Dissertations / Theses on the topic 'Network modelling'
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Gudmundsson, Gudmundur Stefan. "Essays in network modelling." Doctoral thesis, Universitat Pompeu Fabra, 2018. http://hdl.handle.net/10803/663096.
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This thesis consists of two chapters on time series modelling. The first chapter introduces a class of vector autoregressive (VAR) models with a community structure for large panels of time series. In the model, the series are parti-tioned into latent groups such that spillovers are stronger within groups than between them. We then propose an algorithm that uses the eigenvectors of a function of the estimated autoregressive matrices to recover the communities. We study the properties of the procedure and establish its consistency. The algorithm motivates us to suggest a regularised VAR estimator, which per-forms favourably relative to a number of alternatives in a forecasting exercise. The methodology is applied to study clustering in industrial production for a set of major economies. The second chapter introduces a class of partial correlation network models with a community structure. The series form unknown groups, where correlation is higher within groups than otherwise. We propose an algorithm that consistently detects the communities using the eigenvectors of the sample covariance matrix. The procedure is used to analyse real activity clustering in the U.S. and Europe.Aquesta tesi consisteix en dos capítols sobre models de dades de sèries temporals. El primer capítol introdueix una classe de models de vector autoregressius (VAR) amb una estructura de comunitat per panels de dades de sèries temporals. En el model, les sèries es parteixen en grups latents de tal manera que els spillover són ées forts dins de grups que entre ells. Llavors proposem un algoritme que utilitza el vector d’eigen d’una funció de les matrius autoregressives estimades per recuperar les comunitats. Estudiem les propietats del procediment i establim la seva consistència. L’algoritme ens motiva a suggerir un estimador regulat del VAR, el qual actua favorablement en relació a un nombre d’alternatives en una exercici d’ estimació. La metodologia s’aplica per estudiar el clustering en la producció industrial per un conjunt d’economies importants. El segon capítol introdueix una classe de models de xarxa de correlació parcials amb una estructura de comunitat. La èerie forma grups desconeguts, on la correlació és més alta dins de grups que altrament. Proposem un algoritme que detecta consistentment les comunitats que utilitzen els vectors d’eigen de la matriu de mostra de covariáncia. El procediment s’utilitza per analitzar el clustering en l’activitat real en els EUA i Europa.
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Filion, Yves R. "Extended dynamic network modelling." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/MQ58667.pdf.
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Roadknight, C. M. "Transparent neural network modelling." Thesis, Nottingham Trent University, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.314107.
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Dalton, Sarah. "Modelling the Perinatal Network System." Thesis, University of Westminster, 2018. https://westminsterresearch.westminster.ac.uk/item/q559v/modelling-the-perinatal-network-system.
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The topic is that hospital capacity for patient beds runs short. We wish to predict when this will occur. An inter-disciplinary approach to this problem is taken incorporating a Management Science/Operational Research perspective. The subject is the Perinatal Network System, which is described, analysed and modelled. An illustrative Case Study is taken of an English local neonatal unit, where new-born babies are cared for. The focus is High dependency cots. Recommendations produced are subject to human factors and implementation difficulties. In this work, Systems Thinking facilitates an understanding of relationships; Enterprise Architecture helps embed the context and address complexity; while Clinical Medicine underpins decision-making for individual patients. Research outputs include the Conceptual Research Framework, a Quality Metric, a Cot Predictor Tool and a Markovian model Design, which can be adapted in the future. Furthermore there is the milieu or connective ‘glue’, to provide unity. The methodology or Enterprise Modelling helps address the issue by facilitating understanding of both overview and detail.
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Liu, Wei 1975. "Network traffic modelling and analysis." Thesis, McGill University, 2005. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=82613.
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In all-photonic networks, both transmission and switching is performed in the optical domain, without optoelectronic conversion for the data traversing the network. An accurate traffic model is critical in an agile all-photonic network (AAPN) which has the ability to dynamically allocate bandwidth to traffic flows as the demand varies.This thesis focuses on traffic modelling and analysis. A novel traffic model is proposed which can capture the traffic behaviours in all-photonic networks. The new model is based on a study of existing traffic modelling literature. It combines the time-varying Poisson model, gravity model and fractional Gaussian noise. This model can be used for the short-range traffic prediction. We examine Long-Range Dependence and test the time constancy of scaling parameters using the tools designed by Abry and Veitch, to analyze empirical and synthesized traffic traces.
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Bergmann, Daniel. "Genetic network modelling and inference." Thesis, University of Nottingham, 2010. http://eprints.nottingham.ac.uk/11209/.
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Modelling and reconstruction of genetic regulatory networks has developed in a wide field of study in the past few decades, with the application of ever sophisticated techniques. This thesis looks at how models for genetic networks have been developed from simple Boolean representations to more complicated models that take into account the inherent stochasticity of the biological system they are modelling. Statistical techniques are used to help predict the interaction between genes from microarray data in order to recover genetic regulatory networks and provide likely candidates for interactions that can be experimentally verified. The use of Granger causality is applied to statistically assess the effect of one gene upon another and modifications to this are presented, with bootstrapping used to understand the variability present within the parameters. Given the large amounts of data to be analysed from microarray experiments, clustering techniques are used to help reduce the computational burden and novel algorithms are developed to make use of such clustered data. Variability within clusters is also considered, by developing a novel approach with the use of principal component analysis. These algorithms that are developed are implemented with an observed dataset from Xenopus Laevis that has many genes but few timepoints in order to assess their effectiveness under such limited data. Predictions of likely interactions between genes are provided from the algorithms developed and their limitations discussed. Using extra information is considered, where a further dataset of gene knockout data is used to verify the predictions made for one particular gene.
