Department: Physics ![[clear]](close-x.png "Remove this limiter")
35 matches in the database.
These are records: 1 - 30.
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1.
Acosta, Roberto I.
Ostwald Ripening of Iron (Fe) Catalyst Nanoparticles on Aluminum Oxide Surfaces (Al2O3) for the Growth of Carbon Nanotubes .
Degree: MS, Physics, 2010, Wright State University
► Theoretical models have proposed that the nucleation and growth mechanism of carbon…
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▼ Theoretical models have proposed that the nucleation and growth mechanism of carbon nanotubes (CNTs) has been affected by the catalytic activity of transition metals. The catalyst behavior during growth has been mainly associated as the responsible mechanism for the termination of CNT growth. Although several hypotheses have been developed to explain this mechanism, is still today an unresolved phenomenon. It was recently shown that the Ostwald ripening of iron (Fe) nanoparticles played a dominant role in the termination of CNT growth. The Ostwald ripening mechanism was further investigated as a function of thermal annealing in Hydrogen (H2) for iron (Fe) catalyst nanoparticles on various surfaces of aluminum oxide (i.e. sputtered alumina (a-Al2O3), and C- face sapphire (α-Al2O3)).Experimental results showed that the growth kinetics of Fe nanoparticles on a-Al2O3 and α-Al2O3 obeyed the Ostwald ripening mechanism. The proportionality constant (K) for the kinetic equation of the Lyfshitz-Slyozov-Wagner (LSW) theory was calculated for a-Al2O3 and α-Al2O3, Ka-Al2O3 = 1.423 x 10-29 m3 s-1, and Kα-Al2O3 = 7.145 x 10-29 m3 s-1. The log-normal particle size distribution for the Fe nanoparticles was studied as a function of annealing time in H2 for 5, 10, and 15 minutes. It was found that the ripening of the particles is dependent on the surface, where a-Al2O3 < α-Al2O3. Then, after the growth of SWNTs, the particle size distribution of Fe was also investigated on C- and A- face sapphire surfaces. Experimental results showed that the Ostwald ripening rate of the catalyst nanoparticles is higher for the A- face than the C- face sapphire. The synthesis of SWNTs resulted in randomly oriented tubes on the C- face sapphire; as opposed to aligned tubes on the A- face sapphire surfaces. The SWNTs aligned along the specific crystalline directions corresponding to the anisotropic pseudo-1D array of Al atoms on the sapphire surface. The Ostwald ripening effect and the synthesis of SWNTs, was characterized by atomic force microscopy (AFM), scanning electron microscopy (SEM), and Raman Spectroscopy. Due to experimental constraints, a theoretical prediction to modify the LSW theory was not developed at this instance. It is predicted that the particle size distribution will not agree with the LSW theory or with modified LSW equations, probably due to other conditions not included in the Ostwald ripening theory. This disagreement may be due to the existence of multiple and complex variables linked to the growth of CNTs, which are not taken into account in modern coarsening theories. Therefore, it is essential to further quantify all the associated variables that are responsible for the termination growth mechanism of CNTs. The development of a robust kinetic equation that can be coupled to experimentations would be necessary for the achievement of a more realistic Ostwald ripening model.
Advisors/Committee Members: Deibel, Jason.
Subjects: Physics
Keywords: Ostwald ripening; CNT; carbon; nanotubes; catalyst; iron; CVD; growth; kinetics; coarsening
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2.
Benasutti, Patrick B.
Electronic and Structural Properties of Silicene and Graphene Layered Structures.
Degree: MS, Physics, 2012, Wright State University
► Graphene is a two-dimensional nanomaterial with useful and novel properties, but it…
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▼ Graphene is a two-dimensional nanomaterial with useful and novel properties, but it is a material that does not integrate well with the current silicon microchip infrastructure. Silicene could solve this problem, as it is made of silicon yet retains the novel properties that make graphene desirable. This thesis will outline density functional calculations of a newly proposed structure involving the combination of these two materials. The structure includes silicene layered on graphene in such a manner that it composes a superlattice. It will be examined using the ab-initio density functional theory software Quantum Espresso. This superlattice structure is proposed to have an increase in electronic transport as well as higher binding energy versus standard graphene. Examination of the proposed superlattice is accomplished by using PBE-GGA functionals versus a previous LDA methodology. In conclusion, the results confirm the pattern of increased binding energy in the superlattice as well as increased electron transport, but the amount of increase in the electron transport is not the same as the accepted results. The desirable structural effects of graphene are maintained by the data.
Advisors/Committee Members: Lew Yan Voon, Lok C.
Subjects: Physics
Keywords: Silicene, Quantum Espresso, Graphene, Superlattice
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3.
Bernard, Benjamin.
On the Quantization Problem in Curved Space.
Degree: MS, Physics, 2012, Wright State University
► The nonrelativistic quantum mechanics of particles constrained to curved surfaces is studied.…
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▼ The nonrelativistic quantum mechanics of particles constrained to curved surfaces is studied. There is open debate as to which of several approaches is the correct one. After a review of existing literature and the required mathematics, three approaches are studied and applied to a sphere, spheroid, and triaxial ellipsoid. The first approach uses differential geometry to reduce the problem from a three dimensional problem to a two-dimensional problem. The second approach uses three dimensions and holds one of the separated wavefunctions and its associated coordinate constant. A third approach constrains the particle in a three-dimensional space between two parallel surfaces and takes the limit as the distance between the surfaces goes to zero. Analytic methods, finite element methods, and perturbation theory are applied to the approaches to determine which are in agreement. It is found that the differential geometric approach has the most agreement. Constrained quantum mechanics has application in materials science, where topological surface states are studied. It also has application as a simplified model of Carbon-60, graphene, and silicene structures. It also has application as in semiclassical quantum gravity, where spacetime is a pseudo-Riemannian manifold, to which the particles are constrained.
