View All Items

Title: Theoretical and Experimental Studies for Tailoring the Electromagnetic Surface Properties of Conductive Materials.
Creator: Jennings, Jeffrey, Vaidyanathan, Raj, Kar, Aravinda, Coffey, Kevin, Challapalli, Suryanarayana, Brisbois, Elizabeth, Yu, Xiaoming, University of Central Florida
Abstract / Description: Induction in leaded, implanted medical devices exposed to radio frequency (RF) magnetic fields during magnetic resonance imaging (MRI) produce Joule heating in adjacent tissues causing various issues, including death. Given the importance of MRI as a diagnostic tool and the growth in leaded device-related treatments, identification of a solution ensuring their compatibility is of great interest. Electromagnetic (EM) surface property tailoring in lead materials to change their inductive...
Show moreInduction in leaded, implanted medical devices exposed to radio frequency (RF) magnetic fields during magnetic resonance imaging (MRI) produce Joule heating in adjacent tissues causing various issues, including death. Given the importance of MRI as a diagnostic tool and the growth in leaded device-related treatments, identification of a solution ensuring their compatibility is of great interest. Electromagnetic (EM) surface property tailoring in lead materials to change their inductive response by adding functionally-graded, heterogeneous surface layers is a possible solution. However, non-uniform EM properties introduce two challenges: the added complexity of analyses and characterization of the graded region. This dissertation addresses these complexities.An Helmholtz coil and other loops positioned in a coaxial array were used to create and monitor inductive fields that were mathematically related to the induced current in closed, circular loops with electrical conductivities ranging from 1.0 to 57 megaSiemens per meter. Magnetic flux densities up to 14 microTesla at frequencies from 30 to 100 MHz were evaluated for specimens with varying loop and wire diameters. Induced current results show a linear relationship with flux density and strongly depend on the sample geometry, but not on conductivity. Trends within the data matched well with those predicted by theory that considered such a loop.An equivalent length, semi-analytical approach modeled induced current through a graded EM property region and considered effective conductivities. Predicted results for transmissivity through Pt-doped titanium foils and effective conductivity in round wire Sn-modified Cu samples show good agreement with experimental data. The Joule heating experiment used for wire testing also demonstrates a means for characterizing conductor surface properties. Two new technologies derived from this research including an RF magnetic field imaging technique and a contoured loop array for applying therapeutic controlled RF magnetic fields are also described.
Show less
Date Issued: 2018
Identifier: CFE0007756, ucf:52378
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007756

Title: Mathematical Investigation of the Spatial Spread of an Infectious Disease in a Heterogeneous Environment.
Creator: Gaudiello, Arielle, Shuai, Zhisheng, Nevai, A, Song, Zixia, Mohapatra, Ram, Quintana-Ascencio, Pedro, University of Central Florida
Abstract / Description: Outbreaks of infectious diseases can devastate a population. Researchers thus study the spread of an infection in a habitat to learn methods of control. In mathematical epidemiology, disease transmission is often assumed to adhere to the law of mass action, yet there are numerous other incidence terms existing in the literature. With recent global outbreaks and epidemics, spatial heterogeneity has been at the forefront of these epidemiological models.We formulate and analyze a model for...
Show moreOutbreaks of infectious diseases can devastate a population. Researchers thus study the spread of an infection in a habitat to learn methods of control. In mathematical epidemiology, disease transmission is often assumed to adhere to the law of mass action, yet there are numerous other incidence terms existing in the literature. With recent global outbreaks and epidemics, spatial heterogeneity has been at the forefront of these epidemiological models.We formulate and analyze a model for humans in a homogeneous population with a nonlinear incidence function and demographics of birth and death. We allow for the combination of host immunity after recovery from infection or host susceptibility once the infection has run its course in the individual. We compute the basic reproduction number, R0, for the system and determine the global stability of the equilibrium states. If R0(<)= 1, the population tends towards a disease-free state. If R0 (>)1, an endemic equilibrium exists, and the disease is persistent in the population. This work provides the framework needed for a spatially heterogeneous model. The model is then expanded to include a set of cities (or patches), each of which is structured from the homogeneous model. Movement is introduced, allowing travel between the cities at different rates. We assume there always exists a potentially non-direct route between two cities, and the movement need not be symmetric between two patches. Further, each city has its own nonlinear incidence function, demographics, and recovery rates, allowing for realistic interpretations of country-wide network structures. New global stability results are established for the disease-free equilibrium and endemic equilibrium, the latter utilizing a graph theoretic approach and Lyapunov functions. Asymptotic profiles are determined for both the disease-free equilibrium and basic reproduction number as the diffusion of human individuals is faster than the disease dynamics. A numerical investigation is performed on a star network, emulating a rural-urban society with a center city and surrounding suburbs. Numerical simulations give rise to similar and contrasting behavior for symmetric movement to the proposed asymmetric movement. Conjectures are made for the monotonicty of the basic reproduction number in terms of the diffusion of susceptible and infectious individuals. The limiting behavior of the system as the diffusion of susceptibles halts is shown to experience varying behavior based on the location of hot spots and biased movement.
Show less
Date Issued: 2019
Identifier: CFE0007637, ucf:52463
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007637

