Local transient rheological behavior of concentrated suspensions

This paper reports experiments on the shear transient response of concentrated non-Brownian suspensions. The shear viscosity of the suspensions is measured using a wide-gap Couette rheometer equipped with a Particle Image Velocimetry (PIV) device that allows measuring the velocity field. The suspensions made of PMMA particles (31$\mu$m in diameter) suspended in a Newtonian index- and density-matched liquid are transparent enough to allow an accurate measurement of the local velocity for particle concentrations as high as 50%. In the wide-gap Couette cell, the shear induced particle migration is evidenced by the measurement of the time evolution of the flow profile. A peculiar radial zone in the gap is identified where the viscosity remains constant. At this special location, the local particle volume fraction is taken to be the mean particle concentration. The local shear transient response of the suspensions when the shear flow is reversed is measured at this point where the particle volume fraction is well defined. The local rheological measurements presented here confirm the macroscopic measurements of Gadala-Maria and Acrivos (1980). After shear reversal, the viscosity undergoes a step-like reduction, decreases slower and passes through a minimum before increasing again to reach a plateau. Upon varying the particle concentration, we have been able to show that the minimum and the plateau viscosities do not obey the same scaling law with respect to the particle volume fraction. These experimental results are consistent with the scaling predicted by Mills and Snabre (2009) and with the results of numerical simulation performed on random suspensions [Sierou and Brady (2001)]. The minimum seems to be associated with the viscosity of an isotropic suspension, or at least of a suspension whose particles do not interact through non-hydrodynamic forces, while the plateau value would correspond to the viscosity of a suspension structured by the shear where the non-hydrodynamic forces play a crucial role

Embeddings of SL(2,Z) into the Cremona group

Geometric and dynamic properties of embeddings of SL(2,Z) into the Cremona group are studied. Infinitely many non-conjugate embeddings which preserve the type (i.e. which send elliptic, parabolic and hyperbolic elements onto elements of the same type) are provided. The existence of infinitely many non-conjugate elliptic, parabolic and hyperbolic embeddings is also shown. In particular, a group G of automorphisms of a smooth surface S obtained by blowing-up 10 points of the complex projective plane is given. The group G is isomorphic to SL(2,Z), preserves an elliptic curve and all its elements of infinite order are hyperbolic.Comment: to appear in Transformation Group

FTY720 (fingolimod) modulates the severity of viral-induced encephalomyelitis and demyelination.

BackgroundFTY720 (fingolimod) is the first oral drug approved by the Food and Drug Administration for treatment of patients with the relapsing-remitting form of the human demyelinating disease multiple sclerosis. Evidence suggests that the therapeutic benefit of FTY720 occurs by preventing the egress of lymphocytes from lymph nodes thereby inhibiting the infiltration of disease-causing lymphocytes into the central nervous system (CNS). We hypothesized that FTY720 treatment would affect lymphocyte migration to the CNS and influence disease severity in a mouse model of viral-induced neurologic disease.MethodsMice were infected intracranially with the neurotropic JHM strain of mouse hepatitis virus. Infected animals were treated with increasing doses (1, 3 and 10 mg/kg) of FTY720 and morbidity and mortality recorded. Infiltration of inflammatory virus-specific T cells (tetramer staining) into the CNS of FTY720-treated mice was determined using flow cytometry. The effects of FTY720 treatment on virus-specific T cell proliferation, cytokine production and cytolytic activity were also determined. The severity of neuroinflammation and demyelination in FTY720-treated mice was examined by flow cytometry and histopathologically, respectively, in the spinal cords of the mice.ResultsAdministration of FTY720 to JHMV-infected mice resulted in increased clinical disease severity and mortality. These results correlated with impaired ability to control viral replication (P < 0.05) within the CNS at days 7 and 14 post-infection, which was associated with diminished accumulation of virus-specific CD4+ and CD8+ T cells (P < 0.05) into the CNS. Reduced neuroinflammation in FTY720-treated mice correlated with increased retention of T lymphocytes within draining cervical lymph nodes (P < 0.05). Treatment with FTY720 did not affect virus-specific T cell proliferation, expression of IFN-γ, TNF-α or cytolytic activity. FTY720-treated mice exhibited a reduction in the severity of demyelination associated with dampened neuroinflammation.ConclusionThese findings indicate that FTY720 mutes effective anti-viral immune responses through impacting migration and accumulation of virus-specific T cells within the CNS during acute viral-induced encephalomyelitis. FTY720 treatment reduces the severity of neuroinflammatory-mediated demyelination by restricting the access of disease-causing lymphocytes into the CNS but is not associated with viral recrudescence in this model

