Dissertations / Theses on the topic 'Dispersion'

La première partie de cette thèse concerne l'étude du problème de Cauchy pour l'équation de KdV quasi-linéaire.On établit un théorème d'existence locale obtenu grâce à des propriétés structurelles et des techniques de jauge qui permettent de compenser les pertes de dérivées apparentes dans les estimations a priori.Dans la seconde partie, les propriétés de stabilité orbitale co-périodique et modulationnelle sont explorées numériquement en exploitant des critères algébriques tous établis à partir d'une même intégrale d'action et de ses dérivées secondes. Notre méthode utilise des quadratures numériques suivies de différences finies afin de calculer la matrice hessienne de l'intégrale d'action. Le comportement asymptotique de cette matrice nous pousse à prêter beaucoup d'attention à l'étude des ondes de grande période ou de faible amplitude. Les résultats numériquesprésentés fournissent de nombreuses informations en lien avec des questions ouvertes.On effectue également des simulations directes sur le système d' ÉDP original pour étudier à la fois le comportement des ondes périodiques sous différents types de perturbations, et les solutions de problèmes de Cauchy avec donnée initiale discontinue. Pour ces derniers, on s'attend à observer des chocs dispersifs, dont la compréhension est basée sur le problème de Gurevich-Pitaevskii, où les équations modulées à la Whitham sont utilisées pour approcher la zone oscillante des chocs. On compare des simulations directes aux solutions idéales du problème de Gurevich-Pitaevskii, en commençant par la célèbre équation de KdV
The first part of this manuscript presents a well-posedness result for a quasilinear version of the KdV equation.The proof takes advantage of structural properties and gauge techniques to deal with apparent loss of derivativesin a priori estimates.In the second part, we investigate the modulational and orbital coperiodic stability of periodic waves by computingalgebraic criteria involving the same abbreviated action integral and its second order derivatives. Our methoduses numerical integrations followed by finite differences to compute the Hessian matrix of the action integral.We pay attention to the asymptotic behavior of this matrix in the large period and small amplitude limits. Thenumerical results about stability give some new insight on several analytical open questions.Finally, direct numerical computations are done on the original system of PDEs to study the behavior of periodictraveling waves under various kinds of perturbations and the solutions of Cauchy problem with discontinuousinitial data. For the latter, we expect dispersive shock waves to arise. The building block for understandingdispersive shocks is known as the Gurevich-Pitaevskii problem, in which modulated equations 'a la Whitham'are used as an approximate model for the oscillatory zone. We compare direct numerical simulations to idealizedsolutions of Gurevich-Pitaevskii problems, starting with the famous KdV equation

In fiber optic communication systems, the main linear phenomenon that causes optical pulse broadening is called dispersion, which limits the transmission data rate and distance. The principle nonlinear effect, called self-phase modulation, can also limit the system performance by causing spectral broadening. Hence, to achieve the optimal system performance, high data rate and low bandwidth occupancy, those effects must be overcome or compensated. In a nonlinear dispersive fiber, properties of a transmitting pulse: width, chirp, and spectra, are changed along the way and are complicated to predict. Although there is a well-known differential equation, called the Nonlinear Schrodinger Equation, which describes the complex envelope of the optical pulse subject to the nonlinear and dispersion effects, the equation cannot generally be solved in closed form. Although, the split-step Fourier method can be used to numerically determine pulse properties from this nonlinear equation, numerical results are time consuming to obtain and provide limited insight into functional relationships and how to design input pulses. One technique, called the Variational Method, is an approximate but accurate way to solve the nonlinear Schrodinger equation in closed form. This method is exploited throughout this thesis to study the pulse properties in a nonlinear dispersive fiber, and to explore ways to compensate dispersion for both single link and concatenated link systems. In a single link system, dispersion compensation can be achieved by appropriately pre-chirping the input pulse. In this thesis, the variational method is then used to calculate the optimal values of pre-chirping, in which: (i) the initial pulse and spectral width are restored at the output, (ii) output pulse width is minimized, (iii) the output pulse is transform limited, and (iv) the output time-bandwidth product is minimized. For a concatenated link system, the variational calculation is used to (i) show the symmetry of pulse width around the chirp-free point in the plot of pulse width versus distance, (ii) find the optimal dispersion constant of the dispersion compensation fiber in the nonlinear dispersive regime, and (iii) suggest the dispersion maps for two and four link systems in which initial conditions (or parameters) are restored at the output end. The accuracy of the variational approximation is confirmed by split-step Fourier simulation throughout this thesis. In addition, the comparisons show that the accuracy of the variational method improves as the nonlinear effects become small.
Master of Science

Alkylketene dimer, AKD, dispersions are used in the paper industry to obtain paper grades with a hydrophobic character i.e. resistance to sorption of water. AKD is used in neutral to alkaline internal sizing, pH in the interval of 6-9. AKD dispersions consist of wax particles emulsified in water. The particles are electrostatically and in most cases also sterically stabilized by cationic polyelectrolytes. The size of the particles is usually in the range of 0.5-2 µm in diameter. The idea of having cationic particles is that they are supposed to be deposited onto the negatively charged fiber surfaces, heterocoagulation. An increased usage of recycled pulp and a closure of the wet-end circuits of the paper machine will lead to increasing levels of dissolved and colloidal substances. These substances could be detrimental by affecting the AKD deposition onto the fiber material and the colloidal stability i.e. induce flocculation of sizing particles. Flocculation could lead to an inhomogeneous distribution of the sizing agent. The aims addressed in this thesis were the following: to investigate if high levels of shear, electrolyte concentration, anionic polymers and surfactants could affect the colloidal stability and induce flocculation of differently designed AKD dispersions to study the migration of AKD and the influence of extractives on the migration to study the sizing efficiency and retention using flocculated dispersions The colloidal stability of the dispersions was tested under shear by measuring the particle size distribution and the microelectrophoretic mobility. The migration of AKD through paper sheets with defined thickness and through paper sheets impregnated with extractives was analyzed with contact angle measurements on stored samples. The sizing efficiency of flocculated AKD was determined by measuring 60-second Cobb and contact angles on laboratory sheets. The retention of AKD was determined by quantitative analysis of the AKD content in the laboratory sheets using alkaline hydrolysis followed by solvent extraction and quantification with capillary gas chromatography. It was shown that anionic polymers and surfactants could seriously affect the colloidal stability of the dispersions, while shear and electrolyte concentration had a small influence. Dispersions with a high surface charge flocculates easier than dispersions with a low surface charge in process water from the wet-end of a linerboard paper machine. The flocculation rate is fast and occurs on the same time scale as deposition onto fines and fibers. The AKD agglomerates could be up to 30 µm in diameter even at high levels of shear. The AKD diffusion coefficient in paper sheets was estimated to be 10-11 m2/s at a temperature above the melting point of the wax. The results indicate that extractives do not interfere with the AKD migration. A reasonable explanation is that migration occurs via the vapor phase. It was also shown that sizing with flocculated AKD improved the sizing efficiency significantly due to increased retention. This clearly indicates that migration is efficient and that agglomerates can be used for internal sizing provided that the flocculation process is controlled. The conventional picture that the sizing agents must be very evenly distributed to achieve efficient sizing could, from the viewpoint of these results, be questioned. The process of sizing with pre-flocculated AKD dispersions is the subject of a patent application. Even if this thesis is focused on AKD dispersions, the obtained knowledge should be possible to transfer to other sizing systems. The emulsification process for rosin and ASA is based on the same principles as for AKD.
Godkänd; 2002; 20070222 (ysko)

Thesis (M.Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2001.
Includes bibliographical references (leaves 83-87).
by Samuel Tin Bo Wong.
M.Eng.

The linearized Einstein equation describing graviton propagation through a chiral medium appears to be helicity dependent. We analyze features of the corresponding spectrum in a collision-less regime above a flat background. In the long wave-length limit, circularly polarized metric perturbations travel with a helicity dependent group velocity that can turn negative giving rise to a new type of an anomalous dispersion. We further show that this chiral anomalous dispersion is a general feature of polarized modes propagating through chiral plasmas extending our result to the electromagnetic sector.

