Showing papers on "Magnetic field published in 1992"
TL;DR: The observed isotropic giant magnetoresistance (GMR) in nonmultilayer magnetic systems using granular magnetic solids is shown to occur in magnetically inhomogeneous media containing nonaligned ferromagnetic entities on a microscopic scale.
Abstract: We have observed isotropic giant magnetoresistance (GMR) in nonmultilayer magnetic systems using granular magnetic solids. We show that GMR occurs in magnetically inhomogeneous media containing nonaligned ferromagnetic entities on a microscopic scale. The GMR is determined by the orientations of the magnetization axes, the density, and the size of the ferromagnetic entities.
1,465 citations
TL;DR: A quantitative electrostatic theory of the gate-induced confinement of two-dimensional electron gas (2DEG) in the quantum Hall regime is proposed and enables results obtained in experimental studies of edge-state equilibration to be explained.
Abstract: We propose a quantitative electrostatic theory of the gate-induced confinement of two-dimensional electron gas (2DEG) in the quantum Hall regime. The self-consistent electrostatic potential in the region occupied by 2DEG changes in a steplike manner due to the formation of alternating strips of compressible and incompressible electron liquids. We obtain the dependence of positions and widths of these strips on the filling factor. Incompressible strips are shown to be much more narrow than the compressible ones. The relationship between the widths of the adjacent compressible and incompressible strips is found to be universal: It does not depend on the strip number, magnetic field, or gate voltage. Our theory enables us to explain results obtained in experimental studies of edge-state equilibration.
668 citations
TL;DR: In this paper, the authors extend the canonical exponential potential scalar field inflation modified hot big bang model by adding an inflation epoch coupling, between the scalar fields responsible for inflation and an Abelian gauge field.
Abstract: We extend the canonical exponential potential scalar field inflation modified hot big bang model by adding an inflation epoch coupling, between the scalar field Φ responsible for inflation and an Abelian gauge field A μ , ∞e αΦ F μν F μν (where F μν =∂ μ A ν −∂ ν A μ and α is a parameter)
666 citations
TL;DR: In this article, the authors investigated three mechanisms that promote the loss of magnetic flux from an isolated neutron star, including buoyant rise and dragging by superfluid neutron vectors, and found that the drift speed is proportional to the second power of the magnetic field strength.
Abstract: We investigate three mechanisms that promote the loss of magnetic flux from an isolated neutron star. Ohmic decay produces a diffusion of the magnetic field with respect to the charged particles. It proceeds at a rate that is inversely proportional to the electric conductivity and independent of the magnetic field strength. Ohmic decay occurs in both the fluid core and solid crust of a neutron star, but it is too slow to directly affect magnetic fields of stellar scale. Ambipolar diffusion involves a drift of the magnetic field and charged particles relative to the neutrons. The drift speed is proportional to the second power of the magnetic field strength if the protons form a normal fluid. Variants of ambipolar diffusion include both the buoyant rise and the dragging by superfluid neutron
vortices of magnetic flux tubes. Ambipolar diffusion operates in the outer part of the fluid core where the
charged particle composition is homogeneous, protons and electrons being the only species. The charged particle
flux associated with ambipolar diffusion decomposes into a solenoidal and an irrotational component. Both components are opposed by frictional drag. The irrotational component perturbs the chemical equilibrium between neutrons, protons, and electrons, thus generating pressure gradients that effectively choke it. The solenoidal component is capable of transporting magnetic flux from the outer core to the crust on a short time scale. Magnetic flux that threads the inner core, where the charged particle composition is inhomogeneous, would be permanently trapped unless particle interactions could rapidly smooth departures from chemical equilibrium. Magnetic fields undergo a Hall drift related to the Hall component of the electric field. The drift speed is proportional to the magnetic field strength. Hall drift occurs throughout a neutron star. Unlike ohmic decay and ambipolar diffusion which are dissipative, Hall drift conserves magnetic energy. Thus, it cannot by itself be responsible for magnetic field decay. However, it can enhance the rate of ohmic dissipation. In the solid crust, only the electrons are mobile and the tangent of the Hall angle is large. There, the evolution of the magnetic field resembles that of vorticity in an incompressible fluid at large Reynolds number. This leads us to speculate that the magnetic field undergoes a turbulent cascade terminated by ohmic dissipation at small scales. The small-scale components of the magnetic field are also transported by Hall drift waves from the inner crust where ohmic dissipation is slow to the outer crust where it is rapid. The diffusion of magnetic flux through the crust takes ~ 5 x 10^8/B_(12) yr, where B_(12) is the crustal magnetic field strength measured in units of 10^(12) G.
