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- Title
- HIGH VOLTAGE BIAS TESTING AND DEGRADATION ANALYSIS OF PHOTOVOLTAIC MODULES.
- Creator
-
Hadagali, Vinaykumar, Dhere, Neelkanth, University of Central Florida
- Abstract / Description
-
This thesis mainly focuses on two important aspects of the photovoltaic modules. The first aspect addressed the high voltage bias testing and data and degradation analysis of high voltage biased thin film photovoltaic modules. The second aspect addressed the issues of reliability and durability of crystalline silicon module. Grid-connected photovoltaic systems must withstand high voltage bias in addition to harsh environmental conditions such as intermittent solar irradiance, high humidity,...
Show moreThis thesis mainly focuses on two important aspects of the photovoltaic modules. The first aspect addressed the high voltage bias testing and data and degradation analysis of high voltage biased thin film photovoltaic modules. The second aspect addressed the issues of reliability and durability of crystalline silicon module. Grid-connected photovoltaic systems must withstand high voltage bias in addition to harsh environmental conditions such as intermittent solar irradiance, high humidity, heat and wind. a-Si:H thin-film photovoltaic modules with earlier generation SnO2:F transparent conducting oxide (TCO) on the front glass installed on the FSEC High Voltage Test Bed were monitored since December 2001. The data was collected on a daily basis and analyzed. The leakage currents for some chosen time period were calculated and compared with the measured values. Current-voltage characteristic measurements were carried out to check any reduction in the power. Samples were cored and extracted for analysis from one of the -600 V biased modules. Leakage currents in high-voltage-biased laminates specially prepared with improved SnO2:F TCO are being monitored in the hot and humid climate in Florida. Negatively-biased modules showed clear signs of delamination. The leakage currents in high-voltage biased photovoltaic modules are functions of both temperature and relative humidity. Photovoltaic module leakage conductance was found to be thermally stimulated with a characteristic activation energy that depends on relative humidity. The adhesional strength was lost completely in the damaged area. Leakage current values from support to ground in new, unframed laminates fabricated with improved SnO2:F TCO layer were ~100 times lower under the high voltage bias in hot and humid environment. Information on the failure of field deployed modules must be complemented with why and how the modules fail while considering the issues of reliability and durability of crystalline silicon module. At present, all the failure modes have not been identified and failure mechanisms have not been understood. Experience has shown that as the materials and processes are changed, reliability issues that apparently had been resolved resurface. A multicrystalline silicon photovoltaic module that was manufactured by a non-US company and that had shown >50% performance loss in field-deployment of <2 years in hot and dry climate were studied for degradation analysis in comparison with a mc-Si module that was manufactured by the same company and that performed well after 10 years of field-deployment in hot and humid climate.. I-V measurements were carried out to analyze the reduction in photovoltaic parameters. Solder bond strength in mc-Si photovoltaic modules were measured to understand early degradation of performance. Samples were cored and extracted for further analysis. Adhesional strength between the busline metallization and the silicon cell in a newer generation mc-Si photovoltaic module was found to be considerably lower than that in the earlier vintage module. These results can be useful for early detection and diagnosis of field reliability issues and could assist in establishing correlation between long-term field data and observations and accelerated environmental stress testing. It is suggested that more detailed study should be undertaken using unencapsulated strings of crystalline silicon modules so as to avoid complication due to encapsulant creeping beneath the ribbons.
Show less - Date Issued
- 2005
- Identifier
- CFE0000798, ucf:46563
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0000798
- Title
- A SURVEY OF THE BIG FIVE PERSONALITY TRAITS AMONG ELEMENTARY TEACHERS.
- Creator
-
Rohani, Afrina R, Roberts, Sherron, University of Central Florida
- Abstract / Description
-
This research examined the possibility that personality traits play a part in career longevity and job satisfaction in the education field. The current study examined trends among the Big Five personality traits (Openness to Experience, Conscientiousness, Extraversion, Agreeableness, and Neuroticism) and their relation to job satisfaction in the elementary classroom. This researcher hypothesized that some common personality traits that are shared by teachers who persist in the classroom for...
Show moreThis research examined the possibility that personality traits play a part in career longevity and job satisfaction in the education field. The current study examined trends among the Big Five personality traits (Openness to Experience, Conscientiousness, Extraversion, Agreeableness, and Neuroticism) and their relation to job satisfaction in the elementary classroom. This researcher hypothesized that some common personality traits that are shared by teachers who persist in the classroom for five or more years, who are satisfied with their jobs and do not intend to leave. This researcher hypothesized that more experienced teachers would be high in Conscientiousness, and Agreeableness. This researcher hypothesized that less experienced teachers would have Big Five personality scores that are more diverse than those of experienced teachers and that are more representative of the personalities of the general population. This researcher also hypothesized that teachers who score higher in the areas of Neuroticism and lower on Conscientiousness and Extraversion, would be dissatisfied with their jobs. The survey was completed by 202 participants. Experienced teachers (those working in the classroom for five or more years), and less experienced teachers (those working in the classroom for four years or less) completed the Big Five personality survey, along with additional survey questions that assess job satisfaction, and intent to leave. This research found no trend among personality traits in experienced teachers compared to inexperienced teachers. There was, however, a correlation between intention to leave and Neuroticism as well as a correlation between job satisfaction and Neuroticism, Extraversion, and Conscientiousness.
Show less - Date Issued
- 2017
- Identifier
- CFH2000257, ucf:45965
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFH2000257
- Title
- RACE, SOCIO-ECONOMIC STATUS, SCHOOL LEVEL-RESOURCES, AND PARENTAL INFLUENCES ON FCAT SCORES IN FLORIDA: A QUANITATIVE STUDY.
