2,157 research outputs found
Decrumpling membranes by quantum effects
The phase diagram of an incompressible fluid membrane subject to quantum and
thermal fluctuations is calculated exactly in a large number of dimensions of
configuration space. At zero temperature, a crumpling transition is found at a
critical bending rigidity . For membranes of fixed lateral
size, a crumpling transition occurs at nonzero temperatures in an auxiliary
mean field approximation. As the lateral size L of the membrane becomes large,
the flat regime shrinks with .Comment: 9 pages, 4 figure
Dynamics of wrinkles on a vesicle in external flow
Recent experiments by Kantsler et. al. (2007) have shown that the
relaxational dynamics of a vesicle in external elongation flow is accompanied
by the formation of wrinkles on a membrane. Motivated by these experiments we
present a theory describing the dynamics of a wrinkled membrane. Formation of
wrinkles is related to the dynamical instability induced by negative surface
tension of the membrane. For quasi-spherical vesicles we perform analytical
study of the wrinkle structure dynamics. We derive the expression for the
instability threshold and identify three stages of the dynamics. The scaling
laws for the temporal evolution of wrinkling wavelength and surface tension are
established and confirmed numerically.Comment: 4 pages, 2 figure
Three-body problem in heteronuclear mixtures with resonant interspecies interaction
We use the zero-range approximation to study a system of two identical bosons
interacting resonantly with a third particle. The method is derived from
effective field theory. It reduces the three-body problem to an integral
equation which we then solve numerically. We also develop an alternative
approach which gives analytic solutions of the integral equation in coordinate
representation in the limit of vanishing total energy. The atom-dimer
scattering length, the rates of atom-dimer relaxation and three-body
recombination to shallow and to deep molecular states are calculated either
analytically or numerically with a well controlled accuracy for various
energies as functions of the mass ratio, scattering length, and three-body
parameter. We discuss in detail the relative positions of the recombination
loss peaks, which in the universal limit depend only on the mass ratio. Our
results have implications for ongoing and future experiments on Bose-Bose and
Bose-Fermi atomic mixtures.Comment: 13 pages, 8 figures, minor changes, published versio
Bulk and wetting phenomena in a colloidal mixture of hard spheres and platelets
Density functional theory is used to study binary colloidal fluids consisting
of hard spheres and thin platelets in their bulk and near a planar hard wall.
This system exhibits liquid-liquid coexistence of a phase that is rich in
spheres (poor in platelets) and a phase that is poor in spheres (rich in
platelets). For the mixture near a planar hard wall, we find that the phase
rich in spheres wets the wall completely upon approaching the liquid demixing
binodal from the sphere-poor phase, provided the concentration of the platelets
is smaller than a threshold value which marks a first-order wetting transition
at coexistence. No layering transitions are found in contrast to recent studies
on binary mixtures of spheres and non-adsorbing polymers or thin hard rods.Comment: 6 pages, 4 figure
Fluctuation induced interactions between domains in membranes
We study a model lipid bilayer composed of a mixture of two incompatible
lipid types which have a natural tendency to segregate in the absence of
membrane fluctuations. The membrane is mechanically characterized by a local
bending rigidity which varies with the average local lipid
composition . We show, in the case where varies weakly with
, that the effective interaction between lipids of the same type can
either be everywhere attractive or can have a repulsive component at
intermediate distances greater than the typical lipid size. When this
interaction has a repulsive component, it can prevent macro-phase separation
and lead to separation in mesophases with a finite domain size. This effect
could be relevant to certain experimental and numerical observations of
mesoscopic domains in such systems.Comment: 9 pages RevTex, 1 eps figur
Thermal Casimir drag in fluctuating classical fields
A uniformly moving inclusion which locally suppresses the fluctuations of a
classical thermally excited field is shown to experience a drag force which
depends on the dynamics of the field. It is shown that in a number of cases the
linear friction coefficient is dominated by short distance fluctuations and
takes a very simple form. Examples where this drag can occur are for stiff
objects, such as proteins, nonspecifically bound to more flexible ones such as
polymers and membranes.Comment: 4 pages RevTex, 2 figure
Are stress-free membranes really 'tensionless'?
In recent years it has been argued that the tension parameter driving the
fluctuations of fluid membranes, differs from the imposed lateral stress, the
'frame tension'. In particular, stress-free membranes were predicted to have a
residual fluctuation tension. In the present paper, this argument is
reconsidered and shown to be inherently inconsistent -- in the sense that a
linearized theory, the Monge model, is used to predict a nonlinear effect.
Furthermore, numerical simulations of one-dimensional stiff membranes are
presented which clearly demonstrate, first, that the internal 'intrinsic'
stress in membranes indeed differs from the frame tension as conjectured, but
second, that the fluctuations are nevertheless driven by the frame tension.
With this assumption, the predictions of the Monge model agree excellently with
the simulation data for stiffness and tension values spanning several orders of
magnitude
Membrane fluctuations near a plane rigid surface
We use analytical calculations and Monte Carlo simulations to determine the
thermal fluctuation spectrum of a membrane patch of a few tens of nanometer in
size, whose corners are located at a fixed distance above a plane rigid
surface. Our analysis shows that the surface influence on the bilayer
fluctuations can be effectively described in terms of a uniform confining
potential that grows quadratically with the height of the membrane relative
to the surface: . The strength of the harmonic
confining potential vanishes when the corners of the membrane patch are placed
directly on the surface (), and achieves its maximum value when is of
the order of a few nanometers. However, even at maximum strength the
confinement effect is quite small and has noticeable impact only on the
amplitude of the largest bending mode.Comment: Accepted for publication in Phys. Rev.
Path integrals for stiff polymers applied to membrane physics
Path integrals similar to those describing stiff polymers arise in the
Helfrich model for membranes. We show how these types of path integrals can be
evaluated and apply our results to study the thermodynamics of a minority
stripe phase in a bulk membrane. The fluctuation induced contribution to the
line tension between the stripe and the bulk phase is computed, as well as the
effective interaction between the two phases in the tensionless case where the
two phases have differing bending rigidities.Comment: 11 pages RevTex, 4 figure
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