The QSO variability-luminosity-redshift relation

The relationship between variability, luminosity and redshift in the South Galactic Pole QSO sample is examined in an effort to disentangle the effects of luminosity and redshift in the amplitude of the optical variations. The anticorrelation between variability and luminosity found by other authors is confirmed. Our analysis also supports claims that variability increases with redshift, most likely due to an anticorrelation between variability and wavelength. In particular, our parametric fits show that the QSO variability-wavelength relation is consistent with that observed in low-luminosity nearby active galactic nuclei. The results are used to constrain Poissonian-type models. We find that if QSO variability results from a random superposition of pulses, then the individual events must have B-band energies between $\sim 10^{50}$ and a few times $10^{51}$ erg and time-scales of $\sim 2$ yr. Generalized Poissonian models in which the pulse energy and lifetime scale with luminosity are also discussed.Comment: 12 pages, ps-file, 501kB. Also available at http://www.if.ufrgs.br/~cid MNRAS, accepted (31/May/1996

Divergent nematic susceptibility in an iron arsenide superconductor

Within the Landau paradigm of continuous phase transitions, ordered states of matter are characterized by a broken symmetry. Although the broken symmetry is usually evident, determining the driving force behind the phase transition is often a more subtle matter due to coupling between otherwise distinct order parameters. In this paper we show how measurement of the divergent nematic susceptibility of an iron pnictide superconductor unambiguously distinguishes an electronic nematic phase transition from a simple ferroelastic distortion. These measurements also reveal an electronic nematic quantum phase transition at the composition with optimal superconducting transition temperature.Comment: 8 pages, 8 figure

Long Term Variability of SDSS Quasars

We use a sample of 3791 quasars from the Sloan Digital Sky Survey (SDSS) Early Data Release (EDR), and compare their photometry to historic plate material for the same set of quasars in order to study their variability properties. The time base-line we attain this way ranges from a few months to up to 50 years. In contrast to monitoring programs, where relatively few quasars are photometrically measured over shorter time periods, we utilize existing databases to extend this base-line as much as possible, at the cost of sampling per quasar. Our method, however, can easily be extended to much larger samples. We construct variability Structure Functions and compare these to the literature and model functions. From our modeling we conclude that 1) quasars are more variable toward shorter wavelengths, 2) their variability is consistent with an exponentially decaying light-curve with a typical time-scale of ~2 years, 3) these outbursts occur on typical time-scales of ~200 years. With the upcoming first data release of the SDSS, a much larger quasar sample can be used to put these conclusions on a more secure footing.Comment: 16 pages, accepted for publication in AJ, Sept issu

Obscuring Active Galactic Nuclei with Nuclear Starburst Disks

We assess the potential of nuclear starburst disks to obscure the Seyfert-like AGN that dominate the hard X-ray background at z~1. Over 1200 starburst disk models, based on the theory developed by Thompson et al., are calculated for five input parameters: the black hole mass, the radial size of the starburst disk, the dust-to-gas ratio, the efficiency of angular momentum transport in the disk, and the gas fraction at the outer disk radius. We find that a large dust-to-gas ratio, a relatively small starburst disk, a significant gas mass fraction, and efficient angular momentum transport are all important to produce a starburst disk that can potentially obscure an AGN. The typical maximum star-formation rate in the disks is ~10 solar masses per year. Assuming no mass-loss due to outflows, the starburst disks feed gas onto the black hole at rates sufficient to produce hard X-ray luminosities of 10^{43}-10^{44} erg s^{-1}. The starburst disks themselves should be detectable at mid-infrared and radio wavelengths; at z=0.8, the predicted fluxes are ~1 mJy at 24microns and ~10-30 microJy at 1.4GHz. Thus, we predict a large fraction of radio/X-ray matches in future deep radio surveys. The starburst disks should be easily distinguished from AGN in future 100microns surveys by Herschel with expected fluxes of ~5 mJy. Any AGN-obscuring starbursts will be associated with hot dust, independent of AGN heating, resulting in observable signatures for separating galactic and nuclear star-formation. Finally, because of the competition between gas and star-formation, nuclear starbursts will be associated with lower-luminosity AGN. Thus, this phenomenon is a natural explanation for the observed decrease in the fraction of obscured AGN with luminosity.Comment: 13 pages, 12 figures, 3 in color; accepted by Ap

Internationalization of board members and compliance with mandatory disclosure: Empirical study of IFRS 3 (business combinations) in Brazil

The determinants tested in the mandatory disclosure are usually about business and cultural factors. However, the board members have a strong power of decision on the information disclosed, so it is natural that the characteristics of board members can influence the fulfillment of disclosure. This study analyses the level of compliance with IFRS 3 and examines whether it is influenced by the level of internationalization of board members. Our results indicate a moderate level of compliance, which is greater the greater the weight of foreign board members and the weight of board members with training abroad.info:eu-repo/semantics/publishedVersio

The optical-ultraviolet continuum of Seyfert 2 galaxies

This paper aims to understand the continuum of Seyfert 2 galaxies. By fitting the single galaxies in the sample of Heckman et al. (1995) with composite models (shock+ photoionization from the active center), we show that five main components characterize the SED of the continuum. Shocks play an important role since they produce a high temperature zone where soft X-rays are emitted. We show that in the optical-UV range, the slope of the NLR emission reproduces the observed values, and may be the main component of the featureless continuum. The presence of star forming regions cannot be excluded in the circumnuclear region of various Seyfert galaxies. An attempt is made to find their fingerprints in the observed AGN spectra. Finally, it is demonstrated that multi-cloud models are necessary to interpret the spectra of single objects, even in the global investigation of a sample of galaxies.Comment: 26 pages, LaTeX (including 5 Tables) + 17 PostScript figures. To appear in "The Astrophysical Journal

Necrotizing Fasciitis and Middle Ear Infection

A fasceíte necrosante (FN) é uma doença rara em pediatria. Na maior parte dos casos surge como complicação de varicela, sendo a pele habitualmente a porta de entrada e o Streptococcus pyogenes o agente mais frequente. Os autores descrevem um caso clínico de uma criança de 8 anos, previamente saudável que, no contexto de uma otite média aguda medicada com um anti-inflamatório não esteróide (AINE), desenvolve uma infecção invasiva a Streptococcus 13 hemoliticus do grupo A