View All Items

Title: UTILIZATION OF TOTAL MASS AS A CONTROL IN DIFFUSION PROCESSES.
Creator: Salman, Mohamed, Cannon, John, University of Central Florida
Abstract / Description: As motivation for the mathematical problems considered in this work, consider a chamber in the form of a long linear transparent tube. We allow for the introduction or removal of material in a gaseous state at the ends of the tube. The material diffuses throughout the tube with or without reaction with other materials. By illuminating the tube on one side with a light source with a frequency range spanning the absorption range for the material and collecting the residual light that passes...
Show moreAs motivation for the mathematical problems considered in this work, consider a chamber in the form of a long linear transparent tube. We allow for the introduction or removal of material in a gaseous state at the ends of the tube. The material diffuses throughout the tube with or without reaction with other materials. By illuminating the tube on one side with a light source with a frequency range spanning the absorption range for the material and collecting the residual light that passes through the tube with photo-reception equipment, we can obtain a measurement of the total mass of material contained in the tube as a function of time. Using the total mass as switch points for changing the boundary conditions for introduction or removal of material. The objective is to keep the total mass of material in the tube oscillating between two set values such as $m0; \ u(x,0)=0,$ and $u(0,t)=u(1,t)=\psi(t),$ where $\psi(t)=u_0$ for $t_{2k} < t0; \ u(x,0)=0,$ and $u(0,t)=u(1,t)=\psi(t),$ where $\psi(t)=u_0$ for $t_{2k} < t0; \ u(x,0)=0,$ and $-u_x(0,t)=u_x(1,t)=\psi(t),$ where $\psi(t)=1$ for $t_{2k} < t0; \ u(x,0)=0,$ and $-u_x(0,t)=u_x(1,t)=\phi(t),$ where $a=a(x,t,u)$, and $\phi(t)=1$ for $t_{2k} < tShow less
Date Issued: 2005
Identifier: CFE0000551, ucf:46437
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0000551

Title: PROBING RANDOM MEDIA WITH SINGULAR WAVES.
Creator: Schwartz, Chaim, Dogariu, Aristide, University of Central Florida
Abstract / Description: In recent years a resurgence of interest in wave singularities (of which optical vortices are a prominent example), light angular momentum and the relations between them has occurred. Many applications in various areas of linear and non-linear optics have been based on studying effects related to angular momentum and optical vortices. This dissertation examines the use of such wave singularities for studying the light propagation in highly inhomogeneous media and the relationship to angular...
Show moreIn recent years a resurgence of interest in wave singularities (of which optical vortices are a prominent example), light angular momentum and the relations between them has occurred. Many applications in various areas of linear and non-linear optics have been based on studying effects related to angular momentum and optical vortices. This dissertation examines the use of such wave singularities for studying the light propagation in highly inhomogeneous media and the relationship to angular momentum transfer. Angular momentum carried by light can be, in many cases, divided in two terms. The… first one relates to the polarization of light and can be associated, in the quantum description, to the spin of a photon. The second is determined by the electromagnetic …field distribution and, in analogy to atomic physics, is associated with the orbital angular momentum (OAM) of a photon. Under the paraxial approximation appropriate for the case of beam propagation, the two terms do not couple. However, each of them can be modified by the interaction with different media in which the light propagates through processes which involve angular momentum exchange. The decoupling of spin and orbital parts of light angular momentum can not, in general, be assumed for non paraxial propagation in turbid media, especially when backscattering is concerned. In Chapter 3 of this dissertation, scattering effects on angular momentum of light are discussed both for the single and multiple scattering processes. It is demonstrated for the first time that scattering from a spherically symmetric scattering potential, couples the spin and the OAM such that the total angular momentum ‡flux density in conserved in every direction. Remarkably, the conservation of angular momentum occurs also for some classes of multiple scattering trajectories and this phenomenon manifests itself in ubiquitous polarization patterns observed in back-scattering from turbid media. It is newly shown in this dissertation that the polarization patterns a result of OAM carrying optical vortices which have a geometrical origin. These geometrical phase vortices are analyzed using the helicity space approach for optical geometrical phase (Berry phase). This approach, introduced in the con- text of random media, elucidates several aspects specific to propagation in helicity preserving and non-preserving scattering trajectories. Another aspect of singular waves interaction with turbid media relates to singularities embedded in the incident waves. Chapter 4 of the dissertation discusses how the phase distribution associated with an optical vortex leads to changes in the spatial correlations of the electromagnetic field. This change can be used to control the properties of the effect of enhanced backscattering in a way which allows inferring the optical properties of the medium. A detailed theoretical and experimental study of this effect is presented here for the first time for both double-pass geometries and diffusive media. It is also demonstrated that this novel experimental technique can be used to determine the optical properties of turbid media and, moreover, it permits to sense the depth of reflective inclusions in opaque media. When considering a regime of weakly inhomogeneous media, the paraxial approximation is still valid and therefore the spin and OAM do not couple. If, In addition, the medium is optically isotropic then the polarization is not affected. However, when the medium is non-axially symmetric for any specific realization, the OAM does change as a result of interaction with the medium. This effect can be studied using a newly developed method of coherent modes coupling which is presented in Chapter 5. This approach allows studying the power spread across propagating modes which carry different orbital angular momentum. The powerful concept of coherent modes coupling can be applied to fully coherent, fully polarized sources as well to partially coherent, partially polarized ones. An example of this scattering regime is atmospheric turbulence and the propagation through turbulence is thoroughly examined in Chapter 5. The results included in this dissertation are of fundamental relevance for a variety of applications which involves probing different types of random media. Such applications include remote sensing in atmospheric and maritime environments, optical techniques for biomedical diagnostics, optical characterization procedures in material sciences and others.
Show less
Date Issued: 2006
Identifier: CFE0001174, ucf:46852
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0001174

Title: IMPURITY AND INTERDIFFUSION IN THE MAGNESIUM-ALUMINUM SYSTEM.
Creator: Brennan, Sarah, Sohn, Yongho, University of Central Florida
Abstract / Description: Magnesium alloys offer a base of lightweight engineering materials for electronic, military and transportation applications where weight reduction is crucial for higher efficiency. Understanding fundamental diffusion behavior in Mg alloys elicits better materials properties through the optimization of processing techniques and heat treatments, whose material responses are affected by diffusion. The main objective of this study is to provide a clear, comprehensive description of the diffusion...
Show moreMagnesium alloys offer a base of lightweight engineering materials for electronic, military and transportation applications where weight reduction is crucial for higher efficiency. Understanding fundamental diffusion behavior in Mg alloys elicits better materials properties through the optimization of processing techniques and heat treatments, whose material responses are affected by diffusion. The main objective of this study is to provide a clear, comprehensive description of the diffusion behavior in the technically important magnesium-aluminum binary metallic system. In this study, diffusion in the Mg-Al system was observed through solid diffusion couples and thin film specimens in the temperature range of 673-523K. The formation and growth of the intermetallic phases, [two]-Mg2Al3 and [three]-Mg17Al12, and the absence of the [micro]-Mg23Al30 phase was observed. The [two]-Mg2Al3 phase grew thicker, had higher parabolic growth constants and lower activation energy for growth. Concentration-dependent interdiffusion coefficients were determined using the Boltzmann-Matano method. Interdiffusion in the [two]-Mg2Al3 phase was the highest, followed by the [three]-Mg17Al12 phase, the Al solid solution and the Mg solid solution. Intrinsic diffusion coefficients at the marker plane composition of 38 at.% Mg in the [two]-Mg2Al3 were determined from Heumann's method for Mg and Al, for which Al was higher. Extrapolations of the impurity diffusion coefficients in both terminal solid solutions were made and compared to available literature data. The thermodynamic factor, tracer diffusivity and atomic mobility of Mg and Al at the marker plane concentration were estimated using Mg activities in the [two]-Mg2Al3 available from literature. The impurity diffusion of Al and self-diffusion of the stable isotope, 25Mg, in polycrystalline Mg was measured from thin film specimens via depth profiling using secondary ion mass spectrometry. The Al impurity diffusion observed is compared to the extrapolations from the parallel interdiffusion study. The self-diffusion measurements are compared to reported literature values and were observed to be significantly higher. Several reasons for the observed difference in the magnitude of diffusivities are discussed.
Show less
Date Issued: 2011
Identifier: CFE0003984, ucf:48678
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0003984

