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- Title
- SPEEDES: A CASE STUDY OF SPACE OPERATIONS.
- Creator
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Paruchuri, Amith, Rabelo, Luis, University of Central Florida
- Abstract / Description
-
This thesis describes the application of parallel simulation techniques to represent the structured functional parallelism present within the Space Shuttle Operations Flow using the Synchronous Parallel Environment for Emulation and Discrete-Event Simulation (SPEEDES), an object-oriented multi-computing architecture. SPEEDES is a unified parallel simulation environment, which allocates events over multiple processors to get simulation speed up. Its optimistic processing capability minimizes...
Show moreThis thesis describes the application of parallel simulation techniques to represent the structured functional parallelism present within the Space Shuttle Operations Flow using the Synchronous Parallel Environment for Emulation and Discrete-Event Simulation (SPEEDES), an object-oriented multi-computing architecture. SPEEDES is a unified parallel simulation environment, which allocates events over multiple processors to get simulation speed up. Its optimistic processing capability minimizes simulation lag time behind wall clock time, or multiples of real-time. SPEEDES accommodates an increase in process complexity with additional parallel computing nodes to allow sharing of processing loads. This thesis focuses on the process of translating a model of Space Shuttle Operations from a procedural oriented and single processor approach to one represented in a process-driven, object-oriented, and distributed processor approach. The processes are depicted by several classes created to represent the operations at the space center. The reference model used is the existing Space Shuttle Model created in ARENA by NASA and UCF in the year 2001. A systematic approach was used for this translation. A reduced version of the ARENA model was created, and then used as the SPEEDES prototype using C++. The prototype was systematically augmented to reflect the entire Space Shuttle Operations Flow. It was then verified, validated, and implemented.
Show less - Date Issued
- 2005
- Identifier
- CFE0000330, ucf:46286
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0000330
- Title
- DYNAMIC SPEED MONITORING SYSTEM EFFECTIVENESS ON SHARP CURVES.
- Creator
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Persaud, Vasu, Oloufa, Amr, University of Central Florida
- Abstract / Description
-
The design of rural interchanges is of critical concern due to the need for the safe transition of vehicles from one high speed roadways to another and vice versa. This transition is accomplished by entry and exit ramps of various forms. The southbound entry loop ramp at the US 27/ US 192 trumpet interchange in Polk County, Florida does not provide such safe transition since historically there has been a high incidence of vehicular off-tracking. The geometry of the southbound entry ramp...
Show moreThe design of rural interchanges is of critical concern due to the need for the safe transition of vehicles from one high speed roadways to another and vice versa. This transition is accomplished by entry and exit ramps of various forms. The southbound entry loop ramp at the US 27/ US 192 trumpet interchange in Polk County, Florida does not provide such safe transition since historically there has been a high incidence of vehicular off-tracking. The geometry of the southbound entry ramp coupled with high approach speeds are two of the contributing factors. Due to the high cost of interchange modification and ramp realignment, one approach to increasing safety at the interchange is to decrease approach speeds (assumes that speed is a surrogate measure of safety) utilizing a Dynamic Speed Monitoring (DSM) system. The objective of this thesis was to test the effectiveness of such a DSM system at reducing vehicle speeds at the rural US 27/ US 192 trumpet interchange in Polk County, Florida. The system tested was a solar powered, radar based, wireless speed warning system which potentially could be used at traffic locations where it is difficult to secure power and to extended wires. The Measures of Effectiveness (MOEs) for the system were the reduction in mean and variance of speed along with the proportion of vehicles in the higher speed ranges after system implementation. This thesis describes the testing of the DSM effectiveness and involves the documentation of the experiments conducted, the data collected and the analysis of the results. Speed data was collected Before and After installation of the DSM system at two points preceding the southbound entry ramp. Approach speeds were collected at a point 250 feet in advance of the southbound entry ramp curve (also the detection zone of the DSM system radar) and PC speeds were collected at the Point of Curve of southbound entry ramp. Various data sets were analyzed in order to ascertain the systems effectiveness during the day and night, weekdays and weekends, various time periods during the day, and within various speed ranges. The Approach and PC data analysis indicated that the DSM system significantly (at the 95% confidence level) reduced speed mean and variance and increased speed limit/ advisory speed compliance. The Approach mean speed was reduced by 3.58 mph and the PC mean speed was reduced by 1.57 mph. The Approach speed variance was reduced by 3.34 and the PC speed variance was reduced by 0.70 mph. Approach speed limit compliance was increased by 22.27% and PC advisory speed (35 mph) + 5 mph compliance was increased by 11.56% (it was apparent that motorist were utilizing speeds above the advisory speed to navigate the curve). In general, the effectiveness of the DSM system was diminished on weekends as well as during the late night and early morning (12 AM to 7 AM) time periods. This suggested that when there were lower volumes and when motorists' perceived that speed limit enforcement was not as likely, the DSM system effectiveness was reduced. The DSM system resulted in a reduction in the percentage of vehicles utilizing the higher speed ranges (> 45 mph). There was a 62% average reduction in the vehicles that utilized the speed ranges above 57 mph for the Approach data and there was a 36% average reduction in the vehicles that utilized the speed ranges above 45 mph for the PC data. The DSM system resulted in a shift in the distribution of speeds from the higher speed bins to the lower speed bins Before and After installation.
Show less - Date Issued
- 2007
- Identifier
- CFE0001864, ucf:47388
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001864
- Title
- FATAL CRASHES CAUSED BY LIGHT TRUCKS RELATIVE TO CARS: A TEST OF THE OFFSETTING BEHAVIOR HYPOTHESIS.
- Creator
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Zubritsky, Adam, Caputo, Michael, University of Central Florida
- Abstract / Description
-
This thesis presents an econometric test of the offsetting behavior hypothesis concerning drivers of light trucks relative to cars. The main objective is to determine whether drivers of light trucks offset perceived safety benefits associated with larger vehicles by driving more aggressively than drivers of cars, subsequently causing more fatal crashes, holding all else constant. An empirical model using data on pedestrian fatalities across the United States over a five-year period is...
Show moreThis thesis presents an econometric test of the offsetting behavior hypothesis concerning drivers of light trucks relative to cars. The main objective is to determine whether drivers of light trucks offset perceived safety benefits associated with larger vehicles by driving more aggressively than drivers of cars, subsequently causing more fatal crashes, holding all else constant. An empirical model using data on pedestrian fatalities across the United States over a five-year period is developed and analyzed in order to capture the desired results. Estimates provide substantial evidence in support of the offsetting behavior hypothesis. To strengthen the case for driver offsetting behavior beyond previous studies, the model is estimated again using pedalcyclist fatalities. The results also point to interesting conclusions regarding the effects of increased speed limits on the behavior of drivers.
