1,054 research outputs found
SARS-CoV-2 and interferon blockade
© 2020, The Author(s). The response to viral infection generally includes an activation of the adaptive immune response to produce cytotoxic T cells and neutralizing antibodies. We propose that SARS-CoV-2 activates the innate immune system through the renin-angiotensin and kallikrein-bradykinin pathways, blocks interferon production and reduces an effective adaptive immune response. This model has therapeutic implications
Rotation periods of late-type stars in the young open cluster IC 2602
We present the results of a monitoring campaign aimed at deriving rotation
periods for a representative sample of stars in the young (30 Myr) open cluster
IC 2602. Rotation periods were derived for 29 of 33 stars monitored. The
periods derived range from 0.2d (one of the shortest known rotation periods of
any single open cluster star) to about 10d (which is almost twice as long as
the longest period previously known for a cluster of this age). We are able to
confirm 8 previously known periods and derive 21 new ones, delineating the long
period end of the distribution. Despite our sensitivity to longer periods, we
do not detect any variables with periods longer than about 10d. The combination
of these data with those for IC 2391, an almost identical cluster, leads to the
following conclusions:
1) The fast rotators in a 30 Myr cluster are distributed across the entire
0.5 < B-V < 1.6 color range.
2) 6 stars in our sample are slow rotators, with periods longer than 6d.
3) The amplitude of variability depends on both the color and the period. The
dependence on the latter might be important in understanding the selection
effects in the currently available rotation period database and in planning
future observations.
4) The interpretation of these data in terms of theoretical models of
rotating stars suggests both that disk-interaction is the norm rather than the
exception in young stars and that disk-locking times range from zero to a few
Myr.Comment: 23 pages, 8 figures, accepted for publication in the Astrophysical
Journa
Will the recently approved LARES mission be able to measure the Lense-Thirring effect at 1%?
After the approval by the Italian Space Agency of the LARES satellite, which
should be launched at the end of 2009 with a VEGA rocket and whose claimed goal
is a about 1% measurement of the general relativistic gravitomagnetic
Lense-Thirring effect in the gravitational field of the spinning Earth, it is
of the utmost importance to reliably assess the total realistic accuracy that
can be reached by such a mission. The observable is a linear combination of the
nodes of the existing LAGEOS and LAGEOS II satellites and of LARES able to
cancel out the impact of the first two even zonal harmonic coefficients of the
multipolar expansion of the classical part of the terrestrial gravitational
potential representing a major source of systematic error. While LAGEOS and
LAGEOS II fly at altitudes of about 6000 km, LARES will be placed at an
altitude of 1450 km. Thus, it will be sensitive to much more even zonals than
LAGEOS and LAGEOS II. Their corrupting impact \delta\mu has been evaluated by
using the standard Kaula's approach up to degree L=70 along with the sigmas of
the covariance matrices of eight different global gravity solutions
(EIGEN-GRACE02S, EIGEN-CG03C, GGM02S, GGM03S, JEM01-RL03B, ITG-Grace02s,
ITG-Grace03, EGM2008) obtained by five institutions (GFZ, CSR, JPL, IGG, NGA)
with different techniques from long data sets of the dedicated GRACE mission.
It turns out \delta\mu about 100-1000% of the Lense-Thirring effect. An
improvement of 2-3 orders of magnitude in the determination of the high degree
even zonals would be required to constrain the bias to about 1-10%.Comment: Latex, 15 pages, 1 table, no figures. Final version matching the
published one in General Relativity and Gravitation (GRG
Conservative evaluation of the uncertainty in the LAGEOS-LAGEOS II Lense-Thirring test
We deal with the test of the general relativistic gravitomagnetic
Lense-Thirring effect currently ongoing in the Earth's gravitational field with
the combined nodes \Omega of the laser-ranged geodetic satellites LAGEOS and
LAGEOS II.