Advisors/Committee Members: Lew Yan Voon, Lok.
Subjects: Atoms and Subatomic Particles; Condensed Matter Physics; Mathematics; Nanoscience; Nanotechnology; Nuclear Physics; Physics; Quantum Physics; Solid State Physics; Theoretical Mathematics; Theoretical Physics
Keywords: quantum mechanics; differential geometry; constrained quantum mechanics; schrodinger equation; finite element method; spheroid; ellipsoid; sphere; cylinder
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4.
Blank, L. Aaron Jr.
Models of Disordered Media and Predictions of Associated Hydraulic Conductivity.
Degree: MS, Physics, 2006, Wright State University
► In the late 20th century there was a spill of Technetium in…
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▼ In the late 20th century there was a spill of Technetium in eastern Washington State at the US Department of Energy Hanford site. Resulting contamination of water supplies would raise serious health issues for local residents. Therefore, the ability to predict how these contaminants move through the soil is of great interest. The main contribution to contaminant transport arises from being carried along by flowing water. An important control on the movement of the water through the medium is the hydraulic conductivity, K, which defines the ease of water flow for a given pressure difference (analogous to the electrical conductivity). The overall goal of research in this area is to develop a technique which accurately predicts the hydraulic conductivity as well as its distribution, both in the horizontal and the vertical directions, for media representative of the Hanford subsurface. The Hanford subsurface is a disordered sequence of ice-age flood deposits. It is known that concepts from percolation theory are well-suited to addressing transport problems in disordered media. The objective of this thesis was two-fold: (a) to implement techniques using critical path analysis from percolation theory for calculating the distribution of K values for soils with known characteristics, (b) to apply this technique to 53 sets of particle-size data and water retention characteristics taken from soils which represent the area in which the Technetium spill occurred. The research performed should be applicable to other contaminated sites under DOE supervision as well as being relevant for agriculture, climate models, mining and elsewhere.
Advisors/Committee Members: Hunt, Allen.
Keywords: Subsurface Hydrology; Hydraulic Conductivity; Soil Science; Geology; Soil Physics; Percolation Theory
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5.
Buller, Steven Harris.
PHOTOREFRACTIVE THIN FILMS AND POLYMERS FOR USE IN ORGANIC-INORGANIC HYBRID CELLS.
Degree: MS, Physics, 2012, Wright State University
► Two classes of materials were investigated as possible replacements for the bulk…
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▼ Two classes of materials were investigated as possible replacements for the bulk photorefractive windows in inorganic-organic hybrid cells: thin films and polymers. Each material was fabricated and subsequently characterized using two different methods due to their different stages of development. The thin films were characterized by X-ray diffraction while the polymers were characterized by two-beam coupling. Thin films of strontium barium niobate and potassium niobate were grown, using pulsed laser deposition, on four different substrates. It was found that it was possible to grow a thin film of potassium niobate in the correct orientation to replace a bulk photorefractive window. The characterization of the polymers with the use of two beam-coupling showed they required too high of voltages in order to achieve the photorefractive effect and also had sub-optimal phase-shift.
Advisors/Committee Members: Kozlowski, Gregory.
Subjects: Optics
Keywords: photrefractive optics, polymers, thin films
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6.
Bulmer, John Simmons.
Temperature and Frequency Dependent Conduction Mechanisms Within Bulk Carbon Nanotube Materials.
Degree: MS, Physics, 2010, Wright State University
► The resistance of three types of bulk carbon nanotube (CNT) materials (floating…
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▼ The resistance of three types of bulk carbon nanotube (CNT) materials (floating catalyst CNT yarn, forest grown CNT yarn, and super acid spun CNT fiber) was measured from room temperature to 900 C. Fitting the curves to established conduction equations for disordered materials, competing conduction mechanisms pertaining to the material could be determined. Floating catalyst CNT yarn displayed both semiconductive and metallic isotropic behavior with a resistance minimum, similar to the behavior of crystalline graphite. It was found that, at room temperature, the semiconducting contribution-most likely junctions between CNTs-accounted for 99.99% of the overall resistance. The resistance of forest grown CNT yarn and super acid solution spun CNT fiber decreased monotonically with temperature at a rate similar to amorphous carbon. The impedance of all three materials was also measured to 30 MHz. All three materials followed a series resistor inductor circuit, without any resistance decrease as others have found. Finally, the conductivity and specific conductivity of all three materials was compared to metallic benchmarks. While all three materials had a similar conductivity, the floating catalyst CNT yarn had a significantly higher specific conductivity.
Advisors/Committee Members: Kozlowski, Gregory.
Subjects: Physics
Keywords: carbon nanotube, CNT, carbon, yarn, fiber, bulk, conduction mechanism, conductivity, frequency, temperature, dependence, versus, graphitic intercalation compounds, annealing, forest growth, floating catalyst, super acid, LCR, network analyzer
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7.
Cetnar, John S.
Atmospheric Effects on the Propagation of MMW and Sub-MMW Radiation.
