10,478 research outputs found
Electro-Kinetic Instability in a Laminar Boundary Layer Next to an Ion Exchange Membrane
No full textInternational audienceThe electro-kinetic instability in a pressure driven shear flow near an ion exchange membrane is considered. The electrochemical system, through which an electrical potential drop is applied, consists in a polarization layer in contact with the membrane and a bulk. The numerical investigation contained two aspects: analysis of the instability modes and description of the Lagrangian transport of fluid and ions. Regarding the first aspect, the modes were analyzed as a function of the potential drop. The analysis revealed how the spatial distribution of forces controls the dynamics of vortex association and dissociation. In particular, the birth of a counter-clockwise vortex between two clockwise vortices, and the initiation of clusters constituting one or two envelopes wrapping a vortex group, were examined. In regards to the second aspect, the trajectories were computed with the fourth order Runge Kutta scheme for the time integration and with the biquadratric upstream scheme for the spatial and time interpolation of the fluid velocity and the ion flux. The results for the periodic mode showed two kinds of trajectories: the trochoidal motion and the longitudinal one coupled with a periodic transverse motion. For the aperiodic modes, other mechanisms appeared, such as ejection from the mixing layer, trapping by a growing vortex or merging vortices. The analysis of the local velocity field, the vortices' shape, the spatial distribution of the forces and the ion flux components explained these trajectories
Ion transport dependence on the ion pairing/solvation competition in cation-exchange membranes
No full textInternational audienceEffect of ion-pairing on ion partitioning at equilibrium and on transport properties is studied by means of the Poisson–Nernst–Planck (PNP) equations. Owing to the low electrolyte solution relative permittivity (εSεS) and the high ion density in the membrane, the excess terms of the chemical potential must be computed. In this aim, the density functional theory and the binding mean sphere approximation were used in order to extend the PNP equations and to compute the association constant. The counter-ion/fixed-charge-group pairing and the counter-ion/co-ion one were examined. In the case of monovalent fixed charge, the total density of co-ion and the free one decreases with εSεS owing to the solvation contribution. So that it induces a decrease of the membrane system conductivity. If the counter-ion/co-ion pairing is considered, the free co-ion density and the conductivity increase when εSεS reaches small values. However in the ohmic regime, this dependence of the conductivity towards the free co-ion density is not always fulfilled
Influence of the ion-solvent interactions on ionic transport through ion-exchange-membranes
No full textInternational audienceIonic transport through ionic exchange membrane cannot be interpreted by the Nernst-Planck equation if the ion density is high, particularly in the membrane. In order to extend the density range, excess terms must be added to the chemical potential. These terms are computed by considering charged hard spheres embedded in a dielectric continuum. In this aim and owing to heterogeneity of the electrolytic solution the density function theory (DFT) is used. A previous work has been carried out with a homogeneous and amorphous solvent. Here an extension including the finite size of the solvent molecule and the local dielectric properties via the dielectric coefficient is presented. The electro-osmosis is also examined. The selectivity at equilibrium, the density profiles and the voltammograms are analysed. The numerical results obtained with NaCl and CaCl2 show that the physical properties of the solvent decrease the selectivity and increases the conductivity of the membrane systems. In the same time, the dielectric properties increase the electro-osmotic effects on the ionic transport. The approach described in this work can be used to study the solvent confinement effect inside the membrane on the ionic transport
Spatial distribution of mechanical forces and ionic flux in electro-kinetic instability near a permselective membrane
No full textInternational audienceThis paper is devoted to the numerical investigation of electro-kinetic instability in a polarization layer next to a cation-exchange membrane. An analysis of some properties of the electro-kinetic instability is followed by a detailed description of the fluid flow structure and of the spatial distribution of the ionic flux. In this aim, the Stokes-Poisson-Nernst-Planck equation set is solved until the Debye length scale. The results show that the potential threshold of the marginal instability and the current density depend on the logarithm of the concentration at the membrane surface. The size of the stable vortices seems to be an increasing function of the potential drop. The fluid motion is induced by the electric force along the maximum concentration in the extended space charge (ESC) region and by the pressure force in the region around the inner edge of the ESC layer. Two spots of kinetic energy are located in the ESC region and between the vortices. The cationic motion, controlled by the electric field and the convection, presents counter-rotating vortices in the stagnation zone located in the fluid ejection region. The anion transport is also characterized by two independent layers which contain counter-rotating vortices. The first one is in contact with the stationary reservoir. In the second layer against the membrane, the convection, and the electric field control, the transversal motion, the Fickian diffusion, and the convection are dominant in the longitudinal direction. Finally, the longitudinal disequilibrium of potential and pressure along the membrane is analyzed
