Polynomial spline-approximation of Clarke's model

We investigate polynomial spline approximation of stationary random processes on a uniform grid applied to Clarke's model of time variations of path amplitudes in multipath fading channels with Doppler scattering. The integral mean square error (MSE) for optimal and interpolation splines is presented as a series of spectral moments. The optimal splines outperform the interpolation splines; however, as the sampling factor increases, the optimal and interpolation splines of even order tend to provide the same accuracy. To build such splines, the process to be approximated needs to be known for all time, which is impractical. Local splines, on the other hand, may be used where the process is known only over a finite interval. We first consider local splines with quasioptimal spline coefficients. Then, we derive optimal spline coefficients and investigate the error for different sets of samples used for calculating the spline coefficients. In practice, approximation with a low processing delay is of interest; we investigate local spline extrapolation with a zero-processing delay. The results of our investigation show that local spline approximation is attractive for implementation from viewpoints of both low processing delay and small approximation error; the error can be very close to the minimum error provided by optimal splines. Thus, local splines can be effectively used for channel estimation in multipath fast fading channels

The scale free and scale - bound properties of land surfaces: fractal analysis and specific geomorphometry from digital terrain models

The scale-bound view of landsurfaces, being an assemblage of certain landforms, occurring within limited scale ranges, has been challenged by the scale-free characteristics of fractal geometry. This thesis assesses the fractal model by examining the irregularity of landsurface form, for the self-affine behaviour present in fractional Brownian surfaces. Different methods for detecting self-affine behaviour in surfaces are considered and of these the variogram technique is shown to be the most effective. It produces the best results of two methods tested on simulated surfaces, with known fractal properties. The algorithm used has been adapted to consider log (altitude variance) over a sample of log (distances) for: complete surfaces; subareas within surfaces; separate directions within surfaces. Twenty seven digital elevation models of landsurfaces arc re-examined for self- affine behaviour. The variogram results for complete surfaces show that none of these are self-affine over the scale range considered. This is because of dominant slope lengths and regular valley, spacing within areas. For similar reasons subarea analysis produces the non-fractal behaviour of markedly different variograms for separate subareas. The linearity of landforms in many areas, is detected by the variograms for separate directions. This indicates that the roughness of landsurfaces is anisotropic, unlike that of fractal surfaces. Because of difficulties in extracting particular landforms from their landsurfaces, no clear links between fractal behaviour, and landform size distribution could be established. A comparative study shows the geomorphometric parameters of fractal surfaces to vary with fractal dimension, while the geomorphometry of landsurfaces varies with the landforms present. Fractal dimensions estimated from landsurfaces do not correlate with geomorphometric parameters. From the results of this study, real landsurfaces would not appear to be scale- free. Therefore, a scale-bound approach towards landsurfaces would seem to be more appropriate to geomorphology than the fractal alternative

Spatial association in archaeology. Development of statistical methodologies and computer techniques for spatial association of surface, lattice and point processes, applied to prehistoric evidence in North Yorkshire and to the Heslerton Romano-British site.

The thesis investigates the concepts of archaeological spatial association within the context of both site and regional data sets. The techniques of geophysical surveying, surface distribution collection and aerial photography are described and discussed. Several new developments of technique are presented as well as a detailed discussion of the problems of data presentation and analysis. The quantitative relationships between these data sets are explored by modelling them as operands and describing association in terms of operators. Both local and global measures of association are considered with a discussion as to their relative merits. Methods for the spatial association of regional lattice and point processes are developed. A detailed discussion of distance based spatial analysis techniques is presented

Biology, stock assessment and management of the panga Pterogymnus laniarius on the Agulhas Bank, South Africa

