Space and Ground Based Pulsation Data of Eta Bootis Explained with Stellar Models Including Turbulence

The space telescope MOST is now providing us with extremely accurate low frequency p-mode oscillation data for the star Eta Boo. We demonstrate in this paper that these data, when combined with ground based measurements of the high frequency p-mode spectrum, can be reproduced with stellar models that include the effects of turbulence in their outer layers. Without turbulence, the l=0 modes of our models deviate from either the ground based or the space data by about 1.5-4.0 micro Hz. This discrepancy can be completely removed by including turbulence in the models and we can exactly match 12 out of 13 MOST frequencies that we identified as l=0 modes in addition to 13 out of 21 ground based frequencies within their observational 2 sigma tolerances. The better agreement between model frequencies and observed ones depends for the most part on the turbulent kinetic energy which was taken from a 3D convection simulation for the Sun.Comment: 13 pages, 7 figures, ApJ in pres

Comparison of fundamental positive-sequence detectors for highly distorted and unbalanced systems

This paper presents a performance comparison between a PLL and an Adaptive Filter for detecting the positive sequence at the fundamental frequency of any given voltage or current signals of a three-phase system. The comparative analysis was based on the evaluation of a series of steady state performance parameters (phase and amplitude errors, THD and unbalance) and on the response time. The tests were made to study the behaviour of both approaches when working with highly distorted and unbalanced signals. This work was carried out using the computer simulation tool PSCAD/EMTDC.The authors are grateful to FCT (Fundação para a Ciência e a Tecnologia), project funding POCTI/ESE/41170/2001

A microscopic approach to heating rate of ferrofluid droplets by a magnetic field

CNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOCAPES - COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL E NÍVEL SUPERIORIn this work, we study the heating process of colloidal ferrofluids by a magnetic field. The heating of the fluid occurs by the magnetic relaxation of the nanoparticles which provide thermal energy for the host liquid. In the limit of small volumes, the relaxation process occurs through the Neel mechanism since the magnetic nanoparticles present superparamagnetic behavior. Within this limit, we have used a microscopic model for the coupling to phonons and external magnetic field in order to model the relaxation mechanism and to obtain an expression for the heating rate of the fluid as a function of microscopic parameters. The analysis allows determining appropriate conditions for an optimal heating rate for ferrofluids based on superparamagnetic nanoparticles.1254111CNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOCAPES - COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL E NÍVEL SUPERIORCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOCAPES - COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL E NÍVEL SUPERIOR307466/2016-7PNPD 028/2010E.C.S. acknowledges support from the CNPq agency under Grant No. 307466/2016-7. P.A.O. acknowledges financial support from FONDECYT under Grant No. 1140571. F.F.F. and E.C.S. acknowledge CAPES agency financial support (No. CAPES PNPD 028/2010)

Spectroscopic parameters for 451 stars in the HARPS GTO planet search program. Stellar [Fe/H] and the frequency of exo-Neptunes

To understand the formation and evolution of solar-type stars in the solar neighborhood, we need to measure their stellar parameters to high accuracy. We present a catalogue of accurate stellar parameters for 451 stars that represent the HARPS Guaranteed Time Observations (GTO) ``high precision'' sample. Spectroscopic stellar parameters were measured using high signal-to-noise (S/N) spectra acquired with the HARPS spectrograph. The spectroscopic analysis was completed assuming LTE with a grid of Kurucz atmosphere models and the recent ARES code for measuring line equivalent widths. We show that our results agree well with those ones presented in the literature (for stars in common). We present a useful calibration for the effective temperature as a function of the index color B-V and [Fe/H]. We use our results to study the metallicity-planet correlation, namely for very low mass planets. The results presented here suggest that in contrast to their jovian couterparts, Neptune-like planets do not form preferentially around metal-rich stars. The ratio of jupiter-to-neptunes is also an increasing function of stellar metallicity. These results are discussed in the context of the core-accretion model for planet formation.Comment: 11 pages, 8 figures, accepted for publication in Astronomy & Astrophysic

Geologia e zoneamento hidrogeológico da bacia do Rio Preto, DF/GO/MG.

bitstream/item/78956/1/doc-172.pd

Three-point correlation functions from semiclassical circular strings

The strong-coupling limit of three-point correlation functions of local operators can be analyzed beyond the supergravity regime using vertex operators representing spinning string states. When two of the vertex operators correspond to heavy string states having large quantum numbers, while the third operator corresponds to a light state with fixed charges, the correlator can be computed in the large string tension limit by means of a semiclassical approximation. We study the case when the heavy string states are circular string solutions with one AdS_5 spin and three different angular momenta along S^5, for several choices of the light string state.Comment: 13 pages. Latex. v2: Misprints corrected and references adde