This thesis presents a study of the extragalactic radio source population at infrared (IR) and radio wavelengths of the electromagnetic spectrum. The IR/radio emission from these sources can be the result of star−forming processes and/or the result of an accreting supermassive black hole, an active galactic nucleus (AGN). The purpose of this study has been to separate the two different types of emission, determine the dominant process and calculate star formation rates (SFRs) for this population. For the first sample of radio sources, high redshift radio galaxies (HzRGs), polycyclic aromatic hydrocarbon emission has been observed in their mid−IR spectra. For the second sample, the radio sources in the Extended Chandra Deep Field−South (ECDF−S), Herschel photometry was used to infer the contribution of cool dust associated with star formation to the IR emission. Overall, I find that extragalactic radio sources, both those that do and do not contain an AGN, can have a strong component of their IR and/or radio emission from star formation. From this result, I infer they can have exceptional SFRs ("1000sM! yr−1). For the HzRGs, it was also found that they have weak 9.7 μm silicate absorption (!9.7 μm < 0.8). This implies that their mid−IR obscuration is predominantly the result of the dusty torus that surrounds the central engine and not the result of dust in the host galaxy. For the ECDF−S radio sources, AGN and star−forming galaxy contributions to the radio source counts were also determined. I find that sources powered by star formation are responsible for the observed flattening of the counts at "1mJy and a significant portion of these sources host an AGN. The optical morphologies of low−redshift sources are also investigated and Ifind that the faintest sources are mostly either late−type galaxies or irregular/ mergers while the bulk of the bright sources are early−types.

The exoplanet field has been evolving at an astonishing rate: nearly two thousand planets have been detected and many more are awaiting confirmation. Astronomers have begun classifying these planets by mass, radius and orbital parameters, but these numbers tell us only part of the story as we know very little about their chemical composition. Spectroscopic observations of exoplanet atmospheres can provide this missing information, critical for understanding the origin and evolution of these distant worlds. Currently, transit spectroscopy and direct imaging spectroscopy are the most promising methods to achieve this goal. Ground and space-based observations (VLT, Keck Observatory, IRTF, Spitzer Space Telescope, HST) of exoplanets have shown the potentials of the transit method. However, the instruments used in the past ten years were not optimised for this task: the available data are mostly photometric or low resolution spectra with low signal to noise. The interpretation of these --- often sparse --- data is generally a challenge. With the arrival of new facilities (GPI, SPHERE, E-ELT, JWST), and possibly dedicated space instruments such as the Exoplanet Characterisation Observatory (EChO), many questions needed to be tackled in a more systematic way. The focus of this thesis is to provide a theoretical framework to address the question of molecular detectability in exoplanet atmospheres with current and future facilities. The atmospheric components and their spectroscopic signals depend strongly on the planetary temperature and size, therefore I have simulated a significant sample of planets out of a range of sizes and temperatures, to describe comprehensively the chemical compositions that can be expected in those exotic worlds. Such simulations were convolved through instrument simulators to assess performance and limitations of current and future facilities. While my study has been inspired by transit spectroscopy with a hypothetical EChO-like space-based instrument, the methodology and results of this thesis are applicable to observations with other instruments and techniques.

A measurement and a search, both involving high transverse momentum bosons decaying to b-quarks, are performed using a dataset of proton-proton collisions at √s = 8 TeV, collected in 2012 with the ATLAS detector at the LHC, corresponding to an integrated luminosity of 19.5 inverse fb. The production cross section of Z → bb is measured, where the Z boson has high transverse momentum. The measured value of the fiducial cross section is found to be in good agreement with next-to-leading-order Standard Model predictions. A search is made for TeV-scale resonances decaying via a pair of Higgs bosons to the b ̄bb ̄b final state. The graviton excitation, G*, in the bulk Randall-Sundrum model is used as a baseline signal model. No evidence of a resonance is found. Upper limits are set on σ(pp→G*) x BR(G*→HH→bbbb).

