View All Items

Title: In-situ synchrotron studies of turbine blade thermal barrier coatings under extreme environments.
Creator: Knipe, Kevin, Raghavan, Seetha, Gordon, Ali, Kapat, Jayanta, Sohn, Yongho, University of Central Florida
Abstract / Description: Thermal Barrier Coatings have been used for decades to impose a thermal gradient between the hot combustion gases and the underlying superalloy substrate in engine turbine blades. Yttria Stabilized Zirconia (YSZ) is an industry standard high temperature ceramic for turbine applications. The protective coating is adhered to the substrate using a nickel based alloy bond coat. Through exposure to high temperature, a Thermally Grown Oxide (TGO) layer develops at the bond coat-YSZ interface. Large...
Show moreThermal Barrier Coatings have been used for decades to impose a thermal gradient between the hot combustion gases and the underlying superalloy substrate in engine turbine blades. Yttria Stabilized Zirconia (YSZ) is an industry standard high temperature ceramic for turbine applications. The protective coating is adhered to the substrate using a nickel based alloy bond coat. Through exposure to high temperature, a Thermally Grown Oxide (TGO) layer develops at the bond coat-YSZ interface. Large residual stresses develop in these layers due to thermal expansion mismatch that occurs during cool down from high temperature spraying and cyclic operating conditions. Despite their standard use, much is to be determined as to how these residual stresses are linked to the various failure modes. This study developed techniques to monitor the strain and stress in these internal layers during thermal gradient and mechanical conditions representing operating conditions. The thermal gradient is applied across the coating thickness of the tubular samples from infrared heating of the outer coating and forced air internal cooling of the substrate. While thermal and mechanical loading conditions are applied, 2-dimensional diffraction measurements are taken using the high-energy Synchrotron X-Rays and analyzed to provide high-resolution depth-resolved strain. This study will include fatigue comparisons through use of samples, which are both 'as-coated' as well as aged to various stages in a TBC lifespan. Studies reveal that variations in thermal gradients and mechanical loads create corresponding trends in depth resolved strains with the largest effects displayed at or near the bond coat/TBC interface. Single cycles as well as experiments targeting thermal gradient and mechanical effects were conducted to capture these trends. Inelastic behavior such as creep was observed and quantified for the different layers at high temperatures. From these studies more accurate lifespan predictions, material behaviors, and causes of failure modes can be determined. The work further develops measurement and analysis techniques for diffraction measurements in internal layers on a coated tubular sample which can be used by various industries to analyze similar geometries with different applications.
Show less
Date Issued: 2014
Identifier: CFE0005640, ucf:50206
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005640

Title: ATTITUDES TOWARD DIVERSITY AND LIFE IN THE U.S. HELD BY CHILDREN OF HISPANIC IMMIGRANTS: DO THEIR PARENTS PLAY A ROLE?.
Creator: Ruiz, Vanessa, Negy, Charles, University of Central Florida
Abstract / Description: The present study explores how children of Hispanic immigrants (CHIs) perceive life in the U.S., and how they view cultural diversity. Questionnaires were given to 92 non-U.S. born CHIs and one of their non-U.S. born Hispanic immigrant parents (HIPs) who have lived in the U.S. between 1 and 17 years (M yrs = 8.43); their views of the U.S. were assessed along with their acceptance of diversity, acculturative stress, and levels of acculturation. In this study, I found that CHIs generally hold...
Show moreThe present study explores how children of Hispanic immigrants (CHIs) perceive life in the U.S., and how they view cultural diversity. Questionnaires were given to 92 non-U.S. born CHIs and one of their non-U.S. born Hispanic immigrant parents (HIPs) who have lived in the U.S. between 1 and 17 years (M yrs = 8.43); their views of the U.S. were assessed along with their acceptance of diversity, acculturative stress, and levels of acculturation. In this study, I found that CHIs generally hold positive views of the lives in the U.S. and also hold favorable views toward cultural diversity. Furthermore, this study hypothesized that HIPs significantly influence their CHIs attitudes toward both the U.S. and toward cultural diversity. Overall, my findings validated the theoretically based expectation that demonstrates the power of parental attitudes on their children's attitudes. A significant correlation was found between HIPs' attitudes toward the U.S. and their children's attitudes, as well as, CHIs' attitudes toward the U.S. correlating significantly with their perceptions of their parents' attitudes toward the U.S. Multiple and stepwise regressions further confirmed the importance of parental attitudes toward their children's attitudes toward the U.S. and their openness to cultural diversity. Findings from this study provide implications for future research.
Show less
Date Issued: 2015
Identifier: CFH0004875, ucf:45413
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFH0004875

Title: EQUIBIAXIAL FLEXURAL STRENGTH TESTING OF ADVANCE CERAMICS.
Creator: Jordan, Ryan T, Orlovskaya, Nina, Kwok, Kawai; Ghosh, Ranajay, University of Central Florida
Abstract / Description: Ceramics are very important materials with many unique properties used in numerous industrial applications. Ceramics could be very hard and very strong in comparison to metals; however, they are very brittle, thus they are prone to instantaneous and catastrophic failure. Therefore, their reliability is compromised and it is very important to have advanced techniques that allow evaluating their mechanical behavior in many unusual stress states. One of such testing methods is biaxial strength...
Show moreCeramics are very important materials with many unique properties used in numerous industrial applications. Ceramics could be very hard and very strong in comparison to metals; however, they are very brittle, thus they are prone to instantaneous and catastrophic failure. Therefore, their reliability is compromised and it is very important to have advanced techniques that allow evaluating their mechanical behavior in many unusual stress states. One of such testing methods is biaxial strength method, that allows to measure properties not only unidirectional, but also in a biaxial way. The research work for this thesis will be built on design and development of ring-on-ring test jigs that will measure a biaxial strength of thin ceramic disks.
Show less
Date Issued: 2018
Identifier: CFH2000386, ucf:45700
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFH2000386

