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

Numerical modeling of bones is necessary for design of efficient surgical cutting tools that can provide low cutting forces, reduce damage and prevent thermal necrosis of bone tissue. Development of realistic numerical models of cortical bone tissue requires deep knowledge of its deformation behaviour. Deformation mechanisms of bones differ from those of metals, polymers and composites since bones consist of a living tissue with hierarchical microstructure. The aim of this study is to analyse deformation characteristics of the cortical bone tissue from both experimental and numerical perspectives. Initially, Vickers hardness tests were conducted at various anatomical positions on a cross-section of a bovine femur bone to observe location-based variation of its mechanical response. Various load magnitudes ranging between 1 kgf and 100 kgf were applied in the Vickers hardness tests to analyse the effect of anisotropy on damage evolution. These tests were simulated using a finite element scheme to reproduce the mechanical behaviour of bones in indentation. Finally, results of the hardness tests were compared with those obtained from finite element simulations.

Analysis of Deformation Characteristics of Cortical Bone Tissue

The study of time-to-fracture VS external load dependence is studied for a case of crack propagation in stochastic brittle material. The scaling character of such a dependence is proved, which does not change for different types of material's stochasticity.

Effect of stochasticity on scaling properties of crack propagation.

Effect of hybrid machining on structural integrity of aerospace-grade materials

This paper presents a new enhanced computational model of Ultrasonically Assisted Turning (UAT) that is based on the DEFORM 3D FE code and allows transient, coupled thermo-mechanical simulations of both UAT and Conventional Turning (CT) of elasto-plastic materials. The model features 3D oblique chip formation and realistic geometry of a cutting tool. The model is used to analyse the effect of cutting and vibration parameters on cutting forces in UAT. The comparison between efficiency of various vibration directions is also carried out. Optimum values for cutting and vibration parameters are suggested as a result of this numerical study.

Enhanced finite element model of ultrasonically assisted turning

Bones form protective and load-bearing framework of the body. Therefore, their structural integrity is vital for the quality of life. Unfortunately, bones can only sustain a load until a certain limit, beyond which they fail. Therefore, it is essential to study their mechanical and fracture behaviours in order to get an in-depth understanding of the origins of its fracture resistance that, in turn, can assist diagnosis and prevention of bone's trauma. This can be achieved by studying mechanical properties of bone, such as its fracture toughness. Generally, most of bone fractures occur for long bones that consist mostly of cortical bone. Therefore, in this study, only a cortical bone tissue was studied. Since this tissue has an anisotropic behaviour and possesses hierarchical and complex structure, in this paper, an experimental analysis for the fracture toughness of cortical bone tissue is presented in terms of J-integral. The data was obtained using single-edge-notch bending (SENB) cortical specimens of bone tested in a three-point bending setup. Variability of values of fracture toughness was investigated by testing specimens cut from different cortex positions of bovine femur called anterior, posterior, medial, and lateral. In addition, anisotropy ratios of fracture toughness were considered by examining specimens cut from three different orientations: longitudinal, transverse and radial. Moreover, in order to link cortical bone fracture mechanisms with its underlying microstructure, fracture surfaces of specimens from different cortices and along different orientations were studied. Experimental results of this study provide a clear understanding of both variability and anisotropy of cortical bone tissue with regard to its fracture toughness.

http://iopscience.iop.org/article/10.1088/1742-6596/382/1/012045/pdf

Vadim V. Silberschmidt

Papers

Analysis of Deformation Characteristics of Cortical Bone Tissue

Effect of stochasticity on scaling properties of crack propagation.

Effect of hybrid machining on structural integrity of aerospace-grade materials

Enhanced finite element model of ultrasonically assisted turning

Variability and anisotropy of fracture toughness of cortical bone tissue