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Register a new userThe influence of the stationary electric field upon the resonance absorption of microwaves in HeII
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The interaction between electromagnetic microwaves (40-200 GHz) and superfluid helium in a stationary electric field has been investigated experimentally. It is found that the narrow line of resonance absorption at the roton frequency is split in the electric field into two symmetric lines. The splitting magnitude increases almost linearly with the electric field, which suggests a linear Stark effect. The results obtained point of orientational polarizability and dipole moment (10^(-34)C*m) in HeII. It is shown that the spectral line profile consists of two parts - a narrow line of resonance absorption (or induced radiation when superfluid stream are generated) and a broad background. The background with agrees well with the latest neutron data for the roton line.
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Based on interrelation between the thermodynamic and electromechanical phenomena in superfluid helium, the explanation of experimentally found features of microwave interaction in the frequency range of 40-200 GHz is given. Due to fast roton-roton and roton-phonon interactions resonant excitation on frequency correspond to minimal roton energy relaxes and forms a wide pedestal. Alongside these fast processes, there are also slower processes of rotons scattering by microwave photons taking place, which lead to additional absorption of energy of resonant microwaves and to the appearance of a narrow resonant peak on the background of a wide pedestal. The theoretical explanation of the influence which streams exert on resonant absorption of microwaves is given. The critical velocity of stream at which absorption of microwaves was replaced by their radiation is found.
Paper is presented the results of computer simulation. Effect of the dc electric field influence on the propagation of Lamb and SH waves and its temperature coefficients of delay in piezoelectric langasite crystal plate for a lot of cuts and directions have been calculated. There were found the cuts possessing the thermostability and sufficient electromechanical coupling.
Anisotropy of dc electric field influence on the different types of acoustic waves in piezoelectric plate has been investigated by means of computer simulation. Detail calculations have made for bismuth germanium oxide crystals.
The effects of an external electric field on the formation of Liesegang patterns are investigated. The patterns are assumed to emerge from a phase separation process in the wake of a diffusive reaction front. The dynamics is described by a Cahn-Hilliard equation with a moving source term representing the reaction zone, and the electric field enters through its effects on the properties of the reaction zone. We employ our previous results [I. Bena, F. Coppex, M. Droz, and Z. Racz, J. Chem. Phys. {bf 122}, 024512 (2005)] on how the electric field changes both the motion of the front, as well as the amount of reaction product left behind the front, and our main conclusion is that the number of precipitation bands becomes finite in a finite electric field. The reason for the finiteness in case when the electric field drives the reagents towards the reaction zone is that the width of consecutive bands increases so that, beyond a distance $ell_+$, the precipitation is continuous (plug is formed). In case of an electric field of opposite polarity, the bands emerge in a finite interval $ell_-$, since the reaction product decreases with time and the conditions for phase separation cease to exist. We give estimates of $ell_{pm}$ in terms of measurable quantities and thus present an experimentally verifiable prediction of the Cahn-Hilliard equation with a moving source description of Liesegang phenomena.
Paper is presented the results of computer simulation. Effect of the homogeneous dc electric field influence on the propagation of zero and first order Lamb and SH waves in piezoelectric langasite single crystal plates for a lot of cuts and directions have been calculated. Crystalline directions and cuts with maximal and minimal influence of dc electric field have indicated. Effect of hybridization of plate modes has been discussed.
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