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1
Rourke, David E. "Selective pulses in NMR." Thesis, University of Cambridge, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.259620.
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Al-Beshr, Abdullah Saud. "Improved selective pulses for the MR spin-echo experiment." Thesis, University of Nottingham, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.307741.
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Fitzsimons, Paul. "Selective ablation of thin films using ultra-short laser pulses." Thesis, University of Liverpool, 2012. http://livrepository.liverpool.ac.uk/10853/.
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The micro processing of materials using ultra short pulse (USP) lasers with durations in the low picosecond (ps) and femtosecond (fs) range allows for the possibility of precision material removal on both nanometre and micron scales. Precision material removal can be achieved due to the near diffraction limited focus spot size and ultra-short pulse durations, which provide extremely high peak intensities with minimal thermal impact on the surrounding area. The work presented in this thesis is primarily concerned with the selective ablation of thin films deposited on various surfaces, using lasers with picosecond temporal pulse lengths at 1064 nm. As a result, damage to the substrate is negated through exploitation of the difference in linear absorption coefficients between the thin film and substrate. To elucidate the mechanism of selective processing with USP lasers; absorption, single and multi-pulse ablation effects were investigated in both fixed and variable beam positions. A sample of white float glass vacuum coated with indium tin oxide (ITO) was chosen as the material for this study. Experimental results demonstrate that linear absorption (α (λ)) of the ITO and substrate plays a key role in achieving selective thin film ablation. As a direct consequence of the difference in absorption coefficients at 1064 nm, the single (ϕ_th^1 ) and multi (ϕ_th^n ) pulse ablation thresholds of both materials are altered during the high peak intensity exposure. Selective processing was achieved by exploiting the difference between the ablation thresholds of ITO and glass. When irradiated with multiple pulses the ablation threshold of the substrate was observed to decrease with increasing pulse number. This change in threshold fundamentally limits the selective processing window; therefore incubation (S) effects must be considered when determining the viability of selective processing. For the purpose of practical applications, a series of case studies are also presented which attempt to utilise selective materials processing. These investigations were split into industrial and conservation. Industrial case studies focused on successfully micro processing a small thin film ITO circuit using a Spatial Light Modulator and a new low cost solar cell (F doped SnO2); whilst in conservation, the restoration of a pair of Royal gloves and the removal of unwanted bronze gilding is presented. The application of USP lasers in conservation represents a relatively new field of study where little previous research has been carried out. These case studies not only showcase the wide range of USP applications in which selective processing can be applied but also highlight the limitations of this method.
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Sussman, Marshall Stephen. "Design of practical T¦2-selective RF excitation, TELEX, pulses." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp04/mq29272.pdf.
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Geen, Helen Louise. "Design and implementation of band-selective pulses for NMR spectroscopy." Thesis, University of Cambridge, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.359900.
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Kokorin, Denis [Verfasser], and Jürgen [Akademischer Betreuer] Hennig. "Magnetic resonance imaging with spatially-selective pulses using multiple transmission channels = Magnetresonanztomographie mit räumlich-selektiven HF-Pulsen unter Ausnutzung des parallelen Sendens." Freiburg : Universität, 2015. http://d-nb.info/1123482497/34.
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Oliveira, Eduardo Spinelli. "Ablação seletiva de um filme de nitreto de titânio em substrato de carboneto de tungstênio utilizando laser de pulsos ultracurtos." Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/85/85134/tde-16052017-114430/.
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Revestimentos superficiais são aplicados à muitas ferramentas de usinagem na indústria metalúrgica com o intuito de melhorar a eficiência de corte e aumentar sua vida útil. Neste trabalho foram realizados testes para remoção do recobrimento de nitreto de titânio alumínio (TiAlN) em pastilhas de carboneto de tungstênio (WC-Co), utilizando um feixe laser de pulsos ultracurtos. Após a determinação dos limiares de dano do filme e do substrato foram ablacionados na superfície do recobrimento, traços utilizando duas condições de ablação. Inicialmente operou-se no regime de baixa fluência do filme, e posteriormente no regime de baixa fluência do substrato, muito abaixo do limiar do filme, aplicando-se alta sobreposição de pulsos. Um sistema de espectroscopia de emissão atômica induzida por laser (LIBS) foi montado para monitoramento dos materiais presentes no plasma gerado pelo laser, porém o sistema não apresentou sensibilidade suficiente para leitura da baixa intensidade do plasma proveniente do processo e não foi utilizado. Após a análise dos traços por microscopia eletrônica, perfilometria óptica e espectroscopia por fluorescência de Raios-X, não foi possível determinar um processo seguro para realizar a remoção seletiva do filme em questão, porém, devido aos dados obtidos e observações dos resultados em alguns traços, novas possibilidades foram levantadas, abrindo a discussão para a realização de trabalhos futuros.Surface coatings are applied to many cutting tools in the metallurgical industry in order to improve cutting efficiency and extend its useful life. In this work, tests were performed to remove the coating of titanium aluminum nitride (TiAlN) on tungsten carbide (WC-Co) pellets, using an ultrashort laser pulses beam. After determination of the damage thresholds of the film and the substrate, were ablated on the surface of the coating lines using two ablation conditions, it was initially operated on the low fluence regime for the film, and later on the low fluence regime of the substrate, far below the threshold of the film, applying high overlapping pulses. A laser induced breakdown spectroscopy (LIBS) system was set up to monitor the materials present in the plasma generated by the laser, but the system did not present sufficient sensitivity to read the low intensity of the plasma generated in the process and was not used. After the analysis of the traces by electron microscopy, optical profilometer and X-ray fluorescence spectroscopy, it was not possible to determine a safe process to carry out the selective removal of the film in question, however, due to the data obtained and observations of the results in some traces, new possibilities were raised, opening the discussion for future work.
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Kröner, Dominik. "Theory of selective preparation of enantiomers by laser pulses Theorie zur selektiven Präparation von Enantiomeren durch Laserpulse /." [S.l. : s.n.], 2003. http://www.diss.fu-berlin.de/2003/141/index.html.
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Alshehri, Ali. "Micro and Nanostructuring of Polymers by Femtosecond Laser Pulses." Thesis, Université d'Ottawa / University of Ottawa, 2016. http://hdl.handle.net/10393/35356.
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Micro/Nanostructuring of polymers by femtosecond pulses is of extreme importance because it drives applications in photonics and biomedicine. A femtosecond pulse, with an intensity of ∼ 10^13 W/cm^2, is capable of causing an optical breakdown and inducing permanent modification in the material. With such high intensity, and considering the fact that polymers possess high band gaps, the interaction nature is completely nonlinear, and the material can be modified locally on the surface and in bulk. The irradiated regions exhibit fluorescence, and they display new wetting properties as a consequence of the optical breakdown of a material. The optical breakdown can be investigated by studying the nonlinear absorption. In this thesis, we discuss the nonlinear absorption of fs-laser pulses inside polymers using transmission measurements. We show a step– function–like behaviour of the transmission, dropping abruptly to ∼ 20% at the optical breakdown threshold with a ∼ 40 % reduction in the band gap. Utilizing spectroscopy, we show that the laser-modified regions contain randomly distributed nanoclusters. The presence of localized nanoclusters is responsible for exhibiting fluorescence, within ∼ 10 µm3 for a single pulse. This feature was exploited to demonstrate high-density data storage in Polymethyl methacrylate (PMMA) without any special material preparation. We demonstrate up to 20 layers of embedded data that can be stored in a standard 120 mm disc. Storage capacity of 0.2 TBytes/disc can be achieved by adjusting read laser parameters. Besides the fluorescence capability induced in the bulk of polymers, the hydrophilicity shown by the fs–laser modified surface is utilized to study selective cell growth on the micro-structured Polydimethylsiloxane (PDMS) surface. We show that the C2C12 cells and rabbit anti-mouse protein attach preferentially to the modified regions when the surface is modified with low pulse energies. However, in the high pulse energy regime, the laser-modified regions exhibit superhydrophobicity inhibiting cell adhesion.
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Elghobashi, Nadia. "Theory of using few cycle IR and UV laser pulses to control the orientation and selective dissociation of hydrogen bonded anions." [S.l.] : [s.n.], 2005. http://www.diss.fu-berlin.de/2006/23/index.html.
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Mumtaz, Kamran A. "Selective laser melting of Inconel 625 using pulse shaping." Thesis, Loughborough University, 2008. https://dspace.lboro.ac.uk/2134/33630.
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Selective Laser Melting (SLM) is an additive manufacturing technology that consolidates layers of metal powder using a high power laser. The laser's small spot size and relative accuracy facilitates the production of high resolution parts with great complexity that would be otherwise difficult to manufacture using conventional manufacturing techniques (e.g. casting, machining etc.). The possibility to build thin wall high resolution parts complements the technology's main advantage and extends its manufacturing capabilities. The high heat input delivered by the laser and complex melt pool dynamics, requires that laser process parameters are carefully controlled in order to prevent solidified parts from exhibiting poor properties such as a high surface roughness and poor resolution.
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Liu, Maili. "Development and application of pulse methods for selective detection in NMR spectroscopy." Thesis, Birkbeck (University of London), 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.362747.
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Guerra, García Carmen. "High voltage repetitive pulsed nanosecond discharges as a selective source of reactive species." Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/67066.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2011.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 (p. 153-156).
High voltage nanosecond duration discharges can be used in a repetitive manner to create a sustained pool of short lived excited species and ions and long-lived radicals in a gas. Although the suitability of the Repetitive Pulsed Nanosecond Discharge (RPND) technique as a means of creating a non-equilibrium plasma has already been demonstrated, many aspects of these discharges remain unclear. Amongst others, scaling laws as a function of electrical and ow parameters, the exact development characteristics of the dierent regimes encountered, the discharge evolution during the interval between pulses and the hydrodynamic phenomena triggered by the rapid energy deposition need clarification. This work seeks to be an introductory text to the field of nanosecond duration non-thermal discharges and prepare the building blocks to initiate discharge experiments that will hopefully shed some light into these aspects. RPND can be of interest for applications that require a high chemical activity at moderate gas pressures and temperatures and at low power budgets. Amongst others, the RPND technique is a promising method for igniting mixtures and stabilizing flames that would otherwise be unstable, such as in fuel-lean mixtures which are interesting to reduce NOx production. Additionally, certain regimes might produce pressure waves strong enough to excite uid instabilities, if triggered at the right repetition frequency, and enhance mixing. Experiments have been initiated to capture the dierent regimes in low pressure air and also understand the interaction between consecutive pulses. The applied pulses have 10ns duration, amplitude up to 10kV and repetition frequencies up to 30kHz. Future work will extend these experiments in both air and premixed fuel-air mixtures in lean conditions at pressures below 1atm and temperatures up to 1000K and the phenomena observed will be used to propose modeling contributions
by Carmen Guerra García.
S.M.
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Beller, Nicole C. "Selective Pulse Chase-SILAC Labeling of Three-Dimensional Multicellular Spheroids for Global Proteome Analysis." The Ohio State University, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=osu1586292839111678.
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Reddy, Dileep. "Temporal-mode interferometry: A technique for highly selective quantum pulse gating via cascaded frequency conversion in nonlinear optical waveguides." Thesis, University of Oregon, 2018. http://hdl.handle.net/1794/23136.
