Modelling Accretion in Transitional Disks

Transitional disks are protoplanetary disk around young stars that display inner holes in the dust distribution within a few AU, which is accompanied nevertheless by some gas accretion onto the central star. These cavities could possibly be created by the presence of one or more massive planets. If the gap is created by planets and gas is still present in it, then there should be a flow of gas past the planet into the inner region. It is our goal to study the mass accretion rate into the gap and in particular the dependency on the planet's mass and the thermodynamic properties of the disk. We performed 2D hydro simulations for disks with embedded planets. We added radiative cooling from the disk surfaces, radiative diffusion in the disk midplane, and stellar irradiation to the energy equation to have more realistic models. The mass flow rate into the gap region depends, for given disk thermodynamics, non-monotonically on the mass of the planet. Generally, more massive planets open wider and deeper gaps which would tend to reduce the mass accretion into the inner cavity. However, for larger mass planets the outer disk becomes eccentric and the mass flow rate is enhanced over the low mass cases. As a result, for the isothermal disks the mass flow is always comparable to the expected mass flow of unperturbed disks M_d, while for more realistic radiative disks the mass flow is very small for low mass planets (<= 4 M_jup) and about 50% for larger planet masses. For the radiative disks that critical planet mass for the disk to become eccentric is much larger that in the isothermal case. Massive embedded planets can reduce the mass flow across the gap considerably, to values of about an order of magnitude smaller than the standard disk accretion rate, and can be responsible for opening large cavities. The remaining mass flow into the central cavity is in good agreement with the observations.Comment: 10 pages, 29 figures, accepted for publication in Astronomy & Astrophysic

Unraveling the influence of domain knowledge during simulation-based inquiry learning

This study investigated whether the mere knowledge of the meaning of variables can facilitate inquiry learning processes and outcomes. Fifty-seven college freshmen were randomly allocated to one of three inquiry tasks. The concrete task had familiar variables from which hypotheses about their underlying relations could be inferred. The intermediate task used familiar variables that did not invoke underlying relations, whereas the abstract task contained unfamiliar variables that did not allow for inference of hypotheses about relations. Results showed that concrete participants performed more successfully and efficiently than intermediate participants, who in turn were equally successful and efficient as abstract participants. From these findings it was concluded that students learning by inquiry benefit little from knowledge of the meaning of variables per se. Some additional understanding of the way these variables are interrelated seems required to enhance inquiry learning processes and outcomes

Stationary and transient leakage current in the Pauli spin blockade

We study the effects of cotunneling and a non-uniform Zeeman splitting on the stationary and transient leakage current through a double quantum dot in the Pauli spin blockade regime. We find that the stationary current due to cotunneling vanishes at low temperature and large applied magnetic field, allowing for the dynamical preparation of a pure spin ground state, even at large voltage bias. Additionally, we analyze current that flows between blocking events, characterized, in general, by a fractional effective charge $e^*$. This charge can be used as a sensitive probe of spin relaxation mechanisms and can be used to determine the visibility of Rabi oscillations.Comment: v1: 4 pages; v2: 4 pages+ additional supplementary material, version to appear in PR

I\u27m sometimes sad, but know not why

[Verse 1]I\u27m sometimes sad, but know not why, And weep at evening hour;Then gentlest murmurs whisper by,And stillness wakes her power.I\u27m sometimes sad when Cynthia\u27s beamsThe fountains silver o\u27er;I wander then among the elms,Where shadows hide my tear,Where shadows hide my tear. [Verse 2]I\u27m sometimes sad, when friends that were,My sorrows wake anew;They once were here but now they areWhere weeping willows grow!I\u27m sometimes sad, when friends that be,Excite the tender sigh;For soon a long adieu, they\u27ll say!And so must I, must I And so must I, must I. [Verse 3]I\u27m sometimes sad among the crowd,And in the circle glee;And often when the laugh is loud,I go to bend the knee.I\u27m sometimes sad, and think I\u27ve noneTo shed a tear with me!And who for Welwyneer will mourn,When \u27neath the pendant tree?When \u27neath the pendant tree? [Verse 4]Sad world! where is thy soothing pow\u27r,At morn, or vesper mild?Or where when noontide tells the hour,The charm for sorrows child?Tho\u27 sad I roam, tho\u27 drop the tear\u27Mid light, or shadows gloom,Ere long I\u27ll lay me silent there, Low in the peaceful Tomb, Low in the peaceful Tomb

AI meets DA

Der Beitrag beschäftigt sich mit der Diskursmodellierung im Rahmen des Forschungsverbundprojekts Verbmobil, das industrielle und universitäre Forschungseinrichtungen zur Entwicklung eines mobilen Dolmetschcomputers zusammenführte. Dabei wird aufgezeigt, daß sich die Informatik schwer tat, die Erfahrungen der funktionalen Pragmatik einzubinden. Der Nutzen der Diskursanalyse im Rahmen der Pragmatik für die Informatik wird in drei Punkten gesehen: (a) aus einem zweckbezogenen Verständnis sprachlichen Handelns berücksichtigt die DA über die unmittelbar sichtbaren sprachlichen Handlungen auch die gesellschaftlichen Voraussetzungen und Rahmenbedingungen des Handelns und die erschließbaren mentalen Dimensionen ("Einbettung", "Motivierung", "Authentizität" usw.); (b) aus einer funktional-zweckbezogenen Sicht auf die sprachlichen Mittel und ihre Verwendung beim sprachlichen Handeln folgt eine Modellierung des Handelns im Handlungsmuster, das eine adäquatere Diskursmodellierung und Klassifizierung sprachlicher Mittel erlaubt als die in der KI verwendeten flachen Modellierungsverfahren; (c) durch Verwendung computergestützter Werkzeuge, z.B. von Petri-Netzen, werden dynamische Modellierungen möglich, die die statischen Musterdiagramme einerseits abstrakt modellieren, andererseits mit eingegebenen Daten konkrete Musterdurchläufe simulieren; damit werden auch die Grenzen zwischen qualitativen und quantitativen Forschungsmethoden überwindbar.</p