Error-resilient video communications over CDMA networks with a bandwidth constraint.

We present an adaptive video transmission scheme for use in a code-division multiple-access network, which incorporates efficient bandwidth allocation among source coding, channel coding, and spreading under a fixed total bandwidth constraint. We derive the statistics of the received signal, as well as a theoretical bound on the packet drop rate at the receiver. Based on these results, a bandwidth allocation algorithm is proposed at the packet level, which incorporates the effects of both the changing channel conditions and the dynamics of the source content. Detailed simulations are done to evaluate the performance of the system, and the sensitivity of the system to estimation error is presented.     

电能变换领域中随机脉宽调制技术研究概况及展望

相较于传统的脉宽调制技术,随机脉宽调制具备有效的谐波频谱分散能力,从而实现机电负载噪声的削弱。随机脉宽调制技术包括起步的随机开关调制、后续的随机脉冲位置与随机开关频率等3个基本方法。随着电力电子技术的整体发展,随机脉宽调制已从传统的载波调制逐渐拓展到空间矢量调制之中,应用范围日趋广泛,谐波频谱分散与功率谱峰值抑制的效果不断提升。同时,新的优化方案不断被提出,对谐波频谱及功率谱的分散效果亦在不断提高。梳理了随机脉宽调制的研究历程,总结了数种典型的随机脉宽调制的基本原理,并对未来随机脉宽调制的研究方向作出展望,为随机脉宽调制技术的深入研究提供参考。     

镍基单晶合金枝晶典型区域相成分最优化测算法

建立了用于测算镍基单晶高温合金枝晶典型区域相成分的最优化数学模型.根据电子探针对枝晶典型区域成分的测定结果,运用BFGS拟Newton法及CONSTR约束优化算法,可以计算枝晶各典型区域中γ和γ＇相成分.以镍基单晶合金CMSX-2和CMSX-4为对象,对优化测算结果进行了分析,证实了该方法的可行性.     

Boosted Bayesian network classifiers

The use of Bayesian networks for classification problems has received a significant amount of recent attention. Although computationally efficient, the standard maximum likelihood learning method tends to be suboptimal due to the mismatch between its optimization criteria (data likelihood) and the actual goal of classification (label prediction accuracy). Recent approaches to optimizing classification performance during parameter or structure learning show promise, but lack the favorable computational properties of maximum likelihood learning. In this paper we present boosted Bayesian network classifiers, a framework to combine discriminative data-weighting with generative training of intermediate models. We show that boosted Bayesian network classifiers encompass the basic generative models in isolation, but improve their classification performance when the model structure is suboptimal. We also demonstrate that structure learning is beneficial in the construction of boosted Bayesian network classifiers. On a large suite of benchmark data-sets, this approach outperforms generative graphical models such as naive Bayes and TAN in classification accuracy. Boosted Bayesian network classifiers have comparable or better performance in comparison to other discriminatively trained graphical models including ELR and BNC. Furthermore, boosted Bayesian networks require significantly less training time than the ELR and BNC algorithms.     

红外反射式光学系统光机结构设计与分析

为实现红外双波段共孔径光学系统,设计出一种采用大孔径、无焦反射式光学系统,并详细介绍该系统结构.中波和长波MTF值在25线对下均大于0.3.考虑到该光学系统野外使用时复杂的运输环境,利用有限元法对简化后的卡塞格林式望远系统进行低阶振动特性和模态特性分析.通过比较2种材料的模态分析计算结果,最终选取铝合金为金属材料,保证1阶固有频率大于50 Hz,满足野外运输条件,说明该系统结构合理可行.     

弹体头部形状对穿甲爆破弹穿甲性能影响的仿真

为给某穿甲爆破(Armor Piercing High Explosive, APHE)弹优化设计提供参考,运用ANSYS/LS DYNA对某小口径火炮穿甲爆破弹以不同着角、不同着速侵彻不同厚度均质钢靶板的过程进行仿真,得到弹丸穿靶过程中的速度变化规律以及穿靶后的形态、存速和剩余动能等.仿真结果表明：对弹体头部形状和尺寸进行优化设计可以提高弹丸的穿甲性能,其中将弹体头部改为截锥形,弹丸穿靶后剩余动能提高5.3％;弹体头部形状对弹丸穿甲强度也有影响,其中尖锥形最差,截锥形最优;随着着角的增大,弹丸剩余动能越来越小,当着角达到65°时会出现跳弹现象.     

尾翼弹后效开翼原理实验研究

通过对２５模拟尾翼弹丸进行的射击试验，证明了膛口二维流场的存在以及它对弹刃尾翼张开的作用，结果表明，弹丸的尾翼可以在膛口二维气流的作用下在后效期内张开到位，利用这种途径，可以大大简化尾翼弹稳定装置的结构和生产工艺。     

引信球转子运动方程求解的初始条件

给出了质心与形心重合但偏离弹丸旋转轴的引信球转子运动方程组求解的初始条件，讨论了球转子在其腔室内运动的起动特性，包括球转子机构设计参数和弹道环境对球转子运动起动特性的影响．分析表明，球转子的解除保险工作特性不但与球转子的旋转偏心、球转子的直径等因素有关，而且更重要的是还取决于球转子相对于其腔室的初始方位，即球转子与其腔室的初始接触点在球转子上的位置．作为实例，还给出了某引信球转子解除保险运动起动点的计算结果     

电缆夹层防火设计与施工的探讨

从现场实际出发，对火力发电厂电缆夹层防火设计方法与施工方式进行了探讨，针对设计与施工中存在的问题提出了解决方案。