Engineering Commons^™

The Effects Of Low Doses (1 To 500 Kilograys) Of 100-Kev Electrons On Four Polymers, Cynthia Anne Bradbury

Physics Theses & Dissertations

Commercial films of polyetherimide (PEI), polyetheretherimide (PEEI), polyethylene terephthalate (PET), and polycarbonate (PC) were exposed in vacuum to l 00-keV electron radiation to total absorbed doses of l, l 0, l 00, 300, and 500 kilograys. The concentration of radiation-generated radicals, as measured by electron paramagnetic resonance (EPR), increased by over an order of magnitude in all four polymers. Correspondingly, the intensity of the infrared absorption peaks increased uniformly for all doses. Solubility tests resulted in decreased solubility in all polymers. IR, EPR, and solubility suggest dehydrogenation of the aliphatic C-H and phenyl C-H sites. The data indicated that cross …

Viscous Shock Layer Analysis Of Hypersonic Flows Over Long Slender Vehicles, Kam-Pui Lee

Mechanical & Aerospace Engineering Theses & Dissertations

A method for solving the viscous shock-layer equations for hypersonic flows over long slender bodies is presented. The governing equations are solved by employing a spatial-marching implicit finite-difference technique. The two first-order equations, continuity and normal momentum, are solved simultaneously as a coupled set. This method yields a simple and computationally efficient technique.

Flows past hyperboloids and sphere cones with body half angles of five to 35 degrees are considered. The flow conditions included are from high Reynolds numbers at low altitudes to low Reynolds numbers at high altitudes. Detailed comparisons have been made with other predictions and experimental data …

A Finite Element Formulation For The Large Deflection Random Response Of Thermally Buckled Structures, James Eugene Locke

Mechanical & Aerospace Engineering Theses & Dissertations

The effects of temperature and acoustic loading are included in a theoretical finite element large deflection formulation for thin, isotropic plate and beam type structures. Thermal loads are applied as steady-state temperature distributions, and acoustic loads are taken to be stationary and Gaussian with zero mean and uniform magnitude and phase over the surface of the structure. Material properties are considered to be independent of temperature. Also, inplane and rotary inertia terms are assumed to be neglegible, and all inplane edge conditions are taken to be immovable. For the random vibration analysis, cross correlation terms are included.

The nature of …

Application Of Advanced Grid Generation Techniques For Flow Field Computations About Complex Configurations, Monchai Kathong

Mechanical & Aerospace Engineering Theses & Dissertations

In the computation of flow fields about complex configurations, it is very difficult to construct a boundary-fitted coordinate system. An alternative approach is to use several grids at once, each of which is generated independently. This procedure is called the "multiple grids" or "zonal grids" approach, and its applications are investigated in this study. The method is a conservative approach and provides conservation of fluxes at grid interfaces. The Euler equations are solved numerically on such grids for various configurations. The numerical scheme used is the finite-volume technique with a three-stage Runge-Kutta time integration. The code is vectorized and programmed …

Numerical Simulation Of Turbulent Flows Past Three-Dimensional Cavities, Shivakumar Srinivasan

Mechanical & Aerospace Engineering Theses & Dissertations

Computations have been performed to simulate turbulent supersonic, transonic, and subsonic flows past three-dimensional deep, transitional, and shallow cavities. Simulation of these self sustained oscillatory flows has been generated through time accurate solutions of Reynolds averaged full Navier-Stokes equations using the explicit MacCormack scheme. The Reynolds stresses have been modeled, using the Baldwin-Lomax algebraic turbulence model with certain modifications. The computational results include instantaneous and time averaged flow properties everywhere in the computational domain. Time series analyses have been performed for the instantaneous pressure values on the cavity floor. Comparison with experimental data is made in terms of the mean …

Investigation Of Supersonic Chemically Reacting And Radiating Channel Flow, Mortaza Mani

Mechanical & Aerospace Engineering Theses & Dissertations

The two-dimensional time dependent Navier-Stokes equations are used to investigate supersonic flows undergoing finite rate chemical reaction and radiation interaction for a hydrogen-air system. The explicit multi-stage finite volume technique of Jameson is used to advance the governing equations in time until convergence is achieved. The chemistry source term in the species equation is treated implicitly to alleviate the stiffness associated with fast reactions. The multi-dimensional radiative transfer equations for a nongray model are provided for a general configuration, and then reduced for a planer geometry. Both pseudo-gray and nongray models are used to represent the absorption-emission characteristics of the …

Integral Equation Solution Of The Full Potential Equation For Three-Dimensional, Steady, Transonic Wing Flows, Li-Chuan Chu

Mechanical & Aerospace Engineering Theses & Dissertations

An integral equation method for solving the full potential equation has been developed for three dimensional transonic vortex-wing flows. This method is capable of capturing shocks using the Murman-Cole type of finite difference scheme and is capable of predicting accurate and force-free wake shape as well.

