Kliknij ten link, aby zobaczyć inne rodzaje publikacji na ten temat: Phase angle.
Rozprawy doktorskie na temat „Phase angle”
Utwórz poprawne odniesienie w stylach APA, MLA, Chicago, Harvard i wielu innych
Sprawdź 50 najlepszych rozpraw doktorskich naukowych na temat „Phase angle”.
Przycisk „Dodaj do bibliografii” jest dostępny obok każdej pracy w bibliografii. Użyj go – a my automatycznie utworzymy odniesienie bibliograficzne do wybranej pracy w stylu cytowania, którego potrzebujesz: APA, MLA, Harvard, Chicago, Vancouver itp.
Możesz również pobrać pełny tekst publikacji naukowej w formacie „.pdf” i przeczytać adnotację do pracy online, jeśli odpowiednie parametry są dostępne w metadanych.
Przeglądaj rozprawy doktorskie z różnych dziedzin i twórz odpowiednie bibliografie.
1
Maamache, Mustapha. "Phase de berry, angle de annay et etats coherents action angle". Nice, 1993. http://www.theses.fr/1993NICE4625.
Pełny tekst źródłaStreszczenie:
Ce travail de physique theorique porte sur les relations entre la phase de berry et l'angle de hannay qui sont deux notions geometriques decrivant des transports naturels en physique respectivement quantique et classique. Le but principal de ce travail a ete d'elaborer un nouveau formalisme, celui des etats quantiques action angle (generalisation des etats coherents de l'oscillateur harmonique), dans lequel le transport classique apparait comme un cas particulier du transport quantique. Cela a permis non seulement d'etablir plusieurs derivations quantiques inedites de l'angle de hannay, mais aussi d'apporter des eclairages originaux sur la relation entre la phase de berry et l'angle de hannay a travers l'introduction des notions de principe variationnel moyenne ou de minimisation de metriques sur les etats quantiques ou les trajectoires classiques. Le rapport entre la phase de berry et l'angle de hannay a egalement ete examine dans le cas des systemes grassmaniens
2
Magozore, Caxton. "DSP phase angle controlled three phase to single phase uninterruptible power supply". Master's thesis, University of Cape Town, 2003. http://hdl.handle.net/11427/5177.
Pełny tekst źródła
3
Alps, Mike. "The phase transformation friction angle of sand". abstract and full text PDF (free order & download UNR users only), 2007. http://0-gateway.proquest.com.innopac.library.unr.edu/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:1442864.
Pełny tekst źródła
4
Leibly, Frank J. (Frank Joseph). "Measurement and digitization of phase angle modulated sensor data". Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/37753.
Pełny tekst źródła
5
Kok, Yitping. "Phase-referenced Interferometry and Narrow-angle Astrometry with SUSI". Thesis, The University of Sydney, 2013. http://hdl.handle.net/2123/10028.
Pełny tekst źródłaStreszczenie:
This thesis describes the development of an astrometric facility at the Sydney University Stellar Interferometer (SUSI) with an aim to measure at high precision the relative astrometry of bright close binary stars and ultimately to detect the presence of exoplanets within those binary star systems through observations of the systems’ perturbed motion. At the core of the facility is a new beam combiner that is phase-referenced to an existing primary beam combiner in the visible wave- length regime. The latter provides post-processed fringe-tracking information to the former for fringe stabilization and coherent integration of pre-recorded stellar fringes using newly developed data reduction software. Interference fringe packets of a binary star are recorded alternately; first the fringe packet of the primary, then the secondary, finally back to the primary again. The measurement of the fringe packet separation is facilitated by an air-filled differential delay line and a network of interferometer-based metrology systems. Characterizations and initial astronomical observations carried out with the dual beam combiner setup demonstrated for the first time the success of the dual-star phase-referencing technique in visible (~1μm) wavelengths. The current astrometric precision is larger than 100μas while the long term astrometric accuracy is yet to be characterized. In a parallel development, a complementary observing method using only the primary beam combiner is also demonstrated in this thesis. Relative astrometry of binary stars up to ~0.8” separation with this technique has been demonstrated to have precision of better than 100μas. A simple detection limit analysis based on a list of target binary stars estimates up to two exoplanet detections can be achieved with SUSI if the new astrometric facility attains precision of 10μas while the primary beam combiner operates at its designed peak performance. Finally, one new stellar companion was resolved and a preliminary astrometry for another suspected companion was estimated from the astronomical observation data collected throughout the course of this thesis.
6
Morris, Darryl William Seymour. "Low angle protein phasing". Thesis, University of York, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.341631.
Pełny tekst źródła
7
Eaton, Elizabeth Jane. "Paradoxical breathing and arousal from sleep". Thesis, Manchester Metropolitan University, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.320131.
Pełny tekst źródła
8
Sadler, Peter Andrew. "Harmonic elimination and voltage control in three phase AC power converters". Thesis, Manchester Metropolitan University, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.285285.
Pełny tekst źródła
9
Allison, Steven David. "The effects of interblade phase angle on pitch oscillating, transonic, cascade flows". Thesis, University of Salford, 2011. http://usir.salford.ac.uk/26530/.
Pełny tekst źródłaStreszczenie:
A series of compressor blades, aligned as a cascade, situated in a transonic flow has been studied using a two-dimensional Computational Fluid Dynamics (CFD) technique. An objective of the research was to discover, using a CFD code, how the total aerodynamic stability of a compressor cascade was affected by blade pitching oscillations, vibrating at certain interblade phase angles and oscillation frequencies. The analysis focused on the way in which the interblade phase angle, a, is likely to affect the stability of the cascade over a range of oscillation frequencies between 200Hz and 1 OOOHz, for a series of interblade phase angles between 0° and 180°. Two turbulence models were assessed to determine the sensitivity of turbulence coding, namely the Baldwin-Lomax and Johnson-King models. A validation of the CFD code against published data from the NASA Lewis Research Centre was carried out. The interaction of the passage shock, formed between the blades, and on the positive pressure surface of the blade was shown to have the greatest influence on the aerodynamic stability of the cascade; the shocks formed on the suction side had a somewhat smaller effect. Any flow separation, on either the suction or pressure surfaces, was also shown to decrease cascade stability.
10
Cocquerelle, Jean-Louis. "Étude des associations en triphasé : gradateur en angle de phase - transformateur - résistances". Lille 1, 1985. http://www.theses.fr/1985LIL10107.
Pełny tekst źródłaStreszczenie:
Pour régler de façon continue le débit du réseau de distribution dans un récepteur triphasé résistif, à l'aide d'un dispositif présentant de très faibles pertes, il est usuel de disposer un gradateur fonctionnant en "angle de phase" entre la source et la charge. Il est presque toujours nécessaire, dans les équipements de forte puissance, d'ajouter un transformateur. L'analyse du fonctionnement de l'ensemble transformateur - gradateur - charge est très complexe, pour plusieurs raisons :- D'abord, ces dispositifs fonctionnent en commutation libre, c'est à dire que l'on ne peut commander que la mise en conduction des thyristors. - Ensuite, la présence du transformateur modifie totalement, par le couplage magnétique qu'il introduit entre les phases, le comportement du gradateur. En effet, les instants d'extinction des thyristors ne sont pas uniquement dépendant des tensions d'alimentation, mais à la fois du couplage des enroulements, de l'emplacement des composants, du niveau de la charge, ainsi que de l'état magnétique du transformateur. La première partie du mémoire est consacrée à l'étude analytique du fonctionnement en régime permanent. La deuxième partie concerne la comparaison des divers montages, en régime permanent, mais également face à un défaut comme la rupture d'une résistance de charge. Une méthode par simulation est alors introduite, elle permet d'élaborer la meilleure "loi de commande" du gradateur disposé dans une structure donnée.
11
Marais, Sarel Jacobus. "The quadrifilar helix antenna and its application to wide angle phase-steered arrays". Thesis, Stellenbosch : Stellenbosch University, 2007. http://hdl.handle.net/10019.1/21675.
