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

Ion Beam Analysis of Irradiated Materials

With the rapid development of short pulse lasers, femtosecond (fs) lasers have been used in technologies such as materials modification (Vorobyev & Guo, 2008), micromachining (Liu et al., 1997; Gattass & Mazur, 2008), and surface patterning (Miyaji & Miyazaki, 2008). However, details on energy absorption, heat dissipation, and phase transformation during the initial excitation of these intense pulses are poorly understood, despite their importance in determining the final microstructure and morphology of the laser-processed materials. Scientifically, intense laser pulses drive materials into highly non-equilibrium states, which provide us new opportunities in studying the fundamental properties of these states. By carefully controlling the relaxation of the excited materials, it is also possible to create novel metastable structures. Before we can achieve these goals, we need a detailed knowledge on how materials respond to these intense pulses. This is a non-trivial task since the optical, thermodynamics and transport properties can change drastically upon intense laser irradiation. In this chapter, we summarize our recent works on Ag to illustrate some of the complexities involved in both heat transport and absorption at laser fluencies near the melting and ablation threshold. We observe significant heat confinement and absorption enhancement at high laser fluences. These differences derive mainly from the excitation of d-band electrons at high electron temperatures, which significantly changes the electronic properties, although many of the details remain poorly understood. From a more applied consideration, we show that by using fs-pulses, we are able to confine melting and ablation to the very top layers of the materials, which has important implications for pulsed laser deposition of ultra-thin layers and micromachining. Furthermore, we demonstrate that by utilizing the ultrafast quenching of the surface layer after laser excitations, we can create a pure metallic liquid at a temperature as low as 0.6 Tm, where Tm is the melting temperature of the metal. This degree of undercooling has not been achieved by other experimental techniques in pure metals and the transformation kinetics of this far-from-equilibrium state is not well-understood. Indeed, our results show that classical solidification theories cannot explain the experimental results and new atomistic mechanisms are needed in order to explain the measured kinetics.

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Heat Absorption, Transport and Phase Transformation in Noble Metals Excited by Femtosecond Laser Pulses

The large surface area: volume ratios and fine grain size of nanophase materials give rise to novel and exciting structural and electrical properties that are of considerable scientific and technological interest Using copper as a model system we have investigated the sintering of sputtered copper nanoparticles (4-20nm diameter) with a copper substrate in a novel UHV in-situ TEMThe nanoparticles were generated in a UHV chamber built into the side of the column by sputtering in 15Torr Ar They were transported into the microscope in the gas phase and deposited on an electron transparent (001) copper foil mounted on a heated support A typical bright-field (BF) image of the sample immediately after deposition at room temperature is shown in Fig 1 The particles have assumed a random orientation on the substrate and remain stable for many hours at room temperature The presence of both single particles and agglomerates of particles is evident in this image and examples are labelled ‘P’ and ‘A’, respectively

In-Situ Transmission Elecron Microscopy (TEM) Study of the Sintering of Sputtered Copper Nanoparticles on (001) Copper

Fully dynamical computer simulations have been used to study the physical mechanisms of ionized cluster beam deposition. Clusters containing 92 atoms were directed at surfaces with energies per cluster atom ranging from one sixth to three times the cohesive energy of the target. Simulation events employed either Lennard-Jones or Embedded Atom Method potentials. The atoms in the cluster appear to undergo local melting on impact with the substrate. Higher cluster energy increases the spreading of cluster atoms on the substrate and improves epitaxy, but it also increases interdiffusion and produces point defects.

Molecular Dynamics Simulations of Ionized Cluster Beam Deposition

The sintering of copper nanoparticles deposited on a clean (001) copper surface has been studied in real time using a novel in-situ ultrahigh vacuum (UHV) transmission electron microscope with a UHV DC sputtering attachment. The particles were found to assume an initially random orientation on the foil, reorienting upon heating to assume the orientation of the substrate by a mechanism involving classical sintering and grain growth, contrary to expectation. The experiment was inspired by that of Gleiter, where rotation of macroscopic copper balls to low energy configuations was observed upon annealing. We present the results of our study and discuss the differences in reorientation mechanisms in the case of macro- and nano-scale particle sintering. 

Robert S Averback

Papers

Ion Beam Analysis of Irradiated Materials

Heat Absorption, Transport and Phase Transformation in Noble Metals Excited by Femtosecond Laser Pulses

In-Situ Transmission Elecron Microscopy (TEM) Study of the Sintering of Sputtered Copper Nanoparticles on (001) Copper

Molecular Dynamics Simulations of Ionized Cluster Beam Deposition

In-situ TEM study of the sintering of copper nanoparticles on (001) copper