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- Title
- LASER ENHANCED DOPING FOR SILICON CARBIDE WHITE LIGHTEMITTING DIODES.
- Creator
-
Bet, Sachin, Kar, Aravinda, University of Central Florida
- Abstract / Description
-
This work establishes a solid foundation for the use of indirect band gap semiconductors for light emitting application and presents the work on development of white light emitting diodes (LEDs) in silicon carbide (SiC). Novel laser doping has been utilized to fabricate white light emitting diodes in 6H-SiC (n-type N) and 4H-SiC (p-type Al) wafers. The emission of different colors to ultimately generate white light is tailored on the basis of donor acceptor pair (DAP) recombination mechanism...
Show moreThis work establishes a solid foundation for the use of indirect band gap semiconductors for light emitting application and presents the work on development of white light emitting diodes (LEDs) in silicon carbide (SiC). Novel laser doping has been utilized to fabricate white light emitting diodes in 6H-SiC (n-type N) and 4H-SiC (p-type Al) wafers. The emission of different colors to ultimately generate white light is tailored on the basis of donor acceptor pair (DAP) recombination mechanism for luminescence. A Q-switched Nd:YAG pulse laser (1064 nm wavelength) was used to carry out the doping experiments. The p and n regions of the white SiC LED were fabricated by laser doping an n-type 6H-SiC and p-type 4H-SiC wafer substrates with respective dopants. Cr, B and Al were used as p-type dopants (acceptors) while N and Se were used as n-type dopants (donors). Deep and shallow donor and acceptor impurity level states formed by these dopants tailor the color properties for pure white light emission. The electromagnetic field of lasers and non-equilibrium doping conditions enable laser doping of SiC with increased dopant diffusivity and enhanced solid solubility. A thermal model is utilized to determine the laser doping parameters for temperature distribution at various depths of the wafer and a diffusion model is presented including the effects of Fick's diffusion, laser electromagnetic field and thermal stresses due to localized laser heating on the mass flux of dopant atoms. The dopant diffusivity is calculated as a function of temperature at different depths of the wafer based on measured dopant concentration profile. The maximum diffusivities achieved in this study are 4.6110-10 cm2/s at 2898 K and 6.9210-12 cm2/s at 3046 K for Cr in 6H-SiC and 4H-SiC respectively. Secondary ion mass spectrometric (SIMS) analysis showed the concentration profile of Cr in SiC having a penetration depth ranging from 80 nm in p-type 4H-SiC to 1.5 m in n-type 6H-SiC substrates respectively. The SIMS data revealed enhanced solid solubility (2.291019 cm-3 in 6H-SiC and 1.421919 cm-3 in 4H-SiC) beyond the equilibrium limit (31017 cm-3 in 6H-SiC above 2500 C) for Cr in SiC. It also revealed similar effects for Al and N. The roughness, surface chemistry and crystalline integrity of the doped sample were examined by optical interferometer, energy dispersive X-ray spectrometry (EDS) and transmission electron microscopy (TEM) respectively. Inspite of the larger atomic size of Cr compared to Si and C, the non-equilibrium conditions during laser doping allow effective incorporation of dopant atoms into the SiC lattice without causing any damage to the surface or crystal lattice. Deep Level Transient Spectroscopy (DLTS) confirmed the deep level acceptor state of Cr with activation energies of Ev+0.80 eV in 4H-SiC and Ev+0.45 eV in 6H-SiC. The Hall Effect measurements showed the hole concentration to be 1.981019 cm-3 which is almost twice the average Cr concentration (11019 cm-3) obtained from the SIMS data. These data confirmed that almost all of the Cr atoms were completely activated to the double acceptor state by the laser doping process without requiring any subsequent annealing step. Electroluminescence studies showed blue (460-498 nm), blue-green (500-520 nm) green (521-575 nm), and orange (650-690 nm) wavelengths due to radiative recombination transitions between donor-acceptors pairs of N-Al, N-B, N-Cr and Cr-Al respectively, while a prominent violet (408 nm) wavelength was observed due to transitions from the nitrogen level to the valence band level. The red (698-738 nm) luminescence was mainly due to metastable mid-bandgap states, however under high injection current it was due to the quantum mechanical phenomenon pertaining to band broadening and overlapping. This RGB combination produced a broadband white light spectrum extending from 380 to 900 nm. The color space tri-stimulus values for 4H-SiC doped with Cr and N were X = 0.3322, Y = 0.3320 and Z = 0.3358 as per 1931 CIE (International Commission on Illumination) corresponding to a color rendering index of 96.56 and the color temperature of 5510 K. And for 6H-SiC n-type doped with Cr and Al, the color space tri-stimulus values are X = 0.3322, Y = 0.3320 and Z = 0.3358. The CCT was 5338 K, which is very close to the incandescent lamp (or black body) and lies between bright midday sun (5200 K) and average daylight (5500 K) while CRI was 98.32. Similar white LED's were also fabricated using Cr, Al, Se as one set of dopants and B, Al, N as another.
Show less - Date Issued
- 2008
- Identifier
- CFE0002362, ucf:47808
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0002362
- Title
- Do per-capita impact or abundance dominate the impact of an invader? Interactions among neighboring species in context-dependent competition.
- Creator
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Li, Haoyu, Quintana-Ascencio, Pedro, Jenkins, David, Boughton, Elizabeth, University of Central Florida
- Abstract / Description
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Evaluating relative species competitive strength is a central question in community ecology, with strong implications for invasion ecology. Models assessing invader success consider three components: distribution, abundance and per-capita impact. However, relative strength and interactions among these factors remain unclear when applying to specific invasion scenarios. We hypothesized that performance of native and non-native species will vary as a function of direct and indirect effects at...
Show moreEvaluating relative species competitive strength is a central question in community ecology, with strong implications for invasion ecology. Models assessing invader success consider three components: distribution, abundance and per-capita impact. However, relative strength and interactions among these factors remain unclear when applying to specific invasion scenarios. We hypothesized that performance of native and non-native species will vary as a function of direct and indirect effects at different abundances and scales. We conducted a replacement experiment between two dominant grasses in subtropical grasslands (the native Axonopus fissifolius and the non-native Paspalum notatum) in central Florida, USA. Thirty fenced plots (1 m x 3 m each) representing a gradient (15 levels) of increasing non-native groundcover and decreasing native groundcover were set up in November 2017. We transplanted individuals of these two species in subplots (12 subplots and 36 transplants per plot; 1080 plants in total) in a 2*2 factorial design (mixed /single focal species * 2/4 transplants per subplot). Leaf length/number and plant biomass were evaluated at the beginning and end of the experiment along with plot species composition and soil nutrients. Over 92% of transplants of each grass species survived until harvest (11 months). There were significant differences in leaf length, leaf number and plant biomass between conspecific/allospecific subplots. Both P. notatum and A. fissifolius performed better when transplanted in non-native P. notatum subplots. There were also interactions between conspecific/allospecific subplot treatment (direct effects) and the gradient of increasing Paspalum notatum /decreasing Axonopus fissifolius groundcover (indirect effects) treatments. Increasing P. notatum in the whole plot made environments more favorable for both grass species. Effects were consistent for leaf length/number and biomass of the two focal species. More comprehensive evaluation on indirect effects need to be considered when examining competition between non-native species and native species.
