Current Search: Emissions (x)
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Title
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DEVELOPMENT OF A WEIGH-IN-MOTION SYSTEM USING ACOUSTIC EMISSION SENSORS.
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Creator
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Bowie, Jeanne, Radwan, Essam, University of Central Florida
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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.
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Date Issued
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2011
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Identifier
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CFE0003581, ucf:48903
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0003581
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Title
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A 2009 MOBILE SOURCE EMISSIONS INVENTORY OF THE UNIVERSITY OF CENTRAL FLORIDA.
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Creator
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Clifford, Johanna, Cooper, David, University of Central Florida
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Abstract / Description
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This thesis reports on the results of a mobile source emissions inventory for the University of Central Florida (UCF). For a large urban university, the majority of volatile organic compounds (VOC), oxides of nitrogen (NOx), and carbon dioxide (CO2) emissions come from on-road sources: personal vehicles and campus shuttles carrying students, faculty, staff, and administrators to and from the university, as well as university business trips. In addition to emissions from daily commutes, non...
Show moreThis thesis reports on the results of a mobile source emissions inventory for the University of Central Florida (UCF). For a large urban university, the majority of volatile organic compounds (VOC), oxides of nitrogen (NOx), and carbon dioxide (CO2) emissions come from on-road sources: personal vehicles and campus shuttles carrying students, faculty, staff, and administrators to and from the university, as well as university business trips. In addition to emissions from daily commutes, non-road equipment such as lawnmowers, leaf blowers, small maintenance vehicles, and other such equipment utilized on campus contributes to a significant portion to the total emissions from the university. UCF has recently become the second largest university in the nation (with over 56,000 students enrolled in the fall 2010 semester), and contributes significantly to VOC, NOx, and CO2 emissions in Central Florida area. In this project, students, faculty, staff, and administrators were first surveyed to determine their commuting distances and frequencies. Information was also gathered on vehicle type, and age distribution of the personal vehicles of students, faculty, administration, and staff as well as their bus, car-pool, and alternate transportation usage. The EPA approved mobile source emissions model, Motor Vehicle Emissions Simulator (MOVES2010a), was used to calculate the emissions from on-road vehicles, and UCF fleet gasoline consumption records were used to calculate the emissions from non-road equipment and on campus UCF fleet vehicles. The results of the UCF mobile source emissions inventory are reported and compared to a recently completed emissions inventory for the entire three-county area in Central Florida.
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Date Issued
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2011
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Identifier
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CFE0003923, ucf:48704
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0003923
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Title
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2008 EMISSIONS INVENTORY OF CENTRAL FLORIDA.
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Creator
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Ross, Jessica, Cooper, Dr. C. David, University of Central Florida
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Abstract / Description
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An emissions inventory of VOCs, NOx, and CO2 was conducted for three central Florida counties Orange, Seminole, and Osceola (OSO) for calendar year 2008. The inventory utilized three programs: MOBILE6, NONROAD2005, and EDMS (Emissions and Dispersion Modeling System) to model on-road mobile, non-road mobile, and airport emissions, respectively. Remaining point and area source data was estimated from the Florida Department of Environmental Protection (FDEP) and the U.S. Environmental...
Show moreAn emissions inventory of VOCs, NOx, and CO2 was conducted for three central Florida counties Orange, Seminole, and Osceola (OSO) for calendar year 2008. The inventory utilized three programs: MOBILE6, NONROAD2005, and EDMS (Emissions and Dispersion Modeling System) to model on-road mobile, non-road mobile, and airport emissions, respectively. Remaining point and area source data was estimated from the Florida Department of Environmental Protection (FDEP) and the U.S. Environmental Protection Agency's (U.S. EPA) 2008 emissions inventory. The previous OSO emissions inventory was done in 2002 and in the six years between inventories, there have been changes in population, commerce, and pollution control technology in central Florida which have affected the region's emissions. It is important to model VOC and NOx emissions to determine from where the largest proportions are coming. VOCs and NOx are ozone precursors, and in the presence of heat and sunlight, they react to form ozone (O3). Ozone is regulated by the U.S. Environmental Protection Agency through the FDEP. The current standard is 75 parts per billion (ppb) and Orange County's average is 71 ppb. A new standard (which will likely be about 65 ppb) is being developed and is scheduled to be announced by July 2011. If OSO goes into non-attainment, it will need to prepare a contingency plan for how to reduce emissions to submit to the FDEP for approval. The 2008 inventory determined that approximately 71,300 tons of VOCs and 59,000 tons of NOx were emitted that year. The majority of VOCs came from on-road mobile sources (33%) and area sources (43%), while the majority of NOx came from on-road mobile sources (64%) and non-road mobile sources (17%). Other major sources of VOCs included gasoline powered non-road mobile equipment (lawn and garden equipment), consumer solvents, cooking, and gasoline distribution. With the numbers that could be determined for CO2 emissions, on-road mobile and point sources were responsible for 93%. Of the point source CO2 emissions, almost all of it (87%) came from one large coal-fired power plant in Orange County.
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Date Issued
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2011
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Identifier
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CFE0003703, ucf:48834
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0003703
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Title
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The Consequences of a Reduced Superlattice Thickness on Quantum Cascade LASER Performance.
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Creator
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Figueiredo, Pedro, Lyakh, Arkadiy, Peale, Robert, Klemm, Richard, Fathpour, Sasan, University of Central Florida
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Abstract / Description
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Coherent infrared radiation sources are essential for the operability of a wide range of scientific, industrial, military and commercial systems. The importance of the mid-infrared spectral region cannot be understated. Numerous molecules have some vibrational band in this range, allowing for identification of species by means of absorption, emission or some other form of spectroscopy. As such, spectroscopy alone has numerous applications ranging from industrial process control to disease...
