一种基于小波包和双谱的信号分析方法

在高斯噪声背景下,为了尽可能地消除噪声的干扰来提取有用信息,提出了一种基于小波包和双谱对加性高斯噪声信号进行处理的方法。主要利用小波包变换良好的时频分析能力和双谱对高斯噪声不敏感,不但能够抑制噪声、提高信噪比,而且可以得到信号幅度、相位、能量、非线性等丰富的特征信息。最后仿真表明了此方法分析信号的可行性和优越性。     

基于半分析模型的新庙泡叶绿素a浓度反演研究

叶绿素a(Chl-a)含量是反映水体水质的重要参数之一,利用遥感技术监测其浓度具有众多优势.本研究利用2004年5-9月的吉林省新庙泡实测高光谱数据和实验室分析数据,建立了基于三波段的Chl-a浓度反演模型.该模型基于水体叶绿素a、悬浮物、溶解有机物、纯水的生物光学特性分析,优化组合了3个特征波长.结果表明用该方法建立的模型具有一定的物理基础,反演精度较高,其决定系数和均方根误差分别为0.8758、4.98μg·L-1,适合于内陆水体Chi-a含量的定量提取.     

分数卷积及其光学实现

将频域中常规卷积的定义推广到分数域中,得到了分数卷积的频域定义,给出了它的空域表达和光学实现装置,进行了计算机模拟实验。结果表明：分数卷积与常规卷积相比较其峰值降低,但对底座的展宽作用没有变化。此结论对完善分数傅里叶的知识体系具有重要的理论意义,同时为滤波器的设计提供一个新的理论指导。     

Simulation and research of percolation phenomenon in T-ZnOw resin matrix composite

A novel three-dimensional lattice model of tetrapod-like zinc oxide whisker (T-ZnOw) resin matrix composite with a coordination number of 12 is constructed based on the special structure of T-ZnOw; the percolation phenomenon of the system is simulated by the Monte Carlo method,and the percolation threshold is obtained at 23.2%.The critical mixing ratio of T-ZnOw is calculated by considering the practical factors,and the result basically agrees with the reported one.Theoretical calculation shows that the critical mixing ratio mainly depends on the L/D ratio of T-ZnOw,and is also related to the size of T-ZnOw as well as the preparation method of the composite.The microwave absorbing mechanism of T-ZnOw composite is discussed,and conductivity loss and point discharge caused by the polarization effect are regarded to be two important means of energy dissipation.     

Broadcast storm mitigation techniques in vehicular ad hoc networks

Several multihop applications developed for vehicular ad hoc networks use broadcast as a means to either discover nearby neighbors or propagate useful traffic information to other vehicles located within a certain geographical area. However, the conventional broadcast mechanism may lead to the so-called broadcast storm problem, a scenario in which there is a high level of contention and collisions at the link layer due to an excessive number of broadcast packets. While this is a well-known problem in mobile ad hoc wireless networks, only a few studies have addressed this issue in the VANET context, where mobile hosts move along the roads in a certain limited set of directions as opposed to randomly moving in arbitrary directions within a bounded area. Unlike other existing works, we quantify the impact of broadcast storms in VANETs in terms of message delay and packet loss rate in addition to conventional metrics such as message reachability and overhead. Given that VANET applications are currently confined to using the DSRC protocol at the data link layer, we propose three probabilistic and timer-based broadcast suppression techniques: weighted p-persistence, slotted 1-persistence, and slotted p-persistence schemes, to be used at the network layer. Our simulation results show that the proposed schemes can significantly reduce contention at the MAC layer by achieving up to 70 percent reduction in packet loss rate while keeping end-to-end delay at acceptable levels for most VANET applications.     

基于需求的测试用例设计方法研究

本文针对软件的基本特点,介绍了测试用例设计的相关概念,结合软件的需求进行分析,论述了基于需求的测试用例设计的基本过程,给出了以满足功能覆盖为特点的软件测试用例设计方法.     

