6,045 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
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
Effects of organochlorine pesticides on endothelial cell adhesion, proliferation, nitric oxide and superoxide anion productions
National audienc
The Normal College News, March 23, 1911
Contains fulltext :
224795.pdf (Publisher’s version ) (Closed access)In deze bijdrage betogen de auteurs dat het contractuele aansprakelijkheidsrecht slechts zeer beperkte mogelijkheden biedt voor een afnemer van producten en diensten die een cybersecuritycomponent bevatten om schade door digitale onveiligheid in een business to businessrelatie op de leverancier te verhalen. Een combinatie van juridische barrières (vage zorgplichten, exoneratieclausules, moeilijk kwantificeerbare schade, complicaties bij het vaststellen van causaliteit, en bewijsproblemen door informatieasymmetrie) en economische barrières (verschillen in onderhandelingsmacht, hoge kosten en risico’s bij procederen, en mogelijk faillissement van de schadeveroorzaker) zorgt er juist op het terrein van digitale onveiligheid voor dat een aansprakelijkheidszaak meestal niet loont. De auteurs doen aanbevelingen om het geschetste probleem aan te pakken.7 p
Paradoxical effects of the topoisomerase inhibitor, ethoxidine, in the cellular processes leading to angiogenesis on EaHy.926 endothelial cells
Topoisomerase I generates transient single-stranded breaks in DNA and have the capacity to fragment the genome. Thus, this enzyme is the target for some of the most successful anticancer drugs. Ethoxidine, a benzo[c]phenanthridines derivative, was identified as a potent inhibitor of topoisomerase I. As angiogenesis is a critical step in tumorigenesis, this study was designed to test the potential effect of ethoxidine on different processes leading to neovascularisation on EaHy endothelial cells including adhesion, migration and proliferation. Ethoxidine was tested at two concentrations, 100 μM and 10 μM . VEGF (20 ng/mL) was used as control. Adherent cells were evaluated using crystal violet staining, migration using a model of wound healing. Proliferation was analyzed using CyQUANT Cell Proliferation Assay Kit. Both O2- and NO productions were assessed using electronic paramagnetic resonance technique. All the effects of ethoxidine were evaluated at 24 h treatment. Low concentration of ethoxidine promoted migration to the same extent as that produced by VEGF whereas high concentration inhibited this process. Ethoxidine significantly enhanced adhesion at similar level than VEGF at low concentration. It was without effect at high concentration. Although ethoxidine had no effect at low concentration, it significantly reduced cell proliferation at high concentration. At any concentration tested, ethoxidine did not modify basal O2- production. Interestingly, ethoxidine significantly increase NO production at low concentration but it was without effect at high concentration. As control experiment, VEGF enhanced Eahy cells NO production under the same experimental conditions. Altogether, the present study highlights paradoxical effects of ethoxidine depending on the concentration used. At low concentration, it promotes both Eahy cells migration and adhesion without any effect on proliferation. Importantly, these effects were associated with an increase of NO production. In contrast at high concentration, ethoxidine reduced Eahy cells migration and proliferation but had no effect neither on adhesion nor NO release. Of note is the fact that ethoxidine did not alter endothelial cells oxidative stress at any concentration tested. Thus, these data underscore the potential anti-tumoral property of ethoxidine at high concentration and endothelial cells in the present study. The property of ethoxidine in inhibiting proliferation in both cell type probably account for its high antitumor activity
South America: a reservoir of continental carbon - first estimate of changes since 18,000 yr BP
By using geographic and palaeogeographic sketches established for the present situation (before recent deforestation) and for the glacial maximum (about 15,000-18,000 BP) we can estimate the possible total biomass (phytomass) of the South American continent. According to the biomass density used in this first estimate for ten major ecosystems, the results show a possible increase from 140 Gt of carbon (glacial maximum) to 214 Gt C (preindustrial) for the phytomass, and 120 to 180 Gt C for the soils. These preliminary results are possibly only a 60 or 70 percent approximate estimate and could be modified with computation using other palaeogeographic models or another biomass density. It is therefore to underline the urgent need of more field biomass measurements, ecosystems mappings, and palaeostudies to evaluate the part of South America as a future possible sink for the atmospheric carbon dioxide. The Amazonian forest makes of South America an important continental reservoir of carbon for the planet Earth. This continent represents consequently a key zone for the research and knowledge of changes in the biogeochemical cycle of carbon. In order to evaluate more precisely the role it plays we estimated the approximate quantities of carbon in the total phytomass and the carbon in soils for each of the ecosystems represented in Figure 1, both for Present and Last Glacial Maximum landscapes
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