Title: In Quest of Bernstein Inequalities Rational Functions, Askey-Wilson Operator, and Summation Identities for Entire Functions.
Creator: Puwakgolle Gedara, Rajitha, Li, Xin, Mohapatra, Ram, Ismail, Mourad, Xu, Mengyu, University of Central Florida
Abstract / Description: The title of the dissertation gives an indication of the material involved with the connecting thread throughout being the classical Bernstein inequality (and its variants), which provides an estimate to the size of the derivative of a given polynomial on a prescribed set in the complex plane, relative to the size of the polynomial itself on the same set. Chapters 1 and 2 lay the foundation for the dissertation. In Chapter 1, we introduce the notations and terminology that will be used...
Show moreThe title of the dissertation gives an indication of the material involved with the connecting thread throughout being the classical Bernstein inequality (and its variants), which provides an estimate to the size of the derivative of a given polynomial on a prescribed set in the complex plane, relative to the size of the polynomial itself on the same set. Chapters 1 and 2 lay the foundation for the dissertation. In Chapter 1, we introduce the notations and terminology that will be used throughout. Also a brief historical recount is given on the origin of the Bernstein inequality, which dated back to the days of the discovery of the Periodic table by the Russian Chemist Dmitri Mendeleev. In Chapter 2, we narrow down the contents stated in Chapter 1 to the problems we were interested in working during the course of this dissertation. Henceforth, we present a problem formulation mainly for those results for which solutions or partial solutions are provided in the subsequent chapters.Over the years Bernstein inequality has been generalized and extended in several directions. In Chapter \ref{Bern-ineq}, we establish rational analogues to some Bernstein-type inequalities for restricted zeros and prescribed poles. Our inequalities extend the results for polynomials, especially which are themselves improved versions of the classical Erd\"{o}s-Lax and Tur\'{a}n inequalities. In working towards proving our results, we establish some auxiliary results, which may be of interest on their own. Chapters \ref{AW-on-polynomials} and \ref{AW-on-entire} focus on the research carried out with the Askey-Wilson operator applied on polynomials and entire functions (of exponential type) respectively.In Chapter 4, we first establish a Riesz-type interpolation formula on the interval $[-1,1]$ for the Askey-Wilson operator. In consequence, a sharp Bernstein inequality and a Markov inequality are obtained when differentiation is replaced by the Askey-Wilson operator. Moreover, an inverse approximation theorem is proved using a Bernstein-type inequality in $L^2-$space. We conclude this chapter with an overconvergence result which is applied to characterize all $q$-differentiable functions of Brown and Ismail. Chapter \ref{AW-on-entire} is devoted to an intriguing application of the Askey-Wilson operator. By applying it on the Sampling Theorem on entire functions of exponential type, we obtain a series representation formula, which is what we called an extended Boas' formula. Its power in discovering interesting summation formulas, some known and some new will be demonstrated. As another application, we are able to obtain a couple of Bernstein-type inequalities.In the concluding chapter, we state some avenues where this research can progress.
Show less
Date Issued: 2018
Identifier: CFE0007237, ucf:52220
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007237

Title: Modeling Disease Impact of Vibrio-Phage Interactions.
Creator: Botelho, Christopher, Shuai, Zhisheng, Nevai, A, Zhang, Teng, Teter, Kenneth, University of Central Florida
Abstract / Description: Since the work of John Snow, scientists and medical professionals have understood that individuals develop cholera by means of consuming contaminated water. Despite the knowledge(&)nbsp;of cholera's route of infection, many countries have experienced and still experience endemic cholera. Cholera is caused by the Vibrio cholerae (V. cholerae) bacterium and presents with acute diarrhea and vomiting. If untreated, infected individuals may die due to dehydration. Cholera is a disease that most...
Show moreSince the work of John Snow, scientists and medical professionals have understood that individuals develop cholera by means of consuming contaminated water. Despite the knowledge(&)nbsp;of cholera's route of infection, many countries have experienced and still experience endemic cholera. Cholera is caused by the Vibrio cholerae (V. cholerae) bacterium and presents with acute diarrhea and vomiting. If untreated, infected individuals may die due to dehydration. Cholera is a disease that most commonly affects countries with poor infrastructure and water sanitation. Despite efforts to control cholera in such countries, the disease persists. One such example is Haiti which has been experiencing a cholera outbreak since 2010. While there has been much research in the field of microbiology to understand V. cholerae, there has been comparably less research in the field of mathematical biology to understand the dynamics of V. cholerae in the environment. A mathematical model of V. cholerae incorporating a phage population is coupled with a SIRS disease model to examine the impact of vibrio and phage interaction. It is shown that there might exist two endemic equilibria, besides the disease free equilibrium: one in which phage persist in the environment and one in which the phage fail to persist. Existence and stability of these equilibria are established. Disease control strategies based on vibrio and phage interactions are discussed.
Show less
Date Issued: 2019
Identifier: CFE0007604, ucf:52544
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007604

Title: First Principles Studies of Pattern Formations and Reactions on Catalyst Surfaces.
Creator: Le, Duy, Rahman, Talat, Roldan Cuenya, Beatriz, Schelling, Patrick, Sohn, Yongho, University of Central Florida
Abstract / Description: This dissertation undertakes theoretical research into the adsorption, pattern formation, and reactions of atoms, molecules, and layered materials on catalyst surfaces. These investigations are carried out from first-principles calculations of electronic and geometric structures using density functional theory (DFT) for predictions and simulations at the atomic scale. The results should be useful for further study of the catalytic activities of materials and for engineering functional...
Show moreThis dissertation undertakes theoretical research into the adsorption, pattern formation, and reactions of atoms, molecules, and layered materials on catalyst surfaces. These investigations are carried out from first-principles calculations of electronic and geometric structures using density functional theory (DFT) for predictions and simulations at the atomic scale. The results should be useful for further study of the catalytic activities of materials and for engineering functional nanostructures.The first part of the dissertation focuses on systematic first-principles simulations of the energetic pathways of CO oxidation on the Cu2O(100) surface. These simulations show CO to oxidize spontaneously on the O-terminated Cu2O(100) surface by consuming surface oxygen atoms. The O-vacancy on Cu2O(100) then is subsequently healed by dissociative adsorption of atmospheric O2 molecules.The second part discusses the pattern formation of hydrogen on two and three layers of Co film grown on the Cu(111) surface. It is found that increasing the pressure of H2 changes the hydrogen structure from 2H-(2 x 2) to H-p(1 x 1) through an intermediate structure of 6H-(3 x 3).The third part compares the results of different ways of introducing van der Waals (vdW) interactions into DFT simulations of the adsorption and pattern formation of various molecules on certain substrates. Examinations of the physisorption of five nucleobases on graphene and of n-alkane on Pt(111) demonstrate the importance of taking vdW interactions into account, and of doing so in a way that is best suited to the particular system in question. More importantly, as the adsorption of 1,4 diaminebenzene molecules on Au(111) shows inclusion of vdW interactions is crucial for accurate simulation of the pattern formation.The final part carries out first-principles calculations of the geometric and electronic structure of the Moire pattern of a single layer of Molybdenum disulfide (MoS2) on Cu(111). The results reveal three possible stacking types. They also demonstrate that the MoS2 layer to be chemisorbed, albeit weakly, and that, while Cu surface atoms are vertically disordered, the layer itself is not strongly buckled.
Show less
Date Issued: 2012
Identifier: CFE0004224, ucf:48991
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004224

