7,219 research outputs found
Extrasolar planet taxonomy: a new statistical approach
In this paper we present the guidelines for an extrasolar planet taxonomy.
The discovery of an increasing number of extrasolar planets showing a vast
variety of planetary parameters, like Keplerian orbital elements and
environmental parameters, like stellar masses, spectral types, metallicity
etc., prompts the development of a planetary taxonomy. In this work via
principal component analysis followed by hierarchical clustering analysis, we
report the definition of five robust groups of planets. We also discuss the
physical relevance of such analysis, which may provide a valid basis for
disentangling the role of the several physical parameters involved in the
processes of planet formation and subsequent evolution. For instance, we were
able to divide the hot Jupiters into two main groups on the basis of their
stellar masses and metallicities. Moreover, for some groups, we find strong
correlations between metallicity, semi-major axis and eccentricity. The
implications of these findings are discussed.Comment: accepted for publication on Ap
The CorDis Corpus Mark-up and Related Issues
CorDis is a large, XML, TEI-conformant, POS-tagged, multimodal, multigenre corpus representing a significant portion of the political and media discourse on the 2003 Iraqi conflict. It was generated from different sub-corpora which had been assembled by various research groups, ranging from official transcripts of Parliamentary sessions, both in the US and the UK, to the transcripts of the Hutton Inquiry, from American and British newspaper coverage of the conflict to White House press briefings and to transcriptions of American and British TV news programmes. The heterogeneity of the data, the specificity of the genres and the diverse discourse analytical purposes of different groups had led to a wide range of coding strategies being employed to make textual and meta-textual information retrievable.
The main purpose of this paper is to show the process of harmonisation and integration whereby a loose collection of texts has become a stable architecture. The TEI proved a valid instrument to achieve standardisation of mark-up. The guidelines provide for a hierarchical organisation which gives the corpus a sound structure favouring replicability and enhancing the reliability of research. In discussing some examples of the problems encountered in the annotation, we will deal with issues like consistency and re-usability, and will examine the constraints imposed on data handling by specific research objectives. Examples include the choice to code the same speakers in different ways depending on the various (institutional) roles they may assume throughout the corpus, the distinction between quotations of spoken or written discourse and quotations read aloud in the course of a spoken text, and the segmentation of portions of news according to participants interaction and use of camera/voiceover
Image reconstruction from scattered Radon data by weighted positive definite kernel functions
We propose a novel kernel-based method for image reconstruction from scattered Radon data. To this end, we employ generalized Hermite–Birkhoff interpolation by positive definite kernel functions. For radial kernels, however, a straightforward application of the generalized Hermite–Birkhoff interpolation method fails to work, as we prove in this paper. To obtain a well-posed reconstruction scheme for scattered Radon data, we introduce a new class of weighted positive definite kernels, which are symmetric but not radially symmetric. By our construction, the resulting weighted kernels are combinations of radial positive definite kernels and positive weight functions. This yields very flexible image reconstruction methods, which work for arbitrary distributions of Radon lines. We develop suitable representations for the weighted basis functions and the symmetric positive definite kernel matrices that are resulting from the proposed reconstruction scheme. For the relevant special case, where Gaussian radial kernels are combined with Gaussian weights, explicit formulae for the weighted Gaussian basis functions and the kernel matrices are given. Supporting numerical examples are finally presented
The global mass function of M15
Data obtained with the NICMOS instrument on board the Hubble Space Telescope
(HST) have been used to determine the H-band luminosity function (LF) and mass
function (MF) of three stellar fields in the globular cluster M15, located ~7'
from the cluster centre. The data confirm that the cluster MF has a
characteristic mass of ~0.3 Msolar, as obtained by Paresce & De Marchi (2000)
for a stellar field at 4.6' from the centre. By combining the present data with
those published by other authors for various radial distances (near the centre,
at 20" and at 4.6'), we have studied the radial variation of the LF due to the
effects of mass segregation and derived the global mass function (GMF) using
the Michie-King approach. The model that simultaneously best fits the LF at
various locations, the surface brightness profile and the velocity dispersion
profile suggests that the GMF should resemble a segmented power-law with the
following indices: x ~ 0.8 for stars more massive than 0.8 Msolar, x ~ 0.9 for
0.3 - 0.8 Msolar and x ~ -2.2 at smaller masses (Salpeter's IMF would have
x=1.35). The best fitting model also suggests that the cluster mass is ~5.4
10^5 Msolar and that the mass-to-light ratio is on average M/L_V ~ 2.1, with
M/L_V ~ 3.7 in the core. A large amount of mass (~ 44 %) is found in the
cluster core in the form of stellar heavy remnants, which may be sufficient to
explain the mass segregation in M15 without invoking the presence of an
intermediate-mass black hole.Comment: 12 pages, 10 figures, accepted for publication in A&
Partition of unity interpolation using stable kernel-based techniques
In this paper we propose a new stable and accurate approximation technique
which is extremely effective for interpolating large scattered data sets. The
Partition of Unity (PU) method is performed considering Radial Basis Functions
(RBFs) as local approximants and using locally supported weights. In
particular, the approach consists in computing, for each PU subdomain, a stable
basis. Such technique, taking advantage of the local scheme, leads to a
significant benefit in terms of stability, especially for flat kernels.
Furthermore, an optimized searching procedure is applied to build the local
stable bases, thus rendering the method more efficient
RBF approximation of large datasets by partition of unity and local stabilization
We present an algorithm to approximate large dataset by Radial Basis Function
(RBF) techniques. The method couples a fast domain decomposition procedure with a
localized stabilization method. The resulting algorithm can efficiently deal with large
problems and it is robust with respect to the typical instability of kernel methods
Análise quantitativa dp teor de Ăłleo em sementes com RMN de precessĂŁo livre de onda contĂnua (CWFP) on-line.
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