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Title: Investigation of Damage Detection Methodologies For Structural Health Monitoring of Thin-Walled Pressure Vessels.
Creator: Modesto, Arturo, Catbas, Necati, Chopra, Manoj, Zaurin, Ricardo, University of Central Florida
Abstract / Description: There is a need in exploring structural health monitoring technologies for the composite structures particularly aged Composite Overwrapped Pressure Vessels (COPVs) for the current and future implementation of COPVs for space missions. In this study, the research was conducted in collaboration with NASA Kennedy Space Center and also NASA Marshall Space and Flight Center engineers. COPVs have been used to store inert gases like helium (for propulsion) and nitrogen (for life support) under...
Show moreThere is a need in exploring structural health monitoring technologies for the composite structures particularly aged Composite Overwrapped Pressure Vessels (COPVs) for the current and future implementation of COPVs for space missions. In this study, the research was conducted in collaboration with NASA Kennedy Space Center and also NASA Marshall Space and Flight Center engineers. COPVs have been used to store inert gases like helium (for propulsion) and nitrogen (for life support) under varying degrees of pressure onboard the orbiter since the beginning of the Space Shuttle Program. After the Columbia accident, the COPVs were re-examined and different studies (e.g. Laser profilometry inspection, NDE utilizing Raman Spectroscopy) have been conducted and can be found in the literature. To explore some of the unique in-house developed hardware and algorithms for monitoring COPVs, this project is carried out with the following general objectives:1) Investigate the obtaining indices/features related to the performance and/or condition of pressure vessels2) Explore different sensing technologies and Structural Health Monitoring (SHM) systems3) Explore different types of data analysis methodologies to detect damage with particular emphasis on statistical analysis, cross-correlation analysis and Auto Regressive model with eXogeneous input (ARX) models4) Compare differences in various types of pressure vesselsFirst an introduction to theoretical pressure vessels, which are used to compare to actual test specimens, is presented. Next, a background review of the test specimens including their applications and importance is discussed. Subsequently, a review of related SHM applications to this study is presented. The theoretical background of the data analysis methodologies used to detect damage in this study are provided and these methodologies are applied in the laboratory using Composite Overwrapped Pressure Vessels (COPVs) to determine the effectiveness of these techniques. Next another study on the Air Force Research Laboratory (AFRL) Tank that is carried out in collaboration with NASA KSC and NASA MSFC is presented with preliminary results. Finally the results and interpretations of both studies are summarized and discussed.
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Date Issued: 2015
Identifier: CFE0005978, ucf:50770
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005978

Title: Optimal Switch Timing for Piezoelectric-Based Semi-Active Vibration Reduction Techniques.
Creator: Kelley, Christopher, Kauffman, Jeffrey, Das, Tuhin, Xu, Yunjun, University of Central Florida
Abstract / Description: Semi-active vibration reduction techniques switch a piezoelectric transducer between an open circuit and a shunt circuit in a way that reduces vibration. The steady-state vibration amplitude is reduced by exploiting the change in stiffness between states, manipulating the converted electrical energy, or both. Semi-active techniques typically require four switches per vibration cycle. Control laws such as state switching and synchronized switch damping require switches to occur at every...
Show moreSemi-active vibration reduction techniques switch a piezoelectric transducer between an open circuit and a shunt circuit in a way that reduces vibration. The steady-state vibration amplitude is reduced by exploiting the change in stiffness between states, manipulating the converted electrical energy, or both. Semi-active techniques typically require four switches per vibration cycle. Control laws such as state switching and synchronized switch damping require switches to occur at every displacement extrema. Due to the complexity of analyzing a system with discrete switches, these control laws were developed based on intuition. The few analyses that attempt to determine an optimal switching law mathematically only evaluate the system at resonance. This thesis investigates the effects of switch timing on vibration reduction and the frequency dependence of the optimal switch timing control law. Regardless of the switch timing, sensing uncertainties, noise, and modeling errors can cause the switches to occur away from the designed moment. Thus, this work also quantifies the expected degradation in vibration reduction performance due to variations in the designed switch time. Experimental, numerical, and analytical solutions agree that the optimal switch timing of these semi-active techniques depends on frequency. A closed-form solution for the optimal switch timing is derived in terms of well-known, non-dimensional parameters.
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Date Issued: 2016
Identifier: CFE0006336, ucf:51555
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006336

Title: Compressive Sensing and Recovery of Structured Sparse Signals.
Creator: Shahrasbi, Behzad, Rahnavard, Nazanin, Vosoughi, Azadeh, Wei, Lei, Atia, George, Pensky, Marianna, University of Central Florida
Abstract / Description: In the recent years, numerous disciplines including telecommunications, medical imaging, computational biology, and neuroscience benefited from increasing applications of high dimensional datasets. This calls for efficient ways of data capturing and data processing. Compressive sensing (CS), which is introduced as an efficient sampling (data capturing) method, is addressing this need. It is well-known that the signals, which belong to an ambient high-dimensional space, have much smaller...
Show moreIn the recent years, numerous disciplines including telecommunications, medical imaging, computational biology, and neuroscience benefited from increasing applications of high dimensional datasets. This calls for efficient ways of data capturing and data processing. Compressive sensing (CS), which is introduced as an efficient sampling (data capturing) method, is addressing this need. It is well-known that the signals, which belong to an ambient high-dimensional space, have much smaller dimensionality in an appropriate domain. CS taps into this principle and dramatically reduces the number of samples that is required to be captured to avoid any distortion in the information content of the data. This reduction in the required number of samples enables many new applications that were previously infeasible using classical sampling techniques.Most CS-based approaches take advantage of the inherent low-dimensionality in many datasets. They try to determine a sparse representation of the data, in an appropriately chosen basis using only a few significant elements. These approaches make no extra assumptions regarding possible relationships among the significant elements of that basis. In this dissertation, different ways of incorporating the knowledge about such relationships are integrated into the data sampling and the processing schemes.We first consider the recovery of temporally correlated sparse signals and show that using the time correlation model. The recovery performance can be significantly improved. Next, we modify the sampling process of sparse signals to incorporate the signal structure in a more efficient way. In the image processing application, we show that exploiting the structure information in both signal sampling and signal recovery improves the efficiency of the algorithm. In addition, we show that region-of-interest information can be included in the CS sampling and recovery steps to provide a much better quality for the region-of-interest area compared the rest of the image or video. In spectrum sensing applications, CS can dramatically improve the sensing efficiency by facilitating the coordination among spectrum sensors. A cluster-based spectrum sensing with coordination among spectrum sensors is proposed for geographically disperse cognitive radio networks. Further, CS has been exploited in this problem for simultaneous sensing and localization. Having access to this information dramatically facilitates the implementation of advanced communication technologies as required by 5G communication networks.
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Date Issued: 2015
Identifier: CFE0006392, ucf:51509
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006392