Title: SAFETY IMPROVEMENTS ON MULTILANE ARTERIALS A BEFORE AND AFTER EVALUATION USING THE EMPIRICAL BAYES METHOD.
Creator: Devarasetty, Prem Chand, Abdel-Aty, Mohamed, University of Central Florida
Abstract / Description: This study examines the safety effects of the improvements made on multi-lane arterials. The improvements were divided into two categories 1) corridor level improvements, and 2) intersection improvements. Empirical Bayes method, which is one of the most accepted approaches for conducting before-after evaluations, has been used to assess the safety effects of the improvement projects. Safety effects are estimated not only in terms of all crashes but also rear-end (most common type) as well as...
Show moreThis study examines the safety effects of the improvements made on multi-lane arterials. The improvements were divided into two categories 1) corridor level improvements, and 2) intersection improvements. Empirical Bayes method, which is one of the most accepted approaches for conducting before-after evaluations, has been used to assess the safety effects of the improvement projects. Safety effects are estimated not only in terms of all crashes but also rear-end (most common type) as well as severe crashes (crashes involving incapacitating and/or fatal injuries) and also angle crashes for intersection improvements. The Safety Performance Functions (SPFs) used in this study are negative binomial crash frequency estimation models that use the information on ADT, length of the segments, speed limit, and number of lanes for corridors. And for intersections the explanatory variables used are ADT, number of lanes, speed limit on major road, and number of lanes on the minor road. GENMOD procedure in SAS was used to develop the SPFs. Corridor SPFs are segregated by crash groups (all, rear-end, and severe), length of the segments being evaluated, and land use (urban, suburban and rural). The results of the analysis show that the resulting changes in safety following corridor level improvements vary widely. Although the safety effect of projects involving the same type of improvement varied, the overall effectiveness of each of the corridor level improvements were found to be positive in terms of reduction in crashes of each crash type considered (total, severe, and rear-end) except for resurfacing projects where the total number of crashes slightly increased after the roadway section is resurfaced. Evaluating additional improvements carried out with resurfacing activities showed that all (other than sidewalk improvements for total crashes) of them consistently led to improvements in safety of multilane arterial sections. It leads to the inference that it may be a good idea to take up additional improvements if it is cost effective to do them along with resurfacing. It was also found that the addition of turning lanes (left and/or right) and paving shoulders were two improvements associated with a project's relative performance in terms of reduction in rear-end crashes. No improvements were found to be associated with a resurfacing project's relative performance in terms of changes in (i.e., reducing) severe crashes. For intersection improvements also the individual results of each project varied widely. Except for adding turn lane(s) all other improvements showed a positive impact on safety in terms of reducing the number of crashes for all the crash types (total, severe, angle, and rear-end) considered. Indicating that the design guidelines for this work type have to be revisited and safety aspect has to be considered while implementing them. In all it can be concluded that FDOT is doing a good job in selecting the sites for treatment and it is very successful in improving the safety of the sections being treated although the main objective(s) of the treatments are not necessarily safety related.
Show less
Date Issued: 2009
Identifier: CFE0002723, ucf:48148
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0002723

Title: OPTIMAL DUAL FRAMES FOR ERASURES AND DISCRETE GABOR FRAMES.
Creator: Lopez, Jerry, Han, Deguang, University of Central Florida
Abstract / Description: Since their discovery in the early 1950's, frames have emerged as an important tool in areas such as signal processing, image processing, data compression and sampling theory, just to name a few. Our purpose of this dissertation is to investigate dual frames and the ability to find dual frames which are optimal when coping with the problem of erasures in data transmission. In addition, we study a special class of frames which exhibit algebraic structure, discrete Gabor frames. Much work...
Show moreSince their discovery in the early 1950's, frames have emerged as an important tool in areas such as signal processing, image processing, data compression and sampling theory, just to name a few. Our purpose of this dissertation is to investigate dual frames and the ability to find dual frames which are optimal when coping with the problem of erasures in data transmission. In addition, we study a special class of frames which exhibit algebraic structure, discrete Gabor frames. Much work has been done in the study of discrete Gabor frames in $\mathbb^n$, but very little is known about the $\ell^2(\mathbb)$ case or the $\ell^2(\mathbb^d)$ case. We establish some basic Gabor frame theory for $\ell^2(\mathbb)$ and then generalize to the $\ell^2(\mathbb^d)$ case.
Show less
Date Issued: 2009
Identifier: CFE0002614, ucf:48274
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0002614

