共查询到20条相似文献,搜索用时 921 毫秒
1.
《Microwave Theory and Techniques》1974,22(4):365-372
A new method of measuring complex dielectric constants at microwave frequencies by introducing a resonant circuit comprised of the experimental sample within a waveguide is described. The theoretical evaluation of working equations for the complex dielectric constant under the quasi-stationary distribution of the field within the sample is given. In this case, the equations are derived 1) considering the elements as lumped parameters and 2) distributed parameters are treated by means of transmission line equations. The two sets of equations are compared. The working equations are also derived for the condition when the experimental sample takes up the form of a radial line. The accuracy of determining the parameters is computed and experimental results are provided as verification of the applicability of the given method. 相似文献
2.
3.
Performance evaluation of finite normal mixture model-based image segmentation techniques 总被引:3,自引:0,他引:3
Finite normal mixture (FNM) model-based image segmentation techniques adopt the following detection-estimation-classification paradigm: (1) detect the number of image regions by using theoretical information criteria; (2) estimate model parameters by using expectation-maximization (EM)/classification-maximization (CM) algorithms; and (3) classify pixels into regions by using various classifiers. This paper presents a theoretical framework to evaluate the performance of this class of image segmentation techniques. For the detection performance, probabilities of over-detection and under-detection of the number of image regions are defined, and the associated formulae in terms of model parameters and image quality are derived. For the estimation performance, both EM and CM algorithms are showed to produce asymptotically unbiased ML estimates of model parameters in the case of no-overlap. Cramer-Rao bounds of variances of these estimates are derived. For the classification performance, misclassification probability for the Bayesian classifier is defined, and a simple formula based on parameter estimates and classified data is derived to evaluate segmentation errors. This evaluation method provides both theoretically approachable accuracy limits of the techniques and practically achievable performance of the given images. Theoretical and experimental results are in good agreement and indicate that, for images of moderate quality, the detection operation is robust, the parameter estimates are accurate, and the segmentation errors are small. 相似文献
4.
Coupling Characteristics of Planar Dielectric Waveguides of Rectangular Cross Section 总被引:1,自引:0,他引:1
《Microwave Theory and Techniques》1981,29(9):875-880
An approximate analytical method based on experimental results for predicting the coupling characteristics of various coupling structures is described. Expressions for the propagation constants were derived using the generalized effective dielectric constant method. For nonsymmetric coupling structures, the theoretical coupling coefficients were modified by a correction factor. Comparisons between experimental and theoretical results are presented. 相似文献
5.
Ping Yang Zixia Chen 《Electron Devices, IEEE Transactions on》2009,56(10):2243-2249
The aim of this paper is to provide a systematic method to perform experimental test and theoretical evaluation on fatigue characteristics of plastic-ball-grid-array (PBGA) assembly under random vibration. A specified PBGA assembly which contains different structural and material parameters was manufactured. The fatigue characteristics of PBGA assembly under random vibration were tested. Manson-Coffin empirically derived formula and rain-flow algorithm were used to achieve the fatigue life of solder joints. In the meantime, the failure curve (reliability-cycle number curve) can be obtained by using Weibull distribution method when PBGA assembly is on different working situation. Finally, life prediction of corner solder balls was deduced based on three-band technology and cumulative damage index. Test results lay a basis for high-reliability design of PBGA assembly for engineering application. 相似文献
6.
Using a criterion of minimization of total respiratory work during a complete respiratory cycle, an expression has been derived for prediction of the inhalation time/exhalation time ratio. Comparison of calculated results to experimental data is favorable. The expression also predicts a rectangular waveshape during exercise, and this result agrees well with experimental and theoretical findings previously published. 相似文献
7.
8.
The intensity of the light transmitted through a volume holographic grating is measured as a function of incident angle. Material parameters are derived by fitting a theoretical curve to the experimental results. 相似文献
9.
A complete theoretical model for CW and long-pulse dye lasers is developed. The effects of excited singlet-state absorption of pump and laser fight and triplet absorption of pump and laser light are included. Expressions are derived for gain, actual dye transmission, and output power. Experimental work is presented to verify the theory and to obtain values of excited-state absorption cross sections for rhodamine 6G by matching experimental to theoretical curves. 相似文献
10.
