Digital Commons Network^™

Metal Modulation Epitaxy Growth For Extremely High Hole Concentrations Above 10(19) Cm(-3) In Gan, Gon Namkoong, Elaissa Trybus, Kyung Keun Lee, Michael Moseley, W. Alan Doolittle, David C. Look

Applied Research Center Publications

The free hole carriers in GaN have been limited to concentrations in the low 10¹⁸ cm⁻³ range due to the deep activation energy, lower solubility, and compensation from defects, therefore, limiting doping efficiency to about 1%. Herein, we report an enhanced doping efficiency up to ~10% in GaN by a periodic doping, metal modulation epitaxy growth technique. The hole concentrations grown by periodically modulating Ga atoms and Mg dopants were over ~1.5 x 10¹⁹ cm⁻³.

© 2008 American Institute of Physics.

Optimization Of Optical Computed Tomography Techniques For The Synthesis Of Particle Aggregate Models, Patrick Anthony Giordano Jr.

Theses and Dissertations

The characterization of 3-D shapes of particles in geomaterial aggregate mixtures is important for understanding the micro-mechanics of granular materials. Also, numerical synthesis of 3-D particle shapes from their corresponding shape descriptors is required for developing discrete element models (DEMs) that can be used to predict particle contact-forces, and ultimately the shear strength of the aggregate mixture.

Previous work has shown that Fourier-based 3-D shape descriptors can be constructed for aggregate mixtures, using a statistical combination of 2-D projections. Furthermore, optical tomography methods using the Algebraic Reconstruction Technique (ART) algorithm has proved capable of synthesizing 3-D shapes from 2-D projections, …

Interactive Visualization Of Information Hierarchies And Applications On The Web, Confesor Santiago Iii

Theses and Dissertations

The visualization of information hierarchies is concerned with the presentation of abstract hierarchical information about relationships between various entities. It has many applications in diverse domains such as software engineering, information systems, biology, and chemistry. Information hierarchies are typically modeled by an abstract tree, where vertices are entities and edges represent relationships between entities. The aim of visualizing tree drawings is to automatically produce drawings of trees which clearly reflect the relationships of the information hierarchy.

This thesis is primarily concerned with problems related to the automatic generation of area-efficient grid drawings of trees, interactively visualizing information hierarchies, and applying …

Development Of The Impedance-Based Arc-Flash Determination Device (Iadd), Timothy Smith

All Theses

This thesis entitled, 'Development of the Impedance based Arc-Fault Determination Device (IADD)' details the development of a testing device that, when attached to an electrical node on the power system and through observations on voltage, current and phase shift with a step load change, determines the effective Thevenin or Norton impedance at the point of test. This thesis includes discussion of the theory and design process that enables the determination of an equivalent circuit, software development using National Instruments' LabView software development package and suggestions for future development.
The purpose of this thesis is to produce a device that can …

Fabrication, Electrical Characterization, And Annealing Of Al/, Cu/, And Au/4h-Sic Schottky Diodes, Nikhil Karkhanis

All Theses

Schottky diodes were fabricated on n-type 4H-SiC with Nickel ohmic contacts and Aluminum, Copper, and Gold Schottky contacts. An improved and revised fabrication process was developed in the course of this research project. The Schottky diodes were electrically characterized using I-V and C-V measurements to extract electrical parameters which include Schottky barrier height, ideality factor, the diode series resistance, and substrate doping density. Al/4H-SiC and Au/4H-SiC were annealed at 600¼C and 500¼C respectively to improve the Schottky parameters. Schottky barrier height was raised and the ideality factor was reduced in both cases. Significant improvement was observed in the ideality factor …

Distance Estimation Between Transceivers Over Short Distances, Karsten Lowe

All Theses

Three methods for determining distances between a user and a fixed coordinate system are considered. One system is based on 802.11g packet communications, another on HF radio carrier frequency interference, and the final system on a signal transmitted over a radio channel. Emphasis is placed on the use of these systems in indoor, building-sized environments. Tests are performed to examine the effectivness and potential of these methods. None of the suggested methods are determined to be usable. Reasons for their failure are examined.