Show less - Date Issued
- 2005
- Identifier
- CFE0000579, ucf:46469
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0000579
- Title
- DSP IMPLEMENTATION OF DC VOLTAGE REGULATION USING ADAPTIVE CONTROL FOR 200 KW 62000 RPM INDUCTION GENERATOR.
- Creator
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Elkhomri, Othman, Wu, Thomas, University of Central Florida
- Abstract / Description
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The thesis discusses the development of closed loop system to control the DC voltage for 200 kW induction generator rated at a speed of 62000 RPM under different load conditions. The voltage regulation has been implemented using PI controller. A gain scheduling control algorithm has been developed to select the appropriate controller gains with respect to the generator load. Further, a relationship between the generator loads and the controller gains has been established. This relationship...
Show moreThe thesis discusses the development of closed loop system to control the DC voltage for 200 kW induction generator rated at a speed of 62000 RPM under different load conditions. The voltage regulation has been implemented using PI controller. A gain scheduling control algorithm has been developed to select the appropriate controller gains with respect to the generator load. Further, a relationship between the generator loads and the controller gains has been established. This relationship has been modeled using adaptive control technique to vary the gains automatically at any load condition. The adaptive control technique has been successfully generalized for real time DSP implementation to regulate the DC voltage for high speed induction generators rated from 5 kW to 200 kW.
Show less - Date Issued
- 2006
- Identifier
- CFE0001076, ucf:46787
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001076
- Title
- EXPLORING THE POTENTIAL OF COMBINING RAMP METERING AND VARIABLE SPEED LIMIT STRATEGIES FOR ALLEVIATING REAL-TIME CRASH RISK ON URBAN FREEWAYS.
- Creator
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Haleem, Kirolos, Abdel-Aty, Mohamed, University of Central Florida
- Abstract / Description
-
Research recently conducted at the University of Central Florida involving crashes on Interstate-4 in Orlando, Florida has led to the creation of new statistical and neural networks models that are capable of determining the crash risk on the freeway (Abdel-Aty et al., 2004; 2005, Pande and Abdel-Aty, 2006). These models are able to calculate rear-end and lane-change crash risks along the freeway in real-time through the use of static information at various locations along the freeway as well...
Show moreResearch recently conducted at the University of Central Florida involving crashes on Interstate-4 in Orlando, Florida has led to the creation of new statistical and neural networks models that are capable of determining the crash risk on the freeway (Abdel-Aty et al., 2004; 2005, Pande and Abdel-Aty, 2006). These models are able to calculate rear-end and lane-change crash risks along the freeway in real-time through the use of static information at various locations along the freeway as well as real-time traffic data obtained by loop detectors. Since these models use real-time traffic data, they are capable of calculating rear-end and lane-change crash risk values as the traffic flow conditions are changing on the freeway. The objective of this study is to examine the potential benefits of combining two ITS strategies (Ramp Metering and Variable Speed Limits strategies) for reducing the crash risk (both rear-end and lane-change crash risks) along the I-4 freeway. Following this aspect, a 36.25-mile section of I-4 running though Orlando, FL was simulated using the PARAMICS micro-simulation program. Gayah (2006) used the same network to examine the potential benefits of two ITS strategies separately (Route Diversion and Ramp Metering) for reducing the crash risk along the freeway by changing traffic flow parameters. Cunningham (2007) also used the same network to examine the potential benefits of implementing Variable Speed Limits strategy for reducing the crash risk along the freeway. Since the same network is used, the calibration and validation procedures used in this study are the same as these previous two studies. This study simulates three volume loading scenarios on the I-4 freeway. These are 60, 80 and 90 percent loading scenarios. From the final experimental design for the 60 % loading, it was concluded that implementing VSL strategy only was more beneficial to the network than either implementing Ramp Metering everywhere (through the whole network) in conjunction with VSL everywhere or implementing Ramp Metering downtown (in downtown areas only) in conjunction with VSL everywhere. This was concluded from the comparison of the results of this study with the results from Cunningham (2007). However, either implementing Ramp Metering everywhere or downtown in conjunction with VSL everywhere showed safety benefits across the simulated network as well as a reduction in the total travel time. The best case for implementing Ramp Metering everywhere in conjunction with VSL everywhere was using a homogeneous speed zone threshold of 2.5 mph, a speed change distance of half speed zone and a speed change time of 5 minutes in conjunction with a 60 seconds cycle length for the Zone algorithm, a critical occupancy of 0.17 and a 30 seconds cycle length for the ALINEA algorithm. And the best case for implementing Ramp Metering downtown in conjunction with VSL everywhere was using a homogeneous speed zone threshold of 2.5 mph, a speed change distance of half speed zone and a speed change time of 10 minutes in conjunction with a 60 seconds cycle length for the Zone algorithm, a critical occupancy of 0.17 and a 30 seconds cycle length for the ALINEA algorithm. For the 80 % loading, it was concluded that either implementing Ramp Metering everywhere in conjunction with VSL everywhere or implementing Ramp Metering downtown in conjunction with VSL everywhere was more beneficial to the network than implementing VSL strategy only. This was also concluded from the comparison of the results of this study with the results from Cunningham (2007). Moreover, it was concluded that implementing Ramp Metering everywhere in conjunction with VSL everywhere showed higher safety benefits across the simulated network than implementing Ramp Metering downtown in conjunction with VSL everywhere. Also, both of them increased the total travel time a bit, but this was deemed acceptable. Additionally, both of them had successive fluctuations and variations in the average lane-change crash risk vs. time step. The best case for implementing Ramp Metering everywhere in conjunction with VSL everywhere was using a homogeneous speed zone threshold of 5 mph, a speed change distance of half speed zone and a speed change time of 30 minutes in conjunction with a 60 seconds cycle length for the Zone algorithm, a critical occupancy of 0.17 and a 30 seconds cycle length for the ALINEA algorithm. And the best case for implementing Ramp Metering downtown in conjunction with VSL everywhere was using a homogeneous speed zone threshold of 5 mph, a speed change distance of half speed zone and a speed change time of 30 minutes in conjunction with a 60 seconds cycle length for the Zone algorithm, a critical occupancy of 0.17 and a 30 seconds cycle length for the ALINEA algorithm. Searching for the best way to implement both Ramp Metering and VSL strategies in conjunction with each other, an indepth investigation was conducted in order to remove the fluctuations and variations in the crash risk with time step (through the entire simulation period). The entire simulation period is 3 hours, and each time step is 5 minutes, so there are 36 time steps representing the entire simulation period. This indepth investigation led to the idea of not implementing VSL at consecutive zones (using either a gap of one zone or more). Then this idea was applied for the best case of implementing Ramp Metering and VSL everywhere at the 80 % loading, and the successive fluctuations and variations in the crash risk with time step were removed. Moreover, much better safety benefits were found. So, this confirms that this idea was very beneficial to the network. For the 90 % loading, it was concluded that implementing Ramp Metering strategy only (Zone algorithm in downtown areas, and ALINEA algorithm in non downtown areas) was more beneficial to the network than implementing Ramp Metering everywhere in conjunction with VSL everywhere. This was concluded from the comparison of the results of this study with the results from Gayah (2006). However, implementing Ramp Metering everywhere in conjunction with VSL everywhere showed safety benefits across the simulated network as well as a reduction in the total travel time. The best case was using a homogeneous speed zone threshold of 2.5 mph, a speed change distance of the entire speed zone and a speed change time of 20 minutes in conjunction with a 60 seconds cycle length for the Zone algorithm, a critical occupancy of 0.17 and a 30 seconds cycle length for the ALINEA algorithm. In summary, Ramp Metering was more beneficial at congested situations, while Variable Speed Limits were more beneficial at free-flow conditions. At conditions approaching congestion, the combination of Ramp Metering and Variable Speed Limits produced the best benefits. These results illustrate the significant potential of ITS strategies to improve the safety and efficiency of urban freeways.
