Current Search: inverse (x)
Pages


Title

EFFICIENT INVERSION OF THE CONE BEAM TRANSFORM FOR A GENERAL CLASS OF CURVES.

Creator

Kapralov, Mikhail, Katsevich, Alexander, University of Central Florida

Abstract / Description

We extend an efficient cone beam transform inversion formula, proposed earlier for helices, to a general class of curves. The conditions that describe the class are very natural. Curves C are smooth, without selfintersections, have positive curvature and torsion, do not bend too much in a certain sense, and do not admit lines which are tangent to C at one point and intersect C at another point. A domain U is found where reconstruction is possible with a filtered backprojection type algorithm...
Show moreWe extend an efficient cone beam transform inversion formula, proposed earlier for helices, to a general class of curves. The conditions that describe the class are very natural. Curves C are smooth, without selfintersections, have positive curvature and torsion, do not bend too much in a certain sense, and do not admit lines which are tangent to C at one point and intersect C at another point. A domain U is found where reconstruction is possible with a filtered backprojection type algorithm. Results of numerical experiments demonstrate very good image quality. The algorithm developed is useful for image reconstruction in computerized tomography.
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Date Issued

2007

Identifier

CFE0001579, ucf:47120

Format

Document (PDF)

PURL

http://purl.flvc.org/ucf/fd/CFE0001579


Title

ACCIDENTAL INVERSION DURING 3D ROTATION WITH 2DOF INPUT DEVICES.

Creator

Diaz, Derek, Sims, Valerie, University of Central Florida

Abstract / Description

This dissertation focuses on a human operator's ability to perform rotational control of a threedimensional object using twodegrees of freedom (DOF) interface devices. Although input devices designed specifically for 3D interaction exist, devices traditionally used for twodimensional user interaction, such as a mouse or joystick, have become ubiquitous to computer tasks. This research examines a particular humancomputer interaction issue that arises from stimulusresponse...
Show moreThis dissertation focuses on a human operator's ability to perform rotational control of a threedimensional object using twodegrees of freedom (DOF) interface devices. Although input devices designed specifically for 3D interaction exist, devices traditionally used for twodimensional user interaction, such as a mouse or joystick, have become ubiquitous to computer tasks. This research examines a particular humancomputer interaction issue that arises from stimulusresponse compatibility between threedimensional stimuli spaces and 2DOF response sets. The focal point of this research is a phenomenon referred to here as accidental inversion. Accidental inversions occur when an operator erroneously moves a threedimensional object in a direction opposite than was intended. Thus, the effect of accidental inversion results from a mismatch between the operator's intended and actual input. A key assumption in diagnosing the causal factors involved in the accidental inversion effect is contribution from both internal (i.e., having to do with the individual) and external (i.e., having to do with the environment) influences. Three experiments were conducted to study accidental inversion. The first examined population stereotype, a measure of a target population's natural response tendencies to particular stimuli for a particular task. Results indicated a strong population stereotype for horizontal rotations (i.e., yaw) and weak stereotype for vertical rotations (i.e., pitch). This effect was mediated by whether the task was in the context of flight or groundbased movement. The second experiment analyzed the subjective preference for two opposite inputresponse (IR) mappings (i.e., how the system responds to different input into the controlling device) for a task requiring control over vertical rotation. Results indicated that subjective preferences for IR mappings were not heavily polarized. The third experiment also focused on vertical rotational control and examined how subjective preference for a particular IR mapping affected performance. Furthermore, this experiment also examined performance when interference was introduced in the form of a temporary interruption where the participant had to conduct the task using an opposite IR mapping. Results indicated that, upon being interrupted with the opposite IR mapping, the group who used the mapping they subjectively preferred did worse than the group who used the mapping they did not prefer. This research has implications for the design of humanmachine systems requiring humanintheloop threedimensional rotational control. Some humanmachine systems can have significant consequences from even a single mistake caused by a humanoperator accidentally providing the wrong input. Findings from this research lead to two primary recommendations to the design of humanmachine systems: a) an easily accessible and clearly indicated method to select inputresponse mapping which is provided before beginning the actual task, b) be informed of the current inputresponse mapping in use.
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Date Issued

2007

Identifier

CFE0001961, ucf:47454

Format

Document (PDF)

PURL

http://purl.flvc.org/ucf/fd/CFE0001961


Title

Can One Hear...? An Exploration Into Inverse Eigenvalue Problems Related to Musical Instruments.

Creator

Adams, Christine, Nashed, M, Mohapatra, Ram, Kaup, David, University of Central Florida

Abstract / Description

The central theme of this thesis deals with problems related to the question, (")Can one hear the shape of a drum?(") first posed formally by Mark Kac in 1966. More precisely, can one determine the shape of a membrane with fixed boundary from the spectrum of the associated differential operator? For this paper, Kac received both the Lester Ford Award and the Chauvant Prize of the Mathematical Association of America. This problem has received a great deal of attention in the past forty years...
Show moreThe central theme of this thesis deals with problems related to the question, (")Can one hear the shape of a drum?(") first posed formally by Mark Kac in 1966. More precisely, can one determine the shape of a membrane with fixed boundary from the spectrum of the associated differential operator? For this paper, Kac received both the Lester Ford Award and the Chauvant Prize of the Mathematical Association of America. This problem has received a great deal of attention in the past forty years and has led to similar questions in completely different contexts such as (")Can one hear the shape of a graph associated with the Schr(&)#246;dinger operator?("), (")Can you hear the shape of your throat?("), (")Can you feel the shape of a manifold with Brownian motion?("), (")Can one hear the crack in a beam?("), (")Can one hear into the sun?("), etc. Each of these topics deals with inverse eigenvalue problems or related inverse problems. For inverse problems in general, the problem may or may not have a solution, the solution may not be unique, and the solution does not necessarily depend continuously on perturbation of the data. For example, in the case of the drum, it has been shown that the answer to Kac's question in general is (")no.(") However, if we restrict the class of drums, then the answer can be yes. This is typical of inverse problems when a priori information and restriction of the class of admissible solutions and/or data are used to make the problem wellposed. This thesis provides an analysis of shapes for which the answer to Kac's question is positive and a variety of interesting questions on this problem and its variants, including cases that remain open. This thesis also provides a synopsis and perspectives of other types of (")can one hear(") problems mentioned above. Another part of this thesis deals with aspects of direct problems related to musical instruments.
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Date Issued

2013

Identifier

CFE0004643, ucf:49886

Format

Document (PDF)

PURL

http://purl.flvc.org/ucf/fd/CFE0004643


Title

Solution of linear illposed problems using overcomplete dictionaries.

