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

In near-bamboo lines, electromigration-induced damage initiates at polygranular clusters which are longer than a critical length and which act as fast-diffusion segments. It has been proposed that two neighboring subcritical clusters can also lead to damage through the interaction of their stress fields. In order to prove the existence of, and to study, such proximity effects, artificial clusters were generated by creating continuous segments of plastic deformation in single-crystal aluminum lines using nanoindentation. Pairs of segments having different separation distances and lengths were made. In situ electromigration tests showed that these segments generated damage in the form of voids and hillocks even when the individual segments were shorter than the critical length. The void growth rate was found to be a function of the separation distance and segment length. A simple analytical model for the electromigration flux in these structures is shown to be consistent with the measured void growth rates....

Electromigration proximity effects of two neighboring fast-diffusion segments in single-crystal aluminum lines

Pressure sensitive adhesives based on silicone materials are used particularly for skin adhesion, e.g., the fixation of electrocardiogram (ECG) electrodes or wound dressings. However, adhesion to sensitive tissue structures is not sufficiently addressed due to the risk of damage or rupture. We propose an approach in which a poly-(dimethylsiloxane) (PDMS)-based soft skin adhesive (SSA) acts as cellular scaffold for wound healing. Due to the intrinsically low surface free energy of silicone elastomers, functionalization strategies are needed to promote the attachment and spreading of eukaryotic cells. In the present work, the effect of physical adsorption of three different proteins on the adhesive properties of the soft skin adhesive was investigated. Fibronectin adsorption slightly affects adhesion but significantly improves the cellular interaction of L929 murine fibroblasts with the polymeric surface. Composite films were successfully attached to explanted tympanic membranes. This demonstrates the potential of protein functionalized SSA to act as an adhesive scaffold in delicate biomedical applications.

/pdf/a-self-adhesive-elastomeric-wound-scaffold-for-sensitive-3f35winch8.pdf

A Self-Adhesive Elastomeric Wound Scaffold for Sensitive Adhesion to Tissue.

Invar alloys are also of great interest in the form of thin films when dimensional stability at varying temperatures is required. In addition, they offer the benefit of reduced thermal stresses in the construction of micro-devices using incremental deposition methods. The characterization of the films was restricted to the magnetic behavior and the determination of the CTE. In this note, the results of first investigations into the mechanical stress-temperature behavior of thin Fe-Ni films are reported.

Mechanical and thermal expansion behavior of thin Fe-36 wt.-%Ni Invar films

Creep specimens of Inconel MA 6000 with different grain aspect ratios (GAR) ranging from about 4 to 60 were tested at 950\" C at a stress of 230 MPa. The resulting rupture times show a pronounced dependence on the GAR below a value of about 20, where fracture is mainly intergranular. At higher GAR values, the rupture time becomes less sensitive to grain shape, and fracture is predominantly transgranular. These results are interpreted in the light of the hypothesis that sliding of the elongated grains along longitudinal grain boundaries, which is a necessary accommodation mechanism, controls the rate of creep damage accumulation on boundaries perpendicular to the applied stress. A quantitative model for the coupling between the two processes is presented. If it is assumed that the oxide dispersoid introduces a threshold stress for sliding, then the transition in the fracture mode with increasing GAR can be explained quantitatively: The reason is that, above a critical GAR of about 20, the damage-induced shear stress in the longitudinal boundaries lies below the threshold, and sliding and damage accumulation on transverse boundaries are suppressed. This approach results in a quantitative description of the beneficial interaction between elongated grain shape, boundary waviness and oxide dispersion.

/pdf/the-effect-of-grain-shape-on-stress-rupture-of-the-oxide-ts3xm30svo.pdf

Eduard Arzt

Papers

Electromigration proximity effects of two neighboring fast-diffusion segments in single-crystal aluminum lines

A Self-Adhesive Elastomeric Wound Scaffold for Sensitive Adhesion to Tissue.

Mechanical and thermal expansion behavior of thin Fe-36 wt.-%Ni Invar films

The effect of grain shape on stress rupture of the oxide dispersion strengthened superalloy inconel MA 6000

Generating Micro- and Nanopatterns on Polymeric Materials: ARZT:NANOPATTERNS O-BK