A Mechanism for Generation of the Solar Magnetic Field

We apply the mathematical technique of quantum mechanics for studying the process of solar magnetic field generation under conditions where the viscosity is negligible and the rotation velocity of the medium is independent of time. It is assumed that the magnetic field is almost toroidal, axially nonsymmetric, and antisymmetric with respect to the equatorial plane.We show that in the presence of an axisymmetric poloidal component of the hydrodynamic velocity and a radial gradient of the angular velocity of the medium, an oscillating solution growing in time exists for the field. The characteristic frequency of oscillations can exceed the rotation frequency if the rotation of the medium is nonuniform. In the case where the characteristic time of field growth amounts to 10 years, the radial velocity of the medium in the field-generation zone is approximately equal to 10 cm/sec. We also discuss briefly the problem of the existence of two field-generation zones.     

Decay rate of an excited atom in a moving medium

The effect of a uniformly moving medium on the decay rate of an excited atom is calculated. When the local field effects are neglected, the free space decay rate is modified by a factor which is a complicated function of refractive index, permeability, and velocity of the medium. It is shown that the decay rate vanishes if the velocity of the medium exceeds the phase velocity of light in the stationary medium.     

Modes of a rotating dielectric waveguide

Proceeding from the Maxwell differential equations and the Minkowski constitutive equations of the first order with respect to the ratio of the velocity of motion of a medium to the velocity of light in a vacuum, we derived equations for determining the mode structure of a field in a linear isotropic medium with an axially symmetric distribution of the permittivity and the permeability and with the angular velocity of rotation dependent on the distance from the symmetry axis. A waveguide effect was shown to appear even for a homogeneous medium owing to the spatial nonuniformity of the angular velocity. In the case of the quadratic dependence of the angular velocity on the transverse coordinate, the exact solutions for the modes were found in the form of Gaussian beams.     

Electromagnetic radiation in a medium with a velocity gradient

A relativistic expression has been obtained for the curvature of trajectory of the wave vector of an electromagnetic wave in a moving optically transparent medium. It has been shown that the curvature of the trajectory and angular deviation of rays appear in a homogeneous isotropic medium if the gradient of the velocity field in the medium is nonzero. The bending of the trajectory in the medium with the velocity gradient is a firstorder effect in the ratio u/c.     

Dispersion und Absorption transversaler Schallwellen im Magnetfeld

The propagation velocity and absorption of transverse ultrasonic waves have bsen measured in a polycristalline metallic probe as functions of a magnetic field parallel to the direction of propagation. In agreement with the macroscopic theory, these measurements showed, that the propagation velocity was increased by the magnetic field for frequencies below a transition frequency characteristic for the medium. In case of high frequencies the magnetic field causes an absorption. In the dispersion region characterized by the transition frequency, the magnetohydrodynamic Reynolds number is of order one and the magnetically induced changes in propagation velocity and absorption are strongly frequency dependent.     

Concentration and velocity field measurements by magnetic resonance imaging in aperiodic heterogeneous porous media.

Magnetic resonance imaging (MRI) techniques were investigated as a means to obtain concentration and velocity field measurements for the verification of a stochastic model for conservative chemical transport. MRI techniques were successfully applied to obtain one-dimensional breakthrough images and two-dimensional velocity images along the length of an aperiodic heterogeneous porous medium. Experimental moment data showed the concentration field in the experimental model to be slightly positively skewed. Velocity images showed the velocity field to be relatively uniform with no channeling or preferential flow behavior. Measured covariance functions showed evidence of negative correlation in the velocity field. The detailed spatial information provided by these imaging experiments has demonstrated that MRI is a valuable tool for obtaining experimental data for the verification of existing theoretical models.     

Superluminosity,sound propagation,and causality

Different field theories may lead to identical equations of state. Depending on the field theory, from which an equation of state is derived, in the superluminal density domain the sound wave propagation velocity exceeds (does not exceed) the velocity of light, if the field is a medium with normal (anomal) dispersion. Super-light sound violates causality, causality violations lead to logical paradoxies, so superluminal density regions should be regions of anomal dispersion.     

