramics fabricated using these powders were characterized for their microstructure, crystallite size and phase composition. The flexural strength, fracture toughness and micro-hardness of sintered ceramics were measured. High fracture toughness and flexural strength were obtained for sintered bodies with 12 mol% of CeO 2 . Flexural strength and fracture toughness were dependent on CeO 2 concentration, crystallite size and phase composition of sintered bodies. Correlation of data has indicated that the transformable tetragonal phase is the key factor in controlling the fracture toughness and strength of ceramics. It has been demonstrated that the synthesis method is effective to prepare nanocrystalline tetragonal ceria stabilized zirconia powders with improved mechanical properties. Ce-ZrO 2 with 20 wt% alumina was also prepared with flexural strength, 1200 MPa and fracture toughness 9.2 MPa√m. (author)

Effect of calcification on the mechanical stability of plaque based on a three-dimensional carotid bifurcation model

Science.gov (United States)

2012-01-01

Background This study characterizes the distribution and components of plaque structure by presenting a three-dimensional blood-vessel modelling with the aim of determining mechanical properties due to the effect of lipid core and calcification within a plaque. Numerical simulation has been used to answer how cap thickness and calcium distribution in lipids influence the biomechanical stress on the plaque. Method Modelling atherosclerotic plaque based on structural analysis confirms the rationale for plaque mechanical examination and the feasibility of our simulation model. Meaningful validation of predictions from modelled atherosclerotic plaque model typically requires examination of bona fide atherosclerotic lesions. To analyze a more accurate plaque rupture, fluid-structure interaction is applied to three-dimensional blood-vessel carotid bifurcation modelling. A patient-specific pressure variation is applied onto the plaque to influence its vulnerability. Results Modelling of the human atherosclerotic artery with varying degrees of lipid core elasticity, fibrous cap thickness and calcification gap, which is defined as the distance between the fibrous cap and calcification agglomerate, form the basis of our rupture analysis. Finite element analysis shows that the calcification gap should be conservatively smaller than its threshold to maintain plaque stability. The results add new mechanistic insights and methodologically sound data to investigate plaque rupture mechanics. Conclusion Structural analysis using a three-dimensional calcified model represents a more realistic simulation of late-stage atherosclerotic plaque. We also demonstrate that increases of calcium content that is coupled with a decrease in lipid core volume can stabilize plaque structurally. PMID:22336469

Effect of calcification on the mechanical stability of plaque based on a three-dimensional carotid bifurcation model

Directory of Open Access Journals (Sweden)

Wong Kelvin KL

2012-02-01

Full Text Available Abstract Background This study characterizes the distribution and components of plaque structure by presenting a three-dimensional blood-vessel modelling with the aim of determining mechanical properties due to the effect of lipid core and calcification within a plaque. Numerical simulation has been used to answer how cap thickness and calcium distribution in lipids influence the biomechanical stress on the plaque. Method Modelling atherosclerotic plaque based on structural analysis confirms the rationale for plaque mechanical examination and the feasibility of our simulation model. Meaningful validation of predictions from modelled atherosclerotic plaque model typically requires examination of bona fide atherosclerotic lesions. To analyze a more accurate plaque rupture, fluid-structure interaction is applied to three-dimensional blood-vessel carotid bifurcation modelling. A patient-specific pressure variation is applied onto the plaque to influence its vulnerability. Results Modelling of the human atherosclerotic artery with varying degrees of lipid core elasticity, fibrous cap thickness and calcification gap, which is defined as the distance between the fibrous cap and calcification agglomerate, form the basis of our rupture analysis. Finite element analysis shows that the calcification gap should be conservatively smaller than its threshold to maintain plaque stability. The results add new mechanistic insights and methodologically sound data to investigate plaque rupture mechanics. Conclusion Structural analysis using a three-dimensional calcified model represents a more realistic simulation of late-stage atherosclerotic plaque. We also demonstrate that increases of calcium content that is coupled with a decrease in lipid core volume can stabilize plaque structurally.

Stability of biogenic metal(loid) nanomaterials related to the colloidal stabilization theory of chemical nanostructures.

Science.gov (United States)

