1,141 research outputs found
Effects of boundary roughness on a Q-factor of whispering-gallery-mode lasing microdisk cavities
We perform numerical studies of the effect of sidewall imperfections on the
resonant state broadening of the optical microdisk cavities for lasing
applications. We demonstrate that even small edge roughness causes a drastic
degradation of high-Q whispering gallery (WG) mode resonances reducing their
Q-values by many orders of magnitude. At the same time, low-Q WG resonances are
rather insensitive to the surface roughness. The results of numerical
simulation obtained using the scattering matrix technique, are analyzed and
explained in terms of wave reflection at a curved dielectric interface combined
with the examination of Poincare surface of sections in the classical ray
picture.Comment: 4 pages, 3 figure
Defining the risk of human exposure to Australian bat lyssavirus through potential non-bat animal infection
Human infection with Australian bat lyssavirus (ABLV) was first reported in November 1996, six months after the first identification of the virus in a flying fox in May 1996. Only two human cases of ABLV infection have been described to date, although hundreds of potential human exposures to ABLV have been reported. Current public health guidance considers the risk of transmission of ABLV from a dog or cat to a person is very low. Furthermore, owners are advised that although the animal has a remote possibility of being infected with ABLV, it should be observed closely for at least three months and to report any behavioural changes that occur. The authors present two cases where the behaviour of dogs after potential exposure to ABLV posed significant questions for veterinary and public health authorities
Observations of H3+ in the Diffuse Interstellar Medium
Surprisingly large column densities of H3+ have been detected using infrared
absorption spectroscopy in seven diffuse cloud sightlines (Cygnus OB2 12,
Cygnus OB2 5, HD 183143, HD 20041, WR 104, WR 118, and WR 121), demonstrating
that H3+ is ubiquitous in the diffuse interstellar medium. Using the standard
model of diffuse cloud chemistry, our H3+ column densities imply unreasonably
long path lengths (~1 kpc) and low densities (~3 cm^-3). Complimentary
millimeter-wave, infrared, and visible observations of related species suggest
that the chemical model is incorrect and that the number density of H3+ must be
increased by one to two orders of magnitude. Possible solutions include a
reduced electron fraction, an enhanced rate of H2 ionization, and/or a smaller
value of the H3+ dissociative recombination rate constant than implied by
laboratory experiments.Comment: To be published in Astrophysical Journal, March 200
The internal dynamical equilibrium of HII regions: a statistical study
We present an analysis of the integrated Halpha emission line profiles for
the HII region population of the spiral galaxies NGC 1530, NGC 6951 and NGC
3359. We show that 70% of the line profiles show two or three Gaussian
components. The relations between the Halpha luminosity and non-thermal line
width for the HII regions of the three galaxies are studied and compared with
the relation found taken all the HII regions of the three galaxies as a single
distribution. A clearer envelope in non-thermal line width is found when only
those HII regions with non-thermal line width bigger than 13kms are considered.
The linear fit for the envelope is logL=36.8+2.0*log(sigma). The masses of the
HII regions on the envelope using the virial theorem and the mass estimates
from the Halpha luminosity are comparable, which offers evidence that the HII
regions on the envelope are virialized systems, while the remaining regions,
the majority, are not in virial equilibrium.Comment: 19 pages, 10 figures,accepted for publication in A&
A Nitro Enolate Approach to the Synthesis of 4, 5-Disubstituted-2-Aminoimidazoles. Pilot Library Assembly and Screening for Antibiotic and Antibiofilm Activity
This is the published version. Copyright Royal Society of ChemistryA library of 4,5-disubstituted-2-aminoimidazoles was synthesized using a nitroenolate route and then screened for antibiofilm and antimicrobial activity. These compounds displayed notable biofilm dispersal and planktonic microbicidal activity against various Gram-positive and Gram-negative bacteria
Public Health Surveillance for Australian bat lyssavirus in Queensland, Australia, 2000â2001
From February 1, 2000, to December 4, 2001, a total of 119 bats (85 Megachiroptera and 34 Microchiroptera) were tested for Australian bat lyssavirus (ABLV) infection. Eight Megachiroptera were positive by immunofluorescence assay that used cross-reactive antibodies to rabies nucleocapsid protein. A case study of cross-species transmission of ABLV supports the conclusion that a bat reservoir exists for ABLV in which the virus circulates across Megachiroptera species within mixed communities
Nonequilibrium and Nonlinear Dynamics in Geomaterials I : The Low Strain Regime
Members of a wide class of geomaterials are known to display complex and
fascinating nonlinear and nonequilibrium dynamical behaviors over a wide range
of bulk strains, down to surprisingly low values, e.g., 10^{-7}. In this paper
we investigate two sandstones, Berea and Fontainebleau, and characterize their
behavior under the influence of very small external forces via carefully
controlled resonant bar experiments. By reducing environmental effects due to
temperature and humidity variations, we are able to systematically and
reproducibly study dynamical behavior at strains as low as 10^{-9}. Our study
establishes the existence of two strain thresholds, the first, epsilon_L, below
which the material is essentially linear, and the second, epsilon_M, below
which the material is nonlinear but where quasiequilibrium thermodynamics still
applies as evidenced by the success of Landau theory and a simple macroscopic
description based on the Duffing oscillator. At strains above epsilon_M the
behavior becomes truly nonequilibrium -- as demonstrated by the existence of
material conditioning -- and Landau theory no longer applies. The main focus of
this paper is the study of the region below the second threshold, but we also
comment on how our work clarifies and resolves previous experimental conflicts,
as well as suggest new directions of research.Comment: 14 pages, 15 figure
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