Pełny tekst źródłaStreszczenie:
Thesis (MScIng)--University of Stellenbosch, 2007.ENGLISH ABSTRACT: The quadrifilar helix antenna has frequently been employed to provide the wide angle, circularly polarized radiation pattern which is preferable for mobile satellite communications. A detailed study of this antenna and its varieties is presented. When used as an element in wide angle scanning arrays for aeronautical satellite tracking applications, the additional requirement of a low profile with light weight applies. This further complicates the realization of good circular polarization close to the horizon. A top disk is incorporated into various antenna structures in an effort to improve the radiation performance when used within a closely spaced array while reducing the height of the radiating element. The array performance of these elements are investigated which hints at a supported traveling mode aiding the ability to accomplish the wide angle beam steering. Subsequent study of leakywave antennas initiated the study and implementation of leaky-wave structures in phased arrays of quadrifilar helix elements.
AFRIKAANSE OPSOMMING: Die vierledige heliksantenna word dikwels gebruik vir toepassings wat ’n wye, sirkulêr gepolariseerde stralingspatroon benodig. ’n Verskeidenheid van hierdie antennas is noukeurig bestudeer en hul toepaslikheid vir mobiele sattelietkommunikasie ondersoek. Wanneer hierdie antennas in fase gestuurde skikkings gebruik word, word dit ook vereis dat die eenhede liggewig is met ’n lae profiel. Dit bemoeilik die verkryging van goeie sirkulêre polarisasie naby die horison aansienlik. In ’n poging om die wyehoek straling met kort antennas te verbeter, is ’n oorhoofse skyf tot verskillende heliksstrukture toegevoeg. In nou gespasieerde skikkings maak hierdie skywe ’n positiewe bydrae to wyehoekstralingeienskappe. Die invloed van lekmodusse wat binne die struktuur voortplant is ondersoek en gebruik in skikkings waarvan die bundel naby aan die horison gestuur word.
12
Swann, Joshua Michael George. "Characterising pH response in phase separated hydrogels using small angle X-ray scattering". Thesis, University of Sheffield, 2010. http://etheses.whiterose.ac.uk/14968/.
Pełny tekst źródłaStreszczenie:
A range of (methyl methacrylate)-block-poly(2-(diethylamino)ethyl methacrylate)block- poly(methyl methacrylate) [PMMA-block-PDEA-block-PMMA] and poly(methyl methacrylate )-block-poly(methacrylic acid)-block-poly(methyl methacrylate) [PMMA-blockPMAA- block-PMMA] triblock copolymers have been prepared via group transfer and anionic polymerisation respectively. These hydrophilic-hydrophobic block copolymers were characterized with respect to their chemical composition and molecular weights by 1 H and by gel permeation chromatography respectively. Morphological development in solvent cast films were followed using SAXS by monitoring changes in the structure peak. [PM MA-block-PMAA-block-PM MA] triblocks were found to be mechanically weak and therefore not suitable as chemical actuators. Using SAXS the "static" equilibrium molecular response of phase separated films of [PMMA-block-PDEA-block-PMMA] triblock copolymers to changes in pH, ionic strength and salt identity was evaluated. Changes in pH were effected using a controlled set of buffers, namely citric acid, sodium phosphate and ethanol amine. The ionic strength of the buffers was fixed using a series of salts from the Hofmeister series, namely NaAce, NaCl, NaBr, Nal, NaN03 and NaSCN. At a fixed pH and ionic strength the equilibrium expansion ratio of the polymer was found to be highly dependent on the identity of the salt. The extent of swelling was correlated with the surface charge density of the anionic component of the salt. Hydrogels swollen in solution containing more polar anions were found to have a larger expansion ratio. This was explained in terms of the water perturbing effect of the ion. The swelling of the polymer was also monitored as a function of pH. A drastic collapse of the polymer was observed at a specific pH corresponding to the apparent pKa of the PDEA block. The apparent pKa of [PMMA-block-PDEA-block-PMMA] copolymers was found to be dependent on the overall molecular weight, where higher molecular weight material had a lower apparent pKa. Below the apparent pKa the extent of swelling in solutions prepared at 0.1 M ionic strength was found to be dependent on the pH. This has been attributed to the . complex interplay of citrate species in the buffer. The effect of ionic strength on the "swelling was also investigated at fixed pH and salt identity using buffer and simple mineral acid. A modified Donnan theory has been used to interpret the results. SAXS was found to be a highly sensitive technique for measuring the "static response" of the hydrogels. The use of SAXS was also investigated as a technique for measuring the swelling "kinetics" of [PMMA-block-PDEA-block-PMMA] hydrogels. Thin annealed films of hydrogel were swollen in a range of control buffered solutions. The in-situ nature of the technique afforded high resolution data. The kinetics of swelling was monitored by following the change in the structure peak position and its half height peak width, which gave the expansion ratio and diffusive behavior respectively. Swelling stresses induced in the samples made measuring the kinetics problematic and this limited the technique. Finally, to avoid the expense and limited availability of SAXS beam lines a new technique was used to monitor the response of the hydrogels. A diffraction grating was imprinted onto the surface of the hydrogel, and "static" and "kinetic" response was measured by monitoring the change in the diffraction pattern. This technique was found to offer similar accuracy as SAXS, at a Significantly reduced cost.
13
Schmidt, Nico [Verfasser]. "Phase transformation behaviour of polylactide probed by small angle light scattering / Nico Schmidt". Paderborn : Universitätsbibliothek, 2020. http://d-nb.info/1209601370/34.
Pełny tekst źródła
14
Collins, Edward Randolph Jr. "Torque and speed control of single-phase induction motors using an adjustable amplitude and phase angle auxiliary winding power supply". Diss., Georgia Institute of Technology, 1989. http://hdl.handle.net/1853/15472.
Pełny tekst źródła
15
Chavan, Harshad S. "Investigation of ß-phase poly (vinylidene fluoride) films using small-angle x-ray scattering". Cincinnati, Ohio : University of Cincinnati, 2006. http://www.ohiolink.edu/etd/view.cgi?acc%5Fnum=ucin1145990710.
Pełny tekst źródła
16
Polavieja, Gonzalo Garcia de. "Geometric phase and angle for noncyclic adiabatic change, revivals and measures of quantal instability". Thesis, University of Oxford, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.325986.
Pełny tekst źródła
17
CHAVAN, HARSHAD S. "INVESTIGATION OF β-PHASE POLY (VINYLIDENE FLUORIDE) FILMS USING SMALL- ANGLE X-RAY SCATTERING". University of Cincinnati / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1145990710.
Pełny tekst źródła
18
Harada, Tamotsu. "Ultra-Small-Angle Scattering Study of Formation Mechanism and Phase Transition of Colloidal Crystals". Kyoto University, 2001. http://hdl.handle.net/2433/150664.
Pełny tekst źródła
19
Pontoni, Diego. "Small-angle X-ray scattering studies of phase transitions and growth processes on colloidal dispersions". Thesis, King's College London (University of London), 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.271227.
Pełny tekst źródła
20
Xia, Tao. "Frequency Monitoring Network (FNET) Algorithm Improvements and Application Development". Diss., Virginia Tech, 2009. http://hdl.handle.net/10919/77296.
Pełny tekst źródłaStreszczenie:
The Internet Based real-time GPS synchronized wide-area Frequency Monitoring Network (FNET) is an extremely low cost and quickly deployable wide-area frequency measurement system with high dynamic accuracy which consists of Frequency Disturbance Recorder (FDR) distributed to more than 100 places around North America and an Information Management System situated at Virginia Tech. Since its first FDR deployment in 2003, the FNET system has been proved to be able to reliably receive phasor data accurately measured at and instantaneously sent via the Internet from different locations of interest, and efficiently run the analyzing program to detect and record significant system disturbances and subsequently estimate the location of disturbance center, namely the event location, in the electric grid based on the information gathered. The excellent performance of the FNET system so far has made power grid situation awareness and monitoring based on distribution level frequency measurements a reality, and thus advances our understanding of power system dynamics to a higher level and in a broader dimensionality.
Chapter 1 and Chapter 2 of this dissertation briefly introduce the genesis and the architecture of the FNET system, followed by a summary of its concrete implementations. Chapter 3 and Chapter 4 outline FNET frequency estimation algorithm and phase angle estimation algorithm, including their attributes and the new methodologies to enhance them. In Chapter 5, the report discusses the algorithms developed at FNET to detect the frequency disturbance and estimate the disturbance location by the triangulation procedure using real-time frequency data and geographic topology of the FNET units in the power grid where the disturbance occurs. Then, the dissertation proceeds to introduce the FNET angle-based power system oscillation detection and present some research about Matrix Pencil Modal Analysis of FNET phase angle oscillation data in the following two chapters. Lastly, the content of this report is summarized and the future work envisioned in Chapter 8.Ph. D.
