Segui questo link per vedere altri tipi di pubblicazioni sul tema: Kinetic modelling.
Tesi sul tema "Kinetic modelling"
Cita una fonte nei formati APA, MLA, Chicago, Harvard e in molti altri stili
Vedi i top-50 saggi (tesi di laurea o di dottorato) per l'attività di ricerca sul tema "Kinetic modelling".
Accanto a ogni fonte nell'elenco di riferimenti c'è un pulsante "Aggiungi alla bibliografia". Premilo e genereremo automaticamente la citazione bibliografica dell'opera scelta nello stile citazionale di cui hai bisogno: APA, MLA, Harvard, Chicago, Vancouver ecc.
Puoi anche scaricare il testo completo della pubblicazione scientifica nel formato .pdf e leggere online l'abstract (il sommario) dell'opera se è presente nei metadati.
Vedi le tesi di molte aree scientifiche e compila una bibliografia corretta.
1
Munkondya, Ferguson Mukozoke. "Kinetic modelling of leaching". Thesis, Imperial College London, 1989. http://hdl.handle.net/10044/1/47583.
Testo completo
2
Johansson, David. "Kinetic modelling of autoignition phenomena". Licentiate thesis, Stockholm : Kemiteknik, Kungliga Tekniska högskolan, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4516.
Testo completo
3
Gilliland, David. "Kinetic modelling of preservative systems". Thesis, Queen's University Belfast, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.334622.
Testo completo
4
Marsano, Flavio. "Chemical kinetic modelling of hydrocarbon combustion". Thesis, Cardiff University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.402067.
Testo completo
5
Potter, Mark Lee. "Detailed chemical kinetic modelling of propulsion fuels". Thesis, Imperial College London, 2004. http://hdl.handle.net/10044/1/7995.
Testo completo
6
Hagey, H. Louis. "Kinetic modelling of synthesis gas into hydrocarbons". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/NQ58214.pdf.
Testo completo
7
Rizos, Konstantinos-Athanassios. "Detailed chemical kinetic modelling of homogeneous systems". Thesis, Imperial College London, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.407143.
Testo completo
8
Binns, Michael John. "Kinetic modelling of chemical and biochemical networks". Thesis, University of Manchester, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.496236.
Testo completoAbstract (sommario):
The modelling of chemical and biochemical systems is highly dependent on the reaction network of the system. A reaction network should contain all the reactions which can occur in addition to the species involved. However in many cases there will be reactions occurring which are missing from the network. These are called gaps (Reed et al., 2003; Duarte et al, 2004) and occur because the databases of reactions used to build them are incomplete. The main aim of this work is to identify all the reactions which can occur in a given system including the unknown ones. This is accomplished through a new procedure which will be called metabolic network development and is aimed at constructing reaction networks for biochemical systems.
9
Reece, Christian. "Kinetic analysis and modelling in heterogeneous catalysis". Thesis, Cardiff University, 2017. http://orca.cf.ac.uk/103737/.
Testo completoAbstract (sommario):
A combination of Temporal Analysis of Products, Temperature Programmed Reduction, and Density Functional theory techniques have been used to perform kinetic analysis on data from heterogeneous catalysis experiments. A new method of data filtering has been developed for Temporal Analysis of Products, and has been applied to a system of 4 Pt−Mo2C, and the current methodology has been expanded upon to calculate rate coefficients for the oxidation of CO to CO2 via the Boudard reaction. From the kinetic constants it appears that a phase change occurs in the material at approximately 200�C. The current theory for analysing Temperature Programmed Reduction has been applied in a new methodology which is able to perform the deconvolution of thermograms with high accuracy, while also calculating the kinetic parameters related to the reduction processes. This new methodology has been applied to a system of CeO2 calcined at 400, 500 and 600�C and the strengths and limitations of the methodology are explored. From the deconvolution procedure it was found that there are three distinct reduction processes occurring on the CeO2 and that a phase change occurs between 400 and 500�C. Finally Density Functional Theory combined with classical dynamics has been used to explore the mechanism of the hydrogenation of Levulinic Acid to gamma-Valerolactone over a CuZrO2 catalyst. It was found that the Levulinic Acid is more likely to hydrogenate then cyclise, and from using molecular dynamics simulations it was shown that the solvent H2O plays a very important role in the cyclisation of the hydrogenated intermediate.
10
Hameed, Samreen. "Kinetic Analysis and Modelling of Cellulose Pyrolysis". Thesis, Curtin University, 2019. http://hdl.handle.net/20.500.11937/75984.
Testo completoAbstract (sommario):
Pyrolysis is one of the thermochemical techniques to convert biomass into bio-oil, bio-char and gaseous products. This work has focused on modelling the kinetic behaviour of cellulose, which is the most abundant component in any type of biomass, under slow and fast pyrolysis conditions and in the presence of inorganic species using Distributed Activation Energy Model (DAEM). In addition, cellulose pyrolysis product yield has been estimated using Computational Fluid Dynamics (CFD) modelling framework.
11
Altıok, Duygu Tokatlı Figen. "Kinetic modelling of lactic acid production from whey/". [s.l.]: [s.n.], 2004. http://library.iyte.edu.tr/tezler/master/gidamuh/T000471.pdf.
Testo completo
12
Newton, Timothy John. "Computer modelling of poly-#beta#-hydroxybutyrate synthesis in alcaligenes eutrophus". Thesis, University of Newcastle Upon Tyne, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.262922.
Testo completo
13
Mehrvar, Mehrab. "Kinetic modelling and a novel packed bed photocatalytic reactor". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0003/NQ30630.pdf.
Testo completo
14
Gooch, S. D. "Design and mathematical modelling of the kinetic sculpture Blade". Thesis, University of Canterbury. Mechanical Engineering, 2001. http://hdl.handle.net/10092/7844.
Testo completoAbstract (sommario):
Christchurch born artist Len Lye (1901- 1980) built the kinetic sculpture, Blade
(1965), as a prototype for what he perceived to be a much larger work.
This thesis presents a study, which predicts the vibratory response of Blade and develops a design for the sculpture to be built at the largest practical economic size.
Len Lye's aesthetic requirements stipulate that the vibratory blade form of the scaled sculpture must be geometrically similar to the original work and that static similarity should exist between the original and the scaled blades.
Dimensionless formulae are derived and used to study the influence of design parameters and increasing size on structural properties such as natural frequencies, blade forces and moments, and system power requirements. For a solid metal blade of rectangular cross section it is found that the size, which Blade may be scaled, is limited by the magnitude of the bending stresses in the blade material.
Len Lye's specification imposes a set of requirements and constraints on the design, which in addition to economic constraints leads to a variational study which maximises the number of performances per dollar expended on blade materials with increasing size. As a result of this study a titanium alloy 6AI/4V is selected for the scaled blade with a nominal blade length is 3.355m.
To test the validity of the design, frequencies and mode shapes were calculated and a numerical simulation performed. The exact solution for the natural bending frequencies and mode shapes for the blade and the wand are obtained using simple beam theory. The Rayleigh Ritz method is used to calculate the plate frequencies and mode shapes for the blade. The calculated frequencies and mode shapes include the effects of the longitudinal gravitational loading. In this study they are the second and third blade bending frequencies and the third plate mode Len Lye described as the desirable vibrating single and double harmonic blade forms and the shimmering frequency respectively.
For the simulation a mathematical model is developed to describe the dynamics of the interaction of the blade and the wand. The model predicted a swinging phenomenon, which Lye observed in the performance of Blade at the prototype size and regarded as undesirable. A system configuration for the scaled Blade involving a lighter more flexible wand and modified ground motion characteristics predicted a significant reduction of this swinging phenomenon and is incorporated in the design.
Features in the design of the mechanism for the original sculpture were found to be unsatisfactory so a new improved mechanism concept was developed.
The complete design was produced and the system was manufactured and built. The performance of the scaled Blade is found to be consistent with the prediction from the mathematical model.
15
Hamlet, Colin G. "Monochloropropanediols in bread : model dough systems and kinetic modelling". Thesis, University of Nottingham, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.408579.
Testo completo
16
CAMPAJOLA, Carlo. "Modelling financial lead-lag interactions with Kinetic Ising Models". Doctoral thesis, Scuola Normale Superiore, 2020. http://hdl.handle.net/11384/90680.
Testo completo
17
Turner, Clare Ruth. "Laminar kinetic energy modelling for improved laminar-turbulent transition prediction". Thesis, University of Manchester, 2012. https://www.research.manchester.ac.uk/portal/en/theses/laminar-kinetic-energy-modelling-for-improved-laminarturbulent-transition-prediction(404aef03-247f-47ed-852b-b45b2f44a300).html.
Testo completoAbstract (sommario):
This thesis considers the advantages of incorporating laminar kinetic energy modelling into turbulence modelling, in order to predict laminar-turbulent transition. The final aim is to implement an improved transition model into the industrial Finite-Volume code, Code Saturne. The literature review suggests that in order for a RANS-based model to predict transition accurately, modelling of complex, anisotropic phenomena is necessary. The Walters-Cokljat model is shown to compare very well to other transition modelling methods, including correlation-based modelling. The Walters-Cokljat model is a single-point RANS-based model that solves an additional transport equation for laminar kinetic energy. This transition model is especially desirable from an industrial stand-point, due to its single-point RANS basis, with only 3 transport equations. Although this method shows great promise as an industrial tool for transition prediction, results presented here show that there are aspects of the model that require modification. The definition of effective length-scale and the method of accounting for the effects of shear sheltering are the two main areas for consideration. The current definition of effective length-scale is found to be inappropriate for flows with large free-stream length-scales, which are common-place in turbomachinery applications. Another phenomenon commonly found in turbomachinery is separation-induced transition; however, the current function for shear sheltering effects inhibits transition when turbulence intensity is not the forcing factor. Additionally, when reviewed analytically, the definition and placement of the shear sheltering function does not match the observations of Jacobs and Durbin. Alternatives for the definitions of the effective length-scale and the shear sheltering function are proposed. The individual proposals are tested, and steps towards a full working implementation are documented.
18
Shaw, Benjamin Milton. "Statistical issues in kinetic modelling of gas-phase ethylene copolymerization". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape8/PQDD_0007/NQ42976.pdf.
Testo completo
19
Stewart, J. "Applying micro-kinetic techniques to the modelling of automotive catalysis". Thesis, Queen's University Belfast, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.677703.
