Kreisspiegelungen in Möbiusebenen

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Synthesis and reactions of some 3-(2-haloacyl)indoles

The reaction between indole and N-(2-haloacyl)pyridinium salts has been studied. With dioxan as solvent 1-(2-haloacyl)indole (2) was generally the product at low temperatures and 3-(2-haloacyl)indole (1) at high temperatures, as illustrated by the following α-bromopropionylation: Product ratio (1c/2a), 20° (0·01), 40° (0·8) and 60° (8·5). The fact that the a-bromobutyrylation at 60° gave 3-{N-(2-bromobutyryl)-1,4-dihydro-4-pyridyl}indole (6) as the main product, and 3-(2-bromobutyryl)indole (1d) only as a minor product, shows that the 3-acylation is affected by steric hindrance.At high reaction temperature (> 60°) the yield of1 decreased, owing to the formation of 3-indacylpyridinium salts (4).     

Spin resonant optical mixing in InSb — CW-measurements and transient effects

Optical four-wave mixing due to the resonant spin nonlinearity in n-InSb was observed in magnetic fields up to 1.4 T. The mixing of two CO-laser frequencies ω₁ and ω₂ = ω₁ - Δω yields radiation with frequencies ω₁ + 2Δω, ω₁ + Δω, ω₁ - 2Δω, and ω₁ - 3Δω. We found the resonant contribution to the third order nonlinear susceptibility arising from the spin-flip interaction to increase by more than two orders of magnitude when ω₁ is varied from 1760 cm^-1 to 1896 cm^-1. With the lasers working simultaneously Q-switched we observed radiation at ω₁ + Δω and ω₁ - 2Δω due to the mixing caused by the nonparabolicity of the conduction electrons even without an external magnetic field. At the resonant magnetic field the intensity of the mixed radiation is increased by more than one order of magnitude and is also observed when the laser pulses do not hit the sample simultaneously as long as the time difference between the two pulses does not exceed 450 ns. This points to a spin dephasing time T₂ of about 100 ns.     

Buchbesprechungen

Ohne Zusammenfassung     

The evaluation of overlap and Coulomb integrals in complexes with rare-earth or transition-metal central ions

Tables are given to enable effective algorithms to be formed for computer calculation of the overlap and Coulomb integrals with Slater-type orbitals in complexes with rare-earth or transition-metal central ions.     

Lumineszenz- und Leitfähigkeitsuntersuchungen an CaWO4-Einkristallen

Luminescence decay times of CaWO₄ single crystals after excitation with UV-light and electrons and thermoluminescence after irradiation with X-rays and electrons have been investigated. Under certain conditions thermally stimulated and photoconductivity is observed. The experimental results lead to a modification of the usual model of the luminescence centre in CaWO₄.     

Search for a super-allowed β−-decay of H4

If aβ-decaying H⁴ exists a super-allowed transition to the excited analogue state of He⁴ is possible. Such a decay mode was not considered in previous experiments. The reaction Li⁶ (γ, 2p) H⁴ was used to produce H⁴. No super-allowedβ ^?-decay of H⁴ could be observed and upper limits for the production cross section are given.     

Ein Experiment zur Überschreitung der Abbeschen Auflösungsgrenze

It is possible to overcome the Abbe limit of resolution by a factor two. For this one needs the A PRIORI knowledge, that the object is not birefringent or dichroic. That is to say, the object acts identically on both of the independant polarization components of the incident light. Then already one polarization component would be enough to form an image as complete as it is permitted by the lens system and by the aperture. The other polarization component would produce an identical image. Hence the capacity of the other polarization component to carry information from the object plane to the image plane is vasted. This vaste can be avoided by means of a special set up, containing e.g. twoWollaston prism. The result is the doubling in resolution without any increase of the aperture. This has been confirmed experimentally both for coherent and incoherent illumination.