122 research outputs found
Universal G' ∼ L^-3 Law for the Low-Frequency Shear Modulus of Confined Liquids
Get PDFLiquids confined to sub-millimeter scales have remained poorly understood. One of the most striking effects is the large elasticity revealed using good wetting conditions, which grows upon further decreasing the confinement length, L. These systems display a low-frequency shear modulus in the order of 1-10^3 Pa, contrary to our everyday experience of liquids as bodies with a zero low-frequency shear modulus. While early experimental evidence of this effect was met with skepticism and abandoned, further experimental results and, most recently, a new atomistic theoretical framework have confirmed that liquids indeed possess a finite low-frequency shear modulus G', which scales with the inverse cubic power of confinement length L. We show that this law is universal and valid for a wide range of materials (liquid water, glycerol, ionic liquids, non-entangled polymer liquids, isotropic liquids crystals). Open questions and potential applications in microfluidics mechanochemistry, energy, and other fields are highlighted
Blood rheology on modified rheometer surfaces
No full textInternational audienceBackground: Rheology of a bulk sample is a collective phenomenon based on the force transmission through the sample. Conventional rheometry uses steel plates, however, steel is not a physiological contact surface for blood. Blood viscosity and shear moduli might be underestimated in these tests, because the force transmission through the gap is strongly influenced by the contact of the sample to the test surfaces. It was shown that shear moduli are higher when high wetting substrates are used (E. Kume et al.; L. Noirez; U. Windberger et al.).Method: To test blood under near-physiological condition, we modified the test plates by coatings with (1) endothelial cells (HUVECs) grown on a collagen hydrogel, (2) collagen hydrogel without HUVECs, (3) glass that was the substrate for the hydrogel coating, and (4) steel. We tested blood and plasma from healthy human volunteers in oscillating shear flow to assess the blood behavior at near-equilibrium conditions.Results: A linear elastic property was identified by a G´-plateau in both coatings and on glass, but not if both surfaces were made of steel. The highest linear G´-value was obtained on glass and hydrogel surfaces followed by HUVECs, and steel. Yield points were assessed by extrapolating the end of the G´-plateau to the applied shear stress, and revealed the highest values for glass and hydrogel coating, followed by HUVEC seeding. An extended yielding was observed for the modified surfaces, which culminated in a second linear phase until the shear elasticity was finally lost at shear stresses of over 300 mPa. With steel surfaces, elasticity was lost already at 5mPa, demonstrating that the viscoelastic response highly depends on the substrate interaction.Our data indicate that a modification of the boundary surface has deep consequences for flow. To model the flow through biomedical devices, controlled interfacial conditions that reflect the planned application are key parameters
Mise en place de la chimiothérapie à domicile à l'Hôpital Bon Secours de Metz (Première expérience avec les patients du service d'Hématologie traités par Velcade)
No full textLe cancer, véritable fléau de notre société et 1ère cause de mort prématurée en France est devenu l une des préoccupations majeures de santé publique. Ainsi, un plan national de lutte contre le cancer a été mis en place en 2003-2007, prolongé par un second plan cancer 2009-2013. Dans un souci d améliorer la qualité de vie des patients, le plan 2003-2007 a prévu parmi ses 70 mesures de faciliter la prise en charge à domicile, chimiothérapie comprise.C est donc dans ce contexte de mobilisation nationale, auquel s ajoute la saturation de l activité de chimiothérapie au sein des secteurs d Hôpitaux de Jour (HDJ) que l unité de pharmacie clinique cancérologique (UPCC) de l Hôpital Bon Secours de Metz a développé depuis le 10 avril 2007 une activité de chimiothérapie à domicile avec le service d Hématologie.Le premier protocole retenu pour la mise en place de cette activité est un traitement par Velcade®, indiqué chez les patients atteints de myélome multiple. Pendant deux années, nous avons suivi 13 patients traités par ce protocole à leur domicile.Les patients sont très satisfaits de cette prise en charge qui améliore leur confort de vie. Aucun incident n est intervenu lors de l administration de Velcade® à domicile. Cependant, le bilan global de ces deux années d activité reste mitigé. Les professionnels de santé impliqués, hospitaliers et libéraux, rencontrent des difficultés à poursuivre et développer cette activité. Les principales raisons en sont le manque de temps, de coordination et la non prise en compte des coûts de fonctionnement logistique pour l acheminement des préparations au domicile des patients.La chimiothérapie à domicile a sa place comme alternative à l hospitalisation pour des protocoles thérapeutiques bien identifiés, mais a-t-elle un avenir face à l hospitalisation à domicile ?NANCY1-SCD Pharmacie-Odontologie (543952101) / SudocNANCY1-Bib. numérique (543959902) / SudocSudocFranceF
