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

Personalised Nitinol Stent for Focal Plaques: Design and Evaluation

Numerical characterisation of uniformity of fibrous networks

Ultrasonically assisted drilling (UAD) is a novel machining technique suitable for drilling in hard-to-machine quasi-brittle materials such as carbon fibre reinforced polymer composites (CFRP). UAD has been shown to possess several advantages compared to conventional drilling (CD), including reduced thrust forces, diminished burr formation at drill exit and an overall improvement in roundness and surface finish of the drilled hole. Recently, our in-house experiments of UAD in CFRP composites demonstrated remarkable reductions in thrust-force and torque measurements (average force reductions in excess of 80%) when compared to CD with the same machining parameters. In this study, a 3D finite-element model of drilling in CFRP is developed. In order to model acoustic (ultrasonic) softening effects, a phenomenological model, which accounts for ultrasonically induced plastic strain, was implemented in ABAQUS/Explicit. The model also accounts for dynamic frictional effects, which also contribute to the overall improved machining characteristics in UAD. The model is validated with experimental findings, where an excellent correlation between the reduced thrust force and torque magnitude was achieved.

http://iopscience.iop.org/article/10.1088/1742-6596/451/1/012040/pdf

Ultrasonically assisted drilling: A finite-element model incorporating acoustic softening effects

Understanding of bone fracture can improve medical and surgical procedures. Therefore, investigation of the effect of bone’s microstructure and properties as well as loading conditions on crack initiation and propagation is of great importance. In this paper, several modelling approaches are used to study fracture of cortical bone tissue at various length scales and different types of loading. Two major problems are tackled: crack propagation under impact loading and bone cutting in surgical procedures. In the former case, a micro-scale finite-element (FE) fracture model was suggested, accounting for bone’s microstructure and using X-FEM for crack-propagation analysis [1, 2]. The cortical bone tissue was modelled as four-component heterogeneous materials. The morphology of a transverse-radial cross section captured with optical microscopy was used to generate FE models; extensive experimental studies provided necessary mechanical input data [3]. The problem of bone cutting was treated within the framework of tool-bone interaction analysis [4, 5]. A two-domain approach was used, with a process zone simulated using a smooth-particle hydrodynamics method. This zone was embedded in a continuum domain with macroscopic anisotropic properties obtained in experiments. This study is supported by analysis of damage induced by interaction between the cutting tool and the bone tissue using wedge-indentation tests and considering also the anisotropic behaviour of the bone.

Fracture processes in cortical bone: effect of microstructure

Repetitive low-velocity impact loading can result in substantial damage in adhesively bonded joints after few impacts with low force levels compared to other types of loading. The main aim of this paper is to investigate the behavior of adhesive joints subjected to impact fatigue (IF) and standard fatigue (SF) as well as their combinations and compare their effect on damage in single lap joints (SLJs). Damage evolution in both SF and IF regimes is analyzed in terms of the deterioration of residual strength of joints after respective loading histories. Fractography analysis is implemented to correlate the residual stiffness reduction under IF and SF loading with the crack propagation behavior of SLJs.

Vadim V. Silberschmidt

Papers

Personalised Nitinol Stent for Focal Plaques: Design and Evaluation

Numerical characterisation of uniformity of fibrous networks

Ultrasonically assisted drilling: A finite-element model incorporating acoustic softening effects

Fracture processes in cortical bone: effect of microstructure

Analysis of Damage Propagation in Single Lap Joints in Impact Fatigue