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	MHD dynamo
		The MHD (magnetohydrodynamic) dynamo is a fluid example of a dynamo, or electrical generator.
		The MHD dynamo is an active area of research in plasma physics.
		The geophysics and astrophysics communities also have an interest in the MHD dynamo, since it is proposed to be the cause of most geophysical and astrophysical magnetic fields.
	www.ebroadcast.com.au /lookup/encyclopedia/mh/MHD_dynamo.html (121 words)

	Dynamo Conference, NATO 2000, Cargese, participants and abstracts
		Dynamo effect of a helical flow with a superimposed turbulence in a cylinder, R.
		The screw dynamo or so-called Ponomorenko dynamo is able to generate a non-axisymmetric magnetic field in an axisymmetric helical flow and is one of the simplest known dynamo models.
		Starting from a fluid motion capable of dynamo action and a weak magnetic field it was observed that the growing magnetic field destroys the dynamo property of the motion and then decays, and that the system ends up in a state with another motion incapable of dynamo action and zero magnetic field.
	www.math.colostate.edu /~juliana/CARGESE2000/listpt.html (9552 words)

	MHD generator - Wikipedia, the free encyclopedia
		The MHD dynamo is an active area of research in plasma physics and is of great interest to the geophysics and astrophysics communities.
		From their perspective the earth is a global MHD dynamo and with the aid of the particles on the solar wind produces the aurora borealis.
		MHD generators typically reduce the temperature of the conductive substance from plasma temperatures to just over 1000 °C. A second example, which applies to the earth, the differently charged electromagnetic layers produced by the dynamo effect on the earth's geomagnetic field enable the appearance of the aurora borealis.
	en.wikipedia.org /wiki/MHD_dynamo (891 words)

	MHD Magnetic Scale Control: Water,Fluid Treatment MHD Systems: Prevent and Remove Scale: Magenetohydrodynamic Treatment
		The higher conductivity of the liquid (that is the higher the mineralization hence the hardness), the higher the MHD effect.
		The MHD units are conceived with a venturi effect in the magnetic gap to increase the velocity of the fluid.
		The MHD units high efficiency is underscored by the choice of engineers at Amoco’s largest refinery who ran a conclusive test on cooling towers treated with a MHD unit.
	www.mhdsystems.com /mhdsystems/explanation.htm (1162 words)

	Book of abstracts
		Dynamo models have been used to investigate the influence of boundary conditions, such as inhomogeneous heat flux at the core-mantle boundary, different modes of driving convection, or varying size of the inner core during Earth's evolution on the magnetic field.
		The effects of the turbulence, which is necessarily superimposed to the screw flow, on the dynamo are studied in the framework of the mean-field concept.
		Their results challenge the traditional views of kinematic dynamo theory because (i) the modes of the magnetic field with the smallest decay rates appear to be nearly axisymmetric and because (ii) the observed decay rates vary spatially.
	www.fz-rossendorf.de /MHDTag/book.html (2263 words)

	Slow dynamos and fast dynamos
		In fact, it is easily seen that any dynamo which depends on the motion of a rigid conductor for its operation is bound to be a slow dynamo: in the perfectly conducting limit, the magnetic flux linking the conductor could never change, so there would be no magnetic induction.
		The answer is, of course, that an MHD fluid is a non-rigid body, and, thus, its motion possesses degrees of freedom not accessible to rigid conductors.
		At present, the physical existence of fast dynamos has not been conclusively established, since most of the literature on this subject is based on mathematical paradigms rather than actual solutions of the dynamo equation.
	farside.ph.utexas.edu /teaching/plasma/lectures/node71.html (514 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
		Dynamo process The generation of magnetic field by motions of a fluid that conducts electricity, motions driven by some source of energy (e.g.
		Kinematic dynamo --In the theory of fluid dynamos, a self-sustaining dynamo process based on a certain flow pattern, without requiring the flow pattern to be consistent with force balance and other physical considerations.
		MHD is applicable to the Earth's fluid core and also to many plasmas.
	www.phy6.org /earthmag/glossary.htm (5558 words)

