Дисертації з теми "Modelling studies"
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1
Ismail, Raveem. "Modelling studies on global contrails." Thesis, University of Oxford, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.669992.
2
Cullum, Jodie. "Modelling studies of exoplanetary oceans." Thesis, University of East Anglia, 2018. https://ueaeprints.uea.ac.uk/67833/.
Анотація:
The ocean plays a key role in the climate of Earth, and it is therefore expected that any oceans present on an exoplanet would also be a crucial component of the climate system and hence have implications for the habitability of the planet. However, many planetary and oceanic properties cannot be assumed to be the same on an exoplanet as on Earth, and therefore the behaviour of the ocean cannot be assumed. Here, basic land configurations are explored and a single meridional barrier is used throughout the other experiments, as this is the simplest configuration of any substantial land mass. The effect of ocean salinity, at a level both higher and lower than on Earth, is explored for the first time and reversal of the Earth-like meridional overturning circulation is found. The proportionality between mean salinity and salinity gradients in the ocean is established. The impact of planetary rotation period is also investigated, and it is concluded that a longer rotation period results in a greater poleward ocean heat transport, with the additional novel conclusions of a shallower thermocline depth, increased horizontal ocean velocities, and stronger overturning circulation. Finally, existing ocean modelling of a tidally locked configuration is furthered by the addition of different land masses, the extent of the zonal circulation and magnitude of the zonal heat transport is found to have significant dependence on the location of a meridional barrier in the ocean, with resulting dark side mean temperatures varying by over 7 ̋C. The modelling presented here highlights the importance of the consideration of the ocean in exoplanetary climate studies, and its role in planetary habitability.
3
Henderson, Ian A. "Studies related to measurement and modelling." Thesis, University of Strathclyde, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.248871.
4
Oliver, Sophia. "Modelling studies of the atmospheric tides." Thesis, University of Oxford, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.365773.
5
Downing, Anna Kristina. "NMR structural studies and modelling proteins." Thesis, University of Oxford, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.334225.
6
Sands, Zara Amanda. "Modelling studies of DNA recognition events." Thesis, University of Nottingham, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.428950.
7
Ledezma, RosaliÌa Diana DiÌaz. "Three studies in credit risk modelling." Thesis, City University London, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.397858.
8
Square, Lynndle Caroline. "Proton conductivity stability studies by modelling." University of the Western Cape, 2016. http://hdl.handle.net/11394/6121.
Анотація:
Philosophiae Doctor - PhD (Physics)In this thesis, some of the challenges experienced by high temperature polymer electrolyte membrane fuel cells are explored through material modelling techniques. A very important aspect for a fuel cell is that it should have high proton conductivity. As hydrogen enters a fuel cell it gets broken down into its constituents, protons and electrons. The electrons travel to an external load, whilst the protons travel through a diffusive layer, catalyst layer and membrane area, before recombining with oxygen to form water and leave the system. In this particular study, polytetrafluoroethylene and carbon form the diffusive layer, platinum the catalyst and poly(2,5-benzimidazole) doped with phosphoric acid the membrane area. The effects to proton conductivity are investigated as a result of the mixing of materials and adsorption of the phosphoric acid on the platinum active sites. A third study as an alternative avenue for proton conductivity improvements, is also explored. The results from these investigations promotes the idea that polytetrafluoroethylene, which is found in the ionomer layer, should be replaced as its mechanical properties decrease significantly with increase in temperature. Increasing pressure would further promote proton transfer over the doped polymer membrane region.
9
Walker, Jemma. "Bayesian modelling in genetic association studies." Thesis, London School of Hygiene and Tropical Medicine (University of London), 2012. http://researchonline.lshtm.ac.uk/1635516/.
Анотація:
Bayesian Model Selection Approaches are flexible methods that can be utilised to investigate Genetic Association studies in greater detail; enabling us to more accurately pin-point locations of disease genes in complex regions such as the MHC, as well as investigate possible causal pathways between genes, disease and intermediate phenotypes. This thesis is split into two distinct parts. The first uses a Bayesian Multivariate Adaptive Regression Spline Model to search across many highly correlated variants to try to determine which are likely to be the truly causal variants within complex genetic regions and also how each of these variants influences disease status. Specifically, I consider the role of genetic variants within the MHC region on SLE. The second part of the thesis aims to model possible disease pathways between genes, disease, intermediate phenotypes and environmental factors using Bayesian Networks, in particular focussing upon Coronary Heart disease and numerous blood biomarkers and related genes. Bayesian Multivariate Adaptive Regression Spline Model: Genetic association studies have the problem that often many genotypes in strong linkage disequilibrium (LD) are found to be associated with the outcome of interest. This makes it difficult to establish the actual SNP responsible. The aim of this part of the thesis is to investigate Bayesian variable selection methods in regions of high LD. In particular, to investigate SNPs in the major histocompatibility complex (MHC) region associated with systematic lupus erythematosus (SLE). Past studies have found several SNPs in this region to be highly associated with SLE but these SNPs are in high LD with one another. It is desirable to search over all possible regression models in order to find those SNPs that are most important in the prediction of SLE. The Bayesian Multivariate Adapative Regression Splines (BMARS) model used should automatically correct for nearby associated SNPs, and only those directly associated should be included in the model. The BMARS approach will also automatically select the most appropriate disease model for each directly associated variant. It was found that there appear to be 3 separate SNP signals in the MHC region that show association with SLE. The rest of the associations found using simple Frequentist tests are likely to be due to LD with the true signal. Bayesian Networks for Genetic Association Studies: Coronary Heart Disease (CHD) is one of many diseases that result from complicated relationships between both genetic and environmental factors. Identifying causal factors and developing new treatments that target these factors is very difficult. Changes in intermediate phenotypes, or biomarkers, could suggest potential causal pathways, although these have a tendency to group amongst those patients with higher risk of CHD making to difficult to distinguish independent causal relationships. I aim to model disease pathways allowing for intermediate phenotypes as well as genetic and environmental factors. Statistical methodology was developed using directed acyclic graphs (DAGs). Disease outcomes, genes, intermediate phenotypes and possible explanatory variables were represented as nodes in a DAG. Possible models were investigated using Bayesian regression models, based upon the underlying DAG, in a reversible jump MCMC framework. Modelling the data this way allows us to distinguish between direct and indirect effects as well as explore possible directionality of relationships. Since different DAGs can belong to the same equivalence class, some directions of association may become indistinguishable and I am interested in the implications of this. I investigated the integrated associations of genotypes with multiple blood biomarkers linked to CHD risk, focusing particularly on relationships between APOE, CETP and APOB genotypes; HDL- and LDL- cholesterol, triglycerides, C-reactive protein, fibrogen and apolipoproteins A and B. Overview: I will begin by introducing the topics of genetics, statistics and directed acyclic graphs with a background on each (Chapters 2,3 and 4 respectively). Chapter 5 will then detail the analysis and results of the BMARS model. The analysis and results of Bayesian networks for genetic association studies will then be covered in Chapter 6.
