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Title: The Diffusion and Performance of the Accountable Care Organization Model.
Creator: Lin, Yi-ling, Wan, Thomas, Malvey, Donna, Liu, Albert Xinliang, Steen, Julie, University of Central Florida
Abstract / Description: Background: Unity in pursuit of the Triple Aim: better health, better care, and lower per capita cost, can be achieved through a well-designed health care delivery system. The accountable care organizations (ACOs) model is considered a key component of health care delivery system improvement because the model fosters better coordination of care through clinical integration and financial accountability. Within the six Centers for Medicaid (&) Medicare Services (CMS) ACO programs, the Medicare...
Show moreBackground: Unity in pursuit of the Triple Aim: better health, better care, and lower per capita cost, can be achieved through a well-designed health care delivery system. The accountable care organizations (ACOs) model is considered a key component of health care delivery system improvement because the model fosters better coordination of care through clinical integration and financial accountability. Within the six Centers for Medicaid (&) Medicare Services (CMS) ACO programs, the Medicare Shared Savings Program (MSSP) ACO has the largest size with a total of 432 ACOs formed; the service subjects of the MSSP ACO are the fee-for-service beneficiaries. Recently, academicians and researchers have been attracted to exploring ACOs' formation and performance. However, most of the early ACO research types are either descriptive or case study. Also, early researchers had limited access to ACO data sets, so they could utilize only regional and demographic factors to identify the predictors of ACO formation.Purpose: An integrative theoretical framework, Rogers' diffusion of innovation theory and Duncan's POET model, was used to examine ACO formation and performance. The first purpose of this study was to determine the relative influences of contextual variables and ACO characteristic variables on how early an ACO model was adopted. The second purpose was to examine how executives' perceptions of ACO performance and the ACO first-year performance are influenced by the contextual variables, ACO characteristic variables, and timing of the adoption of an ACO model. Methods: A cross-sectional design was formulated to gather data from a survey supplemented by secondary data with the analysis unit at the organization level. Study participants in the ACO survey included 2012, 2013, 2014, and 2015 ACO cohorts. Logistic regression was performed to examine the effects of POET and Rogers' five core characteristics in the early adoption of an ACO model (dichotomous). Additionally, multiple linear regression analysis was used to examine the effects of POET and the timing of adoption of an ACO model in the perceptions of ACO performance. ACO first-year performance dataset consisted only of ACO cohorts from 2012 through 2014. Finally, confirmatory factor analysis and structural equation modeling were conducted to examine the measurement model of the ACO first-year performance and a full latent variable model, respectively. Major Findings: A survey of ACO executives/managers between October 2015 and February 2016 was conducted. The 447 MSSP ACOs in my mailing list yielded a response rate of 13.65 % (n=61). Of the 61 MSSP ACOs, 42 (52.5%) were late adopters whose contractual agreement with CMS started in 2014 or 2015, and 36 (59.0%) were with hospital-based composition. Among ACOs that participated in my survey, their current degree of IT adoption in functionalities (62.27 vs. 52.50 points), usage levels (65.19 vs. 49.49 points), and integration levels (62.24 vs. 53.37 points) were better than their initial years. The multiple logistic regression presented that MSSP ACOs were more likely to be early adopters of a CMS if their service areas had high unemployment rates (OR=2.23; 95% CI: 1.13 - 4.39). In the multiple linear regression analysis, the executives in the early ACOs perceived their organizations as more effective than the late adopters, with 12.65 points higher in an aggregate of eight ACO quality domains (p = .005). Three hundred and seventeen MSSP ACOs, with contractual agreements with CMS before 2015, had retained their year-one performance records (the actual ACO performance with eight quality domains). The variability in the actual ACO performance was explained by the predictor variables of the study with an R-square of 15%. The actual ACO performance was likely to be improved if ACOs had more Medicare assigned beneficiaries or had the hospital-based composition. On the other hand, if ACOs' service areas were located in areas of high poverty concentration, a high unemployment rate, or a lower competitive index, their ACO performance was relatively lower than their counterparts. Implications: The findings suggest that managers should consider strategies to increase economies of scale in size and to have hospital involvement in their ACOs in order to increase effective management. Inadequate capital for information technology improvements is the biggest barrier inhibiting healthcare providers' willingness to join an ACO. Regardless of rural or urban areas, financial support is still important for those potential ACO participants who are planning to invest in necessary infrastructure. ACOs that involved hospitals also showed better performance than those ACOs without hospital involvement. This information may help health policy makers to define core principles of the best ACO model in the future. Conclusions: This study makes a unique contribution using a theoretically integrative framework with Rogers' diffusion of innovation theory coupled with Duncan's POET model to examine ACO formation and ACO performance. In the early ACO adopters, three-fifths of the ACOs had hospital involvement; and the levels of their current IT degree in functionalities, usage levels, and integration levels are higher than the late ACO adopters. This study demonstrates that contextual variables, such as unemployment rates at ACO service areas, relatively influence how early an ACO model was adopted. Executives in the early ACOs had higher perceptions of overall organizational effectiveness as compared with the late adopters. The first-year performance of 2012, 2013, and 2014 ACO cohorts is positively influenced by the size of assigned Medicare beneficiaries and hospital-based ACO and is negatively influenced by the poverty rate, unemployment rate, and market competition scores (Herfindah-Hirschman Index).
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Date Issued: 2016
Identifier: CFE0006347, ucf:51576
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006347

