3,313 research outputs found
Detecting individual gravity modes in the Sun: Chimera or reality?
Over the past 15 years, our knowledge of the interior of the Sun has
tremendously progressed by the use of helioseismic measurements. However, to go
further in our understanding of the solar core, we need to measure gravity (g)
modes. Thanks to the high quality of the Doppler-velocity signal measured by
GOLF/SoHO, it has been possible to unveil the signature of the asymptotic
properties of the solar g modes, thus obtaining a hint of the rotation rate in
the core. However, the quest for the detection of individual g modes is not yet
over. In this work, we apply the latest theoretical developments to guide our
research using GOLF velocity time series. In contrary to what was thought till
now, we are maybe starting to identify individual low-frequency g modes...Comment: Highlight of Astronomy (HoA) proceedings of the JD-11, IAU 2009. 2
pages, 1 figur
A 4 Gyr M-dwarf Gyrochrone from CFHT/MegaPrime Monitoring of the Open Cluster M67
We present stellar rotation periods for late K- and early M-dwarf members of
the 4 Gyr old open cluster M67 as calibrators for gyrochronology and tests of
stellar spin-down models. Using Gaia EDR3 astrometry for cluster membership and
Pan-STARRS (PS1) photometry for binary identification, we build this set of
rotation periods from a campaign of monitoring M67 with the
Canada-France-Hawaii Telescope's MegaPrime wide field imager. We identify 1807
members of M67, of which 294 are candidate single members with significant
rotation period detections. Moreover, we fit a polynomial to the period versus
color-derived effective temperature sequence observed in our data. We find that
the rotation of very cool dwarfs can be explained by a simple solid-body
spin-down between 2.7 and 4 Gyr. We compare this rotational sequence to the
predictions of gyrochronological models and find that the best match is
Skumanich-like spin-down, P_rot \propto t^0.62, applied to the sequence of
Ruprecht 147. This suggests that, for spectral types K7-M0 with near-solar
metallicity, once a star resumes spinning down, a simple Skumanich-like is
sufficient to describe their rotation evolution, at least through the age of
M67. Additionally, for stars in the range M1-M3, our data show that spin-down
must have resumed prior to the age of M67, in conflict with predictions of the
latest spin-down models.Comment: 21 pages, 16 figures, Accepted for publication by Ap
Human Mars Entry, Descent and Landing Architecture Study: Rigid Decelerators
Several technology investments are required to develop Mars human scale Entry, Descent, and Landing (EDL) systems. Studies play the critical role of identifying the most feasible technical paths and high payoff investments. The goal of NASA's Entry, Descent and Landing Architecture Study is to inform those technology investments. In Phase 1 of the study, a point design for one lifting-body-like rigid decelerator vehicle, was developed. In Phase 2, a capsule concept was also considered to determine how it accommodated the human mission requirements. This paper summarizes the concept of operations for both rigid vehicles to deliver a 20-metric ton (t) payload to the surface of Mars. Details of the vehicle designs and flight performance are presented along with a packaging, mass sizing, and a launch vehicle fairing assessment. Finally, recommended technology investments based on the analysis of the rigid vehicles are provided
Studying the dosage-dependent influence of hydrophobic alkoxysilane/siloxane admixtures on the performance of repair micromortars
Cracks sealing in deteriorated concrete often requires the use of repair mortars of compatible composition, good adhesion to the substrate and free of shrinkage. Even where repair mortars properly bond to the substrate, that interface affords a preferred pathway for water ingress. Hydrophobic repair micromortars designed to seal cracks via injection might be one way to solve that problem. This article analyses the effect of adding three hydrophobic products (generic labelled as UCA-TP) comprising silica oligomers, n-octylamine (a surfactant) and polydimethylsiloxane (PDMS) in different proportions (10 wt% of PDMS :UCA-TP10, 28 wt% of PDMS: UCA-TP28 and 56 wt% of PDMS: UCA-TP56) to a fresh repair micromortar. The incorporation of UCA-TP products hastened the early hydration kinetics of repair micromortars, and, at the same time, after 7 days of hydration, declined the total heat released (the higher is the content of UCA-TP product and its proportion of PDMS the lower is the heat of hydration. The inclusion of the hydrophobic products substantially modified the repair micomortar wetting and water transport properties, by inducing a hydrophobic behavior (contact angle >100 degrees) and decreasing water absorption by >60%. Although adding those products to the repair micromortars increased porosity and lowered mechanical performance, 28 d compressive strength was consistently >50 MPa, a value that compared well to the original substrate. Simulated cracks were very effectively sealed by the repair micromortars
Sildenafil restores cognitive function without affecting β-amyloid burden in a mouse model of Alzheimer's disease
Abstract
BACKGROUND AND PURPOSE:
Inhibitors of phosphodiesterase 5 (PDE5) affect signalling pathways by elevating cGMP, which is a second messenger involved in processes of neuroplasticity. In the present study, the effects of the PDE5 inhibitor, sildenafil, on the pathological features of Alzheimer's disease and on memory-related behaviour were investigated.