Degree: MS, Physics, 2010, Wright State University
► This thesis is a study of the propagation of millimeter wavelength (MMW)…
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▼ This thesis is a study of the propagation of millimeter wavelength (MMW) and submillimeter wavelength (sub-MMW) electromagnetic radiation (a.k.a. THz radiation) through the Earth's atmosphere. THz radiation is electromagnetic radiation that exists between the microwave and far infrared regions of the electromagnetic spectrum. It is nonionizing radiation but can penetrate through materials that are opaque to visible light so therefore has many new and useful applications. Unfortunately, THz radiation is heavily attenuated by the Earth's atmosphere as it propagates through it. This therefore represents a challenge to communications and sensing applications at millimeter and sub-millimeter wavelengths. In this work, the general theory of how the atmosphere attenuates propagating THz radiation by absorption and scattering is discussed. From this discussion, we find that water vapor is the constituent of the Earth's atmosphere most responsible for the absorption of THz radiation. The absorption of THz radiation by water vapor was measured at 325 and 620 GHz using steady state or frequency domain absorption spectroscopy. The absorption lines of these frequencies lie in the far wings of a very strong water absorption line at 557 GHz. Spectral line shapes were recorded across a range of pressures and fitted to Voigt profiles. The resulting relationship between the line width and pressure was shown to be linear and very close to published values. Finally, transient signals associated with population and polarization relaxation times were measured at 325 GHz using transient or time domain spectroscopy techniques. Experimental results associated with the steady state and transient measurements will be presented and discussed.
Advisors/Committee Members: Petkie, Douglas.
Subjects: Physics
Keywords: Earth's atmosphere; THz radiation
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8.
Coll Segarra, David.
Dosimetric Effects Near Implanted Vascular Access Ports Under External Electron Beam Radiation.
Degree: MS, Physics, 2010, Wright State University
► Previous studies on dosimetry show important effects for metal vascular access ports…
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▼ Previous studies on dosimetry show important effects for metal vascular access ports for x-rays and electron beams and moderate to no effects for plastic ports for x-ray beams when ports are in the path of the beam. No previous studies exist regarding the effects of electron beams on vascular access ports other than for those made of metal although it has been suggested that electron beam attenuation through non-metal ports may be possible. Measurements of relative ionization through the device and adjacent to the device anteriorly and laterally were taken. A clinical particle accelerator delivered typical clinical electron beams of 6, 9, 12, 16, and 20 MeV through the devices. Results showed a noticeable increase in attenuation in the presence of ports, especially for lower energy beams and little or no variation in scattering measurements.
Advisors/Committee Members: Foy, Brent.
Subjects: Biomedical research; Biophysics; Health; Oncology; Physics; Radiation; Radiology
Keywords: vascular access port; electron beam; dosimetry; attenuation; lateral scatter; backscatter
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9.
Cutlip, James.
Comparison of Two Methods of External Scatter Dose Contributions to the Contralateral Breast.
Degree: MS, Physics, 2008, Wright State University
► The treatment outcomes of many forms of breast cancer have become very…
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▼ The treatment outcomes of many forms of breast cancer have become very favorable. The usual standard of successful treatment of five years without a recurrence is not adequate any longer for breast cancer. Many patients live well beyond this time interval only to have a second malignancy develop in the contralateral breast ten or twenty years later. Boice et al (1992) found that there was a correlation between the amount of dose to the contralateral breast and the likelihood of a secondary malignancy forming. The normal practice today is to use multi-leaf collimators (MLC) to modulate the photon beam in radiation therapy. Due to the limited use of physical compensators, very little data has been presented as to their effectiveness in reducing dose to the contralateral breast. This study will use a Varian 2100 C/D linear accelerator to irradiate a Rando phantom with simulated breast material using both the traditional method and the compensator method. The dose to the contralateral breast will be measured using MOSFETs at various depths in the tissue. The results suggest that the compensators do not reduce the dose to the contralateral breast as effectively as the MLC method. There were a few instances for specific cases where the compensator performed better and these cases require further study for verification and clarity.
Advisors/Committee Members: Foy, Brent.
Subjects: Oncology; Physics; Radiation; Radiology
Keywords: contralateral breast, dose, scatter, compensators, MLC
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10.
Dhanapala, Hembathanthirige Yasas.
Dielectric Constant Measurements Using Atomic Force Microscopy System.
Degree: MS, Physics, 2012, Wright State University
► A new technique to obtain local dielectric constant of thin films was…
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▼ A new technique to obtain local dielectric constant of thin films was developed using atomic force microscopy system. This technique, in addition to other characterization methods such as AFM imaging and X-Ray diffraction, was used to study, as an example, dielectric constant of thin films of 0.3BiScO3 - 0.7BaTiO3. The thin films were fabricated by using pulsed laser deposition technique under following temperature of the substrate: 6500C, 7000C and 7500C. At each temperature, two different oxygen pressures were used in deposition chamber: 50 mTorr and 100 mTorr. Our goal was to find optimal growth conditions with the highest dielectric constant and compare it with their structural properties. In addition, our dielectric constant calculations were generalized to include a wider range of film thicknesses.
Advisors/Committee Members: Kozlowski, Gregory.
Subjects: Physics
Keywords: atomic force microscopy, thin films, dielectric constant, characterization
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11.
Durham, Amanda.
Investigation of the Reflective Properties of a Left-Handed Metamaterial.
