Zur Untersuchung von Versetzungen mit Hilfe der magnetischen Kernresonanz

The line width of the nmr signal is obtained for a statistical distribution of distances and orientations of dislocations as a function of the dislocation density. The quadrupolar part of the line width increases proportional to the root of the dislocation density in the case of first order distortion but is proportional to the dislocation density itself in the case of second order distortion. The total line width passes through a maximum within the range of first order distortion and approaches the value of the undistorted central line which arises from magnetic dipole interaction when the dislocation density becomes sufficiently large. The intensity decay of the nmr signal connected with this line width behaviour will also be presented. In the range of second order distortion the total line width is determined by the constant dipole interaction and the quadrupole interaction of the central line which depends on the dislocation density. Under the assumption of a Gaussian distribution for the line shape a simple expression for this width can be obtained. The calculations are checked for the case of first order distortion by measurements on the Na²³ and Cl³⁵ nmr signals of NaCl single crystals and for the case of second order distortion by measurements on the J¹²⁷ signal of KJ single crystals.     

Stability of a microwave heated fluid Layer

When a time harmonic electromagnetic wave impinges on a slaba certain portion of the wave creates heat within the slab throughdipolar and ohmic heating. The electrical and thermal propertiesof the material dictate the dynamical nature of the heatingprocess, as well as the steady-state temperature profile. Thematerial considered here is a slab of fluid. We consider thecase where the fluid is bounded by thin rigid layers of transparentmaterial. The steady-state heating profile governs the typesof convective motions that can occur and also affects the stabilitycharacteristics of temperature, pressure and velocity perturbationsintroduced in the slab. The main objective here is to examinesuch stability characteristics, initially in the linear regime.Both rigid-rigid and rigid-free configurations are considered.     

First direct observation of strong interaction spin-orbit effects in antiprotonic atoms

The strong ¯p-nucleus spin-orbit interaction was investigated in a measurement of the strong-interaction effects of the 9→8 transition in ¯p ¹⁷⁴Yb at the Low-Energy Antiproton Ring (LEAR) at CERN. This measurement was part of an experimental programme where, for the first time, the fine-structure components of the last observable X-ray transition in a ¯p atom, which carries information on the strong ¯p-nucleus interaction, were resolved and studied individually. The observed splitting ΔE _exp=2408±26 eV consists of the electromagnetic fine-structure splitting ΔE _FS=2350 eV and an additional splitting Δ?=58±26 eV. In addition, one finds a significant difference in the level widths of Δ=195±59 eV with the larger value_?=1216±41 eV for the lower fine-structure level. This experiment follows an earlier measurement on ¯p ¹³⁸Ba, where the transition 8→7 is influenced by the strong interaction. In this case, however, the fine-structure components could not be resolved. The results for¹⁷⁴Yb may be attributed to a spin-orbit (LS) term in the complex strong-interaction potential.     

Radical cyclization of sugar-derived beta-(alkynyloxy)acrylates: synthesis of novel fused ethers

[formula: see text] Tributyltin radical mediated cyclization of carbohydrate-derived beta-(alkynyloxy)acrylates leading to highly functionalized cis- and trans-fused bicyclic ethers of various ring sizes is described. The efficacy of the radical cyclization is nicely illustrated in the iterative construction of a trans-fused tricyclic tetrahydropyran.     

Alkalimanganselenide und -telluride A2Mn3X4 – Synthese,Kristall- und Spinstruktur

Alkali Metal Manganese Selenides and Tellurides – Synthesis, Crystal and Spin Structures The compounds Rb₂Mn₃Se₄, Cs₂Mn₃Se₄, Rb₂Mn₃Te₄ and Cs₂Mn₃Te₄ were synthesized by the reaction of alkali metal carbonates with chalcogen and Mn or MnCO₃ in a stream of hydrogen charged with chalcogen. Structural investigations show that all compounds crystallize in isotypic atomic arrangements (Cs₂Mn₃S₄-type, space group Ibam, Z = 4). Additionally neutron diffraction experiments were carried out and yielded the spin structures of Rb₂Mn₃Se₄ and Cs₂Mn₃Se₄ (Shubnikov space group Ibam'). The structural related selenides ALiMnSe₂ and ALiZnSe₂ (A = K, Rb or Cs) were synthesized by analogous reactions. All these compounds are isotypic and crystallize in the BaZn₂P₂-structure type.