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Pages
- Title
- Wavelength scale resonant structures for integrated photonic applications.
- Creator
-
Weed, Matthew, Schoenfeld, Winston, Moharam, M., Likamwa, Patrick, Delfyett, Peter, Leuenberger, Michael, University of Central Florida
- Abstract / Description
-
An approach to integrated frequency-comb filtering is presented, building from a background in photonic crystal cavity design and fabrication. Previous work in the development of quantum information processing devices through integrated photonic crystals consists of photonic band gap engineering and methods of on-chip photon transfer. This work leads directly to research into coupled-resonator optical waveguides which stands as a basis for the primary line of investigation. These coupled...
Show moreAn approach to integrated frequency-comb filtering is presented, building from a background in photonic crystal cavity design and fabrication. Previous work in the development of quantum information processing devices through integrated photonic crystals consists of photonic band gap engineering and methods of on-chip photon transfer. This work leads directly to research into coupled-resonator optical waveguides which stands as a basis for the primary line of investigation. These coupled cavity systems offer the designer slow light propagation which increases photon lifetime, reduces size limitations toward on-chip integration, and offers enhanced light-matter interaction. A unique resonant structure explained by various numerical models enables comb-like resonant clusters in systems that otherwise have no such regular resonant landscape (e.g. photonic crystal cavities). Through design, simulation, fabrication and test, the work presented here is a thorough validation for the future potential of coupled-resonator filters in frequency comb laser sources.
Show less - Date Issued
- 2013
- Identifier
- CFE0004957, ucf:49568
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004957
- Title
- Microstrip Patch Electrically Steerable Parasitic Array Radiators.
- Creator
-
Luther, Justin, Gong, Xun, Wahid, Parveen, Jones, W, Wu, Xinzhang, Flitsiyan, Elena, University of Central Florida
- Abstract / Description
-
This dissertation explores the expansion of the Electrically Steerable Parasitic Array Radiator (ESPAR) technology to arrays using microstrip patch elements. Scanning arrays of two and three closely-coupled rectangular patch elements are presented, which incorporate no phase shifters. These arrays achieve directive radiation patterns and scanning of up to 26(&)deg; with maintained impedance match. The scanning is effected by tunable reactive loads which are used to control the mutual coupling...
Show moreThis dissertation explores the expansion of the Electrically Steerable Parasitic Array Radiator (ESPAR) technology to arrays using microstrip patch elements. Scanning arrays of two and three closely-coupled rectangular patch elements are presented, which incorporate no phase shifters. These arrays achieve directive radiation patterns and scanning of up to 26(&)deg; with maintained impedance match. The scanning is effected by tunable reactive loads which are used to control the mutual coupling between the elements, as well as additional loads which compensate to maintain the appropriate resonant frequency. The design incorporates theoretical analysis of the system of coupled antennas with full-wave simulation. A prototype of the three-element array at 1 GHz is fabricated and measured to exhibit a maximum gain of 7.4 dBi with an efficiency of 79.1%. Further, the microstrip ESPAR is thoroughly compared to uniformly-illuminated arrays of similar size. To satisfy the need for higher directivity antennas with inexpensive electronic scanning, the microstrip ESPAR is then integrated as a subarray. The three-element subcell fabrication is simplified to a single layer with an inverted-Y groove in the ground plane, allowing for DC biasing without the need for the radial biasing stubs or tuning stubs found in the two-layer design. The 1 GHz ESPAR array employs a corporate feed network consisting of a Wilkinson power divider with switchable delay line phase shifts, ring hybrid couplers, and achieves a gain of 12.1 dBi at boresight with (&)#177;20(&)deg; scanning and low side lobes. This array successfully illustrates the cost savings associated with ESPAR subarray scanning and the associated reduction in required number of phase shifters in the RF front end.
Show less - Date Issued
- 2013
- Identifier
- CFE0005107, ucf:50754
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005107
- Title
- hydro-thermo-mechanical behavior of concrete at elevated temperatures.
- Creator
-
Al Fadul, Manar, Mackie, Kevin, Makris, Nicos, Chopra, Manoj, Kar, Aravinda, University of Central Florida
- Abstract / Description
-
In the light of recent tragic events, such as, natural disasters, arson and terrorism, studying the thermo mechanical behavior of concrete at elevated temperatures has become of special concern. In addition, the fact that concrete has been widely used as a structural material in many critical applications, such as high rise buildings, pressure vessels, and nuclear plants, enhances the potential risk of exposing concrete to high temperatures. Accordingly, the potential damage to large-scale...
