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- Title
- Characterization of Turbulent Flame-Vortex Dynamics for Bluff Body Stabilized Flames.
- Creator
-
Rising, Cal, Ahmed, Kareem, Ghosh, Ranajay, Bhattacharya, Samik, University of Central Florida
- Abstract / Description
-
Modern propulsion systems primarily operate under highly turbulent conditions in order to promote greater efficiency through an increase in mixing. The focus of this thesis is to identify the turbulent flame-vortex interaction to provide insights into the turbulent combustion process. This work is accomplished through the use of turbulent ramjet-style combustor which is stabilized through use of a bluff-body. The facility is equipped with a custom turbulence generator to modulate the incoming...
Show moreModern propulsion systems primarily operate under highly turbulent conditions in order to promote greater efficiency through an increase in mixing. The focus of this thesis is to identify the turbulent flame-vortex interaction to provide insights into the turbulent combustion process. This work is accomplished through the use of turbulent ramjet-style combustor which is stabilized through use of a bluff-body. The facility is equipped with a custom turbulence generator to modulate the incoming turbulence levels to allow flames across various regimes to be analyzed. High-speed particle image velocimetry (PIV) and CH* chemiluminescence diagnostics are implemented to resolve the flow field and flame position. The flame-vortex interaction can be described by the vorticity transport which has four terms; vortex stretching, baroclinic torque, dilatation, and viscous diffusion. The vorticity mechanisms are calculated through the implementation of a Lagrangian tracking scheme, which allows for the individual mechanisms to be decomposed along the path of individual tracks. The mechanisms are compared across different turbulence levels to determine the effects of turbulence on the vorticity mechanisms. The mechanisms are calculated along the flame front as well to determine the individual effects of the vorticity mechanisms on the evolving structure of the turbulent premixed flame. The flame front curvature is also compared across the various turbulence conditions. The results confirm that as the flame-front experiences increased turbulence levels the combustion induced mechanisms of baroclinic torque and dilation decrease, while vortex stretching increases. This is a result of the turbulent energy exchange becoming the controlling factor within the flow-field. In addition, increased flame curvature is experience by the flame front due to increased local baroclinicity and turbulent energy exchange.
Show less - Date Issued
- 2019
- Identifier
- CFE0007714, ucf:52451
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007714
- Title
- Implications of groundwater plume transport and analysis of karst aquifer characteristics in central Florida.
- Creator
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Sandhu, Daljit, Singh, Arvind, Wang, Dingbao, Nam, Boo Hyun, Zheng, Qipeng, University of Central Florida
- Abstract / Description
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Groundwater aquifers make up the primary source of drinking water in Florida. It is imperative to protect and maintain water quality to ensure optimal drinking water conditions. Florida is known for being prone to sinkholes due to karst features. One sinkhole event occurred beneath a phosphogypsum stack, and leaked a large amount of radioactive waste in the Floridan aquifer, raising water quality concerns. To study the behavior of contaminant transport, the radioactive waste plume was modeled...
Show moreGroundwater aquifers make up the primary source of drinking water in Florida. It is imperative to protect and maintain water quality to ensure optimal drinking water conditions. Florida is known for being prone to sinkholes due to karst features. One sinkhole event occurred beneath a phosphogypsum stack, and leaked a large amount of radioactive waste in the Floridan aquifer, raising water quality concerns. To study the behavior of contaminant transport, the radioactive waste plume was modeled by coupling hydraulic and chemistry concepts. Adsorption was studied to see if it can serve as a potential remediation solution to the contaminant waste, using available adsorption knowledge and data from previous studies. Results suggest that simulating mineral adsorption helped limit how far the waste stack would travel in the aquifer, however it would still pose risk in water quality, as drinking water wells are situated along the path of the contaminant plume. Implementation of treatment wells and monitoring would ensure drinking water criteria are met.Acknowledging that the Floridan aquifer contains karst features that consist of limestone fractures and the rock matrix, groundwater flow patterns may be influenced over time. For instance, fractures (or conduits) can conduct larger amounts of groundwater at higher conductivities, which could have implications on groundwater/contaminant transport. To model this process, a karst evolution model utilizing hydraulic and chemistry concepts are applied in a basin in Florida. Results indicate the karst model reproduces head profiles and estimates the age of several conduits. A sensitivity analysis was conducted to investigate how karst evolution is influenced by hydraulic and chemistry parameters. Results show that fracture length has more influence on karst evolution, however other physical parameters show some influence as well.A karst conduit network was simulated for the Silver Springs springshed, based on obtained potentiometric head data. Implementing information on aquifer chemistry and fracture geometry resulted in a unique realization of a karst network. During this process, flow rates change direction, inducing backflow, which can have implications on groundwater resources. Overall, an improved understanding of karst processes can aid in better characterizing conduit flow patterns and improve water resources management.
Show less - Date Issued
- 2019
- Identifier
- CFE0007723, ucf:52427
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007723
- Title
- Electronic and Optoelectronic Transport Properties of Carbon Nanotube/Organic Semiconductor Devices.
- Creator
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Sarker, Biddut, Khondaker, Saiful, Schulte, Alfons, Stolbov, Sergey, Gesquiere, Andre, University of Central Florida
- Abstract / Description
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Organic field effect transistors (OFETs) are of significant research interest due to their promising applications in large area, low-cost electronic devices such as flexible displays, sensor arrays, and radio-frequency identification tags. A major bottleneck in fabricating high-performance OFET is the large interfacial barrier between the metal electrodes and organic semiconductors (OSC) which results in an inefficient charge injection. Carbon nanotubes (CNTs) are considered to be a promising...
Show moreOrganic field effect transistors (OFETs) are of significant research interest due to their promising applications in large area, low-cost electronic devices such as flexible displays, sensor arrays, and radio-frequency identification tags. A major bottleneck in fabricating high-performance OFET is the large interfacial barrier between the metal electrodes and organic semiconductors (OSC) which results in an inefficient charge injection. Carbon nanotubes (CNTs) are considered to be a promising electrode material which can address this challenge.In this dissertation, we demonstrate fabrication of high-performance OFETs using aligned array CNT electrodes and investigate the detailed electronic transport properties of the fabricated devices. The OFETs with CNT electrodes show a remarkable enhancement in the device performance such as high mobility, high current on-off ratio, higher cutoff frequency, absence of short channel effect and better charge carrier injection than those OFETs with metal electrodes. From the low temperature transport measurements, we show that the charge injection barrier at CNT/OSC interface is smaller than that of the metal/OSC interface. A transition from direct tunneling to Fowler-Nordheim tunneling observed in CNT/OSC system shows further evidence of low injection barrier. A lower activation energy measured for the OFETs with CNT electrodes gives evidence of lower interfacial trap states. Finally, OFETs are demonstrated by directly growing crystalline organic nanowires on aligned array CNT electrodes.In addition to investigating the interfacial barrier at CNT/OSC interface, we also studied photoconduction mechanism of the CNT and CNT/OSC nanocomposite thin film devices. We found that the photoconduction is due to the exciton dissociations and charge carrier separation caused by a Schottky barrier at the metallic electrode/CNT interface and diffusion of the charge carrier through percolating CNT networks. In addition, it is found that photoresponse of the CNT/organic semiconductor can be tuned by changing the weight percentage of CNT into the organic semiconductors.
