9,244 research outputs found
Mapping vesicle shapes into the phase diagram: A comparison of experiment and theory
Phase-contrast microscopy is used to monitor the shapes of micron-scale
fluid-phase phospholipid-bilayer vesicles in aqueous solution. At fixed
temperature, each vesicle undergoes thermal shape fluctuations. We are able
experimentally to characterize the thermal shape ensemble by digitizing the
vesicle outline in real time and storing the time-sequence of images. Analysis
of this ensemble using the area-difference-elasticity (ADE) model of vesicle
shapes allows us to associate (map) each time-sequence to a point in the
zero-temperature (shape) phase diagram. Changing the laboratory temperature
modifies the control parameters (area, volume, etc.) of each vesicle, so it
sweeps out a trajectory across the theoretical phase diagram. It is a
nontrivial test of the ADE model to check that these trajectories remain
confined to regions of the phase diagram where the corresponding shapes are
locally stable. In particular, we study the thermal trajectories of three
prolate vesicles which, upon heating, experienced a mechanical instability
leading to budding. We verify that the position of the observed instability and
the geometry of the budded shape are in reasonable accord with the theoretical
predictions. The inability of previous experiments to detect the ``hidden''
control parameters (relaxed area difference and spontaneous curvature) make
this the first direct quantitative confrontation between vesicle-shape theory
and experiment.Comment: submitted to PRE, LaTeX, 26 pages, 11 ps-fi
Massive Three-Dimensional Supergravity From R+R^2 Action in Six Dimensions
We obtain a three-parameter family of massive N=1 supergravities in three
dimensions from the 3-sphere reduction of an off-shell N=(1,0) six-dimensional
Poincare supergravity that includes a curvature squared invariant. The
three-dimensional theory contains an off-shell supergravity multiplet and an
on-shell scalar matter multiplet. We then generalise this in three dimensions
to an eight-parameter family of supergravities. We also find a duality
relationship between the six-dimensional theory and the N=(1,0) six-dimensional
theory obtained through a T^4 reduction of the heterotic string effective
action that includes the higher-order terms associated with the
supersymmetrisation of the anomaly-cancelling \tr(R\wedge R) term.Comment: Latex, 32 Pages, an equation is corrected, a few new equations and a
number of clarifying remarks are adde
Testing for Majorana Zero Modes in a Px+iPy Superconductor at High Temperature by Tunneling Spectroscopy
Directly observing a zero energy Majorana state in the vortex core of a
chiral superconductor by tunneling spectroscopy requires energy resolution
better than the spacing between core states . We show that
nevertheless, its existence can be decisively tested by comparing the
temperature broadened tunneling conductance of a vortex with that of an
antivortex even at temperatures .Comment: 5 pages, 4 figure
Noncommutative Lorentz Symmetry and the Origin of the Seiberg-Witten Map
We show that the noncommutative Yang-Mills field forms an irreducible
representation of the (undeformed) Lie algebra of rigid translations, rotations
and dilatations. The noncommutative Yang-Mills action is invariant under
combined conformal transformations of the Yang-Mills field and of the
noncommutativity parameter \theta. The Seiberg-Witten differential equation
results from a covariant splitting of the combined conformal transformations
and can be computed as the missing piece to complete a covariant conformal
transformation to an invariance of the action.Comment: 20 pages, LaTeX. v2: Streamlined proofs and extended discussion of
Lorentz transformation
Characterization of qutrit channels in terms of their covariance and symmetry properties
We characterize the completely positive trace-preserving maps on qutrits
(qutrit channels) according to their covariance and symmetry properties. Both
discrete and continuous groups are considered. It is shown how each symmetry
group restricts arbitrariness in the parameters of the channel to a very small
set. Although the explicit examples are related to qutrit channels, the
formalism is sufficiently general to be applied to qudit channels
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