Piacenza, Elena; Presentato, Alessandro; Turner, Raymond J

2018-02-25

In the last 15 years, the exploitation of biological systems (i.e. plants, bacteria, mycelial fungi, yeasts, and algae) to produce metal(loid) (Me)-based nanomaterials has been evaluated as eco-friendly and a cost-effective alternative to the chemical synthesis processes. Although the biological mechanisms of biogenic Me-nanomaterial (Bio-Me-nanomaterials) production are not yet completely elucidated, a key advantage of such bio-nanostructures over those chemically synthesized is related to their natural thermodynamic stability, with several studies ascribed to the presence of an organic layer surrounding these Bio-Me-nanostructures. Different macromolecules (e.g. proteins, peptides, lipids, DNA, and polysaccharides) or secondary metabolites (e.g. flavonoids, terpenoids, glycosides, organic acids, and alkaloids) naturally produced by organisms have been indicated as main contributors to the stabilization of Bio-Me-nanostructures. Nevertheless, the chemical-physical mechanisms behind the ability of these molecules in providing stability to Bio-Me-nanomaterials are unknown. In this context, transposing the stabilization theory of chemically synthesized Me-nanomaterials (Ch-Me-nanomaterials) to biogenic materials can be used towards a better comprehension of macromolecules and secondary metabolites role as stabilizing agents of Bio-Me-nanomaterials. According to this theory, nanomaterials are generally featured by high thermodynamic instability in suspension, due to their high surface area and surface energy. This feature leads to the necessity to stabilize chemical nanostructures, even during or directly after their synthesis, through the development of (i) electrostatic, (ii) steric, or (iii) electrosteric interactions occurring between molecules and nanomaterials in suspension. Based on these three mechanisms, this review is focused on parallels between the stabilization of biogenic or chemical nanomaterials, suggesting which chemical-physical mechanisms may be

Measurement of the Earth tides with a MEMS gravimeter.

Science.gov (United States)

Middlemiss, R P; Samarelli, A; Paul, D J; Hough, J; Rowan, S; Hammond, G D

2016-03-31

The ability to measure tiny variations in the local gravitational acceleration allows, besides other applications, the detection of hidden hydrocarbon reserves, magma build-up before volcanic eruptions, and subterranean tunnels. Several technologies are available that achieve the sensitivities required for such applications (tens of microgal per hertz(1/2)): free-fall gravimeters, spring-based gravimeters, superconducting gravimeters, and atom interferometers. All of these devices can observe the Earth tides: the elastic deformation of the Earth's crust as a result of tidal forces. This is a universally predictable gravitational signal that requires both high sensitivity and high stability over timescales of several days to measure. All present gravimeters, however, have limitations of high cost (more than 100,000 US dollars) and high mass (more than 8 kilograms). Here we present a microelectromechanical system (MEMS) device with a sensitivity of 40 microgal per hertz(1/2) only a few cubic centimetres in size. We use it to measure the Earth tides, revealing the long-term stability of our instrument compared to any other MEMS device. MEMS accelerometers--found in most smart phones--can be mass-produced remarkably cheaply, but none are stable enough to be called a gravimeter. Our device has thus made the transition from accelerometer to gravimeter. The small size and low cost of this MEMS gravimeter suggests many applications in gravity mapping. For example, it could be mounted on a drone instead of low-flying aircraft for distributed land surveying and exploration, deployed to monitor volcanoes, or built into multi-pixel density-contrast imaging arrays.

Stabilization of exact nonlinear Timoshenko beams in space by boundary feedback

Science.gov (United States)

Do, K. D.

2018-05-01

Boundary feedback controllers are designed to stabilize Timoshenko beams with large translational and rotational motions in space under external disturbances. The exact nonlinear partial differential equations governing motion of the beams are derived and used in the control design. The designed controllers guarantee globally practically asymptotically (and locally practically exponentially) stability of the beam motions at the reference state. The control design, well-posedness and stability analysis are based on various relationships between the earth-fixed and body-fixed coordinates, Sobolev embeddings, and a Lyapunov-type theorem developed to study well-posedness and stability for a class of evolution systems in Hilbert space. Simulation results are included to illustrate the effectiveness of the proposed control design.

Crystal structure of Earth's inner core: A first-principles study

Science.gov (United States)

Moustafa, S. G.; Schultz, A. J.; Zurek, E.; Kofke, D. A.

2017-12-01

Since the detection of the Earth's solid inner core (IC) by Lehmann in 1936, its composition and crystal structure (which are essential to understand Earth's evolution) have been controversial. While seismological measurements (e.g. PREM) can give a robust estimation of the density, pressure, and elasticity of the IC, they cannot be directly used to determine its composition and/or crystal structure. Experimentally, reaching the extreme IC conditions ( 330 GPa and 6000 K) and getting reliable measurements is very challenging. First-principles calculations provide a viable alternative that can work as a powerful investigative tool. Although several attempts have been made to assess phase stability at IC conditions computationally, they often use a low level of theory for electronic structure (e.g., classical force-field), adopt approximate methods (e.g., quasiharmonic approximation, fixed hcp-c/a), or do not consider finite-size effects. The study of phase stability using accurate first-principles methods is hampered in part by the difficulty of computing the free energy (FE), the central thermodynamic quantity that determines stability, while including anharmonic and finite-size effects. Additional difficulty related to the IC in particular is introduced by the dynamical instability of one of the IC candidate structures (bcc) at low temperature. Recently [1-3], we introduced a novel method (denoted as "harmonically mapped averaging", or HMA) to efficiently measure anharmonic properties (e.g. FE, pressure, elastic modulus) by molecular simulation, yielding orders of magnitude CPU speedup compared to conventional methods. We have applied this method to the hcp candidate phase of iron at the IC conditions, obtaining first-principles anharmonic FE values with unprecedented accuracy and precision [4]. We have now completed and report HMA calculations to assess the phase stability of all IC candidate phases (fcc/hcp/bcc). This knowledge is the prerequisite for

