994 research outputs found

    Simulations of Nonthermal Electron Transport in Multidimensional Flows: Synthetic Observations of Radio Galaxies

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    We have applied an effective numerical scheme for cosmic-ray transport to 3D MHD simulations of jet flow in radio galaxies (see the companion paper by Jones et al. 1999). The marriage of relativistic particle and 3D magnetic field information allows us to construct a rich set of ``synthetic observations'' of our simulated objects. The information is sufficient to calculate the ``true'' synchrotron emissivity at a given frequency using explicit information about the relativistic electrons. This enables us to produce synchrotron surface-brightness maps, including polarization. Inverse-Compton X-ray surface-brightness maps may also be produced. First results intended to explore the connection between jet dynamics and electron transport in radio lobes are discussed. We infer lobe magnetic field values by comparison of synthetically observed X-ray and synchrotron fluxes, and find these ``inverse-Compton'' fields to be quite consistent with the actual RMS field averaged over the lobe. The simplest minimum energy calculation from the synthetic observations also seems to agree with the actual simulated source properties.Comment: 7 pages, 1 figure; to appear in Life Cycles of Radio Galaxies, ed. J. Biretta et al., New Astronomy Review

    Slow Light in Doppler Broadened Two level Systems

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    We show that the propagation of light in a Doppler broadened medium can be slowed down considerably eventhough such medium exhibits very flat dispersion. The slowing down is achieved by the application of a saturating counter propagating beam that produces a hole in the inhomogeneous line shape. In atomic vapors, we calculate group indices of the order of 10^3. The calculations include all coherence effects.Comment: 6 pages, 5 figure

    Abundance and phenology of two pest species, Cacoecimorpha pronubana and Epiphyas postvittana (Lepidoptera: Tortricidae)

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    Cacoecimorpha pronubana (HĂŒbner, [1799]) and Epiphyas postvittana (Walker, 1863) are economically important polyphagous pest species. The larvae of these moths affect a wide range of horticultural crops. We evaluated the seasonal abundance and population dynamics of these two species, hypothesising that both species of moth exhibit similar patterns in their seasonal abundance and respond to abiotic factors. The study was carried out on a wide range of protected ornamental crops grown on a total area of one hectare at a commercial nursery. The study was completed over 5 consecutive years from 2015 to 2019, where both populations were monitored weekly during the months of moth activity, from April to November, using sex pheromone traps to trap the males of both species. The timing and abundance of catches were analysed in relation to local meteorological data. The mean yearly abundance of adult males was 604 ± 23.89 (mean ± SE; C. pronubana) and 1706 ± 167.18 (E. postvittana) also differing significantly between years for both species. There was no influence of any weather measures on the abundance of E. postvittana, but sunshine duration (4.84 ± 0.26 h) and temperature (13.04 ± 0.57°C) affected the mean seasonal abundance of C. pronubana. There was an overall difference in the seasonal pattern of abundance between the species studied. While we demonstrate a seasonal abundance difference between years for C. pronubana, we found no significant seasonal differences for E. postvittana. Improved understanding of seasonal abundance, phenological patterns and inter‐seasonal variations in population dynamics of these two species may be useful in developing forecasting models that can be used in improving integrated pest management strategies for these two pests

    Coherence as ultrashort pulse train generator

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    Intense, well-controlled regular light pulse trains start to play a crucial role in many fields of physics. We theoretically demonstrate a very simple and robust technique for generating such periodic ultrashort pulses from a continuous probe wave which propagates in a dispersive thermal gas media

    Scents and sensibility: Best practice in insect olfactometer bioassays

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    Olfactometers have been used for more than 100 years and are integral to experimental chemical ecology. Studies utilising olfactometer bioassays form the foundation for understanding the behavioural responses of invertebrates to chemical stimuli under standardised laboratory conditions. Widely used olfactometry apparatuses include two-arm olfactometers for binary responses through to four- and six-arm arenas to evaluate more complex behaviours. Despite its prevalence in chemical ecology studies, there has never been a review of experimental best practice in olfactometry. This review critically evaluates both olfactometry methods and applications as well as experimental design and analysis. We aim to outline a standard of good practice to improve experimental design and reporting for studies involving olfactometry, thereby establishing a reference guide to build a robust experimental workflow for olfactometry bioassays

    Current Distribution in the Three-Dimensional Random Resistor Network at the Percolation Threshold

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    We study the multifractal properties of the current distribution of the three-dimensional random resistor network at the percolation threshold. For lattices ranging in size from 838^3 to 80380^3 we measure the second, fourth and sixth moments of the current distribution, finding {\it e.g.\/} that t/Μ=2.282(5)t/\nu=2.282(5) where tt is the conductivity exponent and Μ\nu is the correlation length exponent.Comment: 10 pages, latex, 8 figures in separate uuencoded fil

    Transverse Fresnel-Fizeau drag effects in strongly dispersive media

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    A light beam normally incident upon an uniformly moving dielectric medium is in general subject to bendings due to a transverse Fresnel-Fizeau light drag effect. In conventional dielectrics, the magnitude of this bending effect is very small and hard to detect. Yet, it can be dramatically enhanced in strongly dispersive media where slow group velocities in the m/s range have been recently observed taking advantage of the electromagnetically induced transparency (EIT) effect. In addition to the usual downstream drag that takes place for positive group velocities, we predict a significant anomalous upstream drag to occur for small and negative group velocities. Furthermore, for sufficiently fast speeds of the medium, higher order dispersion terms are found to play an important role and to be responsible for peculiar effects such as light propagation along curved paths and the restoration of the spatial coherence of an incident noisy beam. The physics underlying this new class of slow-light effects is thoroughly discussed

    Destabilization of dark states and optical spectroscopy in Zeeman-degenerate atomic systems

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    We present a general discussion of the techniques of destabilizing dark states in laser-driven atoms with either a magnetic field or modulated laser polarization. We show that the photon scattering rate is maximized at a particular evolution rate of the dark state. We also find that the atomic resonance curve is significantly broadened when the evolution rate is far from this optimum value. These results are illustrated with detailed examples of destabilizing dark states in some commonly-trapped ions and supported by insights derived from numerical calculations and simple theoretical models.Comment: 14 pages, 10 figure

    Existence of superposition solutions for pulse propagation in nonlinear resonant media

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    Existence of self-similar, superposed pulse-train solutions of the nonlinear, coupled Maxwell-Schr\"odinger equations, with the frequencies controlled by the oscillator strengths of the transitions, is established. Some of these excitations are specific to the resonant media, with energy levels in the configurations of Λ\Lambda and NN and arise because of the interference effects of cnoidal waves, as evidenced from some recently discovered identities involving the Jacobian elliptic functions. Interestingly, these excitations also admit a dual interpretation as single pulse-trains, with widely different amplitudes, which can lead to substantially different field intensities and population densities in different atomic levels.Comment: 11 Pages, 6 Figures, presentation changed and 3 figures adde
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