bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the Choice of a Maximal Cluster in the Cluster Variational Method
Authors: Vul David A. , Fontaine Didier de 
Published: March 2011

ABSTRACTAn explanation of the occurrence of unphysical solutions in the cluster variational method is given. A simple algorithm for the construction of an optimal maximal cluster, i.e., a cluster that guarantees correct results for any set of interatomic interactions, is suggested. Examples of optimal maximal clusters for various two- and three-dimensional lattices are presented.
Monte Carlo Simulations of Phase Transformations in Fe-Cr Alloys
Authors: Reinhard L. , Turchi P. E. A. 
Published: March 2011

ABSTRACTPhase stability properties of bcc based Fe-Cr alloys are examined in the framework of the first-principles KKR-CPA-GPM formalism and Monte Carlo simulations. For Fe-rich alloys, ordered configurations are found stable with respect to the random state of the alloy, but unstable with respect to the pure Fe and Cr metals. The results are compared with the ones obtained by using energy parameters extracted from experimental diffuse scattering data.
Pump-Probe Study of Bi1-xSbx Alloys
Authors: Vidal J. , Cheng T.K. , Fung A.W. , Zeiger H.J. , Dresselhaus G. , Dresselhaust M.S. , Ippen E.P. 
Published: March 2011

ABSTRACTBi1-xSbx alloys undergo a semimetal-semiconductor transition at x = 0.065 and 0.22 and are semiconducting between these limits. We investigate this system by means of femtosecond time-resolved experiments, and observe an optical response similar to those in Bi, Sb, Te and Ti2O3. A previously-reported model describes the mechanism of generation of coherent lattice vibrations via the optically excited carriers in this class of materials. As predicted by the model, the modulated reflectivity signal ΔR/R in Bi.88Sb.12 shows a beating oscillatory behavior with the Bi-Bi and Bi-Sb A1g vibrational frequencies. Model-based calculations of the ΔR background relaxation time at different Sb compositions provide understanding of the carrier and lattice dynamics throughout the transition.
Direct Activity Measurements in Liquid Ag-Au=Ge System and its Solution Model Development by Computational Techniques
Authors: Yu Qiling , Howard Stanley M. 
Published: March 2011

ABSTRACTAg activities in the Ag-Au-Ge solution were determined by the mass spectrometric analysis of effusates from a unique valved Knudsen cell at 1416 K. A mathematical model was established for Ag activity coefficient as a function of alloy composition. Activities of Au and Ge were calculated by numerical ternary Gibbs-Duhem integration on a spreadsheet. The data obtained from this investigation show that the activities on all three binary systems occurring in the ternary system are in good agreement with accepted literature values. The behavior of all pseudo binaries was found to be consistent with Darken's quadratic formalism. Darken surface of Ag is shown.
Formation of Intermetallic Phases in Metal Matrix Composites
Authors: Dorfman S. , Fuks D. , Pelleg Joshua 
Published: March 2011

ABSTRACTA theoretical study of the interaction between fibers and a matrix is performed, which is based on several approaches that are connected with the calculation of mixing energy in multicomponent alloys or with the calculation of the diffusion coefficients in such systems. As an example, interatomic potentials for the alloys (Al,Si)-B, (Al,Mg)-B, (Al,Cr)-B, (Al,Mn)-B and (Al,Ga.)-B are calculated. The values of the potential barrier Δu for binary alloys are compared with those in ternary systems. It is shown that alloying of a binary alloy by Si reduces the height of potential in comparison with the binary alloy. Other elements make this barrier higher.
A Dynamical System Theory of Large Deformations and Patterns in Non-Cohesive Solids
Authors: Evesque Pierre , Sornette Didier 
Published: March 2011

ABSTRACTWe propose a dynamical system theory of triaxial-test deformationS and localization bifurcation in brittle media. We apply it to predict that localization may occur in a packing looser than “critical” and that the general localization shape is a spiral staircase in axisymmetric 3-D cells. These two facts have recently been confirmed experimentally. This theory provides a framework for understanding the development of complex deformation patterns from the mechanics of localization and rupture.
Computer Simulation of Fracture in Brittle Polycrystalline Solids: Effect of Modulus Amisotropy
Authors: Ling Shiun , Anderson Michael P. 
Published: March 2011

