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Topic: Dynamo theory


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In the News (Fri 23 Feb 18)

  
  Dynamo Theory (via CobWeb/3.1 planetlab2.cs.umd.edu)   (Site not responding. Last check: 2007-10-03)
Dynamo action describes the sustained conversion of kinetic energy into magnetic energy throughout the bulk of an electrically conducting fluid.
Dynamos are commonly invoked to explain the origin of magnetic fields in the universe.
Despite the many technicalities the themes of dynamo theory are straightforward: what type of velocities are capable of dynamo action, and what are the properties of the generated magnetic fields.
flash.uchicago.edu.cob-web.org:8888 /~cattaneo/Pages/dynamo_theory.htm   (138 words)

  
 Dynamo theory - Wikipedia, the free encyclopedia
Dynamo theory describes the process through which motion of a conductive body in the presence of a magnetic field acts to regenerate that magnetic field.
Dynamo theory of astrophysical bodies uses magnetohydrodynamic equations to investigate how the flow of the conducting materials in the interior of an object can continuously regenerate the magnetic fields of planetary and stellar bodies.
This analysis begins with the magnetohydrodynamic theory version of Ohm’s law once it has been modified to include resistivity (resistivity is the reciprocal of conductivy σ, J is the current density), which is assumed to be a constant in order to further simplify the investigation.
en.wikipedia.org /wiki/Dynamo_theory   (635 words)

  
 Hydromagnetic Dynamo Theory - Scholarpedia
Dynamo theory is a vast field with almost a hundred years of history, starting with early ideas by Joseph Larmor in 1919.
Traditionally, dynamos are divided into kinematic dynamos, where the flow can be considered given, and nonlinear dynamos, where the flow is affected by the magnetic field through the Lorentz force.
There is at present no clear consensus as to whether the solar dynamo operates in the entire convection zone of the sun (distributed dynamo) or whether it works preferentially at the bottom of the convection zone in the so-called tachocline, where the differential rotation changes sharply into a rigidly rotating profile.
www.scholarpedia.org /article/Hydromagnetic_Dynamo_Theory   (1810 words)

  
 On the Geodynamo
The standard theory for the generation of stellar and planetary magnetic fields is "dynamo theory", also known by the formidable sounding title "magnetohydrodynamics" (MHD).
Standard theory holds that fluid circulation in the earth's fluid outer core is the source of the earth's internal magnetic field.
Since standard theory is well endowed along these lines, there seems yet to be little reason for replacing that theory with the as yet poorly developed ideas of the "electric universe" hypothesis.
www.tim-thompson.com /geodynamo.html   (2100 words)

  
 BOOK   (Site not responding. Last check: 2007-10-03)
The equations for passive vectorial transport (dynamo equation) and passive scalar transport are derived on a par, as applications of the theory of stochastic equations with multiplicative noise.
A summary of the elementary physics of the dynamo equation is followed by an analysis of the influence of mean shear flows and resistive effects on the transport coefficients $\alpha$ and $\beta$.
A new approach to the formulation of the electromotive force as well as the theory of differential rotation and meridional circulation is described for use in dynamo theory.
www.kis.uni-freiburg.de /~afm/monografia/monographie.html   (2841 words)

  
 Dynamo Effect   (Site not responding. Last check: 2007-10-03)
The dynamo effect is a geophysical theory that explains the origin of the Earth's main magnetic field in terms of a self-exciting (or self-sustaining) dynamo.
In this dynamo mechanism, fluid motion in the Earth's outer core moves conducting material (liquid iron) across an already existing, weak magnetic field and generates an electric current.
The dynamo theory was proposed by the German-born American physicist Walter M. Elsasser and the British geophysicist Edward Bullard during the mid-1900s.
abyss.uoregon.edu /~js/glossary/dynamo_effect.html   (477 words)

