12,779 research outputs found
Stable resonances and signal propagation in a chaotic network of coupled units
We apply the linear response theory developed in \cite{Ruelle} to analyze how
a periodic signal of weak amplitude, superimposed upon a chaotic background, is
transmitted in a network of non linearly interacting units. We numerically
compute the complex susceptibility and show the existence of specific poles
(stable resonances) corresponding to the response to perturbations transverse
to the attractor. Contrary to the poles of correlation functions they depend on
the pair emitting/receiving units. This dynamic differentiation, induced by non
linearities, exhibits the different ability that units have to transmit a
signal in this network.Comment: 10 pages, 3 figures, to appear in Phys. rev.
Teleportation of continuous variable polarisation states
This paper discusses methods for the optical teleportation of continuous
variable polarisation states. We show that using two pairs of entangled beams,
generated using four squeezed beams, perfect teleportation of optical
polarisation states can be performed. Restricting ourselves to 3 squeezed
beams, we demonstrate that polarisation state teleportation can still exceed
the classical limit. The 3-squeezer schemes involve either the use of quantum
non-demolition measurement or biased entanglement generated from a single
squeezed beam. We analyse the efficacies of these schemes in terms of fidelity,
signal transfer coefficients and quantum correlations
On shotnoise and Brownian motion limits to the accuracy of particle positioning with optical tweezers
This paper examines the fundamental resolution limit of particle positioning with optical tweezers due to the combined effects of Brownian motion and optical shotnoise. It is found that Brownian motion dominates at low signal frequencies, whilst shotnoise dominates at high frequencies, with the exact crossover frequency varying by many orders of magnitude depending on experimental parameters such as particle size and trapping beam power. These results are significant both for analysis of the bandwidth limits of particle monitoring with optical tweezers and for enhancements of optical tweezer systems based on non-classical states of light
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Electrospray synthesis of PLGA TIPS microspheres
We successfully demonstrate the synthesis of polymer microspheres using a single electrospray source, and show their physical characterisation. Electrospray has proven to be a versatile method to manufacture particles, giving tight control over size with quasi-monodisperse size distributions. It is a liquid atomisation technique that generates a monodisperse population of highly charged liquid droplets over a broad size range (nanometres to tens of microns). The droplets contain liquid precursors for the in-flight synthesis of particles, and control over the trajectory of these droplets can be precisely manipulated with the use of electric fields to drive them to a grounded substrate. This study reports a method to synthesize poly(lactic-co-glycolic) acid (PLGA) microspheres using the electrospray and thermally induced phase separation (TIPS) techniques, followed by subsequent freeze-drying, for particle production. These microspheres are of interest as vehicles for controlled drug release systems
Stuffed Black Holes
Initial data corresponding to spacetimes containing black holes are
considered in the time symmetric case. The solutions are obtained by matching
across the apparent horizon different, conformally flat, spatial metrics. The
exterior metric is the vacuum solution obtained by the well known conformal
imaging method. The interior metric for every black hole is regular everywhere
and corresponds to a positive energy density. The resulting matched solutions
cover then the whole initial (Cauchy) hypersurface, without any singularity,
and can be useful for numerical applications. The simpler cases of one black
hole (Schwarzschild data) or two identical black holes (Misner data) are
explicitly solved. A procedure for extending this construction to the multiple
black hole case is also given, and it is shown to work for all time symmetric
vacuum solutions obtained by the conformal imaging method. The numerical
evolution of one such 'stuffed' black hole is compared with that of a pure
vacuum or 'plain' black hole in the spherically symmetric case.Comment: 12 pages, Latex, 4 postscript figures, corrected some typos, new
section about physical interpretatio
Collisions of boosted black holes: perturbation theory prediction of gravitational radiation
We consider general relativistic Cauchy data representing two nonspinning,
equal-mass black holes boosted toward each other. When the black holes are
close enough to each other and their momentum is sufficiently high, an
encompassing apparent horizon is present so the system can be viewed as a
single, perturbed black hole. We employ gauge-invariant perturbation theory,
and integrate the Zerilli equation to analyze these time-asymmetric data sets
and compute gravitational wave forms and emitted energies. When coupled with a
simple Newtonian analysis of the infall trajectory, we find striking agreement
between the perturbation calculation of emitted energies and the results of
fully general relativistic numerical simulations of time-symmetric initial
data.Comment: 5 pages (RevTex 3.0 with 3 uuencoded figures), CRSR-107
Improving teleportation of continuous variables by local operations
We study a continuous-variable (CV) teleportation protocol based on a shared
entangled state produced by the quantum-nondemolition (QND) interaction of two
vacuum states. The scheme utilizes the QND interaction or an unbalanced beam
splitter in the Bell measurement. It is shown that in the non-unity gain regime
the signal transfer coefficient can be enhanced while the conditional variance
product remains preserved by applying appropriate local squeezing operation on
sender's part of the shared entangled state. In the unity gain regime it is
demonstrated that the fidelity of teleportation can be increased with the help
of the local squeezing operations on parts of the shared entangled state that
convert effectively our scheme to the standard CV teleportation scheme.
Further, it is proved analytically that such a choice of the local symplectic
operations minimizes the noise by which the mean number of photons in the input
state is increased during the teleportation. Finally, our analysis reveals that
the local symplectic operation on sender's side can be integrated into the Bell
measurement if the interaction constant of the interaction in the Bell
measurement can be adjusted properly.Comment: 10 pages, 1 figure, discussion of the non-unity gain teleportation is
adde
The Innermost Stable Circular Orbit of Binary Black Holes
We introduce a new method to construct solutions to the constraint equations
of general relativity describing binary black holes in quasicircular orbit.
Black hole pairs with arbitrary momenta can be constructed with a simple method
recently suggested by Brandt and Bruegmann, and quasicircular orbits can then
be found by locating a minimum in the binding energy along sequences of
constant horizon area. This approach produces binary black holes in a
"three-sheeted" manifold structure, as opposed to the "two-sheeted" structure
in the conformal-imaging approach adopted earlier by Cook. We focus on locating
the innermost stable circular orbit and compare with earlier calculations. Our
results confirm those of Cook and imply that the underlying manifold structure
has a very small effect on the location of the innermost stable circular orbit.Comment: 8 pages, 3 figures, RevTex, submitted to PR
Initial Data and Coordinates for Multiple Black Hole Systems
We present here an alternative approach to data setting for spacetimes with
multiple moving black holes generalizing the Kerr-Schild form for rotating or
non-rotating single black holes to multiple moving holes. Because this scheme
preserves the Kerr-Schild form near the holes, it selects out the behaviour of
null rays near the holes, may simplify horizon tracking, and may prove useful
in computational applications. For computational evolution, a discussion of
coordinates (lapse function and shift vector) is given which preserves some of
the properties of the single-hole Kerr-Schild form
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