Radical-cationic photoinitiated copolymerization of isobutylene with isoprene in the presence of vanadium (IV) chloride

EPR spectra of isoprene and isobutylene-isoprene mixture has been studied in the presence of VCl₄ in dark and under irradiation, respectively. Analogously, as with isobutylene, a radical-cation of isoprene is formed under irradiation, and in a mixture of both monomers radical-cations of isobutylene and isoprene are formed side by side. Formation of the isoprene radical-cation prevails even in an excess of isobutylene, that is, in an isobutylene-isoprene ratio of 8:1. Peroxy radicals which inhibit the photochemical copolymerization of isobutylene with isoprene were recorded in the presence of oxygen in isoprene and in the isobutylene-isoprene mixture. The copolymers of isobutylene with isoprene prepared photochemically (unsaturation 1.5–2 mole %) at ?30 to ?78°C had a considerably higher viscometric molecular weight than copolymer samples prepared under the same conditions with AlCl₃ or BF₃ catalysts. According to NMR measurements of butyl rubber samples prepared by photochemical copolymerization, all isoprene is incorporated in the polymer chain as 1,4-structural units.     

Highly sensitive indirect photometric detection of cations by capillary electrophoresis with the cationic dye chrysoidine

The cationic dye, chrysoidine, has been used for the first time as a probe for the indirect photometric detection of cations. The dye has been used as a probe at concentrations of 5 mM, which is roughly an order of magnitude higher than for other cationic dyes used previously for the same purpose, in order to minimise electromigrational dispersion. Baseline instability was minimised by a combination of coating the capillary with poly(ethyleneimine), addition of a neutral polymer to the electrolyte, and the application of a small amount (20 mbar) of hydrodynamic pressure during the separation. Separation of a mixture containing alkali metals, alkaline earths, transition metals and lanthanides was achieved by the addition of 2-hydroxyisobutyric and lactic acid as complexing agents. Excellent peak shapes were observed over a wide range of analyte mobilities due to the moderate mobility of the probe. The high absorptivity (26733 l mol(-1) cm(-1)) provided by chrysoidine in comparison with typically used, less absorbing probes, was reflected in limits of detection which were typically less than 0.5 microM. These are amongst the lowest reported using hydrodynamic injection without the use of large volume stacking methods. The use of 2-hydroxyisobutyric and lactic acids as complexing agents at pH values close to their pKa values provided suitable buffering which was highlighted by very good reproducibility of migration time, corrected peak area and peak height.     

On Dyakonov type theorems for harmonic quasiregular mappings

We prove two Dyakonov type theorems which relate the modulus of continuity of a function on the unit disc with the modulus of continuity of its absolute value. The methods we use are quite elementary, they cover the case of functions which are quasiregular and harmonic, briefly hqr, in the unit disc.     

Phase and signal velocities of waves in dissipative media. Special relativistic theory

The signal and phase velocities (and their frequency dependence) for all possible plane waves in a relativistic gas (of molecules or photons) with dissipation have been determined from the linearized relativistic 13-moment theory. For each direction in 3-space, and for each frequency, one transverse and two longitudinal waves were found. (In addition, some waves are associated with the mass flow and have the mass flow speed.) Of the longitudinal waves, the fast one is a pressure (sound) wave. It is accompanied by a slow longitudinal thermal dissipation wave and a transverse viscous dissipation wave. The pressure wave has a velocity larger than the Laplace adiabatic speed of sound, while the two dissipation waves have a velocity less than the Laplace speed. All the speeds have been expressed explicitly in terms of quantities associated with the state of equilibrium which existed before passage of the wave. It has also been shown that in the ultrarelativistic limit (extremely high temperatures) all signal speeds remain less than the speed of light in vacuo.The major part of this article was presented at the Seminar on Natural Philosophy at The Johns Hopkins University, Baltimore, on November 24, 1971.     

Changes of lipidemia after one month of creatine supplementation

Monatshefte für Chemie - Chemical Monthly - It was proved in two independent experimental studies with the same group of 11 young sportsmen that creatine (CR) given as food supplement...     

Bandwidth matrix selectors for kernel regression

Choosing a bandwidth matrix belongs to the class of significant problems in multivariate kernel regression. The problem consists of the fact that a theoretical optimal bandwidth matrix depends on the unknown regression function which to be estimated. Thus data-driven methods should be applied. A method proposed here is based on a relation between asymptotic integrated square bias and asymptotic integrated variance. Statistical properties of this method are also treated. The last two sections are devoted to simulations and an application to real data.