Open Access. Powered by Scholars. Published by Universities.®
- Discipline
- Institution
- Keyword
- Publication
- Publication Type
Articles 1 - 8 of 8
Full-Text Articles in Engineering Physics
A Monte Carlo Analysis Of Computerized Tomography, Karyl J. Davis
A Monte Carlo Analysis Of Computerized Tomography, Karyl J. Davis
Theses and Dissertations
The purpose of this thesis was to model a computerized tomography device (CT) using Monte Carlo methods to determine the scattered radiation spectrum inside and the dose outside the suite at Wright-Patterson Medical Center and at a generic suite to non-occupational personnel. This was driven by the recent inclusion of the most recent NCRP recommended dose limits into 10CFR20 of 50 mSv, occupational; 1 mSv; non-occupational continuous exposure; and 5 mSv, infrequent exposure. The rotating fan beam of the CT was modeled for MCNP, a general-purpose Monte Carlo n-particle transport modeL The CT target was a standard human phantom defined …
Photoluminescence And Electroluminescence Of Erbium And Neodymium Implanted Semiconductors, James R. Hunter
Photoluminescence And Electroluminescence Of Erbium And Neodymium Implanted Semiconductors, James R. Hunter
Theses and Dissertations
Low temperature photoluminescence (PL) and electroluminescence (EL) measurements were used to study the excitation of erbium- and neodymium-implanted GaAs and AlxGa1-xAs (x=0. 1, 0.3) pn-junctions. The rare-earth (RE) emissions were investigated as a function of ion dose, aluminum mole fraction, laser excitation power, and applied forward bias voltage for the implanted samples. Low temperature PL was also measured from Er doped silicon grown by the metalorganic chemical vapor-phase deposition (MOCVD) method using various growth parameters.. The MOCVD-grown Si samples were studied as a function of metalorganic source temperature, silane (SiH4) flow, growth time, and …
Combination Effects Of Irradiation And Chemical Doping On High Temperature Superconductors, Russell J. Fedewa
Combination Effects Of Irradiation And Chemical Doping On High Temperature Superconductors, Russell J. Fedewa
Honors Theses
The goal of this project is to investigate some methods that improve the critical transport current in high temperature superconductors. A superconductor is a material which can allow an electrical current to flow through it with no resistance. This makes them ideal for a wide variety of applications. Most of the present use is in science or medicine, and show promise in computer circuitry materials and electromagnetic trains. This experiment explores a means of increasing the critical current, the maximum amount of electric current that can pass, and which at present is too low to permit the use of superconductors …
Comparison Of Time-Domain Reflectometry Performance Factors For Several Dielectric Geometries: Theory And Experiments, S. V. Maheshwarla, R. Venkatasubramanian, Robert F. Boehm
Comparison Of Time-Domain Reflectometry Performance Factors For Several Dielectric Geometries: Theory And Experiments, S. V. Maheshwarla, R. Venkatasubramanian, Robert F. Boehm
Electrical & Computer Engineering Faculty Research
We propose three nontraditional dielectric geometries and present an experimental and theoretical analysis and comparison of time domain reflectometry (TDR) performances for them. The traditional geometry (the probes inserted in material of essentially infinite extent) is compared to three nontraditional geometries where the probes are affixed outside of a core sample, inside of a bore, or flat on the surface of a semi-infinite solid. Our derivation relates the velocity of electromagnetic wave propagation to the complex permittivities and permeabilities of the media and the geometry for the three nontraditional configurations. Experimental results for air, styrofoam, dry sand, wet sand of …
Optimal Wavefront Reconstruction For A Coherent Diffracted Field, William W. Arrasmith
Optimal Wavefront Reconstruction For A Coherent Diffracted Field, William W. Arrasmith
Theses and Dissertations
In sheared coherent beam interferometric imaging, an estimate of the average reflectivity profile of the object can be computed from measurements of point to point phase differences in the far field interference pattern and a suitable phase reconstruction technique. The phase difference information is encoded in the irradiance of three identical, shifted and superimposed speckled laser beam patterns. A minimum variance phase reconstruction technique is presented to estimate the phase of the field in the measurement plane from the phase differences and evaluate its performance. Prior knowledge of the phase covariance is used in the minimum variance reconstructor. Analytic calculations …
Supralinear Photoconductivity Of Copper Doped Semi-Insulating Gallium Arsenide, K. H. Schoenbach, R. P. Joshi, F. Peterkin, R. L. Druce
Supralinear Photoconductivity Of Copper Doped Semi-Insulating Gallium Arsenide, K. H. Schoenbach, R. P. Joshi, F. Peterkin, R. L. Druce
Bioelectrics Publications
We report on the intensity dependent supralinear photoconductivity in GaAs:Si:Cu material. The results of our measurements show that the effective carrier lifetime can change over two orders of magnitude with variations in the intensity of the optical excitation. A threshold intensity level has been observed and can be related to the occupancy of the deep copper level. Numerical simulations have also been carried out to analyze the trapping dynamics. The intensity dependent lifetimes obtained from the simulations match the experimental data very well. Finally, based on the nonlinear intensity dependence of the effective lifetimes, a possible low‐energy phototransistor application for …
Energy-Loss Particle Identification In 2-D Silicon Drift Detectors, G. Douglas Maudlin, A. A. Rollefson, Wilfred J. Braithwaite
Energy-Loss Particle Identification In 2-D Silicon Drift Detectors, G. Douglas Maudlin, A. A. Rollefson, Wilfred J. Braithwaite
Journal of the Arkansas Academy of Science
A relatively new type of transducer known as the Silicon Drift Detector (SDD) has been fabricated onto thin silicon wafers. SDD operates like a miniature, high-resolution, 2-D Time-projection chamber. One of these devices can detect two dimensions of an ionizing particle's position, and its integrated electrical charge output level isproportional to the particle's energy loss through the silicon. An array ofSDD's, arranged in three coaxial cylinders, is being considered as part of an instrument surrounding the beam pipe of highly-relativistic colliding beam facility, where it would be used to simultaneously track individual paths of thousands of charged particles emerging from …
Characterization Of Piezoceramic Crosses With Large Range Scanning Capability And Applications For Low Temperature Scanning Tunneling Microscopy, J. A. Helfrich, Shireen Adenwalla, J. B. Ketterson, G. A. Zhitomirsky
Characterization Of Piezoceramic Crosses With Large Range Scanning Capability And Applications For Low Temperature Scanning Tunneling Microscopy, J. A. Helfrich, Shireen Adenwalla, J. B. Ketterson, G. A. Zhitomirsky
Shireen Adenwalla Papers
We have developed a large amplitude piezoceramic scanner which should have numerous applications. Scanning tunneling microscopy (STM) and other scanning probe microscopies predominantly use piezoceramics for the scanning elements. Similarly adaptive optics, high resolution lithography, and micromanipulators are other examples of research which regularly utilize piezoceramic scanners. We present a new geometry for a piezoceramic scanner which allows for both high resolution (~nanometers) and large amplitude (~400 µm) displacements. The cross-shaped geometry makes it possible to produce extremely long pieces with very high tolerances. We have shown its effectiveness by using it as the major component of a low temperature …