Title: Interdiffusion, Crystallography and Mechanical Properties of Nickel Manganese Gallium Alloys.
Creator: Zhou, Le, Sohn, Yongho, Heinrich, Helge, Coffey, Kevin, An, Linan, Orlovskaya, Nina, University of Central Florida
Abstract / Description: NiMnGa Heusler alloys, functioning as either ferromagnetic shape memory alloys or mangetocaloric materials, have both practical applications and fundamental research value. The functional properties of NiMnGa alloys are closely related to the martensitic transformation from high temperature austenitic phase to low temperature martensitic phase. Alloys can be used for room temperature or high temperature applications, depending on the martensitic transformation temperature, which is...
Show moreNiMnGa Heusler alloys, functioning as either ferromagnetic shape memory alloys or mangetocaloric materials, have both practical applications and fundamental research value. The functional properties of NiMnGa alloys are closely related to the martensitic transformation from high temperature austenitic phase to low temperature martensitic phase. Alloys can be used for room temperature or high temperature applications, depending on the martensitic transformation temperature, which is compositional sensitive. The microstructure and crystallography of the martensites can be very complex but are crucial to the optimization of the material performance. In this study, for the first time, a combinatorial study by combining solid-to-solid diffusion couples and various characterization techniques was carried out to fundamentally investigate the NiMnGa ternary alloys. Phase equilibria, interdiffusion behavior, microstructural and crystallographic development, and mechanical properties in NiMnGa alloys were systematically examined. Selected diffusion couples between pure Ni, Ni25Mn75 and four ternary off-stoichiometric NiMnGa alloys (i.e., Ni52Mn18Ga30, Ni46Mn30Ga24, Ni52Mn30Ga18, Ni58Mn18Ga24 in atomic percent) were assembled and annealed at 800, 850 and 900 (&)deg;C for 480, 240 and 120 hours, respectively. The microstructure and concentration profiles of the interdiffusion zone were examined by scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS). Concentration profiles across the interdiffusion zone were further quantified by electron probe micro analysis (EPMA). Detailed microstructure and crystallography of the austenite and martensite were investigated using transmission electron microscopy (TEM). TEM thin foils were prepared by using focused ion beam (FIB) in situ lift out (INLO) technique, which is able to select desired composition from diffusion couples. The mechanical properties, namely reduced elastic modulus and hardness, as a function of composition were assessed via nanoindentation. Solubility values obtained for various phases were mostly consistent with the existing isothermal phase diagrams, but the phase boundary of the ?(Mn) + ? two-phase region was slightly modified. In addition, equilibrium compositions for the ?(Ni) and ?' phases at 900 (&)deg;C were also determined for the respective two-phase regions. Both austenitic and martensitic phases were found at room temperature in each diffusion couple with a clear interphase boundary. The compositions at the interfaces corresponded close to valence electron concentration (e/a) of 7.6, but decreased to lower values when Mn concentration increased to more than 35 at. %. Average effective interdiffusion coefficients for the ? phase over various compositional ranges were determined and reported in the light of temperature-dependence. Ternary interdiffusion coefficients were also determined and examined to assess the ternary diffusional interactions among Ni, Mn and Ga. Ni was observed to interdiffuse the fastest, followed by Mn then Ga. Interdiffusion flux of Ni also has strong influences on the interdiffusion of Mn and Ga with large and negative cross interdiffusion coefficients. The main ternary interdiffusion coefficients exhibited minimum values near 52 at. % Ni concentration. Extensive TEM analyses have been performed for the study of microstructure and crystallography of austenite and martensite from all diffusion couples. Crystallographic variations in martensitic phase, including non-modulated (NM) martensite, modulated (5M or 7M) martensite, were found in the diffusion couples. The 5M and 7M martensites were only found near the interface between austenite and martensite, corresponding to compositions with lower e/a ratio. The NM martensites were found mostly away from the interface region, with high e/a ratios. The tetragonality ratio (c/a) for NM martensite generally increases with e/a ratio, but also depended on the composition. All martensitic microstructure consists of twinned variants with different orientations that were documented using electron diffraction. The twinning relationship along with the c/a ratio was correlated to martensitic transformation temperature. In addition, pre-martensitic state has been clearly observed in the cubic austenitic phase region, with distinctive tweed microstructure originating from the local lattice distortions. Mechanical properties including reduced elastic modulus (Er) and hardness (H) as a function of composition were measured and analyzed by nanoindentation. A decrease of Er and H was observed with Mn or Ni substituting Ga, and Ni substituting Mn for the austenitic phase. However, an opposite trend was found for the martensitic phase. The softening of the elastic constants near the vicinity of martensitic transformation contributed to the sharp decrease in Er and H near the interface region. The measured Er and H had larger scatter for the martensitic phase than those for the austenitic phase. The scatters observed were attributed to the martensitic variants with different orientations. Contribution from the variation in grain orientation or shape memory effect was determined to be small in this investigation.
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Date Issued: 2016
Identifier: CFE0006204, ucf:51108
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006204

Title: Interdiffusion Study of Mg-AA6061 System.
Creator: Fu, Mian, Sohn, Yongho, Coffey, Kevin, An, Linan, University of Central Florida
Abstract / Description: 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.
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Date Issued: 2013
Identifier: CFE0005333, ucf:50521
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005333

Title: Florida Local Government Conservation Planning: Variability, Drivers, and Policy Implications.
Creator: Pannozzo, Pamela, Noss, Reed, Quintana-Ascencio, Pedro, Hinkle, Charles, Knox, Claire, University of Central Florida
Abstract / Description: This study examined the quality of Florida county government conservation planning. To assess conservation planning quality, a theoretical model of conservation planning as prescribed by the conservation science literature was first developed. A plan evaluation coding protocol was applied to local comprehensive plan Conservation Elements to determine the extent to which county-level conservation planning met the theoretical model. A high degree of variability in conservation planning quality...
Show moreThis study examined the quality of Florida county government conservation planning. To assess conservation planning quality, a theoretical model of conservation planning as prescribed by the conservation science literature was first developed. A plan evaluation coding protocol was applied to local comprehensive plan Conservation Elements to determine the extent to which county-level conservation planning met the theoretical model. A high degree of variability in conservation planning quality was found. Highest quality conservation planning occurred in the Gulf coast counties of southwest Florida. Lowest conservation planning quality occurred in the Florida Panhandle counties. The quality of conservation planning of coastal counties was significantly higher than that of inland counties. Significant regional differences were also found, where conservation planning quality in South Florida counties was significantly higher than conservation planning quality in Panhandle counties. Geographic differences in conservation planning quality were likely attributable to significant differences in socioeconomic variables among counties, including differences in education, wealth, and urbanization. Multiple regression analysis using an information theoretic approach was employed to develop a predictive model of conservation planning quality of Florida local governments. The two most plausible predictors in the model were education level of the public and total resources. Local and global spatial autocorrelation analysis were next applied to county conservation planning scores to investigate spatial patterns of conservation planning quality, which were found to be related to the policy process of diffusion. Lastly, current local government conservation planning policy was analyzed for effectiveness and policy recommendations were made. Improving the effectiveness of local conservation planning will require changes in statutory provisions of the state Florida Forever and Growth Management statutes. It will also require a greater commitment on the part of the state of Florida to protect the state's biological resources over the long term.
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Date Issued: 2013
Identifier: CFE0005041, ucf:49971
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005041