Estimates of anelastic dissipation in the Earth's torsional modes

Directory of Open Access Journals (Sweden)

M. CAPUTO

1966-06-01

Full Text Available The decay of the amplitude of the free modes of the
Earth is a potential source of information on the mechanism of dissipation
of the elastic energy of the Earth.
However there are serious difficulties in the interpretation of the decay;
they are caused by several facts. One is the limited length of the significant
part of the record which prohibits to identify the splitting of all the modes
caused by the Earth rotation and also to follow the pattern in its rotation;
another reason is the coupling between modes, caused by the inhomogenities
and the flattening of the Earth, which can transfer energy from one mode
to another. The results available are therefore very few and of poor accuracy.
In order to seek new information on the mechanism of dissipation of
the elastic energy we solve a generalized form of the equation of elastodynamic
in which we have introduced some unspecified operators to represent
the dissipation of the elastic energy. By confronting these operators with
the observations we would hope to find informations on the mechanism
of dissipation. Unfortunately the laws of variation of Q with frequency,
found by various authors who were using different observations, are not in
agreement and are very uncertain. Therefore we can only estimate the
average values of the parameters of the supposed mechanisms of dissipation.
We analyze also the dissipation of energy due to viscous frictions at
the core mantle boundary. This dissipation would be negligible even for
viscosities of the core up to 1010 poise

Thermal response of integral abutment bridges with mechanically stabilized earth walls.

Science.gov (United States)

2013-03-01

The advantages of integral abutment bridges (IABs) include reduced maintenance costs and increased useful life spans. : However, improved procedures are necessary to account for the impacts of cyclic thermal displacements on IAB components, : includi...

A case of the tail wagging the dog? Reverse weathering and Earth's CO2 thermostat.

Science.gov (United States)

Higgins, J. A.

2017-12-01

Feedbacks between climate, the global carbon cycle, and the chemistry of seawater stabilize Earth's surface temperature on geologic timescales and are likely responsible for its habitability over billions of years of Earth history. The most important component of the geologic carbon cycle is the precipitation and burial of carbonate sediments. The amount of carbonate sediment produced depends, in turn, on the alkalinity generated during silicate weathering less the amount consumed during the formation of secondary clay minerals both on the continents and in the ocean. In marine enviroments this process, often referred to as reverse weathering, consumes seawater alkalinity (and cations) via reaction with degraded Al-silicate minerals. Because these reactions constitute a sink of seawater alkalinity, changes in the amount of reverse weathering will lead to imbalances between alkalinity sources and sinks. The net effect is that on timescales greater than the timescale of carbonate compensation (< 10 kyr), changes in reverse weathering will lead to changes in the rate of continental silicate weathering through the dependence of continental silicate weathering on atmospheric CO2 and climate. This mechanism is capable of changing rates of continental silicate weathering without changing either the rate of volcanic outgassing or the rate constant for continental silicate weathering (i.e. through mountain-building or the exposure of different rock types) and as a result represents a unique way of modulating the global carbon cycle and Earth's climate on geologic timescales.

Advancing the Structural Use of Earth-based Bricks: Addressing Key Challenges in the East African Context

Directory of Open Access Journals (Sweden)

Mang Tia

2010-11-01

Full Text Available The research discussed in this paper is a subset of a bigger, NSF funded research project that is directed at investigating the use of sustainable building materials. The deployment context for the research is the hot and humid climate using selected cases from the East African region. The overarching goal for the research is advancing the structural use of earth-based technologies. Significant strides can be made through developing strategies for countering the adverse factors that affect the structural performance of the resulting wall, especially ones related to moisture dynamics. The research was executed in two phases. The first phase was a two-day NSF supported workshop which was held in Tanzania in July 2009. It provided a forum for sharing best practices in earth-based building technologies and developing a research and development roadmap. The priority research areas were broadly classified as optimizing the physio-mechanical properties of earth as a building material and managing socio-cultural impediments. In the second phase of the research, the authors collaborated with researchers from East Africa to conduct experimental work on the optimization of physio-mechanical properties. The specific research issues that have been addressed are: (1 characterizing the chemical reactions that can be linked to deterioration triggered by hygrothermal loads based on the hot and humid context, and; (2 developing a prototype for a simpler, portable, affordable and viable compressed brick production machine. The paper discusses the results from the characterization work that ultimately will be used to design bricks that have specific properties based on an understanding of how different stabilizers affect the hydration process. It also describes a cheaper, portable and more efficient prototype machine that has been developed as part of the follow-up research activities.

Chemical composition and oxidative stability of jussara (Euterpe edulis M.) oil extracted by cold and hot mechanical pressing

International Nuclear Information System (INIS)

Da Cunha, A.L.A.; Freitas, S.P.; Godoy, R.L.O.; Cabral, L.M.C.; Tonon, R.V.

