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

Ultrasonically assisted turning (UAT) is an advanced machining technique, where high frequency vibration (frequency f ≈ 20 kHz, amplitude a ≈ 15 µm) is superimposed on the movement of the cutting tool. Compared to conventional turning (CT), this technique allows significant improvements in processing intractable materials, such as high-strength aerospace alloys, composites and ceramics. Superimposed ultrasonic vibration yields a noticeable decrease in cutting forces, as well as a superior surface finish [1].

Computational modeling of ultrasonically assisted turning

Nano- and micro-indentation studies were carried out to characterise a plasticity mechanism through the evolution of localised shear bands that drive material's deformation at sub-micron length scale. Initial deformation of Zr-based bulk metallic glass (BMG) was investigated with nanoindentation tests using a spherical indenter. The indentation cycle reflects an elastic deformation with the yielding load of approx. 3 mN. For designed cycling indentation, hardening and softening phenomena were observed in nano- and micro-indentations, respectively. High-precision dynamic mechanical relaxation measurements were performed using a Dynamic Mechanical Analyzer (DMA), on decreasing frequency from 160 Hz to 0.1 Hz. A mechanical response of the BMG surface to a concentrated impact load was also studied. The obtained results indicated that the studied Zr-based BMG behaved as an elastic-perfectly plastic material at macroscale with discrete plasticity events at smaller length scales.

https://iopscience.iop.org/article/10.1088/1742-6596/451/1/012009/pdf

Quasi-static and dynamic deformation behaviour of Zr-based bulk metallic glass

The paper describes preliminary experimental studies of magneto-forming technology, undertaken at Loughborough University and using the existing 2 MA/100 kJ Quattro capacitor bank as power supply. Different practical arrangements will be detailed and results presented that illustrate magneto-forming in theta-pinch geometry: • Magneto-forming stainless steel cylinders • Welding stainless steel cylinders with stainless steel cylinders. • Magneto-forming magnesium cylinders. For each arrangement, the results of magneto-forming are analyzed at the interface as well in the adjoined materials in comparison with their pre-manufacture (as delivered) state. The used characterization techniques include micro-and nano-indentation, optical microscopy and scanning electron microscopy.

/pdf/magneto-forming-studies-1osjzhw1pj.pdf

Vadim V. Silberschmidt

Papers

Computational modeling of ultrasonically assisted turning

Quasi-static and dynamic deformation behaviour of Zr-based bulk metallic glass

Magneto-forming studies

In silico evaluation of additively manufactured 316L stainless steel stent in a patient-specific coronary artery.

Modelling the temperature and strain-rate effects of extruded magnesium alloy accounting for deformation slip and twinning