Title: Structure-preserving finite difference methods for linearly damped differential equations.
Creator: Bhatt, Ashish, Moore, Brian, Choudhury, Sudipto, Gurel, Basak, Kauffman, Jeffrey L., University of Central Florida
Abstract / Description: Differential equations (DEs) model a variety of physical phenomena in science and engineering. Many physical phenomena involve conservative or dissipative forces, which manifest themselves as qualitative properties of DEs that govern these phenomena. Since only a few and simplistic models are known to have exact solutions, approximate solution techniques, such as numerical integration, are used to reveal important insights about solution behavior and properties of these models. Numerical...
Show moreDifferential equations (DEs) model a variety of physical phenomena in science and engineering. Many physical phenomena involve conservative or dissipative forces, which manifest themselves as qualitative properties of DEs that govern these phenomena. Since only a few and simplistic models are known to have exact solutions, approximate solution techniques, such as numerical integration, are used to reveal important insights about solution behavior and properties of these models. Numerical integrators generally result in undesirable quantitative and qualitative errors . Standard numerical integrators aim to reduce quantitative errors, whereas geometric (numerical) integrators aim to reduce or eliminate qualitative errors, as well, in order to improve the accuracy of numerical solutions. It is now widely recognized that geometric (or structure-preserving) integrators are advantageous compared to non-geometric integrators for DEs, especially for long time integration.Geometric integrators for conservative DEs have been proposed, analyzed, and investigated extensively in the literature. The motif of this thesis is to extend the idea of structure preservation to linearly damped DEs. More specifically, we develop, analyze, and implement geometric integrators for linearly damped ordinary and partial differential equations (ODEs and PDEs) that possess conformal invariants, which are qualitative properties that decay exponentially along any solution of the DE as the system evolves over time. In particular, we derive restrictions on the coefficient functions of exponential Runge-Kutta (ERK) numerical methods for preservation of certain conformal invariants of linearly damped ODEs. An important class of these methods is shown to preserve the damping rate of solutions of damped linear ODEs. Linearly stability and order of accuracy for some specific cases of ERK methods are investigated. Geometric integrators for PDEs are designed using structure-preserving ERK methods in space, time, or both. These integrators for PDEs are also shown to preserve additional structure in certain special cases. Numerical experiments illustrate higher order accuracy and structure preservation properties of various ERK based methods, demonstrating clear advantages over non-structure-preserving methods, as well as usefulness for solving a wide range of DEs.
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Date Issued: 2016
Identifier: CFE0006832, ucf:51763
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006832

Title: Monitoring Crystal Structure Refinements Using Solid-State NMR Chemical Shift Tensors.
Creator: Kalakewich, Keyton, Harper, James, Campiglia, Andres, Elsheimer, Seth, Chumbimuni Torres, Karin, Masunov, Artem, Moore, Sean, University of Central Florida
Abstract / Description: Inclusion of lattice-fields in density functional theory (DFT) methods has enabled the accurate calculation of solid-state nuclear magnetic resonance (SSNMR) chemical shift tensors. Calculated 13C and 15N tensors (i.e. 3 principle values per nucleus) can be used to monitor crystal structure refinements and to select the correct structure from a large population of computationally generated candidates. In this dissertation, chapter 2 describes a methodology to improve established crystal...
Show moreInclusion of lattice-fields in density functional theory (DFT) methods has enabled the accurate calculation of solid-state nuclear magnetic resonance (SSNMR) chemical shift tensors. Calculated 13C and 15N tensors (i.e. 3 principle values per nucleus) can be used to monitor crystal structure refinements and to select the correct structure from a large population of computationally generated candidates. In this dissertation, chapter 2 describes a methodology to improve established crystal structures from three different diffraction techniques involving geometric refinement monitored using SSNMR tensor values. The calculated 13C tensors for three relatively simple organic compounds (i.e. acetaminophen, naphthalene, and adenosine) are shown to markedly improve upon DFT refinement. The so-called GGA-PBE functional provided the best agreement with experimental data. The use of the three principle values of the tensor is required for such results as the average (i.e. the isotropic) is less accurate. Chapter 3 applies this method to differentiate between hundreds of computationally predicted crystal structures. Typically, lattice energy of each candidate is used to select the correct structure, a process which is seldom successful. Herein, it is demonstrated that when 13C tensors from DFT refined structures are used for structural ranking by comparison to experimental data, only the correct structure agrees with experimental data in all cases. Chapter 4 illustrates the use of 15N tensors to monitor DFT refinement as an alternative to the 13C approach of Chapter 2. 15N tensors have been very difficult to obtain previously, thus a novel experimental method is developed here which improves signal-to-noise by as much as 300% and allows routine measurement. This improvement also improves the accuracy of the tensor values. Overall, the 15N tensors are found to be at least 5 times more sensitive to DFT refinements than 13C values.
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Date Issued: 2017
Identifier: CFE0006888, ucf:51726
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006888

