56 research outputs found
Diffuse Gamma-ray Emission from the Galactic Center - A Multiple Energy Injection Model
We suggest that the energy source of the observed diffuse gamma-ray emission
from the direction of the Galactic center is the Galactic black hole Sgr A*,
which becomes active when a star is captured at a rate of
yr^{-1}. Subsequently the star is tidally disrupted and its matter is accreted
into the black hole. During the active phase relativistic protons with a
characteristic energy erg per capture are ejected. Over
90% of these relativistic protons disappear due to proton-proton collisions on
a timescale years in the small central bulge region with
radius pc within Sgr A*, where the density is cm^{-3}. The
gamma-ray intensity, which results from the decay of neutral pions produced by
proton-proton collisions, decreases according to , where t is
the time after last stellar capture. Less than 5% of relativistic protons
escaped from the central bulge region can survive and maintain their energy for
>10^7 years due to much lower gas density outside, where the gas density can
drop to cm. They can diffuse to a pc region before
disappearing due to proton-proton collisions. The observed diffuse GeV
gamma-rays resulting from the decay of neutral pions produced via collision
between these escaped protons and the gas in this region is expected to be
insensitive to time in the multi-injection model with the characteristic
injection rate of 10^{-5} yr^{-1}. Our model calculated GeV and 511 keV
gamma-ray intensities are consistent with the observed results of EGRET and
INTEGRAL, however, our calculated inflight annihilation rate cannot produce
sufficient intensity to explain the COMPTEL data.Comment: 8 pages, 3 figures, accepted by A&
A microfluidic device for investigating crystal nucleation kinetics
We have developed an original setup using microfluidic tools allowing one to
produce continuously monodisperse microreactors ( nL), and to
control their temperatures as they flow in the microdevice. With a specific
microchannels geometry, we are able to apply large temperature quenches to
droplets containing a KNO solution (up to 50C in 10 s), and then
to follow nucleation kinetics at high supersaturations. By measuring the
probability of crystal presence in the droplets as a function of time, we
estimate the nucleation rate for different supersaturations, and confront our
results to the classical nucleation theory
The Compton Spectrometer and Imager
The Compton Spectrometer and Imager (COSI) is a NASA Small Explorer (SMEX)
satellite mission in development with a planned launch in 2027. COSI is a
wide-field gamma-ray telescope designed to survey the entire sky at 0.2-5 MeV.
It provides imaging, spectroscopy, and polarimetry of astrophysical sources,
and its germanium detectors provide excellent energy resolution for emission
line measurements. Science goals for COSI include studies of 0.511 MeV emission
from antimatter annihilation in the Galaxy, mapping radioactive elements from
nucleosynthesis, determining emission mechanisms and source geometries with
polarization measurements, and detecting and localizing multimessenger sources.
The instantaneous field of view for the germanium detectors is >25% of the sky,
and they are surrounded on the sides and bottom by active shields, providing
background rejection as well as allowing for detection of gamma-ray bursts and
other gamma-ray flares over most of the sky. In the following, we provide an
overview of the COSI mission, including the science, the technical design, and
the project status.Comment: 8 page
The cosipy library: COSI's high-level analysis software
The Compton Spectrometer and Imager (COSI) is a selected Small Explorer
(SMEX) mission launching in 2027. It consists of a large field-of-view Compton
telescope that will probe with increased sensitivity the under-explored MeV
gamma-ray sky (0.2-5 MeV). We will present the current status of cosipy, a
Python library that will perform spectral and polarization fits, image
deconvolution, and all high-level analysis tasks required by COSI's broad
science goals: uncovering the origin of the Galactic positrons, mapping the
sites of Galactic nucleosynthesis, improving our models of the jet and emission
mechanism of gamma-ray bursts (GRBs) and active galactic nuclei (AGNs), and
detecting and localizing gravitational wave and neutrino sources. The cosipy
library builds on the experience gained during the COSI balloon campaigns and
will bring the analysis of data in the Compton regime to a modern open-source
likelihood-based code, capable of performing coherent joint fits with other
instruments using the Multi-Mission Maximum Likelihood framework (3ML). In this
contribution, we will also discuss our plans to receive feedback from the
community by having yearly software releases accompanied by publicly-available
data challenges
COVID-19 symptoms at hospital admission vary with age and sex: results from the ISARIC prospective multinational observational study
Background:
The ISARIC prospective multinational observational study is the largest cohort of hospitalized patients with COVID-19. We present relationships of age, sex, and nationality to presenting symptoms.
