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- Abdo, A. A., et al.
(författare)
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FERMI OBSERVATIONS OF GRB 090902B : A DISTINCT SPECTRAL COMPONENT IN THE PROMPT AND DELAYED EMISSION
- 2009
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Ingår i: Astrophysical Journal Letters. - 2041-8205 .- 0004-637X .- 1538-4357. ; 706:1, s. L138-L144
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Tidskriftsartikel (refereegranskat)abstract
- We report on the observation of the bright, long gamma-ray burst (GRB), GRB 090902B, by the Gamma-ray Burst Monitor (GBM) and Large Area Telescope (LAT) instruments on-board the Fermi observatory. This was one of the brightest GRBs to have been observed by the LAT, which detected several hundred photons during the prompt phase. With a redshift of z = 1.822, this burst is among the most luminous detected by Fermi. Time-resolved spectral analysis reveals a significant power-law component in the LAT data that is distinct from the usual Band model emission that is seen in the sub-MeV energy range. This power-law component appears to extrapolate from the GeV range to the lowest energies and is more intense than the Band component, both below similar to 50 keV and above 100 MeV. The Band component undergoes substantial spectral evolution over the entire course of the burst, while the photon index of the power-law component remains constant for most of the prompt phase, then hardens significantly toward the end. After the prompt phase, power-law emission persists in the LAT data as late as 1 ks post-trigger, with its flux declining as t(-1.5). The LAT detected a photon with the highest energy so far measured from a GRB, 33.4(-3.5)(+ 2.7) GeV. This event arrived 82 s after the GBM trigger and similar to 50 s after the prompt phase emission had ended in the GBM band. We discuss the implications of these results for models of GRB emission and for constraints on models of the extragalactic background light.
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| 5. |
- Mehanna, M., et al.
(författare)
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Geobacter species enhances pit depth on 304L stainless steel in a medium lacking with electron donor
- 2009
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Ingår i: Electrochemistry communications. - : Elsevier BV. - 1388-2481 .- 1873-1902. ; 11:7, s. 1476-1481
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Tidskriftsartikel (refereegranskat)abstract
- Geobacter sulfurreducens bacteria increased the open circuit potential of 304L stainless steel by around 320 mV in only a few hours after inoculation. This represents a significant increase in the corrosion risk. In contrast, the oxidation of acetate, which is catalysed by well-established biofilms, shifted the pitting potential towards positive values. In acetate-lacking media, pitting occurred with and without bacteria in the same range of potential values, but the presence of bacteria drastically increased the size of pits. AFM showed pits more than 10 times broader and deeper due to the presence of bacteria. In the absence of acetate, the masking effect due to acetate oxidation disappeared and the full corrosive effect of the biofilm was revealed. This also fully explains why pitting was predominantly observed close to surface areas where bacterial settlement was the densest. © 2009.
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| 6. |
- Kim, H. J., et al.
(författare)
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A 2.4 GHz concurrent radio transceiver architecture for bluetooth and Wi-Fi
- 2005
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Ingår i: ISIE 2005. - 0780387384 - 9780780387386 ; , s. 1151-1154
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Konferensbidrag (refereegranskat)abstract
- A radio transceiver architecture for concurrent processing of Bluetooth and Wi-Fi (IEE 802.11b) radio signals in the 2.4 GHz ISM band is presented. The architecture is tailored for low power implementation in a standard deep sub-micron CMOS process. It adopts an innovative frequency plan exploiting adaptive frequency hopping for the concurrent processing and of Bluetooth and Wi-Fi radio signals. A link budget analysis is performed to map out system level requirements to block level specifications.
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