惯性冲击对低真空封装的RF MEMS电容开关性能的影响

分析了外界惯性冲击对低真空封装的旁路电容式RF MEMS开关性能的影响.得到了近似计算外界惯性冲击引起位移的解析式.在已知最大容许插入损耗和外部惯性冲击环境条件下,MEMS开关支撑梁的最小机械刚度常数以及外部惯性冲击引起的插入损耗可以根据该式得到.通过RF MEMS电容式开关实例,表明设计低真空封装的RF MEMS电容式开关时应考虑外部环境因素.可见,RF MEMS开关用低真空封装可以减小空气阻尼、改善开关速度和执行电压的同时,开关的性能却容易受外界环境因素的影响.该研究对低真空封装的RF MEMS电容式开关的优化设计很有意义.     

Robust QoS Control for Single Carrier PMP Mode IEEE 802.16 Systems

The IEEE 802.16 WirelessMAN standard provides a comprehensive quality-of-service (QoS) control structure to enable flow isolation and service differentiation over the common wireless network interface. By specifying a particular set of service parameters, the media access control (MAC) mechanisms defined in the standard are able to offer predefined QoS provisioning on a per-connection basis. However, the design of efficient, flexible, and yet robust MAC scheduling algorithms for such QoS provisioning still remains an open topic. This paper proposes a new QoS control scheme for single-carrier point-to-multipoint mode wireless metropolitan area network (WirelessMAN) systems, which enables the predefined service parameters to control the service provided to each uplink and downlink connection. By MAC-PHY cross-layer resource allocation, the proposed scheme is robust against particular wireless link degradation. Detailed simulation experiments are presented to study the performance and to validate the effectiveness of the proposed QoS control scheme.     

Unusual Formation of ZnCo2O4 3D Hierarchical Twin Microspheres as a High‐Rate and Ultralong‐Life Lithium‐Ion Battery Anode Material

A facile two‐step strategy involving a polyol method and subsequent thermal annealing treatment is successfully developed for the large‐scale preparation of ZnCo₂O₄ various hierarchical micro/nanostructures (twin mcrospheres and microcubes) without surfactant assistance. To the best of our knowledge, this is the first report on the synthesis of ZnCo₂O₄ mesoporous twin microspheres and microcubes. More significantly, based on the effect of the reaction time on the morphology evolution of the precursor, a brand‐new crystal growth mechanism, multistep splitting then in situ dissolution recrystallization accompanied by morphology and phase change, is first proposed to understand the formation of the 3D twin microshperes, providing new research opportunity for investigating the formation of novel micro/nanostructures. When evaluated as anode materials for lithium‐ion batteries (LIBs), ZnCo₂O₄ hierarchical microstructures exhibit superior capacity retention, excellent cycling stability at the 5 A g^?1 rate for 2000 cycles. Surprisingly, the ZnCo₂O₄ twin microspheres show an exceptionally high rate capability up to the 10 A g^?1 rate. It should be noted that such super‐high rate performance and cycling stability at such high charge/discharge rates are significantly higher than most work previously reported on ZnCo₂O₄ micro/nanostructures and ZnCo₂O₄‐based heterostructures. The ZnCo₂O₄ 3D hierarchical micro/nanostructures demonstrate the great potential as negative electrode materials for high‐performance LIBs.     

基于改进型模糊神经网络的导弹武器系统生存能力评估

针对导弹武器系统生存能力评估问题,建立了评估的指标体系,给出了指标的隶属函数.利用BP神经网络的自学习、自适应、强容错性,并通过遗传算法（GA）优化BP神经网络的连接权重和阀值,弱化了评价中的人为因素,提高了评价结果的准确性和权威性,解决了BP神经网络存在落入局部最小点和收敛速度慢的问题.实例研究表明,遗传神经网络的评价模型具有有效性和可行性.