Design of Transmission Line for Submillimeter Wave Gyrotron Using Dielectric-Lined Waveguide

The excitation and transmission losses of a dielectric-lined waveguide have been calculated with real, experimentally measured output beams of a submillimeter wave gyrotron. It is shown that for not-so-long transmission lines the coupling losses far exceed the transmission losses in the waveguide.     

Transport Coefficients in Some Stochastic Models of the Revised Enskog Equation

A stochastic model of the revised Enskog equation is considered. A choice of the smearing function suggested by the work of Leegwater is used to apply the model to the repulsive part of the Lennard-Jones potential and the inverse-power soft-sphere potential. The virial coefficients obtained from the equilibrium properties of the models are in excellent agreement with the known exact coefficients for these models. The transport coefficients for the repulsive Lennard-Jones (RLP) model are also computed and appear to be of comparable accuracy to the Enskog-theory coefficients applied directly to a hard-sphere system, although exact results for the RLP with which to make an extensive comparison are not yet available. The pressure and the transport coefficients obtained from the model (shear viscosity, thermal conductivity, and self-diffusion) are compared with the pressure and the corresponding transport coefficients predicted by the Enskog and square-well kinetic theories.     

假火花开关初始放电过程的理论计算

假火花开关具有耐压高、放电电流大及电流上升速率快的优点。本文利用流体模型及当地场近似，对其放电过程进行了理论计算。结果表明，在放电初始阶段，空心阴极效应起关键作用。同时，对不同初始条件（初始电子、离子密度不同）及不同边界条件（开关结构尺寸不同）的放电过程进行了计算。给出了放电时间、放电电流、最佳阴阳极距离和阴极孔尺寸大小。     

<Emphasis Type="Italic">N</Emphasis>-dimensional space-time unit spheres and Lorentz transformation

By using hyperbolic virtual unit of Clifford algebra, the concept of n-dimensional space-time unit spheres is introduced. It is used as n-dimensional Minkowski space-time and Lorentz transformation.     

An Optimum Sectional Waveguide Taper for Quasioptical Transmission Lines

The paper considers an optimum sectional waveguide taper (OSWT) which at a shortest length of the transition region provides nearly adiabatic propagation of the fundamental mode between circular, widely different in diameter quasioptical transmission lines of class hollow dielectric waveguide (HDW). Derived as a consequence of coaxial circular-horn sections, the OSWT offers all the advantages of a simple geometry and lends itself to simple fabrication techniques. The relationships among the critical geometrical parameters and the loss calculation formulae are presented. The comparison studies show that even at a few sections, the OSWT is almost as good in performance as the parabolic taper, but the OSWT is much better from a mechanical viewpoint. And compared to the ordinary linear taper, the OSWT allows essential cut in length and loss with the broadbandness kept. The HDW-based four-sectional OSWT has been fabricated and tested in a quite broad wave range 2,5-8 mm. The testing results lend a good support to the analytical formulae lying at the basis of the design software.     

Nanometer Calibration Particles: What is Available and What is Needed?

Information on available polystyrene calibration spheres is presented regarding the particle diameter, uncertainty in the size, and the width of the size distribution for particles in a size range between 20 and 100nm. The use of differential mobility analysis for measuring the single primary calibration standard in this size range, 100nm NIST Standard Reference Material®1963, is described along with the key factors in the uncertainty assessment. The issues of differences between international standards and traceability to the NIST Standard are presented. The lack of suitable polystyrene spheres in the 20–40nm size range will be discussed in terms of measurement uncertainty and width of the size distributions. Results on characterizing a new class of molecular particles known as dendrimers will be described and the possibilities of using these as size calibration standards for the size range from 3 to 15nm will be discussed.     

离子通道中环形束流分布与场解的自洽理论

考虑环形束流的空间电荷效应与相对论状态下的自磁效应对离子通道——环形束流系统的影响，研究了通道中环形束流的轨道与场解的自洽平衡态.利用动力学理论得到了电子平衡态分布函数以及环形束流的径向位置和通道内电磁场的自洽解.研究发现，相对论束流的自场对系统平衡态有很大影响，并证实了系统自洽平衡态的存在.数值计算给出了束流位置与通道半径间随能量的分布关系以及通道内场随半径分布的规律，为相关器件的设计提供了重要的理论数据. 关键词： 离子通道 环形束流 动力学理论 自洽平衡态     

产生纳米级暗中空光束的方法研究

用时域有限差分法，给出光纤头近场区电场强度模的空间分布.讨论了当光纤纤芯分别取不同尺寸时，对此空间光场强度的影响.要想得到较大范围的暗中空光束，必须增加光纤纤芯尺寸.并且，对光纤纤芯尺寸取一较大值和光纤中空区域尺寸取一较小值时的情况进行讨论，可得在光纤头附近可以出现与光纤中空区域尺寸大小相当的暗斑(10¹ nm量级).但是，暗中空光束中背景光较强.为此，将光纤的空心设计为金属. 发现此时中心暗斑的背景光明显减弱，在近场区域可获得较为理想的暗中空光束.如进一步缩小光纤中空区域尺寸，可以在光纤头附近获得暗斑更小甚至纳米量级的暗中空光束.为获得一种纳米量级的暗中空光束提供一种方法.     

On the Time‐Resolved Optogalvanic Spectra of Neon and Krypton

In this work time resolved optogalvanic signals associated with transitions excited from the first metastable state of neon and krypton have been studied. These gases have similar energy state configurations and it is of significant interest to study their time resolved optogalvanic waveforms resulting from transitions belonging to the states of same quantum numbers. The experimentally observed optogalvanic signals recorded for different discharge currents have been fitted to a theoretical model to obtain parameters that determine amplitudes, instrumental time constants and decay rates of the 1s levels. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Facile one‐pot method of initiator fixation for surface‐initiated atom transfer radical polymerization on carbon hard spheres

An efficient and novel one‐pot process is developed to immobilize the atom transfer radical polymerization (ATRP) initiators onto the surface of fully pyrolyzed carbon hard spheres (CHSs) via a radical trapping process from the in situ thermal decomposition of bis(bromomethylbenzoyl)peroxide. The CHSs do not require any additional preparative treatment prior to the initiator immobilization. Styrene and methyl methacrylate are polymerized onto initiator‐immobilized CHSs by surface‐initiated atomic transfer radical polymerization (SI‐ATRP). Samples are characterized using Fourier transform infrared, thermogravimetric analysis, scanning electron microscopy, and transmission electron microscopy. These methods of characterization confirmed that all the CHSs are coated with a uniform layer of grafted polymer. This efficient, one‐pot immobilization of ATRP‐initiators represents an exceptionally simple route for the rapid preparation of various polymer‐coated carbon‐based nanomaterials using SI‐ATRP. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3314–3322