Title: PHENOMENOLOGY AND EXPERIMENTAL OBSERVATIONS IN HIGH TEMPERATURE TERNARY INTERDIFFUSION.
Creator: Elliott, Abby Lee, Sohn, Yongho, University of Central Florida
Abstract / Description: A new method to extract composition dependent ternary interdiffusion coefficients from a single diffusion couple experiment is presented. The calculations involve direct determination of interdiffusion fluxes from experimental concentration profiles and local integration and differentiation of Onsager's formalism. This new technique was applied to concentration profiles obtained from selected semi-infinite, single-phase diffusion couple experiments in the Cu-Ni-Zn, Fe-Ni-Al, and Ni-Cr-Al...
Show moreA new method to extract composition dependent ternary interdiffusion coefficients from a single diffusion couple experiment is presented. The calculations involve direct determination of interdiffusion fluxes from experimental concentration profiles and local integration and differentiation of Onsager's formalism. This new technique was applied to concentration profiles obtained from selected semi-infinite, single-phase diffusion couple experiments in the Cu-Ni-Zn, Fe-Ni-Al, and Ni-Cr-Al systems. These couples exhibit features such as uphill diffusion and zero flux planes. The interdiffusion coefficients from the new technique along with coefficients reported from other methods are graphed as functions of composition. The coefficients calculated from the new technique are consistent with those determined from Boltzmann-Matano analysis and an alternate analysis based on the concept of average ternary interdiffusion coefficients. The concentration profiles generated from the error function solutions using the calculated interdiffusion coefficients are in good agreement with the experimental profiles including those exhibiting uphill diffusion. The new technique is checked for accuracy and consistency by back-calculating known interdiffusion coefficients; in this exercise, the new method accurately predicts constant diffusivity.After rigorous verification, the new technique is applied to previously unexamined couples in the Ni-Pt-Al system. With Ni as the dependent component, the main coefficients are shown to be relatively constant and the cross coefficients are negative. The interdiffusion coefficient representing the contribution of the concentration gradient of Pt to the interdiffusion flux of Al is relatively large for couples whose Al content is low, indicating that Pt has a significant effect on Al when Al concentration is low.Another important aspect of analyzing diffusional interactions is the movement of single and multi-phase boundaries within a diffusion couple. Phase boundaries for an n-component system are newly classified and boundary movement is analyzed in terms of degrees of freedom. Experimental evidence of a category 2:1 boundary is presented with a solid-to-solid semi-infinite diffusion couple in the Fe-Ni-Al system with two single-phase terminal alloys. The diffusion path for this couple surprisingly passes through the vertex of the equilibrium tie triangle on the phase diagram to exhibit three phase equilibria in a ternary system. Here is shown for the first time experimental verification of this phenomenon.
Show less
Date Issued: 2004
Identifier: CFE0000016, ucf:46101
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0000016

Title: Simultaneous Measurement of Isotope-free Tracer and Interdiffusion Coefficients in Sandwich Type Diffusion Couples.
Creator: Schulz, Esin, Sohn, Yongho, Bai, Yuanli, Florczyk, Stephen, Coffey, Kevin, Orlovskaya, Nina, University of Central Florida
Abstract / Description: The experimental determination of the tracer or self-diffusion coef?cient as a function of composition can be quite burdensome in alloys since separate measurements must be carried out for each alloy composition. A new formalism recently developed by I.V. Belova, N.S. Kulkarni, Y.H. Sohn and G.E. Murch, based on linear response theory combined with the Boltzmann(-)Matano method allows determination of tracer and interdiffusion coef?cients simultaneously from a single, isotope-free solid to...
Show moreThe experimental determination of the tracer or self-diffusion coef?cient as a function of composition can be quite burdensome in alloys since separate measurements must be carried out for each alloy composition. A new formalism recently developed by I.V. Belova, N.S. Kulkarni, Y.H. Sohn and G.E. Murch, based on linear response theory combined with the Boltzmann(-)Matano method allows determination of tracer and interdiffusion coef?cients simultaneously from a single, isotope-free solid to solid diffusion couple experiment. In this study, for the first time, an experimental investigation with an analytical approach based on the new formalism has been carried out in the binary Cu-Ni system. Pure Cu and Ni thin films were deposited in between several binary diffusion couples with varying terminal alloy compositions (such as Cu, Cu-25Ni, Cu-50Ni, Cu-75Ni, Ni). Diffusion couples were then annealed at 800(&)deg;C, 900(&)deg;C and 1000(&)deg;C. After annealing, the couples were water quenched, cross-sectioned, and prepared for compositional characterization. Scanning Electron Microscopy was employed to examine the interdiffusion zone. Energy Dispersive X-ray Spectroscopy was conducted to obtain concentration profiles for quantitative analysis. The superposition of the concentration profiles of thin film and interdiffusion were analyzed for the simultaneous determination of tracer and interdiffusion coefficients. The tracer diffusion coefficient of Cu, tracer diffusion coefficient of Ni and inter-diffusion coefficients simultaneously determined using the experimental methodology based on the novel formalism derived, and produced results consistent with previously reported values determined independently by radiotracer and interdiffusion experiments.
Show less
Date Issued: 2018
Identifier: CFE0007368, ucf:52101
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007368

