Use of a Sagnac interferometer for measurements of linear nonreciprocal birefringence in a transverse magnetic field

A method of measuring phase nonreciprocity in materials using a Sagnac interferometer is proposed and implemented in which the working point is shifted into the region of maximum slope of the interference pattern by means of an absorbing exit mirror. The principal advantage of this method over the laser technique is that there are no stringent constraints on the losses in the materials. This method was used for the first time at 0.83 _μm to measure the nonreciprocal linear birefringence in a LiIO₃ crystal in a transverse magnetic field. Pis’ma Zh. Tekh. Fiz. 23, 30–34 (October 12, 1997)     

Precision of determination of the coordinates of an underwater cable from the results of measurements of its magnetic field

The precision of the coordinates of an underwater cable that are determined from the measurements of the strength of the magnetic field created by the cable is estimated. The maximum total or minimum difference signal of the horizontal component of the field with the use of two sensors as well as the minimum vertical component of the magnetic field with the use of a single sensor are recorded.     

Effect of magnetic field on natural convection in a vertical cylindrical annulus

Natural convection of a low Prandtl number electrically conducting fluid (Pr = 0.054) under the influence of either axial or radial magnetic field in a vertical cylindrical annulus has been numerically studied. The inner and outer cylinders are maintained at uniform temperatures and the horizontal top and bottom walls are thermally insulated. A finite difference scheme consisting of alternating direction implicit (ADI) method and successive line over relaxation (SLOR) method is used to solve the vorticity stream function formulation of the problem. Detailed numerical results of heat transfer rate, temperature and velocity fields have been presented for 1  λ  10, 0.5  A  2, 10³  Ra  10⁶ and 0  Ha_r, Ha_x  10². The computational results reveal that in shallow cavities the flow and heat transfer are suppressed more effectively by an axial magnetic field, whereas in tall cavities a radial magnetic field is more effective. It is also found that the flow oscillations can be suppressed effectively by imposing an external magnetic field. The average Nusselt number increases with radii ratio but decreases with the Hartmann number. Further, the present numerical results are shown to be in good agreement with the available benchmark solutions under the limiting conditions.     

Effect of a non-constant magnetic field on natural convection in a horizontal porous layer heated from the bottom

An analytical and numerical investigation is conducted to study the effect of an electromagnetic field on natural convection in a horizontal shallow porous cavity filled with an electrically conducting fluid. The magnetic field is assumed to be induced by two long wires, carrying current, parallel to the horizontal boundaries of the system. A uniform heat flux is applied to the horizontal walls of the layer while the vertical walls are adiabatic. The governing parameters of the problem under study are the thermal Rayleigh number, Ra, Hartmann number, Ha, position of the electrical wires, d, current intensity ratio, r, and aspect ratio of cavity, A. An analytical solution, valid for a shallow layer (A ? 1), is derived on the basis of the parallel flow approximation. The critical Rayleigh number, Ra _c , for the onset of motion is derived in closed form in terms of the parameters of the problem. For finite-amplitude convection the heat and flow characteristics predicted by the analytical model are found to agree well with a numerical study of the full governing equations.     

Effects of nonuniform temperature gradients on the onset of oscillatory Marangoni convection in a magnetic field

Summary.  This article theoretically studies the onset of oscillatory Marangoni convection in a horizontal layer of an electrically conducting fluid, to which a nonuniform thermal gradient and a uniform magnetic field are applied. The top surface of a fluid layer is deformably free and the bottom is rigid. By means of the linear stability theory and a normal mode analysis, the eigenvalue equations of the perturbed state are solved by using the fourth-order Runge-Kutta-Gill's method with the shooting technique. The computational results are compared with those known from the literature, and the agreement is found out to be generally good. The results indicate that the critical Marangoni number −Ma _c increases with increasing the Chandrasekhar number Q, the Prandtl number Pr, or the Biot number Bi of the upper free surface, but decreases with increasing the Crispation number Cr. As compared with the linear temperature profile, the inverted parabolic temperature profile shows higher −Ma _c values, while the parabolic temperature profile shows lower −Ma _c values. In addition, for the piecewise linear temperature profiles, the influences of thermal depth on the critical Marangoni number are also obtained. Received June 20, 2002; revised September 27, 2002 Published online: March 20, 2003     

