2,316 research outputs found
The Origin of Enhanced Activity in the Suns of M67
We report the results of the analysis of high resolution photospheric line
spectra obtained with the UVES instrument on the VLT for a sample of 15
solar-type stars selected from a recent survey of the distribution of H and K
chromospheric line strengths in the solar-age open cluster M67. We find upper
limits to the projected rotation velocities that are consistent with solar-like
rotation (i.e., v sini ~< 2-3 km/s) for objects with Ca II chromospheric
activity within the range of the contemporary solar cycle. Two solar-type stars
in our sample exhibit chromospheric emission well in excess of even solar
maximum values. In one case, Sanders 1452, we measure a minimum rotational
velocity of vsini = 4 +/- 0.5 km/s, or over twice the solar equatorial
rotational velocity. The other star with enhanced activity, Sanders 747, is a
spectroscopic binary. We conclude that high activity in solar-type stars in M67
that exceeds solar levels is likely due to more rapid rotation rather than an
excursion in solar-like activity cycles to unusually high levels. We estimate
an upper limit of 0.2% for the range of brightness changes occurring as a
result of chromospheric activity in solar-type stars and, by inference, in the
Sun itself. We discuss possible implications for our understanding of angular
momentum evolution in solar-type stars, and we tentatively attribute the rapid
rotation in Sanders 1452 to a reduced braking efficiency.Comment: accepted by Ap
Relations entre contrôle de la source en mémoire épisodique et fonctionnement exécutif dans le vieillissement normal
Les travaux sur le vieillissement cognitif normal suggèrent l\u27existence de difficultés pour le contrôle de la source en mémoire épisodique, en lien avec une diminution du contrôle exécutif. Néanmoins, les approches utilisées dans la littérature ne permettent pas de savoir si toutes les dimensions du contrôle de la source se dégradent avec l\u27âge, ni de savoir si certains processus exécutifs sont plus impliqués que d\u27autres dans la diminution du contrôle de la source. Dans ce travail, nous avons étudié l\u27effet de l\u27âge sur le contrôle de la source à partir de tâches simples et originales évaluant le contrôle interne, le contrôle externe et le contrôle de la réalité. Plusieurs mécanismes exécutifs ont aussi été évalués. Les tâches ont été proposées à 24 participants jeunes et 22 participants âgés en bonne santé appariés par le sexe et le niveau de vocabulaire au Mill Hill. Les résultats ont montré une détérioration du contrôle de la source en mémoire épisodique, surtout pour le contrôle externe, chez les participants âgés. Ce déclin était très lié à la diminution des performances au test de Stroop. Il semblerait donc que le vieillissement normal s\u27accompagne d\u27une baisse assez globale du contrôle de la source en mémoire épisodique et que cette baisse s\u27expliquerait principalement par l\u27altération des compétences inhibitrices
Blind fluorescence structured illumination microscopy: A new reconstruction strategy
In this communication, a fast reconstruction algorithm is proposed for
fluorescence \textit{blind} structured illumination microscopy (SIM) under the
sample positivity constraint. This new algorithm is by far simpler and faster
than existing solutions, paving the way to 3D and/or real-time 2D
reconstruction.Comment: submitted to IEEE ICIP 201
Benzene formation in the inner regions of protostellar disks
Benzene (c-C6H6) formation in the inner 3 AU of a protostellar disk can be
efficient, resulting in high abundances of benzene in the midplane region. The
formation mechanism is different to that found in interstellar clouds and in
protoplanetary nebulae, and proceeds mainly through the reaction between allene
(C3H4) and its ion. This has implications for PAH formation, in that some
fraction of PAHs seen in the solar system could be native rather than inherited
from the interstellar medium.Comment: 9 pages, 2 colour figures, to be published in the Astrophysical
Journal Letter
Internal Dust Correction Factors for Star Formation Rates Derived for Dusty \HII Regions and Starburst Galaxies
Star formation rates in galaxies are frequently estimated using the Balmer
line fluxes. However, these can be systematically underestimated because dust
competes for the absorption of Lyman continuum photons in the ionized gas. Here
we present theoretical correction factors in a simple analytic form. T These
factors scale as the product of the ionization parameter, , and the
nebular O/H abundance ratio, both of which can now be derived from the
observation of bright nebular line ratios. The correction factors are only
somewhat dependent upon the photoelectron production by grains, but are very
sensitive to the presence of complex PAH-like carbonaceous molecules in the
ionized gas, providing that these can survive in such an environment.Comment: 13 pages, 1 figures, Accepted for publication in ApJ. (Feb 1, 2003
Dual Signaling System with an Extended-Tetrathiafulvalene–Phenanthroline Dyad Acting as an Electrooptical Cation Chemosensor
A tetrathiafulvalene donor has been annulated to 2,3-di(1H-2-pyrrolyl)quinoxaline affording a new chemosensor 1, which shows a unique optical selectivity and reactivity for the fluoride ion over other anions in CH2Cl2 leading to a colorimetric response. Electrochemical polymerization of 1 occurred in the presence of fluoride
Iterations of a Riddle: The Reconciliation of Individual and Collective Interests
Scholarships & Prizes Office. University of Sydne
Stable Photoinduced Separated Charge State in Viologen Halometallates: Some Key Parameters
With the aim to define key parameters causing the photochromic properties of (MV)[Bi2Cl8] and (MV)(4)[Bi6Cl26] (MV2+, methylviologen; 1,1-dimethyl-4,4-bipyridinium), the effects of substituting Bi by Sb, Cl by Br, or MV2+ by MOV2+ (1,1-dimethoxy-4,4-bipyridinium) or MeMOV2+ (1-methyl-1-methoxy-4,4-bipyridinium) on the photoinduced charge transfer properties of such viologen halometallates are explored. It appears that only salts containing chlorobismuthate anions undergo a color change upon UV irradiation and that the nature of viologen entities has a key role in the process. We also suggest that a key parameter for observing the stable photoinduced separated charge state in chlorobismuthate viologen hybrids is a high chloride/viologen ratio, rather than the size of the anionic oligomer, as observed in the previously reported unique series (MV)((2n+2)/2)[Bi2nCl8n+2]
On the missing 2175 Angstroem-bump in the Calzetti extinction curve
The aim of the paper is to give a physical explanation of the absence of the
feature in the Calzetti extinction curve. We analyze the dust attenuation of a
homogeneous source seen through a distant inhomogeneous distant screen. The
inhomogeneities are described through an idealized isothermal turbulent medium
where the probability distribution function (PDF) of the column density is
log-normal. In addition it is assumed that below a certain critical column
density the carriers of the extinction bump at 2175 Angstroem are being
destroyed by the ambient UV radiation field. Turbulence is found to be a
natural explanation not only of the flatter curvature of the Calzetti
extinction curve but also of the missing bump provided the critical column
density is N_H >= 10^21 cm^-2. The density contrast needed to explain both
characteristics is well consistent with the Mach number of the cold neutral
medium of our own Galaxy which suggests a density contrast sigma_(rho/) 6.Comment: 6 pages, 6 figures accepted for publication in A&A, section
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