As it is now known that neutrinos oscillate, this entails that lepton number is not a conserved quantity and required modification of the Standard Model. The same mechanism also allows charged leptons to violate lepton number, but at an immeasurable rate. Therefore any observation of e.g. a muon decaying to an electron in the absence of neutrinos would be a signal of physics beyond the Standard Model. A test facility, but also an experiment capable of searching for such a kinematic effect has been set-up in Osaka, Japan. The thesis ‘Initial Measurements at the MuSIC Beam-Line’ documents several exper- iments that were carried out using the MuSIC muon beam in Osaka. The experiments focused on understanding the beam and characterising it. Three main measurements were made: total charged particle flux, muon flux and muon momentum spectrum. Each experiment used plastic scintillators and MPPCs to detect the charged particles. Muons were identified by looking for muon decays between two scintillators. Data acquisition was performed using NIM for signal shaping and logic; and CAMAC or VME for readout via TDC and ADC modules. In addition to direct experimental measurements, a simulation of MuSIC was made using the ‘G4Beamline’ and ‘Geant4’ packages which allowed detailed interrogation of the exper- iment to aid understanding of the results. It also provided a test bed upon which to refine the setup for later measurements. These measurements allow us to confirm the performance of the novel pion capture solenoid which is an integral part of several future experiments (primarily COMET but also proposed neutrino factories). In addition to this core work, the thesis deals with my services writing firmware for the LPD detector being built for the XFEL project in Hamburg, Germany. The firmware is an interface between the generic clock and control card (being developed at UCL) and the custom ASIC (being developed at RAL). The interface was written using VHDL and receives, translates, interprets then transmits control instructions to the detector.

The Kepler Satellite provides unique opportunities in stellar astrophysics, with its observations being of particular importance to the asteroseismology community. With Kepler having a limited target list due to data telemetry limitations, pre-launch time series and colour photometric surveys were undertaken to identify suitable targets for observation. However, none of these combined cadence and depth that matched that derived using Kepler itself. This meant that there were potentially many short period variable sources awaiting discovery which could be observed by Kepler. We therefore chose to initiate a deep, high cadence survey, RATS-Kepler, with a cadence of 1 minute and a depth of g 21 with the aim of recovering astrophysically interesting sources to potentially be observed by Kepler. The work presented here details my role in developing a new data reduction pipeline process, a new variable stars selection algorithm and the subsequent selection of sources for proposals for Kepler short cadence observations. I present the results of our survey, which have been made publicly available to maximise their scientific impact and the Kepler data obtained for the 18 sources which we successfully obtained short cadence observations. I then go on to outline the future of the Kepler mission now that it is unable to continue with its initial mission.

Mitotic chromosome structure is highly important in the packing and safe separation of DNA during cell division. The chromatin fibre, the first packaging of DNA around histone proteins, is coiled into a highly condensed state during the metaphase stage of mitosis where the chromosomes form their characteristic ’X’ shape in order to be split into two daughter cells on cell division. Accessing the 3D structure of the condensed chromatin could provide high resolution information on the location of the genes inside the chromosome during metaphase and the placement of the proteins used in the packaging mechanism. We apply lensless X-ray imaging techniques to chromosomes in an attempt to access their structure. Coherent Diffraction Imaging and Ptychography have potential to achieve wavelength limited resolution in 3D. The techniques directly measure phase that can be used to map the electron density in the sample. Sample preparation is highly important to obtain good quality images from any microscopy technique. We start with studying sample preparations with Fluorescence and Scanning Electron Microscopy to observe the suitability and effects of the protocols. We perform lensless imaging on nuclei and chromosomes prepared with newly designed protocols for this type of X-ray imaging. Images of nuclei were retrieved from the ptychography experiments at 34-ID-C, I-13 and cSAXS. Ptychography was performed with a visible light source on a set of 46 human chromosomes. The images provide a map of electron density that can be used to calculate the mass of chromosomes and nuclei. Mass is a macroscopic structural quantity that can be used to observe the changes to the protein and DNA content in the nucleus during the cell cycle given a high enough resolution. The nuclei measured in this work were in an early mitotic state and gave consistent mass values calculated from the phase measured by ptychography. In the case of chromosomes mass calculated from the ptychography images was used to sort and identify them in a form of karyotyping. This method of identification is novel because it takes into account the whole of the chromosome contents, both protein and DNA, whereas standard methods of karyotyping look at positions of bandsin the chromosomes.

