198 research outputs found
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 âC, 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 mĂ©tasurface acoustique orientables en rĂ©flexion, effective sur une large bande de frĂ©quences, Ă lâaide de cellules actives. La mĂ©tasurface est composĂ©e dâun rĂ©seau de haut-parleurs petits devant la longueur dâonde, dont lâimpĂ©dance acoustique peut ĂȘtre programmĂ©e par contrĂŽle actif afin dâajuster la phase du coefficient de rĂ©flexion en tout point de la mĂ©tasurface. La stratĂ©gie de contrĂŽle sâinspire des RĂ©sonateurs Electroacoustiques Actifs, utilisant un asservissement en courant du transducteur basĂ© sur une captation microphonique devant sa membrane, permettant dâobtenir une large gamme dâimpĂ©dances acoustiques sur un mĂȘme haut-parleur. Ce papier prĂ©sente la mĂ©thodologie de dimensionnement des RĂ©sonateurs Electroacoustiques permettant dâobtenir un angle de rĂ©flexion prĂ©dĂ©fini pour une incidence donnĂ©e, et des validations numĂ©riques et expĂ©rimentales permettent de vĂ©rifier les performances du concept. Lâaspect large-bande du contrĂŽle sera en particulier discutĂ©
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 problÚmes 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
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