We consider the universal central extension of the Lie algebra $Vect (S^1)${math s}$ C^{infty}(S^1)$. The coadjoint representation of this Lie algebra has a natural geometric interpretation by matrix analogues of the Sturm-Liouville operators. This approach leads to new Lie superalgebras generalizing the well-known Neveu-Schwartz algebra.

The equilibrium of non-force-free twisted horizontal magnetic flux tubes is studied including gravity and an arbitrary pressure perturbation on the tube boundary. To solve this free-boundary problem, we use general nonorthogonal flux coordinates and consider the two-dimensional case in which there is no variation of the physical quantities along

The relatively large neutral hydrogen contents and enhanced density of companion galaxies around Seyfert 2 galaxies suggests that tidal interaction could play a major role in the evolution of Seyfert 2 galaxies. Recent observations of the distribution of neutral hydrogen in the active S0 galaxy NGC5252 have shown a disturbed morphology which

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CCD spectroscopic observations from [NeV] lambda3425A to [SIII] lambda9532A of the nucleus and circumnuclear region of the Seyfert 1 NGC 4253 are presented. The nucleus shows circumnuclear emission which is elongated 1.5 kpc to the north-east; the spectrum of this extranuclear emission is well fitted by HII region models with effective temperatures