Open Access. Powered by Scholars. Published by Universities.®

Engineering Commons

Open Access. Powered by Scholars. Published by Universities.®

Articles 1 - 16 of 16

Full-Text Articles in Engineering

Cracking In Cycloaliphatic Epoxy/Aluminum Composite Electrical Bushings, Keith Alan Parker Apr 1999

Cracking In Cycloaliphatic Epoxy/Aluminum Composite Electrical Bushings, Keith Alan Parker

Doctoral Dissertations

The problem of cracking in electrical apparatus bushings as a result of thermal stresses was investigated. The bushings were composed of cycloaliphatic epoxy insulators with embedded aluminum conductors. The problem is due to the difference in coefficients of thermal expansion of the two materials. A solution to the problem had been to coat the conductors before they were formed together with the epoxy insulators. The coating was assumed to prevent cracking by allowing movement between the two materials as their dimensions changed during thermal expansion and contraction. The contribution of the coating was to be established.

The hypothesis was that ...


Preparation And Surface Studies Of Negative Electron Affinity Semiconductors Photocathodes, Khaled A. Elamrawi Apr 1999

Preparation And Surface Studies Of Negative Electron Affinity Semiconductors Photocathodes, Khaled A. Elamrawi

Electrical & Computer Engineering Theses & Disssertations

Fabrication of high quantum efficiency, long lifetime negative electron affinity photocathodes is important for applications such as photomultipliers, image intensifiers, electron beam lithography, electron microscopy, and polarized electron sources. The surface cleanliness of the III-V semiconductor photocathode is crucial in obtaining high photosensitivity.

GaAs(100) and InP(100) photocathodes are prepared by atomic hydrogen cleaning. The cleaning effect on the photocathode performance is discussed. The surface degradation mechanisms which reduce the photocathode lifetime are presented. The photocathode surface cleanliness, structure, and morphology are studied using reflection high-energy electron diffraction (RHEED).

Quantum efficiencies of ∼14% and 8% are obtained for GaAs ...


Characterizing Growth Rates And Growth Rate Dispersion Of Secondary Nuclei As A Function Of Supersaturation , Christopher Michael Jones Jan 1999

Characterizing Growth Rates And Growth Rate Dispersion Of Secondary Nuclei As A Function Of Supersaturation , Christopher Michael Jones

Retrospective Theses and Dissertations

The growth rates of secondary crystal nuclei determine the number of crystals that will reach a size large enough to contribute to the final product mass in a crystallization process. Contact nuclei were chosen for study because crystals nucleated under conditions of low supersaturation are formed by contact or secondary nucleation. High supersaturation levels are required for primary nucleation to occur. Growth rate dispersion complicates the prediction of growth rates and product size distributions. Having growth rate dispersion in a crystallizing system means that despite the population of crystals having all been nucleated and grown under identical conditions, they grow ...


Development Of Highly Magnetostrictive Composites For Applications In Magnetomechanical Torque Sensors , Yonghua Chen Jan 1999

Development Of Highly Magnetostrictive Composites For Applications In Magnetomechanical Torque Sensors , Yonghua Chen

Retrospective Theses and Dissertations

The objective of this work was to investigate and develop a new type of magnetomechanical material with high magnetomechanical response and low hysteresis. This material will be used in electronic torque sensors. A major appreciation could be for advanced steering systems in automobiles which will replace the fuel inefficient hydraulic steering systems currently in use;The effect of the matrix material on the magnetostriction of composites containing highly magnetostrictive particles was studied. Both experimental and modeled results showed that the elastic modulus of the matrix is an important factor determining the magnetostriction of the composite. For a series of composites ...


High Temperature Phase Equilibria Studies In The Bi-Sr-Ca-Cu-O-Ag System , Lawrence Margulies Jan 1999

High Temperature Phase Equilibria Studies In The Bi-Sr-Ca-Cu-O-Ag System , Lawrence Margulies

Retrospective Theses and Dissertations

A variety of experimental techniques were utilized to examine the high temperature phase equilibria in the Bi-Sr-Ca-Cu-0-Ag system. Quenching studies were used to determine the liquid solubility of Ag in the Bi2Sr2CaCu2O8 (Bi2212) melt and the details of the peritectic decomposition pathway of Bi2212 as a function on Ag content and oxygen partial pressure (PO2). A liquid immiscibility region between oxide and Ag liquids in the 8-98 at% range was found above 9000C. Two eutectics were found in the Bi2212-Ag pseudo-binary. On the oxide rich side, a eutectic exists at approximately 4 at% Ag. On the Ag rich side, a ...