This PhD thesis concerns the physics of low-dimensional quantum systems and especially quantum spin ladders. Novel metal-organic compounds (C5H12N)2CuBr4 and (C5H12N)2CuCl4 are investigated as model materials for low-dimensional quantum behavior by neutron scattering experiments and by measurements of magnetic and thermodynamic properties. The experimental results are compared quantitatively to calculations using a variety of theoretical and numerical methods (DMRG, ED) of the ground state and excitations of such systems. Key results are the determination of the Hamiltonian and its exchange parameters of (C5H12N)2CuCl4 studied here for the first time from quantitative modelling of magnetic susceptibility and neutron spectroscopy data. When a magnetic field is applied two quantum critical points occur at which fractionalization of the elementary quasi-particle excitations is ob- served. The characteristic excitation continua are explained by effective spin-chain and t-J models and are observed systematically as a function of magnetic field and temperature. Coherent and incoherent spin Luttinger-liquid physics is observed and for the first time modelled fully quantitatively. The chemical flexibility of the these metal-organic compounds allows continuous solid-state mixtures of Br and Cl resulting in systems with quenched disorder. The rung and leg exchange parameters assume discrete values given by the specific chemical composition of the exchange pathways. The influence of such quenched disorder on the excitations of quantum spin ladders has been studied experimentally. The observed spectra with damped excitations of the unperturbed ladder and more localized modes provide detailed insights into the physics that may be observed in such systems if a magnetic field is applied and so called Bose glass phases are induced.

The work presented in this thesis is motivated by the great commercial impact of organic semiconductors especially in optoelectronics. In particular, we focus our attention on some of the current challenges in organic light-emitting diodes from the point of view of the photophysical properties of materials (i.e. via steady-state and time-resolved photoluminescence characterization) and the device physics. In view of the interest in near-infrared emission, we propose two ways to obtain emission at long wavelength. Firstly, we report a new molecular design of one of the currently best performing polymer for near-infrared light-emitting diodes. We investigate the substitution of sulphur with selenium and find that it is more effective both in terms of photo- and electro-luminescence efficiency than by exploiting higher sulphur-chromophore loadings, while achieving a more important red-shift. Secondly, we explore the tuning of the energy gap through a careful choice of the relative positions of the frontier levels of two organic semiconductors. Following this strategy, we obtain a nearly pure near-infrared electroluminescence with essentially no emission from the single components at any operational voltage. We believe that results obtained are a valuable feedback as they suggest materials design criteria. Given to the potential of phosphorescent materials for obtaining high efficiency OLEDs, we also consider the investigation of a novel emitter based on a wide-gap host co-polymerized with a low-gap phosphorescent emitter for efficient energy transfer. Finally, we report a detailed investigation of the photoluminescence emission at low temperature of the fullerene derivative [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), widely employed as an electron acceptor in organic solar cells. Owing to the availability of solvent-free single-crystals, whose growth has been recently reported by our group, we are able to investigate PCBM optical properties without solvent dependence. Our attempt is to provide significant information on the ordering and relative importance of the relevant excited states in PCBM.

