Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Fast parallel algorithms for short-range molecular dynamics

THE DESIGN AND ANALYSIS OF EXPERIMENTS. By Oscar Kempthorne. New York, John Wiley and Sons, Inc., 1952. 631 pp. $8.50. This book by a teacher of statistics (as well as a consultant for \"experimenters\") is a comprehensive study of the philosophical background for the statistical design of experiment. It is necessary to have some facility with algebraic notation and manipulation to be able to use the volume intelligently. The problems are presented from the theoretical point of view, without such practical examples as would be helpful for those not acquainted with mathematics. The mathematical justification for the techniques is given. As a somewhat advanced treatment of the design and analysis of experiments, this volume will be interesting and helpful for many who approach statistics theoretically as well as practically. With emphasis on the \"why,\" and with description given broadly, the author relates the subject matter to the general theory of statistics and to the general problem of experimental inference. MARGARET J. ROBERTSON

The Design and Analysis of Experiments

The American Society for Testing and Materials (ASTM) is an independent organization devoted to the development of standards.

American Society for Testing and Materials

A positive temperature coefficient is the term which has been used to indicate that an increase in solubility occurs as the temperature is raised, whereas a negative coefficient indicates a decrease in solubility with rise in temperature.

Effect of Temperature

Large-Scale Fabrication of Boron Nitride Nanosheets and Their Utilization in Polymeric Composites with Improved Thermal and Mechanical Properties

Modelling and Simulations of Nanoindentation in Single Crystals

This paper aims to assess the performance of a self-expandable nitinol stent, with lesion-specific design, using a finite-element (FE) method. A superelastic model was adopted to describe the superelasticity of nitinol. Hyperelastic models with damage, calibrated against experimental results, were used to describe the stress-stretch responses of arterial layers and plaque. Abaqus CAE was used to create FE models for a femoral artery with non-uniform diffusive stenosis and a nitinol stent with a lesion-specific design. In numerical simulations, an elastic tube was used to crimp and release the self-expandable stent in the diseased artery. The effect of this lesion-specific design on lumen gain was investigated by employing FE results for a commercial stent with a uniform design as a reference. The obtained results showed that the lesion-specific stent achieved larger lumen area in the artery with diffusive lesions.

Mechanical Performance of Self-expandable Nitinol Stent with Lesion-specific Design

This paper investigates the performance of conventional turning and ultrasonically assisted turning (UAT) processes with plane and textured cutting inserts. Simulations based on the finite-...

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Finite element simulations of conventional and ultrasonically assisted turning processes with plane and textured cutting inserts

Vibration-assisted machining offers a solution to expanding needs for improved machining, especially where accuracy and precision are of importance, such as in micromachining of single crystals of metals and alloys. Crystallographic anisotropy plays a crucial role in determining on overall response to machining. In this study, we intend to address the matter of ultra-precision machining of material at the micron scale using computational modelling. A hybrid modelling approach is implemented that combines two discrete schemes: smoothed particle hydrodynamics and continuum finite elements. The model is implemented in a commercial software ABAQUS/Explicit employing a user-defined subroutine (VUMAT) and used to elucidate the effect of crystallographic anisotropy on a response of face centred cubic (f.c.c.) metals to machining.

http://iopscience.iop.org/article/10.1088/1742-6596/451/1/012038/pdf

Vibration-assisted machining of single crystal

Advanced polymeric materials and polymer based nanocomposites are finding an increasing range of industrial and defence applications. These materials have the potential to improve combat survivability, whilst reducing cost and weight. This study deals with nanocomposites manufactured from blends of low density polyethylene (LDPE) with various nanofillers. The high strain rate behaviour of these materials was investigated using the split Hopkinson pressure bar (SHPB) test. The experimental results for non-reinforced materials were used as a reference to analyse the effect of the nanofillers on the properties and performance of the nano­composites. These results, together with those obtained from other mechanical tests, will be used as input into finite-element analyses to simulate the performance of these materials in lightweight armour applications. In the first step, the finite element model was validated by simulating the SHPB test and comparing the predicted results with those from the experiments. Explicit finite element analysis was used for the simulation. The fully developed model was able to demonstrate the behaviour of the test bar and specimen interaction correctly and reasonably good agreement between predicted and experimental results was observed.

Vadim V. Silberschmidt

Papers

Modelling and Simulations of Nanoindentation in Single Crystals

Mechanical Performance of Self-expandable Nitinol Stent with Lesion-specific Design

Finite element simulations of conventional and ultrasonically assisted turning processes with plane and textured cutting inserts

Vibration-assisted machining of single crystal

Analysis of the High Strain-Rate Behaviour of Polyethylene Based Nanocomposites