5,980 research outputs found
Asteroseismological study of massive ZZ Ceti stars with fully evolutionary models
We present the first asteroseismological study for 42 massive ZZ Ceti stars
based on a large set of fully evolutionary carbonoxygen core DA white dwarf
models characterized by a detailed and consistent chemical inner profile for
the core and the envelope. Our sample comprise all the ZZ Ceti stars with
spectroscopic stellar masses between 0.72 and known to date.
The asteroseismological analysis of a set of 42 stars gives the possibility to
study the ensemble properties of the massive pulsating white dwarf stars with
carbonoxygen cores, in particular the thickness of the hydrogen envelope and
the stellar mass. A significant fraction of stars in our sample have stellar
mass high enough as to crystallize at the effective temperatures of the ZZ Ceti
instability strip, which enables us to study the effects of crystallization on
the pulsation properties of these stars. Our results show that the phase
diagram presented in Horowitz et al. (2010) seems to be a good representation
of the crystallization process inside white dwarf stars, in agreement with the
results from white dwarf luminosity function in globular clusters.Comment: 58 pages, 11 figures, accepted in Ap
Dissipation and memory effects in pure glue deconfinement
We investigate the effects of dissipation in the deconfining transition for a
pure SU(2) gauge theory. Using an effective model for the order parameter, we
study its Langevin evolution numerically, and compare results from local
additive noise dynamics to those obtained considering an exponential non-local
kernel for early times.Comment: 4 pages, 2 figures, to appear in the proceedings of Strong and
Electroweak Matter (SEWM06), BNL, May 200
Remarks on transient photon production in heavy ion collisions
In this note, we discuss the derivation of a formula that has been used in
the literature in order to compute the number of photons emitted by a hot or
dense system during a finite time. Our derivation is based on a variation of
the standard operator-based -matrix approach. The shortcomings of this
formula are then emphasized, which leads to a negative conclusion concerning
the possibility of using it to predict transient effects for the photon rate.Comment: 13 page
Treatment of bimodality in proficiency test of pH in bioethanol matrix
The pH value in bioethanol is a quality control parameter related to its
acidity and to the corrosiveness of vehicle engines when it is used as fuel. In
order to verify the comparability and reliability of the measurement of pH in
bioethanol matrix among some experienced chemical laboratories, reference
material (RM) of bioethanol developed by Inmetro - the Brazilian National
Metrology Institute - was used in a proficiency testing (PT) scheme. There was
a difference of more than one unit in the value of the pH measured due to the
type of internal filling electrolytic solutions (potassium chloride, KCl or
lithium chloride, LiCl) from the commercial pH combination electrodes used by
the participant laboratories. Therefore, bimodal distribution has occurred from
the data of this PT scheme. This work aims to present the possibilities that a
PT scheme provider can use to overcome the bimodality problem. Data from the PT
of pH in bioethanol were treated by two different statistical approaches:
kernel density model and the mixture of distributions. Application of these
statistical treatments improved the initial diagnoses of PT provider, by
solving bimodality problem and contributing for a better performance evaluation
in measuring pH of bioethanol.Comment: 20 pages, 6 figures, Accepted for publication in Accreditation and
Quality Assurance (ACQUAL
Semi-Automated Ontology Generation Process from Industrial Product Data Standards
Ontology development has become an important research area for manufacture industries. Ontologies are one of the most popular methods to achieve semantic interoperability between information systems. In previous works, an ontology network that reuses ontological and non-ontological re-sources have been proposed in order to reach semantic interoperability. Howev-er, processing non-ontological resources to build an ontology is a great time-consuming task. Therefore, this work presents a framework and a prototype tool to support the reuse of the non-ontological resources involved in the develop-ment of the ontology network.Sociedad Argentina de Informática e Investigación Operativa (SADIO
Semi-Automated Ontology Generation Process from Industrial Product Data Standards
Ontology development has become an important research area for manufacture industries. Ontologies are one of the most popular methods to achieve semantic interoperability between information systems. In previous works, an ontology network that reuses ontological and non-ontological re-sources have been proposed in order to reach semantic interoperability. Howev-er, processing non-ontological resources to build an ontology is a great time-consuming task. Therefore, this work presents a framework and a prototype tool to support the reuse of the non-ontological resources involved in the develop-ment of the ontology network.Sociedad Argentina de Informática e Investigación Operativa (SADIO
The sdA problem - II. Photometric and Spectroscopic Follow-up
Subdwarf A star (sdA) is a spectral classification given to objects showing
H-rich spectra and sub-main sequence surface gravities, but effective
temperature lower than the zero-age horizontal branch. Their evolutionary
origin is an enigma. In this work, we discuss the results of follow-up
observations of selected sdAs. We obtained time resolved spectroscopy for 24
objects, and time-series photometry for another 19 objects. For two targets, we
report both spectroscopy and photometry observations. We confirm seven objects
to be new extremely-low mass white dwarfs (ELMs), one of which is a known
eclipsing star. We also find the eighth member of the pulsating ELM class.Comment: Accepted for publication in MNRAS. 19 pages, 30 figures, 6 table
Detection of weak-order phase transitions in ferromagnets by ac resistometry
It is shown that ac resistometry can serve as an effective tool for the
detection of phase transitions, such as spin reorientation or premartensitic
phase transitions, which generally are not disclosed by dc resistivity
measurement. Measurement of temperature dependence of impedance, , allows
one to unmask the anomaly, corresponding to a weak-order phase transition. The
appearance of such an anomaly is accounted for by a change in the effective
permeability of a sample upon the phase transition. Moreover, frequency
dependence of makes it possible to use the frequency of the applied ac
current as an adjusting parameter in order to make this anomaly more
pronounced. The applicability of this method is tested for the rare earth Gd
and Heusler alloy NiMnGa.Comment: 4 pages, 2 figures, to be published in J. Appl. Phys., v.94(5
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