- Creator
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King, Tara, Jasinski, Jana, University of Central Florida
- Abstract / Description
-
There is an abundance of literature that focuses on the standardized test score difference between minority and non-minority students. Within this literature, socio-economic factors, parental influences, and school-level resources have been used to explain the difference in test scores. The purpose of this study is to identify the variables that are thought to significantly influence test score achievement. The data come from the Florida Department of Education and the US Census. Linear...
Show moreThere is an abundance of literature that focuses on the standardized test score difference between minority and non-minority students. Within this literature, socio-economic factors, parental influences, and school-level resources have been used to explain the difference in test scores. The purpose of this study is to identify the variables that are thought to significantly influence test score achievement. The data come from the Florida Department of Education and the US Census. Linear regression analyses results are used to examine the relationship between the independent and the dependent variables. The results showed that overall economic factors are more closely related to FCAT scores than race. More specifically, the percent of students receiving free lunch was negatively correlated with FCAT scores.
Show less - Date Issued
- 2005
- Identifier
- CFE0000896, ucf:46641
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0000896
- Title
- URINALYSIS SCREENING OF DRUGS IN ADULTERATED SAMPLES VIA DIRECT ANALYSIS IN REAL TIME -- HIGH RESOLUTION/ MASS SPECTROMETRY (DART-HR/MS).
- Creator
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Olivieri, Bianca E, Bridge, Candice, University of Central Florida
- Abstract / Description
-
Current screening methods for drug analysis with urine samples includes examination of the sample with an immunoassay. These methods are used to determine the concentration of drug metabolites contained within the sample prior to further confirmatory testing. Drug testing plays a crucial role in maintaining safe workplace environments and safety of individuals. However, a positive result can lead to heavy consequences for the employee including suspension or removal from the workplace....
Show moreCurrent screening methods for drug analysis with urine samples includes examination of the sample with an immunoassay. These methods are used to determine the concentration of drug metabolites contained within the sample prior to further confirmatory testing. Drug testing plays a crucial role in maintaining safe workplace environments and safety of individuals. However, a positive result can lead to heavy consequences for the employee including suspension or removal from the workplace. Therefore, a majority of individuals add commonly known products into the sample to evade detection by developing a false negative result. Although specimen integrity examinations are performed to identify tampering of the sample, these results are typically biased on the experience of the examiner. The purpose of this study was to develop an analytical screening technique that will detect the drug of interest as well as the presence of any additional products that may be added into the sample via Direct Analysis in Real Time � High Resolution/Mass Spectrometry (DART-HR/MS) which is an ambient ionization source that produces fast mass spectrum results that can provide semi-quantitative information of the target metabolite concentration. Although there are various studies that indicate the ability of the DART to detect drug compounds, there are no known studies that have examined how real-world urine samples are analyzed. Additionally, there are no current studies that take into consideration adulteration of the urine sample using the DART method. The results obtained in the study showed the ability for DART to identify molecular protonated peaks indicative of dextroamphetamine and/or the presence of masking agents. While the other target drugs could not be identified using this method, the identification of dextroamphetamine, adulterant products and the deuterated internal standard show promise in using this as a screening technique prior to confirmatory tests. Future work is currently being conducted to optimize the protocol for the evaluation of THC, cocaine and benzodiazepines.
Show less - Date Issued
- 2019
- Identifier
- CFH2000538, ucf:45623
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFH2000538
- Title
- PSYCHOMETRIC DIFFERENCES IN MOTOR FUNCTIONING.
- Creator
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McWaters, Ashley, Fouty, Ed, University of Central Florida
- Abstract / Description
-
Clinical experience has shown that patients performing the Grooved Pegboard Test have difficulty maintaining the manualized right-to-left placement strategy with their left hand. This study sought to investigate possible differences in placement time on the Grooved Pegboard task between participants using the standardized left hand approach and a reversed manualized left hand placement strategy (i.e., left-to-right). The participants included 63 male and female undergraduate volunteers...
Show moreClinical experience has shown that patients performing the Grooved Pegboard Test have difficulty maintaining the manualized right-to-left placement strategy with their left hand. This study sought to investigate possible differences in placement time on the Grooved Pegboard task between participants using the standardized left hand approach and a reversed manualized left hand placement strategy (i.e., left-to-right). The participants included 63 male and female undergraduate volunteers between the ages of 18 and 25 years. All participants had no history of neurologic disease/trauma, or conditions that would affect motor functioning of the right and left upper extremities. Data were analyzed using a 3-way mixed-design ANOVA. Results revealed a significant main effects for gender (F(1, 59) = 5.215, p = .026) and handedness (F(1, 59) = 6.362, p = .014). Of primary interest was the main effect for placement direction, which was not significant, F(1, 59) = .120, p = .731. No significant interaction was observed (all p > .40). Recommendations for the use of this test in applied neuropsychological settings are offered.
Show less - Date Issued
- 2013
- Identifier
- CFH0004510, ucf:45172
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFH0004510
- Title
- PREVALENCE OF HELICOBACTER PYLORI AND HEALTH RELATED RISK FACTORS AT THE UNIVERSITY OF CENTRAL FLORIDA.
- Creator
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Holsonback, Evan, Saleh, Suha, University of Central Florida
- Abstract / Description
-
Helicobacter pylori (H. pylori) is a Gram-negative bacterium that infects and resides in the gastric mucosa of humans. Without treatment, H. pylori infection may cause chronic inflammation of the gastric mucosa. This inflammation creates progressive damage to the lining of the stomach and can lead to multiple diseases located in the upper gastrointestinal region. Worldwide prevalence of H. pylori infection is estimated to be close to 50%. H. pylori has been identified as the primary cause of...