Electromagnetically induced transparency in degenerate two-level systems

The evolution of an electromagnetic wave with slowly varying polarization, which interacts resonantly with the medium formed by degenerate two-level atoms, is studied using the wave function approach under the conditions of electromagnetically induced transparency. It is shown that the amplitude of the wave field propagates at the velocity of light in such a medium. The equation obtained for the polarization parameter has a solution in the form of a simple wave. The breaking length is determined. It is shown that the velocity of propagation of polarization waves may be much smaller than the velocity of light. The proposed approach is common for two-level systems with an arbitrary degeneracy. The case of a system with Zeeman degeneracy is analyzed in detail. The dependence of the velocity of propagation of the polarization structure on the amplitude and polarization is determined for an arbitrary level degeneracy. The evolution of the polarization structure in such a medium is discussed.     

On the stability of capillary waves on the surface of a space-charged dielectric liquid jet moving in a material medium

We have derived and analyzed the dispersion equation for capillary waves with an arbitrary symmetry (with arbitrary azimuthal numbers) on the surface of a space-charged cylindrical jet of an ideal incompressible dielectric liquid moving relative to an ideal incompressible dielectric medium. It has been proved that the existence of a tangential jump of the velocity field on the jet surface leads to a periodic Kelvin–Helmholtz- type instability at the interface between the media and plays a destabilizing role. The wavenumber ranges of unstable waves and the instability increments depend on the squared velocity of the relative motion and increase with the velocity. With increasing volume charge density, the critical value of the velocity for the emergence of instability decreases. The reduction of the permittivity of the liquid in the jet or an increase in the permittivity of the medium narrows the regions of instability and leads to an increase in the increments. The wavenumber of the most unstable wave increases in accordance with a power law upon an increase in the volume charge density and velocity of the jet. The variations in the permittivities of the jet and the medium produce opposite effects on the wavenumber of the most unstable wave.     

有限存贮空间内可燃多孔介质流动和传热的研究

对通风条件下可燃多孔介质库房内的流动和传热特性进行了数值模拟,得到了库房有限空间内的温度场和速度场.通过比较不同的来流温度和入口流速,得到的结果表明:可燃多孔介质(弹药)内部发生化学反应并产生热量,其温度由中心向四周逐渐降低;来流流速越大,越有利于弹药的冷却;在来流速度相同的情况下,来流温度越低,越有利于散热,对于可燃多孔介质(弹药)的贮存越安全;在左侧进风口的上下两边以及可燃多孔介质(弹药)的上方,会形成漩涡.     

Specific dynamics of faster-than-light (in the medium) extremely short optical pulses in an array of carbon nanotubes

Maxwell’s equations for an electromagnetic field propagating in an array of carbon nanotubes have been considered in the case when the velocity of the incident pulse is greater than the speed of light in the medium. The equation for the vector potential of the electromagnetic field has been derived and solved numerically. The dependence of the pulse on its velocity at the entrance to the array of carbon nanotubes has been revealed.     

Generation of magnetic field during shearing motion of a conducting viscous medium

Magnetic field generation in shear flows of an incompressible viscous conducting medium across the flux lines of the initial field created in them is considered in the framework of the plane 1D problem of magnetohydrodynamics. The conditions of free slip and “sticking” are stipulated at the boundary between the flows. The variations of the magnetic field and velocity of shear flow occurring in the moving medium correspond to an Alfven wave “spreading” during its propagation due to dissipative processes in the medium associated with its viscosity and electrical resistance. It is shown that a high-rate shear of metals under explosive or impact loading may lead to generation of megagauss magnetic fields.     

Nonstationary contrasting structures for the generalized Kolmogorov-Petrovskiy-Piskunov equation

The solution to the generalized Kolmogorov-Petrovskiy-Piskunov (GKPP) equation is shown to have a contrasting structure. Contrasting structures (CSs) are characterized by the existence of wide areas with a small field gradient separated by narrow internal transition layers (ITLs) with a large field gradient. The ITLs in an inhomogeneous medium are shown to drift and the drift velocity is determined. The CS drift velocity for the GKPP equation is compared with a simpler model of the reaction-advection-diffusion equation.     