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Zadik, Daniel. "Network modelling of canine metabolism." Thesis, University of Nottingham, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.546533.
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Attenborough, F. R. "The modelling of network polymers." Thesis, University of Liverpool, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.243243.
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This thesis considers the modelling of two and three dimensional molecular networks with a view to being able to predict how the geometry of a network will affect the elastic constants and specifically the Poisson's ratios of the network. Materials with negative Poisson's ratios have much better engineering properties then those with positive Poisson's ratios. Theory states that a network polymer, with negative Poisson's ratios at a molecular level, would have much better properties than most materials with negative Poisson's ratios made to date. Molecular modelling has been used to examine the elastic constants of those two and three dimensional network polymers which are most likely to be synthesised in the near future. Such networks have been predicted to have either large positive or large negative Poisson's ratios depending on the molecular arrangement of the network. Poisson's ratios varying between 0.96 and -0.86 for the three dimensional cases and between -0.9 and 1.26 for the two dimensional cases have been calculated. Young's moduli in the order of 1 GPa have been observed for the three dimensional networks as compared to Young's moduli in the order of 20 - 400 kPa which have been experimentally measured for foam materials. Comparison with local density functional calculations for two 2-D networks with the molecular modelling have confirmed the negative Poisson's ratio in these networks and shown that it is not a function of the molecular modelling packages or force field used. The off-axis properties for both the two and three dimensional networks have been calculated. These show that whilst the networks with a positive Poisson's ratio in the principal axis directions always have a positive Poisson's ratio, those networks with a negative Poisson's ratio in the principal axis directions have off-axis Poisson's ratios that vary between large and positive and large and negative. In general the networks with positive Poisson's ratios are much more isotropic than those with negative Poisson's ratios. Analytical models which model the networks using simple beam theory have been produced for various two and three dimensional networks. These models can be used to predict the elastic constants of a network without the need to do time consumingmolecular modelling calculations to a first approximation. Comparison of the molecular models and analytical models has led to the development a library of force constants for two dimensional networks which can be used to more accurately predict the elastic constants of a network based on a knowledge of the geometry of the network and the constituent `sub-units' from which it is made
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Wang, Hao. "Performance modelling of network management schemes for mobile wireless networks." Thesis, University of Edinburgh, 2009. http://hdl.handle.net/1842/13192.
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Baronikian, Haig. "Modelling and analysis of a computer conferencing system." Thesis, McGill University, 1987. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=63756.
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Randrianandrasana, Michel F. "Finding structures in information networks using the affinity network." Thesis, Aston University, 2011. http://publications.aston.ac.uk/15684/.
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This thesis proposes a novel graphical model for inference called the Affinity Network,which displays the closeness between pairs of variables and is an alternative to Bayesian Networks and Dependency Networks. The Affinity Network shares some similarities with Bayesian Networks and Dependency Networks but avoids their heuristic and stochastic graph construction algorithms by using a message passing scheme. A comparison with the above two instances of graphical models is given for sparse discrete and continuous medical data and data taken from the UCI machine learning repository. The experimental study reveals that the Affinity Network graphs tend to be more accurate on the basis of an exhaustive search with the small datasets. Moreover, the graph construction algorithm is faster than the other two methods with huge datasets. The Affinity Network is also applied to data produced by a synchronised system. A detailed analysis and numerical investigation into this dynamical system is provided and it is shown that the Affinity Network can be used to characterise its emergent behaviour even in the presence of noise.
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Bilal, Muhammad Shahid. "Large Scale Modelling of Striatal Network." Thesis, KTH, Matematik (Inst.), 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-103502.