The dissertation studies traffic dispersion modeling in four parts. In the first part, the dissertation focuses on the Robertson platoon dispersion model which is the most widely used platoon dispersion model. The dissertation demonstrates the importance of the Yu and Van Aerde calibration procedure for the commonly accepted Robertson platoon dispersion model, which is implemented in the TRANSYT software. It demonstrates that the formulation results in an estimated downstream cyclic profile with a margin of error that increases as the size of the time step increases. In an attempt to address this shortcoming, the thesis proposes the use of three enhanced geometric distribution formulations that explicitly account for the time-step size within the modeling process. The proposed models are validated against field and simulated data. The second part focuses on implementation of the Robertson model inside the popular TRANSYT software. The dissertation first shows the importance of calibrating the recurrence platoon dispersion model. It is then demonstrated that the value of the travel time factor β is critical in estimating appropriate signal-timing plans. Alternatively, the dissertation demonstrates that the value of the platoon dispersion factor α does not significantly affect the estimated downstream cyclic flow profile; therefore, a unique value of α provides the necessary precision. Unfortunately, the TRANSYT software only allows the user to calibrate the platoon dispersion factor but does not allow the user to calibrate the travel time factor. In an attempt to address this shortcoming, the document proposes a formulation using the basic properties of the recurrence relationship to enable the user to control the travel time factor indirectly by altering the link average travel time. In the third part of the dissertation, a more general study of platoon dispersion models is presented. The main objective of this part is to evaluate the effect of the underlying travel time distribution on the accuracy and efficiency of platoon dispersion models, through qualitative and quantitative analyses. Since the data used in this study are generated by the INTEGRATION microsimulator, the document first describes the ability of INTEGRATION in generating realistic traffic dispersion effects. The dissertation then uses the microsimulator generated data to evaluate the prediction precision and performance of seven different platoon dispersion models, as well as the effect of different traffic control characteristics on the important efficiency measures used in traffic engineering. The results demonstrate that in terms of prediction accuracy the resulting flow profiles from all the models are very close, and only the geometric distribution of travel times gives higher fit error than others. It also indicates that for all the models the prediction accuracy declines as the travel distance increases, with the flow profiles approaching normality. In terms of efficiency, the travel time distribution has minimum effect on the offset selection and resulting delay. The study also demonstrates that the efficiency is affected more by the distance of travel than the travel time distribution. Finally, in the fourth part of the dissertation, platoon dispersion is studied from a microscopic standpoint. From this perspective traffic dispersion is modeled as differences in desired speed selection, or speed variability. The dissertation first investigates the corresponding steady-state behavior of the car-following models used in popular commercially available traffic microsimulation software and classifies them based on their steady-state characteristics in the uncongested regime. It is illustrated that with one exception, INTEGRATION which uses the Van Aerde car-following model, all the software assume that the desired speed in the uncongested regime is insensitive to traffic conditions. The document then addresses the effect of speed variability on the steady-state characteristics of the car-following models. It is shown that speed variability has significant influence on the speed-at-capacity and alters the behavior of the model in the uncongested regime. A method is proposed to effectively consider the influence of speed variability in the calibration process in order to control the steady-state behavior of the model. Finally, the effectiveness and validity of the proposed method is demonstrated through an example application.
Ph. D.

Cette thèse examine la dispersion multivariée des modelés normales stables Tweedie. Trois estimateurs de fonction variance généralisée sont discutés. Ensuite dans le cadre de la famille exponentielle naturelle deux caractérisations du modèle normal-Poisson, qui est un cas particulier de modèles normales stables Tweedie avec composante discrète, sont indiquées : d'abord par fonction variance et ensuite par fonction variance généralisée. Le dernier fournit la solution à un problème particulier d'équation de Monge-Ampère. Enfin, pour illustrer l'application de la variance généralisée des modèles Tweedie stables normales, des exemples à partir des données réelles sont fournis
This thesis examines the multivariate dispersion of normal stable Tweedie (NST) models. Three generalize variance estimators of some NST models are discussed. Then within the framework of natural exponential family, two characterizations of normal Poisson model, which is a special case of NST models with discrete component, are shown : first by variance function and then by generalized variance function. The latter provides a solution to a particular Monge-Ampere equation problem. Finally, to illustrate the application of generalized variance of normal stable Tweedie models, examples from real data are provided

Solutions to a number of turbulent dispersion problems, involving a contaminant issuing from a steady source into uniform, steady open channel flow, are presented. These problems include the two and three-dimensional dispersion of a neutrally buoyant contaminant and the two-dimensional dispersion of buoyant particles and are modelled with the diffusion equation incorporating turbulent diffusion coefficients. In order to ensure that the solutions simulate the physical processes as accurately as possible the experimentally determined logarithmic velocity profile and the theoretically deduced parabolic diffusivity are used. The solutions take the form of one or two eigenfunction expansions, the eigenfunctions and eigenvalues of which are governed by Sturm-Liouville theory. Generally the power series method for solving ordinary differential equations is employed to derive the eigenfunctions and eigenvalues and in nearly all cases this method is found to be accurate, straightforward in its use and efficient with computing resources. Much useful information is deduced from the eigenfunctions and eigenvalues. The rate at which equilibrium conditions are approached and the ideal source position, that from which the contaminant is most rapidly mixed, come naturally from these quantities. An experimental programme, with the aims of verifying the theoretical solution for vertical dispersion of a neutrally buoyant contaminant and measuring the lateral turbulent diffusion coefficient, is described. The two-dimensional results for vertical mixing strongly support the theoretical predictions, using the measured logarithmic velocity profile and the deduced parabolic diffusivity in the turbulent diffusion equation, and indeed confirm the location of the ideal source derived from theory. The values of the depth-averaged lateral diffusivity obtained from the experiments lie at the lower end of the range of values obtained by other experimentalists. A reanalysis of these previously published results demonstrates that, provided the natural turbulence of a wide channel is the only mixing mechanism present, the depth-averaged lateral diffusivity, non-dimensionalised by the flow depth and shear velocity, is in fact independent of all flow parameters, except when the friction factor is small. The dependence of the rate of lateral spreading on height in the flow and the location of the source demonstrates, at least qualitatively, that the vertical dependence of the lateral diffusivity is in essence the same as the velocity distribution. Verification of the theoretical solution for dispersion of buoyant particles is achieved with the experimental results of Jobson and Sayre (1970) which indicate that the theoretical model is valid for fine particles dispersing in strongly turbulent flow.

This is an experimental and theoretical investigation of the dispersion of a round water jet discharging at various angles into a rectangular channel. A fundamental study of the jet is not only essential for a better understanding of the flow conditions produced by confined water jets but for a scientific approach to the design of hydraulic structures and to determine an efficient form of stilling basin for high velocity discharge from pipe outlets. The Laser Doppler Anemometry (LDA) technique was adapted for measurement of mean velocities and turbulence characteristics,, without any interference in the flow, and was utilised for the investigation of the complex three dimensional circulating flow which was experienced in the channel. In the experiments the inclination of the jet was varied from 45 to 90 degrees to the bed of the channel, while differing ratios of channel width and depth to jet diameter were studied for various Froude numbers. Detailed measurements of velocity decay, normal and lateral velocity profiles, distributions of pressure and turbulence characteristics have been carried out for selected flow conditions relating to the 45 degree oblique and vertical jet in order to determine the flow pattern and head dissipations. The experimental results have been analysed and compared with Glauert Is theory for a radial wall jet as a first approximation neglecting gravity forces when small compared with turbulent forces. Based on these results erosion experiments and model studies using a solid apron and a sand bed downstream, have been conducted to predict the minimum size of an efficient stilling basin and dimensions of any required blocks. Finally generalised design guide-lines and a standard code of practice have been developed for a stilling basin with high velocity pipe outlets. The research work will provide practical information and design procedures for consultants and other organisations working on the design and maintenance of a variety of water projects both in the UK and overseas.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 1986.
MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE.
Vita.
Includes bibliographies.
by Donald Lyle Koch.
Ph.D.