  
 The Need For a New Model of the Earth The Living and Dynamic Earth
Endosymbiotic Theory basically states that the components of the cell (i.e., the organelles) are actually primitive organisms (e.g., bacteria) that formed mutual (symbiotic) relationships that made up a larger organism.
In contrast to a sphere, engineering dynamos have a coil that has two directions of rotation (two fields) that are not equal (two unequal spirals), and bear the shape or symmetry of the face of a clock.
After all, the dynamo theory is seriously flawed if we merely consider the fact that dynamos only reinforce existing fields, and do not provide for the outright generation of a magnetic field.
www.livingcosmos.com /earth.htm   (12423 words)

  
 4.5 The solar dynamo
Kinetic energy is converted to magnetic energy via hydromagnetic dynamo processes and this flux subsequently emerges from the surface, playing a central role in the dynamics of the solar atmosphere and heliosphere.
However, this equation is the starting point for mean-field dynamo theory in which additional approximations are made in order to make the system more tractable.
Most solar dynamo models focus on the axisymmetric component of the field but observations indicate that the magnetic field structure in the solar photosphere and corona is quite complex, with a large non-axisymmetric component (see Section 3.8
solarphysics.livingreviews.org /Articles/lrsp-2005-1/articlesu16.html   (1125 words)

  
 Geomagnetic field decay - CreationWiki   (Site not responding. Last check: 2007-10-03)
The theory is that as lava cools, the magnetic fields of the atoms align with the Earth's field, that as the sea floor spreads a record of Earth's past fields is preserved.
The way the theory is illustrated is with present magnetic field direction and reverse magnetic field direction in nice neat strips across the ocean floor, as produced by the theory.
According to the dynamo theory, the magnetic and rotation axes should nearly always be closely aligned, except for a very relatively short time during a field reversal.
creationwiki.org /index.php?title=Geomagnetic_field_decay   (1159 words)

  
 Magnetic Stars
The theory proposes how a magnetic field is assimilated into a stellar object by the "fossil field hypothesis", and that gaseous nebula cloud holds remnant magnetic fields.
The main weakness of the fossil-field theory has been the lack of known field configurations which are stable enough to survive in a star for the whole of its lifetime.
In one theory, the field is assumed to be generated by convective motions in the core of the star, in same way as the Earth's magnetic field.
www.grantchronicles.com /astro132.htm   (6345 words)

  
 Solar Dynamo Position
From the looping shape of fiery solar flares, to the varying intensity of the solar winds, to the mysterious 11-year sunspot cycle, large-scale events on the surface of the Sun are controlled by strong magnetic fields generated deep in its interior.
The ability to track the solar dynamo's location with increased precision and to measure the conditions there with greater accuracy should allow the researchers to determine how the region changes during the solar cycle.
To determine the solar dynamo's position, the Stanford researchers used a special instrument on the Solar and Heliospheric Observatory (SOHO) spacecraft - a $1.1 billion international project of the European Space Agency and the National Aeronautics and Space Administration - operated by NASA's Goddard Space Flight Center.
soi.stanford.edu /results/agu96.html   (909 words)

  
 Dynamo - Wikipedia, the free encyclopedia
Dynamo theory, a theory relating to magnetic fields of celestial bodies
Loughborough Dynamo F.C. Shepshed Dynamo F.C. FC Dynamo Dresden
Dynamo, one of the 'stalkers' from the 1987 movie The Running Man.
en.wikipedia.org /wiki/Dynamo   (201 words)

  
 The α ω Dynamo
We use as an example the dynamo we predict forms in the accretion disk leading to the massive, central fl hole of presumably every galaxy.
The peculiar circumstance of this astrophysical dynamo avoids the uncertainties of the formation of plumes by convection in stellar atmospheres.
The Ω flow of the dynamo is the differential rotation of this experiment.
www.physics.nmt.edu /~dynamo/The-Dynamo   (743 words)

  
 Ars Technica: HP's Dynamo - Page 1 - (3/2000)   (Site not responding. Last check: 2007-10-03)
Dynamo, a "prototype software dynamic optimizer that transparently accelerates native binaries at runtime".
Even better, the architecture of Dynamo is remarkably similar to Transmeta's Code Morphing, which isn't surprising, because Transmeta hired away a number of researchers that were working on Dynamo.
The Dynamo project was started to investigate issues in what was seen as an increasingly important area -- dynamic translation of non-native binaries to native code.
arstechnica.com /reviews/1q00/dynamo/dynamo-1.html   (681 words)