520 citations
TL;DR: In this article, it is argued that the observed photospheric field should first be corrected for line-of-sight projection and then matched to the radial component of the potential field.
Abstract: It is shown that the line-of-sight matching procedure involved in potential field models of the solar corona do not make good use of the available data because there is strong evidence that the magnetic field is nearly radial, and therefore nonpotential, at the photosphere. It is argued that the observed photospheric field should first be corrected for line-of-sight projection and then matched to the radial component of the potential field. It is shown that this procedure yields much stronger polar fields than the standard method and produces better agreement with high-latitude coronal holes and with white-light structures in the outer corona. The relationship of both methods to the observed inclination angles of polar plumes is also discussed.
497 citations
TL;DR: In this article, the fundamental theory of the geometric phase is summarized in a way suitable for use in molecular systems treated by the Born-Oppenheimer approach, both Abelian and non-Abelian cases are considered.
Abstract: The fundamental theory of the geometric phase is summarized in a way suitable for use in molecular systems treated by the Born-Oppenheimer approach. Both Abelian and non-Abelian cases are considered. Applications discussd include the Abelian geometric phase associated with an intersection of two electronic potential-energy surfaces; screening of nuclei by the electrons from an external magnetic field; non-Abelian gauge potentials in molecular systems with Kramers degeneracy; and the coupling between different electronic levels (Born-Oppenheimer breakdown) represented as a gauge potential. Experimental tests for these systems are discussed, as well as a number of experiments on spin systems.
467 citations
TL;DR: In this paper, an individual gauge for atoms in molecules is presented for relatively accurate ab initio calculations of molecular magnetic response properties, where the magnetic susceptibility and nuclear magnetic shielding tensors can be expressed in terms of the induced current density as a sum of separately determined atomic contributions.
418 citations
TL;DR: In this paper, the fluctuation spectrum that must arise in a mean field dynamo generation of galactic fields if the initial field is weak is considered and a kinetic equation for its evolution is derived and solved.
Abstract: The fluctuation spectrum that must arise in a mean field dynamo generation of galactic fields if the initial field is weak is considered. A kinetic equation for its evolution is derived and solved. The spectrum evolves by transfer of energy from one magnetic mode to another by interaction with turbulent velocity modes. This kinetic equation is valid in the limit that the rate of evolution of the magnetic modes is slower than the reciprocal decorrelation time of the turbulent modes. This turns out to be the case by a factor greater than 3. Most of the fluctuation energy concentrates on small scales, shorter than the hydrodynamic turbulent scales. The fluctuation energy builds up to equipartition with the turbulent energy in times that are short compared to the e-folding time of the mean field. The turbulence becomes strongly modified before the dynamo amplification starts. Thus, the kinematic assumption of the mean dynamo theory is invalid. Thus, the galactic field must have a primordial origin, although it may subsequently be modified by dynamo action.
417 citations
TL;DR: In this article, an exact analytical solution of the governing non-linear boundary layer equation is obtained, showing that an external magnetic field has the same effect on the flow as the viscoelasticity.
Abstract: The flow of a viscoelastic fluid past a stretching sheet in the presence of a transverse magnetic field is considered. An exact analytical solution of the governing non-linear boundary layer equation is obtained, showing that an external magnetic field has the same effect on the flow as the viscoelasticity.
400 citations
Journal Article•
TL;DR: The Ulysses solar wind plasma experiment, termed the Solar Wind Observations Over the Poles of the Sun (SWOOPS) as mentioned in this paper, includes measurements of the solar-wind global properties, the nonlinear MHD disturbances in the solar wind, and the internal state of the plasma.
Abstract: The scientific objectives of the Ulysses solar wind plasma experiment, termed the Solar Wind Observations Over the Poles of the Sun (SWOOPS) include measurements of the solar-wind global properties, the nonlinear MHD disturbances in the solar wind, the internal state of the solar wind plasma, and the solar-wind interaction with Jupiter's magnetic field. In this paper, special attention is given to the two instrumental packages of SWOOPS experiment that will simultaneously perform measurements on electrons and ions of solar plasma: the ion analyzer and the electron analyzer. Results obtained in the initial phases of the SWOOPS experiment are presented.
386 citations
TL;DR: In this paper, the authors measured the small, oscillatory magnetic force (10−14 N) acting on a paramagnetic sample (a few grains of diphenylpicrylhydrazil, weighing < 30 ng) which has been excited into magnetic resonance in the presence of an inhomogeneous magnetic field.
