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Virginia Commonwealth University

Theses/Dissertations

2005

Articles 1 - 11 of 11

Full-Text Articles in Physical Sciences and Mathematics

Stm Studies Of Oxygen Etching Of Silicon Surfaces, Mary L. Willis Jan 2005

Stm Studies Of Oxygen Etching Of Silicon Surfaces, Mary L. Willis

Theses and Dissertations

This study uses atomic force microscopy (AFM) to investigate the oxygen etching behavior of the following silicon surface orientations: (001), (111), (113), (5 5 12) and (112). Most etching was performed at sample temperatures between 650 °C and 800 °C, at pressures of 3.3×10-7 and 1.5×10-7 Torr, and at an exposure of 200 L. Surface orientation strongly influences the morphology resulting from extended etching. The surface orientations that are stable against etching and remain flat include Si(001), Si(111), and Si(113). Such surfaces also include island structures, which result from etching around oxide-induced pinning sites. The density of these islands increases …

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Carbon Monoxide Oxidation On Nanoparticle Catalysts And Gas Phase Reactions Of Small Molecules And Volatile Organics With Metal Cations, Khaled Mohammad Eqab Saoud Jan 2005

Carbon Monoxide Oxidation On Nanoparticle Catalysts And Gas Phase Reactions Of Small Molecules And Volatile Organics With Metal Cations, Khaled Mohammad Eqab Saoud

Theses and Dissertations

This dissertation demonstrates the application of a vapor phase method to synthesize supported and unsupported nanoparticle catalysts for CO oxidation. The method is based on the Laser Vaporization/Controlled Condensation (LVCC) technique. The first part of this dissertation presents the vapor phase synthesis and characterization of gold nanoparticles supported on a variety of oxide supports such as CeO2, TiO2, CuO and MgO.The results indicate that Au nanoparticles supported on CeO2 exhibit higher catalytic activity than Au supported on other oxides. The high activity of the Au/CeO2 catalyst is attributed to the strong interaction of Au with CeO2. The results also indicate …

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Measuring Community Consensus In Facial Characterization Using Spatial Databases And Fuzzy Logic, James Lee Mastros Jan 2005

Measuring Community Consensus In Facial Characterization Using Spatial Databases And Fuzzy Logic, James Lee Mastros

Theses and Dissertations

Spatial databases store geometric objects and capture spatial relationships that can be used to represent key features of the human face. One can search spatial databases for these objects, and seek the relationships between them, using fuzzy logic to provide a natural way to describe the human face for the purposes of facial characterization. This study focuses on community perception of short, average, or long nose length. Three algorithms were used to update community opinion of nose length. All three methods showed similar trends in nose length classification which could indicate that the effort to extract spatial data from images …

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Afm And C-Afm Studies Of Gan Films, Katherine Cooper Jan 2005

Afm And C-Afm Studies Of Gan Films, Katherine Cooper

Theses and Dissertations

This thesis uses the techniques of atomic force microscope (AFM) and conductive AFM (C-AFM) to study the conduction properties of n-type GaN films. A total of 16 samples were examined and grouped according to their surface morphologies and conduction behaviors. The most common type of surface morpliology was that of Ga-rich samples having undulating "hillocks" with interspersed holes. Although most of the samples had this common morphology, their local conduction behaviors were not all similar. Local I-V spectra of the tip-sample Schottky contact could be grouped according to three major types: low leakage, high leakage, and "p-type". The highest quality …

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An Application Of Combinatorial Methods, Yingying Yang Jan 2005

An Application Of Combinatorial Methods, Yingying Yang

Theses and Dissertations

Probability theory is a branch of mathematics concerned with determining the long run frequency or chance that a given event will occur. This chance is determined by dividing the number of selected events by the number of total events possible, assuming these events are equally likely. Probability theory is simply enumerative combinatorial analysis when applied to finite sets. For a given finite sample space, probability questions are usually "just" a lot of counting. The purpose of this thesis is to provide some in depth analysis of several combinatorial methods, including basic principles of counting, permutations and combinations, by specifically exploring …

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Fuzzy Membership Function Initial Values: Comparing Initialization Methods That Expedite Convergence, Stephanie Scheibe Lee Jan 2005

Fuzzy Membership Function Initial Values: Comparing Initialization Methods That Expedite Convergence, Stephanie Scheibe Lee

Theses and Dissertations

Fuzzy attributes are used to quantify imprecise data that model real world objects. To effectively use fuzzy attributes, a fuzzy membership function must be defined to provide the boundaries for the fuzzy data. The initialization of these membership function values should allow the data to converge to a stable membership value in the shortest time possible. The paper compares three initialization methods, Random, Midpoint and Random Proportional, to determine which method optimizes convergence. The comparison experiments suggest the use of the Random Proportional method.

