| This thesis is mainly on the X-ray radiation from radio loud quasars and its dependence on quasar orientation. We compiled a sample of radio-loud quasars which samples over a large range of the radio core-dominance parameter R, including 5 core-dominated quasars (R > 1.0), 4 lobe-dominated quasars (R < 0.5), and 3 quasars with intermediate radio core-dominance. We analyzed their X-ray spectroscopic data from observations taken with the X-ray satellites, mostly with XMM-Newton and some with Chandra. We found that a flat power law component, which dominates at least the hard X-ray band, is needed to fit the X-ray spectra of all the objects in our sample. For core-dominated sources, the average photon index of the flat X-ray component is～1.5. For lobe-dominated sources, the X-ray spectra are best fitted with two power law components, with the average photon index of the flat component being～1.6. The average photon index of the flat component for intermediate core-dominance objects is～1.5.We examined the possible origins of the observed X-ray radiation, namely, emission from core-jets, black hole accretion disk-corona, as well as extended radio jets/lobes. We predicted X-ray emission from jets assuming the dependence of jet X-rays on radio 5 GHz core luminosity, as established in previous studies in the framework of the unified model of radio loud quasars. X-ray emission contributed from disk-corona was estimated from either the optical [O III] emission line luminosity or the optical luminosity at 2500A. By comparing the estimated and the observed X-ray luminosities, we found the following results. For the core-dominated sources in our sample, the observed X-ray luminosities can be satisfactorily explained by X-rays from the relativistic jets, which is produced via likely inverse-Compton radiation and is relativistically beamed. For the lobe-dominated sources, the superposition of the estimated X-rays from both, jets and disk-corona is systematically and significantly smaller than the observed X-ray luminosity, although scatters inherent in the estimation may explain the discrepancy for some individual objects. High spatial resolution X-ray imaging observations with Chandra of some of the sample objects show that the bulk of the X-ray emission comes from the compact, unresolved core of a few kilo-parsec in scale, rather than from diffuse emission of radio lobes or large scale jets. Furthermore, flux and spectral variability in the flat component has also been found in a few objects having more than one epoch observation on timescales of years. Based on these facts, we postulate that the excess flat X-ray emission found in the lobe-dominated sources is actually from the jets, i.e. the X-ray emission from jets in these objects is actually stronger than that predicted by the current unification model. If this is the case, the simple unification model for radio-loud quasars needs to be modified. The underlying physical reason for this finding is not clear. We discussed some possible mechanisms in terms of the dominance of external inverse-Compton scattering in lobe dominated sources, or X-ray and radio jets having different opening angles, or bending jets. We also examined the relationship between the intrinsic power of radio jets with black hole mass, Eddington ratio, and mass accretion rate.Besides the main thesis work above, I was also involved in 3 other research projects, in which I mainly worked on X-ray data analysis. These include studies of a sample of narrow line Seyfert AGN, the newly discovered dwarf AGN with an intermediate mass black hole SDSS J160531.84+174826.1, and the peculiar broad absorption line quasar SDSS J144842.45+042403.1.
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