21
Dowsett, Amy. "The improvement of vehicle noise variability through the understanding of phase angle and NVH analysis methods". Thesis, Loughborough University, 2018. https://dspace.lboro.ac.uk/2134/35880.
Pełny tekst źródłaStreszczenie:
Noise, vibration and harshness (NVH)levels in the luxury automotive industry are used by customers as a subjective method of determining the vehicle quality. This can be achieved by adjusting the vehicle design, where simulations are used to predict the NVH behaviour. Changes can be expensive and time consuming when made after the design stage has been completed, so it is important to produce accurate simulations of the product. Variability exists to some extent in all products, even those just off the production line, however, if a high level of variability exists then only a small portion of products will meet the predicted behaviour. The aim of the project is to provide information that may lead to the reduction of variability in an automotive vehicle. This is achieved by quantifying the statistical spread of FRFs (frequency response function) in a set of nominally identical vehicles. Once overall levels have been calculated, the location of the most variable sources can be identified. Project also seeks to develop new methods of analysis for the system phase response to determine whether further information may be extracted compared to the magnitude response. There are three main themes that run throughout this thesis, with the first being the quantification of variability due to the measurement taking process which is covered in chapter 3. A novel application of a method to separate the measurement variability from the overall system uncertainty was achieved as well as the quantification of the vehicle to- vehicle variability. The second theme that runs through the study concerns the identification of variability sources. This is realised in chapter 4 and chapter 6 as a set of structural and acoustic tests on a luxury sedan door. The trim was found to be held to the door panel by a series of 11 polymer clips and 4 metal screws. The variability of small changes to a significant boundary condition at the door trim was quantified, showing that the removal of rigid clips had a more significant effect on the overall variability that if a loose clip has been removed. It was also found that clips at the corners were the most sensitive to change. The final theme outlines and tests new analysis methods on the phase and compares the statistical spread of the phase with the equivalent spread of the magnitude. Data taken from the same tests was used and for most of the cases the two results were found to be approximately the same.
22
Bucher, Thomas M. Jr. "CAPILLARITY AND TWO-PHASE FLUID TRANSPORT IN MEDIA WITH FIBERS OF DISSIMILAR PROPERTIES". VCU Scholars Compass, 2014. http://scholarscompass.vcu.edu/etd/3653.
Pełny tekst źródłaStreszczenie:
Capillarity is a physical phenomenon that acts as a driving force in the displacement of one fluid by another within a porous medium. This mechanism operates on the micro and nanoscale, and is responsible for countless observable events. This can include applications such as absorption in various hygiene products, self-cleaning surfaces such as water beading up and rolling off a specially-coated windshield, anti-icing, and water management in fuel cells, among many others.
The most significant research into capillarity has occurred within the last century or so. Traditional formulations for fluid absorption include the Lucas–Washburn model for porous media, which is a 1-D model that reduces a porous medium to a series of capillary tubes of some educated equivalent radius. The Richards equation allows for modeling fluid saturation as a function of time and space, but requires additional information on capillary pressure as a function of saturation (pc(S)) in order to solve for absorption. In both approaches, the surface can only possess one fluid affinity. This thesis focuses on developing capillary models necessary for predicting fluid absorption and repulsion in fibrous media. Some of the work entails utilizing approximations based on pore space available to the fluid, which allows for capillary pressure simulation in media with arbitrary fiber orientation. This thesis also presents models for tracking the fluid interface in fibrous media and coatings with simpler geometries such as horizontally and vertically aligned fibers and orthogonal fiber layers. This method hinges on solving for the true fluid interface shape between the fibers based on the balance of forces across it, ensuring the accurate location and total content of fluid in the medium, and therefore accurate pc(S). Using this approach also allows, for the first time, fibers of different fluid affinities to exist in the same structure, to examine their combined influence on fluid behavior. The models in this thesis focus mainly on absorbent fabrics and superhydrophobic coatings, but can be easily expanded for use in other applications such as water filtration from fuel, fluid transport and storage in microchannels, polymer impregnation in fiber-reinforced composite materials, among countless others.
23
Clark, Matthew A. "The Harmonic Distortion Reduction of Phase-Angle Fired SCRs Feeding a Resistive Load using Fuzzy Logic". Wright State University / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=wright1271111941.
Pełny tekst źródła
24
Thakkar, Kairavee K. "A Geometric Analysis of Time Varying Electroencephalogram Vectors". University of Cincinnati / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1613745734396658.
Pełny tekst źródła
25
Uriarte, Fabian. "Modeling, Detection, and Localization of High-Impedance Faults In Low-Voltage Distribution Feeders". Thesis, Virginia Tech, 2003. http://hdl.handle.net/10919/30810.
Pełny tekst źródłaStreszczenie:
High-impedance faults (HIFs) on distribution feeders are abnormal electrical conditions that cannot be detected by conventional protection schemes. These faults pose a threat on human lives when neighboring objects become in contact with the lineâ s bare and energized conductors. An accurate electrical model for a HIF is implemented to investigate typical patterns in the lineâ s current that allow for the detection of these faults. The occurrence of HIFs is detected with harmonic-current phase analysis and localized with recloser-sectionalizer technology as presented in this work. A sectionalizer algorithm is then presented showing the decision criteria for HIF declaration and shown to discriminate against nominal behavior in distribution feeders of similar harmonic content. Finally, it is shown that the algorithm will not produce a misreading when a current transformer enters saturation.Master of Science
26
Chakraborty, Saonti. "SHORT - RANGE ORDER IN THE NEMATIC PHASE OF REDUCED SYMMETRYTHERMOTROPIC MESOGENS". Kent State University / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=kent1385158954.
Pełny tekst źródła
27
Pellegrene, Brittany Ann. "Optimization of Transition Temperatures and Tilt Angle in SmCPA Phase Bent-Core Liquid Crystals". Kent State University Honors College / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=ksuhonors1430258781.
Pełny tekst źródła
28
Miftah, el kheir Laila. "Smart devices for biomedical applications". Thesis, Bourgogne Franche-Comté, 2017. http://www.theses.fr/2017UBFCD054.
Pełny tekst źródłaStreszczenie:
Dans cette thèse, nous nous sommes intéressés aux systèmes intelligents pour des applicationsmédicales et cosmétiques. Ainsi, nous avons conçu et réalisé trois instruments. Le premier estdédié à la mesure de la mouillabilité de la peau. L’originalité de ce dispositif réside en sa capacité àdonner une image 3D de la goûte de la surface de la peau explorée et de donner le comportementdynamique de la goûte. Cette stratégie nous donnera la possibilité de créer de nouvelles basesde données relatives à la mouillabilité de tout le corps humain. En effet, nous disposons que desdonnées sur la mouillabilité de l’avant-bras. Le deuxième instrument intelligent concerne la mesurede la réflectance d’une surface. Ce dispositif assure une mesure de très haute résolution angulairede la BRDF et une très bonne répétabilité de la mesure. Il a été validé sur la peau pour la mesurede l’ éclat. Et enfin le troisième instrument, basé sur une méthode originale de mesure de vibrationà l’aide d’un système de stéréo-vision associée à un motif périodique. Il a été appliqué pour lamesure du mouvement thoracique et abdominal lors de la respiration. Notre principale motivationpour développer ce système fut la réduction des artefacts, dus aux mouvements d’un patient lorsd’un examen radiologiqueSmart Devices have been widely used by health care and cosmetics professionals. Indeed, they helpin many aspects of clinical practice by providing an efficient way for medical diagnosis, supportingbetter clinical decision-making and improving patient outcomes. In this thesis, we have beeninterested in three applications. The first one is related to the wettability measurement, especially forthe human skin. So we propose, a held-hand device that is based on the contact angle measurementto determine skin wettability. Besides, the device allows the visualization of the liquid dropletspreading in both dynamic and static modes. Moreover, it can measure the top and the left views ofthe droplet and provides the 3D droplet and the skin explored area profiles. The second applicationpermits the skin radiance measurement. For this purpose, we propose a miniaturized device havingan original method for the BRDF measurement associated with 3D profile measurement of the areastudied. As regards the third application, it is a non-invasive method for breath measurement that usesa stereovision system and a pseudo-periodic pattern. This system allows a high-resolution threedimensionaldisplacement measurement for the recording of the thoracoabdominal wall respiratorymovement. The devices developed during this research gives us a high accuracy, a good resolutionand repeatability of measurements
29
Oliveira, Pablo Gustavo de. "Ângulo de fase como indicador de desfechos negativos em pacientes cirúrgicos". reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2012. http://hdl.handle.net/10183/61738.
