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Andersen, Jaime. "The gender wage gap : exploring the explanations." Manhattan, Kan. : Kansas State University, 2008. http://hdl.handle.net/2097/760.
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Choueiri, George H. "Experimental Investigations of Flow Development, Gap Instability and Gap Vortex Street Generation in Eccentric Annular Channels." Thèse, Université d'Ottawa / University of Ottawa, 2014. http://hdl.handle.net/10393/31017.
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Isothermal flow development, gap instability, and gap vortex street generation in eccentric annular channels have been studied experimentally. A representative paradigm of a flow in a highly eccentric annular channel was examined for a channel having an inner-to-outer diameter ratio d/D = 0.50 and an eccentricity e = 0.8 for a Reynolds number Re = 7300. Observation of the flow development has identified three distinct regions: the entrance region, the fluctuation-growth region and the rapid-mixing region. Weak quasi-periodic velocity fluctuations were first detected in the downstream part of the entrance region, and grew into very strong ones, reaching peak-to-peak amplitudes in the narrow gap that were nearly 60% of the bulk velocity. The dependence on inlet conditions, d/D, e and Re on the development and structure of flows was also investigated. Experimental conditions covered the ranges: 0 ≤ Re ≤ 19000, 0 ≤ e ≤ 0.9 and d/D = 0.25, 0.50 and 0.75. For Re < 7000, the Strouhal number, the normalized mid-gap axial flow velocity and the axial and cross-flow fluctuation intensities at mid-gap were found to increase with increasing Re and to depend strongly on inlet conditions. At higher Re, however, these parameters reached asymptotic values that were only mildly sensitive to inlet conditions. A map was constructed for the various stages of periodic motions vs. e and Re and it was found that, for e < 0.5 or Re < 1100, the flow was unconditionally stable as far as gap instability is concerned. For e ≤ 0.5, transition to turbulence occurred at Re ≈ 6000, whereas, for 0.6 ≤ e ≤ 0.9, the critical Reynolds number for the formation of periodic motions was found to increase with eccentricity from 1100 for e = 0.6 to 3800 for e = 0.9. The use of an empirically derived "mixing layer Strouhal number" permitted a universal description of gap vortex street periodicity in eccentric annular channels. This study has contributed to our understanding of the physical mechanisms that lead to gap instability and the development of a gap vortex street and the dependence of these flow phenomena on the channel geometry and the dynamic conditions of the flow.
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Lacková, Lucie. "Hodnocení výkonnosti systému DPH v zemích EU." Master's thesis, Vysoká škola ekonomická v Praze, 2014. http://www.nusl.cz/ntk/nusl-201563.
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The thesis assesses measurements of the VAT efficiency. It compares the tax quota, implicit tax rate and VAT revenue ratio. The first chapter deals with theoretical foundations for a flat rate consumption tax. Following chapters discuss the perquisites for VAT efficiency calculations (comparing actual VAT revenue and theoretical amount of tax base). Following chapters assess the above mentioned calculations, with special respect to VAT Revenue Ratio, which is analyzed in detail and to which is presented a comparison across the EU countries. The thesis further analyses Policy Efficiency Ratio (policy gap) and Compliance Efficiency Ratio (compliance gap). In its conclusion it summarizes the information gathered and presents a number of possible improvements.
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Hays, James M. "Student to Teacher Racial/Ethnic Ratios as Contributors to Regional Achievement Gaps, 1999-2008." Thesis, University of North Texas, 2011. https://digital.library.unt.edu/ark:/67531/metadc103326/.
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With the advent of No Child Left Behind legislation in 2002 and its mandates for annual yearly progress for all students, many districts and schools in Texas have had difficulty elevating African American and Hispanic students’ scores. The current study examined these students’ achievement on the annual Texas high-stakes measure as a function of a numerical construct that aligns the race/ethnicity of students when the teacher race is White. Earlier studies have shown that racial/ethnic compatibility between students and teachers improves student achievement in the primary grades. The study, which was set in 10 north Texas school districts and 30 high schools, middle schools, and elementary schools, examined African American and Hispanic students’ achievement on the Texas state assessments in reading and mathematics over a 10-year period. District performance data came from 4,664,192 African American, Hispanic, and White students and 222, 834 White teachers. Campus level data encompassed 188,839 10th graders, 93,573 eighth graders, and 40,083 fourth graders, and 20,471 White teachers. Analysis revealed that, as the ratios of African American and Hispanic students to White teachers increased, the percentages of these two student groups passing the Texas assessments decreased. These patterns differed for White students whose passing percentages increased as these students’ numbers increased relative to White teachers in all settings except in elementary schools. These preliminary findings suggested that racial alignment at the high school and middle school levels might elevate African American and Hispanic achievement. Implications may lead to shifting focus on teacher quality and class size as the primary determinants of student achievement. Findings need validation with further study using larger data sets and sequential grade levels. If validated through further studies involving larger samples, contiguous grade levels, and more sophisticated statistical analysis, this study’s findings may have implications for teacher education curriculum, recruitment of minority teacher candidates, workforce retention, and state policy on class size limits.
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Van, Gaalen Joseph Frank. "Alternative Statistical Methods for Analyzing Geological Phenomena: Bridging the Gap Between Scientific Disciplines." Scholar Commons, 2011. http://scholarcommons.usf.edu/etd/3424.
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When we consider the nature of the scientific community in conjunction with a sense of typical economic circumstances we find that there are two distinct paths for development. One path involves hypothesis testing and evolution of strategies that are linked with iterations in equipment advances. A second, more complicated scenario, can involve external influences whether economic, political, or otherwise, such as the government closure of NASA's space program in 2011 which will no doubt influence research in associated fields. The following chapters are an account of examples of two statistical techniques and the importance of both on the two relatively unrelated geological fields of coastal geomorphology and ground water hydrology.
The first technique applies a multi-dimensional approach to defining groundwater water table response based on precipitation in areas where it can reasonably be assumed to be the only recharge. The second technique applies a high resolution multi-scalar approach to a geologic setting most often restricted to either high resolution locally, or low resolution regionally. This technique uses time-frequency analysis to characterize cuspate patterns in LIDAR data are introduced using examples from the Atlantic coast of Florida, United States. These techniques permit the efficient study of beachface landforms over many kilometers of coastline at multiple spatial scales. From a LIDAR image, a beach-parallel spatial series is generated. Here, this series is the shore-normal position of a specific elevation (contour line). Well-established time-frequency analysis techniques, wavelet transforms, and S-Transforms, are then applied to the spatial series. These methods yield results compatible with traditional methods and show that it is useful for capturing transitions in cuspate shapes. To apply this new method, a land-based LIDAR study allowing for rapid high-resolution surveying is conducted on Melbourne Beach, Florida and Tairua Beach, New Zealand. Comparisons and testing of two different terrestrial scanning stations are evaluated during the course of the field
investigation.
Significant cusp activity is observed at Melbourne Beach. Morphological observations and sediment analysis are used to study beach cusp morphodynamics at the site. Surveys at Melbourne were run ~500 m alongshore and sediment samples were collected intertidally over a five-day period. Beach cusp location within larger scale beach morphology is shown to directly influence cusp growth as either predominantly erosional or accretional. Sediment characteristics within the beach cusp morphology are reported coincident with cusp evolution. Variations in pthesis size distribution kurtosis are exhibited as the cusps evolve; however, no significant correlation is seen between grain size and position between horn and embayment. During the end of the study, a storm resulted in beach cusp destruction and increased sediment sorting.
In the former technique using multi-dimensional studies, a test of a new method for improving forecasting of surficial aquifer system water level changes with rainfall is conducted. The results provide a more rigorous analysis of common predictive techniques and compare them with the results of the tested model. These results show that linear interpretations of response-to-rainfall data require a clarification of how large events distort prediction and how the binning of data can change the interpretation. Analyses show that the binning ground water recharge data as is typically done in daily format may be useful for quick interpretation but only describes how fast the system responds to an event, not the frequency of return of such a response. Without a secure grasp on the nonlinear nature of water table and rainfall data alike, any binning or isolation of specific data carries the potential for aliasing that must be accounted for in an interpretation. The new model is proven capable of supplanting any current linear regression analysis as a more accurate means of prediction through the application of a multivariate technique. Furthermore, results show that in the Florida surficial aquifer system response-to-rainfall ratios exhibit a maxima most often linked with modal stage.
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Desai, Urvi. "Impact of Medicare Part D coverage gap on beneficiaries' adherence to prescription medications." VCU Scholars Compass, 2011. http://scholarscompass.vcu.edu/etd/2571.
