Asteroseismic Theory of Rapidly Oscillating Ap Stars

This paper reviews some of the important advances made over the last decade concerning theory of roAp stars.Comment: 9 pages, 5 figure

Verification of the observer property in discrete event systems

The observer property is an important condition to be satisfied by abstractions of Discrete Event System (DES) models. This technical note presents a new algorithm that tests if an abstraction of a DES obtained through natural projection has the observer property. The procedure, called OP-Verifier, can be applied to (potentially nondeterministic) automata, with no restriction on the existence of cycles of 'non-relevant' events. This procedure has quadratic complexity in the number of states. The performance of the algorithm is illustrated by a set of experiments

In vivo Mononuclear Phagocyte Migration: Paradoxical Effect of Adrenalectomy

The effect of adrenalectomy on neutrophil and monocyte migration into rat peritoneal and pleural cavities was investigated. Carrageenin- or thioglycollate-induced neutrophil emigration into both cavities was enhanced by adrenalectomy. In contrast, monocyte migration into peritoneal cavities induced by these two stimuli was significantl decreased. In pleural cavities, adrenalectomy enhanced the monocyte migration induced by carrageenin but had no effect on that induced by thioglycollate. Administration of physiological doses of glucocorticoids reversed the effect of adrenalectomy on monocyte migration by both stimuli into both cavities. The results support the hypothesis that endogenous glucocorticotds negatively control neutrophil migration independently of the site or type of stimulus. Their role in monocyte migration is, however, dependent on the site of injury and on the type of inflammatory stimulus. There is no obvious explanation for the divergent influence of endogenous glucocorticoids on the monocyte emigration into peritoneal and pleural cavities observed with different stimuli

Influência do espaçamento na bandeja pelos tubetes e da aplicação de fertilizantes de liberação lenta, durante a fase de pré-viveiro, no crescimento, na partição de matéria seca e na nutrição de mudas de dendezeiro.

Este trabalho teve como objetivo verificar a influência do tipo e da dose de adubo de liberação lenta e da distribuição dos tubetes nas bandejas, durante a fase de pré-viveiro, no crescimento, na nutrição e na partição de matéria seca de mudas de dendezeiro

OvHV-2 glycoprotein B delivered by a recombinant BoHV-4 is immunogenic and induces partial protection against sheep-associated malignant catarrhal fever in a rabbit model

An efficacious vaccine for sheep-associated malignant catarrhal fever (SA-MCF) is important for the livestock industry. Research towards SA-MCF vaccine development is hindered by the absence of culture systems to propagate the causative agent, ovine herpesvirus-2 (OvHV-2), which means its genome cannot be experimentally modified to generate an attenuated vaccine strain. Alternative approaches for vaccine development are needed to deliver OvHV-2 antigens. Bovine herpesvirus 4 (BoHV-4) has been evaluated as a vaccine vector for several viral antigens with promising results. In this study, we genetically engineered BoHV-4 to express OvHV-2 glycoprotein B (gB) and evaluated its efficacy as an SA-MCF vaccine using a rabbit model. The construction of a viable recombinant virus (BoHV-4-ADTK-OvHV-2-gB) and confirmation of OvHV-2 gB expression were performed in vitro. The immunization of rabbits with BoHV-4-ADTK-OvHV-2-gB elicited strong humoral responses to OvHV-2 gB, including neutralizing antibodies. Following intra-nasal challenge with a lethal dose of OvHV-2, 42.9% of the OvHV-2 gB vaccinated rabbits were protected against SA-MCF, while all rabbits in the mock-vaccinated group succumbed to SA-MCF. Overall, OvHV-2 gB delivered by the recombinant BoHV-4 was immunogenic and partly protective against SA-MCF in rabbits. These are promising results towards an SA-MCF vaccine; however, improvements are needed to increase protection rates

Detailed numerical simulation of cathode spots in high-current vacuum arcs

A detailed numerical model of cathode spots in high-current vacuum arcs is given. The model provides a complete description of all phases of life of an individual spot taking into account the presence of metal vapor left over from a previous explosion, the interaction of the vaporized plasma from the cathode spot with the cathode surface, and Joule heat generation in the cathode body. Melting and motion of molten metal due to Lorentz force are also accounted for, together with surface tension effects and the pressure exerted by the plasma over the cathode surface. First results are presented and analyzed for copper cathodes with a protrusion and planar cathodes. Emphasis is given to the investigation of the effect of the vaporized plasma and of hydrodynamic processes. No thermal runaway is observed.info:eu-repo/semantics/publishedVersio

Simulating changes in shape of thermionic cathodes during operation of high-pressure arc discharges

A numerical model of current transfer to thermionic cathodes of high-pressure arc discharges is developed with account of deviations from local thermodynamic equilibrium occurring near the cathode surface, in particular, of the near-cathode space-charge sheath, melting of the cathode, and motion of the molten metal under the effect of the plasma pressure, the Lorentz force, gravity, and surface tension. Modelling results are reported for a tungsten cathode of an atmospheric-pressure argon arc and the computed changes in the shape of the cathode closely resemble those observed in the experiment. The modelling has shown that the time scale of change of the cathode shape during arc operation is very sensitive to the temperature attained by the cathode. The fact that the computed time scales conform to those observed in the experiment indicate that the model of non-equilibrium near-cathode layers in high pressure arc discharges, employed in this work, predicts the cathode temperature for a given arc current with adequate accuracy. In contrast, modelling based on the assumption of local thermodynamic equilibrium in the whole arc plasma computation domain up to the cathode surface could hardly produce a similar agreement.info:eu-repo/semantics/publishedVersio

