1,123 research outputs found

    Wall Pressure Coefficients for Low- to High-Rise Buildings

    Get PDF
    Currently, the design of wall cladding and components are based on provisions provided in building codes, such as ASCE 7 for the United States. These codes provide pressure coefficients based on the tributary area, position on the building and the building category. For ASCE 7, low-rise and high-rise buildings are separated by an artificial boundary at 60 ft. (18.2 m). The reasoning for this artificial boundary is unclear. This work investigates the wall pressure coefficients for various buildings, based on aspect ratios, motivated by the large differences in design pressure coefficients for low-rise and high-rise buildings. For this study, a systematic wind tunnel study was performed examining a square plan building with different aspect (i.e., height-to-width ratio) ratios. The wind profile and turbulence intensities were examined to determine the model-scale appropriate for the multiple building heights. Once the model-scale was selected, height configurations of low-rise (H/WH/W\u3e1) buildings were tested. A statistical analysis was performed on these pressure coefficients and these values were converted to GCp (gust factored pressure coefficients) values, as a function of (full-scale) area. The pressure coefficients were compared to studies found in the literature to ensure the reliability of the data. Pressure patterns were observed and the impact of the wind directions was analyzed. Cladding element position and pressure coefficients were compared for the different buildings. The pressure coefficients were compared to ASCE 7. This study concluded that the aspect ratio affected the length of the wall separation bubble, with smaller aspect ratios having more compressed separation bubbles. For positive pressure coefficients, low-rise buildings have different zones of pressure while high-rise buildings are more uniform. For negative pressure (i.e., suction) coefficients, the patterns continually vary with the different aspect ratios. The study showed that there were some aspects of ASCE 7 that were not in good agreement with the data

    Northern Tornadoes Project. Northern Tornadoes Flyover Project: Summary Technical Report of the Year 1 Pilot Study

    Get PDF
    Summary Northern Tornadoes Flyover Project: Summary Technical Report of the Year 1 Pilot Study Gregory A. Kopp, Emilio Hong and Joanne Kennell Faculty of Engineering, University of Western Ontario David Sills Environment and Climate Change Canada 12 January 2018 The objectives of the Year 1 Pilot Study were to (i) develop a methodology for determining tornado occurrence in Northern Ontario, and (ii) obtain research quality data for at least one event. Because of the isolation of many regions, the approach assumed the use of radar data analysis combined with aerial surveys. These objectives were achieved. Aerial surveys were conducted for a total of seven events in Ontario and southern Quebec and 15 confirmed or probable tornadoes identified. Archival geo-tagged imagery was obtained for six of these events. Ten confirmed or probable tornadoes were identified in Ontario, five of which were not in the OSPC database. In addition, 5 tornadoes were confirmed in Quebec. For the 2017 season, the OSPC had a list of 10 verified tornadoes, as of December 21, 2017. The pilot project raises this number to 15. In total, 4 EF2 tornadoes and 1 EF3 tornado were identified via aerial photography. The remainder were EF1 or EF0. UPDATE – 1 March 2021 Based on the analysis of newly available Planet.com high-resolution satellite imagery and the use of related tools, events were reassessed and six additional tornadoes were discovered. However, four tornadoes were reassessed as downbursts. Overall, an additional two tornadoes were added to the 2017 count. The updated events are listed in a revised 2017 summary table appended at the end of this document

    The Parker Instability in 3-D: Corrugations and Superclouds Along the Carina-Sagittarius Arm

    Full text link
    Here we present three-dimensional MHD models for the Parker instability in a thick magnetized disk, including the presence of a spiral arm. The BB-field is assumed parallel to the arm, and the model results are applied to the optical segment of the Carina-Sagittarius arm. The characteristic features of the undular and interchange modes are clearly apparent in the simulations. The undular mode creates large gas concentrations distributed along the arm. This results in a clear arm/inter-arm difference: the instability triggers the formation of large interstellar clouds inside the arms, but generates only small structures with slight density enhancements in the inter-arm regions. The resulting clouds are distributed in an antisymmetric way with respect to the midplane, creating an azimuthal corrugation along the arm. For conditions similar to those of the optical segment of the Carina-Sagittarius arm, it has a wavelength of about 2.4 kpc. This structuring can explain the origin of both HI superclouds and the azimuthal corrugations in spiral arms. The wavelength matches the corrugation length derived with the young stellar groups located in the optical segment of the Carina-Sagittarius arm. Keywords: Galaxy: kinematics and dynamics -- Galaxy: structure -- Instabilities -- ISM: clouds -- ISM: magnetic fields -- ISM: structure -- MHDComment: 29 pages, 12 figures, Latex, Accepted by the Astrophysical Journa

