Zum Mechanismus der Polymerkristallisation

Zusammenfassung Auf der Grundlage der Ergebnisse von Röntgenkleinwinkel-Streuexperimenten und elektroenenmikroskopischen Untersuchungen an verzweigtem Polyethylen wird ein neues Modell zum Ablauf des partiellen Kristallisierens und Schmelzens entwickelt. Im Modell wird der Aufbau der Lamellarstruktur als sukzessive Einschubkristallisation beschrieben, die durch die Konzentration an nichtkristallisierfähigen Einheiten in den amorphen Bereichen gesteuert wird. Die Kinetik der Einschubkristallisation läßt sich durch dilatometrische Experimente verfolgen. Aus vergleichenden Röntgenkleinwinkel- und Ramanstreuexperimenten kann auf eine Anreicherung der Cobausteine an den Lamellenoberflächen geschlossen werden.Preprint zur 30. Hauptversammlung der Kolloid-Gesellschaft, 6.–9. Oktober 1981 in Ulm.     

Forced oscillations of airfoil flows

The effect of background flow oscillations on a transonic airfoil (NACA 0012) flow was investigated experimentally. The oscillations were generated by means of a rotating plate placed downstream of the airfoil. Owing to the expansion and compression waves generated at the plate, the flow over the airfoil flow was drastically disturbed. This resulted in the presence of high intensity oscillations of a shock wave and a separation bubble on the suction surface of the airfoil. For relatively large values of the airfoil angle of attack, weak shock waves (transonic sound waves) were periodically shed upstream of the airfoil.This work was supported by Commission of the European Communities (Communit's Action for Cooperation in Science and Technology with Central and Eastern European Countries).The authors wish to thank Mr P. Koperski for his effective assistance in taking the photographs.     

Thermische und photochemische umsetzungen von acetylenen mit metallcarbonylen—IV : Cycloadditionen von bis[α-oxo-alkinen] in gegenwart von nickeltetracarbonyl

Aryl substituted bis[α-oxo-alkynes] e.g. 1 and 2 with triple bonds, which are able to come in close proximity, yield by the catalytic action of Ni(CO)₄, the quinones 5 and 6 or 7 and 8, respectively. With an excess of added diphenylacetylene or benzoylphenylacetylene, the Diels-Alder adducts 9 and 10 can be obtained. The structural determination of the final products and the reaction mechanism were examined by analysis and measurement of dipole moments, IR, UV, ¹H-NMR, ¹³C-NMR and mass spectra.     

Electron spin polarization in uranium sulfide

We present spin polarization and energy distribution curves of photo-electrons from US and compare them with a density of states calculation based on a cluster method. For photon energies hv ≤ 11 eV the photo-electron spin polarization is negative. Near threshold a structure is observed in the spectra, which is attributed to emission from the 5f-states.     

Multilinearität bei Polyederaddition

Ohne Zusammenfassung     

Die Erzeugung und Bewegung einzelner Versetzungen in Germaniumkristallen

Topographic X-ray pictures are presented showing dislocation sources in plastically deformed germanium crystals. Both internal Frank-Read sources as well as sources at the crystal surface have been observed. Dislocation velocities from 10^?6 to 10^?4 cm/sec have been evaluated.     

BaTiO3 thin-film waveguide modulator with a low voltage-length product at near-infrared wavelengths of 0.98 and 1.55 microm

A BaTiO3 thin-film electro-optic waveguide modulator with a low half-wave voltage-length product has been demonstrated at near-infrared wavelengths of 1-1.6 microm. Half-wave voltage-length products as small as 0.25 and 0.5 V cm were measured for a 5-mm-long device at wavelengths of 973 and 1561 nm, respectively. The effective electro-optic coefficients were calculated as 420 pm/V at 973 nm and 360 pm/V at 1561 nm. Further improvements in device performance by optimizing the ferroelectric domain structure are anticipated.