16,960 research outputs found
The Extreme Ultraviolet and X-Ray Sun in Time: High-Energy Evolutionary Tracks of a Solar-Like Star
Aims. We aim to describe the pre-main sequence and main-sequence evolution of
X-ray and extreme-ultaviolet radiation of a solar mass star based on its
rotational evolution starting with a realistic range of initial rotation rates.
Methods. We derive evolutionary tracks of X-ray radiation based on a
rotational evolution model for solar mass stars and the rotation-activity
relation. We compare these tracks to X-ray luminosity distributions of stars in
clusters with different ages.
Results. We find agreement between the evolutionary tracks derived from
rotation and the X-ray luminosity distributions from observations. Depending on
the initial rotation rate, a star might remain at the X-ray saturation level
for very different time periods, approximately from 10 Myr to 300 Myr for slow
and fast rotators, respectively.
Conclusions. Rotational evolution with a spread of initial conditions leads
to a particularly wide distribution of possible X-ray luminosities in the age
range of 20 to 500 Myrs, before rotational convergence and therefore X-ray
luminosity convergence sets in. This age range is crucial for the evolution of
young planetary atmospheres and may thus lead to very different planetary
evolution histories.Comment: 4 pages, 4 figures, accepted for publication in A&
A Graph-Based Semi-Supervised k Nearest-Neighbor Method for Nonlinear Manifold Distributed Data Classification
Nearest Neighbors (NN) is one of the most widely used supervised
learning algorithms to classify Gaussian distributed data, but it does not
achieve good results when it is applied to nonlinear manifold distributed data,
especially when a very limited amount of labeled samples are available. In this
paper, we propose a new graph-based NN algorithm which can effectively
handle both Gaussian distributed data and nonlinear manifold distributed data.
To achieve this goal, we first propose a constrained Tired Random Walk (TRW) by
constructing an -level nearest-neighbor strengthened tree over the graph,
and then compute a TRW matrix for similarity measurement purposes. After this,
the nearest neighbors are identified according to the TRW matrix and the class
label of a query point is determined by the sum of all the TRW weights of its
nearest neighbors. To deal with online situations, we also propose a new
algorithm to handle sequential samples based a local neighborhood
reconstruction. Comparison experiments are conducted on both synthetic data
sets and real-world data sets to demonstrate the validity of the proposed new
NN algorithm and its improvements to other version of NN algorithms.
Given the widespread appearance of manifold structures in real-world problems
and the popularity of the traditional NN algorithm, the proposed manifold
version NN shows promising potential for classifying manifold-distributed
data.Comment: 32 pages, 12 figures, 7 table
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