Show less - Date Issued
- 2007
- Identifier
- CFE0001840, ucf:47363
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001840
- Title
- EXPERIMENTS IN POOL BOILING HEAT TRANSFER AND NUCLEATIONDYNAMICS OF HIGH PRESSURE REFRIGERANTS.
- Creator
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Joo, Daniel, Kumar, Ranganathan, University of Central Florida
- Abstract / Description
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A high pressure pool boiling experiment of pressurized R134a is designed and built, utilizing thermochromatic liquid crystal techniques. Liquid crystals thermo-chromatography uses encapsulated liquid crystals that are sensitive to temperature. When exposed to hot temperatures the crystal reflect a blue/violet color, and when exposed to cooler temperatures it reflects a red/orange color. The color value or hue is proportional to its temperature. Using this technique this experiment is capable...
Show moreA high pressure pool boiling experiment of pressurized R134a is designed and built, utilizing thermochromatic liquid crystal techniques. Liquid crystals thermo-chromatography uses encapsulated liquid crystals that are sensitive to temperature. When exposed to hot temperatures the crystal reflect a blue/violet color, and when exposed to cooler temperatures it reflects a red/orange color. The color value or hue is proportional to its temperature. Using this technique this experiment is capable of studying the physics and thermodynamics of refrigerants under nucleate pool boiling. The main objective of this experiment was the design of the experimental setup. Various designs were tested and validated, of which all incorporated a pressure resistant chamber constructed out of aluminum and glass viewing ports. Design parameters such as the heating element thickness were verified using a transient FEA thermal model. This model, which was developed in ANSYS, verified that this design would be able to capture the thermal response of the thermochromatic liquid crystals. This analysis concluded that a negligible error of 0.02°C is expected due to transient effects. Difficulties were encountered during early stages of development; most notable were imaging limitations such as low camera frame-rates and poor resolution. Since a TLC technique was used to measure the temperature of the boiling surface, a camera system fast enough to capture the thermal response was needed. At bubble frequencies of 30 nucleations per second, it was necessary for the camera to have much higher frame rates. Through the use of two synchronized cameras, the surface temperature, position, size and shape of the bubbles were recorded simultaneously. Two camera systems were designed and tested. The first system consisted of a high speed CMOS camera capable of capturing 1,000 frames per second, and an RBG CCD color camera capable of 30 Frames per second. However, this system was limited the slow frame rate and low resolution of the RBG camera. The second system used two high resolution and fast shutter speed cameras, which were able to capture fast bubble nucleations. This method required the assumption that under constant operating conditions, the path of one bubble was identical to the next. This method was tested utilizing the high speed camera, and was shown that there was less than a .04% deviation from the path any bubble to that of the next. Detailed analysis of nucleating surface temperatures using thermochromatic liquid crystal technique and temporal-temperature response under various heat flux and at 813.6kPa (118Psia) and 882.5kPa (128Psia) was performed. It is seen that temperature distribution is quite varied in each case. At high pressures the size of nucleation site decreases, giving rise to an increase in the surface temperature. Bubble growth is also analyzed through the use of high speed cameras and compared to temperature distributions. Simultaneous temperature and bubble size measurements provided a correlation between bubble growth and heat transfer. Boiling parameters such as bubble frequency, bubble size, and contact area are also analyzed. From the surface temperature plots, the local and average heat transfer coefficients were calculated as a function of time and bubble dynamics.
Show less - Date Issued
- 2006
- Identifier
- CFE0001489, ucf:47106
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001489
- Title
- DEVELOPING AN OBJECT-ORIENTED APPROACH FOR OPERATIONS SIMULATION IN SPEEDES.
- Creator
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Wasadikar, Amit, Rabelo, Luis, University of Central Florida
- Abstract / Description
-
Using simulation techniques, performance of any proposed system can be tested for different scenarios with a generated model. However, it is difficult to rapidly create simulation models that will accurately represent the complexity of the system. In recent years, Object-Oriented Discrete-Event Simulation has emerged as the potential technology to implement rapid simulation schemes. A number of software based on programming languages like C++ and Java are available for carrying out Object...
Show moreUsing simulation techniques, performance of any proposed system can be tested for different scenarios with a generated model. However, it is difficult to rapidly create simulation models that will accurately represent the complexity of the system. In recent years, Object-Oriented Discrete-Event Simulation has emerged as the potential technology to implement rapid simulation schemes. A number of software based on programming languages like C++ and Java are available for carrying out Object Oriented Discrete-Event Simulation. These software packages establish a general framework for simulation in computer programs, but need to be further customized for desired end-use applications. In this thesis, a generic simulation library is created for the distributed Synchronous Parallel Environment for Emulation and Discrete-Event Simulation (SPEEDES). This library offers classes to model the functionality of servers, processes, resources, transporters, and decisions. The library is expected to produce efficient simulation models in less time and with a lesser amount of coding. The class hierarchy is modeled using the Unified Modeling Language (UML). To test the library, the existing SPEEDES Space Shuttle Model is enhanced and recreated. This enhanced model is successfully validated against the original Arena model.
