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- Title
- PROCESSING AND STUDY OF CARBON NANOTUBE / POLYMER NANOCOMPOSITES AND POLYMER ELECTROLYTE MATERIALS.
- Creator
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Harish, Muthuraman, Huo, Qun, University of Central Florida
- Abstract / Description
-
The first part of the study deals with the preparation of carbon nanotube/polymer nanocomposite materials. The dispersion of multi-walled carbon nanotubes (MWNTs) using trifluoroacetic acid (TFA) as a co-solvent and its subsequent use in polymer nanocomposite fabrication is reported. The use of carbon nanotube/ polymer nanocomposite system for the fabrication of organic solar cells is also studied. TFA is a strong but volatile acid which is miscible with many commonly used organic solvents....
Show moreThe first part of the study deals with the preparation of carbon nanotube/polymer nanocomposite materials. The dispersion of multi-walled carbon nanotubes (MWNTs) using trifluoroacetic acid (TFA) as a co-solvent and its subsequent use in polymer nanocomposite fabrication is reported. The use of carbon nanotube/ polymer nanocomposite system for the fabrication of organic solar cells is also studied. TFA is a strong but volatile acid which is miscible with many commonly used organic solvents. Our study demonstrates that MWNTs can be effectively purified and readily dispersed in a range of organic solvents including dimethyl formamide (DMF), tetrahydrofuran (THF), and dichloromethane when mixed with 10 vol% trifluoroacetic acid (TFA). X-ray photoelectron spectroscopic analysis revealed that the chemical structure of the TFA-treated MWNTs remained intact without oxidation. The dispersed carbon nanotubes in TFA/THF solution were mixed with poly(methyl methacrylate) (PMMA) to fabricate polymer nanocomposites. A good dispersion of nanotubes in solution and in polymer matrices was observed and confirmed by SEM and optical microscopy study. Low percolation thresholds of electrical conductivity were observed from the fabricated MWNT/PMMA composite films. A carbon nanotube/ polymer nanocomposites system was also used for the fabrication of organic solar cells. A blend of single-wall carbon nanotubes (SWNTs) and poly3-hexylthiophene (P3HT) was used as the active layer in the device. The device characteristics showed that the fabrication of the solar cells was successful without any shorts in the circuit. The second part of the study deals with the preparation and characterization of electrode and electrolyte materials for lithium ion batteries. A system of lithium trifluoroacetate/ PMMA was used for its study as the electrolyte in lithium battery. A variety of different processing conditions were used to prepare the polymer electrolyte system. The conductivity of the electrolyte plays a critical role in the high power output of a battery. A high power output requires fast transport of lithium ions for which the conductivity of the electrolyte must be at least 3 x 10^-4 S/cm. Electrochemical Impedance Spectroscopy (EIS) was used to determine the conductivity of the polymer electrolyte films. Among the different processing conditions used to prepare the polymer electrolyte material, wet films of PMMA/salt system prepared by using 10vol% of TFA in THF showed the best results. At about 70wt% loading of the salt in the polymer, the conductivity obtained was about 1.1 x 10^-2 S/cm. Recently, the use of vanadium oxide material as intercalation host for lithium has gained widespread attention. Sol-gel derived vanadium oxide films were prepared and its use as a cathode material for lithium ion battery was studied. The application of carbon nanotubes in lithium ion battery was explored. A carbon nanotube /block copolymer (P3HT-b-PS) composite was prepared and its potential as an anode material was evaluated.
Show less - Date Issued
- 2007
- Identifier
- CFE0001941, ucf:47436
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001941
- Title
- EVALUATION OF THE PHOTO-INDUCED STRUCTURAL MECHANISMS IN CHALCOGENIDE GLASS MATERIALS.
- Creator
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Lopez, Cedric, Richardson, Kathleen, University of Central Florida
- Abstract / Description
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Chalcogenide glasses and their use in a wide range of optical, electronic and memory applications, has created a need for a more thorough understanding of material property variation as a function of composition and in geometries representative of actual devices. This study evaluates compositional dependencies and photo-induced structural mechanisms in As-S-Se chalcogenide glasses. An effective fabrication method for the reproducible processing of bulk chalcogenide materials has been...
Show moreChalcogenide glasses and their use in a wide range of optical, electronic and memory applications, has created a need for a more thorough understanding of material property variation as a function of composition and in geometries representative of actual devices. This study evaluates compositional dependencies and photo-induced structural mechanisms in As-S-Se chalcogenide glasses. An effective fabrication method for the reproducible processing of bulk chalcogenide materials has been demonstrated and an array of tools developed, for the systematic characterization of the resulting material's physical and optical properties. The influence of compositional variation on the physical properties of 13 glasses within the As-S-Se system has been established. Key structural and optical differences have been observed and quantified between bulk glasses and their corresponding as-deposited films. The importance of annealing and aging of the film material and the impact on photosentivity and long term behavior important to subsequent device stability have been evaluated. Photo-induced structures have been created in the thin films using bandgap cw and sub-bandgap femtosecond laser sources and the exposure conditions and their influence on the post-exposure material properties, have been found to have different limitations and driving mechanisms. These mechanisms largely depend on both structural and/or electronic defects, whether initially present in the chalcogenide material or created upon exposure. These defect processes, largely studied previously in individual binary material systems, have now been shown to be consistently present, but varying in extent, across the ternary glass compositions and exposure conditions examined. We thus establish the varying photo-response of these defects as being the major reason for the optical variations observed. Nonlinear optical material properties, as related to the multiphoton processes used in our exposure studies, have been modeled and a tentative explanation for their variation in the context of composition and method of evaluation is presented.
Show less - Date Issued
- 2004
- Identifier
- CFE0000196, ucf:46177
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0000196
- Title
- APPEARANCE-DRIVEN MATERIAL DESIGN.
- Creator
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Colbert, Mark, Hughes, Charles, University of Central Florida
- Abstract / Description
-
In the computer graphics production environment, artists often must tweak specific lighting and material parameters to match a mind's eye vision of the appearance of a 3D scene. However, the interaction between a material and a lighting environment is often too complex to cognitively predict without visualization. Therefore, artists operate in a design cycle, where they tweak the parameters, wait for a visualization, and repeat, seeking to obtain a desired look. We propose the use of...