Pełny tekst źródłaStreszczenie:
Introdução: A Bioimpedância Elétrica (BIA) é um método fácil de usar, rápido, barato, não invasivo e de fácil reprodutibilidade utilizado para verificar as mudanças na composição corporal. O Ângulo de Fase (AF), obtido através da BIA, reflete a relativa contribuição dos fluidos e membranas para o corpo humano, sendo associado como um marcador prognóstico em diversas situações clínicas. Objetivos: Avaliar o AF como indicador de desfechos negativos em pacientes cirúrgicos (ocorrência de infecção e/ou morte e tempo de permanência hospitalar). Metodologia: Foram avaliados pacientes com idade de 18 a 80 anos internados no Hospital de Clínicas de Porto Alegre com indicação de cirurgia eletiva. As avaliações foram realizadas no momento da internação, 48 e 72 horas após a cirurgia. Foram avaliados peso, altura e Índice de Massa Corporal (IMC), estado nutricional através da Avaliação Nutricional Subjetiva Global (ANSG) e Ângulo de Fase através da BIA. Resultados: Foram avaliados 142 pacientes, segundo o IMC, 59,2% dos pacientes foram classificados como eutróficos, 3,5% moderadamente desnutridos e 37,3% apresentaram algum grau obesidade. A avaliação por ANSG verificou que 76,1% dos pacientes estavam eutróficos, 23,2% moderadamente desnutridos e 0,7% desnutridos graves. Os baixos valores para o AF obtidos nas 3 avaliações não se apresentaram como indicadores de desfechos negativos em pacientes cirúrgicos. Conclusões: O AF não se demonstrou um indicador para desfechos negativos em pacientes cirúrgicos.Introduction: Electrical Bioimpedance (BIA) is an easy to use, fast, inexpensive, noninvasive and highly reproducible used to verify the changes in body composition. The Phase Angle (PA), obtained by BIA reflects the relative contribution of fluid and membranes for the human body, being associated as a prognostic marker in various clinical situations. Objectives: To evaluate the AF as an indicator of negative outcomes in surgical patients. Methodology: We studied patients aged 18 to 80 years at the Hospital de Clínicas de Porto Alegre with indication of elective surgery. Evaluations were performed at admission, 48 and 72 hours after surgery. Body weight, height and Body Mass Index (BMI), nutritional status by Subjective Global Assessment (SGA) and Phase Angle through the BIA. Results: According to BMI, 59.2% of patients were classified as eutrophic, 3.5% moderately malnourished and 37.3% had some degree obesity. The assessment by SGA found that 76.1% of patients were eutrophic, 23.2% moderately malnourished and 0.7% severely malnourished. The low values obtained for the AF in three evaluations were not presented as indicators of negative outcomes in surgical patients. Conclusions: AF is not an indicator to show negative outcomes in surgical patients.
30
Li, Biao. "Hydrophobic-Hydrophilic Separation Process for the Recovery of Ultrafine Particles". Diss., Virginia Tech, 2019. http://hdl.handle.net/10919/103278.
Pełny tekst źródłaStreszczenie:
The demands for copper and rare earth elements (REEs) in the U.S. will keep rising due to their applications in green energy technologies. Meanwhile, copper production in the U.S. has been declining over the past five years due to the depletion of high-grade ore deposits. The situation for REEs is worse; there is no domestic supply chain of REEs in the U.S. since the demise of Molycorp, Inc. in 2016. Studies have shown that the rejected materials from copper and coal processing plants contain significant amounts of valuable metals. As such, this rejected material can be considered as potential secondary sources for extracting copper and REEs, which may help combat future supply risks for the supply of copper and REEs in the U.S. However, the valuable mineral particles in these resources are ultrafine in size, which poses considerable challenges to the most widely used fine particle beneficiation technique, i.e., froth flotation. A novel technology called the Hydrophobic-Hydrophilic Separation (HHS) process, developed at Virginia Tech, has been successfully applied to recover fine coal in previous research. The results of research into the HHS process showed that the process has no lower particle size limit, similar to solvent extraction. Therefore, the primary objective of this research is to explore the feasibility of using the new process to recover ultrafine particles of coal, copper minerals, and rare earth minerals (REMs) associated with coal byproducts.
In the present work, a series of laboratory-scale oil agglomeration and HHS tests have been carried out on coal with the objectives of assisting the HHS tests in pilot-scale, and the scale-up of the process. The knowledge gained from this study was successfully applied to solving the problems encountered in the pilot-scale tests. Additionally, a new and more efficient equipment known as the Morganizer has been designed and constructed to break up the agglomerates in oil phase as a means to remove entrained gangue minerals and water. The effectiveness of the new Morganizers has been demonstrated in laboratory-scale HHS tests, which may potentially result in the reduction of capital costs in commercializing the HHS process. Furthermore, the prospect of using the HHS process for processing high-sulfur coals has been explored. The results of this study showed that the HHS process can be used to increase the production of cleaner coal from waste streams.
Application of the HHS process was further extended to recover the micron-sized REMs from a thickener underflow sample from the LW coal preparation plant, Kentucky. The results showed that the HHS process was far superior to the forced-air flotation process. In one test conducted during the earlier stages of the present study, a concentrate assaying 17,590 ppm total REEs was obtained from a 300 ppm feed. In this test, the Morganizer was not used to upgrade the rougher concentrate due to the lack of proper understanding of the fundamental mechanisms involved in converting oil-in-water (o/w) Pickering emulsions to water-in-oil (w/o) Pickering emulsions. Many of the studies has, therefore, been focused on the studies of phase inversion mechanisms. The results showed that phase inversion requires that i) the oil contact angles (θo) of the particles be increased above 90o, ii) the phase volume of oil (ϕo) be increased, and iii) the o/w emulsion be subjected to a high-shear agitation. It has been found that the first criterion can be readily met by using a hydrophobicity-enhancing agent. These findings were applied to produce high-grade REM concentrates from an artificial mixture of micron-sized monazite and silica.
Based on the improved understanding of phase inversion, a modified HHS process has been developed to recover ultrafine particles of copper minerals. After successfully demonstrating the efficacy and effectiveness of this process on a series of artificial copper ore samples, the modified HHS process was used to produce high-grade copper concentrates from a series of cleaner scavenger tails obtained from operating plants.Doctor of Philosophy
Recovery and dewatering of ultrafine particles have been the major challenges in the minerals and coal industries. Based on the thermodynamic advantage that oil droplets form contact angles about twice as large as those obtainable with air bubbles, a novel separation technology called the hydrophobic-hydrophilic separation (HHS) process was developed at Virginia Tech to address this issues. The research into the HHS process previously was only conducted on the recovery of ultrafine coal particles; also, the fundamental aspects of the HHS process were not fully understood, particularly the mechanisms of phase inversion of oil-in-water emulsions to water-in-oil emulsions. As a follow-up to the previous studies, emulsification tests have been conducted using ultrafine silica and chalcopyrite particles as emulsifiers, and the results showed that phase inversion requires high contact angles, high phase volumes, and high-shear agitation. These findings were applied to improve the HHS process for the recovery of ultrafine particles of coal, copper minerals, and rare earth minerals (REMs). The results obtained in the present work show that the HHS process can be used to efficiently recover and dewater fine particles without no lower particle size limits.
31
JUSTICE, RYAN SCOTT. "INTERFACE MORPHOLOGY AND PHASE SEPARATION IN POLYMER DISPERSED LIQUID CRYSTAL (PDLC) COMPOSITES". University of Cincinnati / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1163783056.
Pełny tekst źródła
32
Mickel, Walter. "Geometry controlled phase behavior in nanowetting and jamming". Phd thesis, Université Claude Bernard - Lyon I, 2011. http://tel.archives-ouvertes.fr/tel-00868861.
