The Formation and Role of Vortices in Protoplanetary Disks

We carry out a two-dimensional, compressible, simulation of a disk, including dust particles, to study the formation and role of vortices in protoplanetary disks. We find that anticyclonic vortices can form out of an initial random perturbation of the vorticity field. Vortices have a typical decay time of the order of 50 orbital periods (for a viscosity parameter alpha=0.0001 and a disk aspect ratio of H/r = 0.15). If vorticity is continuously generated at a constant rate in the flow (e.g. by convection), then a large vortex can form and be sustained (due to the merger of vortices). We find that dust concentrates in the cores of vortices within a few orbital periods, when the drag parameter is of the order of the orbital frequency. Also, the radial drift of the dust induces a significant increase in the surface density of dust particles in the inner region of the disk. Thus, vortices may represent the preferred location for planetesimal formation in protoplanetary disks. We show that it is very difficult for vortex mergers to sustain a relatively coherent outward flux of angular momentum.Comment: Sumitted to the Astrophysical Journal, October 20, 199

Cooling Flows of Self-Gravitating, Rotating, Viscous Systems

We obtain self-similar solutions that describe the dynamics of a self-gravitating, rotating, viscous system. We use simplifying assumptions; but explicitly include viscosity and the cooling due to the dissipation of energy. By assuming that the turbulent dissipation of energy is as power law of the density and the speed v_{rms} and for a power-law dependence of viscosity on the density, pressure, and rotational velocity, we investigate turbulent cooling flows. It has been shown that for the cylindrically and the spherically cooling flows the similarity indices are the same, and they depend only on the exponents of the dissipation rate and the viscosity model. Depending on the values of the exponents, which the mechanisms of the dissipation and viscosity determine them, we may have solutions with different general physical properties. The conservation of the total mass and the angular momentum of the system strongly depends on the mechanisms of energy dissipation and the viscosity model.Comment: 19 pages, 5 figures, To appear in ApJ (scheduled for the v574, July 20, 2002

Impact of infection status and cyclosporine on voriconazole pharmacokinetics in an experimental model of cerebral scedosporiosis

Cerebral Scedosporium infections usually occur in lung transplant recipients as well as in immunocompetent patients in the context of near-drowning. Voriconazole is the first-line treatment. The diffusion of voriconazole through the blood-brain barriers in the context of cerebral infection and cyclosporine administration is crucial and remains a matter of debate. To address this issue, the pharmacokinetics of voriconazole were assessed in the plasma, cerebrospinal fluid (CSF), and brain, in an experimental model of cerebral scedosporiosis in rats receiving or not cyclosporine. A single dose of voriconazole (30 mg/kg, i.v.) was administrated to six groups of rats randomized according to the infection status and the cyclosporine dosing regimen (no cyclosporine, a single dose or three doses 15 mg/kg each). Voriconazole concentrations in plasma, CSF, and brain samples were quantified using UPLC-MS/MS and HPLC-UV methods and documented up to 48 hours after administration. Pharmacokinetic parameters were estimated using a non-compartmental approach. Voriconazole pharmacokinetic profiles were similar for plasma, CSF, and the brain in all groups studied. Voriconazole Cmax and AUC0=>48h were significantly higher in the plasma than in the CSF (CSF/plasma ratio, median [range] = 0.5 [0.39-0.55] for AUC0=>48h and 0.47 [0.35 and 0.75] for Cmax). Cyclosporine administration was significantly associated with an increase in voriconazole exposure in the plasma, CSF, and brain. In the plasma but not in the brain, an interaction between the infection and cyclosporine administration reduced the positive impact of cyclosporine on voriconazole exposure. Together these results emphasize the impact of cyclosporine on the brain voriconazole exposure

Dynamics of antibiotic resistance genes and presence of putative pathogens during ambient temperature anaerobic digestion.

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Low frequency Raman studies of multi-wall carbon nanotubes: experiments and theory

In this paper, we investigate the low frequency Raman spectra of multi-wall carbon nanotubes (MWNT) prepared by the electric arc method. Low frequency Raman modes are unambiguously identified on purified samples thanks to the small internal diameter of the MWNT. We propose a model to describe these modes. They originate from the radial breathing vibrations of the individual walls coupled through the Van der Waals interaction between adjacent concentric walls. The intensity of the modes is described in the framework of bond polarization theory. Using this model and the structural characteristics of the nanotubes obtained from transmission electron microscopy allows to simulate the experimental low frequency Raman spectra with an excellent agreement. It suggests that Raman spectroscopy can be as useful regarding the characterization of MWNT as it is in the case of single-wall nanotubes.Comment: 4 pages, 2 eps fig., 2 jpeg fig., RevTex, submitted to Phys. Rev.

Hubble Space Telescope Observations of UV Oscillations in WZ Sagittae During the Decline from Outburst

We present a time series analysis of Hubble Space Telescope observations of WZ Sge obtained in 2001 September, October, November and December as WZ Sge declined from its 2001 July superoutburst. Previous analysis of these data showed the temperature of the white dwarf decreased from ~29,000 K to ~18,000 K. In this study we binned the spectra over wavelength to yield ultraviolet light curves at each epoch that were then analyzed for the presence of the well-known 27.87 s and 28.96 s oscillations. We detect the 29 s periodicity at all four epochs, but the 28 s periodicity is absent. The origin of these oscillations has been debated since their discovery in the 1970s and competing hypotheses are based on either white dwarf non-radial g-mode pulsations or magnetically-channelled accretion onto a rotating white dwarf. By analogy with the ZZ Ceti stars, we argue that the non-radial g-mode pulsation model demands a strong dependence of pulse period on the white dwarf's temperature. However, these observations show the 29 s oscillation is independent of the white dwarf's temperature. Thus we reject the white dwarf non-radial g-mode pulsation hypothesis as the sole origin of the oscillations. It remains unclear if magnetically-funnelled accretion onto a rapidly rotating white dwarf (or belt on the white dwarf) is responsible for producing the oscillations. We also report the detection of a QPO with period ~18 s in the September light curve. The amplitudes of the 29 s oscillation and the QPO vary erratically on short timescales and are not correlated with the mean system brightness nor with each other.Comment: 20 pages, 3 figures, 1 table; accepted for publication in Ap

