2,429 research outputs found
Membrane morphology induced by anisotropic proteins
There are a great many proteins that localize to and collectively generate
curvature in biological fluid membranes. We study changes in the topology of
fluid membranes due to the presence of highly anisotropic, curvature-inducing
proteins. Generically, we find a surprisingly rich phase diagram with phases of
both positive and negative Gaussian curvature. As a concrete example modeled on
experiments, we find that a lamellar phase in a negative Gaussian curvature
regime exhibits a propensity to form screw dislocations of definite burgers
scalar but of both chirality. The induced curvature depends strongly on the
membrane rigidity, suggesting membrane composition can be a factor regulating
membrane sculpting to to curvature-inducing proteins.Comment: 4 pages, 4 figure
Self-Assembly on a Cylinder: A Model System for Understanding the Constraint of Commensurability
A crystal lattice, when confined to the surface of a cylinder, must have a
periodic structure that is commensurate with the cylinder circumference. This
constraint can frustrate the system, leading to oblique crystal lattices or to
structures with a chiral seam known as a "line slip" phase, neither of which
are stable for isotropic particles in equilibrium on flat surfaces. In this
study, we use molecular dynamics simulations to find the steady-state structure
of spherical particles with short-range repulsion and long-range attraction far
below the melting temperature. We vary the range of attraction using the
Lennard-Jones and Morse potentials and find that a shorter-range attraction
favors the line-slip. We develop a simple model based only on geometry and bond
energy to predict when the crystal or line-slip phases should appear, and find
reasonable agreement with the simulations. The simplicity of this model allows
us to understand the influence of the commensurability constraint, an
understanding that might be extended into the more general problem of
self-assembling particles in strongly confined spaces.Comment: 12 pages, 9 figures. Submitted for publication, 201
Thermodynamics of conformal fields in topologically non-trivial space-time backgrounds
We analyze the finite temperature behaviour of massless conformally coupled
scalar fields in homogeneous lens spaces . High and low
temperature expansions are explicitly computed and the behavior of
thermodynamic quantities under thermal duality is scrutinized. The analysis of
the entropy of the different lens spaces in the high-temperature limit points
out the appearance of a topological nonextensive entropy, besides the standard
Stefan-Boltzmann extensive term. The remaining terms are exponentially
suppressed by the temperature. The topological entropy appears as a subleading
correction to the free energy that can be obtained from the determinant of the
lens space conformal Laplacian operator. In the low-temperature limit the
leading term in the free energy is the Casimir energy and there is no trace of
any power correction in any lens space. In fact, the remaining corrections are
always exponentially suppressed by the inverse of the temperature. The duality
between the results of both expansions is further analyzed in the paper.Comment: 21 pages, 2 figure
Charge density and conductivity of disordered Berry-Mondragon graphene nanoribbons
We consider gated graphene nanoribbons subject to Berry-Mondragon boundary
conditions in the presence of weak impurities. Using field--theoretical
methods, we calculate the density of charge carriers (and, thus, the quantum
capacitance) as well as the optical and DC conductivities at zero temperature.
We discuss in detail their dependence on the gate (chemical) potential, and
reveal a non-linear behaviour induced by the quantization of the transversal
momentum.Comment: 17 pages, version accepted for publication in EPJ
Elliptic Phases: A Study of the Nonlinear Elasticity of Twist-Grain Boundaries
We develop an explicit and tractable representation of a twist-grain-boundary
phase of a smectic A liquid crystal. This allows us to calculate the
interaction energy between grain boundaries and the relative contributions from
the bending and compression deformations. We discuss the special stability of
the 90 degree grain boundaries and discuss the relation of this structure to
the Schwarz D surface.Comment: 4 pages, 2 figure
Bjerrum pairing correlations at charged interfaces
Electrostatic correlations play a fundamental role in aqueous solutions. In
this letter, we identify transverse and lateral correlations as two mutually
exclusive regimes. We show that the transverse regime leads to binding by
generalization of Bjerrum pair formation theory, yielding binding constants
from first-principle statistical-mechanical calculations. We compare our
theoretical predictions with experiments on charged membranes and Langmuir
monolayers and find good agreement. We contrast our approach with existing
theories in the strong-coupling limit and on charged modulated interfaces, and
discuss different scenarios that lead to charge reversal and equal-sign
attraction by macro-ions.Comment: 7 pages, 4 figure
Topological mechanics of origami and kirigami
Origami and kirigami have emerged as potential tools for the design of
mechanical metamaterials whose properties such as curvature, Poisson ratio, and
existence of metastable states can be tuned using purely geometric criteria. A
major obstacle to exploiting this property is the scarcity of tools to identify
and program the flexibility of fold patterns. We exploit a recent connection
between spring networks and quantum topological states to design origami with
localized folding motions at boundaries and study them both experimentally and
theoretically. These folding motions exist due to an underlying topological
invariant rather than a local imbalance between constraints and degrees of
freedom. We give a simple example of a quasi-1D folding pattern that realizes
such topological states. We also demonstrate how to generalize these
topological design principles to two dimensions. A striking consequence is that
a domain wall between two topologically distinct, mechanically rigid structures
is deformable even when constraints locally match the degrees of freedom.Comment: 5 pages, 3 figures + ~5 pages S
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