1,095 research outputs found
Stationary and transient Fluctuation Theorems for effective heat flux between hydrodynamically coupled particles in optical traps
We experimentally study the statistical properties of the energy fluxes
between two trapped Brownian particles, interacting through dissipative
hydrodynamic coupling, submitted to an effective temperature difference , obtained by random forcing the position of one trap. We identify effective
heat fluxes between the two particles and show that they satisfy an exchange
fluctuation theorem (xFT) in the stationary state. We also show that after the
sudden application of a temperature gradient , \resub{the total}
hot-cold flux satisfies \resub{a} transient xFT for any integration time
whereas \resub{the total} cold-hot flux only does it asymptotically for long
times
Work fluctuation theorems for harmonic oscillators
The work fluctuations of an oscillator in contact with a thermostat and
driven out of equilibrium by an external force are studied experimentally and
theoretically within the context of Fluctuation Theorems (FTs). The oscillator
dynamics is modeled by a second order Langevin equation. Both the transient and
stationary state fluctuation theorems hold and the finite time corrections are
very different from those of a first order Langevin equation. The periodic
forcing of the oscillator is also studied; it presents new and unexpected short
time convergences. Analytical expressions are given in all cases
On the geometric genus of reducible surfaces and degenerations of surfaces to unions of planes
In this paper we study some properties of degenerations of surfaces whose
general fibre is a smooth projective surface and whose central fibre is a
reduced, connected surface , , which is assumed to be
a union of smooth projective surfaces, in particular of planes. Our original
motivation has been a series of papers of G. Zappa which appeared in the
1940-50's regarding degenerations of scrolls to unions of planes.
Here, we present a first set of results on the subject; other aspects are
still work in progress and will appear later.
We first study the geometry and the combinatorics of a surface like ,
considered as a reduced, connected surface on its own; then we focus on the
case in which X is the central fibre of a degeneration of relative dimension
two over the complex unit disk. In this case, we deduce some of the intrinsic
and extrinsic invariants of the general fibre from the ones of its central
fibre.
In the particular case of a central fibre of a semistable degeneration,
i.e. has only global normal crossing singularities and the total space of
the degeneration is smooth, some of the above invariants can be also computed
by topological methods (i.e., the Clemens-Schmid exact sequence). Our results
are more general, not only because the computations are independent on the fact
that is the central fibre of a degeneration, but also because the
degeneration is not semistable in general.Comment: latex2e, 26 pages, 11 figure
Effective Temperature in a Colloidal Glass
We study the Brownian motion of particles trapped by optical tweezers inside
a colloidal glass (Laponite) during the sol-gel transition. We use two methods
based on passive rheology to extract the effective temperature from the
fluctuations of the Brownian particles. All of them give a temperature that,
within experimental errors, is equal to the heat bath temperature. Several
interesting features concerning the statistical properties and the long time
correlations of the particles are observed during the transition.Comment: to be published in Philosophical Magazin
Failure time and critical behaviour of fracture precursors in heterogeneous materials
The acoustic emission of fracture precursors, and the failure time of samples
of heterogeneous materials (wood, fiberglass) are studied as a function of the
load features and geometry. It is shown that in these materials the failure
time is predicted with a good accuracy by a model of microcrack nucleation
proposed by Pomeau. We find that the time interval between events
(precursors) and the energy are power law distributed and that
the exponents of these power laws depend on the load history and on the
material. In contrast, the cumulated acoustic energy presents a critical
divergency near the breaking time which is % E\sim \left( \frac{\tau
-t}\tau \right) ^{-\gamma }. The positive exponent is independent,
within error bars, on all the experimental parameters.Comment: to be published on European Physical Journa
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