A generalization of the radiation stress tensor

The classical derivation of the radiation stress tensor, for progressive and standing waves, in one dimension, due to Longuet-Higgins and Stewart is generalized to apply to any two-dimensional pattern of waves, standing or progressive, which can be described by a complex velocity potential.     

Olefin metathesis applied to cellulose derivatives—Synthesis,analysis, and properties of new crosslinked cellulose plastic films

New crosslinked cellulose‐based plastic films were synthesized with olefin metathesis as a crosslinking reaction. Microcrystalline cellulose was first dissolved in a lithium chloride/N,N‐dimethylacetamide solvent system and acylated by ω‐undecenoyl chloride under microwave irradiation with N,N‐dimethyl‐4‐aminopyridine as the catalyst. Cellulose unsaturated fatty acyl esters with a degree of substitution (DS) ranging from 1.4 to 2.0 were then crosslinked by olefin metathesis with a first generation Grubbs catalyst. Crosslinking ratios (T) ranging from 20 to 90% were obtained for low catalyst amounts (<1.2%), but gels appeared when T was too high. To avoid this gel formation, cellulose was acylated with a mixture of lauroyl and ω‐undecenoyl chlorides. This internal dilution allowed us to obtain films of every case and various T (varying from 10 to 80% for a catalyst amount below 3.5%). Plastics were characterized by Fourier transform infrared (FTIR) spectroscopy, and the fatty acid mixture resulting from the hydrolysis of cellulose esters were analyzed by gas chromatography (GC) and NMR spectroscopy. Mechanical properties showed that the elastic modulus and tensile failure stress was higher when the plastic films were crosslinked. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 407–418, 2005     

ε-CL-20/F2311 PBXs力学性能和结合能的分子动力学模拟

本文应用分子动力学(MD)模拟方法, 研究高能量密度化合物六硝基六氮杂异伍兹烷(ε-CL-20)与常用高聚物粘结剂F2311所构成的CL-20/F2311高聚物粘结炸药(PBXs)的力学性能和结合能随温度和高聚物浓度而变化的规律. 结果表明, 添加高聚物于主体炸药中, 使其弹性模量减小, 表明刚性减小, 弹性增大, 机械力学性能大为改善; 在一定范围内, 随高聚物F2311在PBXs中浓度的增加,体系结合能从正值变为负值, 而随温度升高,体系的结合能变化不是很明显.     

Application of capillary zone electrophoresis for separation of water-soluble gold monolayer-protected clusters

An effective capillary electrophoretic technique for separating samples of negatively charged, polydisperse, water-soluble gold monolayer-protected cluster (Au MPC) protected by monolayers of N-acetyl-L-cysteine has been developed. The separation mechanisms of the Au MPC in CZE suggest that the larger core sizes Au MPC emerge first from the capillary. The electrophoretic separation depends on pH, buffer concentration, and organic modifiers. The addition of aliphatic alcohols to the run buffer can improve the separation of Au MPC by reducing the EOF and changing the selectivity between the Au MPCs. The enhancement of resolution is attributed to the more significant difference in the charge-to-size ratio between the Au MPCs. The run buffer containing 20 v/v % ethanol provides the best separation for water-soluble Au MPC. Our proposed CE method provides a powerful tool to evaluate and separate the water-soluble Au MPC products.     

Direct partial oxidation of methane to methanol： Reaction zones and role of catalyst location

Direct partial oxidation of methane to methanol was investigated in a specially designed reactor. Methanol yield of about 7%-8% was obtained in gas phase partial oxidation. It was proposed that the reactor could be divided into three reaction zones, namely pre-reaction zone, fierce reaction zone, and post-reaction zone, when the temperature was high enough to initiate a reaction. The oxidation of methane proceeded and was completed mostly in the fierce reaction zone. When the reactant mixture entered the post-reaction zone, only a small amount of produced methanol would bring about secondary reactions, because molecular oxygen had been exhausted in the fierce reaction zone. A catalyst, if necessary, should be placed either in the pre-reaction zone, to initiate a partial oxidation reaction at a lower temperature, or in the fierce reaction zone to control the homogeneous free radical reaction.     

