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

Disclosed are methods for the surface modification of an object in order to increase the adherence of said object. The surface undergoes structuring, whereupon a plurality of projections are formed with a respective foot and head part. The head part possesses a front face pointing away from the surface. The size of each projection is such that all front faces have the same vertical height above the surface and form an adherent contact surface which is interrupted by reciprocal distances between the front faces.

Methods for modifying the surfaces of a solid and microstructured surfaces with increased adherence produced with said methods

Recent advances in bio-inspired microfibrillar adhesives have resulted in technologies that allow reliable attachment to a variety of surfaces. Because capillary and van der Waals forces are consid...

Strong Wet and Dry Adhesion by Cupped Microstructures

Strong single-crystalline Au films tested by a new synchrotron technique

Adhesion measurements on poly(dimethyl)siloxane samples were performed, for the first time, with flat glass probes under controlled tilt angle and the results were compared with measurements from spherical probes of two different radii. Experiments were made on both flat and patterned samples with structure diameters of 4.7 μm and heights of 0.82 μm and 1.95 μm, respectively. Pull-off forces measured with spherical probes showed the usual preload dependence and were independent of misalignment angle. On the other hand, pull-off forces measured with aligned flat probes were preload-independent, but dropped significantly and became preload-dependent with increasing misalignment. This effect was more pronounced for structured samples, where a misalignment by 0.2° resulted in a drop of adhesion by more than 30%. The comparison indicates that measurements from spherical probes underestimate adhesive forces for structured surfaces if compared with aligned flat probes. Finally, we propose a simple model which al...

Adhesion of Flat and Structured PDMS Samples to Spherical and Flat Probes: A Comparative Study

To optimize the tribological performance of miniaturized systems, adequate experimental means are needed. Current microtribometers suffer from inability to ensure parallel flat-on-flat contact and often experience metrological problems related to the geometry of the force sensing element. The present work demonstrates how these limitations can be removed in either homemade or commercial microtribometers by using a self-aligning system of specimen holders and an improved force sensor based on a symmetric design principle. Preliminary tests conducted on a polyvinylsiloxane∕glass tribopair confirm the satisfactory operation of the setup and show no effect of applied load on pull-off force and friction coefficient.

Eduard Arzt

Papers

Methods for modifying the surfaces of a solid and microstructured surfaces with increased adherence produced with said methods

Strong Wet and Dry Adhesion by Cupped Microstructures

Strong single-crystalline Au films tested by a new synchrotron technique

Adhesion of Flat and Structured PDMS Samples to Spherical and Flat Probes: A Comparative Study

Advanced testing of adhesion and friction with a microtribometer