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Theses/Dissertations

1995

Retrospective Theses and Dissertations

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Articles 1 - 30 of 95

Full-Text Articles in Engineering

Neural Networks For Characterizing Magnetic Flux Leakage Signals, Marian M. Chao Jan 1995

Neural Networks For Characterizing Magnetic Flux Leakage Signals, Marian M. Chao

Retrospective Theses and Dissertations

http://www.worldcat.org/oclc/32786804


Multiresolution Wavelet Analysis Of Eeg Signals For The Detection Of Alzheimer's Disease, Robi Polikar Jan 1995

Multiresolution Wavelet Analysis Of Eeg Signals For The Detection Of Alzheimer's Disease, Robi Polikar

Retrospective Theses and Dissertations

No abstract provided.


A Study Of The Behavior Of The Diameter Of The Ascending Aorta When Hemorrhage Is Induced In Mongrel Dogs, Jorge Alberto GarcãƒÂ­A-Zuazaga Jan 1995

A Study Of The Behavior Of The Diameter Of The Ascending Aorta When Hemorrhage Is Induced In Mongrel Dogs, Jorge Alberto GarcãƒÂ­A-Zuazaga

Retrospective Theses and Dissertations

No abstract provided.


An Active Air Spring Suspension System Without Shock Absorber On A Quarter Vehicle Model, Mitchell Alonzo Duncklee Jan 1995

An Active Air Spring Suspension System Without Shock Absorber On A Quarter Vehicle Model, Mitchell Alonzo Duncklee

Retrospective Theses and Dissertations

http://www.worldcat.org/oclc/32803994


Minimizing The Radiated Sound Power With Minimal Structural Modification , Daniel Henry Kruger Jan 1995

Minimizing The Radiated Sound Power With Minimal Structural Modification , Daniel Henry Kruger

Retrospective Theses and Dissertations

In cases where a structure's excitation cannot be altered, the sound radiation from the structure must be minimized by modifying the structure within given design constraints. This dissertation considers minimizing sound radiated by an existing structure with minimal changes to the structure itself. To accomplish this the sound power radiated by a structure was written as a function of the normal surface velocity using the boundary element method. The feasibility of reducing radiated sound power with small patches of constrained layer damping material is proved. Small patches of constrained layer damping material are placed on the structure to effectively ...


Growth Optimization And Characterization Of Gallium Indium Nitride Grown By Electron-Cyclotron-Resonance Plasma-Assisted Molecular-Beam Epitaxy , William O. Liners Jan 1995

Growth Optimization And Characterization Of Gallium Indium Nitride Grown By Electron-Cyclotron-Resonance Plasma-Assisted Molecular-Beam Epitaxy , William O. Liners

Retrospective Theses and Dissertations

The various alloys of gallium indium nitride (GaInN) form a technologically important semiconductor materials system, with potential uses in optoelectronic devices operating in the blue and blue-green region of the visible light spectrum. There has been little work reported on the growth of these materials, and this research addresses fundamental issues related to the epitaxial growth of the nitrides. Our first step in this project was to install an electron cyclotron resonance (ECR) apparatus into our molecular beam epitaxy system. This provided a source for atomic nitrogen needed to grow the nitride materials. We also put together a photoluminescence (PL ...


Development Of An Acoustic Microscope To Measure Residual Stress Via Ultrasonic Rayleigh Wave Velocity Measurements , Jane Carol Johnson Jan 1995

Development Of An Acoustic Microscope To Measure Residual Stress Via Ultrasonic Rayleigh Wave Velocity Measurements , Jane Carol Johnson

Retrospective Theses and Dissertations

High stress in a crucial instrument part can cause failure. Stress detection is one of the aims of nondestructive testing. The velocity change of acoustic waves can be used to detect stress in a material. An acoustic microscope is an instrument which induces and detects acoustic waves and in one mode of operation, is able to measure the velocity of acoustic surface waves. It does this over a very small area and is capable of high spatial resolution;One of the challenges in the measurement of stress is the achievement of high spatial resolution. Since the stress induced velocity shifts ...


