2,026 research outputs found

    The On The Fly Imaging Technique

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    The On-The-Fly (OTF) imaging technique enables single-dish radio telescopes to construct images of small areas of the sky with greater efficiency and accuracy. This paper describes the practical application of the OTF imaging technique. By way of example the implementation of the OTF imaging technique at the NRAO 12 Meter Telescope is described. Specific requirements for data sampling, image formation, and Doppler correction are discussed.Comment: 10 pages, 13 figures, accepted A&

    Representations of world coordinates in FITS

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    The initial descriptions of the FITS format provided a simplified method for describing the physical coordinate values of the image pixels, but deliberately did not specify any of the detailed conventions required to convey the complexities of actual image coordinates. Building on conventions in wide use within astronomy, this paper proposes general extensions to the original methods for describing the world coordinates of FITS data. In subsequent papers, we apply these general conventions to the methods by which spherical coordinates may be projected onto a two-dimensional plane and to frequency/wavelength/velocity coordinates.Comment: 15 Pages, 1 figure, LaTex with Astronomy & Astrophysics macro package, submitted to A&A, related papers at http://www.aoc.nrao.edu/~egreise

    Child with Umbilical Hernia

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    The Negative Stigma Surrounding Mathematics

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    There is a negative stigma that surrounds mathematics in our education system. It is important to bring notice to this for the benefit of future students. There is a lot of research claiming that math is looked down on, but they do not answer why, or what we can do to fix it. Why is there a greater negative stigma around math and not other subjects? What roles to teachers, parents, and peers play in this stigma? In this article, I created a survey for people to answer questions regarding their opinion on math, who they believe typically does well in math, and what affect the people around them contribute to their view of math. As our world is growing technologically, we need teachers to showcase their passion for math to their students. Marissa Greisen is a high school student in the PSU High School Senior Inquiry Program, University Studies Program, Portland State University

    Cosmic ray primary mass composition above the knee: deduction from lateral distribution of electrons

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    Influence of shower fluctuations on the shape of lateral distribution of electrons in EAS of fixed size measured by scintillation counters is analyzed in framework of scaling formalism. Correction factors for the mean square radius of electrons are calculated for the experimental conditions of KASCADE array. Possible improvement of the primary mass discrimination by analysis of lateral distribution of EAS electrons is discussed in detail.Comment: Proceedings of the XIV International Symposium on Very High Energy Cosmic Ray Interaction

    Radio Emission from Cosmic Ray Air Showers: Coherent Geosynchrotron Radiation

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    Cosmic ray air showers have been known for over 30 years to emit pulsed radio emission in the frequency range from a few to a few hundred MHz, an effect that offers great opportunities for the study of extensive air showers with upcoming fully digital "software radio telescopes" such as LOFAR and the enhancement of particle detector arrays such as KASCADE Grande or the Pierre Auger Observatory. However, there are still a lot of open questions regarding the strength of the emission as well as the underlying emission mechanism. Accompanying the development of a LOFAR prototype station dedicated to the observation of radio emission from extensive air showers, LOPES, we therefore take a new approach to modeling the emission process, interpreting it as "coherent geosynchrotron emission" from electron-positron pairs gyrating in the earth's magnetic field. We develop our model in a step-by-step procedure incorporating increasingly realistic shower geometries in order to disentangle the coherence effects arising from the different scales present in the air shower structure and assess their influence on the spectrum and radial dependence of the emitted radiation. We infer that the air shower "pancake" thickness directly limits the frequency range of the emitted radiation, while the radial dependence of the emission is mainly governed by the intrinsic beaming cone of the synchrotron radiation and the superposition of the emission over the air shower evolution as a whole. Our model succeeds in reproducing the qualitative trends in the emission spectrum and radial dependence that were observed in the past, and is consistent with the absolute level of the emission within the relatively large systematic errors in the experimental data.Comment: 17 pages, 18 figures, accepted for publication by Astronomy & Astrophysic

    Underwater Acoustic Detection of Ultra High Energy Neutrinos

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    We investigate the acoustic detection method of 10^18-20 eV neutrinos in a Mediterranean Sea environment. The acoustic signal is re-evaluated according to dedicated cascade simulations and a complex phase dependant absorption model, and compared to previous studies. We detail the evolution of the acoustic signal as function of the primary shower characteristics and of the acoustic propagation range. The effective volume of detection for a single hydrophone is given taking into account the limitations due to sea bed and surface boundaries as well as refraction effects. For this 'benchmark detector' we present sensitivity limits to astrophysical neutrino fluxes, from which sensitivity bounds for a larger acoustic detector can be derived. Results suggest that with a limited instrumentation the acoustic method would be more efficient at extreme energies, above 10^20 eV.Comment: 15 pages, 11 figure
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