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This thesis contains results on type 1 Active Galactic Nuclei detected and studied with INTEGRAL. The sample of sources analysed in the present thesis is based on a complete sample of type 1 AGN extracted from the 3rd IBIS/ISGRI catalogue. Archival X-ray data taken from several observatories, such as XMM-Newton, Chandra, Swift/XRT and ASCA, have been combined together with IBIS spectra, providing for the first time a broad-band spectral analysis of a hard X-ray detected complete sample of type 1 AGN. The principal aim of this work is to study the continuum properties of type 1 AGN, i.e. power law slope, reflection fraction and high energy cut-off, and their relation to spectral modelling of AGN and to synthesis models of the Cosmic Diffuse X-ray Background. The analysis presented in this work covers two subclasses of type 1 AGN: Broad Line Radio Galaxies (BLRG) and Radio Quiet (RQ) type 1 sources. In particular, among BLRG, IGR J21247+5058 is studied in great depth (see chapter 5). This is in fact a very peculiar source, displaying very complex absorption, in the form of two layers partially covering the central emitting source. So far, only one other BLRG was known to require such complexity regarding absorption (namely 4C 445), making IGR 21247+5058 indeed a very peculiar and almost unique AGN. Broad-band spectra of the other seven BLRG present in the INTEGRAL complete sample have been analysed in search for a dichotomy between this population (chapter 6) and their radio quiet counterparts (chapter 7). Several studies have in fact shown in the past that BLRG might behave differently than radio quiet AGN, displaying weaker reprocessing features (i.e. the reflection component and the strength of the iron line), possibly –i– associated with the presence of the jet. In the present study, however, such diversity is not found to be very striking, with the reprocessing features of the analysed sources not being as weak as expected. This could imply a different scenario for the dilution of these features, not involving a jet but rather a different geometry and/or accretion flow efficiency in the accretion disk. The analysis of the complete sample of type 1 AGN also allows a general picture of the average properties of this class of sources to be obtained. The mean power law slope is found to be Г=1.86±0.01, in good agreement with the generally accepted canonical spectral index of 1.9. The average cut-off energy is Ec=104 keV, lower than previously found in other works; the mean reflection fraction is 1.08±0.14. Correlations between the spectral parameters have also been investigated, but most of them remain still to be proven. When considering these results in the framework of AGN spectral modelling, we found that the average Comptonising plasma temperature is typically ∼50 keV with an optical depth ranging from 2 to 5, i.e. the plasma is not too thick. As far as the Cosmic X-ray Diffuse Background is concerned, synthesis models have so far assumed a spectral shape for the CXB with Г=1.9 with no dispersion in values and a high energy cut-off of at least 200 keV. However, the value of Г=1.86 with a dispersion of 0.2 and a cut-off energy with a narrow range of values around 100 keV, as found in the present thesis, could provide a self-consistent modelling of the CXB. The implementation of the information provided in this thesis is clearly very important for CXB synthesis models and represents the next step of this work.

Laser ablation has been investigated as a possible technique for the contactless deflection of Near Earth Asteroids. It is achieved by irradiating the surface of an asteroid with a laser light source. The absorbed heat from the laser beam sublimates the surface, transforming the illuminated material directly from a solid to a gas. The ablated material then forms into a plume of ejecta. This acts against the asteroid, providing a controllable low thrust, which pushes the asteroid away from an Earth-threatening trajectory. The potential of laser ablation is dependent on understanding the physical and chemical properties of the ablation process. The ablation model is based on the energy balance of sublimation and was developed from three fundamental assumptions. Experimental verification was used to assess the viability of the ablation model and its performance in inducing a deflection action. It was achieved by ablating a magnesium-iron silicate rock, under vacuum, with a 90 W continuous wave laser. The laser operated at a wavelength of 808 nm and provided intensities that were below the threshold of plasma formation. The experiment measured the average mass flow rate, divergence geometry and temperature of the ejecta plume and the contaminating effects - absorptivity, height and density - of the deposited ejecta. Results were used to improve the ablation model. A critical discrepancy was in the variation between the previously predicted and experimentally measured mass flow rate of the ablated ejecta. Other improvements have also included the energy absorption within the Knudsen layer, the variation of sublimation temperature with local pressure, the temperature of the target material and the partial re-condensation of the ablated material. These improvements have enabled the performance of the ablation process and the specifications of the laser to be revised. Performance exceeded other forms of electric propulsion that provided an alternative contactless, low thrust deflection method. The experimental results also demonstrated the opportunistic potential of laser ablation. Using existing technologies, with a high technology readiness level, a small and low-cost mission design could demonstrate the technologies, approaches and synergies of a laser ablation mission. The performance of the spacecraft was evaluated by its ability to deflect a small and irregular 4 m diameter asteroid by at least 1 m/s. It was found to be an achievable and measurable objective. The laser ablation system could be successfully sized and integrated into a conventional solar-power spacecraft. Mission mass and complexity is saved by the direct ablation of the asteroid's surface. It also avoids any complex landing and surface operations. Analysis therefore supports the general diversity and durability of using space-based lasers and the applicability of the model's experimental verification.

