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1999

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Articles 1 - 30 of 239

Full-Text Articles in Electrical and Computer Engineering

Method And System For Gas Metal Arc Welding, Yuming Zhang, Liguo E Dec 1999

Method And System For Gas Metal Arc Welding, Yuming Zhang, Liguo E

Electrical and Computer Engineering Faculty Patents

An improved method of gas metal arc welding (GMAW) is disclosed. The method includes utilizing a pulsed current having a variable waveform to ensure the detachment of one-droplet-per-pulse of current. During the welding process, the current is sufficient to produce a droplet at the end of a consumable electrode wire. After the droplet reaches a desired size, the current is lowered to induce an oscillation in the droplet. The current is then increased which, in combination with the momentum created by the oscillation, effects droplet detachment. The oscillation may be monitored by observing the arc voltage to determine a preferred …

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Results Using An Alternative Approach To Channel Equalization Using A Pattern Classification Strategy, Frank M. Caimi, Gamal A. Hassan Dec 1999

Results Using An Alternative Approach To Channel Equalization Using A Pattern Classification Strategy, Frank M. Caimi, Gamal A. Hassan

Electrical Engineering and Computer Science Faculty Publications

In underwater acoustic communication, (ACOMMs), ocean surface and bottom conditions create multi path propagation's for the transmitted signal that result in Inter symbol Interference (ISI) at the receiver. Generally, Equalization, Diversity IBeam forming, and Channel Coding are three independent techniques that are used to improve received signal quality. Equalization compensates for ISI created by a band-limited, time-dispersive channel through implementation of specialized filtering schemes within the receiver. The coefficients of the equalizer need to be continuously adjusted to compensate for the variability in the channel. Since the number of states required by the equalizer (or beam former) is finite, and …

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Near-Band-Gap Cupt-Order-Induced Birefringence In Al0.48Ga0.52Inp2, Mathias Schubert, Tino Hofmann, Bernd Rheinlander, Ines Pietzonka, Torsten Sass, Volker Gottschalch, John A. Woollam Dec 1999

Near-Band-Gap Cupt-Order-Induced Birefringence In Al0.48Ga0.52Inp2, Mathias Schubert, Tino Hofmann, Bernd Rheinlander, Ines Pietzonka, Torsten Sass, Volker Gottschalch, John A. Woollam

Department of Electrical and Computer Engineering: Faculty Publications

The order-induced birefringence in the near-band-gap spectral range (0.75 to 2.5 eV), and its dependence on the degree of ordering η is reported for Al0.48Ga0.52InP2. Transmission and reflection generalized variable angle spectroscopic ellipsometry, dark-field spectroscopy, and cross-polarized reflectance difference spectroscopy (CRDS) are used to determine precisely the room-temperature dielectric functions for polarization parallel and perpendicular to the ordering direction of a series of spontaneously CuPt-ordered samples grown by metalorganic vapor-phase epitaxy. The CRDS technique is introduced as an approach to sense extremely weak anisotropy at oblique angles of incidence. The observed order birefringence is …

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Method For Testing Field Programmable Gate Arrays, Charles E. Stroud, Miron Abramovici Dec 1999

Method For Testing Field Programmable Gate Arrays, Charles E. Stroud, Miron Abramovici

Electrical and Computer Engineering Faculty Patents

A method of testing field programmable gate arrays (FPGAs) includes the step of configuring programmable logic blocks of the FPGAs for completing a built-in self-test. This is followed by the steps of initiating the built-in self-test, generating test patterns with the programmable logic blocks and analyzing a resulting response to produce a pass/fail indication with the programmable logic blocks. More specifically, the configuring step includes establishing a first group of programmable logic blocks as test pattern generators and output response analyzers and a second group of programmable logic blocks as blocks under test. The blocks under test are then repeatedly …

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Dielectric Plug-Loaded Two-Port Transmission Line Measurement Technique For Dielectric Property Characterization Of Granular And Liquid Materials, K. Mubarak, R. Zoughi, Aaron D. Benally, Karl Joseph Bois, Larry F. Handjojo Dec 1999

