Rozprawy doktorskie: „Concentration gradients”

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Zaleski, Christopher John. "Electrochemical concentration gradients in deep eutectic solvents." Thesis, University of Leicester, 2015. http://hdl.handle.net/2381/32232.

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Concentration gradients present in the solution during the redox chemistry of selected metals and conducting polymer (poly(3,4ethylenedioxythiophene) (PEDOT)) films redox cycled in Deep Eutectic Solvents (DES) were observed for the first time through the application of the Probe Beam Deflection (PBD) technique combined with the Electrochemical Quartz Crystal Microbalance (EQCM). Suitability of choline chloride (ChCl) based DES for applications as electrolytes in PEDOT based charge storage devices has also been investigated using EQCM. The combination of carefully optimized experimental parameters (temporally extended chronoamperometry and slow scan rate voltammetry) with modified design of the instrument (reduced probe’s distance of approach) allowed for in-situ observations of electrochemically induced concentration gradients in DES based systems. During the studies of electroactive polymer films, complete determination of mobile species transfers in PEDOT/Ethaline and PEDOT/Propaline systems has been achieved. The application of PBD-EQCM technique in studies of metal electrodeposition from DES allowed for monitoring metal speciation in dynamic and quantitative fashion. EQCM study of ChCl based DES indicated Ethaline as the most promising potential electrolyte for PEDOT based charge storage devices. Additionally, an unusual mass exchange process has been detected in PEDOT/Propaline and PEDOT/Acetaline processes. This work has shown a novel, affordable and non-invasive route for observation of electrode/electrolyte interface processes in DES. The experimental protocol developed can potentially be implemented in further studies of DES as well as Ionic Liquids.

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Gardiner, Allen Brooke. "Measurement of concentration gradients in photoresist films and study of the influence of these gradients on photoresist performance /." Digital version accessible at:, 1999. http://wwwlib.umi.com/cr/utexas/main.

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McQuinn, Chris. "Design of a mechanical device for fabricating protein concentration gradients to study cell adhesion." Thesis, McGill University, 2008. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=18728.

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The binding interaction between specialized proteins within the extracellular matrix (ECM) and specific membrane receptors in cells are pivotal for regulating cell adhesion and migration. Current methods used to generate patterned ECM substrates for the study of migration involve technically complicated devices that are expensive and demand specialized training. Some are also not applicable to the microscopic scale relevant for cells or provide inadequate substrates for growing sensitive cells such as neurons. This Masters thesis introduces an effective method to pattern proteins with micron scale precision at a reasonable financial cost and requires minimal training. The method is based on a device called the squeegee that uses a PDMS (polydimethyl siloxane) barrier to precisely control exposure of protein from solution onto specific areas of a glass surface to regulate adsorption time. The patterns may be produced with a range of proteins on a multitude of glass surfaces. The squeegee method recreated an ECM in the form of graded protein patterns, including continuous gradients and stepped gradients. Mammalian epithelial cells (CHO-K1) were cultured on a surface comprised of a fibronectin stepped gradient and shown to increase in cell spreading with increasing fibronectin surface density. Other proteins were successfully pattered including netrin-1, an important guidance cue in the developing mammalian spinal cord. L'interaction entre les protéines spécialisées qui sont dans la matrice extracellulaire (MEC) et les récepteurs à la limite de la membrane d'un organisme cellulaire est essentielle à la migration des cellules. Les méthodes actuelles pour étudier la migration impliquent l'utilisation d'appareils techniquement complexes, dispendieux et requérant une formation spécifique. De plus, ces méthodes ne sont pas applicables à l'échelle microscopique des organismes cellulaires ou sont inadéquates pour cultiver des cellules spécialisées. Ce mémoire de maîtrise introduit une méthode ayant un faible rapport coût-efficacité pour modeler les protéines avec une précision micrométrique et qui requiert peu de connaissances techniques. Il est possible de produire ces modèles avec une gamme de protéines et sur une multitude de surfaces de verre. La base de cette méthode est un appareil qui est nommé « la racle » qui utilise une barrière de polydimethyl siloxane (PDMS) pour contrôler précisément l'adsorption de protéine d'une solution sur une surface de verre. La méthode qui utilise la racle a permis de recréer des MEC sous forme de gradients de protéines, comprenant aussi bien des pentes continues que des marches d'escalier. Des cellules épithéliales de mammifères (CHO-K1) ont été cultivées sur une surface ayant un gradient de fibronectine en marche d'escalier, les cellules ont montré une augmentation dans leur étalement proportionnelle à la densité de surface de fibronectine.

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Safronov, Grigory. "Formation and disintegration of small-scale concentration gradients of trace metals on aggregate scale." [S.l.] : [s.n.], 2005. http://deposit.ddb.de/cgi-bin/dokserv?idn=974021512.

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Welsche, Mathias Markus [Verfasser], and Roland [Akademischer Betreuer] Zengerle. "Determination of enzyme kinetics in micro concentration gradients = Bestimmung von Enzym-Kinetiken in Mikro-Konzentrationsgradienten." Freiburg : Universität, 2013. http://d-nb.info/1123475792/34.

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Bui, Hanh. "A COMPARISON OF TWO COMMERCIAL STRIPS WITH PREDEFINED ANTIBIOTIC CONCENTRATION GRADIENTS FOR SUSCEPTIBILITY TESTING OF PERIODONTAL BACTERIAL PATHOGENS." Master's thesis, Temple University Libraries, 2013. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/216515.

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Oral Biology M.S. Objectives: Systemic antibiotics are generally recognized as providing a beneficial impact in treatment of both aggressive and chronic periodontitis. Since strains of periodontal pathogens among periodontitis patients may vary in their antibiotic drug resistance, the American Academy of Periodontology recommends antimicrobial susceptibility testing of suspected periodontal pathogens prior to administration of systemic periodontal antibiotic therapy, to reduce the risk of a treatment failure due to pathogen antibiotic resistance. E-test and MIC Test Strip assays are two in vitro antimicrobial susceptibility testing systems employing plastic- and paper-based, respectively, carriers loaded with predefined antibiotic gradients covering 15 two-fold dilutions. To date, no performance evaluations have been carried out comparing the Etest and MIC Test Strip assays in their ability to assess the in vitro antimicrobial susceptibility of periodontal bacterial pathogens. As a result, the purpose of this study was to compare the in vitro performance of E-test and MIC Test Strip assays in assessing minimal inhibitory concentration (MIC) values of four antibiotics frequently utilized in systemic periodontal antibiotic therapy against 11 fresh clinical subgingival isolates of the putative periodontal pathogen, Prevotella intermedia/ nigrescens, and to compare the distribution of P. intermedia/ nigrescens strains identified with interpretative criteria as "susceptible" and "resistant" to each of the four antibiotics using MIC values determined by the two antimicrobial susceptibility testing methods. Methods: Standardized cell suspensions, equivalent to a 2.0 McFarland turbidity standard, were prepared with 11 fresh clinical isolates of P. intermedia/nigrescens, each recovered from the subgingival microbiota of United States chronic periodontitis subjects, and plated onto to the surfaces of culture plates containing enriched Brucella blood agar. After drying, pairs of antibiotic-impregnated, quantitative, gradient diffusion strips from two manufacturers (E-test, bioMérieux, Durham, NC, USA, and MIC Test Strip, Liofilchem s.r.l., Roseto degli Abruzzi, Italy) for amoxicillin, clindamycin, metronidazole, and doxycycline were each placed apart from each other onto the inoculated enriched Brucella blood agar surfaces, so that an antibiotic test strip from each manufacturer was employed per plate against each P. intermedia/ nigrescens clinical isolate for antibiotic susceptibility testing. After 48-72 hours anaerobic jar incubation, individual MIC values for each antibiotic test strip against P. intermedia/nigrescens were read in μg/ml at the point where the edge of the bacterial inhibition ellipse intersected with the antibiotic test strip. MIC50, MIC90, and MIC range were calculated and compared for each of the test antibiotics, with essential agreement (EA) values determined per test antibiotic for the level of outcome agreement between two antimicrobial susceptibility testing methods. In addition, the identification of antibiotic "susceptible" and "resistant" strains among the P. intermedia/nigrescens clinical isolates was determined for each test antibiotic using MIC interpretative criteria from the MIC interpretative standards developed by the European Committee on Antimicrobial Susceptibility Testing (EUCAST) for gram-negative anaerobic bacteria for amoxicillin, clindamycin, and metronidazole findings, and from the French Society of Microbiology breakpoint values for anaerobic disk diffusion testing for doxycycline data. Results: For amoxicillin, higher MIC50 and MIC90 values against the P. intermedia/ nigrescens strains were found with the MIC Test Strip assay than with E-test strips, resulting in a relatively low EA value of 45.5% between the two susceptibility testing methods. A higher percentage of amoxicillin "resistant" P. intermedia/nigrescens strains (72.7%) were identified by MIC Test Strips as compared to E-test strips (54.5%), although both methods found the same proportion of amoxicillin "susceptible" strains (27.3%). For clindamycin, both susceptibility testing methods provided identical MIC values (EA value = 100%), and exactly the same distributions of "susceptible" and "resistant" strains of P. intermedia/nigrescens. For metronidazole, only very poor agreement (EA value = 9.1%) was found between the two susceptibility testing methods, with MIC Test Strips exhibiting markedly higher MIC50 and MIC90 values against P. intermedia/nigrescens as compared to E-test strips. However, the distribution of "susceptible" and "resistant" P. intermedia/ nigrescens were identical between the two susceptibility testing methods. For doxycycline, relatively good agreement (EA value = 72.7%) was found in MIC concentrations between the two susceptibility testing methods, although generally lower MIC values were associated with MIC Test Strips. In addition, identical distributions of "susceptible" and "resistant" P. intermedia/nigrescens were provided by both susceptibility testing methods. Conclusions: Relative to MIC values measured against periodontal strains of P. intermedia/nigrescens, MIC Test Strips gave higher MIC values with amoxicillin and metronidazole, equal MIC values with clindamycin, and lower MIC values with doxycycline, as compared to MIC values measured with the E-test assay. Relative to the identification of antibiotic "susceptible" periodontal P. intermedia/ nigrescens strains, both susceptibility testing methods provided identical findings, suggesting that both methods appear to be interchangeable for clinical decision making in regard to identification of antibiotic-sensitive strains of periodontal P. intermedia/nigrescens. However, for epidemiologic surveillance of drug susceptibility trends, where exact MIC values are important to track over time, the relatively higher proportion of non-exact MIC differences between the two susceptibility testing methods argues against using them interchangeably. Instead, one or the other method should be used consistently for such studies. Further comparative studies of the E-test and MIC Test Strip assays are indicated using other periodontopathic bacterial species besides P. intermedia/ nigrescens, and to assess the reproducibility of MIC values provided by both in vitro susceptibility testing methods over time. Temple University--Theses

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Huraux, Karine. "Morphologies et gradients de concentration induits par le séchage dans des solutions polymères et des gels." Paris 6, 2008. http://www.theses.fr/2008PA066457.

