The cell cortex is a thin network of actin, myosin motors, and associated proteins that underlies the plasma membrane in most eukaryotic cells. It enables cells to resist extracellular stresses, perform mechanical work, and change shape. The actin network undergoes constant reorganisation due to molecular turnover. Hence, cortical structural and mechanical properties depend strongly on the relative turnover rates of its constituents and the actin filament length-distribution, but quantitative data on these dynamics remains elusive. I combined single molecule speckle microscopy and photobleaching experiments with microscopic computer simulations to analyse how molecular binding dynamics of G-actin to filaments sets network turnover and consequently the mechanical properties of the cellular actin cortex in living cells. Using photobleaching experiments, I found that two filament families with very different turnover rates composed the actin cortex: one with fast turnover dynamics and polymerisation resulting from addition of monomers to free barbed-ends and one with slow turnover dynamics with polymerisation resulting from formin-mediated filament growth. I show that filaments in the second subpopulation are on average longer than those in the first and that cofilin-mediated severing of formin-capped filaments contributes to replenishing the filament subpopulation with free barbed-ends. Additionally, I measured the molecular association rates and the distribution of travel-distances of single actin monomers and formin dimers in speckle experiments and showed that this travel-distance distribution is consistent with the actin filament length-distribution found from photobleaching experiments and molecular simulations. Furthermore, I compare the steady state cortex of different cell lines and newly formed cortices in cellular blebs and discuss the role of cross-linkers like α-actinin and myosin mini-filaments in the actin cortex. Together, my results provide a quantitative characterisation of essential mechanisms underlying actin cortex homeostasis.

This thesis presents Density Functional Theory (DFT) modelling results for the V- centre in MgO, and self-trapped holes in the bulk and at the surface of monoclinic (m-)ZrO2. These systems exhibit polaronic self-trapping of a hole, a situation with which conventional DFT struggles due to the self-interaction error (SIE). The V- centre in MgO comprises a hole polaron trapped at a Mg vacancy, and has been the subject of many experimental and theoretical studies. Hybrid DFT was applied within an embedded cluster scheme to investigate how the optical and paramagnetic properties of the centre are affected by the proportion of Hartree-Fock exchange present in the functional, and also to elucidate the nature of the transitions involved in the optical spectrum, which were found to be more complicated than previously thought. Semi-local DFT under periodic boundary conditions, augmented with the cancellation of non-linearity (CON) method to correct for the SIE, was used to determine whether holes self-trap in the bulk of m-ZrO2. Self-trapped holes were found to be stable on the sub-lattice of 3-coordinated (3-C) oxygens, with a trapping energy of 0.13 eV. These hole polarons are highly mobile, but di_use primarily in 2-C planes. Having identified the (-111), (111) and (001) as the three most prevalent facets of a model nanoparticle, the same method as described in the previous paragraph was applied to these surfaces. It was found that self-trapped holes are stable at all under-coordinated oxygen sites, but that they trap particularly strongly at 2-coordinated sites on the (-111) terrace, with a trapping energy of 1.18 eV, while still being relatively mobile. Two model monolayer steps were then constructed by intersecting the (-111) and (111) terraces, and found that trapping was less favourable near the step, in contrast with simpler oxides such as MgO and CaO.

This thesis studies the formation of products of magnetotail reconnection using models and observations. Three studies are presented, the first is an analysis of observations from the Cluster spacecraft, located in different regions of the magnetotail, which allow simultaneous sampling of a Travelling Compression Region (TCR) in the lobe and the underlying magnetic structure in the plasma sheet causing it. Previous work suggests that these structures are created by either single-X-line time-dependent reconnection, forming a flux-bulge, or multiple-X-line reconnection, forming a flux-rope. The observations are analysed and compared to the predictions of these models to determine which mode of reconnection created the structure. The second study presents an adaptation to a single particle model of time-dependent reconnection in the magnetotail previously published by Owen and Cowley (1987). This new model relaxes the cold plasma approximation and assesses the stress balance conditions on reconnected field lines threading the current sheet when the outflow particles have a perpendicular pressure. This is modeled as a result of pitch angle scattering of field-aligned inflow particles as they cross the current sheet on hairpin-like reconnected field lines. The new results show that this accounts for a flux-bulge and a TCR which is consistent with observations. The third study presents a numerical particle model which simulates the evolution of a plasmoid, modeled as a single magnetic field loop in the magnetotail. The model magnetotail has a magnetic, density and velocity gradient along the tail axis. The plasma within the plasmoid splits into two groups, the movement of these groups causes the plasmoid size to oscillate. The initial tailward movement of the plasmoid is caused by the magnetic gradient but continues in its absence due to the net momentum of the plasma inside the plasmoid, with the tailward travelling particles travel faster than the Earthward travelling particles.

