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DEFECTS IN LINBO3 .2. computer-simulation

JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS 1991年第1期52卷 201-210页

作者： DONNERBERG, HJ TOMLINSON, SM CATLOW, CRA UNIV KEELE DEPT CHEM KEELE ST5 5BG STAFFS ENGLAND

Results of our recent shell-model calculations concerning the most important intrinsic and extrinsic defect structures in LiNbO3 are presented. Suitable energy minimization techniques involved in this simulation approach guarantee the full account of crystal relaxation effects upon defects. Li2O-deficiency, reduction-induced changes of the intrinsic defect structure as well as the incorporation modes of impurity ions may consistently be explained. Finally, a detailed description of the Mg incorporation over the whole solution range is given.

关键词： computer-simulation SHELL MODEL MOTT-LITTLETON APPROXIMATION INTRINSIC AND EXTRINSIC DEFECT STRUCTURES MG INCORPORATION IN LINBO3

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NASA Technical Reports Server (Ntrs) 19980006552: Shape Optimization by Bayesian-Validated computer-simulation Surrogates

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2016年

NASA Technical Reports Server (Ntrs) 19980006552: Shape Optimization by Bayesian-Validated computer-simulation Surrogates by NASA Technical Reports Server (Ntrs); NASA Technical Reports Server (Ntrs); published by

关键词： (ntrs) 19980006552: airfoils bayes theorem bayesian-validated computerized simulation computer-simulation construction heat exchangers inclusions nasa technical reports server (ntrs) optimization patera, anthony t. predictions proving reports shapes topology tradeoffs vortices

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A computer simulation study of point defects in diopside and the self-diffusion of Mg and Ca by a vacancy mechanism

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MINERALOGICAL MAGAZINE 1998年第5期62卷 599-606页

作者： Azough, F Freer, R Wright, K Jackson, R Univ Manchester Inst Sci & Technol Ctr Mat Sci Manchester M1 7HS Lancs England Univ Manchester Dept Earth Sci Manchester M13 9PL Lancs England Univ Keele Dept Chem Keele ST5 5BG Staffs England

computer simulation techniques have been used to investigate defect formation and the diffusion of Ca and Mg in diopside. It was found that isolated, non-interacting CaO and MgO Schottky defects had the lowest formation energies (3.66 and 3.97 eV respectively);oxygen Frenkel defects are the most favourable oxygen defects (formation energies 3.93 eV). Magnesium and calcium self-diffusion in the c-direction of diopside is easiest by a vacancy mechanism involving either direct jumps along the c-direction, or double jumps in the b-c plane. In the extrinsic regime, diffusion activation energies for Mg are predicted to be 9.82 eV (direct route) and 1.97 eV (double jump route);for Ca diffusion, activation energies are predicted to be 6.62 eV (direct route) and 5.63 eV (double jump route). If additional vacancies (oxygen or magnesium) are present in the vicinity of the diffusion path, Ca migration energies fall to 1.97-2.59 eV. At elevated temperatures in the intrinsic regime, diffusion activation energies of greater than or equal to 5.95 eV are predicted for Mg self-diffusion and 9.29-10.28 eV for Ca self-diffusion. The values for Ca diffusion are comparable with published experimental data. It is inferred that a divacancy mechanism may operate in diopside crystals.

关键词： computer-simulation point defects diopside vacancy mechanism self-diffusion

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Spatial dispersion of aggregate in concrete a computer simulation study

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computerS AND CONCRETE 2006年第5期3卷 301-312页

作者： Hu, Jing Chen, Huisu Stroeven, Piet Delft Univ Technol Fac Civil Engn & Geosci NL-2628 CN Delft Netherlands

Experimental research revealed that the spatial dispersion of aggregate grains exerts pronounced influences on the mechanical and durability properties of concrete. Therefore, insight into this phenomenon is of paramount importance. Experimental approaches do not provide direct access to three-dimensional spacing information in concrete, however. Contrarily, simulation approaches are mostly deficient in generating packing systems of aggregate grains with sufficient density. This paper therefore employs a dynamic simulation system (with the acronym SPACE), allowing the generation of dense random packing of grains, representative for concrete aggregates. This paper studies by means of SPACE packing structures of aggregates with a Fuller type of size distribution, generally accepted as a suitable approximation for actual aggregate systems. Mean free spacing (lambda) over bar mean nearest neighbour distance (NND) between grain centres (Delta) over bar (3), and the probability density function of Delta(3) are used to characterize the spatial dispersion of aggregate grains in model concretes. Influences on these spacing parameters are studied of volume fraction and the size range of aggregate grains. The values of these descriptors are estimated by means of stereological tools, whereupon the calculation results are compared with measurements. The simulation results indicate that the size range of aggregate grains has a more pronounced influence on the spacing parameters than exerted by the volume fraction of aggregate. At relatively high volume density of aggregates, as met in the present cases, theoretical and experimental values are found quite similar. The mean free spacing is known to be independent of the actual dispersion characteristics (Underwood 1968);it is a structural parameter governed by material composition. Moreover, scatter of the mean free spacing among the serial sections of the model concrete in the simulation study is relatively small, demonstrating th