EXPERIMENTAL APPROACH:
Sildenafil was administered to the Tg2576 transgenic mouse model of Alzheimer's disease and to age-matched negative littermates (controls). Memory function was analysed using the Morris water maze test and fear conditioning tasks. Biochemical analyses were performed in brain lysates from animals treated with saline or with sildenafil.
KEY RESULTS:
Treatment of aged Tg2576 animals with sildenafil completely reversed their cognitive impairment. Such changes were accompanied in the hippocampus by a reduction of tau hyperphosphorylation and a decrease in the activity of glycogen synthase kinase 3β (GSK3β) and of cyclin-dependent kinase 5 (CDK5) (p25/p35 ratio). Moreover, sildenafil also increased levels of brain-derived neurotrophic factor (BDNF) and the activity-regulated cytoskeletal-associated protein (Arc) in the hippocampus without any detectable modification of brain amyloid burden.
CONCLUSIONS AND IMPLICATIONS:
Sildenafil improved cognitive functions in Tg2576 mice and the effect was not related to changes in the amyloid burden. These data further strengthen the potential of sildenafil as a therapeutic agent for Alzheimer's disease
Oxygen abundances in unevolved metal-poor stars from near-UV OH lines
We have performed a detailed oxygen abundance analysis of 23 metal-poor
(-3.0<[Fe/H]<-0.3) unevolved halo stars and one giant through the OH bands in
the near UV, using high-resolution echelle spectra. Oxygen is found to be
overabundant with respect to iron in these stars, with the [O/Fe] ratio
increasing from 0.6 to 1 between [Fe/H]=-1.5 and -3.0. The behavior of the
oxygen overabundance with respect to [Fe/H] is similar to that seen in previous
works based on OI IR triplet data (Abia and Rebolo 1989; Tomkin et al. 1992;
Cavallo, Pilachowski, and Rebolo 1997). Contrary to the previously accepted
picture, our oxygen abundances, derived from low-excitation OH lines, agree
well with those derived from high-excitation lines of the triplet. For nine
stars in common with Tomkin et al. we obtain a mean difference of 0.00+/-0.11
dex with respect to the abundances determined from the triplet using the same
stellar parameters and model photospheres. For four stars in our sample we have
found measurements of the [OI] 6300 A line in the literature, from which we
derive oxygen abundances consistent (average difference 0.09 dex) with those
based on OH lines, showing that the long standing controversy between oxygen
abundances from forbidden and permitted lines in metal-poor unevolved stars can
be resolved. Our new oxygen abundances show a smooth extension of the
Edvardsson et al.'s (1993) [O/Fe] versus metallicity curve to much lower
abundances, with a slope -0.31+/- 0.11 (taking into account the error bars in
both oxygen abundances and metallicities) in the range -3<[Fe/H]<-1.Comment: 17 pages, 8 figures, 3 table
Investigating the properties of granulation in the red giants observed by Kepler
More than 1000 red giants have been observed by NASA/Kepler mission during a
nearly continuous period of ~ 13 months. The resulting high-frequency
resolution (< 0.03 muHz) allows us to study the granulation parameters of these
stars. The granulation pattern results from the convection motions leading to
upward flows of hot plasma and downward flows of cooler plasma. We fitted
Harvey-like functions to the power spectra, to retrieve the timescale and
amplitude of granulation. We show that there is an anti-correlation between
both of these parameters and the position of maximum power of acoustic modes,
while we also find a correlation with the radius, which agrees with the theory.