Testo completoAbstract (sommario):
Kinetic modelling of aftertreatment systems have become a major part of catalyst evaluation and development. A large number of kinetic models have appeared in literature over the past number of decades, varying in application from single reaction models to models capable of simulating a full reaction set for automotive application. All the kinetic models however use either one of two approaches, global kinetics or microkinetics. The kinetic model developed in this work uses both kinetic approaches, allowing the user to select the kinetic approach required for the simulation for each individual reaction. The work presented in this report details the theory behind the kinetic model and development of the micro kinetic and dual kinetic routines. The model is validated against a range of experimental data consisting of end pipe, spatially resolved and vehicle data. Simulations conducted using the -kinetic model proves accurate for each of the kinetic approaches used (global kinetics, micro-kinetics and dual kinetics). with a comparison of each kinetic approach conducted throughout. Integrating micro-kinetics into the kinetic model increased the accuracy of the simulations for the conditions conducted, providing more information for the CO oxidation than previously available using the global kinetic approach. The dual kinetic approach incorporating global kinetics and micro-kinetics provided more accurate results than a purely global kinetic model. The model has been developed to support the further development and expansion of the micro-kinetic reactions.
20
Gonzalez, Calderon Juan David. "Molecular and Kinetic Modelling of the Ammonia Oxidation on Platinum". Thesis, The University of Sydney, 2017. http://hdl.handle.net/2123/17683.
Testo completoAbstract (sommario):
The thesis contributes to the fundamental understanding of the chemistry of ammonia oxidation on platinum. The research concentrates on determining the kinetic and reaction mechanisms for the NH3(g) oxidation with O2(g) on flat and stepped platinum surfaces using first-principles methodologies. The research finds direct applications in the modelling of the NO(g) production from NH3(g), a significant key step in the HNO¬3 manufacture through the Ostwald process. This process is industrially very significant because nearly all of the world's HNO3 is made from NH3(g), and most of the world’s HNO3 production is dedicated to the production of fertilisers. The reactions studied in this work, however, are relevant to other chemical processes of interest such as the selective catalytic oxidation for the removal of NH3(g) from industrial waste streams, and the selective catalytic reduction of NOx. The work carried out seeks fundamental analysis of three main elements of the NH3(g) oxidation, i) the effect of Pt surface morphology towards the formation of N2O(g), ii) the existence of lower activated alternative pathways for NO(g) formation and iii) the effect of the surface coverage on the energetics of selected surface reactions and the adsorption/desorption process. A new thermodynamically-consistent microkinetic model for the NH3(g) oxidation over Pt has been proposed by using the DFT-calculated kinetic parameters on the Pt(211) surface as input parameters. The simulated profiles of NH3(g) conversion and product yields reproduce qualitatively the experimental data obtained previously in our group, for the NH3(g) oxidation over Pt using a micro–tubular reactor. However, sensitivity analysis of the input data suggests small changes to a selected set of values improve the quantitative agreement with experimental observations.
21
Stanford, Natalie Jane. "Towards a full genome-scale model of yeast metabolism". Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/towards-a-full-genomescale-model-of-yeast-metabolism(1c1c018e-3679-4807-ae1b-79d316e09a22).html.
Testo completoAbstract (sommario):
Gaining a quantitative understanding of metabolic behaviour has long been a major scientific goal. Beginning with crude mass balance experiments and progressing through enzyme kinetics, single-pathway models and collaborative efforts such as a community- based yeast reconstruction and onwards to the digital human. The primary goal of this research was to generate a large-scale kinetic metabolic model of yeast metabolism. As a community our ability to produce large-scale dynamic metabolic models has typically been limited by the time and cost involved in obtaining exact measurements of all relevant kinetic parameters. Attempts have been made to bring about a greater understanding by using computational approaches such as flux balance analysis, and also laboratory approaches such as metabolic profiling. Unfortunately these approaches alone do not go far enough to allow for a rich understanding of the metabolic behaviour.Methods were developed that allowed known data such as fluxes, equilibrium constants and metabolite concentrations to be used in first-approximation strategies. These made possible the construction of a thermodynamically consistent model that was reflective of the organism and growth conditions under which the known data were measured. Efforts were made to improve the strategy by developing already known dynamic flux measurement techniques so they were more reflective of the type of data required for constructing the metabolic model. The model constructed, using data from a specific yeast strain in a continuous culture environment, and included 284 reactions. The model showed a reasonable reproduction of system behaviour after perturbations of extracellular glucose above and below the operating conditions, after identification and substitution of just two exact rate laws of reactions that showed high control over the system. The methods developed require little knowledge beyond the stoichiometric matrix in the first instance, and as such, are applicable to any organism that has a reasonably comprehensive network reconstruction available.
22
Meintjes, Maria Magdalena. "Fermentation coupled with pervaporation : a kinetic study / Meintjes M.M". Thesis, North-West University, 2011. http://hdl.handle.net/10394/7283.
Testo completoAbstract (sommario):
Ethanol production through biomass fermentation is one of the major technologies available to produce liquid fuel from renewable energy sources. A major problem associated with the production of ethanol through fermentation remains the inhibition of the yeast Saccharomyces cerevisiae by the produced ethanol. Currently high water dilution rates are used to keep the ethanol concentrations in the fermentation broth at low concentrations, resulting in low yields and increased downstream processing to remove the excess water. Yeast strains that have a high tolerance for ethanol have been isolated but the time and cost associated with doing so poses a challenge.
The fermentation process can be combined with pervaporation, thereby continuously removing ethanol while it is being formed. In this study a mathematical model for ethanol fermentation with yeast, Saccharomyces cerevisiae, coupled with pervaporation was developed. The fermentation of glucose was optimised in the first part of the study and experimental data were obtained to find a kinetic model for fermentation. It was found that an optimum ethanol yield can be obtained with an initial glucose concentration of 15wt%, a yeast concentration of 10 g.L–1, and a pH between 3.5 and 6. The maximum ethanol yield obtained in this study was 0.441g.g–1 (86% of the theoretical maximum) using 15wt% glucose, 10g/L yeast and a pH of 3.5.
Two kinetic models for fermentation were developed based on the Monod model. The substrate–limiting model, predicted fermentation very accurately when the initial glucose concentration was below 20wt%. The second model, the substrate–inhibition model, predicted fermentation very well when high initial glucose concentrations were used but at low glucose concentrations, the substrate–limiting model was more accurate. The parameters for both models were determined by non–linear regression using the simplex optimisation method combined with the Runge–Kutta method.
The PERVAP®4060 membrane was identified as a suitable membrane in this study. The effect of the ethanol content in the feed as well as the influence of the glucose content was investigated. The total pervaporation flux varied with ethanol content of the feed and the highest total flux of 0.853 kg/m2h was obtained at a feed with 20wt% ethanol. The addition of glucose had almost no effect on the ethanol flux but it lowered the water flux, thereby increasing the enrichment factor of the membrane.
The mass transport through the PERVAP®4060 membrane was modelled using the solution–diffusion model and Greenlaw’s model for diffusion coefficients was used. The limiting diffusion coefficient (Di0) and plasticisation coefficients (Bij) were determined by using the Nelder–Mead simplex optimisation method. The theoretical values predicted with the model showed good agreement with the measured experimental values with R2 values above 0.998.
In the third part of this investigation, the kinetic model developed for fermentation was combined with the transport model developed for pervaporation. The combined kinetic model was compared to experimental data and it was found that it could accurately predict fermentation when coupled with pervaporation. This model can be used to describe and better understand the process when fermentation is coupled with pervaporation.Thesis (M.Ing. (Chemical Engineering))--North-West University, Potchefstroom Campus, 2012.
23
Johansson, Dan. "Carbohydrate degradation and dissolution during Kraft cooking : Modelling of kinetic results". Licentiate thesis, Karlstad University, Faculty of Technology and Science, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-1626.
Testo completoAbstract (sommario):
Chemical pulp fibres from wood are commonly used in products associated with packaging as well as with printing and writing. The prevalent way of liberating fibres is by subjecting wood chips to Kraft cooking. This process has a history of almost 130 years and should be both well described and well established. However, new products and new applications that use fibres as an important renewable resource make it all the more important that the properties of fibres be controllable. The properties of wood fibres are influenced by their carbohydrate composition which, in turn, is dependent on the cooking conditions used. This thesis studies the degradation and dissolution of the different carbohydrates during Kraft cooking and summarizes the results in kinetic expressions.
Industrial wood chips from Norway spruce (Picea abies) were cooked at a high liquor-to-wood ratio in an autoclave digester at varying concentrations of hydroxide ions, hydrogen sulphide ions and sodium ions as well as varying temperatures. The pulps were analysed for carbohydrate composition, kappa number, content of hexenuronic acid and the pure cellulose viscosity, i.e. only the cellulose content in the pulp sample was used for calculating the viscosity. Kraft cooking of Eucalyptus urophylla and Eucalyptus grandis was also studied, using industrial liquor-to-wood ratios, to examine the relationship between hexenuronic acids and the amount of xylan in the pulp samples.
For Kraft cooking of Norway spruce it was found that an increase in the concentration of hydroxide ions increased the rate of dissolution of the carbohydrates and the degradation of the cellulose degree of polymerization (DP). However, measured at a kappa number of 30, it is seen that a low hydroxide ion concentration can lower the carbohydrate yield and the pure cellulose viscosity dramatically. The hydroxide ion concentration not only affects the rate of dissolution but also the amount of xylan that reacts in the slower, final phase. Both cellulose and hemicelluloses were found to be affected by the hydrogen sulphide ion concentration. The dissolution of cellulose and hemicelluloses at varying sodium ion concentrations was found to be affected in different directions. The effect of sodium ion concentration on the DP was found to be dependent on the method of evaluation. The pulp viscosity was found to be affected twice as much by the sodium ion concentration than the pure cellulose viscosity was. For Kraft cooking of hardwood it was found that a high xylan yield not always is synonymous with a high hexenuronic acids content.
24
Leamen, Michael. "Kinetic Investigation and Modelling of Multi-Component Polymer Systems with Depropagation". Thesis, University of Waterloo, 2005. http://hdl.handle.net/10012/885.