One of the most important source of systematic uncertainty on the orbits of
the LAGEOS satellites, with respect to the Lense-Thirring signature, is the
bias due to the even zonal harmonic coefficients J_L of the multipolar
expansion of the Earth's geopotential which account for the departures from
sphericity of the terrestrial gravitational potential induced by the
centrifugal effects of its diurnal rotation. The issue addressed here is: are
the so far published evaluations of such a systematic error reliable and
realistic? The answer is negative. Indeed, if the difference \Delta J_L among
the even zonals estimated in different global solutions (EIGEN-GRACE02S,
EIGEN-CG03C, GGM02S, GGM03S, ITG-Grace02, ITG-Grace03s, JEM01-RL03B, EGM2008,
AIUB-GRACE01S) is assumed for the uncertainties \delta J_L instead of using
their more or less calibrated covariance sigmas \sigma_{J_L}, it turns out that
the systematic error \delta\mu in the Lense-Thirring measurement is about 3 to
4 times larger than in the evaluations so far published based on the use of the
sigmas of one model at a time separately, amounting up to 37% for the pair
EIGEN-GRACE02S/ITG-Grace03s. The comparison among the other recent GRACE-based
models yields bias as large as about 25-30%. The major discrepancies still
occur for J_4, J_6 and J_8, which are just the zonals the combined
LAGEOS/LAGOES II nodes are most sensitive to.Comment: LaTex, 12 pages, 12 tables, no figures, 64 references. To appear in
Central European Journal of Physics (CEJP
Major depression, fibromyalgia and labour force participation: A population-based cross-sectional study
BACKGROUND: Previous studies have documented an elevated frequency of depressive symptoms and disorders in fibromyalgia, but have not examined the association between this comorbidity and occupational status. The purpose of this study was to describe these epidemiological associations using a national probability sample. METHODS: Data from iteration 1.1 of the Canadian Community Health Survey (CCHS) were used. The CCHS 1.1 was a large-scale national general health survey. The prevalence of major depression in subjects reporting that they had been diagnosed with fibromyalgia by a health professional was estimated, and then stratified by demographic variables. Logistic regression models predicting labour force participation were also examined. RESULTS: The annual prevalence of major depression was three times higher in subjects with fibromyalgia: 22.2% (95% CI 19.4 – 24.9), than in those without this condition: 7.2% (95% CI 7.0 – 7.4). The association persisted despite stratification for demographic variables. Logistic regression models predicting labour force participation indicated that both conditions had an independent (negative) effect on labour force participation. CONCLUSION: Fibromyalgia and major depression commonly co-occur and may be related to each other at a pathophysiological level. However, each syndrome is independently and negatively associated with labour force participation. A strength of this study is that it was conducted in a large probability sample from the general population. The main limitations are its cross-sectional nature, and its reliance on self-reported diagnoses of fibromyalgia
LARES/WEBER-SAT and the equivalence principle
It has often been claimed that the proposed Earth artificial satellite
LARES/WEBER-SAT-whose primary goal is, in fact, the measurement of the general
relativistic Lense-Thirring effect at a some percent level-would allow to
greatly improve, among (many) other things, the present-day (10^-13) level of
accuracy in testing the equivalence principle as well. Recent claims point
towards even two orders of magnitude better, i.e. 10^-15. In this note we show
that such a goal is, in fact, unattainable by many orders of magnitude being,
instead, the achievable level of the order of 10^-9.Comment: LaTex, 4 pages, no figures, no tables, 26 references. Proofs
corrections included. To appear in EPL (Europhysics Letters
Near and Mid-IR Photometry of the Pleiades, and a New List of Substellar Candidate Members
We make use of new near and mid-IR photometry of the Pleiades cluster in
order to help identify proposed cluster members. We also use the new photometry
with previously published photometry to define the single-star main sequence
locus at the age of the Pleiades in a variety of color-magnitude planes.
The new near and mid-IR photometry extend effectively two magnitudes deeper
than the 2MASS All-Sky Point Source catalog, and hence allow us to select a new
set of candidate very low mass and sub-stellar mass members of the Pleiades in
the central square degree of the cluster. We identify 42 new candidate members
fainter than Ks =14 (corresponding to 0.1 Mo). These candidate members should
eventually allow a better estimate of the cluster mass function to be made down
to of order 0.04 solar masses.
