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Pages
- Title
- Nonviolent action: How it works.
- Creator
-
Lakey, George
- Date Issued
- 1963
- Identifier
- 677387, CFDT677387, ucf:5592
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/FCLA/DT/677387
- Title
- Method for Real-Time Signal Selection for Passive Coherent Location Systems.
- Creator
-
Johnson, Nicholas, Jones, W Linwood, Gong, Xun, Mikhael, Wasfy, Rockway, John, Lichtenberg, Christopher, University of Central Florida
- Abstract / Description
-
Passive coherent location (PCL) systems use signals of opportunity to perform traditional radar detection, targeting, and tracking functions. Traditionally these signals include FM radio, digital TV, GSM, and GPS because of their availability in most urban environments. A benefit of having an abundance of signals is the ability to choose which of those best meet the desired system intentions. For example, one may want to choose a digital TV signal over an FM radio signal due to its range...
Show morePassive coherent location (PCL) systems use signals of opportunity to perform traditional radar detection, targeting, and tracking functions. Traditionally these signals include FM radio, digital TV, GSM, and GPS because of their availability in most urban environments. A benefit of having an abundance of signals is the ability to choose which of those best meet the desired system intentions. For example, one may want to choose a digital TV signal over an FM radio signal due to its range resolution characteristics. This work presents a novel algorithm for characterizing commercial signals for use in a PCL system. By analyzing each signal's ambiguity function in terms of amplitude, transmitter geometry, range and Doppler resolution, and sidelobe levels, a comparative evaluation can be made to decide which signals are best suited for an intended radar function. In addition, this research shows that multiple signals can be combined in the detection process to increase the probability of detection over that of a single signal. Finally, this research investigates the geometric considerations for PCL systems in terms of bistatic radar geometry. The results show zones of linear and non-linear relationships between time delay, range, and Doppler frequency.
Show less - Date Issued
- 2017
- Identifier
- CFE0007123, ucf:51964
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007123
- Title
- PASSIVE WIRELESS SAW SENSORS WITH NEW AND NOVEL REFLECTOR STRUCTURES: DESIGN AND APPLICATIONS.
- Creator
-
Kozlovski, Nikolai, Weeks, Arthur, University of Central Florida
- Abstract / Description
-
Surface acoustic wave (SAW) devices are a solution for today's ever growing need for passive wireless sensors. Orthogonal frequency coding (OFC) together with time division multiplexing (TDM) provides a large number of codes and coding algorithms producing devices that have excellent collision properties. Novel SAW noise-like refector (NLR) structures with pulse position modulation (PPM) are shown to exhibit good auto- and cross-correlation, and anti-collision properties. Multi-track, multi...
Show moreSurface acoustic wave (SAW) devices are a solution for today's ever growing need for passive wireless sensors. Orthogonal frequency coding (OFC) together with time division multiplexing (TDM) provides a large number of codes and coding algorithms producing devices that have excellent collision properties. Novel SAW noise-like refector (NLR) structures with pulse position modulation (PPM) are shown to exhibit good auto- and cross-correlation, and anti-collision properties. Multi-track, multi-transducer approaches yield devices with adjustable input impedances and enhanced collision properties for OFC TDM SAW sensor devices. Each track-transducer is designed for optimum performance for loss, coding, and chip reflectivity. Experimental results and theoretical predictions confirm a constant Q for SAW transducers for a given operational bandwidth, independent of device and transducer embodiment. Results on these new NLR SAW structures and devices along with a new novel 915 MHz transceiver based on a software radio approach was designed, built, and analyzed. Passive wireless SAW temperature sensors were interrogated and demodulated in a spread spectrum correlator system using a new adaptive filter. The first-ever SAW OFC four-sensor operation was demonstrated at a distance of 1 meter and a single sensor was shown to operate up to 3 meters. Comments on future work and directions are also presented.
Show less - Date Issued
- 2011
- Identifier
- CFE0003636, ucf:48851
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003636
- Title
- Passive voice usage in undergraduate STEM textbooks.
- Creator
-
Luo, Huiyuan, Mihai, Florin, Nutta, Joyce, Folse, Keith, Bai, Haiyan, University of Central Florida
- Abstract / Description
-
The present study, a corpus-based quantitative analysis, investigated the use of passive voice in terms of percentage (percentage of total passive usage), constructions (the most commonly used passive forms), and dispersion (the verbs that tended to be associated with passive usage) in college STEM textbooks, more specifically in Science, Technology, Engineering, and Mathematics. The corpus consisted of twenty textbooks with over 1 million running words selected from the textbooks' chapters....
Show moreThe present study, a corpus-based quantitative analysis, investigated the use of passive voice in terms of percentage (percentage of total passive usage), constructions (the most commonly used passive forms), and dispersion (the verbs that tended to be associated with passive usage) in college STEM textbooks, more specifically in Science, Technology, Engineering, and Mathematics. The corpus consisted of twenty textbooks with over 1 million running words selected from the textbooks' chapters. By identifying the main verbs and passive verbs used in the textbooks, the percentage of passive voice usage was calculated. The statistical difference of passive constructions between disciplines was examined by conducting a MANOVA test, and an instrument, the Compleat Lexical Tutor was used to generate a word list of the most commonly-used past participles in passive voice.Results showed that the overall percentage of passive voice usage is over 30%. The MANOVA test revealed a statistically significant difference of passive voice constructions across the four disciplines, i.e. Science, Technology, Engineering, and Mathematics.Implications for teaching suggest that passive voice was an important grammar feature that needs to be taught tor the English as a second/foreign language students who major in the STEM fields. Additionally, the use of passive constructions should be taught differently in reading and writing based on the needs of the four STEM disciplines, due to the significant difference of passive forms usage in these fields.
