声子散射下碳纳米管场效应管建模方法研究

声子散射对碳纳米管场效应管(carbon nanotube field effect transistor, CNTFET)的特性有着不可忽略的影响. 传统研究方法基于弹道输运模型来分析发生声子散射时各参数对器件特性的影响, 进而建立CNTFET声子散射模型.为了降低模型复杂度, 提高仿真计算的速度, 本文深入研究了CNTFET的声子散射影响, 对手性、温度和能量三个参数的变化进行了仿真, 分析了参数对器件特性的影响. 采用线性近似拟合的方式建立了一种新的CNTFET声子散射模型.通过分析散射下电流的变化, 验证了该模型的正确性和有效性.与半经典散射模型相比, 该模型由于不需要进行积分计算, 计算过程较为简单, 降低了运算量. 关键词： 碳纳米管场效应管 声子散射模型 线性近似拟合     

粗糙海面高功率微波传输特性矩量法分析

应用蒙特卡罗方法实现了粗糙海面的仿真与模拟,建立了基于双积分方程的高功率微波（HPM）近海面传输特性矩量法计算模型。模型采用光滑窗函数对均匀平面波进行调制,把均匀平面波入射调制为锥形波,消除了粗糙海面突然被截断而引起的边缘效应的影响;重新推导了锥形波入射下的基尔霍夫近似公式,并在满足基尔霍夫近似的条件下,通过对比分析,验证了模型的正确性;采用模型计算分析了不同海面几何参数和海水媒质参数对HPM近海面传输系数的影响。结果表明:粗糙海面的均方根高度对HPM传输系数影响明显,均方根高度越大,传输系数越小,能量分布越均匀;另外随着海水介电常数实部和虚部的增加,传输系数均有所增加,并且实部的影响更明显。     

基于Rytov积分近似的有限口径定量反演成像（特邀）

提出一种适用于有限口径下高相对介电常数和大尺寸目标物体的反演方法。首先分析了低损耗介质的复折射率，通过有效折射率的计算方法得到有效折射率与介电常数关系；利用高频近似估计对比度函数，通过近似估计散射体内部散射场及其梯度对传统Rytov近似进行数学上的修正，产生无相位条件下Rytov积分近似模型，该模型可以实现定量重建高相对介电常数和大尺寸未知目标的对比度虚部。仿真结果显示有限口径下的Rytov积分近似可以对高介电常数和大尺寸目标的对比度虚部提供精确的形状重建。     

Blumlein型脉冲调制器电容等参数的模拟与计算研究

 采用有限元方法,针对水介质Blumlein结构的Spark-03加速器进行了相关参数的计算。给出了准确的2维CAD模型,对各个部分做了介绍,计算出加速器内部电场分布;利用对电场能量积分的方法,当Blumlein传输线的内筒、中筒分别充电时,对传输线各个部分进行能量积分,给出了加速器各个部分电容的数值;将计算结果与理论值、实验结果相比较,证明了此方法可以更准确的计算加速器电容。应用此方法,可以对不同类型的电容储能型加速器进行参数的模拟计算。     

快Z箍缩物理过程的PSPICE电路模拟方法分析

PSPICE电路模拟方法是脉冲功率驱动源电路模拟设计的一种实用方法。应用PSPICE电路模拟方法，把Z箍缩物理过程的薄壳模型同驱动源的电路模型集中参数有机地结合，应用PSPICE电路模拟方法中的电路积分和微分方法，计算上述微积分方程组，可以得到同驱动源参数相关的Z箍缩零级近似物理参数，如箍缩时间、箍缩速度、内爆动能、负载上的电流、电压等内爆物理量变化规律。     

基于分布参数的制冷装置制冷剂充灌量的研究

采用分布参数积分方法建立了制冷剂积存质量的计算模型,计算模型中考虑到了换热系数对制冷剂积存质量的影响,并利用实验数据与计算结果进行了比较,验证了模型的参考价值。结果表明冷凝器中制冷剂积存质量所占比例最大,是总充灌量的55%~64%,而蒸发器制冷剂积存质量所占比例为17%~32%。     

细致能级光电离与辐射复合速率系数的计算及讨论

在以前所计算的细致能级光电过程截面数据的基础上,用修正的Gramm-Schmidt方法做三次样条函数的最小二乘拟合,在LTE近似条件下,取光子分布函数为Planck分布,自由电子分布函数为Maxwel分布,给出了光电离与辐射复合速率系数积分在样条参数下的表达式,并计算了类氦铷、类氦铌离子光电离与辐射复合速率系数。分析了能级跃迁下的速率系数向轨道跃迁速率系数的过渡关系,并对文[1]给出的半经验公式进行了评价。     

