Amino-acid synthesis in carbonaceous meteorites by aqueous alteration of polycyclic aromatic hydrocarbons

It has been suggested that amino acids and other organic compounds found in carbonaceous meteorites formed by aqueous alteration in the meteorite parent bodies. Observations of carbonaceous material in interstellar grains and interplanetary dust particles indicate that condensed organic compounds may have been present in meteorite parent bodies at the time of aqueous alteration. One group of compounds thought to be representative of this carbonaceous material is the polycyclic aromatic hydrocarbons (PAHs). Recently it was proposed that PAHs condense on SiC grains in the molecular envelopes of carbon-rich red-giant stars, which would allow for their subsequent incorporation into meteorite parent bodies during accretion. This incorporation mechanism is supported by the identification of SiC grains in carbonaceous chondrites. The possibility therefore exists that PAHs, and/or other condensed organic compounds, represent the starting material for aqueous alteration which leads to the formation of amino acids and other water-soluble organic compounds. Here we present calculations of the distribution of aqueous organic compounds in metastable equilibrium with representative PAHs as functions of the fugacities of O2, CO2 and NH3. The results reported here for pyrene and fluoranthene, two PAHs with different structures but the same stoichiometry, differ greatly but indicate that the formation of amino and carboxylic acids is energetically favourable at probable parent-body alteration conditions. The actual reaction mechanisms involved could be revealed by consideration of isotope data for PAHs, amino acids, other organic compounds and carbonates in carbonaceous chondrites.     

频变系统特征问题及其灵敏度分析的扩阶法

当振动系统的物理矩阵（刚度矩阵和／或质量矩阵）是频率的函数时,该特征问题就变为非线性特征问题．由于振型的非正交性,使得非线性特征问题及其灵敏度分析存在困难．针对可展成幂级数形式的非线性特征问题,提出了一种通过初始系统矩阵的扩阶来使原非线性问题线性化的扩阶方法．该方法的优点是：由于在线性化过程中未引入任何误差,因而是精确的;可适用于强非线性特征问题;可求得系统的所有特征值及其灵敏度．数值示例表明,该方法虽很简单,但十分有效．     

磁流变液阻尼器用于转子振动控制的实验研究

实验研究了一种剪切式磁流变流阻尼器在转子振控制中的应用,实验发现,磁流变液阻尼器的刚度和阻尼随施工磁场强度的增加而增大;支承在磁流变液阻尼器上的转子系统的振幅在亚临界区及临界转速处随施加的磁场强度的增加而减小,而在超临界区则随磁场强度的增加而增大;系统的临界转速随磁场强度的增加而升高,通过简单的开关控制,可使转子的振动在全转速区的内达到最小。     

舰艇抗冲瓦隔声性能试验研究

抗冲瓦能够很好地实现对水下非接触爆炸载荷的整体冲击隔离.其特殊的空腔结构是否同时具有隔声性能也广为关注,为此,在某海域港湾内对一艘试验船进行了敷设与未敷设抗冲瓦的声辐射噪声对比试验.试验结果表明,抗冲瓦在广泛的频域内均具有良好的隔声性能.舰艇湿表面敷设抗冲瓦对舰艇本体噪声向水中辐射的抑制效果量级为:0.1～1 kHz频段约为5 dB:1～3 kHz约为10 dB;3 kHz以上15 dB,能够较大地降低舰艇的水中辐射噪声,为提高舰艇整体的隐身性能提供了一种新的技术和方法.     

Methane: an open or shut case?

The author examines conflicting models, especially evidence from Price and Schoell in this issue (see comment), for the creation of ore deposits and the movement of petroleum. The Bakken formation in North Dakota is used as an example of a petroleum reservoir that has not migrated from its original site. Analysis of natural gases at the site indicates a difference in gas distribution between the Bakken site and migratory sites. Controversies are examined in the context of advances in fluid-flow calculations and high-temperature methanogenic reactions.     

环氧丙烷冲击点火的微观研究

利用多种光谱技术提出了一种确定燃料冲击点火延迟时间和临界条件的新方法：先用谱仪确定燃料冲击点火最早出现的中间产物,对于环氧丙烷,氧原子辐射总是先出现;把单色谱仪调至氧原子波长处,并利用压力传感器测得冲击波到达样品的时间便可确定环氧丙烷冲击点火延迟时间。这种方法比国内外常用光电二极管(峰值波长约在800nm)的方法更接近实际值。环氧丙烷受冲击后,冲击点火临界马赫数Mαc＝6。     

Base excision repair and design of small molecule inhibitors of human DNA polymerase β

Base excision repair (BER) can protect a cell after endogenous or exogenous genotoxic stress, and a deficiency in BER can render a cell hypersensitive to stress-induced apoptotic and necrotic cell death, mutagenesis, and chromosomal rearrangements. However, understanding of the mammalian BER system is not yet complete as it is extraordinarily complex and has many back-up processes that complement a deficiency in any one step. Due of this lack of information, we are unable to make accurate predictions on therapeutic approaches targeting BER. A deeper understanding of BER will eventually allow us to conduct more meaningful clinical interventions. In this review, we will cover historical and recent information on mammalian BER and DNA polymerase β and discuss approaches toward development and use of small molecule inhibitors to manipulate BER. With apologies to others, we will emphasize results obtained in our laboratory and those of our collaborators.     

舰艇抗冲瓦整体冲击隔离新概念及其机理研究

基于声阻抗失配原理,提出了舰艇抗冲瓦对水下爆炸冲击的整体隔离新概念.采用波动理论和Taylor平板模型.以冲击波在水、覆盖层、空气层、船体钢中的传播过程为研究对象,建立了实心敷设层结构(消声瓦的简化模型)和带空腔敷设层结构(抗冲瓦)的流固耦合模型.利用Abaqus软件建立舰艇抗冲瓦三维冲击响应模型.算例结果表明,抗冲瓦能够很好地隔离水下爆炸冲击波.大大降低船体结构材料应力和加速度冲击响应峰值,并能在广泛的频域内显著降低舰艇冲击响应.