Title: Vanadium Oxide Microbolometers with Patterned Gold Black or Plasmonic Resonant Absorbers.
Creator: Smith, Evan, Peale, Robert, Khondaker, Saiful, Dove, Adrienne, Boreman, Glenn, University of Central Florida
Abstract / Description: High sensitivity uncooled microbolometers are necessary to meet the needs of the next generation of infrared detectors, which seek low power consumption and production cost without sacrificing performance. Presented here is the design, fabrication, and characterization of a microbolometer with responsivity enhanced by novel highly absorptive coatings. The device utilizes a gold-doped vanadium oxide film in a standard air bridge design. Performance estimations are calculated from current...
Show moreHigh sensitivity uncooled microbolometers are necessary to meet the needs of the next generation of infrared detectors, which seek low power consumption and production cost without sacrificing performance. Presented here is the design, fabrication, and characterization of a microbolometer with responsivity enhanced by novel highly absorptive coatings. The device utilizes a gold-doped vanadium oxide film in a standard air bridge design. Performance estimations are calculated from current theory, and efforts to maximize signal to noise ratio are shown and evaluated. Most notably, presented are the experimental results and analysis from the integration of two different absorptive coatings: a patterned gold black film and a plasmonic resonant structure.Infrared-absorbing gold black was selectively patterned onto the active surfaces of the detector. Patterning by metal lift-off relies on protection of the fragile gold black with an evaporated oxide, which preserves gold black's near unity absorptance. This patterned gold black also survives the dry-etch removal of the sacrificial polyimide used to fabricate the air-bridge bolometers. Infrared responsivity is improved 70% for mid-wave IR and 22% for long-wave IR. The increase in the thermal time constant caused by the additional mass of gold black is a modest 15%. However, this film is sensitive to thermal processing; experimental results indicate a decrease in absorptance upon device heating.Sub-wavelength resonant structures designed for long-wave infrared (LWIR) absorption have also been investigated. Dispersion of the dielectric refractive index provides for multiple overlapping resonances that span the 8-12 ?m LWIR wavelength band, a broader range than can be achieved using the usual resonance quarter-wave cavity engineered into the air-bridge structures. Experimental measurements show an increase in responsivity of 96% for mid-wave IR and 48% for long-wave IR, while thermal response time only increases by 16% due to the increased heat capacity. The resonant structures are not as susceptible to thermal processing as are the gold black films. This work suggests that plasmonic resonant structures can be an ideal method to improve detector performance for microbolometers.
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Date Issued: 2015
Identifier: CFE0006004, ucf:51026
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006004

Title: Development and Implementation of a Streamlined Process for the Creation and Mechanization of Negative Poisson's Ratio Meso-Scale Patterns.
Creator: Shuler, Matthew, Gordon, Ali, Kauffman, Jeffrey L., Ghosh, Ranajay, University of Central Florida
Abstract / Description: This thesis focuses on the development a streamlined process used to create novel meso-scale pattern used to induce negative Poisson's ratio (NPR) behavior at the bulk scale. This process includes, the development, optimization, and implementation of a candidate pattern. Currently, the majority of NPR structures are too porous to be utilized in conventional applications. For others, manufacturing methods have yet to realize the meso-scale pattern. Consequently, new NPR meta-materials must be...
Show moreThis thesis focuses on the development a streamlined process used to create novel meso-scale pattern used to induce negative Poisson's ratio (NPR) behavior at the bulk scale. This process includes, the development, optimization, and implementation of a candidate pattern. Currently, the majority of NPR structures are too porous to be utilized in conventional applications. For others, manufacturing methods have yet to realize the meso-scale pattern. Consequently, new NPR meta-materials must be developed in order to confer transformative thermomechanical responses to structures where transverse expansion is more desirable than contraction. For example, materials at high temperature. Additionally, patterns that take into account manufacturing limitations, while maintaining the properties characteristically attached to negative Poisson's Ratio materials, are ideal in order to utilize the potential of NPR structures. A novel NPR pattern is developed, numerically analyzed, and optimized via design of experiments. The parameters of the meso-structure are varied, and the bulk response is studied using finite element analysis (FEA). The candidate material for the study is Medium-Density Fiberboard (MDF). This material is relevant to a variety of applications where multiaxial stresses, particularly compressive, lead to mechanical fatigue. Samples are fabricated through a laser cutting process, and a comparison is drawn through the use of experimental means, including traditional tensile loading tests and digital image correlation (DIC). Various attributes of the elasto-plasticity responses of the bulk structure are used as objectives to guide the optimization process.
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Date Issued: 2017
Identifier: CFE0006795, ucf:51830
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006795

Title: The conceptual field of proportional reasoning researched through the lived experiences of nurses.
Creator: Deichert, Deana, Dixon, Juli, Haciomeroglu, Erhan, Andreasen, Janet, Hunt, Debra, University of Central Florida
Abstract / Description: Proportional reasoning instruction is prevalent in elementary, secondary, and post-secondary schooling. The concept of proportional reasoning is used in a variety of contexts for solving real-world problems. One of these contexts is the solving of dosage calculation proportional problems in the healthcare field. On the job, nurses perform drug dosage calculations which carry fatal consequences. As a result, nursing students are required to meet minimum competencies in solving proportion...
Show moreProportional reasoning instruction is prevalent in elementary, secondary, and post-secondary schooling. The concept of proportional reasoning is used in a variety of contexts for solving real-world problems. One of these contexts is the solving of dosage calculation proportional problems in the healthcare field. On the job, nurses perform drug dosage calculations which carry fatal consequences. As a result, nursing students are required to meet minimum competencies in solving proportion problems. The goal of this research is to describe the lived experiences of nurses in connection to their use of proportional reasoning in order to impact instruction of the procedures used to solve these problems. The research begins by clarifying and defining the conceptual field of proportional reasoning. Utilizing Vergnaud's theory of conceptual fields and synthesizing the differing organizational frameworks used in the literature on proportional reasoning, the concept is organized and explicated into three components: concepts, procedures, and situations. Through the lens of this organizational structure, data from 44 registered nurses who completed a dosage calculation proportion survey were analyzed and connected to the framework of the conceptual field of proportional reasoning. Four nurses were chosen as a focus of in-depth study based upon their procedural strategies and ability to vividly describe their experiences. These qualitative results are synthesized to describe the lived experiences of nurses related to their education and use of proportional reasoning.Procedural strategies that are supported by textbooks, instruction, and practice are developed and defined. Descriptive statistics show the distribution of procedures used by nurses on a five question dosage calculation survey. The most common procedures used are the nursing formula, cross products, and dimensional analysis. These procedures correspond to the predominate procedures found in nursing dosage calculation texts. Instructional implications focus on the transition between elementary and secondary multiplicative structures, the confusion between equality and proportionality, and the difficulty that like quantities present in dealing with proportions.
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Date Issued: 2014
Identifier: CFE0005781, ucf:50058
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005781

