37 research outputs found
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
Fluctuation theorems for harmonic oscillators
We study experimentally the thermal fluctuations of energy input and
dissipation in a harmonic oscillator driven out of equilibrium, and search for
Fluctuation Relations. We study transient evolution from the equilibrium state,
together with non equilibrium steady states. Fluctuations Relations are
obtained experimentally for both the work and the heat, for the stationary and
transient evolutions. A Stationary State Fluctuation Theorem is verified for
the two time prescriptions of the torque. But a Transient Fluctuation Theorem
is satisfied for the work given to the system but not for the heat dissipated
by the system in the case of linear forcing. Experimental observations on the
statistical and dynamical properties of the fluctuation of the angle, we derive
analytical expressions for the probability density function of the work and the
heat. We obtain for the first time an analytic expression of the probability
density function of the heat. Agreement between experiments and our modeling is
excellent
Thermodynamic time asymmetry in nonequilibrium fluctuations
We here present the complete analysis of experiments on driven Brownian
motion and electric noise in a circuit, showing that thermodynamic entropy
production can be related to the breaking of time-reversal symmetry in the
statistical description of these nonequilibrium systems. The symmetry breaking
can be expressed in terms of dynamical entropies per unit time, one for the
forward process and the other for the time-reversed process. These entropies
per unit time characterize dynamical randomness, i.e., temporal disorder, in
time series of the nonequilibrium fluctuations. Their difference gives the
well-known thermodynamic entropy production, which thus finds its origin in the
time asymmetry of dynamical randomness, alias temporal disorder, in systems
driven out of equilibrium.Comment: to be published in : Journal of Statistical Mechanics: theory and
experimen
Path-integral analysis of fluctuation theorems for general Langevin processes
We examine classical, transient fluctuation theorems within the unifying
framework of Langevin dynamics. We explicitly distinguish between the effects
of non-conservative forces that violate detailed balance, and non-autonomous
dynamics arising from the variation of an external parameter. When both these
sources of nonequilibrium behavior are present, there naturally arise two
distinct fluctuation theorems.Comment: 24 pages, one figur
Non-equilibrium work relations
This is a brief review of recently derived relations describing the behaviour
of systems far from equilibrium. They include the Fluctuation Theorem,
Jarzynski's and Crooks' equalities, and an extended form of the Second
Principle for general steady states. They are very general and their proofs
are, in most cases, disconcertingly simple.Comment: Brief Summer School Lecture Note
The distribution of work performed on a NIS junction
We propose an experimental setup to measure the work performed in a normal-metal/insulator/
superconducting (NIS) junction, subjected to a voltage change and in contact with a thermal bath. We
compute the performed work and argue that the associated heat release can be measured
experimentally. Our results are based on an equivalence between the dynamics of the NIS junction
and that of an assembly of two-level systems subjected to a circularly polarised field, for which we can
determine the work-characteristic function exactly. The average work dissipated by the NIS junction,
as well as its fluctuations, are determined. From the work characteristic function, we also compute the
work probability-distribution and show that it does not have a Gaussian character. Our results allow
for a direct experimental test of the Crooks–Tasaki fluctuation relation.Program of Recruitment of Post Doctoral Researchers for the Portuguese Scientific and Technological System, within the Operational Program Human Potential (POPH) of the QREN, participated by the European Social Fund (ESF) and national funds of the Portuguese Ministry of Education and Science (MEC); Danish National Research Foundation, Project No. DNRF58; National Natural Science Foundation of China, Grant No. 1147425
Fluctuations of the total entropy production in stochastic systems
Fluctuations of the excess heat in an out of equilibrium steady state are
experimentally investigated in two stochastic systems : an electric circuit
with an imposed mean current and a harmonic oscillator driven out of
equilibrium by a periodic torque. In these two linear systems, we study excess
heat that represents the difference between the dissipated heat out of
equilibrium and the dissipated heat at equilibrium. Fluctuation theorem holds
for the excess heat in the two experimental systems for all observation times
and for all fluctuation magnitudes.Comment: 6
Single-molecule experiments in biological physics: methods and applications
I review single-molecule experiments (SME) in biological physics. Recent
technological developments have provided the tools to design and build
scientific instruments of high enough sensitivity and precision to manipulate
and visualize individual molecules and measure microscopic forces. Using SME it
is possible to: manipulate molecules one at a time and measure distributions
describing molecular properties; characterize the kinetics of biomolecular
reactions and; detect molecular intermediates. SME provide the additional
information about thermodynamics and kinetics of biomolecular processes. This
complements information obtained in traditional bulk assays. In SME it is also
possible to measure small energies and detect large Brownian deviations in
biomolecular reactions, thereby offering new methods and systems to scrutinize
the basic foundations of statistical mechanics. This review is written at a
very introductory level emphasizing the importance of SME to scientists
interested in knowing the common playground of ideas and the interdisciplinary
topics accessible by these techniques. The review discusses SME from an
experimental perspective, first exposing the most common experimental
methodologies and later presenting various molecular systems where such
techniques have been applied. I briefly discuss experimental techniques such as
atomic-force microscopy (AFM), laser optical tweezers (LOT), magnetic tweezers
(MT), biomembrane force probe (BFP) and single-molecule fluorescence (SMF). I
then present several applications of SME to the study of nucleic acids (DNA,
RNA and DNA condensation), proteins (protein-protein interactions, protein
folding and molecular motors). Finally, I discuss applications of SME to the
study of the nonequilibrium thermodynamics of small systems and the
experimental verification of fluctuation theorems. I conclude with a discussion
of open questions and future perspectives.Comment: Latex, 60 pages, 12 figures, Topical Review for J. Phys. C (Cond.
Matt
DFT-inspired methods for quantum thermodynamics
In the framework of quantum thermodynamics, we propose a method to
quantitatively describe thermodynamic quantities for out-of-equilibrium
interacting many-body systems. The method is articulated in various
approximation protocols which allow to achieve increasing levels of accuracy,
it is relatively simple to implement even for medium and large number of
interactive particles, and uses tools and concepts from density functional
theory. We test the method on the driven Hubbard dimer at half filling, and
compare exact and approximate results. We show that the proposed method
reproduces the average quantum work to high accuracy: for a very large region
of parameter space (which cuts across all dynamical regimes) estimates are
within 10% of the exact results
Influence of oxidation on mechanical properties of 2.5 D carbon-carbon composite
A 2.5 D laminated Carbon-Carbon composite was studied in the present work. The typical mechanical behaviour of the non-oxidised and of the oxidised composite material was pointed out. The role of oxidation on mechanical properties was estimated. The mechanical characterisation was made by tensile, compression, torsion and Iosipescu tests. Overall, the oxidation leads to a reduction of the initial moduli. This decrease is more important for tests which mechanically request more closely the fibre/matrix interfaces