Current Search: Polarization (x)
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- Title
- PROBING RANDOM MEDIA WITH SINGULAR WAVES.
- Creator
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Schwartz, Chaim, Dogariu, Aristide, University of Central Florida
- Abstract / Description
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In recent years a resurgence of interest in wave singularities (of which optical vortices are a prominent example), light angular momentum and the relations between them has occurred. Many applications in various areas of linear and non-linear optics have been based on studying effects related to angular momentum and optical vortices. This dissertation examines the use of such wave singularities for studying the light propagation in highly inhomogeneous media and the relationship to angular...
Show moreIn recent years a resurgence of interest in wave singularities (of which optical vortices are a prominent example), light angular momentum and the relations between them has occurred. Many applications in various areas of linear and non-linear optics have been based on studying effects related to angular momentum and optical vortices. This dissertation examines the use of such wave singularities for studying the light propagation in highly inhomogeneous media and the relationship to angular momentum transfer. Angular momentum carried by light can be, in many cases, divided in two terms. The first one relates to the polarization of light and can be associated, in the quantum description, to the spin of a photon. The second is determined by the electromagnetic field distribution and, in analogy to atomic physics, is associated with the orbital angular momentum (OAM) of a photon. Under the paraxial approximation appropriate for the case of beam propagation, the two terms do not couple. However, each of them can be modified by the interaction with different media in which the light propagates through processes which involve angular momentum exchange. The decoupling of spin and orbital parts of light angular momentum can not, in general, be assumed for non paraxial propagation in turbid media, especially when backscattering is concerned. In Chapter 3 of this dissertation, scattering effects on angular momentum of light are discussed both for the single and multiple scattering processes. It is demonstrated for the first time that scattering from a spherically symmetric scattering potential, couples the spin and the OAM such that the total angular momentum flux density in conserved in every direction. Remarkably, the conservation of angular momentum occurs also for some classes of multiple scattering trajectories and this phenomenon manifests itself in ubiquitous polarization patterns observed in back-scattering from turbid media. It is newly shown in this dissertation that the polarization patterns a result of OAM carrying optical vortices which have a geometrical origin. These geometrical phase vortices are analyzed using the helicity space approach for optical geometrical phase (Berry phase). This approach, introduced in the con- text of random media, elucidates several aspects specific to propagation in helicity preserving and non-preserving scattering trajectories. Another aspect of singular waves interaction with turbid media relates to singularities embedded in the incident waves. Chapter 4 of the dissertation discusses how the phase distribution associated with an optical vortex leads to changes in the spatial correlations of the electromagnetic field. This change can be used to control the properties of the effect of enhanced backscattering in a way which allows inferring the optical properties of the medium. A detailed theoretical and experimental study of this effect is presented here for the first time for both double-pass geometries and diffusive media. It is also demonstrated that this novel experimental technique can be used to determine the optical properties of turbid media and, moreover, it permits to sense the depth of reflective inclusions in opaque media. When considering a regime of weakly inhomogeneous media, the paraxial approximation is still valid and therefore the spin and OAM do not couple. If, In addition, the medium is optically isotropic then the polarization is not affected. However, when the medium is non-axially symmetric for any specific realization, the OAM does change as a result of interaction with the medium. This effect can be studied using a newly developed method of coherent modes coupling which is presented in Chapter 5. This approach allows studying the power spread across propagating modes which carry different orbital angular momentum. The powerful concept of coherent modes coupling can be applied to fully coherent, fully polarized sources as well to partially coherent, partially polarized ones. An example of this scattering regime is atmospheric turbulence and the propagation through turbulence is thoroughly examined in Chapter 5. The results included in this dissertation are of fundamental relevance for a variety of applications which involves probing different types of random media. Such applications include remote sensing in atmospheric and maritime environments, optical techniques for biomedical diagnostics, optical characterization procedures in material sciences and others.
Show less - Date Issued
- 2006
- Identifier
- CFE0001174, ucf:46852
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001174
- Title
- Inverse Problems in Multiple Light Scattering.
- Creator
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Broky, John, Dogariu, Aristide, Christodoulides, Demetrios, Wu, Shintson, Tamasan, Alexandru, University of Central Florida
- Abstract / Description
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The interaction between coherent waves and material systems with complex optical properties is a complicated, deterministic process. Light that scatters from such media gives rise to random fields with intricate properties. It is common perception that the randomness of these complex fields is undesired and therefore is to be removed, usually through a process of ensemble averaging. However, random fields emerging from light matter interaction contain information about the properties of the...
Show moreThe interaction between coherent waves and material systems with complex optical properties is a complicated, deterministic process. Light that scatters from such media gives rise to random fields with intricate properties. It is common perception that the randomness of these complex fields is undesired and therefore is to be removed, usually through a process of ensemble averaging. However, random fields emerging from light matter interaction contain information about the properties of the medium and a thorough analysis of the scattered light allows solving specific inverse problems. Traditional attempts to solve these kinds of inverse problems tend to rely on statistical average quantities and ignore the deterministic interaction between the optical field and the scattering structure. Thus, because ensemble averaging inherently destroys specific characteristics of random processes, one can only recover limited information about the medium. This dissertation discusses practical means that go beyond ensemble averaging to probe complex media and extract additional information about a random scattering system. The dissertation discusses cases in which media with similar average properties can be differentiated by detailed examination of fluctuations between different realizations of the random process of multiple scattering. As a different approach to this type of inverse problems, the dissertation also includes a description of how higher-order field and polarization correlations can be used to extract features of random media and complex systems from one single realization of the light-matter interaction. Examples include (i) determining the level of multiple scattering, (ii) identifying non-stationarities in random fields, and (iii) extracting underlying correlation lengths of random electromagnetic fields that result from basic interferences. The new approaches introduced and the demonstrations described in this dissertation represent practical means to extract important material properties or to discriminate between media with similar characteristics even in situations when experimental constraints limit the number of realizations of the complex light-matter interaction.
