428 research outputs found
Influence of respiratory and inflammatory parameters preceding intubation on survival of patients with COVID-19 ARDS- A single centre retrospective analysis
It remains unclear if intubation and ventilation earlier in the disease course confers a survival advantage in acute respiratory distress syndrome. Our objective was to determine whether patients with COVID-19 who died following mechanical ventilation were more advanced in their disease compared to survivors. Forty-seven patients admitted directly to our centre received ventilation, of who 26 (57%) patients died. The rate of fall in SpO2:FiO2 ratio (p = 0.478) and increasing respiratory rate (p = 0.948) prior to IMV were similar between survivors and non-survivors. Our data support a trial of continuous positive airway pressure prior to IMV in patients with moderate-to-severe COVID-19 ARDS
COVID-19 and non-COVID ARDS patients demonstrate a distinct response to low dose steroids- A retrospective observational study
Patients with COVID-19 ARDS have distinct physiological and immunological phenotypes compared to patients with non-COVID ARDS. Patients with COVID-19 ARDS (n = 32) had a significant improvement in PaO2: FiO2 ratio (p = 0.046) following low-dose steroid treatment, unlike patients with non-COVID ARDS (n = 16) (p = 0.529). Patients with COVID-19 ARDS had a greater fall in CRP compared to patients with non-COVID ARDS, albeit not statistically significant (p = 0.07). Our novel findings highlight differences in the underlying physiological and immunological phenotypes between COVID-19 and non-COVID ARDS, with implications for future ARDS studies
Spectrophotometric properties of dwarf planet Ceres from the VIR spectrometer on board the Dawn mission
We study the spectrophotometric properties of dwarf planet Ceres in the
VIS-IR spectral range by means of hyper-spectral images acquired by the VIR
imaging spectrometer on board the NASA Dawn mission. Disk-resolved observations
with a phase angle within the interval were used
to characterize Ceres' phase curve in the 0.465-4.05 m spectral range.
Hapke's model was applied to perform the photometric correction of the dataset,
allowing us to produce albedo and color maps of the surface. The -band
magnitude phase function of Ceres was fitted with both the classical linear
model and H-G formalism. The single-scattering albedo and the asymmetry
parameter at 0.55m are and ,
respectively (two-lobe Henyey-Greenstein phase function); the modeled geometric
albedo is ; the roughness parameter is
. Albedo maps indicate small variability
on a global scale with an average reflectance of . Isolated
areas such as the Occator bright spots, Haulani, and Oxo show an albedo much
higher than average. We measure a significant spectral phase reddening, and the
average spectral slope of Ceres' surface after photometric correction is
and at VIS and IR wavelengths, respectively.
Broadband color indices are and . H-G
modeling of the -band magnitude phase curve for gives
and , while the classical linear model provides
and . The comparison with
spectrophotometric properties of other minor bodies indicates that Ceres has a
less back-scattering phase function and a slightly higher albedo than comets
and C-type objects. However, the latter represents the closest match in the
usual asteroid taxonomy.Comment: 14 pages, 20 figures, published online on Astronomy and Astrophysics
on 13 February 2017. Revised to reflect minor changes in text and figures
made in proofs, updated value of V-R and R-
Ceres' opposition effect observed by the Dawn framing camera
The surface reflectance of planetary regoliths may increase dramatically
towards zero phase angle, a phenomenon known as the opposition effect (OE). Two
physical processes that are thought to be the dominant contributors to the
brightness surge are shadow hiding (SH) and coherent backscatter (CB). The
occurrence of shadow hiding in planetary regoliths is self-evident, but it has
proved difficult to unambiguously demonstrate CB from remote sensing
observations. One prediction of CB theory is the wavelength dependence of the
OE angular width. The Dawn spacecraft observed the OE on the surface of dwarf
planet Ceres. We characterize the OE over the resolved surface, including the
bright Cerealia Facula, and to find evidence for SH and/or CB. We analyze
images of the Dawn framing camera by means of photometric modeling of the phase
curve. We find that the OE of most of the investigated surface has very similar
characteristics, with an enhancement factor of 1.4 and a FWHM of 3{\deg} (broad
OE). A notable exception are the fresh ejecta of the Azacca crater, which
display a very narrow brightness enhancement that is restricted to phase angles
{\deg} (narrow OE); suggestively, this is in the range in which CB is
