Influence of wettability on liquid water transport in gas diffusion layer of proton exchange membrane fuel cells (PEMFC)

Water management is a key factor that limits PEFC's performance. We show how insights into this problem can be gained from pore-scale simulations of water invasion in a model fibrous medium. We explore the influence of contact angle on the water invasion pattern and water saturation at breakthrough and show that a dramatic change in the invasion pattern, from fractal to compact, occurs as the system changes from hydrophobic to hydrophilic. Then, we explore the case of a system of mixed wettability, i.e. containing both hydrophilic and hydrophobic pores. The saturation at breakthrough is studied as a function of the fraction of hydrophilic pores. The results are discussed in relation with the water management problem, the optimal design of a GDL and the fuel cell performance degradation mechanisms. We outline how the study could be extended to 3D systems, notably from binarised images of GDLs obtained by X ray microtomography

Multi GPU parallelization of 3D bayesian CT algorithm and its application on real foam reonconstruction with incomplete data set

International audienceA great number of image reconstruction algorithms, based on analytical filtered backprojection, are implemented for X-ray Computed Tomography (CT) [1,2]. The limits of these methods appear when the number of projections is small, and/or not equidistributed around the object. That's the case in the context of dynamic study of fluids in foams for example, the data set are not complete due to the limited acquistion time. In this specific context, iterative algebraic methods are a solution to this lack of data. A great number of them are mainly based on least square criterion. Recently, we proposed a regularized version based on Bayesian estimation approach. The main problem that appears when using such methods as well as any iterative algebraic methods is the computation time and especially for projection and backprojection steps. In this study, first we show how we implemented some main steps of such algorithms which are the forward projection and backward backprojection steps on multi-GPU hardware, and then we show some results on real application of the 3D tomographic reconstruction of metallic foams from a small number of projections. Through this application, we also show the good quality of results as well as a significant speed up of the computation with GPU implementation (300 acceleration factor)

L’engagement comme ressource facilitant l’intégration. Le cas des réfugiés latino-américains en Suède

Les sciences sociales s’interrogent souvent sur la manière de penser l’intégration. De plus en plus influencée par les politistes, la tendance actuelle de la réflexion européenne semble se dégager des seuls aspects sociaux et culturels pour réévaluer, à travers la notion de citoyenneté, la dimension politique de celle ci. L’intégration deviendrait ainsi définie comme le passage « du statut d’immigré à celui de citoyen ». (Rea, Tripier) C’est en partie dans cette démarche que nous souhaitons n..

Nouveaux complexes pinces POCOP, NHCCOP, PIMCOP et PIMIOCOP, et complexes cyclométallés de Ni(II) : synthèse, caractérisation et réactivité

