Regimes of near-wall vortex dynamics in potential flow through gaps

A two-dimensional problem of the motion of a single vortex near an infinite straight wall with singular gaps is solved both analytically, using a point-vortex approach, and numerically based on the method of contour surgery for a vortex patch. The background irrotational flow was generated by a balanced point source-sink system located at the gaps. Three different regimes of vortex evolution were detected and studied in detail: (i) Complete or partial transit, i.e., continuation of the motion along the wall; (ii) complete destruction, i.e., the "penetration" through the sink gap; and (iii) capture in a certain area against the wall between the gaps. These regimes are controlled by three parameters: the ratio of the vortex size and the distance between the gaps, the remoteness of the vortex trajectory from the wall, and the ratio of the intensities of the background flow and the vortex. A bifurcational character of the transition between the regimes was observed. Steady-state solutions were found numerically, including the orbital O state, where the vortex's centroid moves along a constant orbit, while the shape of the vortex changes periodically. Capturing the vortex was usually carried out in a form close to this state. � 2008 American Institute of Physics

Plutonium in locations of local sources and its involvement in global circulation

This paper seeks to compare the volumetric activities of the 239+240Pu and 238Pu isotopes in the surface layer of the atmosphere in the locations of different local sources of radioactive contamination, to characterize these sources as applied to the ratio of the 238Pu and 239+240Pu isotopes, and to estimate the global industry-caused background of plutonium isotopes in the surface atmosphere. Under investigation are an NPP location (the city of Kursk), a territory contaminated as the result of the accident at the Chernobyl NPP (the city of Bryansk), the location of a radiochemical site for the radioactive material reprocessing (PA Mayak in the town of Novogorny, Chelyabinsk Oblast), and the city of Obninsk, the location of nuclear research reactors. The dynamics of the volumetric activity in the locations of interest in 1992–2015 has been reviewed, and the most contaminated areas and the areas with the smallest content of Pu isotopes in the atmosphere's surface layer have been identified. Causes have been revealed for variations in the volumetric activity levels by years and seasonally. The sources of radioactive contamination under consideration have been characterized in terms of the 238Pu–239+240Pu ratio, and the possibility for this ratio to be used to identify the release sources has been evaluated. A much smaller degree of the plutonium isotope involvement in global circulation has been shown based on results of a dedicated study into the volumetric activity of plutonium isotopes at observation points in the Russian subpolar and polar areas, the most distant ones from local sources of the atmospheric Pu release. Throughout the considered period, the volumetric activity of plutonium isotopes in all of the locations of interest was not exceeding the permissible volumetric activity in the inhaled air for the population, as specified in Radiation Safety Regulations NRB-99/2009, which is equal to 2.5 × 10–3 Bq/m3