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Cette thèse présente l’étude de morphologies de surface induites, à la surface de films polymères et de gels, par le séchage. La première partie porte sur la séparation de phases induite par évaporation du solvant dans des films réalisés à partir d’un mélange de deux polymères immiscibles, l’un vitreux, l’autre cristallin à température ambiante, en solvant commun. La morphologie obtenue dépend des conditions de séchage et des propriétés physicochimiques du système. Nous avons mis en évidence, en fonction de la composition du mélange, une inversion de morphologie. L’étude d’une composition donnée permet de distinguer, en fonction de la vitesse de séchage, différents régimes. La seconde partie traite de la formation, à la surface de gels chimiques de polyalcool vinylique, d’instabilités de plissement dépendant des conditions de séchage et de synthèse. Cette morphologie est attribuée à la formation d’une peau vitreuse qui subit, lors de la contraction du gel, une force de compression relaxée par la formation de plis. Nos travaux confirment expérimentalement l’existence de cette peau vitreuse (microscopie à force atomique) et estiment son épaisseur par simulation.

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Kozawa, Kathleen Hiromi. "Investigation of pollution concentrations and pollution concentration gradients in communities adjacent to the ports of Los Angeles and Long Beach using a mobile monitoring platform." Diss., Restricted to subscribing institutions, 2009. http://proquest.umi.com/pqdweb?did=1723112471&sid=1&Fmt=2&clientId=1564&RQT=309&VName=PQD.

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Meierdierks, Jana [Verfasser], and Peter [Akademischer Betreuer] Grathwohl. "Soil-Atmosphere Exchange of PAHs : The Determination of Concentration Gradients with Passive Samplers / Jana Meierdierks ; Betreuer: Peter Grathwohl." Tübingen : Universitätsbibliothek Tübingen, 2019. http://d-nb.info/1205002448/34.

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Anthony, James Lee. "The influence of turbulence, temperature, and nutrient concentration gradients on sediment-water exchanges of nitrogen and phosphorus in lakes." Connect to online resource, 2007. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3284439.

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Abadie, Thomas. "Détection électrochimique de gradients de concentration ou de gouttes générés à l'intérieur d'un canal microfluidique : approche théorique et expérimentale." Thesis, Paris 6, 2016. http://www.theses.fr/2016PA066643/document.

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L'électrochimie permet la mise en œuvre de techniques de détections pertinentes et adaptées aux contraintes de miniaturisation imposées par la conception de laboratoires sur puce. L'objectif de la thèse a été d'étudier la détection d'espèces électroactives circulant à l'intérieur d'un canal microfluidique, sous la forme de gradients de concentration localisés, ou d'espèces contenues à l'intérieur de gouttes. Pour cela, deux approches ont été menées au moyen d'électrodes microbandes intégrées dans des microcanaux. La première a été d'étudier la possibilité de générer puis de détecter électrochimiquement de façon contrôlée des gradients de concentration en écoulement monophasique. Les réponses ampérométriques ont été analysées en fonction des caractéristiques des gradients de concentration après les phases de génération et de propagation. Deux comportements limites ont été mis en évidence par simulations numériques puis vérifiés expérimentalement. La seconde approche a été de mettre en œuvre une détection électrochimique du contenu de gouttes en écoulement diphasique. L'enjeu a été à la fois de démontrer la faisabilité des mesures mais aussi d'établir des relations entre les courants mesurés et les concentrations ou quantités d'espèces à l'intérieur des gouttes. Dans ce cadre, un microdispositif innovant a été proposé puis testé expérimentalement, démontrant la possibilité d'effectuer des électrolyses totales de gouttes Electrochemistry enables the implementation of relevant and appropriate detection techniques to the miniaturization constraints imposed by the design of labs-on-a-chip. The aim of this thesis was to study the detection of electroactive species flowing within microfluidic channels under the form of concentration gradients or microdroplets. Therefore, two approaches were undertaken by means of microband electrodes integrated within microchannels. The first one was to study the opportunity to control the electrochemical generation and detection of concentration gradients in continuous flow. The amperometric responses were analyzed as a function of the characteristics of concentration gradients after the generation and propagation processes. Two boundary behaviours were evidenced by numerical simulations and validated experimentally. The second approach was to implement the electrochemical detection of droplet content in segmented flow. The challenge was both to demonstrate the feasibility of the experiments and to introduce relationships between currents and concentration or amount of species inside droplets. In this context, an innovative microdevice was designed and tested experimentally allowing the total electrolysis of the droplets

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Soulié, Virginie. "Sessile Droplets of Salt Solutions on Inert and Metallic Surfaces : Influence of Salt Concentration Gradients on Evaporation and Corrosion Behaviour." Thesis, Montpellier, 2015. http://www.theses.fr/2015MONTS129/document.

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Dans cette thèse, la dynamique d'évaporation de gouttes sessiles de solutions salines sur des surfaces planes inertes et métalliques a été étudiée et le phénomène de corrosion pour les surfaces ferriques caractérisé. En premier lieu, nous nous sommes intéressés à la dynamique d'évaporation de gouttes sessiles salées sur des surfaces inertes pour une large gamme de concentrations en sel, d'humidité relatives, de tailles de goutte et d'angles de contact. Notre étude révèle les domaines de validité du modèle classique d'évaporation, processus contrôlé par la diffusion de la vapeur dans l'air et met en évidence l'impact de flux (de Marangoni) induits par des gradients de concentration (tension de surface) en sel sur la dynamique d'évaporation et les dépôts salins obtenus après évaporation de la goutte. De plus, nous nous sommes consacrés à l'évolution spatio-temporelle de gouttes sessiles de solutions salines sur des surfaces métalliques. Contrairement au modèle simplifié de la goutte d'Evans, nous avons montré que le processus de corrosion s'étend aux abords de la ligne de contact, avec la formation d'un film périphérique. La ligne triple est déstabilisée par des gradients de tension de surface induits par des variations de composition ionique au cours du processus de corrosion et la migration des cations vers la périphérie de la goutte. Enfin nous avons étudié le phénomène de corrosion du métal induit par l'évaporation de gouttes sessiles salées. Le processus de corrosion, en particulier la localisation des réactions anodiques et cathodiques sur la surface métallique en contact avec la goutte est corrélée à la distribution spatiale du sel au sein de la goutte s'évaporant In this thesis we investigate the evaporation behaviour of sessile droplets of aqueous saline solutions on planar inert and metallic surfaces and characterise the corrosion phenomenon for iron surfaces. First we study the evaporation behaviour of sessile salty droplets on inert surfaces for a wide range of salt concentrations, relative humidities, droplet sizes and contact angles. Our study reveals the range of validity of the well-accepted diffusion-controlled evaporation model and highlights the impact of salt concentration (surface tension) gradients driven Marangoni flows on the evaporation behaviour and the subsequent salt deposit patterns. Furthermore we study the spatial-temporal evolution of sessile droplets from saline solutions on metallic surfaces. In contrast to the simple, generally accepted Evans droplet model, we show that the corrosion spreads ahead of the macroscopic contact line with a peripheral film. The three-phase contact line is destabilized by surface tension gradients induced by ionic composition change during the course of the corrosion process and migrations of cations towards the droplet perimeter. Finally we investigate the corrosion behaviour under drying salty sessile droplets on metallic surfaces. The corrosion process, in particular the location of anodic and cathodic activities over the footprint droplet area is correlated to the spatial distribution of the salt inside the drying droplet

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Perrodin, Pierre. "Intégration d'électrodes dans les canaux microfluidiques : génération et détection d'espèces résolues spatialement et temporellement." Thesis, Paris 6, 2014. http://www.theses.fr/2014PA066238/document.

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L’objectif de cette thèse a été d’étudier, en présence d’un écoulement laminaire, la génération et la détection électrochimiques de gradients locaux de concentration à l’intérieur de canaux microfluidiques. L’influence des paramètres géométriques et hydrodynamiques sur les réponses ampérométriques de microélectrodes a été analysée théoriquement par simulation numérique. Pour cela, plusieurs approches ont été entreprises par le biais de modèles à deux et à trois dimensions afin de résoudre l’équation du transport pour différentes géométries de dispositifs et conditions d’écoulement. Des critères ont été fixés afin de délimiter les régimes et conditions optimales de fonctionnement. Les prévisions issues des calculs ont été testées puis validées à l’aide de mesures expérimentales effectuées à partir de microdispositifs fabriqués au laboratoire. Ainsi, deux concepts innovants ont été définis pour la mise en œuvre au sein de microdispositifs de fonctions combinant microfluidique et électrochimie. Le premier est celui d’une sonde de concentration à très haute résolution temporelle. Le second est la génération d’un gradient linéaire de concentration sur la section d’un canal microfluidique rectangulaire The aim of this thesis was to study the electrochemical generation and electrochemical detection of local concentration gradients within microfluidic channels in presence of a laminar flow. The influence of geometric and hydrodynamic parameters on the amperometric responses of microelectrodes was analyzed theoretically by means of numerical simulations. Several approaches were undertaken using two-dimensional and three-dimensional models in order to solve the transport equation according to the device geometries and flow conditions. Criteria were set to delineate the operating regimes and optimal conditions. Predictions from calculations were tested and validated experimentally using microdevices fabricated in the laboratory. Therefore, two innovative concepts were defined for the implementation of functions within microdevices combining microfluidics and electrochemistry. The first one is a probe of concentration leading to very high temporal resolution. The second one is the generation of a linear concentration gradient over the cross section of a rectangular microfluidic channel

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Pajot, Ségolène. "Synthèse et caractérisation d’oxydes lamellaires riches en lithium et en manganèse obtenus sous la forme de gradients de concentration pour les batteries Li-ion." Thesis, Bordeaux, 2016. http://www.theses.fr/2016BORD0277/document.