ABSTRACTA simulation procedure based on the spring network model has been developed for studying the fracture behavior in brittle, polycrystalline solids. In this 2-D model, the effect of crystalline symmetry is accounted for by imparting to individual bonds a constitutive relationship using the material compliance matrix. Using this model, it was found that the fracture morphology becomes more intragranular in nature with increasing modulus anisotropy. Careful analysis suggests that this is due to the wider stress distributions, and the resulting larger number of cracks generated in the interior of anisotropic grains.
Relationship Between Dilatancy, Stresses and Plastic Dissipation in a Granular Material with Rigid Grains
Authors: Evesque Pierre , Stefani Christian 
Published: March 2011

ABSTRACTBy considering a drained cohesionless granular sample made up of rigid grains and submitted to a triaxial test, we derive an equation relating the dilatancy K, the deviatoric stress q and the confining pressure p to the energy losses D plasticdue to plastic yielding. We demonstrate that the system is contracting (K ≤ 0) at q=0, when q is increasing and that spontaneous uncontrolled yielding begins occurring when dilatancy K is maximum. We also demonstrate the existence of the characteristic state introduced by Luong and Habib and the existence of the critical state of Schofield and Wroth. We give at last a method to determine the plastic losses during a triaxial cell test using the experimental data.
Structure and Elastic Properties of Ni/Cu and Ni/Au Multilayers
Authors: Taiwo Ademola , Yan Hong , Kalonji Gretchen 
Published: March 2011

ABSTRACTThe structure and elastic properties of Ni/Cu and Ni/Au multilayer systems are investigated as a function of the number of Ni monolayers built into the systems. We employed lattice statics simulations with the interatomic potentials described by the embedded-atom method. For the Ni/Cu systems, coherent interfaces and FCC structure are maintained, and no elastic anomaly is found. For the Ni/Au systems, when the Ni layers are thick enough, they undergo a strain-induced phase transformation from FCC to HCP structure. An enhancement of Young’s modulus of these systems is found to be associated with this structural change.
Phonons and Local Elastic Moduli in Symmetrical Tilt Boundaries
Authors: Wang Gui Jin , Vitek V. , Alber I. , Bassani J. 
Published: March 2011

ABSTRACTLattice vibrations and atomic level elastic moduli have been studied for a bicrystal containing a fully relaxed symmetrical tilt boundary in Au. Central force many body potentials have been employed to describe atomic interactions. In the long-wavelength limit the phonons localized at grain boundaries can be identified with Stoneley waves known from continuum analyses. These waves are localized at the grain boundary and their velocity agrees well with that evaluated using the local effective elastic moduli of the interfacial region. However, the usually used continuum model assuming an ideal match across the interface is not sufficient to analyze these waves fully and an explicit description of interfacial properties need to be included into the continuum models of interfaces.
Normal Coordinate Analysis of Benitoite (BaTiSi3O9) and its Constituent Ring
Authors: Kim Charles C. , Bell M. I. , McKeown D. A. 
Published: March 2011

ABSTRACTThe normal modes of vibration and their frequencies are calculated for benitoite, a mineral whose crystal structure (space group D23h) consists of three-membered silicate rings (Si3O9) linked by Ba+2 and Ti+4 ions. The calculation unambiguously assigns the normal modes to the lines in the Raman and infrared spectra and determines the atomic interactions. On the assumption that mode mixings and splittings due to inter-ring interactions are small, the normal frequencies of the isolated ring of C3h, symmetry are determined. The identification of normal modes characteristic of three-membered silicate rings may prove to be a valuable guide in the interpretation of the infrared and Raman spectra of amorphous silicates, potentially leading to new information on the ring statistics of these materials.
Effects of Surface Defects on the Local Electric Field in Inhomogeneous Media
Authors: Ferris Kim F. , Risser Steven M. 
Published: March 2011