Show less - Date Issued
- 2018
- Identifier
- CFE0007047, ucf:52020
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007047
- Title
- A RADAR INTERROGATOR FOR WIRELESS PASSIVE TEMPERATURE SENSING.
- Creator
-
Lambert, Jeffrey, Gong, Xun, University of Central Florida
- Abstract / Description
-
In this thesis I explore radio detection and ranging (RADAR) and software defined radio (SDR) in the context of wireless passive sensor interrogation. A RADAR topology is selected based upon preliminary measurements using ordinary laboratory instrumentation and then used for construction of a prototype X-band wireless measurement system using commercial, off-the-shelf (COTS) components. This research explores the feasibility of wireless passive sensor interrogation through practical...
Show moreIn this thesis I explore radio detection and ranging (RADAR) and software defined radio (SDR) in the context of wireless passive sensor interrogation. A RADAR topology is selected based upon preliminary measurements using ordinary laboratory instrumentation and then used for construction of a prototype X-band wireless measurement system using commercial, off-the-shelf (COTS) components. This research explores the feasibility of wireless passive sensor interrogation through practical application of SDR and RADAR techniques to the interrogation of a wireless passive resonator signal. This work serves as a foundation for further research on sensor interrogation through establishment of critical system parameters in the design of wireless measurement systems.
Show less - Date Issued
- 2011
- Identifier
- CFE0003631, ucf:48886
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003631
- Title
- RF LOW PASS FILTER DESIGN AND FABRICATION USING INTEGRATED PASSIVE DEVICE TECHNOLOGY.
- Creator
-
Li, Heli, Wu, Thomas, University of Central Florida
- Abstract / Description
-
In this thesis, the whole process of design a low pass filter (LPF) for the wireless communication application has been presented. Integrated passive device technology based on GaAs substrate has been utilized to make the LPF. Schematic simulation and electromagnetic simulations are extensively used in the design process. EM simulation is used in the selection of layout design and processing parameters for design optimization of both the inductors and IPD harmonic filters. The effective use...
Show moreIn this thesis, the whole process of design a low pass filter (LPF) for the wireless communication application has been presented. Integrated passive device technology based on GaAs substrate has been utilized to make the LPF. Schematic simulation and electromagnetic simulations are extensively used in the design process. EM simulation is used in the selection of layout design and processing parameters for design optimization of both the inductors and IPD harmonic filters. The effective use of EM simulation enables us to realize the successful development of high performance harmonic filters. To make the optimization be more flexible and also for a deeper understanding of the optimization theory, optimization using genetic algorithm is also implemented. The weight of each targets are adjustable, and a non-uniformly distributed goal for the harmonic rejection range is introduced to achieve better optimization results. The embedded LPF is built and measurement results show good agreement with the simulation data. This kind of very compact, high performance harmonic filters can be used in radio transceiver front-end modules. The realized harmonic filters have insertion loss less than 0.6 dB and harmonic rejections greater than 25 dB with a compact die size of 0.8 mm2.
Show less - Date Issued
- 2006
- Identifier
- CFE0001466, ucf:47091
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001466
- Title
- EVALUATION OF A MICROWAVE RADIATIVE TRANSFER MODEL FOR CALCULATING SATELLITE BRIGHTNESS TEMPERATURE.
- Creator
-
Thompson, Simonetta, Jones, Linwood, University of Central Florida
- Abstract / Description
-
Remote sensing is the process of gathering and analyzing information about the earth's ocean, land and atmosphere using electromagnetic "wireless" techniques. Mathematical models, known as Radiative Transfer Models (RTM), are developed to calculate the observed radiance (brightness temperature) seen by the remote sensor. The RTM calculated brightness temperature is a function of fourteen environmental parameters, including atmospheric profiles of temperature, pressure and moisture, sea...
Show moreRemote sensing is the process of gathering and analyzing information about the earth's ocean, land and atmosphere using electromagnetic "wireless" techniques. Mathematical models, known as Radiative Transfer Models (RTM), are developed to calculate the observed radiance (brightness temperature) seen by the remote sensor. The RTM calculated brightness temperature is a function of fourteen environmental parameters, including atmospheric profiles of temperature, pressure and moisture, sea surface temperature, and cloud liquid water. Input parameters to the RTM model include data from NOAA Centers for Environmental Prediction (NCEP), Reynolds weekly Sea Surface Temperature and National Ocean Data Center (NODC) WOA98 Ocean Salinity and special sensor microwave/imager (SSM/I) cloud liquid water. The calculated brightness temperatures are compared to collocated measurements from the WindSat satellite. The objective of this thesis is to fine tune the RadTb model, using simultaneous environmental parameters and measured brightness temperature from the well-calibrated WindSat radiometer. The model will be evaluated at four microwave frequencies (6.8 GHz, 10.7 GHz, 18.7 GHz, and 37.0 GHz) looking off- nadir for global radiance measurement.
