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- Title
- Theoretical and Computational Studies of the electronic, Structural, Vibrational, and Thermodynamic Properties of Transition Metal Nanoparticles.
- Creator
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Sadatshafaie, Ghazal, Rahman, Talat, Stolbov, Sergey, Ishigami, Masa, Masunov, Artem, University of Central Florida
- Abstract / Description
-
The main objective of this dissertation is to provide better understanding of the atomic configurations, electronic structure, vibrational properties, and thermodynamics of transition metal nanoparticles and evaluate the intrinsic (i.e. size and shape) and extrinsic (i.e. ligands, adsorbates, and support) effects on the aforementioned properties through a simulational approach. The presented research provides insight into better understanding of the morphological changes of the nanoparticles...
Show moreThe main objective of this dissertation is to provide better understanding of the atomic configurations, electronic structure, vibrational properties, and thermodynamics of transition metal nanoparticles and evaluate the intrinsic (i.e. size and shape) and extrinsic (i.e. ligands, adsorbates, and support) effects on the aforementioned properties through a simulational approach. The presented research provides insight into better understanding of the morphological changes of the nanoparticles that are brought about by the intrinsic factors as well as the extrinsic ones. The preference of certain ligands to stabilize specific sizes of nanoparticles is investigated. The intrinsic and extrinsic effects on the electronic structure of the nanoparticles are presented. The physical and chemical properties of the nanoparticles are evaluated through better understanding of the above effects on the experimentally observed properties as well as the applied techniques. The unexpected experimental results are tested and interpreted by deconvolution of the affecting factors. The application of Debye model to nanoparticles is tested and its shortcomings at nanoscale are discussed. Predictions which can provide insight into intelligent choice of candidates to cater to certain properties are provided. The results of this thesis can be used in the future in design and engineering of functionalized materials. We use ab initio calculations based on Density Functional Theory (DFT) to obtain information about the energetics, atomic configuration, and electronic structure of the nanoparticles. Ab initio Molecular Dynamics (MD) is used to study the evolution of the structures of the nanoparticles. To calculate vibrational frequencies, the finite displacement method is employed.
Show less - Date Issued
- 2015
- Identifier
- CFE0006385, ucf:51536
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006385
- Title
- COMPARISON OF THEORETICAL MODELS OF POWER SPECTRAL DENSITY TO THE EXPERIMENTAL VALUE FOR SPECTRUM OF IRRADIANCE FLUCTUATIONS.
- Creator
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Hershberger, Craig, Phillips, Ronald, University of Central Florida
- Abstract / Description
-
A propagation experiment was designed, assembled, and conducted on an extended range to verify theoretical temporal models for weak to strong fluctuation theory. Laser light intensity was propagated over terrain at the Kennedy Space Center (Florida), and detected using optical receivers at a distance of 13.3 Km from the optical source. The intensity data from the experiment was used to generate an experimental Power Spectral Density (PSD) function. The theoretical Mutual Coherence Function ...
Show moreA propagation experiment was designed, assembled, and conducted on an extended range to verify theoretical temporal models for weak to strong fluctuation theory. Laser light intensity was propagated over terrain at the Kennedy Space Center (Florida), and detected using optical receivers at a distance of 13.3 Km from the optical source. The intensity data from the experiment was used to generate an experimental Power Spectral Density (PSD) function. The theoretical Mutual Coherence Function (MCF) and Wave Structure Function (WSF) as set forth by Andrews/Phillips , were evaluated to determine the effective relationship between the statistical moments of the random optical field and the laser light intensity. Two scales of interest were identified (refractive large-scale and diffractive small-scale) and plotted revealing the characteristic shape of each component. In addition, statistical principles applied to the correlation/covariance function relationship and a graphical convolution process were used to generate a theoretical PSD function. Further, utilizing Taylor's "frozen turbulence" hypothesis an analysis of the theoretical temporal covariance function was performed. Functional forms for refractive and diffractive log-irradiance components were developed and used to generate a second theoretical PSD function. Finally, the experimental and theoretical Power Spectral Density functions are plotted on the same graph and a comparison is performed.
Show less - Date Issued
- 2008
- Identifier
- CFE0002403, ucf:47734
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0002403
- Title
- PADE APPROXIMANTS AND ONE OF ITS APPLICATIONS.
- Creator
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fowe, Tame-kouontcho, Mohapatra, Ram, University of Central Florida
- Abstract / Description
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This thesis is concerned with a brief summary of the theory of Padé approximants and one of its applications to Finance. Proofs of most of the theorems are omitted and many developments could not be mentioned due to the vastness of the field of Padé approximations. We provide reference to research papers and books that contain exhaustive treatment of the subject. This thesis is mainly divided into two parts. In the first part we derive a general expression of the Padé...
Show moreThis thesis is concerned with a brief summary of the theory of Padé approximants and one of its applications to Finance. Proofs of most of the theorems are omitted and many developments could not be mentioned due to the vastness of the field of Padé approximations. We provide reference to research papers and books that contain exhaustive treatment of the subject. This thesis is mainly divided into two parts. In the first part we derive a general expression of the Padé approximants and some of the results that will be related to the work on the second part of the thesis. The Aitken's method for quick convergence of series is highlighted as Padé . We explore the criteria for convergence of a series approximated by Padé approximants and obtain its relationship to numerical analysis with the help of the Crank-Nicholson method. The second part shows how Padé approximants can be a smooth method to model the term structure of interest rates using stochastic processes and the no arbitrage argument. Padé approximants have been considered by physicists to be appropriate for approximating large classes of functions. This fact is used here to compare Padé approximants with very low indices and two parameters to interest rates variations provided by the Federal Reserve System in the United States.
Show less - Date Issued
- 2007
- Identifier
- CFE0001682, ucf:47217
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001682
- Title
- UNDERSTANDING AND MODELING PATHWAYS TO THROMBOSIS.
