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

Newtonian quantitative elastohydrodynamic film thickness with linear piezoviscosity

To improve performance of machine components, lubrication is one of the most important factors. Especially for use in extreme environments, researchers look for other solutions rather than common l ...

Elastohydrodynamic performance of a bio-based, non-corrosive ionic liquid

The author questions the accuracy of application of the Roelands equation in pressureviscosity relationships for lubricants. He contends that in the development of his equation when Roelands discarded some vital data on high-viscosity measurements that did not fit his claim of universal applicability. The author suggests that some conclusions based upon calculations using the Roelands equation should be reexamined.

Roelands' missing data:

The nature of the logarithmic traction gradient

The Einstein–Debye relationship gives the time, λ
 EB, for Brownian motion to remove the alignment of polar molecules resulting from an imposed electrical field after the field is removed. Measurements of the dielectric relaxation time and the shear-dependent viscosity in low-molecular-weight liquids, however, show that the theoretical Einstein–Debye rotational relaxation time is much better correlated with the characteristic time in the Carreau law for low-molecular-weight liquids than with the dielectric relaxation time. In fact, the dielectric relaxation time of bis(phenoxyphenoxy)benzene is better approximated by the ratio of viscosity to limiting-high-rate shear modulus. Flow curves for the low molecular weight, monodisperse liquids, di(2-ethylhexyl)phthalate and squalane, can be well-represented by the Carreau law with the Einstein–Debye time as the characteristic time. Doing so yields the standard form for time–temperature–pressure superposition.

https://www.researchgate.net/profile/S_Bair/publication/225109435_A_quantitative_test_of_the_Einstein-Debye_relation_using_the_shear_dependence_of_viscosity_for_low_molecular_weight_liquids/links/02e7e528a440a3005d000000.pdf

Scott Bair

Papers

Newtonian quantitative elastohydrodynamic film thickness with linear piezoviscosity

Elastohydrodynamic performance of a bio-based, non-corrosive ionic liquid

Roelands' missing data:

The nature of the logarithmic traction gradient

A quantitative test of the Einstein–Debye relation using the shear dependence of viscosity for low molecular weight liquids