High-energy laser-pulse self-compression in short gas-filled fibers

We examine the spatiotemporal compression of energetic femtosecond laser pulses within short gas-filled fibers. The study is undertaken using an advanced nonlinear pulse propagation model based on a multimode generalized nonlinear Schrödinger equation that has been modified to include plasma effects. Plasma defocusing and linear propagation effects are shown to be the dominant processes within a highly dynamical mechanism that enables 100-fs pulses to be compressed into the few-cycle regime after <50 mm of propagation. Once the mechanism has been introduced, parameter spaces are explored and compressor designs suitable for performing high-field experiments in situ are presented. We finish by showing how these designs may be extended to novel wavelengths and driving pulses delivered by state-of-the-art high-repetition-rate lasers

Technological Change and the Labour Process - Towards an Analysis of Computerisation in the New Zealand Trading Banks

Within the labour process framework this paper examines the relationship between technological change and processes of control in the New Zealand trading banks. Adopting an historical perspective the author rejects a crude deskilling thesis but concludes that computerisation has served nevertheless to enhance management control. Moreover it is argued that recent changes in the climate of industrial relations in banking can only be understood within the context of changes in technology

Looking at the management sciences through the lens of autopoietic theory

The broad aim of this research has been to employ the various propositions of Humberto Maturana, as derived from his and Francisco Varela's central concept 'Autopoiesis', as a lens or frame through which to critically reflect on both Management Science and major traditions within it. Such reflection has been carried out with both a 'critical' and a 'developmental eye'. From a critical standpoint the research identifies gaps in existing understandings, and suggests ways in which these may be plugged. Used in this mode, the research shows that Autopoietic Theory is a body of knowledge that management scientists, especially inexperienced ones, can turn to as a means of enriching and/or enhancing their practice in distinctive ways, or allowing them to better prepare for it. Used from a developmental standpoint, the research shows how Maturana's epistemological propositions invoke a particular kind of critically reflective Management Science practice, and, how Autopoietic Theory more generally, can stretch the limits of existing practice. In developing these lines of argumentation the main contribution of the work is to remind members of the various Management Science communities that theirs is an activity that is carried out by real human beings first and by impartial scientists second; moreover, that Management Science is an activity that takes place in human, social and organisational contexts. Acknowledgement of this has far reaching ramifications. In that regard, the main contribution of the research can be taken to be an argument in favour of repositioning 'humanity', in all its various facets, much more centrally within the discipline than has been the case hitherto

Direct spatial-temporal discrimination of modes in a photonic lightwave circuit using photon scanning tunnelling microscopy

Multi-mode photonic lightwave circuits (PLCs) provide new avenues for extending the performance of single mode systems. As an example, they can potentially provide increased bandwidth by multiplexing information into different waveguide modes[1]. For practical applications of multi-mode PLCs to be developed, a measurement technique is required to investigate detailed mode profiles and propagation constants in complex circuits. Photon scanning tunnelling microscopy (PSTM) provides a means of experimentally tracking the femtosecond inter-modal delays observed in PLCs with the ability to discriminate modes by their spatial profiles inside the waveguide

Development of a PET radioligand targeting angiogenesis for oncology applications

