172 research outputs found
Action functionals for strings in four dimensions
All possible action functionals on the space of surfaces in that
depend only on first and second derivatives of the functions, entering the
equation of the surface, and satisfy the condition of invariance with respect
to rigid motions are described.Comment: 9 pages, LaTeX, 7 figure
Low-temperature acoustic characteristics of the amorphous alloy Zr41.2Ti13.8Cu12.5Ni10Be22.5
The temperature dependences of the sound velocity v and attenuation alpha of high-frequency (50–160 MHz) sound in the bulk amorphous alloy Zr41.2Ti13.8Cu12.5Ni10Be22.5 are studied at helium temperatures in the normal and superconducting states. The alloy is characterized by a relatively small constant C determining the intensity of interaction between an elastic wave and two-level systems. The density of states of the latter systems is estimated. The peculiarities in the variation of v during the superconducting transition point to the possibility of a gapless superconductivity in a narrow temperature interval near Tc
Dielectric Response and a Phenomenon of a Narrow Band Absorption for a Classical Rotor in a Double Well Potential
The theory of dielectric relaxation in a planar ensemble of polar molecules is presented for a model where dipoles rotate in an intermolecular conservative double well potential, having a profile U = U_0*sin^2(θ). The evolution of the wide band dielectric spectra is demonstrated when the potential depth U_0 is varied; an isotropic and anisotropic medium being taken as examples. The spectra comprise the Debye relaxation and the quasi-resonant Poley absorption region. The rigorous theory is compared with a simplified one which was called the hybrid quasi-elastic bond / extended diffusion model. This approximation is valid for a qualitative description and also for the quantitative one at the large field parameter p = (U_0/((k_B)T))^(1/2). For P >> 1 the spectrum comprises one narrow absorption band and one Debye relaxation region considerably shifted to low frequencies. It is show that in the long lifetime limit τ there exists a minimum absorption band Δν_0(p). The quantity Δν_0 becomes small if the parameter p >> 1.The dielectric relaxation in ice 1 is discussed with regards to this phenomenon
Surface pinning in amorphous ZrTiCuNiBe alloy
We have measured the amplitude and the phase of an electromagnetic (EM) field
radiated from superconductor (amorphous ZrTiCuNiBe alloy) in the mixed state
due to interaction of the flux lattice with an elastic wave. The results
undoubtedly point to an essential contribution of a surface pinning into the
flux lattice dynamics. We propose a model that describes radiation of EM field
from superconductors with non-uniform pinning. The model allows to reconstruct
the viscosity and the Labush parameters from the experimental data. The
behavior of the Labush parameter can be qualitatively explained in terms of the
collective pinning theory with the allowance of thermal fluctuations.Comment: 4 pages, 4 figure
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