Roll Waves in High Gradient Channels

Abstract

Vedernikov's number quantifies the allowable capacity that can be sustained as a stable uniform flow in a high gradient channel, but it does not provide any guidance to the design of freeboard when roll waves exist. Without considering roll waves, high gradient channels are undersized using the uniform flow approach and fail to maintain design integrity. This paper presents revised design curves to determine the stability of flow in high gradient channels. When the design condition exceeds the limiting condition, roll waves should be considered in design. This study applies the model of moving hydraulic jump to simulate roll waves. It provides estimations for wave heights when Froude number is greater than 1.50.     

The geometry of flex tangents to a cubic curve and its parameterizations

We show how the study of the geometry of the nine flex tangents to a cubic produces pseudo-parameterizations, including the ones given by Icart, Kammerer, Lercier, Renault and Farashahi, and infinitely many new ones.     

Least eccentric ellipses for geometric Hermite interpolation

We present a rational Bézier solution to the geometric Hermite interpolation problem. Given two points and respective unit tangent vectors, we provide an interpolant that can reproduce a circle if possible. When the tangents permit an ellipse, we produce one that deviates least from a circle. We cast the problem as a theorem and provide its proof, and a method for determining the weights of the control points of a rational curve. Our approach targets ellipses, but we also present a cubic interpolant that can find curves with inflection points and space curves when an ellipse cannot satisfy the tangent constraints.     

四次C-Bézier曲线的拼接技术研究

为了解决造型设计中复杂曲线难以用单一曲线来表示的问题,研究了一种带形状参数的四次C-Bézier曲线的光滑拼接技术.在对四次C-Bézier曲线基函数及其端点性质分析的基础上,给出了两相邻四次C-Bézier曲线间G1、G2和C1、C2的光滑拼接的充要条件,同时还给出了两相邻四次C-Bézier曲线间光滑拼接的基本步骤和几何造型实例.实例结果表明,所提方法简单有效、易实现,极大地增强了四次C-Bézier曲线表达复杂曲线的能力,可广泛地应用于各种CG/CAD/CAID/CAM造型系统中.     

Low temperature J-resistance curve determination of asphalt concrete using wavelet-Radon transform

A single specimen test using the three point single edge notched beam configuration at low temperatures for obtaining hot mix asphalt （HMA） resistance curves is developed.Resistance curves are obtained for mixtures at six temperature levels of＋5,0,-5,-10,-15,and-20 ℃ and three binder contents of 4％,4.5％,and 5％.Crack extension increments during the test are measured by means of an image processing technique using Radon transform and feature extraction.All the specimens exhibit a rising R-curve,indicating ductility and toughening mechanisms in the ductile-quasi brittle fracture of the mixture.It is observed that the reduction of temperature results in a further tendency of the mixture for unstable crack growth and less subcritical crack length.It is also shown that using the binarization process,an automatic index can be developed that can represent the extent of brittleness and extent of the low temperature in which the cracking has occurred.     

X70钢在模拟酸雨溶液中及其液膜下的腐蚀行为研究

采用交流阻抗法和极化曲线法研究了X70钢在模拟酸雨溶液中及其薄层液膜下的腐蚀行为.研究结果表明:在pH值为2.40³.50的模拟酸雨溶液中,X70钢的阻抗谱表现为一个时间常数,X70钢的腐蚀受电荷传递过程控制.X70钢的腐蚀速率和腐蚀电位随着溶液pH值升高而降低.在薄层液膜下,液膜厚度的减薄抑制了腐蚀的阴、阳极过程.液膜厚度的减薄,电荷传递电阻增大,X70钢的腐蚀速率降低.     

Image denoising using statistical model based on quaternion wavelet domain

Image denoising is the basic problem of image processing.Quaternion wavelet transform is a new kind of multiresolution analysis tools.Image via quaternion wavelet transform,wavelet coefficients both in intrascale and in interscale have certain correlations.First,according to the correlation of quaternion wavelet coefficients in interscale,non-Gaussian distribution model is used to model its correlations,and the coefficients are divided into important and unimportance coefficients.Then we use the non-Gaussian distribution model to model the important coefficients and its adjacent coefficients,and utilize the MAP method estimate original image wavelet coefficients from noisy coefficients,so as to achieve the purpose of denoising.Experimental results show that our algorithm outperforms the other classical algorithms in peak signal-to-noise ratio and visual quality.     

基于词语属性的计算机辅助获取流行词语研究

本文以2005年的1月1日至6月25日新浪网上下载的各类页面上的文本内容为研究资源集合,从中提取出有效词语,对词语的流行程度的判定属性做了定性定量的分析研究,对词语的流行特性进行了定义,在此基础上,引入衡量关注程度的量化方法,并配合依据词语判定属性与时间关系而绘制的走势曲线图,设置淘汰机制与评分机制,得到了候选流行词语,验证了流行词语判定属性规范的合理性,为机器辅助判定词语特性提供了参考数据。