A Comparison Of Thermoelectric Phenomena In Diverse Alloy Systems , Bruce Allan Cook Jan 1999

A Comparison Of Thermoelectric Phenomena In Diverse Alloy Systems , Bruce Allan Cook

Retrospective Theses and Dissertations

A study of the preparation and analysis of selected transport properties of several thermoelectric materials is described. These systems include heavily-doped silicon-germanium solid solutions, ternary half-Heusler intermetallic compounds, electrically-conductive oxides, and rare earth chalcogenides. The alloys were prepared by various techniques (mechanical alloying, vapor phase reaction, or arc melting) depending upon such parameters as ductility, volatility, and chemical reactivity of the components. All materials were characterized for phase purity by x-ray diffraction and for chemical purity by various analytical techniques. Transport properties (electrical resistivity, Seebeck coefficient, and thermal diffusivity) were characterized between 22°C and 1000°C under vacuum conditions ...


The Effect Of Chromate On Adhesion Between Epoxy Coating And Al Substrate, Po-Nien Chen Jan 1999

The Effect Of Chromate On Adhesion Between Epoxy Coating And Al Substrate, Po-Nien Chen

Theses and Dissertations

No abstract provided.


Control Of Tin Compositon And Mold Medium To Reduce The Severity Of Microshrinkage In Copper-Tin Sand Catings, Timothy D. Selleck Jan 1999

Control Of Tin Compositon And Mold Medium To Reduce The Severity Of Microshrinkage In Copper-Tin Sand Catings, Timothy D. Selleck

Theses and Dissertations

No abstract provided.


Use Of Scrap Tires In Civil Engineering Applications , Shiping Yang Jan 1999

Use Of Scrap Tires In Civil Engineering Applications , Shiping Yang

Retrospective Theses and Dissertations

Using scrap tires as construction materials in civil engineering is of growing interest. Whole scrap tires have been used as culverts, retaining walls, and for slope and beach stabilization. Shredded tires have been used as horizontal drains, ravine crossings, highway embankments, lightweight backfill, and road bed support. The practice of these applications needs the engineering properties of scrap tires. This dissertation involves the quantification of the structural and hydraulic properties of whole truck tires as underground culverts, the derivation of a new stress-strain relationship for low-stiffness flexible pipes and its application to a truck tire culvert, and the investigation and ...


Transport Processes In Directional Solidification And Their Effects On Microstructure Development , Prantik Mazumder Jan 1999

Transport Processes In Directional Solidification And Their Effects On Microstructure Development , Prantik Mazumder

Retrospective Theses and Dissertations

The processing of materials with unique electronic, mechanical, optical and thermal properties plays a crucial role in modern technology. The quality of these materials depend strongly on the microstructures and the solute/dopant fields in the solid product, that are strongly influenced by the intricate coupling of heat and mass transfer and melt flow in the growth systems. An integrated research program is developed that include precisely characterized experiments and detailed physical and numerical modeling of the complex transport and dynamical processes. Direct numerical simulation of the solidification process is carried out that takes into account the unsteady thermo-solutal convection ...


Structure And High-Temperature Properties Of Ti5si3 With Interstitial Additions , Jason John Williams Jan 1999

Structure And High-Temperature Properties Of Ti5si3 With Interstitial Additions , Jason John Williams

Retrospective Theses and Dissertations

This study was motivated by the fact that previous research on the structure and properties of Ti5Si3 showed unacceptably inconsistent results. The primary reason for these inconsistencies were due to interstitial contamination of Ti5Si3 by carbon, nitrogen and oxygen. Thus, this study measured the effects that these interstitial atoms have on some of the previously reported properties. These properties of Ti5Si 3Zx (Z = Be C, N or O; x = 0 to 1) include crystalline structure, thermal expansion anisotropy, electronic structure and bonding, and high temperature oxidation resistance. By using pure samples, accurate lattice parameters for pure Ti5Si3 were determined to ...


