Structurally-induced elastic anomalies in a superlattice of (001) twist grain boundaries

1989 ◽  
Vol 4 (6) ◽  
pp. 1427-1443 ◽  
Author(s):  
D. Wolf ◽  
J. F. Lutsko
Keyword(s):  
Grain Boundary ◽  
Elastic Constants ◽  
Mean Field ◽  
Three Dimensional ◽  
Mean Field Model ◽  
Jones Potential ◽  
Embedded Atom ◽  
Atomistic Calculations ◽  
Elastic Anomalies ◽  
Strained Layer Superlattices

It is suggested that the “supermodulus effect” observed for composition-modulated strained-layer superlattices may arise from the presence of the structurally disordered solid interfaces and not necessarily from electronic-structure effects. The latter are excluded by investigating the elastic properties of a so-called grain-boundary superlattice in which chemically identical materials are joined to form a three-dimensional superlattice. Both an embedded-atom-method and Lennard-Jones potential are employed in our zero-temperature atomistic calculations of the elastic constants and moduli of such a superlattice. They yield qualitatively similar results which, for large modulation wavelengths, can be represented by a mean-field model in which the interfacial regions are characterized by a set of effective elastic constants which are different from those of the bulk regions. The appearance of a maximum in the biaxial modulus and a minimum in the shear modulus is shown to arise from the interaction between interfaces. It is also shown that such extreme anomalies appear only in the moduli but not in the elastic constants of the grain-boundary superlattice.

The Study of Defects in Metals Using High Resolution Transmission Electron Microscopy and Atomistic Calculations

1990 ◽  
Vol 183 ◽  
Author(s):  
M. J. Mills ◽  
M. S. Daw
Keyword(s):  
Grain Boundary ◽  
Good Description ◽  
Dislocation Core ◽  
Thin Foil ◽  
Core Structure ◽  
Embedded Atom ◽  
Pair Potentials ◽  
Transmission Electron ◽  
Atomistic Calculations ◽  
Stringent Test

AbstractThe coupling of HRTEM with atomistic calculations is described for the study of grain boundaries and dislocations in aluminum. HRTEM images of the Σ9 (221) [110] grain boundary are compared with molecular statics calculations using both the Embedded Atom Method (EAM) and two pair potentials. Comparison between observed and simulated images are shown to serve as a stringent test of the theoretical methods. Atomistic calculations can in turn provide threedimensional information about the defect structure. Using the EAM, it is also possible to account for the effects of thin foil geometries on the minimim energy configuration of defects. While these effects are found to be minimal for grain boundary structures, the influence of the thin-foil geometries on the core structure of the 60° dislocation in aluminum is discussed. These comparisons indicate that the EAM function provides a good description of grain boundary structures, but fails to reproduce the observed dislocation core structure due to a low predicted value of the intrinsic stacking fault energy (SFE) on the (111). In contrast, the pair potentials used in this study provide reasonable SFE values, but appear to be less accurate for the prediction of the Σ9 (221) [110] grain boundary structures.

scholarly journals DYNAMICAL ASPECTS OF EQUILIBRIUM AND OFF-EQUILIBRIUM SIMULATIONS OF A THREE-DIMENSIONAL HEISENBERG SPIN GLASS

1999 ◽  
Vol 10 (08) ◽  
pp. 1471-1481 ◽  
Author(s):  
H. KAWAMURA ◽  
K. HUKUSHIMA
Keyword(s):  
Glass Transition ◽  
Spin Glass ◽  
Mean Field ◽  
Three Dimensional ◽  
Aging Effect ◽  
Universality Class ◽  
Mean Field Model ◽  
Heisenberg Spin ◽  
The One ◽  
Chiral Glass

Spin-glass and chiral-glass orderings of a three-dimensional isotropic Heisenberg spin glass are studied both by equilibrium and off-equilibrium Monte Carlo simulations with emphasis on their dynamical aspects. The model is found to exhibit a finite-temperature chiral-glass transition without the conventional spin-glass order. Although chirality is an Ising-like quantity from symmetry, universality class of the chiral-glass transition appears to be different from that of the standard Ising spin glass. In the off-equilibrium simulation, while the spin autocorrelation exhibits only an interrupted aging, the chirality autocorrelation persists to exhibit a pronounced aging effect reminiscent of the one observered in the mean-field model.

Conditions for the Occurrence of Abnormal Grain Growth Studied by a 3 D Vertex Dynamics Model

2012 ◽  
Vol 715-716 ◽  
pp. 563-567 ◽  
Author(s):  
M. Syha ◽  
D. Weygand
Keyword(s):  
Grain Boundary ◽  
Grain Growth ◽  
Boundary Energy ◽  
Mean Field ◽  
Three Dimensional ◽  
Abnormal Grain Growth ◽  
Dynamics Model ◽  
Boundary Properties ◽  
The Impact ◽  
Field Approaches

The conditions for the nucleation of abnormal grain growth were investigated using a three dimensional vertex dynamics model. Potentially abnormal growing grains characterized by their size and topological class, respectively and embedded in an isotropic grain ensemble were subjected to annealing varying their grain boundary properties. The simulation results indicate that the classical mean field approaches underestimate the role of the grain boundary energy advantage, while the impact of a mobility advantage is overestimated.