Wafer Probe And Package Test Failure Analysis, Deepa Kalva

All Theses

In recent years, NAND flash memory has gained a lot of momentum in the semiconductor industry and has become an ideal choice for many consumer and communication products. One of the key elements in the successful production of NAND flash memory is to incorporate elaborate testing methods to ensure functionality and reliability before the part reaches the customer. This in turn necessitates the evaluation and understanding of different failure mechanisms, and the development of methodologies to correct problems.
In this thesis, failure analysis was performed on NAND flash memory at wafer and package level. This involved massive data collection and …

Techniques For Improving The Performance Of Coupled Oscillator Arrays, Venkatesh Seetharam

All Dissertations

Coupled oscillator arrays (COAs) have excellent synchronization properties that can be utilized to develop a low cost alternative to phased array systems for beam steering applications. The primary concerns in implementing the COA architecture are the sensitivity to cell-to-cell component variation and poor phase noise performance. Wide injection locking range oscillators reduce the sensitivity to component variation but degrade the array phase noise performance. The objective of this dissertation is to alleviate the concerns hindering the application of COAs by employing techniques to realize COAs with wide mutual injection locking ranges (MILR), improved phase noise characteristics and beam steering capabilities. …

High Quality Molecular Beam Epitaxy Growth And Characterization Of Lead Titanate Zirconate Based Complex-Oxides, Xing Gu

Theses and Dissertations

Research interest in complex oxides has resurged owing to progress in modern epitaxial techniques. Among such oxides, lead-titanate-based thin films such as PbTiO₃ (PTO) and Pb(Zr_xTi_1−x)O₃ (PZT) offer attractive advantages for a wide variety of applications. Moreover, integration between functional oxides with compound semiconductors has the potential to realize multi-functional devices which enjoy the properties from both groups of materials. Ferroelectric materials with a perovskite structure (ABO₃) and semiconductors such as GaN with a hexagonal structure, require a careful choice of a bridge layer and suitable epitaxial technique. Molecular beam epitaxy (MBE) …

The Effect Of Contact Length On Adhesion Between Carbon Nanotubes On Silicon Dioxide, Robert C. Davis, Kaylee Mcelroy, Aaron R. Hopkins

Faculty Publications

The force of adhesion was measured for single walled carbon nanotubes grown over lithographically defined silicon dioxide trenches. We varied contact lengths between the nanotubes and silicon dioxide from 230 to 850 nm. Suspended nanotubes were pushed vertically into the trenches with an atomic force microscope tip, causing them to slip along the surface. Previous work done at shorter contact lengths found that tension was constant with contact length [J. D. Whittaker et al., Nano Lett. 6, 953 (2006)]. This study finds that when the nanotube contact length approaches 1 µm, the tension at which nanotubes slip begins to increase …

College Of Engineering Senior Design Competition Fall 2007, University Of Nevada, Las Vegas

Fred and Harriet Cox Senior Design Competition Projects

Part of every UNLV engineering student’s academic experience, the senior design project stimulates engineering innovation and entrepreneurship. Each student in their senior year chooses, plans, designs, and prototypes a product in this required element of the curriculum. A capstone to the student’s educational career, the senior design project encourages the student to use everything learned in the engineering program to create a practical, real world solution to an engineering challenge.

The senior design competition helps to focus the senior students in increasing the quality and potential for commercial application for their design projects. Judges from local industry evaluate the projects …

Formulation Of Integral Equations Using Analytic Green's Functions In Elliptic Cylindrical And Prolate Spheroidal Coordinates, Adam Schreiber

All Theses

It is desired to develop and present techniques, using analytic Green's functions in elliptic cylindrical coordinates and in prolate spheroidal coordinates, for formulating integral equations for physically practicable structures and sources. Equivalent models for two structures are introduced which serve as guides in the derivation of analytic Greens functions, comprising special functions and satisfying required boundary conditions. Expressions for needed field components are represented in terms of integrals of Greens functions times unknowns, and integral equations follow from the proper relationships among sources and field components needed to satisfy Maxwell's equations.