Show moreHelicobacter pylori (H. pylori) is a Gram-negative bacterium that infects and resides in the gastric mucosa of humans. Without treatment, H. pylori infection may cause chronic inflammation of the gastric mucosa. This inflammation creates progressive damage to the lining of the stomach and can lead to multiple diseases located in the upper gastrointestinal region. Worldwide prevalence of H. pylori infection is estimated to be close to 50%. H. pylori has been identified as the primary cause of peptic ulcer disease, gastric cancer, and mucosa-associated lymphoid tissue lymphoma. The purpose of this study was to identify the prevalence and risk factors associated with H. pylori infection among students, faculty, and staff at the University of Central Florida. A cross-sectional design with a convenience sample was implemented to acquire a study population of 60 participants. The sample was analyzed through the use of a twenty question survey and a rapid blood antibody test kit. The infection rate of the sample was 1.75%. Statistically significant results were found for the relationship between age and upper gastrointestinal symptoms. Trends were also noticed between alcohol consumption, stress levels, and upper gastrointestinal symptoms.
Show less - Date Issued
- 2018
- Identifier
- CFH2000329, ucf:45771
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFH2000329
- Title
- MODIFICATION TO EINSTEIN'S FIELD EQUATIONS IMPOSED BY STRING THEORY AND CONSEQUENCES FOR THE CLASSICAL TESTS OF GENERAL RELATIVITY.
- Creator
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Frye, Christopher, Efthimiou, Costas, University of Central Florida
- Abstract / Description
-
String theory imposes slight modifications to Einstein's equations of general relativity. In Green, Schwarz, and Witten's classic text, the authors claim that the gravitational field equations in empty space should contain, in addition to the Ricci tensor, an extra term which is first order in the string constant alpha-prime and proportional to the Riemann curvature tensor squared. They do admit, however, that this simple modification is just schematic. We show that these modified equations...
Show moreString theory imposes slight modifications to Einstein's equations of general relativity. In Green, Schwarz, and Witten's classic text, the authors claim that the gravitational field equations in empty space should contain, in addition to the Ricci tensor, an extra term which is first order in the string constant alpha-prime and proportional to the Riemann curvature tensor squared. They do admit, however, that this simple modification is just schematic. We show that these modified equations do not admit an isotropic solution. We then investigate the consequences of the modified gravitational equations when they are coupled to the dilaton field. Callan, Myers, and Perry have found a static isotropic solution to these equations. We calculate the additional perihelion precession of Mercury, the added deflection of photons by the sun, and the extra gravitational redshift which should be present if these equations hold. We determine that additional effects due to string theory in each of these cases are quite minuscule.
Show less - Date Issued
- 2013
- Identifier
- CFH0004411, ucf:45087
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFH0004411
- Title
- SUSTAINABLE FAULT-HANDLING OF RECONFIGURABLE LOGIC USING THROUGHPUT-DRIVEN ASSESSMENT.
- Creator
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Sharma, Carthik, DeMara, Ronald, University of Central Florida
- Abstract / Description
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A sustainable Evolvable Hardware (EH) system is developed for SRAM-based reconfigurable Field Programmable Gate Arrays (FPGAs) using outlier detection and group testing-based assessment principles. The fault diagnosis methods presented herein leverage throughput-driven, relative fitness assessment to maintain resource viability autonomously. Group testing-based techniques are developed for adaptive input-driven fault isolation in FPGAs, without the need for exhaustive testing or coding-based...
Show moreA sustainable Evolvable Hardware (EH) system is developed for SRAM-based reconfigurable Field Programmable Gate Arrays (FPGAs) using outlier detection and group testing-based assessment principles. The fault diagnosis methods presented herein leverage throughput-driven, relative fitness assessment to maintain resource viability autonomously. Group testing-based techniques are developed for adaptive input-driven fault isolation in FPGAs, without the need for exhaustive testing or coding-based evaluation. The techniques maintain the device operational, and when possible generate validated outputs throughout the repair process. Adaptive fault isolation methods based on discrepancy-enabled pair-wise comparisons are developed. By observing the discrepancy characteristics of multiple Concurrent Error Detection (CED) configurations, a method for robust detection of faults is developed based on pairwise parallel evaluation using Discrepancy Mirror logic. The results from the analytical FPGA model are demonstrated via a self-healing, self-organizing evolvable hardware system. Reconfigurability of the SRAM-based FPGA is leveraged to identify logic resource faults which are successively excluded by group testing using alternate device configurations. This simplifies the system architect's role to definition of functionality using a high-level Hardware Description Language (HDL) and system-level performance versus availability operating point. System availability, throughput, and mean time to isolate faults are monitored and maintained using an Observer-Controller model. Results are demonstrated using a Data Encryption Standard (DES) core that occupies approximately 305 FPGA slices on a Xilinx Virtex-II Pro FPGA. With a single simulated stuck-at-fault, the system identifies a completely validated replacement configuration within three to five positive tests. The approach demonstrates a readily-implemented yet robust organic hardware application framework featuring a high degree of autonomous self-control.
Show less - Date Issued
- 2008
- Identifier
- CFE0002329, ucf:47813
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0002329
- Title
- Examining Work-To-Rest Ratios To Optimize Upper Body Sprint Interval Training.
- Creator
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Lamonica, Michael, Fukuda, David, Hoffman, Jay, Stout, Jeffrey, Fragala, Maren, University of Central Florida
- Abstract / Description
-
The primary purpose of this study was to compare the metabolic influence of varying work-to-rest ratios during upper body sprint interval training (SIT). Forty-two recreationally trained men were randomized into one of three training groups [10s work bouts with two minutes of rest (10:2, n = 11) or four minutes of rest (10:4, n = 11), or 30s work bouts with four minutes of rest (30:4, n = 10)] or a control group (CON, n = 10). Participants underwent six training sessions over two weeks with...
