393 research outputs found
Dynamiques familiales
L'examen de l'évolution des modèles familiaux en France et en Suède fait ressortir de nombreuses tendances parallèles : accroissement du taux de divorce, baisse des taux de nuptialité et de fécondité, réduction de la taille moyenne des familles, augmentation du nombre de familles monoparentales, diversité des familles recomposées, etc. Les auteurs s'attachent cependant à marquer à quel point le contexte historique et idéologique de cette évolution est très différent d'un pays à l'autre. Tandis que les nouveaux modèles conjugaux se diffusent rapidement en Suède sans y susciter de réactions de rejet, une certaine idéologie française prône un idéal de stabilité conjugale et réclame une politique ouvertement nataliste. La contraception et l'avortement apparaissent naturels à la population suédoise quand ils font toujours l'objet de débats passionnés en France. L'attitude envers l'enfant est très différente entre les deux pays. Pourtant dans l'un et l'autre cas l'évolution des liens familiaux, quoiqu'elle présente un aspect encore expérimental, semble suffisamment radicale pour obliger bientôt à repenser la nature du lien social en général. La procréation artificielle, la confrontation de logiques familiales différentes à travers l'immigration peuvent aussi, dans les années qui viennent, infléchir le sens des dynamiques familiales. (Résumé d'auteur
Intersecting Brane Worlds at One Loop
We develop techniques for one-loop diagrams on intersecting branes. The
one-loop propagator of chiral intersection states on D6 branes is calculated
exactly and its finiteness is shown to be guaranteed by RR tadpole
cancellation. The result is used to demonstrate the expected softening of power
law running of Yukawa couplings at the string scale. We also develop methods to
calculate arbitrary N-point functions at one-loop, including those without
gauge bosons in the loop. These techniques are also applicable to heterotic
orbifold models.Comment: 35 pages, 3 figures; added reference, corrected typos, JHEP styl
BDNF overexpression in mouse hippocampal astrocytes promotes local neurogenesis and elicits anxiolytic-like activities.
The therapeutic activity of selective serotonin (5-HT) reuptake inhibitors (SSRIs) relies on long-term adaptation at pre- and post-synaptic levels. The sustained administration of SSRIs increases the serotonergic neurotransmission in response to a functional desensitization of the inhibitory 5-HT1A autoreceptor in the dorsal raphe. At nerve terminal such as the hippocampus, the enhancement of 5-HT availability increases brain-derived neurotrophic factor (BDNF) synthesis and signaling, a major event in the stimulation of adult neurogenesis. In physiological conditions, BDNF would be expressed at functionally relevant levels in neurons. However, the recent observation that SSRIs upregulate BDNF mRNA in primary cultures of astrocytes strongly suggest that the therapeutic activity of antidepressant drugs might result from an increase in BDNF synthesis in this cell type. In this study, by overexpressing BDNF in astrocytes, we balanced the ratio between astrocytic and neuronal BDNF raising the possibility that such manipulation could positively reverberate on anxiolytic-/antidepressant-like activities in transfected mice. Our results indicate that BDNF overexpression in hippocampal astrocytes produced anxiolytic-/antidepressant-like activity in the novelty suppressed feeding in relation with the stimulation of hippocampal neurogenesis whereas it did not potentiate the effects of the SSRI fluoxetine on these parameters. Moreover, overexpressing BDNF revealed the anxiolytic-like activity of fluoxetine in the elevated plus maze while attenuating 5-HT neurotransmission in response to a blunted downregulation of the 5-HT1A autoreceptor. These results emphasize an original role of hippocampal astrocytes in the synthesis of BDNF, which can act through neurogenesis-dependent and -independent mechanisms to regulate different facets of anxiolytic-like responses
Primordial Black Hole Formation in a Double Inflation Model in Supergravity
It has been recently pointed out that the initial value problem in new
inflation models is naturally solved by supergravity effects if there exists a
pre-inflation before the new inflation. We study this double inflation model in
details and find that density fluctuations on small cosmological scales are
much larger than those on large scales due to peculiar property of the new
inflation. We show that this results in production of primordial black holes
which have masses in a certain parameter region of the
double inflation model. We stress that these black holes may be identified with
MACHOs observed in the halo of our galaxy.Comment: 19 pages (RevTeX file), KUNS-147
A Measurement of Coherent Neutral Pion Production in Neutrino Neutral Current Interactions in NOMAD
We present a study of exclusive neutral pion production in neutrino-nucleus
Neutral Current interactions using data from the NOMAD experiment at the CERN
SPS. The data correspond to muon-neutrino Charged Current
interactions in the energy range GeV. Neutrino
events with only one visible in the final state are expected to result
from two Neutral Current processes: coherent production, {\boldmath
} and single production in
neutrino-nucleon scattering. The signature of coherent production is an
emergent almost collinear with the incident neutrino while 's
produced in neutrino-nucleon deep inelastic scattering have larger transverse
momenta. In this analysis all relevant backgrounds to the coherent
production signal are measured using data themselves. Having determined the
backgrounds, and using the Rein-Sehgal model for the coherent
production to compute the detection efficiency, we obtain {\boldmath } corrected coherent- events with GeV. We measure {\boldmath }.