Dielectric Plug-Loaded Two-Port Transmission Line Measurement Technique For Dielectric Property Characterization Of Granular And Liquid Materials, K. Mubarak, R. Zoughi, Aaron D. Benally, Karl Joseph Bois, Larry F. Handjojo

Electrical and Computer Engineering Faculty Research & Creative Works

There are numerous dielectric property characterization techniques available in the microwave regime each with its own uniqueness, advantages and disadvantages. The two-port completely-filled waveguide (transmission line) technique is a robust measurement approach which is well suited for solid dielectric materials. In this case, the dielectric material can be relatively easily machined to fit inside the waveguide and the subsequent measurement of the scattering parameters of this two-port device renders the dielectric properties of the material filling the waveguide. However, this technique is not well suited for measuring the dielectric properties of granular and liquid materials. These materials are used in …

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Multimode Solution For The Reflection Properties Of An Open-Ended Rectangular Waveguide Radiating Into A Dielectric Half-Space: The Forward And Inverse Problems, R. Zoughi, Aaron D. Benally, Karl Joseph Bois Dec 1999

Multimode Solution For The Reflection Properties Of An Open-Ended Rectangular Waveguide Radiating Into A Dielectric Half-Space: The Forward And Inverse Problems, R. Zoughi, Aaron D. Benally, Karl Joseph Bois

Electrical and Computer Engineering Faculty Research & Creative Works

Open-ended rectangular waveguides are extensively used in nondestructive dielectric material evaluation. The dielectric properties of an infinite-half space of a material are calculated from the measured reflection properties referenced to the waveguide aperture. This calculation relies on a theoretical and numerical derivation of the reflection coefficient likewise referenced to the waveguide aperture. Most of these derivations assume the dominant mode field distribution across the waveguide aperture. However, when dealing with low permittivity and low loss dielectric materials, there may exist significant errors when calculating the dielectric properties from the measured reflection coefficient. These errors have also shown to be more …

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Wide-Bandwidth Multi-Resolutional Analysis Of A Surface-Mounted Pm Synchronous Machine, S. D. Sudhoff, Jerry L. Tichenor, James L. Drewniak Dec 1999

Wide-Bandwidth Multi-Resolutional Analysis Of A Surface-Mounted Pm Synchronous Machine, S. D. Sudhoff, Jerry L. Tichenor, James L. Drewniak

Electrical and Computer Engineering Faculty Research & Creative Works

Advances in power semiconductor devices have led to inverters with unprecedented voltage edge rates. This has decreased inverter switching losses and enabled the use of increasingly higher switching frequencies. However, faster edge rates and higher switching frequencies increase electromagnetic compatibility (EMC) problems, machine insulation stress, bearing currents, and other aspects of system design. Typical computer simulations used to design and evaluate proposed electric drive systems cannot be used to predict these high-frequency effects. A wide-bandwidth multi-resolutional analysis that allows designers to anticipate and quantify high-frequency effects is detailed in this paper. The approach is specifically applied to permanent magnet synchronous …

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Approximation And Optimization Of An Auditory Model For Realization In Vlsi Hardware, Samuel L. Sangregory Dec 1999

Approximation And Optimization Of An Auditory Model For Realization In Vlsi Hardware, Samuel L. Sangregory

Theses and Dissertations

The Auditory Image Model (AIM) is a software tool set developed to functionally model the role of the ear in the human hearing process. AIM includes detailed filter equations for the major functional portions of the ear. Currently, AIM is run on a workstation and requires 10 to 100 times real-time to process audio information and produce an auditory image. An all-digital approximation of the AIM which is suitable for implementation in very large scale integrated circuits is presented. This document details the mathematical models of AIM and the approximations and optimizations used to simplify the filtering and signal processing …