Effect of a variable magnetic field on the instability of a stratified rotating fluid layer in porous medium

The instability of a stratified rotating fluid layer through porous medium in the presence of an inhomogeneous magnetic field is investigated. For exponentially varying density and magnetic field variations, an eigenvalue solution has been obtained. The dispersion relation is obtained and discussed for both the stable and unstable stratifications separately. It is found, for non-porous medium, that for the stable mode of disturbance, the system is always stable, and for the unstable mode of disturbance, it is stabilized only under a certain condition for the Alfvèn velocity, rotation and the stratification parameter. In the latter case, both rotation and magnetic field are found to have a stabilizing effect on the growth rate. In the presence of porous medium, it is found, for real growth rate n, that the inhomogeneous magnetic field has always a stabilizing effect on the considered system. It is found also, for complex growth rate n, that the system is stable for the stable stratification case, while it is stable or unstable for the unstable case under a certain wavenumbers range depending on the Alfvèn velocity and the stratification parameter. The presence of the magnetic field is found to stabilize a certain wavenumbers band, whereas the system was unstable for all wavenumbers in the absence of the magnetic field. Also, the presence of porous medium is found to hide the stabilizing effect played by rotation on the considered system for non-porous medium, i.e., rotation does not have any significant effect on the stability criterion in this case.     

Amplification of an acoustic wave in inhomogeneous Piezoelectric semiconductors

The theory of the amplification of an acoustic wave in an inhomogeneous piezoelectric semiconductor in the presence of a transverse magnetostatic field is developed assuming the explicit dependence of the relaxation time (τ) on the position coordinate. It is found that the implication of the sound wave is possible even if the drift velocity of the electron is smaller than the velocity of sound in the medium.     

On the stability of a cylindrical jet moving in a material medium along an external electrostatic field

A dispersion relation is derived for capillary waves with arbitrary symmetry (with arbitrary azimuthal numbers) on the surface of a jet of an ideal incompressible dielectric liquid moving in an ideal incompressible dielectric medium along an external uniform electrostatic field. A tangential discontinuity in the velocity field on the jet surface is shown to cause Kelvin-Helmholtz periodical instability at the interface and destabilize axisymmetric, flexural, and flexural-deformational waves. Both the flexural and flexural-deformational instabilities have a threshold and are observed not at an arbitrarily small velocity of the jet but starting from a certain finite value. It is shown that the instability of waves generated by the tangential discontinuity of the velocity field is periodic only formally (from the pure mathematical point of view). Actually, the jet disintegrates within the time of instability development, which is shorter than the half-cycle of the wave.     

Time reversal self-adaptive focusing in anisotropic elastic solid medium

In this paper, the time reversal method in an anisotropic elastic solid is theoretically studied for the first time. The transversely isotropic anisotropic medium (6mm crystal structure) is modeled as the anisotropic elastic solid. A unidirectional glass-reinforced epoxy-fiber is chosen as the material of the 6mm anisotropic medium. The time reversal acoustic field is numerically investigated by the ray approximation method. The focused acoustic field has different characteristics in different directions. The focused field is also symmetrical about the principal axes. It is found that the width of the principal lobe of the focused acoustic field reaches the minimum in the maximum group velocity direction and reaches the maximum in the minimum group velocity direction. The relation of the time reversal acoustic field to the parameters of the anisotropic medium is also studied in detail.     

An approach to introducing fractional integro-differentiation in classical electrodynamics

Analogs for Maxwell’s equations with fractional derivatives are obtained using the concepts of an effective current and the velocity of a charged particle in a medium. The calibration invariance is considered and a diffusion-wave equation is found and analyzed for scalar and vector potentials. It is shown that the stochastic nature of charged particle motion in a medium influences the dynamics of an electromagnetic field.     

Quantum-interference effects for gamma radiation under crossing-anticrossing conditions for nuclear levels in an RF field

A new approach to observing the effect of electromagnetically induced transparency in gamma optics is proposed. The propagation of a resonant photon in a ⁵⁷Fe magnetic medium in an applied rf field is considered for this purpose. It is shown that, under crossing-anticrossing conditions, a resonant rf field substantially changes the gamma-optical properties of the medium, which become dependent on the parameters of the field. This opens the possibility for exercising a coherent control of the photon group velocity and a controllable filtration of unpolarized gamma radiation in a sample.     

Chirality dependent component of vortex advection in excitable media

An advective field induces drift of a vortex in excitable media. The component of the drift velocity C( perpendicular ) perpendicular to the field is known to change its sign with the chirality of the vortex. In an experiment with vortices in an electric field in a chemical excitable medium, we have found unexpectedly that C( perpendicular ) changes its sign also independently of chirality with changing composition of the medium. We did not succeed to explain this phenomenon by using existing mathematical models of chemical excitable media. The experiment described calls for more realistic models.(c) 1999 American Institute of Physics.