  
 Theory Group Dynamo
Close to a fl hole a relativistic dynamo theory is required.
We have shown that the shear of the poloidal electric field appears as source term for the flux of the poloidal magnetic field in the axisymmetric dynamo problem.
The turbulent {alpha}{Omega} dynamo is based on mean field MHD, which is not yet availlable in the relativistic context.
www.lsw.uni-heidelberg.de /projects/theory/dynamo.htm   (372 words)

  
 6.6 Comparisons with mean-field theory
Solar dynamo models are generally quite successful in this regard and have provided much insight into the origin of cyclic magnetic activity on the Sun.
Global simulations can be used to help validate mean-field theory although they do not yet possess the resolution or physical conditions to explicitly capture many of the processes which are currently parameterized in dynamo models.
Many of the approximations commonly used in mean-field dynamo theory are not justified by global convection simulations.
solarphysics.livingreviews.org /Articles/lrsp-2005-1/articlesu26.html   (1495 words)

  
 Earth Geo Motor
The premise for the Geomotor theory is that the heat of the interior of the earth causes ionization and separation of charges.
This is definitely not the way the dynamo theory is presented; however, this is the way it has to be in order to have a difference in heat production by forces induced on the solid core.
If the dynamo theory about the inner core were true then there would be no heating and cooling of the earth as has been happening throughout geological time.
earthsgeomotor.com /PageTwentyThree.htm   (450 words)

  
 Explaining Earth's Magnetic Field and Oceanic Magnetic Banding
Instead of a single circulation as in the popular Dynamo Theory, it seems certain that there are actually pairs or quads of counter-rotating convective circulations as shown here (both driven by the red hot-spot that is slightly off-center).
Another complication of this basic Dynamo Theory is that the whole rotating Core would have to be considerably off-center in the Earth, to explain the offset of the line joining the two surface Magnetic Poles.
The fact that this theory suggests that the Earth's Magnetic Field measured at the surface (or in space) is a result of the vector sum of two much stronger but generally opposing source fields, enables straightforward explanation of many of the peculiar characteristics measured in the Earth's Magnetic Field.
mb-soft.com /public/tecto2.html   (7412 words)

  
 [No title]   (Site not responding. Last check: 2007-10-03)
The prevailing theory for the origin of cosmic magnetic fields is that they have been amplified to their present values by the turbulent dynamo inductive action in the protogalactic and galactic medium.
Up to now, in calculation of the turbulent dyanmo, it has been customary to assume that there is no back reaction of the magnetic field on the turbulence, as long as the magnetic energy is less than the turbulent kinetic energy.
In particular, we predict that the magnetic energy growth rate in the magnetized dynamo theory is up to ten times larger than that in the kinematic dynamo theory.
www.pppl.gov /pub_report/2002/PPPL-3672-abs.html   (258 words)

  
 To: All Rcvd: NO Re: What aeon Considers Una Status: Public myrddin!nbn!sgiblab!swrinde!cs   (Site not responding. Last check: 2007-10-03)
Of the rotating electric charge theory, Parkinson writes: For the case of a uniform surface charge it turns out that the external field is a dipole, but the magnitude of the charge needed is 0.14 coul m^-2.
To be sure, the dynamo has problems, including the lack of accurate data on the properties of the core and the extreme computational complexities involved in modelling dynamo processes; but such problems do not negate the fact that the dynamo is the _only_ feasible way to produce Earth's magnetic field.
The differences between a core dynamo and a mantle dynamo may also lead to a field with a greater tilt and off-set from true axial alignment which also contribute to a smaller magnetic field than indicated by the scaling procedure.
www.skepticfiles.org /evolut/magnetic.htm   (2515 words)

  
 Session GI2 - Dynamo Theory and Space Plasmas. (via CobWeb/3.1 planetlab2.cs.umd.edu)   (Site not responding. Last check: 2007-10-03)
We have demonstrated this coherent differential rotation in the laboratory, numerically simulated the dynamo gain, and are building a liquid sodium analogue of the dynamo.
The back reaction of the saturated dynamo forms a force-free field helix that carries all the energy and flux of the dynamo away from the accretion disk and redistributes the field within the clusters and galaxy walls.
However, traditional kinematic mean field dynamo theory has ignored the backreaction of the growing small and large scale field on the kinetic motions.
flux.aps.org.cob-web.org:8888 /meetings/YR00/DPP00/abs/S710.html   (1160 words)