The general objective of this research was to examine the space/time distribution of traffic platoons over a long stretch of roadway with conditions predominant for the southern Arizona urban area. Two sites were chosen for data collection. Both traffic links were one mile long between two successive traffic signals and both were typical of the local low-friction traffic flow conditions. All data were recorded by observers using 20-channel Esterline-Angus recorders. The specifics of the data collection method permitted studying only variables such as the lane of travel, traffic composition, platoon size, traffic volume and the influence of an uphill gradient on platoon behavior. The investigated platoons remained clearly bunched as they progressed downstream along the researched traffic links. The research indicates that it would take much more than a mile (available distance) for the vehicles in the platoon to reach free-flow conditions.

Particles containing 55% divinylbenzene (DVB) have been prepared using dispersion polymerisation. The steric stabilisers that have been utilised are partially hydrolysed poly(vinyl acetate)s, poly(ethylene oxide) and a poly(ethylene oxide) macromonomer in methanolic media. The concentrations of stabiliser, monomer and initiator have been varied to investigate the influence that they have on the particle size and the particle size distribution. The particles have been characterised by scanning electron microscopy (SEM) for a visual impression of the particles in addition to laser diffraction particle size analysis and hydrodynamic chromatography (HDC) for particle size.

River pollution is the contamination of river water by pollutant being discharged directly or indirectly on it. Depending on the degree of pollutant concentration, subsequent negative environmental effects such as oxygen depletion and severe reductions in water quality may occur which affect the whole environment. River pollution can then cause a serious threat for fresh water and as well as the entire living creatures. Dispersion in natural stream is the ability of a stream to dilute soluble pollutants. Different types of pollution, such as accidental spill of toxic chemicals, industrial waste, intermittent discharge from combined sewer overflows and temperature variations produced by thermal outflows, may generate a cloud whose longitudinal spreading strongly affects the pollutant concentration dynamics. Pollutants discharging form a point source is easier to control where as pollutant discharging from non point sources arehardlycontrollable and may represent severe threat to the river ecosystem. The longitudinal dispersion coefficient is used to describe the change in characteristics of a solute cloud from an initial state of high concentration and low spatial variance to a downstream state of lower concentration and higher spatial variance. Therefore, in order to correctly estimate the degree of pollutionwithin a stream and ensure an efficient and informed management of riverine environments,a reliable estimationof the dispersion withinthe stream is a crucial concern. The objective of my research is to develop a mathematical model for determining the dispersion in alluvial river. In order to achieve the goal, a model has been developed which provides an analytical relation for the prediction of the dispersion coefficient in natural streams, given the planimetric configuration of the river and the relevant hydrodynamic and morphodynamic parameters (i.e., width to depth ratio, the sediment grain size, scaled with the flow depth, the Shields stress). One of the most striking features of alluvial rivers is their tendency to develop regular meandering plan forms. Their geometry is in fact characterized by a sequence of symmetrical curves which amplify over time due to erosion processes at the outer bank and deposition at the inner bank. This planimetric pattern affects both the hydrodynamics of the river and the distribution of bed elevations, as well as its hydraulic response, as the average bed slope is progressively reduced along with the flow cross sections. The flow filed that establishes in meandering rivers has clearly a great relevance on the behavior of the pollutant cloud and hence on the dispersion that drives its microscopic evolution. To develop a dispersion coefficient predicting model, the analytical models of flow field establishing in the cross section of a straightriver [TubinoansColombini, 1992] and of a meandering river [Frascati and Lanzoni, 2013] aredeveloped. The two dimensional mass balance equation governing the dynamics of a pollutant is then solved using asymptoticexpression and Morse and Feshbach[1953] formalism. Finally, using the two dimensional spatial distributions of the concentration, the flow depth and the velocity, the dispersion coefficient are obtained. For straight rivers the cross-sectional velocityand the theoretically predicted dispersion coefficients with the field datacollected by Godfrey and Frederick (1970)in two rivers (Clinch River, Copper Creek). The comparison is reasonably good. The performance of the model is also tested with reference to the predictions provided by the model proposed by Deng (2001). The resultant model is found to give prediction closer to 80% of the experimental data,a much better performance agreement with respect to the model of Deng (2001). The results of the model developed to estimate the dispersion coefficients in meandering river, have been compared with the experimental data available in experimental and referring to six different rivers. Also in this case the agreement between the dispersion coefficient predicted theoretically and those calculated on the basis of tracer tests is quite good and better than that ensured by the other theoretical and empirical predictors available in literature
Lo studio della dinamica di un inquinante convenzionale (e.g., BOD) all’interno di un corso d’acqua naturale richiede la conoscenza del campo di moto e della batimetria che si realizzano nel corso d’acqua stesso, delle modalità di immissione (continua o localizzata, accidentale o sistematica) e delle reazioni chimiche a cui l’inquinante è soggetto. L’obiettivo della presente tesi è quello di caratterizzare la distribuzione spazio-temporale della nuvola di inquinante, in modo da poter valutare i carichi inquinanti e controllare il soddisfacimento, o meno, dei requisiti di legge. In particolare, l’attenzione è stata concentrata sul comportamento dell’inquinante nel cosiddetto campo lontano, ovvero a una distanza dalla sorgente tale per cui l’inquinante si è mescolato verticalmente e trasversalmente, distribuendosi quasi uniformemente sulla sezione. In tali condizioni, ai fini applicativi è sufficiente studiare il comportamento della concentrazione media sulla sezione. Tale comportamento è retto dalla classica equazione dell’avvezione-dispersione la cui soluzione, nel caso di immissione istantanea e localizzata di una determinata massa di sostanza inquinante e tratto di corso d’acqua omogeneo, è data dal classico andamento Gaussiano. La stima del coefficiente di dispersione da utilizzare nella suddetta equazione risulta di fondamentale importanza per una corretta previsione del comportamento spazio-temporale dell’inquinante. La struttura di tale coefficiente, d’altra parte, è strettamente legata al campo di moto che si realizza in un alveo naturale e, in particolare, alle deviazioni rispetto ai valori medi sulla sezione della velocità e della concentrazione. Utilizzando le attuali conoscenza relative al campo di moto in alvei a fondo mobile, nella presente tesi viene derivata una soluzione analitica del coefficiente di dispersione dipendente da parametri in ingresso quali il rapporto larghezza-profondità desumibile dalla geometria della sezione, il diametro dei sedimenti, normalizzato con la profondità della corrente, la pendenza del corso d’acqua. Il problema è inizialmente affrontato nel caso di alveo rettilineo e sezione in equilibrio con il trasporto in cui il fondo varia gradualmente in direzione trasversale. Risulta cos`ı possibile suddividere la generica sezione in una zona centrale, dove la profondità della corrente si mantiene approssimativamente costante, e due regioni di sponda, nelle quali la profondità si riduce gradualmente a zero. Il campo di moto calcolato tendendo conto di questa lenta variazione trasversale del fondo (che consente di semplificare opportunamente l’equazione della quantità di moto), raccordato con quello che si realizza nella regione centrale, unitamente all’equazione del bilancio di massa dell’inquinante, consentono di determinare analiticamente il coefficiente di dispersione. Il passo successivo è stato quello di considerare in caso di alvei alluvionali ad andamento meandriforme. Si tratta di una tipologia di configurazione planimetrica molto comune in natura, caratterizzata da una sequenza più o meno regolare di curve alternate. Sfruttando il fatto che molto spesso la curvatura dell’asse del canale è debole, risulta possibile ottenere una soluzione analitica del campo di moto e della topografia del fondo. Tale soluzione, associata all’equazione del bilancio di massa dell’inquinante riscritta in coordinate curvilinee, opportunamente semplificata sfruttando l’ipotesi di deboli curvature, consente di determinare analiticamente il coefficiente di dispersione. Le stime del coefficiente di dispersione ottenute nei casi di alveo rettilineo e ad andamento meandriforme, sono state infine confrontate con i dati di campo reperibili in letteratura, ottenuti tramite campagne di misura con traccianti. Per entrambe le configurazioni planimetriche analizzate(rettilinea e meandriforme), l’accordo tra coefficienti osservati in campo e i risultati delle previsioni teoriche appare generalmente buono e, comunque, decisamente migliore di quello offerto dalle varie formulazioni semi-empiriche e teoriche attualmente disponibili in letteratura

