Spitoni E.,University of Évora |
Matteucci F.,National institute for astrophysics |
Marcon-Uchida M.M.,Southern Cross University of Brazil
Astronomy and Astrophysics | Year: 2013
Context. Galactic fountains and radial gas flows are very important ingredients for modeling the chemical evolution of galactic disks. Aims. Our aim here is to study the effects of galactic fountains and radial gas flows on the chemical evolution of the disk of Andromeda (M 31) galaxy. Methods. We adopt a ballistic method to study the effects of galactic fountains on the chemical enrichment of the M 31 disk by analyzing the landing coordinate of the fountains and the time delay in the pollution of the interstellar gas. To understand the consequences of radial flows, we adopt a very detailed chemical evolution model. Our aim is to study the formation of abundance gradients along the M 31 disk and also compare our results with the Milky Way. Results. We find that the landing coordinate for the fountains in M 31 is no more than 1 kpc from the starting point, thus producing a negligible effect on the chemical evolution of the disk. We find that the delay time in the enrichment process due to fountains is no longer than 100 Myr, and this timescale also produces insignificant effects on the results. Then, we compute the chemical evolution of the M 31 disk with radial gas flows produced by the infall of extragalactic material and fountains. We find that a moderate inside-out formation of the disk, coupled with radial flows of variable speed, can reproduce the observed gradient very well. We also discuss the effects of other parameters, such as a threshold in the gas density for star formation and efficiency of star formation varying with the galactic radius. Conclusions. We conclude that galactic fountains do not affect the chemical evolution of the M 31 disk. Including radial gas flows with an inside-out formation of the disk produces a very good agreement with observations. On the other hand, if radial flows are not considered, one should assume a threshold in the star formation and variable star formation efficiency, besides the inside-out formation to reproduce the data. We conclude that the most important physical processes in creating disk gradients are the inside-out formation and the radial gas flows. More data on abundance gradients both locally and at high redshift are necessary to confirm this conclusion. © ESO, 2013.
Coelho P.R.T.,University of Sao Paulo |
Coelho P.R.T.,Southern Cross University of Brazil
Monthly Notices of the Royal Astronomical Society | Year: 2014
Theoretical stellar libraries have been increasingly used to overcome limitations of empirical libraries, e.g. by exploring atmospheric parameter spaces not well represented in the latter. This work presents a new theoretical library which covers 3000 ≤ Teff ≤ 25 000 K,-0.5 ≤ log g ≤ 5.5 and 12 chemical mixtures covering 0.0017 ≤ Z ≤ 0.049 at both scaledsolar and α-enhanced compositions. This library complements previous ones by providing: (i) homogeneous computations of opacity distribution functions, models atmospheres, statistical surface fluxes and high-resolution spectra; (ii) high-resolution spectra with continua slopes corrected by the effect of predicted lines and (iii) two families of α-enhanced mixtures for each scaled-solar iron abundance, to allow studies of the α-enhancement both at 'fixed iron' and 'fixed Z' cases. Comparisons to observed spectra were performed and confirm that the synthetic spectra reproduce well the observations, although there are wavelength regions which should be still improved. The atmospheric parameter scale of the model library was compared to one derived from a widely used empirical library, and no systematic difference between the scales was found. This is particularly reassuring for methods which use synthetic spectra for deriving atmospheric parameters of stars in spectroscopic surveys © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.
Ruiz L.O.,Southern Cross University of Brazil |
Falceta-Goncalves D.,University of Sao Paulo |
Lanfranchi G.A.,Southern Cross University of Brazil |
Caproni A.,Southern Cross University of Brazil
Monthly Notices of the Royal Astronomical Society | Year: 2013
Theoretical Λcold dark matter (ΛCDM) cosmological models predict a much larger number of low-mass dark matter haloes than has been observed in the Local Group of galaxies. One possible explanation is the increased difficulty of detecting these haloes if most of the visible matter is lost at early evolutionary phases through galactic winds. In this work we study the current models of triggering galactic winds in dwarf spheroidal galaxies (dSph) from supernovae, and study, based on 3D hydrodynamic numerical simulations, the correlation of the mass-loss rates and important physical parameters as the dark matter halo mass and its radial profile, and the star formation rate. We find that the existence of winds is ubiquitous, independent of the gravitational potential. Our simulations revealed that the Rayleigh-Taylor Instability (RTI) may play a major role on pushing matter out of these systems, even for very massive haloes. The instability is responsible for 5-40 per cent of the mass loss during the early evolution of the galaxy, being less relevant at t > 200 Myr. There is no significant difference in the mass-loss rates obtained for the different dark matter profiles studied (NFW and logarithmic). We have also found a correlation between the mass-loss rate and both the halo mass and the rate of supernovae, as already reported in previous works. Besides, the epoch in which most of the baryon galactic matter is removed from the galaxy varies depending on the SN rate and gravitational potential. The later, combined to the importance of the RTI in each model, may change our understanding about the chemical evolution of dwarf galaxies, as well as in the heavy element contamination of the intergalactic medium at high redshifts. © 2012 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.
