1.The GPS (Gigahertz Peaked-Spectrum) and CSS (compact steep-spectrum) radio sources makes up significant fractions of the bright (centimeter-wavelength-selected) radio source population (~10%and ~30%, respectively).
2.Chapter 2 presents the first quasi-simultaneous multi-frequency (2.3, 5.0, 8.4 and 15.4GHz) VLBI observations of the Compact SteepSpectrum (CSS) source 3C 138, and the fast-switching phase-reference observation was used only at 15.4GHz.