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Ce travail présente la mise en oeuvre d’un protocole de synthèse de gradients deconcentration dans les oxydes lamellaires riches en Li et en Mn. Le but a été dedévelopper la formation d’oxydes lamellaires riches en Li et Mn au coeur des agrégatssphériques du matériau actif et, en se rapprochant de la surface, d’enrichir lacomposition de l’oxyde lamellaire en Co et en Ni, afin de combiner une forte densitéd’énergie (apportée par le coeur du gradient) et une excellente stabilité thermique etstructurale (apportée par la surface du gradient). La synthèse a été réalisée en deuxétapes, une co-précipitation pour former un carbonate de métaux de transition suivied’une calcination à haute température pour obtenir le matériau actif lithié. L’influencede différents paramètres (pH, débit d’injection, taille du réacteur, composition, …) surla nature du carbonate à gradient de concentration ainsi formé a été étudiée. De lamême façon, le contrôle du ratio Li/M (ici M = Ni, Co, Mn), de la température et de ladurée de calcination s’est révélé important pour parvenir à maintenir le gradient deconcentration dans le matériau lithié. Le ratio Li/M est également déterminant pourcontrôler la nature des matériaux obtenus (lamellaire - spinelle ou lamellaire –lamellaire). Des caractérisations extrêmement pointues, et complexes à mettre enoeuvre, ont été menées afin d’obtenir des informations pertinentes sur la distributiondes phases au sein des agrégats (composition et structure), de la surface au coeur dugradient : différentes techniques de microscopie (EPMA, MEB-EDX et FIB-STEM) ontainsi été largement utilisées. Les matériaux les plus intéressants ont été étudiés enbatteries Lithium-ion avec une électrode de graphite à la négative, les performancesélectrochimiques et la stabilité thermique à l’état chargé de la batterie sont largementdiscutées par rapport à l’état de l’art et notamment au matériau de coeur riche en Li eten Mn This work describes in details the implementation of the synthesis protocol for theformation of Li- and Mn-rich layered oxides with concentration-gradients. The purposewas to develop the synthesis of Li- and Mn-rich layered oxides in the bulk of sphericalaggregates of active material and, moving to the surface, to enrich the layered oxides’composition with Co and Ni, in order to combine a high energy density (provided bythe bulk) and an excellent thermal and structural stability (provided by the surface).The synthesis was performed in two steps, a coprecipitation to form a transition metalcarbonate followed by a calcination at high temperature to obtain the lithiated activematerial. The influence of several parameters (pH, feeding rate, size of the reactor,composition …) on the nature of the carbonates formed with concentration-gradientswas studied. Similarly, the control of the Li/M ratio (with M = Ni, Co, Mn) and of thetemperature and duration of calcination was revealed to be important to maintain theconcentration-gradient in the lithiated materials. The Li/M ratio is also the keyparameter to control the nature of the materials obtained (layered - spinel or layered -layered). Advanced characterizations, complex to be implemented, were performed inorder to obtain in-depth information on the distribution of phases within the aggregates(composition and structure), from the bulk to the surface: complementary microscopytechniques (EPMA, SEM-EDS and FIB-STEM) were widely used. The most interestingmaterials were studied in Lithium-ion batteries with graphite at the negative electrode,their electrochemical performance and the thermal stability in the charged state of thebattery were compared to the state of art, and particularly to the bulk Li and Mn-richlayered oxide

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Böck, Lorenz [Verfasser], Thomas [Akademischer Betreuer] Sattelmayer, and Dag [Akademischer Betreuer] Bjerketvedt. "Deflagration-to-Detonation Transition and Detonation Propagation in H2-Air Mixtures with Transverse Concentration Gradients / Lorenz Böck. Gutachter: Dag Bjerketvedt ; Thomas Sattelmayer. Betreuer: Thomas Sattelmayer." München : Universitätsbibliothek der TU München, 2015. http://d-nb.info/1075317266/34.

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Bouchaudy, Anne. "Séchage microfluidique de fluides complexes : champs de concentration, diffusion collective et mesure in situ de contraintes." Thesis, Bordeaux, 2018. http://www.theses.fr/2018BORD0192/document.

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Etudier le séchage est un moyen original de caractériser les propriétés de fluides complexes. Cette technique permet de concentrer continûment des fluides : d'un état dilué à un état sec. A l'échelle microfluidique, la manipulation, les observations et les processus qui entrent en jeu sont simplifiés. Ce travail de thèse s'attache à décrire le séchage de ces fluides et plus particulièrement le cas de dispersions colloïdales. Ces travaux présentent deux méthodes pour étudier l'extraction du solvant d'un fluide à l'échelle microfluidique : la micropervaporation et la goutte confinée. Ces techniques ont notamment permis de réaliser des estimations précises de coefficients de diffusion collective sur toute la gamme de concentrations pour un mélange eau/glycérol et pour une dispersion colloïdale de nanoparticules de silice chargées. Par ailleurs, le séchage induit des contraintes mécaniques conséquentes. Ces contraintes peuvent générer des déformations importantes, des phénomènes de délamination ou de fracturation du matériau solidifié. Une méthode originale de mesure in situ de contraintes a été mise en place pendant ces travaux. Les mesures réalisées avec une dispersion colloïdale modèle permettent de mettre en évidence expérimentalement l'apparition de contraintes mécaniques au moment de la transition sol/gel de la dispersion. L'augmentation de la contrainte est ensuite associée au séchage d'un gel poroélastique Drying complex fluids is an original technique to study their properties. Solvent extraction enables the continuous concentration of fluids from a dilute to a solid state. The use of the microfluidic scale allows one to limit side effects and simplify experiments, observations and modeling. This project mainly describes the drying of colloidal dispersions in two confined geometries: microfluidic channels and confined droplets between two plates. With these two techniques, we estimate collective diffusion for a water/glycerol mixture and a model dispersion of charged silica nanoparticles over the whole concentration range. Moreover, the drying of complex fluids often induces mechanical stresses which are the root for deformation, delamination phenomena and cracks. We developed an original technique to measure these stresses in situ. For a model colloidal dispersion, we evidenced experimentally that these forces arise from a liquid to solid state transition. The increase of these stresses is then associated with the drying of a poroelastic gel

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Diaz, Emilie. "Propagation d'ondes, instabilité absolues et convectives d'un écoulement dans un milieu poreux saturé en présence de gradients de température et de concentration et d'un écoulement moyen horizontal." Strasbourg, 2011. http://www.theses.fr/2011STRA6136.

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La convection thermosolutale, due, à la fois, à des gradients de température et de concentration, a de nombreuses applications en milieu naturel et dans le domaine industriel comme la dispersion d'un contaminant dans une nappe phréatique et la dynamique des fluides d'un réservoir géothermique. En utilisant les méthodes de la théorie linéaire bi et tridimensionelle des instabilités absolues et convectives, la nature de l'instabilité est étudiée à l'apparition de la convection dans un modèle de convection dans une couche de milieu poreux saturé horizontale en présence de gradients de concentration et de température et d'un écoulement moyen. Tout d'abord, les modes normaux sont analysés et les valeurs critiques du nombre de Rayleigh thermique verticale, Rv, le nombre d'onde vectorielle, (k, l) et la fréquence, ω, sont obtenus pour un ensemble de valeurs des nombres de Rayleigh thermique et solutal horizontaux, du nombre de Rayleigh solutal vertical et le nombre de Péclet horizontal. Dans les calculs, la méthode de colocation pseudo-spectrale de Chebyshev ayant une haute précision est utilisée. Ensuite, une dichotomie entre l'instabilité absolue et l'instabilité convective à l'émergence de la convection tridimensionnelle dans un ensemble d'état de base donnée par les solutions analytiques exactes des équations d'états du mouvement du modèle est mise en évidence. De plus, nous traitons des cas pour lesquels l'émergence de la convection a le caractère d'instabilité convective. Nous déterminons la valeur de Rv à laquelle la transition de la convection à l'instabilité absolue a lieu et calculons les caractéristiques physiques du paquet d'ondes émergeant absolument instable Thermosolutale convection, due both to temperature and concentration gradients, has many applications in nature and industry. This phenomenon plays a role in the dispersion of a contaminant in ground water and the fluid dynamics of a geothermal reservoir. By using the methods of the theory of two- and three-dimensional linear absolute and convective instabilities, we examine the nature of the instability at the onset of convection in a model of convection in an extended horizontal layer of a saturated porous medium with either horizontal or vertical salinity and inclined temperature gradients, and horizontal throughflow. First, normal modes are analysed and the critical values of the vertical thermal Rayleigh number, Rv, wavenumber vector, (k, l) and frequency, ω, are obtained for a variety of values of the horizontal thermal and salinity Rayleigh numbers, Rh and Sh, respectively, the vertical salinity Rayleigh number Sv and the horizontal Péclet number, Qh. In the computations, a high precision pseudo-spectral Chebyshev-collocation method is used. Then, it is revealed that there exists an absolute/convective instability dichotomy at the onset of three-dimensional convection in a set of the base states given by exact analytic solutions of the equations of motion in the model. Further, we treat the parameter cases in which the onset of convection has the character of convective instability and occurs through longitudinal modes. We determine the value Rvt of Rv at which the transition from convective to absolute instability takes place and compute the physical characteristics of the emerging absolutely unstable wavepacket

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Soulié, Virginie [Verfasser], and Helmuth [Akademischer Betreuer] Moehwald. "Sessile droplets of salt solutions on inert and metallic surfaces : influence of salt concentration gradients on evaporation and corrosion behaviour / Virginie Soulié ; Betreuer: Helmuth Moehwald ; Université de Montpellier." Potsdam : Universität Potsdam, 2015. http://d-nb.info/1218400641/34.

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Merz, Clifford Ronald. "Investigation and evaluation of a bi-polar membrane based seawater concentration cell and its suitability as a low power energy source for energy harvesting/MEMS devices." [Tampa, Fla] : University of South Florida, 2008. http://purl.fcla.edu/usf/dc/et/SFE0002671.

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Kurt, Nilufer, and nilf_k@yahoo com au. "A Study of Channelling Behaviour in Batch Sedimentation." RMIT University. School of Civil and Chemical Engineering, 2006. http://adt.lib.rmit.edu.au/adt/public/adt-VIT20061220.120258.

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Batch sedimentation is a method that enables us to understand the mechanism of compaction and compression of sedimenting slurry. However, batch settling behaviour is a very complex phenomenon that is not easily described fully by a mathematical model. This causes unrealistically large empirical calculations when the thickener size estimations are required. Channelling, reverse concentration gradients and the initial concentration of the slurry have large effects on batch settling. Existing procedures do not provide clear relationships involving these three significant variables. In this study, batch sedimentation phenomena are examined in detail and possible explanations are given to clarify the complex behaviour using recent theories. Modern research has shown that channelling is an unwanted formation because channels can change the concentration at the bottom and top of the bed by carrying a great amount of flocs upwards. Batch sedimentation tests were performed using flocculated slurry of Calcium Carbonate at various initial concentrations such as 250 g/l, 500 g/l, 750 g/l and 1000 g/l to observe channelling and reverse concentration gradients. Flux plots for the batch system reveal behaviour which can be attributed to the upward flow of solids. In addition, photographic methods were used to observe settling processes, channelling mechanisms and flocs in the channels. One of the purposes of this work was to examine the phenomenological solid-liquid separation theory of Buscall and White (1987), which employs the material properties of the local volume fraction, compressive yield stress Py ()ö and hindered settling function R()ö to identify the material behaviour in batch sedimentation. Stepped-pressure filtration and batch settling tests were used to measure the material characteristics for the flocculated CaCO3 suspension. Experimental data were demonstrated using Height versus Time and Height versus Concentration graphs and displayed the possible region of reverse concentration gradients and channelling in the settling bed. Mathematical predictions adopted from Usher (2002) were performed employing material characteristics of the material and graphical documentations were presented. The results of mathematical predictions were compared to the experimental results and the modes of sedimentation explained by Lester et al. (2005). Fundamental theoretical models and experimental observations highlight that the main driving force for channelling is the high-pressure gradient at the bottom of the bed and the most important factors that cause channelling are high initial concentration of slurry and settling time. The predictions also show that the material and flocculant used for the batch settling tests demonstrate important effect on the settling process. The knowledge and information gained from this study is valuable to maximize the thickening process.