关键词： aggregates computer-simulation dispersion SPACE spacing stereology

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Strong layering effects and anomalous dynamical behaviour in confined water at low hydration

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JOURNAL OF PHYSICS-CONDENSED MATTER 2003年第1期15卷 S145-S150页

作者： Rovere, M Gallo, P Univ Roma Tre Dipartimento Fis Ist Nazl Fis Mat Unita Ric Roma Tre I-00146 Rome Italy

Molecular dynamics results on water con fined in a silica pore in the lowhydration regime are presented. Strong layering effects are found due to the hydrophilic character of the substrate. The local properties of water are studied as a function of both temperature and hydration level. The interaction of the thin films of water with the silica atoms induces a strong distortion of the hydrogen bond network. The residence time of the water molecules is dependent on the distance from the surface. Its behaviour shows a transition from a Brownian to a non-Brownian regime on approaching the substrate in agreement with results found in studies of water in contact with globular proteins. The confined liquid at low hydration shows upon supercooling an anomalous behaviour which is rather different to that in the high-hydration regimes already studied.

关键词： Liquid water computer-simulation Glass

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Monte Carlo phase diagram for diblock copolymer melts

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JOURNAL OF CHEMICAL PHYSICS 2006年第2期124卷 24904-1-24904-页

作者： Matsen, MW Griffiths, GH Wickham, RA Vassiliev, ON Univ Reading Dept Phys Reading RG6 6AF Berks England St Francis Xavier Univ Dept Phys Antigonish NS B2G 2W5 Canada

A partial phase diagram is constructed for diblock copolymer melts using lattice-based Monte Carlo simulations. This is done by locating the order-disorder transition (ODT) with the aid of a recently proposed order parameter and identifying the ordered phase over a wide range of copolymer compositions (0.2 <= f <= 0.8). Consistent with experiments, the disordered phase is found to exhibit direct first-order transitions to each of the ordered morphologies. This includes the spontaneous formation of a perforated-lamellar phase, which presumably forms in place of the gyroid morphology due to finite-size and/or nonequilibrium effects. Also included in our study is a detailed examination of disordered cylinder-forming (f=0.3) diblock copolymers, revealing a substantial degree of pretransitional chain stretching and short-range order that set in well before the ODT, as observed previously in analogous studies on lamellar-forming (f=0.5) molecules. (c) 2006 American Institute of Physics.

关键词： MICROPHASE SEPARATION TRANSITION ASYMMETRIC BLOCK-COPOLYMERS computer-simulation POLYMERS BEHAVIOR ORDER

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Temperature effect in a montmorillonite clay at low hydration-microscopic simulation

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MOLECULAR PHYSICS 2004年第18期102卷 1965-1977页

作者： Malikova, N Marry, V Dufrêche, JF Simon, C Turq, P Giffaut, E Univ Paris 06 Lab Liquides Ion & Interfaces Chargees F-75252 Paris 05 France ANDRA F-92298 Chatenay Malabry France

The effect of temperature in the range 0-150degreesC was studied for homo-ionic montmorillonite clays with Na+ and Cs+ compensating ions in low hydration states. Monte Carlo and molecular dynamics simulations were employed to provide both static and dynamic information concerning the interlayer ions and water molecules, and emphasis was laid on the temperature activation of the diffusion coefficients. Principal structural changes were limited to the interlayer water phase, In the monohydrated systems, neither of the cations was seen to enter into the hexagonal cavities of the clay. Cs+ exhibited clear site-to-site diffusion between sites allowing coordination to six oxygen atoms of the clay sheets, this behaviour persisting to high temperatures. Preferential sites for the Na+ counterion were much less well-defined, even at low temperatures. The behaviour of the water phase in the monohydrated states was similar for the two ions. A rapid approach to bulk dynamics was seen in the transition from monohydrated to bihydrated Na-montmorillonite. A detailed quantitative comparison of the temperature activation of diffusion for a two-dimensional water phase and three-dimensional bulk water is presented for the first time.

