介质阻挡放电中的能量转换过程研究

研究了介质阻挡放电过程中的电流强度、电场强度以及电荷分布的演变规律，并对能量转换性质进行了分析.研究结果表明，在一个放电脉冲过程中，外加驱动电源所作的功、电场能量的增量均与起始时刻的壁电荷密度有关，而气体中放电电流所作的功即沉积于气体中的能量与起始时刻的壁电荷密度、放电电流的具体波形无关. 关键词： 介质阻挡放电 壁电荷 动力学过程 能量转换     

The aberration theory of a combined electron focusing–deflection system with a rotating deflection field following the rotation of the electrons

A new type of combined magnetic focusing–electrostatic deflection systems whose orientation of deflection field is rotated synchronously with the beam electrons is proposed. This rotation deflection field can be formed by twistification of tube wall electrode (TWE) deflectors. Formulae are derived for the first-order optical properties, third-order geometrical aberrations and first-order chromatic aberrations of this system. A program was written in FORTRAN for numerical computation. An example is given; the computation results show that compared to the conventional systems, the proposed new system has lower deflection aberration coefficients.     

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根据HCSB-DEMO堆的设计要求,对不同尺寸的聚变堆能产生的聚变功率、中子壁负载和等离子体燃烧时间等进行计算与分析,给出了符合设计要求的堆芯参数。在所选定的堆芯参数条件下进行了零维功率平衡计算分析,给出了3组HCSB-DEMO堆的等离子体初步设计参数。     

Unified semi‐analytical wall boundary conditions for inviscid,laminar or turbulent flows in the meshless SPH method

Wall boundary conditions in smoothed particle hydrodynamics (SPH) is a key issue to perform accurate simulations. We propose here a new approach based on a renormalising factor for writing all boundary terms. This factor depends on the local shape of a wall and on the position of a particle relative to the wall, which is described by segments (in two‐dimensions), instead of the cumbersome fictitious or ghost particles used in most existing SPH models. By solving a dynamic equation for the renormalising factor, we significantly improve traditional wall treatment in SPH, for pressure forces, wall friction and turbulent conditions. The new model is demonstrated for cases including hydrostatic conditions for still water in a tank of complex geometry and a dam break over triangular bed profile with sharp angle where significant improved behaviour is obtained in comparison with the conventional boundary techniques. The latter case is also compared with a finite volume and volume‐of‐fluid scheme. The performance of the model for a two‐dimensional laminar flow in a channel is demonstrated where the profiles of velocity are in agreement with the theoretical ones, demonstrating that the derived wall shear stress balances the pressure gradient. Finally, the performance of the model is demonstrated for flow in a schematic fish pass where both the velocity field and turbulent viscosity fields are satisfactorily reproduced compared with mesh‐based codes. Copyright © 2012 John Wiley & Sons, Ltd.     

Nanosecond Time-Gated Spectroscopy of Laser-Ablation Plume of Human Hair to Detect Calcium for Potential Diagnoses

We demonstrate the nanosecond time-gated spectroscopy of plume luminescence in UV laser ablation of human hair. Clear and sharp peaks of calcium ion (Ca⁺) appear in the spectrum although the Ca content is only 0.1% in human hair. Highly sensitive detection of Ca is thus possible. In the experiment, the peak intensity of Ca⁺ was measured for human hair samples of female subjects over a wide range of age, and compared to the bone mineral density of the lumbar vertebrae of the subjects themselves. Our experimental results suggest that this specific spectroscopy has the potential for novel diagnoses including monitoring of daily Ca intake and a screening diagnosis of osteoporosis. The spectroscopic system and time transition of plume-luminescence spectra are also described.     