Title: Cooperative vs Competitive Goals in Educational Video Games.
Creator: Smith, Peter, Bowers, Clint, McDaniel, Thomas, Kincaid, John, Cannon-Bowers, Janis, University of Central Florida
Abstract / Description: The concept of serious games, or using games and gaming technologies for purposes other than purely entertainment, became popularized with the creation of the Serious Games Initiative in 2002 and has continued to grow. While this trend may appear new, the use of games for learning has a rich history and the idea of using a game as a learning platform is an established concept that had has withstood the test of time. Research in this area must move from if games can teach, to how do we improve...
Show moreThe concept of serious games, or using games and gaming technologies for purposes other than purely entertainment, became popularized with the creation of the Serious Games Initiative in 2002 and has continued to grow. While this trend may appear new, the use of games for learning has a rich history and the idea of using a game as a learning platform is an established concept that had has withstood the test of time. Research in this area must move from if games can teach, to how do we improve games that do. Proponents of serious games suggest that they should improve motivation, time on task, motivation to learn, and a litany of other benefits based primarily on the thought that what works in an entertainment game will work in a learning game. Unfortunately, this might not always be the case. For example, a commonly held misconception in learning games is that competition will motivate learner to succeed, as it motivates players of an entertainment game to continue to play. This is, however, not well supported by the learning science literature. Cooperative goal structures commonly lead to increased motivation to learn as well as improved learning outcomes when compared to competition. This research seeks to provide a framework to view games for learning and more specifically explore the structure of challenge in the context of cooperative and competitive goal structures, as well as explore the use of the word game and how it could possibly modify the expectations of the learner.
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Date Issued: 2012
Identifier: CFE0004603, ucf:49913
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004603

Title: Analytical And Experimental Study Of Monitoring For Chain-Like Nonlinear Dynamic Systems.
Creator: Paul, Bryan, Yun, Hae-Bum, Catbas, Fikret, Chopra, Manoj, University of Central Florida
Abstract / Description: Inverse analysis of nonlinear dynamic systems is an important area of research in the ?eld of structural health monitoring for civil engineering structures. Structural damage usually involves localized nonlinear behaviors of dynamic systems that evolve into different classes of nonlinearity as well as change system parameter values. Numerous parametric modal analysis techniques (e.g., eigensystem realization algorithm and subspace identification method) have been developed for system...
Show moreInverse analysis of nonlinear dynamic systems is an important area of research in the ?eld of structural health monitoring for civil engineering structures. Structural damage usually involves localized nonlinear behaviors of dynamic systems that evolve into different classes of nonlinearity as well as change system parameter values. Numerous parametric modal analysis techniques (e.g., eigensystem realization algorithm and subspace identification method) have been developed for system identification of multi-degree-of-freedom dynamic systems. However, those methods are usually limited to linear systems and known for poor sensitivity to localized damage. On the other hand, non-parametric identification methods (e.g., artificial neural networks) are advantageous to identify time-varying nonlinear systems due to unpredictable damage. However, physical interpretation of non-parametric identification results is not as straightforward as those of the parametric methods. In this study, the Multidegree-of-Freedom Restoring Force Method (MRFM) is employed as a semi-parametric nonlinear identification method to take the advantages of both the parametric and non-parametric identification methods.The MRFM is validated using two realistic experimental nonlinear dynamic tests: (i) large-scale shake table tests using building models with different foundation types, and (ii) impact test using wind blades. The large-scale shake table test was conducted at Tongji University using 1:10 scale 12-story reinforced concrete building models tested on three different foundations, including pile, box and fixed foundation. The nonlinear dynamic signatures of the building models collected from the shake table tests were processed using MRFM (i) to investigate the effects of foundation types on nonlinear behavior of the superstructure and (ii) to detect localized damage during the shake table tests. Secondly, the MRFM was applied to investigate the applicability of this method to wind turbine blades. Results are promising, showing a high level of nonlinearity of the system and how the MRFM can be applied to wind-turbine blades. Future studies were planned for the comparison of physical characteristic of this blade with blades created made of other material.
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Date Issued: 2013
Identifier: CFE0004734, ucf:49818
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004734

Title: STRUCTURAL CAUSES OF SOCIAL CONFLICT IN AFRICA.
Creator: Charland, Lucien, Dolan, Thomas, University of Central Florida
Abstract / Description: Social conflict, as opposed to armed conflict, has received less attention in the field of quantitative research. This paper investigates the structural causes of political violence in 35 African states using data from the Social Conflict in Africa dataset and the Beck and Katz panel corrected standard errors time series regression model. Theoretically, a closed political opportunity structure, combined with a weak state unable to provide public goods, should together produce high levels of...
Show moreSocial conflict, as opposed to armed conflict, has received less attention in the field of quantitative research. This paper investigates the structural causes of political violence in 35 African states using data from the Social Conflict in Africa dataset and the Beck and Katz panel corrected standard errors time series regression model. Theoretically, a closed political opportunity structure, combined with a weak state unable to provide public goods, should together produce high levels of social conflict. The independent variables attempt to operationalize these concepts from four different angles. In this analysis Access to Education and Infrastructure (AEI), Ethno Linguistic Fractionalization (ELF), Freedom in the World Political Rights (FIW), and National Material Capabilities (NMC) were all significant predictors of social conflict. This study found that as the level of ethnic fractionalization and material capabilities within states rose, the frequency of social conflict events also increased. However, as access to infrastructure and political rights declined, the number of social conflict events increased. Wald chi-square and R-square values suggest that the model is complete and has substantial explanatory power.
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Date Issued: 2014
Identifier: CFH0004663, ucf:45314
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFH0004663

