33 research outputs found
Fluctuation-Dissipation Relations and statistical temperatures in a turbulent von K\'arm\'an flow
We experimentally characterize the fluctuations of the non-homogeneous
non-isotropic turbulence in an axisymmetric von K\'arm\'an flow. We show that
these fluctuations satisfy relations analogous to classical
Fluctuation-Dissipation Relations (FDRs) in statistical mechanics. We use these
relations to measure statistical temperatures of turbulence. The values of
these temperatures are found to be dependent on the considered observable as
already evidenced in other far from equilibrium systems.Comment: four pages 2 figures one tabl
Vortex density spectrum of quantum turbulence
The fluctuations of the vortex density in a turbulent quantum fluid are
deduced from local second-sound attenuation measurements. These measurements
are performed with a micromachined open-cavity resonator inserted across a flow
of turbulent He-II near 1.6 K. The power spectrum of the measured vortex line
density is compatible with a (-5/3) power law. The physical interpretation,
still open, is discussed.Comment: Submitted to Europhys. Let
Statistical mechanics of Beltrami flows in axisymmetric geometry: Equilibria and bifurcations
We characterize the thermodynamical equilibrium states of axisymmetric
Euler-Beltrami flows. They have the form of coherent structures presenting one
or several cells. We find the relevant control parameters and derive the
corresponding equations of state. We prove the coexistence of several
equilibrium states for a given value of the control parameter like in 2D
turbulence [Chavanis and Sommeria, J. Fluid Mech. 314, 267 (1996)]. We explore
the stability of these equilibrium states and show that all states are saddle
points of entropy and can, in principle, be destabilized by a perturbation with
a larger wavenumber, resulting in a structure at the smallest available scale.
This mechanism is therefore reminiscent of the 3D Richardson energy cascade
towards smaller and smaller scales. Therefore, our system is truly intermediate
between 2D turbulence (coherent structures) and 3D turbulence (energy cascade).
We further explore numerically the robustness of the equilibrium states with
respect to random perturbations using a relaxation algorithm in both canonical
and microcanonical ensembles. We show that saddle points of entropy can be very
robust and therefore play a role in the dynamics. We evidence differences in
the robustness of the solutions in the canonical and microcanonical ensembles.
A scenario of bifurcation between two different equilibria (with one or two
cells) is proposed and discussed in connection with a recent observation of a
turbulent bifurcation in a von Karman experiment [Ravelet et al., Phys. Rev.
Lett. 93, 164501 (2004)].Comment: 25 pages; 16 figure
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
TSF experiment for comparison of high Reynolds number turbulence in both HeI and HeII: First results
International audienceTSF experiment for comparison of high Reynolds number turbulence in both HeI and HeII: First result
A Deletion in Exon 9 of the LIPH Gene Is Responsible for the Rex Hair Coat Phenotype in Rabbits (Oryctolagus cuniculus)
The fur of common rabbits is constituted of 3 types of hair differing in length and diameter while that of rex animals is essentially made up of amazingly soft down-hair. Rex short hair coat phenotypes in rabbits were shown to be controlled by three distinct loci. We focused on the “r1” mutation which segregates at a simple autosomal-recessive locus in our rabbit strains. A positional candidate gene approach was used to identify the rex gene and the corresponding mutation. The gene was primo-localized within a 40 cM region on rabbit chromosome 14 by genome scanning families of 187 rabbits in an experimental mating scheme. Then, fine mapping refined the region to 0.5 cM (Z = 78) by genotyping an additional 359 offspring for 94 microsatellites present or newly generated within the first defined interval. Comparative mapping pointed out a candidate gene in this 700 kb region, namely LIPH (Lipase Member H). In humans, several mutations in this major gene cause alopecia, hair loss phenotypes. The rabbit gene structure was established and a deletion of a single nucleotide was found in LIPH exon 9 of rex rabbits (1362delA). This mutation results in a frameshift and introduces a premature stop codon potentially shortening the protein by 19 amino acids. The association between this deletion and the rex phenotype was complete, as determined by its presence in our rabbit families and among a panel of 60 rex and its absence in all 60 non-rex rabbits. This strongly suggests that this deletion, in a homozygous state, is responsible for the rex phenotype in rabbits