Show less - Date Issued
- 2005
- Identifier
- CFE0000332, ucf:46278
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0000332
- Title
- SUPER HIGH-SPEED MINIATURIZED PERMANENT MAGNET SYNCHRONOUS MOTOR.
- Creator
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Zheng, Liping, Sundaram, Kalpathy, University of Central Florida
- Abstract / Description
-
This dissertation is concerned with the design of permanent magnet synchronous motors (PMSM) to operate at super-high speed with high efficiency. The designed and fabricated PMSM was successfully tested to run upto 210,000 rpm The designed PMSM has 2000 W shaft output power at 200,000 rpm and at the cryogenic temperature of 77 K. The test results showed the motor to have an efficiency reaching above 92%. This achieved efficiency indicated a significant improvement compared to commercial...
Show moreThis dissertation is concerned with the design of permanent magnet synchronous motors (PMSM) to operate at super-high speed with high efficiency. The designed and fabricated PMSM was successfully tested to run upto 210,000 rpm The designed PMSM has 2000 W shaft output power at 200,000 rpm and at the cryogenic temperature of 77 K. The test results showed the motor to have an efficiency reaching above 92%. This achieved efficiency indicated a significant improvement compared to commercial motors with similar ratings. This dissertation first discusses the basic concept of electrical machines. After that, the modeling of PMSM for dynamic simulation is provided. Particular design strategies have to be adopted for super-high speed applications since motor losses assume a key role in the motor drive performance limit. The considerations of the PMSM structure for cryogenic applications are also discussed. It is shown that slotless structure with multi-strand Litz-wire is favorable for super-high speeds and cryogenic applications. The design, simulation, and test of a single-sided axial flux pancake PMSM is presented. The advantages and disadvantages of this kind of structure are discussed, and further improvements are suggested and some have been verified by experiments. The methodologies of designing super high-speed motors are provided in details. Based on these methodologies, a super high-speed radial-flux PMSM was designed and fabricated. The designed PMSM meets our expectation and the tested results agree with the design specifications. 2-D and 3-D modeling of the complicated PMSM structure for the electromagnetic numerical simulations of motor performance and parameters such as phase inductors, core losses, rotor eddy current loss, torque, and induced electromotive force (back-EMF) are also presented in detail in this dissertation. Some mechanical issues such as thermal analysis, bearing pre-load, rotor stress analysis, and rotor dynamics analysis are also discussed. Different control schemes are presented and suitable control schemes for super high- speed PMSM are also discussed in detail.
Show less - Date Issued
- 2005
- Identifier
- CFE0000762, ucf:46562
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0000762
- Title
- NEW OPTIMAL HIGH EFFICIENCY DSP-BASED DIGITAL CONTROLLER DESIGN FOR SUPER HIGH-SPEED PERMANENT MAGNET SYNCHRONOUS MOTOR.
- Creator
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zhao, limei, Wu, Thomas, University of Central Florida
- Abstract / Description
-
This dissertation investigates digital controller and switch mode power supply design for super high-speed permanent magnet synchronous motors (PMSM). The PMSMs are a key component for the miniaturic cryocooler that is currently under development at the University of Central Florida with support from NASA Kennedy Space Center and the Florida Solar Energy Center. Advanced motor design methods, control strategies, and rapid progress in semiconductor technology enables production of a highly...
Show moreThis dissertation investigates digital controller and switch mode power supply design for super high-speed permanent magnet synchronous motors (PMSM). The PMSMs are a key component for the miniaturic cryocooler that is currently under development at the University of Central Florida with support from NASA Kennedy Space Center and the Florida Solar Energy Center. Advanced motor design methods, control strategies, and rapid progress in semiconductor technology enables production of a highly efficient digital controller. However, there are still challenges for such super high-speed controller design because of its stability, high-speed, variable speed operation, and required efficiency over a wide speed range. Currently, limited research, and no commercial experimental analysis, is available concerning such motors and their control system design. The stability of a super high-speed PMSM is an important issue particularly for open-loop control, given that PMSM are unstable after exceeding a certain applied frequency. In this dissertation, the stability of super high-speed PMSM is analyzed and some design suggestions are given to maximize this parameter. For ordinary motors, the V/f control curve is a straight line with a boost voltage because the stator resistance is negligible and only has a significant effect around the DC frequency. However, for the proposed super high-speed PMSM the situation is quite different because of the motor's size. The stator resistance is quite large compared with the stator reactive impedance and cannot be neglected when employing constant a V/f control method. The challenge is to design an optimal constant V/f control scheme to raise efficiency with constant V/f control. In the development, test systems and prototype boards were built and experimental results confirmed the effectiveness of the dissertation system.
Show less - Date Issued
- 2005
- Identifier
- CFE0000856, ucf:46651
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0000856
- Title
- EVALUATING RAMP METERING AND VARIABLE SPEED LIMITS TO REDUCE CRASH POTENTIAL ON CONGESTED FREEWAYS USING MICRO-SIMULATION.
- Creator
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Dhindsa, Albinder, Abdel-Aty, Mohamed, University of Central Florida
- Abstract / Description
-
Recent research at UCF into defining surrogate measures for identifying crash prone conditions on freeways has led to the introduction of several statistical models which can flag such conditions with a good degree of accuracy. Outputs from these models have the potential to be used as real-time safety measures on freeways. They may also act as the basis for the evaluation of several intervention strategies that might help in the mitigation of risk of crashes. Ramp Metering and Variable Speed...
