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1
Kergosien, Nina. "Instrumentation de plaque composite de type aéronautique pour le contrôle santé intégré." Electronic Thesis or Diss., Ecully, Ecole centrale de Lyon, 2024. http://www.theses.fr/2024ECDL0008.
Анотація:
Des systèmes CSI sont actuellement à l'étude pour vérifier l'intégrité des matériaux composites des aéronefs. Ils permettent d’optimiser la maintenance, en donnant la possibilité de suivre l’état des structures en temps réel ou de contrôler ponctuellement des pièces difficiles d’accès par les méthodes de CND courantes. Les matériaux composites offrent la possibilité d’intégrer un système CSI directement à cœur du matériau. De cette façon, l’instrumentation est protégée de l’environnement et les problématiques de collage en surface sont résolues. L'objectif de cette thèse est de déterminer les effets de l'intégration de transducteurs ultrasonores piézoélectriques à cœur d'un composite PRFC stratifié de type aéronautique sur leur comportement en émission et en réception afin de montrer les avantages et inconvénients d'une telle intégration à cœur pour le monitoring de ces structures par ondes de Lamb. Les transducteurs PZT minces se sont révélés être les transducteurs les plus adaptés à l'intégration, car ils supportent les conditions d'élaboration d'un composite de structures aéronautiques élaboré en autoclave (7 bar et 180°C) et sont capables d'émettre et de recevoir des ondes guidées se propageant dans les plaques. La méthode d'intégration a été adaptée pour préserver l'intégrité des PZT et optimiser leur capacité d'émission d'ondes dans un composite. A cette occasion, la capacité des mesures d'impédance électromécanique à vérifier rapidement l'efficacité de la mise en œuvre de l'intégration a été validée. La caractérisation du champ d'onde qA0 a été réalisée expérimentalement, grâce aux déplacements hors plan mesurées avec un vibromètre laser suite à l'excitation de disques PZT intégrés à des fréquences comprises entre 30 et 200 kHzLa capacité du PZT intégré à détecter un défaut simulé de type aimant est aussi étudiée en essai d'émission-réception et est comparé avec le comportement de PZT couplés en surface de composite. Une étude par modélisation fréquentielle multiphysique a ensuite été réalisée afin de mettre en évidence les phénomènes physiques mis en jeu par l'intégration d'un PZT à cœur de composite. Ainsi, la direction des plis en contact du PZT intégré, la profondeur d'intégration et le couplage du PZT au composite influent sur le mécanisme de transduction ultrasonore. De plus, les contraintes induites par l'actionneur PZT ne permettent pas d'être simplifiées sous forme d'un modèle de type pin-force habituellement utilisé comme chargement d'un PZT en surface de matériau isotrope. En effet, les contraintes induites localement par l'excitation du PZT intégré ne sont pas radiales et dépendent de l'électrode du PZT considérée ainsi que des fréquences de génération d'ondesSHM systems are currently being developed to check the integrity of aircraft composite materials. These systems will help optimize maintenance by enabling real-time monitoring of structural condition, or spot-checking of parts that are difficult to access using conventional NDT methods. Composite materials offer the possibility of integrating a SHM system directly into the material. In this way, the instrumentation is protected from the environment and surface bonding issues are resolved. The aim of this thesis is to determine the effects of integrating piezoelectric transducers into the core of an aeronautical laminated CFRP composite on their Lamb-wave emission and reception abilities, in order to demonstrate the advantages and disadvantages for the design of a defect detection SHM system. Thin PZT transducers proved to be the most suitable ones for integration, as they can withstand the processing conditions of an autoclave-processed composite (7 bar and 180°C). They are also capable of transmitting and receiving guided waves, which are propagating in the plates. Moreover, the integration method was adapted to preserve the integrity of the PZTs and to optimize their ability to transmit waves in a composite. In order to assess the effectiveness of the integration, electromechanical impedance measurements were made a fast checking process. Characterization of qA0 mode wavefield transmitted by embedded PZT was carried out experimentally. Surface-bonded and embedded PZT were excited at frequencies between 30 and 200 kHz, while out-of-plane displacements were measured with a laser vibrometer. The ability of the embedded PZT to detect a simulated magnet-type defect are also studied in pitch-catch tests, and compared with the behavior of surface-bonded PZT to the composite surface. A dynamic finite element modelling study was then conducted to highlight the physical phenomena induced by the integration of a PZT in the composite core. The direction of the plies in contact with the embedded PZT, the depth of integration and the coupling of the PZT with the composite are influencing the ultrasonic transduction mechanism. Furthermore, it appears that the stresses induced by the PZT actuator cannot be simplified by the pin-force model usually used to load a PZT on an isotropic material surface in flaw detection models. These stresses are not radially oriented and depend on the PZT electrode considered, as well as on the wave generation frequencies
2
Zhang, Xu. "Modeling & Performance Analysis of QAM-based COFDM System." University of Toledo / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1310148963.
3
Castro, Sofia Balbina Santos Dias de. "Mode interactions with symmetry." Thesis, University of Warwick, 1993. http://wrap.warwick.ac.uk/4041/.
Анотація:
This thesis deals with steady-state mode interaction problems with symmetry. We prove several results concerning problems invariant under the action of an arbitrary compact Lie group Γ. These include the existence of mixed-mode solutions and secondary Hopf bifurcations. We also consider the unfolding of the equations characterizing such problems. Where appropriate, we distinguish the case when Γ acts trivially on one of the modes. We then apply the results to the problems of the (1,3)-, (1,5)- and (1,3,5)-mode interactions with spherical symmetry. We also consider the (3,5)- and the (1,3,5)-mode interaction problems with SO(3) symmetry.
4
Behrens, Gundula Ragna. "Mode jumping in MCMC." Thesis, University of Bath, 2008. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.478942.
Анотація:
Markov Chain Monte Carlo (MCMC) methods often have difficulties in moving between isolated modes. To understand these difficulties, some MCMC theory and some mode jumping approaches will be reviewed, first in fixed dimension and later in variable dimension. The focus will lie on improving the eficiency of the powerful, but computationally expensive method "tempered transitions". A technique for optimising the method's parameters ("temperatures") will be proposed. It will be demonstrated that the default choice of geometric temperatures can be far from optimal. The tuning technique will then be tested on a hard applied sampling problem, namely on sampling from a fixed-dimensional mixture model. The results will show that the optimisation is robust and performs well and that tempered transitions achieves mode jumping ("label-switching") where standard MCMC fails. Since mixture models are often of variable dimension, it will be verified that tempered transitions and the tuning technique can also be applied in variable-dimensional problems. Tests on a variable-dimensional mixture model will confirm that tempered transitions also improves jumps between dimensions.
5
Potgieter, Marnie. "Cellular effects of Coenzyme Q10 and resveratrol in the SJL/J dysferlinopathy mouse model." Thesis, University of Pretoria, 2010. http://hdl.handle.net/2263/24175.
Анотація:
The muscular dystrophies (MDs) are genetic disorders of muscle degeneration due to mutations in genes that encode a wide variety of proteins. Dysferlinopathy encompasses a large variety of neuromuscular diseases characterized by the absence of dysferlin in skeletal muscle and an autosomal recessive mode of inheritance. Dysferlinopathy can manifest as limb girdle muscular dystrophy type 2B (LGMD 2B), Miyoshi myopathy (MM) or distal myopathy with anterior tibial onset (DMAT). The first symptoms usually appear during the second or third decade of life as clumsiness when running, fatigue when walking long distances and difficulty in climbing stairs. Progression of the disease eventually leads to a loss of ambulation. A deficit in membrane-repair machinery in dysferlinopathy suggested a direct role for dysferlin in the Ca2+-dependent membrane-repair process. Recently, dysferlin has also been implicated in the process of chemotaxis. Evidence exists that free radical mediated injury contributes to the pathogenesis of muscle necrosis in the muscular dystrophies. The imbalance of free radical synthesis and antioxidant capacity has been suggested to contribute to the necrotic process. It is therefore imperative to explore the effect of antioxidant supplementation in the MDs. The present study followed a novel approach in investigating the cellular effects afforded by the supplementation of the SJL/J mouse model for dysferlinopathy with the antioxidants, Coenzyme Q10 (CoQ10) and resveratrol. The study aimed to determine, at cellular level, the histopathology and ultrastructural changes in the SJL/J mouse model following a 90 day trial with antioxidant supplementation. In addition to studying the morphology, the study paid attention to nonspecific parameters. The study mainly focused on the histopathology and ultrastructural alterations in the SJLL/J mouse. In addition the oxidative stress index of the affected quadriceps muscle was determined. The outcome provides evidence that increased oxidative stress levels are present in the SJL/J mouse. Antioxidant supplementation with CoQ10 at 120mg/kg/day or a resveratrol/CoQ10 combination supplementation at 40 and 60mg/kg/day, decreased the levels of oxidative stress and dystrophic markers at a cellular level. In addition, increased physical strength was observed. This thesis provides evidence to create a new platform for combination therapeutic strategies.Thesis (PhD)--University of Pretoria, 2010.
Anatomy
unrestricted
6
Hill, Andrew Stephen. "O(2) equivariant mode interactions." Thesis, University of Warwick, 1988. http://wrap.warwick.ac.uk/99595/.
Анотація:
This thesis uses and develops methods of equivariant bifurcation theory in the context of 0(2) equivariant steady-state and Hopf mode interactions in circumstances where both two and three modes interact. The general actions of the 0(2) orthogonal group are applied to these mode interactions and as an illustration the 0(2) equivariant steady-state/Hopf/Hopf mode interaction is placed in the context of the Taylor-Couette system.
7
Gehre, Christian. "Development of a model of the new born child dummy Q0 /." Düsseldorf : VDI-Verl, 2007. http://bvbr.bib-bvb.de:8991/F?func=service&doc_library=BVB01&doc_number=016244739&line_number=0001&func_code=DB_RECORDS&service_type=MEDIA.
8
Licitra, Floriana. "Pathophysiological and molecular characterization of a mouse model of ARCA2, a recessive cerebellar ataxia associated to Coenzyme Q10 deficiency." Thesis, Strasbourg, 2013. http://www.theses.fr/2013STRAJ096/document.