10
Boyett, Robin Ernest. "Computational studies of hydrophobic porphyrins." Thesis, University of Sussex, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.241621.
11
Gardner, J. M. F. "Synthetic and modelling studies on marine cembranolides." Thesis, University of Cambridge, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.293584.
12
Arinaminpathy, Thayalini. "Modelling and simulation studies of glutamate receptors." Thesis, University of Oxford, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.413984.
13
Kaye, Samantha Louise. "Modelling and simulation studies of NMDA receptors." Thesis, University of Oxford, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.442836.
14
Capener, Charlotte E. "Modelling and simulation studies of potassium channels." Thesis, University of Oxford, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.249241.
15
Law, Richard J. "Modelling and simulation studies of membrane proteins." Thesis, University of Oxford, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.249273.
16
Jiranusornkul, Supat. "Molecular modelling studies of DNA damage recognition." Thesis, University of Nottingham, 2008. http://eprints.nottingham.ac.uk/11303/.
Анотація:
How DNA repair proteins search and recognise the rare sites of damage from the massive numbers of normal DNA remains poorly understood. FapydG (2,6-diamino-4-hydroxy-5-formamidopyrimidine) is one of the most prevalent guanine derived lesions involving opening of the imidazole ring. It is typically repaired by formamidopyrimidine-DNA glycosylase (Fpg) as an initial step in base excision repair; if not repaired, the lesion generates a G: C -+ T: A transversion. Unfortunately, studies on the recognition of FapydG have been hindered by difficulties to synthesise and incorporate the FapydG residue into a DNA duplex. Crystal structures of Fpg-DNA complexes have demonstrated three common recognition events: the protein specifically binding to the extrahelical lesion, bending DNA centred on the damaged base, and flipping the damage into the pocket. Thus, molecular modelling and dynamics simulation have been used to gather dynamical information of those recognition events for damaged and undamaged DNA. The simulations were initially performed when FapydG or G occurs in several dodecamer B-DNA sequences in aqueous solution, then inside the lesion-recognition pocket of Fpg, and during the flipping pathway from the helical stack to an extrahelical position. The influence of the damage on DNA stability and flexibility was first investigated. Energetic analysis revealed that damage to DNA does appear to destabilise the duplex. DNA curvature analysis and a novel combined method of the principal component analysis (PCA) and the Mahalanobis distance (DM) indicated that damaged DNA can adopt the observed protein-bound conformation with lower energetic penalties than its normal counterpart. Results of these studies have provided the validation of DNA bending enhancement by the FapydG lesion. It also suggested that intrinsic DNA bending could be a principal element of how the repair protein locates the lesion from vast expanse of normal bases. Considering the specific recognition of FapydG by Fpg, the aF-/39 loop of the Fpg enzyme may function as a gatekeeping to accommodate the lesion while denying the normal base. Remarkably fluctuating movement of the flipped G residue and the aF-ß9 loop is due to the formation of the non-specific Fpg/G complex with a lower binding energy by 8.4 kcal/mol compared to the specific Fpg/FapydG complex. Free-energy profiles for both damaged and undamaged base flipping were generated from the umbrella sampling simulations and the Weight Histogram Analysis Method (WHAM). An energy barrier for flipping the damage out from the helix is 2.7 kcal/mol higher than its equivalent G and the lesion is highly stabilised inside the pocket. In contrast, G flipping seems to be rapidly rotated out and into the duplex without the formation of a specific complex. These studies could unravel a potentially comprehensive process of the repair protein to find and recognise the lesion through the slow kinetic pathway in which the more deformable damaged DNA is initially located by the protein; the protein subsequently compresses the duplex into an appropriate angle and direction to form a specific protein-DNA complex prior to being flipped and repaired.
17
Dai, F. "Load modelling for power system stability studies." Thesis, University of Manchester, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.578290.
18
Oliver, L. J. "Modelling individual heterogeneity in mark-recapture studies." Thesis, University of Kent, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.595295.
