117 research outputs found
Chandra ACIS-I particle background: an analytical model
Aims: Imaging and spectroscopy of X-ray extended sources require a proper
characterisation of a spatially unresolved background signal. This background
includes sky and instrumental components, each of which are characterised by
its proper spatial and spectral behaviour. While the X-ray sky background has
been extensively studied in previous work, here we analyse and model the
instrumental background of the ACIS-I detector on-board the Chandra X-ray
observatory in very faint mode.
Methods: Caused by interaction of highly energetic particles with the
detector, the ACIS-I instrumental background is spectrally characterised by the
superposition of several fluorescence emission lines onto a continuum. To
isolate its flux from any sky component, we fitted an analytical model of the
continuum to observations performed in very faint mode with the detector in the
stowed position shielded from the sky, and gathered over the eight year period
starting in 2001. The remaining emission lines were fitted to blank-sky
observations of the same period. We found 11 emission lines. Analysing the
spatial variation of the amplitude, energy and width of these lines has further
allowed us to infer that three lines of these are presumably due to an energy
correction artefact produced in the frame store.
Results: We provide an analytical model that predicts the instrumental
background with a precision of 2% in the continuum and 5% in the lines. We use
this model to measure the flux of the unresolved cosmic X-ray background in the
Chandra deep field south. We obtain a flux of for the keV band and for the keV band
Mapping the particle acceleration in the cool core of the galaxy cluster RX J1720.1+2638
We present new deep, high-resolution radio images of the diffuse minihalo in
the cool core of the galaxy cluster RX J1720.1+2638. The images have been
obtained with the Giant Metrewave Radio Telescope at 317, 617 and 1280 MHz and
with the Very Large Array at 1.5, 4.9 and 8.4 GHz, with angular resolutions
ranging from 1" to 10". This represents the best radio spectral and imaging
dataset for any minihalo. Most of the radio flux of the minihalo arises from a
bright central component with a maximum radius of ~80 kpc. A fainter tail of
emission extends out from the central component to form a spiral-shaped
structure with a length of ~230 kpc, seen at frequencies 1.5 GHz and below. We
find indication of a possible steepening of the total radio spectrum of the
minihalo at high frequencies. Furthermore, a spectral index image shows that
the spectrum of the diffuse emission steepens with the increasing distance
along the tail. A striking spatial correlation is observed between the minihalo
emission and two cold fronts visible in the Chandra X-ray image of this cool
core. These cold fronts confine the minihalo, as also seen in numerical
simulations of minihalo formation by sloshing-induced turbulence. All these
observations favor the hypothesis that the radio emitting electrons in cluster
cool cores are produced by turbulent reacceleration.Comment: 16 pages, 11 figures, accepted for publication in The Astrophysical
Journa
Innovative tools and modeling methodology for impact prediction and assessment of the contribution of materials on indoor air quality
International audienceBackground: The combination of more and more airtight buildings and the emission of formaldehyde and other volatile organic compounds (VOCs) by building, decoration and furniture materials lead to lower indoor air quality. Hence, it is an important challenge for public health but also for the preservation of cultural heritage, as for example, artworks in museum showcases and other cultural objects. Indeed, some VOCs such as organic acids or carbonyl compounds may play a role in the degradation of some metallic objects or historic papers. Thus, simple and cost effective sampling tools are required to meet the recent and growing demand of on-site diagnostic of indoor air quality , including emission source identification and their ranking.Results: In this aim, we developed new tools based on passive sampling (Solid-Phase Micro Extraction, SPME) to measure carbonyls compounds (including formaldehyde) and other VOCs and both in indoor air and at the material/ air interface. On one hand, the coupling of SPME with a specially designed emission cell allows the screening and the quantification of the VOCs emitted by building, decoration or furniture materials. On the other hand, indoor air is simply analysed using new vacuum vial sampling combined with VOCs pre-concentration by SPME. These alternative sampling methods are energy free, compact, silent and easy to implement for on-site measurements. They show satisfactory analytical performance as detection limits range from 