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Title: PREDICTING FREQUENCIES AND POWER FOR A CYLINDRICAL CERENKOV SLOW WAVE STRUCTURE.
Creator: HOLSTEIN, DANNY GUY, Florida Atlantic University, Lamborn, Bjorn, Charles E. Schmidt College of Science, Department of Physics
Abstract/Description: The dispersion relation for a dielectrically loaded cylindrical waveguide, both with and without a beam of electrons, is found. It is shown that in the limit of Cerenkov threshold, the frequency goes to infinity. Also, using the fields derived, the Poynting vector is computed. It is shown that the Poynting vector increases and the operating frequency decreases with the thickness of the liner.
Date Issued: 1982
PURL: http://purl.flvc.org/fcla/dt/14136
Subject Headings: Dielectric wave guides, Cherenkov radiation
Format: Document (PDF)

Title: Physical properties of ferrimagnetic bioceramics.
Creator: Kis, Antonella C., Florida Atlantic University, Charles E. Schmidt College of Science, Department of Physics
Abstract/Description: The structural, magnetic and microstructural properties of ferrimagnetic bioglass ceramics (FBC) in the system {0.45(CaO,P2O5) x (0.52-x)SiO2 x xFe 2O3 x 0.03Na2O} with x = 0.05, 0.10, 0.15, 0.20 were studied as a function of composition and heat-treatment temperature. Specimens from each samples series were heattreated at temperatures in the range 600--1000C. X-ray powder diffraction and Rietveld refinement methods, magnetic measurements and scanning electron microscopy with energy...
Show moreThe structural, magnetic and microstructural properties of ferrimagnetic bioglass ceramics (FBC) in the system {0.45(CaO,P2O5) x (0.52-x)SiO2 x xFe 2O3 x 0.03Na2O} with x = 0.05, 0.10, 0.15, 0.20 were studied as a function of composition and heat-treatment temperature. Specimens from each samples series were heattreated at temperatures in the range 600--1000C. X-ray powder diffraction and Rietveld refinement methods, magnetic measurements and scanning electron microscopy with energy dispersive x-ray spectroscopy were used in our studies. Calcium phosphate [Ca3PO4)2], which is the biocompatible component of the materials, and magnetite Fe3O 4 are the two major crystalline phases that were developed in all samples series. In the two series of samples with x = 0.15 and 0.20, calcium phosphate undergoes a gradual transition from the monoclinic to the rhombohedral crystal system (Space Group P21/a, R3c) as the heat-treatment temperature increases from 800 to 1100C. It crystallizes only in R3c in the samples series with x = 0.05 and x = 0.10. Magnetite crystallizes in the orthorhombic system (SG Imma) in weight fractions determined by the heat-treatment temperature. In the system with x = 0.20, magnetite partially converts to hematite (SG R3c) in weight fractions that increase with the heat-treatment temperature. The saturation magnetization of all specimens depends on the starting composition in Fe2O3 while it becomes maximum in samples that were heat-treated at 800°C in all sample series. Magnetization loops show that the energy stored in the material is greatly affected by composition and heat-treatment, but not in a systematic way. SEM and EDX spectra reveal a variety of microstructures that are determined by the processing parameters of each sample. Dendrite structures consisting of Fe and O with crystallites of various sizes form on a glassy matrix of P, Si, Ca and O in the samples series 20G, while very fine surface microstructures are observed in the series 15G.
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Date Issued: 2004
PURL: http://purl.flvc.org/fau/fd/FADT12069
Subject Headings: Physics, Condensed Matter, Engineering, Materials Science
Format: Document (PDF)

Title: Photoemission investigation of the electronic structure in ordered and disordered copper gold.
Creator: Jiang, Yongjin, Florida Atlantic University, Jordan, Robin G., Charles E. Schmidt College of Science, Department of Physics
Abstract/Description: The techniques of x-ray and ultra-violet photoelectron spectroscopies have been used to investigate the electronic structures in ordered (L10-structure) and disordered (fcc) CuAu. Large changes are observed in the valence band regions of the different phases, particularly in the vicinity of the Au-related states. The binding energies of the Cu-2p and Au-4f core levels in the ordered phase are shifted from the pure metal value by 0.27 +- 0.05 eV and 0.30 +- 0.05 eV, respectively. A small...
Show moreThe techniques of x-ray and ultra-violet photoelectron spectroscopies have been used to investigate the electronic structures in ordered (L10-structure) and disordered (fcc) CuAu. Large changes are observed in the valence band regions of the different phases, particularly in the vicinity of the Au-related states. The binding energies of the Cu-2p and Au-4f core levels in the ordered phase are shifted from the pure metal value by 0.27 +- 0.05 eV and 0.30 +- 0.05 eV, respectively. A small reduction of the Au-4f core level shift is found in the disordered phase. Details of the valence band structure and the shifts for the ordered phase are in accord with recently published calculations of the density of states. Investigations of the composition of the surface region using Auger electron spectroscopy indicate that there is excess Au in the surface region, in agreement with previous studies.
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Date Issued: 1991
PURL: http://purl.flvc.org/fcla/dt/14702
Subject Headings: Photoemission, Order-disorder in alloys
Format: Document (PDF)

