20,155 research outputs found

    Prediction of net bedload transport rates obtained in oscillating water tunnels and applicability to real surf zone waves

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    Experimental studies of sediment transport rates due to near shore waves are often conducted in oscillating water tunnels (OWTs). In an OWT, the oscillatory motion produced by the piston propagates almost instantaneously along the entire tunnel. Consequently, unlike the wave motion in the sea or in a wave flume, flow in an OWT is uniform along the tunnel, and second - order wave propagation effects (such as Longuet - Higgins's streaming) are absent. The effect of these hydrodynamic differences between OWT and sea waves on sediment transport rates has generally been neglected. In this paper we present a simple, practical formulation to evaluate bed shear stresses and bed load transport rates due to asymmetric and skewed waves plus a current in an OWT, based on fitting the exact results of a rigorous, analytical model of the OWT wave - current boundary layer. By then accounting for real wave effects we find that wave propagation significantly affects the predicted period - averaged net sediment transport rates. Such real wave effects can therefore not be neglected when comparing near shore transport models with OWT data.Singapore–MIT Alliance for Research and Technology ((SMART) Center for Environmental Sensing and Modeling)Singapore. National Research Foundatio

    Development of a species-specific coproantigen ELISA for human taenia solium taeniasis

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    Taenia solium causes human neurocysticercosis and is endemic in underdeveloped countries where backyard pig keeping is common. Microscopic fecal diagnostic methods for human T. solium taeniasis are not very sensitive, and Taenia saginata and Taenia solium eggs are indistinguishable under the light microscope. Coproantigen (CoAg) ELISA methods are very sensitive, but currently only genus (Taenia) specific. This paper describes the development of a highly species-specific coproantigen ELISA test to detect T. solium intestinal taeniasis. Sensitivity was maintained using a capture antibody of rabbit IgG against T. solium adult whole worm somatic extract, whereas species specificity was achieved by utilization of an enzyme-conjugated rabbit IgG against T. solium adult excretory-secretory (ES) antigen. A known panel of positive and negative human fecal samples was tested with this hybrid sandwich ELISA. The ELISA test gave 100% specificity and 96.4% sensitivity for T. solium tapeworm carriers (N = 28), with a J index of 0.96. This simple ELISA incorporating anti-adult somatic and anti-adult ES antibodies provides the first potentially species-specific coproantigen test for human T. solium taeniasis

    Photon emission as a source of coherent behaviour of polaritons

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    We show that the combined effect of photon emission and Coulomb interactions may drive an exciton-polariton system towards a dynamical coherent state, even without phonon thermalization or any other relaxation mechanism. Exact diagonalization results for a finite system (a multilevel quantum dot interacting with the lowest energy photon mode of a microcavity) are presented in support to this statement

    Moving embedded lattice solitons

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    It was recently proved that isolated unstable "embedded lattice solitons" (ELS) may exist in discrete systems. The discovery of these ELS gives rise to relevant questions such as the following: are there continuous families of ELS?, can ELS be stable?, is it possible for ELS to move along the lattice?, how do ELS interact?. The present work addresses these questions by showing that a novel differential-difference equation (a discrete version of a complex mKdV equation) has a two-parameter continuous family of exact ELS. The numerical tests reveal that these solitons are stable and robust enough to withstand collisions. The model may apply to the description of a Bose-Einstein condensate with dipole-dipole interactions between the atoms, trapped in a deep optical-lattice potential.Comment: 13 pages, 11 figure

    Star Formation Under the Outflow: The Discovery of a Non-Thermal Jet from OMC-2 FIR 3 and its Relationship to the Deeply Embedded FIR 4 Protostar

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    We carried out multiwavelength (0.7-5 cm), multiepoch (1994-2015) Very Large Array (VLA) observations toward the region enclosing the bright far-IR sources FIR 3 (HOPS 370) and FIR 4 (HOPS 108) in OMC-2. We report the detection of 10 radio sources, seven of them identified as young stellar objects. We image a well-collimated radio jet with a thermal free-free core (VLA 11) associated with the Class I intermediate-mass protostar HOPS 370. The jet presents several knots (VLA 12N, 12C, 12S) of non-thermal radio emission (likely synchrotron from shock-accelerated relativistic electrons) at distances of ~7,500-12,500 au from the protostar, in a region where other shock tracers have been previously identified. These knots are moving away from the HOPS 370 protostar at ~ 100 km/s. The Class 0 protostar HOPS 108, which itself is detected as an independent, kinematically decoupled radio source, falls in the path of these non-thermal radio knots. These results favor the previously proposed scenario where the formation of HOPS 108 has been triggered by the impact of the HOPS 370 outflow with a dense clump. However, HOPS 108 presents a large proper motion velocity of ~ 30 km/s, similar to that of other runaway stars in Orion, whose origin would be puzzling within this scenario. Alternatively, an apparent proper motion could result because of changes in the position of the centroid of the source due to blending with nearby extended emission, variations in the source shape, and /or opacity effects.Comment: 16 pages, 4 figures, accepted for publication in The Astrophysical Journa

    Аналіз текстури фрактографічних зображень на основі спектра фрактальних розмірностей Реньї

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    У статті досліджено застосування спектра фрактальних розмірностей Реньї для аналізу текстури фрактографічних зображень. Запропоновано використовувати цей підхід для класифікації типів зламів.В статье исследовано применение спектра фрактальных размерностей Реньи для анализа текстуры фрактографических изображений. Предложено использовать этот подход для классификации типов изломов.Investigated the use of the spectrum of fractal dimensions Renyi for texture analysis fraktohraphic images. Proposed to use this approach for the classification of types of fractures
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