Show moreRecent research at UCF into defining surrogate measures for identifying crash prone conditions on freeways has led to the introduction of several statistical models which can flag such conditions with a good degree of accuracy. Outputs from these models have the potential to be used as real-time safety measures on freeways. They may also act as the basis for the evaluation of several intervention strategies that might help in the mitigation of risk of crashes. Ramp Metering and Variable Speed Limits are two approaches which have the potential of becoming effective implementation strategies for improving the safety conditions on congested freeways. This research evaluates both these strategies in different configurations and attempts to quantify their effect on risk of crash on a 9-mile section of Interstate-4 in the Orlando metropolitan region. The section consists of 17 Loop Detector stations, 11 On-ramps and 10 off-ramps. PARAMICS micro-simulation is used as the tool for modeling the freeway section. The simulated network is calibrated and validated for 5 minute average flows and speeds using loop detector data. Feedback Ramp Metering algorithm, ALINEA, is used for controlling access from up to 7 on-ramps. Variable Speed Limits are implemented based on real-time speed conditions prevailing in the whole 9-mile section. Both these strategies are tested separately as well as collectively to determine the individual effects of all the parameters involved. The results have been used to formulate and recommend the best possible strategy for minimizing the risk of crashes on the corridor. The study concluded that Ramp Metering improves the conditions on the freeway in terms of safety by decreasing variance in speeds and decreasing average occupancy. A safety benefit index was developed for quantifying the reduction in crash risk and it indicated that an optimal implementation strategy might produce benefits of up to 55%. The condition on the freeway section improved with increase in the number of metered ramps. It was also observed that shorter signal cycles for metered ramps were more suitable for metering multiple ramps. Ramp Metering at multiple locations also decreased the segment wide travel-times by 5% and was even able to offset the delays incurred by drivers at the metered on-ramps. Variable Speed Limits (VSL) were individually not as effective as ramp metering but when implemented along with ramp metering, they were found to further improve the safety on the freeway section under consideration. By means of a detailed experimental design it was observed that the best strategy for introducing speed limit changes was to raise the speed limits downstream of the location of interest by 5 mph and not affecting the speed limits upstream. A coordinated strategy - involving simultaneous application of VSL and Ramp Metering - provided safety benefits of up to 56 % for the study section according to the safety benefit index. It also improved the average speeds on the network besides decreasing the overall network travel time by as much as 21%.
Show less - Date Issued
- 2005
- Identifier
- CFE0000913, ucf:46741
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0000913
- Title
- PSYCHOMETRIC DIFFERENCES IN MOTOR FUNCTIONING.
- Creator
-
McWaters, Ashley, Fouty, Ed, University of Central Florida
- Abstract / Description
-
Clinical experience has shown that patients performing the Grooved Pegboard Test have difficulty maintaining the manualized right-to-left placement strategy with their left hand. This study sought to investigate possible differences in placement time on the Grooved Pegboard task between participants using the standardized left hand approach and a reversed manualized left hand placement strategy (i.e., left-to-right). The participants included 63 male and female undergraduate volunteers...
Show moreClinical experience has shown that patients performing the Grooved Pegboard Test have difficulty maintaining the manualized right-to-left placement strategy with their left hand. This study sought to investigate possible differences in placement time on the Grooved Pegboard task between participants using the standardized left hand approach and a reversed manualized left hand placement strategy (i.e., left-to-right). The participants included 63 male and female undergraduate volunteers between the ages of 18 and 25 years. All participants had no history of neurologic disease/trauma, or conditions that would affect motor functioning of the right and left upper extremities. Data were analyzed using a 3-way mixed-design ANOVA. Results revealed a significant main effects for gender (F(1, 59) = 5.215, p = .026) and handedness (F(1, 59) = 6.362, p = .014). Of primary interest was the main effect for placement direction, which was not significant, F(1, 59) = .120, p = .731. No significant interaction was observed (all p > .40). Recommendations for the use of this test in applied neuropsychological settings are offered.
Show less - Date Issued
- 2013
- Identifier
- CFH0004510, ucf:45172
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFH0004510
- Title
- EFFECTS OF GAMIFICATION ON SPEED AND ACCURACY ON AN INTERDEPENDENT PAPER SORTING TASK.
- Creator
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Tinkle, Davis, Salas, Eduardo, University of Central Florida
- Abstract / Description
-
This study examined the effects of gamification, i.e. (what makes games challenging, engaging and fun), and its effects on speed and accuracy on an interdependent paper sorting task. Undergraduate students (N=42) at the University of Central Florida participated by working interdependently in groups to sort numbered pieces of paper into piles before and after either playing video games or doing back-to-back drawing(basic team building exercises). It was hypothesized that participants who...
Show moreThis study examined the effects of gamification, i.e. (what makes games challenging, engaging and fun), and its effects on speed and accuracy on an interdependent paper sorting task. Undergraduate students (N=42) at the University of Central Florida participated by working interdependently in groups to sort numbered pieces of paper into piles before and after either playing video games or doing back-to-back drawing(basic team building exercises). It was hypothesized that participants who played video games would sort pieces of paper into the piles faster and more accurate than those who did back-to-back team exercises. Results showed that playing video games was not better than doing basic team exercises, but that the two tasks were relatively equal. Although groups were formed and dissolved quickly, there was improvement between the pre and posttests. While the experiment did not yield significant results, it is possible that using different video games or different interdependent tasks could foster increases in speed and accuracy compared to back-to-back drawing.
Show less - Date Issued
- 2015
- Identifier
- CFH0004797, ucf:45331
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFH0004797
- Title
- Sleep Disturbances Among Firefighters: The Impact Of Shift Work On Sleep And Cognition.
- Creator
-
Stout, Jeremy, Beidel, Deborah, Bowers, Clint, Paulson, Daniel, Dziegielewski, Sophia, University of Central Florida
- Abstract / Description
-
A comprehensive sleep assessment of 45 firefighters was conducted over 9- days in an effort to determine the impact of their 24 hour work and 48 hour off work schedule on their sleep duration, sleep quality, processing speed, sustained attention, vigilance, and mental health. Chronic patterns of poor sleep are associated with an increased likelihood of performing poorly on tasks that require processing speed and sustained attention/vigilance which could lead to firefighters' suboptimal work...
Show moreA comprehensive sleep assessment of 45 firefighters was conducted over 9- days in an effort to determine the impact of their 24 hour work and 48 hour off work schedule on their sleep duration, sleep quality, processing speed, sustained attention, vigilance, and mental health. Chronic patterns of poor sleep are associated with an increased likelihood of performing poorly on tasks that require processing speed and sustained attention/vigilance which could lead to firefighters' suboptimal work performance or an increased risk of injury. Firefighters completed sleep actigraphy, self- report measures, as well as neuropsychological sub-tests at their beginning of their shift and immediately at the end of their work shift. As measured by actigraphy, firefighters in this sample slept an average of 5 hours and 20.99 minutes at work, which was significantly less than was found in a large sample of U.S. working adults. Firefighters endorsed poor sleep efficiency and poor sleep quality as assessed by self-report and objective actigraphy. One limitation is that only 12 of the 45 firefighters endorsed responding to a nighttime call during the work night that occurred between the two neuropsychological assessments. Comparing changes in neuropsychological performance between firefighters who had disrupted sleep compared to firefighters who did not, significant performances decrements were evident only for the psychomotor vigilance test (PVT) reaction time. If confirmed with a larger sample, the results suggest that reaction time may be a sensitive indicator of decreasing cognitive performance because of sleep loss. Limitations, future study directions, and recommendations are discussed.
