In situ measurement of pressure and strain effects in corundum ceramics

Abstract

An Equipement has been built for the generation of uniaxial pressure and of bending stress respectivety directly in the cavity of an X-band ESR spectrometer. Changes of the structure of paramagnetic centres (Fe³⁺ on Al³⁺ sites) could be detected in materials with a high content of corundum under the innuence of pressure and bending stress. The objects of investigation are not only suitable model system but also have practical relevance. The Fe³⁺-ions, incorporated in the materials react very sensitive on mechanically or thermally induced changes of the state of the matrix. They give insight into the materials at a microscopic level The interpretation of the observed intensity and shift effects is possible on the basis of an adequate spin-hamiltonian.     

A Preisach-based hysteresis model for magnetic and ferroelectric hysteresis

In this paper we present a model for hysteretic nonlinearities with non-local memories. This model can be applied to describe hysteretic material behavior. Common applications are ferromagnetic or ferroelectric materials. Our model consists of an analytic function and a Preisach operator. We define a continuous Preisach weight function and introduce a method for the identification of the model parameters. The model parameters are customized to a set of symmetric hysteresis curves. We verify our model for a soft magnetic material, a hard magnetic material and the ferroelectric behavior of some piezoelectric material. After that, non-symmetric curves like the virgin curve are predicted very well by the model. It is especially useful, if forced magnetization or polarization, that appears beyond technical saturation, come into account.     

Interatomic electronic decay driven by nuclear motion

The interatomic electronic decay after inner-valence ionization of a neon atom by a single photon in a neon-helium dimer is investigated. The excited neon atom relaxes via interatomic Coulombic decay and the excess energy is transferred to the helium atom and ionizes it. We show that the decay process is only possible if the dimer's bond stretches up to 6.2 ?, i.e., to more than twice the equilibrium interatomic distance of the neutral dimer. Thus, it is demonstrated that the electronic decay, taking place at such long distances, is driven by the nuclear motion.     

Synthese,Struktur und einige Reaktionen [N-(N′,N′,N″,N″-tetramethyl)-guanidinyl]-substituierter Phosphorylverbindungen

Synthesis, Structure, and some Reactions of N-(N′,N′,N″,N″-tetramethyl)guanidinyl-substituted Phosphoryl Compounds The tetramethylguanidinyl-substituted phosphoryl compounds 1 – 10 were prepared in the reaction of the appropriate chlorophosphoryl compounds with either N′,N′,N″,N″-tetramethylguanidine (HTMG) or N-trimethylsilyl-(N′,N′,N″,N″-tetramethyl)guanidine (TMSTMG). With methyl iodide 1 reacted with N-alkylation to give the ammonium salt 11. 1 reacted with BF₃ · Et₂O at both imino nitrogen atoms with formation of the bis-BF₃-adduct 12 . The X-ray structure determination of phenylphosphonic acid-bis(N′,N′,N″,N″-tetramethylguanidinide) 3 shows shortened PN-bonds and widened PNC-angles, consistent with the partial double bond character of the PN-bond.     

Cloud point extraction of napropamide and thiabendazole from water and soil

The micellar extraction and enrichment of napropamide and thiabendazole using Genapol X 80 is described. Combined with their quantification by fluorescence, detection limits below 0.2 g/l with recovery rates of up to 95% were achieved. The recovery could be improved by lowering the extraction temperature and purificaton of the surfactants. This extraction method has been applied to the isolation and preconcentration of napropamide from standard soils. Experimental parameters affecting the recovery rates were examined.     

Energies and spatial features for the rotationless bound states of 4He3+(2Sigmag+): a cationic core from helium cluster ionization

Ab initio quantum calculations have been carried out on the helium ionic trimer. The potential energy surface is accurately fitted, especially in the vicinity of the three equivalent minima. The spectrum of bound states for the zero angular momentum is computed and analyzed in detail. Energies and wave functions reveal several interesting features related to the fact that He3+ represents one of the few homonuclear ionic trimers that are linear in their ground vibrational state. At low energies, the triply degenerate eigenfunctions are localized at the potential minimum. With growing excitation energy, however, the wave functions exhibit stronger spatial delocalization.     

Functionally relevant electric-field induced perturbations of the prosthetic group of yeast ferrocytochrome c mutants obtained from a vibronic analysis of low-temperature absorption spectra

We have measured the low temperature (T = 20 K) absorption spectra of the N52A, N52V, N52I, Y67F, and N52AY67F mutants of ferrous Saccharomyces cerevisiae (baker's yeast) cytochrome c. All the bands in the Q0- and Q(v)-band region are split, and the intensity distributions among the split bands are highly asymmetric. The spectra were analyzed by a decomposition into Voigtian profiles. The spectral parameters thus obtained were further analyzed in terms of the vibronic coupling model of Schweitzer-Stenner and Bigman (Schweitzer-Stenner, R.; Bigman, D. J. Phys. Chem. B 2001, 7064-7073) to identify parameters related to electronic and vibronic perturbations of the heme macrocycle. We report that the electronic perturbation is of B(1g) symmetry and reflects the heterogeneity of the electric field at the heme, that is, the difference between the gradients along the perpendicular N-Fe-N axis of the heme core. We found that all the investigated mutations substantially increase this electronic perturbation, so that the spectral properties become similar to those of horse heart cytochrome c. Moreover, the electronic perturbation was found to correlate nonlinearly with the enthalpy changes associated with the reduction of the heme iron. Group theoretical arguments are invoked to propose a simple model which explains how a perturbation of the obtained symmetry can stabilize the reduced state of the heme iron. Finally, vibronic coupling parameters obtained from the analysis of the Q(v)-band region suggest that the investigated mutations decrease the nonplanar deformations of the heme group. This finding was reproduced by a normal mode structural decomposition (NSD) analysis of the N52V and N52VY67F heme conformations obtained from a 1 ns molecular dynamics simulation. We argue that the reduced nonplanarity contributes to the stabilization of the reduced state.