Show moreIn the computer graphics production environment, artists often must tweak specific lighting and material parameters to match a mind's eye vision of the appearance of a 3D scene. However, the interaction between a material and a lighting environment is often too complex to cognitively predict without visualization. Therefore, artists operate in a design cycle, where they tweak the parameters, wait for a visualization, and repeat, seeking to obtain a desired look. We propose the use of appearance-driven material design. Here, artists directly design the appearance of reflected light for a specific view, surface point, and time. In this thesis, we discuss several methods for appearance-driven design with homogeneous materials, spatially-varying materials, and appearance-matching materials, where each uses a unique modeling and optimization paradigm. Moreover, we present a novel treatment of the illumination integral using sampling theory that can utilize the computational power of the graphics processing unit (GPU) to provide real-time visualization of the appearance of various materials illuminated by complex environment lighting. As a system, the modeling, optimization and rendering steps all operate on arbitrary geometry and in detailed lighting environments, while still providing instant feedback to the designer. Thus, our approach allows materials to play an active role in the process of set design and story-telling, a capability that was, until now, difficult to achieve due to the unavailability of interactive tools appropriate for artists.
Show less - Date Issued
- 2008
- Identifier
- CFE0002217, ucf:47913
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0002217
- Title
- SCIENCE INQUIRY KITS AND TEACHER PREPAREDNESS TO TEACH SCIENCE AS INQUIRY IN ELEMENTARY CLASSROOMS.
- Creator
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Clayton, Angela, Jeanpierre, Bobby, University of Central Florida
- Abstract / Description
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The National Science Education Standards (1996) indicate that science education should include inquiry instruction. Many teachers still struggle with how to implement inquiry in their classrooms and a lack of high quality inquiry-based instructional materials has been posited as a hindrance. The purpose of this qualitative study was to observe the instructional practices of three elementary teachers when using an inquiry-based science kit program in their fourth grade classrooms. Teacher...
Show moreThe National Science Education Standards (1996) indicate that science education should include inquiry instruction. Many teachers still struggle with how to implement inquiry in their classrooms and a lack of high quality inquiry-based instructional materials has been posited as a hindrance. The purpose of this qualitative study was to observe the instructional practices of three elementary teachers when using an inquiry-based science kit program in their fourth grade classrooms. Teacher practices and their attitudes towards their preparedness to teach science with the support of the curricular program were examined. Data were collected through pre/post survey comparisons, observations, and a focus group session. Results indicated that these teachers' attitudes were positively impacted. Teachers' access to science kits provided resources which facilitated more inquiry experiences with their students; however, resources alone did not fully address teacher science content needs.
Show less - Date Issued
- 2009
- Identifier
- CFE0002568, ucf:52844
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0002568
- Title
- A Jew from Nebraska: An Actors Attempt at Stand-up Comedy.
- Creator
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Nathan, Jeffrey, Niess, Christopher, Brotherton, Mark, Helsinger, James, University of Central Florida
- Abstract / Description
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Stand-up comedy has been a major influence on American culture and has given the (")Everyman(") the ability to laugh at ourselves. Stand-up comedians have been performing in nightclubs, bars, clubs, and, most importantly, theatres for the past 60 years. Stand-up comedy can take many forms: a monologue of entertaining incidents that form a story, or a string of one-liners, or a succession of jokes. This performance project and thesis is an examination and an attempt at the art form that we...
Show moreStand-up comedy has been a major influence on American culture and has given the (")Everyman(") the ability to laugh at ourselves. Stand-up comedians have been performing in nightclubs, bars, clubs, and, most importantly, theatres for the past 60 years. Stand-up comedy can take many forms: a monologue of entertaining incidents that form a story, or a string of one-liners, or a succession of jokes. This performance project and thesis is an examination and an attempt at the art form that we call stand-up comedy. It will answer the question of what is the best approach to writing comedy for an actor finishing his graduate acting program. It will also challenge the idea of simple joke-telling versus storytelling and examine the following question: Can anyone be a standup comedian? A research of the history, an analysis of the practitioners, and training from graduate studio work will support the discovery of a practical approach to writing and performing a stand-up comedy routine.
Show less - Date Issued
- 2015
- Identifier
- CFE0006046, ucf:50978
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006046
- Title
- Interdiffusion Study of Mg-AA6061 System.
- Creator
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Fu, Mian, Sohn, Yongho, Coffey, Kevin, An, Linan, University of Central Florida
- Abstract / Description
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Magnesium (Mg) is a light-weight metal that has extraordinary physical and chemical properties for many potential applications in automobile, military, and electronics. Aluminum alloys, because of its light-weight, high strength and corrosion resistance have a wide range of commercial applications. Given these two, sometime competing, alloy systems, there are now many applications where the metallurgical compatibility of Mg- and Al-alloys are required for engineering applications. One such...
Show moreMagnesium (Mg) is a light-weight metal that has extraordinary physical and chemical properties for many potential applications in automobile, military, and electronics. Aluminum alloys, because of its light-weight, high strength and corrosion resistance have a wide range of commercial applications. Given these two, sometime competing, alloy systems, there are now many applications where the metallurgical compatibility of Mg- and Al-alloys are required for engineering applications. One such case is the development of diffusion barrier for U-Mo metallic fuel in Al-alloy cladding, where Mg, with its complete immiscibility with U and Mo is being considered as the diffusion barrier. While negligible diffusional interaction between Mg and U-Mo alloys have been reported, diffusional interaction between the Mg and Al-alloy cladding has not been investigated. In this study, solid-to-solid diffusion couples were assembled using discs of pure Mg (99.999 %) and AA6061 Al-alloy. After preparation, Mg was diffusion bonded to AA6061 in sealed quartz capsule at 300(&)deg;, 350(&)deg;, and 400(&)deg;C for 720, 360, and 240 hours, respectively. Scanning electron microscopy was used to inspect the interdiffusion zone, while phase identification was performed using X-ray energy dispersive spectroscopy. One specific phase that exists in the binary Mg-Al system, labeled (")epsilon(") was observed and characterized by transmission electron microscopy. From the preceding data, the growth rates as well as interdiffusion coefficients of the intermetallic phases were extracted and compared to previous investigations using pure Mg and Al.
Show less - Date Issued
- 2013
- Identifier
- CFE0005333, ucf:50521
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005333
- Title
- The Effects of Viewing Sexually Explicit Materials on Men's Body Image Satisfaction, Interest in Pursuing Cosmetic Surgery, and Body Change Behaviors.
- Creator
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Schuster, Elizabeth, Negy, Charles, Renk, Kimberly, Beidel, Deborah, University of Central Florida
- Abstract / Description
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This study examined the effects of viewing sexually explicit media on men's body image, body change behaviors, and esteem in a randomized experimental study. The purpose was to determine if a cause and effect relationship exists between viewing sexually explicit media and body image dissatisfaction in men. Participants were randomized to one of four conditions. They were asked to view a short media clip and then answer a series of questionnaires assessing their current body change strategies ...
