Single tracer technique

Measurement techniques for the gas phase in CFB risers are becoming increasingly more sophisticated and accurate, and many find application in industrial-size equipment. In this section, we classify the different methods into five categories intrusive probes, steady state tracers, impulse (non-steady state) tracers, chemical reaction, and optical tracers. No single tracer technique is capable of quantifying... 

Dispersion in packed tubes with wall effects was part of the CFD study by Magnico (2003), for N — 5.96 and N — 7.8, so the author was able to focus on mass transfer mechanisms near the tube wall. After establishing a steady-state flow, a Lagrangian approach was used in which particles were followed along the trajectories, with molecular diffusion suppressed, to single out the connection between flow and radial mass transport. The results showed the ratio of longitudinal to transverse dispersion coefficients to be smaller than in the literature, which may have been connected to the wall effects. The flow structure near the wall was probed by the tracer technique, and it was observed that there was a boundary layer near the wall of width about Jp/4 (at Ret — 7) in which there was no radial velocity component, so that mass transfer across the layer... 

Work on the biosynthesis of cholesterol began in earnest after Rudolf Schoenheimer and David Rittenberg, at Columbia University, developed isotopic tracer techniques for the analysis of biochemical pathways. In 1941, Rittenberg and Konrad Bloch were able to show that deuterium-labeled acetate (C2H, COO ) was a precursor of cholesterol in rats and mice. In 1949, James Bonner and Barbarin Arreguin postulated that three acetates could combine to form a single five-carbon unit called isoprene. 

Radioactive tracers may be used to determine the amount of a single substance in a mixture. The tracer technique is especially useful where quantitative recovery of the substance in question is difficult or impossible. Basically, the technique involves adding a known amount of the radioactive compound to the mixture and then (after thorough equilibration) reisolating a small amount of the compound. The amount of compound recovered is unimportant, provided it is sufficient to weigh and to count. From the specific activity of the reisolated compound as well as a knowledge of the total number of counts originally added, the amount of... 

Any charge transport by protons must directly correspond to an adequate transport of protonic mass. A straightforward way to determine the true proton conductivity, therefore, is to record directly the proton selfdiffusion coefficient. The traditional way to do this is through tracer techniques. They may be very accurate but require difficult experimental work and measurement periods of the order of days or weeks for a single component and temperature. A further disadvantage is the inherent system perturbation by isotope substitution, which is particularly critical for the substitutions H/ H and... 

Radioactive tracer technique is not single-elemental anymore. In biochemical studies, two radioactive tracers emitting P rays, and for example, are often used together to trace the... 

The diffusion of Pb2+ ions in single-crystal KCl was studied at 200 to 475C. A radioactive tracer technique was used which involved diffusion from a deposited... 

The diffusion of carbon in single and polycrystalline ZrC was measured at 1350 to 2150C, using radioactive tracer techniques. Volume and short-circuit enhanced tracer diffusion coefficients were represented by ... 

The flow patterns for single phase, Newtonian and non-Newtonian liquids in tanks agitated by various types of impeller have been repotted in the literature.1 3 27 38 39) The experimental techniques which have been employed include the introduction of tracer liquids, neutrally buoyant particles or hydrogen bubbles, and measurement of local velocities by means of Pitot tubes, laser-doppler anemometers, and so on. The salient features of the flow patterns encountered with propellers and disc turbines are shown in Figures 7.9 and 7.10. 

The sorption/desorption processes were studied by a batchtype technique. Aqueous solutions were prepared by mixing rock powders with distilled-deionized water. For the sorption experiments, portions of these aqueous solutions were loaded with tracer quantities of a single radioactive nuclide and contacted with wafers of a given rock type. For the desorption experiments, wafers from the sorption experiments were contacted with the remaining portions of the aqueous solutions. 

The striking advantages of STM are atomic resolution, its conceptional transparency and versatility, and the appeal of direct visualisation. STM can be applied to study anisotropic surface mobility, diffusion on inhomogeneous surfaces, or adsorbate interactions and collective transport effects on a local scale. It also a technique where a simultaneous characterization of tracer and chemical diffusion on single crystals is feasible [54]. Surface mobility studies using STM are currently progressing rapidly. 

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