- Creator
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Seligson, John, Kassab, Alain, University of Central Florida
- Abstract / Description
-
Intra-vessel thrombosis leads to serious problems in patient health. Coagulation can constrict blood flow and induce myocardial infarction or stroke. Hemodynamic factors in blood flow promote and inhibit the coagulation cascade. Mechanically, high shear stress has been shown to promote platelet activation while laminar flow maintains plasma layer separation of platelets and endothelial cells, preventing coagulation. These relationships are studied experimentally, however, physical properties...
Show moreIntra-vessel thrombosis leads to serious problems in patient health. Coagulation can constrict blood flow and induce myocardial infarction or stroke. Hemodynamic factors in blood flow promote and inhibit the coagulation cascade. Mechanically, high shear stress has been shown to promote platelet activation while laminar flow maintains plasma layer separation of platelets and endothelial cells, preventing coagulation. These relationships are studied experimentally, however, physical properties of thrombi, such as density and viscosity, are lacking in data, preventing a comprehensive simulation of thrombus interaction. This study incorporates experimental findings from literature to compile a characteristic mechanical property data set for use in thrombosis simulation. The focus of this study's simulation explored how thrombi interact between other thrombi and vessel walls via Volume of Fluid method. The ability to predict thrombosis under specific hemodynamic conditions was also a feature of the data collection. Using patient specific vessel geometry, the findings in this study can be applied to simulate thrombosis scenarios. The possible applications of such a simulation include a more precise method for estimation of patient myocardial infarction or stroke risk and a possible analysis of vessel geometry modification under surgery.
Show less - Date Issued
- 2015
- Identifier
- CFH0004837, ucf:45440
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFH0004837
- Title
- CONVERGENCE OF THE MEAN SHIFT ALGORITHM AND ITS GENERALIZATIONS.
- Creator
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Hu, Ting, Li, Xin, University of Central Florida
- Abstract / Description
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Mean shift is an effective iterative algorithm widely used in image analysis tasks like tracking, image segmentation, smoothing, filtering, edge detection and etc. It iteratively estimates the modes of the probability function of a set of sample data points based in a region. Mean shift was invented in 1975, but it was not widely used until the work by Cheng in 1995. After that, it becomes popular in computer vision. However the convergence, a key character of any iterative algorithm, has...
Show moreMean shift is an effective iterative algorithm widely used in image analysis tasks like tracking, image segmentation, smoothing, filtering, edge detection and etc. It iteratively estimates the modes of the probability function of a set of sample data points based in a region. Mean shift was invented in 1975, but it was not widely used until the work by Cheng in 1995. After that, it becomes popular in computer vision. However the convergence, a key character of any iterative algorithm, has been rigorously proved only very recently, but with strong assumptions. In this thesis, the method of mean shift is introduced systematically first and then the convergence is established under more relaxed assumptions. Finally, generalization of the mean shift method is also given for the estimation of probability density function using generalized multivariate smoothing functions to meet the need for more real life applications.
Show less - Date Issued
- 2011
- Identifier
- CFE0004059, ucf:49133
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004059
- Title
- SURVEY OF METEORITE PHYSICAL PROPERTIES: DENSITY, POROSITY AND MAGNETIC SUSCEPTIBILITY.
- Creator
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Macke, Robert, Britt, Daniel, University of Central Florida
- Abstract / Description
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The measurement of meteorite physical properties (i.e. density, porosity, magnetic susceptibility) supplements detailed chemical and isotopic analyses for small samples (thin sections or ~300 mg portions) by providing whole-rock data for samples massing in the tens of grams. With the advent of fast, non-destructive and non-contaminating measurement techniques including helium ideal-gas pycnometry for grain density, the Archimedean ÂÂ"glass beadÂÂ" method...
Show moreThe measurement of meteorite physical properties (i.e. density, porosity, magnetic susceptibility) supplements detailed chemical and isotopic analyses for small samples (thin sections or ~300 mg portions) by providing whole-rock data for samples massing in the tens of grams. With the advent of fast, non-destructive and non-contaminating measurement techniques including helium ideal-gas pycnometry for grain density, the Archimedean ÂÂ"glass beadÂÂ" method for bulk density and (with grain density) porosity, and the use of low-field magnetometry for magnetic susceptibility, all of which rely on compact and portable equipment, this has enabled a comprehensive survey of these physical properties for a wide variety of meteorites. This dissertation reports on the results of that survey, which spanned seven major museum and university meteorite collections as well as the Vatican collection. Bulk and grain densities, porosities and magnetic susceptibilities are reported for 1228 stones from 664 separate meteorites, including several rare meteorite types that are underrepresented in previous studies. Summarized here are data for chondrites (carbonaceous, ordinary and enstatite) and stony achondrites. Several new findings have resulted from this study. From the use of a ÂÂ"weathering modulusÂÂ" based on grain density and magnetic susceptibility to quantify weathering in finds, it is observed that the degree of weathering of ordinary chondrites is dependent on their initial porosity, which becomes reduced to less than ~8% for all finds, but for enstatite chondrites weathering actually increases porosity. Grain density and magnetic susceptibility, which have been shown to distinguish H, L and LL ordinary chondrites, also may distinguish shergottites, nakhlites and chassignites from each other, but the two groups of enstatite chondrites (EH and EL) remain indistinguishable in these properties. H chondrite finds exhibit a slight negative trend in porosity with increasing petrographic type, and all chondrite falls together exhibit a pronounced negative trend in porosity spanning all petrographic types. The overall trend corresponds roughly to a positive trend in porosities with respect to both degree of oxidation and percentage of matrix. It also corresponds to the macroporosities of analogous asteroids. These traits constrain models of conditions in the solar nebula and the formation of chondrite parent-body precursors.