Title: Characterization, Morphology, Oxidation, and Recession of Silicon Nanowires Grown by Electroless Process.
Creator: Mertens, Robert, Sundaram, Kalpathy, Yuan, Jiann-Shiun, Chow, Louis, Wahid, Parveen, Blair, Richard, University of Central Florida
Abstract / Description: This dissertation presents heretofore undiscovered properties of Silicon Nanowires (SiNWs) grown by electroless process and presents mathematical solutions to the special problems of the oxidation and diffusion of dopants for SiNWs. Also presented here is a mathematical description of morphology of oxidized SiNWs. This dissertation is comprised of several discussions relating to SiNWs growth, oxidation, morphology and doping.In here is presented work derived from a long-term study of SiNWs....
Show moreThis dissertation presents heretofore undiscovered properties of Silicon Nanowires (SiNWs) grown by electroless process and presents mathematical solutions to the special problems of the oxidation and diffusion of dopants for SiNWs. Also presented here is a mathematical description of morphology of oxidized SiNWs. This dissertation is comprised of several discussions relating to SiNWs growth, oxidation, morphology and doping.In here is presented work derived from a long-term study of SiNWs. Several important aspects of SiNWs were investigated and the results published in journals and conference papers. The recession of SiNWs was heretofore unreported by other research groups. In our investigations, this began as a question, (")How far into the substrate does the etching process go when this method is used to make SiNWs?(") Our investigations showed that recession did take place, was controllable and that a number of variables were responsible. The growth mechanism of SiNWs grown by electroless process is discussed at length. The relation of exposed area to volume of solution is shown, derived from experimentation. A relation of Silver used to Si removed is presented, derived from experimentation. The agglomeration of SiNWs grown by the electroless process is presented.The oxidation of SiNWs is a subject of interest to many groups, although most other groups work with SiNWs grown by the VLS process, which is more difficult, time-consuming and expensive to do. The oxidation of planar Silicon (Si) is still a subject of study, even today, after many years of working with and refining our formulae, because of the changing needs of this science and industry. SiNWs oxidation formulae are more complicated than those for planar Si, partly because of their morphology and partly because of their scale. While planar Si only presents one orientation for oxidation, SiNWs present a range of orientations, usually everything between (<)100(>) and (<)110(>) ( the (<)111(>) orientation is usually not presented during oxidation). This complicates the post-oxidation morphology to the extent that, subsequent to oxidation, SiNWs are more rectangular than cylindrical in shape. After etching to remove an oxidation layer from the SiNWs, the rectangular shape shifts 90(&)deg; in orientation.In traditional oxidation, the Deal-Grove formulae are used, but when the oxidation must take place in very small layers, such as with nanoscale devices, the Massoud formulae have to be used. However, even with Massoud, these formulae are not as good because of the morphology. Deal-Grove and Massoud formulae are intended for use with planar Si. We present some formulae that show the change in shape of SiNWs during oxidation, due to their morphology.The diffusion of dopants in SiNWs is a subject few research groups have taken up. Most of the groups who have, use SiNWs grown by the VLS method to make measurements and report findings. In order to measure the diffusion of dopants in SiNWs, a controllable diameter is needed. There are a number of ways to measure diffusion in SiNWs, but none of the ones used so far apply well to SiNWs grown by electroless process. Usually these groups present some mathematical formulae to predict diffusion in SiNWs, but these seem to lack mathematical rigor. Diffusion is a process that is best understood using Fick's Laws, which are applied to the problem of SiNWs in this dissertation.Diffusion is a science with a long history, going back at least 150 years. There are many formulae that can be used in the most common diffusion processes, but the processes involved with the diffusion of dopants in SiNWs is more complex than the simple diffusion processes that are fairly well-understood. Diffusion doping of SiNWs is a multiphase process that is more complex, first because it is multiphase and second because the second step involves a multiplicity of diffusing elements, plus oxidation, which brings on the problems of moving boundaries.In this dissertation, we present solutions to these problems, and the two-step diffusion process for SiNWs.
Show less
Date Issued: 2012
Identifier: CFE0004412, ucf:49366
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004412

Title: ON THE NATURE OF THE FLOW IN A SEPARATED ANNULAR DIFFUSER.
Creator: Dunn, Jason, Kapat, Jayanta, University of Central Florida
Abstract / Description: The combustor-diffuser system remains one of the most studied sections of the turbomachine. Most of these investigations are due to the fact that quite a bit of flow diffusion is required in this section as the high speed flow exits the compressor and must be slowed down to enter the combustor. Like any diffusion process there is the chance for the development of an unfavorable adverse pressure gradient that can lead to flow separation; a cause of drastic losses within a turbine. There are...
Show moreThe combustor-diffuser system remains one of the most studied sections of the turbomachine. Most of these investigations are due to the fact that quite a bit of flow diffusion is required in this section as the high speed flow exits the compressor and must be slowed down to enter the combustor. Like any diffusion process there is the chance for the development of an unfavorable adverse pressure gradient that can lead to flow separation; a cause of drastic losses within a turbine. There are two diffusion processes in the combustor-diffuser system: The flow first exits the compressor into a pre-diffuser, or compressor discharge diffuser. This diffuser is responsible for a majority of the pressure recovery. The flow then exits the pre-diffuser by a sudden expansion into the dump diffuser. The dump diffuser comprises the majority of the losses, but is necessary to reduce the fluid velocity within acceptable limits for combustion. The topic of active flow control is gaining interest in the industry because such a technique may be able to alleviate some of the requirements of the dump diffuser. If a wider angle pre-diffuser with separation control were used the fluid velocity would be slowed more within that region without significant losses. Experiments were performed on two annular diffusers to characterize the flow separation to create a foundation for future active flow control techniques. Both diffusers had the same fully developed inlet flow condition, however, the expansion of the two diffusers differed such that one diffuser replicated a typical compressor discharge diffuser found in a real machine while the other would create a naturally separated flow along the outer wall. Both diffusers were tested at two Reynolds numbers, 5x104 and 1x105, with and without a vertical wall downstream of the exit to replicate the dump diffuser that re-directs the flow from the pre-diffuser outlet to the combustor. Static pressure measurements were obtained along the OD and ID wall of the diffusers to determine the recovered pressure throughout the diffuser. In addition to these measurements, tufts were used to visualize the flow. A turbulent CFD model was also created to compare against experimental results. In the end, the results were validated against empirical data as well as the CFD model. It was shown that the location of the vertical wall was directly related to the amount of separation as well as the separation characteristics. These findings support previous work and help guide future work for active flow control in a separated annular diffuser both computationally and experimentally.
Show less
Date Issued: 2009
Identifier: CFE0002953, ucf:47944
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0002953

Title: STUDY OF DISCHARGE COEFFICIENT AND TRENDS IN FILM COOLING EFFECTIVENESS OF CONICAL HOLES WITH INCREASING DIFFUSION ANGLES.
Creator: Zuniga, Humberto, Kapat, Jayanta, University of Central Florida
Abstract / Description: Previous studies indicate that increasing the diffusion angle in conical film-cooling holes leads to an improvement in their film cooling effectiveness. Discharge coefficient and film cooling effectiveness measurements are conducted to characterize this behavior. Part of the focus of this investigation is to find out how this trend develops and attempt to ascertain the optimum cone angle, if possible. Six test plates, each with one row of eight conical-shaped cooling holes of equal diffusion...
Show morePrevious studies indicate that increasing the diffusion angle in conical film-cooling holes leads to an improvement in their film cooling effectiveness. Discharge coefficient and film cooling effectiveness measurements are conducted to characterize this behavior. Part of the focus of this investigation is to find out how this trend develops and attempt to ascertain the optimum cone angle, if possible. Six test plates, each with one row of eight conical-shaped cooling holes of equal diffusion angles of 0, 1, 2, 3, 6, or 8º, with respect to the hole axis are used in this study. The ratios of the hole exit areas to the inlet areas range from 1 to 2.85. Coolant injection angle for all holes is at 35 degrees to the horizontal, in the direction of the main flow. Coefficients of discharge of all holes are reported under flow conditions. Temperature sensitive paint, TSP, is the technique used to find the temperature distribution downstream of the cooling holes and determine the laterally averaged film-cooling effectiveness. Data are obtained for blowing ratios ranging from 0.5 to 1.5, at a constant density ratio of 1.26. Results and trends are compared with established literature, which also recommends that a cylindrical entry length for diffused holes should be at least 4 diameters long. The effect that an added entry length has on the 3-degree conical plate's cooling effectiveness is also explored. Data are compared to baseline cylindrical holes, as well as to fan-shaped film holes found in open literature. Results indicate that the conical holes with larger diffusion angles provide strikingly even film protection and outperform fan shaped and cylindrical holes under certain conditions over extended downstream distances. Also, the addition of a cylindrical entry length to a conical hole, by providing a manageable metering diameter, should ease their usage while providing the full benefits of the conical geometry which may one day lead to numerous industrial applications.
Show less
Date Issued: 2006
Identifier: CFE0001492, ucf:47087
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0001492

