scholarly journals Generation of coupled global and local magnetic fields by a cellular MHD dynamo

2006 ◽  
Vol 2 (S239) ◽  
pp. 482-487
Author(s):  
A. V. Getling ◽  
R. D. Simitev ◽  
F. H. Busse
Keyword(s):  
Magnetic Fields ◽  
Stationary Regime ◽  
Polar Regions ◽  
Magnetic Structures ◽  
Local Structures ◽  
First Case ◽  
Mhd Dynamo ◽  
Electromagnetic Processes ◽  
Background Fields ◽  
Global And Local

AbstractThe convection-driven MHD dynamo in a rotating spherical shell is simulated numerically. Convection cells are regarded as a connecting link between the global and local electromagnetic processes. Local (in many cases, bipolar) magnetic structures are regularly produced by convection cells. Dynamo regimes in “thick” and “thin” shells are discussed. In the first case, the “general” magnetic field maintained by the dynamo has a sign-alternating dipolar component, which varies cyclically, although not periodically. The local structures, as they disintegrate, change into background fields, which drift toward the poles. From time to time, reversals of the magnetic fields in the polar regions occur, as “new” background fields expel the “old” fields. In the second case, the system settles down to a nearly stationary regime without polarity reversals.

scholarly journals Hydromagnetic dynamos in rotating spherical fluid shells in dependence on the Prandtl number, density stratification and electromagnetic boundary conditions

2014 ◽  
Vol 44 (4) ◽  
pp. 293-312 ◽  
Author(s):  
Tomáš Šoltis ◽  
Ján Šimkanin
Keyword(s):  
Magnetic Field ◽  
Electrical Conductivity ◽  
Magnetic Fields ◽  
Prandtl Number ◽  
Inner Core ◽  
Polar Regions ◽  
Number Density ◽  
Magnetic Diffusion ◽  
Spherical Fluid ◽  
The Magnetic Field

Abstract We present an investigation of dynamo in a simultaneous dependence on the non-uniform stratification, electrical conductivity of the inner core and the Prandtl number. Computations are performed using the MAG dynamo code. In all the investigated cases, the generated magnetic fields are dipolar. Our results show that the dynamos, especially magnetic field structures, are independent in our investigated cases on the electrical conductivity of the inner core. This is in agreement with results obtained in previous analyses. The influence of non-uniform stratification is for our parameters weak, which is understandable because most of the shell is unstably stratified, and the stably stratified region is only a thin layer near the CMB. The teleconvection is not observed in our study. However, the influence of the Prandtl number is strong. The generated magnetic fields do not become weak in the polar regions because the magnetic field inside the tangent cylinder is always regenerated due to the weak magnetic diffusion.

scholarly journals On processes of coloniality and decoloniality of knowledge: notions for analysing the international history of mathematics teaching

ZDM ◽  
2021 ◽  
Author(s):  
Gert Schubring
Keyword(s):  
General Education ◽  
Mathematics Teaching ◽  
History Of Mathematics ◽  
Educational Systems ◽  
Political Processes ◽  
Local Structures ◽  
Novel Approach ◽  
History Of ◽  
Global And Local ◽  
First Time

AbstractThe aspiration of this paper is to develop a novel approach towards investigating the socio-political history of mathematics teaching in educational systems. Traditionally, historical studies are confined to just one country, the author’s country. Broader approaches address international developments by confronting and comparing global and local aspects—revealing general patterns and more specific ‘local’ structures and characteristics. Yet, already in antiquity and medieval times, the specific characteristic of mathematics teaching, namely to operate at the crossroads of general education and vocational training, proved to be intimately tied to the functioning of the particular political system. In pre-modern times, however, a truly international pattern emerged for the first time: European powers conquered, occupied and colonised overseas regions. Given that educational systems were emerging at the same time within these states, they often transmitted elements of these structures to their colonies. This phenomenon included mathematics, and the history of its teaching is analysed here as a part of coloniality. It is shown that this was not a uniform process, and the differences between the various colonial powers are discussed. The involvement of mathematics in the process of decolonisation is addressed, as well as its role in the tension between continued coloniality and movements of decoloniality. Finally, the general framework provided for studying socio-political processes connected with establishing mathematics teaching within public educational systems is applied, in order to analyse recent coloniality practices effected by international achievement studies.