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Numerical simulations play an important role to uncover the dynamic behaviour at the cellular and network levels and accelerate the work in the field of Neuroscience. The modern computational technologies have made it possible to simulate a huge network of neurons which was possible only in theory two decades ago. The simulations of networks of thousand of neurons are carried out on the parallel machine Cray XE6 system, based on the AMD Opteron 12-core which shows good scaling properties. These models can be beneficial for the generation of global behaviour which could not be produced by fewer cells. For example, the effect of inhibition in a striatal network of MSNs is only seen if the number of cells and the synapses are increased sufficiently. The simulated responses of cells are greatly influenced by the numerical scheme. This has been demonstrated using gap junctions between striatal fast spiking inter-neurons. Implicit numerical schemes need to be used in order to get stable and accurate results. The simulations are carried out using serial and parallel implementations on the GENESIS and PGENESIS simulator respectively. The limitations of the simulators have been highlighted by performing several simulation experiments. After exploiting the shortcomings presented in this work, it would be possible to use the insight to investigate biologically relevant questions.Numeriska simuleringar har en stor betydelse när man vill undersöka och förstå dynamiska fenomen på cell- och nätverksnivå. Detta är mycket viktigt för hela neuroområdet. Dagens beräkningsteknologier har gjort det möjligt att simulera stora nätverk av neuroner, vilket knappast var realistiskt för 10-20 år sedan. Simuleringar av nätverk som består av tusentals neuroner kan göras lokalt på KTH på en parallelldator som heter Cray XE6 och som är baserad på AMD Opteron 12-core,med goda skalningsegenskaper. Sådana nätverkssimuleringar är nödvändiga för att undersöka det globala beteendet i nätverket vilket inte kan produceras med färre antal celler. Ett exempel på en nätverkseffekt som endast kan ses i en storskalig modell är hur inhibitionen mellan s.k. medium spiny neurons (MSNs) i det striatal nätverket fungerar. Eftersom inhibitionen mellan varje cellpar är mycket svag behövs input från många celler för att nätverket skall påverkas. Simuleringsresultaten påverkas signifikant av vilken numerisk metod som används. Detta demonstreras med ett striatalt nätverk innehållande s.k. gap junctions (elektriska synapser) mellan striatala fast-spiking interneurons (FS). Implicita numeriska metoder blir nödvändiga för att få stabila och riktiga resultat. Simuleringar görs både seriellt och parallellt med hjälp m.h.a. Genesis simulatorn (PGenesis för parallella implementationer), vilket är en standardsimulator för biofysikaliskt detaljerade neuronmodeller. För att utvärdera Genesis simulatorn och dess svagheter har flera simuleringsexperiment utförts. Insikter från dessa simuleringar, vilka diskuteras i detta arbete, kan hjälpa till att lägga en grund för framtida användning av Genesis för storskaliga simuleringar.
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Brewer, Daniel Simon. "Modelling the p53 gene regulatory network." Thesis, University College London (University of London), 2006. http://discovery.ucl.ac.uk/1445328/.
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p53 is the central protein in the DNA damage response and is part of a complex and extensive gene regulatory network. This network integrates a variety of stress signals to produce the up-regulation of active p53 and a range of effects including apoptosis, growth arrest and DNA damage repair. The p53 system has typically been studied qualitatively as a linear pathway, however this approach is insufficient to gain a full functional under standing of the dynamic nature of the network. In this work a better description of the DNA damage response will be constructed through the use of mathematical techniques. Ordinary differential equations models of the p53 network between DNA damage and p53 up-regulation are proposed, including a model that takes into account various localisation mechanisms. Parameter estimation is required to validate these models with biological data. A number of established techniques axe examined along with a novel method based on linear algebra, collocation and B-splines. To examine the network downstream of p53 and the global response to DNA damage, a "G" time profile (Gg(t)) quantifying the activity driving the formation of each gene is constructed. This is derived from a model of gene transcription, microarray data and mRNA degradation rates. The new parameter estimation technique developed works significantly better than the other techniques examined. Also, it was found that the mechanisms that control the location of p53 significantly contribute to the rapid DNA damage response. The G time profiles suggest that there are four principal transcription activities in the DNA damage response: p53, an early peaking response (possibly AP-1), stopping and restarting the cell cycle, and a double peaked response. The G time profile in combination with a training set of genes can be used to successfully find confirmed p53 targets.
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Krause, Andrew Leslie. "Network modelling of bioactive porous media." Thesis, University of Oxford, 2017. http://ora.ox.ac.uk/objects/uuid:980a0fd8-96a7-4818-904a-0842d4efbd41.
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In this thesis we consider several approaches to modelling interactions between fluid flow and cell proliferation in a bioactive porous medium. This is motivated by models of cell growth within tissue engineering scaffolds placed in perfusion bioreactors. These scaffolds are porous materials used to facilitate nutrient transport to cells placed within them. Recent modelling efforts have sought to understand the influence that cells have on the effective permeability of these tissue scaffolds, and hence on the capacity of the porous medium to facilitate fluid and nutrient transport, which enhances the overall growth of tissue within a scaffold. Contemporary experimental and theoretical studies have emphasized the importance of mechanical forcing on cells due to their environment. We therefore consider simple models of cell growth that assume cells are affected by the fluid itself, either via shear stress, hydrostatic pressure, or local flow rate, and that cell growth influences the local permeability of the scaffold at higher cell densities via pore-blocking. Hence, we are interested in the feedback between cell growth and fluid flow within a bioactive porous medium. It is within this simplified context of fluid-growth interaction that we explore different approaches to modelling the spatial structure of the pore network, and the influence that this has on the cell density distribution throughout the scaffold. Models in the literature are often spatially homogeneous (ODE) or spatially continuous (PDE), only implicitly accounting for the discrete pore network of the medium. The pore and scaffold length scales in typical experiments with perfusion bioreactors can lead to scaffolds with relatively few pores, and it is unclear that macroscopic spatially averaged (homogenized) continuous models will capture features present in small pore networks. We propose a suite of spatially continuous models, modified from existing PDE approaches in the literature, and compare these to discrete lattice (ODE) systems in order to elucidate differences between these modelling paradigms. We also use the structure of the lattice model to explore stochastic analogues that are computationally and theoretically amenable to analysis. We explore behaviours of these models via numerical simulations, bifurcation analyses, and asymptotic reductions to simpler systems. Our lattice modelling approach provides a 'mesoscopic' perspective, where the effective equations governing the cell growth and fluid flow are prescribed as ODEs at each pore. These capture the microscale dynamics at the pore scale, as opposed to homogenization approaches where the microscale is explicitly related to macroscale equations. This also allows us to use tools from dynamical systems theory which are substantially more tractable in the finite dimensional setting of ODEs (with algebraic conditions for the fluid flow), as opposed to the infinite dimensional setting of PDEs (consisting of coupled elliptic and parabolic equations). Additionally, we do not have to worry about issues of numerical convergence or existence of solutions that are important in the spatially continuous setting. Our emphasis on mesoscopic governing equations makes this network-based approach somewhat unique in the tissue engineering community. We demonstrate qualitative and quantitative differences between these continuum and network paradigms, and in particular show behaviours captured by explicitly accounting for the discrete pore network that are not captured in spatially continuous models. For each kind of fluid-cell interaction, we classify behaviours depending on nondimensional model parameters in order to elucidate in what regimes discrete models may provide useful insights into bioactive porous materials. We also discuss computational considerations for analyzing these kinds of models, and in particular suggest that stochastic and discrete models may be easier to simulate in some parameter regimes compared to typical spatially continuous models. Our results suggest several novel approaches to pursue in accounting for the finite discrete nature of bioactive porous media, and we highlight several useful further directions.
