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

Shear-banding is a ubiquitous plastic-deformation mode in materials. In metallic glasses, shear bands are particularly important as they play the decisive role in controlling plasticity and failure at room temperature. While there have been several reviews on the general mechanical properties of metallic glasses, a pressing need remains for an overview focused exclusively on shear bands, which have received tremendous attention in the past several years. This article attempts to provide a comprehensive and up-to-date review on the rapid progress achieved very recently on this subject. We describe the shear bands from the inside out, and treat key materials-science issues of general interest, including the initiation of shear localization starting from shear transformations, the temperature and velocity reached in the propagating or sliding band, the structural evolution inside the shear-band material, and the parameters that strongly influence shear-banding. Several new discoveries and concepts, such as stick-slip cold shear-banding and strength/plasticity enhancement at sub-micrometer sample sizes, will also be highlighted. The understanding built-up from these accounts will be used to explain the successful control of shear bands achieved so far in the laboratory. The review also identifies a number of key remaining questions to be answered, and presents an outlook for the field.

Shear bands in metallic glasses

The Communication program emphasizes theory, research, and application to examine the ways humans communicate, verbally and non-verbally, across a variety of levels and contexts. This is particularly important as communication shapes our ideas and values, gives rise to our politics, consumption and socialization, and helps to define our identities and realities. Its power and potential is inestimable. From the briefest of text messages to the grandest of public declarations, we indeed live within communication and invite you to join us in appreciating its increasing importance in contemporary society. From Twitter and reality television to family relationships and workplace dynamics, communication is about understanding ourselves, our media, our relationships, our culture and how these things connect.

의사 간호사 communication

High-pressure torsion (HPT) method currently receives much attention as a severe plastic deformation (SPD) technique mainly because of the reports of Prof. Ruslan Z. Valiev and his co-workers in 1988. They reported the efficiency of the method in creating ultrafine-grained (UFG) structures with predominantly high-angle grain boundaries, which started the new age of nanoSPD materials with novel properties. The HPT method was first introduced by Prof. Percy W. Bridgman in 1935. Bridgman pioneered application of high torsional shearing stress combined with high hydrostatic pressure to many different kinds of materials such as pure elements, metallic materials, glasses, geological materials (rocks and minerals), biological materials, polymers and many different kinds of organic and inorganic compounds. This paper reviews the findings of Bridgman and his successors from 1935 to 1988 using the HPT method and summarizes their historical importance in recent advancement of materials, properties, phase transformations and HPT machine designs.

A review on high-pressure torsion (HPT) from 1935 to 1988

Ionic liquids are an emerging class of materials with a diverse and extraordinary set of properties. Understanding the origins of these properties and how they can be controlled by design to serve valuable practical applications presents a wide array of challenges and opportunities to the chemical physics and physical chemistry community. We highlight here some of the significant progress already made and future research directions in this exciting area.

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Spotlight on ionic liquids

Department of Chemical Engineering, Colorado School of Mines, Golden CO 80401 Departments of Chemical Engineering, Chemistry and Computer Science, University of Tennessee, Knoxville TN 37996 Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge TN George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta GA 30332 Department of Chemical Engineering and Materials Science, Wayne State University, Detroit MI 48202

Characterizing the high pressure behaviour of lubricant basestocks

An upright suction carpet cleaner is provided with a solid rear axle having wheels mounted on either end thereof and a power assist transmission generally medially mounted therewith. The transmission comprises a housing carrying an input pinion gear driven from the suction fan motor shaft in constant mesh with a pair of contra-rotating face gears freely rotatable upon the axle shaft. A pair of clutch assemblies selectively engage one or the other of the contra rotating face gears in timing relationship with the axle shaft, with the clutch assembly being selectively operable through a bowden cable connection to a shiftable hand grip on the cleaner handle so that slight forward pressure on the hand grip by an operator is effective to engage the forward clutch and provide power assist drive to the cleaner in a forward direction while a slight rearward pressure on the handle grip by the operator provided a power assist in reverse drive. Further, means are provided to lock the transmission in a neutral configuration when the handle is in an upright position.

Power assist drive upright vacuum cleaner and power assist drive system therefor

Quantifying the Inlet Pressure and Shear Stress of Elastohydrodynamic Lubrication

Simply generating a high pressure and containing liquid at high pressure is sometimes considered an achievement in itself. Monoblock pressure vessels have been employed to 4 GPa. However, to advance the understanding of the behavior of liquids in elastohydrodynamic lubrication (EHL) films, it will be necessary to measure the rheological properties of viscous liquids at the pressures of EHL and this requires that the liquid be placed under known stress and that the resulting motion be detected. Motion must be transferred into the high pressure environment and some measurement of force must be transferred outside. The importance of the use of the smallest possible device is emphasized. These requirements can only be met by the application of some innovative experimental techniques which will be explained in detail in this chapter.

Scott Bair

Papers

Characterizing the high pressure behaviour of lubricant basestocks

Power assist drive upright vacuum cleaner and power assist drive system therefor

Quantifying the Inlet Pressure and Shear Stress of Elastohydrodynamic Lubrication

General High-Pressure Experimental Technique

Tribology research at Georgia Tech