Abstract: CONVENTIONAL techniques for measuring magnetic resonance involve the detection of electromagnetic signals induced in a coil or microwave cavity by the collective precession of magnetic moments (from nuclei or electrons) excited by an alternating magnetic field. In a different approach1, isolated electron spins have been detected by scanning tunnelling microscopy, with the spin precession inducing a radiofrequency modulation in the tunnelling current. Here, we describe a new and extremely sensitive method of detection, the principles of which derive from magnetic force microscopy2–5 and a recent proposal6,7 by one of us (J.A.S.). We measure the small, oscillatory magnetic force (10−14 N) acting on a paramagnetic sample (a few grains of diphenylpicrylhydrazil, weighing < 30 ng) which has been excited into magnetic resonance in the presence of an inhomogeneous magnetic field. This force is detected by optically sensing the angstrom-scale vibration of a micromechanical cantilever on which the sample is mounted. The sensitivity of this technique to the spatial distribution of the spins suggests that mechanical detection of magnetic resonance has the potential for imaging microscopic samples in three dimensions. So far, we have achieved a spatial resolution of 19 μm in one dimension.
TL;DR: Local-density-functional calculations on HF molecules within a finite-length tubule, of size 144 atoms, open the way to the study of nanoscale capillarity and to, perhaps, precise control over shielding of specific ``guest'' compounds from external electric and magnetic fields.
Abstract: Fullerene tubules are shown to be highly polarizable ``molecular straws'' capable of ingesting dipolar molecules Local-density-functional calculations on HF molecules within a finite-length tubule, of size 144 atoms, demonstrate this effect The energy of incarceration is several times the thermal ambient at room temperature These calculations, now feasible on desktop workstations, open the way to the study of nanoscale capillarity and to, perhaps, precise control over shielding of specific ``guest'' compounds from external electric and magnetic fields
TL;DR: In this article, the effect of magnetic field on the now characteristics is explored numerically, and it is concluded that the magnetic field tends to make the boundary layer thinner, thereby increasing the wall friction.
Abstract: Magnetohydrodynamic flow of an electrically conducting power-law fluid over a stretching sheet in the presence of a uniform transverse magnetic field is investigated by using an exact similarity transformation. The effect of magnetic field on the now characteristics is explored numerically, and it is concluded that the magnetic field tends to make the boundary layer thinner, thereby increasing the wall friction.
TL;DR: In this article, an analytical solution to the equations of magnetohydrodynamics that can be used to model the effect of a transverse magnetic field on buoyancy driven convection in a two-dimensional cavity was proposed.
TL;DR: In this paper, it was argued that in the limit of small diffusivity only a small amount of flux, many orders of magnitude less than the observed fluxes, can be created by dynamo processes.
Abstract: Astrophysical dynamos operate in the limit of small magnetic diffusivity. In order for magnetic reconnection to occur, very small magnetic structures must form so that diffusion becomes effective. The formation of small-scale fields is accompanied by the stretching of the field lines and therefore by an amplification of the magnetic field strength. The back reaction of the magnetic field on the motions leads to the eventual saturation of the dynamo process, thus posing a constraint on the amount of magnetic flux that can be generated by dynamo action, It is argued that in the limit of small diffusivity only a small amount of flux, many orders of magnitude less than the observed fluxes, can be created by dynamo processes.
TL;DR: Numerical comparisons of the field uniformity generated by Helmholtz coils, or systems of bifilar windings, are made, along with a table of construction details and recommendations for their use in experiments in which large volumes of uniform intensity magnetic exposures are needed.
Abstract: A common mistake in biomagnetic experimentation is the assumption that Helmholtz coils provide uniform magnetic fields; this is true only for a limited volume at their center. Substantial improvements on this design have been made during the past 140 years with systems of three, four, and five coils. Numerical comparisons of the field uniformity generated by these designs are made here, along with a table of construction details and recommendations for their use in experiments in which large volumes of uniform intensity magnetic exposures are needed. Double-wrapping, or systems of bifilar windings, can also help control for the non-magnetic effects of the electric coils used in many experiments. In this design, each coil is wrapped in parallel with two separate, adjacent strands of copper wire, rather than the single strand used normally. If currents are flowing in antiparallel directions, the magnetic fields generated by each strand will cancel and yield virtually no external magnetic field, whereas parallel currents will yield an external field. Both cases will produce similar non-magnetic effects of ohmic heating, and simple measures can reduce the small vibration and electric field differences. Control experiments can then be designed such that the only major difference between treated and untreated groups is the presence or absence of the magnetic field. Double-wrapped coils also facilitate the use of truly double-blind protocol, as the same apparatus can be used either for experimental or control groups.
