German Center for Materials and Coastal Research

Geesthacht, Germany

German Center for Materials and Coastal Research

Geesthacht, Germany
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Onken R.,German Center for Materials and Coastal Research
Ocean Science | Year: 2017

The Regional Ocean Modeling System (ROMS) has been employed to explore the sensitivity of the forecast skill of mixed-layer properties to initial conditions, boundary conditions, and vertical mixing parameterisations. The initial and lateral boundary conditions were provided by the Mediterranean Forecasting System (MFS) or by the MERCATOR global ocean circulation model via one-way nesting; the initial conditions were additionally updated through the assimilation of observations. Nowcasts and forecasts from the weather forecast models COSMO-ME and COSMO-IT, partly melded with observations, served as surface boundary conditions. The vertical mixing was parameterised by the GLS (generic length scale) scheme Umlauf and Burchard (2003) in four different set-ups. All ROMS forecasts were validated against the observations which were taken during the REP14-MED survey to the west of Sardinia. Nesting ROMS in MERCATOR and updating the initial conditions through data assimilation provided the best agreement of the predicted mixed-layer properties with the time series from a moored thermistor chain. Further improvement was obtained by the usage of COSMO-ME atmospheric forcing, which was melded with real observations, and by the application of the k vertical mixing scheme with increased vertical eddy diffusivity. The predicted temporal variability of the mixed-layer temperature was reasonably well correlated with the observed variability, while the modelled variability of the mixed-layer depth exhibited only agreement with the observations near the diurnal frequency peak. For the forecasted horizontal variability, reasonable agreement was found with observations from a ScanFish section, but only for the mesoscale wave number band; the observed sub-mesoscale variability was not reproduced by ROMS. © 2017 The Author(s).

Drescher S.,Martin Luther University of Halle Wittenberg | Garamus V.M.,German Center for Materials and Coastal Research | Garvey C.J.,Australian Nuclear Science and Technology Organisation | Meister A.,Institute of Chemistry | And 2 more authors.
Beilstein Journal of Organic Chemistry | Year: 2017

In the present work, we describe the synthesis of a single-chain, phenylene-modified bolalipid with two phosphocholine head-groups, PC-C18pPhC18-PC, using a Sonogashira cross-coupling reaction as a key step. The aggregation behaviour was studied as a function of temperature using transmission electron microscopy (TEM), differential scanning calorimetry (DSC), Fourier-transform infrared (FTIR) spectroscopy, and small angle neutron scattering (SANS). We show that our new bolalipid self-assembles into nanofibres, which transform into flexible nanofibres at 27 °C and further to small elongated micelles at 45 °C. Furthermore, the miscibility of the bolalipid with bilayer-forming phosphatidylcholines (DMPC, DPPC, and DSPC) was investigated by means of DSC, TEM, FTIR, and small angle X-ray scattering (SAXS). We could show that the PC-C18pPhC18-PC is partially miscible with saturated phosphatidylcholines; however, closed lipid vesicles with an increased thermal stability were not found. Instead, bilayer fragments and disk-like aggregates are formed. © 2017 Drescher et al.; licensee Beilstein-Institut.

Silva E.L.,German Center for Materials and Coastal Research | Hoche D.,German Center for Materials and Coastal Research | Bouali A.C.,German Center for Materials and Coastal Research | Serdechnova M.,German Center for Materials and Coastal Research | And 4 more authors.
Materialwissenschaft und Werkstofftechnik | Year: 2017

This study focuses on the corrosion phenomena occurring between aluminium AA5083 and AZ31 magnesium sheets, joined with a coated steel self-piercing rivet, by punch rivet technology. These assemblies were studied by immersion tests and scanning vibrating electrode technique (SVET) in sodium chloride solutions, in order to evaluate the effects of joint geometry on corrosion resistance. The observed results were also used for validation of transient finite element method (FEM) simulations. A fully coupled continuum model was used to compute the evolution of electrochemically and chemically induced corrosion attack, formation of corrosion products and their influence on the overall system kinetics. Additionally, X-ray diffraction (XRD) analysis of the corrosion products provided evidence for the formation of layered double hydroxides (LDH), which is in accordance with the model outputs. The current study targets the optimization of joint setup for corrosion resistance. The suitability of corrosion simulation for the AZ31-AA5083-Almac ternary galvanic system is shown alongside. The developed modelling approach represents a step forward in terms of digital service-life assessment of multi-material joints. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Wittke P.,TU Dortmund | Klein M.,TU Dortmund | Dieringa H.,German Center for Materials and Coastal Research | Walther F.,TU Dortmund
International Journal of Fatigue | Year: 2015