Testo completoAbstract (sommario):
The phenomenon of depropagation or reverse polymerization for multicomponent polymerizations has been studied in detail. The monomer Alpha-Methyl Styrene (AMS) has been copolymerized with Methyl Methacrylate (MMA) and Butyl Acrylate (BA) at temperatures ranging from 60oC to 140oC and the kinetics have been studied in the form of propagation/cross propagation and depropagation parameters. There have been multiple attempts with varying amounts of success in the past to determine the kinetic parameters for depropagating systems including work by Lowry and Wittmer as well as other modelling methodologies that are not as mechanistic. The most recent development of the mechanistic terminal model is that of the Kruger model. The model is robust and can take into account all special cases as well as all reactions being reversible. The kinetic parameters have been estimated for each of the three binary systems using the Kruger model (MMA/AMS, MMA/BA, BA/AMS). The Alfrey-Goldfinger model is inadequate to describe depropagating terpolymer systems and in order to study them, a new model was developed based upon the binary Kruger model. This new model takes into account a fully depropagating terpolymer system leading to a total of 15 parameters to be estimated. These 15 parameters have the same definitions as those estimated from the binary Kruger model, thus making accurate analysis of the binary systems crucial since these will be used as first estimates for the terpolymer system. Extensive experimental data (composition, conversion and molecular weights) was collected and analysed for the MMA/AMS and BA/AMS systems. For the BA/AMS system both the bulk and solution copolymerizations were studied in detail with the results from the Kruger model not showing a significant difference in the reactivity ratios between the two types of polymerization. For the MMA/AMS system, a bulk study only was done which revealed an interesting phenomenon that points toward a break down of the long chain approximations used for all of the models being studied. For both of these systems, extensive 1H NMR analysis was done to determine the copolymer composition. Data collected in previous research for the MMA/BA system was reanalysed using the Kruger model and it was found that the parameter estimates did not differ significantly from the published values. Extensive benchmarking was done with the newly developed terpolymer model on non-depropagating systems using data from the literature to ensure it worked for the simplest cases. It was found that the model matched the parameter estimates from the literature and in some cases improving upon them to fit the data better. Along with the benchmarking a sensitivity analysis was done which revealed some interesting information. For the MMA/BA/AMS terpolymer system a set of experiments (based upon practical considerations) were performed and the composition of the polymer was determined using 13C NMR instead of the usual 1H NMR due to the difficulty of peak separation for the complex terpolymer. Using the depropagating terpolymer composition data in conjunction with the parameter estimates from the three binary systems allowed for estimation of the 15 kinetic parameters, which showed only minor variation from the binary estimates.
25
Leung, Kai Ming. "Kinetic modelling of hydrocarbon flames using detailed and systematically reduced chemistry". Thesis, Imperial College London, 1995. http://hdl.handle.net/10044/1/7760.
Testo completo
26
Barrett, P. Hugh R. "The kinetic analysis and computer modelling of lipoprotein metabolism in man". Title page, table of contents and abstract only, 1989. http://web4.library.adelaide.edu.au/theses/09PH/09phb274.pdf.
Testo completo
27
Buchanan, Ian 1953. "Kinetic modelling of horseradish peroxidase catalyzed phenol removal for reactor development". Thesis, McGill University, 1996. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=40325.
Testo completoAbstract (sommario):
Horseradish peroxidase (HRP) catalyzes the polymerization of aromatic compounds. These polymers precipitate from solution and may be removed by filtration or sedimentation. The useful lifetime of the enzyme is limited by inactivation which occurs during the removal process; however, the rate of enzyme inactivation is significantly lower in the presence of high molecular mass polyethylene glycol (PEG).An empirical model has been developed to relate phenol concentration after complete batch reaction to the initial concentrations of phenol and HRP, both in the presence and the absence of PEG.
A kinetic model has been developed for the removal process. Enzyme inactivation has been modelled as occurring when free radicals, formed during the catalytic cycle, disrupt the enzyme's active site; and when the enzyme becomes entrapped in the polymers as they form.
The model has been adapted to batch, plug-flow (PFR) and continuous stirred tank reactors (CSTR). The model was calibrated by means of a genetic algorithm using data from bench-scale batch reactors, and validated for batch and plug-flow reactors over a range of phenol concentrations which is normally encountered in industrial effluents. The rate constant associated with enzyme inactivation by free radicals was found to be essentially zero in the presence of PEG.
Calibration of the inactivation rate constants for a CSTR confirmed enzyme inactivation in the presence of PEG to be modelled best by entrapment alone. The estimated value of the rate constant associated with enzyme entrapment in a CSTR was 35% lower than the value estimated for a PFR and batch reactor.
Model simulations and experimental results obtained using a bench-scale multiple-stage CSTR in the presence of PEG showed that the efficiency of enzyme use increased with an increasing number of reactor stages.
These results indicate that a multiple-stage CSTR, to which PEG was added to provide maximum enzyme protection, would be the most favourable environment of those tested during this investigation for the implementation of the HRP-catalyzed process.
28
Xu, Bin. "Coal liquefaction in a flowing-solvent reactor : experiments and kinetic modelling". Thesis, Imperial College London, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.281764.
Testo completo
29
Satheesh, Britto. "Analysis of thermosetting resins using cure kinetic modelling and experimental techniques". Thesis, University of Nottingham, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.603597.
Testo completoAbstract (sommario):
Thermosetting resins undergo irreversible polymerization to form a 3 Dimensional Structure (3D) via a cure reaction. For the present research, properties of thermosetting resins are studied by analysing cure kinetic modelling as well as investigating various additives and fillers to enhance thermal and mechanical propelties for the modified resin composition. Different ratios of Diglycidyl Ether of Bis-Phenol A (DGEBA) are used with aliphatic amidoamine hardener to study the effects of increasing resin content on an epoxy resin/hardener sample. Epoxy/Hardener samples with ratio 2: 1, 3: I and 4: I were studied to investigate the effect of increasing epoxy content on cure and mechanical properties. Analysis using Dynamic Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA) and cure modelling was used to explain the thermal characterization and tests involving tensile, flexural, Scanning Electron Microscopy (SEM) and hardness explain the mechanical property changes when mixing ratio is varied. DSC and TGA results showed the presence of two peaks especially at higher heating rates of non-stoichiometric ratios. Cure kinetic modelling using autocatalytic equation of Cure Rate (du/dt) predicted the bell shaped curve and estimated cure kinetic constants irrespective of the mixing ratio. ABSTRACT Mechanical and thermal property analysis of samples showed that increasing ratio drives brittle behavior for the DGEBA/Hardener samples. The autocatalytic model is also used for investigating thermal behavior of two part epoxy-adhesive sample. Dynamic scans for adhesive were conducted at heating rates of 5, 10 and 15 QC for a temperature ranging from room temperature to 200 QC. The autocatalytic equation still predicted the bell-shaped curve uSll1g cure kinetic constant determined by Borchard and Daniels method. Chitosan a polysaccharide component which is normally found on exoskeleton of shrimps and crabs was added to epoxy resin to alter the chemical :1 and mechanical properties. Here DGEBA was also used as the primary epoxy base with hardener Hexamethylenediamine (HMDA) to create epoxy/hardener blends with different weight percentage of chitosan. Agglomeration at higher loadings of chitosan was confirmed by morphological analysis and this agglomeration inturn compromised the mechanical properties due to the miscibility of chitosan filler in epoxy. There is a considerable change to thermal stability on adding chitosan. This thesis presents new data on the validity of the analytical curing models to determine thermal and mechanical behaviour of epoxy based resins and adhesives. In addition data on chitosan loaded epoxy shows for the first time achievable levels of filler loadings and consequential thermal and mechanical properties.
30
Bennett, Claire Michelle. "Kinetic modelling of recombinant IgG2 biosynthesis in Chinese hamster ovary cells". Thesis, University of Sheffield, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.548539.
Testo completo
31
Ó, Conchúir Breanndán. "Kinetic modelling of transport phenomena at the mesoscale in soft materials". Thesis, University of Cambridge, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.709018.
Testo completo
32
Parker, Mark John. "Kinetic modelling studies of amine-epoxide cure reactions using radiochemical tracers". Thesis, University of Surrey, 1992. http://epubs.surrey.ac.uk/843849/.
Testo completoAbstract (sommario):
The process of curing epoxides with amines has been for many years a route to obtain many useful materials, from everyday substances such as adhesives right through to thermoset resins used in advanced composite manufacture. This work will try to highlight how a combination of chemical and numerical techniques come together to aid the further understanding, of what is an extremely complex reaction. Chapter 1(a) is a general review of epoxy resin curing chemistry, paying particular attention as to how our understanding of the process has developed over several decades, and highlights the various techniques used to study the reaction. Chapter 1(b) describes the experimental approach taken in this work, namely that of using model reactants in combination with radiochemical techniques in order to gain kinetic information about cure reactions. In Chapter 2 the development of the various kinetic models is discussed. It is first described how, and on what basis, various aspects of the cure chemistry are incorporated into the model. One then goes on to describe the numerical analysis applied to the rate equations, and how this is incorporated within the model. The results of the two major aspects of the work are divided into two distinct areas. The first (Chapter 3) deals with the modelling of those reactions using a low initial concentration of primary amine (usually < 0.6M). These systems are devoid of many of the complicating features of cure reactions, and are shown to be modelled to a high degree of accuracy. In essence they are ideal systems, and ones which the initial model (KINET31) used in this study is able to describe. Chapter 3 also describes some studies carried using aromatic diamines, and the modelling performed of these reactions. Chapter 4 on the other hand deals with those reactions which used high initial amine concentrations. By contrast the standard of modelling shown here with KINET31 was much poorer. It is then described how various physical aspects of the cure reaction are investigated in an attempt to highlight the model's inadequacy. It is eventually shown how H-bonding of species, and the formation of pre-complexes, can play a very significant role in cure reactions. When the model is adapted to take these interactions into account a significant improvement is noted (KINET31H). Finally Chapter 5 deals with another interesting aspect of cure reactions, namely that of accelerators. With the model now taking into account the formation of the most are. significant pre-complexes, the reactivities of various -OH type accelerators are investigated.
33
Amos, Terri Emma. "Modelling nanoscale kinetics of radiation damaged surfaces". Thesis, University of Edinburgh, 2015. http://hdl.handle.net/1842/10460.
Testo completoAbstract (sommario):
Materials in nuclear reactors and satellites experience continually damaging radiation which leads to their degradation over time. Currently, a materials safe working lifetime within these environments is estimated with a large, costly, safety margin. The work of this thesis aims to improve the usefulness of an optical technique known as reflection anisotropy spectroscopy (RAS), which once fully characterised could allow materials to be actively monitored in such environments. The intrinsic optical anisotropy of the Cu(110) surface has been exploited to study nanoscale kinetics of ion bombarded surfaces. Within the Cu(110) RA spectrum the 2.1eV peak is particularly sensitive to surface defects and largely unaffected by the bulk of the substrate. Using the Poelsema-Comsa model (which assumes defects scatter surface electronic states within a patch centred on the defect) it can be demonstrated that at finite temperatures the decay of the 2.1eV peak contains information relating to the diffusion of surface defects. A kinetic Monte Carlo simulation has been created to model the destruction of this peak and allows further understanding of the diffusion processes involved. The decay of the 2.1eV peak with ion bombardment has been successfully modelled for a range of temperatures using experimental RAS data for comparison. Through a novel way of analysing RAS data, it has been shown that the total scattering cross section per ion impact decreases with bombardment time, which it is believed to be due to surface diffusion. This could give a novel way of measuring surface diffusion directly from RAS measurements. Clustering of ion induced surface defects has been analysed and the results found are consistent with STM images of the same surface obtained 30 minutes after bombardment. While molecular dynamics calculations have previously attempted to predict the surface topology and defect clustering nanoseconds after impact, using a kinetic Monte Carlo simulation improves on this, demonstrating that diffusion on long time scales (currently inaccessible using molecular dynamics calculations) play an important role in predicting nano-surface topology. 2.1eV peak recovery after surface damage by ion bombardment was also investigated. The peak was found to recover at finite temperatures, which is also seen in experimental data. It was concluded that the surface diffusivity values in the literature are too high and a new value for diffusivity has been calculated by comparing simulation and experimental data.
