Dispersion aspects of periodically amplified soliton transmission systems

This thesis presents improvements to optical transmission systems through the use of optical solitons as a digital transmission format, both theoretically and experimentally. An introduction to the main concepts and impairments of optical fibre on pulse transmission is included before introducing the concept of solitons in optically amplified communications and the problems of soliton system design. The theoretical work studies two fibre dispersion profiling schemes and a soliton launch improvement. The first provides superior pulse transmission by optimally tailoring the fibre dispersion to better follow the power, and hence nonlinearity, decay and thus allow soliton transmission for longer amplifier spacings and shorter pulse widths than normally possible. The second profiling scheme examines the use of dispersion compensating fibre in the context of soliton transmission over existing, standard fibre systems. The limits for solitons in uncompensated standard fibre are assessed, before the potential benefits of dispersion compensating fibre included as part of each amplifier are shown. The third theoretical investigation provides a simple improvement to the propagation of solitons in a highly perturbed system. By introducing a section of fibre of the correct length prior to the first system amplifier span, the soliton shape can be better coupled into the system thus providing an improved "average soliton" propagation model. The experimental work covers two areas. An important issue for soliton systems is pulse sources. Three potential lasers are studied, two ring laser configurations and one semiconductor device with external pulse shaping. The second area studies soliton transmission using a recalculating loop, reviewing the advantages and draw-backs of such an experiment in system testing and design. One particular example of employing the recirculating loop is also examined, using a novel method of pulse shape stabilisation over long distances with low jitter. The future for nonlinear optical communications is considered with the thesis conclusions.

Motivations to deposit:two approaches to Open Educational Resources (OER) within Languages and Social Sciences (LSS) at Aston University

In Spring 2009, the School of Languages and Social Sciences (LSS) at Aston University responded to a JISC (Joint Information Systems Committee) and Higher Education Academy (HEA) call for partners in Open Educational Resources (OER) projects. This led to participation in not one, but two different OER projects from within one small School of the University. This paper will share, from this unusual position, the experience of our English tutors, who participated in the HumBox Project, led by Languages, Linguistics and Area Studies (LLAS) and will compare the approach taken with the Sociology partnership in the C-SAP OER Project , led by the Centre for Sociology, Anthropology and Politics (C-SAP). These two HEA Subject Centre-led projects have taken different approaches to the challenges of encouraging tutors to deposit teaching resources, as on ongoing process, for others to openly access, download and re-purpose. As the projects draw to a close, findings will be discussed, in relation to the JISC OER call, with an emphasis on examining the language and discourses from the two collaborations to see where there are shared issues and outcomes, or different subject specific concerns to consider.

Governance in foreign policy-making in Germany and Poland and Polish-German relations:the role of non-state actors

This thesis examines the influence of non-state actors on Polish-German relations by considering foreign policy-making towards Poland in Germany and vice versa. The approach chosen for this thesis is interdisciplinary and takes into consideration literature from domestic politics (Area Studies), Foreign Policy Analysis and International Relations (IR). The thesis argues that IR, by purely looking into the quality of inter-state relations, too often treats these relations as a result of policies emanating from the relevant governments, without considering the policies’ background. Therefore, the thesis argues that it is necessary to engage with the domestic factors which might explain where foreign policies come from. It points out that non-state actors influence governments’ choices by supplying resources, and by cooperating or competing with the government on an issue at stake. In order to determine the degree of influence that non-state actors can have on foreign policymaking two variables are examined: the institutionalisation of the state relations in question; and the domestic structures of the relevant states. Specifically, the thesis examines the institutionalisation of Polish-German relations, and examines Germany’s and Poland’s domestic structures and their effect on the two states’ foreign policy-making in general. Thereafter, the thesis uses case studies in order to unravel the influence of non-state actors on specific foreign policies. Three case studies are examined in detail: (i) Poland’s EU accession negotiations with regard to the free movement of capital chapter of the acquis communautaire; (ii) Germany’s EU 2004 Eastern Enlargement negotiations with regard to the free movement of workers chapter of the acquis communautaire; and (iii) Germany’s decision to establsh a permanent exhibition in Berlin that will depict the expulsions of millions of Germans from the East following WWII.