Show less - Date Issued
- 2010
- Identifier
- CFE0003424, ucf:48420
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003424
- Title
- The Effect of Parental Population Density on Offspring Immune Function.
- Creator
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Davis, Dana, Fedorka, Kenneth, Savage, Anna, Hoffman, Eric, University of Central Florida
- Abstract / Description
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It is well known that an individual's environment, genetic code, and gene by environment interactions have an effect on its overall phenotype. However, there is a growing body of work that shows that parents can have an effect on their offspring's phenotype beyond the inherited genetic code. Studies have shown that parents may affect their offspring through physiological mechanisms such as egg provisioning and epigenetic effects and through behavioral mechanisms such as maternal care. In many...
Show moreIt is well known that an individual's environment, genetic code, and gene by environment interactions have an effect on its overall phenotype. However, there is a growing body of work that shows that parents can have an effect on their offspring's phenotype beyond the inherited genetic code. Studies have shown that parents may affect their offspring through physiological mechanisms such as egg provisioning and epigenetic effects and through behavioral mechanisms such as maternal care. In many of these cases, the parental effect is triggered by an environmental cue. Previous work has shown that density can impact immune function and cuticle color in insects - two phenotypic traits that are pleiotropically linked. Additional work has shown that parental density can have impacts on offspring immune function, as well. However, previous studies utilized insect species that show a strict density dimorphic phenotype where individuals reared at high densities exhibit increased immune function and much darker cuticles than their low density counterparts, which is not an accurate representation of most insect systems as most insect systems show a more continuous response to density effects. Also, previous work has not determined the parental origin of density effects on offspring immune function and cuticle color. It has been suggested that parental density effects may be due to maternal egg provisioning and that paternal effects may be minimal. However, knowledge of parental origin would give us a better insight into the possible mechanisms of these density driven parental effects and provide a direction for future research. In my study, we used Drosophila melanogaster in order to determine (1) if density affects immune function and cuticle color in a species that shows a continuous response to density, (2) if parental density affects offspring immune function and cuticle color, and (3) if the source of these parental effects are of a maternal origin only or if these effects are of a paternal origin, as well. We found that there is an effect of density on immune function and cuticle color in the parents in a more common insect system and parental density had an effect on offspring phenotype, as well. Most notably, we found that, in addition to the effects of maternal density, these parental effects on offspring phenotype were a response to paternal density, as well.
Show less - Date Issued
- 2017
- Identifier
- CFE0006580, ucf:51355
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006580
- Title
- REGULATION OF VLDL TRAFFICKING BY ORP 10.
- Creator
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Wessels, Philip, Siddiqi, Shadab, University of Central Florida
- Abstract / Description
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Of the challenges facing the improvement of human health, none has taken the forefront quite like the endeavor to discover novel treatments for heart disease. As heart disease has now become the leading cause of death throughout the world , the medical community has made incredible strides in the mission to treat atherosclerosis which is the major contributor to heart disease. Very Low Density Lipoproteins (VLDL) are secreted by the liver and subsequently converted to Low Density Lipoproteins...
Show moreOf the challenges facing the improvement of human health, none has taken the forefront quite like the endeavor to discover novel treatments for heart disease. As heart disease has now become the leading cause of death throughout the world , the medical community has made incredible strides in the mission to treat atherosclerosis which is the major contributor to heart disease. Very Low Density Lipoproteins (VLDL) are secreted by the liver and subsequently converted to Low Density Lipoproteins (LDL). Many factors contribute to the narrowing of the arterial walls, however oxidized LDL is the main factor that leads to the deposition of plaque, leading to atherosclerosis pathologies. Recently, a main focus of research into atherosclerotic processes has been the synthesis and trafficking of VLDL in hepatocytes. The rate-limiting step for the secretion of VLDL from the liver has been determined to be the transport of VLDL from the endoplasmic reticulum (ER) to the Golgi apparatus. VLDL molecules are transported in a specialized transport vesicle the Very Low Density Lipoprotein Transport Vesicle (VTV) . VLDL's core protein, apolipoproteinB-100 (apoB100), is initially lipidated in the ER, and then subsequently delivered to the Golgi apparatus where the VLDL molecule undergoes maturation involving further lipidation and glycosylation of apoB100. Oxysterol Binding Proteins (OSBP) and the sub family OSBP Related Proteins (ORP) have been implicated in many different trafficking processes, mainly the trafficking of sterols, cholesterol, and lipids. Recently, ORP 10 was shown to be a negative regulator of apoB100 secretion in growth medium . Using co-immunoprecipitation, the current study shows that ORP 10 interacts with VLDL's core protein apoB100 directly. Employing an in vitro budding assay, we show that the blocking of ORP 10 with a specific antibody against ORP10 increases VTV formation from the ER. Given that the ER to Golgi pathway is the rate-limiting step in overall VLDL secretion, these findings support the conclusion that ORP 10 is a negative regulator of VLDL trafficking between the ER and Golgi, and that this process is mediated by the ORP 10 protein binding with apoB100.
Show less - Date Issued
- 2015
- Identifier
- CFH0004866, ucf:45491
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFH0004866
- Title
- Simulation Study of a GPRAM System: Error Control Coding and Connectionism.
- Creator
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Schultz, Steven, Wei, Lei, Lin, Mingjie, Yuan, Jiann-Shiun, University of Central Florida
- Abstract / Description
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A new computing platform, the General Purpose Reprsentation and Association Machine is studied and simulated. GPRAM machines use vague measurements to do a quick and rough assessment on a task; then use approximated message-passing algorithms to improve assessment; and finally selects ways closer to a solution, eventually solving it. We illustrate concepts and structures using simple examples.