Title: STRESS AND PERFORMANCE IN UNCERTAINTY-AVOIDING INDIVIDUALS: AN INTRODUCTORY LITERATURE REVIEW.
Creator: Stowers, Kimberly, Salas, Eduardo, University of Central Florida
Abstract / Description: Uncertainty avoidance as a cultural construct has been known to affect worker stress and performance in organizations, but a review of these findings has not been done up until this point. In effort to clarify the relationship between uncertainty avoidance and stress and performance, a comprehensive literature search was performed. Findings from articles on this topic have been presented. In addition, organizational practices for accommodating uncertainty avoidance and other cultural...
Show moreUncertainty avoidance as a cultural construct has been known to affect worker stress and performance in organizations, but a review of these findings has not been done up until this point. In effort to clarify the relationship between uncertainty avoidance and stress and performance, a comprehensive literature search was performed. Findings from articles on this topic have been presented. In addition, organizational practices for accommodating uncertainty avoidance and other cultural dimensions have been explored. This review shows that uncertainty avoidance appears to be linked to higher stress, while its relationship to performance appears to depend on other factors. Best practices for accommodating uncertainty avoidance tend to include enhanced communication and structure. Ideas for future research on this topic are discussed.
Show less
Date Issued: 2013
Identifier: CFH0004450, ucf:45125
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFH0004450

Title: THE RELATIONSHIP BETWEEN CONSUMER DEBT AND MENTAL HEALTH.
Creator: Simmons, Jennifer, Abel, Eileen, University of Central Florida
Abstract / Description: Consumer debt is a growing phenomenon in the US and throughout the world. The beginning of the 21st century has been defined by such an incredible growth in consumer debt that American families have increased their debt relative to personal income four times faster than in the 1990s. Since the Federal Reserve began measuring the amount of American consumer debt and consumer income in the 1980s, consumer debt never exceeded consumer income until 2004 when it reached 104.8% of income. In the...
Show moreConsumer debt is a growing phenomenon in the US and throughout the world. The beginning of the 21st century has been defined by such an incredible growth in consumer debt that American families have increased their debt relative to personal income four times faster than in the 1990s. Since the Federal Reserve began measuring the amount of American consumer debt and consumer income in the 1980s, consumer debt never exceeded consumer income until 2004 when it reached 104.8% of income. In the last two decades, researchers have observed a significant correlation between debt and mental health. The purpose of this thesis is to examine a comprehensive sample of previous quantitative research conducted on the relationship between debt and mental health. This thesis discusses the research in the following categories: 1) increased debt as a contributor to decreased mental health; 2) decreased mental health as a contributor to increased debt; 3) high correlation between debt and mental health risks.
Show less
Date Issued: 2013
Identifier: CFH0004407, ucf:45107
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFH0004407

Title: CROSS-TALK OF RETINOIC ACID AND ADRENERGIC HORMONE SIGNALING MAY INFLUENCE DEVELOPMENT OF CARDIAC CONDUCTION AND RHYTHMICITY IN UTERO.
Creator: Alam, Sabikha, Ebert, Steven, University of Central Florida
Abstract / Description: Stress hormones, adrenaline and noradrenaline, have been shown to be critical for heart development. Mice lacking dopamine beta-hydroxylase (Dbh), an enzyme responsible for synthesis of these adrenergic hormones, die during mid-gestation due to cardiac failure. Prior research showed that adrenergic cells are found within the electrical conduction system of the heart, and adrenergic deficiency leads to slowed cardiac conduction during embryogenesis. Microarray analysis of wild-type (Dbh+/+)...
Show moreStress hormones, adrenaline and noradrenaline, have been shown to be critical for heart development. Mice lacking dopamine beta-hydroxylase (Dbh), an enzyme responsible for synthesis of these adrenergic hormones, die during mid-gestation due to cardiac failure. Prior research showed that adrenergic cells are found within the electrical conduction system of the heart, and adrenergic deficiency leads to slowed cardiac conduction during embryogenesis. Microarray analysis of wild-type (Dbh+/+) and knockout (Dbh-/-) mouse hearts revealed significant differences in expression of retinoic acid (RA) signaling genes. RA signaling has also been shown to be critical for heart development. These data suggest that heart failure due to adrenergic deficiency may be dependent upon RA signaling. This led to the hypothesis that adrenergic hormones promote the development of the electrical conduction system through modulation of RA signaling. To test this, embryonic mouse hearts were cultured with LE 135, a RA receptor blocker. Heart rate, arrhythmic index (AI) and conduction time were measured. Under these conditions there was a marked increase in arrhythmias. Hearts treated with LE 135 showed a mean AI of 0.232+/-0.057 after 24 hours of treatment while when untreated had an AI of 0.083+/-0.028 (p<0.05;n=15). In contrast, there was no significant change in heart rate or conduction speed after 24 hours with or without the retinoic acid receptor blocker. To determine if adrenergic stimulus influences retinoic acid response, an established RA-sensitive reporter cell line was employed. These F9-RARE-LacZ cells were treated with forskolin (cAMP regulator) and isoproterenol (beta-agonist) to measure changes in RA signaling. Evaluation of RA signaling showed an increase in retinoic acid responsiveness when treated with an adrenergic signaling agonist. These results suggest that proper retinoic acid signaling is essential for maintaining cardiac rhythmicity during embryonic development and adrenergic stimulation can influence this response.
Show less
Date Issued: 2011
Identifier: CFH0003831, ucf:44726
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFH0003831