Effect of a pulsed magnetic field on the luminescence of silver chloride single crystals

The phenomenon of a long-term (tens of hours) increase in the intensity of photoluminescence of silver chloride single crystals upon a short-term (tens of seconds) action of a weak (～4 kOe) pulsed magnetic field has been observed for the first time. The observed effect is probably related to the disappearance of vacancy defect complexes present in the initial crystal, which exhibit decomposition via the magnon mechanism under the action of an applied pulsed magnetic field.     

Influence of a magnetic field on natural convection in a shallow porous enclosure saturated with a binary fluid

Summary An analytical and numerical investigation is conducted to study the effect of an electromagnetic field on natural convection in a horizontal shallow porous cavity filled with an electrically conducting binary mixture. A uniform heat flux is applied to the horizontal walls of the layer while the vertical walls are adiabatic. The solutal buoyancy forces are assumed to be induced either by the imposition of constant fluxes of mass on the horizontal boundaries (double diffusive convection) or by temperature gradients (Soret induced convection). Governing parameters of the problem under study are the thermal Rayleigh number, R _T , Hartmann number, Ha, Lewis number, Le, buoyancy ratio, ϕ, aspect ratio, A, and normalized porosity of the porous medium, ɛ. An analytical solution, valid for a shallow layer (A ≫ 1) is derived on the basis of the parallel flow approximation. In the range of the governing parameters considered in this study, a good agreement is found between the analytical predictions and the numerical results obtained by solving the full governing equations.     

Inverse scattering from phaseless measurements of the total field on a closed curve

A new approach for quantitative electromagnetic imaging of scatterers located in free space from phaseless data is proposed and discussed. The procedure splits the problem into two steps. In the first one, we solve a phase-retrieval problem for the total field, thus estimating the amplitude and phase of the scattered field. Careful analysis of properties and possible representations of both scattered and incident fields allow us to introduce a criterion for an optimal choice of the measurement setup and a successful retrieval. Then the complex permittivity profile is reconstructed in the second step by use of the estimated scattered field. Numerical examples are provided to check the whole chain in the presence of noise-corrupted data.     

Effect of level broadening on the photoelectric emission from a single quantum well in ultrathin film under the influence of a quantizing magnetic field

The photoelectric emission from a quasi-two-dimensional electron gas (Q2DEG) in a single quantum well (SQW) formed in wide-gap semiconductor films has been theoretically investigated, under magnetic quantization incorporating Landau level broadening arising due to electron impurity scattering. The photoelectric current density has been computed for a Q2DEG formed in n-type GaAs film and is found to be modified in the presence of level broadening. The photoemission from a quasi-zero-dimensional electron gas (QODEG) formed in the ultrathin film under the influence of a quantizing magnetic field applied normal to the film has also been compared with that for the QODEG formed in a quantum box.     

Faraday isolator based on a TSAG single crystal with compensation of thermally induced depolarization inside magnetic field

A Faraday isolator based on a terbium scandium aluminum garnet (TSAG) single crystal with compensation of thermally induced depolarization inside magnetic field was demonstrated. An isolation ratio of 32 dB at 350 W cw laser radiation power was achieved. Thermally induced depolarization and thermal lens were studied and compared with similar thermal effects arising in the widely used terbium gallium garnet crystal (TGG) for the first time.     

Theory of the excitonic fluctuation in a strong magnetic field. I. Development of the physical picture and a self-consistent Hartree theory

The physical picture of the appearance of the excitonic correlation in a strong magnetic field is developed in an electron-hole system which consists of one conduction band and one valence band. The field is assumed to be sufficiently strong that all the electrons and holes occupy their lowest Landau levels. Kinematical and dynamical aspects of such a truncated system are discussed in detail. The discussion does not deny the possibility of the excitonic phase transition in a strong magnetic field. The essence of the present physics is in the high degeneracy of the single-particle state and the strong shrinking of the electron wave function due to the magnetic field. In order to study the physics explicitly we construct a self-consistent Hartree theory. Further introducing static and local approximations for the excitonic fluctuation. We can determine the quasiparticle state and the fluctuation exactly near the transition point. We present the transition temperature in two limiting cases of the band configuration. We indicate the self-consistent Hartree theory combined with the static and local approximations is an unsatisfactory theory in the light of our physical picture. We also discuss possible improvements of the theory briefly.     