环形空间内凝固问题的研究

首先采用积分近似法中的对数温度分布假定，二次曲线温度颁上假定以及数值计算等三种方法分别求解了内侧冷却，外侧绝热时环形空间内相变介质的凝固问题，然后人分近似解与数值解作了较为详细的比较，接着讨论了环形空间的内径比η１，初始过热度θ１，Ｂｉ数，Ｓｔｅ数等参数对凝固过程的影响；最后得到了两条重要结论，一是当环形空间内外径之比η１大于等于０．６时，可用工作量较小的二次曲线温度分布代替对数温度分布，这样做所     

基于激光吸收光谱技术的非均匀流场气体参数测量研究

为了探索激光吸收光谱技术在非均匀流场中的应用,提出了一种新的实现非均匀流场中气体参数定量测量的方法。预知被测流场中的温度变化范围后,选择在该温度范围内具有近似线性变化特性的谱线,线性拟合该温度范围内的谱线强度,结合实验测量的吸收光谱便可以实现非均匀流场中H₂O组分权重的温度积分平均值和H₂O组分积分平均值的定量测量。两温度分布和高斯温度分布模型的仿真研究证明了该方法的有效性和可靠性。两温度分布模型中的测量结果与理论值的偏差分别小于0.82%和1.10%,而高斯温度分布模型中不同光线中的测量值与理论值的最大偏差分别小于0.9%和3.6%。     

关于实际换能器指向性指数确定的简便方法

指向性指数在评价电声换能器,特别是在声呐应用中,一直是一个重要的参量。但因为它包含三维图案的积分,所以精确地计算和测量这个参数是困难的。因此,在理论上和测量中都广泛使用了近似方法。本文报道中运用的三种近似方法是:1.利用理论近似计算公式计算指向性指数;2.实测波束宽度再作理论近似计算;3.方向性图案测量和图表积分。用这三种方法分别测量和计算了四种换能器的指向性指数。     

Finite element analysis of nano-scale Timoshenko beams using the integral model of nonlocal elasticity

Stress-strain relation in Eringen's nonlocal elasticity theory was originally formulated within the framework of an integral model. Due to difficulty of working with that integral model, the differential model of nonlocal constitutive equation is widely used for nanostructures. However, paradoxical results may be obtained by the differential model for some boundary and loading conditions. Presented in this article is a finite element analysis of Timoshenko nano-beams based on the integral model of nonlocal continuum theory without employing any simplification in the model. The entire procedure of deriving equations of motion is carried out in the matrix form of representation, and hence, they can be easily used in the finite element analysis. For comparison purpose, the differential counterparts of equations are also derived. To study the outcome of analysis based on the integral and differential models, some case studies are presented in which the influences of boundary conditions, nonlocal length scale parameter and loading factor are analyzed. It is concluded that, in contrast to the differential model, there is no paradox in the numerical results of developed integral model of nonlocal continuum theory for different situations of problem characteristics. So, resolving the mentioned paradoxes by means of a purely numerical approach based on the original integral form of nonlocal elasticity theory is the major contribution of present study.     

Non-local defect interaction in one-dimension: weak versus strong non-locality

Defect interaction (kink-antikink interaction) is studied for a prototypical model for non-local interaction. Mathematically, it is a bistable integrodifferential model, where the non-local interaction is performed due to an integral kernel. The system is able to establish domains where it is in one of its two equilibria, separated by defects. It is shown that the defect interaction depends on the asymptotical behavior of the integral kernel. In the weak non-local regime, when the integral kernel decays faster than an exponential at infinitum, the defect interaction is exponentially weak. Hence, this case is qualitatively similar to the local one. On the other hand, in the strong non-local regime, when the integral kernel decays slower than an exponential at infinitum, the defect interaction is ruled by the asymptotical behavior of the integral kernel. In this case, the defect interaction is stronger, and could be characterized, for instance, by a power law. The effect of this transition (from the weak to strong non-locality) on the domain dynamics is discussed.     

