91 research outputs found
Development of a modular CdTe detector plane for gamma-ray burst detection below 100 keV
We report on the development of an innovative CdTe detector plane (DPIX)
optimized for the detection and localization of gamma-ray bursts in the X-ray
band (below 100 keV). DPIX is part of an R&D program funded by the French Space
Agency (CNES). DPIX builds upon the heritage of the ISGRI instrument, currently
operating with great success on the ESA INTEGRAL mission. DPIX is an assembly
of 200 elementary modules (XRDPIX) equipped with 32 CdTe Schottky detectors
(4x4 mm2, 1 mm thickness) produced by ACRORAD Co. LTD. in Japan. These
detectors offer good energy response up to 100 keV. Each XRDPIX is readout by
the very low noise front-end electronics chip IDeF-X, currently under
development at CEA/DSM/DAPNIA. In this paper, we describe the design of XRDPIX,
the main features of the IDeF-X chip, and will present preliminary results of
the reading out of one CdTe Schottky detector by the IDeF-X V1.0 chip. A
low-energy threshold around 2.7 keV has been measured. This is to be compared
with the 12-15 keV threshold of the ISGRI-INTEGRAL and BAT-SWIFT instruments,
which both use similar detector material.Comment: 5 pages, 4 figures in color, Advances in Space Research, COSPAR
meeting, Beijing (2006
Shaping black holes with free fields
Starting from a metric Ansatz permitting a weak version of Birkhoff's theorem
we find static black hole solutions including matter in the form of free scalar
and p-form fields, with and without a cosmological constant \Lambda. Single
p-form matter fields permit multiple possibilities, including dyonic solutions,
self-dual instantons and metrics with Einstein-Kaelher horizons. The inclusion
of multiple p-forms on the other hand, arranged in a homogeneous fashion with
respect to the horizon geometry, permits the construction of higher dimensional
dyonic p-form black holes and four dimensional axionic black holes with flat
horizons, when \Lambda<0. It is found that axionic fields regularize black hole
solutions in the sense, for example, of permitting regular -- rather than
singular -- small mass Reissner-Nordstrom type black holes. Their cosmic string
and Vaidya versions are also obtained.Comment: 38 pages. v2: minor changes, published versio
Polarized emission of GaN/AlN quantum dots : single dot spectroscopy and symmetry-based theory
We report micro-photoluminescence studies of single GaN/AlN quantum dots
grown along the (0001) crystal axis by molecular beam epitaxy on Si(111)
substrates. The emission lines exhibit a linear polarization along the growth
plane, but with varying magnitudes of the polarization degree and with
principal polarization axes that do not necessarily correspond to
crystallographic directions. Moreover, we could not observe any splitting of
polarized emission lines, at least within the spectral resolution of our setup
(1 meV). We propose a model based on the joint effects of electron-hole
exchange interaction and in-plane anisotropy of strain and/or quantum dot
shape, in order to explain the quantitative differences between our
observations and those previously reported on, e.g. CdTe- or InAs-based quantum
dots
Glucose-Dependent Regulation of NR2F2 Promoter and Influence of SNP-rs3743462 on Whole Body Insulin Sensitivity
Background: The Nuclear Receptor 2F2 (NR2F2/COUP-TFII) heterozygous knockout mice display low basal insulinemia and enhanced insulin sensitivity. We previously established that insulin represses NR2F2 gene expression in pancreatic β-cells. The cis-regulatory region of the NR2F2 promoter is unknown and its influence on metabolism in humans is poorly understood. The present study aimed to identify the regulatory regions that control NR2F2 gene transcription and to evaluate the effect of NR2F2 promoter variation on glucose homeostasis in humans. Methodology/Principal Findings: Regulation of the NR2F2 promoter was assessed using gene reporter assays, ChIP and gel shift experiments. The effects of variation at SNP rs3743462 in NR2F2 on quantitative metabolic traits were studied in two European prospective cohorts. We identified a minimal promoter region that down-regulates NR2F2 expression by attenuating HNF4α activation in response to high glucose concentrations. Subjects of the French DESIR population, who carried the rs3743462 T-to-C polymorphism, located in the distal glucose-responsive promoter, displayed lower basal insulin levels and lower HOMA-IR index. The C-allele at rs3743462 was associated with increased NR2F2 binding and decreased NR2F2 gene expression. Conclusions/Significance: The rs3743462 polymorphism affects glucose-responsive NR2F2 promoter regulation and thereby may influence whole-body insulin sensitivity, suggesting a role of NR2F2 in the control of glucose homeostasis in humans. © 2012 Boutant et al
COUP-TFII Controls Mouse Pancreatic β-Cell Mass through GLP-1-β-Catenin Signaling Pathways
Background: The control of the functional pancreatic beta-cell mass serves the key homeostatic function of releasing the right amount of insulin to keep blood sugar in the normal range. It is not fully understood though how beta-cell mass is determined
The Nutritional Induction of COUP-TFII Gene Expression in Ventromedial Hypothalamic Neurons Is Mediated by the Melanocortin Pathway
BACKGROUND: The nuclear receptor chicken ovalbumin upstream promoter transcription factor II (COUP-TFII) is an important coordinator of glucose homeostasis. We report, for the first time, a unique differential regulation of its expression by the nutritional status in the mouse hypothalamus compared to peripheral tissues. METHODOLOGY/PRINCIPAL FINDINGS: Using hyperinsulinemic-euglycemic clamps and insulinopenic mice, we show that insulin upregulates its expression in the hypothalamus. Immunofluorescence studies demonstrate that COUP-TFII gene expression is restricted to a subpopulation of ventromedial hypothalamic neurons expressing the melanocortin receptor. In GT1-7 hypothalamic cells, the MC4-R agonist MTII leads to a dose dependant increase of COUP-TFII gene expression secondarily to a local increase in cAMP concentrations. Transfection experiments, using a COUP-TFII promoter containing a functional cAMP responsive element, suggest a direct transcriptional activation by cAMP. Finally, we show that the fed state or intracerebroventricular injections of MTII in mice induce an increased hypothalamic COUP-TFII expression associated with a decreased hepatic and pancreatic COUP-TFII expression. CONCLUSIONS/SIGNIFICANCE: These observations strongly suggest that hypothalamic COUP-TFII gene expression could be a central integrator of insulin and melanocortin signaling pathway within the ventromedial hypothalamus. COUP-TFII could play a crucial role in brain integration of circulating signal of hunger and satiety involved in energy balance regulation
Smart Sensors and Virtual Physiology Human Approach as a Basis of Personalized Therapies in Diabetes Mellitus
Diabetes mellitus (DM) has a growing incidence and prevalence in modern societies, pushed by the aging and change of life styles. Despite the huge resources dedicated to improve their quality of life, mortality and morbidity rates, these are still very poor. In this work, DM pathology is revised from clinical and metabolic points of view, as well as mathematical models related to DM, with the aim of justifying an evolution of DM therapies towards the correction of the physiological metabolic loops involved. We analyze the reliability of mathematical models, under the perspective of virtual physiological human (VPH) initiatives, for generating and integrating customized knowledge about patients, which is needed for that evolution. Wearable smart sensors play a key role in this frame, as they provide patient’s information to the models
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