34
Bassili, Victor Antoine. "Catalytic amination of 1-methoxy-2-propanol : reaction pathway and kinetic modelling /". Zürich, 1991. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=9351.
Testo completo
35
Biley, Chris. "Thermodynamic and kinetic modelling of iron (III) reduction with sulfur dioxide gas". Thesis, Stellenbosch : Stellenbosch University, 2015. http://hdl.handle.net/10019.1/97120.
Testo completoAbstract (sommario):
Thesis (PhD)--Stellenbosch University, 2015.ENGLISH ABSTRACT: Recent developments in the atmospheric treatment of low-grade nickel laterite ores at Anglo American plc has culminated in the conceptual iron-focused laterite (ARFe) process. In addition to the recovery of nickel and cobalt from laterite ore, this process uniquely aims to recover iron as a saleable by-product. The reduction of soluble iron(III) (Fe(III)) by sulfur dioxide gas (SO2) is central to the ARFe concept and represents a complex, multiphase system involving simultaneous gas-liquid mass transfer, thermodynamic speciation and chemical reaction. The chemistry of iron-containing systems is generally poorly understood and accurately predicting their behaviour is challenging, especially under aggressive hydrometallurgical conditions. The primary objective of this work is the development of an engineering model capable of describing the rate and extent of ferric reduction with SO2 under conditions typical of the ARFe process. Thermodynamic considerations provide a rigorous framework for the interpretation of chemical reactions, however little experimental data are openly available for the associated solution species in acidic iron sulfate systems. A key contribution of this work, and critical for the development of the overall model, is the direct measurement of speciation in iron sulfate solutions. Raman and UV-vis spectroscopy were utilised to make direct speciation measurements in the various subsystems of the Fe2(SO4)3-FeSO4-H2SO4-H2O system that were previously unavailable in the open literature. The FeSO+4 and Fe(SO4)– 2 species were explicitly identified and measurements were supported and rationalised by static computational quantum mechanical calculations and ultimately permit the calibration of a robust, ion-interaction solution model with the explicit recognition of the important solution species up to 1.6 mol/kg Fe2(SO4)3, 0.8 mol/kg H2SO4 over 25 – 90 C. Batch and continuous Fe(III) reduction kinetics were measured and the effects of initial Fe2(SO4)3 and H2SO4 concentrations, temperature and in-situ neutralisation quantified. The retardation effect of sulfuric acid was observed to be the most significant factor influencing the initial reaction rate and the achievable extent of reduction at fixed residence time, which varied between about 20 and 80 % after 180 minutes of reaction. A reaction mechanism that is limited by the slow ligand-to-metal electron transfer in the FeIIISO+3 solution species’ decomposition is proposed and spectroscopic measurements and computational quantum mechanical calculations are used to support this mechanism. A kinetic model, comprising a system of differential mass-balance equations, is incorporated into the thermodynamic framework. This reaction model permits the prediction of kinetic profiles over the full range of experimental conditions and can be incorporated into more elaborate simulation models of the ARFe circuit. The specific original contributions of this work are • The direct measurement of aqueous speciation in the Fe2(SO4)3-H2SO4-H2O system by Raman and UV-vis spectroscopy • The development of a modelling framework to characterise speciation, activity coefficients and solubility in the mixed Fe2(SO4)3-FeSO4-H2SO4-H2O system. • The measurement of Fe(III) reduction kinetics using SO2 in concentrated sulfate solutions as a function of initial composition and temperature. • The development of a solution reaction model of Fe(III) reduction with SO2 that accurately predicts the solution speciation and reaction rate with time as a function of composition and temperature. Lastly, the vast complexity of industrial systems will nearly always result in a lack of specific experimental data that are required for the development of phenomenological models. This work emphasises the crucial role that engineering studies hold in the generation of such data to derive maximum practical value for industrial process development and optimisation.
AFRIKAANSE OPSOMMING: Onlangse ontwikkelinge in die atmosferiese behandeling van lae-graad nikkel lateriet erts by Anglo American plc het gelei tot die konseptuele yster gefokus lateriet (ARFe) proses. Bykommend tot die herwinning van nikkel en kobalt uit laterite erts is hierdie proses uniek en daarop gemik om yster te herwin as ’n verkoopbare by-produk. Die vermindering van oplosbare yster(III) (Fe(III)) met swaeldioksied (SO2) is sentraal tot die ARFe konsep en verteenwoordig ’n komplekse, multifase stelsel wat gelyktydige gas-vloeistof massa-oordrag, termodinamiese spesiasie en chemiese reaksie behels. Die oplossingschemie van ysterstelsels word, oor die algemeen, swak verstaan en om hul gedrag akuraat te voorspel is ’n uitdaging, veral onder aggressiewe hidrometallurgiese kondisies. Die primêre doel van hierdie werk is die ontwikkeling van ’n ingenieursmodel wat die tempo en omvang van yster(III) vermindering met SO2 onder tipiese ARFe proses toestande beskryf. Termodinamiese oorwegings stel ’n streng raamwerk voor vir die interpretasie van chemiese reaksies, alhoewel daar egter min eksperimentele data openlik beskikbaar is vir die gepaardgaande oplossing spesies in suur yster(III) sulfaat stelsels. ’n Belangrike bydrae van hierdie werk, en van kritieke belang vir die ontwikkeling van die algehele model, is die direkte meting van spesiasie in yster(III) sulfaat oplossings. Raman en UV-vis spektroskopie is gebruik om direkte spesiasie metings te maak in die verskillende subsisteme van die Fe2(SO4)3-FeSO4-H2SO4-H2O stelsel wat voorheen nie in die oop literatuur beskikbaar was nie. Die FeSO+4 en Fe(SO4)– 2 spesies is ekplisiet geïdentifiseer, terwyl die metings ondersteun en gerasionaliseer is deur statiese kwantummeganiese berekeninge wat uiteindelik die kalibrasie van ’n robuuste, ioon-interaksie model tot gevolg hê wat ook die belangrike oplossingspesies duidelik beklemtoon tot en met 1.6 mol/kg Fe2(SO4)3, 0.8 mol/kg H2SO4 en tussen 25 – 90°C. Enkellading en kontinue yster(III) verminderingskinetika is gemeet en die gevolge van die aanvanklike Fe2(SO4)3 en H2SO4 konsentrasies, temperatuur en in-situ neutralisasie is gekwantifiseer. Die waargeneemde vertragingseffek van swaelsuur is die mees beduidende faktor wat die aanvanklike reaksietempo en die haalbare reaksie omvangsvermindering na ’n vaste residensietyd van 180 minute bepaal, wat wissel tussen ongeveer 20 en 80%. ’n Reaksiemeganisme word voorgestel wat beperk word deur die stadige ligand-totmetaal elektronoordrag in ontbinding van die Fe(III)SO+3 oplossing-spesies en wat verder deur spektroskopiese metings en kwantummeganiese berekenings ondersteun word. A kinetiese model, wat bestaan uit ’n stelsel van gedifferensieerde massa-balans vergelykings, is in die termodinamiese raamwerk geïnkorporeer. Hierdie reaksie-model laat die voorspelling van kinetiese profiele toe oor die volle omvang van die eksperimentele toestande en kan in meer uitgebreide simulasie modelle van die ARFe proces geinkorporeer word. Die spesifieke en oorspronklike bydraes van hierdie werk is • Die direkte meting van die spesiasie in die Fe2(SO4)3-H2SO4-H2O stelsel deur Raman en UV-vis spektroskopie • Die ontwikkeling van ’n modelraamwerk om spesiasie, aktiwiteitskoëffisiënte en oplosbaarheid in die gemengde Fe2(SO4)3-FeSO4-H2SO4-H2O stelsel te karakteriseer. • Die meting van yster(III) vermideringskinetieka deur SO2 in gekonsentreerde sulfate oplossings te gebruik as ’n funksie van die aanvanklike samestelling en temperatuur. • Die ontwikkeling van ’n oplossingsreaksie-model van yster(III) vermindering met SO2 wat die oplossing-spesiasie en reaksietempo met die tyd as ’n funksie van samestelling en temperatuur akkuraat voorspel. Laastens, die oorgrote kompleksiteit van industriële stelsels sal byna altyd lei tot ’n gebrek van spesifieke eksperimentele data wat nodig is vir die ontwikkeling van fenomenologiese modelle. Hierdie werk beklemtoon die belangrike rol wat ingenieursstudies speel in die generasie van data wat sodanig tot maksimum praktiese waarde vir industriële prosesontwikkeling en optimalisering lei.
36
Mocke, Leanie. "Kinetic modelling of wine fermentations : why does yeast prefer glucose to fructose". Thesis, Stellenbosch : Stellenbosch University, 2013. http://hdl.handle.net/10019.1/80316.
