Search Results - (Author, Cooperation:G. Schubert)

2011-05-14

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

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Chemistry and Pharmacology

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article

1983

Experimentelle Physik ; Flüssigkeit ; Physikunterricht ; Schall ; Synergetik

Vorträge der Frühjahrstagung, Bd. Tagung 1982 (1983) S. 466-480, 3-923835-14-0

German

1089-7666

AIP Digital Archive

Physics

In this study, we carry out numerical simulations of thermal convection in a rapidly rotating spherical fluid shell at high Taylor number Ta and Rayleigh number R with a nonlinear, three-dimensional, time-dependent, spectral-transform code. The parameters used in the simulations are chosen to be in a range which allows us to study two different types of convection, i.e., single column and multi-layered types, and the transition between them. Numerical solutions feature highly time-dependent north–south open columnar convective cells. The cells occur irregularly in longitude, are quasi-layered in cylindrical radius, and maintain alternating bands of mean zonal flow. The complex convective structure and the banded mean zonal flow are results of the high Taylor and Rayleigh numbers. The transition between the two types of convection appears to occur gradually with increasing Rayleigh and Taylor numbers. At a Taylor number of 107 the differential rotation pattern consists of an inner cylindrical region of subrotation and an outer cylindrical shell of superrotation manifest at the outer boundary as an equatorial superrotation and a high latitude subrotation. The differential rotation pattern is similar at Ta=108 and low Rayleigh number. Cylindrical shells of alternately directed mean zonal flow begin to develop at Ta=108 and R=50Rc and at Ta=109 and R=25Rc. This pattern is seen on the outer surface as a latitudinally-banded zonal flow consisting of an equatorial superrotation, a middle and high latitude subrotation, and a polar superrotation. At Ta=109 and R=50Rc the differential rotation appears at the surface as a broad eastward flow in the equatorial region with alternating bands of westward and eastward flow at high latitudes. © 1995 American Institute of Physics.

Electronic Resource

1089-7666

AIP Digital Archive

Physics

Numerical calculations have been carried out of steady, symmetric, three-dimensional modes of convection in internally heated, infinite Prandtl number, Boussinesq fluids at a Rayleigh number of 1.4×104 in a spherical shell with inner/outer radius of 0.55 and in a 3×3×1 rectangular box. Multiple patterns of convection occur in both geometries. In the Cartesian geometry the patterns are dominated by cylindrical cold downflows and a broad hot upwelling. In the spherical geometry the patterns consist of cylindrical cold downwellings centered either at the vertices of a tetrahedron or the centers of the faces of a cube. The cold downflow cylinders are immersed in a background of upwelling within which there are cylindrical hot concentrations (plumes) and hot halos around the downflows. The forced hot upflow return plumes of internally heated spherical convection are fundamentally different from the buoyancy-driven plumes of heated from below convection.

Electronic Resource

1089-7666

AIP Digital Archive

Physics

The equations for three-dimensional, time-dependent convection in a gravitationally modulated fluid layer heated from below are solved numerically using the Galerkin method in space and a Crank–Nicolson scheme in time. Nonlinear solutions are obtained for the Prandtl number of air (0.71) and for two Rayleigh numbers above the value for onset of oscillatory convection. Multiples of the fundamental frequency of oscillatory convection were chosen in order to study the effects of possible resonances of the frequency of gravitational modulation. Modulation causes a transition from traveling wave convection, which persists in the unmodulated case, to standing wave convection and phase locking occurs for moderate values of the amplitude of the dimensionless gravitational modulation (scaled with the standard acceleration of gravity) in the range 0 to 3. For larger values of the modulation amplitude, frequency locking breaks down and chaotic time dependence occurs.

Electronic Resource

1365-246X

Blackwell Publishing Journal Backfiles 1879-2005

Geosciences

bThe Earth is found to equilibrate thermally after a giant impact melts a significant portion of the planet on a time-scale of a few million years. A simple thermal evolution model for the cooling of a terrestrial planet, a prescribed fraction of which is melted during a giant impact, is presented. Two model geometries are considered. The first has a laterally inhomogeneous distribution of melt and solid through a mega-crater geometry and the second has a global magma ocean. The model assumes convective heat transfer in the melt and, in the case of the mega-crater geometry, convection in the solid part of the planet. In the magma-ocean case the solid interior is not convecting. The melt region may cool due to heat transfer to the planet's surface and to the solid region and due to melting of solid. The solid region cools by heat transfer to the planet's surface in the mega-crater model. The viscosities of the melt and the solid are assumed to be dependent on the exponential of the inverse absolute temperature. Convective heat transfer is parametrized by using semi-empirical boundary layer thickness scaling laws. Most model parameters including planetary size are absorbed into a cooling time-scale. Of the remaining parameters of the scaled model, the rate of change of melt viscosity with temperature, the surface temperature and, for small melt fractions, the melt region geometry are most important in determining the cooling time. The initial melt temperature, the heat capacities of the solid and the melt, and the Stefan number, a measure of the latent heat of melting, determine the proportion of the solid that is melted during cooling of the impact melt. It is found that almost the whole planet may melt if the impact originally melted half of the planet and if the initial melt temperature was twice a representative planet melting temperature. For reasonable choices of parameter values it is found that thermal equilibration of the Earth occurs on a time-scale of 1 to 10 million years.

