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Structure and Properties of Polymer-Derived SiBCN Ceramics
Title
Structure and Properties of Polymer-Derived SiBCN Ceramics.
Creator
Chen, Yaohan, An, Linan, Fang, Jiyu, Xu, Chengying, Zhai, Lei, Huo, Qun, Gong, Xun, University of Central Florida
Abstract / Description
Polymer-derived ceramics (PDCs) are a unique class of multifunctional materials synthesized by thermal decomposition of polymeric precursors. Due to their unique and excellent properties and flexible manufacturing capability, PDC is a promising technology to prepare ceramic fibers, coatings, composites and micro-sensors for high-temperature applications. However, the structure-property relationships of PDCs have not been well understood. The lack of such understandings drastically limited the...
Show morePolymer-derived ceramics (PDCs) are a unique class of multifunctional materials synthesized by thermal decomposition of polymeric precursors. Due to their unique and excellent properties and flexible manufacturing capability, PDC is a promising technology to prepare ceramic fibers, coatings, composites and micro-sensors for high-temperature applications. However, the structure-property relationships of PDCs have not been well understood. The lack of such understandings drastically limited the further developments and applications of the materials.In this dissertation, the structure and properties of amorphous polymer-derived silicon carbonitride (SiCN) and silicoboron carbonitride (SiBCN) have been studied. The SiCN was obtained using commercially available polysilazane as pre-ceramic precursor, and the SiBCN ceramics with varied Si-to-B ratio were obtained from polyborosilazanes, which were synthesized by the hydroboration and dehydrocoupling reaction of borane and polysilazane. The structural evolution of polymer-derived SiCN and SiBCN ceramics from polymer to ceramics was investigated by NMR, FTIR, Raman, EPR, TG/DTA, and XRD. The results show a phase-separation of amorphous matrix and a graphitization of (")free(") carbon phase, and suggest that the boron doping has a great influence on the structural evolution. The electric and dielectric properties of the SiCN and SiBCNs were studied by I-V curves, LCR Meter, and network analyzer. A new electronic conduction mechanism and structure model has been proposed to account for the relationships between the observed properties and microstructure of the materials. Furthermore, the SiBCN ceramics showed the improved dielectric properties at characterization temperature up to 1300 (&)#186;C, which allows the fabrication of ultrahigh-temperature wireless microsensors for extreme environments.
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Date Issued
2012
Identifier
CFE0004195, ucf:49014
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0004195
CHEMICAL STRUCTURE - NONLINEAR OPTICAL PROPERTY RELATIONSHIPS FOR A SERIES OF TWO-PHOTON ABSORBING FLUORENE MOLECULES
Title
CHEMICAL STRUCTURE - NONLINEAR OPTICAL PROPERTY RELATIONSHIPS FOR A SERIES OF TWO-PHOTON ABSORBING FLUORENE MOLECULES.
Creator
Hales, Joel McCajah, Van Stryland, Eric W., University of Central Florida
Abstract / Description
This dissertation reports on the investigation of two-photon absorption (2PA) in a series of fluorenyl molecules. Several current and emerging technologies exploit this optical nonlinearity including two-photon fluorescence imaging, three-dimensional microfabrication, site-specific photodynamic cancer therapy and biological caging studies. The two key features of this nonlinearity which make it an ideal candidate for the above applications are its quadratic dependence on the incident...