Show less - Date Issued
- 2019
- Identifier
- CFE0007487, ucf:52685
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007487
- Title
- Theoretical and Experimental Studies for Tailoring the Electromagnetic Surface Properties of Conductive Materials.
- Creator
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Jennings, Jeffrey, Vaidyanathan, Raj, Kar, Aravinda, Coffey, Kevin, Challapalli, Suryanarayana, Brisbois, Elizabeth, Yu, Xiaoming, University of Central Florida
- Abstract / Description
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Induction in leaded, implanted medical devices exposed to radio frequency (RF) magnetic fields during magnetic resonance imaging (MRI) produce Joule heating in adjacent tissues causing various issues, including death. Given the importance of MRI as a diagnostic tool and the growth in leaded device-related treatments, identification of a solution ensuring their compatibility is of great interest. Electromagnetic (EM) surface property tailoring in lead materials to change their inductive...
Show moreInduction in leaded, implanted medical devices exposed to radio frequency (RF) magnetic fields during magnetic resonance imaging (MRI) produce Joule heating in adjacent tissues causing various issues, including death. Given the importance of MRI as a diagnostic tool and the growth in leaded device-related treatments, identification of a solution ensuring their compatibility is of great interest. Electromagnetic (EM) surface property tailoring in lead materials to change their inductive response by adding functionally-graded, heterogeneous surface layers is a possible solution. However, non-uniform EM properties introduce two challenges: the added complexity of analyses and characterization of the graded region. This dissertation addresses these complexities.An Helmholtz coil and other loops positioned in a coaxial array were used to create and monitor inductive fields that were mathematically related to the induced current in closed, circular loops with electrical conductivities ranging from 1.0 to 57 megaSiemens per meter. Magnetic flux densities up to 14 microTesla at frequencies from 30 to 100 MHz were evaluated for specimens with varying loop and wire diameters. Induced current results show a linear relationship with flux density and strongly depend on the sample geometry, but not on conductivity. Trends within the data matched well with those predicted by theory that considered such a loop.An equivalent length, semi-analytical approach modeled induced current through a graded EM property region and considered effective conductivities. Predicted results for transmissivity through Pt-doped titanium foils and effective conductivity in round wire Sn-modified Cu samples show good agreement with experimental data. The Joule heating experiment used for wire testing also demonstrates a means for characterizing conductor surface properties. Two new technologies derived from this research including an RF magnetic field imaging technique and a contoured loop array for applying therapeutic controlled RF magnetic fields are also described.
Show less - Date Issued
- 2018
- Identifier
- CFE0007756, ucf:52378
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007756
- Title
- EFFECTS OF THERMO-MECHANICAL LOADING FROM IN-SITU STUDIES OF EB-PVD THERMAL BARRIER COATINGS.
- Creator
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Jansz, Melan, Raghavan, Seetha, University of Central Florida
- Abstract / Description
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The thermo-mechanical effects on the strain evolution within an EB-PVD thermal barrier coating (TBC) is presented in this work using in-situ characterization. Synchrotron X-ray diffraction at sector 1-ID at the Argonne National Laboratory provided both qualitative and quantitative in-situ data on the strain evolution under a thermal cycle with mechanical loading. The results show that at a critical combination of temperature and load, the stress in the thermally grown oxide (TGO) layer in the...
Show moreThe thermo-mechanical effects on the strain evolution within an EB-PVD thermal barrier coating (TBC) is presented in this work using in-situ characterization. Synchrotron X-ray diffraction at sector 1-ID at the Argonne National Laboratory provided both qualitative and quantitative in-situ data on the strain evolution under a thermal cycle with mechanical loading. The results show that at a critical combination of temperature and load, the stress in the thermally grown oxide (TGO) layer in the TBC reaches a tensile region. These significant findings enhance existing literature showing purely compressive strains within the TGO where mechanical loads have been neglected. The results have important implications on the effects on the overall life of the coating. Depth resolved quantitative strain is presented as contour plots over a thermal cycle highlighting the complementary strains in the adjacent layers including the bond coat and the TBC with time and temperature. Systematic identification of the appropriate peaks within the multi-layer TBC system provides guidelines for future strain studies using high energy X-rays. Piezospectroscopic studies with applied mechanical loading are further presented as verification of the room temperature XRD data for future development of the method as an operational technique to be used outside the laboratory environment
Show less - Date Issued
- 2011
- Identifier
- CFE0004004, ucf:49173
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004004
- Title
- AMORPHOUS PHASE FORMATION IN MECHANICALLY ALLOYED FE-BASED SYSTEMS.
- Creator
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Sharma, Satyajeet, Suryanarayana, C, University of Central Florida
- Abstract / Description
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ABSTRACT Bulk metallic glasses have interesting combination of physical, chemical, mechanical, and magnetic properties which make them attractive for a variety of applications. Consequently there has been a lot of interest in understanding the structure and properties of these materials. More varied applications can be sought if one understands the reasons for glass formation and the methods to control them. The glass-forming ability (GFA) of alloys can be substantially increased by a proper...
Show moreABSTRACT Bulk metallic glasses have interesting combination of physical, chemical, mechanical, and magnetic properties which make them attractive for a variety of applications. Consequently there has been a lot of interest in understanding the structure and properties of these materials. More varied applications can be sought if one understands the reasons for glass formation and the methods to control them. The glass-forming ability (GFA) of alloys can be substantially increased by a proper selection of alloying elements and the chemical composition of the alloy. High GFA will enable in obtaining large section thickness of amorphous alloys. Ability to produce glassy alloys in larger section thicknesses enables exploitation of these advanced materials for a variety of different applications. The technique of mechanical alloying (MA) is a powerful non-equilibrium processing technique and is known to produce glassy (or amorphous) alloys in several alloy systems. Metallic amorphous alloys have been produced by MA starting from either blended elemental metal powders or pre-alloyed powders. Subsequently, these amorphous alloy powders could be consolidated to full density in the temperature range between the glass transition and crystallization temperatures, where the amorphous phase has a very low viscosity. This Dissertation focuses on identifying the various Fe-based multicomponent alloy systems that can be amorphized using the MA technique, studying the GFA of alloys with emphasis on improving it, and also on analyzing the effect of extended milling time on the constitution of the amorphous alloy powder produced at earlier times. The Dissertation contains seven chapters, where the lead chapter deals with the background, history and introduction to bulk metallic glasses. The following four chapters are the published/to be published work, where the criterion for predicting glass formation, effect of Niobium addition on glass-forming ability (GFA), lattice contraction on amorphization, effect of Carbon addition on GFA, and observation of mechanical crystallization in Fe-based systems have been discussed. The subsequent chapter briefly mentions about the consolidation of amorphous powders and presents results of hot pressing and spark plasma sintering on one of the alloy systems. The final chapter summarizes the Dissertation and suggests some prospective research work that can be taken up in future. The Dissertation emphasizes the glass-forming ability, i.e., the ease with which amorphization can occur. In this work the milling time required for amorphization was the indicator/measure of GFA. Although the ultimate aim of this work was to consolidate the Fe-based amorphous alloy powders into bulk so as to undertake mechanical characterization, however, it was first necessary to study the glass forming aspect in the different alloy systems. By doing this a stage has been reached, where different options are available with respect to amorphous phase-forming compositions and the knowledge to improve glass-forming ability via the mechanical alloying technique. This will be ultimately useful in the powder compaction process into various shapes and sizes at optimum pressure and temperature. The study on mechanical crystallization indicates, or in a way defines, a limit to the process of amorphization, and it was also demonstrated that this phenomenon is more common in occurrence than and not as restricted as it was earlier reported to be.