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A new, and thus far only, method to overcome a selectivity barrier in parametrically pumped quantum pulse gates is proposed and experimentally demonstrated for the first time, using frequency conversion of optical temporal modes in second-order nonlinear waveguides. Temporal modes and quantum pulse gates are defined and their utilities are explored. Pulsed operation of three-field and four-field, parametric, optical processes are modeled and numerically investigated. A maximum limit to achievable selectivity for quantum pulse gating in uniform media is discovered and theoretically explained. An interferometric means of overcoming said limit and asymptotically approaching unit selectivity is proposed. The principle is experimentally verified by double-passing specifically shaped optical pulses derived from an ultrafast Ti:sapphire laser through a periodically-poled lithium niobate waveguide phasematched for sum-frequency generation. Further improvements and future implications for quantum technologies are discussed.
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Jensen, Paul. "Ecology of American martens in northern hardwood forests: resource pulses and resource selection across temporal and spatial scales." Thesis, McGill University, 2013. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=114321.
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Effective wildlife management and conservation is based on a sound understanding of ecological processes that operate on multiple temporal and spatial scales and how these processes affect populations. For forest carnivores such as American martens (Martes americana) that have large space requirements, are sensitive to landscape changes, and are closely linked to prey populations, multi-scale studies have the potential to provide useful information for conservation. However, the challenges of collecting data over long time series and broad landscapes are significant. Here, I apply harvest and field-based data to investigate aspects of marten ecology at multiple scales in a northern hardwood forest system. I investigated temporal trends in the relationship among mast-producing trees, small mammal relative abundance, and marten and fisher (Martes pennanti) harvests. A large proportion of the annual variation in harvest success rates for both species could be explained by models including American beech seed production (Fagus grandifolia) as a key predictor variable. Based on these results I hypothesized that marten space use was inversely related to mast crop production (resulting in differential vulnerability to trapping) and tested this hypothesis using location data from radio collared martens. Autumn/winter home range area and daily movement rates differed among years and were greater in mast failure years than those when mast was produced followed by typical winter conditions. However, differences in these metrics were not significant between mast failures and a year when large mast crops were produced followed by a mild winter with reduced snowfall. Thus, the influence of food abundance on marten space use appears to be mediated by winter conditions such as snow depth. Additionally, I investigated marten resource selection at multiple spatial scales within the southern portion of the Northern Appalachians ecoregion (NAP) to better understand 1.) environmental variables constraining the distribution of martens at the southern extent of their range in eastern North America (i.e., first-order species distribution model; SDM), 2.) variables influencing distribution on a more localized landscape (second-order), and 3.) selection of specific forest stand types within home ranges. Of the 3 spatial scales that I examined, martens exhibited the strongest selection at the ecoregional-scale and results supported the hypothesis that a combination of factors including competition with fishers, forest structure/complexity, and land cover were the primary drivers influencing marten distribution in this landscape. In particular, annual snowfall had the greatest relative contribution to the models (42.2-46.3%) and marten presence was associated with mean annual snowfall ≥ 230 cm. These results supported previously hypothesized mechanisms involving relationships among fishers, martens, and snow. Lastly, I discussed how harvest monitoring data can be used to further our understanding of marten-fisher interactions and provided examples of the use of the SDM as a conservation tool. Research presented here identifies novel and unexpected ecological connections among mesocarnivores, small mammals, forest seed production, and snow cover that will assist with the continuation of sustainable harvests and conservation of martens within the northeastern U.S. and southeastern Canada.La gestion et la conservation efficaces de la faune sont basées sur une bonne compréhension des processus écologiques qui opèrent à de multiples échelles spatiales et temporelles et de comment ces processus affectent les populations. Pour les carnivores forestiers, tel que la martre d'Amérique (Martes americana), qui ont besoin de grands espaces, qui sont sensibles aux changements de paysage, et qui sont liés de très près à leurs proies, les études à multiples échelles ont le potentiel d'apporter de l'information utile pour la conservation. Cependant, la collecte de données sur de longues périodes et de vastes paysages représente des défis importants. J'applique ici des données de récolte et de terrain pour examiner des aspects de l'écologie de la martre à de multiples échelles dans une forêt de feuillus à bois dur nordique. J'examine les tendances temporelles dans la relation entre les arbres à paisson, l'abondance relative des petits mammifères, et la récolte de martres et pékans (Martes pennanti). Une large proportion de la variation annuelle du taux de succès de récolte pour les deux espèces a pu être expliquée par des modèles incluant la production de faines d'hêtre à grandes feuilles (Fagus grandifolia) comme variable clé. Basé sur ces résultats, j'ai fait l'hypothèse que l'utilisation de l'espace chez la martre est inversement reliée à la paisson (résultant en une différence de vulnérabilité à la capture) et j'ai testé cette hypothèse en utilisant des données de localisations provenant de martres avec des colliers radio-émetteurs. Les domaines vitaux et les taux de mouvements journaliers automne/hiver différaient entre les années et étaient plus grands lors de faibles paissons que lors de paissons abondantes suivies par des conditions hivernales typiques. Cependant, les différences de ces mesures n'étaient pas significatives entre les faibles paissons et une année avec une paisson abondante suivie d'un hiver doux avec moins de neige. Ainsi, l'influence de l'abondance de nourriture sur l'utilisation de l'espace chez la martre semble être interposée par les conditions hivernales, telle que l'épaisseur de la neige. De plus, j'ai examiné la sélection de ressources chez la martre à de multiples échelles spatiales dans la portion sud de l'écorégion Appalachienne Nord (APN) pour mieux comprendre 1) les variables environnementales qui contraignent la répartition des martres à l'extrême sud de leur distribution nord-américaine de l'est (à savoir, modèle de distribution d'espèce de première ordre; MDE), 2) les variables influençant la distribution de façon plus localisée dans le paysage (deuxième ordre), et 3) la sélection de peuplements forestiers spécifiques dans les domaines vitaux. De ces trois échelles spatiales que j'ai examinées, les martres démontrent la plus forte sélection à l'échelle éco-régionale et les résultats ont supporté l'hypothèse qu'une combinaison de facteurs, incluant la compétition avec les pékans, la structure/complexité forestière, et la couverture du sol sont les conducteurs primaires qui influencent la distribution de la martre dans ce paysage. En particulier, la chute de neige annuelle a eu la plus grande contribution relative dans les modèles (42.2-46.3%) et la présence de martres a été associée avec une chute de neige annuelle moyenne ≥ 230 cm. Ces résultats supportent les mécanismes de l'hypothèse précédente impliquant les relations entre les pékans, les martres, et la neige. Finalement, j'ai discuté de comment les données de suivi de récolte peuvent être utilisées pour comprendre davantage les interactions martre-pékan et ont fourni des exemples d'utilisation de MDE comme outil de conservation. La recherche présentée ici identifie des connections écologiques nouvelles et inattendues entre les mesocarnivores, les petits mammifères, la production forestière de graines, et le couvert de neige qui aideront à la continuation de récolte et de conservation durables des martres.
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Channell, Brent T. "Evaluation and selection of an efficient fuel/air initiation strategy for pulse detonation engines." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2005. http://library.nps.navy.mil/uhtbin/hyperion/05Sep%5FChannell.pdf.
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Thesis (M.S. in Astronautical Engineering)--Naval Postgraduate School, September 2005.Thesis Advisor(s): Christopher M. Brophy. Includes bibliographical references (p. 53-54). Also available online.
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Kosa, Irfan. "Performance of IEEE 802.11a wireless LAN standard over frequency-selective, slowly fading Nakagami channels in a pulsed jamming environment." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2002. http://library.nps.navy.mil/uhtbin/hyperion-image/02Dec%5FKosa.pdf.
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Thesis (M.S. in Electrical Engineering)--Naval Postgraduate School, December 2002.Thesis advisor(s): R. Clark Robertson, Tri Ha. Includes bibliographical references (p. 107-108). Also available online.
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Teotrakool, Kaptan. "Adjustable speed drive bearing fault detection via support vector machine incorporating feature selection using genetic algorithm." Diss., Columbia, Mo. : University of Missouri-Columbia, 2007. http://hdl.handle.net/10355/4845.
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Thesis (Ph. D.)--University of Missouri-Columbia, 2007.The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on March 3, 2008) Vita. Includes bibliographical references.
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Massire, Aurélien. "Non-selective Refocusing Pulse Design in Parallel Transmission for Magnetic Resonance Imaging of the Human Brain at Ultra High Field." Thesis, Paris 11, 2014. http://www.theses.fr/2014PA112180/document.
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En Imagerie par Résonance Magnétique (IRM), l’augmentation du champ magnétique statique permet en théorie de fournir un rapport signal sur bruit accru, améliorant la qualité des images. L’objectif de l’IRM à ultra haut champ est d’atteindre une résolution spatiale suffisamment haute pour pouvoir distinguer des structures si fines qu’elles sont actuellement impossibles à visualiser de façon non-invasive. Cependant, à de telles valeurs de champs magnétiques, la longueur d’onde du rayonnement électromagnétique envoyé pour basculer les spins des protons de l’eau est du même ordre de grandeur que l’objet dont on souhaite faire l’image. Des phénomènes d’interférences sont observés, ce qui se traduit par l’inhomogénéité de ce champ radiofréquence (RF) au sein de l’objet. Ces interférences engendrent des artefacts de signal et/ou de contraste dans les images IRM, et rendent ainsi leur exploitation délicate. Il est donc crucial de fournir des solutions pour atténuer la non-uniformité de l’excitation des spins, à défaut de quoi de tels systèmes ne pourront atteindre leurs pleins potentiels. Pour obtenir des diagnostics pertinents à très haut champ, il est donc nécessaire de créer des impulsions RF homogénéisant l'excitation de l'ensemble des spins (ici du cerveau humain), optimisées pour chaque individu. Pour cela, un système de transmission parallèle (pTX) à 8 canaux a été installé au sein de notre imageur à 7 Tesla. Alors que la plupart des systèmes IRM cliniques n’utilisent qu’un seul canal d’émission, l’extension pTX permet de jouer différentes formes d’impulsions RF de concert. La somme résultante de ces interférences doit alors être optimisée pour atténuer la non-uniformité observée classiquement. L’objectif de cette thèse est donc de synthétiser ce type d’impulsions, en utilisant la pTX. Ces impulsions auront pour contrainte supplémentaire le respect des limitations internationales concernant l'exposition à des champs radiofréquence, qui induit une hausse de température dans les tissus. En ce sens, de nombreuses simulations électromagnétiques et de températures ont été réalisées en introduction de cette thèse, afin d’évaluer la relation entre les seuils recommandés d’exposition RF et l’élévation de température prédite dans les tissus. Cette thèse porte plus spécifiquement sur la conception de l’ensemble des impulsions RF refocalisantes utilisées dans des séquences IRM non-sélectives, basées sur l’écho de spin. Dans un premier temps, seule une impulsion RF a été générée, pour une application simple : l’inversion du déphasage des spins dans le plan transverse. Dans un deuxième temps, sont considérées les séquences à long train d’échos de refocalisation appliquées à l’in vivo. Ici, l’opérateur mathématique agissant sur la magnétisation, et non pas son état final comme il est fait classiquement, est optimisé. Le gain en imagerie à très haut champ est clairement visible puisque les opérations mathématiques (la rotation des spins) voulues sont réalisées avec plus de fidélité que dans le cadre des méthodes de l’état de l’art. Pour cela, la génération de ces impulsions RF combine une méthode d’excitation des spins avec navigation dans l’espace de Fourier, les kT-points, et un algorithme d’optimisation, appelé Gradient Ascent Pulse Engineering (GRAPE), utilisant le contrôle optimal. Cette conception est rapide grâce à des calculs analytiques plus directs que des méthodes de différences finies. La prise en compte d’un grand nombre de paramètres nécessite l’usage de GPUs (Graphics Processing Units) pour atteindre des temps de calcul compatibles avec un examen clinique. Cette méthode de conception d’impulsions RF a été validée expérimentalement sur l’imageur 7 Tesla de NeuroSpin, sur une cohorte de volontaires sainsIn Magnetic Resonance Imaging (MRI), the increase of the static magnetic field strength is used to provide in theory a higher signal-to-noise ratio, thereby improving the overall image quality. The purpose of ultra-high-field MRI is to achieve a spatial image resolution sufficiently high to be able to distinguish structures so fine that they are currently impossible to view in a non-invasive manner. However, at such static magnetic fields strengths, the wavelength of the electromagnetic waves sent to flip the water proton spins is of the same order of magnitude than the scanned object. Interference wave phenomena are then observed, which are caused by the radiofrequency (RF) field inhomogeneity within the object. These generate signal and/or contrast artifacts in MR images, making their exploitation difficult, if not impossible, in certain areas of the body. It is therefore crucial to provide solutions to mitigate the non-uniformity of the spins excitation. Failing this, these imaging systems with very high fields will not reach their full potential.For relevant high field clinical diagnosis, it is therefore necessary to create RF pulses homogenizing the excitation of all spins (here of the human brain), and optimized for each individual to be imaged. For this, an 8-channel parallel transmission system (pTX) was installed in our 7 Tesla scanner. While most clinical MRI systems only use a single transmission channel, the pTX extension allows to simultaneously playing various forms of RF pulses on all channels. The resulting sum of the interference must be optimized in order to reduce the non-uniformity typically seen.The objective of this thesis is to synthesize this type of tailored RF pulses, using parallel transmission. These pulses will have as an additional constraint the compliance with the international exposure limits for radiofrequency exposure, which induces a temperature rise in the tissue. In this sense, many electromagnetic and temperature simulations were carried out as an introduction of this thesis, in order to assess the relationship between the recommended RF exposure limits and the temperature rise actually predicted in tissues.This thesis focuses specifically on the design of all RF refocusing pulses used in non-selective MRI sequences based on the spin-echo. Initially, only one RF pulse was generated for a simple application: the reversal of spin dephasing in the transverse plane, as part of a classic spin echo sequence. In a second time, sequences with very long refocusing echo train applied to in vivo imaging are considered. In all cases, the mathematical operator acting on the magnetization, and not its final state as is done conventionally, is optimized. The gain in high field imaging is clearly visible, as the necessary mathematical operations (that is to say, the rotation of the spins) are performed with a much greater fidelity than with the methods of the state of the art. For this, the generation of RF pulses is combining a k-space-based spin excitation method, the kT-points, and an optimization algorithm, called Gradient Ascent Pulse Engineering (GRAPE), using optimal control.This design is relatively fast thanks to analytical calculations rather than finite difference methods. The inclusion of a large number of parameters requires the use of GPUs (Graphics Processing Units) to achieve computation times compatible with clinical examinations. This method of designing RF pulses has been experimentally validated successfully on the NeuroSpin 7 Tesla scanner, with a cohort of healthy volunteers. An imaging protocol was developed to assess the image quality improvement using these RF pulses compared to typically used non-optimized RF pulses. All methodological developments made during this thesis have contributed to improve the performance of ultra-high-field MRI in NeuroSpin, while increasing the number of MRI sequences compatible with parallel transmission
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Yeago, Taylor Craig. "A Two-Phase Buck Converter with Optimum Phase Selection for Low Power Applications." Thesis, Virginia Tech, 2015. http://hdl.handle.net/10919/51230.