Анотація:
ARCA2 est une ataxie récessive qui se caractérise par une atrophie du cervelet et un léger déficit en coenzyme Q10. Des mutations dans le gène ADCK3 ont été récemment identifiées comme étant la cause d’ARCA2. ADCK3 code pour une kinase mitochondriale atypique, qui pourrait être impliquée dans la biosynthèse du coenzyme Q10. L’objectif de mon projet de thèse était d’élucider la physiopathologie d’ARCA2 en utilisant le modèle murin knockout pour Adck3. J’ai ainsi pu montrer que les souris Adck3-/- reproduisent de nombreux symptômes associés à ARCA2 et constituent un bon modèle pour étudier ARCA2. Au niveau du cervelet, les cellules de Purkinje sont spécifiquement touchées et présentent des anomalies morphologiques et fonctionnelles. Un léger défaut mitochondrial a été observé dans les muscles squelettiques des souris Adck3-/-. Enfin, une analyse transcriptomique de ces deux tissus a révélé des altérations de nombreuses voies, impliquant ADCK3 dans de nouveaux processus cellulairesARCA2 is a form of recessive ataxia characterized by a slow progression of the ataxic phenotype, cerebellar atrophy and mild deficit in Coenzyme Q10. ARCA2 was recently found associated with mutations in the ADCK3 gene that encodes a putativemitochondrial kinase homologous to the yeast Coq8 and the bacterial UbiB proteins, which are required for Coenzyme Q biosynthesis. In order to elucidate the pathophysiology of ARCA2, a constitutive knockout mouse for Adck3 was generated.Adck3-/- mice reproduce many ARCA2 symptoms such as slow progression of the ataxic phenotype and mild Coenzyme Q deficit, suggesting that Adck3-/- mice are a good model to study ARCA2. Strikingly, a morphological and functional impairmentwas found in cerebellar Adck3-/- Purkinje cells, whereas a mild mitochondrial defect was observed in the skeletal muscle of Adck3-/- mice. Interestingly, transcriptomic analyses revealed alteration in a number of molecular pathways implicating ADCK3in novel cellular processes
9
Wan, Derek. "On the supermarket model with memory." Thesis, London School of Economics and Political Science (University of London), 2012. http://etheses.lse.ac.uk/588/.
10
Gopal, Pillay Khuneswari. "Model selection and model averaging in the presence of missing values." Thesis, University of Glasgow, 2015. http://theses.gla.ac.uk/6834/.
Анотація:
Model averaging has been proposed as an alternative to model selection which is intended to overcome the underestimation of standard errors that is a consequence of model selection. Model selection and model averaging become more complicated in the presence of missing data. Three different model selection approaches (RR, STACK and M-STACK) and model averaging using three model-building strategies (non-overlapping variable sets, inclusive and restrictive strategies) were explored to combine results from multiply-imputed data sets using a Monte Carlo simulation study on some simple linear and generalized linear models. Imputation was carried out using chained equations (via the "norm" method in the R package MICE). The simulation results showed that the STACK method performs better than RR and M-STACK in terms of model selection and prediction, whereas model averaging performs slightly better than STACK in terms of prediction. The inclusive and restrictive strategies perform better in terms of prediction, but non-overlapping variable sets performs better for model selection. STACK and model averaging using all three model-building strategies were proposed to combine the results from a multiply-imputed data set from the Gateshead Millennium Study (GMS). The performance of STACK and model averaging was compared using mean square error of prediction (MSE(P)) in a 10% cross-validation test. The results showed that STACK using an inclusive strategy provided a better prediction than model averaging. This coincides with the results obtained through a mimic simulation study of GMS data. In addition, the inclusive strategy for building imputation and prediction models was better than the non-overlapping variable sets and restrictive strategy. The presence of highly correlated covariates and response is believed to have led to better prediction in this particular context. Model averaging using non-overlapping variable sets performs better only if an auxiliary variable is available. However, STACK using an inclusive strategy performs well when there is no auxiliary variable available. Therefore, it is advisable to use STACK with an inclusive model-building strategy and highly correlated covariates (where available) to make predictions in the presence of missing data. Alternatively, model averaging with non-overlapping variables sets can be used if an auxiliary variable is available.
11
Guo, Chuan. "The stochastic volatility Markov-functional model." Thesis, University of Warwick, 2016. http://wrap.warwick.ac.uk/91418/.
Анотація:
In this thesis we study low-dimensional stochastic volatility interest rate models for pricing and hedging exotic derivatives. In particular we develop a stochastic volatility Markov-functional model. In order to implement the model numerically, we further propose a general algorithm by working with basis functions and conditional moments of the driving Markov process. Motivated by a data driven study, we choose a SABR type model as a driving process. With this choice we specify a pre-model and develop an approximation to evaluate conditional moments of the SABR driver which serve as building blocks for the practical algorithm. Having discussed how to set up a stochastic volatility Markov-functional model next we study the calibration of a LIBOR based version of the model with the SABR type driving process. We consider a link between separable SABR LIBOR market models and stochastic volatility LIBOR Markov-functional models. Based on the link we propose a calibration routine to feed in SABR marginals by calibrating to the market vanilla options. Moreover we choose the parameters of the SABR driver by fitting to the market correlation structure. We compare the stochastic volatility Markov-functional model developed in the thesis with one-dimensional (non-stochastic-volatility) swap Markov-functional models in terms of pricing and hedging Bermudan type products. By doing so we investigate effects of correlation structure, implied volatility smiles and the introduction of stochastic volatility on Bermudan type products. Finally we compare Quasi-Gaussian models with Markov-functional models in terms of specification and calibration. In particular we study Quasi-Gaussian models formulated in the Markov-functional model framework to make clear the relationship between the two models.
12
McGrory, Clare Anne. "Variational approximations in Bayesian model selection." Thesis, University of Glasgow, 2005. http://theses.gla.ac.uk/6941/.
Анотація:
The research presented in this thesis is on the topic of the Bayesian approach to statistical inference. In particular it focuses on the analysis of mixture models. Mixture models are a useful tool for representing complex data and are widely applied in many areas of statistics (see, for example, Titterington et al. (1985)). The representation of mixture models as missing data models is often useful as it makes more techniques of inference available to us. In addition, it allows us to introduce further dependencies within the mixture model hierarchy leading to the definition of the hidden Markov model and the hidden Markov random field model (see Titterington (1990)). Chapter 1 introduces the main themes of the thesis. It provides an overview of variational methods for approximate Bayesian inference and describes the Deviance Information Criterion for Bayesian model selection. Chapter 2 reviews the theory of finite mixture models and extends the variational approach and the Deviance Information Criterion to mixtures of Gaussians. Chapter 3 examines the use of the variational approximation for general mixtures of exponential family models and considers the specific application to mixtures of Poisson and Exponential densities. Chapter 4 describes how the variational approach can be used in the context of hidden Markov models. It also describes how the Deviance Information Criterion can be used for model selection with this class of model. Chapter 5 explores the use of variational Bayes and the Deviance Information Criterion in hidden Markov random field analysis. In particular, the focus is on the application to image analysis. Chapter 6 summarises the research presented in this thesis and suggests some possible avenues of future development. The material in chapter 2 was presented at the ISBA 2004 world conference in Viña del Mar, Chile and was awarded a prize for best student presentation.
13
Carr, Ben. "Model subgroups of finite soluble groups." Thesis, University of Warwick, 1998. http://wrap.warwick.ac.uk/111070/.
Анотація:
In this thesis we begin the study of finite groups possessing a model subgroup, where a model subgroup H of a finite group G is defined to be a subgroup satisfying 〖1H〗^(↑G)=∑_(x∊∕π(G))▒X We show that a finite nilpotent group possesses a model subgroup if and only if it is abelian and that a Frobenius group with Frobenius complement C and Frobenius kernel N possesses a model subgroup if and only if (a) N is elementary abelian of order r". (b) C is cyclic of order (r" — 1 )/(rd — 1), for some d dividing n. (c) The finite field F=Frn has an additive abelian subgroup HF of order rd satisfying NormF/K(HF) =K, where K=Frd. We then go on to conjecture that a finite soluble group G possessing a model subgroup is either metabelian or has a normal subgroup N such that G/N is a Frobenius group with cyclic Frobenius complement of order 2" +1 and elementary abelian Frobenius kernel of order 22". We consider a series of cases that need to be excluded in order to prove the conjecture and present some examples that shed light on the problems still to be overcome.
14
Alessandrini, Marco. "Evaluation of the effects of coenzyme Q10 and succinate in a rotenone-induced complex I deficient rat model / by Marco Alessandrini." Thesis, North-West University, 2006. http://hdl.handle.net/10394/491.
Анотація:
Disorders of the mitochondrial respiratory chain have an incidence ranging from 1 in 2,000
to 1 in 5,000, with the most frequent of these cytopathies resulting from causative
alterations within mitochondrial complex I, the first enzyme of the respiratory chain. The
biochemical consequences of a complex I deficiency include, amongst others, failure to
oxidise reduced nicotinamide adenine dinucleotide (NADH), impairment of the Krebs
cycle, elevated blood lactate, lowered adenosine triphosphate (ATP) generation and an
increased production of reactive oxygen species (ROS).
The aim of the investigation was to evaluate the effects of CoQ10 and succinate in a
rotenone-induced animal model. Sprague Dawley rats were dosed with rotenone for a
period of 14 days via oesophageal intubation, resulting in the successful establishment of
a complex I deficient animal model. Upon optimisation of the rotenone concentration, rat
diets were supplemented with high concentrations of either coenzyme Q10 or succinate
for two days in an attempt to alleviate the biochemical manifestations of the rotenone induced
complex I deficiency. Five tissue types were collected and assayed for a total of
seven biochemical parameters, which enabled the establishment of a biochemical profile
of response for each of the tissue groups.
Data generated from the study revealed that rotenone, when dosed in high
concentrations, contributed to the alleviation of serum hydro peroxide levels. This result
was confirmed by the unexpected finding that rotenone itself harboured an antioxidant
capacity equivalent to that of Trolox, the vitamin E analogue generally used for the
determination of antioxidant capacity. It was therefore concluded that rotenone was not
an ideal inhibitor for the evaluation of complex I deficiency and ROS-related investigations
in an animal model. Since this compound is the most widely used inhibitor of complex I,
the data from the study affirms the use of alternative complex l inhibition strategies.