Title: Raman spectroscopic studies of stabilized zirconia at elevated temperatures.
Creator: Lacher, Nathan, Florida Atlantic University, Liu, David, Charles E. Schmidt College of Science, Department of Physics
Abstract/Description: Raman spectroscopy was used to determine the phase structure and phase stability of zirconia mixtures for various elevated temperatures, type and concentration of oxides added to zirconia, and fabrication process. All 8 wt.% yttria samples showed mostly the tetragonal structure at room temperature. Three of the four 8 wt.% yttria samples exhibited the tetragonal structure at elevated temperatures, while no conclusion was inferred for the powdered sample. As compared with yttria, ceria is a...
Show moreRaman spectroscopy was used to determine the phase structure and phase stability of zirconia mixtures for various elevated temperatures, type and concentration of oxides added to zirconia, and fabrication process. All 8 wt.% yttria samples showed mostly the tetragonal structure at room temperature. Three of the four 8 wt.% yttria samples exhibited the tetragonal structure at elevated temperatures, while no conclusion was inferred for the powdered sample. As compared with yttria, ceria is a less effective stabilizer with respect to the zirconia tetragonal structure. A monoclinic transformation between 400 K and 800 K was observed in the 4 wt.% yttria sample which had been processed by rapid quenching. Adding alumina to 4 wt.% yttria did not completely stabilize the tetragonal structure at or above room temperature, making it a less effective stabilizer than yttria or ceria. The phase transformation was responsible for the unusual values in the Gr uneisen parameters obtained for the 4 wt.% yttria sample.
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Date Issued: 1990
PURL: http://purl.flvc.org/fcla/dt/14589
Subject Headings: Zirconium oxide--Spectra, Raman spectroscopy
Format: Document (PDF)

Title: Spectroscopic studies of ZnWO4 and doped ZnWO4 single crystals.
Creator: Wang, Hong, Florida Atlantic University, Charles E. Schmidt College of Science, Department of Physics
Abstract/Description: Zinc tungstate (ZnWO4) is promising as a scintillator and laser host material. However, the presence of color centers limit its applications. It has been found that special annealing techniques or doping with metallic elements such as Nb or Sb can bleach the samples (Zhou et al. 1986a, 1986b, 1989). A group-theoretical analysis of the characteristic lattice vibrational modes for ZnWO4 single crystals is given. The mode assignments have been made. The temperature dependence of the Raman...
Show moreZinc tungstate (ZnWO4) is promising as a scintillator and laser host material. However, the presence of color centers limit its applications. It has been found that special annealing techniques or doping with metallic elements such as Nb or Sb can bleach the samples (Zhou et al. 1986a, 1986b, 1989). A group-theoretical analysis of the characteristic lattice vibrational modes for ZnWO4 single crystals is given. The mode assignments have been made. The temperature dependence of the Raman spectra has been obtained experimentally in various polarization geometries. Anharmonic contributions and interactions between phonons are discussed. Photoluminescence studies of ZnWO4 (colored, color-free), ZnWO4: Nb and ZnWO4:Sb have been carried out in the temperature range from 11 to 430 K. All samples show the blue emission band. An IR emission band with a zero-phonon line (ZPL) has been found in ZnWO4 colored samples only. The lineshape function of the emission bands has been theoretically studied and compared with the experimental results. Radiative, non-radiative and multiphonon transitions have been investigated in the thermal quenching model. The temperature dependences of the intensity, the frequency and the linewidth of the ZPL have been studied. Using the Single Configurational Coordinate model, the linear coupling between electrons and phonons has been analyzed. The quadratic coupling of electrons and phonons has been studied in the Debye approximation. The coupling of electronic transitions to normal vibrational modes, pseudo-localized vibrational modes and localized modes is also discussed.
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Date Issued: 1993
PURL: http://purl.flvc.org/fcla/dt/12346
Subject Headings: Physics, Condensed Matter, Physics, Optics, Engineering, Materials Science
Format: Document (PDF)

