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

The definition of nonwovens is even more complicated. The term nonwoven refers to web-like assemblages of fibers wherein fiber-to-fiber bonding replaces twisting and interlacing. We define a nonwoven as an engineered fabric structure that may contain fibrous and nonfibrous elements and that is often manufactured directly from fibers or filaments and may incorporate other types of fabrics. The difference primarily between a nonwoven and its more traditional counterparts (woven, knitted, and braided structures) is the structure. The fibers or filaments in a nonwoven are not interlaced or interlooped and are somewhat random layered assemblies of fibers held together by a variety of different means. The structure of a nonwoven is defined, therefore, as its fiber orientation distribution function (ODF). Another structural aspect important to consider is the basis weight (mass per unit area—g/m2 or more commonly referred to as gsm) and its uniformity. While ODF may dictate behavior, basis weight uniformity dictates failure. The structure-property relationships in a nonwoven cannot be decoupled from the process utilized to form the nonwoven. Therefore, below, we present a short review of the processes employed in the making of nonwovens followed by a discussion of the structure-process-property relationships and will make an attempt to describe the mechanical properties of one class of nonwovens.

Nonwovens—Structure-process-property relationships

The dynamic mode-II energy release rate (ERR) of the end-loaded split (ELS) test with applied time-dependent displacement is derived for the first time with the effect of vibration included. Dynamic Euler-Bernoulli beams are used together with a deflection condition to simulate contact. To understand the dynamic effect and the relative dynamic contribution from each vibration mode, a ‘dynamic factor’ and a ‘spatial factor’ are defined. It is found that the contribution of the ith vibration mode is dependent on the spatial factor, which is a function of the delamination length and the total length of the ELS specimen. Certain vibration modes are dominant dependent on the spatial factor. In addition, for a given spatial factor, there may be a certain vibration mode, which makes approximately zero contribution to the ERR. The developed theory is verified against results from finite-element method (FEM) simulations and it is in excellent agreement. This work now allows the loading rate-dependent mode-II delamination toughness of materials to be determined by using ELS tests. In addition, it provides understanding of the structural dynamic response in the presence of mode-II delamination and can guide the design of structures to mitigate against vibration-driven delamination.

Theory of dynamic mode-II delamination in end-loaded split tests

A novel 3D continuum shell structure is introduced as inclusion for composite materials with special mechanical properties in this paper. Its geometry is based on a hollow re-entrant tetrahedron. In a composite, such an inclusion can demonstrate a closure effect induced by external compression. Its specific deformation mechanism results in a special character of deformation and affects effective (global) mechanical properties of the composite. A finite-element method is used to explore quantitatively and qualitatively the deformation mechanism of the suggested inclusion and its effect on the overall mechanical performance of the composite. In this study, geometrical features of the inclusion are used as parameters. The obtained results demonstrate that this kind of inclusion could reduce the composite's Poisson's ratio; moreover, its magnitude is adjustable by changing geometrical parameters of the inclusion. Besides, an overall hardening effect is achieved for the composite, with the magnitude of global stiffness also significantly affected by geometrical features of the inclusion. Thus, the developed inclusion actually provides a potential to develop new composites with a tunable Poisson's ratio and enhanced mechanical properties.

/pdf/tailoring-structure-of-inclusion-with-strain-induced-closure-3s5erpbcfh.pdf

Tailoring structure of inclusion with strain-induced closure to reduce Poisson's ratio of composite materials

The use of fiber-reinforced polymer composites (FRPs) in aerospace, automotive, and military applications as well as in energy and naval structures is ever expanding, mainly, due to the weight-saving benefits. To manufacture durable composites parts, understanding their structural behavior under severe loading conditions is critical to designers and end-users. FRPs usually demonstrate a multiplicity of damage mechanisms under varying impact conditions due to their heterogeneous microstructure. A wealth of knowledge is available on a low-velocity impact response of composites, though with continuously emerging advanced materials and structures, established structure–property–performance relationships that could provide guidelines on dynamic impact behavior of composites are rare. A compulsory compliance with extensive testing standards and affirmation to the personnel health and safety makes real-time dynamic impact experiments rather expensive. Repeatability and reliability of their results may also suffer due to the rapid time frame in the absence of a suitable data-acquisition system. Finite-element (FE) models, in such cases, can be used as a virtual simulation tool to help engineers improving design of composite structures exposed to dynamic loading.

8.14 Composites Under Dynamic Loads at High Velocities

Samples in the form of cylindrical plates, additively manufactured using the fused deposition modelling (or filament freeform fabrication, FDM/FFF) technology from polylactide (PLA), polyethylene terephthalate glycol (PETG) and polyetheretherketone (PEEK), were studied in series of in-vitro experiments on the adhesion of rat bone-marrow cells and rat peritoneal cells. Methods of estimation of the absolute number of cells and polymer samples’ mass change were used for the evaluation of cells adhesion, followed by the evaluation of cell-culture supernatants. The results of experiments for both types of cells demonstrated a statistically significant change in the absolute number of cells (variation from 44 to 119%) and the weight of the polymer samples (variation from 0.61 to 2.18%), depending on roughness of sample surface, controlled by a nozzle diameter of a 3D printer as well as printing layer height. It was found that more cells adhere to PLA samples with a larger nozzle diameter and layer height. For PETG samples, the results did not show a clear relationship between cell adhesion and printing parameters. For PEEK samples, on the contrary, adhesion to samples printed with a lower nozzle diameter (higher resolution) is better than to samples printed with a larger nozzle diameter (lower resolution). The difference in results for various polymers can be explained by their chemical structure.

/pdf/biocompatibility-of-3d-printed-pla-peek-and-petg-adhesion-of-17iv794w.pdf

Vadim V. Silberschmidt

Papers

Nonwovens—Structure-process-property relationships

Theory of dynamic mode-II delamination in end-loaded split tests

Tailoring structure of inclusion with strain-induced closure to reduce Poisson's ratio of composite materials

8.14 Composites Under Dynamic Loads at High Velocities

Biocompatibility of 3D-Printed PLA, PEEK and PETG: Adhesion of Bone Marrow and Peritoneal Lavage Cells