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Wang, Aifang. "Relevés de concentrations au voisinage des microélectrodes : étude du transport de masse en régime stationnaire et régime dynamique : élaboration de microélectrodes modifiées par des enzymes." Paris 6, 2008. http://www.theses.fr/2008PA066260.

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Fondées sur un modèle précédemment développé au laboratoire tenant compte des effets de la diffusion et de la convection spontanée sur le transport de masse d’espèces électroactives, des études plus approfondies ont été réalisées afin de mieux comprendre les contributions de chaque mode: diffusion linéaire, diffusion de type hémisphérique, migration, convection spontanée et convection induite par les gradients de densité. Le relevé de profils de concentration au voisinage d’électrodes a été employé au cours d’expériences en électrochimie en régime stationnaire et en regime dynamique. A cette fin, des détections spatiales, hautement résolues, ont été réalisées par ampérométrie en utilisant des ultramicroelectrodes en tant que sondes locales de concentration. Les résultats expérimentaux s’avèrent en bon accord avec les prévisions théoriques issues du modèle lorsqu’il y a notamment influence de la convection spontanée. Les limites de ce modèle ont été aussi établies dans le cas où la convection est induite localement par des gradients de densité. Ce travail ouvre la perspective de cartographier des profils de concentration au voisinage d’électrodes modifiées par des enzymes. Nous présentons ici notre contribution quant à l’élaboration de microélectrodes modifiées par de la glucose oxydase Based on a model previously developed in the laboratory accounting for the influences of diffusion and spontaneous convection on the mass transport of electroactive species, further studies were performed to better understand the contributions of each mode: linear diffusion, hemispherical diffusion, migration, spontaneous convection and convection induced by density gradients. The mapping of concentration profiles in the vicinity of electrodes was realized during electrochemical experiments in steady state and dynamic regimes. Detections with highly spatial resolution were perfomed by amperometry using ultramicroelectrodes as probes of concentration. Experimental results were found in good agreement with the theoretical predictions of the model in particulary when spontaneous convection takes place. The limits of this model were also establihed in case of convection induced locally by density gradients. This work gives the possibility to map concentration profiles above enzyme-modified electrodes. We present here our preliminary contribution about the elaboration of microelectrodes modified by glucose oxidase

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Wilson, Raymond Gary. "A Numerical Analysis of the Influence of Korteweg Stresses on the Flow and Mixing of Miscible Fluids." Cleveland, Ohio : Case Western Reserve University, 2004. http://rave.ohiolink.edu/etdc/view?acc_num=case1081283678.

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Thesis (Ph.D.)--Case Western Reserve University, 2004 Title from PDF (viewed on 01 October 2009) Department of Mechanical Engineering Includes abstract Includes bibliographical references Available online via the OhioLINK ETD Center

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Oliveira, Aline Furtado 1989. "Desenvolvimento de sistema microfluídico baseado em gradiente de concentração difusivo para bioprocessos = Development of microfluidic system based on diffusive concentration gradient for bioprocess." [s.n.], 2014. http://repositorio.unicamp.br/jspui/handle/REPOSIP/266097.

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Orientadores: Lucimara Gaziola de La Torre, Reinaldo Gaspar Bastos Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química Made available in DSpace on 2018-08-25T04:50:36Z (GMT). No. of bitstreams: 1 Oliveira_AlineFurtado_M.pdf: 2165174 bytes, checksum: d3aa7acdee3edc7f222daf3f7a82f910 (MD5) Previous issue date: 2014 Resumo: A microfluídica é uma ciência que opera em pequenos volumes de fluídos dentro de canais em dimensões de micrômetros (10-6 m). Estes sistemas permitem controlar moléculas no espaço e no tempo, gerando resultados rápidos e confiáveis num sistema precisamente controlado e capaz de mimetizar ambientes celulares. Os dispositivos microfluídicos apresentam uma diversidade de geometrias aplicáveis para diversas áreas de pesquisas, sendo que a capacidade de formar gradientes permite avaliar as condições e o desempenho celular microbiano. Assim, este trabalho teve como objetivo desenvolver dispositivos microfluídicos capazes de formar gradiente de concentração difusivo e investigar sua aplicabilidade em bioprocessos. Diante disso, foram propostos três modelos de dispositivos usando materiais biocompatíveis: (i) dispositivo em base de vidro, denominado de Vidro-vidro; (ii) em base de vidro e poli dimetilsiloxano (PDMS), chamado de Vidro-PDMS e (iii) vidro e PDMS modificado quimicamente para tornar a superfície hidrofílica, Vidro-mPDMS. Os três dispositivos foram avaliados quanto à capacidade de formação de gradiente de concentração difusivo, os quais apresentaram um perfil linear. Além disso, validou-se o estudo do comportamento de Saccharomyces cerevisiae ATCC 7754 num gradiente de concentração de glicose de 0 a 40 g/L de glicose, sendo usado o dispositivo vidro-vidro. Foi observado que houve crescimento de células ao longo das câmaras microfluídicas, e isso possibilitou na determinação de parâmetros cinéticos, os quais não apresentaram diferença estatisticamente significativa com o cultivo em batelada convencional. As condições da microfluídica possibilitaram também a determinação da cinética de Monod, usando menores intervalos de gradiente. Portanto, este dispositivo microfluídico mostrou-se uma ferramenta com potencial para investigar comportamento celular frente à diferença de concentração e contribuirá para a otimização de bioprocessos através da determinação de parâmetros cinéticos Abstract: Microfluidic is a science that operates in small amounts of fluids inside channels in dimensions of micrometers (10-6 m). These systems allow the precise control of molecules in space and time, generating fast and reliable results and it can also be used to mimics environment cellular . Microfluidic devices can be produced in diversity of geometries, it can be applied in several scientific areas and especially the formation of concentration gradients can be used to evaluate conditions and performance of microbial cell. Therefore, this work had the objective to develop microfluidic devices that are able to generate diffusive concentration gradients and investigate their applicability in bioprocesses. In this context, we propose three models of microfluidics devices using biocompatible materials: (i) Glass-based device, named glass-glass; (ii) glass and poli dimetilsiloxane (PDMS) based device, Glass-PDMS and (iii) glass and chemically modified PDMS (hydrophilic surface), Glass-mPDMS. The three devices were evaluated by their capacity of generating difusive concentration gradient, demonstrating linear concentration profile. Furthermore, the behavior of Saccharomyces cerevisiae ATCC 7754 inside of glucose concentration gradient ranging from 0 to 40 g/L were validated, using the glass-glass device . It was observed that cell growth along the microfluidic chambers, having determined the kinetic parameters, which was considered statistically similar to conventional batch cultivation. Conditions of microfluidics also allowed determination of the Monod kinetic, using smaller intervals gradient Therefore, the use of concentration gradient in microfluidic device is a potential tool for investigate of microbial cell behavior against the concentration difference and it can contribute to the optimization of bioprocesses through the determination of kinetic parameters Mestrado Desenvolvimento de Processos Biotecnologicos Mestra em Engenharia Química

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Shahnaz, Sabina. "Gas flux estimation from surface gas concentrations." Thesis, Georgia Institute of Technology, 2016. http://hdl.handle.net/1853/55073.

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A gradient-independent model of gas fluxes was formulated and tested. The model is built on the relationship between gas flux and the time history of surface gas concentration, known as half-order derivative (HOD), when the transport of the gas in the boundary layer is described by a diffusion equation. The eddy-diffusivity of gas is parameterized based on the similarity theory of boundary layer turbulence combined with the MEP model of surface heat fluxes. Test of the new model using in-situ data of CO2 concentration and fluxes at several locations with diverse vegetation cover, geographic and climatic conditions confirms its usefulness and potential for monitoring and modeling greenhouse gases. The proposed model may also be used for estimating other GHGS fluxes such as methane (CH4) and Water vapor flux. This proof-of-concept study justifies the proposed model as a practical solution for monitoring and modeling global GHGS budget over remote areas and oceans where ground observations of GHGS fluxes are limited or non-existent. One focus of the on-going research is to investigate its application to producing regional and global distributions of carbon fluxes for identifying sinks and sources of carbon and re-evaluating the regional and global carbon budget at monthly and annual time scales.

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Guélon, Florent. "Déflagration de nuages H2/O2 présentant un gradient de concentration." Orléans, 2003. http://www.theses.fr/2003ORLE2055.

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Pour une meilleure approche de la sécurité industrielle, il est devenu indispensable aujourd'hui de comprendre et maîtriser les explosions de nuages gazeux non-uniformes. Dans ce contexte, sont menées une étude expérimentale et numérique (code FLUENT) de la déflagration d'un nuage H2/ O2 se dispersant dans l'air ambiant. L'analyse expérimentale a permis de : - caractériser les profils de pression générés par l'explosion, - rechercher les limites d'inflammabilité du nuage, - mesurer les vitesses de flamme. Deux points importants vis-à-vis de la sécurité industrielle ressortent de cette étude. - Un nuage diffusant dans l'atmosphère peut être initié en tout point, tant que celui-ci se trouve dans le domaine d'inflammabilité. - Si dans un milieu gazeux uniforme, la célérité de la flamme est constante, cela n'est plus le cas pour un milieu non-uniforme. En effet, la propagation de la flamme est instationnaire et s'accélère dans la direction où le gradient de réactivité est le plus important.

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Khare, Peeyush. "Vertical Concentration Gradient of Influenza Viruses Resuspended from Floor Dust." Thesis, Virginia Tech, 2014. http://hdl.handle.net/10919/49662.

