HDPE/iPP/CB吸波复合材料的导电性能和力学性能研究

利用碳黑（CB）在多相聚合物体系各相中的选择性富集现象，制备出了HDPE／iPP／CB二元聚合物基单层吸波复合材料，使导电相（CB富集相HDPE）为吸波相，有效吸收电磁波能量；非导电相iPP为透波相，作为电磁波进入复合材料的通道．导电性能测试表明，所制备的复合材料中具有明显的渗流现象和二次渗流现象，材料中吸波相和非吸波相并存；力学性能测试表明，适量的CB将增强树脂基体的力学性能，而过量的CB使材料的力学性能下降．分析认为，利用CB在多元聚合物中的选择性富集来制备单层吸波复合材料是一种可行的方法．     

毛泽东晚年宪法观发展嬗变探析

建国后,毛泽东亲自领导制定了1954年宪法,从而构建了“五四宪法”这一新型的法统体系,初步实现了自青年时期以来他所追求的以革命手段来确立人民法统的愿望。在此基础上,1956年前后,毛泽东对民主宪政道路继续作了艰难的探索,形成了许多理论成果。但是,随着社会主义改造的迅速完成和社会主义建设的大规模开始,人民民主专政的精神实质在国家权力运行中却没有能够继续完全得到贯彻落实。“人治”因素逐渐在毛泽东思想中占有重要地位,其原因主要有中国宪政文化先天不足的客观因素,也有毛泽东主观上对宪政、法治的作用认识不足等的主观因素,当今克服其对宪政认识不足的方面,发扬其宪法思想中的精华是新的历史任务。     

Energy transfer mechanism of GdPO4: RE3+ (RE = Tb, Tm) under VUV-UV excitation

Polycrystal of GdPO₄:RE³⁺ (RE=Tb, Tm) phosphors were prepared by solid-state method. Vacuum ultraviolet excitation and emission spectrum and the energy transfer mechanism between the host and dopants of Tb³⁺ and Tm³⁺ were investigated respectively. The emission of Gd³⁺ at 313 nm was enhanced by the strong absorption of CTS of Tm³⁺ at 180 nm in GdPO₄: Tm. It has also been concluded that the excitation of Gd³⁺ is transferred to Tb³⁺ and then emission peaks of ⁵D_J→⁷F_J of Tb³⁺ were observed.     

超高压电网全过程振荡仿真新模型研究

超高压电网振荡模型的准确设计是进行振荡与故障识别算法研究的前提。提出并论证了超高压电网振荡频率变化连续且可导原理,设计出具有连续可导性质的电网振荡频率函数,重新设计了振荡初始与复归阶段的频率变化函数,尤其在振荡复归阶段,使用具有衰减特性的反双曲函数来模拟振荡频率逐步衰减,直至恢复正常的过程。通过典型算例验证了该新模型的有效性。     

吡啶、吡嗪和均三嗪的量子化学理论研究

采用ab initio HF、M P2和B3LYP方法计算了吡啶、吡嗪和均三嗪的几何构型,用ZIN-DO/S法对分子的电子光谱进行了计算,运用GA IO-HF计算了分子的化学位移。结果表明:选用M P2对本文讨论的此类化合物键长键角更为适宜;吡啶的最大吸收波长大于吡嗪的;分子的化学位移与反应活性有密切联系:杂环分子氢原子的δH值愈小,该位置的亲电取代反应活性愈高,杂环分子氢原子的δH值愈大,该位置的亲核取代反应活性愈高。     

IPTV中组播技术的解决方案

文中介绍了IPTV业务的概念,分析了实现IPTV业务的播技术,并讨论了将组播隧道技术和应用层组播技术应用到IPTV中的解决方案.     

FBG传感器在隧道管片结构中的应用

简要介绍了FBG(光纤布拉格光栅)传感器的性能特点和基本工作原理.将FBG传感器应用于地铁隧道混凝土管片的结构力学性能试验中,通过大型压力试验机的分级加载,把粘贴在混凝土管片表面相同部位的FBG传感器和传统电阻应变片的应变进行比较,结果表明两者试验数据吻合良好,为以FBG传感技术为核心的隧道结构健康监测系统的开发和应用提供了科学依据.     

On code design for the Slepian-Wolf problem and lossless multiterminal networks

A Slepian-Wolf coding scheme for compressing two uniform memoryless binary sources using a single channel code that can achieve arbitrary rate allocation among encoders was outlined in the work of Pradhan and Ramchandran. Inspired by this work, we address the problem of practical code design for general multiterminal lossless networks where multiple memoryless correlated binary sources are separately compressed and sent; each decoder receives a set of compressed sources and attempts to jointly reconstruct them. First, we propose a near-lossless practical code design for the Slepian-Wolf system with multiple sources. For two uniform sources, if the code approaches the capacity of the channel that models the correlation between the sources, then the system will approach the theoretical limit. Thus, the great advantage of this design method is its possibility to approach the theoretical limits with a single channel code for any rate allocation among the encoders. Based on Slepian-Wolf code constructions, we continue with providing practical designs for the general lossless multiterminal network which consists of an arbitrary number of encoders and decoders. Using irregular repeat-accumulate and turbo codes in our designs, we obtain the best results reported so far and almost reach the theoretical bounds.     

Progressive image transmission over space-time coded OFDM-based MIMO systems with adaptive modulation

This paper considers a progressive image transmission system over wireless channels by combining joint source-channel coding (JSCC), space-time coding, and orthogonal frequency division multiplexing (OFDM). The BER performance of the space-time coded OFDM-based MIMO system based on a newly built broadband MIMO fading model is first evaluated by assuming perfect channel state information at the receiver for coherent detection. Then, for a given average SNR (hence, BER), a fast local search algorithm is applied to optimize the unequal error protection design in JSCC, subjected to fixed total transmitted energy for various constellation sizes. This design allows the measurement of the expected reconstructed image quality. With this end-to-end system performance evaluation, an adaptive modulation scheme is proposed to pick the constellation size that offers the best reconstructed image quality for each average SNR. Simulation results of practical image transmissions confirm the effectiveness of our proposed adaptive modulation scheme.     

Analysis of a simple step-stress life test with a random stress-change time

This paper studies a variation of a simple step-stress life testing in which the stress change time is random, and the test is subject to type II censoring. We assume that only two order statistics from the test are observed. The first observed order statistic is the stress change time from a low level stress to a high level stress during the testing, and the second observed order statistic is the final failure time when the test is censored. We first present the joint probability distribution of the two order statistics observed from the simple step-stress accelerated life test. Maximum likelihood estimates, and the method of moment estimates for model parameters based on the joint distribution are considered. We also present the exact confidence interval estimates for the model parameters based on various pivotal quantities, and demonstrate the estimation procedure by a simulated example.