4,573 research outputs found
Modulation instability, Akhmediev Breathers and continuous wave supercontinuum generation
Numerical simulations of the onset phase of continuous wave supercontinuum
generation from modulation instability show that the structure of the field as
it develops can be interpreted in terms of the properties of Akhmediev
Breathers. Numerical and analytical results are compared with experimental
measurements of spectral broadening in photonic crystal fiber using nanosecond
pulsesComment: 22 pages, 6 figure
On the statistical interpretation of optical rogue waves
Numerical simulations are used to discuss various aspects of "optical rogue
wave" statistics observed in noise-driven fiber supercontinuum generation
associated with highly incoherent spectra. In particular, we consider how long
wavelength spectral filtering influences the characteristics of the statistical
distribution of peak power, and we contrast the statistics of the spectrally
filtered SC with the statistics of both the peak power of the most red-shifted
soliton in the SC and the maximum peak power across the full temporal field
with no spectral selection. For the latter case, we show that the unfiltered
statistical distribution can still exhibit a long-tail, but the extreme-events
in this case correspond to collisions between solitons of different
frequencies. These results confirm the importance of collision dynamics in
supercontinuum generation. We also show that the collision-induced events
satisfy an extended hydrodynamic definition of "rogue wave" characteristics.Comment: Paper accepted for publication in the European Physical Journal ST,
Special Topics. Discussion and Debate: Rogue Waves - towards a unifying
concept? To appear 201
Diagramming the Social: Relational Method in Research
This book challenges the hyper-production and proliferation of concepts in modern social research. It presents a distinctive methodological response to this tendency through an exploration of one of the most underappreciated yet widely deployed conventions for the analysis of social processes: the creation of diagrammatic relational spaces. Designed to capture social processes in a way that resists reductive and essentialist categories, such spaces have the capacity to produce powerful, systematic analyses that break the spell of concept proliferation and its resultant naively realist approach to explaining the world. Through an exploration of key examples and series of original case studies, the authors demonstrate the application of this approach across a variety of empirical settings and academic disciplines. They thus offer a relational and pragmatic approach to social research that resists current trends characterised by supposedly self-evident data and/or disconnected theory. As such, the book constitutes an important contribution to some of the central questions in current social research, and promises to unsettle and reinvigorate considerations of method across different fields of practice
Postoperative complications associated with external skeletal fixators in cats
OBJECTIVES:
The objective of this study was to quantify complications associated with external skeletal fixators (ESFs) in cats and to identify potential risk factors.
METHODS:
A retrospective review of medical records and radiographs following ESF placement was performed.
RESULTS:
Case records of 140 cats were reviewed; fixator-associated complications (FACs) occurred in 19% of cats. The region of ESF placement was significantly associated with complication development. Complications developed most frequently in the femur (50%), tarsus (35%) and radius/ulna (33%). Superficial pin tract infection (SPTI) and implant failure accounted for 45% and 41% of all FACs, respectively. SPTI occurred more frequently in the femur, humerus and tibia, with implant failure more frequent in the tarsus. No association between breed, age, sex, weight, fracture type (open vs closed), ESF classification, number of pins per bone segment, degree of fracture load sharing, and the incidence or type of FAC was identified. No association between region of placement, breed, age, sex, weight, fracture type (open vs closed), ESF classification, number of pins per bone segment, fracture load sharing and the time to complication development was identified.
CONCLUSIONS AND RELEVANCE:
Complication development is not uncommon in cats following ESF placement. The higher complication rate in the femur, tarsus and radius/ulna should be considered when reviewing options for fracture management. However, cats appear to have a lower rate of pin tract infections than dogs
Fundamental noise limitations to supercontinuum generation in microstructure fiber
Broadband noise on supercontinuum spectra generated in microstructure fiber
is shown to lead to amplitude fluctuations as large as 50 % for certain input
laser pulse parameters. We study this noise using both experimental
measurements and numerical simulations with a generalized stochastic nonlinear
Schroedinger equation, finding good quantitative agreement over a range of
input pulse energies and chirp values. This noise is shown to arise from
nonlinear amplification of two quantum noise inputs: the input pulse shot noise
and the spontaneous Raman scattering down the fiber.Comment: 16 pages with 6 figure
Open Circuit Resonant (SansEC) Sensor for Composite Damage Detection and Diagnosis in Aircraft Lightning Environments
Composite materials are increasingly used in modern aircraft for reducing weight, improving fuel efficiency, and enhancing the overall design, performance, and manufacturability of airborne vehicles. Materials such as fiberglass reinforced composites (FRC) and carbon-fiber-reinforced polymers (CFRP) are being used to great advantage in airframes, wings, engine nacelles, turbine blades, fairings, fuselage and empennage structures, control surfaces and coverings. However, the potential damage from the direct and indirect effects of lightning strikes is of increased concern to aircraft designers and operators. When a lightning strike occurs, the points of attachment and detachment on the aircraft surface must be found by visual inspection, and then assessed for damage by maintenance personnel to ensure continued safe flight operations. In this paper, a new method and system for aircraft in-situ damage detection and diagnosis are presented. The method and system are based on open circuit (SansEC) sensor technology developed at NASA Langley Research Center. SansEC (Sans Electric Connection) sensor technology is a new technical framework for designing, powering, and interrogating sensors to detect damage in composite materials. Damage in composite material is generally associated with a localized change in material permittivity and/or conductivity. These changes are sensed using SansEC. Unique electrical signatures are used for damage detection and diagnosis. NASA LaRC has both experimentally and theoretically demonstrated that SansEC sensors can be effectively used for in-situ composite damage detection
A simple and surprisingly accurate approach to the chemical bond obtained from dimensional scaling
We present a new dimensional scaling transformation of the Schrodinger
equation for the two electron bond. This yields, for the first time, a good
description of the two electron bond via D-scaling. There also emerges, in the
large-D limit, an intuitively appealing semiclassical picture, akin to a
molecular model proposed by Niels Bohr in 1913. In this limit, the electrons
are confined to specific orbits in the scaled space, yet the uncertainty
principle is maintained because the scaling leaves invariant the
position-momentum commutator. A first-order perturbation correction,
proportional to 1/D, substantially improves the agreement with the exact ground
state potential energy curve. The present treatment is very simple
mathematically, yet provides a strikingly accurate description of the potential
energy curves for the lowest singlet, triplet and excited states of H_2. We
find the modified D-scaling method also gives good results for other molecules.
It can be combined advantageously with Hartree-Fock and other conventional
methods.Comment: 4 pages, 5 figures, to appear in Phys. Rev. Letter
On the modulation instability development in optical fiber systems
Extensive numerical simulations were performed to investigate all stages of
modulation instability development from the initial pulse of pico-second
duration in photonic crystal fiber: quasi-solitons and dispersive waves
formation, their interaction stage and the further propagation. Comparison
between 4 different NLS-like systems was made: the classical NLS equation, NLS
system plus higher dispersion terms, NLS plus higher dispersion and
self-steepening and also fully generalized NLS equation with Raman scattering
taken into account. For the latter case a mechanism of energy transfer from
smaller quasi-solitons to the bigger ones is proposed to explain the dramatical
increase of rogue waves appearance frequency in comparison to the systems when
the Raman scattering is not taken into account.Comment: 9 pages, 54 figure
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