187 research outputs found
Gaussian multiplicative Chaos for symmetric isotropic matrices
Motivated by isotropic fully developed turbulence, we define a theory of
symmetric matrix valued isotropic Gaussian multiplicative chaos. Our
construction extends the scalar theory developed by J.P. Kahane in 1985
Intermittency of velocity time increments in turbulence
We analyze the statistics of turbulent velocity fluctuations in the time
domain. Three cases are computed numerically and compared: (i) the time traces
of Lagrangian fluid particles in a (3D) turbulent flow (referred to as the
"dynamic" case); (ii) the time evolution of tracers advected by a frozen
turbulent field (the "static" case), and (iii) the evolution in time of the
velocity recorded at a fixed location in an evolving Eulerian velocity field,
as it would be measured by a local probe (referred to as the "virtual probe"
case). We observe that the static case and the virtual probe cases share many
properties with Eulerian velocity statistics. The dynamic (Lagrangian) case is
clearly different; it bears the signature of the global dynamics of the flow.Comment: 5 pages, 3 figures, to appear in PR
Probing quantum and classical turbulence analogy through global bifurcations in a von K\'arm\'an liquid Helium experiment
We report measurements of the dissipation in the Superfluid Helium high
REynold number von Karman flow (SHREK) experiment for different forcing
conditions, through a regime of global hysteretic bifurcation. Our
macroscopical measurements indicate no noticeable difference between the
classical fluid and the superfluid regimes, thereby providing evidence of the
same dissipative anomaly and response to asymmetry in fluid and superfluid
regime. %In the latter case, A detailed study of the variations of the
hysteretic cycle with Reynolds number supports the idea that (i) the stability
of the bifurcated states of classical turbulence in this closed flow is partly
governed by the dissipative scales and (ii) the normal and the superfluid
component at these temperatures (1.6K) are locked down to the dissipative
length scale.Comment: 5 pages, 5 figure
Lagrangian Velocity Statistics in Turbulent Flows: Effects of Dissipation
We use the multifractal formalism to describe the effects of dissipation on
Lagrangian velocity statistics in turbulent flows. We analyze high Reynolds
number experiments and direct numerical simulation (DNS) data. We show that
this approach reproduces the shape evolution of velocity increment probability
density functions (PDF) from Gaussian to stretched exponentials as the time lag
decreases from integral to dissipative time scales. A quantitative
understanding of the departure from scaling exhibited by the magnitude
cumulants, early in the inertial range, is obtained with a free parameter
function D(h) which plays the role of the singularity spectrum in the
asymptotic limit of infinite Reynolds number. We observe that numerical and
experimental data are accurately described by a unique quadratic D(h) spectrum
which is found to extend from to , as
the signature of the highly intermittent nature of Lagrangian velocity
fluctuations.Comment: 5 pages, 3 figures, to appear in PR
The Peroxisomal 3-keto-acyl-CoA thiolase B Gene Expression Is under the Dual Control of PPARα and HNF4α in the Liver
PPARα and HNF4α are nuclear receptors that control gene transcription by direct binding to specific nucleotide sequences. Using transgenic mice deficient for either PPARα or HNF4α, we show that the expression of the peroxisomal 3-keto-acyl-CoA thiolase B (Thb) is under the dependence of these two transcription factors. Transactivation and gel shift experiments identified a novel PPAR response element within intron 3 of the Thb gene, by which PPARα but not HNF4α transactivates. Intriguingly, we found that HNF4α enhanced PPARα/RXRα transactivation from TB PPRE3 in a DNA-binding independent manner. Coimmunoprecipitation assays supported the hypothesis that HNF4α was physically interacting with RXRα. RT-PCR performed with RNA from liver-specific HNF4α-null mice confirmed the involvement of HNF4α in the PPARα-regulated induction of Thb by Wy14,643. Overall, we conclude that HNF4α enhances the PPARα-mediated activation of Thb gene expression in part through interaction with the obligate PPARα partner, RXRα
Acceleration and vortex filaments in turbulence
We report recent results from a high resolution numerical study of fluid
particles transported by a fully developed turbulent flow. Single particle
trajectories were followed for a time range spanning more than three decades,
from less than a tenth of the Kolmogorov time-scale up to one large-eddy
turnover time. We present some results concerning acceleration statistics and
the statistics of trapping by vortex filaments.Comment: 10 pages, 5 figure
Modeling the pressure Hessian and viscous Laplacian in Turbulence: comparisons with DNS and implications on velocity gradient dynamics
Modeling the velocity gradient tensor A along Lagrangian trajectories in
turbulent flow requires closures for the pressure Hessian and viscous Laplacian
of A. Based on an Eulerian-Lagrangian change of variables and the so-called
Recent Fluid Deformation closure, such models were proposed recently. The
resulting stochastic model was shown to reproduce many geometric and anomalous
scaling properties of turbulence. In this work, direct comparisons between
model predictions and Direct Numerical Simulation (DNS) data are presented.
