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.     

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.     

我国乡镇邮政网点成本收入分析——来自4省(市)的61处乡镇邮政网点的调查

乡镇邮政网点的可持续运营是邮政服务三农、服务农村经济发展的重要保障.结合邮政网络运行特点,运用成本核算方法——作业成本法,建立乡镇邮政网点运营成本模型,并明确了间接成本的分摊依据和方法.实证分析了乡镇邮政网点的成本和收入情况,实证发现,我国乡镇邮政网点业务结构单一,普遍服务业务亏损严重,运营较为困难.最后为促进乡镇邮政网点可持续运营提供一些参考建议.     

A central limit theorem for mabkovian queuing systems

In the paper a central limit theorem for the total busy time of a Markovian queuing system is proved (provided that the system satisfies some simple assumptions), This is based on a stochastic convergence theorem for the average number of services. The latter is presented in a form of “law of large numbers” as well. The case of bounded queue length is particularly analysed.     

序集抽样中$M$估计分布的随机加权逼近

序集抽样是一种适用于准确测量花费太高而排序费用可以忽略不记时的一种抽样方法.讨论了序集抽样下的对于一般分布族M估计的相合性和渐近正态性并且通过随机加权的方法来估计M估计的分布.     

Approximation by randomly weighting method in censored regression model

Censored regression (“Tobit”) models have been in common use, and their linear hypothesis testings have been widely studied. However, the critical values of these tests are usually related to quantities of an unknown error distribution and estimators of nuisance parameters. In this paper, we propose a randomly weighting test statistic and take its conditional distribution as an approximation to null distribution of the test statistic. It is shown that, under both the null and local alternative hypotheses, conditionally asymptotic distribution of the randomly weighting test statistic is the same as the null distribution of the test statistic. Therefore, the critical values of the test statistic can be obtained by randomly weighting method without estimating the nuisance parameters. At the same time, we also achieve the weak consistency and asymptotic normality of the randomly weighting least absolute deviation estimate in censored regression model. Simulation studies illustrate that the performance of our proposed resampling test method is better than that of central chi-square distribution under the null hypothesis. This work was supported by National Natural Science Foundation of China (Grant No. 10471136), PhD Program Foundation of the Ministry of Education of China, and Special Foundations of the Chinese Academy of Sciences and University of Science and Technology of China     

Localization in some discontinuously and randomly driven quantum systems

A charged particle moving in a harmonic, symmetric double well, a square well, or a Morse potential is allowed to interact with a discontinuously reversing spatially homogeneous electric field. Randomly reversing field is seen to cause localization in the quantum system. A critical reversal frequency is seen to exist below which no localization is manifested in the harmonic, double and square well. In the Morse case, there is dissociation if the upper limit of the interval between random kicks exceeds τ_max. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

室温条件下脉冲CO激光辐射特性

CO气体分子发射激光需要在低温(液氮温度附近)时才容易实现。为在常温条件下实现CO的激光输出,采用横向激励大气压(TEA)脉冲放电的方式对CO气体分子在室温条件下的红外发光辐射性能进行了实验研究。在实验所限定的参数条件下,没有获得FO波段激光辐射,仅实现了FB波段的激光输出。典型的指标为:电光转换效率1%,中心波长5.3μm,辐射能量0.22 J,辐射脉宽(FWHM)700 ns,相当于辐射的峰值功率达到0.3 mW左右;当以500 Hz放电脉冲重复频率运转时,常温条件下还获得了大于百瓦量级的高平均功率辐射输出。