16,239 research outputs found
Transition to Chaotic Phase Synchronization through Random Phase Jumps
Phase synchronization is shown to occur between opposite cells of a ring
consisting of chaotic Lorenz oscillators coupled unidirectionally through
driving. As the coupling strength is diminished, full phase synchronization
cannot be achieved due to random generation of phase jumps. The brownian
dynamics underlying this process is studied in terms of a stochastic diffusion
model of a particle in a one-dimensional medium.Comment: Accepted for publication in IJBC, 10 pages, 5 jpg figure
Self-organization of ultrasound in viscous fluids
We report the theoretical and experimental demonstration of pattern formation
in acoustics. The system is an acoustic resonator containing a viscous fluid.
When the system is driven by an external periodic force, the ultrasonic field
inside the cavity experiences different pattern-forming instabilities leading
to the emergence of periodic structures. The system is also shown to possess
bistable regimes, in which localized states of the ultrasonic field develop.
The thermal nonlinearity in the viscous fluid, together with the
far-from-equilibrium conditions, are is the responsible of the observed
effects
A model for conservative chaos constructed from multi-component Bose-Einstein condensates with a trap in 2 dimensions
To show a mechanism leading to the breakdown of a particle picture for the
multi-component Bose-Einstein condensates(BECs) with a harmonic trap in high
dimensions, we investigate the corresponding 2- nonlinear Schr{\"o}dinger
equation (Gross-Pitaevskii equation) with use of a modified variational
principle. A molecule of two identical Gaussian wavepackets has two degrees of
freedom(DFs), the separation of center-of-masses and the wavepacket width.
Without the inter-component interaction(ICI) these DFs show independent regular
oscillations with the degenerate eigen-frequencies. The inclusion of ICI
strongly mixes these DFs, generating a fat mode that breaks a particle picture,
which however can be recovered by introducing a time-periodic ICI with zero
average. In case of the molecule of three wavepackets for a three-component
BEC, the increase of amplitude of ICI yields a transition from regular to
chaotic oscillations in the wavepacket breathing.Comment: 5 pages, 4 figure
Effects of anisotropy in a nonlinear crystal for squeezed vacuum generation
Squeezed vacuum (SV) can be obtained by an optical parametric amplifier (OPA)
with the quantum vacuum state at the input. We are interested in a degenerate
type-I OPA based on parametric down-conversion (PDC) where due to phase
matching requirements, an extraordinary polarized pump must impinge onto a
birefringent crystal with a large \chi(2) nonlinearity. As a consequence of the
optical anisotropy of the medium, the direction of propagation of the pump
wavevector does not coincide with the direction of propagation of its energy,
an effect known as transverse walk-off. For certain pump sizes and crystal
lengths, the transverse walk-off has a strong influence on the spatial spectrum
of the generated radiation, which in turn affects the outcome of any experiment
in which this radiation is employed. In this work we propose a method that
reduces the distortions of the two-photon amplitude (TPA) of the states
considered, by using at least two consecutive crystals instead of one. We show
that after anisotropy compensation the TPA becomes symmetric, allowing for a
simple Schmidt expansion, a procedure that in practice requires states that
come from experimental systems free of anisotropy effects
Projective filtering of a single spatial radiation eigenmode
Lossless filtering of a single coherent (Schmidt) mode from spatially
multimode radiation is a problem crucial for optics in general and for quantum
optics in particular. It becomes especially important in the case of
nonclassical light that is fragile to optical losses. An example is bright
squeezed vacuum generated via high-gain parametric down conversion or four-wave
mixing. Its highly multiphoton and multimode structure offers a huge increase
in the information capacity provided that each mode can be addressed
separately. However, the nonclassical signature of bright squeezed vacuum,
photon-number correlations, are highly susceptible to losses. Here we
demonstrate lossless filtering of a single spatial Schmidt mode by projecting
the spatial spectrum of bright squeezed vacuum on the eigenmode of a
single-mode fiber. Moreover, we show that the first Schmidt mode can be
captured by simply maximizing the fiber-coupled intensity. Importantly, the
projection operation does not affect the targeted mode and leaves it usable for
further applications.Comment: 10 pages, 9 figure