Hidrolisados proteicos possuem propriedades terapêuticas e são absorvidos mais facilmente pelo organismo quando comparados às proteínas, no entanto sua aplicação em alimentos é dificultada por serem higroscópicos, reativos e apresentarem gosto amargo. A microencapsulação por spray chilling pode ser uma alternativa para solucionar essas limitações. Este método de encapsulação consiste na atomização de uma mistura, formada pela dispersão ou emulsão do material ativo com o carreador fundido, em uma câmara com temperatura inferior ao ponto de fusão do carreador, que nessas condições solidifica, formando micropartículas esféricas. O objetivo deste trabalho foi elaborar micropartículas de hidrolisado de proteína de soja utilizando o método de spray chilling e gordura vegetal (PF 51°C) como carreador. Foram realizados ensaios para obtenção das micropartículas avaliando a alimentação por emulsão e dispersãoe diferentes formulações variando a proporção material ativo:encapsulante (1:5 e 1:10), velocidades de rotação no ultra-turrax (6000 e 8000 rpm) e três diferentes temperaturas (60, 70 e 80°C), totalizando dezoito tratamentos. As misturas foram submetidas à análise reológica para determinação de viscosidade e após serem atomizadas em spray chiller as micropartículas obtidas foram caracterizadas por FTIR, Difração de Raio-X, distribuição e tamanho médio por difração a laser e morfologia por microscopia eletrônica de varredura e confocal. Foram obtidas micropartículas lipídicas sólidas esféricas e aglomeradas, o tamanho médio variou de 53,06 ± 2,17 µm e 68,03 ± 14,07 µm, sem diferenças significativas entre os tratamentos. Partículas obtidas pela atomização da emulsão apresentaram poros, todavia exibiram maior capacidade de carregamento do hidrolisado, cerca de 96%, enquanto as obtidas por dispersão apresentaram 54%. Variações durante o preparo da emulsão não proporcionaram alterações na morfologia e tamanho de partícula nas micropartículas, apesar de terem tido influência sobre as propriedades reológicas do sistema. A análise de difração de raios-X indicou que as micropartículas após 90 dias de preparo apresentaram a estrutura na forma polimórfica mais estável. A espectroscopia na região do infravermelho (FTIR) revelou que não ocorreu interação entre os ingredientes independentemente do modo de preparo das micropartículas. Tais resultados demonstram que a técnica de spray chilling é eficiente na microencapsulação de hidrolisado proteico de soja, possibilitando uma futura aplicação em alimentos.
Protein hydrolysates possess therapeutic properties and absorption easier than to proteins; however its application in food is limited due to its bitter taste, hygroscopic and reactivity. Encapsulation byspray chilling could be an alternative to minimize these limitations. This method consists in the atomization of a mixture formed by the dispersion or emulsion of the active material with the molten carrier, into an environment with temperature below the melting point of the carrier, under these conditions it solidifies to form spherical microparticles. The aim of this work was to develop microparticles loaded with hydrolyzed soy protein using the method of spray chilling and vegetable fat (PF 51°C) as carrier. Tests were conducted to obtain microparticles evaluating the feed by emulsion and dispersion and different formulations by varying the proportions active materials:carrier (1:5 and 1:10), homogenization speed by Ultra-Turrax (6000 and 8000 rpm) and temperature (60, 70 and 80°C ), totaling eighteen treatments. The mixtures were subjected to rheological analysis for determination of viscosity and after being atomized at spray chiller obtained microparticles were characterized by infrared spectroscopy and X-ray diffraction, particle size distribution and mean diameter measured using a laser light diffraction instrument and morphology was observed by scanning electron microscopy (SEM) and confocal microscopy. Solid lipid microparticles obtained were spherical and agglomerated the average size between 53.06 ± 2.17 µm and 68.03 ± 14.07 µm, there was no significant difference between formulations. Particles obtained by atomization of emulsion had presence of pores, but exhibited a higher loading capacity of the hydrolyzed, about 96%, while that obtained by dispersion had 54%. Changes during the preparation of the emulsion no provided changes at morphology and particle size of the microparticles, despite having influence on the rheological properties of the system. The analysis of X-ray diffraction showed that the microparticles after 90 days of storage had β polymorphic form. The infrared spectroscopy (FTIR) showed that there was no interaction between the ingredients regardless of the mode of preparation of the microparticles. These results demonstrate that the technique spray chilling is efficient in microencapsulation of soy protein hydrolyzate, allowing future use in foods.

AGÊNCIA NACIONAL DE PETRÓLEO
Neste trabalho é apresentado um estudo sobre a determinação matemática dos valores da dispersão cromática total, do zero de dispersão distribuído e efeitos não lineares em fibras ópticas de dispersão deslocada (DS). Uma metodologia para caracterização das dispersões cromáticas e para os zeros de dispersão local das fibras estudadas é elaborada com a utilização do modelo de fibra degrau equivalente e de aproximações entre as fibras ópticas dos enlaces trabalhados. A relação entre o diâmetro do campo modal e o zero de dispersão cromática distribuído segundo A. Rossaro [6] é discutida e comprovada através da realização de uma série de medidas práticas para a determinação dos efeitos não lineares das fibras de dispersão deslocada dos enlaces da Petrobrás. O objetivo deste trabalho é analisar estes efeitos prejudiciais a transmissão de sinais ópticos de alta velocidade apresentados nos cabos submarinos da Petrobrás entre o Porto de Imbetiba e as plataformas de Pargo I e Pampo I na Bacia de Campos, analisando os resultados obtidos e caracterizando as possibilidades de upgrade destes enlaces.
This work presents a study on the mathematical determination of the total chromatic dispersion, zero dispersion wavelength and nonlinear optical effects in dispersion shifted (DS) fiber optic system. A methodology to determine the chromatic dispersion and zero dispersion wavelength is proposed using the equivalent step index model and the similarity of the total chromatic dispersion measured in fibers of the links under study. The relationship between the mode field diameter and the zero dispersion wavelength according to A. Rossaro [6] is discussed and proven with a series of practical measurements for the determination of the nonlinear effects of the dispersion shifted optical fibers of Petrobras links Imbetiba - Pargo and Imbetiba - Pampo of the Campos Basin.
En este trabajo se presenta un estudio sobre la determinación matemática de los valores de dispersión cromática total, del cero de dispersión distribuido y los efectos no lineales en fibras ópticas de dispersión desplazada (DS). Se elabora una metodología para la caracterización de las dispersiones cromáticas y para los ceros de dispersión local de las fibras estudiadas; utililizando el modelo de fibra escalón equivalente y de aproximaciones entre las fibras ópticas de los enlace. Se discute la relación entre el diámetro del campo modal y el cero de dispersión cromática distribuido según A. Rosaro [6] se comprueba a través de la realización de una serie de medidas prácticas para la determinación de los efectos no lineales de las fibras de dispersión desplazada de los enlaces de la Petrobrás. EL objetivo de este trabajo es analizar los efectos perjudiciales a la transmisión de señales ópticos de alta velocidad que se presentan en los cables submarinos de la Petrobrás entre el Puerto de Imbetiba y las plataformas de Pargo I y Pampo I en la Bacia de Campos, analizando los resultados obtenidos y caracterizando las posibilidades de upgrade de estos enlaces.