Stability Of A Eutectic Interface During Directional Solidification , Seung Hoon Han Jan 1995

Stability Of A Eutectic Interface During Directional Solidification , Seung Hoon Han

Retrospective Theses and Dissertations

Directional solidification of eutectic alloys shows different types of eutectic morphologies. These include lamellar, rod, oscillating and tilting modes. The growth of these morphologies occurs with a macroscopically planar interface. However, under certain conditions, the planar eutectic front becomes unstable and gives rise to a cellular or a dendritic structure. This instability leads to the cellular/dendritic structure of either a primary phase or a two-phase structure. The objective of this work is to develop a fundamental understanding of the instability of eutectic structure into cellular/dendritic structures of a single phase and of two-phases;Experimental studies have been carried ...


Evaluation Of Automatic Vehicle Specific Identification (Avsi) In A Traffic Signal Control System , Alireza Kamyab Jan 1995

Evaluation Of Automatic Vehicle Specific Identification (Avsi) In A Traffic Signal Control System , Alireza Kamyab

Retrospective Theses and Dissertations

Automatic Vehicle Specific Identification (AVSI) is a generic name for advanced vehicle detection systems. By automating the identification of vehicles by sensing the presence of vehicles with roadside detection sites or readers, AVSI is assumed to provide vehicle specific information in traffic signal control systems;In the application of AVSI to traffic signal control systems, as a vehicle passes a reader site, the reader records the arrival time and type of the detected vehicle. The reader would then send the information received to a local microprocessor-based traffic signal controller. The controller's built-in signal control logic would then use the ...


Parallel Surface Reconstruction Through Virtual Milling , Kumaran Kalyanasundaram Jan 1995

Parallel Surface Reconstruction Through Virtual Milling , Kumaran Kalyanasundaram

Retrospective Theses and Dissertations

Surface definition deals with representing a surface analytically using a finite number of parameters and with acceptable levels of error. In the past few years it has become a key discipline in Computational Fluid Dynamics (CFD). Recent advances in computers and numerical algorithms have made it possible for CFD practitioners to attempt flow solutions about complex three-dimensional geometries. The first step in this process is having a numerical representation of the shape. In many cases of interest such a representation already exists; i.e., aircraft designed on a computer. Such Computer-Aided Design (CAD) descriptions do not exist, though, for objects ...


Determining Agricultural Chemical Transport Through The Vadose Zone Using A Large Borehole Cavity , Dean Ivan Olson Jan 1995

Determining Agricultural Chemical Transport Through The Vadose Zone Using A Large Borehole Cavity , Dean Ivan Olson

Retrospective Theses and Dissertations

A large borehole cavity designed to investigate agricultural chemical transport through the vadose zone was installed at the Agronomy-Agricultural Engineering Research Center near Ames, Iowa. The system consisted of a culvert installed vertically in the soil profile with stainless steel suction lysimeters installed radially from the cavity wall. Suction lysimeters were installed at five depths in the soil profile with five replications at each depth to monitor changes in water quality in the vadose zone and below the water table. Electronic tensiometers and a data logger system were installed to continuously monitor matric potential and used to automatically collect water ...


Modeling Recession And Low Flow Characteristics Of Iowa Streams , Ahmad Ali Raaii Jan 1995

Modeling Recession And Low Flow Characteristics Of Iowa Streams , Ahmad Ali Raaii

Retrospective Theses and Dissertations

Available mean daily streamflow data from 143 gaging stations were initially analyzed to characterize recessions and low flows of Iowa streams. The period of record varies between 10 and 115 years for different stations. A computerized mathematical model was used to derive two master recession curves (MRC's)--one for winter and the other for summer--and to calculate the median storage delay factor (K med) for each individual station. These factors were used to estimate the diffusivity of the aquifer(s) contributing base flow to each stream;The MRC's can be used to forecast the general behavior of streams ...


