259 research outputs found
Intermittency in the large N-limit of a spherical shell model for turbulence
A spherical shell model for turbulence, obtained by coupling replicas of
the Gledzer, Okhitani and Yamada shell model, is considered. Conservation of
energy and of an helicity-like invariant is imposed in the inviscid limit. In
the limit this model is analytically soluble and is remarkably
similar to the random coupling model version of shell dynamics. We have studied
numerically the convergence of the scaling exponents toward the value predicted
by Kolmogorov theory (K41). We have found that the rate of convergence to the
K41 solution is linear in 1/N. The restoring of Kolmogorov law has been related
to the behaviour of the probability distribution functions of the instantaneous
scaling exponent.Comment: 10 pages, Latex, 3 Postscript figures, to be published on Europhys.
Let
Growing smooth interfaces with inhomogeneous, moving external fields: dynamical transitions, devil's staircases and self-assembled ripples
We study the steady state structure and dynamics of an interface in a pure
Ising system on a square lattice placed in an inhomogeneous external field. The
field has a profile with a fixed shape designed to stabilize a flat interface,
and is translated with velocity v_e. For small v_e, the interface is stuck to
the profile, is macroscopically smooth, and is rippled with a periodicity in
general incommensurate with the lattice parameter. For arbitrary orientations
of the profile, the local slope of the interface locks in to one of infinitely
many rational values (devil's staircase) which most closely approximates the
profile. These ``lock-in'' structures and ripples dissappear as v_e increases.
For still larger v_e the profile detaches from the interface which is now
characterized by standard Kardar-Parisi-Zhang (KPZ) exponents.Comment: 4 pages, 4 figures, published version, minor change
Points, Walls and Loops in Resonant Oscillatory Media
In an experiment of oscillatory media, domains and walls are formed under the
parametric resonance with a frequency double the natural one. In this bi-stable
system, %phase jumps by crossing walls. a nonequilibrium transition from
Ising wall to Bloch wall consistent with prediction is confirmed
experimentally. The Bloch wall moves in the direction determined by its
chirality with a constant speed. As a new type of moving structure in
two-dimension, a traveling loop consisting of two walls and Neel points is
observed.Comment: 9 pages (revtex format) and 6 figures (PostScript
Turbulence and Multiscaling in the Randomly Forced Navier Stokes Equation
We present an extensive pseudospectral study of the randomly forced
Navier-Stokes equation (RFNSE) stirred by a stochastic force with zero mean and
a variance , where is the wavevector and the dimension . We present the first evidence for multiscaling of velocity structure
functions in this model for . We extract the multiscaling exponent
ratios by using extended self similarity (ESS), examine their
dependence on , and show that, if , they are in agreement with those
obtained for the deterministically forced Navier-Stokes equation (NSE). We
also show that well-defined vortex filaments, which appear clearly in studies
of the NSE, are absent in the RFNSE.Comment: 4 pages (revtex), 6 figures (postscript
Photonic superdiffusive motion in resonance line radiation trapping - partial frequency redistribution effects
The relation between the jump length probability distribution function and
the spectral line profile in resonance atomic radiation trapping is considered
for Partial Frequency Redistribution (PFR) between absorbed and reemitted
radiation. The single line Opacity Distribution Function [M.N. Berberan-Santos
et.al. J.Chem.Phys. 125, 174308 (2006)] is generalized for PFR and used to
discuss several possible redistribution mechanisms (pure Doppler broadening,
combined natural and Doppler broadening and combined Doppler, natural and
collisional broadening). It is shown that there are two coexisting scales with
a different behavior: the small scale is controlled by the intricate PFR
details while the large scale is essentially given by the atom rest frame
redistribution asymptotic. The pure Doppler and combined natural, Doppler and
collisional broadening are characterized by both small and large scale
superdiffusive Levy flight behaviors while the combined natural and Doppler
case has an anomalous small scale behavior but a diffusive large scale
asymptotic. The common practice of assuming complete redistribution in core