Title: SELF-ASSEMBLED LIPID TUBULES: STRUCTURES, MECHANICAL PROPERTIES, AND APPLICATIONS.
Creator: Zhao, Yue, Fang, Jiyu, University of Central Florida
Abstract / Description: Self-assembled lipid tubules are particularly attractive for inorganic synthesis and drug delivery because they have hollow cylindrical shapes and relatively rigid mechanical properties. In this thesis work, we have synthesized lipid tubules of 1,2-bis(tricosa-10,12-dinoyl)-sn-glycero-3-phosphocholine (DC8,9PC) by self-assembly and polymerization in solutions. We demonstrate for the first time that both uniform and modulated molecular tilt orderings exist in the tubule walls, which have been...
Show moreSelf-assembled lipid tubules are particularly attractive for inorganic synthesis and drug delivery because they have hollow cylindrical shapes and relatively rigid mechanical properties. In this thesis work, we have synthesized lipid tubules of 1,2-bis(tricosa-10,12-dinoyl)-sn-glycero-3-phosphocholine (DC8,9PC) by self-assembly and polymerization in solutions. We demonstrate for the first time that both uniform and modulated molecular tilt orderings exist in the tubule walls, which have been predicted by current theories, and therefore provide valuable supporting evidences for self-assembly mechanisms of chiral molecules. Two novel methods are developed for studying the axial and radial deformations of DC8,9PC lipid tubules. Mechanical properties of DC8,9PC tubules are systematically studied in terms of persistence length, bending rigidity, strain energy, axial and radial elastic moduli, and critical force for collapse. Mechanisms of recovery and surface stiffening are discussed. Due to the high aspect ratio of lipid tubules, the hierarchical assembly of lipid tubules into ordered arrays and desired architectures is critical in developing their applications. Two efficient methods for fabricating ordered arrays of lipid tubules on solid substrates have been developed. Ordered arrays of hybrid silica-lipid tubes are synthesized by tubule array-templated sol-gel reactions. Ordered arrays of optical anisotropic fibers with tunable shapes and refractive indexes are fabricated. This thesis work provides a paradigm for molecularly engineered structures.
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Date Issued: 2007
Identifier: CFE0001918, ucf:47486
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0001918

Title: COHORT STUDY OF PAIN BEHAVIORS IN THE ELDERLY RESIDING IN SKILLED NURSING CARE.
Creator: Burfield, Allison, Sole, Mary Lou, University of Central Florida
Abstract / Description: An integral concern across care settings is the prompt intervention for patients suffering with pain. Long-term care (LTC) settings present with unique challenges to assess and manage pain in resident populations. Pain assessment is especially challenging, because residents have varying degrees of cognition to communicate their pain, and clinician/staff knowledge of pain symptoms may be lacking. The purpose of this research was to improve the measurement of pain and outcomes of care for the...
Show moreAn integral concern across care settings is the prompt intervention for patients suffering with pain. Long-term care (LTC) settings present with unique challenges to assess and manage pain in resident populations. Pain assessment is especially challenging, because residents have varying degrees of cognition to communicate their pain, and clinician/staff knowledge of pain symptoms may be lacking. The purpose of this research was to improve the measurement of pain and outcomes of care for the elderly residing in skilled nursing care, especially those with cognitive-impairment. The specific aims of this study were to: 1) Determine the magnitude of the relationship between pain behaviors and a measurement model hypothesized for pain; 2) Test the construct validity of a pain measurement model; 3) Examine the concomitance of pain and cognition in a three-year longitudinal analysis. The research questions answered: 1) Is there a difference in the prevalence of pain in cognitively intact versus cognitively-impaired residents; 2) Can a theoretically derived model of pain aid in detecting pain across all cognitive levels; and 3) Do pain and cognitive status concomitantly correlate? The goal was to examine the covariance model of concomitance of pain and cognition to more accurately construct theoretical models of pain to then include additional resident care factors in future research. Traditional self-reports of pain are often under-assessed and under-treated in the cognitively-impaired (CI) elderly resident. Having additional measures to detect pain beyond self-reports of pain intensity and frequency increases the likelihood of detecting pain in populations with complex symptom presentation. Data collected from skilled nursing facilities offer exceptional opportunities to study resident demographics, characteristics, symptoms, medication use, quality indicators, and care outcomes. The Minimum Data Set-Resident Assessment Instrument (MDS-RAI) 2.0, a nationally required resident assessment tool, must be completed on every resident in a Medicare LTC facility within 14 days of admission, quarterly, annually and with significant changes in resident status. Because the MDS is widely used and recognized in LTC settings, core items from MDS [i.e., pain frequency (J2a) and pain intensity (J2b)] along with additional MDS items hypothesized to signify pain were analyzed in the pilot measurement model. Ten core items from MDS were used: 1) Inappropriate behavior frequency (E4da); 2) Repetitive physical movements; 3) Repetitive verbalizations (E1c); 4) Sad facial expressions (E1l); 5) Crying (E1m); 6) Change in mood (E3); 7) Negative statements (E1a); 8) Pain frequency (J2a); 9) Pain intensity (J2b); and 10) Cumulative pain sites scores. All indicators of pain were significant at the p<.01 level. A longitudinal cohort design was used to answer if a concomitance exists between pain and cognition. Data were collected from MDS annual assessments from 2001, 2002 and 2003 for residents across the United States. The sample consisted of 56,494 residents age 65 years and older with an average age of 83 ±8.2 years. Descriptive statistics, ANOVA and a covariance model were used to evaluate cognition and pain at the three time intervals. ANOVA indicated a significant effect (p<.01) for pain and cognition with protected t-tests indicating scores decreased significantly over time with resident measures of pain and cognition. Results from this study suggest that: 1) Using only pain intensity and frequency, pain prevalence was found in 30% of the pilot population, while 47.7% of cognitively intact residents had documented pain and only 18.2% of the severely CI had documented pain, supporting previous research that pain is potentially under-reported in the CI; 2) Parsimonious measurements models of pain should include dimensions beyond self-reports of pain (i.e., cognitive, affective, behavioral and inferred pain indicators); 3) Model fit was improved by using specific MDS items in the pain construct; 4) Longitudinal analysis revealed relative stability for pain and cognition measures over time (e.g., larger stability or consistency was found in cognitive measures than the measures of pain over the three-year period); 5) Crossed-legged effects between pain and cognition were not consistent; 6) A concomitant relationship was not found between pain and cognition. The relationship was significant (p<.01), but associations were weak (r=0.03 to 0. 08). Pain or cognition should not be used as a predictor of the other in theoretical models for similar populations. The MDS is a reliable instrument to follow resident attributes, quality of care, and patient outcomes over time. The development of more accurate assessments of pain may improve resident care outcomes. Ineffectively intervening on the pain cycle is posited to cause secondary unmet needs that affect the resident's quality of life. Findings support the importance of improving clinical outcomes in the management of pain in the elderly residing in long-term care. Deficits in the treatment of pain highlight the impetus to support health policy change that includes pain treatment as a top health priority and a quality indicator for federally funded programs supporting eldercare.
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Date Issued: 2009
Identifier: CFE0002533, ucf:47660
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0002533