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Analysis Of Perturbation-Based Testing Methodology As Applied To A Real-Time Control System Problem, Richard A. Stutler Jan 2005

Analysis Of Perturbation-Based Testing Methodology As Applied To A Real-Time Control System Problem, Richard A. Stutler

Theses and Dissertations

Perturbation analysis is a software analysis technique used to study the tail function of a program by inserting an error into an executing program using data state mutation. The impact of this induced error on the output is then measured. This methodology can be used to evaluate the effectiveness of a given test set and in fact can be used as a means to derive a test set which provides coverage for a given program. Previous research has shown that there is a "coupling effect" such that test sets that identify simple errors will also identify more complex errors. Thus …

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Feedback Stabilization Of Inverted Pendulum Models, Bruce Cox Jan 2005

Feedback Stabilization Of Inverted Pendulum Models, Bruce Cox

Theses and Dissertations

Many mechanical systems exhibit nonlinear movement and are subject to perturbations from a desired equilibrium state. These perturbations can greatly reduce the efficiency of the systems. It is therefore desirous to analyze the asymptotic stabilizability of an equilibrium solution of nonlinear systems; an excellent method of performing these analyses is through study of Jacobian linearization's and their properties. Two enlightening examples of nonlinear mechanical systems are the Simple Inverted Pendulum and the Inverted Pendulum on a Cart (PoC). These examples provide insight into both the feasibility and usability of Jacobian linearizations of nonlinear systems, as well as demonstrate the concepts …

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Integration Of Vmc++ Into A Commercial Treatment Planning System, Joseph Kingsley Gardner Jan 2005

Integration Of Vmc++ Into A Commercial Treatment Planning System, Joseph Kingsley Gardner

Theses and Dissertations

Recently, there has been interest to integrate VMC++ into the commercial treatment planning system at VCU as another Monte Carlo code option, since it has been shown to increase efficiency dramatically without introducing a significant amount of systematic error. Also, independent validation of VMC++ for photon beams is of interest since this has not been performed previously in literature. This study included several tests required to integrate VMC++. Output factor normalization was performed and found to agree with experiment to within 1% for all field sizes except 1x1 cm2. Geometric validation was successful. Dosimetric validation was performed with respect to …

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Attribute-Level Versioning: A Relational Mechanism For Version Storage And Retrieval, Charles Andrew Bell Jan 2005

Attribute-Level Versioning: A Relational Mechanism For Version Storage And Retrieval, Charles Andrew Bell

Theses and Dissertations

Data analysts today have at their disposal a seemingly endless supply of data and repositories hence, datasets from which to draw. New datasets become available daily thus making the choice of which dataset to use difficult. Furthermore, traditional data analysis has been conducted using structured data repositories such as relational database management systems (RDBMS). These systems, by their nature and design, prohibit duplication for indexed collections forcing analysts to choose one value for each of the available attributes for an item in the collection. Often analysts discover two or more datasets with information about the same entity. When combining this …

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Intelligent Autonomous Data Categorization, Edward Graham Finegan Jan 2005

Intelligent Autonomous Data Categorization, Edward Graham Finegan

Theses and Dissertations

The goal of this research was to determine if the results of a simple comparison algorithm (SCA) could be improved by adding a hyperspace analogue to language model of memory (HAL) layer to form NCA. The HAL layer provides contextual data that otherwise would be unavailable for consideration. It was found that NCA did improve the results when compared to SCA alone. However, NCA added complexity problems that limit its practicality. The complexity of this algorithm is On3 where n is equal to the number of unique symbols in the data. While there is a relativity reasonable soft upper bound …

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