Title: The electronic structure of beta'-nickel-aluminum and its low-index, high-symmetry surfaces.
Creator: Hines, Eric Lawrence, Florida Atlantic University, Charles E. Schmidt College of Science, Department of Physics
Abstract/Description: The electronic structure of beta'-NiAl alloy and its low-index high-symmetry surfaces has been studied with a combination of photocurrent and first-principles electronic structure calculations. Bulk calculations have been performed with both the LMTO and LSMS computational codes, and the core level shifts upon alloying are discussed in detail. Defect formation and bonding mechanisms in off-stoichiometric NiAl are investigated. The electronic structure of the (110), (100) and (111) surfaces...
Show moreThe electronic structure of beta'-NiAl alloy and its low-index high-symmetry surfaces has been studied with a combination of photocurrent and first-principles electronic structure calculations. Bulk calculations have been performed with both the LMTO and LSMS computational codes, and the core level shifts upon alloying are discussed in detail. Defect formation and bonding mechanisms in off-stoichiometric NiAl are investigated. The electronic structure of the (110), (100) and (111) surfaces are investigated using the LMTO and LSMS, and electronic potentials for input to the photocurrent code are evaluated in the surface geometry. Photocurrent calculations for the (110), (100) and (111) surface are presented and compared with high quality experimental measurements. The (100) surface is found to have a double Ni termination. This defect layer is predicted to sustain a magnetic moment. The rippling of the (110) surface is modelled in the photocurrent calculations, and is found to effect the spectral profile in significant ways. The calculated photocurrent spectra are used to predict the surface composition for the (100), (111) and (110) surfaces, and the rippling value of the (110) surface. Agreement with experiment is good. A method for utilizing computational photoemission spectra to predict the structure and composition of metallic surfaces is presented, and its strengths and weaknesses are discussed.
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Date Issued: 1996
PURL: http://purl.flvc.org/fcla/dt/12492
Subject Headings: Physics, Electricity and Magnetism, Physics, Condensed Matter
Format: Document (PDF)

Title: The electronic structure and properties of silver-magnesium alloys.
Creator: Liu, Yan, Florida Atlantic University, Charles E. Schmidt College of Science, Department of Physics
Abstract/Description: The electronic structures of beta'-AgMg and Ag3Mg alloys have been investigated by a combination of photoelectron spectroscopy and first-principles band structure and photocurrent calculations. The study includes the first ever XPS and UPS measurements from the ordered and disordered phases of Ag3Mg. We concentrated mainly on measurements of the valence bands and the core level binding energies for these alloys and their parent metals. The band structures of the ordered alloys and pure metals...
Show moreThe electronic structures of beta'-AgMg and Ag3Mg alloys have been investigated by a combination of photoelectron spectroscopy and first-principles band structure and photocurrent calculations. The study includes the first ever XPS and UPS measurements from the ordered and disordered phases of Ag3Mg. We concentrated mainly on measurements of the valence bands and the core level binding energies for these alloys and their parent metals. The band structures of the ordered alloys and pure metals have been calculated by the SCF-LMTO-ASA method, and the KKR and KKRCPA calculational schemes have been used in order to determine the electronic structures of both ordered and disordered phases of Ag3Mg on an equal footing. For the purpose of interpreting the core level shifts due to alloying, a modified LMTO scheme has been applied, in a supercell geometry, to allow for relaxation effects. In addition, we have shown that the Fermi surface topology may well be an important factor in determining the relative stability of the long period superlattice structure in Ag3Mg. In general, the calculations are in very good agreement with the experimental results. We conclude that the combination of theoretical calculations and photoemission measurements provides a detailed understanding of the electronic structures and the properties of Ag-Mg alloys.
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Date Issued: 1993
PURL: http://purl.flvc.org/fcla/dt/12332
Subject Headings: Physics, Condensed Matter, Engineering, Metallurgy
Format: Document (PDF)