Show moreThis study examined the effects of viewing sexually explicit media on men's body image, body change behaviors, and esteem in a randomized experimental study. The purpose was to determine if a cause and effect relationship exists between viewing sexually explicit media and body image dissatisfaction in men. Participants were randomized to one of four conditions. They were asked to view a short media clip and then answer a series of questionnaires assessing their current body change strategies (e.g., pathogenic weight control practices), interest in risky body behaviors (e.g., cosmetic surgery), esteem (i.e., genital, sexual, and self-esteem), and overall body image satisfaction. It was hypothesized that men exposed to the sexually explicit media condition would evidence more dissatisfaction with their bodies, utilize more body change strategies, and have more interest in risky body change behaviors. It was also hypothesized that men exposed to the sexually explicit condition would evidence poorer self-esteem, sexual esteem, and genital esteem relative to participants in the other conditions. The hypotheses were not supported. There were no significant differences among any of the conditions, including a more specific analysis between the control and sexually explicit conditions. As this differs from findings of similar studies with female participants, it is important for future studies to further examine this topic and to identify protective factors that may exist for men who view sexually explicit materials.
Show less - Date Issued
- 2014
- Identifier
- CFE0005413, ucf:50429
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005413
- Title
- ENVIRONMENTAL DEGRADATION OF OXIDATION RESISTANT AND THERMAL BARRIER COATINGS FOR FUEL-FLEXIBLE GAS TURBINE APPLICATIONS.
- Creator
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Mohan, Prabhakar, Sohn, Yongho, University of Central Florida
- Abstract / Description
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The development of thermal barrier coatings (TBCs) has been undoubtedly the most critical advancement in materials technology for modern gas turbine engines. TBCs are widely used in gas turbine engines for both power-generation and propulsion applications. Metallic oxidation-resistant coatings (ORCs) are also widely employed as a stand-alone protective coating or bond coat for TBCs in many high-temperature applications. Among the widely studied durability issues in these high-temperature...
Show moreThe development of thermal barrier coatings (TBCs) has been undoubtedly the most critical advancement in materials technology for modern gas turbine engines. TBCs are widely used in gas turbine engines for both power-generation and propulsion applications. Metallic oxidation-resistant coatings (ORCs) are also widely employed as a stand-alone protective coating or bond coat for TBCs in many high-temperature applications. Among the widely studied durability issues in these high-temperature protective coatings, one critical challenge that received greater attention in recent years is their resistance to high-temperature degradation due to corrosive deposits arising from fuel impurities and CMAS (calcium-magnesium-alumino-silicate) sand deposits from air ingestion. The presence of vanadium, sulfur, phosphorus, sodium and calcium impurities in alternative fuels warrants a clear understanding of high-temperature materials degradation for the development of fuel-flexible gas turbine engines. Degradation due to CMAS is a critical problem for gas turbine components operating in a dust-laden environment. In this study, high-temperature degradation due to aggressive deposits such as V2O5, P2O5, Na2SO4, NaVO3, CaSO4 and a laboratory-synthesized CMAS sand for free-standing air plasma sprayed (APS) yttria stabilized zirconia (YSZ), the topcoat of the TBC system, and APS CoNiCrAlY, the bond coat of the TBC system or a stand-alone ORC, is examined. Phase transformations and microstructural development were examined by using x-ray diffraction, scanning electron microscopy, and transmission electron microscopy. This study demonstrated that the V2O5 melt degrades the APS YSZ through the formation of ZrV2O7 and YVO4 at temperatures below 747ðC and above 747ðC, respectively. Formation of YVO4 leads to the depletion of the Y2O3 stabilizer and the deleterious transformation of the YSZ to the monoclinic ZrO2 phase. The investigation on the YSZ degradation by Na2SO4 and a Na2SO4 + V2O5 mixture (50-50 mol. %) demonstrated that Na2SO4 itself did not degrade the YSZ, however, in the presence of V2O5, Na2SO4 formed vanadates such as NaVO3 that degraded the YSZ through YVO4 formation at temperature as low as 700ðC. The APS YSZ was found to react with the P2O5 melt by forming ZrP2O7 at all temperatures. This interaction led to the depletion of ZrO2 in the YSZ (i.e., enrichment of Y2O3 in tÃÂ'-YSZ) and promoted the formation of the fluorite-cubic ZrO2 phase. Above 1250ðC, CMAS deposits were observed to readily infiltrate and significantly dissolve the YSZ coating via thermochemical interactions. Upon cooling, zirconia reprecipitated with a spherical morphology and a composition that depended on the local melt chemistry. The molten CMAS attack destabilized the YSZ through the detrimental phase transformation (tÃÂ' -> t -> f + m). Free standing APS CoNiCrAlY was also prone to degradation by corrosive molten deposits. The V2O5 melt degraded the APS CoNiCrAlY through various reactions involving acidic dissolution of the protective oxide scale, which yielded substitutional-solid solution vanadates such as (Co,Ni)3(VO4)2 and (Cr,Al)VO4. The molten P2O5, on the other hand, was found to consume the bond coat constituents significantly via reactions that formed both Ni/Co rich phosphates and Cr/Al rich phosphates. Sulfate deposits such as Na2SO4, when tested in encapsulation, damaged the CoNiCrAlY by Type I acidic fluxing hot corrosion mechanisms at 1000ðC that resulted in accelerated oxidation and sulfidation. The formation of a protective continuous Al2O3 oxide scale by preoxidation treatment significantly delayed the hot corrosion of CoNiCrAlY by sulfates. However, CoNiCrAlY in both as-sprayed and preoxidized condition suffered a significant damage by CaSO4 deposits via a basic fluxing mechanism that yielded CaCrO4 and CaAl2O4. The CMAS melt also dissolved the protective Al2O3 oxide scale developed on CoNiCrAlY by forming anorthite platelets and spinel oxides. Based on the detailed investigation on degradation of the APS YSZ and CoNiCrAlY by various corrosive deposits, an experimental attempt was carried out to mitigate the melt-induced deposit attack. Experimental results from this study demonstrate, for the first time, that an oxide overlay produced by electrophoretic deposition (EPD) can effectively perform as an environmental barrier overlay for APS TBCs. The EPD protective overlay has a uniform and easily-controllable thickness, uniformly distributed closed pores and tailored chemistry. The EPD Al2O3 and MgO overlays were successful in protecting the APS YSZ TBCs against CMAS attack and hot corrosion attack (e.g., sulfate and vanadate), respectively. Furnace thermal cyclic oxidation testing of overlay-modified TBCs on bond-coated superalloy also demonstrated the good adhesive durability of the EPD Al2O3 overlay.
Show less - Date Issued
- 2010
- Identifier
- CFE0003099, ucf:48315
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003099
- Title
- Advanced Nanoscale Characterization of Plants and Plant-derived Materials for Sustainable Agriculture and Renewable Energy.
