Forward Error Correction in Memoryless Optical Modulation

The unprecedented growth in demand for digital media has led to an all-time high in society’s demand for information. This demand will in all likelihood continue to grow as technology such as 3D television service, on-demand video and peer-to-peer networking continue to become more common place. The large amount of information required is currently transmitted optically using a wavelength division multiplexing (WDM) network structure. The need to increase the capacity of the existing WDM network infrastructure efficiently is essential to continue to provide new high bandwidth services to end-users, while at the same time minimizing network providers’ costs. In WDM systems the key to reducing the cost per transported information bit is to effectively share all optical components. These components must operate within the same wavelength limited window; therefore it is necessary to place the WDM channels as close together as possible. At the same time, the correct modulation format must be selected in order to create flexible, cost-effective, high-capacity optical networks. This thesis presents a detailed comparison of Differential Quadrature Phase Shift Keying (DQPSK) to other modulation formats. This comparison is implemented through a series of simulations in which the bit error rate of various modulation formats are compared both with and without the presence of forward error correction techniques. Based off of these simulation results, the top performing modulation formats are placed into a multiplexed simulation to assess their overall robustness in the face of multiple filtering impairments

Reducing turbulence- and transition-driven uncertainty in aerothermodynamic heating predictions for blunt-bodied reentry vehicles

textTurbulent boundary layers approximating those found on the NASA Orion Multi-Purpose Crew Vehicle (MPCV) thermal protection system during atmospheric reentry from the International Space Station have been studied by direct numerical simulation, with the ultimate goal of reducing aerothermodynamic heating prediction uncertainty. Simulations were performed using a new, well-verified, openly available Fourier/B-spline pseudospectral code called Suzerain equipped with a ``slow growth'' spatiotemporal homogenization approximation recently developed by Topalian et al. A first study aimed to reduce turbulence-driven heating prediction uncertainty by providing high-quality data suitable for calibrating Reynolds-averaged Navier--Stokes turbulence models to address the atypical boundary layer characteristics found in such reentry problems. The two data sets generated were Ma[approximate symbol] 0.9 and 1.15 homogenized boundary layers possessing Re[subscript theta, approximate symbol] 382 and 531, respectively. Edge-to-wall temperature ratios, T[subscript e]/T[subscript w], were close to 4.15 and wall blowing velocities, v[subscript w, superscript plus symbol]= v[subscript w]/u[subscript tau], were about 8 x 10-3 . The favorable pressure gradients had Pohlhausen parameters between 25 and 42. Skin frictions coefficients around 6 x10-3 and Nusselt numbers under 22 were observed. Near-wall vorticity fluctuations show qualitatively different profiles than observed by Spalart (J. Fluid Mech. 187 (1988)) or Guarini et al. (J. Fluid Mech. 414 (2000)). Small or negative displacement effects are evident. Uncertainty estimates and Favre-averaged equation budgets are provided. A second study aimed to reduce transition-driven uncertainty by determining where on the thermal protection system surface the boundary layer could sustain turbulence. Local boundary layer conditions were extracted from a laminar flow solution over the MPCV which included the bow shock, aerothermochemistry, heat shield surface curvature, and ablation. That information, as a function of leeward distance from the stagnation point, was approximated by Re[subscript theta], Ma[subscript e], [mathematical equation], v[subscript w, superscript plus sign], and T[subscript e]/T[subscript w] along with perfect gas assumptions. Homogenized turbulent boundary layers were initialized at those local conditions and evolved until either stationarity, implying the conditions could sustain turbulence, or relaminarization, implying the conditions could not. Fully turbulent fields relaminarized subject to conditions 4.134 m and 3.199 m leeward of the stagnation point. However, different initial conditions produced long-lived fluctuations at leeward position 2.299 m. Locations more than 1.389 m leeward of the stagnation point are predicted to sustain turbulence in this scenario.Computational Science, Engineering, and Mathematic

Custom and habit(us): The meaning of traditions and legends in early medieval western Britain

This a post-print, author-produced version of an article accepted for publication in Geografiska Annaler, Series B: Human Geography. Copyright © Blackwell publishing 1999. The definitive version is available at www.blackwell-synergy.comThis paper discusses some well-known legends and hagiographic stories, and explores the context of their production and consumption. From an examination of Welsh foundation legends and Cornish hagiographical accounts, we focus on the methods by which versions of history were used in the Middle Ages to provide a context for fundamental changes in the way in which society was organised. It is found that, far from abandoning traditional versions of history, accounts of the past were promoted that sought to couch newer territorial notions of organisation within existing constructions of identity and mediations with the past. In an examination of the production and reception of these popular stories, we attempt to relate the legends to the generation of communal identity and memory. Consequently, drawing on Bourdieu's notion of habitus, we argue that pre-existing beliefs and customs were an important part in the development of newer institutional structures. Rather than initiating new practices that had no grounding in any particular past, institutional developments gained social currency by being inherently grounded in existing facets of cultural identity. In essence therefore, changing societal and institutional structures were unintentionally couched in the language and understandings of existing structures, so that in many ways a concept of continuity was at the very heart of actual change