Title: Exploring Stress for Novice Teachers' in Low Socio-Economic Elementary Schools Through Breathing Biofeedback.
Creator: Fulchini, Angelica, Dieker, Lisa, Hines, Rebecca, Lue, Martha, Hynes, Mike, University of Central Florida
Abstract / Description: Teachers who serve children of color in schools that support students from low socio-economic status have turnover rates reported to be as high as 70% (SES; Carver-Thomas (&) Darling-Hammond, 2017). Numerous approaches to teacher retention in low SES settings have been discussed in the literature (Chester (&) Beaudin, 1996; Donaldson, 2009; Ingersoll (&) Kralik, 2004; Jacob, 2007; McKinney, Haberman, Stafford-Johnson, (&) Robinson, 2008; McLaurin, Smith, (&) Smillie, 2009; Siwatu, Frazier,...
Show moreTeachers who serve children of color in schools that support students from low socio-economic status have turnover rates reported to be as high as 70% (SES; Carver-Thomas (&) Darling-Hammond, 2017). Numerous approaches to teacher retention in low SES settings have been discussed in the literature (Chester (&) Beaudin, 1996; Donaldson, 2009; Ingersoll (&) Kralik, 2004; Jacob, 2007; McKinney, Haberman, Stafford-Johnson, (&) Robinson, 2008; McLaurin, Smith, (&) Smillie, 2009; Siwatu, Frazier, Osaghae, (&) Starker, 2011; Sutcher, Darling-Hammond, (&) Carver-Thomas, 2016; Taylor (&) Frankenberg, 2009), but the use of emerging biofeedback technology is an unexplored territory. This type of technology could help novice teachers understand basic changes in stress levels through awareness of the body and mind while teaching. Hence, the potential use of biofeedback strategies to reduce stress levels in teachers, in inclusive settings, that serve students with low SES is explored. To help potentially reduce novice teachers' stress levels (Friedman, 2000; Day (&) Hong, 2016; Isenbarger (&) Zembylas, 2006), the researcher explored the effectiveness of biofeedback on breathing rates of teachers in inclusive classrooms serving more than 50% of students from low SES backgrounds. The researcher found, by tracking the rate of stressed breathing of 9 teachers during the instructional day, that teachers reported they were more mindful of their breathing. The researcher found meetings, paperwork, and student behaviors increased their stress and suggested better mentorship as a way to help reduce stress. The paper concludes with implications for practice, and recommendations for future research for teachers is provided.
Show less
Date Issued: 2018
Identifier: CFE0007179, ucf:52266
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007179

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.
Show less
Date Issued: 2019
Identifier: CFE0007538, ucf:52597
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007538

Title: CLASS-E CASCODE POWER AMPLIFIER ANALYSIS AND DESIGN FOR LONG TERM RELIABILITY.
Creator: Kutty, Karan, Yuan, Jiann-Shiun, University of Central Florida
Abstract / Description: This study investigated the Class-E power amplifier operating at 5.2 GHz. Since the operation of this amplifier applies a lot of stress on the switching transistor, a cascode topology was applied in order to reduce the drain-source voltage stress. Such an amplifier was designed and optimized in order to improve stability, power added efficiency, and matching. A layout for the said design was then created to be fabrication-ready using the TSMC 0.18 um technology. Post-layout simulations were...
Show moreThis study investigated the Class-E power amplifier operating at 5.2 GHz. Since the operation of this amplifier applies a lot of stress on the switching transistor, a cascode topology was applied in order to reduce the drain-source voltage stress. Such an amplifier was designed and optimized in order to improve stability, power added efficiency, and matching. A layout for the said design was then created to be fabrication-ready using the TSMC 0.18 um technology. Post-layout simulations were performed in order to realize a more realistic circuit performance with the layout design in mind. Long-term stress effects, such as oxide breakdown, on the key transistors were modeled and simulated in order to achieve an understanding of how leakage currents affect the overall circuit performance. Simulated results were compared and contrasted against theoretical understanding using derived equations. Recommendations for future advancements were made for modification and optimization of the circuit by the application of other stress reduction strategies, variation in the class-E topology, and improvement of the driver stage.
Show less
Date Issued: 2010
Identifier: CFE0003360, ucf:48477
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0003360

Title: Mechanisms of Alpha-Synuclein-Induced Neurodegenertaion in Parkinson's Disease and Stroke.
Creator: Belal, Cherine, Chan, Sic, Ebert, Steven, Self, William, Teter, Kenneth, University of Central Florida
Abstract / Description: Parkinson's disease (PD) is a debilitating neurodegenerative disorder affecting one million Americans. Despite its social and economic impact, the pathological cascades that lead to neuron dysfunction and degeneration in PD are poorly understood. Endoplasmic reticulum (ER) stress has been implicated as an initiator or contributing factor in neurodegenerative diseases including PD. The ER is an organelle central to protein folding and intracellular Ca2+ homeostasis. Perturbations of these...
Show moreParkinson's disease (PD) is a debilitating neurodegenerative disorder affecting one million Americans. Despite its social and economic impact, the pathological cascades that lead to neuron dysfunction and degeneration in PD are poorly understood. Endoplasmic reticulum (ER) stress has been implicated as an initiator or contributing factor in neurodegenerative diseases including PD. The ER is an organelle central to protein folding and intracellular Ca2+ homeostasis. Perturbations of these functions result in ER stress and upregulation of ER stress proteins, of which some have been implicated in counteracting ER stress-induced cell death. The mechanisms that lead to ER stress and how ER stress proteins contribute to the degenerative cascades remain unclear but their understanding is critical to devising effective therapies for PD. Both the accumulation of mutant a-synuclein (aSyn), which causes an inherited form of PD, and the inhibition of mitochondrial complex I function by PD-inducing neurotoxin lead to ER stress. The critical involvement of ER stress in experimental models of PD supports its potential relevance to PD pathogenesis and led us to test the hypothesis whether the homocysteine-inducible ER protein (Herp), an ubiquitin-like domain (UBD) containing ER-resident protein, can counteract mutant Alpha Syn- and neurotoxin- induced pathological cascades.
Show less
Date Issued: 2011
Identifier: CFE0004470, ucf:49310
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004470

