Origin of 1/f3/2noise in GaAs thin-film resistors and MESFET's

This paper addresses the problem of 1/f^3/2low-frequency noise in GaAs thin-film resistors and MESFET's. Experimental data seem to rule out the existence of the so-called "diffusion noise" usually invoked in GaAs devices. Therefore, we propose a new "surface thermal-noise" model based on the existence of lumped thermal-noise generators distributed along the semiconductor-air or semiconductor-dielectric protection interface. The observed dependence of the low-frequency noise on the surface resistance of different MESFET's supports our conclusions.     

A comparison tool between two ASN.1 specifications

ASN.1 (Abstract Syntax Notation number One) is a standardized formal notation used to describe data exchanged between heterogeneous systems. An ASN.1 specification consists of modules which break down into formal definitions. When a protocol is updated, a new version of its ASN. 1 specification is produced. To keep interoperability between applications which support different versions of the same protocol, the specifier has to ensure that the new modules are compatible with the old ones. Our comparator, based on a complete formalization of comparison rules, can indicate the potential incompatibilities between ASN. 1:1997 specifications.     

A comparison between two methods for determining the tracking endurance of organic materials

An experimental investigation of the correlation between two accelerated tests (the Tracking Endurance Wheel and the IEC Publication 112) for determining the tracking endurance of organic materials is reported. It is shown that the qualitative classification of materials in both methods in consistent.     

A comparison of two Crame/spl acute/r-Rao bounds for nonlinear filtering with P/sub d/<1

The paper presents a comparative study of two recently reported Crame/spl acute/r-Rao lower bounds (CRLBs) for nonlinear filtering, both applicable when the probability of detection is less than unity. The first bound is the information reduction factor CRLB; the second is the enumeration method CRLB. The enumeration method is accurate but computationally expensive. We prove in the paper that the information reduction factor bound is overoptimistic, being always less than the enumeration CRLB. The theory is illustrated by two target tracking applications: ballistic object tracking and bearings-only tracking. The simulations studies confirm the theory and reveal that the information reduction factor CRLB rapidly approaches the enumeration CRLB as the scan number increases.     

A comparison between N+-P-P+and P+-N-N+silicon IMPATT diodes

A one-dimensional large-signal computer program that incorporates the material parameters of Si in an exact manner has been employed to compare the efficiency, power output, and other important operating characteristics of both complementary structures of Si IMPATT diodes. The results presented here differ greatly from those already reported by other authors.     

A comparison of two air-stable molecular n-dopants for C60

We compare two air-stable n-dopants for the fullerene C₆₀: AOB and DMBI-POH. Conductivity and Seebeck coefficient measurements were performed at various doping concentrations and the thermal activation of the conductivity was determined. A superlinear increase of conductivity upon doping was found for DMBI-POH doped C₆₀ reaching a maximum conductivity of 5.3 S/cm. In contrast to this, a linear rise of conductivity and an exponential thermal activation of mobility was observed for C₆₀ doped by AOB. This suggests a different doping mechanism for the two compounds.     

A comparison between GO/aperture-field and physical-optics methods of offset reflectors

Both geometrical optics (GO)/aperture-field and physical-optics (PO) methods are used extensively in the diffraction analysis of offset parabolic and dual reflectors. An analytical/numerical comparative study is performed to demonstrate the limitations of the GO/aperture-field method for accurately predicting the sidelobe and null positions and levels. In particular, it is shown that for offset parabolic reflectors and for feeds located at the focal point, the predicted far-field patterns (amplitude) by the GO/aperture-field method will always be symmetric even in the offset plane. This, of course, is inaccurate fur the general case and it is shown that the physical-optics method can result in asymmetric patterns for cases in which the feed is located at the focal point. Representative numerical data are presented and a comparison is made with available measured data.     

A comparison of two conformal methods for FDTD modeling

Two conformal finite-difference time-domain (FDTD) methods are considered, the contour path (CPFDTD) method of Jurgens et al. (see IEEE Trans. Antennas Propagat., vol.40, p.357, 1992) and the overlapping grid (OGFDTD) method of Yee et al. (see IEEE Trans. Antennas Propagat., vol.40, p.1068, 1992). Both TE and TM scattering from a two-dimensional (2-D), perfectly conducting circular cylinder are used to test the accuracy of the methods for curved surfaces. Also, TE and TM scattering from a 2-D, perfectly-conducting rotated square cylinder are used to test the accuracy for corners and edges. It is shown that the conformal method proposed by Yee et al. provide significant improvement in accuracy over the original FDTD algorithm for most of the geometries studied. However, implementation becomes more difficult as the geometries become more complex. The conformal method proposed by Jurgens et al. provide significant improvement in accuracy as well for most of the geometries studied. However, improvement does not occur for the TM case when the square cylinder is not aligned properly with the grid. Implementation of the CPFDTD method is relatively straightforward. For the majority of the cases studied, the OGFDTD method is more accurate than the CPFDTD method     

模板匹配算法的两种实现方法比较

模板匹配算法是图像配准和视频跟踪等系统中常用的一种算法,首先对它进行了详细的分析研究,在此基础上比较了它在VS2010和System Generator两种环境下实现的性能指标。实验结果表明,基于System Generator环境的模板匹配算法效率更高,开发周期更短。     

A comparison of two design methods for MRI magnets

Designs of magnetic resonance imaging (MRI) main magnets obtained from both a functional method and a genetic algorithm method have been compared. While most features in the two approaches are similar, there are several important differences. The functional method leads to fewer coil bundles and a reduced total current, i.e., total ampere turns, (e.g., 6-8 MA) that can be as much as 70% of the total current found with the genetic analysis. While the conclusion about stress is that it is a sensitive function of the choice of wire current density, the designs found with the functional method have a larger hoop stress than that of the genetic design, which may require new or refined manufacturing techniques. Furthermore, the functional approach requires much less computing power (i.e., a personal computer is quite sufficient) while the genetic algorithm method in general demands massively parallel computing techniques. However, in order to search for the optimal magnetic resonance design at a given field strength, it is likely that a combination of these two methods will lead to the best results.     