Show less - Date Issued
- 2012
- Identifier
- CFE0004596, ucf:49217
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004596
- Title
- A STUDY OF THE IMPACT OF INVOLVEMENT AND SEQUENCE IN NARRATIVE PERSUASION.
- Creator
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Lane, Rebekah, Miller, Ann, University of Central Florida
- Abstract / Description
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The purpose of this research was to look more closely at the relationships between narrative and non-narrative persuasive messages, and to begin to determine how and why these message formats might work together. I situated this study within Rogers' roadmap for future theoretical work on entertainment education (E-E), and specifically addressed Slater and Rouner's call for more research on the impact of epilogues in E-E. Synthesizing components of the elaboration likelihood model with recent...
Show moreThe purpose of this research was to look more closely at the relationships between narrative and non-narrative persuasive messages, and to begin to determine how and why these message formats might work together. I situated this study within Rogers' roadmap for future theoretical work on entertainment education (E-E), and specifically addressed Slater and Rouner's call for more research on the impact of epilogues in E-E. Synthesizing components of the elaboration likelihood model with recent theorizing regarding persuasion through narrative, I made predictions regarding the effect of transportation and character identification on perceived salience, attitudes, behavioral intention, and behavior in narrative, argument, and narrative + argument conditions. Undergraduate students were asked to watch one of seven videos. After watching the videos participants were asked to respond to questions reflecting their views of the subject matter in the videos, their experience while watching the videos, and their opinion of the video quality. The questionnaire included scales measuring transportation into the narrative and character development, measures of perceived issue relevance, and persuasion toward the topic of mandatory H1N1 vaccinations. Findings showed no relationship between the narrative format and transportation or perceived salience, however, transportation did predict perceived salience in messages combining both argument and narrative + argument formats. Recommendations were made for modification and future applications of the instruments used in the study and for continued research in the various stages of persuasion through narrative, argumentative, and combined format messaging.
Show less - Date Issued
- 2011
- Identifier
- CFE0004044, ucf:49149
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004044
- Title
- MOBILITY AND SAFETY EVALUATION OF INTEGRATED DYNAMIC MERGE AND SPEED CONTROL STRATEGIES IN WORK ZONES.
- Creator
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Zaidi, Syed, Radwan, Essam, University of Central Florida
- Abstract / Description
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There has been a considerable increase in the amount of construction work on the U.S. national highways. Due to the capacity drop, which is the result of lane closure in work zone area, congestion occurs with a high traffic demand. The congestion increases number and severity of traffic conflicts which raise the potential for accidents; furthermore traffic operational properties of roadway in work zone area become worse. Intelligent Transportation System technologies have been developed and...
Show moreThere has been a considerable increase in the amount of construction work on the U.S. national highways. Due to the capacity drop, which is the result of lane closure in work zone area, congestion occurs with a high traffic demand. The congestion increases number and severity of traffic conflicts which raise the potential for accidents; furthermore traffic operational properties of roadway in work zone area become worse. Intelligent Transportation System technologies have been developed and are being deployed to improve the safety and mobility of traffic in and around work zones. The use of Dynamic Merge Controls (dynamic early merge and dynamic late merge) have been initiated to enhance traffic safety and to smooth traffic operations in work zone areas. The use of variable speed limit (VSL) systems at work zones is also one of those measures. VSL systems improve safety by helping the driver in determining the maximum speed that drivers should travel. Besides adding improvement to safety, they are also expected to improve mobility at the work zones. The main goal of this study was to evaluate the safety and operational effectiveness of the dynamic merge systems in the presence of VSL controls. VISSIM model is utilized to simulate a two-to-one lane configuration when one out of the two lanes in the work zone is closed for traffic. Two scenarios each for early and late simplified dynamic lane merge system (SDLMS) with and without VSLs, whereas one scenario each for the current Motorist Awareness System (MAS) and VSL alone were adopted to assess the effectiveness of these scenarios under different traffic demand volumes and different driversÂÂÂÂ' compliance rates to the messages displayed by the systems. Mean throughputs and travel time were operational measures of effectiveness whereas speed variance and deceleration means were taken as safety surrogate measures. Three different logics were coded each for VSL alone, early SDLMS+VSL and late SDLMS+VSL in calibrated and validated VISSIM model for SDLMS through Vehicle Actuated Programming (VAP) code. It is found that for low and medium volume levels (V0500, V1000 and V1500), there is no significant difference between the Maintenance of Traffic (MOT) plans for mean throughputs. For higher volume levels (V2000 and V2500), late SDLMS with and without VSL produced significantly higher mean throughputs for all compliance rates and truck percentages. This study revealed that VSL increases travel time through the work zone. It is also found out that VSL makes the system safer at higher volumes (2,000 vph and 2,500 vph). Another outcome of this study is that the addition of VSL to the dynamic merge systems helps in improving the overall safety of the system by lowering speed variances and deceleration means of the vehicles travelling through the work zone. The passage of traffic through the work zone is made safer when a speed control is integrated to a dynamic merge system.
Show less - Date Issued
- 2010
- Identifier
- CFE0003519, ucf:48974
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003519
- Title
- DEVELOPMENT OF A WEIGH-IN-MOTION SYSTEM USING ACOUSTIC EMISSION SENSORS.
- Creator
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Bowie, Jeanne, Radwan, Essam, University of Central Florida
- Abstract / Description
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This dissertation proposes a system for weighing commercial vehicles in motion using acoustic emission sensors attached to a metal bar placed across the roadway. The signal from the sensors is analyzed by a computer and the vehicle weight is determined by a statistical model which correlates the acoustic emission parameters to the vehicle weight. Such a system would be portable and low-cost, allowing for the measurement of vehicle weights in much the same way commercial tube and radar...