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Resuspended floor dust constitutes up to sixty percent of the total particulate matter in indoor air. This fraction may also include virus-laden particles that settle on the floor after being emitted by an infected individual. This research focuses on predicting the concentration of influenza A viruses in resuspended dust, generated by people walking in a room, at various heights above the floor. Using a sonic anemometer, we measured the velocity field from floor to ceiling at 10-cm intervals to estimate the magnitude of turbulence generated by walking. The resulting eddy diffusion coefficients varied between 0.06 m2 s-1 and 0.20 m2 s-1 and were maximal at ~0.75-1 m above the floor, approximately the height of the swinging hand. We used these coefficients in an atmospheric transport model to predict virus concentrations as a function of the carrier particle size and height in the room. Results indicate that the concentration of resuspended viruses at 1 m above the floor is about seven times the concentration at 2 m. Thus, shorter people may be exposed to higher concentrations of pathogens in resuspended dust indoors. This study illuminates the possibility that particle resuspension could be a mode of disease transmission. It also emphasizes the importance of considering resuspension of particulate matter when designing ventilation systems and flooring in hospitals and residences. Master of Science

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Tali-Maamar, Nadia. "Modélisation, analyse et commande d'un procédé biotechnologique à gradient spatial de concentration." Toulouse 3, 1994. http://www.theses.fr/1994TOU30031.

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Le procede biotechnologique etudie dans ce memoire est modelise par un systeme d'equations aux derivees partielles non lineaires et non stationnaires. Le modele obtenu est transforme en un systeme d'equations differentielles ordinaires par la methode de collocation orthogonale pour fins de stimulation numerique, d'analyse et, partiellement de synthese de regulateurs. Une etude d'observabilite du systeme en fonction du nombre et de la position des capteurs est exposee. Des algorithmes d'estimation et de commande sont mis en uvre en faisant appel a des techniques non lineaires de type adaptatif exploitant la structure distribuee et non lineaire inherente au modele du bioreacteur a lit fixe etudie. Les differents algorithmes developpes ont ete etudies d'un point de vue theorique puis mis au point en simulation

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Morais, Dayana Campanelli de. "Síntese, processamento e caracterização de vitrocerâmicas com gradiente funcional." Universidade Estadual Paulista (UNESP), 2017. http://hdl.handle.net/11449/152407.

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Submitted by DAYANA CAMPANELLI DE MORAIS null (dayanacampanelli@gmail.com) on 2017-12-22T03:50:36Z No. of bitstreams: 1 para impressão final.pdf: 3931660 bytes, checksum: d52b37974d258d1d9c1647f7cca67f54 (MD5) Approved for entry into archive by Silvana Alvarez null (silvana@ict.unesp.br) on 2018-01-04T18:53:29Z (GMT) No. of bitstreams: 1 morais_dc_me_sjc.pdf: 3931660 bytes, checksum: d52b37974d258d1d9c1647f7cca67f54 (MD5) Made available in DSpace on 2018-01-04T18:53:29Z (GMT). No. of bitstreams: 1 morais_dc_me_sjc.pdf: 3931660 bytes, checksum: d52b37974d258d1d9c1647f7cca67f54 (MD5) Previous issue date: 2017-11-24 Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) O presente estudo teve como objetivo desenvolver vitrocerâmicas de dissilicato de lítio com gradiente funcional de densidade, inspirado no gradiente natural que existe entre o esmalte e a dentina. Primeiramente o vidro de composição: 33,33% mol de Li2O e 66,67% mol de SiO2 foi obtido pelo método fusão/resfriamento. Em seguida foram preparadas amostras com estruturas homogêneas do vidro a base de dissilicato de lítio para determinação dos melhores parâmetros de sinterização. Três diferentes tratamentos térmicos, determinados com base no resultado da análise diferencial de calorimetria foram utilizados: 850 °C/3h; 900 °C/3h e 950 °C/3h. A caracterização desses materiais foi realizada através da difração de raios X, microscopia eletrônica de varredura, método de Arquimedes e ensaio de flexão biaxial (n=10). O tratamento térmico de 950 oC obteve os melhores resultados, sendo o escolhido para a realização das próximas etapas do estudo. Com a finalidade de otimizar a estética, foi adicionada cerâmica feldspática (VITAVM®9) ao vidro SiO2-Li2O na proporção de 10%, 15% e 20% (n=30). Foi observado que a adição de 10% de VM9 não alterou a resistência do material, e quanto maior a quantidade de VM9, maior foi a translucidez e menor foram o módulo elástico e a densidade. Com isso, foram preparadas vitrocerâmicas bioinspiradas com gradiente funcional de densidade nas seguintes sequências de camadas: uma com 10% de VM9, outra com 15% e a última com 20%. Não houve diferença na resistência à flexão biaxial do grupo com gradiente, quando a camada mais densa estava voltada para o lado de tração, com o grupo com 15% de VM9 com estrutura homogênea. A translucidez do grupo com gradiente foi equivalente ao grupo homogêneo mais translúcido, com 20% de VM9. Concluiu-se que foi possível sintetizar uma vitrocerâmica de dissilicato de lítio funcionalmente graduada, onde uma boa resistência mecânica e uma boa translucidez foram unidas.

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Motta, Cecilia Margarida Mendes. "Effect of surface functional groups on chondrocyte behavior using molecular gradients." University of Akron / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=akron1460392374.

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Kaur, Manpreet. "Dual Spin-Cast Thermally Interdiffused Polymeric Photovoltaic Devices." Diss., Virginia Tech, 2011. http://hdl.handle.net/10919/77159.

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An in depth study of the performance of thermally interdiffused concentration gradient polymer photovoltaic devices is carried out with particular attention to the effect of the thickness and the thermal treatments on the power conversion efficiency, short circuit current, open circuit voltage and other key electrical properties. Bilayer films of sequentially spin-cast donor and acceptor materials are exposed to various heat treatments in order to induce the interdiffusion. The depth profiles show concentration gradients in the donor and acceptor as a result of interdiffusion and these devices show an order of magnitude increase in the device performance compared to the bilayer devices. Dual spin-cast poly (3-octylthiophene-2,5-diyl) (P3OT)- [6,6] phenyl C61 butyric acid methyl ester (PCBM) and poly (3-hexylthiophene-2,5-diyl) (P3HT)-PCBM interdiffused devices are studied in detail by varying the thickness of the donor and acceptor layers as well as the annealing conditions for initial polymer layer and the time and temperature of the interdiffusion process. Auger spectroscopy and X-ray photoelectron spectroscopy along with ion beam milling are used to investigate the concentration gradient formed as a result of the interdiffusion. The sulfur signal present in the P3OT and P3HT backbone is detected to identify the concentration profiles in the P3OT-PCBM and P3HT-PCBM devices. The interdiffusion conditions and thickness of the active layers have been optimized to obtain the highest power conversion efficiency. The best device performance of the P3OT-PCBM interdiffused devices is achieved when the interdiffusion is carried out at 150°C for 20 minutes and the P3OT thickness is maintained at 70 nm and the PCBM thickness at 40-50 nm. The highest efficiency achieved for P3OT-PCBM interdiffused devices is 1.0% under AM1.5G solar simulated spectrum. In order to further increase the efficiency, P3OT is replaced by (P3HT) which has higher hole mobility. P3HT- PCBM based concentration gradient devices show improved device performance over P3OT-PCBM devices. Power conversion efficiency of the order of ~3.0% is obtained for P3HT-PCBM interdiffused devices when the interdiffusion is carried out at 150°C for 20 minutes. For both P3OT:PCBM and P3HT:PCBM devices, the optimum performance occurs when the concentration gradient extends across the entire film and is correlated with an increase in the short circuit current density and fill factor as well as a decrease in the series resistance. The results demonstrate that an interdiffused bilayer fabrication approach is a novel and efficient approach for fabrication of polymer solar cell devices. In addition, porphyrin derivative 5, 10, 15, 20-Tetraphenyl-21H, 23H-porphine zinc (ZnTPP) is studied as a new donor material for organic solar cells. ZnTPP: PCBM blend devices are investigated in detail by varying the weight ratio of the donor and acceptor materials in blend devices. The devices with ZnTPP: PCBM in 1:9 ratios showed the best device performance and the efficiency of the order of 0.2% is achieved under AM1.5G solar simulated conditions. Trimetallic Nitride Tempelated (TNT) endohedral fullerenes are also examined in this thesis as the novel acceptor materials. Bulk heterojunction or blend devices are fabricated with P3HT as the donor material and several TNT endohedral fullerenes as the acceptor material. Y3N@C₈₀PCBH based devices which are annealed both before and after the electrode deposition show improvement in the device performance compared to devices that are only annealed before the electrode deposition. The highest power conversion efficiency achieved for TNT endohedral fullerene devices is only 0.06%, suggesting that substantial additional work must be done to optimize the compatibility of the donor and acceptor as well as the device fabrication parameters. Ph. D.

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Jantakananuruk, Nattikarn. "Performance, Temperature and Concentration Profiles in a Non-Isothermal Ammonia-Fueled Tubular SOFC." Digital WPI, 2019. https://digitalcommons.wpi.edu/etd-theses/1295.

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Ammonia has emerged as an attractive potential hydrogen carrier due to its extremely high energy density (hydrogen density), ease of storage and transportation as a liquid, and carbon-free nature. Direct utilization of ammonia in high-temperature solid oxide fuel cells (SOFCs) has been demonstrated over the past decade. Concurrence of in situ endothermic ammonia decomposition and exothermic electrochemical hydrogen oxidation permit efficient heat integration. In this study, the experimental analyses of axial temperature and concentration profiles along the tubular SOFC (t-SOFC) fed directly with ammonia are performed to investigate the coupled ammonia decomposition and hydrogen oxidation reactions as well as the effect of polarization. Fast ammonia decomposition over the Ni catalyst is evident at the inlet of t-SOFC and complete ammonia conversion is confirmed above 600ºC. It is found that direct ammonia-fueled t-SOFC and an equivalent hydrogen-nitrogen fueled t-SOFC provide identical performances. With 100 SCCM of ammonia fuel feed, a maximum power of 12.2 W and fuel utilization of 81% are obtained at 800ºC in a t-SOFC with active area of 32 cm2. The temperature and concentration profiles validate that the efficient heat integration inside ammonia-fueled t-SOFC is feasible if t-SOFC is operated at the temperature of 700ºC and below. The 23-hour performance test and SEM-EDS images of the fresh and used Ni-YSZ cermet surfaces confirm uniform performance and good durability of ammonia t-SOFC.

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Benabbas, Tarik. "Activité électrique de bicristaux de silicium élaborés avec un gradient de concentration en aluminium." Paris 11, 1992. http://www.theses.fr/1992PA112473.