Show moreCoherent infrared radiation sources are essential for the operability of a wide range of scientific, industrial, military and commercial systems. The importance of the mid-infrared spectral region cannot be understated. Numerous molecules have some vibrational band in this range, allowing for identification of species by means of absorption, emission or some other form of spectroscopy. As such, spectroscopy alone has numerous applications ranging from industrial process control to disease diagnosis utilizing breath analysis. However, despite the discovery of the LASER in the 60s, to this day the amount of coherent sources in this range is limited. It is for this reason that the quantum cascade laser has gained such momentum over the past 23 years.Quantum Cascade LASERS (QCL) are semiconductor LASERS which are based on the principle of bandgap engineering. This incredible technique is a testament to the technological maturity of the semiconductor industry. It has been demonstrated that by having precise control of individual material composition (band gap control), thicknesses on the order of monolayers, and doping levels for each individual layer in a superlattice, we have unprecedented flexibility in designing a LASER or detector in the infrared. And although the technology has matured since it's discovery, there still remain fundamental limitations on device performance. In particular, active region overheating limits QCL performance in a high duty cycle mode of operation.In this dissertation, along with general discussion on the background of the QCL, we propose a solution of where by limiting the growth of the superlattice to a fraction of typical devices, we allow for reduction of the average superlattice temperature under full operational conditions. The consequences of this reduction are explored in theory, experiment and system level applications.
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Date Issued
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2017
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Identifier
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CFE0006592, ucf:51273
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0006592
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Title
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A Roughness Correction for Aquarius Ocean Brightness Temperature Using the CONAE MicroWave Radiometer.
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Creator
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Hejazin, Yazan, Jones, W Linwood, Wahid, Parveen, Mikhael, Wasfy, Junek, William, Piepmeier, Jeffrey, University of Central Florida
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Abstract / Description
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Aquarius/SAC-D is a joint NASA/CONAE (Argentine Space Agency) Earth Sciences satellite mission to measure global sea surface salinity (SSS), using an L-band radiometer that measures ocean brightness temperature (Tb). The application of L-band radiometry to retrieve SSS is a difficult task, and therefore, precise Tb corrections are necessary to obtain accurate measurements. One of the major error sources is the effect of ocean roughness that (")warms(") the ocean Tb. The Aquarius (AQ)...
Show moreAquarius/SAC-D is a joint NASA/CONAE (Argentine Space Agency) Earth Sciences satellite mission to measure global sea surface salinity (SSS), using an L-band radiometer that measures ocean brightness temperature (Tb). The application of L-band radiometry to retrieve SSS is a difficult task, and therefore, precise Tb corrections are necessary to obtain accurate measurements. One of the major error sources is the effect of ocean roughness that (")warms(") the ocean Tb. The Aquarius (AQ) instrument (L-band radiometer/scatterometer) baseline approach uses the radar scatterometer to provide this ocean roughness correction, through the correlation of radar backscatter with the excess ocean emissivity.In contrast, this dissertation develops an ocean roughness correction for AQ measurements using the MicroWave Radiometer (MWR) instrument Tb measurements at Ka-band to remove the errors that are caused by ocean wind speed and direction. The new ocean emissivity radiative transfer model was tuned using one year (2012) of on-orbit combined data from the MWR and the AQ instruments that are collocated in space and time. The roughness correction in this paper is a theoretical Radiative Transfer Model (RTM) driven by numerical weather forecast model surface winds, combined with ancillary satellite data from WindSat and SSMIS, and environmental parameters from NCEP. This RTM provides an alternative approach for estimating the scatterometer-derived roughness correction, which is independent. The theoretical basis of the algorithm is described and results are compared with the AQ baseline scatterometer method. Also results are presented for a comparison of AQ SSS retrievals using both roughness corrections.
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Date Issued
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2015
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Identifier
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CFE0005625, ucf:50218
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0005625
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Title
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Non-Degenerate Two Photon Gain in Bulk Gallium Arsenide.
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Creator
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Turnbull, Brendan, Hagan, David, Vanstryland, Eric, Christodoulides, Demetrios, University of Central Florida
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Abstract / Description
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The purpose of this thesis is to investigate the nonlinear phenomena known as doubly-stimulated, non-degenerate two-photon emission (ND-2PE) in Gallium Arsenide (GaAs). 2PE refers to the simultaneous emission of two-photons as electrons move from the conduction band in a direct gap semiconductor to the valence band. Following the same path for describing one-photon emission (1PE) we describe 2PE as a product of the irradiance, I, and the negative of the loss which in this case is two-photon...
Show moreThe purpose of this thesis is to investigate the nonlinear phenomena known as doubly-stimulated, non-degenerate two-photon emission (ND-2PE) in Gallium Arsenide (GaAs). 2PE refers to the simultaneous emission of two-photons as electrons move from the conduction band in a direct gap semiconductor to the valence band. Following the same path for describing one-photon emission (1PE) we describe 2PE as a product of the irradiance, I, and the negative of the loss which in this case is two-photon absorption, ?_2, the negative coming from the population inversion. We attempt to observe 2PE by using a frequency non-degenerate pump-probe experiment in which a third beam optically excites a 4 (&)#181;m thick GaAs sample. We use non-degenerate beams in hopes of utilizing the 3-orders of magnitude enhancement seen in two-photon absorption (2PA) by going to extreme nondegeneracy (END) to enhance 2PE. GaAs is chosen due to the availability of the appropriate wavelengths, the maturity of the GaAs technology, its use in optoelectronic devices and its ability to be electrically pumped. During the experimental development we learn how to effectively etch and manipulate thin GaAs samples and model the transmission spectrum of these samples using thin film transmission matrices. We are able to match the measured transmission spectrum with the theoretical transmission spectrum. Here we etch the bulk GaAs left on the sample leaving only the 4 (&)#181;m thickness of molecular beam epitaxial grown GaAs plus additional layers of aluminum gallium arsenide (AlGaAs). These samples were grown for us by Professor Gregory Salamo of the University of Arkansas.Using the pump-probe experiment on the 4 (&)#181;m GaAs sample, we measure the change of the 2PA due to the presence of optically excited carriers. The goal is to reduce the 2PA signal to zero and then invert the 2PA signal indicating an increase in transmission indicative of 2PE when the population is inverted. Our results show that we achieve a 45% reduction in the 2PA signal in a 4 ?m thick GaAs sample due to the excited carriers. Unfortunately, we currently cannot experimentally determine whether the reduction is strictly due to free-carrier absorption (FCA) of our pump or possibly due to a change in the two-photon absorption coefficient. We measure the transmission of various wavelengths around the bang gap of GaAs as a function of excitation wavelength and achieve a transmittance of ~80% which we attribute to possibly be one photon gain (1PG) at 880 nm. We also go to cryogenic temperatures to concentrate the carriers near the bottom of the conduction band and improve the theoretical gain coefficient for 2PE. Unfortunately, we do not observe a measurable change in 2PA with the addition of optically excited carriers. Along with FCA of our infrared pump we suspect that the difficulties in this first set of experiments are also a result or radiative recombination due to amplified spontaneous emission reducing our free carrier density along with the fact that 4 ?m is too thick for uniform excitation. We now have 1 ?m samples from Professor Gregory Salamo which we hope will give better and more definitive results.
