A generalization of the weighted set covering problem

We study a generalization of the weighted set covering problem where every element needs to be covered multiple times. When no set contains more than two elements, we can solve the problem in polynomial time by solving a corresponding weighted perfect b‐matching problem. In general, we may use a polynomial‐time greedy heuristic similar to the one for the classical weighted set covering problem studied by D.S. Johnson [Approximation algorithms for combinatorial problems, J Comput Syst Sci 9 (1974), 256–278], L. Lovasz [On the ratio of optimal integral and fractional covers, Discrete Math 13 (1975), 383–390], and V. Chvatal [A greedy heuristic for the set‐covering problem, Math Oper Res 4(3) (1979), 233–235] to get an approximate solution for the problem. We find a worst‐case bound for the heuristic similar to that for the classical problem. In addition, we introduce a general type of probability distribution for the population of the problem instances and prove that the greedy heuristic is asymptotically optimal for instances drawn from such a distribution. We also conduct computational studies to compare solutions resulting from running the heuristic and from running the commercial integer programming solver CPLEX on problem instances drawn from a more specific type of distribution. The results clearly exemplify benefits of using the greedy heuristic when problem instances are large. © 2003 Wiley Periodicals, Inc. Naval Research Logistics, 2005     

新中国成立以来军事战略方针的历史演变及启示

编者按:为了学习和宣传党的十七大精神,根据军事科学院政治部的统一部署,我刊特约有关专家撰写了一组稿件载于"本刊特稿"专栏,从军事历史的角度研究和探讨科学发展观对于国防和军队建设的重要指导作用,与广大读者共同学习和理解胡锦涛同志在党的十七大报告中关于国防和军队建设的重要论述.     

舰空导弹试验自动化指挥系统的探讨

分析了舰空导弹飞行试验指挥工作的实际需要,对自动化指挥系统的结构组成和功能进行了分析和设计.提出了系统需要采集的数据信息内容,并对系统信息采集途径进行了可行性分析.重点分析了目标指示等主要信息的数据处理内容和过程.简要介绍了系统可视化设计的内容和实现方法.介绍了自动化系统在实际试验中的应用过程.     

基于低轨道卫星中继的无人机数据链路方案

基于低轨道卫星通信技术,针对高空长航时无人机系统,建立以卫星中继的通信数据链模型.从传统数据链入手,分析其存在的弊端和使用的局限性,并融合现代通信技术,在引用新型编码技术的基础上,给出了新的无人机通信数据链路方案.该设计方案以无人机作战使用实际为基础,极大地提高信息传输能力和信息安全性.     

反红外隐身飞机技术研究

随着隐身技术在军用飞机上的广泛应用,反隐身技术成为赢取未来高技术战争必须研究的课题.以F-117 A和B-2飞机为例,分析了现有的飞机红外隐身技术措施,对红外隐身前后系统作用距离进行估算,重点阐述了未来反红外隐身飞机的技术措施,对飞机反隐身技术的发展提出了展望.     

质量管理八项原则与型号管理——对GJB／Z9001A-2001《质量管理体系要求》标准的理解

阐述质量管理八项原则的基本内涵和相互关系,它是武器装备型号承制单位推进质量管理和贯彻GJB/Z9001A-2001质量管理体系标准必须遵循的基本准则,同时为型号承制单位整体化管理提供一条正确的思路。     

浅探装备军地联合维修保障

随着市场经济和科学技术的发展,军地联合维修保障已成为各国军队装备维修保障的发展趋势。论文从军地联合维修保障的基本认识入手,介绍了外军军地联合维修保障的发展现状,在此基础上,对我国实行装备军地联合维修保障进行了初步探讨。     

Mechanical behavior and failure mechanism of polyurea nanocomposites under quasi-static and dynamic compressive loading

Polyurea is an elastomeric material that can be applied to enhance the protection ability of structures under blast and impact loading.In order to study the compressive mechanical properties of SiC/polyurea nanocomposites under quasi-static and dynamic loading,a universal testing machine and split Hop-kinson pressure bar(SHPB)apparatus were used respectively.The stress-strain curves were obtained on polyurea and its composites at strain rates of 0.001-8000 s-1.The results of the experiment suggested that increase in the strain rates led to the rise of the flow stress,compressive strength,strain rate sensitivity and strain energy.This indicates that all of the presented materials were dependent on strain rate.Moreover,these mechanical characters were enhanced by incorporating a small amount of SiC into polyurea matrix.The relation between yield stress and strain rates were established using the power law functions.Finally,in order to investigate the fracture surfaces and inside information of failed specimens,scanning electron microscopy(SEM)and micro X-ray computed tomography(micro-CT)were used respectively.Multiple voids,crazes,micro-cracks and cracking were observed in fracture surfaces.On the other hand,the cracking propagation was found in the micro-CT slice images.It is essential to understand the deformation and failure mechanisms in all the polyurea materials.     

无铬型防毒浸渍炭的发展与应用

简单回顾了防毒浸渍炭的研究历史,指出了ASC型浸渍炭中六价铬（Cr^6＋）对人体的危害作用,较详细叙述了无铬型浸渍炭的研究和发展过程,根据使用和评价结果评述了无铬型浸渍炭在国内外化学防护领域的应用前景．     

超细粒子对环氧树脂的增韧改性研究

用NW-2辛酯偶联剂改性过的复合氧化锌(ZnO)超细粒子对环氧树脂进行增韧,借助于SEM和力学性能测试手段研究了ZnO粒子的形貌以及NW-2辛酯偶联剂改性复合ZnO粒子在环氧树脂体系中的增韧情况及其机理.结果表明:经过NW-2辛酯偶联剂改性的复合超细ZnO粒子对环氧树脂具备良好的增韧效果.