The panga, Pterogymnus laniarius (Cuvier, 1830), is a South African endemic sparid fish species. On the Agulhas Bank, South Africa it is a commercially important species, caught as bycatch in the hake directed trawlfisheries and targeted by offshore hook-and-linefishers. Recently there has been considerable interest shown in directing further fishing effort on this species. The lack of a suitable management procedure for teleost bycatch in South Africa was the principal reason for undertaking this study. This thesis investigates aspects the panga's life history, particularly those aspects that have management implications. A full knowledge of this species' distribution and abundance was necessary as this could highlight the existence of any nursery areas, ontogenetic migratory patterns and areas of high spawner biomass. The derived parameter estimates were then included as inputs into stock assessment models to determine the status and productivity of the resource. Growth studies based on sectioned sagittal otoliths revealed that the panga was a relatively slow growing fish with ages of 16 years being recorded. Growth was best described by the von Bertalanffy growth model as Lt=379.4(1-e⁻°·¹³⁽t ⁺ ¹·⁷⁸⁾). Total, natural and fishing mortalities were estimated at 0.36 year⁻¹, 0.28 year⁻¹ and 0.08 year ⁻¹, respectively. Detailed histological examination of the gonads revealed that panga is a late gonochorist, males and females maturing after a non-functional intersexual stage. Females mature at approximately 200 mm fork length or 4 years of age. Reproduction occurs throughout the year although there is a slight peak in winter. Gametogenesis was found to be similar to that of other sparid fishes and marine teleosts in general. The panga feeds predominantly on crustaceans with a distinct ontogenetic shift in feeding habits. Juvenile fish feed predominantly in the water column on mysids after which they move to the benthos. Subadult fish feed principally on ophiuroids and amphipods. Adult fish remain on or near the benthos, feeding predominantly on crabs, and on polychaetes, ophiuroids and fishes to a lesser extent. Several aspects of the panga's biology contribute to its ability to sustain a higher fishing pressure than other sympatric sparid species. These include its late gonochoristic reproductive style, protracted spawning season, maturation before recruitment and preference for soft substratum prey that enables it to utilise large areas of the Agulhas Bank. The panga's longevity, slow growth and low natural mortality rate, however, mitigated against these factors and were considered in the stock assessments. A heterogeneous Geographical Information System (GIS) was developed to analyse the distribution and abundance patterns of the panga. The GIS developed in this thesis makes a significant contribution towards the development of a South African Fisheries Information System to analyse and manage fish resources in general and bycatch resources in particular. The GIS developed in this study combines statistical Generalized Additive Modelling and standard GIS methods. Analysis of fourteen biannual fishery independent biomass surveys, disaggregated by life history stage, revealed that a nursery area for immature fish (<23 cm TL or < 4 years of age) exists on the Central Agulhas Bank. After sexual maturation, approximately 40% of the biomass migrated eastwards, colonising large areas of the Eastern Agulhas Bank.ilie location of the nursery area appears to be a result of the pelagic eggs and larvae being advected towards the coast in an anti-cyclonic gyre, stemming off the Agulhas current and later deposited over the Central Agulhas Bank. The weak bottom currents on the Central Agulhas Bank prevented juvenile loss to the Benguela system. The eurytopy of adult fish to various physical variables such as temperature, dissolved oxygen and stronger currents enabled it to reduce conspecific competition and migrate eastwards with distribution primarily determined by depth. Relative biomass estimates revealed a gradual increase in biomass of 5.5% per annum between 1988 and 1995. Predictions from yield-per-recruit, biomass-per-recruit and spawner biomass-per-recruit analyses showed that there was scope for further exploitation. A FSB₅₀ fishing strategy was considered to be the most appropriate fishing strategy as it did not reduce the spawner biomass-per-recruit to less than 50% of unexploited levels. Effort control was considered the most effective management tool as the age-at-50%-selectivity occurred after age-at-sexual maturity and releasing undersized fish was undesirable due to heavy mortalities resulting from severe barotrauma. The panga resource was also assessed using an age-structured production model. The values for the free parameters of the model were estimated using biomass indices derived from fishery-independent trawl surveys. Although the data were fairly uninformative about the productivity of the resource, the results indicated robustly, that the population has recovered from low levels in the mid-1970's and could sustain higher levels of fishing intensity. Risk analysis calculations were used to assess the sustainability of different catch scenarios. The level of sustainable catch was found to be sensitive to the selectivity pattern of the gear utilised. Both stock assessment methods used in this study to investigate the status of the panga resource showed that the resource could theoretically sustain higher catches. It was found that although the stock could be harvested using available fishing methods, the sympatry of this species with other commercial species was of concern as the latter would form a significant bycatch in a panga directed fishery. The failure of current harvesting methods to address the bycatch problem highlights the management problem in South Africa and stresses the need for creativity by both scientists and fishers in designing new and improved methods for selectively harvesting bycatch fish resources. Considering that no suitable method is currently available to fish the panga stock in a directed fishery the fishery should be managed as status quo until some suitable and efficient gear is developed

Advanced tracking and image registration techniques for intraoperative radiation therapy