Patent•
[...]
30 Apr 1992
TL;DR: In this paper, the authors proposed a method to improve the life and printing quality by a method wherein a substrate which comes into contact with an ink has a diaphragm structure, and this diaphrasm is displaced by magnetic force from the outside.
Abstract: PURPOSE:To improve the life and printing quality (high density dot) by a method wherein a substrate which comes into contact with an ink has a diaphragm structure, and this diaphragm is displaced by magnetic force from the outside. CONSTITUTION:Line of magnetic force which is generated by magnets 110, 120 arranged at both sides of an ink jet head goes across the inside of the ink jet head. At this time, electric current is charged in the wiring on a diaphragm 103, conforming to Fleming's rule, force is applied to the wiring 104, i.e., to the upper part or lower part of the diaphragm, in proportion to the strength of the line of magnetic force and the current value. The direction in which the force is applied is determined by the direction of the line of magnetic force and electric current, and by this force, the diaphragm is displaced, and pressure is added to the ink is surrounded by substrates 102 and 105, and the ink drop flies out from an ink discharge port 100.
TL;DR: In this paper, the problem of constructing a time-dependent map of the magnetic field at the core-mantle boundary was considered and the smoothest solution compatible with the observations was proposed.
Abstract: We consider the problem of constructing a time-dependent map of the magnetic field at the core-mantle boundary. We use almost all the available data from the last 300 years to produce two maps, one for the period 1690-1840 and the other for 1840-1990. We represent the spatial dependency of the field using spherical harmonics, the time dependency using a cubic B-spline basis, and seek the smoothest solutions compatible with the observations. We argue that, for observations from permanent magnetic observatories, the most efficient strategy is to use the first differences of annual means; for satellite data, the most efficient strategy is simply to limit the number of data used so as to minimize any tendency to map the crustal field into the core field. The resulting model fits the observatory data better than any previous model. The resulting time-dependent field map exhibits much of the same structure in the field and its secular variation identified in earlier studies.
TL;DR: In this paper, the authors show that externally applied static resonant magnetic perturbations (RMPs) induce stationary magnetic islands, which give rise to a significant degradation in energy and particle confinement, suppression of the sawtooth oscillation and a large change in the impurity ion toroidal velocity.
Abstract: Experimental results from the COMPASS-C tokamak reveal a sharp threshold in amplitude above which externally applied static resonant magnetic perturbations (RMPs) induce stationary magnetic islands. Such islands (in particular, m=2, n=1 islands) give rise to a significant degradation in energy and particle confinement, suppression of the sawtooth oscillation and a large change in the impurity ion toroidal velocity. The observed threshold for inducing stationary (2,1) islands is consistent with a phenomenological resistive MHD model which takes into account plasma rotation (including poloidal flow damping) and externally applied resonant fields. Broadly similar results are found for applied fields other than m=2, n=1. Other results from RMP experiments are also discussed, such as the stabilization of rotating MHD activity, stimulated disruptions and extensions to the disruptive density limit. Finally, the likely effect of field errors on large tokamaks is briefly examined in the light of the COMPASS-C results
TL;DR: In this paper, the authors studied the general relativistic electrodynamics of an isolated, rotating, magnetic neutron star, and derived explicit solutions to the Maxwell equations, and demonstrated the influence of the effects of General Relativity on the creation of an electric field in the afore-mentioned region.
Abstract: We study the general relativistic electrodynamics of an isolated, rotating, magnetic neutron star. We consider the region of a neutron star magnetosphere with steady, space charge limited flow along open magnetic field lines. The explicit solutions to the Maxwell equations are obtained. Being the simplest, this model enables one to carry out analytically a general relativistic treatment, and to demonstrate the influence of the effects of General Relativity on the creation of an electric field in the afore-mentioned region.
TL;DR: In this article, the conservation laws and jump conditions at Alfven and slow resonance points obtained by Sakurai et al. were generalized to include an equilibrium flow, and the assumption that the Eulerian perturbation of total pressure is constant was recovered as the special case of the conservation law for an equilibrium with straight magnetic field lines.
