RESUMO
Large, plume-like internal ice-layer-structures have been observed in radar images from both Antarctica and Greenland, rising from the ice-sheet base to up to half of the ice thickness. Their origins are not yet understood. Here, we simulate their genesis by basal freeze-on using numerical ice-flow modelling and analyse the transient evolution of the emerging ice-plume and the surrounding ice-layer structure as a function of both freeze-on rate and ice flux. We find good agreement between radar observations, modelled ice-plume geometry and internal layer structure, and further show that plume height relates primarily to ice-flux and only secondarily to freeze-on. An in-depth analysis, performed for Northern Greenland of observed spatial plume distribution related to ice flow, basal topography and water availability supports our findings regarding ice flux and suggests freeze-on is controlled by ascending subglacial water flow. Our results imply that widespread basal freeze-on strongly affects ice stratigraphy and consequently ice-core interpretations.
RESUMO
In a retrospective study the results of intravenous digital subtraction angiography (DSA) of renal arteries from 149 hypertensive outpatients investigated 1984 to 1989 at the University of Berne were evaluated. 118 i.v. DSA's (79%) were normal, 10 (7%) were inconclusive and 21 (14%) revealed stenosis. In 16 patients the course of the vessel and the degree of stenosis were verified by intraarterial DSA. In nine patients (6%) a significant stenosis was confirmed and subsequently treated by percutaneous transluminal angioplasty. Renal size was not a predictive parameter for stenosis in this population. Accessory renal arteries were found in 44% of patients with stenosis and only in 18% of those without. The late phase images of i.v. DSA revealed many morphologic abnormalities. The indication for i.v. DSA was assessed according to internationally accepted criteria: 1. severe hypertension, 2. hypertension refractory to treatment, 3. hypertension of sudden onset or aggravation, 4. onset of hypertension in patients younger than 20 or older than 50 years. In the group without stenosis (n = 118) 52 patients (44%) did not fulfill a single one of these criteria, whereas the patients with stenosis (n = 9) had at least one criterion fulfilled. Hypertensive patients should, therefore, only be studied by i.v. DSA if at least one criterion applies. 22,000 SFr. could thus have been saved without loss of medical quality and the treatment options.
