| 1. |
- Abramowski, A., et al.
(författare)
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VHE gamma-ray emission of PKS 2155-304 : spectral and temporal variability
- 2010
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 520, s. A83-
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Tidskriftsartikel (refereegranskat)abstract
- Context. Observations of very high-energy.-rays from blazars provide information about acceleration mechanisms occurring in their innermost regions. Studies of variability in these objects lead to a better understanding of the mechanisms in play. Aims. To investigate the spectral and temporal variability of VHE (>100 GeV) gamma-rays of the well-known high-frequency-peaked BL Lac object PKS 2155-304 with the HESS imaging atmospheric Cherenkov telescopes over a wide range of flux states. Methods. Data collected from 2005 to 2007 were analyzed. Spectra were derived on time scales ranging from 3 years to 4 min. Light curve variability was studied through doubling timescales and structure functions and compared with red noise process simulations. Results. The source was found to be in a low state from 2005 to 2007, except for a set of exceptional flares that occurred in July 2006. The quiescent state of the source is characterized by an associated mean flux level of (4.32 +/- 0.09(stat) +/- 0.86(syst)) x 10(-11) cm(-2) s(-1) above 200 GeV, or approximately 15% of the Crab Nebula, and a power-law photon index of Gamma = 3.53 +/- 0.06(stat) +/- 0.10(syst). During the flares of July 2006, doubling timescales of similar to 2 min are found. The spectral index variation is examined over two orders of magnitude in flux, yielding different behavior at low and high fluxes, which is a new phenomenon in VHE gamma-ray emitting blazars. The variability amplitude characterized by the fractional rms F-var is strongly energy-dependent and is proportional to E-0.19 +/- 0.01. The light curve rms correlates with the flux. This is the signature of a multiplicative process that can be accounted for as a red noise with a Fourier index of similar to 2. Conclusions. This unique data set shows evidence of a low-level.-ray emission state from PKS 2155-304 that possibly has a different origin than the outbursts. The discovery of the light curve ognormal behavior might be an indicator of the origin of aperiodic variability in blazars.
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| 2. |
- Narayanan, Theyencheri, et al.
(författare)
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Recent applications of synchrotron radiation and neutrons in the study of soft matter
- 2017
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Ingår i: Crystallography Reviews. - 0889-311X. ; 23:3, s. 160-226
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Forskningsöversikt (refereegranskat)abstract
- The broad range of applications of synchrotron and neutron scattering in the investigation of soft condensed matter is reviewed. Appropriate combinations of these techniques allow probing the structure and dynamics of these complex systems from sub-nm to micron size scales and picoseconds to seconds and longer time ranges. Applications include a myriad of systems such as polymers, colloids, surfactants, phospholipids, biological macromolecules and functional materials both in bulk and at interfaces. Most studies are performed in situ under the real thermodynamic state of the given system and large ensemble averaged information is readily obtained. The new generations of synchrotron and neutron sources open possibilities for investigating more complex soft matter systems in hitherto unexplored dynamical states.
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| 3. |
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| 4. |
- Harris, Ashleigh, 1976-, et al.
(författare)
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African Street Literature : A Method for an Emergent Form Beyond World Literature
- 2020
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Ingår i: Research in African Literatures. - : Indiana University Press. - 0034-5210 .- 1527-2044. ; 51:2, s. 1-26
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Tidskriftsartikel (refereegranskat)abstract
- This paper begins with the assertion that world literature is in danger of becoming a closed system, whereby literature anticipates its critical reception in both its form and content. Emergent African literary forms are often excluded from the field of world literature precisely because they demand methods of reading that challenge this anticipatory logic. We refer to this emergent literature circulating in African urban spaces as "African street literature." This paper focuses on three such street forms: ephemeral print literature, flash fiction, and spoken word poetry. In all three cases, the literary form registers its situated-ness, and as such its location is co-constructive of the field of the literary text. The methodological intervention that the paper makes explores ways of reading context, material, form, and content as combined and codetermining without losing attention to the literariness of the text under examination.
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| 5. |
- Rasmussen, Lars Kildehöj, et al.
(författare)
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An extrinsic Kalman filter for iterative multiuser decoding
- 2004
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Ingår i: IEEE Transactions on Information Theory. - 0018-9448 .- 1557-9654. ; 50:4, s. 642-648
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Tidskriftsartikel (refereegranskat)abstract
- One powerful approach for multiuser decoding is to iterate between a linear multiuser filter (which ignores coding constraints) and individual decoders (which ignore multiple-access interference). Subject to clearly formulated statistical assumptions and the history of input signals provided by the outer decoders over all previous iterations, an extrinsic Kalman filter is suggested. This approach is motivated by the recent observation that decoder outputs are loosely correlated during initial iterations. Numerical results show that iterative decoding using this filter provides better performance in terms of the supportable load and convergence speed as compared to previously suggested linear-filter-based iterative decoders.
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