Degree: MS, Physics, 2007, Wright State University
► The purpose of this project is to investigate the reflective properties of…
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▼ The purpose of this project is to investigate the reflective properties of a left-handed metamaterial (LHM) through the use of a finite element analysis software called FEMLAB. In the 1960’s, V. Veselago theorized that a material with negative permeability and negative permittivity has a negative index of refraction. In 2000, such a metamaterial was built and demonstrated at microwave frequencies. Previous work had focused on the transmission properties of the metamaterial. In our work, the reflected wave was examined for a LHM subject to an incident transverse electric wave. The different generalizations, first proposed by Veselago, of the Fresnel and Snell’s equations for LHM’s were rederived. We show that the reflectance does not distinguish between normal materials and metamaterials, and, through computational results, that FEMLAB can be used for LHM’s.
Advisors/Committee Members: Lew Yan Voon, Lok.
Keywords: Left-handed; Metamaterial; Reflectivity
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12.
Ford, William Paul.
Development of a Fourier Transform Far Infrared (FTFIR) Spectrometer to Characterize Broadband Transmission Properties of Common Materials in the Terahertz Region.
Degree: MS, Physics, 2006, Wright State University
► With sub-millimeter wave or terahertz devices becoming more readily available, there is…
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▼ With sub-millimeter wave or terahertz devices becoming more readily available, there is interest in developing sensors in this region of the spectra. To support this interest, we have developed a Fourier Transform Far InfraRed (FTFIR) spectrometer to characterize broadband transmission and reflectance coefficients of materials. The spectrometer utilizes a broadband blackbody source, a Michelson interferometer, and silicon bolometer. The path difference in the Michelson is obtained using a linear stage and data acquisition and stage control were both implemented in a Labview programming environment. The details of the experimental setup and experimental results are presented in this thesis. The instrument demonstrated capability to measure the broadband transmission spectra of cloth and cardboard samples and we found that these spectra, which showed transmission < ~0.5 THz and increased in attenuation at higher frequencies, agreed with accepted general trends.
Advisors/Committee Members: Petkie, Doug T.
Subjects: Physics, Optics
Keywords: Terahertz; FTFIR; FTIR; sub-millimeter wave; far-infrared spectroscopy
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13.
Garcia, Aaron Nicholas.
Comparative Investigation of Dosimetric Tools in IMRT.
Degree: MS, Physics, 2007, Wright State University
► Verification of the isodose distribution delivered to the planned tumor volume is…
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▼ Verification of the isodose distribution delivered to the planned tumor volume is required for quality assurance in the clinic. Verification in this context means ensuring that the actual dose delivered to a volume matches the dose that a computerized planning system intended that volume to receive. The computerized planning is performed by a Computerized Medical Systems (CMS) Intensity Modulated Radiation Therapy (IMRT) plan. Two methods of measuring the delivered dose are film dosimetry and diode dosimetry. This project will compare the relative isodose distribution profiles of film dosimetry and MapCheck (Sun Nuclear Corporation, a diode-based dosimetry system) to the relative isodose distribution profile of the CMS IMRT plan. Two IMRT plans were used that were intended to deliver 7500centigray to the prostate. These plans were then performed while measuring the isodose distributions using the above two techniques. The two techniques were compared on the basis of time efficiency and accuracy.
Advisors/Committee Members: Foy, Brent D.
Subjects: Physics, Radiation
Keywords: IMRT
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14.
Guzman-Verri, Gian Giacomo.
Electronic Properties of Silicon-based Nanostructures.
Degree: MS, Physics, 2006, Wright State University
► We have developed a new unifying tight-binding theory that can account for…
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▼ We have developed a new unifying tight-binding theory that can account for the electronic properties of recently proposed Si-based nanostructures, namely, Si graphene-like sheets and Si nanotubes. We considered the sp2s* and sp3 models up to first- and second-nearest neighbors, respectively. Our results show that the corresponding Si nanotubes follow the so-called Hamada's rule. Comparison to a recent ab initio calculation is made.
Advisors/Committee Members: Lew Yan Voon, Lok C.
Subjects: Physics, Condensed Matter
Keywords: Si; nanotubes; graphene; tight-binding; sp2s*; sp3
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15.
Jagoo, Mohammud Zafrullah.
Radio-frequency Heating of Magnetic Nanoparticles.
Degree: MS, Physics, 2012, Wright State University
► In the present study, a power supply capable of converting a direct…
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▼ In the present study, a power supply capable of converting a direct current into an alternating current was built. The frequency of oscillation of the output current could be varied from 174.8 kHz to 726.0 kHz by setting a set of capacitors in resonance. To this power supply is attached a 20-turns copper coil in the shape of a spiral. Because of the high heat generated in the coil, the latter has to be permanently water-cooled. A vacuum pump removes the air between the sample holder and the coil. A fiber optic temperature sensor with an accuracy of 0.001 K was used to measure the temperature of the nanoparticles. Four ferromagnetic nanoparticles (CoFe_2O_4, NiFe_2O_4, Ni_0.5Zn_0.5Fe_2O_4, Co_0.4Ni_0.4Zn_0.2Fe_2O_4) with different magnetic properties were subjected to heating. The heating performance is given by the specific power loss (SPL) which was calculated from the initial slope of the heating curve whereby there is minimum heat loss to the surroundings and the highest SPL was obtained when magnetic field and frequency were highest at 20.6 µT and 348.0 kHz, respectively. When the frequency was changed from 174.8 to 348.0 kHz, the SPL value was double indicating a one-to-one relationship between the frequency and the SPL. No such relationships were found when the magnetic field was increased from 13.8 µT to 20.6 µT. There is also a coercivity and remanent magnetization dependence on the SPL and both of them obey an inverse law. We found that the SPL for Ni_0.5Zn_0.5Fe_2O_4 (GPZ4) was 1.09 ± 0.02 W/g2. Moreover, the sample CoFe_2O_4 (GPZ11) with the highest power loss density (12250 J/m3) measured by the variable sample magnetometer was found to have the lowest SPL (0.135 ± 0.002 W/g2) in the lot. The magnetic field inside the coil is only a fraction the VSM, so when the low magnetic field was turned on, the hysteresis loop opened only to the extent of the minor loop.
