151,454 research outputs found
Absolute magnitudes and kinematics of CP stars from Hipparcos data
The position in the HR diagram and the kinematic characteristics of different
kinds of CP stars of the upper main sequence are obtained using the LM method
(Luri et al., 1996). Most of the CP stars are main sequence stars occupying the
whole width of the sequence. From a kinematic point of view, they belong to the
young disk population (ages < 1.5 Gyr). It has also been found that, on
kinematic grounds, the behaviour of lambda Bootis stars is similar to the one
observed for normal stars of the same spectral range. On the other hand, roAp
and noAp stars show the same kinematic characteristics. The peculiar velocity
distribution function has been decomposed into a sum of three dimensional
gaussians and the presence of Pleiades, Sirius and Hyades moving groups has
been clearly established. Finally, a small number of CP stars are found to be
high-velocity objects.Comment: 8 pages, 1 figure, to appear in: Proc. of the 26th workshop of the
European Working Group on CP stars, eds. P. North, A. Schnell and J.
Ziznovsky, Contrib. Astr. Obs. Skalnate Pleso Vol. 27, No
Gauge-invariant fluctuations of scalar branes
A generalization of the Bardeen formalism to the case of warped geometries is
presented. The system determining the gauge-invariant fluctuations of the
metric induced by the scalar fluctuations of the brane is reduced to a set of
Schr\"odinger-like equations for the Bardeen potentials and for the canonical
normal modes of the scalar-tensor action. Scalar, vector and tensor modes of
the geometry are classified according to four-dimensional Lorentz
transformations. While the tensor modes of the geometry live on the brane
determining the corrections to Newton law, the scalar and and vector
fluctuations exhibit non normalizable zero modes and are, consequently, not
localized on the brane. The spectrum of the massive modes of the fluctuations
is analyzed using supersymmetric quantum mechanics.Comment: 29 pages in Latex styl
Homotopy theory of diagrams
In this paper we develop homotopy theoretical methods for studying diagrams.
In particular we explain how to construct homotopy colimits and limits in an
arbitrary model category. The key concept we introduce is that of a model
approximation. Our key result says that if a category admits a model
approximation then so does any diagram category with values in this category.
From the homotopy theoretical point of view categories with model
approximations have similar properties to those of model categories. They admit
homotopy categories (localizations with respect to weak equivalences). They
also can be used to construct derived functors by taking the analogs of fibrant
and cofibrant replacements.
A category with weak equivalences can have several useful model
approximations. We take advantage of this possibility and in each situation
choose one that suits our needs. In this way we prove all the fundamental
properties of the homotopy colimit and limit: Fubini Theorem (the homotopy
colimit -respectively limit- commutes with itself), Thomason's theorem about
diagrams indexed by Grothendieck constructions, and cofinality statements.
Since the model approximations we present here consist of certain functors
"indexed by spaces", the key role in all our arguments is played by the
geometric nature of the indexing categories.Comment: 95 pages with inde
"Aggregation Bias" DOES explain the PPP puzzle
This article summarizes our views on the role of an "aggregation bias" in explaining the PPP Puzzle, in response to the several papers recently written in reaction to our initial contribution. We discuss in particular the criticisms of Imbs, Mumtaz, Ravn and Rey (2002) presented in Chen and Engel (2005). We show that their contentions are based on: (i) analytical counter-examples which are not empirically relevant; (ii) simulation results minimizing the extent of "aggregation bias"; (iii) unfounded claims on the impact of measurement errors on our results; and (iv) problematic implementation of small-sample bias corrections. We conclude, as in our original paper, that "aggregation bias" goes a long way towards explaining the PPP puzzle
Evolutionary Games on Networks and Payoff Invariance Under Replicator Dynamics
The commonly used accumulated payoff scheme is not invariant with respect to
shifts of payoff values when applied locally in degree-inhomogeneous population
structures. We propose a suitably modified payoff scheme and we show both
formally and by numerical simulation, that it leaves the replicator dynamics
invariant with respect to affine transformations of the game payoff matrix. We
then show empirically that, using the modified payoff scheme, an interesting
amount of cooperation can be reached in three paradigmatic non-cooperative
two-person games in populations that are structured according to graphs that
have a marked degree inhomogeneity, similar to actual graphs found in society.
The three games are the Prisoner's Dilemma, the Hawks-Doves and the Stag-Hunt.
