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Träfflista för sökning "WFRF:(Cooray V.) "

Sökning: WFRF:(Cooray V.)

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  • Cooray, V, et al. (författare)
  • Lightning-induced overvoltages in power lines: Validity of various approximations made in overvoltage calculations
  • 1998
  • Ingår i: IEEE TRANSACTIONS ON ELECTROMAGNETIC COMPATIBILITY. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 0018-9375. ; 40:4, s. 355-363
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • In this paper, the validity of different approximations used in the calculation of induced overvoltages in power lines are investigated, These approximations are as follows: 1) neglect the distortions introduced by the finitely conducting ground on the el
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  • Gao, L, et al. (författare)
  • Simulation of streamer discharges as finitely conducting channels
  • 1999
  • Ingår i: IEEE TRANSACTIONS ON DIELECTRICS AND ELECTRICAL INSULATION. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 1070-9878. ; 6:1, s. 35-42
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • This paper presents a two-dimensional simulation of positive streamers in air at atmospheric pressure in a quasi-uniform electric field. A streamer is assumed to consist of a hemispherical tip and a finitely conducting cylindrical channel with a constant
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  • Roman, F, et al. (författare)
  • Comparison of the breakdown of rod-plane gaps with floating electrode
  • 1998
  • Ingår i: IEEE TRANSACTIONS ON DIELECTRICS AND ELECTRICAL INSULATION. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 1070-9878. ; 5:4, s. 622-624
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • The possible influence of a metal body in a lightning protection system was determined by comparing the electrical breakdown probability of two symmetrical sphere-rod gaps, one conventional and the other with a floating electrode, i.e. a rod with a series
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  • Roman, F, et al. (författare)
  • Corona from floating electrodes
  • 1996
  • Ingår i: JOURNAL OF ELECTROSTATICS. - : ELSEVIER SCIENCE BV. - 0304-3886. ; 37:1-2, s. 67-78
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • It is not unusual to have insulated conducting objects located close to the conductors of a Lightning Protection System. However, the separation of these objects from the Lightning Protection System could vary from a few millimetres to some centimetres. W
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  • Roman, F, et al. (författare)
  • Increase in the visual corona from floating electrodes
  • 1999
  • Ingår i: JOURNAL OF ELECTROSTATICS. - : ELSEVIER SCIENCE BV. - 0304-3886. ; 45:4, s. 243-254
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • The corona and streamer discharges on a floating metallic rod located close to a high-voltage electrode were investigated under the application of both positive and negative 300/3000 mu s switching impulses. The distance between the floating rod and the h
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  • Akyuz, M, et al. (författare)
  • Characteristics of laser-triggered electric discharges in air
  • 2005
  • Ingår i: IEEE Transactions on Dielectrics and Electrical Insulation. - 1070-9878. ; 12:5, s. 1060-1070
  • Tidskriftsartikel (refereegranskat)abstract
    • An experiment of laser-triggered electric discharges has been conducted in a uniform background electric field. By focusing the beam of a pulsed Nd-YAG laser (wavelength 532 nm, pulse duration 5 ns) in a narrow (15 mm) plane-parallel air gap exposed to a dc voltage, streamer discharges and disruptive discharges were triggered.. The laser energy and the background electric field strength were varied in the ranges 0-180 mJ and 0.8-1.4 MV/m, respectively, and the laser plasma was induced either close to the anode, close to the cathode or mid-gap. From images of the electrode gap and from current measurements, the occurrence of and time to the streamer discharge and the disruptive discharge were determined. No distinct level was found of either the laser energy or the plasma energy for the transition from one discharge case to another, even if the general trend was that the energy required for a certain discharge case was reduced when increasing the background electric field. These and other observations make the method of laser triggering a less suitable method for studies of streamer initiation and streamer propagation, but revealed several interesting features of laser-triggered electric discharges.