Анотація:
Since its original derivation, researchers have developed different extensions of the Cormack-Jolly-Seber (CJS) model in order to accommodate variation in the survival and recapture probabilities across the population. More recent developments have allowed each of these probabilities to vary as a function of observable covariates. The relationship between the parameters and covariates is often expressed in the form of a logistic regression. Such regressions are useful because they reduce the overall number of parameters in the model and may offer important ecological insight into the survival and recapture processes. However, the use of covariates in mark-recapture studies also gives rise to two important problems: (1) the covariates may contain missing values; and (2) the covariates may be subject to measurement error. To date, the latter issue has only been addressed in the context of closed population models. In this thesis we demonstrate the effects of measurement error in the CJS model. More specifically, we consider the case where the survival probabilities are modelled as a logistic function of an error-prone time-varying covariate. The covariate is then subject to both missing values and measurement error. Although a conditional likelihood approach can be used to handle the missing values, the resulting model makes no provision for errors in the covariate. A simulation study shows that, when these errors are ignored, the regression coefficients are estimated with bias and the effect of the covariate is understated. Furthermore, the bias becomes more severe as the magnitude of the errors increases. To accommodate measurement error in the model, we use a refinement of the regression calibration (RRC) method, which is based on deriving an approximate model for the survival probabilities given the observed covariate values in terms of the true regression parameters.
19
Wat, Rex Man Shing. "Experimental modelling studies of miscible flooding processes." Thesis, University of Exeter, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.310076.
Анотація:
During the tertiary stage of oil recovery, various chemicals and gases are injected into the reservoir. The success of these processes often depend on the ability of the injected chemicals/gases making contact with the residual hydrocarbon. The accessibility of the individual pore, where the hydrocarbon are trapped, to the injected fluid is therefore important. In many core flooding experiments which simulate such tertiary processes, the effluent profiles of the injected chemical often exhibit the capacitance effect of early breakthrough and long tails. These are mainly due to the fact that not all the pores are accessible to the displacing fluid. In this work, a mass transfer model, using physical meaningful parameters, has been set up to study the capacitance effect. The pore space are divided into a flowing fraction in which the bulk flow of the injected chemical takes place and a stagnant fraction where the chemical can only access by molecular diffusion. The significance and sensitivity of the five model parameters have been studied extensively using computer simulation. The extent of the mass transfer process is characterised by the different sets of family curves. A series of IPA/water miscible displacements using Clashach sandstone have been carried out to provide experimental data for model simulation. The assumption of the stagnant fraction in the form of dead end pores has been supported by the results of hexane/toluene displacements at connate water saturation. Some problems of history matching the experimental results by model simulation have been highlighted. This is mainly caused by the difficulty of establishing an analytical solution for the model equation and the need to optimise simultaneously the five model parameters. Various approach to overcome these problems have been successfully demonstrated in this work and further possible improvement has been identified. The source of numerical dispersion and the different corrective schemes proposed in various papers have been summarised and compared. One of these, the method of lines (MOL) has been used successfully in this work to minimise numerical dispersion. The understanding of the non-equilibrium capacitance effect in porous media is essential in order to interpret the production data and, in particular, laboratory core flooding results correctly. It is also important, for the mathematical model, to use parameters which are physically meaningful to the process itself. The work carried out in this research has provided a detailed study on this subject.
20
Haider, Syed Muhammed Shozeb. "Structural and modelling studies of quadruplex DNA." Thesis, Institute of Cancer Research (University Of London), 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.408250.
21
Grau, Crespo Ricardo. "Computer modelling studies of iron antimonate FeSbOâ‚„." Thesis, Birkbeck (University of London), 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.429418.
22
Larwood, Vivienne Lynne. "Modelling studies of factors affecting gellan gelation." Thesis, University of Surrey, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.320909.
23
Sanderson, Michael George. "Experimental and modelling studies of atmospheric chemistry." Thesis, University of York, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.259802.
24
Hadjigeorgiou, Christina. "Molecular modelling studies on bidentate iron chelators." Thesis, King's College London (University of London), 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.298845.
25
Ellis, Richard Raymond. "MRI and modelling studies of drying phenomena." Thesis, University of Cambridge, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.611581.
26
Collin, Adam John. "Advanced load modelling for power system studies." Thesis, University of Edinburgh, 2013. http://hdl.handle.net/1842/8890.
Анотація:
Although power system load modelling is a mature research area, there is a renewed interest in updating available load models and formulating improved load modelling methodologies. The main drivers of this interest are the introduction of new types of non-conventional (e.g. power electronic interfaced) loads, the requirement to operate power supply systems with increasing levels of renewable distributed generation and the implementation of various load control functionalities (e.g. demand side management). As the majority of existing load models do not allow for a full and precise analysis of these new operating conditions, it is essential to develop new load models and update load modelling techniques. This thesis presents a detailed study of modern loads, focussing on the requirements for their correct representation in power system analysis. The developed models of the individual loads are then combined using a new load aggregation methodology for developing aggregate load models, suitable for the analysis of both existing and future power supply systems (so called ’smart grids’). The methodology uses a circuit-based load modelling approach, as this allows reproduction of the instantaneous current waveforms of the modelled load for any given supply voltage. This approach retains all electrical characteristics of the loads and provides a more realistic representation of some important phenomena (e.g. harmonic cancellation and attenuation due to load and supply system interactions) which are often neglected in traditional load modelling procedures. Case studies of the UK residential and commercial load sectors are presented as illustrations of the load aggregation methodology. The results show significant short-term and long-term temporal variations in the load characteristics, which are not available or reported in the existing literature. This information allows for a more comprehensive assessment of demand-side management functionalities and correlation with locally connected distributed generation. Both of these effects are investigated in the thesis by quantifying the possible extent and range of changes in power system performance for some expected near future changes in load configurations and network operating conditions.
27
Olauson, Jon. "Modelling Wind Power for Grid Integration Studies." Doctoral thesis, Uppsala universitet, Elektricitetslära, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-302837.