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New Neuron Model For Simulating Rotating Electrical Machines And Load Forecasting Problems, D. K. Chaturvedi, P. S. Satsangi, P. K. Kalra Nov 1999

New Neuron Model For Simulating Rotating Electrical Machines And Load Forecasting Problems, D. K. Chaturvedi, P. S. Satsangi, P. K. Kalra

D. K. Chaturvedi Dr.

The existing neuron structure has an aggregation function (usually summation) and its transformation through non-linear filter or squashing or thresholding functions. Such structure of neural networks has a number of disadvantages like large number of neurons, hidden layers and huge training data required for complex function approximations. The present paper proposes new neuron models to overcome the above problems in the existing neural networks. The model has been developed and tested for modelling of electrical machines like DC motor, induction motor and synchronous generator and load forecasting problems using different new neuron models in the neural network like S neuron …

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Study On Electrochemical Reduction Properties Of Nitrobenzene, Chuna Ma, Wenkui Zhang, Hui Huang, Yongping Gan Nov 1999

Study On Electrochemical Reduction Properties Of Nitrobenzene, Chuna Ma, Wenkui Zhang, Hui Huang, Yongping Gan

Journal of Electrochemistry

The electrochemical reduction characteristics of nitrobenzene was extensively investigated by using the techniques such as quasi_steady_state polarization,cyclic voltammetry,fast linear potential sweep method and chronoamperometry in this paper.The electroanalytic properties of Cu,Cu_Hg and Cu_Ni electrodes were evaluated.Based on the study of the transient steping behaviour of nitrobenzene to PAP,the reduction mechanism was discussed.The results showed that the transition steps existed on the electrochemical reduction of nitrobenzene in acidic solution,the reactant is also absorbed on electrodes surface. The control step in the reduction of nitrobenzene was ascribed to the diffusion of nitrobenzene and its electrochemical reductive products in the acid solution.

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Photoelectrochemical Studies On The Tio_2 Nanostructured Porous Film Sensitized By Cyanine Dye, Li Zhang, Maizhi Yang, Xuebin Qiao, Yanzhong Hao, Enqing Gao, Shengmin Cai Nov 1999

Photoelectrochemical Studies On The Tio_2 Nanostructured Porous Film Sensitized By Cyanine Dye, Li Zhang, Maizhi Yang, Xuebin Qiao, Yanzhong Hao, Enqing Gao, Shengmin Cai

Journal of Electrochemistry

The photoelectrochemical behaviors of the TiO 2 nanostructured porous film sensitized by cyanine dye were investigated in this paper.The results showed that the excitaed state level matched the conduction band edge of TiO 2 nanoparticle.Therefore the sensitization of the dye can increase the photocurrent intensity of the TiO 2 nanostructured electrode obviously and results in a red-shift of optical absorption from the ultra_violet region to the visible.As a result,the light_to _electricity conversion efficiency was improved evidently,the maximum value of IPCE has reached 12.1%.

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Studies Of The Electrode Preparation Of Electrode From Lead Carbonate For Lead Acid Battery Ⅰ The Activation Of The Pme, Zhongxu Dai, Dihua Wang, Junwei Jiang, Yunhong Zhou, Jinyun Zou Nov 1999

Studies Of The Electrode Preparation Of Electrode From Lead Carbonate For Lead Acid Battery Ⅰ The Activation Of The Pme, Zhongxu Dai, Dihua Wang, Junwei Jiang, Yunhong Zhou, Jinyun Zou

Journal of Electrochemistry

Lead carbonate which was an intermediate product in lead hydrometallurgy without pollution of lead vapor and sulfur dioxide was selected as electrode material of lead_acid batteries. In the present work,the performances of PbO 2/PbSO 4 or PbSO 4/Pb electrode transformed from PbCO 3 have been investigated by powder microelectrode technique combined with cyclic voltammetry.The results show that the CV characteristics of either negative or positive electrode prepared from PbCO 3 is as good as that of both electrodes made from lead oxide produced by mill machine,when a powder microelectrode with PbCO 3 transformed into PbSO 4 in 1.0 mol/L H …

