A especificação de funções de covariância espaço-temporais é uma das possíveis estratégias para modelagem de processos dos quais observações são tomadas em diferentes posições do espaço e do tempo. Tais funções podem definir processos separáveis ou não separáveis e na sua especificação deve-se garantir que são funções de covariância válidas atendendo a condição de serem positiva definidas. Entre estratégias para obtenção de tais funções estão as de Cressie e Huang (1999) e Gneiting (2002). A primeira se baseia na idéia de obter funções em um espaç de dimensão aumentada a partir de funções válidas no espaço original e necessita de operações no domínio da freqüência. Alternativamente a segunda proposta utiliza combinação de funções completamente monótonas e estritamente crescentes, evitando inversão de representações espectrais. Há ainda poucos relatos de uso e avaliações comparativas das diferentes propostas. Neste trabalho considerou-se a metodologia proposta por Gneiting, com diferentes valores do parâmetro que indica a força da interação entre o espaço e o tempo. Diferentes modelos foram aplicados à dois conjuntos de dados, um referente a estoques de peixe na costa de Portugual, e outro referente à armazenagem de água em um solo com citros. Utilizou-se a implementação no pacote RandomFields do programa R, revisando-se a metodologia e investigando-se a implementação computacional. Para os dois conjuntos de dados o modelo de covariância separável se mostrou adequado para descrever o comportamento das observações disponíveis sendo a escolha do modelo determinada por ajustes de máxima verossimilhança. / The specification of space-time covariance functions is one of the possible strategies to model processes observed at different locations and time points. Such functions can define separable and non-separable processes and must attend the condition of positivedefiniteness. Among the strategies to obtain such valid functions are the ones suggested by Cressie and Huang (1999) and by Gneiting (2002). The former is based on the idea of obtaining valid functions in a space of increased dimension from valid functions on the primary dimension and requires operations in the frequency domain. Alternatively, the latter combines increasing monotone functions avoiding the inversion of spectral representations. There are still few reports of usage and comparisons of the strategies. This work follows Gneiting?s proposals with different values for the space-time interaction parameter. Models were applied for the analysis of two real data sets, one about fish stocks in the Portuguese coast and a second on soil water storage. The implementation on the R package RandomFields was used, with methodology and computational implementation being reviewed. For both case the separable model provided a satisfactory fit, based on maximum likelihood estimation.

A especificação de funções de covariância espaço-temporais é uma das possíveis estratégias para modelagem de processos dos quais observações são tomadas em diferentes posições do espaço e do tempo. Tais funções podem definir processos separáveis ou não separáveis e na sua especificação deve-se garantir que são funções de covariância válidas atendendo a condição de serem positiva definidas. Entre estratégias para obtenção de tais funções estão as de Cressie e Huang (1999) e Gneiting (2002). A primeira se baseia na idéia de obter funções em um espaç de dimensão aumentada a partir de funções válidas no espaço original e necessita de operações no domínio da freqüência. Alternativamente a segunda proposta utiliza combinação de funções completamente monótonas e estritamente crescentes, evitando inversão de representações espectrais. Há ainda poucos relatos de uso e avaliações comparativas das diferentes propostas. Neste trabalho considerou-se a metodologia proposta por Gneiting, com diferentes valores do parâmetro que indica a força da interação entre o espaço e o tempo. Diferentes modelos foram aplicados à dois conjuntos de dados, um referente a estoques de peixe na costa de Portugual, e outro referente à armazenagem de água em um solo com citros. Utilizou-se a implementação no pacote RandomFields do programa R, revisando-se a metodologia e investigando-se a implementação computacional. Para os dois conjuntos de dados o modelo de covariância separável se mostrou adequado para descrever o comportamento das observações disponíveis sendo a escolha do modelo determinada por ajustes de máxima verossimilhança. / The specification of space-time covariance functions is one of the possible strategies to model processes observed at different locations and time points. Such functions can define separable and non-separable processes and must attend the condition of positivedefiniteness. Among the strategies to obtain such valid functions are the ones suggested by Cressie and Huang (1999) and by Gneiting (2002). The former is based on the idea of obtaining valid functions in a space of increased dimension from valid functions on the primary dimension and requires operations in the frequency domain. Alternatively, the latter combines increasing monotone functions avoiding the inversion of spectral representations. There are still few reports of usage and comparisons of the strategies. This work follows Gneiting?s proposals with different values for the space-time interaction parameter. Models were applied for the analysis of two real data sets, one about fish stocks in the Portuguese coast and a second on soil water storage. The implementation on the R package RandomFields was used, with methodology and computational implementation being reviewed. For both case the separable model provided a satisfactory fit, based on maximum likelihood estimation.