Creator

Gupta, Pawan, Pensky, Marianna, Swanson, Jason, Zhang, Teng, Foroosh, Hassan, University of Central Florida

Abstract / Description

In this dissertation, we consider an application of overcomplete dictionaries to the solution of general illposed linear inverse problems. In the context of regression problems, there has been an enormous amount of effort to recover an unknown function using such dictionaries. While some research on the subject has been already carried out, there are still many gaps to address. In particular, one of the most popular methods, lasso, and its variants, is based on minimizing the empirical...
Show moreIn this dissertation, we consider an application of overcomplete dictionaries to the solution of general illposed linear inverse problems. In the context of regression problems, there has been an enormous amount of effort to recover an unknown function using such dictionaries. While some research on the subject has been already carried out, there are still many gaps to address. In particular, one of the most popular methods, lasso, and its variants, is based on minimizing the empirical likelihood and unfortunately, requires stringent assumptions on the dictionary, the socalled, compatibility conditions. Though compatibility conditions are hard to satisfy, it is well known that this can be accomplished by using random dictionaries. In the first part of the dissertation, we show how one can apply random dictionaries to the solution of illposed linear inverse problems with Gaussian noise. We put a theoretical foundation under the suggested methodology and study its performance via simulations and realdata example. In the second part of the dissertation, we investigate the application of lasso to the linear illposed problems with nonGaussian noise. We have developed a theoretical background for the application of lasso to such problems and studied its performance via simulations.
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Date Issued

2019

Identifier

CFE0007811, ucf:52345

Format

Document (PDF)

PURL

http://purl.flvc.org/ucf/fd/CFE0007811


Title

A DIRECT COMPENSATOR PROFILE OPTIMIZATION APPROACH FOR INTENSITY MODULATED RADIATION TREATMENT PLANNING.

Creator

Erhart, Kevin, Divo, Eduardo, University of Central Florida

Abstract / Description

Radiation therapy accounts for treatment of over one million cancer patients each year in the United States alone, and its use will continue to grow rapidly in the coming years. Recently, many important advancements have been developed that greatly improve the outcomes and effectiveness of this treatment technique, the most notable being Intensity Modulated Radiation Therapy (IMRT). IMRT is a sophisticated treatment technique where the radiation dose is conformed to the tumor volume, thereby...
Show moreRadiation therapy accounts for treatment of over one million cancer patients each year in the United States alone, and its use will continue to grow rapidly in the coming years. Recently, many important advancements have been developed that greatly improve the outcomes and effectiveness of this treatment technique, the most notable being Intensity Modulated Radiation Therapy (IMRT). IMRT is a sophisticated treatment technique where the radiation dose is conformed to the tumor volume, thereby sparing nearby healthy tissue from excessive radiation dose. While IMRT is a valuable tool in the planning of radiation treatments, it is not without its difficulties. This research has created, developed, and tested an innovative approach to IMRT treatment planning, coined Direct Compensator Profile Optimization (DCPO), which is shown to eliminate many of the difficulties typically associated with IMRT planning and delivery using solid compensator based treatment. The major innovation of this technique is that it is a direct delivery parameter optimization approach which has adopted a parameterized surface representation using NonUniform Rational BSplines (NURBs) to replace the conventional beamlet weight optimization approach. This new approach brings with it three key advantages: 1) a reduced number of parameters to optimize, reducing the difficulty of numerical optimization; 2) the ability to ensure complete equivalence of planned and actual manufactured compensators; and 3) direct inclusion of delivery device effects during planning with no performance penalties, eliminating the degrading fluencetodelivery parameter conversion process. Detailed research into the affects of the DCPO approach on IMRT planning has been completed and a thorough analysis of the developments is provided herein. This research includes a complete description of the DCPO surface representation scheme, inverse planning process, as well as quantification of the manufacturing constraint control procedure. Results are presented which demonstrate the performance and innovation offered by this new approach and show that the resulting compensator shapes can be manufactured to nearly 100 percent of the designed shape.
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Date Issued

2009

Identifier

CFE0002800, ucf:48099

Format

Document (PDF)

PURL

http://purl.flvc.org/ucf/fd/CFE0002800


Title

Kinematical Modelling and Its Analytical Inverse Kinematic Solution for the Handling Mechanism of an Agricultural Robot.

Creator

Defterli, Sinem, Xu, Yunjun, Lin, KuoChi, Zheng, Qipeng, Song, SangEun, University of Central Florida