Show less - Date Issued
- 2008
- Identifier
- CFE0002025, ucf:47630
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0002025
- Title
- Deconstructing Differences in Effectiveness of Reading Teachers of Ninth Grade Non-Proficient Readers in One Florida School District.
- Creator
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Wysong, Jason, Taylor, Rosemarye, Murray, Barbara, Baldwin, Gordon, Doherty, Walter, Zugelder, Bryan, University of Central Florida
- Abstract / Description
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ABSTRACT This study was undertaken to identify specific instructional and professional differences between the most effective and least effective teachers of ninth grade students enrolled in intensive reading courses in one Florida school district. Teachers from eleven schools were invited to complete a survey that included categorical, Likert, and open-ended response items. Principals and assistant principals at these schools were also invited to complete a similar survey. Teacher...
Show moreABSTRACT This study was undertaken to identify specific instructional and professional differences between the most effective and least effective teachers of ninth grade students enrolled in intensive reading courses in one Florida school district. Teachers from eleven schools were invited to complete a survey that included categorical, Likert, and open-ended response items. Principals and assistant principals at these schools were also invited to complete a similar survey. Teacher respondents were then divided into three effectiveness groups based on the percentage of their students who met 2011-2012 FCAT performance targets established by Florida's value-added learning growth model. Inferential statistics were used to identify specific attributes that differed among the most and least effective teachers. These attributes included years of classroom teaching experience, status of Florida Reading Endorsement, belief in collaboration with others as a source of effectiveness, valuation of classroom strategies including teaching students to self-monitor their progress and cooperative learning activities, and frequency of use of reading strategies including sustained silent reading and paired/partner student readings. School administrators and the most effective classroom teachers reported similar beliefs about valuation and frequency of use of the four aforementioned classroom strategies. Analysis of responses to open-ended response items resulted in the identification of three instructional themes(-)importance of building positive relationships with students, student practice, and student self-reflection(-)and three resource needs(-)increased access to technology, print resources, and professional learning.
Show less - Date Issued
- 2013
- Identifier
- CFE0004963, ucf:49571
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004963
- Title
- Land use effects on energy and water balance-developing a land use adapted drought index.
- Creator
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Cheng, Chi-Han, Nnadi, Fidelia, Chopra, Manoj, Wang, Dingbao, Sumner, David, University of Central Florida
- Abstract / Description
-
Climate change is expected to increase the frequency, intensity and duration of droughts in all parts of the United States (US). Snow packs are disappearing earlier in the spring and summer, with reduced stream-flow. Lower reservoir levels, higher temperatures, and greater precipitation variability have been observed. Drought events in the US have threatened drinking water supplies for communities in Maryland and Chesapeake Bay as observed in 2001 through September 2002; Lake Mead in Las...
Show moreClimate change is expected to increase the frequency, intensity and duration of droughts in all parts of the United States (US). Snow packs are disappearing earlier in the spring and summer, with reduced stream-flow. Lower reservoir levels, higher temperatures, and greater precipitation variability have been observed. Drought events in the US have threatened drinking water supplies for communities in Maryland and Chesapeake Bay as observed in 2001 through September 2002; Lake Mead in Las Vegas in 2000 through 2004; Peace River and Lake Okeechobee in South Florida in 2006; and Lake Lanier in Atlanta, Georgia in 2007. ENSO influences the climate of Florida; where El Ni(&)#241;o years tend to be cooler and wetter, while La Ni(&)#241;a years tend to be warmer and drier than normal in the fall through the spring, with the strongest effect in the winter. Both prolonged heavy rainfall and drought potentially have impacts on land uses and many aspects of Florida's economy and quality of life. Drought indices could integrate various hydrological and meteorological parameters and quantify climate anomalies in terms of intensity, duration, and spatial extent, thus making it easier to communicate information to diverse users. Hence, understanding local ENSO patterns on regional scales and developing a new land use drought index in Florida are critical in agriculture and water resources planning and managements. Current drought indices have limitations and drawbacks such as calculation using climate data from meteorological stations, which are point measurements. In addition, weather stations are scarce in remote areas and are not uniformly distributed. Currently used drought indices like the PDSI and the Standardized Precipitation Index (SPI) could not fully demonstrate the land use effects. Other limitations include no single index that addresses universal drought impact. Hence, there is a renewed interest to develop a new (")Regional Land Use Drought Index (RLDI) that could be applied for various land use areas and serve for short term water resources planning. In this study, the first and second research topics investigated water and energy budgets on the specific and important land use areas (urban, forest, agriculture and lake) in the State of Florida by using the North American Regional Reanalysis (NARR) reanalysis data. NARR data were used to understand how drought events, EI Ni(&)#241;o, La Ni(&)#241;a, and seasonal and inter-annual variations in climatic variables affect the hydrologic and energy cycle over different land use areas. The results showed that the NARR data could provide valuable, independent analysis of the water and energy budgets for various land uses in Florida. Finally, the high resolution land use (32km(&)#215;32km) adapted drought indices were developed based on the NARR data from 1979 to 2002. The new regional land use drought indices were developed from normalized Bowen ratio and the results showed that they could reflect not only the level of severity in drought events resulting from land use effects, but also La Ni(&)#241;a driven drought impacts.
Show less - Date Issued
- 2012
- Identifier
- CFE0004344, ucf:49410
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004344
- Title
- Deconstructing Differences in Effectiveness of Teachers of Tenth Grade Non-Proficient Readers in One Florida School District.
- Creator
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Williams, Mary, Taylor, Rosemarye, Doherty, Walter, Murray, Barbara, Baldwin, Gordon, Zugelder, Bryan, University of Central Florida
- Abstract / Description
-
Despite an intense focus and considerable financial commitment to remediate non-proficient readers in high school, the large suburban school district that was the target of this study had been unable to consistently improve student achievement in the lowest 25% of students as measured by outcomes on the FCAT Reading. Scholarly literature on high school reading had focused mostly on evaluation of curriculum rather than on teacher practices. A clear understanding of these differences in...