“Enquête sur l’auteur. Entretien avec Pierre Bayard”
No full textInternational audience05/04/2019 “Enquête sur l’auteur. Entretien avec Pierre Bayard” [“Investigation into the Author. Interview with Pierre Bayard”], event for bachelor’s and master’s students in French and comparative literature, Lorraine University
Impact of dynamic processes on the cloupling between fluid transport and precipitate deposition
No full textInternational audienceWe present a Lagrangian approach to study the clogging evolution of a one-dimensional homogeneous micro-fractured medium by deposition of one chemical species. Semi-analytical expressions are determined by means of the mass balance equations of #uid and solute in which the chemical and hydrodynamic disequilibrium makes an important dynamic contribution to the clogging mechanism. We describe some aspects of the coupling between the #uid transport and the chemical reaction with a qualitative analysis of these expressions by comparing the clogging evolution as a function of the imposed boundary conditions. In particular, a feedback e!ect underlies the solute transport if the pressure is imposed. Its analysis reveals a competition between local scales and large scales ampli"ed by the variation rate of the porosity, so that we have to distinguish the clogging process at short times and at long times. By means of the Lagrangian formulation, we are able to "nd an accurate analytical expression of the hydraulic conductivity of the overall medium. But it is necessary to use the successive approximation method to obtain quantitative results for the other quantities. Applications to heterogeneous media modeled by capillary tubes networks have displayed similar hydrodynamic behavior compared to homogeneous media if the deposition kinetics is not too sensitive to heterogeneities
Is There Market Power in the French Comte Cheese Market?
No full textAn NEIO approach is used to measure seller market power in the French Comté cheese market, characterised by government-approved supply control. The estimation is performed on quarterly data at the wholesale stage over the period 1985-2005. Three different elasticity shifters are included in the demand specification, and the supply equation accounts for the existence of the European dairy quota policy. The market power estimate is small and statistically insignificant. Monopoly is rejected, as well as weak forms of Cournot oligopoly. Results appear to be robust to the choice of functional form, and suggest little effect of the supply control scheme on consumer prices.Supply control, NEIO, protected designation of origin, Marketing,
The aesthetics of Pierre Boulez
No full textTo enable the reader to find references as quickly and easily as possible, I have grouped all references together in the bibliography in alphabetical order. Texts by the same author are distinguished first by year and second, if there are several texts from the same year, by letter. Interviews and writing collaborations (including published correspondence) involving Boulez are also ordered alphabetically. The year given at the beginning of each bibliographical entry is, in the majority of cases, the year in which the text was first published (not necessarily the year of the edition cited). For all writings written by Boulez, I have provided the original title under which the text in question was first published (usually in French). Many articles have subsequently been translated into English and therefore I have decided to provide page references for both versions. For all texts by writers other than Boulez, I have cited the version of the text I have used. Wherever possible, I have cited the existing English translations of texts originally written in French. However, on many occasions I have considered it necessary to make alterations to the published translations. This is particularly applicable to Boulez on Music Today (1971) and Orientations (1986), both of which display an often heavy-handed and rather inaccurate approach to the task of translating specific concepts employed by Boulez. In contrast. Stocktakings of an Apprenticeship (1991) has required only occasional minor amendments. All changes to the published English translations are acknowledged in the corresponding footnote. None of the material m this thesis has previously been submitted for a degree in this or any other University. The copyright of this thesis rests with the author. No quotation from it should be published without prior written consent and information from it should be acknowledged. I have received permission to exceed the word limit from the Graduate School Committee at the University of Durham
