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Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures Processing, Measurement, and Phenomena 2000年第4期18卷 2322-2327页

作者： Yifei Zhang Yulia Smorchkova C. Elsass Stacia Keller James Ibbetson Steven DenBaars Umesh Mishra Jasprit Singh Applied Physics Program University of Michigan Ann Arbor Michigan 48109 Department of Electrical Engineering and Computer Science University of Michigan Ann Arbor Michigan 48109-2122 Department of Electrical and Computer Engineering University of California Santa Barbara California 93106 Department of Electrical Engineering and Computer Engineering University of Michigan Ann Arbor Michigan 48109

The AlGaN/GaN heterostructure is important for both electronic and optoelectronic devices. In addition to having a large band gap, the heterostructure has a strong piezoelectric effect and a large spontaneous polarization. This allows one to incorporate a large electric field (>106 V/cm) and high sheet charge (>1013 cm−2) without doping. Theoretical studies are done to examine how polarization effects controls the sheet charge density. The studies also focus on how interface roughness, aluminum mole fraction in the barrier, impurity scattering, sheet charge density, and phonon scattering influence mobility. Results are compared with experimental studies on samples grown by both molecular beam epitaxy (MBE) and metalorganic chemical vapor deposition (MOCVD). We find that interface roughness is a dominant source of scattering in the samples reported. Due to the variation in growth techniques we find that the MBE samples have a smoother interface quality compared to the MOCVD samples. By carefully fitting the experimental data we present results on interface roughness parameters for MBE and MOCVD samples.

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A room temperature unipolar quantum dot intersubband long wavelength (13.3 /spl mu/m) laser

A room temperature unipolar quantum dot intersubband long wa...

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IEEE Photonics Conference (IPC)

作者： S. Krishna P. Bhattacharya J. Singh J. Urayama T.B. Norris P.J. McCann K. Namjou Applied Physics Program Department of Electrical Engineering and Computer Science University of Michigan Ann Arbor MI USA School of Electrical and Computer Engineering University of Oklahama Norman OK USA

Summary form only given. We report the room temperature operation of a novel unipolar self-organized quantum dot FIR laser (13.3 /spl mu/m) based on transitions between discrete bound electron states in self-organized... 详细信息

关键词： Quantum dot lasers US Department of Transportation Electrons Infrared detectors Stationary state Finite impulse response filter Land surface temperature Infrared spectra Spectroscopy Laser radar

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Direct Classification with Indirect Data 00

Direct Classification with Indirect Data

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Annual Conference on Neural Information Processing Systems

作者： Timothy X Brown Interdisciplinary Telecommunications Program Dept. of Electrical and Computer Engineering University of Colorado Boulder 80309-0530

We classify an input space according to the outputs of a real-valued function. The function is not given, but rather examples of the function. We contribute a consistent classifier that avoids the unnecessary complexi... 详细信息

ISBN: (纸本)0262122413

关键词： Taxonomy Output Mentoring Classifiers

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Quantum Confinement in Nanocrystalline Si Superlattices

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MRS Online Proceedings Library 2000年第1期592卷 359-364页

作者： G. F. Grom P. M. Fauchet L. Tsybeskov J. P. McCaffrey H. J. Labbé D. J. Lockwood Department of Mechanical Engineering Materials Science Program USA Department of Electrical and Computer Engineering University of Rochester Rochester USA Institute for Microstructural Sciences National Research Council Ottawa Canada

Photoconductance spectroscopy was used to probe the effects of quantum confinement in nanocrystalline (nc)-Si/amorphous (a)-SiO2 superlattices (SLs). A Metal-Oxide-Semiconductor (MOS)-like structure with the nc-Si SL incorporated in the oxide was fabricated to study charging/discharging processes in Si nanocrystals. The fine structure observed in photoconductance spectra at low temperatures was interpreted in terms of singularities in the carrier density of states, possibly due to energy quantization. In addition, a low-resistance sample exhibited photocurrent oscillations with a frequency of several kHz, which could be a manifestation of sequential resonant carrier tunneling in the nc-Si/a-SiO2 SL.