ABSTRACTSurface defects both focus the local electric field and enhance its intensity in the vicinity of the defect. Using a finite element model of an inhomogeneous dielectric film, we have examined the relationship between the defect shape and local electric field in the film and defect. We find that raised defect regions that are peaked have the largest local fields while the slope of removed regions has little effect on the field in raised defects. Both peaked and flat surface defects can lead to large enhancements of the local electric field above that predicted by effective medium approximation (EMA) methods.
Order-Disorder Transformation in Cu3AAu: A Molecular Dynamics Study
Authors: Cleri Fabrizio , Mazzone Giorgio , Enea Vittorio Rosato 
Published: March 2011

ABSTRACTThe order-disorder transformation in CU3Au has been investigated using a combined Molecular Dynamics and Cluster Variation Method approach. Free energy minimization has been performed using the Natural Iteration technique. The calculated temperature dependence of enthalpy, lattice dynamics, short-range and long-range order parameters have been successfully compared with experimental data.
H Motion in Pd and Nb: A Molecular-Dynamics Study
Authors: Li Yinggang , Wahnström Göran 
Published: March 2011

ABSTRACTBased on realistic many-body potentials molecular-dynamics simulations are carried out for PdH0.03 and NbH0.02. The H motion is investigated at two different temperatures, T = 300 and 600K, paying attention to the vibrational and diffusive motion. We find that the motion of H in Nb, a bcc metal, is more complicated than in Pd, a fee metal, and the differences are discussed. When detailed comparison is made with quasielastic neutron scattering data for H in Pd at 600K, we argue that in order to characterize the diffusion correctly, one has to include nonadiabatic effects.
Computer Modelling of Dynamically-Induced Dislocation Patterning
Authors: Devincre Benoit , Pontikis Vassilis 
Published: March 2011

ABSTRACTThe evolution of a random and initially homogeneous distribution of parallel and infinitely extended edge dislocations is studied by using elastic energy minimization without and in presence of a periodic external stress, τa. During the energy minimization without external stress (relaxation), randomly distributed dislocation dipoles are formed whereas, when the external stress is acting, the dislocations condense in walls. We investigated the spatial periodicity of this microstructure, λ, as a function of, τa, and of the total dislocation density. The elastic energy of the stress-induced microstructure is found to be comparable to the value obtained by relaxation. Thereby, emphasis is given to the dynamical character of patterning. A phenomenological model has been developed, explaining the correlation between λ and τa found in the simulations and comparing favorably with existing experimental data.
Embedded - Atom - Method Interatomic Potentials for BCC - Iron
Authors: Simonelli G. , Pasianot R. , Savino E.J. 
Published: March 2011

ABSTRACTAn embedded-atom-method (EAM) interatomic potential [1] for bcc-iron is derived. It is fitted exactly to the lattice parameter, elastic constants, an approximation to the unrelaxed vacancy formation energy, and Rose's expression for the cohesive energy [2]. Formation energies and relaxation volumes of point defects are calculated. We find that the relative energies of the defect configurations depend on the functional fitting details of the potential considered, mainly its range: the experimental interstitial configuration of lowest energy can be reproduced by changing this parameter. This result is confirmed by calculating the same defect energies using other EAM potentials, based on the ones developed by Harrison et al. [3].
Can the Strength of Brittle Materials be Enhanced?
Authors: Monette L. , Anderson M. P. , Grest G. S. 
Published: March 2011

ABSTRACTWe have employed a two-dimensional computer model to study the effect of volume fraction of second phase constituents on load transfer (stiffness) and strength in brittle short-fiber composites, i.e. composites containing a random distribution of aligned fibers, and brittle particulate composites. We find that the efficiency of load transfer to the second phase consituent increases with volume fraction in particulate composites, while it decreases for short-fiber composites. The strength of brittle particulate composites is found to decrease, while the strength of brittle short-fiber composites marginally increases only at fiber volume fractions equal or greater than 0.25.
Massively Parallel Molecular Dynamics Simulations of Two-dimensional Materials at High Strain Rates
Authors: Wagner Norman J. , Holian Brad Lee 
Published: March 2011