Title: INTERDIFFUSION ANALYSIS FOR NICOCRALY AND NIAL VS. VARIOUS SUPERALLOYS.
Creator: Perez, Emmanuel, Sohn, Yong-Ho, University of Central Florida
Abstract / Description: Hot section components in gas turbines can be NiCoCrAlY-coated to provide the component with an Al reservoir that maintains a protective oxide layer on its surface. Over the service life of the component, the coatings degrade by composition and phase changes due to oxidation/hot-corrosion, and multicomponent interdiffusion from and into the superalloy substrate. In this study, the rate of Al interdiffusion into selected Ni-base superalloys using various diffusion couples of two-phase...
Show moreHot section components in gas turbines can be NiCoCrAlY-coated to provide the component with an Al reservoir that maintains a protective oxide layer on its surface. Over the service life of the component, the coatings degrade by composition and phase changes due to oxidation/hot-corrosion, and multicomponent interdiffusion from and into the superalloy substrate. In this study, the rate of Al interdiffusion into selected Ni-base superalloys using various diffusion couples of two-phase NiCoCrAlY (beta + gamma) and single beta-phase NiAl with the selected alloys is measured. The diffusion couples were examined with an emphasis on the composition-dependence of Al interdiffusion. Microstructural analysis of the NiCoCrAlY vs. superalloys couples is performed to examine the dependence of coatings lifetime on the superalloy composition. The beta-NiAl diffusion couples were analyzed to determine the integrated, apparent and average effective interdiffusion coefficient as a function of superalloy's composition. Concentration profiles were obtained by EPMA of the NiAl vs. superalloy diffusion couples. Findings of this study show that the lifetimes of NiCoCrAlY are heavily dependent on superalloy compositions. The rate of interdiffusion in the diffusion couples is affected by the refractory precipitate phase microstructure structures in the interdiffusion zones as well as by component interactions. The results of the beta-NiAl diffusion couples show that increasing concentrations of Cr, Mo and Ti in the superalloy increase the Al effective interdiffusion coefficient into the superalloy, while increasing concentrations of Al, Ta and W reduce it. Thus NiCoCrAlY-superalloy systems may be designed to produce optimal microstructures in the interdiffusion zone and minimize Al interdiffusion by consideration of these diffusional interactions.
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Date Issued: 2005
Identifier: CFE0000681, ucf:46486
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0000681

Title: Laser Spark Ignition of Counter-flow Diffusion Flames: Effects of diluents and diffusive-thermal properties.
Creator: Sime Segura, Fidelio, Deng, Weiwei, Chen, Ruey-Hung, Kapat, Jayanta, University of Central Florida
Abstract / Description: A pulsed Nd:YAG laser is used to study laser spark ignition of methane counter-flow diffusion flames with the use of helium and argon as diluents to achieve a wide range of variations in transport properties. The global strain rate and Damk(&)#246;hler number on successful ignition were investigated for the effects of Lewis number and transport properties, which are dependent on the diluent type and dilution level. A high-speed camera is used to record the ignition events and a software is...
Show moreA pulsed Nd:YAG laser is used to study laser spark ignition of methane counter-flow diffusion flames with the use of helium and argon as diluents to achieve a wide range of variations in transport properties. The global strain rate and Damk(&)#246;hler number on successful ignition were investigated for the effects of Lewis number and transport properties, which are dependent on the diluent type and dilution level. A high-speed camera is used to record the ignition events and a software is used for pre-ignition flow field and mixing calculations. It is found that the role of effective Lewis number on the critical global strain rate, beyond which ignition is not possible, is qualitatively similar that on the extinction strain rate. With the same level of dilution, the inert diluent with smaller Lewis number yields larger critical global strain rate. The critical Damk(&)#246;hler number below which no ignition is possible is found to be within approximately 20% for all the fuel-inert gas mixtures studied. When successful ignition takes place, the ignition time increases as the level of dilution of argon is increased. The ignition time decreases with increasing level of helium dilution due to decreases in thermal diffusion time, which causes rapid cooling of the flammable layer during the ignition process. However, the critical strain for ignition with helium dilution rapidly decreases as the dilution level is increased. The experimental results show that with the increase of strain rate the time to steady flame decreases, and that with the increase of dilution level time for the flame to become steady increases. For the same level of dilution, the time for steady flame is observed to be longer for He-diluted flames than for Ar-diluted flames due to its thermal diffusivity being larger than that of Ar.
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Date Issued: 2012
Identifier: CFE0004295, ucf:49467
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004295

Title: EXPERIMENTAL STUDY OF PROFILES OF IMPLANTED SPECIES INTO SEMICONDUCTOR MATERIALS USING SECONDARY ION MASS SPECTROMETRY.
Creator: Salman, Fatma, Chow, Lee, University of Central Florida
Abstract / Description: ABSTRACT The study of impurity diffusion in semiconductor hosts is an important field that has both fundamental appeal and practical applications. Ion implantation is a good technique to introduce impurities deep into the semiconductor substrates at relatively low temperature and is not limited by the solubility of the dopants in the host. However ion implantation creates defects and damages to the substrate. Annealing process was used to heal these damages and to activate the dopants. In...
Show moreABSTRACT The study of impurity diffusion in semiconductor hosts is an important field that has both fundamental appeal and practical applications. Ion implantation is a good technique to introduce impurities deep into the semiconductor substrates at relatively low temperature and is not limited by the solubility of the dopants in the host. However ion implantation creates defects and damages to the substrate. Annealing process was used to heal these damages and to activate the dopants. In this study, we introduced several species such as alkali metals (Li, Na, K), alkali earth metals (Be, Ca,), transition metals (Ti, V, Cr, Mn) and other metals (Ga, Ge) into semiconductor substrates using ion implantation. The implantation energy varies form 70 keV to 200 keV and the dosages vary between ~ 1.0x1012 and ~5.0x1015 atoms/cm2. The samples are annealed at different temperatures from 300°C to 1000°C and for different time intervals. The redistribution behaviors of the implanted ions are studied experimentally using secondary ion mass spectrometry (SIMS). We observed some complex distribution behaviors due to the defects created during the process of ion implantation. The diffusivities of some impurities are calculated and compared to previous data. It was found that the diffusivities of implanted impurities is related to the dosages, annealing temperatures and the defects and damages caused by ion implantation. Additionally, as we go from one type of semiconductor to another, the diffusion behavior of the impurities shows a different trend.
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Date Issued: 2007
Identifier: CFE0001791, ucf:47269
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0001791

Title: INFLUENCE OF ELECTRON TRAPPING ON MINORITY CARRIER TRANSPORT PROPERTIES OF WIDE BAND GAP SEMICONDUCTORS.
Creator: Tirpak, Olena, Chernyak, Leonid, University of Central Florida
Abstract / Description: Minority carrier transport properties and the effects of electron irradiation/injection were studied in GaN and ZnO containing dopants known to form acceptor states deep within the materials' bandgap. Minority carrier diffusion length and lifetime changes were investigated using Electron Beam Induced Current (EBIC) method, cathodoluminescence spectroscopy, spectral photoresponse and persistent photoconductivity measurements. It is shown that electron irradiation by the beam of a scanning...
Show moreMinority carrier transport properties and the effects of electron irradiation/injection were studied in GaN and ZnO containing dopants known to form acceptor states deep within the materials' bandgap. Minority carrier diffusion length and lifetime changes were investigated using Electron Beam Induced Current (EBIC) method, cathodoluminescence spectroscopy, spectral photoresponse and persistent photoconductivity measurements. It is shown that electron irradiation by the beam of a scanning electron microscope results in a significant increase of minority carrier diffusion length. These findings are supported by the cathodoluminescence measurements that demonstrate the decay of near-band-edge intensity as a consequence of increasing carrier lifetime under continuous irradiation by the electron beam. Temperature-dependent measurements were used to determine the activation energies for the electron irradiation-induced effects. The latter energies were found to be consistent with the involvement of deep acceptor states. Based on these findings, the effects of electron irradiation are explained via the mechanism involving carrier trapping on these levels. Solid-state electron injection was also shown to result in a similar increase of minority carrier lifetime and diffusion length. Solid-state injection was carried out by applying the forward bias to a ZnO homojunction and resulted in a significant improvement of the peak photoresponse of the junction. This improvement was unambiguously correlated with the increase of the minority carrier diffusion length due to electron injection.
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Date Issued: 2007
Identifier: CFE0001710, ucf:47325
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0001710