Abstract / Description

Early detection of the crop diseases helps to prevent failure in the amount and the quality of the production. In agricultural robotics, the idea of a disease detection robot is a fresh and an innovative hotbutton topic. The exclusion of the diseased parts from the strawberry plants for further analyses is one of the main tasks of a recently developed strawberry robot. To this purpose, the handling mechanism in the robot needs to achieve an accurate manipulation task to reach the target....
Show moreEarly detection of the crop diseases helps to prevent failure in the amount and the quality of the production. In agricultural robotics, the idea of a disease detection robot is a fresh and an innovative hotbutton topic. The exclusion of the diseased parts from the strawberry plants for further analyses is one of the main tasks of a recently developed strawberry robot. To this purpose, the handling mechanism in the robot needs to achieve an accurate manipulation task to reach the target. Reaching, cutting and storing the diseased leaf are challenging and delicate processes during the procedure of the handling mechanism operation in the field.The manipulation task of the mechanism is succeeded when the inverse kinematic relations from workspace to joint space are defined properly. The inverse kinematic analysis is usually subjected to the restrictions due to the limitations in mechanical design of the mechanism, hardware components and operation environment of the robots as well as the morphology of the target. This study proposes a set of analytical algorithms to solve the inverse kinematics problem of the handling mechanism under certain constraints. First, proposed analytical approach is based on the calculation of the joint variables by solving only the 3D position information of the target since the output from image processing algorithms of vision subsystem in the ground robot is only the location of the diseased point. The position of target point is the only output from vision subsystem and this data will be given as an input to the proposed algorithms. Second, the mechanism has certain restrictions on its geometrical construction and the joint actuators' capacity. Hence, these restrictions limit the range of joint variables to be solved. Due to sudden and unpredicted nature of field conditions, the quickness of handling mechanism inverse kinematics solution's execution has a vital effect on the success of the picking task of the robot. Another essential factor is to use the battery life of the robot effectively, by minimizing energy consumption. Therefore, the effectiveness of the proposed algorithm is decided by comparing the developed performance indices of consumed energy and CPU time cost via numerical solution namely, a nonlinear constrained optimization method under same restrictions of inverse kinematics problem. Performance of both algorithms is observed by the simulations in MATLAB(&)#174; and laboratory setup experiments.
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Date Issued

2016

Identifier

CFE0006291, ucf:51588

Format

Document (PDF)

PURL

http://purl.flvc.org/ucf/fd/CFE0006291


Title

Online Path Planning and Control Solution for a Coordinated Attack of Multiple Unmanned Aerial Vehicles in a Dynamic Environment.

Creator

VegaNevarez, Juan, Qu, Zhihua, Haralambous, Michael, Xu, Yunjun, University of Central Florida

Abstract / Description

The role of the unmanned aerial vehicle (UAV) has significantly expanded in the military sector during the last decades mainly due to their cost effectiveness and their ability to eliminate the human life risk. Current UAV technology supports a variety of missions and extensive research and development is being performed to further expand its capabilities. One particular field of interest is the area of the low cost expendable UAV since its small price tag makes it an attractive solution for...
Show moreThe role of the unmanned aerial vehicle (UAV) has significantly expanded in the military sector during the last decades mainly due to their cost effectiveness and their ability to eliminate the human life risk. Current UAV technology supports a variety of missions and extensive research and development is being performed to further expand its capabilities. One particular field of interest is the area of the low cost expendable UAV since its small price tag makes it an attractive solution for target suppression. A swarm of these low cost UAVs can be utilized as guided munitions or kamikaze UAVs to attack multiple targets simultaneously. The focus of this thesis is the development of a cooperative online path planning algorithm that coordinates the trajectories of these UAVs to achieve a simultaneous arrival to their dynamic targets. A nonlinear autopilot design based on the dynamic inversion technique is also presented which stabilizes the dynamics of the UAV in its entire operating envelope. A nonlinear high fidelity six degrees of freedom model of a fixed wing aircraft was developed as well that acted as the main test platform to verify the performance of the presented algorithms
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Date Issued

2012

Identifier

CFE0004613, ucf:49925

Format

Document (PDF)

PURL

http://purl.flvc.org/ucf/fd/CFE0004613


Title

EFFICIENT CONE BEAM RECONSTRUCTION FOR THE DISTORTED CIRCLE AND LINE TRAJECTORY.

Creator

Konate, Souleymane, Katsevich, Alexander, University of Central Florida

Abstract / Description

We propose an exact filtered backprojection algorithm for inversion of the cone beam data in the case when the trajectory is composed of a distorted circle and a line segment. The length of the scan is determined by the region of interest , and it is independent of the size of the object. With few geometric restrictions on the curve, we show that we have an exact reconstruction. Numerical experiments demonstrate good image quality.

Date Issued

2009

Identifier

CFE0002530, ucf:47669

Format

Document (PDF)

PURL

http://purl.flvc.org/ucf/fd/CFE0002530


Title

AN INVERSE ALGORITHM TO ESTIMATE THERMAL CONTACT RESISTANCE.

Creator

Gill, Jennifer, Kassab, Alain, University of Central Florida

Abstract / Description

Thermal systems often feature composite regions that are mechanically mated. In general, there exists a significant temperature drop across the interface between such regions which may be composed of similar or different materials. The parameter characterizing this temperature drop is the thermal contact resistance, which is defined as the ratio of the temperature drop to the heat flux normal to the interface. The thermal contact resistance is due to roughness effects between mating surfaces...
Show moreThermal systems often feature composite regions that are mechanically mated. In general, there exists a significant temperature drop across the interface between such regions which may be composed of similar or different materials. The parameter characterizing this temperature drop is the thermal contact resistance, which is defined as the ratio of the temperature drop to the heat flux normal to the interface. The thermal contact resistance is due to roughness effects between mating surfaces which cause certain regions of the mating surfaces to loose contact thereby creating gaps. In these gap regions, the principal modes of heat transfer are conduction across the contacting regions of the interface, conduction or natural convection in the fluid filling the gap regions of the interface, and radiation across the gap surfaces. Moreover, the contact resistance is a function of contact pressure as this can significantly alter the topology of the contact region. The thermal contact resistance is a phenomenologically complex function and can significantly alter prediction of thermal models of complex multicomponent structures. Accurate estimates of thermal contact resistances are important in engineering calculations and find application in thermal analysis ranging from relatively simple layered and composite materials to more complex biomaterials. There have been many studies devoted to the theoretical predictions of thermal contact resistance and although general theories have been somewhat successful in predicting thermal contact resistances, most reliable results have been obtained experimentally. This is due to the fact that the nature of thermal contact resistance is quite complex and depends on many parameters including types of mating materials, surface characteristics of the interfacial region such as roughness and hardness, and contact pressure distribution. In experiments, temperatures are measured at a certain number of locations, usually close to the contact surface, and these measurements are used as inputs to a parameter estimation procedure to arrive at the soughtafter thermal contact resistance. Most studies seek a single value for the contact resistance, while the resistance may in fact also vary spatially. In this thesis, an inverse problem (IP) is formulated to estimate the spatial variation of the thermal contact resistance along an interface in a twodimensional configuration. Temperatures measured at discrete locations using embedded sensors appropriately placed in proximity to the interface provide the additional information required to solve the inverse problem. A superposition method serves to determine sensitivity coefficients and provides guidance in the location of the measuring points. Temperature measurements are then used to define a regularized quadratic functional that is minimized to yield the contact resistance between the two mating surfaces. A boundary element method analysis (BEM) provides the temperature field under current estimates of the contact resistance in the solution of the inverse problem when the geometry of interest is not regular, while an analytical solution can be used for regular geometries. Minimization of the IP functional is carried out by the LevenbergMarquadt method or by a Genetic Algorithm depending on the problem under consideration. The Lcurve method of Hansen is used to choose the optimal regularization parameter. A series of numerical examples are provided to demonstrate and validate the approach.
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Date Issued