Title: STRUCTURAL, ELECTRONIC, VIBRATIONAL AND THERMODYNAMICAL PROPERTIES OF SURFACES AND NANOPARTICLES.
Creator: Yildirim, Handan, Rahman, Talat S., University of Central Florida
Abstract / Description: The main focus of the thesis is to have better understanding of the atomic and electronic structures, vibrational dynamics and thermodynamics of metallic surfaces and bi-metallic nanoparticles (NPs) via a multi-scale simulational approach. The research presented here involves the study of the physical and chemical properties of metallic surfaces and NPs that are useful to determine their functionality in building novel materials. The study follows the Ã‚Â"bottom-upÃ&...
Show moreThe main focus of the thesis is to have better understanding of the atomic and electronic structures, vibrational dynamics and thermodynamics of metallic surfaces and bi-metallic nanoparticles (NPs) via a multi-scale simulational approach. The research presented here involves the study of the physical and chemical properties of metallic surfaces and NPs that are useful to determine their functionality in building novel materials. The study follows the Ã‚Â"bottom-upÃ‚Â" approach for which the knowledge gathered at the scale of atoms and NPs serves as a base to build, at the macroscopic scale, materials with desired physical and chemical properties. We use a variety of theoretical and computational tools with different degrees of accuracy to study problems in different time and length scales. Interactions between the atoms are derived using both Density Functional Theory (DFT) and Embedded Atom Method (EAM), depending on the scale of the problem at hand. For some cases, both methods are used for the purpose of comparison. For revealing the local contributions to the vibrational dynamics and thermodynamics for the systems possessing site-specific environments, a local approach in real-space is used, namely Real Space GreenÃ‚Â's Function method (RSGF). For simulating diffusion of atoms/clusters and growth on metal surfaces, Molecular Statics (MS) and Molecular Dynamics (MD) methods are employed.
Show less
Date Issued: 2010
Identifier: CFE0003064, ucf:48300
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0003064

Title: GRADUATED STUDENTS WITH AUTISM SPECTRUM DISORDERS AND THEIR PARENTS: LIVED EXPERIENCES IN PUBLIC HIGH SCHOOL.
Creator: Uhle, Karen, Martin, Suzanne, University of Central Florida
Abstract / Description: ABSTRACT With a dramatic increase in the prevalence of students with autism spectrum disorders (ASD), including those with high-functioning autism and Asperger's syndrome, educators are challenged to meet the educational needs of a complex and widely diverse group of exceptional learners. The focus of this research was to gain insight into the experiences of the graduated student with autism and his/her parent(s) during the student's time in public school. This study had three research...
Show moreABSTRACT With a dramatic increase in the prevalence of students with autism spectrum disorders (ASD), including those with high-functioning autism and Asperger's syndrome, educators are challenged to meet the educational needs of a complex and widely diverse group of exceptional learners. The focus of this research was to gain insight into the experiences of the graduated student with autism and his/her parent(s) during the student's time in public school. This study had three research questions: 1) What were the lived experiences of students with ASD who graduated from an urban public high school in the southeast United States?; 2) What were the lived experiences of the parents of the graduated students with ASD?; and, 3) Were there common themes between the graduated students' lived experiences and the parent's lived experiences? Five graduated students and their parents were interviewed in this qualitative, phenomenological study. Explicitation of the interview data identified three themes for the graduated student group: a) challenges with learning due to having an ASD; b) difficulty making friends; and, c) involvement in their educational process. Four themes were present in the parent group: a) challenges with learning due to having an ASD; b) difficulty making friends; c) establishment of a relationship with the school; and, d) preparation for post-secondary experiences. The graduated student group agreed with the parent group on 16 of the 20 interview questions. Responses for each graduated student were compared to the responses of his/her own parent(s). Recommendations were made for future research.
Show less
Date Issued: 2011
Identifier: CFE0003719, ucf:48801
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0003719

Title: Analysis and Simulation for Homogeneous and Heterogeneous SIR Models.
Creator: Wilda, Joseph, Shuai, Zhisheng, Brennan, Joseph, Nevai, A, University of Central Florida
Abstract / Description: In mathematical epidemiology, disease transmission is commonly assumed to behave in accordance with the law of mass action; however, other disease incidence terms also exist in the literature. A homogeneous Susceptible-Infectious-Removed (SIR) model with a generalized incidence term is presented along with analytic and numerical results concerning effects of the generalization on the global disease dynamics. The spatial heterogeneity of the metapopulation with nonrandom directed movement...
Show moreIn mathematical epidemiology, disease transmission is commonly assumed to behave in accordance with the law of mass action; however, other disease incidence terms also exist in the literature. A homogeneous Susceptible-Infectious-Removed (SIR) model with a generalized incidence term is presented along with analytic and numerical results concerning effects of the generalization on the global disease dynamics. The spatial heterogeneity of the metapopulation with nonrandom directed movement between populations is incorporated into a heterogeneous SIR model with nonlinear incidence. The analysis of the combined effects of the spatial heterogeneity and nonlinear incidence on the disease dynamics of our model is presented along with supporting simulations. New global stability results are established for the heterogeneous model utilizing a graph-theoretic approach and Lyapunov functions. Numerical simulations confirm nonlinear incidence gives raise to rich dynamics such as synchronization and phase-lock oscillations.
Show less
Date Issued: 2015
Identifier: CFE0005906, ucf:50872
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005906

Title: Applied problem solving in children with ADHD: The mediating roles of working memory and mathematical calculation.
Creator: Friedman, Lauren, Rapport, Mark, Beidel, Deborah, Vasquez, Eleazar, University of Central Florida
Abstract / Description: The difficulties children with ADHD experience solving applied math problems (i.e., word problems) are well documented; however, the independent and/or interactive contribution of cognitive processes underlying these difficulties is not fully understood and warrant scrutiny. The current study examines two primary cognitive processes integral to children's ability to solve applied math problems: working memory (WM) and math calculation ability (i.e., the ability to utilize specific facts,...
Show moreThe difficulties children with ADHD experience solving applied math problems (i.e., word problems) are well documented; however, the independent and/or interactive contribution of cognitive processes underlying these difficulties is not fully understood and warrant scrutiny. The current study examines two primary cognitive processes integral to children's ability to solve applied math problems: working memory (WM) and math calculation ability (i.e., the ability to utilize specific facts, skills, or processes related to basic math operations stored in long-term memory). Thirty-six boys with ADHD-combined presentation and 33 typically developing (TD) boys aged 8-12 years old were administered multiple counterbalanced tasks to assess upper (central executive [CE]) and lower level (phonological [PH STM] and visuospatial [VS STM] short-term memory) WM processes, and standardized measures of mathematical abilities. Bias-corrected, bootstrapped mediation analyses revealed that CE ability fully mediated between-group differences in applied problem solving whereas math calculation ability partially mediated the relation. Neither PH STM nor VS STM was a significant mediator. When modeled together via serial mediation analysis, CE in tandem with math calculation ability fully mediated the relation, explained 79% of the variance, and provided a more parsimonious explication of ADHD-related deficits in applied math ability. Results suggest that interventions designed to address applied math difficulties in children with ADHD will likely benefit from targeting basic knowledge of math facts and skills while simultaneously promoting the active interplay among these skills and CE processes.
Show less
Date Issued: 2017
Identifier: CFE0006593, ucf:51300
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006593