Title: The electronic structure and properties of equi-atomic CuAu.
Creator: Xu, Xumou, Florida Atlantic University, Charles E. Schmidt College of Science, Department of Physics
Abstract/Description: The electronic structure of equi-atomic CuAu has been investigated by a combination of photoelectron spectroscopy and first-principles band structure calculations. The study includes the first ever ARUPS and ARAES measurements from a single crystal of CuAu I. We have studied in detail the energy dispersion and shifts of a Tamm state on the (001) and (100) surfaces and we determined the surface lattice constants and the dependencies of the energy shifts on atomic concentration and geometry....
Show moreThe electronic structure of equi-atomic CuAu has been investigated by a combination of photoelectron spectroscopy and first-principles band structure calculations. The study includes the first ever ARUPS and ARAES measurements from a single crystal of CuAu I. We have studied in detail the energy dispersion and shifts of a Tamm state on the (001) and (100) surfaces and we determined the surface lattice constants and the dependencies of the energy shifts on atomic concentration and geometry. Two new surface states were found on the two surfaces and their properties have been investigated. Comparisons between the valence band spectra from the two samples of CuAu I have been carried out and the results show that the different atomic arrangements in the crystal do not have a significant effect on the band structure. We also compared spectra from the alloy with those from the parent metals. A series of calculations of the electronic structure of CuAu I has been carried out by the SCF-LMTO-ASA and RKKR methods. We found that the superzone boundaries that are created when the CuAu II phase is formed destroy appreciable regions of Fermi surface, thus, favoring the latter phase. The positions of the new boundaries are related directly to the period of the long period superlattice and we have investigated their dependence on the e/a ratio and pressure. The results are in very good agreement with previous experimental measurements. We also calculated the Fermi surfaces of three disordered Cu-Au alloys near the equi-atomic composition using the KKR-CPA scheme. The results have shown strong evidence that the Fermi surface topology may play an important role in stabilizing and determining the modulation of the LPS in CuAu II.
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Date Issued: 1995
PURL: http://purl.flvc.org/fcla/dt/12423
Subject Headings: Physics, Condensed Matter
Format: Document (PDF)

Title: The multiple scattering approach to the electronic structure of ordered solids, impurities, and alloys.
Creator: Wang, Yang, Florida Atlantic University, Charles E. Schmidt College of Science, Department of Physics
Abstract/Description: In this dissertation, multiple scattering theory (MST) plays a fundamental role. It is applied to develop the electronic structure calculation techniques for ordered solids, single impurities and binary alloys. The most accurate fast-band-theory technique based on the MST is the quadratic Korringa-Kohn-Rostoker (QKKR) method. A method for carrying out the self-consistent QKKR calculation for ordered compounds is derived and applied to palladium hydride. The application of the QKKR method to...
Show moreIn this dissertation, multiple scattering theory (MST) plays a fundamental role. It is applied to develop the electronic structure calculation techniques for ordered solids, single impurities and binary alloys. The most accurate fast-band-theory technique based on the MST is the quadratic Korringa-Kohn-Rostoker (QKKR) method. A method for carrying out the self-consistent QKKR calculation for ordered compounds is derived and applied to palladium hydride. The application of the QKKR method to single impurity problems is also examined. In order to study phase diagrams of binary alloys, a new approach, called the embedded cluster Monte Carlo (ECMC) method, is developed. It is used to calculate the miscibility gap in the Pd-Rh alloy phase diagram to an accuracy that has never before been achieved. A non-magnetic calculation for Cu-Ni alloys is also provided. These calculations required the mastery of Korringa-Kohn-Rostoker coherent-potential-approximation methods and the development of embedded cluster codes.
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Date Issued: 1993
PURL: http://purl.flvc.org/fcla/dt/12333
Subject Headings: Physics, Condensed Matter, Engineering, Materials Science
Format: Document (PDF)