关键词： INTERLAYER MOLECULAR-STRUCTURE MONTE-CARLO-simulation X-RAY-DIFFRACTION ELEVATED PRESSURES NEUTRON-DIFFRACTION computer-simulation SWELLING PROPERTIES CA-MONTMORILLONITE SOLID INTERFACE WATER

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Frequency Domain Acoustic Radiance Transfer for Real-Time Auralization

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ACTA ACUSTICA UNITED WITH ACUSTICA 2009年第1期95卷 106-117页

作者： Siltanen, Samuel Lokki, Tapio Savioja, Lauri Aalto Univ Dept Media Technol Helsinki 02015 Finland

A method for modeling room acoustics and auralizing the results in real time with a moving listener is presented. The acoustics modeling is based on the acoustic radiance transfer technique which is capable of modeling arbitrary reflection properties of different materials. The novel idea of implementing this technique in frequency domain allows modeling of all frequencies at once as the time domain technique requires separate runs for each frequency band. Since the auralization of the results requires scaling, adding, and delaying responses as well as convolving them with head-related impulse responses, the massive parallel computation capacity of modern graphics hardware is utilized. Thus, realistic interactive walkthroughs are possible in typical room models with a stationary source.

关键词： PRINCIPAL COMPONENTS-ANALYSIS 3RD ROUND-ROBIN computer-simulation IMPULSE RESPONSES MODEL SOUND

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Phase and interfacial behavior of partially miscible symmetric Lennard-Jones binary mixtures

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JOURNAL OF CHEMICAL PHYSICS 2005年第18期123卷 4507-1-4507-9页

作者： Diaz-Herrera, E Ramirez-Santiago, G Moreno-Razo, JA Univ Autonoma Metropolitana Iztapalapa Dept Fis Mexico City 09340 DF Mexico Univ Nacl Autonoma Mexico Inst Fis Mexico City 01000 DF Mexico

We have carried out extensive equilibrium molecular-dynamics simulations to study quantitatively the topology of the temperature versus density phase diagrams and related interfacial phenomena in a partially miscible symmetric Lennard-Jones binary mixture. The topological features are studied as a function of miscibility parameter, alpha=epsilon(AB)/epsilon(AA). Here epsilon(AA)=epsilon(BB) and epsilon(AB) stand for the parameters related to the attractive part of the intermolecular interactions for similar and dissimilar particles, respectively. When the miscibility varies in the range 0

关键词： MOLECULAR-DYNAMICS simulation LIQUID-VAPOR INTERFACE ATTRACTIVE-YUKAWASYSTEM CRITICAL END-POINTS computer-simulation SURFACE FLUID TENSION VANDERWAALS

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Structural and transport properties in the Ag₃SI system:: a molecular dynamics study of alpha, beta and molten phases

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JOURNAL OF PHYSICS-CONDENSED MATTER 2004年第3期16卷 181-194页

作者： Matsunaga, S Madden, PA Nagaoka Natl Coll Technol Div Gen Educ Nagaoka Niigata 9408532 Japan Univ Oxford Phys & Theoret Chem Lab Oxford OX1 3QZ England

Structural properties of the beta phase and transport properties of the superionic (alpha), beta and molten phases of Ag3SI are investigated by molecular dynamics simulation (MD), using Vashishta-Rahman (VR)-type potentials. In the beta phase, the pair distribution functions are quite different from those in the alpha phase, because anions form the order arrangement in a bcc structure in the beta phase, whereas anions occupy the lattice points randomly in the alpha phase. The silver distributions obtained in the beta phase are in good agreement with experimental results, which are quite different from those in the alpha phase, as we reported in a previous paper. The conductivities obtained in the alpha and beta phases by MD are also in good agreement with experiments. The frequency dependent diffusion coefficients in the alpha and beta phases, which are derived from the temporal Fourier transformation of the velocity autocorrelation function, have similar features to the neutron TOF spectra data.

关键词： Und silbersulfidjodid ag3sj Superionic conductor ag3si computer-simulation Ionic-conductivity Motion Alpha-ag3si Diffraction Mixtures Order Alloy

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