880 research outputs found
CS, HC3N and CH3CCH multi-line analyses towards starburst galaxies. The evolution of cloud structures in the central regions of galaxies
We aim to study the properties of the dense molecular gas towards the inner
few 100 pc of four nearby starburst galaxies dominated both by photo
dissociation regions (M82) and large-scale shocks (NGC253, IC342 and Maffei2),
and to relate the chemical and physical properties of the molecular clouds with
the evolutionary stage of the nuclear starbursts. We have carried out
multi-transitional observations and analyses of three dense gas molecular
tracers, CS, HC3N and CH3CCH, using Boltzmann diagrams in order to determine
the rotational temperatures and column densities of the dense gas, and using a
Large Velocity Gradients model to calculate the H2 density structure in the
molecular clouds. The CS and HC3N data indicate the presence of density
gradients in the molecular clouds, showing similar excitation conditions, and
suggesting that they arise from the same gas components. In M82, CH3CCH has the
highest fractional abundance determined in a extragalactic source (10^-8). The
density and the chemical gradients found in all galaxies can be explained in
the framework of the starburst evolution. The young shock-dominatedstarburst
galaxies, like presumably Maffei2, show a cloud structure with a rather uniform
density and chemical composition which suggests low star formation activity.
Molecular clouds in galaxies with starburst in an intermediate stage of
evolution, such as NGC253 and IC342, show clouds with a large density contrast
(two orders of magnitude) between the denser regions (cores) and the less dense
regions (halos) of the molecular clouds and relatively constant chemical
abundance. Finally, the galaxy with the most evolved starburst, M82, has clouds
with a rather uniform density structure, large envelopes of atomic/molecular
gas subjected to UV photodissociating radiation from young star clusters, and
very different chemical abundances of HC3N and CH3CCH.Comment: 14 pages + 1 appendix of 2 pages; 7 figures. Accepted for publication
in Astronomy and Astrophysic
The relationship between copyright and contract law
Contracts lie at the heart of the regulatory system governing the creation and dissemination of cultural products in two respects: (1) The exclusive rights provided by copyright law only turn into financial reward, and thus incentives to creators, through a contract with a third party to exploit protected material. (2) From a user perspective purchases of protected material may take the form of a licensing contract, governing behaviour after the initial transaction.
Thus, a review of the relationship between copyright and contract law has to address both supply- and demand-side issues. On the supply side, policy concerns include whether copyright law delivers the often stated aim of securing the financial independence of creators. Particularly acute are the complaints by both creators and producers that they fail to benefit from the exponential increase in the availability of copyright materials on the Internet. On the demand side, the issue of copyright exceptions and their policy justification has become central to a number of reviews and consultations dealing with digital content. Are exceptions based on user needs or market failure? Do exceptions require financial compensation? Can exceptions be contracted out by licence agreements?
This report (i) reviews economic theory of contracts, value chains and transaction costs, (ii) identifies a comprehensive range of regulatory options relating to creator and user contracts, using an international comparative approach, (iii) surveys the empirical evidence on the effects of regulatory intervention, and (iv) where no evidence is available, extrapolates predicted effects from theory
Molecular Gas Properties of the Giant Molecular Cloud Complexes in the Arms and Inter-arms of the Spiral Galaxy NGC 6946
Combining observations of multiple CO lines with radiative transfer modeling
is a very powerful tool to investigate the physical properties of the molecular
gas in galaxies. Using new observations as well as literature data, we provide
the most complete CO ladders ever generated for eight star-forming regions in
the spiral arms and inter-arms of the spiral galaxy NGC 6946, with observations
of the CO(1-0), CO(2-1), CO(3-2), CO(4-3), CO(6-5), 13CO(1-0) and 13CO(2-1)
transitions. For each region, we use the large velocity gradient assumption to
derive beam-averaged molecular gas physical properties, namely the gas kinetic
temperature (T_K), H2 number volume density n(H2) and CO number column density
N(CO). Two complementary approaches are used to compare the observations with
the model predictions: chi-square minimisation and likelihood. The physical
conditions derived vary greatly from one region to the next: T_K=10-250 K,
n(H2)=10^2.3-10^7.0 cm^-3 and N(CO)=10^15.0-10^19.3 cm^-2. The spectral line
energy distribution (SLED) of some of these extranuclear regions indicates a
star-formation activity that is more intense than that at the centre of our own
Milky Way. The molecular gas in regions with a large SLED turnover transition
(J_max>4) is hot but tenuous with a high CO column density, while that in
regions with a low SLED turnover transition (J_max<=4) is cold but dense with a
low CO column density. We finally discuss and find some correlations between
the physical properties of the molecular gas in each region and the presence of
young stellar population indicators (supernova remnants, HII regions, HI holes,
etc.)Comment: 23 pages, 11 figures, MNRAS, Accepte
ISM chemistry in metal rich environments: molecular tracers of metallicity
In this paper we use observations of molecular tracers in metal rich and
alpha-enhanced galaxies to study the effect of abundance changes on molecular
chemistry. We selected a sample of metal rich spiral and star bursting objects
from the literature, and present here new data for a sample of early-type
galaxies (ETGs). We conducted the first survey of CS and methanol emission in
