1,753 research outputs found
Dark Matter Annihilation in Substructures Revised
Upcoming -ray satellites will search for Dark Matter annihilations in
Milky Way substructures (or 'clumps'). The prospects for detecting these
objects strongly depend on the assumptions made on the distribution of Dark
Matter in substructures, and on the distribution of substructures in the Milky
Way halo. By adopting simplified, yet rather extreme, prescriptions for these
quantities, we compute the number of sources that can be detected with upcoming
experiments such as GLAST, and show that, for the most optimistic particle
physics setup ( GeV and annihilation cross section cm s), the result ranges from zero to
hundred sources, all with mass above . However, for a fiducial DM
candidate with mass GeV and cm s,
at most a handful of large mass substructures can be detected at ,
with a 1-year exposure time, by a GLAST-like experiment. Scenarios where
micro-clumps (i.e. clumps with mass as small as ) can be
detected are severely constrained by the diffuse -ray background
detected by EGRET.Comment: Version accepted for publication in MNRAS. Other subhalos mass
function slopes added. All-sky analysis performed. Boost factors added. High
resolution figures for all models in http://www2.iap.fr/users/bertone/Clumps
Anisotropy probe of galactic and extra-galactic Dark Matter annihilations
We study the flux and the angular power spectrum of gamma-rays produced by
Dark Matter (DM) annihilations in the Milky Way (MW) and in extra-galactic
halos. The annihilation signal receives contributions from: a) the smooth MW
halo, b) resolved and unresolved substructures in the MW, c) external DM halos
at all redshifts, including d) their substructures. Adopting a self-consistent
description of local and extra-galactic substructures, we show that the
annihilation flux from substructures in the MW dominates over all the other
components for angles larger than O(1) degrees from the Galactic Center, unless
an extreme prescription is adopted for the substructures concentration. We also
compute the angular power spectrum of gamma-ray anisotropies and find that, for
an optimistic choice of the particle physics parameters, an interesting
signature of DM annihilations could soon be discovered by the Fermi LAT
satellite at low multipoles, l<100, where the dominant contribution comes from
MW substructures with mass M>10^4 solar masses. For the substructures models we
have adopted, we find that the contribution of extra-galactic annihilations is
instead negligible at all scales.Comment: 14 pages, 7 figure
UB CCD photometry of the old, metal rich, open clusters NGC 6791, NGC 6819 and NGC 7142
We report on a UV-oriented imaging survey in the fields of the old,
metal-rich open clusters, NGC 6791, NGC 6819 and NGC 7142. These three clusters
represent both very near and ideal stellar aggregates to match the distinctive
properties of the evolved stellar populations, as in elliptical galaxies and
bulges of spirals. The CMD of the three clusters is analyzed in detail, with
special emphasis to the hot stellar component. We report, in this regard, one
new extreme horizontal-branch star candidate in NGC 6791. For NGC 6819 and
7142, the stellar luminosity function points to a looser radial distribution of
faint lower Main Sequence stars, either as a consequence of cluster dynamical
interaction with the Galaxy or as an effect of an increasing fraction of binary
stars toward the cluster core, as actually observed in NGC 6791 too.Comment: 12 pages with 15 Figures & 5 Tables. To appear in the Astronomical
Journa
A critical appraisal of ATLAS9 and NextGen 5 model atmospheres
The fitting atmosphere parameters (Teff, g, and [Fe/H]) for over 300 stars in
the Gunn & Striker and Jacoby et al. catalogs have been obtained relying on the
Kurucz (1992) ATLAS9 and Hauschildt et al (1999) NextGen5 synthesis models. The
output results are compared, and a critical appraisal of both theoretical codes
is performed.Comment: 2 pages, 2 figures; proceedings of "New Quests in Stellar
Astrophysics: The link between Stars and Cosmology", 26-30 March, 2001,
Puerto Vallarta, Mexico, eds. M. Chavez, A. Bressan, A. Buzzoni & D. Mayya,
to be published by the Kluwer Academic Publisher
The Temporal Expression of Adipokines During Spinal Fusion
Background Context
Adipokines are secreted by white adipose tissue and have been associated with fracture healing. Our goal was to report the temporal expression of adipokines during spinal fusion in an established rabbit model.
Purpose
Our goal was to report the temporal expression of adipokines during spinal fusion in an established rabbit model.
Study Design
The study design included a laboratory animal model.
Methods
New Zealand white rabbits were assigned to either sham surgery (n=2), unilateral posterior spinal fusion (n=14), or bilateral posterior spinal fusion (n=14). Rabbits were euthanized 1–6 and 10 weeks out from surgery. Fusion was evaluated by radiographs, manual palpation, and histology. Reverse transcription-polymerase chain reaction on the bone fusion mass catalogued the gene expression of leptin, adiponectin, resistin, and vascular endothelial growth factor (VEGF) at each time point. Results were normalized to the internal control gene, glyceraldehyde-3-phosphate dehydrogenase (GAPDH) (2^ΔCt), and control bone sites (2^ΔΔCt). Quantitative data were analyzed by two-factor analysis of variance (p\u3c.05).
Results
Manual palpation scores, radiograph scores, and histologic findings showed progression of boney fusion over time (p
Conclusions
Leptin expression is likely associated with the maturation phase of bone fusion. Adiponectin and resistin may play a role early on during the fusion process. Our results suggest that leptin expression may be upstream of VEGF expression during spinal fusion, and both appear to play an important role in bone spinal fusion
The Abundance of New Kind of Dark Matter Structures
A new kind of dark matter structures, ultracompact minihalos (UCMHs) was
proposed recently. They would be formed during the radiation dominated epoch if
the large density perturbations are existent. Moreover, if the dark matter is
made up of weakly interacting massive particles, the UCMHs can have effect on
cosmological evolution because of the high density and dark matter annihilation
within them. In this paper, one new parameter is introduced to consider the
contributions of UCMHs due to the dark matter annihilation to the evolution of
cosmology, and we use the current and future CMB observations to obtain the
constraint on the new parameter and then the abundance of UCMHs. The final
results are applicable for a wider range of dark matter parametersComment: 4 pages, 1 tabl
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