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In this thesis I use X-ray observations to study the cores and extended structures of radio-loud AGN, to determine their structure, accretion properties and the impact they have on their surroundings. I use new Chandra data and archival XMM-Newton observations ofMarkarian 6 to look for evidence of emission from shocked gas around the external radio bubbles, using spatially resolved regions in Chandra and spectral analysis of the XMM data. The results show that the bubbles in Mrk 6 are indeed driving a shock into the halo of the host galaxy, with a Mach number of 3.9. I also find that the spectrum of the AGN has a variable absorbing column, which changes from 8 × 1021 atoms cm−2 to 3 × 1023 atoms cm−2 on short timescales (2-6 years). This is probably caused by a clump of gas close to the central AGN, passing in front of us at the moment of the observation. Using new and archival Chandra observations of the Circinus galaxy, I match them to pre-existing radio, infrared and optical data to study the kpc-scale emission. As for Mrk 6, I find that the radio bubbles in Circinus are driving a shock into the interstellar medium of the host galaxy, with Mach numbers M 2.7–3.6 and M 2.8–5.3 for the W and E shells respectively. Comparing the results with those we previously obtained for Centaurus A, NGC 3801 and Mrk 6, I show that the total energy in the lobes (thermal+kinetic) scales approximately with the radio power of the parent AGN. The spatial coincidence between the X-ray and edge-brightened radio emission in Circinus resembles the morphology of some SNR shocks, a parallel that has been expected for AGN, but has never been observed before. I investigate what underlying mechanisms both types of systems may have in common, arguing that, in Circinus, the edge-brightening in the shells may be accounted for by a B field enhancement caused by shock compression, but do not preclude some local particle acceleration. I also carry out a systematic study of the X-ray emission from the cores in the 0.02 < z < 0.7 2Jy sample, using Chandra and XMM-Newton observations. I combine the results with the mid-IR, optical emission line and radio luminosities, and compare them with those of the 3CRR sources, to show that the low-excitation objects in our sample show all the signs of radiatively inefficient accretion. I study the effect of the jet-related emission on the various luminosities, confirming that it is the main source of soft X-ray emission for our sources. I also find strong correlations between the accretion-related luminosities, and identify several sources whose optical classification is incompatible with their accretion properties. I derive the bolometric and jet kinetic luminosities for the sample and find a difference in the total Eddington rate between the low and high-excitation populations, with the former peaking at 1 per cent and the latter at 20 per cent Eddington. There is, however, an overlap between the two, indicating that a simple Eddington switch may not be possible. The apparent independence of jet kinetic power and radiative luminosity in the highexcitation population in our plots allows us to test the hypothesis in which jet production and radiatively efficient accretion are in fact independent processes that can coexist in high-excitation objects.

This thesis describes the results of the experimental investigations into some new geometrical configurations in plate-like structures materialising one-dimensional (1D) acoustic black holes for flexural waves (wedges of power-law profile) and two-dimensional (2D) acoustic black holes for flexural waves (circular indentations of power-law profile). Such acoustic black holes allow the user to reduce the amplitudes of the vibration responses of plate-like structures to a maximum effect, while not increasing the mass of the structures. This thesis also suggests some new real world practical applications for this damping technique. Initially, the effects of geometrical and material imperfections on damping flexural vibrations in plates with attached wedges of power-law profile (1D black holes) were investigated, demonstrating that this method of damping is robust enough for practical applications. Then, damping of flexural vibrations in turbofan blades with trailing edges tapered according to a power-law profile has been investigated. In addition, experimental investigations into power-law profiled slots within plates have been also conducted. Another important configuration under investigation was that of circular indentations (pits) of power-law profile within the plate. In the case of quadratic or higher-order profiles, such indentations materialise 2D acoustic black holes for flexural waves. To increase the damping efficiency of power-law profiled indentations, the absorption area has been enlarged by increasing the size of the central hole in the pit, while keeping the edges sharp. The next step of investigation in this thesis was using multiple indentations of power-law profile (arrays of 2D black holes). It was shown that not only do multiple indentations of power-law profile provide substantial reduction in the damping of flexural vibrations, but also a substantial reduction in radiated sound power. The experimental results have been obtained also for a cylindrical plate incorporating a central hole of quadratic profile. They are compared to the results of numerical predictions, thus validating the results and the experimental technique. Investigations into the effects of indentations of power-law profile made in composite plates and panels and their subsequent inclusion into composite honeycomb sandwich panels are also reported. These indentations again act as 2D acoustic black holes for flexural waves and they effectively damp flexural vibrations within the panels. It was also demonstrated that these indentations can be enclosed in smooth surfaced panels and that no additional damping layer is required to induce the acoustic black hole effect in composite structures. In conclusion, it has been confirmed in this thesis that one and two-dimensional acoustic black holes represent an effective method of damping flexural vibrations and reducing the associated structure-borne sound. Furthermore, this thesis has shown that acoustic black holes can be efficiently employed in practical applications, such as trailing edges of jet engine fan blades, composite panels, and composite honeycomb sandwich structures.