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Le but de ce travail est d'aborder l'aspect semi-quantitatif de la recombinaison aux joints de grains dans le silicium, en relation avec leur microstructure. Nous avons pour cela elabore par croissance directionnelle h. E. M. (heat exchange method), en collaboration avec le c. E. C. M. De vitry, des bicristaux de silicium de purete electronique, dotes d'un gradient de concentration en aluminium. Il a ete montre que l'aluminium present en concentration importante dans le semiconducteur, diminue la longueur de diffusion des porteurs minoritaires en se placant sur des sites autres que les sites accepteurs. Precisons tout de meme que l'objectif principal de cette recherche n'est pas tant l'etude du role de l'aluminium dans le silicium, ce sujet ayant fait l'objet de nombreuses etudes, mais plutot, de tenter d'etablir une correspondance, a l'echelle la plus fine possible, entre la microstructure liee a la presence d'une impurete, et l'activite electrique des joints de grains. Nous avons dans ce but entrepris une serie d'observations en microscopie electronique en transmission des joints de grains afin de suivre l'evolution de la microstructure des defauts en relation avec le gradient de concentration en impurete. La microstructure des joints est ensuite correlee a leur comportement electrique au moyen d'une technique d'injection de porteurs sur diodes minces. Cette technique developpee au laboratoire, a permis de montrer avec une resolution spatiale de l'ordre de 100 nm que la recombinaison des porteurs au niveau des joints speciaux dans le silicium, est localisee au niveau des precipites intergranulaires. L'activite electrique des joints de grains est donc essentiellement a caractere extrinseque

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Sikorsky, Alison A. "Concentration enhancement and device fabrication for the improved performance of gradient elution moving boundary electrophoresis." Thesis, University of Maryland, College Park, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=3644192.

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Many recent efforts in the field of microfluidics have been focused on reducing the size and the complexity of devices and on simplifying the methods of analysis performed with them. Gradient elution moving boundary electrophoresis (GEMBE) is a recently described counterflow electrophoresis method that was developed to simplify the analysis of ions in complex matrices. In this thesis, the improvement of the limit of detection of GEMBE and reduction of the GEMBE channel length is investigated. Integration of simple and robust device components required for the successful adaptation of many analytical methods to multiplexed and field-portable devices often has negative effects on detection sensitivity, such as in the optical detection components in a capillary electrophoresis (CE) system. One of the simplest methods to improve sensitivity in the CE field is known as sample stacking. This method involves preparing the sample in a buffer with a different concentration (and conductivity) than that of the run buffer, such that when an electric field is applied the analyte concentration is increased at the boundary between the two different buffer concentrations. A method in which the sample is prepared in a buffer at a lower concentration than the run buffer has been implemented. This method achieves a significantly greater signal enhancement than expected for sample stacking. The concentration enhancement ability of this method is demonstrated utilizing GEMBE with channel current detection. Current GEMBE device construction methods impose limitations on the minimum length of the separation channel. One technique well suited for minimizing the size of the GEMBE separation channel is multiphoton absorption polymerization (MAP). Because MAP is a non-linear optical fabrication method, polymerization is limited to a small region near the focal point of a laser beam. As a result, three-dimensional structures with small feature sizes can be easily created. The 3D capabilities of MAP have been exploited to create channels with circular cross sections and &sim;300 &mgr;m lengths for GEMBE. The integration of device components fabricated with MAP and molded with PMDS allows visualization of the GEMBE separations, and provides insights into the effect of channel length on GEMBE step width.

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Sparks, Christopher S. "Concentration gradient patterns of traffic and non-traffic generated aerosols: Ultrafine, PM2.5, and coarse particles." University of Cincinnati / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1314302308.

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Gopal, Anamika. "Effects of Thickness, Morphology and Molecular Structure of Donor and Acceptor Layers in Thermally Interdiffused Polymer Photovoltaics." Diss., Virginia Tech, 2007. http://hdl.handle.net/10919/27279.

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An in-depth study of concentration gradients in thermally-interdiffused polymer – fullerene photovoltaic devices, with a focus on thickness and heat treatments, is presented in this thesis. Device performance is improved from the bilayer by the creation of a concentration gradient of the donor and acceptor materials throughout the active layer of the device. Concentration gradients are expected to improve device performance by optimizing the charge transfer, transport and collection processes. This is achieved through heat-induced interdiffusion of the two materials at temperatures above the glass transition temperature of the polymer. Investigation of the poly(3-octylthiophene) (P3OT) – C₆₀ system show a three-fold improvement in the external quantum efficiencies (EQE) as compared with bilayer devices. Auger spectroscopy, combined with argon-ion beam milling, serves to record the concentration depth profile and identify concentration gradients in the device through detection of the sulfur in the P3OT backbone. Concentration gradients are optimized to yield the best devices through a thickness variation study conducted on the P3OT – C₆₀ system for fixed thermal interdiffusion conditions at 118 °C for 5 minutes. An optimum thickness of 40 to 60 nm is obtained for the two materials that yields the ideal morphology of a concentration gradient as recorded by Auger spectroscopy. For such devices, the concentration gradient is seen to extend through the device, ending in a thin layer of pure material at each electrode. A monochromatic power conversion efficiency of 2.05% is obtained for 5.3 mW/cm²⁺ illumination at 470 nm. A brief study is also presented to optimize the concentration gradient profile through variations of the thermal parameters. The dependence of the concentration gradient on the interdiffusion time and temperature is investigated. The merits of heat treatment on the crystallinity of P3OT and the overall device performance are also discussed. It is shown in some case that devices with annealed P3OT layers show almost twice the EQE as non-annealed P3OT layer devices. Potential alternatives for C₆₀ in interdiffused devices with P3OT have been presented. [6,6]-phenyl C₆₁-butyric acid methyl ester (PCBM), a well-investigated acceptor for blend devices, is studied as an acceptor in concentration gradient devices. A method for spin-coating uniform bilayers of P3OT and PCBM, without solution damage to either layer, is presented. A thermal variation study of the interdiffusion conditions on this system indicated higher interdiffusion temperatures and times are preferred for P3OT – PCBM systems. For interdiffusion at 150 °C for ten minutes, EQE values approaching 35 % at 500 nm are obtained. Auger spectroscopy studies on this system yielded the same conclusions about the concentration gradient device morphology that gives optimum device output. 1:1 and 1:2 blends of P3OT – PCBM are also studied. The influence of various thermal treatments on these devices is described. The endohedral fullerene Sc₃N@C₈₀ is introduced as a new acceptor material. The endohedral fullerene consists of Sc₃N cluster enclosed in a C₈₀ cage. An order of magnitude increase is seen in device performance upon sublimation of these molecules on a P3OT layer confirming its effectiveness as an acceptor. Preliminary studies done on this system indicated the need for greater thermal treatment to produce optimum concentration gradients. An in depth study for varying temperatures and times is presented. The best device performance was seen for interdiffusion at 160 °C for 25 minutes. The endohedral fullerene devices also show a long-term deterioration and so best result are presented from a set of devices fabricated within the same time period. The study of these three donor-acceptor systems confirms that the conclusions on the thickness dependence and device performance study conducted for the P3OT – C₆₀ system extend to other acceptors. A model of EQE for varying thicknesses based on absorption in the interdiffused concentration gradient regions is also presented. This model effectively highlights the influence of P3OT layer thickness on the trends observed in the EQE. It did not, however, reproduce the experimental thickness variation results for varying C₆₀ thicknesses. Incorporation of the effects of the electric field intensity distribution is expected to correct for this. Suggestions have been given on how this might be achieved. Ph. D.

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Awwad, Yousef Ahmad. "The Effect of Interleukin-1 (IL-1) Concentration on Single Cell NF-kappaB Activation in a Gradient-Generating Microfluidic Device." Thesis, Virginia Tech, 2011. http://hdl.handle.net/10919/35315.

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Interleukin-1 (IL-1) is a multifunctional cytokine produced primarily by activated monocytes/macrophages and by a variety of other cell types. IL-1 plays an integral role in the immuno-inflammatory response of the body to a variety of stimuli including infection, trauma and other bodily injuries. Once IL-1 is released from the synthesizing cell, it acts as a hormone, initializing a variety of responses in different cells and tissues. These responses are believed to be crucial to survival and are termed acute-phase responses. NF-ÎºB is a family of dimeric transcription factors that control the expression of hundreds of genes which regulate cellular stress responses, cell division, apoptosis, and inflammation. NF-ÎºB dwells in the cytoplasm of the cell until activation in response to a wide range of extracellular stimuli including signaling molecules such as cytokines. NF-ÎºB regulates transcription and gene expression through nucleocytoplasmic transport. Most previous studies on NF-ÎºB activation have been performed using bulk assays to look at populations of cells. Determining cell variance at a single-cell level is crucial in understanding the full mechanisms of drug response. The goal of this study is to analyze the effects of variant concentrations of IL-1Î² on the activation of NF-ÎºB in individual cells through use of a microfluidic gradient generator. The gradient generator was adopted from Jeon et al and used principles of diffusive mixing and splitting of flows in order create a solute concentration gradient. A soft lithography procedure was used. Briefly, the design was printed on a transparency using a high resolution printer. A master of the design is then created using an SU-8 photoresist and UV light to imprint the design on a silicon wafer. The master is then used to create a Polydimethylsiloxane (PDMS) mold of the design which can be irreversibly attached to a glass slide through oxidation in order to close off the microfluidic channels. FITC-conjugated Î²-Casein (a protein with similar molecular weight to IL-1Î²) was used in order to verify the gradient generated by the design. The concentration gradient was analyzed by measuring fluorescent intensity of images taken under a UV light microscope and found to agree with microfluidic simulations run on COMSOL. A procedure for culturing cells in a microfluidic device was then adapted from Jeon that is explained in detail in Chapter 3. Two main trends were revealed; firstly, as IL-1Î² concentration decreased, the percent of cells activated also decreased. Secondly, as IL-1Î² concentration decreased, the activation time of the responding cells increased. Cells were observed to act in a single-cell manner; in which multiple cells subjected to the same concentration would not all respond in the same fashion. No major activation threshold was observed but two minor thresholds were; the first at 0.02 ng/mL IL-1Î² where activation levels drop from 20% to around 5%. The second around 1 ng/mL, in which all greater concentrations show nearly complete activation of all cells exposed. Of the cells that activated, the activation times were recorded and analyzed as well. In general, a decrease in IL-1Î² concentration caused cells to take longer to activate. Concentrations greater than 5 ng/mL responded on average in 30 minutes with a significant amount of variation. Between 5 ng/mL and 0.1 ng/mL, activation time increased as IL-1Î² concentration decreased in a linear fashion when concentration was plotted on a base-10 log scale. Below 0.1 ng/mL, the trend disappears and an average activation time of around 95 minutes is observed that no longer depended on concentration. This is interesting because fewer and fewer cells are activating in this concentration range but activation time follows no trend and remains partially stochastic with times ranging from 80 to 105 minutes. The previous results were all observed with a continuous flow and stimulation of the cells. Experiments were also run by only exposing the cells to the IL-1Î² for 10 minutes and then replacing the flow with a buffer. These studies yielded interesting results; the fraction of activated cells reported the same trends and values as those that were continuously stimulated. The activation times, however, were delayed between 10 and 20 minutes but otherwise followed the same trend as the continuous stimulation. These results suggest that a brief exposure to an external stimulant is all it takes for the cascade of intercellular events to take place and cause NF-ÎºB translocation. Master of Science

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37

Lin, Shu-Ling. "Electric Field Gradient Focusing-UV Detection for Protein Analysis." Diss., CLICK HERE for online access, 2006. http://contentdm.lib.byu.edu/ETD/image/etd1372.pdf.