Title: Interdiffusion reaction between uranium-zirconium and iron.
Creator: Park, Young Joo, Sohn, Yongho, Coffey, Kevin, Fang, Jiyu, University of Central Florida
Abstract / Description: U-Zr metallic fuels cladded in Fe-alloys are being considered for application in an advanced Sodium-Cooled Fast Reactor (SFR) that can recycle the U-Zr fuels and minimize the long-lived actinide waste. To understand the complex fuel-cladding chemical interaction of the U-Zr metallic fuel with Fe-alloys, a systematic multicomponent diffusion study was carried out using solid-to-solid diffusion couples. The U-10 wt.% Zr vs. pure Fe diffusion couples were assembled and annealed at temperatures,...
Show moreU-Zr metallic fuels cladded in Fe-alloys are being considered for application in an advanced Sodium-Cooled Fast Reactor (SFR) that can recycle the U-Zr fuels and minimize the long-lived actinide waste. To understand the complex fuel-cladding chemical interaction of the U-Zr metallic fuel with Fe-alloys, a systematic multicomponent diffusion study was carried out using solid-to-solid diffusion couples. The U-10 wt.% Zr vs. pure Fe diffusion couples were assembled and annealed at temperatures, 630, 650 and 680(&)deg;C for 96 hours. Development of microstructure, phase constituents, and compositions developed during the thermal anneals were examined by scanning electron microscopy, transmission electron microscopy and X-ray energy dispersive spectroscopy. A complex microstructure consisting of several layers that include phases such as U6Fe, UFe2, ZrFe2, ?-U, ?-U, Zr-precipitates, ?, ?, and ? was observed. Multi-phase layers were grouped based on phase constituents and microstructure, and the layer thicknesses were measured to calculate the growth constant and activation energy. The local average compositions through the interaction layer were systematically determined, and employed to construct semi-quantitative diffusion paths on isothermal U-Zr-Fe ternary phase diagrams at respective temperatures. The diffusion paths were examined to qualitatively estimate the diffusional behavior of individual components and their interactions. Furthermore, selected area diffraction analyses were carried out to determine, for the first time, the exact crystal structure and composition of the ?, ? and ?-phases. The ?, ? and ?-phases were identified as Pnma(62) Fe(Zr,U), I4/mcm(140) Fe(Zr,U)2, and I4/mcm(140) U3(Zr,Fe), respectively.
Show less
Date Issued: 2013
Identifier: CFE0004908, ucf:49616
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004908

Title: Multifunctional and Responsive Polyelectrolyte Nanostructures.
Creator: Malhotra, Astha, Zhai, Lei, Kolpashchikov, Dmitry, Ye, Jingdong, Chumbimuni Torres, Karin, Santra, Swadeshmukul, Fang, Jiyu, University of Central Florida
Abstract / Description: A polyelectrolyte complex is formed by mixing two oppositely charged polyelectrolytes in a solution. The electrostatic interactions between partially charged polymeric chains lead to the formation of a stable complex while avoiding the use of covalent cross linkers. Since complex formation can improve the stability of polyelectrolyte and metal ions in polyelectrolyte can provide various functionalities, PECs incorporated with metal ions are promising candidates for manufacturing stable and...
Show moreA polyelectrolyte complex is formed by mixing two oppositely charged polyelectrolytes in a solution. The electrostatic interactions between partially charged polymeric chains lead to the formation of a stable complex while avoiding the use of covalent cross linkers. Since complex formation can improve the stability of polyelectrolyte and metal ions in polyelectrolyte can provide various functionalities, PECs incorporated with metal ions are promising candidates for manufacturing stable and multifunctional structures. While the coordination of metal ions and polyelectrolytes has been extensively investigated in solutions and multilayer films, to our knowledge, no research has been performed to study the effect of metal ion/polyelectrolyte interactions on PECs structures and properties. The following research demonstrates the impact of different metal ions in controlling PEC structure morphology and applications. These discoveries indicate great potential of metal ions in PECs to fabricate functional PEC nanostructures.The research investigates the effect of the interactions between different metal ions and polyelectrolytes on the morphology and properties of PECs, explore the fabrication of different structures using embedded metal ions and understand the impact of metal ion/polyelectrolyte interactions on the nanoparticle structures. The research concludes: 1) incorporating metal ions of different valence into PECs introduces metal ion/polyelectrolyte interactions that can tune the morphology of PECs; 2) metal ion/polyelectrolyte interactions can be used to control the PECs swelling properties and stability in aqueous solutions; 3) the release of embedded metal ions from PECs to aqueous solutions is affected by metal ion/polyelectrolyte interactions; and 4) the embedded metal ions function as a reagent reservoir for various applications to produce functional structures. ?
Show less
Date Issued: 2014
Identifier: CFE0005833, ucf:50918
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005833