The Interplay Of Long-Range Magnetic Order And Single-Ion Anisotropy In Rare Earth Nickel Germanides , Zahirul Islam Jan 1999

The Interplay Of Long-Range Magnetic Order And Single-Ion Anisotropy In Rare Earth Nickel Germanides , Zahirul Islam

Retrospective Theses and Dissertations

This dissertation is concerned with the interplay of long-range order and anisotropy in the tetragonal RNi2Ge2 (R = rare earth) family of compounds. Microscopic magnetic structures were studied using both neutron and x-ray resonant exchange scattering (XRES) techniques;The magnetic structures of Tb, Dy, Eu and Gd members have been determined using high-quality single-crystal samples. TbNi2Ge2 and DyNi2Ge2 order in an amplitude modulated structure below TN, with propagation vectors (0 0 ∼ 0.758) and (0 0 ∼ 0.75), respectively. Below Tt < TN, the structures are equal moment commensurate , described by three modulations, (0 0 ¾) and its third harmonic (0 0 ¼), (½ ½ 0) and (½ ½ ½), respectively. Whereas the Tb compound is uniaxial with moments along the c&d4; axis in both phases, its Dy neighbor has an ordered in-plane component. XRES is the probe of choice for the study of neutron-opaque Eu and Gd members. While EuNi2Ge2 has a simple antiferromagnetic state, (0 0 1), with moments in the basal plane, GdNi2Ge 2 orders with an incommensurate modulation, (0 0 ∼ 0.793) at TN. There is an ordered component along c&d4; in the Gd compound below TN but above Tt. Below Tt, Gd moment is locked to the basal plane;This work has correlated a strong Fermi surface nesting to the magnetic ordering in the RNi2Ge2 compounds. Generalized susceptibility, c0 (q), calculations found nesting to be responsible for both incommensurate ordering wave vector in GdNi2Ge 2, and the commensurate structure in EuNi2Ge 2. A continuous transition from incommensurate to commensurate magnetic structures via band filling is predicted. The surprisingly higher TN in EuNi2Ge2 than that in GdNi 2Ge2 is also explained;Next, all the metamagnetic phases in TbNi2Ge2 with an applied field along the c&d4; axis have been characterized with neutron diffraction measurements. A "mixed phase" model for the first metamagnetic structure consisting of fully-saturated as well as reduced-moment Tb ions is presented. The moment reduction may be due to moment instability which is possible if the exchange is comparable to the low-lying CEF level splitting and the ground state is a singlet. In such a case, certain Tb sites may experience a local field below the critical value needed to reach saturation.


Backscattering And Attenuation During The Propagation Of Ultrasonic Waves In Duplex Titanium Alloys , Paul Donald Panetta Jan 1999

Backscattering And Attenuation During The Propagation Of Ultrasonic Waves In Duplex Titanium Alloys , Paul Donald Panetta

Retrospective Theses and Dissertations

This dissertation reports results from studies of the interactions between the microstructure/macrostructure of titanium alloys and propagating ultrasonic waves. Attention is focused on the interactions which cause backscattering and attenuation. Experimental studies will be reported which show that the phase aberration contribution to attenuation does not remove energy from the propagating beam, and a physical picture is developed. A simple ray model which encompasses the ideas presented in the physical picture is used to predict attenuation for propagation in single phase materials with elongated grains. In addition, a general theory for attenuation that includes some degree of multiple scattering ...


High Pressure Crystallization Of Purafect® Subtilisin , Ruta Yeshwant Waghmare Jan 1999

High Pressure Crystallization Of Purafect® Subtilisin , Ruta Yeshwant Waghmare

Retrospective Theses and Dissertations

The aim of this work was to study the effect of high pressure on kinetics of subtilisin crystallization and to use high pressure as a means to better understand the mechanism of crystallization;It is known that the effect of hydrostatic pressure on conformation varies with the protein being studied. To determine the effect of high pressure on the conformation of subtilisin, activity assays were used in addition to FTIR spectroscopy. Pressures up to 100 MPa were found to cause no irreversible conformational changes in subtilisin;To study the effect of high pressure on subtilisin crystallization, a factorial experiment was ...


The Thermographic Nondestructive Evaluation Of Iron Aluminide Green Sheet, Michael L. Watkins Jan 1999

The Thermographic Nondestructive Evaluation Of Iron Aluminide Green Sheet, Michael L. Watkins

Dissertations, Theses, and Masters Projects

The recent development of manufacturing techniques for the fabrication of thin iron aluminide sheet requires advanced quantitative methods for on-line inspection. An understanding of the mechanisms responsible for flaws and the development of appropriate flaw detection methods are key elements in an effective quality management system. The first step in the fabrication of thin FeAl alloy sheet is the formation of a green sheet by cold rolling FeAl powder mixed with organic binding agents. The green sheet composite has a bulk density, which is typically less than about 3.6 g/cc. The finished sheet, with a density of about ...


Fabrications And Characterizations Of Boron Containing Polyimides For Radiation Shielding, Christopher Scott Pugh Jan 1999

Fabrications And Characterizations Of Boron Containing Polyimides For Radiation Shielding, Christopher Scott Pugh

Dissertations, Theses, and Masters Projects

No abstract provided.