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Theparod, Thitiya. "Network modelling for sexually transmitted diseases." Thesis, Lancaster University, 2015. http://eprints.lancs.ac.uk/82239/.
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The aim of this thesis is to propose suitable mathematical models for the analysis of sexually transmitted disease epidemics. We are interested in a closed population, where infections are only transmitted through heterosexual contacts. The population is hence divided into two groups: male and female. Individuals are classified according to gender, relationship and disease status. Both stochastic and deterministic SIS models are employed. The stochastic models are formulated in terms of a Markov process with a finite state space. Two main models are constructed and quantities of interest such as the basic reproduction number and endemic level of the sexually transmitted disease (STD) are obtained. The first model is formulated to describe dynamics of STDs, where the sexual behaviour is considered “faithful”. By being faithful, we mean individuals are monogamous, and there are no casual sexual contacts (one-night stands). The early stages of the epidemic are approximated by a 2-type branching process. This allows us to compute the following quantities of interest, the threshold parameter (R0) and the probability of extinction. In order to study the endemic level, it is helpful to use the deterministic (ODE) approximation of the stochastic SIS epidemic. The behaviour about the endemic equilibrium is studied using an Ornstein-Uhlenbeck process. Stochastic simulations are utilised to obtain the mean time to extinction. The second model is an extension of the first model, where casual sexual contacts (one - night stands) are included in the model. The model is again a Markov process but its analysis is more involved. A key difference is now a 5 type branching process is used to approximate the initial stages of the epidemic, to determine the threshold parameter (R0) and the probability of extinction. Other quantities of interest are studied through similar approaches. Medication use is studied as a control measure in this thesis. We introduce a new parameter (v) governing the medication use into both models. Throughout we study the effect of the control strategies on the key quantities of interest highlighted above.
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Rasouli, Mohammad. "Trip distribution modelling using neural network." Thesis, Curtin University, 2014. http://hdl.handle.net/20.500.11937/669.
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In this research a new generalized regression neural network (GRNN) model has been researched to estimate the distribution of journey to work trips. As a case study, the model was applied to the journey to work trips in the City of Mandurah in Western Australia. The results of the GRNN model were compared with the well-known doubly-constrained gravity model and the Back-Propagation model and its superiority over these models has been demonstrated.
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Gabrys, Bogdan. "Neural network based decision support : modelling and simulation of water distribution networks." Thesis, Nottingham Trent University, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.387534.
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Yaveroglu, Omer Nebil. "Graphlet correlations for network comparison and modelling : World Trade Network example." Thesis, Imperial College London, 2013. http://hdl.handle.net/10044/1/25523.
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We propose methods on two fundamental graph theoretic problems: (1) network comparison, and (2) network modelling. Our methods are applied to five real-world network types, with an emphasis on world trade networks (WTNs), which we choose due to the world's current economic crisis. Finding topological similarities of complex networks is computationally intractable due to NP-Completeness of the subgraph isomorphism problem. Hence, simple heuristics have been used for this purpose. The most sophisticated heuristics are based on graph spectra and small subnetworks including graphlets. Among these, graphlets are preferred since spectra do not provide a direct real-world interpretation of network structure. However, current graphlet-based techniques can be improved. We improve graphlet-based heuristics by defining a new network topology descriptor, Graphlet Correlation Matrix (GCM), which eliminates all redundancies and quantifies the dependencies in graphlet properties. Then, we introduce a new network distance measure, Graphlet Correlation Distance (GCD), that compares GCMs of two networks. We show that GCD has the best network classification performance, is highly noise-tolerant, and is computationally efficient. Using this methodology, we highlight a three-layer organization in the WTNs: core, broker, and periphery. Furthermore, we uncover the link between the dynamic changes in oil price and trade network topology. Network models should shed light on the rules governing the formation of real networks. Using GCD, we identify models that fit five real-world network types. However, none of these standard network models fit WTNs. Hence, we introduce two new network models: one that mimics the Gravity Model of Trade, and the other that mimics brokerage / peripheral positioning of a country in WTN. Also, we show that economic wealth indicators of a country are predictive of its future brokerage position. Finally, we use exponential-family random graph modelling approach to build a generic framework that enables modelling based on any graphlet property.
