CCD检测激光束折散宽度及在柱面镜曲率半径测量中的应用

本文介绍一种检测柱面镜曲率半径方法。该方法的基本原理是利用准直激光束通过柱面镜产生扇形折射光束,折射光束散开的宽度同柱面镜曲率半径直接相关。利用线阵CCD和微机数据处理系统,可以高精度确定折散光束宽度,进而确定出柱面半径。将这种检测技术应用于汽车灯配光镜柱面半径测量,测量精度达到2%。     

A Paraxial approximation of the problem of formation of nonparaxial conical and toroidal electron beams of an arbitrary cross section

A paraxial solution is constructed for the problem of calculation of forming electrodes for non-paraxial cuts from converging and diverging flows in a spherical diode and a Meltzer flow with circular paths. The solution is expressed in elementary functions for the case of a cone. For example, computations for a square on a sphere (the first approximation of the approximation of a contour) and a toroid with a circular cross section are presented.     

Specific features of photoelectric properties of layered films of amorphous hydrogenated silicon

Temperature dependences of photoconductivity of layered and conventional undoped films of amorphous hydrogenated silicon have been studied within a wide range of temperatures (130–420 K) and illumination intensities (0.1–60 mW cm⁻²). It is established that a higher photosensitivity of layered films compared with conventional films is governed by a low dark conductivity of layered films as a consequence of a deeper position of the equilibrium Fermi level in the band gap and the absence of temperature quenching of photoconductivity in these films. It is shown that these specific features of electrical and photoelectric properties of layered films can be attributed to a low concentration of silicon dangling bonds in comparison with the concentration of oxygen-related acceptor centers, which feature a larger capture coefficient for holes.     

Analysis of the current-voltage characteristic of solar cells

The parameters for the generation-recombination current and diffusion current of a solar cell including series and shunt resistance are determined experimentally by a new method through applying equal current steps to the cell rather than voltage steps. This allows a simple evaluation of the generation-recombination current term in the presence of a low shunt resistance of the cell. In a second measuring cycle the series resistance and the diffusion current term of the cell are determined in a similar way. The presented method is a relative simple and low-cost analysis and it allows a quick and accurate on-line determination of the parameters of the current-voltage characteristic, especially for silicon solar cells.     

数字式甲烷测量仪器示值测量结果不确定度评定

作者在建立计量标准时,将多个规程囊括到一个标准项目中,节省人力和物力.简单的介绍了合并后的不确定度分析及评定过程.     

Capacitance of transmission line of parallel cylinders in thepresence of dielectric coating

The paper presents a method for the evaluation of variation of capacitance of a dielectric coated two-wire line of parallel cylinders, each of unit radius with a change in thickness of the dielectric along the radial direction. A conformal transformation is used to transform the conductor and dielectric boundaries to appropriate contours extending over a fixed region along the imaginary axis in the transformed plane. Approximating the continuous curve obtained through transformation of dielectric boundaries by a very large number of discrete steps, the expression for the capacitance is derived in the form of a definite integral. Numerical data on capacitance as a function of width of the dielectric in the absence and presence of a conducting ground plane are presented     

Analysis of efficiency of magnetic stimulation

Magnetic stimulation can activate excitable tissues noninvasively. However, this method requires high energy to operate and can produce equipment heat that leads to inefficient stimulation. In this study, a comprehensive optimization of efficiency for magnetic stimulation has been conducted. A total of 16 781 coil designs were tested in order to determine the optimal coil geometry and inductance for neural excitation. Induced electric fields were calculated to find the optimal stimulation site (OSS) of a given coil. The threshold energy of a magnetic pulse for neural excitation was then calculated based on the transmembrane responses of a nerve model. Simulation results show that there exists an optimal inductance, as a consequence of an optimal pulse duration, corresponding to a minimum threshold energy. A longer pulse width is required to obtain the maximum efficiency for axons with slower membrane dynamics, a longer coil-to-fiber distance, and greater values of resistance (R) and capacitance (C) of the resistance-inductance-capacitance circuit. The optimal geometry features a minimum coil height, suggesting a flat coil design for optimal efficiency. The dimension of the optimal coil design increases with the coil-to-fiber distance. Moreover, the cloverleaf design achieves the highest efficiency for infinitely long fibers whereas the butterfly design is optimal for terminating or bending fibers.     