Show less - Date Issued
- 2012
- Identifier
- CFE0004656, ucf:49888
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004656
- Title
- MULTILAYERED PLANAR PERIODIC SUBWAVELENGTH MICROSTRUCTURES FOR GENERATING AND DETECTING CIRCULARLY POLARIZED THERMAL INFRARED RADIATION.
- Creator
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Wadsworth, Samuel, Boreman, Glenn, University of Central Florida
- Abstract / Description
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Generation and detection of circularly-polarized (CP) radiation in the 8- to 12-[micro]m band of the infrared (IR) spectrum is crucial for polarization sensing and imaging scenarios. There is very little naturally occurring CP radiation in the long-wave IR band, so that useful functionalities may be obtained by exploiting preferential radiation and transmission characteristics of engineered metamaterials. Conventional CP devices in the IR utilize birefringent crystals, which are typically...
Show moreGeneration and detection of circularly-polarized (CP) radiation in the 8- to 12-[micro]m band of the infrared (IR) spectrum is crucial for polarization sensing and imaging scenarios. There is very little naturally occurring CP radiation in the long-wave IR band, so that useful functionalities may be obtained by exploiting preferential radiation and transmission characteristics of engineered metamaterials. Conventional CP devices in the IR utilize birefringent crystals, which are typically bulky and expensive to manufacture. The operation of these devices is generally optimized at a single wavelength. Imaging in the long-wave IR is most often broadband, so that achromatic CP-device behavior is highly desirable from a flux-transfer viewpoint. Also, size, weight and cost are significant drivers in the design of practical IR systems. Thus a solution is sought with a convenient thin planar form factor. This dissertation will demonstrate a novel planar periodic subwavelength-microstructured approach derived from classical radiofrequency meanderline designs that are able to generate CP radiation over a broad IR band while maintaining a low fabrication profile. We investigate issues regarding efficiency as a function of the number of layers in the device structure; reflective, transmissive, and emissive behavior; strategies for broadband achromatization; and thermal-isolation requirements between the active blackbody reservoir and the top of the planar device, to achieve a given degree of polarization. Theoretical, numerical, and experimental findings are presented that confirm the feasibility of this class of devices for use in a wide variety of situations, from polarization imaging and spectroscopy to industrial laser processing and machining.
Show less - Date Issued
- 2011
- Identifier
- CFE0003935, ucf:48686
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003935
- Title
- National Security and Political Polarization.
- Creator
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Funderburke, Joseph, Handberg, Roger, Pollock, Philip, Ilderton, Nathan, Kubiak, Jeffrey, University of Central Florida
- Abstract / Description
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This dissertation explores how partisan polarization among the political elites (the President and key Members of Congress) impacts national security decision-making. The research examines the relationship over time beginning at the start of the Cold War through 2014. In doing so, the research tests several hypotheses to determine the nature of the relationship and what the implications might be for future U.S. national security policy-making. There are three different approaches used in the...
Show moreThis dissertation explores how partisan polarization among the political elites (the President and key Members of Congress) impacts national security decision-making. The research examines the relationship over time beginning at the start of the Cold War through 2014. In doing so, the research tests several hypotheses to determine the nature of the relationship and what the implications might be for future U.S. national security policy-making. There are three different approaches used in the research centered on the same theory of partisan polarization. The first approach examines changes in the level of polarization and defense budgets each year. The second explores the impact of partisan polarization on the outcome of key roll-call votes on national security legislation. Lastly, the third approach studies the changes in polarization relative to the Presidents' decision to use force. Poole and Rosenthal (1984) argue that political polarization has increased among the political elite since the 1960s and the Republicans and Democrats continue to move further apart ideologically (Gray et al. 2015). I argue that the combined effect of polarization and a growing ideological divide between the two major political parties puts our collective national security at risk. Using analytical regression time series models and a qualitative analysis, the findings suggests that rising partisan polarization presents a clear and present threat to our national security.
Show less - Date Issued
- 2019
- Identifier
- CFE0007458, ucf:52662
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007458
- Title
- EFFECTS OF POLARIZATION AND COHERENCE ON THE PROPAGATION AND THE DETECTION OF STOCHASTIC ELECTROMAGNETIC BEAMS.
- Creator
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Salem, Mohamed, Rolland, Jannick, University of Central Florida
- Abstract / Description
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Most of the physically realizable optical sources are radiating in a random manner given the random nature of the radiation of a large number of atoms that constitute the source. Besides, a lot of natural and synthetic materials are fluctuating randomly. Hence, the optical fields that one encounters, in most of the applications are fluctuating and must be treated using random or stochastic functions. Within the framework of the scalar-coherence theory, one can describe changes of the...
Show moreMost of the physically realizable optical sources are radiating in a random manner given the random nature of the radiation of a large number of atoms that constitute the source. Besides, a lot of natural and synthetic materials are fluctuating randomly. Hence, the optical fields that one encounters, in most of the applications are fluctuating and must be treated using random or stochastic functions. Within the framework of the scalar-coherence theory, one can describe changes of the properties of any stochastic field such as the spectral density and the spectral degree of coherence on propagation in any linear medium, deterministic or random. One of the frequently encountered random media is the atmospheric turbulence, where the fluctuating refractive index of such medium severely degrades any signal propagating through it; especially it causes intensity fades of the signal. The usage of stochastic beams at the transmitter instead of deterministic ones has been suggested sometime ago to suppress the severe effects of intensity fluctuations caused by the atmospheric turbulence. In this dissertation, we study the usage of partially coherent beams in long path propagation schemes through turbulent atmosphere such as one frequently encounters in remote sensing, in the use of communication systems, and in guiding. Also the used detection scheme at the receiver is important to quantify the received signal efficiently, hence we compare the performance of incoherent (direct) detection versus coherent (heterodyne) detection upon the use of either one of them at the receiver of the communication system of beams propagating in turbulent atmosphere and namely we evaluate the signal-to-noise-ratio (SNR) for each case. The scalar-coherence theory ignored the vector nature of stochastic fields, which should be taken into account for some applications such as the ones that depend on the change of the polarization of the field. Recently generalization for the scalar-coherence theory including the vector aspects of the stochastic beams has been formulated and it is well-known as the unified theory of coherence and polarization of stochastic beams. The use of the unified theory of coherence and polarization makes it possible to study both the coherence properties and the polarization properties of stochastic electromagnetic beams on propagation in any linear media. The central quantity in this theory is a 2 × 2 matrix that describes the statistical ensemble of any stochastic electromagnetic beam in the space-frequency domain or its Fourier transform in the space-time domain. In this dissertation we derive the conditions that the cross-spectral density matrix of a so-called planar, secondary, electromagnetic Gaussian Schell-model source has to satisfy in order to generate a beam propagating in vacuum. Also based on the unified-theory of coherence and polarization we investigate the subtle relationship between coherence and polarization under general circumstances. Besides we show the effects of turbulent atmosphere on the degree of polarization and the polarization state of a partially coherent electromagnetic beam, which propagates through it and we compare with the propagation in vacuum. The detection of the optical signals is important; hence it affects the fidelity of the communication system. In this dissertation we present a general analysis for the optical heterodyne detection of stochastic electromagnetic beams. We derive an expression for the SNR when two stochastic electromagnetic beams are mixed coherently on a detector surface in terms of the space-time domain representation of the beams, the beam coherence polarization matrices. We evaluate also the heterodyne efficiency of a heterodyne detection system for stochastic beams propagating in vacuum and we discuss the dependence of the heterodyne efficiency of the detection process on the changes in the beam parameters as the beam propagates in free space.