Show moreIn the light of recent tragic events, such as, natural disasters, arson and terrorism, studying the thermo mechanical behavior of concrete at elevated temperatures has become of special concern. In addition, the fact that concrete has been widely used as a structural material in many critical applications, such as high rise buildings, pressure vessels, and nuclear plants, enhances the potential risk of exposing concrete to high temperatures. Accordingly, the potential damage to large-scale structures during the course of the fire, besides the possible loss of human life, emphasizes the necessity to better understand the thermo-structural behavior and failure mechanism of concrete exposed to elevated temperatures. In this study, a one-dimensional model that describes coupled heat and mass transfer phenomena in heated concrete was developed. The mathematical model is based on the fully implicit finite difference scheme. The control volume approach was employed in the formulation of the finite difference equations. The primary variables considered in the analysis are temperature, vapor density, and pore pressure of the gaseous mixture. Several phenomena have been taken into account, such as evaporation, condensation, and dehydration process. Temperature, pressure, and moisture dependent properties of both gaseous and solid phases were also considered. Moreover, the proposed model is capable of predicting pore pressure values with a sufficient accuracy, which could be significantly important for the prediction of spalling and fire resistance of concrete. The two dimensional coupled heat and mass transfer problem was then studied by extending the proposed one dimensional model so that it can be applicable in solving two-dimensional problems. Output from the numerical model showed that the maximum values of temperature, pressure, and moisture content occur in the corner zone of the concrete cross section, in which the pore pressure builds up right next to the moisture pocket towards the center. In addition, the model demonstrates the capability to solve the coupled problem in situations involving non symmetric boundary conditions, in which conducting a one dimensional analysis is of no use. The contour plots of the temperature, pressure, and moisture were also presented.Simulation results clearly indicate the capability of the proposed model to capture the complex behavior of the concrete exposed to elevated temperatures in two dimensional systems and to adequately predict the coupled heat and mass transfer phenomena of the heated concrete over the entire flow domain. In order to predict the structural behavior of reinforced concrete members exposed to elevated temperatures, a three-dimensional fiber beam model was developed in this study to compute the mechanical responses of reinforced concrete structures at elevated temperatures by using the well-known sectional analysis approach. The temperature distributions obtained from the two-dimensional coupled heat and mass transfer analysis were used as an input to the strength analysis. The model also accounts for the various strain components that might generate in concrete and steel due to the effect of high temperatures. The constitutive models that describe the structural behavior of concrete and steel at elevated temperatures were also presented. In order to establish the validity of the proposed fiber model, a sequentially coupled thermo mechanical analysis was implemented, in which the model predictions were compared against measured data from tests with good qualitative agreement. The developed model can be considered as an efficient and powerful tool to promptly assess the structural behavior and the integrity of the structure during emergency situations, such as fire events.
Show less - Date Issued
- 2017
- Identifier
- CFE0006551, ucf:51340
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006551
- Title
- The Influence of Stigma on Quality of Life and Relationship Satisfaction for Prostate Cancer Survivors and Their Partners.
- Creator
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Wood, Andrew, Barden, Sejal, Daire, Andrew, Lambie, Glenn, Munyon, Matthew, Conley, Abigail, University of Central Florida
- Abstract / Description
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The purpose of this study was to examine the relationships between stigma, quality of life (QoL), and relationships satisfaction for prostate cancer (PCa) survivors and their intimate and/or romantic partners. The investigator tested a theoretical model that stigma (as measured by the Social Impact Scale [SIS; Fife (&) Wright, 2000]) influenced QoL (as measured by the Functional Assessment of Cancer Therapy (-) Prostate [FACT-P; Esper et al., 1997] and the Functional Assessment of Cancer...
Show moreThe purpose of this study was to examine the relationships between stigma, quality of life (QoL), and relationships satisfaction for prostate cancer (PCa) survivors and their intimate and/or romantic partners. The investigator tested a theoretical model that stigma (as measured by the Social Impact Scale [SIS; Fife (&) Wright, 2000]) influenced QoL (as measured by the Functional Assessment of Cancer Therapy (-) Prostate [FACT-P; Esper et al., 1997] and the Functional Assessment of Cancer Therapy (-) General Population [FACT-GP; Cella et al., 1993]) and relationship satisfaction (as measured by the Couples Satisfaction Index [CSI; Funk (&) Rogge, 2007]) for both PCa survivors and their partners (N = 72 couples). The investigator hypothesized that stigma would have a negative influence on both QoL and relationship satisfaction. Further, exploratory research questions pertained to the influence of race on stigma, QoL, and relationship satisfaction, as well as examining difference in experiences of stigma based on demographic variables (e.g., age and income).The results of the structural equation model analyses identified that stigma negatively influenced QoL (R2 = .84, p (<) .05) and relationship satisfaction (R2 = .19, p (<) .05) for both PCa survivors and their partners. Race did not have statistically significant (p (>) .05) relationships with stigma, QoL, or relationship satisfaction and stigma was not found to be statistically different (p (>) .05) based on demographic variables. Implications of the results of the study include (a) practical implications for PCa survivors and their partners; (b) strategies for effective individual, group, and couples-based counseling; (c) need for counselor educators to prepare counselors to work with medically ill populations and cancer survivors; (d) PCa stigma instrument development; and (e) the necessity to examine research with couples in a dyadic fashion.
Show less - Date Issued
- 2015
- Identifier
- CFE0005742, ucf:50112
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0005742
- Title
- INELASTIC DYNAMIC BEHAVIOR AND DESIGN OF HYBRID COUPLED WALL SYSTEMS.
- Creator
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Hassan, Mohamed Ali, El-Tawil, Sherif, University of Central Florida
- Abstract / Description
-
A key consideration in seismic design of buildings is to ensure that the lateral load resisting system has an appropriate combination of strength, stiffness and energy dissipation capacity. Hybrid coupled wall systems, in which steel beams are used to couple two or more reinforced concrete shear walls in series, can be designed to have these attributes and therefore have the potential to deliver good performance under severe seismic loading. This research presents an investigation of the...