Title: MULTIPLE SCATTERING OF LIGHT IN INHOMOGENEOUS MEDIA AND APPLICATIONS.
Creator: Mujat, Claudia, Dogariu, Aristide, University of Central Florida
Abstract / Description: Light scattering-based techniques are being developed for non-invasive diagnostics of inhomogeneous media in various fields, such as medicine, biology, and material characterization. However, as most media of interest are highly scattering and have a complex structure, it is difficult to obtain a full analytical solution of the scattering problem without introducing approximations and assumptions about the properties of the system under consideration. Moreover, most of the previous studies...
Show moreLight scattering-based techniques are being developed for non-invasive diagnostics of inhomogeneous media in various fields, such as medicine, biology, and material characterization. However, as most media of interest are highly scattering and have a complex structure, it is difficult to obtain a full analytical solution of the scattering problem without introducing approximations and assumptions about the properties of the system under consideration. Moreover, most of the previous studies deal with idealized scattering situations, rarely encountered in practice. This dissertation provides new analytical, numerical, and experimental solutions to describe subtle effects introduced by the properties of the light sources, and by the boundaries, absorption and morphology of the investigated media. A novel Monte Carlo simulation was developed to describe the statistics of partially coherent beams after propagation through inhomogeneous media. The Monte Carlo approach also enabled us to study the influence of the refractive index contrast on the diffusive processes, to discern between different effects of absorption in multiple scattering, and to support experimental results on inhomogeneous media with complex morphology. A detailed description of chromatic effects in scattering was used to develop new models that explain the spectral dependence of the detected signal in applications such as imaging and diffuse reflectance measurements. The quantitative and non-invasive characterization of inhomogeneous media with complex structures, such as porous membranes, diffusive coatings, and incipient lesions in natural teeth was then demonstrated.
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Date Issued: 2004
Identifier: CFE0000048, ucf:46143
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0000048

Title: A RELATIONAL DIFFUSION NETWORK STUDY OF SYNCHRONOUS AND ASYNCHRONOUS INTERNET-BASED FACULTY'S PERSONAL NETWORK EXPOSURE MODELS RELATED TO DISCUSSIONS ABOUT TEACHING ONLINE.
Creator: Pick, Dorothy, Orwig, Gary, University of Central Florida
Abstract / Description: For many faculty, teaching online represents a new instructional delivery method, requiring the development of new teaching skills. This exploratory investigation builds upon Rogers' (2003) Diffusion of Innovations theory and communication channels to describe the influence of faculty discussions on their perceptions and decisions about teaching and learning. A sequential explanatory mixed-methods research design, using both sociometric and phenomenological methodologies, guided the...
Show moreFor many faculty, teaching online represents a new instructional delivery method, requiring the development of new teaching skills. This exploratory investigation builds upon Rogers' (2003) Diffusion of Innovations theory and communication channels to describe the influence of faculty discussions on their perceptions and decisions about teaching and learning. A sequential explanatory mixed-methods research design, using both sociometric and phenomenological methodologies, guided the exploration of faculty personal network exposure models and social learning opportunities. The study utilized online survey and open-ended interview instruments for the investigation. Faculty from several colleges at the University of Central Florida voluntarily completed the survey instrument identifying with whom, how, and why they discuss teaching online, including the influence of these discussions. In-depth interviews offered internal descriptions of their personal networks. Survey results established baseline data for demographic and future comparisons and identified concerns, issues, and trends unique to synchronous and asynchronous Internet-based faculty development and support needs. Phenomenological data produced the emergent categories and themes used to investigate and explain faculty's communication channel usage and social learning experiences. Similarities between diffusion and knowledge research findings and participants reflected more conformity than anticipated. Differences in communication channel and learning style preferences and usage and faculty's 24/7 work life needs, present challenges to administrators and educators responsible for providing development and support systems.
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Date Issued: 2006
Identifier: CFE0000967, ucf:46712
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0000967

Title: EFFECTS OF BINARY SOLVENT SYSTEM ON MORPHOLOGY OF PARTICLES.
Creator: Besana, Patrick, Deng, Weiwei, University of Central Florida
Abstract / Description: Recent advancements in cancer research has led to the synthesis of a new drug known as docetaxel. Meant to replace paclitaxel, its more natural counterpart whose ingredients are difficult to obtain, the drug is known to effectively treat a wide array of cancers, including breast cancer, ovarian cancer, and prostate cancer. The establishment of a synthetic alternative to paclitaxel has increased its bioavailability, thereby lowering the cost needed to utilize the drug. Still, the limiting...
Show moreRecent advancements in cancer research has led to the synthesis of a new drug known as docetaxel. Meant to replace paclitaxel, its more natural counterpart whose ingredients are difficult to obtain, the drug is known to effectively treat a wide array of cancers, including breast cancer, ovarian cancer, and prostate cancer. The establishment of a synthetic alternative to paclitaxel has increased its bioavailability, thereby lowering the cost needed to utilize the drug. Still, the limiting factor in minimizing costs is the method in which the drug is processed. Current methods in drug processing have their limitations, which include the introduction of impurities and a low effective yield due to poor powder geometry. Thus, the goal of this study looks to explore a new way to process the drug in a more efficient manner. In this study, a new method for processing docetaxel is explored on in great detail. A more direct method of using electrospray deposition is utilized for the creation of monodisperse nanoparticles, with the main intention of increasing the efficiency at which the drug is processed and prepared for drug delivery to the patient by means of injection. A key feature in electrospray deposition is its ability to produce droplets that are sized homogenously. These droplets eventually evaporate at homogenous rates. These two concepts have been exploited to consistently produce nanoparticles of the cancer drug, which is made possible by the fact that the minimal variation in droplet sizes has easily translated to minimal variation in dry particle sizes. Compared to other methods of drug processing, one other benefit that electrospray deposition conveys is that through evaporation, virtually all impurities and unwanted foreign material are eliminated. Moreover, a binary solvent system is investigated in more detail in this study, so as to determine its effects on both the evaporation of the solvent and the diffusion of the drug into nanoparticles. From there, material and geometric properties of the electrospray nozzle were explored upon in great detail, with the main goal of being able to produce a cone jet that consistently dissociates into monodisperse droplets. At the same time, controllable properties of the electrospray atomizer were investigated and continuously modified. Modifications in both the components of the solution and the operating temperature were also considered to enhance both the electrospray deposition process and the geometry of the particles. Scanning electron microscopy (SEM) characterization is continuously utilized to determine suitability of results obtained in experiments. Ultimately, the goal of this study is to determine the ideal conditions (solvent ratios, flow rate, operating temperature, electrospray atomizer nozzle configurations, etc.) in which spherical docetaxel particles sized at 100-200 nm can be produced.
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Date Issued: 2015
Identifier: CFH0004872, ucf:45412
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFH0004872