Title: Electronic Structure of Metal (Al, Cu) Doped Carbon Nanotubes and the Resultant Conduction of the Hybrid Materials.
Creator: Jiang, Jingyin, Chen, Quanfang, Zhai, Lei, Fang, Jiyu, Bai, Yuanli, Stolbov, Sergey, University of Central Florida
Abstract / Description: Due to the exceptional strength, stiffness and excellent electrical and thermal properties, carbon nanotubes (CNTs) have been regarded as promising candidates for advanced nanoelectronics and multifunctional nanocomposites. In this dissertation, the interaction of CNTs with metals have been investigated and the resultant electrical conduction have been analyzed, aiming to develop innovative avenues to best utilize CNTs' potential. In order to do so, quantum mechanics calculations have been...
Show moreDue to the exceptional strength, stiffness and excellent electrical and thermal properties, carbon nanotubes (CNTs) have been regarded as promising candidates for advanced nanoelectronics and multifunctional nanocomposites. In this dissertation, the interaction of CNTs with metals have been investigated and the resultant electrical conduction have been analyzed, aiming to develop innovative avenues to best utilize CNTs' potential. In order to do so, quantum mechanics calculations have been carried out to study that how to obtain greater electrical conduction by doping metals (Cu, Al) which tailor the electronic structure of three different types of metal-CNT interactions, : 1) encapsulation of atoms inside the CNTs, 2) adsorption of atoms onto CNT surface, and 3) substitutional doping. Models of different doping methods were built and optimized with Density Functional Theory (DFT). And in conjunction with non-equilibrium Green's function, the electronic structure and the conducting properties were then calculated.Through this study, both metallic and semiconducting CNTs have been used. Metallic CNT (5, 5) encapsulated with copper chains have been first investigated with an emphasis on the electronic structure and the resultant conductance. The Density of States (DOS) have showed that the encapsulation of Cu effectively introduced more states around the fermi level. And due to the interaction between copper and CNTs, the conductance of the metallic CNTs-Cu system can be significantly increased.In addition to copper, aluminum has been also introduced for the study. The electronic structure and transport properties of hybrid nanowires consisting of aluminum chains adsorbed on a single-wall semiconducting CNT (10, 0) have been calculated. The band structure and DOS of the hybrid nanowires have showed that the adsorption of Al can effectively reduce the band gap. And with more than 4 Al chains adsorbed, the CNT has transformed from semiconducting to conducting. The transmission eigenstates further indicated that both Al chains and the modified nanotube were responsible for the increased conduction in the hybrid nanowires. The resultant conductance of CNT (10, 0)/Al hybrid nanowire is about 40% greater than that of pure Cu nanowire with the same diameter. In order to utilize the extraordinary conductance in CNT(10,0)/Al hybrid nanowire, it is also important to investigate the end-contact between the hybrid nanowire with Al electrodes. During this work the transmission spectrum at different bias voltage were calculated to study the I-V characteristics and the electrical contact resistances at the interfaces. The results have suggested that the electrical contact resistances between Al electrodes and the hybrid nanowire is significantly lower than that of Al-pure CNT contacts, although the actual contact resistance is directional dependent that the contact resistance is reduced to 20% of that Al-pure CNT along the longitudinal direction.The possibility of substitutional doping of Cu and Al in both metallic and semiconducting CNTs were also investigated. The formation energies have showed that Al doping was more energy favorable than Cu doping in both cases. And by doping of Al or Cu, a metallic tube experienced a higher conductance and a semiconducting tube has transited to conducting.In summary, different doping methods could modify the conducting property of nanotubes. Encapsulation of Cu in metallic CNT results in a significant conductance increment. Adsorption of Al transforms semiconducting CNT to conducting and reduces the contact resistance between the nanowire and Al electrode. Substitutional doping of Cu or Al transits semiconducting nanotube to conducting and enhance the conductance of metallic nanotube.
Show less
Date Issued: 2017
Identifier: CFE0006607, ucf:51274
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006607