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INTRODUCTION: Medicare Part D provides prescription drug coverage to seniors through a benefit plan with a major deductible inserted in the middle. It is important to study the extent to which this structure affects seniors’ adherence to prescription medications. Therefore, this study had the following objectives: (1) To identify characteristics of beneficiaries reaching and not reaching the coverage gap, (2) To study the entry and exit times from the coverage gap, (3) To study the impact of a complete gap in coverage on beneficiaries’ adherence to prescription medications, (4) To study the impact of a partial gap in coverage on beneficiaries’ adherence to prescription medications METHODS: This was a retrospective quasi-experimental analysis with matched control groups using a nationally representative sample of Part D enrollees from 2008 Centers for Medicare and Medicaid (CMS) datasets. Adherence to each oral medication taken for one or more of the seven pre-defined therapeutic classes before and after reaching the coverage gap was measured using the Medication Possession Ratio (MPR). Appropriate statistical tests for significance were performed for each analysis RESULTS: A quarter of our sample (24.42%) reached the coverage gap in 2008. Most of the beneficiaries reaching the coverage gap did so by end of September. Those reaching the coverage gap and losing all coverage experienced significantly greater reductions in adherence (3% more for beta-blockers to 9% more for oral anti-diabetic agents), compared to those not reaching the coverage gap. A considerable proportion of beneficiaries stopped taking medications in both the groups and the proportion of beneficiaries considered adherent also dropped in both the groups during the coverage gap period. CONCLUSIONS: Medicare Part D beneficiaries face significant barriers to adherence and this is especially highlighted among those reaching the coverage gap. Interventions to improve adherence in this group should target all beneficiaries, especially those with several chronic conditions.
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Dwivedi, Bhakti. "Impact of molecular evolutionary footprints on phylogenetic accuracy a simulation study /." Dayton, Ohio : University of Dayton, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1250807136.
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Taghvatalab, Golnaz. "The Economics of Marriage and Divorce in Iran." Diss., Virginia Tech, 2012. http://hdl.handle.net/10919/77981.
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This dissertation consists of four chapters on the economics of marriage and divorce in Iran. The first chapter outlines major forces driving the recent transitions in Iran's marriage market. Age structure of the population, the rise of women's education, marriage and divorce laws, and fertility decline are the four main forces influencing marriage transitions, that is, the age of marriage, couple's age and education gaps, quality of marriage (stability, education status of children), and women's power within marriage.
Chapter two looks at the change in age structure that influences the sex ratio. I consider the influence of the sex ratio on couples' age and education gaps using data from multiple national surveys from 1984-2007. The findings of this chapter show that a lower sex ratio, i.e. a greater supply of marriage-age women, increases the bargaining power of men at the time of marriage and thereby increases their ability to marry younger and more educated women.
In chapter three, I evaluate the effects of demographic change, the sex ratio, and policy change, particularly the provision of family planning programs through health clinics on delayed marriage in rural Iran. I use data from Iran's 2000 Demographic and Health Survey to estimate a hazard model of timing of marriage. The results show that a lower sex ratio decreases the chances of a woman finding a man five years older, and easier access to family planning decreases her probability of marriage.
In chapter four, I provide a legal history of Iran's marriage and divorce laws and then discuss how changes in the legal structure of marriage and divorce alter the terms of marital bargaining and force women to circumvent inequitable Iranian laws to improve their position. Then, I present a model of how Mahrieh could improve a woman's position within the household in light of the unequal divorce rights favoring men. As women cannot exit their marriage, they request a conditional and legally enforceable bond known as Mahrieh from their husbands to secure themselves against the risks of divorce or maltreatment within marriage.Ph. D.
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Sun, Yu. "Theoretical and Experimental Studies on the Minimum Size 2-edge-connected Spanning Subgraph Problem." Thèse, Université d'Ottawa / University of Ottawa, 2013. http://hdl.handle.net/10393/24198.
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A graph is said to be 2-edge-connected if it remains connected after the deletion of any single edge. Given an unweighted bridgeless graph G with n vertices, the minimum size 2-edge-connected spanning subgraph problem (2EC) is that of finding a 2-edge-connected spanning subgraph of G with the minimum number of edges. This problem has important applications in the design of survivable networks. However, because
the problem is NP-hard, it is unlikely that efficient methods exist for solving it. Thus efficient methods that find solutions that are provably close to optimal are sought.
In this thesis, an approximation algorithm is presented for 2EC on bridgeless cubic graphs which guarantees to be within 5/4 of the optimal solution value, improving on the previous best proven approximation guarantee of 5/4+ε for this problem. We also focus on the linear programming (LP) relaxation of 2EC, which provides important lower bounds for 2EC in useful solution techniques like branch and bound. The “goodness” of this lower bound is measured by the integrality gap of the LP relaxation for 2EC, denoted by α2EC. Through a computational study, we find the exact value of α2EC for graphs with small n. Moreover, a significant improvement is found for the lower bound on the value of α2EC for bridgeless subcubic graphs, which improves the known best lower bound on α2EC from 9/8 to 8/7.
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Antoun, labib Joseph. "Modélisation des écoulements confinés entre un stator et un rotor ultra-rapide." Thesis, Paris, ENSAM, 2016. http://www.theses.fr/2016ENAM0079/document.
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Le projet e-MECA : electro-Mécanique Embarquée à Compacité Améliorée, dont l’objectif est de concevoir une machine ultra compacte et ultra rapide à une puissance utile de 12Kw, trouve son application dans les véhicules mild et full hybrides. Ce type de machine présente en effet un fort potentiel de déploiement industriel en très grandes séries à des prix abordables. Pour ces machines, les pertes de charge liées aux écoulements dans le jeu constituent des enjeux essentiels pour les constructeurs. La présente étude porte sur le moyen d’identifier de ces pertes des machines électriques ultra-compactes et ultra-rapides (50 000 rpm).Cette thèse a pour objet l’étude des pertes aérauliques dans l’espace entre le rotor et le stator d’une machine électrique ultra-rapide (≈ 250 m/s) et ultra-compacte (0,5mm - 2mm d’entrefer), en cherchant à répondre aux spécifications élaborées par nos partenaires dans le cadre du projet e-MECAThe project e-MECA: electromechanical engineering Embarked in Improved Compactness, the objective of which is to design a machine with a small gap and high speed rotor with a useful power of 12Kw, finds its application in mild and hybrid vehicle. This type of machine indeed presents a high potential in the industrial deployment in very big series to affordable prices. The losses in these machines are linked to the flow in the gap has a significant importance for the manufacturers. This study aims to identify these losses for the ultra-compact and ultrafast electric machines (50 000 rpm).This thesis is a study of the air losses in the space between the rotor and the stator of an ultra-fast electric machine (≈ 250 m/s) and ultra-compact (0,5mm - 2mm of air-gap). This study was done to meet the specifications that had been elaborated by our partners in the e-MECA project
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Arsenyev, Sergey A. "Photonic band gap structures for superconducting radio-frequency particle accelerators." Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/107281.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Nuclear Science and Engineering, 2016.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 175-181).
This thesis presents the design and testing of the first multi-cell superconducting accelerating cavity with a photonic band gap (PBG) coupler cell. The structure serves as a building block for superconducting radio-frequency (SRF) electron accelerators. It has five accelerating cells: four cells of elliptical shape, commonly used for SRF cavities, and one PBG cell in the middle. The purpose of the PBG cell is to damp unwanted Higher-Order electromagnetic Modes (HOMs) in the structure. Strong HOM damping is highly desirable for SRF cavities because it increases maximum achievable beam current by reducing the negative effect that HOMs have on the propagating electron beam. In the presented structure, effective HOM damping is achieved because of the inherent frequency selective properties of the PBG cell. The HOM spectrum in the five-cell cavity was carefully analyzed using eigenmode and wakefield simulations with good agreement between the two methods. The simulations showed that most of the dangerous HOMs were damped to fairly low external quality factors on the order of 102-104. This in principle implies that the new multicell cavity will support much higher beam currents than achievable in conventional SRF cavities that are not optimized for high-current operation. The improved HOM damping does not significantly compromise the accelerating properties of the cavity which are comparable to those of the cavities that only use the elliptical cells. Additionally, the PBG cavity does not need HOM couplers on the beam-pipe sections of the structure, and hence for the same amount of acceleration has a shorter length in the direction of the propagating beam. The five-cell cavity was fabricated of high purity niobium. Fabrication and tuning mechanisms were successfully tested on a copper prototype before being implemented for the niobium cavity. The accelerating gradient profile in the tuned niobium cavity matched the desired profile within a 5% accuracy. Two cryogenic tests were conducted with the five-cell cavity. The first test did not succeed due to a problem with the low quality factor of the cavity's accelerating mode. The problem was identified as a poor waveguide joint in the fundamental power coupler. Modifications were made to the waveguide joint and a second cryogenic test was conducted. In the second test, the high cavity quality factor was demonstrated at the temperature of 4.2 K for accelerating gradients up to 3 MV/m. The measured value of the cavity's quality factor with all ports closed was 1.55 x 108, in agreement with the prediction. This agreement indicated that the implemented surface treatment was effective in the cavity, including the complex PBG cell. No cavity leaks were observed during the tests in superfluid helium, proving the reliability of the fabrication process which included difficult electron-beam welds. No hard barriers in the accelerating gradient were observed during the test, indicating the absence of fundamental limits to cavity's operation for the gradient of at least several MV/m. A series of room-temperature experiments were conducted to measure external quality factors of six dangerous HOMs in the fabricated five-cell cavity. The measurements agreed with the simulations, showing all of the measured Q-factors below 3 x 103. Effective HOM damping, together with the ability to support accelerating gradients of multiple MV/m at cryogenic temperatures, makes the cavity an attractive candidate for future high-current accelerators.
by Sergey A. Arsenyev.