I have divided this dissertation into three chapters: introduction to organic solar cells, thermo-chemical lithography of a conjugated polymer, and triplet emitters in organic solar cells (OSCs). The first chapter introduces OSCs giving the background necessary to understand the problem of simultaneous optimisation of exciton dissociation and charge transport. The second chapter deals with scanning thermo-chemical lithography (SThL) of PPV on indium-tin oxide (ITO) by means of a thermal AFM, i.e. an AFM that has a hot probe scanning across the surface, to ultimately pattern the active layer of an OSC. I investigate the influence of the thermal conductivity of the substrate on the lithography by combining finite element simulations of the heat transfer and experimental results. The model explains the rather substrate-independent feature size observed during experiments and it is found that for the highest resolution features, there exists a small gap of unconverted polymer near the substrate, which is why SThL is possible on high thermal conductivity substrates such as gold. In the third chapter I report experimental findings regarding the inclusion of triplet emitters in organic photovoltaic cells. The idea is to increase the exciton diffusion length (L) of the primary photoexcitations by converting them into triplet excitons, which are known to have longer lifetimes and hence offer the potential of increased exciton diffusion lengths. Several host systems were chosen, among them P3HT:PC61BM, MDMO-PPV:PC61BM and PBTTT:bis-PC61BM. As phosphorescent molecules I used Cu-complexes and different Ir-complexes. Results on MDMO-PPV:PC61BM blends and bilayer devices showed a promising increase in the short-circuit current density (Jsc) partly supported by an increase in the incident photon to current efficiency peak in the polymer absorption wavelength range. The overall achievability of the idea is critically discussed and a 1D random walk model used to estimate possible improvements of Jsc upon increases in L.

In this thesis we formulate sophisticated quasiclassical techniques to describe corre- lated electron dynamics in atoms and diatomic molecules that are either absorbing a single photon or are driven by strong infrared laser fields. The first part of this thesis concerns the multi-electron ionisation in atoms following single-photon absorption. For excess photon energies close to threshold, the Wannier threshold law predicts that the electrons escape in the most symmetric way. We describe the single-photon quadru- ple ionisation from the ground state of beryllium. Surprisingly, we find that close to threshold the four electrons escape on the apexes of a triangular pyramid, while Wan- nier threshold law predicts a regular tetrahedron. We explain this unexpected breakup pattern using non-linear analysis for the fixed points of the Coulomb four-body sys- tem. We then focus on time-resolving the attosecond collision sequences that underlie single-photon multi-electron ionisation. We formulate how to time resolve intra-atomic correlated electron dynamics during the escape of two electrons. Specifically, we show how to compute the “collision” time, using the inter-electronic angle as a function of the phase between the triggering and the streaking laser fields. We also demonstrate how this two-electron streak camera captures the different ionisation dynamics for different electron energy sharings. We then proceed to generalise the two electron streak camera to account for realistic experimental conditions. In the final part of this thesis, we ad- dress correlated electron dynamics during the breakup of diatomic molecules driven by intense infrared laser fields. We concentrate on the two pathways leading to the forma- tion of highly excited neutral atoms. In particular, we show how for high ellipticites of the infrared laser field two-electron effects are “switched” off. Moreover, we find that the two dimensional momentum distribution of the escaping electron, in the formation of highly excited neutral atoms, carries the imprint of one-electron effects with increasing ellipticity of the infrared laser field.

The development and testing of two novel hyperspectral cameras intended to fly on a small Unmanned Aerial Vehicle (UAV) and give simultaneous views of the sky and ground over a spherical field of view in the visible and near-infrared is described. These measurements are intended to be gathered concurrent with satellite and ground observations and used in the vicarious calibration of Earth Observation satellite sensors. Hence, stringent accuracy demands guided the project. These were researched as part of a collaborative study into satellite inter-comparison over Dome C, Antarctica, which found typical agreement in Top-of-Atmosphere reflectance between different sensors and other comparison studies of < 3%. A literature review revealed that vicarious calibration, normally performed over bright desert targets, should be carried out over vegetation. The first hyperspectral camera developed employs a bespoke conical mirror coupled with an AOTF. This proof-of-concept system was found to be an innovative step towards a device to continuously capture downwelling and upwelling spectral radiance in the Solar Principal Plane for long periods without reorientation. This makes it extremely useful in studies of the backscattering peak of vegetation angular reflectance. The second camera uses a LCTF and a fisheye lens that trades spectral resolution for improved Out-Of-Band Stray Light and spatial/angular resolution to overcome the limitations of the first camera. Testing revealed the LCTF-based camera meets almost all requirements for vicarious calibration when deployed from either the ground or a low altitude UAV platform. Novel use of the fisheye lens was performed by imaging horizontally to capture both upward and downward hemispheres to allow simultaneous viewing of ground and sky. Less than 4% absolute radiometric accuracy was achieved, but the inter-pixel flat-field calibration of a 190 degree FoV imager presents an original problem that this project reveals is not adequately addressed in the literature.

