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We investigate various aspects of the proton structure in this thesis. The first addresses the distribution of the proton spin among its constituents, quarks and gluons. We derive the framework of distribution functions for these constituents and study the properties of the polarized distributions which describe the spin structure of the proton. A determination of the polarized distributions on the basis of present experimental data is presented and options for future measurements are critically evaluated. A second aspect under consideration is the phenomenology of hard diffractive electron-proton scattering. We show how diffractive interaction and hard scattering can be disentangled and suggest experimental tests for this interpretation. Finally, we illustrate how the knowledge on the proton structure can be used for the computation of observables in proton-antiproton collisions, confirming or extending our knowledge of the physics of elementary particles.

The acceleration of charged particles with ultrafast terahertz electromagnetic radiation could enable new, and improve many of aspects of, accelerator applications. These include providing shorter electron bunches for ultrafast time-resolved pump-probe spectroscopy, enabling complex longitudinal profiles to be imparted onto charged particle bunches and significantly improving the ability to synchronise an accelerator to an external laser. In this thesis I present investigations into terahertz radiation sources that enabled the generation of terahertz radiation with attractive properties for accelerator based applications. Specific attention has been paid to temporally tunable sources that generate strong longitudinally polarised electric field components as these enable a free-space co-linear interaction geometry to be implemented. A simulation describing the propagation of radiation from such sources has been developed. Terahertz sources have been designed and the radiation generated characterised via electro optic detection. These include a radially biased photoconductive antenna (PCA) based source of which the longitudinally polarised terahertz electric field component was found to have an amplitude of 2.22 kVcm-1 as well as a near-single cycle temporal profile. This radially biased PCA was used in conjunction with the Accelerators and Lasers in Combined Experiments (ALICE) energy recovery linear accelerator at the Daresbury Laboratory in an electron acceleration experiment. To enable higher longitudinally polarised terahertz electric field strengths to be obtained, as well as the ability to temporally tune the terahertz radiation, generation within non-linear optical crystals was investigated. Magnesium-oxide doped stoichiometric lithium niobate (MgO:SLN) was investigated as a possible candidate due to its high non-linear susceptibility tensor and reported ability to impose temporal tuning directly from the pump laser beam. A scheme consisting of two MgO:SLN crystals each generating a separate linear polarised terahertz pulse which were then combined via a lens was designed and built. Electro optic detection techniques were used to characterise the radiation generated from this source. Peak terahertz electric fields amplitudes of 11.6 kVcm-1 and 47 kVcm-1 were measured for both the longitudinally and transversely polarised field components respectively. Temporal profiles measured from both the longitudinally and transversely polarised electric field components showed electric field periods of approximately 300 fs. This method of generating terahertz radiation employed a pulse-front tilt technique. Allowing for the same scaling as recently reported in the literature for MgO:SLN generation techniques, which will in principle allow this method to scale to longitudinally polarised terahertz electric field profiles in excess of 1 MVcm-1.

No description available.

[Truncated abstract.] An apparatus has been built, tested and characterised with greatly increased precision and accuracy to enable spin-polarised electron impact explorations of angular momentum effects in atoms. A combination of experimental, computational and interpretative studies has revealed new phenomena. In zinc the polarisation of the radiated photons from excited and ionised-with-excited atoms was measured in terms of integrated Stokes parameters (P1, P2 and P3) and related to electron exchange and spin-orbit interaction using normalised state multipoles.

In nature, both fundamental and sophisticated ecological functionality alike are driven by the display or, conversely, the concealment of colour and visual contrast. Through scientific investigation, the evolutionary genius manifested in numerous light manipulating biological systems has provided many blueprints for innovative photonic devices and other smart materials. The development of innovative bioinspired materials that harness the optical properties exhibited by chiral structures, such as those found in certain Scarabaeidae, offer widespread potential. In this thesis, the species-specific circularly polarised optical behaviour corresponding to a variety of Scarabaeidae beetles is investigated. The helicoidal morphology giving rise to circularly polarised photonic properties is first described for several beetles displaying a narrowband colour appearance. A structural analysis of the native surface structures encountered in these species is presented alongside a discussion of their role in defining the species' optical characteristics. Experimental measurements of the circularly polarised scattering behaviour are presented and discussed with respect to the electron microscopy and surface morphology measurements comprising the structural analysis. Following this, the origins of the subtle differences in the metallic colour appearance of several broadband coleopteran structures are deciphered. The broadband response of these species is attributed to chirped configurations of the helicoidal lamellar structure, elucidated using electron microscopy. Results of this structural analysis are applied to theoretical simulations of the structures' electromagnetic response and consolidate experimental measurements of the circularly polarised reflectance. Rigorous experimental measurement demonstrated that the circularly polarised spectral response is relatively robust to small structural defects or `biological noise'. Building from this, the intraspecific colour variation displayed in the species Chrysina aurigans is a useful lens through which the nuances of the chirped multilayer structure are further examined. As a result, this work provides detailed insights into the fine-tuning of chirped biological photonic systems. Likewise, the topic of biological wave retarders is afforded significant attention, primarily with reference to the biological half-wave plate encountered in the cuticle structure of Chrysina resplendens. A rigorous analysis of the photonic system in C. resplendens is presented, leading to novel conclusions describing this system's opto-structural relationship. Additionally, this thesis reports, for the first time, the presence of a biological wave retarder in the cuticle structure of Chrysina cupreomarginata.

