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

Note: Times Cited: 875 Reference EPFL-ARTICLE-206025doi:10.1021/cr0501846View record in Web of Science URL: ://WOS:000249839900009 Record created on 2015-03-03, modified on 2017-05-12

Complex Hydrides for Hydrogen Storage

Materials Challenges in Nuclear Energy

Many traditional approaches for strengthening steels typically come at the expense of useful ductility, a dilemma known as strength-ductility trade-off. New metallurgical processing might offer the possibility of overcoming this. Here we report that austenitic 316L stainless steels additively manufactured via a laser powder-bed-fusion technique exhibit a combination of yield strength and tensile ductility that surpasses that of conventional 316L steels. High strength is attributed to solidification-enabled cellular structures, low-angle grain boundaries, and dislocations formed during manufacturing, while high uniform elongation correlates to a steady and progressive work-hardening mechanism regulated by a hierarchically heterogeneous microstructure, with length scales spanning nearly six orders of magnitude. In addition, solute segregation along cellular walls and low-angle grain boundaries can enhance dislocation pinning and promote twinning. This work demonstrates the potential of additive manufacturing to create alloys with unique microstructures and high performance for structural applications.

https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=1443&context=ameslab_manuscripts

Additively manufactured hierarchical stainless steels with high strength and ductility

Handbook of SiC properties for fuel performance modeling

https://eprints.lib.hokudai.ac.jp/dspace/bitstream/2115/57439/1/SSC195%2070-73.pdf

Physical properties of α-Fe upon the introduction of H, He, C, and N

Defect-flow-induced grain boundary migration with segregation under electron irradiation

Mechanical properties of unirradiated and irradiated reduced-activation martensitic steels with and without nickel compared to properties of commercial steels

An Fe-9Cr-2W-0.25V-0.07Ta-0.1C (9Cr-2WVTa) steel has a smaller prior-austenite grain size than this same composition without tantalum (9Cr-2WV) when the steels are given a similar heat treatment. Except for prior-austenite grain size, the microstructures of the steels are similar before irradiation, and they develop similar changes in microstructure during irradiation. Nevertheless, the 9Cr-2WVTa shows less effect of irradiation on the Charpy behavior. To determine the effect of grain size on the Charpy properties of the 9Cr-2WV and 9Cr-2WVTa, specimens of the two steels were given various normalization heat treatments to produce different prior austenite grain sizes, and the tensile and impact properties were determined. For the smaller prior-austenite grain sizes, the 9Cr-2WV steel had impact properties similar to or better than those of the 9Cr-2WVTa steel. Differences in the microstructures of the steels were used to explain the observations and what they mean for developing steels with improved properties.

Effect of Heat Treatment and Tantalum on Microstructure and Mechanical Properties of Fe-9Cr-2W-0.25V Steel

The reaction mechanism of the (de)hydrogenation of a LiNH2 + LiH mixture with a nanoscale catalyst has been investigated. In this research, the position of each solid phase was examined by transmission electron microscopy (TEM). The observation showed that LiH particles, around 100 nm in size, formed around LiNH2 in the hydrogenation process. According to in situ TEM observation of the dehydrogenation process, the LiH particles became smaller as they reacted with LiNH2. Fine particles of Li2NH with crystallites of size 30–40 nm formed on the surface of the LiNH2. It indicated that H+ from the LiNH2 moved to the interface and combined with H− from the LiH in the dehydrogenation process, consequently H2 was released. At the same time, Li+ ions diffused from the LiH to the LiNH2 through the interface and Li2NH formed. On the other hand, it was confirmed that the catalyst was located at the interface between the LiH and LiNH2. It was found that the catalyst had the effect of improving the migration of Li+ from LiH to LiNH2.

Naoyuki Hashimoto

Papers

Physical properties of α-Fe upon the introduction of H, He, C, and N

Defect-flow-induced grain boundary migration with segregation under electron irradiation

Mechanical properties of unirradiated and irradiated reduced-activation martensitic steels with and without nickel compared to properties of commercial steels

Effect of Heat Treatment and Tantalum on Microstructure and Mechanical Properties of Fe-9Cr-2W-0.25V Steel

A solid–solid reaction enhanced by an inhomogeneous catalyst in the (de)hydrogenation of a lithium–hydrogen–nitrogen system