A Deletion in Exon 9 of the LIPH Gene Is Responsible for the Rex Hair Coat Phenotype in Rabbits (Oryctolagus cuniculus)
The fur of common rabbits is constituted of 3 types of hair differing in length and diameter while that of rex animals is essentially made up of amazingly soft down-hair. Rex short hair coat phenotypes in rabbits were shown to be controlled by three distinct loci. We focused on the “r1” mutation which segregates at a simple autosomal-recessive locus in our rabbit strains. A positional candidate gene approach was used to identify the rex gene and the corresponding mutation. The gene was primo-localized within a 40 cM region on rabbit chromosome 14 by genome scanning families of 187 rabbits in an experimental mating scheme. Then, fine mapping refined the region to 0.5 cM (Z = 78) by genotyping an additional 359 offspring for 94 microsatellites present or newly generated within the first defined interval. Comparative mapping pointed out a candidate gene in this 700 kb region, namely LIPH (Lipase Member H). In humans, several mutations in this major gene cause alopecia, hair loss phenotypes. The rabbit gene structure was established and a deletion of a single nucleotide was found in LIPH exon 9 of rex rabbits (1362delA). This mutation results in a frameshift and introduces a premature stop codon potentially shortening the protein by 19 amino acids. The association between this deletion and the rex phenotype was complete, as determined by its presence in our rabbit families and among a panel of 60 rex and its absence in all 60 non-rex rabbits. This strongly suggests that this deletion, in a homozygous state, is responsible for the rex phenotype in rabbits
Nuclear Organization and Dynamics of 7SK RNA in Regulating Gene Expression
We have identified 7SK RNA to be enriched in nuclear speckles. Knock-down of 7SK results in the mislocalization of nuclear speckle constituents, and the transcriptional up-regulation of a reporter gene locus. 7SK RNA transiently associates with the locus upon transcriptional down-regulation correlating with the displacement of pTEF-b
The Mechanism of Release of P-TEFb and HEXIM1 from the 7SK snRNP by Viral and Cellular Activators Includes a Conformational Change in 7SK
The positive transcription elongation factor, P-TEFb, is required for the production of mRNAs, however the majority of the factor is present in the 7SK snRNP where it is inactivated by HEXIM1. Expression of HIV-1 Tat leads to release of P-TEFb and HEXIM1 from the 7SK snRNP in vivo, but the release mechanisms are unclear.We developed an in vitro P-TEFb release assay in which the 7SK snRNP immunoprecipitated from HeLa cell lysates using antibodies to LARP7 was incubated with potential release factors. We found that P-TEFb was directly released from the 7SK snRNP by HIV-1 Tat or the P-TEFb binding region of the cellular activator Brd4. Glycerol gradient sedimentation analysis was used to demonstrate that the same Brd4 protein transfected into HeLa cells caused the release of P-TEFb and HEXIM1 from the 7SK snRNP in vivo. Although HEXIM1 binds tightly to 7SK RNA in vitro, release of P-TEFb from the 7SK snRNP is accompanied by the loss of HEXIM1. Using a chemical modification method, we determined that concomitant with the release of HEXIM1, 7SK underwent a major conformational change that blocks re-association of HEXIM1.Given that promoter proximally paused polymerases are present on most human genes, understanding how activators recruit P-TEFb to those genes is critical. Our findings reveal that the two tested activators can extract P-TEFb from the 7SK snRNP. Importantly, we found that after P-TEFb is extracted a dramatic conformational change occurred in 7SK concomitant with the ejection of HEXIM1. Based on our findings, we hypothesize that reincorporation of HEXIM1 into the 7SK snRNP is likely the regulated step of reassembly of the 7SK snRNP containing P-TEFb