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

In this critical review, metal oxides-based materials for electrochemical supercapacitor (ES) electrodes are reviewed in detail together with a brief review of carbon materials and conducting polymers. Their advantages, disadvantages, and performance in ES electrodes are discussed through extensive analysis of the literature, and new trends in material development are also reviewed. Two important future research directions are indicated and summarized, based on results published in the literature: the development of composite and nanostructured ES materials to overcome the major challenge posed by the low energy density of ES (476 references).

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A review of electrode materials for electrochemical supercapacitors

Recent years have seen a rapid growth of interest by the scientific and engineering communities in the thermal properties of materials. Heat removal has become a crucial issue for continuing progress in the electronic industry, and thermal conduction in low-dimensional structures has revealed truly intriguing features. Carbon allotropes and their derivatives occupy a unique place in terms of their ability to conduct heat. The room-temperature thermal conductivity of carbon materials span an extraordinary large range--of over five orders of magnitude--from the lowest in amorphous carbons to the highest in graphene and carbon nanotubes. Here, I review the thermal properties of carbon materials focusing on recent results for graphene, carbon nanotubes and nanostructured carbon materials with different degrees of disorder. Special attention is given to the unusual size dependence of heat conduction in two-dimensional crystals and, specifically, in graphene. I also describe the prospects of applications of graphene and carbon materials for thermal management of electronics.

Thermal properties of graphene and nanostructured carbon materials

Recent years witnessed a rapid growth of interest of scientific and engineering communities to thermal properties of materials. Carbon allotropes and derivatives occupy a unique place in terms of their ability to conduct heat. The room-temperature thermal conductivity of carbon materials span an extraordinary large range – of over five orders of magnitude – from the lowest in amorphous carbons to the highest in graphene and carbon nanotubes. I review thermal and thermoelectric properties of carbon materials focusing on recent results for graphene, carbon nanotubes and nanostructured carbon materials with different degrees of disorder. A special attention is given to the unusual size dependence of heat conduction in two-dimensional crystals and, specifically, in graphene. I also describe prospects of applications of graphene and carbon materials for thermal management of electronics.

Thermal Properties of Graphene, Carbon Nanotubes and Nanostructured Carbon Materials

Organic phase-change material for enhanced energy storage was prepared by adding SiO2 particles in a certain proportion into molten palmitic acid (PA) with stirring and intensive sonication at a constant temperature. The thermal properties of the SiO2/PA composite were experimentally characterized. As compared with the pure PA, the latent heat capacity of the composite with addition of 3 wt% SiO2 particles is increased by 51.7 kJ/kg, reaching 214.7 kJ/kg, which is the highest value among the composites tested with varying SiO2 ratio from 1 to 5 wt%; the thermal conductivity of the 3 wt% SiO2/PA composite is also increased by 12% at 30 oC (solid state) and 7% at 70 oC (liquid state), respectively. A water heater was built and tested with embedded capsules containing the 3 wt% SiO2/PA composite and pure PA, respectively. The lab-built phase-change water heater is much smaller in size than an ordinary household water heater in comparison and uses reduced electrical power. However, it responds faster and has a larger volume ratio of hot water output to water heater size. During the 2 turning-off test, the water heater with 3 wt% SiO2/PA can provide 2.23 times hot water of heater size; while the ordinary water heater can only provide 1.41 times hot water volume of tank size.

Using organic phase-change materials for enhanced energy storage in water heaters: an experimental study

Temperature adjustable thermal conductivity and thermal contact resistance for liquid metal/paraffin/olefin block copolymer interface material

Enhancement of the heat transfer of the cold side is one of the approaches to improve the performance of thermoelectric generator systems (TEGs). In order to investigate viability and further performance of the TEG for waste heat recovery in industry area, a small low-temperature waste heat thermoelectric generator setup has been constructed with graphene oxide (GO) nanofluids as coolants in the paper. The results showed excellent stability of GO nanofluids through the preparation of two-step method to be applied in the TEGs .The highest open output voltage of TEG system were obtained by 0.15% weight fraction of GO nanofluids as coolant when the temperature difference (△T) was designed at 95K and the hot side temperature was fixed at 373K in the TEGs. Compared with conventional glycol-water base fluid as coolant, the highest open voltage enhancement ratio has reached 65.26% in the TEGs.

The preparation, characterization and application of glycol aqueous base graphene oxide nanofluid

As typical absorbing solar energy collectors, direct absorption solar collectors (DASCs) have shown great potentials in solar energy utilization. However, due to the instability and discontinuities of solar energy, it is difficult for the heat source output sustainably. Fabrication of direct solar energy storage system is appealing, which can combine the DASCs system and the phase change materials (PCMs) storage system in one unit. In our current work, using biomass-derived porous carbons (PC) as solar energy absorbance materials and adipic acid (AA) as PCMs in a direct solar storage system, integrations of solar energy collection, photo-thermal conversion and long-term energy storage have been achieved. The photothermal conversion efficiency of AA+7 wt% PC is as high as 93.83%. The thermal conductivity of the AA+7 wt% PC is 1.18 W/(m·K), which is 149% higher than pure AA (0.45 W/(m·K)). The PC-CPCMs have the advantages of no subcooling, and the energy storage density can reach 195.05 J/g. The environmental benign and cheap biomass porous carbons based composite PCMs encapsulated in direct solar energy storage systems pave a new avenue for high utilization of solar energy. It can meet thermal energy demands independent of weather conditions and time effects. • A novel direct solar energy storage system is designed and fabricated. • The system integrates the solar thermal collection with the PCMs storage systems. • Environmental benign biomass-derived carbons are used as light-capturing materials. • PC-CPCMs possess good solar energy absorption and energy storage. • AA+7wt%PC has photothermal conversion efficiency as high as 93.83%. 

Popcorn-derived porous carbon based adipic acid composite phase change materials for direct solar energy storage systems

Lead sulfide (PbS), a promising medium-temperature thermoelectric material, is a cheap and excellent substitute for lead pyride. However, its high thermal conductivity limits its thermoelectric properties strongly. In this paper, the nanocomposites with PbS matrix and organic conducting polymer polyparaphenylene (PPP) supplement are introduced to decrease the thermal conductivity by mechanical mixing method. The experimental results show that the thermal conductivity of PbS–PPP nanocomposites significantly decreases and the minimum thermal conductivity is 0.43 W m−1 K−1, which can be obtained when the mass ratio of the PPP is 3% at 773 K. Consequently, the figure of merit (ZT) of PbS–PPP nanocomposites reaches as large as 0.5, which is 52.40% of magnitude higher than that of pure PbS. Therefore, it is an effective way to improve the thermoelectric properties of PbS by introducing the organic conducting polymer PPP. This work may shed light on developing high-performance thermoelectric materials via organic–inorganic nanocomposites at the intermediate temperature range.

Huaqing Xie

Papers

Using organic phase-change materials for enhanced energy storage in water heaters: an experimental study

Temperature adjustable thermal conductivity and thermal contact resistance for liquid metal/paraffin/olefin block copolymer interface material

The preparation, characterization and application of glycol aqueous base graphene oxide nanofluid

Popcorn-derived porous carbon based adipic acid composite phase change materials for direct solar energy storage systems

Raising the thermoelectric performance of PbS with low-content polyparaphenylene