A multi-flow model for microquasars

We present a new picture for the central regions of Black Hole X-ray Binaries. In our view, these central regions have a multi-flow configuration which consists in (1) an outer standard accretion disc down to a transition radius r_J, (2) an inner magnetized accretion disc below r_J driving (3) a non relativistic self-collimated electron-proton jet surrounding, when adequate conditions for pair creation are met, (4) a ultra relativistic electron-positron beam. This accretion-ejection paradigm provides a simple explanation to the canonical spectral states, from radio to X/gamma-rays, by varying the transition radius r_J and disc accretion rate independently. Large values of r_J and low accretion rate correspond to Quiescent and Hard states. These states are characterized by the presence of a steady electron-proton MHD jet emitted by the disc below r_J. The hard X-ray component is expect to form at the jet basis. When r_J becomes smaller than the marginally stable orbit r_i, the whole disc resembles a standard accretion disc with no jet, characteristic of the Soft state. Intermediate states correspond to situations where r_J ~ r_i. At large accretion rate, an unsteady pair cascade process is triggered within the jet axis, giving birth to flares and ejection of relativistic pair blobs. This would correspond to the luminous intermediate state, with its associated superluminal motions.Comment: 12 pages, 3 figures. Proceedings of ``High Energies in the Highlands'', Fort-William, 27 June-1 July 200

Sensitivity distribution of Venturia inaequalis to fenarimol in Québec apple orchards

Cette étude a été faite dans le but d'établir le seuil de sensibilité du Venturia inaequalis au fenarimol, un inhibiteur de la biosynthèse de l'ergostérol. Au cours de la saison 1988, des isolats du V. inaequalis ont été prélevés dans 26 vergers commerciaux du Québec pour un total de 576 isolats monoconidiens. La sensibilité au fenarimol a été établie par des tests d'inhibition de la croissance radiale du mycélium. Les valeurs de ED50 obtenues pour les 26 vergers ont varié de 0,024 à 5,212 μg mL-1 pour une moyenne de 0,156 μ g mL-1. Une réduction de sensibilité, exprimée en valeur de ED50, a été observée dans trois vergers, soit pour 4,51% des isolats testés. Les isolats sensibles avaient un ED50 moyen de 0,079 μg mL-1, et les isolats de sensibilité réduite démontraient un ED50 de 1,714 (μg mL-1, ce qui représente un facteur de résistance de 22. Quatre populations ont été identifiées en fonction de la distribution de fréquence des valeurs de ED50.This study was initiated to quantify the baseline sensitivity of apple scab (Venturia inaequalis) to fenarimol, an ergosterol synthesis-inhibiting fungicide. In 1988, 576 monoconidial isolates of Venturia inaequalis were collected from 26 commercial orchards throughout Quebec. Sensitivity to fenarimol was assessed by radial growth inhibition assay. The ED50 values for the 26 orchards ranged from 0.024 to 5.212 (μ g mL-1 with a mean ED50 of 0.156 μg ml-1. Reduced sensitivity, expressed as ED50, was found in three orchards for an overall frequency of 4.51% of isolates. Sensitive isolates had a mean ED50 of 0.079 μg ml-1, whereas isolates with reduced sensitivity had a mean ED50 of 1.714 μ g mL-1, yielding a resistance factor of about 22. Four populations were identified based on the frequency distribution of ED50 values

A closed form for the electrostatic interaction between two rod-like charged objects

We have calculated the electrostatic interaction between two rod-like charged objects with arbitrary orientations in three dimensions. we obtained a closed form formula expressing the interaction energy in terms of the separation distance between the centers of the two rod-like objects, $r$, their lengths (denoted by $2l_1$ and $2l_2$), and their relative orientations (indicated by $\theta$ and $\phi$). When the objects have the same length ($2l_1=2l_2=l$), for particular values of separations, i.e for $r\leq0.8 l$, two types of minimum are appeared in the interaction energy with respect to $\theta$. By employing the closed form formula and introducing a scaled temperature $t$, we have also studied the thermodynamic properties of a one dimensional system of rod-like charged objects. For different separation distances, the dependence of the specific heat of the system to the scaled temperature has been studied. It is found that for $r<0.8 l$, the specific heat has a maximum.Comment: 10 pages, 9 figures, 1 table, Accepted by J. Phys.: Condens. Matte

Transport of Cosmic Rays in Chaotic Magnetic Fields

The transport of charged particles in disorganised magnetic fields is an important issue which concerns the propagation of cosmic rays of all energies in a variety of astrophysical environments, such as the interplanetary, interstellar and even extra-galactic media, as well as the efficiency of Fermi acceleration processes. We have performed detailed numerical experiments using Monte-Carlo simulations of particle propagation in stochastic magnetic fields in order to measure the parallel and transverse spatial diffusion coefficients and the pitch angle scattering time as a function of rigidity and strength of the turbulent magnetic component. We confirm the extrapolation to high turbulence levels of the scaling predicted by the quasi-linear approximation for the scattering frequency and parallel diffusion coefficient at low rigidity. We show that the widely used Bohm diffusion coefficient does not provide a satisfactory approximation to diffusion even in the extreme case where the mean field vanishes. We find that diffusion also takes place for particles with Larmor radii larger than the coherence length of the turbulence. We argue that transverse diffusion is much more effective than predicted by the quasi-linear approximation, and appears compatible with chaotic magnetic diffusion of the field lines. We provide numerical estimates of the Kolmogorov length and magnetic line diffusion coefficient as a function of the level of turbulence. Finally we comment on applications of our results to astrophysical turbulence and the acceleration of high energy cosmic rays in supernovae remnants, in super-bubbles, and in jets and hot spots of powerful radio-galaxies.Comment: To be published in Physical Review D, 20 pages 9 figure