Show less - Date Issued
- 2007
- Identifier
- CFE0001932, ucf:47445
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001932
- Title
- POLARIMETRIC CHARACTERIZATION OF RANDOM ELECTROMAGNETIC BEAMS AND APPLICATIONS.
- Creator
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Mujat, Mircea, Dogariu, Aristide, University of Central Florida
- Abstract / Description
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The polarimetric properties of random electromagnetic beams provide new means for characterizing random media. A novel interferometric technique is introduced for controlling the polarimetric, spectral, and coherence characteristics of random electromagnetic beams. Several new techniques are presented for measuring the state of polarization and the polarization transfer through scattering media. The polarimetric signatures of different particulate systems are related to their structural...
Show moreThe polarimetric properties of random electromagnetic beams provide new means for characterizing random media. A novel interferometric technique is introduced for controlling the polarimetric, spectral, and coherence characteristics of random electromagnetic beams. Several new techniques are presented for measuring the state of polarization and the polarization transfer through scattering media. The polarimetric signatures of different particulate systems are related to their structural properties and to the size distribution, shape, orientation, birefringent or dichroic properties of the particles. Various scattering regimes and different geometries are discussed for applications relevant to the bio-medical field, material science, and remote sensing.
Show less - Date Issued
- 2004
- Identifier
- CFE0000049, ucf:46132
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0000049
- Title
- THE STUDENT DEBT CRISIS AND POLITICAL POLARIZATION IN THE MILLENNIAL GENERATION.
- Creator
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Wallace, Dylan, Kinsey, Barbara, University of Central Florida
- Abstract / Description
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According to the Pew Research Center, the modern wave of political polarization began in 1994, and is the strongest today than it has ever been during the 23-year period. (2007) Polarization in the US party system is evidenced by several factors including: growing consistent partisan views, partisan antipathy, ideological bubbles, growing difference in preferences, a shrinking political center, and the lack of political compromise. (Pew Research Center 2014) The question I attempt to answer...
Show moreAccording to the Pew Research Center, the modern wave of political polarization began in 1994, and is the strongest today than it has ever been during the 23-year period. (2007) Polarization in the US party system is evidenced by several factors including: growing consistent partisan views, partisan antipathy, ideological bubbles, growing difference in preferences, a shrinking political center, and the lack of political compromise. (Pew Research Center 2014) The question I attempt to answer in this thesis is on the factors associated with political polarization within the millennial generation. One of the most pressing issues to this generation is what is known as the Student Loan Crisis, which is the $1.45 Trillion dollars Americans owe to private and federal lenders to attend college. (StudentLoanHero.com). In this thesis, I argue that economic inequality, via the student loan crisis, contributes to political polarization within the millennial generation. My analysis takes place at the level of the individual. I conduct a statistical analysis using the 2016 American National Election Survey Dataset, to test whether political polarization, operationalized as ideological and partisan polarization, is associated with polarization on economic issues that I link to wealth inequality in the millennial generation, controlling for polarization on social issues, interest in politics, and income. The main finding is that party/ideological polarization is positive and significantly related to polarization on economic issues in the millennial generation; whether or not the Student Loan Crisis underlies this link requires further study.
Show less - Date Issued
- 2018
- Identifier
- CFH2000381, ucf:45773
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFH2000381
- Title
- POLARIZATION DEPENDENT TWO-PHOTON ABSORPTION PROPERTIES OF CHIRAL MOLECULES.
- Creator
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Toro, Carlos, Hernandez, Florencio, University of Central Florida
- Abstract / Description
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Molecules that are non-superimposable on their mirror image are named chiral or optically active compound. Over the years, molecular chirality has played an essential role in the understanding of fundamental aspects associated the origin of life, drug and food technologies and, asymmetric catalysis, among others. Moreover, most of the groundbreaking discoveries and advances made in this field have happened due to the development of spectroscopic techniques based on the natural asymmetry of...
