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Related Concept Videos

Magnetic Fields01:27

Magnetic Fields

A moving charge or a current creates a magnetic field in the surrounding space, in addition to its electric field. The magnetic field exerts a force on any other moving charge or current that is present in the field. Like an electric field, the magnetic field is also a vector field. At any position, the direction of the magnetic field is defined as the direction in which the north pole of a compass needle points.
A magnetic field is defined by the force that a charged particle experiences...
Magnetic Damping01:17

Magnetic Damping

Eddy currents can produce significant drag on motion, called magnetic damping. For instance, when a metallic pendulum bob swings between the poles of a strong magnet, significant drag acts on the bob as it enters and leaves the field, quickly damping the motion.
If, however, the bob is a slotted metal plate, the magnet produces a much smaller effect. When a slotted metal plate enters the field, an emf is induced by the change in flux; however, it is less effective because the slots limit the...
Atomic Nuclei: Nuclear Relaxation Processes01:23

Atomic Nuclei: Nuclear Relaxation Processes

In the absence of an external magnetic field, nuclear spin states are degenerate and randomly oriented. When a magnetic field is applied, the spins begin to precess and orient themselves along (lower energy) or against (higher energy) the direction of the field. At equilibrium, a slight excess population of spins exists in the lower energy state. Because the direction of the magnetic field is fixed as the z-axis,  the precessing magnetic moments are randomly oriented around the z-axis. This...
Energy In A Magnetic Field01:24

Energy In A Magnetic Field

If a magnetic field is sustained, there must be a current in a closed circuit or loop, implying some energy has been spent in creating the field. If this energy is not dissipated via the circuit's resistance, it is stored in the field.
Take an ideal inductor with zero resistance. Although it's practically impossible, assume that the coil's resistance is so small that it is practically negligible. The loss of the field's energy to dissipate thermal energy (or heat) is thus negligible.
The energy...
Magnetic Field Lines01:19

Magnetic Field Lines

The representation of magnetic fields by magnetic field lines is very useful in visualizing the strength and direction of the magnetic field. Each of the magnetic field lines forms a closed loop. The field lines emerge from the north pole (N), loop around to the south pole (S), and continue through the bar magnet back to the north pole.
Magnetic field lines follow several hard-and-fast rules:
Ferromagnetism01:31

Ferromagnetism

Materials like iron, nickel, and cobalt consist of magnetic domains, within which the magnetic dipoles are arranged parallel to each other. The magnetic dipoles are rigidly aligned in the same direction within a domain by quantum mechanical coupling among the atoms. This coupling is so strong that even thermal agitation at room temperature cannot break it. The result is that each domain has a net dipole moment. However, some materials have weaker coupling, and are ferromagnetic at lower...

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Geomagnetic Field (Gmf) and Plant Evolution: Investigating the Effects of Gmf Reversal on Arabidopsis thaliana Development and Gene Expression
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Geomagnetic Field (Gmf) and Plant Evolution: Investigating the Effects of Gmf Reversal on Arabidopsis thaliana Development and Gene Expression

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Mechanisms for magnetic field reversals.

F Pétrélis1, S Fauve

  • 1Laboratoire de Physique Statistique, CNRS UMR 8550, Ecole Normale Supérieure, 24 rue Lhomond, 75005 Paris, France. petrelis@lps.ens.fr

Philosophical Transactions. Series A, Mathematical, Physical, and Engineering Sciences
|March 10, 2010
PubMed
Summary

This review covers fluid dynamo models explaining magnetic field reversals. A simple mechanism is proposed, explaining features in paleomagnetic records, simulations, and experiments, and applicable to large-scale flows.

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Geomagnetic Field (Gmf) and Plant Evolution: Investigating the Effects of Gmf Reversal on Arabidopsis thaliana Development and Gene Expression
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Fabrication of Magnetic Nanostructures on Silicon Nitride Membranes for Magnetic Vortex Studies Using Transmission Microscopy Techniques
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Area of Science:

  • Geophysics
  • Plasma Physics
  • Fluid Dynamics

Background:

  • Turbulent flows of electrically conducting fluids generate magnetic fields (fluid dynamos).
  • Understanding magnetic field reversals is crucial for geophysics and astrophysics.
  • Previous models have attempted to explain these complex phenomena.

Purpose of the Study:

  • To review existing models of magnetic field reversals in fluid dynamos.
  • To present a novel, simple mechanism explaining observed reversal features.
  • To demonstrate the applicability of this mechanism to paleomagnetic records, simulations, and experiments.

Main Methods:

  • Literature review of fluid dynamo models.
  • Description of a proposed simple reversal mechanism.
  • Analysis of paleomagnetic data, numerical simulations, and experimental results.

Main Results:

  • A comprehensive overview of current fluid dynamo reversal models is provided.
  • The proposed simple mechanism successfully explains key features observed in various contexts.
  • The mechanism's versatility is demonstrated across different scales and systems.

Conclusions:

  • The presented simple mechanism offers a unified explanation for magnetic field reversals.
  • This model enhances our understanding of Earth's magnetic field behavior and other astrophysical dynamos.
  • Further research can explore the implications of this mechanism in diverse turbulent systems.