438 research outputs found
Efficiency at maximum power output for an engine with a passive piston
Efficiency at maximum power (MP) output for an engine with a passive piston
without mechanical controls between two reservoirs is theoretically studied. We
enclose a hard core gas partitioned by a massive piston in a
temperature-controlled container and analyze the efficiency at MP under a
heating and cooling protocol without controlling the pressure acting on the
piston from outside. We find the following three results: (i) The efficiency at
MP for a dilute gas is close to the Chambadal-Novikov-Curzon-Ahlborn (CNCA)
efficiency if we can ignore the side wall friction and the loss of energy
between a gas particle and the piston, while (ii) the efficiency for a
moderately dense gas becomes smaller than the CNCA efficiency even when the
temperature difference of reservoirs is small. (iii) Introducing the Onsager
matrix for an engine with a passive piston, we verify that the tight coupling
condition for the matrix of the dilute gas is satisfied, while that of the
moderately dense gas is not satisfied because of the inevitable heat leak. We
confirm the validity of these results using the molecular dynamics simulation
and introducing an effective mean-field-like model which we call stochastic
mean field model.Comment: 24 pages, 13 figure
Roles of Dry Friction in Fluctuating Motion of Adiabatic Piston
The motion of an adiabatic piston under dry friction is investigated to
clarify the roles of dry friction in non-equilibrium steady states. We clarify
that dry friction can reverse the direction of the piston motion and causes a
discontinuity or a cusp-like singularity for velocity distribution functions of
the piston. We also show that the heat fluctuation relation is modified under
dry friction.Comment: 8 pages, 4 figure
Minimal Model of Stochastic Athermal Systems: Origin of Non-Gaussian Noise
For a wide class of stochastic athermal systems, we derive Langevin-like
equations driven by non-Gaussian noise, starting from master equations and
developing a new asymptotic expansion. We found an explicit condition whereby
the non-Gaussian properties of the athermal noise become dominant for tracer
particles associated with both thermal and athermal environments. Furthermore,
we derive an inverse formula to infer microscopic properties of the athermal
bath from the statistics of the tracer particle. We apply our formulation to a
granular motor under viscous friction, and analytically obtain the angular
velocity distribution function. Our theory demonstrates that the non-Gaussian
Langevin equation is the minimal model of athermal systems.Comment: 10 pages, 5 figure
Simulation of granular jet: Is granular flow really a "perfect fluid?"
We perform three-dimensional simulations of a granular jet impact for both
frictional and frictionless grains. Small shear stress observed in the
experiment[X. Cheng et al., Phys. Rev. Lett. 99, 188001 (2007) ] is reproduced
through our simulation. However, the fluid state after the impact is far from a
perfect fluid, and thus, similarity between granular jets and quark gluon
plasma is superficial, because the observed viscosity is finite and its value
is consistent with the prediction of the kinetic theory.Comment: 8 pages 11 figures(9 figures: text, 2 figures: supplementary
material) 2 tables. To be published in Phys. Rev.
Geometric pumping induced by shear flow in dilute liquid crystalline polymer solutions
We investigate nonlinear rheology of dilute liquid crystalline polymer
solutions under time dependent two-directional shear flow. We analyze the
Smoluchowski equation, which describes the dynamics of the orientation of a
liquid crystalline polymer, by employing technique of the full counting
statistics. In the adiabatic limit, we derive the expression for time
integrated currents generated by a Berry-like curvature. Using this expression,
it is shown that the expectation values of the time-integrated angular velocity
of a liquid crystalline polymer and the time-integrated stress tensor are
generally not zero even if the time average of the shear rate is zero. The
validity of the theoretical calculations is confirmed by direct numerical
simulations of the Smoluchowski equation. Nonadiabatic effects are also
investigated by simulations and it is found that the time-integrated stress
tensor depends on the speed of the modulation of the shear rate if we adopt the
isotropic distribution as an initial state.Comment: 22 pages, 2 figure
Integrable Cosmological Models From Higher Dimensional Einstein Equations
We consider the cosmological models for the higher dimensional spacetime
which includes the curvatures of our space as well as the curvatures of the
internal space. We find that the condition for the integrability of the
cosmological equations is that the total space-time dimensions are D=10 or D=11
which is exactly the conditions for superstrings or M-theory. We obtain
analytic solutions with generic initial conditions in the four dimensional
Einstein frame and study the accelerating universe when both our space and the
internal space have negative curvatures.Comment: 10 pages, 2 figures, added reference, corrected typos(v2),
explanation improved and references and acknowledgments added, accepted for
publication in PRD(v3
Theory of law of the power spectrum in dissipative flows
It is demonstrated that law of the power spectrum with the
angular frequency in dissipative flows is produced by the emission of
dispersive waves from the antikink of an congested domain. The analytic theory
predicts the spectrum is proportional to for relatively low
frequency and for high frequency.Comment: 11 pages, 2 figure
The anomalous behavior of coefficient of normal restitution in the oblique impact
The coefficient of normal restitution in an oblique impact is theoretically
studied. Using a two-dimensional lattice models for an elastic disk and an
elastic wall, we demonstrate that the coefficient of normal restitution can
exceed one and has a peak against the incident angle in our simulation.
Finally, we explain these phenomena based upon the phenomenological theory of
elasticity.Comment: 4 pages, 4 figures, to be appeared in PR
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