59 research outputs found
COSIMA-Rosetta calibration for in-situ characterization of 67P/Churyumov-Gerasimenko cometary inorganic compounds
20 pages, 3 figures, 5 tablesInternational audienceCOSIMA (COmetary Secondary Ion Mass Analyser) is a time-of-flight secondary ion mass spectrometer (TOF-SIMS) on board the Rosetta space mission. COSIMA has been designed to measure the composition of cometary dust grains. It has a mass resolution m/{\Delta}m of 1400 at mass 100 u, thus enabling the discrimination of inorganic mass peaks from organic ones in the mass spectra. We have evaluated the identification capabilities of the reference model of COSIMA for inorganic compounds using a suite of terrestrial minerals that are relevant for cometary science. Ground calibration demonstrated that the performances of the flight model were similar to that of the reference model. The list of minerals used in this study was chosen based on the mineralogy of meteorites, interplanetary dust particles and Stardust samples. It contains anhydrous and hydrous ferromagnesian silicates, refractory silicates and oxides (present in meteoritic Ca-Al-rich inclusions), carbonates, and Fe-Ni sulfides. From the analyses of these minerals, we have calculated relative sensitivity factors for a suite of major and minor elements in order to provide a basis for element quantification for the possible identification of major mineral classes present in the cometary grains
Inference on the Nature and the Mass of Earth's Late Veneer from Noble Metals and Gases
Noble metals and gases are very sensitive to the late accretion to the Earth
of asteroids and comets. We present mass balance arguments based on these
elements that indicate that 0.7E22-2.7E22 kg of extraterrestrial bodies struck
the Earth after core formation and that comets comprised less than 1E-5 by mass
of the impacting population. These results imply that the dynamics of asteroids
and comets changed drastically with time and that biogenic elements and
prebiotic molecules were not delivered to the Earth by comets but rather by
carbonaceous asteroids.Comment: 10 pages, 2 figures, 1 table, submitted to JG
Carbon-rich dust in comet 67P/Churyumov-Gerasimenko measured by COSIMA/Rosetta
Cometary ices are rich in CO2, CO and organic volatile
compounds, but the carbon content of cometary dust was only measured for
the Oort Cloud comet 1P/Halley, during its flyby in 1986. The COmetary
Secondary Ion Mass Analyzer (COSIMA)/Rosetta mass spectrometer
analysed dust particles with sizes ranging from 50 to 1000Â ÎŒm, collected
over 2 yr, from 67P/Churyumov-Gerasimenko (67P), a Jupiter family
comet. Here, we report 67P dust composition focusing on the elements C
and O. It has a high carbon content (atomic | |â )
close to the solar value and comparable to the 1P/Halley data. From
COSIMA measurements, we conclude that 67P particles are made of nearly
50 per cent organic matter in mass, mixed with mineral phases that are
mostly anhydrous. The whole composition, rich in carbon and non-hydrated
minerals, points to a primitive matter that likely preserved its
initial characteristics since the comet accretion in the outer regions
of the protoplanetary disc.</p
Nitrogen-to-carbon atomic ratio measured by COSIMA in the particles of comet 67P/ChuryumovâGerasimenko
The COmetary Secondary Ion Mass Analyzer (COSIMA) on board the Rosetta mission has analysed numerous cometary dust particles collected at very low velocities (a few m sâ1)
in the environment of comet 67P/ChuryumovâGerasimenko (hereafter 67P).
In these particles, carbon and nitrogen are expected mainly to be part
of the organic matter. We have measured the nitrogen-to-carbon (N/C)
atomic ratio of 27 cometary particles. It ranges from 0.018 to 0.06 with
an averaged value of 0.035 ± 0.011. This is compatible with the
measurements of the particles of comet 1P/Halley and is in the lower
range of the values measured in comet 81P/Wild 2 particles brought back
to Earth by the Stardust mission. Moreover, the averaged value
found in 67P particles is also similar to the one found in the insoluble
organic matter extracted from CM, CI and CR carbonaceous chondrites and
to the bulk values measured in most interplanetary dust particles and
micrometeorites. The close agreement of the N/C atomic ratio in all
these objects indicates that their organic matters share some
similarities and could have a similar chemical origin. Furthermore,
compared to the abundances of all the detected elements in the particles
of 67P and to the elemental solar abundances, the nitrogen is depleted
in the particles and the nucleus of 67P as was previously inferred also
for comet 1P/Halley. This nitrogen depletion could constrain the
formation scenarios of cometary nuclei.</p
Predictive value of flat-panel CT for haemorrhagic transformations in patients with acute stroke treated with thrombectomy
International audienc
Transcranial Doppler for middle cerebral artery stenosis assessment: how to grasp the tool?
