Further bounds for waiting time distributions and their means in the case ρ<1

In the paper exponential bounds for the instationary and stationary waiting time d.f.'s in GI/GI/1/∞, derived by several authors partly using martingale theory arguments, are improved with the help of monotonicity properties. Further it is shown that Ne?eptjrenko's bound for the rate of convergence of the mean waiting time in single server queues Is also valid for many server queues with ρ < 1.     

不同磁路下微型ECR中和器电子引出的模拟研究

电子回旋共振(ECR)中和器是微型ECR离子推力器的重要组成部分,其引出的电子用于中和ECR离子源的离子束流,避免了航天器表面电荷堆积,并且电子引出性能对推力器的整体性能起着重要作用.为了分析影响微型ECR中和器电子引出的因素,本文建立了二维轴对称PIC/MCC计算模型,通过数值模拟研究不同磁路结构对中和器的电子引出,及不同腔体长度对壁面电流损失的影响.计算结果表明, ECR区位置和引出孔附近磁场构型对中和器的电子引出性能至关重要.当ECR区位于天线上游,电子在迁移扩散中易损失,并且电子跨过引出孔前电势阱所需的能量更高.如果更多磁力线平行通过引出孔,中和器引出相同电子电流所需电压较小.当ECR区被天线切割或位于下游时,电子更易沿磁力线迁移到引出孔附近,从而降低了收集板电压.研究了同一磁路结构下不同腔体长度对电子引出的影响,发现增加腔体长度,使得更多平行轴线的磁力线通过引出孔从而避免电子损失在引出板表面,增加了引出电子电流.研究结果有助于设计合理的中和器磁路和腔体尺寸.     

The side chain effects on TPD-based copolymers: the linear chain leads to a higher jsc

Abstract

Alkyl substituents appended to polymers play the determining role on self-assembly and film-forming properties, and on device performance. In this work, we highlight the effects of the linear and branched flexible chains appended to the acceptor moiety (A) in D-A type copolymers. Two thieno[3,4-c]-pyrrole-4,6-dione (TPD) based copolymers PT1 and PT2 with different alkyl chains, were designed and synthesized. By comparison their UV-vis absorptions, HOMO/LUMO energy levels, as well as the characters in polymer solar cells, the influences of alkyl chains were investigated. Both copolymers showed molecular weights of 21?kDa and similar optical properties with a medium band gap of 1.93?eV, while PT2 with the branched chain exhibited a lower HOMO than that of PT1 (?5.43 vs???5.37?eV). In bulk heterojunction (BHJ) solar cells, PT1 with a linear chain presented a short circuit current (J_sc) of 6.76?mA cm^?2, open circuit voltage (V_oc) of 0.89?V and power conversion efficiency (PCE) of 2.92%. To the contrary, PT2 showed a J_sc of 3.53?mA cm^?2, V_oc of 0.99?V, delivering a relatively lower PCE of 2.05%. The result indicates that appending a linear alkyl chain to the TPD unit could sufficient enhance the J_sc value of the related polymer.     

Multidimensional gas chromatography for the characterization of permanent gases and light hydrocarbons in catalytic cracking process

An integrated gas chromatographic system has been successfully developed and implemented for the measurement of oxygen, nitrogen, carbon monoxide, carbon dioxide and light hydrocarbons in one single analysis. These analytes are frequently encountered in critical industrial petrochemical and chemical processes like catalytic cracking of naphtha or diesel fuel to lighter components used in gasoline. The system employs a practical, effective configuration consisting of two three-port planar microfluidic devices in series with each other, having built-in fluidic gates, and a mid-point pressure source. The use of planar microfluidic devices offers intangible advantages like in-oven switching with no mechanical moving parts, an inert sample flow path, and a leak-free operation even with multiple thermal cycles. In this way, necessary features such as selectivity enhancement, column isolation, column back-flushing, and improved system cleanliness were realized. Porous layer open tubular capillary columns were employed for the separation of hydrocarbons followed by flame ionization detection. After separation has occurred, carbon monoxide and carbon dioxide were converted to methane with the use of a nickel-based methanizer for detection with flame ionization. Flow modulated thermal conductivity detection was employed to measure oxygen and nitrogen. Separation of all the target analytes was achieved in one single analysis of less than 12 min. Reproducibility of retention times for all compounds were found to be less than 0.1% (n = 20). Reproducibility of area counts at two levels, namely 100 ppm_v and 1000 ppm_v over a period of two days were found to be less than 5.5% (n = 20). Oxygen and nitrogen were found to be linear over a range from 20 ppm_v to 10,000 ppm_v with correlation coefficients of at least 0.998 and detection limits of less than 10 ppm_v. Hydrocarbons of interest were found to be linear over a range from 200 ppb_v to 1000 ppm_v with correlation coefficients of greater than 0.999 and detection limits of less than 100 ppb_v.     