Finally, the data was suggestive of the fact that both coenzyme Q10 and succinate
exclusively improved isolated components of the biochemical profile. Results generated in
this study thus support current therapeutic intervention where patients receive a
combination of vitamins and cofactors as part of a management strategy for the
mitochondrial cytopathies.Thesis (Ph.D. (Biochemistry))--North-West University, Potchefstroom Campus, 2007.
15
Zhou, Yan. "Bayesian model comparison via sequential Monte Carlo." Thesis, University of Warwick, 2014. http://wrap.warwick.ac.uk/62064/.
Анотація:
The sequential Monte Carlo (smc) methods have been widely used for modern scientific computation. Bayesian model comparison has been successfully applied in many fields. Yet there have been few researches on the use of smc for the purpose of Bayesian model comparison. This thesis studies different smc strategies for Bayesian model computation. In addition, various extensions and refinements of existing smc practices are proposed in this thesis. Through empirical examples, it will be shown that the smc strategies can be applied for many realistic applications which might be difficult for Markov chain Monte Carlo (mcmc) algorithms. The extensions and refinements lead to an automatic and adaptive strategy. This strategy is able to produce accurate estimates of the Bayes factor with minimal manual tuning of algorithms. Another advantage of smc algorithms over mcmc algorithms is that it can be parallelized in a straightforward way. This allows the algorithms to better utilize modern computer resources. This thesis presents work on the parallel implementation of generic smc algorithms. A C++ framework within which generic smc algorithms can be implemented easily on parallel computers is introduced. We show that with little additional effort, the implementations using this framework can provide significant performance speedup.
16
Underhill, Nick. "Efficient and context-dependent Bayesian model selection." Thesis, University of Warwick, 2016. http://wrap.warwick.ac.uk/89267/.
Анотація:
In this thesis, we argue that the development of a number of context-dependent modifications to standard model selection approaches are warranted from an applied statistical standpoint, where we would generally accept that not only is no candidate model likely to be correct, but also that different models may be preferred for different purposes. To achieve this we propose three types of modification. First, we consider modifications to Bayes factor selection which proceed by specialising the Bayes factor to particular variables of interest, or as an alternative, by placing vague, adaptive priors on variables of less interest. We suggest that, particularly when the analyst wishes to assess models in light of a specific utility, scoring rules have an important role to play, and propose a new bias corrected score based information criterion which can be tailored to the utility at hand. Finally, we present results on a modular assessment framework for ‘big’ models whose components can be expressed in terms of exponential families. Such an approach allows components of the broader model to be assessed individually, and the assessments combined into an overall model score. We believe that this enables the analyst to allow certain judgements about data assessment periods and exchangeability of future data to be accommodated. We conclude with a discussion of areas for further research.
17
Patrascoiu, Octavian. "Model driven language engineering." Thesis, University of Kent, 2005. https://kar.kent.ac.uk/14352/.
Анотація:
Modeling is a most important exercise in software engineering and development and one of the current practices is object-oriented (OO) modeling. The Object Management Group (OMG) has defined a standard object-oriented modeling language the Unified Modeling Language (UML). The OMG is not only interested in modeling languages; its primary aim is to enable easy integration of software systems and components using vendor-neutral technologies. This thesis investigates the possibilities for designing and implementing modeling frameworks and transformation languages that operate on models and to explore the validation of source and target models. Specifically, we will focus on OO models used in OMG's Model Driven Architecture (MDA), which can be expressed in terms of UML terms (e.g. classes and associations). The thesis presents the Kent Modeling Framework (KMF), a modeling framework that we developed, and describes how this framework can be used to generate a modeling tool from a model. It then proceeds to describe the customization of the generated code, in particular the definition of methods that allows a rapid and repeatable instantiation of a model. Model validation should include not only checking the well-formedness using OCL constraints, but also the evaluation of model quality. Software metrics are useful means for evaluating the quality of both software development processes and software products. As models are used to drive the entire software development process it is unlikely that high quality software will be obtained using low quality models. The thesis presents a methodology supported by KMF that uses the UML specification to compute the design metrics at an early stage of software development. The thesis presents a transformation language called YATL (Yet Another Transformation Language), which was designed and implemented to support the features provided by OMG's Request For Proposal and the future QVT standard. YATL is a hybrid language (a mix of declarative and imperative constructions) designed to answer the Query/Views/Transformations Request For Proposals issued by OMG and to express model transformations as required by the Model Driven Architecture (MDA) approach. Several examples of model transformations, which have been implemented using YATL and the support provided by KMF, are presented. These experiments investigate different knowledge areas as programming languages, visual diagrams and distributed systems. YATL was used to implement the following transformations: * UML to Java mapping * Spider diagrams to OCL mapping * EDOC to Web Services
18
Zhang, Fan. "Parameter estimation and model fitting of stochastic processes." Thesis, University of Warwick, 2011. http://wrap.warwick.ac.uk/51576/.
Анотація:
Multiscale methods such as averaging and homogenization have become an increasingly interesting topic in stochastic time series modelling. When applying the averaged/ homogenized processes to applications such as parameter estimation and filtering problems, the resulting asymptotic properties are often weak. In this thesis, we focus on the above mentioned multiscale methods applied on Ornstein-Uhlenbeck processes. We find that the maximum likelihood based estimators for the drift and diffusion parameters derived from the averaged/homogenized systems can use the corresponding marginal multiscale data as observations, and still provide a strong convergence to the true value as if the observations are from the averaged/homogenized systems themselves. The asymptotic distribution for the estimators are studied in this thesis for the averaging problem, while that of the homogenization problem exhibit more difficulties and will be an interest of future work. In the case when applying the multiscale methods to the Kalman filter of Ornstein-Uhlenbeck systems, we study the convergence between the marginal covariance and marginal mean of the full scale system and those of the averaged/homogenized systems, by measuring their discrepancies. In Part III, we study real world projects of time series modelling in the field of econometrics. Chapter 7 presents a modelling project on interest rate time series from the well known Nelson-Siegel yield curve model. The methodology shows a development from standard Vector Autoregressive model to Bayesian based heteroscedastic regression model. Gibbs sampling is used as theMonte Carlo method. Chapter 8 presents a model comparison in modelling a portfolio of economic indices between constant correlation GARCH and Dynamic Conditional Correlation GARCH models. It compares the two models suitability in capturing the effect of "volatility clustering".
19
Adamou, Maria. "Bayesian optimal designs for the Gaussian Process Model." Thesis, University of Southampton, 2014. https://eprints.soton.ac.uk/373881/.
Анотація:
This thesis is concerned with methodology for finding Bayesian optimal designs for the Gaussian process model when the aim is precise prediction at unobserved points. The fundamental problem addressed is that the design selection criterion obtained from the Bayesian decision theoretic approach is often, in practice, computationally infeasible to apply. We propose an approximation to the objective function in the criterion and develop this approximation for spatial and spatio-temporal studies, and for computer experiments. We provide empirical evidence and theoretical insights to support the approximation. For spatial studies, we use the approximation to find optimal designs for the general sensor placement problem, and also to find the best sensors to remove from an existing monitoring network. We assess the performance of the criterion using a prospective study and also from a retrospective study based on an air pollution dataset. We investigate the robustness of designs to misspecification of the mean function and correlation function in the model through a factorial sensitivity study that compares the performance of optimal designs for the sensor placement problem under different assumptions. In computer experiments, using a Gaussian process model as a surrogate for the output from a computer model, we find optimal designs for prediction using the proposed approximation. A comparison is made of optimal designs obtained from commonly used model-free methods such as the maximin criterion and Latin hypercube sampling via both the space-filling and prediction properties of the designs. For spatio-temporal studies, we extend our proposed approximation to include both space and time dependency and investigate the approximation for a particular choice of separable spatio-temporal correlation function. Two cases are considered: (i) the temporal design is fixed and an optimal spatial design is found; (ii) both optimal temporal and spatial designs are found. For all three of the application areas, we found that the choice of optimal design depends on the degree and the range of the correlation in the Gaussian process model.
20
Chen, Weiwei. "A coupled left ventricle and systemic arteries model." Thesis, University of Glasgow, 2015. http://theses.gla.ac.uk/7037/.