Testo completoAbstract (sommario):
Thesis (MSc)--Stellenbosch University, 2013.ENGLISH ABSTRACT: In the present-day competitive global market, wine industries are constantly aiming to improve the wine-making process,including the role of yeast. The most commonly used wine yeast is Saccharomyces cerevisiae, which is able to produce high quality wines, but problem fermentations do sometimes arise. The occurrence of stuck and sluggish fermentations pose a serious problem leading to loss of productivity and quality. Although the precise mechanism leading to stuck fermentations is unknown, they are often correlated with high fructose to glucose ratios in the wine-must. S. cerevisiae is a glucophylic yeast, indicating its preference for consuming glucose over fructose. Both these hexose sugars are present in unfermented wine must, mostly in equal concentrations. As fermentation progresses, glucose is consumed at a faster rate than fructose, leading to an increase in the fructose to glucose ratio. Yeast are left with the undesirable fructose at the later stages of fermentation, when the environmental stresses on the yeast can lead to stuck or sluggish fermentation. This residual fructose can lead to undesirable sweetness, as fructose is about twice as sweet as glucose. Even with the extensive research into yeast metabolism, there is as yet no definitive explanation as to why yeasts ferment glucose faster than fructose. This study aimed to investigate the mechanism responsible for the faster consumption of glucose over fructose of a commercially used wine yeast strain S. cerevisiae VIN 13. The first two steps of sugar metabolism, uptake and phosphorylation, were investigated as the possible sites of discrepancy in fermentation rates. Enzyme rates and affinities for both glucose and fructose as substrates for the relevant enzymes were experimentally determined. These kinetic parameter values were used to improve an existing model of yeast glycolytic pathway to model wine fermentations. The feasibility of constructing and validating a kinetic model of wine fermentations were investigated, by comparing model predicted fluxes with experimentally determined fluxes. Another aspect of this study was an investigation into the effect of hexose sugar type on fermentation profiles. Wine fermentations were done with only one hexose sugar as carbon source to determine if it has an effect on the flux through metabolism. This work succeeded in the construction of a kinetic model that distinguished between glucose and fructose as carbon source. The glucose was consumed faster than fructose, with control lying in the hexose transport step. It was also established that fermentation prfiles of fermentations with only one sugar was the same for both one sugar type fermentations. Fermentation with either glucose or fructose as the sole carbohydrate source had the same specfic production and consumption rates as normal fermentations with both sugars. Construction of detailed kinetic models can aid in the metabolic and cellular engineering of novel yeast strains. By identifying the importance of hexose transport, and thus the glucophilic character of the yeast, in flux control, yeast transporters can be targeted for strain improvement. This may in turn lead to more effective fermentation practices for controlling problem fermentations, or to the development of novel strains that utilizes fructose in the same manner as glucose, and in so doing lower the risk of stuck or sluggish wine fermentation.
AFRIKAANSE OPSOMMING: In die hedendaagse kompeterende wynmark is wynmakers aanhoudend besig om die wynmaak proses te verbeter en dit sluit die verbetering van wyngis in. Die mees algemeenste gebruikte wyngis is Saccharomyces cerevisiae, omdat dit wyn van gehalte produseer, maar probleem fermentasies kom wel voor. Die verskynsel van vasval of stadige fermentasies kan lei tot die verlies van produksie en kwaliteit. Die oorsaak van probleem fermentasies is gewoontlik veelvoudig, maar die verhouding van glukose tot fruktose in die wyn-mos kan ongunstig raak om fermentasies te onderhou. S. cerevisiae is 'n glukofiliese gis, wat sy voorkeur om glukose bo fruktose te gebruik beskryf. Albei hierdie heksose suikers is teenwoordig in ongefermenteerde wyn-mos, meestal in gelyke hoeveelhede. Soos fermentasies vorder word glukose vinniger verbruik as fruktose wat lei tot 'n toename in die fruktose tot glukose verhouding. Die gis moet dus die fruktose in die later stadium van fermentasie gebruik wanneer die omgewings druk op die gis kan lei tot probleem fermentasies. Die oorblywende fruktose kan lei tot ongewenste soetheid aangesien fruktose twee keer soeter is as glukose. Selfs met die ekstensiewe navorsing met betrekking tot gis metabolisme is daar nog nie 'n verduideliking hoekom gis glukose vinniger as fruktose gebruik nie. Hierdie studie het beoog om die meganisme wat lei tot die vinniger verbruik van glukose oor fruktose te ondersoek vir 'n kommersieël gebruikte gis S. cerevisiae VIN 13. Die eerste twee stappe van suiker metabolisme, suiker opname en fosforilasie, was ondersoek as die moontlike punt van die verskil in fermentasie tempo. Ensiem snelhede en affiniteite vir beide glukose en fruktose as substrate vir die ensieme van belang was eksperimenteel bepaal. Hierdie waardes is gebruik om 'n bestaande model van gis glikolise aan te pas vir wyn fermentasies. Die uitvoerbaarheid van saamstel en valideer van 'n kinetiese model van wyn fermentasies was ondersoek, deur model voorspelde fluksie waardes met eksperimentele fluksie waardes te vergelyk. 'n Ander aspek van die studie was die ondersoek van die effek van heksose suiker tipe op fermentasie profiel. Wyn fermentasies is gedoen met slegs een heksose suiker as koolstof bron om te bepaal of dit 'n invloed het op die fluksie deur metabolisme. Hierdie werk het daarin geslaag om 'n kinetiese model saamtestel wat onderskei tussen glukose en fruktose as koolstof bron. Die glukose is vinniger verbruik as fruktose, met beheer gesetel in die heksose opname stap. Dit was ook vasgestel dat fermentasie profiele van fermentasies met slegs een suiker nie verskil het vir fermentasies met slegs fruktose of glukose. Fermentasies met slegs een suiker het dieselfde spesifieke produksie en konsumpsie tempo gehad as die normale fermentasie met albei suikers. Die konstruksie van 'n gedetailleerde kinetiese model kan gebruik word in die metaboliese en sellulêre ontwikkeling van nuwe gisstamme. Deur die ontdekking van die belangrikheid van heksose opname in fluksie beheer, wat lei tot die glukofiliese karakter van gis, kan gis opname geteiken word vir gis ontwikkeling. Dit mag om die beurt lei tot meer effektiewe fermentasie praktyk in die beheer van probleem fermentasies, of die ontwikkeling van nuwe stamme wat fruktose in dieselfde manier as glukose benut, en sodoende die risiko van vasval of stadige wyn fermentasies verlaag.
National Research Foundation
Post-graduate Merit Bursary
37
Storr, Mark Timothy. "Computer modelling of the mode of action of gas hydrate kinetic inhibitors". Thesis, University of Warwick, 2001. http://wrap.warwick.ac.uk/79629/.
Testo completoAbstract (sommario):
This thesis reports an investigation of two families of potential gas hydrate inhibitor: quaternary amine carboxylates and sulphonates. Molecular dynamics simulations of the inhibitors have been performed both in liquid water and at the surface of a thin hydrate film under natural gas. Trajectories were analysed to determine inhibitor effects upon the structure of the water and the stability of the gas hydrate lattice. TIP conditions for the thin film study were determined from the calculated stability of a structure II gas hydrate under pressure. All three studies were analysed using radial distribution functions, time correlation functions, and order parameters to probe the underlying structure. To complement the computer modelling study, an experimental investigation of one of the amine sulphonates, N,N ,N-tributylammonium-l-(3-propylsulphonate), and one established inhibitor, polyvinylpyrrolidone was performed. These measured the effect of the inhibitor on nucleation time, crystal growth and morphology for both tetrahydrofuran and ethane hydrate. Results from the liquid water simulations indicate that bulk water is largely unaffected by the inhIbitors, while solvated water shows increased short- and long-range structure. Hydrate pressures were determined from the thin film simulations. A transition to a high-pressure phase was also found at around 20 kbar. These results are consistent with experimental data. Pressures in the middle of the hydrate stability zone were adopted for the subsequent inhibitor simulations. Inhibitor behaviour at the interface showed signs of relaxation of the gas hydrate water network, while for solvated water there was a contraction in the water network for the carboxylates head group. The experimental investigation revealed the amine sulphonate to be a more effective kinetic inhibitor of hydrate formation than polyvinylpyrrolidone. This was achieved by delaying nucleation, along with some growth modifying properties.
38
Catarino, Maria Teresa Nunes Mangas. "Thermodynamic and kinetic modelling of the redox properties of tetrahaem cytochromes C3". Doctoral thesis, Faculdade de Ciências e Tecnologia, 1998. http://hdl.handle.net/10362/4763.
Testo completoAbstract (sommario):
Dissertação apresentada para obtenção do grau de Doutor em Bioquímica,especialidade Bioquímica-Física, pela Universidade Nova de Lisboa, Faculdade de Cincias e TecnologiaThe work presented in this thesis concerns the description and modelling of the thermodynamic and kinetic properties of tetrahaem cytochromes C3 isolated from different Desulfovibrio spp.. Sulfate-reducing bacteria produce tetrahaem cytochrome C3 in large quantities. This small (13 - 15 kD) protein is located in the periplasmic space of the cells,where it has been proposed to work as a cofactor of the enzyme hydrogenase. The four haems in cytochrome C3 are covalently bound to the protein through thioether linkages with cysteinyl residues and all display bis-histidinyl axial coordination. Although the degree of homology between the amino acid sequence of cytochromes C3 isolated from different organisms is low, the architecture of the haem core, is strictly conserved. The modelling of the thermodynamic properties of this protein has to take into account the fact that the four haems display different, interacting, and pH dependent redox potentials. Various approaches are described and discussed in this thesis, giving special emphasis to models which include both haem-haem and haem-proton interactions. To explain the pH dependence of the NMR resonances, the acid/base (NB) model was developed under the assumption that the protein could undergo a proton-linked conformational change, each conformation being characterised by a different set of microscopic redox potentials and haemhaem interacting potentials. The model of five interacting centres, developed later, demonstrated that it is not necessary to make any structural assumptions and that the experimental data can be simulated using fewer parameters, which are therefore better defined. According to this model, the thermodynamic properties of cytochrome C3 can be described by the intrinsic microscopic parameters of one acid/base and four redox centres plus the two-site interactions established between the five centres, namely, six haem-haem interactions plus four haem-proton interactions. Application of this model to NMR and visible redox titrations enabled the accurate determination of the complete set of microscopic parameters that characterise the thermodynamic behaviour of cytochromes C3 isolated from D. gigas and D. vulgaris. It is apparent from the values of the thermodynamic parameters that these cytochromes are able to perform a concerted two-electron step, which is coupled to the simultaneous uptake or release of protons, depending on the direction of the electron flow. These properties allow cytochrome C3 to work as an energy transducing system. However, since kinetic control of the electron and proton transfer steps is essential to achieve energy transduction, the kinetic properties of cytochrome C3 isolated from D. gigas are described and analysed in the second half of this thesis, making use of a specially developed kinetic model.
39
Coleman, Matthew. "Flux balance techniques for modelling metabolic networks and comparison with kinetic models". Thesis, University of Nottingham, 2018. http://eprints.nottingham.ac.uk/50999/.
