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- Ackermann, M., et al.
(författare)
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In-flight measurement of the absolute energy scale of the Fermi Large Area Telescope
- 2012
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Ingår i: Astroparticle physics. - : Elsevier BV. - 0927-6505 .- 1873-2852. ; 35:6, s. 346-353
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Tidskriftsartikel (refereegranskat)abstract
- The Large Area Telescope (LAT) on-board the Fermi Gamma-ray Space Telescope is a pair-conversion telescope designed to survey the gamma-ray sky from 20 MeV to several hundreds of GeV. In this energy band there are no astronomical sources with sufficiently well known and sharp spectral features to allow an absolute calibration of the LAT energy scale. However, the geomagnetic cutoff in the cosmic ray electron-plus-positron (CRE) spectrum in low Earth orbit does provide such a spectral feature. The energy and spectral shape of this cutoff can be calculated with the aid of a numerical code tracing charged particles in the Earth's magnetic field. By comparing the cutoff value with that measured by the LAT in different geomagnetic positions, we have obtained several calibration points between ∌6 and ∌13 GeV with an estimated uncertainty of ∌2%. An energy calibration with such high accuracy reduces the systematic uncertainty in LAT measurements of, for example, the spectral cutoff in the emission from gamma ray pulsars.
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2. |
- Wirsel, SGR, et al.
(författare)
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Four or more species of Cladosporium sympatrically colonize Phragmites australis
- 2002
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Ingår i: Fungal Genetics and Biology. - : Elsevier BV. - 1087-1845. ; 35:2, s. 99-113
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Tidskriftsartikel (refereegranskat)abstract
- A collection of Cladosporium has been recovered from common reed growing at Lake Constance (Germany). High-resolution cryo-scanning electron microscopy revealed that Cladosporium isolates from reed are diverse. Morphologically, we distinguished three species, viz. C. herbarum, C. oxysporum, and Cladosporium sp. Internal transcribed spacer (ITS) sequence analysis supported these results and, moreover, separated the most common species, C. oxysporum, into two subclades. Two additional phylogenies were generated to gain support for this finding. The first, differentiating fungi by their capacities to metabolize different carbon sources, showed correlation with morphology. The second, based on actin gene sequences, showed the same overall topology as that of the ITS tree, but resulted in a higher resolution indicating the existence of four or more species of Cladosporium on reed. A nested PCR assay targeting variable sequences within actin introns indicated that these four species sympatrically colonize reed. There was no evidence for mutual exclusion on or within the host or specialization for host habitats or organs.
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