Oscillations of a bubble separated from an air cavity under compression caused by magnetic field in a magnetic fluid

Based on the concept of mapping the free surface geometry of a weakly magnetic medium by the topography of isolines of the magnetic field strength magnitude, the shape of the free surface of a magnetic fluid is studied in the static state at two stages: the initial stage, where an annular magnet is moving toward the surface of the magnetic fluid column in a tube, and at the stage where the air cavity is pressed to the bottom. It is shown that the separation of bubbles from the air cavity occurs at the magnet axis in the immediate vicinity of the magnet symmetry plane. A method and an experimental setup are proposed to investigate possible electromagnetic indication of the size of air bubbles formed in the magnetic fluid. The results of an experimental study of bubble separation from an air cavity held in the magnetic fluid and compressed by the pondermotive forces of the magnetic field are discussed. The results may be of importance for designing a new technique for metering small gas shots to a reactor.     

Elastic properties of magnetic materials

This review discusses the theoretical aspects of magnetoelastic coupling with emphasis on the magnetic perturbation of elastic properties. The basic theory of magnetostriction is set out with application to ferromagnets, ferrimagnets and antiferromagnets, and is followed by a discussion of the physical origin of the magnetoelastic coupling coefficients in both localized and itinerant magnetic systems. Magnetic contributions to elastic compliance are then discussed and sound velocity anomalies near magnetic phase transitions investigated, including the cooperative Jahn-Teller limit for which the acoustic mode itself drives a structural transition even when magnetic ordering does not occur. The review concludes with discussion of magnetoelastic (or mixed magnon-phonon) waves in low temperature magnetically ordered phases and with a study of local striction phenomena in magnetically dilute materials. The latter leads to a recognition of internal rearrangement modes which may also be present in concentrated magnetic systems, and which may or may not couple significantly to bulk homogenous strain.     

Elastic wave diffraction by a circular cavity

Inhomogeneous waves running along concave surfaces shed homogeneous pressure and shear waves governed by continuous directional spectra. The quantification of diffraction based upon conservation of energy and momentum permits ray modelling.     

Annoyance caused by the sounds of a magnetic levitation train

In a laboratory study, the annoyance caused by the passby sounds from a magnetic levitation (maglev) train was investigated. The listeners were presented with various sound fragments. The task of the listeners was to respond after each presentation to the question: "How annoying would you find the sound in the preceding period if you were exposed to it at home on a regular basis?" The independent variables were (a) the driving speed of the maglev train (varying from 100 to 400 km/h), (b) the outdoor A-weighted sound exposure level (ASEL) of the passbys (varying from 65 to 90 dB), and (c) the simulated outdoor-to-indoor reduction in sound level (windows open or windows closed). As references to the passby sounds from the maglev train (type Transrapid 08), sounds from road traffic (passenger cars and trucks) and more conventional railway (intercity trains) were included for rating also. Four important results were obtained. Provided that the outdoor ASELs were the same, (1) the annoyance was independent of the driving speed of the maglev train, (2) the annoyance caused by the maglev train was considerably higher than that caused by the intercity train, (3) the annoyance caused by the maglev train was hardly different from that caused by road traffic, and (4) the results (1)-(3) held true both for open or closed windows. On the basis of the present results, it might be expected that the sounds are equally annoying if the ASELs of the maglev-train passbys are at least 5 dB lower than those of the intercity train passbys. Consequently, the results of the present experiment do not support application of a railway bonus to the maglev-train sounds.     

Detection of the dirac monopole with magnetic levitation

Recently it was suggested that an experiment by Mikhailov should be reproduced to confirm the existence of magnetic charge on ferromagnetic aerosols. At the present time, there is controversy about the results of Mikhailov's experiment in regard to a reanalysis by Akers. In this paper, an experiment is proposed to resolve the discrepancy between Mikhailov's earlier results and the latest value for the Dirac charge.     

The magneto-optical properties of an ensemble of ellipsoidal dielectric particles in a magnetic fluid

The paper deals with an analytical investigation of magnetic birefringence in a dilute suspension of ellipsoidal dielectric particles in a magnetic fluid. The major axes of particles tend to line up along the field because of the difference in the “demagnetizing” coefficients along and across the ellipsoid axis, which brings about a multiple increase in the optical anisotropy of the system. Formulas are derived which describe the field dependence of magnetization of the system and of the difference between the refractive indices for ordinary and extraordinary rays. It is demonstrated that, given the bulk concentration of impurity particles of several percent, the magnetization of the system varies insignificantly, while the birefringence signal may increase by two orders of magnitude.     

Crossing in the magnetic force-gap hysteresis curve of magnetic levitation systems with a high-Tc superconductor

For the magnetic levitation system consisting of a high-T_c superconductor and permanent magnet, the relation curve of magnetic force with gap between these two components is known as a hysteresis loop, that is, the approaching and departing portions envelop a complete one, and generally these two portions do not cross each other. However, in some special cases this crossing arises, and makes the complete loop broken. In this paper, by the numerical simulation of the magnetic force-gap curve in large numbers of physical and geometrical parameters, two typical crossings were found. To investigate the crossing and explore its physical causes, for one of the crossings, the current density in the superconductor was further calculated and its magnitude and vector distribution at the gaps nearby where the crossing arises were obtained. Based on these calculation results and an adequate discussion, the conclusion was induced that the crossing in the magnetic force-gap hysteresis curve results from applied magnetic field’s incomplete and insufficient penetrating in superconductor.     

