Energy-efficient adaptive sensor scheduling for target tracking in wireless sensor networks

Sensor scheduling is essential to collaborative target tracking in wireless sensor networks (WSNs). In the existing works for target tracking in WSNs, such as the information-driven sensor query (IDSQ), the tasking sensors are scheduled to maximize the information gain while minimizing the resource cost based on the uniform sampling intervals, ignoring the changing of the target dynamics and the specific desirable tracking goals. This paper proposes a novel energyefficient adaptive sensor scheduling approach that jointly selects tasking sensors and determines their associated sampling intervals according to the predicted tracking accuracy and tracking energy cost. At each time step, the sensors are scheduled in alternative tracking mode, namely, the fast tracking mode with smallest sampling interval or the tracking maintenance mode with larger sampling interval, according to a specified tracking error threshold. The approach employs an extended Kalman filter (EKF)-based estimation technique to predict the tracking accuracy and adopts an energy consumption model to predict the energy cost. Simulation results demonstrate that, compared to a non-adaptive sensor scheduling approach, the proposed approach can save energy cost significantly without degrading the tracking accuracy.     

Seamless handover between unicast and multicast multimedia streams

With the deployment of heterogeneous networks, mobile users are expecting ubiquitous connectivity when using applications. For bandwidth-intensive applications such as Interact Protocol Television （IPTV）, multimedia contents are typical- ly transmitted using a multicast delivery method due to its bandwidth efficiency. However, not all networks support multicasting. Multicasting alone could lead to service disruption when the users move from a multicast-capable network to a non-multicast network. In this paper, we propose a handover scheme called application layer seamless switching （ALSS） to provide smooth real-time multimedia delivery across unicast and multicast networks. ALSS adopts a soft handover to achieve seamless playback during the handover period. A real-time streaming testbed is implemented to investigate the overall handover performance, espe- cially the overlapping period where both network interfaces are receiving audio and video packets. Both the quality of service （QoS） and objective-mapped quality of experience （QoE） metrics are measured. Experimental results show that the overlapping period takes a minimum of 56 and 4 ms for multicast-to-unicast （M2U） and unicast-to-multicast （U2M） handover, respectively. The measured peak signal-to-noise ratio （PSNR） confirms that the frame-by-frame quality of the streamed video during the handover is at least 33 dB, which is categorized as good based on ITU-T recommendations. The estimated mean opinion score （MOS） in terms of video playback smoothness is also at a satisfactory level.     

基于数字图像的非均质岩土工程材料的数值分析方法

提出了一种基于数字图像的非均质岩土工程结构的二维数值分析方法。以花岗岩为例,先将岩石的表面图像导入计算机中;然后采用基于彩色空间的数字图像技术将组成花岗岩的几种主要材料:长石、石英和黑云母一一分辨出来并再现岩石的细观结构;再通过一个简单的线性转换,将图像细观结构转换为矢量细观结构;最后,岩石的矢量细观结构可以与数值计算方法--有限元法或有限差分法结合,从而实现非均质岩石材料的力学分析。采用有限差分法FLAC程序来分析岩石的破坏过程。传统室内试验数值模拟表明材料的细观结构对应力分布和破坏模式有着明显的影响,基于数字图像的数值分析方法可以真实地实现岩土工程材料的非均质分析。     

GM(1,1)模型在水电工程软弱岩石力学试验分析中的应用

应用灰色控制理论,对泥质岩石软化试验中的主要力学参数数据进行建模分析,提出了描述和预测膨胀岩石软化和水解作用过程中的非线性力学特性GM（1,1）模型．     

金刚石钻进比功及风化花岗岩实时分级研究

基于钻进过程监测系统在不同花岗岩地基金刚石钻进中监测数据,对钻进比功及其变化特性进行分析。结果表明,金刚石钻进比功随岩石风化程度的减弱而增大,具有明显的分区性。在软的全风化及强风化花岗岩中,金刚石钻进比功值低于冲击凿碎比功值;在中等硬度的风化花岗岩中,金刚石钻进比功值与冲击凿碎比功值接近;在硬度较大的微风化花岗岩中,金刚石钻进比功大于冲击凿碎比功。由此可知,在中等硬度的花岗岩中,用冲击凿碎比功来估计金刚石钻进比功才是合适的。这与旋转钻进只适于中硬以下岩层的实际相吻合。最后,提出采用比功变化曲线进行分区,并结合比功均值指标与上界指标对岩体进行实时分级的方法。     

模型嵌岩桩试验及数值分析

由于嵌岩桩的极限承载力很高,在现场试验中很难将其加载至破坏和监测破坏时嵌岩段摩阻力的分布特征。采用室内模型试验方法对桩1混凝土及桩1岩石界面的摩阻特性进行研究。试验中对两个嵌岩桩模型进行荷载试验,将其中一个加载至破坏。试验结果表明,破坏发生在桩/混凝土界面,而桩身及岩体内部均保持完好。另外,桩/岩石界面上的摩阻力分布是非均匀的;模型桩破坏时在嵌岩段上部产生的摩阻力远大于下部的值。数值模拟结果表明,摩阻力的这种分布特性是因为桩周岩体变形所在界面所产生的法向压应力的影响。试验结果说明,对于建造在高强度岩体中的嵌岩桩,其承载力特性极大地取决于桩/岩石界面的摩阻特性,而摩阻力的分布又受到桩周岩体变形的影响。     

基于最小二乘的N-S方程算子分裂有限元法

提出一种新的求解N S方程的有限元法,即基于最小二乘的N S方程算子分裂有限元法。该算法采用算子分裂法将N S方程分解成扩散项和对流项:扩散项时间离散采用向后差分格式,空间离散采用标准Galerkin有限元法;对流项时间离散采用向后差分格式,空间离散采用最小二乘有限元法。应用该算法对方腔流和后台阶流进行数值模拟,方腔流数值计算结果与标准解吻合很好;在后台阶流数值模拟中给出了不同雷诺数下的流场特征和速度对比曲线,所得计算结果与试验结果吻合较好,表明基于最小二乘的N S方程算子分裂有限元法具有较好的收敛性和较高的精度。     

非饱和渗流分析在FLAC3D中的实现和应用

基于FLAC3D内置的FISH语言,对其渗流模型进行了扩展。将实验室测得的原状黄土土水特征曲线,利用MATLAB实现了参数拟合。将拟合参数编写为子程序,在每步渗流分析中加以调用,从而实现非饱和土的渗流模拟。利用该方法与有限元法分别模拟3种边界条件下的一维入渗问题,并比较模拟结果。经验证,结果吻合。其结果对研究非饱和土理论及扩展FLAC3D在非饱和土数值计算方面的应用均具有一定的意义。     

岩石脆性破裂的重正化研究及数值模拟

针对脆性岩石细观强度非均匀、离散性特征 ,利用重正化群理论建立了岩石临界破坏重正化模型 ,系统研究了岩石宏观临界强度和细观强度的定量关系 ,采用条件概率方法处理模型中细观单元间的应力转移 ,从而求得岩石临界破裂时的临界概率P ,着重研究了岩石均质度与岩石峰值强度的理论关系。此外 ,利用岩石破裂过程分析程序 (RFPA)模拟了岩石单轴压缩下细观破裂演化至宏观破裂的全过程。研究结果表明 ,数值模拟和重正化群得到的岩石峰值强度十分吻合