9,927 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
Scarred eigenstates for quantum cat maps of minimal periods
In this paper we construct a sequence of eigenfunctions of the ``quantum
Arnold's cat map'' that, in the semiclassical limit, show a strong scarring
phenomenon on the periodic orbits of the dynamics. More precisely, those states
have a semiclassical limit measure that is the sum of 1/2 the normalized
Lebesgue measure on the torus plus 1/2 the normalized Dirac measure
concentrated on any a priori given periodic orbit of the dynamics. It is known
(the Schnirelman theorem) that ``most'' sequences of eigenfunctions
equidistribute on the torus. The sequences we construct therefore provide an
example of an exception to this general rule. Our method of construction and
proof exploits the existence of special values of Planck's constant for which
the quantum period of the map is relatively ``short'', and a sharp control on
the evolution of coherent states up to this time scale. We also provide a
pointwise description of these states in phase space, which uncovers their
``hyperbolic'' structure in the vicinity of the fixed points and yields more
precise localization estimates.Comment: LaTeX, 49 pages, includes 10 figures. I added section 6.6. To be
published in Commun. Math. Phy
A search for clusters and groups of galaxies on the line of sight towards 8 lensed quasars
In this paper we present new ESO/VLT FORS1 and ISAAC images of the fields
around eight gravitationally lensed quasars: CTQ414, HE0230-2130,
LBQS1009-0252, B1030+074, HE1104-1805, B1359+154, H1413+117 and HE2149-2745.
When available and deep enough, HST/WFPC2 data were also used to infer the
photometric redshifts of the galaxies around the quasars. The search of galaxy
overdensities in space and redshift, as well as a weak-shear analysis and a
mass reconstruction are presented in this paper. We find that there are most
probably galaxy groups towards CTQ414, HE0230-2130, B1359+154, H1413+117 and
HE2149-2745, with a mass ~ 4x10^14 M_sol h^-1. Considering its photometric
redshift, the galaxy group discovered in the field around HE1104-1805 is
associated with the quasar rather than with the lensing potential.Comment: 14 pages, 11 figures(.jpg
Electromagnetic topology: Characterization of internal electromagnetic coupling
The main principles are presented of a method dealing with the resolution of electromagnetic internal problems: Electromagnetic Topology. A very interesting way is to generalize the multiconductor transmission line network theory to the basic equation of the Electromagnetic Topology: the BLT equation. This generalization is illustrated by the treatment of an aperture as a four port junction. Analytical and experimental derivations of the scattering parameters are presented. These concepts are used to study the electromagnetic coupling in a scale model of an aircraft, and can be seen as a convenient means to test internal electromagnetic interference
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
CH observations toward the Orion Bar
CH is one of the first radicals to be detected in the interstellar
medium. Its higher rotational transitions have recently become available with
the Herschel Space Observatory. We aim to constrain the physical parameters of
the CH emitting gas toward the Orion Bar. We analyse the CH line
intensities measured toward the Orion Bar CO Peak and Herschel/HIFI maps of
CH, CH, and HCO, and a NANTEN map of [CI]. We interpret the observed
CH emission using radiative transfer and PDR models. Five rotational
transitions of CH have been detected in the HIFI frequency range toward the
CO peak. A single component rotational diagram gives a rotation temperature
of ~64 K and a beam-averaged CH column density of 410
cm. The measured transitions cannot be explained by any single parameter
model. According to a non-LTE model, most of the CH column density produces
the lower- CH transitions and traces a warm ( ~ 100-150 K)
and dense ((H)~10-10 cm) gas. A small fraction of the
CH column density is required to reproduce the intensity of the highest-
transitions (=9-8 and N=10-9) originating from a high density
((H)~510 cm) hot ( ~ 400 K) gas. The
total beam-averaged CH column density in the model is 10 cm.
Both the non-LTE radiative transfer model and a simple PDR model representing
the Orion Bar with a plane-parallel slab of gas and dust suggest, that CH
cannot be described by a single pressure component, unlike the reactive ion
CH, which was previously analysed toward the Orion Bar CO peak. The
physical parameters traced by the higher rotational transitions
(=6-5,...,10-9) of CH may be consistent with the edges of dense clumps
exposed to UV radiation near the ionization front of the Orion Bar.Comment: Proposed for acceptance in A&A, abstract abridge
The diversity of the EU approach to law enforcement:Towards a coherent model inspired by a law and economics approach
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