An accurate parallel genetic algorithm to schedule tasks on a cluster

Recent breakthroughs in the mathematical estimation of parallel genetic algorithm parameters are applied to the NP-complete problem of scheduling multiple tasks on a cluster of computers connected by a shared bus. Numerous adjustments to the original method of parameter estimation were made in order to accurately reflect differences in the problem model. The parallel scheduler used m-ary encoding and included a shared communication bus constraint. Fitness was an indirect computation requiring an evaluation of the meaning and implications (i.e., effect on communication time) of the encoding. The degree of correctness was defined as the “nearness” to the optimal schedule that could be obtained in a limited amount of time. Experiments reveal that the parallel scheduling algorithm developed very accurate schedules when the modified parameter guidelines were used. This article describes the scheduling problem, the parallel genetic scheduler, the adjustments made to the mathematical estimations, the quality of the schedules that were obtained, and the accuracy of the schedules compared to mathematically predicted expected values.     

Effect of large β-Si3N4 particles on the thermal conductivity of β-Si3N4 ceramics

Mean-field micromechanics model, the rule of mixture is applied to the prediction of the thermal conductivity of sintered β-Si₃N₄, considering that the microstructure of β-Si₃N₄ is composed of a uniform matrix phase (which contains grain boundaries and small grains of Si₃N₄) and the purified large grains (⩾2 μm in diameter) of Si₃N₄. Experimental results and theoretical calculations showed that the thermal conductivity of Si₃N₄ is controlled by the amount of the purified large grains of Si₃N₄. The present study demonstrates that the high thermal conductivity of β-Si₃N₄ can be explained by the precipitation of high purity grains of β-Si₃N₄ from liquid phase.     

La(Mg1/2Ti1/2)O3–La2/3TiO3 microwave dielectric ceramics

Structure and microwave dielectric properties were studied in the (1−x)La(Mg_1/2Ti_1/2)O₃–xLa_2/3TiO₃ system. Ceramics with this composition in the 0⩽x⩽0.5 range were processed from powders obtained by a citrate-based chemical route. Structure of these perovskite solid solutions changed from orthorhombic for x=0.1 and 0.3 to pseudocubic for x=0.5. Microwave and radio frequency measurements revealed increase in permittivity and temperature coefficient of the resonant frequency τ_f with increasing of La_2/3TiO₃ content. Close to zero τ_f value was found near to x=0.5 composition of (1−x)La(Mg_1/2Ti_1/2)O₃–x La_2/3TiO₃.     

Solvothermal synthesis of nanocrystalline KTaO3: Effect of solvent dielectric constant

A set of KTaO₃ nanopowders has been prepared at T = 180 °C using various aliphatic alcohols and water as solvents. Pronounced connection between the solvent type and potassium tantalate structures was found. Structural X-ray, TEM and Raman scattering experiments have shown that the solvent dielectric constant ? is an important critical parameter. At ? ～ 24 the cubic perovskite-type phase was formed. Mixed perovskite and pyrochlore phases were formed at larger values of ?. Only pure pyrochlore phase is realized when ? ～ 80. Pyrochlore-free perovskite-structure nanopowder phase formation with the particle size of ～18 and 28 nm was achieved when ethanol and isopropanol solvents were used. Under annealing the coherent domain size decreased down to 6 and 18 nm respectively, since the amorphous phase crystallized. Crystallinity of both as-prepared and annealed powder is the best when isopropanol solvent is used.     

Kinetic performance of hydrogen generation enhanced by AlCl3 via hydrolysis of MgH2 prepared by hydriding combustion synthesis