Show moreDespite an intense focus and considerable financial commitment to remediate non-proficient readers in high school, the large suburban school district that was the target of this study had been unable to consistently improve student achievement in the lowest 25% of students as measured by outcomes on the FCAT Reading. Scholarly literature on high school reading had focused mostly on evaluation of curriculum rather than on teacher practices. A clear understanding of these differences in practice will inform future decisions related to staffing, scheduling, and professional learning. This study sought to identify the underlying professional and instructional differences between the most effective and least effective teachers of tenth grade intensive reading courses through teacher and principal/assistant principal surveys along with teacher evaluation data. This study revealed with regards to a teacher's preparation to teach reading (research question one), that years of experience in the classroom and years of experience as a high school reading teacher were the only significant factors that influenced a teacher's effectiveness. For research questions two and three; which had to do with the beliefs and professional practices of the teacher, the educationally relevant belief that the more effective teachers were more confident about their abilities than their less effective peers was noted. Research question four provided the data with regards to the general classroom teaching strategies and the adolescent reading strategies the effective teachers employed. This data revealed that the more effective teachers implemented posting and communicating daily and long term learning goals more frequently than their less effective peers. In addition, the general classroom teaching practices of efficient use of learning time, establishing and maintaining classroom routines, and checking for understanding proved to be educationally relevant. Additionally, the adolescent reading strategies of sustained silent reading, paired/partner readings, and students reading one-on-one with teacher, were educationally relevant as well. Finally, in regards to research question five, it was of statistical significance that administrators valued the use of the general classroom teaching strategy of posting and communicating daily and long term learning goals and were able to recognize the use of this strategy when observing and evaluating the teachers.?
Show less - Date Issued
- 2013
- Identifier
- CFE0004960, ucf:49573
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004960
- Title
- THERMO-MECHANICAL CHARACTERIZATION OF HIGH-TEMPERATURE SHAPE MEMORY NI-TI-PD WIRES.
- Creator
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Fox, Matthew, Vaidyanathan, Rajan, University of Central Florida
- Abstract / Description
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Actuator applications of shape memory alloys have typically been limited by their phase transformation temperatures to around 100 degrees C. However, recently with a focus on aerospace and turbomachinery applications there have been successful efforts to increase the phase transformation temperatures. Several of these alloy development efforts have involved ternary and quaternary elemental additions (e.g., Pt, Pd, etc.) to binary NiTi alloys. Experimentally assessing the effects of varying...
Show moreActuator applications of shape memory alloys have typically been limited by their phase transformation temperatures to around 100 degrees C. However, recently with a focus on aerospace and turbomachinery applications there have been successful efforts to increase the phase transformation temperatures. Several of these alloy development efforts have involved ternary and quaternary elemental additions (e.g., Pt, Pd, etc.) to binary NiTi alloys. Experimentally assessing the effects of varying composition and thermo-mechanical processing parameters can be cost intensive, especially when expensive, high-purity elemental additions are involved. Thus, in order to save on development costs there is value in establishing a methodology that facilitates the fabrication, processing and testing of smaller specimens, rather than larger specimens from commercial billets. With the objective of establishing such a methodology, this work compares thermo-mechanical test results from bulk dog-bone tensile Ni29.5Ti50.5Pd20 samples (7.62 mm diameter) with that of thin wires (100 μm-150 µm diameter) extracted from comparable, untested bulk samples by wire electrical-discharge machining (EDM). The wires were subsequently electropolished to different cross-sections, characterized with Scanning Electron Microscopy, Transmission Electron Microscopy and Energy Dispersive X-Ray Spectroscopy to verify the removal of the heat affected zone following EDM and subjected to Laser Scanning Confocal Microscopy to accurately determine their cross-sections before thermo-mechanical testing. Stress-strain and load-bias experiments were then performed on these wires using a dynamic mechanical analyzer and compared with results established in previous studies for comparable bulk tensile specimens. On comparing the results from a bulk tensile sample with that of the micron-scale wires, the overall thermomechanical trends were accurately captured by the micron-scale wires for both the constrained recovery and monotonic tensile tests. Specifically, there was good agreement between the stress-strain response in both the martensitic and austenitic phases, the transformation strains at lower stresses in constrained recovery, and the transformation temperatures at higher stresses in constrained recovery. This work thus validated that carefully prepared micron-diameter samples can be used to obtain representative bulk thermo-mechanical properties, and is useful for fabricating and optimizing composition and thermo-mechanical processing parameters in prototype button melts prior to commercial production. This work additionally assesses potential applications of high temperature shape memory alloy actuator seals in turbomachinery. A concept for a shape memory alloy turbine labyrinth seal is also presented. Funding support from NASA's Fundamental Aeronautics Program, Supersonics Project (NNX08AB51A) and Siemens Energy is acknowledged.
Show less - Date Issued
- 2009
- Identifier
- CFE0002813, ucf:48102
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0002813
- Title
- SAFETY IMPROVEMENTS ON MULTILANE ARTERIALS A BEFORE AND AFTER EVALUATION USING THE EMPIRICAL BAYES METHOD.
- Creator
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Devarasetty, Prem Chand, Abdel-Aty, Mohamed, University of Central Florida
- Abstract / Description
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This study examines the safety effects of the improvements made on multi-lane arterials. The improvements were divided into two categories 1) corridor level improvements, and 2) intersection improvements. Empirical Bayes method, which is one of the most accepted approaches for conducting before-after evaluations, has been used to assess the safety effects of the improvement projects. Safety effects are estimated not only in terms of all crashes but also rear-end (most common type) as well as...
Show moreThis study examines the safety effects of the improvements made on multi-lane arterials. The improvements were divided into two categories 1) corridor level improvements, and 2) intersection improvements. Empirical Bayes method, which is one of the most accepted approaches for conducting before-after evaluations, has been used to assess the safety effects of the improvement projects. Safety effects are estimated not only in terms of all crashes but also rear-end (most common type) as well as severe crashes (crashes involving incapacitating and/or fatal injuries) and also angle crashes for intersection improvements. The Safety Performance Functions (SPFs) used in this study are negative binomial crash frequency estimation models that use the information on ADT, length of the segments, speed limit, and number of lanes for corridors. And for intersections the explanatory variables used are ADT, number of lanes, speed limit on major road, and number of lanes on the minor road. GENMOD procedure in SAS was used to develop the SPFs. Corridor SPFs are segregated by crash groups (all, rear-end, and severe), length of the segments being evaluated, and land use (urban, suburban and rural). The results of the analysis show that the resulting changes in safety following corridor level improvements vary widely. Although the safety effect of projects involving the same type of improvement varied, the overall effectiveness of each of the corridor level improvements were found to be positive in terms of reduction in crashes of each crash type considered (total, severe, and rear-end) except for resurfacing projects where the total number of crashes slightly increased after the roadway section is resurfaced. Evaluating additional improvements carried out with resurfacing activities showed that all (other than sidewalk improvements for total crashes) of them consistently led to improvements in safety of multilane arterial sections. It leads to the inference that it may be a good idea to take up additional improvements if it is cost effective to do them along with resurfacing. It was also found that the addition of turning lanes (left and/or right) and paving shoulders were two improvements associated with a project's relative performance in terms of reduction in rear-end crashes. No improvements were found to be associated with a resurfacing project's relative performance in terms of changes in (i.e., reducing) severe crashes. For intersection improvements also the individual results of each project varied widely. Except for adding turn lane(s) all other improvements showed a positive impact on safety in terms of reducing the number of crashes for all the crash types (total, severe, angle, and rear-end) considered. Indicating that the design guidelines for this work type have to be revisited and safety aspect has to be considered while implementing them. In all it can be concluded that FDOT is doing a good job in selecting the sites for treatment and it is very successful in improving the safety of the sections being treated although the main objective(s) of the treatments are not necessarily safety related.