Detection of copper(II) sulfate’s uniformity and its thermal behavior in flammability of cotton fabric

Blue vitriol (copper(II) sulfate pentahydrate), CuSO₄·5H₂O has been chosen and investigated for its effectiveness as a flame-retardant, when impregnated into cotton fabric (cotton with a plain structure; woven 180 g m⁻², with 22 numbers of yarns per 10 mm). Using the vertical flame test, the extent of resistance to burning of the specimens has been determined. The impregnation was accomplished via dipping and stirring of bone-dried, weighed fabrics into the individual and suitable concentrations of the salt at room temperature. Afterwards the samples were squeeze rolled and dried horizontally at 110°C for 30 min in an oven and cooled in a desiccator and reweighed with an analytical precision. They were then kept under ordinary conditions overnight prior the fulfillment of the vertical flame test. The efficient quantities of the aforesaid salt expressed in g per 100 g dry fabric have been determined in an average figure of 12.75%. Estimation of uniformity in a selected sample was carried out via a spectrophotometer and results are in favor of the heterogeneous distribution of the salt in the fabric’s middle sectors. However initial and final parts of specimen showed to be rather uniformed. Thermogravimetric analysis of the pure cotton and the treated ones with insufficient and effective amounts of the salt were fulfilled and their thermograms were compared and commented. The results obtained for the effect of copper(II) sulfate comply with ‘The Dust or Wall Effect Theory’. This action is also assigned to the condensed phase retardation.     

Participation of ions in promoting intermolecular associations of cell wall polysaccharides

The physiological functions of the two ions, Ca²⁺ and H⁺, in controlling mechanical properties of plant cell wall are reviewed. The interactions of these ions with major cell wall polysaccharides during cell growth and development are described. Experimental results for Ca²⁺/H⁺-induced molecular associations of some polysaccharides in solutions are also given. This article aims to bridge the understandings of molecular associations in solutions (in vitro) with those occurring in cell wall matrix of high order structure (in vivo).     

The delay of transition of a laminar boundary layer over compliant wall

In a previous paper^[1], a method has been developed to study the stability characteristics of laminar boundary layers over compliant walls. In this paper, the effect of double layered compliant wall and Kramer type compliant wall on delaying the transition is investigated, and it is shown that there does exist the possibility to delay the transition by applying such compliant walls. The project supported by the National Natural Science Foundation of China.     

大风区铁路沿线挡风墙积沙机理及优化措施的风洞实验研究

位于兰州至新疆的兰新二线是世界上首条穿越大风区的高速铁路,途径著名的烟墩风区、百里风区、三十里风区及达坂城风区,风区段铁路里程长达 462.4 km,占新疆段线路总长的 65.1${\%}$,大风对铁路的运营、养护和运输造成很大危害. 为了降低大风对通行列车的危害,兰新铁路沿线设置了大量挡风墙. 挡风墙发挥作用的同时,也带来了铁路沿线的积沙问题. 为了解决这一工程实践的现实问题,本文提出了在现有挡风墙背风侧的不同位置处,设立第二道挡墙以减弱铁路积沙的治理思路,并开展了对应条件下对现有单道挡风墙、以及在现有单道挡风墙背风侧坡顶处和坡脚处设置第二道挡墙,共计3种情景的风洞模拟实验,发现设置第二道挡墙后距轨道线路高0.1 m处的沙粒水平速度、数密度、输沙通量及沉积率较无第二道挡墙时明显减少,介于8%$\sim$12${\%}$,51%$\sim$69${\%}$,20%$\sim$73${\%}$以及26%$\sim $38${\%}$,而且在现有单道挡风墙背风侧坡顶部增设第二道挡风墙的效果更好. 因此,本文的研究成果有助于优化大风区已有铁路沿线、城镇等防沙治沙工程措施.      

Holographic visualization of laser-induced plume in pulsed laser welding

High-speed holographic interferometry was applied to the experimental study of a laser-induced plasma plume in pulsed laser welding. We adopted two kinds of holographic interferometers for visualizing and imaging the refractive index distribution of the plume and vaporized metal; a real-time holographic interferometer with a high-speed camera and a double-pulsed holographic interferometer with a dual-reference-beam module. The high-speed photographs of the weld plume were compared with the visualized images by holographic interferometer. The experimental results show the process of generation and propagation of the laser-induced plume and give the feasibility of quantitative measurement of the density distribution of the laser-induced plume and vaporized metal in laser welding.