[en] The nature and the magnitude of the spin exchange interaction between the electrons within the half-filled band (HFB) arising as result of intermolecular π-π interaction between polymethine radicals in a two-dimensional Langmuir film has been investigated theoretically using the band theory of open-shell π-electron systems. It is shown that a favorable slipped geometry of the radicals in stacks is responsible for the nature of magnetic interaction: either ferromagnetic or anti-ferromagnetic

[en] This memo aims to provide an overview of environmentally harmful subsidies in the Netherlands. Eliminating environmentally harmful subsidies is an important first step toward including the environmental effects in prices and weigh the use of natural resources explicitly in decisions made by citizens, businesses and governments. Particularly in the sectors energy, transport and agriculture significant amounts of environmentally harmful subsidies are available. For the Netherlands this amounts to 5-10 billion euros in 2010. The exact amount is difficult to estimate depends strongly on the definition and the method of calculation. This also goes for determining the hazardous effects on the environment.

[en] The Ruhrverband operates a total of 118 municipal wastewater treatment works. Predominantly, biological treatment is applied. Supplementary to common analyses the digested sludges are investigated concerning radioactivity since 1960. Thus, the additional loading resulting from fall out and wash out after the reactor accident on 26 April 1986 in Chernobyl could be precisely recorded. Prior to the description of the effects of the Chernobyl accident on river water, potable water and on wastewater sludges, a short background information on the occurrence of the accident and its consequences for the F.R.G. is given. (author)

[en] Allenes, substituted with radicalic groups (CH₂^z.ccirf, NH₂^z.ccirf⁺, HN-O^z.ccirf) at the terminal carbon atoms, have been investigated theoretically by ab initio methods. It is shown that the 1,3-dimethyleneallene and the 1,3-diaminoallene dication are molecules with triplet ground states due to the formation of carbene-like triplet state structures. In contrast, the closed-shell singlet state and the triplet state are degenerate for the 1,3-dinitroxideallene due to orthogonally arranged and hence decoupled π-electron systems. (Copyright (c) 1999 Elsevier Science B.V., Amsterdam. All rights reserved.)

[en] It has been shown that a symmetry lowering from a state with higher symmetry to a state with lower symmetry (D_(2m)d → C_(2m)) occurs in 1-D polymers with polymethine fragments as elementary units when electron-vibration interaction is taken into account. The investigations are carried out using an extended Su-Schrieffer-Heeger method, where the electron-electron interaction is taken into account

[en] The excitation function and momentum distribution of η^′ mesons have been measured in photon induced reactions on ¹²C in the energy range of 1250–2600 MeV. The experiment was performed with tagged photon beams from the ELSA electron accelerator using the Crystal Barrel and TAPS detectors. The data are compared to model calculations to extract information on the sign and magnitude of the real part of the η^′-nucleus potential. Within the model, the comparison indicates an attractive potential of −(37±10(stat)±10(syst)) MeV depth at normal nuclear matter density. Since the modulus of this depth is larger than the modulus of the imaginary part of the η^′-nucleus potential of −(10±2.5) MeV, determined by transparency ratio measurements, a search for resolved η^′-bound states appears promising

[en] ω photoproduction off hydrogen and deuterium has been studied with the tagged photon beam of the ELSA accelerator in Bonn for photon energies up to 2.0 GeV. The ω meson has been identified via the ω → π⁰γ → γγγ decay mode, using the combined setup of the Crystal Barrel/TAPS detector systems. Both inclusive and exclusive analyses have been carried out. Differential and total cross-sections have been derived for ω mesons produced off free protons and off protons and neutrons bound in deuterium. The cross-section for the production off the bound neutron is found to be a factor of ∼ 1.3 larger than the one off the bound proton in the incident beam energy region 1.2 GeV < E_γ < 1.6 GeV. For higher incident beam energies this factor goes down to ∼ 1.1 at 2.0 GeV. The cross-sections of this work have been used as normalization for transparency ratio measurements. (orig.)