Title: Phase transformation and growth kinetics in reaction zone between uranium alloy and zirconium diffusion barrier.
Creator: Park, Young Joo, Sohn, Yongho, Coffey, Kevin, Fang, Jiyu, University of Central Florida
Abstract / Description: U-10wt.%Mo (U10Mo) alloy as a part of monolithic fuel system is being developed under Material Management and Minimization Reactor Conversion (MMMRC) program, tasked with replacing high-enriched uranium (HEU) fuel with low-enriched uranium (LEU) fuel in civilian research and test reactors. Use of U10Mo fuel alloy entails a Zr diffusion barrier to avoid the undesirable interdiffusion and reactions between the U10Mo and Al-alloy cladding. To better understand the interaction between these fuel...
Show moreU-10wt.%Mo (U10Mo) alloy as a part of monolithic fuel system is being developed under Material Management and Minimization Reactor Conversion (MMMRC) program, tasked with replacing high-enriched uranium (HEU) fuel with low-enriched uranium (LEU) fuel in civilian research and test reactors. Use of U10Mo fuel alloy entails a Zr diffusion barrier to avoid the undesirable interdiffusion and reactions between the U10Mo and Al-alloy cladding. To better understand the interaction between these fuel system constituents, microstructural development and diffusion kinetics in U-Mo-Zr, U-Zr and fuel plate assembly processed by co-rolling and hot isostatic pressing (HIP) were investigated using a variety of analytical techniques accompanying scanning electron microscopy and transmission electron microscopy.Phase constituents, microstructure and diffusion kinetics between U10Mo and Zr were examined using solid-to-solid diffusion couples annealed at 650 (&)deg;C for 240, 480 and 720 hours. Concentration profiles were mapped as diffusion paths on the isothermal ternary phase diagram. Within the diffusion zone, single-phase layers of (?U,?Zr) were observed along with a discontinuous layer of Mo2Zr between the ?Zr and ?U layers. In the vicinity of Mo2Zr phase, islands of ?Zr phase were also found. In addition, acicular ?Zr and U6Zr3Mo phases were observed within the ?U(Mo). Growth rate of the interdiffusion-reaction zone was determined to be 1.81 (&)#215; 10-15 m2/sec at 650 (&)deg;C, however with an assumption of a certain incubation period.Investigation for interdiffusion and reaction between U and Zr were carried out using solid-to-solid diffusion couples annealed at 580, 650, 680 and 710 (&)deg;C. The interdiffusion and reaction layer consisted of ?U containing Zr acicular precipitate, ?' (oC4-variant) and (?U,?Zr) solid solution at 650, 680 and 710 (&)deg;C. The ?-UZr2 phase, instead of (?U,?Zr) solid solution phase, was observed in the couple annealed at 580 (&)deg;C. The interdiffusion fluxes and coefficients were determined for the ?U, (?U,?Zr) and ?-UZr2 (580 ?C only) phases using both Sauer-Freise and Boltzmann-Matano analyses. For the ?'-phase with negligible concentration gradient, integrated interdiffusion coefficients were determined via Wagner method. Marker plane was found in (?U,?Zr) (cI2) solid solution from the couples annealed at 650, 680 and 710 (&)deg;C and ?-UZr2 from the couple at 580 (&)deg;C. Intrinsic diffusion coefficients at the compositions corresponding to the marker plane were determined based on Heumann analysis: U intrinsically diffused an order magnitude faster than Zr. Arrhenius temperature-dependence, Darken relation, and comparison to existing literature data demonstrated consistency in results.Monolithic fuel plate assembly was fabricated by sequential process of (1) co-rolling to laminate the Zr barrier onto the U10Mo fuel alloy and (2) HIP to encase the fuel laminated with Zr, within the Al-alloy 6061 (AA6061). In this study, HIP process was carried out as functions of temperature (520, 540, 560 and 580 (&)deg;C for 90 minutes), time (45, 60, 90, 180 and 345 minutes at 560 (&)deg;C) with ramp-cool rate (35, 70 and 280 (&)deg;C/hour). At the interface between the U10Mo and Zr, following the co-rolling, the UZr2 phase was observed to develop adjacent to Zr, and the ?U phase was found between the UZr2 and U10Mo. Mo2Zr was found as precipitates mostly within the ?U phase. Observable growth due to HIP was only observed for the (Al,Si)3Zr phase found at the Zr/AA6061 interface, however, with a large activation energy of 457 kJ/mol. Decomposition of ?U into ?U and ?' was observed in the U10Mo alloy. The volume fraction of ? and ?' increased as the HIP temperature and ramp-cool rate decreased. The UC-UO2 inclusions within the U10Mo fuel alloy were observed, but the volume percent of the UC-UO2 inclusions within the U10Mo alloy, ranging from approximately 0.5 to 1.8, did not change as functions of HIP temperature and holding time. However, the inclusions located near the surface of the U10Mo alloy, were frequently observed to interfere the uniformity of interdiffusion and reaction between the U10Mo alloy and Zr diffusion barrier. The regions of limited interaction between the U10Mo and Zr barrier associated with UC-UO2 inclusions decreased with an increase in HIP temperature, however no significant trend was observed with an increase in HIP duration at 560 (&)deg;C.
Show less
Date Issued: 2016
Identifier: CFE0006371, ucf:51499
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006371

Title: Interdiffusion and Impurity Diffusion in Magnesium Solid Solutions.
Creator: Kammerer, Catherine, Sohn, Yongho, Coffey, Kevin, Suryanarayana, Challapalli, Gordon, Ali, University of Central Florida
Abstract / Description: Magnesium, being lightweight, offers potential to be developed into extensive structural applications. The transportation segment has particular interest in Mg and Mg alloy for applications where reduced vehicle weight is proportional to increased fuel efficiency. Aluminum and zinc are two of the most common alloying elements in commercial Mg alloys. They improve the physical properties of Mg through solid solution strengthening and precipitation hardening. Diffusion plays a key role in the...
Show moreMagnesium, being lightweight, offers potential to be developed into extensive structural applications. The transportation segment has particular interest in Mg and Mg alloy for applications where reduced vehicle weight is proportional to increased fuel efficiency. Aluminum and zinc are two of the most common alloying elements in commercial Mg alloys. They improve the physical properties of Mg through solid solution strengthening and precipitation hardening. Diffusion plays a key role in the kinetics of and microstructural development during solidification and heat treatment. However, there is limited diffusion data available for Mg and Mg alloys. In particular, because Al is mono-isotopic, tracer diffusion data is not available. Interdiffusion of Mg solid solution with Zn also does not exist in literature. The diffusional interaction of Al and Zn in Mg solid solution at temperatures ranging from 623 (-) 723K was examined using solid-to-solid diffusion couple method. The objective of this thesis is two-fold: first, is the examination of interdiffusion in the Mg solid solution phase of the binary Mg-Al and Mg-Zn systems; second, is to explore non-conventional analytical methods to determine impurity diffusion coefficients. The quality of diffusion bonding was examined by optical microscopy and scanning electron microscopy with X-ray energy dispersive spectroscopy, and concentration profiles were determined using electron probe microanalysis with pure standards and ZAF matrix correction. Analytical methods of concentration profiles based on Boltzmann-Matano analysis for binary alloys are presented along with compositional dependent interdiffusion coefficients. As the concentration of Al or Zn approaches the dilute ends, an analytical approach based on the Hall method was employed to estimate the impurity diffusion coefficients.Zinc was observed to diffuse faster than Al, and in fact, the impurity diffusion coefficient of Al was smaller than the self-diffusion coefficient of Mg. In the Mg solid solution with Al, interdiffusion coefficients increased by an order of magnitude with an increase in Al concentration. Activation energy and pre-exponential factor for the average effective interdiffusion coefficient in Mg solid solution with Al was determined to be 186.8 KJ/mole and 7.69 x 10-1 m^2/sec. On the other hand, in the Mg solid solution with Zn, interdiffusion coefficients did not vary significantly as a function of Zn concentration. Activation energy and pre-exponential factor for the average effective interdiffusion coefficient in Mg solid solution with Zn was determined to be 129.5 KJ/mole and 2.67 x 10-4 m^2/sec. Impurity diffusion coefficients of Al in Mg was determined to have activation energy and pre-exponential factor of 144.1 KJ/mole and 1.61 x 10-4 m^2/sec. Impurity diffusion coefficients of Zn in Mg was determined to have activation energy and pre-exponential factor of 109.8 KJ/mole and 1.03 x 10-5 m^2/sec. Temperature and composition-dependence of interdiffusion coefficients and impurity diffusion coefficients are examined with respect to reported values in literature, thermodynamic factor, ?, diffusion mechanisms in hexagonal close packed structure, and experimental uncertainty.
Show less
Date Issued: 2013
Identifier: CFE0004699, ucf:49851
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004699

