Combined use of small-angle neutron scattering and atom probe tomography for the analysis of precipitates in a Fe-15 m% Co-25 m% Mo alloy

Atom probe tomography (APT) measurements were conducted to analyze nm-sized precipitates in a Fe-25 m% Co-15 m% Mo model alloy. Calculation of isoconcentration surfaces and application of cluster-search algorithms yielded the chemical compositions of matrix and precipitates. Small-angle neutron scattering (SANS) was performed in order to calculate the ratio of magnetic to nuclear scattering. This so-called A-ratio was compared with values calculated from the chemical information derived from the atom probe data. For this, the magnetism of the precipitates has to be taken into account. Ab-initio studies have been carried out to determine the magnetic moment of the precipitate phase. The results show that the extremely fine precipitates are ferromagnetic and exhibit near-equilibrium composition. In the very early stage of decomposition, however, the composition is different from near-equilibrium. The influences of the magnetism of the precipitates as well as of artifacts from atom probe measurements on the obtained results are discussed.     

Variational dimension of random sequences and its application

A concept of variational dimension is introduced for a random sequence with stationary increments. In the Gaussian case, the variational dimension in the limit coincides with the Hausdorff dimension of a proper random process. Applications of the concept are illustrated by examples of neurological data and network traffic analysis.     

Development of an HPLC-NMR method for the determination of PAHs in soil samples - a comparison with conventional methods

A hyphenated HPLC-(1)H NMR method for the identification and quantification of PAHs in soil samples has been developed and applied to a PAH reference sample provided by the Federal Institute for Materials Research and Testing (BAM, Berlin, Germany). The results were compared with those obtained by HPLC-DAD, HPLC-F, and GC-MS analyses of the same sample.     

Solid-phase microextraction-gas chromatography-mass spectrometry of biologically active substances in water samples

High-flow pneumatically assisted electrospray ionization mass spectrometry (ESI-MS) has been extensively used for the characterization and determination of peptides and peptide hormones available for biomedical research and therapeutic applications. The aim of this study was to optimize a method of characterization and determination of a mixture of peptide hormones with therapeutic interest by liquid chromatography (LC) coupled to ESI-MS. In this work the linear solvation energy relationship methodology was used in order to optimize the mobile phase to be used in the LC separation of the peptide hormone series and the operational parameters of the source and analyzer of ESI were also optimized to obtain the best signal stability and the highest sensitivity. To validate the proposed method for peptide hormone analysis, quality parameters were determined and satisfactory results were obtained. Likewise, the method detection limit was picomole level for most of the peptides employing selected-ion monitoring of the [M+nH]n+ ions.     

The Krein-Milman theorem in operator convexity

We generalize the Krein-Milman theorem to the setting of matrix convex sets of Effros-Winkler, extending the work of Farenick-Morenz on compact C-convex sets of complex matrices and the matrix state spaces of C-algebras. An essential ingredient is to prove the non-commutative analogue of the fact that a compact convex set may be thought of as the state space of the space of continuous affine functions on .

     

On the Relaxation of Energetic Electrons in Plasmas

The impact of individual collision processes on the relaxation of the velocity distribution function of a group of electrons, initially localized in a narrow region at relatively high energies, has been studied. By having recourse to solutions of the non-stationary Boltzmann equation and to corresponding Monte-Carlo simulations, the temporal behaviour of electrons in CO₂ plasmas, both in the absence and the presence of an external dc field, has been investigated. A microphysical interpretation of observed relaxation phenomena, based on the data relevant to the individual collision processes, is also given.