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Date Issued
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2013
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Identifier
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CFE0004762, ucf:49776
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0004762
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Title
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A STUDY OF CENTRAL FLORIDA NONROAD VOC AND NOX EMISSIONS AND POTENTIAL ACTIONS TO REDUCE EMISSIONS.
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Creator
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Radford, Michael, Cooper, C. David, University of Central Florida
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Abstract / Description
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Ground-level ozone is harmful to the human respiratory system, as well as the environment. The national EPA 8-hour ozone standard for ground-level ozone was reduced from 85 parts per billion (ppb) to 75 ppb in 2008, and trends from previous years show that some of the counties in Central Florida could be in danger of violation. Violation means "non attainment" status; in which the county is ordered by EPA to develop specific implementation plans to reduce its emissions. The objective of this...
Show moreGround-level ozone is harmful to the human respiratory system, as well as the environment. The national EPA 8-hour ozone standard for ground-level ozone was reduced from 85 parts per billion (ppb) to 75 ppb in 2008, and trends from previous years show that some of the counties in Central Florida could be in danger of violation. Violation means "non attainment" status; in which the county is ordered by EPA to develop specific implementation plans to reduce its emissions. The objective of this study was to compile an emissions inventory of volatile organic compounds (VOCs) and nitrogen oxides (NOx) from nonroad equipment in Osceola, Seminole, and Orange Counties (OSO) in Central Florida, and to develop possible action steps to reduce those emissions. This is important because VOC and NOx emissions are precursors to ground-level ozone. Thus, compiling emissions inventories is important to identify high VOC and NOx emitters. Mobile and point sources have long been the highest emitters of VOC and NOx and have therefore been targeted and monitored since the Clean Air Act of 1970, but the nonroad sources (such as construction and lawn equipment) have only been regulated since the 1990s. Using the NONROAD and NMIM modeling programs, the highest nonroad emitters of VOC for Central Florida were found to be lawn/garden equipment, and boating equipment, emitting a combined percentage of 77% of the total nonroad mobile source VOC. Construction equipment contributed 67% of the total nonroad mobile source emissions of NOx in Central Florida. The components of these categories were also analyzed to find the largest individual sources of VOC and NOx. Of the individual sources, lawn mowers and outboard boat engines were found to be the largest sources of VOCs. Of the NOx sources, all the construction equipment components had a relatively similar level of NOx emissions. Next, action steps were developed to reduce emissions, focusing on the high emitters, along with an estimated cost and feasibility for each measure. Of these steps, implementing a ban on leafblowers, and reducing use of lawn mowers, edgers, trimmers, etc. seemed to be the most effective for reducing VOCs. Although these are effective measures, the cost and feasibility of both pose challenges. The best action step for reducing NOx emissions in construction equipment seemed to be by simply reducing idling of equipment on job sites. This also poses challenges in feasibility and enforcement by management. Further, constant on/off cycles could result in decreasing the useful life of the older construction equipment. Finally, a survey was conducted with various construction managers and companies to find out the typical equipment and quantity needed for land clearing/grubbing, as well as the typical use, idling time, and total project time for each piece of equipment on a 10-acre site, under various conditions. The purpose of the study was to develop a rough estimate for the average amount of VOC and NOx emissions that will be produced per acre of land clearing activities, and to estimate the emissions reductions and cost savings if idling of the equipment was reduced.
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Date Issued
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2009
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Identifier
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CFE0002850, ucf:48064
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0002850
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Title
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Life-cycle Greenhouse Gas Emissions and Water Footprint of Residential Waste Collection and Management Systems.
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Creator
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Maimoun, Mousa, Reinhart, Debra, McCauley, Pamela, Cooper, David, University of Central Florida
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Abstract / Description
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Three troublesome issues concerning residential curbside collection (RCC) and municipal solid waste (MSW) management systems in the United States motivated this research. First, reliance upon inefficient collection and scheduling procedures negatively affect RCC efficiency, greenhouse gas (GHG) emissions, and cost. Second, the neglected impact of MSW management practices on water resources. Third, the implications of alternative fuels on the environmental and financial performance of waste...
