直排型DF/HF化学激光器扩压器喉道最佳长度实验研究

 为了研究扩压器喉道长度对直排型连续波DF/HF化学激光器起动特性的影响,建立了一套化学激光器气流通道双喷管小型实验模型。在无二次流的条件下,通过选用喉道长度不同的扩压器进行实验,分别得到对应的起动压力和工作压力,并将起动压力和工作压力的大小作为评价扩压器喉道长度优劣的依据。实验数据显示,对于该特定结构的直排型DF/HF激光器气流通道双喷管实验模型,扩压器喉道最佳长度为等效直径的17倍。     

大功率TEA CO2激光器旋转火花开关电极烧蚀实验

旋转火花开关系统工作在整个放电回路条件最为恶劣和苛刻的环节中,主要用于实现TEA CO2激光器脉冲放电工作过程的控制。该系统的性能直接决定了激光器的主要技术指标,是关系到激光器能否实现大面积均匀辉光放电的核心关键技术之一。本文介绍了这种旋转开关系统的设计、组成和工作原理,并针对影响开关寿命的放电电极烧蚀问题开展了相应的实验研究工作,有效地解决了旋转火花开关电极的使用寿命问题。实际应用结果显示：旋转火花开关系统不仅完全满足激光器的技术要求,而且稳定脉冲放电工作寿命达到了107次。     

High operating temperature SWIR p+–n FPA based on MBE-grown HgCdTe/Si(0 1 3)

The characteristics of SWIR (1.6–3 μm) 320 × 256 and 1024 × 1024 focal plane arrays (FPA’s) based on n-type In-doped HgCdTe heteroepitaxial layers are reported. The HgCdTe layers were grown by molecular beam epitaxy on silicon substrates with ZnTe and CdTe buffer layers. p–n junctions were formed by arsenic ion implantation into HgCdTe film. Reverse current in the temperature range from 210 to 330 K was found to be limited by the diffusion mechanism. At the same time in the temperature range from 140 to 210 K the reverse current was dominated by the thermal generation of charge carriers through deep traps located in the middle of the band gap. At 170 K NETD was less than 40 mK.     

Operating characteristics of MX/G/1 queue with N-policy

We consider aM ^X/G/1 queueing system withN-policy. The server is turned off as soon as the system empties. When the queue length reaches or exceeds a predetermined valueN (threshold), the server is turned on and begins to serve the customers. We place our emphasis on understanding the operational characteristics of the queueing system. One of our findings is that the system size is the sum of two independent random variables: one has thePGF of the stationary system size of theM ^X/G/1 queueing system withoutN-policy and the other one has the probability generating function _j=0 ^N=1 _j z ^j/ _j=0 ^N=1 _j , in which _j is the probability that the system state stays atj before reaching or exceedingN during an idle period. Using this interpretation of the system size distribution, we determine the optimal thresholdN under a linear cost structure.     

纳米级随机粗糙表面微观滑动摩擦力的计算研究

表面形貌很大程度上决定了摩擦副的摩擦性能, 而所有的表面都不可能是绝对光滑的.由于摩擦表面形貌的随机性, 决定了实际的摩擦过程具有随机性的特点, 因此为了获得与随机形貌对应的摩擦特性, 建立合理的随机摩擦模型是必要的. 本文基于Lennard-Jones势能建立了纳米级随机粗糙表面和原子级光滑的刚性平面间的随机摩擦模型; 模型中, 界面势能由法向载荷和界面间平衡距离决定.通过数值计算的方法, 推导了微观滑动摩擦力的计算公式和摩擦力与法向载荷之间的关系. 研究结果表明摩擦力随着法向载荷的增加而增加, 但不是线性增长. 结果也说明界面间的表面势能可能是微观摩擦力的本质起源. 关键词： 随机粗糙表面 Lennard-Jones势能 微滑动摩擦力 微摩擦     

矩形波纹过模周期慢波结构色散特性及其单模工作分析

 通过数值模拟，给出了一种求解矩形波纹过模周期慢波结构TM_0n模的色散关系的简便方法；研究了周期慢波系统平均半径、波纹周期、波纹幅度等结构参数对本征模式色散特性的影响；讨论了周期慢波系统中表面波与体积波的存在条件；分析了过模周期慢波系统仍能工作在单模状态下的原因。结果表明，过模周期慢波系统中，当结构参数满足一定条件，且与束电压、束半径匹配，使电子束与TM₀₁模同步点位于π模附近，此时TM₀₁模的总场是表面波，在两种选模机制作用下系统可实现TM₀₁单模工作。     

Long Paths and Cycles in Dynamical Graphs

We study the large-time dynamics of a Markov process whose states are finite directed graphs. The number of the vertices is described by a supercritical branching process, and the edges follow a certain mean-field dynamics determined by the rates of appending and deleting. We find sufficient conditions under which asymptotically a.s. the order of the largest component is proportional to the order of the graph. A lower bound for the length of the longest directed path in the graph is provided as well. We derive an explicit formula for the limit as time goes to infinity, of the expected number of cycles of a given finite length. Finally, we study the phase diagram.     

Low-voltage blue-phase liquid crystal display with single-penetration electrodes

A blue-phase liquid crystal display (BPLCD) with single–penetration (S-P) electrodes is proposed to reduce the operating voltage. X-shape inclined-electric field is induced by the S-P electrodes with 2 ~ 3 μm height, which can lower the operating voltage by ~45%, and improve the transmittance compared with BPLCD with conventional in-plane electrodes. Moreover, the wide viewing angle and very small image distortion index can be obtained in this structure with a half-wave biaxial film. The proposed structure shows simple etching control and easy one-drop filling process of blue-phase liquid crystal compared with dual-convex-penetration electrodes.     

Dissipativity analysis of memristive neural networks with time‐varying delays and randomly occurring uncertainties

Dissipativity theory is a very important concept in the field of control system. In this paper, we pay attention to the problem of dissipativity analysis of memristive neural networks with time‐varying delay and randomly occurring uncertainties(ROUs). Under the framework of Filippov solution, differential inclusion theory, by employing a proper Lyapunov functional, and some inequality techniques, the dissipativity criteria are obtained in terms of LMIs. It should be noteworthy that the uncertainty terms as well as the ROUs are separately taken into consideration, in which the uncertainties are norm‐bounded and the ROUs obey certain mutually uncorrelated Bernoulli‐distributed white noise sequences. Finally, the effectiveness of the proposed method will be verified via numerical example. Copyright © 2015 John Wiley & Sons, Ltd.     

具有大量椭圆颗粒/孔洞随机分布区域的计算机模拟及其改进三角形自动网格生成算法

针对颗粒／孔洞为椭圆形状并且呈随机分布的多相复合材料给出了一种计算机模拟方法，同时针对这样复杂的二维区域提供了一个改进的快速自动三角形网格剖分算法。最后用实例说明了算法的有效性。此算法可以推广到三维情形、裂纹材料等。