Show moreThis dissertation proposes a system for weighing commercial vehicles in motion using acoustic emission sensors attached to a metal bar placed across the roadway. The signal from the sensors is analyzed by a computer and the vehicle weight is determined by a statistical model which correlates the acoustic emission parameters to the vehicle weight. Such a system would be portable and low-cost, allowing for the measurement of vehicle weights in much the same way commercial tube and radar counters routinely collect vehicle speed and count. The system could be used to collect vehicle speed and count data as well as weight information. Acoustic emissions are naturally occurring elastic waves produced by the rapid release of energy within a material. They are caused by deformation or fracturing of a solid due to thermal or mechanical stress. Acoustic emission sensors have been developed to detect these waves and computer software and hardware have been developed to analyze and provide information about the waveforms. Acoustic emission testing is a common form of nondestructive testing and is used for pressure vessel testing, leak detection, machinery monitoring, structural integrity monitoring, and weld monitoring, among other things (Miller, 1987). For this dissertation, acoustic emission parameters were correlated to the load placed on the metal test bar to determine the feasibility of using a metal test bar to measure the weight of a vehicle in motion. Several experiments were done. First, the concept was tested in a laboratory setting using an experimental apparatus. A concrete cylinder was mounted on a frame and rotated using a motor. The metal test bar was applied directly to the surface of the cylinder and acoustic emission sensors were attached to each end of the bar. As the cylinder rotated, a motorcycle tire was pushed up against the cylinder using a scissor jack to simulate different loads. The acoustic emission response in the metal test strip to the motorcycle tire rolling over it was detected by the acoustic emission sensors and analyzed by the computer. Initial examinations of the data showed a correlation between the force of the tire against the cylinder and the energy and count of the acoustic emissions. Subsequent field experiments were performed at a weigh station on I-95 in Flagler County, Florida. The proposed weigh-in-motion system (the metal test bar with attached acoustic emission sensors) was installed just downstream of the existing weigh-in-motion scale at the weigh station. Commercial vehicles were weighed on the weigh station weigh-in-motion scale and acoustic emission data was collected by the experimental system. Test data was collected over several hours on two different days, one in July 2008 and the other in April 2009. Initial examination of the data did not show direct correlation between any acoustic emission parameter and vehicle weight. As a result, a more sophisticated model was developed. Dimensional analysis was used to examine possible relationships between the acoustic emission parameters and the vehicle weight. In dimensional analysis, a dimensionally correct equation is formed using measurable parameters of a system. The dimensionally correct equation can then be tested using experimental data. Dimensional analysis revealed the possible relationships between the acoustic emission parameters and the vehicle weight. Statistical models for weight using the laboratory data and using the field data were developed. Dimensional analysis variables as well as other relevant measurable parameters were used in the development of the statistical models. The model created for the April 2009 dataset was validated, with only 27 lbs average error in the weight calculation as compared with the weight measurement made with the weigh station weigh-in-motion scale. The maximum percent error for the weight calculation was 204%, with about 65% of the data falling within 30% error. Additional research will be needed to develop an acoustic emission weigh-in-motion system with adequate accuracy for a commercial product. Nevertheless, this dissertation presents a valuable contribution to the effort of developing a low-cost acoustic emission weigh-in-motion scale. Future research needs that were identified as part of this dissertation include: Examination of the effects of pavement type (flexible or rigid), vehicle speeds greater than 50 mph, and temperature Determination of the best acoustic emission sensor for this system Exploration of the best method to separate the data from axles which pass over the equipment close together in time (such as tandem axles) Exploration of the effect of repeated measures on improving the accuracy of the system.
Show less - Date Issued
- 2011
- Identifier
- CFE0003581, ucf:48903
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003581
- Title
- CHARACTERIZATION OF MOTILITY ALTERATIONS CAUSED BY THE IMPAIRMENT OF DYNEIN/DYNACTIN MOTOR PROTEIN COMPLEX.
- Creator
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Nandini, Swaran, King, Stephen, Kim, Yoon-Seong, Estevez, Alvaro, University of Central Florida
- Abstract / Description
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Transport of intracellular cargo is an important and dynamic process required for cell maintenance and survival. Dynein is the motor protein that carries organelles and vesicles from the cell periphery to the cell center along the microtubule network. Dynactin is a protein that activates dynein for this transport process. Together, dynein and dynactin forms a motor protein complex that is essential for transport processes in all the vertebrate cells. Using fluorescent microscope based live...
Show moreTransport of intracellular cargo is an important and dynamic process required for cell maintenance and survival. Dynein is the motor protein that carries organelles and vesicles from the cell periphery to the cell center along the microtubule network. Dynactin is a protein that activates dynein for this transport process. Together, dynein and dynactin forms a motor protein complex that is essential for transport processes in all the vertebrate cells. Using fluorescent microscope based live cell imaging techniques and kymograph analyses, I studied dynein/dynactin disruptions on the intracellular transport in two different cell systems. In one set of experiments, effects of dynein heavy chain (DHC) mutations on the vesicular motility were characterized in the fungus model system Neurospora crassa. I found that many DHC mutations had a severe transport defect, while one mutation linked to neurodegeneration in mice had a subtle effect on intracellular transport of vesicles. In a different set of experiments in mammalian tissue culture CAD cells, I studied the effects of dynactin knockdown and dynein inhibition on mitochondrial motility. My results indicated that reductions in dynactin levels decrease the average number of mitochondrial movements and surprisingly, increase the mitochondrial run lengths. Also, I determined that the dynein inhibitory drug Ciliobrevin causes changes in mitochondrial morphology and decreases the number of mitochondrial movements inside cells. Overall, my research shows that distinct disruptions in the dynein and dynactin motor complex alters intracellular motility, but in different ways. So far, my studies have set the ground work for future experiments to analyze the motility mechanism of motor proteins having mutations that lead to neurodegenerative disorders.
Show less - Date Issued
- 2013
- Identifier
- CFE0004897, ucf:49664
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004897
- Title
- Financial evaluation of milege based user fees for Florida's transportation funding.
- Creator
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Moradi, Massoud, Al-Deek, Haitham, Radwan, Ahmed, Abdel-Aty, Mohamed, Uddin, Nizam, University of Central Florida
- Abstract / Description
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ABSTRACTMotor fuel taxes have been collected as a principal source of highway funding for close to a century. They account for approximately two thirds of all the highway user fees and about half of all highway expenditures. Federal fuel taxes have not kept pace with the inflation in general and increasing traffic demand and resulting construction, maintenance and operation costs of the transportation assets in particular.Lack of political will, combined with rising anti-tax sentiment among...
Show moreABSTRACTMotor fuel taxes have been collected as a principal source of highway funding for close to a century. They account for approximately two thirds of all the highway user fees and about half of all highway expenditures. Federal fuel taxes have not kept pace with the inflation in general and increasing traffic demand and resulting construction, maintenance and operation costs of the transportation assets in particular.Lack of political will, combined with rising anti-tax sentiment among the populace, has kept the federal tax level not only well below its initial intents, but also at a unsustainable level in future.Mileage based user fees are possibly an alternative to the fuel taxes, which have been the main mechanism for funding the transportation system.Mileage based user fees have been successfully utilized in many parts of the world with glowing results. Germany's (")TollCollect("), a quasi government enterprise has utilized GPS technology in collecting the users' fee from the truck operators. The system has been a financial engine providing much needed funding for many major transportation projects. Oregon Department of Transportation, in a federally co-funded pilot project, examined the practicality of the mileage based user fee collection at the fuel pumps. According to the Oregon study, there are not any major technical difficulties in mileage based user fee collection at the pump. Study participants (general motorist) did not express any objection to the mileage based user fee collection.This dissertation evaluates revenue impacts of several pricing policies including: Current per gallon fuel taxes, conversion to a mileage based user fee, time of day user fee application, area type user fee and congestion priced user fees. State of Florida's years 2015-2035 fuel revenue forecast is used as a case study. A model is constructed to estimate annual vehicle miles travelled for the analyses period. Fuel efficiencies, current per gallon fuel taxes and their corresponding mileage-based user fee equivalents are the input to a financial model developed for comparisons. Results demonstrate that decrease in fuel revenues due to vehicles fuel efficiency improvements can be offset by replacing current per gallon fuel taxes with a mileage-based user fee. Pricing the user fee according to area type, roadway classification, time of day and congestion level can not only generate more revenues but also assist in demand management.