	Magnetohydrodynamics Summary
		MHD is accomplished by forcing an electrically conducting fluid or a plasma through a channel with a magnetic field applied across it and electrodes placed at right angles to flow and field (Figure 1).
		To achieve extra high efficiencies, MHD is combined in a binary thermodynamic cycle with a conventional steam plant to add an extra 40 percent to the total power output and to boost the overall combined efficiency into the 60 percent range.
		MHD is potentially a natural choice for conversion of high temperature energy output from future nuclear power plants whether fission or fusion driven.
	www.bookrags.com /Magnetohydrodynamics (3133 words)

	Subcritical Transition to Turbulence
		Dynamo action, the spontaneous generation of a magnetic field in a flow of conducting fluid, is supposed to be at the origin of the planets and stars magnetic fields.
		This is mainly due to the fact that to build a dynamo, one must use liquid sodium, with all its incumbent dangers.
		Moreover, the dynamo will work only if the advection of the magnetic field and generation of current are fast compared to dissipation - namely if the magnetic Reynolds number exceeds a critical value, which strongly depends on the geometry of the flow.
	www-drecam.cea.fr /spec/Pres/Git/MHD/mhd.htm (1033 words)

	Library - Eötvös University, Department of Astronomy
		An important ingredient in recent models of the dynamo mechanism is the meridional flow of material, which is believed to originate from turbulent stresses in the solar convection zone.
		The expression is used to predict the shape of the spatial spectrum and the rms level of the plasma fluctuations in the lower part of the solar atmosphere.
		The dynamo action of unstable magnetic flux tubes due to magnetic buoyancy in a rotating stellar convection zone is summarized and the implications of a flux tube dynamo with a threshold in field strength for dynamo action is discussed in connection with the observed variability of solar and stellar magnetic activity.
	icsip.elte.hu /astro/en/library/padeu/padeu_vol_13.html (2670 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)

	5. Geodynamo Modeling
		Dynamo models that solve the induction equation alone are called `kinematic', and several such geodynamos models have been integrated.
		The main challenge today is to solve the fully dynamic dynamo problem, sometimes also called `the MHD dynamo problem' or `the fully self--consistent dynamo problem', in which the induction equation is solved and the equation of motion for the fluid.
		Because of Cowling's theorem, a true MHD dynamo model should be 3D, but a supercomputer is then required to integrate it numerically.
	www.agu.org /revgeophys/roberp01/node5.html (1777 words)

	Magnetohydrodynamics - Wikipedia, the free encyclopedia
		Such dynamos work by stretching magnetic field lines that thread through turbulent or sheared flows in a conductive fluid: the total length of magnetic field line in a particular volume determines the strength of the magnetic field, so stretching the field lines increases the magnetic field.
		MHD applies quite well to astrophysics since over 99% of baryonic matter content of the Universe is made up of plasma, including stars, the interplanetary medium (space between the planets), the interstellar medium (space between the stars), nebulae and jets.
		MHD power generation fueled by potassium-seeded coal combustion gas showed potential for more efficient energy conversion (the absence of solid moving parts allows operation at higher temperatures), but failed due to cost prohibitive technical difficulties.
	en.wikipedia.org /wiki/Magnetohydrodynamics (2138 words)

	about MDE (Site not responding. Last check: 2007-11-02)
		The MHD dynamo is a process by which kinetic energy in flowing, conducting fluids can be spontaneously converted into magnetic energy.
		This grant supports studies of MHD phenomena in a new laboratory at the University of Wisconsin where key questions pertinent to the MHD dynamo will be investigated.
		To investigate and study magnetic field generation in the laboratory requires an ample volume of a sufficiently conducting liquid such as sodium, moving with a sufficiently high velocity to stretch and amplify magnetic fields.
	uw.physics.wisc.edu /~forest/Dynamo/aboutmde.htm (393 words)

