Ein Polarimeter zur Messung schneller chemischer Reaktionen

Zusammenfassung Es wird ein Polarimeter vorgestellt, das die Messung schneller Änderungen der optischen Drehung gestattet. Als Meßprinzip wird eine Art Zweistrahlverfahren benutzt. Die Drehung wird in ein Signal umgesetzt, das dieser Drehung direkt proportional ist und das zur Kompensation dieser Drehung verwendet wird. Durch das Kompensationsverfahren bleibt die Messung der optischen Drehung unbeeinflußt von eventuell gleichzeitig stattfindenden Extinktionsänderungen. Die Zeitkonstante des Gerätes beträgt etwa 20 s. Die Auflösung ist durch das Schrotrauschen begrenzt und beträgt bei der angegebenen Zeitkonstante etwa ± 15 Milligrad.Wir danken der Deutschen Forschungsgemeinschaft für die Förderung dieser Untersuchungen.     

State of order in isotactic polyhexylethylene

Cooling slowly from the melt and annealing at 250 K for a month isotactic polyhexylethylene becomes partially crystalline. The degree of crystallinity, calculated according to the method of Hermans and Weidinger, is 0.3. The wide-angle x-ray diffraction diagram shows seven reflections, not completely independent of one another. These x-ray data do not allow an exact determination of the structure. The main chins possibly form quaternary helices (e. g., 4/1 or 7/2 helices) and the side chains are arranged in triclinic structure. The unit cell may be monoclinic: a ～ 0.56 nm, b ～ 3.8 nm, c ～ 0.76 nm (in case of a 4/1 helix), β ? 97° The melting temperature is 278 K and the heat of fusion amounts to 30 J/g.     

Block Preconditioners in the Parallel Toolbox

We present a parallel solver for second order scalar PDE called The Parallel Toolbox. We investigate certain performance issues which arise when high performance compute nodes with a relatively slow network interconnect are used. These performance issues motivate the introduction of block methods which reduce network usage and thus increase parallel performance. First benchmarks computed on a GPU cluster evaluate the success of this attempt. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

State of order in blends of poly(butylene terephthalate) with poly(ethylene terephthalate) or polycarbonate

Blends of PBT with PET or PC were studied by X-ray diffraction and DSC for different conditions of crystallization. PBT and PET crystallize very similarly, though they are recognized as partially compatible in the melt. In the PBT/PC blends X-ray diffraction examinations show crystallization of PC after 4 h of annealing. In the melt, both components are compatible. T_g-calculations indicate a plasticizing effect. In both kinds of blends, PBT crystallizes faster than PC or PET. Fast crystallization processes were examined by X-ray diffraction measurements with synchrotron radiation.     

Experimentelle Bestimmung der Supraleitungsparameter einiger Verbindungen vom β-Wolframtyp aus Magnetisierungsmessungen

A complete analysis of magnetization curves is given for bulk sintered samples of Nb₃Sn with low hysteresis and for finely powdered sintered and melted samples of Nb₃Sn, Nb₃Al, V₃Si and V₃Ga. The Ginzburg-Landau parameterκ and the penetration depthλ of weak magnetic fields is calculated from the temperature dependence of the thermodynamic and upper critical fieldsH _c andH _c2. The slope of theH _c ?T curve is about 360 Oe/°K and approximately the same for all measured samples. There is an extremely high increase of the lower critical fieldH _c1 if the grain size approachesλ. The occurence of field expulsion and partially reversible magnetization curves of sintered Nb₃Sn samples with high sintering temperatures and high pore volumes is explained by means of connections between single grains which have lower transition temperatures.     

Ordnungszustände im system polyamid-6 und polyamid-6, 6

Blends of PA-6 and PA-6,6 were studied by DSC for different conditions of crystallization. All samples were characterized by x-ray diffraction. From dilute solution the components crystallize in separate modifications. In the melt both components are compatible. PA-6- and PA-6,6-segments are linked together. During rapid quenching of the melt in the samples of about equal composition of PA-6 and PA-6,6 a modification is formed possibly built by a three-dimensional network of hydrogen bonds between PA-6- and PA-6,6-segments. If the samples of the same composition are annealed at 25 K below the melting temperatures of PA-6 and PA-6,6 for 3 hours in each case a modification appears as in quenched samples in addition to only partially ordered crystallites of PA-6 and PA-6,6. Despite optimal annealing there is no complete separation of the components.     

Three-dimensional micro-XRF under cryogenic conditions: a pilot experiment for spatially resolved trace analysis in biological specimens

Three-dimensional micro-XRF is a recently developed microprobe which facilitates three-dimensional resolved chemical analyses with a resolution of around 20 μm. Arbitrary sites or sections of samples can be investigated without the need to section specimens physically. In this paper we demonstrate the use of the microprobe in combination with a cold nitrogen gas stream for the cryogenic fixation of specimens. A 3D micro-XRF setup at the new microfocus beamline at BESSY II was equipped with a nitrogen cryogenic stream. The distribution of Ca, Fe, Zn and Cu across virtual cross sections of a water-rich sample, the root of common duckweed, could be investigated without further sample preparation. This paper demonstrates the capabilities of 3D micro-XRF under cryogenic conditions for investigations of biological specimens.