Caproni A.,Southern Cross University of Brazil |
Abraham Z.,University of Sao Paulo |
Monteiro H.,Federal University of Itajubá
Monthly Notices of the Royal Astronomical Society | Year: 2013
BL Lacertae is the prototype of the BL Lac class of active galactic nuclei, exhibiting intensive activity on parsec (pc) scales, such as intense core variability and multiple ejections of jet components. In particular, in previousworks the existence of precession motions in the pc-scale jet of BL Lacertae has been suggested. In this work we revisit this issue, investigating temporal changes of the observed right ascension and declination offsets of the jet knots in terms of our relativistic jet-precession model. The seven free parameters of our precession model were optimized via a heuristic cross-entropy method, comparing the projected precession helix with the positions of the jet components on the plane of the sky and imposing constraints on their maximum and minimum superluminal velocities. Our optimized best model is compatible with a jet having a bulk velocity of 0.9824c, which is precessing with a period of about 12.1 yr in the observer's reference frame and changing its orientation in relation to the line of sight between 4° and 5°, approximately. Assuming that the jet precession has its origin in a supermassive binary black hole system, we show that the 2.3-yr periodic variation in the structural position angle of the very-long-baseline interferometry (VLBI) core of BL Lacertae reported by Stirling et al. is compatible with a nutation phenomenon if the secondary black hole has a mass higher than about six times that of the primary black hole. © 2012 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.
Vinolo M.A.R.,University of Sao Paulo |
Hirabara S.M.,Southern Cross University of Brazil |
Curi R.,University of Sao Paulo
Current Opinion in Clinical Nutrition and Metabolic Care | Year: 2012
Purpose of review: It has been demonstrated that fatty acids (FAs) are physiological ligands of G-protein-coupled receptors (GPRs). Activation of the GPRs (40, 41, 43, 84, 119 and 120) by FAs or synthetic agonists modulates several responses. In this review, we discuss the current knowledge on the actions of FA-activated GPRs and their relevance in normal and pathological conditions. Recent findings: Studies have shown that FA-activated GPRs modulate hormone secretion (incretin, insulin and glucagon), activation of leukocytes and several aspects of metabolism. Summary: Understanding GPR actions and their involvement in the development of insulin-resistance, β-cell failure, dyslipidemia and inflammation associated with obesity, type 2 diabetes, metabolic syndrome and cardiovascular diseases is important for the comprehension of the mechanisms underlying these pathological conditions and for the establishment of new and effective interventions. © 2012 Wolters Kluwer Health | Lippincott Williams & Wilkins.
de Melo J.P.B.C.,Southern Cross University of Brazil |
Frederico T.,Brazilian Technological Institute of Aeronautics
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2012
The issue of the contribution of zero-modes to the light-front projection of the electromagnetic current of phenomenological models of vector particles vertices is addressed in the Drell-Yan frame. Our analytical model of the Bethe-Salpeter amplitude of a spin-1 fermion-antifermion composite state gives a physically motivated light-front wave function symmetric by the exchange of the fermion and antifermion, as in the ρ-meson case. We found that among the four independent matrix elements of the plus component in the light-front helicity basis only the 0 → 0 one carries zero-mode contributions. Our derivation generalizes to symmetric models, important for applications, the above conclusion found for a simplified non-symmetrical form of the spin-1 Bethe-Salpeter amplitude with photon-fermion point-like coupling and also for a smeared fermion-photon vertex model. © 2012 Elsevier B.V.