Show less - Date Issued
- 2004
- Identifier
- CFE0000318, ucf:46280
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0000318
- Title
- Excellent Surface Passivation for High Efficiency C_Si Solar Cells.
- Creator
-
Bakhshi, Sara, Schoenfeld, Winston, Abdolvand, Reza, Sundaram, Kalpathy, Davis, Kristopher, University of Central Florida
- Abstract / Description
-
Semiconductor surface clean is sometimes perceived as costly but long recognized as pivotal in determining the final semiconductor device performance and yield. In this contribution, we investigated the effectiveness of crystalline silicon surface cleaning by a simple UV-ozone process in comparison to the industry standard RCA clean for silicon photovoltaic applications. We present a unique method of processing the silicon surface effectively by UV-ozone cleaning. Despite being simple, UV...
Show moreSemiconductor surface clean is sometimes perceived as costly but long recognized as pivotal in determining the final semiconductor device performance and yield. In this contribution, we investigated the effectiveness of crystalline silicon surface cleaning by a simple UV-ozone process in comparison to the industry standard RCA clean for silicon photovoltaic applications. We present a unique method of processing the silicon surface effectively by UV-ozone cleaning. Despite being simple, UV-ozone cleaning results in a superior surface passivation quality that is comparable to high-quality RCA clean. When used as a stack dielectric(-)UV-ozone oxide overlaid by aluminum oxide(-)the thickness of UV-ozone oxide plays an important role in determining the passivation quality. Of all treatment times, 15 min of UV-ozone treatment results in an outstanding passivation quality, achieving the effective carrier lifetime of 3 ms and saturation current density of 5 fA/cm2. In addition, we present a simple and effective technique to extract values of electron/hole capture cross-section for the purpose of analyzing the interface passivation quality from already measured surface recombination parameters of saturation current density, interfacial trap density and total fixed charge, instead of measuring on the separately prepared metal-insulated-semiconductor (MIS) samples by the techniques: frequency-dependent parallel conductance or deep-level transient spectroscopy.
Show less - Date Issued
- 2018
- Identifier
- CFE0007154, ucf:52313
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007154
- Title
- WIRELESSLY SENSING RESONATE FREQUENCY OF PASSIVE RESONATORS WITH DIFFERENT Q VALUES.
- Creator
-
Lukacs, Mathew, Gong, Xun, University of Central Florida
- Abstract / Description
-
Numerous techniques exist for measuring temperature using passive devices such as SAW filters. However, SAW filters have a significant limitation regarding high temperature environments exceeding 1000C. There are several applications for a high temperature sensor in this range, most notably heat flux or temperature in turbine engines. For these environments, an alternative to SAW filters is to use a passive resonator. The resonate frequency will vary depending on the environment temperature....
Show moreNumerous techniques exist for measuring temperature using passive devices such as SAW filters. However, SAW filters have a significant limitation regarding high temperature environments exceeding 1000C. There are several applications for a high temperature sensor in this range, most notably heat flux or temperature in turbine engines. For these environments, an alternative to SAW filters is to use a passive resonator. The resonate frequency will vary depending on the environment temperature. Understanding how the frequency changes with temperature will allow us to determine the environmental temperature. In order for this approach to work, it is necessary to induce resonance in the device and measure the resonance frequency. However, the extreme high temperature makes wired connections impractical, therefore wireless interrogation is necessary. To be practical a system of wireless interrogation of up to 20cm is desired.
Show less - Date Issued
- 2011
- Identifier
- CFE0003709, ucf:48828
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003709
- Title
- The Frequency of the Passive Voice in Freshman Academic Books.
- Creator
-
Moreb, Basma, Folse, Keith, Mihai, Florin, Young, Beth, University of Central Florida
- Abstract / Description
-
The use of passive voice has long been an area of difficulty for English learners. Celce-Murcia (&) Larsen-Freeman (2015) noted that it is learning when to use the English passive that presents the greatest long-term challenge to ESL/EFL students(") (p. 352). Because textbooks are a source of language input for English learners, this study investigated the frequency of passive voice verbs in samples from four academic textbooks in courses commonly taken by freshmen. The study also examined...
Show moreThe use of passive voice has long been an area of difficulty for English learners. Celce-Murcia (&) Larsen-Freeman (2015) noted that it is learning when to use the English passive that presents the greatest long-term challenge to ESL/EFL students(") (p. 352). Because textbooks are a source of language input for English learners, this study investigated the frequency of passive voice verbs in samples from four academic textbooks in courses commonly taken by freshmen. The study also examined whether there are significant differences between the frequencies by textbook. The data was collected from four General Education Plan (GEP) subject textbooks used in freshman classes at a large metropolitan university in the southeastern United States, namely English composition, history, psychology, and biology. The data was then compiled into a corpus of approximately 20,000 words created specifically for the current study, with 5,000 words randomly and sequentially selected from each of the four textbooks. The study utilized a table created by Folse (2009) to analyze differences between the basic passive voice tenses found in the textbooks. The study examined the be-passives, get-passives, and have-passives and their frequency in different tenses. The findings revealed that passive voice occurred in academic textbooks with an overall frequency of 7.06% (of all conjugated verbs). The results also found significant differences between the academic genres (p (<) 0.05). In this particular corpus, passive voice occurred more in biology than in the other subjects. Therefore, the results of the study indicated a need to explicitly teach the basic be-passive voice to English language learners to all English learners, but teachers also need to be especially aware that certain university subjects (e.g., biology) use more passive voice verb forms than others.
