Nonlinear scattering of acoustic waves by natural and artificially generated subsurface bubble layers in sea

The paper describes nonlinear effects due to a biharmonic acoustic signal scattering from air bubbles in the sea. The results of field experiments in a shallow sea are presented. Two waves radiated at frequencies 30 and 31-37 kHz generated backscattered signals at sum and difference frequencies in a bubble layer. A motorboat propeller was used to generate bubbles with different concentrations at different times, up to the return to the natural subsurface layer. Theoretical consideration is given for these effects. The experimental data are in a reasonably good agreement with theoretical predictions.     

Conductivity of disordered graphene at half filling

We study electron transport properties of a monoatomic graphite layer (graphene) with different types of disorder at half filling. We show that the transport properties of the system depend strongly on the symmetry of disorder. We find that the localization is ineffective if the randomness preserves one of the chiral symmetries of the clean Hamiltonian or does not mix valleys. We obtain the exact value of minimal conductivity 4e²/πh in the case of chiral disorder. For long-range disorder (decoupled valleys), we derive the effective field theory. In the case of smooth random potential, it is a symplectic-class sigma-model including a topological term with θ=π. As a consequence, the system is at a quantum critical point with a universal value of the conductivity of the order of e²/h. When the effective time reversal symmetry is broken, the symmetry class becomes unitary, and the conductivity acquires the value characteristic for the quantum Hall transition.     

Josephson effect in a Coulomb-blockaded SINIS junction

The problem of a Josephson current through a Coulomb-blocked nanoscale superconductor-normal-superconductor structure with tunnel contacts is reconsidered. Two different contributions to the phase-biased supercurrent I(?) are identified, which are dominant in the limits of weak and strong Coulomb interaction. Full expression for the free energy valid at arbitrary Coulomb strength is found. The current derived from this free energy interpolates between known results for weak and strong Coulomb interaction as the phase bias changes from 0 to π. In the broad range of Coulomb strength, the current-phase relation is substantially nonsinusoidal and qualitatively different from the case of semiballistic SNS junctions. The Coulomb interaction leads to the appearance of a local minimum in the current at some intermediate value of the phase difference applied to the junction.     

Internal solitons in laboratory experiments: comparison with theoretical models

Nonlinear internal solitary waves observed in laboratory experiments are discussed from the standpoint of their relation to different soliton theories, from the classical integrable models such as the Korteweg-de Vries, Gardner, Benjamin-Ono, and Joseph-Kubota-Ko-Dobbs equations and their modifications, through the nonintegrable models describing higher-order nonlinear effects, viscosity, rotation, and cylindrical spreading, to the strongly nonlinear models. First, these theoretical models are briefly described and, then, laboratory data and their comparison with the theory are presented.     

Application of three-dimensional resonant acoustic spectroscopy method to rock and building materials.

This paper presents the experimental and theoretical results of applying resonant acoustic spectroscopy (RAS) to determine elastic parameters and losses in such consolidated granular materials as rock and building bricks. First, the theoretical aspects of the RAS method are outlined. A computer code for the rectangular and cylindrical samples was developed and tested. The results of experiments on specimens of rock and ceramic brick are then described. Finally, a modification of the previously published RUS algorithm is presented which permits a significant reduction in computing time for elongated samples.     

Coherent-mode representation of partially coherent imagery

A new method for calculating image intensity distribution in partially coherent illumination is described. The method is based on the coherent-mode representation of the cross-spectral density function of illumination field and allows considerable reduction of the computational effort needed for image intensity calculation in comparison with the direct method. The computational efficiency of the method is larger the more coherent is the illumination in a global sense. An example of calculating image intensity for Schell-model illumination is compared with theoretical results.     

An ultrasonic method for measuring stresses in engineering materials

A ‘multiparameter’ method for indirect evaluation of intrinsic anisotropy values for prestressed engineering materials is discussed. The proposed method is based on simultaneous measurement of both the velocity of elastic waves and the parameters, characterizing the frequency dispersion and/or attenuation. Preliminary experimental demonstrations of the feasibility of such methods for common engineering materials are presented.     

Paraxial Approximation of Modern Radiometry for Beamlike Wave Propagation

A new approach to the construction of a system of the generalized radiometric quantities expressed in terms of the cross-spectral density function of the wave field is proposed. The key distinction of this approach lies in the fact that the initial hypothesis of beamlike wave propagation allows to invoke the paraxial approximation when deducing the generalized radiant flux. Within the framework of this approach the new expressions for the generalized radiant emittance, the generalized radiant intensity and the generalized radiance are derived. All the proposed generalized radiometric characteristics represent physically measurable quantities and, hence, may be used in practical radiometry. The results obtained in this paper can be regarded as a particular case of the modern radiometry theory in paraxial approximation for beamlike wave propagation.On leave from Kiev Polytechnic Institute, Ukraine.