Show less - Date Issued
- 2018
- Identifier
- CFE0007251, ucf:52190
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007251
- Title
- Design of Low-Capacitance Electrostatic Discharge (ESD) Protection Devices in Advanced Silicon Technologies.
- Creator
-
Dong, Aihua, Sundaram, Kalpathy, Fan, Deliang, Gong, Xun, Wei, Lei, Salcedo, Javier, University of Central Florida
- Abstract / Description
-
Electrostatic discharge (ESD) related failure is a major IC reliability concern and this is particularly true as technology continues shrink to nano-metric dimensions. ESD design window research shows that ESD robustness of victim devices keep decreasing from 350nm bulk technology to 7nm FinFET technologies. In the meantime, parasitic capacitance of ESD diode with same It2 in FinFET technologies is approximately 3X compared with that in planar technologies. Thus transition from planar to...
Show moreElectrostatic discharge (ESD) related failure is a major IC reliability concern and this is particularly true as technology continues shrink to nano-metric dimensions. ESD design window research shows that ESD robustness of victim devices keep decreasing from 350nm bulk technology to 7nm FinFET technologies. In the meantime, parasitic capacitance of ESD diode with same It2 in FinFET technologies is approximately 3X compared with that in planar technologies. Thus transition from planar to FinFET technology requires more robust ESD protection however the large parasitic capacitance of ESD protection cell is problematic in high-speed interface design. To reduce the parasitic capacitance, a dual diode silicon controlled rectifier (DD-SCR) is presented in this dissertation. This design can exhibit good trade-offs between ESD robustness and parasitic capacitance characteristics. Besides, different bounding materials lead to performance variations in DD-SCRs are compared. Radio frequency (RF) technology is also demanded low capacitance ESD protection. To address this concern, a ?-network is presented, providing robust ESD protection for 10-60 GHz RF circuit. Like a low pass ? filter, the network can reflect high frequency RF signals and transmit low frequency ESD pulses. Given proper inductor value, networks can work as robust ESD solutions at a certain Giga Hertz frequency range, making this design suitable for broad band protection in RF input/outputs (I/Os). To increase the holding voltage and reduce snapback, a resistor assist triggering heterogeneous stacking structure is presented in this dissertation, which can increase the holding voltage and also keep the trigger voltage nearly as same as a single SCR device.
Show less - Date Issued
- 2018
- Identifier
- CFE0007172, ucf:52251
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007172
- Title
- Intrinsic Modulation Response Modeling and Analysis for Lithographic Vertical-Cavity Surface-Emitting Lasers.
- Creator
-
Li, Mingxin, Deppe, Dennis, Fathpour, Sasan, Wu, Shintson, Malocha, Donald, University of Central Florida
- Abstract / Description
-
Vertical-cavity surface-emitting lasers (VCSELs) have been greatly improved and successfully commercialized over the past few decades owing to their ability to provide both mode and current confinement that enables low energy consumption, high efficiency and high modulation speed. However, further improvement of oxide VCSELs is limited by the nature of the oxide aperture because of self-heating, internal strain and difficulties in precise size control. In this dissertation, VCSELs using...
Show moreVertical-cavity surface-emitting lasers (VCSELs) have been greatly improved and successfully commercialized over the past few decades owing to their ability to provide both mode and current confinement that enables low energy consumption, high efficiency and high modulation speed. However, further improvement of oxide VCSELs is limited by the nature of the oxide aperture because of self-heating, internal strain and difficulties in precise size control. In this dissertation, VCSELs using lithographic approach are demonstrated to overcome the limitations of oxide VCSELs, in which an intra-cavity phase shifting mesa is applied to define the device size and provide optical mode and electrical current confinement instead of an oxide aperture. A newly developed model of intrinsic modulation response is proposed and analyzed to focus on the thermal limit of the modulation speed of VCSELs. The results show that both the temperature dependent differential gain and stimulated emission rate impact laser speed and the stimulated emission rate dominates the speed limit. Thermal limits of modulation response are compared for oxide and lithographic VCSELs for various sizes. The results predict that the intrinsic modulation response can be significantly increased by using lithographic VCSELs due to low thermal resistance and reduced mode volume while maintaining high efficiency. The intrinsic bandwidth could exceed 100 GHz for a 2-?m-diameter lithographic VCSEL. Combined with low electrical parasitics, it is expected to produce over 100 Gb/s data rate from a single directly modulated laser. VCSELs designed for high speed are discussed and their characteristics are demonstrated.
Show less - Date Issued
- 2016
- Identifier
- CFE0006346, ucf:51556
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006346
- Title
- ROLLBACK-ABLE RANDOM NUMBER GENERATORS FOR THE SYNCHRONOUS PARALLEL ENVIRONMENT FOR EMULATION AND DISCRETE-EVENT SIMULATION (SPEEDES).
- Creator
-
Narayanan, Ramaswamy Karthik, Rabelo, Luis, University of Central Florida
- Abstract / Description
-
Random Numbers form the heart and soul of a discrete-event simulation system. There are few situations where the actions of the entities in the process being simulated can be completely predicted in advance. The real world processes are more probabilistic than deterministic. Hence, such chances are represented in the system by using various statistical models, like random number generators. These random number generators can be used to represent a various number of factors, such as length of...
Show moreRandom Numbers form the heart and soul of a discrete-event simulation system. There are few situations where the actions of the entities in the process being simulated can be completely predicted in advance. The real world processes are more probabilistic than deterministic. Hence, such chances are represented in the system by using various statistical models, like random number generators. These random number generators can be used to represent a various number of factors, such as length of the queue. However, simulations have grown in size and are sometimes required to run on multiple machines, which share the various methods or events in the simulation among themselves. These Machines can be distributed across a LAN or even the internet. In such cases, to keep the validity of the simulation model, we need rollback-able random number generators. This thesis is an effort to develop such rollback able random number generators for the Synchronous Parallel Environment for Emulation and Discrete-Event Simulation (SPEEDES) environment developed by NASA. These rollback-able random number generators will also add several statistical distribution models to the already rich SPEEDES library.
