On the dislocation image in the Bragg Case

In the Bragg case of X-ray diffraction the image of the dislocations with large screw component is examined. It is shown that the traditional white-black contrast is completed with an additional narrow black contrast. The experiments were performed by means of the double crystal spectrometer. The CuK radiation and silicon single crystals were used.     

Über Vorzeichenwechsel einiger arithmetischer Funktionen. II

Ohne Zusammenfassung     

Asymptotic degeneracy of the transfer matrix spectrum for systems with interfaces: Relation to surface stiffness and step free energy

Two- and three-dimensional Ising-type systems are considered in the finite-cross-section cylindrical geometry. An interface is forced along the cylinder (strip in 2d) by the antiperiodic or +– boundary conditions. Detailed predictions are presented for the largest asymptotically degenerate set of the transfer matrix eigenvalues. For rough interfaces, i.e., for 0<T<T _c in 2d,T _R<T<T _c in 3d, the eigenvalues are split algebraically, and the spectral gaps are governed by thesurface stiffness coefficient. For rigid interfaces, i.e., 0<T<T _R in 3d, the eigenvalues are split exponentially, with the gaps determined by thestep free energy.     

Rheological investigation of aqueous solutions of poly(vinyl alcohol) during aging II. Influence of experimental conditions on dissolution and aging

The influence of the temperature and time of heating during dissolution on the aging of concentrated aqueous solutions of poly(vinyl alcohol) and aging at different temperatures are described. Changes occuring during aging are interpreted on the basis of non-Newtonian viscosity and normal stress measurements.     

Rapid radiochemical separation and determination of chlorine,bromine and iodine in water samples using ion exchange

On the basis of tracer experiments, a simple and rapid radiochemical separation method for simultaneous determination of I^–, Br^– and Cl^– in one aliquot of a water sample (only 2–4 ml) has been developed. The method is based on short irradiation of the water sample and separation of the halogens using sequential ion exchange columns filled with Dowex 1×8, 100–200 mesh anionic resin prepared in I^–/I₂, Br^–/Br₂ and Cl^– form. After washing the columns with an appropriate volume of 2% NaCl solution, the resins were transferred to vials and activities of the isolated radionuclides¹²⁸I,⁸²Br and³⁸Cl measured together with standards in a well type or on a coaxial Ge detector connected to a Canberra 90 multichannel analyzer. Besides high chemical yields, from the -spectra of the isolated radionuclides, it is evident that high decontamination fac-The paper was presented at the MTAA-8, Vienna, September 1991.     

The normal coordinate analysis of hydrogen bonded adducts of chloroacetic acids with dimethyl sulphoxide

The modified valence force field and the potential energy distribution were calculated for adducts of mono-, di-, and trichloroacetic acids with dimethyl sulphoxide. The calculated force constants gave a good fit to the experimental frequencies of normal adducts and their OD and CD₃ analogues. The hydrogen bond strength increases from mono- to trichloroacetic acid and this is reflected in the decrease of the K_O-H force constant and increase of k_O?h.     

Dependence of the retention volumes of additional streaming current responses and of the column void volume on mobile phase composition

Summary The influence of the alcohol content of the mobile phase and water, acetic acid and aniline as mobile phase additives on the generation and shape of two additional changes of the streaming current, generated inside the liquid chromatography column by injection of any sample and recorded before the responses of retained solutes, was studied in a normal-phase system using silica gel as the stationary phase. The mobile phases were based on a n-heptane-1-propanol mixtures. Under the same conditions the relationships between the column interparticle volume, the column void volume and the total liquid volume in the column and the retention volumes of these two streaming current responses, having the form of chromatographic peaks, were studied. The column void volume was identified with the retention volume of n-octane. The total liquid volume in the column (column hold-up) was calculated from the weight loss of the column wetted with water at first and then dried in nitrogen stream. The retention volume of the first streaming current response equals the column interparticle volume disregarding the mobile phase composition. If the 95∶5 n-heptane-1-propanol mobile phase contains water up to 80% of its saturated concentration (up to 0.114% by vol.), the retention volume of the second response agrees with the total volume of the liquid in the silica gel column, with a precision better than 2%. At a higher relative water saturation the retention volume of the second response increases, while the column void volume decreases. Both changes are explained by the spontaneous formation of a highly polar stagnant liquid in the pores of the silica gel.     

Water-anion vibrational coupling in some crystallohydrates

In treating the vibrational spectra of crystallohydrates, it is usually assumed that the water molecules vibrate independently (or nearly so) from the rest of the structural units and, consequently, the bands which shift on deuteration are automatically assigned to water modes (internal or external). In a number of hydrates of metal carboxylates, however, we were able to detect indications of water-anion vibrational coupling.     

Selection of carrier for immobilization of fructosyltransferase from Aureobasidium pullulans

The study deals with the development of an immobilized biocatalyst for the production of fructooligosaccharides. Several commercial anion-exchange resins and polymethacrylate carriers were tested for the immobilization either by the direct attachment of fructosyltransferase or by the attachment accompanied by simultaneous glutaraldehyde crosslinking in the pH range from 5.7 to 7.1. On the basis of the efficiency of immobilization and the storage stability, Amberlite IRA 900 and Dowex Marathon MSA were selected as the best carriers for fructosyltransferase immobilization by direct attachment at pH 5.7. Regular paper An erratum to this article is available at .     

Catalysis of hydrosilylation of carbon-carbon multiple bonds: Recent progress

Recent progress in the catalytic hydrosilylation of organic and organosilicon compounds containing carbon-carbon multiple bonds is reviewed. Related to this, dehydrogenative silylation is also discussed. During the last decade new hydrosilylation catalysts, predominantly homogenous and heterogenous transition methal complexes, have been developed. These catalysts offer not only increased efficiency and turnover rate but also improved regioselectivity and stereoselectivity; moreover, there has been development in the mechanistic rationale behind these improvements. Application and extension of these basic chemical advances are found in many areas including polyorganosiloxane curing, hydrosilylation polymerization, polysiloxane functionalization, and silicon-containing dendrimer development.