Methods:
International, prospective observational study of 60â109 hospitalized symptomatic patients with laboratory-confirmed COVID-19 recruited from 43 countries between 30 January and 3 August 2020. Logistic regression was performed to evaluate relationships of age and sex to published COVID-19 case definitions and the most commonly reported symptoms.
Results:
âTypicalâ symptoms of fever (69%), cough (68%) and shortness of breath (66%) were the most commonly reported. 92% of patients experienced at least one of these. Prevalence of typical symptoms was greatest in 30- to 60-year-olds (respectively 80, 79, 69%; at least one 95%). They were reported less frequently in children (â€â18 years: 69, 48, 23; 85%), older adults (â„â70 years: 61, 62, 65; 90%), and women (66, 66, 64; 90%; vs. men 71, 70, 67; 93%, each Pâ<â0.001). The most common atypical presentations under 60 years of age were nausea and vomiting and abdominal pain, and over 60 years was confusion. Regression models showed significant differences in symptoms with sex, age and country.
Interpretation:
This international collaboration has allowed us to report reliable symptom data from the largest cohort of patients admitted to hospital with COVID-19. Adults over 60 and children admitted to hospital with COVID-19 are less likely to present with typical symptoms. Nausea and vomiting are common atypical presentations under 30 years. Confusion is a frequent atypical presentation of COVID-19 in adults over 60 years. Women are less likely to experience typical symptoms than men
Analyse et modélisation du changement climatique - 2° édition du Livre blanc Escrime
International audienc
Vulnérabilité des ressources en eau au changement global en zone méditerranéenne - Le projet Vulcain. Compte-rendu de fin de projet
The Mediterranean region has been pointed out as a « hot spot » in terms of climate change, withsevere warming and precipitations decrease. Moreover, the intense population growth rate willprobably deepen its water resources structural deficit. In the future, the water scarcity level will dependon both the withdrawals and the climate evolution. The VULCAIN project proposes a method toanalyze and compare the climate and socio-economic change impacts on the water resources of thePyrĂ©nĂ©es Orientales department (figure 1). Future climate and drinking/agricultural water usescenarios have been built and their impact on the water resources of the study zone wascharacterized and compared, with a description of the associated uncertainties. The results allowedthe vulnerability characterization based on future water resources to water use budget. The mainissues of the vulnerability of the studied territory have been identified, which are currently integratedby the water managers to structure their adaptation strategies.La rĂ©gion mĂ©diterranĂ©enne est considĂ©rĂ©e comme un « hot spot » du changement climatique, affectĂ©epar une poursuite du rĂ©chauffement et une diminution des prĂ©cipitations. Par ailleurs, le rapideaccroissement dĂ©mographique observĂ© risque dâaggraver son dĂ©ficit structurel en termes deressource en eau. Dans le futur, le niveau de raretĂ© de lâeau devrait dĂ©pendre Ă la fois de lâĂ©volutiondes prĂ©lĂšvements et du climat. Le projet VULCAIN propose une mĂ©thode dâĂ©tude et de comparaisondes impacts du changement climatique et socio-Ă©conomique sur les ressources en eau sur ledĂ©partement des PyrĂ©nĂ©es Orientales (figure 1). AprĂšs avoir Ă©laborĂ© des scĂ©narios de climat etdâĂ©volution des usages eau potable et agricoles, leur impact sur les ressources en eau du territoire aĂ©tĂ© caractĂ©risĂ© Ă lâaide de modĂšles et comparĂ©, en veillant Ă identifier les sources dâincertitudes quileur sont associĂ©es. Les rĂ©sultats ont permis de caractĂ©riser la vulnĂ©rabilitĂ© en se basant sur un bilanentre ressources et usages futurs. Ce travail a permis dâidentifier les enjeux en termes de vulnĂ©rabilitĂ©sur le territoire Ă©tudiĂ© et dâalimenter les structures de gestion pour leur rĂ©flexion en termes destratĂ©gies dâadaptation
Simulation des changements climatiques au cours du XXI<sup>e</sup> siÚcle incluant l'ozone stratosphérique
Simulation of climate changes during the 21-st century including stratospheric ozone
International audienc
- âŠ