- Date Issued
- 2012
- Identifier
- CFE0004437, ucf:49361
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004437
- Title
- DENSITY FUNCTIONAL THEORY STUDY OF MOLECULES AND CRYSTALS CONTAINING D AND F METALS.
- Creator
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Gangopadhyay, Shruba, Masunov, Artem, University of Central Florida
- Abstract / Description
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Density Functional Theory (DFT) method is applied to study the crystal structure of transition metal and lanthanide oxides, as well as molecular magnetic complexes. DFT is a widely popular computational approach because it recasts a many-body problem of interacting electrons into an equivalent problem of non-interacting electrons, greatly reducing computational cost. We show that for certain structural properties like phase stability, lattice parameter and oxygen migration energetics pure DFT...
Show moreDensity Functional Theory (DFT) method is applied to study the crystal structure of transition metal and lanthanide oxides, as well as molecular magnetic complexes. DFT is a widely popular computational approach because it recasts a many-body problem of interacting electrons into an equivalent problem of non-interacting electrons, greatly reducing computational cost. We show that for certain structural properties like phase stability, lattice parameter and oxygen migration energetics pure DFT can give good agreement with experiments. But moving to more sensitive properties like spin state energetic certain modifications of standard DFT are needed. First we investigated mixed ionic-electronic conducting perovskite type oxides with a general formula ABO3 (where A =Ba, Sr, Ca and B = Co, Fe, Mn). These oxides often have high mobility of the oxygen vacancies and exhibit strong ionic conductivity. They are key materials that nd use in several energy related applications, including solid oxide fuel cell (SOFC), sensors, oxygen separation membranes, and catalysts. Different cations and oxygen vacancies ordering are examined using plane wave pseudopotential density functional theory. We nd that cations are completely disordered, whereas oxygen vacancies exhibit a strong trend for aggregation in L-shaped trimer and square tetramer structure. On the basis of our results, we suggest a new explanation for BSCF phase stability. Instead of linear vacancy ordering, which must take place before the phase transition into brownmillerite structure, the oxygen vacancies in BSCF prefer to form the nite clusters and preserve the disordered cubic structure. This structural feature could be found only in the rst-principles simulations and cannot be explained by the effect of the ionic radii alone. In order to understand vacancy clustering and phase stability in oxygen-deficient barium strontium cobalt iron oxide (BSCF), we predict stability and activation energies for oxygen vacancy migration. Using symmetry constrained search and Nudged Elastic Band method, we characterize the transition states for an oxygen anion moving into a nearby oxygen vacancy site that is surrounded by different cations and find the activation energies to vary in the range 30-50 kJ/mol in good agreement with experimental data. Next we study spin alignments of single molecule magnets (SMM). SMMs are a class of polynuclear transition metal complexes, which characterized by a large spin ground state and considerable negative anisotropy. These properties lead to a barrier for the reversal of magnetization. For these reasons SMM are expected to be promising materials for molecular spintronics and quantum computing applications. To design SMM for quantum computation, we need to accurately predict their magnetic properties. The most important property is, Heisenberg exchange coupling constant (J). This constant appears in model Heisenberg Hamiltonian that can be written in general form as here Jij represents the coupling between the two magnetic centers i and j with the spin states Si and Sj. The positive J values indicate the ferromagnetic ground state and the negative ones indicate the antiferromagnetic ground state. We found pure DFT is not accurate enough to predict J values. We employ density functionals with a Hubbard U term that helps to counteract the unphysical delocalization of electrons due to errors in pure exchange-correlation functionals. Unlike most previous DFT+U studies, we calibrate U parameters for both metal and ligand atoms using five binuclear manganese complexes as the benchmarks. We note delocalization of the spin density onto acetate ligands due to À-back bonding, inverting spin-polarization of the acetate oxygen atoms relative to that predicted from superexchange mechanism. This inversion may affect performance of the models assuming strict localization of the spins on magnetic centers for the complexes with bridging acetate ligands. Next, we apply DFT+U methodology for Mn12(mda) and Mn12(ada) complexes to calculate all six nearest neighbor Jij value. Our result shows both qualitative and quantitative agreement with experiments unlike other DFT studies. Using the optimized geometry of the ground spin state instead of less accurate experimental geometry was found to be crucial for this good agreement. The protocol tested in this study can be applied for the rational design of single-molecule magnets for molecular spintronics and quantum computing applications. Finally we apply hybrid DFT methodology to calculate geometrical parameters for cerium oxides. We review the experimental and computational studies on the cerium oxide nanoparticles, as well as stoichiometric phases of bulk ceria. Electroneutral and nonpolar pentalayers are identified as building blocks of type A sesqioxide structure. The idealized structure of the nanoparticles is described as dioxide covered by a single pentalayer of sesquioxide, which explains the exceptional stability of subsurface vacancies in nanoceria. The density functional theory (DFT) predictions of the lattice parameters and bulk moduli for the Ce(IV) and Ce(III) oxides at the hybrid DFT level are also presented. The calculated values for both compounds agree with experiment and allow to predict changes in the lattice parameter with decreasing size of the nanoparticles. The results validate hybrid DFT as a promising method for future study the structure of oxygen vacancies and catalytic properties of ceria nanoparticles.
Show less - Date Issued
- 2011
- Identifier
- CFE0003741, ucf:48762
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003741
- Title
- SIMULATION OF PHOTOCHROMIC COMPOUNDS USING DENSITY FUNCTIONAL THEORY METHODS.
- Creator
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Patel, Pansy, Masunov, Artem, University of Central Florida
- Abstract / Description
-
This Thesis describes the systematic theoretical study aimed at prediction of the essential properties for the functional organic molecules that belong to diarylethene (DA) family of compounds. Diarylethenes present the distinct ability to change color under the influence of light, known as photochromism. This change is due to ultrafast chemical transition from open to closed ring isomers (photocyclization). It can be used for optical data storage, photoswitching, and other photonic...