Show moreThree troublesome issues concerning residential curbside collection (RCC) and municipal solid waste (MSW) management systems in the United States motivated this research. First, reliance upon inefficient collection and scheduling procedures negatively affect RCC efficiency, greenhouse gas (GHG) emissions, and cost. Second, the neglected impact of MSW management practices on water resources. Third, the implications of alternative fuels on the environmental and financial performance of waste collection where fuel plays a significant rule. The goal of this study was to select the best RCC program, MSW management practice, and collection fuel. For this study, field data were collected for RCC programs across the State of Florida. The garbage and recyclables generation rates were compared based on garbage collection frequency and use of dual-stream (DS) or single-stream (SS) recyclables collection system. The assessment of the collection programs was evaluated based on GHG emissions, while for the first time, the water footprint (WFP) was calculated for the most commonly used MSW management practices namely landfilling, combustion, and recycling. In comparing alternative collection fuels, two multi-criteria decision analysis (MCDA) tools, TOPSIS and SAW, were used to rank fuel alternatives for the waste collection industry with respect to a multi-level environmental and financial decision matrix. The results showed that SS collection systems exhibited more than a two-fold increase in recyclables generation rates, and a ~2.2-fold greater recycling efficiency compared to DS. The GHG emissions associated with the studied collection programs were estimated to be between 36 and 51 kg CO2eq per metric ton of total household waste (garbage and recyclables), depending on the garbage collection frequency, recyclables collection system (DS or SS) and recyclables compaction. When recyclables offsets were considered, the GHG emissions associated with programs using SS were estimated between -760 and -560, compared to between -270 and -210 kg CO2eq per metric ton of total waste for DS programs. In comparing the WFP of MSW management practices, the results showed that the WFP of waste landfilling can be reduced through implementing bioreactor landfilling. The WFP of electricity generated from waste combustion was less than the electricity from landfill gas. Overall, the WFP of electricity from MSW management practices was drastically less than some renewable energy sources. In comparing the WFP offsets of recyclables, the recycling of renewable commodities, e.g. paper, contributed to the highest WFP offsets compared to other commodities, mainly due to its raw material acquisition high WFPs. This suggests that recycling of renewable goods is the best management practice to reduce the WFP of MSW management. Finally, the MCDA of alternative fuel technologies revealed that diesel is still the best option, followed by hydraulic-hybrid waste collection vehicles (WCVs), then landfill gas (LFG) sourced natural gas, fossil natural gas and biodiesel. The elimination of the fueling station criterion from the financial criteria ranked LFG-sourced natural gas as the best option; suggesting that LFG sourced natural gas is the best alternative to fuel WCV when accessible. In conclusion, field data suggest that RCC system design can significantly impact recyclables generation rate and efficiency, and consequently determine environmental and economic impact of collection systems. The WFP concept was suggested as a method to systematically assess the impact of MSW management practices on water resources. A careful consideration of the WFP of MSW management practices and energy recovered from MSW management facilities is essential for the sustainable appropriation of water resources and development.
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Date Issued
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2015
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Identifier
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CFE0005656, ucf:50174
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0005656
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Title
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Microscopic Assessment of Transportation Emissions on Limited Access Highways.
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Creator
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Abou-Senna, Hatem, Radwan, Ahmed, Abdel-Aty, Mohamed, Al-Deek, Haitham, Cooper, Charles, Johnson, Mark, University of Central Florida
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Abstract / Description
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On-road vehicles are a major source of transportation carbon dioxide (CO2) greenhouse gas emissions in all the developed countries, and in many of the developing countries in the world. Similarly, several criteria air pollutants are associated with transportation, e.g., carbon monoxide (CO), nitrogen oxides (NOx), and particulate matter (PM). The need to accurately quantify transportation-related emissions from vehicles is essential. Transportation agencies and researchers in the past have...
Show moreOn-road vehicles are a major source of transportation carbon dioxide (CO2) greenhouse gas emissions in all the developed countries, and in many of the developing countries in the world. Similarly, several criteria air pollutants are associated with transportation, e.g., carbon monoxide (CO), nitrogen oxides (NOx), and particulate matter (PM). The need to accurately quantify transportation-related emissions from vehicles is essential. Transportation agencies and researchers in the past have estimated emissions using one average speed and volume on a long stretch of roadway. With MOVES, there is an opportunity for higher precision and accuracy. Integrating a microscopic traffic simulation model (such as VISSIM) with MOVES allows one to obtain precise and accurate emissions estimates. The new United States Environmental Protection Agency (USEPA) mobile source emissions model, MOVES2010a (MOVES) can estimate vehicle emissions on a second-by-second basis creating the opportunity to develop new software (")VIMIS 1.0(") (VISSIM/MOVES Integration Software) to facilitate the integration process. This research presents a microscopic examination of five key transportation parameters (traffic volume, speed, truck percentage, road grade and temperature) on a 10-mile stretch of Interstate 4 (I-4) test bed prototype; an urban limited access highway corridor in Orlando, Florida. The analysis was conducted utilizing VIMIS 1.0 and using an advanced custom design technique; D-Optimality and I-Optimality criteria, to identify active factors and to ensure precision in estimating the regression coefficients as well as the response variable.The analysis of the experiment identified the optimal settings of the key factors and resulted in the development of Micro-TEM (Microscopic Transportation Emissions Meta-Model). The main purpose of Micro-TEM is to serve as a substitute model for predicting transportation emissions on limited access highways to an acceptable degree of accuracy in lieu of running simulations using a traffic model and integrating the results in an emissions model. Furthermore, significant emission rate reductions were observed from the experiment on the modeled corridor especially for speeds between 55 and 60 mph while maintaining up to 80% and 90% of the freeway's capacity. However, vehicle activity characterization in terms of speed was shown to have a significant impact on the emission estimation approach.Four different approaches were further examined to capture the environmental impacts of vehicular operations on the modeled test bed prototype. First, (at the most basic level), emissions were estimated for the entire 10-mile section (")by hand(") using one average traffic volume and average speed. Then, three advanced levels of detail were studied using VISSIM/MOVES to analyze smaller links: average speeds and volumes (AVG), second-by-second link driving schedules (LDS), and second-by-second operating mode distributions (OPMODE). This research analyzed how the various approaches affect predicted emissions of CO, NOx, PM and CO2. The results demonstrated that obtaining accurate and comprehensive operating mode distributions on a second-by-second basis improves emission estimates. Specifically, emission rates were found to be highly sensitive to stop-and-go traffic and the associated driving cycles of acceleration, deceleration, frequent braking/coasting and idling. Using the AVG or LDS approach may overestimate or underestimate emissions, respectively, compared to an operating mode distribution approach.Additionally, model applications and mitigation scenarios were examined on the modeled corridor to evaluate the environmental impacts in terms of vehicular emissions and at the same time validate the developed model (")Micro-TEM("). Mitigation scenarios included the future implementation of managed lanes (ML) along with the general use lanes (GUL) on the I-4 corridor, the currently implemented variable speed limits (VSL) scenario as well as a hypothetical restricted truck lane (RTL) scenario. Results of the mitigation scenarios showed an overall speed improvement on the corridor which resulted in overall reduction in emissions and emission rates when compared to the existing condition (EX) scenario and specifically on link by link basis for the RTL scenario.The proposed emission rate estimation process also can be extended to gridded emissions for ozone modeling, or to localized air quality dispersion modeling, where temporal and spatial resolution of emissions is essential to predict the concentration of pollutants near roadways.