- Creator
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Soliman, Mikhael, Tetard, Laurene, Vaidyanathan, Raj, Kang, Hyeran, Santra, Swadeshmukul, Zhai, Lei, Chumbimuni Torres, Karin, University of Central Florida
- Abstract / Description
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The need for nanoscale, non-invasive functional characterization has become more significant with advances in nano-biotechnology and related fields. Exploring the ultrastructure of plant cell walls and plant-derived materials is necessary to access a more profound understanding of the molecular interactions in the systems, in view of a rational design for sustainable applications. This, in turn, relates to the pressing requirements for food, energy and water sustainability experienced...
Show moreThe need for nanoscale, non-invasive functional characterization has become more significant with advances in nano-biotechnology and related fields. Exploring the ultrastructure of plant cell walls and plant-derived materials is necessary to access a more profound understanding of the molecular interactions in the systems, in view of a rational design for sustainable applications. This, in turn, relates to the pressing requirements for food, energy and water sustainability experienced worldwide.Here we will present our advanced characterization approach to study the effects of external stresses on plants, and resulting opportunities for biomass valorization with an impact on the food-energy-water nexus.First, the adaption of plants to the pressure imposed by gravity in poplar reaction wood will be discussed. We will show that a multiscale characterization approach is necessary to reach a better understanding of the chemical and physical properties of cell walls across a transverse section of poplar stem. Our Raman spectroscopy and statistical analysis reveals intricate variations in the cellulose and lignin properties. Further, we will present evidence that advanced atomic force microscopy can reveal nanoscale variations within the individual cell wall layers, not attainable with common analytical tools. Next, chemical stresses, in particular the effect of Zinc-based pesticides on citrus plants, will be considered. We will show how multiscale characterization can support the development of new disease management methods for systemic bacterial diseases, such as citrus greening, of great importance for sustainable agriculture. In particular, we will focus on the study of new formulations, their uptake and translocation in the plants following different application methods. Lastly, we will consider how plant reactions to mechanical and chemical stresses can be controlled to engineer biomass for valorization applications. We will present our characterization of two examples: the production of carbon films derived from woody lignocellulosic biomass and the development of nanoscale growth promoters for food crop. A perspective of the work and discussion of the broader impact will conclude the presentation.
Show less - Date Issued
- 2018
- Identifier
- CFE0007415, ucf:52717
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007415
- Title
- Quantum Chemical Studies for the Engineering of Metal Organic Materials.
- Creator
-
Rivera Jacquez, Hector, Masunov, Artem, Balaeff, Alexander, Harper, James, Heider, Emily, Zou, Shengli, Kaden, William, University of Central Florida
- Abstract / Description
-
Metal Organic Materials (MOM) are composed of transition metal ions as connectors and organic ligands as linkers. MOMs have been found to have high porosity, catalytic, and optical properties. Here we study the gas adsorption, color change, and non-linear optical properties of MOMs. These properties can be predicted using theoretical methods, and the results may provide experimentalists with guidance for rational design and engineering of novel MOMs. The theory levels used include semi...
Show moreMetal Organic Materials (MOM) are composed of transition metal ions as connectors and organic ligands as linkers. MOMs have been found to have high porosity, catalytic, and optical properties. Here we study the gas adsorption, color change, and non-linear optical properties of MOMs. These properties can be predicted using theoretical methods, and the results may provide experimentalists with guidance for rational design and engineering of novel MOMs. The theory levels used include semi-empirical quantum mechanical calculations with the PM7 Hamiltonian and, Density Functional Theory (DFT) to predict the geometry and electronic structure of the ground state, and Time Dependent DFT (TD-DFT) to predict the excited states and the optical properties.The molecular absorption capacity of aldoxime coordinated Zn(II) based MOMs (previously measured experimentally) is predicted by using PM7 Theory level. The 3D structures were optimized with and without host molecules inside the pores. The absorption capacity of these crystals was predicted to be 8H2 or 3N2 per unit cell. When going beyond this limit, the structural integrity of the bulk material becomes fractured and microcrystals are observed both experimentally and theoretically.The linear absorption properties of Co(II) based complexes are known to change color when the coordination number is altered. In order to understand the mechanism of this color change TD-DFT methods are employed. The chromic behavior of the Co(II) based complexes studied was confirmed to be due to a chain in coordination number that resulted in lower metal to ligand distances. These distances destabilize the occupied metal d orbitals, and as a consequence of this, the metal to ligand transition energy is lowered enough to allow the crystals to absorb light at longer wavelengths.Covalent organic frameworks (COFs) present an extension of MOM principles to the main group elements. The synthesis of ordered COFs is possible by using predesigned structures andcarefully selecting the building blocks and their conditions for assembly. The crystals formed by these systems often possess non-linear optical (NLO) properties. Second Harmonic Generation (SHG) is one of the most used optical processes. Currently, there is a great demand for materials with NLO optical properties to be used for optoelectronic, imaging, sensing, among other applications. DFT calculations can predict the second order hyperpolarizability ?2 and tensor components necessary to estimate NLO. These calculations for the ?2 were done with the use of the Berry's finite field approach. An efficient material with high ?2 was designed and the resulting material was predicted to be nearly fivefold higher than the urea standard.Two-photon absorption (2PA) is another NLO effect. Unlike SHG, it is not limited to acentric material and can be used development of in vivo bio-imaging agents for the brain. Pt(II) complexes with porphyrin derivatives are theoretically studied for that purpose. The mechanism of 2PA enhancement was identified. For the most efficient porphyrin, the large 2PA cross-section was found to be caused by a HOMO-LUMO+2 transition. This transition is strongly coupled to 1PA allowed Q-band HOMO-LUMO states by large transition dipoles. Alkyl carboxyl substituents delocalize the LUMO+2 orbital due to their strong ?-acceptor effect, enhancing transition dipoles and lowering the 2PA transition to the desirable wavelengths range.The mechanism 2PA cross-section enhancement of aminoxime and aldoxime ligands upon metal addition of is studied with TD-DFT methods. This mechanism of enhancement is found to be caused by the polarization of the ligand orbitals by the metal cation. After polarization an increase in ligand to ligand transition dipole moment. This enhancement of dipole moment is related to the increase in 2PA cross-sections.
Show less - Date Issued
- 2015
- Identifier
- CFE0005990, ucf:50777
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005990
- Title
- Light-Matter Interactions of Plasmonic Nanostructures.
