矩形平面直流磁控溅射装置工作区域磁场分析

通过分析磁场对磁控溅射过程的影响,总结出了矩形平面直流磁控溅射装置工作区域磁场的设计原则,并给出了两种磁体结构.采用有限元方法对一套装置的磁场进行了计算,磁场计算结果与测量值吻合较好.基于上述分析计算,研究了磁场分布对靶材刻蚀形貌的影响,并进一步提出了具体的磁场改进措施.采用分流条垫补方法可以改进磁场分布,如果磁场水平分量呈马鞍形分布,靶材的利用率可以提高,采用磁极斜面结构对磁场分布的改进意义不大.另外,错开磁体间安装接缝和对永磁体精确充磁能够有效提高工作区域磁场分布的均匀性.     

Sintering study of Ti6Al4V powders with different particle sizes and their mechanical properties

Ti6Al4V powders with three different particle size distributions (0-20, 20-45, and 45-75 μm) were used to evaluate the effect of the particle size distribution on the solid-state sintering and their mechanical properties. The sintering kinetics was determined by dilatometry at temperatures from 900 to 1260℃. The mechanical properties of the sintered samples were evaluated by microhardness and compression tests. The sintering kinetics indicated that the predominant mechanism depends on the relative density irrespective of the particle size used. The mechanical properties of the sintered samples are adversely affected by increasing pore volume fraction. The elastic Young's modulus and yield stress follow a power law function of the relative density. The fracture behavior after compression is linked to the neck size developed during sintering, exhibiting two different mechanisms of failure:interparticle neck breaking and intergranular cracking in samples with relative densities below and above of 90%, respectively. The main conclusion is that relative density is responsible for the kinetics, mechanical properties, and failure behavior of Ti6Al4V powders.     

Hydroxylation of demethoxy-Q6 constitutes a control point in yeast coenzyme Q6 biosynthesis

Coenzyme Q is a lipid molecule required for respiration and antioxidant protection. Q biosynthesis in Saccharomyces cerevisiae requires nine proteins (Coq1p–Coq9p). We demonstrate in this study that Q levels are modulated during growth by its conversion from demethoxy-Q (DMQ), a late intermediate. Similar conversion was produced when cells were subjected to oxidative stress conditions. Changes in Q₆/DMQ₆ ratio were accompanied by changes in COQ7 gene mRNA levels encoding the protein responsible for the DMQ hydroxylation, the penultimate step in Q biosynthesis pathway. Yeast coq null mutant failed to accumulate any Q late biosynthetic intermediate. However, in coq7 mutants the addition of exogenous Q produces the DMQ synthesis. Similar effect was produced by over-expressing ABC1/COQ8. These results support the existence of a biosynthetic complex that allows the DMQ₆ accumulation and suggest that Coq7p is a control point for the Q biosynthesis regulation in yeast. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Received 04 September 2008; received after revision 22 October 2008; accepted 23 October 2008     

Causally productive activities

This paper suggests and discusses an answer to the following question: What distinguishes causal from non-causal or coincidental co-occurrences? The answer derives from Elizabeth Anscombe’s idea that causality is a highly abstract concept whose meaning derives from our understanding of specific causally productive activities (e.g., pulling, scraping, burning), and from her rejection of the assumption that causality can be informatively understood in terms of actual or counterfactual regularities.