脉冲等离子体推力器羽流的粒子模拟

目前微小卫星正在积极地发展中,脉冲等离子体推力器是其推进系统的一个重要发展方向,为了能够将PPT成功地运用于空间,需对其羽流进行研究.将DSMC(Direct Simulation Monte-Carlo)/PIC(Particle in Cell)流体混合算法与一维MHD放电模型相结合,一体化模拟NASA Glenn PPT羽流,对不同出口偏转角的羽流场进行模拟,并与实验结果进行了比较.计算结果显示引入出口速度的偏转角提高了模型的羽流扩散能力,羽流的扩散角是影响羽流的一个主要因素.     

军事供应链不确定性产生机理研究

军事供应链中不可避免地存在不确定性。构建了军事供应链不确定性产生机理的概念模型,从需求、供应、环境三个方面分析了军事供应链不确定性产生的原因,同时,对军事供应链中可能存在的各种不确定性进行了讨论,明确了加剧不确定性影响的因素是军事供应链系统的复杂性。具体表现为军事供应链成员交互关系的复杂性和军事供应链网络结构的复杂性。提出正是由于这两个原因的存在,对军事供应链的保障性能产生了巨大的影响。     

P波段中功率混合集成放大器设计与制作

文中介绍了P 波段6瓦功率放大器的研制过程,讨论了有关理论和实际问题。该放大器采用微带和集中参数混合电路形式,具有体积小,结构紧凑,调试方便,性能稳定的特点。该电路已成功地用于某雷达整机。     

潜艇上浮运动数值计算方法的研究与验证

预报潜艇上浮运动是探索研究潜艇上浮运动控制规律以及潜艇安全上浮的前提。就潜艇上浮运动的数值计算方法和计算流程进行了详细介绍,对数值计算方法中的湍流模型及离散格式等进行了优选。基于模型上浮试验结果,对数值计算的不确定度进行了分析且对数值计算结果进行了验证。证明了该数值计算的可靠性,并发现数值计算结果与试验结果很接近,验证了该数值计算方法的可行性,说明该数值计算方法和试验可为潜艇上浮运动的研究提供参考和借鉴。     

一类不确定大系统的分散变结构模型跟随控制

针对一类具有不确定参数和外界扰动的非线性大系统 ,在子系统互连项上界具有多项式形式的条件下 ,提出了一种分散变结构模型跟随控制器设计方案。该控制器不需要未知参数变化、外界扰动以及子系统互连上界的先验信息 ,能够通过自适应率对上述信息进行在线估计。在保证闭环大系统渐近稳定的条件下 ,同时实现了各个子系统滑动模态的存在性和可达性。理论分析和仿真结果验证了本文所提方案的有效性     

Putin – the masked nemesis of the strategy of ambiguity

Recent events demonstrate the complex and adaptive approach employed by Russia to reassert influence in Europe. The changing face of Russia’s strategy commenced in 2007 when it launched a crippling cyber-attack against Estonia. This was followed by a large Russian conventional attack against Georgia in 2008, occupying two large areas of the nation. 2014 witnessed the Russian annexation of Crimea where in just a week, Russia seized control of Crimea “without firing a shot.” The annexation of Crimea was rapidly followed by a Russian inspired and led subversive war in eastern Ukraine. The common thread among these diverse Russian operations is its use of ambiguity to confound and confuse decision makers in the West.     

神经规则与案例融合的专家系统知识表示和推理

为了对专家系统中的知识进行表示,并使得推理变得更加准确高效,介绍了一种结合符号规则、神经网络和案例的方法。该方法是把一种混合规则,即神经规则和案例结合在一起。它与传统的基于符号规则推理不同的是,即使有一些未知的输入,也可以执行基于神经规则的推理。实验证明,与传统的专家系统比较,混合推理可以提高故障诊断的效率和精确度。     

用非概率理论分析混合不确定性结构的可靠性

针对不确定性结构可靠性分析中的输入变量分布参数具有不确定性和输入变量为区间模型的混合不确定性结构展开研究。考虑到可用信息最少的情况,将分布参数的不确定性描述为区间模型。通过等概率转换方法将随机变量与其分布参数进行分离,使问题转化为随机与区间变量混合的可靠性问题,建立了混合不确定性问题的可靠性分析模型。基于非概率可靠性理论,建立混合不确定结构分析模型的二级极限状态函数并结合Kriging代理模型建立了高效的求解方法。将所建立的混合不确定模型应用于飞行器结构的不确定性分析中,验证了所建模型的合理性和所提方法的高效性和准确性。     

Exact likelihood inference for the exponential distribution under generalized Type‐I and Type‐II hybrid censoring

Chen and Bhattacharyya [Exact confidence bounds for an exponential parameter under hybrid censoring, Commun Statist Theory Methods 17 (1988), 1857–1870] considered a hybrid censoring scheme and obtained the exact distribution of the maximum likelihood estimator of the mean of an exponential distribution along with an exact lower confidence bound. Childs et al. [Exact likelihood inference based on Type‐I and Type‐II hybrid censored samples from the exponential distribution, Ann Inst Statist Math 55 (2003), 319–330] recently derived an alternative simpler expression for the distribution of the MLE. These authors also proposed a new hybrid censoring scheme and derived similar results for the exponential model. In this paper, we propose two generalized hybrid censoring schemes which have some advantages over the hybrid censoring schemes already discussed in the literature. We then derive the exact distribution of the maximum likelihood estimator as well as exact confidence intervals for the mean of the exponential distribution under these generalized hybrid censoring schemes. © 2004 Wiley Periodicals, Inc. Naval Research Logistics, 2004     

Optimization of schedule stability and efficiency under processing time variability and random machine breakdowns in a job shop environment

The ability to cope with uncertainty in dynamic scheduling environments is becoming an increasingly important issue. In such environments, any disruption in the production schedule will translate into a disturbance of the plans for several external activities as well. Hence, from a practical point of view, deviations between the planned and realized schedules are to be avoided as much as possible. The term stability refers to this concern. We propose a proactive approach to generate efficient and stable schedules for a job shop subject to processing time variability and random machine breakdowns. In our approach, efficiency is measured by the makespan, and the stability measure is the sum of the variances of the realized completion times. Because the calculation of the original measure is mathematically intractable, we develop a surrogate stability measure. The version of the problem with the surrogate stability measure is proven to be NP‐hard, even without machine breakdowns; a branch‐and‐bound algorithm is developed for this problem variant. A tabu search algorithm is proposed to handle larger instances of the problem with machine breakdowns. The results of extensive computational experiments indicate that the proposed algorithms are quite promising in performance. © 2011 Wiley Periodicals, Inc. Naval Research Logistics, 2011