A study of the propagation of moving striations in inert gases by means of artificial feedback

A study is made of the propagation of moving striations in inert gases. The method elaborated in [6] combined with the optical method of photo-multipliers was used. The results of the measurements show that despite the fact that the striations themselves move from anode to cathode, their propagation takes place in the opposite direction. Measurements with artificial feedback further confirmed the conclusions reached in [1] and [2] on the mechanism of self-excitation of the striations by means of feedback over the external discharge circuit.In conclusion the authors thank Prof. V. Kunzl and M. Novák for valuable remarks and K. Jakoubková for help in the experiments.     

Resonance properties of the vocal folds: in vivo laryngoscopic investigation of the externally excited laryngeal vibrations

The study presents the first attempt to investigate resonance properties of the living vocal folds by means of laryngoscopy. Laryngeal vibrations were excited via a shaker placed on the neck of a male subject and observed by means of videostroboscopy and videokymography (VKG). When the vocal folds were tuned to the phonation frequency of 110 Hz and sinusoidal vibration with sweeping frequency (in the range 50-400 Hz) was delivered to the larynx, three clearly pronounced resonance peaks at frequencies around 110, 170, and 240 Hz were identified in the vocal fold tissues. Different modes of vibration of the vocal folds, observed as distinct lateral-medial oscillations with one, two, and three half-wavelengths along the glottal length, respectively, were associated with these resonance frequencies. At the external excitation frequencies below 100 Hz, vibrations of the ventricular folds, aryepiglottic folds and arytenoid cartilages were dominant in the larynx.     

Oscillation and nonoscillation of perturbed nonlinear equations with p-Laplacian

In this paper, we analyze oscillatory properties of perturbed half-linear differential equations (i.e., equations with one-dimensional p-Laplacian). The presented research covers the Euler and Riemann–Weber type equations with very general coefficients. We prove an oscillatory result and a nonoscillatory one, which show that the studied equations are conditionally oscillatory (i.e., there exists a certain threshold value that separates oscillatory and nonoscillatory equations). The obtained criteria are easy to use. Since the number of perturbations is arbitrary, we solve the oscillation behavior of the equations in the critical setting when the coefficients give exactly the threshold value. The results are new for linear equations as well.     

Oxidation of AISI 304L stainless steel surface with atomic oxygen

Oxidation of stainless steel surface in oxygen atmosphere was investigated by Auger electron spectroscopy (AES) depth profiling. The samples made of AISI 304L stainless steel were exposed to highly non-equilibrium oxygen atmosphere at different temperatures between 300 and 800 K and for different periods between 5 and 600 s. The degree of dissociation of oxygen molecules was of the order of 10%. A thin oxide layer formed on the stainless steel surface consisted of the iron oxide. The thickness depended on the sample temperature. At room temperature it was 7 nm, and it remained the same up to 200 °C. With further increase of temperature, the thickness of the oxide layer increased and reached 40 nm at 450 °C. The thickness was independent of exposure time. The results were explained by two mechanisms of oxide growth. Up to 200 °C the oxidation was run by electro-migration, while at higher temperatures the thermal induced migration prevailed.     

Nickel Poisoning of a Cracking Catalyst Unravelled by Single-Particle X-ray Fluorescence-Diffraction-Absorption Tomography

Ni contamination from crude oil in the fluid catalytic cracking (FCC) process is one of the primary sources of catalyst deactivation, thereby promoting dehydrogenation–hydrogenation and speeding up coke growth. Herein, single-particle X-ray fluorescence, diffraction and absorption (μXRF-μXRD-μXAS) tomography is used in combination with confocal fluorescence microscopy (CFM) after thiophene staining to spatially resolve Ni interaction with catalyst components and study zeolite degradation, including the processes of dealumination and Brønsted acid sites distribution changes. The comparison between a Ni-lean particle, exposed to hydrotreated feedstock, and a Ni-rich one, exposed to non-hydrotreated feedstock, reveals a preferential interaction of Ni, found in co-localization with Fe, with the γ-Al₂O₃ matrix, leading to the formation of spinel-type hotspots. Although both particles show similar surface zeolite degradation, the Ni-rich particle displays higher dealumination and a clear Brønsted acidity drop.     

Almost periodic homogeneous linear difference systems without almost periodic solutions

Almost periodic homogeneous linear difference systems are considered. It is supposed that the coefficient matrices belong to a group. The aim was to find such groups that the systems having no non-trivial almost periodic solution form a dense subset of the set of all considered systems. A closer examination of the used methods reveals that the problem can be treated in such a generality that the entries of coefficient matrices are allowed to belong to any complete metric field. The concepts of transformable and strongly transformable groups of matrices are introduced, and these concepts enable us to derive efficient conditions for determining what matrix groups have the required property.     

Anti-bacterial treatment of polyethylene by cold plasma for medical purposes

Polyethylene (PE) is one of the most widely used polymers in many industrial applications. Biomedical uses seem to be attractive, with increasing interest. However, PE it prone to infections and its additional surface treatment is indispensable. An increase in resistance to infections can be achieved by treating PE surfaces with substances containing antibacterial groups such as triclosan (5-Chloro-2-(2,4-dichlorophenoxy)phenol) and chlorhexidine (1,1'-Hexamethylenebis[5-(4-chlorophenyl)biguanide]). This work has examined the impact of selected antibacterial substances immobilized on low-density polyethylene (LDPE) via polyacrylic acid (PAA) grafted on LDPE by low-temperature barrier discharge plasma. This LDPE surface treatment led to inhibition of Escherichia coli and Staphylococcus aureus adhesion; the first causes intestinal disease, peritonitis, mastitis, pneumonia, septicemia, the latter is the reason for wound and urinary tract infections.     

A note on successive complexometric determination of thorium and rare earths

An improved method for successive determination of thorium and rare earths is described. It is based on the EDTA titration of thorium at pH 2 (Xylenol Orange as indicator) followed by addition of acetylacetone-acetone mixture, adjustment of the pH to 5-5.5 with hexamine, and by further EDTA titration of rare earths with the same indicator.