Show moreA key consideration in seismic design of buildings is to ensure that the lateral load resisting system has an appropriate combination of strength, stiffness and energy dissipation capacity. Hybrid coupled wall systems, in which steel beams are used to couple two or more reinforced concrete shear walls in series, can be designed to have these attributes and therefore have the potential to deliver good performance under severe seismic loading. This research presents an investigation of the seismic behavior of this type of structural system. System response of 12- and 18-story high prototypes is studied using transient finite element analyses that accounts for the most important aspects of material nonlinear behavior including concrete cracking, tension stiffening, and compressive behavior for both confined and unconfined concrete as well as steel yielding. The developed finite element models are calibrated using more detailed models developed in previous research and are validated through numerous comparisons with test results of reinforced concrete walls and wall-beam subassemblages. Suites of transient inelastic analyses are conducted to investigate pertinent parameters including hazard level, earthquake record scaling, dynamic base shear magnification, interstory drift, shear distortion, coupling beam plastic rotation, and wall rotation. Different performance measures are proposed to judge and compare the behavior of the various systems. The analyses show that, in general, hybrid coupled walls are particularly well suited for use in regions of high seismic risk. The results of the dynamic analyses are used to judge the validity of and to refine a previously proposed design method based on the capacity design concept and the assumption of behavior dominated by the first vibration mode. The adequacy of design based on the pushover analysis procedure as promoted in FEMA-356 (2000) is also investigated using the dynamic analysis results. Substantial discrepancies between both methods are observed, especially in the case of the 18-story system. A critical assessment of dynamic base shear magnification is also conducted, and a new method for estimating its effects is suggested. The method is based on a modal combination procedure that accounts for presence of a plastic hinge at the wall base. Finally, the validity of limitations in FEMA-368 (2000) on building height, particularly for hybrid coupled wall systems, is discussed.
Show less - Date Issued
- 2004
- Identifier
- CFE0000047, ucf:46086
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0000047
- 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
-
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
- CHARACTERIZATION OF DISPERSION AND RESIDUAL STRESS IN NANOPARTICLE REINFORCED HYBRID CARBON FIBER COMPOSITES.
- Creator
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Selimov, Alex, Raghavan,Seetha, University of Central Florida
- Abstract / Description
-
Hybrid carbon fiber reinforced composites are a new breed of materials that are currently being explored and characterized for next generation aerospace applications. Through the introduction of secondary reinforcements, such as alumina nanoparticles, hybrid properties including improved mechanical properties and stress sensing capabilities can be achieved. In order to maximize these properties, it is necessary to achieve a homogeneous dispersion of particulate filler. Utilizing the...
Show moreHybrid carbon fiber reinforced composites are a new breed of materials that are currently being explored and characterized for next generation aerospace applications. Through the introduction of secondary reinforcements, such as alumina nanoparticles, hybrid properties including improved mechanical properties and stress sensing capabilities can be achieved. In order to maximize these properties, it is necessary to achieve a homogeneous dispersion of particulate filler. Utilizing the photoluminescent properties of alumina, it is possible to compare local levels of particle concentration through emission intensities as a way to determine the effectiveness of the tested manufacturing parameters in increasing material homogeneity. Parameters of these photoluminescence emissions have been established to be stress dependent, which allows for in situ residual stress measurements. It is shown here that the application of silane coupling agents as particle surface treatments improves particle dispersion when compared to untreated samples. Reactive silane coupling agent (RSCA) treatments were found to provide for greater dispersion improvements when compared to non-reactive silane coupling agents (NRSCA). Higher resolution investigations into these samples found that treatment with a reactive coupling agent altered the stress state of particles concentrated around the fiber from a tensile stress state to a compressive stress state. This is proposed to result from bonding of the reactive groups on the coupling agent to the organic groups on the carbon fibers which adjusts the stress state of the particle. Future mechanical tests will verify the effects of the particle surface functionalization treatments on mechanical properties of the composites.
Show less - Date Issued
- 2016
- Identifier
- CFH0000233, ucf:44669
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFH0000233
- Title
- Mode coupling in space-division multiplexed systems.
- Creator
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Liu, Huiyuan, Li, Guifang, Likamwa, Patrick, Amezcua Correa, Rodrigo, Chanda, Debashis, University of Central Florida
- Abstract / Description
-
Even though fiber-optic communication systems have been engineered to nearly approach the Shannon capacity limit, they still cannot meet the exponentially-growing bandwidth demand of the Internet. Space-division multiplexing (SDM) has attracted considerable attention in recent years due to its potential to address this capacity crunch. In SDM, the transmission channels support more than one spatial mode, each of which can provide the same capacity as a single-mode fiber. To make SDM practical...
Show moreEven though fiber-optic communication systems have been engineered to nearly approach the Shannon capacity limit, they still cannot meet the exponentially-growing bandwidth demand of the Internet. Space-division multiplexing (SDM) has attracted considerable attention in recent years due to its potential to address this capacity crunch. In SDM, the transmission channels support more than one spatial mode, each of which can provide the same capacity as a single-mode fiber. To make SDM practical, crosstalk among modes must be effectively managed. This dissertation presents three techniques for crosstalk management for SDM. In some cases such as intra-datacenter interconnects, even though mode crosstalk cannot be completely avoided, crosstalk among mode groups can be suppressed in properly-designed few-mode fibers to support mode group-multiplexed transmission. However, in most cases, mode coupling is unavoidable. In free-space optical (FSO) communication, mode coupling due to turbulence manifests as wavefront distortions. Since there is almost no modal dispersion in FSO, we demonstrate the use of few-mode pre-amplified receivers to mitigate the effect of turbulence without using adaptive optics. In fiber-optic communication, multi-mode fibers or long-haul few-mode fibers not only suffer from mode crosstalk but also large modal dispersion, which can only be compensated electronically using multiple-input-multiple-output (MIMO) digital signal processing (DSP). In this case, we take the counterintuitive approach of introducing strong mode coupling to reduce modal group delay and DSP complexity.