Title: Experimental and Numerical Investigation of Aerodynamic Unsteadiness in a Gas Turbine Midframe.
Creator: Golsen, Matthew, Kapat, Jayanta, Vasu Sumathi, Subith, Sultanian, Bijay, University of Central Florida
Abstract / Description: As modern gas turbines implement more and more complex geometry to increase life and efficiency, attention to unsteady aerodynamic behavior becomes more important. Computational optimization schemes are contributing to advanced geometries in order to reduce aerodynamic losses and increase the life of components. These advanced geometries are less representative of cylinder and backward facing steps which have been used as analogous geometries for most aerodynamic unsteadiness research. One...
Show moreAs modern gas turbines implement more and more complex geometry to increase life and efficiency, attention to unsteady aerodynamic behavior becomes more important. Computational optimization schemes are contributing to advanced geometries in order to reduce aerodynamic losses and increase the life of components. These advanced geometries are less representative of cylinder and backward facing steps which have been used as analogous geometries for most aerodynamic unsteadiness research. One region which contains a high degree of flow unsteadiness and a direct influence on engine performance is that of the MidFrame. The MidFrame (or combustor-diffuser system) is the region encompassing the main gas path from the exit of the compressor to the inlet of the first stage turbine. This region contains myriad flow scenarios including diffusion, bluff bodies, direct impingement, high degree of streamline curvature, separated flow, and recirculation. This represents the most complex and diverse flow field in the entire engine. The role of the MidFrame is to redirect the flow from the compressor into the combustion system with minimal pressure loss while supplying high pressure air to the secondary air system. Various casing geometries, compressor exit diffuser shapes, and flow conditioning equipment have been tested to reduce pressure loss and increase uniformity entering the combustors. Much of the current research in this area focuses on aero propulsion geometries with annular combustors or scaled models of the power generation geometries. Due to the complexity and size of the domain accessibility with physical probe measurements becomes challenging. The current work uses additional measurement techniques to measure flow unsteadiness in the domain. The methodology for identifying and quantifying the sources of unsteadiness are developed herein. Sensitivity of MidFrame unsteadiness to compressor exit conditions is shown for three different velocity profiles. The result is an extensive database of measurements which can serve as a benchmark for radical new designs to ensure that the unsteadiness levels do not supersede previous successful levels.
Show less
Date Issued: 2013
Identifier: CFE0004851, ucf:49682
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004851

Title: Diffusion and reaction in selected uranium alloy system.
Creator: Huang, Ke, Sohn, Yongho, An, Linan, Xu, Chengying, Coffey, Kevin, Heinrich, Helge, University of Central Florida
Abstract / Description: U-Mo metallic fuels with Al alloys as the matrix/cladding are being developed as low enriched uranium fuels under the Reduced Enrichment for Research and Test Reactor (RERTR) program. Significant interactions have been observed to occur between the U-Mo fuel and the Al alloy during fuel processing and irradiation. U-Zr metallic fuels with stainless steel claddings have been developed for the generation IV sodium fast reactor (SFR). The fuel cladding chemical interaction (FCCI) induced by the...
Show moreU-Mo metallic fuels with Al alloys as the matrix/cladding are being developed as low enriched uranium fuels under the Reduced Enrichment for Research and Test Reactor (RERTR) program. Significant interactions have been observed to occur between the U-Mo fuel and the Al alloy during fuel processing and irradiation. U-Zr metallic fuels with stainless steel claddings have been developed for the generation IV sodium fast reactor (SFR). The fuel cladding chemical interaction (FCCI) induced by the interdiffusion of components was also observed. These interactions induce deleterious effects on the fuel system, such as thinning of the cladding layer, formation of phases with undesirable properties, and thermal cracking due to thermal expansion mismatches and changes in molar volume. The interaction between the fuel and the cladding involves multi-component interdiffusion. To determine the ternary interdiffusion coefficients using a single diffusion couple, a new method based on regression via the matrix transformation approach is proposed in this study. This new method is clear in physical meaning and simple in mathematical calculation. The reliability and accuracy of this method have been evaluated through application to three case studies: a basic asymptotic concentration profile, a concentration profile with extrema and a smoothed concentration profile with noise. Generally, this new method works well in all three cases.In order to investigate the interdiffusion behavior in U-Mo alloys, U vs. Mo diffusion couples were assembled and annealed in the temperature range of 650 to 1000(&)deg;C. The interdiffusion microstructures and concentration profiles were examined via scanning electron microscopy (SEM) and electron probe microanalysis (EPMA), respectively. Interdiffusion coefficients and activation energies were calculated as functions of temperature and Mo composition. The intrinsic diffusion coefficients of U and Mo at the marker composition were also determined. The activity of U and the thermodynamic factor of the U-Mo alloy have been calculated using the ideal solution, the regular solution, and the subregular solution models based on the molar excess Gibbs free energy of the U-Mo alloy. The calculated intrinsic diffusivities of U and Mo along with the thermodynamic factor of the U-Mo alloy were employed to estimate the atomic mobilities and the vacancy wind effects of U and Mo according to Manning's description.To explore potential diffusion barrier materials for reducing the fuel cladding chemical interaction between the U-Mo fuel and the Al alloy matrix/cladding, the interdiffusion behavior between U-Mo alloys and Mo, Zr, Nb and Mg were systematically studied. U-10wt.%Mo vs. Mo, Zr and Nb diffusion couples were annealed in the temperature range from 600 to 1000(&)deg;C. A diffusion couple between U-7wt.%Mo and Mg was annealed at 550(&)deg;C for 96 hours. SEM and transmission electron microscopy (TEM) were applied to characterize the microstructure of the interdiffusion zone. X-ray energy dispersive spectroscopy (XEDS) and EPMA were utilized to examine the concentration redistribution and the phase constituents. For the U-Mo vs. Mo diffusion couples, the interdiffusion coefficients at high Mo concentrations ranging from 22 to 32 at.%Mo were determined for the first time. In the U-Mo vs. Zr diffusion couples, the Mo2Zr phase was found at the interface. The diffusion paths were estimated and investigated according to the Mo-U-Zr ternary phase diagram. Thermal cracks and pure U precipitates were found within the diffusion zone in the U-Mo vs. Nb system. The growth rate of the interdiffusion zone was found to be lower by about 103 times for Zr, 105 times for Mo and 106 times for Nb compared to those observed in the U-10wt.%Mo vs. Al or Al-Si systems. For the diffusion couple of U-Mo vs. Mg, the U-Mo was bonded very well to the Mg and there was negligible diffusion observed even after 96 hours annealing at 550(&)deg;C.For a more fundamental understanding of the complex diffusion behavior between U-Zr fuels and their stainless steel claddings, U vs. Fe, Fe-15wt.%Cr and Fe-15wt.%Cr-15wt.%Ni diffusion couples were examined to investigate the interdiffusion behaviors between U and Fe and the effects of the alloying elements Cr and Ni. The diffusion couples were annealed in the temperature range from 580 to 700(&)deg;C for various times. Two intermetallic phases, U6Fe and UFe2, developed in all of the diffusion couples with the U6Fe layer growing faster than the UFe2 layer. For the diffusion couples of U vs. Fe, extrinsic growth constants, intrinsic growth constants, integrated interdiffusion coefficients and activation energies in each phase were calculated. The results suggest that U6Fe impeded the growth of UFe2, and the boundary condition change caused by the allotropic transformation of U played a role in the growth of the U6Fe and UFe2 layers. The reasons why U6Fe grew much faster than UFe2 are also discussed. The additions of Cr and Ni into Fe affected the growth rates of U6Fe and UFe2. The solubility of Cr and Ni in U6Fe and UFe2 were determined, and it was found that Cr diffused into U more slowly than Fe or Ni.
Show less
Date Issued: 2012
Identifier: CFE0004548, ucf:49238
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004548

