对短跑“速度障碍”成因及其克服的研究

田径运动是各项运动的基础.而短跑又是田径运动的基础。短跑水平上不去,将影响到整个田径运动水平的提高。因此,提高短跑运动水平具有重要意义。在实际训练中,经常产生影响和阻碍短跑成绩提高的令教练员十分棘手的“速度障碍”。只有研究和分析“速度障碍”的成因,采取切实有效的方法和手段来克服速度障碍,才能保证短跑运动水平的提高。     

PWM模拟信号光电耦合隔离电路的研制

本文提出一种运用PWM(脉冲调宽)原理设计低价格、低漂移、高线性模拟信号光电耦合隔离电路的方案。这种方案仅用普通的光电耦合器件。实验结果表明,这种隔离电路的非线性度不劣于0.02％,温度漂移低于0.002％/℃。本文还讨论了光电耦合器件的关断时间t_（OFF）对隔离电路动态范围的影响,并着重指出,关断时间温度系数（?）是影响隔离电路温度稳定性的主要因素。     

Lactate dehydrogenase and glutamate dehydrogenase activities in the circumventricular organs of rat brain following neonatal monosodium glutamate

Glutamate (glu) an excitatory neurotransmitter amino acid, is present in high concentrations in the mammalian central nervous system and is the most abundant amino acid in our daily diet. In the present study the activities of lactate dehydrogenase (LDH) and glutamate dehydrogenase (GDH) were evaluated in the circumventricular organs (CVO) of the brain in 25-day-old rats following MSG administration at a dose of 4 mg/g b.wt during the first ten days of life. The results show the LDH activity increased to 265% of that in the control (p<0.001), whereas GDH activity was significantly decreased (p<0.05), The great elevation in LDH, a cytoplasmic marker enzyme, is apparently due to cytoskeletal changes brought about as a consequence of glu toxicity, whereas lowered GDH activity indicates altered glu homostasis in the blood-brain-barrier deficient areas following neonatal exposure to glu.     

A relevant in vitro rat model for the evaluation of blood-brain barrier translocation of nanoparticles

Poly(MePEG₂₀₀₀cyanoacrylate-co-hexadecylcyanoacrylate) (PEG-PHDCA) nanoparticles have demonstrated their capacity to reach the rat central nervous system after intravenous injection. For insight into the transport of colloidal systems across the blood-brain barrier (BBB), we developed a relevant in vitro rat BBB model consisting of a coculture of rat brain endothelial cells (RBECs) and rat astrocytes. The RBECs used in our model displayed and retained structural characteristics of brain endothelial cells, such as expression of P-glycoprotein, occludin and ZO-1, and immunofluorescence studies showed the specific localization of occludin and ZO1. The high values of transendothelial electrical resistance and low permeability coefficients of marker molecules demonstrated the functionality of this model. The comparative passage of polyhexadecylcyanoacrylate and PEG-PHDCA nanoparticles through this model was investigated, showing a higher passage of PEGylated nanoparticles, presumably by endocytosis. This result was confirmed by confocal microscopy. Thanks to a good in vitro/in vivo correlation, this rat BBB model will help in understanding the mechanisms of nanoparticle translocation and in designing new types of colloidal carriers as brain delivery systems.Received 4 March 2005; accepted 14 April 2005     

Decision-making at the surface of the intact or barrier disrupted skin: potential applications for vaccination or therapy

The skin is a highly accessible organ and constitutes an active immunological site. Both these properties make this surface an attractive route for what promises to be a cost-effective, simple, practical and needle-free delivery of vaccines and immunomodulators. Less obvious is the fact that the state of the skin barrier can influence quantitative and qualitative aspects of antigen-specific immune responses. The everyday decision-making at the skin epithelium concerns the choice between the induction of an immune response and the establishment of a state of non-responsiveness (tolerance). This decision is influenced by various factors such as the dose, the route (intact vs barrier-disrupted skin), the cytokine microenvironment and the nature of the antigenic stimulus. By increasing our understanding of how immune responses are regulated in the epidermis we can envisage the development of immunisation protocols aimed at eliciting a protective immune response or inducing tolerance, with direct applications to preventive or therapeutic vaccination, respectively.Received 29 November 2004; received after revision 2 February 2005; accepted 22 February 2005     

磁场调制下单层石墨烯势垒结构的隧穿特性

利用传递矩阵方法,在多方势垒基础上,采用渐近手段,研究了单层石墨烯不同势垒结构(方势垒和劈形势垒)的隧穿特性,结果发现势垒形状影响隧穿特性.对于2种形状的势垒结构,无论是透射系数还是平均电导率,既展现出相同的特点,又有明显不同之处.通过比较透射系数与平均电导率,得出各自的特点,为实际设计纳米器件提供理论基础.     

疯牛病防治的研究进展

疯牛病是由朊病毒引起的一种致死性人畜共患神经退行性疾病.根据近年来国际上有关疯牛病防治的研究进展,并结合本课题组最近在该领域的研究成果,以新的角度,主要从疯牛病的风险因素、演化、种间传播、防治药物和监控体系等方面做以综述,旨在为我国各级政府在“后疯牛病时期”制定相应的疯牛病的防治政策提供参考.     

带扩散扰动的对偶风险模型的门槛分红策略

研究了一类带干扰(布朗运动)的对偶风险模型,此模型可以用来模拟证券公司的盈余过程(经营收入).利用无穷小分析法,求出了公司在破产前总分红现值期望函数(分红函数)满足的微积分方程组,导出了与该微积分方程组等价的更新方程组.最后,在指数分布收入情形下,我们给出了分红函数在特例下的一般解.     

α-乙酰基二硫缩烯酮在TiCl4催化下的酰化反应机理研究

在B3LYP/6-311G(p)理论水平上研究α-乙酰基二硫缩烯酮在TiCl4催化下的酰化反应的微观反应机理.优化反应过程中的反应物、中间体、过渡态和产物的结构,同时采用了极化连续介质模型(PCM)对各个驻点进行了单点能计算以模拟在CH2Cl2溶剂中的反应过程,并且应用了自然轨道理论(NBO)和分子中的原子理论(AIM)分析了这些物质的成键特征和轨道间的相互作用.计算结果得到此反应在TiCl4催化情况下的活化能小于没有催化剂情况下的活化能,证明了在TiCl4催化剂参加的情况下有利于此反应的进行,溶剂效应也较大程度地降低了此反应的活化能.     

楼板配筋率对板筋参与梁端抗弯的影响

针对现浇楼板在框架梁端实际抗弯中具有参与作用的情况,采用有限元软件ABAQUS对不同楼板配筋率的钢筋混凝土框架结构在侧向荷载作用下的受力情况进行了分析.研究表明,现浇楼板配筋率会影响现浇楼板中的板筋在框架梁端实际抗弯的参与程度,在梁柱同等配筋的情况下,楼板配筋率高的框架梁端的实际承载能力要大于楼板配筋率低的结构的实际承载能力,因此,在进行有效翼缘宽度的选取时,应将现浇楼板配筋率列入考虑范围.