- Creator
-
Reed, Jennifer, Zou, Shengli, Belfield, Kevin, Zhai, Lei, Hernandez, Eloy, Vanstryland, Eric, University of Central Florida
- Abstract / Description
-
Light interaction with matter has long been an area of interest throughout history, spanning many fields of study. In recent decades, the investigation of light-matter interactions with nanostructures has become an intense area of research in the field of photonics. Metallic nanostructures, in particular, are of interest due to the interesting properties that arise when interacting with light. The properties are a result of the excitation of surface plasmons which are the collective...
Show moreLight interaction with matter has long been an area of interest throughout history, spanning many fields of study. In recent decades, the investigation of light-matter interactions with nanostructures has become an intense area of research in the field of photonics. Metallic nanostructures, in particular, are of interest due to the interesting properties that arise when interacting with light. The properties are a result of the excitation of surface plasmons which are the collective oscillation of the conduction electrons in the metal. Since the conduction electrons can be thought of as harmonic oscillators, they are quantized in a similar fashion. Just as a photon is a quantum of oscillations of an electromagnetic field, the plasmon is a quantum of electron oscillations of a metal. There are three types of plasmons:1. Bulk plasmons, also called volume plasmons, are longitudinal density fluctuations which propagate through a bulk metal with an eigenfrequency of ?_p called the plasma frequency.2. Localized surface plasmons are non-propagating excitations of the conduction electrons of a metallic nanoparticle coupled to an electromagnetic field. 3. Surface plasmon polaritons are evanescent, dispersive propagating electromagnetic waves formed by a coupled state between a photon and the excitation of the surface plasmons. They propagate along the surface of a metal-dielectric interface with a broad spectrum of eigenfrequencies from ?=0 to ?= ?_p??2. Plasmonics is a subfield of photonics which focuses on the study of surface plasmons and the optical properties that result from light interacting with metal films and nanostructures on the deep subwavelength scale. In this thesis, plasmonic nanostructures are investigated for optical waveguides and other nanophotonic applications through computational simulations primarily base on electrodynamic theory. The theory was formulated by several key figures and established by James Clerk Maxwell after he published a set of relations which describe all classical electromagnetic phenomena, known as Maxwell's equations. Using methods based on Maxwell's equations, the optical properties of metallic nanostructures utilizing surface plasmons is explored. In Chapter 3, light propagation of bright and dark modes of a partially and fully illuminated silver nanorod is investigated for waveguide applications. Then, the origin of the Fano resonance line shape in the scattering spectra of a silver nanorod is investigated. Next, in Chapter 4, the reflection and transmission of a multilayer silver film is simulated to observe the effects of varying the dielectric media between the layers on light propagation. Building on the multilayer film work, metal-insulator-metal waveguides are explored by perforating holes in the bottom layer of a two layer a silver film to investigate the limits of subwavelength light trapping, confinement, and propagation. Lastly, in Chapter 5, the effect of surface plasmons on the propagation direction of electromagnetic wave around a spherical silver nanoparticle which shows an effective negative index of refraction is examined. In addition, light manipulation using a film of silver prisms with an effective negative index of refraction is also investigated. The silver prisms demonstrate polarization selective propagation for waveguide and optical filter applications. These studies provide insight into plasmonic mechanisms utilized to overcome the diffraction limit of light. Through better understanding of how to manipulating light with plasmonic nanostructures, further advancements in nanophotonic technologies for applications such as extremely subwavelength waveguides, sensitive optical detection, optical filters, polarizers, beam splitters, optical data storage devices, high speed data transmission, and integrated subwavelength photonic circuits can be achieved.
Show less - Date Issued
- 2013
- Identifier
- CFE0005049, ucf:49964
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005049
- Title
- A COMPARATIVE ANALYSIS OF GREEN ROOF DESIGNS INCLUDING DEPTH OF MEDIA, DRAINAGE LAYER MATERIALS, AND POLLUTION CONTROL MEDIA.
- Creator
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Kelly, Matt, Cooper, C. David, University of Central Florida
- Abstract / Description
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Population growth has lead to an increase in development and impervious areas in urban settings. Post-development conditions cause several problems for stormwater management such as limited space for stormwater storage systems and the conveyance of pollution picked up by runoff to near by water bodies. Green Roofs with cisterns have been shown to attenuate the peak flow of storm events and reduce the pollution load leaving a site and entering nearby water bodies. The purpose of this research...
Show morePopulation growth has lead to an increase in development and impervious areas in urban settings. Post-development conditions cause several problems for stormwater management such as limited space for stormwater storage systems and the conveyance of pollution picked up by runoff to near by water bodies. Green Roofs with cisterns have been shown to attenuate the peak flow of storm events and reduce the pollution load leaving a site and entering nearby water bodies. The purpose of this research is to expand the available research data on green roofs with cisterns by investigating the water quality and hydrology effects of different green roof designs including depth of media, an additional pollution control layer beneath the growth media, and different drainage layer materials. Furthermore, a comparison study is performed on the cistern water quality, direct filtrate water quality, and control roof filtrate water quality. Results show that phosphorus concentrations are lower when using a pollution control layer beneath the growing media, and that evapotransporation and filtrate factor values from the 4-inch media and the 8-inch media are approximately equal for one year. However, hydrograph results show that the 8-inch media design has a lower peak flow and longer attenuation when compared to the 4-inch media design for a single storm event. Furthermore, the drainage layer material has no significant effect on the water quality or hydrology of the green roof discharge. The data also emphasizes the importance and effectiveness of the incorporation of a cistern into a green roof system.
Show less - Date Issued
- 2008
- Identifier
- CFE0002107, ucf:47552
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0002107
- Title
- TWO-PHOTON 3D OPTICAL DATA STORAGE VIA FLUORESCENCE MODULATION OF FLUORENE DYES BY PHOTOCHROMIC DIARYLETHENES.
- Creator
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Corredor, Claudia, Belfield, Kevin D., University of Central Florida
- Abstract / Description
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Three-dimensional (3D) optical data storage based on two-photon processes provides highly confined excitation in a recording medium and a mechanism for writing and reading data with less cross talk between multiple memory layers, due to the quadratic dependence of two photon absorption (2PA) on the incident light intensity. The capacity for highly confined excitation and intrinsic 3D resolution affords immense information storage capacity (up to 1012 bits/cm3). Recently, the use of...