Title: Density-Functional Theory+Dynamical Mean-Field Theory Study of the Magnetic Properties of Transition-Metal Nanostructures.
Creator: Kabir, Alamgir, Rahman, Talat, Kara, Abdelkader, Del Barco, Enrique, Kik, Pieter, University of Central Florida
Abstract / Description: In this thesis, Density Functional Theory (DFT) and Dynamical Mean-Field Theory (DMFT) approaches are applied to study the magnetic properties of transition metal nanosystems of different sizes and compositions. In particular, in order to take into account dynamical electron correlation effects (time-resolved local charge interactions), we have adopted the DFT+DMFT formalism and made it suitable for application to nanostructures. Preliminary application of this DFT+DMFT approach, using...
Show moreIn this thesis, Density Functional Theory (DFT) and Dynamical Mean-Field Theory (DMFT) approaches are applied to study the magnetic properties of transition metal nanosystems of different sizes and compositions. In particular, in order to take into account dynamical electron correlation effects (time-resolved local charge interactions), we have adopted the DFT+DMFT formalism and made it suitable for application to nanostructures. Preliminary application of this DFT+DMFT approach, using available codes, to study the magnetic properties of small (2 to 5-atom) Fe and FePt clusters provide meaningful results: dynamical effects lead to a reduction of the cluster magnetic moment as compared to that obtained from DFT or DFT+U (U being the Coulomb repulsion parameter). We have subsequently developed our own nanoDFT+DMFT code and applied it to examine the magnetization of iron particles containing10-147 atoms. Our results for the cluster magnetic moments are in a good agreement with experimental data. In particular, we are able to reproduce the oscillations in magnetic moment with size as observed in the experiments. Also, DFT+DMFT does not lead to an overestimation of magnetization for the clusters in the size range of 10-27 atoms found with DFT and DFT+U. On application of the nanoDFT+DMFT approach to systems with mixed geometry (-) Fe2O3 film, which are periodic (infinitely extended), in two directions, and finite in the third. Similar to DFT+U, we find that the surface atom magnetic moments are smaller compared to the bulk. However, the absolute values of the surface atoms magnetic moments are smaller in DFT+DMFT. In parallel, we have carried out a systematic study of magnetic anisotropy in bimetallic L10 FePt nanoparticles (20-484 atoms) by using two DFT-based approaches: direct and the torque method. We find that the magnetocrystalline anisotropy (MCA) of FePt clusters is larger than that of the pure Fe and Pt ones. We explain this effect by a large hybridization of 3d Fe- and 5d Pt-atom orbitals, which lead to enhancement of the magnetic moment of the Pt atom, and hence to a larger magnetic anisotropy because of large spin-orbit coupling of Pt atoms. In addition, we find that particles whose (large) central layer consists of Pt atoms, rather than Fe, have larger MCA due to stronger hybridization effects. Such 'protected' MCA, which does not require protective cladding, can be used in modern magnetic technologies.
Show less
Date Issued: 2015
Identifier: CFE0006038, ucf:50971
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006038

Title: The Impact of Job Experience Training on Executive Functioning Skills for Students with Language Impairments.
Creator: Elliott, Christopher, Martin, Suzanne, Boote, David, Hopp, Carolyn, Whiteman, JoAnn, Cerasale, Mark, University of Central Florida
Abstract / Description: The collaborative efforts of families, educators, and policy makers have mergedvocational training with special education services for students with disabilities. The Individuals with Disabilities Education Act of 2004 introduced mandates for schools to provide transition services for students with disabilities based on three areas of need: a) education, b) employment,and independent living. This legislation has led to more work-based learning programs that meet the postsecondary needs for...
Show moreThe collaborative efforts of families, educators, and policy makers have mergedvocational training with special education services for students with disabilities. The Individuals with Disabilities Education Act of 2004 introduced mandates for schools to provide transition services for students with disabilities based on three areas of need: a) education, b) employment,and independent living. This legislation has led to more work-based learning programs that meet the postsecondary needs for students with disabilities. Despite this increase in work-based learning programs many students with disabilities are still unable to make successful transitions into postsecondary outcomes. Using a mixed method design, this study examined the impact of a Job Experience Training (JET) program on the executive functioning skills of seven young men (15 to 18 years of age) over the course of seven weeks at an assisted living facility. Resultsof the teacher evaluations showed the students were capable of completing tasks, making individual goals, and increasing executive functioning skills while participating in the JET program. Conversely, the results from the parent and student assessments showed little to no change in executive functioning skills once the participants were outside the context of theassisted living facility. Future research is encouraged to examine a longitudinal study across multiple job sites that evaluates and measures the students' ability to transfer executive functioning skills to other contexts and further investigate mentoring as the core teaching strategy of a JET program.
Show less
Date Issued: 2014
Identifier: CFE0005161, ucf:50714
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005161

Title: Charge and Spin Transport in Low-Dimensional Materials.
Creator: Ahmadi, Amin, Mucciolo, Eduardo, Del Barco, Enrique, Ishigami, Masa, Guo, Jing, University of Central Florida
Abstract / Description: My research has been focused on two main areas. First, electronic transports in chiral carbonnanotubes in the presence of charged adatoms. To study such systems we employed recursiveGreens function technique to evaluate the conductance using the Landauer formula. Comparingwith the experimental data, we determined the effective amplitude and the range of scatteringpotentials. In addition, using a similar approach we explained qualitatively an unusual conductancefeature in a metallic carbon...
Show moreMy research has been focused on two main areas. First, electronic transports in chiral carbonnanotubes in the presence of charged adatoms. To study such systems we employed recursiveGreens function technique to evaluate the conductance using the Landauer formula. Comparingwith the experimental data, we determined the effective amplitude and the range of scatteringpotentials. In addition, using a similar approach we explained qualitatively an unusual conductancefeature in a metallic carbon nanotube. The second part of my study was concerned to the dynamicalspin injection and spin currents in low-dimensional materials. We have developed an atomisticmodel to express the injected spin current in terms of the systems Greens function. The newformulation provides a framework to study the spin injection and relaxation of a system with anarbitrary structure.
Show less
Date Issued: 2017
Identifier: CFE0006550, ucf:51343
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006550

