Cette Thèse de Doctorat est consacrée à l'étude des écoulements cisaillés réactifs supersoniques et plus particulièrement à la dynamique des jets compressibles fortement sous détendus. Ce type d'écoulement est rencontré dans un certain nombre d'applications relatives, par exemple, à l'injection d'hydrogène dans les superstatoréacteurs ou bien à l'allumage de moteurs fusées. Il est aussi représentatif du percement de réservoirs à haute pression. Ce travail s'appuie sur l'emploi d'un outil de simulation numérique haute fidélité: CREAMS (Compressible REActive Multi-species Solver). Ce code de calcul met en oeuvre des schémas numériques d'ordre élevé: schéma d' intégration d'ordre 3 en temps et d'ordre 7 et 8 en espace. Il s'appuie sur une description des termes de transport moléculaire et des termes sources chimiques la plus précise possible (transport détaillé et chimie complexe). Les simulations réalisées dans des conditions inertes permettent de caractériser l'importance des interactions choc/turbulence avec une attention particulière accordée au mélange turbulent à petite échelle. Les simulations réactives de jets fortement sous détendus d' hydrogène montrent les difficultés d'allumage et de stabilisation de la combustion pour ce type de conditions, même en présence d'un apport externe d' énergie. Enfin, l'analyse d'un jet représentatif d'un allumeur de moteur fusée révèle certaines spécificités de l'auto-allumage dans ces conditions non-prémélangées rapides. / This dissertation is devoted to the study of sheared supersonic reactive flows and more specifically the dynamics of highly underexpanded jets. Such complex compressible turbulent flow conditions are of praclical interest for scramjets as well as rocket engines applications. Similar condit ions may also be found during the accidentai releases of flammable substances into the atmosphere during high pressure vessel rupture or venting. This work is conducted with a high fidelity computational solver: CREAMS (Compressible Multi-reactive species Solver). It uses high precision numerical schemes third-order Runge Kutta scheme for time integration, plus a combination of seventh and eighth-order centered and WENO schemes for spatial integration. The molecular transport terms and chemical sources terms are handled with the most accurate descriptions, i. e., including detailed transport and chemistry. Inert flow simulations allow to characterize the importance of shock/turbulence interactions with a special emphasis placed on the small-scale scalar mixing. Highly under-expanded reactive hydrogen jet simulations underline the specific difficulties associated to ignition and combustion stabilization even in the presence of an external deposit of energy. Finally, the analysis of the rocket engine igniter jet reveals some specific features of self-ignition phenomena in such non-premixed conditions.

Thesis--Auburn University, 2009. / Abstract. Includes bibliographical references (p. 57-69).

Introdução: A estabilidade fisica de sistemas emulsionados pode ser avaliada através de avaliação da distribuição de gotículas, propriedades reológicas, termoanálise, microscopia, entre outras técnicas. Objetivo: Avaliar a estabilidade fisica de emulsões obtidas com diferentes concentrações de emulsificantes aniônicos (A - cetil fosfato de potássio 3, 5 e 7%) e não-iônicos (N monoestearato de glicerila, 3, 5 e 7%), e a influência da transposição de escala de produção. Metodologia: Avaliação da distribuição das gotículas formadas através de difração de raio laser, análise reológica do tipo fluxo, microscopia e termogravimetria. Resultados e Conclusão: Os valores de 90% das gotículas foram menores que 92,66 µm; 50,28µm e 38,80µm, respectivamente para 3, 5 e 7% de emulsificante N. No sistema A, 90% das gotículas foram menores que 3,85µm; 4,89µm e 63,57µm, para 3, 5 e 7%, respectivamente. O aumento de escala de produção influenciou ambos os sistemas, com aumento de viscosidade: Sistema A: de 6,614 Pa.s para 81,55 Pa.s e Sistema N - de 3,366 Pa.s para 7,153 Pa.s no sistema N. Na análise TG, somente água livre pôde ser detectada no sistema N e, no sistema A, água interlamelar e livre puderam ser detectadas (inicial e em estabilidade) / lntroduction: The physical stability of emulsions can be evaluated through droplets distribution evaluation, rheological properties, thermal analysis, microscopy and others. Objective: Evaluate the physical stability of emulsions containg different concentrations of anionic (A - potassium cetyl phosphate 3, 5 e 7%) and non-ionic emulsifiers (N - glyceril monostearate, 3, 5 e 7%), and the influence ofthe scale-up processo Methodology: Evaluate the droplets distribution with laser diffraction, rheology analysis, microscopy and thermogravimetry (TG). Results and Conc1usion: The values of 90% of the droplets were below 92.66 µm, 50.28µm and 38.80µm, respectively for 3, 5 and 7% ofN emulsifier. For system A, 90% ofthe droplets were below 3.85µm, 4.89µm and 63.57µm, for 3, 5 and 7%. The scale-up process influenced both systems, with an increase in the viscosity on system A from 6.614 Pa.s to 81.55 Pa.s and from 3.366 Pa.s to 7.153 Pa.s for system N. ln the TG analysis, only bulk water could be detected in system N and, in the system A, both interlamellar and bulk water were detected (initial and stability).

