无线传感器网络中一种能量高效的skyline查询算法

针对分布式无线传感器网络环境下的skyline查询问题,提出了KSkySenor算法,有效地从传感器网络中获取更有意义的skyline结果;KSkySenor算法对感知数据进行预处理计算每个元组的支配能力,按照支配能力与各维度值之和对其进行排序,设计了一个基于聚簇的结构用于收集所有传感器读数,提出了一个剪枝方法用于渐进的从传感器网中获取skyline结果集;实验中分别改变传感器网络规模大小、数据维度、支配属性个数k,对KSkySensor算法进行测试,实验结果表明KSkySenor算法与先前的skyline查询处理算法相比具有很高效率,减少了无线传感器网络中的数据传输量,延长了网络生命周期。     

基于DIJKSTRA的无线传感器网络分簇路由算法

为加快无线传感器网络最优路径搜索速度、减少路径寻优能量消耗和延长网络寿命,提出了基于改进的DIJKSTRA算法的无线传感器网络分簇路由算法;运用DIJKSTRA算法在无线传感器网络内以多跳接力的方式来搜寻从源节点到目的节点的最短路径;结合能耗优化策略,避免网络能耗热点问题,实现网络能耗均衡;通过与基于蚁群算法的路由算法对比分析,基于Dijkstra的网络分簇路由算法能优化网络分簇并建立较优传输路径,其快速收敛性能减缓了网络中簇头节点的能耗,延长了网络寿命,提高了网络鲁棒性。     

有向传感器网络中热释电红外传感器节点部署及仿真研究

针对有向传感器网络（Directional Sensor Networks, DSNs）探测区域中PIR（Pyroelectric Infrared Sensor）传感器节点部署问题,设计了4种基于几何形状的节点部署方案,计算了各部署方案的节点密度。基于修改后的TIS测试编写仿真算法,在Matlab平台上对各节点部署方案进行了仿真实验,统计不同部署方案下的目标检测率,并对实验数据进行分析。结果表明,设计的4种部署方案的目标检测率均高于随机部署约10%;等腰三角形部署方案适用于节点数目充足的情况,能实现探测区域全覆盖,目标检测率可达80%以上;正方形部署方案适用于节点数目有限的情况,能实现探测区域大部分覆盖,目标检测率可达75%以上。     

一种无线传感器网络多级异构分簇路由协议

JP+1]研究了无线传感器网络,提出了一种适合大规模应用的无线传感器网络体系结构,并提出了一种新的路由协议——多级异构分簇路由协议;该协议将无线传感器网络节点分成4种类型,根据簇头间平均跳数、簇头能耗等因素选举出第一级簇头节点;利用通信能耗、节点能耗以及跳数3个方面作为启发因子,寻找第一级簇头到第二级簇头间的最佳路径;基于NS2平台对该路由协议进行了仿真实验,并与LEACH协议进行比较;仿真结果表明:在大规模的应用中,该路由协议能有效地降低节点的平均能耗、延长网络生存时间。     

基于DS证据理论和压缩感知的WSN数据融合策略设计

为了降低WSN数据量和延长网络生命周期,设计了一种基于DS证据理论和压缩感知的WSN混合数据融合策略;首先,在分簇协议的基础上引入了基于DS证据理论和压缩感知的混合模型,然后,采用改进的DS对所有簇成员节点的基本信度分配函数进行加权处理,在簇头处采用加权和归一化的信度分配函数计算证据对各命题的支持程度,将支持程度较大的若干命题作为DS融合结果,在此基础上采用压缩感知方法通过构造测量矩阵对融合结果进行稀疏化表示,并在基站处对稀疏信号进行重构;仿真实验表明,文中方法能有效地实现数据融合,且和其他方法相比,具有重构误差较小和网络生命周期较长的优点,具有较大的优越性。     

基于概率假设密度的无线传感器网络多目标跟踪算法

针对无线传感器网络多目标跟踪过程中杂波难以去除以及由数据关联复杂带来的计算复杂度高的问题,将概率假设密度滤波器应用于无线传感器网络,以更好地对多目标状态信息进行融合估计;首先,建立簇-树型无线传感器网络模型,并运用随机有限集理论对目标状态模型和传感器观测模型进行描述;然后,根据目标与节点之间的距离设置观测阈值,当传感器节点测量值小于观测阈值时,概率假设密度滤波器将实时对该组测量数据进行处理,从而实现传感器网络对目标状态的联合检测与跟踪;仿真结果表明,在无线传感器网络的多目标跟踪应用中,该算法比粒子滤波算法具有更高的跟踪效率和精度。     

