BSC信道下线性分组码的差错概率下界分析

针对BSC信道,提出了一种线性分组码的最大似然译码差错概率下界的计算方法.根据最大似然译码算法原理,首先将译码差错概率转化为差错事件的联合概率,基于改进的Dawson-Sankoff界的优化准则,推导出BSC信道下线性分组码差错冗余事件的判决准则,最后得到差错概率下界的计算表达式.该下界只依赖于码字的Hamming重量...     

抗战初期晋察冀边区的县政权建设

县政权,是中共政权系统承上启下的一个重要环节。抗战初期,晋察冀边区的县政权建设经历了起步与发展的历程。晋察冀边区的县政权虽属初建,却在探索实践中不断发展,其不仅表现为县政权组织构成和主要职能的组建与嬗变,亦表现为县政权会议制度的创建与改进,都体现了延续与渐变的因时而易的特点。在这过程中,中国共产党坚决实行抗日民主政策,团结社会各阶层,不断扩大民众的民主权利,实行民主决策,促进了敌后抗日根据地的建设,更好地适应了战时变局,为其后的中共县政权建设积累了宝贵的经验。     

Fabrication and analysis of TIG welding-brazing butt joints of in-situ TiB2/7050 composite and TA2

Lightweight hybrid structures of Al MMCs and titanium alloy dissimilar materials have great prospect in the defence industry application. So, it is necessary to join Al MMCs with Ti metal to achieve this structural design. In this work, in-situ TiB2/7050 composite and TA2 were firstly attempted to join by TIG welding-brazing technique. The result was that the intact welding-brazing butt joint was successfully fabricated. The joint presents dual characteristics, being a brazing on TA2 side and a welding on TiB2/7050 side. At brazing joint side, ER4043 filler metal effectively wets on TA2 under TIG heating condition, and a continuous interfacial reaction layer with 1—3μm is formed at welded metal/TA2 interface. The whole interfacial reaction layers are composed of Ti(AlSi)3 intermetallic compounds (IMCs), but their morphologies at the different regions present obvious distinguishes. The microhardness of the reaction layers is as much as 141—190 HV. At welding joints side, the fusion zone appears the equixaed crystal structure, and the grain sizes are much smaller than those of welded metal, which is attributed to the effect of TiB2 particulates from the melted TiB2/7050 on acceleration formation and inhibiting growth for the new crystal nucleus. The tensile test results show that average tensile strength of the optimal welding-brazing joint is able to achieve 138 MPa. The failure of the tensile joint occurs by quasi-cleavage pattern, and the cracks initiate from the IMCs layer at the groove surface of TA2 and propagate into the welded metal.     

张爱萍国防科技思想探析

张爱萍作为新中国国防科技事业的主要领导者,在领导和组织国防科技事业中,为后人留下了极其丰厚和宝贵的精神财富。本文从国防科技要坚持与国家建设协调发展的基本方针、坚持独立自主加强对外交流的发展途径和坚持"统一、协同、一致"的科学管理等三个方面,对张爱萍国防科技思想进行总结和探讨,以期对国防科技事业提供历史借鉴。     

Turkey’s strategic choice: buy or make weapons?

Turkey has been investing in its national defence industrial base since the 1980s. As with other developing countries, Turkey’s motivations for investing in national defence industries can be boiled down to the pursuit of defence autarky, economic benefits and international prestige. However, after 40 years of investment, Turkey is unable to reach the primary goals of defence industrialisation. We argue that three factors are important to understanding Turkey’s persistence in these primary goals. First, Turkey believes that there is an overall improvement in its defence industrial capabilities and the goal of autarky is still reachable. Second, increased defence exports support the belief that Turkish defence industries have become sustainable and the trend will continue in the future. The third reason, perhaps most important of all, has to do with the domestic political gains of defence industrialisation: the AKP uses defence industry and indigenous weapon systems for prestige and, therefore, garners broader support.