Title: ON THE USE OF VARIABLE COHERENCE IN INVERSE SCATTERING PROBLEMS.
Creator: Baleine, Erwan, Dogariu, Aristide, University of Central Florida
Abstract / Description: Even though most of the properties of optical fields, such as wavelength, polarization, wavefront curvature or angular spectrum, have been commonly manipulated in a variety of remote sensing procedures, controlling the degree of coherence of light did not find wide applications until recently. Since the emergence of optical coherence tomography, a growing number of scattering techniques have relied on temporal coherence gating which provides efficient target selectivity in a way achieved only...
Show moreEven though most of the properties of optical fields, such as wavelength, polarization, wavefront curvature or angular spectrum, have been commonly manipulated in a variety of remote sensing procedures, controlling the degree of coherence of light did not find wide applications until recently. Since the emergence of optical coherence tomography, a growing number of scattering techniques have relied on temporal coherence gating which provides efficient target selectivity in a way achieved only by bulky short pulse measurements. The spatial counterpart of temporal coherence, however, has barely been exploited in sensing applications. This dissertation examines, in different scattering regimes, a variety of inverse scattering problems based on variable spatial coherence gating. Within the framework of the radiative transfer theory, this dissertation demonstrates that the short range correlation properties of a medium under test can be recovered by varying the size of the coherence volume of an illuminating beam. Nonetheless, the radiative transfer formalism does not account for long range correlations and current methods for retrieving the correlation function of the complex susceptibility require cumbersome cross-spectral density measurements. Instead, a variable coherence tomographic procedure is proposed where spatial coherence gating is used to probe the structural properties of single scattering media over an extended volume and with a very simple detection system. Enhanced backscattering is a coherent phenomenon that survives strong multiple scattering. The variable coherence tomography approach is extended in this context to diffusive media and it is demonstrated that specific photon trajectories can be selected in order to achieve depth-resolved sensing. Probing the scattering properties of shallow and deeper layers is of considerable interest in biological applications such as diagnosis of skin related diseases. The spatial coherence properties of an illuminating field can be manipulated over dimensions much larger than the wavelength thus providing a large effective sensing area. This is a practical advantage over many near-field microscopic techniques, which offer a spatial resolution beyond the classical diffraction limit but, at the expense of scanning a probe over a large area of a sample which is time consuming, and, sometimes, practically impossible. Taking advantage of the large field of view accessible when using the spatial coherence gating, this dissertation introduces the principle of variable coherence scattering microscopy. In this approach, a subwavelength resolution is achieved from simple far-zone intensity measurements by shaping the degree of spatial coherence of an evanescent field. Furthermore, tomographic techniques based on spatial coherence gating are especially attractive because they rely on simple detection schemes which, in principle, do not require any optical elements such as lenses. To demonstrate this capability, a correlated lensless imaging method is proposed and implemented, where both amplitude and phase information of an object are obtained by varying the degree of spatial coherence of the incident beam. Finally, it should be noted that the idea of using the spatial coherence properties of fields in a tomographic procedure is applicable to any type of electromagnetic radiation. Operating on principles of statistical optics, these sensing procedures can become alternatives for various target detection schemes, cutting-edge microscopies or x-ray imaging methods.
Show less
Date Issued: 2006
Identifier: CFE0001387, ucf:47005
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0001387

Title: LOW REYNOLDS NUMBER WATER FLOW CHARACTERISTICS THROUGH RECTANGULAR MICRO DIFFUSERS/NOZZLES WITH A PRIMARY FOCUS ON MAJOR/MINOR PRESSURE LOSS, STATIC PRESSURE RECOVERY, AND FLOW SEPARATION.
Creator: Hallenbeck, Kyle, Chew, Larry, University of Central Florida
Abstract / Description: The field of microfluidics has recently been gathering a lot of attention due to the enormous demand for devices that work in the micro scale. The problem facing many researchers and designers is the uncertainty in using macro scaled theory, as it seems in some situations they are incorrect. The general idea of this work was to decide whether or not the flow through micro diffusers and nozzles follow the same trends seen in macro scale theory. Four testing wafers were fabricated using PDMS...
Show moreThe field of microfluidics has recently been gathering a lot of attention due to the enormous demand for devices that work in the micro scale. The problem facing many researchers and designers is the uncertainty in using macro scaled theory, as it seems in some situations they are incorrect. The general idea of this work was to decide whether or not the flow through micro diffusers and nozzles follow the same trends seen in macro scale theory. Four testing wafers were fabricated using PDMS soft lithography including 38 diffuser/nozzle channels a piece. Each nozzle and diffuser consisted of a throat dimension of 100μm x 50μm, leg lengths of 142μm, and half angles varying from 0o – 90o in increments of 5o. The flow speeds tested included throat Reynolds numbers of 8.9 – 89 in increments of 8.9 using distilled water as the fluid. The static pressure difference was measured from the entrance to the exit of both the diffusers and the nozzles and the collected data was plotted against a fully attached macro theory as well as Idelchik's approximations. Data for diffusers and nozzles up to HA = 50o hints at the idea that the flow is neither separating nor creating a vena contracta. In this region, static pressure recovery within diffuser flow is observed as less than macro theory would predict and the losses that occur within a nozzle are also less than macro theory would predict. Approaching a 50o HA and beyond shows evidence of unstable separation and vena contracta formation. In general, it appears that there is a micro scaled phenomenon happening in which flow gains available energy when the flow area is increased and looses available energy when the flow area decreases. These new micro scaled phenomenon observations seem to lead to a larger and smaller magnitude of pressure loss respectively.
Show less
Date Issued: 2008
Identifier: CFE0002391, ucf:47772
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0002391

Title: End to End Brain Fiber Orientation Estimation Using Deep Learning.
Creator: Puttashamachar, Nandakishore, Bagci, Ulas, Shah, Mubarak, Rahnavard, Nazanin, Sundaram, Kalpathy, University of Central Florida
Abstract / Description: In this work, we explore the various Brain Neuron tracking techniques, one of the most significant applications of Diffusion Tensor Imaging. Tractography is a non-invasive method to analyze underlying tissue micro-structure. Understanding the structure and organization of the tissues facilitates a diagnosis method to identify any aberrations which can occurwithin tissues due to loss of cell functionalities, provides acute information on the occurrences of brain ischemia or stroke, the...
Show moreIn this work, we explore the various Brain Neuron tracking techniques, one of the most significant applications of Diffusion Tensor Imaging. Tractography is a non-invasive method to analyze underlying tissue micro-structure. Understanding the structure and organization of the tissues facilitates a diagnosis method to identify any aberrations which can occurwithin tissues due to loss of cell functionalities, provides acute information on the occurrences of brain ischemia or stroke, the mutation of certain neurological diseases such as Alzheimer, multiple sclerosis and so on. Under all these circumstances, accurate localization of the aberrations in efficient manner can help save a life. Following up with the limitations introduced by the current Tractography techniques such as computational complexity, reconstruction errors during tensor estimation and standardization, we aim to elucidate these limitations through our research findings. We introduce an End to End Deep Learning framework which can accurately estimate the most probable likelihood orientation at each voxel along a neuronal pathway. We use Probabilistic Tractography as our baseline model to obtain the training data and which also serve as a Tractography Gold Standard for our evaluations. Through experiments we show that our Deep Network can do a significant improvement over current Tractography implementations by reducing the run-time complexity to a significant new level. Our architecture also allows for variable sized input DWI signals eliminating the need to worry about memory issues as seen with the traditional techniques. The advantageof this architecture is that it is perfectly desirable to be processed on a cloud setup and utilize the existing multi GPU frameworks to perform whole brain Tractography in minutes rather than hours. The proposed method is a good alternative to the current state of the art orientation estimation technique which we demonstrate across multiple benchmarks.
Show less
Date Issued: 2017
Identifier: CFE0007292, ucf:52156
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007292

