10,364 research outputs found
Collisional excitation of HC3N by para- and ortho-H2
New calculations for rotational excitation of cyanoacetylene by collisions
with hydrogen molecules are performed to include the lowest 38 rotational
levels of HC3N and kinetic temperatures to 300 K. Calculations are based on the
interaction potential of Wernli et al. A&A, 464, 1147 (2007) whose accuracy is
checked against spectroscopic measurements of the HC3N-H2 complex. The quantum
coupled-channel approach is employed and complemented by quasi-classical
trajectory calculations. Rate coefficients for ortho-H2 are provided for the
first time. Hyperfine resolved rate coefficients are also deduced. Collisional
propensity rules are discussed and comparisons between quantum and classical
rate coefficients are presented. This collisional data should prove useful in
interpreting HC3N observations in the cold and warm ISM, as well as in
protoplanetary disks.Comment: 8 pages, 2 tables, 4 figures, accepted for publication in MNRA
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]
Rotational Excitation of HC_3N by H_2 and He at low temperatures
Rates for rotational excitation of HC3N by collisions with He atoms and H2
molecules are computed for kinetic temperatures in the range 5-20K and 5-100K,
respectively. These rates are obtained from extensive quantum and
quasi-classical calculations using new accurate potential energy surfaces
(PES)
Contracting for liability limitation
Today terrorism has become a world-wide phenomenon which does not stop at the European borders. Following the 9/11 attacks on the World Trade Centre and terrorist attacks in Paris, Madrid and London, concerns have arisen in Europe about potential liability exposure for terrorism-related damage. This book tackles the problem of civil liability for damage caused by terrorist acts from several angles. The authors expertly deliver a comprehensive analysis of terrorism-related risk under international and EU law and the national tort law systems of seven representative EU Member States. They also provide a comparison of the situation in Europe to the liability environment in the US. Risk mitigation strategies are considered and critically assessed, as are alternative systems for redressing terrorism-related risks. The book concludes with a reflection on the analysis and presents possible strategies for future regulation by the European lawmakers
Collisional excitation of singly deuterated ammonia NHD by H
The availability of collisional rate coefficients with H is a
pre-requisite for interpretation of observations of molecules whose energy
levels are populated under non local thermodynamical equilibrium conditions. In
the current study, we present collisional rate coefficients for the NHD /
para--H() collisional system, for energy levels up to (735 K) and for gas temperatures in the range K. The
cross sections are obtained using the essentially exact close--coupling (CC)
formalism at low energy and at the highest energies, we used the
coupled--states (CS) approximation. For the energy levels up to
(215 K), the cross sections obtained through the CS formalism are
scaled according to a few CC reference points. These reference points are
subsequently used to estimate the accuracy of the rate coefficients for higher
levels, which is mainly limited by the use of the CS formalism. Considering the
current potential energy surface, the rate coefficients are thus expected to be
accurate to within 5\% for the levels below , while we estimate
an accuracy of 30\% for higher levels
Collisional excitation of water by hydrogen atoms
We present quantum dynamical calculations that describe the rotational
excitation of HO due to collisions with H atoms. We used a recent, high
accuracy potential energy surface, and solved the collisional dynamics with the
close-coupling formalism, for total energies up to 12 000 cm. From these
calculations, we obtained collisional rate coefficients for the first 45 energy
levels of both ortho- and para-HO and for temperatures in the range T =
5-1500 K. These rate coefficients are subsequently compared to the values
previously published for the HO / He and HO / H collisional
systems. It is shown that no simple relation exists between the three systems
and that specific calculations are thus mandatory
Upper bound on the density of Ruelle resonances for Anosov flows
Using a semiclassical approach we show that the spectrum of a smooth Anosov
vector field V on a compact manifold is discrete (in suitable anisotropic
Sobolev spaces) and then we provide an upper bound for the density of
eigenvalues of the operator (-i)V, called Ruelle resonances, close to the real
axis and for large real parts.Comment: 57 page
On the influence of collisional rate coefficients on the water vapour excitation
Water is a key molecule in many astrophysical studies. Its high dipole moment
makes this molecule to be subthermally populated under the typical conditions
of most astrophysical objects. This motivated the calculation of various sets
of collisional rate coefficients (CRC) for HO (with He or H) which are
necessary to model its rotational excitation and line emission. We performed
accurate non--local non--LTE radiative transfer calculations using different
sets of CRC in order to predict the line intensities from transitions that
involve the lowest energy levels of HO (E 900 K). The results obtained
from the different CRC sets are then compared using line intensity ratio
statistics. For the whole range of physical conditions considered in this work,
we obtain that the intensities based on the quantum and QCT CRC are in good
agreement. However, at relatively low H volume density ((H)
10 cm) and low water abundance ((HO) 10), these
physical conditions being relevant to describe most molecular clouds, we find
differences in the predicted line intensities of up to a factor of 3 for
the bulk of the lines. Most of the recent studies interpreting early Herschel
Space Observatory spectra used the QCT CRC. Our results show that although the
global conclusions from those studies will not be drastically changed, each
case has to be considered individually, since depending on the physical
conditions, the use of the QCT CRC may lead to a mis--estimate of the water
vapour abundance of up to a factor of 3
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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