两种蚀刻法制作埋嵌电容PCB的对比研究

蚀刻法是埋嵌电容技术中研究与应用较多的方法。文章研究了双面蚀刻一次层压与单面蚀刻两次层压这两种工艺方法,并指出了两种方法加工埋嵌电容PCB工艺过程的关键点。通过电容值测量及回流焊测试,对比分析了不同工艺方法对埋嵌电容PCB的容值精确度及耐热性能的影响,明确了这两种工艺方法的优缺点。     

Performance comparison of two text marking methods

A text document typically consists of a collection of regular structures such as words, lines, and paragraphs, a slight movement of which seems less perceptible than, say, dithering of the document image. We exploit this property to watermark formatted text documents by shifting slightly certain lines and words in order to discourage illicit distribution. We analyze two methods for reliable document identification in the presence of severe distortions introduced by photocopying, facsimile transmission, and other processing. The correlation method uses document profiles directly for detection. To eliminate the effect of certain distortions, the centroid method bases its decision on the distances between the centroids of adjacent profile blocks. We present the maximum likelihood detectors for both methods and evaluate their relative performance. Our analysis indicates that line-shift generally has a smaller error than word-shift detection, and that the correlation detector outperforms the centroid detector provided certain distortions can be accurately compensated for before detection is attempted. These results have been applied to implement a marking and identification system and preliminary experimental results have been very promising     

多波长掺铒光纤激光器技术研究

掺铒光纤激光器（EDFL）是光通信与光传感领域中最有发展前途的光源之一,目前已有多种方法实现了掺铒光纤激光器多个波长的稳定输出.本文分析了各种在EDFL中产生多波长振荡的机理,并讨论了未来的发展趋势.     

Comparison between two asymptotic methods

Two complete asymptotic expansions of an integral with many simple pole singularities and a first-order, isolated, saddle point evaluated by two different methods are compared. It is shown that both expansions are exactly the same (term by term) inside and outside the transition regions.     

A comparison of methods to evaluate potential integrals

Several methods are developed and used to evaluate potential integrals which occur in the numerical solution of electromagnetic scattering or radiation from electrically thin elements. Exact and approximate representations are obtained for potential integrals with constant, trigonometric, or polynomial distribution functions. Each integrand and integral is displayed graphically over a broad range of parameters. The computational accuracy and efficiency of these representations are compared with direct numerical quadrature.     

A comparison between two kinds of equivalent currents to analyze conducting bodies with apertures using moment methods: Application to horns with symmetry of revolution

A system of integral equations (SIE) based on the unique-hess theorem that uses only electric equivalent currents (EEC) is formulated to analyze conducting bodies with apertures. This SIE is compared with an SIE that uses both electric and magnetic equivalent currents (EMEC). In general, to solve both SIE's numerically difficult computations of Cauchy principal-value integrals with highly singular kernels are required. These integrals appear when computing electric (magnetic) fields created by magnetic (electric) currents. Their evaluation can be avoided using the EEC approach in many practical cases when the main interest is in the radiation patterns of aperture antennas. The two SIE's are compared by carrying out an analysis of rotationally symmetric horns using the moment method (MM) in its formulation for bodies of revolution. Numerical results of electric currents and radiation patterns are presented for small horns of various geometries. These results compare quite well with measurements for both SIE's. However, the central processing unit (CPU) time for the EEC formulation is an order of magnitude smaller than for the EMEC formulation.     

A qualitative comparison between two semiconductor laser amplifierequivalent circuit models

Two different forms of equivalent circuit models have been independently proposed for semiconductor laser amplifiers. These have interesting similarities in their equivalent circuits. A comparison is made of the models in terms of derivation, completeness, applications, and computing speed. Results from the transmission line laser model (TLLM) are presented and show the effects of input power, carrier inhomogeneities, and front facet reflectivity on two-input intermodulation distortion     

A comparison between two routing protocols: OSPF and IS-IS

A comparison is made of the open shortest path first (OSPF) and intermediate system-to-intermediate system (IS-IS) routing protocols in terms of their ability to route internet protocol (IP) traffic. Common characteristics of the two protocols are briefly indicated. The differences between the two are explored with respect to packet encoding, area partitions, level 2 partitions, injection of level 2 information, authentication, designated router election, link state packet propagation, synchronized parameter setting, and neighbor initialization     

Bandlimited 1/fα-noise source

CMOS imagers generate both white noise and low frequency noise with a power spectral density proportional to 1/f^α with 0.5<α<2.0. To characterise on-chip/off-chip amplifiers or CDS circuits, white noise sources are available commercially, but not low frequency noise sources. A practical bandlimited 1/f^α -noise constructed using a white noise source is presented