4,821 research outputs found
A strict lower-limit EBL: Applications on gamma-ray absorption
A strict lower limit flux for the extragalactic background light from
ultraviolet to the far-infrared photon energies is presented. The spectral
energy distribution is derived using an established EBL model based on galaxy
formation. The model parameters are chosen to fit the lower limit data from
number count observations in particular recent results by the SPITZER infrared
space telescope. A lower limit EBL model is needed to calculate guaranteed
absorption due to pair production in extragalactic gamma-ray sources as in TeV
blazars.Comment: Comments: 4 pages, 2 figures, submitted to proceedings of "4th
Heidelberg International Symposium on High Energy Gamma-Ray Astronomy 2008
On the equivalence of N=1 brane worlds and geometric singularities with flux
We consider Kaluza Klein reductions of M-theory on the Z_N orbifold of the
spin bundle over S^3 along two different U(1) isometries. The first one gives
rise to the familiar ``large N duality'' of the N=1 SU(N) gauge theory in which
the UV is realized as the world-volume theory of N D6-branes wrapped on S^3,
whereas the IR involves N units of RR flux through an S^2. The second reduction
gives an equivalent version of this duality in which the UV is realized
geometrically in terms of an S^2 of A_{N-1} singularities, with one unit of RR
flux through the S^2. The IR is reached via a geometric transition and involves
a single D6 brane on a lens space S^3/Z_N or, alternatively, a singular
background (S^2\times R^4)/Z_N, with one unit of RR flux through S^2 and,
localized at the singularities, an action of their stabilizer group in the U(1)
RR gauge bundle, so that no massless twisted states occur. We also consider
linear sigma-model descriptions of these backgrounds.Comment: 25 pages, LaTeX; v2: one reference added, published versio
320g Ionization-Heat Cryogenic Detector for Dark Matter Search in the EDELWEISS Experiment
The EDELWEISS experiment used in 2001 a 320g heat-and-ionization cryogenic Ge
detector operated in a low-background environment in the Laboratoire Souterrain
de Modane for direct WIMP detection. This detector presents an increase of more
than 4 times the mass of previous detectors. Calibrations of this detector are
used to determine its energy resolution and fiducial volume, and to optimize
the detector design for the 1kg phase of the EDELWEISS-I experiment. Analysis
of the calibrations and characteristics of a first series of 320g-detectors are
presented.Comment: 4 pages, 3 figure
Simultaneous X-ray and optical spectroscopy of the Oef supergiant lambda Cep
Probing the structures of stellar winds is of prime importance for the
understanding of massive stars. Based on their optical spectral morphology and
variability, the stars of the Oef class have been suggested to feature
large-scale structures in their wind. High-resolution X-ray spectroscopy and
time-series of X-ray observations of presumably-single O-type stars can help us
understand the physics of their stellar winds. We have collected XMM-Newton
observations and coordinated optical spectroscopy of the O6Ief star lambda Cep
to study its X-ray and optical variability and to analyse its high-resolution
X-ray spectrum. We investigate the line profile variability of the He II 4686
and H-alpha emission lines in our time series of optical spectra, including a
search for periodicities. We further discuss the variability of the broadband
X-ray flux and analyse the high-resolution spectrum of lambda Cep using
line-by-line fits as well as a code designed to fit the full high-resolution
X-ray spectrum consistently. During our observing campaign, the He II 4686 line
varies on a timescale of ~18 hours. On the contrary, the H-alpha line profile
displays a modulation on a timescale of 4.1 days which is likely the rotation
period of the star. The X-ray flux varies on time-scales of days and could in
fact be modulated by the same 4.1 days period as H-alpha, although both
variations are shifted in phase. The high-resolution X-ray spectrum reveals
broad and skewed emission lines as expected for the X-ray emission from a
distribution of wind-embedded shocks. Most of the X-ray emission arises within
less than 2R* above the photosphere.Comment: Accepted for publication in Astronomy & Astrophysic