The International Linear Collider (ILC) is a proposed future e\(^+\)e\(^-\) linear collider which will make precise measurements of the Standard Model of Particle Physics. Novel detector systems with unprecedented performance are required to allow these measurements. This thesis focuses on the validation of a Digital Electromagnetic Calorimeter (DECAL) which infers the energy of the incident particles by counting the number of pixel fired (particles) in the shower rather than the energy deposited.The TPAC sensor has been developed for use as the active layer of a DECAL and its properties have been studied during beam tests at CERN and DESY. Data from these tests has been used to validate the DECAL concept by showing that pixel multiplicity increases with incident particle energy and material depth as expected for electromagnetic shower development. The radiation hardness of the TPAC sensors was also evaluated with a reduction in the signal to noise ratio of 8 % observed at doses up to 200 krad. The semileptonic decay of e\(^+\)e\(^-\) \(\rightarrow\) ttH has been studied at 1 TeV to evaluate the performance of the International Large Detector (ILD) yielding a predicted uncertainty on the measurement of the top Higgs Yukawa coupling of 6.9% with 1000 fb\(^-\)\(^1\) of data. An investigation into the effect of the inclusion of a DECAL has yielded results consistent with a conventional calorimeter system.

The main focus of this work is to make use of a novel tool in the cosmologist's toolbox when it comes to constraining the parameters of the peculiar velocity fields of the nearby Universe called ROBUST, whose unique properties and lack of reliance on secondary distance indicators sets it apart from other available constraining techniques, rendering it potentially very useful for future upcoming surveys such as the LSST and the SKA. While ROBUST proves itself more than adequate in constraining parameters in a mock controlled environment with the IRAS PSCz survey, it begins to struggle when applied to the real-world 2MRS survey, primarily due to an inherent fault in the survey that causes it to not function properly with the program. These problems persist even when we begin to make use of one of the ancillary tools developed in conjunction with ROBUST, namely relative entropy, despite it once again continuing to function adequately across multiple mock realisations. It is the conclusion of this work that while ROBUST is not successful in recovering values for the cosmological parameters we seek to constrain, this does not necessarily negate its viability for use with upcoming surveys, as it has proven itself successful in determining exclusion intervals on the value of the linear redshift distortion parameter β for real world surveys that are in very good agreement with the generally small values computed by contemporary velocity-velocity constraining techniques such as VELMOD and χ2 minimisation, while also confidently ruling out the results of older density-density constraining techniques such as POTENT that favour values closer to unity.

This explanatory essay discusses the rationale, methods and observational results using modern commercial, off the shelf (COTS) equipment in meteor astronomy. Much of the work is directed at developing spectroscopic observations and combining multi station observations to provide both orbital and compositional information about meteoroids. Papers are presented illustrating examples of the observations made and the significance of the results is discussed. COTS equipment is used primarily due to the reduced unit cost of such items. The cost of a typical system as used in this work, is in the region of £1000 for the camera, lens and grating (at time of writing).