2005

Identifier

CFE0000748, ucf:46582

Format

Document (PDF)

PURL

http://purl.flvc.org/ucf/fd/CFE0000748


Title

APPLICATION OF TRAINED PODRBF TO INTERPOLATION IN HEAT TRANSFER AND FLUID MECHANICS.

Creator

Ashley, Rebecca A, Kassab, Alain, University of Central Florida

Abstract / Description

To accurately model or predict future operating conditions of a system in engineering or applied mechanics, it is necessary to understand its fundamental principles. These may be the material parameters, defining dimensional characteristics, or the boundary conditions. However, there are instances when there is little to no prior knowledge of the system properties or conditions, and consequently, the problem cannot be modeled accurately. It is therefore critical to define a method that can...
Show moreTo accurately model or predict future operating conditions of a system in engineering or applied mechanics, it is necessary to understand its fundamental principles. These may be the material parameters, defining dimensional characteristics, or the boundary conditions. However, there are instances when there is little to no prior knowledge of the system properties or conditions, and consequently, the problem cannot be modeled accurately. It is therefore critical to define a method that can identify the desired characteristics of the current system without accumulating extensive computation time. This thesis formulates an inverse approach using proper orthogonal decomposition (POD) with an accompanying radial basis function (RBF) interpolation network. This method is capable of predicting the desired characteristics of a specimen even with little prior knowledge of the system. This thesis first develops a conductive heat transfer problem, and by using the truncated POD  RBF interpolation network, temperature values are predicted given a varying Biot number. Then, a simple bifurcation problem is modeled and solved for velocity profiles while changing the mass flow rate. This bifurcation problem provides the data and foundation for future research into the left ventricular assist device (LVAD) and implementation of POD  RBF. The trained POD  RBF inverse approach defined in this thesis can be implemented in several applications of engineering and mechanics. It provides model reduction, error filtration, regularization and an improvement over previous analysis utilizing computational fluid dynamics (CFD).
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Date Issued

2018

Identifier

CFH2000279, ucf:45782

Format

Document (PDF)

PURL

http://purl.flvc.org/ucf/fd/CFH2000279


Title

TRACKING ERROR OF LEVERAGED AND INVERSE ETFS.

Creator

Romano, John, Gilkeson, Jim, University of Central Florida

Abstract / Description

Tracking ability of leveraged and inverse exchange traded funds can be very important to investors looking for a dependable return. If the investor wants to put their money on a certain index they feel strongly about, they expect their investment vehicle to track that return appropriately. Over the years, we have seen tremendous growth in the exchange traded fund industry. In 2006, leveraged and inverse funds were introduced to the market, allowing investors to take leveraged and directional...
Show moreTracking ability of leveraged and inverse exchange traded funds can be very important to investors looking for a dependable return. If the investor wants to put their money on a certain index they feel strongly about, they expect their investment vehicle to track that return appropriately. Over the years, we have seen tremendous growth in the exchange traded fund industry. In 2006, leveraged and inverse funds were introduced to the market, allowing investors to take leveraged and directional trades on indices. These investment vehicles can be traded as easily as any stock, and therefore need some attention. Since any novice investor can access and trade these funds, they need to be aware of the risks they are taking. In this study, I test whether the ProShares S&P tracking leveraged and inverse exchange traded funds track their appropriate index multiple as promised. I did this by running regressions on each fund against the appropriate multiple of their underlying indices. I did this for funds of different market capitalization, for different holding periods, and with different amounts of leverage, to compare how these funds track in different conditions. I found that the large cap funds tend to track the best, with the small cap funds tracking the worst. I also find that tracking error tends to increase with longer holding periods. I find that the distribution of excess returns becomes less normal over longer holding periods, and begins to flatten out and widen. There does not seem to be a concrete conclusion as to whether or not the amount of leverage affects the tracking ability of the funds. I end up with mixed results when comparing amounts of leverage by model fit and by tracking error. Direction also does not seem to play any role in the tracking ability of these funds.
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Date Issued

2012

Identifier

CFH0004184, ucf:44893

Format

Document (PDF)

PURL

http://purl.flvc.org/ucf/fd/CFH0004184


Title

INVERSE BOUNDARY ELEMENT/GENETIC ALGORITHM METHOD FOR RECONSTRUCTION OF MULTIDIMENSIONAL HEAT FLUX DISTRIBUTIONS WITH FILM COOLING APPLICATIONS.

