On the problem of the simulation of the acoustic path of an angle transducer during ultrasonic testing of thin welded joints

The results of theoretical and experimental studies of signals from high-frequency angle transducers during ultrasonic testing of thin-welded joints are presented. The effect of the quasi-bending of an acoustic beam of a piezoelectric transducer at high frequencies is confirmed. The appropriate testing parameters for such welded joints are recommended.     

Simulation of the supersonic turbulent flow around a cylinder with coaxial disks

The turbulent axisymmetric flow around a stepped body — a cylinder with coaxial front and rear disks — has been calculated with the aid of a VP2/3 package based on multiblock computational technologies and the generalized procedure of pressure correction. The computational model has been tested with the example of a supersonic flow around a sphere. The numerical forecasts made with the use of Spalart–Allmares shear stress transfer and eddy viscosity transfer models have been compared with the data of the aeroballistic experiment, wind tunnel tests, and the results of the calculation of the flow around the disk–cylinder arrangement by a simplified zonal model in a wide range of variation of the incident flow Mach number (from 1.5 to 4). We have obtained a good agreement between the calculated transverse flow density distributions in the front stalling zone and those determined from the interferograms for the wave-drag-rational disk–cylinder arrangement. The influence of the rear disk on the drag of the disk–cylinder–disk arrangement has been estimated.     

Synthesis and properties of 99Tc(I) and 99m Tc(I) hexacarbonyl in aqueous solutions

A procedure was developed for preparing Tc(CO)₆ClO₄ by carbonylation of a solution of technetium(I) tricarbonyltriaqua complex in 2 M HClO₄ in a pressure vessel at 100–170°C and CO pressure of 150 atm. The hexacarbonyltechnetium cation in solution was characterized by IR and ⁹⁹Tc NMR spectroscopy, and also by high-performance liquid chromatography (HPLC). The effect of particular acid and of synthesis conditions on the yield of the hexacarbonyltechnetium cation was examined, and the stability of this cation in aqueous solutions was evaluated. Conditions were found for preparing an aqueous solution containing ^99m Tc(CO) ₆ ⁺ .     

La4Ni3O10±δ – BaCe0.9Y0.1O3-δ cathodes for proton ceramic fuel cells; short-circuiting analysis using BaCe0.9Y0.1O3-δ symmetric cells

Protonic ceramic fuel cells are a promising technology for energy conversion and chemical synthesis in the intermediate temperature range (400–600 °C). Nevertheless, a major restriction to their wider implementation concerns their relatively high cathode polarisation resistance that can become performance limiting as working temperatures decrease. As potential new cathode materials, high order nickelates can be attractive candidates as they exhibit high electrical conductivities at lower temperatures due to their metallic behaviour. In the current work, we investigate the performance of La₄Ni₃O_10±δ and La₄Ni₃O_10±δ–BaCe_0.9Y_0.1O_3-δ composite cathodes, deposited on a BaCe_0.9Y_0.1O_3-δ (BCY10), proton-conducting electrolyte in the temperature range 350–550 °C. The study is performed in symmetrical cell configuration to permit separation of the electrode performance from the overall cell behaviour. For such experiments, possible internal short-circuiting of the electrolyte in oxidising conditions can arise from the presence of p-type electronic conductivity in the BCY10 electrolyte, causing underestimation of measured polarisation resistances. The current work corrects for such factors by knowledge of the transference numbers of the BCY10 electrolyte and the use of a parallel short-circuiting resistor in the equivalent circuit model. The results underscore that the cathode characteristics are highly dependent on the electronic leakage, especially at higher temperatures, and that suitable correction of data is imperative before discussion. Corrected values for polarisation resistance in wet O₂ reveal the composite cathode shows an improvement of total polarisation resistance by a factor of 1.5. The analysis on the oxygen reduction reaction mechanism allows the rate-limiting processes between the electrodes to be differentiated, with the low-frequency term, corresponding to surface processes, being the dominant polarisation resistance and the most improved on formation of the composite. Overall performance analysis indicates that the results from this work are in line with some of the best cathodes currently reported.     

Synergistic effects of zirconium- and aluminum co-doping on the thermoelectric performance of zinc oxide

This work aims to explore zirconium as a possible dopant to promote thermoelectric performance in bulk ZnO-based materials, both within the single-doping concept and on simultaneous co-doping with aluminum. At 1100–1223 K mixed-doped samples demonstrated around ～2.3 times increase in ZT as compared to single-doped materials, reaching ～0.12. The simultaneous presence of aluminum and zirconium imposes a synergistic effect on electrical properties provided by their mutual effects on the solubility in ZnO crystal lattice, while also allowing a moderate decrease of the thermal conductivity due to phonon scattering effects. At 1173 K the power factor of mixed-doped Zn_0.994Al_0.003Zr_0.003O was 2.2–2.5 times higher than for single-doped materials. Stability tests of the prepared materials under prospective operation conditions indicated that the gradual increase in both resistivity and Seebeck coefficient in mixed-doped compositions with time may partially compensate each other to maintain a relatively high power factor.     

Comparison of physical and numerical modeling of supersonic flow over a cone

Results of a multiapproach study of flow of ideal and viscous gases over conical bodies are evaluated. The experiments were performed with a ballistic device using interferometry.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 55, No. 2, pp. 209–212, August, 1988.     

Microconsuming 8–12 GHz GaN Power Amplifiers

Russian Microelectronics - This paper describes a cascade circuit of a gallium nitride (GaN) power amplifier whose chip area is smaller by factors of 4 to 6 than that of traditional amplifiers on...