Low corrosion resistance of magnesium alloys strongly limits their application range. This study aims at the investigation of corrosion influence on microstructure and depending mechanical properties of newly developed magnesium alloy Mg-4Al-2Ba-2Ca. The fatigue properties of this creep-resistant magnesium alloy were investigated under three corrosive environments: double distilled water, 0.01 and 0.1molL-1 NaCl solutions. Potentiodynamic polarization measurements and immersion tests were performed to estimate the corrosion behaviour. Specimen surfaces were observed using light and scanning electron microscopy for microstructure-related assessment of corrosion mechanisms. The corrosion fatigue behaviour was characterized in continuous load increase tests using plastic strain and electrochemical measurements. Continuous load increase tests allow estimating the fatigue limit and determining the failure stress amplitude with one single specimen. Fatigue results showed a significant decrease in the estimated fatigue limit and determined failure stress amplitude with increasing corrosion impact of the environments. This corrosion-structure-property relation was quantitatively described by means of model-based correlation approaches and failure hypotheses. Plastic strain amplitude and deformation-induced changes in electrochemical measurands can be equivalently applied for precise corrosion fatigue assessment. © 2015 Elsevier Ltd.

Klein M.,TU Dortmund | Kuhlmann F.,TU Dortmund | Wittke P.,TU Dortmund | Dieringa H.,German Center for Materials and Coastal Research | Walther F.,TU Dortmund
Materials and Corrosion | Year: 2014

The corrosion behavior as well as the microstructure in initial state and after corrosive deterioration were investigated for the newly developed Mg-Al-Ba-Ca alloy DieMag422. In order to investigate the corrosion behavior, potentiodynamic polarization measurements and immersion tests were performed in different NaCl concentrations. The microstructure was observed using light microscopy and combined SEM and EDX studies of the specimens before and after corrosive deterioration. Potentiodynamic polarization measurements and immersion tests showed that DieMag422 has a strong susceptibility to corrosion in NaCl solutions. Light microscope and SEM studies revealed that the difference in the corrosion behavior can be attributed to the different occurrence of the anodic a-Mg phase and the cathodic Ca-rich phase. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Holck O.,BAM Federal Institute of Materials Research and Testing | Holck O.,Fraunhofer Institute for Reliability and Microintegration | Bohning M.,BAM Federal Institute of Materials Research and Testing | Heuchel M.,German Center for Materials and Coastal Research | And 4 more authors.
Journal of Membrane Science | Year: 2013

Detailed atomistic simulations were carried out for swelling polymer/gas systems related to experimental sorption and dilation data for CO2 and CH4 in three glassy polymers (polysulfone PSU, the polyimide 6FDA-TrMPD, and a polymer of intrinsic microporosity PIM-1) at 308K (35°C) and pressures up to 50bar. Corresponding experiments were performed with a gravimetric sorption balance and a dilatometer based on a capacitance distance sensor. For each polymer/gas system molecular packing models were prepared and equilibrated for two reference states: the pure polymer is taken as reference for the respective "unswollen" state and similarly the state of the highest penetrant pressure reached in the corresponding experiment is taken to represent the "swollen" state. Models for the latter were constructed in agreement with experimental data (pressure, temperature, gas concentration and volume dilation). Concentration-pressure isotherms of each polymer/gas system were obtained using Grand Canonical Monte Carlo (GCMC) simulations for both reference states (depleted of gas molecules), which are in good agreement with the experimental data in the respective pressure range. As expected these isotherms - due to the simulation technique used, merely based on hole-filling in a static host matrix - do not represent the sorption behavior over a broader range of gas pressures which may involve significant structural rearrangements as well as swelling and relaxational phenomena. Nevertheless, a linear combination of the two GCMC-isotherms allows the interpolation in order to describe the nonlinear gas sorption in the glassy polymers under investigation covering the penetrant pressure range between the reference states in good agreement with the experimental results. © 2012 Elsevier B.V.

Li Z.,Northeastern University China | Zhang Y.,CNRS Study of Microstructures, Mechanics and Material Sciences lab | Zhang Y.,University of Lorraine | Esling C.,CNRS Study of Microstructures, Mechanics and Material Sciences lab | And 5 more authors.
Applied Physics Letters | Year: 2014

The influences of uniaxial compressive stress on martensitic transformation were studied on a polycrystalline Ni-Mn-Ga bulk alloy prepared by directional solidification. Based upon the integrated in-situ neutron diffraction measurements, direct experimental evidence was obtained on the variant redistribution of seven-layered modulated (7M) martensite, triggered by external uniaxial compression during martensitic transformation. Large anisotropic lattice strain, induced by the cyclic thermo-mechanical treatment, has led to the microstructure modification by forming martensitic variants with a strong 〈0 1 0〉7M preferential orientation along the loading axis. As a result, the saturation of magnetization became easier to be reached. © 2014 AIP Publishing LLC.