Introdução: A estabilidade fisica de sistemas emulsionados pode ser avaliada através de avaliação da distribuição de gotículas, propriedades reológicas, termoanálise, microscopia, entre outras técnicas. Objetivo: Avaliar a estabilidade fisica de emulsões obtidas com diferentes concentrações de emulsificantes aniônicos (A - cetil fosfato de potássio 3, 5 e 7%) e não-iônicos (N monoestearato de glicerila, 3, 5 e 7%), e a influência da transposição de escala de produção. Metodologia: Avaliação da distribuição das gotículas formadas através de difração de raio laser, análise reológica do tipo fluxo, microscopia e termogravimetria. Resultados e Conclusão: Os valores de 90% das gotículas foram menores que 92,66 µm; 50,28µm e 38,80µm, respectivamente para 3, 5 e 7% de emulsificante N. No sistema A, 90% das gotículas foram menores que 3,85µm; 4,89µm e 63,57µm, para 3, 5 e 7%, respectivamente. O aumento de escala de produção influenciou ambos os sistemas, com aumento de viscosidade: Sistema A: de 6,614 Pa.s para 81,55 Pa.s e Sistema N - de 3,366 Pa.s para 7,153 Pa.s no sistema N. Na análise TG, somente água livre pôde ser detectada no sistema N e, no sistema A, água interlamelar e livre puderam ser detectadas (inicial e em estabilidade) / lntroduction: The physical stability of emulsions can be evaluated through droplets distribution evaluation, rheological properties, thermal analysis, microscopy and others. Objective: Evaluate the physical stability of emulsions containg different concentrations of anionic (A - potassium cetyl phosphate 3, 5 e 7%) and non-ionic emulsifiers (N - glyceril monostearate, 3, 5 e 7%), and the influence ofthe scale-up processo Methodology: Evaluate the droplets distribution with laser diffraction, rheology analysis, microscopy and thermogravimetry (TG). Results and Conc1usion: The values of 90% of the droplets were below 92.66 µm, 50.28µm and 38.80µm, respectively for 3, 5 and 7% ofN emulsifier. For system A, 90% ofthe droplets were below 3.85µm, 4.89µm and 63.57µm, for 3, 5 and 7%. The scale-up process influenced both systems, with an increase in the viscosity on system A from 6.614 Pa.s to 81.55 Pa.s and from 3.366 Pa.s to 7.153 Pa.s for system N. ln the TG analysis, only bulk water could be detected in system N and, in the system A, both interlamellar and bulk water were detected (initial and stability).

Les produits cosmétiques sont des substances utilisées pour entretenir ou modifier l'aspect des parties superficielles du corps humain (telles que la peau, les ongles ou les cheveux). Dans de nombreux pays d’Afrique et d’Asie et dans certaines communautés africaines immigrantes, plusieurs femmes et parfois des hommes utilisent des produits contenant des agents actifs tels que le mercure, l’hydroquinone et le propionate de clobétasol pour éclaircir leur peau. Ces principaux agents sont toxiques et leur présence dans les cosmétiques est règlementée, voire interdite, dans plusieurs pays. Dans notre étude, nous avons déterminé les concentrations de ces ingrédients dans plusieurs produits utilisés en Afrique de l’Ouest et au Canada. Nous avons également exploré l’effet de ces produits sur le microbiome cutané. Nos résultats révèlent que 68 à 84% des crèmes et 7.5 à 65% des savons dépassent les normes lorsqu’on considère l’interdiction de mercure, d’hydroquinone et de propionate de clobétasol et les concentrations déclarées sur les étiquettes ne sont pas souvent fiables. Selon la diversité de Shannon, il semble y avoir plus d’équitabilité, et donc moins de dominance dans le groupe des femmes utilisant les crèmes éclaircissantes que dans le groupe des femmes qui ne les utilisent pas. Par ailleurs, nous n’avons pas trouvé de différences significatives au niveau du microbiome cutané du groupe avec crèmes et sans crèmes au niveau du phylum et du genre. Cependant, d’autres méthodes plus approfondies avec plus d’échantillonnage pourraient révéler à des échelles plus fines (espèces, souches, etc.) l’effet de ces produits sur le microbiome cutané. / Cosmetics are substances used to maintain or change the appearance of external parts of the human body (such as skin, nails or hair). In many countries of Africa and Asia and in some immigrant African communities, many women and sometimes men use products containing active agents such as mercury, hydroquinone and clobetasol propionate to lighten their skin. These main active agents are toxic and their presence in cosmetics is regulated or even banned in several countries. In our study, we determined the concentrations of these ingredients in many products used in West Africa and Canada. In addition, we also explored the effect of these products on the skin microbiome. Our results reveal that 68 to 84% of cream and 7.5 to 65% of soaps exceed the standards when considering mercury, hydroquinone and clobetasol propionate ban in lightening products and concentrations of the three compounds declared on labels of soaps and creams usually did not correspond to concentrations actually measured. According to Shannon diversity index, there seems to be more evenness, less dominance in group of African women with creams than in those without cream. Moreover, we have not found significant differences in the skin microbiome of the group with creams and the one without creams at the phylum and genus level. However, additional detailed studies with more sampling methods could reveal at finer scales (species, strains, etc.) the effect of these products on the human skin microbiome.

