2,405 research outputs found

    Satellite data relay and platform locating in oceanography. Report of the In Situ Ocean Science Working Group

    Get PDF
    The present and future use of satellites to locate offshore platforms and relay data from in situ sensors to shore was examined. A system of the ARGOS type will satisfy the increasing demand for oceanographic information through data relay and platform location. The improved ship navigation provided by the Global Positioning System (GPS) will allow direct observation of currents from underway ships. Ocean systems are described and demand estimates on satellite systems are determined. The capabilities of the ARGOS system is assessed, including anticipated demand in the next decade

    The onset of a small-scale turbulent dynamo at low magnetic Prandtl numbers

    Full text link
    We study numerically the dependence of the critical magnetic Reynolds number Rmc for the turbulent small-scale dynamo on the hydrodynamic Reynolds number Re. The turbulence is statistically homogeneous, isotropic, and mirror--symmetric. We are interested in the regime of low magnetic Prandtl number Pm=Rm/Re<1, which is relevant for stellar convective zones, protostellar disks, and laboratory liquid-metal experiments. The two asymptotic possibilities are Rmc->const as Re->infinity (a small-scale dynamo exists at low Pm) or Rmc/Re=Pmc->const as Re->infinity (no small-scale dynamo exists at low Pm). Results obtained in two independent sets of simulations of MHD turbulence using grid and spectral codes are brought together and found to be in quantitative agreement. We find that at currently accessible resolutions, Rmc grows with Re with no sign of approaching a constant limit. We reach the maximum values of Rmc~500 for Re~3000. By comparing simulations with Laplacian viscosity, fourth-, sixth-, and eighth-order hyperviscosity and Smagorinsky large-eddy viscosity, we find that Rmc is not sensitive to the particular form of the viscous cutoff. This work represents a significant extension of the studies previously published by Schekochihin et al. 2004, PRL 92, 054502 and Haugen et al. 2004, PRE, 70, 016308 and the first detailed scan of the numerically accessible part of the stability curve Rmc(Re).Comment: 4 pages, emulateapj aastex, 2 figures; final version as published in ApJL (but with colour figures

    The Ursinus Weekly, November 24, 1958

    Get PDF
    Y holds seminar Nov. 19; Marriage problem is topic • Fireside chats to be held Dec. 3 at prof\u27s home • C. Carpenter has poem published in anthology • Administrative regulation • Mayes, Francis \u2762 representatives to MSGA • New pledges announced by Alpha Psi Omega • De Gaulle and France topic at second Forum of Fall semester • Who\u27s who honors 12 leading Ursinus seniors • Senior Ball to be held at Sunnybrook Dec. 5 • W.S.G.A. presents plaque to winning frosh team • Editorial: Thanksgiving • Letters to the editor • Review: Joan of Lorraine • Slightly allegorical • U.C. soccermen lose last three games; Finish 2-6-1 • Prospects for U.C. basketball team looking up • Varsity hockey finishes with 4-2-1; J.V. is 6-0-1 • Football squad drops two games 12-0, 34-6 • Sorority bids • American hist. students begin tour program • Fine art of datinghttps://digitalcommons.ursinus.edu/weekly/1372/thumbnail.jp

    The International Pulsar Timing Array: First Data Release

    Get PDF
    The highly stable spin of neutron stars can be exploited for a variety of (astro)physical investigations. In particular, arrays of pulsars with rotational periods of the order of milliseconds can be used to detect correlated signals such as those caused by gravitational waves. Three such \u27pulsar timing arrays\u27 (PTAs) have been set up around the world over the past decades and collectively form the \u27International\u27 PTA (IPTA). In this paper, we describe the first joint analysis of the data from the three regional PTAs, i.e. of the first IPTA data set. We describe the available PTA data, the approach presently followed for its combination and suggest improvements for future PTA research. Particular attention is paid to subtle details (such as underestimation of measurement uncertainty and long-period noise) that have often been ignored but which become important in this unprecedentedly large and inhomogeneous data set. We identify and describe in detail several factors that complicate IPTA research and provide recommendations for future pulsar timing efforts. The first IPTA data release presented here (and available on-line) is used to demonstrate the IPTA\u27s potential of improving upon gravitational-wave limit

    Ecotypic Differentiation in Response to Photoperiodism in Several Species of Amaranthus