Advisors/Committee Members: Kozlowski, Gregory.
Subjects: Physics
Keywords: magnetic nanoparticles; specific power loss; ferromagnetic; hysteresis loop
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16.
Kamanalu, Sunil S.
Proximity and Thickness Estimation of Aluminum 3003 Alloy Metal Sheets Using Multi-Frequency Eddy Current Sensor.
Degree: MS, Physics, 2010, Wright State University
► The research work is focused on conducting a feasibility study on a…
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▼ The research work is focused on conducting a feasibility study on a new “non-contact” single probe dual coil inductive sensor for sensing the proximity and thickness of Aluminum (Al) 3003 alloy metal sheets, which is a non-magnetic metal. A bulk of the research and development work has already been done in the area of non-destructive testing (NDT) using eddy current technology targeted to various applications like corrosion detection, material thickness, material conductivity, etc. The research work presented in this thesis uses the prior research and development work completed in NDT as a platform for conducting this study to estimate proximity and thickness of Aluminum 3003 alloy metal sheets, which is not considered a flaw detection application. Some of the current technologies in the area of eddy current NDT for proximity and thickness estimation, each with its own limitations, include single probe ‘contact' sensors for magnetic metals, single probe ‘non-contact' sensors with separation distance of less than 1 mm and dual probe sensors that requires probes on both sides of the metal sheet. A swept multi-frequency scanning technique is used together with an automated data collection system to measure and collect output voltage and phase difference data over a wide range of frequencies. The skin effect in conductors and its associated property of skin depth is used to extract proximity and thickness information from the data collected, and then correlated with reference values to validate the results. Experimental results show the output voltage and phase difference of the sensor is dependent on the metal parameters (resistivity ‘ρ', permeability ‘μ', thickness ‘T') and coil parameters (diameter ‘D', frequency ‘F', lift-off ‘L'). Further, proximity is estimated from output voltage difference, and metal thickness (single/double) is estimated from phase difference independent of lift-off, which is a novel approach for thickness detection. The test sensor provides an accurate measure of proximity and thickness of Al 3003 alloy from a single sided measurement with varying lift-off, overcoming the limitations of other sensor configurations.
Advisors/Committee Members: Petkie, Douglas T.
Subjects: Aerospace materials; Electrical engineering; Electromagnetism; Engineering; Physics
Keywords: coil; EDDY CURRENT; output voltage; voltage difference; voltage; KHz; lift-off
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17.
Kemp, Izaak Vincent.
Sub-mm Wave Imaging and Waveguiding Techniques for Non-Destructive Materials Evaluation.
Degree: MS, Physics, 2009, Wright State University
► Sub-mm wave technology (also known as Terahertz/THz) is a rapidly developing field…
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▼ Sub-mm wave technology (also known as Terahertz/THz) is a rapidly developing field of electro-optics which has great potential in a variety of applications. Generally defined as the band of the electro-magnetic spectrum with frequencies spanning from 300 GHz to 30 THz, sub-mm waves are non-ionizing and are capable of passing through a wide range of dielectric substances making them well suited for imaging purposes such as non-destructive materials evaluation (NDE). Because of their high sensitivity to metals and ability to penetrate surface obscurants such as paint, oil, and epoxy sub-mm waves are capable of imaging corrosion damage on metallic surfaces as well as burn damage in composites routinely used in aerospace structures, with resolution comparable to many of the currently employed NDE techniques. In order to avoid failure of components during operation, many aircraft parts are replaced earlier than necessary leading to higher costs that could be reduced if the degree of damage in the component material could be determined non-destructively without requiring contact with the section to be imaged, thus a portable real-time sub-mm wave imaging system if developed would posses significant promise in the NDE market. We have developed a sub-mm wave imaging system and have compiled a library of images which successfully demonstrate the potential of such a system in evaluating aerospace materials. However there are still many unsolved issues related to the propagation of sub-mm wave radiation that need to be addressed before a practical system can be produced for use in the field. One major problem is that all of the substances which posses the refractive index profile and absorption coefficients necessary for the production of a sub-mm waveguide equivalent to fiber-optic cables are crystalline, making them impractical for use in NDE applications. Since the sub-mm wave imaging systems we have researched are active a practical NDE system would either need a compact source or a method of propagating sub-mm radiation over substantial distances to the sample to be imaged. One proposed method is the utilization of what are known as Sommerfield-Zenneck waves, or surface plasmon polaritons (SPPs). These surface electron density waves are capable of propagating over large distances and many metals posses SPP modes with frequencies in the sub-mm wave band. In addition to our NDE efforts, we have constructed a wire waveguide capable of exciting and transmitting these modes, and have characterized a number of its properties via imaging of the diffracted outgoing wave.
Advisors/Committee Members: Petkie, Doug.
Subjects: Physics
Keywords: Terahertz NDE materials evaluation
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18.
