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.     

面向容错的对地观测卫星实时任务调度研究

提出一种面向容错的对地观测卫星任务调度模型,该模型采用主版本/副版本技术可以实现对任意时刻一颗卫星失效时的容错.在容错调度模型的基础上,提出了一种卫星容错调度算法FTSS.FTSS采用重叠技术,有效提高了卫星资源利用率.此外,FTSS采用了任务合成策略可以有效减少实际执行任务的个数从而进一步提高系统的可调度性.为了验证FTSS算法的性能,本文通过模拟实验对FTSS与其它3个基准算法进行了比较分析.实验结果表明FTSS优于其它算法,适合卫星实时任务容错调度.     

A pseudo‐spectral method that uses an overlapping multidomain technique for the numerical solution of sine‐Gordon equation in one and two spatial dimensions

In this article, we study an explicit scheme for the solution of sine‐Gordon equation when the space discretization is carried out by an overlapping multidomain pseudo‐spectral technique. By using differentiation matrices, the equation is reduced to a nonlinear system of ordinary differential equations in time that can be discretized with the explicit fourth‐order Runge–Kutta method. To achieve approximation with high accuracy in large domains, the number of space grid points must be large enough. This yields very large and full matrices in the pseudo‐spectral method that causes large memory requirements. The domain decomposition approach provides sparsity in the matrices obtained after the discretization, and this property reduces storage for large matrices and provides economical ways of performing matrix–vector multiplications. Therefore, we propose a multidomain pseudo‐spectral method for the numerical simulation of the sine‐Gordon equation in large domains. Test examples are given to demonstrate the accuracy and capability of the proposed method. Numerical experiments show that the multidomain scheme has an excellent long‐time numerical behavior for the sine‐Gordon equation in one and two dimensions. Copyright © 2013 John Wiley & Sons, Ltd.     

激光精密切割不锈钢薄板的工艺研究

采用Nd∶YAG脉冲激光器对不锈钢进行了精密切割。系统研究了工艺参数对切缝宽度和切缝质量的影响规律。结果表明,缝宽随激光功率密度、频率以及脉宽的增加而加大;提高激光输出重复频率,不仅有利于提高加工质量,而且可以增大切割速度,提高加工效率。在此基础上,导出了光斑重叠度和极限切割速度的计算公式,利用此公式估算的脉冲激光切割的极限速度与实验结果符合很好     

径向基函数神经网络用于重叠色谱峰解析

 在高斯基径向基函数神经网络 (RBFNN)学习算法中引入了鲁棒性和随机全局寻优的两阶段遗传算法 :结构学习和参数优化。通过两阶段学习算法的交替使用 ,使网络具有结构自学习和参数优化的能力 ,而后将网络应用于组分数未知的重叠色谱峰解析。该方法具有不需人为干预 ,可自动确定网络结构即组分数的优点 ;并且解析精度较高 ,适用于多组分重叠色谱峰的解析 ;对完全重叠色谱峰也具有良好的解析能力。     

光波导放大器中的光场与铒浓度分析之间重迭的分析

本文在忽略放大自发辐射（ASE）和上转过程影响的情况下,用重迭因子的方法,得到了980nm波段泵浦的掺饵光波导放大器增益的隐式解析解、泵浦光沿波导方向分布的函数关系式和泵浦阈值功率的解析表达式。详细讨论了重迭因子对增益、泵浦阈值功率和波导中任意位置泵浦光分布的影响。     

复杂网络的重叠社区及社区间的结构洞识别

大数据环境下如何有效地、准确地识别复杂网络的重叠社区是近年来学者关注的重点.本文提出一种基于多标签传播方式MLPS（Multiple Label Propagation Strategy）的重叠社区识别算法,该算法首先利用影响力最大化模型选取初始种子集合并赋予它们唯一的标签,然后采用结点间的相似性和影响传播特性共同作用于标签的传播迭代过程,迭代停止后将具有相同标签的结点划分为同一社区.通过合成网络和真实网络的实验验证了MLPS算法具有较高的准确度和模块度,且具有接近线性的时间复杂度.另外,在对MLPS算法输出的重叠结构进行分析的基础上,本文提出社区间的结构洞识别算法SHCDA（Structural Holes Between Communities Detection Algorithm）,该算法通过分析重叠结构和重叠结点的位置特征,计算重叠结点作为结构洞的得分,最后输出top-k结构洞.本文在不同特性的数据集上进行实验,结果证明了SHCDA算法具有最好的准确度.     

梯度折射率成象光纤光学特性与光纤长度的关系

梯度折射率(GRIN)成象光纤的光学特性与光纤长度的关系是光纤应用中一个重要问题。本文从理治与测量方面说明光纤长度与光纤光学特性如:物象距,最大半视场角、最大场高、有效数值孔径、照度分布以及MTF的关系。