Анотація:
Mathematical modelling and computational simulation are effective tools in studying the function of the cardiovascular system and diagnosing the progress of diseases in this system, especially when clinical experiments or measurements are limited or not capable to proceed. A variety of models have been developed related to different segments in the cardiovascular system, such as the heart, the valves, the systemic arteries and the pulmonary arteries, etc. Among these studies, modelling the left ventricle (LV) and systemic arteries (SA) have drawn a great deal of attention in the last several decade due to the high pressure and high morbidity of the systemic circulation. The recent models range from lumped-parameter models, one-dimensional models to three-dimensional models,which expand our understanding of the function of the left ventricle and systemic arteries respectively, but few of them considered the interaction between two parts. Thus, the propose of this thesis is to develop a dynamic cardiac-vascular model to study the pressure and flow wave interactions in the systemic circulation. Here we employs two advanced models, a three-dimensional finite-strain structure-based LV, and a one-dimensional dynamic physiologically-based model for the systemic arteries, to complete a coupled LV-SA model. The LV model is based on Gao et al. [35]’s work. In this model, the fluid-structure interaction (FSI) is described by an Immersed Boundary (IB) approach, in which an incompressible solid is immersed in a viscous incompressible fluid, and solved by a Lagrangian Finite Element (FE) method [40]. The systemic circulation model is employed from Olufsen et al. [90]’s work, which consists of two groups of arteries, the large arteries and the small arteries or vascular beds. The large-arteries model uses a LaxWendroff scheme to compute the cross-sectional area-averaged flow and pressure based on physiological parameters of the arterial tree. The vascular beds are modelled as asymmetric structured tree, to provide outflow boundary conditions at the end of each terminal vessel in the network of large arteries. The coupling is achieved by matching the pressure and flow rate at the aortic root, i.e. the circulation model feeds back the pressure as a boundary condition to the LV model, and the flow rate from the LV is used as the inflow for the circulation model. The function of the aortic valve (AV) is modelled as follows: the AV opens when the pressure in the LV just exceeds the pressure in the proximal aorta adjacent to the valve; the AV closes when the flow rate is negative (referring to backflow) at the boundary plane in the LV proximal to the AV. The governing equations of the system is solved by a combined immersed boundary finite element (IB/FE) method, and the LaxWendroff scheme of Olufsen et al. [90]. To investigate the cardio-vascular interactions under different conditions in the LV-SA system, this thesis first simulate a standard case defined by using parameters based on measurements of healthy LV and healthy systemic arteries from two healthy subjects, and then simulating four disease-related cases based on different pathological conditions in the LV-SA model, i.e. stiffening of the large arteries, functional rarefaction, increasing heart beat rate (by shortening the systemic diastolic phase) and varied end-of-diastolic pressure. The results of pathological cases are compared with the standard case to provide a more insightful change of the pressure/flow interaction, and the change of LV contractility. To better understand the cardiac-valvular-vascular interactions, a lumped-parameter AV model is coupled in the LV-SA model to further develop it into a more detailed LV-AV-SA model. Compared to the LV-SA model (no AV), when a normal AV condition is used in the coupled LV-AV-SA model, the active tension of the LV and the peak LV pressure at early systole slightly increases, but the peak flow rate and the cardiac output barely changed. While, when a mild stenosis AV condition is applied in the LV-AV-SA model, the LV function changes dramatically, especially a dramatically increase of the peak LV pressure and the peak active tension of the LV. This indicates that the valve condition is also important in studying cardiac-vascular interactions, especially for diseased valve conditions that the effects are huge and cannot be ignored. In order to study how the valvular region affects the cross-valve pressure difference, we reconstruct the valvular region in the LV based on the mid-systolic CMR images, which shows a 93% increase of the cross-sectional area in the valvular region than early systole. The cross-valve pressure drop decreases dramatically with a expanded valvular region compared with the narrower valvular region in previous LV-SA model. This indicates that the a local stenosis in the valvular region may have significant effects on the heart function, and a better description of modelling the expanding procedure of the valvular region is needed to predict more physiological results. This thesis is a step forward for studying the cardiac-valvular-vascular interactions in the systemic circulation, and can provide dynamic pressure and flow waveforms in the LV and long the systemic arteries. Moreover, this model not only verifies the effects of pethological conditions but also quantifies change of pressure, flow rate and ventricular inotropy in the LV-SA system, which is important progress and has barely been studied before. Further approach of this work is to develop a patient-specific model in the future to diagnose the progress of disease, as well as providing practical treatment strategy.
21
Monks, Thomas. "Comparing model reuse with model building : an empirical study of learning from simulation." Thesis, University of Warwick, 2011. http://wrap.warwick.ac.uk/55525/.
Анотація:
What are the benefits of involving decision makers in simulation model development? Do decision makers learn more about their problem if they are involved in model development than if they had been excluded? This thesis presents an experiment which compares decision maker learning outcomes and process in two different types of discrete-event simulation (DES) study. The first is a traditional simulation project where decision makers take the role of domain experts and are involved in the building of a simulation model through to its use. The second is where a model is reused rather than built. Sixty four undergraduate participants were individually involved in one of three experimental conditions: development of an A&E simulation model and its subsequent use; development of the same model, but with less time for model use; or were presented with the model already developed and asked to reuse it. Participants of each condition were then allowed to run the model, change variables and review results in an attempt to improve the performance of the system. Learning was measured at two levels: attitude change, to infer learning about a business problem, and transfer of learning, to infer a deeper learning. Results indicated that, firstly, model building aided participant's discovery of aspects of the problem that were previously unconsidered. However, attitudes about these novel aspects of the problem were only converted to transferable knowledge when experimentation was not limited. Secondly, participants that reused the model learnt about the model through quick cycles of experimentation followed by validation, although these tended to be focused on factors with which participants were most familiar. In fact, model reuse participants learnt more following this approach than by scrutinizing the results of each scenario in detail. Little empirical evidence exists to support the discussions and the view that involvement in model building aids learning. This thesis contributes to this debate by providing insight into the mechanisms that in uence learning. Moreover, results suggest that learning from experimentation when reusing a model is also valid, although the process followed may be different. Of course, there are limitations to the approach used to perform the comparison. For instance, the experiment uses novice decision makers and measures attitude immediately after the experiment. Refl ection on such points is used to aid the generation of testable hypotheses that can be explored in future research.
22
Overstall, Antony Marshall. "Default Bayesian model determination for generalised linear mixed models." Thesis, University of Southampton, 2010. https://eprints.soton.ac.uk/170229/.
Анотація:
In this thesis, an automatic, default, fully Bayesian model determination strategy for GLMMs is considered. This strategy must address the two key issues of default prior specification and computation. Default prior distributions for the model parameters, that are based on a unit information concept, are proposed. A two-phase computational strategy, that uses a reversible jump algorithm and implementation of bridge sampling, is also proposed. This strategy is applied to four examples throughout this thesis.
23
Hollmann, Claudia. "A cognitive human behaviour model for pedestrian behaviour simulation." Thesis, University of Greenwich, 2015. http://gala.gre.ac.uk/13831/.
Анотація:
Pedestrian behaviour simulation models are being developed with the intention to simulate human behaviour in various environments in both non-emergency and emergency situations. These models are applied with the objective to understand the underlying causes and dynamics of pedestrian behaviour and how the environment or the environment’s intrinsic procedures can be adjusted in order to provide an improvement of human comfort and safety. In order to realistically model pedestrian behaviour in complex environments, the specific human behaviour patterns which govern their behaviour need to be represented. It is thereby of importance to understand the causal chains between the surrounding conditions and the pedestrians’ behaviours: the impact of the environment’s purpose and facilities as well as the pedestrians’ individual goals on the pedestrians’ planning and route choice behaviour; the influence of emergent stimuli on the pedestrians’ plans and environment usage; the influence of the pedestrians’ environment usage under normal usage conditions on the pedestrians’ behaviour in response to a potential alarm event. In this thesis, a framework is developed for modelling advanced individual pedestrian behaviours and especially purpose-driven environment usage. The framework thereby aims to assist building and facility planners in improving a building’s layout in terms of pedestrian experience and walking routes. In this thesis, a comprehensive review on how individual pedestrian behaviour and the pedestrians’ environment usage are realised in current pedestrian behaviour simulation models has been undertaken. In addition, current theories on human decision making, goal-driven behaviour and emotion modelling have been surveyed from the research fields of artificial intelligence, virtual reality simulation, human psychology and human behavioural sciences. From this survey, theories suitable for this thesis’ cause have been identified and combined for the proposed Cognitive Pedestrian Agent Framework (CPAF). The proposed framework contains a sophisticated human decision making model, a multi-faceted individual knowledge representation, a model to realise situational and contextual awareness, and a novel realisation of a human path planning heuristic. The proposed framework has been demonstrated in the simulation of a building usage-cycle use case. Further, it has been outlined how the proposed framework could be used to model experiential alarm response behaviour.
24
Sammut, Fiona. "Using generalized linear models to model compositional response data." Thesis, University of Warwick, 2016. http://wrap.warwick.ac.uk/89876/.
Анотація:
This work proposes a multivariate logit model which models the influence of explanatory variables on continuous compositional response variables. This multivariate logit model generalizes an elegant method that was suggested previously by Wedderburn (1974) for the analysis of leaf blotch data in the special case of J = 2, leading to our naming this new approach as the generalized Wedderburn method. In contrast to the logratio modelling approach devised by Aitchison (1982, J. Roy Stat. Soc. B.), the multivariate logit model used under the generalized Wedderburn approach models the expectation of a compositional response variable directly and is also able to handle zeros in the data. The estimation of the parameters in the new model is carried out using the technique of generalized estimating equations (GEE). This technique relies on the specification of a working variance-covariance structure. A working variance-covariance structure which caters for the specific variability arising in compositional data is derived. The GEE estimator that is used to estimate the parameters of the multivariate logit model is shown to be invariant to the values of the correlation and dispersion parameters in the working variance-covariance structure. Due to this invariance property and the fact that the estimating equations used under the generalized Wedderburn method are linear and unbiased, the GEE estimator achieves full efficiency across a wide class of potential dispersion and correlation matrices for the compositional response variables. As for any other GEE estimator, the estimator used in the generalized Wedderburn method is also asymptotically unbiased and consistent, provided that the marginal mean model specification is correct. The theoretical results derived in this thesis are substantiated by simulation experiments, and properties of the new model are also studied empirically on some classic datasets from the literature.
25
Veerapen, Parmaseeven Pillay. "Recurrence relationships and model monitoring for Dynamic Linear Models." Thesis, University of Warwick, 1991. http://wrap.warwick.ac.uk/109386/.
Анотація:
This thesis considers the incorporation and deletion of information in Dynamic Linear Models together with the detection of model changes and unusual values. General results are derived for the Normal Dynamic Linear Model which naturally also relate to second order modelling such as occurs with the Kalman Filter, linear least squares and linear Bayes estimation. The incorporation of new information, the assessment of its influence and the deletion of old or suspect information are important features of all sequential models. Many dynamic sequential models exhibit conditioned, independence properties. Important results concerning conditional independence in normal models are established which provide the framework and the tools necessary to develop neat procedures and to obtain appropriate recurrence relationships for data incorporation and deletion. These are demonstrated in the context of dynamic linear models, with particularly simple procedures for discount regression models. Appropriate model and forecast monitoring mechanisms are required to detect model changes and unusual values. Cumulative Sum (Cusum) techniques widely used in quality control and in model and forecast monitoring have been the source of inspiration in this context. Bearing in mind that a single sided Cusum may be regarded essentially as a sequence of sequential tests, such a Cusum is, in many cases, equivalent to a Sequence of Sequential Probability Ratio Tests in many cases, as for example in the case of the Exponential Family. A relationship between Cusums and Bayesian decision is established for a useful class of linear loss functions. It is found to apply to the Normal and other important practical cases. For V- mask Cusum graphs, a particularly interesting result which emerges is the interpretation of the distance of the V vertex from the latest plotted point as the prior precision in terms of a number of equivalent observations.