Electronic Resource

1365-2761

Blackwell Publishing Journal Backfiles 1879-2005

Biology

Medicine

Abstract. Trophonts of Pisdnoodinium pillulare (Schäperclaus, 1954), a common ectoparasite of freshwater aquarium fish, are attached to host cells by means of a specialized structure, the attachment disc. Unlike other dinoflagellate genera parasitic on fish and invertebrates, this disc features nail-like organelles, the rhizocysts. Head-parts of the rhizocysts are inverted in separate compartments, rhizothecas, in the sole of the disc while their long shafts are firmly embedded in the cytoplasm of cells of the host epidermis or gill epithelium. The attachment inflicts a serious injury on the host cells which may ultimately be destroyed. Rhizocysts originate in the subnuclear cytoplasm from where they migrate into the attachment disc. There are other specialized organelles and inclusions; fibrous vesicles, membraneous bodies, striated tubular bodies and paracrystalline bodies. Pisdnoodinium has well-developed chloroplasts. While its cytological adaptations indicate a nutritional dependence on the host, there is no evidence of ingestion of host-derived particulate material. Pisdnoodinium may derive an essential part of its nutrition from photosynthesis.

Electronic Resource

1476-4687

Nature Archives 1869 - 2009

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

[Auszug] Calculations of tidal dissipation in Europa have been only partly successful in accounting for a tidal heating rate large enough to prevent the solidification of an internal ocean. Cassen et al.8 corrected their original work4 and concluded that a subsurface liquid water layer would be rather ...

Electronic Resource

1476-4687

Nature Archives 1869 - 2009

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

[Auszug] It has been argued that frictional heating along slip zones between subducting and overriding plates provides the heat for partial melting1'2. At hot spots the suggested sources of heat are more controversial, ranging from shear heating in the asthenosphere3 to more vague sources associated with ...

Electronic Resource

1476-4687

Nature Archives 1869 - 2009

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

[Auszug] REISZ et al.1 consider, in the preceding letter, two conceptually important points regarding the lunar transfer function inversions which we reported2,3. That work used a symmetric confining current theory so that the dark hemisphere diamagnetic cavity effect was ignored, as we pointed out at that ...

Electronic Resource

1476-4687

Nature Archives 1869 - 2009

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

[Auszug] On Mars, the strong magnetization in the highland crust of the southern hemisphere and the absence of magnetic anomalies at the Hellas and Argyre impact basins have been taken as signs that the core dynamo that once drove the planet's magnetic field turned off more than 4 billion years ...

Electronic Resource

1476-4687

Nature Archives 1869 - 2009

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

[Auszug] The atmosphere of Jupiter has a complex circulation which, until recently, has been observable only at the cloud tops,; the mechanisms driving the winds, and the nature of the interior circulation, remained unknown. Recent analyses of the radio signal from the Galileo probe, obtained during its ...

Electronic Resource

1476-4687

Nature Archives 1869 - 2009

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

[Auszug] On Galileo's first inbound pass following orbital insertion, the magnetometer2 measurements followed reasonably closely the predictions from a recent model of the magnetic field of Jupiter's magnetosphere3 that we refer to as the KK96 model. (This model consists of the O6 model4 of Jupiter's ...

Electronic Resource

1476-4687

Nature Archives 1869 - 2009

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

[Auszug] The Galileo spacecraft has been orbiting Jupiter since 7 December 1995, and encounters one of the four galilean satellites—Io, Europa, Ganymede and Callisto—on each orbit. Initial results from the spacecraft's magnetometer, have indicated that neither Europa nor Callisto have an ...

Electronic Resource

1476-4687

Nature Archives 1869 - 2009

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

[Auszug] The ice-rich surface of the jovian satellite Europa is sparsely cratered, suggesting that this moon might be geologically active today. Moreover, models of the satellite's interior indicate that tidal interactions with Jupiter might produce enough heat to maintain a subsurface liquid water ...

Electronic Resource

1476-4687

Nature Archives 1869 - 2009

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

[Auszug] Galileo's first encounter with Callisto took place on 4 November 1996, and the gravity signal was detected in the radio Doppler data recorded during the encounter. The data analysis was accomplished by fitting a parametrized orbital model to the radio Doppler data by weighted nonlinear least ...

Electronic Resource

1476-4687

Nature Archives 1869 - 2009

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

[Auszug] The data were analysed by fitting a parametrized orbital model to the radio Doppler data by weighted nonlinear least squares8"10. The two encounters between Galileo and Ganymede (on 27 June and 6 September 1996) were analysed independently. Ganymede's external gravitational field was modelled by ...

Electronic Resource

0012-821X

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Geosciences

Physics

Electronic Resource

0012-821X

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Geosciences

Physics

Electronic Resource

0012-821X

Elsevier Journal Backfiles on ScienceDirect 1907 - 2002

Geosciences

Physics

Electronic Resource