Title: USING ANTENNA TILE-ASSISTED SUBSTRATE DELIVERY TO IMPROVE THE DETECTION LIMITS OF DEOXYRIBOZYME BIOSENSORS.
Creator: Cox, Amanda, Kolpashchikov, Dmitry, University of Central Florida
Abstract / Description: One common limitation of enzymatic reactions is the diffusion of a substrate to the enzyme active site and/or the release of the reaction products. These reactions are known as diffusion-controlled. Overcoming this limitation may enable faster catalytic rates, which in the case of catalytic biosensors can potentially lower limits of detection of specific analyte. Here we created an artificial system to enable deoxyribozyme (Dz) 10-23 based biosensor to overcome its diffusion limit. The sensor...
Show moreOne common limitation of enzymatic reactions is the diffusion of a substrate to the enzyme active site and/or the release of the reaction products. These reactions are known as diffusion-controlled. Overcoming this limitation may enable faster catalytic rates, which in the case of catalytic biosensors can potentially lower limits of detection of specific analyte. Here we created an artificial system to enable deoxyribozyme (Dz) 10-23 based biosensor to overcome its diffusion limit. The sensor consists of the two probe strands, which bind to the analyzed nucleic acid by Watson-Crick base pairs and, upon binding re-form the catalytic core of Dz 10-23. The activated Dz 10-23 cleaves the fluorophore and quencher-labeled DNA-RNA substrate which separates the fluorophore from the quencher thus producing high fluorescent signal. This system uses a Dz 10-23 biosensor strand associated to a DNA antenna tile, which captures the fluorogenic substrate and channels it to the reaction center where the Dz 10-23 cleaves the substrate. DNA antenna tile captures fluorogenic substrate and delivers it to the activated Dz 10-23 core. This allows for lower levels of analyte to be detected without compromising the specificity of the biosensor. The results of this experiment demonstrated that using DNA antenna, we can create a synthetic environment around the Dz 10-23 biosensor to increase its efficiency and allow for lower levels of analyte to be detected without using amplification techniques like PCR.
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Date Issued: 2015
Identifier: CFH0004887, ucf:45432
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFH0004887

Title: EMERGING AND DISRUPTIVE TECHNOLOGIES FOR EDUCATION: AN ANALYSIS OF PLANNING, IMPLEMENTATION, AND DIFFUSION IN FLORIDAÃ‚Â'S ELEVEN STATE UNIVERSITY SYSTEM INSTITUTIONS.
Creator: Bradford, Deborah, Cintron, Rosa, University of Central Florida
Abstract / Description: The purpose of the study was to understand and appreciate the methodologies and procedures used in determining the extent to which an information technology (IT) organization within the eleven member State University Systems (SUS) of Florida planned, implemented, and diffused emerging educational technologies. Key findings found how critical it was that flexibility be given during the planning stages and not rely on standardized models which may or may not be of use any longer. Research also...
Show moreThe purpose of the study was to understand and appreciate the methodologies and procedures used in determining the extent to which an information technology (IT) organization within the eleven member State University Systems (SUS) of Florida planned, implemented, and diffused emerging educational technologies. Key findings found how critical it was that flexibility be given during the planning stages and not rely on standardized models which may or may not be of use any longer. Research also found that the SUS institutions have to be prepared to organize and preserve the deluge of digital data if they intended to remain relevant as a Ã‚Â"towerÃ‚Â" of knowledge transmissions. The literature found that institutions of higher education needed to keep abreast of the new technologies, new pedagogies, and never before open-access concepts because authors found these ideas were converging and producing an unprecedented period of innovation in learning. Furthermore, the implications of perpetual connectivity to information, peers, and teachers garnered a great deal of attention among educational technologists. However, those implications had not been gauged, especially in FloridaÃ‚Â's SUS institutions. A survey of those institutions regarding how technologies were planned for, implemented logically, and thoroughly diffused, along with lessons learned could potentially save resources and ensure FloridaÃ‚Â's institutions continue to be on higher learningÃ‚Â's forefront.
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Date Issued: 2010
Identifier: CFE0002989, ucf:47932
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0002989

Title: THE EFFECT OF APPLYING WIKIS IN AN ENGLISH AS A FOREIGN LANGUAGE (EFL) CLASS IN TAIWAN.
Creator: Chen, Yu-ching, Witta, Lea, University of Central Florida
Abstract / Description: Incorporating technology into learning has brought major benefits to learners and has greatly changed higher education. Since there is limited number of experimental research investigating the effectiveness of applying wikis, this study collected experimental data to investigate its effectiveness. The purpose of the study was to examine the effectiveness of applying wikis in terms of students' learning outcomes, to investigate the changes regarding students' attitude towards language...
Show moreIncorporating technology into learning has brought major benefits to learners and has greatly changed higher education. Since there is limited number of experimental research investigating the effectiveness of applying wikis, this study collected experimental data to investigate its effectiveness. The purpose of the study was to examine the effectiveness of applying wikis in terms of students' learning outcomes, to investigate the changes regarding students' attitude towards language learning, to explore the communication channels in wikis that facilitate students' interaction in the e-learning environment as well as students' experience of using wikis. Results showed that there existed statistically significant difference between the group with and without wikis, which means the group applying wikis performed better in listening and reading abilities. When compared with the non-wiki group, the wiki group had a more favorable attitude towards the class, their English ability improvement, and cooperative learning. Moreover, the students agreed that wikis helped them complete their assignment, they felt comfortable in the wiki environment, and it was easy for them to use wikis. From the experiences of using wikis shared by the students, they provided recommendations about the interface and the edit functions in the wiki environment. Their interaction with other team members and the course material increased but they expressed that the main interaction was through face-to-face and instant message software. Finally, the wiki environment allowed students to fulfill their role duties, cooperate, negotiate, manage their contribution, and modeling from each other.
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Date Issued: 2008
Identifier: CFE0002227, ucf:47919
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0002227

