带轴向场自由电子激光器的增益

给出了带轴向场自由电子激光器的增益,并讨论了轴向场的效应。     

A three-loop method for determining the radiation characteristicsof an electrically small source

A method for determining the radiation characteristics of an electrically small source is proposed. The source is located at the center of three orthogonal loop antennas, each terminated with identical loads at diametrically opposite points. The electrically small source is represented by equivalent electric and magnetic dipole moments, and these dipole moments can be determined from the appropriate combinations of the loop responses     

New instabilities of free-electron laser with an axial guide magnetic field

In this paper, the unperturbed orbits, their stable conditions and the single-pass gain of a free-electron laser have been treated with a single-particle theory to show the existence of a couple of new instabilities and moreover, to discuss their effects. Numerical analyses reveal that the new instabilities will probably affect the operation of free-electron laser when the guide field increases and get into the vicinity of its stability boundary.     

A note on the theory of scattering from an irregular surface

Integral formulas are developed directly from vector field theory for scattering by a perfectly conducting irregular surface at very short wavelengths. It is shown that, in the optical limit, the back-scattered field has no cross polarized component. When the integrals are evaluated asymptotically by the method of stationary phase, it turns out that to a first approximation the back scattering cross section is proportional to the average number of specular points which are illuminated at a given angle of incidence and to the geometric mean of the principal radii of curvature at those points. The scattering problem is, thus, transformed to a problem in the statistical geometry of irregular surfaces.     

A generation method of insulator region proposals based on edge boxes

High-quality insulator region proposals play important roles in the process of transmission line inspection images. A generation method of insulator region proposals based on edge boxes is proposed in this paper, and edge boxes are applied to the localization of insulators in inspection images creatively. We take a series of operations to generate insulator region proposals:K-means cluster is used on curvature scale space (CSS) points extracted from edge images, the most appropriate cluster number is chosen, and the circle is drawn on the insulator subclass. We consider the characteristics of insulators’ edge images, and combine these characteristics with edge boxes. As a result, more insulator region proposals are displayed. The experimental results show that our method can effectively reduce the interference area, meanwhile, has high quality of region proposals with fast calculation speed.     

Effects of an axial magnetic field on the output power of a pulsed xenon laser

Data indicating the effects of an axial magnetic field on the output power of a pulsed xenon laser are presented. The output power increased significantly with increasing axial magnetic field only for low output power levels.     

A new method for determining the FET small-signal equivalentcircuit

A method to determine the small-signal equivalent circuit of FETs is proposed. This method consists of a direct determination of both the extrinsic and intrinsic small-signal parameters in a low-frequency band. This method is fast and accurate, and the determined equivalent circuit fits the S-parameters well up to 26.5 GHz     

A novel method for determining the nature of time series

The delay vector variance (DVV) method, which analyzes the nature of a time series with respect to the prevalence of deterministic or stochastic components, is introduced. Due to the standardization within the DVV method, it is possible both to statistically test for the presence of nonlinearities in a time series, and to visually inspect the results in a DVV scatter diagram. This approach is convenient for interpretation as it conveys information about the linear or nonlinear nature, as well as about the prevalence of deterministic or stochastic components in the time series, thus unifying the existing approaches which deal either with only deterministic versus stochastic, or the linear versus nonlinear aspect. The results on biomedical time series, namely heart rate variability (HRV) and functional Magnetic Resonance Imaging (fMRI) time series, illustrate the applicability of the proposed DVV-method.     

An efficient method for determining threshold voltage, seriesresistance and effective geometry of MOS transistors

An accurate and robust method of extracting the threshold voltage, the series resistance and the effective geometry of MOS transistors is presented. The method is based on efficient nonlinear optimization using an iterative linear regression procedure which usually converges in less than four rounds. Thereby extracted parameters are obtained from analytical expressions for the solutions to a linear system of equations whereby time consuming numerical differentiations are avoided. MOSFET parameters are explicitly identified as parameters of an underlying widely used device model that is a good approximation for operation in the linear region. The method is particularly suitable for process characterization and can be used on as few as twelve data points (three data points from each of four different size transistors). By connecting external resistors in series with the transistors, we show that the extracted values of the parameters are independent of the series resistance     

Gain characteristics of an axial gas discharge interacting with atransverse rotating magnetic field

Gain measurements within an axial discharge interacting with a transverse rotating magnetic field are presented. The effects of applied voltage and magnetic field strength on centerline gain are discussed. This is followed by an investigation of the radial gain profile and the saturation intensity. Observed values of the small signal gain and the saturation intensity were 0.85 m^-1 and 160 W/cm², respectively     

An investigation of the effect of an axial magnetic field on the He-Cd+laser

The drastic effect that a weak axial magnetic field can have upon the output of an He-Cd+ metal vapor laser is reported. A 37-percent increase in output power has been observed for a tube current of 55 mA and magnetic field strength of 70 G. Also described are parametric and spectroscopic studies performed to elucidate the cause of the large power output change.     

