Numerical simulation of the flow within and over an intersection model with Reynolds-averaged Navier--Stokes method

In this study, the Reynolds-averaged Navier--Stokes (RANS) method is employed to simulate the flow within and over an intersection model with three kinds of $k$--$\varepsilon$ turbulence closure schemes, namely, standard model, renormalization group (RNG) model and realizable $k$--$\varepsilon$model. The comparison between the simulated and observed flow fields shows that the RANS simulation with all the three turbulence models cannot completely and accurately reproduce the observed flow field in all details. A detailed comparison between the predicted profiles of wind velocities and the measured data shows that the realizable $k$--$\varepsilon$ model is the best one among the three turbulence closure models in general. However, the extent to which the improvement is achieved by the realizable $k$--$\varepsilon$ model is still not enough to completely and accurately describe the turbulent flow in a relatively complex environment.     

Application of the second—order ground—state correlation and random—phase approximation on photoionization cross section of manganese

Using the many-body perturbation theory,we have calculated the photoionization cross section of 3p and 3d subshells of the neutral manganese,and discussed the second-order ground-state correlation and random-phase approx-imation correlations in detail.This is the first theoretical calculation for manganese as far as we know .our calculated results are more consistent with the experimental results than those given by other methods in the literature.     

高密度体系光电离截面新表达式的应用

利用实验光谱学的Beer Lambert定律和介质中的麦克斯韦方程组，建立了精确的光吸收（光电离）截面表达式，并通过一个随体系粒子数密度和宏观复介电常数而变化的变换函数，将严格截面公式与Fano和Cooper 1968年建立的理想气体的光电离截面公式直接联系起来.建议：1)当知道某密度下正确的体系宏观复介电常数β,γ时，可直接由严格表达式求得高密度下非理想状态的正确光电离截面；2)或当知道该体系的粒子微观极化率η,ζ和其理想气体的精确截面时，用上述变换公式间接求得其他密度时的光电离截面.对氩原子和氙原子的应用表明：当缺乏β,γ时，可由某一合理的宏观电极化率物理（例如克劳修斯-莫索缔）模型来计算β,γ，从而获得高密度体系的截面.这样获得的结果符合被散射物质的光电离（光吸收）截面随体系粒子数密度增大而增加的客观散射现象.而且，考虑了高密度真实体系中粒子间相互作用的宏观电极化率模型越正确，如此求得的散射截面的误差就越小. 关键词： 光电离截面 光吸收截面 介电常数 极化率     

C20F20分子电子输运性质的第一性原理研究

利用第一性原理密度泛函理论和非平衡格林函数方法研究了C₂₀F₂₀分子的电子输运性质. 计算得到了C₂₀F₂₀分子的平衡电导为0385 G₀ 其I-V曲线表现出较好的线性特性. 在有限偏压范围内具有较稳定的电导值, 可以用于制备稳恒电阻分子器件. 关键词： 20F₂₀分子')" href="#">C₂₀F₂₀分子 电子输运 分子器件     

Variation of photoabsorption cross section of atomic silver from isolated to condensed conditions

The influence of the local-field on the photoabsorption cross section of the atomic silver is studied in detail by using the Clausius--Mossotti (CM) model and the Onsager model separately. The variations of the photoabsorption cross section of atomic silver with number density and radius of the environmental interaction cavity are studied systematically by using more general expressions for the photoabsorption cross sections, proposed by Sun et al recently. It has proved to be reasonable to model the optical response properties of bulky material by coupling the property of isolated atom with the environmental effects in the present work.     

离子通道中毒对耦合随机Hodgkin-Huxley神经元集体激发行为的影响

四乙铵（tetraethylammonium）和河豚毒素（tetrodotoxin）可以分别使神经元细胞钾离子和钠离子通道中毒,从而导致电导降低和有效通道数减少。数值模拟研究了钾离子和钠离子通道中毒对耦合Hodgkin-Huxley神经元集体激发（collective spiking）行为的影响。发现对于一定数目的神经元,随离子通道簇面积（patchsize）的变化,离子通道中毒既可以增强也可以降低集体激发的规则性（regularity）;当簇面积大小固定时,对于较小和较大的簇面积,钾离子和钠离子通道中毒可以分别降低和增强集体激发的规则性,但二者变化的簇面积范围不同。对于某个簇面积,二者的效果可能相反。这一结果与离子通道中毒对单个神经元膜电势激发的影响不同,反映了神经元耦合作用、离子通道中毒导致的电导降低和离子通道噪声增强三者间的相互作用和影响。     

Femtosecond control of photoionization and photodissociation of sodium iodine molecules by laser pulse

Wave packet propagation techniques are used to find experimentally reliable laser parameters that yield optimal production.The photoionization and photodissociation dynamics of sodium iodine molecules are interpreted into several channels.Several frequencies are found to be suitable for NaI molecules during the photoionization and dissociation processes.Photon-dressed excited states and electron-dressed ionic continuum states facilitate the search for available laser parameters.     

Ab initio investigations of the charge transport properties of endohedral M@C20（M=Na and K）metallofullerenes

Using density functional theory and quantum transport calculations based on nonequilibum Green’s function formalism,we investigate the charge transport properties of endohedral M@C 20 (M=Na and K) metallofullerenes.Our results show that the conductance of C 20 fullerene can be obviously improved by insertion of alkali atom at its centre.Both linear and nonlinear sections are found on the I-V curves of the Au-M@C 20-Au two-probe systems.The novel negative differential resistance behaviour is also observed in Na@C 20 molecule but not in K@C 20.     

边界振动的微腔中的二能级原子

采用全量子理论，对注入腔内的二能级原子、单模腔场和振动边界(视为频率为ω_m的量子谐振子)构成的系统，在相互作用绘景中，求解了该系统的态函数随时间的演化关系，在此基础上得到了原子布居数随时间的演化关系，结果显示布居数在初始值附近振荡，这说明边界的振动是周期性的，它对原子布居数的影响也是周期性的. 关键词： 边界振动的微腔 二能级原子 布居数     

平均速度近似为瞬时速度造成系统误差的多方法研究——以倾斜气垫导轨法测量重力加速度实验设计为例

匀变速直线运动加速度计算公式应用中，最基本的物理观念是几个物理量之间存在着“一一对应”关系。在倾斜气垫导轨法测量重力加速度实验中，滑块运动的瞬时速度无法准确测量，只能用平均速度代替，造成了公式应用中要求的物理量之间的“一一对应”关系被破坏，产生了无法克服的系统误差。本文设计了匀加速和匀减速直线运动两种实验情境，分别用控制变量法、数学解析法和图像法等多种方法研究了不同实验情境的系统误差，将系统误差分析与物理观念构建建立了联系，分析了挡光片宽度d、加速情境滑块静止释放时离第一个光电门的距离L、减速情境滑块静止时离第二个光电门距离M、两光电门间距S和气垫导轨倾角θ等参量对该系统误差的影响，研究表明：d、S、L或W参量对该系统误差都有影响；d值的大小是造成该系统误差的主要因素；θ参量无影响；应用公式(1)计算重力加速度值更精确。