Show less - Date Issued
- 2016
- Identifier
- CFE0006695, ucf:51929
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006695
- Title
- MISCONCEPTIONS ABOUT SILENCE AND PASSIVITY: HOW AMERICAN STUDENTS PERCEIVE ASIAN INTERNATIONAL STUDENTS' USE OF PASSIVITY WITHIN THE CLASSROOM.
- Creator
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Nuru, Audra, Weger, Harry, University of Central Florida
- Abstract / Description
-
Asian international students (AIS) are becoming increasingly more populous in American universities each year. While AIS are enrolled in the same required classes as American students, it has been observed that frequent interaction between AIS and American students is rather uncommon. Due to obvious social hesitation between the two groups of students during classroom discussion, the study presented was initiated in order to unveil possible reasons for this social integration dilemma. Social...
Show moreAsian international students (AIS) are becoming increasingly more populous in American universities each year. While AIS are enrolled in the same required classes as American students, it has been observed that frequent interaction between AIS and American students is rather uncommon. Due to obvious social hesitation between the two groups of students during classroom discussion, the study presented was initiated in order to unveil possible reasons for this social integration dilemma. Social Attractiveness, Perceived Homophily and Attributional Confidence scales were selected in order to determine possible factors contributing to this dilemma. In order to pursue explanations for the dormant socialization between the two groups of students during class, a survey was administered to a convenience sampling of 426 undergraduate students enrolled in upper-level courses at the University of Central Florida. Results indicated that passive classroom behavior was perceived as less socially desirable by American students. In fact, participants determined that students reflecting passive classroom behavior were less socially attractive, less similar, and less predictable than students that demonstrated active classroom behavior. Ethnicity factors did not play a key role in determining social appeal. These findings provide evidence that the social integration dilemma facing AIS and American students has much more to do with perceived social behavior and cultural differences regarding classroom behavior than with racial prejudice or ethnicity factors.
Show less - Date Issued
- 2008
- Identifier
- CFE0002415, ucf:47733
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0002415
- Title
- ON-CHIP SPIRAL INDUCTOR/TRANSFORMER DESIGN AND MODELING FOR RF APPLICATIONS.
- Creator
-
Chen, Ji, Liou, Juin, University of Central Florida
- Abstract / Description
-
Passive components are indispensable in the design and development of microchips for high-frequency applications. Inductors in particular are used frequently in radio frequency (RF) IC's such as low-noise amplifiers and oscillators. High performance inductor has become one of the critical components for voltage controlled oscillator (VCO) design, for its quality factor (Q) value directly affects the VCO phase noise. The optimization of inductor layout can improve its performance, but the...
Show morePassive components are indispensable in the design and development of microchips for high-frequency applications. Inductors in particular are used frequently in radio frequency (RF) IC's such as low-noise amplifiers and oscillators. High performance inductor has become one of the critical components for voltage controlled oscillator (VCO) design, for its quality factor (Q) value directly affects the VCO phase noise. The optimization of inductor layout can improve its performance, but the improvement is limited by selected technology. Inductor performance is bounded by the thin routing metal and small distance from lossy substrate. On the other hand, the in-accurate inductor modeling further limits the optimization process. The on-chip inductor has been an important research topic since it was first proposed in early 1990's. Significant amount of study has been accomplished and reported in literature; whereas some methods have been used in industry, but not released to public. It is of no doubt that a comprehensive solution is not exist yet. A comprehensive study of previous will be first address. Later author will point out the in-adequacy of skin effect and proximity effect as cause of current crowding in the inductor metal. A model method embedded with new explanation of current crowding is proposed and its applicability in differential inductor and balun is validated. This study leads to a robust optimization routine to improve inductor performance without any addition technology cost and development.
Show less - Date Issued
- 2006
- Identifier
- CFE0001364, ucf:46962
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001364
- Title
- DESIGN AND SIMULATION FOR ENCODED PN-OFC SAW SENSOR SYSTEMS.
- Creator
-
Pavlina, John, Malocha, Donald, University of Central Florida
- Abstract / Description
-
Surface acoustic wave (SAW) sensors provide versatility in that they can offer wireless, passive operation in numerous environments. Various SAW device embodiments may also be employed for retrieval of the sensed data. Single sensor systems typically use a single carrier frequency and a simple device embodiment since tagging is not required. However, it is necessary in a multi-sensor environment to both identify the sensor and retrieve the information. Overlapping sensor data signals in time...
