This paper presents a comparison of three topologies of multilevel inverters applied to drive an induction motor of 500 kVA/4.16 kV rating. The multilevel inverters analyzed are the following: a ...neutral-point-clamped inverter, a symmetrical cascaded multilevel inverter, and a hybrid asymmetrical cascaded multilevel inverter. The performance indexes used in the comparison are total harmonic distortion, first-order distortion factor, second-order distortion factor, common-mode voltage, semiconductor power loss distribution, and heat-sink volume. The multilevel inverters are designed to present 99% efficiency at the nominal operating point, and the aforementioned performance indexes are compared for distinct values of amplitude modulation depth.
This study identifies the main results and research opportunities based on 52 hedge accounting-related studies, published in Scopus indexing journals from 2007-2019. The study was classified in five ...investigation groups based on their main topic, with Risk Management and Hedge Accounting being the topic most studied (18) and Regulatory Environment the least studied (six). The results show that during the period analysed, the journal with the largest number of publications on hedge accounting is in the United States of American and the most common origin of the journals is the United Kingdom (21). We have identified different research opportunities for each of the five groups and some general opportunities. The main opportunities relate to comparatives researches, considering samples from different countries, the development of methodologies for teaching hedge accounting and models for effectiveness measurement, the study of enterprise risk and disclosure analysis, and research on the impact of Covid-19 on hedge accounting through risk management. The study differs by identifying five classification groups for papers on hedge accounting, since prior studies didn't carry out such classification. The groups are: i) Regulatory Environment, ii) Academic Research, iii) Evolution of Hedge Accounting and Disclosure, iv) Hedge Effectiveness and v) Risk Management and Hedge Accounting. Furthermore, this study is, to our knowledge, the first bibliometric review done about hedge accounting. The paper is relevant to researchers because it points out opportunities for future studies, enabling the production of new research for a topic considered to be complex.
We report the first blazar detection by AGILE. AGILE detected 3C 454.3 during a period of strongly enhanced optical emission in 2007 July. AGILE observed the source with a dedicated repointlng during ...the period 2007 July 24-30 with its two co-aligned imagers, the Gamma-Ray Imaging Detector and the hard X-ray imager Super-AGILE sensitive in the 30 MeV to 50 GeV and 18-60 keV ranges, respectively. Over the entire period, AGILE detected y-ray emission from 3C 454.3 at a significance level of 13.8 a with an average flux (E > 100 MeV) of (280 plus or minus 40) x 10 super(-5) photons cm-2, s-1. The y-ray flux appears to be variable toward the end of the observation. No emission was detected by Super-AGILE in the energy range 20-60 keV, with a 3 o upper limit of 2.3 x 10 super(-3) photons cm-2 S-1. The Y-ray flux level of 3C 454.3 detected by AGILE Is the highest ever detected for this quasar and among the most intense Y-ray fluxes ever detected from fiat-spectrum radio quasars.
Terrestrial gamma-ray flashes (TGFs) are very short bursts of high-energy photons and electrons originating in Earth's atmosphere. We present here a localization study of TGFs carried out at ...gamma-ray energies above 20 MeV based on an innovative event selection method. We use the AGILE satellite Silicon Tracker data that for the first time have been correlated with TGFs detected by the AGILE Mini-Calorimeter. We detect 8 TGFs with gamma-ray photons of energies above 20 MeV localized by the AGILE gamma-ray imager with an accuracy of ∼5-10° at 50 MeV. Remarkably, all TGF-associated gamma rays are compatible with a terrestrial production site closer to the subsatellite point than 400 km. Considering that our gamma rays reach the AGILE satellite at 540 km altitude with limited scattering or attenuation, our measurements provide the first precise direct localization of TGFs from space.
The AGILE satellite detects Terrestrial Gamma‐ray Flashes (TGFs) in the 0.35–100 MeV energy range using its Mini‐Calorimeter (MCAL) instrument with an average detection rate of 10 TGFs/month. Thanks ...to its Low Earth Orbit with only 2.5 degree of inclination, AGILE guarantees an unprecedented exposure above the equator, where both lightning activity and TGF detection peak. Here we report the comparison between the AGILE TGFs detected between March 2009 and February 2010 and full climatology lightning worldwide distribution based on satellite optical observations from LIS (Lightning Imaging Sensor) and OTD (Optical Transient Detector) instruments. This approach is complementary to the one‐to‐one TGF/lightning correlations by ground‐based sferics measurements. Based on mono and bi‐dimensional Kolmogorov‐Smirnov tests, we show that the AGILE TGFs and time‐averaged global lightning in the equatorial area are not drawn from the same distribution. However, we find significant regional differences in the degree of correlation as well as in the TGF/lightning ratio. In the case of south east Asia we find a 87% probability for the TGF and lightning being samples of the same distribution. This result supports the idea that the physical conditions at play in TGF generation can have strong geographical and climatological modulation. Based on the assumption that the observed range of TGF/flash ratio holds at all latitudes we can estimate a global rate of ≃ 220 ÷ 570 TGFs per day. The observed TGF/flash geographical modulation as well as the TGF global rate estimate are in agreement with previous observations.
