Bilateral bounds for the shear and torsion factors: comments on elementary derivations

This paper proposes a new simple derivation of bilateral bounds for the strain energy–based shear and torsion factors, χ _i , of an elastic beam together with some comments about the coherence of the current formulations. A rearrangement of the definition as a mean over the cross-section and an original decomposition of the shear stress in two parts—τ _eqv that is equivalent to the external force and a residual Δτ—allow (i) to interpret (χ − 1) as the mean quadratic deviation of the shear field with respect to the distribution τ _eqv and (ii) to easily evaluate an upper bound, using minimal information about the stress field. In this formulation, the lower bound becomes trivial. Several numerical examples illustrate the accuracy and suitability of the results obtained.     

Acceleration of Brownian particle diffusion parallel to a fast random field with a short spatial period

It is shown that a spatially periodic random field fluctuating rapidly near zero with a fairly small spatial period may substantially accelerate the diffusion of Brownian particles parallel to this field. Pis’ma Zh. Tekh. Fiz. 24, 9–15 (November 12, 1998)     

Induced of zeeman coherence in an ensemble of cesium atoms interacting with a two-frequency (microwave+rf) magnetic field

Interference between Zeeman states corresponding to the forbidden magnetic-dipole transition ΔF=0, Δm _F=2 is reported in connection with the simultaneous interaction of 6² S _1/2 cesium atoms with a resonant microwave field and an rf field which varies at twice the Larmor frequency and is directed perpendicular to a static magnetic field H ₀=0.2 Oe. Pis’ma Zh. Tekh. Fiz. 24, 89–93 (July 26, 1998)     

Magnetic hysteresis and dissipative losses in superconducting films

An analysis is made of the response of thin-film superconductors to an oscillating magnetic field. The field strengths for defreezing and expulsion of the flux are determined. A hysteresis curve is plotted for the sample over the entire oscillation cycle of the magnetic field. The dissipative loss power is determined as a function of the amplitude of the alternating field. Pis’ma Zh. Tekh. Fiz. 23, 27–33 (June 12, 1997)     

Spin-orbit interaction in the field of an optical vortex of a few-mode fiber

A quantum-mechanical analog of the spin-orbit interaction operator is constructed for the fields of optical CV vortices and TE and TM modes in an optical fiber. It is shown that the polarization correction δβ to the propagation constant, which is the mean value of this operator, is a measure of the “level splitting” of the propagation constant in the scalar case. The difference in the operation of the individual parts of the operator on the fields of CV vortices and on the fields of TM and TE modes is indicative of the presence of two different physical processes — circular and linear birefringence in the locally isotropic optical fiber. The conversion of the “scalar” field to a vector field e ₁ as a consequence of the spin-orbit interaction operator can be regarded as resulting from a re-radiation of the additional field e ₁ by the vortex field , which rotates around the optical axis of the fiber. In this picture the additional field e ₁ can be regarded as being a “relativistic” correction to the vortex field for the distortions of the main field and arising as a result of the rotation of the field of the optical vortex in the medium of the few-mode fiber. Zh. Tekh. Fiz. 24, 87–93 (October 26, 1998)     

Magnetoplasmon modes in the response of a mesoscopic particle of a semimetal or a nonmagnetic insulator

The macroscopic features of the behavior of a mesoscopic particle in a magnetic field are investigated for mesoscopic particles possessing the properties of a semimetal or a nonmagnetic insulator. It is shown that for a fixed value of the magnetic field the frequency of the Alfve’n magnetoplasma mode falls off monotonically (as 1/R) as the radius of the particle increases. Pis’ma Zh. Tekh. Fiz. 23, 16–21 (December 12, 1997)     

Stress field at the boundary of a wedge-shaped twin

A model is proposed to calculate the stress field at the boundary of a wedge-shaped twin which can allow for its degree of coherence. It is shown that the stress field decreases exponentially with increasing distance from the twinning boundary. Pis’ma Zh. Tekh. Fiz. 23, 1–6 (November 26, 1997)     

Interaction between relativistic charged particles and an extended strong rf field

An investigation is made of the interaction between relativistic charged particles and a high-intensity microwave electric field over long interaction lengths. The microwave field has no magnetic component over the entire interaction length. It is shown that the interaction of the relativistic particles has features which depend on the relation between the incoming particle energy and the field strength. In particular, part of a monoenergetic particle beam may be accelerated by the beam’s own energy with some of the energy being transferred from the beam to the field. Pis’ma Zh. Tekh. Fiz. 24, 80–86 (May 26, 1998)     

Anisotropy of 63Ni diffusion in single-crystal silicon iron in a static magnetic field

An investigation is made of the influence of a static magnetic field on the diffusion of ⁶³Ni in single-crystal silicon iron. It is established that the diffusion coefficient depends on the annealing temperature, the external magnetic field strength, the direction of the Ni concentration gradient, and the crystallographic orientation of the sample, but does not depend on the direction of the field. Pis’ma Zh. Tekh. Fiz. 23, 33–38 (March 12, 1997)     