No description available.

Tactile perception is considered an important contributor to the overall consumer experience of a product. However, what physical properties that create the specifics of tactile perception, are still not completely understood. This thesis has researched how many dimensions that are required to differentiate the surfaces perceptually, and then tried to explain these dimensions in terms of physical properties, by interconnecting human perception measurements with various physical measurements. The tactile perception was assessed by multidimensional scaling or magnitude estimation, in which methods human participants assign numbers to how similar pairs of surfaces are perceived or to the relative quantity of a specified perceptual attribute, such as softness, smoothness, coarseness and coolness. The role of friction and surface texture in tactile perception was investigated in particular detail, because typically tactile exploration involves moving (at least) one finger over a textured surface. A tactile approach for measuring friction was developed by means of moving a finger over the surfaces, mounted on a force sensor. The contribution of finger friction to tactile perception was investigated for surfaces of printing papers and tissue papers, as well as for model surfaces with controlled topography. The overarching research goal of this thesis was to study, systematically, the role of texture in tactile perception of surfaces. The model surfaces displayed a sinusoidal texture with a characteristic wavelength and amplitude, fabricated by surface wrinkling and replica molding techniques. A library of surfaces was manufactured, ranging in wavelengths from 270 nm up to 100 µm and in amplitudes from 7 nm up to 6 µm. These surfaces were rigid and cleanable and could therefore be reused among the participants. To my knowledge, this is the first time in a psychophysical experiment, that the surface texture has been controlled over several orders of magnitude in length scale, without simultaneously changing other material properties of the stimuli. The finger friction coefficient was found to decrease with increasing aspect ratio (amplitude/wavelength) of the model surfaces and also with increasing average surface roughness of the printing papers. Analytical modeling of the finger’s interaction with the model surfaces shows how the friction coefficient increases with the real contact area, and that the friction mechanism is the same on both the nanoscale and microscale. The same interaction mechanism also explains the friction characteristics of tissue paper. Furthermore, it was found that the perceptions of smoothness, coarseness, coolness and dryness are satisfactorily related to the real contact area at the finger-surface interface.  It is shown that it is possible to discern perceptually among both printing papers and tissue papers, and this differentiation is based on either two or three underlying dimensions. Rough/smooth and thin/thick were the two main dimensions of surface feel found for the printing papers, whereas friction and wavelength were strongly related to the perceptual cues employed in scaling the model surfaces. These experimental results support the duplex theory of texture perception, which holds that both a “spatial sense”; used to discriminate the roughest textures from the others, and a “vibration sense”; used to discriminate among the smoother textures, are involved. The perception of what is considered rough and smooth depends on the experimental stimulus context. It is concluded that friction is important for human differentiation of surface textures below about 10 µm in surface roughness, and for larger surface textures, friction is less important or can even be neglected. The finger friction experiments also allowed the following conclusions to be drawn: (i) The interindividual variation in friction coefficients is too large to allow direct comparison; however, the trends in relative friction coefficients for a group of participants are the same. (ii) Lipids are transferred to the test surface of study, and this lowers the friction. (iii) Many of the studies point to a characteristic frequency during sliding of about 30 Hz, which is both characteristic of the resonance frequency of skin and the expected frequency associated with the fingerprints. (iv) The applied load in surface interrogation is in fact regulated in response to the friction force. The limits in tactile perception were indirectly researched by similarity scaling experiments on the model surfaces. Wrinkle wavelengths of 760 nm and 870 nm could be discriminated from untextured reference surfaces, whereas 270 nm could not. The amplitude of the wrinkles so discriminated was