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Studies On Methods Of Fuel Cells Electrodes Preparation, Jun Gu, Sheng Sui, Guangqiang Li, Zhitong Sui Nov 1999

Studies On Methods Of Fuel Cells Electrodes Preparation, Jun Gu, Sheng Sui, Guangqiang Li, Zhitong Sui

Journal of Electrochemistry

In fuel cells,the structure of electrodes is an important factor which effect the cell performance.To improve the structure and the performance of electrodes,a new method of providing fuel cell electrodes is proposed in this paper.PTFE(polytetrafluoroethylene) and ethyne black was ground for about half an hour in a high_speed grinder,then the catalyst was added into the grinder and milled for an hour.This milled catalyst was transferred into a mixer followed by the addition of surface_active agent. After a suspension was formed,it was filtered under vacuum condition.Then a thin uniform filter_cake of the catalyst was formed,which was rolled together with a current_collecting …

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The Electrochemical Behaviors Of Superoxide Dismutase At Promoter Modified Gold Electrode, Xiaqin Wu, Xiaoyun Meng, Zhesu Wang, Zongrang Zhang Nov 1999

The Electrochemical Behaviors Of Superoxide Dismutase At Promoter Modified Gold Electrode, Xiaqin Wu, Xiaoyun Meng, Zhesu Wang, Zongrang Zhang

Journal of Electrochemistry

The electron_transfer process of superoxide dismutase was investigated by cyclic voltammetry at the 4,4'_dithiodipyridine,L_cysteine,histidine and arginine modified gold wire electrodes repectively.The quasi_reversible behavior was observed at L_cysteine modified gold electrode.An irreversible electrochemical behavior has been observed at hisdinine modified gold wire electrode.

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High Performance Proton Exchange Membrane Fuel Cells, Jingrong Yu, Baolian Yi, Ming Han, Xiaoliang Cheng, Zhigang Shao, Jingxin Zhang Nov 1999

High Performance Proton Exchange Membrane Fuel Cells, Jingrong Yu, Baolian Yi, Ming Han, Xiaoliang Cheng, Zhigang Shao, Jingxin Zhang

Journal of Electrochemistry

Proton_exchange membrane fuel cells(PEMFC) using a perfluorosulfonic acid proton exchange membrane as an electrolyte can simplify water and electrolyte management.In this paper,the effects of thickness of PEM on the performance of PEMFC were studied.The Nafion_112 PEM and low platinum loading E_TEK electrode yielded very high power density,of the order of 0.95 W/cm 2.The energy_conversion efficiency,the degree of platinum utilization and stability for PEMFC using Nafion 112 and E_TEK electrode were also investigated.

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Electro Oxidation Of Phenol On Sno_2/Ti Electrodes Prepared By Thermal Oxidation, Qingsong Zhang, Huihuang Wu Nov 1999

Electro Oxidation Of Phenol On Sno_2/Ti Electrodes Prepared By Thermal Oxidation, Qingsong Zhang, Huihuang Wu

Journal of Electrochemistry

A SnO 2/Ti electrode prepared by thermal oxidation was used as the anode for galvanostatic electrolysis in acidic solution containing phenol, the time_dependances of phenol concentration,chemical oxygen demand in solution(COD)and instantaneous current efficiency were determined during electrolysis.The results show that with the SnO 2/Ti anode instead of Pt,the COD significantly decreases at the same charge passage, and average current efficiency of oxidation increases by three times The mechanism for phenol oxidation at two electrodes was discussed.

