Stokes问题的非协调广义差分法

本文提出解Stokes问题的非协调广义差分法,速度用不连续分片线性函数逼近,压力用分片常数函数逼近。速度近似按‖.‖_h模,压力近似按L²模都具有最优的逼近阶误差估计。本文还给出了数值计算结果。     

KdV孤子的含时微扰理论

研究了周期性含时微扰对KdV(Korteweg de Vries)孤子的影响. 将微扰项展为时间变量的傅里叶级数,发现其常数项是导致长期项的根源. 在一阶近似下,消除长期项,求出了孤子参数(高度、宽度和速度)随时间的缓慢变化. 傅氏级数中的其他项决定了微扰对孤子波形的一阶修正. 关键词： KdV孤子 孤子微扰论     

梯度倾斜相关测量水平C_n~2和横向风速廓线的理论与仿真研究

根据Rytov近似以及泰勒湍流冻结假设,推导出以不同距离的前向散射光为信标的水平路径上梯度倾斜角的相关表达式.基于该表达式,在理论上提出了计算湍流强度与横向风速的新方法,并通过数值仿真对该方法进行了初步验证.结果表明,在5%高斯误差情况下,大气折射结构常数和风速的计算结果与理论真值在整体变化上具有较好的一致性,线性相关系数分别能达到0.8与0.9.该方法能够得到不同湍流与风速条件下的湍流强度廓线以及风速廓线,为反演大气湍流强度以及风速提供了一种新思路.     

微平行管道内Jeffrey流体的非定常电渗流动

研究了微平行管道内线性黏弹性流体的非定常电渗流动, 其中线性黏弹性流体的本构关系是由Jeffrey流体模型来描述的. 利用Laplace变换法, 求解了线性化的Poisson-Boltzmann方程、 非定常的柯西动量方程和Jeffrey流体本构方程, 给出了黏弹性Jeffrey流体电渗速度的解析表达式, 分析了无量纲弛豫时间λ₁和滞后时间λ₂对速度剖面的影响. 发现滞后时间为零时, 弛豫时间越小, 速度剖面图越接近牛顿流体的速度剖面图; 随着弛豫时间和滞后时间的增加, 速度振幅也变得越来越大, 随着时间的增加, 速度逐渐趋于恒定. 关键词： 双电层 微平行管道 Jeffrey流体 非定常电渗流动     

采用BP神经网络研究C-F键核自旋偶合常数

通常理论研究核自旋偶合常数的方法是基于线性模型进行拟合和预测，该方法在拟合和预测中仍有较大误差. 本文在前面工作的基础上，提出了基于非线性模型对C-F键核自旋偶合常数进行研究的观点，采用BP神经网络方法对C-F键核自旋偶合常数的函数关系式进行拟合，并用拟合结果对4种化合物的偶合常数进行预测. 结果表明，采用非线性的BP神经网络方法其训练效果与预测效果均优于线性模型方法；其预测误差对文中的4种化合物不超过0.40%.     

q振子光场模型的光与物质相互作用的非线性理论

建立了一个以q振子为光场模型的光与物质相互作用的非线性理论,求得了薛定谔方程的形式解,并用微扰法求出一级近似的发射概率和吸收概率,同时求解了共振条件的拉比问题。在q→1时,恢复为普通线性理论。 关键词：     

第一原理计算稀磁半导体(In1-xMnx)As的晶格常数,磁性和电子结构

用紧束缚近似线性Muffin-tin轨道的方法计算了稀磁半导体(In1-xMnx)As(x=1/2,1/4和1/8)的晶格常数,磁性和电子结构.给出了Mn掺杂浓度的变化对(In1-xMnx)As的晶格常数,磁性和电子结构的影响.     