Show less - Date Issued
- 2009
- Identifier
- CFE0002723, ucf:48148
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0002723
- Title
- DESIGN AND MODELING OF RADIATION HARDENED LATERAL POWER MOSFETS.
- Creator
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Landowski, Matthew, Shen, Zheng, University of Central Florida
- Abstract / Description
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Galactic-cosmic-rays (GCR) exist in space from unknown origins. A cosmic ray is a very high energy electron, proton, or heavy ion. As a GCR transverses a power semiconductor device, electron-hole-pairs (ehps) are generated along the ion track. Effects from this are referred to as single-event-effects (SEEs). A subset of a SEE is single-event burnout (SEB) which occurs when the parasitic bipolar junction transistor is triggered leading to thermal runaway. The failure mechanism is a complicated...
Show moreGalactic-cosmic-rays (GCR) exist in space from unknown origins. A cosmic ray is a very high energy electron, proton, or heavy ion. As a GCR transverses a power semiconductor device, electron-hole-pairs (ehps) are generated along the ion track. Effects from this are referred to as single-event-effects (SEEs). A subset of a SEE is single-event burnout (SEB) which occurs when the parasitic bipolar junction transistor is triggered leading to thermal runaway. The failure mechanism is a complicated mix of photo-generated current, avalanche generated current, and activation of the inherent parasitic bipolar transistor. Current space-borne power systems lack the utility and advantages of terrestrial power systems. Vertical-double-diffused MOSFETs (VDMOS) is by far the most common power semiconductor device and are very susceptible to SEEs by their vertical structure. Modern space power switches typically require system designers to de-rate the power semiconductor switching device to account for this. Consequently, the power system suffers from increased size, cost, and decreased performance. Their switching speed is limited due to their vertical structure and cannot be used for MHz frequency applications limiting the use of modern digital electronics for space missions. Thus, the Power Semiconductor Research Laboratory at the University of Central Florida in conjunction with Sandia National Laboratories is developing a rad-hard by design lateral-double-diffused MOSFET (LDMOS). The study provides a novel in-depth physical analysis of the mechanisms that cause the LDMOS to burnout during an SEE and provides guidelines for making the LDMOS rad-hard to SEB. Total dose radiation, another important radiation effect, can cause threshold voltage shifts but is beyond the scope of this study. The devices presented have been fabricated with a known total dose radiation hard CMOS process. Single-event burnout data from simulations and experiments are presented in the study to prove the viability of using the LDMOS to replace the VDMOS for space power systems. The LDMOS is capable of higher switching speeds due to a reduced drain-gate feedback capacitance (Miller Capacitor). Since the device is lateral it is compatible with complimentary-metal-oxide-semiconductor (CMOS) processes, lowering developing time and fabrication costs. High switching frequencies permit the use of high density point-of-load conversion and provide a fast dynamic response.
Show less - Date Issued
- 2009
- Identifier
- CFE0002795, ucf:48113
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0002795
- Title
- THE TYLER PERRY EFFECT: EXAMINING THE INFLUENCE OF BLACK MEDIA IMAGES ON THE BLACK IDENTITY.
- Creator
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Jackson, Nicole, Musambira, George, University of Central Florida
- Abstract / Description
-
This study investigated the influence of Tyler Perry's House of Payne and Meet the Browns on black viewers' racial identity, based on a survey of 145 members of four predominantly African American churches in the Central Florida area. Mirroring Allen, Dawson, and Brown's (1989) model of an African American racial belief system, this study proposed that both shows would positively influence three dimensions of the black identity including closeness to blacks, black separatism, and the belief...
Show moreThis study investigated the influence of Tyler Perry's House of Payne and Meet the Browns on black viewers' racial identity, based on a survey of 145 members of four predominantly African American churches in the Central Florida area. Mirroring Allen, Dawson, and Brown's (1989) model of an African American racial belief system, this study proposed that both shows would positively influence three dimensions of the black identity including closeness to blacks, black separatism, and the belief in positive stereotypes about blacks, while negatively influencing the dimension that emphasizes negative stereotypes about blacks. Socioeconomic status and religiosity were also hypothesized to predict exposure to both shows. The results show that while House of Payne positively influenced two dimensions of the black identity including closeness to blacks and the belief in positive stereotypes about blacks, Meet the Browns did not have a statistically significant relationship with any of the dimensions of the black identity. Additionally, results showed mixed support for the relationship between socioeconomic status, religiosity, and show exposure. While education had a negative relationship with exposure to both House of Payne and Meet the Browns, the income variable revealed no significant results with either show. Lastly, religiosity was shown to be a significant predictor of exposure to House of Payne, but not Meet the Browns. The findings suggest that Perry's shows may be considered by viewers as more beneficial than harmful to viewers to their racial identity and experience, which contradicts the critiques of his images as reverberating with negative stereotypical images of the past. Findings also suggest the importance of education and religion to black socialization patterns.
Show less - Date Issued
- 2011
- Identifier
- CFE0003957, ucf:48708
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003957
- Title
- TRUST ON THE WEB: THE IMPACT OF SOCIAL CONSENSUS ON INFORMATION CREDIBILITY.
- Creator
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Del Giudice, Katherine, Hancock, Peter, University of Central Florida
- Abstract / Description
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Models of the need-driven information search and the information appraisal process were formed from a comprehensive literature review of factors affecting perceived credibility and trust in online information. The social component of online credibility has not, to date, been thoroughly researched. This componentÃÂ's impact on the development of the perceived credibility of online information was examined in two experiments. In the first experiment, the impact of...
Show moreModels of the need-driven information search and the information appraisal process were formed from a comprehensive literature review of factors affecting perceived credibility and trust in online information. The social component of online credibility has not, to date, been thoroughly researched. This componentÃÂ's impact on the development of the perceived credibility of online information was examined in two experiments. In the first experiment, the impact of positive, mixed, and negative social feedback on the development of the perceived credibility of a web page was evaluated. In the second experiment, the effect of social feedback on credibility was examined under two levels of motivation for information use to investigate whether social feedback becomes less important as motivation to obtain quality information increases. The results of Experiment 1 suggest that type of feedback can influence perceived web page credibility. Pages with negative audience feedback received the lowest credibility ratings, while pages with positive audience feedback received the highest credibility ratings. Pages with mixed or no audience feedback received higher credibility ratings than pages with negative feedback, but lower credibility ratings than pages with positive feedback. In Experiment 2, high motivation did not impact the number of web page elements participants reported that they used to determine credibility. High motivation for information use also did not reduce the impact of audience feedback on perceived credibility.