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Investigation Of Sodium Hypophosphite Anodic Oxidizing Behavior In The Process Of Acid Electroless Nickel Deposition, Meiyuan Wang, Yafei Kuang, Yan Xu Nov 1999

Investigation Of Sodium Hypophosphite Anodic Oxidizing Behavior In The Process Of Acid Electroless Nickel Deposition, Meiyuan Wang, Yafei Kuang, Yan Xu

Journal of Electrochemistry

The anodic oxidizing behavior of sodium hypophosphite in the process of electroless nickle deposition(pH=5.5) was investigated with the linear potential sweep method and alternating current impedance.The results indicated that,the oxidation of NaH 2PO 2 was a complicated electrochemical process and affected by the concentration of NaH 2PO 2, the temperature of the bath,the sweep rate and the existence of nickel ion. The NaH 2PO 2 electrooxidation reaction was very likely preceded by heterogeneous interface transformation process,which might be the control step of the whole anodic process.

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Numerical Calculation Of Diffraction Coefficients From Building Edges Using Fdtd Method, Weiting Cai Nov 1999

Numerical Calculation Of Diffraction Coefficients From Building Edges Using Fdtd Method, Weiting Cai

FIU Electronic Theses and Dissertations

Finite Difference Time Domain (FDTD) Method and software are applied to obtain diffraction waves from modulated Gaussian plane wave illumination for right angle wedges and Fast Fourier Transform (FFT) is used to get diffraction coefficients in a wideband in the illuminated lit region. Theta and Phi polarization in 3-dimensional, TM and TE polarization in 2-dimensional cases are considered respectively for soft and hard diffraction coefficients. Results using FDTD method of perfect electric conductor (PEC) wedge are compared with asymptotic expressions from Uniform Theory of Diffraction (UTD). Extend the PEC wedges to some homogenous conducting and dielectric building materials for diffraction …

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Method For Testing Field Programmable Gate Arrays, Charles E. Stroud, Miron Abramovici Nov 1999

Method For Testing Field Programmable Gate Arrays, Charles E. Stroud, Miron Abramovici

Electrical and Computer Engineering Faculty Patents

A method of testing field programmable gate arrays (FPGAs) includes the step of configuring programmable logic blocks of the FPGAs for completing a built-in self-test. Specifically, the FPGA under test may be configured to act as an iterative logic array wherein a first group of programmable logic blocks are configured as test pattern generators, output response analyzers and helper cells, and a second group of programmable logic blocks are configured as blocks under test. The blocks under test are then repeatedly reconfigured in order to completely test each block under test in all possible modes of operation. The first and …

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Method Of Arc Welding Using Dual Serial Opposed Torches, Yuming Zhang, Shaobin Zhang Nov 1999

Method Of Arc Welding Using Dual Serial Opposed Torches, Yuming Zhang, Shaobin Zhang

Electrical and Computer Engineering Faculty Patents

An improved method of arc welding uses a single power supply connected to opposed welding torches placed on both sides of a workpiece. Each torch is connected to a different polarity lead of the power supply and forms a separate arc with the workpiece. When a current is supplied to the first torch, it is guided from the first electrode, through the first arc, the workpiece, the second arc, and to the electrode of the second torch. This guiding function improves the penetration, concentration, as well as the directional stability of the arc. This permits the effective and efficient welding …

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Electroluminescent Device Comprising A Transparent Structured Electrode Layer Made From A Conductive Polymer, Aemilianus G. J. Staring, David Braun Nov 1999

Electroluminescent Device Comprising A Transparent Structured Electrode Layer Made From A Conductive Polymer, Aemilianus G. J. Staring, David Braun

Electrical Engineering

A description is given of an electroluminescent (EL) device (1) composed of polymeric LEDs comprising an active layer (7) of a conjugated polymer and a transparent polymeric electrode layer (5) having electroconductive areas (51) as electrodes. Like the active layer (7), the electrode layer (5) can be manufactured in a simple manner by spin coating. The electrode layer (5) is structured into conductive electrodes (51) by exposure to UV light. The electrodes (9) and (51) jointly form a matrix of LEDs for a display. When a flexible substrate (3) is used, a very bendable EL device is obtained.