26
Wang, Jinghua. "A hybrid model for large scale simulation of unsteady nonlinear waves." Thesis, City University London, 2016. http://openaccess.city.ac.uk/14575/.
Анотація:
A hybrid model for simulating rogue waves in random seas on a large time and space scale is proposed in this thesis. It is formed by combining the derived fifth order Enhanced Nonlinear Schrödinger Equation based on Fourier transform (ENLSE-5F), the fully nonlinear Enhanced Spectral Boundary Integral (ESBI) method and its simplified version. The numerical techniques and algorithm for coupling three models on time scale are provided. Using them, and the switch between the three models during the computation is triggered automatically according to wave nonlinearities. Numerical tests are carried out and the results indicate that this hybrid model could simulate rogue waves both accurately and efficiently. In some cases showed, the hybrid model is more than 10 times faster than just using the ESBI method.
27
Karaki, Muath. "Composition operators on model spaces." Doctoral thesis, Université Laval, 2015. http://hdl.handle.net/20.500.11794/25834.
Анотація:
Cette thèse est consacrée à l'étude des opérateurs de composition sur les espaces modèles. Soit φ une fonction analytique du disque unité dans lui même et soit θ une fonction intérieure, c'est à dire une fonction holomorphe et bornée par 1 dont les limites radiales sur le cercle sont de module 1 presque partout par rapport à la mesure de Lebesgue. A cette fonction θ, on associe l'espace modèle Kθ, défini comme l'ensemble des fonctions f ∈ H2 qui sont orthogonales au sous-espace θH2. Ici H2 est l'espace de Hardy du disque unité. Ces sous-espaces sont importants en théorie des opérateurs car ils servent à modéliser une large classe de contractions sur un espace de Hilbert. Le premier problème auquel nous nous intéressons concerne la compacité d'un opérateur de composition Cφ vu comme opérateur de Kθ dans H2. Récemment, Lyubarskii et Malinnikova ont obtenu un joli critère de compacité pour ces opérateurs qui fait intervenir la fonction de comptage de Nevanlinna du symbole φ. Ce critère généralise le critère classique de Shapiro. Dans une première partie de la thèse, nous généralisons ce résultat de Lyubarskii-Malinnikova à une classe plus générale de sous-espaces, à savoir les espaces de de Branges-Rovnyak ou certains de leurs sous-espaces. Les techniques utilisées sont en particulier des inégalités fines de type Bernstein pour ces espaces. Le deuxième problème auquel nous nous intéressons dans cette thèse concerne l'invariance de Kθ sous l'action de Cφ. Ce problème nous amène à considérer une structure de groupe sur le disque unité du plan complexe via les automorphismes qui fixent le point 1. A travers cette action de groupe, chaque point du disque produit une classe d'équivalence qui se trouve être une suite de Blaschke. On montre alors que les produits de Blaschke correspondants sont des solutions "minimales" d'une équation fonctionnelle ψ∘φ=λψ , où λ est une constante unimodulaire et φ un automorphisme du disque unité. Ces résultats sont ensuite appliqués au problème d'invariance d'un espace modèle par un opérateur de composition.This thesis concerns the study of composition operators on model spaces. Let φ be an analytic function on the unit disc into itself and let θ be an inner function, that is a holomorphic function bounded by 1 such that the radial limits on the unit circle are of modulus 1 almost everywhere with respect to Lebesgue measure. With this function θ, we associate the model space Kθ, defined as the set of functions f ∈ H2, which are orthogonal to the subspace θH2. Here, H2 is the Hardy space on the unit disc. These subspaces are important in operator theory because they are used to model a large class of contractions on Hilbert space. The first problem which we are interested in concerns the compactness of the composition operator Cφ as an operator on H2 into H2. Recently, Lyubarskii and Malinnikova have obtained a nice criterion for the compactness of these operators which is related to the Nevanlinna counting function. This criterion generalizes the classical criterion of Shapiro. In the first part of the thesis, we generalize this result of Lyubarskii-Malinnikova to a more general class of subspaces, known as de Branges-Rovnyak spaces or some subspaces of them. The techniques that are used are particular Bernstein type inequalities of these spaces. The second problem in which we are interested in this thesis concerns the invariance of Kθ under Cφ. We present a group structure on the unit disc via the automorphisms which fix the point 1. Then, through the induced group action, each point of the unit disc produces an equivalence class which turns out to be a Blaschke sequence. Moreover, the corresponding Blaschke products are minimal solutions of the functional equation ψ∘φ=λψ , where λ is a unimodular constant and φ is an automorphism of the unit disc. These results are applied in the invariance problem of the model spaces by the composition operator.
28
Smaus, Jan-Georg. "Modes and types in logic programming." Thesis, University of Kent, 1999. https://kar.kent.ac.uk/21739/.
Анотація:
This thesis deals with two themes: (1) construction of abstract domains for mode analysis of typed logic programs; (2) verification of logic programs using non-standard selection rules. (1) Mode information is important mainly for compiler optimisations. The precision of a mode analysis depends partly on the expressiveness of the abstract domain. We show how specialised abstract domains may be constructed for each type in a typed logic program. These domains capture the degree of instantiation of a term very precisely. The domain construction procedure is implemented using the Godel language and tested on some example programs to demonstrate the viability and high precision of the analysis. (2) We provide verification methods for logic programs using selection rules other than the usual left-to-right selection rule. We consider five aspects of verification: termination; and freedom from (full) unification, occur-check, foundering, and errors related to built-ins. The methods are based on assigning a mode, input or output, to each argument position of each predicate. This mode is only fixed with respect to a particular execution. For termination, we first identify a class of predicates which terminate under the assumption that derivations are input-consuming, meaning that in each derivation step, the input arguments of the selected atom do not become instantiated. Input-consuming derivations can be realised using block declarations, which test that certain argument positions of the selected atom are non-variable. To show termination for a program where not all predicates terminate under the assumption that derivations are input-consuming, we make the stronger assumption that derivations are left-based. This formalises the ''default left-to-right'' selection rule of Prolog. To the best of our knowledge, this work is the first formal and comprehensive approach to this kind of termination problem. The results on the other four aspects are mainly generalisations of previous results assuming the left-to-right selection rule.
29
Shiers, N. L. "Gaussian latent tree model constraints for linguistics and other applications." Thesis, University of Warwick, 2016. http://wrap.warwick.ac.uk/80590/.
Анотація:
The relationships between languages are often modelled as phylogenetic trees whereby there is a single shared ancestral language at the root and contemporary languages appear as leaves. These can be thought of as directed acyclic graphs with hidden variables, specifically Bayesian networks. However, from a statistical perspective there is often no formal assessment of the suitability of these latent tree models. A lot of the work that seeks to address this has focused on discrete variable models. However, when observations are instead considered as functional data, the high dimensional approximations are often better considered in a Gaussian context. The high dimensional data is often inefficiently stored and so the first challenge is to project this data to a low dimension while retaining the information of interest. One approach is to use the newly developed tool named separable-canonical variate analysis to form a basis. Extending the techniques for assessing latent tree model compatibility to beyond discrete variables, the complete set of Gaussian tree constraints are derived for the first time. This set comprises equations and inequality statements in terms of correlations of observed variables. These statements must in theory be adhered to for a Gaussian latent tree model to be appropriate for a given data set. Using the separable-canonical variate analysis basis to obtain a truncated representation, the suitability of a phylogenetic tree can then be plainly assessed. However, in practice it is desirable to allow for some sampling error and as such probabilistic tools are developed alongside the theoretical derivation of Gaussian tree constraints. The proposed methodology is implemented in an in-depth study of a real linguistic data set to assess the phylogenies of five Romance languages. This application is distinctive as the data set consists of acoustic recordings, these are treated as functional data, and moreover these are then being used to compare languages in a phylogenetic context. As a consequence a wide range of theory and tools are called upon from the multivariate and functional domains, and the powerful new separable-canonical function analysis and separable-canonical variate analysis are used. Utilising the newly derived Gaussian tree constraints for hidden variable models provides a first insight into features of spoken languages that appear to be tree-compatible.
30
Dunbar, Oliver. "A diffuse interface model of surfactants in multi-phase flow." Thesis, University of Warwick, 2017. http://wrap.warwick.ac.uk/99133/.
Анотація:
We investigate a free boundary problem arising in fluid dynamics, by modelling multiple incompressible fluids over subdomains with different material quantities, and in the presence of surface tension reducing chemicals known as surfactants. We construct a free energy for this system, and we require it obey the second law of thermodynamics, leading to the formulation of an energy minimisation problem (the sharp problem). This problem is degenerate, so we regularise it by constructing a new energy of Ginzburg-Landau type, parametrised by a (small) constant ε > 0 and when ε → 0 the sharp problem is recovered in the sense of Γ-convergence. This multi-phase energy is formed from a multiwell potential and gradient term, and the minimisers are known as phase field variables. The phase field variables approximate characteristic functions of the subdomains, and the model is rewritten as functions of them. Beneficially, the energy analysis can be repeated as before to obtain a diffuse interface model. We construct and perform numerical analysis of a novel discretisation scheme for a Cahn-Hilliard Navier-Stokes system. Here we create a fractional-theta coupling scheme which is importantly proved to be of second order in time. The key property of this scheme is that it uses weighted operator splitting to separate the different nonlinearities that appear in a Cahn-Hilliard Navier-Stokes system. That is, the Cahn-Hilliard multiwell potential, the incompressibility condition and the convection. We discuss stability and the extension to surfactants. We implement the novel scheme in DUNE (Distributed Unified Numerics Environment), a finite element package and use simulation to run tests to validate the stability and consistency of the schemes, convergence of the diffuse interface model with respect to its parametrisation, and flexibility for the code development.
31
Than, Soe Muang. "Vibration-based finite element model updating and structural damage identification." Thesis, University of Greenwich, 2013. http://gala.gre.ac.uk/11451/.