Show moreThis Thesis describes the systematic theoretical study aimed at prediction of the essential properties for the functional organic molecules that belong to diarylethene (DA) family of compounds. Diarylethenes present the distinct ability to change color under the influence of light, known as photochromism. This change is due to ultrafast chemical transition from open to closed ring isomers (photocyclization). It can be used for optical data storage, photoswitching, and other photonic applications. In this work we apply Density Functional Theory methods to predict 6 of the related properties: (i) molecular geometry; (ii) resonant wavelength; (iii) thermal stability; (iv) fatigue resistance; (v) quantum yield and (vi) nanoscale organization of the material. In order to study sensitivity at diode laser wavelengths, we optimized geometry and calculated vertical absorption spectra for a benchmark set of 28 diarylethenes. Bond length alternation (BLA) parameters and maximum absorption wavelengths (λmax) are compared to the data presently available from X-ray diffraction and spectroscopy experiments. We conclude that TD-M05/6-31G*/PCM//M05-2X/6-31G*/PCM level of theory gives the best agreement for both the parameters. For our predictions the root mean square deviation (RMSD) are below 0.014 Å for the BLAs and 25 nm for λmax. The polarization functions in the basis set and solvent effects are both important for this agreement. Next we consider thermal stability. Our results suggest that UB3LYP and UM05-2X functionals predict the activation barrier for the cycloreversion reaction within 3-4 kcal/mol from experimental value for a set of 7 photochromic compounds. We also study thermal fatigue, defined as the rate of undesirable photochemical side reactions. In order to predict the kinetics of photochemical fatigue, we investigate the mechanism of by-product formation. It has been established experimentally that the by-product is formed from the closed isomer; however the mechanism was not known. We found that the thermal by-product pathway involves the bicyclohexane (BCH) ring formation as a stable intermediate, while the photochemical by-product formation pathway may involve the methylcyclopentene diradical (MCPD) intermediate. At UM05-2X/6-31G* level, the calculated barrier between the closed form and the BCH intermediate is 51.2 kcal/mol and the barrier between the BCH intermediate and the by-product 16.2 kcal/mol. Next we investigate two theoretical approaches to the prediction of quantum yield (QY) for a set of 14 diarylethene derivatives at the validated M05-2X/6-31G* theory level. These include population of ground-state conformers and location of the pericycylic minimum on the potential energy surface 2-A state. Finally, we investigate the possibility of nanoscale organization of the photochromic material based on DNA template, as an alternative to the amorphous polymer matrix. Here we demonstrate that Molecular Dynamic methods are capable to describe the intercalation of π-conjugated systems between DNA base pairs and accurately reproduced the available photophysical properties of these nanocomposites. In summary, our results are in good agreement with the experimental data for the benchmark set of molecules we conclude that Density Functional Theory methods could be successfully used as an important component of material design strategy in prediction of accurate molecular geometry, absorption spectra, thermal stability of isomers, fatigue resistance, quantum yield of photocyclization and photophysical properties of nanocomposites.
Show less - Date Issued
- 2010
- Identifier
- CFE0003136, ucf:48633
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003136
- Title
- HIGH CURRENT DENSITY LOW VOLTAGE ISOLATED DC-DC CONVERTERSWITH FAST TRANSIENT RESPONSE.
- Creator
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Yao, Liangbin, Batarseh, Issa, University of Central Florida
- Abstract / Description
-
With the rapid development of microprocessor and semiconductor technology, industry continues to update the requirements for power supplies. For telecommunication and computing system applications, power supplies require increasing current level while the supply voltage keeps decreasing. For example, the Intel's CPU core voltage decreased from 2 volt in 1999 to 1 volt in 2005 while the supply current increased from 20A in 1999 to up to 100A in 2005. As a result, low-voltage high-current...
Show moreWith the rapid development of microprocessor and semiconductor technology, industry continues to update the requirements for power supplies. For telecommunication and computing system applications, power supplies require increasing current level while the supply voltage keeps decreasing. For example, the Intel's CPU core voltage decreased from 2 volt in 1999 to 1 volt in 2005 while the supply current increased from 20A in 1999 to up to 100A in 2005. As a result, low-voltage high-current high efficiency dc-dc converters with high power-density are demanded for state-of-the-art applications and also the future applications. Half-bridge dc-dc converter with current-doubler rectification is regarded as a good topology that is suitable for high-current low-voltage applications. There are three control schemes for half-bridge dc-dc converters and in order to provide a valid unified analog model for optimal compensator design, the analog state-space modeling and small signal modeling are studied in the dissertation and unified state-space and analog small signal model are derived. In addition, the digital control gains a lot of attentions due to its flexibility and re-programmability. In this dissertation, a unified digital small signal model for half-bridge dc-dc converter with current doubler rectifier is also developed and the digital compensator based on the derived model is implemented and verified by the experiments with the TI DSP chip. In addition, although current doubler rectifier is widely used in industry, the key issue is the current sharing between two inductors. The current imbalance is well studied and solved in non-isolated multi-phase buck converters, yet few discusse this issue in the current doubler rectification topology within academia and industry. This dissertation analyze the current sharing issue in comparison with multi-phase buck and one modified current doubler rectifier topology is proposed to achieve passive current sharing. The performance is evaluated with half bridge dc-dc converter; good current sharing is achieved without additional circuitry. Due to increasing demands for high-efficiency high-power-density low-voltage high current topologies for future applications, the thermal management is challenging. Since the secondary-side conduction loss dominates the overall power loss in low-voltage high-current isolated dc-dc converters, a novel current tripler rectification topology is proposed. Theoretical analysis, comparison and experimental results verify that the proposed rectification technique has good thermal management and well-distributed power dissipation, simplified magnetic design and low copper loss for inductors and transformer. That is due to the fact that the load current is better distributed in three inductors and the rms current in transformer windings is reduced. Another challenge in telecommunication and computing applications is fast transient response of the converter to the increasing slew-rate of load current change. For instance, from Intel's roadmap, it can be observed that the current slew rate of the age regulator has dramatically increased from 25A/uS in 1999 to 400A/us in 2005. One of the solutions to achieve fast transient response is secondary-side control technique to eliminate the delay of optocoupler to increase the system bandwidth. Active-clamp half bridge dc-dc converter with secondary-side control is presented and one industry standard 16th prototype is built and tested; good efficiency and transient response are shown in the experimental section. However, one key issue for implementation of secondary-side control is start-up. A new zero-voltage-switching buck-flyback isolated dc-dc converter with synchronous rectification is proposed, and it is only suitable for start-up circuit for secondary-side controlled converter, but also for house-keeping power supplies and standalone power supplies requiring multi-outputs.