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Date Issued
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2012
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Identifier
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CFE0004777, ucf:49788
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0004777
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Title
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Ignition Studies of Oxy-Syngas/CO2 Mixtures Using Shock Tube for Cleaner Combustion Engines.
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Creator
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Barak, Samuel, Vasu Sumathi, Subith, Kapat, Jayanta, Ahmed, Kareem, University of Central Florida
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Abstract / Description
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In this study, syngas combustion was investigated behind reflected shock waves in order to gain insight into the behavior of ignition delay times and effects of the CO2 dilution. Pressure and light emissions time-histories measurements were taken at a 2 cm axial location away from the end wall. High-speed visualization of the experiments from the end wall was also conducted. Oxy-syngas mixtures that were tested in the shock tube were diluted with CO2 fractions ranging from 60% - 85% by volume...
Show moreIn this study, syngas combustion was investigated behind reflected shock waves in order to gain insight into the behavior of ignition delay times and effects of the CO2 dilution. Pressure and light emissions time-histories measurements were taken at a 2 cm axial location away from the end wall. High-speed visualization of the experiments from the end wall was also conducted. Oxy-syngas mixtures that were tested in the shock tube were diluted with CO2 fractions ranging from 60% - 85% by volume. A 10% fuel concentration was consistently used throughout the experiments. This study looked at the effects of changing the equivalence ratios (?), between 0.33, 0.5, and 1.0 as well as changing the fuel ratio (?), hydrogen to carbon monoxide, from 0.25, 1.0 and 4.0. The study was performed at 1.61-1.77 atm and a temperature range of 1006-1162K. The high-speed imaging was performed through a quartz end wall with a Phantom V710 camera operated at 67,065 frames per second. From the experiments, when increasing the equivalence ratio, it resulted in a longer ignition delay time. In addition, when increasing the fuel ratio, a lower ignition delay time was observed. These trends are generally expected with this combustion reaction system. The high-speed imaging showed non-homogeneous combustion in the system, however, most of the light emissions were outside the visible light range where the camera is designed for. The results were compared to predictions of two combustion chemical kinetic mechanisms: GRI v3.0 and AramcoMech v2.0 mechanisms. In general, both mechanisms did not accurately predict the experimental data. The results showed that current models are inaccurate in predicting CO2 diluted environments for syngas combustion.
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Date Issued
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2018
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Identifier
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CFE0006974, ucf:52909
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0006974
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Title
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Wireless Power Transfer for Space Applications: System Design and Electromagnetic Compatibility Compliance of Radiated Emissions.
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Creator
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Vazquez Ramos, Gabriel, Yuan, Jiann-Shiun, Sundaram, Kalpathy, Wu, Xinzhang, Soto Toro, Felix, University of Central Florida
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Abstract / Description
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This dissertation evaluates the possibility of wireless power transfer (WPT) systems for space applications, with an emphasis in launch vehicles (rockets). After performing literature review for WPT systems, it was identified that magnetic resonance provides the more suited set of characteristics for this application. Advanced analysis, simulation and testing were performed to magnetic resonance WPT systems to acquire system performance insight. This was accomplished by evaluating/varying...
Show moreThis dissertation evaluates the possibility of wireless power transfer (WPT) systems for space applications, with an emphasis in launch vehicles (rockets). After performing literature review for WPT systems, it was identified that magnetic resonance provides the more suited set of characteristics for this application. Advanced analysis, simulation and testing were performed to magnetic resonance WPT systems to acquire system performance insight. This was accomplished by evaluating/varying coupling configuration, load effects and magnetic element physical characteristics (i.e. wire material, loop radius, etc.). It was identified by analysis, circuit simulation and testing that the best coupling configuration for this application was series-series and series-shunt with Litz wire loop inductors. The main concern identified for the implementation of these systems for space applications was radiated emissions that could potentially generate electromagnetic interference (EMI). To address this EMI concern, we developed the Electromagnetic Compatibility Radiated Emissions Compliance Design Evaluation Approach for WPT Space Systems. This approach systematically allocates key analyses, simulations and tests procedures to predict WPT EMC compliance to NASA's EMC standard Mil-Std-461E/F. Three prototype/magnetic elements were successfully assessed by implementing the WPT EMC design approach. The electric fields intensity generated by the WPT prototypes/magnetic elements tested were: 30.02 dBuV/m, 28.90 dBuV/m and 82.13 dBuV/m (requirement limit: 140 dBuV/m). All three prototypes successfully transferred power wirelessly and successfully met the NASA EMC requirements.
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Date Issued
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2012
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Identifier
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CFE0004448, ucf:49344
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0004448
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Title
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Investigating New Guaiazulenes and Diketopyrropyrroles for Photonic Applications.
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Creator
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Ghazvini Zadeh, Ebrahim, Belfield, Kevin, Campiglia, Andres, Yuan, Yu, Zou, Shengli, Cheng, Zixi, University of Central Florida
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Abstract / Description
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?-Conjugated systems have been the focus of study in recent years in order to understand their charge transport and optical properties for use in organic electronic devices, fluorescence bioimaging, sensors, and 3D optical data storage (ODS), among others. As a result, several molecular building blocks have been designed, allowing new frontiers to be realized. While various successful building blocks have been fine-tuned at both the electronic and molecular structure level to provide advanced...