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Undergraduate Research Participation In Electrical Engineering, John F. Vetelino Nov 1999

Undergraduate Research Participation In Electrical Engineering, John F. Vetelino

University of Maine Office of Research Administration: Grant Reports

The Electrical Engineering Department at the University of Maine will offer ten undergraduate students the opportunity to participate in research. The available research projects include: 1. Microwave Acoustic solid State Sensors, 2. Robotics, Computer Vision and Neural Processing, 3. Communications Devices and Applications, 4. Motion Control, 5. Microprocessing/Instrumentation Applications, 6. Macroscopic and Microscopic Characterization of Metallic Films, and 7. Power Systems Applications. in addition to extensive University of Maine facilities, the students will also have access to facilities at nearby industries such as Bangor Hydro Electric Power and Central Maine Power Companies, James River, Champion and Scott paper Companies, Digital …

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Knowledge Based Neural Network For Voltage Contingency Selection And Ranking, Sn Singh, L Srivastava, Jd Sharma Nov 1999

Knowledge Based Neural Network For Voltage Contingency Selection And Ranking, Sn Singh, L Srivastava, Jd Sharma

SN Singh PhD

No abstract provided.

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Crossover Photonic Switching Network With Cmos/Seed Smart Pixel Device And 2d Optical Fiber Bundle Array, Fengguang Luo, Mingcui Cao, Qiaoyan Hu, Anjun Wan, Jun Xu, Cong Deng, Deming Liu Nov 1999

Crossover Photonic Switching Network With Cmos/Seed Smart Pixel Device And 2d Optical Fiber Bundle Array, Fengguang Luo, Mingcui Cao, Qiaoyan Hu, Anjun Wan, Jun Xu, Cong Deng, Deming Liu

Electro-Optics and Photonics Faculty Publications

A 16 X 16 Crossover photonic switching network with hybrid integrated CMOS/SEED smart pixel device and 2D optical fiber bundle array I/O access device is reported in this paper. SEEd array devices ar used as light receivers and transmitters, while CMOS devices make efficient logical processing. 4 X 40 2D multilayer optical fiber bundle arrays are fabricated and are used as I/O access devices in the crossover photonic switching network. The center to center spacing between adjacent optical fibers in the same layer of the fiber array is 125micrometers , and the spacing between adjacent layers is 250micrometers . Displacing …

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Piezoelectric Doping In Alingan/Gan Heterostructures, M. Asif Khan, J. W. Yang, Grigory Simin, R. Gaska, M. S. Shur, A. D. Bykovski Nov 1999

Piezoelectric Doping In Alingan/Gan Heterostructures, M. Asif Khan, J. W. Yang, Grigory Simin, R. Gaska, M. S. Shur, A. D. Bykovski

Faculty Publications

We report on the piezoelectricdoping and two-dimensional (2D) electron mobility in AlInGaN/GaN heterostructures grown on 6H–SiC substrates. The contribution of piezoelectricdoping to the sheet electron density was determined using an In-controlled built-in strain-modulation technique. Our results demonstrate that in strained AlGaN/GaN heterostructures, the piezoelectric field generates at least 50% of the 2D electrons. The strain modulation changes the potential distribution at the heterointerface, which, in turn, strongly affects the 2D electron mobility, especially at cryogenic temperatures. The obtained results demonstrate the potential of strain engineering and piezoelectricdoping for GaN-based electronics.

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Low-Frequency Noise In N-Gan With High Electron Mobility, M. E. Levinshtein, S. L. Rumyantsev, D. C. Look, R. J. Molnar, M. Asif Khan, Grigory Simin, V. Adivarahan, M. S. Shur Nov 1999

Low-Frequency Noise In N-Gan With High Electron Mobility, M. E. Levinshtein, S. L. Rumyantsev, D. C. Look, R. J. Molnar, M. Asif Khan, Grigory Simin, V. Adivarahan, M. S. Shur

