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Determination of Sr, Ba, Rb, and Cs in biological reference materials using a radiochemical group separation procedure
Mizera, Jiří ; Řanda, Zdeněk
Strontium, barium, rubidium, and cesium in selected, predominantly biological, reference materials was determined using neutron activation analysis (NAA) in two different analytical modes - instrumental NAA with epithermal neutrons, and NAA with radiochemical group separation of Sr-Ba and Rb-Cs (RNAA). The RNAA procedure was based on decomposition of irradiated samples by alkaline-oxidative fusion followed by precipitation of Sr and Ba sulfates, and sorption of Rb and Cs onto ammonium phosphomolybdate.
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Zpracování informací získaných z termochromních kapalných krystalů
Tesař, Václav ; Randa, Zdeněk
Thermochromic liquid crystals respond to local changes of temperature by varying the colour of reflected light. Their use in experiments with anisothermal fluid flows seems to be simple - just taking pictures of the colours on the walls exposed to the fluid flow. However, practical extraction of quantitative informationfrom the pictures is not straightforward and brings a number of pitfalls. Unfortunately, these details are generally not found in available literature since most authors mention these practical procedure aspects very briefly, if at all. The present paper concentrates on these practical steps following them on a practicalexample of an investigation of an impinging jet, presenting the experience acquired in such investigations.
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Kalibrace clonkové tratě rotačním průtokoměrem a rezonance systému
Randa, Zdeněk ; Tesař, Václav ; Hrubý, Jan
Rotary piston flowmeters (RPF) are widely used for accurate measurement of gas flow rates. We used it to calibrate a Koennecke-type quadrant nozzle flowmeter. The evaluated discharge coefficient exhibited strange local maxima, even exceeding unity. The phenomenon was sensitive to the length of the tubes connecting the RPF with the calibrated quadrant nozzle. One possible explanation, discussed in the present paper, is the local maxima to be due to acoustic resonance in the system, excited by periodic character of the flow through the RPF. Another possibility is that the also the inertia of the pistons plays a role, the air providing the spring action.
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Měření přestupu tepla a frekvence oscilací s fluidickým generátorem syntetizovaného impaktního proudu
Tesař, Václav ; Trávníček, Zdeněk ; Kordík, Jozef ; Randa, Zdeněk
The paper discusses recent results of an experimental research of annular impinging hybrid-synthetic jets generated by a no-moving-part fluidic actuator. The actuator is based on a new principle and the first part of the paper discusses the basic configuration idea and the relationship with earlier hybrid-synthetic jet generators. The next part of the paper provides information of a strange phenomenon – an unexpected high-temperature region found on the impingement surface. Also discussed are the measurements of the oscillation frequency. The most important result is the substantial increase of heat transfer efficiency compared with the steady flow from the same nozzles.
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