Show less - Date Issued
- 2019
- Identifier
- CFE0007831, ucf:52806
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007831
- Title
- Multiphase Flow Modeling of Molten Metal Atomization at High Gas Pressure.
- Creator
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Hanthanan Arachchilage, Kalpana, Kumar, Ranganathan, Sohn, Yongho, Kassab, Alain, Shivamoggi, Bhimsen, University of Central Florida
- Abstract / Description
-
The high-pressure gas atomization is well known as one of the best powder manufacturing processes due to its controllability over powder size distribution. However, with the continuous improvement of new alloys, optimizing the operating parameters to maximize the yield is costly and time-consuming. Therefore, it is essential to understand the high-pressure gas atomization process and the effects of different operational parameters on the powder size distribution.Two-phase numerical...
Show moreThe high-pressure gas atomization is well known as one of the best powder manufacturing processes due to its controllability over powder size distribution. However, with the continuous improvement of new alloys, optimizing the operating parameters to maximize the yield is costly and time-consuming. Therefore, it is essential to understand the high-pressure gas atomization process and the effects of different operational parameters on the powder size distribution.Two-phase numerical simulations are performed to capture the interfacial dynamic during the atomization process and to obtain the effects of gas pressure, melt flow rate, and thermophysical properties of atomizing gas and the molten metal. The Volume of Fluid (VOF) model is used to capture the melt-gas interface, and in-house post-processing code is developed to obtain the droplet size distributions. Three-dimensional geometry of an annular-slit close-coupled gas atomizer is utilized to investigate the primary atomization process. The current grid resolution is sufficient forcapturing primary atomization and some characteristics of the secondary atomization, but it is not adequate to capture all the length scales in secondary atomization. Qualitative comparisons of the cumulative volume graphs indicate that this numerical approach is capable of capturing the trends in the atomization process as in the experiments. It is found that a combination of several interfacial instabilities governs the atomization process. Simulations corresponding to different gas pressures show that the atomizationcharacteristics remain unchanged irrespective of the gas pressure. However, it is found that the rate of the evolution and the effectiveness of the atomization process increases with the gas pressure. Three melts (aluminum, steel, and an artificial material with intermediate thermophysical properties) are used to investigate the effects of the molten metal properties and found that the rate of the atomization process decreases with increasing melt density, and the yield of the atomized powder is seen to increase. The flow characteristics remain unchanged for all three melts. The melt flow is strongly correlated with flow characteristics and interfacial instability.
Show less - Date Issued
- 2019
- Identifier
- CFE0007814, ucf:52342
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007814
- Title
- BEAM-STEERABLE AND RECONFIGURABLE REFLECTARRAY ANTENNAS FOR HIGH GAIN SPACE APPLICATIONS.
- Creator
-
Karnati, Kalyan, Gong, Xun, Wahid, Parveen, Jones, W Linwood, Wu, Thomas, Cho, Hyoung Jin, University of Central Florida
- Abstract / Description
-
Reflectarray antennas uniquely combine the advantages of parabolic reflectors and phased array antennas. Comprised of planar structures similar to phased arrays and utilizing quasi-optical excitation similar to parabolic reflectors, reflectarray antennas provide beam steering without the need of complex and lossy feed networks. Chapter 1 discusses the basic theory of reflectarray and its design. A brief summary of previous work and current research status is also presented. The inherent...
Show moreReflectarray antennas uniquely combine the advantages of parabolic reflectors and phased array antennas. Comprised of planar structures similar to phased arrays and utilizing quasi-optical excitation similar to parabolic reflectors, reflectarray antennas provide beam steering without the need of complex and lossy feed networks. Chapter 1 discusses the basic theory of reflectarray and its design. A brief summary of previous work and current research status is also presented. The inherent advantages and drawbacks of the reflectarray are discussed.In chapter 2, a novel theoretical approach to extract the reflection coefficient of reflectarray unit cells is developed. The approach is applied to single-resonance unit cell elements under normal and waveguide incidences. The developed theory is also utilized to understand the difference between the TEM and TE10 mode of excitation. Using this theory, effects of different physical parameters on reflection properties of unit cells are studied without the need of full-wave simulations. Detailed analysis is performed for Ka-band reflectarray unit cells and verified by full-wave simulations. In addition, an approach to extract the Q factors using full-wave simulations is also presented. Lastly, a detailed study on the effects of inter-element spacing is discussed.Q factor theory discussed in chapter 2 is extended to account for the varying incidence angles and polarizations in chapter 3 utilizing Floquet modes. Emphasis is laid on elements located on planes where extremities in performance tend to occur. The antenna element properties are assessed in terms of maximum reflection loss and slope of the reflection phase. A thorough analysis is performed at Ka band and the results obtained are verified using full-wave simulations. Reflection coefficients over a 749-element reflectarray aperture for a broadside radiation pattern are presented for a couple of cases and the effects of coupling conditions in conjunction with incidence angles are demonstrated. The presented theory provides explicit physical intuition and guidelines for efficient and accurate reflectarray design.In chapter 4, tunable reflectarray elements capacitively loaded with Barium Strontium Titanate (BST) thin film are shown. The effects of substrate thickness, operating frequency and deposition pressure are shown utilizing coupling conditions and the performance is optimized. To ensure minimum affects from biasing, optimized biasing schemes are discussed. The proposed unit cells are fabricated and measured, demonstrating the reconfigurability by varying the applied E-field. To demonstrate the concept, a 45 element array is also designed and fabricated. Using anechoic chamber measurements, far-field patterns are obtained and a beam scan up to 25o is shown on the E-plane.Overall, novel theoretical approaches to analyze the reflection properties of the reflectarray elements using Q factors are developed. The proposed theoretical models provide valuable physical insight utilizing coupling conditions and aid in efficient reflectarray design. In addition, for the first time a continuously tunable reflectarray operating at Ka-band is presented using BST technology. Due to monolithic integration, the technique can be extended to higher frequencies such as V-band and above.
