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

Deposits of clastic carbonate-dominated (calciclastic) sedimentary slope systems in the rock record have been identified mostly as linearly-consistent carbonate apron deposits, even though most ancient clastic carbonate slope deposits fit the submarine fan systems better. Calciclastic submarine fans are consequently rarely described and are poorly understood. Subsequently, very little is known especially in mud-dominated calciclastic submarine fan systems. Presented in this study are a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) that reveals a >250 m thick calciturbidite complex deposited in a calciclastic submarine fan setting. Seven facies are recognised from core and thin section characterisation and are grouped into three carbonate turbidite sequences. They include: 1) Calciturbidites, comprising mostly of highto low-density, wavy-laminated bioclast-rich facies; 2) low-density densite mudstones which are characterised by planar laminated and unlaminated muddominated facies; and 3) Calcidebrites which are muddy or hyper-concentrated debrisflow deposits occurring as poorly-sorted, chaotic, mud-supported floatstones. These

Phd by thesis

J. Appl. Cryst.の発刊に際して

Diamond-like carbon (DLC) is a metastable form of amorphous carbon with significant sp3 bonding. DLC is a semiconductor with a high mechanical hardness, chemical inertness, and optical transparency. This review will describe the deposition methods, deposition mechanisms, characterisation methods, electronic structure, gap states, defects, doping, luminescence, field emission, mechanical properties and some applications of DLCs. The films have widespread applications as protective coatings in areas, such as magnetic storage disks, optical windows and micro-electromechanical devices (MEMs).

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Diamond-like amorphous carbon

Mechanical properties of nanocrystalline materials

Understanding the liquid-solid phase transition has long been of scientific interest, owing to its singular importance in the processing of materials with desired microstructures. Presently, however, little is known about the atomic mechanisms controlling this process. Using molecular dynamics simulations, we find a surprising connection between the crystallization behavior of metals at extreme undercoolings and the properties of interstitial atoms in the crystalline phase. We show first that the activation energy of crystallization in a number of metals at the kinetically controlled regime is precisely the same as the migration energy of self-interstitials atom in the crystalline state. We then show, contrary to the present thought, that the advance of a planar solid-liquid interface in Fe at low temperatures is controlled by thermally activated jumps of a small fraction of the atoms on the liquid side of the interface, and remarkably these atoms have the same 110 dumbbell interstitialcy structure as observed for interstitials in crystalline Fe.

https://iopscience.iop.org/article/10.1209/0295-5075/79/26005/pdf

Atomic mechanisms controlling crystallization behaviour in metals at deep undercoolings

Chemical mixing and self-organization of Nb precipitates in Cu during severe plastic deformation

Radiation-enhanced diffusion of Cu and Au tracer impurity atoms during ${\mathrm{Kr}}^{+}$ irradiation has been measured in amorphous ${\mathrm{Ni}}_{50}$${\mathrm{Zr}}_{50}$ and ${\mathrm{Ni}}_{35}$${\mathrm{Zr}}_{65}$ alloys in the range 80-573 K. At low temperatures, the spreading of the thin impurity layers was due to ion beam mixing and was independent of temperature. Above \ensuremath{\cong}400 K, the diffusion coefficient of Cu in ${\mathrm{Ni}}_{50}$${\mathrm{Zr}}_{50}$ shows Arrhenius behavior with an apparent activation enthalpy of \ensuremath{\cong}0.55 eV, and it depends on the square root of dose rate. The radiation-enhanced diffusion coefficient is greater for Cu than Au and is also larger in the Zr-rich alloy.

Radiation-enhanced diffusion in amorphous Ni-Zr alloys

MgO and Al2O3 crystals have been implanted with Ne ions at temperatures between 90 K and 720 K and the damaged layers were investigated by optical absorption spectroscopy and X-ray diffraction. The damage production is discussed in terms of the number of F-centers, of the change of the lattice parameter, and of the diffuse scattering intensity close to Bragg reflections. The stability of the defects was tested in addition by subsequent subthreshold e−-irradiations. No effect of an applied electric field on the defect production is observed for both oxides.

Robert S Averback

Papers

Atomic mechanisms controlling crystallization behaviour in metals at deep undercoolings

Chemical mixing and self-organization of Nb precipitates in Cu during severe plastic deformation

Radiation-enhanced diffusion in amorphous Ni-Zr alloys

Defects in ion implanted and electron irradiated Mgo and Al2O3

Radiation-annealing effects in energetic displacement cascades