Show less - Date Issued
- 2007
- Identifier
- CFE0001814, ucf:47336
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001814
- Title
- DENSITY-FUNCTIONAL THEORY APPLIED TO PROBLEMS IN CATALYSIS AND ELECTROCHEMISTRY.
- Creator
-
Kumar, Santosh, Schelling, Patrick, University of Central Florida
- Abstract / Description
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We study the structure and energetics of water molecules adsorbed at ceria (111) surfaces below one monolayer coverage using density-functional theory. The results of this study provide a theoretical framework for interpreting recent experimental results on the redox properties of water at ceria (111) surfaces. In particular, we have computed the structure and energetics of various absorption geometries at stoichiometric ceria (111) surface. In contrast to experiment results, we do not find a...
Show moreWe study the structure and energetics of water molecules adsorbed at ceria (111) surfaces below one monolayer coverage using density-functional theory. The results of this study provide a theoretical framework for interpreting recent experimental results on the redox properties of water at ceria (111) surfaces. In particular, we have computed the structure and energetics of various absorption geometries at stoichiometric ceria (111) surface. In contrast to experiment results, we do not find a strong coverage dependence of the adsorption energy. For the case of reduced surface, our results show that it may not be energetically favorable for water to oxidize oxygen vacancy site at the surface. Instead, oxygen vacancies tend to result in water more strongly binding to the surface. The result of this attractive water-vacancy interaction is that the apparent concentration of oxygen vacancies at the surface is enhanced in the presence of water. Finally, we discuss this problem with reference to recent experimental and theoretical studies of vacancy clustering at the (111) ceria surface. We also describe the simulation results for the structure and dynamics of liquid water using the SIESTA electronic structure approach. We find that the structure of water depends strongly on the particular basis set used. Applying a systematic approach to varying the basis set, we find that the basis set which results in good agreement with experimental binding energies for isolated water dimers also provides a reasonable description of the radial distribution functions of liquid water. We show that the structure of liquid water varies in a systematic fashion with the choice of basis set. Comparable to many other first-principle studies of liquid water using gradient-corrected density functionals, the liquid is found to be somewhat overstructured. The possibility of further improvements through a better choice of the basis set is discussed. We find that while improvements are likely to be possible, application to large-scale systems will require use of a computational algorithm whose computational cost scales linearly with system size. Finally, we study the molecular and atomic adsorption of oxygen on the gold nano-clusters. We show multiple stable and metastable structures for atomically and molecularly adsorbed oxygen to the gold cluster. We plan to predict the reaction pathway and calculate activation energy barrier for desorption of molecular oxygen from the atomically adsorbed gold cluster which is very important for any catalytic reaction occurring using gold nanoparticles.
Show less - Date Issued
- 2006
- Identifier
- CFE0001211, ucf:46938
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001211
- Title
- DERIVING THE DENSITY OF STATES FOR GRANULAR CONTACT FORCES.
- Creator
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Metzger, Philip, Bhattacharya, Aniket, University of Central Florida
- Abstract / Description
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The density of single grain states in static granular packings is derived from first principles for an idealized yet fundamental case. This produces the distribution of contact forces P_f(f) in the packing. Because there has been some controversy in the published literature over the exact form of the distribution, this dissertation begins by reviewing the existing empirical observations to resolve those controversies. A method is then developed to analyze Edwards' granular contact force...
Show moreThe density of single grain states in static granular packings is derived from first principles for an idealized yet fundamental case. This produces the distribution of contact forces P_f(f) in the packing. Because there has been some controversy in the published literature over the exact form of the distribution, this dissertation begins by reviewing the existing empirical observations to resolve those controversies. A method is then developed to analyze Edwards' granular contact force probability functional from first principles. The derivation assumes Edwards' flat measure -- a density of states (DOS) that is uniform within the metastable regions of phase space. A further assumption, supported by physical arguments and empirical evidence, is that contact force correlations arising through the closure of loops of grains may be neglected. Then, maximizing a state-counting entropy results in a transport equation that can be solved numerically. For the present it has been solved using the "Mean Structure Approximation," projecting the DOS across all angular coordinates to more clearly identify its predominant features in the remaining stress coordinates. These features are: (1) the Grain Factor related to grain stability and strong correlation between the contact forces on the same grain, and (2) the Structure Factor related to Newton's third law and strong correlation between neighboring grains. Numerical simulations were then performed for idealized granular packings to permit a direct comparison with the theory, and the data including P_f(f) were found to be in excellent agreement. Where the simulations and theory disagree, it is primarily due to the coordination number Z because the theory assumes Z to be a constant whereas in disordered packings it is not. The form of the empirical DOS is discovered to have an elegant, underlying pattern related to Z. This pattern consists entirely of the functional forms correctly predicted by the theory, but with only slight parameter changes as a function of Z. This produces significant physical insight and suggests how the theory may be generalized in the future.