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Ma, Yanrui. "Facile Fabrication of One- and Two-Dimensional Orthogonal Peptide Concentration Gradient Surfaces for Directed Stem Cell Differentiation." University of Akron / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=akron1405936934.

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39

Vyas, Chandni Atul. "Rapid Detection of Biogenic Amines using Capillary Electrophoresis and Gradient Elution Isotachophoresis." Diss., Temple University Libraries, 2010. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/112673.

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Chemistry Ph.D. The metabolism of amino acids produces important chemical signaling molecules called neurotransmitters, which are responsible for carrying out important actions within the human body. There are approximately one hundred identified neurotransmitters. Neurotransmitter study is important due to their involvement in biological, physiological, pharmacological, and pathological functions. Commonly employed methods for neurotransmitter detection are mainly based upon microdialysis. However, the methods suffer from disadvantages. Microdialysis fails to determine the absolute concentration of analytes and therefore requires it to be tied in with an analytical technique such as high performance liquid chromatography or capillary electrophoresis. Although high performance liquid chromatography is the most powerful analytical technique to date, it necessitates high maintenance and suffers from poor temporal resolution. While capillary electrophoresis affords more rapid separations than high performance liquid chromatography, it suffers from poor concentration limits of detection and requires large sample dilutions of highly conductive samples, such as biological fluids. Consequently, research is focused on detection of various amino acids and neurotransmitters employing novel analytical techniques along with traditional capillary electrophoresis. First, a method was developed using traditional capillary electrophoresis with laser induced fluorescence detection to detect two major excitatory neurotransmitters, glutamate and aspartate in planaria. The method was later applied to detect several biogenic amines using micellar electrokinetic chromatography with laser induced fluorescence detection in planaria to study the effect of feeding on the levels of biogenic amines within individual planaria homogenates. The concentration sensitivity issue of capillary electrophoresis led to the use of a new method for sensitive neurotransmitter measurements, gradient elution isotachophoresis. Gradient elution isotachophoresis is an efficient capillary-based enrichment and separation technique based on balancing hydrodynamic counter-flow against electrophoresis. Enrichment is achieved with the aid of high concentrations of leading electrolyte in the counter-flow solution that creates an ionic interface near the capillary inlet. Discrete electrolyte spacers or carrier ampholyte mixtures are used to separate analyte zones. The method was applied to the enrichment and separation of physiologically relevant concentrations of aspartate and glutamate labeled with dansyl chloride, phenyl isothiocyanate, or carboxyfluorescein, succinimidyl ester in artificial cerebrospinal fluid using ultraviolet absorbance detection. Finally, gradient elution isotachophoresis was combined with capillary zone electrophoresis to eliminate the use of spacers and provide rapid separations and enrichment. The technique was applied for the detection of biogenic amines in a glass microfluidic device. Temple University--Theses

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40

Gruselle, Catherine. "Etude du développement d'une flamme soumise à un gradient de concentration : Rôle de la stratification et des EGR." Phd thesis, INSA de Rouen, 2014. http://tel.archives-ouvertes.fr/tel-01005306.

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La combustion stratifiée, qui consiste à brûler un mélange carburant/oxydant inhomogène, et la combustion diluée, consistant à ajouter une quantité limitée de gaz brûlés, sont deux technologies utilisées dans les moteurs à piston pour réduire leur consommation. Cette thèse est dédiée à l'étude de l'allumage dans ces deux types de milieux en régimes laminaire et turbulent. Un nouveau schéma cinétique pour la combustion propane/air a été dérivé et combiné à deux approches de modélisation différentes : la chimie complexe et une approche de chimie tabulée de type FPI. Dans le cas laminaire, les deux approches de modélisation donnent des résultats similaires et un modèle simple a mis en évidence l'importance de la dynamique des gaz frais et des gaz brûlés sur le développement du noyau. Dans le cas turbulent, plusieurs techniques d'analyse ont montré la dépendance de la vitesse absolue de la flamme au champ de vitesse moyen et la décorrélation des fluctuations locales de richesse.

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Gruselle, Catherine. "Etude du développement d’une flamme soumise à un gradient de concentration : Rôle de la stratification et des EGR." Thesis, Rouen, INSA, 2014. http://www.theses.fr/2014ISAM0003/document.

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La combustion stratifiée, qui consiste à brûler un mélange carburant/oxydant inhomogène, et la combustion diluée, consistant à ajouter une quantité limitée de gaz brûlés, sont deux technologies utilisées dans les moteurs à piston pour réduire leur consommation. Cette thèse est dédiée à l’étude de l’allumage dans ces deux types de milieux en régimes laminaire et turbulent. Un nouveau schéma cinétique pour la combustion propane/air a été dérivé et combiné à deux approches de modélisation différentes : la chimie complexe et une approche de chimie tabulée de type FPI. Dans le cas laminaire, les deux approches de modélisation donnent des résultats similaires et un modèle simple a mis en évidence l’importance de la dynamique des gaz frais et des gaz brûlés sur le développement du noyau. Dans le cas turbulent, plusieurs techniques d’analyse ont montré la dépendance de la vitesse absolue de la flamme au champ de vitesse moyen et la décorrélation des fluctuations locales de richesse Stratified combustion, which consists in burning an inhomogeneous fuel/air mixture, and diluted combustion, which consists in adding a limited quantity of burnt gases, are two technologies used in internal combustion engines to reduce fuel consumption. This Ph.D is devoted to the study of ignition in these two types of combustion in laminar and turbulent regimes. A new kinetic scheme for propane/air combustion has been derived and combined to two modeling approaches: finite-rate chemistry and an FPI tabulated chemistry approach. In the laminar case, both approaches give similar results and a simplified model has highlighted the importance of fresh and burnt gases dynamics on the kernel development. In the turbulent case, several techniques of analysis have shown the dependency of absolute flame speed on the mean fluid velocity and the lack of correlation to the local equivalence ratio

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42

Teerapanich, Pattamon. "Fluorescence-based nanofluidic biosensor platform for real-time measurement of protein binding kinetics." Thesis, Toulouse 3, 2015. http://www.theses.fr/2015TOU30239/document.

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L'analyse cinétique d'interactions de protéines offre une multitude d'informations sur les fonctions physiologiques de ces molécules au sein de l'activité cellulaire, et peut donc contribuer à l'amélioration des diagnostics médicaux ainsi qu'à la découverte de nouveaux traitements thérapeutiques. La résonance plasmonique de surface (SPR) est la technique de biodétection optique de référence pour les études cinétiques d'interaction de molécules biologiques. Si la SPR offre une détection en temps réel et sans marquage, elle nécessite en revanche des équipements coûteux et sophistiqués ainsi que du personnel qualifié, limitant ainsi son utilisation au sein de laboratoires de recherche académiques. Dans ces travaux de thèse, nous avons développé une plateforme de biodétection basée sur l'utilisation de nanofentes biofonctionnalisées combinées avec une détection par microscopie à fluorescence. Ce système permet l'observation en temps réel d'interactions protéines-protéines et la détermination des constantes cinétiques associées, avec des temps de réponse optimisés et une excellente efficacité de capture. La fonctionnalité du système a été démontrée par l'étude des cinétiques d'interaction de deux couples modèles de différentes affinités : le couple streptavidine/biotine et le couple IgG de souris/anti-IgG de souris. Une très bonne cohérence entre les constantes cinétiques extraites, celles obtenues par des expériences similaires réalisées en SPR et les valeurs rapportées dans la littérature montre que notre approche pourrait être facilement applicable pour l'étude cinétique d'interactions de protéines avec une sensibilité allant jusqu'au pM, sur une large gamme de constantes de dissociation. De plus, nous avons intégré un générateur de gradient de concentrations microfluidique en amont de nos nanofentes, permettant ainsi des mesures simultanées de cinétiques d'interactions à différentes concentrations d'analyte en une seule expérience. Ce système intégré offre de nombreux avantages, tels qu'une réduction de la consommation des réactifs et des temps d'analyse par rapport aux approches séquentielles classiques. Cette technologie innovante pourrait ainsi être un outil précieux non seulement pour les domaines du biomédical et de la médecine personnalisée mais aussi pour la recherche fondamentale en chimie et biologie Kinetic monitoring of protein-protein interactions offers fundamental insights of their cellular functions and is a vital key for the improvement of diagnostic tests as well as the discovery of novel therapeutic drugs. Surface plasmon resonance (SPR) is an established biosensor technology routinely used for kinetic studies of biomolecular interactions. While SPR offers the benefits of real-time and label-free detection, it requires expensive and sophisticated optical apparatus and highly trained personnel, thus limiting the accessibility of standard laboratories. In this PhD project, we have developed an alternative and cost-effective biosensor platform exploiting biofunctionalized nanofluidic slits, or nanoslits, combined with a bench-top fluorescence microscope. Our approach enables the visualization of protein interactions in real-time with the possibility to determine associated kinetic parameters along with optimized response times and enhanced binding efficiency. We have demonstrated the effectiveness of our devices through kinetic studies of two representative protein-receptor pairs with different binding affinities: streptavidin-biotin and mouse IgG/anti-mouse IgG interactions. Good agreement of extracted kinetic parameters between our device, SPR measurements and literature values indicated that this approach could be readily applicable to study kinetics of protein interactions with sensitivity down to 1 pM on a large scale of dissociation constants. In addition, we have incorporated a microfluidic gradient generator to our validated nanoslit device, which has allowed one-shot parallel kinetic measurements to be realized in a single-experiment. This integrated system provides advantages of diminished material consumption and analysis time over the conventional kinetic assays. We believe that this innovative technology will drive future advancements not only in the discipline of biomedical and personalized medicine, but also in basic chemical/biological research

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43

Sahnoun, Mohamed Aymen. "Contribution à la modélisation et au contrôle de trajectoire de Trackers photovoltaïques à haute concentration (HCPV)." Thesis, Paris, ENSAM, 2015. http://www.theses.fr/2015ENAM0043/document.

