Engineering Commons^™

Study Of Cathodoluminescence In Semiconductors, Mandakini V. Kale

Electrical & Computer Engineering Theses & Dissertations

Cathodoluminescence in Zn doped GaAs and ZnSe, the materials of interest for electron-beam controlled semiconductor switches, has been investigated. A new diagnostic technique, using telescopic setup of lenses, was developed to study the spatially resolved cathodoluminescence. The setup eliminated the light, other than rays from the sample, parallel to the optical axis, resulting in an enhanced spatial resolution. At high e-beam energies, light was detected, from the Zn layer region in the GaAs. It is proposed to be due to the radiative recombination of electron-hole pairs, created by the e-beam. For the polycrystalline ZnSe no light emission was detected. This …

Linearized Dynamics Of Space Structures With Articulated Appendages, Gopichand Koganti

Mechanical & Aerospace Engineering Theses & Dissertations

The inherent difficulties of the conventional spacecraft design, which first considered the optimization with respect to structural variables and then with respect to control variables, have led to the concept of Controls-Structures Interactive Design. The success of the CSI design of Space structures without articulated appendages has prompted the extension of the CSI design to systems with articulated appendages. The presentation is of two parts, the first part deals with the derivations of the equations of motion and the second part deals with the eigenvalue/vector approximations.

Three approaches, namely: the multibody approach, the finite element based approach with hinge joints …

Experimental Study Of Transition In A Supersonic Free Shear Layer, Rudolph A. King

Mechanical & Aerospace Engineering Theses & Dissertations

The transition behavior of a free shear layer above a cavity with high and low levels of freestream acoustic disturbances has been investigated at Mach 3.5 in the Supersonic Low-Disturbance Pilot Tunnel located at NASA Langley Research Center. Schlieren photography, mean pitot pressure data, and hot-wire surveys were used to detect transition locations. The transition Reynolds numbers obtained were between Re_Tr = 3.6 x 10⁵ and 5.3 x 10⁵ in good agreement with conventional ("noisy") wind tunnel results. The study indicated that the effects of a decrease in freestream noise on Re_Tr were minimal but, as …

An Experimental Investigation Of Composite Sensors For Crack Length Measurement, Manickam Ramasamy

Mechanical & Aerospace Engineering Theses & Dissertations

Structural defects such as cracks can cause catastrophic failure in engineering components or structures. There are many techniques to measure the crack growth in materials and are commercially available. In this thesis, bondable crack length measurement gages have been investigated and these gages give electrical signal as the output and measure the crack length continuously. Silver paint, nickel powder impregnated epoxy and carbon powder impregnated polymer composite gages are investigated and tests are conducted by resistance measurement method with simple instrumentation and by potential drop method with a constant current output source. Rectangular shape gages have been investigated and as …

Finite Element Frequency Domain Solution Of Nonlinear Panel Flutter With Temperature Effects And Fatigue Life Analysis, David Yongxiang Xue

Mechanical & Aerospace Engineering Theses & Dissertations

A frequency domain solution method for nonlinear panel flutter with thermal effects using a consistent finite element formulation has been developed. The von Karman nonlinear strain-displacement relation is used to account for large deflections, the quasi-steady first-order piston theory is employed for aerodynamic loading and the quasi-steady thermal stress theory is applied for the thermal stresses with a given change of the temperature distribution, ΔΤ (x, y, z). The equation of motion under a combined thermal-aerodynamic loading can be mathematically separated into two equations and then solved in sequence: (1) thermal-aerodynamic postbuckling and (2) limit-cycle oscillation. The Newton-Raphson iteration technique …

Domain Limitations And Interface Requirements For Expert Developed Knowledge Based Systems, Bernard Lee Lewis

Engineering Management & Systems Engineering Theses & Dissertations

The expanded use of graphical, case-based and object oriented techniques in expert systems creation has made it more practical for domain experts to develop their own applications. This thesis focuses on the elements necessary in an expert/developer interface and looks at various forms and techniques that exemplify such an approach. The spreadsheet metaphor is used for an interface or managed set of interfaces that a domain expert can use in building his own expert system or prototype. criteria are established for such interfaces and recent commercial offerings that make expert-created knowledge-bases more practical are reviewed for techniques that qualify. Approaches …