First, statistical properties of A are described using conditional averages of
strain skewness, enstrophy production, energy transfer and vorticity
alignments, conditioned upon invariants of A. These conditionally averaged
quantities are found to be described accurately by the stochastic model. More
detailed comparisons that focus directly on the terms being modeled in the
closures are also presented. Specifically, conditional statistics associated
with the pressure Hessian and the viscous Laplacian are measured from the model
and are compared with DNS. Good agreement is found in strain-dominated regions.
However, some features of the pressure Hessian linked to rotation dominated
regions are not reproduced accurately by the model. Geometric properties such
as vorticity alignment with respect to principal axes of the pressure Hessian
are mostly predicted well. In particular, the model predicts that an
eigenvector of the rate-of-strain will be also an eigenvector of the pressure
Hessian, in accord to basic properties of the Euler equations. The analysis
identifies under what conditions the Eulerian-Lagrangian change of variables
with the Recent Fluid Deformation closure works well, and in which flow regimes
it requires further improvements.Comment: 16 pages, 10 figures, minor revisions, final version published in
Phys. Fluid
Universal intermittent properties of particle trajectories in highly turbulent flows
We present a collection of eight data sets, from state-of-the-art experiments
and numerical simulations on turbulent velocity statistics along particle
trajectories obtained in different flows with Reynolds numbers in the range
. Lagrangian structure functions from all data sets
are found to collapse onto each other on a wide range of time lags, revealing a
universal statistics, and calling for a unified theoretical description.
Parisi-Frisch Multifractal theory, suitable extended to the dissipative scales
and to the Lagrangian domain, is found to capture intermittency of velocity
statistics over the whole three decades of temporal scales here investigated.Comment: 5 pages, 1 figure; content changed, references update
Altered Energy Homeostasis and Resistance to Diet-Induced Obesity in KRAP-Deficient Mice
Obesity and related metabolic disorders have become leading causes of adult morbidity and mortality. KRAP (Ki-ras-induced actin-interacting protein) is a cytoskeleton-associated protein and a ubiquitous protein among tissues, originally identified as a cancer-related molecule, however, its physiological roles remain unknown. Here we demonstrate that KRAP-deficient (KRAP−/−) mice show enhanced metabolic rate, decreased adiposity, improved glucose tolerance, hypoinsulinemia and hypoleptinemia. KRAP−/− mice are also protected against high-fat diet-induced obesity and insulin resistance despite of hyperphagia. Notably, glucose uptake in the brown adipose tissue (BAT) in KRAP−/− mice is enhanced in an insulin-independent manner, suggesting that BAT is involved in altered energy homeostasis in KRAP−/− mice, although UCP (Uncoupling protein) expressions are not altered. Of interest is the down-regulation of fatty acid metabolism-related molecules, including acetyl-CoA carboxylase (ACC)-1, ACC-2 and fatty acid synthase in the liver of KRAP−/− mice, which could in part account for the metabolic phenotype in KRAP−/− mice. Thus, KRAP is a novel regulator in whole-body energy homeostasis and may be a therapeutic target in obesity and related diseases
Bronchial epithelial spheroids: an alternative culture model to investigate epithelium inflammation-mediated COPD
<p>Abstract</p> <p>Background</p> <p>Chronic obstructive pulmonary disease (COPD) is characterized by abnormal lung inflammation that exceeds the protective response. Various culture models using epithelial cell lines or primary cells have been used to investigate the contribution of bronchial epithelium in the exaggerated inflammation of COPD. However, these models do not mimic <it>in vivo </it>situations for several reasons (e.g, transformed epithelial cells, protease-mediated dissociation of primary cells, etc.). To circumvent these concerns, we developed a new epithelial cell culture model.</p> <p>Methods</p> <p>Using non transformed non dissociated bronchial epithelium obtained by bronchial brushings from COPD and non-COPD smokers, we developed a 3-dimensional culture model, bronchial epithelial spheroids (BES). BES were analyzed by videomicroscopy, light microscopy, immunofluorescence, and transmission electron microscopy. We also compared the inflammatory responses of COPD and non-COPD BES. In our study, we chose to stimulate BES with lipopolycaccharide (LPS) and measured the release of the pro-inflammatory mediators interleukin-8 (IL-8) and leukotriene B4 (LTB4) and the anti-inflammatory mediator prostaglandin E2 (PGE2).</p> <p>Results</p> <p>BES obtained from both COPD and non-COPD patients were characterized by a polarized bronchial epithelium with tight junctions and ciliary beating, composed of basal cells, secretory cells and ciliated cells. The ciliary beat frequency of ciliated cells was not significantly different between the two groups. Of interest, BES retained their characteristic features in culture up to 8 days. BES released the inflammatory mediators IL-8, PGE2 and LTB4 constitutively and following exposure to LPS. Interestingly, LPS induced a higher release of IL-8, but not PGE2 and LTB4 in COPD BES (p < 0.001) which correlated with lung function changes.</p> <p>Conclusion</p> <p>This study provides for the first time a compelling evidence that the BES model provides an unaltered bronchial surface epithelium. More importantly, BES represent an attractive culture model to investigate the mechanisms of injuring agents that mediate epithelial cell inflammation and its contribution to COPD pathogenesis.</p
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