排序方式: 共有98条查询结果,搜索用时 15 毫秒
21.
王胜兵 《海军工程大学学报》1991,(4)
本文引入带权的 Sobolev 空间,讨论了奇型线性问题:(?)((?)u)/((?)t)-1/x~(?)(x~aa(x)u′)′=f(t,x) (x,t)∈1×J(?)/((?)x)u(t,0)=u(t,1)=0 t∈Ju(0,x)=φ(x) x∈I式中 I=(0,1),J=[0,T],0<α<3的有限元方法,并在适当条件下,给出了最佳估计:‖u_(?)-u‖_(0,2,a)≤ch~2{‖φ‖_(2,2,a)+[integral 0 to t (‖u‖~2_(2,2,a)+‖u_(?)‖~2_(2,2,a)dt]~(1/2)}‖u_(?)-u‖_(1,2,a)≤ch~2{‖φ‖_(2,2,a)+[integral 0 to t (‖u‖~2_(2,2,a)+‖u_(?)‖~2_(2,2,a)dt]~(1/2)} 相似文献
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1 引言 Leapfrog sCF具有低灵敏度特性。但在低通情况下,由于开关电容模拟输人电阻的近似性,使得Lcapfrog scF的灵敏度特性变差二。文献[2贻出了设计低灵敏度scF的状态空间法,描述了满足低灵敏度和零灵敏度的矩阵条件,·但未给出寻求满足一定条件的变换矩阵的系统方法。本文在文献口汹基础上,导出了具 相似文献
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Marvin G. Weinbaum 《Small Wars & Insurgencies》2017,28(1):34-56
Pakistan has an uneven history of dealing with insurgencies and extremism. This article identifies the various campaigns and policies employed to defeat militants and deal with violent extremism. It describes the major anti-state groups and how Pakistan’s military and civilian leaders, relying on the related strategies of selectivity, gradualism and containment, have allowed militancy and terrorism to thrive. This article finds that while the elites and the public may have belatedly come to appreciate the existential internal threats these groups pose to the country, there are strong reasons to doubt the state’s full commitment to its promises to take meaningful action. 相似文献
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《防务技术》2022,18(12):2160-2169
Most finite element models of small arms focus on an idealized barrel, typically one with a perfectly straight bore centerline. Using five different experimentally measured bore centerlines, this investigation analyzes the effect centerline nonlinearity has on projectile exit conditions. This includes the effect of rotating a centerline through several orientations. Modeled using Abaqus/Explicit, this dynamic analysis simulates a single firing cycle for each centerline. Projectile jump is calculated for each model as a measure of the effects of warped centerlines. The warped centerlines have a small effect on barrel dynamics. 相似文献
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J. M. Quinn 《Defence and Peace Economics》2013,24(5):536-554
This study models the structural sources of variation in the use of selective (discriminate) repression within 89 civil wars fought between 1981 and 2005. The severity of repressive violence is modeled as a function of the amount of territory being contested by the insurgents. This idea is operationalized using measures of the location, size, and density of insurgency violence. The analysis finds evidence that the repressive behavior of both governments and rebel groups is linked to conflict geography. Governments violate physical integrity rights more frequently and kill more civilians the greater the overall amount of territory under contestation. Rebels kill more civilians in highly dispersed insurgencies that lack a clear epicenter. 相似文献
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ABSTRACTIn 2014, an affiliate of the Islamic State of Iraq and Syria emerged in Afghanistan. Wilayat Khorasan, or ISIS-K, intends to secure Afghanistan to legitimize the Islamic State’s caliphate across the ‘Khorasan Province’ including portions of Central Asia, China, Iran, the Indian Subcontinent, and Southeast Asia. While the group’s intent is clear, its capability confounds analysts. The authors argue that Wilayat Khorasan is likely the Islamic State’s most viable and lethal regional affiliate based on an expansionist military strategy. This is designed to enable the group’s encirclement of Jalalabad City in Nangarhar Province and is foundational to its expanded operational reach, regionalization, and lethality. Since 2016, the US-led Coalition’s counter-terrorism strategy has disrupted ISIS-K’s critical requirements and prevented external attacks. Yet, raids and strikes alone will not defeat ISIS-K. They must be calibrated against an institution-building approach that legitimizes Afghanistan’s government and redresses grievances that ISIS-K exploits to resolve. 相似文献
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分析了单星观测模式下的天基测控系统的可行性,并针对该观测模式下轨道确定中法矩阵的特点,提出了一种基于压缩估计的定轨方法,该方法对法矩阵进行变换,避免了法矩阵奇异造成的误差传递。证明了当满足一定条件时,该压缩方法的估计精度要高于传统的定轨方法。并结合单星观测的特殊性,提出了误差传递因子,设计了单星观测下的压缩估计定轨算法。最后以单星模式下的天基测控系统作为仿真背景进行了仿真试验。结果表明,该压缩估计可有效提高单星观测模式下的轨道确定精度。 相似文献
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本文讨论在给定的热源温度和压缩比的情况下,涉及活塞惯性且过程进行的速率有限,只考虑传热不可逆影响的内可逆卡诺制冷机的制冷系数与利润率的关系,得到了一些有意义的结论,为实际制冷机设计提供了一个新的理论依据。 相似文献
30.
冯定斌 《海军工程大学学报》1991,(1)
本文探讨了形如 Ex_(k+1)=Ax_k+Bu_k 的定常离散描述器系统的状态调节问题,得出了一个用至多 n 步使描述器从状态 x_0到达原点的闭环反馈控制律μ_k=Kx_k。 相似文献