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This paper treats the stability of two superposed gravitating streams rotating about the axis transverse to the horizontal magnetic field. The critical wave number for instability is found to be affected by rotation for propagation perpendicular to the axis about which the system rotates. The critical wave number for instability is not affected by rotation when waves propagate along the axis of rotation. The critical wave number is affected by both the magnetic field and the streaming velocity in both cases. Both the magnetic field and the rotation are stabilizing, while the streaming velocity is destabilizing.

Introduction The last 30 years were crucial for understanding the taxonomy and diversity of the orchid subtribe Pleurothallidinae. At the end of the 18th century, less than 40 species representing this group were known, and most of them were classified in Epidendrum L. (today this genus is included in the subtribe Laeliinae).

abstract. The distribution patterns of Neotropical orchid genus Diodonopsis were analysed and the location of its glacial refugia was reconstructed. The possible changes in the coverage of suitable niches of Diodonopsis representatives were evaluated using three different scenarios. The results of ecological niche modeling indicated that the range of studied taxa is in regression since last glacial maximum. The climatic niches of three Diodonopsis species are well separated.

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