In recent years, a range of detailed palaeoclimatic reconstructions have shown indications of a connection between changes in solar activity and Earth's climate. However, a process that may explain such a relationship has yet to be reliably demonstrated. One proposed mechanism concerns the theoretical link between the solar-modulated galactic cosmic ray (GCR) flux and Earth's cloud cover. Several microphysical pathways have been suggested which could account for this relationship, including (i) changes in the concentration of cloud condensation nuclei by an ion-mediated growth of aerosol particles, and (ii) the accumulation of charge at cloud boundaries predicted to influence the ability of cloud droplets to grow by scavenging processes. This work uses an original epoch-superpositional (composite) methodology to present new indications of statistically significant relationships between the rate of GCR flux (measured from neutron monitor sites across the globe) and changes in the rate of numerous large-scale atmospheric parameters (derived from satellite, reanalysis and weather station datasets) over daily timescales. Attempts are made to reproduce the observed anomalous atmospheric responses within a general circulation model. The results strongly suggest that some of the observed anomalies may be causally related to cloud changes and, furthermore, provide some support for possible links between the GCR flux, cloud anomalies and atmospheric responses. This relationship appears to be sensitive to changes in the rate of GCR flux and is also likely constrained by internal conditions.

Gravitational wave detectors are a new class of observatories aiming to detect gravitational waves from cosmic sources. All-reflective interferometer configurations have been proposed for future detectors, replacing transmissive optics with diffractive elements, thereby reducing thermal issues associated with power absorption. However, diffraction gratings introduce additional phase noise, creating more stringent conditions for alignment stability, and further investigations are required into all-reflective interferometers. A suitable mathematical framework using Gaussian modes is required for analysing the alignment stability using diffraction gratings. Such a framework was created, whereby small beam displacements are modelled using a modal technique. It was confirmed that the original modal-based model does not contain the phase changes associated with grating displacements. Experimental tests verified that the phase of a diffracted Gaussian beam is independent of the beam shape. Phase effects were further examined using a rigorous time-domain simulation tool. These findings show that the perceived phase difference is based on an intrinsic change of coordinate system within the modal-based model, and that the extra phase can be added manually to the modal expansion. This thesis provides a well-tested and detailed mathematical framework that can be used to develop simulation codes to model more complex layouts of all-reflective interferometers.

New Extreme Ultra-Violet (EUV) observations of the solar corona, obtained by the Coronal Diagnostic Spectrometer (CDS) instrument on board the NASA/ESA Solar and Heliospheric Observatory (SOHO) are presented. The CDS instrument for the first time has provided the opportunity of observing a large number of emission lines from a wide range of ions of different elements. The spectral and spatial resolution of the CDS instrument has allowed the simultaneous application of a wide range of spectroscopic diagnostic techniques to determine the temperature distribution, densities and elemental abundances in the solar plasma. A differential emission measure (DEM) diagnostic technique has been used to infer the temperature structure and the element abundances. The importance of including DEM effects in the element abundance analysis is demonstrated. A complete in-flight cross-calibration between all the CDS detectors (NIS and €115, 150-785 A), is presented here for the first time. The level of accuracy and completeness of the CHIANTI atomic database, used throughout this thesis, has allowed the identification of the many hundreds of spectral lines observed in the CDS spectra, resulting in several new line identifications. An assessment of the €115 solar spectra is presented, showing that, in spite of complexities, €115 spectra are useful for diagnostic analyses. Many discrepancies (in particular with the Li-like ions) between theory and CDS observations are highlighted. It is shown that some of these may be explained by inaccurate ionization equilibrium calculations. Coronal hole densities, temperatures, DEMs, and relative element abundances from both off-limb (plume and inter-plume regions) and on-disc observations are derived and compared with quiet sun values. These included (August 1996) a large equatorial hole, the Elephant's Trunk, probably the best example of a coronal hole observed by SOHO. Coronal hole densities in both coronal (N 1x10 8 cm 3 ) and transition region (Ne = lxlO'° cm 3 ) plasma were found to be about a factor of 2 lower than in the quiet sun, with much lower emission measures at temperatures above 106 K. Moreover, in the transition region, the cell-centres in both coronal holes and quiet sun regions show consistently higher densities (factor of 2) compared to those in the network. Relative element abundances show approximately photospheric values for the coronal holes, with an indication of element abundance variation .(neon in particular) with the supergranular structure. On-disc EUV observations of coronal hole plumes have been performed. This allowed a spectroscopic characterisation of plumes to be obtained for the first time, leading to the first identification of a low-latitude plume near sun-centre. Plumes are shown to be quasi-isothermal structures, with temperatures T 7 - 8x10 5 K. Abundance analyses (using transition region lines) reveal a small FIP effect in these plumes, together with a decreased Ne/O abundance ratio (compared to photospheric).