Testo completoAbstract (sommario):
A variety of techniques used to model metabolic networks are examined, both kinetic (ODE) models and flux balance (FB) models. These models are applied to a case study network describing CO and CO2 metabolism in Clostridium autoethanogenum, bacteria which can produce both ethanol and butanediol from a source of carbon monoxide. ODE and FB methods are also used to model a variety of simpler networks. By comparing the results from these simpler networks, the strengths and weaknesses of each examined method are highlighted, and ultimately, insight is gained into the conclusions that can be drawn from each model. ODE models have commonly been used to model metabolism in both in vivo and in vitro contexts, allowing the dynamic behaviour of wildtype bacteria to be examined, as well as that of mutants. An ODE model is formed for the C. autoethanogenum network. By exploring a range of parameter schemes, the possible long timescale behaviours of the model are fully determined. The model is able to exhibit both steady states, and also states in which metabolite concentrations grow indefinitely in time. By considering the scalings of these concentrations in the long timescale, six different non-steady behaviours are categorised and one steady. For a small range of parameter schemes, the model is able to exhibit both steady and unsteady behaviours in the long timescale, depending on initial conditions. FB methods are also applied to the same network. First flux balance analysis (FBA) is used to model the network in steady state. By imposing a range of constraints on the model, limits on levels of flux in the network that are required for a steady-state are found. In particular, boundaries on the ratio of inputs into the network are calculated, outside of which steady states cannot exist. Comparing the steady state regions predicted by FBA and our ODE model, it is found that the FBA model predicts a wider range of conditions leading to steady state. FBA is only able to observe a network in steady state, so an extension of FBA, known as dynamic flux balance analysis (dFBA), is used to examine non-steady-state behaviours. dFBA predicts similar long term non-steady behaviour to the ODE models, with states in which concentrations of some metabolites are able to grow indefinitely in time. These dFBA states do not precisely match those found by the ODE model, and states that cannot be observed in the ODE model are also found, suggesting that other ODE models for the same network could exhibit different long timescale behaviours. The examples considered clarify the strengths and weaknesses of each approach and the nature of insight into metabolic behaviour each provides.
40
BONANOMI, NICOLA. "Experimental investigation and gyro-kinetic modelling of turbulent transport in thermonuclear plasmas". Doctoral thesis, Università degli Studi di Milano-Bicocca, 2018. http://hdl.handle.net/10281/198976.
Testo completoAbstract (sommario):
ITER (International Thermonuclear Experimental Reactor) rappresenterà un passo fondamentale per la realizzazione della fusione termonucleare controllata. Tra i problemi ancora aperti, il controllo del trasporto turbolento è cruciale per ITER, che richiederà alti valori di temperatura, densità e confinamento del plasma. Questo lavoro si focalizza su quattro aspetti riguardanti il trasporto di calore turbolento nel centro del plasma: l'effetto delle impurezze leggere, l'effetto delle particelle veloci, il ruolo delle instabilità su scala elettronica e delle interazioni multi-scala e l'effetto della massa della specie ionica principale del plasma (effetto isotopico). L'esecuzione e l'analisi di esperimenti in plasmi in L-mode nel tokamak JET è affiancata dall'uso di simulazioni giro-cinetiche con il codice GENE e da test dei modelli quasi-lineari TGLF e QuaLiKiz, usati per la predizione di plasmi di ITER. Il trasporto turbolento è principalmente dovuto a instabilità su scale dell'ordine del raggio di Larmor ionico ed elettronico causate dai gradienti della temperatura ionica ed elettronica oltre una soglia in tali gradienti. Sopra tale soglia, il flusso turbolento cresce con un tasso che determina quanto le temperature sono rigide rispetto a un incremento della potenza di riscaldamento. Soglia e livello di rigidità sono usate in questa tesi per caratterizzare lo stato turbolento del plasma in diverse condizioni. Sono misurate sperimentalmente e comparate con le predizioni numeriche per una validazione dei modelli utilizzati. Le instabilità su scala elettronica sono state trovate fondamentali per spiegare il flusso di calore elettronico sperimentale. Una forte interazione tra scale ioniche ed elettroniche è stata osservata, i modi su scala elettronica essendo più forti quando i modi su scala ionica sono vicini alla stabilità, come sarà in ITER. TGLF è in buon accordo con le simulazioni giro-cinetiche ed è adatto per predizioni qualitative di questi effetti in scenari futuri. Riguardo alle impurezze leggere, le densità di 3He,Be,C,N e Ne e hanno differenti profili radiali negli stessi plasmi, mentre le simulazioni predicono lo stesso profilo per tutte le impurezze. Plasmi in cui N è stato iniettato hanno gradienti di Ti più alti, ben riprodotti e spiegati dalle simulazioni giro-cinetiche. TGLF e QuaLiKiz hanno punti di disaccordo con le simulazioni giro-cinetiche. Indicazioni sui miglioramenti necessari sono state fornite. Una prima prova sperimentale di una forte stabilizzazione del trasporto di calore dovuta alle particelle veloci è stata ottenuta in plasmi con bassa rotazione. Le simulazioni giro-cinetiche indicano due principali meccanismi di stabilizzazione. Uno elettrostatico legato a interazioni risonanti onde-particelle veloci, uno elettromagnetico e sensibile alla pressione del plasma. Anche la funzione di distribuzione delle particelle veloci è determinante. Questi meccanismi non sono ancora stati introdotti nei modelli quasi-lineari. Infine, plasmi di deuterio sono stati comparati con plasmi di idrogeno con simili parametri. Te e Te sono più basse in plasmi di idrogeno e le differenze partono dal bordo del plasma. Nessuna differenza sostanziale è stata osservata nel trasporto di calore a bassa potenza, ma ad alta potenza, quando le particelle veloci sono importanti, il loro effetto di stabilizzazione è minore in plasmi di idrogeno. Una spiegazione è stata trovata nella diversa pressione delle particelle veloci, che in H è la metà di quella in D , a causa di diverse configurazioni dei sistemi di riscaldamento. In conclusione, differenti aspetti del trasporto di calore turbolento sono stati studiati in plasmi L-mode del JET. Un'interpretazione dei risultati sperimentali è stata ottenuta con l'aiuto di simulazioni giro-cinetiche, e alcuni effetti fisici rilevanti per ITER sono stati identificati. Indicazioni sulla validità e su possibili miglioramenti dei modelli utilizzati sono state ottenute.ITER (International Thermonuclear Experimental Reactor) will represent a fundamental step in the realization of controlled thermonuclear fusion. Among the problems still open, the understanding of the turbulent transport in the plasma is crucial for ITER, that will require high plasma temperature, density and confinement. This work focuses on four topics related to the thermal transport in a tokamak plasma core: the effects of light impurities, the effects of fast particles, the role of electron scale turbulence and multi-scale interactions and the effects of the plasma main ion mass (isotope effect). It covers the execution and analysis of experiments in JET tokamak L-mode plasmas, the use of local gyro-kinetic simulations (using the GENE code) to model the plasma and the test of the quasi-linear models TGLF and QuaLiKiz, used for ITER predictions. The turbulent transport in a tokamak is mainly due to instabilities on scales of the order of ion or electron Larmor radius driven by the ion and electron temperature gradients over a threshold in these gradients. Above the threshold, the turbulent flux increases with a rate that determines how stiff the temperature profiles are against an increase of heating power. Threshold and stiffness are key concepts used in this thesis to characterize the turbulent state of plasmas in different conditions. They are measured experimentally and compared to the theoretical predictions, providing a deeper insight into the plasma behavior and a stringent validation procedure for the models. Electron scale modes have been found determinant to explain the experimental electron heat flux and stiffness. A strong interaction between ion and electron scales was also found, with electron modes being strongest in conditions where ion scale modes are marginal stable, as will be the case in ITER. The TGLF model is in good agreement with the multi-scale gyro-kinetic simulations and can therefore be suitable for at least a qualitative exploration of these effects in future scenarios. Regarding the light impurities, the density profiles of 3He,Be,C,N and Ne show different peaking in the same plasmas, whilst theory predicts similar peaking for all the impurities. Discharges with N injection show higher peaking of Ti, well explained and reproduced by gyro-kinetic simulations. TGLF and QuaLiKiz show several discrepancies with the gyro-kinetic simulations. Indications have been provided on the improvements needed. A first experimental evidence of a strong thermal transport stabilization due to fast ions has been obtained in plasmas with low rotation. Gyro-kinetic simulations indicate two main stabilization mechanisms. One is electrostatic and related to a resonant wave-fast particle interaction, one is electromagnetic and sensitive to the total plasma pressure. The fast ion distribution function has also an influence on the level of the stabilization. These mechanisms are still not included in the quasilinear models. Finally, D plasmas have been compared to H plasmas with similar operational settings. Te and Ti are lower in H plasmas, the difference starting at the plasma edge. No substantial differences have been observed in the thermal transport in the plasma core at low power, but at high power, when fast ions are important, their stabilization effects appear less strong in H plasmas. An explanation has been found in the differences between the fast ion populations, with H plasmas featuring ~1/2 of the fast ion pressure in D, due to the different parameters of the heating systems. In conclusion, different aspects of thermal turbulent transport have been studied in JET L-mode plasmas. An interpretation of the experimental results has been reached with the help of gyro-kinetic simulations, and some physical effects have been evidenced to be relevant for future ITER scenarios. Some important indications on the validity and on possible improvements of the available numerical models have been obtained.
41
Zhao, Wei. "Dehydrogenation mechanisms of methyl-cyclohexane on γ-alumina supported platinum subnanometric-clusters : DFT coupled with experimental kinetics and kinetic modelling". Thesis, Lyon, 2017. http://www.theses.fr/2017LYSEN052/document.