Key Points
TGFs are spatially consistent with the global lightning distribution
The TGF/flash ratio is 8 × 10−5 leading to a global rate of 300 TGFs/day
Context. We report the detection by the AGILE (Astro-rivelatore Gamma a Immagini LEggero) satellite of an intense gamma-ray flare from the source AGL J1511-0909, associated with the powerful quasar ...PKS 1510-089, during ten days of observations from 23 August to 1 September 2007. Aims. During the observation period, the source was in optical decrease following a flaring event monitored by the GLAST-AGILE Support Program (GASP) of the Whole Earth Blazar Telescope (WEBT). The simultaneous gamma-ray, optical, and radio coverage allows us to study the spectral energy distribution and the theoretical models based on the synchrotron and inverse Compton (IC) emission mechanisms. Methods. AGILE observed the source with its two co-aligned imagers, the Gamma-Ray Imaging Detector and the hard X-ray imager Super-AGILE sensitive in the 30 MeV $\div$ 50 GeV and 18 $\div$ 60 keV bands, respectively. Results. Between 23 and 27 August 2007, AGILE detected gamma-ray emission from PKS 1510-089 when this source was located ~$50^\circ$ off-axis, with an average flux of $(270 \pm 65)$ $\times$ 10-8 photons cm-2 s-1 for photon energy above 100 MeV. In the following period, 28 August-1 September, after a satellite re-pointing, AGILE detected the source at ~$35^\circ$ off-axis, with an average flux (E > 100 MeV) of $(195 \pm 30)$ $\times$ 10-8 photons cm-2 s-1. No emission was detected by Super-AGILE, with a 3-σ upper limit of 45 mCrab in 200 ks. Conclusions. The spectral energy distribution is modelled with a homogeneous one-zone synchrotron self Compton (SSC) emission plus contributions by external photons: the SSC emission contributes primarily to the X-ray band, whereas the contribution of the IC from the external disc and the broad line region match the hard gamma-ray spectrum observed.
Preliminary results on TeV sources search with AGILE Rappoldi, A.; Longo, F.; Argan, A. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
02/2011, Letnik:
630, Številka:
1
Journal Article
Recenzirano
During its first 2 years of operation, the gamma-ray AGILE satellite almost completed a full study of the gamma-ray sky. This paper presents the preliminary results of the systematic study performed ...on the AGILE data to search for GeV counterparts and to derive flux upper limits of the TeV sources detected by various instruments (MAGIC, HESS, VERITAS, Cangaroo, MILAGRO, ARGO,
…
.).
The well-known Crab Nebula is at the center of the SN1054 supernova remnant. It consists of a rotationally powered pulsar interacting with a surrounding nebula through a relativistic particle wind. ...The emissions originating from the pulsar and nebula have been considered to be essentially stable. Here, we report the detection of strong gamma-ray (100 mega-electron volts to 10 giga-electron volts) flares observed by the AGILE satellite in September 2010 and October 2007. In both cases, the total gamma-ray flux increased by a factor of three compared with the non-flaring flux. The flare luminosity and short time scale favor an origin near the pulsar, and we discuss Chandra Observatory x-ray and Hubble Space Telescope optical follow-up observations of the nebula. Our observations challenge standard models of nebular emission and require power-law acceleration by shock-driven plasma wave turbulence within an approximately 1-day time scale.
Super-massive black holes in active galaxies can accelerate particles to relativistic energies, producing jets with associated -ray emission. Galactic 'microquasars', which are binary systems ...consisting of a neutron star or stellar-mass black hole accreting gas from a companion star, also produce relativistic jets, generally together with radio flares. Apart from an isolated event detected in Cygnus X-1, there has hitherto been no systematic evidence for the acceleration of particles to gigaelectronvolt or higher energies in a microquasar, with the consequence that we are as yet unsure about the mechanism of jet energization. Here we report four -ray flares with energies above 100 MeV from the microquasar Cygnus X-3 (an exceptional X-ray binary that sporadically produces radio jets). There is a clear pattern of temporal correlations between the -ray flares and transitional spectral states of the radio-frequency and X-ray emission. Particle acceleration occurred a few days before radio-jet ejections for two of the four flares, meaning that the process of jet formation implies the production of very energetic particles. In Cygnus X-3, particle energies during the flares can be thousands of times higher than during quiescent states.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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