We present archival ROSAT data for three recently identified, nearby (D < 70 pc), young (∼ 10−40 Myr) stellar associations: the TW Hydrae Association, the Tucana-Horologium Association, and the β Pic Moving Group. The distributions of ROSAT X-ray hardness ratios (HR1, HR2) for these three groups, whose membership is dominated by low-mass, weak-lined T Tauri stars, are tightly clustered and very...

We review recent observational results which suggest that magnetically channeled accretion in T Tauri stars is a highly time dependent process on timescales ranging from hours to months.

flow cytometry (fcm) was used to determine the ploidy levels of six different populationsof agropyron cristatum (l.) gaertn. (poaceae) in iran, using a diploid cultivated barley (hordeumvulgare l.) as an internal reference. according to flow cytometric data, tetraploid (2n = ± 28) andhexaploid (2n = ± 42) levels were detected among the examined populations and these results weresupported by chr...

The research presents the problem of liquidation dumps substandard raw materials zeolite-containing rocks Holinsky deposit, measures for reclamation disturbed lands. most effective way to restore ecosystems is renaturation. Time intervals succession are considered. Renaturation lands consists 6 stages. Possible dominant plants proposed options considered in detail: Stipa lessingiana, Poa platen...