Intermittent Behaviour in Axisymmetric Mean-Field Dynamo Models in Spherical Shells     

Andrew Tworkowski  Reza Tavakol  Axel Brandenburg  John M. Brooke  David Moss  & Ilkka Tuominen 《Monthly notices of the Royal Astronomical Society》1998,296(2):287-295

Axisymmetric mean-field dynamo models in spherical shells are shown to be capable of producing temporally intermittent behaviour. This is of potential importance since (i) it is, as far as we are aware, the first time such behaviour has been produced internally by a mean-field dynamo model in a spherical shell, without requiring any additional assumptions or truncations, and (ii) it may be characteristic of the type of behaviour observed in the long-term record of solar activity, such as Maunder minima. We also show that these types of behaviour persist when the functional form of the alpha quenching is altered and also occur over intervals of the shell thickness and the dynamo number.  相似文献   

The radial disc structure around a magnetic neutron star: analytic and semi-analytic solutions     

Axel Brandenburg  & Chris G. Campbell 《Monthly notices of the Royal Astronomical Society》1998,298(1):223-230

The radial structure of a thin accretion disc is calculated in the presence of a central dipole magnetic field aligned with the rotation axis. The problem is treated using a modified expression for the turbulent magnetic diffusion, which allows the angular momentum equation to be integrated analytically. The governing algebraic equations are solved iteratively between 1 and 10⁴ stellar radii. An analytic approximation is provided that is valid near the disruption radius at about 100 stellar radii. At that point, which is approximately 60 per cent of the Alfvén radius and typically about 30 per cent of the corotation radius, the disc becomes viscously unstable. This instability results from the fact that both radiation pressure and opacity caused by electron scattering become important. This in turn is a consequence of the magnetic field which leads to an enhanced temperature in the inner parts. This is because the magnetic field gives rise to a strongly enhanced vertically integrated viscosity, so that the viscous torque can balance the magnetic torque.  相似文献   

Der untersilurische Brandschiefer von Kuckers (Estland)     

Axel Born 《International Journal of Earth Sciences》1914,5(4):313-317

Ohne Zusammenfassung  相似文献   

Die schwedische Hochgebirgsfrage und die Häufigkeit der Überschiebungen     

Axel Hamberg 《International Journal of Earth Sciences》1912,3(4):219-236

Ohne Zusammenfassung  相似文献   

Der Einfluß einiger aÜßerer Faktoren auf die geschiechtliche Entwicklung und die Segmentbildung bei Anaitides mucosa (Annelida, Polychaeta, Phyllodocidae)     

Axel  Röhrkasten 《Marine Ecology》1984,5(2):135-142

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Robustness of truncated α Ω dynamos with a dynamic α     

Covas  Eurico  Tworkowski  Andrew  Tavakol  Reza  Brandenburg  Axel 《Solar physics》1997,172(1-2):3-9

In a recent work (Covas et al., 1996), the behaviour and the robustness of truncated dynamos with a dynamic were studied with respect to a number of changes in the driving term of the dynamic equation, which was considered previously by Schmalz and Stix (1991) to be of the form AB. Here we review and extend our previous work and consider the effect of adding a quadratic quenching term of the form |B|². We find that, as before, such a change can have significant effects on the dynamics of the related truncated systems. We also find intervals of (negative) dynamo numbers, in the system considered by Schmalz and Stix (1991), for which there is sensitivity with respect to small changes in the dynamo number and the initial conditions, similar to what was found in our previous work. This latter behaviour may be of importance in producing the intermittent type of behaviour observed in the Sun.  相似文献   

Melt evolution in felsic dikes inferred from the composition of gahnite in two new occurrences,Pala Chief and Elizabeth R composite dikes,California     

Adriana Heimann  Jason A. Yonts  Michael A. Wise 《Mineralogy and Petrology》2016,110(6):731-746

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Mechanisms rectifying the annual mean response of tropical Atlantic rainfall to precessional forcing     

Michelle Tigchelaar  Axel Timmermann 《Climate Dynamics》2016,47(1-2):271-293

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The role of floating mucilage in the invasive spread of the benthic microalga Chrysophaeum taylorii          下载免费PDF全文

Sarah Caronni  Maria Anna Delaria  Kirsten Heimann  Giovanni Macri  Augusto Navone  Pieraugusto Panzalis  Giulia Ceccherelli 《Marine Ecology》2016,37(4):867-876

Chrysophaeum taylorii Lewis & Bryan (Pelagophyceae) is a mucilage‐producing benthic microalga that has recently begun to spread in the Mediterranean Sea, where a range expansion is occurring. This paper presents the results of three field experiments that aimed to increase the knowledge on mucilage provision mechanisms for this benthic microalga and to evaluate the importance of mucilage in its range expansion. By means of two correlative field experiments (several years of data were considered to encompass the variability of mucilage cover) we found that, on the sea bottom, mucilage cover does not depend on epilithic cell density and that both its cover and settling are affected by water flow. We also tested the hypothesis that cells embedded in floating mucilage fall on the underlying substratum, where their abundance depends on water flow. To this aim, in the field we manipulated the presence of floating mucilaginous aggregates in cages with different levels of exposure to winds. The abundance of C. taylorii cells on the substratum under cages with mucilage was compared with that of two control treatments: cages without mucilage and mucilage in still water, in the field and lab, respectively. The results suggested that mucilage can represent an excellent strategy for the species to disperse, as C. taylorii cells fall from the floating mucilage and, if the water flow is unimportant, settle on hard substrata just underneath the cage. This study enriches the portfolio of knowledge of the dispersal strategies of microalgae and contributes to the understanding of the spread of invasive species.  相似文献   

New structural and U–Pb zircon data from Anafi crystalline basement (Cyclades,Greece): constraints on the evolution of a Late Cretaceous magmatic arc in the Internal Hellenides     

Silviu O. Martha  Wolfgang Dörr  Axel Gerdes  Rainer Petschick  Janina Schastok  Paraskevas Xypolias  Gernold Zulauf 《International Journal of Earth Sciences》2016,105(7):2031-2060

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