In this thesis, an antenna reduction technique in Multiple Input Multiple Output (MIMO) systems, which is called Code Shift Keying (CSK) Modulation, is introduced. With the use of Walsh Hadamard orthogonal spreading codes, we overcome the biggest drawback of conventional Spatial Modulation (SM) which is the antenna index estimation errors due to channel correlation. Also SM fails to perform in non normalised channel conditions. The combination of orthogonal spreading codes and antenna devices, as a means to convey information at the receiver, results in a remarkable performance improvement at the receiver.Moreover, an improved scheme that uses half the amount of spreading codes so as to represent the total number of information bits has been introduced leading to an important reduction in bandwidth usage. By maintaining the net spreading levels of the system we attain remarkable performance improvements.A technique called Polarisation Assisted Space Shift Keying Modulation (PASSK) has also been proposed which manages to exploit the polarisation domain and it is able to outperform the conventional SM technique as well as the Maximal Ratio Receiver Combine (MRRC) and Vertical-Bell Laboratories Layered Space-Time (V-BLAST) schemes. A new precoding scheme that manages to either eliminate or exploit the cross polarisation effects has also been proposed as a complementary study of the PASSK scheme.As modern and future communications show a rising demand for higher data transmission rates, network coding is increasingly incorporated in wireless communication standards. In harmonisation with this trend, this thesis discusses the main state-of-art network coding schemes. The contribution here includes a number of innovative schemes that are able to further increase throughput. Finally, the employment of network coding is discussed in conjunction with CSK Modulation resulting to further improvement in terms of throughput as well as Bit Error Rate (BER) performance at the cost of increased bandwidth usage.

Magnetic recording media refers to the disc shaped thin film magnetic medium present inside the hard disk drive of a computer. Magnetic recording is an important function of the hard disk drive by which information such as text, pictures, audio and videos are stored. Information is broken down to a simple binary format and is stored as magnetised bits along the tracks of the disk forming the hard drive. Over the years advancements in research on the type of magnetic materials used has allowed increased data storage capacities by reducing magnetic bit sizes. It is with this advancement in magnetic data storage, that we have today's hard disk drive technology, which uses a perpendicular magnetic medium to store data. A perpendicular magnetic medium is a multi-layered magnetic thin film structure with the topmost layer comprising nanoscale magnetic grains of high perpendicular anisotropy. The topmost recording layer (RL) is mapped into individual bits of 80-100 nm² area that consist of 5-10 nm diameter CoCrPt grains, embedded in an oxide matrix. A bit area is defined to ensure a significant number of stable grains allowing data to be stored in each bit as a ‘0' or a ‘1' depending on its switched magnetic state. The magnetic grains if sputtered below a threshold grain size tend to suffer from thermal fluctuation and instability due to super-paramagnetic effects, hence bringing limitations to grain size. As a result of this, research in recent years has been directed at introducing a softer magnetic exchange coupled composite (ECC) layer above the recording layer. This layer facilitates the delicate balance of switching smaller grains with strong magneto-crystalline anisotropy at lower magnetic fields, by exchange coupling with the CoCrPt grains in the recording layer. However this technique of increasing the efficiency in the perpendicular magnetic medium by introducing ‘facilitating' layers is an area that is still being widely researched and understood. Although numerous surface and bulk analysis techniques exist to study magnetic and surface properties of these materials, there is limited information on the structural and magnetic properties of these materials at the nanoscale level. The reported work investigates the structural and magnetic properties of the magnetic grains and multi-layers in the perpendicular magnetic medium using polarised neutron scattering and reflectivity techniques. The work investigates the structural and magnetic properties of the CoCrPt grains, apart from understanding the CoCrPt magnetic grain switching. The work also investigates the magnetisation in the layers of the thin film perpendicular media structure using polarised neutron reflectivity (PNR). Using polarised small angle neutron scattering (PolSANS), it has been shown that ferromagnetic ordered core region of the CoCrPt grain in the recording layer is smaller than the physical CoCrPt granular structure. The magnetic switching behaviour of the CoCrPt grain at different magnetic fields is also analysed and the experimental PolSANS data is fitted with non-interacting size-dependent analytical grain switching models. This result provides significant evidence that the magnetic anisotropy increases with grain size, with larger magnetic grains having larger magnetic anisotropy. Polarised neutron scattering experiments are carried out with the magnetically softer exchange coupled composite (ECC) layer included in the thin film magnetic structure. The first experiments investigate if the ECC layer contributes to the nuclear and magnetic interference scattering term in the experimenting scattering data. The experiments clearly show that there is no contribution from the ECC layer in the nuclear and magnetic scattering interference term. The role of the ECC layer in the magnetic switching process is then investigated at different magnetic fields. The ECC layer was found to influence the size-dependent magnetic grain switching of the CoCrPt grains in the recording layer and a detailed investigation is presented in the reported work. Polarised neutron reflectivity (PNR) experiments have also been carried out with the ECC layer on the perpendicular magnetic media samples. These experiments investigate the composition and thickness of the thin film structure, while also providing information on the magnetic state of the thin films under the influence of an in-plane magnetic field. The in-plane magnetisation in the recording and ECC layer is determined at different in-plane magnetic fields. The magnetisation values determined for the ECC layer and the recording layer (RL) at different in-plane magnetic fields help better understand the differences in their magnetic properties.