2017-01-01

The aim of this work was to evaluate the effect of mechanical pressing on jussara oil yield, oxidative stability and carotenoid profile with or without heat application. Firstly, jussara pulp was centrifuged for juice extraction, and the resulting cake was dried until reaching 10% moisture content. Then, oil extraction was performed in an expeller press at 25 ºC (cold pressing) and at 50 ºC (hot pressing). The process performance was evaluated by the oil yield, and the crude jussara oil was characterized for fatty acid composition, acid value, carotenoid profile and oxidative stability. Jussara oil contained 74% unsaturated fatty acids, mainly oleic and linoleic acids (48% and 24%, respectively). The oil yield was almost twice as high for the hot process as compared to the cold one. Additionally, hot pressing resulted in 25% higher total carotenoid content as compared to cold pressing, with β-carotene as the most abundant one. Hot and cold pressing showed no difference in oil oxidative stability and fatty acid composition. [es

International Conference and Advanced School Planet Earth

CERN Document Server

Jeltsch, Rolf; Pinto, Alberto; Viana, Marcelo

2015-01-01

The focus of this volume is research carried out as part of the program Mathematics of Planet Earth, which provides a platform to showcase the essential role of mathematics in addressing problems of an economic and social nature and creating a context for mathematicians and applied scientists to foster mathematical and interdisciplinary developments that will be necessary to tackle a myriad of issues and meet future global economic and social challenges. Earth is a planet with dynamic processes in its mantle, oceans and atmosphere creating climate, causing natural disasters, and influencing fundamental aspects of life and life-supporting systems. In addition to these natural processes, human activity has developed highly complex systems, including economic and financial systems; the World Wide Web; frameworks for resource management, transportation, energy production and utilization; health care delivery, and social organizations. This development has increased to the point where it impacts the stability and ...

Ternary rare earth sulfide CaCe2S4: Synthesis and characterization of stability, structure, and photoelectrochemical properties in aqueous media

Science.gov (United States)

Sotelo, Paola; Orr, Melissa; Galante, Miguel Tayar; Hossain, Mohammad Kabir; Firouzan, Farinaz; Vali, Abbas; Li, Jun; Subramanian, Mas; Longo, Claudia; Rajeshwar, Krishnan; Macaluso, Robin T.

2018-06-01

A red-orange rare earth ternary chalcogenide, CaCe2S4, was prepared in powder form by solid-state synthesis. The structural details of this compound were determined by powder X-ray diffraction. The optical band gap of CaCe2S4 was determined by diffuse reflectance spectroscopy (DRS) to be 2.1 eV, consistent with the observed red-orange color. Quantitative colorimetry measurements also support the observed color and band gap of CaCe2S4. Both direct and indirect optical transitions were gleaned from Tauc analyses of the DRS data. Photoelectrochemistry experiments on CaCe2S4 films showed n-type semiconductor behavior. Analyses of these data via the Butler-Gärtner model afforded a flat-band potential of - 0.33 V (vs. Ag/AgCl/KCl 4 M) in pH 9 aqueous sulfite electrolyte. The potential and limitations of this material for solar water splitting and photocatalytic environmental remediation (e.g., dye photodegradation) are finally presented against the backdrop of its photoelectrochemical stability and surface hole transfer kinetics in aqueous electrolytes.

Stabilization of classic and quantum systems

International Nuclear Information System (INIS)

Buts, V.A.

2012-01-01

It is shown that the mechanism of quantum whirligig can be successfully used for stabilization of classical systems. In particular, the conditions for stabilization of charged particles and radiation fluxes in plasma are found.

Exploiting sequence and stability information for directing nanobody stability engineering.

Science.gov (United States)

Kunz, Patrick; Flock, Tilman; Soler, Nicolas; Zaiss, Moritz; Vincke, Cécile; Sterckx, Yann; Kastelic, Damjana; Muyldermans, Serge; Hoheisel, Jörg D

2017-09-01

Variable domains of camelid heavy-chain antibodies, commonly named nanobodies, have high biotechnological potential. In view of their broad range of applications in research, diagnostics and therapy, engineering their stability is of particular interest. One important aspect is the improvement of thermostability, because it can have immediate effects on conformational stability, protease resistance and aggregation propensity of the protein. We analyzed the sequences and thermostabilities of 78 purified nanobody binders. From this data, potentially stabilizing amino acid variations were identified and studied experimentally. Some mutations improved the stability of nanobodies by up to 6.1°C, with an average of 2.3°C across eight modified nanobodies. The stabilizing mechanism involves an improvement of both conformational stability and aggregation behavior, explaining the variable degree of stabilization in individual molecules. In some instances, variations predicted to be stabilizing actually led to thermal destabilization of the proteins. The reasons for this contradiction between prediction and experiment were investigated. The results reveal a mutational strategy to improve the biophysical behavior of nanobody binders and indicate a species-specificity of nanobody architecture. This study illustrates the potential and limitations of engineering nanobody thermostability by merging sequence information with stability data, an aspect that is becoming increasingly important with the recent development of high-throughput biophysical methods. Copyright © 2017 The Authors. Published by Elsevier B.V. All rights reserved.

