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567 results on '"Godin, Oleg A."'

299. Retrieval of Green’s functions of elastic waves from thermal fluctuations of fluid-solid systems.

Author

Godin, Oleg A.

Subjects
*ELASTIC waves, *ENERGY dissipation, *PHONONS, *THERMODYNAMIC equilibrium, *RADIO transmitter-receivers, *FLUCTUATIONS (Physics)
Abstract

Fluctuation-dissipation and flow reversal theorems are used to study long-range correlation of thermal phonons in a stationary heterogeneous mechanical system comprised of arbitrary inhomogeneous fluid flow and anisotropic solid. At thermal equilibrium, with an appropriate choice of physical observables to characterize thermal fluctuations within the fluid and within the solid, the general integral expression for the two-point correlation function of the fluctuations reduces to a linear combination of deterministic Green’s functions, which describe wave propagation in opposite directions between the two points. It is demonstrated that the cross-correlation of thermal noise contains as much information about the environment as can be obtained in active reciprocal transmission experiments with transceivers placed at the two points. These findings suggest a possible application of ambient noise cross-correlation to passive acoustic characterization of inhomogeneous flows in fluid-solid systems in laboratory and geophysical settings. [ABSTRACT FROM AUTHOR]

Published
2009
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300. Sound transmission through water-air interfaces: new insights into an old problem.

Author

Godin, Oleg A.

Subjects
*SOUND, *WAVELENGTHS, *AIR, *UNDERWATER acoustics, *COMPRESSIBILITY
Abstract

A water-air interface is usually an almost perfect reflector of acoustic waves. It was found recently that the interface becomes anomalously transparent and the power flux in the wave transmitted into air increases dramatically when a compact underwater sound source approaches the interface within a fraction of wavelength. The phenomenon is robust with respect to the roughness of the interface and to the variation of air and water parameters and may have significant geophysical and biological implications. This review article discusses the properties of the interface and the physical mechanisms leading to the anomalous transparency. [ABSTRACT FROM AUTHOR]

Published
2008
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