Show less - Date Issued
- 2005
- Identifier
- CFE0000328, ucf:46292
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0000328
- Title
- EXAMINING DYNAMIC VARIABLE SPEED LIMIT STRATEGIES FOR THE REDUCTION OF REAL-TIME CRASH RISK ON FREEWAYS.
- Creator
-
Cunningham, Ryan, Abdel-Aty, Mohamed, University of Central Florida
- Abstract / Description
-
Recent research at the University of Central Florida involving crashes on Interstate-4 in Orlando, Florida has led to the creation of new statistical models capable of determining the crash risk on the freeway (Abdel-Aty et al., 2004; 2005, Pande and Abdel-Aty, 2006). These models are able to calculate the rear-end and lane-change crash risks along the freeway in real-time through the use of static information at various locations along the freeway as well as the real-time traffic data...
Show moreRecent research at the University of Central Florida involving crashes on Interstate-4 in Orlando, Florida has led to the creation of new statistical models capable of determining the crash risk on the freeway (Abdel-Aty et al., 2004; 2005, Pande and Abdel-Aty, 2006). These models are able to calculate the rear-end and lane-change crash risks along the freeway in real-time through the use of static information at various locations along the freeway as well as the real-time traffic data obtained by loop detectors. Since these models use real-time traffic data, they are capable of calculating rear-end and lane-change crash risk values as the traffic flow conditions are changing on the freeway. The objective of this study is to examine the potential benefits of variable speed limit implementation techniques for reducing the crash risk along the freeway. Variable speed limits is an ITS strategy that is typically used upstream of a queue in order to reduce the effects of congestion. By lowering the speeds of the vehicles approaching a queue, more time is given for the queue to dissipate from the front before it continues to grow from the back. This study uses variable speed limit strategies in a corridor-wide attempt to reduce rear-end and lane-change crash risks where speed differences between upstream and downstream vehicles are high. The idea of homogeneous speed zones was also introduced in this study to determine the distance over which variable speed limits should be implemented from a station of interest. This is unique since it is the first time a dynamic distance has been considered for variable speed limit implementation. Several VSL strategies were found to successfully reduce the rear-end and lane-change crash risks at low-volume traffic conditions (60% and 80% loading conditions). In every case, the most successful treatments involved the lowering of upstream speed limits by 5 mph and the raising of downstream speed limits by 5 mph. In the free-flow condition (60% loading), the best treatments involved the more liberal threshold for defining homogeneous speed zones (5 mph) and the more liberal implementation distance (entire speed zone), as well as a minimum time period of 10 minutes. This treatment was actually shown to significantly reduce the network travel time by 0.8%. It was also shown that this particular implementation strategy (lowering upstream, raising downstream) is wholly resistant to the effects of crash migration in the 60% loading scenario. In the condition approaching congestion (80% loading), the best treatment again involved the more liberal threshold for homogeneous speed zones (5 mph), yet the more conservative implementation distance (half the speed zone), along with a minimum time period of 5 minutes. This particular treatment arose as the best due to its unique capability to resist the increasing effects of crash migration in the 80% loading scenario. It was shown that the treatments implementing over half the speed zone were more robust against crash migration than other treatments. The best treatment exemplified the greatest benefit in reduced sections and the greatest resistance to crash migration in other sections. In the 80% loading scenario, the best treatment increased the network travel time by less than 0.4%, which is deemed acceptable. No treatment was found to successfully reduce the rear-end and lane-change crash risks in the congested traffic condition (90% loading). This is attributed to the fact that, in the congested state, the speed of vehicles is subject to the surrounding traffic conditions and not to the posted speed limit. Therefore, changing the posted speed limit does not affect the speed of vehicles in a desirable manner. These conclusions agree with Dilmore (2005).
Show less - Date Issued
- 2007
- Identifier
- CFE0001723, ucf:47309
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001723
- Title
- DRIVING SIMULATOR VALIDATION AND REAR-END CRASH RISK ANALYSIS AT A SIGNALISED INTERSECTION.
- Creator
-
Chilakapati, Praveen, Abdel-Aty, Mohamed, University of Central Florida
- Abstract / Description
-
In recent years the use of advanced driving simulators has increased in the transportation engineering field especially in evaluating safety countermeasures. The driving simulator at UCF is a high fidelity simulator with six degrees of freedom. This research aims at validating the simulator in terms of speed and safety with the intention of using it as a test bed for high risk locations and to use it in developing traffic safety countermeasures. The Simulator replicates a real world...
Show moreIn recent years the use of advanced driving simulators has increased in the transportation engineering field especially in evaluating safety countermeasures. The driving simulator at UCF is a high fidelity simulator with six degrees of freedom. This research aims at validating the simulator in terms of speed and safety with the intention of using it as a test bed for high risk locations and to use it in developing traffic safety countermeasures. The Simulator replicates a real world signalized intersection (Alafaya trail (SR-434) and Colonial Drive (SR-50)). A total of sixty one subjects of age ranging from sixteen to sixty years were recruited to drive the simulator for the experiment, which consists of eight scenarios. This research validates the driving simulator for speed, safety and visual aspects. Based on the overall comparisons of speed between the simulated results and the real world, it was concluded that the UCF driving simulator is a valid tool for traffic studies related to driving speed behavior. Based on statistical analysis conducted on the experiment results, it is concluded that SR-434 northbound right turn lane and SR-50 eastbound through lanes have a higher rear-end crash risk than that at SR-50 westbound right turn lane and SR-434 northbound through lanes, respectively. This conforms to the risk of rear-end crashes observed at the actual intersection. Therefore, the simulator is validated for using it as an effective tool for traffic safety studies to test high-risk intersection locations. The driving simulator is also validated for physical and visual aspects of the intersection as 87.10% of the subjects recognized the intersection and were of the opinion that the replicated intersection was good enough or realistic. A binary logistic regression model was estimated and was used to quantify the relative rear-end crash risk at through lanes. It was found that in terms of rear-end crash risk SR50 east- bound approach is 23.67% riskier than the SR434 north-bound approach.
Show less - Date Issued
- 2006
- Identifier
- CFE0001391, ucf:46964
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001391
- Title
- Spray_Deposited Titanium-Oxide Films For Infrared Optics, Photonics, And Solar Cell Applications.
