Current Search: Orbiter (x)
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Title
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High power fiber lasers and fiber devices.
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Creator
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Sanjabieznaveh, Zeinab, Amezcua Correa, Rodrigo, Chang, Zenghu, Argenti, Luca, Richardson, Martin, Schulzgen, Axel, University of Central Florida
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Abstract / Description
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Fiber lasers and fiber amplifiers have experienced considerable improvements in recent years and demonstrated remarkable power scalability. However, due to high optical intensity in the core, the performance of high power fiber lasers is limited by detrimental nonlinear processes, such as four-wave mixing, self-phase modulation, stimulated Brillouin scattering, and stimulated Raman scattering. To mitigate nonlinear effects, very large mode area (LMA) fibers, which exhibit a mode field...
Show moreFiber lasers and fiber amplifiers have experienced considerable improvements in recent years and demonstrated remarkable power scalability. However, due to high optical intensity in the core, the performance of high power fiber lasers is limited by detrimental nonlinear processes, such as four-wave mixing, self-phase modulation, stimulated Brillouin scattering, and stimulated Raman scattering. To mitigate nonlinear effects, very large mode area (LMA) fibers, which exhibit a mode field diameter larger than 30 ?m have been developed. However, for larger core sizes the discrimination capabilities of conventional fiber designs decrease, consequently, LMA fibers are not strictly single mode which ultimately at high average powers results in sudden degradation of the output beam of a fiber laser or amplifier, namely, modal instability (MI). To suppress higher order modes (HOMs) in LMA fibers, various techniques have been proposed such as large pitch fibers (LPFs), differential bend loss for HOMs, leakage channel fibers, mode filtering with tapers, and chirally coupled cores. This thesis is divided into two parts. In the first two chapters, I focus on simulation, design and characterization of advanced high power fiber amplifiers. In the first chapter, I study the numerical modeling of the MI in active LMA fibers. Using a high fidelity time dependent computer model based on beam propagation method (BPM), taking laser gain and thermal effects into account, I show that engineering pump scheme is a promising technique leading to an appreciable threshold increase in a fiber amplifier. As an example I demonstrate that bi-directional pump scheme increases the instabilities threshold by a factor of ~30% with respect to the forward pump configuration. In the second chapter, I present a novel design of microstructured large pitch, LMA asymmetric rod-type fiber to achieve higher MI threshold. By eliminating mirror symmetries in the cladding of the LPF through six high refractive index germanium-doped silica inclusions, we reduce the overlap of the LP1m-like modes with the core region, which leads to strong HOM delocalization and enhanced preferential gain for the fundamental mode in active fibers. The third and fourth chapters of this thesis are focused on all-fiber mode multiplexers for communication applications. In the third chapter, I present an all-fiber mode selective photonic lantern mode multiplexer designed for launching into few-mode multicore fibers (FM-MCFs). This device is capable of selectively exciting LP01, LP11a and LP11b modes in a seven core configuration resulting in 21 spatial channels, with less than 38 dB crosstalk and with insertion loss below 0.4 dB. This device can be a critical component for the evolution of high capacity, high-density space division multiplexing (SDM) transmission networks based on MCFs.In the fourth chapter, I demonstrate for the first time, an all-fiber orbital angular momentum (OAM) mode multiplexer to efficiently generate and simultaneously multiplex multiple OAM modes within a broad spectral range of at least 550 nm. This innovative all-fiber passive design provides simultaneous multiplexing of multiple orthogonal OAM modes in a single fiber device with low loss and at low design complexity, therefore, it is of grand utility in variety of applications in classical and modern optical studies.
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Date Issued
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2017
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Identifier
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CFE0006956, ucf:51632
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0006956
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Title
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Dynamical Formation of Protoplanetesimals.