Title: Ferrimagnetic bioglass ceramics in simulated body fluid: Electron, X-ray and neutron scattering studies.
Creator: Papanearchou, Nearchos I., Florida Atlantic University, Charles E. Schmidt College of Science, Department of Physics
Abstract/Description: The effect of simulated body fluid (SBF) on the crystal structure and surface structure properties of Ferrimagnetic Bioglass Ceramics (FBC) as a function of the time of immersion in SBF was studied. The materials examined were prepared with a systematic variation of the composition of the oxides in the system [0.45(CaO, P2O5) (0.52-x)SiO2 xFe2O3 0.03Na2O] and the heat treatment temperature. X-ray powder diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive x-ray...
Show moreThe effect of simulated body fluid (SBF) on the crystal structure and surface structure properties of Ferrimagnetic Bioglass Ceramics (FBC) as a function of the time of immersion in SBF was studied. The materials examined were prepared with a systematic variation of the composition of the oxides in the system [0.45(CaO, P2O5) (0.52-x)SiO2 xFe2O3 0.03Na2O] and the heat treatment temperature. X-ray powder diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive x-ray spectroscopy (EDX), neutron powder diffraction (NPD) and Rietveld refinement methods were used in our studies. The in vitro experiments demonstrated the bioactivity of the FBC through formation of hydroxyapatite (HAp). It varies with the composition of the FBC, annealing temperature, and time of immersion of the samples in SBF in a non-systematic way. SEM and EDX studies showed that pores appear on the surface of some specimens, while a surface layer of Si, P, and Ca partially covers the Fe, O dendrites of the original samples. Formation and size of pores was determined by the specific processing parameters of the samples. Quantitative phase analysis of the neutron diffraction patterns revealed a phase transition of the calcium phosphate from hexagonal to monoclinic, in weight percentages depended on the composition of the as-prepared FBC and time of immersion in SBF. The weight percentage of the ferrimagnetic phase [Fe3O4] is less affected by immersion in SBF. Inclusion of magnetic scattering of the neutrons in the Rietveld refinement process improved the quality of the fit between calculated and experimental diffraction patterns, resulting in a reduction of the weighted pattern residuals Rwp from 0.15 to 0.07.
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Date Issued: 2005
PURL: http://purl.flvc.org/fcla/dt/12169
Subject Headings: Health Sciences, Radiology, Biophysics, General
Format: Document (PDF)

Title: MEASUREMENTS OF TERRESTRIAL OH ABUNDANCES BY SPECTROSCOPIC OBSERVATION OF RESONANCE ABSORPTION OF SUNLIGHT.
Creator: SPERANZA, PATRICK DANIEL, Florida Atlantic University, Charles E. Schmidt College of Science, Department of Physics
Abstract/Description: Measurements of the atmospheric hydroxyl radical (OH) abundance were made at Boca Raton, Florida, (26° 22' N, 80° 6' W) during the period March 14 through April 9, 1977. Observations were made on the P1(1) line of the A^2sigma+ - x^2pi(0,0) rotation band of OH at 3081.7A. By the use of the high resolution Pepsios (poly-etalon pressure scanning interferometric optical spectrometer) spectrometer, the narrow absorption curve due to terrestrial OH was distinguished from the broad solar Fraunhofer...
Show moreMeasurements of the atmospheric hydroxyl radical (OH) abundance were made at Boca Raton, Florida, (26° 22' N, 80° 6' W) during the period March 14 through April 9, 1977. Observations were made on the P1(1) line of the A^2sigma+ - x^2pi(0,0) rotation band of OH at 3081.7A. By the use of the high resolution Pepsios (poly-etalon pressure scanning interferometric optical spectrometer) spectrometer, the narrow absorption curve due to terrestrial OH was distinguished from the broad solar Fraunhofer line. Measurements of the amount of atmospheric OH absorption indicated an average vertical column abundance of (2.0 +- 0.8) (10^13) molecules/cm^2 for this observation period.
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Date Issued: 1977
PURL: http://purl.flvc.org/fcla/dt/13848
Subject Headings: Hydroxides--Absorption and adsorption, Atmospheric ozone
Format: Document (PDF)

Title: MODE-MODE COUPLING OF PLASMA WAVES IN SYSTEMS WITH STRONG NON-LINEARITIES.
Creator: LODDEN, JAMES ALAN, Florida Atlantic University, Charles E. Schmidt College of Science, Department of Physics
Abstract/Description: The coupled equations of motion describing electrostatic plasma oscillations are derived using a collective coordinate approach. The boundary between the physical and nonphysical regions of phase space is discussed. The two mode case is studied in detail for both small and large initial disturbances. For small initial disturbances the motion was found to be periodic. For large initial disturbances, non-periodic growing solutions were found that approached one of two asymptotic limits. For...
Show moreThe coupled equations of motion describing electrostatic plasma oscillations are derived using a collective coordinate approach. The boundary between the physical and nonphysical regions of phase space is discussed. The two mode case is studied in detail for both small and large initial disturbances. For small initial disturbances the motion was found to be periodic. For large initial disturbances, non-periodic growing solutions were found that approached one of two asymptotic limits. For these solutions, the variables became infinitely large in a finite time.
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Date Issued: 1976
PURL: http://purl.flvc.org/fcla/dt/13828
Subject Headings: Coupled mode theory, Plasma waves
Format: Document (PDF)