Title: MICROSCOPIC SURFACE TEXTURES CREATED BY INTERFACIAL FLOW INSTABILITIES.
Creator: Gu, Jing, Weiwei Deng, Dr., University of Central Florida
Abstract / Description: In nature, microscopic surface textures impact useful function, such as the drag reduction of shark skin (Dean & Bhushan, 2010) and superhydrophobicity of the lotus leaf(Pan, Kota, Mabry, & Tuteja, 2013). In this study, we explore these phenomena by re-creating microscopic surface textures via the method of interfacial flow instability in drying polyvinylidene fluoride (PVDF) acetone solutions. In general, PVDF films can be made using either spin coating or electrospray deposition with...
Show moreIn nature, microscopic surface textures impact useful function, such as the drag reduction of shark skin (Dean & Bhushan, 2010) and superhydrophobicity of the lotus leaf(Pan, Kota, Mabry, & Tuteja, 2013). In this study, we explore these phenomena by re-creating microscopic surface textures via the method of interfacial flow instability in drying polyvinylidene fluoride (PVDF) acetone solutions. In general, PVDF films can be made using either spin coating or electrospray deposition with various weight concentrations in acetone. In order to study the morphology of the porous structure of PVDF films, wet deposition samples were fabricated by spin coating or near-field electrospray. Possible theories are discussed and examined to explain the formation of these porous structures resulting in development of a well-controlled method to create porous PVDF films with various pore sizes and pore densities. All samples are characterized and found to exhibit superhydrophobicity and drag reduction. To connect porous PVDF film morphology to the established field of dry particle fabrication, PVDF particle synthesis by far-field electrospray is also reviewed and discussed. An established method to generate polymer particles of different morphologies in other polymers (Almeria-Diez, 2012) by electrospray drying is confirmed using PVDF as well. Due to the ability of scalable and re-configurable electrospray, the microscopic surface textures can be applied to areas of any size to reduce drag or impart water-repelling properties.
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Date Issued: 2013
Identifier: CFH0004479, ucf:45066
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFH0004479

Title: STRUCTURAL HEALTH MONITORING WITH EMPHASIS ON COMPUTER VISION, DAMAGE INDICES, AND STATISTICAL ANALYSIS.
Creator: ZAURIN, RICARDO, CATBAS, F. NECATI, University of Central Florida
Abstract / Description: Structural Health Monitoring (SHM) is the sensing and analysis of a structure to detect abnormal behavior, damage and deterioration during regular operations as well as under extreme loadings. SHM is designed to provide objective information for decision-making on safety and serviceability. This research focuses on the SHM of bridges by developing and integrating novel methods and techniques using sensor networks, computer vision, modeling for damage indices and statistical approaches....
Show moreStructural Health Monitoring (SHM) is the sensing and analysis of a structure to detect abnormal behavior, damage and deterioration during regular operations as well as under extreme loadings. SHM is designed to provide objective information for decision-making on safety and serviceability. This research focuses on the SHM of bridges by developing and integrating novel methods and techniques using sensor networks, computer vision, modeling for damage indices and statistical approaches. Effective use of traffic video synchronized with sensor measurements for decision-making is demonstrated. First, some of the computer vision methods and how they can be used for bridge monitoring are presented along with the most common issues and some practical solutions. Second, a conceptual damage index (Unit Influence Line) is formulated using synchronized computer images and sensor data for tracking the structural response under various load conditions. Third, a new index, Nd , is formulated and demonstrated to more effectively identify, localize and quantify damage. Commonly observed damage conditions on real bridges are simulated on a laboratory model for the demonstration of the computer vision method, UIL and the new index. This new method and the index, which are based on outlier detection from the UIL population, can very effectively handle large sets of monitoring data. The methods and techniques are demonstrated on the laboratory model for damage detection and all damage scenarios are identified successfully. Finally, the application of the proposed methods on a real life structure, which has a monitoring system, is presented. It is shown that these methods can be used efficiently for applications such as damage detection and load rating for decision-making. The results from this monitoring project on a movable bridge are demonstrated and presented along with the conclusions and recommendations for future work.
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Date Issued: 2009
Identifier: CFE0002890, ucf:48039
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0002890

