4,829 research outputs found

    Holographic field theory models of dark energy in interaction with dark matter

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    We discuss two lagrangian interacting dark energy models in the context of the holographic principle. The potentials of the interacting fields are constructed. The models are compared with CMB distance information, baryonic acoustic oscilations, lookback time and the Constitution supernovae sample. For both models the results are consistent with a non vanishing interaction between dark sectors - with more than three standard deviations of confidence for one of them. Moreover, in both cases, the sign of coupling is consistent with dark energy decaying into dark matter, alleviating the coincidence problem.Comment: arXiv admin note: substantial text overlap with arXiv:0912.399

    Fan Loops Observed by IRIS, EIS and AIA

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    A comprehensive study of the physical parameters of active region fan loops is presented using the observations recorded with the Interface Region Imaging Spectrometer (IRIS), the EUV Imaging Spectrometer (EIS) on-board Hinode and the Atmospheric Imaging Assembly (AIA) and the Helioseismic and Magnetic Imager (HMI) on-board the Solar Dynamics Observatory (SDO). The fan loops emerging from non-flaring AR~11899 (near the disk-center) on 19th November, 2013 are clearly discernible in AIA 171~{\AA} images and those obtained in \ion{Fe}{8} and \ion{Si}{7} images using EIS. Our measurements of electron densities reveal that the footpoints of these loops are approximately at constant pressure with electron densities of logNe=\log\,N_{e}= 10.1 cm3^{-3} at log[T/K]=5.15\log\,[T/K]=5.15 (\ion{O}{4}), and logNe=\log\,N_{e}= 8.9 cm3^{-3} at log[T/K]=6.15\log\,[T/K]=6.15 (\ion{Si}{10}). The electron temperature diagnosed across the fan loops by means of EM-Loci suggest that at the footpoints, there are two temperature components at log[T/K]=4.95\log\,[T/K]=4.95 and 5.95, which are picked-up by IRIS lines and EIS lines respectively. At higher heights, the loops are nearly isothermal at log[T/K]=5.95\log\,[T/K]=5.95, that remained constant along the loop. The measurement of Doppler shift using IRIS lines suggests that the plasma at the footpoints of these loops is predominantly redshifted by 2-3~km~s1^{-1} in \ion{C}{2}, 10-15~km~s1^{-1} in \ion{Si}{4} and  ~15{--}20~km~s1^{-1} in \ion{O}{4}, reflecting the increase in the speed of downflows with increasing temperature from log[T/K]=4.40\log\,[T/K]=4.40 to 5.15. These observations can be explained by low frequency nanoflares or impulsive heating, and provide further important constraints on the modeling of the dynamics of fan loops.Comment: Accepted for publication in The Astrophysical Journal; 8 Figures, 11 page

    Correspondence between Loop-inspired and Braneworld Cosmology

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    Braneworld scenarios are motivated by string/M-theory and can be characterized by the way in which they modify the conventional Friedmann equations of Einstein gravity. An alternative approach to quantum gravity, however, is the loop quantum cosmology program. In the semi-classical limit, the cosmic dynamics in this scenario can also be described by a set of modified Friedmann equations. We demonstrate that a dynamical correspondence can be established between these two paradigms at the level of the effective field equations. This allows qualitatively similar features between the two approaches to be compared and contrasted as well as providing a framework for viewing braneworld scenarios in terms of constrained Hamiltonian systems. As concrete examples of this correspondence, we illustrate the relationships between different cosmological backgrounds representing scaling solutions

    Collaboration Versus Cheating

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    We outline how we detected programming plagiarism in an introductory online course for a master's of science in computer science program, how we achieved a statistically significant reduction in programming plagiarism by combining a clear explanation of university and class policy on academic honesty reinforced with a short but formal assessment, and how we evaluated plagiarism rates before SIGand after implementing our policy and assessment.Comment: 7 pages, 1 figure, 5 tables, SIGCSE 201

    Measuring Market Valuation of Amman Stock Exchange Industrial Sectors: Tobin’s Q Ratio as Investors’ Market Performance Indicator

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    This research investigation purported to present the market valuation of Amman Stock Exchange Industrial Sectors utilizing the Tobin’s Q ratio to serve as performance indicator among Jordanian industrial firms. The most specific research objectives addressed in this research work were to evaluate the Amman Stock Exchange Industry market performance, present the trend in Q ratio valuation during the study period, and to recommend some guiding principles to enrich investors in making the right investment decisions. The research paper is anchored on the concepts of Chung and Pruitt (1994) who have developed a simple approximation of Tobin’s q. For the methodology, the researchers made use of the 49 sample companies from all industrial public traded company sectors listed in the Amman Stock Exchange (ASE) clustered based on the Amman Stock Exchange classification as published in their publications inclusive of 2008-2015. The sectors included the Pharmaceutical & Medical Industries, Chemical Industries, Paper & Cartoon Industries, Food & Beverage, Tobacco & Cigarettes, Mining & Extraction Industries, Engineering & Construction, Electrical Industries, Textile, and Leather & Clothing......
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