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Gonzalez, Hosta Joan. "Dynamical Modelling of a Metabolic Reaction Network." Thesis, KTH, Reglerteknik, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-106221.
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In a cell culture system, a lot of compounds are involved considering the ones contained in the medium (extracellular) and the intracellular environment. Studies of the different system behaviours adopted due to variations in the medium concentrations are typically based on empirical or statistical approaches when working with such an amount of compounds. In this paper is presented a method to develop a dynamical model of a cell culture system which can predict the evolution of the medium compounds and cell growth along the time for this kind of systems. The method has been implemented as a standardised tool that can be used for any kind of biological system when a pre-defined metabolic network and data of different states are available. In parallel to this project, a medium where the exact concentrations of all the compounds are known and should let the cells live properly have been developed by the KTH Division of Bioprocess. The system corresponding to the experiments carried out to develop the medium has been modelled using the proposed method. The results have been analysed and the conclusions, requirements and drawbacks of the model have been discussed.
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Xie, Qingsheng. "Network manufacturing systems : modelling, implementation and applications." Thesis, Leeds Beckett University, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.435466.
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Barry, Thomas Andrew Linden. "Modelling of methods for wireless network access." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ40463.pdf.
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Tupas, Ronald-Ray Tiñana. "Artificial neural network modelling of filtration performance." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape4/PQDD_0011/MQ59890.pdf.
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Huang, Yan, and 黃艷. "Neural network modelling of coastal algal blooms." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2001. http://hub.hku.hk/bib/B43894872.
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Hind, Alan. "Parallel simulation techniques for telecommunication network modelling." Thesis, Durham University, 1994. http://etheses.dur.ac.uk/5520/.
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In this thesis, we consider the application of parallel simulation to the performance modelling of telecommunication networks. A largely automated approach was first explored using a parallelizing compiler to speed up the simulation of simple models of circuit-switched networks. This yielded reasonable results for relatively little effort compared with other approaches. However, more complex simulation models of packet- and cell-based telecommunication networks, requiring the use of discrete event techniques, need an alternative approach. A critical review of parallel discrete event simulation indicated that a distributed model components approach using conservative or optimistic synchronization would be worth exploring. Experiments were therefore conducted using simulation models of queuing networks and Asynchronous Transfer Mode (ATM) networks to explore the potential speed-up possible using this approach. Specifically, it is shown that these techniques can be used successfully to speed-up the execution of useful telecommunication network simulations. A detailed investigation has demonstrated that conservative synchronization performs very well for applications with good look ahead properties and sufficient message traffic density and, given such properties, will significantly outperform optimistic synchronization. Optimistic synchronization, however, gives reasonable speed-up for models with a wider range of such properties and can be optimized for speed-up and memory usage at run time. Thus, it is confirmed as being more generally applicable particularly as model development is somewhat easier than for conservative synchronization. This has to be balanced against the more difficult task of developing and debugging an optimistic synchronization kernel and the application models.
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Jolliffe, Andrew Donald. "Modelling ventilation in the human tracheobronchial network." Thesis, University of Hertfordshire, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.365986.
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Weng, Jialai. "On advanced channel modelling for network planning." Thesis, University of Sheffield, 2016. http://etheses.whiterose.ac.uk/22361/.
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With the increasing demand for high speed wireless network services, the next generation wireless networks are proposed to use advanced wireless communication technologies. These technologies include massive MIMO, mmWave and distributed MIMO. In order to deploy wireless networks equipped with these technologies, channel models capturing the channel features and characteristics of these wireless technologies are essential in the planning and optimisation of networks. However, conventional channel models lack the capability to support these next generation network technologies. In this PhD thesis, I investigated the channel models for the next generation wireless technologies, including massive MIMO, mmWave communications and distributed MIMO. I developed channel models for network planning and optimisation based on conventional ray launching algorithms for these wireless technologies. The models have been validated and applied to optimise network performance. The existing challenge in wireless channel modelling is the improvement of modelling accuracy without increasing modelling complexity. In order to achieve this goal, a new calibration method is developed to improve the accuracy of the predication model when measurements are available. Moreover, in order to use the channel models as an effective tool in wireless network planning and optimisation, a new wireless capacity definition from radio propagation perspective is also investigated. It provides insight to the physical limit of wireless channel capacity from a radio propagation perspective.
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Cowley, Daniel J. "Modelling species movement using electric network theory." Thesis, University of Bristol, 2015. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.678206.
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McLoone, Sean Francis. "Neural network training for modelling and control." Thesis, Queen's University Belfast, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.337109.
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Huang, Yan. "Neural network modelling of coastal algal blooms." Hong Kong : University of Hong Kong, 2001. http://sunzi.lib.hku.hk/hkuto/record.jsp?B25248510.
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Athanasiadis, Ignatios. "Hydro-mechanical network modelling of porous geomaterials." Thesis, University of Glasgow, 2017. http://theses.gla.ac.uk/8204/.