Kirby E.N.,California Institute of Technology |
Lanfranchi G.A.,Southern Cross University of Brazil |
Simon J.D.,Carnegie Institution of Washington |
Cohen J.G.,California Institute of Technology |
Guhathakurta P.,University of California at Santa Cruz
Astrophysical Journal | Year: 2011
We present metallicity distribution functions (MDFs) for the central regions of eight dwarf satellite galaxies of the Milky Way: Fornax, Leo I and II, Sculptor, Sextans, Draco, Canes Venatici I, and Ursa Minor. We use the published catalog of abundance measurements from the previous paper in this series. The measurements are based on spectral synthesis of iron absorption lines. For each MDF, we determine maximum likelihood fits for Leaky Box, Pre-Enriched, and Extra Gas (wherein the gas supply available for star formation increases before it decreases to zero) analytic models of chemical evolution. Although the models are too simplistic to describe any MDF in detail, a Leaky Box starting from zero metallicity gas fits none of the galaxies except Canes Venatici I well. The MDFs of some galaxies, particularly the more luminous ones, strongly prefer the Extra Gas Model to the other models. Only for Canes Venatici I does the Pre-Enriched Model fit significantly better than the Extra Gas Model. The best-fit effective yields of the less luminous half of our galaxy sample do not exceed 0.02 Z⊙, indicating that gas outflow is important in the chemical evolution of the less luminous galaxies. We surmise that the ratio of the importance of gas infall to gas outflow increases with galaxy luminosity. Strong correlations of average [Fe/H] and metallicity spread with luminosity support this hypothesis. © 2011. The American Astronomical Society.
Rojas E.,Southern Cross University of Brazil |
El-Bennich B.,Southern Cross University of Brazil |
De Melo J.P.B.C.,Southern Cross University of Brazil
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2014
We study ground and radial excitations of flavor singlet and flavored pseudoscalar mesons within the framework of the rainbow-ladder truncation using an infrared massive and finite interaction in agreement with recent results for the gluon-dressing function from lattice QCD and Dyson-Schwinger equations. Whereas the ground-state masses and decay constants of the light mesons as well as charmonia are well described, we confirm previous observations that this truncation is inadequate to provide realistic predictions for the spectrum of excited and exotic states. Moreover, we find a complex conjugate pair of eigenvalues for the excited D(s) mesons, which indicates a non-Hermiticity of the interaction kernel in the case of heavy-light systems and the present truncation. Nevertheless, limiting ourselves to the leading contributions of the Bethe-Salpeter amplitudes, we find a reasonable description of the charmed ground states and their respective decay constants. © 2014 American Physical Society.
Genovese W.J.,Southern Cross University of Brazil
Photomedicine and laser surgery | Year: 2010
OBJECTIVE: To review the literature regarding the use of surgical lasers in hemangioma treatment and to report a clinical case involving diode laser. BACKGROUND: Hemangiomas are benign vascular proliferations consisting of numerous capillary structures and are especially common on the tongue, lips, jugal mucous membrane, and gums. A number of treatment modalities have been proposed for hemangioma treatment. METHODS: The patient was referred for evaluation complaining of chewing difficulty because of swelling in the right area of the upper lip, with no previous trauma. The lesion was located in the internal right jugal mucous membrane, measured 4 x 4 cm(2), presented a bluish coloration, and was diagnosed as a hemangioma. The treatment selected was surgical removal using gallium arsenide (GaAs) diode laser at 980 nm wavelength, with 4.0 W of power. RESULTS: During surgery, complications including hemorrhage were not observed, and no scarring developed after surgery. CONCLUSIONS: The use of GaAs high-potency diode laser in the treatment of hemangioma reduced bleeding during surgery, with a consequent reduction in operating time, and promoted rapid postoperative hemostasis. It is safe for use on large lesions and easy to manage, and postoperative problems, including potential scarring, and discomfort are minimal.
Coelho P.,Southern Cross University of Brazil |
Gadotti D.A.,European Southern Observatory
Astrophysical Journal Letters | Year: 2011
We obtained stellar ages and metallicities via spectrum fitting for a sample of 575 bulges with spectra available from the Sloan Digital Sky Survey. The structural properties of the galaxies have been studied in detail in 2009 by Gadotti and the sample contains 251 bulges in galaxies with bars. Using the whole sample, where galaxy stellar mass distributions for barred and unbarred galaxies are similar, we find that bulges in barred and unbarred galaxies occupy similar loci in the age versus metallicity plane. However, the distribution of bulge ages in barred galaxies shows an excess of populations younger than ∼4 Gyr, when compared to bulges in unbarred galaxies. Kolmogorov-Smirnov statistics confirm that the age distributions are different with a significance of 99.94%. If we select sub-samples for which the bulge stellar mass distributions are similar for barred and unbarred galaxies, this excess vanishes for galaxies with bulge mass log M < 10.1 M ⊙, while for more massive galaxies we find a bimodal bulge age distribution for barred galaxies only, corresponding to two normal distributions with mean ages of 10.4 and 4.7Gyr. We also find twice as much active galactic nuclei among barred galaxies, as compared to unbarred galaxies, for low-mass bulges. By combining a large sample of high-quality data with sophisticated image and spectral analysis, we are able to find evidence that the presence of bars affects the mean stellar ages of bulges. This lends strong support to models in which bars trigger star formation activity in the centers of galaxies. © 2011. The American Astronomical Society. All rights reserved.