535 research outputs found
IDeF-X ASIC for Cd(Zn)Te spectro-imaging systems
Joint progresses in Cd(Zn)Te detectors, microelectronics and interconnection
technologies open the way for a new generation of instruments for physics and
astrophysics applications in the energy range from 1 to 1000 keV. Even working
between -20 and 20 degrees Celsius, these instruments will offer high spatial
resolution (pixel size ranging from 300 x 300 square micrometers to few square
millimeters), high spectral response and high detection efficiency. To reach
these goals, reliable, highly integrated, low noise and low power consumption
electronics is mandatory. Our group is currently developing a new ASIC detector
front-end named IDeF-X, for modular spectro-imaging system based on the use of
Cd(Zn)Te detectors. We present here the first version of IDeF-X which consists
in a set of ten low noise charge sensitive preamplifiers (CSA). It has been
processed with the standard AMS 0.35 micrometer CMOS technology. The CSA are
designed to be DC coupled to detectors having a low dark current at room
temperature. The various preamps implemented are optimized for detector
capacitances ranging from 0.5 up to 30 pF.Comment: 8 pages, 11 figures, IEEE NSS-MIC conference in Rome 2004, submitted
to IEEE TNS, correction in unit of figure
ORIGAMIX, a CdTe-based spectro-imager development for nuclear applications
The Astrophysics Division of CEA Saclay has a long history in the development
of CdTe based pixelated detection planes for X and gamma-ray astronomy, with
time-resolved imaging and spectrometric capabilities. The last generation,
named Caliste HD, is an all-in-one modular instrument that fulfills
requirements for space applications. Its full-custom front-end electronics is
designed to work over a large energy range from 2 keV to 1 MeV with excellent
spectroscopic performances, in particular between 10 and 100 keV (0.56 keV FWHM
and 0.67 keV FWHM at 13.9 and 59.5 keV). In the frame of the ORIGAMIX project,
a consortium based on research laboratories and industrials has been settled in
order to develop a new generation of gamma camera. The aim is to develop a
system based on the Caliste architecture for post-accidental interventions or
homeland security, but integrating new properties (advanced spectrometry,
hybrid working mode) and suitable for industry. A first prototype was designed
and tested to acquire feedback for further developments. In this study, we
particularly focused on spectrometric performances with high energies and high
fluxes. Therefore, our device was exposed to energies up to 700 keV (133Ba,
137Cs) and we measured the evolution of energy resolution (0.96 keV at 80 keV,
2.18 keV at 356 keV, 3.33 keV at 662 keV). Detection efficiency decreases after
150 keV, as Compton effect becomes dominant. However, CALISTE is also designed
to handle multiple events, enabling Compton scattering reconstruction, which
can drastically improve detection efficiencies and dynamic range for higher
energies up to 1408 keV (22Na, 60Co, 152Eu) within a 1-mm thick detector. In
particular, such spectrometric performances obtained with 152Eu and 60Co were
never measured before with this kind of detector.Comment: Nuclear Instruments and Methods in Physics Research Section A:
Accelerators, Spectrometers, Detectors and Associated Equipment. Available
online 9 January 2015, ISSN 0168-9002
(http://www.sciencedirect.com/science/article/pii/S0168900215000133).
