Engineering Commons^™

Metamodeling Aspects Of Model Conceptualization, Wayne W. Wakeland

Complex Systems Faculty Publications and Presentations

This paper suggests a technique for improving the conceptualization of models. The key aspect of this technique is to set aside the main model for a period of time during the model conceptualization process and focus on building a "watchdog" submodel. The primary purpose of the watchdog submodel is to assure that the main model remains internally consistent during its operation. In the experience of this author, such a submodel can help to identify model conceptualization errors and to determine if a model is sufficiently "robust" to adequately replicate the behavior of the system being modeled.

This is not a …

Principles And Clinical Applications Of Magnetic Resonance, Rao P. Gullapalli, Teresa T. Evans, Roger M. Hawk

Journal of the Arkansas Academy of Science

A review is presented which covers the basic theory of nuclear magnetic resonance (NMR) with regard to angular momentum, magnetic moments, and the classical mechanical description of the NMR experiment. Longitudinal (T,) and Transverse (T2) relaxation times are defined as well as the basic pulse sequences used for their measurement. In particular, the 180°-t-90° and the Hahn Spin Echo pulse sequences are described in detail. Basic Magnetic Resonance Imaging (MRI) theory is discussed with regard to slice selection, frequency encoding, and phase encoding to define the imaged volume element. The equations defining the amount of Tt , T2 , and …

Effect Of Central Station Photovoltaic Plant On Power System Security, Badrul H. Chowdhury

Electrical and Computer Engineering Faculty Research & Creative Works

The value of photovoltaic (PV) plants to electric utilities is investigated under constraints of power system security. It is suggested that the generally adopted methods of analysis for determining the capacity credit, energy displacement, and production cost savings due to the PV plants have neglected the adverse conditions that may arise out of a random preselection of a substation where PV power is injected into the system. The author presents an extensive approach to determining the realistic value of a PV plant to the utility. The method consists of using a power flow algorithm to determine system conditions under specific …

Analysis Of Wind Power Integration With Power System Planning, Badrul H. Chowdhury

Electrical and Computer Engineering Faculty Research & Creative Works

No abstract provided.

A Review Of Recent Advances In Economic Dispatch, Badrul H. Chowdhury, S. Rahman

Electrical and Computer Engineering Faculty Research & Creative Works

A survey is presented of papers and reports that address various aspects of economic dispatch. The time period considered is 1977-88. Four related areas of economic dispatch are identified and papers published in the general areas of economic dispatch are classified into these. These areas are: optimal power flow, economic dispatch in relation to AGC, dynamic dispatch, and economic dispatch with nonconventional generation sources.

Effect Of Viscoplastic Flow Rules On The Initiation And Growth Of Shear Bands At High Strain Rates, R. C. Batra, Chang-Soo Kim

Mechanical and Aerospace Engineering Faculty Research & Creative Works

Marchand and Duffy have reported detailed measurements of the temperature and strain as a shear band develops in a HY-100 steel. Assuming their torsional tests in thin-wall tubes can be adequately modeled by a viscoplastic block undergoing overall adiabatic simple shearing deformations, we investigate the effect of modeling the viscoplastic response of the material by a.power law, and flow rules proposed by Litonski, Bodner and Partom, and Johnson and Cook. Each of these flow rules is first calibrated by using the test data at a nominal strain-rate of 3300 s-1. Then predictions from the use of these flow rules at …

A Two-Dimensional Analog Vlsi Circuit For Detecting Discontinuities In Early Vision, John G. Harris, Christof Koch, Jin Luo

Electrical and Computer Engineering Faculty Research & Creative Works

A large number of computer vision algorithms for finding intensity edges, computing motion, depth, and color, and recovering the three-dimensional shape of objects have been developed within the framework of minimizing an associated "energy" or "cost" functional. Particularly successful has been the introduction of binary variables coding for discontinuities in intensity, optical flow field, depth, and other variables, allowing image segmentation to occur in these modalities. The associated nonconvex variational functionals can be mapped onto analog, resistive networks, such that the stationary voltage distribution in the network corresponds to a minimum of the functional. The performance of an experimental analog …

Transistor-Based Measurements Of Electron Injection Currents In P-Type Gaas Doped 1018–1020 Cm-3, M. E. Klausmeier-Brown, M. R. Melloch, Mark S. Lundstrom