一种红外热像仪模拟训练器的设计

介绍了红外热像仪模拟训练器需求产生的背景,提出了一种基于SOPC的红外热像仪模拟训练器设计思路,并用基于FPGA芯片的NIOS嵌入式系统实现了该样品.该模拟训练器样品具有低成本、低功耗、高仿真度的特点.     

Experimental study of burnout of microwave bipolar transistors under action of a series of electric pulses

Burnout of silicon transistors under the action of a periodic train of electric pulses is experimentally studied. A numerical model and a more physically demonstrative analytical model of the pulse-to-pulse heat accumulation are in qualitative and, to a certain extent, quantitative agreement with the measured results. It is demonstrated that catastrophic failure takes place at a melting point of silicon but additional heat is needed for melting of low-temperature eutectics.     

Analysis of absorbing characteristics of thin-type absorber forgeneralized conditions of incident wave

The treatment of a thin absorber as a boundary condition, taking the arbitrary thickness of the absorber into account, is presented. To verify this approach, the equivalent circuit is applied to the terminal model of a coaxial line and rectangular waveguides. Its validity is verified by changing the medium constant, frequency, and angle and polarization of the obliquely incident wave. To illustrate the application of the approach to a complicated structure, the reflecting and scattering characteristics of an aircraft model are presented     

Modeling of TE cooling of pump lasers

The pump laser is a key module in optical amplifiers for long-haul fiber optic telecommunication systems. Its core component is a semiconductor laser diode mounted on a thermoelectric cooler. It is of crucial importance to maintain the laser diode temperature in a narrow range during operation in order to achieve satisfactory performance and reliability of the module. Therefore, a proper thermal management solution is very important to the pump module design. In this paper, a three-dimensional finite element analysis on thermoelectric cooling is presented. The modeling results show good agreement with the experimental results obtained by IR thermometry. When the heat source has a high power dissipation and a small footprint compared to the size of the heat sink, the spreading resistance becomes important. To analyze the maximum performance of the heat sink, both single and dual pump module configurations are considered.     

Measurement of broadening of pulses in glass fibres

In the letter is reported the measurement of broadening of pulses in glass fibres using a GaAs injection laser diode as an emitter and a germanium photodiode as a detector. We found broadening of about 5 ps/m for a multimode fibre and 0.6 ps/m for a self-focusing glass fibre.     

Analysis of target response of FM-CW radar

Detection and location of different targets buried in ground or constructional walls depends to a great extent on the knowledge of expected target return response. The analysis of the target-radar response for FM-CW ground probing radar is performed with the aid of a signal flow diagram relating the target response and the radar performance. A plane wave model for the radar radiated electromagnetic waves is adopted and the analysis is carried out for two typical targets; a finite thickness slab and a sphere. Computed returns based on this analysis are compared with those obtained experimentally from a 1-2 GHz FM-CW radar scheme and a very close agreement is found. A computational study is conducted on the response of planar target model, and important conclusions are reached upon relevant to ground probing problem.     

A contribution of image processing to the diagnosis of diabetic retinopathy--detection of exudates in color fundus images of the human retina

In the framework of computer assisted diagnosis of diabetic retinopathy, a new algorithm for detection of exudates is presented and discussed. The presence of exudates within the macular region is a main hallmark of diabetic macular edema and allows its detection with a high sensitivity. Hence, detection of exudates is an important diagnostic task, in which computer assistance may play a major role. Exudates are found using their high grey level variation, and their contours are determined by means of morphological reconstruction techniques. The detection of the optic disc is indispensable for this approach. We detect the optic disc by means of morphological filtering techniques and the watershed transformation. The algorithm has been tested on a small image data base and compared with the performance of a human grader. As a result, we obtain a mean sensitivity of 92.8% and a mean predictive value of 92.4%. Robustness with respect to changes of the parameters of the algorithm has been evaluated.     