Title: LASER ENHANCED DOPING FOR SILICON CARBIDE WHITE LIGHTEMITTING DIODES.
Creator: Bet, Sachin, Kar, Aravinda, University of Central Florida
Abstract / Description: This work establishes a solid foundation for the use of indirect band gap semiconductors for light emitting application and presents the work on development of white light emitting diodes (LEDs) in silicon carbide (SiC). Novel laser doping has been utilized to fabricate white light emitting diodes in 6H-SiC (n-type N) and 4H-SiC (p-type Al) wafers. The emission of different colors to ultimately generate white light is tailored on the basis of donor acceptor pair (DAP) recombination mechanism...
Show moreThis work establishes a solid foundation for the use of indirect band gap semiconductors for light emitting application and presents the work on development of white light emitting diodes (LEDs) in silicon carbide (SiC). Novel laser doping has been utilized to fabricate white light emitting diodes in 6H-SiC (n-type N) and 4H-SiC (p-type Al) wafers. The emission of different colors to ultimately generate white light is tailored on the basis of donor acceptor pair (DAP) recombination mechanism for luminescence. A Q-switched Nd:YAG pulse laser (1064 nm wavelength) was used to carry out the doping experiments. The p and n regions of the white SiC LED were fabricated by laser doping an n-type 6H-SiC and p-type 4H-SiC wafer substrates with respective dopants. Cr, B and Al were used as p-type dopants (acceptors) while N and Se were used as n-type dopants (donors). Deep and shallow donor and acceptor impurity level states formed by these dopants tailor the color properties for pure white light emission. The electromagnetic field of lasers and non-equilibrium doping conditions enable laser doping of SiC with increased dopant diffusivity and enhanced solid solubility. A thermal model is utilized to determine the laser doping parameters for temperature distribution at various depths of the wafer and a diffusion model is presented including the effects of Fick's diffusion, laser electromagnetic field and thermal stresses due to localized laser heating on the mass flux of dopant atoms. The dopant diffusivity is calculated as a function of temperature at different depths of the wafer based on measured dopant concentration profile. The maximum diffusivities achieved in this study are 4.6110-10 cm2/s at 2898 K and 6.9210-12 cm2/s at 3046 K for Cr in 6H-SiC and 4H-SiC respectively. Secondary ion mass spectrometric (SIMS) analysis showed the concentration profile of Cr in SiC having a penetration depth ranging from 80 nm in p-type 4H-SiC to 1.5 m in n-type 6H-SiC substrates respectively. The SIMS data revealed enhanced solid solubility (2.291019 cm-3 in 6H-SiC and 1.421919 cm-3 in 4H-SiC) beyond the equilibrium limit (31017 cm-3 in 6H-SiC above 2500 C) for Cr in SiC. It also revealed similar effects for Al and N. The roughness, surface chemistry and crystalline integrity of the doped sample were examined by optical interferometer, energy dispersive X-ray spectrometry (EDS) and transmission electron microscopy (TEM) respectively. Inspite of the larger atomic size of Cr compared to Si and C, the non-equilibrium conditions during laser doping allow effective incorporation of dopant atoms into the SiC lattice without causing any damage to the surface or crystal lattice. Deep Level Transient Spectroscopy (DLTS) confirmed the deep level acceptor state of Cr with activation energies of Ev+0.80 eV in 4H-SiC and Ev+0.45 eV in 6H-SiC. The Hall Effect measurements showed the hole concentration to be 1.981019 cm-3 which is almost twice the average Cr concentration (11019 cm-3) obtained from the SIMS data. These data confirmed that almost all of the Cr atoms were completely activated to the double acceptor state by the laser doping process without requiring any subsequent annealing step. Electroluminescence studies showed blue (460-498 nm), blue-green (500-520 nm) green (521-575 nm), and orange (650-690 nm) wavelengths due to radiative recombination transitions between donor-acceptors pairs of N-Al, N-B, N-Cr and Cr-Al respectively, while a prominent violet (408 nm) wavelength was observed due to transitions from the nitrogen level to the valence band level. The red (698-738 nm) luminescence was mainly due to metastable mid-bandgap states, however under high injection current it was due to the quantum mechanical phenomenon pertaining to band broadening and overlapping. This RGB combination produced a broadband white light spectrum extending from 380 to 900 nm. The color space tri-stimulus values for 4H-SiC doped with Cr and N were X = 0.3322, Y = 0.3320 and Z = 0.3358 as per 1931 CIE (International Commission on Illumination) corresponding to a color rendering index of 96.56 and the color temperature of 5510 K. And for 6H-SiC n-type doped with Cr and Al, the color space tri-stimulus values are X = 0.3322, Y = 0.3320 and Z = 0.3358. The CCT was 5338 K, which is very close to the incandescent lamp (or black body) and lies between bright midday sun (5200 K) and average daylight (5500 K) while CRI was 98.32. Similar white LED's were also fabricated using Cr, Al, Se as one set of dopants and B, Al, N as another.
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Date Issued: 2008
Identifier: CFE0002362, ucf:47808
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0002362

Title: Experimental and numerical investigation of a novel adsorption bed design for cooling applications.
Creator: Abdelhady, Ramy, Chow, Louis, Mansy, Hansen, Das, Tuhin, Duranceau, Steven, University of Central Florida
Abstract / Description: A global challenge is to develop environmentally friendly, affordable, compact and sustainable technologies to provide heating and cooling power. Adsorption cooling (AC) technology is one of the most promising ways to solve the environmental issues and cut down the energy consumption related to the traditional air conditioning and refrigeration systems. However, AC systems still suffer from poor heat and mass transfer inside the adsorption bed, which is the main obstacle to commercialization...
Show moreA global challenge is to develop environmentally friendly, affordable, compact and sustainable technologies to provide heating and cooling power. Adsorption cooling (AC) technology is one of the most promising ways to solve the environmental issues and cut down the energy consumption related to the traditional air conditioning and refrigeration systems. However, AC systems still suffer from poor heat and mass transfer inside the adsorption bed, which is the main obstacle to commercialization of adsorption cooling units. The main goal of this study is designing an efficient adsorption cooling cycle. In this research work, an in-depth scaling analysis of heat and mass transfer in an adsorption packed bed has been performed to identify and quantify how the effective thermal diffusivity of an adsorption bed and the surface diffusion rate of an adsorbate in a nanoporous adsorbent affect the specific cooling power of an adsorption cooling system. The main goal of this study is to derive new scaling parameters that can be used to specify the optimal bed dimensions and select the appropriate adsorbate/adsorbent pair to achieve the maximum cooling power. As the choice of a suitable working pair is critical for an adsorption cooling cycle, an experimental setup is designed and built to measure the adsorption kinetics and isotherms of any working pair accurately. This setup is also able to measure the dynamic performance of an adsorption bed. The equilibrium uptakes of Fuji silica-gels Type-RD and RD-2060 (manufactured by Fuji Silysia, Japan), which are commonly used in adsorption cooling systems, are measured experimentally. Based on the adsorption rate and the adsorbent temperature measured simultaneously, a new approach is proposed to measure the surface diffusivity in the temperature and pressure ranges typical of those during the operating conditions of adsorption cooling systems. In addition, the experimental measurements from the lab-scale adsorption bed are used to validate the numerical models that are commonly used for estimating the SCP of AC cycle. By using the scaling parameters driven from the scaling analysis, a newly designed packed bed for use in AC systems is proposed and evaluated in this research. The proposed design consists of repeated packed bed cells (modules). Each module is an open-cell aluminum foam packed with silica gel to enhance the overall thermal conductivity of the bed from 0.198 to 5.8 W/m.K. the experimental test rig is used to evaluate the performance on the new adsorption bed. The effect of pores per inch (PPI) of the foam, silica-gel particle size, bed height and adsorption isotherm of different types of silica gel on the bed performance are investigated.
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Date Issued: 2019
Identifier: CFE0007422, ucf:52702
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007422