Show moreThe primary purpose of this study was to compare the metabolic influence of varying work-to-rest ratios during upper body sprint interval training (SIT). Forty-two recreationally trained men were randomized into one of three training groups [10s work bouts with two minutes of rest (10:2, n = 11) or four minutes of rest (10:4, n = 11), or 30s work bouts with four minutes of rest (30:4, n = 10)] or a control group (CON, n = 10). Participants underwent six training sessions over two weeks with four to six 'all-out' sprints. During pre- and post-intervention visits, participants underwent a graded exercise test to determine maximal oxygen consumption (V?O2peak) and peak power output (PPO), four constant-work rate trials to determine critical power (CP), anaerobic working capacity (W'), and electromyographic fatigue threshold (EMGFT), and an upper body Wingate test to determine peak power (PP), mean power (MP), and total work (TW). Oxygen consumption and blood lactate during the Wingate test generated estimates of oxidative, glycolytic, and ATP-PCr energy system provisions. An analysis of covariance was performed on all testing measurements collected at post with the associated pre-values used as covariates. V?O2peak was greater in 30:4 (p = .007) and 10:2 (p = .036) compared to CON and PPO was greater in 30:4 than CON (p = .007). No differences were observed between groups in CP (p = .530), W' (p = .900), EMGFT (p = .692), PP (p = .692), MP (p = .290), or TW (p = .291). Relative energy contribution (p = .026) and energy expenditure (p = .019) of the ATP-PCr energy system was greater in 10:4 compared to CON. SIT protocols with larger work-to-rest ratios induce enhanced aerobic adaptions, whereas smaller work-to-rest ratios may enhance ATP-PCr utilization in the upper body over a short-term two-week intervention.
Show less - Date Issued
- 2018
- Identifier
- CFE0007036, ucf:51978
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007036
- Title
- HOW DO SITUATIONAL JUDGMENT TESTS AND SITUATIONAL INTERVIEWS COMPARE? AN EXAMINATION OF CONSTRUCT AND CRITERION-RELATED VALIDITY.
- Creator
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Gunter, James, Fritzsche, Barbara, University of Central Florida
- Abstract / Description
-
This study replicated and extended an earlier study by Banki and Latham (2010) and developed an equivalent SJT and SI in order to examine whether the two methods correlated differently with cognitive ability, personality, job experience, and job performance. The results of this study showed that the SJT and SI only correlated .20 and that the correlations for the SI with Extraversion, customer service experience, and overall work experience were significantly different from the correlations...
Show moreThis study replicated and extended an earlier study by Banki and Latham (2010) and developed an equivalent SJT and SI in order to examine whether the two methods correlated differently with cognitive ability, personality, job experience, and job performance. The results of this study showed that the SJT and SI only correlated .20 and that the correlations for the SI with Extraversion, customer service experience, and overall work experience were significantly different from the correlations for the SJT. Participants felt that the SJT and SI provided the same opportunity to perform oneÂÂ's skills and level of scoring consistency. However, participants felt significantly more anxiety during the SI than the SJT. The practical and theoretical implications of these findings are discussed.
Show less - Date Issued
- 2010
- Identifier
- CFE0003522, ucf:48941
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003522
- Title
- The Impact of Timed Versus Untimed Standardized Tests On Reading Scores Of Third Grade Students in Title I Schools.
- Creator
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Haniff, Ruthie, Stewart, Martha, Holt, Larry, Platt, Jennifer, Clark, Margaret, Purmensky, Kerry, University of Central Florida
- Abstract / Description
-
The purpose of this study was to investigate the extent to which the performance of Title I third grade students in a central Florida School District differed on tests dministered under timed and untimed conditions. Further examined was the literature on reasons for the achievement gap which centered around seven different themes: (a) standardized testing, (b) achievement gap data and identified factors (c) deficit theory, (d) cultural mismatch theory, (e) extended time accommodations, (f)...
Show moreThe purpose of this study was to investigate the extent to which the performance of Title I third grade students in a central Florida School District differed on tests dministered under timed and untimed conditions. Further examined was the literature on reasons for the achievement gap which centered around seven different themes: (a) standardized testing, (b) achievement gap data and identified factors (c) deficit theory, (d) cultural mismatch theory, (e) extended time accommodations, (f) test anxiety and stress, and (g) timed versus untimed tests.Six Title I schools participated in this study by assigning 194 students to take the 2006 Released FCAT Reading Test under either timed or untimed conditions. Although there were no interactions between the covariates and testing conditions, those who were in the free or reduced lunch program or were in exceptional education programs had lower FCAT scores than those who were not. However, when school was included as a moderator, there was a statistically significant interaction between testing conditions and schools on FCAT scores indicating that the relationship between testing conditions and FCAT scores varied for each individual school.A factorial ANCOVA was conducted, and it was found that the mean differences between students who took the timed and untimed 2006 FCAT Reading Test varied from school to school after accounting for the covariates. For two schools, those students who took the untimed tests scored higher than those who took the timed tests. In contrast, those students who took the untimed tests scored lower than those students who took thetimed test for one of the schools. There was no statistically significant difference for three of the schools.A factorial MANCOVA was used to compare reading performance on the 2006 Reading FCAT between the timed and untimed groups on domain specific tests. The relationship between testing condition and FCAT scores for each domain specific test varied depending on the individual school. Therefore, it could not be concluded from these analyses that testing conditions would consistently result in increases or decreases of student performance on standardized domain specific tests.
Show less - Date Issued
- 2012
- Identifier
- CFE0004381, ucf:49407
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004381
- Title
- A NOVEL EXPERIMENTAL APPROACH USING A RECONFIGURABLE TEST SETUP FOR COMPLEX NONLINEAR DYNAMIC SYSTEMS.
- Creator
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Rank, Aaron, Yun, Hae-Bum, University of Central Florida
- Abstract / Description
-
Experimental nonlinear dynamics is an important area of study in the modern engineering field, with engineering applications in structural dynamics, structural control, and structural health monitoring. As a result, the discipline has experienced a great influx of research efforts to develop a versatile and reliable experimental methodology. A technical challenge in many experimental studies is the procurement of a device that exhibits the desired nonlinear behavior. As a result, many...