Show moreThree-dimensional (3D) optical data storage based on two-photon processes provides highly confined excitation in a recording medium and a mechanism for writing and reading data with less cross talk between multiple memory layers, due to the quadratic dependence of two photon absorption (2PA) on the incident light intensity. The capacity for highly confined excitation and intrinsic 3D resolution affords immense information storage capacity (up to 1012 bits/cm3). Recently, the use of photochromic materials for 3D memory has received intense interest because of several major advantages over current optical systems, including their erasable/rewritable capability, high resolution, and high sensitivity. This work demonstrates a novel two-photon 3D optical storage system based on the modulation of the fluorescence emission of a highly efficient two-photon absorbing fluorescent dye (fluorene derivative) and a photochromic compound (diarylethene). The feasibility of using efficient intermolecular Förster Resonance Energy Transfer (RET) from the non-covalently linked two-photon absorbing fluorescent fluorene derivative to the photochromic diarylethene as a novel read-out method in a two-photon optical data storage system was explored. For the purpose of the development of this novel two-photon 3D optical storage system, linear and two-photon spectroscopic characterization of commercial diarylethenes in solution and in a polymer film and evidence of their cyclization (O→C) and cycloreversion (C→O) reactions induced by two-photon excitation were undertaken. For the development of a readout method, Resonance Energy Transfer (RET) from twophoton absorbing fluorene derivatives to photochromic compounds was investigated under one and two-photon excitation. The Förster's distances and critical acceptor concentrations were determined for non-bound donor-acceptor pairs in homogeneous molecular ensembles. To the best of my knowledge, modulation of the two-photon fluorescence emission of a dye by a photochromic diarylethene has not been reported as a mechanism to read the recorded information in a 3D optical data storage system. This system was demonstrated to be highly stable and suitable for recording data in thick storage media. The proposed RET-based readout method proved to be non-destructive (exhibiting a loss of the initial fluorescence emission less than 20% of the initial emission after 10,000 readout cycles). Potential application of this system in a rewritable-erasable optical data storage system was proved. As part of the strategy for the development of diarylethenes optimized for 3D optical data storage, derivatives containing π-conjugated fluorene molecules were synthesized and characterized. The final part of this reasearch demonstrated the photostability of fluorine derivatives showing strong molecular polarizability and high fluorescence quantum yields. These compounds are quite promising for application in RET-based two-photon 3D optical data storage. Hence, the photostability of these fluorene derivatives is a key parameter to establish, and facilitates their full utility in critical applications.
Show less - Date Issued
- 2007
- Identifier
- CFE0001662, ucf:47210
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001662
- Title
- FACTORS THAT INFLUENCE TRANSFER OF HAZARDOUS MATERIAL TRAINING: THE PERCEPTION OF SELECTED FIRE-FIGHTER TRAINEES AND SUPERVISORS.
- Creator
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Bhati, Divya, Gary Orwig, Stephen A. Sivo,, University of Central Florida
- Abstract / Description
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This study examined the influence of factors on transfer of training and was based on the work of Broad and Newstrom (1992). For the purpose of this study the Broad and Newstrom (1992) transfer of training barriers are rephrased into positive statements. The nine transfer of training factors are: (1) reinforcement on the job; (2) little interference from immediate (work) environment; (3) supportive organizational culture; (4) trainees' perception of training programs being practical; (5)...
Show moreThis study examined the influence of factors on transfer of training and was based on the work of Broad and Newstrom (1992). For the purpose of this study the Broad and Newstrom (1992) transfer of training barriers are rephrased into positive statements. The nine transfer of training factors are: (1) reinforcement on the job; (2) little interference from immediate (work) environment; (3) supportive organizational culture; (4) trainees' perception of training programs being practical; (5) trainees' perception of relevant training content; (6) trainees' being comfortable with change and associated effort; (7) trainer being supportive and inspiring; (8) trainees' perception of training being well designed/delivered, and (9) peer support. This study explored the degree to which these factors influenced transfer of training in terms of on-the-job application. The study found supportive organizational culture to be the strongest predictor of transfer of training to on-the-job application. In addition, the degree of influence of Broad and Newstrom's (1992) nine factors varied with the thirteen locations. The study also found perception gaps between fire fighter trainees and their supervisor on factors influencing transfer of training. They differed on four factors: Supportive organizational culture, Perception of training programs being practical, Trainer being supportive and inspiring, and Perception of training being well designed/delivered.
Show less - Date Issued
- 2007
- Identifier
- CFE0001850, ucf:47353
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001850
- Title
- REVERSION OF POLY-PHOSPHATES TO ORTHO-PHOSPHATES IN WATER DISTRIBUTION SYSTEMS.
- Creator
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shekhar, avinash, taylor, james, University of Central Florida
- Abstract / Description
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Orthophosphates and polyphosphates are rarely present at significant levels in raw water source but are purposefully added to the water in various forms to inhibit corrosion, iron oxidation (red water), or calcium carbonate precipitation (scale formation). Orthophosphates serve as building blocks for polyphosphates, which includes structures in linear chain, branched chains (metaphosphate) and "glassy" polyphosphate polymers. The advantage of polyphosphates over ortho phosphates lies in the...
Show moreOrthophosphates and polyphosphates are rarely present at significant levels in raw water source but are purposefully added to the water in various forms to inhibit corrosion, iron oxidation (red water), or calcium carbonate precipitation (scale formation). Orthophosphates serve as building blocks for polyphosphates, which includes structures in linear chain, branched chains (metaphosphate) and "glassy" polyphosphate polymers. The advantage of polyphosphates over ortho phosphates lies in the fact that they slowly revert to orthophosphates and thus provide corrosion inhibition action over longer period of time in distribution systems. A study was completed for Tampa Bay Water on water distribution systems in a changing water quality environment. Blended orthophosphates was used as one of the corrosion inhibitors to study its effects on metal release and thus justify its application in comparison to other corrosion inhibitors like orthophosphates, zinc orthophosphates and silicates. This work focuses on the study of reversion of polyphosphates to ortho phosphates. A first-order model was developed that quantifies reversion as a function of the hydraulic residence time and initial poly phosphate concentration. The same model was used in two different forms one for the hybrid lines and the other for single material lines. The results from single material lines (estimated by a non linear least square regression using ANOVA) showed that the reversion rate was highest for galvanized pipe followed by unlined cast iron, lined cast iron and the lowest rate in PVC. The first-order reversion rate constant in PVC was almost two log orders less than galvanized line. A high first-order rate constant for the galvanized pipe could be attributed to a rougher surface, large surface area, reaction with the wall surface, pipe material or a combination of these effects. The results from the hybrid PDSs (estimated by an algebraic manipulation of the first-order reaction) substantially agree with the results obtained from the single material lines, with the exception of the PVC material. The data from the hybrid lines confirms that the reversion rate constant is greatest for exposure to galvanized pipe materials, but the hybrid data indicate that the rate constant associated with PVC is somewhat larger than the constants determined for either LCI or UCI. Once an overall first-order rate expression was established, efforts were made to find a relation between polyphosphate reversions with bulk water quality. None of the major water quality parameters were found to significantly affect the reversion. This observation may be attributable to a similar water quality over the study duration. A positive correlation was found between first-order reversion rate constant and temperature. An empirical equation (modified Arrhenius equation) that relates the first-order reversion rate constant with temperature was developed that showed a strong sensitivity to temperature. The results from this study could be used to predict the stability of polyphosphates in distribution systems with varying pipe materials and temperature.
