Metall-Schwefelstickstoff-Verbindungen. 17. Die Verbindungen HgN2S · NH3 und 2Hg(NH3)2I2 · S4N4

Metal Sulphur Nitrogen Compounds. 17. Compounds HgN₂S · NH₃ and Hg(NH₃)₂I₂ · S₄N₄ The crystal and molecular structures of the known compounds HgN₂S · NH₃ and of the new inclusion compound 2Hg(NH₃)₂I₂ · S₄N₄ are reported. HgN₂S · NH₃ is orthorhombic, space group Pbca with a = 5.548, b = 10.158, c = 14.919 Å, Z = 8. In the dimeric molecules two Hg atoms are bridged to form eight-membered rings . In addition, each Hg is coordinated by an NH₃ molecule and by an N atom of an adjacent ring. This results in a two-dimensional network. 2Hg(NH₃)₂I₂ · S₄N₄ is tetragonal, space group P4₂/nmc, a = 8.948, c = 13.188 Å, Z = 2. It is an inclusion compound with S₄N₄ molecules in the holes of the lattice of the large Hg(NH₃)₂I₂ tetrahedra.     

Long-range tail produced by the CDD ambiguity in a static model

An aspect of a potential-model analogy of the customary CDD ambiguity is studied. Starting from the idea that the known CDD ambiguity in theS-matrix produces an ambiguity in the determination of potentials, the influence of CDD poles upon the long-range behaviour of potentials in the relativistic (Klein-Gordon) static model is demonstrated. Generation of the long-range tail by CDD poles is investigated in terms of a scattering inversion-problem formalism, based on theN/D equations extended off the mass shell.     

Permeability of heterogeneous gels

Gels made by radical copolymerization of monofunctional and difunctional monomer units in the presence of swelling medium will tend to be heterogeneous. A case in point is acrylamide co-polymerized with N,N′-methylene bis-acrylamide in water. Such gels can be assumed to be two-phasic with both phases gels, but of different average concentration and average degree of cross-linking. As Weiss and Silberberg have shown, permeability can be used to characterize the distribution in space. In this paper, their earlier model is expanded and improved by considering specifically the permeability of each of the two phases and taking into account that each of these phases separately must have come into swelling equilibrium with the swelling medium, water. It can be shown that only the length of the Kuhn statistical element remains as a free parameter in this model. Essentially the same value of this parameter, however, accurately accounts for the measured permeability. It is found that at an overall volume fraction of about 0.16, the two-phase structure tends to disappear. For higher degrees of crosslinking, this occurs because the more dilute phase takes over the entire space; for more lightly crosslinked systems, the more concentrated phase takes over. The heterogeneity of the distribution lies in the nanometer range and reasonable agreement between the results obtainable from permeability and from viscoelasticity can be demonstrated. These results are consistent with the model for the polymerization process.     

Über s-reguläre Graphen

Let G be a graph of valency d = 1 + p^rn with p prime and n < p. It is shown that if the automorphism group of G contains a subgroup A which acts as a regular permutation group on the set of s-arcs in G then s ≤ 7 and s ≠ 6; if d = p^r + 1, r = 2^r, v ≥ 1 an integer, p ≠ 2, then s = 1.