The vector fields admitting one-parameter spatial symmetry group and their reduction

For a n-dimensional vector fields preserving some n-form, the following conclusion is reached by the method of Lie group. That is, if it admits an one-parameter, n-form preserving symmetry group, a transformation independent of the vector field is constructed explicitly, which can reduce not only dimesion of the vector field by one, but also make the reduced vector field preserve the corresponding ( n - 1)-form. In partic ular, while n = 3, an important result can be directly got which is given by Me,ie and Wiggins in 1994.

孔心平行电极间赝火花放电的有效极距

20年代,胡刚复先生为我国度量衡统一确定一个市制,对米、千克、升的公制有一个3、2、1的简单比例关系。这一制度沿用至今,不仅已被科技界视为当然,且更广泛便利人民生活,定将一直延续下去。反观当时我国各地方、各行业,如营造尺、16两、大斗小称等度量衡各异的混乱;以及今日美、英等国被英尺、磅、加仑的英制零星折算产生的经常困扰;特别是对工程及商务所带来的经济损失,以致积重难返的窘态。可以悟出胡先生这一简明建议的重大功绩,堪与两千年前同文同轨、权衡悉依秦制的炎黄文明相映生辉。在纪念胡先生百周年时,谨撰此文,寓意于简单3、2、1系数的巧合,借以颂扬胡先生的功绩。

严格求解夹层圆柱壳在轴压下的轴对称失稳问题

本文在文献[1]的基础上,用严格的方法求解两端简支的夹层圆柱壳在均匀轴压下的轴对称失稳问题.内、外表层很薄弹性模量又大,按薄壳理论处理;夹心较厚弹性模量又相当小,横向剪切变形的影响必须考虑,在研究夹层壳的整体失稳尤其是局部失稳时,横向的拉伸和压缩变形也不可忽略,用数学弹性力学的方法处理.本文导得了可求解轴对称整体失稳和局部失稳临界载荷的超越方程,用数值计算的方法可算得临界载荷的最小值.对于整体失稳的情况,给出算例,与夹层壳理论的解作了比较.

中子星的吸积流动

本文分析中子星的吸积流动,其中磁轴与自转轴重合.吸积盘内缘区域的波阻将使盘内的角速度偏离开普勒速度而减小,引力势能使流体加热和加速.吸积盘中有两类流动.完全亚声速流动的引力势能主要使吸积流加热.另一种流动有跨声速过渡和激波.这两种流动都表明,吸积盘的高温区域都位于过渡区中,而外部区域中气体温度不高.还计算了中子星磁层中的吸积流动.在极区距几个中子星半径处,气体被急剧加热,产生X射线辐射,形成热斑.这些结果与中子星吸积流动的主要特征一致.

窄缝内汽液两相临界流实验研究

本文实验研究了高过冷水在窄缝内形成的汽液两相临界流动现象,考察了水的泄漏率与容器内压、温度、流道几何尺寸等影响因素之间的关系,给出了一个简单的拟单相流预测关系式,和实验数据的比较表明,该关系式可以较好地预测高过冷水在窄缝内形成的气液两相临界流动现象。

Chemical equilibrium analysis and CFD simulation of coal combustion and NOx formation

A full two-fluid model of reacting gas-particle flows with an algebraic unified second-order moment (AUSM) turbulence-chemistry model is used to simulate Beijing coal combustion and NOx formation. The sub-models are the k-epsilon-kp two-phase turbulence model, the EBU-Arrhenius volatile and CO combustion model, the six-flux radiation model, coal devolatilization model and char combustion model. The blocking effect on NOx formation is discussed. In addition, the chemical equilibrium analysis is used to predict NOx concentration at different temperature. Results of CID simulation and chemical equilibrium analysis show that, optimizing air dynamic parameters can delay the NOx formation and decrease NOx emission, but it is effective only in a restricted range. In order to decrease NOx emission near to zero, the re-burning or other chemical methods must be used.

Developing A Microfluidic-Based System To Quantify Cell Capture Efficiency

Micro-fabrication technology has substantial potential for identifying molecular markers expressed on the surfaces of tissue cells and viruses. It has been found in several conceptual prototypes that cells with such markers are able to be captured by their antibodies immobilized on microchannel substrates and unbound cells are flushed out by a driven flow. The feasibility and reliability of such a microfluidic-based assay, however, remains to be further tested. In the current work, we developed a microfluidic-based system consisting of a microfluidic chip, an image grabbing unit, data acquisition and analysis software, as well as a supporting base. Specific binding of CD59-expressed or BSA-coupled human red blood cells (RBCs) to anti-CD59 or anti-BSA antibody-immobilized chip surfaces was quantified by capture efficiency and by the fraction of bound cells. Impacts of respective flow rate, cell concentration, antibody concentration and site density were tested systematically. The measured data indicated that the assay was robust. The robustness was further confirmed by capture efficiencies measured from an independent ELISA-based cell binding assay. These results demonstrated that the system developed provided a new platform to effectively quantify cellular surface markers effectively, which promoted the potential applications in both biological studies and clinical diagnoses.

Absolute phase control of spectra effects in a two-level medium driven by two-color ultrashort laser pulses

Using a omega-3 omega combination scenario, we investigate the absolute phase control of the spectra effects for ultrashort laser pulses propagating in a two-level medium. It is found that the higher spectral components can be controlled by the absolute phases. In particular, different absolute phase combinations can lead to the buildup or split of the even harmonics. (c) 2006 Elsevier B.V. All rights reserved.

Radius of curvature measurements for laser beams: A simple method

A simple method for measuring the radius of curvature of laser beams is introduced. It has been developed to estimate the astigmatic aberration of a diode laser. Compared with the interferornetry, this method is convenient and straightforward. (c) 2005 Elsevier GmbH. All rights reserved.

空间CCD凝视成像跟踪系统的作用距离分析

在充分考虑了空间背景光辐射特性以及漫反射目标对相干光和自然光的不同反射特性的基础上,利用信号检测的统计学方法,导出了空间电荷耦合器件(CCD)凝视成像跟踪系统分别在激光照明主动跟踪模式和太阳光照明被动跟踪模式下的作用距离表达式。结果表明,空间CCD凝视成像跟踪系统在脉冲能量为1mJ的激光照明主动跟踪模式下可对1m2空间漫反射目标实现10km量级范围内的跟踪;而利用太阳光照明的被动跟踪模式下的跟踪距离可达几百千米。