Magnetostatic analog of Love surface elastic waves

The possibility of the existence of a magnetostatic analog of Love surface elastic waves is predicted. They appear in situations where the conditions for the existence of magnetostatic volume waves hold in the upper layer of a ferromagnetic bilayer, but not in the lower layer. Zh. Tekh. Fiz. 68, 85–90 (October 1998)     

Scattering of spin waves by a rectilinear edge dislocation

The propagation of volume spin waves in an unbounded easy-axis magnet containing a rectilinear edge dislocation is studied theoretically. The spin-wave scattering amplitudes are calculated in the Born approximation. It is shown that the spin-wave scattering amplitude vanishes for certain values of the scattering angle. The dependence of the scattering angle on the angle of incidence of the spin waves is found for this case. The transport scattering cross section of spin waves is found. Fiz. Tverd. Tela (St. Petersburg) 40, 2056–2058 (November 1998)     

Magnetostatic volume waves in exchange-coupled ferrite films

The influence of exchange coupling of layers on the propagation of magnetostatic dipole volume waves in normally and tangentially magnetized two-layer epitaxial ferrite structures is investigated. It is shown that the indicated influence is manifested in the form of dynamic spin pinning effects on the interlayer boundary and formation of a common dipole-exchange wave spectrum for the entire structure. In this case, at the synchronism frequencies of the dipole and exchange waves the losses of the dipole waves grow and anomalous segments appear in the dispersion. In films magnetized in the “hard” direction relative to the axis of normal uniaxial surface anisotropy the magnetostatic dipole volume waves can interact resonantly with the surface spin waves supported by the boundaries with pinned spins. Zh. Tekh. Fiz. 68, 97–110 (July 1998)     

Parametric interaction of magnetostatic waves with a nonstationary local pump

A solution is obtained for the general problem of the nonstationary interaction of backward volume magnetostatic waves in films of yttrium-iron garnet with local parametric pumping. In the case of a large pump region, l≫λ, where λ is the wavelength of the backward volume magnetostatic waves, the problem reduces to a system of truncated equations for two packets of counter propagating waves. In the opposite case, l<λ, the exact problem of parametric interactions of the eigenmodes of a ferrite film (both counterpropagating and in the same direction) is solved numerically. Both cases are studied experimentally and good qualitative and quantitative agreement is obtained with the theory. For the first time, the reversal of a wave front and the time reversal of the shape of backward volume magnetostatic wave pulses are observed and a change in the propagation time for the peak of the signal pulse and a reduction in its width owing to pumping are recorded. Two operating regimes are identified for a nonstationary parametric backward volume magnetostatic wave amplifier with local pumping, which differ in the ratio of the duration of the pump pulse to the transit time for the wave through the local pump region, and the effect of the parametric excitation of two-dimensional spin waves on the interaction of backward volume magnetostatic waves with a local nonstationary parametric pump is determined. Zh. éksp. Teor. Fiz. 116, 2192–2211 (December 1999)     

Field distribution of magnetostatic waves in a tangentially magnetized ferromagnetic slab

The field distribution of magnetostatic surface and volume waves as they propagate at an arbitrary angle to a constant field in a tangentially magnetized ferromagnetic slab (Damon-Eschbach waves) is investigated. Snapshots of the magnetic field lines of the wave are constructed. The variation of the magnetic field distribution with thickness is qualitatively identified for a volume wave as it propagates at an angle equal to the cutoff angle of the surface wave, as a result of which the sinusoidal profile of the wave over thickness almost discontinuously acquires an additional phase difference. Zh. Tekh. Fiz. 69, 82–86 (January 1999)     

Surface waves of the potential type at the interface between a metal and an inhomogeneous medium

A study is made of surface waves of the potential type propagating along the interface between a metal and a plasma of nonuniform density, with the thermal motion of the electrons taken into account. Dispersion relation for these waves are derived and solved for a linear plasma density profile. The influence of the nonuniformity of the plasma density on the dispersion properties of the waves is studied. Cases of negative and positive gradients are considered. Zh. Tekh. Fiz. 69, 80–83 (July 1999)     

Scattering by 2D particles deposited on a dielectric planar waveguide: a near-field and far-field study

Abstract

Scattering of a plane wave by 2D particles (i.e. rods) placed on a dielectric planar waveguide is studied by means of a volume integral approach. The visualization of the near-field surrounding one or two rods points out the role of the guided waves in the interaction between the particles. In the far-field, a peak in the retroreflection direction, as well as secondary peaks, are observed. Different mechanisms involving multiple scattering of the guided waves are proposed.     