Анотація:
When wind power and other intermittent renewable energy (IRE) sources begin to supply a significant part of the load, concerns are often raised about the inherent intermittency and unpredictability of these sources. In order to study the impact from higher IRE penetration levels on the power system, integration studies are regularly performed. The model package presented and evaluated in Papers I–IV provides a comprehensive methodology for simulating realistic time series of wind generation and forecasts for such studies. The most important conclusion from these papers is that models based on coarse meteorological datasets give very accurate results, especially in combination with statistical post-processing. Advantages with our approach include a physical coupling to the weather and wind farm characteristics, over 30 year long, 5-minute resolution time series, freely and globally available input data and computational times in the order of minutes. In this thesis, I make the argument that our approach is generally preferable to using purely statistical models or linear scaling of historical measurements. In the variability studies in Papers V–VII, several IRE sources were considered. An important conclusion is that these sources and the load have very different variability characteristics in different frequency bands. Depending on the magnitudes and correlations of these fluctuation, different time scales will become more or less challenging to balance. With a suitable mix of renewables, there will be little or no increase in the needs for balancing on the seasonal and diurnal timescales, even for a fully renewable Nordic power system. Fluctuations with periods between a few days and a few months are dominant for wind power and net load fluctuations of this type will increase strongly for high penetrations of IRE, no matter how the sources are combined. According to our studies, higher capacity factors, more offshore wind power and overproduction/curtailment would be beneficial for the power system.
28
Moral, Rafael de Andrade. "Statistical modelling of data from insect studies." Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/11/11134/tde-06042018-153400/.
Анотація:
Data from insect studies may present different features. Univariate responses may be analyzed using generalized linear models (continuous and discrete data), survival models (time until event data), mixed effects models (longitudinal data), among other methods. These models may be used to analyse data from experiments which assess complex ecological processes, such as competition and predation. In that sense, computational tools are useful for researchers in several fields, e.g., insect biology and physiology, applied ecology and biological control. Using different datasets from entomology as motivation, as well as other types of datasets for illustration purposes, this work intended to develop new modelling frameworks and goodness-of-fit assessment tools. We propose accelerated failure rate mixed models with simultaneous location and scale modelling with regressors to analyse time-until-attack data from a choice test experiment. We use the exponential, Weibull and exponentiated-Weibull models, and assess goodness-of-fit using half-normal plots with simulation envelopes. These plots are the subject of an entire Chapter on an R package, called hnp, developed to implement them. We use datasets from different types of experiments to illustrate the use of these plots and the package. A bivariate extension to the N-mixture modelling framework is proposed to analyse longitudinal count data for two species from the same food web that may interact directly or indirectly, and example datasets from ecological studies are used. An advantage of this modelling framework is the computation of an asymmetric correlation coefficient, which may be used by ecologists to study the degree of association between species. The jointNmix R package was also developed to implement the estimation process for these models. Finally, we propose a goodness-of-fit assessment tool for bivariate models, analogous to the half-normal plot with a simulation envelope, and illustrate the approach with simulated data and insect competition data. This tool is also implemented in an R package, called bivrp. All software developed in this thesis is made available freely on the Comprehensive R Archive Network.Dados provenientes de estudos com insetos podem apresentar características diferentes. Respostas univariadas podem ser analisadas utilizando-se modelos lineares generalizados (dados contínuos e discretos), modelos de análise de sobrevivência (dados de tempo até ocorrência de um evento), modelos de efeitos mistos (dados longitudinais), dentre outros métodos. Esses modelos podem ser usados para analisar dados provenientes de experimentos que avaliam processos ecológicos complexos, como competição e predação. Nesse sentido, ferramentas computacionais são úteis para pesquisadores em diversos campos, por exemplo, biologia e fisiologia de insetos, ecologia aplicada e controle biológico. Utilizando diferentes conjuntos de dados entomológicos como motivação, assim como outros tipos de dados para ilustrar os métodos, este trabalho teve como objetivos desenvolver novos modelos e ferramentas para avaliar a qualidade do ajuste. Foram propostos modelos de tempo de vida acelerado mistos, com modelagem simultânea dos parâmetros de locação e de escala com regressores, para analisar dados de tempo até ataque de um experimento que avaliou escolha de predadores. Foram utilizados modelos exponencial, Weibull e Weibull-exponenciado, e a qualidade do ajuste foi avaliada utilizando gráficos meio-normais com envelope de simulação. Esses gráficos são o assunto de um Capítulo inteiro sobre um pacote para o software R, chamado hnp, desenvolvido para implementá-los. Foram utilizados conjuntos de dados de diferentes tipos de experimentos para ilustrar o uso desses gráficos e do pacote. Uma extensão bivariada para os modelos chamados \"N-mixture\" foi proposta para analisar dados longitudinais de contagem para duas espécies pertencentes à mesma teia trófica, que podem interagir direta e indiretamente, e conjuntos de dados provenientes de estudos ecológicos são usados para ilustrar a abordagem. Uma vantagem dessa estratégica de modelagem é a obtenção de um coeficiente de correlação assimétrico, que pode ser utilizado por ecologistas para inferir acerca do grau de associação entre espécies. O pacote jointNmix foi desenvolvido para implemetar o processo de estimação para esses modelos. Finalmente, foi proposta uma ferramenta de avaliação de qualidade do ajuste para modelos bivariados, análoga ao gráfico meio-normal com envelope de simulação, e a metodologia _e ilustrada com dados simulados e dados de competição de insetos. Essa ferramenta está também implementada em um pacote para o R, chamado bivrp. Todo o software desenvolvido nesta tese está disponível, gratuitamente, na Comprehensive R Archive Network (CRAN).