Show less - Date Issued
- 2005
- Identifier
- CFE0000381, ucf:46325
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0000381
- Title
- SMOOTHING PARAMETER SELECTION IN NONPARAMETRIC FUNCTIONAL ESTIMATION.
- Creator
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Amezziane, Mohamed, Ahmad, Ibrahim, University of Central Florida
- Abstract / Description
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This study intends to build up new techniques for how to obtain completely data-driven choices of the smoothing parameter in functional estimation, within the confines of minimal assumptions. The focus of the study will be within the framework of the estimation of the distribution function, the density function and their multivariable extensions along with some of their functionals such as the location and the integrated squared derivatives.
- Date Issued
- 2004
- Identifier
- CFE0000307, ucf:46314
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0000307
- Title
- EFFECTS OF THE SOIL PROPERTIES ON THE MAXIMUM DRY DENSITY OBTAINED FROM THE STANDARD PROCTOR TEST.
- Creator
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Arvelo, Andres, Kuo, Shiou-san, University of Central Florida
- Abstract / Description
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In the construction of highways, airports, and other structures, the compaction of soils is needed to improve its strength. In 1933 Proctor developed a laboratory compaction test to determine the maximum dry density of compacted soils, which can be used for specifications of field compaction. The Compaction of soils is influenced by many factors, the most common are the moisture content, the soil type and the applied compaction energy. The objective of this research is the analysis of the...
Show moreIn the construction of highways, airports, and other structures, the compaction of soils is needed to improve its strength. In 1933 Proctor developed a laboratory compaction test to determine the maximum dry density of compacted soils, which can be used for specifications of field compaction. The Compaction of soils is influenced by many factors, the most common are the moisture content, the soil type and the applied compaction energy. The objective of this research is the analysis of the maximum dry density values based on the soil classification and characterization. The method of choice in the determination of the maximum dry density from different soils was the Standard Proctor Test following the procedure for the standard Proctor test as is explained in ASTM Test Designation D-698. From this investigation, the maximum dry density of eight types of sands was obtained, the sands were classified by using the Unified Soil Classification System. The influence on the maximum dry density of the type of sands, type of fines, amount of fines and distribution of the grain size was determined, followed by a sensitivity analysis that measured the influence of these parameters on the obtained maximum dry density. The research revealed some correlations between the maximum dry density of soils with the type of fines, the fines content and the Uniformity Coefficient. These correlations were measured and some particular behavioral trends were encountered and analyzed. It was found that well-graded sands have higher maximum dry density than poorly graded when the soils have the same fines content, also it was encountered that plastic fines tend to increase the maximum dry density.
Show less - Date Issued
- 2004
- Identifier
- CFE0000261, ucf:46237
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0000261
- Title
- EXAMINATION OF THE REHABILITATION PROTOCOL OF TRAUMATIC TRANSFEMORAL AMPUTEES AND HOW TO PREVENT BONE MINERAL DENSITY LOSS.
- Creator
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Jenkinson, Emily R, Fisher, Thomas, University of Central Florida
- Abstract / Description
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The purpose of this literature review was to identify any adaptations that could be made to the rehabilitation process for Traumatic Transfemoral Amputees. Traumatic Transfemoral Amputation is particularly debilitating with the amputees encountering many obstacles throughout the rehabilitation process. These obstacles can prevent the return to pre-morbid functioning. With an ever-increasing number of amputees within the United States, it is imperative the rehabilitation process be addressed....
Show moreThe purpose of this literature review was to identify any adaptations that could be made to the rehabilitation process for Traumatic Transfemoral Amputees. Traumatic Transfemoral Amputation is particularly debilitating with the amputees encountering many obstacles throughout the rehabilitation process. These obstacles can prevent the return to pre-morbid functioning. With an ever-increasing number of amputees within the United States, it is imperative the rehabilitation process be addressed. This literature review addresses possible adjustments in the initial stages of rehabilitation examining the post-operative, pre-prosthetic, and prosthetic rehabilitation stage to enhance the physical functioning for the amputee. This comprehensive literature review encompassing 63 academic and medical journals analyzes the research literature regarding each of the three stages of the post-operative procedure. The literature review synthesizes the research findings to see how procedures may be adapted to reduce the risk of further co-morbidities such as loss of bone mineral density and disuse atrophy. Loss of bone mineral density and disuse atrophy are the major contributing factors to the amputees decreased mobility. Reducing this loss can be addressed within the initial post-operative, pre-prosthetic, and prosthetic rehabilitation stages. Further research is required to examine the efficacy of these alterations in relation to this specific population.
Show less - Date Issued
- 2017
- Identifier
- CFH2000268, ucf:45964
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFH2000268
- Title
- HIGH SPEED TURBO TCM OFDM FOR UWB AND POWERLINE SYSTEM.
- Creator
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WANG, YANXIA, Wei, Lei, University of Central Florida
- Abstract / Description
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Turbo Trellis-Coded Modulation (TTCM) is an attractive scheme for higher data rate transmission, since it combines the impressive near Shannon limit error correcting ability of turbo codes with the high spectral efficiency property of TCM codes. We build a punctured parity-concatenated trellis codes in which a TCM code is used as the inner code and a simple parity-check code is used as the outer code. It can be constructed by simple repetition, interleavers, and TCM and functions as standard...