Micromagnetics of rare-earth efficient permanent magnets

Science.gov (United States)

Fischbacher, Johann; Kovacs, Alexander; Gusenbauer, Markus; Oezelt, Harald; Exl, Lukas; Bance, Simon; Schrefl, Thomas

2018-05-01

The development of permanent magnets containing less or no rare-earth elements is linked to profound knowledge of the coercivity mechanism. Prerequisites for a promising permanent magnet material are a high spontaneous magnetization and a sufficiently high magnetic anisotropy. In addition to the intrinsic magnetic properties the microstructure of the magnet plays a significant role in establishing coercivity. The influence of the microstructure on coercivity, remanence, and energy density product can be understood by using micromagnetic simulations. With advances in computer hardware and numerical methods, hysteresis curves of magnets can be computed quickly so that the simulations can readily provide guidance for the development of permanent magnets. The potential of rare-earth reduced and rare-earth free permanent magnets is investigated using micromagnetic simulations. The results show excellent hard magnetic properties can be achieved in grain boundary engineered NdFeB, rare-earth magnets with a ThMn12 structure, Co-based nano-wires, and L10-FeNi provided that the magnet’s microstructure is optimized.

Accretion disc origin of the Earth's water.

Science.gov (United States)

Vattuone, Luca; Smerieri, Marco; Savio, Letizia; Asaduzzaman, Abu Md; Muralidharan, Krishna; Drake, Michael J; Rocca, Mario

2013-07-13

Earth's water is conventionally believed to be delivered by comets or wet asteroids after the Earth formed. However, their elemental and isotopic properties are inconsistent with those of the Earth. It was thus proposed that water was introduced by adsorption onto grains in the accretion disc prior to planetary growth, with bonding energies so high as to be stable under high-temperature conditions. Here, we show both by laboratory experiments and numerical simulations that water adsorbs dissociatively on the olivine {100} surface at the temperature (approx. 500-1500 K) and water pressure (approx. 10⁻⁸ bar) expected for the accretion disc, leaving an OH adlayer that is stable at least up to 900 K. This may result in the formation of many Earth oceans, provided that a viable mechanism to produce water from hydroxyl exists. This adsorption process must occur in all disc environments around young stars. The inevitable conclusion is that water should be prevalent on terrestrial planets in the habitable zone around other stars.

Stability of Hyperthermophilic Proteins

DEFF Research Database (Denmark)

Stiefler-Jensen, Daniel

stability by randomly generate mutants and lengthy screening processes to identify the best new mutants. However, with the increase in available genomic sequences of thermophilic or hyperthermophilic organisms a world of enzymes with intrinsic high stability are now available. As these organisms are adapted...... to life at high temperatures so are their enzymes, as a result the high stability is accompanied by low activity at moderate temperatures. Thus, much effort had been put into decoding the mechanisms behind the high stability of the thermophilic enzymes. The hope is to enable scientist to design enzymes...... in the high stability of hyperthermophilic enzymes. The thesis starts with an introduction to the field of protein and enzyme stability with special focus on the thermophilic and hyperthermophilic enzymes and proteins. After the introduction three original research manuscripts present the experimental data...

Stovetop Earth Pecan Pie

Science.gov (United States)

Robin, C. M.

2005-12-01

Many fluid mechanical experiments with direct applications to Earth Science are performed with sugary syrups using conceptually straightforward procedures. Corn syrup has indeed proven to be a godsend for those studying convection and related non-linear phenomena. In addition, however, it gives experimentalists a deep physical intuition for the interior workings of hot planets. The basic concepts behind plate tectonics and mantle convection are not difficult; indeed, although they may not be aware of it, most students probably have a basic intuitive understanding of fluid mechanics gained in their daily life. However, the large size and long time scale of geophysical processes may be quite intimidating to young students. Even a simple geophysical experiment requires a complicated array of coolers, heaters and measuring and recording equipment. It is of interest to introduce students to the geodynamical concepts that can be visualized in a high-tech lab using familiar processes and equipment. Using a homemade apparatus and grocery store supplies, I propose using a 'Stove-top Earth pecan pie' to introduce simple geodynamic concepts to middle- and high-school students. The initially cold syrup heats up and the pecans begin to float (continent formation), the syrup begins to convect (mantle convection), and convection slows down after the heat is removed (secular cooling). Even Wilson cycles can be simulated by moving the pan to one side or the other of the stovetop or heating element. The activity formally introduces students to convection and its application to the earth, and makes them think about plate motion, heat transfer, scaling, and experimental procedures. As an added bonus, they can eat their experiments after recess!

A new program in earth system science education

Science.gov (United States)

Huntress, Wesley; Kalb, Michael W.; Johnson, Donald R.

1990-01-01

A program aimed at accelerating the development of earth system science curricula at the undergraduate level and at seeding the establishment of university-based mechanisms for cooperative research and education among universities and NASA has been initiated by the Universities Space Research Association (USRA) in conjunction with NASA. Proposals were submitted by 100 U.S. research universities which were selected as candidates to participate in a three-year pilot program to develop undergraduate curricula in earth system science. Universities were then selected based upon peer review and considerations of overall scientific balance among proposed programs. The program will also aim to integrate a number of universities with evolving earth system programs, linking them with a cooperative curriculum, shared faculty, and NASA scientists in order to establish a stronger base for earth systems related education and interdisciplinary research collaboration.