Thermal Characterization Of Carbon Monoxide Oxidation Catalysts Using Thermogravimetric Analysts And Differential Scanning Calorimetry, Rene A. Bartgis

Chemistry & Biochemistry Theses & Dissertations

Catalysts composed of platinum and/or palladium on tin (IV) oxide supports, with and without silica gel, as well as catalysts composed of gold on manganese oxide, have been developed for the recombination of carbon monoxide and oxygen to form carbon dioxide for use in carbon dioxide lasers. A thermogravimetric method and a differential scanning calorimetric method have been developed for the thermal characterization of these catalysts. The mass loss data and the enthalpy changes determined as the catalysts lost water were then related to existing activity data for these catalysts. No relationship was found between the thermal data and the …

Parallel-Vector Computation For Geometrically Nonlinear Frame Structural Analysis And Design Sensitivity Analysis, Majdi A. Baddourah

Civil & Environmental Engineering Theses & Dissertations

Parallel-vector algorithms are presented for solving the geometrically nonlinear structural problems and obtaining design sensitivity information. A new algorithm is also presented for parallel generation and assembly of the finite element stiffness and mass matrices. The presented assembly algorithm is based on a node-by-node approach rather than the more conventional element-by-element approach. Three different methods, Newton Raphson, Modified Newton Raphson, and the BFGS, are used in the analysis of the nonlinear structural problems. A study is made to determine the performance of each of the mentioned methods in a parallel-vector computer environment. Medium to large-scale, practical problems are solved to …

Conceptual Design Of Dual Cam Mechanisms Using Graph Theory, Raymond Lee Mcclendon

Mechanical & Aerospace Engineering Theses & Dissertations

This paper presents the theory of graphs and how they can be applied to the conceptual design of dual-cam mechanisms. The graph theory was used to validate the results of previous authors (Hain and Pryor). Several applications of dual cam mechanisms are reviewed.

Algorithms using a process of bit mapping were used to developed all possible non-isomorphic graphs for various classes of mechanisms. A classification method was developed using common occurring substructures found in the graphs. This classification scheme was used for conversion of graphs into schematics. Once the results of Hain were verified, the investigation turned to mechanisms with …

Finite Element Analysis Of Nonlinear Panel Flutter Of Rectangular Composite Plates Under A Uniform Thermal Load, Lain Ross Dixon

Mechanical & Aerospace Engineering Theses & Dissertations

A finite element formulation is developed to analyze large-amplitude panel flutter of arbitrarily laminated composite plates subjected to a uniform temperature change. The plates considered are anisotropic composite, thin rectangular panels. The aerodynamic pressure load is modeled through the use of the first-order piston theory. The equations of motion for the oscillating plate are determined from the principle of virtual work. Two different solution procedures are given to determine the panel motions. The first procedure, which considers only the aerodynamic load, solves the panel limit-cycle motions by employing the linearized updated-mode with a nonlinear time function (LUM/NTF) approximation. The second …

Application Of Sensitivity Analysis To The Euler Equations, Vamshi Mohan Korivi

Mechanical & Aerospace Engineering Theses & Dissertations

An approximation method is presented for efficiently predicting the changes which occur in a steady-state numerical solution of the Euler equations as a consequence of a small change in the geometric shape of the domain. The method is extended to develop a general procedure for calculating aerodynamic sensitivity derivatives with respect to variations of geometric shape. The techniques are implemented using an upwind cell centered finite volume formulation, and are applied to two test cases, (1) a subsonic nozzle (M_∞ = 0.85), and (2) a supersonic inlet (M_∞ = 2.0). Conventional numerical solutions are first obtained for flow …

Dynamic Test/Analysis Correlation Using Reduced Analytical Models, Paul E. Mcgowan

Mechanical & Aerospace Engineering Theses & Dissertations

Test/analysis correlation is an important aspect of the verification of analysis models which are used to predict on-orbit response characteristics of large space structures. This thesis summarizes the study of using reduced analysis models for performing dynamic test/analysis correlation. The reduced test-analysis model (TAM) has the same number of degrees-of-freedom (DOF) as the number of test measurements. This allows the direct comparison of modal parameters between ground vibration test results and finite element model (FEM) analysis results. The TAM can also be used for pre-test analysis and to aid in the post-test mathematical model updating process.