Title: Magnetic, thermodynamic, and structural studies of manganese oxides.
Creator: Terashita, Hirotoshi, Florida Atlantic University, Charles E. Schmidt College of Science, Department of Physics
Abstract/Description: Magnetic, thermodynamic, and structural properties of the manganese oxides La1-xCa xMnO3 are studied. Neutron powder diffraction reveals two distinct crystallographic phases as well as two magnetic (ferromagnetic and antiferromagnetic) phases for 0.08
Show moreMagnetic, thermodynamic, and structural properties of the manganese oxides La1-xCa xMnO3 are studied. Neutron powder diffraction reveals two distinct crystallographic phases as well as two magnetic (ferromagnetic and antiferromagnetic) phases for 0.08 < x < 0.14. Details of the compositional dependence of the phase fractions is discussed in the context of local ferromagnetism. Comparisons of magnetic and crystallographic properties are made to the analogous electron-doped Ca1- yLayMnO3 (0 < y < 0.20) system. Thermodynamic properties of La1- xCaxMnO 3 (0 < x < 0.54) are investigated for possible applications in magnetic refrigeration. A maximum magnetic entropy change of 5.5 J/kg K and a corresponding temperature change of 2 K are estimated for x = 0.28. The magnetocaloric effect in antiferromagnetic and charge-ordering compounds is found to be small.
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Date Issued: 2005
PURL: http://purl.flvc.org/fau/fd/FADT12133
Subject Headings: Physics, Condensed Matter
Format: Document (PDF)

Title: Hamiltonian Methods in the Quantization of Gauge Systems.
Creator: Vaulin, Ruslan, Florida Atlantic University, Miller, Warner A., Charles E. Schmidt College of Science, Department of Physics
Abstract/Description: The new formalism for quantization of gauge systems based on the concept of the dynamical Hamiltonian recently introduced as a basis for the canonical theory of quantum gravity was considered in the context of general gauge theories. This and other Hamiltonian methods, that include Dirac's theory of extended Hamiltonian and the Hamiltonian reduction formalism were critically examined. It was established that the classical theories of constrained gauge systems formulated within the framework...
Show moreThe new formalism for quantization of gauge systems based on the concept of the dynamical Hamiltonian recently introduced as a basis for the canonical theory of quantum gravity was considered in the context of general gauge theories. This and other Hamiltonian methods, that include Dirac's theory of extended Hamiltonian and the Hamiltonian reduction formalism were critically examined. It was established that the classical theories of constrained gauge systems formulated within the framework of either of the approaches are equivalent. The central to the proof of equivalence was the fact that the gauge symmetries resuIt in the constraints of the first class in Dirac's terminology that Iead to redundancy of equations of motion for some of the canonica variables. Nevertheless, analysis of the quantum theories showed that in general, the quantum theory of the dynamical Hamiltonian is inequivalent to those of the extended Hamiltonian and the Hamiltonian reduction. The new method of quantization was applied to a number of gauge systems, including the theory of relativistic particle, the Bianchi type IX cosmological model and spinor electrodynamics along side with the traditional methods of quantization. In all of the cases considered the quantum theory of the dynamical Hamiltonian was found to be well-defined and to possess the appropriate classical limit. In particular, the quantization procedure for the Bianchi type IX cosmological spacetime did not run into any of the known problems with quantizing the theory of General Relativity. On the other hand, in the case of the quantum electrodynamics the dynamical Hamiltonian approach led to the quantum theory with the modified self-interaction in the matter sector. The possible consequence of this for the quantization of the full theory of General Relativity including the matter fields are discussed.
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Date Issued: 2006
PURL: http://purl.flvc.org/fau/fd/FA00000882
Subject Headings: Quantum field theory, Mathematical physics, Evolution equations, Nonlinear, Hamiltonian systems
Format: Document (PDF)

Title: Measurements of output factors for small photon fields up to 10 cm x 10 cm.
Creator: Bacala, Angelina, Pella, Silvia, Charles E. Schmidt College of Science, Department of Physics
Abstract/Description: Field output factors (OF) for photon beams from a 6 MV medical accelerator were measured using five different detectors in a scanning water phantom. The measurements were taken for square field sizes of integral widths ranging from 1 cm to 10 cm for two reference source-to-surface distances (SSD) and depths in water. For the diode detectors, square field widths as small as 2.5 mm were also studied. The photon beams were collimated by using either the jaws or the multileaf collimators....
Show moreField output factors (OF) for photon beams from a 6 MV medical accelerator were measured using five different detectors in a scanning water phantom. The measurements were taken for square field sizes of integral widths ranging from 1 cm to 10 cm for two reference source-to-surface distances (SSD) and depths in water. For the diode detectors, square field widths as small as 2.5 mm were also studied. The photon beams were collimated by using either the jaws or the multileaf collimators. Measured OFs are found to depend upon the field size, SSD, depth and also upon the type of beam collimation, size and type of detector used. For field sizes larger than 3 cm x 3 cm, the OF measurements agree to within 1% or less. The largest variation in OF occurs for jawsshaped field of size 1 cm x 1cm, where a difference of more than 18% is observed.
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Date Issued: 2013
PURL: http://purl.flvc.org/fau/fd/FA0004003
Subject Headings: Integrated circuits, Photonics, Quantum electrodynamics, Quantum theory
Format: Document (PDF)

