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- D. Elstner, R. Arlt
- 1997

Following earlier suggestions to replace the ensemble average used in the mean-eld electrodynamics by an averaging over the azimuthal coordinate we consider the basic coeecients in the turbulent electromotive force (EMF) as time-dependent functions. The well-known coeecients and T { both in the relevant tensorial formulations { are derived from one and the… (More)

- L. Jouve, A. S. Brun, +9 authors A. G. Kosovichev
- 2008

Context. The solar magnetic activity and cycle are linked to an internal dynamo. Numerical simulations are an efficient and accurate tool to investigate such intricate dynamical processes. Aims. We present the results of an international numerical benchmark study based on two-dimensional axisymmetric mean field solar dynamo models in spherical geometry. The… (More)

- G. Rüdiger, R. Arlt, D. Shalybkov
- 2002

The hydrodynamic stability of accretion disks is considered. The particular question is whether the combined action of a (stable) vertical density stratification and a (stable) radial differential rotation gives rise to a new instability for nonax-isymmetric modes of disturbances. The existence of such an instability is not suggested by the well-known… (More)

Received ; accepted – 2 – ABSTRACT Because of the lack of reliable sunspot observation, the quality of sunspot number series is poor in the late 18th century, leading to the abnormally long solar cycle (1784–1799) before the Dalton minimum. Using the newly recovered solar drawings by the 18–19th century observers Staudacher and Hamilton, we construct the… (More)

- R. Arlt, A. Brandenburg
- 2001

The origin of large scale magnetic fields in accretion discs is investigated. Using global three-dimensional simulations of accretion disc turbulence, a recent suggestion of Vishniac & Cho (2001, ApJ 550, 752) is reexamined , according to which large scale fields in accretion discs could be understood without explicitly invoking the usual helicity effect.… (More)

- G R Udiger, L Primavera, R Arlt, D Elstner
- 1997

The possibility that the magnetic shear-ow instability (alsòBalbus-Hawley' instability) might give rise to turbulence in a thin accretion disk is investigated through numerical simulations. The study is linear and the uid disk is supposed to be incompressible and diierentially rotating with a simple velocity proole with / R ?q. The simplicity of the model… (More)

- S Hubrig, J F González, R Arlt
- 2008

The important result achieved in our recent study of a large sample of HgMn stars using UVES at the VLT and FEROS at the ESO 2.2 m telescope is the finding that most HgMn stars exhibit spectral variability of various chemical elements, proving that the presence of an inhomogeneous distribution on the surface of these stars is a rather common characteristics… (More)

- R Arlt, G R Udiger
- 2008

A 2D mean-field MHD code for spheres is used to check the nonlinear interplay between dynamo-induced magnetic fields and the differential rotation in convection zones. The magnetic back-reaction is threefold: Lorentz force,-quenching and-quenching. If only the Malkus-Proctor feedback is used then the dynamo shows an interesting nonperiodic behavior which,… (More)

- June, Gautier Mathys, +32 authors Aysegul Teker
- 2013