Area summation in human vision at and above detection threshold

The initial image-processing stages of visual cortex are well suited to a local (patchwise) analysis of the viewed scene. But the world's structures extend over space as textures and surfaces, suggesting the need for spatial integration. Most models of contrast vision fall shy of this process because (i) the weak area summation at detection threshold is attributed to probability summation (PS) and (ii) there is little or no advantage of area well above threshold. Both of these views are challenged here. First, it is shown that results at threshold are consistent with linear summation of contrast following retinal inhomogeneity, spatial filtering, nonlinear contrast transduction and multiple sources of additive Gaussian noise. We suggest that the suprathreshold loss of the area advantage in previous studies is due to a concomitant increase in suppression from the pedestal. To overcome this confound, a novel stimulus class is designed where: (i) the observer operates on a constant retinal area, (ii) the target area is controlled within this summation field, and (iii) the pedestal is fixed in size. Using this arrangement, substantial summation is found along the entire masking function, including the region of facilitation. Our analysis shows that PS and uncertainty cannot account for the results, and that suprathreshold summation of contrast extends over at least seven target cycles of grating. © 2007 The Royal Society.

Studies on the deactivation and reactivation of spent hydroprocessing catalyst

A study is reported on the deactivation of hydroprocessing catalysts and their reactivation by the removal of coke and metal foulants. The literature on hydrotreating catalyst deactivation by coke and metals deposition, the environmental problems associated with spent catalyst disposal, and its reactivation/rejuvenation process were reviewed. Experimental studies on catalyst deactivation involved problem analysis in industrial hydroprocessing operations, through characterization of the spent catalyst, and laboratory coking studies. A comparison was made between the characteristics of spent catalysts from fixed bed and ebullating bed residue hydroprocessing reactor units and the catalyst deactivation pattern in both types of reactor systems was examined. In the laboratory the nature of initial coke deposited on the catalyst surface and its role on catalyst deactivation were studied. The influence of initial coke on catalyst surface area and porosity was significant. Both catalyst acidity and feedstock quality had a remarkable influence on the amount and the nature of the initial coke. The hydroenitrogenation function (HDN) of the catalyst was found to be deactivated more rapidly by the initial coke than the hydrodesulphurization function (HDS). In decoking experiments, special attention was paid to the initial conditions of coke combustion, since the early stages of contact between the coke on the spent catalyst surface and the oxygen are crucial in the decoking process. An increase in initial combustion temperature above 440oC and the oxygen content of the regeneration gas above 5% vanadium led to considerable sintering of the catalyst. At temperatures above 700oC there was a substantial loss of molybdenum from the catalyst, and phase transformations in the alumina support. The preferred leaching route (coked vs decoked form of spent catalyst) and a comparison of different reagents (i.e., oxalic acid and tartaric acid) and promoters (i.e., Hydrogen Peroxide and Ferric Nitrate) for better selectivity in removing the major foulant (vanadium), characterization and performance evaluation of the treated catalysts and modelling of the leaching process were addressed in spent catalyst rejuvenation studies. The surface area and pore volume increased substantially with increasing vanadium extraction from the spent catalyst; the HDS activity showed a parallel increase. The selectivity for leaching of vanadium deposits was better, and activity recovery was higher, for catalyst rejuvenated by metal leaching prior to decoking.

Studies in three phase gas-liquid-solid fluidised systems

The work is a logical continuation of research started at Aston some years ago when studies were conducted on fermentations in bubble columns. The present work highlights typical design and operating problems that could arise in such systems as waste water, chemical, biochemical and petroleum operations involving three-phase, gas-liquid-solid fluidisation; such systems are in increasing use. It is believed that this is one of few studies concerned with `true' three-phase, gas-liquid-solid fluidised systems, and that this work will contribute significantly to closing some of the gaps in knowledge in this area. The research work was mainly experimentally based and involved studies of the hydrodynamic parameters, phase holdups (gas and solid), particle mixing and segregation, and phase flow dynamics (flow regime and circulation patterns). The studies have focused particularly on the solid behaviour and the influence of properties of solids present on the above parameters in three-phase, gas-liquid-solid fluidised systems containing single particle components and those containing binary and ternary mixtures of particles. All particles were near spherical in shape and two particle sizes and total concentration levels were used. Experiments were carried out in two- and three-dimensional bubble columns. Quantitative results are presented in graphical form and are supported by qualitative results from visual studies which are also shown as schematic diagrams and in photographic form. Gas and solid holdup results are compared for air-water containing single, binary and ternary component particle mixtures. It should be noted that the criteria for selection of the materials used are very important if true three-phase fluidisation is to be achieved: this is very evident when comparing the results with those in the literature. The fluid flow and circulation patterns observed were assessed for validation of the generally accepted patterns, and the author believes that the present work provides more accurate insight into the modelling of liquid circulation in bubble columns. The characteristic bubbly flow at low gas velocity in a two-phase system is suppressed in the three-phase system. The degree of mixing within the system is found to be dependent on flow regime, liquid circulation and the ratio of solid phase physical properties. Evidence of strong `trade-off' of properties is shown; the overall solid holdup is believed to be a major parameter influencing the gas holdup structure.