Oxidation Studies On Small Atom Doped Ti5si3 , Andrew Jason Thom Jan 1995

Oxidation Studies On Small Atom Doped Ti5si3 , Andrew Jason Thom

Retrospective Theses and Dissertations

Several Ti5Si3Zx compositions (Z = B,C,N,O and 0 ≤ x ≤ 1) were arc-melted, and powder x-ray diffraction indicates the materials maintain the Mn5Si3-type structure of undoped Ti5Si3. Single crystal x-ray diffraction verifies that the ternary additions occupy the normally vacant interstitial sites in the Mn5Si3-type structure. Interstitial nitrogen and oxygen also significantly increase the density of Ti5Si3;Coefficient of thermal expansion (CTE) of Ti5Si3 was measured by the method of high temperature x-ray diffraction. CTE along the c-axis is substantially larger than along the a-axis ([alpha] a = 8.68 ± 0.14 and [alpha] c = 20.4 ± 0.4 ppm ...


Surface And Sub-Surface Ablation Cell Design For Remote (Robotic) Radioactive Soil Analysis Using Laser Ablation-Inductively Coupled-Atomic Emission Spectrometry/Mass Spectrometry La-Icp-Aes/Ms , Reza Bashirzadeh Jan 1995

Surface And Sub-Surface Ablation Cell Design For Remote (Robotic) Radioactive Soil Analysis Using Laser Ablation-Inductively Coupled-Atomic Emission Spectrometry/Mass Spectrometry La-Icp-Aes/Ms , Reza Bashirzadeh

Retrospective Theses and Dissertations

There are approximately 1800 uncontrollable hazardous waste sites across the United States. The Department of Energy (DOE) is responsible for cleaning up several of these sites that were contaminated as a result of producing weapon-grade nuclear fuels in different states since the 1940s. Site characterization is the first and a very critical step in the remediation program of a radioactive contaminated site. During this process, all the necessary information about location, level, and chemical composition of the contaminated sites must be collected for the clean up planning. Ames Laboratory, one of the U.S. Department of Energy sites, has adopted ...


Crop And Tillage Management Effects On Water Flow And Nitrate-Nitrogen Loss Through Subsurface Drains , David L. Bjorneberg Jan 1995

Crop And Tillage Management Effects On Water Flow And Nitrate-Nitrogen Loss Through Subsurface Drains , David L. Bjorneberg

Retrospective Theses and Dissertations

Data were collected from subsurface drains on 36, 0.4-ha plots at Iowa State University's Northeast Research Farm near Nashua, IA to determine crop and tillage management effects on water flow and nitrate-N loss through subsurface drains. From 1990 to 1992, four tillage systems (chisel plow, moldboard plow, ridge till and no-till) were used with two crop rotations (continuous corn (Zea mays L.) and corn-soybean (Glycine max L. (Herr.)) rotation) and a single-spring fertilizer application. From 1993 to 1995, tillage systems were reduced to chisel plow and no-till, while fertilizer management changed to include single-spring fertilizer, spring-summer split fertilizer ...


Analytical Investigation Of The Effect Of Material And Geometric Imperfections On Buckling Strength Of Spherical Shells , Rama Krishna Challa Jan 1995

Analytical Investigation Of The Effect Of Material And Geometric Imperfections On Buckling Strength Of Spherical Shells , Rama Krishna Challa

Retrospective Theses and Dissertations

Spherical shells are extensively used as structural elements. As they are subjected to different loading conditions, compressive membrane forces develop causing failure due to compressive stability. In order that the shells perform their design function adequately, sufficient design margins should exist. These design margins are established by means of experimental tests and numerical analysis. Comparisons between classical, theoretical and experimental results for spherical shells subjected to external pressure loading demonstrated large discrepancies. These discrepancies are attributable to material and geometric imperfections resulting from fabrication methods.;Sufficient design information with respect to the imperfections is required to perform numerical analyses. The ...


