133 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
Dynamics of a Liquid Crystal close to the Fr\'eedericksz transition
We report experimental and numerical evidences that the dynamics of the
director of a liquid crystal driven by an electric field close to the critical
point of the Fr\'eedericksz Transition(FT) is not described by a
Landau-Ginzburg (LG) equation as it is usually done in literature. The reasons
are related to the very crude approximations done to obtain this equation, to
the finite value of the anchoring energy and to small asymmetries on boundary
conditions. We also discuss the difference between the use of LG equation for
the statics and the dynamics. These results are useful in all cases where FT is
used as an example for other orientational transitions
Slow crack growth : models and experiments
The properties of slow crack growth in brittle materials are analyzed both
theoretically and experimentally. We propose a model based on a thermally
activated rupture process. Considering a 2D spring network submitted to an
external load and to thermal noise, we show that a preexisting crack in the
network may slowly grow because of stress fluctuations. An analytical solution
is found for the evolution of the crack length as a function of time, the time
to rupture and the statistics of the crack jumps. These theoretical predictions
are verified by studying experimentally the subcritical growth of a single
crack in thin sheets of paper. A good agreement between the theoretical
predictions and the experimental results is found. In particular, our model
suggests that the statistical stress fluctuations trigger rupture events at a
nanometric scale corresponding to the diameter of cellulose microfibrils.Comment: to be published in EPJ (European Physical Journal
Comment on ''Measurement of Effective Temperatures in an Aging Colloidal Glass''
We measure the fluctuations of the position of a silica bead trapped by an
optical tweezers during the aging of a Laponite suspension. We find that the
effective temperature is equal to the bath temperature
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
Heat fluctuations for harmonic oscillators
Heat fluctuations of a harmonic oscillator in contact with a thermostat and
driven out of equilibrium by an external deterministic force are studied
experimentally and theoretically within the context of Fluctuation Theorems. We
consider the case of a periodic forcing of the oscillator, and we calculate the
analytic probability density function of heat fluctuations. The limit of large
time is discussed and we show that heat fluctuations satisfy the conventional
fluctuation theorem, even if a different fluctuation relation exists for this
quantity. Experimental results are also given for a transient state.Comment: Submitted to Europhysics Letter
Thermal response of nonequilibrium RC-circuits
We analyze experimental data obtained from an electrical circuit having
components at different temperatures, showing how to predict its response to
temperature variations. This illustrates in detail how to utilize a recent
linear response theory for nonequilibrium overdamped stochastic systems. To
validate these results, we introduce a reweighting procedure that mimics the
actual realization of the perturbation and allows extracting the susceptibility
of the system from steady state data. This procedure is closely related to
other fluctuation-response relations based on the knowledge of the steady state
probability distribution. As an example, we show that the nonequilibrium heat
capacity in general does not correspond to the correlation between the energy
of the system and the heat flowing into it. Rather, also non-dissipative
aspects are relevant in the nonequilbrium fluctuation response relations.Comment: 2 figure
On the transient Fluctuation Dissipation Theorem after a quench at a critical point
The Modified Fluctuation Dissipation Theorem (MFDT) proposed by G. Verley et
al. {\it (EPL 93, 10002, (2011))} for non equilibrium transient states is
experimentally studied. We apply MFDT to the transient relaxation dynamics of
the director of a liquid crystal after a quench close to the critical point of
the Fr\'eedericksz transition (Ftr), which has several properties of a second
order phase transition driven by an electric field. Although the standard
Fluctuation Dissipation Theorem (FDT) is not satisfied, because the system is
strongly out of equilibrium, the MFDT is perfectly verified during the
transient in a system which is only partially described by Landau-Ginzburg (LG)
equation, to which our observation are compared. The results can be useful in
the study of material aging
On the heat flux and entropy produced by thermal fluctuations
We report an experimental and theoretical analysis of the energy exchanged
between two conductors kept at different temperature and coupled by the
electric thermal noise. Experimentally we determine, as functions of the
temperature difference, the heat flux, the out-of- equilibrium variance and a
conservation law for the fluctuating entropy, which we justify theoretically.
The system is ruled by the same equations of two Brownian particles kept at
different temperatures and coupled by an elastic force. Our results set strong
constrains on the energy exchanged between coupled nano-systems kept at
different temperature.
Statistical properties of the energy exchanged between two heat baths coupled by thermal fluctuations
We study both experimentally and theoretically the statistical properties of
the energy exchanged between two electrical conductors, kept at different
temperature by two different heat reservoirs, and coupled by the electric
thermal noise. Such a system is ruled by the same equations as two Brownian
particles kept at different temperatures and coupled by an elastic force. We
measure the heat flowing between the two reservoirs, the thermodynamic work
done by one part of the system on the other, and we show that these quantities
exhibit a long time fluctuation theorem. Furthermore, we evaluate the
fluctuating entropy, which satisfies a conservation law. These experimental
results are fully justified by the theoretically analysis. Our results give
more insight into the energy transfer in the famous Feymann ratchet widely
studied theoretically but never in an experiment.Comment: arXiv admin note: substantial text overlap with arXiv:1301.431
- …