8,592 research outputs found
Geodesic Transport Barriers in Jupiter's Atmosphere: A Video-Based Analysis
Jupiter's zonal jets and Great Red Spot are well known from still images. Yet
the planet's atmosphere is highly unsteady, which suggests that the actual
material transport barriers delineating its main features should be
time-dependent. Rare video footages of Jupiter's clouds provide an opportunity
to verify this expectation from optically reconstructed velocity fields.
Available videos, however, provide short-time and temporally aperiodic velocity
fields that defy classical dynamical systems analyses focused on asymptotic
features. To this end, we use here the recent theory of geodesic transport
barriers to uncover finite-time mixing barriers in the wind field extracted
from a video captured by NASA's Cassini space mission. More broadly, the
approach described here provides a systematic and frame-invariant way to
extract dynamic coherent structures from time-resolved remote observations of
unsteady continua
Measuring topology in a laser-coupled honeycomb lattice: From Chern insulators to topological semi-metals
Ultracold fermions trapped in a honeycomb optical lattice constitute a
versatile setup to experimentally realize the Haldane model [Phys. Rev. Lett.
61, 2015 (1988)]. In this system, a non-uniform synthetic magnetic flux can be
engineered through laser-induced methods, explicitly breaking time-reversal
symmetry. This potentially opens a bulk gap in the energy spectrum, which is
associated with a non-trivial topological order, i.e., a non-zero Chern number.
In this work, we consider the possibility of producing and identifying such a
robust Chern insulator in the laser-coupled honeycomb lattice. We explore a
large parameter space spanned by experimentally controllable parameters and
obtain a variety of phase diagrams, clearly identifying the accessible
topologically non-trivial regimes. We discuss the signatures of Chern
insulators in cold-atom systems, considering available detection methods. We
also highlight the existence of topological semi-metals in this system, which
are gapless phases characterized by non-zero winding numbers, not present in
Haldane's original model.Comment: 30 pages, 12 figures, 4 Appendice
Generalized 4 4 Matrix Formalism for Light Propagation in Anisotropic Stratified Media: Study of Surface Phonon Polaritons in Polar Dielectric Heterostructures
We present a generalized 4 4 matrix formalism for the description of
light propagation in birefringent stratified media. In contrast to previous
work, our algorithm is capable of treating arbitrarily anisotropic or
isotropic, absorbing or non-absorbing materials and is free of discontinous
solutions. We calculate the reflection and transmission coefficients and derive
equations for the electric field distribution for any number of layers. The
algorithm is easily comprehensible and can be straight forwardly implemented in
a computer program. To demonstrate the capabilities of the approach, we
calculate the reflectivities, electric field distributions, and dispersion
curves for surface phonon polaritons excited in the Otto geometry for selected
model systems, where we observe several distinct phenomena ranging from
critical coupling to mode splitting, and surface phonon polaritons in
hyperbolic media
Numerical Relativity: A review
Computer simulations are enabling researchers to investigate systems which
are extremely difficult to handle analytically. In the particular case of
General Relativity, numerical models have proved extremely valuable for
investigations of strong field scenarios and been crucial to reveal unexpected
phenomena. Considerable efforts are being spent to simulate astrophysically
relevant simulations, understand different aspects of the theory and even
provide insights in the search for a quantum theory of gravity. In the present
article I review the present status of the field of Numerical Relativity,
describe the techniques most commonly used and discuss open problems and (some)
future prospects.Comment: 2 References added; 1 corrected. 67 pages. To appear in Classical and
Quantum Gravity. (uses iopart.cls
Stability and Quasinormal Modes of Black holes in Tensor-Vector-Scalar theory: Scalar Field Perturbations
The imminent detection of gravitational waves will trigger precision tests of
gravity through observations of quasinormal ringing of black holes. While
General Relativity predicts just two polarizations of gravitational waves, the
so-called plus and cross polarizations, numerous alternative theories of
gravity predict up to six different polarizations which will potentially be
observed in current and future generations of gravitational wave detectors.
Bekenstein's Tensor-Vector-Scalar (TeVeS) theory and its generalization fall
into one such class of theory that predict the full gamut of six polarizations
of gravitational waves. In this paper we begin the study of quasinormal modes
(QNMs) in TeVeS by studying perturbations of the scalar field in a spherically
symmetric background. We show that, at least in the case where superluminal
propagation of perturbations is not present, black holes are generically stable
to this kind of perturbation. We also make a unique prediction that, as the
limit of the various coupling parameters of the theory tend to zero, the QNM
spectrum tends to times the QNM spectrum induced by scalar
perturbations of a Schwarzschild black hole in General Relativity due to the
intrinsic presence of the background vector field. We further show that the QNM
spectrum does not vary significantly from this value for small values of the
theory's coupling parameters, however can vary by as much as a few percent for
larger, but still physically relevant parameters.Comment: Published in Physical Review
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