Analyses of experiments and a functional model for ship rolling

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.Simulation techniques and a Volterra functional polynomial are applied as two alternative methods of calculating ship roll response to irregular waves. The roll motion is modeled by a single degree of freedom differential equation, with two alternative nonlinear damping functions. Estimation techniques are developed to obtain the coefficients of the damping functions from decay tests and from forced rolling tests. A linear plus quadratic form of damping function is found to be slightly preferable to a linear plus cubic form. The roll response process is found to be non-Gaussian, and characterised by negative values of the coefficient of kurtosis. Simulation results agree well with results obtained from the functional polynomial for low response levels, but show increasing disagreement as the response level increases, due to divergence of the functional polynomial representation. Analyses of results from model tests in irregular waves and from sea trials confirm the non-Gaussian nature of the roll response. A "constrained" form of the generalised gamma distribution function is found to provide an improved fit to the roll maxima and tothe roll minima, as compared to the Rayleigh distribution. The model tests also show some asymmetry in the roll response, which is not predicted by the theoretical model. It is suggested that this asymmetry may primarily be due to the combined effect of horizontal drift forces and the restraining system used to keep the model on station.Financial support was obtained from: Dr.Techn. Georg Vedeler's Fund for Ship Research; A.S Veritas Research; the Overseas Research Students - ORS Awards Scheme; and the Royal Norwegian Council for Scientific and Industrial Research

De la cosmologie à la formation des galaxies : que nous apprennent les grandes structures de l'Univers ?

This thesis by publication is devoted to the theoretical understanding of the large-scale structure of the Universe and its role in the context of cosmology and galaxy formation. The birth and evolution of galaxies occur within the large cosmic highways drawn by the cosmic web and the natural question which arises is whether galaxies retain a memory of the large-scale cosmic flows from which they emerge. To address this key question, we will first show that in cosmological simulations, the spin of galaxies and the direction of their host filament are correlated in a mass-dependent way. This signal will be shown to be qualitatively understood in the context of hierarchical structure formation. An analytic model which explicitly takes into account the anisotropy of the cosmic web will complement this qualitative understanding by reproducing the measured correlations. Those ideas are important to understand the evolution of galaxy morphology but also to understand the intrinsic alignments of galaxies that contaminate cosmological probes like cosmic shear experiments. We will in particular measure this contamination directly from a state-of-the-art hydrodynamical simulation. In a second part, we will address the question of how to efficiently use large-scale structure data to probe the cosmological model describing our Universe by measuring its topology and geometry and using perturbation theory in the weakly and even mildly non-linear regime. The major contribution of this work is to analytically study the effect of redshift space distortions and non-linear collapse of structures on the topology, geometry and statistics of the cosmic density field.Dans cette thèse sur articles, nous nous intéressons aux grandes structures de l’Univers et à leur rôle fondamental pour la cosmologie et la formation des galaxies. Les galaxies naissent et grandissent au sein des filaments de la toile cosmique soulevant la question de l’impact de ces filaments sur les propriétés galactiques telles que la morphologie. Pour étudier cette question fondamentale, nous allons dans un premier temps montrer que dans les simulations numériques de l’Univers, le spin des galaxies est fortement lié à la direction de leur filament hôte avec un comportement qui dépend de leur masse. Ces corrélations spin-filament seront expliquées qualitativement dans le contexte de la formation hiérarchique des structures cosmologiques. Un modèle analytique tenant compte de l’anisotropie de la toile cosmique complètera ce tableau en reproduisant les corrélations observées. Ces idées sont importantes pour comprendre la morphologie des galaxies mais aussi les alignements intrinsèques qui peuvent certaines sondes cosmologiques basées sur la mesure de l’astigmatisme cosmique. Nous allons en particulier mesurer cette contamination dans une simulation hydrodynamique. Dans la seconde partie de ce manuscrit, nous nous poserons la question de comment extraire efficacement de l’information de la toile cosmique en mesurant sa topologie et sa géométrie et en utilisant la théorie perturbative dans un régime quasi-linéaire, la pierre angulaire de ce travail reposant sur l’étude analytique de l’impact de l’effondrement non-linéaire des structures et des distorsions en espace des redshifts sur la statistique du champ de densité cosmique