- Creator
-
Alhasan, Sarmad, Peale, Robert, Sundaram, Kalpathy, Mikhael, Wasfy, Abdolvand, Reza, Kar, Aravinda, University of Central Florida
- Abstract / Description
-
Self-assembled TiO2 foam-like films, were grown by the water based Streaming Process for ElectrodelessElectrochemical Deposition (SPEED). The morphology of the 1 m thick films consistsof a tangled ropy structure with individual strands of 200 nm diameter and open pores of 0.1to 3 micron dimensions. Such films are advantageous for proposed perovskite solar cell comprisingCH3NH3PbI3 absorber with additional inorganic films as contact and conduction layers,all deposited by SPEED. Lateral film...
Show moreSelf-assembled TiO2 foam-like films, were grown by the water based Streaming Process for ElectrodelessElectrochemical Deposition (SPEED). The morphology of the 1 m thick films consistsof a tangled ropy structure with individual strands of 200 nm diameter and open pores of 0.1to 3 micron dimensions. Such films are advantageous for proposed perovskite solar cell comprisingCH3NH3PbI3 absorber with additional inorganic films as contact and conduction layers,all deposited by SPEED. Lateral film resistivity is in the range 20 - 200 k-cm, increasing withgrowth temperature, while sheet resistance is in the range 2 ?? 20 108 /Sq. Xray diffractionconfirms presence of TiO2 crystals of orthorhombic class (Brookite). UV-vis spectroscopy showshigh transmission below the expected 3.2 eV TiO2 bandgap. Transmittance increases with growthtemperature. This is a Ropy TiO2 thin film.We also prepared a Smooth TiO2 thin film. Self-assembled TiO2 film deposited by aqueous-spraydeposition was investigated to evaluate morphology, crystalline phase, and infrared optical constants.The Anatase nano-crystalline film had 10 nm characteristic surface roughness sparselypunctuated by defects of not more than 200 nm amplitude. The film is highly transparent throughoutthe visible to wavelengths of 12 m. The indirect band gap was determined to be 3.2 eV. Importantfor long-wave infrared applications is that dispersion in this region is weak compared with themore commonly used dielectic SiO2 for planar structures. The low-cost, large-area, atmosphericpressure,chemical spray deposition method allows conformal fabrication on flexible substrates forlong-wave infrared photonics.For comparison TiO2 films deposited by electron-beam evaporation were evaluated to determinemorphology, crystalline phase, and optical transparency.The evaporated TiO2 film was amorphous but crystallized into Anatase phase after annealing.Such film is attractive as electron conductor of unprecedented thinness and flexibility for proposedperovskite solar cell comprising CH3NH3PbI3 absorber with additional inorganic films as contactand conduction layers. The spray deposition method would allow conformal solar cell fabricationon flexible substrates for wearable power generation. Band gap of Evaporated TiO2 film is 4.0 eV.We prepared BaTiO3 thin film to know infrared pyroelectric response.Self-assembled nano-crystalline BaTiO3 films on stainless steel foil substrates, were grown by thewater based Streaming Process for Electrodeless Electrochemical Deposition (SPEED). SPEED isan aqueous process that deposits self-assembled nano-crystalline inorganic thin films over largeareas, without a vacuum, providing a scalable and manufacturing friendly process to fabricatedurable films. The morphology of the 1m thick films comprises single crystals of micron dimensionsimbedded in a matrix of nanocrystals. XRD confirms presence of BaTiO3 crystals ofhexagonal phase for samples annealed at 500C. Subsequent annealing at 600C transforms thefilm to the cubic phase. Potential applications include dielectric layers, capacitors, waveguides,ferroelectric RAM, pyroelectric infrared detectors, and phosphors. Characterization of infraredpyroelectric response at 10m wavelength shows an initially good sensitivity that reversibly decaysover a period of days due to water vapor absorption. A short-lived photo-response due topoling of the hydrated sample is also observed. We studied BaTiO3 to know hysteresis loop.Pyroelectric photoresponse of aqueous spray deposited thin films containing BaTiO3 nano-crystalsis reported. X-ray diffraction data indicate the presence of hexagonal BaTiO3 nano-crystals with20 nm crystalline domains in a matrix of some as yet unidentified nano-crystalline material.When the film is annealed at 600C, the X-ray pattern changes significantly and indicates a conversionto one of the non-hexagonal phases of BaTiO3 as well as a complete change in the matrix.With suitable amplifier, the measured photoresponse was 40V/W.Ferroelectric hysteresis on a film with significant presence of hexagonal BaTiO3 shows saturatedpolarization which is about 5-times smaller than for the bulk tetragonal phase.
Show less - Date Issued
- 2017
- Identifier
- CFE0006710, ucf:51899
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006710
- Title
- Cryogenic performance projections for ultra-small oxide-free vertical-cavity surface-emitting lasers.
- Creator
-
Bayat, Mina, Deppe, Dennis, Li, Guifang, Schoenfeld, Winston, Lyakh, Arkadiy, University of Central Florida
- Abstract / Description
-
Small-sized vertical-cavity surface-emitting laser (VCSEL) may offer very low power consumption along with high reliability for cryogenic data transfer. Cryogenic data transfer has application in supercomputers and superconducting for efficient computing and also focal plane array cameras operating at 77 K, and at the lower temperature of 4 K for data extraction from superconducting circuits. A theoretical analysis is presented for 77 K and 4 K operation based on small cavity, oxide-free...
Show moreSmall-sized vertical-cavity surface-emitting laser (VCSEL) may offer very low power consumption along with high reliability for cryogenic data transfer. Cryogenic data transfer has application in supercomputers and superconducting for efficient computing and also focal plane array cameras operating at 77 K, and at the lower temperature of 4 K for data extraction from superconducting circuits. A theoretical analysis is presented for 77 K and 4 K operation based on small cavity, oxide-free VCSEL sizes of 2 to 6 (&)#181;m, that have been shown to operate efficiently at room temperature. Temperature dependent operation for optimally-designed VCSELs are studied by calculating the response of the laser at 77 K and 4 K to estimate their bias conditions needed to reach modulation speed for cryogenic optical links. The temperature influence is to decrease threshold for reducing temperature, and to increase differential gain for reducing temperature. The two effects predict very low bias currents for small cavity VCSELs to reach needed data speed for cryogenic optical data links. Projections are made for different cavity structures (half-wave cavity and full-wave cavity) shown that half-wave cavity structure has better performance. Changing the number of top-mirror pairs has also been studied to determine how cavity design impacts speed and bit energy. Our design and performance predictions paves the way for realizing highly efficient, ultra-small VCSEL arrays with applications in optical interconnects.
Show less - Date Issued
- 2019
- Identifier
- CFE0007782, ucf:52330
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007782