Density, structure and dynamics of water: the effect of Van der Waals interactions
It is known that ab initio molecular dynamics (AIMD) simulations of liquid
water, based on the generalized gradient approximation (GGA) to density
functional theory (DFT), yield structural and diffusive properties in
reasonable agreement with experiment only if artificially high temperatures are
used in the simulations. The equilibrium density, at normal conditions, of DFT
water has been recently shown by Schmidt et al. [J. Phys. chem. B, 113, 11959
(2009)] to be underestimated by different GGA functionals for exchange and
correlation, and corrected by the addition of interatomic pair potentials to
describe van derWaals (vdW) interactions. In this contribution we present a
DFTAIMD study of liquid water using several GGA functionals as well as the van
der Waals density functional (vdW-DF) of Dion et al. [Phys. Rev. Lett. 92,
246401(2004)]. As expected, we find that the density of water is grossly
underestimated by GGA functionals. When a vdW-DF is used, the density improves
drastically and the experimental diffusivity is reproduced without the need of
thermal corrections. We analyze the origin of the density differences between
all the functionals. We show that the vdW-DF increases the population of
non-H-bonded interstitial sites, at distances between the first and second
coordination shells. However, it excessively weakens the H-bond network,
collapsing the second coordination shell. This structural problem is partially
associated to the choice of GGA exchange in the vdW-DF. We show that a
different choice for the exchange functional is enough to achieve an overall
improvement both in structure and diffusivity.Comment: 11 pages, 9 figures, submitted. Revised versio
Conformal Spinning Quantum Particles in Complex Minkowski Space as Constrained Nonlinear Sigma Models in U(2,2) and Born's Reciprocity
We revise the use of 8-dimensional conformal, complex (Cartan) domains as a
base for the construction of conformally invariant quantum (field) theory,
either as phase or configuration spaces. We follow a gauge-invariant Lagrangian
approach (of nonlinear sigma-model type) and use a generalized Dirac method for
the quantization of constrained systems, which resembles in some aspects the
standard approach to quantizing coadjoint orbits of a group G. Physical wave
functions, Haar measures, orthonormal basis and reproducing (Bergman) kernels
are explicitly calculated in and holomorphic picture in these Cartan domains
for both scalar and spinning quantum particles. Similarities and differences
with other results in the literature are also discussed and an extension of
Schwinger's Master Theorem is commented in connection with closure relations.
An adaptation of the Born's Reciprocity Principle (BRP) to the conformal
relativity, the replacement of space-time by the 8-dimensional conformal domain
at short distances and the existence of a maximal acceleration are also put
forward.Comment: 33 pages, no figures, LaTe
Introduction: Tricksters, humour and activism
This special issue, entitled ‘The Trickster Activist in Global Humour and Comedy’, investigates the relevance of the concept of the trickster for explaining activist expressions that emanate from comedians, or that appear in comedy and humour more generally. Comedy has traditionally been viewed as an aesthetic or entertainment medium. It has often been charged with encouraging stereotype and the affirmation of mainstream audience beliefs. Despite this, we argue, there have been moments in recent history where comedians have given their performances an increased level of social and political consciousness that resonates with the public at large, or with sections of the public. Comedians, we argue, are able to reach this level of social commentary due to their potential to become tricksters. Paradoxically, the mythical trickster is a liminal entity, one that is adept at destruction as well as creation, or at conservativism as well radicalism. The articles in this issue explore the complexity of the trickster concept, showing some of the polysemy involved in the social activism enabled by comedy and humour
Lorentz-Violating Electrostatics and Magnetostatics
The static limit of Lorentz-violating electrodynamics in vacuum and in media
is investigated. Features of the general solutions include the need for
unconventional boundary conditions and the mixing of electrostatic and
magnetostatic effects. Explicit solutions are provided for some simple cases.
Electromagnetostatics experiments show promise for improving existing
sensitivities to parity-odd coefficients for Lorentz violation in the photon
sector.Comment: 9 page
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