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

抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Microstructures and properties of high-entropy alloys

Mechanical properties of nanocrystalline materials

Mechanical alloying (MA) is a solid-state powder processng technique involving repeated welding, fracturing, and rewelding of powder particles in a high-energy ball mill. Originally developed to produce oxide-dispersion strengthened (ODS) nickel- and iron-base superalloys for applications in the aerospace industry, MA has now been shown to be capable of synthesizing a variety of equilibrium and non-equilibrium alloy phases starting from blended elemental or prealloyed powders. The non-equilibrium phases synthesized include supersaturated solid solutions, metastable crystalline and quasicrystalline phases, nanostructures, and amorphous alloys. Recent advances in these areas and also on disordering of ordered intermetallics and mechanochemical synthesis of materials have been critically reviewed after discussing the process and process variables involved in MA. The often vexing problem of powder contamination has been analyzed and methods have been suggested to avoid/minimize it. The present understanding of the modeling of the MA process has also been discussed. The present and potential applications of MA are described. Wherever possible, comparisons have been made on the product phases obtained by MA with those of rapid solidification processing, another non-equilibrium processing technique.

Mechanical Alloying And Milling

Elektronenmikroskopische Untersuchungen an dispersionsgehärteten Superlegierungen / Electron-Microscopic Investigations of Dispersion- Strengthened Superalloys

The resistivities of individual multi-walled pure/boron doped carbon nanotubes have been measured in the temperature range from 25 to 300 °C. The connection patterns were formed by depositing two-terminal tungsten wires on a nanotube using focused-ion-beam lithography. A semiconductor-like behavior was found for both B-doped and pure carbon nanotubes. B-doped nanotubes have a reduced room-temperature resistivity (7.4×10−7–7.7×10−6 Ωm) as compared to pure nanotubes (5.3×10−6–1.9×10−5 Ωm). The activation energy derived from the resistivity vs. temperature Arrhenius plots was found to be smaller for the B-doped (58–78 meV) than for the pure multi-walled nanotubes (190–290 meV).

Temperature dependence of the resistivity of individual multi-walled pure/boron doped carbon nanotubes at elevated temperatures

Response to comment on: Size effects on yield strength and strain hardening for ultra-thin Cu films with and without passivation: A study by synchrotron and bulge test techniques

Human epithelial cancer cells are known to exhibit a reorganization of their keratin cytoskeleton and an attendant change in their elastic stiffness upon incubation with a natural lipid. The change in the keratin network was modeled and the model structures were computationally deformed using a Finite Element Method. The simulation results show a marked difference in the mechanical behavior of the cells for tensile and compressive loading conditions. In the former case, the elastic compliance increases in agreement with experimental findings. We interpret this increase by applying principles of structural engineering and suggest that cells may generally use these principles to regulate their cytoskeletal architecture.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S1946427400084530

A Model for the Increased Elastic Compliance in Human Cancer Cells

In this work, NiAl films deposited by magnetron co-sputtering onto silicon substrates with compositions between 45.0 and 51.5 at-% Al and a thickness of 1.2 μm were studied. The films exhibited grain sizes comparable to the film thickness. Furthermore, the films were found to have fiber textures with the strongest component being (110) for the very Ni-rich and (111) for the stoichiometric and Al-rich films. The residual stresses in the Ni-rich and stoichiometric films after annealing were found to be independent of composition, while the Al-rich films showed a significant decrease in film stress. This stress drop can be related to severe cracking in the Al-rich films, which has not been observed in the stoichiometric and Ni-rich films, indicating that the fracture toughness depends on composition. Based on a simple estimate, the fracture toughness of these Al-rich films was determined to be in the range of 1 to 2 MPa m-1/2, which is somewhat smaller than commonly reported bulk values for polycrystalline NiAl.

Eduard Arzt

Papers

Elektronenmikroskopische Untersuchungen an dispersionsgehärteten Superlegierungen / Electron-Microscopic Investigations of Dispersion- Strengthened Superalloys

Temperature dependence of the resistivity of individual multi-walled pure/boron doped carbon nanotubes at elevated temperatures

Response to comment on: Size effects on yield strength and strain hardening for ultra-thin Cu films with and without passivation: A study by synchrotron and bulge test techniques

A Model for the Increased Elastic Compliance in Human Cancer Cells

The Role of Chemical Composition for the Ductility and Microstructure of Thin NiAl Films