Department of Electrical and Computer Engineering Faculty Publications

Measurements of electron currents injected into p+‐GaAs are presented for molecular beam epitaxially grown material doped from 2×1018 to 8×1019 cm−3 with Be. The collector current versus base‐emitter voltage characteristics of n‐p+‐n GaAs homojunction bipolar transistors are analyzed, and the results are interpreted in terms of the quantity (n0Dn), where n0 is the equilibrium minority‐carrier concentration and Dn is the minority‐carrier diffusion coefficient. The results are consistent with earlier measurements of (n0Dn) made using metalorganic chemical vapor deposited p+‐n GaAs solar …

High‐Efficiency Al0.22ga0.78as Solar Cells Grown By Molecular Beam Epitaxy, Michael R. Melloch, S. P. Tobin, C. Bajgar, A. Keshavarzi, T. B. Stellwag, G. B. Lush, Mark S. Lundstrom, K. Emery

Department of Electrical and Computer Engineering Faculty Publications

The quality of pn junction photodetectors made of Al0.2Ga0.8As has been investigated as a first step in the optimization of tandem solar cells. We have obtained 1 sun AM1.5 efficiencies of 16.1% for 0.25 cm2 Al0.22Ga0.78As solar cellsfabricated from molecular beam epitaxy (MBE) material. This efficiency is 3.2 percentage points higher than the previously best reported efficiency of 12.9% for an Al0.2Ga0.8As solar cell fabricated from MBE material.

Surface Passivation Effects Of As2s3 Glass On Self‐Aligned Algaas/Gaas Heterojunction Bipolar Transistors, H. L. Chuang, M. S. Carpenter, Michael R. Melloch, Mark S. Lundstrom, E. Yablonovitch, T. J. Gmitter

Department of Electrical and Computer Engineering Faculty Publications

A recently developed As₂S₃ chemical treatment was used to passivate the perimeters of self‐aligned heterojunction bipolar transistors (HBTs). The As₂S₃chemical treatment significantly lowered the base current resulting in a two order of magnitude reduction in the collector current density at which dc current gain was observed (β=1). No degradation with time has been observed in the electrical characteristics of the chemically treated HBTs. This absence of degradation is attributed to the impermeability to oxygen of the As2S3 glass which coats the perimeter of the HBT after chemical treatment.

Orientation-Dependent Perimeter Recombination In Gaas Diodes, T. B. Stellwag, Michael R. Melloch, Mark S. Lundstrom, M. S. Carpenter, R. F. Pierret

Department of Electrical and Computer Engineering Faculty Publications

Perimeter recombination currents affect the performance of GaAs-based devices such as solar cells, heterojunction bipolar transistors, and injection lasers. We report that the n SEf 2 perimeter recombination current has a strong orientation dependence. More than a factor of five variation in the surface recombination current at mesa-etched edges has been observed. These results suggest that with proper device design, perimeter recombination currents could be substantially reduced.

Instrument Matrix Of The Four-Detector Photopolarimeter: Physical Meaning Of Its Rows And Columns And Constraints On Its Elements, R. M.A. Azzam

Electrical Engineering Faculty Publications

The four-detector photopolarimeter (FDP) is an arrangement of four photodetectors for measuring the state of polarization of light. The output current vector I of the FDP is related to the input Stokes vector S by I = AS, where A is the instrument matrix. The rows of A can be viewed as projection operators that determine the output currents of the detectors. This leads to the recognition of four special totally polarized input states, each of which maximizes the output of one detector. The associated four orthogonal states produce minimum signals. Because each detector is absorptive and its output is …

Ground Exploitation Using A Binary Phase-Only Optical Correlator, Samuel Peter Kozaitis, Sandra L. Halby, Wesley E. Foor

Electrical Engineering and Computer Science Faculty Publications

Experimental results of an optical binary phase-only correlator using aerial imagery for ground exploitation is presented. The correlator uses magnetooptic spatial light modulators (SLMs) for dynamic operation. Input images to the correlator originate from actual aerial imagery containing aircraft and a variety of distortions. Digital image processing techniques are used on images before being input into the optical correlator to enhance the performance of the system. Filters or templates used as a database for the system are derived from models of aircraft. Rotation and scale invariance is achieved through an adaptive filtering technique in which filters are displayed sequentially against …

Electrical Properties Of Hydrogenated Diamond, Sacharia Albin, Linwood Watkins

Electrical & Computer Engineering Faculty Publications

Hydrogen passivation of deep traps in diamond is demonstrated. Current‐voltage (I‐V) characteristics of polycrystalline thin film and bulk diamond were studied before and after hydrogenation. On hydrogenation, all the samples showed several orders of magnitude increase in conductivity. Hydrogenation was carried out under controlled conditions to study the changes in the I‐V characteristics of the samples. The concentration of uncompensated traps was varied systematically by hydrogenation. The concentration of electrically active hydrogen was determined from the I‐V data. It is shown that hydrogenation is an alternative to deep‐level transient spectroscopy, suitable for …

Measurement Of Magnetic Fluctuations By O-X Mode Conversion, L. L. Vahala, G. Vahala, N. Bretz

Electrical & Computer Engineering Faculty Publications

The possibility of measuring magnetic fluctuations in a fusion plasma is considered by examining the O→X mode conversion. Under certain conditions and with good angular resolution, this mode conversion can be attributed to the presence of magnetic fluctuations even though the level of these fluctuations is much lower than that of density fluctuations. Some nonideal effects such as mode polarization mismatch at the plasma edge are also discussed.