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The microstructure of porous geomaterials strongly influences macroscopic hydro-mechanical properties, such as fluid retention, conductivity and stiffness. These properties are of importance for predicting the performance of many engineering applications, such as waste barriers and flood defence embankments. Predicting these properties with confidence requires a thorough understanding of processes at the microscale and their effect on macroscopic phenomenological properties. For unsaturated geomaterials, providing this understanding requires still further research. In this study, network models representing processes in the pore structure and solid skeleton were developed with the aim to improve the required understanding to link processes at the micro-scale to macroscopic properties. The objectives were to develop a new coupled hydro-mechanical network model, with main application the improvement of understanding of the influence of microstructure on the retention behaviour and conductivity of porous geomaterials, the mechanical response in the form of the elastic stiffness, and their interaction. The model is valid for investigation of transport and mechanical aspects geomaterials such as concrete, rocks, sand and clay soils with length scales of the pore radii spanning from sub-μm to mm. In the present network models, the microstructure of the material is idealised by means of a network of voids for the transport response and a network of grains/particles representing the solid skeleton response. For the transport network, the void structure is idealised by spheres representing large voids and pipes for the interconnecting narrow throats. The structural network of grains is modelled by rigid polyhedra connected by springs which contain information related to the constitutive response of the skeleton. The geometry of the networks is determined by dual irregular Delaunay and Voronoi tessellations based on random sets of points. For the transport network, the spheres and pipes were placed on the Voronoi polyhedral vertices and along the ridges, respectively. The mechanical elements were placed on the edges of the Delaunay tetrahedra. In addition to the irregular arrangement of elements, microstructural heterogeneity was introduced by assigning the radii of the spheres and pipes as well as the polyhedra contact areas from probability distributions. New techniques to provide Periodic Boundary Conditions for representative cells generated by the irregular networks were developed. Another new feature of the model is a pore scaling technique which improves the modelling of the retention behaviour. For being able to perform simulations of representative cells of the coupled networks, the model was implemented in a finite element framework. The correct development and implementation of the network models was verified by comparison with a range of analytical solutions. Furthermore, a sensitivity study was performed to investigate the qualitative macroscopic response of the material in the form of retention behaviour, conductivity and stiffness for important model parameters. For the influence of the cell size on the macroscopic properties, it was found that for large cell sizes, the macroscopic response of the model is independent of a change of the cell size. For all macroscopic properties investigated, the mean converges to a representative value. Furthermore, the standard deviation approaches zero for large cells for almost all cases. Only for a small range of very low conductivities for highly unsaturated conditions, the standard deviation did not decrease with increasing cell size, which was attributed to the occurrence of percolation. In addition to the verification part, a calibration strategy was developed for the transport part of the model. Then, the model was used to predict the relative conductivity of unsaturated geomaterials reported in the literature. The agreement between the numerical prediction and the experimental results for degree of saturation and relative permeability was found to be very good. The model presented possibility to predict evolution of relative permeability when calibrated to match retention experimental data.
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Holzhauer, Sascha [Verfasser]. "Dynamic Social Networks in Agent-based Modelling : Increasingly Detailed Approaches of Network Initialisation and Network Dynamics / Sascha Holzhauer." Kassel : Kassel University Press, 2017. http://d-nb.info/1137030445/34.
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Littlewort, G. C. "Neural network analysis and simulation." Thesis, University of Oxford, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.292677.
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Holovatch, T. "Complex transportation networks : resilience, modelling and optimisation." Thesis, Coventry University, 2011. http://curve.coventry.ac.uk/open/items/eafefd84-ff08-43cf-a544-597ee5e63237/1.
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Wahab, Junaid, and Zubair Ali. "Improved Energy Modelling of Wireless Personal Area Network." Thesis, Halmstad University, School of Information Science, Computer and Electrical Engineering (IDE), 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:hh:diva-2615.
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Wireless sensors networks are used in a variety of environments ranging from environment
monitoring such as humidity and temperature, to environments like patient monitoring, habitat
monitoring etc. Sometimes sensors are deployed in inaccessible or hazardous places, and they
are battery operated; recharging or changing the sensor’s battery is almost impossible.
In such scenarios, where the battery can not be recharged or changed, it is crucial to know in
advance how long the battery will last so that the old sensor node can be replaced by a new
one. Normally, in order to effectively utilize the battery the components of a wireless sensor
node are turned off when not needed.
This paper presents an in-depth analysis of the importance of switching sensor node
components, and its impact on the life time prediction. A new energy model is presented
which caters for the current and time consumed in switching from one mode to another. A
comparison is made between scenarios where current consumption while switching is catered
with the one where it is not catered. This was achieved by using on chip fuel gauge, with
some limitation, which was verified by using digital multimeter.
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Urquhart, Andrew J. "Accuracy of low voltage electricity distribution network modelling." Thesis, Loughborough University, 2016. https://dspace.lboro.ac.uk/2134/21799.
