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

J. Appl. Cryst.の発刊に際して

Nanocrystals are fundamental to modern science and technology. Mastery over the shape of a nanocrystal enables control of its properties and enhancement of its usefulness for a given application. Our aim is to present a comprehensive review of current research activities that center on the shape-controlled synthesis of metal nanocrystals. We begin with a brief introduction to nucleation and growth within the context of metal nanocrystal synthesis, followed by a discussion of the possible shapes that a metal nanocrystal might take under different conditions. We then focus on a variety of experimental parameters that have been explored to manipulate the nucleation and growth of metal nanocrystals in solution-phase syntheses in an effort to generate specific shapes. We then elaborate on these approaches by selecting examples in which there is already reasonable understanding for the observed shape control or at least the protocols have proven to be reproducible and controllable. Finally, we highlight a number of applications that have been enabled and/or enhanced by the shape-controlled synthesis of metal nanocrystals. We conclude this article with personal perspectives on the directions toward which future research in this field might take.

Shape‐Controlled Synthesis of Metal Nanocrystals: Simple Chemistry Meets Complex Physics?

Microstructures and properties of high-entropy alloys

2.2. MOFs with Metal Active Sites 4614 2.2.1. Early Studies 4614 2.2.2. Hydrogenation Reactions 4618 2.2.3. Oxidation of Organic Substrates 4620 2.2.4. CO Oxidation to CO2 4626 2.2.5. Phototocatalysis by MOFs 4627 2.2.6. Carbonyl Cyanosilylation 4630 2.2.7. Hydrodesulfurization 4631 2.2.8. Other Reactions 4632 2.3. MOFs with Reactive Functional Groups 4634 2.4. MOFs as Host Matrices or Nanometric Reaction Cavities 4636

Engineering Metal Organic Frameworks for Heterogeneous Catalysis

The microstructural changes brought about by irradiating α-iron containing a distribution of platelet α″-nitrate precipitates with fast neutrons at 355 K are described. With increasing irradiation dose these underwent radiation-induced dissolution. By a dose of 4 × 1022 neutrons m-2(E> 1 MeV) many had been replaced by rafts of small precipitates apparently lying within the pre-irradiation boundaries of the original precipitates. Others were apparently unaffected, while a small number had partially dissolved and appeared as regions of undisturbed platelet surrounded by rafts of small precipitates. At higher doses, an increasing fraction of the precipitates were affected. At a dose of 7.5 × 1023 n m -2 no larger precipitates remained and a homogeneous population of small dislocation loops and precipitates was observed, whilst at 8.4 × 1023 n m -2 no visible damage or precipitation remained. Post-irradiation annealing at 593 K of foils irradiated to a dose of 4 × 1021 n m-2 gave rise to dislocation ...

Dissolution of nitride precipitates in iron by low-dose neutron irradiation

Thermal annealing, irradiation with electrons (25-300 keV), and irradiation with photons (hν = 233-388 eV) have been used to stimulate the crystallization of isolated amorphous zones in Si, Ge, GaAs, GaP and InP Transmission electron microscopy and computer image analysis were used to determine the crystallization processes For all materials, thermally stimulated crystallization occurred only at temperatures above 373 K The electron-stimulated crystallization rate is sensitive to the electron energy Initially, the rate decreases with increasing energy until it reaches a minimum at about one half the threshold displacement energy and then it increases It is insensitive to the irradiation temperature between 90 and 300 K and to the crystal orientation The effective diameter of the amorphous zone initially shrinks linearly with increasing electron dose For the laser-induced crystallization experiments the crystallization rate in Si, but not in Ge, was sensitive to the temperature, with a faster rate

Crystallization of isolated amorphous zones in semiconductors

https://par.nsf.gov/servlets/purl/10135651

Radiation-resistant nanotwinned austenitic stainless steel

Les mecanismes de fragilisation par l'hydrogene des aciers inoxydables austenitiques type AISI 316 recuits et sensibilises ont ete etudies in-situ par microscopie electronique haute tension. L'influence de l'hydrogene sur les transformations de phase induites par la deformation, la vitesse de generation des dislocations et la vitesse de propagation des fissures a ete analysee.

Ian M. Robertson

Papers

Dissolution of nitride precipitates in iron by low-dose neutron irradiation

Crystallization of isolated amorphous zones in semiconductors

Radiation-resistant nanotwinned austenitic stainless steel

HVEM studies of the effects of hydrogen on the deformation and fracture of AISI type 316 austenitic stainless steel

Influence of internal hydrogen content on the evolved microstructure beneath fatigue striations in 316L austenitic stainless steel