The Object-Oriented Design Of A Hardware Description Language Analyser For The Diades Silicon Compiler System, Lian Yang

Dissertations and Theses

This thesis is one of the first to introduce a systematic and general Source Language Analysis System (called SLA) for a high -level synthesis system.

Threaded Octree Structures For Fast Neighbor Voxel Processing In A Parallel Ray Tracer, B.R. Naveen Chandra

Dissertations and Theses

In the field of Computer Graphics, Ray Tracing has so far been the the best algorithm for rendering of realistic three dimensional images created by mathematical models. Ray Tracing is also known for its very large computation times, where the computation depends on the picture resolution, the number of objects and the complexity of the scene.

Contours Of Constant Pseudo-Brewster Angle In The Complex Є Plane And An Analytical Method For The Determination Of Optical Constants, R. M.A. Azzam, Ericson E. Ugbo

Electrical Engineering Faculty Publications

The locus of all points in the complex plane of the dielectric function є[є_r + jє_i = |є| exp(jθ)], that represent all possible interfaces characterized by the same pseudo-Brewster angle θ_pB of minimum p reflectance, is derived in the polar form: |є| = l cos(ζ/3), where l = 2(tan²Φ_pB)k, ζ = arccos(- cosθ cos²Φ_pB/k³), and k = (1 - 2/3 sin²Φ_pB)½. Families of iso-Φ_pB contours for (I) 0° ≤ Φ_pB ≤ …

Enhanced Magneto-Optic Kerr Effects In Thin Magnetic/Metallic Layered Structures, William A. Mcgahan, Liang-Yao Chen, Z. S. Shan, David J. Sellmyer, John A. Woollam

Department of Electrical and Computer Engineering: Faculty Publications

Enhanced Kerr rotation spectra are measured in thin magnetic layers on silver. Also, variable angle of incidence spectroscopic ellipsometry is employed to measure the optical dielectric function of both the thin magnetic layer and the underlying thick silver layer. These results are explained quantitatively using the electromagnetic theory for reflection of light from multiple layers of isotropic and gyrotropic materials.

Dynamic Behavior Of Co₂ Lasers, Li Zhang

Dissertations and Theses

Spontaneous pulsations have been observed in the output of a CO₂ laser. The temporal waveforms, transverse mode patterns, and laser lines are simultaneously measured under various operation conditions. The experimental data show that these pulsations have a direct connection with the transverse modes. We interpret the oscillations as being caused by mode beating, and the frequency shift of the oscillation as resulting from mode pulling. The theoretical explanations for these effects are in good agreement with the experimental results.

Endless State-Of-Polarization Control For Coherent Optical Communication Systems Using Nematic Liquid Crystal, Scott H. Rumbaugh

Dissertations and Theses

One of the obstacles to coherent fiber-optic communications is the unpredictable polarization drift which necessitates the use of an active polarization controlling system to match the polarizations of the signal and local oscillator. The polarization match must be maintained during the reset of any of the finite range components to prevent loss of data. We present a novel and practical system which uses three liquid crystal devices for the polarization matching process. Also, the required reset control algorithm and its derivation are described in detail.

Ellipsometric Study Of Al2O3/Ag/Si And Sio2/Ag/Quartz Ashed In An Oxygen Plasma, Bhola N. De, John A. Woollam

Department of Electrical and Computer Engineering: Faculty Publications

Using monolayer-sensitive variable angle of incidence spectroscopic ellipsometry, the silver oxide growth on a silver mirror, coated with an Al₂ O₃ or SiO₂ protective layer, was investigated. The oxidation was done in a pure oxygen plasma asher. The resulting silver oxide growth was monitored accurately as a function of exposure time in the plasma asher. It was found that silver was converted to silver oxide under the protective coating, during ashing of a sample. The optical constants of a dense silver oxide thin film, created by oxidizing in the asher, were also measured.