The resonance spectrum of the nucleon gives direct information on the dynamics and interactions of its constituents. This offers an important challenge to the theoretical models of nucleon structure, including the emerging Lattice QCD predictions, conformal field theories and more phenomenological, QCD-based approaches. Although the various models predict different features for the excitation spectra, the experimental information is currently of too poor quality to differentiate between these models. Pion photoproduction from the nucleon is a powerful probe of the spectrum as most resonances are expected to couple to the pion decay channel. However, cross-sections alone are not sensitive enough to allow identification of the underlying excitation spectrum, as the resonances have energy widths larger than their separations. A major world effort is underway to additionally measure polarisation observables in the production process. For a model-independent analysis a “complete” set of single- and doublepolarisation observables needs to be measured in experiments involving polarised beams, targets and a means of determining recoil nucleon polarisation. In particular, the beam asymmetry is a critical observable for the constraint of partial wave analyses (PWA) used to extract the nucleon excitation spectrum from the data. Almost all of the available world data on the beam asymmetry has been taken on the proton, with the neutron dataset sparse, containing only three experiments at fixed angles and in a limited photon energy range. The lack of extensive data on the neutron is a major deficiency, as different resonances have very different electromagnetic couplings to the proton and neutron. As a result, the data from the two targets will have very different relative contributions from, and sensitivities to, the spectrum of nucleon resonances. Moreover, neutron data is essential for the separation of the isoscalar and isovector components of the reaction amplitudes. This thesis presents a very high statistics measurement of the photon beam asymmetry on the neutron with close-to-complete angular coverage and a wide range of invariant mass (1610 – 2320 MeV) extending over the third resonance region, where the excitation spectrum is particularly ill defined. The experiment was conducted at the Thomas Jefferson National Accelerator Facility (JLab) using a tagged, linearly polarised photon beam, a liquid deuterium target and the CEBAF Large Acceptance Spectrometer (CLAS). The quality and quantity of the data has allowed an invariantmass resolution of 10 MeV and an angular resolution of 0.1 in the cosine of the centre-of-mass pion production angle, θ. Good agreement is evident in the regions where there is kinematic overlap with sparse previous data. Comparison of the new data is made with the two main partial wave analyses, SAID andMAID. Significant discrepancy is observed at backward θ with SAID (across most of the energy range) and MAID (up to ∼ 1750 MeV) and also below ∼ 35◦ in θ with both analyses. This extensive new dataset will help significantly to constrain partial wave analyses and will be a crucial part of the current world effort to use meson photoproduction to tackle long-standing uncertainties in the fundamental excitation spectrum of the nucleon. As a first step towards this the refitting of the SAID partial wave analysis incorporating the new data was carried out and shows very significant changes in the properties of the magnetic P11, P13, D13, D35, F15, G17 and G19 partial waves.

The physics of the series Pr_yY_1-yBa₂Cu₃O_6+x, and ability of Pr to suppress superconductivity, has been a subject of frequent discussions in the literature for more than a decade. This thesis describes a polarised neutron diffraction (PND) experiment performed on PrBa₂Cu₃O_6.24 designed to find out something about the electron structure. This experiment pushed the limits of what can be done using the PND technique. The problem is one of a limited number of measured Fourier components that need to be inverted to form a real space image. To accomplish this inversion the maximum entropy technique has been employed. In some cases, the maximum entropy technique has the ability to increase the resolution of ‘inverted’ data immensely, but this ability is found to depend critically on the choice of constants used in the method. To investigate this a Bayesian robustness analysis of the maximum entropy method is carried out, resulting in an improvement of the maximum entropy technique for analysing PND data. Some results for nickel in the literature have been re-analysed and a comparison is made with different maximum entropy algorithms. Equipped with an improved data analysis technique and carefully measured PND data for PrBa₂Cu₃O_6.24 a number of new interesting features are observed, putting constraints on existing theoretical models of Pr_yY_1-yBa₂Cu₃O_6+x and leaving room for more questions to be answered.