On singular univariate specializations of bivariate hypergeometric functions

It is tempting to evaluate F₂(x,1) and similar univariate specializations of Appell's functions by evaluating the apparent power series at x=0 straight away using the Gauss formula for ₂F₁(1). But this kind of naive evaluation can lead to errors as the ₂F₁(1) coefficients might eventually diverge; then the actual power series at x=0 might involve branching terms. This paper demonstrates these complications by concrete examples.     

Influence of the retardation of the multiplexing element in a dual channel Q-switched laser

We present an experimental and numerical analysis, how deviations of the multiplexer-retardation influence the output power of a time-multiplexed dual channel laser. The laser has two different channels, each one with its own gain medium. The channels are time-multiplexed by a single crystal photo-elastic modulator. It enables to double the repetition rate and output power of the laser. However, as multiplexing is based on polarization-switching, the retardation of the modulator should be kept within certain limits. By experimental measurement and theoretical analysis, we determine the operational window within which the retardation should be kept to avoid additional losses into the resonator. The analysis was done for two configurations of the laser setup, namely with and without a quarter-wave plate.     

A Monte Carlo simulation of diffusion-controlled reactions in inhomogeneous systems

A random-walk model has been developed to treat the kinetics of reactions taking place in spurs at different solute concentrations. The dependence of the molecular yields on solute concentration has been studied using Monte Carlo techniques for simulation of the formation of spurs and of the random movement of the reactive species.     

The role of transition metals in oxidative degradation of cellulose

The role of transition metals in oxidative degradation of cellulose has been studied. Degradation experiments with model papers and studies of hydroxyl radical production in solution have been performed with Fe, Cu, Mn, Co, Cr, Ni, and Zn. Rates of production of hydroxyl radicals in solution have been estimated using the radical scavenger N,N′-(5-nitro-1,3-phenylene)bisglutaramide in the pH interval 7-9. Hydroxyl radical production during degradation of Cu-containing cellulose has been studied. To gain a better insight into chemistry behind degradation processes, chemiluminometric experiments were also performed.The experiments provide strong evidence that the role of transition metals during the oxidative degradation of cellulose is catalytic. A correlation between the behaviour of transition metals in solution and in paper was established at low contents of transition metal in paper.     

Radical intermediates induced by porphyrin triplets

In the photochemical reactions of triplets of both protoporphyrin-IX-dimethyl-ester (PP) and haematoporphyrin dihydrochloride (HP) with alpha-phenyl-ethyl hydroperoxide (HROOH) in C6H6 at room temperature, both O-O and C-C bonds are broken yielding alkoxy and carbon-centred radicals. The ruptures of C-C and O-H bonds were observed in the photochemical reaction of PP with tert-butanol in the same solvent, yielding alkoxy and carbon-centred radicals at lambda greater than or equal to 366 nm, while HP did not react photochemically with tert-butanol at lambda greater than or equal to 334 nm.     

A possible construction of chemical reaction networks

The chemical reaction networks and the sequence networks represent the pathways of a complex chemical process. In order to study the pathways separately the systematization of the elementary processes included in the possible mechanism is inevitable.This systematization was realized by a special procedure based on linear algebraic methods and enabled us to select the corresponding processes from the possible mechanism. The efficiency of the procedure has been illustrated by its application to the liquid phase oxidation of ethylbenzene and the elementary processes have been selected using a computer program.     

Hydrogenation of acetylene–ethylene mixtures on Pd catalysts: study of the surface mechanism by computational approaches. Metal dispersion and catalytic activity

The hydrogenation mechanism of acetylene–ethylene mixtures on Pd catalysts under different experimental conditions was studied by employing a time-dependent Monte Carlo approach set to use a fixed series of event probabilities. The dependence of the catalyst activity and selectivity on the sizes of the metal particles was simulated at microscopic level and the results, also refined by fitting procedures, suggested proper explanations for the apparent nonuniformity of the related experimental findings. The use of the steric hindrance parameter of the surface species and the available surface energy on the metallic catalyst sites was decisive for reproducing the experimental results. Received: 16 September 1999 / Accepted: 3 February 2000 / Published online: 2 May 2000     

Precipitation from homogeneous solution : Precipitation of molybdenum as sulfide with thioacetamide

The determination of molybdenum with thioacetamide by precipitation of molybdenum sulfide from homogeneous solution has been studied. The optimum acidity is about 0.75 N in perchloric acid and a two-fold excess of reagent suffices. Pressure flasks and large excesses of reagent are unnecessary. Heating for 60 min at boiling water -temperatures yields quantitative precipitation.     

Evaluation of a method for treatment of iron gall ink corrosion on paper

Iron gall ink was the most widely used writing ink for paper from the Middle Ages to the twentieth century. Unfortunately, the ink ingredients contain corrosive transition metal ions and acids that cause severe damage to the paper carrier. New or improved paper conservation methods for iron gall ink stabilization are constantly sought. The aim of the study was evaluation of a recently proposed stabilization treatment, adapted to lower relative humidity, applied to various model and historical paper samples containing iron gall ink. The effect of stabilization treatment on paper samples during artificial thermal aging was followed by the determination of the molecular weight distribution by size exclusion chromatography and colorimetry. Migration of iron and copper compounds from the ink lines was monitored by laser ablation inductively coupled plasma mass spectrometry. The results demonstrate that effective stabilization of iron gall ink-containing paper can be successfully achieved by interleaving with papers impregnated with the antioxidant tetrabutylammonium bromide and alkaline buffer under experimental conditions. Negative side effects of the stabilization treatment, such as migration of iron or copper ions from the ink lines and changes of color after the treatment and after accelerated thermal degradation, were limited, proving that the proposed stabilization treatment can be considered for future use by conservators.     

Normalized Leonard pairs and Askey-Wilson relations

Let V denote a vector space with finite positive dimension, and let (A, A^∗) denote a Leonard pair on V. As is known, the linear transformations A, A^∗ satisfy the Askey-Wilson relations