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91.
快速反击战术是当今足球比赛的重要特征之一,影响运动员快速能力的因素体现在跑速、动作结构、动作速率、传球速度等六个方面,足球比赛中应注重培养运动员的快速反击意识、节奏感和抢截能力。 相似文献
92.
Knowledge of the seismic velocity structure at the top of the Earth's inner core is important for deciphering the physical processes responsible for inner-core growth. Previous global seismic studies have focused on structures found 100 km or deeper within the inner core, with results for the uppermost 100 km available for only isolated regions. Here we present constraints on seismic velocity variations just beneath the inner-core boundary, determined from the difference in travel time between waves reflected at the inner-core boundary and those transmitted through the inner core. We found that these travel-time residuals-observed on both global seismograph stations and several regional seismic networks-are systematically larger, by about 0.8 s, for waves that sample the 'eastern hemisphere' of the inner core (40 degrees E to 180 degrees E) compared to those that sample the 'western hemisphere' (180 degrees W to 40 degrees E). These residuals show no correlation with the angle at which the waves traverse the inner core; this indicates that seismic anisotropy is not strong in this region and that the isotropic seismic velocity of the eastern hemisphere is about 0.8% higher than that of the western hemisphere. 相似文献
93.
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). 相似文献
94.
Interaction of reelin signaling and Lis1 in brain development 总被引:1,自引:0,他引:1
Assadi AH Zhang G Beffert U McNeil RS Renfro AL Niu S Quattrocchi CC Antalffy BA Sheldon M Armstrong DD Wynshaw-Boris A Herz J D'Arcangelo G Clark GD 《Nature genetics》2003,35(3):270-276
Loss-of-function mutations in RELN (encoding reelin) or PAFAH1B1 (encoding LIS1) cause lissencephaly, a human neuronal migration disorder. In the mouse, homozygous mutations in Reln result in the reeler phenotype, characterized by ataxia and disrupted cortical layers. Pafah1b1(+/-) mice have hippocampal layering defects, whereas homozygous mutants are embryonic lethal. Reln encodes an extracellular protein that regulates layer formation by interacting with VLDLR and ApoER2 (Lrp8) receptors, thereby phosphorylating the Dab1 signaling molecule. Lis1 associates with microtubules and modulates neuronal migration. We investigated interactions between the reelin signaling pathway and Lis1 in brain development. Compound mutant mice with disruptions in the Reln pathway and heterozygous Pafah1b1 mutations had a higher incidence of hydrocephalus and enhanced cortical and hippocampal layering defects. Dab1 and Lis1 bound in a reelin-induced phosphorylation-dependent manner. These data indicate genetic and biochemical interaction between the reelin signaling pathway and Lis1. 相似文献
95.
YUZhengquan FANBaoliang DAIYunping ZHENGMing MINHuiling WANGMeili WANGLili FEIJing LINing 《科学通报(英文版)》2003,48(21):2331-2335
Human lysozyme is a 130-aa (amino acid) alkaline polypeptide, and has both anti-bacterial and anti-viral properties which make it an important component of human natural immunity system. As a first step toward the ultimate goal of improving the anti-bacterial properties of bovine and ovine milk, a transgenic mouse that contains the genomic DNA sequence of the human lysozme gene has been generated for the first time. From 83 mice generated by microinjection, a total of 6 positive transgenic mice were identified by PCR and Southern blot. F1 mice positive for transgene in lines were also detected by PCR. This shows that transgene could be transmitted from founder transgenic mice to their offspring. Recombinant human lysozyme (rHlys) was found in the whey of 3 female positive transgenic mice by Western blot. The highest concentration of rHlys for transgenic mice was 0.2mg/mL. The antibacterial activity of the whey for transgenic mice was highly enhanced up to 0.4 times as much as that of human, while that of non-transgenic mouse was very low. Although the lysozyme activity of transgenic mice is still lower than that of human, the rHlys exhibits the same specific activity as that of human lysozyme. It provides a strong basis for further studies into the possible application of rHlys express in mammary gland. 相似文献
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98.
城市固体垃圾热解设备与特性研究 总被引:2,自引:0,他引:2
针对无筛分城市垃圾热解的实用技术进行了研究,开发出内热源和外热源联合使用的垃圾热解设备.同时对设备的温度变化、垃圾热解特性、产气规律以及影响热解气热值的主要因素等进行了详细的分析.结果表明:实用热解设备的产气率高,理想热解温度在700℃以下.垃圾热解气中H2的体积分数达15.2%,C2H4,C2H6,C3H6和CH4的体积分数总和是10%,热解气的平均热值为7546.4 kJ/m3.设备运行稳定且温度特性满足设计要求. 相似文献
99.
采用大中心孔设计方法成功地研制了高集成度空间机械臂模块化关节.该关节具有多种传感器,包括位置传感器、力矩传感器、温度传感器等,它的所有电气系统都集成在关节内部,包括传感系统、驱动系统、控制系统和电源系统.采用中心孔走线方式实现了关节的内部走线,避免了空间环境对导线及其传输信号的影响.针对所设计的关节进行了必要的关节性能实验,结果表明该模块化关节具有高刚度、大负载特点,其关节的位置输出能精确跟踪期望的轨迹,位置精度非常高,达到了0.01°. 相似文献
100.
利用蒽甲醇对单壁碳纳米管进行了化学修饰,并利用透射电镜、紫外可见吸收光谱、荧光光谱、拉曼光谱对修饰后的单壁碳纳米管进行了表征分析.通过对比吸附前后的紫外可见吸收光谱发现,吸附后的光谱强度下降大约57.1%,说明单壁碳纳米管吸附上了蒽甲醇.通过拉曼光谱分析发现,吸附后单壁碳纳米管的拉曼光谱中主要峰的位置向长波方向移动了6~7cm^-1,认为拉曼光谱发生移动的原因是单壁碳纳米管吸附蒽甲醇前后状态的改变导致的. 相似文献