On certain positive linear operators in polynomial weight spaces

We consider certain modified Szász-Mirakyan operators A _n (f;r) in polynomial weight spaces of functions of one variable and we study approximation properties of these operators. This revised version was published online in June 2006 with corrections to the Cover Date.     

Mass spectrometry of 3-oxothiazolo[3,2-a] and [3,2-c]pyrimidin-5-ones. Correlation of the intensities of the M+. and the selected fragment ions

The mass spectral fragmentation of eight new 3-oxothiazolo[3,2-a] and [3,2-c]pyrimidin-5-ones were investigated. Fragmentation pathways are proposed on the basis of accurate mass and metastable transition measurements. The correlation between the intensities of M^+. and the selected fragment ions of these compounds is discussed. The data obtained created the basis for distinguishing isomers and metamers.     

Orthogonal hexatic smectic phase-rare or common?

The hexatic smectic B (Hex B) phase is commonly encountered among hydrogen-bonded liquid crystal materials. Among enaminoketone and Schiff's base compounds, twenty homologous series (c. 10² compounds) exhibiting orthogonal mono-or bi-layer hexatic phases were identified by combined microscopy and DSC. Phase transitions from crystal B (CrB) of S_f to Hex B as well as from Hex B to S_f, S_a or S_c phases were observed within the range 50 to 190°C. Temperature ranges of the Hex B phase detectable by DSC varied from 0.2 to 20°C. Within two groups of three-ring enaminoketones, the formation of the Hex B phase was found to be controlled by both inductive and mesomeric components of the Hammett constants of the terminal substituents of the molecules.     

The influence of thiourea on the electroreduction of Zn2+ ions in various supporting electrolytes in respect to the cap-pair effect

The mechanism of the cap-pair effect was examined with respect to its acceleration of the electro-reduction of Zn²⁺ ions in NaCIO₄, NaCl and NaBr. It was found that the presence of thiourea in the solution increased the rate of the electrode process; a role is played in the acceleration by the composition of zinc complexes formed in the bulk of the solution.     

Investigation of the self association of higher fatty alcohols and acids on chromatographic sorbents

Summary Three different sorbents, one with high activity (silica gel), the second with medium activity (cellulose powder) and the third having low activity (chromatographic paper) were compared in respect of their usefulness for the evaluation of the self association of selected higher fatty alcohols and acids. The obtained results are correlated with IR spectroscopic data and theoretical considerations.     

Automated determination of nitrate in waters with a reduction column in a microcomputer-based stopped-flow sample processing system

An automated method for the determination of nitrate in waters with a microcomputer-based stopped-flow mixing system is described. Nitrate is reduced to nitrite with a copperized cadmium—silver alloy or cadmium tube column fitted to the stopped-flow system. Nitrite is determined using fast kinetic, multi-point or single-point procedures with N-(1-naphthyl)ethylenediamine dihydrochloride as the color reagent. Reduction time parameters are evaluated and optimized. Water samples in the range of 0.025–3 ppm NO^-₃—N can be processed with a throughput of up to 100 samples per hour and a detection limit of 0.013 ppm. Interference studies show that cyanide; dichromate, iodide, sulfide, copper and tin ions cause negative results.     

A New Route to Light Emitting Organic Materials Based on Triazine Derivatives

Novel light-emitting organic materials comprising conjugated oligomers chemically attached via a flexible spacer to an electron–or hole-conducting core were synthesized by Stille cross-coupling methodology and designed for tunable charge injection and optical properties. The hyperbranched structures have been characterized by ¹H NMR, ¹³C NMR, and UV-VIS spectroscopy. The obtained structures show good stability in common organic solvents such as CHCl₃, toluene, and CH₂Cl₂ and exhibit excellent thermal stability. A preliminary electroluminescence properties were also investigated. This class of materials will help to balance charge injection and transport and to spread out the charge recombination zone, thereby significantly improving the device efficiency and lifetime of unpolarized and polarized OLEDs.