Cette thèse traite de la chimie des complexes pinces de Ni(II) ainsi que des complexes cyclométallés de Ni(II) comportant au moins un motif phosphinite. Elle se divise en trois parties. La première concerne la synthèse, la caractérisation, le mécanisme de formation et la réactivité des complexes pinces de Ni(II) à base de ligand de type POCOP 1,3-(i-Pr2PO)2C6H4. De nouveaux ligands de type R-(POCOP) = κP,κC,κP-{Rn-2,6-( R'2PO)2C6H4-n}; Rn = 4-OMe, 4-Me, 4-CO2Me, 3-OMe, 3- CO2Me, 3,5-t-Bu2 ; R' = i-Pr, t-Bu ont été synthétisés suite à l'addition de chlorophosphine ClPR'2 à une solution de résorcinol ou dérivés en présence de base. La synthèse des complexes R-(POCOP)Ni(Br) s'effectue à partir du ligand correspondant en présence de base, et de {NiBr2(NCiPr)}n. Ce nouveau précurseur de nickel est synthétisé à partir de brome de nickel métallique dans l'isobutyronitrile. Il est stable sous atmosphère inerte et sa solubilité dans les solvants polaires permet d'étudier les synthèses des complexes en milieu homogène. Le mécanisme de formation des complexes portant des ligand pinces (PCsp3P) 1,3-(i- Pr2PCH2CH2)2CH2, (POCsp3OP) 1,3-(i-Pr2POCH2)2CH2, (PCsp2P) 1,3-(i- Pr2PCH2)2C6H4, Rn-(POCsp2OP) 1,3-(i-Pr2PO)2C6H4-n via nickellation du lien C-H a été investigué avec une méthode de réaction de compétition. Cette étape a été déterminée comme étant de nature électrophile. Les complexes résultants ont été complètement caractérisés. Une corrélation a notamment été effectuée entre le déplacement chimique du Cipso en spectroscopie RMN 13C et le potentiel d'oxydation Eox en voltamétrie cyclique. Une nouvelle méthode de synthèse directe verte "one pot" a été mise en place. En faisant réagir à 75 °C un mélange hétérogène de II résorcinol, de chlorodiisopropylphosphine et de nickel métallique en poudre, on obtient le complexes pince (POCOP)Ni(Cl) avec des rendements allant jusqu'à 93%. La réactivité de ces complexes POCOP a été investiguée pour des réactions de fluorination et trifluorométhylation des halogénures d'alkyle. La synthèse du (POCOP)Ni(F) a lieu à partir de précurseur (POCOP)Ni(X) (X=Br, Cl), en présence d'un large excès de fluorure d'argent AgF. Ce complexe catalyse la fluorination du bromure de benzyle et peut être converti en (POCOP)Ni(CF3) en présence de réactif du Ruppert, Me3SiCF3. La réaction entre (POCOP)Ni(CF3) et le bromure de benzyle dans les solvants aromatiques mène à la conversion totale du complexe en (POCOP)Ni(Br) et à l'inattendue benzylation du solvant aromatique utilisé. La seconde partie concerne la synthèse des nouveaux complexes non symétriques à base de ligands comportant un motif imidazolo-phosphine (PIMCOP) 3-[2-(R2P)-C3H2N2]-(R2PO)-C6H3, imidazoliophosphine (PIMIOCOP) 3-[2-(R2P)-3- (CH3)-C3H2N2]-(R2PO)-C6H3] et carbène N-hétérocyclique (NHCCOP). La double déprotonation du 3-hydroxyphenyl-imidazole suivi de l'addition de deux équivalents de chlorodiphenylphosphine mène à l'obtention du ligand PIMCOP 3-[3-(CH3)- C3H2N2]-(R2PO)-C6H3. L'étape de nickellation a lieu comme dans le cas des composés (POCOP)Ni. La méthylation du motif imidazole du (PIMCOP)Ni(Br) par le triflate de méthyle MeOTf, donne le dérivé (PIMIOCOP)Ni(Br). Ce dernier est converti en (NHCCOP)Ni(Br) après l'addition de chlorure de tétraéthylamonium NEt4Cl. Les analogues i-Pr2P de ces complexes sont synthétisés en remplaçant ClPPh2 par ClPiPr2. On obtient les espèces cationiques [(PIMCOP)Ni(NCCH3)][OTf], [(PIMIOCOP)Ni(NCCH3)][OTf]2 et III [(NHCCOP)Ni(NCCH3)][OTf] suite à l'addition en solution dans l'acétonitrile de triflate d'argent AgOTf. Ces espèces ont été utilisés comme catalyseurs pour la synthèse d'amidine à partir de benzonitrile et de diverse amines aliphatiques. Enfin des complexes orthonickellés trans-Ni[(ĸ2-P,C-P(OC6H4)-(iPr2)( iPr2P(OC6H5))]Br à base de phosphinite ont été synthétisés et caractérisés. Les ligands sont synthétisés par réaction d'un phénol et de chlorodiisopropylphosphine en présence de base. L'ajout de {NiBr2(NCiPr)}n et de triéthylamine permet l'orthométallation