7,149 research outputs found
Thermodynamics of the dead-zone inner edge in protoplanetary disks
In protoplanetary disks, the inner boundary between the turbulent and laminar
regions could be a promising site for planet formation, thanks to the trapping
of solids at the boundary itself or in vortices generated by the Rossby wave
instability. At the interface, the disk thermodynamics and the turbulent
dynamics are entwined because of the importance of turbulent dissipation and
thermal ionization. Numerical models of the boundary, however, have neglected
the thermodynamics, and thus miss a part of the physics. The aim of this paper
is to numerically investigate the interplay between thermodynamics and dynamics
in the inner regions of protoplanetary disks by properly accounting for
turbulent heating and the dependence of the resistivity on the local
temperature. Using the Godunov code RAMSES, we performed a series of 3D global
numerical simulations of protoplanetary disks in the cylindrical limit,
including turbulent heating and a simple prescription for radiative cooling. We
find that waves excited by the turbulence significantly heat the dead zone, and
we subsequently provide a simple theoretical framework for estimating the wave
heating and consequent temperature profile. In addition, our simulations reveal
that the dead-zone inner edge can propagate outward into the dead zone, before
staling at a critical radius that can be estimated from a mean-field model. The
engine driving the propagation is in fact density wave heating close to the
interface. A pressure maximum appears at the interface in all simulations, and
we note the emergence of the Rossby wave instability in simulations with
extended azimuth. Our simulations illustrate the complex interplay between
thermodynamics and turbulent dynamics in the inner regions of protoplanetary
disks. They also reveal how important activity at the dead-zone interface can
be for the dead-zone thermodynamic structure.Comment: 16 pages, 16 figures. Accepted in Astronomy and Astrophysic
Quasi-classical rate coefficient calculations for the rotational (de)excitation of H2O by H2
The interpretation of water line emission from existing observations and
future HIFI/Herschel data requires a detailed knowledge of collisional rate
coefficients. Among all relevant collisional mechanisms, the rotational
(de)excitation of H2O by H2 molecules is the process of most interest in
interstellar space. To determine rate coefficients for rotational de-excitation
among the lowest 45 para and 45 ortho rotational levels of H2O colliding with
both para and ortho-H2 in the temperature range 20-2000 K. Rate coefficients
are calculated on a recent high-accuracy H2O-H2 potential energy surface using
quasi-classical trajectory calculations. Trajectories are sampled by a
canonical Monte-Carlo procedure. H2 molecules are assumed to be rotationally
thermalized at the kinetic temperature. By comparison with quantum calculations
available for low lying levels, classical rates are found to be accurate within
a factor of 1-3 for the dominant transitions, that is those with rates larger
than a few 10^{-12}cm^{3}s^{-1}. Large velocity gradient modelling shows that
the new rates have a significant impact on emission line fluxes and that they
should be adopted in any detailed population model of water in warm and hot
environments.Comment: 8 pages, 2 figures, 1 table (the online material (4 tables) can be
obtained upon request to [email protected]
Electron-impact rotational and hyperfine excitation of HCN, HNC, DCN and DNC
Rotational excitation of isotopologues of HCN and HNC by thermal
electron-impact is studied using the molecular {\bf R}-matrix method combined
with the adiabatic-nuclei-rotation (ANR) approximation. Rate coefficients are
obtained for electron temperatures in the range 56000 K and for transitions
among all levels up to J=8. Hyperfine rates are also derived using the
infinite-order-sudden (IOS) scaling method. It is shown that the dominant
rotational transitions are dipole allowed, that is those for which . The hyperfine propensity rule is found to be stronger
than in the case of HeHCN collisions. For dipole allowed transitions,
electron-impact rates are shown to exceed those for excitation of HCN by He
atoms by 6 orders of magnitude. As a result, the present rates should be
included in any detailed population model of isotopologues of HCN and HNC in
sources where the electron fraction is larger than 10, for example in
interstellar shocks and comets.Comment: 12 pages, 4 figures, accepted in MNRAS (2007 september 3
Entropy of complex relevant components of Boolean networks
Boolean network models of strongly connected modules are capable of capturing
the high regulatory complexity of many biological gene regulatory circuits. We
study numerically the previously introduced basin entropy, a parameter for the
dynamical uncertainty or information storage capacity of a network as well as
the average transient time in random relevant components as a function of their
connectivity. We also demonstrate that basin entropy can be estimated from
time-series data and is therefore also applicable to non-deterministic networks
models.Comment: 8 pages, 6 figure
Les effets de l’âge et du sexe des candidats en question : une étude des biais évaluatifs et du discours de la discrimination en situation de recrutement.
International audienc
Composition pour retarder l'initiation tumorale de cellules cancereuses chez un mammifère à risque
La présente invention concerne une composition préventive antitumorale comprenant une quantité pharmaceutiquement efficace d\u27au moins un antagoniste du récepteur AT2 de l\u27angiotensine II pour son application comme médicament afin de prévenir le développement de cancers chez un mammifère à risque. La présente invention concerne également un procédé de prévention du développement de cancer chez un mammifère à risque, ainsi qu\u27un kit de prévention du développement de cancers
Effects of organochlorine pesticides on endothelial cell adhesion, proliferation, nitric oxide and superoxide anion productions
National audienc
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