Electrons on a dielectric liquid-vapor interface. Stability in presence of normal magnetic field

The capillary wavelength instability of a charged liquid surface due to coupling between surface deformation and charge compression may be modified by altering the transport properties of the charges along the surface. For gas-like electrons, a normal magnetic field lessens the charge density softening of the capillary mode and renders the damped transverse mode unstable at exactly the same charge conditions at which the capillary mode goes unstable in zero field. For solid-like electrons exhibiting shear elasticity, on the other hand, the magnetic field has little effect on the softening of the surface deformation modes. Systems to which these considerations are applicable are electrons on and under a liquid helium surface, and ions at the demixtion interface of ³He-⁴He mixtures.     

Effect of magnetic properties of a composite superconductor on losses in variable magnetic field. Part 2: Experiment

The theory developed in Part 1 of this paper is compared with the results of experimental measurements of losses in multi-filamentary superconductors in a transverse field. The losses have been measured for different magnetic field variation patterns (sinusoidal, triangular, trapezoidal, single pulses). The numerical results obtained with the aid of the theory are in fairly good agreement with the experimental data. In the majority of the actual cases, analytical expressions for losses can be used.     

磁流体薄片中聚焦激光束对交流磁场的相位独立响应

报导了磁流体薄片中聚焦激光束在探测50Hz交流磁场时产生与磁场相位无关响应的效应。聚焦于并通过磁流体薄片的633nm激光束的偏转角仅与交流磁场的幅度相关。为了探寻其机理，还研究了磁流体中聚焦激光束对开／关磁场或激光的瞬态响应。提出了基于磁熵守恒的磁流体中磁性粒子密度再分布正反馈模型来解释这一效应。这一模型也可以预 磁流体中一种磁－热失稳现象。     

Magnetoelastic modeling of circular cylindrical shells immersed in a magnetic field. Part I: Magnetoelastic loads considering finite dimensional effects

Determination of magnetoelastic loads acting on a perfectly electro-conductive circular cylindrical shell immersed in a uniform applied magnetic field is addressed. The finite dimensional effects related to the finite length and finite thickness of the shell are taken into consideration. Fourier integral method is used to derive the singular integral equations governing the distributed magnetoelastic loads. As special cases, determination of magnetoelastic loads via discarding the thickness effect are obtained from the general formulation, and the magnetoelastic loads of infinitely long shells are derived. Magnetoelastic loads on plate strips or infinite plates are also reduced from the general formulation. To the best of the authors’ knowledge, this represents the first work devoted to the analytical determination of magnetoelastic loads on circular cylindrical shells considering the finite length and thickness effects.     

Description of the process of magnetization of hollow cylindrical rods from soft magnetic materials in a homogeneous quasi-static magnetic field of a solenoid. Hysteresis loop

On the basis of the arctangential approximation of the magnetic hysteresis loop of the material and the expression for the central demagnetization coefficient of hollow cylindrical rods from soft magnetic materials, a method for calculating the hysteresis loops of these rods in a homogeneous quasi-static field of a solenoid is proposed. Calculation and comparison to experimental data of the basic parameters of the magnetic loops hysteresis of hollow cylindrical rods with a different value of the demagnetization coefficient have been made. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 80, No. 6, pp. 181–188, November–December, 2007.     

The anisotropic effect of a weak magnetic field on the photoconductivity of C<Subscript>60</Subscript> single crystals

The effect of crystal orientation on the photogeneration of free charge carriers was studied for C₆₀ single crystals in a weak magnetic field. The photoconductivity sharply depends on the orientation of magnetic field with respect to the crystallographic directions, showing a 5–8% increase for seven axes of the C₆₀ crystal.