Title: The Comparison of the School District Curriculum Alignment with Algebra Content Standards.
Creator: Lipscomb, Karen, Murray, Barbara, Doherty, Walter, Baldwin, Lee, Pawlas, George, University of Central Florida
Abstract / Description: The purpose of this study was to analyze school district curriculum alignment with state and national standards to find content omissions that may contribute to low Algebra End-of-Course exam scores in ninth grade. The study primarily looked for algebra course content omissions in the algebra, functions, and statistics' domains of the algebra curriculum. These three categories were chosen because low achievement for ninth grades students was recorded in each category for a Medium Sized Rural...
Show moreThe purpose of this study was to analyze school district curriculum alignment with state and national standards to find content omissions that may contribute to low Algebra End-of-Course exam scores in ninth grade. The study primarily looked for algebra course content omissions in the algebra, functions, and statistics' domains of the algebra curriculum. These three categories were chosen because low achievement for ninth grades students was recorded in each category for a Medium Sized Rural School District. The study also examined the pre-algebra curriculum for a Medium Sized Rural School District to see if alignment was present with the algebra curriculum. Embedded skills needed for algebra success were also recorded to develop an in-depth look at the curriculum alignment. The embedded skills are skills that should be mastered before students are placed in the pre-algebra course.The algebra state standards were compared with the Medium Sized Rural School District local algebra standards. From the local standards, 95 coded algebra skills were established as pertinent for mastery of algebra content. The 95 coded algebra skills were used in the constant comparison document analysis to find content omissions in the algebra curriculum, the pre-algebra curriculum, and the algebra textbook. The 95 algebra coded skills were also examined individually to record embedded skills needed for mastery of each skill. An additional study was performed on the amount of time given to the mastery of the 95 algebra coded skills or performance tasks.The following results were found in this research for curriculum alignment. In a Medium Size Rural School District, the algebra curriculum and algebra textbook were analyzed for the presence of 95 essential performance tasks in search for missing content. The algebra curriculum and algebra textbook were both found to be aligned with the algebra state standards. These findings allow educators to look at other factors that may contribute to low performance on the Algebra End-of-Course exam. Content omissions were found in the pre-algebra curriculum that showed a lack of alignment with the algebra course. Also, 77 embedded skills were recorded as prerequisites to algebra mastery. Last, the amount of material to be mastered in a ninth grade algebra course may be too numerous for ninth grade algebra students to master the material.
Show less
Date Issued: 2016
Identifier: CFE0006348, ucf:51574
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006348

Title: The Role of the Y-Chromosome in the Evolution of Autosomally Coded Traits.
Creator: Kutch, Ian, Fedorka, Kenneth, Vonkalm, Laurence, Hoffman, Eric, University of Central Florida
Abstract / Description: Recent work indicates that the Y-chromosome of the fruit fly Drosophila melanogaster can influence gene regulation on the autosomes and X chromosome. This newly discovered function of the Y has the potential to dramatically shape the regulatory evolution of numerous genes that reside throughout the genome; even for genes that code for both male and female traits. Given that the mechanism underlying the Y-linked influence on gene expression in D. melanogaster appears to exist in other...
Show moreRecent work indicates that the Y-chromosome of the fruit fly Drosophila melanogaster can influence gene regulation on the autosomes and X chromosome. This newly discovered function of the Y has the potential to dramatically shape the regulatory evolution of numerous genes that reside throughout the genome; even for genes that code for both male and female traits. Given that the mechanism underlying the Y-linked influence on gene expression in D. melanogaster appears to exist in other independently evolved heterogametic sex chromosomes, the evolutionary implications of Y-linked regulatory variation (YRV) deserves to be explored. These implications include the potential for Y-chromosomes to facilitate the adaptive evolution of sexually dimorphic gene expression, and the potential for the Y to constrain evolutionary rates in both males and females (depending on the nature of the YRV effect). Unfortunately, the evolutionary implications of this potentially widespread and significant phenomenon have yet to be explored. My dissertation addresses this knowledge gap by determining the influence YRV has on the evolution of autosomally coded traits in D. melanogaster. First, we address the potential for selection to shape YRV by determining if YRV (i) exists within natural populations (i.e. where natural selection operates), and (ii) has any influence on male fitness-related autosomal traits. Second, we address if YRV can facilitate the adaptive evolution of sexually dimorphic gene expression by testing for the presence of Y-linked additive genetic variation. To this end, we investigate the physiological properties of select Y-chromosomes across multiple genetic backgrounds. Third, we address if YRV can constrain adaptive evolution for autosomally coded traits by employing artificial selection on replicate populations that contain either multiple Y-chromosomes (i.e. contain YRV) or only a single Y-chromosome (no YRV). The following studies present evidence that YRV does exist within populations where natural selection operates. We show significant levels of YRV on X-linked and autosomal immune gene expression in wild caught D. melanogaster from a single natural population. Furthermore, YRV effects on immune related genes show a significantly positive correlation to a male fly's ability to fight an immune challenge (an important aspect of organismal fitness). Estimated physiological properties of YRV support previous interpopulation studies showing strong non-additive effect dependent on the autosomal genetic background with which Y-chromosome's are paired with. Physiological epistasis can manifest as additive genetic variation on a population level, but our experimental evolution study suggest that YRV constrains rather than facilitates the evolution of the autosomal coded geotaxis behavior. Ultimately, this dissertation provides evidence that YRV has the potential to influence how autosomal traits evolve and that population level studies of YRV indicate a potential constraint to the adaptive evolution of autosomal traits. If these trends are common and YRV is a wide spread phenomenon, Y-chromosomes have the potential to influence how autosomal traits evolve.
Show less
Date Issued: 2017
Identifier: CFE0006756, ucf:51873
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006756

Title: Declarative Memory, Theory of Mind, and Community Functioning in Schizophrenia.
Creator: Deptula, Andrew, Bedwell, Jeffrey, Paulson, Daniel, Sims, Valerie, Fiore, Stephen, University of Central Florida
Abstract / Description: Cognitive impairments are highly prevalent in individuals with schizophrenia and are now considered hallmark features of the disorder. Over the past decade, considerable evidence has demonstrated the functional significance of social and nonsocial cognitive impairments in individuals with schizophrenia. However, the nature of the relationship between specific domains of social and nonsocial cognition and how they relate to functional outcome in this population is less clear. In particular,...
Show moreCognitive impairments are highly prevalent in individuals with schizophrenia and are now considered hallmark features of the disorder. Over the past decade, considerable evidence has demonstrated the functional significance of social and nonsocial cognitive impairments in individuals with schizophrenia. However, the nature of the relationship between specific domains of social and nonsocial cognition and how they relate to functional outcome in this population is less clear. In particular, declarative memory impairment has been suggested to have critical consequences for the everyday life of individuals with schizophrenia and may play a role in their social integration difficulties. Preliminary evidence also indicates that theory of mind (ToM) may be an important intermediary between nonsocial cognition and functional outcome. The current study aimed to better understand the relationships between declarative memory, ToM, and functional outcome in individuals with schizophrenia.
Show less
Date Issued: 2016
Identifier: CFE0006096, ucf:51207
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006096