Show less - Date Issued
- 2010
- Identifier
- CFE0003240, ucf:48540
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003240
- Title
- Dairy calcium advertising awareness, attitudes and behavior : a survey of 13-17 year-old females.
- Creator
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Cooper, Michele, Davis, Robert H., Arts and Sciences
- Abstract / Description
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University of Central Florida College of Arts and Sciences Thesis; In April 1984, at a conference convened by the National Institutes of Health, a panel of experts issued a statement listing calcium as a "mainstay in the prevention and management of osteoporosis." Osteoporosis, or "brittle bone disease," affects one out of every four American women over 5 0 and is the 12th leading cause of death in the United States. In January 1985, the National Dairy Promotion and Research Board began...
Show moreUniversity of Central Florida College of Arts and Sciences Thesis; In April 1984, at a conference convened by the National Institutes of Health, a panel of experts issued a statement listing calcium as a "mainstay in the prevention and management of osteoporosis." Osteoporosis, or "brittle bone disease," affects one out of every four American women over 5 0 and is the 12th leading cause of death in the United States. In January 1985, the National Dairy Promotion and Research Board began emphasizing dietary calcium in the promotion of milk and dairy products. Television commercials and print advertising were developed which focused on the calcium contained in dairy products and stressed the importance of this nutrient to a woman's diet. Recent consumer research conducted by Market Facts, Inc. of Chicago indicates that this positive calcium message designed to increase dairy product intake may not be effectively reaching the 13-24 year old female. The study shows that subjects in this age group report that they are doing less about their calcium deficiencies than subjects who were studied prior to the time that the dietary calcium advertising began. In addition, the research indicates that those women who are taking steps to increase calcium intake are less likely to use dairy products. Teenage females offer the dairy industry a challenging opportunity. While average male milk consumption jumps dramatically during the ages of 13-19, average female milk consumption experiences only a slight increase. Reaching this audience at this habit-forming age end changing their attitudes and behavior could provide lifelong use of dairy products. The purpose of this study is to determine the efficacy of past dairy calcium advertising messages in affecting the health attitudes and dietary behavior of 13-17 year old women in Florida.
Show less - Date Issued
- 1987
- Identifier
- CFR0004326, ucf:52991
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFR0004326
- Title
- Nanoelectronic Devices using Carbon Nanotubes and Graphene Electrodes: Fabrication and Electronic Transport Investigations.
- Creator
-
Kang, Narae, Khondaker, Saiful, Leuenberger, Michael, Zhai, Lei, University of Central Florida
- Abstract / Description
-
Fabrication of high-performance electronic devices using the novel semiconductors is essential for developing future electronics which can be applicable in large-area, flexible and transparent displays, sensors and solar cells. One of the major bottlenecks in the fabrication of high-performance devices is a large interfacial barrier formation at metal/semiconductor interface originated from Schottky barrier and interfacial dipole barrier which causes inefficient charge injection at the...
Show moreFabrication of high-performance electronic devices using the novel semiconductors is essential for developing future electronics which can be applicable in large-area, flexible and transparent displays, sensors and solar cells. One of the major bottlenecks in the fabrication of high-performance devices is a large interfacial barrier formation at metal/semiconductor interface originated from Schottky barrier and interfacial dipole barrier which causes inefficient charge injection at the interface. Therefore, having a favorable contact at electrode/semiconductor is highly desirable for high-performance devices fabrication.In this dissertation, the fabrication of nanoelectronic devices and investigation of their transport properties using carbon nanotubes (CNTs) and graphene as electrode materials will be shown. I investigated two types of devices using (i) semiconducting CNTs, and (ii) organic semiconductors (OSC). In the first part of this thesis, I will demonstrate the fabrication of high-performance solution-processed highly enriched (99%) semiconducting CNT thin film transistors (s-CNT TFTs) using densely aligned arrays of metallic CNTs (m-CNTs) for source/drain electrodes. From the electronic transport measurements at room temperature, significant improvements of field-effect mobility, on-conductance, transconductance and current on/off ratio for m-CNT/s-CNT devices were found compared to control palladium (Pd contacted s-CNT devices. From the temperature dependent transport investigation, a lower Schottky barrier height for the m-CNT/s-CNT devices was found compared to the devices with control metal electrodes. The enhanced device performance can be attributed to the unique device geometry as well as strong ?- ? interaction at m-CNT/s-CNT interfaces. In addition, I also investigated s-CNT TFTs using reduced graphene oxide (RGO) electrodes.In the second part of my thesis, I will demonstrate high-performance organic field-effect transistors (OFETs) using different types of graphene electrodes. I show that the performance of OFETs with pentacene as OSC and RGO as electrode can be continuously improved by increasing the carbon sp2 fraction of RGO. The carbon sp2 fractions of RGO were varied by controlling the reduction time. When compared to control Pd electrodes, the mobility of the OFETs shows an improvement of ?200% for 61% sp2 fraction RGO, which further improves to ?500% for 80% RGO electrode. Similarly, I show that when the chemical vapor deposition (CVD) graphene film is used as electrodes in fabricating OFET, the better performance is observed in comparison to RGO electrodes. Our study suggests that, in addition to ?-? interaction at graphene/pentacene interface, the tunable electronic properties of graphene as electrode have a significant role in OFETs performance. For a fundamental understanding of the interface, we fabricated short-channel OFETs with sub-100nm channel length using graphene electrode. From the low temperature electronic transport measurements, a lower charge injection barrier was found compared to control metal electrode. The detailed investigations reported in this thesis clearly indicated that the use of CNT and graphene as electrodes can improve the performance of future nanoelectronic devices.
Show less - Date Issued
- 2015
- Identifier
- CFE0006039, ucf:50982
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006039
- Title
- Parallel fabrication and transport properties of carbon nanotube single electron transistors.
- Creator
-
Islam, Muhammad, Khondaker, Saiful, Chow, Lee, Stolbov, Sergey, Zhai, Lei, University of Central Florida
- Abstract / Description
-
Single electron transistors (SET) have attracted significant attention as a potential building block for post CMOS nanoelectronic devices. However, lack of reproducible and parallel fabrication approach and room temperature operation are the two major bottlenecks for practical realization of SET based devices. In this thesis, I demonstrate large scale single electron transistors fabrication techniques using solution processed single wall carbon nanotubes (SWNTs) and studied their electron...