Show moreMolecules that are non-superimposable on their mirror image are named chiral or optically active compound. Over the years, molecular chirality has played an essential role in the understanding of fundamental aspects associated the origin of life, drug and food technologies and, asymmetric catalysis, among others. Moreover, most of the groundbreaking discoveries and advances made in this field have happened due to the development of spectroscopic techniques based on the natural asymmetry of the enantiomers and their ability to preferentially absorb right or left polarized light. For instance, circular dichroism (CD), which measures the difference in absorption between these two states of polarized light, has emerged as one of the most useful spectroscopic methods to identify and characterize chiral compounds. Unfortunately, CD is based on linear absorption which, in most common organic molecules, takes place in the UV region of the spectrum where the majority of organic solvents absorb as well. This certainly imposes limitations in the indiscriminated applicability of this technique to the study of chiral chromophores of biological interest in non-aqueous solutions. Consequently, a systematic and comprehensive characterization of the electronic and optical properties of such molecular entities still remains a major issue to be addressed. On this regard, nonlinear optics offers new alternatives to overcome some of the shortcomings of the standard linear CD-based spectroscopy. In order to surmount the existent limitations in this field and deepen in the fundamental understanding of chiral systems, we have mainly directed the attention of our research to the experimental and theoretical study of the polarization dependent two-photon absorption (2PA) of several chiral azo-compounds and binaphthol derivatives in solution. The first part of this dissertation (Chapters I-IV) covers a full characterization of the linear and nonlinear optical properties of a series of non-chiral and chiral azo derivatives. The combination of experimental techniques such as absorption, fluorescence, excitation anisotropy, circular dichroism, two-photon absorption and two-photon absorption circular-linear dichroism in combination with density functional theory calculations allowed us to unambiguously distinguish and assign the spectral position of the main electronic transitions (n-* and -*) in azobenzene derivatives. Our results represent a major contribution to the understanding of the electronic structure of these organic chromophores which have been reported of potential interest in the design of optoelectronic devices. Then, Chapter V describes the development of a novel experimental technique called the synchronized double L-scan for the study of polarization dependent multiphoton absorption in chiral samples. The high sensitivity of this technique resides in the use of ÃÂ"twinÃÂ" pulses to account for energy and mode fluctuations of the excitation pulse when determining absorption nonlinearities as a function of the light polarization. The robustness of this method was validated by measuring the first ever reported two-photon absorption circular dichroism (2PA-CD) spectrum on a chiral binaphthol derivative in solution. Finally, Chapters VI and VII compile an ample experimental and theoretical investigation of the chirality-dependent 2PA of axial enantiomers in solution. We combined the use of the synchronized double L-scan technique with state-of-the-art density functional theory calculations to provide a precise and reliable description of the contribution of the different electronic excited states to the 2PA-CD and 2PA-CLD spectra. Our findings are foreseen to have a tremendous impact in the comprehension of some of the most fundamental aspects of chiral phenomena.
Show less - Date Issued
- 2010
- Identifier
- CFE0003284, ucf:48529
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003284
- Title
- DESIGN OF A WIDEBAND DUAL-POLARIZED CAVITY BACKED SLOT ANTENNA.
- Creator
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Paryani, Rajesh, Wahid, Parveen F, University of Central Florida
- Abstract / Description
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A new technique for designing wideband dual-polarized cavity-backed slot antennas is presented. The structure is in the form of a double-resonant, dual-polarized slot antenna backed by a shallow substrate integrated cavity with a depth of approximately one tenth the free space wavelength. The presence of the cavity behind the slot enhances the antennaÃÂ's directivity and reduces the possibility of surface wave propagation in the antenna substrate when the element is...
Show moreA new technique for designing wideband dual-polarized cavity-backed slot antennas is presented. The structure is in the form of a double-resonant, dual-polarized slot antenna backed by a shallow substrate integrated cavity with a depth of approximately one tenth the free space wavelength. The presence of the cavity behind the slot enhances the antennaÃÂ's directivity and reduces the possibility of surface wave propagation in the antenna substrate when the element is used in an array environment. Moreover, the dual-polarized nature of this radiating element may be exploited to synthesize any desired polarization (vertical, horizontal, RHCP, or LHCP). The double-resonant behavior observed in this substrate-integrated cavity-backed slot antenna (SICBSA) is utilized to enhance its bandwidth compared to a typical cavity-backed slot antenna. A prototype of the proposed antenna is fabricated and tested. Measurement results indicate that a bandwidth of 19%, an average gain of 5.3 dB, and a wideband differential isolation of 30 dB can be achieved using this technique. The principles of operation along with the measurement results of the fabricated prototype are presented and discussed in this dissertation. The SICBSA is investigated as a candidate for use as an array element. A uniform two element phased array is demonstrated to locate the main beam from boresight to thirty degrees. The potential effects of mutual coupling and surface wave propagation are considered and analyzed.
Show less - Date Issued
- 2010
- Identifier
- CFE0003066, ucf:48295
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003066
- Title
- THE EFFECTS OF ECOTOURISM ON POLAR BEAR BEHAVIOR.
- Creator
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Eckhardt, Gillian, Waterman, Jane, University of Central Florida
- Abstract / Description
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Polar bears spend the majority of their lives on the sea ice, where they gain access to seals and mates. In western Hudson Bay, the sea ice melts for three to four months in the summer, and polar bears there are forced onto land. These bears live on their fat reserves for the duration of the iceless period, until temperatures get colder in the fall and freeze up begins. The aggregation of polar bears near Churchill, Manitoba during the ice free period has led to a thriving tourist industry,...
Show morePolar bears spend the majority of their lives on the sea ice, where they gain access to seals and mates. In western Hudson Bay, the sea ice melts for three to four months in the summer, and polar bears there are forced onto land. These bears live on their fat reserves for the duration of the iceless period, until temperatures get colder in the fall and freeze up begins. The aggregation of polar bears near Churchill, Manitoba during the ice free period has led to a thriving tourist industry, with a large influx of tourists visiting Churchill in the fall in a six to eight week period, yet little is known about the impacts of this industry on the biology of the bears. This study investigated the effect of tourist vehicles and human presence on the behavior of polar bears over the fall of 2003 and 2004. Overall time budgets were estimated for bears, and the behavior of males and females was compared. Females spent significantly less time lying and more time in locomotion than males. Time budgets were also estimated for bears in the presence and absence of tourist vehicles. Bears spent less time lying and more time in a sit/stand position in the presence of vehicles. Air temperature had no significant effect on the time budgets of polar bears. Tundra vehicle approaches were manipulated to determine effects on polar bear behavior, and to investigate any variables that significantly affected response, including habituation. A response was defined as any sudden whole body movement or change in position or behavior at the time of approach. A total of 25% of all bears responded to the experimental vehicle approach. For bears that responded to approach, the average distance at response was 43 m. The average speed of the vehicle was 0.66 ± 0.02 m/s (range 0.23 to 1.15 m/s). Approach variables that significantly influenced the likelihood of response of a bear to an approaching vehicle included angle of approach and vehicle speed. Direct approaches, in which the bear was in the path of the moving vehicle, had a higher probability of eliciting a response than indirect approaches, in which the vehicle stayed to one side of the bear at all times. Higher speeds of the vehicle increased the probability of a response by a bear. Behaviors of the bear that significantly predicted a response were shifting of the body and smacking of the lips. A playback study was conducted to determine the effects of human induced sound on polar bears. There was no significant effect of human sound on polar bears. Results presented here provide the first experimental evidence of variables in the tourist industry that affect polar bear behavior, and the first evidence of behavioral cues predicting a response to vehicle approach.