Title: Reading comprehension deficits in children with ADHD: The mediating roles of working memory and orthographic conversion.
Creator: Friedman, Lauren, Rapport, Mark, Beidel, Deborah, Vasquez, Eleazar, University of Central Florida
Abstract / Description: Reading comprehension deficits in children with ADHD are well-established; however, limited information exists concerning the cognitive mechanisms that contribute to these deficits and the extent to which they interact with one another. The current study examines two broad cognitive processes known to be involved in children's reading comprehension abilities(-)(a) working memory (i.e., central executive processes [CE], phonological short-term memory [PH STM], and visuospatial short-term...
Show moreReading comprehension deficits in children with ADHD are well-established; however, limited information exists concerning the cognitive mechanisms that contribute to these deficits and the extent to which they interact with one another. The current study examines two broad cognitive processes known to be involved in children's reading comprehension abilities(-)(a) working memory (i.e., central executive processes [CE], phonological short-term memory [PH STM], and visuospatial short-term memory [VS STM]) and (b) orthographic conversion(-)to elucidate their unique and interactive contribution to ADHD-related reading comprehension deficits. Thirty-one children with ADHD and 30 typically developing (TD) children aged 8 to 12 years (M = 9.64, SD = 1.22) were administered multiple counterbalanced tasks assessing WM and orthographic conversion processes. Relative to TD children, children with ADHD exhibited significant deficits in PH STM (d = -0.66), VS STM (d = -0.84), CE (d = -1.24) and orthographic conversion (d = -0.85). Bias-corrected, bootstrapped mediation analyses revealed that CE and orthographic conversion processes modeled separately, partially mediated ADHD-related reading comprehension impairments, whereas PH STM and VS STM did not. CE and orthographic conversion modeled jointly fully mediated ADHD-related reading comprehension deficits wherein orthographic conversion's large magnitude influence on reading comprehension occurred indirectly through CE's impact on the orthographic system. The findings suggest that adaptive cognitive interventions designed to improve reading-related outcomes in children with ADHD may benefit by including modules that train CE and orthographic conversion processes independently and interactively.
Show less
Date Issued: 2016
Identifier: CFE0006103, ucf:51210
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006103

Title: Psychopathology and Functional Impairment in Adolescents with Social Anxiety Disorder.
Creator: Mesa, Franklin, Beidel, Deborah, Cassisi, Jeffrey, Neer, Sandra, University of Central Florida
Abstract / Description: Although social anxiety disorder is most often diagnosed during adolescence, few investigations have examined the clinical presentation of this disorder exclusively in adolescents. Prior studies have demonstrated that some clinical features of SAD in adolescents are unique relative to younger children with the condition. Furthermore, the extant literature on daily functional impairment in this population is limited. In this investigation, multiple areas of functioning were examined in...
Show moreAlthough social anxiety disorder is most often diagnosed during adolescence, few investigations have examined the clinical presentation of this disorder exclusively in adolescents. Prior studies have demonstrated that some clinical features of SAD in adolescents are unique relative to younger children with the condition. Furthermore, the extant literature on daily functional impairment in this population is limited. In this investigation, multiple areas of functioning were examined in adolescents with SAD (n = 16) and normal control adolescents (n = 14): specific social skills, subjective distress and physiological reactivity during one speech performance task and one social interaction task; alcohol use and expectancies; subjective and objective quality of sleep; and daily distressing social activities. No differences were observed in sleep actigraphy, self-reported sleep difficulties, alcohol use, or alcohol expectancies. Adolescents with SAD reported greater distress during both analogue tasks relative to NC adolescents. During the speech task, adolescents with SAD exhibited significantly greater speech latency (4.42 seconds vs. 1.75 seconds) and spoke significantly less (83.09 seconds vs. 167.75 seconds) than NC adolescents. Additionally, SAD participants manifested greater skin conductance during the speech task. During the social interaction, adolescents with SAD asked significantly fewer questions (2.20 vs. 7.07) and required significantly more confederate prompts (2.33 vs. 1.14) to stimulate interaction. Finally, adolescents with SAD reported more frequent anxiety-provoking situations in their daily lives and greater avoidance of these situations, including answering questions in class, assertive communication, and interacting with a group. The findings are discussed with respect to the current understanding of alcohol use, quality of sleep, and social functioning in adolescents with SAD.
Show less
Date Issued: 2013
Identifier: CFE0004891, ucf:49648
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004891

Density Functional Theory (5)	+ -
density functional theory (5)	+ -
Empirical Bayes (4)	+ -
Highway Safety Manual (4)	+ -
working memory (4)	+ -

Executive Function (3)	+ -
Safety Performance Functions (3)	+ -
executive function (3)	+ -
fNIRS (3)	+ -
meshless methods (3)	+ -
Aging (2)	+ -
Bootstrap (2)	+ -
CaR-FA-X (2)	+ -
Catalysis (2)	+ -
Crash Modification Factors (2)	+ -
Functional Near-Infrared Spectroscopy (2)	+ -
Functions (2)	+ -
Lyapunov functions (2)	+ -
Parenting (2)	+ -
Phospholipase A2 (2)	+ -
Rumination (2)	+ -
Transferability (2)	+ -
atmospheric turbulence (2)	+ -
discriminant function analysis (2)	+ -
executive functions (2)	+ -
functional near-infrared spectroscopy (2)	+ -
global stability (2)	+ -
gold nanoparticles (2)	+ -
meta-analysis (2)	+ -
neuropsychology (2)	+ -

ETD Collection (104)	+ -
Honors Collection (15)	+ -

English (117)	+ -
Engilsh (2)	+ -

University of Central Florida (118)	+ -
Abdel-Aty, Mohamed (8)	+ -
Rapport, Mark (7)	+ -
Lee, JaeYoung (6)	+ -
Paulson, Daniel (6)	+ -

Search In

Pages

Pages

Sort Results By:

Narrow results by:

Topical Subject

Collection

Type of Resource

Language

Creator

Format

Owner