Mención Internacional en el título de doctorIntraoperative electron radiation therapy (IOERT) is a technique used to deliver radiation to the surgically opened tumor bed without irradiating healthy tissue. Treatment planning systems and mobile linear accelerators enable clinicians to optimize the procedure, minimize stress in the operating room (OR) and avoid transferring the patient to a dedicated radiation room. However, placement of the radiation collimator over the tumor bed requires a validation methodology to ensure correct delivery of the dose prescribed in the treatment planning system. In this dissertation, we address three well-known limitations of IOERT: applicator positioning over the tumor bed, docking of the mobile linear accelerator gantry with the applicator and validation of the dose delivery prescribed. This thesis demonstrates that these limitations can be overcome by positioning the applicator appropriately with respect to the patient’s anatomy. The main objective of the study was to assess technological and procedural alternatives for improvement of IOERT performance and resolution of problems of uncertainty. Image-to-world registration, multicamera optical trackers, multimodal imaging techniques and mobile linear accelerator docking are addressed in the context of IOERT. IOERT is carried out by a multidisciplinary team in a highly complex environment that has special tracking needs owing to the characteristics of its working volume (i.e., large and prone to occlusions), in addition to the requisites of accuracy. The first part of this dissertation presents the validation of a commercial multicamera optical tracker in terms of accuracy, sensitivity to miscalibration, camera occlusions and detection of tools using a feasible surgical setup. It also proposes an automatic miscalibration detection protocol that satisfies the IOERT requirements of automaticity and speed. We show that the multicamera tracker is suitable for IOERT navigation and demonstrate the feasibility of the miscalibration detection protocol in clinical setups. Image-to-world registration is one of the main issues during image-guided applications where the field of interest and/or the number of possible anatomical localizations is large, such as IOERT. In the second part of this dissertation, a registration algorithm for image-guided surgery based on lineshaped fiducials (line-based registration) is proposed and validated. Line-based registration decreases acquisition time during surgery and enables better registration accuracy than other published algorithms. In the third part of this dissertation, we integrate a commercial low-cost ultrasound transducer and a cone beam CT C-arm with an optical tracker for image-guided interventions to enable surgical navigation and explore image based registration techniques for both modalities. In the fourth part of the dissertation, a navigation system based on optical tracking for the docking of the mobile linear accelerator to the radiation applicator is assessed. This system improves safety and reduces procedure time. The system tracks the prescribed collimator location to solve the movements that the linear accelerator should perform to reach the docking position and warns the user about potentially unachievable arrangements before the actual procedure. A software application was implemented to use this system in the OR, where it was also evaluated to assess the improvement in docking speed. Finally, in the last part of the dissertation, we present and assess the installation setup for a navigation system in a dedicated IOERT OR, determine the steps necessary for the IOERT process, identify workflow limitations and evaluate the feasibility of the integration of the system in a real OR. The navigation system safeguards the sterile conditions of the OR, clears the space available for surgeons and is suitable for any similar dedicated IOERT OR.La Radioterapia Intraoperatoria por electrones (RIO) consiste en la aplicación de radiación de alta energía directamente sobre el lecho tumoral, accesible durante la cirugía, evitando radiar los tejidos sanos. Hoy en día, avances como los sistemas de planificación (TPS) y la aparición de aceleradores lineales móviles permiten optimizar el procedimiento, minimizar el estrés clínico en el entorno quirúrgico y evitar el desplazamiento del paciente durante la cirugía a otra sala para ser radiado. La aplicación de la radiación se realiza mediante un colimador del haz de radiación (aplicador) que se coloca sobre el lecho tumoral de forma manual por el oncólogo radioterápico. Sin embargo, para asegurar una correcta deposición de la dosis prescrita y planificada en el TPS, es necesaria una adecuada validación de la colocación del colimador. En esta Tesis se abordan tres limitaciones conocidas del procedimiento RIO: el correcto posicionamiento del aplicador sobre el lecho tumoral, acoplamiento del acelerador lineal con el aplicador y validación de la dosis de radiación prescrita. Esta Tesis demuestra que estas limitaciones pueden ser abordadas mediante el posicionamiento del aplicador de radiación en relación con la anatomía del paciente. El objetivo principal de este trabajo es la evaluación de alternativas tecnológicas y procedimentales para la mejora de la práctica de la RIO y resolver los problemas de incertidumbre descritos anteriormente. Concretamente se revisan en el contexto de la radioterapia intraoperatoria los siguientes temas: el registro de la imagen y el paciente, sistemas de posicionamiento multicámara, técnicas de imagen multimodal y el acoplamiento del acelerador lineal móvil. El entorno complejo y multidisciplinar de la RIO precisa de necesidades especiales para el empleo de sistemas de posicionamiento como una alta precisión y un volumen de trabajo grande y propenso a las oclusiones de los sensores de posición. La primera parte de esta Tesis presenta una exhaustiva evaluación de un sistema de posicionamiento óptico multicámara comercial. Estudiamos la precisión del sistema, su sensibilidad a errores cometidos en la calibración, robustez frente a posibles oclusiones de las cámaras y precisión en el seguimiento de herramientas en un entorno quirúrgico real. Además, proponemos un protocolo para la detección automática de errores por calibración que satisface los requisitos de automaticidad y velocidad para la RIO demostrando la viabilidad del empleo de este sistema para la navegación en RIO. Uno de los problemas principales de la cirugía guiada por imagen es el correcto registro de la imagen médica y la anatomía del paciente en el quirófano. En el caso de la RIO, donde el número de posibles localizaciones anatómicas es bastante amplio, así como el campo de trabajo es grande se hace necesario abordar este problema para una correcta navegación. Por ello, en la segunda parte de esta Tesis, proponemos y validamos un nuevo algoritmo de registro (LBR) para la cirugía guiada por imagen basado en marcadores lineales. El método propuesto reduce el tiempo de la adquisición de la posición de los marcadores durante la cirugía y supera en precisión a otros algoritmos de registro establecidos y estudiados en la literatura. En la tercera parte de esta tesis, integramos un transductor de ultrasonido comercial de bajo coste, un arco en C de rayos X con haz cónico y un sistema de posicionamiento óptico para intervenciones guiadas por imagen que permite la navegación quirúrgica y exploramos técnicas de registro de imagen para ambas modalidades. En la cuarta parte de esta tesis se evalúa un navegador basado en el sistema de posicionamiento óptico para el acoplamiento del acelerador lineal móvil con aplicador de radiación, mejorando la seguridad y reduciendo el tiempo del propio acoplamiento. El sistema es capaz de localizar el colimador en el espacio y proporcionar los movimientos que el acelerador lineal debe realizar para alcanzar la posición de acoplamiento. El sistema propuesto es capaz de advertir al usuario de aquellos casos donde la posición de acoplamiento sea inalcanzable. El sistema propuesto de ayuda para el acoplamiento se integró en una aplicación software que fue evaluada para su uso final en quirófano demostrando su viabilidad y la reducción de tiempo de acoplamiento mediante su uso. Por último, presentamos y evaluamos la instalación de un sistema de navegación en un quirófano RIO dedicado, determinamos las necesidades desde el punto de vista procedimental, identificamos las limitaciones en el flujo de trabajo y evaluamos la viabilidad de la integración del sistema en un entorno quirúrgico real. El sistema propuesto demuestra ser apto para el entorno RIO manteniendo las condiciones de esterilidad y dejando despejado el campo quirúrgico además de ser adaptable a cualquier quirófano similar.Programa Oficial de Doctorado en Multimedia y ComunicacionesPresidente: Raúl San José Estépar.- Secretario: María Arrate Muñoz Barrutia.- Vocal: Carlos Ferrer Albiac

