254 research outputs found
The LOFT Burst Alert System and its Burst On-board Trigger
The ESA M3 candidate mission LOFT (Large Observatory For x-ray Timing) has
been designed to study strong gravitational fields by observing compact
objects, such as black-hole binaries or neutron-star systems and supermassive
black-holes, based on the temporal analysis of photons collected by the primary
instrument LAD (Large Area Detector), sensitive to X-rays from 2 to 50 keV,
offering a very large effective area (>10 m 2 ), but a small field of view
({\o}<1{\deg}). Simultaneously the second instrument WFM (Wide Field Monitor),
composed of 5 coded-mask camera pairs (2-50 keV), monitors a large part of the
sky, in order to detect and localize eruptive sources, to be observed with the
LAD after ground-commanded satellite repointing. With its large field of view
(>{\pi} sr), the WFM actually detects all types of transient sources, including
Gamma-Ray Bursts (GRBs), which are of primary interest for a world-wide
observers community. However, observing the quickly decaying GRB afterglows
with ground-based telescopes needs the rapid knowledge of their precise
localization. The task of the Loft Burst Alert System (LBAS) is therefore to
detect in near- real-time GRBs (about 120 detections expected per year) and
other transient sources, and to deliver their localization in less than 30
seconds to the observers, via a VHF antenna network. Real-time full resolution
data download to ground being impossible, the real-time data processing is
performed onboard by the LBOT (LOFT Burst On-board Trigger system). In this
article we present the LBAS and its components, the LBOT and the associated
ground-segment.Comment: Proc. SPIE 9144, Space Telescopes and Instrumentation 2014:
Ultraviolet to Gamma Ray, 91446
Carbon sequestration in the deep Atlantic enhanced by Saharan dust
sinking rates of particulate organicmatter. Here we present a two-year time series of sediment trap observations of particulate organic carbon flux to 3,000m depth, measured directly in two locations: the dust-rich central North Atlantic gyre and the dust-poor South Atlantic gyre. We find that carbon fluxes are twice as high and a higher proportion of primary production is exported to depth in the dust-rich North Atlantic gyre. Low stable nitrogen isotope ratios suggest that high fluxes result from the stimulation of nitrogen fixation and productivity following the deposition of dust-borne nutrients. Sediment traps in the northern gyre also collected intact colonies of nitrogen-fixing Trichodesmium species. Whereas ballast in Enhanced atmospheric input of dust-borne nutrients and minerals to the remote surface ocean can potentially increase carbon uptake and sequestration at depth. Nutrients can enhance primary productivity, and mineral particles act as ballast, increasing the southern gyre is predominantly biogenic, dust-derived mineral particles constitute the dominant ballast element during the enhanced carbon fluxes in the northern gyre. We conclude that dust deposition increases carbon sequestration in the North Atlantic gyre through the fertilization of the nitrogen-fixing community in surface waters and mineral ballasting of sinking particles
Background Light in Potential Sites for the ANTARES Undersea Neutrino Telescope
The ANTARES collaboration has performed a series of {\em in situ}
measurements to study the background light for a planned undersea neutrino
telescope. Such background can be caused by K decays or by biological
activity. We report on measurements at two sites in the Mediterranean Sea at
depths of 2400~m and 2700~m, respectively. Three photomultiplier tubes were
used to measure single counting rates and coincidence rates for pairs of tubes
at various distances. The background rate is seen to consist of three
components: a constant rate due to K decays, a continuum rate that
varies on a time scale of several hours simultaneously over distances up to at
least 40~m, and random bursts a few seconds long that are only correlated in
time over distances of the order of a meter. A trigger requiring coincidences
between nearby photomultiplier tubes should reduce the trigger rate for a
neutrino telescope to a manageable level with only a small loss in efficiency.Comment: 18 pages, 8 figures, accepted for publication in Astroparticle
Physic
Transcriptomic Analysis Highlights Time-specific Embryonic Adaptation of Mice to the Lack of PrP
The physiological function of the PrP remains largely elusive. Its invalidation does not affect mouse survival and induces subtle phenotypes. To potentially assess this conundrum, we first comparatively analyzed the adult brain transcriptome of wild-type mice with that of transgenic mice invalidated at this locus either at the zygotic (Zürich PrP0/0 mice) or adult stages (NFH-Cre-Lox mice). Only subtle differences could be evidenced in the adult brains following microarray and QPCR analyses. When performed at an early adult stage, neuronal Prnp disruption appeared to sequentially induce an oxidative stress response and a nervous system remodeling, but it involved a limited number of only slightly modified genes. In sharp contrast, analysis at early embryonic stages, 7.5 and 8.5 dpc, just after the suspected normal time set of the Prnp locus activation, led to a transient perturbation of the transcriptome involving a larger number of genes and pointing to potential pathways related to the PrP physiological function. Overall, our data suggests an early adaptation of the mouse to the potentially detrimental lack of PrP during embryogenesis while its presence is less influential or redundant at later developmental stages
The ANTARES Optical Beacon System
ANTARES is a neutrino telescope being deployed in the Mediterranean Sea. It
consists of a three dimensional array of photomultiplier tubes that can detect
the Cherenkov light induced by charged particles produced in the interactions
of neutrinos with the surrounding medium. High angular resolution can be
achieved, in particular when a muon is produced, provided that the Cherenkov
photons are detected with sufficient timing precision. Considerations of the
intrinsic time uncertainties stemming from the transit time spread in the
photomultiplier tubes and the mechanism of transmission of light in sea water
lead to the conclusion that a relative time accuracy of the order of 0.5 ns is
desirable. Accordingly, different time calibration systems have been developed
for the ANTARES telescope. In this article, a system based on Optical Beacons,
a set of external and well-controlled pulsed light sources located throughout
the detector, is described. This calibration system takes into account the
optical properties of sea water, which is used as the detection volume of the
ANTARES telescope. The design, tests, construction and first results of the two
types of beacons, LED and laser-based, are presented.Comment: 21 pages, 18 figures, submitted to Nucl. Instr. and Meth. Phys. Res.
Towards a standard typology of endogenous landslide seismic sources
The objective of this work is to propose a standard classification of seismic
signals generated by gravitational processes and detected at close distances
(<1 km). We review the studies where seismic instruments have been
installed on unstable slopes and discuss the choice of the seismic
instruments and the network geometries. Seismic observations acquired at 13
unstable slopes are analyzed in order to construct the proposed typology. The
selected slopes are affected by various landslide types (slide, fall, topple
and flow) triggered in various material (from unconsolidated soils to
consolidated rocks). We investigate high-frequency bands (>1 Hz) where
most of the seismic energy is recorded at the 1 km sensor to source
distances. Several signal properties (duration, spectral content and
spectrogram shape) are used to describe the sources. We observe that similar
gravitational processes generate similar signals at different slopes. Three
main classes can be differentiated mainly from the length of the signals, the
number of peaks and the duration of the autocorrelation. The classes are the
“slopequake” class, which corresponds to sources potentially occurring
within the landslide body; the “rockfall” class, which corresponds to
signals generated by rock block impacts; and the “granular flow” class,
which corresponds to signals generated by wet or dry debris/rock flows.
Subclasses are further proposed to differentiate specific signal properties
(frequency content, resonance, precursory signal). The signal properties of
each class and subclass are described and several signals of the same class
recorded at different slopes are presented. Their potential origins are
discussed. The typology aims to serve as a standard for further comparisons
of the endogenous microseismicity recorded on landslides.</p
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