An analysis of coastal zone management in England and the Netherlands

The coastal zone is an area of crucial economic and ecological significance, which has increasingly been recognised in land-use planning. Within the coastal zone, integrating land-use planning and environmental management is recognised as one way to minimise trade-offs of interest between economic development and environmental objectives. Many governments are currently discussing the potential role of integrated coastal zone management (CZM) within their planning systems, while some international organisations promote CZM as a means to counter the loss of coastal resources due to human occupation of the coast.This thesis examines how the coastal zone in the United Kingdom is perceived and how effectively CZM is being promoted as a planning model to secure sustainable coastal development through the integration of planning policies. Policy integration is not a quixotic quest, but a model suggesting appropriate methods to manage and reduce conflicts. Any planning model can be traceable to varying assumptions and propositions from political thought, which in turn arises from different political practices. Each CZM plan thus reflects the planning and policy culture of its national system.In order to provide a context within which to assess the UK approach, the development of CZM in the Netherlands is also examined. Both national planning systems have comprehensive statutory land-use planning systems, while marine issues are controlled sectorally by central government. Neither administration has a national CZM policy framework. This thesis therefore includes a comparison of two management plans: the Wash Estuary Management Plan and Integraal Beleidsplan Voordelta. By comparing the organisational structures, policy development and implementation, the case studies provide an insight into the national CZM planning strategy currently being followed in the UK. Finally, the thesis concludes by identifying ways in which CZM might be further improved in the UK and also integrated into European approaches that have recently been initiated

Equal possibilities not restricted opportunity: A critical reflection on the experiences of ‘Vocational’ transition within the context of post-16 sports education

This PhD study explores the transitional experiences of working class students between institutions of Further Education and Higher Education within the field of post-16 sports education. It draws its empirical illustration from the interview and ethnographic data collected over an 18 month period between October 2007 and July 2009 from a group of six students who had enrolled on a vocational FDSc Foundation Degree qualification. The study is comprised of two interrelated parts: Part I of the study illustrates the conceptual and methodological considerations which have driven the exploration of the student experience. The theoretical approach for investigating these experiences is informed by the structurationist perspective of Rob Stones (Stones, 2005). Stones conceptualises the relations between agent and structure four interlinked areas: External Structures, Internal Structures, Active Agency and Outcomes. Conceptualising transitional experience in this manner offers possibilities for a more contextually sensitive, refined, developed and ultimately adequate ontology of structuration. In further developing the framework, the study draws upon the sociological understanding of Basil Bernstein and Pierre Bourdieu. The incorporation of these two distinguishable but related perspectives allows the framework to inform an understanding of the interconnections between the sanctioned practices of a context, the role of agents within a context and the power capacities that are derived from these relations (Mouzelis, 1991; Morrison, 2005). In doing so, it provides a number of lenses in understanding the practices and relations between Further and Higher Education and the consequences of this for agents who enter this transition. Part II critically reflects on the participants experiences. Drawing upon data collected at three institutions: Hope Further Education College (HFEC), Fawlty University-College (FUC) and Ivory Tower University (ITU), the study discusses and explores in depth how the relations between the participants and the external structures of the institutions begin to form three identifiable and conceptually distinguishable transitional experiences which are seen to be either Empowering, Fragmented or Failed. In reflecting upon such relations and experiences, the study suggests that discourses of opportunity surrounding vocational qualifications forwarded to these students prior to, and during their course, is rather more complex than previously illustrated and for some functions as more of a myth than empowering discourse. Rather than providing equal possibility, the relations and transitional experiences that are currently produced only afford restricted opportunities to students choosing this vocational pathway within post-16 sports education. In conclusion, the study begins to discuss the implications of the relations and experiences highlighted for present and prospective relations and practices, asking whether change is possible, creating equal possibilities, not restricted opportunity

Non-optimality of the Greedy Algorithm for subspace orderings in the method of alternating projections

The method of alternating projections involves projecting an element of a Hilbert space cyclically onto a collection of closed subspaces. It is known that the resulting sequence always converges in norm and that one can obtain estimates for the rate of convergence in terms of quantities describing the geometric relationship between the subspaces in question, namely their pairwise Friedrichs numbers. We consider the question of how best to order a given collection of subspaces so as to obtain the best estimate on the rate of convergence. We prove, by relating the ordering problem to a variant of the famous Travelling Salesman Problem, that correctness of a natural form of the Greedy Algorithm would imply that $\mathrm{P}=\mathrm{NP}$, before presenting a simple example which shows that, contrary to a claim made in the influential paper [Kayalar-Weinert, Math. Control Signals Systems, vol. 1(1), 1988], the result of the Greedy Algorithm is not in general optimal. We go on to establish sharp estimates on the degree to which the result of the Greedy Algorithm can differ from the optimal result. Underlying all of these results is a construction which shows that for any matrix whose entries satisfy certain natural assumptions it is possible to construct a Hilbert space and a collection of closed subspaces such that the pairwise Friedrichs numbers between the subspaces are given precisely by the entries of that matrix.Comment: To appear in Results in Mathematic

A statistical simulation of magnetic particle alignment in sediments

Sedimentary magnetizations are fundamental to palaeomagnetism, but the mechanisms that control remanence acquisition remain poorly constrained. Observed sedimentary natural remanent magnetizations are often orders of magnitude smaller than the saturatio