Keywords: CdTe; X-ray; Gamma-ray; Spectrometry; Charge-sharing; Astrophysics
Instrumentation; Nuclear Instrumentation; Gamma-ray camera
Numerical implementation of isolated horizon boundary conditions
We study the numerical implementation of a set of boundary conditions derived from the isolated horizon formalism, and which characterize a black hole whose horizon is in quasiequilibrium. More precisely, we enforce these geometrical prescriptions as inner boundary conditions on an excised sphere, in the numerical resolution of the conformal thin sandwich equations. As main results, we first establish the consistency of including in the set of boundary conditions a constant surface gravity prescription, interpretable as a lapse boundary condition, and second we assess how the prescriptions presented recently by Dain et al. for guaranteeing the well-posedness of the conformal transverse traceless equations with quasiequilibrium horizon conditions extend to the conformal thin sandwich elliptic system. As a consequence of the latter analysis, we discuss the freedom of prescribing the expansion associated with the ingoing null normal at the horizon
Compton telescope with coded aperture mask: Imaging with the INTEGRAL/IBIS Compton mode
Compton telescopes provide a good sensitivity over a wide field of view in
the difficult energy range running from a few hundred keV to several MeV. Their
angular resolution is, however, poor and strongly energy dependent. We present
a novel experimental design associating a coded mask and a Compton detection
unit to overcome these pitfalls. It maintains the Compton performance while
improving the angular resolution by at least an order of magnitude in the field
of view subtended by the mask. This improvement is obtained only at the expense
of the efficiency that is reduced by a factor of two. In addition, the
background corrections benefit from the coded mask technique, i.e. a
simultaneous measurement of the source and background. This design is
implemented and tested using the IBIS telescope on board the INTEGRAL satellite
to construct images with a 12' resolution over a 29 degrees x 29 degrees field
of view in the energy range from 200 keV to a few MeV. The details of the
analysis method and the resulting telescope performance, particularly in terms
of sensitivity, are presented
The ECLAIRs micro-satellite mission for gamma-ray burst multi-wavelength observations
Gamma-ray bursts (GRB), at least those with a duration longer than a few
seconds are the most energetic events in the Universe and occur at cosmological
distances. The ECLAIRs micro-satellite, to be launched in 2009, will provide
multi-wavelength observations of GRB, to study their astrophysics and to use
them as cosmological probes. Furthermore in 2009 ECLAIRs is expected to be the
only space borne instrument capable of providing a GRB trigger in near
real-time with sufficient localization accuracy for GRB follow-up observations
with the powerful ground based spectroscopic telescopes available by then. A
"Phase A study" of the ECLAIRs project has recently been launched by the French
Space Agency CNES, aiming at a detailed mission design and selection for flight
in 2006. The ECLAIRs mission is based on a CNES micro-satellite of the
"Myriade" family and dedicated ground-based optical telescopes. The satellite
payload combines a 2 sr field-of-view coded aperture mask gamma-camera using
6400 CdTe pixels for GRB detection and localization with 10 arcmin precision in
the 4 to 50 keV energy band, together with a soft X-ray camera for onboard
position refinement to 1 arcmin. The ground-based optical robotic telescopes
will detect the GRB prompt/early afterglow emission and localize the event to
arcsec accuracy, for spectroscopic follow-up observations.Comment: 7 pages, 1 figure, proceedings of the conference "New Developments in
Photodetection", Beaune (France), June 25005. Submitted to NIM-A (Elsevier
Science
Probing the Slope of Cluster Mass Profile with Gravitational Einstein Rings: Application to Abell 1689
The strong lensing modelling of gravitational ``rings'' formed around massive
galaxies is sensitive to the amplitude of the external shear and convergence
produced by nearby mass condensations. In current wide field surveys, it is now
possible to find out a large number of rings, typically 10 gravitational rings
per square degree. We propose here, to systematically study gravitational rings
around galaxy clusters to probe the cluster mass profile beyond the cluster
strong lensing regions. For cluster of galaxies with multiple arc systems, we
show that rings found at various distances from the cluster centre can improve
the modelling by constraining the slope of the cluster mass profile. We outline
the principle of the method with simple numerical simulations and we apply it
to 3 rings discovered recently in Abell~1689. In particular, the lens modelling
of the 3 rings confirms that the cluster is bimodal, and favours a slope of the
mass profile steeper than isothermal at a cluster radius \sim 300 \kpc. These
results are compared with previous lens modelling of Abell~1689 including weak
lensing analysis. Because of the difficulty arising from the complex mass
distribution in Abell~1689, we argue that the ring method will be better
implemented on simpler and relaxed clusters.Comment: Accepted for publication in MNRAS. Substantial modification after
referee's repor
The Wide-Field X and Gamma-Ray Telescope ECLAIRs aboard the Gamma-Ray Burst Multi-Wavelength Space Mission SVOM