Show moreThis dissertation reports on the investigation of two-photon absorption (2PA) in a series of fluorenyl molecules. Several current and emerging technologies exploit this optical nonlinearity including two-photon fluorescence imaging, three-dimensional microfabrication, site-specific photodynamic cancer therapy and biological caging studies. The two key features of this nonlinearity which make it an ideal candidate for the above applications are its quadratic dependence on the incident irradiance and the improved penetration into absorbing media that it affords. As a consequence of the burgeoning field which exploits 2PA, it is a goal to find materials that exhibit strong two-photon absorbing capabilities. Organic materials are promising candidates for 2PA applications because their material properties can be tailored through molecular engineering thereby facilitating optimization of their nonlinear optical properties. Fluorene derivatives are particularly interesting since they possess high photochemical stability for organic molecules and are generally strongly fluorescent. By systematically altering the structural properties in a series of fluorenyl molecules, we have determined how these changes affect their two-photon absorbing capabilities. This was accomplished through characterization of both the strength and location of their 2PA spectra. In order to ensure the validity of these results, three separate nonlinear characterization techniques were employed: two-photon fluorescence spectroscopy, white-light continuum pump-probe spectroscopy, and the Z-scan technique. In addition, full linear spectroscopic characterization was performed on these molecules along with supplementary quantum chemical calculations to obtain certain molecular properties that might impact the nonlinearity. Different designs in chemical architecture allowed investigation of the effects of symmetry, solvism, donor-acceptor strengths, conjugation length, and multi-branched geometries on the two-photon absorbing properties of these molecules. In addition, the means to enhance 2PA via intermediate state resonances was investigated. To provide plausible explanations for the experimentally observed trends, a conceptually simple three level model was employed. The subsequent correlations found between chemical structure and the linear and nonlinear optical properties of these molecules provided definitive conclusions on how to properly optimize their two-photon absorbing capabilities. The resulting large nonlinearities found in these molecules have already shown promise in a variety of the aforementioned applications.
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Date Issued
2004
Identifier
CFE0000005, ucf:46103
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0000005
CATEGORICAL PROPERTIES OF LATTICE-VALUED CONVERGENCE SPACES
Title
CATEGORICAL PROPERTIES OF LATTICE-VALUED CONVERGENCE SPACES.
Creator
Flores, Paul, Richardson, Gary, University of Central Florida
Abstract / Description
This work can be roughly divided into two parts. Initially, it may be considered a continuation of the very interesting research on the topic of Lattice-Valued Convergence Spaces given by Jäger [2001, 2005]. The alternate axioms presented here seem to lead to theorems having proofs more closely related to standard arguments used in Convergence Space theory when the Lattice is L=.Various Subcategories are investigated. One such subconstruct is shown to be isomorphic to the category of...
Show moreThis work can be roughly divided into two parts. Initially, it may be considered a continuation of the very interesting research on the topic of Lattice-Valued Convergence Spaces given by Jäger [2001, 2005]. The alternate axioms presented here seem to lead to theorems having proofs more closely related to standard arguments used in Convergence Space theory when the Lattice is L=.Various Subcategories are investigated. One such subconstruct is shown to be isomorphic to the category of Lattice Valued Fuzzy Convergence Spaces defined and studied by Jäger . Our principal category is shown to be a topological universe and contains a subconstruct isomorphic to the category of probabilistic convergence spaces discussed in Kent and Richardson when L=. Fundamental work in lattice-valued convergence from the more general perspective of monads can be found in Gähler . Secondly, diagonal axioms are defined in the category whose objects consist of all the lattice valued convergence spaces. When the latter lattice is linearly ordered, a diagonal condition is given which characterizes those objects in the category that are determined by probabilistic convergence spaces which are topological. Certain background information regarding filters, convergence spaces, and diagonal axioms with its dual are given in Chapter 1. Chapter 2 describes Probabilistic Convergence and associated Diagonal axioms. Chapter 3 defines Jäger convergence and proves that Jäger's construct is isomorphic to a bireflective subconstruct of SL-CS. Furthermore, connections between the diagonal axioms discussed and those given by Gähler are explored. In Chapter 4, further categorical properties of SL-CS are discussed and in particular, it is shown that SL-CS is topological, cartesian closed, and extensional. Chapter 5 explores connections between diagonal axioms for objects in the sub construct δ(PCS) and SL-CS. Finally, recommendations for further research are provided.
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Date Issued
2007
Identifier
CFE0001715, ucf:47292
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0001715
INVESTIGATION OF THE EFFECT OF EDGE-OXIDIZED GRAPHENE OXIDE (EOGO) ON THE PROPERTIES OF CEMENT COMPOSITES
Title
INVESTIGATION OF THE EFFECT OF EDGE-OXIDIZED GRAPHENE OXIDE (EOGO) ON THE PROPERTIES OF CEMENT COMPOSITES.