Show moreSingle electron transistors (SET) have attracted significant attention as a potential building block for post CMOS nanoelectronic devices. However, lack of reproducible and parallel fabrication approach and room temperature operation are the two major bottlenecks for practical realization of SET based devices. In this thesis, I demonstrate large scale single electron transistors fabrication techniques using solution processed single wall carbon nanotubes (SWNTs) and studied their electron transport properties. The approach is based on the assembly of individual SWNTs via dielectrophoresis (DEP) at the selected position of the circuit and formation of tunnel barriers on SWNT. Two different techniques: i) metal-SWNT Schottky contact, and ii) mechanical templating of SWNTs were used for tunnel barrier creation.Low temperature (4.2K) transport measurement of 100 nm long metal-SWNT Schottky contact devices show that 93% of the devices with contact resistance (RT) (>) 100 K? show SET behavior. Majority (90%) of the devices with 100 K? (<) RT (<) 1 M?, show periodic, well-de?ned Coulomb diamonds with a charging energy ~ 15 meV, represents single electron tunnelling through a single quantum dot (QD), defined by the top contact. For high RT ((>) 1M?), devices show multiple QDs behaviors, while QD was not formed for low RT ((<) 100 K?) devices. From the transport study of 50 SWNT devices, a total of 38 devices show SET behavior giving an yield of 76%. I also demonstrate room temperature operating SET by using mechanical template technique. In mechanical template method individual SWNT is placed on top of a Al/Al2O3 local gate which bends the SWNT at the edge and tunnel barriers are created. SET devices fabricated with a template width of ~20 nm shows room temperature operation with a charging energy of ~150 meV. I also discussed the detailed transport spectroscopy of the devices.
Show less - Date Issued
- 2015
- Identifier
- CFE0006037, ucf:50987
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006037
- Title
- A Priori Analysis of Error and Bias in Value-Added Models.
- Creator
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Lavery, Matthew, Hahs-Vaughn, Debbie, Sivo, Stephen, Bai, Haiyan, Amrein-Beardsley, Audrey, University of Central Florida
- Abstract / Description
-
Over the past 20 years, value-added models (VAMs) have become increasingly popular in educational assessment and accountability policies because of the sophisticated statistical controls these models use to purportedly isolate the effect of a single teacher on the learning gains of his or her students. The present research uses a Monte Carlo simulation study design in order to investigate whether VAMs are able to provide accurate estimates of teacher effectiveness when all assumptions are met...
Show moreOver the past 20 years, value-added models (VAMs) have become increasingly popular in educational assessment and accountability policies because of the sophisticated statistical controls these models use to purportedly isolate the effect of a single teacher on the learning gains of his or her students. The present research uses a Monte Carlo simulation study design in order to investigate whether VAMs are able to provide accurate estimates of teacher effectiveness when all assumptions are met and to determine how robust the models are to endogenous peer effects and nonrandom assignment of students to classroom. The researcher generates three years of simulated achievement data for 18,750 students taught by 125 teachers, and analyzes this data with a linear mixed model similar to the SAS(&)#174; EVAAS(&)#174; Multivariate Response Model (MRM; M1), a basic covariate adjustment model (M2), and variations on these models designed to estimate random classroom effects. Findings indicate that the modified EVAAS may be too computationally onerous to be of practical use, and that modified covariate adjustment models do not perform significantly differently than the basic covariate adjustment model. When all assumptions are met, M1 is more accurate than M2, but both models perform reasonably well, misclassifying fewer than 5% of teachers on average. M1 is more robust to endogenous peer effects than M2, however both models misclassified more teachers than when all assumptions are met. M2 is more robust to nonrandom assignment of students than M1. Assigning teachers a balanced schedule of nonrandom classes with low, medium, and high prior achievement seemed to mitigate the problems that nonrandom assignment caused for M1, but made M2 less accurate. Implications for practice and future research are discussed.
Show less - Date Issued
- 2016
- Identifier
- CFE0006344, ucf:51568
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006344
- Title
- POLYURETHANE FIBER REINFORCED POLYMER STRENGTHENING OF SHEAR DEFICIENT REINFORCED CONCRETE BEAMS.
- Creator
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Al-Lebban, Yasir, Mackie, Kevin, Chopra, Manoj, Makris, Nicos, Gou, Jihua, University of Central Florida
- Abstract / Description
-
The use of externally-bonded fiber-reinforced polymer (FRP) composites has been established as an effective means for the strengthening of shear-deficient reinforced concrete (RC) flexural members. Epoxy-based wet layup systems were predominantly employed in previous studies. In this study, carbon FRP pre-impregnated with polyurethane resin is utilized in strengthening shear-deficient RC beams and compared to an epoxy resin. Fourteen small-scale (96 in span, 6 in width, and 12 in height) and...
Show moreThe use of externally-bonded fiber-reinforced polymer (FRP) composites has been established as an effective means for the strengthening of shear-deficient reinforced concrete (RC) flexural members. Epoxy-based wet layup systems were predominantly employed in previous studies. In this study, carbon FRP pre-impregnated with polyurethane resin is utilized in strengthening shear-deficient RC beams and compared to an epoxy resin. Fourteen small-scale (96 in span, 6 in width, and 12 in height) and five large-scale (132 in span, 12 in width, and 17 in height) flexural specimens were tested, considering FRP system type (polyurethane versus epoxy), size effect, shear span-to-depth ratio, FRP configuration (U-wraps versus side bonding), and FRP scheme (sheets versus strips with 45o or 90o). Experimental strength testing under four-point loading demonstrated similar or enhanced shear capacity when strengthening by the polyurethane compared to the epoxy composite systems.The shear behavior of polyurethane-based FRP composite system is investigated in this research using analytical and numerical approaches. A closed-form mechanics-based analytical model, utilizing the principle of effective FRP stress and upper-bound theorem, illustrated that the shear behavior and debonding mechanism were dependent on both FRP composite and bond characteristics. The analytical model is expressed in terms of shear crack opening crossed by the FRP laminate and gives good agreement with experimental results. The finite element analysis (FEA) model shows that the stresses in the FRP are not in single direction as in the coupon tests, and the biaxial stress states should be taken into consideration.The structural behavior of RC members strengthened with externally-bonded FRP composites is mobilized through the composite action technique. Bond stress can be defined as the shear stress acting in the interface between FRP and concrete. It is of crucial importance to evaluate the failure mode behavior. Debonding (loss of adhesion) failure is one of the most common modes of failure encountered in shear strengthening RC members in practice. Numerous constitutive bond-slip models have been proposed and derived numerically and mathematically based on experimental data with an assumption that the FRP width bp is taken as a variable and all stresses or strains at the same longitudinal coordinate (L direction) are uniform. No attention has been given to study the bond states of stress which are mainly altered by the inclined shear cracks in concrete. A new bond-slip law was proposed to address the biaxial two-dimensional (2D) states of stress problem. Numerical solution by finite difference (FD) was conducted to solve four partial differential equations per node (2 for FRP and 2 for concrete in each direction) with appropriate boundary conditions to obtain the stresses, slips, and strains based on the proposed bond-slip model. A new experimental setup was proposed to represent the 2D bond-slip model by lap shear tests in both directions by laminating two perpendicular strips on concrete blocks with the proposed strain profile. Experimental calibration has been carried out by using nonlinear least-squares regression (fitting) of the experimental strain data with the numerical FD equations to obtain the bond-slip parameters for the 2D FRP-to-concrete polyurethane interface system.
Show less - Date Issued
- 2017
- Identifier
- CFE0006852, ucf:51737
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006852
- Title
- Scientific transformations: a philosophical and historical analysis of cosmology from Copernicus to Newton.