Title: From Excited Charge Dynamics to Cluster Diffusion: Development and Application of Techniques Beyond DFT and KMC.
Creator: Acharya, Shree Ram, Rahman, Talat, Chow, Lee, Stolbov, Sergey, Wu, Annie, University of Central Florida
Abstract / Description: This dissertation focuses on developing reliable and accurate computational techniques which enable the examination of static and dynamic properties of various activated phenomena using deterministic and stochastic approaches. To explore ultrafast electron dynamics in materials with strong electron-electron correlation, under the influence of a laser pulse, an ab initio electronic structure method based on time-dependent density functional theory (TDDFT) in combination with dynamical mean...
Show moreThis dissertation focuses on developing reliable and accurate computational techniques which enable the examination of static and dynamic properties of various activated phenomena using deterministic and stochastic approaches. To explore ultrafast electron dynamics in materials with strong electron-electron correlation, under the influence of a laser pulse, an ab initio electronic structure method based on time-dependent density functional theory (TDDFT) in combination with dynamical mean field theory (DMFT) is developed and applied to: 1) single-band Hubbard model; 2) multi-band metal Ni; and 3) multi-band insulator MnO. The ultrafast demagnetization in Ni reveal the importance of memory and correlation effects, leading to much better agreement with experimental data than previously obtained, while for MnO the main channels of charge response are identified. Furthermore, an analytical form of the exchange-correlation kernel is obtained for future applications, saving tremendous computational cost. In another project, size-dependent temporal and spatial evolution of homo- and hetero-epitaxial adatom islands on fcc(111) transition metals surfaces are investigated using the self-learning kinetic Monte Carlo (SLKMC) method that explores long-time dynamics unbiased by apriori selected diffusion processes. Novel multi-atom diffusion processes are revealed. Trends in the diffusion coefficients point to the relative role of adatom lateral interaction and island-substrate binding energy in determining island diffusivity. Moreover, analysis of the large data-base of the activation energy barriers generated for multitude of diffusion processes for variety of systems allows extraction of a set of descriptors that in turn generate predictive models for energy barrier evaluation. Finally, the kinetics of the industrially important methanol partial oxidation reaction on a model nanocatalyst is explored using KMC supplemented by DFT energetics. Calculated thermodynamics explores the active surface sites for reaction components including different intermediates and energetics of competing probable reaction pathways, while kinetic study attends to the selectivity of products and its variation with external factors.
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Date Issued: 2018
Identifier: CFE0006965, ucf:52910
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006965

Title: Impact of Ionizing Radiation and Electron Injection on Carrier Transport Properties in Narrow and Wide Bandgap Semiconductors.
Creator: Lee, Jonathan, Flitsiyan, Elena, Chernyak, Leonid, Peale, Robert, Orlovskaya, Nina, University of Central Florida
Abstract / Description: This study investigated the minority carrier properties of wide and narrow bandgap semiconductors. Included specifically are wide bandgap materials GaN and ?-Ga2O3, and narrow bandgap InAs/GaSb type-II strain-layer superlattice. The importance of minority carrier behavior in bipolar device performance is utmost because it is the limiting component in current conduction. The techniques used to determine minority carrier properties include electron beam induced current (EBIC) and...
Show moreThis study investigated the minority carrier properties of wide and narrow bandgap semiconductors. Included specifically are wide bandgap materials GaN and ?-Ga2O3, and narrow bandgap InAs/GaSb type-II strain-layer superlattice. The importance of minority carrier behavior in bipolar device performance is utmost because it is the limiting component in current conduction. The techniques used to determine minority carrier properties include electron beam induced current (EBIC) and cathodoluminescence (CL) spectroscopy. The CL spectroscopy is complemented with time-resolved CL (TRCL) for direct measurement of carrier radiative recombination lifetime. The minority carrier properties and effect of high energy radiation is explored. The GaN TRCL results suggested an activation energy effecting carrier lifetime of about 90 meV which is related to nitrogen vacancies. The effects of 60Co gamma radiation are demonstrated and related to the effects of electron injection in GaN-based devices. The effects of various high energy radiations upon Si-doped ?-Ga2O3 minority carrier diffusion length and radiative lifetime are measured. The non-irradiated sample thermal activation energies found for minority carrier diffusion length were 40.9 meV, related to shallow Si-donors in the material. The CL results demonstrate that the bandgap of 4.9 eV is slightly indirect. The thermal activation energy decreased on 1.5 MeV electron irradiation but increased for 10 MeV proton irradiation. The increase in energy was related to higher order defects and their complexes, and influenced recombination lifetime significantly. Finally, the diffusion length is reported for narrow bandgap InAs/GaSb superlattice structure and the effect of 60Co gamma radiation is demonstrated.In general, the defects introduced by high energy radiations decreased minority carrier diffusion length, except for 60Co gamma on AlGaN/GaN HEMT devices and high-temperature proton irradiated ?-Ga2O3.
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Date Issued: 2018
Identifier: CFE0007217, ucf:52239
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007217