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Power consumption of smart cameras varies significantly between sleep mode and active mode, and a smart camera operates in sleep mode for 80 — 90% of time for typical use. To prolong the battery life of smart cameras, it is essential to increase the power converter efficiency for light load, while being able to manage heavy load. The power stage of traditional buck converter is optimized for maximum load, at the cost of light-load efficiency. Wei proposed a multiphase buck converter incorporating the baby-buck concept and optimum number of phases (ONP) control. This thesis research investigated Wei's multiphase buck converter to improve the light-load efficiency for smart cameras as the target application.
The proposed two-phase buck converter aims to provide power for microprocessors of smart cameras. The input voltage of the converter is 5 V DC, and the output voltage is 1.2 V DC with power dissipation range of 25 mA (30 mW) for light load and 833 mA (1 W) for heavy load. Three methods are considered to improve light-load efficiency: adopting baby-buck concept, adapting ONP control for low-power range, and implementing a pulse frequency modulation (PFM) control scheme with discontinuous conduction mode (DCM) to lower switching frequency. The first method is to adopt the baby-buck concept through power stage design of each phase to optimize efficiency for a specific load range. The baby-buck phase is optimized for light load and the heavy-load phase is designed to handle the processors maximum power consumption. The second method performs phase selection from sensed load current information. Rather than have all phases active for heavy-load as in ONP control, optimum phase selection (OPS) control is introduced to adaptively select between phases based on load current. Due to low-power constraints, OPS is more efficient for the medium to heavy-load range. The transition between phases due to load change is also investigated. The third and final method implements PFM control with DCM to lower switching frequency and reduce switching and driving losses under light load. PFM is accomplished with a constant on-time (COT) valley current mode controller, which uses the inductor current information and output voltage to generate switching signals for both the top and bottom switches. The baby-buck phase enters DCM to lower switching frequency under very light load, while the heavy-load phase remains in continuous conduction mode (CCM) throughout its load range.
The proposed two-phase buck converter is designed and prototyped using discrete components. Efficiency of the two-phase converter and a power loss breakdown for each block in the control scheme were measured. The efficiency ranges from 64% to 81% for light load ranging of 30 mW to 200 mW, and the efficiency ranges from 81% to 88% for heavy load ranging from 200 mW to 1 W. The majority loss is due to controllers, which are responsible for 37 % (8.6 mW) for light load of 60 mW and for 10.9 % (9 mW) for heavy load of 600 mW. The gate driver loss is considerable for heavy load of 600 mW, consuming 11.9% (9.8mW). The converter has a 10 mV overshoot voltage for a load step-down from 225 mA to 25 mA, and it has 65 mV overshoot voltage for a load step-up from 25 mA to 225 mA. Although, a fair comparison is difficult due to use of discrete parts for OPS control, the proposed converter shows reasonably good efficiency and performance.Master of Science
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BANNARI-CHRISTIEANS, SOUAD. "Selection de ferments aromatiques pour saucisson sec. Controle d implantation des bacteries par technique d electrophorese en champ pulse." Clermont-Ferrand 2, 1998. http://www.theses.fr/1998CLF21012.
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Les criteres de qualites sensorielles sont privilegies par le consommateur pour le choix des produits alimentaires. Ceci est particulierement vrai pour le saucisson sec qui est consomme en l'etat et choisi, des l'achat, a son aspect et a son odeur. Le produit devra aussi repondre a l'attente du consommateur par son gout et sa flaveur. Pour se demarquer sur le marche, l'industriel francais souhaite des produits types du point de vue aromatique. Aussi, l'objectif de cette etude est de selectionner des ferments aromatiques pour saucisson sec et de controler l'implantation des bacteries par des techniques de denombrements microbiologiques classiques et moleculaires telle que l'electrophorese en champ pulse (r-ecp), adaptee pour la premiere fois aux bacteries du saucisson sec. Une collection de bacteries (staphylocoques, lactobacilles et levures) a ete constituee a partir de saucissons de fabrications industrielles, artisanales et fermieres. Apres identification biochimique, seules les especes susceptibles d'etre employees comme ferments starters ont ete retenues. Les staphylocoques sont representes essentiellement par l'espece s. Xylosus, les lactobacilles par l. Curvatus, l. Sake, l. Plantarum et les levures par c. Famata et c. Zeylanoides. Dans un premier temps, la selection des differentes bacteries isolees a ete effectuee selon leur proprietes biochimiques, a savoir, la lipolyse pour les staphylocoques et les levures, la proteolyse pour les lactobacilles et les staphylocoques et l'acidification pour les lactobacilles. La diversite genetique des differentes bacteries selectionnees a ete ulterieurement evaluee par rapd et r-ecp. Cette etape a permis d'eliminer les souches genetiquement identiques et d'etablir les profils des bacteries retenues pour ulterieurement verifier leur implantation et leur potentiel aromatisant. Les premiers essais de fabrication ont permis de selectionner six staphylocoques (lipolytiques et/ou proteolytiques), cinq lactobacilles acidifiants et deux levures lipolytiques. Ces differentes souches ont ete retenues pour leur potentiel aromatique et pour leur capacite d'implantation. En effet, lors des differentes fabrications experimentales, le controle d'implantation des bacteries ensemencees a revele que les techniques classiques de denombrements microbiologiques ne permettent pas de juger de la bonne implantation des micro-organismes. Dans le cas ou les souches ne sont pas presentes, les denombrements microbiologiques sont corrects alors que les profils obtenus par r-ecp sont identiques a ceux de la melee non ensemencee. Les micro-organismes endogenes (de la melee) peuvent donc supplanter les levains apportes en debut de fabrication. Les essais realises a partir d'associations entre lactobacilles et staphylocoques selectionnes ont amene a en retenir six performantes (l153 + s16, l153 + s19, l153 + s20, l10 + s19, l10 + s20 et l33 + s20). Les 3 staphylocoques s16, s19 et s20 appartiennent a l'espece s. Xylosus, s19 est proteolytique, s16 lipolytique et s20 a la fois lipolytique et proteolytique. Les lactobacilles l33 (l. Plantarum) et l153 (l. Sake) ne sont pas proteolytiques et montrent un pouvoir acidifiant modere, alors que l10 (l. Curvatus) est proteolytique et tres acidifiant. Ces resultats nous ont amene a conclure que la lipolyse et la proteolyse des bacteries sont en partie responsables de la flaveur caracteristique du saucisson sec. Les differentes associations testees par les sept industriels impliques dans ce projet ont permis de souligner plus specialement l'effet aromatisant de deux associations : s19+l10 et s20+l153, juge plus important que le levain temoin actuellement commercialise.
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Nolis, Fañanás Pau. "Disseny i aplicació de nous mètodes de RMN. Avenços en polarització creuada heteronuclear, mètodes d'estat de spin selectius i adquisició simultània de diferents espectres." Doctoral thesis, Universitat Autònoma de Barcelona, 2007. http://hdl.handle.net/10803/3253.
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La present tesi doctoral és un compendi dels treballs publicats en revistes científiques d'àmbit internacional durant el transcurs del període formatiu de tercer cicle a la Universitat Autònoma de Barcelona. Durant aquest període s'han dissenyat noves metodologies (seqüències de pulsos) de Ressonància Magnètica Nuclear basades en l'espectroscòpia bidimensional de detecció inversa. Aquestes es discuteixen tant des d'un punt de vista teòric del desenvolupament metodològic així com des del punt de vista de nova aplicabilitat. S'han fet aven?os en diferents camps d'investigació: la polarització creuada heteronuclear en mostres líquides, els mètodes d'estat de spin selectiu i mètodes amb adquisició simultània de diferents espectres. I s'ha demostrat la seva utilitat en el camp de l'elucidació estructural de molècules orgàniques i biomolècules.The present thesis is a compendium of the work published in international scientific journals during the formative period of third cycle at the Universitat Autònoma de Barcelona. During this period new Nuclear Magnetic Resonance methodologies (pulse sequences) based on inverse detection spectroscopy have been developed. Those are discussed from the theoretical point of view of the methodological development as well as from the point of view of new application. Advances at different research fields have been performed: heteronuclear cross polarization in liquid state, spin state selective methodologies and methods for the simultaneous acquisition of two spectra within a single experiment. The utility of the new pulse sequences herein presented is demonstrated for the structural analysis of biomolecules and organic compounds.