This thesis explores the properties of distant galaxies in the Universe, in particular their redshifts, morphologies, evolutionary history and star formation processes within them. The first part is concerned with photometric redshift estimation. I present different photo-z methods and compare them using a sample of Luminous Red Galaxies (LRGs). Photo-z design studies are then carried out for the upcoming Dark Energy Survey as well as the planned space-based Euclid mission. I show the importance of adding near infra-red data to optical data in obtaining accurate redshift estimates for both these projects and how this may prove crucial for some of the cosmological analysis intended with them. In Chapter 5, I present automated morphological classifications for ∼ 1 million objects from the Sloan Digital Sky Survey and compare them to visual classifications of the same objects obtained as part of the Galaxy Zoo project. I find that a neural network is able to reproduce the human classifications to an accuracy of better than 90%. In Chapter 6 I study the evolution of the luminosity and mass functions of LRGs using spectroscopic data. I find that these objects are mainly composed of old stars that were formed very early in the history of the Universe and also that the most massive objects were already well assembled at redshifts of ∼0.8 in direct contradiction with predictions of most current models of galaxy formation. Chapter 7 presents an alternative means of determining the approximate nature of the stellar initial mass function of extragalactic systems by considering timescales for low-mass star formation in different environments. I find that a galaxy’s metallicity is a key parameter in determining the shape of its IMF and make some predictions about trends in molecular emission in different extragalactic systems with different IMFs.

A precision measurement of the mass and width of the W boson is presented. The W bosons are produced in proton antiproton collisions occurring at a centre of mass energy of 1.96 TeV at the Tevatron accelerator. The data used for the analyses is collected by the Collider Detector at Fermilab (CDF) and corresponds to an average integrated luminosity of 350 pb−1 for the W width analysis for the electron and muon channels and an average integrated luminosity of 2350 pb−1 for the W mass analysis. The mass and width of the W boson is extracted by fitting to the transverse mass distribution, with the peak of the distribution being most sensitive to the mass and the tail of the distribution sensitive to the width. The W width measurement in the electron and muon channels is combined to give a final result of 2032 ± 73 MeV. The systematic uncertainty on the W mass from the recoil of the W boson against the initial state gluon radiation is discussed. A systematic study of the recoil in Z \rightarrow e+e− events where one electron is reconstructed in the central calorimeter and the other in the plug calorimeter and its effect on the W mass is presented for the first time in this thesis.

This thesis is related to the growth of structure in the late-time Universe. It addresses both the measurement of this structure and the use of such information in constraining fundamental underlying physics. This includes the gravitational framework and the sum of the three neutrinos’mass. The thesis starts by using weak gravitational lensing data (CFHTLS) to constrain a modification of gravity that is invoked to provide the observed accelerated expansion in the Universe. This is shown to disfavour the model in question. It is, however, incapable of placing any bounds on the growth parameter that represents extensions to gravity. The future of weak lensing in probing general relativity is illustrated with forecasts on the growth signature and power spectrum parameter using the proposed Euclid probe. A measurement is made on the clustering of Luminous Red Galaxies (LRGs) in the Universe. This represents a new photometric galaxy clustering angular power spectrum: MegaZ LRG Data Release 7 (DR7). The cosmological constraints are demonstrated to be competitive with spectroscopic surveys and complementary to the WMAP5 data. Specifically, bounds of f_b \equiv \Omega _b / \Omega _m = 0.173 \pm 0.046 and \Omega_m = 0.260 \pm 0.035 are placed. Potential systematics in the data are discussed and examined. The work concludes by placing one of the most stringent constraints available of the sum of the three neutrino masses. By combining cosmic microwave background information, distance measures from supernovae and baryon acoustic oscillations with growth from the MegaZ LRG galaxy clustering data, produced earlier, the limit is found to be \sum m_v < 0.281 eV at the 95% confidence level.

This thesis first presents a relatively straight forward approach for detecting galaxy clusters using spectroscopic data. A friend-of-friends algorithm based on that of Huchra & Geller (1982) is implemented with linking parameters that take into account selection effects on the the 2dF-SDSS and QSO (2SLAQ) Luminous Red Galaxy Survey (Cannon et al. 2006). The linking parameters are constrained using a mock halo catalogue. The galaxy groups and clusters found with this method have an average velocity dispersion of \sigma v = 467:97 kms-1 and an average size of R clt = 0:78 h-1Mpc. Cluster masses are estimated using the cluster velocity dispersions and appear consistent with values expected for genuine structures. The spectroscopic cluster catalogue is then used to calibrate and compare with a more complex method for detecting clusters using photometric redshifts based on the method of Botzler et al. (2004). The spectroscopic cluster catalogue can be reproduced by around 38% and up to 80% if matching is made only to groups and clusters with six or more members. This code is also applied to the Megaz-LRG DR7 catalogue (Collister & Lahav 2004) producing two catalogues. One that appears to have a good level of completeness relative to the 2SLAQ spectroscopic catalogue. A spectroscopic follow up of some preliminary results from the photometric cluster finder was made using the Anglo-Australian Telescope, which show that the majority of the clusters analysed are genuine and approximate masses can be estimated from the cluster velocity dispersions. Finally, some initials results from on going work in the Dark Energy Survey collaboration are presented, which cover simulated galaxy photometric redshift and colour analysis as well as cluster detection.