radiation and frequency coherence in the wings of the spectral distribution is
incompatible with the breakdown of superdiffusion in combined natural and
Doppler broadening conditions
Mid-Air Haptic Interfaces for Interactive Digital Signage and Kiosks
European Union’s Horizon 202
Field Theory And Second Renormalization Group For Multifractals In Percolation
The field-theory for multifractals in percolation is reformulated in such a
way that multifractal exponents clearly appear as eigenvalues of a second
renormalization group. The first renormalization group describes geometrical
properties of percolation clusters, while the second-one describes electrical
properties, including noise cumulants. In this context, multifractal exponents
are associated with symmetry-breaking fields in replica space. This provides an
explanation for their observability. It is suggested that multifractal
exponents are ''dominant'' instead of ''relevant'' since there exists an
arbitrary scale factor which can change their sign from positive to negative
without changing the Physics of the problem.Comment: RevTex, 10 page
Elastic turbulence in curvilinear flows of polymer solutions
Following our first report (A. Groisman and V. Steinberg, \sl Nature , 53 (2000)) we present an extended account of experimental observations of
elasticity induced turbulence in three different systems: a swirling flow
between two plates, a Couette-Taylor (CT) flow between two cylinders, and a
flow in a curvilinear channel (Dean flow). All three set-ups had high ratio of
width of the region available for flow to radius of curvature of the
streamlines. The experiments were carried out with dilute solutions of high
molecular weight polyacrylamide in concentrated sugar syrups. High polymer
relaxation time and solution viscosity ensured prevalence of non-linear elastic
effects over inertial non-linearity, and development of purely elastic
instabilities at low Reynolds number (Re) in all three flows. Above the elastic
instability threshold, flows in all three systems exhibit features of developed
turbulence. Those include: (i)randomly fluctuating fluid motion excited in a
broad range of spatial and temporal scales; (ii) significant increase in the
rates of momentum and mass transfer (compared to those expected for a steady
flow with a smooth velocity profile). Phenomenology, driving mechanisms, and
parameter dependence of the elastic turbulence are compared with those of the
conventional high Re hydrodynamic turbulence in Newtonian fluids.Comment: 23 pages, 26 figure
Wave Propagation in Stochastic Spacetimes: Localization, Amplification and Particle Creation
Here we study novel effects associated with electromagnetic wave propagation
in a Robertson-Walker universe and the Schwarzschild spacetime with a small
amount of metric stochasticity. We find that localization of electromagnetic
waves occurs in a Robertson-Walker universe with time-independent metric
stochasticity, while time-dependent metric stochasticity induces exponential
instability in the particle production rate. For the Schwarzschild metric,
time-independent randomness can decrease the total luminosity of Hawking
radiation due to multiple scattering of waves outside the black hole and gives
rise to event horizon fluctuations and thus fluctuations in the Hawking
temperature.Comment: 26 pages, 1 Postscript figure, submitted to Phys. Rev. D on July 29,
199
Open Clusters IC 4665 and Cr 359 and a Probable Birthplace of the Pulsar PSR B1929+10
Based on the epicyclic approximation, we have simulated the motion of the
young open star clusters IC 4665 and Collinder 359. The separation between the
cluster centers is shown to have been minimal 7 Myr ago, 36 pc. We have
established a close evolutionary connection between IC 4665 and the
Scorpius-Centaurus association -- the separation between the centers of these
structures was pc 15 Myr ago. In addition, the center of IC 4665
at this time was near two well-known regions of coronal gas: the Local Bubble
and the North Polar Spur. The star HIP 86768 is shown to be one of the
candidates for a binary (in the past) with the pulsar PSR B1929+10. At the
model radial velocity of the pulsar km s, a close
encounter of this pair occurs in the vicinity of IC 4665 at a time of -1.1 Myr.
At the same time, using currently available data for the pulsar B1929+10 at its
model radial velocity km s, we show that the hypothesis
of Hoogerwerf et al. (2001) about the breakup of the Oph--B1929+10
binary in the vicinity of Upper Scorpius (US) about 0.9 Myr ago is more
plausible.Comment: 19 pages, 8 figure
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