Title: Multi-scale fluid-structure interaction model analysis of patient-specific geometry for optimization of lvad outflow graft implantation: an investigation aimed at reducing stroke risk.
Creator: Prather, Ray, Kassab, Alain, Mansy, Hansen, Bai, Yuanli, Divo, Eduardo, DeCampli, William, University of Central Florida
Abstract / Description: A Left Ventricular Assist Device (LVAD), is a mechanical pump capable of(&)nbsp;providing circulatory myocardium relief when used as bridge-to-transplantation by reducing the workload of a failing heart, with the additional bonus of allowing for cardiac recovery when used as destination therapy. The newer generations of continuous flow VADs are essentially axial or radial flow pumps, and while these devices are capable their efficiency depends upon fluid composition and flow field patterns....
Show moreA Left Ventricular Assist Device (LVAD), is a mechanical pump capable of(&)nbsp;providing circulatory myocardium relief when used as bridge-to-transplantation by reducing the workload of a failing heart, with the additional bonus of allowing for cardiac recovery when used as destination therapy. The newer generations of continuous flow VADs are essentially axial or radial flow pumps, and while these devices are capable their efficiency depends upon fluid composition and flow field patterns. The most devastating complication of VAD therapy is caused by embolization of thrombi formed within the LVAD or inside the heart into the brain leading to stroke. Anticoagulation management and improved LVADs design has reduced stroke incidence, however, investigators have recently reported the incidence of thromboembolic cerebral events is still significant and ranges from 14% to 47% over a period of 6-12 months. Blood clots may cause obstruction of critical vessels, such as cerebral arteries, reducing brain oxygenation and resulting in devastating consequences like major neurocognitive malfunction and complications which can be fatal.The hypothesis that incidence of stroke can be significantly reduced by adjusting the VAD outflow cannula implantation to direct dislodged thrombi away from the cerebral vessels has been recently supported by a series of steady flow computations assuming rigid vessel walls for the vasculature. Such studies have shown as much as a 50% reduction in embolization rates depending on outflow cannula implantation. In this study, a pulsatile fully compliant vessel wall model is developed to further establish this hypothesis. A time-dependent multi-scale Eulerian Computational Fluid Dynamics (CFD) analysis of patient-specific geometry models of the VAD-bed vasculature is coupled with a 3D Finite Element Analysis (FEA) of the mechanical response of the vascular walls to establish the VAD assisted hemodynamics. A Lagrangian particle tracking algorithm is used to determine the embolization rates of thrombi emanating from the cannula or other possible thrombogenic locations such as the aortic root. This multiscale Eulerian-Lagrangian pulsatile fluid-structure coupled paradigm allows for a fully realistic model of the hemodynamics of interest. The patient-specific geometries obtained from CT scan are implemented into the numerical domain in two modes. In the 3D CFD portion of the problem, the geometry accounts solely for the flow volume where the fluid is modelled as constant density and non-Newtonian under laminar pulsatile flow conditions. The blood-thrombus ensemble in treated as a two-phase flow, handled by an Eulerian-Lagrangian coupled scheme to solve the flow field and track particle transport. Thrombi are modelled as constant density spherical particles. Particle interactions are limited to particle-to-wall and particle-to-fluid, while particle-to-particle interaction are neglected for statistical purposes. On the other hand, with the help of Computer Aided Design (CAD) software a patient-specific aortic wall geometry with variable wall thickness is brought into the numerical domain. FEA is applied to determine the aortic wall cyclic displacement under hydrodynamic loads. To properly account for wall deformation, the arterial wall tissue incorporates a hyperelastic material model based on the anisotropic Holzapfel model for arteries. This paradigm is referred to as Fluid Structure Interaction (FSI) and allows structural analysis in conjunction with flow investigation to further monitor pathological flow patterns. The FSI model is driven by time dependent flow and pressure boundary conditions imposed at the boundaries of the 3D computational domain through a 50 degree of freedom 0D lumped parameter model (LPM) electric circuit analog of the peripheral VAD-assisted circulation.Results are presented for a simple vessel model of the ascending aorta to validate the anisotropic fiber orientation implementation. Arterial wall dilation is measured between 5-20% in the range reported in literature. Hemodynamics of the VAD assisted flow in a patient-derived geometry computed using rigid vessels walls are compared to those for a linearly elastic vessel wall model and a hyperelastic anisotropic vessel wall model. Moreover, the thromboembolization rates are presented and compared for pulsatile hemodynamics in rigid and compliant wall models. Pulsatile flow solutions for embolization probabilities corroborate the hypothesis that tailoring the LVAD cannula implantation configuration can significantly reduce thromboembolization rates, and this is consistent with indications from previous steady-flow calculations.
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Date Issued: 2018
Identifier: CFE0007077, ucf:52017
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007077

Title: Identifying Type of Expertise as a Means to Measure CRM Knowledge Structures.
Creator: Jimenez, Camilo, Jentsch, Florian, Shumaker, Randall, Burke, Shawn, Sims, Valerie, University of Central Florida
Abstract / Description: Crew Resource Management (CRM) training has evolved since its inception in the 1980s to better accommodate the operational needs of flight crews. However, even as the aviation and research communities have pointed to the potential benefit of providing CRM training, some criticism continues to emerge periodically which claims that there is no concrete evidence of its impact on flight deck performance and safety. Therefore, it is imperative to develop tools that allow researchers and, more...
Show moreCrew Resource Management (CRM) training has evolved since its inception in the 1980s to better accommodate the operational needs of flight crews. However, even as the aviation and research communities have pointed to the potential benefit of providing CRM training, some criticism continues to emerge periodically which claims that there is no concrete evidence of its impact on flight deck performance and safety. Therefore, it is imperative to develop tools that allow researchers and, more importantly, practitioners, to more effectively and objectively assess training effectiveness and identify whether or not desired CRM behaviors are being put to practice during line operations.This study focused on evaluating pilots' CRM schemas and identifying differences in CRM knowledge structures among pilots. Differences in CRM knowledge and opinions about training could be an indication of the existence of what Hatano and Inagaki (1986) have described as two distinct types of expertise, namely, routine and adaptive expertise. The study sought to identify differences among routine and adaptive expert pilots in CRM knowledge structures (schemas), their perceptions on the value and efficacy of current CRM training evaluation, along with their opinion on how CRM training effectiveness could be more accurately assessed. Results from over 250 pilots showed that, in general, participants had a positive view of CRM training and training evaluation, regardless of their type of expertise. Some evidence of potential differences in the structural knowledge of CRM between routine and adaptive experts, as well as, differences in their opinions about CRM training, evaluation, and automation on the flight deck was also identified. Additionally, analysis of survey scores and free response items indicate the existence of a third category of experts, between routine and adaptive expertise (whom I call transitional experts). The study results provide evidence that assessment of CRM schemas could potentially be used as a way to evaluate CRM training effectiveness. The results of the study also indicate that identification of specific training needs for each group of expert may be possible through the assessment of CRM schemas and type of expertise. Implications for practice and theory, limitations of the study, and suggestions for future research are also provided.
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Date Issued: 2018
Identifier: CFE0007200, ucf:52264
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007200