Offshore Supply Vessel Design Studies with Application of Expert Systems

This thesis deals in depth with the design, operational and economic characteristics of offshore supply vessels, including pure supply and anchor handling/tug/supply types. The design characteristics investigated in this thesis include the main dimensions, hullform, stability, group weights, capacity and powering. The hullform of the offshore supply vessel is developed using the initial sketch technique where the vessel is divided into four boundary curves, that is, stem profile, parallel middle body and stem profile. The operational characteristics examine the seakeeping and manoeuvring behaviour, and the modelling of the supply operation of offshore supply vessels. The seakeeping characteristics are analysed using strip theory, while the manoeuvring characteristics are based on established empirical formulae. The modelling of the supply operation simulates the operating pattern of such vessels supplying materials to drilling platforms. Economic studies incorporated in this thesis served as a base for economic evaluation of each design. The required freight rate is used as a measure of merit for the owner operating the vessel, while the minimum charter rate is used if the owner is to charter the vessel. The computer is used as the principal tool in this thesis and a digital computer program algorithm has been developed to carry out the task. The computer program is written using expert system programming. Instead of using one of the languages used in expert system programming such as Lisp or Prolog, a well known commercial expert system shell, Leonardo, is used. The programs have been carefully written so that the user can interact with the system, the interaction can be merely to request continuation of the calculation or discuss the next step, with the system giving guidance, advice and stimulation. In general, three major programs have been developed. They are a. an iterative design program for offshore supply vessels, b. an interactive optimisation design program which involves mathematical optimisation procedures, and c. an operational modelling program for the offshore supply vessels. This thesis also considers methods of incorporating uncertainties in the preliminary design of offshore supply vessels. Apart from reviewing the existing methods of incorporating uncertainties in ship design studies, two methods are examined, Certainty Theory and Bayes' Rule. A program is written to incorporate uncertainties in the selection of main engine and propulsion units for the offshore supply vessels