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Creator
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Whizin, Akbar, Colwell, Joshua, Fernandez, Yan, Klemm, Richard, Lewis, Mark, Moore, Brian, University of Central Florida
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Abstract / Description
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The seeds of planetesimals that formed in the gaseous protoplanetary disk (PPD) have many barriers to overcome in their growth from millimeter to meter-sized and larger bodies. Centimeter-sized aggregates are weakly bound and self-gravity is almost non-existent so surface forces play a critical role in holding small loosely-bound rubble-piles together. Their orbital motions and effects form disk processes impart relative velocities leading to collisions so understanding the macroscopic disk...
Show moreThe seeds of planetesimals that formed in the gaseous protoplanetary disk (PPD) have many barriers to overcome in their growth from millimeter to meter-sized and larger bodies. Centimeter-sized aggregates are weakly bound and self-gravity is almost non-existent so surface forces play a critical role in holding small loosely-bound rubble-piles together. Their orbital motions and effects form disk processes impart relative velocities leading to collisions so understanding the macroscopic disk environment is also necessary. To this end we analyze the dynamics of particles in Saturn's F ring as an analogue to understanding the orbital evolution of proto-planetesimals embedded in a PPD. We also study how the mechanical, material, and collisional properties affect the dynamical accretion of cm-sized bodies. The collisional outcomes can be determined by a set of definable collision parameters, and experimental constraints on these parameters will improve formation models for planetesimals. We have carried out a series of microgravity laboratory collision experiments of small aggregates to determine under what conditions collisional growth can occur for protoplanetary aggregates. We measure coefficients of restitution, sticking and fragmentation thresholds, compressive strengths, and sticking probabilities for collision velocities of 1 - 200 cm/s, then compare the results of our experiments with results from a collisional N-body code that includes adhesion between particles. We find that cm-sized aggregates are very weakly bound and require high internal cohesion to avoid fragmentation in agreement with simulations. The threshold for sticking is found to be under 10 cm/s and the fragmentation threshold near 1 m/s. Quiescent regions in the mid-plane of the disk may cultivate abnormally low relative velocities permitting sticking to occur (~1 cm/s), however, without a well-defined path to formation it is difficult to determine whether collisional accretion as a mechanism can overcome low thresholds for sticking and fragmentation. We discuss this research's implications to both the meter-barrier and planetesimal formation.
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Date Issued
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2016
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Identifier
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CFE0006196, ucf:51103
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0006196
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Title
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EVALUATION OF SPACE SHUTTLE TILE SUBNOMINAL BONDS.
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Creator
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Snapp, Cooper, Moslehy, Faissal, University of Central Florida
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Abstract / Description
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This study researched the history of Space Shuttle Reusable Surface Insulation which was designed and developed for use on the United States Orbiter fleet to protect from the high heating experienced during reentry through Earth's atmosphere. Specifically the tile system which is attached to the structure by the means of an RTV adhesive has experienced situations where the bonds are identified as subnominal. The history of these subnominal conditions is presented along with a recent...
Show moreThis study researched the history of Space Shuttle Reusable Surface Insulation which was designed and developed for use on the United States Orbiter fleet to protect from the high heating experienced during reentry through Earth's atmosphere. Specifically the tile system which is attached to the structure by the means of an RTV adhesive has experienced situations where the bonds are identified as subnominal. The history of these subnominal conditions is presented along with a recent identification of a subnominal bond between the Strain Isolation Pad and the tile substrate itself. Tests were run to identify the cause of these subnominal conditions and also to show how these conditions were proved to be acceptable for flight. The study also goes into cases that could be used to identify subnominal conditions on tile as a non-destructive test prior to flight. Several options of non-destructive testing were identified and recommendations are given for future research into this topic. A recent topic is also discussed in the instance where gap fillers were identified during the STS-114 mission that did not properly adhere to the substrate. The gap fillers were found protruding past the Outer Mold Line of the vehicle which required an unprecedented spacewalk to remove them to allow for a safe reentry through the atmosphere.
