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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 (0.52x)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 heattreatment temperature. Specimens from each samples series were heattreated at temperatures in the range 6001000C. Xray 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 (0.52x)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 heattreatment temperature. Specimens from each samples series were heattreated at temperatures in the range 6001000C. Xray powder diffraction and Rietveld refinement methods, magnetic measurements and scanning electron microscopy with energy dispersive xray 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 heattreatment 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 heattreatment temperature. In the system with x = 0.20, magnetite partially converts to hematite (SG R3c) in weight fractions that increase with the heattreatment temperature. The saturation magnetization of all specimens depends on the starting composition in Fe2O3 while it becomes maximum in samples that were heattreated at 800°C in all sample series. Magnetization loops show that the energy stored in the material is greatly affected by composition and heattreatment, 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.
Show less  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 xray and ultraviolet photoelectron spectroscopies have been used to investigate the electronic structures in ordered (L10structure) and disordered (fcc) CuAu. Large changes are observed in the valence band regions of the different phases, particularly in the vicinity of the Aurelated states. The binding energies of the Cu2p and Au4f 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 xray and ultraviolet photoelectron spectroscopies have been used to investigate the electronic structures in ordered (L10structure) and disordered (fcc) CuAu. Large changes are observed in the valence band regions of the different phases, particularly in the vicinity of the Aurelated states. The binding energies of the Cu2p and Au4f 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 Au4f 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.
Show less  Date Issued
 1991
 PURL
 http://purl.flvc.org/fcla/dt/14702
 Subject Headings
 Photoemission, Orderdisorder 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.
Show less  Date Issued
 1990
 PURL
 http://purl.flvc.org/fcla/dt/14589
 Subject Headings
 Zirconium oxideSpectra, 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 grouptheoretical 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 grouptheoretical 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, colorfree), 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 zerophonon 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, nonradiative 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, pseudolocalized vibrational modes and localized modes is also discussed.
Show less  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'nickelaluminum and its lowindex, highsymmetry 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 lowindex highsymmetry surfaces has been studied with a combination of photocurrent and firstprinciples 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 offstoichiometric NiAl are investigated. The electronic structure of the (110), (100) and (111) surfaces...
Show moreThe electronic structure of beta'NiAl alloy and its lowindex highsymmetry surfaces has been studied with a combination of photocurrent and firstprinciples 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 offstoichiometric 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.
Show less  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 silvermagnesium 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 firstprinciples 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 firstprinciples 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 SCFLMTOASA 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 AgMg alloys.
Show less  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 equiatomic CuAu.
 Creator
 Xu, Xumou, Florida Atlantic University, Charles E. Schmidt College of Science, Department of Physics
 Abstract/Description

The electronic structure of equiatomic CuAu has been investigated by a combination of photoelectron spectroscopy and firstprinciples 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 equiatomic CuAu has been investigated by a combination of photoelectron spectroscopy and firstprinciples 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 SCFLMTOASA 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 CuAu alloys near the equiatomic composition using the KKRCPA 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.
Show less  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 fastbandtheory technique based on the MST is the quadratic KorringaKohnRostoker (QKKR) method. A method for carrying out the selfconsistent 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 fastbandtheory technique based on the MST is the quadratic KorringaKohnRostoker (QKKR) method. A method for carrying out the selfconsistent 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 PdRh alloy phase diagram to an accuracy that has never before been achieved. A nonmagnetic calculation for CuNi alloys is also provided. These calculations required the mastery of KorringaKohnRostoker coherentpotentialapproximation methods and the development of embedded cluster codes.
Show less  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, Xray 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) (0.52x)SiO2 xFe2O3 0.03Na2O] and the heat treatment temperature. Xray powder diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive xray...
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) (0.52x)SiO2 xFe2O3 0.03Na2O] and the heat treatment temperature. Xray powder diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive xray 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 nonsystematic 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 asprepared 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.
Show less  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 (polyetalon 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 (polyetalon 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.
Show less  Date Issued
 1977
 PURL
 http://purl.flvc.org/fcla/dt/13848
 Subject Headings
 HydroxidesAbsorption and adsorption, Atmospheric ozone
 Format
 Document (PDF)
 Title
 MODEMODE COUPLING OF PLASMA WAVES IN SYSTEMS WITH STRONG NONLINEARITIES.
 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, nonperiodic 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, nonperiodic growing solutions were found that approached one of two asymptotic limits. For these solutions, the variables became infinitely large in a finite time.
Show less  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 La1xCa 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 La1xCa 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 electrondoped 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 chargeordering compounds is found to be small.
Show less  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 welldefined 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 selfinteraction 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.
Show less  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 sourcetosurface 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 sourcetosurface 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.
Show less  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 nanoscale, 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 selfconsistent multiple scattering (LSMS) method is the method of choice for such calculations because it has a technical feature called orderN scaling....
Show moreDesigning materials, particularly at the nanoscale, 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 selfconsistent multiple scattering (LSMS) method is the method of choice for such calculations because it has a technical feature called orderN scaling. We describe an implementation of the LSMS for massively parallel supercomputers using kspace and realspace 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 nanoparticle embedded in an iron aluminide crystal matrix.
Show less  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 twodimensional 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 twodimensional 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 nonlinearly coupled equations are derived to study finite, layered, pseudotwodimensional forest fires. Critical states can be predicted by evaluating these nonlineady coupled equations.
Show less  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 KantowskiSachs 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 KleinGordon equation in quantum mechanics and Schrodingerbased or KleinGordon 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 KleinGordon equation in quantum mechanics and Schrodingerbased or KleinGordon 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 KantowskiSachs 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 spacetime where the concept of time is derived by imposing the constraints as expectation values over the true dynamicaldegrees of freedom of the gravitational field. Thus, we obtained a Schrodinger type wave equation instead of the WheelerDeWitt 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 oneloop renormalized effective potential for the massive self interacting &PHgr;6 theory the spatially homogenous and anisotropic KantowkiSachs Universe. We concluded that regularizing the theory in (3 + 1) dimensional spacetime may not be possible. Finally, we looked at the time evolution of the critical temperature that is associated with our model.
Show less  Date Issued
 2005
 PURL
 http://purl.flvc.org/fau/fd/FADT12125
 Subject Headings
 Physics, General
 Format
 Document (PDF)
 Title
 The tightbinding coherent potential approximation embedded cluster method Monte Carlo approach and approximations to the quadratic KorringaKohnRostoker 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 longrange characteristics of an alloy. However, since it is a singlesite 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 shortrange order effects. The tightbinding coherentpotential 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 longrange characteristics of an alloy. However, since it is a singlesite 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 shortrange order effects. The tightbinding coherentpotential 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 KorringaKohnRostoker method is developed and is applied to a system consisting of one metal.
Show less  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 waterequivalent phantom and a waterfilled 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.
Show less  Date Issued
 2021
 PURL
 http://purl.flvc.org/fau/fd/FA00013731
 Subject Headings
 Skin, Radiotherapy, Electron beams
 Format
 Document (PDF)