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Modeling and evaluating electricity options markets with intelligent agents

Modeling and evaluating electricity options markets with int...

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International Conference on Electric Utility Deregulation and Restructuring and Power Technologies (DRPT)

作者： D.W. Lane C.W. Richter G.B. Sheble Systems Engineering Program Iowa State University Ames IA USA Electrical and Computer Engineering Department Iowa State University Ames IA USA

Under deregulation, the formation of electricity markets is a topic of great interest in the power industry and in financial institutions worldwide. Using derivative financial instruments (including options) becomes important for hedging against uncertainty and managing risk-limiting exposure to adverse market conditions. Black and Scholes' equation is often used to value options, but its validity is questionable due to assumptions that may not hold for electricity, most notably the assumption of log-normally distributed prices for the underlying commodity. In this research, a put options market for electricity is modeled. Adaptive agents trade in this market to maximize profit. They are not forced to use an explicit economic or financial model (e.g., Black-Scholes) in their valuation. A genetic algorithm (GA) is used to find alternate valuations that are used to generate buy and sell signals. The results show that it is possible to evolve profitable valuations for use with buying and selling options in this simple model. Reasons for and implications of this finding (e.g., that Black-Scholes may not be a good method for pricing electricity derivatives) are discussed.

关键词： Cost accounting Electricity supply industry deregulation Electricity supply industry Power industry Instruments Uncertainty Financial management Risk management Equations Power system economics

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Convergence analysis of an oversampled subband adaptive filtering structure with local errors

Convergence analysis of an oversampled subband adaptive filt...

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IEEE International Symposium on Circuits and Systems (ISCAS)

作者： M.R. Petraglia R.G. Alves P.S.R. Diniz COPPE-Program of Electrical Engineering Federal University of Rio de Janeiro Rio de Janeiro Rio de Janeiro Brazil Department of Electrical and Computer Engineering Concordia University Montreal QUE Canada

Subband adaptive filtering has been recently studied by a large number of researchers. The main alternatives are structures with critical sampling and noncritical sampling, and structures that use local errors and global error in the adaptive algorithm. In this paper a theoretical convergence analysis for the case of an oversampled subband adaptive altering structure with local errors is presented. The convergence rate and misadjustment of the algorithm can be estimated from the results of this analysis. computer simulations are presented to illustrate the convergence behavior of the subband adaptive algorithm and to verify the theoretical results.

关键词： Convergence Adaptive filters Finite impulse response filter Filter bank computer errors Sampling methods Adaptive algorithm Algorithm design and analysis computer simulation Prototypes

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Spreadsheet model for MorphoSys RC array

Spreadsheet model for MorphoSys RC array

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IEEE International Conference on Electronics, Circuits and Systems (ICECS)

作者： H. Diab E. Abdennour N. Mansour Department of Electrical and Computer Eng'g Faculty of Engineering and Architecture American University of Beirut Beirut Lebanon Computer Science Program Lebanese American University Beirut Lebanon

ISBN: (纸本)0780365429

This paper introduces reconfigurable computing and MorphoSys, which is a reconfigurable system. It also explains the architecture of its reconfigurable hardware part. Then, it presents two spreadsheet models for the operation of this reconfigurable device. The first spreadsheet performs the modelling through formulas, while the second does it numerically. These spreadsheet models serve as design and debugging tools.

关键词： Registers Hardware computer architecture Application software Reduced instruction set computing Multiplexing Numerical models Debugging Application specific integrated circuits Parallel processing

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On the Perception of Transients: Applying Psychophysical Constraints to Improve Audio Analysis and Synthesis 26

On the Perception of Transients: Applying Psychophysical Con...