A preliminary study of thermo-mechanical stability of carbon S-phase formed in austenitic stainless steel

Energy Technology Data Exchange (ETDEWEB)

Li, Wei; Chiu, Yu Long; Dong, Hanshan, E-mail: wsgddf@hotmail.com [School of Metallurgy and Materials, College of Physical and Engineering Sciences, The University of Birmingham, Birmingham (United Kingdom)

2010-07-01

Carbon S-phase was generated in the surface of AISI316 austenitic stainless steel by plasma carburising at 500°C for 10h in a gas mixture of 1.5%CH4 and 98.5%H{sub 2}. The thermo-mechanical stability of the carbon S-phase was studied by stressing the 'dog-bone' tensile specimens in the range of 0-200MPa at temperatures ranging from 400 to 500°C for 100-150h. Post-test characterisation was conducted using XRD, SEM, TEM and micro-indentation. The experimental results demonstrate that when tested at a fix temperature the thickness of the carbon S-phase layer increased with the stress applied to the tensile specimens during the thermo-mechanical stability tests. This indicates that tensile stress promotes the diffusion of carbon in the carbon-S-phase. When stressed at 400°C the microstructure of the carbon S-phase was not affected by the stress level; however, when stressed at 450 and 500°C for 100MPa or above, the corrosion resistance of the carbon S-phase slightly deteriorated. The application of a tensile stress during annealing of S-phase layer can retard the deduction of its hardness. This is believed to be related to the early stage precipitation of carbides in the S-phase, which could be facilitated by the applied tensile stress during thermal annealing. (author)

Numerical simulation of head top coal's stability control of fully mechanized longwall mining with sublevel caving face in large dip seam

Energy Technology Data Exchange (ETDEWEB)

Li, W.; Wan, Z.; Jiang, F.; Jia, P. [Beijing Science and Technology University, Beijing (China)

2008-07-01

Stability control of the head face's top-coal is one of the key techniques of realising high production and high efficiency in coal mining in fully mechanized top-coal caving face. The characteristics of the stress in the overlying strata of the fully mechanized top-coal caving face and the top coal were analysed using FLAC{sup 3D}. The results show that the tip-to-face top-coal generates a large deformation while it is in the stress-relaxed area. The top-coal in the front of the wall appears to be the failure area for the effect of the abutment pressure that spreads over the coal seam. The surrounding rock of the upper face end is the key part strengthened the control of the rib spalling. The first and frequent appearing phenomenon of losing stability of the powered supports is that the back base of the hydraulic power supports in the top of the face slips. Increasing the quality of support and so on can maintain the stability of surrounding rock. 4 refs., 7 figs., 1 tab.

Stability of matter

International Nuclear Information System (INIS)

Thirring, W.

1985-01-01

Basing on quantum mechanics and the simple Hamiltonian consisting of kinetic energy and Coulomb potential, heuristic arguments and estimates are used to guess the essential stability properties of many-particle systems. In view of applications in astrophysics, gravitation as a second potential and thermodynamic arguments are added. The guesses thus obtained are confronted with known exact results. The connection between the stabilities against explosion and against implosion, and thermodynamic stability is considered. In systems with a particle number larger than approx= 10 54 (corresponding to the Jupiter mass) gravitational energy prevails over the electrostatic energy and determines the history of a star. Negative specific heat accompanies life and death of a star. Finally the role of stability and instability in the universe for life is outlined. (G.Q.)

Synthesis and physicochemical investigation of 3-nitro-5-aminobenzoates of rare earths

International Nuclear Information System (INIS)

Makushova, G.N.; Zakharova, T.V.; Shilova, L.I.

1994-01-01

The compounds of cerium subgroup rare earth with 3-nitro-5-aminobenzoic acid of composition Ln(C 7 H 5 N 2 O 4 ) 3 ·nH 2 O, where Ln-La, Ce, Pr, Nd, Sm, Eu; n=4-14 not yet described in literature were obtained. Rare earth 3-nitro-5-aminobenzoates were individual crystal substances, as shown by X-ray diffraction; their interplanar distances were calculated. Thermal stability of the derived compounds was studied by means of thermography and thermal gravimetry. The interval of dehydration and start of decomposition of anhydrous salts was determined

MOCVD and ALD of rare earth containing multifunctional materials. From precursor chemistry to thin film deposition and applications

International Nuclear Information System (INIS)

Milanov, Andrian Petrov

2010-01-01

The present thesis deals with the development of metal-organic complexes of rare elements. They should be used as novel precursors for the production of rare earth thin films by metal-organic chemical vapor deposition (MOCVD) and Atomic Layer Deposition (ALD). Within the work two precursor classes were examined, the tris-Malonato-complexes as well as the tris-Guanidinato-complexes of a series of rare earth metals. The latter showed excellent properties regarding to their volatility, their thermal stability, the defined decomposition and high reactivity towards water. They have been successfully used as precursors for the MOCVD of rare earth oxide layers. By using of a gadolinium guanidinate it could also be shown that the rare earth guanidinates are promising precursors for ALD of rare earth oxide and MOCVD of rare earth nitride layers. [de

Stability of iron-rich magnesiowüstite in Earth's lower mantle

Science.gov (United States)

Ohta, K.; Fujino, K.; Kuwayama, Y.; Kondo, T.; Shimizu, K.; Ohishi, Y.