29
Laskiewicz, Marek. "Casual modelling of businesses." Thesis, Queen Mary, University of London, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.300105.
30
Ellis, Dianne D. "Structural studies of phosphines and phosphites." Thesis, University of Bristol, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.482802.
31
Hand, Karen Jayne. "Computational studies of protein-ligand interactions." Thesis, University of York, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.282271.
32
Greaves, Richard Brian. "Computational studies of protein structure and function." Thesis, University of York, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.387165.
33
King, Matthew James Stuart. "Experimental and modelling studies of transient slug flow." Thesis, Imperial College London, 1998. http://hdl.handle.net/10044/1/8270.
34
Downing, Anna Kristina. "N.M.R. structural studies and modelling of modular proteins." Thesis, University of Oxford, 1993. https://ora.ox.ac.uk/objects/uuid:a8c88faa-08ee-4374-a384-b7116c551ef1.
Анотація:
This thesis focuses on structural studies of the fibronectin type 1 module (F1) of tissue-type plasminogen activator (t-PA) and the N-terminal src homology 2 (SH2) module of the p85α subunit of phosphatidylinositol-3-OH kinase (PI3-kinase). t-PA plays a key role in the dissolution of blood clots. It is the only serine protease that binds to the fibrin network of a thrombus and localises its activity to the site of a clot. The t-PA F1 module is critical to t-PA fibrin binding. This module was produced for structural studies using a yeast alpha secretion system. N.m.r. data collected on the purified protein were used to calculate a high resolution structure of the module. The structures of the t-PA finger and the seventh type 1 module from human fibronectin were compared and found to be strikingly similar. Topological differences between the two molecules suggested that one face of the t-PA finger engages in domain-domain interactions in the intact protein. A model of the intact t-PA was constructed and used to explain differences in the biological activity of the two naturally abundant glycosylated variants of the molecule. The SH2 module binds sequence-specifically to intracellular phosphorylated tyrosines on receptor tyrosine kinases and thus mediates cell signalling pathways which lead ultimately to changes in cell growth and differentiation. The 3-dimensional structure of the N-terminal SH2 of the p85α subunit of PI3-kinase was computed and compared to the v-src SH2 complexed with low affinity phosphopeptides in order to assess the conformational changes associated with phosphopeptide binding. Finally, the structures of two homologous SH2 modules were modelled to identify possible high affinity protein-peptide interactions responsible for the variation in phosphopeptide affinity of SH2 modules. The predicted interactions were subsequently observed in two high affinity SH2-peptide complexes.
35
Li, Yazhuo. "Crystallographic and molecular modelling studies of NQO2-complexes." Thesis, University of Nottingham, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.537673.
36
Bailey, J. "Theoretical modelling studies of aggregation and molecular interactions." Thesis, University of Cambridge, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.596263.
Анотація:
Understanding the interactions between dye molecules and their constituent moieties will lead to an improvement in the design of new molecules with the appropriate properties. Here, we use computational methods to investigate the relative stability of the three tautomers of hydroxy-triazine, and how they interact with themselves in the gas phase, in aqueous solution and in the solid state. Ab initio and density functional theory (DFT) methods were used to establish the relative gas phase stability of the tautomers, showing two of the tautomers to be significantly more stable than the third. Thermodynamic cycles were calculated using ab initio free energies of salvation and gas phase energies. The crystal phase investigation involved data mining of the Cambridge Structural Database and generating hypothetical crystal structures which were subjected to lattice energy minimisations. The interactions were investigated in the gas phase by minimising small clusters of the tautomers, treated as rigid molecules, from a number of random starting conformations. Molecule dynamics simulations looked at the behaviour in solution, while the lattice energy minimisations and the CSD were again used to look at solid phase interactions. The above methods were also incorporated into further investigations of the interactions between these tautomers and another important dye-related molecule, morpholine, both as an additive and as a covalently bonded fraction. Whole dye molecules containing these substructures, were then studied using the above methods, as well as UV-Vis spectroscopic analysis to calculate dimerisation equilibrium constants. Finally the computational methods were applied to look at the effects of substituents on the interactions of zinc phthalocyanine.
37
Basse, Britta. "Case studies in mathematical modelling for biological conservation." Thesis, University of Canterbury. Mathematics & Statistics, 1999. http://hdl.handle.net/10092/4804.
Анотація:
The use of mathematical modelling as a tool for investigating selected topics in conservation
biology is the focus of this thesis.
A continuous system of partial and ordinary differential equations model the age structured
population dynamics of a cohort of endemic, threatened New Zealand North Island
brown kiwi, Apteryx mantelli. Critical predation and recruitment rates of immature birds are
estimated. Stoats, Mustela erminea, are the main predator of immature kiwi. A refinement
to the model allows the calculation of acceptable stoat densities. In order to reduce stoats
to this critical density, a linear system of ordinary differential equations, representing an
acute secondary poisoning regime, is solved. An optimal secondary poisoning scheme, which
minimises the number of prey poisoned and the amount of poison used, is found. The minimum
area required for pest control is estimated by simulating the dispersal of sub-adult kiwi
using a discrete random walk approach. Simulations and a discrete age structured model are
used to investigate pulsed management strategies for both kiwi and kokako, Callaeas cinerea
wilsoni. Finally, a two dimensional discrete random walk is generalised and a continuous
diffusion equation is derived. A diffusion equation is incorporated into a S1 R (Susceptible,
Infected, Recovered) model representing the natural spread of Rabbit Haemorrhagic Disease
from a point source in rabbit, Oryctolagus cuniculus cuniculus, populations. The speed
for the virus, dependant on certain model parameters, is found and the minimum initial
population density, below which the wave of infection will not travel, is estimated.