Show moreExperimental nonlinear dynamics is an important area of study in the modern engineering field, with engineering applications in structural dynamics, structural control, and structural health monitoring. As a result, the discipline has experienced a great influx of research efforts to develop a versatile and reliable experimental methodology. A technical challenge in many experimental studies is the procurement of a device that exhibits the desired nonlinear behavior. As a result, many researchers have longed for a versatile, but accurate, testing methodology that has complete freedom to simulate a wide range of nonlinearities and stochastic behaviors. The objective of this study is to develop a reconfigurable test setup as a tool to be used in a wide range of nonlinear dynamic studies. The main components include a moving mass whose restoring force can accurately be controlled and reprogrammed (with software) based upon measured displacement and velocity readings at each time step. The device offers control over nonlinear characteristics and the equation of dynamic motion. The advantage of having such an experimental setup is the ability to simulate various types of nonlinearities with the same test setup. As a result, the data collected can be used to help validate nonlinear modeling, system identification, and stochastic analysis studies. A physical test apparatus was developed, and various mechanical, electrical, and programming calibrations were performed for reliable experimental studies. To display potential uses for the reconfigurable approach, examples are presented where the device has been used to create physical data for use in change detection and deterioration studies. In addition, a demonstration is presented of the device's ability to physically simulate a large-scale orifice viscous damper, devices commonly used for vibration mitigation in bridges and buildings. For a large-scale viscous damper, physical testing is required to ensure structural design properties. However, due to the large scale of the dampers, expensive dynamic loading tests can be carried out at a very limited number of facilities. Using the reconfigurable test setup, the dynamic signature of the large-scale viscous damper can accurately be simulated with pre-collected data. The development of a system capable of emulating the restoring force of a nonlinear device with software is a novel approach and requires further calibration for increased reliability and accuracy. A discussion regarding the challenges faced when developing the methodology is presented and possible solutions are recommended. The methodology introduced by this apparatus is very promising. The device is a valuable experimental tool for researchers and designers, allowing for physical data collection, modeling, analysis, and validation of a wide class of nonlinear phenomena that commonly occur in a wide variety of engineering applications.
Show less - Date Issued
- 2011
- Identifier
- CFE0003982, ucf:48654
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003982
- Title
- Predictive modeling for assessing the reliability of bypass diodes in Photovoltaic modules.
- Creator
-
Shiradkar, Narendra, Sundaram, Kalpathy, Schoenfeld, Winston, Atia, George, Abdolvand, Reza, Xanthopoulos, Petros, University of Central Florida
- Abstract / Description
-
Solar Photovoltaics (PV) is one of the most promising renewable energy technologies for mitigating the effect of climate change. Reliability of PV modules directly impacts the Levelized Cost of Energy (LCOE), which is a metric for cost competitiveness of any energy technology. Further reduction in LCOE of PV through assured long term reliability is necessary in order to facilitate widespread use of solar energy without the need for subsidies. This dissertation is focused on frameworks for...
Show moreSolar Photovoltaics (PV) is one of the most promising renewable energy technologies for mitigating the effect of climate change. Reliability of PV modules directly impacts the Levelized Cost of Energy (LCOE), which is a metric for cost competitiveness of any energy technology. Further reduction in LCOE of PV through assured long term reliability is necessary in order to facilitate widespread use of solar energy without the need for subsidies. This dissertation is focused on frameworks for assessing reliability of bypass diodes in PV modules. Bypass diodes are critical components in PV modules that provide protection against shading. Failure of bypass diode in short circuit results in reducing the PV module power by one third, while diode failure in open circuit leaves the module susceptible for extreme hotspot heating and potentially fire hazard. PV modules, along with the bypass diodes are expected to last at least 25 years in field. The various failure mechanisms in bypass diodes such as thermal runaway, high temperature forward bias operation and thermal cycling are discussed. Operation of bypass diode under shading is modeled and method for calculating the module I-V curve under any shading scenario is presented. Frameworks for estimating the diode temperature in field deployed modules based on Typical Meteorological Year (TMY) data are developed. Model for predicting the susceptibility of bypass diodes for thermal runaway is presented. Diode wear out due to High Temperature Forward Bias (HTFB) operation and Thermal Cycling (TC) is studied under custom designed accelerated tests. Overall, this dissertation is an effort towards estimating the lifetime of bypass diodes in field deployed modules, and therefore, reducing the uncertainty in long term reliability of PV modules.
Show less - Date Issued
- 2015
- Identifier
- CFE0006001, ucf:51023
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006001
- Title
- Site Specific Sinkhole risk assessment in Central Florida using Cone Penetration Testing.
- Creator
-
Shamet, Ryan, Nam, Boo Hyun, Chopra, Manoj, Wang, Dingbao, University of Central Florida
- Abstract / Description
-
As Florida's population is expanding and greater fluctuations in groundwater levels are being recorded, Central Florida has been experiencing a higher frequency of sinkhole occurrences than ever before in recorded history. Sinkholes in Central Florida are formed by a combination of bedrock weathering and overburden soil erosion due to the groundwater recharge and are a part of Florida's past and future geology. The initial stage of a sinkhole is referred to as soil raveling and is the most...
