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Mayer C.,Bavarian Academy of science | Fowler A.C.,University of Limerick | Lambrecht A.,University of Innsbruck | Scharrer K.,University of Swansea
Journal of Glaciology | Year: 2011

Between 2003 and 2007, North Gasherbrum Glacier on the northeastern slope of the Karakoram mountains in Asia underwent a dramatic acceleration, during which a velocity wave propagated down the glacier. There was a significant transfer of ice from up-glacier downstream, which resulted in a strong surface elevation increase over the lower tongue, but only a moderate advance of the glacier snout. We interpret this behaviour as that of a glacier surge, and we explain the observations by means of a simple version of the Kamb drainage-switching theory.

Cicha I.,Friedrich - Alexander - University, Erlangen - Nuremberg | Worner A.,Friedrich - Alexander - University, Erlangen - Nuremberg | Urschel K.,Friedrich - Alexander - University, Erlangen - Nuremberg | Beronov K.,Bavarian Academy of science | And 4 more authors.
Stroke | Year: 2011

Background and Purpose: Rupture of atherosclerotic plaques is one of the main causes of ischemic strokes. The aim of this study was to investigate carotid plaque vulnerability markers in relation to blood flow direction and the mechanisms leading to plaque rupture at the upstream side of carotid stenoses. Methods: Frequency and location of rupture, endothelial erosion, neovascularization, and hemorrhage were determined in longitudinal sections of 80 human carotid specimens. Plaques were immunohistochemically analyzed for markers of vulnerability. Plaque geometry was measured to reconstruct shape profiles of ruptured versus stable plaques and to perform computational fluid dynamics analyses. Results: In 86% of ruptured plaques, rupture was observed upstream. In this region, neovascularization and hemorrhage were increased, along with increased immunoreactivity of vascular endothelial and connective tissue growth factor, whereas endothelial erosion was more frequent downstream. Proteolytic enzymes, mast cell chymase and cathepsin L, and the proapoptotic protein Bax showed significantly higher expression upstream as compared with the downstream shoulder of atherosclerotic lesions. Comparison of geometric profiles for ruptured and stable plaques showed increased longitudinal asymmetry of fibrous cap and lipid core thickness in ruptured plaques. The specific geometry of plaques ruptured upstream induced increased levels of shear stress and increased pressure drop between the upstream and the downstream plaque shoulders. Conclusions: Vulnerability of the upstream plaque region is associated with enhanced neovascularization, hemorrhage, and cap thinning induced by proteolytic and proapoptotic mechanisms. These processes are reflected in structural plaque characteristics, analyses of which could improve the efficacy of vascular diagnostics and prevention. © 2011 American Heart Association, Inc.

Krukau A.,Max Planck Institute of Colloids and Interfaces | Krukau A.,Bavarian Academy of science | Knecht V.,Max Planck Institute of Colloids and Interfaces | Knecht V.,Albert Ludwigs University of Freiburg | Lipowsky R.,Max Planck Institute of Colloids and Interfaces
Physical Chemistry Chemical Physics | Year: 2014

Molecular motors such as kinesin are essential for many biological processes. These motors have two motor domains, which bind to tubulin filaments, hydrolyze ATP, and transduce the released chemical energy into directed movements. The general principles of this chemomechanical coupling are now well-established but the underlying molecular mechanisms remain elusive because small conformational changes within large proteins are difficult to detect experimentally. Here, we use atomistic molecular dynamics simulations to monitor such changes within a single motor domain of KIF1A, which belongs to the kinesin-3 motor family. The nucleotide binding pocket of this domain can be empty or occupied by ATP or ADP. For these three nucleotide states, we determine the mobility of the backbone of the protein, both in solution and attached to tubulin. Only one subdomain of the motor domain is found to exhibit a strongly increased mobility upon binding to tubulin: the neck linker that presumably acts as a mechanical transmitter to the other motor domain in dimeric kinesin-3 motors. Furthermore, upon binding to tubulin, the neck linker mobility becomes sensitive to the bound nucleotide and is highly increased after phosphate release, which implies undocking of this linker from the core of the motor domain. These simulation results are consistent with experimental data from EPR spectroscopy, FRET, and cryo-electron microscopy. A detailed analysis of our simulation data also reveals that the undocking of the neck linker in the ADP-kinesin-tubulin state arises from allosteric interactions between the nucleotide and tubulin and that the β-sheet core undergoes a twist both during phosphate release and ATP binding. The computational approach used here can be applied to other motor domains and mechanoenzymes in order to identify allosteric interactions between the subdomains of these proteins. This journal is © 2014 the Owner Societies.