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Fjeld, Hans Erik. "Application of Parallel Programming in a Automatic Detector for a Pulsed MTD Radar system : Automatic Detection and Fast Ordered Selection Algorithms." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for elektronikk og telekommunikasjon, 2012. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-18490.
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Automatic CFAR Detection is to be implemented in a real time pulsed MTD radar system, used in a mar-itime application.The CFAR should be able to have good detection properties in bad weather conditions, where rough seastates, heavy downpour and high winds are expected.Sucient detection properties may be achieved using an Ordered Statistics based CFAR to generate detec-tion threshold for the MTD radar video signal.The MTD video is the coherent raw video of the signal ltered in a bandpass lter bank, separating theDoppler frequency space of the video into a number of individual Doppler channels.The Doppler frequency shift relates to a velocity, implying that every Doppler channel represents a velocityspace, so that targets and clutter may further resolved by their relative Doppler velocityCFAR algorithms are applied to all the test cells in the MTD video signal. These algorithms have to estimatea threshold that is used at discriminating real targets from clutter in all the velocity channels of the MTDvideo.A good threshold estimate is to have a low probability of false detections, and a high probability of declaringactual targets.This is to be valid in all clutter conditions, even when one or multiple targets are surrounded by non-stationary clutter and closely spaced.The Ordered Statistics algorithms involves using the k'th largest value of the test window as a mean clutterpower estimate for its corresponding test cell.The ordered statistics model makes a threshold selection based on the rank of the samples. A task withcomplexity increasing as a function of window length and k parameter.This task is to be performed on a large number of test cells in a system running real time. In a real timeradar system, all processing have to be done before the next scan becomes available.Radian AS works on developing a PC based MTD Radar system for a pulsed Doppler radar.The radar interfaces the PC through a PCI Express radar receiver card developed by Radian AS.This thesis investigates the application of parallel programming in C/C++ in order to achieve real time au-tomatic detection in a PC based MTD radar. Two means of parallel programming are considered, involvingexploitation of multi core CPU architecture as well as using a dedicated GPU as a co processor.OpenMP is an Open Source library with compiler instructions for running tasks in parallel over multiplecores in a CPU. It is easily incorporated into C/C++ code, and may be used with most multi core CPUs.nVidia has made GP-GPU computing available to the public through CUDA, selling CUDA enabled graphicscards and providing the tools as well as documentation needed for a programmer to be able to use the GPUas co processor.CUDA C integrates the SIMT abstractions of CUDA, and a programmer may write C code that is compiledand executed on the GPU.Dierent implementations of the OS-CFAR algorithm for threshold estimation are implemented using CUDAand OpenMP.The dierent implementations are evaluated and compared to each other in terms of the results gatheredfrom executing them on MTD video.The experiences drawn from this work is concluded with respect to the application of parallel programming,and further recommendations for the future of the project of making a PC based pulsed MTD Radar signalprocessor.This thesis introduces a CUDA algorithm for high throughput ordered selection using short window lengthson a large number of cells under test.An algorithm developed in C for the project assignment leading up to this thesis is enabled openMP, alongwith a C++ STL algorithm, for performing ordered statistics ranked selection on the CPU. In addition, theCUDA OS-CFAR algorithm is ported to C with openMP.The three implementations in C/C++ are compared to the CUDA C implementation.
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Kalogrias, Christos. "Performance analysis of the IEEE 802.11A WLAN standard optimum and sub-optimum receiver in frequency-selective, slowly fading Nakagami channels with AWGN and pulsed noise jamming." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2004. http://library.nps.navy.mil/uhtbin/hyperion/04Mar%5FKalogrias.pdf.
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Thesis (M.S. in Electrical Engineering and M.S. in Systems Engineering)--Naval Postgraduate School, March 2004.Thesis advisor(s): Clark Robertson. Includes bibliographical references (p. 143). Also available online.
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Lyon, Robert James. "Why are pulsars hard to find?" Thesis, University of Manchester, 2016. https://www.research.manchester.ac.uk/portal/en/theses/why-are-pulsars-hard-to-find(f15226ec-355d-4794-b2b8-e0a8e793948e).html.
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Searches for pulsars during the past fifty years, have been characterised by two problems making their discovery difficult: i) an increasing volume of data to be searched, and ii) an increasing number of `candidate' pulsar detections arising from that data, requiring analysis. Whilst almost all are caused by noise or interference, these are often indistinguishable from real pulsar detections. Deciding which candidates should be studied is therefore difficult. Indeed it has become known as the `candidate selection problem'. This thesis presents an interdisciplinary study of the selection problem, with the aim of developing a new method able to mitigate it. Specifically for future pulsar surveys undertaken with the Square kilometre Array (SKA). Through a combination of critical literature evaluations, theoretical modelling exercises, and empirical investigations, the selection problem is described in-depth here for the first time. It is shown to be characterised by the dominance of Gaussian distributed noise signals, a factor that no existing selection method accounts for. It also reveals the presence of a significant trend in survey data rates, which suggest that candidate selection is transitioning from an off-line processing procedure, to an on-line, and real-time, decision making process. In response, a new real-time machine learning based method, the GH-VFDT, is introduced in this thesis. The results presented here show that a significant improvement in selection performance can be achieved using the GH-VFDT, which utilises a learning procedure optimised for data characterised by skewed class distributions. Whilst the principled development of new numerical features that maximise the separation between pulsars and Gaussian noise, have also greatly improved GH-VFDT pulsar recall. It is therefore concluded that the sub-optimal performance of existing selection systems, is due to a combination of poor feature design, insensitivity to noise, and an inability to deal with skewed class distributions.
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Tada, Masaru. "Coherent time evolution of highly excited Rydberg states in pulsed electric field : Opening a stringent way to selectively field-ionize the highly excited states." 京都大学 (Kyoto University), 2001. http://hdl.handle.net/2433/150822.
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Attar, H., M. Bönisch, M. Calin, L. C. Zhang, K. Zhuravleva, A. Funk, S. Scudino, C. Yang, and J. Eckert. "Comparative study of microstructures and mechanical properties of in situ Ti–TiB composites produced by selective laser melting, powder metallurgy, and casting technologies." Cambridge University Press, 2014. https://tud.qucosa.de/id/qucosa%3A39023.
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This study presents results of selective laser melting (SLM), powder metallurgy (PM), and casting technologies applied for producing Ti–TiB composites from Ti–TiB₂ powder. Diffraction patterns and microstructural investigations reveal that chemical reaction occurred between Ti and TiB₂ during all the three processes, leading to the formation of Ti–TiB composites. The ultimate compressive strength of SLM-processed and cast samples are 1421 and 1434 MPa, respectively, whereas the ultimate compressive strengths of PM-processed 25%, 29%, and 36% porous samples are 510, 414, and 310 MPa, respectively. The Young’s moduli of porous composite samples are 70, 45, and 23 GPa for 25%, 29%, and 36% porosity levels, respectively, and are lower than those of SLM-processed (145 GPa) and cast (142 GPa) samples. Fracture analysis of the SLM-processed and cast samples shows shear fracture and microcracks across the samples, whereas failure of porous samples occurs due to porosities and weak bonds among particles.
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Zhang, Rui. "Impact of emerging technologies on the cell disruption and fractionation of microalgal biomass." Thesis, Compiègne, 2020. http://www.theses.fr/2020COMP2548.
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Ce travail de recherche se concentre sur l'extraction et le fractionnement des biomolécules à partir de microalgues par des traitements physiques: les champs électriques pulsés (CEP), les décharges électriques de hautes tensions (DEHT) et les ultrasons (US). Dans cette étude, trois espèces de microalgues Nannochloropsis sp., Phaeodactylum tricornutum (P. tricornutum) et Parachlorella kessleri (P. kessleri) ont été étudiées. Les espèces ont différentes formes cellulaires, structure et contenu intracellulaire. L'effet des techniques testées sur l'extraction des biomolécules a été mis en évidence à travers une analyse quantitative et qualitative: suivi du rendement des composés ioniques, des glucides, des protéines, des pigments et des lipides. Une étude comparative des traitements physiques (CEP, DEHT et US), à la même énergie, pour la libération des biomolécules intracellulaires à partir des trois espèces de microalgues, a permis de mieux comprendre les différents mécanismes de désintégration. Pour chaque microalgue, à la même énergie consommée, le traitement par DEHT s'est révélé le plus efficace en terme d'extraction des glucides, tandis que les US sont plus efficaces pour l'extraction des protéines et des pigments. Le traitement par CEP a été moins efficace en terme du rendement d’extraction. Cependant, la meilleure sélectivité (extraction des glucides) a été obtenue en utilisant les CEP ou les DEHT. Les prétraitements physiques (CEP, DEHT ou US) des suspensions plus concentrées suivis d'une homogénéisation haute pression (HHP) de suspensions diluées ont permis d'améliorer l'efficacité de l'extraction et de diminuer la consommation énergétique totale et le nombre de passages. Le prétraitement physique permet de réduire la pression mécanique de l’HHP, pour atteindre le même rendement d’extraction. Pour la valorisation maximale de la biomasse de microalgues, une procédure d'extraction assistée par DEHT (40 kV/cm, 1-8 ms) suivie de plusieurs étapes d'extraction aqueuses et non aqueuses semble être utile pour l'extraction sélective et le fractionnement de différentes biomolécules à partir de microalgues. Des effets significatifs du prétraitement HVED sur l'extraction par solvant organique des pigments (chlorophylles, caroténoïdes) et des lipides ont été observésThis research work focuses on extraction and fractionation of bio-molecules from microalgae using physical treatments: pulsed electric fields (PEF), high voltage electrical discharges (HVED) and ultrasonication (US) techniques. In this study, three microalgae species Nannochloropsis sp., Phaeodactylum tricornutum (P. tricornutum) and Parachlorella kessleri (P. kessleri) were investigated. These species have different cell shapes, structure and intracellular contents. The effects of tested techniques on extraction of bio-molecules have been highlighted in a quantitative and qualitative analysis by evaluating the ionic components, carbohydrates, proteins, pigments and lipids. A comparative study of physical treatments (PEF, HVED and US) at the equivalent energy input for release of intracellular bio-molecules from three microalgal species allowed us to better understand the different disintegration mechanisms. For each microalga at the same energy consumption, the HVED treatment proved to be the most efficient for extraction of carbohydrates, while the US treatment for extraction of proteins and pigments. In general, the smallest efficiency was observed for the PEF treatment. However, the highest selectivity towards carbohydrates can be obtained using the mild PEF or HVED technique. The preliminary physical treatments (PEF, HVED or US) of more concentrated suspensions followed by high pressure homogenization (HPH) of diluted suspensions allowed improving the extraction efficiency and decreasing the total energy consumption. The physical pretreatments permit to reduce the mechanical pressure of the HPH and number of passes, to reach the same extraction yield. For the maximum valorisation of microalgal biomass, extraction procedure assisted by HVED treatment (40 kV/cm, 1-8 ms) followed by aqueous and non-aqueous extraction steps seems to be useful for selective extraction and fractionation of different bio-molecules from microalgae. The significant effects of HVED pre-treatment on organic solvent extraction of pigments (chlorophylls, carotenoids) and lipids were also observed
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Benmamas, Arezki Lotfi. "Valorisation des systèmes d’éclairage à LED en fin de cycle de vie." Thesis, Troyes, 2021. http://www.theses.fr/2021TROY0044.