Controllable emission properties of an atom inside a cavity by manipulating the atom outside the cavity

Consider a pair of two-level atoms initially in the EPR singlet state. Then we put one atom into a cavity. It is shown that the emission properties of the atom inside the cavity are much affected by the manipulation of the atom outside the cavity.     

On levitation of diamagnetic bodies in a magnetic field

Various methods for calculating the force characteristics of a suspension ensuring levitation of diamagnetic bodies of various origin and shape are considered. The method of calculation is based on the computation of the energy of interaction of a body upon its displacement from the center of suspension for an arbitrary configuration of the suspending field. The method of quasi-homogeneous approximation is considered and compared with the method for calculating the force characteristics based on the general formula for the magnetic energy. The necessary and sufficient conditions for conservative stability of the equilibrium state are formulated, and the stability domain is determined. It is shown that the stability domain depends on the size of the body. Calculations of force characteristics are performed specifically for the suspension of a diamagnetic sphere. The dependences of forces and stiffnesses on the magnetic field strength are obtained, which makes it possible to analyze the stability of confinement of the diamagnetic sphere in the field of the system of circular currents.     

Experimental study of magnetic forces on normal and null flux coil arrangements in the inductive levitation system

We report on measurements of lift and drag forces exerted by various small-scale current-carrying superconducting coils, placed near a large rotating disk. In detail we have studied the influences of shape and arrangement of the coils, as well as the influences of plate thickness, velocity and suspension height. In some experiments the drag force was measured under constant load condition. Most of the experimental results are compared with exact calculations based upon the general theory recently given by Miericke and Urankar [1] for infinitely wide but arbitrarily thick sheet tracks. The agreement between experiment and theory was generally good, and we believe that predictions for large-scale systems can be made with confidence.     

Collapse dynamics of liquid bridges investigated by time-varying magnetic levitation

Using a novel technique that facilitates temporal control over the total body force on a liquid, an unexpected scaling relationship was discovered for the collapse time of a liquid bridge. A paramagnetic liquid was suspended between the tips of two collinear rods in a strong magnetic field gradient that was adjusted to compensate gravity. A sudden change of the magnet current, corresponding to a change of Bond number, resulted in a deformation and ultimate collapse of the liquid bridge. The collapse time was found to be independent of the bridge length when other parameters were held constant.     

The energy injection into a fluid by stochastic volume forces and random stirring forces

The wavenumber spectrum of the stationary energy injection rate into an incompressible fluid described by the Navier-Stokes equations is evaluated for some simple realizations of stochastic volume as well as stirring forces. A general relation between energy injection, fluid's response, and force correlations is derived which was previously shown to be particularly simple for Gaussian distributed forces with white noise frequency spectrum. For two kinds of such model volume forces the energy injection rates are calculated: Fluid volume elements of variable size around randomly chosen positions are forced in one model centralsymmetrically in the other one anti-symmetrically under inversion with various force density profiles. The circumstances under which both models display an energy injection rate k ^–1 into a bandd k around the wavenumberk are discussed. As a simple realization of stochastic stirring forces externally moved hard spheres immersed in the fluid are considered. The equation of motion and energy balance for the velocity field of the combined system is discussed. The spectral distribution of energy injection by stirring is shown to be that of a volume force model.     

Elastic scattering of a photon by an atom with an open shell

In the nonrelativistic approximation, the absolute values and the forms of the differential cross sections of the anomalous elastic scattering of a linearly polarized x-ray photon by manganese and copper atoms in the energy region of the ionization threshold of the 1s shell are calculated for the wave functions of one-electron states. We take into account the multiparticle effects of relaxation of atomic shells in the field of core vacancies, multiplet splitting, the configuration interaction, and Auger and radiative decays of vacancies, as well as the processes of double excitation/ionization of the ground state of the atom. The calculation results are in good agreement with the synchrotron experiment.     

Elastic tension effect on magnetic properties of ferromagnetic films

The present work describes the results achieved in investigating the influence of mechanical stresses on the processes of quasi-static magnetization reversal, the dynamic characteristics and the creep of the domain walls of Fe-Ni films with Ni content from 60% to 90% and the thickness from 150 to 3000 .     

Instability of the flat surface of a magnetic fluid in a cylindrical cavity in the presence of a vertical magnetic field

The problem of a magnetic liquid which completely fills a vertical cylindrical cavity in an undeformable horizontal layer of a magnet having the same magnetic properties as the liquid is considered. The entire system is immersed in a uniform vertical magnetic field. in a linear formulation of the problem an approximate solution in the form of series is obtained for the evolution of an initial small deviation of the free surface of the liquid from its flat equilibrium shape. An experiment is performed which shows that the initially flat free surface takes on a stable domed shape as the field strength is increased (from zero) and that a further increase in the field in a certain restricted range leads to the formation of an annular corrugation. The structures observed, which are the result of the nonlinear stage in the development of the initial perturbation, are qualitatively similar to the first two modes of the solution obtained. Zh. Tekh. Fiz. 68, 23–30 (January 1998)     

Interaction of a droplet magnetic fluid with a variable magnetic field

The subject of investigation is the effective magnetic susceptibility of a droplet magnetic fluid. It is found that the rotation of such a medium causes the intriguing behavior of its magnetization due to the probing-field-induced deformation of droplet aggregates followed by their reorientation under rotation. To confirm this, the deformation of droplet aggregates subjected to a variable magnetic field is studied. In the case of the variable magnetic field, the threshold strength causing deformation is much lower than in the case of the constant field and depends on the field frequency.