CENP-A Is Dispensable for Mitotic Centromere Function after Initial Centromere/Kinetochore Assembly
Human centromeres are defined by chromatin containing the histone H3 variant CENP-A assembled onto repetitive alphoid DNA sequences. By inducing rapid, complete degradation of endogenous CENP-A, we now demonstrate that once the first steps of centromere assembly have been completed in G1/S, continued CENP-A binding is not required for maintaining kinetochore attachment to centromeres or for centromere function in the next mitosis. Degradation of CENP-A prior to kinetochore assembly is found to block deposition of CENP-C and CENP-N, but not CENP-T, thereby producing defective kinetochores and failure of chromosome segregation. Without the continuing presence of CENP-A, CENP-B binding to alphoid DNA sequences becomes essential to preserve anchoring of CENP-C and the kinetochore to each centromere. Thus, there is a reciprocal interdependency of CENP-A chromatin and the underlying repetitive centromere DNA sequences bound by CENP-B in the maintenance of human chromosome segregation
The EDELWEISS Experiment : Status and Outlook
The EDELWEISS Dark Matter search uses low-temperature Ge detectors with heat
and ionisation read- out to identify nuclear recoils induced by elastic
collisions with WIMPs from the galactic halo. Results from the operation of 70
g and 320 g Ge detectors in the low-background environment of the Modane
Underground Laboratory (LSM) are presented.Comment: International Conference on Dark Matter in Astro and Particle Physics
(Dark 2000), Heidelberg, Germany, 10-16 Jul 2000, v3 minor revision
FIRBACK Source Counts and Cosmological Implications
FIRBACK is a one of the deepest surveys performed at 170 microns with ISOPHOT
onboard ISO, and is aimed at the study of cosmic far infrared background
sources. About 300 galaxies are detected in an area of four square degrees, and
source counts present a strong slope of 2.2 on an integral "logN-logS" plot,
which cannot be due to cosmological evolution if no K-correction is present.
The resolved sources account for less than 10% of the Cosmic Infrared
Background at 170 microns. In order to understand the nature of the sources
contributing to the CIB, and to explain deep source counts at other
wavelengths, we have developed a phenomenological model, which constrains in a
simple way the luminosity function evolution with redshift, and fits all the
existing deep source counts from the mid-infrared to the submillimetre range.
Images, materials and papers available on the FIRBACK web:
http://wwwfirback.ias.u-psud.fr wwwfirback.ias.u-psud.frComment: proceedings of "ISO Surveys of a Dusty Universe", eds. D. Lemke, M.
Stickel, K. Wilke, Ringberg, 8-12 Nov 1999, to appear in Springer 'Lecture
Notes of Physics'. 8 pages, 7 eps figures, .sty include
A Temporally Dynamic Gut Microbiome in Atlantic Salmon During Freshwater Recirculating Aquaculture System (RAS) Production and Post-seawater Transfer
This study was funded by the UKRI project ROBUSTSMOLT (BBSRC BB/S004270/1 and BB/S004432/1). There was also cofunding from the Scottish Aquaculture Innovation Centre. ACKNOWLEDGMENTS The authors would like to thank John Richmond and staff at MOWI and the Centre for Genome Enabled Biology and Medicine (CGEBM) at the University of Aberdeen, particularly Dr. Ewan Campbell, for help with amplification protocols, conducting 16S library preparation and sequencing. The datasets presented in this study can be found in online repositories. The names of the repository/repositories and accession number(s) can be found below: https://www.ncbi.nlm.nih.gov/bioproject/PRJNA729215.Peer reviewedPublisher PD
Dark Matter Search in the Edelweiss Experiment
Preliminary results obtained with 320g bolometers with simultaneous
ionization and heat measurements are described. After a few weeks of data
taking, data accumulated with one of these detectors are beginning to exclude
the upper part of the DAMA region. Prospects for the present run and the second
stage of the experiment, EDELWEISS-II, using an innovative reversed cryostat
allowing data taking with 100 detectors, are briefly described.Comment: IDM 2000, 3rd International Workshop on the Identification of Dark
Matter, York (GB), 18-22/09/2000, v2.0 minor modification
- …