A theory of wave scattering from an inhomogeneous layer with an irregular interface

Bistatic wave scattering from a layer of Rayleigh scatterers with an irregular interface is investigated by combining the doubling method in volume scattering with the Kirchhoff method in rough surface scattering. Theoretical results are shown illustrating the effect of the rough interface. It is found that for scattered and incident angles near the vertical, the rough interface causes a substantial increase relative to the plane interface in both the like and cross-scattering coefficients over all azimuth angles. However, for large scattered and incident angles, the reverse is true except for azimuth angles around the specular direction. It is interesting to note that while one dominant peak of the like polarized scattering coefficient occurs along the specular direction, two dominant peaks of the cross-polarized scattering coefficient may appear symmetrically with respect to the specular direction. In backscattering, the surface roughness causes a peak to appear in both the like and cross-scattering coefficients at near vertical incidence and also a decrease of these coefficients at large incidence angles.     

A temperature-variation-sensitive method for determining the optical constants of uniaxial crystals

A simple temperature-variation-sensitive method is proposed for determining the thickness of a plate fabricated from a uniaxial crystal and the crystal’s refractive indexes with errors of less than 10^?3 μm and 10^?6, respectively. It is shown that optical parameters are determined via this method with an accuracy limited by temperature fluctuations inside the crystal. The temperature coefficients of the refractive indexes and linear expansion coefficients that were determined experimentally for a plane-parallel plate cut out of artificial crystalline quartz in parallel to its optical axis are presented.     

反演卷云激光雷达比的新方法

激光雷达比(消光系数与后向散射系数之比)是 卷云的重要光学特性之一,提出了一种通过 Mie散射激光雷达回波信号反演卷云激光雷达比的新方法。以云底气溶胶的消光系数 和卷云的光学 厚度两个参量为约束条件,构建以云顶气溶胶的消光系数和卷云的激光雷达比为未知参量的 非线性方程 组,采用粒子群算法求非线性方程组的数值解,同时获得云顶气溶胶的消光系数和卷云的激 光雷达比。使 用Mie散射激光雷达真实回波信号进行了实验验证,结果表明,本文方法是有效的,并且具 有迭代次数少、收敛速度快的优点。     

牛奶中三聚氰胺浓度测定的一种新方法

对三聚氰胺牛奶溶液在紫外光激发下的荧光光谱进行了测量,用小波变换(WT)处理荧光光谱,结合径向基函数神经网络(RBFNN),建立了检测牛奶中三聚氰胺浓度的模型。对6种三聚氰胺牛奶溶液样本的浓度进行检测,检测结果相对误差分别为1.19%、2.99%、1.06%、1.43%、2.12%和3.83%。实验结果表明,该方法能快捷、准确地测定三聚氰胺在牛奶中的含量。     

一种分析光纤共聚焦系统轴向光强的方法

在携带光纤或传像束的共聚焦系统中,光场在光纤或传像束的端面要发生改变,不能用通常的空间线性不变方法分析系统成像过程。根据单模光纤的传输特性,获得光纤的有效点扩散函数,提出利用光纤空间平均函数描述系统空间变成像过程的方法,模拟出光纤共聚焦系统的轴向光强分布,对比由光波动理论所得结果,显示该方法在光纤输出光斑的有效尺寸较小时能用于分析携带光纤或传像束的共聚焦系统且更简便。     

SEM是判断滑坡稳定性的有效方法

滑坡是一种严重的地质灾害,常常造成大量的财产损失和人身伤亡。仅在1998年我国发生了不同规模的崩塌、滑坡等突发性地质灾害多达18万处,其中规模较大的有447处,1万多人受伤,1157人死亡,50多万间房屋被毁坏,经济损失达270亿元*。随着城市的发展和土地利用,特别是大型工程项目的建设,导致人们面临的滑坡问题越来越严重。因此,滑坡已成为全球科学研究、工程研究和工程实践以及土地利用政策研究的重点。近几年,我们利用扫描电镜和X射线衍射仪等手段先后对重钢高焦炉滑坡、巴东黄土滑坡、万州乌龙池滑坡、袁家蹬滑坡、秭归淹锅沙坝滑坡、白水河…