We also use new IRAC data, in particular the images obtained at 8 um, in
order to comment briefly on interstellar dust in and near the Pleiades. We
confirm, as expected, that -- with one exception -- a sample of low mass stars
recently identified as having 24 um excesses due to debris disks do not have
significant excesses at IRAC wavelengths. However, evidence is also presented
that several of the Pleiades high mass stars are found to be impacting with
local condensations of the molecular cloud that is passing through the Pleiades
at the current epoch.Comment: Accepted to ApJS; data tables and embedded-figure version available
at http://spider.ipac.caltech.edu/staff/stauffer/pleiades07
The chromospheric emission of solar-type stars in the young open clusters IC 2391 and IC 2602
In this paper we present chromospheric emission levels of the solar-type
stars in the young open clusters IC 2391 and IC 2602. High resolution
spectroscopic data were obtained for over 50 F, G, and K stars from these
clusters over several observing campaigns using the University College London
Echelle Spectrograph on the 3.9-m Anglo-Australian Telescope. Unlike older
clusters, the majority (28/52) of the solar-type stars in the two clusters are
rapid-rotators (vsini > 20 km/s) with five of the stars being classified as
ultra-rapid rotators (vsini > 100 km/s). The emission levels in the Calcium
infrared triplet lines were then used as a measure of the chromospheric
activity of the stars. When plotted against Rossby number (NR) the star's
chromospheric emission levels show a plateau in the emission for Log(NR) < -1.1
indicating chromospheric saturation similar to the coronal saturation seen in
previously observed X-ray emission from the same stars. However, unlike the
coronal emission, the chromospheric emission of the stars show little evidence
of a reduction in emission (i.e. supersaturation) for the ultra-rapid rotators
in the clusters. Thus we believe that coronal supersaturation is not the result
of an overall decrease in magnetic dynamo efficiency for ultra-rapid rotators.Comment: 19 pages, 14 figures, Landscape tables in separate tex file, Accepted
by MNRA
Accretion-related properties of Herbig Ae/Be stars. Comparison with T Tauris
We look for trends relating the mass accretion rate (Macc) and the stellar
ages (t), spectral energy distributions (SEDs), and disk masses (Mdisk) for a
sample of 38 HAeBe stars, comparing them to analogous correlations found for
classical T Tauri stars. Our goal is to shed light on the timescale and
physical processes that drive evolution of intermediate-mass pre-main sequence
objects.
Macc shows a dissipation timescale \tau = 1.3^{+1.0}_{-0.5} Myr from an
exponential law fit, while a power law yields Macc(t) \propto t^{-\eta}, with
\eta = 1.8^{+1.4}_{-0.7}. This result is based on our whole HAeBe sample (1-6
Msun), but the accretion rate decline most probably depends on smaller stellar
mass bins. The near-IR excess is higher and starts at shorter wavelengths (J
and H bands) for the strongest accretors. Active and passive disks are roughly
divided by 2 x 10^{-7} Msun/yr. The mid-IR excess and the SED shape from the
Meeus et al. classification are not correlated with Macc. We find Macc \propto
Mdisk^{1.1 +- 0.3}. Most stars in our sample with signs of inner dust
dissipation typically show accretion rates ten times lower and disk masses
three times smaller than the remaining objects.
The trends relating Macc with the near-IR excess and Mdisk extend those for T
Tauri stars, and are consistent with viscous disk models. The differences in
the inner gas dissipation timescale, and the relative position of the stars
with signs of inner dust clearing in the Macc-Mdisk plane, could be suggesting
a slightly faster evolution, and that a different process - such as
photoevaporation - plays a more relevant role in dissipating disks in the HAeBe
regime compared to T Tauri stars. Our conclusions must consider the mismatch
between the disk mass estimates from mm fluxes and the disk mass estimates from
accretion, which we also find in HAeBe stars.Comment: 11 pages, 7 figures, 1 appendix. Accepted in A&
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