微重力条件下气／液两相流压降实验研究

利用俄罗斯IL-76失重飞机对微重力条件下方形截面管道内的水/气两相流压降进行了实验研究．利用本次微重力气／液两相流压降实验结果对一些目前常用的基于地面常重力实验结果的两相流压降预测模型(均相模型、Lockhart-Martinelli—Chisholm模型和Friedel模型)在微重力条件下的适用性进行了评估．比较发现,均相模型和Lockhart-Martinelli—Chisholm模型预测结果和实验数据差异很大;而Friedel模型的预测结果尽管也与实验数据有着明显的差别,但在这些模型中是误差最小的．因此,可以利用Friedel模型来对微重力气／液两相流压降进行初步预估,而新的、更精确的模型将依赖于更有物理意义的分析方法及不同重力条件下气／液两相流压降实验的结果．     

Crystal structure of the human angiotensin-converting enzyme-lisinopril complex

Angiotensin-converting enzyme (ACE) has a critical role in cardiovascular function by cleaving the carboxy terminal His-Leu dipeptide from angiotensin I to produce a potent vasopressor octapeptide, angiotensin II. Inhibitors of ACE are a first line of therapy for hypertension, heart failure, myocardial infarction and diabetic nephropathy. Notably, these inhibitors were developed without knowledge of the structure of human ACE, but were instead designed on the basis of an assumed mechanistic homology with carboxypeptidase A. Here we present the X-ray structure of human testicular ACE and its complex with one of the most widely used inhibitors, lisinopril (N2-[(S)-1-carboxy-3-phenylpropyl]-L-lysyl-L-proline; also known as Prinivil or Zestril), at 2.0 A resolution. Analysis of the three-dimensional structure of ACE shows that it bears little similarity to that of carboxypeptidase A, but instead resembles neurolysin and Pyrococcus furiosus carboxypeptidase--zinc metallopeptidases with no detectable sequence similarity to ACE. The structure provides an opportunity to design domain-selective ACE inhibitors that may exhibit new pharmacological profiles.     

Regulated degradation of a class V myosin receptor directs movement of the yeast vacuole

Normal cellular function requires that organelles be positioned in specific locations. The direction in which molecular motors move organelles is based in part on the polarity of microtubules and actin filaments. However, this alone does not determine the intracellular destination of organelles. For example, the yeast class V myosin, Myo2p, moves several organelles to distinct locations during the cell cycle. Thus the movement of each type of Myo2p cargo must be regulated uniquely. Here we report a regulatory mechanism that specifically provides directionality to vacuole movement. The vacuole-specific Myo2p receptor, Vac17p, has a key function in this process. Vac17p binds simultaneously to Myo2p and to Vac8p, a vacuolar membrane protein. The transport complex, Myo2p-Vac17p-Vac8p, moves the vacuole to the bud, and is then disrupted through the degradation of Vac17p. The vacuole is ultimately deposited near the centre of the bud. Removal of a PEST sequence (a potential signal for rapid protein degradation) within Vac17p causes its stabilization and the subsequent 'backward' movement of vacuoles, which mis-targets them to the neck between the mother cell and the bud. Thus the regulated disruption of this transport complex places the vacuole in its proper location. This may be a general mechanism whereby organelles are deposited at their terminal destination.     

A gene expression atlas of the central nervous system based on bacterial artificial chromosomes

The mammalian central nervous system (CNS) contains a remarkable array of neural cells, each with a complex pattern of connections that together generate perceptions and higher brain functions. Here we describe a large-scale screen to create an atlas of CNS gene expression at the cellular level, and to provide a library of verified bacterial artificial chromosome (BAC) vectors and transgenic mouse lines that offer experimental access to CNS regions, cell classes and pathways. We illustrate the use of this atlas to derive novel insights into gene function in neural cells, and into principal steps of CNS development. The atlas, library of BAC vectors and BAC transgenic mice generated in this screen provide a rich resource that allows a broad array of investigations not previously available to the neuroscience community.     

High-performance thin-film transistors using semiconductor nanowires and nanoribbons

Thin-film transistors (TFTs) are the fundamental building blocks for the rapidly growing field of macroelectronics. The use of plastic substrates is also increasing in importance owing to their light weight, flexibility, shock resistance and low cost. Current polycrystalline-Si TFT technology is difficult to implement on plastics because of the high process temperatures required. Amorphous-Si and organic semiconductor TFTs, which can be processed at lower temperatures, but are limited by poor carrier mobility. As a result, applications that require even modest computation, control or communication functions on plastics cannot be addressed by existing TFT technology. Alternative semiconductor materials that could form TFTs with performance comparable to or better than polycrystalline or single-crystal Si, and which can be processed at low temperatures over large-area plastic substrates, should not only improve the existing technologies, but also enable new applications in flexible, wearable and disposable electronics. Here we report the fabrication of TFTs using oriented Si nanowire thin films or CdS nanoribbons as semiconducting channels. We show that high-performance TFTs can be produced on various substrates, including plastics, using a low-temperature assembly process. Our approach is general to a broad range of materials including high-mobility materials (such as InAs or InP).