Анотація:
Damage and material deterioration could lead to structural failure with unknown consequences. Structural health monitoring strategy based on vibration measurements for existing aging structures offers a promising technique for effectively managing the deteriorating structures. The main objectives of this research are to develop a procedure for finite element model updating by using incomplete modal data identified from vibration measurements, to develop real time structural damage detecting method by directly using vibration measurements and then identify the damage at detailed location and extend in the structure on the basis of the validated numerical model. A steel frame model structure was constructed in the laboratory for finite element model updating and structural damage detection. Forced vibration testing was undertaken on the model structure and dynamic response such as accelerations were measured by using sensors installed. Modal analyses are then carried out to identify modal parameters such as frequencies, mode shapes and damping from the vibration measurements. Structural damage scenarios were simulated by breaking bracing members of the model structure, and modal parameter of the damaged structures were also identified and analysed. An effective approach for directly updating finite element model from measured incomplete modal data with a regularised iterative algorithm is then presented. The exact relationship between the perturbation of structural parameters and the modal properties of the dynamic structure is developed. Numerical simulation investigations and experimental study of a laboratory tested space steel frame model and practical application to the Canton Tower benchmark problem are undertaken to verify the accuracy and effectiveness of the proposed model updating method. Finally, a new approach for real time structural damage detection by using acceleration measurements is presented. Structural damage is characterised at element level by introducing damage parameters which can indicate the location and severity of damage in the structure. The relationship between the damage parameters and the measured dynamic response is then established from the governing equation of the dynamic structure. Numerical examples of cantilever beams, plane frame, and braced frames are adopted to demonstrate the effectiveness of the proposed method. The new proposed technique performs well and produces stable and reliable results, which could be used for real time damage assessment during the event of earthquake and explosion.
32
Gibiansky, Ekaterina. "Population pharmacokinetics : model-free approach and nonlinear mixed-effects modelling." Thesis, University of Greenwich, 1999. http://gala.gre.ac.uk/8654/.
Анотація:
The work is devoted to the application and further development of modern statistical methods to study pharmacokinetics of drugs. Specifically, it deals with applications and development of repeated measures analysis, so called 'population approach' methods, in the field of pharmacokinetics. hi the first part of the thesis, a new, model-free approach is developed and tested. It introduces a model-free measure of patient's exposure to drugs, and then investigates the relationships between the exposure level and covariates using various statistical techniques. Classification tree models (CART) and regression analysis are used to study various subpopulations of interest. It is shown, via simulations, that the model-free method is capable to identify predictors of exposure in a wide range of variability in the data. The non-linear mixed effect modelling is used to confirm the results of the model-free investigation. Model-free approach is successfully applied to several drugs. Non-linear Mixed Effects population models developed for the same data agree with its results. Limits of the new method are also identified. Specifically, it does not allow the estimation of the variability: either the within-subject (intra-individual) variability in response, or between-subject (inter-individual) variability of the pharmacokinetic parameters in the population. The second part of the thesis is devoted to applications of the Non-linear Mixed Effect methodology to population pharmacokinetics and dose-response analysis. Population pharmacokinetic and dose-response models of several drugs are developed. Pharmacokinetic models allow for complete characterisation of the drug's pharmacokinetics and its relationships to safety and efficacy. The developed models are used to explore the relationships between the exposure (individual Bayes estimates) and demographic predictors of exposure, and safety and efficacy of the drug. Finally, the developed models are used in simulations to guide the design of new studies.
33
Touloupou, Panayiota. "Bayesian inference and model selection for partially observed stochastic epidemics." Thesis, University of Warwick, 2016. http://wrap.warwick.ac.uk/88361/.
Анотація:
Over the past decades, statistical models have been established as an important tool for understanding the transmission dynamics of infectious diseases. Inference in such models can be challenging due to the strong dependencies in the actual epidemic process, as well as the fact that observations often rely in diagnostic tests that have imperfect sensitivities. Moreover, samples are often taken with very low temporal resolution, which leads to the actual dynamics being only partially observed. Data augmentation techniques implemented within the framework of Markov chain Monte Carlo (MCMC) methods can tackle these problems by taking into account the unobserved dynamics of transmission and thus have been widely employed in practice. Despite the methodological advances in the context of partially observed epidemic models, there are still several open challenges that remain to be addressed. One of the key challenges is the establishment of model comparison techniques that can be efficiently applied in problems involving a large amount of missing information. In this thesis, we describe a framework based on importance sampling which provides estimates of the marginal likelihood and is well suited for applications in this complex setting. Until recently, the study of infectious diseases in large scale populations has been challenging due to the computationally intensive methods needed to these models. One further contribution of this thesis is the development of a data augmentation MCMC algorithm that can be used in both Markovian and non-Markovian epidemic models. Our algorithm achieves good computational efficiency and therefore can be viewed as an alternative to existing approaches, particularly for applications on big datasets. The last part of the thesis is concerned with epidemic data containing additional information regarding the strain of a pathogen with which individuals are infected. Quantifying the interactions between the different strains of pathogens is crucial in order to obtain a complete understanding of the disease but statistical methods for this type of problem are still in the early stages of development. Motivated by this demand, we construct a model that incorporates this additional information and propose a statistical algorithm for inference. The model improves upon existing methods in the sense that it allows for both imperfect diagnostic test sensitivities and strain misclassification. Finally, extensive simulation studies are conducted in order to assess the performance of our methods, while the utility of the developed methodologies is demonstrated on data obtained from two longitudinal studies of Escherichia coli in cattle.
34
Jaeg, Tiphaine. "Exploring the mitochondrial function in muscle and molecular dysregulation in cerebellum in a mouse model for ARCA2, a recessive ataxia with coenzyme Q10 deficiency." Thesis, Strasbourg, 2017. http://www.theses.fr/2017STRAJ082/document.
Анотація:
ARCA2 est une ataxie autosomique récessive rare, caractérisée par une atrophie du cervelet et un léger déficit en Coenzyme Q10 (CoQ). La majorité des patients présentent des signes neurologiques supplémentaires comme l’épilepsie ou l’intolérance à l’exercice. La maladie est due à des mutations dans le gène COQ8A qui semble encoder une protéine kinase-like atypique, impliquée dans la biosynthèse du CoQ. Pour comprendre les mécanismes physiopathologiques, une souris Coq8a knock-out (KO) constitutif a été générée et récapitule les symptômes observés chez les patients. Le but de ce travail de thèse était de mieux comprendre certains aspects, notamment l’intolérance à l’exercice et l’ataxie. Malgré un déficit en CoQ dans les muscles, aucun défaut de respiration mitochondriale n’a été détecté dans un modèle cellulaire de muscle. Néanmoins, dans le cervelet, les niveaux de transcrits de 27 gènes sont dérégulés, précocement dans l’apparition de la pathologie chez les souris KO. Les voies métaboliques vont être explorées, ce qui devrait permettre de relier la fonction de COQ8A au taux de CoQ et aux symptômes observés chez les patientsARCA2, a rare form of recessive ataxia, is characterized by early onset progressive ataxia, cerebellar atrophy and a mild Coenzyme Q10 deficiency. Most of the patients show additional neurological signs such as epilepsy and exercise intolerance. Mutations in the COQ8A gene lead to ARCA2. COQ8A is suggested as being an unorthodox protein kinase like, with a regulatory role in CoQ biosynthesis, in mammals. To better understand ARCA2, a constitutive Coq8a knock-out (KO) mouse model was generated, which recapitulates most of the patient’s symptoms. Here we report the use of cellular models and the affected tissues to uncover the molecular signature of COQ8A loss and CoQ deficit. Despite CoQ deficit in the muscle, no mitochondrial bioenergetics defect was uncovered. In parallel, we have identified, by RT-qPCR, a key set of genes that are dysregulated in cerebellum, very early on in the pathology. We are currently investigating these pathways to uncover the link with COQ8A function. Altogether, our experiments will shed light on the early molecular events that lead to ARCA2 and may help draw a link between COQ8A function, CoQ pools and the symptoms observed in patients
35
Rama, Krishnan. "Fermion flavour observables : renormalisation invariants and model building using discrete symmetries." Thesis, University of Warwick, 2012. http://wrap.warwick.ac.uk/56802/.
Анотація:
We very briefly review the current status of flavour physics with much of the emphasis on the experimental and the theoretical aspects of neutrino oscillations. Later we move on to study flavour symmetric constraints among observables like the Koide formula and present a novel speculation in this context. Our research on the renormalisation evolution of flavour symmetric observables leads us to the discovery of exact one-loop evolution invariants in the Standard Model. Then we shift our attention towards model building. We construct a model based on the discrete group C3 x C3 x C3 and successfully describe the flavour physics in the leptonic sector including the recent observation of non-zero mixing angle 013. Here both the charged-lepton and the neutrino mass matrices have a common circulant-plusdiagonal form. Later we use the previously published “Simplest Neutrino" texture as the starting point to construct another model based on the discrete group S4. We redefine the flavour basis in a non-standard way and use the “u-t" rotated basis of S4 in model building. Like in the previous model, here also we use the recent experimental data for fitting and make predictions.
36
Tạ, Ngọc Trí. "Results on the number of zero modes of the Weyl-Dirac operator." Thesis, Lancaster University, 2009. http://eprints.lancs.ac.uk/30804/.
Анотація:
For a given magnetic potential A one can define the Weyl-Dirac operator σ·(-i∇-A) on R³. An L² eigenfunction of σ·(-i∇-A) corresponding to 0 is called a zero mode. In this thesis we will be concerned with the zero mode problem for the Weyl-Dirac operator and some related problems. The main results are: (i) upper bounds for the number of zero modes of the Weyl-Dirac operator in three dimensions when scaling a given magnetic field. A similar version for the Dirac operator in two dimensions is also obtained. There are also related results to estimate the number of zero modes of the massless Dirac operator, and the dimension of the eigenspaces at threshold energies for the Dirac operator with positive mass. (ii) construction of Dirac operators on the unit ball S² of R³ as well as the determination of their spectrum in case of "constant" magnetic fields. We also show another proof for the Aharonov-Casher theorem for S² based on results about spectral properties of Dirac operators that we have obtained. (iii) a formula giving the number of zero modes of the Weyl-Dirac operator for a special magnetic field, which is the result of pullbacks from the "constant" volume form of S². We also obtain a lower bound for the number of zero modes for the Weyl-Dirac operator corresponding to certain scaled magnetic fields; the magnetic fields are parallel to fibres of the Hopf fibration (pulled-back to R³ using inverse stereographic projection).