Ph. D.
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Van, Hout Daniel Richard. "Heat Transfer and Film Cooling Performance on a Transonic Converging Nozzle Guide Vane Endwall With Purge Jet Cooling and Dual Cavity Slashface Leakage." Thesis, Virginia Tech, 2020. http://hdl.handle.net/10919/100799.
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The following study presents an experimental and computational investigation on the effects of implementing a dual cavity slashface configuration and varying slashface coolant leakage mass flow rate on the thermal performance for a 1st stage nozzle guide vane axisymmetric converging endwall. An upstream doublet staggered cylindrical hole jet cooling scheme provides additional purged coolant with consistent conditions throughout the investigation. The effects are measured in engine representative transonic mainstream and coolant flow conditions where Mexit = 0.85, Reexit = 1.5 × 106, freestream turbulence intensity of 16%, and a coolant density ratio of 1.95.
Four combinations of slashface Fwd and Aft cavity mass flow rate are experimentally analyzed by comparing key convective heat transfer parameters. Data is collected and reduced using a combination of IR thermography and a linear regression technique to map endwall heat transfer performance throughout the passage. A flow visualization study is employed using 100 cSt oil-based paint to gather qualitative insights into the endwall flow field. A complimentary CFD study is carried out to gather additional understanding of the endwall flow ingestion and egression behavior as well as comparing performance against a conventional cavity configuration.
Experimental comparisons indicate slashface mass flow rate variations have a minor effect on passage film cooling coverage. Instead, coolant coverage across the passage is primarily driven by upstream purge coolant. However, endwall heat transfer coefficient is reduced as much as 20% in mid-passage areas as leakage flow decreases. This suggests that changes in leakage flow maintains a first order correlation in altering passage aerodynamics that, despite relatively consistent film cooling coverage, also leads to significant changes in net heat flux reduction in the passage.
Endwall flow behavior proves to be complex along the gap interface showing signs of ingestion, egression, and tangential flow varying spatially throughout the gap. CFD comparisons suggests that a dual cavity configuration varies the gap static pressure distribution closer to the mainstream pressure throughout the passage in high speed applications compared to a single cavity configuration. The resulting decelerating flow creates a more stable endwall flow profile and favorable coolant environment by reducing boundary layer thinning and shear interaction in near gap endwall tangential flow.Master of Science
Gas turbines are often exposed to high temperatures as they convert hot, energetic gas streams into mechanical motion. As turbines receive higher temperature gases, their efficiency increases and reduces waste. However, these temperatures can get too hot for turbine parts. To survive these high temperatures, turbine components are often assembled with a gap in between to allow the part to expand and contrast when it heats and cools. Relatively cold air is also fed into the gap to help prevent hot gases from entering. This cold air can also feed into other pathways to flow onto the turbine component's surface and act as an insulating layer to the hot gas and protect the component from overheating. The study presented investigates an assembly gap, referred to as a slashface gap, found in the middle of a vane located immediately after gas combustion with cold air leaking through. One unique aspect of this study is that there are two pathways for cold air, or coolant, to leak through when, typically, there is only one. The slashface gap lies on a wall which the vanes are attached to, referred to as the endwall. Multiple small holes on the endwall in between the combustor and vanes jet out coolant to try and protect the endwall from hot gases. These holes, called jump cooling holes, point out towards the vanes and angled more shallowly so that the holes do not face directly up from the endwall. The holes are angled as they are meant to gracefully spray coolant to cover and insulate the endwall instead of mixing with the hot air above. The experiments found that changing how much coolant is leaked through the slashface has little effect on how much coolant from jump cooling holes covered the endwall. However, smaller slashface leaks better protect the endwall from the hot gas by forcing it to move smoother and give off less heat across the endwall rather than a tumbling like manner. The experiment is modeled on a computer simulation to determine the differences of a slashface gap with the typical one coolant pathway and the coolant dual pathway configuration that is tested in the experiments. This simulation discovered that having two coolant pathways significantly reduces how much hot gas and jump cooling coolant enters and leaves the slashface gap. This makes the surrounding airflow along the endwall travel more smoothly and does not give off as much heat as if a single coolant pathway configuration is used instead.
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Rocha, Chrystianne. "Gap filler adaptativo para sistema ISDB-Tb." Universidade Presbiteriana Mackenzie, 2014. http://tede.mackenzie.br/jspui/handle/tede/1440.
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Previous issue date: 2014-08-07This master thesis presents the proposal of assigning the cognitive ability to a gap filler. Differently from the usual repeaters found on the market, the adaptive gap filler is able to automatically monitor tuned channels with the intention of verifying if the protection ratio described in Resolution nº398 from Anatel is being respected. Spectrum sensing techniques and the concepts related to coverage area will be addressed. Tests were carried out on the Matlab and GNU Radio Software with the purpose of analyzing the adaptive gap filler performance on real channels.
Este trabalho apresenta a proposta de atribuir ao gap filler a capacidade cognitiva . Diferentemente dos repetidores encontrados no mercado, o gap filler adaptativo tem como função monitorar, de forma autônoma, os canais sintonizados para verificar se a relação de proteção descrita na Resolução nº 398 da Anatel está sendo respeitada. Como fundamentos dessa proposta são abordadas as técnicas de sensoriamento do espectro e os conceitos relacionados às áreas de cobertura. Em uma abordagem prática, os testes foram desenvolvidos no Matlab e no GNU Radio, em que se analisa a atuação do gap filler adaptativo em canais reais.
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MacDonald, Nicholas Roy. "Bridging the gap : synthetic radio observations of numerical simulations of extragalactic jets /." Halifax, N.S. : Saint Mary's University, 2008.
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Gao, Bo. "Passive UHF RFID tag using electromagnetic band gap (EBG) material for metallic objects tracking /." View abstract or full-text, 2007. http://library.ust.hk/cgi/db/thesis.pl?MECH%202007%20GAO.
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Schurig, Philipp [Verfasser]. "Radio frequency sputter deposition of the transparent conducting wide band gap oxide Ga2O3 / Philipp Schurig." Gießen : Universitätsbibliothek, 2021. http://d-nb.info/1230476172/34.
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Leite, Adriana Ribeiro. "Regulação das junções comunicantes (GAP junctions) em cultura de ilhotas pancreaticas de ratos recem-nascidos." [s.n.], 2002. http://repositorio.unicamp.br/jspui/handle/REPOSIP/313990.
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Orientadores : Carla Beatriz Collares-Buzato, Antonio Carlos BoscheroDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Biologia
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Resumo: As junções comunicantes (JCs) ou gap junctions são canais intercelulares formados pela união de dois hemicanais ou conexons, os quais são formados por proteínas integrais pertencentes à família das conexinas (Cx). Estudos em ilhotas pancreáticas têm demonstrado que a comunicação intercelular, via junções comunicantes, é fundamental para adequada biossíntese, estoque e liberação de insulina pelas células b pancreáticas. Condições que promovem a formação de JCs aumentam a secreção e biossíntese deste hormônio. Por outro lado, o bloqueio dos canais ou ruptura das JCs na célula 13 resultam em comprometimento do processo secretório. Ilhotas pancreáticas de fetos e recém-nascidos de ratos exibem uma resposta secretória de insulina reduzida em comparação às ilhotas de animais adultos. Cultivo prolongado de ilhotas pancreáticas, bem como o tratamento in vitro com hormônios somatotróficos, como a prolactina, induzem maturação deste processo de acoplamento estímulo-secreção. Esta tese teve como objetivo investigar os possíveis mecanismos intracelulares de regulação das JCs pela cultura prolongada e pelo tratamento in vitro com prolactina em ilhotas pancreáticas de ratos recém-nascidos. Para tal, foi avaliada a localização, o grau de expressão gênica e o conteúdo celular das proteínas integrantes das JCs, as conexinas 43 e 36, bem como o grau de adesão celular pela expressão da b -catenina nas ilhotas nestas condições experimentais. Foram executados os seguintes protocolos: 1) tratamento in vitro com prolactina (2mg/mL/dia) durante 7 dias, 2) cultivo das ilhotas por períodos variando de 1 a 7 dias e 3) cultivo por 3 dias em concentrações variáveis de glicose no meio de cultura. Foi detectado um aumento significativo da secreção de insulina após o tratamento com prolactina, tempo prolongado de cultivo e concentração crescente de glicose no meio. Este resultado indica que tais condições experimentais induzem maturação do processo de secreção de insulina em ilhotas pancreáticas de ratos recém-nascidos. O tratamento crônico com prolactina também induziu um aumento na expressão de Cx43 e b -catenina, como demonstrado por Westem Blot. Ambas proteínas juncionais foram detectadas por imunocitoquímica na região de contato intercelular nas células das ilhotas. Quanto ao efeito da cultura per se, foi observada uma correlação entre o tempo de cultivo e o aumento na expressão celular de Cx43, Cx36 e b -catenina. No caso das conexinas, a cultura prolongada também resultou em aumento da transcrição gênica, como detectado pelo método de RT-PCR. Quando foram analisadas as variações de expressão das conexinas em resposta à glicose, somente a Cx36 pareceu ser regulada por concentrações crescentes deste secretagogo no meio de cultura. Esses resultados, tomados em conjunto, sugerem que a regulação das conexinas nas ilhotas pancreáticas pela prolactina, glicose e outros fatores contidos no meio de cultura podem ser importantes no processo de maturação das células 13 em condições de cultivo
Mestrado
Fisiologia
Mestre em Biologia Funcional e Molecular
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Kumar, Amrendra. "Effective fracture geometry obtained with large water sand ratio." [College Station, Tex. : Texas A&M University, 2008. http://hdl.handle.net/1969.1/ETD-TAMU-2359.
