High-spin states in97Tc

The level scheme of⁹⁷Tc was studied by gamma ray spectroscopy using the⁹⁴Zr(⁶Li, 3nγ)⁹⁷Tc reaction. New levels and spins and parities were established.⁹⁷Tc is compared with the neighbouring even-even nucleus and with the results of an IBFM calculation.     

Influence of exchange fields in hybrid pairing superconductors,I: Ground states

Hybrid pairing superconductors with two bands of localized and delocalized states in the presence of uniform molecular fields and a finite displacement of the bands at the Fermi level are analyzed in mean field theory.At zero temperature, in addition to the usual BCS like ground state, agapless superconducting state withfinite spin polarization can be realized. The appearance of this state is somewhat analogous to the occurrence of the Fulde Ferrell state in a single band superconductor with an exchange field.We comment on the relevance of this model for heavy-fermion superconductors.Work performed within the research program of Sonderforschungsbereich 125 Aachen-Jülich-Köln     

Niedermolekulare diorganozinn-sauerstoff-verbindungen: di-t-butyl- und di-t-amylzinnoxid

Di-t-butyltin oxide (t-Bu₂SnO)₃ and di-t-amyltin oxide (t-Am₂SnO)₃ were synthesized by hydrolysis of the diorganotin dichlorides. Their molecular and crystal structures were investigated by X-ray diffraction techniques and vibrational spectroscopy. Both compounds form isolated molecules with planar six-membered tin-oxygen rings.     

Unusual critical behaviour of ferromagnetic superconductors

Electromagnetic effects are believed to play an important role in ferromagnetic superconductors (FMS). As an, to date, unobserved consequence of the electromagnetic coupling of the superconducting and the magnetic order parameter, we predict the possibility of Lifshitz point critical behaviour in FMS. In particular we present a detailed mean field investigation of the (T, x)-phase diagram of Er_1?xHo_xRh₄B₄ in the neighbourhood of the “modified Lifshitz point”, which separates the normal paramagnetic, the superconducting paramagnetic and the normal ferromagnetic phases.     

High spin states in73Se observed by the reaction70Ge(α,nγ)

⁷³Se has been investigated by the reaction⁷⁰Ge(α, nγ). Gamma excitation functions (E _α=10–16 MeV), gamma angular distributions (E _α=18 MeV) and gamma-gamma coincidences (E _α=15 MeV)) have been taken. A level scheme has been established, spins and partities have been assigned. States of a rotational band on the 151.2 keV (5/2^?) state and an anomalous band have been identified. Nuclear Reaction⁷⁰Ge(α,nγ)E _α=15 and 18 MeV; measuredE _γ,I _γ,γ-γ-coin.,γ-angular distribution,γ-excitation function.⁷³Se deduced levels,J, π. Enriched target, Ge(Li).     

Structural Analogues Of Aporphines Part 1: Synthesis of Apomorphines with the Catechol Moiety Replaced by 5-membered Heterocycles

Analogues of apomorphine (1) having the catechol moiety replaced by pyrrole (→ 10 , 18 ), pyrazole (→ 12 ), isoxazole (→ 13 , 14 ), thiazole (→ 16 ) and thiadiazole (→ 20 ) ring systems have been synthesized from the key intermediate ketone 6 .     

Percolation of diffusional creep: a new universality class

We study the percolation aspects of diffusional "Coble" creep on heterogeneous grain boundary networks, assuming free grain boundary sliding. A novel percolation threshold is obtained for the honeycomb lattice when two representative types of grain boundaries are randomly distributed, p(cc)=0.5416+/-0.0036. The creep viscosity diverges near the percolation threshold with power-law exponents t=1.69+/-0.09 and s=1.88+/-0.12, different from the standard conduction and rigidity percolation exponents. The moments of both the force and flux distributions all conform to finite-size scaling at p(cc), but with new exponents. These new scaling behaviors seen in the creeping system are proposed to arise from the unique coupling of both force and flux balances in the network.     

Hydrogen transfer vs proton transfer in 7-hydroxy-quinoline.(NH3)3: a CASSCF/CASPT2 study

Multiconfigurational CASSCF and CASPT2 calculations were performed to investigate the enol --> keto tautomerization in the lowest singlet excited state of the 7-hydroxyquinoline.(NH3)3 cluster. Two different reaction mechanisms were explored. The first one corresponds to that proposed previously by Tanner et al. (Science 2003, 302, 1736) on the basis of experimental observations and CASSCF optimizations under Cs-symmetry constraints. This mechanism comprises four consecutive steps and involves nonadiabatic transitions between the valence 1pipi* state and a pisigma* Rydberg-type state, resulting in hydrogen-atom transfer. Single-point CASPT2 calculations corroborate that for Cs-symmetry pathways hydrogen-atom transfer is clearly preferred over proton transfer. The second mechanism, predicted by CASSCF optimizations without constraints, implies proton transfer along a pathway on the 1pipi* surface in which one or more ammonia molecules depart significantly from the molecular plane defined by the hydroxyquinoline ring. The results suggest that both mechanisms may be competitive with proton transfer being somewhat favorable over hydrogen-atom transfer.     

Connectivity and percolation behaviour of grain boundary networks in three dimensions

Grain boundary networks are subject to crystallographic constraints at both triple junctions (first-order constraints) and quadruple nodes (second-order constraints). First-order constraints are known to influence the connectivity and percolation behaviour in two-dimensional grain boundary networks, and here we extend these considerations to fully three-dimensional microstructures. Defining a quadruple node distribution (QND) to quantify both the composition and isomerism of quadruple nodes, we explore how the QNDs for crystallographically consistent networks differ from that expected in a randomly assembled network. Configurational entropy is used to quantify the relative strength of each type of constraint (i.e., first- and second-order), with first-order triple junction constraints accounting for at least 75% of the non-random correlations in the network. As the dominant effects of constraint are captured by considering the triple junctions alone, a new analytical model is presented which allows the 3-D network connectivity to be estimated from data on 2-D microstructural sections. Finally, we show that the percolation thresholds for 3-D crystallographically consistent networks differ by as much as ±0.07 from those of standard percolation theory.