Show more?-Conjugated systems have been the focus of study in recent years in order to understand their charge transport and optical properties for use in organic electronic devices, fluorescence bioimaging, sensors, and 3D optical data storage (ODS), among others. As a result, several molecular building blocks have been designed, allowing new frontiers to be realized. While various successful building blocks have been fine-tuned at both the electronic and molecular structure level to provide advanced photophysical and optoelectronic characteristics, the azulene framework has been under-appreciated despite its unique electronic and optical properties. Among several attributes, azulenes are vibrant blue naturally occurring hydrocarbons that exhibit large dipolar character, coupled with stimuli-responsive behavior in acidic environments. Additionally, the non-toxic nature and the accompanying eco-friendly feature of some azulenes, namely guaiazulene, may set the stage to further explore a more (")green(") route towards photonic and conductive materials.The first part of this dissertation focuses on exploiting guaiazulene as a natural building block for the synthesis of chromophores with varying stimuli-responsiveness. Results described in Chapter 1 show that extending the conjugation of guaiazulene through its seven-membered ring methyl group with aromatic substituents dramatically impacts the optical properties of the guaiazulenium carbocation. Study of these ?(-)stabilized tropilium ions enabled establishing photophysical structure-property trends for guaiazulene-terminated ?-conjugated analogs under acidic conditions, including absorption, emission, quantum yield, and optical band gap patterns. These results were exploited in the design of a photosensitive polymeric system with potential application in the field of three dimensional (3D) optical data storage (ODS).Chapter 2 describes the use of guaiazulene reactive sites (C-3 and C-4 methyl group) to generate a series of cyclopenta[ef]heptalenes that exhibit strong stimuli-responsive behavior. The approach presents a versatile route that allows for various substrates to be incorporated into the resulting cyclopenta[ef]heptalenes, especially after optimization that led to devising a one-pot reaction toward such tricyclic systems. Examining the UV-vis absorption profiles in neutral and acidic media showed that the extension of conjugation at C(4) of the cyclopenta[ef]heptalene skeleton results in longer absorption maxima and smaller optical energy gaps. Additionally, it was concluded that these systems act as sensitizers of a UV-activated ((<) 300 nm) photoacid generator (PAG), via intermolecular photoinduced electron transfer (PeT), upon which the PAG undergoes photodecomposition resulting in the generation of acid.In a related study, the guaiazulene methyl group at C-4 was employed to study the linear and nonlinear optical properties of 4-styrylguaiazulenes, having the same ?(-)donor with varying ?-spacer. It was realized that the conjugation length correlates with the extent of bathochromic shift of the protonated species. On the other hand, a trend of decreasing quantum yield was established for this set of 4-styrylguaiazulenes, which can be explained by the increasingly higher degree of flexibility.The second part of this dissertation presents a comprehensive investigation of the linear photophysical, photochemical, and nonlinear optical properties of diketopyrrolopyrrole (DPP)-based derivatives, including two-photon absorption (2PA), femtosecond transient absorption, stimulated emission spectroscopy, and superfluorescence phenomena. The synthetic feasibility, ease of modification, outstanding robustness, and attractive spectroscopic properties of DPPs have motivated their study for fluorescence microscopy applications, concluding that the prepared DPP's are potentially suitable chromophores for high resolution stimulated emission depletion (STED) microscopy.
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Date Issued
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2015
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Identifier
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CFE0006034, ucf:50986
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0006034
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Title
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An On-orbit Calibration Procedure for Spaceborne Microwave Radiometers Using Special Spacecraft Attitude Maneuvers.
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Creator
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Farrar, Spencer, Jones, W Linwood, Mikhael, Wasfy, Wahid, Parveen, Gaiser, Peter, University of Central Florida
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Abstract / Description
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This dissertation revisits, develops, and documents methods that can be used to calibrate spaceborne microwave radiometers once in orbit. The on-orbit calibration methods discussed within this dissertation can provide accurate and early results by utilizing Calibration Attitude Maneuvers (CAM), which encompasses Deep Space Calibration (DSC) and a new use of the Second Stokes (SS) analysis that can provide early and much needed insight on the performance of the instrument. This dissertation...
Show moreThis dissertation revisits, develops, and documents methods that can be used to calibrate spaceborne microwave radiometers once in orbit. The on-orbit calibration methods discussed within this dissertation can provide accurate and early results by utilizing Calibration Attitude Maneuvers (CAM), which encompasses Deep Space Calibration (DSC) and a new use of the Second Stokes (SS) analysis that can provide early and much needed insight on the performance of the instrument. This dissertation describes pre-existing and new methods of using DSC maneuvers as well as a simplified use of the SS procedure. Over TRMM's 17 years of operation it has provided invaluable data and has performed multiple CAMs over its lifetime. These maneuvers are analyzed to implement on-orbit calibration procedures that will be applied for future missions. In addition, this research focuses on the radiometric calibration of TMI that will be incorporated in the final processing (Archive/Legacy of the NASA TMI 1B11 brightness temperature data product). This is of importance since TMI's 17-year sensor data record must be vetted of all known calibration errors so to provide the final stable data for science users, specifically, climatological data records.
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Date Issued
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2015
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Identifier
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CFE0005611, ucf:50208
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0005611
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Title
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THE APPLICATION OF TWO-PHOTON ABSORBING PROBES IN LYSOSOMAL, ZINC ION SENSING AND FOLATE RECEPTOR-TARGETED BIOIMAGING.
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Creator
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WANG, XUHUA, Belfield, Kevin D., University of Central Florida
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Abstract / Description
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Two-photon fluorescence microscopy (2PFM) has become a powerful technique for bioimaging in non-invasive cancer diagnosis and also investigating the mechanization and original of a variety of diseases by tracking various biological processes. Because the fluorescence emission by two photon absorbing (2PA) is directly proportional to the square of the intensity of excitation light, this intrinsic property of 2PA provides 2PFM great advantages over traditional one-photon fluorescence microscopy...