Background: This study seeks to model aspects of the regeneration of radiata pine (Pinus radiata D.Don) seedlings under a range of environmental conditions. This study investigated whether “hybrid” mechanistic models, which predict plant growth and development using empirical representations of plant physiological responses to the environment, could provide a realistic alternative to conventional empirical regeneration models. Objectives: The objectives of this study were to 1) identify the functional relationships between the environmental conditions controlling germination, establishment and growth of radiata pine seedlings, under a range of those environmental conditions as specified by temperature and available light and soil water; and 2) specify those functional relationships in hybrid mechanistic (“hybrid”) models. Methods: Radiata pine seedling germination and growth were measured under controlled environmental conditions (incubators for seed germination, growth cabinets for seedlings), and results used to adapt, parameterise and test two published hybrid models; one for germination (the hydrothermal time model); and one for seedling growth in the first six months after germination, based on plant radiation use efficiency (RUE). The hydrothermal model was tested by incubating commercial radiata pine seeds under factorial combinations of temperature and water potentials where germination was likely to occur (12.5 ºC to 32.5 ºC and 0 MPa to –1.2 MPa.). 100 seeds were germinated for each factorial combination. The hydrothermal germination model was fitted to the germination data using non-linear regression modles, will allowed simultaneous estimation of all modle parameters. Seedlings were grown in controlled growth cabinets, and their RUE was calculated as the ratio of net primary production (NPP, specified in terms of an increase in oven dry biomass), to PAR intercepted or absorbed by a seedling. Estimation of seedling RUE required development of novel techniques for non-destructive estimation of seedling oven dry weight, and measurement of PAR interception by seedlings. The effect of varying PAR flux density on RUE was tested by measuring RUE of seedlings grown at 125, 250 and 500 µmol m⁻² s⁻¹. In a second experiment, the effect of deficits in available soil water on RUE was tested by measuring RUE of seedlings grown under 250 µmol m⁻² s⁻¹ PAR flux, and at different levels of available soil water. Available soil water was specified by a soil moisture modifier factor (ƒθ) which ranges between 1 for moist soils and 0 for soils where there is insufficient water for seedling growth. This soil moisture modifier had not previously been applied in studies of tree seedling growth. Temperatures for both seedling experiments were a constant 17.5 ºC (day) and 12.5 ºC (night). Results: Hydrothermal time models accurately described radiata pine seed germination. Model predictions were closely correlated with actual seed germination over the full range of temperature and water potentials where germination was likely to occur (12.5 ºC to 32.5 ºC and 0 MPa to –1.2 MPa. The minimum temperature for germination (base temperature) was 9.0 ºC. Optimum temperatures for germination ranged from ~20ºC for slow-germinating seeds to ~27 ºC for the fastest germinating seeds. The minimum water potential for seed germination varied within the seed population, with an approximately normal distribution (base water potential = –1.38 MPa, standard deviation of 0.48 MPa). In the process of developing the model, a novel explanation for the decline in germination rates at supra-optimal temperatures was developed (Section 3.4.6), based on earlier models proposed by Alvarado & Bradford (2002) and Rowse & Finch-Savage (2003). This explanation was that the decline in germination rate was not driven just by temperature, but by accumulated hydrothermal time above the base temperature for germination (T₀). This in turn raised the base soil water potential (Ψb) towards 0, so that the reduction in germination rate arose from a reduced accumulation of hydro-time, rather than from thermal denaturation of enzymes facilitating germination – the conventional explanation for non-linear accumulation of thermal