Pair Creation at Shocks: Application to the High Energy Emission of Compact objects

We investigate the effect of pair creation on a shock structure. Actually, particles accelerated by a shock can be sufficiently energetic to boost, via Inverse Compton (IC) process for example, surrounding soft photons above the rest mass electron energy and thus to trigger the pair creation process. The increase of the associated pair pressure is thus able to disrupt the plasma flow and possibly, for too high pressure, to smooth it completely. Reversely, significant changes of the flow velocity profile may modify the distribution function of the accelerated particles, modifying consequently the pair creation rate. Stationary states are then obtained by solving self-consistently for the particle distribution function and the flow velocity profile. We discuss our results and the application of these processes to the high energy emission and variability of compact objects.Comment: 14 pages, 7 figures (uses newpasp.sty included). To appear in Proc. of "X-ray astronomy 2000",(Palermo Sep. 2000), Eds. R. Giacconi, L. Stella, S. Serio, ASP Conf. Series, in pres

Characterization of neutrophils and macrophages from ex vivo cultured murine bone marrow for morphologic maturation and functional responses by imaging flow cytometry

Neutrophils and macrophages differentiate from common myeloid progenitors in the bone marrow, where they undergo unique nuclear morphologic changes as they mature into fully functional phagocytes. These changes include condensation of chromatin, the most pronounced exhibited by mature neutrophils. Both myeloid cells acquire multiple functions critical to their ability to kill pathogens, including phagocytosis, the production of proteolytic enzymes and reactive oxygen species (ROS), and in the case of neutrophils, release of nuclear material known as nuclear extracellular traps (NETs). Studies on these functions often rely on the use of cells acquired from mature mouse tissues, but these tend to produce limited numbers of cells. Strategies to analyze the morphologic features and functional responses of these cells include the use of conventional brightfield or fluorescence microscopy to examine changes in nuclear structure, internalization of fluorescein-labeled bacterial or yeast particles, or release of nuclear material. Flow cytometry also is often used, especially for identifying changes in the expression of lineage-specific cell surface markers and ROS production. However, each of these techniques presents certain limitations. Here we describe methods to generate abundant populations highly enriched for neutrophils or macrophages from previously frozen, ex vivo cultured mouse bone marrow. We then apply state-of-the-art imaging flow cytometry, which combines the resolution of microscopy with the speed of flow cytometry, to analyze each lineage for changes in nuclear structure and expression of key cell surface markers. Different gating and masking strategies are applied to characterize phagocytosis of pH-dependent fluorescein-labeled E. coli, ROS production, and NET release by neutrophils. We also demonstrate that neutrophils engulfing E. coli bioparticles produce NETs in a process we term PhagoNETosis. Together these assays reveal the power of imaging flow cytometry for simultaneously assessing the maturation features and functional responses of these critical mediators of innate immunity

Applying Magnetized Accretion-Ejection Models to Microquasars: a preliminary step

We present in this proceeding some aspects of a model that should explain the spectral state changes observed in microquasars. In this model, ejection is assumed to take place only in the innermost disc region where a large scale magnetic field is anchored. Then, in opposite to conventional ADAF models, the accretion energy can be efficiently converted in ejection and not advected inside the horizon. We propose that changes of the disc physical state (e.g. transition from optically thick to optically thin states) can strongly modify the magnetic accretion-ejection structure resulting in the spectral variability. After a short description of our scenario, we give some details concerning the dynamically self-consistent magnetized accretion-ejection model used in our computation. We also present some preliminary results of spectral energy distribution.Comment: Proceeding of the fith Microquasar Workshop, June 7 - 13, 2004, Beijing, China. Accepted for publication in the Chinese Journal of Astronomy and Astrophysic

A unified accretion-ejection paradigm for Black Hole X-ray Binaries

We present a new picture for the central regions of Black Hole X-ray Binaries. In our view, these central regions have a multi-flow configuration which consists in (1) an outer standard accretion disc down to a transition radius r_J, (2) an inner magnetized accretion disc below r_J driving (3) a non relativistic self-collimated electron-proton jet surrounding, when adequate conditions for pair creation are met, (4) a ultra relativistic electron-positron beam. This accretion-ejection paradigm provides a simple explanation to the canonical spectral states by varying the transition radius r_J and disc accretion rate independently. Large values of r_J correspond to the Quiescent state for low $\dot m$ and the Hard state for larger $\dot m$. These states are characterized by the presence of a steady electron-proton MHD jet emitted by the disc below r_J. The hard X-ray component is expected to form at the jet basis. When r_j becomes smaller than the marginally stable orbit r_i, the whole disc resembles a standard accretion disc, characteristic of the Soft state. Intermediate states correspond to situations where r_J ~ r_i. At large $\dot m$, an unsteady pair cascade process is triggered within the jet axis, giving birth to ejection of relativistic pair blobs. This would correspond to the luminous intermediate state, with its associated superluminal motions. The variation of r_J independently of $\dot m$ is a necessary ingredient in this picture, arising from the presence of a large scale vertical magnetic field threading the disc.Comment: 15 pages, 2 figures. Accepted by A&A main journa