Show moreTwo-photon fluorescence microscopy (2PFM) has become a powerful technique for bioimaging in non-invasive cancer diagnosis and also investigating the mechanization and original of a variety of diseases by tracking various biological processes. Because the fluorescence emission by two photon absorbing (2PA) is directly proportional to the square of the intensity of excitation light, this intrinsic property of 2PA provides 2PFM great advantages over traditional one-photon fluorescence microscopy (1PFM), including high 3D spatial localization, less photodamage and interference from biological tissue because of using longer wavelength excitation (700-1300 nm). However, most 2PA probes are hydrophobic and their photostabilities are questionable, severely limiting their biological and medical applications. In addition, probes with significant specificity for certain organelles for tracking cellular processes or metal ions for monitoring neural transmission are somewhat rare. Moreover, it is also very significant to deliver the probes to specific disease sites for early cancer diagnosis. In order to increase the water solubility of probes, polyethylene glycol (PEG) was introduced to a fluorene-based 2PA probe LT1 for lysosomal 2PFM cell imaging. The 2PFM bioimaging application of the novel two-photon absorbing fluorene derivative LT1, selective for the lysosomes of HCT 116 cancer cells is described in Chapter II. Linear and nonlinear photophysical and photochemical properties of the probe were investigated to evaluate the potential of the probe for 2PFM lysosomal imaging. After the investigation of the cytotoxicity of this new probe, colocalization studies of the probe with commercial lysosomal probe Lysotracker Red in HCT 116 cells were conducted. A high colocalization coefficient (0.96) was achieved and demonstrated the specific localization of the probe in lysosomes. A figure of merit, FM, was introduced by which all fluorescent probes for 2PFM can be compared. LT1 was demonstrated to have a number of properties that far exceed those of commercial lysotracker probes, including much higher 2PA cross sections, good fluorescence quantum yield, and, importantly, high photostability, all resulting in a superior figure of merit. Consequently, 2PFM was used to demonstrate lysosomal tracking with LT1. In addition to lysosomes, it is also very significant to investigate the physiological roles of free metal ions in biological processes, especially Zn2+, because Zn2+ normally serves either as the catalytic elements in enzymatic activity centers or as structural elements in enzymes and transcription factors. However, biocompatible and effective Zn2+ probes for 2PFM bioimaging are infrequent. In Chapter III, 2PFM bioimaging with a hydrophilic 2PA Zn2+ sensing fluorescent probe, bis(1,2,3-triazolyl)fluorene derivative, is described. 2PFM bioimaging of the probe in living HeLa cancer cells was demonstrated. The results revealed a significant fluorescence increase upon introduction of Zn2+ into the cancer cells, and a reversible Zn2+ binding to the probe was also demonstrated, providing a robust probe for two-photon fluorescence zinc ion sensing. Early cancer diagnosis is another critical application for 2PFM, but there are still huge challenges for this new technique in clinical areas. Most 2PA probes with large two-photon absorbing cross sections and fluorescence quantum efficiency are synthetically more accessible in hydrophobic forms. In order to increase the efficiency of the probes and minimize the effect of the probe on the human body, delivery of the probe specifically to cancer sites is desired. The synthesis and characterization of narrow dispersity organically modified silica nanoparticles (SiNPs), diameter ~30 nm, entrapping a hydrophobic two-photon absorbing fluorenyl dye, are reported in Chapter IV. The surface of the SiNPs was functionalized with folic acid to specifically deliver the probe to folate receptor (FR) over-expressing HeLa cells, making these folate 2PA dye-doped SiNPs potential candidates as probes for two-photon fluorescence microscopy (2PFM) bioimaging. In vitro studies using FR over-expressing HeLa cells demonstrated specific cellular uptake of the functionalized nanoparticles. However, when the concentration of the dye in SiNPs increased for higher signal output, the fluorescence quantum efficiency of a probe normally decreases because of self-quenching. In Chapter V, a near-infrared (NIR) emitting probe is reported to overcome this limitation through both aggregate-enhanced fluorescence emission and aggregate enhanced two-photon absorption. The dye was encapsulated in SiNPs and the surface of the nanoparticles was functionalized with PEG followed by a folic acid derivative to specifically target folate receptors. NIR emission is important for deep tissue imaging. In vitro studies using HeLa cells that upregulate folate receptors indicated specific cellular uptake of the folic acid functionalized SiNP nanoprobe. Meanwhile, the probe was also investigated for live animal imaging by employing mice bearing HeLa tumors for in vivo studies. Ex vivo 2PFM tumor imaging was then conducted to achieve high quality 3D thick tissue tumor images.
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Date Issued
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2011
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Identifier
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CFE0003640, ucf:48891
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0003640
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Title
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OPTICAL AND PHYSICAL PROPERTIES OF CERAMIC CRYSTAL LASER MATERIALS.
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Creator
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Simmons, Jed, Bass, Michael, University of Central Florida
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Abstract / Description
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Historically ceramic crystal laser material has had disadvantages compared to single crystal laser material. However, progress has been made in the last decade and a half to overcome the disadvantages associated with ceramic crystal. Today, because of the promise of ceramic crystal as a high power laser material, investigation into its properties, both physical and optical, is warranted and important. Thermal expansion was measured in this thesis for Nd:YAG (yttrium aluminum garnet) ceramic...
Show moreHistorically ceramic crystal laser material has had disadvantages compared to single crystal laser material. However, progress has been made in the last decade and a half to overcome the disadvantages associated with ceramic crystal. Today, because of the promise of ceramic crystal as a high power laser material, investigation into its properties, both physical and optical, is warranted and important. Thermal expansion was measured in this thesis for Nd:YAG (yttrium aluminum garnet) ceramic crystal using an interferometric method. The interferometer employed a spatially filtered HeNe at 633 nm wavelength. Thermal expansion coefficients measured for the ceramic crystal samples were near the reported values for single crystal Nd:YAG. With a similar experimental setup as that for the thermal expansion measurements, dn/dT for ceramic crystal Nd:YAG was measured and found to be slightly higher than the reported value for single crystal. Depolarization loss due to thermal gradient induced stresses can limit laser performance. As a result this phenomenon was modeled for ceramic crystal materials and compared to single crystals for slab and rod shaped gain media. This was accomplished using COMSOL Multiphysics, and MATLAB. Results indicate a dependence of the depolarization loss on the grain size where the loss decreases with decreased grain size even to the point where lower loss may be expected in ceramic crystals than in single crystal samples when the grain sizes in the ceramic crystal are sufficiently small. Deformation-induced thermal lensing was modeled for a single crystal slab and its relevance to ceramic crystal is discussed. Data indicates the most notable cause of deformation-induced thermal lensing is a consequence of the deformation of the top and bottom surfaces. Also, the strength of the lensing along the thickness is greater than the width and greater than that due to other causes of lensing along the thickness of the slab. Emission spectra, absorption spectra, and fluorescence lifetime were measured for Nd:YAG ceramic crystal and Yb:Lu2O3 ceramic crystal. No apparent inhomogeneous broadening appears to exist in the Nd:YAG ceramic at low concentrations. Concentration and temperature dependence effects on emission spectra were measured and are presented. Laser action in a thin disk of Yb:Y2O3 ceramic crystal was achieved. Pumping was accomplished with a fiber coupled diode laser stack at 938 nm. A slope efficiency of 34% was achieved with maximum output energy of 28.8 mJ/pulse.