All tumours must become vascularised in order to survive and metastasise, and initiate angiogenesis through the dysregulated and uncontrolled release of pro-angiogenic factors. Such uncontrolled angiogenesis leads to highly disordered and abnormal vasculature and is widely recognised as a hallmark of cancer. The major angiogenic pathway hyper-activated in cancer is the VEGF-VEGFR₂ signalling system. Anti-angiogenic therapies have been developed, but there is no accepted way of determining which patients will respond. The development of a molecular imaging probe targeting VEGFR₂ through the use of PET represents one way to achieve this. Currently, there are no PET imaging probes which exhibit the required characteristics. Therefore, the initial focus of this project was to synthesise novel probes based around existing suitable pharmacophores. Initial libraries focusing on urea or indole motifs, lacked either routes to a radiolabelling precursor or selectivity on biological testing, and were abandoned. A third library based around the only known selective VEGFR₂ inhibitor 5-((7-benzyloxyquinazolin-4-yl)amino)-4-fluoro-2-methylphenol 98, ZM323881, was developed. Synthesis of 98 proceeded via the Dimroth rearrangement in three steps, with a shorter synthesis time, use of less toxic reagents and easier purification than published methods. Initial kinase profiling revealed 98 also targeted closely related kinases; VEGFR₁, VEGFR₃, RET, PDGFRα. Known inhibitor 98 and closely related analogue 4-fluoro-5-((7- (4-fluorobenzyl)oxy))quinazoline-4-yl)amino)-2-methylphenol 101 exhibited activity against VEGFR₂, 4.75 nM and 7.5 nM respectively. The quinazoline focused library was selected for radiolabelling. Initial radiolabelling revealed a debenzylation reaction occurring, to produce 4-(2-fluoro-5-hydroxy-4-methylphenyl)amino quinazolin-7-ol 166 during the radiolabelling reaction. Radiolabelling analogue 7-(benzyloxy)-N-(4-bromo—fluorophenyl)quinazolin-4-amine 123, via the Dimroth rearrangement was troublesome and requires more optimisation, due the presence of the de-cyanation by-product. Initial biological testing presented in this thesis does not rule out the quinazoline library from its use as a PET imaging agent and further in vitro characterisation is required

Experimental demonstration of a high-flux capillary based XUV source in the high ionisation regime

High harmonic generation (HHG) has proven to be a fascinating and incredibly useful nonlinear optical phenomenon and has led to the realisation of tabletop sources of coherent extreme ultraviolet (XUV) radiation. Capillary based geometries in particular have attracted a great deal of attention due to their lengthy interaction regions and the potential to phase-match the HHG process leading to a large increase in XUV flux. Unfortunately due to plasma induced nonlinear and dispersive effects the simple phase-matching mechanism detailed in [1] cannot be scaled to high energy pump pulses and high gas pressures. In this work we have used a computational model [2] to design a capillary that can support a broad interaction region well-suited to quasi-phase-matching (QPM) while simultaneously reducing the effect that XUV reabsorption has on the output flux of the source. This modelling work has involved adjusting both the capillary length and gas density profile (figure 1a) in order to produce rapid oscillations in the radially integrated ionization fraction (figure 1b) coupled with a rapid decrease in gas pressure at the capillary exit. Our theory suggests that these oscillations are driven by a nonlinear self-compression process modulating the intensity of the pump pulse as it propagates through the plasma-filled waveguide [3]. Subsequent experimental work has shown an increase in XUV flux of almost 50 times over our previous capillary-based source (see figure 1c), and preliminary estimates suggest a photon flux of 1012 photons s-1 harmonic-1 in the 45 eV spectral region

The use of traditional and unconventional culturing methods for the discovery of antimicrobial compounds derived from marine microorganisms

The main aim is to evaluate the content of marine biofilms and different marine bacteria for antimicrobial potential. Hypothesis: antimicrobial compounds can be produced in the presence of other bacterial species; in the context of Winogradsky columns that simulate a naturalistic environment, and in the proximity to other species in the case of marine bacterial isolates. For this main aim and hypothesis, the following subgoals are defined: 1. Document any antimicrobial production by marine bacteria from different marine sources, using a co-culture approach. 2. Document the bacterial content of biofilm in Winogradsky columns (WC) from the seashore, using different techniques. 3. Evaluate the antibacterial production in the bacterial content from Winogradsky biofilms by performing diffusing assays, MIC assays in combinations with chromatographic methods

Quantum efficiency measurements in oxygen-containing gallium lanthanum sulphide glasses and fibers doped with Pr³⁺

The quantum efficiency of Pr3+ emission at 1.3µm from the 1G4 - 3H5 transition is measured in Gallium Lanthanum Sulphide (GLS) glass containing varying quantities of lanthanum oxide. The variation of quantum efficiency with host composition is described, and the variation of quantum efficiency with pump wavelength in oxide-containing hosts is compared to a model of the effect of the addition of oxygen on the spectroscopy of the Pr ion. Oxide-containing GLS glasses can show quantum efficiencies of up to 84% of that of pure GLS, while retaining considerably better thermal and glass-forming properties. No degradation of quantum efficiency is seen when GLS glass is pulled into fiber form