Show moreSurface acoustic wave (SAW) sensors provide versatility in that they can offer wireless, passive operation in numerous environments. Various SAW device embodiments may also be employed for retrieval of the sensed data. Single sensor systems typically use a single carrier frequency and a simple device embodiment since tagging is not required. However, it is necessary in a multi-sensor environment to both identify the sensor and retrieve the information. Overlapping sensor data signals in time and frequency present problems when attempting to collect the sensed data at the receiver. This dissertation defines a system simulation environment exclusive to SAW sensors. The major parameters associated with a multi-device system include the transmitter, the channel, and the receiver characteristics. These characteristics are studied for implementation into the simulation environment. A coupling of modes (COM) model for SAW devices is utilized as an accurate software representation of the various SAW devices. Measured device results are presented and compared with COM model predictions to verify performance of devices and system. Several coding techniques to alleviate code collisions and detection errors were investigated and evaluated. These specialized techniques apply the use of time, frequency, and spatial diversity to the devices. Utilizing these multiple-access techniques a multi-device system is realized. An optimal system based on coding technique, frequency of operation, range, and related parameters is presented. Funding for much of this work was provided through STTR contracts from NASA Kennedy Space Center.
Show less - Date Issued
- 2010
- Identifier
- CFE0003124, ucf:48630
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003124
- Title
- Study of Surface Passivation Behavior of Crystalline Silicon Solar Cells.
- Creator
-
Ali, Haider, Schoenfeld, Winston, Coffey, Kevin, Gaume, Romain, Thomas, Jayan, Chanda, Debashis, University of Central Florida
- Abstract / Description
-
To achieve efficiencies approaching the theoretical limit of 29.4% for industrially manufactured solar cells based on crystalline silicon, it is essential to have very low surface recombination velocities at both the front and rear surfaces of the silicon substrate. Typically, the substrate surfaces feature contacted and uncontacted regions, and recombination should be limited for both to maximize the energy conversion efficiency.Uncontacted silicon surfaces are often passivated by the...
Show moreTo achieve efficiencies approaching the theoretical limit of 29.4% for industrially manufactured solar cells based on crystalline silicon, it is essential to have very low surface recombination velocities at both the front and rear surfaces of the silicon substrate. Typically, the substrate surfaces feature contacted and uncontacted regions, and recombination should be limited for both to maximize the energy conversion efficiency.Uncontacted silicon surfaces are often passivated by the deposition of silicon nitride (SiNx) or an aluminum oxide film with SiNx as capping layer (Al2O3/SiNx stack). Further, proper surface preparation and cleaning of Si wafers prior to deposition also plays an important role in minimizing surface recombination. In the present work, the effect of various cleans based on different combinations of HCl, HF, HNO3, and ozonated deionized water (DIO3) on surface passivation quality of boron-diffused and undiffused {100} n-type Cz Si wafers was studied. It was observed that for SiNx passivated Si, carrier lifetime was strongly influenced by cleaning variations and that a DIO3-last treatment resulted in higher lifetimes. Moreover, DIO3+HF+HCl?HF?DIO3 and HNO3?HF?HNO3 cleans emerged as potential low-cost alternatives to HCl/HF clean in the photovoltaics industry.Transmission electron microscopy (TEM) studies were carried out to get insight into the origin of variation in carrier lifetimes for different cleans. Changes in the surface cleans used were not found to have a significant impact on Al2O3/SiNx passivation stacks.ivHowever, an oxide-last cleaning step prior to deposition of SiNx passivation layers was found to create a 1-2 nm SiOx tunnel layer resulting in excellent carrier lifetimes.For contacted regions, low surface recombination can be achieved using passivated carrier selective contacts, which not only passivate the silicon surface and improve the open circuit voltage, but are also carrier selective. This means they only allow the majority carrier to be transported to the metal contacts, limiting recombination by reducing the number of minority carriers. Typically, carrier selectivity is achieved using a thin metal oxide layer, such as titanium oxide (TiO2) for electron-selective contacts and molybdenum oxide (MoOx) for hole-selective contacts. This is normally coupled with a very thin passivation layer (e.g., a-Si:H, SiOx) between the silicon wafer and the contact.In the present work, TiO2-based electron-selective passivated rear contacts were investigated for n-type c-Si solar cells. A low efficiency of 9.8% was obtained for cells featuring a-Si:H/TiO2 rear contact, which can be attributed to rapid degradation of surface passivation of a-Si:H upon FGA at 350(&)deg;C due to hydrogen evolution leading to generation of defect states which increases recombination and hence a much lower Voc of 365 mV is obtained. On the other hand, 21.6% efficiency for cells featuring SiO2/TiO2 rear contact is due to excellent passivation of SiO2/TiO2 stack upon FGA anneal, which can be attributed to the presence of 1-2 nm SiO2 layer whose passivation performance improves upon FGA at 350(&)deg;C whereas presence of large number of oxygen vacancies in TiO2-x reduces rear contact resistivity.vLikewise, MoOx-based contacts were investigated as hole-selective front contacts for an n-type cell with a boron-doped emitter. It has been previously reported that cell efficiencies up to 22.5% have been achieved with silicon heterojunction solar cells featuring a front contact wherein MoOx is inserted between a-Si:H(i) and hydrogenated indium oxide (IO:H). However, device performance and FF degrades upon annealing beyond 130(&)deg;C. In this work, contact resistivity measurements by TLM technique in combination with TEM studies revealed that degradation of device performance is due to oxygen diffusion into MoOx upon annealing in air which reduces concentration of oxygen vacancies in MoOx and increases contact resistivity. The increase in contact resistivity reduces FF resulting in deterioration of device performance.
