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- Michael, Eli, et al.
(författare)
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Hubble Space Telescope Observations of High-Velocity Lyα and Hα Emission from Supernova Remnant 1987A : The Structure and Development of the Reverse Shock
- 2003
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 593, s. 809-830
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Tidskriftsartikel (refereegranskat)abstract
- We present two-dimensional line profiles of high-velocity (~+/-12,000 km s-1) Lyα and Hα emission from supernova remnant 1987A obtained with the Space Telescope Imaging Spectrograph between 1997 September and 2001 September (days 3869-5327 after the explosion). This emission comes from hydrogen in the debris that is excited and ionized as it passes through the remnant's reverse shock. We use these profiles to measure the geometry and development of the reverse-shock surface. The observed emission is confined within ~+/-30° about the remnant's equatorial plane. At the equator, the reverse shock has a radius of ~75% of the distance to the equatorial ring. We detect marginal differences (6%+/-3%) between the location of the reverse-shock front in the northeast and southwest parts of the remnant. The radius of the reverse shock surface increases for latitudes above the equator, a geometry consistent with a model in which the supernova debris expands into a bipolar nebula. Assuming that the outer supernova debris has a power-law density distribution, we can infer from the reverse-shock emission light curve an expansion rate (in the northeast part of the remnant) of 3700+/-900kms-1, consistent with the expansion velocities determined from observations in radio (Manchester et al.) and X-ray (Park et al.; Michael et al.) wavelengths. However, our most recent observation (at day 5327) suggests that the rate of increase of mass flux across the northeast sector of the reverse shock has accelerated, perhaps because of deceleration of the reverse shock caused by the arrival of a reflected shock created when the blast wave struck the inner ring. Resonant scattering within the supernova debris causes Lyα photons created at the reverse shock to be directed preferentially outward, resulting in a factor of ~5 difference in the observed brightness of the reverse shock in Lyα between the near and far sides of the remnant. Accounting for this effect, we compare the observed reverse-shock Lyα and Hα fluxes to infer the amount of interstellar extinction by dust as E(B-V)=0.17+/-0.01 mag. We also notice extinction by dust in the equatorial ring with E(B-V)~0.02-0.08 mag, which implies dust-to-gas ratios similar to that of the LMC. Since Hα photons are optically thin to scattering, the observed asymmetry in brightness of Hα from the near and far sides of the remnant represents a real asymmetry in the mass flux through the reverse shock of ~30%. We discuss future observational strategies that will permit us to further investigate the reverse-shock dynamics and resonant scattering of the Lyα line and to constrain better the extinction by dust within and in front of the remnant.
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| 5. |
- Andersson, Anders, et al.
(författare)
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A transcriptional timetable of autumn senescence
- 2004
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Ingår i: Genome Biology. - : Springer Science and Business Media LLC. - 1465-6906 .- 1474-760X. ; 5:4, s. R24-
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Tidskriftsartikel (refereegranskat)abstract
- Background We have developed genomic tools to allow the genus Populus (aspens and cottonwoods) to be exploited as a full-featured model for investigating fundamental aspects of tree biology. We have undertaken large-scale expressed sequence tag (EST) sequencing programs and created Populus microarrays with significant gene coverage. One of the important aspects of plant biology that cannot be studied in annual plants is the gene activity involved in the induction of autumn leaf senescence. Results On the basis of 36,354 Populus ESTs, obtained from seven cDNA libraries, we have created a DNA microarray consisting of 13,490 clones, spotted in duplicate. Of these clones, 12,376 (92%) were confirmed by resequencing and all sequences were annotated and functionally classified. Here we have used the microarray to study transcript abundance in leaves of a free-growing aspen tree (Populus tremula) in northern Sweden during natural autumn senescence. Of the 13,490 spotted clones, 3,792 represented genes with significant expression in all leaf samples from the seven studied dates. Conclusions We observed a major shift in gene expression, coinciding with massive chlorophyll degradation, that reflected a shift from photosynthetic competence to energy generation by mitochondrial respiration, oxidation of fatty acids and nutrient mobilization. Autumn senescence had much in common with senescence in annual plants; for example many proteases were induced. We also found evidence for increased transcriptional activity before the appearance of visible signs of senescence, presumably preparing the leaf for degradation of its components.