$A study on the plasticity and fracture of AISI 4340 steel under different loading conditions considering heat treatment and micromechanics$

Title: A study on the plasticity and fracture of AISI 4340 steel under different loading conditions considering heat treatment and micromechanics.
Creator: Ghazali, Sami, Bai, Yuanli, Kassab, Alain, Kwok, Kawai, Nam, Boo Hyun, University of Central Florida
Abstract / Description: Accurate predictions of material strength under different loading conditions with large plastic deformation and ductile fracture are of great importance. This dissertation aims to develop an essential understanding of ductile fracture of AISI 4340 steel alloy using both empirical and micromechanics based models. For this purpose, 29 specimens of different geometries with different heat-treatments were designed to investigate the effects of stress states. These specimens are: (a) 13 round bars...
Show moreAccurate predictions of material strength under different loading conditions with large plastic deformation and ductile fracture are of great importance. This dissertation aims to develop an essential understanding of ductile fracture of AISI 4340 steel alloy using both empirical and micromechanics based models. For this purpose, 29 specimens of different geometries with different heat-treatments were designed to investigate the effects of stress states. These specimens are: (a) 13 round bars with different notches (axial symmetric tension); (b) 13 flat grooved specimens with different grooves; (c) 3 small round cylinders. Mechanical tests up to fracture were conducted on these specimens to characterize the influence of hydrostatic stress and Lode angle on material plasticity and fracture. Scanning electron microscopy (SEM) observations were performed on both original and fractured specimens to investigate different micromechanical revelations and features. The plasticity model with pressure and Lode angle effects (PPL model) and the modified Mohr-Coulomb (MMC) fracture criterion were used to predict plastic flow and fracture initiation behaviors under different loading conditions in finite element simulations. A model optimization method using ISIGHT was set up to achieve simulation results that were well correlated with experimental data. The effects of heat-treatment on material strength and ductility of AISI 4340 steel were also discussed. This work was further carried onto the microvoids based metal plasticity theory. The well-known Gurson-Tvergaard-Needleman (GTN) model was calibrated for AISI 4340 steel. It is found that the GTN model is not sufficient in simulating test data for the 16 Rockwell hardness plane strain specimens. Therefore, The GTN model is modified to include the Lode angle dependence on matrix material plasticity. It is also found that using afixed or constant microvoid volume fraction at failure (ff) for all loading conditions is inadequate. Following a similar derivation of the MMC fracture model, the microvoid volume fraction at failure (ff) becomes a function of both stress triaxiality and Lode angle. This new criterion is named (GTN-MMC). The proposed plasticity and fracture models were implemented into ABAQUS through a user-defined material subroutine (VUMAT) for FE simulations. Good correlations were achieved between experimental results and numerical simulations
Show less
Date Issued: 2018
Identifier: CFE0007004, ucf:52026
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0007004

Title: VIBRATIONAL AND MECHANICAL PROPERTIES OF 10 MOL % SC2O3-1 MOL % CEO2- ZRO2 ELECTROLYTE CERAMICS FOR SOLID OXIDE FUEL CELLS.
Creator: Lukich, Svetlana, Orlovskaya, Nina, University of Central Florida
Abstract / Description: Solid Oxide Fuel Cells (SOFCs) are emerging as a potential breakthrough energy conversion technology for clean and efficient production of electricity and heat from hydrogen and hydro-carbon fuels. Sc0.1Ce0.01ZrO2 electrolytes for Solid Oxide Fuel Cells are very promising materials because their high ionic conductivity in the intermediate temperature range 700oC-800oC. The vibration response of cubic and rhombohedral (β) 10 mol%Sc2O3 - 1 mol%CeO2 - ZrO2 (Sc0.1Ce0.01ZrO2 ) both at room...
Show moreSolid Oxide Fuel Cells (SOFCs) are emerging as a potential breakthrough energy conversion technology for clean and efficient production of electricity and heat from hydrogen and hydro-carbon fuels. Sc0.1Ce0.01ZrO2 electrolytes for Solid Oxide Fuel Cells are very promising materials because their high ionic conductivity in the intermediate temperature range 700oC-800oC. The vibration response of cubic and rhombohedral (β) 10 mol%Sc2O3 - 1 mol%CeO2 - ZrO2 (Sc0.1Ce0.01ZrO2 ) both at room and high-temperatures is reported. The in-situ heating experiments and ex-situ indentation experiments were performed to characterize the vibrational behavior of these important materials. A temperature and stress-assisted phase transition from cubic to rhombohedral phase was detected during in-situ Raman spectroscopy experiments. While heating and indentation experiments performed separately did not cause the transition of the cubic phase into the rhombohedral structure under the performed experimental conditions and only broadened or strained peaks of the cubic phase could be detected, the heating of the indented (strained) surface leaded to the formation of the rhombohedral Sc0.1Ce0.01ZrO2. Both temperature range and strained zone were estimated by in situ heating and 2D mapping, where a formation of rhombohedral or retention of cubic phase has been promoted. The mechanical properties, such as Young's modulus, Vickers hardness, indentation fracture resistance, room and high temperature four point bending strength and SEVNB fracture toughness along with the stress – strain deformation behavior in compression, of 10 mol% Sc2O3 – 1 mol % CeO2 - ZrO2 (ScCeZrO2) ceramics have been studied. The chosen composition of the ScCeZrO2 has very high ionic conductivity and, therefore, is very promising oxygen ion conducting electrolyte for the intermediate temperature Solid Oxide Fuel Cells. Therefore, its mechanical behavior is of importance and is presented in this study.
Show less
Date Issued: 2009
Identifier: CFE0002914, ucf:52845
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0002914