ETGs, detecting 7 objects in CS, and 5 in methanol emission. We find evidence
to support the hypothesis that CS is a better tracer of dense star-forming gas
than HCN. We suggest that the methanol emission in these sources is driven by
dust mantle destruction due to ionisation from high mass star formation, but
cannot rule out shocks dominating in some sources. The derived source averaged
CS/methanol column densities and rotation temperatures are similar to those
found in normal spiral and starburst galaxies, suggesting dense clouds are
little affected by the differences between galaxy types. Finally we used the
total column density ratios for our galaxy samples to show for the first time
that some molecular tracers do seem to show systematic variations that appear
to correlate with metallicity, and that these variations roughly match those
predicted by chemical models. Using this fact, the chemical models of Bayet et
al. (2012b), and assumptions about the optical depth we are able to roughly
predict the metallicity of our spiral and ETG sample, with a scatter of ~0.3
dex. We provide the community with linear approximations to the relationship
between the HCN and CS column density ratio and metallicity. Further study will
clearly be required to determine if this, or any, molecular tracer can be used
to robustly determine gas-phase metallically, but that a relationship exists at
all suggests that in the future it may be possible to calibrate a metallicity
indicator for the molecular interstellar medium (abridged).Comment: 14 pages, 9 figures. MNRAS, accepte
A lambda=3 mm molecular line survey of NGC1068. Chemical signatures of an AGN environment
We aimed to study the molecular composition of the interstellar medium (ISM)
surrounding an Active Galactic Nucleus (AGN), by making an inventory of
molecular species and their abundances, as well as to establish a chemical
differentiation between starburst galaxies and AGN. We used the IRAM-30 m
telescope to observe the central 1.5-2 kpc region of NGC1068, covering the
frequencies between 86.2 GHz and 115.6 GHz. Using Boltzmann diagrams, we
calculated the column densities of the detected molecules. We used a chemical
model to reproduce the abundances found in the AGN, to determine the origin of
each detected species, and to test the influence of UV fields, cosmic rays, and
shocks on the ISM. We identified 24 different molecular species and
isotopologues, among which HC3N, SO, N2H+, CH3CN, NS, 13CN, and HN13C are
detected for the first time in NGC1068. We obtained the upper limits to the
isotopic ratios 12C/13C=49, 16O/18O=177 and 32S/34S=5. Our chemical models
suggest that the chemistry in the nucleus of NGC1068 is strongly influenced by
cosmic rays, although high values of both cosmic rays and far ultraviolet (FUV)
radiation fields also explain well the observations. The gas in the nucleus of
NGC1068 has a different chemical composition as compared to starburst galaxies.
The distinct physical processes dominating galaxy nuclei (e.g. C-shocks, UV
fields, X-rays, cosmic rays) leave clear imprints in the chemistry of the gas,
which allow to characterise the nucleus activity by its molecular abundances.Comment: 16 pages, 6 figures, 7 tables. Accepted for publication in Astronomy
and Astrophysic
Les déterminants de la dynamique entrepreneuriale dans les régions françaises (1994-2003)
Cet article cherche à évaluer les déterminants de la dynamique entrepreneuriale dans les régions françaises pour la période 1993-2004. On estime dans ce but un modèle dynamique de panel par la méthode de Blundell et Bond (1998) pour expliquer le taux de création d'entreprise (rapporté à la population régionale). L'hypothèse d'Holcombe (1998) selon laquelle la création d'entreprise s'explique par elle-même est en premier lieu confirmée. Il apparaît également que le niveau de chômage et le revenu disponible ont un effet positif sur la création régionale d'entreprise. La taille des entreprises jouerait, à l'inverse, négativement comme une barrière à l'entrée. Enfin, l'importance statistique des effets spécifiques individuels amène à penser que les facteurs institutionnels et culturels doivent être mieux pris en considération au niveau régional.dynamique entrepreneuriale, modèle dynamique de panel, régions françaises
Differential responses of the mosquito Aedes albopictus from the Indian Ocean region to two chikungunya isolates
International audienceBACKGROUND: Aedes aegypti and Aedes albopictus are both vectors of chikungunya virus (CHIKV). The two Aedes species co-exist in the Indian Ocean region and were involved in the 2005-2006 CHIKV outbreaks. In the Reunion Island, a single mutation in the viral envelope has been selected that leads to high levels of replication in Ae. albopictus, and a short extrinsic incubation period as the virus could be found in saliva as early as two days after infection. An important question is whether this variant is associated with adverse effects impacting some mosquito life-history traits such as survival and reproduction. RESULTS: We performed experimental infections using three mosquito strains of Ae. aegypti Mayotte and Ae. albopictus (Mayotte and Reunion), and two CHIKV strains (E1-226A and E1-226V). Ae. aegypti Mayotte were similarly susceptible to both viral strains, whereas Ae. albopictus Mayotte and Ae. albopictus Reunion were more susceptible to CHIKV E1-226V than to E1-226A. In terms of life-history traits measured by examining mosquito survival and reproduction, we found that: (1) differences were observed between responses of mosquito species to the two viruses, (2) CHIKV infection only affected significantly some life-history traits of Ae. albopictus Reunion and not of the other two mosquito strains, and (3) CHIKV reduced the lifespan of Ae. albopictus Reunion and shortened the time before egg laying. CONCLUSION: We demonstrated that CHIKV only reduces the survival of Ae. albopictus from the Reunion Island. By laying eggs just before death, reproduction of Ae. albopictus from the Reunion Island is not reduced since other parameters characterizing oviposition and hatching were not affected
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