Creator

Silieti, Mahmood, Kassab, Alain, University of Central Florida

Abstract / Description

A methodology is formulated for the solution of the inverse problem concerned with the reconstruction of multidimensional heat fluxes for film cooling applications. The motivation for this study is the characterization of complex thermal conditions in industrial applications such as those encountered in film cooled turbomachinery components. The heat conduction problem in the metal endwall/shroud is solved using the boundary element method (bem), and the inverse problem is solved using a...
Show moreA methodology is formulated for the solution of the inverse problem concerned with the reconstruction of multidimensional heat fluxes for film cooling applications. The motivation for this study is the characterization of complex thermal conditions in industrial applications such as those encountered in film cooled turbomachinery components. The heat conduction problem in the metal endwall/shroud is solved using the boundary element method (bem), and the inverse problem is solved using a genetic algorithm (ga). Thermal conditions are overspecified at exposed surfaces amenable to measurement, while the temperature and surface heat flux distributions are unknown at the film cooling hole/slot walls. The latter are determined in an iterative process by developing two approaches. The first approach, developed for 2d applications, solves an inverse problem whose objective is to adjust the film cooling hole/slot wall temperatures and heat fluxes until the temperature and heat flux at the measurement surfaces are matched in an overall heat conduction solution. The second approach, developed for 2d and 3d applications, is to distribute a set of singularities (sinks) at the vicinity of the cooling slots/holes surface inside a fictitious extension of the physical domain or along cooling hole centerline with a given initial strength distribution. The inverse problem iteratively alters the strength distribution of the singularities (sinks) until the measuring surfaces heat fluxes are matched. The heat flux distributions are determined in a postprocessing stage after the inverse problem is solved. The second approach provides a tremendous advantage in solving the inverse problem, particularly in 3d applications, and it is recommended as the method of choice for this class of problems. It can be noted that the ga reconstructed heat flux distributions are robust, yielding accurate results to both exact and errorladen inputs. In all cases in this study, results from experiments are simulated using a full conjugate heat transfer (cht) finite volume models which incorporate the interactions of the external convection in the hot turbulent gas, internal convection within the cooling plena, and the heat conduction in the metal endwall/shroud region. Extensive numerical investigations are undertaken to demonstrate the significant importance of conjugate heat transfer in film cooling applications and to identify the implications of various turbulence models in the prediction of accurate and more realistic surface temperatures and heat fluxes in the cht simulations. These, in turn, are used to provide numerical inputs to the inverse problem. Single and multiple cooling slots, cylindrical cooling holes, and fanshaped cooling holes are considered in this study. The turbulence closure is modeled using several twoequation approach, the fourequation turbulence model, as well as five and seven moment reynolds stress models. The predicted results, by the different turbulence models, for the cases of adiabatic and conjugate models, are compared to experimental data reported in the open literature. Results show the significant effects of conjugate heat transfer on the temperature field in the film cooling hole region, and the additional heating up of the cooling jet itself. Moreover, results from the detailed numerical studies presented in this study validate the inverse problem approaches and reveal good agreement between the bem/ga reconstructed heat fluxes and the cht simulated heat fluxes along the inaccessible cooling slot/hole walls
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Date Issued

2004

Identifier

CFE0000166, ucf:52896

Format

Document (PDF)

PURL

http://purl.flvc.org/ucf/fd/CFE0000166


Title

PARAMETER ESTIMATION IN HEAT TRANSFER AND ELASTICITY USING TRAINED PODRBF NETWORK INVERSE METHODS.

Creator

Rogers, Craig, Kassab, Alain, University of Central Florida

Abstract / Description

In applied mechanics it is always necessary to understand the fundamental properties of a system in order to generate an accurate numerical model or to predict future operating conditions. These fundamental properties include, but are not limited to, the material parameters of a specimen, the boundary conditions inside of a system, or essential dimensional characteristics that define the system or body. However in certain instances there may be little to no knowledge about the systems...
Show moreIn applied mechanics it is always necessary to understand the fundamental properties of a system in order to generate an accurate numerical model or to predict future operating conditions. These fundamental properties include, but are not limited to, the material parameters of a specimen, the boundary conditions inside of a system, or essential dimensional characteristics that define the system or body. However in certain instances there may be little to no knowledge about the systems conditions or properties; as a result the problem cannot be modeled accurately using standard numerical methods. Consequently, it is critical to define an approach that is capable of identifying such characteristics of the problem at hand. In this thesis, an inverse approach is formulated using proper orthogonal decomposition (POD) with an accompanying radial basis function (RBF) network to estimate the current material parameters of a specimen with little prior knowledge of the system. Specifically conductive heat transfer and linear elasticity problems are developed in this thesis and modeled with a corresponding finite element (FEM) or boundary element (BEM) method. In order to create the truncated PODRBF network to be utilized in the inverse approach, a series of direct FEM or BEM solutions are used to generate a statistical data set of temperatures or deformations in the system or body, each having a set of various material parameters. The data set is then transformed via POD to generate an orthonormal basis to accurately solve for the desired material characteristics using the LevenbergMarquardt (LM) algorithm. For now, the LM algorithm can be simply defined as a direct relation to the minimization of the Euclidean norm of the objective Least Squares function(s). The trained PODRBF inverse technique outlined in this thesis provides a flexible by which this inverse approach can be implemented into various fields of engineering and mechanics. More importantly this approach is designed to offer an inexpensive way to accurately estimate material characteristics or properties using nondestructive techniques. While the PODRBF inverse approach outlined in this thesis focuses primarily in application to conduction heat transfer, elasticity, and fracture mechanics, this technique is designed to be directly applicable to other realistic conditions and/or industries.
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Date Issued

2010

Identifier

CFE0003267, ucf:48517

Format

Document (PDF)

PURL

http://purl.flvc.org/ucf/fd/CFE0003267


Title

Dynamical spin injection in graphene.