Creator
Alharbi, Yousef, Nam, Boo Hyun, Chopra, Manoj, Zaurin, Ricardo, Kwok, Kawai, University of Central Florida
Abstract / Description
The use of edge-oxidized graphene oxide (EOGO), produced by a mechanochemical ?process that allow to deliver a product suitable for large-scale production at affordable cost, as ?an additive in cement composites was investigated. Comprehensive experimental tests were ?conducted to investigate the effect of EOGO on the properties of cement composites. The ?experimental tests were designed for three subtasks: (1) investigation of the performance of ?EOGO and its mixing method on the strength,...
Show moreThe use of edge-oxidized graphene oxide (EOGO), produced by a mechanochemical ?process that allow to deliver a product suitable for large-scale production at affordable cost, as ?an additive in cement composites was investigated. Comprehensive experimental tests were ?conducted to investigate the effect of EOGO on the properties of cement composites. The ?experimental tests were designed for three subtasks: (1) investigation of the performance of ?EOGO and its mixing method on the strength, pore structure and microstructure of EOGO-?cement composites, (2) evaluation of the rheological and fluidity behavior of EOGO-cement ?paste and mortar, and (3) investigation of the mechanism of the enhanced workability of ?EOGO-concrete. EOGO content ranged from 0.01% to 1% and two mix design methods were ?employed for cement paste and mortar to explore an optimum and feasible mix design of ?EOGO. Compressive and flexural strength tests were conducted to investigate the mechanical ?performance of EOGO-cement composites. Total porosity and water sorptivity were performed ?to investigate the pore structure of EOGO-cement paste and mortar. Furthermore, petrographic ?analyses were conducted to characterize the microstructure of EOGO-cement composites. ?Imaged based-mini-slump and flow table tests were performed to measure the fluidity of ?EOGO-cement paste and mortar. The rheological properties of EOGO-cement paste were ?measured through viscometer test. The mechanism of the enhanced workability of EOGO-?concrete was investigated by performing slump and water absorption of aggregate in cement ?paste tests. The key findings are (1) the addition of EOGO into cement composites improves the ?compressive and flexural strength, (2) 0.05% of EOGO is the optimum content to improve the ?strength and pore structure of EOGO-cement composites, (3) the addition of EOGO reduces the ?fluidity and increases the viscosity of EOGO-cement composites, (4) the addition of EOGO ?improves the workability of concrete, and (5) dry-mix design is feasible and more practical for ?large-scale production.?
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Date Issued
2019
Identifier
CFE0007425, ucf:52721
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0007425
THE CONTEXTUAL IMPACT OF INCOME INEQUALITY ON SOCIAL CAPITAL AND ADVERSE SOCIAL OUTCOMES
Title
THE CONTEXTUAL IMPACT OF INCOME INEQUALITY ON SOCIAL CAPITAL AND ADVERSE SOCIAL OUTCOMES.
Creator
Schiff, Jeannie, Wan, Thomas, University of Central Florida
Abstract / Description
An interdisciplinary approach to policy and governance recognizes that many social welfare problems are interrelated, and policy-makers have long recognized a need to address the root causes of these problems. There is much evidence that income inequality is one of these root causes but research suggesting the effect of income inequality is mediated by social capital has complicated the relationship, as have theories of causality that take different approaches. This study takes an ecological...
Show moreAn interdisciplinary approach to policy and governance recognizes that many social welfare problems are interrelated, and policy-makers have long recognized a need to address the root causes of these problems. There is much evidence that income inequality is one of these root causes but research suggesting the effect of income inequality is mediated by social capital has complicated the relationship, as have theories of causality that take different approaches. This study takes an ecological approach to these issues to test the relationship between income inequality, social capital and selected adverse outcomes proposed by the relative income hypothesis. The relative income hypothesis posits that the impact of income inequality on adverse outcomes is mediated by social capital. The study used a retrospective cross-sectional design to analyze county-level data for the year 2000 with a structural equation model composed of three constructs: income inequality, modeled by four common measures; a social capital construct based on a model developed by Rupasingha, Goetz and Freshwater (2006); and an adverse outcomes construct designed as a parsimonious measure of social outcomes in four public affairs disciplinary areas. The test of the path presumed by the relative income hypothesis revealed both a direct effect of income inequality and indirect effect of inequality through social capital. However, the direct effect of income inequality on outcomes was significantly larger than the indirect effect, indicating the relationship is moderated, rather than mediated, by social capital. Since the impact of social capital on the selected adverse outcomes was relatively small, and the final model failed to achieve statistical significance, the relative income hypothesis that income inequality exerts its primary effect on outcomes through social capital was rejected.