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Si l’éclairage solide permet une réduction conséquente de la consommation d’électricité, reste posé la problématique des dispositifs à base de LED. Cette thèse associée au projet RECYLED a consisté à identifier puis à développer des méthodes et des procédés en fonction des typologies des dispositifs (lampes, tubes et luminaires) et ce en vue d’une valorisation et d’une réutilisation de certains composants élémentaires. L’objectif, par une approche globale, incluant à la fois les aspects techniques, économiques et environnementaux était d’aboutir à un taux de recyclage de 80%. Trois scénarii ont été identifiés pour le recyclage des lampes et des tubes à LED, la réutilisation, le broyage et le désassemblage des lampes et des tubes à LED. Des études des déchets et des produits commercialisés, ont été menées afin de caractériser le gisement et de dimensionner les solutions de traitement proposées et estimer le potentiel de valorisation global. Concernant le désassemblage identifié comme le point bloquant, la technologie des puissances pulsées reposant sur la fragmentation est proposée. En ce qui concerne les tubes des solutions purement mécaniques ont été validées. Les méthodes proposées permettent d'obtenir un taux de valorisation matière de 74% pour les lampes et 94% pour les tubes. Ces taux sont à relier avec les prévisions estimées pour 2030 dans le cadre de ce travail qui aboutissent à un gisement annuel maximal évalué pour les lampes à LED à 2600 tonnes et pour les tubes et dalles à LED à 1600 tonnesWhile solid-state lighting allows for a significant reduction in electricity consumption, the problem of the end-of-life of the LED-based devices remains. This thesis associated with the RECYLED project consisted in identifying and then developing methods and processes according to the typologies of the devices (lamps, tubes and luminaires) with a view to recovery and reuse of certain elementary components. The objective, through a comprehensive approach, including both technical, economic and environmental aspects, was to achieve a recycling rate of 80%. Three scenarios have been identified for the recycling of LED lamps and tubes, reuse, shredding and disassembly. Studies of waste and marketed products have been carried out in order to characterize the deposit and size the proposed treatment solutions and estimate the overall recovery potential. Regarding the disassembly identified as the blocking point, the technology of pulsed powers based on fragmentation is proposed. With regard to the tubes, purely mechanical solutions have been validated. The proposed methods make it possible to obtain a material recovery rate of 74% for the lamps and 94% for the tubes. These rates are to be linked with the forecasts estimated for 2030 as part of this work, which lead to a maximum annual deposit estimated for LED lamps at 2600 tons and for LED tubes and panels at 1600 tons
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Okell, Thomas William. "Assessment of collateral blood flow in the brain using magnetic resonance imaging." Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:7e63bcf2-22bf-49e5-81ec-1644217605ae.
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Collateral blood flow is the compensatory flow of blood to the tissue through secondary channels when the primary channel is compromised. It is of vital importance in cerebrovascular disease where collateral flow can maintain large regions of brain tissue which would otherwise have suffered ischaemic damage. Traditional x-ray based techniques for visualising collateral flow are invasive and carry risks to the patient. In this thesis novel magnetic resonance imaging techniques for performing vessel-selective labelling of brain feeding arteries are explored and developed to reveal the source and extent of collateral flow in the brain non-invasively and without the use of contrast agents. Vessel-encoded pseudo-continuous arterial spin labelling (VEPCASL) allows the selective labelling of blood water in different combinations of brain feeding arteries that can be combined in post-processing to yield vascular territory maps. The mechanism of VEPCASL was elucidated and optimised through simulations of the Bloch equations and phantom experiments, including its sensitivity to sequence parameters, blood velocity and off-resonance effects. An implementation of the VEPCASL pulse sequence using an echo-planar imaging (EPI) readout was applied in healthy volunteers to enable optimisation of the post-labelling delay and choice of labelling plane position. Improvements to the signal-to-noise ratio (SNR) and motion-sensitivity were made through the addition of background suppression pulses and a partial-Fourier scheme. Experiments using a three-dimensional gradient and spin echo (3D-GRASE) readout were somewhat compromised by significant blurring in the slice direction, but showed potential for future work with a high SNR and reduced dropout artefacts. The VEPCASL preparation was also applied to a dynamic 2D angiographic readout, allowing direct visualisation of collateral blood flow in the brain as well as a morphological and functional assessment of the major cerebral arteries. The application of a balanced steady-state free precession (bSSFP) readout significantly increased the acquisition efficiency, allowing the generation of dynamic 3D vessel-selective angiograms. A theoretical model of the dynamic angiographic signal was also derived, allowing quantification of blood flow through specified vessels, providing a significant advantage over qualitative x-ray based methods. Finally, these methods were applied to a number of patient groups, including those with vertebro-basilar disease, carotid stenosis and arteriovenous malformation. These preliminary studies demonstrate that useful clinical information regarding collateral blood flow can be obtained with these techniques.
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Handouzi, Wahida. "Traitement d'information mono-source pour la validation objective d'un modèle d'anxiété : application au signal de pression sanguine volumique." Thesis, Université de Lorraine, 2014. http://www.theses.fr/2014LORR0237/document.
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La détection et l’évaluation des émotions sont des domaines qui suscitent un grand intérêt par de nombreuses communautés tant au niveau des sciences humaines que des sciences exactes. Dans cette thèse nous nous intéressons à la reconnaissance de l’anxiété sociale qui est une peur irrationnelle ressentie par une personne lors de toute forme de relation sociale. L’anxiété peut être révélée par un ensemble de traits physiques et physiologiques tels que l’intonation de la voix, les mimiques faciales, l’augmentation du rythme cardiaque, le rougissement… etc. L’avantage de l’utilisation des mesures physiologiques est que les individus ne peuvent pas les manipuler, c’est une source continue de données et chaque émotion est caractérisée par une variation physiologique particulière. Dans ce travail, nous proposons un système de mesure d’anxiété basé sur l’utilisation d’un seul signal physiologique « signal de pression sanguine volumique (Blood volume pulse BVP)». Le choix d’un seul capteur limite la gêne des sujets due au nombre de capteurs. De ce signal nous avons sélectionné des paramètres pertinents représentant au mieux les relations étroites du signal BVP avec le processus émotionnel de l’anxiété. Cet ensemble de paramètres est classé en utilisant les séparateurs à vastes marges SVM. Les travaux engagés dans le domaine de la reconnaissance des émotions utilisent fréquemment, pour support d’information, des données peu fiables ne correspondant pas toujours aux situations envisagées. Ce manque de fiabilité peut être dû à plusieurs paramètres parmi eux la subjectivité de la méthode d’évaluation utilisée (questionnaire, auto-évaluation des sujets, …etc.). Nous avons développé une approche d’évaluation objective des données basée sur les dynamiques des paramètres sélectionnés. La base de données utilisée a été enregistrée dans notre laboratoire dans des conditions réelles acquises sur des sujets présentant un niveau d’anxiété face aux situations sociales et qui ne sont pas sous traitement psychologique. L’inducteur utilisé est l’exposition à des environnements virtuels représentant quelques situations sociales redoutées. L’étape d’évaluation, nous a permis d’obtenir un modèle de données fiable pour la reconnaissance de deux niveaux d’anxiété. Ce modèle a été testé dans une clinique spécialisée dans les thérapies cognitives comportementales (TCC) sur des sujets phobiques. Les résultats obtenus mettent en lumière la fiabilité du modèle construit notamment pour la reconnaissance des niveaux d’anxiété sur des sujets sains ou sur des sujets phobiques ce qui constitue une solution au manque de données dont souffrent les différents domaines de reconnaissancesDetection and evaluation of emotions are areas of great interest in many communities both in terms of human and exact sciences. In this thesis we focus on social anxiety recognition, which is an irrational fear felt by a person during any form of social relationship. Anxiety can be revealed by a set of physical and physiological traits such as tone of voice, facial expressions, increased heart rate, flushing ... etc. The interest to the physiological measures is motivated by them robustness to avoid the artifacts created by human social masking, they are a continuous source of data and each emotion is characterized by a particular physiological variation. In this work, we propose a measurement system based on the use of a single physiological signal "Blood volume pulse BVP". The use of a single sensor limits the subjects’ discomfort. From the BVP signal we selected three relevant features which best represents the close relationship between this signal and anxiety status. This features set is classified using support vector machine SVM. The work undertaken in the field of emotion recognition frequently use, for information support, unreliable data do not always correspond to the situations envisaged. This lack of reliability may be due to several parameters among them the subjectivity of the evaluation method used (self-evaluation questionnaire, subjects…etc.). We have developed an approach to objective assessment of data based on the dynamics of selected features. The used database was recorded in our laboratory under real conditions acquired in subjects with a level of anxiety during social situations and who are not under psychological treatment. The used stimulus is the exposition to virtual environments representing some feared social situations. After the evaluation stage, we obtained a reliable model for the recognition of two levels of anxiety. The latter was tested in a clinic specializing in cognitive behavioral therapy (CBT) on phobic subjects. The results highlight the reliability of the built model specifically for the recognition of anxiety levels in healthy subjects or of phobic subjects, what constitutes a solution to the lack of data affecting different areas of recognition
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Ghasemi, Negareh. "Improving ultrasound excitation systems using a flexible power supply with adjustable voltage and frequency to drive piezoelectric transducers." Thesis, Queensland University of Technology, 2012. https://eprints.qut.edu.au/61091/1/Negareh_Ghasemi_Thesis.pdf.
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The ability of a piezoelectric transducer in energy conversion is rapidly expanding in several applications. Some of the industrial applications for which a high power ultrasound transducer can be used are surface cleaning, water treatment, plastic welding and food sterilization. Also, a high power ultrasound transducer plays a great role in biomedical applications such as diagnostic and therapeutic applications. An ultrasound transducer is usually applied to convert electrical energy to mechanical energy and vice versa. In some high power ultrasound system, ultrasound transducers are applied as a transmitter, as a receiver or both. As a transmitter, it converts electrical energy to mechanical energy while a receiver converts mechanical energy to electrical energy as a sensor for control system. Once a piezoelectric transducer is excited by electrical signal, piezoelectric material starts to vibrate and generates ultrasound waves. A portion of the ultrasound waves which passes through the medium will be sensed by the receiver and converted to electrical energy. To drive an ultrasound transducer, an excitation signal should be properly designed otherwise undesired signal (low quality) can deteriorate the performance of the transducer (energy conversion) and increase power consumption in the system. For instance, some portion of generated power may be delivered in unwanted frequency which is not acceptable for some applications especially for biomedical applications.
To achieve better performance of the transducer, along with the quality of the excitation signal, the characteristics of the high power ultrasound transducer should be taken into consideration as well. In this regard, several simulation and experimental tests are carried out in this research to model high power ultrasound transducers and systems. During these experiments, high power ultrasound transducers are excited by several excitation signals with different amplitudes and frequencies, using a network analyser, a signal generator, a high power amplifier and a multilevel converter. Also, to analyse the behaviour of the ultrasound system, the voltage ratio of the system is measured in different tests. The voltage across transmitter is measured as an input voltage then divided by the output voltage which is measured across receiver. The results of the transducer characteristics and the ultrasound system behaviour are discussed in chapter 4 and 5 of this thesis.
Each piezoelectric transducer has several resonance frequencies in which its impedance has lower magnitude as compared to non-resonance frequencies. Among these resonance frequencies, just at one of those frequencies, the magnitude of the impedance is minimum. This resonance frequency is known as the main resonance frequency of the transducer. To attain higher efficiency and deliver more power to the ultrasound system, the transducer is usually excited at the main resonance frequency. Therefore, it is important to find out this frequency and other resonance frequencies. Hereof, a frequency detection method is proposed in this research which is discussed in chapter 2.
An extended electrical model of the ultrasound transducer with multiple resonance frequencies consists of several RLC legs in parallel with a capacitor. Each RLC leg represents one of the resonance frequencies of the ultrasound transducer. At resonance frequency the inductor reactance and capacitor reactance cancel out each other and the resistor of this leg represents power conversion of the system at that frequency. This concept is shown in simulation and test results presented in chapter 4.
