69 research outputs found
Energy and Vorticity Spectra in Turbulent Superfluid He from to
We discuss the energy and vorticity spectra of turbulent superfluid He in
all the temperature range from up to the phase transition "
point", K. Contrary to classical developed turbulence
in which there are only two typical scales, i.e. the energy injection and
the dissipation scales , here the quantization of vorticity introduces
two additional scales, i.e the vortex core radius and the mean vortex
spacing . We present these spectra for the super- and normal-fluid
components in the entire range of scales from to including the
cross-over scale where the hydrodynamic eddy-cascade is replaced by the
cascade of Kelvin waves on individual vortices. At this scale a bottleneck
accumulation of the energy was found earlier at .
We show that even very small mutual friction dramatically suppresses the
bottleneck effect due to the dissipation of the Kelvin waves. Using our results
for the spectra we estimate the Vinen "effective viscosity" in the
entire temperature range and show agreement with numerous experimental
observation for .Comment: 20 pages, 5 figure
Statistical distributions in the folding of elastic structures
The behaviour of elastic structures undergoing large deformations is the
result of the competition between confining conditions, self-avoidance and
elasticity. This combination of multiple phenomena creates a geometrical
frustration that leads to complex fold patterns. By studying the case of a rod
confined isotropically into a disk, we show that the emergence of the
complexity is associated with a well defined underlying statistical measure
that determines the energy distribution of sub-elements,``branches'', of the
rod. This result suggests that branches act as the ``microscopic'' degrees of
freedom laying the foundations for a statistical mechanical theory of this
athermal and amorphous system
Temperature suppression of Kelvin-wave turbulence in superfluids
Kelvin waves propagating on quantum vortices play a crucial role in the
phenomenology of energy dissipation of superfluid turbulence. Previous
theoretical studies have consistently focused on the zero-temperature limit of
the statistical physics of Kelvin-wave turbulence. In this letter, we go beyond
this athermal limit by introducing a small but finite temperature in the form
of non-zero mutual friction dissipative force; A situation regularly
encountered in actual experiments of superfluid turbulence. In this case we
show that there exists a new typical length-scale separating a quasi-inertial
range of Kelvin wave turbulence from a far dissipation range. The letter
culminates with analytical predictions for the energy spectrum of the
Kelvin-wave turbulence in both of these regimes
Energy Spectra of Superfluid Turbulence in He
In superfluid He turbulence is carried predominantly by the superfluid
component. To explore the statistical properties of this quantum turbulence and
its differences from the classical counterpart we adopt the time-honored
approach of shell models. Using this approach we provide numerical simulations
of a Sabra-shell model that allows us to uncover the nature of the energy
spectrum in the relevant hydrodynamic regimes. These results are in qualitative
agreement with analytical expressions for the superfluid turbulent energy
spectra that were found using a differential approximation for the energy flux
The Effective Temperature in Elasto-Plasticity of Amorphous Solids
An effective temperature which differs from the bath
temperature is believed to play an essential role in the theory of
elasto-plasticity of amorphous solids. The definition of a measurable in the literature on sheared solids suffers however from being connected
to a fluctuation-dissipation theorem which is correct only in equilibrium. Here
we introduce a natural definition of based on measurable
structural features without recourse to any questionable assumption. The value
of is connected, using theory and scaling concepts, to the flow
stress and the mean energy that characterize the elasto-plastic flow.Comment: 4 pages, 5 figure
Interplay between Polymer Chain Conformation and Nanoparticles Assembly in Model Industrial Silica/Rubber Nanocomposites
International audienceThe question of the influence of nanoparticles (NP) on chain dimensions in polymer nanocomposites(PNC) has been treated mainly through the fundamental way using theoretical or simulation tools andexperiments on well-defined model PNC. Here we present the first experimental study about theinfluence of NP on the polymer chain conformation for PNC designed to be as close as possible toindustrial systems employed in tire industry. PNC are silica nanoparticles dispersed into a Styrene-Butadiene-Rubber (SBR) matrix whose NP dispersion can be managed by NP loading with interfacialcoating or coupling additives usually employed in the manufacturing mixing process. We associatedspecific chain (d) labeling, and the so-called Zero Average Contrast (ZAC) method, with SANS, in-situSANS and SAXS/TEM experiments to extract the polymer chain scattering signal at rest for non-crosslinked and under stretching for cross-linked PNCs. NP loading, individual clusters or connectednetwork, as well as the influence of the type, the quantity of interfacial agent and the influence of theelongation rate have been evaluated on the chain conformation and on its related deformation. Weclearly distinguish the situations where the silica is perfectly matched from the unperfected matching bydirect comparison of SANS and SAXS structure factor. Whatever the silica matching situation, theadditive type and quantity and the filler content, there is no thus significant change in the polymerdimension for NP loading up to 15% v/v within a range of 5%. One can see an extra scatteringcontribution at low Q, as often encountered, enhanced for non-perfect silica matching but also visiblefor perfect filler matching. This contribution can be qualitatively attributed to specific h or d chainsadsorption onto the NP surface inside the NP cluster that modifying the average scattering neutroncontrast of the silica cluster. Under elongation, NP act as additional cross-linking junction preventingchain relaxation giving a deformation of the chain with NP closer to theoretical phantom networkprediction than for pure matrix
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