Interactions in multicomponent systems containing surfactants. System silver iodide — methylene blue and sodium dodecyl sulphate

The precipitation and dissolution of AgI in the presence of methylene blue (MB · Cl) and sodium dodecyl sulphate (NaDS) was followed by X-ray diffraction analysis.At high MB · Cl concentration, the absence of AgI precipitates was observed, which is explained by considering the redox process MB⁺ + 2I^– MB^– + I₂. The decrease in I^– concentration causes dissolution or inhibition of growth of solid AgI which is significant at relatively high MB · Cl concentrations. The addition of NaDS causes the disappearance of these effects, which is explained by the incorporation of MB in NaDS micelles.These explanations are supported by the potentiometric measurements using Ag/Ag₂S and Pt electrodes.     

Ermüdungserscheinungen der infrarotbestrahlten Silber-Cäsium-Photokathoden

Zusammenfassung In dieser Arbeit werden die Erscheinungen der normalen und anomalen, durch Infrarotstrahlung verursachten und von uns schon früher an diesen Photokatoden beobachteten Ermüdung von Silber-Cäsium-Photokathoden untersucht. Diese Erscheinungen wurden an durchsichtigen sowie undurchsichtigen, durch verschiedene Technologien zubereiteten Photokathoden festgestellt. Es wurden Messungen der Strahlungsintensitäts-, Temperatur- und Spektralverteilungsabhängigkeit der normalen und anomalen Ermüdung durchgeführt. Es werden die Ursachen der Unübereinstimmigkeit im Vergleich mit Arbeiten von De Boer und Teves besprochen. Ferner wurden die Zeitverläufe der Ermüdung bei der Abwechslung der Bestrahlungs- und Dunkelzyklen studiert.

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Emission and absorption of plane impulsive gravitational waves

Emission and absorption of plane impulsive waves of radiation by a thin shell of dust are studied. At the moment of interaction local conservation laws apply. An impulsive gravitational wave does not participate in the energy balance. Rather, it is associated with a change in isotropy of the source (absorber). Changes in the kinetic energy of the source exactly match the changes in its rest mass.     

On embedding expanders into ℓ p spaces

In this note we show that the minimum distortion required to embed alln-point metric spaces into the Banach space ℓ _p is between (c ₁/p) logn and (c ₂/p) logn, wherec ₂>c ₁>0 are absolute constants and 1≤p<logn. The lower bound is obtained by a generalization of a method of Linial et al. [LLR95], by showing that constant-degree expanders (considered as metric spaces) cannot be embedded any better. Research supported by Czech Republic Grant GAČR 201/94/2167 and Charles University grants No. 351 and 361.     

Antioxidants and stabilizers-XXXVI. The activity of phenolic antioxidants with substituents containing O,S or N atoms in the stabilization of polypropylene

The antioxidative activities of phenols derived from 2,6-di-tert. butyl-4-methylphenol (1) and 2,4-dimethyl-6-tert.butylphenol (and containing at position 4 or 2 to the hydroxyl group a substituent with the heteroatoms O, S or N) have been investigated. The highest activity was observed with the compounds of type (I) containing sulphur. The oxidation of isotactic polypropylene stabilized with all sulphur derivatives under investigation was clearly retarded even after the induction period.     

The effect of preferential solvation on the kinetic order of alkyl methacrylate polymerization in benzene

The kinetic order of the polymerization of n-alkylmethacrylates with respect to monomer in benzene (fractional and greater than one) has been interpreted as due to concentration changes of a monomer at the site of reaction caused by preferential solvation of the growing macromolecule by benzene. Correlation of the rates of polymerization at 30° with determined monomer concentrations in the close vicinity of the polymer chain gives kinetic orders of 1±0.05 for both n-butyl- and n-dodecyl-methacrylates. The coefficient of preferential solvation at 30° for the polymers investigated is between 0.1 and 0.4 [cm³ g^?1] depending on the composition of the mixture of benzene and monomer. The coordination numbers 3 and 4 needed for calculation of the composition of the solvent in the solvating layer correspond to theoretical views on polymer solutions.