Testo completoAbstract (sommario):
Le reformage catalytique vise à transformer les naphtas en aromatiques à haut indice d'octane et à produire simultanément du dihydrogène. Le catalyseur utilisé est composé d’agrégats sub-nanométriques à base de platine hautement dispersées sur un support d’alumine-gamma dont le comportement en réaction pose de nombreuses questions. Nous étudions expérimentalement et théoriquement une réaction modèle qui sonde les sites métalliques, la déshydrogénation du methyl-cyclohexane en toluène. Une compréhension détaillée à l'échelle atomique des mécanismes impliqués et des paramètres cinétiques est nécessaire. Nous avons mise en œuvre des calculs DFT (PBE et PBE-dDsC) sur un modèle pertinent Pt13/alumine-gamma, afin de déterminer les intermédiaires, les états de transition et leurs enthalpies libres. Le mécanisme a été exploré via des étapes séquentielles de rupture des liaisons C-H. Une reconstruction des agrégats se produit le long du chemin réactionnel, mettant en évidence sa fluctionalité (confirmée par dynamique moléculaire). Les enthalpies libres d’activation de la rupture C-H, de migration d’hydrogène et de reconstruction de l’agrégat ont été systématiquement déterminées à T=625 K. L'enthalpie libre la plus élevée (ΔrG‡=95 kJ/mol) est trouvée pour la troisième rupture de liaison C-H sur le methyl-cyclohexène. L'intermédiaire le plus stable est le produit adsorbé {toluène+H2}. Cependant, d’autres étapes de rupture C-H ou de désorption du toluène sont compétitives. Les constantes de vitesse des étapes élémentaires obtenues par DFT sont introduites dans 8 modèles cinétiques différents de type Langmuir-Hinshelwood (LH). La nature de l'étape déterminante de la vitesse a été choisie en fonction des constantes de vitesse de chaque étape élémentaire individuelle, ou de la prise en compte de séquences d’étapes limitantes, grâce à une analyse de type « energetic span ». Nous avons finalement expérimentalement réalisé des tests catalytiques sur Pt/γ-alumine (0.3 wt% Pt) à différentes températures, temps de contact, pressions partielles d’hydrogène et de méthylcyclohexane, pour obtenir des données cinétiques expérimentales. L'enthalpie d'activation apparente de 196 kJ/mol calculée par l’un des meilleurs modèles LH (3ème rupture C-H limitante) est proche de l’expérience (195 kJ/mol). De plus, l’évolution des vitesses de réaction en fonction des pressions partielles d'hydrogène et de méthylcyclohexane est discutée au regard de l’expérience et des modèles. Même si les tendances sont recouvrées par les modèles, des écarts théorie-expérience sont mis au jour, ce qui ouvre des perspectives vers une modélisation microcinétique futureCatalytic reforming aims at transforming naphta into high octane aromatics and producing simultaneously dihydrogen. The catalyst used is composed of platinum-based sub-nanometric clusters highly dispersed on a gamma-alumina support which behavior under reaction conditions is the subject of numerous questions. We investigate experimentally and theoretically one model reaction probing the metal sites, the dehydrogenation of methyl-cyclohexane into toluene. A detailed atomic scale understanding of the mechanisms involved, and their related kinetic parameters, is required. We undertook DFT calculations with PBE and PBE-dDsC functionals on a relevant Pt13/γ-alumina model, in order to determine the intermediates, transition states and their free energies. The reaction mechanism was explored by assuming sequential C-H breaking steps. Reconstructions of the cluster and hydrogen migrations occur along the reaction pathway, highlighting its high fluctionality (also confirmed by molecular dynamics). Free energies of activation for C-H bond breaking, H migration and cluster’s reconstruction were systematically determined at T=625 K. The highest activation Gibbs free energy (ΔrG‡=95 kJ/mol) is found for the third C-H bond breaking on methyl-cyclohexene, while the most stable intermediate is the {toluene+H2} adsorbed product. However, other C-H bond breaking steps and eventually toluene desorption may compete. A comparison with the Pt (111) surface is also given. Rate constants of elementary steps estimated by DFT are introduced in 8 Langmuir-Hinshelwood (LH) kinetic models based on a single rate determining step (RDS) concept, or on a limiting steps sequence deduced from an energetic span analysis. We finally carried out experimental tests on Pt/γ-alumina catalysts (0.3 wt% Pt) at various temperatures, space times, hydrogen and methyl-cyclohexane partial pressures, to provide experimental kinetic data. The calculated apparent activation enthalpy is predicted to be 196 kJ/mol in close agreement with the experimental one (195 kJ/mol) for the best LH model (third C-H bond breaking as RDS). Moreover, the dependence of reaction rates on hydrogen and methyl-cyclohexane partial pressures are discussed with respect to experimental trends and models. Although the main trends are recovered by the kinetic model, some discrepancies are revealed. This work paves the way for a future microkinetic modeling
42
Angeloudis, Athanasios. "Numerical and experimental modelling of flow and kinetic processes in serpentine disinfection tanks". Thesis, Cardiff University, 2014. http://orca.cf.ac.uk/58914/.
Testo completoAbstract (sommario):
New water directives impose strict regulations to reduce the footprint of treatment operations and contaminant levels, which suggest a performance review of water treatment facilities, including disinfection contact tanks. Serpentine contact tank units suggest plug flow to be the optimal hydrodynamic condition at which disinfection performance is maximized. However, previous studies indicate that flow exhibits a residence time distribution (RTD) which can be significantly distorted from what is dictated by plug flow. Over the years, there has been rising concern over the impact of such digressions from optimal hydraulic conditions on microbe inactivation and the regulation of potentially carcinogenic Disinfection By-Products (DBPs). With the growth of computing power and the advancement of computational models, the potential of contact tank water disinfection optimization by means of numerical modelling techniques can be assessed. In this study, Acoustic Doppler Velocity (ADV) and fluorescent tracer dye measurement campaigns are carried out to assess the hydraulic efficiency of a serpentine contact tank physical model and evaluating appropriate indicators. Then, three-dimensional Computational Fluid Dynamics (CFD) models are set up to simulate the hydrodynamic and solute transport processes for a variety of contact tank geometries examining the effects of inlet design, baffling configuration and tank scale. The simulation capability to reproduce the actual conditions is attested through comparisons against available laboratory results. The CFD approach is subsequently refined with appropriately selected kinetic models, describing the processes of disinfectant decay, pathogen inactivation and DBP formation. Results highlight that computational models can become invaluable tools for the simulation of disinfection processes as they can reproduce the conditions encountered experimentally to a satisfactory extent. Moreover, the optimization of hydraulic efficiency, as studied numerically, facilitates more uniform disinfectant contact time which corresponds to greater levels of pathogen inactivation and a more controlled by-product accumulation.
43
Håkansson, David. "Aerothermal and Kinetic Modelling of a Gas Turbine Dry Low Emission Combustion System". Thesis, KTH, Strömningsmekanik och Teknisk Akustik, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-298477.
Testo completoAbstract (sommario):
Growing environmental concerns are causing a large transformation within the energy industry. Within the gas turbine industry, there is a large drive to develop improved modern dry-low emission combustion systems. The aim is to enable gas turbines to run on green fuels like hydrogen, while still keeping emission as NOx down. To design these systems, a thorough understanding of the aerothermal and kinetic processes within the combustion system of a gas turbine is essential. The goal of the thesis was to develop a one-dimensional general network model of the combustion system of Siemens Energy SGT-700, which accurately could predict pressure losses, mass flows, key temperatures, and emissions. Three models were evaluated and a code that emulated some aspects of the control system was developed. The models and the code were evaluated and compared to each other and to test data from earlier test campaigns performed on SGT-700 and SGT-600. Simulations were also carried out with hydrogen as the fuel. In the end, a model of the SGT-700 combustion chamber was developed and delivered to Siemens Energy. The model had been verified against test data and predictions made by other Siemens Energy thermodynamic calculation software, for a range of load conditions. The preforms of the model, when hydrogen was introduced into the fuel mixture, were also tested and compared to test dataEn växande medvetenhet kring klimatfrågan, har medfört stora förändringar i energibranschen. I och med detta behöver även gasturbinindustrin förbättra de nuvarande dry-low emissions systemen och göra det möjligt för gasturbiner att förbränna gröna bränslen som väte. Samtidigt måste också utsläppen av NOx hållas nere. För att kunna utforma dessa system behövs en fullständig förståelse för de aerotermiska och kinetiska processerna i en gasturbins förbränningskammare. Målet med detta examensarbete var att utveckla en endimensionell generell nätverksmodell för förbränningssystemet i Siemens Energys SGT-700. Modellen skulle noggrant kunna förutsäga tryckförluster, massflöden, viktiga temperaturer samt utsläpp. Tre modeller utvärderades och en kod som emulerade vissa aspekter av styrsystemet utvecklades också. Modellerna och koden utvärderades och jämfördes mot varandra och även mot testdata från tidigare testserier som utfördes på SGT-700 och SGT-600. Simuleringar utfördes också med väte som bränsle. Slutligen levererades en modell av SGT-700 förbränningskammaren till Siemens Energy. Modellen har verifierats för en rad olika lastfall, mot testdata och data som genererats av andra termodynamisk beräkningsprogram som utvecklats av Siemens Energy. Hur modellen uppförde sig när väte var introducerat in i olika lastfall jämfördes också mot testdata
44
Ostergaard, Kasper Korsholm. "Gas hydrate stability in the petroleum industry and its application in gas-liquid separation". Thesis, Heriot-Watt University, 2000. http://hdl.handle.net/10399/574.
Testo completo
45
EMVALOMENOS, Gaelle. "Quantitative Methods For Detection of Transient Changes in Endogenous Dopamine For Preclinical PET Studies". Thesis, The University of Sydney, 2021. https://hdl.handle.net/2123/25710.
Testo completoAbstract (sommario):
This thesis investigates quantitative methods for the characterisation of dopamine (DA) release in preclinical PET. The goal was to develop methodologies that improve quantification of the PET signal and test to what extent these techniques can reliably detect subtle DA fluctuations. Ultimately, reliable quantification could help to better understand the role of DA in human brain conditions.
The focus of this work is kinetic modelling, whose accuracy depends on different factors, from the quality of the measured imaging data to the interpretation of parameter estimates. An investigation of the model, linear parametric neurotransmitter PET (lp-ntPET), that enables the description of time-varying DA changes, was performed in 3 contexts.
First, its performance was tested in a Bayesian framework, the PET-ABC method. Second, it was evaluated in 1D-simulations by varying the activations and the priors, to study their effects on uncertainty in the estimates. Third, a [11C]raclopride study was performed in monkeys using the high sensitivity MiniExplorer, where different amphetamine doses were injected to induce variable DA releases. Finally, towards exploiting the synergies of PET/fMRI data in the future, a preclinical PET insert was evaluated in 3 configurations: as a standalone unit, in the MR bore and with the MR pulsing.
In conclusion, the results of the studies showed that the lp-ntPET model used in conjunction with PET-ABC is a robust quantitative method that not only provides parameter estimates and their uncertainties but also statistically sound inferences about model preference. Further, PET-ABC is able to reliably estimate parameters describing transient DA release in preclinical studies. The PET insert presented good performance in all configurations, enabling future investigation of parallel analysis of fMRI and PET data for improved parameter estimation.
46
Green, Caroline Elizabeth. "An experimental and modelling investigation into the solid-phase extraction of pollutants from water". Thesis, University College London (University of London), 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.322408.
Testo completo
47
Araujo, Leandro Goulart de. "Photo-oxidative degradation of bisphenol A by H2O2/UV: process study and kinetic modelling". Universidade de São Paulo, 2018. http://www.teses.usp.br/teses/disponiveis/3/3137/tde-17072018-111837/.
