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

An introduction to heat transfer

Review of the proton exchange membranes for fuel cell applications

Emerging challenges and materials for thermal management of electronics

Recent development of polymer electrolyte membranes for fuel cells.

The effect of pore size and porosity on thermal management performance of phase change material infiltrated microcellular metal foams

A method for solvent-free fabrication of porous polymer using solid-state foaming and ultrasound for tissue engineering applications.

http://www-personal.umich.edu/~hpeng/publications/Chen-Li%20humidifier%20paper.pdf

An experimental study and model validation of a membrane humidifier for PEM fuel cell humidification control

High-voltage spinel cathodes LiMn1.5Ni0.5O4 are promising candidates for large-scale energy-storage applications such as electric vehicles. However, the widespread adoption of this high-voltage spinel cathode is hampered by severe capacity fade, particularly at elevated temperatures, resulting from aggressive formation of a thick solid-electrolyte interphase (SEI) layer through side reactions with the electrolyte at the high operating voltage, cationic ordering between Mn4+ and Ni2+ ions in the crystal lattice, and formation of a rock salt LixNi1−xO impurity phase. While these issues have been explored, the wide variation in physical and electrochemical properties with different synthesis methods is not fully understood. In this investigation, we present how the synthesis conditions of the co-precipitation method influence the microstructure and morphology through nucleation and growth of crystals in solution. The samples were prepared by two similar wet-chemical routes and were characterized by microscopy and electrochemical methods to determine the role of microstructure and morphology in the electrochemical performance. Various factors such as the degree of cation ordering between Mn4+ and Ni2+, Mn3+ content, Ni–Mn ratio in the sample, change in lattice parameter with the state of charge, and surface crystal planes were examined to develop a better understanding of the factors influencing the electrochemical performance. It is found that the surface crystal planes, the arrangement of lithium ions near the surface, and the lithium diffusion mechanism have a dominant effect on the capacity retention and rate performance.

Octahedral and truncated high-voltage spinel cathodes: the role of morphology and surface planes in electrochemical properties

A fabrication process to produce functionally graded porous polymer via supercritical carbon dioxide (ScCO2) foaming is reported in this paper. It utilizes a partial gas saturation technique to obtain non-equilibrium gas concentration profiles in thermoplastic polymer. Once foamed the polymer material obtains a graded foam–solid-foam structure with varying pore size distributions. This functionally graded material fabrication method was studied with polymethyl methacrylate (PMMA) under a ScCO2 saturation condition. A diffusion model was developed to estimate the gas diffusion coefficient and to predict the gas concentration profiles inside the polymer samples. Scanning electron microscopy images were used to analyze the effects of partial saturation on the graded porous structure. Mechanical properties of the foamed samples were characterized using a three-point bending test. It was found that the gas concentration profiles resulted from partial saturation corresponded well to the graded structure after foaming. The proportion of the foam and solid regions inside the polymer sample can be manipulated by controlling the partial saturation profile. The test results also suggested that the graded foam structure could be optimized to achieve desirable mechanical properties.

Wei Li

Papers

The effect of pore size and porosity on thermal management performance of phase change material infiltrated microcellular metal foams

A method for solvent-free fabrication of porous polymer using solid-state foaming and ultrasound for tissue engineering applications.

An experimental study and model validation of a membrane humidifier for PEM fuel cell humidification control

Octahedral and truncated high-voltage spinel cathodes: the role of morphology and surface planes in electrochemical properties

Fabrication of functionally graded porous polymer via supercritical CO2 foaming