via une étape de nickellation C-H. Un intermédiaire trans- [NiBr2{PiPr2(OC6H5)}2] de cette réaction a été isolé. Le complexe dimère peut réagir avec des espèces électrophiles mener à l'ortho-fonctionnalisation de la phosphinite.This thesis describes the chemistry of Ni (II) pincer and cyclonickelated complexes bearing at least one phosphinite moiety. The content is divided into three parts. A first study concerns the synthesis, the characterization, the mechanism of formation and the reactivity of nickel complexes bearing a ligand POCOP (1,3-(i- Pr2PO)2C6H4). New ligands R-(POCOP) = κP,κC,κP-{Rn-2,6-( R'2PO)2C6H3-n}; Rn = 4-OMe, 4-Me, 4-CO2Me, 3-OMe, 3-CO2Me, 3,5-t-Bu2 ; R' = i-Pr, t-Bu have been synthesized by addition of chlorophosphine in presence of base in a resorcinol or derivatives solution. The synthesis of R-(POCOP)Ni(Br) complexes occurred by reacting the corresponding ligand in presence of base and{NiBr2(NCiPr)}n. This new nickel precursor is synthesized in isobutyronitrile with bromine and metallic nickel powder. It is stable under inert atmosphere and its solubility in polar solvents allowed the study of those complexes in homogenous solution. Mechanism of formation of complexes bearing pincer ligands (PCsp3P) 1,3-(i-Pr2PCH2CH2)2CH2, (POCsp3OP) 1,3-(i-Pr2POCH2)2CH2, (PCsp2P) 1,3-(i-Pr2PCH2)2C6H4, Rn-(POCsp2OP) 1,3-(i- Pr2PO)2C6H4-n via C-H nickelation has been investigated by a method of competition reactions. The nickelation step was determined to be electrophilic. New {Rn-2,6-( R'2PO)2C6H4-n} ligands and corresponding nickel bromine complexes were characterized including linear correlation between 13C NMR chemical shift of ipso carbon (Cipso) and oxidation potential Eox. A new greener methodology for the one pot synthesis of (POCOP)Ni(Cl) from metallic nickel has been developed. Reacting at 75 °C at mixture of resorcinol, chlorodiisopropylphosphine and nickel power gives (POCsp2OP)Ni(Cl) up to 93 %. Reactivity of this complex has been investigated for fluorination and trifluoromethylation of benzyl halides. Synthesis of (POCOP)Ni(F) occurred starting from (POCOP)Ni(X) (X=Br, Cl) with excess of silver fluoride AgF. This complex catalyzes the fluorination of benzyl bromide and can be converted into (POCOP)Ni(CF3) using Ruppert reagent Me3SiCF3. Reaction of (POCOP)Ni(CF3) with benzyl bromide leads to its complete conversion into (POCOP)Ni(Br) and to the unexpected benzylation of the used aromatic solvent. The second part concerns the synthesis of new unsymmetrical complexes bearing imidazolo-phosphine moiety (PIMCOP) 3-[2-(R2P)-C3H2N2]-(R2PO)-C6H3, imidazoliophosphine (PIMIOCOP) 3-[2-(R2P)-3-(CH3)-C3H2N2]-(R2PO)-C6H3] and N-heterocyclique carbene (NHCCOP). (PIMCOP) ligands were synthesized by double deprotonation of 3-hydroxyphenyl-imidazole followed by addition of two equivalents of chlorodiphenylphosphine. Nickelation occured in a similar route as (POCOP)Ni. Methylation of the imidazole moiety of (PIMCOP)Ni(Br) using MeOTf leads the (PIMIOCOP)Ni(Br) complex. The latter can be converted into (NHCCOP)Ni(Br) after addition of tetraethylamonium chloride NEt4Cl. Analogs PiPr2 of those complexes are synthesized replacing ClPPh2 by ClPiPr2. Cationic species [(PIMCOP)Ni(NCCH3)][OTf], [(PIMIOCOP)Ni(NCCH3)][OTf]2 et [(NHCCOP)Ni(NCCH3)][OTf] are obtained reacting their bromo homologue complexes with silver triflate in acetonitrile. Those species are used to catalyze amidine synthesis from benzonitrile with various aliphatic amines. Finally orthonickellated complexes trans-Ni[(ĸ2-P,C-P(OC6H4)-(iPr2)( iPr2P(OC6H5))]Br, and dimeric specie {Ni(μ-Br){κ2-P,C-PiPr2(OC6H4)}}2 have been synthesized and characterized. Phosphinite ligand was synthesized reacting phenol and ClPiPr2 in presence of base. Nickellation occured heating in solution {NiBr2(NCiPr)}n and base. An intermediate trans-[NiBr2{PiPr2(OC6H5)}2] of this reaction has been isolated. Ortho-functionalization of diisopropyl phosphinite can be achieved by reacting dimeric complex with electrophilic species