Show moreAs Florida's population is expanding and greater fluctuations in groundwater levels are being recorded, Central Florida has been experiencing a higher frequency of sinkhole occurrences than ever before in recorded history. Sinkholes in Central Florida are formed by a combination of bedrock weathering and overburden soil erosion due to the groundwater recharge and are a part of Florida's past and future geology. The initial stage of a sinkhole is referred to as soil raveling and is the most effective time to perform soil improvement measures, such as grouting, to mitigate further expansion of a subterranean void. Subsurface exploration tests, commonly implemented by geotechnical engineers for site characterization, have been shown to detect these sinkhole anomalies even when no signs of subsidence are evident on the ground surface. Secondary geophysical testing has also been proven to detect sinkhole raveling anomalies, but at the expense of additional time and money added to the specific project. In this study, current practices in detecting premature sinkholes were expanded upon with a primary focus on Cone Penetrometer testing data (CPT). Cone Penetrometer tests provide valuable high-resolution quantitative information regarding the discrete strength characteristics of relatively loose sandy and clayey subsoil. CPTs are also much quicker and cleaner to perform when compared to other subsurface testing procedures (e.g. Standard penetration tests). Therefore, CPTs were chosen for this study to understand how they can be implemented to assess risk of future sinkhole collapse, or other karst construction concerns, in Central Florida specific soils. By implementing the findings presented in this report, Geotechnical engineers and contractors in central Florida will be able to practically evaluate the size and severity of potential forming sinkhole without the use of additional subsurface geophysical testing. The results of this study hope to eliminate extraneous testing costs, as well as maximize the efficiency of estimating mitigation products and procedures required all while still ensuring a safe design in Central Florida's highly karst areas.
Show less - Date Issued
- 2017
- Identifier
- CFE0006657, ucf:51246
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006657
- Title
- WALL HEAT TRANSFER EFFECTS IN THE ENDWALL REGION BEHIND A REFLECTED SHOCK WAVE AT LONG TEST TIMES.
- Creator
-
Frazier, Corey, Petersen, Eric, University of Central Florida
- Abstract / Description
-
Shock-tube experiments are typically performed at high temperatures (>1200K) due to test-time constraints. These test times are usually ~1 ms in duration and the source of this short, test-time constraint is loss of temperature due to heat transfer. At short test times, there is very little appreciable heat transfer between the hot gas and the cold walls of the shock tube and a high test temperature can be maintained. However, some experiments are using lower temperatures (approx. 800K) to...
Show moreShock-tube experiments are typically performed at high temperatures (>1200K) due to test-time constraints. These test times are usually ~1 ms in duration and the source of this short, test-time constraint is loss of temperature due to heat transfer. At short test times, there is very little appreciable heat transfer between the hot gas and the cold walls of the shock tube and a high test temperature can be maintained. However, some experiments are using lower temperatures (approx. 800K) to achieve ignition and require much longer test times (up to 15 ms) to fully study the chemical kinetics and combustion chemistry of a reaction in a shock-tube experiment. Using mathematical models, analysis was performed studying the effects of temperature, pressure, shock-tube inner diameter, and test-port location at various test times (from 1 – 20 ms) on temperature maintenance. Three models, each more complex than the previous, were used to simulate test conditions in the endwall region behind the reflected shock wave with Ar and N2 as bath gases. Temperature profile, thermal BL thickness, and other parametric results are presented herein. It was observed that higher temperatures and lower pressures contributed to a thicker thermal boundary layer, as did shrinking inner diameter. Thus it was found that a test case such as 800K and 50 atm in a 16.2-cm-diameter shock tube in Argon maintained thermal integrity much better than other cases – pronounced by a thermal boundary layer < 1 mm thick and an average temperature > 799.9 K from 1–20 ms.
Show less - Date Issued
- 2007
- Identifier
- CFE0001593, ucf:47162
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001593
- Title
- Sinkhole Monitoring Using Groundwater Table Data.
- Creator
-
Tu, Ton, Yun, Hae-Bum, Nam, Boo Hyun, Wang, Dingbao, University of Central Florida
- Abstract / Description
-
Florida might be one of the most sinkhole-active areas on the earth. Due to its unpredictability and significance of occurrence, the development of sinkhole monitoring techniques is imperative to minimize sinkhole-induced hazards. Several methods have been used to evaluate sinkhole risks, including destructive methods, such as Standard Penetrating Tests (SPT) and Cone Penetrating Tests (CPT), geophysical method, and sensor-based groundwater monitoring method. However, few studies are...
Show moreFlorida might be one of the most sinkhole-active areas on the earth. Due to its unpredictability and significance of occurrence, the development of sinkhole monitoring techniques is imperative to minimize sinkhole-induced hazards. Several methods have been used to evaluate sinkhole risks, including destructive methods, such as Standard Penetrating Tests (SPT) and Cone Penetrating Tests (CPT), geophysical method, and sensor-based groundwater monitoring method. However, few studies are available for comprehensive understanding of spatiotemporal sinkhole mechanism by combining different exploration methods under realistic experimental conditions. The objective of this study is to understand spatiotemporal sinkhole mechanism, using SPT, CPT, ground penetrating radar (GPR), and piezo pressure sensors tested at actual sinkhole sites. A small-scale test was conducted prior to the field test to validate data analysis technique using piezo pressure sensors, developed in this study. Eight piezo pressure sensors were used located at different distances from the sinkhole center to measure the ground water levels (GWLs) during artificially made sinkhole events. A total of 24 scaled tests was conducted with different sinkhole soil thickness and initial GWL. The cone of water depression was observed during the tests, which indicates there are strong relationship between sinkhole and sinkhole occurrence. A novel peak-counting method was developed and validated to estimate spatiotemporal relations of the relations between GWLs and sinkhole collapse patterns.The field test was conducted at an active sinkhole site in Lake county, Florida to determine locations of points of breach and to monitor fluctuation GWL over time. Twenty piezometer sensors were installed, and the GWLs were monitored for three months at 30-min sampling rate. The daily moving average of GWL was calculated and visualized in ArcGIS map to understand spatiotemporal behavior of GWL at different locations from sinkhole positions. The monitoring results were compared with CPT, SPT and GPR results that were conducted prior to the piezo sensor installations. Strong correlations were observed between CPT, SPT, GPR and GWL results. From the results, it can be concluded that size and shape of the cone of water depression depend on dimensions of point discharges and properties of surrounding soil.
Show less - Date Issued
- 2016
- Identifier
- CFE0006511, ucf:51383
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006511
- Title
- The nuclear test-ban treaty: Gateway to peace.