ABSTRACTLarge scale molecular dynamics simulations on a massively parallel computer are performed to investigate the mechanical behavior of 2-dimensional materials. A model embedded atom many- body potential is examined, corresponding to “ductile” materials. A parallel MD algorithm is developed to exploit the architecture of the Connection Machine, enabling simulations of > 106atoms. A model spallation experiment is performed on a 2-D triagonal crystal with a well-defined nanocrystalline defect on the spall plane. The process of spallation is modelled as a uniform adiabatic expansion. The spall strength is shown to be proportional to the logarithm of the applied strain rate and a dislocation dynamics model is used to explain the results. Good predictions for the onset of spallation in the computer experiments is found from the simple model. The nanocrystal defect affects the propagation of the shock front and failure is enhanced along the grain boundary.
Quantitative X-Ray Diffraction Analysis of Titanate Waste Forms and its Application to Damage Ingrowth
Authors: White T.J. , Mitamura H. 
Published: March 2011

ABSTRACTQuantitative powder X-ray diffraction was used to analyse the phase assemblages of titanate nuclear waste ceramics doped with 244Cm and accumulating a-decay doses up to 1.24 × 1018 alpha-decay-events g−1. Among the Cm-bearing phases, perovskite is more susceptible to damage than zirconolite. Phases devoid of curium (hollandite and freudenbergite) experience a flux of ionizing radiation, and may also undergo radiation-induced structural degradation. The analysis demonstrated that at a dose of 1.24 × 1018 alpha-decay-events g−1 approximately 20 wt% of the waste phases remain aperiodic after annealing for 2 hours at 800°C.
Uranium and Rare Earth Partitioning in Synroc
Authors: Smith K. L. , Lumpkin G. R. , Blackford M. G. 
Published: March 2011

ABSTRACTImproved AEM techniques were used to investigate three Synrocs containing 10 wt/ simulated HLW and a fourth sample with ∼18 wt/ simulated HLW. One of the 10 wt./ loaded Synrocs also contained an addition of 1.0 wt/ Na2O and another contained an addition of 2.0 wt/ Fe2O3. This work is part of a larger study initiated with the objective of determining if the bulk composition of Synroc affects the partitioning of elements between individual phases. Results from the four samples in this study show that, as expected, elemental partitioning is mainly controlled by the ionic radius criterion, with smaller Y, Gd, and U ions having a preference for zirconolite and the larger Ce and Nd ions favouring perovskite. Additions of Na and Fe lead to the formation of CAT and loveringite at the expense of rutile or Magneli phases, but only have minor effects on partitioning coefficients. Partitioning coefficients, DZ/P, for REE, Y, and U in the four Synrocs are the same (within experimental error).
The Reaction of SRL 202 Glass in J-13 and DIW
Authors: Ebert W. L. , Bates J. K. , Buck E. C. 
Published: March 2011

ABSTRACTStatic leach tests were performed in both 304L stainless steel and Teflon vessels using a synthetic high-level waste glass with either deionized water (DIW) or a tuff groundwater solution as the leachant to assess the effects of the vessel and the initial leachant composition on the extent and nature of the glass reaction. The tests were performed using monolith samples at 340 m−1 and crushed samples at 2000 m−1 for times up to 1 year. The results show less silicon is released from the glass into the groundwater solution than into DIW at both high and low glass surface area/leachant volume ratios (SA/V), but the alkali metal and boron releases are not affected by the leachant used. Tests performed in a stainless steel vessel resulted in slightly lower leachate pH values, but similar reaction rates to those performed in a Teflon vessel, as measured by the boron release. Blank tests with DIW or EJ-13 in the vessels showed the Teflon vessels to release small amounts of fluoride (1 to 2 ppm) and to acidify the DIW slightly (4.0 < pH < 5.6). The pH values of blank tests with EJ-13 increased from 8.2 to about 8.6 in steel and to about 9.2 in Teflon vessels. The slightly higher pH values attained in Teflon vessels are attributed to outgassing of CO2 during the test.
Enhancement of the Glass Corrosion in the Presence of Clay Minerals: Testing Experimental Results with an Integrated Glass Dissolution Model
Authors: Curti Enzo , Godon N. , Vernaz E.Y. 
Published: March 2011