Pełny tekst źródłaStreszczenie:
This thesis is devoted to several aspects of geometry and morphology in wetting problems and hard sphere packings. First, we propose a new method to simulate wetting and slip on nanostructured substrates: a phase field model associated with a dynamical density theory approach. We showed omniphobicity, meaning repellency, no matter the chemical properties of the liquid on monovalued surfaces, i.e. surfaces without overhangs, which is in contradiction with the macroscopic Cassie-Baxter-Wenzel theory, can produce so-called We checked systematically the impact of the surface parameters on omniphobic repellency, and we show that the key ingredient are line tensions, which emerge from needle shaped surface structures. Geometrical effects have also an important influence on glassy or jammed systems, for example amorphous hard sphere systems in infinite pressure limit. Such hard sphere packings got stuck in a so-called jammed phase, and we shall demonstrate that the local structure in such systems is universal, i.e. independent of the protocol of the generation. For this, robust order parameters - so-called Minkowski tensors - are developed, which overcome robustness deficiencies of widely used order parameters. This leads to a unifying picture of local order parameters, based on geometrical principles. Furthermore, we find with the Minkowski tensor analysis crystallization in jammed sphere packs at the random closed packing point
33
Rapolu, Prakash. "Capillarity Effect on Two-phase Flow Resistance in Microchannels". University of Cincinnati / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1204082574.
Pełny tekst źródła
34
Bhatta, Fanindra P. "Phase Separation in Binary Lipid Monolayers Bilayers: Experiment and Theory". Kent State University / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=kent1322501214.
Pełny tekst źródła
35
Rauchecker, Maximilian [Verfasser], Harald [Akademischer Betreuer] Garcke, Mathias [Akademischer Betreuer] Wilke i Gieri [Akademischer Betreuer] Simonett. "Evolution of interfaces in two-phase problems with ninety degree contact angle / Maximilian Rauchecker ; Harald Garcke, Mathias Wilke, Gieri Simonett". Regensburg : Universitätsbibliothek Regensburg, 2019. http://d-nb.info/1201160642/34.
Pełny tekst źródła
36
Chae, Chun Sik. "Studies of the Interferometric Phase and Doppler Spectra of Sea Surface Backscattering Using Numerically Simulated Low Grazing Angle Backscatter Data". The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1331074430.
Pełny tekst źródła
37
Bleier, Blake J. "Droplet-Based Approaches to Probe Complex Behavior in Colloidal Fluids with High Composition Resolution". Research Showcase @ CMU, 2018. http://repository.cmu.edu/dissertations/1173.
Pełny tekst źródłaStreszczenie:
In this work, microfluidic and millifluidic droplets are utilized to study and control complex fluid behavior with high composition resolution. Different techniques are used on two length scales to create unique approaches towards the same goal of merging droplet-based experiments with classical colloidal characterization experiments. First, a microfluidic dehydrating droplet device is characterized and a procedure established by concentrating a phase separating organic-inorganic system on chip and using geometric calculations to determine composition. The device is then expanded to a more complex, particle-polymer system to investigate suspension stability and interparticle behavior. A model system containing silica particles and PEO polymer is found to transition from a bridging flocculation mechanism to polymer-coated particle jamming based on the mass ratio of polymer to particle. Lastly, a phase separating particle-polymer system consisting of polystyrene particles and hydroxyethyl cellulose is concentrated on-chip. Interparticle interactions are controlled by varying particle size, polymer size, and polymer type and the effects on phase behavior are examined. Droplet experiments are scaled-up to millifluidic droplets and concentration gradients are used to produce high composition resolution in place of time, used in the dehydrating microfluidic experiments. A novel, millifluidic containment device is created to study aggregation and sedimentation in droplets containing carbon black and OLOA surfactant suspended in dodecane. A slow increase in stabilization behavior is observed as opposed to the previously observed sharp “on-off” effect. The droplet production technique is then improved to achieve more complex composition paths and the device is expanded for a small angle neutron scattering (SANS) application. SANS is performed on flowing droplets with varying concentration to map interparticle interactions and phase behavior of complex particulate systems. Feasibility of device is demonstrated and preliminary model systems of silica particles and polymer, salt, and surfactant are analyzed and characterized.
38
Tang, Xuanping. "Effect of Surface State on Water Wetting and Carbon Dioxide Corrosion in Oil-water Two-phase Flow". Ohio University / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1304638556.
Pełny tekst źródła
39
Lopian, Tobias. "Characterization of a metal-extracting water-poor microemulsion". Thesis, Montpellier, 2017. http://www.theses.fr/2017MONTT206/document.
Pełny tekst źródłaStreszczenie:
Le recyclage des terres rares à partir de déchets électroniques n'a toujours pas trouvé une réalisation industrielle significative. L'une des raisons est le manque de procédures de séparation optimisées en raison de connaissances fondamentales médiocres sur ces systèmes. En raison des similitudes chimiques et physiques de ces métaux, la conception d'une formulation efficace, adaptative et prédictive est toujours hors de portée des possibilités. L'interprétation supramoléculaire de la formation complexe dans la phase organique est de plus en plus importante au cours des dernières années. C'est l'approche la plus prometteuse permettant l'explication de divers phénomènes, tels que la formation de la troisième phase et les signaux forts dans de petites expériences de diffusion et de revenir à des méthodes bien connues de la science des tensioactifs. Notre contribution à une compréhension plus complète dans cette matière est l'analyse du comportement électrodynamique de ces phases et la corrélation de ces résultats avec les résultats des propriétés d'auto-assemblage et du transport de masse dans ces médias. Pour cette étude, nous avons spécifiquement conçu un modèle de référence, en passant un processus d'extraction à ses quatre composants fondamentaux: l'extracteur avant l'extraction (acide Di-(2-éthylhexyl) phosphorique, HDEHP), l'extrait après extraction (son sel de sodium, NaDEHP ), le toluène comme diluant apolaire et de l'eau. Un prisme de phase de Gibbs a été préparé (illustré sur la figure 1), où l'axe z donne le rapport de HDEHP à NaDEHP, ce qui représente le développement d'une extraction. Couvrant le domaine de basse fréquence, la spectroscopie d'impédance a été la méthode de choix afin de déterminer la conductivité dépendant de la fréquence. En utilisant la spectroscopie de relaxation diélectrique, nous révélons des processus dynamiques rapides à haute fréquence. Des mesures combinées SAXS et SANS ont été effectuées pour comparer les tendances électrodynamiques avec les propriétés d'agrégation et les interactions entre groupes. Deux phénomènes ont été identifiés comme responsables du profil de conductivité dans les systèmes micellaires inverse: la formation d'agrégats chargés par la dissimulation et la percolation. Tout au long du système de référence, ces deux processus ont été sondés en fonction de trois variables: la concentration totale d'agent d'extraction, le rapport eau-agent tensioactif et le rapport Na: H. En tant que résultat majeur, l'eau joue un rôle important dans les deux processus. En cas de percolation, les agrégats inverse ne peuvent pas fusionner en l'absence d'eau. Par conséquent, la conductivité électrique est interdite. Dans les systèmes dilués, l'eau facilite le processus de dismutation, entraînant une augmentation de la conductivitéRecycling of rare earths from electronic waste has still not found a significant industrial realization. One reason is the lack of optimized separation procedures due to poor fundamental knowledge on these systems. Due to the chemical and physical similarities of these metals, designing an efficient, adaptive and predictive formulation is still out of scope of possibilities. The supramolecular interpretation of complex-formation in the organic phase has gained an increasing importance in the last years. It is the most promising approach allowing the explanation of diverse phenomena, such as third phase formation and strong signals in small scattering experiments and to revert to methods well known from surfactant science. Our contribution towards a more complete understanding in this matter is the analysis of the electrodynamic behaviour of such phases and the correlation of these findings with the results of self-assembly properties and mass transport in these media.For this study, we specifically designed a reference model, breaking an extraction process down to its four fundamental components: The extractant before extraction (Di-(2-ethylhexyl)phosphoric acid, HDEHP), the extractant after extraction (its sodium salt, NaDEHP), toluene as apolar diluent and water. A Gibbs phase prism has been prepared (illustrated in Figure 1), where the z-axis gives the ratio of HDEHP to NaDEHP, representing the development of an extraction. Covering the low frequency-domain, impedance spectroscopy has been the method of choice in order to determine the frequency-dependent conductivity. Using dielectric relaxation spectroscopy, we reveal fast dynamic processes at high frequencies. Combined SAXS and SANS measurements have been performed to compare the electrodynamic trends with aggregation properties and intercluster interactions.Two phenomena have been identified to be responsible for the conductivity profile in reverse micellar systems: the formation of charged aggregates through dismutation and percolation. Throughout the reference system, these two processes have been probed as function of three variables: total extractant concentration, the water-to-surfactant ratio and the Na:H-ratio. As a major result, water plays a significant role in both processes. In case of percolation, reverse aggregates are not able to merge in the absence of water. Therefore, electrical conductivity is prohibited. In dilute systems, water facilitates the dismutation–process leading to an increase in conductivity
40
Zhang, Di. "Analysis and Design of Paralleled Three-Phase Voltage Source Converters with Interleaving". Diss., Virginia Tech, 2010. http://hdl.handle.net/10919/27579.