Optimal Sizing And Location Of Static And Dynamic Reactive Power Compensation, Wenjuan Zhang

Doctoral Dissertations

The key of reactive power planning (RPP), or Var planning, is the optimal allocation of reactive power sources considering location and size. Traditionally, the locations for placing new Var sources were either simply estimated or directly assumed. Recent research works have presented some rigorous optimization-based methods in RPP. Different constraints are the key of various optimization models, identified as Optimal Power Flow (OPF) model, Security Constrained OPF (SCOPF) model, and Voltage Stability Constrained OPF model (VSCOPF).

First, this work investigates the economic benefits from local reactive power compensation including reduced losses, shifting reactive power flow to real power flow, and …

Electro-Thermal Modeling Of Sic Power Electronic Systems, Hui Zhang

Doctoral Dissertations

As the development of Silicon (Si) semiconductor technology slows down due to its material limitations, more and more attention is being paid to wide bandgap material based semiconductor technology. Silicon Carbide (SiC) has been widely recognized as the material for next generation power electronic devices. However, a great deal of work needs to be done before SiC power devices can be widely applied. This dissertation addresses this need and has conducted research on the modeling of SiC power electronic system. More specifically, a method for system modeling of a SiC power system based on basic physics and device tests is …

Life Cycle Aware Computing: Reusing Silicon Technology, John Y. Oliver, Rajeevan Amirtharajah, Venkatesh Akella, Roland Geyer, Frederic T. Chong

Electrical Engineering

Despite the high costs associated with processor manufacturing, the typical chip is used for only a fraction of its expected lifetime. Reusing processors would create a "food chain" of electronic devices that amortizes the energy required to build chips over several computing generations.

Agricultural Applications For Electromagnetic Exposure, H. Aliakbarian, A. Enayati, Hossein Ameri Mahabadi, M. Ashayer Soltani

Hossein Ameri Mahabadi

Despite the advances in bug controlling and antifreezing operations of agricultural products, the devastation of Sunne pests and freezing is still enormous. Traditional treatments such as chemical insecticides for bug controlling and covering to avoid freezing have not been sufficient. In the presented paper, new ideas of using electromagnetic treatment for anti-freezing operation, pre-harvest Sunne pest control, and Orchid flower control are introduced.

A Fast Image Super-Resolution Algorithm Using An Adaptive Wiener Filter, Russell C. Hardie

Electrical and Computer Engineering Faculty Publications

A computationally simple super-resolution algorithm using a type of adaptive Wiener filter is proposed. The algorithm produces an improved resolution image from a sequence of low-resolution (LR) video frames with overlapping field of view. The algorithm uses subpixel registration to position each LR pixel value on a common spatial grid that is referenced to the average position of the input frames. The positions of the LR pixels are not quantized to a finite grid as with some previous techniques. The output high-resolution (HR) pixels are obtained using a weighted sum of LR pixels in a local moving window. Using a …

Collaborative Routing Algorithm For Wireless Sensor Network Longevity, Shishir Bashyal, Ganesh K. Venayagamoorthy

Electrical and Computer Engineering Faculty Research & Creative Works

This study proposes a new parameter for evaluating longevity of wireless sensor networks after showing that the existing parameters do not properly evaluate the performance of algorithms in increasing longevity. This study also proposes an ant inspired Collaborative Routing Algorithm for Wireless Sensor Network Longevity (CRAWL) that has scalability and adaptability features required in most wireless sensor networks. Using the proposed longevity metrics and implementing the algorithm in simulations, it is shown that CRAWL is much more adaptive to non-uniform distribution of available energy in sensor networks. The performance of CRAWL is compared to that of a non-collaborative algorithm. Both …

Analysis And Characterization Of A Sige Bicmos Low Power Operational Amplifier, Archana Yarlagadda

