Phonon-assisted exciton transitions in spherical GaAs nanocrystals embedded in SiO2 matrices have been studied by means of selective excitation spectroscopy. The optical and acoustic phononassisted optical transitions appear in the photoluminescence excitation, photoluminescence linenarrowing, and photoluminescence hole-burning spectra at low temperatures. Both direct (zerophonon) and phonon-as...

1 We suggest that high-mass black holes; i.e., black holes of several solar masses, can be formed in binaries with low-mass main-sequence companions, provided that the hydrogen envelope of the massive star is removed in common envelope evolution which begins only after the massive star has finished He core burning. Our evolution scenario naturally explains the gap (low probability region) in th...

In this paper, a method is proposed to determine the basic properties of γ-ray loud blazars, among them the central black hole mass, M , the Doppler factor, δ, the propagation angle of the γ-rays with respect to the symmetric axis of a twotemperature accretion disk, Φ, and the distance (i.e. the height above the accretion disk), d at which the γ-rays are created, for seven γ-ray loud blazars wi...