Full textAbstract:
The connection of high penetrations of new low carbon technologies such as PV and electric vehicles onto the distribution network is expected to cause power quality problems and the thermal capacity of feeder cables may be exceeded. Replacement of existing infrastructure is costly and so feeder cables are likely to be operated close to their hosting capacity. Network operators therefore require accurate simulation models so that new connection requests are not unnecessarily constrained. This work has reviewed recent studies and found a wide range of assumptions and approximations that are used in network models. A number of these have been investigated further, focussing on methods to specify the impedances of the cable, the impacts of harmonics, the time resolution used to model demand and generation, and assumptions regarding the connectivity of the neutral and ground conductors. The calculation of cable impedances is key to the accuracy of network models but only limited data is available from design standards or manufacturers. Several techniques have been compared in this work to provide guidance on the level of detail that should be included in the impedance model. Network modelling results with accurate impedances are shown to differ from those using published data. The demand data time resolution has been shown to affect estimates of copper losses in network cables. Using analytical methods and simulations, the relationship between errors in the loss estimates and the time resolution has been demonstrated and a method proposed such that the accuracy of loss estimates can be improved. For networks with grounded neutral conductors, accurate modelling requires the resistance of grounding electrodes to be taken into account. Existing methods either make approximations to the equivalent circuit or suffer from convergence problems. A new method has been proposed which resolves these difficulties and allows realistic scenarios with both grounded and ungrounded nodes to be modelled. In addition to the development of models, the voltages and currents in a section of LV feeder cable have been measured. The results provide a validation of the impedance calculations and also highlight practical difficulties associated with comparing simulation models with real measurement results.
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Lee, Yong Wha. "Modelling and dynamic routing for computer queueing network." Thesis, University of Ottawa (Canada), 1985. http://hdl.handle.net/10393/4678.
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Leung, Chi-chung. "Modelling complex network dynamics a statistical physics approach /." Click to view the E-thesis via HKUTO, 2006. http://sunzi.lib.hku.hk/hkuto/record/B38324611.
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Konstatinos, Sasloglou. "Channel measurements and modelling for sensor network applications." Thesis, University of Strathclyde, 2010. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=12833.
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Qadir, Fayyaz Mahmood. "Incorporating reliability into network modelling for policy analysis." Thesis, University of Leeds, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.522974.
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Leung, Chi-chung, and 梁志聰. "Modelling complex network dynamics: a statistical physics approach." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2006. http://hub.hku.hk/bib/B38324611.
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Vince, Emma Pierina. "Using neural network modelling to detect eating disorders." Thesis, University of Bath, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.426288.
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Gomez, E. Ribes. "Wavelet neural network algorithms and architectures : nonlinear modelling." Thesis, Queen's University Belfast, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.273393.
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Wu, Z.-D. "Performance modelling of Cambridge ring based local network." Thesis, University of Kent, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.376339.
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Whitlock, Mark E. "A Bayesian approach to road traffic network modelling." Thesis, University of Kent, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.311262.
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Harvey, David Robert. "Neural network modelling of a planar walking biped." Thesis, University of Portsmouth, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.422899.
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Pirouti, Marouf. "Modelling and analysis of a district heating network." Thesis, Cardiff University, 2013. http://orca.cf.ac.uk/45201/.
Full textAbstract:
District heating systems have the potential to contribute to the UK renewable energy targets. However, there are a number of economic barriers which would have to be addressed in order to make district heating competitive in comparison with alternative heating technologies. The objective of this research was to model and analyse a district heating network and develop an optimisation method to calculate the minimum capital investment, heat losses and pump energy consumption. Firstly, modelling and analysis of a district heating network was conducted to obtain district heating design cases with minimum annual total energy consumption, annual total exergy consumption and annualised cost. Then through the analysis, a two-stage programming model was developed which synthesised design and optimal operation of a district heating network. The optimisation was used to minimise annual total energy consumption, annual total exergy consumption or annualised cost of the heat network by selecting suitable pump and pipe sizes, taking into account different parameters such as target pressure loss, temperature regime and operating strategy. The optimisation technique was used to investigate two different case studies, with high and low heat density. In all cases, a variable flow and variable supply temperature operating method was found to be beneficial. Design cases with minimum annual total energy consumption and annualised cost used rather small pipe diameters and large pressure drops. To achieve the minimum annual total exergy consumption a design case with larger pipe diameters and smaller pressure loss was found to be desirable. It was observed that by reducing the water temperature and increasing temperature difference between supply and return pipes, the annual total energy consumption, annual total exergy consumption and the annualised cost were reduced. It was also shown that district heating in an area with high heat density is more energy efficient and cost effective.
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Tsertou, Athanasia. "Modelling interference in a CSMA/CA wireless network." Thesis, University of Edinburgh, 2006. http://hdl.handle.net/1842/14589.
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Initially, a systematic characterisation of all the possible ways in which two communicating pairs of nodes can interfere with each other is made. Using this as a building block and assuming independence of the stations, an estimate for the network throughput can be derived. The latter proves to be quite accurate for symmetric networks and manages to follow the performance trends in an arbitrary network. Following this, a more detailed Markovian-based mathematical model is proposed for the analysis of the hidden node case. This approach does not rely on common assumptions, such as renewal theory and node synchronisation, and is highly accurate, independently of the system parameters, unlike prior methods. Moreover, the usual decoupling approximation is not adopted; on the contrary, a joint view of the competing stations is taken into consideration. The model is firstly developed based on the assumption that the network stations employ a constant contention window for their backoff process. However, later in the thesis this assumption is relaxed, and performance curves are derived for the case when the stations employ the Binary Exponential Backoff Scheme, as is the case in practice. The Markovian state space is kept relatively small by employing an iterative technique that computes the unknown distributions. The adoption of this technique makes the analysis computationally efficient.
