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We investigate flow of liquid which is partially filled in a cylindrical container horizontally rotating about its axis of symmetry. Even if the rotation is slow enough to keep the liquid–gas interface almost undeformed, convection cells whose circulation axis is perpendicular to the container's rotational axis can be sustained. We conduct experiments by particle image velocimetry and direct numerical simulations with the S-CLSVOF and immersed boundary methods to reveal the condition of the Reynolds number, the aspect ratio of the container and the filling ratio of liquid for the onset of these convection cells. When the filling ratio is not too large, as the Reynolds number increases, convection cells appear through a pitchfork bifurcation in an infinitely long cylinder. This bifurcation becomes imperfect in the case of a finite-length cylinder. In contrast, when the filling ratio is large enough, convection cells appear through a subcritical bifurcation. Through these investigations, it becomes evident that the axial wavelength of sustained convection cells is an increasing function of the filling ratio in an infinitely long cylinder. In practice, to sustain intense convection cells, we should use a cylinder with the length equal to an integer multiple of the wavelength of the most unstable mode in the infinite-length cylinder. Although we focus on the liquid-pool regime with small Froude numbers, the critical Reynolds number for the pitchfork bifurcation weakly depends on the Froude number. This dependence is explained by considering the changes in the effective filling ratio and the convection velocity. [ABSTRACT FROM AUTHOR]

The Japanese black salamander, Hynobius nigrescens, is endemic to Japan and breeds in still water. Egg sacs of three colors (white, intermediate, and transparent) have been identified to date. However, the cause of this variation is not well understood. Therefore, we conducted a survey within the Ryohaku Mountains, where genetic differences are assumed to be small, and investigated egg sac color type in 10 spawning ponds. Our results confirmed that the ratio of the intermediate and transparent types increases with altitude. Regarding egg sac color type at each altitude, all egg sacs found above 740 m asl were white, whereas the transparent and intermediate types began to appear from at or above 740 m. As altitude increased, the incidence of the white type decreased and that of the transparent and intermediate types increased. In addition, a redundancy analysis was performed to determine the relationship between egg sac color and the topographical and meteorological conditions and to clarify the results for each pond. The analysis revealed that maximum snow depth was strongly correlated with an increase in the number of egg sacs of intermediate and transparent types. [ABSTRACT FROM AUTHOR]