Nonlinear instability of density-independent orbital-free kinetic energy functionals

We study in this article the mathematical properties of a class of orbital-free kinetic energy functionals. We prove that these models are linearly stable but nonlinearly unstable, in the sense that the corresponding kinetic energy functionals are not bounded from below. As a matter of illustration, we provide an example of an electronic density of simple shape the kinetic energy of which is negative.Comment: 14 pages, 1 figur

Commitment and the Modern Union: Assessing the Link Between Premarital Cohabitation and Subsequent Marital Stability

In recent years, the incidence of premarital cohabitation has increased dramatically in many countries of Western Europe and in the United States. As cohabitation becomes a more common experience, it is increasingly important to understand the links between cohabitation and other steps in the process of family formation and dissolution. We focus on the relationship between pre- marital cohabitation and subsequent marital stability, and analyze data from the 1981 Women in Sweden survey using a hazards model approach. Our results indicate that women who premaritally cohabit have almost 80 percent higher marital dissolution rates than those who do not cohabit. Women who cohabit for over three years prior to marriage have over 50 percent higher dissolution rates than women who cohabit for shorter durations. Last, cohabitors and non-cohabitors whose marriages have remained intact for eight years appear to have identical dissolution rates after that time. In addition, we provide evidence that strongly suggests a weaker commitment, on the part of those who cohabit premaritally, to the institution of marriage.

Les Petits opérateurs privés de la distribution d'eau à Maputo : d'un problème à une solution ? Regards croisés

Consultable sur Internet : http://www.afd.fr/webdav/site/afd/shared/PUBLICATIONS/RECHERCHE/Scientifiques/Documents-de-travail/085-document-travail.pdfNational audienceA Maputo, le réseau officiel d'approvisionnement en eau potable ne dessert qu'une petite partie des habitants de l'agglomération. De nombreux habitants, en particulier ceux de la périphérie de la ville, n'ont d'autre choix que de s'approvisionner auprès de divers fournisseurs informels. C'est ainsi que sont apparus dans les années 1990 des systèmes autonomes de distribution de l'eau gérés par des petits opérateurs locaux. Si la présence de Petits opérateurs privés (POP) est commune dans les pays en développement, la spécificité de ceux de Maputo réside dans leur prolifération exceptionnelle (450 opérateurs desservent plus de 350 000 personnes). Ils ont dévelop- pé des options techniques robustes, modulaires et rentables, et certains d'entre eux se comportent en véritables entrepreneurs malgré le caractère informel de leur activité. A tel point que leur modèle apparaît aujourd'hui prometteur pour la desserte des zones périurbaines et que les autorités locales, appuyées par les bailleurs de fonds, ont défini une véritable stratégie à leur égard. Pourtant, les POP ont à l'origine été ignorés par les autorités publiques, puis considérés comme des concurrents illégaux du fournisseur officiel. Il est dès lors intéressant de reconstituer les événements qui ont conduit à un tel changement de perception avec une approche d'analyse des politiques publiques. Ainsi, le modèle de la " fenêtre d'opportunité " de J. Kingdon, qui postule la convergence de différents courants (courant " des problèmes "," des solutions ", et " de la politique ") comme facteur explicatif d'une politique publique, est éclairant pour saisir ce qui a rendu l'intégration des POP possible. Raisonner en termes de " réseaux " permet également d'identifier le rôle, d'un côté de la petite communauté de spécialistes internationaux des dispositifs alternatifs de distribution d'eau, et de l'autre des organisations mozambicaines cherchant à construire un compromis social sur les POP du quartier de Laulane

San Francisco\u27s Doom

https://digitalcommons.library.umaine.edu/mmb-vp/2420/thumbnail.jp

The origin of the complex character of the ohmic impedance

The local and global Ohmic response for an electrode exhibiting geometry-induced potential and/or current distributions has recently been shown to be represented by a frequency-dependent complex impedance. A physical explanation for this result is provided in terms of the radial contribution to local current density and the decrease in current density along the current lines. Experiments performed with Cu/Al and Mg/Al galvanic couples show that, in regions where a radial current density does not exist, the local Ohmic impedance is independent of position; whereas, in regions where the radial current density cannot be neglected, the local Ohmic impedance is a function of position. Simulations performed on recessed electrodes show that, even in the absence of a radial current, an axial variation of current density gives rise to a complex Ohmic impedance. The complex character of the Ohmic impedance shows that an equivalent circuit, using the usual two-terminal resistor to represent the Ohmic contribution of the electrolyte, provides an inadequate representation of an electrode with geometry-induced current and potential distributions