随着宽带雷达技术的发展,经典窄带信号参数估计的克拉美罗(CR)界已经不能再作为参数估计算法的评估标准。该文以宽带频率步进雷达为应用背景,首先推导了宽带频率步进信号参数估计的CR界,给出了Fisher信息阵元的闭合表达式。然后深入揭示了宽带CR界的特性,证明了频率步进信号参数估计的性能不仅与信号带宽、信噪比有关,还会受到相对带宽的影响。最后验证了窄带CR界只是宽带CR界的一个特例,宽带CR界综合考虑了宽带模型下各种因素的影响,在理论分析中有更加全面的指导意义。 相似文献
11.
The problem of adaptive detection of signals contaminated with Middleton's class-A impulsive noise and transmitted over a fast time-varying frequency-selective fading channel is addressed. Adaptive algorithms are derived to update the estimate of the channel parameters to the detector. A theoretical performance evaluation of the detector is provided. Computer simulations are performed to validate the theoretical developments. 相似文献
12.
13.
14.
A new theoretical approach to the determination of the critical temperature of spinodal decomposition of alloys is suggested. The approach is based on the inclusion of the dependences of elementary excitations existing in the system on the alloy composition. It is shown that the most substantial effect on the critical temperature is produced by equilibrium plasma oscillations. An analytical expression for the critical temperature in terms of the band -structure parameters of the alloy is derived. The role of other excitations existing in the system is analyzed. The calculated critical temperatures are correlated with the currently available theoretical and experimental results. 相似文献
15.
16.
激光参数及激光超声探测方法对超声信号影响 总被引:1,自引:0,他引:1
文中通过激光超声激发过程理论模型,获得激光超声信号的波形特点,并分析相关参数对激发超声信号的影响。应用两种不同的激光超声探测方法对激光超声信号进行探测,即分别采用超声探头和基于双波混合干涉的光学探测方式搭建两种实验装置。实验针对入射激光参数对激发超声信号的影响及两种探测方法获得激光超声信号的特点进行分析。通过实验验证了理论分析结果,得出入射激光参数会影响激发超声的幅度,而基于双波混合干涉的光学探测方式可以获得更为完整的超声波形信息。 相似文献
17.
The differential-capacitance technique for the evaluation of doping profiles of the low-doped side of strongly asymmetrical p-n junctions may be extended to diffused junctions, provided that the actual profile is approximated by an exponential function. An easy fit between experimental and theoretical curves allows evaluation of the two parameters of the exponential approximation. 相似文献
18.
Effros M. Visweswariah K. Kulkarni S.R. Verdu S. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》2002,48(5):1061-1081
The Burrows Wheeler transform (1994) is a reversible sequence transformation used in a variety of practical lossless source-coding algorithms. In each, the BWT is followed by a lossless source code that attempts to exploit the natural ordering of the BWT coefficients. BWT-based compression schemes are widely touted as low-complexity algorithms giving lossless coding rates better than those of the Ziv-Lempel codes (commonly known as LZ'77 and LZ'78) and almost as good as those achieved by prediction by partial matching (PPM) algorithms. To date, the coding performance claims have been made primarily on the basis of experimental results. This work gives a theoretical evaluation of BWT-based coding. The main results of this theoretical evaluation include: (1) statistical characterizations of the BWT output on both finite strings and sequences of length n → ∞, (2) a variety of very simple new techniques for BWT-based lossless source coding, and (3) proofs of the universality and bounds on the rates of convergence of both new and existing BWT-based codes for finite-memory and stationary ergodic sources. The end result is a theoretical justification and validation of the experimentally derived conclusions: BWT-based lossless source codes achieve universal lossless coding performance that converges to the optimal coding performance more quickly than the rate of convergence observed in Ziv-Lempel style codes and, for some BWT-based codes, within a constant factor of the optimal rate of convergence for finite-memory sources 相似文献
19.
针对光纤陀螺工程化对超辐射发光二极管(SLD)光源筛选的需求,开展了光源筛选和评价方法的试验和理论分析研究。通过构建光纤陀螺光源综合调试和检测系统,对SLD光源所有外部可获取特征进行了实时监测。测试和理论分析结果表明,SLD的离散特性主要受光源内部组件特性的影响;在散热充分的情况下,SLD的离散性可近似由TEC等效内阻、温控电流、热敏电阻温度系数和发光芯片功率来表征;SLD光源的常规评价指标与上述指标相结合,可更为完备地对光源进行筛选。另外,构建的光纤陀螺光源综合调试和检测系统也可直接作为光源筛选系统。 相似文献
20.
An expression for the tunnelling current between the silicon bands and the traps located in the silicon nitride, in thin-oxide m.n.o.s. memory transistors under low-field conditions, is derived. The theoretical results are compared with available experimental data, and the parameters for the trap distribution are calculated. The agreement with experimental results is satisfactory. 相似文献