Zur Oxydationsreaktion von Magnetit

Verlauf des Oxydationsvorganges von Magnetiten verschiedener Herkunft. Ergebnisse der gravimetrischen und der Differentialthermoanalyse sowie der Röntgenstrukturuntersuchung. Sättigungsmagnetisierung des oxydierten Magnetits. Mößbauerspektren des Magnetits bei verschiedenen Oxydationsgraden. Einflüsse auf den Mechanismus und die Kinetik des Oxydationsvorganges des Magnetits.     

Neural networks and adaptive expert systems in the CSA approach

According to many authors, neural networks and adaptive expert systems may provide the foundations of sixth-generation computers. Neural networks use lower hardware-like concepts and they are based on continuous and numeric type computation. On the other hand, adaptive expert systems use inference rules and perform high-level symbolic computations. the approaches may seem to be totally different, but they do exhibit similar properties: learning, flexibility, parallel search, generalization, and association. This article takes up the problem of the design of a common model for neural networks and adaptive expert systems. For this purpose the Calculus of Self-Modifiable Algorithms, a general tool for problem solving, is used. This joint approach to expert systems and neural networks emphasize their analogies, rather than their differences. © 1993 John Wiley & Sons, Inc.     

New methods for high current fast ion beam production by laser-driven acceleration

An overview of the last experimental campaigns on laser-driven ion acceleration performed at the PALS facility in Prague is given. Both the 2 TW, sub-nanosecond iodine laser system and the 20 TW, femtosecond Ti:sapphire laser, recently installed at PALS, are used along our experiments performed in the intensity range 10(16)-10(19) W∕cm(2). The main goal of our studies was to generate high energy, high current ion streams at relatively low laser intensities. The discussed experimental investigations show promising results in terms of maximum ion energy and current density, which make the laser-accelerated ion beams a candidate for new-generation ion sources to be employed in medicine, nuclear physics, matter physics, and industry.     

Shot-to-shot reproducibility in the emission of fast highly charged metal ions from a laser ion source

The generation of fast highly charged metal ions with the use of the sub-nanosecond Prague Asterix Laser System, operated at a fundamental wavelength of 1315 nm, is reported. Particular attention is paid to shot-to-shot reproducibility in the ion emission. Au and Pd targets were exposed to intensities up to 5 × 10(16) W∕cm(2). Above the laser intensity threshold of ～3 × 10(14) W∕cm(2) the plasma is generated in a form of irregular bursts. The maximum energy of protons constituting the leading edge of the fastest burst reaches a value up to 1 MeV. The fast ions in the following bursts have energy gradually decreasing with the increasing burst number, namely, from a value of about 0.5 MeV∕charge regardless of the atomic number and mass of the ionized species.     

Epoxidation of 1-butene-3-ol over titanium silicalite TS-2 catalyst under autogenic pressure

Epoxidation of 1-butene-3-ol (1B3O) with 30 wt% hydrogen peroxide over TS-2 catalyst has been studied with methanol as a solvent and at elevated pressure (autogenic). The influence of temperature in the range of 20-120 degrees C, the molar ratio of 1B3O/H(2)O(2) 1:1-5:1, methanol concentration 5-90 wt%, TS-2 catalyst concentration 0.1-5.0 wt% and the reaction time 0.5-5.0 h have been investigated. The process was described by the following functions: the selectivity of transformation to 1,2-epoxybutane-3-ol (1,2EB3) in relation to 1B3O consumed, the selectivity of transformation to organic compounds in relation to H(2)O(2) consumed and the conversions of 1B3O and hydrogen peroxide. The major product of epoxidation is 1,2EB3, a compound with many applications.     

Effect of Mg and Ti doping on the luminescence of Y2O2S:Eu

The Y₂O₂S:Eu³⁺,Mg²⁺,Ti^IV (x_Eu = 0.028, x_Mg = 0.086, x_Ti = 0.03) materials were prepared with the flux fusion method. According to X-ray powder diffraction, the materials had the hexagonal crystal structure. The emission of Y₂O₂S:Eu³⁺,Mg²⁺,Ti^IV was centered at 627 nm (λ_exc : 250 nm) due to the ⁵D₀ → ⁷F₂ transition of Eu³⁺. The excitation spectra (λ_em : 627 nm) showed broad bands at 240 and 320 nm due to the O²⁻ → Eu³⁺ and S²⁻ → Eu³⁺ charge transfer transitions, respectively. The latter band can also overlap with the Ti → Eu³⁺ energy transfer. In the excitation spectra with synchrotron radiation, in addition to the O²⁻ → Eu³⁺ and S²⁻ → Eu³⁺ charge transfer transitions, excitation over the band gap was observed at 4.8 eV (258 nm). The red persistent luminescence due to the ⁵D₀ → ⁷F₂ emission from Eu³⁺ residing in the regular Y³⁺ site of the host was ca. 10 min with 1 min fluorescent lamp irradiation. In addition, a very broad band was observed at 600 nm probably due to the Ti³⁺ emission.     

Changes to polyphenols in the process of production of must and wines from blackcurrants and cherries. Part I. Total polyphenols and phenolic acids

The effect of pulp treatment on the qualitative and quantitative changes to polyphenol compounds exhibiting antioxidant properties, in musts and wines from blackcurrants and cherries was investigated. The following variants of pulp treatment were used: hot maceration, hot maceration and pulp pectinolysis with Rohapect MA Plus and Pektopol PM preparations, and also pulp pectinolysis with Rohapect and Pektopol preparations. Blackcurrant musts contained from 4800 to 6600 mg l^-1 of total polyphenols and cherry musts from 3060 to 3920 mg l^-1. The fermentation process caused a decrease in polyphenols content of approximately 25%. In production of fruit wines, the pulp treatment method had a considerable effect on the total content of polyphenols. In blackcurrant wines the highest extraction of polyphenols was obtained after pectinolysis with a Rohapect preparation. In the case of cherry wines the highest content of these compounds was extracted during pectinolysis with a Pektopol preparation. In musts and wines the presence of the following compounds, derivatives of hydroxycinnamic acid, was determined: neochlorogenic, chlorogenic, caffeic, p-coumaric and ferulic acids. The content of neochlorogenic acid was the highest both in musts and wines from blackcurrants and cherries and amounted to 41.7-126.3 mg l^-1, and 24.7-35.3 mg l^-1 respectively for blackcurrants and 74.3-87.7 mg l^-1and 44.5-71.4 mg l^-1 respectively for cherries. The enzymatic preparation Pektopol PM contained an enzyme acting as depsidase. It broke down chlorogenic acid and other compounds to simple phenolic acids (caffeic acid, p-coumaric acid).     

Examination of the causes of a bucket wheel fracture in a bucket wheel excavator

A bucket wheel excavator failure occurred in a brown-coal mine. The failure was caused by a fractured shaft of the bucket wheel. An attempt to determine the causes of the bucket wheel shaft fracture has been made. To that end, the character of changing loads and their maximum amplitudes has been determined by performing measurements on the excavator. A discreet model of the shaft was built and a numerical simulation of the shaft operation using the FEM method was achieved. An analysis of the materials in the fracture area was also implemented. Macroscopic and microscopic images of the fracture area are provided. The shaft fracture was mainly caused by a non-metallic inclusion located below the surface of the shaft as a result of its being rolled. Moreover, it was discovered that the shaft had not been heat-treated.