To excite a high power ultrasound transducer, a high power signal is required. Multilevel converters are usually applied to generate a high power signal but the drawback of this signal is low quality in comparison with a sinusoidal signal. In some applications like ultrasound, it is extensively important to generate a high quality signal. Several control and modulation techniques are introduced in different papers to control the output voltage of the multilevel converters. One of those techniques is harmonic elimination technique. In this technique, switching angles are chosen in such way to reduce harmonic contents in the output side. It is undeniable that increasing the number of the switching angles results in more harmonic reduction. But to have more switching angles, more output voltage levels are required which increase the number of components and cost of the converter. To improve the quality of the output voltage signal with no more components, a new harmonic elimination technique is proposed in this research. Based on this new technique, more variables (DC voltage levels and switching angles) are chosen to eliminate more low order harmonics compared to conventional harmonic elimination techniques. In conventional harmonic elimination method, DC voltage levels are same and only switching angles are calculated to eliminate harmonics. Therefore, the number of eliminated harmonic is limited by the number of switching cycles. In the proposed modulation technique, the switching angles and the DC voltage levels are calculated off-line to eliminate more harmonics. Therefore, the DC voltage levels are not equal and should be regulated. To achieve this aim, a DC/DC converter is applied to adjust the DC link voltages with several capacitors. The effect of the new harmonic elimination technique on the output quality of several single phase multilevel converters is explained in chapter 3 and 6 of this thesis.
According to the electrical model of high power ultrasound transducer, this device can be modelled as parallel combinations of RLC legs with a main capacitor. The impedance diagram of the transducer in frequency domain shows it has capacitive characteristics in almost all frequencies. Therefore, using a voltage source converter to drive a high power ultrasound transducer can create significant leakage current through the transducer. It happens due to significant voltage stress (dv/dt) across the transducer. To remedy this problem, LC filters are applied in some applications. For some applications such as ultrasound, using a LC filter can deteriorate the performance of the transducer by changing its characteristics and displacing the resonance frequency of the transducer. For such a case a current source converter could be a suitable choice to overcome this problem. In this regard, a current source converter is implemented and applied to excite the high power ultrasound transducer. To control the output current and voltage, a hysteresis control and unipolar modulation are used respectively. The results of this test are explained in chapter 7.
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Vacano, Bernhard von [Verfasser]. "Chemically selective microspectroscopy with broadband shaped femtosecond laser pulses / Bernhard von Vacano." 2008. http://d-nb.info/988370875/34.
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Wang, Chung-Han, and 王崇翰. "Selective Induction of Cell Death and the Dead Cell Detachment from a Microfabricated Cell Culture Substrate Using Femtosecond Laser Pulses." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/16326588422921529673.
Full textAbstract:
碩士國立交通大學
應用化學系碩博士班
103
Construction of bio-functional devices has become one of the most important technologies for studying cellular behaviour. We aim at providing a new methodology to construct living-cell network on a culture substrate toward cell-based devices. Such devices may play an important role in controlling cellular functions such as development, proliferation, migration, differentiation and death. In order to realize the cell-based devices, induction of cell death without affecting the neighbours should be controlled. Because cell maturation is a sophisticated process involving many cell functions, the condition of individual cells is varying during this period. Furthermore, when the cells finishing their roles, they kill themselves to make places to other kinds of cells for maturing tissues. The types of cell death frequently occurs naturally in normal tissue maturation cycle. The purpose of this thesis is to find out a condition for inducing death of individual cells to remove them by utilising femtosecond laser ablation. The relation among laser parameters, cell death and the detachment of dead cell was investigated with HepG2 cell iii (human liver hepatocellular carcinoma cell line). The micro-fabricated cell culture substrate was applied to monitoring individual cells. The cells can be arranged linearly as a monolayer on a micro-pattern. When intense femtosecond laser pulses are tightly focused into a single living cell, ablation is induced as a result of multi-photon absorption. If the laser power is enough high to generate cavitation bubbles, bursting of a single cell is induced to release intracellular toxins to extracellular environment. In this case, surrounding cells receive fatal damages. In contrast, a relatively low power was set just to kill a target single cell in short period without affecting adjacent cells. We found that the target HepG2 cells were detached from the micro-fabricated pattern with 96% reproducibility. Our methodology for control of specific cell death and their detachment by utilising femtosecond laser will contribute to the development of cell-based devices. It will play a significant role in study of selectively controlling cell functions, for example, cell renewal and cell death in near future. In addition, this ability for temporally and spatially controlling cellular and tissue damages and removing an individual specific cells will receive much attention from the view point of regeneration studies.
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Kröner, Dominik [Verfasser]. "Theory of selective preparation of enantiomers by laser pulses = Theorie zur selektiven Präparation von Enantiomeren durch Laserpulse / vorgelegt von Dominik Kröner." 2003. http://d-nb.info/96791163X/34.
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Elghobashi, Nadia [Verfasser]. "Theory of using few cycle IR and UV laser pulses to control the orientation and selective dissociation of hydrogen bonded anions / vorgelegt von Nadia Elghobashi." 2005. http://d-nb.info/978587529/34.
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Patel, Arun Kumar. "Design of Novel NMR Methodologies to address diverse challenging problems in Chemistry." Thesis, 2021. https://etd.iisc.ac.in/handle/2005/5216.
Full textAbstract:
The thesis entitled “Design of Novel NMR Methodologies to address diverse challenging problems in Chemistry” discusses the design of number of novel NMR methodologies which have broader utility and, also the extensive investigations carried out on the weak molecular interactions like Hydrogen bonding. The applications of the novel sequences to address various challenging problems encountered in chemistry have been demonstrated. The first part of the thesis discusses the manipulation of the spin dynamics for the development of two novel NMR methodologies. The first developed methodology is cited as PASS-J¬-Resolved, which is used for the extraction of the scalar coupling information for a selected proton along with combating the inherent sensitivity issue of Clean-G-SERF experiment. Unlike Clean-G-SERF experiment, the new sequence not only yields the active couplings, but also the passive coupling information. Further, to enhance the resolution of PASS-J-Resolved experiment, another experiment cited as PASS-J-Resolved-NOAP has been developed in which the final spectrum is obtained from the inphase terms which yield the spectrum with enhanced resolution. The distinct advantages of these experimental techniques have been demonstrated by extracting the coupling information for a selected proton from the complex spectra of β-butyrolactone and strychnine. Another new pulse sequence developed is the Phase Modulated (PM) one-dimensional TOCSY. The phase modulation of the chosen spin relative to other spins can be achieved by appropriate manipulation of the delay period before the isotropic mixing. It helps to differentiate different spin systems, based on the 180-degree phase difference between the selectively excited proton with the remaining spins or by nullifying the signal of the chosen spin. The wide utility of this methodology has been demonstrated on; the spin systems identification in a multicomponent mixture, identification of α- and β- anomers of glucose and suppression of residual water peak and providing the solution for enantiomeric discrimination in challenging situations. In another direction, the investigations on the hydrogen bond (HB) have been carried out by the extensive utility of NMR experiments on the synthesised binaphthalene benzamide derivatives. The application of various multinuclear and multidimensional NMR experiments indubitably established the existence of HB in all the synthesised molecules. Two-dimensional experiments like HOESY on the fluorine substituted molecule confirmed the close spatial proximity between 19F and 1H, conducive for HB interactions. The 15N-1H HSQC experiment aided in the determination of both scalar couplings and the couplings mediated through HB. All the NMR experimental findings are corroborated by theoretical computations, using DFT based approaches, such as, QTAIM and NCI. Single crystal XRD structure of the fluoro-derivative is also obtained which aided in ascertaining the spatial proximity between the fluorine and hydrogen atom, and confirmed the NMR observations. From the XRD structure, the reason for the retention of strong HB in the high polarity solvents like DMSO-d6 has been understood.Indian Institute of Science
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"Wavelength selection and switching in short pulses generated from semiconductor lasers." 2000. http://library.cuhk.edu.hk/record=b5890470.
Full textAbstract:
by Chow Kin Kee.Thesis (M.Phil.)--Chinese University of Hong Kong, 2000.
Includes bibliographical references.
Abstracts in English and Chinese.
Abstract --- p.ii
Acknowledgment --- p.v
Table of Contents --- p.vi
Chapter 1. --- Introduction --- p.1
Chapter 1.1 --- Ultra-short Pulse Generation in Semiconductor Lasers --- p.2
Chapter 1.2 --- Wavelength Selection and Switching in Short Pulses Generated from Semiconductor Laser --- p.4
Chapter 1.3 --- Structure of the Thesis --- p.6
Reference --- p.8
Chapter 2. --- Principles and Theories --- p.10
Chapter 2.1 --- Principle of Wavelength Switching in Self-Seeded Laser --- p.11
Chapter 2.2 --- Principle of Synchronous Injection Seeding of two Lasers --- p.15
Chapter 2.3 --- Principle of Fast Spectral Improvement in DFB Laser with Optical Feedback --- p.17
Chapter 2.4 --- Principle of Spectrally Resolved Analysis --- p.19
Reference --- p.24
Chapter 3. --- Switching Dynamics between Single-Mode and Dual-Mode Pulse Emissions from a Self-Seeded Laser Diode --- p.25
Chapter 3.1 --- Introduction --- p.26
Chapter 3.2 --- Experimental Details and Discussion --- p.28
Chapter 3.3 --- Summary --- p.37
Reference --- p.38
Chapter 4. --- Spectrally Resolved Analysis of Fast Tuning in Single-Mode Pulses Generated from Mutually Injection-Seeded Fabry- Perot Laser Diodes --- p.40
Chapter 4.1 --- Introduction --- p.41
Chapter 4.2 --- Experimental Details and Discussion --- p.42
Chapter 4.3 --- Summary --- p.51
Reference --- p.52
Chapter 5. --- Fast Spectral Improvement in Gain-Switched Pulses Generated from a Distributed Feedback Laser with Weak Optical Feedback --- p.54
Chapter 5.1 --- Introduction --- p.55
Chapter 5.2 --- Experimental Details and Discussion --- p.57
Chapter 5.3 --- Summary --- p.65
Reference --- p.66
Chapter 6. --- Conclusion and Future Work --- p.67
Chapter 6.1 --- Conclusion --- p.67
Chapter 6.2 --- Future Works --- p.69
Reference --- p.71
Appendices --- p.A-l
Appendix A. List of Publications --- p.A-l
Appendix B. Modeling of Self-Seeded Fabry-Perot Laser --- p.A-2
Appendix C. List of Figures --- p.A-4
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Lau, Angus. "Frequency-selective Methods for Hyperpolarized 13C Cardiac Magnetic Resonance Imaging." Thesis, 2012. http://hdl.handle.net/1807/34779.
Full textAbstract:
Heart failure is a complex clinical syndrome in which the heart cannot pump sufficient blood and nutrients to the organs in the body. Increasingly, alterations in cardiac energetics are being implicated as playing an important role in the pathogenesis of heart failure. An understanding of specific metabolic switches which occur during the development of heart failure in patients would be greatly beneficial as a new diagnostic method and for the development of new therapies for patients with failing hearts.
This thesis deals with the non-invasive assessment of metabolism in the heart. New magnetic resonance imaging (MRI) methods for metabolic characterization of the heart using hyperpolarized carbon-13 MRI are presented. Spatially resolved images of hyperpolarized 13C substrates and their downstream products can provide insight into real-time metabolic processes occurring in vivo, within minutes of injection of a pre-polarized 13C-labeled substrate. Conventional 3D spectroscopic acquisitions require in excess of 100 excitations, making it challenging to acquire full cardiac and respiratory-gated, whole-heart metabolic volumes.