Abstract: The Hollweg et al. (1990) analysis of MHD surface waves in a stationary equilibrium is extended. The conservation laws and jump conditions at Alfven and slow resonance points obtained by Sakurai et al. (1990) are generalized to include an equilibrium flow, and the assumption that the Eulerian perturbation of total pressure is constant is recovered as the special case of the conservation law for an equilibrium with straight magnetic field lines and flow along the magnetic field lines. It is shown that the conclusions formulated by Hollweg et al. are still valid for the straight cylindrical case. The effect of curvature is examined.
TL;DR: In this article, the authors investigated the nonlinear evolution of the accretion disk magnetic shear instability through a series of numerical simulations and found that the most rapid growth occurs for very small radial and azimuthal wavenumbers, leading to coherent magnetic field structure in planes parallel to the disk.
Abstract: The nonlinear evolution of the recently identified accretion disk magnetic shear instability is investigated through a series of numerical simulations. Finite-difference computations of the equations of compressible MHD are carried out on an axisymmetric shearing sheet system with periodic boundary conditions designed to approximate a local region within an accretion disk. Initial field configurations that include some net vertical component evolve into a nonlinear, exponentially growing solution with large poloidal velocities and magnetic fields with energies comparable to the thermal energy density. The stability of a purely azimuthal field configuration is examined, and it is found that nonaxisymmetric instability is present, but with a growth time measured in tens of orbital periods. In general, the most rapid growth occurs for very small radial and azimuthal wavenumbers, leading to coherent magnetic field structure in planes parallel to the disk. It is suggested that this instability is a key ingredient for the generation of magnetic fields in disks.
01 Feb 1992-Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms
TL;DR: In this paper, an electrostatic electron spectrometer combining both high resolution and large luminosity is presented. But the energy resolution of the electrostatic filter is determined by the ratio of the magnetic fields at the source and in the analyzing plane.
Abstract: We have built an electrostatic electron spectrometer combining both high resolution and large luminosity. The instrument consists essentially of two superconducting solenoids separated by a system of ring electrodes of 4 m in length. Source and detector are placed in the high-field regions of the superconducting solenoids, whereas the repellent analyzing electrostatic potential of the ring electrodes peaks at the minimum of the magnetic field in between these solenoids. The magnetic guiding field provides (i) the acceptance of the full foreward solid angle of 2π, (ii) the transformation of the transverse cyclotron motion into longitudinal motion parallel to the magnetic field. The energy resolution of the electrostatic filter is determined by the ratio of the magnetic fields at the source and in the analyzing plane. It is typically 5 × 10 3 in our case. The spectrometer will serve first of all to investigate the limits of the rest mass of the electron antineutrino from 3 H 2 s-decay. It has been tested by measuring conversion lines from a 83m Kr source which yielded an energy of Eγ = 32151.5(11) eV for the corresponding nuclear transition.
TL;DR: In this paper, the authors presented a summary of the theory and experimental measurements on the production of high-density plasmas using radio-frequency excitation of helicon waves.
Abstract: This work concerns a search for novel plasma generators with applications to materials processing and advanced accelerators and radiation sources. Experimental measurements, together with a summary of the theory, are presented on the production of high‐density plasmas using radio‐frequency (rf) excitation of helicon waves. Plasma densities above 3 × 1013 cm−3 have been achieved with 2 kW of rf power. The required power agrees with classical diffusion theory. The scaling of density with magnetic field agrees with the theory of helicon waves. The effect of different antenna designs is demonstrated. Unexpected observations include: (a) a density maximum occurring at very low magnetic fields, (b) an increase in peak density with nonuniform fields, and (c) the strong effects of dc wall potentials on the behavior of the discharge. Tentative explanations of these phenomena are presented.
TL;DR: In this article, direct simulations of turbulent compressible hydromagnetic convection above a stable overshoot layer are presented, where spontaneous dynamo action occurs followed by saturation, with most of the generated magnetic field appearing as coherent flux tubes in the vicinity of strong downdrafts, where both the generation and destruction of magnetic field is most vigorous.
Abstract: Results are presented from direct simulations of turbulent compressible hydromagnetic convection above a stable overshoot layer. Spontaneous dynamo action occurs followed by saturation, with most of the generated magnetic field appearing as coherent flux tubes in the vicinity of strong downdrafts, where both the generation and destruction of magnetic field is most vigorous. Whether or not this field is amplified depends on the sizes of the magnetic Reynolds and magnetic Prandtl numbers. Joule dissipation is balanced mainly by the work done against the magnetic curvature force. It is this curvature force which is also responsible for the saturation of the dynamo.