Testo completoAbstract (sommario):
Bisphenol A (BPA) is widely used in the production of plastics, epoxy resins and polycarbonates. It is a toxic, endocrine disruptor compound. Different studies have shown the presence of BPA in several environmental systems, classifying it as a worldwide persistent pollutant which may act synergistically with other pollutants. In this context, advanced oxidation processes (AOP) have received great attention due to their ability to degrade pollutants with such characteristics, through their transformation into less hazardous compounds or even their mineralization. Although there are investigations on the use of AOPs for BPA degradation, systematic studies on the effects of process variables, coupled with the statistical interpretation of the results are virtually non-existent. Furthermore, to the best of our knowledge, a rigorous kinetic model has not yet been proposed for the degradation of this pollutant by the H2O2/UV process. The objective of this work was to evaluate BPA degradation by the H2O2/UV process, investigating the effects of the initial H2O2 concentration and the specific rate of photons emission (EP,0) by means of a Doehlert experimental design, combined with the response surface methodology. The experiments were performed in a photochemical tubular reactor equipped with a 254-nm UV lamp, for [H2O2]0 and EP,0 in the ranges 1.6-9.6 mmol L-1 and 0.87 × 1018-3.6 × 1018 photons L-1 s-1, respectively. Total BPA degradation was achieved after 60 min of irradiation in all experiments. The best conditions were [H2O2]0 = 7.6 mmol L-1 and EP,0 = 3.6 × 1018 photons L-1 s-1, for which the best performance was obtained regarding the BPA degradation rate, BPA degradation after 15 min, and the second highest TOC removal after 180 min. However, in most experiments less than 75% TOC removal was observed, with 95% mineralization obtained only for the superior [H2O2]0 and EP,0. A mathematical model was developed, considering the reactor characteristics and the radiation field, based on the line source with parallel emission (LSPP) approach, in combination with the radiative transfer equation (RTE), mass balances, and a detailed kinetic model of the H2O2/UV process. The steady-state approximation was applied for all radical species. In the estimation of unknown kinetic constants, the non-linear least squares method was employed. The model was able to satisfactorily fit experimental BPA and H2O2 concentrations as a function of time. This work shows that the H2O2/UV process is a good alternative for BPA removal from aqueous streams, with total degradation of the target compound and adequate percent mineralization under optimal operating conditions. Such conditions may serve as first guidelines for pilot-plant and industrial processes operation. In addition, simulations using the proposed kinetic model may provide useful information for the design and scale-up of pre- or post-treatment of effluents containing this pollutant.O bisfenol A (BPA) é amplamente utilizado na fabricação de plásticos, resinas epóxi e policarbonatos. Trata-se de um composto tóxico e um desregulador endócrino. Diferentes estudos evidenciam a presença do BPA em diversos compartimentos ambientais em todo planeta, identificando-o como um poluente persistente e resistente à degradação biológica, que apresenta efeitos sinergéticos com outros poluentes. Nesse contexto, os processos oxidativos avançados (POA) têm recebido atenção devido a sua capacidade em degradar poluentes com tais características, transformando-os em compostos menos perigosos ou até mesmo mineralizando-os totalmente. Apesar de haver trabalhos na literatura acerca da utilização de POA para degradação de BPA, estudos sistemáticos dos efeitos de variáveis de processo junto com a interpretação estatística dos resultados são virtualmente inexistentes. Além disso, até onde se sabe um modelo cinético rigoroso ainda não foi proposto para a degradação desse poluente por meio do processo H2O2/UV. Este trabalho teve por objetivo avaliar a degradação do BPA pelo processo H2O2/UV, investigando os efeitos da concentração inicial de H2O2 e da taxa específica de emissão de fótons (EP,0) por meio de um projeto experimental Doehlert, combinado com a análise de superfície de resposta. Os experimentos foram realizados em um reator tubular fotoquímico equipado com uma lâmpada UV de 254 nm, para [H2O2]0 e EP,0 entre 1,6-9,6 mmol L-1 e 0,87 × 1018 - 3,6 × 1018 fótons L-1 s-1, respectivamente. Todos os experimentos sob H2O2/UV resultaram em total degradação do BPA após 60 min de irradiação. Nesse caso, as melhores condições foram [H2O2]0 = 7,6 mmol L-1 e EP,0 = 3,6 × 1018 fótons L-1 s-1, para as quais se obteve o melhor desempenho quanto à taxa de degradação de BPA e à remoção após 15 min, e a segunda maior remoção de COT após 180 min. Entretanto, na maioria dos experimentos menos de 75% de remoção de COT foram observados, com 95% de mineralização obtida apenas para os maiores [H2O2]0 e EP,0. Elaborou-se um modelo matemático que considera as características do reator utilizado e o campo de radiação, baseado no modelo de fonte linear de emissão em planos paralelos (LSPP), combinado à equação de transferência radiativa (RTE), aos balanços materiais e a um modelo cinético detalhado do processo H2O2/UV. Foi empregada a aproximação de estado estacionário para todas as espécies radicalares. Na estimativa das constantes cinéticas desconhecidas, utilizou-se o método de mínimos quadrados não linear. Esse modelo foi capaz de ajustar satisfatoriamente as concentrações experimentais de BPA e de H2O2 em função do tempo. Este trabalho mostra que o processo H2O2/UV constitui uma alternativa conveniente para a degradação de BPA em matrizes aquosas, com total degradação do composto alvo e porcentagem de mineralização adequada nas condições ótimas de operação. Tais condições podem servir como diretrizes iniciais de processamento em escalas piloto e industrial. Por sua vez, simulações empregando o modelo matemático proposto permitem gerar informações úteis para projeto e aumento de escala de processos de pré- ou pós-tratamento de efluentes contendo esse poluente.
48
Adiamah, Delali. "Genome-scale integrative modelling of gene expression and metabolic networks". Thesis, University of Manchester, 2012. https://www.research.manchester.ac.uk/portal/en/theses/genomescale-integrative-modelling-of-gene-expression-and-metabolic-networks(4fb25bda-2890-4b64-94e1-3e5b538cd1a5).html.
Testo completoAbstract (sommario):
The elucidation of molecular function of proteins encoded by genes is a major challenge in biology today. Genes regulate the amount of proteins (enzymes) needed to catalyse a metabolic reaction. There are several works on either the modelling of gene expression or metabolic network. However, an integrative model of both is not well understood and researched. The integration of both gene expression and metabolic network could increase our understanding of cellular functions and aid in analysing the effects of genes on metabolism. It is now possible to build genome-scale models of cellular processes due to the availability of high-throughput genomic, metabolic and fluxomic data along with thermodynamic information. Integrating biological information at various layers into metabolic models could also improve the robustness of models for in silico analysis. In this study, we provide a software tool for the in silico reconstruction of genome-scale integrative models of gene expression and metabolic network from relevant database(s) and previously existing stoichiometric models with automatic generation of kinetic equations of all reactions involved. To reduce computational complexity, compartmentalisation of the cell as well as enzyme inhibition is assumed to play a negligible role in metabolic function. Obtaining kinetic parameters needed to fully define and characterise kinetic models still remains a challenge in systems biology. Parameters are either not available in literature or unobtainable in the lab. Consequently, there have been numerous methods developed to predict biological behaviour that do not require the use of detailed kinetic parameters as well as techniques for estimation of parameter values based on experimental data. We present an algorithm for estimating kinetic parameters which uses fluxes and metabolites to constrain values. Our results show that our genetic algorithm is able to find parameters that fit a given data set and predict new biological states without having to re-estimate kinetic parameters.
49
Lloyd, Adam L. "Modelling silver thin film growth on zinc oxide". Thesis, Loughborough University, 2017. https://dspace.lboro.ac.uk/2134/24860.
Testo completoAbstract (sommario):
Ag thin film growth on ZnO substrates has been investigated theoretically using multi-timescale simulation methods. The models are based on an atomistic approach where the interactions between atoms are treated classically using a mixture of fixed and variable charge potential energy functions. After some preliminary tests it was found that existing fixed charge potential functions were unreliable for surface growth simulations. This resulted in the development of a ReaxFF variable charge potential fitted to Ag/ZnO surface interactions. Ab initio models of simple crystal structures and surface configurations were used for potential fitting and testing. The dynamic interaction of the Ag atoms with the ZnO surface was first investigated using single point depositions, via molecular dynamics, whereby the Ag impacted various points on an irreducible symmetry zone of the ZnO surface at a range of energies. This enabled the determination of the relative numbers of atoms that could penetrate, reflect or bond to the surface as a function of incident energy. The results showed that at an energy of up to 10 eV, most atoms deposited adsorbed on top of the surface layer. The second part of the dynamic interaction involved a multi-timescale technique whereby molecular dynamics (MD) was used in the initial stages followed by an adaptive kinetic Monte Carlo (AKMC) approach to model the diffusion over the surface between impacts. An impact energy of 3 eV was chosen for this investigation. Ag was grown on various ZnO surfaces including perfect polar, O-deficient and surfaces with step edges. Initial growth suggests that Ag prefers to be spread out across a perfect surface until large clusters are forced to form. After further first layer growth, subsequent Ag atoms begin to deposit on the existing Ag clusters and are unlikely to join the first layer. Ag island formation (as mentioned within the literature) can then occur via this growth mechanism. O-deficient regions of ZnO surfaces result in unfavourable Ag adsorption sites and cause cluster formation to occur away from O-vacancies. In contrast, ZnO step edges attract deposited Ag atoms and result in the migration of surface Ag atoms to under-coordinated O atoms in the step edge. Various improvements have been made to the existing methodology in which transitions are determined. A new method for determining defects within a system, by considering the coordination number of atoms, is shown to increase the number of transitions found during single ended search methods such as the relaxation and translation (RAT) algorithm. A super-basin approach based on the mean rate method is also introduced as a method of accelerating a simulation when small energy barriers dominate. This method effectively combines states connected by small energy barriers into a single large basin and calculates the mean time to escape such basin. To accelerate growth simulations further and allow larger systems to be considered, a lattice based adaptive kinetic Monte Carlo (LatAKMC) method is developed. As off-lattice AKMC and MD results suggest Ag resides in highly symmetric adsorption sites and that low energy deposition events lead to no penetrating Ag atoms or surface deformation, the on-lattice based approach is used to grow Ag on larger perfect polar ZnO surfaces. Results from the LatAKMC approach agree with off-lattice AKMC findings and predict Ag island formation. Critical island sizes of Ag on ZnO are also approximated using a mean rate approach. Single Ag atoms are placed above an existing Ag cluster and all transition states are treated as belonging to a single large super-basin . Results indicate that small Ag clusters on the perfect ZnO surface grow in the surface plane until a critical island size of around 500 atoms is reached. Once a critical island size is reached, multiple Ag ad-atoms will deposit on the island before existing Ag atoms join the cluster layer and hence islands will grow upwards. A marked difference is seen for second layer critical island sizes; second layer Ag islands are predicted to be two orders of magnitude smaller (< 7 atoms). This analysis suggests that Ag on ZnO (0001) may exhibit Stranski-Krastanov (layer plus island) growth.
50
Bhattacharya, Subhamoy [Verfasser], e Matthias [Akademischer Betreuer] Kraume. "Solvent-free chemo-enzymatic epoxidation: Experimental and kinetic modelling studies / Subhamoy Bhattacharya. Betreuer: Matthias Kraume". Berlin : Universitätsbibliothek der Technischen Universität Berlin, 2012. http://d-nb.info/1021976318/34.
Testo completo