37
Macdonald, Craig. "The voting model for people search." Thesis, University of Glasgow, 2009. http://theses.gla.ac.uk/609/.
Анотація:
The thesis investigates how persons in an enterprise organisation can be ranked in response to a query, so that those persons with relevant expertise to the query topic are ranked first. The expertise areas of the persons are represented by documentary evidence of expertise, known as candidate profiles. The statement of this research work is that the expert search task in an enterprise setting can be successfully and effectively modelled using a voting paradigm. In the so-called Voting Model, when a document is retrieved for a query, this document represents a vote for every expert associated with the document to have relevant expertise to the query topic. This voting paradigm is manifested by the proposition of various voting techniques that aggregate the votes from documents to candidate experts. Moreover, the research work demonstrates that these voting techniques can be modelled in terms of a Bayesian belief network, providing probabilistic semantics for the proposed voting paradigm. The proposed voting techniques are thoroughly evaluated on three standard expert search test collections, deriving conclusions concerning each component of the Voting Model, namely the method used to identify the documents that represent each candidate's expertise areas, the weighting models that are used to rank the documents, and the voting techniques which are used to convert the ranking of documents into the ranking of experts. Effective settings are identified and insights about the behaviour of each voting technique are derived. Moreover, the practical aspects of deploying an expert search engine such as its efficiency and how it should be trained are also discussed. This thesis includes an investigation of the relationship between the quality of the underlying ranking of documents and the resulting effectiveness of the voting techniques. The thesis shows that various effective document retrieval approaches have a positive impact on the performance of the voting techniques. Interestingly, it also shows that a `perfect' ranking of documents does not necessarily translate into an equally perfect ranking of candidates. Insights are provided into the reasons for this, which relate to the complexity of evaluating tasks based on ranking aggregates of documents. Furthermore, it is shown how query expansion can be adapted and integrated into the expert search process, such that the query expansion successfully acts on a pseudo-relevant set containing only a list of names of persons. Five ways of performing query expansion in the expert search task are proposed, which vary in the extent to which they tackle expert search-specific problems, in particular, the occurrence of topic drift within the expertise evidence for each candidate. Not all documentary evidence of expertise for a given person are equally useful, nor may there be sufficient expertise evidence for a relevant person within an enterprise. This thesis investigates various approaches to identify the high quality evidence for each person, and shows how the World Wide Web can be mined as a resource to find additional expertise evidence. This thesis also demonstrates how the proposed model can be applied to other people search tasks such as ranking blog(ger)s in the blogosphere setting, and suggesting reviewers for the submitted papers to an academic conference. The central contributions of this thesis are the introduction of the Voting Model, and the definition of a number of voting techniques within the model. The thesis draws insights from an extremely large and exhaustive set of experiments, involving many experimental parameters, and using different test collections for several people search tasks. This illustrates the effectiveness and the generality of the Voting Model at tackling various people search tasks and, indeed, the retrieval of aggregates of documents in general.
38
Uluat, Mehmet Fatih. "Model-based Approach To The Federation Object Model Independence Problem." Master's thesis, METU, 2007. http://etd.lib.metu.edu.tr/upload/3/12608672/index.pdf.
Анотація:
One of the promises of High Level Architecture (HLA) is the reusability of
simulation components. Although HLA supports reusability to some extent with
mechanisms provided by Object Model Template (OMT), when the developer
wants to use an existing federate application within another federation with a
different Federation Object Model (FOM) problem arises. She usually has to
modify the federate code and rebuilt it. There have been some attempts to solve
this problem and they, in fact, accomplish this to some extent but usually they fall
short of providing flexible but also a complete mapping mechanism. In this work,
a model based approach that mainly focuses on Declaration, Object and
Federation Management services is explored. The proposed approach makes use
of Model Integrated Computing (MIC) and .NET 2.0 technologies by grouping
federate transitioning activities into three well-defined phases, namely, modeling,
automatic code generation and component generation. As a side product, a .NET
2.0 wrapper to Runtime Infrastructure (RTI) has been developed to help
developers create IEEE 1516 compatible .NET 2.0 federates in a programming
language independent way.
39
Kasal, Ozcan. "Model Theory Of Derivation Spaces." Phd thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/2/12611715/index.pdf.
Анотація:
In this thesis, the notion of the derivation spaces is introduced. In a suitable two-sorted language, the first order theory of these structures is studied. In particular, it is shown that the theory is not companionable. In the last section, the language is expanded by predicate symbols for a dependence relation. In this language it is shown that the extension of the corresponding theory has a model companion. It is shown that the model companion is a complete, unstable theory which does not eliminate quantifiers.
40
Nazar, Faizan Q. "Electronic structure of defects in the Thomas-Fermi-von-Weizsäcker model of crystals." Thesis, University of Warwick, 2017. http://wrap.warwick.ac.uk/91552/.
Анотація:
In this thesis, we establish a locality property for solutions to the Thomas-Fermi-von Weizsäcker (TFW) equations. This is a system of coupled PDEs that models the ground state electron density corresponding to a given nuclear arrangement. The locality property is a pointwise stability estimate for the TFW equations, that demonstrates the exponential response of the electron density to a perturbation of the nuclei. We show that this result holds for the TFW when using either the Coulomb or the Yukawa potential to treat the interaction of charged particles. We then use the locality result to prove several consequences for the TFW ground state, which includes generalising results from [14] regarding the neutrality of infinite systems and also showing the uniform convergence of ground states when passing to the limit from the Yukawa to the Coulomb model. Our main application is the construction of site energies from the TFW energy. The locality result implies that the response of each site energy decays exponentially with respect to a perturbation of the nuclear arrangement. Using these site energies, we then formulate the lattice relaxation problem, that was initially formulated in [23], to consider the response of a perfect crystal lattice to the introduction of a point defect. The site energies allow us to formulate a variational problem over a space of deformations of the lattice, show this problem is well-posed and finally establish the decay properties of minimisers.
41
Lee, Min Cherng. "Multiple imputation for missing data and statistical disclosure control for mixed-mode data using a sequence of generalised linear models." Thesis, University of Southampton, 2014. https://eprints.soton.ac.uk/366481/.
Анотація:
Multiple imputation is a commonly used approach to deal with missing data and to protect confidentiality of public use data sets. The basic idea is to replace the missing values or sensitive values with multiple imputation, and we then release the multiply imputed data sets to the public. Users can analyze the multiply imputed data sets and obtain valid inferences by using simple combining rules, which take the uncertainty due to the presence of missing values and synthetic values into account. It is crucial that imputations are drawn from the posterior predictive distribution to preserve relationships present in the data and allow valid conclusions to be made from any analysis. In data sets with different types of variables, e.g. some categorical and some continuous variables, multivariate imputation by chained equations (MICE) (Van Buuren (2011)) is a commonly used multiple imputation method. However, imputations from such an approach are not necessarily drawn from a proper posterior predictive distribution. We propose a method, called factored regression model (FRM) to multiply impute missing values in such data sets by modelling the joint distribution of the variables in the data through a sequence of generalised linear models. We use data augmentation methods to connect the categorical and continuous variables and this allows us to draw imputations from a proper posterior distribution. We compare the performance of our method with MICE using simulation studies and on a breastfeeding data. We also extend our modelling strategies to incorporate different informative priors for the FRM to explore robust regression modelling and the sparse relationships between the predictors. We then apply our model to protect confidentiality of the current population survey (CPS) data by generating multiply imputed, partially synthetic data sets. These data sets comprise a mix of original data and the synthetic data where values chosen for synthesis are based on an approach that considers unique and sensitive units in the survey. Valid inference can then be made using the combining rules described by Reiter (2003). An extension to the modelling strategy is also introduced to deal with the presence of spikes at zero in some of the continuous variables in the CPS data.
42
Schweigler, Mario. "A unified model for inter- and intra-processor concurrency." Thesis, University of Kent, 2006. https://kar.kent.ac.uk/14444/.
Анотація:
Although concurrency is generally perceived to be a `hard' subject, it can in fact be very simple --- provided that the underlying model is simple. The occam-pi parallel processing language provides such a simple yet powerful concurrency model that is based on CSP and the pi-calculus. This thesis presents pony, the occam-pi Network Environment. occam-pi and pony provide a new, unified, concurrency model that bridges inter- and intra-processor concurrency. This enables the development of distributed applications in a transparent, dynamic and highly scalable way. The author specified the layout of the pony system as presented in this thesis, and carried out about 90% of the implementation. This thesis is structured into three main parts, as well as an introduction and an appendix. In the introduction, the need for a unified concurrency model is examined in detail. Thereupon, the pony environment is presented as a solution that provides such a unified model. The first part of this thesis is concerned with the usage of the pony environment for the development of distributed applications. It presents the interface between pony and the user-level code, as well as pony's configuration and a sample application. The second part presents the design and implementation of the pony environment. It explains the internal structure of pony, the implementation of pony's components and public processes, and the integration of pony in the KRoC compiler. The third part evaluates pony's performance and contains the final conclusions. It presents a number of performance tests and concludes with a discussion of the work presented in this thesis, along with an outline of possible future research.
43
Zakaria, Mohamed Ramzy. "The hybrid model, and adaptive educational hypermedia frameworks." Thesis, University of Nottingham, 2004. http://eprints.nottingham.ac.uk/14247/.
Анотація:
The amount of information on the web is characterised by being enormous, as is the number of users with different goals and interests. User models have been utilized by adaptive hypermedia systems generally and adaptive educational hypermedia systems (AEHS) particularly to personalize the amount of information they have with respect to each individual's knowledge, background and goals. As a result of the research described herein, a user model called the Hybrid Model has been developed. This model is both generic and abstract, and it extends other models used by AEHS by measuring users' knowledge levels with respect to different knowledge domains simultaneously by utilising well known techniques in the world of user modelling, specifically the Overlay model (which has been modified) and the Stereotype model. Therefore, using the Hybrid Model, AEHS will not be restricted to a single knowledge domain at anyone time. Thus, by implementing the Hybrid model, those systems can manage users' knowledge globally with respect to the deployed knowledge domains. The model has been implemented experimentally in an educational hypermedia system called WHURLE (Web-based Hierarchal Universal Reactive Learning Environment) to verify its aim - managing users' knowledge globally. Moreover, this implementation has been tested successfully through a user trial as an adaptive revision guide for a Biological Anthropology Course. Furthermore, the infrastructure of the WHURLE system has been modified to embrace the objective of the Hybrid Model. This has led to a novel design that provides the system with the capability of utilising different user models easily without affecting any of its component modules.