thought to dominate. We do not find a wavelength dependence for the width of
the broad OE, and lack the data to investigate the dependence for the narrow
OE. The prediction of a wavelength-dependent CB width is rather ambiguous. The
zero-phase observations allow us to determine Ceres' visible geometric albedo
as . A comparison with other asteroids suggests that
Ceres' broad OE is typical for an asteroid of its spectral type, with
characteristics that are primarily linked to surface albedo. Our analysis
suggests that CB may occur on the dark surface of Ceres in a highly localized
fashion.Comment: Credit: Schr\"oder et al, A&A in press, 2018, reproduced with
permission, \copyright ES
Cometary dust collected by MIDAS on board Rosetta II. Particle shape descriptors and pristineness evaluation
The MIDAS (Micro-Imaging Dust Analysis System) atomic force microscope on
board the Rosetta comet orbiter investigated and measured the 3D topography of
a few hundred nm to tens of m sized dust particles of
67P/Churyumov-Gerasimenko with resolutions down to a few nanometers, giving
insights into the physical processes of our early Solar System. We analyze the
shapes of the cometary dust particles collected by MIDAS on the basis of a
recently updated particle catalog with the aim to determine which structural
properties remained pristine. We develop a set of shape descriptors and metrics
such as aspect ratio, elongation, circularity, convexity, and particle
surface/volume distribution, which can be used to describe the distribution of
particle shapes. Furthermore, we compare the structure of the MIDAS dust
particles and the clusters in which the particles were deposited to those found
in previous laboratory experiments and by Rosetta/COSIMA. Finally, we combine
our findings to calculate a pristineness score for MIDAS particles and
determine the most pristine particles and their properties. We find that the
morphological properties of all cometary dust particles at the micrometer scale
are surprisingly homogeneous despite originating from diverse cometary
environments (e.g., different collection targets that are associated with
cometary activities/source regions and collection velocities/periods). We next
find that the types of clusters found by MIDAS show good agreement with those
defined by previous laboratory experiments, however, there are some differences
to those found by Rosetta/COSIMA. Based on our result, we rate 19 out of 1082
MIDAS particles at least moderately pristine, i.e., they are not substantially
flattened by impact, not fragmented, and/or not part of a fragmentation
cluster.Comment: 40 pages, 31 figures, 1 online tabl
The contamination of the surface of Vesta by impacts and the delivery of the dark material
The Dawn spacecraft observed the presence of dark material, which in turn
proved to be associated with OH and H-rich material, on the surface of Vesta.
The source of this dark material has been identified with the low albedo
asteroids, but it is still a matter of debate whether the delivery of the dark
material is associated with a few large impact events, to micrometeorites or to
the continuous, secular flux of impactors on Vesta. The continuous flux
scenario predicts that a significant fraction of the exogenous material
accreted by Vesta should be due to non-dark impactors likely analogous to
ordinary chondrites, which instead represent only a minor contaminant in the
HED meteorites. We explored the continuous flux scenario and its implications
for the composition of the vestan regolith, taking advantage of the data from
the Dawn mission and the HED meteorites. We used our model to show that the
stochastic events scenario and the micrometeoritic flux scenario are natural
consequences of the continuous flux scenario. We then used the model to
estimate the amounts of dark and hydroxylate materials delivered on Vesta since
the LHB and we showed how our results match well with the values estimated by
the Dawn mission. We used our model to assess the amount of Fe and siderophile
elements that the continuous flux of impactors would mix in the vestan
regolith: concerning the siderophile elements, we focused our attention on the
role of Ni. The results are in agreement with the data available on the Fe and
Ni content of the HED meteorites and can be used as a reference frame in future
studies of the data from the Dawn mission and of the HED meteorites. Our model
cannot yet provide an answer to the fate of the missing non-carbonaceous
contaminants, but we discuss possible reasons for this discrepancy.Comment: 31 pages, 7 figures, 4 tables. Accepted for publication on the
journal ICARUS, "Dark and Bright Materials on Vesta" special issu
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