Undamped self-oscillations in a compensated semiconductor under conditions of impurity breakdown in the presence of a magnetic field

Conditions for the generation of undamped self-oscillations in a compensated semiconductor in the presence of a magnetic field are studied. Pis’ma Zh. Tekh. Fiz. 23, 62–66 (August 26, 1997)     

Mechanism of field-enhanced self-sustaining secondary electron emission in porous dielectrics

A model is proposed for field-enhanced self-sustaining electron emission in secondary-emission porous dielectrics. It is shown that the mechanism for the formation of primary electrons at the metal-porous dielectric interface is field emission from the metal, and the electric field of the required intensity for field emission is formed by redistribution of the field in the layer as a result of the avalanche formation of secondary electrons. Pis’ma Zh. Tekh. Fiz. 24, 13–18 (October 12, 1998)     

Use of magnetic field screening by high-temperature superconducting films to switch microwave signals

The efficiency with which YBCO films screen an alternating magnetic field near the superconducting transition was measured. In the decimeter range measurements were made of the characteristics of a switch whose operating principle was based on the change in the screening of an alternating magnetic field by a superconducting transition. Pis’ma Zh. Tekh. Fiz. 24, 76–81 (July 12, 1998)     

Experimental study of the temperature stability of magnetic field sensors based on Bi12SiO20 crystals

The temperature characteristics of the conversion coefficient of the sensitive element on a fiber-optic magnetic field probe based on a Bi₁₂SiO₂₀ crystal are studied experimentally. A laboratory model of the sensitive element of a magnetic field sensor is built, and the temperature drift of the conversion coefficient is found to be ∼0.15% over the temperature interval from +15 to +70 °C. Pis’ma Zh. Tekh. Fiz. 24, 26–33 (June 12, 1998)     

Photorefractive surface waves in sillenite crystals in an alternating-sign electric field

A theoretical model is proposed for photorefractive TE surface waves in a sillenite crystal located in an alternating-sign electric field Pis’ma Zh. Tekh. Fiz. 23, 48–53 (March 26, 1997)     

Formation of a honeycomb domain structure in magnetic films

An analysis is made of the possible formation of a honeycomb domain structure directly from a labyrinth structure in uniaxial magnetic films exposed to a series of uniform magnetic field pulses. It is shown that the scenario for the formation of a honeycomb structure depends on the pulse parameters and on the magnitude of the static magnetizing magnetic field. Pis’ma Zh. Tekh. Fiz. 23, 46–51 (May 12, 1997)     

An <Emphasis Type="Italic">hp</Emphasis>-adaptive finite element/boundary element coupling method for electromagnetic problems

We present an hp-version of the finite element / boundary element coupling method to solve the eddy current problem for the time-harmonic Maxwell’s equations. We use H(curl, Ω -conforming vector-valued polynomials to approximate the electric field in the conductor Ω and surface curls of continuous piecewise polynomials on the boundary Γ of Ω to approximate the twisted tangential trace of the magnetic field on Γ. We present both a priori and a posteriori error estimates together with a three-fold hp-adaptive algorithm to compute the fem/bem coupling solution with appropriate distributions of polynomial degrees on suitably refined meshes.     

Two-feedback-loop oscillator with chaotic dynamics

This paper contains new results relating to an intensively developing field — the study of dynamic chaos. It is shown that the introduction of auxiliary wide-band feedback in an autostochastic oscillator with delay transforms chaotic oscillations into quasimonochromatic oscillations. Pis’ma Zh. Tekh. Fiz. 23, 75–79 (January 26, 1997)     

Polarization Effect in ESR of Co Doped CuGeO<Subscript>3</Subscript>

Electron spin resonance of a single crystal of CuGeO₃ doped with 2% of Co has been studied at f = 99 GHz in temperature range 1.8–50 K. Contributions to ESR absorption from Cu²⁺ chains and from Co²⁺ ions were derived. It is found that functions obtained for ESR integrated intensities: Curie-Weiss for Cu²⁺ (χCu ∼ C _Cu/(T + Θ), with Θ = 92 K) and Curie for Co²⁺ (χCo ∼ C _Co/T) are well consistent with temperature dependence of static magnetic susceptibility. Strong dependence of ESR absorption on polarization of oscillating magnetic field was discovered for Co²⁺ contribution. Polarization effect was studied for magnetic field applied along a, b and c directions. Values of g-factors of resonance lines are presented.     

The Oktupol’ galathea electric-discharge confinement system

A new electric-discharge plasma confinement system based on an octupole magnetic field is described. The results of experiments with a confinement system using argon are reported. Pis’ma Zh. Tekh. Fiz. 25, 57–61 (September 12, 1999)