Title: CLASS F AND INVERSE CLASS F POWER AMPLIFIER SUBJECT TO ELECTRICAL STRESS EFFECT.
Creator: Skaria, Giji, Yuan, Jiann, University of Central Florida
Abstract / Description: This study investigated the Class F and inverse Class F RF power amplifier operating at 5.8 GHz. The major challenging issue in design and implementation of CMOS power transistor is the breakdown voltage especially in sub-micron CMOS technologies. In order to eliminate this problem a Cascode topologies were implemented to reduce the Drain-to-Source voltage (stress). A Cascode Class F & Inverse Class F RF power amplifier were designed, and optimized in order to improve efficiency and...
Show moreThis study investigated the Class F and inverse Class F RF power amplifier operating at 5.8 GHz. The major challenging issue in design and implementation of CMOS power transistor is the breakdown voltage especially in sub-micron CMOS technologies. In order to eliminate this problem a Cascode topologies were implemented to reduce the Drain-to-Source voltage (stress). A Cascode Class F & Inverse Class F RF power amplifier were designed, and optimized in order to improve efficiency and reliability using 0.18[micro]m CMOS technology process. A 50% decrease in the stress has been achieved in the Cascode class-F and Inverse class F amplifiers. The sensitivity and temperature effect were investigated using BSIM-4 model. Such an amplifier was designed and optimized for a good sensitivity. A substrate bias circuit was implemented to achieve a good sensitivity. Recommendations were made for future advancements for modification and optimization of the class F and inverse class F circuit by the application of other stress reduction strategies, and improvement of the substrate bias circuit for a better sensitivity.
Show less
Date Issued: 2011
Identifier: CFE0004030, ucf:49161
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004030

Title: EVOLUTION OF MICROSTRUCTURE AND RESIDUAL STRESS IN DISC-SHAPE EB-PVD THERMAL BARRIER COATINGS AND TEMPERATURE PROFILE OF HIGH PRESSURE TURBINE BLADE.
Creator: Mukherjee, Sriparna, Sohn, Yongho, University of Central Florida
Abstract / Description: A detailed understanding of failure mechanisms in thermal barrier coatings (TBCs) can help develop reliable and durable TBCs for advanced gas turbine engines. One of the characteristics of failure in electron beam physical vapor deposited (EB-PVD) TBCs is the development of instability, named rumpling, at the interface between (Ni, Pt)Al bond coat and thermally grown oxide (TGO). In this study, thermal cycling at 1100[degrees]C with 1 hr dwell time was carried out on 25.4mm disc specimens of...
Show moreA detailed understanding of failure mechanisms in thermal barrier coatings (TBCs) can help develop reliable and durable TBCs for advanced gas turbine engines. One of the characteristics of failure in electron beam physical vapor deposited (EB-PVD) TBCs is the development of instability, named rumpling, at the interface between (Ni, Pt)Al bond coat and thermally grown oxide (TGO). In this study, thermal cycling at 1100[degrees]C with 1 hr dwell time was carried out on 25.4mm disc specimens of TBCs that consisted of EB-PVD coated ZrO2-7wt.%Y2O3, (Pt,Ni)Al bond coat, and CMSX-4 Ni-based superalloy. At specific fraction of lifetime,TBCs were examined by electron microscopy and photostimulated luminescence (PL). Changes in the average compressive residual stress of the TGO determined by PL and the magnitude of rumpling, determined by tortuosity from quantitative microstructural analyses, were examined with respect to the furnace thermal cyclic lifetime and microstructural evolution of TBCs. The combination of elastic strain energy within the TGO and interfacial energy at the interface between the TGO and the bond coat was defined as the TGO energy, and its variation with cyclic oxidation time was found to remain approximately constant ~135J/m2 during thermal cycling from 10% to 80% thermal cyclic lifetime. Parametric study at ~135J/m2 was performed and variation in residual stress with rumpling for different oxide scale thicknesses was examined. This study showed that the contribution of rumpling in residual stress relaxation decreased with an increase in TGO thickness. High pressure turbine blades serviced for 2843 hours and in the as coated form were also examined using electron microscopy and photostimulated luminescence. The difference in residual stress values obtained using PL on the suction and pressure sides of as-coated turbine blade were discussed. The presence of a thick layer of deposit on the serviced blade gave signals from stress free alpha-Al2O3 in the deposit, not from the TGO. The TGO growth constant data from the disc-shape TBCs, thermally cycled at 1100[degrees]C, and studies by other authors at different temperatures but on similar EB-PVD coated TBCs with (Pt, Ni)Al bond coat and CMSX-4 Ni- based superalloy were used to determine the temperature profile at the YSZ/bond coat interface. The interfacial temperature profiles of the serviced blade and the YSZ thickness profile were compared to document the variable temperature exposure at the leading edge, trailing edge, suction and the pressure side.
Show less
Date Issued: 2011
Identifier: CFE0003927, ucf:48700
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0003927