Show less - Date Issued
- 2017
- Identifier
- CFE0006554, ucf:51351
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006554
- Title
- Microwave Radiometer (MWR) Evaluation of Multi-Beam Satellite Antenna Boresight Pointing Using Land-Water Crossings, for the Aquarius/SAC-D Mission.
- Creator
-
Clymer, Bradley, Jones, W Linwood, Mikhael, Wasfy, Flitsiyan, Elena, University of Central Florida
- Abstract / Description
-
This research concerns the CONAE Microwave Radiometer (MWR), on board the Aquarius/SAC-D platform. MWR's main purpose is to provide measurements that are simultaneous and spatially collocated with those of NASA's Aquarius radiometer/scatterometer. For this reason, knowledge of the MWR antenna beam footprint geolocation is crucial to mission success.In particular, this thesis addresses an on-orbit validation of the MWR antenna beam pointing, using calculated MWR instantaneous field of view ...
Show moreThis research concerns the CONAE Microwave Radiometer (MWR), on board the Aquarius/SAC-D platform. MWR's main purpose is to provide measurements that are simultaneous and spatially collocated with those of NASA's Aquarius radiometer/scatterometer. For this reason, knowledge of the MWR antenna beam footprint geolocation is crucial to mission success.In particular, this thesis addresses an on-orbit validation of the MWR antenna beam pointing, using calculated MWR instantaneous field of view (IFOV) centers, provided in the CONAE L-1B science data product. This procedure compares L-1B MWR IFOV centers at land/water crossings against high-resolution coastline maps. MWR IFOV locations versus time are computed from knowledge of the satellite's instantaneous location relative to an earth-centric coordinate system (provided by on-board GPS receivers), and a priori measurements of antenna gain patterns and mounting geometry.Previous conical scanning microwave radiometer missions (e.g., SSM/I) have utilized observation of rapid change in brightness temperatures (T_B) to estimate the location of land/water boundaries, and subsequently to determine the antenna beam-pointing accuracy. In this thesis, results of an algorithm to quantify the geolocation error of MWR beam center are presented, based upon two-dimensional convolution between each beam's gain pattern and land-water transition. The analysis procedures have been applied to on-orbit datasets that represent land-water boundaries bearing specific desirable criteria, which are also detailed herein. The goal of this research is to gain a better understanding of satellite radiometer beam-pointing error and thereby to improve the geolocation accuracy for MWR science data products.
Show less - Date Issued
- 2015
- Identifier
- CFE0005591, ucf:50269
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005591
- Title
- AN OCEAN SURFACE WIND VECTOR MODEL FUNCTION FOR A SPACEBORNE MICROWAVE RADIOMETER AND ITS APPLICATION.
- Creator
-
Soisuvarn, Seubson, Jones, W. Linwood, University of Central Florida
- Abstract / Description
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Ocean surface wind vectors over the ocean present vital information for scientists and forecasters in their attempt to understand the Earth's global weather and climate. As the demand for global wind velocity information has increased, the number of satellite missions that carry wind-measuring sensors has also increased; however, there are still not sufficient numbers of instruments in orbit today to fulfill the need for operational meteorological and scientific wind vector data. Over the...
Show moreOcean surface wind vectors over the ocean present vital information for scientists and forecasters in their attempt to understand the Earth's global weather and climate. As the demand for global wind velocity information has increased, the number of satellite missions that carry wind-measuring sensors has also increased; however, there are still not sufficient numbers of instruments in orbit today to fulfill the need for operational meteorological and scientific wind vector data. Over the last three decades operational measurements of global ocean wind speeds have been obtained from passive microwave radiometers. Also, vector ocean surface wind data were primarily obtained from several scatterometry missions that have flown since the early 1990's. However, other than SeaSat-A in 1978, there has not been combined active and passive wind measurements on the same satellite until the launch of the second Advanced Earth Observing Satellite (ADEOS-II) in 2002. This mission has provided a unique data set of coincident measurements between the SeaWinds scatterometer and the Advanced Microwave Scanning Radiometer (AMSR). AMSR observes the vertical and horizontal brightness temperature (TB) at six frequency bands between 6.9 GHz and 89.0 GHz. Although these measurements contain some wind direction information, the overlying atmospheric influence can easily obscure this signal and make wind direction retrieval from passive microwave measurements very difficult. However, at radiometer frequencies between 10 and 37 GHz, a certain linear combination of vertical and horizontal brightness temperatures causes the atmospheric dependence to be nearly cancelled and surface parameters such as wind speed, wind direction and sea surface temperature to dominate the resulting signal. This brightness temperature combination may be expressed as ATBV-TBH, where A is a constant to be determined and the TBV and TBH are the brightness temperatures for the vertical and horizontal polarization respectively. In this dissertation, an empirical relationship between the AMSR's ATBV-TBH and SeaWinds' surface wind vector retrievals was established for three microwave frequencies: 10, 18 and 37 GHz. This newly developed model function for a passive microwave radiometer could provide the basis for wind vector retrievals either separately or in combination with scatterometer measurements.