Peculiarities of metal electrodeposition inside a flow-through porous electrode with low initial conductivity in oxidant containing solution

The earlier developed dynamic model of a flow-through electrode is used for studying how the variations in initial conductivity of a porous matrix κ_s,ini and a metal deposit affect the rate of metal deposition from an oxidant-containing solution for the direct-flow operation mode of the porous electrode. It is found that in contrast to an oxidant-free solution in which the decrease of κ_s,ini improves the uniformity of deposit distribution inside the porous cathode and increases the deposit final mass m _f, the opposite situation is observed in the presence of an oxidant, namely, a decrease in κ_s,ini, under otherwise similar conditions reduces the deposit mass and leads to its specific spatial distribution. The final metal deposit is divided into two separate fragments (rear and front) with a region of low conductivity of the initial porous matrix in between. Dynamics of the current and metal redistribution within the porous electrode, the reasons for the formation and stabilization of the rear fragment of coating, the correlation between the metal deposition rate and changes in the anodic zone position and intensity are discussed. It is shown that with the appearance of a specific profile of deposit distribution, the dependence of m _f on the metal conductivity develops a limit that differs considerably from the deposit final mass for an equipotential porous electrode.     

Effect of solution volume on the rate of metal recovery and its distribution in porous cathode

By means of earlier developed dynamic model of porous electrode, numerical analysis is given of the effect of the division into smaller parts of optimal volume V _opt of metal-containing solution circulating through the porous electrode, which ensures both achieving of the metal preset recovery and the prescribed final porosity in the critical cross-section of the porous cathode, most strongly filled with the deposit. It is shown that the result depends significantly on the presence (or absence) of oxidant ions in the solution. In the absence of oxidant, the division of V _opt is desirable; it entails some improving of the distribution uniformity and increase in the deposit eventual mass. On the contrary, in the presence of oxidant such a division brings about marked negative consequences: (1) the metal deposit stronger localization at the porous electrode front edge and (2) decrease in the deposit’s final mass. It was shown that these phenomena result from the formation of anodic zone in the porous electrode rear side in the initial stage of the processing of the second and subsequent portions of solution. This is promoted by low polarization in this part of the porous electrode and the presence of a soluble metal deposited here during the final stage of electrolysis of the solution preceding portion.     

Thermal activation and deactivation of grown‐in defects limiting the lifetime of float‐zone silicon

By studying the minority carrier lifetime in recently manufactured commercially available n‐ and p‐type float‐zone (FZ) silicon from five leading suppliers, we observe a very large reduction in the bulk lifetime when FZ silicon is heat‐treated in the range 450–700 °C. Photoluminescence imaging of these samples at the wafer scale revealed concentric circular patterns, with higher recombination occurring in the centre, and far less around the periphery. Deep level transient spectroscopy measurements indicate the presence of recombination active defects, including a dominant center with an energy level at ～E_v + 0.5 eV. Upon annealing FZ silicon at temperatures >1000 °C in oxygen, the lifetime is completely recovered, whereby the defects vanish and do not reappear upon subsequent annealing at 500 °C. We conclude that the heat‐treatments at >1000 °C result in total annihilation of the recombination active defects. Without such high temperature treatments, the minority carrier lifetime in FZ silicon is unstable and will affect the development of high efficiency (>24%) solar cells and surface passivation studies.     

Direct correlation of microstructure and device performance of liquid phase crystallized Si thin film solar cells on glass

Si thin films on glass grown by liquid phase crystallization (LPC) exhibit large grains resembling those in multicrystalline Si wafers. The present work gives direct insight into how planar defects in LPC‐Si thin films influence the device performance of the corresponding solar cells by acquiring electron‐backscatter diffraction maps and measuring solar cell parameters on the same identical positions. By this approach, it was possible to demonstrate how low scanning velocities of the laser line during the crystallization lead to lower densities of grain boundaries, to improved charge‐carrier diffusion lengths, and hence to improved device performances.

     

超高效液相色谱法同时测定食品塑料包装材料中的紫外吸收剂和抗氧化剂

超声萃取结合超高效液相色谱(UPLC)技术,建立了食品塑料包装材料中14种紫外吸收剂及抗氧化剂(UV-0,UV-9,UV-71,UV-329,UV-326,UV-327,UV-234,UV-360,抗氧化剂2246,抗氧化剂425,TH-1790,抗氧化剂3114,抗氧化剂1010和抗氧化剂1076)的高通量检测方法。样品经三氯甲烷-甲醇超声提取,C18色谱柱分离后,乙腈和0.1%甲酸水为流动相梯度洗脱,二极管阵列检测器测定。14种物质在一定的浓度范围内线性关系良好,相关系数(r2)均不低于0.999 2,方法定量下限(S/N=10)为8.0~33.0 mg/kg,平均回收率为83.6%~116.2%,相对标准偏差(RSD,n=6)为1.3%~9.5%。方法具有前处理简单、净化效果好等特点,适用于食品塑料包装中14种紫外吸收剂及抗氧化剂的同时测定。