液体静压导轨支承油膜的有限元分析

介绍了液体静压导轨支承的设计,并对其油膜压力分布进行了研究.根据流体润滑理论及雷诺方程,构建了导轨油膜压力的数学物理模型,提出了运用有限元法进行油膜刚度及导轨承载能力的分析与计算方法.借助非线性有限元软件Marc对一个应用实例进行了分析与计算,得到油膜压力的分布云图和曲线,求解出了油膜刚度和导轨的承载能力.计算结果表明,该方法计算结果精确,可以满足设计要求.     

DPA:一种动态环境下QoS单播路由算法

目前Internet网络环境下,网络参数的随时变化容易造成路由过期,从而使提供的QoS路由无效,为此提出了一种适合参数动态变化的单播QoS路由算法(DPA),该算法在路径代价随时间不断变化的情况下能够自主地选择最优路由节点,解决多约束QoS单播路由选择不精确的问题.实验表明,本路由算法自适应性和扩展性较好,同时在路由选择方面比传统的路由算法能够提供更好的QoS路由.     

Robust image hashing using non-uniform sampling in discrete Fourier domain

This paper proposes a robust image hashing method in discrete Fourier domain that can be applied in such fields as image authentication and retrieval. In the pre-processing stage, image resizing and total variation based filtering are first used to regularize the input image. Then the secondary image is obtained by the rotation projection, and the robust frequency feature is extracted from the secondary image after discrete Fourier transform. More sampling points are chosen from the low- and middle-frequency component to represent the salient content of the image effectively, which is achieved by the non-uniform sampling. Finally, the intermediate sampling feature vectors are scrambled and quantized to produce the resulting binary hash securely. The security of the method depends entirely on the secret key. Experiments are conducted to show that the present method has satisfactory robustness against perceptual content-preserving manipulations and has also very low probability for collision of the hashes of distinct images.     

Peri-Watchdog: Hunting for hidden botnets in the periphery of online social networks

In order to evade detection of ever-improving defense techniques, modern botnet masters are constantly looking for new communication platforms for delivering C&C (Command and Control) information. Attracting their attention is the emergence of online social networks such as Twitter, as the information dissemination mechanism provided by these networks can naturally be exploited for spreading botnet C&C information, and the enormous amount of normal communications co-existing in these networks makes it a daunting task to tease out botnet C&C messages.Against this backdrop, we explore graph-theoretic techniques that aid effective monitoring of potential botnet activities in large open online social networks. Our work is based on extensive analysis of a Twitter dataset that contains more than 40 million users and 1.4 billion following relationships, and mine patterns from the Twitter network structure that can be leveraged for improving efficiency of botnet monitoring. Our analysis reveals that the static Twitter topology contains a small-sized core sugraph, after removing which, the Twitter network breaks down into small connected components, each of which can be handily monitored for potential botnet activities. Based on this observation, we propose a method called Peri-Watchdog, which computes the core of a large online social network and derives the set of nodes that are likely to pass botnet C&C information in the periphery of online social network. We analyze the time complexity of Peri-Watchdog under its normal operations. We further apply Peri-Watchdog on the Twitter graph injected with synthetic botnet structures and investigate the effectiveness of Peri-Watchdog in detecting potential C&C information from these botnets.To verify whether patterns observed from the static Twitter graph are common to other online social networks, we analyze another online social network dataset, BrightKite, which contains evolution of social graphs formed by its users in half a year. We show not only that there exists a similarly relatively small core in the BrightKite network, but also this core remains stable over the course of BrightKite evolution. We also find that to accommodate the dynamic growth of BrightKite, the core has to be updated about every 18 days under a constrained monitoring capacity.     

求解泊松方程的紧致修正法

将紧致格式与低阶格式结合,构造紧致格式的修正项,并将修正项加入到源项中进行求解,得到了一种基于非均分网格求解泊松方程的紧致修正法,且将该方法应用于二维和三维泊松方程的数值求解中。数值计算结果表明:紧致修正方法的精度高于经典方法的精度,但四阶紧致修正方法比二阶经典方法对网格的依赖性强。     

全日制村镇供水管网经济流速的计算

村镇供水管网设计是一项系统工程,选择合理的经济流速对于降低管网的总费用与运行费用是非常必要的。考虑资金的时间价值,结合山东省某村镇的农村供水工程实例,得出了适合该村镇供水管网设计的经济流速。该方法可为全日制村镇供水工程设计提供参考。     

A new image fusion performance metric based on visual information fidelity

Because subjective evaluation is not adequate for assessing work in an automatic system, using an objective image fusion performance metric is a common approach to evaluate the quality of different fusion schemes. In this paper, a multi-resolution image fusion metric using visual information fidelity (VIF) is presented to assess fusion performance objectively. This method has four stages: (1) Source and fused images are filtered and divided into blocks. (2) Visual information is evaluated with and without distortion information in each block. (3) The visual information fidelity for fusion (VIFF) of each sub-band is calculated. (4) The overall quality measure is determined by weighting the VIFF of each sub-band. In our experiment, the proposed fusion assessment method is compared with several existing fusion metrics using the subjective test dataset provided by Petrovic. We found that VIFF performs better in terms of both human perception matching and computational complexity.