Creator

Singh, Simranjeet, Del Barco, Enrique, Mucciolo, Eduardo, Ishigami, Masa, Hill, Stephen, University of Central Florida

Abstract / Description

Within the exciting current trend to explore novel lowdimensional systems, the possibility to injectpure spin currents in graphene and other twodimensional crystals has attracted considerableattention in the past few years. The theoretical prediction of large spin relaxation times and experimentally observed mesoscopicscale spin diffusion lengths places graphene as a promising base system for future spintronics devices. This is due to the unique characteristics intrinsic to the two...
Show moreWithin the exciting current trend to explore novel lowdimensional systems, the possibility to injectpure spin currents in graphene and other twodimensional crystals has attracted considerableattention in the past few years. The theoretical prediction of large spin relaxation times and experimentally observed mesoscopicscale spin diffusion lengths places graphene as a promising base system for future spintronics devices. This is due to the unique characteristics intrinsic to the twodimensional lattice of carbon atoms forming graphene, such as the lack of nuclear spins and weak spinorbit coupling of the charge carriers. Interestingly for some spintronic applications, the latter can be chemically and physically engineered, with large induced spinorbit couplings found in functionalized graphene sheets. Understanding spin injection, spin current and spin dynamics in graphene is of a great interest, both from the fundamental and applied points of view.This thesis presents an experimental study of dynamical generation of spin currents in macroscopic graphene sheets by means of spin pumping from the precessing magnetization of an adjacent ferromagnet. The spin pumping characteristics are studied by means of ferromagnetic resonance (FMR) measurements in Permalloy/graphene (Py/Gr) bilayers. Changes in the FMR linewidth induced by the presence of graphene (when compared to studies with only Py films) correspond to an increase in the Gilbert damping in the ferromagnetic layer (proportional to the FMR linewidth) and interpreted as a consequence of spin pumping at the Py/Gr interface driven by the Py magnetization dynamics (i.e., magnetic induced by the microwave stimulus). FMR experiments are performed on different FM/Gr interfaces, completing a set of studies designed to systematically identify and eliminate damping enhancement arising from processes other than spin pumping. Remarkably, a substantial enhancement of the Gilbert damping observed in Py/Gr strips with graphene protruding a few micrometers from the strip sides is univocally associated to spin pumping at the quasionedimensional interface between the Py strip edges and graphene. This increase in the FMR linewidth compares with observations in other bilayer systems, in where thick (thicker than the spin diffusionlength) layers of heavy metals with strong spinorbit coupling are employed as the nonmagneticlayer, indicating that spin relaxation in chemically grown graphene must be greatly enhanced in order to account for the losses of angular momentum lost by the ferromagnet. The fundamentalimplications of the results presented in this thesis point to a nontrivial nature of the spin pumping mechanism owing to the twodimensionality of the nonmagnetic layer (i.e., graphene).In addition, a spintronics device designed to interconvert charge and spin currents has been designed. A highfrequency microwave irradiation lockin modulation technique is employed todetect the small electrical voltages generated by the inverse spin Hall effect (ISHE). As a proofof principle, a successful spincharge interconversion in Py/Ptbased devices is experimentally demonstrated in this thesis. The challenges associated with the spincharge interconversion in twodimensional devices are discussed and systematically addressed, and a potential device geometry for measuring the ISHE in Py/Grbased systems is provided.
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Date Issued

2014

Identifier

CFE0005552, ucf:50284

Format

Document (PDF)

PURL

http://purl.flvc.org/ucf/fd/CFE0005552


Title

Electrical Conductivity Imaging via Boundary Value Problems for the 1Laplacian.

Creator

Veras, Johann, Tamasan, Alexandru, Mohapatra, Ram, Nashed, M, Dogariu, Aristide, University of Central Florida

Abstract / Description

We study an inverse problem which seeks to image the internal conductivity map of a body by one measurement of boundary and interior data. In our study the interior data is the magnitude of the current density induced by electrodes. Access to interior measurements has been made possible since the work of M. Joy et al. in early 1990s and couples two physical principles: electromagnetics and magnetic resonance. In 2007 Nachman et al. has shown that it is possible to recover the conductivity...
Show moreWe study an inverse problem which seeks to image the internal conductivity map of a body by one measurement of boundary and interior data. In our study the interior data is the magnitude of the current density induced by electrodes. Access to interior measurements has been made possible since the work of M. Joy et al. in early 1990s and couples two physical principles: electromagnetics and magnetic resonance. In 2007 Nachman et al. has shown that it is possible to recover the conductivity from the magnitude of one current density field inside. The method now known as Current Density Impedance Imaging is based on solving boundary value problems for the 1Laplacian in an appropriate Riemann metric space. We consider two types of methods: the ones based on level sets and a variational approach, which aim to solve specific boundary value problem associated with the 1Laplacian. We will address the Cauchy and Dirichlet problems with full and partial data, and also the Complete Electrode Model (CEM). The latter model is known to describe most accurately the voltage potential distribution in a conductive body, while taking into account the transition of current from the electrode to the body. For the CEM the problem is nonunique. We characterize the nonuniqueness, and explain which additional measurements fix the solution. Multiple numerical schemes for each of the methods are implemented to demonstrate the computational feasibility.
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Date Issued

2014

Identifier

CFE0005437, ucf:50388

Format

Document (PDF)

PURL

http://purl.flvc.org/ucf/fd/CFE0005437


Title

ELECTRICAL CAPACITANCE VOLUME TOMOGRAPHY OF HIGH CONTRAST DIELECTRICS USING A CUBOID GEOMETRY.