Canonical orbital contributions to the magnetic fields induced by global and local diatropic and paratropic ring currents

2017 ◽  
Vol 38 (30) ◽  
pp. 2594-2604 ◽  
Author(s):  
Nickolas D. Charistos ◽  
Anastasios G. Papadopoulos ◽  
Thomas A. Nikopoulos ◽  
Alvaro Muñoz-Castro ◽  
Michael P. Sigalas
Keyword(s):  
Magnetic Fields ◽  
Ring Currents ◽  
Global And Local

Correlation between crystallographic superstructure and magnetic structures in finite magnetic fields: A neutron study on a single crystal ofHo2PdSi3

2010 ◽  
Vol 82 (17) ◽  
Author(s):  
Matthias Frontzek ◽  
Fei Tang ◽  
Peter Link ◽  
Astrid Schneidewind ◽  
Jens-Uwe Hoffman ◽  
...  
Keyword(s):  
Magnetic Fields ◽  
Single Crystal ◽  
Magnetic Structures

scholarly journals Experimental Study of the Orientation of Magnetic Fields in the Corona

1971 ◽  
Vol 43 ◽  
pp. 580-587 ◽  
Author(s):  
P. Charvin
Keyword(s):  
Magnetic Field ◽  
Experimental Study ◽  
Magnetic Fields ◽  
Large Scale ◽  
Coronal Line ◽  
Magnetic Structures ◽  
Polarization Measurements ◽  
First Results

We present polarization measurements obtained in 1970 in the green coronal line with a new coronameter located at the Pic du Midi. The analysis of these data has been conducted with the theory given by the writer in 1964 and 1965. It appears that magnetic field orientations in the Corona can be deduced from the above measurements. First results showing large scale magnetic structures are presented.

scholarly journals Dynamo in Astrophysics

1990 ◽  
Vol 140 ◽  
pp. 83-89
Author(s):  
A.A. Ruzmaikin
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Turbulent Flow ◽  
Large Scale ◽  
Spiral Galaxies ◽  
Clusters Of Galaxies ◽  
Magnetic Structures ◽  
Random Magnetic Field ◽  
Astrophysical Objects

The fast dynamo acting in a turbulent flow explains the origin of magnetic fields in astrophysical objects. Stellar cycles and large-scale magnetic fields in spiral galaxies reflect the behaviour of a mean magnetic field. Intermittent magnetic structures in clusters of galaxies are associated with random magnetic field.

scholarly journals Global and Local Structures of Bifurcation Curves of ODE with Nonlinear Diffusion

2018 ◽  
Vol 2018 ◽  
pp. 1-7
Author(s):  
Tetsutaro Shibata
Keyword(s):  
Mathematical Model ◽  
Eigenvalue Problem ◽  
Nonlinear Diffusion ◽  
Nonlinear Term ◽  
Nonlinear Eigenvalue Problem ◽  
Maximum Norm ◽  
Bifurcation Parameter ◽  
Local Structures ◽  
Global And Local ◽  
The Mathematical Model

We consider the nonlinear eigenvalue problem Duu′′+λfu=0, u(t)>0, t∈I≔(0,1), u(0)=u(1)=0, where D(u)=uk, f(u)=u2n-k-1+sin⁡u, and λ>0 is a bifurcation parameter. Here, n∈N and k (0≤k<2n-1) are constants. This equation is related to the mathematical model of animal dispersal and invasion, and λ is parameterized by the maximum norm α=uλ∞ of the solution uλ associated with λ and is written as λ=λ(α). Since f(u) contains both power nonlinear term u2n-k-1 and oscillatory term sin⁡u, it seems interesting to investigate how the shape of λ(α) is affected by f(u). The purpose of this paper is to characterize the total shape of λ(α) by n and k. Precisely, we establish three types of shape of λ(α), which seem to be new.

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