17,728 research outputs found
High Speed Chaos in Optical Feedback System with Flexible Timescales
We describe a new opto-electronic device with time-delayed feedback that uses
a Mach-Zehnder interferometer as passive nonlinearity and a semiconductor laser
as a current-to-optical-frequency converter. Bandlimited feedback allows tuning
of the characteristic time scales of both the periodic and high dimensional
chaotic oscillations that can be generated with the device. Our implementation
of the device produces oscillations in the frequency range of tens to hundreds
of MHz. We develop a model and use it to explore the experimentally observed
Andronov-Hopf bifurcation of the steady state and to estimate the dimension of
the chaotic attractor.Comment: 7 pages, 6 figures, to be published in IEEE J. Quantum Electro
The strategies that peanut and nut-allergic consumers employ to remain safe when travelling abroad
Copyright @ 2012 Barnett et al.; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The article has been made available through the Brunel Open Access Publishing Fund.Background: An understanding of the management strategies used by food allergic individuals is needed as a prerequisite to improving avoidance and enhancing quality of life. Travel abroad is a high risk time for severe and fatal food allergic reactions, but there is paucity of research concerning foreign travel. This study is the first to investigate the experiences of, and strategies used by peanut and tree nut allergic individuals when travelling abroad. Methods: Thirty-two adults with a clinical history of reaction to peanuts or tree nuts consistent with IgE-mediated allergy participated in a qualitative interview study. Results: Travel abroad was considered difficult with inherent risks for allergic individuals. Many participants recounted difficulties with airlines or restaurants. Inconsistency in managing allergen avoidance by airlines was a particular risk and a cause of frustration to participants. Individuals used a variety of strategies to remain safe including visiting familiar environments, limiting their activities, carrying allergy information cards in the host language, preparing their own food and staying close to medical facilities. Conclusions: Participants used a variety of allergen avoidance strategies, which were mostly extensions or modifications of the strategies that they use when eating at home or eating-out in the UK. The extended strategies reflected their recognition of enhanced risk during travel abroad. Their risk assessments and actions were generally well informed and appropriate. A need for airline policy regarding allergy to be declared and adhered to is needed, as is more research to quantify the true risks of airborne allergens in the cabin. Recommendations arising from our study are presented.This study is funded by the UK Food Standards Agency under project code T07058
Injection locking of two frequency-doubled lasers with 3.2 GHz offset for driving Raman transitions with low photon scattering in Ca
We describe the injection locking of two infrared (794 nm) laser diodes which
are each part of a frequency-doubled laser system. An acousto-optic modulator
(AOM) in the injection path gives an offset of 1.6 GHz between the lasers for
driving Raman transitions between states in the hyperfine split (by 3.2 GHz)
ground level of Ca. The offset can be disabled for use in
Ca. We measure the relative linewidth of the frequency-doubled beams
to be 42 mHz in an optical heterodyne measurement. The use of both injection
locking and frequency doubling combines spectral purity with high optical
power. Our scheme is applicable for providing Raman beams across other ion
species and neutral atoms where coherent optical manipulation is required.Comment: 3 pages, 3 figure
Earth-like sand fluxes on Mars
Strong and sustained winds on Mars have been considered rare, on the basis of surface meteorology measurements and global circulation models, raising the question of whether the abundant dunes and evidence for wind erosion seen on the planet are a current process. Recent studies showed sand activity, but could not determine whether entire dunes were moving—implying large sand fluxes—or whether more localized and surficial changes had occurred. Here we present measurements of the migration rate of sand ripples and dune lee fronts at the Nili Patera dune field. We show that the dunes are near steady state, with their entire volumes composed of mobile sand. The dunes have unexpectedly high sand fluxes, similar, for example, to those in Victoria Valley, Antarctica, implying that rates of landscape modification on Mars and Earth are similar
Controlling Fast Chaos in Delay Dynamical Systems
We introduce a novel approach for controlling fast chaos in time-delay
dynamical systems and use it to control a chaotic photonic device with a
characteristic time scale of ~12 ns. Our approach is a prescription for how to
implement existing chaos control algorithms in a way that exploits the system's
inherent time-delay and allows control even in the presence of substantial
control-loop latency (the finite time it takes signals to propagate through the
components in the controller). This research paves the way for applications
exploiting fast control of chaos, such as chaos-based communication schemes and
stabilizing the behavior of ultrafast lasers.Comment: 4 pages, 4 figures, to be published in Physical Review Letter
Cosmology on a Three-Brane
In this paper a general solution is found for a five dimensional orbifold
spacetime that induces a cosmology on a three-brane. Expressions for the
energy density and pressure on the brane in terms of the brane metric are
derived. Given a metric on the brane it is possible to find five dimensional
spacetimes that contain the brane. This calculation is carried out for an
inflationary universe and for a metric that corresponds to a radiation
dominated universe in standard cosmology. It is also shown that any
cosmology can be embedded in a flat five dimensional orbifold spacetime and the
equation of the three-brane surface is derived. For an inflationary universe it
is shown that the surface is the usual hyperboloid representation of de Sitter
space, although it is embedded in an orbifold spacetime.Comment: 11 pages, LaTex. New solutions with a cosmological constant have been
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