Show less - Date Issued
- 2005
- Identifier
- CFE0000544, ucf:46441
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0000544
- Title
- SELECTIVE MODE EXCITATION IN SPECIALTY WAVEGUIDES USING MICRO OPTICAL ELEMENTS.
- Creator
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Mohammed, Waleed, Johnosn, Eric, University of Central Florida
- Abstract / Description
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Although optical fibers and specialty waveguides are the base of majority of today's telecom and light delivery applications, fabrication deformation, nonlinearity and attenuation limit the bandwidth of the data being transmitted or the amount of power carried by these systems. One-way to overcome these limitations without changing the fibers design or fabrication is to engineer the input light in order to excite a certain mode or a group of modes with unique optical properties. Diffractive...
Show moreAlthough optical fibers and specialty waveguides are the base of majority of today's telecom and light delivery applications, fabrication deformation, nonlinearity and attenuation limit the bandwidth of the data being transmitted or the amount of power carried by these systems. One-way to overcome these limitations without changing the fibers design or fabrication is to engineer the input light in order to excite a certain mode or a group of modes with unique optical properties. Diffractive and micro optics are highly effective for selectively coupling light to specific modes. Using micro optics, mode selective coupling can be achieved through several matching schemes: phase only, phase and amplitude, or phase, amplitude and polarization. The main scope of this work is the design and fabrication of novel optical elements that overcome the limitations of these light delivery systems, as well as the characterization and analysis of their performance both experimentally and using numerical simulation
Show less - Date Issued
- 2004
- Identifier
- CFE0000171, ucf:46163
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0000171
- Title
- POLARIZATION-INDEPENDENT LIQUID CRYSTAL DEVICES.
- Creator
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Lin, Yi-Hsin, Wu, Shin-Tson, University of Central Florida
- Abstract / Description
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Liquid crystal (LC) devices can be operated as amplitude modulators and phase modulators. LC amplitude modulation is commonly used in liquid crystal display (LCD) while phase-only modulation is useful for laser beam steering, tunable grating, prism, lens, and other photonic devices. Most LC devices are polarization dependent and require at least one polarizer. As a result, the optical efficiency is low. To enhance display brightness, a power hungry backlight has to be used leading to a high...
Show moreLiquid crystal (LC) devices can be operated as amplitude modulators and phase modulators. LC amplitude modulation is commonly used in liquid crystal display (LCD) while phase-only modulation is useful for laser beam steering, tunable grating, prism, lens, and other photonic devices. Most LC devices are polarization dependent and require at least one polarizer. As a result, the optical efficiency is low. To enhance display brightness, a power hungry backlight has to be used leading to a high power consumption and short battery life. In a LC phase modulator, the polarization dependent property complicates the laser beam steering system. It is highly desirable to develop new operating mechanisms that are independent of the incident light polarization. In this dissertation, we have developed eight polarization-independent liquid crystal operation principles: three of them are aimed for displays and the other five are for phase modulators. For amplitude modulations, a new polymer-dispersed liquid crystal (PDLC) and two new dye-doped LC gels are polarizer-free by combining light scattering with dye-absorption effects. In phase modulation, we explore five device concepts: PDLC and Polymer-Stabilized Cholesteric Texture (PSCT), homeotropic LC gels, thin polymer film separated double-layered structure, and double-layered LC gels. In the low voltage regime, both PDLC and PSCT have a strong light scattering. However, as the voltage exceeds a certain level, the phase modulation is scattering-free and is independent of polarization. The homeotropic LC gels do not require any biased voltage and the response time is still fast. Although the remaining phase in these devices is small, they are still useful for micro-photonic device applications. To increase the phase change, thin polymer film separated double-layered structure is a solution. The orthogonal arrangement of top and bottom LC directors results in polarization independence. However, the response time is slow. Similarly, double-layered LC gels are not only polarization independent but also fast response due to the established polymer network.
Show less - Date Issued
- 2006
- Identifier
- CFE0000983, ucf:46706
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0000983
- Title
- Hybrid Integrated Photonic Platforms and Devices.
- Creator
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Chiles, Jeffrey, Fathpour, Sasan, Vodopyanov, Konstantin, Khajavikhan, Mercedeh, Chanda, Debashis, University of Central Florida
- Abstract / Description
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Integrated photonics has the potential to revolutionize optical systems by achieving drastic reductions in their size, weight and power. Remote spectroscopy, free-space communications and high-speed telecommunications are critical applications that would benefit directly from these advancements. However, many such applications require extremely wide spectral bandwidths, leading to significant challenges in their integration. The choice of integrated platform influences the optical...
Show moreIntegrated photonics has the potential to revolutionize optical systems by achieving drastic reductions in their size, weight and power. Remote spectroscopy, free-space communications and high-speed telecommunications are critical applications that would benefit directly from these advancements. However, many such applications require extremely wide spectral bandwidths, leading to significant challenges in their integration. The choice of integrated platform influences the optical transparency and functionality which can be ultimately achieved. In this work, several new platforms and technologies have been developed to meet these needs. First, the silicon-on-lithium-niobate (SiLN) platform is discussed, on which the first compact, integrated electro-optic modulator in the mid-infrared has been demonstrated. Next, results are shown in the development of the all-silicon-optical-platform (ASOP), an ultra-stable suspended membrane approach which offers broad optical transparency from 1.2 to 8.5 um and enables efficient nonlinear frequency conversion in the mid-IR. This fabrication approach is then taken further with (")anchored-membrane waveguides,(") (T-Guides) enabling single-mode and single-polarization waveguiding over a span exceeding 1.27 octaves. Afterward, a new photonic technology enabling integrated polarization beam-splitters and polarizers over unprecedented bandwidths is introduced, called topographically anisotropic photonics (TAP). Next, results on high-performance microphotonic chalcogenide glass waveguides are presented. Finally, several integrated photonics concepts suitable for further work will be discussed, such as augmentations to T-Guides and a novel technique for quasi-phase-matching.
