243 research outputs found
Theory of Electric Field-Induced Photoluminescence Quenching in Disordered Molecular Solids
The dynamics of excitons in disordered molecular solids is studied
theoretically, taking into account migration between different sites,
recombination, and dissociation into free charge carriers in the presence of an
electric field. The theory is applied to interpret the results of electric
field-induced photoluminescence (PL) quenching experiments on molecularly doped
polymers by Deussen et al. [Chem. Phys. 207, 147 (1996)]. Using an
intermolecular dissociation mechanism, the dependence of the PL quenching on
the electric field strength and the dopant concentration, and the time
evolution of the transient PL quenching can be well described. The results
constitute additional proof of the distinct exciton dissociation mechanisms in
conjugated polymer blends and molecularly doped polymers.Comment: 4 pages RevTeX, 3 Postscript figure
Interstellar extinction towards the inner Galactic Bulge
DENIS observations in the J (1.2 micron) and K_S (2.15 micron) bands together
with isochrones calculated for the RGB and AGB phase are used to draw an
extinction map of the inner Galactic Bulge. The uncertainty in this method is
mainly limited by the optical depth of the Bulge itself. A comparison with
fields of known extinction shows a very good agreement. We present an
extinction map for the inner Galactic Bulge (approx. 20 sq. deg.)Comment: 4 pages, 4 figures, accepted for publication in A&A as a letter, see
also http://www-denis.iap.fr/articles/extinction
Holstein polaron in the presence of disorder
Non-local, inhomogeneous and retarded response observed in experiments is
reproduced by introducing the Inhomogeneous Momentum Average (IMA) method to
study single polaron problems with disorder in the on-site potential and/or
spatial variations of the electron-phonon couplings and/or phonon frequencies.
We show that the electron-phonon coupling gives rise to an additional
inhomogeneous, strongly retarded potential, which makes instant approximations
questionable. The accuracy of IMA is demonstrated by comparison with results
from the approximation free Diagrammatic Monte Carlo (DMC) method. Its
simplicity allows for easy study of many problems that were previously
unaccessible. As an example, we show how inhomogeneities in the electron-phonon
coupling lead to nonlocal, retarded response in scanning tunneling microscopy
(STM) images.Comment: 4 pages, 3 figure
Welfare regimes and social cohesion regimes: do they express the same values?
Welfare regime types are classified according to the role played by three main institutions, namely the market, the state and the family. They can be reinterpreted as systems of exchanges for providing resources based on the main principles of liberty, equality and solidarity. Depending on the different possible dialectical relations between these three principles, they lead to different social cohesion regimes. This paper is the first attempt to empirically test this hypothesis at a European level by elaborating a measure of social cohesion based on values and creating a typology of social cohesion regimes. In comparison to welfare regimes, it invites to go one step further by considering the articulation between the three main principles and proposes a more precise classification for countries. The results invite further research on the links between welfare and social cohesion regimes. The analysis is based on data from the 2008 European Values Study (EVS) in 43 countries using principal component analysis, multidimensional scaling and cluster analyses
ISOGAL-DENIS detection of red giants with weak mass loss in the Galactic Bulge
The ISOGAL project is a survey of the stellar populations, structure, and
recent star formation history of the inner disk and bulge of the Galaxy. ISOGAL
combines 15 and 7micron ISOCAM observations with DENIS IJKs data to determine
the nature of a source and the interstellar extinction. In this paper we report
an ISOGAL study of a small field in the inner Galactic Bulge (l=0deg, b=1.0deg,
area=0.035 sq. deg) as a prototype of the larger area ISOGAL survey of the
inner Galaxy. The five wavelengths of ISOGAL+DENIS, together with the
relatively low and constant extinction in front of this specific field, allow
reliable determination of the nature of the sources. The primary scientific
result of this paper is evidence that the most numerous class of ISOGAL
15micron sources are Red Giants in the Galactic bulge and central disk, with
luminosities just above or close to the RGB tip and weak mass-loss rates. They
form loose sequences in the magnitude-colour diagrams [15]/Ks-[15] and
[15]/[7]-[15]. Their large excesses at 15micron with respect to 2micron and
7micron is due to circumstellar dust produced by mass-loss at low rates. These
ISOGAL results are the first systematic evidence and study of dust emission at
this early stage (''Intermediate'' AGB), before the onset of the large
mass-loss phase. It is thus well established that efficient dust formation is
already associated with such low mass-loss rates during this early phase.Comment: 15 pages, 9 figures, accepted for publication in Astronomy and
Astrophysics Journa
Acceleration disturbances and requirements for ASTROD I
ASTRODynamical Space Test of Relativity using Optical Devices I (ASTROD I)
mainly aims at testing relativistic gravity and measuring the solar-system
parameters with high precision, by carrying out laser ranging between a
spacecraft in a solar orbit and ground stations. In order to achieve these
goals, the magnitude of the total acceleration disturbance of the proof mass
has to be less than 10−13 m s−2 Hz−1/2 at 0.1 m Hz. In this
paper, we give a preliminary overview of the sources and magnitude of
acceleration disturbances that could arise in the ASTROD I proof mass. Based on
the estimates of the acceleration disturbances and by assuming a simple
controlloop model, we infer requirements for ASTROD I. Our estimates show that
most of the requirements for ASTROD I can be relaxed in comparison with Laser
Interferometer Space Antenna (LISA).Comment: 19 pages, two figures, accepted for publication by Class. Quantum
Grav. (at press
- …