Plane-strain propagation of a fluid-driven fracture during injection and shut-in: Asymptotics of large toughness

This paper considers the problem of plane-strain fluid-driven fracture propagating in an impermeable elastic medium under condition of large toughness or, equivalently, of low fracturing fluid viscosity. We construct an explicit solution for a fracture propagating in the toughness-dominated regime when the energy dissipated in the viscous fluid flow inside the fracture is negligibly small compared to the energy expended in fracturing the solid medium. The next order corrections in viscosity to this limiting solution are then derived, allowing the range of problem parameters corresponding to the toughness-dominated regime to be established. The first-order small viscosity (large toughness) solution is shown to provide an excellent approximation of the solution for the crack length in the wide range of the viscosity parameter. Furthermore, this solution, when combined with the first-order small-toughness solution of Garagash and Detournay [Journal of Applied Mechanics, 2005], provides a simple analytical approximation of the crack length solution in practically the entire range of viscosity (toughness). It is also shown that the established method of asymptotic expansion in small parameter is equally applicable to study other small effects (e.g., fluid inertia) on the otherwise toughness-dominated solution. A solution for the fracture evolution during shut-in (i.e., after fluid injection rate is suddenly stopped) is also obtained. This solution, which corresponds to a slowing fracture evolving towards the toughness-dominated steady state, draws attention to the possibility of substantial fracture growth after fluid injection is ceased especially under conditions when the fracture propagation during injection phase is dominated by viscous dissipation.     

混沌优化的仿射尺度搜索算法研究

为了求解单目标线性规划问题,提出了基于混沌优化（COA）算法的仿射尺度搜索（AFS）算法,即混沌AFS算法。使用混沌优化算法以迭代方式从随机初始点中得到优化的初始点;将得到的初始解点作为仿射尺度搜索算法的起始点来提高仿射尺度搜索算法的性能;通过搜索单目标线性规划决策变量域得到可行的近似最优解。实验结果表明,相比传统的AFS算法,在求解单目标线性优化问题时所提混沌AFS算法明显降低了目标值的偏差,同时大大地减少了迭代次数及CPU运行时间。     

一种具有RST不变性的2D/3D轨迹相似性度量

具有旋转、缩放、平移不变性的轨迹相似性度量是实现精准手语识别、相似轨迹检索等的关键环节,常规的相似性度量往往不满足这一要求,特别是不具备旋转不变性。提出一种具有旋转、缩放、平移不变性的轨迹相似性度量方法,该方法首先对轨迹进行滤波、归一化、等间距重采样等预处理操作,然后对任意两条待比较的轨迹估计最优旋转矩阵,从而消除旋转对距离度量的干扰。该方法对二维、三维轨迹数据均适用,计算复杂度为[ON],与曲率、挠率等不变量相比,该方法对轨迹噪声不敏感。     

基于多维标度和奇异值分解的视频水印算法

针对于网络中的视频资源的知识产权问题,提出一种基于多维标度(MDS)和奇异值分解( SVD)的视频水印算法。该方法首先利用MDS把原始视频各帧投影到二维平面上,然后利用SVD的方法把水印信息嵌入到视频帧与其在二维平面上投影点之间的差值上。实验证明,该算法对随机噪声干扰和诸如旋转、平移、裁剪等空间同步失真的攻击有较强的鲁棒性;另外,该算法对帧丢弃、帧插入等时间同步失真也具有一定程度的鲁棒性。     

关于无标度网络中Hub节点的研究

无标度网络中少量节点的连接数非常大(称为Hub节点),而大量节点的连接数则非常少。通过理论和仿真两方面的研究,发现复杂网络中Hub节点的度值、数量与度分布指数具有直接关系。研究表明,度分布指数等于2是无标度网络中度分布指数的一个临界值。     

基于压缩感知和LBG算法的SAR数据压缩与重构方法

针对如何大幅压缩SAR海量数据并获得有效的重构结果以完成SAR场景目标的高分辨成像问题,本文提出利用压缩感知（Compressed Sensing, CS）和Linde-Buzo-Gray （LBG）算法共同完成。对于SAR所接收到的回波信号,首先依据CS理论构造随机高斯噪声观测矩阵对回波信号进行降维处理,然后,利用LBG算法对CS压缩后的数据再进行压缩编码以达到进一步大幅压缩的目的。对于数据重构问题,同样分为两步:一是利用LBG算法编码的逆过程进行解码恢复,二是依据CS理论利用平滑L0（smooth L0, SL0）算法重构原始回波信号。在此基础上,再利用传统频率变标（Frequency Scaling, FS）SAR成像算法进行高分辨成像。仿真结果证明了本文方法的有效性。      

Ozone Treatment of Cooling Water: Results of a Full-Scale Performance Evaluation

This paper is the first technical status report of a continuing evaluation of ozone treatment for cooling tower water. Data will be presented that illustrate the results of ozone treatment in a 3,400-ton air-conditioning cooling system at the Oak Ridge Y-12 Plant, Oak Ridge, Tennessee, which is operated by Martin Marietta Energy Systems, Inc., for the U.S. Department of Energy. Heat transfer data and equipment inspections confirm that a threshold surface temperature exists, below which heat exchange surfaces remain free of mineral scale. Heat exchange surfaces that exceed the temperature threshold experience calcium carbonate scaling. The temperature threshold effect may explain why ozone treatment has been reported as a successful treatment for air conditioning cooling towers, but has not been successful in higher temperature process cooling systems. Plans for future ozone investigations will be discussed.     

The Connectionist Construction of Psychological Spaces

The application of connectionist learning procedures to the development of psychological internal representations requires a constraining theory of mental structure. The psychological space construct is advanced for this role and, consequently, a connectionist network which learns the multi-dimensionally scaled representations of a set of stimuli is developed. The model assumes that the function relating similarity to distance in psychological space is an exponential decay function, operates under the family of Minkowskian metrics and is able to determine the appropriate dimensionality of the psychological spaces it derives. The model is demonstrated on both separable and integral stimuli, and the validity of its application of gradient descent optimization principles over the city-block metric is examined. Several modelling extensions are discussed, including means by which the model might learn more general psychophysical mappings, and be able to derive internally the measures of psychological similarity currently provided through a similarity matrix.     

非均匀子波空间采样定理

本文从非均匀采样出发，详细研究了非均匀采样的Ｗａｌｔｅｒ子波空间采样定理的存在条件，给出了Ｓｈａｎｎｏｎ采样定理的一类非均匀采样形式，对紧支尺度函数张成的子波空间，给出了一类非均匀采样方法，使得对该空间中任意紧支信号，非均匀采样成为可能，文中还指出了非均匀紧支子汉空间采样的优点，数值实例验证了理论的正确性。     

Analysis of nano-scale MOSFET including uniaxial and biaxial strain

In this paper, we focus on uniaxial and biaxial strain technologies, and we also investigate an optimum combination of strain method and channel direction. We linked the first principles band calculation program to the FUJITSU ensemble full band Monte Carlo simulator FALCON directly, which enables to incorporate arbitrary Si band structures such as uniaxial and biaxial strained-Si into device characteristics analysis. We show that the combination of biaxial tensile strain and <100> current for NMOS, and compressive uniaxial strain and <110> channel for PMOS are optimum methods for current enhancement. However, considering technological difficulties and process cost, it is one of the candidate methods to use the combination of uniaxial tensile strain and <100> channel direction for NMOS and that of uniaxial compressive strain and <110> channel direction for PMOS.