对称陀螺分子NH3的高温谱线强度研究

在直接计算分子配分函数的基础上,将无转动跃迁偶极矩平方近似为一常数,计算了对称陀螺分子NH₃ 0300 a—0000 s跃迁在高温下的线强度.在296K,计算的分子总配分函数与HITRAN数据库的结果符合很好,只有0.19%的百分误差.计算的跃迁线强度在2000 K和3000K的高温与HITRAN数据库的结果也符合相当好,最大百分误差分别为-0.65%和-1.77%.这就表明分子配分函数和线强度的高温计算是可靠的.在此基础上,计算被扩展到更高温度,报道了对称陀螺分子NH_{3< 关键词： 高温光谱 对称陀螺分子 配分函数 氨}     

ReSi1.75电子结构的第一性原理研究

基于第一性原理全势线性缀加平面波方法和局域密度近似(LDA)，对ReSi_1.75的基态晶格属性进行了研究. 结构优化的结果表明，ReSi_1.75的基态平衡晶格常数比实验值小约0.6%. 在LDA计算基础上，考虑局域的Re的d电子库仑作用，用LDA+U方法计算了ReSi_1.75的电子结构，发现当U_eff=U-J=4.4eV时，能带结构呈半导体性质. 具有0.12eV 关键词： 1.75')" href="#">ReSi_1.75 局域密度近似 自相互修正作用 电子结构     

考虑非常数自旋扭矩时LLS方程的微扰解

不将自旋扭矩因子近似为一个常数,利用Melnikov微扰方法推导了LLS方程解的表达式,通过VC与MATLAB混和编程进行计算,计算结果显示,与将自旋扭矩因子视为常数的情况相比较,自旋扭矩为磁化强度函数时的磁化强度运动轨道在离开未扰轨道初期仅在未扰轨道附近做微小振动,在翻转时刻附近有较大振荡,并且所预言的磁化强度翻转时刻相对提前. 关键词： 自旋扭矩 磁化强度 LLS方程 微扰     

Escape probabilities from a spherical shell medium

The particle escape probability from a spherical shell medium containing internal sources is obtained by solving exactly the integral equation for the total flux. The Galerkin method is used to obtain numerical results, which is a simple and efficient method to study such a problem.     

Discrete dynamics and metastability: Mean first passage times and escape rates

The problem of escape from a domain of attraction is applied to the case of discrete dynamical systems possessing stable and unstable fixed points. In the presence of noise, the otherwise stable fixed point of a nonlinear map becomes metastable, due to noise-induced hopping events, which eventually pass the unstable fixed point. Exact integral equations for the moments of the first passage time variable are derived, as well as an upper bound for the first moment. In the limit of weak noise, the integral equation for the first moment, i.e., the mean first passage time (MFPT), is treated, both numerically and analytically. The exponential leading part of the MFPT is given by the ratio of the noise-induced invariant probability at the stable fixed point and unstable fixed point, respectively. The evaluation of the prefactor is more subtle: It is characterized by a jump at the exit boundaries, which is the result of a discontinuous boundary layer function obeying an inhomogeneous integral equation. The jump at the boundary is shown to be always less than one-half of the maximum value of the MFPT. On the basis of a clear-cut separation of time scales, the MFPT is related to the escape rate to leave the domain of attraction and other transport coefficients, such as the diffusion coefficient. Alternatively, the rate can also be obtained if one evaluates the current-carrying flux that results if particles are continuously injected into the domain of attraction and captured beyond the exit boundaries. The two methods are shown to yield identical results for the escape rate of the weak noise result for the MFPT, respectively. As a byproduct of this study, we obtain general analytic expressions for the invariant probability of noisy maps with a small amount of nonlinearity.     

GaN光电阴极表面势垒对电子逸出几率的影响

针对GaN光电阴极表面势垒对电子逸出几率的影响问题,应用玻尓兹曼分布和基于Airy函数的传递矩阵法计算了GaN光电阴极的电子逸出几率,发现电子逸出几率主要由I势垒决定,II势垒对电子逸出几率的影响有限.利用自行研制的GaN光电阴极激活评估实验系统,测试了透射式GaN光电阴极样品的激活光电流.实验发现,Cs单独激活引起电子逸出几率的显著增加,而Cs单独充分激活后的Cs/O交替激活对电子逸出几率的影响有限.理论计算结果与激活光电流测试结果一致,其原因是Cs单独激活对降低真空能级的贡献远大于Cs/O共同激活.     