Pełny tekst źródłaStreszczenie:
Three-phase voltage source converters(VSCs) have become the converter of choice in many ac medium and high power applications due to their many advantages, including low harmonics, high power factor, and high efficiency. Modular VSCs have also been a popular choice as building blocks to achieve even higher power, primarily through converter paralleling. In addition to high power ratings, paralleling converters can also provide system redundancy through the so-called (N+1) configuration for improved availability, as well as allow easy implementation of converter power management. Interleaving can further improve the benefit of paralleling VSCs by reducing system harmonic currents, which potentially can increase system power density. There are many challenges to implement interleaving in paralleled VSCs system due to the complicated relationships in a three-phase power converter system. In addition, to maximize the benefit of interleaving, current knowledge of symmetric interleaving is not enough. More insightful understanding of this PWM technology is necessary before implement interleaving in a real paralleled VSCs system.
In this dissertation, a systematic methodology to analyze and design a paralleled three-phase voltage source converters with interleaving is developed. All the analysis and proposed control methods are investigated with the goal of maximizing the benefit of interleaving based on system requirement.
The dissertation is divided into five sections. Firstly, a complete analysis studying the impact of interleaving on harmonic currents in ac and dc side passive components for paralleled VSCs is presented. The analysis performed considers the effects of modulation index, pulse-width-modulation (PWM) schemes, interleaving angle and displacement angle. Based on the analysis the method to optimize interleaving angle is proposed. Secondly, the control methods for the common mode (CM) circulating current of paralleled three-phase VSCs with discontinuous space-vector modulation (DPWM) and interleaving are proposed. With the control methods, DPWM and interleaving, which is a desirable combination, but not considered possible, can be implemented together. In addition, the total flux of integrated inter-phase inductor to limit circulating current can be minimized. Thirdly, a 15 kW three phase ac-dc rectifier is built with SiC devices. With the technologies presented in this dissertation, the specific power density can be pushed more than 2kW/lb. Fourthly, the converter system with low switching frequency is studied. Special issues such as beat phenomenon and system unbalance due to non-triplen carrier ratio is explained and solved by control methods. Other than that, an improved asymmetric space vector modulation is proposed, which can significantly reduce output current total harmonic distortion (THD) for single and interleaved VSCs system. Finally, the method to protect a system with paralleled VSCs under the occurrence of internal faults is studied. After the internal fault is detected and isolated, the paralleled VSCs system can continue work. So system reliability can be increased.Ph. D.
41
Silva, Taís Kereski da. "Avaliação do comportamento do ângulo de fase e da dinamometria manual em pacientes submetidos à cirurgia cardíaca : estudo de coorte prospectivo". reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2016. http://hdl.handle.net/10183/148173.
Pełny tekst źródłaStreszczenie:
Introdução: O ângulo de fase (AF), derivado da análise de bioimpedância elétrica (BIA), tem sido interpretado como indicador de integridade da membrana celular; e a dinamometria manual têm sido usados como indicadores de prognóstico em algumas situações clínicas. Objetivos: avaliar o comportamento do AF e da dinamometria manual em pacientes submetidos à cirurgia cardíaca e associá-los com EuroSCORE e desfechos clínicos. Métodos: Estudo de coorte prospectivo com 50 pacientes submetidos à cirurgia cardíaca, com idade ≥18 anos, entre janeiro de 2015 e outubro de 2015. O AF e a dinamometria manual foram aferidos em três momentos: pré-operatório, pré-alta hospitalar e três meses após à cirurgia. Também foram coletadas as seguintes variáveis: tempo de circulação extracorpórea (CEC), isquemia, ventilação mecânica (VM), tempo de internação na Unidade de Terapia Intensiva (UTI) e tempo de internação hospitalar após à cirurgia e foi calculado o EuroSCORE. Resultados: Os pacientes foram de predominância do sexo masculino 32 (64%) com idade média de 62,8 ± 10,2 anos, tempo de estadia na UTI de 3 dias (2 – 23), tempo de internação pré-operatória de 7 (5 – 61) dias e EuroSCORE 4 (0 – 10) dias. Houve redução do AF, com diferença entre o período pré-operatório e os dois momentos de avaliação no pós-operatório (p<0,001). Quando a dinamometria manual foi avaliada ao longo do tempo foi observada uma redução entre o préoperatório e a pré-alta hospitalar (p<0,001) e recuperação dessa nos três meses após à cirurgia (p<0,001). A VM e o EuroSCORE tiveram correlação inversa com o AF e a dinamometria manual nos três momentos. A correlação do AF no período pré-operatório do EuroScore p=0,007 e o segundo e o terceiro momento p<0,001, e para os três momentos da VM (p<0,001), respectivamente. Já a correlação da dinamometria manual no primeiro e no segundo momento com o EuroSCORE e a VM p <0,001 e no terceiro momento p=0,010 e p=0,018, respectivamente. Conclusões: O AF e a dinamometria manual parecem estar associados ao tempo de VM, tempo de internação na UTI e tempo de internação no pós-operatório em pacientes submetidos à cirurgia cardíaca.Background and aims: The phase angle (PA), derived from bioelectrical impedance analysis (BIA), have been interpreted as cell membrane integrity indicator; and the handgrip strength (HGS) have been used as prognostic indicators in some clinical situations. This study aims to evaluate the PA and HGS behavior in patients undergoing cardiac surgery and associate these with clinical outcomes and prognostic. Methods: Cohort prospective study of consecutive recruited patients undergoing cardiac surgery aged ≥18 years. The PA and HGS were measured at three set points: preoperatively, hospital predischarge and three months after surgery. Were also collected: time of cardiopulmonary bypass (CPB), ischemia, mechanical ventilation (MV), length of stay (LOS) in Intensive Care Unit (ICU) and LOS after surgery and calculated the EuroSCORE. Results: A decrease in PA was observed between the preoperative and the two postoperative stages (p<0.001). When the HGS was evaluated over time was seen a reduction between preoperative and predischarge (p<0.001) and a recovery in three months after surgery (p<0.001). The MV and EuroSCORE had an inverse association with PA and HGS in three stages. PA correlation in the first stage of the EuroSCORE p=0.007 and the second and third stage p<0.001, and for the three stages of MV (p<0.001), respectively. In HGS correlation in the first and second stage of the EuroSCORE and MV p<0,001 and in the third stage p=0.010 and p=0.018, respectively. Conclusion: PA and HGS appears to be related to MV time, LOS in ICU and LOS after surgery in patients undergoing cardiac surgery.
42
Wang, Chuanyun. "Investigation on Interleaved Boost Converters and Applications". Diss., Virginia Tech, 2009. http://hdl.handle.net/10919/28635.
Pełny tekst źródłaStreszczenie:
With the rapid evolving IT technologies, today, the power factor correction (PFC) design is facing many challenges, such as power scalability, high entire-load-range efficiency, and high power density. Power scalability is a very desirable and cost-effective approach in the PFC design in order to keep up with serversâ growing power requirements. Higher power density can eventually reduce the converter cost and allows for accommodating more equipment in the existing infrastructures. Driven strongly by economic and environmental concerns, high entire-load-range efficiency is more and more required by various organizations and programs, such as the U.S. Energy Star, Climate Savers, and German Blue Angel. Today, the existing boost PFC is reaching its limitations to meet these challenges simultaneously. Using the cutting-edge semiconductor devices, further efficiency improvement at light load is still needed. There are limited approaches available for increasing the power density due to the large EMI filter and inductor size.