2012-12-01

At ambient conditions, MgO periclase and FeO wüstite form a solid solution (Mg1-xFex)O, named ferropericlase (x ≤ 0.5) and magnesiowüstite (x > 0.5). (Mg1-xFex)O ferropericlase is considered to be a major component of Earth's lower mantle, and may play an important role for its structure and dynamics. Iron-rich magnesiowüstite also needs to be considered because of possible iron enrichment at the core-mantle boundary region [e.g., Nomura et al., 2011]. Recent laser-heated diamond anvil cell experiments on FeO revealed that NaCl-type (B1) structured FeO underwent an insulator-metal transition at about 70 GPa and 1800 K without any structural transformation [Fischer et al., 2011; Ohta et al., 2012]. These results imply that the metallic B1 FeO would require a two-phase field for the MgO-FeO binary system due to different chemical bonding between insulating MgO and metallic FeO. We performed simultaneous electrical conductivity and x-ray diffraction measurements on (Mg0.20Fe0.80)O and (Mg0.05Fe0.95)O magnesiowüstite up to 140 GPa and 2100 K, and then examined recovered samples by using analytical transmission electron microprobe. We obtained some evidences for the dissociation of (Mg0.05Fe0.95)O into lighter and heavier phases than starting material occurring above 70 GPa and 1900 K, which is most likely due to the metallization of FeO component. On the other hand, we did not observe such dissociation and metallization in (Mg0.20Fe0.80)O. Observed dissociation in (Mg0.05Fe0.95)O might contribute to the heterogeneity in seismic wave and electrical conductivity at the Earth's core-mantle boundary region.

How did Earth not End up like Venus?

Science.gov (United States)

Jellinek, M.; Lenardic, A.; Weller, M. B.

2017-12-01

Recent geodynamic calculations show that terrestrial planets forming with a chondritic initial bulk composition at order 1 AU can evolve to be either "Earth-like" or "Venus-like": Both mobile- and stagnant-lid tectonic regimes are permitted, neither solution is an explicitly stronger attractor and effects related to differences in Sun-Earth distance are irrelevant. What factors might then cause the thermal evolutionary paths of Earth and Venus to diverge dynamically at early times? At what point in Earth's evolution did plate tectonics emerge and when and how did this tectonic mode gain sufficient resilience to persist over much of Earth's evolution? What is the role of volatile cycling and climate: To what extent have the stable climate of Earth and the greenhouse runaway climate of Venus enforced their distinct tectonic regimes over time? In this talk I will explore some of the mechanisms potentially governing the evolutionary divergence of Earth and Venus. I will first review observational constraints that suggest that Earth's entry into the current stable plate tectonic mode was far from assured by 2 Ga. Next I will discuss how models have been used to build understanding of some key dynamical controls. In particular, the probability of "Earth-like" solutions is affected by: 1) small differences in the initial concentrations of heat producing elements (i.e., planetary initial conditions); 2) long-term climate change; and 3) the character of a planet's early evolutionary path (i.e., tectonic hysteresis).

Mathematics applied to fluid mechanics and stability; Proceedings of the Conference, Rensselaer Polytechnic Institute, Troy, NY, Sept. 9-11, 1985

International Nuclear Information System (INIS)

Drew, D.A.; Flaherty, J.E.

1986-01-01

The mathematical analysis of fluid mechanics and stability and its applications in science and engineering are examined in reviews and reports. Topics addressed include Taylor-vortex flow, isothermal fluid-film lubrication theories, the morphology of spiral galaxies, rotating-fluid problems in ballistics, coupled Lorenz oscillators, the connection between chaos and turbulence, plane-front alloy solidification versus free-surface Benard convection, and the nonlinear stability of spiral flow between rotating cylinders with a small gap. Consideration is given to resonance conditions for forced two-dimensional channel flows, the secondary bifurcation of standing surface waves in rectangular basins, instability in the flow of granular materials, and the supercritical dynamics of baroclinic disturbances

Preliminary treatment of chlorinated streams containing fission products: mechanisms leading to crystalline phases in molten chloride media

International Nuclear Information System (INIS)

Hudry, D.