Numerical Investigation Of Type Ii Non-Newtonian De/Anti-Icing Fluid Effects On Take-Off Performance For General Aviation Aircraft , Dennis James Cronin Jan 1995

Numerical Investigation Of Type Ii Non-Newtonian De/Anti-Icing Fluid Effects On Take-Off Performance For General Aviation Aircraft , Dennis James Cronin

Retrospective Theses and Dissertations

Ground icing, while preventable with glycol based freezing point depressant fluids, accounts for nearly 40-50 civil accidents a year according to one account. More viscous than Type I fluids, Type II fluids are inherently non-linear in their shear stress-rate of strain relationship having smaller relative viscosity at higher shear rates. The non-linearity makes properly scaled wind-tunnel testing difficult and computational methods are employed in this study to look at the aerodynamic effects of the deicing fluid on global performance during typical take-off maneuvers for general aviation. The method is tested on a two-dimensional NACA 0012 airfoil under typical take-off simulation ...


A Predictive Model Of The Hf Noise Environment At Satellite Heights , Marisa Mccoy Jan 1995

A Predictive Model Of The Hf Noise Environment At Satellite Heights , Marisa Mccoy

Retrospective Theses and Dissertations

The radio noise background is an area of continuing research and measurement. In many cases, the background noise becomes the primary limiting factor in a communication system's sensitivity. The issue of HF (1-30 MHz) interference from terrestrial sources is especially pertinent to space-based low-frequency radio astronomy. Radio astronomy observations in the HF portion of the electromagnetic spectrum could result in new insights into astrophysical processes. However, this particular part of the spectrum is mostly inaccessible from the ground due to the effects of the Earth's ionosphere;The objective of this research is to determine to what extent terrestrial ...


Adaptive Nonlinear Attitude Control Of Spacecraft , Cheng Tang Jan 1995

Adaptive Nonlinear Attitude Control Of Spacecraft , Cheng Tang

Retrospective Theses and Dissertations

Three adaptive nonlinear control approaches are proposed for attitude control of a Space Station. These control algorithms avoid the need for linearization, either by truncating a Taylor series or by a feedback linearization approach, which poses some difficulties in the presence of both uncertain mass properties and external disturbances. Global stability of the Space Station is guaranteed;A conventional linear-quadratic regulator synthesis technique is investigated. This linear control scheme provides a natural way to select control gains for the known spacecraft system parameters. Simulation results reveal that the uncertain mass property causes the nonlinear Space Station to be uncontrollable;On ...


The Effect Of Learning Problem-Solving Methods On Learning To Program In The Basic Language , Yen-Chu Hung Jan 1995

The Effect Of Learning Problem-Solving Methods On Learning To Program In The Basic Language , Yen-Chu Hung

Retrospective Theses and Dissertations

This study was designed to compare learning problem-solving methods versus non problem-solving activity (word-processing) on subsequent learning to program in the BASIC language. It also examined a method to provide students with increased knowledge and skills to enable them to learn how to program;A pretest-posttest control group design was used in this experiment with random assignment of subjects to one of three groups. Experiment groups one (deduction group) and two (induction group) first received the pretest and learning problem-solving methods; then group one received deduction instruction while group two received induction instruction, both followed by learning BASIC language programming ...


Design Of Developmental Test Programs For One-Shot Systems With Two State Reliability , Mu-Yeh Huang Jan 1995

Design Of Developmental Test Programs For One-Shot Systems With Two State Reliability , Mu-Yeh Huang

Retrospective Theses and Dissertations

This dissertation considers efficient developmental testing for one-shot systems (for example, missiles) that are destroyed in testing or first normal use, where there is the possibility of "reliability growth" of the basic system design as a result of redesigns following failed developmental tests. We consider situations where the cost of redesign is negligible and there is a fixed procurement budget covering both system development and purchase, each developmental test produces either a binary (success-failure) or a continuous outcome. The analysis offered here is intended as an answer to the question "How much testing is enough?" posed by Seglie (1992) in ...


Analysis Of Nonlinear Modal Interaction And Its Effect On Control Performance In Stressed Power Systems Using Normal Forms Method , Chih-Ming Lin Jan 1995

Analysis Of Nonlinear Modal Interaction And Its Effect On Control Performance In Stressed Power Systems Using Normal Forms Method , Chih-Ming Lin

Retrospective Theses and Dissertations

In this research the nonlinear modal interaction and the effect of the interaction on the stressed power system dynamic behavior including excitation control performance are discussed. A systematic scheme based on the normal forms method for the determination of nonlinear interaction between fundamental modes and excitation control modes in a stressed power system is developed;In a stressed power system, the interarea mode phenomenon may occur under large disturbance. Recent investigations revealed that the interarea mode may be among the power system fundamental modes of oscillation associated with the nonlinear modal interaction. If there is significant interaction, the controls will ...