Etnografia e fotografia: reflexões sobre as fotografias etnográficas de Pierre Fatumbi Verger
No full textDissertação (mestrado) - Universidade Federal de Santa Catarina, Centro de Filosofia e Ciências Humanas. Programa de Pós-graduação em Antropologia Social, Florianópolis, 2009A relação entre a fotografia e a etnografia nos estudos da Antropologia, apesar de antiga e densa, é incerta e complexa. Se por um lado a fotografia é a cada dia mais utilizada nos trabalhos antropológicos, por outro sua potencialidade como algo além da ilustração e de uma técnica de interação com o Outro é pouco explorada. A partir do exemplo, do legado, da trajetória de vida e, principalmente, da obra de Pierre Fatumbi Verger, esta pesquisa se dedica a analisar essa relação. Francês radicado na Bahia na década de 1940, Verger é conhecido mundialmente tanto por seu trabalho como fotógrafo quanto pelas suas pesquisa etnográficas. Há, entretanto, uma indefinição quanto à razão desse reconhecimento, e examinar as suas razões oferece um profícuo campo de reflexão sobre a pesquisa etnográfica, especialmente quando relacionada ao universo das imagens fotográficas. A Fundação Pierre Verger é a instituição que atualmente abriga o acervo do fotógrafo-etnógrafo e onde foi realizada a pesquisa de campo através da qual, aliada à leitura de fotografias relacionadas ao candomblé em suas manifestações na África e na Bahia, foi criada uma metodologia de análise das fotografias que privilegia as interações e os diálogos como espaço de construção de definições sobre a etnografia. Pelo contato com a Fundação, seus freqüentadores e o acervo fotográfico ali disponibilizado, esta pesquisa pretende refletir sobre a etnografia e a construção de um olhar etnográfico em relação direta com o exercício da fotografia.The relationship between photography and ethnography in anthropological studies, albeit ancient and deep, is uncertain and complex. Photography has been increasingly used in anthropological researches but it´s potencial as something beyond illustration and it´s interaction with the Other as a technique is very little explored. This research is dedicated to the analysis of this relationship by taking the work of Pierre Fatumbi Verger, his life and legacy. A French man, rooted in Bahia, Brasil, in the decade of 1940, Verger is known worldwide for his work as a photographer as well as for his etnographic studies. However, the reason of this recognition is undefined and examining the reason for these indefinitions can be a fruitful field of reflection concerning ethnographic researches, especially when related to the photographic universe. The Pierre Verger Foundation is the institution that hosts his photographic and ethnographic collection and it´s also where the field research of this work took place. Through the field research combined with the readings of photographs related to candomblé and it´s manifestations in Africa and Bahia, a photographic analysis methodology was created that privilege interaction and dialogue as a way to build definitions about ethnography. By the contact with the Foundation, it´s users and it´s available photographic collection, this research intends to reflect about the ethnography and the creation of an ethnographic view in direct relation to the exercise of photography
A Emergência Do Autor Pierre Rivièrethe Emergence Of The Pierre Rivière Author
No full textNesse artigo apresento uma análise do caso de parricídio / fraticídio cometido por um jovem camponês francês, nascido na comuna de Courvaudon, Pierre Rivière que em 3 de junho de 1835, aos vinte anos, assassinou a golpes de foice sua mãe grávida de sete meses, sua irmã de 18 anos, e seu irmão de sete anos. O livro intitulado Eu, Pierre Rivière, que degolei minha mãe, minha irmã e meu irmão produzido pelo trabalho de uma equipe de pesquisadores, no Collège de France, sob a coordenação de Michel Foucault em 1973, apresenta em seu conjunto notícias de jornais, testemunhos, interrogatórios, laudos médicos e uma gama de diferentes discursos. Para empreender a análise do nó entre a escrita e o assassinato, utilizo a relação entre a escrita e o autor demarcando o personagem Rivière no desdobramento, na ordem do corpo e da linguagem. Palavras-chave Função autor; Corpo; Linguagem; Pierre Rivière; Michel Foucault Abstract This paper has as aim to present an analysis of the case of patricide / fratricide cometed by a French Countryman, Pierre Rivière, who was born in the commune of Courvaudon, who, on July 3rd, 1835, at age of 20, killed his mother, his brother and sister with a sickle. His mother was in the seventh month of pregnancy, his sister was 18 and his brother was 7 years old. The book, whose name was “I, Pierre Riviere, Having Slaughtered My Mother, My Sister, and My Brother ...: A Case of Parricide in the Nineteenth Century” was produced by a group of researchers at the Collège de France, under the coordination of Michel Foucault in 1973, has a set of newspaper news, witnesses, inquiring, forensic medical reports and a variety of different texts. To understand and analyze the writings and the homicide, the relationship between writing and the author is used, marking the character Rivière unfolding body and language. Keywords Function author; Body; Language; Pierre Rivière; Michel Foucault80227-24
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