Detailed numerical simulation of cathode spots in vacuum arcs: Interplay of different mechanisms and ejection of droplets

A model of cathode spots in high-current vacuum arcs is developed with account of all the poten tially relevant mechanisms: the bombardment of the cathode surface by ions coming from a pre existing plasma cloud; vaporization of the cathode material in the spot, its ionization, and the inter action of the produced plasma with the cathode; the Joule heat generation in the cathode body; melting of the cathode material and motion of the melt under the effect of the plasma pressure and the Lorentz force and related phenomena. After the spot has been ignited by the action of the cloud (which takes a few nanoseconds), the metal in the spot is melted and accelerated toward the periph ery of the spot, with the main driving force being the pressure due to incident ions. Electron emis sion cooling and convective heat transfer are dominant mechanisms of cooling in the spot, limiting the maximum temperature of the cathode to approximately 4700–4800 K. A crater is formed on the cathode surface in this way. After the plasma cloud has been extinguished, a liquid-metal jet is formed and a droplet is ejected. No explosions have been observed. The modeling results conform to estimates of different mechanisms of cathode erosion derived from the experimental data on the net and ion erosion of copper cathodes.info:eu-repo/semantics/publishedVersio

The fundamental parameters of the roAp star 10 Aql

Due to the strong magnetic field and related abnormal surface layers existing in rapidly oscillating Ap stars, systematic errors are likely to be present when determining their effective temperatures, which potentially compromises asteroseismic studies of these pulsators. Using long-baseline interferometry, our goal is to determine accurate angular diameters of a number of roAp targets to provide a temperature calibration for these stars. We obtained interferometric observations of 10 Aql with the visible spectrograph VEGA at the CHARA array. We determined a limb-darkened angular diameter of 0.275+/-0.009 mas and deduced a linear radius of 2.32+/-0.09 R_sun. We estimated the star's bolometric flux and used it, in combination with its parallax and angular diameter, to determine the star's luminosity and effective temperature. For two data sets of bolometric flux we derived an effective temperature of 7800+/-170 K and a luminosity of 18+/-1 L_sun or of 8000+/-210 K and 19+/-2 L_sun. We used these fundamental parameters together with the large frequency separation to constrain the mass and the age of 10 Aql, using the CESAM stellar evolution code. Assuming a solar chemical composition and ignoring all kinds of diffusion and settling of elements, we obtained a mass of 1.92 M_sun and an age of 780 Gy or a mass of 1.95 M_sun and an age of 740 Gy, depending on the considered bolometric flux. For the first time, we managed to determine an accurate angular diameter for a star smaller than 0.3 mas and to derive its fundamental parameters. In particular, by only combining our interferometric data and the bolometric flux, we derived an effective temperature that can be compared to those derived from atmosphere models. Such fundamental parameters can help for testing the mechanism responsible for the excitation of the oscillations observed in the magnetic pulsating stars

Evidence for a spectroscopic direct detection of reflected light from 51 Peg b

The detection of reflected light from an exoplanet is a difficult technical challenge at optical wavelengths. Even though this signal is expected to replicate the stellar signal, not only is it several orders of magnitude fainter, but it is also hidden among the stellar noise. We apply a variant of the cross-correlation technique to HARPS observations of 51 Peg to detect the reflected signal from planet 51 Peg b. Our method makes use of the cross-correlation function of a binary mask with high-resolution spectra to amplify the minute planetary signal that is present in the spectra by a factor proportional to the number of spectral lines when performing the cross correlation. The resulting cross-correlation functions are then normalized by a stellar template to remove the stellar signal. Carefully selected sections of the resulting normalized CCFs are stacked to increase the planetary signal further. The recovered signal allows probing several of the planetary properties, including its real mass and albedo. We detect evidence for the reflected signal from planet 51 Peg b at a significance of 3\sigma_noise. The detection of the signal permits us to infer a real mass of 0.46^+0.06_-0.01 M_Jup (assuming a stellar mass of 1.04\;M_Sun) for the planet and an orbital inclination of 80^+10_-19 degrees. The analysis of the data also allows us to infer a tentative value for the (radius-dependent) geometric albedo of the planet. The results suggest that 51Peg b may be an inflated hot Jupiter with a high albedo (e.g., an albedo of 0.5 yields a radius of 1.9 \pm 0.3 R_Jup for a signal amplitude of 6.0\pm0.4 x 10^-5). We confirm that the method we perfected can be used to retrieve an exoplanet's reflected signal, even with current observing facilities. The advent of next generation of observing facilities will yield new opportunities for this type of technique to probe deeper into exoplanets.Comment: 9 pages, 6 figure