2008-10-01

The world of the nuclear power gets ready for profound modifications so that 'the atom' can aspire in conformance with long-lasting energy: it is what we call the development of generation IV nuclear systems. So, the new pyrochemical separation processes for the spent fuel reprocessing are currently being investigated. Techniques in molten chloride media generate an ultimate flow (with high chlorine content) which cannot be incorporated in conventional glass matrices. This flow is entirely water-soluble and must be conditioned in a chemical form which is compatible with a long-term disposal. This work of thesis consists in studying new ways for the management of the chlorinated streams loaded with fission products (FP). To do it, a strategy of selective FP extraction via the in situ formation of crystalline phases was retained. The possibility of extracting rare earths in the eutectic LiCl-KCl was demonstrated via the development of a new way of synthesis of rare earth phosphates (TRPO 4 ). As regards alkaline earths, the conversion of strontium and barium chlorides to the corresponding tungstates or molybdates was studied in different solvents. Mechanisms leading to the crystalline phases in molten chloride media were studied via the coupling of NMR and XRD techniques. First of all, it has been shown that these mechanisms are dependent on the stability of the used precursors. So in the case of the formation of rare earth phosphates the solvent is chemically active. On the other hand, in the case of the formation of alkaline earth tungstates it would seem that the solvent plays the role of structuring agent which can control the ability to react of chlorides. (author)

Surfactant-assisted dispersion of carbon nanotubes: mechanism of stabilization and biocompatibility of the surfactant

Science.gov (United States)

Singh, Raman Preet; Jain, Sanyog; Ramarao, Poduri

2013-10-01

Nanoparticles (NPs) are thermodynamically unstable system and tend to aggregate to reduce free energy. The aggregation property of NPs results in inhomogeneous exposure of cells to NPs resulting in variable cellular responses. Several types of surfactants are used to stabilize NP dispersions and obtain homogenous dispersions. However, the effects of these surfactants, per se, on cellular responses are not completely known. The present study investigated the application of Pluronic F68 (PF68) for obtaining stable dispersion of NPs using carbon nanotubes as model NPs. PF68-stabilized NP suspensions are stable for long durations and do not show signs of aggregation or settling during storage or after autoclaving. The polyethylene oxide blocks in PF68 provide steric hindrance between adjacent NPs leading to stable NP dispersions. Further, PF68 is biocompatible in nature and does not affect integrity of mitochondria, lysosomes, DNA, and nuclei. Also, PF68 neither induce free radical or cytokine production nor does it interfere with cellular uptake mechanisms. The results of the present study suggest that PF68-assisted dispersion of NPs produced suspensions, which are stable after autoclaving. Further, PF68 does not interfere with normal physiological functions suggesting its application in nanomedicine and nanotoxicity evaluation.

Surfactant-assisted dispersion of carbon nanotubes: mechanism of stabilization and biocompatibility of the surfactant

International Nuclear Information System (INIS)

Singh, Raman Preet; Jain, Sanyog; Ramarao, Poduri

2013-01-01

Nanoparticles (NPs) are thermodynamically unstable system and tend to aggregate to reduce free energy. The aggregation property of NPs results in inhomogeneous exposure of cells to NPs resulting in variable cellular responses. Several types of surfactants are used to stabilize NP dispersions and obtain homogenous dispersions. However, the effects of these surfactants, per se, on cellular responses are not completely known. The present study investigated the application of Pluronic F68 (PF68) for obtaining stable dispersion of NPs using carbon nanotubes as model NPs. PF68-stabilized NP suspensions are stable for long durations and do not show signs of aggregation or settling during storage or after autoclaving. The polyethylene oxide blocks in PF68 provide steric hindrance between adjacent NPs leading to stable NP dispersions. Further, PF68 is biocompatible in nature and does not affect integrity of mitochondria, lysosomes, DNA, and nuclei. Also, PF68 neither induce free radical or cytokine production nor does it interfere with cellular uptake mechanisms. The results of the present study suggest that PF68-assisted dispersion of NPs produced suspensions, which are stable after autoclaving. Further, PF68 does not interfere with normal physiological functions suggesting its application in nanomedicine and nanotoxicity evaluation

Preformulation stability study of the EGFR inhibitor HKI-272 (Neratinib) and mechanism of degradation.

Science.gov (United States)

Lu, Qinghong; Ku, Mannching Sherry

2012-03-01

The stability in solution of HKI-272 (Neratinib) was studied as a function of pH. The drug is most stable from pH 3 to 4, and degradation rate increases rapidly around pH 6 and appears to approach a maximum asymptotic limit in the range of pH 812. Pseudo first-order reaction kinetics was observed at all pH values. The structure of the major degradation product indicates that it is formed by a cascade of reactions within the dimethylamino crotonamide group of HKI-272. It is assumed that the rate-determining step is the initial isomerization from allyl amine to enamine functionality, followed by hydrolysis and subsequent cyclization to a stable lactam. The maximum change in degradation rate as a function of pH occurs at about pH 6, which corresponds closely to the theoretical pKa value of the dimethylamino group of HKI-272 when accounting for solvent/temperature effects. The observed relationship between pH and degradation rate is discussed, and a self-catalyzed mechanism for the allylamine-enamine isomerization reaction is proposed. The relevance of these findings to other allylamine drugs is discussed in terms of the relative stability of the allylic anion intermediate through which, the isomerization occurs.