Kleismit, Richard A.
EVANESCENT MICROWAVE MICROSCOPY OF PORCINE SKIN TISSUE.
Degree: MS, Physics, 2008, Wright State University
► This thesis describes the application of a custom designed λ/4 resonant coaxial…
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▼ This thesis describes the application of a custom designed λ/4 resonant coaxial probe to measurements of the complex permittivity of in vitro freshly excised porcine skin tissue. The dielectric properties of the organic material within the near field of the tip of the probe frustrates the electric field and measurably changes the resonant frequency and quality factor Q of the coaxial sensor, where the change in resonant frequency and quality factor of a tuned resonance is measured as a function of tip-sample separation. The design of the probe enables better spatial resolution than previously developed probes. The following studies were performed: (1) measurement of the complex permittivity of porcine tissue over a range of frequencies revealed values consistent with published literature; (2) the change in quality factor from the probe measurements was compared to a visual microscope analysis of histological slices from the same skin location, indicating that subsurface structures such as capillary beds, ducts of exocrine sweat glands, and vein lumen ducts can be detected; and (3) measurements of the dielectric properties of a puncture wound and several burn lesions of varying severity revealed easily detectable changes, indicating that the probe has potential for evaluating and monitoring skin conditions. In addition, a new quantitative two point relationship between the real and imaginary parts of the materials complex permittivity related to the resonant frequency and quality factor shift using the method of images is developed, presented, and used in the above described skin studies. The two-point model describing the probe tip-sample interaction is capable of producing quantitative complex permittivity values for organic and biological materials.
Advisors/Committee Members: Foy, Brent.
Subjects: Physics
Keywords: evanescent, sensor, microwave, biomaterial characterization
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19.
Lindsey, Rhett Ellis.
The Derivation and Testing of Three-Dimensional Line Equations That Predict the Location of Brachytherapy Sources.
Degree: MS, Physics, 2010, Wright State University
► In High Dose Rate brachytherapy, a catheter is placed inside the body…
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▼ In High Dose Rate brachytherapy, a catheter is placed inside the body and a radioactive source is allowed to dwell at specific positions to treat a tumor. In normal usage, anatomical images acquired before the treatment are used to plan dwell positions, and then the plan is executed without further verifying source locations during treatment. However, slight errors in catheter positioning and shifts in internal anatomy cause variations in source position. In this study, a general method for determining dwell positions during treatment is evaluated. For this method, the treatment source exposes the tumor to radiation and creates an image on a film after the radiation passes through a constructed phantom. 3D line reconstruction is then used to back-extrapolate to the source location. Experiments are performed for several types of catheter movement. Two methods of identifying image locations and two mathematical methods for back-extrapolation are evaluated.
Advisors/Committee Members: Foy, Brent.
Subjects: Health; Health care; Oncology; Physics; Public health; Radiation; Radiology
Keywords: Brachytherapy; Source Location; Medical Physics; Three-Dimensional Line Equation
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20.
Massie, Michael Todd.
Respiratory-Gated IMRT Quality Assurance with Motion in Two Dimensions.
Degree: MS, Physics, 2010, Wright State University
► Intensity modulated radiation therapy (IMRT) plans can be further customized to each…
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▼ Intensity modulated radiation therapy (IMRT) plans can be further customized to each patient with the use of a four-dimensional (4D) respiratorygated computed tomography (CT), with time being the fourth dimension. The 4D respiratory-gated CT allows for the internal margin (IM), the expansion of the tumor volume that accounts for physiologic motions, to be addressed in the treatment planning process and no longer assumes that the treatments will be delivered to a fixed or rigid patient anatomy. Delivering the IMRT plan with a gated technique limits the treatment to a duty cycle when the target motion is at a minimum. The goal of this project is to study respiratory-gated IMRT quality assurance (QA) results for tumor motion in two dimensions and develop a guideline for acceptable limits on tumor motion and field size. Respiratory-gated IMRT QA was performed for four field sizes and varying amounts of motion with a fixed duty cycle using Sun Nuclearʼs MapCHECK and MotionSIM XY/4D products. The treated and planned dose planes were compared and errors were evaluated using standard acceptance conditions.
Advisors/Committee Members: Foy, Brent.
Subjects: Physics
Keywords: IMRT; QA; Respiratory-Gated; Intensity Modulated Radiation Therapy
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21.
Miles, Jared A.
Determining Metastable Densities in an Argon Discharge Through Optical Emission Spectroscopy.
Degree: MS, Physics, 2010, Wright State University
► A plasma diagnostic technique has been experimentally demonstrated where optical emission measurements…
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▼ A plasma diagnostic technique has been experimentally demonstrated where optical emission measurements of relative intensities of spectral lines in the violet range were combined with available electron-impact cross sections to yield absolute Ar metastable species concentration. An enabling factor of this analysis was that the electron excitation pattern was quite different between the Ar ground state and the metastable state. The result of this pattern was that the optical spectrum was unique depending on whether the emission was generated by direct excitation from the ground state, or by stepwise excitation from one of the metastable states. This study has shown that a model combining Ar excitation cross sections can fit the experimental spectral distributions by varying the ratio of the metastable state density and the E/N within the discharge. The absolute density obtained through optical emission spectroscopy was compared to measurements using laser diode absorption in order to confirm the results.
Advisors/Committee Members: Clark, Jerry.
Subjects: Physics
Keywords: argon; metastable; emission spectroscopy
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22.