Show less - Date Issued
- 2006
- Identifier
- CFE0001493, ucf:47088
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001493
- Title
- HIGH POWER MODE-LOCKED SEMICONDUCTOR LASERS AND THEIR APPLICATIONS.
- Creator
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Lee, Shinwook, Delfyett, Peter, University of Central Florida
- Abstract / Description
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In this dissertation, a novel semiconductor mode-locked oscillator which is an extension of eXtreme Chirped Pulse Amplification (XCPA) is investigated. An eXtreme Chirped Pulse Oscillator (XCPO) implemented with a Theta cavity also based on a semiconductor gain is presented for generating more than 30ns frequency-swept pulses with more than 100pJ of pulse energy and 3.6ps compressed pulses directly from the oscillator. The XCPO shows the two distinct characteristics which are the scalability...
Show moreIn this dissertation, a novel semiconductor mode-locked oscillator which is an extension of eXtreme Chirped Pulse Amplification (XCPA) is investigated. An eXtreme Chirped Pulse Oscillator (XCPO) implemented with a Theta cavity also based on a semiconductor gain is presented for generating more than 30ns frequency-swept pulses with more than 100pJ of pulse energy and 3.6ps compressed pulses directly from the oscillator. The XCPO shows the two distinct characteristics which are the scalability of the output energy and the mode-locked spectrum with respect to repetition rate. The laser cavity design allows for low repetition rate operation <100MHz. The cavity significantly reduces nonlinear carrier dynamics, integrated self phase modulation (SPM), and fast gain recovery in a Semiconductor optical Amplifier (SOA). Secondly, a functional device, called a Grating Coupled Surface Emitting Laser (GCSEL) is investigated. For the first time, passive and hybrid mode-locking of a GCSEL is achieved by using saturable absorption in the passive section of GCSEL. To verify the present limitation of the GCSEL for passive and hybrid mode-locking, a dispersion matched cavity is explored. In addition, a Grating Coupled surface emitting Semiconductor Optical Amplifier (GCSOA) is also investigated to achieve high energy pulse. An energy extraction experiment for GCSOA using stretched pulses generated from the colliding pulse semiconductor mode-locked laser via a chirped fiber bragg grating, which exploits the XCPA advantages is also demonstrated. Finally, passive optical cavity amplification using an enhancement cavity is presented. In order to achieve the interferometric stability, the Hänsch-Couillaud Method is employed to stabilize the passive optical cavity. The astigmatism-free optical cavity employing an acousto-optic modulator (AOM) is designed and demonstrated. In the passive optical cavity, a 7.2 of amplification factor is achieved with a 50 KHz dumping rate.
Show less - Date Issued
- 2008
- Identifier
- CFE0002093, ucf:47555
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0002093
- Title
- Surface Acoustic Wave (SAW) Cryogenic Liquid and Hydrogen Gas Sensors.
- Creator
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Fisher, Brian, Malocha, Donald, Gong, Xun, Likamwa, Patrick, Richie, Samuel, Youngquist, Robert, University of Central Florida
- Abstract / Description
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This research was born from NASA Kennedy Space Center's (KSC) need for passive, wireless and individually distinguishable cryogenic liquid and H2 gas sensors in various facilities. The risks of catastrophic accidents, associated with the storage and use of cryogenic fluids may be minimized by constant monitoring. Accidents involving the release of H2 gas or LH2 were responsible for 81% of total accidents in the aerospace industry. These problems may be mitigated by the implementation of a...
Show moreThis research was born from NASA Kennedy Space Center's (KSC) need for passive, wireless and individually distinguishable cryogenic liquid and H2 gas sensors in various facilities. The risks of catastrophic accidents, associated with the storage and use of cryogenic fluids may be minimized by constant monitoring. Accidents involving the release of H2 gas or LH2 were responsible for 81% of total accidents in the aerospace industry. These problems may be mitigated by the implementation of a passive (or low-power), wireless, gas detection system, which continuously monitors multiple nodes and reports temperature and H2 gas presence. Passive, wireless, cryogenic liquid level and hydrogen (H2) gas sensors were developed on a platform technology called Orthogonal Frequency Coded (OFC) surface acoustic wave (SAW) radio frequency identification (RFID) tag sensors. The OFC-SAW was shown to be mechanically resistant to failure due to thermal shock from repeated cycles between room to liquid nitrogen temperature. This suggests that these tags are ideal for integration into cryogenic Dewar environments for the purposes of cryogenic liquid level detection. Three OFC-SAW H2 gas sensors were simultaneously wirelessly interrogated while being exposed to various flow rates of H2 gas. Rapid H2 detection was achieved for flow rates as low as 1ccm of a 2% H2, 98% N2 mixture. A novel method and theory to extract the electrical and mechanical properties of a semiconducting and high conductivity thin-film using SAW amplitude and velocity dispersion measurements were also developed. The SAW device was shown to be a useful tool in analysis and characterization of ultrathin and thin films and physical phenomena such as gas adsorption and desorption mechanisms.?
Show less - Date Issued
- 2012
- Identifier
- CFE0004536, ucf:49258
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004536
- Title
- Mechanism of Hip Dysplasia and Identification of the Least Energy Path for its Treatment by using the Principle of Stationary Potential Energy.