Show less - Date Issued
- 2012
- Identifier
- CFE0004416, ucf:49378
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004416
- Title
- CONTROLLED ASSEMBLY AND ELECTRONIC TRANSPORT STUDIES OF SOLUTION PROCESSED CARBON NANOTUBE DEVICES.
- Creator
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Stokes, Paul, Khondaker, Saiful I., University of Central Florida
- Abstract / Description
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Developing techniques for the parallel fabrication of Complementary Metal Oxide Semiconductor (CMOS) compatible single walled carbon nanotube (SWNT) electronic devices is of great importance for nanoelectronic applications. In this thesis, solution processed SWNTs in combination with AC dielectrophoresis (DEP) were utilized to fabricate CMOS compatible SWNT field effect transistors (FETs) and single electron transistors (SETs) with high yield and their detailed electronic transport properties...
Show moreDeveloping techniques for the parallel fabrication of Complementary Metal Oxide Semiconductor (CMOS) compatible single walled carbon nanotube (SWNT) electronic devices is of great importance for nanoelectronic applications. In this thesis, solution processed SWNTs in combination with AC dielectrophoresis (DEP) were utilized to fabricate CMOS compatible SWNT field effect transistors (FETs) and single electron transistors (SETs) with high yield and their detailed electronic transport properties were studied. Solution processing of SWNTs is attractive not only for the high throughput and parallel manufacturing of SWNT devices but also due to the ease of processing at room temperature, and compatibility with various substrates. However, it is generally believed that solution processing introduces defects and can degrade electronic transport properties. The results presented in this dissertation show that devices assembled from stable solutions of SWNT can give rise to high quality FET devices at room temperature and relatively clean SET behavior at low temperature. This is a strong indication that there are no or few intrinsic defects in the SWNTs. The dissertation will also discuss the controlled fabrication of size tunable SWNT SET devices using a novel mechanical template approach which offers a route towards the parallel fabrication of room temperature SET devices. The approach is based on the formation of two tunnel barriers created in a SWNT a distance L apart by bending the SWNT at the edge of a local Al/Al2O3 bottom gate. The local gate tunes individual electrons one by one in the device and defines the size of the quantum dot though its width. By tuning both the back gate and local gate, it is possible to tune the transparency of tunnel barriers and the size of the quantum dot further. Detailed transport spectroscopy of these devices will be presented.
Show less - Date Issued
- 2010
- Identifier
- CFE0003061, ucf:48310
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003061
- Title
- SINGLE-ELECTRON TRANSPORT SPECTROSCOPY STUDIES OF MAGNETIC MOLECULES AND NANOPARTICLES.
- Creator
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Haque, Md. Firoze, del Barco, Enrique, University of Central Florida
- Abstract / Description
-
Magnetic nanoparticles and molecules, in particular ferromagnetic noble metal nanoparticles, molecular magnet and single-molecule magnets (SMM), are perfect examples to investigate the role of quantum mechanics at the nanoscale. For example, SMMs are known to reverse their magnetization by quantum tunneling in the absence of thermal excitation and show a number of fundamental quantum mechanical manifestations, such as quantum interference effects. On the other hand, noble metal nanoparticles...
Show moreMagnetic nanoparticles and molecules, in particular ferromagnetic noble metal nanoparticles, molecular magnet and single-molecule magnets (SMM), are perfect examples to investigate the role of quantum mechanics at the nanoscale. For example, SMMs are known to reverse their magnetization by quantum tunneling in the absence of thermal excitation and show a number of fundamental quantum mechanical manifestations, such as quantum interference effects. On the other hand, noble metal nanoparticles are found to behave ferromagnetically for diameters below a few nanometers. Some of these manifestations are still intriguing, and novel research approaches are necessary to advance towards a more complete understanding of these exciting nanoscale systems. In particular, the ability to study an isolated individual nanoscale system (i.e just one molecule or nanoparticle) is both challenging technologically and fundamentally essential. It is expected that accessing to the energy landscape of an isolated molecule/nanoparticle will allow unprecedented knowledge of the basic properties that are usually masked by collective phenomena when the systems are found in large ensembles or in their crystal form. Several approaches to this problem are currently under development by a number of research groups. For instance, some groups are developing deposition techniques to create patterned thin films of isolated magnetic nanoparticles and molecular magnets by means of optical lithography, low-energy laser ablation, or pulsed-laser evaporation or specific chemical functionalization of metallic surfaces with special molecular ligands. However, it is still a challenge to access the properties of an individual molecule or nanoparticle within a film or substrate. I have studied molecular nanomagnets and ferromagnetic noble metal nanoparticles by means of a novel experimental approach that mixes the chemical functionalization of nano-systems with the use of single-electron transistors (SETs). I have observed the Coulomb-blockade single-electron transport response through magnetic gold nanoparticles and single-molecule magnet. In particular, Coulomb-blockade response of a Mn4-based SET device recorded at 240 mK revealed the appearance of two diamonds (two charge states) with a clear switch between one and the other is indicative of a conformational switching of the molecule between two different states. The excitations inside the diamonds move with magnetic field. The curvature of the excitations and the fact of having them not going down to zero energy for zero magnetic field, indicated the presence of magnetic anisotropy (zero-field splitting) in the molecule. In addition, the high magnetic field slope of the excitations indicates that transitions between charge states differ by a net spin value equal to 9 (dS = 9), as expected from the behavior of Mn4 molecules in their crystalline form. Anticrossings between different excitations are indicative of quantum superpositions of the molecular states, which are observed for the first time in transport measurements through and individual SMM.
Show less - Date Issued
- 2011
- Identifier
- CFE0003718, ucf:48776
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003718
- Title
- Econometric Modeling Analysis of Public Transit Ridership: Application for Orlando Region.
- Creator
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Rahman, Moshiur, Eluru, Naveen, Abdel-Aty, Mohamed, Yasmin, Shamsunnahar, Uddin, Nizam, University of Central Florida
- Abstract / Description
-
Policy makers are considering several alternatives to counter the negative externalities of personal vehicle dependence. Towards this end, public transit investments are critical in growing urban regions such as Orlando, Florida. Transit system managers and planners mostly rely on statistical models to identify the factors that affect ridership as well as quantifying the magnitude of the impact on the society. These models provide vital feedback to agencies on the benefits of public transit...
Show morePolicy makers are considering several alternatives to counter the negative externalities of personal vehicle dependence. Towards this end, public transit investments are critical in growing urban regions such as Orlando, Florida. Transit system managers and planners mostly rely on statistical models to identify the factors that affect ridership as well as quantifying the magnitude of the impact on the society. These models provide vital feedback to agencies on the benefits of public transit investments which in turn act as lessons to improve the investment process. We contribute to public transit literature by addressing several methodological challenges for transit ridership modeling. Frist, we examine the impact of new transit investments (such as an addition of commuter rail to an urban region) on existing transit infrastructure (such as the traditional bus service already present in the urban region). The process of evaluating the impact of new investments on existing public transit requires a comprehensive analysis of the before and after measures of public transit usage in the region. Second, we accommodate for the presence of common unobserved factors associated with spatial factors by developing a spatial panel model using stop level public transit boarding and alighting data. Third, we contribute to literature on transit ridership by considering daily boarding and alighting data from a recently launched commuter rail system (SunRail). The model system developed will allow us to predict ridership for existing stations in the future as well as potential ridership for future expansion sites. Fourth, we accommodate for potential endogeneity between bus headway and ridership by proposing a simultaneous model system of headway and ridership. Finally, a cost benefit analysis exercise is conducted for examining the impact of Sunrail on the region.