Effects Of Shallow Water Tables On Soil Aeration, Water Quality, And Physiological Growth Of Soybean , Tahir Sarwar Jan 1995

Effects Of Shallow Water Tables On Soil Aeration, Water Quality, And Physiological Growth Of Soybean , Tahir Sarwar

Retrospective Theses and Dissertations

This study was conducted to investigate the effects shallow water table depths on soil aeration, groundwater quality and on some physiological growth and yield parameters of soybean. The experiments were conducted in two environmentally controlled growth chambers using sixteen lysimeters. Water table (WT) treatments were established on 37 day after planting (DAP), at depths of 0.15-, 0.30-, 0.45- and 0.60-m below the soil surface. Soil aeration status was determined by measuring soil oxygen concentrations at 0.15-, 0.30-, 0.60-m depths in the lysimeters. Effects of water table depths on groundwater quality were determined by ...


Amino Acid Composition Of Soil Organic Matter And Nitrogen Transformations In Soils Under Different Management Systems , Zachary Ngewoh Senwo Jan 1995

Amino Acid Composition Of Soil Organic Matter And Nitrogen Transformations In Soils Under Different Management Systems , Zachary Ngewoh Senwo

Retrospective Theses and Dissertations

Studies of amino acid composition of soil organic matter extracted from 10 Iowa surface soils and from surface soils of two long-term rotation experiments showed that, with the exception of asparagine plus aspartic acid and glutamine plus glutamic acid, the other 13 amino acids, expressed as percentages of total amino acid extracted, were very uniform among the soils. The total amino acid extracted was significantly correlated with organic C (r = 0.79[superscript]\*\*) and clay content (r = 0.76[superscript]\*\*), but not with total N. Expressed as percentages of organic C and N in soils, the amounts extracted ranged from ...


Optimal Turning Maneuvers For Six-Degree-Of-Freedom High Angle-Of-Attack Aircraft Models , Jen-Nai Chou Jan 1995

Optimal Turning Maneuvers For Six-Degree-Of-Freedom High Angle-Of-Attack Aircraft Models , Jen-Nai Chou

Retrospective Theses and Dissertations

Various Minimum-Time Turning Maneuvers for two high angle-of-attack, six-degree-of-freedom, aircraft models have been investigated. The primary aircraft model is for a nonlinear 6-DOF F-16 fighter aircraft with high angle-of-attack maneuverability. The other model is for a linearized 6-DOF F-18 fighter which also can be flown in the high angle-of-attack range. Standard 6-DOF equations are employed except that the Quaternion attitude representation system is used instead of Euler Angles to avoid the pitch angle singularity of Euler Angles;These Optimal Control problems have been transformed into Nonlinear Programming problems via Parameter Optimization techniques. Different parameterization techniques were tested on the Van ...


Low Temperature Epitaxial Silicon Growth Using Electron Cyclotron Resonance Plasma Deposition , Scott Jeffrey Deboer Jan 1995

Low Temperature Epitaxial Silicon Growth Using Electron Cyclotron Resonance Plasma Deposition , Scott Jeffrey Deboer