Show less - Date Issued
- 2007
- Identifier
- CFE0001832, ucf:47350
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001832
- Title
- ALTERNATIVE FOAM TREATMENTS FOR THE SPACE SHUTTLE'S EXTERNAL TANK.
- Creator
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Dreggors, Kirsten, Nayfeh, Jamal, University of Central Florida
- Abstract / Description
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The Space Shuttle Columbia accident and the recent excitement surrounding Discovery's return to space brought excessive media attention to the foam products used on the External Tank (ET). In both cases, videos showed chunks of foam or ablative material falling away from the ET during lift off. This led to several years of investigation and research into the exact cause of the accident and potential solutions to avoid the problem in the future. Several design changes were made prior to the...
Show moreThe Space Shuttle Columbia accident and the recent excitement surrounding Discovery's return to space brought excessive media attention to the foam products used on the External Tank (ET). In both cases, videos showed chunks of foam or ablative material falling away from the ET during lift off. This led to several years of investigation and research into the exact cause of the accident and potential solutions to avoid the problem in the future. Several design changes were made prior to the return to flight this year, but the ET still shed foam during lift off. Since the Columbia accident, the loss of foam on ETs has been a significant area of interest for NASA, United Space Alliance, and Lockheed Martin. The Columbia Accident Investigation Board did not evaluate alternative materials but certainly highlighted the need for change. The majority of the research previously concentrated on improving the design and/or the application process of the current materials. Within recent years, some research and testing has been done to determine if a glass microsphere composite foam would be an acceptable alternative, but this work was overcome by the need for immediate change to return the shuttle to flight in time to deliver supplies to the International Space Station. Through a better understanding of the foam products currently used on the ET, other products can be evaluated for future space shuttle flights and potential applications on new space vehicles. The material properties and the required functionality of alternative materials can be compared to the current materials to determine if suitable replacement products exist. This research also lends itself to the development of future space flight and unmanned launch vehicles. In this paper, the feasibility of alternative material for the space shuttle's external tank will be investigated. Research on what products are used on the ET and a set of functional requirements driving the selection of those materials will be presented. The material properties of the current ET foam products will be collected and an evaluation of how those materials' properties meet the functional requirements will be accomplished. Then significant research on polymeric foams and ablative materials will be completed to learn how these various products can be applied in this industry. With this research and analysis, the knowledge gained will be used to select and evaluate the effectiveness of an alternate product and to determine feasibility of a product change with the current ET and the importance of maintaining the shuttle launch schedule. This research will also be used to evaluate the potential application of the alternative product on future platforms. There are several possible outcomes to this research. This research could result in a recommended change to the ET foam material or a perfectly acceptable alternative material that could result in a cost or schedule impact if implemented. It is also possible that there exists no suitable alternative material given the existing functional requirements. In any case, the alternative material could have future applications on new space vehicles. A set of results from the research and analysis will be provided along with a recommendation on a future material for use on space vehicles.
Show less - Date Issued
- 2005
- Identifier
- CFE0000787, ucf:46566
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0000787
- Title
- FINITE ELEMENT ANALYSIS OF LEFT-HANDED WAVEGUIDES.
- Creator
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Vellakkinar Balasubramaniam, Satish, Wu, Thomas X, University of Central Florida
- Abstract / Description
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In this work, waveguides with simultaneous negative dielectric permittivity and magnetic permeability, otherwise known as left-handed waveguides, are investigated. An approach of formulating and solving an eigenvalue problem with finite element method resulting in the dispersion relation of the waveguides is adopted in the analysis. Detailed methodology of one-dimensional scalar and two-dimensional vector finite element formulation for the analysis of grounded slab and arbitrary shaped...
Show moreIn this work, waveguides with simultaneous negative dielectric permittivity and magnetic permeability, otherwise known as left-handed waveguides, are investigated. An approach of formulating and solving an eigenvalue problem with finite element method resulting in the dispersion relation of the waveguides is adopted in the analysis. Detailed methodology of one-dimensional scalar and two-dimensional vector finite element formulation for the analysis of grounded slab and arbitrary shaped waveguides is presented. Based on the analysis, for waveguides with conventional media, excellent agreement of results is observed between the finite element approach and the traditional approach. The method is then applied to analyze left-handed waveguides and anomalous dispersion of modes is found. The discontinuity structure of a left-handed waveguide sandwiched between two conventional dielectric slab waveguides is analyzed using mode matching technique and the results are discussed based on the inherent nature of the materials. The scattering characteristics of a parallel plate waveguide partially filled with left-handed and conventional media are also analyzed using finite element method with eigenfunction expansion technique.
Show less - Date Issued
- 2004
- Identifier
- CFE0000296, ucf:46208
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0000296
- Title
- FEMTOSECOND LASER WRITTEN VOLUMETRIC DIFFRACTIVE OPTICAL ELEMENTS AND THEIR APPLICATIONS.
- Creator
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Choi, Jiyeon, Richardson, Martin, University of Central Florida
- Abstract / Description
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Since the first demonstration of femtosecond laser written waveguides in 1996, femtosecond laser direct writing (FLDW) has been providing a versatile means to fabricate embedded 3-D microstructures in transparent materials. The key mechanisms are nonlinear absorption processes that occur when a laser beam is tightly focused into a material and the intensity of the focused beam reaches the range creating enough free electrons to induce structural modification. One of the most useful features...
Show moreSince the first demonstration of femtosecond laser written waveguides in 1996, femtosecond laser direct writing (FLDW) has been providing a versatile means to fabricate embedded 3-D microstructures in transparent materials. The key mechanisms are nonlinear absorption processes that occur when a laser beam is tightly focused into a material and the intensity of the focused beam reaches the range creating enough free electrons to induce structural modification. One of the most useful features that can be exploited in fabricating photonic structures is the refractive index change which results from the localized energy deposition. The laser processing system for FLDW can be realized as a compact, desktop station, implemented by a laser source, a 3-D stage and focusing optics. Thus, FLDW can be readily adopted for the fabrication of the photonic devices. For instance, it has been widely employed in various areas of photonic device fabrication such as active and passive waveguides, couplers, gratings, opto-fluidics and similar applications. This dissertation describes the use of FLDW towards the fabrication of custom designed diffractive optical elements (DOE's). These are important micro-optical elements that are building blocks in integrated optical devices including on-chip sensors and systems. The fabrication and characterization of laser direct written DOEs in different glass materials is investigated. The design and performance of a range of DOE's is described, especially, laser-written embedded Fresnel zone plates and linear gratings. Their diffractive efficiency as a function of the fabrication parameters is discussed and an optimized fabrication process is realized. The potential of the micro-DOEs and their integration shown in this dissertation will impact on the fabrication of future on-chip devices involving customized DOEs that will serve great flexibility and multi-functional capability on sensing, imaging and beam shaping.
