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

The application of the new quantitative elastohydrodynamics, which employs real properties of the liquid lubricant, to practical tribology problems obviously requires property measurements at high ...

Density Scaling of the Thermal Conductivity of a Jet Oil

Guegan and coworkers have addressed the important problem of friction of elastohydrodynamic contacts in the mixed regime. Any attempt at understanding friction in the mixed regime must address the friction in the full-film regime. To analyze fiction for the full film, they used a common, but unsupported, assumption that the friction curve is a rheological flow curve. The inconsistency can be demonstrated by integration over the contact with the assumed Eyring equation employing the known pressure dependence of the viscosity and also by a full numerical simulation which yields the same sinh friction curve without using the Eyring assumption.

Comment on “The Relationship Between Friction and Film Thickness in EHD Point Contacts in the Presence of Longitudinal Roughness” by Guegan, Kadiric, Gabelli, & Spikes

Experimental investigation of friction in entrapped elastohydrodynamic contacts

Shear Band Analysis for Lubricants Based on a Viscoelastic Plasticity Model

A specially designed falling body viscometer has been used to obtain low shear viscosities of dilute solutions of high molecular weight polyethylene in decalin and for detecting phase transitions at high pressures. The method provides valuable rheological data at pressures that correspond to those in lubrication and some extrusion processes. In addition, the method enables detection of phase transitions, such as crystallization, that result in detectable changes in rheology. The influence of pressures as high as 0.6 GPa (∼ 80,000 psi) is illustrated here through a study of crystallization, with verification from light scattering and calorimetry.

Low shear viscosity and crystallization in dilute solutions of polymers at high pressures: Falling body viscometry of high molecular weight polyethylene solutions

Scott Bair

Papers

Density Scaling of the Thermal Conductivity of a Jet Oil

Comment on “The Relationship Between Friction and Film Thickness in EHD Point Contacts in the Presence of Longitudinal Roughness” by Guegan, Kadiric, Gabelli, & Spikes

Experimental investigation of friction in entrapped elastohydrodynamic contacts

Shear Band Analysis for Lubricants Based on a Viscoelastic Plasticity Model

Low shear viscosity and crystallization in dilute solutions of polymers at high pressures: Falling body viscometry of high molecular weight polyethylene solutions