Faculty Publications

We report on the results of measurements of low frequency noise in n-type gallium nitride (GaN) grown on sapphire with 300 K electron mobility of 790 cm2/V s. The noise spectra have the form of 1/f noise with a Hooge parameter α of approximately 5×10−2. This value of α is two orders of magnitude smaller than that observed before in n-GaN. The obtained results show that the level of flicker noise in GaN, just like that in GaAs and Si, strongly depends on the structural perfection of the material (the amplitude of the 1/f …

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Accuracy Of Scatterometer-Derived Winds Using The Cramer-Rao Bound, David G. Long, Travis E. Oliphant Nov 1999

Accuracy Of Scatterometer-Derived Winds Using The Cramer-Rao Bound, David G. Long, Travis E. Oliphant

Faculty Publications

A wind scatterometer makes measurements of the normalized radar-backscatter coefficient O of the ocean surface. To retrieve the wind, a geophysical model function (GMF), which relates O to the near-surface wind, is used. The wind vector can be estimated using maximum-likelihood techniques from several O measurements made at different azimuth angles. The probability density of the measured O is assumed to be Gaussian with a variance that depends on the true O and therefore, depends on the wind through the GMF. With this model for wind estimation, the Cramer-Rao (C-R) bound is derived for wind estimation, and its implications for …

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Coulomb Crystals And Glasses For Self-Assembly Of Nanoparticles, P. F. Williams, A. Belolipetski, A. Goussev, M. E. Markes Oct 1999

Coulomb Crystals And Glasses For Self-Assembly Of Nanoparticles, P. F. Williams, A. Belolipetski, A. Goussev, M. E. Markes

P. F. (Paul Frazer) Williams Publications

Under proper conditions, small particles may be suspended in a regularly-spaced array called a Coulomb crystal. In this paper we discuss the application of this phenomenon to the self-assembly of nanoparticles in a lattice-lie array on a substrate. Issues associated with depositing the particles, and the size and lattice spacing of the particles are discussed.

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Carrier Concentration And Lattice Absorption In Bulk And Epitaxial Silicon Carbide Determined Using Infrared Ellipsometry, Thomas E. Tiwald, John A. Woollam, Stefan Zollner, Jim Christiansen, R. B. Gregory, T. Wetteroth, S. R. Wilson, Adrian R. Powell Oct 1999

Carrier Concentration And Lattice Absorption In Bulk And Epitaxial Silicon Carbide Determined Using Infrared Ellipsometry, Thomas E. Tiwald, John A. Woollam, Stefan Zollner, Jim Christiansen, R. B. Gregory, T. Wetteroth, S. R. Wilson, Adrian R. Powell

Department of Electrical and Computer Engineering: Faculty Publications

We have measured the dielectric function of bulk nitrogen-doped 4H and 6H SiC substrates from 700 to 4000 cm-1 using Fourier-transform infrared spectroscopic ellipsometry. Photon absorption by transverse optical phonons produces a strong reststrahlen band between 797 and 1000 cm-1 with the effects of phonon anisotropy being observed in the region of the longitudinal phonon energy (960 to 100 cm-1). The shape of this band is influenced by plasma oscillations of free electrons, which we describe with a classical Drude equation. For the 6H-SiC samples, we modify the Drude equation to account for the strong effective …

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Temperature Dependence Of Electrical And Optical Modulation Responses Of Quantum-Well Lasers, T. Keating, Xiaomin Jin, Shun Lien Chuang, K. Hess Oct 1999

Temperature Dependence Of Electrical And Optical Modulation Responses Of Quantum-Well Lasers, T. Keating, Xiaomin Jin, Shun Lien Chuang, K. Hess

Electrical Engineering

We present theory and experiment for high-speed optical injection in the absorption region of a quantum-well laser and compare the results with those of electrical injection including the carrier transport effect. We show that the main difference between the two responses is the low-frequency roll-off. By using both injection methods, we obtain more accurate and consistent measurements of many important dynamic laser parameters, including the differential gain, carrier lifetime, K factor, and gain compression factor. Temperature-dependent data of the test laser are presented which show that the most dominant effect is the linear degradation of differential gain and injection efficiency …

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