Title: ZrB2-SiC BASED ULTRA HIGH TEMPERATURE CERAMIC COMPOSITES: MECHANICAL PERFORMANCE AND MEASUREMENT AND DESIGN OF THERMAL RESIDUAL STRESSES FOR HYPERSONIC VEHICLE APPLICATIONS.
Creator: Stadelmann, Richard, Orlovskaya, Nina, Kumar, Ranganathan, Raghavan, Seetha, University of Central Florida
Abstract / Description: Ultra-high temperature ceramics (UHTCs), such as ZrB2-based ceramic composites, have been identified as next generation candidate materials for leading edges and nose cones in hypersonic air breathing vehicles. Mechanical performance of ceramic composites play an important role in the ultra-high temperature applications, therefore SiC is added to ZrB2 as a strengthening phase to enhance its mechanical performance. The high melting temperatures of both ZrB2 and SiC, as well as the ability of...
Show moreUltra-high temperature ceramics (UHTCs), such as ZrB2-based ceramic composites, have been identified as next generation candidate materials for leading edges and nose cones in hypersonic air breathing vehicles. Mechanical performance of ceramic composites play an important role in the ultra-high temperature applications, therefore SiC is added to ZrB2 as a strengthening phase to enhance its mechanical performance. The high melting temperatures of both ZrB2 and SiC, as well as the ability of SiC to form SiO2 refractory oxide layers upon oxidation make ZrB2-SiC ceramics very suitable for aerospace applications. Thermal residual stresses appearing during processing are unavoidable in sintered ZrB2-SiC ceramic composites. Residual microstresses appear at the microstructural level (intergranular microstresses) or at the crystal structure level (intragranular microstresses). These microstresses are of enormous importance for the failure mechanisms in ZrB2-SiC ceramics, such as ratio of the trans- and intergranular fracture; crack branching or bridging, microcracking, subcritical crack growth and others, as they govern crack propagation(-)induced energy dissipation and affect the toughness and strength of the ceramic material. Therefore, understanding the evolution of residual stress state in processed ZrB2-SiC ceramic composites and accurate measurements of these stresses are of high priority. In the present research the ZrB2-17vol%SiC, ZrB2-32vol%SiC, and ZrB2-45vol%SiC ultra-high temperature particulate ceramic composites were sintered using both Hot Pressing (HP) and Spark Plasma Sintering (SPS) techniques. The mechanical performance of the ZrB2-SiC composites was investigated using 3- and 4-point bending techniques for measurements of instantaneous fracture strength and fracture toughness. Resonant Ultrasound Spectroscopy was used for measurement of Young's, shear, and bulk moduli as well as Poisson's ratio of the composites. The distribution of thermal residual stresses and the effect of the applied external load on their re-distribution was studied using micro-Raman spectroscopy. Piezospectroscopic coefficients were determined for all compositions of ZrB2-SiC ceramic under study and their experimentally obtained values were compared with the piezospectroscopic coefficients both published in the literature and calculated using theoretical approach. Finally, the novel ZrB2-IrB2-SiC ceramic composites were also produced using Spark Plasma Sintering (SPS), where IrB2 powder was synthesized using mechanochemical route. It is expected that the IrB2 additive phase might contribute to the improved overall oxidation resistance of ZrB2 based ultra-high temperature ceramic composites.
Show less
Date Issued: 2015
Identifier: CFE0006008, ucf:51004
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006008

Title: The Effect of the Great Recession on Local Goverment Policy in Florida.
Creator: Levey, Richard, Martin, Lawrence, Zhang, Ning, Lawther, Wendell, Hawkins, Christopher, University of Central Florida
Abstract / Description: The length and depth of the Great Recession of 2008 provides an opportunity to examine the policy behavior of local governments unlike any window since the 1930's post Depression era. Utilizing Peterson's (1981) City Limits typology as a framework for local government policy allows for an evaluation of whether or not the economic downturn caused local governments to change their relative expenditures between policy categories. The City Limits typology has been widely used in the literature to...
Show moreThe length and depth of the Great Recession of 2008 provides an opportunity to examine the policy behavior of local governments unlike any window since the 1930's post Depression era. Utilizing Peterson's (1981) City Limits typology as a framework for local government policy allows for an evaluation of whether or not the economic downturn caused local governments to change their relative expenditures between policy categories. The City Limits typology has been widely used in the literature to explain how expenditures define a local government's role in economic development. The typology has had limited use in a pre-post natural experimental research design to determine if a local government has 'shifted' policy priorities as measured by changes in expenditures among and between policy categories. This research design and the use Peterson's framework combine for a study that has not yet been conducted under similar conditions.Most of the existing literature, including the research from the 1980's, failed to account for inter-state differences that directly affect local government expenditures and policy. Concentrating solely on Florida local governments, this study eliminates the confounding nature of a national study and ensures that the unit of analysis is comparable for research purposes. The study utilizes actual expenditure data for all cities and counties in Florida from FY2006 through FY2011. The research tests for the relationships between changes in policy priorities from pre- to post-recession, and the type of government, form of government, and various socio-economic factors.The research contributes to a new body of knowledge that is just beginning to emerge in the literature about how local governments respond to periods of extreme fiscal stress. The findings suggest that cities and counties had an inverse response from pre- to post-recession with cities shifting toward developmental expenditures and counties prioritizing allocational spending. Differences were also found between forms of government. In addition, the density of population was found to contribute differently to shifts in expenditures for cities and counties. The study identifies emerging patterns that can help local governments understand past behavior and better anticipate future economic downturns.
Show less
Date Issued: 2015
Identifier: CFE0005971, ucf:50782
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005971

