Elastic instability in stratified core annular flow

We study experimentally the interfacial instability between a layer of dilute polymer solution and water flowing in a thin capillary. The use of microfluidic devices allows us to observe and quantify in great detail the features of the flow. At low velocities, the flow takes the form of a straight jet, while at high velocities, steady or advected wavy jets are produced. We demonstrate that the transition between these flow regimes is purely elastic -- it is caused by viscoelasticity of the polymer solution only. The linear stability analysis of the flow in the short-wave approximation captures quantitatively the flow diagram. Surprisingly, unstable flows are observed for strong velocities, whereas convected flows are observed for low velocities. We demonstrate that this instability can be used to measure rheological properties of dilute polymer solutions that are difficult to assess otherwise.Comment: 4 pages, 4 figure

Phase field modeling of electrochemistry I: Equilibrium

A diffuse interface (phase field) model for an electrochemical system is developed. We describe the minimal set of components needed to model an electrochemical interface and present a variational derivation of the governing equations. With a simple set of assumptions: mass and volume constraints, Poisson's equation, ideal solution thermodynamics in the bulk, and a simple description of the competing energies in the interface, the model captures the charge separation associated with the equilibrium double layer at the electrochemical interface. The decay of the electrostatic potential in the electrolyte agrees with the classical Gouy-Chapman and Debye-H\"uckel theories. We calculate the surface energy, surface charge, and differential capacitance as functions of potential and find qualitative agreement between the model and existing theories and experiments. In particular, the differential capacitance curves exhibit complex shapes with multiple extrema, as exhibited in many electrochemical systems.Comment: v3: To be published in Phys. Rev. E v2: Added link to cond-mat/0308179 in References 13 pages, 6 figures in 15 files, REVTeX 4, SIUnits.sty. Precedes cond-mat/030817

Évolution des anticorps chez les bovins après immunisation contre la brucellose par le vaccin tué H. 38.

Au cours de 5 expériences portant sur 164 bovins et durant de 3 mois à 2 ans, la cinétique des agglutinines et sensibilisatrices induites chez les bovins, âgés de 7 à 18 mois selon l’expérience, par le vaccin antibrucellique tué, souche Br. melitensis 53 H. 38 a été étudiée seule ou comparée aux effets similaires d’autres vaccins. Les anticorps post-vaccinaux créés chez les bovins par le vaccin H. 38 disparaissent plus vite que ceux dus au vaccin B. 19. On constate l’absence de taux diagnostique (normes F. A. O./O. M. S.) d’agglutinine (100 U. I.) ou de sensibilisatrice (titre 1/4) 2 à 3 mois après la vaccination par H. 38. L’absence de taux de suspicion aux normes de la C. E. E. et françaises se note 5 à 6 mois après la vacci nation par 53 H. 38. Les réactions d’agglutination et de Fixation du Complément sont négatives un an après la vaccination, bien avant que les vaches aient 30 mois. Le vaccin tué, souche Br. melitensis 53 H. 58 ne ris que donc pas d’interférer avec des programmes de prophylaxie anti brucellique mettant en jeu la recherche des anticorps spécifiques.In five experiments on 164 cattle, each of a duration from 3 months to 2 years, the behaviour of agglutinating and C. F. antibodies created on bovine 7 to 18 months old, depending on the experiment, bv Br. melitensis strain 53 H. 38 killed vaccine is studied alone or in comparison with similar effects of other antibrucellosis vaccines. Post vaccinal antibodies due to H. 38 vaccine disapear more quickely than those induced on bovine by strain 19 vaccine. There stand no specific agglutininins at the F. A. O./W. H. 0. diagnostic level (100 I. U.) or C. F. antibodies (titer 1/4) 2 to 3 months after H. 38 vaccination. Five to 0 months after such a vaccination, there are no brucella antibodies at the suspicous titer (30 I. V.) retained by European and French authorities. The are no remains of either antibodies one year after H. 38 vac cination, long before cattle has reached 30 months of age. Thus, the killed in adjuvant, Br. melitensis strain H. 38, vaccine will not interfer with campagns of animal brucellosis control using a test policy

Mesures de facteurs spectroscopiques de 61Ni par réaction (d, p) en régime sous-coulombien

Nous avons utilisé la réaction (d, p) en régime sous-coulombien pour mesurer les facteurs spectroscopiques de deux états excités par transferts l = 0 et l = 2 dans 61Ni au voisinage de 4,8 MeV. Nos résultats confirment que la règle de somme pour le remplissage des couches 3s1/2 et 2d n'est satisfaite qu'à 50 % dans 61Ni

A Practical Catalytic Reductive Amination of Carboxylic Acids

We report reductive alkylation reactions of amines using carboxylic acids as nominal electrophiles. The two-step reaction exploits the dual reactivity of phenylsilane and involves a silane-mediated amidation followed by a Zn(OAc)2-catalyzed amide reduction. The reaction is applicable to a wide range of amines and carboxylic acids and has been demonstrated on a large scale (305 mmol of amine). The rate differential between the reduction of tertiary and secondary amide intermediates is exemplified in a convergent synthesis of the antiretroviral medicine maraviroc. Mechanistic studies demonstrate that a residual 0.5 equivalents of carboxylic acid from the amidation step is responsible for the generation of silane reductants with augmented reactivity, which allow secondary amides, previously unreactive in zinc/phenylsilane systems, to be reduced

Préparation et contrôle de l’activité d’un sérum anti-colibacillaire plurispécifique

Saint Aubert G. de, Valette L. R., Papageorgiou C. Préparation et contrôle de l’activité d’un sérum anti-colibacillaire plurispéciflque. In: Bulletin de l'Académie Vétérinaire de France tome 118 n°9, 1965. pp. 439-446

Spécificité, fidélité et sensibilité des antigènes pulloriques de dépistage

Papageorgiou C., Valette L., Béranger G., Joubert L. Spécificité, fidélité et sensibilité des antigènes pulloriques de dépistage. In: Bulletin de l'Académie Vétérinaire de France tome 121 n°3, 1968. pp. 107-117

On twisted Fourier analysis and convergence of Fourier series on discrete groups

We study norm convergence and summability of Fourier series in the setting of reduced twisted group $C^*$-algebras of discrete groups. For amenable groups, F{\o}lner nets give the key to Fej\'er summation. We show that Abel-Poisson summation holds for a large class of groups, including e.g. all Coxeter groups and all Gromov hyperbolic groups. As a tool in our presentation, we introduce notions of polynomial and subexponential H-growth for countable groups w.r.t. proper scale functions, usually chosen as length functions. These coincide with the classical notions of growth in the case of amenable groups.Comment: 35 pages; abridged, revised and update