11,482 research outputs found
False Vacuum Transitions - Analytical Solutions and Decay Rate Values
In this work we show a class of oscillating configurations for the evolution
of the domain walls in Euclidean space. The solutions are obtained
analytically. Phase transitions are achieved from the associated fluctuation
determinant, by the decay rates of the false vacuum.Comment: 6 pages, improved to match the final version to appear in EP
Homogeneous abundance analysis of dwarf, subgiant and giant FGK stars with and without giant planets
We have analyzed high-resolution and high signal-to-noise ratio optical
spectra of nearby FGK stars with and without detected giant planets in order to
homogeneously measure their photospheric parameters, mass, age, and the
abundances of volatile (C, N, and O) and refractory (Na, Mg, Si, Ca, Ti, V, Mn,
Fe, Ni, Cu, and Ba) elements. Our sample contains 309 stars from the solar
neighborhood (up to the distance of 100 pc), out of which 140 are dwarfs, 29
are subgiants, and 140 are giants. The photospheric parameters are derived from
the equivalent widths of Fe I and Fe II lines. Masses and ages come from the
interpolation in evolutionary tracks and isochrones on the HR diagram. The
abundance determination is based on the equivalent widths of selected atomic
lines of the refractory elements and on the spectral synthesis of C_2, CN, C I,
O I, and Na I features. We apply a set of statistical methods to analyze the
abundances derived for the three subsamples. Our results show that: i) giant
stars systematically exhibit underabundance in [C/Fe] and overabundance in
[N/Fe] and [Na/Fe] in comparison with dwarfs, a result that is normally
attributed to evolution-induced mixing processes in the envelope of evolved
stars; ii) for solar analogs only, the abundance trends with the condensation
temperature of the elements are correlated with age and anticorrelated with the
surface gravity, which is in agreement with recent studies; iii) as in the case
of [Fe/H], dwarf stars with giant planets are systematically enriched in [X/H]
for all the analyzed elements, except for O and Ba (the former due to
limitations of statistics), confirming previous findings in the literature that
not only iron has an important relation with the planetary formation; and iv)
giant planet hosts are also significantly overabundant for the same metallicity
when the elements from Mg to Cu are combined together.Comment: 20 pages, 16 figures, 8 table
On the Spinor Representation
A systematic study of the spinor representation by means of the fermionic
physical space is accomplished and implemented. The spinor representation space
is shown to be constrained by the Fierz-Pauli-Kofink identities among the
spinor bilinear covariants. A robust geometric and topological structure can be
manifested from the spinor space, wherein, for instance, the first and second
homotopy groups play prominent roles on the underlying physical properties,
associated to the fermionic fields.Comment: 16 page
Chemical Evolution of the Galaxy Based on the Oscillatory Star Formation History
We model the star formation history (SFH) and the chemical evolution of the
Galactic disk by combining an infall model and a limit-cycle model of the
interstellar medium (ISM). Recent observations have shown that the SFH of the
Galactic disk violently variates or oscillates. We model the oscillatory SFH
based on the limit-cycle behavior of the fractional masses of three components
of the ISM. The observed period of the oscillation ( Gyr) is reproduced
within the natural parameter range. This means that we can interpret the
oscillatory SFH as the limit-cycle behavior of the ISM. We then test the
chemical evolution of stars and gas in the framework of the limit-cycle model,
since the oscillatory behavior of the SFH may cause an oscillatory evolution of
the metallicity. We find however that the oscillatory behavior of metallicity
is not prominent because the metallicity reflects the past integrated SFH. This
indicates that the metallicity cannot be used to distinguish an oscillatory SFH
from one without oscillations.Comment: 21 pages LaTeX, to appear in Ap
A new limit for the NW RÃo de la Plata Craton Border at about 24ºS (Argentina) detected by Magnetotellurics
Old South American structures constitute a puzzle where the RÃo de la Plata craton is the most important clue in the assembly of SW Gondwana. The present study was performed to improve the knowledge resulting from all the previous magnetotelluric (MT) studies focused particularly on characterizing the western border of the Rio de la Plata Craton. MT data were acquired along an approximately NW-SE 750 km profile at about 24ºS, from the Sub Andean Ranges in the province of Salta (NW) to the boundary Formosa Province frontier (SE) next to Paraguay River. Distortion and structure dimensionality analysis indicates that MT responses are two-dimensional with a NS strike orientation, consistent with the regional geological strike. A 2D inversion of the data provided a model showing a sharp lateral discontinuity, possibly associated with cratonic structures. The high resistivity (> 5000 ohm-m) observed, from about the middle of the profile toward its eastern end, may be interpreted as the terranes accreted to the RÃo de la Plata Craton during Neoproterozoic to Cambrian times, or even as the RÃo de la Plata Craton itself. Along the profile from the surface to a depth of about 10 km the resistivity model shows a significant resistivity variation in the structure. The resistive block identified at the western end of the profile represents the Sub Andean system. The markedly enhanced low-resistivity structure (~ 1 to 10 ohm-m) corresponds to a sedimentary pile whose thickness decreases from NW to SE
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