0.05 to 0.1 µg m −3 with an average Relative Standard Deviation (RSD) of 18 %. They already have been applied to monitoring of indoor air quality and building material emissions for a 6 months period. The data obtained were in agreement with the prediction of a physical monozonal model which considers building materials both as VOC sources and sinks and air exchange rate in one single room ("box model").Conclusion: Results are promising, even if more data are required to complete validation, and the model could be envisaged as a predictive tool for indoor air quality. This new integrated approach involving measurements and mod-eling could be easily transposed to historic environments and to the preservation of cultural heritage
LoCuSS: Hydrostatic Mass Measurements of the High- Cluster Sample -- Cross-calibration of Chandra and XMM-Newton
We present a consistent analysis of Chandra and XMM-Newton observations of an
approximately mass-selected sample of 50 galaxy clusters at -- the
"LoCuSS High- Sample". We apply the same analysis methods to data from
both satellites, including newly developed analytic background models that
predict the spatial variation of the Chandra and XMM-Newton backgrounds to
and precision respectively. To verify the cross-calibration of
Chandra and XMM-Newton-based cluster mass measurements, we derive the mass
profiles of the 21 clusters that have been observed with both satellites,
extracting surface brightness and temperature profiles from identical regions
of the respective datasets. We obtain consistent results for the gas and total
hydrostatic cluster masses: the average ratio of Chandra- to XMM-Newton-based
measurements of and at are and
, respectively with an intrinsic scatter of for gas
masses and for hydrostatic masses. Comparison of our hydrostatic mass
measurements at with the latest LoCuSS weak-lensing results indicate
that the data are consistent with non-thermal pressure support at this radius
of . We also investigate the scaling relation between our hydrostatic
cluster masses and published integrated Compton parameter
measurements from the Sunyaev-Zel'dovich Array. We measure a scatter in mass at
fixed of at , which is consistent with
theoretical predictions of scatter.Comment: 21 pages, 11 figure
ACTAPOL : un chantier de recherche sur les conventionnels
Derrière l’acronyme ACTAPOL se cache un projet financé par l’Agence nationale de la recherche, intitulé : « Acteurs et action politique en Révolution. Les conventionnels ». Conçu et porté par des membres des équipes de l’IRHiS (Lille 3, Hervé Leuwers), du GRHis (Rouen, Michel Biard) et du CHEC (Clermont-Ferrand 2, Philippe Bourdin) qui, traditionnellement, consacrent une part notable de leurs travaux aux révolutions du tournant des XVIIIe et XIXe siècles, le programme s’est déployé parallèlem..
Diffusion of n-alkanes in MFI-type zeolites: a comparative study with different measuring techniques
CHEX-MATE: pressure profiles of 6 galaxy clusters as seen by SPT and Planck
Pressure profiles are sensitive probes of the thermodynamic conditions and
the internal structure of galaxy clusters. The intra-cluster gas resides in
hydrostatic equilibrium within the Dark Matter gravitational potential.
However, this equilibrium may be perturbed, e.g. as a consequence of thermal
energy losses, feedback and non-thermal pressure supports. Accurate measures of
the gas pressure over the cosmic times are crucial to constrain the cluster
evolution as well as the contribution of astrophysical processes. In this work
we presented a novel algorithm to derive the pressure profiles of galaxy
clusters from the Sunyaev-Zeldovich (SZ) signal measured on a combination of
Planck and South Pole Telescope (SPT) observations. The synergy of the two
instruments made it possible to track the profiles on a wide range of spatial
scales. We exploited the sensitivity to the larger scales of the Planck
High-Frequency Instrument to observe the faint peripheries, and the higher
spatial resolution of SPT to solve the innermost regions. We developed a
two-step pipeline to take advantage of the specifications of each instrument.
We first performed a component separation on the two data-sets separately to
remove the background (CMB) and foreground (galactic emission) contaminants.
Then we jointly fitted a parametric pressure profile model on a combination of
Planck and SPT data. We validated our technique on a sample of 6 CHEX-MATE
clusters detected by SPT. We compare the results of the SZ analysis with
profiles derived from X-ray observations with XMM-Newton. We find an excellent
agreement between these two independent probes of the gas pressure structure.Comment: 19 pages, 13 figures, submitted to A&
Extracorporeal Membrane Oxygenation for Severe Acute Respiratory Distress Syndrome associated with COVID-19: An Emulated Target Trial Analysis.