Simplification of first-line antibacterial regimen for complicated appendicitis in children was associated with better adherence to guidelines, and reduced use of antibiotics
International audienceAcute appendicitis in children requires early surgery and short-course antibiotics active against Enterobacteriaceae and anaerobes. Although an aminoglycoside-containing three-drug regimen has been used successfully for decades, simpler regimens with similar efficacy are increasingly used. This study evaluated the impact of a switch from the combination of cefotaxime, metronidazole and gentamicin (regimen 1) to piperacillin/tazobactam (regimen 2) as first-line regimen for complicated acute appendicitis in children. In total, 171 children were enrolled [median (IQR) age, 10 (6-13) years], treated with regimen 1 (nâŻ=âŻ80) or regimen 2 (nâŻ=âŻ91) following surgery for complicated acute appendicitis. The two groups were comparable except for surgical approach (through laparoscopy in 46% vs. 88% for regimens 1 and 2, respectively; P < 0.001). Post-operative complications and duration of hospital stay were similar. Deviations from antibacterial treatment protocol decreased from 36% (29/80) to 14% (13/91) (P < 0.001), with a dramatic reduction in antibacterial treatment duration from median (IQR) of 15 (12-16) days to 5 (5-8) days (P < 0.001). Post-operative intra-abdominal abscess developed in 32 children (18.7%). Female sex (ORâŻ=âŻ2.76, 95% CI 1.18-6.48; PâŻ=âŻ0.02) and sepsis/septic shock on admission (ORâŻ=âŻ4.72, 95% CI 1.12-19.97; PâŻ=âŻ0.035) were independently associated with post-operative intra-abdominal abscess, but not antibacterial regimen. This study shows that simplification of first-line antibacterial regimen for complicated appendicitis in children was associated with reduced protocol deviation, reduced duration of antibiotics, and similar outcomes (post-operative complications and duration of hospital stay)
Correction to: COVID-19-associated acute cerebral venous thrombosis: clinical, CT, MRI and EEG features
Effectiveness and complications of ultrasound-guided subclavian vein cannulation in children and neonates
International audienceBackground The ultrasound (US)-guided supraclavicular approach to subclavian vein (Sup-SCV) catheterisation in children has recently been described and evaluated in a small cohort. The aim of this study was to assess this technique in a large paediatric cohort including neonates. Methods We conducted a prospective observational study between November 2010 and December 2013 which included 615 children divided into two groups according to their weight: Group 1 †5 kg (n = 124), Group 2 > 5 kg (n = 491). All procedures were performed under general anaesthesia by an anaesthesiologist or a supervised resident. The success rates of catheter insertion, the number of punctures required, the procedure time, and the complication rates were analysed. Results Sup-SCV catheterisation was successful in 98% of the cases and was higher in Group 2 than in Group 1 (99.4% versus 92.7%, P < 0.001). The success rate after the first attempt was higher and the incidence of multiple attempts (℠3 punctures) was lower in Group 2 than in Group 1(84.2% versus 64.5%, P < 0.001 and 4.5% versus 19.4%, P < 0.001). The success rate was similar between right and left cannulations (P = 0.404), and according to physician experience (P = 1.000). Procedure time was fast in both groups with a median time for all procedures of 40 [30-90] seconds. Among the procedures recorded, only five arterial punctures and no cases of pneumothorax were observed. Conclusion US-guided Sup-SCV catheterisation appears to be fast and safe in children and neonates, even if it remains a little more difficult to achieve in lower-weight patient
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