Creator

Nurge, Mark, Schelling, Patrick, University of Central Florida

Abstract / Description

An Electrical Capacitance Volume Tomography system has been created for use with a new image reconstruction algorithm capable of imaging high contrast dielectric distributions. The electrode geometry consists of two 4 x 4 parallel planes of copper conductors connected through custom built switch electronics to a commercially available capacitance to digital converter. Typical electrical capacitance tomography (ECT) systems rely solely on mutual capacitance readings to reconstruct images of...
Show moreAn Electrical Capacitance Volume Tomography system has been created for use with a new image reconstruction algorithm capable of imaging high contrast dielectric distributions. The electrode geometry consists of two 4 x 4 parallel planes of copper conductors connected through custom built switch electronics to a commercially available capacitance to digital converter. Typical electrical capacitance tomography (ECT) systems rely solely on mutual capacitance readings to reconstruct images of dielectric distributions. This dissertation presents a method of reconstructing images of high contrast dielectric materials using only the self capacitance measurements. By constraining the unknown dielectric material to one of two values, the inverse problem is no longer illdetermined. Resolution becomes limited only by the accuracy and resolution of the measurement circuitry. Images were reconstructed using this method with both synthetic and real data acquired using an aluminum structure inserted at different positions within the sensing region. Comparisons with standard two dimensional ECT systems highlight the capabilities and limitations of the electronics and reconstruction algorithm.
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Date Issued

2007

Identifier

CFE0001591, ucf:47119

Format

Document (PDF)

PURL

http://purl.flvc.org/ucf/fd/CFE0001591


Title

Estimation and clustering in statistical illposed linear inverse problems.

Creator

Rajapakshage, Rasika, Pensky, Marianna, Swanson, Jason, Zhang, Teng, Bagci, Ulas, Foroosh, Hassan, University of Central Florida

Abstract / Description

The main focus of the dissertation is estimation and clustering in statistical illposed linear inverse problems. The dissertation deals with a problem of simultaneously estimating a collection of solutions of illposed linear inverse problems from their noisy images under an operator that does not have a bounded inverse, when the solutions are related in a certain way. The dissertation defense consists of three parts. In the first part, the collection consists of measurements of temporal...
Show moreThe main focus of the dissertation is estimation and clustering in statistical illposed linear inverse problems. The dissertation deals with a problem of simultaneously estimating a collection of solutions of illposed linear inverse problems from their noisy images under an operator that does not have a bounded inverse, when the solutions are related in a certain way. The dissertation defense consists of three parts. In the first part, the collection consists of measurements of temporal functions at various spatial locations. In particular, we studythe problem of estimating a threedimensional function based on observations of its noisy Laplace convolution. In the second part, we recover classes of similar curves when the class memberships are unknown. Problems of this kind appear in many areas of application where clustering is carried out at the preprocessing step and then the inverse problem is solved for each of the cluster averages separately. As a result, the errors of the procedures are usually examined for the estimation step only. In both parts, we construct the estimators, study their minimax optimality and evaluate their performance via a limited simulation study. In the third part, we propose a new computational platform to better understand the patterns of RfMRI by taking into account the challenge of inevitable signal fluctuations and interpretthe success of dynamic functional connectivity approaches. Towards this, we revisit an autoregressive and vector autoregressive signal modeling approach for estimating temporal changes of the signal in brain regions. We then generate inverse covariance matrices fromthe generated windows and use a nonparametric statistical approach to select significant features. Finally, we use Lasso to perform classification of the data. The effectiveness of theproposed method is evidenced in the classification of RfMRI scans
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Date Issued

2019

Identifier

CFE0007710, ucf:52450

Format

Document (PDF)

PURL

http://purl.flvc.org/ucf/fd/CFE0007710


Title

EXPERIMENTAL AND THEORETICAL STUDY OF THE OPTICAL PROPERTIES OF SEMICONDUCTOR QUANTUM DOTS.

Creator

Nootz, Gero, Cuenya , Beatriz, University of Central Florida

Abstract / Description

The aim of this dissertation is to gain a better understanding of the unique electronic structure of lead salt quantum dots (QDs) and its influences on the nonlinear optical (NLO) properties as well as the time dynamics of the photogenerated charge carriers. A variety of optical techniques such as Zscan, twophoton excited fluorescence and timeresolved pump probe spectroscopy are used to measure these properties. The onephoton as well as the degenerate and nondegenerate twophoton...
Show moreThe aim of this dissertation is to gain a better understanding of the unique electronic structure of lead salt quantum dots (QDs) and its influences on the nonlinear optical (NLO) properties as well as the time dynamics of the photogenerated charge carriers. A variety of optical techniques such as Zscan, twophoton excited fluorescence and timeresolved pump probe spectroscopy are used to measure these properties. The onephoton as well as the degenerate and nondegenerate twophoton absorption (2PA) spectra are measured and the electronic wave functions from a fourband envelope function formalism are used to model the results. We observe local maxima in the 2PA spectra for QD samples of many different sizes at energies where only 1PA is predicted by the model. This is similar to the previously measured transitions in the 1PA spectra which are not predicted by the model but accrue at the energies of the twophoton allowed transitions. Most importantly we observe 2PA peaks for all samples at the energy of the first onephoton allowed transition. This result can only be understood in terms of symmetry breaking and therefore is strong evidence that other transitions, not predicted by the model if the selection rules are left intact, also have the origin in the lifted spatial symmetry of the wave functions. On the other hand, the uniquely symmetric eigenenergies of these quantumconfined energy states in the conduction and valance bands explain the observed trend toward larger twophoton crosssections as the quantum confinement is increased in smaller QDs. Moreover, this unique feature is shown to reduce the possible relaxation channels for photoexcited carriers, which is confirmed experimentally by the reduced carrier relaxation rate as compared to CdSe QDs which lack this symmetry. Carrier multiplication (CM), a process in which several electrons are excited by the absorption of a single photon is studied in PbS QDs. We show that for PbS QDs with radius smaller than 2.5 nm the parameters of CM get very close to the theoretical optimum. Nextgeneration solar cells operating under these ideal conditions could potentially have conversion efficiency of up to 42%. This compares favorably to the 30% efficiency limit of a single junction silicon solar cell.
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Date Issued

2010

Identifier

CFE0003396, ucf:48413

Format

Document (PDF)

PURL

http://purl.flvc.org/ucf/fd/CFE0003396


Title

ESTIMATION OF OCEANIC RAINFALL USING PASSIVE AND ACTIVE MEASUREMENTS FROM SEAWINDS SPACEBORNE MICROWAVE SENSOR.