Show less - Date Issued
- 2018
- Identifier
- CFE0007583, ucf:52577
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007583
- Title
- Analysis of Driver Behavior Modeling in Connected Vehicle Safety Systems Through High Fidelity Simulation.
- Creator
-
Jamialahmadi, Ahmad, Pourmohammadi Fallah, Yaser, Rahnavard, Nazanin, Chatterjee, Mainak, University of Central Florida
- Abstract / Description
-
A critical aspect of connected vehicle safety analysis is understanding the impact of human behavior on the overall performance of the safety system. Given the variation in human driving behavior and the expectancy for high levels of performance, it is crucial for these systems to be flexible to various driving characteristics. However, design, testing, and evaluation of these active safety systems remain a challenging task, exacerbated by the lack of behavioral data and practical test...
Show moreA critical aspect of connected vehicle safety analysis is understanding the impact of human behavior on the overall performance of the safety system. Given the variation in human driving behavior and the expectancy for high levels of performance, it is crucial for these systems to be flexible to various driving characteristics. However, design, testing, and evaluation of these active safety systems remain a challenging task, exacerbated by the lack of behavioral data and practical test platforms. Additionally, the need for the operation of these systems in critical and dangerous situations makes the burden of their evaluation very costly and time-consuming. As an alternative option, researchers attempt to use simulation platforms to study and evaluate their algorithms. In this work, we introduce a high fidelity simulation platform, designed for a hybrid transportation system involving both human-driven and automated vehicles. We decompose the human driving task and offer a modular approach in simulating a large-scale traffic scenario, making it feasible for extensive studying of automated and active safety systems. Furthermore, we propose a human-interpretable driver model represented as a closed-loop feedback controller. For this model, we analyze a large driving dataset to extract expressive parameters that would best describe different driving characteristics. Finally, we recreate a similarly dense traffic scenario within our simulator and conduct a thorough analysis of different human-specific and system-specific factors and study their effect on the performance and safety of the traffic network.
Show less - Date Issued
- 2018
- Identifier
- CFE0007573, ucf:52578
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007573
- 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
- A Macro-Level Sustainability Assessment Framework for Optimal Distribution of Alternative Passenger Vehicles.
- Creator
-
Onat, Nuri, Tatari, Omer, Nam, Boo Hyun, Oloufa, Amr, Pazour, Jennifer, University of Central Florida
- Abstract / Description
-
Although there are many studies focusing on the environmental impacts of alternative vehicle options, social and economic dimensions and trade-off relationships among all of these impacts were not investigated sufficiently. Moreover, most economic analyses are limited to life cycle cost analyses and do not consider macro-level economic impacts. Therefore, this thesis aims to advance the Life Cycle Sustainability Assessment literature and electric vehicle sustainability research by presenting...
Show moreAlthough there are many studies focusing on the environmental impacts of alternative vehicle options, social and economic dimensions and trade-off relationships among all of these impacts were not investigated sufficiently. Moreover, most economic analyses are limited to life cycle cost analyses and do not consider macro-level economic impacts. Therefore, this thesis aims to advance the Life Cycle Sustainability Assessment literature and electric vehicle sustainability research by presenting a novel combined application of Multi Criteria Decision Making techniques with Life Cycle Sustainability Assessment for decision analysis. With this motivation in mind, this research will construct a compromise-programming model (multi-objective optimization method) in order to calculate the optimum vehicle distribution in the U.S. passenger car fleet while considering the trade-offs between environmental, economic, and social dimensions of the sustainability. The findings of this research provide important insights for policy makers when developing strategies to estimate optimum vehicle distribution strategies based on various environmental and socio-economic priorities. For instance, compromise programming results can present practical policy conclusions for different states which might have different priorities for environmental impact mitigation and socio-economic development. Therefore, the conceptual framework presented in this work can be applicable for different regions in U.S. and decision makers can generate balanced policy conclusions and recommendations based on their environmental, economic and social constraints. The compromise programming results provide vital guidance for policy makers when optimizing the use of alternative vehicle technologies based on different environmental and socio-economic priorities. This research also effort aims to increase awareness of the inherent benefits of Input-Output based a Life Cycle Sustainability Assessment and multi-criteria optimization.
Show less - Date Issued
- 2015
- Identifier
- CFE0005858, ucf:50901
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005858
- Title
- Differential Expression Of Proteins Involved In VLDL Trafficking Causes Reduced VLDL Secretion In Male Ames Dwarf Mice.
- Creator
-
Ahmed Moinuddin, Faisal, Siddiqi, Shadab, Masternak, Michal, Naser, Saleh, University of Central Florida
- Abstract / Description
-
Cardiovascular diseases (CVDs) have been recorded as the number one cause of death worldwide, accounting for 32% of total deaths annually. More than two-thirds of all CVD cases are associated with atherosclerosis, which is the accumulation of fats and other substances causing plaque formation in the interior walls of major arteries. This leads to narrowing of the lumen and hardening of the arteries, ultimately resulting in angina, heart attack and/or stroke. Studies have shown that the...