Blind separation of instantaneous mixtures of nonstationary sources

Most source separation algorithms are based on a model of stationary sources. However, it is a simple matter to take advantage of possible nonstationarities of the sources to achieve separation. This paper develops novel approaches in this direction based on the principles of maximum likelihood and minimum mutual information. These principles are exploited by efficient algorithms in both the off-line case (via a new joint diagonalization procedure) and in the on-line case (via a Newton-like procedure). Some experiments showing the good performance of our algorithms and evidencing an interesting feature of our methods are presented: their ability to achieve a kind of super-efficiency. The paper concludes with a discussion contrasting separating methods for non-Gaussian and nonstationary models and emphasizing that, as a matter of fact, “what makes the algorithms work” is-strictly speaking-not the nonstationarity itself but rather the property that each realization of the source signals has a time-varying envelope     

SAR图像特征数据立方体的构造

图像数据立方体的建立有助于图像数据的基于视觉内容的分析和多种知识的挖掘,包括汇总、分类、比较、关联和聚类.图像数据立方体对于图像分析是很有用的模型.实现一个维数很大的数据立方体是很困难的.但如果维数不够,则会使图像的建模范围过于粗糙、受到限制和不精确的扩展.因此,如何设计出既能满足效率要求,又能有足够的表达能力的图像数据立方体,是个亟待研究的问题.文中借鉴前人的思路和方法,构造了SAR图像立方体的模型.     

Determination of Range of Effectiveness of Transmitter Harmonic Output Filtering

The actual effectiveness of a transmitter harmonic filter, when inserted in the transmission line to the antenna, can vary over a wide range which extends both above and below the standard characteristic-impedance circuit insertion-loss values. The location in this range varies with interconnecting transmission line lengths. An example discussed here shows that the actual insertion loss of a 60 db filter could be anywhere between 10 db and 94 db. Furthermore, the transmitter harmonic power delivered to an antenna, in the absence of a filter, can also vary with the length of the interconnecting transmission line. These effects are produced by changes in mismatch loss which occur as the length of interconnecting transmission line is varied. The purpose of this paper is to show how to determine the range of variation of such effects. Included are some sample calculations and the results of limited experimental tests.     

Determination of the age distribution of sea ice from Lagrangianobservations of ice motion

A procedure for monitoring the local age distribution of the Arctic sea ice cover is presented. The age distribution specifies the area covered by ice in different age classes. In the authors' approach, a regular array of grid points is defined initially on the first image of a long time series, and an ice tracker finds the positions of those points in all subsequent images of the series. These Lagrangian points mark the corners of a set of cells that move and deform with the ice cover. The area of each cell changes with each new image or time step. A positive change indicates that ice in a new age class was formed in the cell. A negative change is assumed to have ridged the youngest ice in the cell, reducing its area. The ice in each cell ages as it progresses through the time series. The area of multiyear ice in each cell is computed using an ice classification algorithm. Any area that is not accounted for by the young ice or multiyear ice is assigned to a category of older first-year ice. The authors thus have a fine age resolution in the young end of the age distribution, and coarse resolution for older ice. The age distribution of the young ice can be converted to a thickness distribution using a simple empirical relation between accumulated freezing-degree days and ice thickness, or using a more complicated thermodynamic model. The authors describe a general scheme for implementing this procedure for the Arctic Ocean from fall freeze-up until the onset of melt in the spring. The concept is illustrated with a time series of five ERS-1 SAR images spanning a period of 12 days. Such a scheme could be implemented with RADARSAT SAR imagery to provide basin-wide ice age and thickness information     

The k-Diameter of a Kind of Circulant Graph

The terminology and notion in this paper are similar to Ref.[1], all graphs discussed here are finite and simple. The diameter d(G) of a graph G is the maximal distance between pairs of vertices of G. The connectivity of G is the minimum number of vertices needed to be removed in order to disconnect the graph. When a network is modeled as a graph,a vertex represents a node of processor (or a station) and an edge between two vertices is the link (or connection) between those two processors. I…     

几种DOA估计算法的性能分析

在其他条件相同的情况下比较了Bartlett，Capon和Music算法的性能。Bartlett算法使波束形成的输出功率相对于某个输入信号为最大；Capon算法使噪声以及来自非信源方向的任何干扰所贡献的功率为最小，但又能保持信源方向上信号功率不变；Mustc算法是一种超分辨的方法，属于特征结构的子空间方法，因而有较高的分辨率。仿真结果征明了在其他条件相同的情况下，Music算法的性能量化。