	[56.13] A Proposed Laboratory Experiment on Dynamo Action in a Liquid Metal Torus (Site not responding. Last check: 2007-11-02)
		The explanation of the observed magnetic fields is given by dynamo theories based on an MHD description of the electrically conductive media.
		The present proposal calls for a laboratory experiment to study dynamo processes, especially the \alpha-effect (an electromotive force along the mean magnetic field arising from turbulence), in an axisymmetrical geometry in order to provide fundamental data which can be quantitatively compared with leading dynamo theories.
		Motivated by recent observations of dynamo effects in a toroidal laboratory plasma, an axisymmetrical torus filled with liquid metal is considered, with flows generated by propellers and external magnetic fields applied by coils.
	www.aas.org /publications/baas/v31n3/aas194/542.htm (256 words)

	Global nonlinear low frequency activity is among the most important phenomena in present-day fusion experiments (Site not responding. Last check: 2007-11-02)
		In its present form, NIMROD solves all but the continuity equation; however, the current advection terms in Ohm’s law and all nonadiabatic terms in the pressure equations have not been implemented, and the stress tensor term in the momentum equation is presently an isotropic kinematic viscosity.
		The effects may have an impact on the dynamo and magnetic fluctuation level at small aspect ratio, where poloidal coupling is strong.
		MHD tearing mode with kinematic viscosity equivalent to electrical diffusivity in a periodic cylinder with close-fitting conducting shell.
	www.cs.sandia.gov /~sjplimp/papers/HTML/plasma99/plasma99.html (2864 words)

	Dynamos in the protoplanetary accretion disc (Site not responding. Last check: 2007-11-02)
		Furthermore, the low temperature in the extensive parts of a protoplanetary disc translates into the low ionisation regime, which is maintained by nonthermal ionisation processes (Umebayashi and Nakano 1988 [24], Stepinski 1992 [22]).
		In the absence of an external field, the dynamo generates a field with a quadrupole symmetry as shown on Fig.
		As in the case of the standard disc dynamo, the field inside the disc is dominated by its toroidal component.
	www.lpi.usra.edu /science/tom/mn/node5.html (1355 words)

	Hall dynamo (Site not responding. Last check: 2007-11-02)
		The new expression is highly nonlinear in the magnetic field and the electric current, since the helicity of the electron flow velocity is strongly affected during the growth of the magnetic field.
		The expression is also nonlinear in the amplitude of the Hall effect, and therefore the dependence of the efficiency of the dynamo with the amplitude of the Hall effect is not expected to be monotonic.
		We perform direct numerical simulations of the MHD and the Hall-MHD system to study the grow and nonlinear evolution of magnetic fields in presence of dynamo action.
	www.iafe.uba.ar /plasmas/hall_dyn.html (598 words)

	Dipole field generation by an MHD dynamo
		A magnetic field is generated by the thermal convection motion of an electrically conducting fluid in a rotating spherical shell.
		It is shown that a strong dipole field is spontaneously generated by the MHD dynamo.
		The dipole field generation is closely related to the columnar structure of the convection motion, which is characteristic of the rotating spherical convection.
	stacks.iop.org /0741-3335/39/A83 (235 words)

	A model of the nonlinear turbulent dynamo
		A model of nonlinear evolution and saturation of the turbulent MHD dynamo
		A physical picture of the ensuing nonlinear evolution of the MHD dynamo is proposed.
		It is found that, while the shift of the bulk of the magnetic energy from the subviscous scales to the velocity scales may be possible, it occurs very slowly - at the resistive, rather than dynamical, timescale (for galaxies, this means that the generation of large-scale magnetic fields cannot be explained by this mechanism).
	stacks.iop.org /1367-2630/4/84 (360 words)

	NSC Project 2005036
		Large scale dynamo action might be essential for matching observations of protoplanetary nebulae (PPNs) and planetary nebulae (PNs).
		This approach is supported by a semi-quantitative theoretical physical model, in which mean-field dynamo action in both a PPN /PN star and a surrounding accretion disk, drives MHD winds whose power is sufficiently large to explain the high observed kinetic luminosities.
		Our MHD codes are thus well suited to be adapted to study numerically the formation of PPNs and PNs according to the above proposed physical model.
	www.nsc.liu.se /projects/previousprojects/project_2005036.html (327 words)