Show less - Date Issued
- 2015
- Identifier
- CFE0006040, ucf:50963
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006040
- Title
- Mode Evolution in Fiber Based Devices for Optical Communication Systems.
- Creator
-
Huang, Bin, Li, Guifang, Amezcua Correa, Rodrigo, Abouraddy, Ayman, Chen, Haoshuo, University of Central Florida
- Abstract / Description
-
Space division multiplexing (SDM) is the most promising way of increasing the capacity of a single fiber. To enable the few mode fiber (FMF) or multi-mode fiber (MMF) transmission system, several major challenges have to be overcome. One is the urgent need of ideal mode multiplexer, the second is the perfect amplification for all spatial modes, another one is the modal delay spread (MDS) due to group velocity difference of spatial modes. The main subject of this dissertation is to model,...
Show moreSpace division multiplexing (SDM) is the most promising way of increasing the capacity of a single fiber. To enable the few mode fiber (FMF) or multi-mode fiber (MMF) transmission system, several major challenges have to be overcome. One is the urgent need of ideal mode multiplexer, the second is the perfect amplification for all spatial modes, another one is the modal delay spread (MDS) due to group velocity difference of spatial modes. The main subject of this dissertation is to model, fabricate and characterize the mode multiplexer for FMF transmission. First, we designed a novel resonant mode coupler (structured directional coupler pair). After that, we studied the adiabatic mode multiplexer (photonic lantern). 6-mode photonic lantern using graded-index (GI) MMFs is proposed and demonstrated, which alleviates the adiabatic require-ment and improves mode selectivity. Then, 10-mode photonic lantern is demonstrated using novel double cladding micro-structured drilling-hole preform, which alleviates the adiabatic requirement and demonstrate a feasible way to scale up the lantern modes. Also, multi-mode photonic lantern is studied for high order input modes. In addition, for the perfect amplification of the modes, cladding pump method is demonstrated. The mode selective lantern designed and fabricated can be used for the characterization of few mode amplifier with swept wavelength interferometer (SWI). Also, we demonstrated the application of the use of the few mode amplifier for the turbulence-resisted preamplified receiver. Besides, for the reduction of MDS, the long period grating for introducing strong mode mixing is demonstrated.
Show less - Date Issued
- 2017
- Identifier
- CFE0006884, ucf:51720
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006884
- Title
- Exploring Relationship Quality as a Dyadic Mediator of Adverse Childhood Experiences and Health for Economically Disadvantaged Couples.
- Creator
-
Wheeler, Naomi, Barden, Sejal, Lambie, Glenn, Young, Mark, Carlson, Ryan, Taylor, Dalena, Daire, Andrew, University of Central Florida
- Abstract / Description
-
The purpose of this research study was to investigate the directional relationships between Adverse Childhood Experiences (ACE; Felitti et al., 1998), relationship quality (as measured by the Relationship Assessment Scale [Hendrick, 1988] and the Behavioral Self-Regulation for Effective Relationships Scale [Wilson, Charker, Lizzio, Halford, (&) Kimlin, 2005]), and health (as measured by the OQ 45.2 [Lambert et al., 2004] and a Brief Medical History Questionnaire [Daire, Wheeler, (&) Liekweg,...
Show moreThe purpose of this research study was to investigate the directional relationships between Adverse Childhood Experiences (ACE; Felitti et al., 1998), relationship quality (as measured by the Relationship Assessment Scale [Hendrick, 1988] and the Behavioral Self-Regulation for Effective Relationships Scale [Wilson, Charker, Lizzio, Halford, (&) Kimlin, 2005]), and health (as measured by the OQ 45.2 [Lambert et al., 2004] and a Brief Medical History Questionnaire [Daire, Wheeler, (&) Liekweg, 2014]) among economically disadvantaged couples. The theorized model included a dyadic structure and mediation of ACE and health by relationship quality using the Actor-Partner Interdependence Mediation Model (APIMeM). The researcher employed structural equation modeling analyses and the APIMeM to investigate the model fit with archival and enrollment data from 503 heterosexual couples in a relationship education program. The majority of participants (76.9%) also identified a racial or ethnic minority background. Final results indicated a good fit for the model to the sample data and explained a significant portion of variance in health (i.e., 82.3% for men [a large effect], 56.5% for women [a large effect]). Significant findings included: (a) ACE exerted an effect on health indirectly through relationship quality (i.e., 98.05% of the male total actor effect, 57.4% of the female total actor effect); (b) ACE exerted a direct effect on health for women; (c) overall ACE, relationship quality, and health were significantly related at the actor-level; and (d) a dyadic influence between male and female reports of ACE, relationship quality, and health contributed to the overall model fit. Discussion of results, implications for practice, recommendations for future research, and study limitations are provided.
Show less - Date Issued
- 2017
- Identifier
- CFE0006673, ucf:51229
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006673
- Title
- Dar's nobody looking but de owl and de moon.
