We have analysed several multiwavelength optical observations (Hα, Hβ, Hǫ, Ca ii H & K, Ca ii IRT lines) of chromospherically active binary system OU Gem, taken in three observation runs: March 1996, April 1998 (using the SOFIN spectrograph and the Nordic Optical Telescope) and January 1999 (using the ESA-MUSICOS spectrograph and the Isaac Newton Telescope). The spectra show double Hα and Hβ ab...

Extending the results in (B.M.) on one dimensional interacting fermions in a periodic potential we study the infrared behaviour of the two points Schwinger function in the lled band case. If the fermions are spinless such behaviour is completely determined and it depends on the ratio between the amplitude of the gap and the strength of the interaction. If the ratio is large the Schwinger functi...

An example of discontinuity of the energy-momentum tensor moving at superluminal velocity is discussed. It is shown that the gravita-tional Mach cone is formed. The power spectrum of the corresponding Cherenkov radiation is evaluated.

We discuss the impact of modal filtering in Legendre spectral methods, both on accuracy and stability. For the former, we derive sufficient conditions on the filter to recover high order accuracy away from points of discontinuity. Computational results confirm that less strict necessary conditions appear to be adequate. We proceed to discuss a instability mechanism in polynomial spectral method...

We present new optical spectral observations of 3G71, the previously suspected optical counterpart of the hard X-ray source 1H2214+589. The spectra of 3G71 exhibit many forbidden lines, unusually intense H-Balmer emission lines and the approximately B5 spectral type. Such spectral features, together with its large IRAS infrared color excess and associated with nebulosity, provide evidences that...