    Irrelevance of photon events distinguishability in a class of Bell experiments

    Get PDF
    We show that the possibility of distinguishing between single- and two-photon detection events, usually not met in the actual experiments, is not a necessary requirement for proof that the experiments of Alley and Shih [Phys. Rev. Lett. 61, 2921 (1988)] and Ou and Mandel [Phys. Rev. Lett. 61, 50 (1988)] are modulo a fair sampling assumption, valid tests of local realism. We also give the critical parameters for the experiments to be unconditional tests of local realism, and show that some other interesting phenomena (involving bosonic-type particle indistinguishability) can be observed during such tests

    Search for Gravitational Wave Bursts from Six Magnetars

    Get PDF
    Soft gamma repeaters (SGRs) and anomalous X-ray pulsars (AXPs) are thought to be magnetars: neutron stars powered by extreme magnetic fields. These rare objects are characterized by repeated and sometimes spectacular gamma-ray bursts. The burst mechanism might involve crustal fractures and excitation of non-radial modes which would emit gravitational waves (GWs). We present the results of a search for GW bursts from six galactic magnetars that is sensitive to neutron star f-modes, thought to be the most efficient GW emitting oscillatory modes in compact stars. One of them, SGR 0501+4516, is likely similar to 1 kpc from Earth, an order of magnitude closer than magnetars targeted in previous GW searches. A second, AXP 1E 1547.0-5408, gave a burst with an estimated isotropic energy >10(44) erg which is comparable to the giant flares. We find no evidence of GWs associated with a sample of 1279 electromagnetic triggers from six magnetars occurring between 2006 November and 2009 June, in GW data from the LIGO, Virgo, and GEO600 detectors. Our lowest model-dependent GW emission energy upper limits for band-and time-limited white noise bursts in the detector sensitive band, and for f-mode ringdowns (at 1090 Hz), are 3.0 x 10(44)d(1)(2) erg and 1.4 x 10(47)d(1)(2) erg, respectively, where d(1) = d(0501)/1 kpc and d(0501) is the distance to SGR 0501+4516. These limits on GW emission from f-modes are an order of magnitude lower than any previous, and approach the range of electromagnetic energies seen in SGR giant flares for the first time.United States National Science FoundationScience and Technology Facilities Council of the United KingdomMax-Planck-SocietyState of Niedersachsen/GermanyItalian Istituto Nazionale di Fisica NucleareFrench Centre National de la Recherche ScientifiqueAustralian Research CouncilCouncil of Scientific and Industrial Research of IndiaIstituto Nazionale di Fisica Nucleare of ItalySpanish Ministerio de Educacion y CienciaConselleria d'Economia Hisenda i Innovacio of the Govern de les Illes BalearsFoundation for Fundamental Research on Matter supported by the Netherlands Organisation for Scientific ResearchPolish Ministry of Science and Higher EducationFoundation for Polish ScienceRoyal SocietyScottish Funding CouncilScottish Universities Physics AllianceNational Aeronautics and Space Administration NNH07ZDA001-GLASTCarnegie TrustLeverhulme TrustDavid and Lucile Packard FoundationResearch CorporationAlfred P. Sloan FoundationRussian Space AgencyRFBR 09-02-00166aIPN JPL Y503559 (Odyssey), NASA NNG06GH00G, NASA NNX07AM42G, NASA NNX08AC89G (INTEGRAL), NASA NNG06GI896, NASA NNX07AJ65G, NASA NNX08AN23G (Swift), NASA NNX07AR71G (MESSENGER), NASA NNX06AI36G, NASA NNX08AB84G, NASA NNX08AZ85G (Suzaku), NASA NNX09AU03G (Fermi)Astronom