- Creator
-
United States. Dept. of State
- Date Issued
- 1961
- Identifier
- 1745497, CFDT1745497, ucf:4781
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/FCLA/DT/1745497
- Title
- Emotional Labor and Identity Management Among HIV Counselors and Testers.
- Creator
-
Caldwell, James, Anthony, Amanda, Donley, Amy, Gay, David, University of Central Florida
- Abstract / Description
-
Emotional labor, an idea first developed by Arlie Hochschild, became a main component of work developing the field of sociology of emotions. Emotion labor provides a conceptual framework for understanding the outward and inward emotional experiences that are deemed either appropriate or inappropriate during interactions with others, specifically in the workplace. A product and derivation of this emotional labor is carefully outlined display rules. These rules vary from position to position,...
Show moreEmotional labor, an idea first developed by Arlie Hochschild, became a main component of work developing the field of sociology of emotions. Emotion labor provides a conceptual framework for understanding the outward and inward emotional experiences that are deemed either appropriate or inappropriate during interactions with others, specifically in the workplace. A product and derivation of this emotional labor is carefully outlined display rules. These rules vary from position to position, but are often part and parcel of work in the human services sector. This labor can be understood as resulting from the employee's adherence to display rules, which may or may not match the employees' organically felt or perceived emotions at the time. The current study draws from these conceptual frameworks and emotion work typologies introduced by Arlie Hochschild to analyze in-depth, the emotional labor performed by HIV Testers; this study does so through the analytical categories of Bodily Emotion Work, Expressive Emotion Work, and Cognitive Emotion Work. While the current study upholds many conclusions of prior research related to human services, and high rates of emotional labor, this study contributes through introducing the term Emotional Tuning. As based in the dynamic of emotional labor existing between HIV Testers and the patients that they serve, this study puts forth the term Emotional Tuning as the process of one individual scanning or reviewing the emotional state of another. The individual then acts accordingly, based on their interpretation of the other's emotional state, to help influence that emotional state, typically by matching or contrasting with that emotional state. This research contributes by expanding on prior research of emotion work and emotion labor through the specific field of client-based counseling, as there is no known prior research that has delved specifically into the work performed by HIV Testers and the rich experiences had by those delivering HIV results and sexual education, particularly as the emotional labor being studied is not commodified. Such topics as HIV status and sexual health education have been, even recently, overshadowed by stigma. Many Testers in the current study found HIV work to be both the hardest and most rewarding experience of their life. The current study looked closely at the effect that this emotional work had on both the testers interviewed, and the patients they serve and has broad implications for both tester training and client support initiatives.
Show less - Date Issued
- 2016
- Identifier
- CFE0006274, ucf:51036
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006274
- Title
- ANISOTROPY EVOLUTION DUE TO SURFACE TREATMENT ON 3D-PRINTED FUSED DEPOSITION MODELING (FDM) OF ACRYLONITRILE BUTADIENE STYRENE (ABS).
- Creator
-
Lozinski, Blake E, Kassab, Alain, University of Central Florida
- Abstract / Description
-
Purpose: This paper will present insight to the methodology and results of the experimental characterization of Acrylonitrile Butadiene Styrene (ABS) using Fused Deposition Modeling (FDM). The work in this research explored the effects of print orientation, surface treatment, and ultraviolet (UV) light degradation with the utilization of Digital Image Correlation (DIC) on ABS tensile specimens. Design/methodology: ABS specimens were printed at three build orientations (flat (0 degrees), 45...
Show morePurpose: This paper will present insight to the methodology and results of the experimental characterization of Acrylonitrile Butadiene Styrene (ABS) using Fused Deposition Modeling (FDM). The work in this research explored the effects of print orientation, surface treatment, and ultraviolet (UV) light degradation with the utilization of Digital Image Correlation (DIC) on ABS tensile specimens. Design/methodology: ABS specimens were printed at three build orientations (flat (0 degrees), 45 degrees, and up-right (90 degrees)). Each of these specimens were treated with three different surface treatments including a control (acrylic paint, Cyanoacrylate, and Diglycidyl Bisphenol A) followed by exposure to UV light to the respective batches. This experiment design will provide tensile direction properties with the effect of thermoset coatings and UV degradation. Dogbone FDM specimens based on ASTM standard D638 type IV were printed on a Stratasys Dimension SST (Soluble Support Technology) 1200es 3D Printer and loaded into a MTS Landmark Servohydraulic Test Systems. Analysis was preformed on the fracture section of the tensile specimens utilized DIC and comparing Ultimate Tensile Strength (UTS) and Ultimate Fracture Strength (UFS). Findings: From the results UV light did not play a large factor in the strength of the specimens. The print orientation showed the largest anisotropic behavior where some specimens experienced as much as a 54% difference in ultimate tensile strength. Thermoset coated specimens experienced a maximum of 2% increase in strength for the Cyanoacrylate and Diglycidyl Bisphenol A specimens where the acrylic paint and natural did not. Several findings were of value when looking at the stress strain plots. Originality/value: This paper provides knowledge to the limited work on print build orientation, thermoset coatings and, UV light on ABS specimens. Very little to no work has been done on these three properties. This paper can serve as the foundation of future work on external applications on ABS plastics.
Show less - Date Issued
- 2017
- Identifier
- CFH2000269, ucf:45825
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFH2000269
- Title
- UV-LIGA COMPATIBLE ELECTROFORMED NANO-STRUCTURED MATERIALS FOR MICRO MECHANICAL SYSTEMS.
- Creator
-
LI, BO, Chen, Quanfang, University of Central Florida
- Abstract / Description
-
UV-LIGA is a microfabrication process realzed by material deposition through microfabricated molds. UV photolithography is conducted to pattern precise thick micro molds using UV light sensitive materials, mostly SU-8, and electroforming is performed to fabricate micro metallic structures defined by the micro molds. Therefore, UV-LIGA is a bottom-up in situ material-addition process. UV-LIGA has received broad attention recently than LIGA a micro molding fabrication process using X-ray to...
