The structural, magnetic and magneto-optical properties of iron oxides (wustite, magnetite, Hematite and maghemite), yttrium iron garnet (YIG) and calcium doped YIG (Ca:YIG) thin films prepared by pulsed laser deposition (PLD) technique were studied. The properties of iron oxides films grown on sapphire substrate were found to be dependent on the annealing temperature of the target and the oxygen pressure (PO2) during the ablation. For example, the high annealing temperature of the target and base pressure give wustite, whereas a lower annealing temperature with same oxygen pressure and conditions give magnetite. In addition, the fraction of Fe3+ ions increases with increasing the oxygen pressure, which leads to pure maghemite at PO2 more than 100 mTorr. YIG thin films were grown on gadolinium gallium garnet (GGG) and yttrium aluminium garnet (YAG) substrates. The GGG substrate was found to cause a lower lattice strain (ɛ= 0.016%) in YIG lattice compared to YAG substrates (ɛ=1.12%). The oxygen pressure was also found to affect the magnetic and magneto optical properties of YIG thin films. For example, YIG/GGG films prepared at PO2 =400 mTorr were found to have magnetic properties close to bulk YIG with saturation magnetisation (Ms= 143 emu/cm3) and coercive field (Hc) < 1 Oe. These insights were used to prepare Ca:YIG thin films. The Ca:YIG films showed an increase in the oxygen vacancies, a decrease in Ms and high strain; with increasing the amount of doped Ca+2 ion. It also found that all the Ca:YIG/GGG films contain about 5% Fe2+ at this PO2. For example, the film that contains x=0.05 has a reduction in the magnetisation of about 18% from the pure YIG/GGG thin film. Lower PO2 led to the occurrence of Fe2+ ions in the tetrahedral sites of YIG and increased the oxygen vacancies that reduced Ms.

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It is now accepted that there is a co-evolution between galaxies and their central super massive black holes (SMBHs). Primarily, cosmological simulations suggest that accreting SMBHs (or Active Galactic Nuclei, AGN) must somehow quench their hosts' star-formation rates (SFRs). In contrast, empirical results report that there is no evidence of a strong (anti-)correlation between SFR and X-ray luminosity (a proxy for AGN power). In this thesis, we aim to investigate further this apparent contradiction between AGNs and their host star-forming properties. The hypothesis we test is that a powerful AGN will have a higher impact on a low mass host galaxy than on a high mass one. Therefore, instead of the previously used X-ray luminosity, we investigate the relationship between the X-ray luminosity relative to the host stellar mass (a proxy for Eddington ratio) and the host SFR. We first used a sample of 1620 X-ray selected AGNs, for which we measured Eddington ratios and their host far-infrared luminosities (a proxy for SFR) that we corrected for AGN contamination. By doing this, we found a slight enhancement of SFR at higher Eddington ratios when compared to the SFR of star-forming galaxies with similar stellar masses that do not host AGNs. Furthermore, the change in the star-forming properties at higher Eddington ratio indicates that the Eddington ratio distribution must change with the host star-forming properties. To investigate further how the Eddington ratio distribution of AGNs changes with the star-forming properties of their hosts, we used a model for which we assumed the Eddington ratio distribution simply split between star-forming and quiescent galaxies. Overall, we find that our model is able to reproduce the X-ray luminosity function but fails to reproduce the flat relationship between SFR and X-ray luminosity. Finally, we found that this can be resolved if we introduce a mass-dependency into our model.

In this thesis we investigate the role of the cell nucleus in processes that involve nucleus deformation. To begin with, we mathematically model the motion of molecular motors, using an asymmetric particle model, as a method to describe one force generation mechanism within a cell. This model is used to explore the effects of molecular motors working in tandem while attached to a single object, such as the cell nucleus. We then move on to developing a analysis tool for use with images of nucleus deformation. This computational tool uses a simulated annealing energy minimisation method with classical elasticity to determine the deformation of the nucleus between images, and from the deformation field, make predictions about the traction force on the surface of the nucleus which caused the observed deformations. We begin by treating the nucleus as a homogeneous elastic solid and calculating the traction force to cause the deformations observed of nuclei as they pass through channels containing constrictions. We then developed a second model of the nucleus, where it is instead treated as a thin homogeneous elastic shell. The shell model of the nucleus was then applied to the same images of nuclei passing through channels, and the resulting traction forces compared with the solid model results. Both the solid and shell models of the nucleus were then developed further to calculate the traction force on a deforming nucleus, when using three dimensional images in the form of a series of z stacks as input. We also combine the traction force calculations with an iterative method to calculate Poisson’s ratio from experimental images and compared this with previously published data of nuclei.

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