Mitchell, William D.
Polarization Reversal in Potassium Titanyl Phosphate.
Degree: MS, Physics, 2007, Wright State University
► Mitchell, William D. M.S., Department of Physics, Wright State University, 2007.…
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▼ Mitchell, William D. M.S., Department of Physics, Wright State University, 2007. Polarization reversal in both hydrothermal and flux grown potassium titanyl phosphate was studied using square pulses at room temperature from 1600 V/mm to 5000 V/mm. Maximum switching current and inverse switching time data is compared to the ferroelectric polarization reversal model developed by Fatuzzo and Merz in the last century. Room temperature calculation of spontaneous polarization is reported and compared to that of potassium titanyl phosphate in the literature.
Advisors/Committee Members: Lew Yan Voon, Lok C.
Subjects: Physics, Condensed Matter
Keywords: KTP, domain reversal, spontaneous polarization
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23.
Morales-Masis, Monica.
Fabrication and Study of ZnO Micro- and Nanostructures.
Degree: MS, Physics, 2007, Wright State University
► ZnO micro-structures and nano-structures have been grown on two types of substrate…
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▼ ZnO micro-structures and nano-structures have been grown on two types of substrate by reacting condensed Zn vapor with oxygen. The source material was either pure zinc powder or zinc acetate which was either evaporated or decomposed. This was done in the temperature range 500 C to 650 C, in a flowing Ar plus oxygen ambient at atmospheric pressure. Variations in the carrier gas composition, gas flow rate and the position of the substrate in the furnace were found to control the formation and the morphology of the nanostructures. Scanning electron microscopy images of samples grown from a Zn powder source show forested needles approximately 100 nm in diameter by 1 micrometers long, and faceted rods from 500 nm to 700 nm thick. Samples grown from Zn acetate show the formation of nano crystals (from ~100nm to ~300nm) dispersed across the substrates. Photoluminescence measurements at 4.2K show a dominant line at ~3.36 eV with additional features at 3.32 and 3.37 eV. The line widths are ~3.5 meV indicating good quality material. The usual green-band emission is also observed. Hall measurements and CV profiling were attempted but they were unsuccessful due to the inability to make good contacts.
Advisors/Committee Members: Farlow, Gary.
Subjects: Physics, Condensed Matter
Keywords: ZnO, nanostructures, growth, photoluminescence
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24.
Moran, Benjamin L.
Analytical Chemical Sensing Using High Resolution Terahertz/Submillimeter Wave Spectroscopy.
Degree: MS, Physics, 2012, Wright State University
► A highly sensitive and selective Terahertz gas sensor used to analyze a…
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▼ A highly sensitive and selective Terahertz gas sensor used to analyze a complex mixture of Volatile Organic Compounds (VOCs) has been developed. To best demonstrate analytical capabilities of a THz chemical sensor, we chose to perform analytical quantitative analysis of a certified gas mixture using a prototype gas phase chemical sensor that couples a commercial preconcentration system (Entech 7100A) to a custom high resolution THz spectrometer. A Method TO-14A certified mixture of thirty-nine VOCs was purchased. Twenty-six of the thirty-nine chemicals were identified as suitable for THz spectroscopic detection. The Entech 7100A system is designed and marketed as an inlet system for Gas Chromatography Mass Spectrometry (GC-MS) instruments with a specific focus on TO-14A sampling methods and has been incorporated into our spectrometer. Its preconcentration efficiency is high for the thirty-nine chemicals in the mixture used for this study and our preliminary results confirm this for many of the selected VOCs. Presented are the results of this study which will serve as a basis for our ongoing research in environmental sensing and exhaled human breath.
Advisors/Committee Members: Medvedev, Ivan.
Subjects: Physics
Keywords: Breath Analysis; Rotational Spectroscopy; Terahertz; THz; Preconcentration; T0-14A; Submillimeter Wave Spectroscopy
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25.
Munbodh, Kineshma.
Evanescent Microwave Characterization of carbon Nanotube Films Grown on Silicon Carbide Substrate.
Degree: MS, Physics, 2007, Wright State University
► The electromagnetic characterization of carbon nanotube films (CNT) grown by the surface…
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▼ The electromagnetic characterization of carbon nanotube films (CNT) grown by the surface decomposition of silicon carbide (SiC) has been performed. The CNT films formed on the carbon and silicon terminated face of the SiC substrate were uncapped by an annealing process at a temperature of 4000 C with dwelling time up to 60 minutes in oxygen or carbon dioxide atmosphere. X-Y scans of the quality factor were used to deduce the local conductive properties of the films measured by evanescent microwave microscopy. Real and imaginary permittivity values, as determined by these electromagnetic measurements, provided valuable information for future field emission testing on these films. A theoretical model, adapted from the literature, was used to find the real and imaginary component of the permittivity of the CNT films. The results showed improvement in the surface conductivity of the samples after the annealing treatment.
Advisors/Committee Members: Kozlowski, Gregory.
Subjects: Physics, General
Keywords: CNT; CNT films; Si-face; NANOTUBE; CARBON NANOTUBE; CARBON; Fig
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26.
Niklas, Andrew John.
Characterization of Structured Nanomaterials using Terahertz Frequency Radiation.
