345 research outputs found
Erwachsenenbildung und Inklusion: eine intersektionale Perspektivierung
No full textPenkwitt M, Schreiber-Barsch S, Curdt W. Erwachsenenbildung und Inklusion: eine intersektionale Perspektivierung. Debatte. Beiträge zur Erwachsenenbildung. Accepted;8(1)
Non-LTE modelling of prominence fine structures using hydrogen Lyman-line profiles
No full textDate of Acceptance: 10/03/2015Aims. We perform a detailed statistical analysis of the spectral Lyman-line observations of the quiescent prominence observed on May 18, 2005. Methods. We used a profile-to-profile comparison of the synthetic Lyman spectra obtained by 2D single-thread prominence fine-structure model as a starting point for a full statistical analysis of the observed Lyman spectra. We employed 2D multi-thread fine-structure models with random positions and line-of-sight velocities of each thread to obtain a statistically significant set of synthetic Lyman-line profiles. We used for the first time multi-thread models composed of non-identical threads and viewed at line-of-sight angles different from perpendicular to the magnetic field. Results. We investigated the plasma properties of the prominence observed with the SoHO/SUMER spectrograph on May 18, 2005 by comparing the histograms of three statistical parameters characterizing the properties of the synthetic and observed line profiles. In this way, the integrated intensity, Lyman decrement ratio, and the ratio of intensity at the central reversal to the average intensity of peaks provided insight into the column mass and the central temperature of the prominence fine structures.Peer reviewe
Updates to the SUMER Spectral Atlas
No full textWe present a reworked version of the SUMER spectral atlas (Curdt et al., 2001). New identifications are given for more than 100 emission lines; entries were corrected or added to the list. The solar emission curve - spectral radiance versus wavelength - in the SUMER spectral range is now available in digital format as electronic supplementary material. To reveal the true solar emission, second-order photons from the Lyman continuum have been discarded near the long wavelength section in the first order of diffraction
The Balmer Lines of He II in the Blue Wing of the Hydrogen Lyman alpha Line Observed in a Quiescent Prominence
No full textInternational audienceWe revisit the prominence observations in the Lyman α line of Curdt et al. (Astron. Astrophys. 511, L4, 2010) and focus on the bump in the blue wing of the line, which we identify with He ii Balmer lines. We determine the transition candidates, derive an upper limit for the width of the profile and an associated non-thermal velocity close to 0 km s−1, with the assumption that the kinetic temperature is equal to the formation temperature. We compare the total intensity with the corresponding H Lyman α intensity and find a ratio much lower than that measured by Ebadi, Vial, and Ajabshirizadeh (Solar Phys. 257, 91, 2009) in other Lyman lines. We confirm this result with observations performed by Schwartz et al. (private communication, 2014), we discuss a possible interpretation, and suggest that this issue needs to be addressed closely in future observations
The Lyman alpha profile of quiescent prominences
No full textAims. As the result of a novel observing technique, we publish for the first time SoHO-SUMER observations of the true spectral line profile of hydrogen Lyman-alpha in quiescent prominences. Because SoHO is not in Earth orbit, our high-quality data set is free of geocoronal absorption. We studied the line profile to complement earlier observations of the higher Lyman lines and to substantiate recent model predictions. Methods. We applied the reduced-aperture observing mode to two prominence targets and did a statistical analysis of the line profiles in both data sets. In particular, we investigated the shape of the profile, the radiance distribution, and the line shape-to-radiance interrelation. We also compared Ly-alpha data to co-temporal lambda 1206 Si III data. Results. We find that the average profile of Ly-alpha has a blue-peak dominance and is reversed more if the line-of-sight is perpendicular to the field lines. The contrast of Ly-alpha prominence emission rasters is very low, and the radiance distribution differs from the log-normal distribution of the disk. Features in the Si III line are not always co-spatial with Ly-alpha emission. Conclusions. Our empirical results support recent multi-thread models, which predict that asymmetries and depths of the self-reversal depend on the orientation of the prominence axis relative to the line-of-sight.Astronomy & AstrophysicsSCI(E)EI5ARTICLE3null51
The redshifted network contrast of transition region emission