Each of the developments described in this thesis is intended to advance cardiac hyperpolarized 13C metabolic imaging towards a routine, clinical exam which can be used for prognosis and treatment optimization in patients with cardiovascular disease. The major technical development is a new interleaved-frequency, time-resolved MRI pulse sequence that can provide robust and reliable measurements of cardiac metabolic signals. The technique was applied to several realistic pre-clinical models of cardiac disease and the work presented will hopefully lead towards significant improvement in the management of patients with heart failure.
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Liao, Ping-Chun, and 廖品竣. "Selective Harmonic Elimination for a 24-pulse Inverter Based on Zig-zag Connected Transformer." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/nr7v8w.
Full textAbstract:
碩士國立臺灣科技大學
電機工程系
99
In this paper, a zig-zag transformer applied in the 24 pulse voltage source inverter is presented, the zig-zag transformer provides the isolation between the input and output side of the system, it can additionally suppress and eliminate harmonics except the 24n ± 1 orders(n=1,2,3…). Thus the selective harmonic elimination pulse width modulation (SHE-PWM) method is used to control the inverter in the proposed system. This method yields the advantage of low switching frequency, low switching losses, the direct control of the fundamental harmonic component, and the elimination for particular harmonics. So this method is highly suitable for the apparatus with suppression to specific harmonics in high power applications. Furthermore, SHE techniques usually perform one quarter-wave symmetry. In addition to generate the one half-wave symmetry waveform, this thesis also control the fundamental of the output voltage in system, eliminating 23rd, 25th, 47th, and 49th harmonics. Discussion and analysis to the half-wave symmetrical waveforms is conducted in the thesis to further improve the power quality and permits the inverter being operated with low switching frequency. The lowest harmonic order left in the output voltage is 71st. Compared to those voltage source inverters with low switching frequency, the proposed scheme yields lower harmonic distortion and higher power quality in the output voltage. In this thesis, MATLAB analysis and simulation, and finally to verify the feasibility of implementation.
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(9760571), Ahmad Enosh Kazem. "PREBIOTIC POTENTIAL OF A WIDE SELECTION OF TUBERS, GRAINS, AND PULSES IN COMPARISON TO FRUCTO-OLIGOSACCHARIDE." Thesis, 2020.
Find full textAbstract:
The most common food and supplement prebiotic fiber is inulin – most commonly extracted from chicory root. Fructo-oligosaccharide (FOS) is a smaller version of inulin, both containing mainly fructose units with β-1,2 linkages. FOS/inulin has been used, and studied, as a prebiotic for decades. The potential of alternative prebiotics intrinsic in whole foods, such as in tubers, grains, vegetables, and pulses – the world’s most common staple crops – are not as commonly recognized as prebiotics, though have this potential if fermentable in the gut. If such alternative sources of prebiotic ingredients could be established it would allow for cheaper, possibly more effective, and more diverse food product development options beyond FOS/inulin.
This study demonstrates the potential of tubers, grains, and pulses as prebiotics in relation to their in vitro human fecal fermentation rate, short chain fatty acid (SCFA) production, and microbiota indicators of alpha diversity and impact on key bacterial genera. Fecal samples were obtained from three diverse healthy human donors and used as the initial bacterial inoculum to simulate conditions in the human gut (colon). Substrates (n=35), after undergoing an upper gastrointestinal tract simulated digestion, were fermented by each individual donors’ inoculum separately, and measurements after 6, 12, and 24 h of fermentation were made on gas production, SCFA metabolite production, and microbiome composition.
The results of this study establish high fermentability and potential prebiotic effects of dietary fibers from tubers, grains, and pulses. Whole foods, ground and cooked the same way, produced dietary fibers that were largely insoluble, but surprisingly fermentable with high SCFA levels, mostly slow fermentation profiles indicating high tolerability, and mostly promoting diverse microbiota responses compared to FOS. Generally, whole food fibers had higher fermentability than similar isolated fibers. Overall, the processing steps, such as atmospheric or pressure cooking, tested in some pulses did not detract, or add to, the prebiotic abilities of the substrates. Each food fiber substrate had unique effects on the gut microbiota parameters tested. Gut microbiome compositional responses to the same substrate varied significantly among the three donors, but notably SCFA metabolite responses were similar among donors.
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Ke, Jhih-Jheng, and 柯志正. "Preliminary Investigation on the Optimization of Heteronuclear Decoupling During Selective Refocusing Pulse in Solid State Nuclear Magnetic Resonance." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/mq6rbd.
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Heras, I., M. Krause, G. Abrasonis, A. Pardo, J. L. Endrino, E. Guillén, and R. Escobar-Galindo. "Advanced characterisation and optical simulation for the design of solar selective coatings based on carbon:transition metal carbide nanocomposites." 2019. https://hzdr.qucosa.de/id/qucosa%3A33924.
Full textAbstract:
Solar selective coatings based on carbon transition metal carbide nanocomposite absorber layers were designed. Pulsed filtered cathodic arc was used for depositing amorphous carbon: metal carbide (a-C:MeC, Me = V, Mo) thin films. Composition and structure of the samples were characterized by ion beam analysis, X-ray diffraction, Raman spectroscopy, and transmission electron microscopy. The optical properties were determined by ellipsometry and spectrophotometry. Three effective medium approximations (EMA), namely Maxwell-Garnett, Bruggeman, and Bergman, were applied to simulate the optical behaviour of the nanocomposite thin films. Excellent agreement was achieved between simulated and measured reflectance spectra in the entire wavelength range by using the Bergman approach, where in-depth knowledge of the nanocomposite thin film microstructure is included. The reflectance is shown to be a function of the metal carbide volume fraction and its degree of percolation, but not dependent on whether the nanocomposite microstructure is homogeneous or a self-organized multilayer. Solar selective coatings based on an optimized a-C:MeC absorber layer were designed exhibiting a maximum solar absorptance of 96% and a low thermal emittance of ~5 and 15% at 25 and 600ºC, respectively. The results of this study can be considered as predictive design tool for nanomaterial-based optical coatings in general.
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"Model selection and optimization of the sodium ion channel through the use of single and ensemble pulse protocols." Tulane University, 2003.
Find full textAbstract:
Nonequilibrium Response Spectroscopy (NRS), the technique of using rapidly fluctuating voltage pulses in the study of ion channels is applied here. NRS is known to drive an ensemble of ion channels far from equilibrium where it has been argued that new details of ion channel kinetics can be studied under nonequilibrium conditions. In this study, single pulse NRS technique with custom designed waveforms built from wavelets are used. Two series of experiments were implemented using custom designed pulses, which were obtained using a pulse search algorithm with suitable 'cost functionals' as constraints in the design of the pulse. The use of NRS pulses in model selection was investigated, as well as an in the analysis of model topology through parametric optimization. Electrophysiological recordings (whole cell ionic current measurements) were made from mammalian cells (HEK 293) which stably expressed the sodium ion channel. Wavelet analysis of the model response and the experimental data is introduced. Its effectiveness in the data analysis is demonstrated in the unique plots of the wavelet transforms. The results show how these new NRS pulses can be applied in a systematic way to study ion channels gating kineticsacase@tulane.edu
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Wei, I.-Lun, and 魏薏倫. "Pulse generation from picosecond to sub-nanosecond regime by mode selection in low-repetition-rate passively mode-locked Nd:YVO4 lasers." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/pbunv8.
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Boby, Mathews. "Multilevel Dodecagonal and Octadecagonal Voltage Space Vector Structures with a Single DC Supply Using Basic Inverter Cells." Thesis, 2017. http://etd.iisc.ac.in/handle/2005/3712.
Full textAbstract:
Multilevel converters have become the direct accepted solution for high power converter applications. They are used in wide variety of power electronic applications like power transmission and distribution, electric motor drives, battery management and renewable energy management to name a few. For medium and high voltage motor drives, especially induction motor drives, the use of multilevel voltage source inverters have become indispensible. A high voltage multilevel inverter could be realized using low voltage switching devices which are easily available and are of low cost. A multilevel inverter generates voltage waveforms of very low harmonic distortion by switching between voltage levels of reasonably small amplitude differences. Thus the dv/dt of the output voltage waveform is small and hence the electromagnetic interference generated is less. Because of better quality output generation, the switching frequency of the multilevel inverters could be reduced to control the losses. Thus, a multilevel converter stands definitely a class apart in terms of performance from a conventional two-level inverter. Many multilevel inverter topologies for induction motor drives are available in the literature. The basic multilevel topologies are the neutral point clamped (NPC) inverter, flying capacitor (FC) inverter and the cascaded H-bridge (CHB) inverter. Various other hybrid multilevel topologies have been proposed by using the basic multilevel inverter topologies. It is also possible to obtain multilevel output by using conventional two-level inverters feeding an open-end winding induction motor from both sides.
All the conventional multilevel voltage source inverters generate hexagonal (6 sided polygons) voltage space vector structures. When an inverter with hexagonal space vector structure is operated in the over modulation range, significant low order harmonics are generated in the phase voltage output. Over modulation operation is required for the full utilization of the available DC-link voltage and hence maximum power generation. Among the harmonics generated, the fifth and seventh harmonics are of significant magnitudes. These harmonics generate torque ripple in the motor output and are undesirable in high performance motor drive applications. The presence of these harmonics further creates problems in the closed loop current control of a motor, affecting the dynamic performance. Again, the harmonic currents generate losses in the stator windings. Therefore, in short, the presence of harmonic voltages in the inverter output is undesirable.
Many methods have been proposed to eliminate or mitigate the effect of the harmonics. One solution is to operate the inverter at high switching frequency and thereby push the harmonics generated to high frequencies. The stator leakage inductance offers high impedance to the high frequency harmonics and thus the harmonic currents generated are negligible. But, high switching frequency brings switching losses and high electromagnetic interference generation in the drive system. And also, high switching frequency operation is effective only in the linear modulation range. Another solution is to use passive harmonic filters at the inverter output. For low order harmonics, the filter components would be bulky and costly. The loss created by the filters degrades the efficiency of the drive system as well. The presence of a filter also affects the dynamic performance of the drive system during closed loop operation. Special pulse width modulation (PWM) techniques like selective harmonic elimination (SHE) PWM can prevent the generation of a particular harmonic from the phase voltage output. The disadvantages of such schemes are limited modulation index, poor dynamic performance and extensive offline computations. An elegant harmonic elimination method is to generate a voltage space vector structure having more number of sides like a dodecagon (12 sided polygons) or an octadecagon (18 sided polygons) rather than a hexagon.
Inverter topologies generating dodecagonal voltage space vector structure eliminate fifth and seventh order harmonics, represented as 6n 1; n = odd harmonics, from the phase voltages and hence from the motor phase currents, throughout the entire modulation range. The first harmonics appearing the phase voltage are the 11th and 13th harmonics. Another advantage is the increased linear modulation range of operation for a given DC-link voltage, because geometrically dodecagon is closer to circle than a hexagon. An octadecagonal structure eliminates the 11th and 13th harmonics as well from the phase voltage output. The harmonics present in the phase voltage are of the order 18n 1; n = 1; 2; 3; :::. Thus the total harmonics distortion (THD) of the phase voltage is further improved. The linear modulation range also gets enhanced compared to hexagonal and dodecagonal structures. Multilevel dodecagonal and octadecagonal space vector structures combines the advantages of both multilevel structure and dodecagonal and octadecagonal structure and hence are very attractive solutions for high performance induction motor drive schemes. Chapter 1 of this thesis introduces the multilevel in-verter topologies generating hexagonal, dodecagonal and octadecagonal voltage space vector structures. Inverter topologies generating multilevel dodecagonal and octadecago-nal voltage space vector structures have been proposed before but using multiple DC sources delivering active power. The presence of more than one DC source in the inverter topology makes the back to back operation (four-quadrant operation) of the drive system difficult. And also the drive system becomes more costly and bulky. This thesis proposes induction motor drive schemes generating multilevel dodecagonal and octadecagonal volt-age space vector structures using a single DC source.