This confirms previous important observations that, under certain conditions,
cooperation may emerge in such network-structured populations, even though
standard replicator dynamics for mixing populations prescribes equilibria in
which cooperation is totally absent in the Prisoner's Dilemma, and it is less
widespread in the other two games.Comment: 20 pages, 8 figures; to appear on BioSystem
Self-Deception as Affective Coping. An Empirical Perspective on Philosophical Issues
In the philosophical literature, self-deception is mainly approached through the analysis of paradoxes. Yet, it is agreed that self-deception is motivated by protection from distress. In this paper, we argue, with the help of findings from cognitive neuroscience and psychology, that self-deception is a type of affective coping.
First, we criticize the main solutions to the paradoxes of self-deception. We then present a new approach to self-deception. Self-deception, we argue, involves three appraisals of the distressing evidence: (a) appraisal of the strength of evidence as uncertain, (b) low coping potential and (c) negative anticipation along the lines of Damasio’s somatic marker hypothesis. At the same time, desire impacts the treatment of flattering evidence via dopamine. Our main proposal is that self-deception involves emotional mechanisms provoking a preference for immediate reward despite possible long-term negative repercussions. In the last part, we use this emotional model to revisit the philosophical paradoxes
Investigation of the Praesepe cluster. III. Radial velocity and binarity of the F5-K0 Klein-Wassink stars
Coravel observations of 103 F5-K0 stars in the Praesepe cluster yielded 24
spectroscopic binaries (3 are non-members), and 20 orbits were determined, with
periods from 4 to 7400 days. Based on a complete sample in the colour range
0.40 < B-V < 0.80 (80 stars, including KW 244 = TX Cnc), the companion star
fraction CSF = 0.45. The percentage of spectroscopic binaries with P < 1000d is
20% (16/80). The combined photometric and spectroscopic analysis showed that 12
among 18 single-lined spectroscopic binaries are located within the "single"
star sequence in the (V,B-V) diagram and cannot be detected by the photometric
analysis in the UBV system. In addition, seven photometrically analysed
binaries were not detected with the radial velocity observations, but are
confirmed members. The number of single:binary:triple stars is 47:30:3.Comment: 10 pages, 3 tables, 7 eps figures. Accepted for A&A. LaTe
Shallow vs deep learning architectures for white matter lesion segmentation in the early stages of multiple sclerosis
In this work, we present a comparison of a shallow and a deep learning
architecture for the automated segmentation of white matter lesions in MR
images of multiple sclerosis patients. In particular, we train and test both
methods on early stage disease patients, to verify their performance in
challenging conditions, more similar to a clinical setting than what is
typically provided in multiple sclerosis segmentation challenges. Furthermore,
we evaluate a prototype naive combination of the two methods, which refines the
final segmentation. All methods were trained on 32 patients, and the evaluation
was performed on a pure test set of 73 cases. Results show low lesion-wise
false positives (30%) for the deep learning architecture, whereas the shallow
architecture yields the best Dice coefficient (63%) and volume difference
(19%). Combining both shallow and deep architectures further improves the
lesion-wise metrics (69% and 26% lesion-wise true and false positive rate,
respectively).Comment: Accepted to the MICCAI 2018 Brain Lesion (BrainLes) worksho
Asymptotics of Random Contractions
In this paper we discuss the asymptotic behaviour of random contractions
, where , with distribution function , is a positive random
variable independent of . Random contractions appear naturally in
insurance and finance. Our principal contribution is the derivation of the tail
asymptotics of assuming that is in the max-domain of attraction of an
extreme value distribution and the distribution function of satisfies a
regular variation property. We apply our result to derive the asymptotics of
the probability of ruin for a particular discrete-time risk model. Further we
quantify in our asymptotic setting the effect of the random scaling on the
Conditional Tail Expectations, risk aggregation, and derive the joint
asymptotic distribution of linear combinations of random contractions.Comment: 25 page
Genome-to-genome analysis highlights the effect of the human innate and adaptive immune systems on the hepatitis C virus
Outcomes of hepatitis C virus (HCV) infection and treatment depend on viral and host genetic factors. Here we use human genome-wide genotyping arrays and new whole-genome HCV viral sequencing technologies to perform a systematic genome-to-genome study of 542 individuals who were chronically infected with HCV, predominantly genotype 3. We show that both alleles of genes encoding human leukocyte antigen molecules and genes encoding components of the interferon lambda innate immune system drive viral polymorphism. Additionally, we show that IFNL4 genotypes determine HCV viral load through a mechanism dependent on a specific amino acid residue in the HCV NS5A protein. These findings highlight the interplay between the innate immune system and the viral genome in HCV control
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