Direct raycasting of unstructured cell-centered data by discontinuity Roe-average computation

In the field of computational fluid dynamics (CFD), the upwind finite volume method (FVM) is widely applied to solve 3D flows with discontinuity phenomena (e.g., shock waves). It produces unstructured data at the center of each cell (cell-centered data) with the flow discontinuity constraint on the inner-face between face-neighboring cells. For visualization, existing approaches with interpolation usually pre-extrapolate cell-centered data into cell-vertexed data (data values given at cell vertices) and only handle cell-vertexed data during actual rendering, which unconsciously depress the rendering accuracy and violate the discontinuity constraint. In this paper, we propose a novel method to visualize cell-centered data directly avoiding extrapolation and keep the discontinuity in the rendering data on the framework of multi-pass raycasting. During resampling, the field is reconstructed using the original cell-centered data value and the cell-gradient estimated by Green–Gauss theorem. To keep the discontinuity, we reconstruct the field at an inner-face resampled point using both the face-adjacencies and get two discontinuous field values. Then the field is obtained by computing Roe-average of the two. The analysis and experiments demonstrate that our approach gains a high-accuracy reconstruction and leads to a high-quality image.     

Active noise control in a forced-air cooling system

This paper discusses the design methodology for the active noise control of sound disturbances in a forced-air cooling system. The active sound cancellation algorithm uses the framework of output-error based optimization of a linearly parametrized filter for feedforward sound compensation to select microphone location and demonstrate the effectiveness of active noise cancellation in a small portable data projector. Successful implementation of the feedforward based active noise controller on a NEC LT170 data projector shows a 20–40 dB reduction per frequency point in the spectrum of external noise of the forced-air cooling system can be obtained over a broad frequency range from 1 to 5 kHz. A total noise reduction (unweighted) of 9.3 dB is achieved.     

社会网络中紧密度模型分析

针对社会网络中节点的复杂性,以及节点间关系的不确定性,本文采用中心性和凝聚子群对社会网络进行建模分析,并通过MATLAB进行仿真实验验证,从而在复杂的网络中选择出有效的中心节点。通过对节点的管理和利用,实现对整个社会网络管理的科学性,严谨性。通过模型的理论分析,我们可以设想该方法将对社会网络知识的传播,有效信息的发布,社会网络的稳定等起到有的放矢的作用。因而此研究具有良好的实践价值。     

校园局域网常见故障的解决办法及网络安全问题

本文对校园局域网络常见的故障以及网络安全问题作简要分析,从硬件与软件的角度针对不同类型故障,分别分析了产生的原因,探讨了一些解决问题的方法,这对校园网络管理和维护工作具有一定的借鉴意义。     

一种多级运动目标检测算法

为了提高Javed等提出的运动目标三级检测算法的稳定性,文中对其处理方法做出改进;在像素级处理阶段,采用每一个像素点及其邻域组成的集合作为特征矢量来描述图像,对YUV格式的彩色图像的不同颜色分量分别建立混合高斯模型,得到背景模型后,计算出Sobel边缘检测得到的边缘点的统计分布;在区域级处理阶段,将彩色图像分割与背景建模结合起来,得到具有精确边缘的运动目标,并利用边缘信息消除干扰目标;实验结果表明,即使在前景纹理、颜色比较一致且与背景对比不是很明显的情况下,改进后的方法也能完整地检测出运动目标.     

Phase change materials in the ternary system NH4Cl+CaCl2+H2O

Solubility isotherms of the ternary system (NH₄Cl+CaCl₂+H₂O) were elaborately determined at T= (273.15 and 298.15) K by using the isothermal method. In the equilibrium phase diagram, there are two solubility branches corresponding to the solid phases CaCl₂⋅6H₂O and NH₄Cl. Invariant point compositions are 36.32 wt% CaCl₂ and 3.4 wt% NH₄Cl at 273.15 K, and 45.86 wt% CaCl₂ and 5.22 wt% NH₄Cl at 298.15 K. A Pitzer-Simonson-Clegg thermodynamic model was applied to represent the thermodynamic properties of this ternary system and to construct a partial phase diagram of the ternary system at temperatures between (273.15 and 323.15) K. It was found in the predicted solubility phase diagram that the double salt 2NH₄Cl⋅CaCl₂⋅3H₂O, found by other authors at (323.1 and 348.1) K, will disappear at temperatures below 298.15 K. Besides, it was found that there are two peritectic points in the ternary system with peritectic temperatures at 299.65 K and 298.15 K, and the former peritectic point falls just on the line between the composition points of NH₄Cl and CaCl₂⋅6H₂O. According to phase rule, a solution made of this point will begin to crystallize at 299.65 K and end at 298 K and therefore can be acted as a “pseudo eutectic” phase change material (PCM). A heat storing and releasing experiment of 50 grams of the PCM was carried out, obtaining a satisfying result.     

基于移动平均线组合和支持向量机的股市趋势研究

证券投资是一种高风险、高收益的理财方式,而对市场运行趋势的良好把握有助于投资者回避风险、把握机会。提出基于多条移动平均线斜率组合和支持向量机算法,判断当前市场运行趋势,从而采取相应的投资策略。模拟实验证明,该方法取得了良好的效果。     

H.264帧内预测模式选择快速算法的研究

提出一种适用于H.264帧内预测的快速算法,利用相邻像素间的梯度筛选预测模式来避免不必要的预测模式计算。实验结果表明:用全I帧编码,该算法在图像质量和输出码率基本不变的情况下,编码时间大约节省了60%。