The X and Gamma-ray telescope ECLAIRs is foreseen to be launched on a low
Earth orbit (h=630 km, i=30 degrees) aboard the SVOM satellite (Space-based
multi-band astronomical Variable Objects Monitor), a French-Chinese mission
with Italian contribution. Observations are expected to start in 2013. It has
been designed to detect and localize Gamma-Ray Bursts (GRBs) or persistent
sources of the sky, thanks to its wide field of view (about 2 sr) and its
remarkable sensitivity in the 4-250 keV energy range, with enhanced imaging
sensitivity in the 4-70 keV energy band. These characteristics are well suited
to detect highly redshifted GRBs, and consequently to provide fast and accurate
triggers to other onboard or ground-based instruments able to follow-up the
detected events in a very short time from the optical wavelength bands up to
the few MeV Gamma-Ray domain.Comment: Proccedings of the "2008 Nanjing GRB Conference", June 23-27 2008,
Nanjing, Chin
Inhibitory Control on a Stop Signal Task in Tourette Syndrome before and after Deep Brain Stimulation of the Internal Segment of the Globus Pallidus
As part of the first randomized double-blind trial of deep brain stimulation (DBS) of the globus pallidus (GPi) in Tourette syndrome, we examined the effect of stimulation on response initiation and inhibition. A total of 14 patients with severe Tourette syndrome were recruited and tested on the stop signal task prior to and after GPi-DBS surgery and compared to eight age-matched healthy controls. Tics were significantly improved following GPi-DBS. The main measure of reactive inhibition, the stop signal reaction time did not change from before to after surgery and did not differ from that of healthy controls either before or after GPi-DBS surgery. This suggests that patients with Tourette syndrome have normal reactive inhibition which is not significantly altered by GPi-DBS
The mass profile of early-type galaxies in overdense environments: the case of the double source plane gravitational lens SL2SJ02176-0513
SL2SJ02176-0513 is a remarkable lens for the presence of two multiply-imaged
systems at different redshifts lensed by a foreground massive galaxy at : a bright cusp arc at and an additional
double-image system at an estimated redshift of based on
photometry and lensing geometry. The system is located about 400 kpc away from
the center of a massive group of galaxies. Mass estimates for the group are
available from X-ray observations and satellite kinematics. Multicolor
photometry provides an estimate of the stellar mass of the main lens galaxy.
The lensing galaxy is modeled with two components (stars and dark matter), and
we include the perturbing effect of the group environment, and all available
constraints. We find that classic lensing degeneracies, e.g. between external
convergence and mass density slope, are significantly reduced with respect to
standard systems and infer tight constraints on the mass density profile: (i)
the dark matter content of the main lens galaxy is in line with that of typical
galaxies ; (ii) the required mass
associated with the dark matter halo of the nearby group is consistent with
X-ray and weak-lensing estimates (); (iii)
accounting for the group contribution in the form of an external convergence,
the slope of the mass density profile of the main lens galaxy alone is found to
be , consistent with the isothermal ()
slope. We demonstrate that multiple source plane systems together with good
ancillary dataset can be used to disentangle local and environmental effects.Comment: 10 pages, 6 figures, submitted to A&
Synaptotagmin I, a molecular target for steroid hormone signaling controlling the maturation of sexual behavior in an insect
As in vertebrates, the insect steroid hormones, especially 20-hydroxyecdysone (20E), initiate and regulate sexual behavior by acting on the central nervous system. This 20E action is, in part, triggered by transcriptional events mediated through the binding of 20E to a heterodimer comprising the ecdysone receptor (EcR) and ultraspiracle (USP). However, to date, our knowledge about this genomic steroid pathway remains incomplete. In moths, males detect female sex pheromones, eliciting stereotyped sexual behavior. In Agrotis ipsilon males, the behavioral response and the neuronal sensitivity to sex pheromone in the olfactory center, the antennal lobe (AL), increase with age. We recently showed that 20E controlled this age-dependent olfactory plasticity via the activation of an EcR/USP-dependent pathway in the AL. Here, we cloned the gene encoding A. ipsilon synaptotagmin I (AisytI), a presynaptic vesicle protein known to act as a calcium sensor in neurotransmitter release. AisytI was expressed in the AL, where its amount increased with age, whereas its knockdown inhibited the sex pheromone-oriented flight of males. 20E administration to males induced AL AisytI expression in a dose-dependent and time-dependent manner. Moreover, A. ipsilon EcR silencing caused decreases in AL AisytI expression and the behavioral response to sex pheromone. Our results show that the synaptotagmin I gene is a target gene for the genomic steroid signaling that controls the expression of insect sexual behavior by acting on central sex pheromone processing. This study thus represents a significant advance in our understanding of the steroid actions that influence neural functions, and thereby behavioral plasticity, in various organisms
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