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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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A stereoscopic ranging system using standard PC technology

A stereoscopic ranging system using standard PC technology

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International Symposium on Underwater Technology

作者： N. Nelissen R. Koch A. Duncan Physics and Energy Studies Program Murdoch University Murdoch WA Australia Australian Maritime Engineering CRC Curtin University of Technology Bentley Australia

A stereoscopic ranging system is currently being developed as a key source of positional information for an underwater ROV station keeping system. Advancements in PC technology make it possible to use a relatively simple image capture card and a PC as a platform for the fast capture and processing of video images. We make use of the extensive capabilities of fast data buses and the high processing power of fast PCs with Pentium II or III processors. Using this approach we are developing an image processing system that is largely manufacturer independent and promises a good path for both hardware and software upgrading in the future.

关键词： Hardware Image processing Remotely operated vehicles Australia Personal communication networks Computer architecture Software packages Manufacturing processes Control systems Prototypes

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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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Improved in vivo abdominal image quality using real-time estimation and correction of wavefront arrival time errors

Improved in vivo abdominal image quality using real-time est...

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IEEE Symposium (IUS) Ultrasonics

作者： K.W. Rigby C.L. Chalek B.H. Haider R.S. Lewandowski M. O'Donnell L.S. Smith D.G. Wildes GE Corporate Research and Development Center Schenectady NY USA Department of Biomedical Engineering and Applied Physics Program University of Michigan Ann Arbor MI USA

ISBN: (纸本)0780363655

The speed of sound varies with tissue type, yet commercial ultrasound imagers assume it is constant. Sound speed variation in abdominal fat and muscle layers is widely believed to be largely responsible for poor image contrast and resolution in some patients. The simplest model of the abdominal wall assumes that it adds a spatially varying time delay to the ultrasound wavefront. We describe an adaptive imaging system consisting of a GE LOGIQ 700 imager connected to a multi-processor computer. Arrival time errors for each beamforming channel, estimated by correlating each channel signal with the beamsum signal, are used to correct the imager's transmit and receive beamforming time delays at the image frame rate. A multi-row transducer provides two dimensional sampling of wavefront arrival time errors. After beamforming time delay correction, we observe significant improvement in abdominal images of healthy male volunteers, including increased contrast of blood vessels, increased brightness of liver tissue, and improved definition of the renal capsule and splenic boundary.

关键词： In vivo Abdomen Image quality Ultrasonic imaging Delay effects Array signal processing Computer errors Muscles Spatial resolution Image resolution

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Three dimensional nonlinear optical fiber simulation using the FDTD method

Three dimensional nonlinear optical fiber simulation using t...

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Antennas and Propagation Society International Symposium

作者： D. Sullivan M. Kuzyk Department of Electrical Engineering University of Idaho Moscow ID USA Chair Materials Science Program Physics Department Washington State University Pullman WA USA

A previous paper addressed the simulation of nonlinear optical fibers using the finite difference time domain (FDTD) method in one dimension. The three-dimensional problem presents substantial logistical problems because the FDTD method requires a relatively high sampling density per wavelength making simulation over distances of several wavelengths difficult. Several techniques are described to make such a simulation possible with limited computer resources. Among them is a moving problem space which holds the pulse in the middle and moves the background medium passed the pulse. Fourier and wavelet analyses are used to characterize the pulse.

关键词： Optical fibers Finite difference methods Optical pulses Optical propagation Wavelet analysis Fourier transforms Time domain analysis Computational modeling Analytical models Pulse shaping methods

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Coherence between one random and one periodic signal-application to the EEG during sensory stimulation

Coherence between one random and one periodic signal-applica...

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Annual International Conference of the IEEE engineering in Medicine and Biology Society (EMBC)

作者： A.M.F.L. Miranda de Sa D.M. Simpson A. Fernando Biomedical Engineering Program Federal University of Rio de Janeiro Rio de Janeiro Brazil Department of Medical Physics Leicester Royal Infirmary Leicester UK

ISBN: (纸本)0780364651

Coherence between a pulse train representing periodic stimuli and the EEG has been used in the objective detection of steady-state evoked potentials, based on its sampling distribution under the null hypothesis of no responses. In order to use this coherence as a measure of the strength of responses, its sample distribution must be established under the alternative hypothesis. In this paper, the statistics of coherence estimates between one random and one periodic signal is investigated, with the aim of obtaining its confidence limits and the probability of detecting a response, if such is present. The results are then verified in Monte Carlo simulations and applied to the EEG of 14 subjects.

关键词： Electroencephalography Sampling methods Statistical distributions Biomedical measurements Brain modeling Steady-state Probability physics education Biomedical engineering Testing

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Polarization effects and transport in AlGaN/GaN system

Journal of Vacuum Science & Technology B: Microelectronics a...

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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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Developing a high speed beamformer using the TMS320C6201 digital signal processor

Developing a high speed beamformer using the TMS320C6201 dig...