Show moreCardiovascular diseases (CVDs) have been recorded as the number one cause of death worldwide, accounting for 32% of total deaths annually. More than two-thirds of all CVD cases are associated with atherosclerosis, which is the accumulation of fats and other substances causing plaque formation in the interior walls of major arteries. This leads to narrowing of the lumen and hardening of the arteries, ultimately resulting in angina, heart attack and/or stroke. Studies have shown that the pathogenesis of atherosclerosis and associated CVDs is strongly linked to elevated secretion of liver-specific lipoproteins called very-low-density-lipoprotein (VLDL). VLDLs are crucial lipoproteins responsible for transportation of triacylglycerides (TAGs), chemically inert particles that are physiologically significant for their energy storing capacity, from the liver to peripheral tissues. These VLDL particles are synthesized in the lumen of the endoplasmic reticulum (ER) of hepatocytes, transported from the ER to the cis-Golgi in special transport vesicles called VLDL-transport-vesicles (VTVs) and secreted into plasma through a highly regulated secretory pathway. Previous studies from our laboratory have shown that VTV-mediated ER-to-Golgi VLDL trafficking is the rate-limiting step in overall VLDL secretion from hepatocytes into plasma. In this project, we investigated intracellular VLDL trafficking and VLDL secretion in Ames dwarf (Prop1df, df/df) mice, a mutant mouse model homozygous for a recessive mutation at Prop1 gene locus (Prop1df) having deficiency of growth hormone (GH), thyroid stimulating hormone (TSH) and prolactin (PRL). This model is characteristic of prolonged longevity (~50% longer) and improved insulin sensitivity in comparison to their wild-type (N) counterparts. Ames dwarf (df/df) mice have recently been shown to have highly reduced plasma TAG levels, associating them with reduced susceptibility to atherosclerosis and associated CVDs. The underlying mechanism responsible for reduced VLDL secretion in Ames dwarf mice is yet to be characterized. We hypothesize that VTV-mediated trafficking of VLDL is reduced in Ames dwarf mice because of reduced expression of proteins regulating VLDL and VTV formation. To test our hypothesis, we first performed VTV-budding assay using cellular fractions isolated separately from Ames dwarf (df/df) and wild-type (N) mice livers. Our results show a significant (45%) reduction in VTV-budding process in Ames dwarf (df/df) mice compared to wild-type (N). Next we performed 2-dimensional differential gel electrophoresis (2-DIGE) on VTV and whole cell lysate (WCL) samples in order to examine the differences in protein expression and to have highly specific protein separation. ExPASy database was used to analyze protein spots that allowed us in identifying proteins specifically expressed in each of the mouse groups. Employing western blotting, samples (ER, cytosol, VTV and WCL) from both sets of mice were tested for expression levels of VLDL and VTV associated proteins (ApoB100, Sec22b, CideB, MTP, Apo-A1 and Apo-AIV) with ?-actin as the loading control. Significant differences in expression level of these proteins were observed which strongly suggest that the formation of VTV from ER in male Ames dwarf (df/df) mice is reduced compared to wild-type (N). Overall, we conclude that the differential expression of proteins required for VLDL transport causes reduced VLDL secretion in male Ames dwarf (df/df) mice.
Show less - Date Issued
- 2015
- Identifier
- CFE0005916, ucf:50829
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005916
- Title
- Modeling and Solving Large-scale Stochastic Mixed-Integer Problems in Transportation and Power Systems.
- Creator
-
Huang, Zhouchun, Zheng, Qipeng, Xanthopoulos, Petros, Pazour, Jennifer, Chang, Ni-bin, University of Central Florida
- Abstract / Description
-
In this dissertation, various optimization problems from the area of transportation and power systems will be respectively investigated and the uncertainty will be considered in each problem. Specifically, a long-term problem of electricity infrastructure investment is studied to address the planning for capacity expansion in electrical power systems with the integration of short-term operations. The future investment costs and real-time customer demands cannot be perfectly forecasted and...
Show moreIn this dissertation, various optimization problems from the area of transportation and power systems will be respectively investigated and the uncertainty will be considered in each problem. Specifically, a long-term problem of electricity infrastructure investment is studied to address the planning for capacity expansion in electrical power systems with the integration of short-term operations. The future investment costs and real-time customer demands cannot be perfectly forecasted and thus are considered to be random. Another maintenance scheduling problem is studied for power systems, particularly for natural gas fueled power plants, taking into account gas contracting and the opportunity of purchasing and selling gas in the spot market as well as the maintenance scheduling considering the uncertainty of electricity and gas prices in the spot market. In addition, different vehicle routing problems are researched seeking the route for each vehicle so that the total traveling cost is minimized subject to the constraints and uncertain parameters in corresponding transportation systems.The investigation of each problem in this dissertation mainly consists of two parts, i.e., the formulation of its mathematical model and the development of solution algorithm for solving the model. The stochastic programming is applied as the framework to model each problem and address the uncertainty, while the approach of dealing with the randomness varies in terms of the relationships between the uncertain elements and objective functions or constraints. All the problems will be modeled as stochastic mixed-integer programs, and the huge numbers of involved decision variables and constraints make each problem large-scale and very difficult to manage. In this dissertation, efficient algorithms are developed for these problems in the context of advanced methodologies of optimization and operations research, such as branch and cut, benders decomposition, column generation and Lagrangian method. Computational experiments are implemented for each problem and the results will be present and discussed. The research carried out in this dissertation would be beneficial to both researchers and practitioners seeking to model and solve similar optimization problems in transportation and power systems when uncertainty is involved.
Show less - Date Issued
- 2016
- Identifier
- CFE0006328, ucf:51559
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006328
- Title
- A New Multidimensional Psycho-Physical Framework for Modeling Car-Following in a Freeway Work Zone.
- Creator
-
Lochrane, Taylor, Al-Deek, Haitham, Radwan, Essam, Oloufa, Amr, Harb, Rami, Uddin, Nizam, University of Central Florida
- Abstract / Description
-
As the United States continues to build and repair the ageing highway infrastructure, the bearing of freeway work zones will continue to impact the capacity. To predict the capacity of a freeway work zone, there are several tools available for engineers to evaluate these work zones but only microsimulation has the ability to simulate the driver behavior. One of the limitations of current car-following models is that they only account for one overall behavioral condition. This dissertation...
Show moreAs the United States continues to build and repair the ageing highway infrastructure, the bearing of freeway work zones will continue to impact the capacity. To predict the capacity of a freeway work zone, there are several tools available for engineers to evaluate these work zones but only microsimulation has the ability to simulate the driver behavior. One of the limitations of current car-following models is that they only account for one overall behavioral condition. This dissertation hypothesizes that drivers change their driving behavior as they drive through a freeway work zone compared to normal freeway conditions which has the potential to impact traffic operations and capacity of work zones. Psycho-physical car-following models are widely used in practice for simulating car-following. However, current simulation models may not fully capture car-following driver behavior specific to freeway work zones. This dissertation presents a new multidimensional psycho-physical framework for modeling car-following based on statistical evaluation of work zone and non-work zone driver behavior. This new framework is close in character to the Wiedemann model used in popular traffic simulation software such as VISSIM. This dissertation used two methodologies for collecting data: (1) a questionnaire to collect demographics and work zone behavior data and (2) a real-time vehicle data from a field experiment involving human participants. It is hypothesized that the parameters needed to calibrate the multidimensional framework for work zone driver behavior can be derived statistically by using data collected from runs of an Instrumented Research Vehicle (IRV) in a Living Laboratory (LL) along a roadway. The design of this LL included the development of an Instrumented Research Vehicle (IRV) to capture the natural car-following response of a driver when entering and passing through a freeway work zone. The development of a Connected Mobile Traffic Sensing (CMTS) system, which included state-of-the-art ITS technologies, supports the LL environment by providing the connectivity, interoperability and data processing of the natural, real-life setting. The IRV and CMTS system are tools designed to support the concept of a LL which facilitates the experimental environment to capture and calibrate natural driver behavior. The objective is to have these participants drive the instrumented vehicle and collect the relative distance and the relative velocity between the instrumented vehicle and the vehicle in the front of the instrumented vehicle. A Phase I pilot test was conducted with 10 participants to evaluate the experiment and make any adjustments prior to the full Phase II driver test. The Phase II driver test recruited a group of 64 participants to drive the IRV through an LL set up along a work zone on I-95 near Washington D.C. in order to validate this hypothesis In this dissertation, a new framework was applied and it demonstrated that there are four different categories of car-following behavior models each with different parameter distributions. The four categories are divided by traffic condition (congested vs. uncongested) and by roadway condition (work zone vs. non-work zone). The calibrated threshold values are presented for each of these four categories. By applying this new multidimensional framework, modeling of car-following behavior can enhance vehicle behavior in microsimulation modeling.This dissertation also explored driver behavior through combining vehicle data and survey techniques to augment the model calibrations to improve the understanding of car-following behavior in freeway work zones. The results identify a set of survey questions that can potentially guide the selection of parameters for car-fallowing models. The findings presented in this dissertation can be used to improve the performance of driver behavior models specific to work zones. This in return will more acutely forecast the impact a work zone design has on capacity during congestion.
