4,299 research outputs found
Spreading of Perturbations in Long-Range Interacting Classical Lattice Models
Lieb-Robinson-type bounds are reported for a large class of classical
Hamiltonian lattice models. By a suitable rescaling of energy or time, such
bounds can be constructed for interactions of arbitrarily long range. The bound
quantifies the dependence of the system's dynamics on a perturbation of the
initial state. The effect of the perturbation is found to be effectively
restricted to the interior of a causal region of logarithmic shape, with only
small, algebraically decaying effects in the exterior. A refined bound, sharper
than conventional Lieb-Robinson bounds, is required to correctly capture the
shape of the causal region, as confirmed by numerical results for classical
long-range chains. We discuss the relevance of our findings for the
relaxation to equilibrium of long-range interacting lattice models.Comment: 4+6 pages, 3+2 figure
Poincar\'e profiles of groups and spaces
We introduce a spectrum of monotone coarse invariants for metric measure
spaces called Poincar\'{e} profiles. The two extremes of this spectrum
determine the growth of the space, and the separation profile as defined by
Benjamini--Schramm--Tim\'{a}r. In this paper we focus on properties of the
Poincar\'{e} profiles of groups with polynomial growth, and of hyperbolic
spaces, where we deduce a connection between these profiles and conformal
dimension. As applications, we use these invariants to show the non-existence
of coarse embeddings in a variety of examples.Comment: 55 pages. To appear in Revista Matem\'atica Iberoamerican
Is nonlinear propagation responsible for the brassiness of elephant trumpet calls?
African elephants (Loxodonta africana) produce a broad diversity of sounds ranging from infrasonic rumbles to much higher frequency trumpets. Trumpet calls are very loud voiced signals given by highly aroused elephants, and appear to be produced by a forceful expulsion of air through the trunk. Some trumpet calls have a very distinctive quality that is unique in the animal kingdom, but resemble the "brassy" sounds that can be produced with brass musical instruments such as trumpets or trombones.
Brassy musical sounds are characterised by a flat spectral slope caused by the nonlinear propagation of the source wave as it travels through the long bore of the instrument. The extent of this phenomenon, which normally occurs at high intensity levels (e.g. fortissimo), depends on the fundamental frequency (F0) of the source as well as on the length of the resonating tube.
Interestingly, the length of the vocal tract of the elephant (as measured from the vocal folds to the end of the trunk) approximates the critical length for shockwave formation, given the fundamental frequency and intensity of trumpet calls. We suggest that this phenomenon could explain the unique, distinctive brassy quality of elephant trumpet calls
Hydrodynamics of operator spreading and quasiparticle diffusion in interacting integrable systems
We address the hydrodynamics of operator spreading in interacting integrable
lattice models. In these models, operators spread through the ballistic
propagation of quasiparticles, with an operator front whose velocity is locally
set by the fastest quasiparticle velocity. In interacting integrable systems,
this velocity depends on the density of the other quasiparticles, so
equilibrium density fluctuations cause the front to follow a biased random
walk, and therefore to broaden diffusively. Ballistic front propagation and
diffusive front broadening are also generically present in non-integrable
systems in one dimension; thus, although the mechanisms for operator spreading
are distinct in the two cases, these coarse grained measures of the operator
front do not distinguish between the two cases. We present an expression for
the front-broadening rate; we explicitly derive this for a particular
integrable model (the "Floquet-Fredrickson-Andersen" model), and argue on
kinetic grounds that it should apply generally. Our results elucidate the
microscopic mechanism for diffusive corrections to ballistic transport in
interacting integrable models.Comment: Published versio
Beyond the 2nd Fermi Pulsar Catalog
Over thirteen times more gamma-ray pulsars have now been studied with the
Large Area Telescope on NASA's Fermi satellite than the ten seen with the
Compton Gamma-Ray Observatory in the nineteen-nineties. The large sample is
diverse, allowing better understanding both of the pulsars themselves and of
their roles in various cosmic processes. Here we explore the prospects for even
more gamma-ray pulsars as Fermi enters the 2nd half of its nominal ten-year
mission. New pulsars will naturally tend to be fainter than the first ones
discovered. Some of them will have unusual characteristics compared to the
current population, which may help discriminate between models. We illustrate a
vision of the future with a sample of six pulsars discovered after the 2nd
Fermi Pulsar Catalog was written.Comment: 6 pages, to appear in the proceedings of "The Fast and the Furious:
Energetic Phenomena in Isolated Neutron Stars, Pulsar Wind Nebulae and
Supernova Remnants",ESAC, Madrid, Spain, 22 - 24 May 2013
http://xmm.esac.esa.int/external/xmm_science/workshops/2013_science/, to be
published as a regular issue of the Astronomische Nachrichten / Astronomical
Notes (AN
The geographical significance of the first five-year development programme of Trinidad and Tobago 1958 to 1962
Not availabl
Inhomogeneous Gain Saturation in EDF: Experiment and Modeling
Erbium-Doped Fiber Amplifiers can present holes in spectral gain in
Wavelength Division Multiplexing operation. The origin of this inhomogeneous
saturation behavior is still a subject of controversy. In this paper we present
both an experimental methods and a gain's model. Our experimental method allow
us to measure the first homogeneous linewidth of the 1.5 m erbium emission
with gain spectral hole burning consistently with the other measurement in the
literature and the model explains the differences observed in literature
between GSHB and other measurement methods
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