无线传感器网络多跳路由协议研究

目的：无线传感器网络发展迅速,但传感器的高能耗问题成为制约其发展的主要瓶颈,高效节能的路由协议设计成为研究热点。方法：针对目前无线传感器网络常用的LEACH路由协议存在的簇首能耗过分集中、簇首分布不均衡问题,提出了改进的路由协议EEACRA,在总结、分析LEACH路由协议现有问题的基础上,给出了EEACRA路由协议的簇首选取门限值、簇首位置调整算法和基于能量代价最小的簇间多跳路由算法的实现方法,同时给出了具体的实现EEACRA协议的工作流程和关键算法。在MATLAB环境下对LEACH路由协议和EEACRA路由协议进行了仿真,对比了不同能耗降低措施对网络能耗降低的贡献。结果：仿真结果表明EEACRA路由协议的网络稳定期较LEACH路由协议有较大的改善。结论：证明了改进的路由协议EEACRA可以有效地提高网络的稳定期。     

基于人工蜂群的无线传感器网络能耗均衡算法

由于无线传感器网络中的节点链路状况、数据传输能耗及节点剩余能量的限制,造成网络中部分感知节点寿命缩短,影响网络生存周期,提出了一种基于人工蜂群算法的WSNs能耗均衡算法,优化网络能耗均衡,从而提高网络寿命;文章给出了网络能耗相应的数学模型及优化求解算法,介绍人工蜂群算法的寻找食物过程,阐述了人工蜂群算法在网络能耗均衡方面的实现步骤;通过实验仿真证明,文章提到的算法与LEACH分簇算法、蚁群优化算法相比,具有更好的能耗和负载均衡能量、丢包率和时延性,有效地提高了网络生存周期。     

多体作用对氦原子团簇He9压缩特性的贡献

 采用Lowdin方法计算了处于压缩状态的氦原子团簇He₉体心立方向型的排斥势及其多体分量，并由此计算出团簇微观压强及其多体分压强。结果发现，多体作用对氦原子团簇He₉压缩特性贡献较大。在相同体积下，由两体近似方法计算的体系压强比多原子体系实际压强偏高10%~30%；考虑三体分压强修正后，近似理论的计算值又会偏低1.5%~10%；只有同时考虑三体、四体修正后，近似理论计算值与实际多原子体系的压强值基本一致。团簇He₉所表现出的压缩特性与固态氦的实验结果相符合。     

能量收集传感器网络中改进的能耗管理方案研究

能量收集传感器平台为网络协议的设计开辟了新的领域。为了支持网络的运行,能耗率不得高于能量收集率,否则,传感器节点会最终耗尽它们的能量。与资源处于静态的传统网络资源分配问题相比,充电速率的时间可变性带来了新的挑战。在本文中,我们首先研究了一种基于高效对偶分解和次梯度策略的算法QuickFix,计算出数据采样率和路由。然而,再次充电发生波动时的时标可能会快于传统方法的收敛时间,进而导致电池断电和溢出,这会造成采样丢失和能量收集机会丢失。为了解决这一动态问题,我们提出一种本地算法SnapIt,通过对采集率进行调节以维持电池电量在目标水平上。基于TOSSIM模拟器的性能评估表明,QuickFix和SnapIt联合起来可以跟踪网络瞬时最优效用,同时维持电池电量处于目标水平。与基于余压的IFRC相比,本文方法使总体数据速率平均提升42%,同时显著提升了网络效用。     

Guided-Wave Two-Dimensional Acousto-Optic Scanner Using Proton-Exchanged Lithium Niobate Waveguide

Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.     

Hybrid Wavelength and Code Division Multiple Access in Optical Networks

A review of schemes for multiple access in fiber optic networks shows that a hybrid of wavelength and code division multiple access (WCDMA) combines the best features of both. In particular, the hybrid scheme retains the large information carrying capacity of wavelength division multiple access (WDMA) and flexibility of code division multiple access (CDMA). In this paper WDMA, optical CDMA (OCDMA), and WCDMA networks are discussed. In OCDMA networks, concept of incoherent and coherent coding including inverse decoding and matched filter is introduced. The delay performance of both WDMA and WCDMA networks, under the simple suboptimum access protocols based on cyclic search, is computed. It has been shown quantitatively that tuning delay significantly affects the delay performance of both WDMA and WCDMA networks. Futhermore, delay performance of WCDMA networks is always better than the WDMA networks for the same tuning delay, load, and number of users.     

