29 research outputs found
Energy flow between two hydrodynamically coupled particles kept at different effective temperatures
We measure the energy exchanged between two hydrodynamically coupled
micron-sized Brownian particles trapped in water by two optical tweezers. The
system is driven out of equilibrium by random forcing the position of one of
the two particles. The forced particle behaves as it has an "effective
temperature" higher than that of the other bead. This driving modifies the
equilibrium variances and cross-correlation functions of the bead positions: we
measure an energy flow between the particles and an instantaneous
cross-correlation, proportional to the effective temperature difference between
the two particles. A model of the interaction which is based on classical
hydrodynamic coupling tensors is proposed. The theoretical and experimental
results are in excellent agreement
Information and thermodynamics: Experimental verification of Landauer's erasure principle
We present an experiment in which a one-bit memory is constructed, using a
system of a single colloidal particle trapped in a modulated double-well
potential. We measure the amount of heat dissipated to erase a bit and we
establish that in the limit of long erasure cycles the mean dissipated heat
saturates at the Landauer bound, i.e. the minimal quantity of heat necessarily
produced to delete a classical bit of information. This result demonstrates the
intimate link between information theory and thermodynamics. To stress this
connection we also show that a detailed Jarzynski equality is verified,
retrieving the Landauer's bound independently of the work done on the system.
The experimental details are presented and the experimental errors carefully
discusse
Fluctuations in an aging system: absence of effective temperature in the sol-gel transition of a quenched gelatin sample
We study the fluctuations of a Brownian micro particle trapped with optical
tweezers in a gelatin solution undergoing a fast local temperature quench below
the sol-gel transition. Contrary to what was previously reported, we observe no
anomalous fluctuations in the particle's position that could be interpreted in
terms of an effective temperature. A careful analysis with ensemble averages
shows only equilibrium-like properties for the fluctuations, even though the
system is clearly aging. We also provide a detailed discussion on possible
artifacts that could have been interpreted as an effective temperature, such as
the presence of a drift or a mixing in time and ensemble averages in data
analysis. These considerations are of general interest when dealing with
non-ergodic or non-stationary systems
Detailed Jarzynski Equality applied on a Logically Irreversible Procedure
International audienceA single bit memory system is made with a brownian particle held by an optical tweezer in a double-well potential and the work necessary to erase the memory is measured. We show that the minimum of this work is close to the Landauer's bound only for very slow erasure procedure. Instead a detailed Jarzynski equality allows us to retrieve the Landauer's bound independently on the speed of this erasure procedure. For the two separated subprocesses, i.e. the transition from state 1 to state 0 and the transition from state 0 to state 0, the Jarzynski equality does not hold but the generalized version links the work done on the system to the probability that it returns to its initial state under the time-reversed procedure
A general fluctuation-response relation for noise variations and its application to driven hydrodynamic experiments
The effect of a change of noise amplitudes in overdamped diffusive systems is
linked to their unperturbed behavior by means of a nonequilibrium
fluctuation-response relation. This formula holds also for systems with
state-independent nontrivial diffusivity matrices, as we show with an
application to an experiment of two trapped and hydrodynamically coupled
colloids, one of which is subject to an external random forcing that mimics an
effective temperature. The nonequilibrium susceptibility of the energy to a
variation of this driving is an example of our formulation, which improves an
earlier version, as it does not depend on the time-discretization of the
stochastic dynamics. This scheme holds for generic systems with additive noise
and can be easily implemented numerically, thanks to matrix operations
Suspensions rhéo-épaississantes - Principes et applications
International audienceShear-thickening is observed in dense particulate suspensions and consists in a severe increase of the suspension viscosity above an onset stress. This behavior, which is very useful for certain technological applications, can also be an issue in some industrial processes. Shear thickening was considered a puzzle for a long time. It can now be explained as a frictional transition thanks to a recent theoretical model. This paper presents this model and its numerical and experimental validations. Different applications which may emerge from the understanding of this phenomenon are then discussed.Le rhéo-épaississement est un phénomène observé dans certaines suspensions denses de particules. Il consiste en une augmentation parfois brutale de leur viscosité lorsqu'elles sont soumises à une forte contrainte. Ce comportement, très utile pour certaines applications tech-nologiques, peut aussi s'avérer problématique dans certains processus industriels. Longtemps resté une énigme, le rhéo-épaississement est désormais décrit de façon cohérente par le modèle de transition frictionnelle. Cet article présente ce modèle ainsi que les études numériques et expérimentales qui le valident. Sont ensuite abordées différentes perspectives d'applications offertes par la compréhension de ce phénomène. Résumé Shear-thickening is observed in dense particulate suspensions and consists in a severe increase of the suspension viscosity above an onset stress. This behavior, which is very useful for certain technological applications, can also be an issue in some industrial processes. Shear thickening was considered a puzzle for a long time. It can now be explained as a frictio-nal transition thanks to a recent theoretical model. This paper presents this model and its numerical and experimental validations. Different applications which may emerge from the understanding of this phenomenon are then discussed
Simultaneous 3D measurement of the translation and rotation of finite size particles and the flow field in a fully developed turbulent water flow
We report a novel experimental technique that measures simultaneously in
three dimensions the trajectories, the translation, and the rotation of finite
size inertial particles together with the turbulent flow. The flow field is
analyzed by tracking the temporal evolution of small fluorescent tracer
particles. The inertial particles consist of a super-absorbent polymer that
renders them index and density matched with water and thus invisible. The
particles are marked by inserting at various locations tracer particles into
the polymer. Translation and rotation, as well as the flow field around the
particle are recovered dynamically from the analysis of the marker and tracer
particle trajectories. We apply this technique to study the dynamics of
inertial particles much larger in size (Rp/{\eta} \approx 100) than the
Kolmogorov length scale {\eta} in a von K\'arm\'an swirling water flow
(R{\lambda} \approx 400). We show, using the mixed (particle/fluid) Eulerian
second order velocity structure function, that the interaction zone between the
particle and the flow develops in a spherical shell of width 2Rp around the
particle of radius Rp. This we interpret as an indication of a wake induced by
the particle. This measurement technique has many additional advantages that
will make it useful to address other problems such as particle collisions,
dynamics of non-spherical solid objects, or even of wet granular matter.Comment: 18 pages, 7 figures, submitted to "Measurement Science and
Technology" special issue on "Advances in 3D velocimetry
Marangoni stress induced by rotation frustration in a liquid foam
International audienceThe role of surface tension gradients in the apparent viscosity of liquid foams remains largely unexplained. In this article, we develop a toy-model based on a periodic array of 2D hexagonal bubbles, each bubble being separated from its neighbors by a liquid film of uniform thickness. The two interfaces of this thin liquid film are allowed to slide relatively to each other, thus shearing the liquid phase in between. We solve the dynamics under external shear of this minimal system and we show that the continuity of the surface tension around the whole bubble is the relevant condition to determine the bubble rotation rate and the energy dissipation. This result is expected to be robust in more complex situations and illustrates that thin film dynamics should be solve at the scale of the whole bubble interface when interface rheology matters