    Get PDF
    Amaranthus retroflexus, A. hybridus and A. powellii were grown in a uniform garden at Ames from seed collected over a wide geographic area. Intraspecific variability in flowering response to photoperiod was studied. There was a significant correlation between date of flowering and the collection site

    Education & Entrepreneurship: Implications For Contemporary Microfinance

    Get PDF
    In world regions receiving direct foreign aid, beneficiaries of aid often lack the education required to remove themselves from poverty. Micro-lending refers to the initiation of small loans to the neediest of borrowers who are unable to secure traditional financing from financial intermediaries. In order for micro-lending to thrive as a viable alternative to traditional government aid, borrowers must not only receive a loan, but also an education in business to fully equip borrowers with necessary resources to establish and operate a prosperous business entity. The authors will argue for the provision of increased educational resources and discuss the disparities between the US model of education and that of third-world nations. Furthermore, the authors will prescribe steps to develop educational materials and train micro-credit borrowers to better guarantee the viability of microfinance

    Method to estimate ISCO and ring-down frequencies in binary systems and consequences for gravitational wave data analysis

    Get PDF
    Recent advances in the description of compact binary systems have produced gravitational waveforms that include inspiral, merger and ring-down phases. Comparing results from numerical simulations with those of post-Newtonian (PN), and related, expansions has provided motivation for employing PN waveforms in near merger epochs when searching for gravitational waves and has encouraged the development of analytic fits to full numerical waveforms. The models and simulations do not yet cover the full binary coalescence parameter space. For these yet un-simulated regions, data analysts can still conduct separate inspiral, merger and ring-down searches. Improved knowledge about the end of the inspiral phase, the beginning of the merger, and the ring-down frequencies could increase the efficiency of both coherent inspiral-merger-ring-down (IMR) searches and searches over each phase separately. Insight can be gained for all three cases through a recently presented theoretical calculation, which, corroborated by the numerical results, provides an implicit formula for the final spin of the merged black holes, accurate to within 10% over a large parameter space. Knowledge of the final spin allows one to predict the end of the inspiral phase and the quasinormal mode ring-down frequencies, and in turn provides information about the bandwidth and duration of the merger. In this work we will discuss a few of the implications of this calculation for data analysis.Comment: Added references to section 3 14 pages 5 figures. Submitted to Classical and Quantum Gravit

    Coordinated SuperDARN THEMIS ASI observations of mesoscale flow bursts associated with auroral streamers

    Full text link
    Nightside auroral zone localized flow channels, typically associated with auroral poleward boundary intensifications and streamers, are an important component of high‐latitude ionospheric plasma dynamics. We investigate the structure of these flow channels using two‐dimensional line‐of‐sight flow observations from the Super Dual Auroral Radar Network (SuperDARN) radars and auroral images from the Time History of Events and Macroscale Interactions during Substorms (THEMIS) ground‐based all‐sky imager (ASI) array. Radar echoes captured <~500 km horizontal distance from the radars were mainly used to detect small‐scale flow structures that would otherwise be missed or poorly resolved in long‐range radar echoes. After identifying 135 auroral streamers in the ASI images at close‐radar capture locations, we examined the associated ionospheric flow data in the radar echoes. Flow bursts and streamers are invariably correlated in all events. The flow bursts are often directed equatorward and appear simultaneously with the streamers. Equatorward flows are located just to the east of the streamers. Less frequently (~10% of the time), a poleward flow enhancement was detected even when a streamer propagated equatorward, the poleward flow enhancement being located to the west of the auroral streamer, or to the east of the equatorward flow enhancement, consistently with the spatial relationship between flow shear and upward field‐aligned currents in plasma sheet flow bursts. The azimuthal width of the flow channel is, on average, ~75 km, and the azimuthal offset of the equatorward flow channel relative to the auroral streamer is ~57 km eastward. This study demonstrates the capability of radar‐imager pairs for identifying the 2‐D structure of localized flows associated with plasma sheet flow bursts. Key Points Structure of flow channels using SuperDARN radars and THEMIS ASI is investigated Simultaneous flow bursts and streamers are invariably correlated in all events 3‐D structure of flows consistent with plasma flow shears around a BBF channelPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/106072/1/jgra50744.pd
    corecore