44
Pasos, Jose E. "Mean-variance optimal portfolios for Lévy processes and a singular stochastic control model for capacity expansion." Thesis, London School of Economics and Political Science (University of London), 2018. http://etheses.lse.ac.uk/3771/.
Анотація:
In the first part of the thesis, the problem of determining the optimal capacity expansion strategy for a firm operating within a random economic environment is studied. The underlying market uncertainty is modelled by means of a general one-dimensional positive diffusion with possible absorption at 0. The objective is to maximise a performance criterion that involves a general running payoff function and associates a cost with each capacity increase up to the first hitting time of 0, at which time the firm defaults. The resulting optimisation problem takes the form of a degenerate twodimensional singular stochastic control problem that is explicitly solved. The general results are further illustrated in the special cases in which market uncertainty is modelled by a Brownian motion with drift, a geometric Brownian motion or a square-root mean-reverting process such as the one in the CIR model. The second part of the thesis presents a study of mean-variance portfolio selection for asset prices modelled by Lévy processes under conic constraints on trading strategies. In this context, the combination of the price processes’ jumps and the trading constraints gives rise to a new qualitative behaviour of the optimal strategies. The existence and the behaviour of the optimal strategies are related to different no-arbitrage conditions that can be directly expressed in terms of the Lévy triplet. This allows for a fairly complete characterisation of mean-variance optimal portfolios under conic constraints.
45
Al-Karkhi, Tahani. "Population dynamics and pattern formation in an info-chemical mediated tri-trophic plankton model." Thesis, University of Essex, 2018. http://repository.essex.ac.uk/22828/.
Анотація:
In this thesis, we study a spatio–temporal prey–predator model of plankton. This model has spatial interaction terms which represent a plankton dynamics that includes info–chemical mediated trophic interactions. We consider both a simplified two species model which has been studied in the literature (mostly in biological terms) and an extended, four-species model. In the latter, the grazing pressure of microzooplankton (M) on phytoplankton (P) is controlled through external infochemical (C) mediated predation by copepods (Z). We undertake a stability analysis of both the two species model and the four species model and compare the system dynamics. In relation to this, the critical conditions for Turing instability are derived; these are necessary and sufficient. Furthermore, we consider the degenerated situation wherein Turing bifurcation and Hopf bifurcation occur simultaneously. We also consider under what conditions Turing patterns are exhibited and under what conditions spatiotemporal patterns are observed generally. The Transient Turing instability of spatial interactions –exhibited by the two species model–is introduced and investigated in a number of ways. We also study the effects of the paradox of enrichment. This paradox led to a loss of stability in the four species model after this was derived from the two species model by expansion and by the addition of resources. Further, a numerical continuation technique was used to determine the existence of multiple stationary patterns.
46
Finch, Sam. "The random cluster model on the tree : Markov chains, random connections and boundary conditions." Thesis, University of Warwick, 2010. http://wrap.warwick.ac.uk/47385/.
Анотація:
The Fortuin-Kasteleyn random cluster model was adapted to the tree by Häggström [38] who considered a Gibbs specification corresponding to "wired boundary conditions" on the tree. Grimmett and Janson [36] generalized this idea by considering boundary conditions defined by equivalence relations on the set of rays of the tree. In this thesis we continue this project by defining a new object, a "random connection;" a type of random equivalence relation that allows us to redefine what is meant by a cluster of edges on the tree. Our definition is general enough to include Grimmett and Janson's boundary conditions. The random connection approach allows us to reconnect the random cluster model on the tree with Bernoulli bond percolation and we define two critical probabilities for bond percolation on a tree associated with each random connection that allow us to identify three behavioral phases of the associated random cluster model. We consider some examples of random connections defined by equivalence relations, including the "open" boundary conditions described in [36] where we are able to describe the behaviour of the random cluster model exactly and "Mandelbrot" bondary conditions described by a map from the boundary of a tree to the unit square that defines fractal percolation. In addition we adapt work of Zachary [66] to the wired random cluster model on a tree so as to prove a conjecture of Häggström concerning uniqueness of the Gibbs measure for large bond strengths.
47
Vasquez, Louella J. "High precision multifractal analysis in the 3D Anderson model of localisation." Thesis, University of Warwick, 2010. http://wrap.warwick.ac.uk/3811/.
Анотація:
This work presents a large scale multifractal analysis of the electronic state in the vicinity of the localisation-delocalisation transition in the three-dimensional Anderson model of localisation using high-precision data and very large system sizes of up to L3 = 2403. The multifractal analysis is implemented using box- and system- size scaling of the generalized inverse participation ratios employing typical and ensemble averaging techniques. The statistical analysis in this study has shown that in the thermodynamic limit a proposed symmetry relation in the multifractal exponents is true for the 3D Anderson model in the orthogonal universality class. Better agreement with the symmetry is found when using system-size scaling with ensemble averaging in which a more complete picture of the multifractal spectrum f(α) is also obtained. A complete profile of f(α) has negative fractal dimensions and shows the contributions coming from the tails of the distribution. Various boxpartitioning approaches have been carefully studied such as the use of cubic and non-cubic boxes, periodic boundary conditions to enlarge the system, and single and multiple origins in the partitioning grid. The most reliable method is equal partitioning of a system into cubic boxes which has also been shown to be the least numerically expensive. Furthermore, this work gives an expression relating f(α) and the probability density function (PDF) of wavefunction intensities. The relation which contains a finite-size correction provides an alternative and simpler method to obtain f(α) directly from the PDF in which f(α) is interpreted as the scaleinvariant distribution at criticality. Finally, a generalization of standard multifractal analysis which is applicable to the critical regime and not just at the critical point is presented here. Using this generalization together with finite-size scaling analysis, estimates of critical disorder and critical exponent based on exact diagonalization have been obtained that are in excellent agreement, supporting for the first time previous results of transfer matrix calculations.
48
Rizzo, Michael. "A model for flexible telephone services based on negotiating agents." Thesis, University of Kent, 1996. https://kar.kent.ac.uk/21341/.
49
Kister, Alexander Karl. "Sample path large deviations for the Laplacian model with pinning interaction in (1+1)-dimension." Thesis, University of Warwick, 2015. http://wrap.warwick.ac.uk/79699/.
Анотація:
We consider the (1+1) dimensional Laplacian model with pinning interaction. This is a probabilistic model for a polymer or an interface that is attracted to the zero line. Without the pinning interaction, the Laplacian model is a Gaussian field (Φi)iEΛN, where ΛN = {1, 2, ..., N - 1}. The covariance matrix of this field is given by the inverse of Φ -> 1/2 ENi=0(ΔΦi)2, where Δ is the discrete Laplacian. Furthermore the values at {-1, 0, N, N+1} are fixed boundary values. The pinning interaction is introduced by giving the field a reward each time it touches the zero line. Depending on the reward the model with pinning and the one without pinning show different behaviour. Caravenna and Deuschel [10] study the localisation behaviour of the polymer. The model is delocalised if the number of times a typical field touches the zero line is of order o(N). The authors of [10] show that for zero boundary conditions there is a critical reward such that for smaller rewards the model is delocalised whilst for larger rewards the model is localised. In this thesis we study the behaviour of the empirical profile of the field. We show that for non zero boundary conditions there is a critical reward such that for smaller rewards the empirical profile for the model with pinning and the one for the model without pinning behave in the same way whilst for larger rewards the empirical profile of the model with pinning interaction is attracted to the zero line.
50
Kokkola, N. "A double-error correction computational model of learning." Thesis, City, University of London, 2017. http://openaccess.city.ac.uk/18838/.
Анотація:
In this thesis, the Double Error model, a general computational model of real-time learning is presented. It builds upon previous real-time error-correction models and assumes that associative connections form not only between stimuli and reinforcers, but between all types of stimuli in a connectionist network. The stimulus representation uses temporally-distributed elements with memory traces, and a process of expectation-based attentional modulation for both reinforcers and non-reinforcing stimuli is introduced. A modified error-correction learning rule is proposed, which incorporates both an error-term for the predicted and predicting stimulus. The static asymptote of learning familiar from other models of learning is replaced by a similarity measure between the activities of said stimuli, resulting in more temporally correlated stimulus representations forming stronger associative links. Associative retrieval based on previously formed associative links result in the model predicting mediated learning and pre-exposure effects. As a general model of learning, it accounts for phenomena predicted by extant learning models. For instance, its usage of error-correction learning produces a natural account of cue-competition effects such as blocking and overshadowing. Its elemental framework, which incorporates overlapping sets of elements to represent stimuli, leads to it predicting non-linear discriminations including biconditional discriminations and negative patterning. The observation that adding a cue to an excitatory compound stimulus leads to a lower generalization decrement as compared to removing a cue from said compound also follows from this representational assumption. The model further makes a number of unique predictions. The apparent contradiction of mediated learning in backward blocking and mediated conditioning proceeding in opposite directions is predicted through the model’s dynamic asymptote. Latent inhibition is accounted for as occurring through both learning and selective attention. The selective attention of the model likewise produces emergent effects when instantiated in the real-time dynamics of the model, predicting that the relatively best predictor of an outcome can sustain the largest amount of attention when compared to poorer predictors of said outcome. The model is evaluated theoretically, through simulations of learning experiments, and mathematically to demonstrate its generality and formal validity. Further, a simplified version of the model is contrasted against other models on a simple artificial classification task, showcasing the power of the fully-connected nature of the model, as well as its second error term in enabling the model’s performance as a classifier. Finally, numerous avenues of future work have been explored. I have completed a proof-of-concept deep recurrent network extension of the model, instantiated with reference to machine learning theory, and applied the second error term of the model to modulating backpropagation in time of a vanilla RNN. Both the former and latter were applied to a natural language processing task.