time at supra-optimal temperatures for plant development. Upwards adjustment (towards 0 MPa) of base water potentials of germinating seeds occurred also at very cold temperatures in combination with high water potentials. In both cases (very cold or else supra-optimal temperatures) this upwards adjustment in base water potentials prevented germination of part of the seed population, and is proposed as a mechanism which enables seed populations to “hedge their bets” when germinating under less than ideal germination conditions. RUE of young germinated radiata pine seedlings growing in a controlled growth cabinet was not significantly different over a range of constant PAR flux densities. Mean RUE’s were 3.22, 2.82 and 2.58 g MJ⁻¹ at 125, 250 and 500 µmol m⁻² s⁻¹ respectively. In the second experiment, the novel use of a soil moisture modifier (ƒθ) to predict RUE of seedlings subjected to water stress proved successful within a limited range of soil water stress conditions. Measured seedling transpiration and stomatal conductance were closely correlated but seedling photosynthesis was less correlated with available soil water. This result suggests that photosynthesis was not coupled with stomatal conductance when PAR flux was 250 µmol m⁻² s⁻¹, which is well below saturating irradiance for C₃ plants. Conclusions: The use of hybrid, quasi-mechanistic models to describe tree seedling growth has been seldom explored, which necessitated the development of novel experimental and analytical techniques for this study. These included a predictive model of germination decline at sub- and supra-optimal temperatures; a method for accurately estimating seedling dry weights under a range of PAR flux densities; and a novel method for estimating light interception by small seedlings. The work reported in this thesis showed that existing hybrid models (the hydrothermal time germination model and the RUE model) can be adapted to model germination and growth of radiata pine seedlings under controlled environmental conditions. Nonetheless, further research is needed before the models can be confidently used as an alternative to conventional empirical models to model regeneration in “real-world” forests. Research priorities are the performance of hydrothermal germination models under variable field conditions, and the use of the soil moisture modifier for seedlings growing on a range of soil textures and under a range of PAR fluxes.

Made available in DSpace on 2014-12-17T15:26:38Z (GMT). No. of bitstreams: 1 Patricia Borchardt Santos.pdf: 378137 bytes, checksum: e27ccc5c056aa17d7bd2ca2c8b64458f (MD5) Previous issue date: 2009-12-01 / We presented in this work two methods of estimation for accelerated failure time models with random e_ects to process grouped survival data. The _rst method, which is implemented in software SAS, by NLMIXED procedure, uses an adapted Gauss-Hermite quadrature to determine marginalized likelihood. The second method, implemented in the free software R, is based on the method of penalized likelihood to estimate the parameters of the model. In the _rst case we describe the main theoretical aspects and, in the second, we briey presented the approach adopted with a simulation study to investigate the performance of the method. We realized implement the models using actual data on the time of operation of oil wells from the Potiguar Basin (RN / CE). / Apresentamos neste trabalho dois m?todos de estima??o para modelos de tempo de falha acelerado com efeito aleat?rio para tratar de dados de sobreviv?ncia correlacionados. O primeiro m?todo, que est? implementado no software SAS, atrav?s do procedimento NLMIXED, utiliza a quadratura Gauss-Hermite adaptada para obter a verossimilhan?a marginalizada. O segundo m?todo, implementado no software livre R, est? baseado no m?todo da verossimilhan?a penalizada para estimar os par?metros do modelo. No primeiro caso descrevemos os principais aspectos te?ricos e, no segundo, apresentamos brevemente a abordagem adotada juntamente com um estudo de simula??o para investigar a performance do m?todo. Realizamos uma aplica??o dos modelos usando dados reais sobre o tempo de funcionamento de po?os petrol?feros da Bacia Potiguar (RN/CE).