Thoma M.,Bavarian Academy of science | Thoma M.,Alfred Wegener Institute for Polar and Marine Research | Grosfeld K.,Alfred Wegener Institute for Polar and Marine Research | Mayer C.,Bavarian Academy of science | Pattyn F.,Free University of Colombia
Annals of Glaciology | Year: 2012

Several hundred subglacial lakes have been identified beneath Antarctica so far. Their interaction with the overlying ice sheet and their influence on ice dynamics are still subjects of investigation.While it is known that lakes reduce the ice-sheet friction towards a free-slip basal boundary condition, little is known about how basal melting and freezing at the lake/ice interface modifies the ice dynamics, thermal regime and ice rheology. In this diagnostic study we simulate the Vostok Subglacial Lake area with a coupled full Stokes 3-D ice-flow model and a 3-D lake-circulation model. The exchange of energy (heat) and mass at the lake/ice interface increases (decreases) the temperature in the ice column above the lake by up to 10% in freezing (melting) areas, resulting in a significant modification of the highly nonlinear ice viscosity. We show that basal lubrication at the bottom of the ice sheet has a significant impact not only on the ice flow above the lake itself, but also on the vicinity and far field. While the ice flow crosses Vostok Subglacial Lake, flow divergence is observed and modelled. The heterogeneous basal-mass-balance pattern at the lake/ice interface intensifies this divergence. Instead of interactive coupling between the ice-flow model and the lake-flow model, only a single iteration is required for a realistic representation of the ice/water interaction. In addition, our study indicates that simplified parameterizations of the surface temperature boundary condition might lead to a velocity error of 20% for the area of investigation. © 2012 Publishing Technology.

Thoma M.,Alfred Wegener Institute for Polar and Marine Research | Thoma M.,Bavarian Academy of science | Grosfeld K.,Alfred Wegener Institute for Polar and Marine Research | Barbi D.,Alfred Wegener Institute for Polar and Marine Research | And 4 more authors.
Geoscientific Model Development | Year: 2014

Glaciers and ice caps exhibit currently the largest cryospheric contributions to sea level rise. Modelling the dynamics and mass balance of the major ice sheets is therefore an important issue to investigate the current state and the future response of the cryosphere in response to changing environmental conditions, namely global warming. This requires a powerful, easy-to-use, versatile multi-approximation ice dynamics model. Based on the well-known and established ice sheet model of Pattyn (2003) we develop the modular multi-approximation thermomechanic ice model RIMBAY, in which we improve the original version in several aspects like a shallow ice-shallow shelf coupler and a full 3D-grounding-line migration scheme based on Schoof's (2007) heuristic analytical approach. We summarise the full Stokes equations and several approximations implemented within this model and we describe the different numerical discretisations. The results are cross-validated against previous publications dealing with ice modelling, and some additional artificial set-ups demonstrate the robustness of the different solvers and their internal coupling. RIMBAY is designed for an easy adaption to new scientific issues. Hence, we demonstrate in very different set-ups the applicability and functionality of RIMBAY in Earth system science in general and ice modelling in particular.

Determann J.,Alfred Wegener Institute for Polar and Marine Research | Thoma M.,Alfred Wegener Institute for Polar and Marine Research | Thoma M.,Bavarian Academy of science | Grosfeld K.,Alfred Wegener Institute for Polar and Marine Research | Massmann S.,Federal Maritime and Hydrographic Agency
Annals of Glaciology | Year: 2012

Ice flow from the ice sheets to the ocean contains the maximum potential contributing to future eustatic sea-level rise. In Antarctica most mass fluxes occur via the extended ice-shelf regions covering more than half the Antarctic coastline. The most extended ice shelves are the Filchner-Ronne and Ross Ice Shelves, which contribute ≈30% to the total mass loss caused by basal melting. Basal melt rates here show small to moderate average amplitudes of <0.5ma-1. By comparison, the smaller but most vulnerable ice shelves in the Amundsen and Bellinghausen Seas show much higher melt rates (up to 30ma-1), but overall basal mass loss is comparably small due to the small size of the ice shelves. The pivotal question for both characteristic ice-shelf regions, however, is the impact of ocean melting, and, coevally, change in ice-shelf thickness, on the flow dynamics of the hinterland ice masses. In theory, iceshelf back-pressure acts to stabilize the ice sheet, and thus the ice volume stored above sea level.We use the three-dimensional (3-D) thermomechanical ice-flow model RIMBAY to investigate the ice flow in a regularly shaped model domain, including ice-sheet, ice-shelf and open-ocean regions. By using melting scenarios for perturbation studies, we find a hysteresis-like behaviour. The experiments show that the system regains its initial state when perturbations are switched off. Average basal melt rates of up to 2ma-1 as well as spatially variable melting calculated by our 3-D ocean model ROMBAX act as basal boundary conditions in time-dependent model studies. Changes in ice volume and grounding-line position are monitored after 1000 years of modelling and reveal mass losses of up to 40 Gt a-1. © 2012 Publishing Technology.

Bentel K.,Norwegian University of Life Sciences | Gerlach C.,Bavarian Academy of science
International Association of Geodesy Symposia | Year: 2014

A closed-loop simulation is set up in order to study in detail regional gravity modelling from GRACE-type observations. Thereby, potential differences between two satellites are simulated from a pre-defined mass trend signal, superimposed to a static background gravity model. These simulated observations are used for regional gravity field analysis with spherical radial basis functions. Finally, we use EOF analysis to identify the trend in gravity potential from a time series of 15-days quasi-static snapshots. Regional gravity modelling on the sphere is fairly complex and introduces approximation errors and artificial effects. In order not to mix up these errors with noise from the observations, we currently use noise-free observations. The model provides a versatile tool for detailed investigation of the data analysis method. Validation of the results is performed by comparison of input and output gravity change. © Springer-Verlag Berlin Heidelberg 2014.