Laminar burning velocity of liquefied petroleum gas mixtures

This thesis reports experimental and theoretical studies of the laminar burning velocity of liquefied petroleum gas (LPG) measured using the constant volume bomb method. The test rig designed at Loughborough University was a rigid and spherical chamber with central ignition. The LPG gas used in this study is a mixture of propane and n-butane with volume percentage of n-butane ranging from 0 to 100. The laminar burning velocities of the LPG/air mixtures have been determined over a range of equivalence ratios (0.7 to 1.4), unburnt gas pressures and temperatures (0.5 to 37 bar and 293 to 530 K respectively). With the measured pressure/time history in the constant volume combustion chamber, a new combustion model, which was developed based on a commonly used two-zone combustion model, was used to determine the laminar burning velocity. To obtain a more accurate value of the laminar burning velocity, the assumptions in the two-zone combustion model were analysed, and two effects were considered in the new combustion model, i.e. the effect of flame thickness and the effect of temperature gradient in the burnt gas zone. [Continues.

Influence of low-speed aerodynamic performance on airport community noise

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2008.Includes bibliographical references (p. 145-149).Properly assessing proposed aviation policies requires a thorough trade study of noise, emissions, fuel consumption, and cost. Aircraft low-speed aerodynamic performance is an important driver of all these impacts, and this thesis presents the development of an aerodynamic tool capable of accurately estimating key low-speed performance characteristics using aircraft geometry information typical of that available in the preliminary phase of aircraft design. The goal of this thesis is to use the low-speed aerodynamic estimates to present the sensitivity of aircraft noise to aircraft configuration and operational procedures, and then to identify improved procedures to reduce the cost, fuel use, and noise of current aircraft. The low-speed aerodynamic method developed in this work is comparable to aircraft manufacturer initial design tools. It requires about fifteen seconds on a modem computer and has been developed to a sufficient level of accuracy through a calibration study using Boeing flight test data, NASA wind tunnel results, and an empirically-tuned Lockheed method. The low-speed method is generally capable of predicting a drag polar, drag as a function of lift, to within one-percent. It also determines the changes of the drag polar due to high-lift devices, both slat and flap deployment, to within about three-percent. In addition, the method contains correlations to predict the variations of lift with angle of attack and the maximum lift coefficient; these predictions have errors around ten-percent and five-percent, respectively. The estimates produced by the method are of appropriate fidelity to properly model aircraft flight trajectories for fuel bum and noise estimates within larger environmental impact assessment models.(cont.) The results of simulations of the mandated takeoff and landing noise certification procedure show that noise is reduced insignificantly by small modifications to the airframe. This is largely because, for the current aircraft fleet, engine noise dominates both takeoff and landing noise, and only methods to reduce the required thrust or increase the aircraft altitude will significantly decrease noise. For landing, significant reductions in noise, on the order of 12%, were found by increasing the approach speed, which decreases required thrust, and by steepening the approach path, which keeps the aircraft higher above the ground when outside the airport boundaries. The results of an optimization study estimating the Pareto Frontier of departure procedures for a 747-200 aircraft show that compared to the standard departure at maximum takeoff weight, a reduction in time to climb of two minutes, in fuel consumption of 1,300 Ibm, and in land area exposed to a sound level 55 EPNdB of 100 square miles can be mutually achieved.by Andrew March.S.M

Fifth Annual Workshop on Space Operations Applications and Research (SOAR 1991), volume 2

Papers given at the Space Operations and Applications Symposium, host by the NASA Johnson Space Center on July 9-11, 1991 are given. The technical areas covered included intelligent systems, automation and robotics, human factors and life sciences, and environmental interactions