1,081 research outputs found
Directional wave spectra observed during JONSWAP 1973
Estimates of the directional wave spectrum obtained from the meteorological buoy of the University of Hamburg and a pitch-and-roll buoy of the Institute of Oceanographic Sciences are reported from a series of measurements made within the framework of the Joint North Sea Wave Project during September 1973. Three main aspects were considered. First, the properties and parameterization of the directional spectrum were studied when the waves were generated by steady winds without any significant swell contribution. The results do not support the parameterization proposed by Mitsuyasu et al. (1975) and are in agreement with a parameterization in which the peak frequency is the relevant scale parameter. Second, comparisons are made between two independent methods of fitting the data exactly by means of a maximum likelihood technique (Long and Hasselmann, 1979) and a least-squares technique. The two methods give very similar fits to the observed data. Finally, the response of the directional wave spectrum to veering winds is considered and a simple model is constructed as a first attempt to describe some of the observations
Functional renormalization group in the broken symmetry phase: momentum dependence and two-parameter scaling of the self-energy
We include spontaneous symmetry breaking into the functional renormalization
group (RG) equations for the irreducible vertices of Ginzburg-Landau theories
by augmenting these equations by a flow equation for the order parameter, which
is determined from the requirement that at each RG step the vertex with one
external leg vanishes identically. Using this strategy, we propose a simple
truncation of the coupled RG flow equations for the vertices in the broken
symmetry phase of the Ising universality class in D dimensions. Our truncation
yields the full momentum dependence of the self-energy Sigma (k) and
interpolates between lowest order perturbation theory at large momenta k and
the critical scaling regime for small k. Close to the critical point, our
method yields the self-energy in the scaling form Sigma (k) = k_c^2 sigma^{-}
(k | xi, k / k_c), where xi is the order parameter correlation length, k_c is
the Ginzburg scale, and sigma^{-} (x, y) is a dimensionless two-parameter
scaling function for the broken symmetry phase which we explicitly calculate
within our truncation.Comment: 9 pages, 4 figures, puplished versio
Topological Defects and the Spin Glass Phase of Cuprates
We propose that the spin glass phase of cuprates is due to the proliferation
of topological defects of a spiral distortion of the antiferromagnet order. Our
theory explains straightforwardly the simultaneous existence of short range
incommensurate magnetic correlations and complete a-b symmetry breaking in this
phase. We show via a renormalization group calculation that the collinear
O(3)/O(2) symmetry is unstable towards the formation of local non-collinear
correlations. A critical disorder strength is identified beyond which
topological defects proliferate already at zero temperature.Comment: 7 pages, 2 figures. Final version with some changes and one replaced
figur
Differential approximation for Kelvin-wave turbulence
I present a nonlinear differential equation model (DAM) for the spectrum of
Kelvin waves on a thin vortex filament. This model preserves the original
scaling of the six-wave kinetic equation, its direct and inverse cascade
solutions, as well as the thermodynamic equilibrium spectra. Further, I extend
DAM to include the effect of sound radiation by Kelvin waves. I show that,
because of the phonon radiation, the turbulence spectrum ends at a maximum
frequency where
is the total energy injection rate, is the speed of sound and
is the quantum of circulation.Comment: Prepared of publication in JETP Letter
Dynamics of lattice pinned charge stripes
We study the transversal dynamics of a charged stripe (quantum string) and
show that zero temperature quantum fluctuations are able to depin it from the
lattice. If the hopping amplitude t is much smaller than the string tension J,
the string is pinned by the underlying lattice. At t>>J, the string is depinned
and allowed to move freely, if we neglect the effect of impurities. By mapping
the system onto a 1D array of Josephson junctions, we show that the quantum
depinning occurs at t/J = 2 / pi^2. Besides, we exploit the relation of the
stripe Hamiltonian to the sine-Gordon theory and calculate the infrared
excitation spectrum of the quantum string for arbitrary t/J values.Comment: 4 pages, 2 figure
No evidence of skin infection with Chlamydia pneumoniae in patients with cutaneous T cell lymphoma
Recently, Chlamydia pneumoniae-specific DNA and antigens were reported in the skin of patients with Mycosis fungoides (MF), the most common form of cutaneous T-cell lymphomas. In order to revalidate these data we analyzed skin sections of patients with MF for the expression of three different chlamydial antigens and C. pneumoniae DNA by immunohistochemistry and PCR according to previously described protocolls. Neither C. pneumoniae-specific DNA sequences nor antigens were detected in any of the skin biopses from 24 MF patients tested, suggesting that further studies are needed to establish any pathogenetic relevance of C. pneumoniae in MF
Energy spectra of the ocean's internal wave field: theory and observations
The high-frequency limit of the Garrett and Munk spectrum of internal waves
in the ocean and the observed deviations from it are shown to form a pattern
consistent with the predictions of wave turbulence theory. In particular, the
high frequency limit of the Garrett and Munk spectrum constitutes an {\it
exact} steady state solution of the corresponding kinetic equation.Comment: 4 pages, one color figur
- …