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IEEE Symposium (IUS) Ultrasonics

作者： C.R. Hazard G.R. Lockwood Biomedical Engineering Program Ohio State Uinversity Columbus OH USA Department of Biomedical Engineering Cleveland Clinic Foundation Cleveland OH USA Department of Physics Queen''s University Kingston ONT Canada

ISBN: (纸本)0780363655

We are developing a synthetic aperture beamformer for a realtime 3D imaging system. The beamformer consists of a network of multi-processor digital signal processor (DSP) boards which provide the processing speed and flexibility required for realtime 3D beamforming. The system uses high speed memory buffers and a ribbon cable interface between DSP boards to allow channel to channel transfers to occur in parallel. Each channel has a 12 bit A/D, a C6201 DSP which calculates delayed signal values using linear interpolation, and a DSP for summing. Dividing the summing and delaying tasks reduces the input/output (I/O) burden. Restricting the A/D sampling frequency to an integer multiple of four times the center frequency of the ultrasound signal further reduces the I/O burden. An algorithm optimized for the C6201 calculates a single demodulated point in 25 ns. A multi-resolution look up table algorithm produces an 8 bit estimate of the log compressed envelope signal in less than 25 ns per point. Simulations of the radiation pattern formed using three transmit pulses show secondary lobes below -50 dB.

关键词： Digital signal processing Delay Frequency Signal processing algorithms Digital signal processors Array signal processing Interpolation Sampling methods Ultrasonic imaging Brain modeling

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Nitrogen atom energy distributions in a hollow-cathode planar sputtering magnetron

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Physical Review E - Statistical, Nonlinear, and Soft Matter physics 2000年第2期61卷 1904-1911页

作者： Wang, Zhehui Cohen, Samuel A. Ruzic, David N. Goeckner, M.J. Los Alamos National Laboratory Los AlamosNM87545 United States Plasma Physics Laboratory Princeton University P.O. Box 451 PrincetonNJ08543 United States Department of Nuclear Plasma and Radiological Engineering University of Illinois UrbanaIL61801 United States Electrical Engineering Program Plasma Science Laboratory University of Texas at Dallas P.O. Box 830688 M/S EC33 DallasTX75083 United States

Energy distributions of nitrogen atoms (N) in a hollow-cathode planar sputtering magnetron were obtained by use of optical emission spectroscopy. A characteristic line, N I 8216.3 A˚, well separated from molecular nitrogen emission bands, was identified. Jansson's nonlinear spectral deconvolution method, refined by minimization of xw2, was used to obtain the optimal deconvolved spectra. These showed nitrogen atom energies from 1 eV to beyond 500 eV. Based on comparisons with VFTRIM computer code results, it is proposed that the energetic N's are generated from N2+ ions after these ions are accelerated through the sheath and dissociatively reflect from the cathode. ©2000 The American Physical Society.

关键词： Cathodes

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Health risks due to radon in drinking water (vol 33, pg 921, 2000)

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ENVIRONMENTAL SCIENCE & TECHNOLOGY 2000年第11期34卷 2371-2371页

作者： Hopke, PK Borak, TB Doull, J Cleaver, JE Eckerman, KF Gundersen, LCS Harley, NH Hess, CT Kinner, NE Kopecky, KJ McKone, TE Sextro, RG Simon, SL Department of Chemistry Clarkson University Potsdam New York 13699-5810 Department of Radiological Health Sciences Colorado State University Ft. Collins Colorado 80523 University of Kansas Medical Center Kansas City Kansas 66160-7417 Department of Dermatology University of California at San Francisco San Francisco California 94143-0750 Life Sciences Division Oak Ridge National Laboratory Oak Ridge Tennessee 37831-0117 Mineral Resources Program U.S. Geological Survey Reston Virginia 20192 Nelson Institute of Environmental Medicine New York University Medical Center New York New York 10016 Department of Physics University of Maine Orono Maine 04469-5709 Department of Civil Engineering University of New Hampshire Durham New Hampshire 03824-3591 Fred Hutchinson Cancer Research Center Seattle Washington 98109-4417 School of Public Health University of California Berkeley California 94720-7360 Environmental Energy Technologies Division Lawrence Berkeley National Laboratory Berkeley California 94720 and BRER National Research Council 2102 Constitution Avenue NW Washington D.C. 20418

Following more than a decade of scientific debate about the setting of a standard for 222Rn in drinking water, Congress established a timetable for the promulgation of a standard in the 1996 Amendments to the Safe Drinking Water Act As a result of those Amendments, the EPA contracted with the National Academy of Sciences to undertake a risk assessment for exposure to radon in drinking water. In addition, the resulting committee was asked to address several other scientific issues including the national average ambient 222Rn concentration and the increment of 222Rn to the indoor-air concentration arising from the use of drinking water in a home. A new dosimetric analysisof the cancer risk to the stomach from ingestion was performed. The recently reported risk estimates developed by the BEIR Vt Committee for inhalation of radon decay products were adopted. Because the 1996 Amendments permit states to develop programs in which mitigation of air-producing health-rsik reductions equivalent to that which would be achieved by treating the drinking water, the scientific issues involved in such "multimedia mitigation programs" were explored.

关键词： GOVERNMENT policy Drinking water Radon Health

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