Show moreTurbo Trellis-Coded Modulation (TTCM) is an attractive scheme for higher data rate transmission, since it combines the impressive near Shannon limit error correcting ability of turbo codes with the high spectral efficiency property of TCM codes. We build a punctured parity-concatenated trellis codes in which a TCM code is used as the inner code and a simple parity-check code is used as the outer code. It can be constructed by simple repetition, interleavers, and TCM and functions as standard TTCM but with much lower complexity regarding real world implementation. An iterative bit MAP decoding algorithm is associated with the coding scheme. Orthogonal Frequency Division Multiplexing (OFDM) modulation has been a promising solution for efficiently capturing multipath energy in highly dispersive channels and delivering high data rate transmission. One of UWB proposals in IEEE P802.15 WPAN project is to use multi-band OFDM system and punctured convolutional codes for UWB channels supporting data rate up to 480Mb/s. The HomePlug Networking system using the medium of power line wiring also selects OFDM as the modulation scheme due to its inherent adaptability in the presence of frequency selective channels, its resilience to jammer signals, and its robustness to impulsive noise in power line channel. The main idea behind OFDM is to split the transmitted data sequence into N parallel sequences of symbols and transmit on different frequencies. This structure has the particularity to enable a simple equalization scheme and to resist to multipath propagation channel. However, some carriers can be strongly attenuated. It is then necessary to incorporate a powerful channel encoder, combined with frequency and time interleaving. We examine the possibility of improving the proposed OFDM system over UWB channel and HomePlug powerline channel by using our Turbo TCM with QAM constellation for higher data rate transmission. The study shows that the system can offer much higher spectral efficiency, for example, 1.2 Gbps for OFDM/UWB which is 2.5 times higher than the current standard, and 39 Mbps for OFDM/HomePlug1.0 which is 3 times higher than current standard. We show several essential requirements to achieve high rate such as frequency and time diversifications, multi-level error protection. Results have been confirmed by density evolution. The effect of impulsive noise on TTCM coded OFDM system is also evaluated. A modified iterative bit MAP decoder is provided for channels with impulsive noise with different impulsivity.
Show less - Date Issued
- 2006
- Identifier
- CFE0000943, ucf:46745
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0000943
- Title
- CHARACTERISTICS OF THE ADULT FEMALE ENDURANCE RUNNER: A SURVEY.
- Creator
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Gabriel, Stephanie F, Rothschild, Carey, University of Central Florida
- Abstract / Description
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Objective: This study investigated the behaviors and characteristics of the adult female endurance runner and potential components of the female athlete triad (FAT). The FAT consists of three components that are interrelated: low energy availability, menstrual dysfunction, and low bone mineral density. Low energy availability may occur with or without disordered eating. Reproduction becomes non-essential leading to irregular menstrual cycles. A reduction in estrogen levels may contribute to...
Show moreObjective: This study investigated the behaviors and characteristics of the adult female endurance runner and potential components of the female athlete triad (FAT). The FAT consists of three components that are interrelated: low energy availability, menstrual dysfunction, and low bone mineral density. Low energy availability may occur with or without disordered eating. Reproduction becomes non-essential leading to irregular menstrual cycles. A reduction in estrogen levels may contribute to low bone mineral density which may lead to stress fractures. Research investigating the FAT has primarily focused on adolescent and young adult females. Adult females training for endurance events may also be at risk for the FAT. Method: A survey was constructed and distributed to females in a local half-marathon and marathon training group in Central Florida. The data was collected at one point in time and no additional follow-up was required. The survey aimed to identify specific behaviors and characteristics related to components of the FAT and determine the potential prevalence in a small sample of female endurance athletes aged 18 and older. Results: 72 females with a mean age of 40.92(± 9.61) years completed the survey. Subjects had an average height of 163.60(±6.41) cm, weighed an average of 62.24(±10.05) kg and had 10 years of running experience. Conclusion: Adult female endurance runners demonstrate behaviors and characteristics that may be indicative of the FAT. Participants demonstrated signs of inadvertent or intentional low energy availability. These characteristics can be due to either body dissatisfaction or wanting to increase performance.
Show less - Date Issued
- 2017
- Identifier
- CFH2000173, ucf:45926
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFH2000173
- Title
- Spatial distribution and abundance of large green turtles on foraging grounds in the Florida Keys, USA.
- Creator
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Welsh, Ryan, Mansfield, Kate, Quintana-Ascencio, Pedro, Gorham, Jonathan, University of Central Florida
- Abstract / Description
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Discerning distribution, density, and abundance of organisms is essential for conservation and management of imperiled species. However, simple counts of sampled individuals are often not adequate to make such estimates, this is especially true for large and highly mobile marine animals. Green turtles (Chelonia mydas) are a highly migratory, long-lived, late-maturing, marine megafauna, that is beginning to recover from severe global population declines. Distance sampling techniques can be...
Show moreDiscerning distribution, density, and abundance of organisms is essential for conservation and management of imperiled species. However, simple counts of sampled individuals are often not adequate to make such estimates, this is especially true for large and highly mobile marine animals. Green turtles (Chelonia mydas) are a highly migratory, long-lived, late-maturing, marine megafauna, that is beginning to recover from severe global population declines. Distance sampling techniques can be used to generate estimates of abundance of green turtles in foraging grounds which have been relatively unstudied in the Northeastern Atlantic basin, filling in important data gaps in a species that is of critical conservation concern. The Quicksands foraging grounds located west of Key West, Florida, USA is used by both sub-adult and adult green turtles. Standardized transects were performed 18 times between 2006 (-) 2018, and using the collected data; abundances, spatial distribution and evidence of spatial segregation were generated through density surface models and null mode analysis. Densities of foraging green turtles rival some of the largest densities known in the world. Spatial segregation of the two size classes is evident on the foraging ground and may be attributed to differing predator detection and avoidance strategies of the size classes Finally, given the high densities of animals found on the foraging grounds and the rise in general population levels of green turtles and drop in population of green turtle predators (i.e. large sharks), concern is raised for the long term sustainably of the Quicksands seagrass pastures.
Show less - Date Issued
- 2019
- Identifier
- CFE0007874, ucf:52767
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007874