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Simpson, Gabriël Pieter. "Relevant cost and financial ratio principles applied in a small business / G.P. Simpson." Thesis, North-West University, 2012. http://hdl.handle.net/10394/9837.
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Cost-Volume-Profit (CVP) analysis and financial ratios are all managerial accounting and financial accounting tools that can help managers to make informative business decisions within their organisations. In addition, certain strategic tools such as Porters five forces, SWOT analysis, identifying of core principles, the compilation of the vision and mission statement will empower the small to medium business to be successful as an entrepreneurial venture.
The problem arises in many small to medium business (SMEs), that once growth occurs and important decisions needs to be made, which may include relocation of the business and buying of capital equipment. The owners of these ventures struggle to make informative decisions.
The general objective of this research is to apply financial and managerial accounting principles as well as strategy principles to a small business called Envirocare Laboratories. The aim of this research is to empower the small business owner with these tools to ensure success in future ventures.
Literature on financial, managerial and strategic principles advises that the objectives, measurements and targets should be aligned with the SMEs long-term goals and performance.
An empirical study done with the owner of the SME called Envirocare, has indicated serious shortcomings in terms of understanding how long-term goals are defined and the objectives achieved. The most important conclusion includes that certain capital expenditure projects have been viable, that the SME has been adding value to the economy and that the current strategy needs to be revised to include long-term goal planning.Thesis (MBA)--North-West University, Potchefstroom Campus, 2013.
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Grant, Marcus Paul. "Computer control of air-gas ratio for nozzle mix systems." Thesis, Coventry University, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.390222.
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Mei, Xiangyang. "Preparation of pyramidal textured GaP p-n junctions and their applications to alpha radio-voltaic cells, ARVCs." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ33972.pdf.
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Lyall, Michael Eric. "Heat Transfer from Low Aspect Ratio Pin Fins." Thesis, Virginia Tech, 2006. http://hdl.handle.net/10919/33470.
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The performance of many engineering devices from power electronics to gas turbines is limited by thermal management. Pin fins are commonly used to augment heat transfer by increasing surface area and increasing turbulence. The present research is focused on but not limited to internal cooling of turbine airfoils using pin fins. Although the pin fins are not limited to a single shape, circular cross-sections are most common.
The present study examines heat transfer from a single row of circular pin fins with the row oriented perpendicular to the flow. The configurations studied have spanwise spacing to pin diameter ratios of two, four, and eight. Low aspect ratio pin fins were studied whereby the channel height to pin diameter was unity. The experiments are carried out for a Reynolds number range of 5000 to 30,000. Heat transfer measurements are taken on both the pin and on the endwall covering several pin diameters upstream and downstream of the pin row. The results show that the heat transfer augmentation relative to open channel flow is highest for the smallest spanwise spacing for the lowest Reynolds number flows. The results also indicate that the pin fin heat transfer is higher than on the endwall.Master of Science
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Chen, Bing-Hung. "Inductively coupled radio-frequency discharges." Thesis, University of Oxford, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.244566.
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Wu, Yichao. "RF circuit applications of enhancement-mode AlGaN/GaN HEMTs /." View abstract or full-text, 2007. http://library.ust.hk/cgi/db/thesis.pl?ECED%202007%20WUY.
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Kolevatov, Sergej. "A contribution to bridge the design gap between software and hardware for complex signal processing systems in mobile communications." Aachen Shaker, 2009. http://d-nb.info/1001974972/04.
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Callet, Guillaume. "Caractérisation et modélisation de transistors HEMT AlGaN/GaN et InAlN/GaN pour l’amplification de puissance en radio-fréquences." Limoges, 2011. https://aurore.unilim.fr/theses/nxfile/default/3c0fde17-3720-49cd-9824-bd071826245e/blobholder:0/2011LIMO4033.pdf.
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Ce document traite de la caractérisation de composants HEMT à base de GaN en vue de leur modélisation. Une caractérisation exhaustive des transistors à base d’InalN/GaN et AlGaN/GaN est réalisée. Une importance particulière est donnée aux méthodes de caractérisation thermique, avec l’utilisation de la méthode 3ω pour la mesure de l’impédance thermique. Une étude des facteur d’échelle du modèle linéaire est également abordée. Le modèle non-linéaire présenté est développé afin d’élargir son champ d’application à l’amplification de puissance et à la commutation. Enfin, il est utilisé pour la réalisation du premier amplificateur de puissance utilisant la technologie InAlN en bande KaThis report deals with the characterization of GaN HEMTs devices in order to create their model. An exhaustive characterization has been realized for AlInN/GaN and AlGaN/GAN based HEMTs. A special care has been given to the different thermal characterization methods, with the use of the 3ω method for the measurement of the thermal impedance. A study of scaling rules for small-signal model is presented. The non-linear model presented is developed in order to extend his application domain to the power amplification and power switches. Finally it is used in the design of the first poser amplifier base on AlInN technology in Ka-band
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An, Yan. "The Potential of Bulk and Amino-Acid Specific Isotope Ratio Mass Spectrometry of Human Hair in Forensic and Clinical Applications." Ohio University / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1363701887.
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Carvalho, Paulo Moreira de. "Modeling the electrical submersible jet pump producing high gas-liquid-ratio petroleum wells /." Digital version accessible at:, 1998. http://wwwlib.umi.com/cr/utexas/main.
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Bolyard, Jason D. "Evaluation of an air-to-fuel ratio derived exhaust flow rate for in-use emissions testing." Morgantown, W. Va. : [West Virginia University Libraries], 2005. https://eidr.wvu.edu/etd/documentdata.eTD?documentid=4302.
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Thesis (M.S.)--West Virginia University, 2005.Title from document title page. Document formatted into pages; contains xi, 88 p. : ill. (some col.), col. map. Includes abstract. Includes bibliographical references (p. 59-63).
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Sundstrom, Linda-Marie. "Internet radio: Identifying administrative and regulatory gaps in a cyberspace world without borders." CSUSB ScholarWorks, 2002. https://scholarworks.lib.csusb.edu/etd-project/2137.
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The purpose of this paper is to identify gaps in regulatory policies resulting from the emergence of Internet radio. To accomplish this purpose, the paper seeks to: 1) provide insights into agencies that may have direct involvement in potentially regulating Internet radio; 2) explore the concepts of jurisdiction in cyberspace; and 3) address the regulatory challenges that exist when traditional country borders no longer apply.
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Muccio, Zeland. "Isotope ratio mass spectrometry a rapidly developing tool for forensic samples /." Ohio : Ohio University, 2010. http://www.ohiolink.edu/etd/view.cgi?ohiou1263488205.
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Lawson, Seth Augustus. "Heat Transfer from Multiple Row Arrays of Low Aspect Ratio Pin Fins." Thesis, Virginia Tech, 2007. http://hdl.handle.net/10919/31190.