This is the most precise measurement of the coherent production to
date.Comment: 23 pages, 9 figures, accepted for publication in Phys. Lett.
Partonic flow and -meson production in Au+Au collisions at = 200 GeV
We present first measurements of the -meson elliptic flow
() and high statistics distributions for different
centralities from = 200 GeV Au+Au collisions at RHIC. In
minimum bias collisions the of the meson is consistent with the
trend observed for mesons. The ratio of the yields of the to those of
the as a function of transverse momentum is consistent with a model
based on the recombination of thermal quarks up to GeV/,
but disagrees at higher momenta. The nuclear modification factor () of
follows the trend observed in the mesons rather than in
baryons, supporting baryon-meson scaling. Since -mesons are
made via coalescence of seemingly thermalized quarks in central Au+Au
collisions, the observations imply hot and dense matter with partonic
collectivity has been formed at RHIC.Comment: 6 pages, 4 figures, submit to PR
Measurement of Transverse Single-Spin Asymmetries for Di-Jet Production in Proton-Proton Collisions at GeV
We report the first measurement of the opening angle distribution between
pairs of jets produced in high-energy collisions of transversely polarized
protons. The measurement probes (Sivers) correlations between the transverse
spin orientation of a proton and the transverse momentum directions of its
partons. With both beams polarized, the wide pseudorapidity () coverage for jets permits separation of Sivers functions for the valence
and sea regions. The resulting asymmetries are all consistent with zero and
considerably smaller than Sivers effects observed in semi-inclusive deep
inelastic scattering (SIDIS). We discuss theoretical attempts to reconcile the
new results with the sizable transverse spin effects seen in SIDIS and forward
hadron production in pp collisions.Comment: 6 pages total, 1 Latex file, 3 PS files with figure
Energy and system size dependence of \phi meson production in Cu+Cu and Au+Au collisions
We study the beam-energy and system-size dependence of \phi meson production
(using the hadronic decay mode \phi -- K+K-) by comparing the new results from
Cu+Cu collisions and previously reported Au+Au collisions at \sqrt{s_NN} = 62.4
and 200 GeV measured in the STAR experiment at RHIC. Data presented are from
mid-rapidity (|y|<0.5) for 0.4 < pT < 5 GeV/c. At a given beam energy, the
transverse momentum distributions for \phi mesons are observed to be similar in
yield and shape for Cu+Cu and Au+Au colliding systems with similar average
numbers of participating nucleons. The \phi meson yields in nucleus-nucleus
collisions, normalised by the average number of participating nucleons, are
found to be enhanced relative to those from p+p collisions with a different
trend compared to strange baryons. The enhancement for \phi mesons is observed
to be higher at \sqrt{s_NN} = 200 GeV compared to 62.4 GeV. These observations
for the produced \phi(s\bar{s}) mesons clearly suggest that, at these collision
energies, the source of enhancement of strange hadrons is related to the
formation of a dense partonic medium in high energy nucleus-nucleus collisions
and cannot be alone due to canonical suppression of their production in smaller
systems.Comment: 20 pages and 5 figure
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