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).     

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.     

Quantitation of naproxen by quenching of phosphorescence from a ternary complex of 2-bromo-6-methoxynaphthalene and α-cyclodextrin

A unique method, based on the measurement of phosphorescence lifetimes, is reported for use in analytically detecting the widely used anti-inflammatory drug naproxen. The reciprocal phosphorescence lifetime of a ternary complex containing α-cyclodextrin and 2-bromo-6-methoxynaphthalene increases linearly with naproxen concentration and has a quenching constant of 2.1 ± 0.05 × 10⁶ M⁻¹ s⁻¹. Similar behavior is observed for quenching by the sodium salt of naproxen that has a quenching constant of 1.8 × 10⁶ ± 0.05 M⁻¹ s⁻¹. The experimental sensitivity is sufficient to permit measurements of naproxen concentrations differing by 11 μg/ml. Phosphorescence lifetime measurements reveal that the quenching mechanism does not involve displacement of the unrelaxed triplet-state guest molecule by naproxen from the complex and may occur by energy transfer or electron transfer.     

Proximity induced enhancement of the Curie temperature in hybrid spin injection devices

We investigate the increase of the Curie temperature T(C) in a lateral spin injection geometry where the ferromagnetic (Ga,Mn)As injector and detector contacts are capped by a thin iron film. Because of interlayer coupling between Fe and (Ga,Mn)As T(C) gets enhanced by nearly 100% for the thinnest (Ga,Mn)As films. The use of the proximity effect might pave the way for practical implementation of spintronic devices.     

Nonadiabatic superconductivity in K3C60 and Rb3C60

We discuss the validity of Migdal–Eliashberg theory applied to the superconductor fullerides K₃C₆₀ and Rb₃C₆₀. Recently, the relevant superconductor properties have been measured, like the isotope coefficient, the energy gap and critical temperatures for these compounds and compared with their optical properties. They all present a very disperse band of phonon frequencies, running from very small to very large energies, the latter being close to the Fermi edge. Therefore, these materials exceed the limit of validity of the adiabatic Migdal theorem, measured with a nonadiabatic parameter m=w₀/E_F, where w₀ is a characteristic phonon frequency and E_F=250 meV, the Fermi level. We examine previous theories incorporating vertex corrections into the Eliashberg equations to deal with such a situation. We compare these approaches by calculating the critical temperatures using a multimodal Eliashberg spectral function ²F(w) to study the contribution of the various phononic modes. We arrive at the conclusion that the optical modes, not the intramolecular ones, are among those which maximize T_c independently of including vertex corrections or not. This result goes in the direction to understand why doped fullerides A₃C₆₀ are superconductors.     

Lifshitz-point behaviour of ferromagnetic superconductors

The critical behaviour of the electromagnetically coupled superconductor magnet system is investigated by means of a generalized mean field theory and a renormalization group analysis. We show that in the presence of a genuine anisotropy in systems with an additional pressure-like parameter (like concentration in pseudo-ternary ferromagnetic superconductors (FMS), e.g. Er_1?x Ho _x Rh₄B₄) the indirect coupling between superconducting and magnetic order parameters (i.e. gauge coupling) can lead to a peculiar kind of critical behaviour characterized by Lifshitz points (LP). These points (quite generally) occur as merging points of three phases: a (magnetically) disordered phase, a homogeneously ordered phase and a modulated phase. In FMS the latter phase may result from exchange screening by supercurrents. This unusual critical behaviour is found in two varieties:

1. a regular LP which may occur on the lower transition line of a reentrant FMS
2. a similar but slightly different critical point which we term modified Lifshitz point (MLP), and which is to be expected at the merging point of the upper and lower superconducting transition lines with the magnetic order disorder transition lines in the (x, T) phase diagrams of FMS's.

     

Analysis of the fusariotoxins zearalenone and vomitoxin (deoxynivalenol) in human foods and animal feeds by high-performance liquid chromatography (HPLC)

Summary HPLC procedures for analyses of the fusariotoxins zearalenone and vomitoxin in individual food- and feedstuffs as well as in mixed feed are described. Zearalenone is separated on a column with polar stationary phase (25 cm × 4.6 mm i.d., particle size 7 m), eluted with a chloroform-isooctane (75/25, v/v)+1.5% methanol mixture and detected fluorometrically. The quantitative determination was possible in all analyzed samples with a detection limit of 2g/kg with 70–80% recovery. Vomitoxin is fractionated by HPLC (C ₁₈ ¹ column, 25 cm×4 mm i.d., 5 m particle size) with water-methanol (60/40, v/v) mobile phase and determined by combining GLC or TLC with UV detection. The detection limit in mixed feed with interfering substances was 25 g/kg (recovery 25–35%). The separation by HPLC makes preparation of pure vomitoxin possible. The described methods are fast, simple and low cost and are suitable for routine analyses.     

8-Sila-4-stanna-s-tetrahydroindacenes as synthons for Me2Si-bridged zirconocenes: formation from biscyclopentadienyl silanes by reaction with aminostannanes

Alkyl-substituted bis(cyclopentadienyl)dimethylsilanes react with Me₂Sn(NEt₂)₂ and with (Me₂N)₄Sn to yield correspondingly substituted, meso-configurated RS-8-sila-4-stanna-s-tetrahydroindacene and axially symmetric RR,SS-4-spiro-bis(8-sila-4-stanna-s-tetrahydroindacene) compounds, respectively, which are stereoselectively converted by reaction with ZrCl₄ to the corresponding meso- and rac-configurated ansa-zirconocene complexes.     

Zum Valenzwinkelproblem einfacher Moleküle

Ohne Zusammenfassung     

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.