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).

/pdf/diamond-like-amorphous-carbon-3pczopr0z7.pdf

Diamond-like amorphous carbon

Mechanical properties of nanocrystalline materials

The sintering and deformation kinetics of nanocrystalline (n-) TiO2 were studied. It was found that pressureless sintering yields densities above 95 % with modest increase in grain size whereas pressure assisted sintering (1GPa) results in high density samples without grain growth. In addition compression tests were performed. Large true strains up to 0.6 and strain rates as high as 8 × 10−5 s−1 were observed at 810°C without fracturing. The sintering and creep results are discussed in terms of the microstructure and diffusion coefficients in n-TiO2.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S1946427400360559

Low Temperature Sintering and Deformation of Nanocrystalline TiO2

Nanocavities in Ge(111) created by 5 keV Xe ion irradiation are characterized by ex situ transmission electron microscopy and Rutherford backscattering spectrometry. Nanocavities nucleate near the surface and then undergo thermal migration. Nanocavities with an average diameter of 10 nm and areal density of $5.1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}{\mathrm{nm}}^{\ensuremath{-}2}$ are observed at $500\ifmmode^\circ\else\textdegree\fi{}\mathrm{C},$ while nanocavities with an average diameter of 2.9 nm and areal density of $3.1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}{\mathrm{nm}}^{\ensuremath{-}2}$ are observed at $400\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}.$ The estimated Xe gas pressure inside the nanocavities is 0.035 GPa at $500\ifmmode^\circ\else\textdegree\fi{}\mathrm{C},$ much smaller than the estimated equilibrium pressure 0.38 GPa. This result suggests that the nanocavities grow beyond equilibrium size at $500\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}.$ The nanocavities are annihilated at the surface to form surface pits by the interaction of displacement cascades of keV Xe ions with the nanocavities. These pits are characterized by in situ scanning tunneling microscopy. Pits are created on Ge(111) and Ge(001) at temperatures $\ensuremath{\sim}250--305\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ by keV Xe ions even when less than a bilayer (monolayer) of surface material is removed.

http://arxiv.org/pdf/cond-mat/0307581.pdf

Formation and annihilation of nanocavities during keV ion irradiation of Ge

Surface defects created by 20 keV Xe ion irradiation of Ge(1 1 1)

Ion‐beam mixing in AlxGa1−xAs and InP matrices was measured as a function of irradiation temperature using 1 MeV Kr ion irradiation. For these III–V compound semiconductors, the mixing increased with temperature up to a critical temperature Tc at which point it precipitously dropped. Tc was identified as the amorphous‐to‐crystalline transition temperature in these materials under 1 MeV Kr irradiation.

Temperature dependence of ion-beam mixing in III-V semiconductors

Data are presented demonstrating the use of MeV oxygen ion implantation and subsequent annealing procedures to induce compositional disordering and to create a semiinsulating region simultaneously within an AlAs-GaAs superlattice. High dose oxygen implantation yields a compositionally disordered region 3500A wide centered 1.25 µm below the surface of the superlattice, as determined by secondary ion mass spectrometry (SIMS) analysis. More extensive disordering of the superlattice occurs at lower implantation temperatures. Current-voltage measurements indicate the formation of a semiinsulating layer which is thermally stable to at least 850° C. The semi-insulating properties of the implanted superlattice are assigned to the disorder-enhanced formation of Al-O pairs and the substitutional introduction of deep level states.

Robert S Averback

Papers

Low Temperature Sintering and Deformation of Nanocrystalline TiO2

Formation and annihilation of nanocavities during keV ion irradiation of Ge

Surface defects created by 20 keV Xe ion irradiation of Ge(1 1 1)

Temperature dependence of ion-beam mixing in III-V semiconductors

Compositional disordering and the formation of semi-insulating layers in AIAs-GaAs superlattices by MeV oxygen implantation