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Date Issued
2010
Identifier
CFE0003205, ucf:48574
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0003205
A multi-scale approach to study Solid Oxide Fuel Cells: from Mechanical Properties and Crystal Structure of the Cell's Materials to the Development of an Interactive and Interconnected Educational Tool
Title
A multi-scale approach to study Solid Oxide Fuel Cells: from Mechanical Properties and Crystal Structure of the Cell's Materials to the Development of an Interactive and Interconnected Educational Tool.
Creator
Aman, Amjad, Orlovskaya, Nina, Xu, Yunjun, Das, Tuhin, University of Central Florida
Abstract / Description
Solid Oxide Fuel Cells are energy conversion devices that convert chemical energy of a fuel directly into electrical energy. They are known for being fuel-flexible, have minimal harmful emissions, ideal for combined heat and power applications, highly energy-efficient when combined with gas or steam turbines. The current challenges facing the widespread adoption these fuel cells include cost reduction, long-term testing of fully integrated systems, improving the fuel cell stack and system...
Show moreSolid Oxide Fuel Cells are energy conversion devices that convert chemical energy of a fuel directly into electrical energy. They are known for being fuel-flexible, have minimal harmful emissions, ideal for combined heat and power applications, highly energy-efficient when combined with gas or steam turbines. The current challenges facing the widespread adoption these fuel cells include cost reduction, long-term testing of fully integrated systems, improving the fuel cell stack and system performance, and studies related to reliability, robustness and durability. The goal of this dissertation is to further the understanding of the mechanical properties and crystal structure of materials used in the cathode and electrolyte of solid oxide fuel cells, as well as to report on the development of a supplementary educational tool that could be used in course related to fuel cells. The first part of the dissertation relates to the study of LaCoO3 based perovskites that are used as cathode material in solid oxide fuel cells and in other energy-related applications. In-situ neutron diffraction of LaCoO3 perovskite during uniaxial compression was carried out to study crystal structure evolution and texture development. In this study, LaCoO3 was subjected to two cycles of uniaxial loading and unloading with the maximum stress value being 700-900 MPa. The in-situ neutron diffraction revealed the dynamic crystallographic changes occurring which is responsible for the non-linear ferroelastic deformation and the appearance of hysteresis in LaCoO3. At the end of the first cycle, irreversible strain was observed even after the load was removed, which is caused by non-recoverable domain reorientation and texture development. At the end of the second cycle, however, no irreversible strain was observed as domain reorientation seemed fully recovered. Elastic constants were calculated and Young's modulus was estimated for LaCoO3 single crystals oriented along different crystallographic directions. The high temperature mechanical behavior study of LaCoO3 based perovskites is also of prime importance as solid oxide fuel cells operate at high temperatures. Incidentally, it was observed that as opposed to the behavior of most materials, LaCoO3 exhibits stiffening between 700 oC to 900 oC, with the Young's modulus going from a value of ~76 GPa at room temperature to ~120 GPa at 900 oC. In-situ neutron diffraction, XRD and Raman spectroscopy were used to study structural changes occurring in the material as it was heated. The results from these experiments will be discussed.The next portion of the dissertation will focus on electrolytes. Numerical simulation was carried out in order to predict the non-linear load-stress relationship and estimation of biaxial flexure strength in layered electrolytes, during ring-on-ring mechanical testing.Finally, the development of an interactive and inter-connected educational software is presented that could serve as a supplementary tool to teach fuel cell related topics.
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Date Issued
2016
Identifier
CFE0006436, ucf:51467
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0006436
Modeling Repair Patches of Ship Hull and Studying the Effect of Their Orientation on Stresses
Title
Modeling Repair Patches of Ship Hull and Studying the Effect of Their Orientation on Stresses.
