Teltow, Germany
Teltow, Germany

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Syromyatnikov V.G.,RAS Petersburg Nuclear Physics Institute | Schebetov A.F.,RAS Petersburg Nuclear Physics Institute | Lott D.,Geesthacht GmbH | Bulkin A.P.,RAS Petersburg Nuclear Physics Institute | And 2 more authors.
Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment | Year: 2011

A wide-aperture fan neutron supermirror analyzer of polarization is presented in the paper. The analyzer has been made in PNPI (Gatchina, Russia) for the neutron reflectometer NeRo in GKSS (Geesthacht, Germany). The analyzer is installed in front of the two coordinate position-sensitive detector with sensitive area 250×250 mm2. The neutron wavelength is 4.35 Å. The analyzer consists of 90 channels, and its entrance cross-section is 90×160 mm2. In the paper, the results of tests of the analyzer are presented. © 2010 Elsevier B.V. All rights reserved.

Pistidda C.,Geesthacht GmbH | Pistidda C.,Karlsruhe Institute of Technology | Garroni S.,Geesthacht GmbH | Garroni S.,Autonomous University of Barcelona | And 11 more authors.
Journal of Physical Chemistry C | Year: 2010

The hydrogen absorption mechanism of the 2NaH + MgB2 system has been investigated in detail. Depending on the applied hydrogen pressure, different intermediate phases are observed. In the case of absorption measurements performed under 50 bar of hydrogen pressure, NaBH4 is found not to be formed directly. Instead, first an unknown phase is formed, followed upon further heating by the formation of NaMgH3 and a NaH-NaBH4 molten salt mixture; only at the end after heating to 380 °C do the reflections of the crystalline NaBH4 appear. In contrast, measurements performed at lower hydrogen pressure (5 bar of H 2), but under the same temperature conditions, demonstrate that the synthesis of NaBH4 is possible without occurrence of the unknown phase and of NaMgH3. This indicates that the reaction path can be tuned by the applied hydrogen pressure. The formation of a NaH-NaBH4 molten salt mixture is observed also for the measurement performed under 5 bar of hydrogen pressure with the formation of free Mg. However, under this pressure condition the formation of crystalline NaBH4 is observed only during cooling at 367 °C. For none of the applied experimental conditions has it been possible to achieve the theoretical gravimetric hydrogen capacity of 7.8 wt %. © 2010 American Chemical Society.

Neffe A.T.,Geesthacht GmbH | Neffe A.T.,University of Potsdam | Zaupa A.,Geesthacht GmbH | Zaupa A.,University of Potsdam | And 4 more authors.
Macromolecular Rapid Communications | Year: 2010

Molecular models of gelatin-based materials formed the basis for the knowledge-based design of a physically cross-linked polymer system. The computational models with 25 wt-% water content were validated by comparison of the calculated structural properties with experimental data and were then used as predictive tools to study chain organization, cross-link formation, and estimation of mechanical properties. The introduced tyrosinederived side groups, desaminotyrosine (DAT) and desaminotyrosyl tyrosine (DATT), led to the reduction of the residual helical conformation and to the formation of physical net-points by π-π interactions and hydrogen bonds. At 25 wt.-% water content, the simulated and experimentally determined mechanical properties were in the same order of magnitude. The degree of swelling in water decreased with increasing the number of inserted aromatic functions, while Young's modulus, elongation at break, and maximum tensile strength increased. (Figure Presented) © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Wagermaier W.,Geesthacht GmbH | Zander T.,Geesthacht GmbH | Hofmann D.,Geesthacht GmbH | Kratz K.,Geesthacht GmbH | And 4 more authors.
Macromolecular Rapid Communications | Year: 2010

The dual- and triple-shape effects of multiphase polymer networks that contain two crystallizable chain segments have been assessed in situ by combining X-ray measurements with thermomechanical investigations. The studied polymer, named CLEG, is a multiphase polymer network of crystallizable poly(ε-caprolactone) (PCL) with grafted polyethylene glycol) (PEG) side chains. Wideangle (WAXS) and small-angle X-ray scattering (SAXS) measurements were combined with temperature-controlled in situ tensile testing experiments. This integrated approach enables systematic investigation and interpretation of relevant structural features during the programming procedures and the thermally-induced recovery process. Main results concern the combined effect of PCL and PEG crystals on shape fixation, the specific role of low-melting PCL crystallites in the fixation of the low temperature temporary shape, and the different orientation behavior of PCL and PEG crystals during certain stages of the programming procedure. These results demonstrate that crystal orientation effects are dominant for the PCL crystals. The effects of the low temperature PCL crystals could only be investigated when synchrotron radiation was applied. These findings indicate the great potential of in situ X-ray investigations for the creation of design-relevant knowledge about the microscopic foundations of dual- and triple-shape effects in appropriate polymer systems. (Figure Presented) © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Lendlein A.,Geesthacht GmbH | Lendlein A.,Berlin Brandenburg Center for Regenerative Therapies | Behl M.,Geesthacht GmbH | Kamlage S.,Geesthacht GmbH
NATO Science for Peace and Security Series A: Chemistry and Biology | Year: 2010

Degradable shape-memory polymer networks intended for biomedical applications are highlighted. These polymer networks were synthesized from oligo(ε-caprolactone)dimethacrylate (PCL), or oligo[(L-lactide)-ran- glycolide]dimethacrylate (PLG), or from starlike hydroxytelechelic oligo[(rac-lactide)-co-glycolide] and a low molecular weight linker. While the thermal transition related to the switching phase is a melting point in case of the PCL-based materials, the switching transition of oligo[(L-lactide)-ran- glycolide]dimethacrylate networks and copolyesterurethane networks is a glass transition. In this chapter, the influence of the nature of thermal transition on the shape-memory behavior of polymer networks is described. Furthermore, different polymer network architectures are introduced, which enable the tailoring of polymer network properties as well as the shape-memory capability. © 2010 Springer Science+Business Media B.V.

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