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| 6. |
- Anghinolfi, Francisco, et al.
(författare)
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DTMROC-S: Deep submicron version of the readout chip for the TRT detector in ATLAS
- 2002
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Ingår i: 8th Workshop On Electronics For LHC Experiments. ; , s. 95-99
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Konferensbidrag (refereegranskat)abstract
- A new version of the circuit for the readout of the ATLAS straw tube detector, TRT [1], has been developed in a deep-submicron process. The DTMROC-S is fabricated in a commercial 0.25μm CMOS IBM technology, with a library hardened by layout techniques [2]. Compared to the previous version of the chip [3] done in a 0.8μm radiation-hard CMOS and despite of the features added for improving the robustness and testability of the circuit, the deep-submicron technology results in a much smaller chip size that increases the production yield and lowers the power consumption.
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| 7. |
- Balkau, Beverley, et al.
(författare)
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Frequency of the WHO metabolic syndrome in European cohorts, and an alternative definition of an insulin resistance syndrome
- 2002
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Ingår i: Diabetes & Metabolism. - 1878-1780. ; 28:5, s. 364-376
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: To describe the frequency, in some European populations, of the World Health Organisation (WHO) defined metabolic syndrome and to compare the frequency of this syndrome with an alternative definition for non-diabetic subjects, called the insulin resistance syndrome proposed by the European Group for the Study of Insulin Resistance (EGIR). METHODS: Investigators of eight European studies contributed, according to a written protocol, the frequencies of abnormalities of these two syndromes, by sex and age class, as well as the overall frequencies of the syndromes and the average number of abnormalities: 8200 men and 9363 women were included. RESULTS: The frequency of both syndromes increased with age and was almost always higher in men than women for a given age. In non-diabetic subjects the frequency of the WHO syndrome varied between 7% and 36% for men 40 to 55 years; for women of the same age, between 5% and 22%. The EGIR syndrome was less frequent than the WHO syndrome (1% to 22% in men, 1% to 14% in women 40-55 years), and in men this was mainly due to the differing definitions of central obesity, as the WHO definition included overall obesity, BMI > or = 30 kg/m(2). CONCLUSIONS: There is great variability in the frequency of the syndrome between different populations, due to the differing frequencies of the abnormalities and no doubt to the differing methodologies of measurement. Prospective studies and advances in the knowledge of physio-pathological mechanisms are required to determine the most appropriate and practical definition of the syndrome.
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| 9. |
- Bergström, Sture, et al.
(författare)
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Gränsgångare över Öresund
- 2003
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Ingår i: Festskrift till Gustaf Lindencrona. - 9139009173
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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| 10. |
- Bindler, Richard, et al.
(författare)
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Pre-industrial atmospheric pollution: Was it important for the pH of acid-sensitive Swedish lakes?
- 2002
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Ingår i: Ambio. - 0044-7447. ; 31:6, s. 460-465
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Tidskriftsartikel (refereegranskat)abstract
- Acid rain has caused extensive surface water acidification in Sweden since the mid-20(th) century. Sulfur emissions from fossil-fuel burning and metal production were the main sources of acid deposition. In the public consciousness acid deposition is strongly associated with the industrial period, in particular the last 50 years. However, studies of lake-water pH development and atmospheric pollution, based on analyses of lake sediment deposits, have shown the importance of a long-term perspective. Here, we present a conceptual argument, using the sediment record, that large-scale atmospheric acid deposition has impacted the environment since at least Medieval times. Sulfur sources were the pre-industrial mining and metal industries that produced silver, lead and other metals from sulfide ores. This early excess sulfur deposition in southern Sweden did not cause surface water acidification; on the contrary, it contributed to alkalization, i.e. increased pH and productivity of the lakes. Suggested mechanisms are that the excess sulfur caused enhanced cation exchange in catchment soils, and that it altered iron-phosphorus cycling in the lakes, which released phosphorus and increased lake productivity
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