    Search for Gravitational Waves from Low Mass Compact Binary Coalescence in LIGO's Sixth Science Run and Virgo's Science Runs 2 and 3

    Get PDF
    We report on a search for gravitational waves from coalescing compact binaries using LIGO and Virgo observations between July 7, 2009 and October 20, 2010. We searched for signals from binaries with total mass between 2 and 25 solar masses; this includes binary neutron stars, binary black holes, and binaries consisting of a black hole and neutron star. The detectors were sensitive to systems up to 40 Mpc distant for binary neutron stars, and further for higher mass systems. No gravitational-wave signals were detected. We report upper limits on the rate of compact binary coalescence as a function of total mass, including the results from previous LIGO and Virgo observations. The cumulative 90%-confidence rate upper limits of the binary coalescence of binary neutron star, neutron star- black hole and binary black hole systems are 1.3 x 10^{-4}, 3.1 x 10^{-5} and 6.4 x 10^{-6} Mpc^{-3}yr^{-1}, respectively. These upper limits are up to a factor 1.4 lower than previously derived limits. We also report on results from a blind injection challenge.Comment: 11 pages, 5 figures. For a repository of data used in the publication, go to: . Also see the announcement for this paper on ligo.org at: <http://www.ligo.org/science/Publication-S6CBCLowMass/index.php

    A First Search for coincident Gravitational Waves and High Energy Neutrinos using LIGO, Virgo and ANTARES data from 2007

    Get PDF
    We present the results of the first search for gravitational wave bursts associated with high energy neutrinos. Together, these messengers could reveal new, hidden sources that are not observed by conventional photon astronomy, particularly at high energy. Our search uses neutrinos detected by the underwater neutrino telescope ANTARES in its 5 line configuration during the period January - September 2007, which coincided with the fifth and first science runs of LIGO and Virgo, respectively. The LIGO-Virgo data were analysed for candidate gravitational-wave signals coincident in time and direction with the neutrino events. No significant coincident events were observed. We place limits on the density of joint high energy neutrino - gravitational wave emission events in the local universe, and compare them with densities of merger and core-collapse events.Comment: 19 pages, 8 figures, science summary page at http://www.ligo.org/science/Publication-S5LV_ANTARES/index.php. Public access area to figures, tables at https://dcc.ligo.org/cgi-bin/DocDB/ShowDocument?docid=p120000

    Implementation and testing of the first prompt search for gravitational wave transients with electromagnetic counterparts

    Get PDF
    Aims. A transient astrophysical event observed in both gravitational wave (GW) and electromagnetic (EM) channels would yield rich scientific rewards. A first program initiating EM follow-ups to possible transient GW events has been developed and exercised by the LIGO and Virgo community in association with several partners. In this paper, we describe and evaluate the methods used to promptly identify and localize GW event candidates and to request images of targeted sky locations. Methods. During two observing periods (Dec 17 2009 to Jan 8 2010 and Sep 2 to Oct 20 2010), a low-latency analysis pipeline was used to identify GW event candidates and to reconstruct maps of possible sky locations. A catalog of nearby galaxies and Milky Way globular clusters was used to select the most promising sky positions to be imaged, and this directional information was delivered to EM observatories with time lags of about thirty minutes. A Monte Carlo simulation has been used to evaluate the low-latency GW pipeline's ability to reconstruct source positions correctly. Results. For signals near the detection threshold, our low-latency algorithms often localized simulated GW burst signals to tens of square degrees, while neutron star/neutron star inspirals and neutron star/black hole inspirals were localized to a few hundred square degrees. Localization precision improves for moderately stronger signals. The correct sky location of signals well above threshold and originating from nearby galaxies may be observed with ~50% or better probability with a few pointings of wide-field telescopes.Comment: 17 pages. This version (v2) includes two tables and 1 section not included in v1. Accepted for publication in Astronomy & Astrophysic

    Swift follow-up observations of candidate gravitational-wave transient events