Show moreUV-LIGA is a microfabrication process realzed by material deposition through microfabricated molds. UV photolithography is conducted to pattern precise thick micro molds using UV light sensitive materials, mostly SU-8, and electroforming is performed to fabricate micro metallic structures defined by the micro molds. Therefore, UV-LIGA is a bottom-up in situ material-addition process. UV-LIGA has received broad attention recently than LIGA – a micro molding fabrication process using X-ray to pattern the micro molds. LIGA is an expansive and is limited in access. In comparing to LIGA, the UV-LIGA is a cost effective process, and is widely accessible and safe. Therefore, it has been extensively used for the fabrication of metallic micro-electro-mechanical-systems (MEMS). The motivation of this research was to study micro mechanical systems fabricated with nano-structured metallic materials via UV-LIGA process. Various micro mechanical systems with high-aspect-ratio and thick metallic structures have been developed and are presented in this desertation. A novel micro mechanical valve has been developed with nano-structured nickel realized with UV-LIGA fabrication technique. Robust compact valves are crucial for space applications where payload and rubstaness are critically concerned. Two types of large flow rate robust passive micro check valve arrays have been designed, fabricated and tested for robust hydraulic actuators. The first such micro valve developed employs nanostructured nickel as the valve flap and single-crystal silicon as the substrates to house inlet and outlet channels. The Nano-structured nickel valve flap was fabricated using the UV-LIGA process developed and the microchannels were fabricated by deep reactive etching (DRIE) method. The valves were designed to operate under a high pressure (>10MPa), able to operate at high frequencies (>10kHz) in cooperating with the PZT actuator to produce large flow rates (>10 cc/s). The fabricated microvalves weigh 0.2 gram, after packing with a novel designated valve stopper. The tested results showed that the micro valve was able to operate at up to 14kHz. This is a great difference in comparison to traditional mechanical valves whose operations are limited to 500 Hz or less. The advantages of micro machined valves attribute to the scaling laws. The second type of micro mechanical valves developed is a in situ assembled solid metallic (nickel) valves. Both the valve substrates for inlet and outlet channels and the valve flap, as well as the valve stopper were made by nickel through a UV-LIGA fabrication process developed. Continuous multiple micro molds fabrication and molding processes were performed. Final micro mechanical valves were received after removing the micro molds used to define the strutures. There is no any additional machining process, such as cutting or packaging. The alignment for laminated fabrication was realized under microscope, therefore it is a highly precise in situ fabrication process. Testing results show the valve has a forward flow rate of19 cc/s under a pressure difference of 90 psi. The backward flow rate of 0.023 cc/s, which is negligible (0.13%). Nano-structured nickel has also been used to develop laminated (sandwiched) micro cryogenic heater exchanger with the UV-LIGA process. Even though nickel is apparently not a good thermal conductor at room temperature, it is a good conductor at cryogentic temerpature since its thermal conductivity increases to 1250 W/k·m at 77K. Micro patterned SU-8 molds and electroformed nickel have been developed to realize the sandwiched heat exchanger. The SU-8 mold (200mm x 200mm x50mm) array was successfully removed after completing the nickel electroforming. The second layer of patterned SU-8 layer (200mm x 200mm x50mm, as a thermal insulating layer) was patterned and aligned on the top of the electroformed nickel structure to form the laminated (sandwiched) micro heat exchanger. The fabricated sandwiched structure can withstand cryogenic temperature (77K) without any damages (cracks or delaminations). A study on nanocomposite for micro mechanical systems using UV-LIGA compatible electroforming process has been performed. Single-walled carbon nanotubes (SWNTs) have been proven excellent mechanical properties and thermal conductive properties, such as high strength and elastic modulus, negative coefficient of thermal expansion (CTE) and a high thermal conductivity. These properties make SWNT an excellent reinforcement in nanocomposite for various applications. However, there has been a challenge of utilizing SWNTs for engineering applications due to difficulties in quality control and handling – too small (1-2nm in diameter). A novel copper/SWNT nanocomposite has been developed during this dissertational research. The goal of this research was to develop a heat spreader for high power electronics (HPE). Semiconductors for HPE, such as AlGaN/GaN high electron mobility transistors grown on SiC dies have a typical CTE about 4~6x10-6/k while most metallic heat spreaders such as copper have a CTE of more than 10x10-6/k. The SWNTs were successfully dispersed in the copper matrix to form the SWNT/Cu nano composite. The tested composite density is about 7.54 g/cm3, which indicating the SWNT volumetric fraction of 18%. SEM pictures show copper univformly coated on SWNT (worm-shaped structure). The measured CTE of the nanocomposite is 4.7 x 10-6/°C, perfectly matching that of SiC die (3.8 x 10-6/°C). The thermal conductivity derived by Wiedemann-Franz law after measuring composit's electrical conductivity, is 588 W/m-K, which is 40% better than that of pure copper. These properties are extremely important for the heat spreader/exchanger to remove the heat from HPE devices (SiC dies). Meanwhile, the matched CTE will reduce the resulted stress in the interface to prevent delaminations. Therefore, the naocomposite developed will be an excellent replacement material for the CuMo currently used in high power radar, and other HPE devices under developing. The mechanical performance and reliability of micro mechanical devices are critical for their application. In order to validate the design & simulation results, a direct (tensile) test method was developed to test the mechanical properties of the materials involved in this research, including nickel and SU-8. Micro machined specimens were fabricated and tested on a MTS Tytron Micro Force Tester with specially designed gripers. The tested fracture strength of nanostructured nickel is 900±70 MPa and of 50MPa for SU-8, resepctively which are much higher than published values.
Show less - Date Issued
- 2005
- Identifier
- CFE0000478, ucf:46372
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0000478