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The heat transfer characteristics through arrays of pin fins were studied for the further development of internal cooling methods for turbine airfoils. Low aspect ratio pin fin arrays were tested through a range of Reynolds numbers between 5000 and 30,000 to determine the effects of pin spacing as well as aspect ratio on pin and endwall heat transfer. Experiments were also conducted to determine the independent effects of pin spacing and aspect ratio on arrays with different flow incidence angles. The pin Nusselt numbers showed almost no dependence on pin spacing or flow incidence angle. Using an infrared thermogaphy technique, spatially-resolved Nusselt numbers were measured along the endwalls of each array. The endwall results showed that streamwise spacing had a larger effect than spanwise spacing on array-averaged Nusselt numbers. Endwall heat transfer patterns showed that arrays with flow incidence angles experienced less wake interaction between pins than arrays with perpendicular flow, which caused a slight decrease in heat transfer in arrays with flow incidence angles. The effect of flow incidence angle on array-average Nusselt number was greater at tighter pin spacings. Even though the pin Nusselt number was independent of pin spacing, the ratio of pin-to-endwall Nusselt number was dependent on flow conditions as well as pin spacing. The pin aspect ratio had little effect on the array-average Nusselt number for arrays with perpendicular flow; however, the effect of flow incidence angle on array-average Nusselt number increased as aspect ratio decreased.Master of Science
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Bilgili, Hulusi Birol. "Pressure, Gas Ratio And Operation Voltage Optimization Of A Helium-neon Laser." Master's thesis, METU, 2005. http://etd.lib.metu.edu.tr/upload/3/12605917/index.pdf.
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Aim of this thesis is to investigate the optimum working parameters of a helium-neon laser. Partial pressure ratios, total pressures of the gases and voltage-current characteristics were studied. The analysis of the results includes the minor factors (impurity, volume, etc.) and their effects to main parameters (laser power, voltage, current). Tables, which were formed by measured optical parameters as wavelength and power, converted to graphs and from these graphs optimal working conditions for the laser are obtained.
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Giebel, Brian M. "Advancement and Application of Gas Chromatography Isotope Ratio Mass Spectrometry Techniques for Atmospheric Trace Gas Analysis." Scholarly Repository, 2011. http://scholarlyrepository.miami.edu/oa_dissertations/610.
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The use of gas chromatography isotope ratio mass spectrometry (GC-IRMS) for compound specific stable isotope analysis is an underutilized technique because of the complexity of the instrumentation and high analytical costs. However stable isotopic data, when coupled with concentration measurements, can provide additional information on a compounds production, transformation, loss, and cycling within the biosphere and atmosphere. A GC-IRMS system was developed to accurately and precisely measure δ13C values for numerous oxygenated volatile organic compounds (OVOCs) having natural and anthropogenic sources. The OVOCs include methanol, ethanol, acetone, methyl ethyl ketone, 2-pentanone, and 3-pentanone. Guided by the requirements for analysis of trace components in air, the GC-IRMS system was developed with the goals of increasing sensitivity, reducing dead-volume and peak band broadening, optimizing combustion and water removal, and decreasing the split ratio to the IRMS. The technique relied on a two-stage preconcentration system, a low-volume capillary reactor and water trap, and a balanced reference gas delivery system. Measurements were performed on samples collected from two distinct sources (i.e. biogenic and vehicle emissions) and ambient air collected from downtown Miami and Everglades National Park. However, the instrumentation and the method have the capability to analyze a variety of source and ambient samples. The measured isotopic signatures that were obtained from source and ambient samples provide a new isotopic constraint for atmospheric chemists and can serve as a new way to evaluate their models and budgets for many OVOCs. In almost all cases, OVOCs emitted from fuel combustion were enriched in 13C when compared to the natural emissions of plants. This was particularly true for ethanol gas emitted in vehicle exhaust, which was observed to have a uniquely enriched isotopic signature that was attributed to ethanol’s corn origin and use as an alternative fuel or fuel additive. Results from this effort show that ethanol’s unique isotopic signature can be incorporated into air chemistry models for fingerprinting and source apportionment purposes and can be used as a stable isotopic tracer for biofuel inputs to the atmosphere on local to regional scales.
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Lara, Peinado Javier. "Minding the spectrum gaps : First steps toward developing a distributed white space sensor grid for cognitive radios." Thesis, KTH, Radio Systems Laboratory (RS Lab), 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-123548.
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The idea that the radio spectrum is growing ever more scarce has become commonplace, and is being reinforced by the recent bidding wars among telecom operators. New wireless applications tend to be deployed in the relatively narrow unlicensed frequency bands, worsening the problem of interference for all users. However, not all frequency bands are in use in every location all the time, creating temporal and spatial gaps (also known as white spaces) that cognitive radio systems aim to take advantage of. In order to achieve that, such systems need to be able to constantly scan large chunks of the radio spectrum to keep track of which frequency bands are locally available any given moment, thus allowing users to switch to one of these unoccupied frequency bands once the current band becomes unusable (or less useful). This requirement of wideband sensing capabilities often translates into the need to install specialized radio components, raising the costs of such systems, and is often at odds with the focus on monitoring the current band as is done by traditional wireless devices. The goal of this master’s thesis project is to simplify cognitive radio systems by shifting the wideband sensing functionality to a specialized and inexpensive embedded platforms that will act as a white space sensor, thus freeing cognitive radio users from this task and making it easier to integrate dynamic spectrum management techniques into existing systems. To do that a wireless sensor gateway platform developed by a previous master’s thesis has been repurposed as a prototype white space detector and tested against several wireless transmitters. The aim is to develop a standalone platform that can be deployed all around an area to collect data that can be used to create a geographical map of the use of the spectrum. Such a system should require as little maintenance as possible, thus auto-update and self-configuring features have been implemented in the detector, as well as a simple scanning protocol that allows for remote configuration of the wideband sensing parameters. Furthermore, a basic server has been developed to aggregate and display the data provided by the different sensors.Tanken att radiospektrum blir allt knappare har blivit vardagsmat, och förstärks av de senaste budgivning krig mellan teleoperatörer. Nya trådlösa applikationer tenderar att sättas i de relativt smala olicensierade frekvensband, förvärrade problemet med störningar för alla användare. Men inte alla frekvensband som används i varje plats hela tiden, skapar tidsmässiga och rumsliga luckor (även känd som vita fläckar) som kognitiva radiosystem syftar till att dra nytta av. För att uppnå detta, sådana system måste hela tiden kunna scanna stora delar av radiospektrum för att hålla reda på vilka frekvensband är lokalt tillgängliga varje givet ögonblick, vilket gör omkopplaren när den nuvarande bandet blir obrukbar. Det här kravet på bredbands avkänning kapaciteter översätter ofta in behovet av att installera specialiserade radiokomponenter, höja kostnaderna för sådana system, och är ofta i strid med fokus på övervakning av strömmen band med traditionella trådlösa enheter. Målet med detta examensarbete är att förenkla kognitiva radiosystem med wideband avkänning funktionalitet till en specialiserad och billig inbäddad plattform som kommer att fungera som ett vitt utrymme sensor, vilket frigör kognitiva radio användare från denna uppgift och gör det enklare att integrera dynamiskt spektrum förvaltning tekniker i befintliga system. För att göra det en trådlös sensor gateway plattform som utvecklats av ett tidigare examensarbete har apterat som en prototyp blanktecken detektor och testas mot flera trådlösa sändare. Målet är att utveckla en fristående plattform som kan sättas runt för att skapa en geografisk karta av användningen av spektrum och kräva så lite underhåll som möjligt, har automatisk uppdatering och självkonfigurerande funktioner implementerats i detektorn, samt som en enkel scanning protokoll som möjliggör fjärrkonfiguration av den bredbandiga avkänningsparametrarna. Dessutom har en grundläggande server utvecklats för att aggregera och visa uppgifterna från de olika sensorerna.
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Gomes, Jorge Miguel Abrantes de Almeida. "GaN power amplifier for satellite communications." Master's thesis, Universidade de Aveiro, 2014. http://hdl.handle.net/10773/13704.
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Mestrado em Engenharia Electrónica e TelecomunicaçõesThe satellite communications have become a valid alternative to conventional communications, through fiber or copper, in situations of catastrophe or even as complement to improve the quality of the services provided at a worldwide scale. Recently, radio frequency engineers have worked towards a reliable solution to replace the travelling wave tube amplifiers on board of the satellite communications. Despite the travelling wave tube amplifiers reveal a good performance, its weight, size and cost are a serious technical problem to the main satellite manufacturers. However, this scenario tends to change due to the exploitation of the Gallium Nitride technology in high power, efficiency and frequency applications. The objective of this work involves an implementation of two power amplifiers in class B, resorting to a Gallium Nitride transistors and using different types of planar transmission lines, for a 5.8GHz frequency which is often used in uplink transmissions for C-band or even in recent applications of wireless power transmission. The best results were obtained for the microstrip lines power amplifier, achieving 34.1dBm of output power, 62.35% of drain efficiency at saturation and a small-gain of 17dB.
