4,137 research outputs found
Restoring a fluctuation-dissipation theorem in a nonequilibrium steady state
In a nonequilibrium steady state, the violation of the
fluctuation-dissipation theorem (FDT) is connected to breaking detailed
balance. For the velocity correlations of a driven colloidal particle we
calculate an explicit expression of the FDT violation. The equilibrium form of
the FDT can be restored by measuring the velocity with respect to the local
mean velocity.Comment: streamlined derivation and minor change
Thermodynamics of genuine non-equilibrium states under feedback control
For genuine non-equilibrium states that even at fixed external control
parameter exhibit dissipation, we extend the Hatano-Sasa equality to processes
with feedback control. The resulting bound on the maximal extractable work is
substantially sharper than what would follow from applying the Sagawa-Ueda
equality to transitions involving such states. For repeated measurements at
short enough intervals, the power thus extracted can even exceed the average
cost of driving as demonstrated explicitly with a simple, analytically solvable
example.Comment: 5 pages, 3 figure
Extracting work from a single heat bath through feedback
Work can be extracted from a single heat bath if additional information is
available. For the paradigmatic case of a Brownian particle in a harmonic
potential, whose position has been measured with finite precision, we determine
the optimal protocol for manipulating the center and stiffness of the potential
in order to maximize this work in a finite-time process. The bound on this work
imposed by a generalized second law inequality involving information can be
reached only if both position and stiffness of the potential are controlled and
the process is quasistatic. Estimates on the power delivered by such an
"information machine" operating cyclically follow from our analytical results.Comment: 6 pages, 3 figure
Critical behavior of interacting surfaces with tension
Wetting phenomena, molecular protrusions of lipid bilayers and membrane
stacks under lateral tension provide physical examples for interacting surfaces
with tension. Such surfaces are studied theoretically using functional
renormalization and Monte Carlo simulations. The critical behavior arising from
thermally-excited shape fluctuations is determined both for global quantities
such as the mean separation of these surfaces and for local quantities such as
the probabilities for local contacts.Comment: 13 pages, 17 figures; accepted for publication in The European
Physical Journa
Swinging and tumbling of elastic capsules in shear flow
The deformation of an elastic micro-capsule in an infinite shear flow is
studied numerically using a spectral method. The shape of the capsule and the
hydrodynamic flow field are expanded into smooth basis functions. Analytic
expressions for the derivative of the basis functions permit the evaluation of
elastic and hydrodynamic stresses and bending forces at specified grid points
in the membrane. Compared to methods employing a triangulation scheme, this
method has the advantage that the resulting capsule shapes are automatically
smooth, and few modes are needed to describe the deformation accurately.
Computations are performed for capsules both with spherical and ellipsoidal
unstressed reference shape. Results for small deformations of initially
spherical capsules coincide with analytic predictions. For initially
ellipsoidal capsules, recent approximative theories predict stable oscillations
of the tank-treading inclination angle, and a transition to tumbling at low
shear rate. Both phenomena have also been observed experimentally. Using our
numerical approach we could reproduce both the oscillations and the transition
to tumbling. The full phase diagram for varying shear rate and viscosity ratio
is explored. While the numerically obtained phase diagram qualitatively agrees
with the theory, intermittent behaviour could not be observed within our
simulation time. Our results suggest that initial tumbling motion is only
transient in this region of the phase diagram.Comment: 20 pages, 7 figure
Profiling of fine and coarse particle mass : Case studies of Saharan dust and Eyjafjallajökull/Grimsvötn volcanic plumes
© Author(s) 2012. This work is distributed under the Creative Commons Attribution 3.0 LicenseThe polarization lidar photometer networking (POLIPHON) method introduced to separate coarse-mode and fine-mode particle properties of Eyjafjallajokull volcanic aerosols in 2010 is extended to cover Saharan dust events as well. Furthermore, new volcanic dust observations performed after the Grimsvotn volcanic eruptions in 2011 are presented. The retrieval of particle mass concentrations requires mass-specific extinction coefficients. Therefore, a review of recently published mass-specific extinction coefficients for Saharan dust and volcanic dust is given. Case studies of four different scenarios corroborate the applicability of the profiling technique: (a) Saharan dust outbreak to central Europe, (b) Saharan dust plume mixed with biomass-burning smoke over Cape Verde, and volcanic aerosol layers originating from (c) the Eyjafjallajokull eruptions in 2010 and (d) the Grimsvotn eruptions in 2011. Strong differences in the vertical aerosol layering, aerosol mixing, and optical properties are observed for the different volcanic eventsPeer reviewe
Gravity-Induced Shape Transformations of Vesicles
We theoretically study the behavior of vesicles filled with a liquid of
higher density than the surrounding medium, a technique frequently used in
experiments. In the presence of gravity, these vesicles sink to the bottom of
the container, and eventually adhere even on non - attractive substrates. The
strong size-dependence of the gravitational energy makes large parts of the
phase diagram accessible to experiments even for small density differences. For
relatively large volume, non-axisymmetric bound shapes are explicitly
calculated and shown to be stable. Osmotic deflation of such a vesicle leads
back to axisymmetric shapes, and, finally, to a collapsed state of the vesicle.Comment: 11 pages, RevTeX, 3 Postscript figures uuencode
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