Title: Nanocomposite Coating Mechanics via Piezospectroscopy.
Creator: Freihofer, Gregory, Raghavan, Seetha, Gou, Jihua, Bai, Yuanli, Schulzgen, Axel, University of Central Florida
Abstract / Description: Coatings utilizing the piezospectroscopic (PS) effect of alpha alumina could enable on the fly stress sensing for structural health monitoring applications. While the PS effect has been historically utilized in several applications, here by distributing the photo-luminescent material in nanoparticle form within a matrix, a stress sensing coating is created. Parallel to developing PS coatings for stress sensing, the multi-scale mechanics associated with the observed PS response of...
Show moreCoatings utilizing the piezospectroscopic (PS) effect of alpha alumina could enable on the fly stress sensing for structural health monitoring applications. While the PS effect has been historically utilized in several applications, here by distributing the photo-luminescent material in nanoparticle form within a matrix, a stress sensing coating is created. Parallel to developing PS coatings for stress sensing, the multi-scale mechanics associated with the observed PS response of nanocomposites and their coatings has been applied to give material property measurements, providing an understanding of particle reinforced composite behavior.Understanding the nanoparticle-coating-substrate mechanics is essential to interpreting the spectral shifts for stress sensing of structures. In the past, methods to experimentally measure the mechanics of these embedded nano inclusions have been limited, and much of the design of these composites depend on computational modeling and bulk response from mechanical testing. The PS properties of Chromium doped alumina allow for embedded inclusion mechanics to be revisited with unique experimental setups that probe the particles state of stress under applied load to the composite. These experimental investigations of particle mechanics will be compared to the Eshelby theory and its derivative theories in addition to the nanocomposite coating mechanics. This work discovers that simple nanoparticle load transfer theories are adequate for predicting PS properties in an intermediate volume fraction range. With fundamentals of PS nanocomposites established, the approach was applied to selected experiments to prove its validity. In general it was observed that the elastic modulus values calculated from the PS response were similar to that observed from macroscale strain measurements such as a strain gage. When simple damage models were applied to monitor the elastic modulus, it was observed that the rate of decay for the elastic modulus was much higher for the PS measurements than for the strain gage.A novel experiment including high resolution PS maps with secondary strain maps from digital image correlation is reviewed on an open hole tension, composite coupon. The two complementary measurements allow for a unique PS response for every location around the hole with a spatial resolution of 400 microns. Progression of intermediate damage mechanisms was observed before digital image correlation indicated them. Using the PS nanocomposite model, elastic modulus values were calculated. Introducing an elastic degradation model with some plastic deformation allows for estimation of material properties during the progression of failure.This work is part of a continuing effort to understand the mechanics of a stress sensing PS coating. The mechanics were then applied to various experimental data that provided elastic property calculations with high resolution. The significance is in the experimental capture of stress transfer in particulate composites. These findings pave the way for the development of high resolution stress-sensing coatings.
Show less
Date Issued: 2014
Identifier: CFE0005614, ucf:50223
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005614

Title: THE EFFECTS OF AUDITORY STIMULI ON STRESS LEVELS OF ADULT PATIENTS IN THE CRITICAL CARE SETTING.
Creator: Ellermets, Jessica, Heglund, Stephen, University of Central Florida
Abstract / Description: The purpose of this review of literature is to explore the effects of interventional and environmental auditory stimuli on the adult critical care population. Current research has yet to compare and contrast the effectiveness of various interventional auditory stimuli on stress relief, an oversight this thesis aims to remedy. Modern day critical care settings demand the identification of the most therapeutic interventional auditory stimulus and the most stress-inducing environmental stimuli,...
Show moreThe purpose of this review of literature is to explore the effects of interventional and environmental auditory stimuli on the adult critical care population. Current research has yet to compare and contrast the effectiveness of various interventional auditory stimuli on stress relief, an oversight this thesis aims to remedy. Modern day critical care settings demand the identification of the most therapeutic interventional auditory stimulus and the most stress-inducing environmental stimuli, so that interventions can be made to optimize patient stress levels and improve outcomes. Suggestions will be made on how to simultaneously reduce harmful or stress inducing auditory stimuli in the critical care setting and implement the optimal stress-relieving interventional auditory stimuli.
Show less
Date Issued: 2015
Identifier: CFH0004853, ucf:45482
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFH0004853