Show less - Date Issued
- 2016
- Identifier
- CFE0006447, ucf:51408
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006447
- Title
- MICRO-OPTIC-SPECTRAL-SPATIAL-ELEMENTS (MOSSE).
- Creator
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Mehta, Alok, Johnson, Eric, University of Central Florida
- Abstract / Description
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Over a wide range of applications, optical systems have utilized conventional optics in order to provide the ability to engineer the properties of incident infra-red fields in terms of the transmitted field spectral, spatial, amplitude, phase, and polarization characteristics. These micro/nano-optical elements that provide specific optical functionality can be categorized into subcategories of refractive, diffractive, multi-layer thin film dichroics, 3-D photonic crystals, and polarization...
Show moreOver a wide range of applications, optical systems have utilized conventional optics in order to provide the ability to engineer the properties of incident infra-red fields in terms of the transmitted field spectral, spatial, amplitude, phase, and polarization characteristics. These micro/nano-optical elements that provide specific optical functionality can be categorized into subcategories of refractive, diffractive, multi-layer thin film dichroics, 3-D photonic crystals, and polarization gratings. The feasibility of fabrication, functionality, and level of integration which these elements can be used in an optical system differentiate which elements are more compatible with certain systems than others. With enabling technologies emerging allowing for a wider range of options when it comes to lithographic nano/micro-patterning, dielectric growth, and transfer etching capabilities, optical elements that combine functionalities of conventional optical elements can be realized. Within this one class of optical elements, it is possible to design and fabricate components capable of tailoring the spectral, spatial, amplitude, phase, and polarization characteristics of desired fields at different locations within an optical system. Optical transmission filters, polarization converting elements, and spectrally selective reflecting components have been investigated over the course of this dissertation and have been coined MOSSE,' which is an acronym for micro-optic-spectral-spatial-elements. Each component is developed and fabricated on a wafer scale where the thin film deposition, lithographic exposure, and transfer etching stages are decoupled from each other and performed in a sequential format. This facilitates the ability to spatially vary the optical characteristics of the different MOSSE structures across the surface of the wafer itself.
Show less - Date Issued
- 2007
- Identifier
- CFE0001962, ucf:47457
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001962
- Title
- WIDE VIEWING ANGLE LIQUID CRYSTAL DISPLAYS.
- Creator
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Hong, Qi, Wu, Shin-Tson, University of Central Florida
- Abstract / Description
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In this dissertation, novel phase compensation technologies are applied to the designs of wide viewing angle and high transmittance liquid crystal displays. First, a design of wide viewing angle liquid crystal displays utilizing crossed linear polarizers is proposed. The designed multi-domain vertical-alignment liquid crystal display predicts superb contrast ratio over wide viewing angles. Next, to increase the bright state transmittance while maintain the high contrast. Finally, to reduce...
Show moreIn this dissertation, novel phase compensation technologies are applied to the designs of wide viewing angle and high transmittance liquid crystal displays. First, a design of wide viewing angle liquid crystal displays utilizing crossed linear polarizers is proposed. The designed multi-domain vertical-alignment liquid crystal display predicts superb contrast ratio over wide viewing angles. Next, to increase the bright state transmittance while maintain the high contrast. Finally, to reduce the cost and improve the applicability of the broadband and wide-view circular polarizer, the device configuration of the broadband and wide-view circular polarizer is significantly simplified by the application of biaxial compensation films. The produced states of polarization remain close to the ideal circular polarization over a wide range of incident angles within the visual spectrum. With this circular polarizer, the presented wide-view liquid crystal display predicts high contrast ratio as well as high and uniform transmittance over wide viewing angles within the visual spectrum. ratio, wide viewing angle circular polarizers are developed. The produced states of polarization are very close to the ideal circular state of polarization over a wide range of incident angles within the visual spectrum. This guarantees not only high contrast ratio but also high and uniform transmittance.
Show less - Date Issued
- 2006
- Identifier
- CFE0001378, ucf:46963
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001378
- Title
- Sub-Terahertz Spin Pumping from an Insulating Antiferromagnet.
- Creator
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Vaidya, Priyanka, Del Barco, Enrique, Neupane, Madhab, Nakajima, Yasuyuki, Hernandez, Florencio, University of Central Florida
- Abstract / Description
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The combination of the spin transfer torque and spin Hall effects, or their reciprocal dynamical spin pumping and inverse spin Hall effects, respectively, enable reading and controlling the magnetization state in spintronics devices which are at the verge of mass commercialization as the next generation of energy-efficient and fast magnetic random-access memory applications with the use of ferromagnetic elements, e.g., the spin valve. However, these effects have remained elusive in...
Show moreThe combination of the spin transfer torque and spin Hall effects, or their reciprocal dynamical spin pumping and inverse spin Hall effects, respectively, enable reading and controlling the magnetization state in spintronics devices which are at the verge of mass commercialization as the next generation of energy-efficient and fast magnetic random-access memory applications with the use of ferromagnetic elements, e.g., the spin valve. However, these effects have remained elusive in antiferromagnetic-based devices up to date, despite the fascinating advantages offered by the absence of stray fields (zero net magnetization), Terahertz spin dynamics, and the widespread availability of metallic, insulating and semiconducting antiferromagnetic materials. In this thesis I report the first demonstration of sub-Terahertz dynamical spin pumping at the interface between an antiferromagnet and a non-magnetic material; more specifically a uniaxial insulating antiferromagnet MnF2 and heavy metal Pt. The measured ISHE signal generated by the corresponding spin-charge current interconversion in the platinum layer is modulated by the handedness of the circularly polarized sub-THz irradiation. This effect results directly from the opposite chirality of each of the fundamental dynamical modes of the antiferromagnet. Contrary to the case of ferromagnets, this observation in an antiferromagnetic system allows unambiguously differentiating coherent spin pumping from incoherent spin Seeback effect, by which electric signals result from thermal activation. A complete study of the generated electric signals at the antiferromagnetic resonances, the spin-flop mode and the transition between the two regimes as the microwave polarization is continuously varied from circular to linear polarizations enabled an understanding of the different phenomena governing interconversion of spin dynamics and charge currents at the MnF2/Pt interface.