All specific models discussed throughout the thesis are generic by nature and can be
applied to a diverse range of subjects.
38
Khan, Nasar Ahmed. "Modelling and mass transfer studies in continuous crystallisers." Thesis, Teesside University, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.410867.
39
Pardo-Benito, J. Mauricio. "Modelling studies on freeze-drying of coffee extracts." Thesis, University of Reading, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.394175.
40
Rabias, Ioannis. "Theoretical and computational modelling studies of conducting polymers." Thesis, University of Surrey, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.310151.
41
Bentley, Mark Stephen. "Space weathering on mercury : laboratory studies and modelling." Thesis, Open University, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.413806.
42
Parkin, Andrew. "Crystallographic and modelling studies of transition metal complexes." Thesis, University of Edinburgh, 2002. http://hdl.handle.net/1842/12767.
Анотація:
Molecular mechanics techniques have been applied to the investigation of the formation of transition metal complexes. In addition to the determination of many relevant crystal structures, the two major projects carried out were: a) molecular structures within the crystalline forms of copper(I) ligated by phosphine and alkoxide or aryloxide ligands, and b) modes of extraction of salicylaldimine derivatives for metal salt transport. Copper(I) is observed to crystallise with phosphine and alkoxide or aryloxide ligands in five different structural motifs. The formation of these structural motifs was rationalised in terms of electronic and steric effects. Electronic effects were approximated to the pKa of the alkoxide or aryloxide ligand. Steric effects were modelled using molecular mechanics calculations. Parameters for molecular mechanics were obtained from the Cambridge Structural Database. The results show that the formation of molecular structures can indeed be justified this way, and some structures have been predicted. Recently White and Tasker have proposed a novel method of "metal salt" extraction based on derivatives of the salicylaldimine ligand. The addition of pendant tertiary amines to this ligand allows the encapsulation of an anion, and thus transport of the entire "metal salt". This has been particularly successful for square planar copper(II) salts. Molecular mechanics calculations were employed to model the possible structures formed in the solution species to aid design of improved extractants for nickel(II). Parameters for molecular mechanics were obtained from the Cambridge Structural Database. The results enabled rationalisation of the poor performance of the original design, and the design of species with improved geometries for anion encapsulation.
43
Yang, He. "Numerical modelling studies on asymmetries in tropical cyclones." Thesis, University of Reading, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.646002.
Анотація:
Hurricanes are the most destructive of all weather systems. Conditions necessary for their formation are well known, but not those sufficient to guarantee their occurrence. A thorough understanding of their structure, the physical and dynamical processes which operate within them, and their interactions with the large-scale environmental flow are necessary if accurate forecasts are to be made of their development and tracks. In the present study, both 2-D (axisymmetric) and 3-D (asymmetric), two-layer (plus the boundary layer) numerical models have been developed. The 2 -D model is used to investigate the essential characteristics of the symmetric flow component of tropical cyclones. The heating rate, which is computed at the mid-level in the model, is related to the vortexflow itself. It consists of three parts: moisture convergence over the whole column, Ekman pumping and surface evaporation. The moisture convergence is found to be crucial in providing latent heating released by condensation of water vapour sufficient to compensate adiabatic ascent cooling. The Ekman pumping plays an important role as a 'contractor', i.e. to cause the maximum winds to concentrate towards the centre, and consequent intensification of the modelled vortex. The surface evaporation, although relatively S11UJU, spreads over a larger area than the other two. It is found to beessentialformaintenance of the mature stage.
44
Mulvihill, Daniel Martin. "Studies of frictional interface behaviour : experiments and modelling." Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:54e18b10-1167-40f1-9dc9-0ca529a56f34.
Анотація:
Predictive models of structures containing frictional joints presently suffer from poor descriptions of interface behaviour at the joints. This thesis aims to address this shortfall by furthering the physical understanding of parameters affecting interface behaviour such as friction and contact stiffness. Aspects of friction and contact stiffness relevant to the characterisation of fretting joints are investigated by a combined modelling and experimental approach. Friction and wear behaviour in gross-slip fretting are investigated by in-line and rotational fretting tests. New 3D topography parameters are found to be useful in the analysis of surfaces during fretting. Wear-scar shape is found to be dependent on material. A phenomenon whereby friction increases during the gross-slip phase of individual cycles is found to be due to wear-scar interaction primarily through the interference of local features distributed over the contact area. These features are similar in size to the applied fretting stroke. A simple model to explain the behaviour is put forward which shows that wear-scar shape determines the form of the friction variation. A finite-element (FE) model of the interaction of an elastic-plastic asperity junction is used to predict sliding friction coefficients. The modelling differs from previous work by: permitting greater asperity overlaps, enforcing an interface shear strength, and allowing material failure. The results are also used to predict friction coefficients for a stochastic rough surface. The magnitudes of the predicted friction coefficients are generally representative of experimental measurements. Results suggest that friction arises from both plasticity and tangential interface adhesion. Contact stiffness is studied for both fretting and non-fretting. A technique to isolate the true interface stiffness from results derived from load-deflection data is developed by comparing experimental and FE results. In the fretting wear case, comparison of tangential contact stiffness results in the literature with FE results reveals an interface whose compliance dominates the response to the extent that stiffness is proportional to contact area. In fretting tests such as this, wear debris is thought to be a factor contributing to high interface compliance. Non-fretting experiments performed here show that, at higher pressures, interface domination is reduced as the contact approaches the smooth case. Experiments are performed where contact stiffness is measured simultaneously by both ultrasound and digital image correlation. The effect of normal and tangential loading upon the contact stiffness (normal and tangential) is investigated. Experimental evidence showing that ultrasound measures an ‘unloading’ stiffness while DIC measures a ‘loading’ stiffness is obtained for the case of tangential loading where the ‘DIC stiffness’ decreases with increasing tangential load whereas the ‘ultrasound stiffness’ remains approximately constant. On average, ultrasound gives magnitudes 3.5 and 2.5 times stiffer than the DIC results for the normal and tangential stiffness cases, respectively. The difference in magnitudes can largely be physically explained, and is relatively small considering the significant differences between the techniques. Therefore, both methods can claim to give valid measurements of contact stiffness – though each has its own limitations which are outlined herein.