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Murray-Smith, Roderick. "A local model network approach to nonlinear modelling." Thesis, University of Strathclyde, 1994. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=27067.
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This thesis describes practical learning systems able to model unknown nonlinear dynamic processes from their observed input-output behaviour. Local Model Networks use a number of simple, locally accurate models to represent a globally complex process, and provide a powerful, flexible framework for the integration of different model structures and learning algorithms. A major difficulty with Local Model Nets is the optimisation of the model structure. A novel Multi-Resolution Constructive (MRC) structure identification algorithm for local model networks is developed. The algorithm gradually adds to the model structure by searching for 'complexity' at ever decreasing scales of 'locality'. Reliable error estimates are useful during development and use of models. New methods are described which use the local basis function structure to provide interpolated state-dependent estimates of model accuracy. Active learning methods which automatically construct a training set for a given Local Model structure are developed, letting the training set grow in step with the model structure - the learning system 'explores' its data set looking for useful information. Local Learning methods developed in this work are explicitly linked to the local nature of the basis functions and provide a more computationally efficient method, more interpretable models and, due to the poor conditioning of the parameter estimation problem, often lead to an improvement in generalisation, compared to global optimisation methods. Important side-effects of normalisation of the basis functions are examined. A new hierarchical extension of Local Model Nets is presented: the Learning Hierarchy of Models (LHM), where local models can be sub-networks, leading to a tree-like hierarchy of softly interpolated local models. Constructive model structure identification algorithms are described, and the advantages of hierarchical 'divide-and-conquer' methods for modelling, especially in high dimensional spaces are discussed. The structures and algorithms are illustrated using several synthetic examples of nonlinear multivariable systems (dynamic and static), and applied to real world examples. Two nonlinear dynamic applications are described: predicting the strip thickness in an aluminium rolling mill from observed process data, and modelling robot actuator nonlinearities from measured data. The Local Model Nets reliably constructed models which provided the best results to date on the Rolling Mill application.
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Birch, Jenna. "Modelling financial markets using methods from network theory." Thesis, University of Liverpool, 2015. http://livrepository.liverpool.ac.uk/2028739/.
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This thesis discusses how properties of complex network theory can be used to study financial time series, in particular time series for stocks on the DAX 30. First, we make a comparison between three correlation-based networks: minimum spanning trees; assets graphs and planar maximally filtered graphs. A series of each of these network types is created for the same dataset of time series' of DAX 30 stocks and we consider what information each network can provide about the relationship between the stock prices from the underlying time series. We also analyse two specific time periods in further detail - a period of crisis and a period of recovery for the German economy. Next, we look at the structure and representations of planar maximally filtered graphs and in particular we consider the vertices that form the 3-cliques and 4-cliques [Tumminello et al. (2005)] state '... normalizing quantities are n_s - 3 for 4-cliques and 3n_s - 8 for 3-cliques. Although we lack a formal proof, our investigations suggest that these numbers are the maximal number of 4-cliques and 3-cliques, respectively, that can be observed in a PMFG of n_s elements.' Within this thesis we provide a proof for these quantities and a different construction algorithm. Finally, rather than correlation-based networks, we discuss two relatively new types of networks: visibility graphs and the geometrically simpler horizontal visibility graphs. We review the field's that these networks have already been applied to and consider if this is an appropriate method to apply to financial time series - specifically stock prices. We also consider using horizontal visibility graphs as a method for distinguishing between random and chaotic series within stock price time series.
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Jia, Nan. "Refinery hydrogen network optimisation with improved hydroprocessor modelling." Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/refinery-hydrogen-network-optimisation-with-improved-hydroprocessor-modelling(e9fe6201-0e62-4b10-b51d-fe747f811ea1).html.
Full textAbstract:
Heavier crude oil, tighter environmental regulations and increased heavy-end upgrading in the petroleum industry are leading to the increased demand for hydrogen in oil refineries. Hence, hydrotreating and hydrocracking processes now play increasingly important roles in modern refineries. Refinery hydrogen networks are becoming more and more complicated as well. Therefore, optimisation of overall hydrogen networks is required to improve the hydrogen utilisation in oil refineries. In previous work for hydrogen management many methodologies have been developed for H2 network optimisation, all with fixed H2/Oil ratio and H2 partial pressure for H2 consumers, which may be too restrictive for H2 network optimisation. In this work, a variable H2/Oil and H2 partial pressure strategy is proposed to enhance the H2 network optimisation, which is verified and integrated into the optimisation methodology. An industrial case study is carried out to demonstrate the necessity and effectiveness of the approach. Another important issue is that existing binary component H2 network optimisation has a very simplistic assumption that all H2 rich streams consist of H2 and CH4 only, which leads to serious doubts about the solution's validity. To overcome the drawbacks in previous work, an improved modelling and optimisation approach has been developed. Light-hydrocarbon production and integrated flash calculation are incorporated into a hydrogen consumer model. An optimisation framework is developed to solve the resulting NLP problem. Both the CONOPT solver in GAMS and a simulated annealing (SA) algorithm are tested to identify a suitable optimisation engine. In a case study, the CONOPT solver out-performs the SA solver. The pros and cons of both methods are discussed, and in general the choice largely depends on the type of problems to solve.