Degree: MS, Physics, 2012, Wright State University
► Measurements that use terahertz frequency radiation to characterize materials are beneficial for…
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▼ Measurements that use terahertz frequency radiation to characterize materials are beneficial for scientists trying to determine the physical parameters that govern the interaction of electromagnetic waves and matter at those frequencies. Results will be presented of time domain terahertz spectroscopy measurements taken in forward and backward scattering directions from vertically aligned arrays of multi‐walled carbon nanotubes and thin films of perforated copper. The intent of this research is to both corroborate results from independent research groups conducting similar experiments and to further increase understanding in the scientific community with respect to carbon nanotube reflection phenomena at terahertz frequencies.
Advisors/Committee Members: Deibel, Jason.
Subjects: Physics
Keywords: Wright State University
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27.
Oh, Jaesung.
Fabrication of Silver Nanoparticles by Solution Phase Method and Physical Characterization of Their Arrays.
Degree: MS, Physics, 2007, Wright State University
► Synthesis of silver nanostructures has been an active research area for many…
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▼ Synthesis of silver nanostructures has been an active research area for many decades because of their importance in biological sensing, imaging, electronics, optoelectronics and catalysis. In particular, much effort has been devoted to the controlled synthesis of silver nanowires because of their potential use as interconnects or active components in fabricating nanoscale devices. The solution phase method is used here to form Ag nanoparticles by reducing silver nitrate with ethylene glycol heated to 160°C. The additional presence of polyvinyl pyrrolidone plays a role of stabilizer to prevent an agglomeration and/or a capping agent to produce highly anisotropic nanowires. Silver nanoparticles are extracted from the highly viscous ethylene glycol through centrifugation, filtration, decanting and dilution in de-ionized water. The monodispersed silver nanomaterials are self-assembled into ordered arrays on a glass substrate by the drop-coating method. SEM and AFM micrographs are presented to characterize the microstructure of these nanomaterials and their arrays. Their physical characterizations are discussed by using evanescent microwave microscopy. In particular, values of resonant frequencies and Q-factors of silver nanoparticle arrays measured by evanescent microwave microscope are used to fit to theoretical model allowing calculation their relative local conductivities.
Advisors/Committee Members: Kozlowski, Gregory.
Subjects: Physics, General
Keywords: silver nanoparticles
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28.
Owens, Lindsay.
Characterization of Ceramic Composite Materials Using Terahertz Non-Destructive Evaluation Techniques.
Degree: MS, Physics, 2012, Wright State University
► The characterization of defects such as rust, voids, etc. on materials and…
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▼ The characterization of defects such as rust, voids, etc. on materials and the analysis and prediction of strain and stress induced breakdown are well known applications of non-destructive evaluation (NDE) techniques. THz radiation has been suggested as an effective NDE tool for use in the field of ceramics and ceramic matrix composite materials (CMC), via THz spectroscopy and imaging. The goal of this research is to monitor the progression of thermal and mechanical damage applied to the CMC materials using terahertz spectroscopic imaging in order to create a predictive model that will correlate THz imaging data of these materials to environmental stress exposure.
Advisors/Committee Members: Deibel, Jason.
Subjects: Physics
Keywords: terahertz; non-destuctive evalution; ceramics
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29.
Patel, Jay.
GROWTH AND CHARACTERIZATION OF CARBON NANOMATERIALS.
Degree: MS, Physics, 2011, Wright State University
► In this thesis, single and multi-layered graphene films were epitaxially grown on…
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▼ In this thesis, single and multi-layered graphene films were epitaxially grown on either Si-face or C-face of SiC single crystal substrates. The film growth conditions, such as decomposition temperatures and pressures, and their surface morphologies were optimized. These films were then characterized by using surface analysis tools including SEM, TEM, AFM evanescent wave microscopy and electron educed spectroscopy. In addition to studying graphene decomposed from SiC crystals, carbon nanotube material was fabricated using a floating catalyst technique. These carbon nanotube material was then studied for potential cathode applications in this thesis. Field emission properties of these cathodes was measured and compared between carbon nanotubes grown by the floating catalyst technique and carbon nanotube material fabricated from a super acid solution spinning process. The result found that carbon nanotube material produced from the floating catalyst method supported the highest emission currents. As a result of this research, carbon nanotube field emitters fabricated from this method are now being studied in a wide range of vacuum electronic applications.
Advisors/Committee Members: Kozlowski, Gregory.
Subjects: Physics
Keywords: carbon nanotube, field emission, cathode, graphene
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30.
Prater, Brock Andrew.
Experimental Comparison of ACR and ICAMRL Magnetic Resonance Imaging Accreditation Protocols.
Degree: MS, Physics, 2010, Wright State University
► Two primary accrediting bodies exist for magnetic resonance imaging systems: the American…
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▼ Two primary accrediting bodies exist for magnetic resonance imaging systems: the American College of Radiology (ACR) and the Intersocietal Commission for the Accreditation of Magnetic Resonance Laboratories (ICAMRL), each of which defines specific standards for specific image quality criteria at which MRI images must be produced. An MRI clinic that wishes to show a commitment to image quality may do so by becoming accredited by one of these organizations of their choosing. The limits of these image criteria were compared to demonstrate the standards of each accrediting body. Images were produced that fell well within the standards of both accrediting organization, and subsequent images were produced at the limits of ACR and ICAMRL standards respectively. These images were first produced using a phantom to quantify a difference in criteria standards, then images were produced using a human patient to show a qualitative difference in criteria standards for clinical applications.
Advisors/Committee Members: Foy, Brent.
Subjects: Physics
Keywords: Slice Thickness; Slice; ACR; ACCREDITATION; ICAMRL; Spatial Resolution; phantom
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