3,653 research outputs found
On the Rapid Increase of Intermittency in the Near-Dissipation Range of Fully Developed Turbulence
Intermittency, measured as log(F(r)/3), where F(r) is the flatness of
velocity increments at scale r, is found to rapidly increase as viscous effects
intensify, and eventually saturate at very small scales. This feature defines a
finite intermediate range of scales between the inertial and dissipation
ranges, that we shall call near-dissipation range. It is argued that
intermittency is multiplied by a universal factor, independent of the Reynolds
number Re, throughout the near-dissipation range. The (logarithmic) extension
of the near-dissipation range varies as \sqrt(log Re). As a consequence,
scaling properties of velocity increments in the near-dissipation range
strongly depend on the Reynolds number.Comment: 7 pages, 7 figures, to appear in EPJ
Fermi liquid theory of ultra-cold trapped Fermi gases: Implications for Pseudogap Physics and Other Strongly Correlated Phases
We show how Fermi liquid theory can be applied to ultra-cold Fermi gases,
thereby expanding their "simulation" capabilities to a class of problems of
interest to multiple physics sub-disciplines. We introduce procedures for
measuring and calculating position dependent Landau parameters. This lays the
ground work for addressing important controversial issues: (i) the suggestion
that thermodynamically, the normal state of a unitary gas is indistinguishable
from a Fermi liquid (ii) that a fermionic system with strong repulsive contact
interactions is associated with either ferromagnetism or localization; this
relates as well to He and its p-wave superfluidity.Comment: 4 pages, 2 figures, revised versio
Heat Transfer in Turbulent Rayleigh-Benard Convection below the Ultimate Regime
A Rayleigh-B\'enard cell has been designed to explore the Prandtl (Pr)
dependence of turbulent convection in the cross-over range and for
the full range of soft and hard turbulences, up to Rayleigh number . The set-up benefits from the favourable characteristics of cryogenic
helium-4 in fluid mechanics, in-situ fluid property measurements, and special
care on thermometry and calorimetric instrumentation. The cell is cylindrical
with . The effective heat transfer has been
measured with unprecedented accuracy for cryogenic turbulent convection
experiments in this range of Rayleigh numbers. Spin-off of this study include
improved fits of helium thermodynamics and viscosity properties. Three main
results were found. First the dependence exhibits a bimodality of the
flow with difference in for given and . Second, a
systematic study of the side-wall influence reveals a measurable effect on the
heat transfer. Third, the dependence is very small or null : the
absolute value of the average logarithmic slope is smaller
than 0.03 in our range of , which allows to disciminate between
contradictory experiments [Ashkenazi \textit{et al.}, Phys. Rev.Lett. 83:3641
(1999)][Ahlers \textit{et al.}, Phys.Rev.Lett. 86:3320 (2001)].Comment: submitted for publication to JLTP (august 2003
Thinking the Difference: On Feminism and Postcolony [review essay]
The recent publication in France of two volumes on South Asian feminism and its reception in the West—Danielle Haase-Dubosc et al.’s Enjeux contemporains du féminisme indien (2002) and Martine Van Woerkens’ Nous ne sommes pas des fleurs: deux siècles de combats féministes en Inde (2010)—has raised several key issues regarding the complex and somewhat ambiguous collusion between feminist thought and postcolonial theory. Much has been written (Kiswar 1985, Chatterjee 1993, Sarkar 1999 & 2001) ..
Unified Multifractal Description of Velocity Increments Statistics in Turbulence: Intermittency and Skewness
The phenomenology of velocity statistics in turbulent flows, up to now,
relates to different models dealing with either signed or unsigned longitudinal
velocity increments, with either inertial or dissipative fluctuations. In this
paper, we are concerned with the complete probability density function (PDF) of
signed longitudinal increments at all scales. First, we focus on the symmetric
part of the PDFs, taking into account the observed departure from scale
invariance induced by dissipation effects. The analysis is then extended to the
asymmetric part of the PDFs, with the specific goal to predict the skewness of
the velocity derivatives. It opens the route to the complete description of all
measurable quantities, for any Reynolds number, and various experimental
conditions. This description is based on a single universal parameter function
D(h) and a universal constant R*.Comment: 13 pages, 3 figures, Extended version, Publishe
Empirical distributions of Chinese stock returns at different microscopic timescales
We study the distributions of event-time returns and clock-time returns at
different microscopic timescales using ultra-high-frequency data extracted from
the limit-order books of 23 stocks traded in the Chinese stock market in 2003.
We find that the returns at the one-trade timescale obey the inverse cubic law.
For larger timescales (2-32 trades and 1-5 minutes), the returns follow the
Student distribution with power-law tails. With the decrease of timescale, the
tail becomes fatter, which is consistent with the vibrational theory.Comment: 14 Elsart page including 2 tables and 3 figure
A Simple Analytical Model of Evaporation in the Presence of Roots
Root systems can influence the dynamics of evapotranspiration of water out of
a porous medium. The coupling of evapotranspiration remains a key aspect
affecting overall root behavior. Predicting the evapotranspiration curve in the
presence of roots helps keep track of the amount of water that remains in the
porous medium. Using a controlled visual set-up of a 2D model soil system
consisting of monodisperse glass beads, we first perform experiments on actual
roots grown in partially saturated systems under different relative humidity
conditions. We record parameters such as the total mass loss in the medium and
the resulting position of the receding fronts and use these experimental
results to develop a simple analytical model that predicts the position of the
evaporating front as a function of time as well as the total amount of water
that is lost from the medium due to the combined effects of evaporation and
transpiration. The model is based on fundamental principles of evaporation flux
and includes empirical assumptions on the quantity of stoma in the leaves and
the transition time between regime 1 and regime 2. The model also underscores
the importance of a much prolonged root life as long as the root is exposed to
a partially saturated zone composed of a mixture of air and water. Comparison
between the model and experimental results shows good prediction of the
position of the evaporating front as well as the total mass loss from
evapotranspiration in the presence of real root systems. These results provide
additional understanding of both complex evaporation phenomenon and its
influence on root mechanisms.Comment: 10 pages, 6 figure
Spatially heterogeneous dynamics in a thermosensitive soft suspension before and after the glass transition
The microscopic dynamics and aging of a soft thermosensitive suspension was
investigated by looking at the thermal fluctuations of tracers in the
suspension. Below and above the glass transition, the dense microgel particles
suspension was found to develop an heterogeneous dynamics, featured by a non
Gaussian Probability Distribution Function (PDF) of the probes' displacements,
with an exponential tail. We show that non Gaussian shapes are a characteristic
of the ensemble-averaged PDF, while local PDF remain Gaussian. This shows that
the scenario behind the non Gaussian van Hove functions is a spatially
heterogeneous dynamics, characterized by a spatial distribution of locally
homogeneous dynamical environments through the sample, on the considered time
scales. We characterize these statistical distributions of dynamical
environments, in the liquid, supercooled, and glass states, and show that it
can explain the observed exponential tail of the van Hove functions observed in
the concentrated states. The intensity of spatial heterogeneities was found to
amplify with increasing volume fraction. In the aging regime, it tends to
increase as the glass gets more arrested.Comment: 19 pages, 10 figures, Soft Matter accepte
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