45
Glasspool, David William. "Modelling serial order in behaviour : studies of spelling." Thesis, University College London (University of London), 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.391254.
46
Lindblad, Louise. "Modelling and Simulation ofGNC/AOCS Systemsfor Conceptual Studies." Thesis, KTH, Mekanik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-202627.
Анотація:
The preliminary design of Guidance, Navigation, and Control (GNC) algorithms andAttitude and Orbital Control Systems (AOCS) for spacecraft plays an important rolein the planning of a space mission. Many missions require accurate positioning andattitude control to be able to full the mission objectives. In an early phase of conceptualstudies, trade-os have to be made to the GNC/AOCS subsystem designand compromises with respect to other subsystem designs have to be taken intoaccount. This demands for the possibility of rapid prototyping where design parameters,such as the choice of sensors and actuators, can be changed easily to assessthe compliance to the mission requirements. This thesis presents the modelling ofGNC/AOCS components for a toolbox created in the MATLAB/Simulink environment.The resulting toolbox is a user-friendly tool, which simplies the creationof GNC/AOCS system simulations for conceptual studies. A number of completesimulations were constructed to demonstrate the capabilities of the toolbox.
47
Klyukin, Yury Igorevich. "Modelling and analytical studies of magmatic-hydrothermal processes." Diss., Virginia Tech, 2017. http://hdl.handle.net/10919/84442.
Анотація:
Hydrothermal processes play a major role in transporting mass and energy in Earth’s crust. These processes rely on hydrothermal fluid, which is dissolving, transporting and precipitating minerals and distribute heat. The composition of the hydrothermal fluid is specific for various geological settings, but in most cases it can be approximated by H₂O-NaCl-CO₂ fluid composition. The flow of hydrothermal fluid is controlled by differences in temperature, pressure and/or density of the fluid and hydraulic conductivity of the rock. In my work, I was focused on modeling of the hydrothermal fluid properties and experimental characterization of fluid that formed emerald deposit in North Carolina, USA. The dissertation based on the result of three separate projects.
The first project has been dedicated to characterization of the H₂O-NaCl hydrothermal fluid ability to transport mass and energy. This ability of the fluid is defined by a change in fluid density and enthalpy in response to changing pressure or temperature. In this project we quantified the derivatives of mass, enthalpy and SiO₂ solubility in wide range of pressure, temperature and composition (PTx) of H₂O-NaCl fluid. Our study indicated that the PT region in which fluid is most efficiently can transport mass and energy, located in the critical region near liquid-vapor phase boundary and the sensitivity to changing pressure-temperature conditions decrease with increasing salinity.
In second project we developed the revised H₂O-NaCl viscosity model. Revised model to calculate the viscosity of H₂O-NaCl reproduces experimental data with ±10% precision in PTx range where experimental data available and follows expected trends outside of the range. This model is valid over the temperature range from the H₂O solidus (~0 °C) to ~1,000 °C, from ~0.1 MPa to ≤500 MPa, and for salinities from 0-100 wt.% NaCl.
The third project has been focused on the characterization of formation conditions of the emerald at North American Emerald Mine, Hiddenite, North Carolina, USA. The emerald formation conditions defined as 120-220 MPa, 450-625 °C using stable isotope, Raman spectrometry, and fluid inclusion analysis. Hydrothermal fluid had a composition of CO2-H2O±CH4, which indicates mildly reducing environment of emerald growth.Ph. D.
48
Masenya, Mamago Adolphina. "Computational modelling studies of precious mixed metals sulphides." Thesis, University of Limpopo, 2016. http://hdl.handle.net/10386/1725.
Анотація:
Thesis (MSc. (Physics)) -- University of Limpopo, 2016The stabilities of PtS to PdS and PdS to PtS were investigated using density functional theory within the generalized gradient approximation. Their structural, electronic and mechanical properties were determined to show their stability and the effect of pressure on different compositions. We found good correlation of calculations with available ex-perimental data. The lattice parameters were observed to fluctuate with increasing con-centration for both systems. Furthermore, heats of formation were calculated to deter-mine the relative structural stability of the systems. They predict that the most stable structure is Pd50S50 P42/mmc and Pt25Pd25S50 P42/mmc being the least stable. Pd12.5Pt37.5S50 P42/m is the most stable and Pd50S50 P42/m being the least stable struc-ture. The Pt37.5Pd12.5S50 P1 was said to be the most stable structure and Pd50S50 P1 be-ing the least stable. The phonon dispersion calculations show that Pt50S50 P42/mmc, Pd50S50 P42/mmc, Pd12.5Pt37.5S50 P42/m and Pt50S50 P1 (derived from P42/mmc) are me-chanically stable, consistent with calculated elastic constants. The Pt25Pd25S50 P42/mmc show soft modes, which are due to vibrations of Pt and Pd atoms in the x - y plane which suggests the instability of the structure, in agreement with C66 being negative, and consistent with heats of formation. The lattice parameters decreased steadily with increasing pressure. An anomaly was observed in Pt50S50 P1 (derived from P42/mmc), where the c lattice parameter was found to increase with increasing pressure. The elec-tronic density of states (DOS) were performed on all compositions. The DOS were sub-jected to pressure and it was generally noted that the band gap increases with increas-ing pressure. It was observed that the smaller the band gap, the more stable the struc-ture. Furthermore, phonon dispersions under pressure show that compounds with the P42/mmc and P1 (from P42/mmc) symmetries display the mixing of lower and upper en-ergy bands at pressures above 30 GPa.