Show less - Date Issued
- 2019
- Identifier
- CFE0007870, ucf:52776
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0007870
- Title
- Evaluating Corrosion Control Alternatives for a Reverse Osmosis, Nanofiltration and Anion-Exchange Blended Water Supply.
- Creator
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Wilder, Rebecca, Duranceau, Steven, Randall, Andrew, Zhang, Husen, University of Central Florida
- Abstract / Description
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The research reported herein describes the study activities performed by University of Central Florida (UCF) on behalf of the Town of Jupiter Water Utilities (Town). The Town recently changed its water treatment operations from a combination of reverse osmosis (RO), lime softening (LS) and anion-exchange (IX) to a combination of RO, IX and nanofiltration (NF). Although this treatment change provided enhanced water to the surrounding community in terms of better contaminant removal and reduced...
Show moreThe research reported herein describes the study activities performed by University of Central Florida (UCF) on behalf of the Town of Jupiter Water Utilities (Town). The Town recently changed its water treatment operations from a combination of reverse osmosis (RO), lime softening (LS) and anion-exchange (IX) to a combination of RO, IX and nanofiltration (NF). Although this treatment change provided enhanced water to the surrounding community in terms of better contaminant removal and reduced DBP formation potential, integration of the NF process altered finished water quality parameters including pH, alkalinity and hardness. There was concern that these changes could result in secondary impacts related to accelerated corrosion of distribution system components and subsequent regulatory compliance. In addition, replacement of the LS process altered the in-plant blending operations by creating an unstable intermediate blend composed of RO and IX waters. There were concerns that this intermediate blend was affecting the integrity of in-plant hydraulic conveyance components.UCF developed a corrosion monitoring study to assess the potential impacts related to internal corrosion, water quality and regulatory compliance after integrating NF into the existing water supply. The intended purpose was to further highlight the complexities of corrosion, describe a unique approach to corrosion monitoring as well as offer various recommendations for corrosion control in a system that relies on a blended water supply. Research was conducted in three phases to address the in-plant and distribution system corrosion issues separately and identify appropriate corrosion control treatment alternatives. The three test phases included: a baseline conditions assessment to compare corrosion of the intermediate RO-IX blend with the finished water blend (RO-IX-NF); an in-plant corrosion control evaluation; and a distribution system corrosion control evaluation.A test apparatus was constructed and operated at the Town's facilities to monitor corrosion activity of mild steel, copper and lead solder metal components. The test apparatus consisted of looped PVC pipe segments housed with electrochemical probes and metal coupons to monitor corrosion rates of the metallic components. Electrochemical probes containing metal electrodes were used to obtain instantaneous corrosion rates by means of the Linear Polarization Resistance (LPR) technique while the metal coupons were gravimetrically evaluated for weight loss. The electrochemical probes permitted daily monitoring of each metal's corrosion rates while metal coupons were analyzed at the conclusion of testing and used for comparison. Different test waters flowed through the corrosion rack according to each test phase and relative corrosion rates were compared to evaluate corrosion control techniques.Study findings indicated that the intermediate blend was more corrosive, in general, then the final blend; however, research also indicated that the final blend of water was increasing lead and copper concentrations within the distribution system. An orthophosphate corrosion inhibitor was evaluated for in-plant corrosion control. The inhibitor's performance was assessed by comparing mild steel corrosion rates with and without the chemical. In addition, secondary impacts related to introduction of the chemical were evaluated by pre-corroding the metallic components prior to the introduction of the inhibitor. Results indicated that the inhibitor marginally decreased corrosion rates and increased the turbidity of the water supply. Based on these observations, it was concluded that the inhibitor was not a viable solution for in-plant corrosion control. To resolve in-plant corrosion issues, recommendations were made for modification of in-plant blending operations to eliminate the corrosive intermediate blend from the process allowing the RO, IX and NF treated waters to be blended in a common location. The effectiveness of a poly/ortho blended phosphate chemical inhibitor was evaluated for reducing lead and copper corrosion to resolve distribution corrosion issues. A 50/50 poly/ortho blend was selected because of its analogous use in similar municipal water facilities. Metallic corrosion rates, particularly lead and copper, were compared with and without the inhibitor to assess the performance of the chemical. Like the previous test phase, the metallic components were pre-corroded prior to the chemical's introduction to determine if secondary impacts could result from its presence. Results indicated that lead and copper corrosion rates were lower in the presence of the inhibitor, and secondary impacts related to increased turbidity were not observed for this chemical. Based on these results, it was recommended that a poly/ortho blended phosphate be used to decrease lead and copper corrosion within the Town's distribution system.
Show less - Date Issued
- 2012
- Identifier
- CFE0004460, ucf:49349
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004460
- Title
- NEAR-FIELD OPTICAL INTERACTIONS AND APPLICATIONS.
- Creator
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Haefner, David, Dogariu, Aristide, University of Central Florida
- Abstract / Description
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The propagation symmetry of electromagnetic fields is affected by encounters with material systems. The effects of such interactions, for example, modifications of intensity, phase, polarization, angular spectrum, frequency, etc. can be used to obtain information about the material system. However, the propagation of electromagnetic waves imposes a fundamental limit to the length scales over which the material properties can be observed. In the realm of near-field optics, this limitation is...
