Oberfl?chenuntersuchungen zur Phosphatisierung von unlegierten Stahlblechen

Zusammenfassung Unterschiedliche Ergebnisse im Korrosionsverhalten von zwei unlegierten, phosphatierten Feinblechsorten mit Farbauftrag wurden auf die Korngrößendifferenz der Phosphatdeckschicht zurückgeführt. Zur Klärung des Keimbildungs und Wachstumsverhaltens der Phosphatkristalle wurden chemische Analysen im Oberflächenbereich der Walzproben mit der Ionenmikrosonde vorgenommen. Die Ausbildung einer Adsorptionsschicht mit hohen Kohlenstoffanteilen konnte mit durch den Walzvorgang hervorgerufenen Konzentrationsänderungen der Eisenbegleitelemente in m-tiefen Oberflächenschichten in Zusammenhang gebracht und deren Einfluß diskutiert werden.

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Surface examinations for the phosphatization of non-alloyed steel sheets

Summary Differences in the results of corrosion tests of two non-alloyed phosphatized and painted steel sheets were related to differences in the grain sizes of their phosphate coating. Chemical analysis in the surface region of the rolled steel samples was made by an Ion Microprobe to determine nucleation and growth of the phosphate crystals. The formation of an adsorption layer with high carbon content could be related to the concentration changes of the non-alloyed elements in m-deep surface layers; this relationship is discussed.

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Wir danken dem Conselho National de Desenvolvimento Científico e Tecnológico (CNPq) für finanzielle Unterstützung.     

Study of inclusive neutral current interactions of neutrinos and antineutrinos

We report on results from a study of hadron-energy distributions for ν and $\text{ν}$ inclusive neutral current interactions. There is no significant variation of the neutral to charged current total cross-section ratios R_ν and $\text{R}\text{ν}$ with neutrino energy. The space-time structure of neutral currents is dominated by V?A, with a significant admixture of V+A. The Weinberg-Salam model is in agreement with all data if sin²θ_w=0.24±0.02.     

The magnetic field influence on bridge-assisted electron transfer

The influence of an external magnetic field on the rate of electron transfer is studied theoretically for the case of a donor-acceptor complex with paramagnetic ions as bridging sites. We demonstrate for a bridge with a single and with two paramagnetic ions that the applied magnetic field causes a blocking effect of the electron transfer. Each paramagnetic ion staying in its electronic ground state is assumed to reduce its spin from if the transferred electron is coupled to it. Such a spin reduction determines the magnetic field dependence of the transfer rate in a specific manner. The magnetic field dependence is derived at low temperatures in utilizing the Wigner 6j-symbols method. For the case of two paramagnetic ions per bridge the exchange interaction between them has been additionally included into the calculations. It is responsible for the step-like dependence of the rate constant on the magnetic field, as well as for the creation of a rather narrow field-strength region where the rate constant drops to zero.     

Anisotropy induced in a silver chloride emulsion by two successive beams of white light perpendicularly polarized

This paper is a study of the anisotropy induced in a silver chloride photographic emulsion by two successive beams of white light, linearly polarized at right angle. After the first exposure, the colloidal medium contains silver ellipsoids e generated by the photolysis of silver chloride and silver ellipsoids e_b resulting of the partial destruction of some of the previous ones by long wavelengths. This medium is then illuminated by the second beam linearly polarized at right angle of the first beam. Short wavelengths induced silver ellipsoids e′ identical to the ellopsoids e but rotated through π/2 with respect to them. As in the first exposure, some of them are partly broken up and transformed into ellipsoids e′_b identical to ellipsoids e_b but the direction of their major axis. Moreover, the long wavelengths of second exposure transform some of the particles e and e_b generated during the first exposure, into smaller ellipsoids e_eb and e_bb. Finally, the colloidal medium resulting of these two exposures, contains silver chloride and six sorts of silver particles. By calculating the indices of the medium, we show that the wavelengths characterizing the zero birefringence and zero dichroism of the emulsion are dependent on the energies recorded during each of the exposures.     

Sound localization of frequency-modulated sinusoids by Old World monkeys

Directional hearing acuity, as measured by the minimum audible angle (MAA), was determined in four Old World monkeys, Macaca radiata. The acoustic stimuli were linear changes in frequency (sweeps) for different frequency ranges and sweep rates. The sweeps ranged between 0.5 and 1.3 kHz, at two durations, 100 and 200 ms. In upsweeps which began at 0.5 kHz and were 200 ms in duration, MAA decreased as sweep rate and frequency range increased. These thresholds were compared to MAAs of sweeps which traversed the same range of frequencies but at a different rate, to MAAs of sweeps with identical rates but over different frequency ranges, and to the MAAs of downsweeps. These comparisons indicated that range, and not sweep rate, exerts the greatest effect on the MAA. Interaural phase differences derived from the upper limits of the frequency range are discussed as potential FM localization cues.     

Determination of glycyrrhetinic acid in human plasma by high-performance liquid chromatography.

A high-performance liquid chromatographic (HPLC) method has been developed for measuring 18 beta-glycyrrhetinic acid (GRA) in human plasma in the range of 0.1-3 micrograms/ml. The acetate ester of GRA is added to the plasma as an internal standard, plasma proteins are denatured with urea to release GRA, and the GRA and the internal standard are extracted in an ion-pairing solid-phase extraction process. An isocratic, reversed-phase HPLC separation is used, followed by ultraviolet absorbance detection at 248 nm. The results from the analysis of five GRA-fortified plasma pools show a mean relative standard deviation of 7% and are accurate to within 10%. With evaporative concentration of the extract, the limit of detection for GRA in plasma is approximately 10 ng/ml.     

Evidence for non-axial shapes in81, 82, 83Kr

Excitations up to I=12 have been found in⁸²Kr during an (α, 2n) in-beam experiment. Several levels are interpreted as due to (g9/2)² neutron excitations. A comparison with g9/2 neutron bands in^{81, 83}Kr and with cranked shell model calculations indicates non-axial deformation in connection with a rotation-aligned band starting with an 8⁺ level. Non-collective excitations, 8⁺ (and 6⁺), have been interpreted as deformation-aligned two-neutron states.     

Comparative studies of methylmercury determination in biological and environmental samples

Some parameters affecting the accuracy of various approaches to methylmercury (MeHg) determination in biological and environmental samples were studied. Different isolation techniques (ion-exchange, extraction, volatilization, distillation) and final measurement via cold vapour atomic absorption spectroscopy (CV AA) or gas chromatography (GC) were compared. Results obtained by the various isolation techniques are comparable for almost all biological and environmental samples, except for soils and some sediments, where disagreement between the results obtained by GC and CV AA was found. In order to resolve these problems, a new separation technique based on distillation of MeHg from the sample followed either by CV AA or GC was developed. The new method results in very good recovery and reproducibility (95 ± 2%) for all samples examined (fish, mussel, shrimp, blood, hair, algae, sediment, etc.), is specific for MeHg and provides for its differentiation from other species by an indirect CV AA determination. Gas-chromatographic measurement of the isolated MeHg using different packings and conditioning of the columns is also discussed. The distillation method with GC detection is advantageous in producing cleaner chromatograms and in prolonging the life-time of the packing and the intervals between reconditioning.