1,224 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
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Investigations of biomimetic light energy harvesting pigments
This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at Los Alamos National Laboratory (LANL). Nature uses chlorophyll and other porphyrinic pigments to capture and transfer light energy as a preliminary step in photosynthesis. The design of synthetic assemblies of light harvesting and energy directing pigments has been explored through synthesis and characterization of porphyrin oligomers. In this project, pigment electronic and vibrational structures have been explored by electrochemistry and dynamic and static optical measurements. Transient absorption data reveal energy transfer between pigments with lifetimes on the order of 20--200 picoseconds, while Raman data reveal that the basic porphyrin core structure is unperturbed relative to the individual monomer units. These two findings, along with an extensive series of experiments on the oxidized oligomers, reveal that coupling between the pigments is fundamentally weak, but sufficient to allow facile energy transfer as the predominant excited state process. Modeling of the expected quantum yields for energy transfer within a variety of arrays was accomplished, thereby providing a tool to guide synthetic goals
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
The debris disk host star HD 61005: a member of the Argus Association?
HD 61005 is a nearby young solar type star that shows a large infrared excess
due to a debris disk. The disk has been recently imaged from ground and space,
with indications of several components. Some characteristics of the disk
suggest the presence of planetary companions around the star, that remain
undetected in deep adaptive optics imaging. For a better understanding of the
system we aim to refine the determination of the stellar parameters, with
emphasis on the stellar age and system orientation. We used ASAS and Hipparcos
photometry and FEROS spectra to determine the rotation period, radial and
rotational velocity, chromospheric emission, effective temperature, and
chemical composition. We find no indication of any misalignment between the
star rotation axis and the disk. The standard age calibrations applied to
several indicators yield an age close to that of the Pleiades (120 Myr);
however the kinematic properties strongly support its membership in the younger
(40 Myr) Argus association, which also includes the IC 2391 open cluster.
Detailed comparison of the properties of HD 61005 and IC 2391 members shows
that the characteristics of HD 61005 are compatible with membership to the
Argus association, once its rather slow rotation is taken into account, because
lithium and other age indicators are somewhat correlated with stellar rotation
at a fixed age. We also identify systematic differences between the field and
cluster population of the Argus association, which are probably selection
effects, so we suggest that additional members with slower rotation and lower
activity level are waiting to be identified.Comment: A&A, in press, 13 pages, 11 figure
Low-mass members of the young cluster IC 4665 and pre-main-sequence lithium depletion
We have used fibre spectroscopy to establish cluster membership and examine
pre-main-sequence (PMS) lithium depletion for low-mass stars (spectral types F
to M) in the sparse young (~30 Myr) cluster IC 4665. We present a filtered
candidate list of 40 stars that should contain 75 per cent of single cluster
members with V of 11.5 to 18 in the central square degree of the cluster.
Whilst F- and G-type stars in IC 4665 have depleted little or no lithium, the
K- and early M-type stars have depleted more Li than expected when compared
with similar stars in other clusters of known age. An empirical age estimate
based on Li-depletion among the late-type stars of IC 4665 would suggest it is
older than 100 Myr. This disagrees entirely with ages determined either from
the nuclear turn-off, from isochronal matches to low-mass stars or from the
re-appearance of lithium previously found in much lower mass stars (the
``lithium depletion boundary''). We suggest that other parameters besides age,
perhaps composition or rotation, are very influential in determining the degree
of PMS Li-depletion in stars with M greater than 0.5 Msun. Further work is
required to identify and assess the effects of these additional parameters,
particularly to probe conditions at the interface between the sub-photospheric
convection zone and developing radiative core. Until then, PMS Li depletion in
F- to early M-type stars cannot be confidently used as a precise age indicator
in young clusters, kinematic groups or individual field stars.Comment: Accepted for publication in MNRA
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
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