La dispersion natale est un processus durant lequel les individus se déplacent de leur domaine natal vers leur domaine de reproduction. Ce processus fondamental pour la dynamique et la persistance des populations passe par l'évitement de la consanguinité ou la capacité des individus à atteindre et coloniser de nouveaux habitats contenant des ressources ou des partenaires sexuels. La dispersion peut donc comporter de nombreux bénéfices pour les individus disperseurs. Cependant, elle peut également être coûteuse pour les individus, en raison d'une augmentation de la mortalité ou des blessures, une dépense énergétique élevée, ou enfin la perte d'un habitat natal favorable ou de temps à allouer à une autre activité. L'expression du phénotype de dispersion au niveau populationnel dépend donc de la balance entre coûts et bénéfices, et la théorie prévoit que les disperseurs devraient être contre-sélectionnés si les coûts deviennent supérieurs aux bénéfices engendrés par la dispersion. Dans le contexte actuel de changements globaux, on peut s'attendre à ce que (1) les coûts de la dispersion augmentent avec la dégradation de l'environnement et (2) à ce que cette augmentation des coûts de la dispersion diminue le succès et la portée géographique de ce processus, au travers de mécanismes évolutifs. De plus, les coûts de la dispersion devraient varier avec le type de déplacement effectué par l'individu disperseur, et par conséquent, on peut se demander (3) quelles tactiques alternatives de dispersion un individu pourrait adopter dans un environnement contrasté. Au cours de ce doctorat, mon objectif était de travailler sur ces trois hypothèses en utilisant deux jeux de données portant sur deux populations de chevreuils distinctes (données GPS en Haute-Garonne et données de Capture-Marquage-Recapture dans les Deux-Sèvres, France), ainsi qu'une approche par modélisation. Tout d'abord, j'ai montré que, malgré leur bonne condition physique, les disperseurs subissent des coûts de mortalité, reproduction et croissance. J'ai également montré que le changement climatique pourrait augmenter les coûts de mortalité chez ces individus. Parallèlement à ces variations de coûts, j'ai aussi mis en évidence que la dispersion avait diminué au cours des 30 dernières années de plus de 30% chez les deux sexes. Ensuite, j'ai identifié l'existence d'au moins six tactiques alternatives de dispersion chez le chevreuil, caractérisées par des phénologies, durées et amplitudes différentes, ce qui pourrait induire différentes répercussions en termes de coûts et de dynamique de population. Enfin, mes analyses de modélisation suggèrent que la dispersion pourrait évoluer de sorte à observer davantage de mouvements tortueux ou de courte distance quand les coûts de mortalité augmentent, ce qui limiterait la portée géographique de la dispersion. De façon générale, ces résultats soulignent les effets préoccupants que les changements globaux pourraient avoir sur les coûts et sur l'évolution de la dispersion. Ce processus étant à la fois espèce et condition dépendant, davantage d'études portant sur les impacts des changements globaux sur les coûts de la dispersion, idéalement prenant en considération les tactiques alternatives de dispersion, nous permettront de mieux prédire comment les espèces pourraient faire face aux changements globaux
Natal dispersal is a process by which individuals move from their natal to reproductive ranges which is fundamental for population dynamics and persistence. Through for example the limitation of inbreeding or the capacity it provides to reach and colonize new habitats containing resources or mates, it can be highly beneficial to dispersing individuals. However, dispersal can also be costly for the individuals, through increased mortality or attrition, energy expenditure, or lost habitat opportunities and time. Its expression at the population level thus depends on the balance between costs and benefits, and theory states that dispersal may become counter-selected if costs outweigh benefits. In the current context of global change, we may expect (1) dispersal costs to increase with the degradation of environments and (2) increased dispersal costs to decrease dispersal success and geographical reach through evolutionary mechanisms. Moreover, because dispersal costs may vary with actual dispersal movement, we may wonder what are the discrete alternative tactics roe deer may use in contrasting environments (3). In this PhD, I aimed to address these three perspectives using two roe deer datasets from two geographically distinct populations (GPS data in Haute-Garonne and Capture-Mark-Recapture data in Deux-Sèvres, France), as well as a modelling approach. First, I show that, despite having a good body condition, dispersers incur costs in terms of mortality, reproduction and growth, and that climate change may increase mortality costs. Concomitant to these variations in costs, I also found that realised dispersal has diminished over the past 30 years by more than 30% in both sexes. Second, I identified at least six alternative dispersal tactics in roe deer, characterised by different movement timing, amplitude and duration, which may imply different outcomes in terms of costs and population dynamics. Lastly, my analyses suggest that dispersal might evolve towards tortuous and short distance movements when mortality costs increase, limiting the geographical reach of dispersal. Overall, these results highlight the concerning effects global changes may have on dispersal costs and dispersal evolution. Because dispersal is a species and context dependent process, more studies addressing the impacts of global changes on dispersal costs, ideally incorporating alternative dispersal tactics, will provide valuable information to better predict how species may cope with environmental changes

With growing trend in "cloud computing" and increase in the data moving into the Internet, the need to store large amounts of data by service providers such as Google, Yahoo and Microsoft has increased over time. Now, more than ever, there is a need to efficiently and securely store large amounts of data. This thesis presents an implementation of a Ramp Scheme that confidentially splits a data file into a configurable number of parts or shares of equal size such that a subset of those shares can recover the data entirely. Furthermore, the implementation supports a threshold for data compromise and data verification to verify that the data parts have not been tampered with. This thesis addresses two key problems faced in large-scale data storage, namely, data availability and confidentiality.

Demand uncertainty has been recognized as one factor that may cause price dispersion in perfectly competitive markets with costly and perishable capacity. With the persistence of the degree of price dispersion in increasingly competitive markets, demand uncertainty has become more important for us to understand the phenomenon of fare inequality. This dissertation consists of three related studies on this topic. In the first study, Prescott (1975) model is extends by incorporating the heterogeneity of customers' reservation values. The model shows that the equilibrium price dispersion also depends on the mix of customers and their reservation values. With customer segmentation based on reservation values, the equilibrium price dispersion is more efficient than what can be achieved without segmentation. In the airline industry context, the model implies that different prices can exist simultaneously in the market and carriers would provide more seats if they can segment their travelers. This sheds light on an alternative motivation for airlines to require Saturday night stay over other than the practice of price discrimination. In the second study, a price simulation in the airline industry is conducted. The stochastic demand for coach class, nonstop, air travel service on the observed routs is calculated. Then a market price schedule based on Prescott's model is simulated by using nonparametric method. The comparison between the simulated price distribution and the actual price distribution provides evidence that on average more than 60 percent of the fare inequality on the observed routes can be accounted for by cost variation due to demand uncertainty under the condition of perfect competition. At last, an empirical model is specified to explore the relationship between route demand uncertainty and carrier price dispersion in U.S. air travel markets. The results demonstrate that the effect of route demand uncertainty on carrier price dispersion varies with the market structure. In monopoly market, the route demand uncertainty has no effect on carrier price dispersion. While in duopoly and competitive markets, the increase of route demand uncertainty is associated with the decrease of the carrier price dispersion. Furthermore, the negative relationship is magnified when the market becomes more competitive.

Since the introduction of derivatives into the modern financial market, volatility based tradingstrategies have emerged as important tools for asset managers. Since the financial crisis apopular trading strategy has been dispersion trading, however few published studies ofdispersion trading exist. This thesis aim to perform a study of how dispersion strategies performand their characteristics. This is achieved by finding basic common dispersion trading strategies,isolate and evaluate their attributes to then draw conclusions in general about dispersion trading.Three basic dispersion strategies are found based on vanilla option spreads and their performanceis back-tested. It was found that the strategies delivered positive return with low marketcorrelation and acceptable risk. It is also found that transaction costs is a key-factors tosuccessfully use dispersion trading. Thus it is a vital factor to consider when creating adispersion based trading strategy. An interesting topic for further research is how trading signalssuch as the implied correlation and the implied volatility spread can be used to increaseprofitability. As well to model market impact from dispersion trading.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2006.
Includes bibliographical references (p. 171-183).
Vegetation is ubiquitous in rivers, estuaries and wetlands, strongly influencing both water conveyance and mass transport. The plant canopy affects both mean and turbulent flow structure, and thus both advection and dispersion. Accurate prediction of the fate and transport of nutrients, microbes, dissolved oxygen and other scalars depends on our ability to quantify vegetative impacts. In this thesis, the focus is on longitudinal dispersion, which traditionally has been modeled by drawing analogy to rough boundary layers. This approach is inappropriate in many cases, as the vegetation provides a significant dead zone, which may trap scalars and augment dispersion. The dead zone process is not captured in the rough boundary model. This thesis describes a new theoretical model for longitudinal dispersion in a vegetated channel, which isolates three separate contributory processes. To evaluate the performance of the model, tracer experiments and velocity measurements were conducted in a laboratory flume. Results show that the mechanism of exchange between the free stream and the vegetated region is critical to the overall dispersion, and is primarily controlled by the canopy density.
(cont.) A numerical random walk particle-tracking model was developed to assess the uncertainty associated with the experimental data. Results suggest that the time scale required to obtain sound experimental data in tracer studies is longer than the commonly used Fickian time scale.
by Enda Murphy.
S.M.