  
 Origin of The Earth's Magnetism
Currents create a magnetic field--a distribution of magnetic forces--and the essence of the self-sustaining dynamo problem is to find solutions such that the resulting magnetic field is also the input field required for generating the current in the first place.
One limitation, related to the failure of Blackett's theory, is that any electric circuit rotating like a solid body will not produce "dynamo currents." Even if part of the circuit follows the axis of rotation, and can therefore be viewed as non-rotating, solid rotation will not create any currents.
Glatzmaier and collaborators have conducted some interesting simulations of the dynamo process, with realistic behavior, although limitations of computer speed forced them to simplify the properties of the liquid core.
www.phy6.org /earthmag/dynamos2.htm   (1210 words)

  
 MHD dynamo theory
The basic premise of dynamo theory is that all astrophysical bodies which contain anomalously long-lived magnetic fields also contain highly conducting fluids (e.g.
It is not surprising, therefore, that dynamo theory tends to be extremely complicated, and is far from completely understood, at present.
It is clear from examining this type of data that dynamo magnetic fields (and velocity fields) are essentially chaotic in nature, exhibiting strong random variability superimposed on more regular quasi-periodic oscillations.
farside.ph.utexas.edu /teaching/plasma/lectures/node69.html   (770 words)

  
 Glossary of Terms
A self-excited dynamo (of either kind) is one in which the generated current creates the magnetic field by which the dynamo operates.
Initially, "kinematic dynamo theory" asked whether dynamo processes were at all possible, and after some decades of study, the answer was "yes." "MHD (magneto-hydrodynamic) dynamo theory" searches for dynamos which also satisfy consistent pressure and force structures.
A dynamo process occurring in a fluid that conducts electricity.
www.drpawluk.com /glossary.htm   (4597 words)

  
 Stirring Up a Magnetic Field
Such a "technical dynamo" is quite different from a fluid dynamo, explains Gunter Gerbeth of the Rossendorf Research Center in Dresden, Germany.
According to fluid dynamo theory, the flowing liquid stretches and distorts the seed field, which induces electric currents.
This is an important verification of the idea that dynamos generate the magnetic fields in planets and stars, says Roberts.
focus.aps.org /story/v5/st20   (594 words)

  
 INI Programme DYN
Dynamo theory is the theory of spontaneous generation of magnetic fields in conducting fluids, with application to planetary, stellar and galactic systems.
The theory has relevance also to the dynamics of fusion plasma.
the nature of dynamo action in the limit of very high conductivity in the sun, stars and galaxy; in these contexts turbulence plays a critical and ill-understood role; but model problems (e.g.
www.newton.cam.ac.uk /programmes/DYN/index.html   (228 words)

  
 David Moss's Home Page   (Site not responding. Last check: 2007-10-03)
Magnetic fields in astrophysics: dynamo theory; the origin and evolution of stellar magnetic fields; the generation and maintenance of galactic magnetic fields, and their influence on the interstellar medium.
Axel Brandenburg at Univ of Newcastle (UK)/NORDITA (Denmark): stellar, galactic and planetary dynamos.
Dynamo models", Moss D., Shukurov A., Sokoloff D., Beck R., Fletcher A., 2001, Astron.
www.ma.man.ac.uk /~moss   (1413 words)

  
 12V dynamo theory   (Site not responding. Last check: 2007-10-03)
This is possible because the dynamo can be assumed to be a constant current device.
The SON is highly efficient (even more so at 12V) and will cause at 12v less resistance than a conventional bottle generator at 3 watts.
The SON dynamo can supply 12V-6w from approx 20 kp/h (12 mph) onwards (see graph) At slow speeds it is to be preferred to revert to 6V, one bright light being superior over two dim yellow ones.
www.m-gineering.nl /son12vg.htm   (239 words)

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