Mass Flow and Accretion through gaps in Accretion Discs

We study the structure and dynamics of the gap created by a protoplanet in an accretion disc. The hydrodynamic equations for a flat, two-dimensional, non-selfgravitating protostellar accretion disc with an embedded, Jupiter sized protoplanet on a circular orbit are solved. To simulate possible accretion of mass onto the protoplanet we continually remove mass from the interior of the planet's Roche lobe which is monitored. Firstly, it is shown that consistent results independent on numerical issues (such as boundary or initial conditions, artificial viscosity or resolution) can be obtained. Then, a detailed parameter study delineates the influence of the disc viscosity and pressure on the magnitude of the accretion rate. We find that, even after the formation of a gap in the disc, the planet is still able to accrete more mass from the disc. This accretion occurs from regions of the disc which are radially exterior and interior to the planet's orbital radius. The rate depends on the magnitude of the viscosity and vertical thickness of the disc. For a disc viscosity alpha=10^{-3} and vertical thickness H/r=0.05 we estimate the time scale for the accumulation of one Jupiter mass to be of order hundred thousand years. For a larger(smaller) viscosity and disc thickness this accretion rate is increasing(decreasing). For a very small viscosity (alpha < 5 10^{-4}) the mass accretion rate through the gap onto the planet is markedly reduced, and the corresponding accretion time scale becomes larger than the viscous evolution time of the disc.Comment: 15 pages, Latex, uses MN Latex style v1.4, accepted by MN. Paper, figures and mpeg simulation available at http://www.tpi.uni-jena.de/~wak/research/gap/gap.htm

Orbital Stability of Planets in Binary Systems: A New Look at Old Results

About half of all known stellar systems with Sun-like stars consist of two or more stars, significantly affecting the orbital stability of any planet in these systems. This observational evidence has prompted a large array of theoretical research, including the derivation of mathematically stringent criteria for the orbital stability of planets in stellar binary systems, valid for the "coplanar circular restricted three-body problem". In the following, we use these criteria to explore the validity of results from previous theoretical studies.Comment: 3 pages, 1 figure; submitted to: Exoplanets: Detection, Formation and Dynamics, IAU Symposium 249, eds. Y.-S. Sun, S. Ferraz-Mello, and J.-L. Zhou (Cambridge: Cambridge University Press

Editorial Board

Editors-in Chief E. Lars Phillips Mike Wilson Executive Editors Carrie Gibadlo Michelle Tafoya Articles Editor Lucas Hamilton Online Editors Aaron Brann Tyler M. Stockton Business Editor Paige Griffith Intake Editor James Murnion Staff Luc Brodhead Jason Colling Briad Geer Eli Inabnit Marin Keyes Nicholas LeTang Brandon Shannon Megan Timm Constance Van Kley Connor Walker Caitlin Williams Kristen Zadick Faculty Advisor Anthony Johnston

Iluminismo e religião: ruptura ou continuidade?

This article, through a review of a portion of the relevant literature, problematizes the way in which the connection between the Enlightenment and religion has traditionally been explained, principally by a historiography excessively focused on the 18th century French experience. Alternatively, this article argues that “continuity,” rather than “rupture,” more adequately describes this relationship. However, continuity, as understood here, excludes neither tension nor transformation. If, on the one hand, the Enlightenment is much more akin to religion than has been previously recognized, on the other hand, it has to a great extent shaped modern understanding of religion. This revision of the relationship between the Enlightenment and religion suggests the need to rethink the very identity of the Enlightenment and the issue of secularization. The article uses as a guide the German debate surrounding the question, “What is the Enlightenment?” It concludes with an analysis of Kant’s famous contribution to this debate.A partir de uma revisão de parte da literatura recente sobre o tema, este artigo busca problematizar a maneira pela qual Iluminismo e religião foram tradicionalmente articulados, sobretudo por uma historiografia excessivamente focada na experiência do século XVIII francês. Em contraposição, este artigo argumenta que “continuidade” é um termo que expressa de forma mais adequada essa relação do que o termo “ruptura”. No entanto, continuidade, como se defende, não exclui tensões nem tampouco transformações. Se, de um lado, o Iluminismo é muito mais próximo da religião do que se reconhece; de outro, ele modelou em larga medida o entendimento moderno da religião. A revisão da relação entre Iluminismo e religião implica também repensar a própria identidade do Iluminismo e a questão da secularização. O artigo toma o debate alemão em torno da questão “o que é Iluminismo?” como fio condutor do comentário, que se encerra com uma análise da famosa contribuição de Kant a esse debate