- Creator
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Zwawi, Mohammed abdulwahab m, Moslehy, Faissal, Kassab, Alain, Mansy, Hansen, Divo, Eduardo, University of Central Florida
- Abstract / Description
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Developmental dysplasia of the hip (DDH) is a common newborn condition where the femoral head is not located in its natural position in the acetabulum (hip socket). Several treatment methods are being implemented worldwide to treat this abnormal condition. One of the most effective methods of treatment is the use of Pavlik Harness, which directs the femoral head toward the natural position inside the acetabulum. This dissertation presents a developed method for identifying the least energy...
Show moreDevelopmental dysplasia of the hip (DDH) is a common newborn condition where the femoral head is not located in its natural position in the acetabulum (hip socket). Several treatment methods are being implemented worldwide to treat this abnormal condition. One of the most effective methods of treatment is the use of Pavlik Harness, which directs the femoral head toward the natural position inside the acetabulum. This dissertation presents a developed method for identifying the least energy path that the femoral head would follow during reduction. This is achieved by utilizing a validated computational biomechanical model that allows the determination of the potential energy, and then implementing the principle of stationary potential energy. The potential energy stems from strain energy stored in the muscles and gravitational potential energy of four rigid-body components of lower limb bones. Five muscles are identified and modeled because of their effect on DDH reduction. Clinical observations indicate that reduction with the Pavlik Harness occurs passively in deep sleep under the combined effects of gravity and the constraints of the Pavlik Harness.A non-linear constitutive equation, describing the passive muscle response, is used in the potential energy computation. Different DDH abnormalities with various flexion, abduction, and hip rotation angles are considered, and least energy paths are identified. Several constraints, such as geometry and harness configuration, are considered to closely simulate real cases of DDH. Results confirm the clinical observations of two different pathways for closed reduction. The path of least energy closely approximated the modified Hoffman-Daimler method. Release of the pectineus muscle favored a more direct pathway over the posterior rim of the acetabulum. The direct path over the posterior rim of the acetabulum requires more energy. This model supports the observation that Grade IV dislocations may require manual reduction by the direct path. However, the indirect path requires less energy and may be an alternative to direct manual reduction of Grade IV infantile hip dislocations. Of great importance, as a result of this work, identifying the minimum energy path that the femoral head would travel would provide a non-surgical tool that effectively aids the surgeon in treating DDH.?
Show less - Date Issued
- 2015
- Identifier
- CFE0006022, ucf:51000
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006022
- Title
- Integrated Microwave Resonator/Antenna Structures for Sensor and Filter Applications.
- Creator
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Cheng, Haitao, Gong, Xun, Wahid, Parveen, Wu, Thomas, Kapoor, Vikram, An, Linan, University of Central Florida
- Abstract / Description
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This dissertation presents design challenges and promising solutions for temperature and pressure sensors which are highly desirable for harsh-environment applications, such as turbine engines. To survive the harsh environment consisting of high temperatures above 1000oC, high pressures around 300 psi, and corrosive gases, the sensors are required to be robust both electrically and mechanically. In addition, wire connection of the sensors is a challenging packaging problem, which remains...
Show moreThis dissertation presents design challenges and promising solutions for temperature and pressure sensors which are highly desirable for harsh-environment applications, such as turbine engines. To survive the harsh environment consisting of high temperatures above 1000oC, high pressures around 300 psi, and corrosive gases, the sensors are required to be robust both electrically and mechanically. In addition, wire connection of the sensors is a challenging packaging problem, which remains unresolved as of today. In this dissertation, robust ceramic sensors are demonstrated for both high temperature and pressure measurements. Also, the wireless sensors are achieved based on microwave resonators.Two types of temperature sensors are realized using integrated resonator/antennas and reflective patches, respectively. Both types of the sensors utilize alumina substrate which has a temperature-dependent dielectric constant. The temperature in the harsh environment is wirelessly detected by measuring the resonant frequency of the microwave resonator, which is dependent on the substrate permittivity. The integrated resonator/antenna structure minimizes the sensor dimension by adopting a seamless design between the resonator sensor and antenna. This integration technique can be also used to achieve an antenna array integrated with cavity filters. Alternatively, the aforementioned reflective patch sensor works simultaneously as a resonator sensor and a radiation element. Due to its planar structure, the reflective patch sensor is easy for design and fabrication. Both temperature sensors are measured above 1000oC.A pressure sensor is also demonstrated for high-temperature applications. Pressure is detected via the change in resonant frequency of an evanescent-mode resonator which corresponds to cavity deformation under gas pressure. A compact sensor size is achieved with a post loading the cavity resonator and a low-profile antenna connecting to the sensor. Polymer-Derived-Ceramic (PDC) is developed and used for the sensor fabrication. The pressure sensor is characterized under various pressures at high temperatures up to 800oC. In addition, to facilitate sensor characterizations, a robust antenna is developed in order to wirelessly interrogate the sensors. This specially-developed antenna is able to survive a record-setting temperature of 1300oC.
Show less - Date Issued
- 2014
- Identifier
- CFE0005473, ucf:50335
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005473