- Date Created
- 1900s
- Identifier
- DP0015466
- Format
- Set of related objects
- PURL
- http://purl.flvc.org/ucf/fd/DP0015466
- Title
- STRUCTURE-FUNCTION ANALYSIS OF THE DROSOPHILA STUBBLE TYPE II TRANSMEMBRANE SERINE PROTEASE.
- Creator
-
Morgan, Rachel, von Kalm, Laurence, University of Central Florida
- Abstract / Description
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Hormonally-triggered regulatory hierarchies play a major role in organismal development. Disruption of a single member of such a hierarchy can lead to irregular development and disease. Therefore, knowledge of the members involved and the mechanisms controlling signaling through such pathways is of great importance in understanding how resulting developmental defects occur. Type II transmembrane serine proteases (TTSPs) make up a family of cell surface-associated proteases that play important...
Show moreHormonally-triggered regulatory hierarchies play a major role in organismal development. Disruption of a single member of such a hierarchy can lead to irregular development and disease. Therefore, knowledge of the members involved and the mechanisms controlling signaling through such pathways is of great importance in understanding how resulting developmental defects occur. Type II transmembrane serine proteases (TTSPs) make up a family of cell surface-associated proteases that play important roles in the development and homeostasis of a number of mammalian tissues. Aberrant expression of TTSPs is linked to several human disorders, including deafness, heart and respiratory disease and cancer. However, the mechanism by which these proteases function remains unknown. The ecdysone-responsive Stubble TTSP of Drosophila serves as a good model in which to study the functional mechanism of the TTSP family. The Stubble protease interacts with the intracellular Rho1 (RhoA) pathway to control epithelial development in imaginal discs. The Rho1 signaling pathway regulates cellular behavior via control of gene expression and actin cytoskeletal dynamics. However, the mechanism by which the Stubble protease interacts with the Rho1 pathway to control epithelial development, in particular leg imaginal disc morphogenesis, has yet to be elucidated. The Stubble protein consists of several conserved domains. One approach to a better understanding of the mechanism of action of Stubble in regulating Rho1 signaling is to define which of the conserved domains within the protease are required for proper function. Sequence analysis of twelve recessive Stubble mutant alleles has revealed that the proteolytic domain is essential for proper function. Alleles containing mutations which disrupt regions of the protease domain necessary for protease activation or substrate binding, as well as those with deletions or truncations that remove some portion of the proteolytic domain, result in defective epithelial development in vivo. In contrast, mutations in other regions of the Stubble protein, including the disulfide-knotted and cytoplasmic domains, were not observed. Another important step for defining the connection between Stubble and Rho1 signaling is to identify a Stubble target that acts as an upstream regulator of the Rho1 pathway. We performed a genetic screen in which 97 of the 147 Drosophila non-olfactory and non-gustatory G-protein-coupled receptors (GPCRs), a family of proteins that has been shown to be protease-activated and to activate Rho1 signaling, were tested for interactions with a mutant allele of Stubble. We found 4 genomic regions uncovering a total of 7 GPCRs that interact genetically when in heterozygous combination with a Stubble mutant. Further analysis of these genes is necessary to determine if any of these GPCRs is targeted by Stubble during activation of the Rho1 pathway.
Show less - Date Issued
- 2008
- Identifier
- CFE0002285, ucf:47875
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0002285
- Title
- RESPONSE-CALIBRATION TECHNIQUES FOR ANTENNA-COUPLED INFRARED SENSORS.
- Creator
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Krenz, Peter, Boreman, Glenn, University of Central Florida
- Abstract / Description
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Infrared antennas are employed in sensing applications requiring specific spectral, polarization, and directional properties. Because of their inherently small dimensions, there is significant interaction, both thermal and electromagnetic, between the antenna, the antenna-coupled sensor, and the low-frequency readout structures necessary for signal extraction at the baseband modulation frequency. Validation of design models against measurements requires separation of these effects so that the...
Show moreInfrared antennas are employed in sensing applications requiring specific spectral, polarization, and directional properties. Because of their inherently small dimensions, there is significant interaction, both thermal and electromagnetic, between the antenna, the antenna-coupled sensor, and the low-frequency readout structures necessary for signal extraction at the baseband modulation frequency. Validation of design models against measurements requires separation of these effects so that the response of the antenna-coupled sensor alone can be measured in a calibrated manner. Such validations will allow confident extension of design techniques to more complex infrared-antenna configurations. Two general techniques are explored to accomplish this goal. The extraneous signal contributions can be measured separately with calibration structures closely co-located near the devices to be characterized. This approach is demonstrated in two specific embodiments, for removal of cross-polarization effects arising from lead lines in an antenna-coupled infrared dipole, and for removal of distributed thermal effects in an infrared phased-array antenna. The second calibration technique uses scanning near-field microscopy to experimentally determine the spatial dependence of the electric-field distributions on the signal-extraction structures, and to include these measured fields in the computational electromagnetic model of the overall device. This approach is demonstrated for infrared dipole antennas which are connected to coplanar strip lines. Specific situations with open-circuit and short-circuit impedances at the termination of the lines are investigated.
Show less - Date Issued
- 2010
- Identifier
- CFE0003177, ucf:48606
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003177
- Title
- EXPLORING THE RELATIONSHIP BETWEEN MARITAL EXPECTATIONS AND MARITAL SATISFACTION BETWEEN MARRIED AFRICAN IMMIGRANT COUPLES AND UNITED STATES BORN MARRIED COUPLES.