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Date Issued
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2007
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Identifier
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CFE0001764, ucf:47273
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Format
-
Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0001764
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Title
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Improvements on Instrumentation to Explore the Multidimensionality of Luminescence Spectroscopy.
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Creator
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Moore, Anthony, Campiglia, Andres, Chumbimuni Torres, Karin, Harper, James, Rex, Matthew, Lee, Woo Hyoung, University of Central Florida
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Abstract / Description
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This dissertation presents experimental and instrumentation developments that take full advantage of the multidimensional nature of line narrowing spectroscopy at liquid nitrogen (77 K) and liquid helium (4.2 K) temperatures. The inconvenience of sample freezing procedures is eliminated with the aid of cryogenic fiber optic probes. Rapid collection of multidimensional data formats such as wavelength time matrices, excitation emission matrices, time-resolved excitation emission matrices and...
Show moreThis dissertation presents experimental and instrumentation developments that take full advantage of the multidimensional nature of line narrowing spectroscopy at liquid nitrogen (77 K) and liquid helium (4.2 K) temperatures. The inconvenience of sample freezing procedures is eliminated with the aid of cryogenic fiber optic probes. Rapid collection of multidimensional data formats such as wavelength time matrices, excitation emission matrices, time-resolved excitation emission matrices and time resolved excitation emission cubes is made possible with the combination of a pulsed tunable dye laser, a spectrograph and an intensifier-charged coupled device. These data formats provide unique opportunities for processing vibrational luminescence data with second order multivariate calibration algorithms. The use of cryogenic fiber optic probes is extended to commercial instrumentation. An attractive feature of spectrofluorimeters with excitation and emission monochromators is the possibility to record synchronous spectra. The advantages of this approach, which include narrowing of spectral bandwidth and simplification of emission spectra, were demonstrated with the direct analysis of highly toxic dibenzopyrene isomers. The same is true for the collection of steady-state fluorescence excitation-emission matrices. These approaches provide a general solution to unpredictable spectral interference, a ubiquitous problem for the analysis of organic pollutants in environmental samples of unknown composition. Since commercial spectrofluorimeters are readily available in most academic institutions, industrial settings and research institutes, the developments presented here should facilitate the widespread application of line-narrowing spectroscopic techniques to the direct determination, no chromatographic separation, of highly toxic compounds in complex environmental matrixes of unknown composition.
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Date Issued
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2015
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Identifier
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CFE0005847, ucf:50934
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Format
-
Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0005847
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Title
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The Behavior of Cerium Oxide Nanoparticles in Polymer Electrolyte Membranes in Ex-Situ and In-Situ Fuel Cell Durability Tests.
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Creator
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Pearman, Benjamin, Hampton, Michael, Blair, Richard, Clausen, Christian, Seal, Sudipta, Campiglia, Andres, Yestrebsky, Cherie, Mohajeri, Nahid, University of Central Florida
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Abstract / Description
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Fuel cells are known for their high efficiency and have the potential to become a major technology for producing clean energy, especially when the fuel, e.g. hydrogen, is produced from renewable energy sources such as wind or solar. Currently, the two main obstacles to wide-spread commercialization are their high cost and the short operational lifetime of certain components.Polymer electrolyte membrane (PEM) fuel cells have been a focus of attention in recent years, due to their use of...
Show moreFuel cells are known for their high efficiency and have the potential to become a major technology for producing clean energy, especially when the fuel, e.g. hydrogen, is produced from renewable energy sources such as wind or solar. Currently, the two main obstacles to wide-spread commercialization are their high cost and the short operational lifetime of certain components.Polymer electrolyte membrane (PEM) fuel cells have been a focus of attention in recent years, due to their use of hydrogen as a fuel, their comparatively low operating temperature and flexibility for use in both stationary and portable (automotive) applications.Perfluorosulfonic acid membranes are the leading ionomers for use in PEM hydrogen fuel cells. They combine essential qualities, such as high mechanical and thermal stability, with high proton conductivity. However, they are expensive and currently show insufficient chemical stability towards radicals formed during fuel cell operation, resulting in degradation that leads to premature failure. The incorporation of durability improving additives into perfluorosulfonic acid membranes is discussed in this work.Cerium oxide (ceria) is a well-known radical scavenger that has been used in the biological and medical field. It is able to quench radicals by facilely switching between its Ce(III) and Ce(IV) oxidation states.In this work, cerium oxide nanoparticles were added to perfluorosulfonic acid membranes and subjected to ex-situ and in-situ accelerated durability tests.The two ceria formulations, an in-house synthesized and commercially available material, were found to consist of crystalline particles of 2 (-) 5 nm and 20 (-) 150 nm size, respectively, that did not change size or shape when incorporated into the membranes.At higher temperature and relative humidity in gas flowing conditions, ceria in membranes is found to be reduced to its ionic form by virtue of the acidic environment. In ex-situ Fenton testing, the inclusion of ceria into membranes reduced the emission of fluoride, a strong indicator of degradation, by an order of magnitude with both liquid and gaseous hydrogen peroxide. In open-circuit voltage (OCV) hold fuel cell testing, ceria improved durability, as measured by several parameters such as OCV decay rate, fluoride emission and cell performance, over several hundred hours and influenced the formation of the platinum band typically found after durability testing.
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Date Issued
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2012
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Identifier
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CFE0004789, ucf:49731
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0004789
Pages