The SCANning Doppler Imager, SCANDI, is a new all-sky development on the network of UCL Fabry Perot Interferometers, FPI, in the Arctic region. It is able to provide high temporal and spatial resolution measurements on the upper atmosphere, in scales of minutes and tens of kilometres. This is a step change from the single look direction provided by a standard FPI. SCANDI’s mechanics, control-software, data analysis and calibration methods are presented. This includes details on techniques that are specific to the instrument’s all-sky capability. The meso-scale data are of particular interest to developments in atmospheric models, which look for increasingly small-scale structures. An ionospheric cusp study utilising SCANDI is able to provide direct neutral measurements at high spatial resolution. It indicates Joule heating is likely to be one of the main sources which contributes to atmospheric cusp density upwelling. The neutral cusp results also complement the CHAMP satellite density data and are able to demonstrate the neutral thermosphere has a considerable meso-scale structure reflecting its response to the cusp dynamics. The temperature variation over the recent solar-cycle in years 1999-2009 is analysed, which covers the extended solar minimum of cycle 23/24. It is also the longest continual period of FPI observation from a single site that has been analysed. The dataset demonstrates that the polar cap neutral temperature is unaffected by the unusually low solar activity, possibly because of high latitude geomagnetic contributions. The difference between measurements and MSIS model results are explored, which demonstrate MSIS unexpectedly over-estimated the neutral temperature by 200 K at this solar maximum. It indicates MSIS is unable to recreate the low temperatures in this unusually weak solar cycle. A new technique was also developed for the study of FPI long term neutral temperature by modelling the red and green-line emission profiles. It is demonstrated that the FPI-measured temperature can be lowered by ∼50K because of variations in the width of the emission height profile and peak altitude. This needs to be considered in long-term temperature trend analysis, especially where looking for trends of as small as a few Kelvin.

The drive to continue Moore’s Law by shrinking electrical components down to the ultimate limit has led to a great deal of interest in atomic and molecular-scale electronics, in which individual atoms and molecules can be used as circuit elements. More recent proposals also seek to exploit the magnetic properties of these nanoscale objects in new applications in information technology and spintronics. In typical device geometries, the magnetic element is coupled to electrical leads, and these interactions can strongly affect the properties of the quantum system. Using scanning tunneling microscopy and spectroscopy, we study the effects of inter- actions between individual magnetic atoms and molecules that are separated from an underlying metallic surface by a thin insulating layer of copper nitride (Cu2N). By utilising the different growth phases of the Cu2N, we show that the position of magnetic molecules can be controlled, and that the properties of a molecule can be controlled through the binding site. For electrical transport through a junction containing an individual iron phthalocya- nine (FePc) molecule on Cu2N, we observe two novel magnetoresistance behaviours that arise from negative differential resistance (NDR) that shifts by unexpectedly large amounts in a magnetic field. Because voltage is dropped asymmetrically in this double barrier junction, the FePc can become transiently charged when its states are aligned with the Fermi energy of the Cu, resulting in the observed NDR effect. Furthermore, the asymmetric coupling magnifies the observed voltage sensitivity of the magnetic field dependence of the NDR, which inherently is on the scale of the Zeeman energy, by almost two orders of magnitude. These findings represent a new basis for making magnetoresistance devices at the single molecule scale. Fur- thermore, the enhancement of the energy scales created by asymmetric coupling of the junction can be used in conjunction with other multi-step tunnelling processes to allow for the investigation of phenomena that would otherwise be difficult to observe. We also show that it is possible to interact with the f-shell magnetic moment when a bis(phthalocyaninato)Dy(III) complex (DyPc2) is strongly coupled to the Cu(001) surface. DyPc2 is a single molecule magnet, a type of molecule which may have applications in both spintronic and quantum computing applications. A Fano lineshape is observed at the Fermi energy, which is caused by the interference between tunnelling into the continuum and into a resonance created by the Kondo effect. By mapping the variance of the amplitude of the Fano line shape we are able to show that the ligand states create the continuum states and the 4f states create the Kondo resonance.