18,168 research outputs found
Breaking the core-envelope symmetry in p-mode pulsating stars
It has been shown that there is a potential ambiguity in the asteroseismic
determination of the location of internal structures in a pulsating star. We
show how, in the case of high-order non-radial acoustic modes, it is possible
to remove this ambiguity by considering modes of different degree. To support
our conclusions we have investigated the seismic signatures of sharp density
variations in the structure of quasi-homogeneous models.Comment: 3 pages, 3 figures, accepted for publication in Astronomy and
Astrophysic
Representation of Nelson Algebras by Rough Sets Determined by Quasiorders
In this paper, we show that every quasiorder induces a Nelson algebra
such that the underlying rough set lattice is algebraic. We
note that is a three-valued {\L}ukasiewicz algebra if and only if
is an equivalence. Our main result says that if is a Nelson
algebra defined on an algebraic lattice, then there exists a set and a
quasiorder on such that .Comment: 16 page
(Unmet)needs: A challenging concept and a complex social construction
This paper is based on an investigation entitled "Unmet Needs in Portugal - Tradition
and emerging trends". Among other objectives, the study in question sought to develop
an operative notion of needs, interpreting them as generated by the non-achievement
of individual aspirations / expectations, through mismatch between opportunities and
capabilities, in a dynamic process between the social context of action and the individual.
Of the six case studies conducted within the scope of the research, we extracted the
analysis of how two of those groups (adults in transition to retirement and adults in
training transition) face the complex relationship that involves the satisfaction of their
needs. We chose the first group because it allows us to analyse how these (older) adults
live an important period of transition and the consequent recomposition of their needs
that this stage of life (the transition to retirement) entails. In the case of adults in training
transition, we use the testimonies of this group as an aid to understand how learning
processes (at least, formal ones) interfere with the questioning, perception and
achievement of the unmet needs. Therefore, a better understanding of the possible
centrality of education in contributing to the satisfaction of needs, and its impact on
well-being.info:eu-repo/semantics/publishedVersio
Porto Oscillation Code (POSC)
The Porto Oscillation Code (POSC) has been developed in 1995 and improved
over the years, with the main goal of calculating linear adiabatic oscillations
for models of solar-type stars. It has also been used to estimate the
frequencies and eigenfunctions of stars from the pre-main sequence up to the
sub-giant phase, having a mass between 0.8 and 4 solar masses.
The code solves the linearised perturbation equations of adiabatic pulsations
for an equilibrium model using a second order numerical integration method. The
possibility of using Richardson extrapolation is implemented. Several options
for the surface boundary condition can be used. In this work we briefly review
the key ingredients of the calculations, namely the equations, the numerical
scheme and the output.Comment: Accepted for publication in Astrophysics and Space Science
The dynamics of corporate credit risk: an intensity-based econometric analysis
Lucas, A. [Promotor
Parameter Driven Multi-state Duration Models: Simulated vs Approximate Maximum Likelihood Estimation
Likelihood based inference for multi-state latent factor intensity models is hindered by the fact that exact closed-form expressions for the implied data density are not available. This is a common and well-known problem for most parameter driven dynamic econometric models. This paper reviews, adapts and compares three different approaches for solving this problem. For evaluating the likelihood, two of the methods rely on Monte Carlo integration with importance sampling techniques. The third method, in contrast, is based on fully deterministic numerical procedures. A Monte Carlo study is conducted to illustrate the use of each method, and assess its corresponding finite sample performance
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