- Creator
-
Castillo, Manuel-Albert, Jones, Donald, Dandrow, Edward, Garbayo, Luciana, University of Central Florida
- Abstract / Description
-
The purpose of this thesis is to show a transformation around the scientific revolution from the sixteenth to seventeenth centuries against a Whig approach in which it still lingers in the history of science. I find the transformations of modern science through the cosmological models of Nicholas Copernicus, Johannes Kepler, Galileo Galilei and Isaac Newton. Since of the enormous content, I shall only pay particular attention to Copernicus and Newton in which the emerging sciences transformed...
Show moreThe purpose of this thesis is to show a transformation around the scientific revolution from the sixteenth to seventeenth centuries against a Whig approach in which it still lingers in the history of science. I find the transformations of modern science through the cosmological models of Nicholas Copernicus, Johannes Kepler, Galileo Galilei and Isaac Newton. Since of the enormous content, I shall only pay particular attention to Copernicus and Newton in which the emerging sciences transformed the cosmos on what Alexandre Koyr(&)#233; calls from a (")closed world to infinite universe(").As an interdisciplinary approach, I used the methods and inquiries from philosophy and history to explain the cosmological transformation in the sciences. The first part deals on the philosophic content of Michel Foucault and Thomas Kuhn which help to provide insight though their systematic thoughts are incompatible. The second part deals in the historic contents from Copernicus' doctrine, De revolutionibus, to Newton's mechanics, Principia. My ultimate outcome is to demonstrate the multi-perspective dimension of knowledge in which interdisciplinary studies shows transformation of the sciences and its effects on history
Show less - Date Issued
- 2017
- Identifier
- CFE0006862, ucf:51738
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006862
- Title
- Analysis of Driving Behavior at Expressway Toll Plazas using Driving Simulator.
- Creator
-
Saad, Moatz, Abdel-Aty, Mohamed, Eluru, Naveen, Lee, JaeYoung, University of Central Florida
- Abstract / Description
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The objective of this study is to analyze the driving behavior at toll plazas by examining multiple scenarios using a driving simulator to study the effect of different options including different path decisions, various signs, arrow markings, traffic conditions, and extending auxiliary lanes before and after the toll plaza on the driving behavior. Also, this study focuses on investigating the effect of drivers' characteristics on the dangerous driving behavior (e.g. speed variation, sudden...
Show moreThe objective of this study is to analyze the driving behavior at toll plazas by examining multiple scenarios using a driving simulator to study the effect of different options including different path decisions, various signs, arrow markings, traffic conditions, and extending auxiliary lanes before and after the toll plaza on the driving behavior. Also, this study focuses on investigating the effect of drivers' characteristics on the dangerous driving behavior (e.g. speed variation, sudden lane change, drivers' confusion). Safety and efficiency are the fundamental goals that transportation engineering is always seeking for the design of highways. Transportation agencies have a crucial challenging task to accomplish traffic safety, particularly at the locations that have been identified as crash hotspots. In fact, toll plaza locations are one of the most critical and challenging areas that expressway agencies have to pay attention to because of the increasing traffic crashes over the past years near toll plazas.Drivers are required to make many decisions at expressway toll plazas which result in drivers' confusion, speed variation, and abrupt lane change maneuvers. These crucial decisions are mainly influenced by three reasons. First, the limited distance between toll plazas and the merging areas at the on-ramps before the toll plazas. In additional to the limited distance between toll plazas and the diverging areas after the toll plazas at the off-ramps. Second, it is also affected by the location and the configuration of signage and pavement markings. Third, drivers' decisions are affected by the different lane configurations and tolling systems that can cause drivers' confusion and stress. Nevertheless, limited studies have explored the factors that influence driving behavior and safety at toll plazas. There are three main systems of the toll plaza, the traditional mainline toll plaza (TMTP), the hybrid mainline toll plaza (HMTP), and the all-electronic toll collection (AETC). Recently, in order to improve the safety and the efficiency of the toll plazas, most of the traditional mainline toll plazas have been converted to the hybrid toll plazas or the all-electronic toll collection plazas. This study assessed driving behavior at a section, including a toll plaza on one of the main expressways in Central Florida. The toll plaza is located between a close on-ramp and a nearby off-ramp. Thus, these close distances have a significant effect on increasing driver's confusion and unexpected lane change before and after the toll plaza. Driving simulator experiments were used to study the driving behavior at, before and after the toll plaza. The details of the section and the plaza were accurately replicated in the simulator. In the driving simulator experiment, Seventy-two drivers with different age groups were participated. Subsequently, each driver performed three separate scenarios out of a total of twenty-four scenarios. Seven risk indicators were extracted from the driving simulator experiment data by using MATLAB software. These variables are average speed, standard deviation of speed, standard deviation of lane deviation, acceleration rate, standard deviation of acceleration (acceleration noise), deceleration rate, and standard deviation of deceleration (braking action variation). Moreover, various scenario variables were tested in the driving simulator including different paths, signage, pavement markings, traffic condition, and extending auxiliary lanes before and after the toll plaza. Divers' individual characteristics were collected from a questionnaire before the experiment. Also, drivers were filling a questionnaire after each scenario to check for simulator sickness or discomfort. Nine variables were extracted from the simulation questionnaire for representing individual characteristics including, age, gender, education level, annual income, crash experience, professional drivers, ETC-tag use, driving frequency, and novice international drivers. A series of mixed linear models with random effects to account for multiple observations from the same participant were developed to reveal the contributing factors that affect driving behavior at toll plazas. The results uncovered that all drivers who drove through the open road tolling (ORT) showed higher speed and lower speed variation, lane deviation, and acceleration noise than other drivers who navigate through the tollbooth. Also, the results revealed that providing adequate signage, and pavement markings are effective in reducing risky driving behavior at toll plazas. Drivers tend to drive with less lane deviation and acceleration noise before the toll plaza when installing arrow pavement markings. Adding dynamic message sign (DMS) at the on-ramp has a significant effect on reducing speed variation before the toll plaza. Likewise, removing the third overhead sign before the toll plaza has a considerable influence on reducing aggressive driving behavior before and after the toll plaza. This result may reflect drivers' desire to feel less confusion by excessive signs and markings. Third, extending auxiliary lanes with 660 feet (0.125 miles) before or after the toll plaza have an effect on increasing the average speed and reducing the lane deviation and the speed variation at and before the toll plaza. It also has an impact on increasing the acceleration noise and the braking action variation after the toll plaza. Finally, it was found that in congested conditions, participants drive with a lower speed variation and lane deviation before the toll plaza but with a higher acceleration noise after the toll plaza. On the other hand, understanding drivers' characteristics is particularly important for exploring their effect on risky driving behavior. Young drivers (18-25) and old drivers (older than 50 years) consistently showed a higher risk behavior than middle age drivers (35 to 50). Also, it was found that male drivers are riskier than female drivers at toll plazas. Drivers with high education level, drivers with high income, ETC-tag users, and drivers whose driving frequency is less than three trips per day are more cautious and tend to drive at a lower speed.
Show less - Date Issued
- 2016
- Identifier
- CFE0006492, ucf:51391
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006492