Optohydrodynamics of soft fluid interfaces : Optical and viscous nonlinear effects

Recent experimental developments showed that the use of the radiation pressure, induced by a continuous laser wave, to control fluid-fluid interface deformations at the microscale, represents a very promising alternative to electric or magnetic actuation. In this article, we solve numerically the dynamics and steady state of the fluid interface under the effects of buoyancy, capillarity, optical radiation pressure and viscous stress. A precise quantitative validation is shown by comparison with experimental data. New results due to the nonlinear dependence of the optical pressure on the angle of incidence are presented, showing different morphologies of the deformed interface going from needle-like to finger-like shapes, depending on the refractive index contrast. In the transient regime, we show that the viscosity ratio influences the time taken for the deformation to reach steady state

Eddies and interface deformations induced by optical streaming

We study flows and interface deformations produced by the scattering of a laser beam propagating through non-absorbing turbid fluids. Light scattering produces a force density resulting from the transfer of linear momentum from the laser to the scatterers. The flow induced in the direction of the beam propagation, called 'optical streaming', is also able to deform the interface separating the two liquid phases and to produce wide humps. The viscous flow taking place in these two liquid layers is solved analytically, in one of the two liquid layers with a stream function formulation, as well as numerically in both fluids using a boundary integral element method. Quantitative comparisons are shown between the numerical and analytical flow patterns. Moreover, we present predictive simulations regarding the effects of the geometry, of the scattering strength and of the viscosities, on both the flow pattern and the deformation of the interface. Finally, theoretical arguments are put forth to explain the robustness of the emergence of secondary flows in a two-layer fluid system

Influence of the spatial correlation structure of an elastic random medium on its scattering properties

International audienceIn the weakly heterogeneous regime of elastic wave propagation through a random medium, transport and diffusion models for the energy densities can be set up. In the isotropic case, the scattering cross sections are explicitly known as a function of the wave number and the correlations of the Lamé parameters and density. In this paper, we discuss the precise influence of the correlation structure on the scattering cross sections, mean free paths and diffusion parameter, and separate that influence from that of the correlation length and variance. We also analyze the convergence rates towards the low-and high-frequency ranges. For all analyses, we consider five different correlation structures, that allow us to explore a wide range of behaviors. We identify that the controlling factors for the low-frequency behavior are the value of the Power Spectral Density Function (PSDF) and its first non-vanishing derivative at the origin. In the high frequency range, the controlling factor is the third moment of the PSDF (which may be unbounded)

Impact of aging on the soft error rate of 6T SRAM for planar and bulk technologies

This paper evaluates the impact of aging on the radiation sensitivity of 6T SRAMfor two planar bulk technologies. This study ismotivated by the growing impact of aging and radiation effects on the reliability of CMOS technology. Amodelling methodology dedicated to this newphenomenon is proposed. Thismodelling uses the radiation modelling device MUSCA SEP3 and an electrical aging modelling. First, the impact of aging on SEE sensitivity is studied through a parametric modeling of the threshold voltages of the transistors composing the 6T SRAM. Then, an operative avionics environment is modelled in order to evaluate the consequences on reliability

Previous Leisure-Time Physical Activity Dose Dependently Decreases Ischemic Stroke Severity

In the present subanalysis of a cross-sectional study showing the favorable effect of prior transient ischemia, leisure-time physical activity, and lipid-lowering drug therapy on stroke severity, we aimed to evaluate whether previous physical activity was dose dependently associated to minor stroke (NIHSS 0–3) and to identify possible underlying factors. Among 362 consecutive patients, less severe stroke was related to weekly exercise duration prior to stroke (no exercise: 36.1%; <2 hours: 49.3%; 2–5 hours: 58.8%; >5 hours: 64.0%; P = 0.003). Only weak and moderate exercise practices were protective (weak: 50.0%; moderate: 79.3%; heavy: 22.2%; P < 0.0001). Such a beneficial effect was observed independently of age and was associated with a trend to a lower frequency of arterial hypertension, alcohol abuse, and a better metabolic profile. Besides other therapeutic approaches, physical activity may be a simple way to decrease cerebral ischemia severity

