Stability and nonlinear adjustment of vortices in Keplerian flows

We investigate the stability, nonlinear development and equilibrium structure of vortices in a background shearing Keplerian flow. We make use of high-resolution global two-dimensional compressible hydrodynamic simulations. We introduce the concept of nonlinear adjustment to describe the transition of unbalanced vortical fields to a long-lived configuration. We discuss the conditions under which vortical perturbations evolve into long-lived persistent structures and we describe the properties of these equilibrium vortices. The properties of equilibrium vortices appear to be independent from the initial conditions and depend only on the local disk parameters. In particular we find that the ratio of the vortex size to the local disk scale height increases with the decrease of the sound speed, reaching values well above the unity. The process of spiral density wave generation by the vortex, discussed in our previous work, appear to maintain its efficiency also at nonlinear amplitudes and we observe the formation of spiral shocks attached to the vortex. The shocks may have important consequences on the long term vortex evolution and possibly on the global disk dynamics. Our study strengthens the arguments in favor of anticyclonic vortices as the candidates for the promotion of planetary formation. Hydrodynamic shocks that are an intrinsic property of persistent vortices in compressible Keplerian flows are an important contributor to the overall balance. These shocks support vortices against viscous dissipation by generating local potential vorticity and should be responsible for the eventual fate of the persistent anticyclonic vortices. Numerical codes have be able to resolve shock waves to describe the vortex dynamics correctly.Comment: 12 pages, 10 figure

FUSE Observations of the Dwarf Novae UU Aql, BV Cen, and CH UMa in Quiescence

We report on FUSE spectra of three U Gem-type, long period, dwarf novae, UU Aql, BV Cen and CH UMa taken during their quiescence intervals. We discuss the line identifications in their spectra and attempt to characterize the source(s) of their FUV flux distribution. Archival IUE spectrum of CH UMa and BV Cen in quiescence were identified as having a matching flux level with the FUSE spectra and these were combined with each FUSE spectrum to broaden the wavelength coverage and further constrain model fits. Multi-component synthetic spectral fits from our model grids, consisting of single temperature white dwarfs, two-temperature white dwarfs, accretion disks and white dwarfs plus accretion disks, were applied to the FUSE spectra alone and to the combined FUSE + IUE spectra. We present the results of our model analyses and their implications.Comment: accepted in AJ, 26 pages, 6 tables, 8 figures (5 color, 3 b/w

Far Ultraviolet Spectroscopic Explorer Spectroscopy of the Nova-like BB Doradus

We present an analysis of the Far Ultraviolet Spectroscopic Explorer ({\it{FUSE}}) spectra of the little-known southern nova-like BB Doradus. The spectrum was obtained as part of our Cycle 8 {\it FUSE} survey of high declination nova-like stars. The FUSE spectrum of BB Dor, observed in a high state, is modeled with an accretion disk with a very low inclination (possibly lower than 10deg). Assuming an average WD mass of 0.8 solar leads to a mass accretion rate of 1.E-9 Solar mass/year and a distance of the order of 650 pc, consistent with the extremely low galactic reddening in its direction. The spectrum presents some broad and deep silicon and sulfur absorption lines, indicating that these elements are over-abundant by 3 and 20 times solar, respectively

Scedosporium apiospermum complex Catalase A1 and Cu-Zn SOD recombinant proteins are useful tools for serodiagnosis of Scedosporium infection

International audienc

Production de protéines recombinantes de Scedosporium apiospermum, Cu,Zn superoxide dismutase et catalase, pour l’amélioration et la standardisation du sérodiagnostic des infections à Scedosporium apiospermum chez les patients atteints de mucoviscidose

National audienc

Pharmacokinetics of voriconazole and posaconazole administered in experimental models of disseminated scedosporiosis with cerebral involvement

International audienc

Platelet inhibition by low-dose aspirin but not by clopidogrel reduces the axon-reflex current-induced vasodilation in humans