Juen M.,Bavarian Academy of science | Mayer C.,Bavarian Academy of science | Lambrecht A.,Bavarian Academy of science | Han H.,CAS Lanzhou Cold and Arid Regions Environmental and Engineering Research Institute | Liu S.,CAS Lanzhou Cold and Arid Regions Environmental and Engineering Research Institute
Cryosphere | Year: 2014

To quantify the ablation processes on a debris covered glacier, a simple distributed ablation model has been developed and applied to a selected glacier. For this purpose, a set of field measurements was carried out to collect empirical data. A morphometric analysis of the glacier surface enables us to capture statistically the areal distribution of topographic features that influence debris thickness and consequently ablation. Remote-sensing techniques, using high-resolution satellite imagery, were used to extrapolate the in situ point measurements to the whole ablation area and to map and classify melt-relevant surface types. As a result, a practically applicable method is presented that allows the estimation of ablation on a debris covered glacier by combining field data and remote-sensing information. The sub-debris ice ablation accounts for about 24% of the entire ice ablation, while the percentage of the moraine covered area accounts for approximately 32% of the entire glacierized area. Although the ice cliffs occupy only 1.7% of the debris covered area, the melt amount accounts for approximately 12% of the total sub-debris ablation and 2.5% of the total ablation respectively. Our study highlights the influence of debris cover on the response of the glacier terminus in a particular climate setting. Due to the fact that melt rates beyond 0.1 m of moraine cover are highly restricted, the shielding effect of the debris cover dominates over the temperature and elevation dependence of the ablation in the bare ice case. © Author(s) 2014.

Lerf A.,Bavarian Academy of science | Wagner F.E.,TU Munich
Hyperfine Interactions | Year: 2016

Ferrogallic inks were used for at least two millennia before they became obsolete in the 20th century. The chemistry of such inks is, however, still largely unclear. Today it is of particular interest for the conservation of old manuscripts. 57Fe Mössbauer spectra of the ink on historical documents showed the presence of Fe(II) oxalate and of Fe(III) sites presumably representing iron oxihydroxides. To obtain more information on the behaviour of ink on paper we have performed Mössbauer studies at 300 and 4.2 K on iron gall inks prepared from FeSO4⋅7H2O and tannin. These inks were either written on paper or isolated as a precipitate by centrifugation. In the dried precipitate there is still a strong contribution of the FeSO4⋅7H2O which is absent in the same ink written on paper, for which a broad ferrous component with a quadrupole splitting (QS) of about 2.5 mm/s was found. The dominant Fe(III) site present in all inks on paper with QS ≈ 0.82 mm/s is not Fe(III) gallate and different from the precipitates. We propose that nanoparticulate oxidic clusters or molecular composites covered by a shell of polymerized oxidation products of the phenols are formed on the paper. © 2016, Springer International Publishing Switzerland.

Weber M.,Bavarian Academy of science | Braun L.,Bavarian Academy of science | Mauser W.,Ludwig Maximilians University of Munich | Prasch M.,Ludwig Maximilians University of Munich
Geografia Fisica e Dinamica Quaternaria | Year: 2010

The hydrological model of the Danubia decision support system allows the sources of runoff to be determined according to glaciermelt, snowmelt and rain at any location of the Upper Danube river network. The analysis shows for the past decade 1991-2000 that in glacierized head watersheds (e.g., Vent gauging station, 35% glacier area) there is about an equal amount of runoff originating from icemelt, snowmelt and rain (about 33 % each). Further downstream the portion of icemelt decreases sharply even under present-day conditions with the effect that ultimately 2 % of annual runoff is of glacial origin in Passau/Achleiten (basin area of about 77,000 km 2, current glaciation 0.5%), while about 3/4 originates from rain and 1/4 from snowmelt. This latter fraction is about twice as high as found for subbasins lying exclusively in the lowlands with no connection to the alpine region. Using the regionally adapted Remo scenario data based on the AlB emission scenario of IPCC, the future development of runoff sources is calculated, taking into account the dynamics of glacierized area reduction using the SURGES glacier model (Subscale Regional Glacier Extension Simulator). In about 30 years, the mean icemelt fraction in the glaciated head watersheds will be less than half of the one observed in the decade from 1991 to 2000. The proportion of snowmelt will be about the same, and rain contribution will increase by 50% to about half of annual specific runoff. After the confluence of the Inn River with the Danube at Passau, the portion from icemelt will be negligible, and 80% of runoff will be from rain and 20% from snowmelt after the year 2030. With the anticipated warming over the whole year and the drying out of the summer season the Alps' capacity to export water will diminish, and water availability will be reduced, mainly through the loss of summer precipitation and increased evaporation, and not so much due to the loss of glaciermelt.

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