374 research outputs found
Curvature singularity and film-skating during drop impact
We study the influence of the surrounding gas in the dynamics of drop impact
on a smooth surface. We use an axisymmetric 3D model for which both the gas and
the liquid are incompressible; lubrication regime applies for the gas film
dynamics and the liquid viscosity is neglected. In the absence of surface
tension a finite time singularity whose properties are analysed is formed and
the liquid touches the solid on a circle. When surface tension is taken into
account, a thin jet emerges from the zone of impact, skating above a thin gas
layer. The thickness of the air film underneath this jet is always smaller than
the mean free path in the gas suggesting that the liquid film eventually wets
the surface. We finally suggest an aerodynamical instability mechanism for the
splash.Comment: 5 figure
Granular Pressure and the Thickness of a Layer Jamming on a Rough Incline
Dense granular media have a compaction between the random loose and random
close packings. For these dense media the concept of a granular pressure
depending on compaction is not unanimously accepted because they are often in a
"frozen" state which prevents them to explore all their possible microstates, a
necessary condition for defining a pressure and a compressibility
unambiguously. While periodic tapping or cyclic fluidization have already being
used for that exploration, we here suggest that a succession of flowing states
with velocities slowly decreasing down to zero can also be used for that
purpose. And we propose to deduce the pressure in \emph{dense and flowing}
granular media from experiments measuring the thickness of the granular layer
that remains on a rough incline just after the flow has stopped.Comment: 10 pages, 2 figure
A 2-D asymmetric exclusion model for granular flows
A 2-D version of the asymmetric exclusion model for granular sheared flows is
presented. The velocity profile exhibits two qualitatively different behaviors,
dependent on control parameters. For low friction, the velocity profile follows
an exponential decay while for large friction the profile is more accurately
represented by a Gaussian law. The phase transition occurring between these two
behavior is identified by the appearance of correlations in the cluster size
distribution. Finally, a mean--field theory gives qualitative and quantitative
good agreement with the numerical results.Comment: 13 pages, 5 figures; typos added, one definition change
Cavitation induced by explosion in a model of ideal fluid
We discuss the problem of an explosion in the cubic-quintic superfluid model,
in relation to some experimental observations. We show numerically that an
explosion in such a model might induce a cavitation bubble for large enough
energy. This gives a consistent view for rebound bubbles in superfluid and we
indentify the loss of energy between the successive rebounds as radiated waves.
We compute self-similar solution of the explosion for the early stage, when no
bubbles have been nucleated. The solution also gives the wave number of the
excitations emitted through the shock wave.Comment: 21 pages,13 figures, other comment
Asymptotic behaviour of the Rayleigh--Taylor instability
We investigate long time numerical simulations of the inviscid
Rayleigh-Taylor instability at Atwood number one using a boundary integral
method. We are able to attain the asymptotic behavior for the spikes predicted
by Clavin & Williams\cite{clavin} for which we give a simplified demonstration.
In particular we observe that the spike's curvature evolves like while
the overshoot in acceleration shows a good agreement with the suggested
law. Moreover, we obtain consistent results for the prefactor coefficients of
the asymptotic laws. Eventually we exhibit the self-similar behavior of the
interface profile near the spike.Comment: 4 pages, 6 figure
Vortices in condensate mixtures
In a condensate made of two different atomic molecular species, Onsager's
quantization condition implies that around a vortex the velocity field cannot
be the same for the two species. We explore some simple consequences of this
observation. Thus if the two condensates are in slow relative translation one
over the other, the composite vortices are carried at a velocity that is a
fraction of the single species velocity. This property is valid for attractive
interaction and below a critical velocity which corresponds to a saddle-node
bifurcation.Comment: 4 pages, 3 figure
Visual Field Analysis: A reliable method to score left and right eye use using automated tracking
Brain and behavioural asymmetries have been documented in various taxa. Many of these asymmetries involve preferential left and right eye use. However, measuring eye use through manual frame-by-frame analyses from video recordings is laborious and may lead to biases. Recent progress in technology has allowed the development of accurate tracking techniques for measuring animal behaviour. Amongst these techniques, DeepLabCut, a Python-based tracking toolbox using transfer learning with deep neural networks, offers the possibility to track different body parts with unprecedented accuracy. Exploiting the potentialities of DeepLabCut, we developed Visual Field Analysis, an additional open-source application for extracting eye use data. To our knowledge, this is the first application that can automatically quantify leftâright preferences in eye use. Here we test the performance of our application in measuring preferential eye use in young domestic chicks. The comparison with manual scoring methods revealed a near perfect correlation in the measures of eye use obtained by Visual Field Analysis. With our application, eye use can be analysed reliably, objectively and at a fine scale in different experimental paradigms
Stability and individual variability of social attachment in imprinting
Filial imprinting has become a model for understanding memory, learning and social behaviour in neonate animals. This mechanism allows the youngs of precocial bird species to learn the characteristics of conspicuous visual stimuli and display affiliative response to them. Although longer exposures to an object produce stronger preferences for it afterwards, this relation is not linear. Sometimes, chicks even prefer to approach novel rather than familiar objects. To date, little is known about how filial preferences develop across time. This study aimed to investigate filial preferences for familiar and novel imprinting objects over time. After hatching, chicks were individually placed in an arena where stimuli were displayed on two opposite screens. Using an automated setup, the duration of exposure and the type of stimuli were manipulated while the time spent at the imprinting stimulus was monitored across 6 days. We showed that prolonged exposure (3 days vs 1 day) to a stimulus produced robust filial imprinting preferences. Interestingly, with a shorter exposure (1 day), animals re-evaluated their filial preferences in functions of their spontaneous preferences and past experiences. Our study suggests that predispositions influence learning when the imprinting memories are not fully consolidated, driving animal preferences toward more predisposed stimuli
A continuous non-linear shadowing model of columnar growth
We propose the first continuous model with long range screening (shadowing)
that described columnar growth in one space dimension, as observed in plasma
sputter deposition. It is based on a new continuous partial derivative equation
with non-linear diffusion and where the shadowing effects apply on all the
different processes.Comment: Fast Track Communicatio
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