61 research outputs found
Monodisperse Dry Granular Flows on Inclined Planes : Role of Roughness
Recent studies have pointed out the importance of the basal friction on the
dynamics of granular flows. We present experimental results on the influence of
the roughness of the inclined plane on the dynamics of a monodisperse dry
granular flow. We found experimentally that it exists a maximum of the friction
for a given relative roughness. This maximum is shown to be independent of the
angle of the slope. This behavior is observed for four planes with different
bump sizes (given by the size of the beads glued on the plane) from 200 microns
to 2 mm. The relative roughness corresponding to the maximum of the friction
can be predicted with a geometrical model of stability of one single bead on
the plane. The main parameters are the size of the bumps and the size of the
flowing beads. In order to obtain a higher precision, the model also takes into
account of the spacing between the bumps of the rough plane. Experimental
results and model are in good agreement for all the planes we studied. Other
parameters, like the sphericity of the beads, or irregularities in the
thickness of the layer of glued particles, are shown to be of influence on the
friction.Comment: 17 pages, 15 figures, submitted to EPJ
Beyond the personal–anonymous divide: agency relations in powers of attorney in France in the eighteenth and nineteenth centuries
Powers of attorney are often interpreted as evidence of trust among the parties involved. We build a novel dataset of notarized powers of attorney, capturing a wide variety of agency relationships in four large French commercial cities in the eighteenth and nineteenth centuries, to test hypotheses on the relational basis of economic relationships. We find little support for the idea of a radical shift from personal to anonymous relationships during our period. Our results point to more nuanced transformations. The preference for proxies in the same occupation as the principal somewhat declined, while professional proxies emerged and principals used relational chains, especially involving notaries, to find proxies.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/151849/1/ehr12784_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/151849/2/ehr12784.pd
Functional Implication of Dp71 in Osmoregulation and Vascular Permeability of the Retina
Functional alterations of Müller cells, the principal glia of the retina, are an early hallmark of most retina diseases and contribute to their further progression. The molecular mechanisms of these reactive Müller cell alterations, resulting in disturbed retinal homeostasis, remain largely unknown. Here we show that experimental detachment of mouse retina induces mislocation of the inwardly rectifying potassium channels (Kir4.1) and a downregulation of the water channel protein (AQP4) in Müller cells. These alterations are associated with a strong decrease of Dp71, a cytoskeleton protein responsible for the localization and the clustering of Kir4.1 and AQP4. Partial (in detached retinas) or total depletion of Dp71 in Müller cells (in Dp71-null mice) impairs the capability of volume regulation of Müller cells under osmotic stress. The abnormal swelling of Müller cells In Dp71-null mice involves the action of inflammatory mediators. Moreover, we investigated whether the alterations in Müller cells of Dp71-null mice may interfere with their regulatory effect on the blood-retina barrier. In the absence of Dp71, the retinal vascular permeability was increased as compared to the controls. Our results reveal that Dp71 is crucially implicated in the maintenance of potassium homeostasis, in transmembraneous water transport, and in the Müller cell-mediated regulation of retinal vascular permeability. Furthermore, our data provide novel insights into the mechanisms of retinal homeostasis provided by Müller cells under normal and pathological conditions
Genetic Deletion of Laminin Isoforms β2 and γ3 Induces a Reduction in Kir4.1 and Aquaporin-4 Expression and Function in the Retina
Glial cells such as retinal Müller glial cells are involved in potassium ion and water homeostasis of the neural tissue. In these cells, inwardly rectifying potassium (Kir) channels and aquaporin-4 water channels play an important role in the process of spatial potassium buffering and water drainage. Moreover, Kir4.1 channels are involved in the maintenance of the negative Müller cell membrane potential. The subcellular distribution of Kir4.1 and aquaporin-4 channels appears to be maintained by interactions with extracellular and intracellular molecules. Laminins in the extracellular matrix, dystroglycan in the membrane, and dystrophins in the cytomatrix form a complex mediating the polarized expression of Kir4.1 and aquaporin-4 in Müller cells.The aim of the present study was to test the function of the β2 and γ3 containing laminins in murine Müller cells. We used knockout mice with genetic deletion of both β2 and γ3 laminin genes to assay the effects on Kir4.1 and aquaporin-4. We studied protein and mRNA expression by immunohistochemistry, Western Blot, and quantitative RT-PCR, respectively, and membrane currents of isolated cells by patch-clamp experiments. We found a down-regulation of mRNA and protein of Kir4.1 as well as of aquaporin-4 protein in laminin knockout mice. Moreover, Müller cells from laminin β2 and γ3 knockout mice had reduced Kir-mediated inward currents and their membrane potentials were more positive than those in age-matched wild-type mice.These findings demonstrate a strong impact of laminin β2 and γ3 subunits on the expression and function of both aquaporin-4 and Kir4.1, two important membrane proteins in Müller cells
Targeted inactivation of dystrophin gene product Dp71: phenotypic impact in mouse retina
Bidisperse granular avalanches on inclined planes: A rich variety of behaviors
Experiments were performed to provide insight into the
flow behavior and structure of bimodal mixtures of grains in
gravity-driven, free-surface flows. Unsteady unconfined flows
were produced by releasing instantaneously a dry granular mass,
composed of two particle sizes, over a rough inclined plane. As a
result of size segregation, the small particles are found at the
bottom of the flow and final deposit, the large particles are
found at the free surface, but also on the lateral borders and at
the front of the flow. The lateral and vertical inhomogeneous
repartitions of particles lead to two main effects that are
completely absent in monodispersed flows. The outline effect
results from the accumulation of large beads on the periphery of
the flow depending on the value of the relative friction of each
particle species on the plane. This effect in turn causes a
narrowing of the flow and/or an increase of length of the final
deposit. The interface effect results of the interaction between
layers of different size particles and causes the modification of
the thickness of the deposit. These effects occur simultaneously
and their combination leads to a great variety of behaviors. In
this investigation, evidence of the diversity of behaviors is
presented as the size ratio, relative friction and concentration
of each particle species are varied
Expression of Dp71 in Müller glial cells: a comparison with utrophin- and dystrophin-associated proteins.
International audienceThe abnormal retinal electrophysiology observed in patients with Duchenne muscular dystrophy (DMD) has been attributed to an altered expression of C-terminal products of the dystrophin gene. It has been shown that Dp260 is expressed by photoreceptor cells, whereas Dp71 is present in glial cells. The present study was intended to identify all known members of the dystrophin superfamily and their associated proteins expressed in Müller glial cells (MGC)
Expression of Dp71 in Müller glial cells: a comparison with utrophin- and dystrophin-associated proteins.
International audienceThe abnormal retinal electrophysiology observed in patients with Duchenne muscular dystrophy (DMD) has been attributed to an altered expression of C-terminal products of the dystrophin gene. It has been shown that Dp260 is expressed by photoreceptor cells, whereas Dp71 is present in glial cells. The present study was intended to identify all known members of the dystrophin superfamily and their associated proteins expressed in Müller glial cells (MGC)
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