47 research outputs found
The Incompressible Navier-Stokes Equations From Black Hole Membrane Dynamics
We consider the dynamics of a d+1 space-time dimensional membrane defined by
the event horizon of a black brane in (d+2)-dimensional asymptotically
Anti-de-Sitter space-time and show that it is described by the d-dimensional
incompressible Navier-Stokes equations of non-relativistic fluids. The fluid
velocity corresponds to the normal to the horizon while the rate of change in
the fluid energy is equal to minus the rate of change in the horizon
cross-sectional area. The analysis is performed in the Membrane Paradigm
approach to black holes and it holds for a general non-singular null
hypersurface, provided a large scale hydrodynamic limit exists. Thus we find,
for instance, that the dynamics of the Rindler acceleration horizon is also
described by the incompressible Navier-Stokes equations. The result resembles
the relation between the Burgers and KPZ equations and we discuss its
implications.Comment: 5 pages; v2: expanded discussion to clarify a few points, title
slightly change
3-D Perturbations in Conformal Turbulence
The effects of three-dimensional perturbations in two-dimensional turbulence
are investigated, through a conformal field theory approach. We compute scaling
exponents for the energy spectra of enstrophy and energy cascades, in a strong
coupling limit, and compare them to the values found in recent experiments. The
extension of unperturbed conformal turbulence to the present situation is
performed by means of a simple physical picture in which the existence of small
scale random forces is closely related to deviations of the exact
two-dimensional fluid motion.Comment: Discussion of intermittency improved. Figure include
The role of tank-treading motions in the transverse migration of a spheroidal vesicle in a shear flow
The behavior of a spheroidal vesicle, in a plane shear flow bounded from one
side by a wall, is analysed when the distance from the wall is much larger than
the spheroid radius. It is found that tank treading motions produce a
transverse drift away from the wall, proportional to the spheroid eccentricity
and the inverse square of the distance from the wall. This drift is independent
of inertia, and is completely determined by the characteristics of the vesicle
membrane. The relative strength of the contribution to drift from tank-treading
motions and from the presence of inertial corrections, is discussed.Comment: 16 pages, 1 figure, Latex. To appear on J. Phys. A (Math. Gen.
Drag forces on inclusions in classical fields with dissipative dynamics
We study the drag force on uniformly moving inclusions which interact
linearly with dynamical free field theories commonly used to study soft
condensed matter systems. Drag forces are shown to be nonlinear functions of
the inclusion velocity and depend strongly on the field dynamics. The general
results obtained can be used to explain drag forces in Ising systems and also
predict the existence of drag forces on proteins in membranes due to couplings
to various physical parameters of the membrane such as composition, phase and
height fluctuations.Comment: 14 pages, 7 figure