2,461 research outputs found
Angular Momentum Evolution of Stars in the Orion Nebula Cluster
(Abridged) We present theoretical models of stellar angular momentum
evolution from the Orion Nebula Cluster (ONC) to the Pleiades and the Hyades.
We demonstrate that observations of the Pleiades and Hyades place tight
constraints on the angular momentum loss rate from stellar winds. The observed
periods, masses and ages of ONC stars in the range 0.2--0.5 M, and the
loss properties inferred from the Pleiades and Hyades stars, are then used to
test the initial conditions for stellar evolution models. We use these models
to estimate the distribution of rotational velocities for the ONC stars at the
age of the Pleiades (120 Myr). The modeled ONC and observed Pleiades
distributions of rotation rates are not consistent if only stellar winds are
included. In order to reconcile the observed loss of angu lar momentum between
these two clusters, an extrinsic loss mechanism such as protostar-accretion
disk interaction is required. Our model, which evolves the ONC stars with a
mass dependent saturation threshold normalized such that at 0.5 \m, and which includes a distribution of disk lifetimes
that is uniform over the range 0--6 Myr, is consistent with the Pleiades. This
model for disk-locking lifetimes is also consistent with inferred disk
lifetimes from the percentage of stars with infrared excesses observed in young
clusters. Different models, using a variety of initial period distributions and
different maximum disk lifetimes, are also compared to the Pleiades. For
disk-locking models that use a uniform distribution of disk lifetimes over the
range 0 to , the acceptable range of the maximum lifetime is Myr.Comment: 21 pages, 7 figures, submitted to Ap
From Jeopardy! to Jaundice: The Medical Liability Implications of Dr. Watson and Other Artificial Intelligence Systems
In this article, the author offers information on need of reframing the laws that can encourage innovative technology\u27s growth to overcome the healthcare shortages and enhance the quality of patients care. It suggests that an approach of law for assessing the liability against artificial intelligence systems and robotics for advanced health care is required in the U.S
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
Structure-function relationships of the polypyrimidine tract binding protein
Abstract.: The polypyrimidine tract binding protein (PTB) is a 58-kDa RNA binding protein involved in multiple aspects of mRNA metabolism including splicing regulation, polyadenylation, 3′end formation, internal ribosomal entry site-mediated translation, RNA localization and stability. PTB contains four RNA recognition motifs (RRMs) separated by three linkers. In this review we summarize structural information on PTB in solution that has been gathered during the past 7 years using NMR spectroscopy and small-angle X-ray scattering. The structures of all RRMs of PTB in their free state and in complex with short pyrimidine tracts, as well as a structural model of PTB RRM2 in complex with a peptide, revealed unusual structural features that provided new insights into the mechanisms of action of PTB in the different processes of RNA metabolism and in particular splicing regulatio
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
Communiquer avec une personne atteinte de la maladie d’Alzheimer : Apports des neurosciences cognitives et affectives
Modelling the effect of carbon on deformation behaviour of twinning induced plasticity steels
In this article, a physical model describing the deformation behaviour of Twinning Induced Plasticity(TWIP) steels has been extended to include the effect of carbon content. The experimental validation and the analysis show that carbon mainly controls the maximum number of dislocations piled up at the twin boundary, resulting in the increase of back-stresses (i.e. kinematic hardening) and therefore the work hardening rate. This explanation seems to be in agreement with recent TEM observations. © The Author(s) 2011. This article is published with open access at Springerlink.com. © Springer Science+Business Media, LLC 2011.published_or_final_versionSpringer Open Choice, 21 Feb 201
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