Surface-type waves on the boundary of a metal with a plasma-molecular medium

The influence of the molecular subsystem on the properties of surface-type waves (STW’s) propagating along a plasma-metal boundary is examined with consideration of the thermal motion of the electrons. The dynamics of the molecular subsystem is described using the equation for the polarization vector, which is equivalent to a quantum-mechanical treatment of a rarefied gas with phenomenological consideration of the dissipation. A dispersion equation for surface-type waves is obtained. The molecular subsystem influences both the phase velocity of the waves and the penetration depth. In the case of a weakly ionized medium there is a forbidden frequency band for surface-type waves. Zh. Tekh. Fiz. 67, 47–49 (December 1997)     

Investigations of the structure of porous titanium nickelide after thermal treatment

Methods of optical metallography, scanning electron microscopy, and x-ray structural and spectral microanalyses are used to investigate the structural features of porous titanium nickelide produced by the method of self-propagating high-temperature synthesis (SHS) after its thermal treatment. It is demonstrated that the clearly expressed structural-phase inhomogeneity observed in porous titanium nickelide after SHS is retained after thermal treatment. During thermal treatment with increase in the annealing temperature, the volume fraction of the Ti₂Ni phase enriched in titanium remains essentially unchanged; it is redistributed over the sample volume. The volume fraction of the TiNi₃ phase increases and nonuniformity in its density distribution over the sample volume, caused by the chemical inhomogeneity of the matrix, is observed. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 86–92, October, 2008.     

Induced modulation instability of spin waves in ferromagnetic films

Induced modulation instability of backward volume spin waves in ferromagnetic films is investigated. It is found that the nonlinearity of the spin system of a ferromagnetic sample can greatly enrich the spectrum by excitation of spin waves at close frequencies and, in consequence, result in the appearance of a sequence of soliton-like pulses. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 11, 828–832 (10 December 1998)     

Polyimides Containing Azobenzene Side Units: Properties and Correlation with Conformational Parameters

Two series of aromatic polyimides differing by the bridging group between imide rings, polymers a, b, and c, having C?O linkages and polymers d, e, and f, having C(CF₃)₂ groups, have been obtained by polycondensation reaction of aromatic dianhydrides with aromatic diamines containing substituted azobenzene groups. These polymers with good solubility in polar amidic solvents, were able to form transparent flexible films and showed high thermal stability. Conformational parameters of the polymers were calculated by the Monte Carlo method with allowance for hindered rotation. Several physical properties of these polymers, such as solubility, glass transition temperature (T_g), and initial decomposition temperature (T_onset) were measured and discussed in relation to the volume factor of the macromolecular chains. The volume factor is equal to ratio of the Van der Waals volume of the pendent group to the Van der Waals volume of the repeating unit of the main chain.     

Propagation of magnetostatic waves in unsaturated ferrite films with a strip domain structure

The propagation of surface and volume magnetostatic waves in unsaturated films of yttrium iron garnet is studied experimentally for the case when the wavelength greatly exceeds the domain width, while the domain width is comparable to the film thickness. The characteristics of these waves are examined for symmetric linear, asymmetric linear, and symmetric zigzag strip domain structures in the films. These characteristics cannot be explained by a theory based on averaging the magnetization over all the domains. Zh. éksp. Teor. Fiz. 111, 1016–1031 (March 1997)     

Parametric interaction of volume magnetostatic waves in a ferrite film with spatiotemporal modulation of the magnetic field

Effects of the resonant Bragg scattering of magnetostatic backward volume waves on the periodic structure of a conductive meander pattern with an alternating current are analyzed theoretically and compared with experiment. It is shown that unlike a static grating, a dynamic grating causes a frequency shift of the scattered wave. It is proposed that this phenomenon be utilized for effective control of the intermodal conversion of magnetostatic waves. Zh. Tekh. Fiz. 68, 105–112 (May 1998)     

Lattice Boltzmann simulation of 3-dimensional natural convection heat transfer of CuO/water nanofluids

The present study investigated fluid flow and natural convection heat transfer in an enclosure embedded with isothermal cylinder. The purpose was to simulate the three-dimensional natural convection by thermal lattice Boltzmann method based on the D3Q19 model. The effects of suspended nanoparticles on the fluid flow and heat transfer analysis have been investigated for different parameters such as particle volume fraction, particle diameters, and geometry aspect ratio. It is seen that flow behaviors and the average rate of heat transfer in terms of the Nusselt number (Nu) are effectively changed with different controlling parameters such as particle volume fraction (5 % ≤ φ ≤ 10 %), particle diameter (d _p = 10 nm to 30 nm) and aspect ratio (0.5 ≤ AR ≤ 2) with fixed Rayleigh number, Ra = 10⁵. The present results give a good approximation for choosing an effective parameter to design a thermal system.     