TL;DR: Low-temperature measurements of the frequency-dependent magnetic noise and magnetic susceptibility of nanometer-scale antiferromagnetic horse-spleen ferritin particles are reported, using an integrated dc SQUID microsusceptometer, indicating that this behavior results from macroscopic quantum tunneling of the Neel vector of the Antiferromagnets.
Abstract: We report low-temperature measurements of the frequency-dependent magnetic noise and magnetic susceptibility of nanometer-scale antiferromagnetic horse-spleen ferritin particles, using an integrated dc SQUID microsusceptometer. A sharply defined resonance near 1 MHz develops below T\ensuremath{\sim}0.2 K. The behavior of this resonance as a function of temperature, applied magnetic field, and particle concentration indicates that it results from macroscopic quantum tunneling of the N\'eel vector of the antiferromagnets.
TL;DR: Data suggest an important role for magnetic field exposure in altering cellular processes, and changes in transcript levels, assessed by slot-blot analysis, have been found to parallel the changes in gene transcription.
TL;DR: The finite-difference time-domain method is used to calculate induced current densities for the anatomically based model of the human body for the various orientations of the time-varying magnetic fields, namely from side to side, front to back, or from top to bottom of the model, respectively.
Abstract: We have used the finite-difference time-domain (FDTD) method to calculate induced current densities in a 1.31-cm (nominal 1/2 in) resolution anatomically based model of the human body for exposure to purely electric, purely magnetic, and combined electric and magnetic fields at 60 Hz. This model based on anatomic sectional diagrams consists of 45,024 cubic cells of dimension 1.31 cm for which the volume-averaged tissue properties are prescribed. It is recognized that the conductivities of several tissues (skeletal muscle, bone, etc.) are highly anisotropic for power-line frequencies. This has, however, been neglected in the first instance and will be included in future calculations. Because of the quasi-static nature of coupling at the power-line frequencies, a higher quasi-static frequency f' may be used for irradiation of the model, and the internal fields E' thus calculated can be scaled back to the frequency of interest, e.g., 60 Hz. Since in the FDTD method one needs to calculate in the time domain until convergence is obtained (typically 3-4 time periods), this frequency scaling to 5-10 MHz for f' reduces the needed number of iterations by over 5 orders of magnitude. The data calculated for the induced current and its variation as a function ofmore » height are in excellent agreement with the data published in the literature. The average current densities calculated for the various sections of the body for the magnetic field component (H) are considerably smaller (by a factor of 20-50) than those due to the vertically polarized electric field component when the ratio E/H is 377 ohms. We have also used the previously described impedance method to calculate the induced current densities for the anatomically based model of the human body for the various orientations of the time-varying magnetic fields, namely from side to side, front to back, or from top to bottom of the model, respectively. 34 refs.« less
TL;DR: In this article, the authors present numerical computations of linear kinematic dynamos associated with periodic smooth flows, with diffusion explicitly included, for diffusion times up to 10,000 times greater than the turnover time.
Abstract: MANY astrophysical magnetic fields are thought to arise by dynamo action due to internal fluid motions, but the natural timescale for magnetic field growth is the diffusion timescale, which in realistic astrophysical applications is very large1. A fast dynamo is one that operates on the much shorter turnover timescale of the generating fluid flow, and the analytical intractability of smooth flows with diffusion has prompted the use of many ingenious models2–10, differing from the true problem in having a modified or time-dependent diffusion or singularities in the flow field. Here we adopt a straightforward approach and present numerical computations of linear kinematic dynamos associated with periodic smooth flows, with diffusion explicitly included. Examples of time-varying flows depending on two spatial coordinates give convincing evidence of fast dynamo action for diffusion times up to 10,000 times greater than the turnover time. A three-dimensional steady flow shows similar behaviour, although computations have not beencarried out so far and the asymptotic behaviour is less clear. All these flows have large regions where particle paths are chaotic.
TL;DR: In this article, a self-similar solution for relativistic winds driven by rotating magnetic fields is constructed, which can attain supermagnetosonic speeds with high Lorentz factors.
Abstract: A class of self-similar solutions for relativistic winds driven by rotating magnetic fields is constructed. These winds are collimated to cylindrical jet flows of finite radii and may attain supermagnetosonic speeds with high Lorentz factors. Most of the flow acceleration results from the 'magnetic nozzle' effect and occurs beyond the fast magnetosonic point, which is typically located a few light cylinder radii from the rotation axis. Approximate equipartition between the electromagnetic and flow kinetic energies is generally achieved for these jets, in contrast to the radial wind case in which the flow is magnetically dominated at all radii.