- Creator
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Ngazimbi, Evadne, Daire, Andrew, University of Central Florida
- Abstract / Description
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ABSTRACT Marriage is still considered a universal institution in many countries worldwide. Marriage provides benefits for wives, husbands, children, families, and communities. Why Marriage Matters (Wilcox et al., 2005), outlined the benefits of marriage, including improved physical and mental health, biological and social benefits for husbands, wives, children and families in America. In sub-Saharan Africa benefits emanating from marriage included increased survival rates for young children ...
Show moreABSTRACT Marriage is still considered a universal institution in many countries worldwide. Marriage provides benefits for wives, husbands, children, families, and communities. Why Marriage Matters (Wilcox et al., 2005), outlined the benefits of marriage, including improved physical and mental health, biological and social benefits for husbands, wives, children and families in America. In sub-Saharan Africa benefits emanating from marriage included increased survival rates for young children (Omariba & Boyle, 2007); reduced maternal morbidity and mortality rates for women due to reduced risks from self-inflicted abortions (Garenne, Tollman, Kahn, Collins, & Ngwenya, 2001); and improved economic management in homes due to exchanging gender-specific tasks within households (Gezon, 2002). Despite these benefits, approximately half the marriages in the United States end in divorce (Raley & Bumpass, 2003; Smith, 2007). Reduced marital satisfaction leads to dissolution of marriages in the U. S. Marital expectations were associated with marital satisfaction (Juvva & Bhatti, 2006). The purpose of this study was to investigate the relationship between marital expectations and marital satisfaction between African immigrant and United States born married couples. The independent variable was marital expectations, measured with the Marital Expectations Questionnaire (MEQ, Ngazimbi & Daire, 2008). The dependent variables were marital satisfaction, measured by the Relationship Assessment Scale (RAS, Hendrick, 1988), and the Relationship Pleasure Scale (RPS, PAIRS Foundation, 1993). The participants were recruited from nine sites in six states located in three geographical regions. The regions were the Midwest, the West and the Pacific Northwest. They were recruited through faith-based leaders. Participants consisted of 87 couples and 35 individuals who participated without their spouses. This was a mixed methods design. In the quantitative section, three instruments were used to collect data: the MEQ, the RAS, and the RPS. The first section of the MEQ contained four open-ended questions which were used to collect qualitative data. Significant differences were found in the relationships between marital expectations and marital satisfaction between African immigrants and non-immigrants. Qualitative differences and similarities were found between African immigrant and U. S. born married couples. Implications of the findings are discussed for research, counselor education and clinical practice.
Show less - Date Issued
- 2009
- Identifier
- CFE0002629, ucf:48224
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0002629
- Title
- Injection Locking of Semiconductor Mode-Locked Lasers for Long-Term Stability of Widely Tunable Frequency Combs.
- Creator
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Williams, Charles, Delfyett, Peter, Hagan, David, Likamwa, Patrick, Vanstryland, Eric, DeSalvo, Richard, University of Central Florida
- Abstract / Description
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Harmonically mode-locked semiconductor lasers with external ring cavities offer high repetition rate pulse trains while maintaining low optical linewidth via long cavity storage times. Single frequency injection locking generates widely-spaced and tunable frequency combs from these harmonically mode-locked lasers, while stabilizing the optical frequencies. The output is stabilized long-term with the help of a feedback loop utilizing either a novel technique based on Pound-Drever-Hall...
Show moreHarmonically mode-locked semiconductor lasers with external ring cavities offer high repetition rate pulse trains while maintaining low optical linewidth via long cavity storage times. Single frequency injection locking generates widely-spaced and tunable frequency combs from these harmonically mode-locked lasers, while stabilizing the optical frequencies. The output is stabilized long-term with the help of a feedback loop utilizing either a novel technique based on Pound-Drever-Hall stabilization or by polarization spectroscopy. Error signals of both techniques are simulated and compared to experimentally obtained signals. Frequency combs spaced by 2.5 GHz and ~10 GHz are generated, with demonstrated optical sidemode suppression of unwanted modes of 36 dB, as well as RF supermode noise suppression of 14 dB for longer than 1 hour. In addition to the injection locking of actively harmonically mode-locked lasers, the injection locking technique for regeneratively mode-locked lasers, or Coupled Opto-Electronic Oscillators (COEOs), is also demonstrated and characterized extensively.
Show less - Date Issued
- 2013
- Identifier
- CFE0004774, ucf:49805
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004774
- Title
- TOWARD A THEORY OF PRACTICAL DRIFT IN TEAMS.
- Creator
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Bisbey, Tiffany, Salas, Eduardo, University of Central Florida
- Abstract / Description
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Practical drift is defined as the unintentional adaptation of routine behaviors from written procedure. The occurrence of practical drift can result in catastrophic disaster in high-reliability organizations (e.g. the military, emergency medicine, space exploration). Given the lack of empirical research on practical drift, this research sought to develop a better understanding by investigating ways to assess and stop the process in high-reliability organizations. An introductory literature...