Show moreThe propagation symmetry of electromagnetic fields is affected by encounters with material systems. The effects of such interactions, for example, modifications of intensity, phase, polarization, angular spectrum, frequency, etc. can be used to obtain information about the material system. However, the propagation of electromagnetic waves imposes a fundamental limit to the length scales over which the material properties can be observed. In the realm of near-field optics, this limitation is overcome only through a secondary interaction that couples the high-spatial-frequency (but non-propagating) field components to propagating waves that can be detected. The available information depends intrinsically on this secondary interaction, which constitutes the topic of this study. Quantitative measurements of material properties can be performed only by controlling the subtle characteristics of these processes. This dissertation discusses situations where the effects of near-field interactions can be (i) neglected in certain passive testing techniques, (ii) exploited for active probing of static or dynamic systems, or (iii) statistically isolated when considering optically inhomogeneous materials. This dissertation presents novel theoretical developments, experimental measurements, and numerical results that elucidate the vectorial aspects of the interaction between light and nano-structured material for use in sensing applications.
Show less - Date Issued
- 2010
- Identifier
- CFE0003095, ucf:48318
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0003095
- Title
- Control of Metal-Release and Tuberculation in a Silica-Laden Groundwater Distribution System on the Volcanic Island of Lana'i.
- Creator
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Myers, Samantha, Duranceau, Steven, Sadmani, A H M Anwar, Lee, Woo Hyoung, University of Central Florida
- Abstract / Description
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A corrosion control study for two distinct water distribution systems (WDS) has been completed for the Pulama Lana'i Water Company (Pulama). This project evaluated the use of chemical inhibitors to control corrosion and tuberculation within the Manele Bay WDS and the Lana'i City WDS. Pulama provides water to a population of 3,100 residents and is considering incorporating alternative water supplies in the future. Hence, knowing baseline corrosion rates within the WDS was desired.Several...
Show moreA corrosion control study for two distinct water distribution systems (WDS) has been completed for the Pulama Lana'i Water Company (Pulama). This project evaluated the use of chemical inhibitors to control corrosion and tuberculation within the Manele Bay WDS and the Lana'i City WDS. Pulama provides water to a population of 3,100 residents and is considering incorporating alternative water supplies in the future. Hence, knowing baseline corrosion rates within the WDS was desired.Several groundwater wells feed each of the WDS's; however, water quality between wells varies. Well water supplied to the WDS's is generally of high quality, therefore, the historical treatment method has been limited to disinfection prior to distribution. The distribution system consists of several materials of construction, which includes galvanized iron. Valves and pipes within the WDS were experiencing visible corrosion and tuberculation believed to be responsible for variable pressure drop throughout portions of the system.In this work, two corrosion racks, each consisting of two parallel loops, were designed, constructed, and installed at each site. One loop was maintained as a control while the other loop was used for testing alternative corrosion inhibitors. The racks utilized metal sample coupons and linear polarization resistance probes to provide data on corrosion rates of selected metals of interest.Results indicated that the water in Manele Bay experienced no noticeable change between the test loop and control loop when a corrosion inhibitor was added. A first experiment found the corrosion rates reached baseline steady(-)state at 4,000 operational hours. A second experiment found that the corrosion rates reached baseline steady(-)state at 2,200 operational hours. During these two experiments, the addition of a phosphate or silica(-)based inhibitor neither reduced nor increased the corrosion rates of mild steel, lead, and copper.Results from Lana'i City indicated that inhibitors offered little to no positive effect between the control condition and the test condition. During the first experiment, baseline corrosion was reached after 2,400 hours. The addition of a phosphate inhibitor did not reduce nor increase the corrosion rates of mild steel and lead. However, the corrosion rate of copper increased to 1.0mpy from 0.22mpy. The corrosion rate remained elevated after inhibitor feed was terminated. The second experiment reached baseline corrosion rates at 1,400 operational hours. The use of silica inhibitor neither reduced nor increased the corrosion rate of mil steel, lead, and copper.Since corrosion inhibitors were found to be ineffective, a valve exercise and replacement program for Pulama's assets was recommended. This program included: (1) developing a detailed asset inventory, (2) implementing operation and maintenance tasks, (3) forming a valve replacement plan, and (4) establishing long range financial planning. An opinion of probable replacement cost for 200 new valves was conceptually estimated to approximate 3.3 million dollars expended over a 20 year time frame.
Show less - Date Issued
- 2016
- Identifier
- CFE0006152, ucf:51152
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0006152
- Title
- Institutional vs. Non-Institutional Sources of Presidential Influence: Explaining Congressional-Presidential Relations in the Age of Polarization.
- Creator
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Culp, Derek, Ilderton, Nathan, Lanier, Drew, Houghton, David, University of Central Florida
- Abstract / Description
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This thesis examines the determinants of presidential success with Congress. Seven essential sources of presidential power in the current era of party polarization were derived from the extant literature, and these factors were delineated into the institutional (formal) and non-institutional (informal) policymaking tools of the presidency. Variables that explain presidential legislative success include: intraparty support in Congress, the use of veto bargaining, executive orders and signing...
Show moreThis thesis examines the determinants of presidential success with Congress. Seven essential sources of presidential power in the current era of party polarization were derived from the extant literature, and these factors were delineated into the institutional (formal) and non-institutional (informal) policymaking tools of the presidency. Variables that explain presidential legislative success include: intraparty support in Congress, the use of veto bargaining, executive orders and signing statements (institutional factors); as well as public approval, 'going public,' and strategic lobbying of Congress (non-institutional factors). Case studies of the presidencies of Bill Clinton and George W. Bush analyze the role of these policymaking tools in four key legislative battles of each presidency. Regression models were constructed to test the effect of these variables on presidential legislative success. The case studies elucidate the relationship between non-institutional factors and their subsequent impact on key presidential policy priorities, particularly the interaction between public approval and going public. Findings indicate a positive relationship between a president's strategic bargaining ability with Congress and subsequent legislative success. Findings also show no significant relationship between intraparty support and presidential success when focusing on only key legislative battles between the executive and legislative branches, contrary to the findings of prior research. Future research might examine the various relationships between these policymaking tools and how they affect the nature of presidential power in the current era of heightened party polarization and ideological homogeneity.
Show less - Date Issued
- 2013
- Identifier
- CFE0004832, ucf:49705
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004832