Masters Theses

Integrated circuit design for space applications can require radiation immunity, cryogenic operation and low power consumption. This thesis provides analysis and characterization of a SiGe BiCMOS low power operational amplifier (op amp) designed for lunar surface applications. The op amp has been fabricated on a commercially available 0.35-micron Silicon-Germanium (SiGe) BiCMOS process. The Heterojunction bipolar transistors (HBT) available in the SiGe process have been used in this op amp to take advantage of the total ionizing dose (TID) irradiation immunity and superb cryogenic operation, along with PMOS devices that show better TID immunity than their NMOS counterparts. The key features …

Load Shedding Algorithm Using Voltage And Frequency Data, Poonam Joshi

All Theses

Under frequency load shedding schemes have been widely used, to restore power system stability post major disturbances. However, the analysis of recent blackouts suggests that voltage collapse and voltage-related problems are also important concerns in maintaining system stability. For this reason, both frequency and voltage need to be taken into account in load shedding schemes. The research undertaken here considers both parameters in designing a load shedding scheme to determine the amount of load to be shed and its appropriate location. An introduction about the need for a load shedding scheme and the purpose of doing research on this particular …

Design Of Alu And Cache Memory For An 8 Bit Alu, Pravin Chander Chandran

All Theses

The design of an ALU and a Cache memory for use in a high performance processor was examined in this thesis. Advanced architectures employing increased parallelism were analyzed to minimize the number of execution cycles needed for 8 bit integer arithmetic operations. In addition to the arithmetic unit, an optimized SRAM memory cell was designed to be used as cache memory and as fast Look Up Table.
The ALU consists of stand alone units for bit parallel computation of basic integer arithmetic operations. Addition and subtraction were performed using Kogge Stone parallel prefix hardware operating at 330MHz. A high performance …

Impedance Matching And PspiceR Simulation Of One Atmosphere Uniform Glow Discharge Plasma (Oaugdp™) Reactor/Actuator Systems, Zhiyu Chen

Masters Theses

This thesis addresses two important issues relevant to One Atmosphere Uniform Glow Discharge Plasma (OAUGDP™) reactors and actuators ¾ impedance matching and PSpice^R simulation.

An OAUGDP™ reactor/actuator with the plasma energized can be modeled as a capacitor in parallel with a resistor. In addition, the non-ideality of the transformer between the RF power supply and the plasma reactor/actuator introduces an imaginary component in its impedance. Thus, the load of the RF power supply, as seen by its output terminals, is highly reactive. An impedance mismatch resulting from the absence of a matching network will cause a large reflected power …

A Standard Cmos Compatible Bandgap Voltage Reference With Post-Process Digitally Tunable Temperature Coefficient, Sam D. Caylor

Masters Theses

An essential element of most robust analog/mixed-signal systems is a stable and precise bandgap voltage reference (BGR). CMOS compatible BGR circuits are generally limited by variability in output drift over temperature due to process variations. In this work a CMOS BGR is developed that provides simple, digitally-controlled post-process (i.e., post fabrication) trimming. The trimming is achieved through MOSFET switches used to adjust a current gain factor for the thermal voltage referenced current within the BGR circuit. This current is proportional to absolute temperature (PTAT). The PTAT current is injected into a series connected resistor and diode to ultimately provide an …

Improved Covariance Model Parameter Estimation Using Rna Thermodynamic Properties, Jennifer A. Smith, Kay C. Wiese

Electrical and Computer Engineering Faculty Publications and Presentations

Covariance models are a powerful description of non-coding RNA (ncRNA) families that can be used to search nucleotide databases for new members of these ncRNA families. Currently, estimation of the parameters of a covariance model (state transition and emission scores) is based only on the observed frequencies of mutations, insertions, and deletions in known ncRNA sequences. For families with very few known members, this can result in rather uninformative models where the consensus sequence has a good score and most deviations from consensus have a fairly uniform poor score. It is proposed here to combine the traditional observed-frequency information with …

Deconvolution And Segmentation Of Ground Penetrating Radar Images, Vincent Krause

Masters Theses

Ground Penetrating Radar is a valuable tool for infrastructure condition evaluation as well as in archaeology and geology. The image produced by a GPR scan can be difficult to interpret due to the weak reflection amplitude, the overlap of reflections, and due to outside interference. This thesis proposes an algorithm to automate GPR scan interpretation. This will enable maintenance engineers to read GPR scans quickly and accurately.