Motormanagement Systeme im modernen Kraftfahrzeug werden zunehmend umfangreicher und komplexer. Die Steuergeräte als zentrale Komponente dieser Systeme werden in ihrer Funktionalität durch Hard- und Software bestimmt. Sie sind das Ergebnis eines langen Entwicklungs- und Fertigungsprozesses. Fahrversuche und Versuche am Motorenprüfstand zum Test von Steuergeräten sind sehr zeit- und kostenintensiv. Eine Alternative ist der Test von Steuergeräten außerhalb ihrer realen Umgebung. Das Steuergerät wird dabei auf einem Hardware-in-the-Loop-Prüfstand betrieben. Die große Zahl von Einzelfunktionen und miteinander verknüpften Funktionen des Steuergerätes erfordert einen strukturierten und reproduzierbaren Ablauf beim Test. Diese Tests sind aber erst nach Fertigstellung eines Motorprototypen möglich, da die Parameter der vorhandenen Modelle aus den gemessenen Prüfstandsdaten ermittelt werden. Eine weitere Fragestellung zu diesem Thema bezieht sich auf die Modelltiefe: Heutige Modelle basieren auf Daten, die über einem Arbeitsspiel gemittelt werden. Untersuchungen wie z.B. der Momentanbeschleunigung von Kurbelwellen sind somit nicht möglich. Aus diesem Grund untersucht diese Arbeit Strategien im Hinblick auf den modellbasierten Test von Motormanagement Systemen. Dabei wird das Potenzial zur Zeiteinsparung bei einem neuen Motormodell großer Tiefe betrachtet.

Les études menées permettent de prendre en main un système depuis l’identification jusqu’à la commande robuste des systèmes non entiers. Les principes de la platitude permettent de parvenir à la planification de trajectoire à condition de connaître le modèle du système, d’où l’intérêt de l’identification des paramètres du système. Les principaux travaux de cette thèse concernent l’identification de système par modèles non entiers, la génération et la poursuite robuste de trajectoire par l’application des principes de la platitude aux systèmes non entiers.Le chapitre 1 rappelle les définitions et propriétés de l’opérateur non entier ainsi que les diverses méthodes de représentation d’un système non entier. Le théorème de stabilité est également remémoré. Les algèbres sur les polynômes non entiers et sur les matrices polynômiales non entières sont introduites pour l’extension de la platitude aux systèmes non entiers.Le chapitre 2 porte sur l’identification par modèle non entier. Après un état de l’art sur les méthodes d’identification par modèle non entier, deux contextes sont étudiés : en présence de bruit blanc et en présence de bruit coloré. Dans chaque cas, deux estimateurs optimaux (sur la variance et le biais) sont propos´es : l’un, en supposant une structure du modèle connue et d’ordres de dérivation fixés, et l’autre en combinant des techniques de programmation non linéaire qui optimise à la fois les coefficients et les ordres de dérivation.Le chapitre 3 établit l’extension des principes de la platitude aux systèmes non entiers.La platitude des systèmes non entiers linéaires en proposant différentes approches telles que les fonctions de transfert et la pseudo-représentation d’état par matrices polynômiales est étudiée.La robustesse du suivi de trajectoire est abordée par la commande CRONE. Des exemples de simulations illustrent les développements théoriques de la platitude au travers de la diffusion thermique sur un barreau métallique.Enfin, le chapitre 4 est consacré à la validation des contributions en identification, en planification de trajectoire et en poursuite robuste sur un système non entier réel : un barreau métallique est soumis à un flux de chaleur. / The general theme of the work enables to handle a system, from identification to robust control. Flatness principles tackle path planning unless knowing the system model, hence the system parameter identification necessity. The principal contribution of this thesis deal with system identification by non integer models and with robust path tracking by the use of flatness principles for fractional models.Chapter 1 recalls the definitions and properties of a fractional operator and also the various representation methods of a fractional system. The stability theorem is also brought to mind. Fractional polynomial and fractional polynomial matrice algebras are introduced for the extension of flatness principles for fractional systems.Chapter 2 is about non integer model identification. After a state of the art on system identification by non integer model. Two contexts are considered : in presence of white noise and of colored noise. In each situation, two optimal (in variance and bias sense) estimators are put forward : one, when considering a known model structure with fixed differentiating orders, and another one by combining nonlinear programming technics for the optimization of coefficients and differentiating orders.Chapter 3 establishes the extension of flatness principles to fractional systems. Flatness of linear fractional systems are studied while considering different approaches such as transfer functions or pseudo-state-space representations with polynomial matrices. Path tracking robustness is ensured with CRONE control. Simulation examples display theoretical developments on flatness through thermal diffusion on a metallic rod. Finally, Chapter 4 is devoted to validate the contributions to system identification, to trajectory planning and to robust path tracking on a real fractional system : a metallic rod submitted to a heat flux.