Les "vagues voyageuses" du campagnol terrestre en Franche-Comté

Dans les prairies d'altitude, les dégâts provoqués par le campagnol terrestre posent un problème économique et agricole récurrent depuis le début des années 70. Dans la lutte contre cette peste agricole, l'utilisation croissante d'un anticoagulant rodenticide, la bromadiolone, a en plus considérablement augmenté la mortalité de nombreuses espèces animales, notamment de rapaces (légalement protégés), de renards et de sangliers. Dès le début du siècle, les recherches sur les variations de populations de rongeurs ont montré que la densité de certaines espèces de petits mammifères (lemmings, campagnols, etc.) fluctue de manière plus ou moins cyclique

Influence of Lipid Profiles on the Risk of Hemorrhagic Transformation after Ischemic Stroke: Systematic Review

Background: It has been suggested that low cholesterol levels might be associated with an increased risk of hemorrhagic transformation (HT) in patients with acute cerebral ischemia. We systematically reviewed the literature to determine the influence of lipid profiles on the HT risk. Methods: We searched PubMed from 1966 and EMBASE from 1980 for studies that investigated the association between lipid profiles and HT. We performed a meta-analysis (weighted mean difference method) for the comparison between presence and absence of HT (all or symptomatic) for total, low-density-lipoprotein (LDL) and high-density-lipoprotein (HDL) cholesterol, and triglycerides. Results: Eight studies investigating 1,763 patients were eligible, but none was designed specifically to address this question. All studies recruited acute stroke patients selected on the presumed cause of cerebral ischemia or treatment received. The meta-analysis showed that: (i) patients with all HT had lower LDL cholesterol levels (p = 0.008) but no difference in HDL cholesterol levels (p = 0.066), total cholesterol (p = 0.129) and triglycerides (p = 0.900); (ii) patients with symptomatic HT had lower total cholesterol levels (p = 0.035) but did not differ in LDL (p = 0.056) and HDL cholesterol (p = 0.138) and triglyceride (p = 0.851) levels. Conclusion: HT is associated with baseline total and LDL cholesterol levels, but the mechanism of this association needs to be explored to identify preventive strategies

Impact of the neutrophil response to granulocyte colony-stimulating factor on the risk of hemorrhage when used in combination with tissue plasminogen activator during the acute phase of experimental stroke

BACKGROUND: Granulocyte colony-stimulating factor (G-CSF) is a pharmacologic agent inducing neutrophil mobilization and a new candidate for neuroprotection and neuroregeneration in stroke. Its effects when used in combination with tissue plasminogen activator (tPA) were explored during the acute phase of ischemic stroke. METHODS: We used a middle cerebral artery occlusion (MCAO) model of cerebral ischemia, associated with treatment with tPA, in male spontaneously hypertensive rats (SHR). Granulocyte colony-stimulating factor (G-CSF; 60 μg/kg) was injected just before tPA. Neutrophil response in peripheral blood and in the infarct area was quantified in parallel to the infarct volume. Protease matrix metallopeptidase 9 (MMP-9) release from circulating neutrophils was analyzed by immunochemistry and zymography. Vascular reactivity and hemorrhagic volume in the infarct area was also assessed. RESULTS: Twenty four hours after ischemia and tPA, G-CSF administration induced a significant increase of neutrophils in peripheral blood (P <0.05). At 72 hours post-ischemia, G-CSF was significantly associated with an increased risk of hemorrhage in the infarct area (2.5 times more likely; P <0.05) and significant cerebral endothelium-dependent dysfunction. Ex vivo, an increased MMP-9 release from neutrophils after tPA administration correlated to the increased hemorrhagic risk (P <0.05). In parallel, G-CSF administration was associated with a decreased neutrophil infiltration in the infarct area (-50%; P <0.05), with a concomitant significant neuroprotective effect (infarct volume: -40%; P <0.05). CONCLUSIONS: We demonstrate that G-CSF potentiates the risk of hemorrhage in experimental stroke when used in combination with tPA by inducing neutrophilia. This effect is concomitant to an increased MMP-9 release from peripheral neutrophils induced by the tPA treatment. These results highlight the potential hemorrhagic risk of associating G-CSF to thrombolysis during the acute phase of stroke