Viscosity and Electrical Conductivity of Aqueous NaCl Solutions with Dissolved CO2

AbstractWith the perspective of long term CO2 storage, thermodynamic data are necessary for the simulations of CO2 injection in aquifers of depleted oil reservoirs. We focus here on the determination of the resistivity and viscosi ty of aqueous NaCl solutions with dissolved CO2. It is well known that dissolved CO2 increases slightly the water density. Recently, Bando et al. (2004) measured the viscosity of CO2 saturated brines and found an increase of viscosity with increasing amoun t of dissolved CO2. For resistivity, no data is available to our knowledge.We evaluated the effect of dissolved CO2 simultaneously on the resistivity and viscosity of three NaCl solutions covering the range of salinity usually encountered in potential CO2 storage geological formations. At a constant temperature of 35 ∘C, we show that the variation of resistivity and viscosity are proportional to the amount of dissolved CO2. For viscosity, our data are in agreement with previous observations. The observed variations are small, at maximum of the order of 10%. The increase of viscosity is well correlated with the variation of conductivity because ions are moving in a more viscous solvent and th erefore conductivity decreases. For the temperature dependence, w e used the Arps model to describe the measured variation of conductivity as a function of temperature. We propose a simple model to take into account the small modifications of conductivity and viscosity as a function of the dissolved CO2 fraction and temperature. Finally, we examine two potential impact s of these findings

Constant-pressure sound waves in non-Hermitian disordered media

When waves impinge on a disordered material they are back-scattered and form a highly complex interference pattern. Suppressing any such distortions in the free propagation of a wave is a challenging task with many applications in a number of different disciplines. In a recent theoretical proposal, it was pointed out that both perfect transmission through disorder as well as a complete suppression of any variation in a wave intensity can be achieved by adding a continuous gain-loss distribution to the disorder. Here we show that this abstract concept can be implemented in a realistic acoustic system. Our prototype consists of an acoustic waveguide containing several inclusions that scatter the incoming wave in a passive configuration and provide the gain or loss when being actively controlled. Our measurements on this non-Hermitian acoustic metamaterial demonstrate unambiguously the creation of a reflectionless scattering wave state that features a unique form of discrete constant-amplitude pressure waves. In addition to demonstrating that gain-loss additions can turn localised systems into transparent ones, we expect our proof-of-principle demonstration to trigger interesting new developments not only in sound engineering, but also in other related fields such as in non-Hermitian photonics

Active Su-Schrieffer-Heeger-like System

An acoustic dimer composed of two electronically controlled electro-acoustic resonators is presented in view of exploring one-dimensional topological phenomena.Comment: 9 pages, 9 figure

Développement et validation d'une métasurface acoustique orientable large bande composée de résonateurs électroacoustiques actifs

Nous proposons un concept de métasurface acoustique orientables en réflexion, effective sur une large bande de fréquences, à l’aide de cellules actives. La métasurface est composée d’un réseau de haut-parleurs petits devant la longueur d’onde, dont l’impédance acoustique peut être programmée par contrôle actif afin d’ajuster la phase du coefficient de réflexion en tout point de la métasurface. La stratégie de contrôle s’inspire des Résonateurs Electroacoustiques Actifs, utilisant un asservissement en courant du transducteur basé sur une captation microphonique devant sa membrane, permettant d’obtenir une large gamme d’impédances acoustiques sur un même haut-parleur. Ce papier présente la méthodologie de dimensionnement des Résonateurs Electroacoustiques permettant d’obtenir un angle de réflexion prédéfini pour une incidence donnée, et des validations numériques et expérimentales permettent de vérifier les performances du concept. L’aspect large-bande du contrôle sera en particulier discuté

Toward Wideband Steerable Acoustic Metasurfaces with Arrays of Active Electroacoustic Resonators

We introduce an active concept for achieving acoustic metasurfaces with steerable reflection properties, effective over a wide frequency band. The proposed active acoustic metasurface consists in a surface array of subwavelength loudspeakers diaphragms, each with programmable individual active acoustic impedances allowing for local control over the different reflection phases over the metasurface. The active control framework used for controlling the reflection phase over the metasurface is derived from the Active Electroacoustic Resonator concept. Each unit-cell simply consists of a current-driven electrodynamic loudspeaker in a closed box, whose acoustic impedance at the diaphragm is judiciously adjusted by connecting an active electrical control circuit. The control is known to achieve a wide variety of acoustic impedances on a single loudspeaker diaphragm used as an acoustic resonator, with the possibility to shift its resonance frequency by more than one octave. The paper presents a methodology for designing such active metasurface elements. An experimental validation of the achieved individual reflection coefficients is presented, and full wave simulations present a few examples of achievable reflection properties, with a focus on the bandwidth of operation of the proposed control concept

Immunological markers after long-term treatment interruption in chronically HIV-1 infected patients with CD4 cell count above 400 x 10(6) cells/l.

OBJECTIVE: To analyse immunological markers associated with CD4+ lymphocyte T-cell count (CD4+) evolution during 12-month follow-up after treatment discontinuation. METHOD: Prospective observational study of chronically HIV-1 infected patients with CD4+ above 400 x 10(6) cells/l. RESULTS: CD4+ changes took place in two phases: an initial rapid decrease in the first month (-142 x 10(6) cells/l on average), followed by a slow decline (-17 x 10(6) cells/l on average) The second slope of CD4+ decline was not correlated with the first and only baseline plasma HIV RNA was associated with it. The decline in CD4+ during the first month was steeper in patients with higher CD4+ and weaker plasma HIV RNA baseline levels. Moreover, the decline was less pronounced (P < 10(-4)) in patients with CD4+ nadir above 350 x 10(6) cells/l (-65 x 10(6) cells/l per month) in comparison with those below 350 x 10(6) cells/l (-200 x 10(6) cells/l per month). A high number of dendritic cells (DCs) whatever the type was associated with high CD4+ at the time of treatment interruption and its steeper decline over the first month. Moreover, the myeloid DC level was stable whereas the lymphoid DC count, which tended to decrease in association with decrease in CD4+, was negatively correlated with the HIV RNA load slope. CONCLUSIONS: The results support the use of the CD4+ nadir to predict the CD4+ dynamic after treatment interruption and consideration of the CD4+ count after 1-month of interruption merely reflects the 12-month level of CD4+. Although DCs seem to be associated with the CD4+ dynamic, the benefit of monitoring them has still to be defined

Surveillance passive dans l'Internet

International audienceAfin d'obtenir les informations nécessaires à une bonne gestion des ressources de leur réseau, les opérateurs placent des sondes passives sur les liens de leurs points de présence. Dans cet article, nous donnons des écritures en programmes linéaires mixtes des problèmes de placement de sondes simples ou avec échantillonnage, et donnons une stratégie pour la maintenance de la surveillance partielle de trafics dynamiques dans un point de présence. Ces formulations améliorent les résultats de deux articles récents de la littérature