This thesis deals with the planning and implementation of construction project by the contractor. In the theoretical part, I wrote the basic concepts of project management, construction participants and temporal models of construction. Furthermore, I focused on the public procurement and its by tendering documentation. In the practical part I focused on a specific project, where I proposed an alternative course of the contract and the contract followed from its very beginning to evaluation.

Motormanagement Systeme im modernen Kraftfahrzeug werden zunehmend umfangreicher und komplexer. Die Steuergeräte als zentrale Komponente dieser Systeme werden in ihrer Funktionalität durch Hard- und Software bestimmt. Sie sind das Ergebnis eines langen Entwicklungs- und Fertigungsprozesses. Fahrversuche und Versuche am Motorenprüfstand zum Test von Steuergeräten sind sehr zeit- und kostenintensiv. Eine Alternative ist der Test von Steuergeräten außerhalb ihrer realen Umgebung. Das Steuergerät wird dabei auf einem Hardware-in-the-Loop-Prüfstand betrieben. Die große Zahl von Einzelfunktionen und miteinander verknüpften Funktionen des Steuergerätes erfordert einen strukturierten und reproduzierbaren Ablauf beim Test. Diese Tests sind aber erst nach Fertigstellung eines Motorprototypen möglich, da die Parameter der vorhandenen Modelle aus den gemessenen Prüfstandsdaten ermittelt werden. Eine weitere Fragestellung zu diesem Thema bezieht sich auf die Modelltiefe: Heutige Modelle basieren auf Daten, die über einem Arbeitsspiel gemittelt werden. Untersuchungen wie z.B. der Momentanbeschleunigung von Kurbelwellen sind somit nicht möglich. Aus diesem Grund untersucht diese Arbeit Strategien im Hinblick auf den modellbasierten Test von Motormanagement Systemen. Dabei wird das Potenzial zur Zeiteinsparung bei einem neuen Motormodell großer Tiefe betrachtet.

Cette thèse traite de l’identification de systèmes dynamiques à partir de données échantillonnées à pas variable. Ce type de données est souvent rencontré dans les domaines biomédical, environnemental, dans le cas des systèmes mécaniques où un échantillonnage angulaire est réalisé ou lorsque les données transitent sur un réseau. L’identification directe de modèles à temps continu est l’approche à privilégier lorsque les données disponibles sont échantillonnées à pas variable ; les paramètres des modèles à temps discret étant dépendants de la période d’échantillonnage. Dans une première partie, un estimateur optimal de type variable instrumentale est développé pour estimer les paramètres d’un modèle Box-Jenkins à temps continu. Ce dernier est itératif et présente l’avantage de fournir des estimées non biaisées lorsque le bruit de mesure est coloré et sa convergence est peu sensible au choix du vecteur de paramètres initial. Une difficulté majeure dans le cas où les données sont échantillonnées à pas variable concerne l’estimation de modèles de bruit de type AR et ARMA à temps continu (CAR et CARMA). Plusieurs estimateurs pour les modèles CAR et CARMA s’appuyant sur l’algorithme Espérance-Maximisation (EM) sont développés puis inclus dans l’estimateur complet de variable instrumentale optimale. Une version étendue au cas de l’identification en boucle fermée est également développée. Dans la deuxième partie de la thèse, un estimateur robuste pour l'identification de systèmes à retard est proposé. Cette classe de systèmes est très largement rencontrée en pratique et les méthodes disponibles ne peuvent pas traiter le cas de données échantillonnées à pas variable. Le retard n’est pas contraint à être un multiple de la période d’échantillonnage, contrairement à l’hypothèse traditionnelle dans le cas de modèles à temps discret. L’estimateur développé est de type bootstrap et combine la méthode de variable instrumentale itérative pour les paramètres de la fonction de transfert avec un algorithme numérique de type gradient pour estimer le retard. Un filtrage de type passe-bas est introduit pour élargir la région de convergence pour l’estimation du retard. Tous les estimateurs proposés sont inclus dans la boîte à outils logicielle CONTSID pour Matlab et sont évalués à l’aide de simulation de Monte-Carlo / The output of a system is always corrupted by additive noise, therefore it is more practical to develop estimation algorithms that are capable of handling noisy data. The effect of white additive noise has been widely studied, while a colored additive noise attracts less attention, especially for a continuous-time (CT) noise. Sampling issues of CT stochastic processes are reviewed in this