694 research outputs found
Fluctuation Theorems for Entropy Production and Heat Dissipation in Periodically Driven Markov Chains
Asymptotic fluctuation theorems are statements of a Gallavotti-Cohen symmetry
in the rate function of either the time-averaged entropy production or heat
dissipation of a process. Such theorems have been proved for various general
classes of continuous-time deterministic and stochastic processes, but always
under the assumption that the forces driving the system are time independent,
and often relying on the existence of a limiting ergodic distribution. In this
paper we extend the asymptotic fluctuation theorem for the first time to
inhomogeneous continuous-time processes without a stationary distribution,
considering specifically a finite state Markov chain driven by periodic
transition rates. We find that for both entropy production and heat
dissipation, the usual Gallavotti-Cohen symmetry of the rate function is
generalized to an analogous relation between the rate functions of the original
process and its corresponding backward process, in which the trajectory and the
driving protocol have been time-reversed. The effect is that spontaneous
positive fluctuations in the long time average of each quantity in the forward
process are exponentially more likely than spontaneous negative fluctuations in
the backward process, and vice-versa, revealing that the distributions of
fluctuations in universes in which time moves forward and backward are related.
As an additional result, the asymptotic time-averaged entropy production is
obtained as the integral of a periodic entropy production rate that generalizes
the constant rate pertaining to homogeneous dynamics
Can a combination of the conformal thin-sandwich and puncture methods yield binary black hole solutions in quasi-equilibrium?
We consider combining two important methods for constructing
quasi-equilibrium initial data for binary black holes: the conformal
thin-sandwich formalism and the puncture method. The former seeks to enforce
stationarity in the conformal three-metric and the latter attempts to avoid
internal boundaries, like minimal surfaces or apparent horizons. We show that
these two methods make partially conflicting requirements on the boundary
conditions that determine the time slices. In particular, it does not seem
possible to construct slices that are quasi-stationary and avoid physical
singularities and simultaneously are connected by an everywhere positive lapse
function, a condition which must obtain if internal boundaries are to be
avoided. Some relaxation of these conflicting requirements may yield a soluble
system, but some of the advantages that were sought in combining these
approaches will be lost.Comment: 8 pages, LaTeX2e, 2 postscript figure
Active and driven hydrodynamic crystals
Motivated by the experimental ability to produce monodisperse particles in
microfluidic devices, we study theoretically the hydrodynamic stability of
driven and active crystals. We first recall the theoretical tools allowing to
quantify the dynamics of elongated particles in a confined fluid. In this
regime hydrodynamic interactions between particles arise from a superposition
of potential dipolar singularities. We exploit this feature to derive the
equations of motion for the particle positions and orientations. After showing
that all five planar Bravais lattices are stationary solutions of the equations
of motion, we consider separately the case where the particles are passively
driven by an external force, and the situation where they are self-propelling.
We first demonstrate that phonon modes propagate in driven crystals, which are
always marginally stable. The spatial structure of the eigenmodes depend solely
on the symmetries of the lattices, and on the orientation of the driving force.
For active crystals, the stability of the particle positions and orientations
depends not only on the symmetry of the crystals but also on the perturbation
wavelengths and on the crystal density. Unlike unconfined fluids, the stability
of active crystals is independent of the nature of the propulsion mechanism at
the single particle level. The square and rectangular lattices are found to be
linearly unstable at short wavelengths provided the volume fraction of the
crystals is high enough. Differently, hexagonal, oblique, and face-centered
crystals are always unstable. Our work provides a theoretical basis for future
experimental work on flowing microfluidic crystals.Comment: 10 pages, 10 figure
Microtubule length dependence of motor traffic in cells
In living cells, motor proteins, such as kinesin and dynein can move
processively along microtubule (MT), and also detach from or attach to MT
stochastically. Experiments have found that, the traffic of motor might be
jammed, and various theoretical models have been designed to understand this
traffic jam phenomenon. But previous studies mainly focus on motor
attachment/detachment rate dependent properties. Recent experiment of Leduc
{\it et al.} found that the traffic jam formation of motor protein kinesin
depends also on the length of MT [Proc. Natl. Acad. Sci. U.S.A. {\bf 109},
6100-6105 (2012)]. In this study, the MT length dependent properties of motor
traffic will be analyzed. We found that MT length has one {\it critical value}
, traffic jam occurs only when MT length . The jammed length of MT
increases with total MT length, while the non-jammed MT length might not change
monotonically with the total MT length. The critical value increases with
motor detachment rate from MT, but decreases with motor attachment rate to MT
Milagrito: a TeV air-shower array
Milagrito, a large, covered water-Cherenkov detector, was the world's first
air-shower-particle detector sensitive to cosmic gamma rays below 1 TeV. It
served as a prototype for the Milagro detector and operated from February 1997
to May 1998. This paper gives a description of Milagrito, a summary of the
operating experience, and early results that demonstrate the capabilities of
this technique.Comment: 38 pages including 24 figure
Prenatal exposure to maternal cigarette smoking and structural properties of the human corpus callosum
Alterations induced by prenatal exposure to nicotine have been observed in experimental (rodent) studies. While numerous developmental outcomes have been associated with prenatal exposure to maternal cigarette smoking (PEMCS) in humans, the possible relation with brain structure is less clear. Here we sought to elucidate the relation between PEMCS and structural properties of human corpus callosum in adolescence and early adulthood in a total of 1,747 youth. We deployed three community-based cohorts of 446 (age 25–27 years, 46% exposed), 934 (age 12–18 years, 47% exposed) and 367 individuals (age 18–21 years, 9% exposed). A mega-analysis revealed lower mean diffusivity in the callosal segments of exposed males. We speculate that prenatal exposure to maternal cigarette smoking disrupts the early programming of callosal structure and increases the relative portion of small-diameter fibres.</p
Health promotion: results of focus groups with African-American men
http://dx.doi.org/10.1016/j.jomh.2010.11.00
Multidimensional Conservation Laws: Overview, Problems, and Perspective
Some of recent important developments are overviewed, several longstanding
open problems are discussed, and a perspective is presented for the
mathematical theory of multidimensional conservation laws. Some basic features
and phenomena of multidimensional hyperbolic conservation laws are revealed,
and some samples of multidimensional systems/models and related important
problems are presented and analyzed with emphasis on the prototypes that have
been solved or may be expected to be solved rigorously at least for some cases.
In particular, multidimensional steady supersonic problems and transonic
problems, shock reflection-diffraction problems, and related effective
nonlinear approaches are analyzed. A theory of divergence-measure vector fields
and related analytical frameworks for the analysis of entropy solutions are
discussed.Comment: 43 pages, 3 figure
Search for Heavy Neutral and Charged Leptons in e+ e- Annihilation at LEP
A search for exotic unstable neutral and charged heavy leptons as well as for
stable charged heavy leptons is performed with the L3 detector at LEP.
Sequential, vector and mirror natures of heavy leptons are considered. No
evidence for their existence is found and lower limits on their masses are set
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