Title: An Investigation of College Student-Athletes' Mental Health Stigma, Help-Seeking Attitudes, Depression, Anxiety, and Life Stress Scores Using Structural Equation Modeling.
Creator: Tabet, Saundra, Lambie, Glenn, Barden, Sejal, Taylor, Dalena, Wood, Eric, Jahani, Shiva, University of Central Florida
Abstract / Description: The purpose of this study was to investigate the directional relationship between student-athletes' degree of mental health stigma, help-seeking attitudes, depression, anxiety, and life stress scores. This investigation tested the theoretical model that student-athletes' (N = 621) degree of mental health stigma (as measured by the Perceived Devaluation-Discrimination Scale (-) Adapted [PDD-A; Eisenberg et al., 2009]) contributed to their attitudes towards help-seeking (as measured by the...
Show moreThe purpose of this study was to investigate the directional relationship between student-athletes' degree of mental health stigma, help-seeking attitudes, depression, anxiety, and life stress scores. This investigation tested the theoretical model that student-athletes' (N = 621) degree of mental health stigma (as measured by the Perceived Devaluation-Discrimination Scale (-) Adapted [PDD-A; Eisenberg et al., 2009]) contributed to their attitudes towards help-seeking (as measured by the Attitudes Toward Seeking Professional Psychological Help (-) Short Form [ATSPPH-SF; Fisher (&) Farina, 1995]) and levels of depression (as measured by the Patient Health Questionnaire (-) 9 [PHQ-9; Kroenke et al., 2001]), anxiety (as measured by the Generalized Anxiety Disorder - 7 [GAD-7; Spitzer et al., 2006]), and life stress (as measured by the College Student-Athlete Life Stress Scale [CSALSS; Lu et al., 2012]). Specifically, the researcher tested the hypothesized directional relationship that student-athletes with a greater amount of mental health stigma would have (a) decreased positive help-seeking attitudes and (b) increased levels of depression, anxiety, and life stress. The results of the structural equation model (SEM) analyses identified that student-athletes' amount of mental health stigma contributed to help-seeking attitudes (25.6% of the variance), but not levels of depression (.16% of the variance), anxiety (.09% of the variance), or life stress (.81% of the variance). Specifically, student-athletes' degree of mental health stigma shared a strong negative relationship (-.506) with attitudes towards seeking professional psychological help. Further, the results identified that personal stigma mediates the relationship between public stigma and help-seeking attitudes. Implications of the findings include (a) greater knowledge of the importance student-athletes' mental health stigma and attitudes toward receiving help; (b) increased understanding for counselors of student-athletes mental health needs; and (c) insight into practices for institutions of higher education as they implement mental health initiatives within intercollegiate athletics.
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Date Issued: 2019
Identifier: CFE0007538, ucf:52597
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007538

Title: The influence of an annual meeting on the sense of community of association members, their satisfaction, and future intentions.
Creator: Hahm, Jee Yeon, Breiter, Deborah, Wang, Youcheng, Fjelstul, Jill, Boote, David, Severt, Kimberly, University of Central Florida
Abstract / Description: Over the past decade, many studies have provided some understanding on what influences association members' decision to attend a meeting; however, more systematic and theoretical research is necessary. The decision making process of attendees is a complicated human behavior practice. The major contribution of this study is adopting the sense of community (SOC) model from psychology to gain a better understanding of the attendee behavior. By doing so, this study will add a theoretical...
Show moreOver the past decade, many studies have provided some understanding on what influences association members' decision to attend a meeting; however, more systematic and theoretical research is necessary. The decision making process of attendees is a complicated human behavior practice. The major contribution of this study is adopting the sense of community (SOC) model from psychology to gain a better understanding of the attendee behavior. By doing so, this study will add a theoretical foundation to the existing research in the meeting industry. Also, this study will contribute to the SOC research in psychology by applying the concept to a different setting. This study investigates whether annual conferences build a SOC among association members. First, the SOC of association members at the conference will be analyzed. Second, the influence of SOC on members' satisfaction with the conference will be studied. Lastly, the direct and indirect relationship between SOC and future intentions (i.e., return to next meeting, membership renewal, and membership recommendation) will be examined. Data was collected through an intercept survey approach at three annual conferences of national/international associations. The questionnaire consisted of four sections: sense of community, satisfaction with the conference, future intentions, and member profile. Confirmatory factor analysis was conducted to test the factor structure and structural equation modeling was used to examine the relationships, and Spearman's rank order correlation was used to see the strength of the relationship between respondent characteristics and sense of community. The results showed that sense of community was a strong predictor of future intentions. Implications, limitations, and suggestions for future research are discussed in the final chapter.
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Date Issued: 2012
Identifier: CFE0004543, ucf:49247
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004543

Title: Essays on the Effect of Excess Compensation and Governance Changes on Firm Value.
Creator: Dah, Mustafa, Frye, Melissa, Whyte, Ann, Gatchev, Vladimir, Schnitzlein, Charles, Campbell, Terry, University of Central Florida
Abstract / Description: This dissertation consists of three essays on the effect of excess compensation and corporate governance changes on the firm's performance. The first paper utilizes a cost minimization stochastic frontier approach to investigate the efficiency of director total compensation. Our findings suggest that board members are over compensated. We show that, on average, the director actual compensation level is above the efficient compensation level by around 63%. Our results suggest that an increase...
Show moreThis dissertation consists of three essays on the effect of excess compensation and corporate governance changes on the firm's performance. The first paper utilizes a cost minimization stochastic frontier approach to investigate the efficiency of director total compensation. Our findings suggest that board members are over compensated. We show that, on average, the director actual compensation level is above the efficient compensation level by around 63%. Our results suggest that an increase in director excess compensation decreases the likelihood of CEO turnover, reduces the turnover-performance sensitivity, and increases managerial entrenchment. Thus, the surplus in director compensation is directly associated with managerial job security and entrenchment. Furthermore, although director excess compensation is not significantly inversely related to the firm's future performance, it has an indirect negative effect on future performance through its impact on the entrenchment-performance relationship. Therefore, this essay proposes that the overcompensation of directors is directly associated with a board culture predicated by mutual back-scratching and collusion between the CEO and the board members. The second essay tests the effect of an exogenous shock, the Sarbanes-Oxley Act (SOX) of 2002, on the structure of corporate boards and their efficiency as a monitoring mechanism. The results suggest an increase in the participation of independent directors at the expense of insiders. Consequently, we investigate the implications of board composition changes on CEO turnover and firm value. We document a noticeable reduction in CEO turnover in the post-SOX period. We also demonstrate that, after SOX, a board dominated by independent directors is less likely to remove a CEO due to poor performance. Finally, we highlight a negative association between the change in board composition and firm value. We propose that our findings are predicated on an off equilibrium result whereby firms were forced to modify their endogenously chosen board composition. Therefore, contrary to the legislators' objectives, we suggest that the change in board structure brought about inefficient monitoring and promoted an unfavorable tradeoff between independent directors and insiders. The third essay examines the relationship between the firm's governance structure and its value during different economic conditions. We show that both relative industry turnover and CEO entrenchment increase during economic downturns. We also find that relative industry turnover and managerial entrenchment have opposite impacts on the value of the firm throughout the recessionary period. While industry turnover leads to an appreciation in firm value, managerial entrenchment reduces shareholders' wealth. The negative impact of managerial entrenchment on firm value, however, outweighs the positive impact of industry turnover. Accordingly, we propose that a recession provides managers with a good opportunity to camouflage their behavior and extract more private benefits and, thus, blame the poor performance on bad economic conditions.
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Date Issued: 2012
Identifier: CFE0004202, ucf:49029
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004202

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