Herein, four methods for …

Investigation Of Radiative Interactions In Supersonic Chemically Reacting Channel Flows, Almuttil M. Thomas

Mechanical & Aerospace Engineering Theses & Dissertations

Analyses and numerical procedures are presented to investigate the radiative interactions of absorbing emitting species in chemically reacting supersonic flow in various ducts. The two-dimensional time dependent Navier-Stokes equations in conjunction with radiative flux equation are used to investigate supersonic flows undergoing finite rate chemical reaction in a hydrogen air system. The specific problem considered is the flow of premixed radiating gas between parallel plates. Specific attention is directed in investigating the radiative contribution of H2O, OH and NO under realistic physical and flow conditions. Results are presented for the radiative flux obtained for different gases and for various combination …

Parallel-Vector Design Sensitivity Analysis In Structural Dynamics, Yongxing Zhang

Civil & Environmental Engineering Theses & Dissertations

In this study, the design sensitivity analysis is for the purpose of providing constraint derivative information for structural optimization under dynamic loads. Various existing formulations are reviewed, and the direct differentiation method is justified as the best one for design sensitivity analysis in structural dynamics. An alternative formulation for design sensitivity analysis with direct differentiation method is developed. The alternative formulation works efficiently with the reduced system of dynamic equations, and it eliminates the need for expensive and complicated eigenvector derivatives, which is required in the existing reduced system formulation. The relationship of the alternative formulation and the existing reduced …

Purification And Characterization Of The Prostate Cancer-Associated Antigen: 7e11-C5, Qi Feng

Theses and Dissertations in Biomedical Sciences

A murine monoclonal antibody (MAb), 7E11-C5, recognizes a prostate organ-specific antigen. Under reducing conditions, the 7E11-C5 antigen exhibited major 100-Kd and minor 70-Kd bands, suggesting that the antigen comprises two peptide chains. The antigen was detected in pooled normal human seminal plasma, xenograft tissue extract of a prostate adenocarcinoma cell line, LNCaP, and tissue extracts of benign prostatic hyperplasia (BPH) and prostate carcinomas, but was not identified in any of the non-prostate tissue extracts tested. Antibodies of the three major prostate-associated antigens (prostatic acid phosphatase (PAP), prostate specific antigen (PSA) and prostate secretory protein (PSP)) were unable to block the …

Integrated System Identification And Adaptive State Estimation For Control Of Flexible Space Structures, Chung-Wen Chen

Mechanical & Aerospace Engineering Theses & Dissertations

Accurate state information is crucial for control of flexible space structures in which the state feedback strategy is used. The performance of a state estimator relies on accurate knowledge about both the system and its disturbances, which are represented by system model and noise covariances respectively. For flexible space structures, due to their great flexibility, obtaining good models from ground testing is not possible. In addition, the characteristics of the systems in operation may vary due to temperature gradient, reorientation, and deterioration of material, etc. Moreover, the disturbances during operation are usually not known. Therefore, adaptive methods for system identification …

A Robust Approach To Human-Computer Interface Design Using The Taguchi Method, Billie Mitchell Reed

Engineering Management & Systems Engineering Theses & Dissertations

The application of Dr. Genichi Taguchi's approach for design optimization, called Robust Design, to the design of human-computer interface software is investigated. The Taguchi Method is used to select a near optimum set of interface design alternatives to improve user acceptance of the resulting interface software product with minimum sensitivity to uncontrollable noise caused by human behavioral characteristics.