Show morePractical drift is defined as the unintentional adaptation of routine behaviors from written procedure. The occurrence of practical drift can result in catastrophic disaster in high-reliability organizations (e.g. the military, emergency medicine, space exploration). Given the lack of empirical research on practical drift, this research sought to develop a better understanding by investigating ways to assess and stop the process in high-reliability organizations. An introductory literature review was conducted to investigate the variables that play a role in the occurrence of practical drift in teams. Research was guided by the input-throughput-output model of team adaptation posed by Burke, Stagl, Salas, Pierce, and Kendall (2006). It demonstrates relationships supported by the results of the literature review and the Burke and colleagues (2006) model denoting potential indicators of practical drift in teams. Research centralized on the core processes and emergent states of the adaptive cycle; namely, shared mental models, team situation awareness, and coordination. The resulting model shows the relationship of procedure—practice coupling demands misfit and maladaptive violations of procedure being mediated by shared mental models, team situation awareness, and coordination. Shared mental models also lead to team situation awareness, and both depict a mutual, positive relationship with coordination. The cycle restarts when an error caused by maladaptive violations of procedure creates a greater misfit between procedural demands and practical demands. This movement toward a theory of practical drift in teams provides a conceptual framework and testable propositions for future research to build from, giving practical avenues to predict and prevent accidents resulting from drift in high-reliability organizations. Suggestions for future research are also discussed, including possible directions to explore. By examining the relationships reflected in the new model, steps can be taken to counteract organizational failures in the process of practical drift in teams.
Show less - Date Issued
- 2014
- Identifier
- CFH0004636, ucf:45300
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFH0004636
- Title
- Cavity-Coupled Plasmonic Systems for Enhanced Light-Matter Interactions.
- Creator
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Vazquez-Guardado, Abraham, Chanda, Debashis, Christodoulides, Demetrios, Abouraddy, Ayman, Moharam, Jim, Leuenberger, Michael, University of Central Florida
- Abstract / Description
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Light-matter interaction is a pivotal effect that involves the synergetic interplay of electromag- netic fields with fundamental particles. In this regard localized surface plasmons (LSP) arise from coherent interaction of the electromagnetic field with the collective oscillation of free electrons in confined sub-wavelength environments. Their most attractive properties are strong field en- hancements at the near field, highly inhomogeneous, peculiar temporal and spatial distributions and...
Show moreLight-matter interaction is a pivotal effect that involves the synergetic interplay of electromag- netic fields with fundamental particles. In this regard localized surface plasmons (LSP) arise from coherent interaction of the electromagnetic field with the collective oscillation of free electrons in confined sub-wavelength environments. Their most attractive properties are strong field en- hancements at the near field, highly inhomogeneous, peculiar temporal and spatial distributions and unique polarization properties. LSP systems also offer a unique playground for fundamental electromagnetic physics where micro-scale systemic properties can be studied in the macro-scale. These important properties and opportunities are brought up in this work where I study hybrid cavity-coupled plasmonic systems in which the weak plasmonic element is far-field coupled with the photonic cavity by properly tuning its phase. In this work I preset the fundamental understand- ing of such a complex systems from the multi-resonance interaction picture along experimental demonstration. Using this platform and its intricate near fields I further demonstrate a novel mech- anism to generate superchiral light: a field polarization property that adds a degree of freedom to light-matter interactions at the nanoscale exploited in advanced sensing applications and surface effect processes. Finally, the detection of non-chiral analytes, such as proteins, neurotransmit- ters or nanoparticles, and more complex chiral analytes, such as proteins and its conformation states, amino acids or chiral molecules at low concentrations is demonstrated in several biosensing applications. The accompanied experiential demonstrations were accomplished using the nanoim- printing technique, which places the cavity-coupled hybrid plasmonic system as a unique platform towards realistic applications not limited by expensive lithographic techniques.
Show less - Date Issued
- 2018
- Identifier
- CFE0007418, ucf:52708
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007418
- Title
- Light Matter Interaction in Single Molecule Magnets.
- Creator
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Cebulka, Rebecca, Del Barco, Enrique, Klemm, Richard, Mucciolo, Eduardo, Luis, Fernando, University of Central Florida
- Abstract / Description
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This dissertation includes a series of experimental realizations which focus on studying the coupling between photons and single-molecule magnets (SMMs) in both the weak and strong coupling regimes. In the weak coupling regime, the aim is to achieve coherent control over the time evolution of the spin of SMMs while applying rapid microwave pulses at sub-Kelvin temperatures, where polarization of the spin bath may be achieved without large magnetic fields, allowing the suppression of dipolar...
Show moreThis dissertation includes a series of experimental realizations which focus on studying the coupling between photons and single-molecule magnets (SMMs) in both the weak and strong coupling regimes. In the weak coupling regime, the aim is to achieve coherent control over the time evolution of the spin of SMMs while applying rapid microwave pulses at sub-Kelvin temperatures, where polarization of the spin bath may be achieved without large magnetic fields, allowing the suppression of dipolar dephasing. The continuing results of this experiment will be to provide a window into fundamental sources of decoherence in single-crystal SMMs in an energy range not thoroughly investigated. We expect that these conditions would allow us to study the quantum dynamics of the spins as governed by the intrinsic molecular magnetic anisotropy, which should give rise to non-well-defined Rabi oscillations of the spin state, including metastable precessional spin states. In the strong coupling regime, high quality factor superconducting CPW resonators have been designed and fabricated to investigate the vacuum Rabi splitting between a photon and the SMM spin. The proposed setup will permit measurements of coherent collective coupling between molecular spins and a low number of photons, ideally down to a single photon. This experiment may ultimately provide the opportunity for reaching the strong coupling regime with a single spin. Finally, this thesis also documents a research study into the impact of service-learning methodology on students' depth of learning and critical thinking skills during a novel nanoscale science and technology course offered in the UCF Physics Dept. The overall learning of students was assessed and results clearly showed improvement in both multiple choice pre/post-tests and critical reflection papers. We associate this improvement at least partially to the service-learning experience.
Show less - Date Issued
- 2019
- Identifier
- CFE0007442, ucf:52728
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007442