As comunicações via satélite têm-se tornado uma alternativa válida às vias de comunicações convencionais, como a fibra e o cobre, em situações de catástrofe ou até como complemento para melhorar a qualidade de serviços disponibilizados à escala global. Recentemente, os engenheiros de rádio frequência têm trabalhado para encontrar uma solução definitiva e fiável para a substituição dos amplificadores a válvulas nos satélites de comunicações. Apesar destes amplificadores apresentarem uma performance de destaque, o seu tamanho, peso, consumo e custo são sérios problemas para as empresas especializadas na sua construção. Contudo, o panorama tende a mudar devido à exploração da tecnologia de Nitreto de Gálio em aplicações de alta potência, frequência e eficiência. O objetivo desta trabalho passa pela implementação de dois amplificadores de potência em classe B, recorrendo a transístores de Nitreto de Gálio e usando diferentes linhas de transmissão planares, para a frequência de 5.8GHz que é frequentemente usada em transmissões uplink na banda C, ou mesmo nas recentes aplicações de transferência de energia sem fios. Os melhores resultados foram obtidos pela implementação em linhas microstrip, atingindo os 34.1dBm de potência de saída, 62.35% de eficiência na saturação e um ganho máximo de 17dB.
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Wirth, Douglas A. "An experimental investigation of the effect of temporal equivalence ratio fluctuations on NOx̳ emissions in premixed flames /." This resource online, 1993. http://scholar.lib.vt.edu/theses/available/etd-06062008-144729/.
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Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1993.On t.p. "x̳" is subscript. Vita. Abstract. Includes bibliographical references (leaves 179-185). Also available via the Internet.
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Dasgupta, Abhijeet. "High efficiency S-Band vector power modulator design using GaN technology." Thesis, Limoges, 2018. http://www.theses.fr/2018LIMO0021/document.
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L’évolution des systèmes de télécommunications, liée à une demande sans cesse croissante en termes de débit et de volume de données, se concrétise par le développement de systèmes proposant des bandes passantes très larges, des modulations à très hautes efficacités spectrales, de la flexibilité en puissance et en fréquence d’émission. Par ailleurs, la mise en œuvre de ces dispositifs doit se faire avec un souci permanent d’économie d’énergie d’où la problématique récurrente de l’amplification de puissance RF qui consiste à allier au mieux rendement, linéarité et bande passante. L’architecture conventionnelle d’une chaine d’émission RF consiste dans une première étape à réaliser l’opération de modulation-conversion de fréquence (Modulateur IQ) puis dans une deuxième étape l’opération de conversion d’énergie DC-RF (Amplificateur de Puissance), ces deux étapes étant traditionnellement traitées de manière indépendante. L’objectif de ces travaux de thèse est de proposer une approche alternative qui consiste à combiner ces deux opérations dans une seule et même fonction : le modulateur vectoriel de puissance à haute efficacité énergétique. Le cœur du dispositif, conçu en technologie GaN, repose sur un circuit à deux étages de transistors HEMT permettant d’obtenir un gain en puissance variable en régime de saturation. Il est associé à un modulateur de polarisation multi-niveaux spécifique également en technologie GaN. Le dispositif réalisé a permis de générer directement, à une fréquence de 2.5 GHz, une modulation vectorielle 16QAM (100Msymb/s) de puissance moyenne 13 W, de puissance crête 25W avec un rendement global de 40% et une linéarité mesurée par un EVM à 5%The evolution of telecommunications systems, linked to a constantly increasing demand in terms of data rate and volume, leads to the development of systems offering very wide bandwidths, modulations with very high spectral efficiencies, increased power and frequency flexibilities in transmitters. Moreover, the implementation of such systems must be done with a permanent concern for energy saving, hence the recurring goal of the RF power amplification which is to combine the best efficiency, linearity and bandwidth. Conventional architectures of RF emitter front-ends consist in a first step in performing the frequency modulation-conversion operation (IQ Modulator) and then in a second step the DC-RF energy conversion operation (Power Amplifier), these two steps being usually managed independently. The aim of this thesis is to propose an alternative approach that consists in combining these two operations in only one function: a high efficiency vector power modulator. The core of the proposed system is based on a two-stage GaN HEMT circuit to obtain a variable power gain operating at saturation. It is associated with a specific multi-level bias modulator also design using GaN technology. The fabricated device generates, at a frequency of 2.5 GHz, a 16QAM modulation (100Msymb/s) with 13W average power, 25W peak power, with an overall efficiency of 40% and 5% EVM
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Shaw, Carl Robert. "Optical and radio H I studies of the fine-scale structure of the interstellar gas." Thesis, Queen's University Belfast, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.388191.
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Ghomashi, Hossein. "Modelling the combustion in a dual fuel HCCI engine : investigation of knock, compression ratio, equivalence ratio and timing in a Homogeneous Charge Compression Ignition (HCCI) engine with natural gas and diesel fuels using modelling and simulation." Thesis, University of Bradford, 2013. http://hdl.handle.net/10454/7344.
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This thesis is about modelling of the combustion and emissions of dual fuel HCCI engines for design of “engine combustion system”. For modelling the combustion first the laminar flamelet model and a hybrid Lagrangian / Eulerian method are developed and implemented to provide a framework for incorporating detailed chemical kinetics. This model can be applied to an engine for the validation of the chemical kinetic mechanism. The chemical kinetics, reaction rates and their equations lead to a certain formula for which the coefficients can be obtained from different sources, such as NASA polynomials [1]. This is followed by study of the simulation results and significant findings. Finally, for investigation of the knock phenomenon some characteristics such as compression ratio, fuel equivalence ratio, spark timing and their effects on the performance of an engine are examined and discussed. The OH radical concentration (which is the main factor for production of knock) is evaluated with regard to adjustment of the above mentioned characteristic parameters. In the second part of this work the specification of the sample engine is given and the results obtained from simulation are compared with experimental results for this sample engine, in order to validate the method applied in AVL Fire software. This method is used to investigate and optimize the effects of parameters such as inlet temperature, fuels ratio, diesel fuel injection timing, engine RPM and EGR on combustion in a dual fuel HCCI engine. For modelling the dual fuel HCCI engine AVL FIRE software is applied to simulate the combustion and study the optimization of a combustion chamber design. The findings for the dual fuel HCCI engine show that the mixture of methane and diesel fuel has a great influence on an engine's power and emissions. Inlet air temperature has also a significant role in the start of combustion so that inlet temperature is a factor in auto-ignition. With an increase of methane fuel, the burning process will be more rapid and oxidation becomes more complete. As a result, the amounts of CO and HC emissions decrease remarkably. With an increase of premixed ratio beyond a certain amount, NOX emissions decrease. With pressure increases markedly and at high RPM, knock phenomenon is observed in HCCI combustion.
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Sibold, Ridge Alexander. "The Effect of Density Ratio on Steep Injection Angle Purge Jet Cooling for a Converging Nozzle Guide Vane Endwall at Transonic Conditions." Thesis, Virginia Tech, 2019. http://hdl.handle.net/10919/102650.
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The study presented herein describes and analyzes a detailed experimental investigation of the effects of density ratio on endwall thermal performance at varying blowing rates for a typical nozzle guide vane platform purge jet cooling scheme. An axisymmetric converging endwall with an upstream doublet staggered cylindrical hole purge jet cooling scheme was employed. Nominal exit flow conditions were engine representative and as follows: {rm Ma}_{Exit} = 0.85,
{rm Re}_{Exit,C_{ax}} = 1.5 times {10}^6, and large-scale freestream Tu = 16%. Two blowing ratios were investigated corresponding to the upper and lower engine extrema. Each blowing ratio was investigated amid two density ratios; one representing typical experimental neglect of density ratio, at DR = 1.2, and another engine representative density ratio achieved by mixing foreign gases,
DR = 1.95. All tests were conducted on a linear cascade in the Virginia Tech Transonic Blowdown Wind Tunnel using IR thermography and transient data reduction techniques. Oil paint flow visualization techniques were used to gather quantitative information regarding the alteration of endwall flow physics due two different blowing rates of high-density coolant. High resolution endwall adiabatic film cooling effectiveness, Nusselt number, and Net Heat Flux Reduction contour plots were used to analyze the thermal effects.
The effect of density is dependent on the coolant blowing rate and varies greatly from the high to low blowing condition. At the low blowing condition better near-hole film cooling performance and heat transfer reduction is facilitated with increasing density. However, high density coolant at low blowing rates isn't adequately equipped to penetrate and suppress secondary flows, leaving the SS and PS largely exposed to high velocity and temperature mainstream gases. Conversely, it is observed that density ratio only marginally affects the high blowing condition, as the momentum effects become increasingly dominant. Overall it is concluded density ratio has a first order impact on the secondary flow alterations and subsequent heat transfer distributions that occur as a result of coolant injection and should be accounted for in purge jet cooling scheme design and analysis.
Additionally, the effect of increasing high density coolant blowing rate was analyzed. Oil paint flow visualization indicated that significant secondary flow suppression occurs as a result of increasing the blowing rate of high-density coolant. Endwall adiabatic film cooling effectiveness, Nusselt number, and NHFR comparisons confirm this. Low blowing rate coolant has a more favorable thermal impact in the upstream region of the passage, especially near injection. The low momentum of the coolant is eventually dominated and entrained by secondary flows, providing less effectiveness near PS, near SS, and into the throat of the passage. The high momentum present for the high blowing rate, high-density coolant suppresses these secondary flows and provides enhanced cooling in the throat and in high secondary flow regions. However, the increased turbulence impartation due to lift off has an adverse effect on the heat load in the upstream region of the passage. It is concluded that only marginal gains near the throat of the passage are observed with an increase in high density coolant blowing rate, but severe thermal penalty is observed near the passage onset.Master of Science
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Rasco, Clark Joseph. "Demographic trends in the European Union: political and strategic implications." Thesis, Monterey California. Naval Postgraduate School, 2004. http://hdl.handle.net/10945/1526.