Creator
Enwegy, Halima, Moslehy, Faissal, Kassab, Alain, Bai, Yuanli, University of Central Florida
Abstract / Description
The hull is the most important structural part of any maritime vessel. It must be adequately designed to withstand the harsh sailing environmental conditions and associated forces. In the past, the basic material used to manufacture the ship hull was wood, where the hull was usually shaped as cylindrical wooden shanks. In the present, hull designs have developed to steel columns or stiffened panels that are made of different types of materials. Panels that are stiffened orthogonally in two or...
Show moreThe hull is the most important structural part of any maritime vessel. It must be adequately designed to withstand the harsh sailing environmental conditions and associated forces. In the past, the basic material used to manufacture the ship hull was wood, where the hull was usually shaped as cylindrical wooden shanks. In the present, hull designs have developed to steel columns or stiffened panels that are made of different types of materials. Panels that are stiffened orthogonally in two or more directions and have nine independent material constants are defined as orthotropic panels, and they achieve high specific strength.This thesis presents the effect of different patch orientations on the resulting strain and stress concentrations at the area of interaction between the panel and the patch. As it is known, the behavior of stiffened plates is affected by several important parameters, e.g., length to width ratio of the panel, stiffener geometry and spacing, aspect ratio for plates between stiffeners, plate slenderness, von Mises stresses, initial distortions, boundary conditions, and type of loading. A finite element model of the ship hull has been developed and run on ABAQUS (commercially available finite element software). The stiffened panel and patch are modeled as equivalent orthotropic plates made of steel. The panel edges are considered to be simply supported, and uniaxial tension was applied to the equivalent stiffened panel in addition to the lateral pressure (from water interaction). The developed model successfully predicted the optimal orientation of the panel for maximum stress concentration reduction. Moreover, in order to minimize the severe conditions caused by the mismatch that occurs if the material properties of the patch and the panel are the same during the patching process, it is necessary to stiffened the patch more than the panel. The developed model also suggested that an isotropic layer be added at the interaction to decrease the severity of arising stresses.
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Date Issued
2014
Identifier
CFE0005162, ucf:50701
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0005162
Daytona Highlands
Title
Daytona Highlands: Florida's suburb of hills and lakes.
Creator
PALMM (Project)
Abstract / Description
Folded brochure advertising the suburb Daytona Highlands which was started in 1924 as a golf and country club style community. It features the Tarragona Tower entrance, part of which still stands today.
Date Issued
1924
Identifier
AAC3718QF00001/29/200704/19/200715327BnamI D0QF, FHP C CF 2007-01-29, FIPS12127, FCLA url 20070409xOCLC, 123286911, CF00001740, 2703411, ucf:21832
Format
E-book
PURL
http://purl.flvc.org/fcla/tc/fhp/CF00001740.jpg
THE INCOMPATIBILITY OF FREEDOM OF THE WILL AND ANTHROPOLOGICAL PHYSICALISM
Title
THE INCOMPATIBILITY OF FREEDOM OF THE WILL AND ANTHROPOLOGICAL PHYSICALISM.
Creator
Gonzalez, Ariel, Rodgers, Travis, University of Central Florida
Abstract / Description
Many contemporary naturalistic philosophers have taken it for granted that a robust theory of free will, one which would afford us with an agency substantial enough to render us morally responsible for our actions, is itself not conceptually compatible with the philosophical theory of naturalism. I attempt to account for why it is that free will (in its most substantial form) cannot be plausibly located within a naturalistic understanding of the world. I consider the issues surrounding an...
Show moreMany contemporary naturalistic philosophers have taken it for granted that a robust theory of free will, one which would afford us with an agency substantial enough to render us morally responsible for our actions, is itself not conceptually compatible with the philosophical theory of naturalism. I attempt to account for why it is that free will (in its most substantial form) cannot be plausibly located within a naturalistic understanding of the world. I consider the issues surrounding an acceptance of a robust theory of free will within a naturalistic framework. Timothy O'Connor's reconciliatory effort in maintaining both a scientifically naturalist understanding of the human person and a full-blooded theory of agent-causal libertarian free will is considered. I conclude that Timothy O'Connor's reconciliatory model cannot be maintained and I reference several conceptual difficulties surrounding the reconciliation of agent-causal libertarian properties with physical properties that haunt the naturalistic libertarian.
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Date Issued
2014
Identifier
CFH0004628, ucf:45292
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFH0004628