Title: SUPPORT SYSTEMS IN ADOLESCENTS WITH TYPE 1 DIABETES MELLITUS AND THE RELATIONSHIP TO DIABETES-RELATED STRESS, CONFLICT, AND METABOLIC CONTROL.
Creator: Foarde, Samuel, LaManna, Jacqueline, University of Central Florida
Abstract / Description: The purpose of this integrated review of the literature was to explore the effects of social support on diabetes-related stress, conflict, and metabolic control in adolescents with type 1 diabetes mellitus (T1DM). Social support was examined in four subgroups: adolescents with T1DM, family caregivers, peers, and teachers. Relevant findings in the literature revealed a significant deficiency of research devoted to adolescent males with diabetes as well as fathers as primary and secondary...
Show moreThe purpose of this integrated review of the literature was to explore the effects of social support on diabetes-related stress, conflict, and metabolic control in adolescents with type 1 diabetes mellitus (T1DM). Social support was examined in four subgroups: adolescents with T1DM, family caregivers, peers, and teachers. Relevant findings in the literature revealed a significant deficiency of research devoted to adolescent males with diabetes as well as fathers as primary and secondary caregivers. Studies highlighted the importance of fostering autonomy and positive self-image in adolescents with T1DM and described effective interventions to improve diabetes-related stress, reduce disease-related conflict, and improve metabolic control. Findings suggested that nurses caring for adolescents with T1DM and their families should foster positive, open communication, while identifying barriers to problem solving, coping, stress, and optimal glycemic control. Interventions that educate caregivers and peers on how to better communicate and provide support are critical in fostering positive psychological and physiological outcomes in the adolescent with T1DM. The findings of this study may provide guidance in the way that nurses assess, identify, and counsel adolescents with TIDM regarding their disease management and access to support systems.
Show less
Date Issued: 2013
Identifier: CFH0004324, ucf:45057
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFH0004324

Title: The Relationship Between Married Partners' Individual and Relationship Distress: An Actor-Partner Analysis of Low-income, Racially and Ethnically Diverse Couples in Relationship Education.
Creator: Munyon, Matthew, Young, Mark, Hagedorn, William, Daire, Andrew, Sivo, Stephen, University of Central Florida
Abstract / Description: Couples experiencing relationship distress often require professional help, such as counseling and couple and relationship education (CRE). Research recently discovered that among couples in counseling, a circular relationship exists between individual and relationship distress(-)stress begets stress. Until this study, a similar examination had not been conducted among couples selecting CRE. This study examined the relationship between individual and relationship distress among married...
Show moreCouples experiencing relationship distress often require professional help, such as counseling and couple and relationship education (CRE). Research recently discovered that among couples in counseling, a circular relationship exists between individual and relationship distress(-)stress begets stress. Until this study, a similar examination had not been conducted among couples selecting CRE. This study examined the relationship between individual and relationship distress among married couples that had children, were from predominantly low-income and racially and ethnically diverse backgrounds, and selected CRE. A correlational research design was employed and framed in the social interdependence theory. The actor-partner interdependence model was conducted within a three-level hierarchical model. The results confirmed that a circular relationship exists between individual and relationship distress(-)distress begets distress. Within the circular model of individual and relational functioning, personal individual distress predicted partner individual distress as well as personal and partner relationship distress, and personal relationship distress predicted personal individual distress and partner relationship distress. The extent to which distress begot distress was stronger among women, those with low income, and those who were unemployed. The results also revealed a continuum of individual and relational functioning. Dyad members interact along a continuum from intrapersonal individual functioning to interpersonal relational functioning. The continua meet at the nexus of negotiation or the heart of interpersonal interaction, where dyad members communicate and make decisions, among other actions. Implications related to the findings of this study as well as inspirations for future research are discussed.
Show less
Date Issued: 2012
Identifier: CFE0004284, ucf:49529
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004284

stress (37)	+ -
Stress (17)	+ -
PTSD (6)	+ -
anxiety (5)	+ -
coping (5)	+ -

burnout (4)	+ -
exposure therapy (4)	+ -
health (4)	+ -
residual stress (4)	+ -
College Students (3)	+ -
Coping (3)	+ -
Nurse (3)	+ -
acculturative stress (3)	+ -
compassion fatigue (3)	+ -
posttraumatic stress disorder (3)	+ -
secondary traumatic stress (3)	+ -
synchrotron (3)	+ -
Anxiety (2)	+ -
Ceramics (2)	+ -
Compassion Fatigue (2)	+ -
Cortisol (2)	+ -
ER stress (2)	+ -
Emergency Department (2)	+ -
FEA (2)	+ -
Finite Element Analysis (2)	+ -
Hill Yield Criterion (2)	+ -
Inconel 718 (2)	+ -
Latinos (2)	+ -
Lode angle (2)	+ -
Mechanical Testing (2)	+ -

ETD Collection (101)	+ -
Honors Collection (31)	+ -

University of Central Florida (132)	+ -
Bowers, Clint (10)	+ -
Beidel, Deborah (9)	+ -
Orlovskaya, Nina (8)	+ -
Raghavan, Seetha (8)	+ -

Gou, Jihua (7)	+ -
Bai, Yuanli (6)	+ -
Gordon, Ali (6)	+ -
Hancock, Peter (6)	+ -
Renk, Kimberly (5)	+ -
Sohn, Yongho (5)	+ -
Andrews, Diane (4)	+ -
Lambie, Glenn (4)	+ -
Neer, Sandra (4)	+ -
Self, William (4)	+ -
Bedwell, Jeffrey (3)	+ -
Ebert, Steven (3)	+ -
Ghosh, Ranajay (3)	+ -
Heglund, Stephen (3)	+ -
Jentsch, Florian (3)	+ -
Kwok, Kawai (3)	+ -
Negy, Charles (3)	+ -
Salas, Eduardo (3)	+ -
Sole, Mary Lou (3)	+ -
Szalma, James (3)	+ -
Vaidyanathan, Raj (3)	+ -
Young, Mark (3)	+ -
Zhang, Ning (3)	+ -
Abel, Eileen (2)	+ -
Bushy, Angeline (2)	+ -

Search In

Pages

Pages

Sort Results By:

Narrow results by:

Topical Subject

Collection

Type of Resource

Language

Creator

Format

Owner