419 research outputs found
Measurement and modeling of three-dimensional sound intensity variations due to shallow-water internal waves
Author Posting. © Acoustical Society of America, 2005. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 117 (2005): 613-625, doi:10.1121/1.1828571.Broadband acoustic data (30–160 Hz) from the SWARM'95 experiment are analyzed to investigate acoustic signal variability in the presence of ocean internal waves. Temporal variations in the intensity of the received signals were observed over periods of 10 to 15 min. These fluctuations are synchronous in depth and are dependent upon the water column variability. They can be explained by significant horizontal refraction taking place when the orientation of the acoustic track is nearly parallel to the fronts of the internal waves. Analyses based on the equations of vertical modes and horizontal rays and on a parabolic equation in the horizontal plane are carried out and show interesting frequency-dependent behavior of the intensity. Good agreement is obtained between theoretical calculations and experimental data.This work was supported
by the Ocean Acoustics Program at the Office of Naval
Research (ONR Grants N00014-01-1-0114 to U.D., and
N00014-04-1-0016 to R.P.I.) and by the Russian Foundation
For Basic Research (RFBR Grant 03-05-64568-a)
Fermi liquid theory of electronic topological transitions and screening anomalies in metals
General expressions for the contributions of the Van Hove singularity (VHS)in
the electron density of states to the thermodynamic potential \Omega connected with the Lifshitz
electronic topological transition (ETT) is found. Screening anomalies due to
virtual transitions between VHS and the Fermi level are considered. It is shown
that, in contrast with the one-particle picture of ETT, the singularities in
$\Omega turns out to be two-sided for interacting electrons.Comment: 8 pages RevTeX, with minor corrections (Introduction and Conclusions
are rewritten, new references are added), to appear in Physical review
Acoustic multipath arrivals in the horizontal plane due to approaching nonlinear internal waves
Author Posting. © Acoustical Society of America, 2011. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 129 (2011): EL141-EL147, doi:10.1121/1.3553374.Simultaneous measurements of acoustic wave transmissions and a nonlinear internal wave packet approaching an along-shelf acoustic path during the Shallow Water 2006 experiment are reported. The incoming internal wave packet acts as a moving frontal layer reflecting (or refracting) sound in the horizontal plane. Received acoustic signals are filtered into acoustic normal mode arrivals. It is shown that a horizontal multipath interference is produced. This has previously been called a horizontal Lloyd’s mirror. The interference between the direct path and the refracted path depends on the mode number and frequency of the acoustic signal. A mechanism for the multipath interference is shown. Preliminary modeling results of this dynamic interaction using vertical modes and horizontal parabolic equation models are in good agreement with the observed data
Atomic Collapse and Quasi-Rydberg States in Graphene
Charge impurities in graphene can host an infinite family of Rydberg-like
resonance states of massless Dirac particles. These states, appearing for
supercritical charge, are described by Bohr-Sommerfeld quantization of
collapsing classical trajectories that descend on point charge, in analogy to
Rydberg states relation with planetary orbits. We argue that divalent and
trivalent charge impurities in graphene is an ideal system for realization of
this atomic collapse regime. Strong coupling of these states to the Dirac
continuum via Klein tunneling leads to striking resonance effects with direct
signatures in transport, local properties and enhancement of the Kondo effect.Comment: 5 pages, 4 figure
Theory of optically forbidden d-d transitions in strongly correlated crystals
A general multiband formulation of linear and non-linear optical response
functions for realistic models of correlated crystals is presented. Dipole
forbidden d-d optical transitions originate from the vertex functions, which we
consider assuming locality of irreducible four-leg vertex. The unified
formulation for second- and third-order response functions in terms of the
three-leg vertex is suitable for practical calculations in solids. We
illustrate the general approach by consideration of intraatomic spin-flip
contributions, with the energy of 2J, where J is a Hund exchange, in the
simplest two-orbital model.Comment: 9 pages, 4 figures, to appear in J. Phys. Cond. Matte
Nature of non-magnetic strongly-correlated state in delta-plutonium
Ab-initio relativistic dynamical mean-field theory is applied to resolve the
long-standing controversy between theory and experiment in the "simple"
face-centered cubic phase of plutonium called delta-Pu. In agreement with
experiment, neither static nor dynamical magnetic moments are predicted. In
addition, the quasiparticle density of states reproduces not only the peak
close to the Fermi level, which explains the large coefficient of electronic
specific heat, but also main 5f features observed in photoelectron
spectroscopy.Comment: 9 pages, 3 figure
Observation and theoretical description of the pure Fano-effect in the valence-band photo-emission of ferromagnets
The pure Fano-effect in angle-integrated valence-band photo-emission of
ferromagnets has been observed for the first time. A contribution of the
intrinsic spin polarization to the spin polarization of the photo-electrons has
been avoided by an appropriate choice of the experimental parameters. The
theoretical description of the resulting spectra reveals a complete analogy to
the Fano-effect observed before for paramagnetic transition metals. While the
theoretical photo-current and spin difference spectra are found in good
quantitative agreement with experiment in the case of Fe and Co only a
qualitative agreement could be achieved in the case of Ni by calculations on
the basis of plain local spin density approximation (LSDA). Agreement with
experimental data could be improved in this case in a very substantial way by a
treatment of correlation effects on the basis of dynamical mean field theory
(DMFT).Comment: 11 pages, 3 figures accepted by PR
Effect of Holstein phonons on the electronic properties of graphene
We obtain the self-energy of the electronic propagator due to the presence of
Holstein polarons within the first Born approximation. This leads to a
renormalization of the Fermi velocity of one percent. We further compute the
optical conductivity of the system at the Dirac point and at finite doping
within the Kubo-formula. We argue that the effects due to Holstein phonons are
negligible and that the Boltzmann approach which does not include inter-band
transition and can thus not treat optical phonons due to their high energy of
eV, remains valid.Comment: 13 pages, 4 figure
The Aharonov-Bohm effect for massless Dirac fermions and the spectral flow of Dirac type operators with classical boundary conditions
We compute, in topological terms, the spectral flow of an arbitrary family of
self-adjoint Dirac type operators with classical (local) boundary conditions on
a compact Riemannian manifold with boundary under the assumption that the
initial and terminal operators of the family are conjugate by a bundle
automorphism. This result is used to study conditions for the existence of
nonzero spectral flow of a family of self-adjoint Dirac type operators with
local boundary conditions in a two-dimensional domain with nontrivial topology.
Possible physical realizations of nonzero spectral flow are discussed.Comment: 15 pages, 6 figures. Submitted to Theoretical and Mathematical
Physics. v2: A change has been made to the paragraph describing the previous
work of M. Prokhorov
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