Paramagnetic defects in BaTiO3 and their role in light-induced charge transport — Optical studies

On the basis of a previous identification of paramagnetic defects in nominally undoped as grown BaTiO₃ single crystals, we have investigated the changes of the concentrations of these centers and their optical absorptions under illumination with light of varying wavelengths. The most pronounced charge transfers occur by hole ionization of Fe⁴⁺ and — to a lesser extent — of Cr⁵⁺ and Cr⁴⁺. At low temperatures the created holes are trapped in the form of O^–-ions next to Al³⁺ or unknown acceptor defects. Corresponding Fe⁴⁺ and O^– absorptions have been identified.     

Investigation of the reaction order for nucleophilic substitution of dialkyl methylphosphonates by alkoxides

The rate of nucleophilic substitution at the phosphorus centre of dialkyl methylphosphonates by methoxide and ethoxide has been studied to investigate the possible involvement of hexacoordinated phosphorus species in this reaction. For alkoxide concentrations less than ca. 1.5 M the rate increases with the square of alkoxide concentration. However, consideration of the activity of the alkoxides, represented by an appropriate acidity function, reveals that only one equivalent of alkoxide is involved in the rate-determining step. Thus, there is no requirement to invoke the intermediacy of a hexacoordinated species in the reaction pathway. © John Wiley & Sons, Inc.     

Eine Kennzeichnung der angeordneten Loops durch monotone Abbildungen

Ohne Zusammenfassung     

Characterization of carbide phases in high speed tool steels

A study is reported on carbides electrolytically extracted from two different types of high speed tool steels as quenched and after tempering. According to X-ray diffraction analysis and EDS microanalysis, Mössbauer spectra show the presence of MC and M₆C in every analysed sample. Only a few substitutional Fe atoms should be present in MC and they give a minor contribution to the Mössbauer spectrum. A model for evaluating the Mössbauer spectrum of M₆C is proposed which is based on the symmetry of lattice sites occupied by Fe atoms and partially substituted by other metallic atoms. The proposed model also allows to get information on the amount of this substitution.     

Charm production in two-photon collisions: Calculation of the leading nonperturbative contribution in QCD

The leading nonperturbative contribution to the cross section of charm production in two-photon collisions is calculated in QCD. Operator expansion is used and the c-quark interaction with vacuum gluon condensate is taken into account. As a result, the moments of the charm contribution to the photon structure function are obtained. The moments with sufficiently high numbers turn out to be sensitive to the gluon condensate.     

Deformations of incompressible bodies with free boundaries

Communicated by C. Dafermos     

Scattering of scalar fields by rough surfaces. Accounting for multiple scattered waves

Physical Engineering Institute, Moscow. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 34, No. 5, pp. 565–574, May, 1991.