RATIONALE: Whether COVID patients may benefit from extracorporeal membrane oxygenation (ECMO) compared with conventional invasive mechanical ventilation (IMV) remains unknown. OBJECTIVES: To estimate the effect of ECMO on 90-Day mortality vs IMV only Methods: Among 4,244 critically ill adult patients with COVID-19 included in a multicenter cohort study, we emulated a target trial comparing the treatment strategies of initiating ECMO vs. no ECMO within 7 days of IMV in patients with severe acute respiratory distress syndrome (PaO2/FiO2 <80 or PaCO2 ≥60 mmHg). We controlled for confounding using a multivariable Cox model based on predefined variables. MAIN RESULTS: 1,235 patients met the full eligibility criteria for the emulated trial, among whom 164 patients initiated ECMO. The ECMO strategy had a higher survival probability at Day-7 from the onset of eligibility criteria (87% vs 83%, risk difference: 4%, 95% CI 0;9%) which decreased during follow-up (survival at Day-90: 63% vs 65%, risk difference: -2%, 95% CI -10;5%). However, ECMO was associated with higher survival when performed in high-volume ECMO centers or in regions where a specific ECMO network organization was set up to handle high demand, and when initiated within the first 4 days of MV and in profoundly hypoxemic patients. CONCLUSIONS: In an emulated trial based on a nationwide COVID-19 cohort, we found differential survival over time of an ECMO compared with a no-ECMO strategy. However, ECMO was consistently associated with better outcomes when performed in high-volume centers and in regions with ECMO capacities specifically organized to handle high demand. This article is open access and distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives License 4.0 (http://creativecommons.org/licenses/by-nc-nd/4.0/)
Imagerie et spectro-imagerie X appliquées à l'étude des propriétés du milieu intergalactique dans les amas de galaxies en cours de coalescence
PARIS-BIUSJ-Thèses (751052125) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF
The importance of H2O in arc magmas for the formation of porphyry Cu deposits
Porphyry copper deposits (PCDs) hosted in subvolcanic intrusions at convergent margins are the primary world's copper resources. However, the set of magmatic processes that lead to the generation of ore-bearing magmatic provinces remains unclear. In this paper we review the systematic of Cu evolution during arc magma differentiation using new and existing global compilations of whole rock geochemistry data. We trace the Cu evolution from primitive arc magmas through lower crustal plutonic to volcanic rocks. We focus on the well-known tholeiitic and calc-alkaline fractionation sequences, where arc tholeiitic series represents damp primitive melts (2 wt% H₂O) that differentiate with iron depletion. Our study shows that the Cu concentration in primitive arc basalts (~80 ppm) is indistinguishable from that of primitive melts formed at mid-ocean ridges (MORBs) implying that Cu is mainly sourced from the mantle wedge in arcs with a limited contribution from the subducted oceanic lithosphere. A global compilation of plutonic rocks whole rock geochemistry (lower crustal cumulates and derivative melts) indicate no systematic difference in Cu concentrations between cumulates associated with tholeiitic or calc-alkaline series. Yet a complementary global compilation of arc volcanic whole rock geochemistry highlights the contrasting behavior of Cu in tholeiitic and calc-alkaline series during magmatic differentiation. In tholeiitic arc series, Cu shows an incompatible or compatible behavior during magma differentiation influenced by the crustal thickness. In calk-alkaline arc series, Cu is compatible during magma differentiation independently to the crustal thickness. This relates to the timing of sulfide saturation, which is controlled by the liquid lines of descent (LLD) and/or crustal thickness at redox conditions relevant for arc magmas. We demonstrate that the initial melt H₂O content in primitive arc melts controls the LLD and the volume of remaining melt mass at fluid saturation. We show that the remaining H₂O-saturated melt mass positively correlates with the total mass of Cu transferred into degassing fluids. The mass of extractable Cu ranges from ~3 to ~10 Mt (i.e., large PCD) for calc-alkaline series, and ranges from ~0.3 to ~2.5 Mt for tholeiitic series. The ore-forming potential of calc-alkaline arc magmas is at least ~4 to ~10 times higher relative to tholeiitic arc magmas. Despite the compatible behavior of Cu during magmatic differentiation, we propose that a single stage model for the formation of large economic PCDs (as opposed to multi-stage model for Cu-sulfides storage and remobilization) is most applicable for the calc-alkaline melts. The importance of the initial melt H₂O content ultimately reflects the key role of flux melting associated with wet calc-alkaline series and high ore-forming potential, in opposition to decompression melting associated with damp tholeiitic series in arc.National Science Foundation (Grant EAR-1552202
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