National Research Foundation
49
Alessandri, Jacopo <1989>. "Coastal modelling studies for forecasting and remediation solutions." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2022. http://amsdottorato.unibo.it/10075/1/Alessandri_Jacopo_Tesi.pdf.
Анотація:
The coastal area along the Emilia-Romagna (ER), in the Italian side of the northern Adriatic Sea, is considered to implement an unstructured numerical ocean model with the aim to develop innovative tools for the coastal management and a forecasting system for the storm surge risk reduction. The Adriatic Sea has been the focus of several studies because of its peculiar dynamics driven by many forcings acting at basin and local scales. The ER coast is particularly exposed to storm surge events. In particular conditions, winds, tides and seicehs may combine and contribute to the flooding of the coastal area. The global sea level rise expected in the next decades will increase even more the hazard along the ER and Adriatic coast. Reliable Adriatic and Mediterranean scale numerical ocean models are now available to allow the dynamical downscaling of very high-resolution models in limited coastal areas. In this work the numerical ocean model SHYFEM is implemented in the Goro lagoon (named GOLFEM) and along the ER coast (ShyfER) to test innovative solutions against sea related coastal hazards. GOLFEM was succesfully applied to analyze the Goro lagoon dynamics and to assess the dynamical effects of human interventions through the analysis of what-if scenarios. The assessment of storm surge hazard in the Goro lagoon was carried out through the development of an ensemble storm surge forecasting system with GOLFEM using forcing from different operational meteorological and ocean models showing the fundamental importance of the boundary conditions. The ShyfER domain is used to investigate innovative solutions against storm surge related hazard along the ER coast. The seagrass is assessed as a nature-based solution (NBS) for coastal protection under present and future climate conditions. The results show negligible effects on sea level but sensible effects in reducing bottom current velocity.
50
Lima, Alessandra Vallim [UNESP]. "Niche Modelling: a comparison between modelling methods best applied for Cnidaria niche dispersion studies." Universidade Estadual Paulista (UNESP), 2017. http://hdl.handle.net/11449/150823.
Анотація:
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Nas ultimas décadas, modelagem de nicho ecológico vem recebendo maior atenção em diversas áreas da biologia devido a evolução dos computadores pessoais e aumento dos dados disponíveis utilizados para a modelagem. Os resultados obtidos podem ser utilizados em ações preventivas, tais quais manejo de espécie e acompanhamento da distribuição de espécies invasoras. Desde o aumento dessa popularidade, diversos algoritmos estão disponíveis e testes estão em andamento para averiguar suas performances em relação a diferentes filos. Invertebrados marinhos, mais especificamente cnidários, apresentam poucos estudos nesse ramo, devendo receber mais atenção nos próximos anos devido ao aumento global das populações de aguas vivas (blooms), e branqueamento em quase todos os recifes de corais. Devido a essa lacuna em informação, este grupo foi escolhido para comparar três algoritmos. Utilizamos o MAXENT, GARP e AquaMaps em suas formas de desktop e os selecionamos baseado em outros estudos comparando algoritmos. Utilizamos diferentes organismos do filo cnidária, Lychnorhiza lucerna, Chrysaora lactea, Phyllorhiza punctata, Tamoya haplonema, Ceriantheomorphe brasiliensis e Mussismilia hispida, para comparar os algoritmos e averiguar qual demonstrou melhor performance. Nossos resultados mostram que o MAXENT superou os outros algoritmos tanto com relação a Área Sob a Curva ROC (AUC), quanto com relação aos mapas de distribuição. O GARP apresentou resultados variados com mapas generalizados e AquaMaps foi o menos confiável. Nossos resultados são similares aqueles encontrados em diversas publicações, significando então, que o MAXENT é o algoritmo mais confiável em se tratando da modelagem de nicho desses organismos.
Recently, ecological niche modelling has been receiving more attention in several areas in biology, due to the evolution of personal computers, and the increasing availability of data used in modelling. The results obtained can be used in preventive actions such as species management and invasive species distribution. Since its increasing popularity, several algorithms are available and undergoing tests regarding their performance towards different phylum. Marine invertebrates, more specifically cnidarians, present few studies on this field, and should receive closer attention in the next years due to worldwide increases in jellyfish population (blooms), and bleaching in almost every known shallow water coral reef. Because of this gap of information, we chose this still poor studied group to compare three algorithms. We used MAXENT, GARP and AquaMaps in its desktop form and selected them based on other studies comparing algorithms. Our aim was to, based on different organisms of the phylum Cnidaria, Lychnorhiza lucerna, Chrysaora lactea, Phyllorhiza punctata, Tamoya haplonema, Ceriantheomorphe brasiliensis and Mussismilia hispida, compare those algorithms and examine which one performed the best. Our results shown that MAXENT outperformed the other algorithms both regarding de Area Under the ROC Curve (AUC) and the map distribution. GARP show varying results with generalized maps and AquaMaps was the least accurate of them. Our results are similar to those found in other papers, thus meaning that MAXENT is the most reliable software when it comes to modelling these animals.