Design alternatives for interaction with personal micro-computers are identified. Several important and representative alternatives are chosen as design parameters for the Taguchi matrix experiment. A noise field with three human behavioral characteristics as noise factors were chosen as a representative noise array. …

An Experimental Study On Anisotropic Behavior Of Granular Materials, Jong Woon Choi

Civil & Environmental Engineering Theses & Dissertations

Two types of mixtures of glass bead assemblies (large beads and small beads) were used to investigate the source of the anisotropy of granular materials in volume change behaviors during shearing process. Most tests (7 series) were conducted in the conventional triaxial device while a series of the experiments were in the hollow cylinder test device. All the specimens were first isotropically consolidated up to 137.9 kPa and were subjected to shearing in triaxial compression and triaxial extension modes with a constant effective mean normal stress (137.9 kPa). The test results indicated that all the specimens had a strong but …

An Experimental And Analytical Investigation Of Wing Flutter On A Trial Rotor V/Stol Aircraft, David L. Soistmann

Mechanical & Aerospace Engineering Theses & Dissertations

A wind tunnel model based on a trail rotor vehicle concept was tested for wing flutter in the subsonic flow regime. The wind tunnel model was flutter tested in the forward flight mode only. From this test it was determined that this conceptual vehicle may be susceptible to wing flutter. However, the flutter encountered was not catastrophic but was of the limited amplitude type. The trailing rotor blades were found to have a positive aerodynamic damping effect on flutter. The flutter mechanism for each flutter point was due to a coupling of the first wing bending and first wing torsion …

Simulation And Measurement Of The Radiant Field Produced By Quartz Heating Systems, Travis Lee Turner

Mechanical & Aerospace Engineering Theses & Dissertations

A method is developed for predicting the radiant heat flux distribution produced by tungsten-filament tubular quartz heating systems with reflectors. The method is an application of Monte Carlo simulation, which takes the form of a ray tracing or random walk scheme. The method is applied to four systems of increasing complexity including; a single unreflected lamp, a single lamp with a flat reflector, a single lamp with a parabolic reflector, and up to six lamps in a six-lamp contoured reflector heating unit. The general methodology of the Monte Carlo method is discussed and applied to the simulation of thermal radiation. …

On Shock Capturing For Liquid And Gas Media, Tze Jang Chen

Mathematics & Statistics Theses & Dissertations

The numerical investigation of shock phenomena in gas or liquid media where a specifying relation for internal energy is absent poses special problems. Classically, for gas dynamics the usual procedure is to employ a splitting scheme to remove the source terms from the Euler equations, then up-wind biased shock capturing algorithms are built around the Riemann problem for the system which remains. However, in the case where the Euler equations are formulated in the term of total enthalpy, a technical difficulty associated with equation splitting forces a pressure time derivative to be treated as a source term. This makes it …

The Solution Of A Singular Integral Equation Arising From A Lifting Surface Theory For Rotating Blades, Mark H. Dunn

Mathematics & Statistics Theses & Dissertations

A technique is presented for the solution of a linear, two dimensional, singular, Volterra integral equation of the first kind. The integral equation, originally developed by Farassat and Myers, is derived from the basic equations of linearized acoustics and models the lifting force experienced by an infinitesimally thin surface moving tangent to itself. As a particular application, the motion of modern high speed aircraft propellers (Advanced Technology Propellers) is considered. The unknown propeller blade surface pressure distribution is approximated by a piecewise constant function and the integral equation is solved numerically by the method of collocation. Certain simplifying assumptions applied …

Cathodoluminescence Of Gaas, Tyler Smith

Electrical & Computer Engineering Theses & Dissertations

Cathodoluminescence of band-gap radiation across the bulk of a proposed semiconductor switch has been studied. Such a device relies on the efficient use of cathodoluminescence to modulate the conductivity of the switch. Diagnostics were configured to measure the intensity of band-gap radiation across the bulk of several switch samples. The measured results were compared to calculations based on a four energy level band-gap model which included two deep levels EL2 and HL10.

Q Improvement Of A 5.2 Ghz Te011 Cavity By Incorporating Y1Ba2Cu3O7-X, R. Joseph Leclear

Electrical & Computer Engineering Theses & Dissertations

Research is undertaken to apply high temperature superconducting material to improve the quality factor (Q) of a 5.2 GHz cylindrical resonant cavity. In particular, the approach is to electrophoretically deposit polycrystalline Y₁Ba₂Cu₃O_7-x (YBCO) on the conducting surface of the cavity cylinder. Spalling of the YBCO ceramic coating due to expansion and contraction of the cavity during sintering and testing is overcome by segmenting the cylinder. Results show that the Q of the cavity is increased over that of a copper cavity at temperatures below 60 K. At 20 K, improvement exceeds a factor …