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  • Bakx, Tom, 1990, et al. (författare)
  • A dusty protocluster surrounding the binary galaxy HerBS-70 at z = 2.3
  • 2024
  • Ingår i: Monthly Notices of the Royal Astronomical Society. - 0035-8711 .- 1365-2966. ; 530:4, s. 4578-4596
  • Tidskriftsartikel (refereegranskat)abstract
    • We report on deep SCUBA-2 observations at 850 μm and NOrthern Extended Millimetre Array (NOEMA) spectroscopic measurements at 2 mm of the environment surrounding the luminous, massive (M∗ ≈ 2 × 1011 M☉) Herschel-selected source HerBS-70. This source was revealed by previous NOEMA observations to be a binary system of dusty star-forming galaxies at z = 2.3, with the east component (HerBS-70E) hosting an active galactic nucleus. The SCUBA-2 observations detected, in addition to the binary system, 21 sources at >3.5σ over an area of ∼25 square comoving Mpc with a sensitivity of 1σ850 = 0.75 mJy. The surface density of continuum sources around HerBS-70 is three times higher than for field galaxies. The NOEMA spectroscopic measurements confirm the protocluster membership of three of the nine brightest sources through their CO(4–3) line emission, yielding a volume density 36 times higher than for field galaxies. All five confirmed sub-mm galaxies in the HerBS-70 system have relatively short gas depletion times (80−500 Myr), indicating the onset of quenching for this protocluster core due to the depletion of gas. The dark matter halo mass of the HerBS-70 system is estimated around 5 × 1013 M☉, with a projected current-day mass of 1015 M☉, similar to the local Virgo and Coma clusters. These observations support the claim that DSFGs, in particular the ones with observed multiplicity, can trace cosmic overdensities.
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  • Bendo, G. J., et al. (författare)
  • The bright extragalactic ALMA redshift survey (BEARS) – II. Millimetre photometry of gravitational lens candidates
  • 2023
  • Ingår i: Monthly Notices of the Royal Astronomical Society. - 0035-8711 .- 1365-2966. ; 522:2, s. 2995-3017
  • Tidskriftsartikel (refereegranskat)abstract
    • We present 101- and 151-GHz ALMA continuum images for 85 fields selected from Herschel observations that have 500-μm flux densities >80 mJy and 250–500-μm colours consistent with z > 2, most of which are expected to be gravitationally lensed or hyperluminous infrared galaxies. Approximately half of the Herschel 500-μm sources were resolved into multiple ALMA sources, but 11 of the 15 brightest 500-μm Herschel sources correspond to individual ALMA sources. For the 37 fields containing either a single source with a spectroscopic redshift or two sources with the same spectroscopic redshift, we examined the colour temperatures and dust emissivity indices. The colour temperatures only vary weakly with redshift and are statistically consistent with no redshift-dependent temperature variations, which generally corresponds to results from other samples selected in far-infrared, submillimetre, or millimetre bands but not to results from samples selected in optical or near-infrared bands. The dust emissivity indices, with very few exceptions, are largely consistent with a value of 2. We also compared spectroscopic redshifts to photometric redshifts based on spectral energy distribution templates designed for infrared-bright high-redshift galaxies. While the templates systematically underestimate the redshifts by ∼15 per cent, the inclusion of ALMA data decreases the scatter in the predicted redshifts by a factor of ∼2, illustrating the potential usefulness of these millimetre data for estimating photometric redshifts.
