1,752 research outputs found
Nonparametrically consistent depth-based classifiers
We introduce a class of depth-based classification procedures that are of a
nearest-neighbor nature. Depth, after symmetrization, indeed provides the
center-outward ordering that is necessary and sufficient to define nearest
neighbors. Like all their depth-based competitors, the resulting classifiers
are affine-invariant, hence in particular are insensitive to unit changes.
Unlike the former, however, the latter achieve Bayes consistency under
virtually any absolutely continuous distributions - a concept we call
nonparametric consistency, to stress the difference with the stronger universal
consistency of the standard NN classifiers. We investigate the finite-sample
performances of the proposed classifiers through simulations and show that they
outperform affine-invariant nearest-neighbor classifiers obtained through an
obvious standardization construction. We illustrate the practical value of our
classifiers on two real data examples. Finally, we shortly discuss the possible
uses of our depth-based neighbors in other inference problems.Comment: Published at http://dx.doi.org/10.3150/13-BEJ561 in the Bernoulli
(http://isi.cbs.nl/bernoulli/) by the International Statistical
Institute/Bernoulli Society (http://isi.cbs.nl/BS/bshome.htm
Binary populations and stellar dynamics in young clusters
We first summarize work that has been done on the effects of binaries on
theoretical population synthesis of stars and stellar phenomena. Next, we
highlight the influence of stellar dynamics in young clusters by discussing a
few candidate UFOs (unconventionally formed objects) like intermediate mass
black holes, Eta Carinae, Zeta Puppis, Gamma Velorum and WR 140.Comment: Contributed paper IAU 250: Massive Stars as Cosmic Engine
Tyler shape depth
In many problems from multivariate analysis, the parameter of interest is a
shape matrix, that is, a normalized version of the corresponding scatter or
dispersion matrix. In this paper, we propose a depth concept for shape matrices
that involves data points only through their directions from the center of the
distribution. We use the terminology Tyler shape depth since the resulting
estimator of shape, namely the deepest shape matrix, is the median-based
counterpart of the M-estimator of shape of Tyler (1987). Beyond estimation,
shape depth, like its Tyler antecedent, also allows hypothesis testing on
shape. Its main benefit, however, lies in the ranking of shape matrices it
provides, whose practical relevance is illustrated in principal component
analysis and in shape-based outlier detection. We study the invariance,
quasi-concavity and continuity properties of Tyler shape depth, the topological
and boundedness properties of the corresponding depth regions, existence of a
deepest shape matrix and prove Fisher consistency in the elliptical case.
Finally, we derive a Glivenko-Cantelli-type result and establish almost sure
consistency of the deepest shape matrix estimator.Comment: 28 pages, 5 figure
The formation and evolution of very massive stars in dense stellar systems
The early evolution of dense stellar systems is governed by massive single
star and binary evolution. Core collapse of dense massive star clusters can
lead to the formation of very massive objects through stellar collisions
( 1000 \msun). Stellar wind mass loss determines the evolution and final
fate of these objects, and decides upon whether they form black holes (with
stellar or intermediate mass) or explode as pair instability supernovae,
leaving no remnant. We present a computationaly inexpensive evolutionary scheme
for very massive stars that can readily be implemented in an N-body code. Using
our new N-body code 'Youngbody' which includes a detailed treatment of massive
stars as well as this new scheme for very massive stars, we discuss the
formation of intermediate mass and stellar mass black holes in young starburst
regions. A more detailed account of these results can be found in Belkus et al.
2007.Comment: 2 pages, 2 figures. To appear in conference proceedings for IAUS246,
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