Interleaved multi-channel boost PFC is a promising candidate to meet those challenges, but the interleaved boost converter is a less explored area. On the other hand, the multi-channel interleaved buck converter for the VR application has been intensively studied and thoroughly explored. One basic approach of this study is trying to extend the existing knowledge and techniques obtained from multiphase buck converters to the multi-channel interleaved boost converters since there are similarities existed between the multi-phase buck and the multi-channel boost converters.
The existing studies about the interleaving impact on the EMI filter design are based on the time domain ripple cancellation effect. This approach is good enough for most of the filter designs. However, unlike the conventional filter designs, the EMI filter design is a specification related process. Both the EMI standard and the EMI measurement are based on the frequency domain spectrum. Limited by the existing analysis approaches, it is difficult to provide a clear picture about how exactly the multi-channel interleaving will impact the EMI filter design. The interleaving impact on the Common Mode (CM) noise also has not been studied in any existing literatures for the same reason. In this study, the frequency domain analysis method was adopted. With the double Fourier integral transformation, a closed-form expression of all the harmonics of the noise sources can be obtained. With all the detailed phase relationship of the switching frequency harmonics and all the side band harmonics, the multi-channel interleaving impact on both the differential mode (DM) and CM filter design can be clearly understood and summarized. According to the design curves provided, the EMI filter size can be effectively reduced by properly choosing the interleaving channel number and the switching frequency. The multi-channel interleaving impact on the output capacitor current ripple is also studied and summarized in this dissertation.
It should be pointed out that interleaving only reduces the total input and output current ripples; the inductor current in each channel still has large ripple if small inductance is used. Similar to the multi-phase buck converter, coupling inductors result in different equivalent inductances for input current ripple and inductor current ripple for boost converters. Keeping the inductor current ripple magnitude the same, inverse coupling inductors between the interleaved channels can reduce the inductor size. However, the DM filter size is increased due to larger input current. Based on the investigation on the total magnetic component weight, inverse coupling inductor can reduce the total magnetic component weight. The reduction is more pronounced for lower switching frequency design when the inductor size is dominating among the total magnetic components.
Based on the harmonic cancellation, and with all the detailed phase relationship of the switching frequency harmonics and all the side band harmonics, a novel phase angle control method is proposed to maximize the reduction of the EMI filter. For example, in a 2-channel interleaved PFC, just by changing the interleaving scheme to 90 degree phase shift, 39% total volume reduction of the EMI filter can be achieved. The proposed phase angle controlled multi-channel PFC is experimentally demonstrated and verified on a digital controlled 4-channel PFC. The phase angle control method proposed in the multi-channel boost converter can be applied back to the multi-phase buck converter as well. The harmonic cancellation principle will be the same as the multi-channel boost converter. The same benefits can be obtained when the requirement is defined in the frequency domain, e.g. the EMI Standard.
The interleaved multi-channel configuration makes it possible to implement the phase-shedding to improve the PFC light load efficiency. By decreasing the number of active channels according to the load, the PFC light load efficiency can be optimized. However, shedding phases can reduce the ripple cancellation effect as well, which will result in the EMI noise increase and losing the benefit on the EMI filter. By applying the proposed phase-shedding with phase angle control strategy, the phase shedding impact on the EMI filter design can be minimized. The light load efficiency can be improved without compromising the EMI filter size. Then, adaptive frequency controlled PFC is proposed to further improve the PFC light load efficiency. The proposed light load efficiency improvement strategies are combined and implemented on the platform of the digital controlled 4-channel PFC. The benefit of improving the light load efficiency is experimentally verified. The EMI performance is also evaluated with the EMI measurement results obtained from the PFC prototype.
Following the same approach explored, the benefits of interleaved boost converter can be further extended other applications, such as the boost converter in the Hybrid Electric Vehicles (HEV) and photovoltaic (PV) system.Ph. D.
43
Alquist, Keith Eldred III. "Structural studies of phase behavior in 1,6-dicyanohexane/urea and 1,6-diisocyanohexane/urea inclusion compounds". Thesis, Kansas State University, 2014. http://hdl.handle.net/2097/18814.
Pełny tekst źródłaStreszczenie:
Master of ScienceDepartment of Chemistry
Mark Hollingsworth
The crystal structures of the inclusion compounds 1,6-diisocyanohexane/urea and 1,6-dicyanohexane/urea were refined at several temperatures from X-ray data. These urea inclusion compounds are commensurate structures with host:guest ratios of 6:1. In contrast with the ordinary helical topology of the urea host, these structures have stacked loop topologies of the host hydrogen bonds and crystallize in space group P21/n. At room temperature, both structures are distorted along [001] from hexagonal metric symmetry. As in earlier studies of 1-chloro-6-cyanohexane/urea, cooling 1,6-diisocyanohexane/urea gives rise to an exothermic phase transition (Hº = -856 cal mol 1, Sº = -5 cal mol-1 K-1) at 175 K that results in the cooperative translation of guest molecules by 5.5 Å along the channel axis. In the low temperature form, 1,6-diisocyanohexane/urea is distorted along [100], much like X(CH2)6Y, where X, Y = Br, Cl. Although the crystal structure of 1,6-dicyanohexane/urea is essentially isomorphous with that of the high temperature form of 1,6-diisocyanohexane/urea, it does not undergo an equivalent phase transition at low temperatures. Both of these systems exhibit dynamic disorder between two gauche conformers of the guest, which have mean planes of the alkyl chains lying within 1º of [100] (major conformer) and approximately 14º from [001] (minor conformer). The temperature dependence of site occupancy factors for the disordered sites yielded enthalpy differences between major and minor sites in 1,6-diisocyanohexane/urea and 1,6-dicyanohexane/urea of 216 and 127 cal mol 1, respectively. Since the low temperature form of 1,6-diisocyanohexane/urea is distorted along [100], this is favored at low temperatures by an increased concentration of the major conformer, which predominates in 1,6-dibromohexane/urea and congeners. In 1,6-diisocyanohexane/urea, the phase transition to the low temperature form occurs at a threshold concentration for the major conformer of 67%. With its shallower temperature dependence, 1,6-dicyanohexane/urea should not reach this threshold population until approximately 92 K, at which temperature the system cannot overcome the barrier for cooperative translation of guests along the channel axis.
44
Korejčík, Michal. "Návrh transformátoru s regulací fáze pro laboratorní výuku". Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2012. http://www.nusl.cz/ntk/nusl-219412.
Pełny tekst źródłaStreszczenie:
This thesis deals with a power flow control in the electric power system. An overview of FACTS devices is introduced; their basic characteristics as well as examples of their application are discussed. A significant part of this thesis investigates phase shifting transformers (PST´s), which seem to be suitable for implementation in the transmission system of the Czech Republic. The PST´s are useful devices that control active power flows on cross-border lines and regulate unwanted and unexpected power flows. Basic types and characteristics of the PST´s are discussed. In chapter 7 is designed laboratory task that should validate the regulatory capabilities of the transformer PST. Designs of models of individual parts of this laboratory task are presented. In the last part of this thesis the regulation effect of the PST is validated in the GLF/AES program.
45
Zhang, Xuning. "Passive Component Weight Reduction for Three Phase Power Converters". Diss., Virginia Tech, 2014. http://hdl.handle.net/10919/47788.
Pełny tekst źródłaStreszczenie:
Over the past ten years, there has been increased use of electronic power processing in alternative, sustainable, and distributed energy sources, as well as energy storage systems, transportation systems, and the power grid. Three-phase voltage source converters (VSCs) have become the converter of choice in many ac medium- and high-power applications due to their many advantages, such as high efficiency and fast response. For transportation applications, high power density is the key design target, since increasing power density can reduce fuel consumption and increase the total system efficiency. While power electronics devices have greatly improved the efficiency, overall performance and power density of power converters, using power electronic devices also introduces EMI issues to the system, which means filters are inevitable in those systems, and they make up a significant portion of the total system size and cost. Thus, designing for high power density for both power converters and passive components, especially filters, becomes the key issue for three-phase converters.
This dissertation explores two different approaches to reducing the EMI filter size. One approach focuses on the EMI filters itself, including using advanced EMI filter structures to improve filter performance and modifying the EMI filter design method to avoid overdesign. The second approach focuses on reducing the EMI noise generated from the converter using a three-level and/or interleaving topology and changing the modulation and control methods to reduce the noise source and reduce the weight and size of the filters.