Propagation Of Millimeter Wave Signals In Forests Using The Equation Of Radiative Transfer With Strong Forward Scattering Phase Functions, Nack Yang Cho

Dissertations

A forest is a highly scattering medium at millimeter wave frequencies. The propagation of cw millimeter wave signals in forests has been studied previously, both theoretically and experimentally. Published experimental data verified that continuous wave transmission is possible over lengths of the order of a few hundred meters and that a forest acts to strongly scatter energy in the forward direction. The cw studies yielded the determination of the range dependence, beam broadening effects and depolarization effects of millimeter wave signals in a forest. However, pulse broadening effects, which are of importance particularly in the case of digital signal transmission, …

An Approach To Pattern Recognition Of Multifont Printed Alphabet Using Conceptual Graph Theory And Neural Networks, Ihab A. Harb

Dissertations and Theses

This thesis describes an approach for accomplishing a pattern recognition task using conceptual graph theory and neural networks (NNs). The set of patterns to be recognized are the capital letters of six different fonts of the English alphabet, plus two shifted and six rotated versions of each. The letters are represented to the neural network on a 16x16 input grid (256 "sensor lines"). A standard classification encoding for such patterns is to use a 26-bit vector (26 lines at the NN's output), one bit corresponding to each letter. Experiments with such an encoding yielded results with poor generalization capability. A …

Scattering By A Narrow Gap In An Impedance Plane, John R. Natzke

Faculty Publications - Department of Electrical Engineering and Computer Science

No abstract provided.

Triggering In Trigatron Spark Gaps: A Fundamental Study, P. F. Williams, F. E. Peterkin

P. F. (Paul Frazer) Williams Publications

The trigatron has been in widespread use as a demand-triggered, high-voltage switch for more than 40 years. In spite of the popularity and maturity of the technology, there persists an uncertainty over the basic physical mechanism(s) responsible for triggering breakdown in the devices. We present the results of an empirical study of trigatrons that demonstrates that breakdown is initiated by a streamer launched from the trigger pin, independent of the trigger spark. We compare our results with those of previous workers, and discuss the generality of our conclusions.

Transient Stability Hierarchical Control In Multimachine Power Systems, A Rubbai, F. Eugenio Villaseca

Electrical and Computer Engineering Faculty Publications

The authors present the optimal transient stability control problem in a hierarchical structure for multimachine power systems. The two-level structure retains the local closed-loop controls, thereby easing its implementation on existing systems. The formulation accounts for nonlinearities and interconnections, and the optimization of the system transient performance is obtained with less computational effort. Since the computations are distributed among the many local feedback subsystems, the storage and solution times are considerably less than those required by a single overall centralized controller. This advantage becomes much stronger as the system size increases. For illustration purposes, this technique was applied successfully to …

Use Of Technology For Undergraduate Engineering Education, B. A. Black, J. S. Demetry, J. G. Harris, J. R. Jones

Electrical Engineering

California Polytechnic State University, Rose-Hulman Institute of Technology, University of Alabama at Birmingham, and Worcester Polytechnic Institute have formed a consortium to develop an alternative learning environment centered around a workstation comprised of a personal computer interfaced to a video disk and laboratory instrumentation. The first phase in their collective effort has involved the development of four instructional modules in the fundamentals of electrical engineering. The results of the first phase efforts are presented. They demonstrate how four different universities can work together to agree on standards, and to prepare instructional material that can be shared. The second phase will …

Accurate Calibration Of The Four-Detector Photopolarimeter With Imperfect Polarizing Optical Elements, R. M.A. Azzam, Ali G. Lopez

Electrical Engineering Faculty Publications

The first three columns of the instrument matrix A of the four-detector photopolarimeter (FDP) are determined by Fourier analysis of the output current vector I(P) as a function of the azimuth angle P of the incident linearly polarized light. Therefore 12 of the 16 elements of A are measured free of the imperfections of the (absent) quarter-wave retarder (QWR). The effect of angular beam deviation by the polarizer is compensated for by taking the average, (1/2) [I(P) + I(P + 180°)], of the FDP output at 180°-apart, optically equivalent, angular positions of the polarizer. The remaining fourth column of A …

The Electrical Characteristics Of Semi-Insulating Gallium Arsenide A Material For High Power Switches, David Clifton Stoudt

Electrical & Computer Engineering Theses & Dissertations

An experimental study of the electrical characteristics of semi-insulating gallium arsenide has been performed. The goal of this research was to aid in the development of an electron-beam controlled high-power semiconductor switch. The electrical characteristics were found to be heavily dependent on the deep level configuration of the material being investigated. Two methods of deep level characterization are discussed and their results are compared to the information given by the material manufacturer. Studies were conducted to determine both the steady-state and transient dark current characteristics of the switch. Along with being a function of the applied voltage and the deep …