Bayesian estimation of Dirichlet mixture model with variational inference

In statistical modeling, parameter estimation is an essential and challengeable task. Estimation of the parameters in the Dirichlet mixture model (DMM) is analytically intractable, due to the integral expressions of the gamma function and its corresponding derivatives. We introduce a Bayesian estimation strategy to estimate the posterior distribution of the parameters in DMM. By assuming the gamma distribution as the prior to each parameter, we approximate both the prior and the posterior distribution of the parameters with a product of several mutually independent gamma distributions. The extended factorized approximation method is applied to introduce a single lower-bound to the variational objective function and an analytically tractable estimation solution is derived. Moreover, there is only one function that is maximized during iterations and, therefore, the convergence of the proposed algorithm is theoretically guaranteed. With synthesized data, the proposed method shows the advantages over the EM-based method and the previously proposed Bayesian estimation method. With two important multimedia signal processing applications, the good performance of the proposed Bayesian estimation method is demonstrated.     

图像质量快速盲检测及其在视觉系统中的应用

提出了一种新的图像质量快速盲检测方法,以锐利度作为图像质量准则,而锐利度可以归结为图像的模糊特性,并由边缘信息估计得到。为了提高系统效率,采用边缘对比度的估计方法,并以边缘对比度作为边缘锐利度的判据准则。分析了邻近边缘的相互影响,因而只需从有限的边缘点来提取出合理的线扩展函数(LSF),进而得到模糊参数。在LSF计算中,采用一种新的插值计算方法。实验结果表明:当图像不是特别模糊时,测量结果是准确的。     

Linux 2.6内核调度机制剖析与改进①

详细剖析了Linux 2.6内核进程调度的时机、调度策略、调度有关的重要数据结构、O(1)调度算法实现,以及Linux 2.6内核新引入的内核抢占机制。为了使Linux 2.6内核支持硬实时应用,提出了改进的最小裕度优先调度算法。该算法通过引入抢占阈值,从而减少颠簸现象造成的系统资源浪费,并提高了实时处理效率。     

自动应答系统中自然语言理解技术的研究*

自动应答系统（QAS）是一种基于因特网的高性能软件系统。它的核心技术是基于自然语言理解的相关技术,包括知识库和语料库的建设、文本的切分和标注、句子的语法分析和语义分析等。重点论述了自动应答系统中知识信息的语义网络表示和LSF随机化句法分析模型,以及自动应答系统的结构与组成,并对LSF模型进行了参数训练,实践证明这些技术是可行的、高效的。     

嵌入式Linux路由器中同步PPP的实现方案

分析了在做入式Linux路由器上实现同步PPP的问题并设计了几种解决方案。通过对各种方案的对比确定了一种最优方案，并将其实现。实验结果表明，该方案可以有效地进行同步PPP的PAP和CHAP认证以及NCP协商，并能够达到同步串口速率为2Mbps。     

凝视热成像系统MTF测试技术分析

概述了目前进行高成像系统ＭＴＦ测试的几个主要方法，着重分析了其中的斜缝法和激光散斑法各自解决问题的工作原理，技术特点及技术关键，指出，对于凝视成像系统的ＭＴＦ测试，这是两种比较值得研究和推广的技术。     

LPC与LSF转换算法的比较研究

线性预测法是语音信号处理中的核心技术。在语音信号的处理中,常常需要将线性预测的LPC系数与LSF参数相互转换。本文根据Chebyshev多项式求根法,研究了几种由LPC求解LSF的算法,分析了它们各自的特点及相互关系。分析并推导了由LSF求解LPC的算法。     

基于PointCPP-LSF方法的航天筒段薄壁件滚弯成形质量分析

为解决传统圆柱拟合方法对参数初值具有较高依赖性而导致无法满足航天筒段薄壁件滚弯成形质量检测精度及速度要求的问题,提出一种PointCPP-LSF方法,以实现航天筒段薄壁件滚弯成形质量分析.基于点云深度学习建立面向圆柱参数预测的点云网络(PointCPP)模型以获得可靠的圆柱参数初值,然后基于改进的最小二乘拟合(LSF)...     

Development of realistic design fire time-temperature curves for the testing of cold-formed steel wall systems

Fire resistance rating of light gauge steel frame (LSF) wall systems is obtained from fire tests based on the standard fire time-temperature curve. However, fire severity has increased in modern buildings due to higher fuel loads as a result of modern furniture and light weight constructions that make use of thermoplastics materials, synthetic foams and fabrics. Some of these materials are high in calorific values and increase both the spread of fire growth and heat release rate, thus increasing the fire severity beyond that of the standard fire curve. Further, the standard fire curve does not include a decay phase that is present in natural fires. Despite the increasing usage of LSF walls, their behavior in real building fires is not fully understood. This paper presents the details of a research study aimed at developing realistic design fire curves for use in the fire tests of LSF walls. It includes a review of the characteristics of building fires, previously developed fire time-temperature curves, computer models and available parametric equations. The paper highlights that real building fire time-temperature curves depend on the fuel load representing the combustible building contents, ventilation openings and thermal properties of wall lining materials, and provides suitable values of many required parameters including fuel loads in residential buildings. Finally, realistic design fire time-temperature curves simulating the fire conditions in modern residential buildings are proposed for the testing of LSF walls.     

激光立体成形TC4钛合金的热力场演化

激光立体成形能够实现高性能复杂零件的精确成形,但成形过程中的高温度梯度极易导致残余应力和变形,最终影响构件的几何精度和力学性能。通过搭建基板单边夹持原位热变形测量系统,探究了多道多层TC4钛合金成形件在激光立体成形过程中基板温度、变形的演化规律,分析了不同扫描策略对构件热应力场的影响。研究结果表明,构件的变形发展受其热历史驱使,扫描策略对成形件的热变形具有显著影响。