Title: Phonon Modulation by Polarized Lasers for Material Modification.
Creator: Chen, Sen-Yong, Kar, Aravinda, Vaidyanathan, Rajan, Harvey, James, Likamwa, Patrick, University of Central Florida
Abstract / Description: Magnetic resonance imaging (MRI) has become one of the premier non-invasive diagnostic tools, with around 60 million MRI scans applied each year. However, there is a risk of thermal injury due to radiofrequency (RF) induction heating of the tissue and implanted metallic device for the patients with the implanted metallic devices. Especially, MRI of the patients with implanted elongated devices such as pacemakers and deep brain stimulation systems is considered contraindicated. Many efforts,...
Show moreMagnetic resonance imaging (MRI) has become one of the premier non-invasive diagnostic tools, with around 60 million MRI scans applied each year. However, there is a risk of thermal injury due to radiofrequency (RF) induction heating of the tissue and implanted metallic device for the patients with the implanted metallic devices. Especially, MRI of the patients with implanted elongated devices such as pacemakers and deep brain stimulation systems is considered contraindicated. Many efforts, such as determining preferred MRI parameters, modifying magnetic field distribution, designing new structure and exploring new materials, have been made to reduce the induction heating. Improving the MRI-compatibility of implanted metallic devices by modifying the properties of the existing materials would be valuable.To evaluate the temperature rise due to RF induction heating on a metallic implant during MRI procedure, an electromagnetic model and thermal model are studied. The models consider the shape of RF magnetic pulses, interaction of RF pulses with metal plate, thermal conduction inside the metal and the convection at the interface between the metal and the surroundings. Transient temperature variation and effects of heat transfer coefficient, reflectivity and MRI settings on the temperature change are studied.Laser diffusion is applied to some titanium sheets for a preliminary study. An electromagnetic and thermal model is developed to choose the proper diffusant. Pt is the diffusant in this study. An electromagnetic model is also developed based on the principles of inverse problems to calculate the electromagnetic properties of the metals from the measured magnetic transmittance. This model is used to determine the reflectivity, dielectric constant and conductivity of treated and as-received Ti sheets. The treated Ti sheets show higher conductivity than the as-received Ti sheets, resulting higher reflectivity.A beam shaping lens system which is designed based on vector diffraction theory is used in laser diffusion. Designing beam shaping lens based on the vector diffraction theory offers improved irradiance profile and new applications such as polarized beam shaping because the polarization nature of laser beams is considered. Laser Pt diffusion are applied on the titanium and tantalum substrates using different laser beam polarizations. The concentration of Pt and oxygen in those substrates are measured using Energy Dispersive X-Ray Spectroscopy (EDS). The magnetic transmittance and conductivity of those substrates are measured as well. The effects of laser beam polarizations on Pt diffusion and the magnetic transmittance and conductivity of those substrates are studied. Treated Ti sheets show lower magnetic transmittance due to the increased conductivity from diffused Pt atoms. On the other hand, treated Ta sheets show higher magnetic transmittance due to reduced conductivity from oxidation. Linearly polarized light can enhance the Pt diffusion because of the excitation of local vibration mode of atoms.Laser Pt diffusion and thermo-treatment were applied on the Ta and MP35N wires. The Pt concentration in laser platinized Ta and MP35N wires was determined using EDS. The ultimate tensile strength, fatigue lives and lead tip heating in real MRI environment of those wires were measured. The lead tip hating of the platinized Ta wires is 42 % less than the as-received Ta wire. The diffused Pt increases the conductivity of Ta wires, resulting in more reflection of magnetic field. In the case of the platinized MP35N wire, the reduction in lead tip heating was only 1 (&)deg;C due to low concentration of Pt. The weaker ultimate tensile strength and shorter fatigue lives of laser-treated Ta and MP35N wires may attribute to the oxidation and heating treatment.
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Date Issued: 2012
Identifier: CFE0004500, ucf:49269
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004500

Title: Aerodynamic Characteristics of a Gas Turbine Exhaust Diffuser with an Accompanying Exhaust Collection System.
Creator: Bernier, Bryan, Kapat, Jayanta, Deng, Weiwei, Raghavan, Seetha, University of Central Florida
Abstract / Description: The effects of an industrial gas turbine's Exhaust Collector Box (ECB) geometry on static pressure recovery and total pressure loss were investigated in this study experimentally and computationally. This study aims to further understand how exit boundary conditions affect the performance of a diffuser system as well as the accuracy of industry standard computational models. A design of experiments approach was taken using a Box-Behnken design method for investigating three geometric...
Show moreThe effects of an industrial gas turbine's Exhaust Collector Box (ECB) geometry on static pressure recovery and total pressure loss were investigated in this study experimentally and computationally. This study aims to further understand how exit boundary conditions affect the performance of a diffuser system as well as the accuracy of industry standard computational models. A design of experiments approach was taken using a Box-Behnken design method for investigating three geometric parameters of the ECB. In this investigation, the exhaust diffuser remained constant through each test, with only the ECB being varied. A system performance analysis was conducted for each geometry using the total pressure loss and static pressure recovery from the diffuser inlet to the ECB exit. Velocity and total pressure profiles obtained with a hotwire anemometer and Kiel probe at the exit of the diffuser and at the exit of the ECB are also presented in this study. A total of 13 different ECB geometries are investigated at a Reynolds number of 60,000. Results obtained from these experimental tests are used to investigate the accuracy of a 3-dimensional RANS with realizable k-? turbulence model from the commercial software package Star-CCM+. The study confirms the existence of strong counter-rotating helical vortices within the ECB which significantly affect the flow within the diffuser. Evidence of a strong recirculation zone within the ECB was found to force separation within the exhaust diffuser which imposed a circumferentially asymmetric pressure field at the inlet of the diffuser. Increasing the ECB width proved to decrease the magnitude of this effect, increasing the diffuser protrusion reduced this effect to a lesser degree. The combined effect of increasing the ECB Length and Width increased the expansion area ratio, proving to increase the system pressure recovery by as much as 19% over the nominal case. Additionally, the realizable k-? turbulence model was able to accurately rank all 13 cases in order by performance; however the predicted magnitudes of the pressure recovery and total pressure loss were poor for the cases with strong vortices. For the large volume cases with weak vortices, the CFD was able to accurately represent the total pressure loss of the system within 5%.
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Date Issued: 2012
Identifier: CFE0004517, ucf:49296
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004517

Diffusion (14)	+ -
diffusion (14)	+ -
interdiffusion (5)	+ -
GaN (3)	+ -
Interdiffusion (3)	+ -

diffusion length (3)	+ -
diffusion of innovations (3)	+ -
Aluminum (2)	+ -
CATER (2)	+ -
DFT (2)	+ -
Diffuser (2)	+ -
Intermetallics (2)	+ -
Magnesium (2)	+ -
Nanoindentation (2)	+ -
Separation (2)	+ -
TEM (2)	+ -
cathodoluminescence (2)	+ -
diffusion coefficient (2)	+ -
impurity diffusion (2)	+ -
ionic strength (2)	+ -
molybdenum (2)	+ -
nanofiltration (2)	+ -
uranium (2)	+ -
zirconium (2)	+ -
Ab-initio (1)	+ -
Accountable Care Organizations (1)	+ -
Adsorption cooling cycle (1)	+ -
Aerodynamics (1)	+ -
Al (1)	+ -
Al2O3 (1)	+ -

ETD Collection (58)	+ -
Honors Collection (2)	+ -

University of Central Florida (60)	+ -
Sohn, Yongho (12)	+ -
Coffey, Kevin (11)	+ -
Kapat, Jayanta (5)	+ -
Sundaram, Kalpathy (4)	+ -

An, Linan (3)	+ -
Chernyak, Leonid (3)	+ -
Chow, Lee (3)	+ -
Chow, Louis (3)	+ -
Deng, Weiwei (3)	+ -
Dogariu, Aristide (3)	+ -
Duranceau, Steven (3)	+ -
Fang, Jiyu (3)	+ -
Heinrich, Helge (3)	+ -
Orlovskaya, Nina (3)	+ -
Rahman, Talat (3)	+ -
Stolbov, Sergey (3)	+ -
Yuan, Jiann-Shiun (3)	+ -
Blair, Richard (2)	+ -
Brown, Timothy (2)	+ -
Gordon, Ali (2)	+ -
Kammerer, Catherine (2)	+ -
Kar, Aravinda (2)	+ -
Kara, Abdelkader (2)	+ -
Kolpashchikov, Dmitry (2)	+ -
Lee, Woo Hyoung (2)	+ -
Park, Young Joo (2)	+ -
Perez, Emmanuel (2)	+ -
Roldan Cuenya, Beatriz (2)	+ -
Sadmani, A H M Anwar (2)	+ -

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