A comparative study of 'joined-up' working in three regeneration programme case studies

This research concerns the development of coordination and co-governance within three different regeneration programmes within one Midlands city over the period from 1999 to 2002. The New Labour government, in office since 1997, had an agenda for ‘joining-up’ government, part of which has had considerable impact in the area of regeneration policy. Joining-up government encompasses a set of related activities which can include the coordination of policy-making and service delivery. In regeneration, it also includes a commitment to operate through co-governance. Central government and local and regional organisations have sought to put this idea into practice by using what may be referred to as network management processes. Many characteristics of new policies are designed to address the management of networks. Network management is not new in this area, it has developed at least since the early 1990s with the City Challenge and Single Regeneration Budget (SRB) programmes as a way of encouraging more inclusive and effective regeneration interventions. Network management theory suggests that better management can improve decision-making outcomes in complex networks. The theories and concepts are utilised in three case studies as a way of understanding how and why regeneration attempts demonstrate real advances in inter-organisational working at certain times whilst faltering at others. Current cases are compared to the historical case of the original SRB programme as a method of assessing change. The findings suggest that: The use of network management can be identified at all levels of governance. As previous literature has highlighted, central government is the most important actor regarding network structuring. However, it can be argued that network structuring and game management are both practised by central and local actors; Furthermore, all three of the theoretical perspectives within network management (Instrumental, Institutional and Interactive), have been identified within UK regeneration networks. All may have a role to play with no single perspective likely to succeed on its own. Therefore, all could make an important contribution to the understanding of how groups can be brought together to work jointly; The findings support Klijn’s (1997) assertion that the institutional perspective is dominant for understanding network management processes; Instrumentalism continues on all sides, as the acquisition of resources remains the major driver for partnership activity; The level of interaction appears to be low despite the intentions for interactive decision-making; Overall, network management remains partial. Little attention is paid to the issues of accountability or to the institutional structures which can prevent networks from implementing the policies designed by central government, and/or the regional tier.

Magnetoencephalography:technical improvements in image co-registration and studies of visual cortical oscillations

The work presented in this thesis is divided into two distinct sections. In the first, the functional neuroimaging technique of Magnetoencephalography (MEG) is described and a new technique is introduced for accurate combination of MEG and MRI co-ordinate systems. In the second part of this thesis, MEG and the analysis technique of SAM are used to investigate responses of the visual system in the context of functional specialisation within the visual cortex. In chapter one, the sources of MEG signals are described, followed by a brief description of the necessary instrumentation for accurate MEG recordings. This chapter is concluded by introducing the forward and inverse problems of MEG, techniques to solve the inverse problem, and a comparison of MEG with other neuroimaging techniques. Chapter two provides an important contribution to the field of research with MEG. Firstly, it is described how MEG and MRI co-ordinate systems are combined for localisation and visualisation of activated brain regions. A previously used co-registration methods is then described, and a new technique is introduced. In a series of experiments, it is demonstrated that using fixed fiducial points provides a considerable improvement in the accuracy and reliability of co-registration. Chapter three introduces the visual system starting from the retina and ending with the higher visual rates. The functions of the magnocellular and the parvocellular pathways are described and it is shown how the parallel visual pathways remain segregated throughout the visual system. The structural and functional organisation of the visual cortex is then described. Chapter four presents strong evidence in favour of the link between conscious experience and synchronised brain activity. The spatiotemporal responses of the visual cortex are measured in response to specific gratings. It is shown that stimuli that induce visual discomfort and visual illusions share their physical properties with those that induce highly synchronised gamma frequency oscillations in the primary visual cortex. Finally chapter five is concerned with localization of colour in the visual cortex. In this first ever use of Synthetic Aperture Magnetometry to investigate colour processing in the visual cortex, it is shown that in response to isoluminant chromatic gratings, the highest magnitude of cortical activity arise from area V2.