The time dimension in measurements of population health

As recently attested by the Millennium Declaration (United Nations, 2000), the health of populations is a concern for both governments and civil society: three of the eight Millennium Development Goals are defined in terms of health objectives. It is therefore reasonable to enquire what it means when we claim population health improves or declines. We should also know how to measure such changes. Since the Millennium Declaration does not answer these questions, we infer that concern for population health on the part of governments and civil society is not necessarily accompanied by clear concepts regarding its definition and measurement. Nevertheless, substantial technical progress on population health measurement has been made recently (see, for example, Murray and Lopez, 1996). In addition, there is a substantial body of older work on life expectancy and related measures (for an overview, see Keyfitz and Caswell, 2005). Life expectancy, in addition to being one of the oldest population health measures, might also be the only one to have successfully established itself in popular and political conceptions. As we argue in the following, this very success conceals subtle technical points that have confounded, at least to some degree, further developments in population health measurement

Untangling hotel industry’s inefficiency: An SFA approach applied to a renowned Portuguese hotel chain

The present paper explores the technical efficiency of four hotels from Teixeira Duarte Group - a renowned Portuguese hotel chain. An efficiency ranking is established from these four hotel units located in Portugal using Stochastic Frontier Analysis. This methodology allows to discriminate between measurement error and systematic inefficiencies in the estimation process enabling to investigate the main inefficiency causes. Several suggestions concerning efficiency improvement are undertaken for each hotel studied.info:eu-repo/semantics/publishedVersio

Stochastic calculus and derivatives pricing in the Nigerian stock market

Led by the Central Bank of Nigeria (CBN) and the Nigerian Stock Exchange (NSE), policy makers, investors and other stakeholders in the Nigerian Stock Market consider the introduction of derivative products in Nigerian capital markets essential for their investment and risk management needs. This research foregrounds these interests through detailed theoretical and empirical review of derivative pricing models. The specific objectives of the research include: 1) To explore the key stochastic calculus models used in pricing and trading financial derivatives (e.g. the Black-Scholes model and its extensions); 2) To examine the investment objectives fulfilled by derivatives; 3) To investigate the links between the stylized facts in the Nigerian Stock Market (NSM), the risk management techniques to be adopted, and the workings of the pricing models; and 4) To apply the research results to the NSM, by comparing the investment performance of selected derivative pricing models under different market scenarios, represented by the stylized facts of the underlying assets and market characteristics of the NSM. The foundational concepts that underpin the research include: stochastic calculus models of derivative pricing, especially the Black-Scholes (1973) model; its extensions; the practitioners’ Ad-Hoc Black Scholes models, which directly support proposed derivative products in the NSM; and Random Matric Theory (RMT). RMT correlates market data from the NSM and Johannesburg Stock Exchange (JSE) and facilitates possible simulation of non-existing derivative prices in the NSM, from those in the JSE. Furthermore, the research explores in detail the workings of different derivative pricing models, for example various structures for the Ad-Hoc Black Scholes models, using selected underlying asset prices, to determine the applicability of the models in the NSM. The key research findings include: 1) ways to estimate the parameters of the stochastic calculus models; 2) exploring the benefits of introducing pioneer derivative products in the NSM, including risk hedging, arbitrage, and price speculation; 3) using NSM stylized facts to calibrate selected derivative pricing models; and 4) explaining how the results could be used in future experimental modelling to compare the investment performance of selected models. By way of contributions to knowledge, this is the first study known to the researcher that provides in-depth review of the theoretical and empirical underpinnings of derivative pricing possible in the NSM. This forms the basis for the Black Scholes approach to asset pricing of European option contract, which is the kind of call/put option contract that is being adopted in the NSM. The research provides the initial foundations for effective derivatives trading in the NSM. By explaining the heuristics for developing derivative products in the NSM from JSE information, the research will support future work in this important area of study