Determination of porous glass surface free energy components from contact angles

The contact angles of water drops and diiodomethane drops on pellets made of controlled porosity glasses have been measured. The surface of the glasses was modified by thermal treatment at 873 K which led to an increase in the surface concentration of boron atoms. Glass modified with Carbowax 20M (polyethylene glycol) and fully hydroxylated glass have also been studied. Using the measured contact angles and modified Young equation, the dispersion and nondispersion components of the glass surface free energy have been calculated. The values show that with increasing heating time (increasing surface density of boron atoms) an increase in the surface polarity takes place. However, the polarity of the same samples decreases after treatment with Carbowax, increasingly so with higher boron atom concentrations.     

Allotropic phase transformations induced by ultraviolet power laser irradiation of graphite

Optically induced allotropic phase transformations of carbon were studied. Under irradiation with a laser beam of 337.1 nm wavelength, at an energy density of 1.9 mJ per 0.1 mm², graphite transformed into -carbin, and amorphous carbon-film transformed into rhombohedral graphite with no evidence of high-temperature effects. The transformations differ from the changes occurring due to heating alone. We suggest that the results could be explained by the one-photon excitation and recombination of electrons.     

Allotropie phase transformation induced by UV power laser irradiation of boron nitride

The optically induced allotropic phase transformations of boron nitride were studied. Under irradiation with laser beam of 337.1 nm wavelength, at energy density of 1.9mJ per 0.1 mm² a hexagonal boron nitride transformed into the cubic form. The suggestion is made that the results obtained could be explained by the multiphoton excitation and recombination of electrons.     

Sensing properties of the CB-PCV composites for chlorinated hydrocarbon vapours

The conductivity measurements of carbon black (CB)-polyvinyl chloride (PCV) composite in a tetrachloride (CCl₄), trichloromethane (chloroform, CHCl₃) or methylene chloride (CH₂Cl₂) vapour ambient have been performed. The composite contains 20% Chezacarb K2 carbon black and was prepared as a plastic strip. Based on the =f(t) dependence, three methods to determine the vapour concentration,c, are presented. The investigations could allow one to construct a CCl₄ and CHCl₃ vapour detector.     

A universal dependence for thermal conductivity of metals and dilute alloys

A universal curve relating the maximum of thermal conductivity and its respective temperature with the residual electrical resistivity has been proposed for metals and dilute alloys. Based on the equation of that curve, a comparative analysis of selected literature data of thermal conductivity of metals, which have residual electrical resistivity in the range 10^–11<₀<10^–5. cm, have been performed. Using the data for 33 metals, confirmation of the Wiedemann-Franz law for the impurity component/T of thermal conductivity was obtained, which means that _th/_el1, where _th and _el are the parameters of the electron-lattice defect interaction obtained from measurements of thermal and electrical conductivity, respectively. Examples of the failure of the Wiedemann-Franz law are also presented, exhibiting the values of _th/_el in the range 0.16 to 25. Measurements of thermal conductivity in the range 2 to 20 K and determination of the residual electrical resistivity for the samples of Cd doped with Zn and quenched were performed, resulting in values _th/_el1.     

Ion sputtering and its biomedical applications. Theoretical concepts and practical consequences. Clinical implications and potential use

It is the purpose of the paper to promote the ion beam sputtering technique and its biomedical applications among not only ion beam users but also other research workers, and especially, among biologists and medical doctors. The objectives of this article are threefold. Firstly, it supplies a conceptual background for discussing the main question of this work, i.e. biomedical applications of sputtering. Secondly, the title issue and some related problems, important in the biomedical use, are widely presented and discussed. Finally, clinical implication and potential applications are shown.     

Effect of Ca2+ and Mg2+ ions on the sintering and spectroscopic properties of cr-doped yttrium aluminum garnet ceramics

In this work, we investigated the effects of Ca²⁺ and Mg²⁺ ions and annealing temperature on the spectroscopic parameters of chromium-doped yttrium aluminum garnet ceramics (Cr:YAG). Samples were obtained with either a separate or a simultaneous addition of calcium and magnesium oxides. To achieve this, aqueous suspensions were prepared using Y₂O₃, Al₂O₃, Cr₂O₃, MgO, and CaO high-purity powders as raw materials. The obtained suspensions were freeze-granulated, pressed into pellets, debinded, and subjected to reactive sintering in vacuum at 1715°C for 6 h. Each material was annealed in air with temperatures between 1300 and 1700°C. Samples were also compared to Cr:YAG ceramics with the addition of silica as a sintering aid. All the materials obtained were then exposed to 445 nm excitation, and emission spectra in the visible and infrared wavelengths were recorded. The results showed that the emission spectra of Cr:YAG ceramics varied according to the annealing conditions: as-sintered samples exhibited strong emissions of around 680 nm and, after air annealing, of around 1400 nm. This phenomenon is attributed to the Cr³⁺→Cr⁴⁺ transition. Samples doped solely with MgO exhibited the highest emission intensity in the infrared region. Thus, Mg²⁺ ions provided the best conversion efficiency of chromium ions.     

Stability of nonlinear 2D systems described by the continuous-time Roesser model

This paper considers systems with two-dimensional dynamics (2D systems) described by the continuous-time nonlinear state-space Roesser model. The sufficient conditions of exponential stability in terms of vector Lyapunov functions are established. These conditions are then applied to analysis of the absolute stability of a certain class of systems comprising a linear continuous-time plant in the form of the Roesser model with a nonlinear characteristic in the feedback loop, which satisfies quadratic constraints. The absolute stability conditions are reduced to computable expressions in the form of linear matrix inequalities. The obtained results are extended to the class of continuous-time systems governed by the Roesser model with Markovian switching. The problems of absolute stability and stabilization via state- and output-feedback are solved for linear systems of the above class. The solution procedures for these problems are in the form of algorithms based on linear matrix inequalities.