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26th International computer Music Conference, ICMC 2000

作者： Wakefield, Gregory H. Heller, Laurie M. Carney, Laurel H. Mellody, Maureen Department of Electrical Engineering and Computer Science University of Michigan Ann ArborMI48109 United States Naval Submarine Medical Research Laboratory GrotonCT06359 United States Hearing Research Center Dept. of Biomedical Engineering Boston University BostonMA02215 United States Applied Physics Program University of Michigan United States

In a psychophysical experiment, a wideband, 4-ms noise is compared with spectrally smoothed versions of the noise. To isolate on the magnitude spectrum, the phase spectrum is controlled by assigning the same random phase spectrum to both the original and smoothed signals. Depending on the choice of phase spectrum, discrimination thresholds for spectral shape vary from a maximum spectral deviation of 2-3 dB to as much as 25 dB. The exact source of this effect remains an open question. However, it suggests that not all transients require the same signal fidelity. Given a proper characterization of the perceptual response, it may be possible to reduce the size of the codebook required to maintain acceptable perceptual results. © 2000 ICMC. All Rights Reserved.

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Prediction of excess noise factor and frequency response for thin avalanche photodiodes

Prediction of excess noise factor and frequency response for...

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IEEE Photonics Conference (IPC)

作者： M.M. Hayat M.A. Saleh Ohhyun Kwon B.E.A. Saleh M.C. Teich Dept. of Electr. & Comput. Eng. Dayton Univ. OH USA Department of Electrical and Computer Engineering Boston University Boston MA USA Electro-Optics Program and the Department of Electrical and Computer Engineering University of Dayton Dayton OH USA

Summary form only given. Recent experimental measurements from InP and InAlAs avalanche photodiodes (APDs) with thin multiplication regions, collected by J.C. Campbell and collaborators at the University of Texas at Austin, show that, for a fixed gain the excess noise factor is significantly lower than that predicted by the conventional McIntyre theory. The observed dependence of the noise on the multiplication-region width cannot be explained using the conventional theory in which the excess noise factor is a function only of the mean gain and the ionization coefficient ratio. In the dead-space-multiplication theory (DSMT), a carrier must travel a certain distance, called the dead space, before gaining sufficient energy for impact ionisation to occur. Because this dead space regularizes the ionisation locations, the randomness of the avalanching mechanism is reduced. For thin multiplication-region APDs, this effect is proportionally higher and thus the noise is lower. We applied the DSMT to the experimental results for GaAs and AlGaAs and more recently for InP and InAlAs APDs. We were able to fit the ionization coefficients associated with devices of various thicknesses, as a function of the electric field, within the confines of a single exponential model.

关键词： Frequency response Avalanche photodiodes Ionization Indium phosphide Gallium arsenide Bandwidth Electronic mail Indium compounds Signal to noise ratio Space exploration

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Classification and estimation of ultrasound speckle noise with neural networks

Classification and estimation of ultrasound speckle noise wi...

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IEEE Symposium on Bioinformatics and Bioengineering (BIBE)

作者： M.P. Wachowiak A.S. Elmaghraby R. Smolikova J.M. Zurada Electrical and Computer Eng. Department University of Louisville Louisville KY USA Computer Science and Engineering Program University of Louisville Louisville KY USA Computer Eng. and Computer Science Department University of Louisville Louisville KY USA

Presents a neural-based approach to classifying and estimating the statistical parameters of speckle noise found in biomedical ultrasound images. Speckle noise, a very complex phenomenon, has been modeled in a variety of different ways: and there is currently no clear consensus as to its precise statistical characteristics. In this study, different neural network architectures are used to classify ultrasound images contaminated with three types of noise, based upon three one-parameter statistical distributions. At the same time: the parameter is estimated. It is expected that accurate characterization of ultrasound speckle noise will benefit existing post-processing methods, and may lead to new refinements in these techniques.

关键词： Ultrasonic imaging Speckle Neural networks Additive noise computer science Parameter estimation computer networks Statistical distributions Adaptive filters Biomedical computing

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