This dissertation is divided into five chapters. Chapter 1 describes the motivations and objectives of this research. After an examination of the surveyed results from the literature, the challenges in this research area are addressed. Chapter 2 studies system-level EMI modeling and EMI filter design methods for voltage source converters. Filter-design-oriented EMI modeling methods are proposed to predict the EMI noise analytically. Based on these models, filter design procedures are improved to avoid overdesign using in-circuit attenuation (ICA) of the filters. The noise propagation path impedance is taken into consideration as part of a detailed discussion of the interaction between EMI filters, and the key design constraints of inductor implementation are presented. Based on the modeling, design and implementation methods, the impact of the switching frequency on EMI filter weight design is also examined. A two-level dc-fed motor drive system is used as an example, but the modeling and design methods can also be applied to other power converter systems.
Chapter 3 presents the impact of the interleaving technique on reducing the system passive weight. Taking into consideration the system propagation path impedance, small-angle interleaving is studied, and an analytical calculation method is proposed to minimize the inductor value for interleaved systems. The design and integration of interphase inductors are also analyzed, and the analysis and design methods are verified on a 2 kW interleaved two-level (2L) motor drive system. Chapter 4 studies noise reduction techniques in multi-level converters. Nearest three space vector (NTSV) modulation, common-mode reduction (CMR) modulation, and common-mode elimination (CME) modulation are studied and compared in terms of EMI performance, neutral point voltage balancing, and semiconductor losses. In order to reduce the impact of dead time on CME modulation, the two solutions of improving CME modulation and compensating dead time are proposed. To verify the validity of the proposed methods for high-power applications, a 100 kW dc-fed motor drive system with EMI filters for both the AC and DC sides is designed, implemented and tested. This topology gains benefits from both interleaving and multilevel topologies, which can reduce the noise and filter size significantly. The trade-offs of system passive component design are discussed, and a detailed implementation method and real system full-power test results are presented to verify the validity of this study in higher-power converter systems. Finally, Chapter 5 summarizes the contributions of this dissertation and discusses some potential improvements for future work.Ph. D.
46
Park, Daniel Joseph. "B1 Mapping for Magnetic Resonance Imaging". BYU ScholarsArchive, 2014. https://scholarsarchive.byu.edu/etd/5750.
Pełny tekst źródłaStreszczenie:
Magnetic Resonance Imaging (MRI) is a non-ionizing form of medical imaging which has practical uses in diagnosing, characterizing, and studying diseases in vivo. Current clinical practice utilizes a highly trained radiologist to view MR images and qualitatively diagnose, characterize, or study a disease. There is no easy way to compare qualitative data. That is why developing quantitative measures in MRI show promise. Quantitative measures of disease can be compared across a population, MRI sites, and over time. Osteoarthritis is one disease where those who have it may benefit from the development of quantitative MRI measures. Those benefits may include earlier diagnosis and treatment of the disease or treatment which may halt or even reverse the damage from the disease.The work presented in this dissertation focuses on analyzing and developing new methods of radiofrequency (B1) field mapping to improve quantitative MRI measures. The dissertation opens with an introduction and a brief primer on MRI physics, followed by an introduction to B1 and flip-angle mapping in MRI (Chapters 1-3). Chapter 4 presents a careful statistical analysis of a recent and popular B1 mapping method, the Bloch-Siegert shift (BSS) method, along with a comparison of the technique to other common B1 mapping methods. The statistical models developed in chapter 4 are verified using both Monte Carlo simulation and actual MRI experiments in phantoms. Chapter 5 analyzes and details the potential errors introduced in B1 mapping when a 3D slab-selective excitation is employed. A method for correcting errors introduced by 3D slab-selective B1 mapping is then introduced in chapter 6, along with metrics to quantify the error involved. The thesis closes with a summary of other scientific contributions made by the author in chapter 7. The chapters comprising the bulk of the presented research (4-7) are briefly summarized below. Chapter 4, the statistical analysis of B1 mapping methods, demonstrates the effectiveness of deriving the B1 estimate from the phase of the MR image. These techniques are shown to perform particularly well in low signal-to-noise ratio (SNR) applications. However, there are benefits and drawbacks of each B1 mapping technique. The BSS method deposits a significant amount of radiofrequency (RF) power into the patient, causing a concern that tissue heating may occur. The Phase-Sensitive (PS) method of B1 mapping outperforms the other techniques in many situations, but suffers from significant sensitivity to off-resonance. The Dual-Angle (DA) method is very simple to implement and the analysis is straightforward, but it can introduce significant mean bias in the estimate. No B1 mapping technique performs well for all situations. Therefore, the best B1 mapping method needs to be determined for each situation. The work in chapter 4 provides guidance for that choice. Many B1 mapping techniques rely on a linear relationship between flip angle and transmit voltage. That assumption breaks down when a 3D slab-selective excitation is used. 3D slab-selective excitation is a common technique used to reduce the field-of-view (FOV) in MRI, which can directly reduce scan time. The problem with slab-selective excitation in conjunction with B1 mapping has been documented, but the potential errors in B1 estimation have never been properly analyzed across different techniques. The analysis in chapter 5 demonstrates that the errors introduced in B1 mapping using a slab-selective excitation in conjunction with the ubiquitous DA B1 mapping method can be significant. It is then shown that another B1 mapping technique, the Actual Flip Angle Imaging (AFI) method, doesn't suffer from the same limitation. The analysis presented in Chapter 6 demonstrates that some errors introduced by 3D slab-selective B1 mapping may be modeled and corrected allowing the use of 3D slab-selective excitation to reduce field-of-view, and potentially reduce scan time. The errors are modeled and corrected with a general numerical method using Bloch simulations. The general method is applied to the DA method as an example, but is general and could easily be extended to other methods as well. Finally, a set of metrics are proposed and briefly explored that can be used to better understand the topology and severity of errors introduced into B1 mapping methods. With a better understanding of the errors introduced, the need for correction can be determined. Chapter 7 details other significant ancillary contributions made by the author including: (1) presentation of a new B1 mapping method, the decoupled RF-pulse phase-sensitive B1 mapping method, which has potential for parallel transmit MRI; (2) demonstration of an ultra-short TE method which has potential for imaging Alzheimers brain lesions in vivo; (3) introduction of a new steady-state diffusion tensor imaging technique; (4) phase-sensitive B1 mapping in sodium is demonstrated, a feat not previously demonstrated; (5) a comparison between a dual-tuned and single-tuned sodium coil; (6) introduction of a water- and fat-separation technique using multiple acquisition SSFP; (7) an inter-site and inter-vendor quantitative MRI study is introduced; (8) a relaxation and contrast optimization for laryngeal imaging at 3T is introduced; and (9) diffusion imaging with insert gradients is introduced.
47
Kurepa, Alexandra. "Radially Symmetric Solutions to a Superlinear Dirichlet Problem in a Ball". Thesis, North Texas State University, 1987. https://digital.library.unt.edu/ark:/67531/metadc330725/.
Pełny tekst źródła
48
Boariu, Florin Loredan [Verfasser], Friedrich [Gutachter] Reinert, Matthias [Gutachter] Bode i Fakher [Gutachter] Assaad. "The "Hidden-Order" Phase Transition of URu2Si2 : Investigated by Angle-Resolved Photoelectron Spectroscopy / Florin Loredan Boariu. Gutachter: Friedrich Reinert ; Matthias Bode ; Fakher Assaad". Würzburg : Universität Würzburg, 2014. http://d-nb.info/1111886830/34.
Pełny tekst źródła
49
Kinder, S. H. "Small angle neutron scattering and #gamma#-ray scattering for the study of second phase precipitation in semiconductor silicon and the Nimonic superalloy PE16". Thesis, University of Reading, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.378199.
Pełny tekst źródła
50
"Phase Oscillator". Master's thesis, 2015. http://hdl.handle.net/2286/R.I.29899.
Pełny tekst źródłaStreszczenie:
abstract: A control method based on the phase angle is used to control oscillating systems. The phase oscillator uses the sine and cosine of the phase angle to change key properties of a mass-spring-damper system, including amplitude, frequency, and equilibrium. An inverted pendulum is used to show a further application of the phase oscillator. Two methods of control based on the phase oscillator are used for swing-up and balancing of the pendulum. The first control method involves two separate stages. The scenarios where this control works are discussed. The second control method uses variable coefficients to result in a smooth transition between swing-up and balancing.Dissertation/Thesis
Masters Thesis Mechanical Engineering 2015