Abstract
Resumo Este estudo visa a identificar como mecanismos de controle externo e interno da governança corporativa, tipicamente considerados no setor empresarial privado, são aplicados ou transformados para o setor público nas empresas estatais. A partir de uma revisão do problema de agência e dos mecanismos propostos para sua mitigação no contexto empresarial, este estudo analisa a situação da governança das empresas estatais no Brasil e em Portugal, com vistas a comparar as soluções adotadas nos dois países e as necessidades de desenvolvimento. Além de compartilhar histórias e fundamentos culturais comuns, esses países são caracterizados como ambientes de pouca segurança aos investidores e fragilidade de instrumentos de solução de litígios, por estruturas de propriedade concentradas e por mercados de capitais ainda insuficientes para pressionar o comportamento das empresas, condições que fragilizam os mecanismos de mercado de controle externo e amplificam a influência das peculiaridades das questões internas de governança das estatais. As análises apontam significativas evoluções recentes nas práticas de governança das estatais, mas identificam desafios que ainda precisam ser direcionados.

Abstract
The broadening of atomic emission lines by high-velocity motion of gas near accreting supermassive black holes is an observational hallmark of quasars(1). Observations of broad emission lines could potentially constrain the mechanism for transporting gas inwards through accretion disks or outwards through winds(2). The size of regions for which broad emission lines are observed (broad-line regions) has been estimated by measuring the delay in light travel time between the variable brightness of the accretion disk continuum and the emission lines(3)-a method known as reverberation mapping. In some models the emission lines arise from a continuous outflow(4), whereas in others they arise from orbiting gas clouds(5). Directly imaging such regions has not hitherto been possible because of their small angular size (less than 10(-4) arcseconds(3,6)). Here we report a spatial offset (with a spatial resolution of 10(-5) arcseconds, or about 0.03 parsecs for a distance of 550 million parsecs) between the red and blue photo-centres of the broad Paschen-alpha line of the quasar 3C 273 perpendicular to the direction of its radio jet. This spatial offset corresponds to a gradient in the velocity of the gas and thus implies that the gas is orbiting the central supermassive black hole. The data are well fitted by a broad-line-region model of a thick disk of gravitationally bound material orbiting a black hole of 3 x 10(8) solar masses. We infer a disk radius of 150 light days; a radius of 100-400 light days was found previously using reverberation mapping(7-9). The rotation axis of the disk aligns in inclination and position angle with the radio jet. Our results support the methods that are often used to estimate the masses of accreting supermassive black holes and to study their evolution over cosmic time.

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The energy sector is evolving rapidly, namely due to the increasing importance of renewable energy sources. The connection of large amounts of wind power generation poses new challenges for the dynamic voltage stability analysis of an electric power system, which has to be studied. In this paper, the traditional Doubly-Fed Induction Generator model is employed. Based on this model, a crowbar and chopper circuit is set up to protect the turbine during the short-circuit period. The EUROSTAG software package was used for the simulation studies of the system, and numerical results were obtained. Conclusions are drawn that provide a better understanding of the influence of crowbar and chopper protection on Doubly-Fed Induction Generators (DFIG), during low voltage ride through, in a system with wind power generation.

Abstract