Grashorn S.,German Center for Materials and Coastal Research | Lettmann K.A.,Carl von Ossietzky University | Wolff J.-O.,Carl von Ossietzky University | Badewien T.H.,Carl von Ossietzky University | Stanev E.V.,German Center for Materials and Coastal Research
Ocean Dynamics | Year: 2015

An unstructured-grid model (FVCOM) coupled to a surface wave model (FVCOM-SWAVE) with two different setups is used to investigate the hydrodynamic and wave energy conditions during a moderate wind and a storm situation in the southern North Sea. One setup covers the whole North Sea with moderately increased grid resolution at the coast, whereas the other is a very high-resolution Wadden Sea setup that is one-way coupled to the coarser North Sea model. The results of both model setups are validated, compared to each other and analysed with a focus on longshore currents and wave energy. The numerical results show that during storm conditions, strong wave-induced longshore currents occur in front of the East Frisian Wadden Sea islands with current speeds up to 1 m/s. The model setup with the higher resolution around the islands shows even stronger currents than the coarser setup. The wave-current interaction also influences the surface elevation by raising the water level in the tidal basins. The calculated wave energies show large differences between moderate wind and storm conditions with time-averaged values up to 200 kW/m. © 2015, Springer-Verlag Berlin Heidelberg.

Riabtseva A.,Lviv Polytechnic | Mitina N.,Lviv Polytechnic | Grytsyna I.,Ukrainian Academy of Sciences | Boiko N.,Ukrainian Academy of Sciences | And 4 more authors.
European Polymer Journal | Year: 2016

Branched polymeric surfactants composed of grafted non-ionic polyethylene glycol (PEG) and anionic polyelectrolyte chains were synthesized via radical polymerization initiated by the comb-like PEG-containing polyperoxide. Above definite concentration in solution, these surfactants form micelle-like structures (MLS). The MLS formed by branched polymeric molecules are of larger size in comparison with size of MLS formed by the initial PEG-containing polyperoxide that is caused mainly by different mechanism of their self-organization and morphology of formed MLS. The availability of grafted polyelectrolyte chains in the MLS provides a possibility of their use as the containers for immobilization of bio-active substances and nucleation of the inorganic nanoparticles, as well as formation of their stable colloidal systems in water in a wide pH range. Noticeable compaction and narrowed size distribution of the MLS were revealed after immobilization of doxorubicin (Dox) molecules or Fe2O3 nanocrystals. MLS-based systems were used for delivery of Dox and maghemite particles at treatment of tumor cells. Both MLS-based formulations of Dox and Fe2O3 were efficiently engulfed by rat glioma C6 cells. A significant (10 times) decrease in the effective therapeutic dose of Dox was found when this drug was delivered by a MLS-based formulation of Dox. That effect might be explained by a specific structure and functionality of the novel carrier used for immobilization of drug that should be delivered to target cells. © 2016 Elsevier Ltd. All rights reserved.

Codling G.,Lancaster University | Halsall C.,Lancaster University | Ahrens L.,Swedish University of Agricultural Sciences | Del Vento S.,Lancaster University | And 4 more authors.
Environmental Pollution | Year: 2014

Per- and polyfluoroalkyl substances (PFAS) were measured systematically in a snowpack in northern Sweden to determine chemical behaviour during seasonal melt. Average PFAS concentrations were generally low, but displayed a wide range with median (range) concentrations of PFOA and PFOS of 66.5 pg L-1 (ND-122) and 20.5 pg L-1 (2.60-253) respectively. Average concentrations of the shorter chain, C4 and C5 perfluoroalkyl carboxylates (PFCAs) and perfluoroalkyl sulfonates (PFSAs), were ∼10-fold higher. Differences in the PFAS concentrations and profile were observed between surface snow and deeper layers, with evidence of PFAS migration to deeper snow layers as melt progressed. Chemical loads (ng m-2) for C4-9 PFCAs decreased gradually as melt progressed, but increased for C4, C6-8 PFSAs and the longer chain C10-12 PFCAs. This enrichment in the diminishing snowpack is an unusual phenomenon that will affect PFAS elution with meltwater and subsequent entry to catchment surface waters. © 2014 Elsevier B.V. All rights reserved.

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