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Approved for public release, distribution is unlimitedThis thesis analyzes adverse demographic trends in the European Union, including sub-replacement birthrates and increasing median ages. It investigates the implications of these trends for the EU's prospects for becoming a stronger and more influential actor in international affairs. Pressures arising from population trends in and near the EU could ultimately affect national and EU cohesion, governmental effectiveness, and social stability. Absent remedial measures, social programs in some EU countries will be unsustainable due to the mounting financial burden of pensions and health care for growing elderly populations. Such financial obligations hinder funding other national programs, including modernized military capabilities. Nationalism and national identity are at issue in immigrant integration and assimilation efforts. The role of population trends with regard to the growing threat of radical Islamic fundamentalism is explored. The thesis concludes with policy recommendations that might be considered to avert the looming economic, social, and security crises that may result from these demographic trends. In short, the security and financial consequences foreshadowed by the current demographic trends of an aging, economically weaker, and socially conflicted European Union could present dramatic implications for the vital national interests of the United States.
Lieutenant, United States Navy
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Clavijo, William Paul. "Low-temperature Fabrication Process for Integrated High-Aspect Ratio Metal Oxide Nanostructure Semiconductor Gas Sensors." VCU Scholars Compass, 2017. http://scholarscompass.vcu.edu/etd/4781.
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This work presents a new low-temperature fabrication process of metal oxide nanostructures that allows high-aspect ratio zinc oxide (ZnO) and titanium dioxide (TiO2) nanowires and nanotubes to be readily integrated with microelectronic devices for sensor applications. This process relies on a new method of forming a close-packed array of self-assembled high-aspect-ratio nanopores in an anodized aluminum oxide (AAO) template in a thin (2.5 µm) aluminum film deposited on a silicon and lithium niobate substrate (LiNbO3). This technique is in sharp contrast to traditional free-standing thick film methods and the use of an integrated thin aluminum film greatly enhances the utility of such methods. We have demonstrated the method by integrating ZnO nanowires, TiO2 nanowires, and multiwall TiO2 nanotubes onto the metal gate of a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor), and the delay line of a surface acoustic wave (SAW) device to form an integrated ChemFET (Chemical Field-Effect Transistor) and a orthogonal frequency coded (OFC) SAW gas sensor. The resulting metal oxide nanostructures of 1-1.7 µm in height and 40-100 nm in diameter offer an increase of up to 220X the surface area over a standard flat metal oxide film for sensing applications.
The metal oxide nanostructures were characterized by SEM, EDX, TEM and Hall measurements to verify stoichiometry, crystal structure and electrical properties. Additionally, the electrical response of ChemFETs and OFC SAW gas sensors with ZnO nanowires, TiO2 nanowires, and multiwall TiO2 nanotubes were measured using 5-200 ppm ammonia as a target gas at room temperature (24ºC) showing high sensitivity and reproducible testing results.
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Cambridge, Shevonn Nathaniel. "The effect of compression ratio on emissions from an alcohol-fueled engine." Thesis, This resource online, 1992. http://scholar.lib.vt.edu/theses/available/etd-09122009-040220/.
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Brockdorf, Kathleen Louise. "A Graphene/RF Gas Sensor." Wright State University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=wright1574345655987416.
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Liang, Dong Cuan. "Development and characterization of atmospheric pressure radio frequency capacitively coupled plasmas for analytical spectroscopy." Thesis, University of British Columbia, 1990. http://hdl.handle.net/2429/30590.
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An atmospheric pressure radio frequency capacitively coupled plasma (CCP) has been developed and characterized for applications in atomic emission spectrometry (AES), atomic absorption spectrometry (AAS) and gas chromatography (GC).
The CCP torch was initially designed as an atom reservoir for carrying out elemental analysis using atomic absorption. Functionally, the device consists of two parts, the CCP discharge tube and the tantalum strip electrothermal vaporization sample introduction system. The torch design provides for very effective energy transfer from the power supply to the plasma by capacitive coupling. Therefore, the plasma can be generated at atmospheric pressure with a flexible geometry. The plasma can be operated at very low rf input powers (30-600 W) enabling optimal conditions for atom resonance line absorption measurements. Absorption by the analyte takes place within the plasma discharge which is characterized by a long path length (20 cm) and low support gas flow rate (0.2 L/Min). Both of these characteristics ensure a relatively long residence time. The device exhibits linear calibration plots and provides sensitivities in the range of 3.5-40 pg. A preliminary measurement gave a Fe I excitation temperature of approximately 4000 K for the discharge. At this temperature, potential chemical interferences are likely to be minimal. Chemical interferences for Fe, Al, As, Ca, Co, Cd, Li, Mo and Sr were negligible in the determination of silver. Chloride interference, which is prevalent in GF-AAS, was not found. The amount of Ag found in a SMR#1643b (NIST) water sample was 9.5 ± 0.5 ng/g which fell in the certified range of 9.8 ± 0.8 ng/g. Spikes of 30 ng/g and 60 ng/g of silver were added to the SRM and recoveries were found to be in a range from 105 % to 96.2 %. The RSD obtained for 7 replicates of 270 pg silver was 4.6 %.
The results for the CCP AES are even more promising. The interferences of thirteen elements are negligible in the determination of silver. The chloride interference was not found. The detection limits for Ag, Cd, Li, Sb and B are 0.7, 0.7, 2, 80 and 400 pg respectively. The amount of silver found in a SRM#1643b (NIST) water sample was 9.3 ± 0.5 ng/g which also fell in the certified range of 9.8 ±0.8 ng/g. Spikes of 30 ng/g and 60 ng/g of silver were added into the SRM#1643b (NIST) samples; the recoveries were found to range from 97 % to 104 %. The RSD obtained for 7 analyses of 270 pg silver were 1.5 % for CCP-AES. It was also found that the signal to noise ratios (S/N) are higher in the AES mode than those in the AAS mode in the same CCP atomizer.
In order to exploit advantages inherent in both GF-AAS and I CP-AES, an atmospheric pressure capacitively coupled plasma sustained inside a graphite furnace was developed. This source combines the high efficiency of atomization in furnaces and the high efficiency of the excitation in atmospheric pressure plasmas. In general, plasma sources are able to effectively excite high-lying excited states for most metals and non-metals and can also ionize vaporized elements. Therefore the possibility exists of using non-resonance lines to avoid the effects of self-absorption at high analyte concentrations. Ion lines may also be used in cases where they provide better sensitivity or freedom from spectral interferences. This source also offers the ability to independently optimize vaporization and excitation. However, the most important aspect of this new source is that it can be used for simultaneous, multielement determinations of small sized samples in a graphite furnace atomizer, a design which has been proven to be effective over many years of use. Preliminary quantitative characteristics of this new atmospheric pressure plasma emission source have been studied. The detection limit for Ag of 0.3 pg is lower than the value of 0.4 pg reported for GF-AAS.
Variants of the CCP, including a gas chromatography (GC) detector, combinations of laser ablation - CCP, rf sputtering - CCP direct solid analysis, and its application as an intense spectral lamp have been developed and are reported in this dissertation.Science, Faculty of
Chemistry, Department of
Graduate
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Dupuis, Sebastien. "Influence des ratios de co-expression précis Cx43 : Cx45 sur la formation des canaux de jonction et leurs propriétés électriques." Thesis, Bordeaux, 2016. http://www.theses.fr/2016BORD0375/document.
