365 research outputs found
Representation of Photonic Crystals and Their Localized Modes Through the Use of Fourier-Bessel Expansions
Photonic crystal (PhC) geometry is typically characterized by its translational symmetry. However, it can be treated based on the rotationally symmetry through the use of Fourier-Bessel expansions about the center of rotation. Fourier-Bessel expansions of the inverse dielectric of the structures and the transverse electric (TE) localized modes extract the rotational symmetry that is present. The results show that in PhCs and photonic quasi-crystals, the localized Hzfield contains only the rotational orders that correspond to the rotational order of the dielectric plus and minus the rotational order of the corresponding perfect state. This relationship indicates the potential for simplification within the master equation in cylindrical coordinates that will require further examination
Characterisation of the inshore fish assemblages of the Pilbara and Kimberley coasts
All of the objectives of this project have been met by documenting the following: the overall catch of the key commercial, recreational and charter boat fish species; the species composition and relative abundance of the inshore demersal finfish resource from the shoreline outward to a depth of 30 m along the inner continental shelf in north-western Australia; and the nursery areas of the major commercial and recreational fish species in the Pilbara and Kimberley regions
Complex Kerr Geometry and Nonstationary Kerr Solutions
In the frame of the Kerr-Schild approach, we consider the complex structure
of Kerr geometry which is determined by a complex world line of a complex
source. The real Kerr geometry is represented as a real slice of this complex
structure. The Kerr geometry is generalized to the nonstationary case when the
current geometry is determined by a retarded time and is defined by a
retarded-time construction via a given complex world line of source. A general
exact solution corresponding to arbitrary motion of a spinning source is
obtained. The acceleration of the source is accompanied by a lightlike
radiation along the principal null congruence. It generalizes to the rotating
case the known Kinnersley class of "photon rocket" solutions.Comment: v.3, revtex, 16 pages, one eps-figure, final version (to appear in
PRD), added the relation to twistors and algorithm of numerical computations,
English is correcte
Gauged motion in general relativity and in Kaluza-Klein theories
In a recent paper [1] a new generalization of the Killing motion, the {\it
gauged motion}, has been introduced for stationary spacetimes where it was
shown that the physical symmetries of such spacetimes are well described
through this new symmetry. In this article after a more detailed study in the
stationary case we present the definition of gauged motion for general
spacetimes. The definition is based on the gauged Lie derivative induced by a
threading family of observers and the relevant reparametrization invariance. We
also extend the gauged motion to the case of Kaluza-Klein theories.Comment: 42 pages, revised version, typos correction along with some minor
changes, Revtex forma
Glassy dynamics in granular compaction: sand on random graphs
We discuss the use of a ferromagnetic spin model on a random graph to model
granular compaction. A multi-spin interaction is used to capture the
competition between local and global satisfaction of constraints characteristic
for geometric frustration. We define an athermal dynamics designed to model
repeated taps of a given strength. Amplitude cycling and the effect of
permanently constraining a subset of the spins at a given amplitude is
discussed. Finally we check the validity of Edwards' hypothesis for the
athermal tapping dynamics.Comment: 13 pages Revtex, minor changes, to appear in PR
Calibration of Plastic Phoswich Detectors for Charged Particle Detection
The response of an array of plastic phoswich detectors to ions of has been measured from =12 to 72 MeV. The detector response has been
parameterized by a three parameter fit which includes both quenching and high
energy delta-ray effects. The fits have a mean variation of with
respect to the data.Comment: 17 pages, 5 figure
Aperiodicity in one-way Markov cycles and repeat times of large earthquakes in faults
A common use of Markov Chains is the simulation of the seismic cycle in a
fault, i.e. as a renewal model for the repetition of its characteristic
earthquakes. This representation is consistent with Reid's elastic rebound
theory. Here it is proved that in {\it any} one-way Markov cycle, the
aperiodicity of the corresponding distribution of cycle lengths is always lower
than one. This fact concurs with observations of large earthquakes in faults
all over the world
On Mason's rigidity theorem
Following an argument proposed by Mason, we prove that there are no
algebraically special asymptotically simple vacuum space-times with a smooth,
shear-free, geodesic congruence of principal null directions extending
transversally to a cross-section of Scri. Our analysis leaves the door open for
escaping this conclusion if the congruence is not smooth, or not transverse to
Scri. One of the elements of the proof is a new rigidity theorem for the
Trautman-Bondi mass.Comment: minor typos correcte
Semi-automatic enrichment of crowdsourced synonymy networks: the WISIGOTH system applied to Wiktionary
International audienceSemantic lexical resources are a mainstay of various Natural Language Processing applications. However, comprehensive and reliable resources are rare and not often freely available. Handcrafted resources are too costly for being a general solution while automatically-built resources need to be validated by experts or at least thoroughly evaluated. We propose in this paper a picture of the current situation with regard to lexical resources, their building and their evaluation. We give an in-depth description of Wiktionary, a freely available and collaboratively built multilingual dictionary. Wiktionary is presented here as a promising raw resource for NLP. We propose a semi-automatic approach based on random walks for enriching Wiktionary synonymy network that uses both endogenous and exogenous data. We take advantage of the wiki infrastructure to propose a validation "by crowds". Finally, we present an implementation called WISIGOTH, which supports our approach
- …