Title: Computational methods in metallic alloys within multiple scattering theory.
Creator: Rusanu, Aurelian, Florida Atlantic University, Charles E. Schmidt College of Science, Department of Physics
Abstract/Description: Designing materials, particularly at the nano-scale, is an important scientific research area. It includes a large spectrum of basic science and technological developments. In order to provide results that are relevant to real materials, quantum mechanical simulations involving thousands to millions of atoms must be carried out. The locally self-consistent multiple scattering (LSMS) method is the method of choice for such calculations because it has a technical feature called order-N scaling....
Show moreDesigning materials, particularly at the nano-scale, is an important scientific research area. It includes a large spectrum of basic science and technological developments. In order to provide results that are relevant to real materials, quantum mechanical simulations involving thousands to millions of atoms must be carried out. The locally self-consistent multiple scattering (LSMS) method is the method of choice for such calculations because it has a technical feature called order-N scaling. We describe an implementation of the LSMS for massively parallel supercomputers using k-space and real-space methods. For magnetic materials, the constrained local moment approach and the exchange interaction method are used. We demonstrate our approach by calculating the electronic and magnetic structure of an iron nano-particle embedded in an iron aluminide crystal matrix.
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Date Issued: 2005
PURL: http://purl.flvc.org/fcla/dt/12176
Subject Headings: Physics, Condensed Matter
Format: Document (PDF)

Title: Critical behavior of forest fires: Theory and numerical simulations.
Creator: Lu, Huizong, Florida Atlantic University, Charles E. Schmidt College of Science, Department of Physics
Abstract/Description: Forest fire is an integral part of natural ecosystems. Understanding the mechanisms governing the formation and propagation of forest fire is imperative for effectively managing the natural resources of a forest and minimizing or eliminating damages caused by uncontrolled forest fire. Numerical simulation of two-dimensional forest fires indicates that there is a critical state at which the fire is likely to spread to the entire forest. The effects of wind conditions and multiple tree species...
Show moreForest fire is an integral part of natural ecosystems. Understanding the mechanisms governing the formation and propagation of forest fire is imperative for effectively managing the natural resources of a forest and minimizing or eliminating damages caused by uncontrolled forest fire. Numerical simulation of two-dimensional forest fires indicates that there is a critical state at which the fire is likely to spread to the entire forest. The effects of wind conditions and multiple tree species are studied using numerical simulations and various Mean Field Approximations. Results from the analytical calculations agree well with numerical simulations for square lattice forest fire. Other lattice structures are also investigated. Mathematical models with non-linearly coupled equations are derived to study finite, layered, pseudo-two-dimensional forest fires. Critical states can be predicted by evaluating these non-lineady coupled equations.
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Date Issued: 2000
PURL: http://purl.flvc.org/fcla/dt/12645
Subject Headings: Agriculture, Forestry and Wildlife
Format: Document (PDF)