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Les canaux de jonctions (CJ) composés des connexines (Cxs) assurent la communication intercellulaire directe qui par leur propriétés électriques régulent la propagation du potentiel d’action (PA) cardiaque. Dans les myocytes ventriculaires Cx43 et Cx45 exprimées à des niveaux et ratios physiopathologiques variables assurent cette fonction. Cette étude détermine la contribution de Cx43 et Cx45 dans la formation des CJ et leurs propriétés électriques. La lignée cellulaire épithéliale de foie de rat exprimant la Cx43 endogène et transfectée de manière stable pour exprimer des ratios Cx43:Cx45 précis a été utilisée. Les propriétés électriques des CJ ont été obtenues par double voltage clamp sur paires de cellules. L’expression de la Cx45 diminue le couplage électrique et augmente la dépendance au potentiel de jonction indépendamment du ratio. Les cinétiques de désactivation sont ralenties avec l’augmentation du niveau d’expression de Cx45 et les cinétiques de restitution sont modifiées en fonction du ratio. Les conductances unitaires suggèrent la formation de CJ composés de Cx43 et Cx45. La diminution du niveau d’expression de Cx43 par ARNi anti-Cx43 entraine une diminution du couplage électrique tandis que les autres propriétés électriques restent inchangées. Ces résultats montrent une contribution spécifique de Cx43 et Cx45 dans la régulation de la formation et des propriétés électriques des CJ caractérisées. Ces propriétés seront corrélées à la participation des CJ dans la régulation de la propagation du PA en fonction des profils d’expression des Cxs en conditions physiologiques et pathologiquesGap junction channels (GJCs), composed of connexins (Cxs) allow a direct intercellular communication that ensures the cardiac action potential (AP) propagation. Cx43 and Cx45 co-expressed in ventricular myocytes with changing expression levels and ratios in the healthy and the diseased heart ensure this function. The purpose of this study is to determine the contribution of Cx43 and Cx45 on the formation of GJCs and their electrical properties. Rat Liver Epithelial cells that endogenously express Cx43 and stably transfected to co-express accurate Cx43:Cx45 ratios have been used. The electrical properties of GJCs at each ratios were obtained by performing dual voltage clamp recordings on cell pairs. Expression of Cx45 decreases the electrical coupling and increases the voltage dependence independently of the ratio. The kinetics of deactivation are slowed with the increases of Cx45 level of expression and the kinetics of recovery are modified in a Cx43:Cx45 ratio dependent manner. Unitary conductances suggest a formation of GJCs composed by Cx43 and Cx45. The decreases of Cx43 level of by a SiRNA treatment induces a decrease of the electrical coupling, while other electrical properties are not affected. Our data show a specific contribution of Cx43 and Cx45 in regulation of the GJCs characterized by specific electrical properties. Such properties will be correlated to the function of GJCs in regulating the AP propagation in the specific patterns of expression of Cxs in the healthy and diseased heart
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Wirth, Douglas A. "An experimental investigation of the effect of temporal equivalence ratio fluctuations on NOx emissions in premixed flames." Diss., Virginia Tech, 1993. http://hdl.handle.net/10919/37948.
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Eshghi, Hosein. "Electron and hole transport in GaN and InGaN." Thesis, University of Surrey, 2000. http://epubs.surrey.ac.uk/2237/.
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Dawson, Daniel. "Stable hydrogen isotope ratios of individual hydrocarbons in sediments and petroleum." Curtin University of Technology, Department of Applied Chemistry, 2006. http://espace.library.curtin.edu.au:80/R/?func=dbin-jump-full&object_id=16839.
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Early research into the stable hydrogen isotopic compositions (δD) of petroleum involved bulk deuterium/hydrogen (D/H) measurements which, while providing some useful information, had to contend with the analysis of complex mixtures of hydrocarbons, and alteration resulting from the rapid exchange of nitrogen-, oxygen- and sulphur-bound hydrogen. The use of gas chromatography-isotope ratio mass spectrometry (GC-irMS) overcomes these problems by allowing the analysis of individual compounds containing only the most isotopically conservative aliphatic carbon-bound (C-bound) hydrogen. This project investigates the geochemical utility and reliability of compound-specific δD values, with the aim to better understand and exploit this analytical capability. To demonstrate the source diagnostic potential of compound-specific δD values, normal and branched alkanes extracted from series of immature bog-head coals (torbanites) were analysed. The torbanites contain immature organic matter predominantly from a single, freshwater algal source, i.e. Botryococcus braunii (B. braunii). The δD values of n-alkanes reflect the climate regime at the time of deposition of the torbanites, and vary mainly in response to the δD values of the source meteoric waters in their depositional environments. n-Alkanes from torbanites deposited at high latitude in a glacial climate are depleted in D by up to 70% relative to those from a torbanite deposited at low latitude under a tropical climate regime. Torbanites deposited in a mid-latitude region under cool-temperate conditions contain n-alkanes with δD values falling in between those of n-alkanes from tropical and glacial torbanites.The δD values of the n-alkanes also reflect their multiple source inputs. For example, a saw-toothed profile of n-alkane δD values in Australian torbanites is attributed to a dual-source system: a predominant B. braunii input, with a minor terrestrial plant input to odd-carbon-numbered n-alkanes in the range n-C20 [subscript] to n-C29 [subscript]. The δD values of n-alkanes and isoprenoids (pristane and phytane) differ significantly in two Permian torbanites from Australia, thought to be reflective of the offset between the δD values of their precursors in extant organisms. The torbanite data indicate that a biological δD signal has been preserved for at least 260–280 million years, extending the utility of δD values for palaeoclimate studies. To elucidate the effect of sedimentary processes on the δD values of petroleum hydrocarbons, three sedimentary sequences have been studied. These comprise one from the Perth Basin (Western Australia) and two from the Vulcan Sub-basin (northern Australia) covering a wide range of maturities, i.e. 0.53–1.6% vitrinite reflectance (Ro). The δD values of n-alkanes extracted from immature-early mature sediments (marine shales/siltstones and mudstones) are consistent with that expected of marine-derived n-alkyl lipids. The hydrocarbons become enriched in D with increasing maturity. The large (ca. 115%) biologically-derived offset between the δD values of n-alkanes and acyclic isoprenoids from immature sediments gradually decreases with increasing maturity, as the isoprenoids become enriched in D more rapidly than the n-alkanes. The D-enrichment in isoprenoids correlates strongly with Ro and traditional molecular maturity parameters.
This suggests that H/D exchange during maturation occurs via a mechanism involving carbocation-like intermediates, which proceeds more rapidly with compounds containing tertiary carbon centres. Significant epimerisation of pristane and phytane coincides with their D-enrichment, suggesting that hydrogen exchange occurs at their tertiary carbons. A mechanism is proposed which can account for both H/D exchange and the epimerisation of pristane and phytane in the sedimentary environment. Pristane and phytane extracted from a post-mature sediment from the Paqualin-1 sequence are significantly enriched in D (ca. 40%) relative to the n-alkanes, indicating that D-enrichment persists at very high maturity, and is more pronounced for the regular isoprenoids than the n-alkanes. This supports the notion that H/D exchange causes the observed shift in δD values, rather than free-radical hydrogen transfer. The differences between the δD values of pristane and phytane show opposite trends in the Perth Basin and Vulcan Sub-basin sediments. In the Perth Basin, phytane is enriched in D relative to pristane, likely due to a dominant algal source. In the Vulcan Sub-basin, pristane is enriched in D relative to phytane, and thus is attributed to a lower relative input of algal organic matter. The variance of the δD values of pristane and phytane is generally consistent throughout the maturity range and provides evidence that pristane and phytane exchange hydrogen at similar rates. δD analysis of crude oils and condensates reservoired in the Perth Basin and Vulcan Sub-basin has been carried out to evaluate potential applications in oil-source correlation.
The n-alkanes from crude oils and condensates are often more enriched in D than n-alkanes extracted from their supposed source rocks, and the oils also show relatively small differences between the δD values of n-alkanes and isoprenoids. These results suggest significant H/D exchange has occurred, implying that the liquids were generated from mature source rocks. A Perth Basin crude oil (Gage Roads-1) thought to be derived from a lacustrine/terrestrial source contains hydrocarbons that are significantly depleted in D relative to Perth Basin oils derived from a marine source, attributed to variability in the isotopic composition of marine and terrestrial source waters. δD values of n-alkanes from Vulcan Sub-basin crude oils and condensates are largely consistent with their prior classification into two groups: Group A, having a marine source affinity; and Group B, having a terrigenous source affinity. Some oils and condensates are suggested to be mixtures of Group A and Group B hydrocarbons, or Group A hydrocarbons and other as yet unknown sources. An exception is a former Group A oil (Tenacious-1) containing n-alkanes that are enriched in D relative to those from other Group A oils and condensates, attributed to mixing with another source of more mature hydrocarbons. The n-alkane δD profile appears to be indicative of source and sedimentary processes. One Perth Basin crude oil (Dongara-14) contains lower-molecular-weight n-alkanes that are depleted in D relative to higher-molecular-weight n-alkanes, attributed to a mixed marine/terrestrial source.
Group A crude oils and condensates from the Vulcan Sub-basin display a ‘bowl-shaped’ profile of n-alkane δD values. An upward inflection in the n-alkane δD profile from n-C11 [subscript] to n-C15 [subscript] is suggested to represent the addition of D-enriched lower-molecular-weight n-alkanes from a more mature wet gas/condensate to an initial charge of lower maturity oil. Ultimately, this project has demonstrated that the δD values of individual petroleum hydrocarbons can be used to elucidate the nature of source organic matter and depositional environments. The preservation potential of lipid δD values is greater than previously thought, although it is clear that H/D exchange accompanying maturation can have a significant effect on the δD values of certain hydrocarbons. Thus, great care must be taken when interpreting δD values of individual hydrocarbons, particularly those derived from sediments of high thermal maturity.