28,866 research outputs found
Interactions between Membrane Inclusions on Fluctuating Membranes
We model membrane proteins as anisotropic objects characterized by
symmetric-traceless tensors and determine the coupling between these
order-parameters and membrane curvature. We consider the interactions between
transmembrane proteins that respect up-down (reflection) symmetry of bilayer
membranes and that have circular or non-circular cross-sectional areas in the
tangent-plane of membranes. Using a field theoretic approach, we find
non-entropic interactions between reflection-symmetry-breaking
transmembrane proteins with circular cross-sectional area and entropic
interactions between transmembrane proteins with circular
cross-section that do not break up-down symmetry in agreement with previous
calculations. We also find anisotropic interactions between
reflection-symmetry-conserving transmembrane proteins with non-circular
cross-section, anisotropic interactions between
reflection-symmetry-breaking transmembrane proteins with non-circular
cross-section, and non-entropic many-particle interactions among
non-transmembrane proteins. For large , these interactions might provide the
dominant force inducing aggregation of the membrane proteins.Comment: REVTEX, 29 pages with 4 postscript figures compressed using uufiles.
Introduction and Discussion sections revised. To appear in J. Phys. France I
(September
Disclination Asymmetry in Deformable Hexatic Membranes and the Kosterlitz-Thouless Transitions
A disclination in a hexatic membrane favors the development of Gaussian
curvature localized near its core. The resulting global structure of the
membrane has mean curvature, which is disfavored by curvature energy. Thus a
membrane with an isolated disclination undergoes a buckling transition from a
flat to a buckled state as the ratio of the bending rigidity
to the hexatic rigidity is decreased. In this paper we
calculate the buckling transition and the energy of both a positive and a
negative disclination. A negative disclination has a larger energy and a
smaller critical value of at buckling than does a positive
disclination. We use our results to obtain a crude estimate of the
Kosterlitz-Thouless transition temperature in a membrane. This estimate is
higher than the transition temperature recently obtained by the authors in a
renormalization calculation.Comment: REVTEX, 16 pages with 5 postscript figures compressed using uufiles.
Accepted for publication in J. Phys. France
General polygamy inequality of multi-party quantum entanglement
Using entanglement of assistance, we establish a general polygamy inequality
of multi-party entanglement in arbitrary dimensional quantum systems. For
multi-party closed quantum systems, we relate our result with the monogamy of
entanglement to show that the entropy of entanglement is an universal
entanglement measure that bounds both monogamy and polygamy of multi-party
quantum entanglement.Comment: 4 pages, 1 figur
Violation of Bell's inequality using classical measurements and non-linear local operations
We find that Bell's inequality can be significantly violated (up to
Tsirelson's bound) with two-mode entangled coherent states using only homodyne
measurements. This requires Kerr nonlinear interactions for local operations on
the entangled coherent states. Our example is a demonstration of
Bell-inequality violations using classical measurements. We conclude that
entangled coherent states with coherent amplitudes as small as 0.842 are
sufficient to produce such violations.Comment: 6 pages, 5 figures, to be published in Phys. Rev.
Disruption of Molecular Clouds by Expansion of Dusty H II Regions
Dynamical expansion of H II regions around star clusters plays a key role in
dispersing the surrounding dense gas and therefore in limiting the efficiency
of star formation in molecular clouds. We use a semi-analytic method and
numerical simulations to explore expansion of spherical dusty H II regions and
surrounding neutral shells and the resulting cloud disruption. Our model for
shell expansion adopts the static solutions of Draine (2011) for dusty H II
regions and considers the contact outward forces on the shell due to radiation
and thermal pressures as well as the inward gravity from the central star and
the shell itself. We show that the internal structure we adopt and the shell
evolution from the semi-analytic approach are in good agreement with the
results of numerical simulations. Strong radiation pressure in the interior
controls the shell expansion indirectly by enhancing the density and pressure
at the ionization front. We calculate the minimum star formation efficiency
required for cloud disruption as a function of the cloud's
total mass and mean surface density. Within the adopted spherical geometry, we
find that typical giant molecular clouds in normal disk galaxies have
%, with comparable gas and radiation pressure
effects on shell expansion. Massive cluster-forming clumps require a
significantly higher efficiency of % for disruption,
produced mainly by radiation-driven expansion. The disruption time is typically
of the order of a free-fall timescale, suggesting that the cloud disruption
occurs rapidly once a sufficiently luminous H II region is formed. We also
discuss limitations of the spherical idealization.Comment: 23 pages, 14 figures; Accepted for publication in Ap
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