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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 nonaxisymmetric modes of disturbances. The existence of such an instability is not suggested by the well-known(More)
Digitized images of the drawings by J.C. Staudacher were used to determine sunspot positions for the period of 1749–1796. From the entire set of drawings, 6285 sunspot positions were obtained for a total of 999 days. Various methods have been applied to find the orientation of the solar disk which is not given for the vast majority of the drawings by(More)
Stars of spectral classes A and late B are almost entirely radiative. CP stars are a slowly rotating subgroup of these stars. It is possible that they possessed long-lived accretion disks in their T Tauri phase. Magnetic coupling of disk and star leads to rotational braking at the surface of the star. Microscopic viscosities are extremely small and will not(More)
Ultrasonography performed on 517 patients presenting as surgical emergencies permitted many specific diagnoses. In 95 % of patients with bile duct pathology, diagnosis was correct. In patients with pancreatitis, ultrasonography was sufficiently reliable only in stage II and beyond. When acute appendicitis was suspected, ultrasonography was of great(More)
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 solar butterfly diagram, i.e. the(More)
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)