No full textAims. We study the VUV emission of the quiet Sun and the net redshift of transition region lines in the SUMER spectral range. We aim at establishing a link with atmospheric processes and interpreting the observed downflow as the most evident part of the prevailing global coronal mass transport. Methods. We rank and arrange all pixels of a monochromatic raster scan by radiance and define equally-sized bins of bright, faint, and medium-bright pixels. Comparing the bright pixels with the faint pixels, we determine the spectrally-resolved network contrast for 19 emission lines. We then compare the contrast centroids of these lines with the position of the line itself. We establish a relationship between the observed redshift of the network contrast with the line formation temperature. Results. We find that the network contrast is offset in wavelength compared to the emission line itself. This offset, if interpreted as redshift, peaks at middle transition region temperatures and is 10 times higher than the previously reported net redshift of transition region emission lines. We demonstrate that the brighter pixels are more redshifted, causing both a significant shift of the network contrast profile and the well-known net redshift. We show that this effect can be reconstructed from the radiance distribution. This result is compatible with loop models, which assume downflows near both footpoints.Astronomy & AstrophysicsSCI(E)EI9ARTICLE2L13-L1649
Search strategy analysis of Tg4-42 Alzheimer Mice in the Morris Water Maze reveals early spatial navigation deficits
No full textAbstract Spatial disorientation is one of the earliest symptoms in Alzheimer’s disease and allocentric deficits can already be detected in the asymptomatic preclinical stages of the disease. The Morris Water Maze (MWM) is used to study spatial learning in rodent models. Here we investigated the spatial memory of female 3, 7 and 12 month-old Alzheimer Tg4-42 mice in comparison to wild-type control animals. Conventional behavior analysis of escape latencies and quadrant preference revealed spatial memory and reference memory deficits in female 7 and 12 month-old Tg4-42 mice. In contrast, conventional analysis of the MWM indicated an intact spatial memory in 3 month-old Tg4-42 mice. However, a detailed analysis of the swimming strategies demonstrated allocentric-specific memory deficits in 3 month-old Tg4-42 mice before the onset of severe memory deficits. Furthermore, we could show that the spatial reference memory deficits in aged Tg4-42 animals are caused by the lack of allocentric and spatial strategies. Analyzing search strategies in the MWM allows to differentiate between hippocampus-dependent allocentric and hippocampus-independent egocentric search strategies. The spatial navigation impairments in young Tg4-42 mice are well in line with the hypometabolism and synaptic deficits in the hippocampus. Therefore, analyzing search strategies in the Tg4-42 model can be a powerful tool for preclinical drug testing and identifying early therapeutic successes.Open-Access-Publikationsfonds 202
The Ly-α profile and center-to-limb variation of the quiet Sun
No full textAims. We study the emission of the hydrogen Lyman-alpha line in the quiet Sun, its center-to-limb variation, and its radiance distribution. We also compare quasi-simultaneous Ly-alpha and Ly-beta line profiles. Methods. We used the high spectral and spatial resolution of the SUMER spectrometer and completed raster scans at various locations along the disk. For the first time, we used a method to reduce the incoming photon flux to a 20%-level by partly closing the aperture door. We also performed a quasi-simultaneous observation of both Ly-alpha and Ly-beta at the Sun center in sit-and-stare mode. We infer the flow characteristic in the Ly-alpha map from variations in the calibrated lambda 1206 Si III line centroids. Results. We present the average profile of Ly-alpha, its radiance distribution, its center-to-limb behaviour, and the signature of flows on the line profiles. Little center-to-limb variation and no limb brightening are observed in the profiles of the Ly-alpha line. In contrast to all other lines of the Lyman series, which have a red-horn asymmetry, Ly-alpha has a robust and -except for dark locations -dominating blue-horn asymmetry. There appears to be a brightness-to-asymmetry relationship. A similar and even clearer trend is observed in the downflow-to-asymmetry relationship. This important result is consistent with predictions from models that include flows. However, the absence of a clear center-to-limb variation in the profiles may be more indicative of an isotropic field than a mainly radial flow. Conclusions. It appears that the ubiquitous hydrogen behaves in a similar way to a filter that dampens all signatures of the line formation by processes in both the chromosphere and transition region.Astronomy & AstrophysicsSCI(E)EI19ARTICLE1L9-L1249
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