The proposed algorithm framework uses an optimization-based deconvolution technique followed by a segmentation process. Each column of the image is deconvoluted and thus reducing them to a list of ordered pairs of reflection …

Evaluation Of Losses In Hid Electronic Ballast Using Silicon Carbide Mosfets, Lakshmi Reddy Gopi Reddy

Masters Theses

HID lamps are used in applications where high luminous intensity is desired. They are used in a wide range of applications from gymnasiums to movie theatres, from parking lots to indoor aquaria, from vehicle headlights to indoor gardening. They require ballasts during start-up and also during operation to regulate the voltage and current levels. Electronic ballasts have advantages of less weight, smooth operation, and less noisy over electromagnetic ballasts. A number of topologies are available for the electronic ballast where control of power electronic devices is exploited to achieve the performance of a ballast for lighting. A typical electronic ballast …

An Estimation Of Distribution Improved Particle Swarm Optimization Algorithm, Raghavendra V. Kulkarni, Ganesh K. Venayagamoorthy

Electrical and Computer Engineering Faculty Research & Creative Works

PSO is a powerful evolutionary algorithm used for finding global solution to a multidimensional problem. Particles in PSO tend to re-explore already visited bad solution regions of search space because they do not learn as a whole. This is avoided by restricting particles into promising regions through probabilistic modeling of the archive of best solutions. This paper presents hybrids of estimation of distribution algorithm and two PSO variants. These algorithms are tested on benchmark functions having high dimensionalities. Results indicate that the methods strengthen the global optimization abilities of PSO and therefore, serve as attractive choices to determine solutions to …

Fabrication And A Study On The Wetting Properties Of Nanostructured Surfaces, Meenaa Kalyanaraman

Masters Theses

Fluid behavior at the microscale exhibits large surface to volume ratios increasing the significance of interfacial phenomena. We have studied two microfluidic phenomena that utilize interplay between microstructure and chemical composition. The first one causes liquid droplets to roll off from surfaces with a very high contact angle. This phenomenon is called superhydrophobic behavior, can be controlled by several tuning parameters. The second one changes the wettability of liquids on a dielectric coated surface with electric potential. The experimental studies were done by first fabricating an ordered array of glass nanocones. Fiber drawing and differential glass etching processes were used …

A 64-Channel Mixed-Signal Data Acquisition System For A Solid-State High Efficiency Neutron Detector Array, Anthony Gene Antonacci

Masters Theses

This thesis presents the design of multiple analog and digital blocks required to implement a desired solid-state data acquisition system for the High Efficiency Neutron Detector Array (HENDA) project under the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory (ORNL). This system encloses and is an extension of prior work described in [1] and [2]. The first prototype chip, named Patara, contained a charge sensitive front-end amplifier [2], and a semi-Gaussian shaper with baseline restore circuitry [1]. Patara III, described in this thesis, involved the addition of the following system components; two comparators, a selectable synchronous/asynchronous digital …

Electromagnetic Simulation For Inhomogeneous Interconnect And Packaging Structures, Lijun Jiang, Barry J. Rubin, Yuan Liu, Jason D. Morsey, Alina Deustch

Electrical and Computer Engineering Faculty Research & Creative Works

The paper contains a novel mechanism for full wave electromagnetic simulation of complicated inhomogeneous structures, such as on-chip interconnects, IC packaging, antennas, and scattering objects. It uses only Equivalent Principle based EFIE instead of both EFIE and MFIE to establish the surface integral equations for practical inhomogeneous structure so that a much more simplified formulation process is needed in the EM simulation procedure. To overcome the numerical error of K operator in the formulation, a new analytical solution to the K operator for general full-wave integral equations is provided. Numerical results are demonstrated to verify the proposed algorithm. © 2007 …