We previously showed a prolonged inhibition of current-induced vasodilation (CIV) after a single oral high dose of aspirin. In this study, we tested the hypothesis of platelet involvement in CIV. Nine healthy volunteers took 75 mg aspirin/day, 98 mg of clopidogrel bisulfate/day, or placebo for 4 days. CIV was induced by two consecutive 1-min anodal current applications (0.08 mA/cm2) through deionized water with a 10-min interval. CIV was measured with laser Doppler flowmetry and expressed as a percentage of baseline cutaneous vascular conductance: %Cb. In a second experiment in 10 volunteers, aspirin and placebo were given as in experiment 1, but a 26-h delay from the last aspirin intake elapsed before ACh iontophoresis and postocclusive hyperemia were studied in parallel to CIV. In experiment 1, the means ± SE amplitude of CIV was 822 ± 314, 313 ± 144, and 746 ± 397%Cb with placebo, aspirin (P < 0.05 from placebo and clopidogrel), and clopidogrel (NS from placebo), respectively. In experiment 2, CIV impairment with aspirin was confirmed: CIV amplitudes were 300 ± 99, and 916 ± 528%Cb under aspirin and placebo, respectively (P < 0.05), whereas vasodilation to ACh iontophoresis (322 ± 74 and 365 ± 104%Cb) and peak postocclusive hyperemia (491 ± 137 and 661 ± 248%Cb) were not different between aspirin and placebo, respectively. Low-dose aspirin, even 26 h after oral administration, impairs CIV, while ACh-mediated vasodilation and postocclusive hyperemia are preserved. If platelets are involved in the neurovascular mechanism triggered by galvanic current application in humans, it is likely to occur through the cyclooxygenase but not the ADP pathway. a significant increase in skin blood flow (SkBF) has been observed in response to non-noxious galvanic current application in humans. This current-induced vasodilation (CIV) has been described as the result of an axon reflex (3) and disappears in locally anesthetized or chronically capsaicin-treated skin. Then CIV depends on capsaicin-sensitive fibers and is an interesting model of the neurovascular interaction following non-noxious stimulation (11, 16). Prostaglandins are synthesized by cyclooxygenases (COX) and play a key role as mediators in the vascular response observed during CIV. COX are expressed in a large variety of human tissues, including endothelium, smooth muscles, nerves, and platelets (29). We recently reported a long-lasting inhibition of CIV (>5 days) following a single high (1,000 mg) oral dose of aspirin (11, 12, 40), which irreversibly blocks both isoforms of COX (COX-1 and COX-2). COX of neuronal origin does not seem responsible for this long-lasting effect (13). This long-lasting inhibition of CIV is consistent with the time required to resynthesize unblocked platelets after oral single-dose aspirin leading to the hypothesis that platelets participate in the vascular response to CIV. Indeed, a single oral high dose of aspirin irreversibly inactivates the platelet COX pathway for the duration of the life of the platelets (∼10 days) (1, 36). Indomethacin, a nonspecific COX inhibitor devoid of effect on vanilloid receptors and acid-sensing ion channels (41), abolished CIV, confirming that the inhibition of CIV by aspirin likely resulted from its effect on COX (and not on vanilloid receptors or on acid-sensing ion channels). Furthermore, the specific COX-2 inhibitor, celecoxib, failed to affect CIV, suggesting that CIV is mainly a COX-1-dependent phenomenon (39). Together, with the long-lasting effect of a single oral high dose of aspirin, the fact that COX-1 isoform participates in CIV raises the question of a possible platelet involvement in the axon-reflex CIV. Although there is, to date, no in vivo proof of a direct platelet-mediated vasodilation in humans, the hypothesis of a platelet involvement in axon-reflex vasodilation and other vasodilator mechanisms has previously been explored in vitro (15, 23, 31). Those authors provided evidence for a direct in vitro platelet-mediated endothelium-dependent vasodilation in preconstricted arteries but mainly by the ADP pathway. To investigate whether the platelet COX and ADP pathways are involved in vivo in CIV, we inhibited platelet function by aspirin (a platelet COX inhibitor) or clopidogrel (a platelet ADP-receptor inhibitor). Our hypothesis was that if platelets are involved, both clopidogrel and low-dose aspirin would impair the current-induced vasodilation

Biofilm colonizing the Nam Theun 2 power plant Penstock (Lao PDR) - mechanism and potential evolution

Biofilms are the most common bacterial life mode on Earth. These tri-dimension bacterial structures occur at a substratum-liquid interface. Due to their intrinsic properties(niche for pathogens, resistance to biocide treatments, etc.), they cause major problems in various industries. In water systems, the physical and chemical characteristics of biofilms (viscoelastic behavior, roughness) may lead to the lowering of flow velocity. A rough biofilm has developed in the Penstock of the Nam Theun 2 hydropower plant (Khammouane Province, Lao PDR). This biofilm is thought to lead to additional head losses and to slightly affect the power production. The mineral, chemical and microbiological compositions of the biofilm were investigated in order to propose solutions to reduce its effect. Samples were taken during two water drainages in 2011 and 2012. In order to complete the knowledge from the water quality monitoring, major elements, trace elements and rare earth element (REE) contents in samples were measured using ICP-AES and ICP-MS. Crystalline phases were identified and quantified by X-ray diffraction (XRD). The microbial composition of the biofilm was first assessed by culture (2011) and then monitored according to the location and the time after water drainage by molecular biology methods (2012). Results show that the chemical composition of the biofilm is dominated by ferric iron Fe3+ and its mineralogy is mostly constituted of lepidocrocite and magnesioferrite. The bacterial population was dominated by beta-Proteobacteria but population profiles varied strongly according to the layer of the biofilm, the nature of the substratum and the time during which the biofilm was subjected to the conditions of the water drainage. These observations are concordant with the modification of the biofilm properties and the reduction in head losses when returning to functioning regimes in the Penstoc

Simulations of dust-trapping vortices in protoplanetary discs

Local three-dimensional shearing box simulations of the compressible coupled dust-gas equations are used in the fluid approximation to study the evolution of different initial vortex configurations in a protoplanetary disc and their dust-trapping capabilities. The initial conditions for the gas are derived from an analytic solution to the compressible Euler equation and the continuity equation. The solution is valid if there is a vacuum outside the vortex. In the simulations the vortex is either embedded in a hot corona, or it is extended in a cylindrical fashion in the vertical direction. Both configurations are found to survive for at least one orbit and lead to accumulation of dust inside the vortex. This confirms earlier findings that dust accumulates in anticyclonic vortices, indicating that this is a viable mechanism for planetesimal formation.Comment: 15 pages, 13 figures, accepted for publication in A&