An investigation of x‐ray escape for an HPGe detector

X‐ray escape peaks for a planar HPGe detector were investigated for a point source of photons with 59.5 keV energy. The effect of the solid angle for the incident photons on the escape probability of Ge K x‐rays was studied using collimators with varying apertures. A Monte Carlo program was also developed to estimate the probability of escape for various mechanisms and routes. The experimental and simulation results showed that the escape probability is essentially constant for a wide range of collimator radii, but at first starts to increase and then becomes constant when the side surface of the detector becomes accessible for escape with larger collimators. Copyright © 2003 John Wiley & Sons, Ltd.     

表面势垒对梯度掺杂GaN光电阴极电子逸出几率的影响

研究表面势垒对梯度掺杂GaN光电阴极电子逸出几率的影响.计算梯度掺杂透射式GaN光电阴极的电子能量分布及逸出几率,结果显示梯度掺杂与均匀掺杂相比,可以获得更大的电子逸出几率;I势垒对电子逸出几率的影响显著,而Ⅱ势垒影响较小.利用GaN光电阴极多信息量测试系统,测试两种GaN阴极样品的光电流.实验结果表明,梯度掺杂GaN样品比均匀掺杂电子逸出几率更大;单独进行Cs激活形成的I势垒对电子逸出几率有显著影响,而Cs/O共同激活形成的Ⅱ势垒对其影响较小.     

铟封前后透射式GaAs光电阴极光谱响应特性的测试与分析

利用自行研制的光谱响应测试仪工程化样机,对透射式GaAs光电阴极在高温激活结束、低温激活结束以及铟封成管后的光谱响应特性进行了测试。结果显示,铟封后阴极整个响应波段的光谱响应下降,长波响应受到最显著的影响,表现为800~815 nm之间长波响应大幅度衰减,截止波长和峰值波长向短波移动,峰值响应和积分灵敏度减小,最终的光谱响应曲线变得平坦。阴极参量的计算结果反映铟封后阴极的表面逸出几率降低,说明铟封引起阴极表面激活层发生变化,使得能量较低的长波段光生电子不容易逸出,阴极长波响应和灵敏度随之降低。进一步分析了铟封过程中影响阴极表面激活层的因素。     

Photon escape probabilities for stark-broadened lyman series lines

A simple formula is derived for the escape probability of photons in optically thick resonance lines of hydrogenic ions. The result is valid whenever quasi-static Stark broadening predominates in the line wings, a condition that is satisfied in most laser-produced plasmas. In contrast to impact (Lorentzian) broadening, Stark broadening tends to decrease the probability of photon escape as the plasma density increases.     

GaAs光电阴极稳定性的光谱响应测试与分析

利用光谱响应测试仪对激活后的反射式GaAs(Cs,O)光电阴极进行了稳定性测试,获得了阴极随时间变化的光谱响应曲线,并表征了阴极在衰减过程中的性能参数变化.结果表明:积分灵敏度和峰值响应随着时间不断下降,截止波长向短波推移,表面逸出几率的下降是阴极衰减的直接原因.不同波长下光谱响应的衰减速率并不相同,波长越长,衰减速率越大,因此激活台内阴极在灵敏度衰减的同时长波响应能力也在不断下降.     

Escape probability of O 1s photoelectrons leaving copper oxide

The escape probability of O 1s photoelectrons as a function of depth of origin in CuO has been studied experimentally and by the Monte Carlo technique. It has been proved experimentally that the escape probability in the direction of X-ray propagation is no longer described by a simple exponential law but is a complex function with a maximum at a depth of 4–10 Å. The mean escape depth is derived from the experimental data and is compared with the results of theory; satisfactory agreement is obtained.