Effect ofγ-radiation on the spectral luminescence characteristics of impure cadmium tungstate crystals

Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·10⁴ Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.     

Femtosecond Transform-Limited Pulse Generation by Compensating for the Linear Chirp of SPM Spectra in Dispersion Shifted Fibers

A simple technique of pulse compression, based on the linear chirp compensation of self-phase modulation (SPM) spectra in dispersion shifted fibers, is demonstrated. The optimization procedure is carried out, for a short span of a single-mode fiber, using a parabolic law, which describes the behavior of the squared output pulse width versus the pump peak power in the case of Gaussian pulses. The experimental results give a minimum pulse duration of 233 fs, which is in good agreement with the model. Shorter and coherent pulses, down to 90 fs, have been obtained by inserting an interference filter at the optical output.     

Sorting of bending magnets for the SSRF booster

The Shanghai Synchrotron Radiation Facility(SSRF)booster ring,a full energy injector for the storage ring,is deigned to accelerate the electron beam energy from 150MeV to 3.5GeV that demands high extraction efficiency at the extraction energy with low beam loss rate when electrons are ramping.Closed orbit distortion(COD)caused by bending magnet field uniformity errors which affects the machine performance harmfully could be effectively reduced by bending magnet location sorting.Considering the affections of random errors in measurement,both ideal sorting and realistic sorting are studied based on measured bending magnet field uniformity errors and one reasonable combination of bending magnets which can reduce the horizontal COD by a factor of 5is given as the final installation sequence of the booster bending magnets in this paper.     

Measurement of nonlinear coefficient of optical fiber based on small chirped soliton transmission

We measure the waveform and phase curves of short optical pulses before and after transmission over different lengths of fibers by use of the pulse analyzer with the frequency-resolved optical gating (FROG),and numerically simulate pulse evolution under the experimental conditions.The nonlinear coefficient of the fiber is given by comparing the experimental results with the numerical ones.Difference between the experiment and numerical simulation is analyzed.     

Resonance scattering of canonical elastic shells in absorbing fluid medium

Resonance scattering of elastic spherical shell and cylindrical shell while the surrounding fluid medium has absorption is studied. The normal mode solution derived using exact elastic theory and the separation of variables is still applicable. However, the scattering form function has to be modified for the absorbing medium, otherwise the unreasonable result would be obtained. The backscattering form function in the absorbing medium is redefined, and the form function of elastic spherical and cylindrical shell with vacuum or solid matter filled is calculated in various absorption conditions. The results show that the absorption of surrounding fluid leads to notable attenuation of the coincidence resonances in the mid-frequency, but it has a little influence on the low-frequency resonance scattering induced by the filler inside the shell.     

Single-beam self-referenced phase-sensitive surface plasmon resonance sensor with high detection resolution

A versatile and low-cost single-beam self-referenced phase-sensitive surface plasmon resonance(SPR)sensing system with ultra-high resolution performance is presented.The system exhibits a root-mean-square phase fluctuation of ±0.0028.over a period of 45 min.i.e.a resolution of±5.2×10-9 refractive index units.The enhanced performance has been achieved through the incorporation of three design elements:a true single-beam configuration enabling complete self-referencing so that only the phase change associated with SPR gets detected,a differential measurement scheme to eliminate spurious signals not related to the sensor response,and the elimination of retardation drifts by incorporating temperature stabilization in the liquid crystal phase modulato .Our design should bring the detection sensitivity of non-labeling SPR biosensing closer to that achievable by conventional fluorescence-based techniques.     

Influences of SiO2 protective layers and annealing on the laser-induced damage threshold of Ta2O5 films

Ta2O5 films are prepared on BK7 substrates with conventional electron beam evaporation deposition.The effects of SiO2 protective layers and annealing on the laser-induced damage threshold (LIDT) of the films are investigated.The results show that SiO2 protective layers exert little influence on the electric field intensity(EFI)distribution,microstructure and microdefect density but increase the absorption slightly.Annealing iS effective on decreasing the microdefect density and the absorption of the films.Both SiO2 protective layers and annealing are beneficial to the damage resistance of the films and the latter is more effective to improve the LIDT.Moreover,the maximal LIDT of Ta2O5 films is achieved by the combination of SiO2 protective layers and annealing.