	ANS : Store : Electronic Articles
		A gas core reactor (GCR) with magnetohydrodynamic (MHD) power converter and cascading power cycle forms the basis for a Generation IV concept that is expected to set the upper performance limits in sustainability and power conversion efficiency among all existing and proposed fission powered systems.
		The hot working fluid exiting a topping cycle MHD generator has sufficient heat to drive a conventional helium Brayton cycle with 35% thermal efficiency as well as a superheated steam Rankine cycle, with up to 40% efficiency, which recovers the waste heat from the intermediate Brayton cycle.
		The high-temperature direct-energy conversion capability of an MHD dynamo combined with an already sophisticated steam-powered turbine industry knowledge base allows the cascading cycle design to achieve breakthrough first-law energy efficiencies previously unheard of in the nuclear power industry.
	www.ans.org /store/index.cgi?i=E120000-nt-145-3-311-318 (403 words)

	Exeter Fluids and MHD Abstracts (Site not responding. Last check: 2007-11-02)
		In the kinematic dynamo problem a fluid motion is specified arbitrarily and the induction equation is solved for non-decaying magnetic fields; it forms part of the larger magnetohydrodynamic (MHD) dynamo problem in which the fluid flow is buoyancy-driven.
		The boundary effect is first removed by surrounding the dynamo region with a thick layer of quiescent conducting fluid, and then studied numerically by progressively reducing the thickness of this layer to zero.
		The insulating boundary contributes to the difficulty of obtaining dynamo action, and to the numerical difficulties encountered.
	www.maths.ex.ac.uk /~CAJones/abstracts/1996abs/sg.html (444 words)

	[59.06] MHD Turbulent Dynamo in Astrophysics: Theory and Numerical Simulation (Site not responding. Last check: 2007-11-02)
		Astrophysical dynamo theory studies the generation of large-scale magnetic fields from small-scale turbulence in many celestial objects.
		By considering both the time-dependent term and the boundary effect term in the equation of magnetic helicity, we are able to show, both analytically and numerically, that dynamo effect may not be quenched by large magnetic Reynolds numbers in astrphysical systems.
		Another open question on dynamo process is the concern that fast growing small-scale magnetic field would swamp velocity field entirely so that dynamo effect will not happen in systems of large magnetic Prandtl number, for example, the Galaxy.
	www.aas.org /publications/baas/v32n4/aas197/213.htm (343 words)

	Interaction between rotation, convection and magnetic fields in the Sun and solar-type stars (Site not responding. Last check: 2007-11-02)
		It is now clear that mean-field dynamo theory needs to be reformulated in such a way that magnetic helicity conservation is incorporated, and this is currently being undertaken by various groups (e.g.
		The main reason for this could be the absence of a realistic treatment of the base of the convection zone or of the upper boundary and the near-surface shear layer.
		We also aim to study in detail dynamo-relevant processes in the crucial shear layers both near the base and near the top of stellar convection zones, including mechanisms of magnetic field amplification, formation of magnetic structures including flux tubes, their buoyant rise and the alpha effect resulting from the interaction of these structures with rotation.
	www.nordita.dk /~brandenb/tmp/project (770 words)

	Discussion
		In this paper we have studied the process of magnetic field generation in thin accretion discs via the MHD dynamo.
		Tentatively assuming that a wind launched either centrifugally (inner disc) or gravitationally (outer disc) is able to eventually open up field lines, we may conclude that the magnetic field resulting from the dynamo action in the absence of an ambient field could lead to a bipolar, symmetric wind.
		This is because the dynamo field is concentrated in its toroidal component, and only a very small fraction of its total strength is available for a vertical component.
	www.lpi.usra.edu /science/tom/mn/node6.html (1698 words)

	Dipole field generation by an MHD dynamo (Site not responding. Last check: 2007-11-02)
		Computer simulation of magnetohydrodynamic dynamo in a rotating spherical shell is performed.
		Time developments of the magnetic field and the velocity field are self-consistently calculated by solving the MHD equations.
		The magnetic field is amplified by the MHD dynamo.
	flux.aps.org /meetings/BAPSDPP96/abs/S430002.html (375 words)

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