Creator

Ahmad, Khalil, Jones, Linwood, University of Central Florida

Abstract / Description

The Ku band microwave remote sensor, SeaWinds, was developed at the National Aeronautics and Space Administration (NASA) Jet Propulsion Laboratory (JPL). Two identical SeaWinds instruments were launched into space. The first was flown onboard NASA QuikSCAT satellite which has been orbiting the Earth since June 1999, and the second instrument flew onboard the Japanese Advanced Earth Observing Satellite II (ADEOSII) from December 2002 till October 2003 when an irrecoverable solar panel failure...
Show moreThe Ku band microwave remote sensor, SeaWinds, was developed at the National Aeronautics and Space Administration (NASA) Jet Propulsion Laboratory (JPL). Two identical SeaWinds instruments were launched into space. The first was flown onboard NASA QuikSCAT satellite which has been orbiting the Earth since June 1999, and the second instrument flew onboard the Japanese Advanced Earth Observing Satellite II (ADEOSII) from December 2002 till October 2003 when an irrecoverable solar panel failure caused a premature end to the ADEOSII satellite mission. SeaWinds operates at a frequency of 13.4 GHz, and was originally designed to measure the speed and direction of the ocean surface wind vector by relating the normalized radar backscatter measurements to the near surface wind vector through a geophysical model function (GMF). In addition to the backscatter measurement capability, SeaWinds simultaneously measures the polarized radiometric emission from the surface and atmosphere, utilizing a ground signal processing algorithm known as the QuikSCAT / SeaWinds Radiometer (QRad / SRad). This dissertation presents the development and validation of a mathematical inversion algorithm that combines the simultaneous active radar backscatter and the passive microwave brightness temperatures observed by the SeaWinds sensor to retrieve the oceanic rainfall. The retrieval algorithm is statistically based, and has been developed using collocated measurements from SeaWinds, the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) rain rates, and Numerical Weather Prediction (NWP) wind fields from the National Centers for Environmental Prediction (NCEP). The oceanic rain is retrieved on a spacecraft wind vector cell (WVC) measurement grid that has a spatial resolution of 25 km. To evaluate the accuracy of the retrievals, examples of the passiveonly, as well as the combined active / passive rain estimates from SeaWinds are presented, and comparisons are made with the standard TRMM rain data products. Results demonstrate that SeaWinds rain measurements are in good agreement with the independent microwave rain observations obtained from TMI. Further, by applying a threshold on the retrieved rain rates, SeaWinds rain estimates can be utilized as a rain flag. In order to evaluate the performance of the SeaWinds flag, comparisons are made with the Impact based Multidimensional Histogram (IMUDH) rain flag developed by JPL. Results emphasize the powerful rain detection capabilities of the SeaWinds retrieval algorithm. Due to its broad swath coverage, SeaWinds affords additional independent sampling of the oceanic rainfall, which may contribute to the future NASA's Precipitation Measurement Mission (PMM) objectives of improving the global sampling of oceanic rain within 3 hour windows. Also, since SeaWinds is the only sensor onboard QuikSCAT, the SeaWinds rain estimates can be used to improve the flagging of raincontaminated oceanic wind vector retrievals. The passiveonly rainfall retrieval algorithm (QRad / SRad) has been implemented by JPL as part of the level 2B (L2B) science data product, and can be obtained from the Physical Oceanography Distributed Data Archive (PO.DAAC).
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Date Issued

2007

Identifier

CFE0001969, ucf:47441

Format

Document (PDF)

PURL

http://purl.flvc.org/ucf/fd/CFE0001969


Title

SemiAnalytical Solutions of Nonlinear Differential Equations Arising in Science and Engineering.

Creator

Dewasurendra, Mangalagama, Vajravelu, Kuppalapalle, Mohapatra, Ram, Rollins, David, Kumar, Ranganathan, University of Central Florida

Abstract / Description

Systems of coupled nonlinear differential equations arise in science and engineering are inherently nonlinear and difficult to find exact solutions. However, in the late nineties, Liao introduced Optimal Homotopy Analysis Method (OHAM), and it allows us to construct accurate approximations to the systems of coupled nonlinear differential equations.The drawback of OHAM is, we must first choose the proper auxiliary linear operator and then solve the linear higherorder deformation equation by...
Show moreSystems of coupled nonlinear differential equations arise in science and engineering are inherently nonlinear and difficult to find exact solutions. However, in the late nineties, Liao introduced Optimal Homotopy Analysis Method (OHAM), and it allows us to construct accurate approximations to the systems of coupled nonlinear differential equations.The drawback of OHAM is, we must first choose the proper auxiliary linear operator and then solve the linear higherorder deformation equation by spending lots of CPU time. However, in the latest innovation of Liao's " Method of Directly Defining inverse Mapping (MDDiM)" which he introduced to solve a single nonlinear ordinary differential equation has great freedom to define the inverse linear map directly. In this way, one can solve higher order deformation equations quickly, and it is unnecessary to calculate an inverse linear operator.Our primary goal is to extend MDDiM to solve systems of coupled nonlinear ordinary differential equations. In the first chapter, we will introduce MDDiM and briefly discuss the advantages of MDDiM Over OHAM. In the second chapter, we will study a nonlinear coupled system using OHAM. Next three chapters, we will apply MDDiM to coupled nonlinear systems arise in mechanical engineering to study fluid flow and heat transfer. In chapter six we will apply this novel method to study coupled nonlinear systems in epidemiology to investigate how diseases spread throughout time. In the last chapter, we will discuss our conclusions and will propose some future work. Another main focus is to compare MDDiM with OHAM.
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Date Issued

2019

Identifier

CFE0007624, ucf:52551

Format

Document (PDF)

PURL

http://purl.flvc.org/ucf/fd/CFE0007624
Pages