283 research outputs found
Spectroscopie dans l'infrarouge lointain de molécules d'intérêt astrophysique
Cette thèse a été consacrée à l étude en laboratoire plusieurs molécules d intérêt astrophysique par spectroscopie par transformation de Fourier dans l infrarouge lointain afin de montrer les possibilités offertes par cette gamme spectrale en matière de spectroscopie vibrationnelle et rotationnelle, notamment grâce à l utilisation du rayonnement synchrotron. Nous nous sommes intéressés à des molécules relativement lourdes, dérivées du naphtalène, pour lesquelles nous avons pu observer les bandes de vibrations de plus basses fréquences. Nous avons également développé différents dispositifs de décharge permettant d étudier la spectroscopie rotationnelle de molécules instables : molécules légères à haute température et radicaux de petite taille.This thesis has been dedicated to the laboratory far-infrared Fourier transform spectroscopy of several molecules of astrophysical interest in order to demonstrate the interest of this spectral region for vibrational and rotational spectroscopy, in particular using synchrotron radiation. Low frequency vibrational spectra of nine naphthalene derivatives, relatively heavy molecules, have been studied. Several discharge set-ups have also been developed in order to study rotational spectroscopy of transient species: high temperature light molecules and small radicals.PARIS11-SCD-Bib. électronique (914719901) / SudocSudocFranceF
Generalized Gibbs ensembles for time dependent processes
An information theory description of finite systems explicitly evolving in
time is presented for classical as well as quantum mechanics. We impose a
variational principle on the Shannon entropy at a given time while the
constraints are set at a former time. The resulting density matrix deviates
from the Boltzmann kernel and contains explicit time odd components which can
be interpreted as collective flows. Applications include quantum brownian
motion, linear response theory, out of equilibrium situations for which the
relevant information is collected within different time scales before entropy
saturation, and the dynamics of the expansion
Sequence structure emission in The Red Rectangle Bands
We report high resolution (R~37,000) integral field spectroscopy of the
central region (r<14arcsec) of the Red Rectangle nebula surrounding HD44179.
The observations focus on the 5800A emission feature, the bluest of the
yellow/red emission bands in the Red Rectangle. We propose that the emission
feature, widely believed to be a molecular emission band, is not a molecular
rotation contour, but a vibrational contour caused by overlapping sequence
bands from a molecule with an extended chromophore. We model the feature as
arising in a Polycyclic Aromatic Hydrocarbon (PAH) with 45-100 carbon atoms.Comment: 13 pages, 9 figures, accepted for publication in ApJ. A version of
the paper with full resolution figures is available at:
http://www.aao.gov.au/local/www/rgs/Sequence-Structure
Control of silver-polymer aggregation mechanism by primary particle spatial correlations in dynamic fractal-like geometry
Silver nanocrystals have been prepared by reacting silver nitrate with
ascorbic acid in aqueous solution containing a low concentration of a
commercial polynaphtalene sulphonate polymer (Daxad 19). Various crystalline
morphologies have been obtained simply by tuning the reaction temperature. We
have investigated the nanoparticle formation mechanism at three different
temperatures by in situ and time resolved Small Angle X ray Scattering
measurements. By modeling the scattering intensity with interacting spherical
particles in a fractal-like polymer-Ag matrix, we found signatures of
nucleation, growth and assembly of primary particles of about 15-20 nm. We
observed how the time evolution of both spatial correlations between primary
particles and the dynamic fractal geometry of the polymer-Ag matrix could
influence and determine both the aggregation mechanism and the morphology of
forming nanostructures in solution
Formalism of collective electron excitations in fullerenes
We present a detailed formalism for the description of collective electron
excitations in fullerenes in the process of the electron inelastic scattering.
Considering the system as a spherical shell of a finite width, we show that the
differential cross section is defined by three plasmon excitations, namely two
coupled modes of the surface plasmon and the volume plasmon. The interplay of
the three plasmons appears due to the electron diffraction of the fullerene
shell. Plasmon modes of different angular momenta provide dominating
contributions to the differential cross section depending on the transferred
momentum.Comment: 11 pages, 2 figures; submitted to the special issue "Atomic Cluster
Collisions: Structure and Dynamics from the Nuclear to the Biological Scale"
of Eur. Phys. J.
Formalism for Multiphoton Plasmon Excitation in Jellium Clusters
We present a new formalism for the description of multiphoton plasmon
excitation processes in jellium clusters. By using our method, we demonstrate
that, in addition to dipole plasmon excitations, the multipole plasmons
(quadrupole, octupole, etc) can be excited in a cluster by multiphoton
absorption processes, which results in a significant difference between plasmon
resonance profiles in the cross sections for multiphoton as compared to
single-photon absorption. We calculate the cross sections for multiphoton
absorption and analyse the balance between the surface and volume plasmon
contributions to multipole plasmons.Comment: 29 pages, 1 figur
When a duck is not a duck; a new interdisciplinary synthesis for environmental radiation protection
This consensus paper presents the results of a workshop held in Essen, Germany in September 2017, called to examine critically the current approach to radiological environmental protection. The meeting brought together participants from the field of low dose radiobiology and those working in radioecology. Both groups have a common aim of identifying radiation exposures and protecting populations and individuals from harmful effects of ionising radiation exposure, but rarely work closely together. A key question in radiobiology is to understand mechanisms triggered by low doses or dose rates, leading to adverse outcomes of individuals while in radioecology a key objective is to recognise when harm is occurring at the level of the ecosystem. The discussion provided a total of six strategic recommendations which would help to address these questions.Funding was provided for this workshop by the International Union for Radioecology and the University of Duisburg-Essen
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