3 research outputs found
Experimental test of the Gallavotti-Cohen fluctuation theorem in turbulent flows
We test the fluctuation theorem from measurements in turbulent flows. We
study the time fluctuations of the force acting on an obstacle, and we consider
two experimental situations: the case of a von K\'arm\'an swirling flow between
counter-rotating disks (VK) and the case of a wind tunnel jet. We first study
the symmetries implied by the Gallavotti-Cohen fluctuation theorem (FT) on the
probability density distributions of the force fluctuations; we then test the
Sinai scaling. We observe that in both experiments the symmetries implied by
the FT are well verified, whereas the Sinai scaling is established, as
expected, only for long times
Work and heat fluctuations in two-state systems: a trajectory thermodynamics formalism
Two-state models provide phenomenological descriptions of many different
systems, ranging from physics to chemistry and biology. We investigate work
fluctuations in an ensemble of two-state systems driven out of equilibrium
under the action of an external perturbation. We calculate the probability
density P(W) that a work equal to W is exerted upon the system along a given
non-equilibrium trajectory and introduce a trajectory thermodynamics formalism
to quantify work fluctuations in the large-size limit. We then define a
trajectory entropy S(W) that counts the number of non-equilibrium trajectories
P(W)=exp(S(W)/kT) with work equal to W. A trajectory free-energy F(W) can also
be defined, which has a minimum at a value of the work that has to be
efficiently sampled to quantitatively test the Jarzynski equality. Within this
formalism a Lagrange multiplier is also introduced, the inverse of which plays
the role of a trajectory temperature. Our solution for P(W) exactly satisfies
the fluctuation theorem by Crooks and allows us to investigate
heat-fluctuations for a protocol that is invariant under time reversal. The
heat distribution is then characterized by a Gaussian component (describing
small and frequent heat exchange events) and exponential tails (describing the
statistics of large deviations and rare events). For the latter, the width of
the exponential tails is related to the aforementioned trajectory temperature.
Finite-size effects to the large-N theory and the recovery of work
distributions for finite N are also discussed. Finally, we pay particular
attention to the case of magnetic nanoparticle systems under the action of a
magnetic field H where work and heat fluctuations are predicted to be
observable in ramping experiments in micro-SQUIDs.Comment: 28 pages, 14 figures (Latex
Characterization of Fluorinated Polymers by Atmospheric-Solid-Analysis-Probe High-Resolution Mass Spectrometry (ASAP/HRMS) Combined with Kendrick-Mass-Defect Analysis
Fluorinated
polymers are a diverse and important class of polymers
with unique applications. However, characterization of fluorinated
polymers by conventional mass spectrometric methods is challenging
because (i) their high fluorine contents make them insoluble or only
sparingly soluble in most common solvents and (ii) commonly used matrices
employed for MALDI do not desorb or ionize them efficiently. In this
work, atmospheric-solid-analysis-probe (ASAP) high-resolution orbitrap
mass spectrometry (HRMS) was used as a new tool for the molecular
characterization of various fluorinated polymers, including polyvinylidene
fluoride (PVDF) and fluorinated copolymers containing PVDF and chlorotrifluoroethylene
(KEL-F 800) or PVDF and hexafluoropropylene (Viton A and Tecnoflon).
The major peaks of the observed distributions were assigned compositions,
but the high number of species required the use of an alternative
method to treat such complex data. Kendrick-mass defects (KMD) were
calculated on the basis of the “common-to-all” vinylidene
difluoride repeating unit. By plotting the KMD as a function of the
nominal Kendrick masses (NKM), specific patterns based on homologous
series emerged. Kendrick maps were therefore drawn to simplify the
mass spectra and provide confident peak assignments through homologous-series
recognition. A specific fingerprint for each polymer has been identified,
and the ability to discern the four species present in a blend through
KMD analysis was demonstrated