CCD非线性效应对剪切干涉法波前检测的影响

利用径向剪切干涉法检测高功率激光波前时,由于探测器CCD非线性效应,在频谱中引入了除基频外的二级、三级等高次频谱分量,增加了频谱混叠的可能,使得对有用信息提取困难,降低了波前检测精度。从理论上分析了CCD非线性效应产生高次频谱分量和导致频谱混叠的原因,给出非线性条件下避免频谱混叠的条件,提出了通过提高空间载频的方法来减小或消除CCD非线性效应导致的频谱混叠。计算机模拟和实验结果表明,该方法能够有效抑制频谱混叠并显著提高波前检测精度。     

高能核-核碰撞中粒子的(赝)快度分布与重叠柱模型

应用重叠柱模型描述了高能核-核碰撞中带电粒子的快度(或赝快度)分布. 对目前加速器上的固定靶实验而言, 观察到了相同相对强度的纵向流, 两个完全重叠的热化柱能够描述实验数据. 在更高能量范围(4A TeV以上), 观察到了更强的纵向流, 这时需要两个部分重叠的热化柱来描述实验数据. 用重叠柱模型计算得到的(赝)快度分布与1A GeV到100A TeV能区的实验结果符合.     

Beam overlapping in a multipass Ti:sapphire amplifier based on a parabolic mirror

According to laser beam transporting in a multipass Ti:sapphire amplifier based on a parabolic mirror, the influential factors to induce astigmatism are analyzed. The beam waists of the laser beam transporting in the multipass amplifier are calculated by ABCD law in sagittal and tangential planes, respectively, and are compared with each other. Our analyses of these influential factors provide valuable data to optimize this design of multipass Ti:sapphire amplifier, and our experimental results of getting Gaussian beam from such a kind of amplifier confirmed our theoretical analyses.     

Non‐self‐overlapping structured grid generation on an n‐sided surface

Most existing meshing algorithms for a 2D or shell figure requires the figure to have exactly four sides. Generating structured grids in the n‐sided parametric region of a trimmed surface thus usually requires to first partition the region into four‐sided sub‐regions. We address the automatic structured grid generation problem in an n‐sided region by fitting a planar Gregory patch so that the partition requirement is naturally avoided. However, self‐overlapping may occur in some portions of the algebraically generated grid; this severely limits its usage in most of engineering and scientific applications where a grid system with no self‐intersecting is strictly required. To solve the problem, we use a functional optimization approach to move grid nodes in the u?v domain of the trimmed surface to eliminate the self‐overlapping. The derivatives of a Gregory patch, which are extremely difficult to compute analytically, are not required in our method. Thus, our optimization algorithm compares favourably at least in terms of speed with some other mesh optimization algorithms, such as the elliptic PDE method. In addition, to overcome the difficulty of guessing a good initial position of every grid node for the conjugate gradient method, a progressive optimization algorithm is incorporated in our optimization. Experiment results are given to illustrate the usefulness and effectiveness of the presented method. Copyright © 2004 John Wiley & Sons, Ltd.     

基于有限回传链路的小基站网络重叠协作方法研究

采用一种小区间重叠协作的方法,解决了基于有限回传链路的小基站网络中的干扰管理问题。提出了一种新的基于下行协同波束赋形的小区间重叠协作算法,用于消除小基站网络中不同小基站之间的下行干扰,提高系统吞吐量。仿真结果显示,提出的算法能够显著提升以吞吐量为指标的系统性能。     

基于改进水平集方法的粘连细胞分割

传统水平集方法对粘连细胞分割效果差,同时在分割过程中需要不断地重新初始化水平集函数。为了解决传统水平集方法在粘连细胞分割上的不足,提出了一种基于颜色特征的水平集方法。该方法将能够约束水平集函数与符号距离函数之间偏差的变分公式作为内部能量项,从而无需重新初始化水平集函数;把结合图像颜色特征信息的能量函数作为模型的外部能量项,以改进粘连细胞的分割效果。实验结果表明,该方法能有效地分割粘连细胞,算法实现比较简单。     

Partially overlapping channel assignment for WLANs using SINR interference model

The use of multiple channels in 802.11 wireless local area networks can improve network performance. Many efforts have been done to better exploit multiple non‐overlapped channels. However, the number of orthogonal channels in the Institute of Electrical and Electronics Engineers 802.11 standards is very much limited. Recent studies indicate that we can improve the full‐range channel utilization and the network throughput by properly utilizing the partially overlapping channels. However, little work was focused on channel assignment for partially overlapping channels. In this paper, we investigate the problem of partially overlapping channel assignment to improve the performance of 802.11 wireless networks based on the Signal to Interference–Noise Ratio interference model. Using the Signal to Interference–Noise Ratio model, we deduce a direct relationship between maximizing system throughput and minimizing total interference when partially overlapping channels are employed. After that, we propose a greedy method to minimize the total interference for throughput maximization. We evaluate our algorithm through extensive simulations and compare its performances with those of the state‐of‐the‐art. Copyright © 2013 John Wiley & Sons, Ltd.     

Effects of variable viscosity on pulsatile flow of blood in a tapered stenotic flexible artery

The objective of the present study is to investigate the effects of variable viscosity on incompressible laminar pulsatile flow of blood through an overlapping doubly constricted tapered artery. To mimic the realistic situation, wall of the artery is taken to be flexible, and physiologically relevant pulsatile flow is introduced. The governing equations of blood flow are made dimensionless. A coordinate transformation is used to make the overlapping doubly constricted wall geometry of tube to a straight tube. Taking advantage of the Stream function–Vorticity formulation, the system of partial differential equations is then solved numerically by finite difference approximations. Effects of Reynolds number, Strouhal number, degree of contraction, tapering angle, and viscosity parameters are presented graphically and analyzed. The results show that formation of stenosis and tapering disturb the flow field significantly, and degree of stenosis is more important in influencing blood flow compared with tapering.     

A cost-effective ultra-dense WDM PON system with speed of 12.5 Gbit/s and channel spacing of 12.5 GHz

In this paper, an experimental scheme for cordwood color division multiplexing（CDM） visible light communication（VLC） system is proposed. The principle and structure of the experimental scheme are described. Right angle prisms and band-pass filter are used to make the unit of the optical collector and splitter. We can add or subtract the unit as we need. The cordwood CDM-VLC system can also be effectively used as a model to accomplish color shift keying and color division duplexing. The experimental system provides a new way for researching VLC.