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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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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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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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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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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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Biophysical and spectral characteristics of cool- and warm-season grasslands under three land management practices in Eastern Kansas

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Natural Resources Research 2000年第4期9卷 321-331页

作者： Guo, Xulin Price, Kevin P. Stiles, James M. Kansas Applied Remote Sensing Program (KARS) Department of Geography University of Kansas Lawrence KS 66045 2335 Irving Hill Road United States Radar Systems and Remote Sensing Laboratory (RSL) Department of Electrical Engineering and Computer Science University of Kansas Lawrence KS 66045 2335 Irving Hill Road United States Lawrence KS 66045 2335 Irving Hill Road United States

Grasslands are the largest of the Earth's four major vegetation types and are among the most agriculturally productive lands. Grassland management practices alter biophysical factors, such as plant species composition, soil structure and chemistry, and primary productivity. Large-scale changes in land management practices can have significant impacts on available natural resources, therefore impacting a regional socioeconomics. For these reasons, an improved understanding of the geographic distribution of changing land management practices and how these changes affect grassland biophysical characteristics of an area is critical to improve land use planning and practices. This study investigated the spectral characteristics, as measured using satellite remotely sensed data, of three land management practices [grazing, haying, and management under Conservation Reserve program (CRP)] on areas dominated by cool- and warm-season grasslands. The satellite imagery was acquired in May, July, and September in 1997 over Douglas County, Kansas. Biomass, vegetation cover, and species richness data were collected around the satellite overflight periods. Our results indicate that the biophysical characteristics and spectral reflectances are significantly different among the three management practices over cool- and warm-season grasslands. Interestingly, sites grazed by livestock had the highest species richness and the highest forb cover, although the total cover is almost the same as the other practices, and they have the highest near-infrared reflectance throughout the growing season. © 2000 International Association for Mathematical Geology.

关键词： Landsat Tallgrass prairie Thematic Mapper (TM)

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GA-based kernel optimization for pattern recognition: theory for EHW application

GA-based kernel optimization for pattern recognition: theory...

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Congress on Evolutionary Computation

作者： M. Yasunaga T. Nakamura I. Yoshihara J.H. Kim Institute Information Science and Electrical University of Tsukuba Tsukuba Ibaraki Japan Doctoral Program of Engineering University of Tsukuba Tsukuba Ibaraki Japan Miyazaki University Miyazaki Japan The Center for Advanced Computer Studies University of Louisiana Lafayette LA USA

An extension of the kernel-based pattern recognition method using a genetic algorithm is proposed. The method is suited to evolvable pattern recognition hardware using FPGAs. In the conventional method one common kernel function is used in the superposition to make discrimination functions. In the extended method each region of the kernel function is optimized individually. For the kernel-region optimization we use a genetic algorithm to solve a large combinatorial problem almost impossible to solve using any brute-force search. A chromosome represents the kernel region in an n-dimensional pattern space, and each locus corresponds to one of the candidates (genes) for an edge length of the kernel region. We have applied the extended method to a sonar spectrum recognition problem and obtained a recognition accuracy of 83.9%, which is much higher than the 62.0% obtained using the conventional kernel-based method and is also better than 82.7% obtained using the nearest neighbor method and the 83.0% obtained using a neural network (backpropagation algorithm). We have analyzed the individually optimized kernel regions and shown that the GA process automatically extracts features in the patterns and embeds the features in the kernel regions.

关键词： Kernel Pattern recognition Genetic algorithms Hardware Field programmable gate arrays Optimization methods Biological cells Sonar applications Nearest neighbor searches Neural networks

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1.54 μm Electroluminescence from Erbium-Doped Porous Silicon Composites for Photonic Applications

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physica status solidi (a) 2000年第1期182卷

作者： H.A. Lopez P.M. Fauchet Materials Science Program and Department of Electrical and Computer Engineering University of Rochester Rochester NY 14627 USA

We have fabricated erbium-doped porous silicon (PSi) devices and demonstrated stable room-temperature electroluminescence (EL) at 1.54 μm under both forward and reverse bias conditions. Erbium was infiltrated into the nanostructured matrix of PSi (≤ 10 19 cm —3 ) by cathodic electrochemical migration of the ions followed by high temperature annealing (950–1100 °C). The devices exhibit an exponential EL dependence in both bias conditions as a function of driving current and voltage. External quantum efficiencies of 0.01% have been obtained. The EL intensity in reverse bias and the transport properties of the devices show large temperature dependences. From the differences in temperature, electrical, and EL characteristics in forward and reverse biases, we believe that different excitation mechanisms are responsible for the EL.

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Porous Silicon Encapsulated Nematic Liquid Crystals for Electro-Optic Applications

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physica status solidi (a) 2000年第1期182卷

作者： M.V. Wolkin S. Chan P.M. Fauchet Program in Materials Science and Department of Electrical and Computer Engineering University of Rochester Rochester NY 14627 USA

In this study we present the fabrication, the optical characterization and the electrical operation of a high quality, nanometer-sized, silicon-based light modulator made of nematic liquid crystals (LC) encapsulated into porous silicon (PSi) multilayer matrix. We first demonstrate the infiltration procedure and characterize the cell's reflectance and photoluminescence (PL) before and after infiltration. Then we examine the LC molecular alignment, and show that their long axis is positioned along the pore walls. Therefore, the electrical control of an interference filter is achieved by applying a field horizontal to the pore's directionality. We also demonstrate that by applying up to 10 V the molecules reorient, the effective refractive index is modulated by as much as Δ n = 0.15, and the reflectance spectra is red shifted.

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