Numerical Simulation of Concentrated Emulsion Flows

1998 ◽  
Vol 120 (4) ◽  
pp. 824-832 ◽  
Author(s):  
Michael Loewenberg
Keyword(s):  
Shear Flow ◽  
Numerical Simulations ◽  
Mean Field ◽  
Three Dimensional ◽  
Cylindrical Tube ◽  
Shear Thinning ◽  
Mean Field Model ◽  
Numerical Predictions ◽  
Pressure Driven Flow ◽  
Concentrated Emulsion

The macroscopic flow and detailed microphysics of a concentrated emulsion are described with three-dimensional numerical simulations. Numerical predictions for deformable drop interactions in shear-flow are in very close agreement to direct microscopic measurements. The results illustrate that drop deformation stabilizes drops against coalescence. Numerical simulations are used to describe an emulsion in shear flow at dispersed-phase volume fractions up to 30 percent. Shear-thinning viscosities and large normal stresses are found. The results are used to describe pressure-driven flow of a concentrated emulsion in a cylindrical tube. Blunted macroscopic velocity profiles and shear-thinning apparent viscosities are predicted. Our results suggest that some features of moderately concentrated emulsion flows can be predicted by an effective mean-field model.

SPONTANEOUS FISSION HALF-LIVES IN VARIOUS MACROSCOPIC-MICROSCOPIC MODELS

2011 ◽  
Vol 20 (02) ◽  
pp. 532-538 ◽  
Author(s):  
Z. ŁOJEWSKI
Keyword(s):  
Spontaneous Fission ◽  
Mean Field ◽  
Three Dimensional ◽  
Superheavy Nuclei ◽  
Dynamical Programming ◽  
Mean Field Model ◽  
Macroscopic Models ◽  
Microscopic Models ◽  
Theoretical Investigations ◽  
Fission Barriers

The problem of describing spontaneous fission for the entire region of superheavy nuclei is continually present in theoretical investigations. This study outlines the results of the calculations of fission barriers and spontaneous fission half-lives for superheavy nuclei in the region of Z =100-122 using a mean field model. We examine four distinct macroscopic models and two types of pairing interactions. Our approach is based on the deformed Woods-Saxon potential. Spontaneous fission half-lives are calculated using a multi-dimensional dynamical-programming method, where the action integral is minimized within a three dimensional deformation space (β2, β4, β6).

scholarly journals Crystal Plasticity Modeling of Anisotropic Hardening and Texture Due to Dislocation Transmutation in Twinning

Materials ◽  
2018 ◽  
Vol 11 (10) ◽  
pp. 1855 ◽  
Author(s):  
Robert Allen ◽  
Laszlo Toth ◽  
Andrew Oppedal ◽  
Haitham El Kadiri
Keyword(s):  
Mechanical Response ◽  
Volume Fraction ◽  
Mean Field ◽  
Three Dimensional ◽  
Dislocation Core ◽  
Modeling Framework ◽  
Mean Field Model ◽  
Dynamic Simulations ◽  
Damage Initiation ◽  
Strain Behavior

In crystalline materials, dislocations are three-dimensional lattice distortions that systematically distort twin interfaces that they encounter. This results in dislocation dissociation events and changes in the atomic structure of the interface. The manner in which the interface distorts drive the product of the dissociation event, and consequently, the incident dislocation core and the magnitude and relative direction of the Burgers vector govern these slip-twin interaction phenomena. Recent characterization studies using transmission electron microscopy as well as advanced molecular dynamic simulations have shown that slip dislocations, whether striking or struck by a {10 1 ¯ 2} twin boundary, dissociate into a combination of twinning disconnections, interfacial disclinations (facets), jogs, and other types of dislocations engulfed inside the twin domains, called transmuted dislocations. While twinning disconnections were found to promote twin propagation, the dislocations incorporated inside the twin are of considerable importance to hardening and damage initiation as they more significantly obstruct slip dislocations accommodating plasticity of the twins. In this work, the dislocation transmutation event and its effect on hardening is captured using a dislocation density based hardening model contained in a visco-plastic self-consistent mean-field model. This is done by allowing the twins to increase their dislocation densities, not only by virtue of slip inside the twin, but also through dislocations that transmute from the parents as the twin volume fraction increases. A correspondence matrix rule is used to determine the type of converted dislocations while tracking and parameterizing their evolution. This hypothesis provides a modeling framework for capturing slip-twin interactions. The model is used to simulate the mechanical response of pure Mg and provides a more physically based approach for modeling stress-strain behavior.

scholarly journals On the Throughput Optimization in Large-Scale Batch-Processing Systems

2021 ◽  
Vol 48 (3) ◽  
pp. 128-129
Author(s):  
Sounak Kar ◽  
Robin Rehrmann ◽  
Arpan Mukhopadhyay ◽  
Bastian Alt ◽  
Florin Ciucu ◽  
...  
Keyword(s):  
Large Scale ◽  
Mean Field ◽  
Queueing Network ◽  
Processing System ◽  
Batch Size ◽  
System Throughput ◽  
Throughput Optimization ◽  
Mean Field Model ◽  
Optimal Batch Size ◽  
Globally Attractive

We analyze a data-processing system with n clients producing jobs which are processed in batches by m parallel servers; the system throughput critically depends on the batch size and a corresponding sub-additive speedup function that arises due to overhead amortization. In practice, throughput optimization relies on numerical searches for the optimal batch size which is computationally cumbersome. In this paper, we model this system in terms of a closed queueing network assuming certain forms of service speedup; a standard Markovian analysis yields the optimal throughput in w n4 time. Our main contribution is a mean-field model that has a unique, globally attractive stationary point, derivable in closed form. This point characterizes the asymptotic throughput as a function of the batch size that can be calculated in O(1) time. Numerical settings from a large commercial system reveal that this asymptotic optimum is accurate in practical finite regimes.

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