Title: Fundamental core effects in Co-Cr-Fe-Ni based high entropy alloys.
Creator: Mehta, Abhishek, Sohn, Yongho, Coffey, Kevin, Kushima, Akihiro, Jiang, Tengfei, Stolbov, Sergey, University of Central Florida
Abstract / Description: High entropy alloys (HEAs) are near equiatomic multi-principal-element-alloys (MPEAs) which are different from traditional solvent-based multicomponent alloys. Based on initial work by Yeh and Co-workers, they were proposed to exhibit four (")core(") effects: high entropy, sluggish diffusion, lattice distortion, and cocktail effect. Present work investigates two of the four (")core(") effects, i.e. high entropy and sluggish diffusion effects, in Co-Cr-Fe-Ni based transition metal high entropy...
Show moreHigh entropy alloys (HEAs) are near equiatomic multi-principal-element-alloys (MPEAs) which are different from traditional solvent-based multicomponent alloys. Based on initial work by Yeh and Co-workers, they were proposed to exhibit four (")core(") effects: high entropy, sluggish diffusion, lattice distortion, and cocktail effect. Present work investigates two of the four (")core(") effects, i.e. high entropy and sluggish diffusion effects, in Co-Cr-Fe-Ni based transition metal high entropy alloys. Solid-to-solid diffusion couple approach was adopted to investigate, these core effects. Experimental results contradicts the (")high entropy(") effect based on thermodynamics analysis: that the HEAs with low entropy of mixing may be thermodynamically more stable than the HEA of similar constituent elements with high entropy of mixing. In such cases, enthalpy of mixing can also play a vital role in stabilizing the HEA with lower entropy of mixing. Measurement of diffusion coefficients (i.e. both interdiffusion and tracer diffusion coefficients) in HEAs and its comparison with conventional solvent-based multicomponent alloys suggests that diffusion is not always sluggish in high entropy alloys. Contrary to previous findings, larger fluctuations in lattice potential energy (LPE) of an alloy may not always result in anomalously slow diffusion, in comparison to alloy systems which exhibits smaller fluctuation in LPE. Findings from his dissertation provide a (")controversial(") understanding of high entropy alloys, and alloy development strategies in the future for the most aggressive applications such as those found in gas turbines and nuclear reactors. As these applications will certainly require the knowledge of high temperature stability and nature of diffusion under extreme application environment.
Show less
Date Issued: 2019
Identifier: CFE0007501, ucf:52645
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007501

Title: THREE STUDIES RELATED TO THE INSTITUTIONALIZATION OF INTERNATIONAL FINANCIAL REPORTING STANDARDS.
Creator: Alon, Anna, Dwyer, Peggy, University of Central Florida
Abstract / Description: This dissertation consists of three separate, but related, studies on the institutionalization of International Financial Reporting Standards (IFRS). The first study examines the relationship between the national variables and the level of IFRS adoption. Theoretical insights regarding the level of national IFRS adoption come from the world-level institutional theory (Meyer et. al., 1997). Archival data are utilized for the study. The findings indicate that countries with weaker national...
Show moreThis dissertation consists of three separate, but related, studies on the institutionalization of International Financial Reporting Standards (IFRS). The first study examines the relationship between the national variables and the level of IFRS adoption. Theoretical insights regarding the level of national IFRS adoption come from the world-level institutional theory (Meyer et. al., 1997). Archival data are utilized for the study. The findings indicate that countries with weaker national governance structures and lower economic development demonstrate the highest level of commitment to IFRS. Nationalism was found to influence the extent of adoption. The study contributes to IFRS adoption literature by recognizing the multi-level possibilities of IFRS adoption and discovering the factors that drive the degree of IFRS adoption on a national level. The second study examines the ongoing change in the U.S. accounting regulation related to IFRS. The specific event investigated is an historic ruling by the Securities and Exchange Commission (SEC) made in 2007 to accept IFRS filings from foreign issuers. This move toward acceptance of IFRS by the primary U.S. regulator is of academic interest because it represents an opportunity to study regulatory institutional change. The event is analyzed using a qualitative study of the rhetoric found in the comment letters submitted to the SEC. The following theoretical frameworks were used to interpret the qualitative findings: a model of institutional change (Greenwood et. al., 2002), the role of rhetoric in legitimating institutional change (Suddaby & Greenwood, 2005), and the agents of change model (Djelic & Quack, 2003b). The conversation of opponents and proponents through the comment letters revealed the struggle of the participants to legitimize their positions. As expected, rhetorical themes associated with the moral and pragmatic legitimacy of their positions were utilized. Unexpectedly, the shifting site of regulation and the related power of SEC were troubling for proponents and opponents of the change. The study contributes to transnational accounting regulation literature in a number of ways. It presents a synthesis of different theoretical perspectives to investigate institutional change in accounting regulation. It also deepens the understanding of how institutional change is theorized by evaluating the rhetoric of domestic, foreign, and transnational participants. The third study evaluates the diffusion of IFRS in developing countries, using the specific case of Russia. The study investigates whether individual perceptions of various aspects of financial reporting and reforms are associated with IFRS adoption. Particularly of interest is whether there are differences between voluntary adopters and those for which adoption was mandated. The data were obtained from a 2007 survey exploring RussiaÃ‚Â's transition to IFRS. In general, adopters had a more positive view of transition toward IFRS and financial reforms in Russia. Further, the perceptions of reforms by adopters did not vary based on whether the adoption was required by a national or a foreign mandate. The study contributes both theoretically and empirically to the literature on IFRS in developing countries. Taken together, these three studies focus on issues that have not been addressed previously in the accounting literature. They will advance the international accounting literature on factors related to IFRS adoption, regulations, and influences.
Show less
Date Issued: 2010
Identifier: CFE0003286, ucf:48543
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0003286

Title: Propagation Failure in Discrete Inhomogeneous Media Using a Caricature of the Cubic.
Creator: Lydon, Elizabeth, Moore, Brian, Choudhury, Sudipto, Kaup, David, University of Central Florida
Abstract / Description: Spatially discrete Nagumo equations have widespread physical applications, including modeling electrical impulses traveling through a demyelinated axon, an environment typical in multiple scle- rosis. We construct steady-state, single front solutions by employing a piecewise linear reaction term. Using a combination of Jacobi-Operator theory and the Sherman-Morrison formula we de- rive exact solutions in the cases of homogeneous and inhomogeneous diffusion. Solutions exist only under certain...
Show moreSpatially discrete Nagumo equations have widespread physical applications, including modeling electrical impulses traveling through a demyelinated axon, an environment typical in multiple scle- rosis. We construct steady-state, single front solutions by employing a piecewise linear reaction term. Using a combination of Jacobi-Operator theory and the Sherman-Morrison formula we de- rive exact solutions in the cases of homogeneous and inhomogeneous diffusion. Solutions exist only under certain conditions outlined in their construction. The range of parameter values that satisfy these conditions constitutes the interval of propagation failure, determining under what circumstances a front becomes pinned in the media. Our exact solutions represent a very specific solution to the spatially discrete Nagumo equation. For example, we only consider inhomogeneous media with one defect present. We created an original script in MATLAB which algorithmically solves more general cases of the equation, including the case for multiple defects. The algorithmic solutions are then compared to known exact solutions to determine their validity.
Show less
Date Issued: 2015
Identifier: CFE0005831, ucf:50903
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005831

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)	+ -

Search In

Pages

Pages

Sort Results By:

Narrow results by:

Topical Subject

Collection

Type of Resource

Language

Creator

Format

Owner