In Chapter 2, an induction motor drive scheme generating a six-concentric multilevel dodecagonal voltage space vector structure using a single DC source is proposed for an open-end winding induction motor. In the topology, two three-level inverters drive an open-end winding IM, one inverter from each side. DC-link of primary inverter is from a DC source (Vdc) which delivers the entire active power, whereas the secondary inverter DC-link is maintained by a capacitor at a voltage of 0:289Vdc, which is self-balanced during the inverter operation. The PWM scheme implemented ensures low switching frequency for primary inverter. Secondary inverter operates at a small DC-link voltage. Hence, switching losses are small for both primary and secondary inverters. An open-loop V/f scheme was used to test the topology and modulation scheme.
In the work proposed in Chapter 3, the topology and modulation scheme used in the first work is modified for a star connected induction motor. Again, the scheme uses only a single DC source and generates a six-concentric multilevel space vector struc-ture. The power circuit topology is realized using a three-level flying capacitor (FC) inverter cascaded with an H-bridge (CHB). The capacitors in the CHB inverter are maintained at a voltage level of 0:1445Vdc. The FC inverter switches between volt-age levels of [Vdc; 0:5Vdc; 0] and the CHB inverter switches between voltage levels of [+01445Vdc; 0; 0:1445Vdc]. The PWM scheme generates a quasi-square waveform output from the FC inverter. This results in very few switchings of the FC inverter in a funda-mental cycle and hence the switching losses are controlled. The CHB inverter switches Ch. 0: at high frequency compared to the FC inverter and cancels the low order harmonics (6n 1; n = odd) generated by the FC inverter. Even though the CHB operates at higher switching frequency, the switchings are at low voltage thereby controlling the losses. The linear modulation range of operation is extended to 48:8Hz for a base frequency of 50Hz. An open-loop V/f scheme was used to test the topology and modulation scheme.
In Chapter 4, a nine-concentric multilevel octadecagonal space vector structure is proposed for the first time, again using a single DC source. The circuit topology remains same as the work in Chapter 3, except that the CHB capacitor voltage is maintained at 0:1895Vdc. The 5th; 7th; 11th and 13th harmonics are eliminated from the phase voltage output. The linear modulation range is enhanced to 49:5Hz for a base speed of 50Hz. An open-loop V/f scheme and rotor field oriented control scheme were used to test the proposed drive system.
All the proposed drive schemes have been extensively simulated and tested in hard-ware. Simulation was performed in MATLAB-SIMULINK environment. For implement-ing the inverter topology, SKM75GB12T4 IGBT modules were used. The control al-gorithms were implemented using a DSP (TI’s TMS320F28334) and an FPGA (Xilinx Spartan XC3S200). A 1kW , 415V , 4-pole induction motor was used for the experiment purpose.
The above mentioned induction motor drive schemes generate phase voltage outputs in which the low order harmonics are absent. The linear modulation range is extended near to the base frequency of operation compared to hexagonal space vector structure. In the inverter topologies, the secondary inverters or the CHB inverters functions as harmonic filters and delivers zero active power. The primary inverter in the topologies switches at low frequency, reducing the power loss. Single DC source requirement brings down the cost of the system as well as permitting easy four-quadrant operation. This is also advantageous in battery operated systems like EV applications. With these features and advantages, the proposed drive schemes are suitable for high performance, medium voltage induction motor drive applications.
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Boby, Mathews. "Multilevel Dodecagonal and Octadecagonal Voltage Space Vector Structures with a Single DC Supply Using Basic Inverter Cells." Thesis, 2017. http://etd.iisc.ernet.in/2005/3712.
Full textAbstract:
Multilevel converters have become the direct accepted solution for high power converter applications. They are used in wide variety of power electronic applications like power transmission and distribution, electric motor drives, battery management and renewable energy management to name a few. For medium and high voltage motor drives, especially induction motor drives, the use of multilevel voltage source inverters have become indispensible. A high voltage multilevel inverter could be realized using low voltage switching devices which are easily available and are of low cost. A multilevel inverter generates voltage waveforms of very low harmonic distortion by switching between voltage levels of reasonably small amplitude differences. Thus the dv/dt of the output voltage waveform is small and hence the electromagnetic interference generated is less. Because of better quality output generation, the switching frequency of the multilevel inverters could be reduced to control the losses. Thus, a multilevel converter stands definitely a class apart in terms of performance from a conventional two-level inverter. Many multilevel inverter topologies for induction motor drives are available in the literature. The basic multilevel topologies are the neutral point clamped (NPC) inverter, flying capacitor (FC) inverter and the cascaded H-bridge (CHB) inverter. Various other hybrid multilevel topologies have been proposed by using the basic multilevel inverter topologies. It is also possible to obtain multilevel output by using conventional two-level inverters feeding an open-end winding induction motor from both sides.
All the conventional multilevel voltage source inverters generate hexagonal (6 sided polygons) voltage space vector structures. When an inverter with hexagonal space vector structure is operated in the over modulation range, significant low order harmonics are generated in the phase voltage output. Over modulation operation is required for the full utilization of the available DC-link voltage and hence maximum power generation. Among the harmonics generated, the fifth and seventh harmonics are of significant magnitudes. These harmonics generate torque ripple in the motor output and are undesirable in high performance motor drive applications. The presence of these harmonics further creates problems in the closed loop current control of a motor, affecting the dynamic performance. Again, the harmonic currents generate losses in the stator windings. Therefore, in short, the presence of harmonic voltages in the inverter output is undesirable.
Many methods have been proposed to eliminate or mitigate the effect of the harmonics. One solution is to operate the inverter at high switching frequency and thereby push the harmonics generated to high frequencies. The stator leakage inductance offers high impedance to the high frequency harmonics and thus the harmonic currents generated are negligible. But, high switching frequency brings switching losses and high electromagnetic interference generation in the drive system. And also, high switching frequency operation is effective only in the linear modulation range. Another solution is to use passive harmonic filters at the inverter output. For low order harmonics, the filter components would be bulky and costly. The loss created by the filters degrades the efficiency of the drive system as well. The presence of a filter also affects the dynamic performance of the drive system during closed loop operation. Special pulse width modulation (PWM) techniques like selective harmonic elimination (SHE) PWM can prevent the generation of a particular harmonic from the phase voltage output. The disadvantages of such schemes are limited modulation index, poor dynamic performance and extensive offline computations. An elegant harmonic elimination method is to generate a voltage space vector structure having more number of sides like a dodecagon (12 sided polygons) or an octadecagon (18 sided polygons) rather than a hexagon.
Inverter topologies generating dodecagonal voltage space vector structure eliminate fifth and seventh order harmonics, represented as 6n 1; n = odd harmonics, from the phase voltages and hence from the motor phase currents, throughout the entire modulation range. The first harmonics appearing the phase voltage are the 11th and 13th harmonics. Another advantage is the increased linear modulation range of operation for a given DC-link voltage, because geometrically dodecagon is closer to circle than a hexagon. An octadecagonal structure eliminates the 11th and 13th harmonics as well from the phase voltage output. The harmonics present in the phase voltage are of the order 18n 1; n = 1; 2; 3; :::. Thus the total harmonics distortion (THD) of the phase voltage is further improved. The linear modulation range also gets enhanced compared to hexagonal and dodecagonal structures. Multilevel dodecagonal and octadecagonal space vector structures combines the advantages of both multilevel structure and dodecagonal and octadecagonal structure and hence are very attractive solutions for high performance induction motor drive schemes. Chapter 1 of this thesis introduces the multilevel in-verter topologies generating hexagonal, dodecagonal and octadecagonal voltage space vector structures. Inverter topologies generating multilevel dodecagonal and octadecago-nal voltage space vector structures have been proposed before but using multiple DC sources delivering active power. The presence of more than one DC source in the inverter topology makes the back to back operation (four-quadrant operation) of the drive system difficult. And also the drive system becomes more costly and bulky. This thesis proposes induction motor drive schemes generating multilevel dodecagonal and octadecagonal volt-age space vector structures using a single DC source.
In Chapter 2, an induction motor drive scheme generating a six-concentric multilevel dodecagonal voltage space vector structure using a single DC source is proposed for an open-end winding induction motor. In the topology, two three-level inverters drive an open-end winding IM, one inverter from each side. DC-link of primary inverter is from a DC source (Vdc) which delivers the entire active power, whereas the secondary inverter DC-link is maintained by a capacitor at a voltage of 0:289Vdc, which is self-balanced during the inverter operation. The PWM scheme implemented ensures low switching frequency for primary inverter. Secondary inverter operates at a small DC-link voltage. Hence, switching losses are small for both primary and secondary inverters. An open-loop V/f scheme was used to test the topology and modulation scheme.
In the work proposed in Chapter 3, the topology and modulation scheme used in the first work is modified for a star connected induction motor. Again, the scheme uses only a single DC source and generates a six-concentric multilevel space vector struc-ture. The power circuit topology is realized using a three-level flying capacitor (FC) inverter cascaded with an H-bridge (CHB). The capacitors in the CHB inverter are maintained at a voltage level of 0:1445Vdc. The FC inverter switches between volt-age levels of [Vdc; 0:5Vdc; 0] and the CHB inverter switches between voltage levels of [+01445Vdc; 0; 0:1445Vdc]. The PWM scheme generates a quasi-square waveform output from the FC inverter. This results in very few switchings of the FC inverter in a funda-mental cycle and hence the switching losses are controlled. The CHB inverter switches Ch. 0: at high frequency compared to the FC inverter and cancels the low order harmonics (6n 1; n = odd) generated by the FC inverter. Even though the CHB operates at higher switching frequency, the switchings are at low voltage thereby controlling the losses. The linear modulation range of operation is extended to 48:8Hz for a base frequency of 50Hz. An open-loop V/f scheme was used to test the topology and modulation scheme.
In Chapter 4, a nine-concentric multilevel octadecagonal space vector structure is proposed for the first time, again using a single DC source. The circuit topology remains same as the work in Chapter 3, except that the CHB capacitor voltage is maintained at 0:1895Vdc. The 5th; 7th; 11th and 13th harmonics are eliminated from the phase voltage output. The linear modulation range is enhanced to 49:5Hz for a base speed of 50Hz. An open-loop V/f scheme and rotor field oriented control scheme were used to test the proposed drive system.
All the proposed drive schemes have been extensively simulated and tested in hard-ware. Simulation was performed in MATLAB-SIMULINK environment. For implement-ing the inverter topology, SKM75GB12T4 IGBT modules were used. The control al-gorithms were implemented using a DSP (TI’s TMS320F28334) and an FPGA (Xilinx Spartan XC3S200). A 1kW , 415V , 4-pole induction motor was used for the experiment purpose.
The above mentioned induction motor drive schemes generate phase voltage outputs in which the low order harmonics are absent. The linear modulation range is extended near to the base frequency of operation compared to hexagonal space vector structure. In the inverter topologies, the secondary inverters or the CHB inverters functions as harmonic filters and delivers zero active power. The primary inverter in the topologies switches at low frequency, reducing the power loss. Single DC source requirement brings down the cost of the system as well as permitting easy four-quadrant operation. This is also advantageous in battery operated systems like EV applications. With these features and advantages, the proposed drive schemes are suitable for high performance, medium voltage induction motor drive applications.