We finally compare our results with 3D models of the convection.Comment: 4 pages, 1 figure. To appear in the ASP proceedings of "The 61st
Fujihara seminar: Progress in solar/stellar physics with helio- and
asteroseismology", 13th-17th March 2011, Hakone, Japa
Phosphoethanolamine and omega-3 in patients with asthma
The effect of omega-3 (n-3) in asthma has been inconclusive. One explanation for it may be the low incorporation of these fatty acids in clinical studies. Phosphoethanolamine (PEtn) can increase the synthesis of phosphatidylethanolamine, which can, in turn, increase the incorporation of n-3 in cell membranes. The aim of this study is to evaluate the effect of synthetic PEtn in patients with asthma who are receiving n-3. This randomized, double-blind, placebo-controlled study was carried out over a two month period by using spirometry, the Asthma Control Test questionnaire (ACT) and medicine intake. Forty-one patients with asthma were studied. Twenty-one patients received n-3 daily (1.080 mg of EPA, 720 mg of DHA) and 800 mg of PEtn (PEtn group), and twenty patients received the same doses of n-3 and placebo (control group). All patients continued receiving their conventional treatment for asthma. The hospital ethics committee approved the study. Five patients of each group required systemic corticosteroids, being the total consumption, smaller in the PEtn group (127.4 mg of prednisone/patient versus 416.0 mg of prednisone/patient in the control group, p-value = 0.0269). There were no significant differences in the changing of ATC and FEV1, as well as in the intake of formoterol or budesonide between the groups. In this study, patients who received phosphoethanolamine and omega-3 needed a smaller dose of systemic corticosteroid for asthma control than patients who only received omega-3. However, as the trial was conducted on a small scale, more studies are necessary
Boron in Very Metal-Poor Stars
We have observed the B I 2497 A line to derive the boron abundances of two
very metal-poor stars selected to help in tracing the origin and evolution of
this element in the early Galaxy: BD +23 3130 and HD 84937. The observations
were conducted using the Goddard High Resolution Spectrograph on board the
Hubble Space Telescope. A very detailed abundance analysis via spectral
synthesis has been carried out for these two stars, as well as for two other
metal-poor objects with published spectra, using both Kurucz and OSMARCS model
photospheres, and taking into account consistently the NLTE effects on the line
formation. We have also re-assessed all published boron abundances of old disk
and halo unevolved stars. Our analysis shows that the combination of high
effective temperature (Teff > 6000 K, for which boron is mainly ionized) and
low metallicity ([Fe/H]<-1) makes it difficult to obtain accurate estimates of
boron abundances from the B I 2497 A line. This is the case of HD 84937 and
three other published objects (including two stars with [Fe/H] ~ -3), for which
only upper limits can be established. BD +23 3130, with [Fe/H] ~ -2.9 and
logN(B)_NLTE=0.05+/-0.30, appears then as the most metal-poor star for which a
firm measurement of the boron abundance presently exists. The evolution of the
boron abundance with metallicity that emerges from the seven remaining stars
with Teff < 6000 K and [Fe/H]<-1, for which beryllium abundances were derived
using the same stellar parameters, shows a linear increase with a slope ~ 1.
Furthermore, the B/Be ratio found is constant at a value ~ 20 for stars in the
range -3<[Fe/H]<-1. These results point to spallation reactions of ambient
protons and alpha particles with energetic particles enriched in CNO as the
origin of boron and beryllium in halo stars.Comment: 38 pages, 11 Encapsulated Postscript figures (included), uses
aaspp4.sty. Accepted for publication in The Astrophysical Journal. The
preprint is also available at: http://www.iac.es/publicaciones/preprints.htm
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