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Dans une optique de maximisation de la production et de réduction des coûts d’installation, de maintenance et d’entretien des trackers solaires, qui permettent d’orienter les modules photovoltaïques à haute concentration (HCPV), ces travaux de thèse se focalisent sur l’amélioration de la précision et la réduction du coût de la stratégie de génération de la trajectoire du tracker. Dans un premier temps, un simulateur de tracker HCPV est développé offrant une étude de l’influence de la performance du suivi du soleil sur la production des modules HCPV, permettant ainsi une étude et une comparaison des stratégies de génération de trajectoires. Le simulateur est basé sur un modèle comportemental de module HCPV monté sur tracker permettant de prédire la puissance maximale du module HCPV en fonction de l’erreur de position du tracker face au soleil, de l’ensoleillement direct et de la température. Une première stratégie de commande dite de référence a été implémentée sur ce simulateur. C’est une commande hybride qui repose sur un viseur solaire pour corriger l’erreur de poursuite par un calcul astronomique. Ensuite, afin d’améliorer les performances et de réduire les coûts de cette stratégie, une nouvelle approche sans capteur est développée en se basant sur une méthode d’optimisation du gradient de puissance pour la génération de la trajectoire du tracker. Une étude complémentaire est également exposée afin de mettre en évidence des algorithmes de recherche de la puissance maximale (MPPT) pouvant offrir des temps de réponse suffisamment rapides pour ne pas affecter la qualité de l’évaluation du gradient de puissance. Dans ce contexte, une commande MPPT P&O améliorée par un réseau de neurones à complexité réduite est proposée, assurant un compromis entre précision, simplicité et rapidité This work focuses on improving the accuracy and on reducing the cost of the tracker generating trajectory strategy, in order to maximize the production and to reduce the installation and the maintenance cost of a solar tracker orienting high concentrated photovoltaic modules (HCPV). Initially, we propose a behavioral modeling of the HCPV module mounted on a dual axis tracker in order to study the influence of the tracking performance on the module power production. Then, this simulator can be used to test control strategies and to compare their performance. Firstly, a classical control strategy is implemented in the simulator. It is based on a hybrid control operating an astronomical calculation to follow the sun path, and a sun sensor to correct the tracking error. A sensorless strategy is proposed in this work to reduce the cost of the HCPV tracker control. This strategy is based on a gradient optimization algorithm to generate the tracker trajectory and to catch the sun path. Tested on the simulator, this strategy presents the same accuracy as the classical strategy while being less costly. The last study proposed in this thesis work concerns maximum power point tracking (MPPT) algorithms, in order to respond to a given problem relating to the practical implementation of gradient algorithm. In this context, we propose an original optimization of the P&O MPPT control with a neural network algorithm leading to a significant reduction of the computational cost required to train it. This approach, which is ensuring a good compromise between accuracy and complexity is sufficiently fast to not affect the quality of the evaluation of the gradient

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44

Kaminski, Myriam. "Modélisation de l'endommagement en fatigue des superalliages monocristallins pour aubes de turbines en zone de concentration de contrainte." Phd thesis, École Nationale Supérieure des Mines de Paris, 2007. http://tel.archives-ouvertes.fr/tel-00268736.

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Les aubes de turbine Haute Pression des moteurs d'avion, constituées du superalliage monocristallin AM1, sont refroidies par un circuit complexe de microcanalisations, situé en bord d'attaque et près du bord de fuite. Il peut constituer des sites privilégiés d'endommagement et d'amorçage de fissures, qu'il est indispensable de prendre en compte dans le dimensionnement en fatigue des aubes de turbines. Ce travail a consisté, dans un premier temps, à réaliser une étude expérimentale sur des éprouvettes perforées de trous de différents diamètres. Elle a permis de mettre en évidence qualitativement et quantitativement l'effet du gradient de contrainte sur l'amorçage de fissure. Cependant, la contrainte locale maximale (ou la déformation maximale) ne peut suffire dans un critère de rupture, car elle surestime le risque de rupture, ne prenant pas en compte les effets d'échelle ou de géométrie. Une méthode de moyenne volumique a alors été proposée pour prendre en compte le gradient de contrainte dans le calcul de durée de vie et a ainsi permis d'améliorer les prévisions de durée de vie.Parallèlement, un modèle d'endommagement de fatigue anisotrope, qui couple plasticité et endommagement, en s'attachant particulièrement à décrire la phase de micro-amorçage, a été développé. L'identification et la validation du modèle ont été réalisées à partir d'une base de données expérimentales conséquente sur l'AM1 et sur les essais sur éprouvettes perforées réalisés au cours de ce travail. Afin de prendre en compte les effets de gradient dans les zones à forte concentration de contrainte, la méthode de moyenne volumique a été appliquée avec ce modèle et a fourni des résultats encourageants.

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Crumley, Mariana Neubauer. "The effects of a reduced fractional inspired oxygen concentration on ventilation and A-a oxygen gradient in isoflurane anesthetized horses." Thesis, Kansas State University, 2011. http://hdl.handle.net/2097/13258.

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Master of Science Department of Clinical Sciences Rose M. McMurphy Hypoventilation (PaCO2 > 45 mmHg) and large P(A-a)O2 gradients due to V/Q mismatch and shunt, are common during isoflurane anesthesia in horses. A fraction of inspired oxygen < 50% has been shown to improve ventilation and decrease intra-operative atelectasis in humans and some animals. The study compared the effects of two different fractions of inspired oxygen, 50% versus > 95%, on ventilation, respiratory pattern, and P(A-a)O2 gradient in isoflurane anesthetized horses. Eight mature horses were sedated with IV xylazine (1.0 mg/kg) and anesthetized with diazepam (0.05 mg/kg) and ketamine (2.2 mg/kg) twice. Anesthesia was maintained with isoflurane (ET1.5 vol%) in either 50 or > 95% oxygen for 90 minutes. Both treatments were randomly assigned to each horse with a one week interval in between treatments. Horses were positioned in dorsal recumbency, connected to a preloaded circle breathing system and allowed to spontaneously ventilate. Measurements included inspiratory and expiratory peak flow and time, tidal volume, respiratory frequency, ETCO2, CO2, O2, PaO2, PaCO2, pH, SaO2, heart rate, and arterial blood pressure. Calculated values included PAO2, P(A-a)O2, P(A-a)O2 rate of change, and physiologic dead space. FiO2 of 50% resulted in a lower PaO2, SaO2, PAO2, and P(A-a)O2. No significant change in PaCO2, ventilatory pattern, or any remaining measured variables was observed (p<0.05). The use of 50% oxygen and nitrogen as the carrier gas did not significantly change the ventilatory characteristics or improve oxygenation in isoflurane anesthetized horses. Repeatable respiratory rhythms characteristics were observed for horses while inspiring 50% and > 95% oxygen. A high A-a oxygen gradient with an equal rate of change overtime was still observed during both treatments.

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Sesanga, N'tshuika Bill. "Optimisation de gammes : application à la conception des machines synchrones à concentration de flux." Thesis, Grenoble, 2011. http://www.theses.fr/2011GRENT012/document.

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Les travaux de cette thèse portent sur l’optimisation de gammes dans laconception des machines synchrones à concentration de flux. Dans un premier temps, unmodèle de dimensionnement multi physique dédié à l’optimisation a été développé pourchaque machine retenue pour cette étude. Un modèle analytique pour la structure à bobinagereparti et un modèle semi-analytique à base de réseaux de réluctances pour la machineà bobinage sur dents. Dans un second temps, nous avons validé nos modèles par comparaisonavec des essais expérimentaux. L’aspect gamme de notre étude nous a contraints à fairecette validation sur différentes machines et pour différents points de fonctionnement. Unepremière phase d’optimisation classique, réalisée grâce au couplage de nos modèles avec uneméthode déterministe à base de gradient a montré la possibilité d’optimiser nos machines.Une démarche originale d’optimisation de gammes basée sur le partage des composants aété mise au point. Son application sur une série de machines a montré que la discrétisationoptimale de tôles dans un diamètre donné est fonction de la vitesse des machines The works of this thesis concern the ranges optimization for radial synchronousmachines conception. At first, a multiphysical sizing model dedicated to optimizationwas developed for every retained machine for our study. An analytical model for distributedwinding structure and a semi-analytical model with network reluctances for concetratedwinding motors. Secondly, we validated the models by comparison with the experimentalmesures. The range aspect of the study forced us to make this validation on variousmachines and for various operating points. A first phase of classic optimization, whichis realized due to the coupling of the models with a gradient based determinist methodshowed the possibility to optimize the motors. An original approach of range optimizationbased on the components sharing was developed. Its application on a series of motors showedthat, the optimal discretization of steel sheets in a given diameter is a function of themotor speed

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Boulesteix, Rémy. "Densification du grenat d'yttrium et d'aluminium pur ou dopé sous forme de céramiques transparentes : relation entre microstructure et propriétés optiques : élaboration de matériaux à gradient de concentration en néodyme." Limoges, 2009. http://www.theses.fr/2009LIMO4040.

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Heath, Kristy Marie. "Fluid Mud Formation in the Petitcodiac River, New Brunswick, Canada." Thesis, Boston College, 2009. http://hdl.handle.net/2345/922.

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Thesis advisor: Gail C. Kineke Experiments were conducted in the Petitcodiac River in New Brunswick, Canada during June and August 2006 to study high-concentrations of suspended sediment in a turbulent system. This study will evaluate the conditions necessary for fluid mud formation by investigating 1) the suppression of turbulence at gradient Richardson numbers greater than 0.25; 2) a threshold condition for the amount of sediment a flow can maintain in a turbulent suspension; and 3) the influence of flocculation on vertical suspended-sediment transport. Direct measurements of salinity, temperature, current velocity, and suspended-sediment concentration were collected during accelerating and decelerating flows and when fluid mud formed. In June, current velocities were typically above 1 m s-1 and suspended-sediment concentrations were generally less than 10 g l -1. In August, current velocities were typically less than 1.5 m s-1, suspended-sediment concentrations were greater than 10 g l -1, and a high-concentration bottom layer formed rapidly during decelerating flood currents. Gradient Richardson numbers for concentrations greater than 10 g l -1 were generally greater than 0.25, suggesting strong density gradients have the ability to suppress turbulence. Results from the Petitcodiac suggest a carrying capacity threshold might exist, but is based on a critical gradient Richardson number between 1.0 and 2.0 rather than the previously accepted value of 0.25. Differences in the evolution of disaggregated grain size distributions for settling suspensions suggest flocculation plays an important role for fluid mud formation by enhancing settling of fine sediments Thesis (MS) — Boston College, 2009 Submitted to: Boston College. Graduate School of Arts and Sciences Discipline: Geology and Geophysics

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Beckert, Steffen, Frank Stallmach, Jens Kullmann, and Dirk Enke. "Concentration dependent self-diffusion coefficients of aqueous electrolyte solutions in bulk phase and confined in porous glasses measured by pulsed field gradient NMR." Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-184977.

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Beckert, Steffen, Frank Stallmach, Jens Kullmann, and Dirk Enke. "Concentration dependent self-diffusion coefficients of aqueous electrolyte solutions in bulk phase and confined in porous glasses measured by pulsed field gradient NMR." Diffsuion fundamentals 16 (2011) 38, S. 1-2, 2011. https://ul.qucosa.de/id/qucosa%3A13773.

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