An analytical model to estimate the performance of an indoor barrier at low-medium frequencies

Indoor barriers are now widely used for sound insulation. This paper examines the performance of indoor barriers in the low-medium frequency range and analyses the interaction between different natural modes of a room-barrier-room system. Morse proposed a theoretical model to calculate the sound field in a coupled-room, but this model neglects the surface integral of the boundary values of sound pressure. To estimate the performance of a barrier in an indoor environment, an analytical model is proposed that modifies the Green’s function for a non-rigid boundary enclosure and approximates the surface integral by a pre-estimated sound pressure based on Morse’s model. An additional approximation has been made in the proposed model to neglect the coupling area in the calculation of the surface integral. The proposed model used to predict the insertion loss of the barrier is verified by the experimental results using a 1:5 scale model. The predicted results agree well with the measured results at lower frequencies.     

Breakdown of the coherent state path integral: two simple examples

We show how the time-continuous coherent state path integral breaks down for both the single-site Bose-Hubbard model and the spin-path integral. Specifically, when the Hamiltonian is quadratic in a generator of the algebra used to construct coherent states, the path integral fails to produce correct results following from an operator approach. As suggested by previous authors, we note that the problems do not arise in the time-discretized version of the path integral.     

一种可稳定计算Pekeris波导中声场的波数积分方法

提出一种可稳定计算Pekeris波导中声场的波数积分方法,并在此基础上开发出一个数值模型,可用于提供Pekeris波导中声场的精确、稳定的数值解。在这个方法中,由于与深度有关的波动方程齐次解中所有的上行波与下行波均采用了合理的归一化表示,从而得到的系统方程是无条件稳定的。在简正波方法中,割线积分一般只对近场有显著影响。因此,传统的简正波模型一般都忽略割线积分对声场的贡献。但是,如果某号简正波离割线非常近,则割线积分对非常远距离的声场仍可能有显著影响。在这种情况下,传统的简正波模型由于忽略割线积分的贡献,从而得到的声场结果是不准确的。本文通过数值算例比较本文提出的波数积分模型与传统的简正波模型。数值结果表明,本文提出的模型可以提供精确、稳定的Pekeris波导中声场的数值解,而在某些情况下传统的简正波模型得到的声场结果是不准确的。因此,本文提出的模型可以作为Pekeris波导中声传播问题的标准模型使用。      

Treatment of Confinement in the Faddeev Approach to Three-Quark Problems

We present a method to solve the Faddeev integral equations of the semirelativistic constituent quark model. In such a model the quark–quark interaction is modeled by an infinitely rising confining potential and the kinetic energy is taken in a relativistic form. We solve the integral equations in Coulomb–Sturmian basis. This basis facilitates an exact treatment of the confining potentials.     

Quantum Cosmology with Hyperbolic Potential

For an FRW model with a minimally coupled scalar field having hyperbolic(exponential) potential we evaluate the wave function both by solving theWheeler-Dewitt (WD) equation and by evaluating the path integral. The WDequation is solved in configuration as well as in momentum space, while thepath integral is evaluated by dividing the lapse integral into a number of pieces.     

Instability of Solution of Phase Retrieval in Direct Diffraction Phase-Contrast Imaging with Partially Coherent X-Ray Source

The theoretical model of direct diffraction phase-contrast imaging with partially coherent x-ray source is expressed by an operator of multiple integral. It is presented that the integral operator is linear. The problem of its phase retrieval is described by solving an operator equation of multiple integral. It is demonstrated that the solution of the phase retrieval is unstable. The numerical simulation is performed and the result validates that the solution of the phase retrieval is unstable.     

Artifact analysis and image enhancement in three-dimensional computational integral imaging using smooth windowing technique

We propose an artifact analysis in computational integral imaging and the image enhancement method based on the analysis using the smooth windowing technique. Blurring and lenslet artifacts, which are major problems in computational integral imaging, are defined and analyzed using a signal model. Applying a smooth and continuous window such as the triangular window to computational integral imaging reconstruction provides a dramatic improvement in terms of image quality. Experimental results are presented to show the validity of our method. To our best knowledge, this is the first trial to control a window function in computational integral imaging.     

Integral sliding mode control for offshore steel jacket platforms

This paper is concerned with robust integral sliding mode control for an offshore steel jacket platforms subject to nonlinear wave-induced force and parameter perturbations. A robust integral sliding mode controller is designed to stabilize the dynamic model of the offshore steel jacket platform. It is shown through simulation results that the robust integral sliding mode control scheme can reduce the internal oscillations of the offshore steel jacket platform dramatically; and the performance of the offshore steel jacket platform under the robust integral sliding mode control scheme is better than the ones under the nonlinear control scheme and the dynamic output feedback control scheme.