Elektrometrische Bestimmung von Vanadium und Uran allein, gemeinsam und neben Eisen

Ohne Zusammenfassung     

Universality of the double scaling limit in random matrix models

We study unitary random matrix ensembles in the critical case where the limiting mean eigenvalue density vanishes quadratically at an interior point of the support. We establish universality of the limits of the eigenvalue correlation kernel at such a critical point in a double scaling limit. The limiting kernels are constructed out of functions associated with the second Painlevé equation. This extends a result of Bleher and Its for the special case of a critical quartic potential. The two main tools we use are equilibrium measures and Riemann‐Hilbert problems. In our treatment of equilibrium measures we allow a negative density near the critical point, which enables us to treat all cases simultaneously. The asymptotic analysis of the Riemann‐Hilbert problem is done with the Deift‐Zhou steepest‐descent analysis. For the construction of a local parametrix at the critical point we introduce a modification of the approach of Baik, Deift, and Johansson so that we are able to satisfy the required jump properties exactly. © 2005 Wiley Periodicals, Inc.     

Raman scattering from antiferromagnetic spin fluctuations

A microscopic theory for the scattering of light from spin fluctuation pair modes in the two-dimensional Hubbard model is presented. Two-spin fluctuation processes with opposite momenta near the antiferromagnetic wave vectorQ=(, ) are shown to contribute in particular to the low energy part of the Raman cross section. We explicitly investigate the influence of the Raman vertex function that describes the coupling of the Raman vertex function that describes the coupling of the light to the electrons and distinguishes between the different scattering geometries. In addition we explore the dependence on the correlation strength and on the temperature.     

Intramolecular carbonyl?carbonyl interactions in W, Mo and Fe complexes containing the η-N-maleimidato ligand: X-ray, DFT and AIM studies

The crystal structures of (η⁵-C₅H₅)W(CO)₃(η¹-N-maleimidato) and (η⁵-C₅H₅)Fe(CO)₂(η¹-N-maleimidato) complexes were determined by single crystal X-ray diffraction. The molecular geometries of both structures are compared with those of the Mo analog of the W complex and ethyl-N-maleimide in order to find a relation between the geometrical features and the rate constants of the addition reaction of the sulfhydryl group of biomolecules to the ethylenic bond of the maleimidato fragment. For a deeper insight into the problem DFT calculation were performed. An analysis of atomic charges, using the CHELPG scheme, and of theoretical electron density function, using the AIM theory, was performed. In the (η⁵-C₅H₅)W(CO)₃(η¹-N-maleimidato), likewise in its Mo analog, the carbonyl?carbonyl interaction was found both for experimental and calculated structures. It is probably the first approach to explain this type of intramolecular interactions acting in organometallic compounds. This interaction can play the essential role in the reaction mechanism of nucleophilic addition to the maleimidato moiety. The AIM investigations indicate also the differences in the character of bonding between the η-N-maleimidato ligand and the central metal atom.     

Surface-induced hydrogelation

The first azo dye that gels from its aqueous solution was synthesized and its moist hydrogel was investigated with electron microscopy and atomic force microscopy; the anionic azo dye in aqueous solution forms a hydrogel on cationic surfaces even at concentrations 50 times below the minimal gelation concentration.     

Preparation and Crystal Structure of MnBiS<Subscript>2</Subscript>Br

Summary. Black single crystals of MnBiS₂Br were obtained by the reaction of stoichiometric amounts of α-MnS, Bi, S, and BiBr₃ (3:2:3:1) at 600°C for 4 weeks. The compound crystallises in the monoclinic system, space group C2/m, with a = 12.767(2), b = 3.9468(4), c = 9.574(1) ?, β = 90.87(2)°, and Z = 4. The crystal structure refinement based on 720 reflections converged at R = 0.0244 and wR2 = 0.0579, respectively. MnBiS₂Br forms a layer structure consisting of MnS₆ octahedra, MnS₂Br₄ octahedra, and BiS₃₊₂ pyramids.