Gases and particles released by volcanoes pose a serious hazard to humans and society. Emis-sions can be transported over long distances before being reduced to harmless concentrations.Knowing which areas are, or will be, exposed to volcanic emissions is an important part inreducing the impact on human health or society. In this thesis, the dispersion of volcanic emis-sions is studied using a set of atmospheric models. Two case studies have been performed, onestudying potential ash emission from future eruptions on Iceland, and a second covering SO2 emissions from Mt. Nyiragongo in D.R. Congo The first study covers long range (∼1,000 km) dispersion of fine ash from explosive erup-tions. Three years of meteorological data are used to repeatedly simulate five eruption scenarios.The resulting concentrations of airborne ash at different times relative the onset of each eruptionis compared to current and previous threshold concentrations used by air traffic controllers. Theash hazard showed a seasonal variation, with a higher probability of efficient eastward transportin winter, compared to summer; summer eruptions pose a more persistent hazard. In the second study, emissions of SO2 from passive degassing at Mt. Nyiragongo is studiedover a one–year period. The meteorological impact on the dispersion is studied by assigninga fixed emission source. Furthermore, flux measurements from the remote sensing data areused to improve the description of the emission source. Gases are generally transported to thenorth-west in June–August and to the south-west in December–January. A diurnal variation dueto land breeze around lake Kivu contributes to high concentrations of SO2 along the northernshore during the night. Daily averaged concentrations in the city of Goma (∼15 km SW of thesource) exceeded the European Union’s air quality standard (125 μg/m 3 ) for 120-210 days overa one year period.
Gas- och partikelutsl ̈app fr ̊an vulkaner utg ̈or en fara för människor och för vårt samhälle. Utsläppen kan transporteras över långa avstånd innan de reduceras till ofarliga halter. Att kännatill vilka områden som utsätts, eller kommer utsättas, för utsläppen är ett viktigt verktyg för att minska påverkan påv folkhälsa och samhället. I den här avhandlingen studeras spridningen av utsläpp från vulkaner med hjälp av en uppsättning atmosfärsmodeller. Två fallstudier har utförts,en fokuserar på vulkanaska från potentiella framtida utbrott på Island, den andra studerar SO2 -ustl äpp fr ̊an Nyiragongo i Demokratiska Republiken Kongo. Den f ̈orsta studien beskriver l ̊angv ̈aga (∼1,000 km) transport av aska från explosiva utbrott.Tre är av meteorologiska data används för att modellera spridningen från fem olika utbrotts-scenarier för varierande vädersituationer. Koncentrationen av luftburen aska studeras vid olikatidpunkter relativt utbrottens starttid och j ̈amf ̈ors med tidigare samt befintliga gränsvärden för flygtrafik. Sannolikheten för skadliga halter aska varierar med årstid, med en högre sannolikhetför effektiv transport österut under vintermånaderna, jämfört med sommarmånaderna; sommar-utbrott är istället mer benägna att orsaka långvariga problem över specifika områden. I den andra studien modelleras utsl ̈app av SO 2 från passiva utsläpp vid Nyiragongo över en ettårsperiod. Den meteorologiska effekten på spridningen studeras genom att använda en konatant utsläppskälla. Dessutom studeras spridningen mer i detalj genom att använda fjärranalysdata för att bättre uppskatta utsläppen. Gaserna transporteras i regel mot nordväst i juni–augusti ochmot sydväst i december–februari. En sjö-/landbriscirkulation runt Kivusjön orsakar höga halterav SO2 längs sjöns norra strand nattetid. Dygnsmedelkoncentrationer av SO2 i provinshuvud-staden Goma (∼15 km sydväst om Nyiragongo) överskred EU-riktlinjer (125 μg/m3 ) under 120-210 dagar under en ettårsperiod.

When simulating a molecular system, a cutoff distance for interactions is often used to speed up the simulations. This is made at the cost of neglecting some interactions which will lead to inaccurate results for energy, pressure components and surface tension (for systems with surfaces). To compensate for the neglected long-range interactions, continuum corrections can be added to the surface tension, system energies and pressures. For a homogenous isotropic system this is straight-forward but for a system with a surface it is more complicated. In this work we have derived expressions for the corrections to the surface tension, system energies and pressures that are more general than previous results. When these corrections are added to multi-component systems with a surface (or single-component systems with vacuum) they compensate for the change in surface tension, system energy and pressures due to the finite cutoff. When simulating systems with no Coulomb-interactions, the structure of the system may change significantly if the cutoffs are too short. If this is the case then these corrections alone will not be enough. The solution is to add corrections to the force acting on each molecule added during the simulation, which we derive in this work. This solves the structural problem at low cutoffs and makes it possible to calculate an accurate surface tension independent of cutoff.

Gases and particles released by volcanoes pose a serious hazard to humans and society. Emissions can be transported over long distances before being reduced to harmless concentrations. Knowing which areas are, or will be, exposed to volcanic emissions is an important part inreducing the impact on human health and society. In this thesis, the dispersion of volcanic emissions is studied using a set of atmospheric models. The work includes contribution to the development of the Lagrangian Particle Dispersion Model FLEXPART-WRF. Three case studies have been performed, one studying potential ash emissions from potential future eruptions on Iceland, a second covering SO2 emissions from Mt. Nyiragongo in D.R. Congo, and a third studying the SO2 emission rate of the Holuhraun eruption (Iceland) in 2014–2015. The first study covers volcanic ash hazard for air traffic over Europe. Three years of meteorological data are used to repeatedly simulate dispersion from different eruption scenarios. The simulations are used to study the probability of hazardous concentrations in ash in European airspace. The ash hazard shows a seasonal variation with a higher probability of efficient eastward transport in winter, while summer eruptions pose a more persistent hazard. In the second study, regional gas exposure around Mt. Nyiragongo is modelled using flux measurements to improve the description of the emission source. Gases are generally transported to the north-west in June–August and to the south-west in December–January. A diurnal variation due to land breeze around lake Kivu contributes to high concentrations of SO2 along the northern shore during the night. Potentially hazardous concentrations are occasionally reached in populated areas in the region, but mainly during the nights. The third study uses inverse dispersion modelling to determine the height and emission rates based on traverse measurements of the plume at 80–240 km from the source. The calculated source term yields better agreement with satellite observations compared to commonly used column sources. The work in this thesis presents improvements in dispersion modelling of volcanic emissions through improved models, more accurate representation of the source terms, and through incorporating new types of measurements into the modelling systems.
Gas- och partikelutsläpp från vulkaner utgör en fara för människor och för vårt samhälle. Utsläppen kan transporteras över långa avstånd innan de reduceras till oskadliga halter. Att känna till vilka områden som utsätts för, eller kommer utsättas för, utsläppen är ett viktigt verktyg föratt minska påverkan på folkhälsa och samhälle. I avhandlingen studeras spridningen av utsläpp från vulkanutbrott med hjälp av en uppsättning numeriska atmosfärsmodeller. Den Lagrangiska Partikelspridningsmodellen FLEXPART-WRF har förbättrats och applicerats för spridningsmodellering av vulkanutbrott. Tre studier har utförts, en fokuserar på vulkanaska från potentiella framtida utbrott på Island, den andra studerar SO2-ustläpp från vulkanen Nyiragongo i Demokratiska Republiken Kongo, och den tredje studerar SO2-ustläpp från utbrottet i Holuhraun (Island) 2014–2015. Den första studien uppskattar sannolikheten för att vulkanaska från framtida vulkanutbrott på Island ska överskrida de gränsvärden som tillämpas för flygtrafik. Tre år av meteorologisk data används för att simulera spridningen från olika utbrottsscenarier. Sannolikheten för skadliga halter aska varierar med årstid, med en högre sannolikhet för effektiv transport österut under vintermånaderna, sommarutbrott är istället mer benägna att orsaka långvariga problem överspecifika områden. In den andra studien undersöks spridningen av SO2 från Nyiragongo över en ettårsperiod. Flödesmätningar av plymen används för att förbättra källtermen i modellen. Gaserna transporteras i regel mot nordväst i juni–augusti och mot sydväst i december–februari En dygnsvariation, kopplad till mesoskaliga processer runt Kivusjön, bidrar till förhöjda halter av SO2 nattetid längs Kivusjöns norra kust. Potentiellt skadliga halter av SO2 uppnås av och till i befolkade områden men huvudsakligen nattetid. Den tredje studien utnyttjar inversmodellering för att avgöra plymhöjd och gasutsläpp baserat på traversmätningar av plymen runt 80–240 km från utsläppskällan. Den beräknade källtermen resulterar i bättre överensstämmelse mellan modell- och satellitdata jämfört med enklare källtermer. Arbetet i den här avhandlingen presenterar flertalet förbättringar för spridningsmodellering av vulkanutbrott genom bättre modeller, nogrannare beskrivning av källtermer, och genom nya metoder för tillämpning av olika typer av mätdata.

