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

Interfacial debonding in compacted graphite iron: effect of thermal loading

Additive manufacturing emerges as an innovative technology to fabricate medical stents used to treat blocked arteries. However, there is a lack of direct comparison of underlying microstructure and mechanical properties of additively manufactured and commercial stents. In this study, additively manufactured and commercial 316 L stainless steel stents were investigated comparatively, with electrochemical polishing being used to improve the surface finish of the former stent. Microstructural characterisation of both stents was carried out through optical microscopy, scanning electron microscopy, and electron backscatter diffraction. Their hardness and elastic modulus were studied using Berkovich nanoindentation, with an emphasis on the effect of grain orientation. In addition, spherical nanoindentation was used to generate indentation stress-strain curves based on load-displacement responses. The obtained results showed that electrochemical polishing was effective in diminishing the average surface roughness, with a reduction of Ra value from 8.45 µm to 5.96 µm. The additively manufactured stent demonstrated the hierarchical grain microstructure with columnar grains and cellular sub-grains, as opposed to equiaxed fine grains and twins in the commercial stent. The hardness and modulus of additively manufactured stents were higher than those of the commercial ones. The grains close to the (111) orientation exhibited the highest hardness and elastic modulus followed by (101) and (001) orientations. The indentation stress-strain curves, yield strength, and hardening behaviour were similar for the additively manufactured and commercial stents. This work provides a fundamental understanding of the microstructure and properties of the additively manufactured stent and represents an important step towards innovative manufacturing of stents. 

A Comparative Study of Microstructures and Nanomechanical Properties of Additively Manufactured and Commercial Metallic Stents

Glass fabric-reinforced polymer (GFRP) composites used in wind turbine blades are usually exposed to large-deflection bending impacts caused by wind storms, heavy rainfall, water splashes and hailstones in the offshore; and sand and dust impingement in the desert environments. Such loadings can cause deterioration of structural integrity and load-bearing capacity of the blade structure due to induced damage in the form of matrix cracking, delamination and fibre fracture. These types of damage mechanisms become more detrimental and pose a threat to the fatigue life of the turbine blades. In this work, first the load-bearing and energy absorbing capability of woven GFRP laminates is investigated under impact loading. Experimental tests are conducted to characterise the behaviour of GFRP composites under large-deflection dynamic bending in Izod type impact tests using Resil impactor. Impact tests are performed at various energy levels to determine the ultimate fracture toughness of the laminates. In these tests, the material demonstrated interply delamination damage due to weaker matrix at low energy levels. At higher impact energies, apart from delamination, the material also exhibited permanent deflection instead of catastrophic fabric fracture. The latter was due to the visco-elasto-plastic nature of the glass fibres apart from the thermoplastic matrix. The deformation behaviour and delamination damage ensued by dynamic loading is also studied by developing three-dimensional finite element (FE) model in Abaqus/Explicit commercial package. In FE model, multiple layers of bilinear cohesive-zone elements are defined at the damage locations. Stress-based criteria and fracture-mechanics techniques are used to assess damage initiation and its progression, respectively. Numerical results gave good correlation when compared to the dynamic response observed in experiments. The methodology developed here can be employed in damage tolerant design of wind turbine composite blades subjected to similar impact loading conditions.

/pdf/analysis-of-impact-induced-damage-in-composites-for-wind-el83l622ot.pdf

Analysis of impact induced damage in composites for wind turbine blades

Non-contact imaging photoplethysmography (iPPG) to detect pulsatile blood microcirculation in tissue has been selected as a successor to low spatial resolution and slow scanning blood perfusion techniques currently employed by clinicians. The proposed iPPG system employs a novel illumination source constructed of multiple high power LEDs with narrow spectral emission, which are temporally modulated and synchronised with a high performance sCMOS sensor. To ensure spectrum stability and prevent thermal wavelength drift due to junction temperature variations, each LED features a custom-designed thermal management system to effectively dissipate generated heat and auto-adjust current flow. The use of a multi-wavelength approach has resulted in simultaneous microvascular perfusion monitoring at various tissue depths, which is an added benefit for specific clinical applications. A synchronous detection algorithm to extract weak photoplethysmographic pulse-waveforms demonstrated robustness and high efficiency when applied to even small regions of 5 mm2. The experimental results showed evidences that the proposed system could achieve noticeable accuracy in blood perfusion monitoring by creating complex amplitude and phase maps for the tissue under examination.

/pdf/noncontact-blood-perfusion-mapping-in-clinical-applications-59tywg9ajp.pdf

Vadim V. Silberschmidt

Papers

Interfacial debonding in compacted graphite iron: effect of thermal loading

A Comparative Study of Microstructures and Nanomechanical Properties of Additively Manufactured and Commercial Metallic Stents

Analysis of impact induced damage in composites for wind turbine blades

Noncontact blood perfusion mapping in clinical applications

Finite element modelling of thermally bonded nonwovens: Effect of manufacturing parameters on tensile stiffness