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

Reversible and switchable adhesion of elastomeric microstructures has attracted significant interest in the development of grippers for object manipulation. Their applications, however, have often been limited to dry conditions and adhesion of such deformable microfibrils in the fluid environment is less understood. In the present study, we performed adhesion tests in silicone oil using single cylindrical microfibrils of a flat-punch shape with a radius of 80 µm. Stiff fibrils were created using three-dimensional printing of an elastomeric resin with an elastic modulus of 500 MPa, and soft fibrils, with a modulus of 3.3 MPa, were moulded in polyurethane. Our results suggest that adhesion is dominated by hydrodynamic forces, which can be maximized by stiff materials and high retraction velocities, in line with theoretical predictions. The maximum pull-off stress of stiff cylindrical fibrils is 0.6 MPa, limited by cavitation and viscous fingering, occurring at retraction velocities greater than 2 µm s−1. Next, we add a mushroom cap to the microfibrils, which, in the case of the softer material, deforms upon retraction and leads to a transition to a hydrostatic suction regime with higher pull-off stresses ranging from 0.7 to 0.9 MPa. The effects of elastic modulus, fibril size and viscosity for underwater applications are illustrated in a mechanism map to provide guidance for design optimization.

Attachment of bioinspired microfibrils in fluids: transition from a hydrodynamic to hydrostatic mechanism

PROBLEM TO BE SOLVED: To provide a vacuum gripping device which transmits larger tangential force to an object with the same negative pressure. SOLUTION: This invention relates to the vacuum gripping device for sticking to the object 32 provided with a negative pressure generating part 14, a sucker 20, and a sucker retainer 12. The sucker 20 is provided with a sealing edge part 22 forming a sucking chamber 26 close to the object and a contact surface 28 contacting the object 32 when an inside of the sucking chamber is in a negative pressure state. The sucking chamber 26 is fluidly connected to the negative pressure generating part 14. The contact surface 28 is provided with a plurality of bar shaped, thin plate shaped or pin shaped elements, and the elements form micro structures. COPYRIGHT: (C)2004,JPO&NCIPI

Vacuum gripping device

The wafer curvature technique was used to analyze stresses in fine-grained, 50 nm to 2 μm thick Au films on silicon substrates between room temperature and 500°C. The microstructural evolution was analyzed by scanning electron microscopy (SEM), focused ion beam (FIB) microscopy and transmission electron microscopy (TEM). In situ heating experiments inside a scanning electron microscope provided a comparison between the morphological development and the stress-temperature behavior of the film. Hillock formation was observed, but it can only partially account for the stress relaxation measured by the wafer curvature technique.

Hillock formation and thermal stresses in thin Au films on Si substrates

Grain growth in thin films is usually accompanied by texture evolution due to the crystallographic dependencies of surface, interface and strain energies. In this work the driving forces for grain growth for a 1 and 5 μm thick Cu thin film on a polyimide substrate are calculated assuming biaxial and uniaxial stress. While the results for the biaxial stress state are used to explain observed textures, for the case of uniaxial stress predictions suggest new ways to control the texture of thin films.

Strain Energy Effects on Texture Evolution in Thin Films: Biaxial vs. Uniaxial Stress State

Der Kriechbruch der oxiddispersionsgeharteten Superlegierung INCONEL MA 6000 wurde als Funktion der Kornstreckung und der Belastungsrichtung untersucht. Metallographische Beobachtungen zeigen eine starke Neigung zur Ausbildung von Kriechporen an Korngrenzen, die senkrecht zur auseren Spannung liegen. Die starke Abhangigkeit der Bruchzeit von dem Kornstreckungsverhaltnis und der Spannungsrichtung wird im Rahmen eines Modells interpretiert, das das Ausmas der Behinderung der Schadigungsentwicklung durch benachbarte Kroper als entscheidend fur das Bruchverhalten annimmt. Es folgt, das Feinkornbereiche vermieden werde mussen, um das volle Potential der Dispersionshartung ausschopfen zu konnen.

/pdf/the-role-of-grain-boundaries-in-high-temperature-creep-51gaayp3w5.pdf

Eduard Arzt

Papers

Attachment of bioinspired microfibrils in fluids: transition from a hydrodynamic to hydrostatic mechanism

Vacuum gripping device

Hillock formation and thermal stresses in thin Au films on Si substrates

Strain Energy Effects on Texture Evolution in Thin Films: Biaxial vs. Uniaxial Stress State

The role of grain boundaries in high temperature creep fracture of an oxide dispersion strengthened superalloy