Show less - Date Issued
- 2014
- Identifier
- CFE0005521, ucf:50326
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005521
- Title
- Genetic and biochemical characterization of the roles of two putative purine transporters in the infectious cycle of Borrelia burgdorferi.
- Creator
-
Jain, Sunny, Jewett, Mollie, Naser, Saleh, Self, William, Vonkalm, Laurence, University of Central Florida
- Abstract / Description
-
Lyme disease, the most common tick borne disease in United States, is caused by the bacterial pathogen Borrelia burgdorferi. In nature, B. burgdorferi exists in an enzootic infectious cycle between an arthropod vector and mammalian hosts. Identification and characterization of the genes essential for B. burgdorferi survival throughout its infectious cycle is an important step toward understanding the molecular mechanisms involved in B. burgdorferi pathogenesis. B. burgdorferi contains a small...
Show moreLyme disease, the most common tick borne disease in United States, is caused by the bacterial pathogen Borrelia burgdorferi. In nature, B. burgdorferi exists in an enzootic infectious cycle between an arthropod vector and mammalian hosts. Identification and characterization of the genes essential for B. burgdorferi survival throughout its infectious cycle is an important step toward understanding the molecular mechanisms involved in B. burgdorferi pathogenesis. B. burgdorferi contains a small genome, which lacks the genes encoding for the enzymes required for de novo synthesis of amino acids, fatty acids and nucleic acid precursors. Therefore, the spirochete is dependent upon the host environment for the uptake of these essential nutrients. Purines are required for the synthesis of nucleotides for the biosynthesis of DNA and RNA. Due to the lack of de novo purine synthesis, the ability of B. burgdorferi to salvage purines from its host environments is essential to its survival. While the enzymes critical for the B. burgdorferi purine salvage pathway are known, the transporters involved in the uptake of purines from the host environments are not. The work in this thesis is focused on identification of the genes encoding purine permeases in B. burgdorferi and genetic and biochemical characterization of their functions in the infectious cycle of B. burgdorferi. Here, we demonstrate that homologous genes bbb22 and bbb23 present on circular plasmid 26 encode for purine permeases, which are important for transport of hypoxanthine, adenine and guanine. Furthermore, genes bbb22-23 together were essential for B. burgdorferi infection in mice. BBB22 and BBB23 share 78% amino acid identify. And although, individually both BBB22 and BBB23 were found to be capable of purine transport, BBB22 has higher affinity for hypoxanthine and adenine compared to BBB23. Moreover, the bbb22 gene alone was sufficient to restore mouse infectivity to spirochetes lacking both bbb22 and bbb23, whereas, bbb23 was not. Nonetheless, the spirochete loads in the tissues of mice infected with B. burgdorferi carrying bbb22 alone were significantly reduced compared to B. burgdorferi carrying both bbb22 and bbb23, demonstrating the importance of the two genes together for the spirochetes to achieve wild type levels of infection. In ticks, genes bbb22 and bbb23 were dispensable for spirochete survival but contributed to spirochete replication in fed larvae. The replication of spirochetes lacking bbb22-23 in larval ticks was restored to wild type levels by the reintroduction of the low affinity purine transporter encoded by bbb23 alone. Overall, we have identified a purine transport system in B. burgdorferi, which is essential for spirochete survival in the mammalian host and contributes to spirochete replication in the tick vector. As B. burgdorferi lacks typical virulence factors and toxins, these studies highlight the critical role of physiological functions in the virulence of this pathogen. Moreover, the BBB22-23 in vivo essential transport system may represent a novel therapeutic target to deliver antimicrobial drugs to treat Lyme disease.
Show less - Date Issued
- 2014
- Identifier
- CFE0005511, ucf:50303
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005511
- Title
- The Phenomenological Experience of Narrative Transportation.
- Creator
-
Buchanan, William, Fiore, Stephen, Weger, Harry, Miller, Ann, University of Central Florida
- Abstract / Description
-
Previous research has attempted to identify consequences of mental transportation into narrative worlds. While scales have been developed and validated to measure readers' levels of transportation, the objective quantification has left researchers at a descriptive disadvantage for the full range of qualitative responses to this phenomenon. This study presents a qualitative method of inquiry designed to get at the experience of narrative transportation as it is lived: the phenomenological...
Show morePrevious research has attempted to identify consequences of mental transportation into narrative worlds. While scales have been developed and validated to measure readers' levels of transportation, the objective quantification has left researchers at a descriptive disadvantage for the full range of qualitative responses to this phenomenon. This study presents a qualitative method of inquiry designed to get at the experience of narrative transportation as it is lived: the phenomenological interview. Interview transcripts were inductively analyzed for common themes that indicate intersubjective features of narrative experience. Four main themes were identified, which were composed of 22 base-level experiences reported by participants. These findings corroborated the extant literature and provided a nuanced understanding of the phenomenon as it is lived.
Show less - Date Issued
- 2013
- Identifier
- CFE0004657, ucf:49883
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004657
- Title
- Real-time traffic safety evaluation models and their application for variable speed limits.
- Creator
-
Yu, Rongjie, Abdel-Aty, Mohamed, Radwan, Ahmed, Madani Larijani, Kaveh, Ahmed, Mohamed, Wang, Xuesong, University of Central Florida
- Abstract / Description
-
Traffic safety has become the first concern in the transportation area. Crashes have cause extensive human and economic losses. With the objective of reducing crash occurrence and alleviating crash injury severity, major efforts have been dedicated to reveal the hazardous factors that affect crash occurrence at both the aggregate (targeting crash frequency per segment, intersection, etc.,) and disaggregate levels (analyzing each crash event). The aggregate traffic safety studies, mainly...