Le transfert de masse d'un contaminant passif (cas du traceur) dans un milieu poreux heterogene constitue par des inclusions spheriques impermeables de meme diametre, reparties de facon stationnaire, aleatoire et statistiquement homogene dans une matrice poreuse uniforme, est etudie theoriquement. La diffusivite longitudinale effective est calculee pour les temps longs, en mettant en uvre la methode generale proposee par batchelor et hinch, pour l'etude des suspensions diluees. Dans le cas des nombres de peclet eleves et des faibles concentrations volumiques en inclusions, la dispersion mecanique est proportionnelle au peclet et varie de facon non lineaire avec la concentration volumique. En vue de proceder a la validation de ces resultats, une installation experimentale a ete realisee et une serie de tests de qualification effectues

Un champ de turbulence bidimensionnelle est caracterise par trois elements de base: les structures coherentes ou la rotation domine, un premarecage turbulent a la peripherie des tourbillons qui est domine par les deformations et, enfin, un marecage constitue par le milieu residuel entre les tourbillons ou la rotation equilibre la deformation. Dans le cadre de cette topographie nous etudions les comportements statistiques de la dispersion lagrangienne aux differentes echelles d'espace et de temps en considerant deux points essentiels: i) les limites de tolerance des approches purement euleriennes; ii) les ouvertures favorisees par les analyses lagrangiennes. Nous proposons une modelisation qui permet de cartographier la valeur asymptotique a grande echelle du coefficient de dispersion absolue dans le cas non homogene et qui complete celle deja existante dans le cas homogene 2-d. La dispersion relative dans les cascades d'enstrophie et d'energie est ensuite etudiee analytiquement et a l'aide des experiences numeriques. Nous nous interessons en particulier a ses comportements statistiques dans le domaine inertiel de la cascade d'energie et analysons les conditions d'observations de la loi auto-similaire de richardson. Nous montrons qu'il existe des zones privilegiees d'affluence particulaire au sein desquelles les predictions auto-similaires sont mieux verifiees et qui sont des sieges de mecanisme de cascade inverse. Nous proposons, enfin, une nouvelle formulation de la loi de richardson dans la cascade d'energie d'une turbulence bidimensionnelle

Dispersion remains, today, a highly topical subject. Our group has been interested in characterizing this phenomenon by pulsed-field-gradient NMR technique. Direct measurement of the dispersion coefficient can be done with a Pulsed Gradient Spin Echo (PGSE) sequence by assuming that the asymptotic regime is reached. In unsteady state, the propagator formalism is used. To better understand these measurements, the NMR experiment is modeled using a stochastic simulation (random walks) and compared with experimental results. The comparison is made for the simple case of Poiseuille flow in a circular tube (Taylor-Aris dispersion).

L'activité humaine a un impact significatif sur la vadose, une zone située au-dessus des nappes phréatiques, qui n'est que partiellement saturée en eau. La vadose peut être polluée par les activités agricoles ou industrielles, ce qui constitue une menace pour les ressources en eau. De plus, la saturation varie considérablement, notamment en raison des sécheresses plus fréquentes dues au changement climatique. Prévoir le transport de contaminants en milieux insaturées est donc essentiel. Cependant, la compréhension de la dispersion dans les milieux poreux insaturés reste limitée, en raison de l'interaction complexe des flux multiphasiques non miscibles avec le milieu poreux. Les modèles traditionnels tels que le modèle Fickien, décrit par l'équation d'Advection-Diffusion, ne parviennent pas à rendre compte avec précision de la dispersion dans les milieux poreux insaturés. L'objectif est d'aborder la question du transport dans les milieux poreux insaturés en identifiant les propriétés pertinentes à l'échelle du pore pour comprendre la dispersion à plus grande échelle. Il s'agit notamment de déterminer si la dispersion est fickienne ou non-fickienne, ce qui est crucial pour prédire la propagation des polluants. Une double approche est adoptée : des expériences de transport à l'échelle du pore et des simulations de Lattice Boltzmann. La visualisation directe des fluides dans les milieux poreux est un défi. Nous utilisons donc des micromodèles, réseaux poreux transparents interconnectés, pour permettre la visualisation optique à l'échelle du pore. Tout d'abord, un dispositif expérimental micromodèle a été établi et optimisé pour étudier l'écoulement et le transport multiphasiques. Des méthodes d'analyse ont été développées, ainsi que des techniques de caractérisation de la dispersion par l'analyse des moments spatiaux. Une première série d'expériences mène à des résultats préliminaires, l'évolution de la saturation et des distributions de phases avec le nombre capillaire a été caractérisée. Les expériences de transport réalisées pour toute la gamme de saturation montrent que la dispersion augmente à mesure que la saturation diminue. Cependant, l'analyse des faibles saturations s'est avérée difficile en raison de l'augmentation significative de la dispersion et des limites imposées par la taille du micromodèle, empêchant l'étude de la dispersion à long terme. Pour surmonter cette limitation, des simulations Lattice-Boltzmann ont été utilisées pour l'écoulement et le transport, car elles sont flexibles en taille et seulement limitées par le temps de calcul. Toutefois, simuler la distribution de deux phases après un écoulement multiphasique dans un milieu poreux complexe reste un défi. Générer des images à grande échelle de milieux poreux insaturés à partir de données expérimentales s'est donc avéré nécessaire pour observer la dispersion à temps long. Un algorithme de statistique multipoints (MPS) a été utilisé pour générer à la fois des images de milieux poreux non saturés plus larges et un grand ensemble de d'images plus petites pour augmenter la signification statistique de l'étude. Des simulations d'écoulement et de transport ont été réalisées sur l'ensemble des images générées afin d'explorer l'influence de la saturation sur l'écoulement et le transport. Cette étude révèle que la diminution de la saturation augmente de manière significative l'hétérogénéité de l'écoulement, ce qui entraîne une dispersion accrue. Notamment, la nature non fickienne de l'écoulement tend à être plus prononcée à faible saturation. De plus, la transition d'un transport fickien à un transport non fickien dépend du nombre de Peclet. Il existe une compétition entre l'advection et la diffusion dans des conditions saturées, ce qui entraîne un régime Fickien diffusif pour les faibles nombres de Peclet. Cependant, le transport en conditions non saturées est principalement advectif, même à faible nombre de Peclet, et présente donc un comportement non Fickien
Human activity has a significant impact on the vadose zone, an area located below the land surface and above the water tables, only partially saturated with water. The vadose is susceptible to pollution from agricultural or industrial activities, posing a threat to water resources. Plus, saturation levels vary greatly, especially with the increasing frequency of droughts due to climate change. Hence, predicting contaminant transport in unsaturated conditions is crucial. However, the understanding of dispersion in unsaturated porous media remains limited, due to the complex interaction of multiphase non-miscible flows with the porous medium. Traditional models such as the Fickian model, described by the Advection-Diffusion Equation, fail to accurately capture dispersion in unsaturated porous media.The objective is to address the issue of transport in unsaturated porous media by identifying relevant properties at the pore scale to understand dispersion at a larger scale. One of the goals is to determine whether dispersion follows Fickian or non-Fickian behavior, as this understanding is crucial for predicting the spreading of pollutant in the vadose zone.To investigate transport in unsaturated porous media, a dual approach is being employed: pore scale transport experiments and Lattice Boltzmann simulations. Direct visualization of fluid structure in natural porous media is challenging. Thus, we use micromodels, transparent interconnected porous networks, to enable optical visualization at the pore scale. First, a micromodel experimental setup was established and optimized to study multiphase flow and transport. Analysis methods were developed, along with techniques for characterizing dispersion through spatial moment analysis.A series of experiments were conducted to obtain initial results on multiphase flow and dispersion. The evolution of saturation and phase distributions with the capillary number was characterized. Transport experiments were performed for the entire range of saturations, showing that dispersion increases as saturation decreases. However, analyzing low saturations was challenging due to the significant increase in dispersion and limitations imposed by the micromodel size, preventing the study of long-term dispersion.To overcome this limitation, Lattice Boltzmann simulations were used for flow and transport, as there is no size limitation except for computational time. However, simulating the distribution of two phases after a multiphase flow in a complex porous medium remains challenging. Generating large-scale images of unsaturated porous media based on experimental data was then crucial for observing late-time dispersion. Machine learning techniques, specifically the Multiple Point Statistic algorithm, were employed to generate images of wider unsaturated porous media and a large dataset of smaller images to increase the statistical significance of the study.Flow and transport simulations were conducted using the generated image dataset to explore the influence of saturation on flow and transport. This involved examining flow properties under saturated and unsaturated conditions. The nature of transport, specifically whether it exhibited Fickian or non-Fickian behavior was investigated. Furthermore, the effect of the Peclet number (a measure of the balance between advection and diffusion) on dispersion for different saturation levels was analyzed.This study revealed that decreasing saturation significantly increases flow heterogeneity, leading to increased dispersion. Notably, the non-Fickian nature of flow tends to be more pronounced with low saturations. Plus, the transition from Fickian to non-Fickian depends on the Peclet number. There is a competition between advection and diffusion in saturated conditions, resulting in a diffusive Fickian regime for low Peclet numbers. However, transport in unsaturated conditions is mainly advective, even at low Peclet, and thus displays a non-Fickian behavior