Magnesium hydride (MgH₂) is a very promising hydrogen storage material and it has been paid more and more attention on the application of supplying hydrogen on-board because the theoretical hydrogen yield is up to 1703 mL/g when it reacts with water. However, the hydrolysis reaction is inhibited rapidly by the passivation layer of Mg(OH)₂ formed on the surface of MgH₂. This paper reports that high purity MgH₂ (～98.7 wt%) can be readily obtained by the process of hydriding combustion synthesis (HCS) and the hydrogen generation via hydrolysis of the as-prepared HCSed MgH₂ can be dramatically enhanced by the addition of AlCl₃ in hydrolysis solutions. An excellent kinetics of hydrogen generation of 1487 mL/g in 10 min and 1683 mL/g in 17 min at 303 K was achieved for the MgH₂-0.5 M AlCl₃ system, in which the theoretical hydrogen yield (1685 mL/g) of the HCSed product was nearly reached. The mechanism of the hydrolysis kinetics enhancement was demonstrated by the generation of a large amounts of H⁺ from the Al³⁺ hydrolysis and the pitting corrosion (Cl^?) of the Mg(OH)₂ layer wrapped on the surface of MgH₂ even at a low temperature. In addition, the apparent activation energies for the MgH₂ hydrolysis in the 0.1 M AlCl₃ and 0.5 M AlCl₃ solutions are decreased to 34.68 kJ/mol and 21.64 kJ/mol, respectively, being far superior to that of reported in deionized water (58.06 kJ/mol). The results suggest that MgH₂ + AlCl₃ system may be used as a promising hydrogen generation system in practical application of supplying hydrogen on-board.     

Influence of chloride salts on hydrogen generation via hydrolysis of MgH2 prepared by hydriding combustion synthesis and mechanical milling

The effects of chloride salts (NaCl, MgCl₂ and NH₄Cl) on the hydrolysis kinetics of MgH₂ prepared by hydriding combustion synthesis and mechanical milling (HCS+MM) were discussed. X-ray diffraction (XRD) analyses show that high-purity MgH₂ was successfully prepared by HCS. Hydrolysis performance test results indicate that the chloride salt added during the milling process is favorable to the initial reaction rate and hydrogen generation yield within 60 min. A MgH₂–10% NH₄Cl composite exhibits the best performance with the hydrogen generation yield of 1311 mL/g and a conversion rate of 85.69% in 60 min at room temperature. It is suggested that the chloride salts not only play as grinding aids in the milling process, but also create fresh surface of reactive materials, favoring the hydrolysis reaction.     

Nanoporous copper fabricated from Zr65Cu17.5Fe10Al7.5 amorphous alloy and its electrocatalytic oxidation performance

A series of bi-continuous and uniform nanoporous structures were fabricated successfully through chemical dealloying from quaternary Zr₆₅Cu_17.5Fe₁₀Al_7.5 amorphous ribbons in hydrofluoric acid (HF) solutions under a free corrosion condition. Nanoporous structures obtained from dealloying amorphous ribbons for 5 h in 0.02 M,0.035 M and 0.05 M HF solutions have mean pore sizes of 30–40 nm. A three-dimensional bi-continuous nanoporous copper (NPC) structure formed on Zr₆₅Cu_17.5Fe₁₀Al_7.5 ribbon alloys has pore sizes of 44.91 nm,52.60 nm and 57.37 nm, respectively, after immersion in 0.02 M HF solution for 15 h, 20 h, and 25 h. It shows that the pore size of NPC structure increases with increasing the dealloying time. The cyclic voltammetry (CV) results reveal that all NPC structures have the obvious electrocatalytic ability to the oxidation of (CH₂OH)₂ solution, compared with the initial amorphous ribbon without oxidation peak on CV curve. Zr-Cu-Fe-Al amorphous alloys can be new candidates for fabricating NPC structures.     

The biomethane producing potential in China: A theoretical and practical estimation

Biomethane has been developed rapidly in many countries as a renewable energy which upgraded from biogas. China also began to pay attention to it even though we still at a initial stage, primarily, understanding the biomethane potential and development prospect, choosing appropriate biomass as the biomethane source is very important. In this work, the theoretical and practical biomethane producing potential from five main biomass resources in China were estimated with appropriate methods based on the data collected, and during calculation, two appropriate energy crops were assumed to be planted on marginal lands for biomethane production. Our estimation showed that the theoretical and practical biomethane potentials in China can reach to 888.78 and 316.30 billion m³ per year, agricultural waste should be the preferential development biomass, and planting energy crops on marginal lands is the most promising way to enhance biomethane production in China. Finally, biomethane is compared with natural gas, and the result showed that 48.15% of the practical biomethane potential can meet the total Chinese natural gas consumption in 2013.