Title: Cosmological studies with spatially homogenous models and quantum field effects in Kantowski-Sachs universe.
Creator: Sabir, Abdenour, Florida Atlantic University, Charles E. Schmidt College of Science, Department of Physics
Abstract/Description: Perhaps constructing a complete theory of quantum gravity, has been one of the greatest challenges for theoretical physicists in the last few decades, a theory that would reconcile general relativity and quantum mechanics. Addressing this issue, we are drawing a parallel between the Schrodinger and Klein-Gordon equation in quantum mechanics and Schrodinger-based or Klein-Gordon based wave equation in canonical quantum gravity. In particular we analyze the quantum geometrodynamics Schrodinger...
Show morePerhaps constructing a complete theory of quantum gravity, has been one of the greatest challenges for theoretical physicists in the last few decades, a theory that would reconcile general relativity and quantum mechanics. Addressing this issue, we are drawing a parallel between the Schrodinger and Klein-Gordon equation in quantum mechanics and Schrodinger-based or Klein-Gordon based wave equation in canonical quantum gravity. In particular we analyze the quantum geometrodynamics Schrodinger equation for a homogeneous cosmological model and we study the quantum field effects for the &PHgr;6 scalar field in Kantowski-Sachs universe. In essence, we present a unified view of quantum gravity by establishing a parallel between our study and the usual quantum mechanics. Thus, the first part of this dissertation deals with the quantization of Bianchi type IX space-time where the concept of time is derived by imposing the constraints as expectation values over the true dynamical-degrees of freedom of the gravitational field. Thus, we obtained a Schrodinger type wave equation instead of the Wheeler-DeWitt which is associated with the problem of time in quantum gravity [1]. The main technical difference between our proposed equation and other quantum cosmology approaches is in our treatment of the constraints. Ordinarily, the equation cannot be solved simply by separating the coordinates variables, and only under some specific conditions imposed on the background that one may obtain exact analytical expressions. In the second part, we evaluated the one-loop renormalized effective potential for the massive self interacting &PHgr;6 theory the spatially homogenous and anisotropic Kantowki-Sachs Universe. We concluded that regularizing the theory in (3 + 1) dimensional space-time may not be possible. Finally, we looked at the time evolution of the critical temperature that is associated with our model.
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Date Issued: 2005
PURL: http://purl.flvc.org/fau/fd/FADT12125
Subject Headings: Physics, General
Format: Document (PDF)

Title: The tight-binding coherent potential approximation embedded cluster method Monte Carlo approach and approximations to the quadratic Korringa-Kohn-Rostoker method.
Creator: Horvath, Eva Antoinette, Florida Atlantic University, Charles E. Schmidt College of Science, Department of Physics
Abstract/Description: The coherent potential approximation (CPA) can yield information about the long-range characteristics of an alloy. However, since it is a single-site theory, the effect of the local environment cannot be taken into account. The CPA can be extended to more than one site using the embedded cluster method, thereby including short-range order effects. The tight-binding coherent-potential approximation embedded cluster method can be used to generate the densities of states corresponding to all...
Show moreThe coherent potential approximation (CPA) can yield information about the long-range characteristics of an alloy. However, since it is a single-site theory, the effect of the local environment cannot be taken into account. The CPA can be extended to more than one site using the embedded cluster method, thereby including short-range order effects. The tight-binding coherent-potential approximation embedded cluster method can be used to generate the densities of states corresponding to all possible configurations of any cluster, but in particular a cluster consisting of an atom and its nearest neighbors. It is then demonstrated that the interaction energies can be calculated and used in conjunction with the Monte Carlo approach to generate the phase diagram of an alloy. In addition, the formalism for two new approximations to the Quadratic Korringa-Kohn-Rostoker method is developed and is applied to a system consisting of one metal.
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Date Issued: 1992
PURL: http://purl.flvc.org/fcla/dt/12321
Subject Headings: Physics, Condensed Matter
Format: Document (PDF)

Title: Machined brass skin collimation with variable thickness for electron therapy.
Creator: Gomez, Facenda Alianna, Ouhib, Zoubir, Florida Atlantic University, Department of Physics, Charles E. Schmidt College of Science
Abstract/Description: Skin collimation in electron therapy ensures sharper penumbra and maximal protection to adjacent critical structures. It also provides a better clinical dose to the target and avoids recurrences at the periphery. The thickness of the electron skin collimation must be adequate for shielding purposes, not too thick to cause discomfort to the patient and be conformal to the skin. This study assessed the clinical potential of machined brass skin collimation with variable thickness. Brass...
Show moreSkin collimation in electron therapy ensures sharper penumbra and maximal protection to adjacent critical structures. It also provides a better clinical dose to the target and avoids recurrences at the periphery. The thickness of the electron skin collimation must be adequate for shielding purposes, not too thick to cause discomfort to the patient and be conformal to the skin. This study assessed the clinical potential of machined brass skin collimation with variable thickness. Brass transmission factors for 6, 9, and 12 MeV electron beams were measured and used to determine the skin collimation clinically acceptable thickness. Dosimetric performance of the variable thickness skin collimation was evaluated for 9 MeV electrons within a rectilinear water-equivalent phantom and a water-filled head phantom. Results showed the variable thickness skin collimation is dosimetrically equivalent to the uniform thickness collimation. Favorable dosimetric advantages for brass skin collimation for small electron fields were achieved.
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Date Issued: 2021
PURL: http://purl.flvc.org/fau/fd/FA00013731
Subject Headings: Skin, Radiotherapy, Electron beams
Format: Document (PDF)

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