Retrospective Theses and Dissertations

The development of a process for the low temperature (<600° C) growth of epitaxial silicon is an important technological issue. Conventional growth processes involve temperatures in excess of 1000° C. At these temperatures autodoping and impurity redistribution limit the feature size achievable in VLSI fabrication. As the typical feature sizes move into the submicron region, new processes for epitaxial silicon deposition will be needed. Another application for a low temperature growth process is the fabrication of solar cells on inexpensive metallurgical grade silicon wafers. Impurity diffusion from the wafer during conventional epitaxial silicon growth limits the quality of the solar cells if expensive high purity wafers are not used. We have used electron cyclotron resonance (ECR) plasma deposition to grow high quality epitaxial silicon films on silicon wafers. This growth technique relies on the deposition of silicon from a highly energetic hydrogen and silane plasma. The presence of the hydrogen in the plasma provides reactive etching of the silicon surface during growth. This reduces the oxygen and carbon contamination in the film as well as increasing the number of available growth sites on the surface by displacing the adsorbed hydrogen. By optimizing the growth pressure, substrate temperature, microwave power, substrate bias and silane to hydrogen ratio we have developed a process which provides enhanced growth rates and good uniformity at temperatures (425-575° C) significantly below those used in conventional processes. The structural and electrical properties of the films have been characterized using SEM, TEM, Raman spectroscopy, UV reflectance, spreading resistance profiles, Hall mobility measurements, and both four-point probe and van der Pauw resistivity measurements.


Knowledge And Decision Support For Variable Rate Application Of Materials In Prescription Farming , Jack Robert Ambuel Jan 1995

Knowledge And Decision Support For Variable Rate Application Of Materials In Prescription Farming , Jack Robert Ambuel

Retrospective Theses and Dissertations

One major goal of prescription farming is to optimize application rates for seed fertilizer, and other agricultural inputs as a function of location within a field. There are four main components of a variable rate application system: (1) A method of determining the location of farm equipment (e.g. combines, tractors) within a field. (2) A system for controlling the application rate of materials (seeds, fertilizers, pesticides). (3) The capability to measure the results using a real time yield monitor. (4) An algorithm or prescription for determining what rates of materials to apply at each location. In this dissertation it ...


Flocculation Kinetics Using Dual Coagulants: Effects Of Temperature, Addition Sequence, Rapid Mixing, And Sulfate , Bashaar Yakoub Ammary Jan 1995

Flocculation Kinetics Using Dual Coagulants: Effects Of Temperature, Addition Sequence, Rapid Mixing, And Sulfate , Bashaar Yakoub Ammary

Retrospective Theses and Dissertations

The effects of temperature, rapid mixing time and intensity, sulfate, and coagulant addition sequence of dual coagulants on the flocculation kinetics were studied. Either ferric nitrate alone or a cationic polymer alone or in combination as dual coagulants were used. The flocculation kinetics were monitored using mainly a Photometric Dispersion Analyzer (PDA). An Automatic Image Analyzer was also used in a limited number of experiments to monitor the flocculation kinetics. Kaolinite clay (with four concentrations: 5, 25, 50, and 100 mg/L) suspended in distilled water with added salinity was used at two temperatures (5 or 23°C) and two ...


Unstructured Grid Algorithms For Two- And Three-Dimensional Flows On Parallel Computers , Thomas Hans Ramin Jan 1995

Unstructured Grid Algorithms For Two- And Three-Dimensional Flows On Parallel Computers , Thomas Hans Ramin

Retrospective Theses and Dissertations

The Navier-Stokes equations are solved numerically for two-and three-dimensional viscous laminar flows. The domain is discretized using triangular control volumes in two dimensions and tetrahedra in three dimensions, using existing grid generators. The flow solvers are implemented on a variety of computers, including distributed memory parallel computers;A finite-volume approach is used to discretize the governing flow equations in conservation law form using conserved variables. A cell centered approach is used where the unknowns are computed at the center of each control volume. Both explicit and implicit solution strategies are pursued. In the two-dimensional version of the algorithm an explicit ...


Image Fusion Using Multi-Resolution Decomposition And Lmmse Filter , Jaewon Yim Jan 1995

Image Fusion Using Multi-Resolution Decomposition And Lmmse Filter , Jaewon Yim

Retrospective Theses and Dissertations

The subject of data fusion utilizing heterogeneous sensors has received significant attention in recent years. Each of the sensors provides a limited perspective of the desired information. A heterogeneous sensor environment combined with a procedure for synergistically combining data from each of the transducers can potentially lead to a more comprehensive and accurate estimate of the desired information. An example of a field that can profit from the application of data fusion techniques is the area of nondestructive evaluation (NDE);This dissertation is concerned with developing efficient image fusion techniques for NDE applications. This dissertation begins with a brief description ...