基于单片机和光电开关的通用计数器设计

At presrent, the photoelectric switch is more and more widely used in the industrial automation equipment.It can be finished counting industrial products by using the characteristic of the photoelectric switch which can detect the objects without touching them. This design uses the modular design method,including power-supply module, The photoelectric conversion module, optocoupler isolation circuit module, power off protection module, matrix keyboard module, counting module and The display module. It mainly uses 51 single-chip microcomputer to control the system,uses the keilC51 software to design program,uses the Proteus software to complete the simulation. Through the experiment, it proves the design is feasible.     

基于LVDT的新型信号调理电路的设计研究

LVDT线性可变差动变压器,其输出信号为两个线圈的差动电压信号,能够实时的、高准确性的将机械位移信号转化成电信号。传统LVDT信号调理电路存在不易散热、检测修复困难、性价比低、适用范围窄等问题,本文设计了一种新型LVDT信号调理电路,该信号调理电路由驱动电路、整流归一化电路和滤波放大电路组成,测试结果能够匹配LVDT的输出信号特性,达到LVDT信号调理的各项指标要求,实验结果表明本设计具有一定的可行性。     

Universal point sets for planar three-trees

For every $n\in \mathbb{N}$, we present a set $S_n$ of $O(n^{3/2}\log n)$ points in the plane such that every planar 3-tree with n vertices has a straight-line embedding in the plane in which the vertices are mapped to a subset of $S_n$. This is the first subquadratic upper bound on the cardinality of universal point sets for planar 3-trees, as well as for the class of 2-trees and serial parallel graphs.     

石墨烯嵌锂的拉曼成像

锂离子电池由于具有高能量密度,高循环寿命,低自放电率的优势,成为当前使用最为广泛的储能器件。层状材料是极为常用的负极材料,其微观嵌锂行为的研究对提高电池的能量密度和循环寿命有重要意义。本工作发展了一种新的平板微电池结构,可用于研究锂离子在各类二维层状纳米材料中的嵌锂行为。我们用机械剥离的单片少层石墨烯为正极,热蒸镀的锂金属为负极,构成石墨烯电池,用恒电压放电的方法进行嵌锂测试。采用拉曼成像技术收集石墨烯G峰信号的空间分布,实现对锂的嵌入过程的显微观测。发现了锂在石墨烯中沿层间扩散迁移,以及石墨烯断层对锂扩散的阻碍作用。这些结果有助于理解放电时锂在石墨烯电极中扩散过程,并且这项研究开发的平板微电池结构可用于多种材料的电化学过程中的微观过程表征,同时可实现与光学、电学、电子显微学等多种表征手段的兼容,具有较好的应用前景。     

类Liu系统在水声微弱信号检测中的应用研究

利用三阶混沌系统构造了一种新的微弱信号检测系统——类Liu系统, 对类Liu 系统进行了深度的理论分析. 类Liu系统中, 当输入待测信号幅值大于某临界值时, 系统可达到平衡点S₀, S₀中系统变量x平衡于摄动力信号, 系统变量y, z收敛于零态, 且S₀ 对应的Lyapunov指数小于零. 通过Matlab仿真、Multisim电路仿真以及实际电路证明了类Liu系统的周期态收敛性及广域检测性, 解决了传统Duffing系统进行微弱信号检测时周期态不收敛、只能进行窄域检测等问题, 同时谱级信噪比范围仍可达-46.57 dB. 类Liu系统采用了全新的设计理念, 具有较高的实用价值, 对未来海洋物联网中的水声通信有一定参考价值.