Contrast integration over area is extensive: a three-stage model of spatial summation

Classical studies of area summation measure contrast detection thresholds as a function of grating diameter. Unfortunately, (i) this approach is compromised by retinal inhomogeneity and (ii) it potentially confounds summation of signal with summation of internal noise. The Swiss cheese stimulus of T. S. Meese and R. J. Summers (2007) and the closely related Battenberg stimulus of T. S. Meese (2010) were designed to avoid these problems by keeping target diameter constant and modulating interdigitated checks of first-order carrier contrast within the stimulus region. This approach has revealed a contrast integration process with greater potency than the classical model of spatial probability summation. Here, we used Swiss cheese stimuli to investigate the spatial limits of contrast integration over a range of carrier frequencies (1–16 c/deg) and raised plaid modulator frequencies (0.25–32 cycles/check). Subthreshold summation for interdigitated carrier pairs remained strong (~4 to 6 dB) up to 4 to 8 cycles/check. Our computational analysis of these results implied linear signal combination (following square-law transduction) over either (i) 12 carrier cycles or more or (ii) 1.27 deg or more. Our model has three stages of summation: short-range summation within linear receptive fields, medium-range integration to compute contrast energy for multiple patches of the image, and long-range pooling of the contrast integrators by probability summation. Our analysis legitimizes the inclusion of widespread integration of signal (and noise) within hierarchical image processing models. It also confirms the individual differences in the spatial extent of integration that emerge from our approach.

Remote sensing applied to land use and erosion hazard studies in Jamaica

The northern half of the parish of St. Catherine in Jamaica was selected as a test area to study, by means of remote sensing, the problems of soil erosion in a tropical environment. An initial study was carried out to determine whether eroded land within this environment could be successfully interpreted and mapped from the available 1: 25,000 scale aerial photographs. When satisfied that a sufficiently high percentage of the eroded land could be interpreted on the aerial photographs the main study was initiated. This involved interpreting the air photo cover of the study area for identifying and classifying land use and eroded land, and plotting the results on overlays on topographic base maps. These overlays were then composited with data on the soils and slopes of the study area. The areas of different soil type/slope/land use combinations were then measured, as was the area of eroded land for each of these combinations. This data was then analysed in two ways. The first way involved determining which of the combinations of soil type, slope and land use were most and least eroded and, on the basis of this, to draw up recommendations concerning future land use. The second analysis was aimed at determining which of the three factors, soil type, slope and land use, was most responsible for determining the rate of erosion. Although it was possible to show that slope was not very significant in determining the rate of erosion, it was much more difficult to separate the effects of land use and soil type. The results do, however, suggest that land use is more significant than soil type in determining the rate of erosion within the study area.

Volcanogenic mineralisation in the limestone lake area, Saskatchewan, Canada

This thesis describes the geology, geochemistry and mineralogy of a Lower Proterozoic, metamorphosed volcanogenic Cu-Zn deposit, situated at the western end of the Flin Flon greenstone belt. Stratabound copper mineralisation occurs in silicified and chloritoid-bearing alteration assemblages within felsic tuffs and is mantled by thin (< 3m) high-grade sphalerite layers. Mineralisation is underlain by garnet-hornblende bearing Lower Iron Formation (LIF), and overlain by garnet-grunerite bearing Upper Iron Formation (UIF). Distinctive trace element trends, involving Ti and Zr, in mineralised and footwall felsic tuffs are interpreted to have formed by fractionation associated with a high-level magma chamber in a caldera-type environment. Discrimination diagrams for basaltic rocks are interpreted to indicate their formation in an environment similar to that of recent, primitive, tholeiitic island arcs. Microprobe studies of key mineral phases demonstrate large and small scale chemical variations in silicate phases related to primary lithological, rather than metamorphic, controls. LIF is characterised by alumino-ferro-tschermakite and relatively Mn-poor, Ca-rich garnets, whereas UIF contains manganoan grunerite and Mn-rich garnets. Metamorphic mineral reactions are considered and possible precursor assemblages identified for garnet-, and chloritoid-bearing rocks. Chloritoid-bearing rocks are interpreted as the metamorphosed equivalents of iron-rich feeder zones formed near the surface. The iron-formations are thought to represent iron-rich sediments formed on the sea floor formed from the venting of the ore fluids. Consideration of various mineral assemblages leads to an estimate for peak metamorphic conditions of 450-500oC and > 4Kb total pressure. Comparisons with other volcanogenic deposits indicate affinities with deposits of `Mattabi-type' from the Archean of Ontario. An extrapolation of the main conclusions of the thesis to adjacent areas points to the presence of a number of geologically similar localities with potential for mineralisation.

