Aggregate stability of ZrO2 aqueous sols in electrolyte solutions

The aggregate stability of submicron and nanosized ZrO₂ aqueous sols of different origins and different dispersities at pH 3–10 in the KCl concentration range 10^?3–10^?1 M is investigated by flow ultramicroscopy and photometry. The results obtained are analyzed in the framework of the extended Derjaguin-Landau-Verwey-Overbeek theory and the Muller-Martynov theory of reversible aggregation. The extension of boundary layers of water near the surface of the ZrO₂ particles is estimated.     

Effect of p-n junction overheating on degradation of silicon high-power pulsed IMPATT diodes

The thermal limits of the two-drift impact avalanche and transit-time (IMPATT) diode operating in the pulsed mode in the 8-mm wavelength region with a microwave power as high as 30–35 W have been estimated. It is shown that p-n junction overheat at an operating pulse length of 300 ns and a supply current amplitude of 11.3–15 A amounts to 270–430°C relative to an ambient medium. The temperature limit of junction overheating, above which IMPATT diodes rapidly degrade, was determined as 350°C. The presented results of X-ray phase analysis and depth profiles of Au-Pt-Ti-Pd-Si ohmic contact components confirm thermal limits of the IMPATT diode operating in the pulsed mode.

     

Occupational and occupationally determined diseases

Medical definitions of occupational and professionally conditioned pathology are given in the article together with relevant examples. With the view to account appropriately occupational pathology in accordance with its severity classification based on the degree of working capacity loss is presented. Notions of acute occupational disease (intoxication) and professional accident are determined. International list of occupational diseases is considered. Suggestions intended at promotion of safe working conditions are made on perfection of the Ukrainian list.     

Cross flow around a cylinder at periodic disturbances in the boundary layer by electrolysis bubbles

Particularities of dynamic flow control in an open-loop system around a cylinder with a boundary layer by means of periodic generation of microbubbles are presented. Experiments were carried out in the range of Reynolds numbers of Re = (0.3?1.2) × 10⁵. It is shown that this method provides very similar results as in the case of continuous generation of microbubbles; however, the energy expenditure is two times less. The effect can be explained by the delayed response of the boundary layer separation on the disturbance cutoff. Lock-in modes of the natural vortex shedding frequency f _N and the frequency of forced oscillations f _E, as well as superposition of these frequencies, are registered. Maximal values of the amplitude of the drag and lift oscillations are registered in the range of low frequencies (f _E/f _N < 0.07).     

Coherent-interface-induced strain in large lattice-mismatched materials:A new approach for modeling Raman shift

Strain engineering as one of the most powerful techniques for tuning optical and electronic properties of Ⅲ-nitrides requires reliable methods for strain invest...     

Cavitation technologies for dispergation and homogenization

The results of tests carried out in industrial conditions are presented. They allow one to propose cavitation technologies of dispergation and homogenization for fabricating emulsions and suspensions under the action of ultrasonic, hydrodynamic, and hydroacoustic cavitation. The dispergation regimes were found for materials with various physicochemical properties, including viscous media (natural juices with pulp) and materials with a lamella structure (bentonite). Cavitation effects intensify dispergation processes and allow one to produce materials with submicronic dimension of the particles; this considerably increases the sedimentation period of the suspensions.     

Structural transformations in ZnS:Cu in the course of thermal annealing

The influence of annealing at 800°C on the photoluminescence, electron spin resonance, and X-ray diffraction spectra of powder-like ZnS:Cu, obtained by the self-propagating high-temperature synthesis of a charge, consisting of Zn, S, and CuCl, is studied. It is shown that variation in the material’s heating rate up to the annealing temperature leads to a nonmonotonic variation in the spectral location and full-width at half-maximum of the photoluminescence band in the blue-green spectral region, as well as in the Mn²⁺ paramagnetic center concentration. It is established that the cubic and hexagonal ZnS phases, as well as the ZnO and CuZn phases, are present in the powder after synthesis. It is shown that annealing of the obtained powder at 800°C leads to three processes: the transformation of the hexagonal ZnS phase into the cubic phase, the oxidation of ZnS and CuZn, and the diffusion of Cu into the bulk of the ZnS microcrystals from the CuZn phase. A model attributing the observed variations in luminescence and electron spin resonance spectra to the diffusion of Cu and Mn impurities into the microcrystal bulk, particularly from the CuZn phase, and to their accumulation at extended defects is suggested.