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  • Berta, S., et al. (författare)
  • z -GAL: A NOEMA spectroscopic redshift survey of bright Herschel galaxies: III. Physical properties
  • 2023
  • Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 678
  • Tidskriftsartikel (refereegranskat)abstract
    • The z-GAL survey observed 137 bright Herschel-selected targets with the IRAM Northern Extended Millimeter Array, with the aim to measure their redshift and study their properties. Several of them have been resolved into multiple sources. Consequently, robust spectroscopic redshifts have been measured for 165 individual galaxies in the range 0.8., <., z., <., 6.5. In this paper we analyse the millimetre spectra of the z-GAL sources, using both their continuum and line emission to derive their physical properties. At least two spectral lines are detected for each source, including transitions of 12CO, [CI], and H2O. The observed 12CO line ratios and spectral line energy distributions of individual sources resemble those of local starbursts. In seven sources the para-H2O (211-202) transition is detected and follows the IR versus H2O luminosity relation of sub-millimetre galaxies. The molecular gas mass of the z-GAL sources is derived from their 12CO, [CI], and sub-millimetre dust continuum emission. The three tracers lead to consistent results, with the dust continuum showing the largest scatter when compared to 12CO. The gas-to-dust mass ratio of these sources was computed by combining the information derived from 12CO and the dust continuum and has a median value of 107, similar to star-forming galaxies of near-solar metallicity. The same combined analysis leads to depletion timescales in the range between 0.1 and 1.0 Gyr, which place the z-GAL sources between the main sequence' of star formation and the locus of starbursts. Finally, we derived a first estimate of stellar masses "modulo possible gravitational magnification "by inverting known gas scaling relations: the z-GAL sample is confirmed to be mostly composed by starbursts, whereas ∼25% of its members lie on the main sequence of star-forming galaxies (within ±0.5 dex).
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  • Cooray, V (författare)
  • A model for negative first return strokes in lightning flashes
  • 1997
  • Ingår i: PHYSICA SCRIPTA. - : ROYAL SWEDISH ACAD SCIENCES. - 0281-1847. ; 55:1, s. 119-128
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • A model is introduced to describe negative first return strokes in lightning ground hashes. The basic assumptions made are similar to those used previously to describe the subsequent return strokes. The model predictions are in general agreement with expe
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  • Cooray, V (författare)
  • A model for positive return strokes
  • 1995
  • Ingår i: ELECTROSTATICS 1995. - : IOP PUBLISHING LTD. - 0951-3248. ; 143, s. 363-371
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • A model to describe positive return strokes is presented. The basic concepts used in the model are essentially similar to those used previously to describe negative first return strokes. However, laboratory experiments indicate that the mechanism of neutr
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  • Cooray, V (författare)
  • Energy dissipation in lightning flashes
  • 1997
  • Ingår i: JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES. - : AMER GEOPHYSICAL UNION. ; 102:D17, s. 21401-21410
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • In this paper the amounts of energy dissipation in different stages of ground flashes are estimated by electrostatic energy considerations. In the analysis the cloud is modeled using the typical charge configuration given by Malan [1963]. The leader stage
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  • Cox, P., et al. (författare)
  • z-GAL: A NOEMA spectroscopic redshift survey of bright Herschel galaxies: I. Overview
  • 2023
  • Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 678
  • Tidskriftsartikel (refereegranskat)abstract
    • Using the IRAM NOrthern Extended Millimetre Array (NOEMA), we conducted a Large Programme (z-GAL) to measure redshifts for 126 bright galaxies detected in the Herschel Astrophysical Large Area Survey (H-ATLAS), the HerMES Large Mode Survey (HeLMS), and the Herschel Stripe 82 (HerS) Survey. We report reliable spectroscopic redshifts for a total of 124 of the Herschel-selected galaxies. The redshifts are estimated from scans of the 3 and 2-mm bands (and, for one source, the 1-mm band), covering up to 31 GHz in each band, and are based on the detection of at least two emission lines. Together with the Pilot Programme, where 11 sources had their spectroscopic redshifts measured, our survey has derived precise redshifts for 135 bright Herschel-selected galaxies, making it the largest sample of high-z galaxies with robust redshifts to date. Most emission lines detected are from 12CO (mainly from J = 2 1 to 5 4), with some sources seen in [CI] and H2O emission lines. The spectroscopic redshifts are in the range 0.8
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  • Resultat 1-50 av 81

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