We investigate black hole-host galaxy scaling relations in cosmological simulations with a self-consistent black hole growth and feedback model. Our sub-grid accretion model captures the key scalings governing angular momentum transport by gravitational torques from galactic scales down to parsec scales, while our kinetic feedback implementation enables the injection of outflows with properties chosen to match observed nuclear outflows (star formation-driven winds are not included to isolate the effects of black hole feedback). We show that 'quasar mode' feedback can have a large impact on the thermal properties of the intergalactic medium and the growth of galaxies and massive black holes for kinetic feedback efficiencies as low as 0.1 per cent relative to the bolometric luminosity. None the less, our simulations indicate that the black hole-host scaling relations are only weakly dependent on the effects of black hole feedback on galactic scales, since black hole feedback suppresses the growth of galaxies and massive black holes by a similar amount. In contrast, the rate at which gravitational torques feed the central black hole relative to the host galaxy star formation rate governs the slope and normalization of the black hole-host correlations. Our results suggest that a common gas supply regulated by gravitational torques is the primary driver of the observed co-evolution of black holes and galaxies.

Two contrasting notions have been put forward on how social capital may influence individual effectiveness in organizations. Burt (1992) sets forth the informational and control advantages that are possible by building an open network characterized by large numbers of structural holes. In contrast, Coleman (1990) and Simmel (1950) have suggested that network closure, exemplified by large numbers of Simmelian ties, enables actors to develop trust, cohesiveness, and norms which contribute to effectiveness. Simmelian ties are strong, reciprocal ties shared by three actors. It is proposed that an actor's network cannot be dominated by both structural holes and Simmelian ties. Thus, this study examines whether a moderating variable is at work. It is proposed that the actor's task interdependence in the workplace influences the relationship between network closure and individual effectiveness. Actors in less task interdependent environments will benefit especially from the information and control benefits afforded by a network characterized by structural holes. Conversely, actors in highly interdependent environments will benefit especially from the creation of trust and cooperation that result from large numbers of Simmelian ties. Data was collected on 113 subjects in three organizations. Subjects were asked to rate the strength of their relationship with all organization members and their own level of task interdependence. Contrary to expectations, nearly all subjects reported high levels of task interdependence. Raters in each organization provided individual effectiveness measures for all subjects. Hypotheses were tested using hierarchical set regression and bivariate correlation. The results indicated support for the hypothesized relationship of Simmelian ties with task interdependence. When examining all cases, no support was found for the hypothesized relationship of structural holes and Simmelian ties with individual effectiveness and of structural holes with task interdependence. Nonetheless, additional analyses provided some indication of an association between Simmelian ties and individual effectiveness. Task interdependence did not moderate the relationships between either Simmelian ties or structural holes and individual effectiveness.

吀e so-called "trumpet" initial data has recently received mu挀 a琀ention as a potential candidate for the natural black hole initial data to be used in 3+1 numerical relativity simulations with 1+log foliation. In this work we first derive a variant of the maximal trumpet initial data that is made to move on the numerical grid by the means of a Lorentz boost and write a numerical code that constructs this boosted trumpet initial data. We also write a numerical code for calculating the Krets挀mann scalar from the 3+1 variables, to be used in analysing the data from our simulations. With the help of those two codes, we study the behaviour of the boosted trumpet initial data when evolved with the BSSN formulation of the Einstein equations, using 1+log slicing and the Γ-driver shi昀 condition.

In 2009 Bañados, Silk and West described the possibility of principally unbounded collision energies in the centre-of-mass frame for the particle collisions in the vicinity of black holes. Their work attracted a big response. This thesis aims to summarise the results of a number of the articles about the topic and puts these results into a new, broader context. It also presents some generalisations of the existing results, especially for models of magnetised black holes. The main subject of interest is the question, whether the unbounded collision energies can be achieved in a single-scattering or multiple-scattering process which was first formulated by Grib, Pavlov and Zaslavskii. Variety of methods is summarised. A considerable attention is paid to the limiting near-horizon description, which is further developed in order to derive new links and relations among known results, particularly between the purely theoretical work dealing with the geometry of degenerate horizons and their vicinity and more astrophysical articles about magnetic fluxes. Powered by TCPDF (www.tcpdf.org)

All massive nearby galaxies, including our own, host supermassive black holes. Active galactic nuclei (AGN) are seen when such black holes accrete, and when they produce powerful jets of synchrotron-emitting plasma, they are termed radio-loud AGN. The close correlation between black hole mass and galaxy bulge mass in elliptical galaxies indicates that AGN feedback may be the key to the regulation of galaxy formation. It is thus necessary to fully understand the structure of AGN, the way that they are fuelled, and their duty cycle, in order to study the feedback processes and get a clear picture of galaxy formation. In this thesis, independent methods are developed to constrain the accretion disk and radio jet angles to the line of sight. H IX emission from a sub-sample of high-redshift quasars is measured from near-infrared spectroscopy and modelled as sums of different components, including the characteristic double-peaked profile which results from a thin, rotating accretion disk. Comparing the models using Bayesian evidence, almost all quasars were found to have infrared spectra consistent with the presence of a disk. The jet inclination angles of the same set of quasars were constrained by fitting a model, including the effect of Doppler boosting and the receding torus model for dust obscuration, to the radio \ spectral energy distribution. The fitted disk and jet angles correlate strongly, and are consistent with a model in which the radio jets are launched orthogonally to the plane of the accretion disk, as expected if the jet is powered by energy drawn from the spin of the black hole. Both disk and jet angles correlate with the observed linear source size, which is a projection effect; when deprojected using the fitted angles, the distribution of source sizes agrees with a scenario in which the sources expand into the surrounding medium at a constant rate up to ~ 1 Mpc and then shut off, probably as the nuclei become quiescent. The accretion disk angle was found to correlate weakly with the low-frequency radio luminosity, which provides direct, albeit tenuous, evidence for the receding torus model.