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Date Issued
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2006
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Identifier
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CFE0000947, ucf:46754
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0000947
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Title
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Smooth and Non-Smooth Traveling Wave Solutions of Some Generalized Camassa-Holm Equations.
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Creator
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Rehman, Taslima, Choudhury, Sudipto, Nevai, Andrew, Rollins, David, University of Central Florida
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Abstract / Description
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In this thesis we employ two recent analytical approaches to investigate the possible classes of traveling wave solutions of some members of recently derived integrable family of generalized Camassa-Holm (GCH) equations. In the first part, a novel application of phase-plane analysis is employed to analyze the singular traveling wave equations of four GCH equations, i.e. the possible non-smooth peakon, cuspon and compacton solutions. Two of the GCH equations do no support singular traveling...
Show moreIn this thesis we employ two recent analytical approaches to investigate the possible classes of traveling wave solutions of some members of recently derived integrable family of generalized Camassa-Holm (GCH) equations. In the first part, a novel application of phase-plane analysis is employed to analyze the singular traveling wave equations of four GCH equations, i.e. the possible non-smooth peakon, cuspon and compacton solutions. Two of the GCH equations do no support singular traveling waves. We generalize an existing theorem to establish the existence of peakon solutions of the third GCH equation. This equation is found to also support four segmented, non-smooth M-wave solutions. While the fourth supports both solitary (peakon) and periodic (cuspon) cusp waves in different parameter regimes.In the second part of the thesis, smooth traveling waves of the four GCH equations are considered. Here, we use a recent technique to derive convergent multi-infinite series solutions for the homoclinic and heteroclinic orbits of their traveling-wave equations, corresponding to pulse and front (kink or shock) solutions respectively of the original PDEs. Unlike the majority of unaccelerated convergent series, high accuracy is attained with relatively few terms. Of course, the convergence rate is not comparable to typical asymptotic series. However, asymptotic solutions for global behavior along a full homoclinic/heteroclinic orbit are currently not available.
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Date Issued
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2013
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Identifier
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CFE0004918, ucf:49637
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0004918
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Title
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AUTONOMOUS CONTROLS ALGORITHMFOR FORMATION FLYING OF SATELLITES.
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Creator
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Santiago, Luis, Johnson, Roger, University of Central Florida
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Abstract / Description
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This document describes the design and analysis of the Navigation, Guidance and Control System for the KnightSat project. The purpose for the project is to test and demonstrate new technologies the Air Force would be interested in for research and development. The primary mission of KnightSat is to show how a constellation of satellites can maintain relative position with each other autonomously using the Microwave Electro Thermal (MET) thruster. The secondary mission is to use multiple...
Show moreThis document describes the design and analysis of the Navigation, Guidance and Control System for the KnightSat project. The purpose for the project is to test and demonstrate new technologies the Air Force would be interested in for research and development. The primary mission of KnightSat is to show how a constellation of satellites can maintain relative position with each other autonomously using the Microwave Electro Thermal (MET) thruster. The secondary mission is to use multiple satellite imagery to obtain 3 dimensional stereo photographs of observable terrain. Formation flying itself has many possible uses for future applications. Selected missions that require imaging or data collection can be more economically accomplished using smaller multiple satellites. The MET thruster is a very efficient, but low thrust alternative that can provide thrust for a very long time, hence provide the low thrust necessary to maintain the satellites at a constant separation. The challenge is to design a working control algorithm to provide the desired output data to be used to command the MET thrusters. The satellites are to maintain a constant relative distance from each other, and use the least amount of fuel possible. If one satellite runs out of fuel before the other, it would render the constellation less useful or useless. Hence, the satellites must use the same amount of fuel in order to maintain an optimal operational duration on orbit.
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Date Issued
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2006
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Identifier
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CFE0001171, ucf:46854
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Format
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Document (PDF)
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PURL
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http://purl.flvc.org/ucf/fd/CFE0001171