approximately 10 nm, suggesting that nanotechnology may well have a role to play in haptics and tactile perception. / Taktil perception bidrar starkt till den sammantagna upplevelsen av en produkt, men hur materials olika ytegenskaper påverkar och styr perceptionen är ännu inte helt klart. Den här avhandlingen undersöker hur många och vilka egenskaper som är viktiga när känslan mellan två ytor jämförs. Tillvägagångssättet är tvärvetenskapligt där fysikaliska mätningar kopplas ihop med perceptions mätningar där människor används som instrument. Två typer av perceptionsförsök har utförts, multidimensionell skalning där försökspersoner sätter siffror på hur lika två ytor känns, samt magnitud estimation där i stället intensiteten på specifika perceptuella storheter som t.ex. upplevt lenhet, upplevd mjukhet och upplevd strävhet bedömdes. Eftersom taktil perception innebär kontakt samt relativ rörelse mellan hud och ytor, har fokus i avhandlingen varit att undersöka hur friktion och ytans struktur (ytråhet) påverkar och bidrar till den taktila perceptionen. Förutom fysikaliska mätningar på friktion och ytstruktur har värmekonduktivitet, mjukhet samt olika standard mätningar inom pappersindustrin mätts. En metod för att mäta friktion mellan ett finger och olika ytor har utvecklats för att i möjligaste mån återspegla friktionskomponenten i upplevt taktil perception. Friktionskoefficienter beräknades och jämfördes mellan alla ytor. De stimuli som har studerats är tryckpapper och mjukpapper samt modellytor, gjorda för att systematiskt undersöka hur ytstruktur påverkar perceptionen. Tillverkningsmetoden för modellytorna valdes så att ytorna var tåliga och kunde tvättas och därmed återanvändas. Strukturen på ytorna bestod av ett vågformat mönster där våglängden varierade mellan 270 nm och 100 µm och amplituden mellan 7 nm och 6 µm. Enligt vår vetskap är det första gången som strukturer i de här skalorna har gjorts utan att samtidigt ändra andra material egenskaper. Friktionskoefficienten minskade med ökad kvot mellan amplituden och våglängden på modellytorna samt med ytråheten på tryckpappren. En analytisk modell tillämpades på kontakten mellan ett finger och ytorna som visade att friktionskoefficienten beror av den verkliga kontaktarean. För de mycket grövre mjukpappren uppmättes inga stora skillnader i friktion förmodligen för att kontakarean mellan de olika mjukpapprena var lika. Den faktiska kontakarean visade sig också vara viktig för perceptionen av lenhet, strävhet, torrhet och svalhet. Det visade sig vara en stor perceptuell skillnad mellan olika typer av tryckpapper och mjukpapper utifrån hur stimuli placerade sig på en taktil karta. För de tre materialen användes enbart två alternativt tre egenskaper hos materialet för att särskilja mellan alla olika par. För tryckpapper verkade en viktig dimension kunna beskrivas av alla de perceptuella och fysikaliska egenskaper som har med kontaktarean att göra, d.v.s. lenhet, svalhet, torrhet, ytråhet, värmekonduktivitet samt friktion. För att taktilt särskilja mellan olika ytor där bara strukturen är varierade, kunde friktion och våglängden relateras till spridningen i kartan. Båda studierna stödjer duplex theory of texture perception, där ett spatialt sinne används för att särskilja en av de grövre ytorna från en slät, och ett vibrationssinne för att särskilja mellan olika släta strukturer. Friktionen visade sig alltså vara en viktig fysikalisk egenskap för strukturer under åtminstone 10 µm i ytråhet. Från fingerfriktions mätningar kunde även följande slutsatser dras: (i) Stora skillnader i friktionskoefficient mellan olika personer uppmättes, men trenderna mellan olika individer var samma, vilket gör att relativa skillnader i friktion från en individ är representativa. (ii) Lipider (fingerfett) som överförs från fingret till ytan vid kontakt sänker friktionen. (iii) Frekvensinnehållet i friktionskraften varierar mellan olika ytor och den frekvenstopp som ses vid 30 Hz kan möjligtvis bero på fingrets struktur eller resonansfrekvensen på huden. (iv) Den pålagda kraften under en friktionsmätning visar sig omedvetet regleras av den friktionskraft som fingret möter under rörelse.  Hur små strukturer som kan diskrimineras har indirekt undersökts genom likhetsförsöket på modellytorna där försökspersoner skulle bedöma hur lika alla par av ytor kändes. Resultaten visade att ytorna med våglängder på 760 nm och 870 nm upplevdes olika jämfört med referens ytor utan något systematiskt mönster, medan ytan med 270 nm i våglängd inte kunde särskiljas. Amplituden på ytan som kunde diskrimineras var endast ca 10 nm, vilket indikerar att nanoteknologi mycket väl kan bidra inom haptiken och för att i framtiden kontrollera den taktila perceptionen. / <p>QC 20121026</p>