Using nanofluid saturated porous media to enhance free convective heat transfer around a spherical electronic device

The thermophysical properties of the nanofluid saturated porous media are used in this work to optimize the thermal design of a spherical electronic device. Quantification of free convective heat transfer has been numerically determined by means of the finite volume method using the SIMPLE algorithm. The Rayleigh number based on the component diameter and water characteristics varies between 6.5x10⁶ and 1.32x10⁹, given the power generated during operation of this active component. The latter is disposed in the center of another sphere maintained isothermal. Its cooling is achieved by means of a porous medium saturated with a water based - Copper nanofluid whose volume fraction varies between 0 (pure water) and 10%. The thermal conductivity of the porous material's matrix ranges from 0 to 40 times that of the base fluid (water). Results of this work show that convective heat transfer systematically increases with this ratio according to a function depending on the Rayleigh number in the whole range of the considered volume fraction. The average Nusselt number also increases with the Rayleigh number according to a conventional power type law while influence of the fraction volume is moderate in the 2-10% range. The results are in agreement with those of previous works for particular thermal conditions. In order to optimize the thermal design of this electronic device, a correlation is proposed, allowing determination of the Nusselt number for any combination of the three influencing parameters for applications in various engineering fields, includind electronics.     

Ion pickup by the intrinsic low-frequency Alfvén waves with a spectrum

Ion pickup by a monochromatic low-frequency Alfvén wave, which propagates along the background magnetic field, has recently been investigated in a low beta plasma (Lu and Li 2007 Phys. Plasmas 14 042303). In this paper, the monochromatic Alfvén wave is generalized to a spectrum of Alfvén waves with random phase. It finds that the process of ion pickup can be divided into two stages. First, ions are picked up in the transverse direction, and then phase difference (randomization) between ions due to their different parallel thermal motions leads to heating of the ions. The heating is dominant in the direction perpendicular to the background magnetic field. The temperatures of the ions at the asymptotic stage do not depend on individual waves in the spectrum, but are determined by the total amplitude of the waves. The effect of the initial ion bulk flow in the parallel direction on the heating is also considered in this paper.     

Effect of initial texture on texture evolution in cold-rolled AA 5182 aluminium alloy

AA 5182 aluminium alloy with a strong cube texture was cold rolled to different reductions along the following directions: firstly, the original rolling direction; secondly, at angles of 22.5 and 45° to the original rolling direction. The evolution of texture in the cold-rolled samples with different initial textures was then investigated by X-ray diffraction. The texture evolution was quantified by mathematical formulae of texture volume fractions and rolling true strain. The results show that initial texture has a strong influence on the evolution of rolling texture. AA 5182 aluminium alloy with an initial rotated-cube (r-cube) (45° normal direction r-cube) texture exhibits the fastest rate of formation of the β fibre. The rate of formation of the β fibre decreases as the initial texture changes from the r-cube texture to the cube texture. The relationship between the rate of formation of the β fibre (k _β value in the mathematical formula for the volume fraction of the β fibre) and the initial texture (M _cube and M _r-cube: the volume fractions of the cube and r-cube components respectively) can be expressed as k _β ?=?0.37???0.03(M _cube /5.41???M _r???cube /5.64).     

Moment-volume instabilities in alloys with compositions around the C14 laves phase

We measured the thermal expansion and the specific heat of Ti_xFe_100-x alloys with x = 30.5, 32.5 and 35, all with hexagonal C14 laves phase structure (MgZn₂) like TiFe₂, and determine the temperature dependence of the magnetic contributions to the thermal expansion and the specific heat c_mag. For fixed composition and c mag ( T ) show the same type of behavior, demonstrating that both anomalies are of the same microscopic nature. They originate from moment-volume fluctuations (antiferromagnetic Invar-effect) as a comparison with total energy calculations as a function of atomic volume and moment for TiFe₂ reveals. Received: 26 January 1998 / Accepted: 17 April 1998     

Preparation and heat transfer properties of nanoparticle-in-transformer oil dispersions as advanced energy-efficient coolants

Three kinds of nanofluids are prepared by dispersing Al₂O₃ and AlN nanoparticles-in-transformer oil. The thermal conductivity of the nanoparticle–oil mixtures increases with particle volume fraction and thermal conductivity of the solid particle itself. The AlN nanoparticles at a volume fraction of 0.5% can increase the thermal conductivity of the transformer oil by 8% and the overall heat transfer coefficient by 20%. From the natural convection test using a prototype transformer, the cooling effect of Al₂O₃/AlN-oil nanofluids on the heating element and oil itself is confirmed. However, the excess quantity of surfactant has a harmful effect on viscosity, thermal property, chemical stability, and thus it is strongly recommended to control the addition of the surfactant with great care.