ABSTRACTRecent glass dissolution experiments, conducted at 90°C in the presence of potential backfill materials, indicate remarkably faster glass corrosion in the presence of clay, compared to tests where the glass is leached either alone or with alternative backfill materials. This effect correlates with the clay content in the backfill, and may be attributed to the removal of silica from solution. Sorption, or dissolution with reprecipitation of a silica-rich clay, have been proposed as possible mechanisms for the silica consumption.The results of some experiments have been tested against a glass dissolution model, in which a widely used kinetic equation for glass corrosion is coupled with diffusive silica transport through a single porosity, linearly sorbing medium, which represents the backfilling. Because the glass corrosion rates imposed by the kinetic equation are inversely proportional to the silicic acid concentration of the leachant contacting the glass, the model predicts enhanced glass dissolution if silica is sorbed by the porous medium.The experimental data proved to be consistent with the predicted enhancement of the glass dissolution. Moreover, the model-estimated distribution coefficients for silica sorption (Kd) fall within the range of values extracted from available literature data, thus supporting the hypothesis that the observed high corrosion rates are due to sorption of silica on the clay mineral surfaces.
Does Fully Radioactive Glass Behave Differently than Simulated Waste Glass?
Authors: Feng X. , Bates J. K. , Bradley C. R. , Buck E. C. 
Published: March 2011

ABSTRACTStatic tests at SA/V (ratio of surface area of glass to solution volume) 20,000 m−1 on SRL 200 glass compositions show that, at long test periods, the simulated nuclear waste glass (nonradioactive) leaches faster than the corresponding radioactive glass by a factor of about 40, although comparative tests, done through 560 days, at lower SA/V, 2000 m−1, indicate little difference in the leach behavior of the two types of glasses. The similarity in leach behavior between radioactive and simulated glasses at SAN of 2000 m−1 or lower is also observed for SRL 165/42 and 131/11 compositions. The accelerated glass reaction with the simulated glass 200S is associated with the formation of crystalline phases such as clinoptilolite (or potassium feldspar), and a pH excursion. The radiation field generated by the fully radioactive glass reduces the solution pH. This lower pH, in turn, may retard the onset of increased reaction rate. The radiation field generated by the radioactive glasses does not directly affect the stability of the glass surface alteration layer under those conditions where the radioactive and simulated glasses react at the same rate. These results suggest that the fully radioactive nuclear waste glass 200R may maintain a much lower leach rate than the simulated 200S, if the lower pH in the 200R leachate can be sustained. Meaningful comparison tests between radioactive and simulated nuclear waste glasses should include long-term and high SA/V tests.
Evaluation of Some Low-Activation Structural Materials for Minimizing Radioactive Waste Production by Future Nuclear Fusion Power Plants
Authors: Donato Aldo 
Published: March 2011

ABSTRACTTaking into account the neutron activation (Bq/kWht) and the environmental impact in terms of Ingestion Toxic Potential IT (m3 H2O/kWht) of radioactive wastes coming from several low-activation structural material candidates for future nuclear fusion power reactors, the contribution of the material chemical composition elements and impurities to the overall radioactivity and IT has been assessed. The chemical impurities, also at very low concentrations, have been ascertained to give, in many cases, a considerable contribution to the radwastes environmental impact, as in the case of SiC/SiC fiber composites materials or low-activation martensitic steels.The orign of impurities origin has been identified and efforts to use this information in the material production processes for nuclear fusion application are suggested.
in-situ Electrochemical Characterization of Grouted Radioactive Waste
Authors: Kruger Albert A. , Gu Jingyan , Tomkiewicz Micha 
Published: March 2011

ABSTRACTThis work is based upon the notion that a grid of electrodes will be incorporated in the slurry of radioactive waste and grout-forming solids. These electrodes will remain in the hardened grout, and will serve to monitor the ionic concentration of the liquids contained within the matrix, the structural integrity of the matrix, and the rates of out-diffusion of the electrolytes. Ultimately, we will investigate four techniques: (1) ionic conductivity, (2) electrochemical potential, (3) cyclic voltammetry, and (4) impedance measurements. Eventually, the results will be correlated with present quality verification methods, which include recovering samples and following the Toxicity Characteristic Leach Procedure (or other such accepted standard tests). This paper presents the preliminary results of a recently initiated effort.