Functional neuroimaging and behavioural studies on global form processing in the human visual system

Magnetoencephalography (MEG), functional magnetic resonance imaging (fMRI) and behavioural experiments were used to investigate the neural processes underlying global form perception in human vision. Behavioural studies using Glass patterns examined sensitivity for detecting radial, rotational and horizontal structure. Neuroimaging experiments using either Glass patterns or arrays of Gabor patches determined the spatio-temporal neural responseto global form. MEG data were analysed using synthetic aperture magnetometry (SAM) to spatially map event-related cortical oscillatory power changes: the temporal sequencing of activity within a discrete cortical area was determined using a Morlet wavelet transform. A case study was conducted to determine the effects of strbismic amblyopia on global form processing: all other observers were normally-sighted. The main findings from normally-sighted observers were: 1) sensitivity to horizontal structure was less than for radial or rotational structure; 2) the neural response to global structure was a reduction in cortical oscillatory power (10-30 Hz) within a network of extrastriate areas, including V4 and V3a; 3) the extend of reduced cortical power was least for horizontal patters; 4) V1 was not identified as a region of peak activity with either MEG or fMRI. The main findings with the strabismic amblyope were: 1) sensitivity for detection of radial, rotational, and horizontal structure was reduced when viewed with the amblyopic- relative to the fellow- eye; 2) cortical power changes within V4 to the presentation of rotational Glass patterns were less when viewed with the amblyopic- compared with the fellow- eye. The main conclusions are: 1) a network of extrastriate cortical areas are involved in the analysis of global form, with the most prominent change in neural activity being a reduction in oscillatory power within the 10-30 Hz band; 2) in strabismic amblyopia, the neuronal assembly associated with form perception in extrastriate cortex may be dysfunctional, the nature of this dysfunction may be a change in the normal temporal pattern of neuronal discharges; 3) MEG, fMRI and behavioural measures support the notion that different neural processes underlie the perception of horizontal as opposed to radial or rotational structure.

The development of calibration and adaptive filtering procedures for neuromagnetic studies of human visual function

This thesis first considers the calibration and signal processing requirements of a neuromagnetometer for the measurement of human visual function. Gradiometer calibration using straight wire grids is examined and optimal grid configurations determined, given realistic constructional tolerances. Simulations show that for gradiometer balance of 1:104 and wire spacing error of 0.25mm the achievable calibration accuracy of gain is 0.3%, of position is 0.3mm and of orientation is 0.6°. Practical results with a 19-channel 2nd-order gradiometer based system exceed this performance. The real-time application of adaptive reference noise cancellation filtering to running-average evoked response data is examined. In the steady state, the filter can be assumed to be driven by a non-stationary step input arising at epoch boundaries. Based on empirical measures of this driving step an optimal progression for the filter time constant is proposed which improves upon fixed time constant filter performance. The incorporation of the time-derivatives of the reference channels was found to improve the performance of the adaptive filtering algorithm by 15-20% for unaveraged data, falling to 5% with averaging. The thesis concludes with a neuromagnetic investigation of evoked cortical responses to chromatic and luminance grating stimuli. The global magnetic field power of evoked responses to the onset of sinusoidal gratings was shown to have distinct chromatic and luminance sensitive components. Analysis of the results, using a single equivalent current dipole model, shows that these components arise from activity within two distinct cortical locations. Co-registration of the resulting current source localisations with MRI shows a chromatically responsive area lying along the midline within the calcarine fissure, possibly extending onto the lingual and cuneal gyri. It is postulated that this area is the human homologue of the primate cortical area V4.

Electrophysiological studies of the visual pathways in Alzheimer's and Parkinson's disease

It is known that parallel pathways exist within the visual system. These have been described as magnocellular and parvocellular as a result of the layered organisation of the lateral geniculate nucleus and extend from the retina to the cortex. Dopamine (DA) and acetylcholine (ACH) are neurotransmitters that are present in the visual pathway. DA is present in the retina and is associated with the interplexiform cells and horizontal cells. ACH is also present in the retina and is associated with displaced amacrine cells; it is also present in the superior colliculus. DA is found to be significantly depleted in the brain of Parkinson's disease (PD) patients and ACH in Alzheimer's disease (AD) patients. For this reason these diseases were used to assess the function of DA and ACH in the electrophysiology of the visual pathway. Experiments were conducted on young normals to design stimuli that would preferentially activate the magnocellular or parvocellular pathway. These stimuli were then used to evoke visual evoked potentials (VEP) in patients with PD and AD, in order to assess the function of DA and ACH in the visual pathway. Electroretinograms (ERGs) were also measured in PD patients to assess the role of DA in the retina. In addition, peripheral ACH function was assessed by measuring VEPs, ERGs and contrast sensitivity (CS) in young normals following the topical instillation of hyoscine hydrobromide (an anticholinergic drug). The results indicate that the magnocellular pathway can be divided into two: a cholinergic tectal-association area pathway carrying luminance information, and a non-cholinergic geniculo-cortical pathway carrying spatial information. It was also found that depletion of DA had very little effect on the VEPs or ERGs, confirming a general regulatory function for this neurotransmitter.