Quantified HI Morphology V: HI Disks in the Virgo Cluster

We explore the quantified morphology of atomic hydrogen (HI) disks in the Virgo cluster. These galaxies display a wealth of phenomena in their Hi morphology, e.g., tails, truncation and warps. These morphological disturbances are related to the ram-pressure stripping and tidal interaction that galaxies undergo in this dense cluster environment. To quantify the morphological transformation of the HI disks, we compute the morphological parameters of CAS, Gini, and M20 and our own GM for 51 galaxies in 48 HI column density maps from the VIVA project. Some morphological phenomena can be identified in this space of relatively low resolution HI data. Truncation of the HI disk can be cleanly identified via the Concentration parameter (C<1) and Concentration can also be used to identify HI deficient disks (1<C<5). Tidal interaction is typically identified using combinations of these morphological parameters, applied to (optical) images of galaxies. We find that some selection criteria (Gini-M20, Asymmetry, and a modified Concentration-M20) are still applicable for the coarse (~15" FWHM) VIVA HI data. The phenomena of tidal tails can be reasonably well identified using the Gini-M20 criterion (60% of galaxies with tails identified but with as many contaminants). Ram-pressure does move HI disks into and out of most of our interaction criteria: the ram-pressure sequence identified by Vollmer et al. (2009) tracks into and out of some of these criteria (Asymmetry based and the Gini-M20 selections, but not the Concentration-M20 or the GM based ones). Therefore, future searches for interaction using HI morphologies should take ram-pressure into account as a mechanism to disturb HI disks enough to make them appear as gravitationally interacting. One mechanism would be to remove all the HI deficient (C<5) disks from the sample, as these have undergone more than one HI removal mechanism.Comment: 10 pages, 3 figures, accepted by MNRAS, appendixes not include

Die Studierendenbefragung in Deutschland: best3 : Studieren mit einer gesundheitlichen Beeinträchtigung

[no abstract available

Die Studierendenbefragung in Deutschland: 22.Sozialerhebung : Die wirtschaftliche und soziale Lage der Studierenden in Deutschland 2021

[no abstract available

Accelerated aortic 4D flow cardiovascular magnetic resonance using compressed sensing: applicability, validation and clinical integration

Background Three-dimensional time-resolved phase-contrast cardiovascular magnetic resonance (4D flow CMR) enables the quantification and visualisation of blood flow, but its clinical applicability remains hampered by its long scan time. The aim of this study was to evaluate the use of compressed sensing (CS) with on-line reconstruction to accelerate the acquisition and reconstruction of 4D flow CMR of the thoracic aorta. Methods 4D flow CMR of the thoracic aorta was acquired in 20 healthy subjects using CS with acceleration factors ranging from 4 to 10. As a reference, conventional parallel imaging (SENSE) with acceleration factor 2 was used. Flow curves, net flows, peak flows and peak velocities were extracted from six contours along the aorta. To measure internal data consistency, a quantitative particle trace analysis was performed. Additionally, scan-rescan, inter- and intraobserver reproducibility were assessed. Subsequently, 4D flow CMR with CS factor 6 was acquired in 3 patients with differing aortopathies. The flow patterns resulting from particle trace visualisation were qualitatively analysed. Results All collected data were successfully acquired and reconstructed on-line. The average acquisition time including respiratory navigator efficiency with CS factor 6 was 5:02 +/- 2:23 min while reconstruction took approximately 9 min. For CS factors of 8 or less, mean differences in net flow, peak flow and peak velocity as compared to SENSE were below 2.2 +/- 7.8 ml/cycle, 4.6 +/- 25.2 ml/s and - 7.9 +/- 13.0 cm/s, respectively. For a CS factor of 10 differences reached 5.4 +/- 8.0 ml/cycle, 14.4 +/- 28.3 ml/s and - 4.0 +/- 12.2 cm/s. Scan-rescan analysis yielded mean differences in net flow of - 0.7 +/- 4.9 ml/cycle for SENSE and - 0.2 +/- 8.5 ml/cycle for CS factor of 6. Conclusions A six- to eightfold acceleration of 4D flow CMR using CS is feasible. Up to a CS acceleration rate of 6, no statistically significant differences in measured flow parameters could be observed with respect to the reference technique. Acquisitions in patients with aortopathies confirm the potential to integrate the proposed method in a clinical routine setting, whereby its main benefits are scan-time savings and direct on-line reconstruction