Exact ground state of a spin ladder with a quantum phase transition

We introduce a spin ladder with Ising interactions along the legs and intrinsically frustrated Heisenberg-like ferromagnetic interactions on the rungs. The model is solved exactly in the subspaces relevant for the ground state by mapping to the quantum Ising model, and we show that a first order quantum phase transition separates the classical from quantum regime, with the spin correlations on the rungs being either ferromagnetic or antiferromagnetic, and different spin excitations in both regimes. The present case resembles the quantum phase transition found in the compass model in one and two dimensions.     

Application of EPR Spectroscopy to Examination of Free Radical Formation in Thermally Sterilized Flumetasone

Thermal formation of free radicals in flumetasone sterilized according to the pharmaceutical norms at 160, 170 and 180 °C was examined by electron paramagnetic resonance (EPR) spectroscopy. The microbiological analysis was done. Similar free radical concentrations were measured for flumetasone sterilized at 160 and 170 °C. The concentration was considerably higher than that for flumetasone sterilized at 180 °C. Fast spin–lattice relaxation processes, homogeneously broadened EPR lines, and complex free radicals system characterize the heated flumetasone. Free radicals were not observed 30 days after thermal sterilization. Optimal temperatures of sterilization of flumetasone are 160 and 170 °C.     

Impedance spectroscopy of vanadium modified BaBi<Subscript>2</Subscript>Nb<Subscript>2</Subscript>O<Subscript>9</Subscript> ceramics

In recent years a wide range of Aurivillius layered materials have been introduced. These novel materials are produced in many various forms such as fibers, thin films as well as bulk by using a number of processing routes. As advanced materials they are they have many interesting properties which include a number of useful electrical properties related to separated grain and grain boundary conductivity, impedance, activation energies, etc. In this paper these properties are described and discussed in detail. The electrical properties of the vanadium doped BaBi₂Nb₂O₉ ceramic was measured over a wide range of temperatures by impedance spectroscopy (IS). The separated grain activation energy, calculated from Arrhenius characteristics at temperatures between room temperature and 600 °C, was 1 eV for 0 at.% of vanadium dopant and 1.2 eV for 10 at.%, whereas the activation energies in the grain boundary region were 0.97 and 1.15 eV, respectively. The obtained results suggest the significant role of vanadium dopant, causing ordering the crystalline structure.     

Cu(II) recognition materials: Fluorophores grafted on mesoporous silica supports

There were designed and synthesized naphthalene and pyrene derivatives consisting of fluorophore group and of receptor fragment with donor N and O atoms. These fluorosensors were covalently attached by grafting carboxyl group to surfaces of silica xerogel or mesoporous silicas (MCM-41 and MCM-48) functionalized either with 3-aminopropyl or 3-glycidoxypropyl groups. The pyrene derivatives 2 and 3 covalently grafted on MCM-48 silica functionalized with 3-aminopropyl groups are potential recognition elements of a fluorescence chemical sensor.Fluorescence emission of the prepared recognition materials is quenched specifically owing to photoinduced electron transfer (PET) effect after coordination reactions with Cu(II) ions. Moreover, both the materials exhibit selectivity for Cu(II) ions in aqueous solutions in presence of such metal ions as: alkali, alkaline earth and transition. During UV irradiation the studied recognition elements undergo slowly photochemical degradation.     

Asymptotic distribution of the discriminant function

This paper describes discrimination among multivariate autoregressive processes by the Bayes method. The asymptotic distribution of the discriminant function and estimation of the probability of misclassification are investigated.     

Subthreshold kaon production in Au on Au collisions at 1 GeV/u

Subthreshold kaon production in¹⁹⁷ Au+¹⁹⁷ Au collisions at 1.0 GeV/u has been investigated with the Kaon Spectrometer at SIS. At _lab =44±4 we found aK ⁺/p ratio of>3 · 10^–4 for the momentum range 650 MeV/c to 1150 MeV/c.Dedicated to Prof. Dr. P. Kienle on the occasion of his 60th birthday     

Electronic structure and magnetism in 4d-transition metal clusters

We analyze the stability of magnetic states obtained within the tight-binding model for cubooctahedral (O_h) and icosahedral (I_h) clusters of early 4d (Y, Zr, Nb, Mo, and Tc) transition metals. Several metastable magnetic clusters are identified which suggests the existence of multiple magnetic solutions in realistic systems. A bulk-like parabolic behavior is observed for the binding energy of O_h and I_h clusters as a function of the atomic number along the 4 d-series. The charge transfer on the central atom changes sign, while the average magnetic moments present an oscillatory behavior as a function of the number of d electrons in the cluster. Our results are in agreement with other theoretical calculations. Received: 20 November 1997 / Received in final form: 9 March 1998 / Accepted: 30 March 1998