9,149 research outputs found
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
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
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
The magnetic precursor of L1448-mm: Excitation differences between ion and neutral fluids
Shock modelling predicts an electron density enhancement within the magnetic
precursor of C-shocks. Previous observations of SiO, H13CO+, HN13C and H13CN
toward the young L1448-mm outflow showed an over-excitation of the ion fluid
that was attributed to an electron density enhancement in the precursor. We
re-visit this interpretation and test if it still holds when we consider
different source morphologies and kinetic temperatures for the observed
molecules, and also give some insight on the spatial extent of the electron
density enhancement around L1448-mm.
We estimate the opacities of H13CO+ and HN13C by observing the J=3\to2 lines
of rarer isotopologues to confirm that the emission is optically thin. To model
the excitation of the molecules, we use the large velocity gradient (LVG)
approximation with updated collisional coefficients to i) re- analyse the
observations toward the positions where the over-excitation of H13CO+ has
previously been observed [i.e. toward L1448- mm at offsets (0,0) and (0,-10)],
and ii) to investigate if the electron density enhancement is still required
for the cases of extended and compact emission, and for kinetic temperatures of
up to 400 K. We also report several lines of SiO, HN13C and H13CO+ toward new
positions around this outflow, to investigate the spatial extent of the
over-excitation of the ions in L1448-mm. From the isotopologue observations, we
find that the emission of H13CO+ and HN13C from the precursor is optically thin
if this emission is extended. Using the new collisional coefficients, an
electron density enhancement is still needed to explain the excitation of
H13CO+ for extended emission and for gas temperatures of\le 400 K toward
L1448-mm (0,-10), and possibly also toward L1448-mm (0,0). For compact emission
the data cannot be fitted. We do not find any evidence for the over-excitation
of the ion fluid toward the newly observed positions around L1448-mm.
The observed line emission of SiO, H13CO+ and HN13C toward L1448-mm (0,0) and
(0,-10) is consistent with an electron density enhancement in the precursor
component, if this emission is spatially extended. This is also true for the
case of high gas temperatures (\le400 K) toward the (0,-10) offset. The
electron density enhancement seems to be restricted to the southern, redshifted
lobe of the L1448-mm outflow. Interferometric images of the line emission of
these molecules are needed to confirm the spatial extent of the over-excitation
of the ions and thus, of the electron density enhancement in the magnetic
precursor of L1448-mm.Comment: Accepted for publication in A&A; 9 pages, 3 figure
An Implicit Tensor-Mass solver on the GPU for soft bodies simulation
International audienceThe realistic and interactive simulation of deformable objects has become a challenge in Computer Graphics. In this paper, we propose a GPU implementation of the resolution of the mechanical equations, using a semi-implicit as well as an implicit integration scheme. At the contrary of the classical FEM approach, forces are directly computed at each node of the discretized objects, using the evaluation of the strain energy density of the elements. This approach allows to mix several mechanical behaviors in the same object. Results show a notable speedup of 30, especially in the case of complex scenes. Running times shows that this efficient implementation may contribute to make this model more popular for soft bodies simulations
Topological properties of quantum periodic Hamiltonians
We consider periodic quantum Hamiltonians on the torus phase space
(Harper-like Hamiltonians). We calculate the topological Chern index which
characterizes each spectral band in the generic case. This calculation is made
by a semi-classical approach with use of quasi-modes. As a result, the Chern
index is equal to the homotopy of the path of these quasi-modes on phase space
as the Floquet parameter (\theta) of the band is varied. It is quite
interesting that the Chern indices, defined as topological quantum numbers, can
be expressed from simple properties of the classical trajectories.Comment: 27 pages, 14 figure
The IRAM-30m line survey of the Horsehead PDR: IV. Comparative chemistry of H2CO and CH3OH
Aims. We investigate the dominant formation mechanism of H2CO and CH3OH in
the Horsehead PDR and its associated dense core. Methods. We performed deep
integrations of several H2CO and CH3OH lines at two positions in the Horsehead,
namely the PDR and dense core, with the IRAM-30m telescope. In addition, we
observed one H2CO higher frequency line with the CSO telescope at both
positions. We determine the H2CO and CH3OH column densities and abundances from
the single-dish observations complemented with IRAM-PdBI high-angular
resolution maps (6") of both species. We compare the observed abundances with
PDR models including either pure gas-phase chemistry or both gas-phase and
grain surface chemistry. Results. We derive CH3OH abundances relative to total
number of hydrogen atoms of ~1.2e-10 and ~2.3e-10 in the PDR and dense core
positions, respectively. These abundances are similar to the inferred H2CO
abundance in both positions (~2e-10). We find an abundance ratio H2CO/CH3OH of
~2 in the PDR and ~1 in the dense core. Pure gas-phase models cannot reproduce
the observed abundances of either H2CO or CH3OH at the PDR position. Both
species are therefore formed on the surface of dust grains and are subsequently
photodesorbed into the gas-phase at this position. At the dense core, on the
other hand, photodesorption of ices is needed to explain the observed abundance
of CH3OH, while a pure gas-phase model can reproduce the observed H2CO
abundance. The high-resolution observations show that CH3OH is depleted onto
grains at the dense core. CH3OH is thus present in an envelope around this
position, while H2CO is present in both the envelope and the dense core itself.
Conclusions. Photodesorption is an efficient mechanism to release complex
molecules in low FUV-illuminated PDRs, where thermal desorption of ice mantles
is ineffective.Comment: 12 pages, 5 tables, 7 figures; Accepted for publication in A&
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