Show moreTraffic safety has become the first concern in the transportation area. Crashes have cause extensive human and economic losses. With the objective of reducing crash occurrence and alleviating crash injury severity, major efforts have been dedicated to reveal the hazardous factors that affect crash occurrence at both the aggregate (targeting crash frequency per segment, intersection, etc.,) and disaggregate levels (analyzing each crash event). The aggregate traffic safety studies, mainly developing safety performance functions (SPFs), are being conducted for the purpose of unveiling crash contributing factors for the interest locations. Results of the aggregate traffic safety studies can be used to identify crash hot spots, calculate crash modification factors (CMF), and improve geometric characteristics. Aggregate analyses mainly focus on discovering the hazardous factors that are related to the frequency of total crashes, of specific crash type, or of each crash severity level. While disaggregate studies benefit from the reliable surveillance systems which provide detailed real-time traffic and weather data. This information could help in capturing microlevel influences of the hazardous factors which might lead to a crash. The disaggregate traffic safety models, also called real-time crash risk evaluation models, can be used in monitoring crash hazardousness with the real-time field data fed in. One potential use of real-time crash risk evaluation models is to develop Variable Speed Limits (VSL) as a part of a freeway management system. Models have been developed to predict crash occurrence to proactively improve traffic safety and prevent crash occurrence.In this study, first, aggregate safety performance functions were estimated to unveil the different risk factors affecting crash occurrence for a mountainous freeway section. Then disaggregate real-time crash risk evaluation models have been developed for the total crashes with both the machine learning and hierarchical Bayesian models. Considering the need for analyzing both aggregate and disaggregate aspects of traffic safety, systematic multi-level traffic safety studies have been conducted for single- and multi-vehicle crashes, and weekday and weekend crashes. Finally, the feasibility of utilizing a VSL system to improve traffic safety on freeways has been investigated. This research was conducted based on data obtained from a 15-mile mountainous freeway section on I-70 in Colorado. The data contain historical crash data, roadway geometric characteristics, real-time weather data, and real-time traffic data. Real-time weather data were recorded by 6 weather stations installed along the freeway section, while the real-time traffic data were obtained from the Remote Traffic Microwave Sensor (RTMS) radars and Automatic Vechicle Identification (AVI) systems. Different datasets have been formulated from various data sources, and prepared for the multi-level traffic safety studies. In the aggregate traffic safety investigation, safety performance functions were developed to identify crash occurrence hazardous factors. For the first time real-time weather and traffic data were used in SPFs. Ordinary Poisson model and random effects Poisson models with Bayesian inference approach were employed to reveal the effects of weather and traffic related variables on crash occurrence. Two scenarios were considered: one seasonal based case and one crash type based case. Deviance Information Criterion (DIC) was utilized as the comparison criterion; and the correlated random effects Poisson models outperform the others. Results indicate that weather condition variables, especially precipitation, play a key role in the safety performance functions. Moreover, in order to compare with the correlated random effects Poisson model, Multivariate Poisson model and Multivariate Poisson-lognormal model have been estimated. Conclusions indicate that, instead of assuming identical random effects for the homogenous segments, considering the correlation effects between two count variables would result in better model fit. Results from the aggregate analyses shed light on the policy implication to reduce crash frequencies. For the studied roadway segment, crash occurrence in the snow season have clear trends associated with adverse weather situations (bad visibility and large amount of precipitation); weather warning systems can be employed to improve road safety during the snow season. Furthermore, different traffic management strategies should be developed according to the distinct seasonal influence factors. In particular, sites with steep slopes need more attention from the traffic management center and operators especially during snow seasons to control the excess crash occurrence. Moreover, distinct strategy of freeway management should be designed to address the differences between single- and multi-vehicle crash characteristics.In addition to developing safety performance functions with various modeling techniques, this study also investigates four different approaches of developing informative priors for the independent variables. Bayesian inference framework provides a complete and coherent way to balance the empirical data and prior expectations; merits of these informative priors have been tested along with two types of Bayesian hierarchical models (Poisson-gamma and Poisson-lognormal models). Deviance Information Criterion, R-square values, and coefficients of variance for the estimations were utilized as evaluation measures to select the best model(s). Comparisons across the models indicate that the Poisson-gamma model is superior with a better model fit and it is much more robust with the informative priors. Moreover, the two-stage Bayesian updating informative priors provided the best goodness-of-fit and coefficient estimation accuracies.In addition to the aggregate analyses, real-time crash risk evaluation models have been developed to identify crash contributing factors at the disaggregate level. Support Vector Machine (SVM), a recently proposed statistical learning model and Hierarchical Bayesian logistic regression models were introduced to evaluate real-time crash risk. Classification and regression tree (CART) model has been developed to select the most important explanatory variables. Based on the variable selection results, Bayesian logistic regression models and SVM models with different kernel functions have been developed. Model comparisons based on receiver operating curves (ROC) demonstrate that the SVM model with Radial basis kernel function outperforms the others. Results from the models demonstrated that crashes are likely to happen during congestion periods (especially when the queuing area has propagated from the downstream segment); high variation of occupancy and/or volume would increase the probability of crash occurrence.Moreover, effects of microscopic traffic, weather, and roadway geometric factors on the occurrence of specific crash types have been investigated. Crashes have been categorized as rear-end, sideswipe, and single-vehicle crashes. AVI segment average speed, real-time weather data, and roadway geometric characteristics data were utilized as explanatory variables. Conclusions from this study imply that different active traffic management (ATM) strategies should be designed for three- and two-lane roadway sections and also considering the seasonal effects. Based on the abovementioned results, real-time crash risk evaluation models have been developed separately for multi-vehicle and single-vehicle crashes, and weekday and weekend crashes. Hierarchical Bayesian logistic regression models (random effects and random parameter logistic regression models) have been introduced to address the seasonal variations, crash unit level's diversities, and unobserved heterogeneity caused by geometric characteristics. For the multi-vehicle crashes: congested conditions at downstream would contribute to an increase in the likelihood of multi-vehicle crashes; multi-vehicle crashes are more likely to occur during poor visibility conditions and if there is a turbulent area that exists downstream. Drivers who are unable to reduce their speeds timely are prone to causing rear-end crashes. While for the single-vehicle crashes: slow moving traffic platoons at the downstream detector of the crash occurrence locations would increase the probability of single-vehicle crashes; large variations of occupancy downstream would also increase the likelihood of single-vehicle crash occurrence.Substantial efforts have been dedicated to revealing the hazardous factors that affect crash occurrence from both the aggregate and disaggregate level in this study, however, findings and conclusions from these research work need to be transferred into applications for roadway design and freeway management. This study further investigates the feasibility of utilizing Variable Speed Limits (VSL) system, one key part of ATM, to improve traffic safety on freeways. A proactive traffic safety improvement VSL control algorithm has been proposed. First, an extension of the traffic flow model METANET was employed to predict traffic flow while considering VSL's impacts on the flow-density diagram; a real-time crash risk evaluation model was then estimated for the purpose of quantifying crash risk; finally, the optimal VSL control strategies were achieved by employing an optimization technique of minimizing the total predicted crash risks along the VSL implementation area. Constraints were set up to limit the increase of the average travel time and differences between posted speed limits temporarily and spatially. The proposed VSL control strategy was tested for a mountainous freeway bottleneck area in the microscopic simulation software VISSIM. Safety impacts of the VSL system were quantified as crash risk improvements and speed homogeneity improvements. Moreover, three different driver compliance levels were modeled in VISSIM to monitor the sensitivity of VSL's safety impacts on driver compliance levels. Conclusions demonstrate that the proposed VSL system could effectively improve traffic safety by decreasing crash risk, enhancing speed homogeneity, and reducing travel time under both high and moderate driver compliance levels; while the VSL system does not have significant effects on traffic safety enhancement under the low compliance scenario. Future implementations of VSL control strategies and related research topics were also discussed.
Show less - Date Issued
- 2013
- Identifier
- CFE0005283, ucf:50556
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005283