Analytical Modeling And Simulation For Investigation Of A Digital Gas Filter Correlation Radiometer, Catherine P. Mcgowan

Electrical & Computer Engineering Theses & Dissertations

This thesis investigates a digital gas filter correlation radiometer called the Tropospheric Radiometer for Atmospheric Chemistry and Environmental Research (TRACER), which will be used to remotely measure carbon monoxide at three levels in the troposphere. The nadir-viewing radiometer measures the differential absorption of radiation through the atmosphere at 4.67@m and 2.33pm wavelengths. This thesis develops an analytical model of the TRACER measurement process to evaluate the effect of varying certain system parameters on the measurement. The independent sampling criterion and the response of linear systems to random signals are explained. A parametric simulation model is also developed to evaluate the …

The Breakdown Mechanism Of Hollow Cathode Discharge, Mai Tuyet Ngo

Electrical & Computer Engineering Theses & Dissertations

In a low pressure discharge, if the cathode incorporates a cylindrical or slit shaped hole, the discharge current can be several orders of magnitude higher than in one with plane parallel electrodes under the same pressure and voltage conditions. In this work hollow cathode discharges in Helium under the influence of variable parameters such as gas pressure, applied voltage, electrode gap spacing, external magnetic field, etc., are investigated by means of electrical and optical diagnostic techniques.

The results indicate that a hollow cathode discharge develops in two stages. The initial breakdown occurs along the longest straight path of the system, …

Signal Processing Methodologies For An Acoustic Fetal Heart Rate Monitor, Robert A. Pretlow Iii

Electrical & Computer Engineering Theses & Dissertations

Research and development is presented of real time signal processing methodologies for the detection of fetal heart tones within a noise-contaminated signal from a passive acoustic sensor. A linear predictor algorithm is utilized for detection of the heart tone event and additional processing derives heart rate. The linear predictor is adaptively "trained" in a least mean square error sense on generic fetal heart tones recorded from patients. A real time monitor system is described which outputs to a strip chart recorder for plotting the time history of the fetal heart rate. The system is validated in the context of the …

An Erasable Optical Memory Based On Stimulated Electronic Transition Concept, James D. Satira

Electrical & Computer Engineering Theses & Dissertations

Erasable optical memory systems with a high storage density and a large data transfer rate are required for many real time data acquisition systems such as those placed aboard NASA's space born platforms. A new concept for erasable optical memory involving stimulated electronic transitions (SET) will meet these requirements. The SET concept useful in erasable optical storage systems was demonstrated in MgS and SrS doped with Eu and Sm. The optical properties of these materials were studied. The reading and writing wavelengths for these samples were determined to be 950 and 514 nm respectively. The peaks of the emission spectra …

Finite Element Analysis Of Thermal Post-Buckling And Vibrations Of Thermally Buckled Composite Plates, Charles Clifton Gray

Mechanical & Aerospace Engineering Theses & Dissertations

The development of supersonic and hypersonic flight vehicles such as the High Speed Civil Transport and the National Aero-Space Plane has created an increased need for analysis of structures at very high temperatures. Bisplinghoff and Pian, Yang and Han, and Dokmeci and Boley have conducted experimental and analytical studies to determine the effect of elevated temperatures on the vibration characteristics of isotropic plates, Chen and Chen, and Meyers and Hyer have clone studies on thermal buckling and post-buckling of composite plates, respectively.

The thermal loads which will be imposed on the new high speed aircraft will be too great for …

Simulation Of 3-D Viscous Flow Around A Nozzle-Afterbody At High Speeds, Wendy B. Hoffman

Mechanical & Aerospace Engineering Theses & Dissertations

Turbulent shear flows at supersonic and hypersonic speeds around a nozzle-afterbody are numerically simulated and investigated. The specific application is for the flow around the nozzle-afterbody of a generic hypersonic vehicle. Accurate simulation of viscous, separating flows is not an easy task, and it is complicated by turbulence modeling concerns. A main objective of this study is to numerically simulate the afterbody flowfield while addressing the turbulence modeling problem. The viscous flow considered i~ this study is characterized by three-dimensional corner flows, shock boundary layer interactions, plume flow, shear layers, and cross-flow separations. Accurate simulation of this flow requires solution …