Side-chain liquid-crystalline polyacrylates: Experimental evidence of a coexistence of a double main-chain confinement inside the smectic layer
No full textDetailed profiles providing the main-chain/mesogen organisation
within the smectic layers have been deduced from neutron diffraction
measurements, by combination of the coherent scattering length
profiles of the fully hydrogenated and the partially deuterated
side-chain liquid-crystal polymers. Two different sites of the
molecule (either on the main chain or on the mesogen extremity)
have been labelled to prove that main chains can occupy the central
zone of the mesogenic layers whereas most of them remains confined
between the layers of mesogens. This surprising result can be
explained considering symmetry arguments
Unexpected thermo-elastic effects in liquid glycerol by mechanical deformation
Get PDFIt is commonly accepted that shear waves do not propagate in a liquid medium. The shear wave energy is supposed to dissipate nearly instantaneously. This statement originates from the difficulty to access “static” shear stress in macroscopic liquids. In this paper, we take a different approach. We focus on the stability of the thermal equilibrium while the liquid (glycerol) is submitted to a sudden shear strain at sub-millimeter scale. The thermal response of the deformed liquid is unveiled. The liquid exhibits simultaneous and opposite bands up to about +0.04 to −0.04 °C temperature variation, while keeping the global thermal balance unchanged. The sudden thermal changes and the long thermal relaxation highlight the ability of the liquid to convert the step strain energy in non-uniform thermodynamic states. The thermal effects depend nearly linearly on the amplitude of the deformation supporting the hypothesis of a shear wave propagation (elastic correlations) extending up to several hundreds micrometers. This new physical effect can be explained in terms of the underlying phonon physics of confined liquids, which unveils a hidden solid-like response with many similarities to glassy systems
L’échographie pleuro-pulmonaire pour le pneumologue [Lung and pleural space ultrasonography for pulmonologist]
No full textIn the past twenty years ultrasound has been the subject of renewed interest in lung exploration in the broad sense. The necessity of accessing a means of rapid exploration at the bed of the patient in a critical situation has led to the development of a pleuro-pulmonary ultrasound semiology to make it a diagnostic tool of choice which exceeds the strict framework intensive care units and emergency services. With the diagnosis of thoracic tumors or the exploration of interstitial syndromes, it tends to integrate more into the daily practice of the pulmonologist. This article is a review of the possibilities offered by ultrasound in the field with its advantages and limitations
Identification of thermal shear bands in a low molecular weight polymer melt under oscillatory strain field
No full textInternational audienceWe present real-time micro-thermal measurements of the response of viscous fluids (low molecular weight unentangled and entangled polymer melts) submitted to an oscillatory mechanical shear strain (in conditions of conventional viscoelastic measurements). We show that thermal changes occur at the early steps of the applied deformation. A succession of thermodynamic states is identified showing the formation of non-uniform temperature shear bands along the strain direction. These thermal shear bands indicate the coexistence of cold and warm zones appearing in phase with the deformation. The synchronism of the temperature variation with the mechanical strain reveals a reversible process of elastic type indicating that viscous liquids might exhibit thermoelastic behaviors
Microstructure and concentration fluctuations in alcohol–Toluene andalcohol-Cyclohexane binary liquids: A small angle neutronscattering study
No full textInternational audienceThe origin of concentration fluctuations in a series of binary liquids is examined by small angle neutron scatteringin relation with H-bonded micellar clusters and the aggregation of alcohol-rich domains, which is also related tothe well-known observation of a prepeak in diffraction spectra of alcohols. The results suggest that concentrationfluctuations do not arise from size variation and re-arrangement of the mesoscopic domains but from themicellar-clusters themselves. We evaluate the scattering intensity at small angles and deduce the Ornstein–Zernike correlation lengths, the Bhatia-Thornton concentration fluctuations and the Kirkwood–Buff integrals.An alternative approach, based on the Guinier approximation was applied, indicating that the observed inhomogeneitycould be related to spherical particles with diameter comparable to the H-bonded multimers. We comparethe structure factor of different systems when varying the molecular interactions: the alcohol–solventinteraction has been tuned with Toluene and Cyclohexane aprotic solvents, and the amphiphilic character ofthe alcohol, by going from Tert-butanol to Ethanol and Methanol
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