thesis, several sampling schemes are presented. Estimation of a CT stochastic process is studied. An expectation-maximization-based (EM) method to CT autoregressive/autoregressive moving average model is developed, which gives accurate estimation over a large range of sampling interval. Estimation of CT Box-Jenkins models is also considered in this thesis, in which the noise part is modeled to improve the performance of plant model estimation. The proposed method for CT Box-Jenkins model identification is in a two-step and iterative framework. Two-step means the plant and noise models are estimated in a separate and alternate way, where in estimating each of them, the other is assumed to be fixed. More specifically, the plant is estimated by refined instrumental variable (RIV) method while the noise is estimated by EM algorithm. Iterative means that the proposed method repeats the estimation procedure several times until a optimal estimate is found. Many practical systems have inherent time-delay. The problem of identifying delayed systems are of great importance for analysis, prediction or control design. The presence of a unknown time-delay greatly complicates the parameter estimation problem, essentially because the model are not linear with respect to the time-delay. An approach to continuous-time model identification of time-delay systems, combining a numerical search algorithm for the delay with the RIV method for the dynamic has been developed in this thesis. In the proposed algorithm, the system parameters and time-delay are estimated reciprocally in a bootstrap manner. The time-delay is estimated by an adaptive gradient-based method, whereas the system parameters are estimated by the RIV method. Since numerical method is used in this algorithm, the bootstrap method is likely to converge to local optima, therefore a low-pass filter has been used to enlarge the convergence region for the time-delay. The performance of the proposed algorithms are evaluated by numerical examples

This thesis provides a general methodology for classifying and describing many combinatoric problems, systematising and finding theoretical expressions for quantities of interest, and investigating their feasible numerical evaluation. Unifying notation and definitions are provided. Our knowledge of random allocations is also extended. This is achieved by investigating new processes, generalising known processes, and by providing a formal structure and innovative techniques for analysing them. The random allocation models described in this thesis can be classified as occupancy urn models, in which we have a sequence of urns and throw balls into them, and investigate static, waiting-time and dynamic processes. Various structures are placed on the relationship(s) between cells, balls, and the selection of items being distributed, including varieties, batch arrivals, taboo sets and blocking sets. Static, waiting-time and dynamic processes are investigated. Both without-replacement and with-replacement sampling types are considered. Emphasis is placed on the distributions of waiting-times for one or more events to occur measured from the time a particular event occurs; this begins as an abstraction and generalisation of a model of departures of cars parked in lanes. One of several additional determinations is the platoon size distribution. Models are analysed using combinatorial analysis and Markov Chains. Global attributes are measured, including maximum waits, maximum room required, moments and the clustering of completions. Various conversion formulae have been devised to reduce calculation times by several orders of magnitude. New and extended applications include Queueing in Lanes, Cake Displays, Coupon Collector's Problem, Sock-Sorting, Matching Dependent Sets (including Genetic Code Attribute Matching and the game SET), the Zig-Zag Problem, Testing for Randomness (including the Cake Display Test, which is a without-replacement test similar to the standard Empty Cell test), Waiting for Luggage at an Airport, Breakdowns in a Network, Learning Theory and Estimating the Number of Skeletons at an Archaeological Dig. Fundamental, reduction and covering theorems provide ways to reduce the number of calculations required. New combinatorial identities are discovered and a well-known one is proved in a combinatorial way for the first time. Some known results are derived from simple cases of the general models. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1309598 / Thesis (Ph.D.) -- University of Adelaide, School of Mathematical Sciences, 2007