Reversing type II migration: resonance trapping of a lighter giant protoplanet

We present a mechanism related to the migration of giant protoplanets embedded in a protoplanetary disc whereby a giant protoplanet is caught up, before having migrated all the way to the central star, by a lighter outer giant protoplanet. This outer protoplanet may get captured into the 2:3 resonance with the more massive one, in which case the gaps that the two planets open in the disc overlap. Two effects arise, namely a squared mass weighted torque imbalance and an increased mass flow through the overlapping gaps from the outer disc to the inner disc, which both play in favour of an outwards migration. Indeed under the conditions presented here, which describe the evolution of a pair of protoplanets respectively Jupiter and Saturn sized, the migration is reversed, while the planets semi-major axis ratio is constant and the eccentricities are confined to small values by the disc material. The long-term behaviour of the system is briefly discussed, and could account for the high eccentricities observed for the extrasolar planets with semi-major axis a>0.2 AU.Comment: 5 pages, 4 figures. Accepted for publication in MNRA

Propaganda pombalina em França: tradução, visualização, radicalização

The fact that Pombal is today one of the most important actors of enlightened absolutism is due above all to his comprehensive reform program, which included virtually all political fields of action of the 18th century. At least as important, however, is the fact that he accompanied his measures with extremely intensive public relations work: Pombal had understood how important it was to get public opinion in Europe on his side, because especially those reforms that threatened the traditional rights and positions of power of the Catholic Church were the subject of controversial debate in a Europe divided along confessional lines. France played an important role in the European battle of opinion: French intellectuals and publicists dominated international public opinion, and French was the language of the educated and enlightened. This paper will therefore examine how Pombal's propaganda functioned in France and what significance French translations and adaptations had for the European battle of opinion.O facto de Pombal ser hoje um dos mais importantes atores do despotismo esclarecido deve-se sobretudo ao seu abrangente programa de reformas aberto a praticamente todos os campos de atuação política do século xviii. Igualmente importante, também, é o facto de ter acompanhado as suas medidas com um trabalho de relações públicas extremamente intenso: Pombal compreendera a importância de ter a opinião pública europeia do seu lado porque precisamente aquelas reformas que ameaçavam os direitos e cargos tradicionais de poder da Igreja Católica foram objeto de um debate controverso numa Europa dividida por linhas confessionais. A França desempenhou um papel importante na batalha europeia de opinião: os intelectuais e publicitários franceses dominaram a opinião pública internacional e o francês era a língua falada pela população educada e ilustrada. Este artigo examinará, portanto, a propaganda de Pombal em França e o papel das traduções e adaptações na batalha de opinião pública.info:eu-repo/semantics/publishedVersio

The impact of the spacecraft system SÄNGER on the composition of the middle atmosphere

A two-dimensional chemical model and physical considerations are used to estimate the impact of the spacecraft system SÄNGER on stratospheric and mesospheric ozone in relation to other spacecraft and other anthropogenic perturbations. Perturbations of middle atmospheric NOy H2O and H2 concentrations, and their impact on the radiative balance of the atmosphere, including contrail formation, are discussed. It is found, that in case of about 24 launches per year the perturbations due to SÄGER are about negligible on a global scale. However, if a SÄGER version would be used for a hypersonic fleet of commercial aircraft a serious ozone depletion is predicted. © 1992 by Wax Planck Society

Editorial Board

Editors-in Chief Nicholas LeTang Constance Van Kley Executive Editors Kristen Meredith Megan Timm Symposium Editors Brandon Shannon Caitlin Williams Articles Editors Luc Brodhead Marin Keyes Online Editor Brian Geer Business Editor Elijah Inabnit Intake Editor Connor Walker Staff Erik Anderson Katy Brautigam Tim Brothwell Morgan Changler Victoria Dettman Emily Gutierrez Dillon Haskell Cori Losing Molly McCarty Rachel Pannabecker Hannah Wilson Faculty Advisor Anthony Johnston