Prosper-Alphonse Isaac (1858-1924)

Décorateur pour l’Art nouveau et graveur sur bois à la manière japonaise, Prosper-Alphonse Isaac (1858-1924) se passionna toute sa vie pour l’art japonais. Pendant une quarantaine d’années, il constitua une riche collection d’objets japonais et d’estampes qui, plus qu’une source d’inspiration, se trouve à l’origine de son œuvre de décorateur et de graveur. De tempérament discret et peu sûr de lui, il demeura longtemps dans l’ombre des grands japonisants tels que Siegfried Bing, Edmond de Goncourt ou Théodore Duret. Il contribua pourtant activement à l’essor de la gravure japonaise en France, en s’associant avec d’autres pour créer la Société des Amis de l’art japonais, en participant activement à la Société franco-japonaise qui voulait renforcer les liens entre les deux pays et en militant pour son entrée dans les musées, par de multiples dons. Mais ce qui occupa véritablement les trente dernières années de sa vie fut l’apprentissage de la gravure sur bois à la manière japonaise, auprès de Yoshijiro Urushibara (1889-1953), jeune graveur japonais de passage à Paris au début du siècle. Celui-ci lui livra les secrets de la xylographie japonaise, qu’Isaac avait commencé à découvrir quelques années plus tôt par l’étude attentive des Méthodes de dessin de Kitao Keisai Masayoshi (1764-1824). Grâce à Urushibara et aux outils qu’il lui fit parvenir du Japon, Isaac devint en quelques années un des plus fins connaisseurs de la gravure sur bois japonaise et multiplia, dès lors, les occasions de transmettre ce qu’il savait aux artistes et collectionneurs français, tous passionnés par le Japon.Art nouveau decorative artist and Japanese-style woodblock printmaker Prosper-Alphonse Isaac (1858-1924) was a lifelong enthusiast of Japanese art. For more than 40 years he assembled a rich collection of Japanese prints and artefacts, which was more than mere inspiration to him: it was the source of his art. Shy and unassuming, he lived for a long time in the shadow of the great figures of Japonism like Siegfried Bing, Edmond de Goncourt and Théodore Duret. Still, he took an active part in the development of Japanese woodblock printing in France: he was one of the founders of the Friends of Japanese Art Society and an active member of the French-Japanese society whose mission was to strengthen the ties between the two countries. He also contributed to bringing Japanese woodcuts into museum collections through many donations. The focus of the last 30 years of his life was the mastering of Japanese woodblock engraving under Yoshijiro Urushibara (1889-1953), a young Japanese printmaker who stayed in Paris at the turn of the century. Under his guidance Isaac learned the secrets of the craft he first discovered a few years before through careful study of the Methods of Cursive Drawing by Kitao Keisa Masayoshi (1764-1824). Urushibara supplied him with tools from Japan, and in a few years Isaac became one of the most talented experts of Japanese woodblock printmaking. From then on he never missed a chance to pass on his lore to Japan enthusiasts, artists and collectors alike

Defocus test and defocus correction in full-field optical coherence tomography

We report experimental evidence and correction of defocus in full-field OCT of biological samples due to mismatch of the refractive index of biological tissues and water. Via a metric based on the image quality, we demonstrate that we are able to compensate this index-induced defocus and to recover a sharp image in depth.Comment: 7 pages, 3 figures, minor changes, 1 figure adde

Hydraulic simulations to evaluate and predict design and operation of the Chashma Right Bank Canal

Irrigation systems / Irrigation canals / Flow control / Velocity / Canal regulation techniques / Hydraulics / Simulation models / Design / Operations / Crop-based irrigation / Distributary canals / Water delivery / Policy / Protective irrigation / Water allocation / Water requirements / Sedimentation / Water distribution / Equity / Water conveyance / Pakistan / Chashma Right Bank Canal

Suspended sediment behaviour modeling in irrigation canals of Pakistan: operation, maintenance and sedimentation in irrigation canals

Irrigation canals / Sedimentation / Models / Operations / Maintenance / Simulation / Hydraulics / Calibrations / Pakistan

Parallélisation sur GPU d'un algorithme de reconstruction 3D bayésien en tomographie X.

An important number of image reconstruction algorithms are implemented in the literature on X-ray CT (Computed Tomography) data. The main family of methods are analytical, mainly filtered backprojection which are implemented generally in medical imaging for their fast reconstruction time. The limits of these methods appear when the number of projections is small, and/or not equidistributed around the object. In this specific context, iterative algebraic methods are implemented. A great number of them are mainly based on least square criterion. We propose a regularized version of iterative algorithms to improve results. The main problem that appears when using iterative algebraic methods is the computation time and especially for projection and backprojection steps. We propose to implement some steps of the iterations on GPU hardware. We present an original method based on a Bayesian statistical method for 3D tomographic reconstructions. The main interest is to apply it in a context of non-consistent data sets, for example with a small number of projections. We show a good quality of results and a significant speed up of the calculation with GPU implementation

GPU implementation of a 3D bayesian CT algorithm and its application on real foam reconstruction

5 pagesInternational audienceA great number of image reconstruction algorithms, based on analytical filtered backprojection, are implemented for X-ray Computed Tomography (CT) [1, 3]. The limits of these methods appear when the number of projections is small, and/or not equidistributed around the object. In this specific context, iterative algebraic methods are implemented. A great number of them are mainly based on least square criterion. Recently, we proposed a regularized version based on Bayesian estimation approach. The main problem that appears when using such methods as well as any iterative algebraic methods is the computation time and especially for projection and backprojection steps. In this paper, first we show how we implemented some main steps of such algorithems which are the forward projection and backward backprojection steps on GPU hardware, and then we show some results on real application of the 3D tomographic reconstruction of metallic foams from a small number of projections. Through this application, we also show the good quality of results as well as a significant speed up of the computation with GPU implementation