Quasars are strong sources of electromagnetic energy, powered by a central engine in the vicinity of a supermassive black hole. Blazars are a special group of active galactic nuclei that are believed to have their relativistic jets pointing toward the Earth at a small angle. Nonthermal emission from relativistic jets usually extends from radio to GeV or even TeV γ-ray. One important feature of blazar emission is its variability over almost the whole electromagnetic waveband. Mohamed is interested in the variability study of blazar (particularly at High Energy band), using the powerful tool ‘continuously all-sky monitoring Fermi Large Area Telescope’, which gives important clues on the black hole-jet systems.