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

[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

Single layer transition metal sulfides (SLTMS) such as MoS{sub 2}, WS{sub 2}, and ReS{sub 2}, play an important role in catalytic processes such as the hydrofining of petroleum streams, and are involved in at least two of the slurry-catalyst hydroconversion processes that have been proposed for upgrading heavy petroleum feed and other sources of hydrocarbon fuels such as coal and shale oils. Additional promising catalytic applications of the SLTMS are on the horizon. The physical, chemical, and catalytic properties of these materials are reviewed in this report. Also discussed are areas for future research that promise to lead to advanced applications of the SLTMS.

Catalytic properties of single layers of transition metal sulfide catalytic materials.

In industries such as aerospace, petrochemistry and automobile, many parts of different machines are under environment which shows high temperature and high pressure, and have their proneness to wear and corrosion. Therefore, the wear resistibility and stability under high temperature need to be further improved. Nowadays, Laser cladding (LC) is widely used in machine parts repairing and functional coating due to its advantages such as lower dilution rate, small heat-affected zone and good metallurgical bonding between coating and substrate. In this paper, LC is introduced in detail from aspects of process simulation, monitoring and parameter optimization. At the same time, the paper gives a comprehensive review over LC material system as high entropy alloys (HEAs), amorphous alloy and single crystal alloy have been gradually showing their advantages over traditional metal materials in LC. In addition, the applications of LC in functional coatings and in maintenance of machine parts are also outlined. Also, the existing problems and the development trend of LC is discussed then.

Recent research and development status of laser cladding: A review

Modeling of thermal behavior and mass transport in multi-layer laser additive manufacturing of Ni-based alloy on cast iron

High-entropy alloy (HEA) coatings of AlCoCrFeNiTix (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0) were fabricated on AISI1045 steel by laser cladding. X-Ray diffraction (XRD) was used to investigate the phase composition of the coatings. The microstructure of coatings was analyzed using a scanning electron microscopy (SEM) and transmission electron microscopy (TEM). X-Ray diffraction (XRD) was used to investigate the phase composition of the coatings. The potentiodynamic polarization behaviour of coatings and substrate was studied. The composition of passive film on the corroded surface of the coating was identified by X-Ray photoelectron spectroscopy (XPS). The phase composition analysis showed that the coating was mainly composed of disordered body-centered cubic (BCC) solid solution phase (Fe-Cr) and ordered BCC phase (Al-Ni). The microstructure of the coatings was mainly composed of equiaxed polygonal grains, micro-nano particles of TiC and nanoparticles of Al2O3. The spinodal decomposition structure of Fe-Cr enrichment and Al-Ni-Ti enrichment was found in grains. The introduction of Ti led to passivation behavior of the coating during corrosion process. The components of the passive film were Al2O3, TiO2, Ti2O3, Cr2O3 and Cr(OH)3. The AlCoCrFeNiTi HEA coating showed the best corrosion resistance.

Microstructural characterization and corrosion behaviour of AlCoCrFeNiTix high-entropy alloy coatings fabricated by laser cladding

AlCoCrFeNiTix (x = 0, 0.2, 0.4, 0.6, 0.8, 1.0) HEA coatings reinforced by in-situ TiC particles were successfully prepared on AISI1045 steel via laser cladding. The coatings are made up of two BCC phases identified as Fe-Cr and Al-Ni phases, and a few in-situ TiC phases with a shape of granular in micro-nano scale. Ti element prefers to dissolve into the Al-Ni phase and refines the equiaxed grains. The AlCoCrFeNiTi1.0 HEA composite coating with the highest volume fraction of TiC particles phase (2.6%) exhibits the highest average microhardness (860.1 HV0.3). It is found that the composite coating is strengthened by the effect of solid solution strengthening, dispersion strengthening, and fine-grain strengthening. The wear behaviour of the coatings was tested at 25 °C and 600 °C, respectively. The micromorphology and chemical composition analysis of the wear scars show that oxidation wear occurs in addition to adhesive wear during the wear process at 600 °C. The oxidation products are identified as Al2O3, CoO, Cr2O3, Fe2O3, Fe3O4, and NiO in terms of the calculation of flash temperature and Gibbs free energy. The calculation results of wear rates show that the AlCoCrFeNiTi1.0 composite coating exhibits the best wear resistance.

Microstructure and high temperature wear behaviour of in-situ TiC reinforced AlCoCrFeNi-based high-entropy alloy composite coatings fabricated by laser cladding

Microstructural evolution and bonding characteristic in multi-layer laser cladding of NiCoCr alloy on compacted graphite cast iron

AlCoCrFeNiSix (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5) high-entropy alloy (HEA) coatings were deposited on the surface of AISI 304 stainless steel via laser cladding technology with different content of Si element. The evolution in microstructure, microhardness, and wear behavior of the coatings was investigated comprehensively to explore the effect of Si element. The results showed that the HEA coatings consisted of disordered Fe-Cr and ordered Al-Ni solid solution phases with a body-centered cubic (BCC) structure. Si element dissolved into the solid solutions, leading to lattice distortion. As Si content increased, the microstructure was refined, and a small quantity of Cr23C6 phase was precipitated along the grain boundaries. The microhardness of the coatings was linearly proportionate to Si content. The quantitative analysis revealed that the improvement of microhardness was dominated by the effect of dislocation strengthening, rather than solution strengthening and fine-grain strengthening. With the increase in Si content, the average friction coefficient and wear rate of the HEA coatings were all reduced remarkably, and the main wear mechanism evolved from adhesive wear, abrasive wear and delamination wear to oxidation wear. These phenomena were believed to be associated with the formation of the oxide film on the worn surface, which was identified as Fe2O3, Fe3O4, Cr2O3, SiO2, and SiO.

Hao Liu

Papers

Modeling of thermal behavior and mass transport in multi-layer laser additive manufacturing of Ni-based alloy on cast iron

Microstructural characterization and corrosion behaviour of AlCoCrFeNiTix high-entropy alloy coatings fabricated by laser cladding

Microstructure and high temperature wear behaviour of in-situ TiC reinforced AlCoCrFeNi-based high-entropy alloy composite coatings fabricated by laser cladding

Microstructural evolution and bonding characteristic in multi-layer laser cladding of NiCoCr alloy on compacted graphite cast iron

Effect of Si addition on microstructure and wear behavior of AlCoCrFeNi high-entropy alloy coatings prepared by laser cladding