710 research outputs found

    Dependence of the optical continuous spectrum of quasars on their red-shift

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    Dependence of optical continuous spectrum of quasi-stellar sources on red shif

    An Induction Accelerator of Cosmic Rays on the Axis of an Accretion Disk

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    The structure and magnitude of the electric field created by a rotating accretion disk with a poloidal magnetic field is found for the case of a vacuum approximation along the axis. The accretion disk is modeled as a torus filled with plasma and the frozen-in magnetic field. The dimensions and location of the maximum electric field are found, as well as the energy of the accelerated particles. The gravitational field is assumed to be weak.Comment: 10 pages, 4 figure

    Spectral ageing in the era of big data : Integrated versus resolved models

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    This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society. © 2017 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.Continuous injection models of spectral ageing have long been used to determine the age of radio galaxies from their integrated spectrum; however, many questions about their reliability remain unanswered. With various large area surveys imminent (e.g. LOw Frequency ARray, MeerKAT, MurchisonWidefield Array) and planning for the next generation of radio interferometers are well underway (e.g. next generationVLA, SquareKilometreArray), investigations of radio galaxy physics are set to shift away from studies of individual sources to the population as a whole. Determining if and how integrated models of spectral ageing can be applied in the era of big data is therefore crucial. In this paper, I compare classical integrated models of spectral ageing to recent well-resolved studies that use modern analysis techniques on small spatial scales to determine their robustness and validity as a source selection method. I find that integrated models are unable to recover key parameters and, even when known a priori, provide a poor, frequency-dependent description of a source's spectrum. I show a disparity of up to a factor of 6 in age between the integrated and resolved methods but suggest, even with these inconsistencies, such models still provide a potential method of candidate selection in the search for remnant radio galaxies and in providing a cleaner selection of high redshift radio galaxies in z - α selected samples.Peer reviewe

    Reconnection in pulsar winds

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    The spin-down power of a pulsar is thought to be carried away in an MHD wind in which, at least close to the star, the energy transport is dominated by Poynting flux. The pulsar drives a low-frequency wave in this wind, consisting of stripes of toroidal magnetic field of alternating polarity, propagating in a region around the equatorial plane. The current implied by this configuration falls off more slowly with radius than the number of charged particles available to carry it, so that the MHD picture must, at some point, fail. Recently, magnetic reconnection in such a structure has been shown to accelerate the wind significantly. This reduces the magnetic field in the comoving frame and, consequently, the required current, enabling the solution to extend to much larger radius. This scenario is discussed and, for the Crab Nebula, the range of validity of the MHD solution is compared with the radius at which the flow appears to terminate. For sufficiently high particle densities, it is shown that a low frequency entropy wave can propagate out to the termination point. In this case, the "termination shock" itself must be responsible for dissipating the wave.Comment: LaTeX 13 pages, 3 figures, typos remove

    Local vibrational density of states in disordered graphene

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    Local vibrational density of states for disordered graphene has been calculated via Green’s functions method. Disordered material has been modeled with Bethe lattice. Density of states does not include particularities specific for ideal graphene

    Radio astronomical space system of aperture synthesis: Filling of the spatial frequency spectrum

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    The information potential of radio astronomical space systems of aperture synthesis is examined. Ground based and space radio telescopes are included


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    Detector of internal combustion engine’s crankshaft torsional vibrations based on accelerometer method is designed. It consists of a measuring and transmitting part, which is mounted on the crankshaft of a diesel engine or the propeller shaft of a vessel and a receiving and recording part placed remotely. The measuring and transmitting parts of detector is easily mounted on area of the shaft of the vessel important for the measurement, which are difficult to access for other methods of vibration measuring. It allows directly in real time to measure the tangential accelerations of the shaft without interfering in the propulsion unit work. Carrying out such measurements allows to control the arising torsional stresses and signalling the excess of their safety limit. The measurement results of engine's pulsations of rotation of the crankshaft, arising during operation, allow to watchkeeping engineer to analyze the quality of the working process of each engine’s cylinder in real time and at different operating modes of the vessel. This analysis makes it possible to assess the technical condition of the engine’s parts and assemblies (cylinder liner, piston, o-rings), the quality of the fuel equipment of the diesel engine and, in general, allows to control the technical condition of the entire engine

    Synchrotron aging and the radio spectrum of SN 1993J

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    We combine the GMRT low frequency radio observations of SN 1993J with the VLA high frequency radio data to get a near simultaneous spectrum around day 3200 since explosion. The low frequency measurements of the supernova determine the turnover frequency and flux scale of the composite spectrum and help reveal a steepening in the spectral index, Δα0.6\Delta \alpha \sim 0.6, in the optically thin part of the spectrum. This is the first observational evidence of a break in the radio spectrum of a young supernova. We associate this break with the phenomenon of synchrotron aging of radiating electrons. From the break in the spectrum we calculate the magnetic field in the shocked region independent of the equipartition assumption between energy density of relativistic particles and magnetic energy density. We determine the ratio of these two energy densities and find that this ratio is in the range: 8×1065×1048\times 10^{-6}-5\times 10^{-4}. We also predict the nature of the evolution of the synchrotron break frequency with time, with competing effects due to diffusive Fermi acceleration and adiabatic expansion of the radiative electron plasma.Comment: 12 pages, 2 figures. Accepted for publication in ApJ

    On Scattering of Electromagnetic Waves by a Wormhole

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    We consider scattering of a plane electromagnetic wave by a wormhole. It is found that the scattered wave is partially depolarized and has a specific interference picture depending on parameters of the wormhole and the distance to the observer. It is proposed that such features can be important in the direct search of wormholes