This study examines the relationship between in ation and price dispersion during the hyperin ationary episode in Brazil. We look at micro data on price dynamics through the perspective of dispersion at the store level, building on the informational consequences of high price dispersion. Rather than focus on which theoretical framework best explains the relative price variability seen on the data, we focus on a top-down approach to the information embedded in prices: we analyze price setting behavior from the perspective of economic segments as whole and from the perspective of each seller taken individually. In the former case we seek to answer the following: do higher levels of in ation favor higher price dispersion? In the latter, we focus on the time-series properties of each of more than 150 real price trajectories in both high and low in ation periods. We provide further empirical evidence of the loss of information embedded in prices, be it deriving from greater overall dispersion or from a greater volatility in each seller\'s price trajectory relative to its peers\'. Our findings extend previous results, accounting for a higher level of in ation, a longer time span and a broader selection of items.
Este trabalho investiga a relação entre inflação e dispersão de preços durante a experiência de hiperinflação vivida no Brasil. Estudamos micro dados de preços sob a perspectiva da dispersão no nível do vendedor, buscando evidências das consequências informacionais de uma alta dispersão de preços. Ao invés de investigar qual arcabouço teórico melhor explica a variabilidade de preços relativos encontrada nos dados, focamos em uma abordagem sobre a informação incorporada nos preços que vai do geral para o particular: analisamos primeiramente a formação de preços de maneira agregada e depois sob o ponto de vista do vendedor individualmente. No primeiro caso queremos responder à seguinte pergunta: níveis maiores de inflação geram níveis maiores de dispersão de preços? No segundo caso, focamos nas características das séries temporais de mais de 150 trajetórias de preços reais tanto para o período de alta inflação quanto para o período pós-estabilização. Fornecemos evidências empíricas adicionais da diminuição do caráter informacional dos preços, resultante tanto de uma maior dispersão das distribuições de preços, quanto da maior volatilidade na trajetória individual dos preços, relativamente aos preços dos concorrentes. Nossos resultados estendem trabalhos anteriores uma vez que considera um ambiente de inflação mais alta e mais volátil, um horizonte de tempo maior e uma seleção mais ampla de produtos.

Dans ce travail de thèse, on s'est applique à rechercher une meilleure connaissance des processus et procédés de dispersion-broyage. Dans un premier temps, on s'est efforcé de trouver un moyen adéquat pour caractériser le degré de dispersion obtenu lors de cette opération. C'est dans le cadre de cette partie que l'on a effectué des mesures de permittivité de suspension, que l'on a ensuite essayé de relier avec les propriétés des différents composants. Dans une seconde partie, on s'est intéressé à l'utilisation d'un broyeur à billes à agitation rapide comme moyen de dispersion-broyage. Cet appareil pouvant fonctionner en continu, une étude du transport de matière (mesure de distribution de temps de séjour) a été effectuée pour avoir une bonne connaissance des temps de séjour des particules dans la chambre de broyage. L'influence de différents paramètres opératoires a été étudiée, et l'on a compare les D. T. S. Obtenues à partir de plusieurs méthodes. Enfin des essais de broyage-dispersion ont été effectués en variant les conditions opératoires et les résultats ont été interprétés à l'aide des théories classiques du broyage

This thesis presents a study on the production of microbubble dispersions from rhamnolipid biosurfactant and the mechanism and factors that impact upon the effectiveness of the dispersion for improving bioremediation efficiency, with a specific focus on the use of microbubble dispersion as a carrier for contaminant-degrading bacteria within a bioremediation scenario. Microbubble dispersion is a suspension of a large number of minute spherical gas bubbles encapsulated in a soapy liquid film in an aqueous surfactant solution. Microbubble dispersion has promising potential for enhancing in situ bioremediation owing to its advantages over air sparging, bioventing and surfactant injection. Characterisation studies investigated the stability, size distribution and gas hold-up properties of the rhamnolipid microbubble dispersion. Drainage experiments and contact angle measurements were performed to identify factors that influence P.putida and R.erythropolis adhesion to microbubble dispersion. Fluorescence microscopy was used to investigate the interaction of P.putida and R.erythropolis and hexadecane, a model NAPLcontaminant on the microbubble surface. The LW-AB surface thermodynamic model was applied to quantify the interaction energy to better understand the bacteria/microbubble and bacteria/contaminant/microbubble interactions. The findings of the characterisation studies support that rhamnolipid microbubble dispersion had comparable properties to the synthetic surfactants reported in this study and in the literature. The stability of the rhamnolipid microbubble dispersion, prepared at rhamnolipid concentrations of 500 mg/L, 1,000 mg/L and 4,000 mg/L, was in the range from 385 to 546 seconds. The gas hold-up in the dispersion was fairly constant ranging from 67% to 72%, and majority of the microbubbles were in the size range of 20 μm to 140 μm. The bacterial drainage experiments, coupled with surface free energy calculation by the LWAB model, showed that rhamnolipid microbubble dispersion was more effective in delivering hydrophilic P.putida than hydrophobic R.erythropolis. Bacterial cell surface hydrophobicity and rhamnolipid concentration were demonstrated as two key factors to control when making the microbubble dispersion an effective bacterial carrier. Furthermore, fluorescence microscopic images revealed that rhamnolipid microbubble dispersion might potentially overcome the problem of limited contaminant bioavailability by improving P.putida and R.erythropolis bacterial contact with hexadecane immobilised at the microbubble surface.
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Society benefits considerably from large scale industrial activities. However, these activities can have undesirable side effects which must be adequately controlled and monitored; the motivation for this thesis is risk assessment. Industrial processes often involve large amounts of hazardous, liquified gases, and accidental release of such substances poses a threat to nearby populations. Accidentally released gases are often denser than air and this thesis addresses the physics of dense gas dispersion. As dense gas clouds tend to adopt low-lying configurations, a shallow layer model (in which physical properties of the cloud are depth averaged) is indicated for simulating dense gas dispersion. This type of model has been comparatively neglected up to the present but is useful because it is capable of simulating the effect of complex terrain such as valleys and mountain ranges. This thesis presents a computationally validated and physically realistic shallow layer model for dense gas dispersion. A computational model has been developed to simulate the mathematical model. This model uses the flux correction scheme of Zalesak, generalized to account for complex terrain. The computational model is validated against a number of theoretical results. The model is then compared with a body of experimental data including large scale field trials, laboratory experiments, and established integral models. A case study, in which the present model was used on a real hazard site, is presented.