Show less - Date Issued
- 2009
- Identifier
- CFE0002958, ucf:47984
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0002958
- Title
- DESIGN AND EXPERIMENTAL STUDY OF AN INTEGRATED VAPOR CHAMBER THERMAL ENERGY STORAGE SYSTEM.
- Creator
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Kota, Krishna, CHOW, LOUIS, University of Central Florida
- Abstract / Description
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Future defense, aerospace and automotive technologies involve electronic systems that release high pulsed waste heat like during high power microwave and laser diode applications in tactical and combat aircraft, and electrical and electronic systems in hybrid electric vehicles, which will require the development of an efficient thermal management system. A key design issue is the need for fast charging so as not to overheat the key components. The goal of this work is to study the fabrication...
Show moreFuture defense, aerospace and automotive technologies involve electronic systems that release high pulsed waste heat like during high power microwave and laser diode applications in tactical and combat aircraft, and electrical and electronic systems in hybrid electric vehicles, which will require the development of an efficient thermal management system. A key design issue is the need for fast charging so as not to overheat the key components. The goal of this work is to study the fabrication and technology implementation feasibility of a novel high energy storage, high heat flux passive heat sink. Key focus is to verify by theory and experiments, the practicability of using phase change materials as a temporary storage of waste heat for heat sink applications. The reason for storing the high heat fluxes temporarily is to be able to reject the heat at the average level when the heat source is off. Accordingly, a concept of a dual latent heat sink intended for moderate to low thermal duty cycle electronic heat sink applications is presented. This heat sink design combines the features of a vapor chamber with rapid thermal energy storage employing graphite foam inside the heat storage facility along with phase change materials and is attractive owing to its passive operation unlike some of the current thermal management techniques for cooling of electronics employing forced air circulation or external heat exchangers. In addition to the concept, end-application dependent criteria to select an optimized design for this dual latent heat sink are presented. A thermal resistance concept based design tool/model has been developed to analyze and optimize the design for experiments. The model showed that it is possible to have a dual latent heat sink design capable of handling 7 MJ of thermal load at a heat flux of 500 W/cm2 (over an area of 100 cm2) with a volume of 0.072 m3 and weighing about 57.5 kg. It was also found that with such high heat flux absorption capability, the proposed conceptual design could have a vapor-to-condenser temperature difference of less than 10 0C with a volume storage density of 97 MJ/m3 and a mass storage density of 0.122 MJ/kg. The effectiveness of this heat sink depends on the rapidness of the heat storage facility in the design during the pulse heat generation period of the duty cycle. Heat storage in this heat sink involves transient simultaneous laminar film condensation of vapor and melting of an encapsulated phase change material in graphite foam. Therefore, this conjugate heat transfer problem including the wall inertia effect is numerically analyzed and the effectiveness of the heat storage mechanism of the heat sink is verified. An effective heat capacity formulation is employed for modeling the phase change problem and is solved using finite element method. The results of the developed model showed that the concept is effective in preventing undue temperature rise of the heat source. Experiments are performed to investigate the fabrication and implementation feasibility and heat transfer performance for validating the objectives of the design i.e., to show that the VCTES heat sink is practicable and using PCM helps in arresting the vapor temperature rise in the heat sink. For this purpose, a prototype version of the VCTES heat sink is fabricated and tested for thermal performance. The volume foot-print of the vapor chamber is about 6"X5"X2.5". A custom fabricated thermal energy storage setup is incorporated inside this vapor chamber. A heat flux of 40 W/cm2 is applied at the source as a pulse and convection cooling is used on the condenser surface. Experiments are done with and without using PCM in the thermal energy storage setup. It is found that using PCM as a second latent system in the setup helps in lowering the undue temperature rise of the heat sink system. It is also found that the thermal resistance between the vapor chamber and the thermal energy storage setup, the pool boiling resistance at the heat source in the vapor chamber, the condenser resistance during heat discharging were key parameters that affect the thermal performance. Some suggestions for future improvements in the design to ease its implementation and enhance the heat transfer of this novel heat sink are also presented.
Show less - Date Issued
- 2008
- Identifier
- CFE0002332, ucf:47802
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0002332
- Title
- A Framework for Miniaturized Mechanical Characterization of Tensile, Creep, and Fatigue Properties of SLM Alloys.
- Creator
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Torres-Caceres, Jonathan, Orlovskaya, Nina, Xu, Yunjun, Das, Tuhin, University of Central Florida
- Abstract / Description
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With the heightened design complexity that may be achieved through additive manufacturing (AM) comes an equally complex set of distinct material characteristics. To properly characterize new materials for use in selective laser melting (SLM), extensive analysis is necessary. Traditional testing techniques, however, can be prohibitive in time and cost incurred. The small punch test (SPT) has been developed for such purposes, where material is scarce or costly. Although lacking standardization,...
Show moreWith the heightened design complexity that may be achieved through additive manufacturing (AM) comes an equally complex set of distinct material characteristics. To properly characterize new materials for use in selective laser melting (SLM), extensive analysis is necessary. Traditional testing techniques, however, can be prohibitive in time and cost incurred. The small punch test (SPT) has been developed for such purposes, where material is scarce or costly. Although lacking standardization, SPT has been successfully employed with various materials to assess material properties such as the yield and ultimate strength and verified by traditional testing results. With the accompaniment of numerical simulations for use in the inverse method and determining correlation factors, several methods exist for equating SPT results with traditional results. There are, however, areas of weakness with SPT which require development, and the solution of the inverse method can be demanding of time and resources. Additionally, the combination of SPT and SLM is relatively unexplored in literature, though studies have shown that SPT is sensitive to the types of structures and unique material characteristics present in SLM components. The present research therefore focuses on developing a framework for characterizing SLM materials via the small punch test. Several types of SLM materials in various orientations and processing states are small punch tested to evaluate the ability of the SPT to track the effects of these as they cause the materials to evolve. A novel cyclic test method is proposed to fill the gap in SPT fatigue testing. Results from these tests are evaluated via numerical modelling using the inverse method solved with the least squares method. Samples were also inspected using digital microscopy to connect fracture morphology to processing parameter variations. A framework is thus presented with which SPT may be utilized to more economically and expeditiously characterize SLM materials.
Show less - Date Issued
- 2018
- Identifier
- CFE0007109, ucf:51952
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007109