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

다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

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

The physical and chemical properties of nanophase materials rely on their crystal and surface structures. Transmission electron microscopy (TEM) is a powerful and unique technique for structure characterization. The most important application of TEM is the atomic-resolution real-space imaging of nanoparticles. This article introduces the fundamentals of TEM and its applications in structural determination of shape-controlled nanocrystals and their assemblies. By forming a nanometer size electron probe, TEM is unique in identifying and quantifying the chemical and electronic structure of individual nanocrystals. Electron energy-loss spectroscopy analysis of the solid-state effects and mapping the valence states are even more attractive. In situ TEM is demonstrated for characterizing and measuring the thermodynamic, electric, and mechanical properties of individual nanostructures, from which the structure−property relationship can be registered with a specific nanoparticle/structure.

Transmission Electron Microscopy of Shape-Controlled Nanocrystals and Their Assemblies

Alloying has long been used to confer desirable properties to materials. Typically, it involves the addition of relatively small amounts of secondary elements to a primary element. For the past decade and a half, however, a new alloying strategy that involves the combination of multiple principal elements in high concentrations to create new materials called high-entropy alloys has been in vogue. The multi-dimensional compositional space that can be tackled with this approach is practically limitless, and only tiny regions have been investigated so far. Nevertheless, a few high-entropy alloys have already been shown to possess exceptional properties, exceeding those of conventional alloys, and other outstanding high-entropy alloys are likely to be discovered in the future. Here, we review recent progress in understanding the salient features of high-entropy alloys. Model alloys whose behaviour has been carefully investigated are highlighted and their fundamental properties and underlying elementary mechanisms discussed. We also address the vast compositional space that remains to be explored and outline fruitful ways to identify regions within this space where high-entropy alloys with potentially interesting properties may be lurking. High-entropy alloys have greatly expanded the compositional space for alloy design. In this Review, the authors discuss model high-entropy alloys with interesting properties, the physical mechanisms responsible for their behaviour and fruitful ways to probe and discover new materials in the vast compositional space that remains to be explored.

High-entropy alloys

Mechanistic Study of Dark Etching Regions in Bearing Steels Due to Rolling Contact Fatigue

Silicon Nitride Based Ceramic Nanocomposites.

For understanding the tribological behaviour of the system bearing/lubrkcant we have investigated reaction layers formed by lubricants with low wear protection and high wear protection on thrust cylindrical roller bearings made of 100Cr6 steel. Electron Probe Micro Analysis (EP MA) measurements were used to analyse the oxygen coverage across the whole layer, which is a direct measure for the thickness of the reaction layer. Transmission Electron Microscopy (TEM) investigations reveale that the reaction layers at the rolling contact are formed by an amorphous phase with embedded nanocrystalline iron oxide particles. For a sample with good wear protection the layer consists of an ultra-thin oxide with less than 10 nm thickness and extremely low surface roughness. In contrast, a sample with low wear protection exhibited an uneven reaction layer with a thickness varying between 0 -130 nm and a three times higher surface roughness as the sample with high wear protecton. Furthermore, tribological mutation (tribomutation) of the steel was found in regions of about 150 - 400 nm in thickness below the surface. These regions are characterised by a strongly plastically deformed fine grained structure whitch exists below the contact parts of the reaction layer in both the high wear protection system as well as the low wear protection system. The nanomechanical behaviour of the different tribological layers were investigated by a combination of nanoindentation and atomic force microscopy (AFM). The determined effective Young's moduli show substatial differences for the reaction layers on the two different systems. However, they become very similar for the both tribological systems with increasing penetration depth into the tribomutation layer. Our results indicate that wear protection not only relies on the reaction layer itself but also on the properties of the combined system of reaction and tribomution layer. A new tribological model has been develop on the basis of our present results.

Elektronenmikroskopische und Rastersonden-Untersuchungen des Verschleißschutzes durch Reaktionsschichten in langsam laufenden Wälzlagern

Author(s): Josten, Elisabeth; Raftrey, David; Hierro-Rodriguez, Aurelio; Sorrentino, Andrea; Aballe, Lucia; Lipinska-Chwalek, Marta; Jansen, Thomas; Hoflich, Katja; Kroncke, Hanno; Dubourdieu, Catherine; Burgler, Daniel E; Mayer, Joachim; Fischer, Peter | Abstract: The scientific and technological exploration of artificially designed three-dimensional magnetic nanostructures opens the path to exciting novel physical phenomena, originating from the increased complexity in spin textures, topology, and frustration in three dimensions. Theory predicts that the equilibrium magnetic ground state of two-dimensional systems which reflects the competition between symmetric (Heisenberg) and antisymmetric (Dzyaloshinskii-Moriya interaction (DMI)) exchange interaction is significantly modified on curved surfaces when the radius of local curvature becomes comparable to fundamental magnetic length scales. Here, we present an experimental study of the spin texture in an 8 nm thin magnetic multilayer with growth-induced in-plane anisotropy and DMI deposited onto the curved surface of a 1.8 {\mu}m long non-magnetic carbon nanowire with a 67 nm radius. Using magnetic soft x-ray tomography the three-dimensional spin configuration in this nanotube was retrieved with about 30nm spatial resolution. The transition between two vortex configurations on the two ends of the nanotube with opposite circulation occurs through a domain wall that is aligned at an inclined angle relative to the wire axis. Three-dimensional micromagnetic simulations support the experimental observations and represent a visualization of the curvature-mediated DMI. They also allow a quantitative estimate of the DMI value for the magnetic multilayered nanotube.

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Joachim Mayer

Papers

Mechanistic Study of Dark Etching Regions in Bearing Steels Due to Rolling Contact Fatigue

Silicon Nitride Based Ceramic Nanocomposites.

Elektronenmikroskopische und Rastersonden-Untersuchungen des Verschleißschutzes durch Reaktionsschichten in langsam laufenden Wälzlagern

Curvature-mediated spin textures in magnetic multi-layered nanotubes

Formation of the reaction zone between tin-copper brazing fillers and aluminum-silicon-magnesium alloys : Experiments and thermodynamic analysis