HST FUV spectroscopy of the short orbital period recurrent nova CI Aql: Implications for white dwarf mass evolution

An HST COS Far UV spectrum (1170 A to 1800 A) was obtained for the short orbital period recurrent novae (T Pyxidis subclass), CI Aquilae. CI Aql is the only classical CV known to have two eclipses of sensible depth per orbit cycle and also have pre- and post-outburst light curves that are steady enough to allow estimates of mass and orbital period changes. Our FUV spectral analysis with model accretion disks and NLTE high gravity photospheres, together with the Gaia parallax, reveal CI Aql's FUV light is dominated by an optically thick accretion disk with an accretion rate of the order of $4\times 10^{-8}$ $M_{\odot}/yr$. Its database of light curves, radial velocity curves, and eclipse timings is among the best for any CV. Its orbit period ($P$), $dP/dt$, and reference time are re-derived via simultaneous analysis of the three data types, giving a dimensionless post-outburst $dP/dt$ of $-2.49\pm 0.95\times 10^{-10}$. Lack of information on loss of orbital to rotational angular momentum leads to some uncertainty in the translation of $dP/dt$ to white dwarf mass change rate, $dM_1/dt$, but within the modest range of $+4.8\times 10^{-8}$ to $+7.8\times 10^{-8}$ $M_{\odot} /yr$. The estimated white dwarf mass change through outburst for CI Aql, based on simple differencing of its pre- and post outburst orbit period, is unchanged from the previously published $+5.3 \times 10^{-6} M_{\odot}$. At the WD's estimated mass increase rate, it will terminate as a Type Ia supernova within 10 million years

White Dwarf Heating and Subsequent Cooling in Dwarf Nova Outbursts

We follow the time dependent thermal evolution of a white dwarf (WD) undergoing sudden accretion in a dwarf nova outburst, using both simulations and analytic estimates. The post-outburst lightcurve clearly separates into early times when the WD flux is high, and late times when the flux is near the quiescent level. The break between these two regimes, occurring at a time of order the outburst duration, corresponds to a thermal diffusion wave reaching the base of the freshly accreted layer. Our principal result is that long after the outburst, the fractional flux perturbation about the quiescent flux decays as a power law with time (and {\it not} as an exponential). We use this result to construct a simple fitting formula that yields estimates for both the quiescent flux and the accreted column, i.e. the total accreted mass divided by WD surface area. The WD mass is not well constrained by the late time lightcurve alone, but it can be inferred if the accreted mass is known from observations. We compare our work with the well-studied outburst of WZ Sge, finding that the cooling is well described by our model, giving an effective temperature $T_{\rm eff}=14,500 {\rm K}$ and accreted column $\Delta y\approx10^6 {\rm g cm^{-2}}$, in agreement with the modeling of Godon et al. To reconcile this accreted column with the accreted mass inferred from the bolometric accretion luminosity, a large WD mass $\gtrsim1.1M_\odot$ is needed. Our power law result is a valuable tool for making quick estimates of the outburst properties. We show that fitting the late time lightcurve with this formula yields a predicted column within 20% of that estimated from our full numerical calculations.Comment: Accepted for publication in The Astrophysical Journal, 10 pages, 8 figure

Differential climatic conditions drive growth of Acacia tortilis tree in its range edges in Africa and Asia

DATA AVAILABILITY STATEMENT : The full data are available on Figshare at https://doi.org/10.6084/m9.figshare.21779819.SUPPORTING INFORMATION : APPENDIX S1. Supplementary tables. APPENDIX S2. Supplementary figures.PREMISE : Tree growth is a fundamental biological process that is essential to ecosystem functioning and water and element cycling. Climate exerts a major impact on tree growth, with tree species often requiring a unique set of conditions to initiate and maintain growth throughout the growing season. Still, little is known about the specific climatic factors that enable tree growth in savannah and desert tree species. Among the global tree species, Acacia tortilis occupies one of the largest distribution ranges (crossing 6500 km and 54 latitudes), spanning large parts of Africa and into the Middle East and Asia. METHODS : Here we collected climate data and monitored Acacia tortilis tree growth (continuous measurements of stem circumference) in its southern and northern range edges in South Africa (SA) and Israel (IL), respectively, to elucidate whether the growth–climate interactions were similar in both edges. RESULTS : Growth occurred during the summer (between December and March) in SA and in IL during early summer and autumn (April–June and October–November, respectively). Surprisingly, annual growth was 40% higher in IL than in SA. Within the wide distribution range of Acacia tortilis, our statistical model showed that climatic drivers of tree growth differed between the two sites. CPNCLUSIONS : High temperatures facilitated growth at the hot and arid IL site, while high humidity permitted growth at the more humid SA site. Our results confer an additional understanding of tree growth adaptation to extreme conditions in Acacia's world range edges, a major point of interest with ongoing climate change.http://wileyonlinelibrary.com/journal/AJBZoology and Entomolog