Reading the full potential equation as Poisson's equation, the solution for the velocity field has been expressed in terms of an integral equation using Green's theorem. The solution consists of a surface integral of vorticity distribution on the wing and its free-vortex sheets and a volume integral of source distribution within a computational region …

Full-Potential Integral Solutions For Steady And Unsteady Transonic Airfoils With And Without Embedded Euler Domains, Hong Hu

Mechanical & Aerospace Engineering Theses & Dissertations

The integral equation solution of the full-potential equation is presented for steady and unsteady transonic airfoil flow problems. The method is also coupled with an embedded Euler domain solution to treat flows with strong shocks for steady flows.

For steady transonic flows, three integral equation schemes are well developed. The first two schemes are based on the integral equation solution of the full-potential equation in terms of the velocity field. The Integral Equation with Shock-Capturing (IE-SC) and the Integral Equation with Shock-Capturing Shock-Fitting (IE-SCSF) schemes have been developed. The IE-SCSF scheme is an extension of the IE-SC scheme, which consists …

A Bulk Optically Controlled Semiconductor Switch, Rudolf K.F. Germer, Karl H. Schoenbach, Stephen G.E. Pronko

Bioelectrics Publications

Turn‐on and turn‐off of bulk semiconductor switches, based on excitation and quenching of photoconductivity, respectively, have been demonstrated with copper‐doped II‐VI semiconductor crystals. The increase of the conductivity (turn‐on) was realized with a xenon flash‐lamp pulse of 15‐μs duration. A reduction of the conductivity (turn‐off) was obtained by irradiating the samples with IR light using an 8‐ns Nd:YAG laser pulse (YAG denotes yttrium aluminum garnet). For turn‐on in CdS:Cu the conductivity follows the xenon flash excitation. The turn‐off time constant was 250 ns. ZnS and ZnSe crystals showed a slower response. A memory effect for the IR light was observed.

Raman Scattering Characterization Of The Microscopic Structure Of Semi-Insulating Polycrystalline Si Thin Films, D.J. Olego, H. Baumgart

Electrical & Computer Engineering Faculty Publications

Raman scattering experiments were carried out to study the microscopic structure of semi-insulating polycrystalline Si (SIPOS) thin films prepared by low-pressure chemical vapor deposition. The samples contain 18, 25, and 30 at. % of oxygen and after growth they were annealed at 900 and 1000°C for 30 min. The Raman spectra show in the vibrational region of the optical frequencies of Si two bands, which arise from scattering in crystalline grains and disordered forms of Si. The behavior of these bands as a function of oxygen content and annealing temperatures was established in detail. The crystallinelike band peaks below the …

Strains In Si-Onsio2 Structures Formed By Oxygen Implantation: Raman Scattering Characterization, D.J. Olego, H. Baumgart, G.K. Celler

Electrical & Computer Engineering Faculty Publications

Low-temperature Raman scattering measurements were carried out to characterize Si-on-SiO₂ structures formed by oxygen implantation and subsequent furnace or lamp annealing. The experiments were conducted with 413.1 nm laser light to probe only the thin Si layers at the top of the structures. The Raman spectra of the furnace-annealed samples are red shifted and broadened when compared with a virgin Si surface. The shifts and broadenings decrease with increasing annealing temperatures but they are still present in samples annealed above 1250°C for 3 h. No shifts or broadenings affect the Raman peaks of the layers, which were lamp annealed …

An Optically Controlled Closing And Opening Semiconductor Switch, K. H. Schoenbach, V. K. Lakdawala, R. Germer, S. T. Ko

Electrical & Computer Engineering Faculty Publications

A concept for a bulk semiconductor switch is presented, where the conductivity is increased and reduced, respectively, through illumination with light of different wavelengths. The increase in conductivity is accomplished by electron ionization from deep centers and generation of bound holes. The reduction of conductivity is obtained by hole ionization from the excited centers and subsequent recombination of free electrons and holes. The transient behavior of electron and hole density in a high power semiconductor (GaAs:Cu) switch is computed by means of a rate equation model. Changes in conductivity by five orders of magnitude can be obtained.

Dynamic Allocation Of Responsibility Between Operators With Different Models Of System Information Using Computer-Mediated Communication, Michele Terranova

Psychology Theses & Dissertations

This research focused on the effectiveness of two operator teams for dynamic control of a process simulation. The responsibility for system optimization and failure detection was shared by the operators through computer-mediated communication. System information was displayed to both operators by one of three mental models of the systems: an alphanumeric/separable representation, a graphic/integral system representation, or both representations. The following team-display configurations were used: primary operator with graphic display, support operator with alphanumeric (GRAL); primary operator with alphanumeric display, support operator with graphic (ALGR); both operators with alphanumeric displays (BOAL); both operators with graphic displays (BOGR); and both operators …

A Simple Solid-Phase Electrophoretic Procedure For The Separation Of Plasmid Dna, Linda Ann Simurra

Biological Sciences Theses & Dissertations

A method was developed for extraction of plasmid DNA from bacterial cells embedded in agarose blocks. Cell - containing blocks were treated with various lysing reagents and inserted into the wells of an agarose gel. Upon electrophoresis the plasmid DNA migrated out of the embedding block and into the gel leaving intact chromosomal DNA in the well. This method was tested with various organisms and found to be effective for plasmid isolation. In comparison to "traditional" procedures, this new method is less tedious since chemical separation of plasmids is not required prior to electrophoresis. Also, a higher yield of plasmid …