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Dissertationen zum Thema „Chemical kinetics“
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1
Heard, Dwayne Ellis. „Laser studies of chemical kinetics“. Thesis, University of Oxford, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.258025.
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2
Kononova, Anna. „Memetic computing in chemical kinetics“. Thesis, University of Leeds, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.531526.
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3
Biasca, Rodger Joseph. „Chemical kinetics of SCRAMJET propulsion“. Thesis, Massachusetts Institute of Technology, 1988. http://hdl.handle.net/1721.1/35949.
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4
Justi, Rosa da Silva. „Models of teaching of chemical kinetics“. Thesis, University of Reading, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.388404.
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5
Chen, Tianjiao S. M. Massachusetts Institute of Technology. „Experimental characterization and chemical kinetics study of chemical looping combustion“. Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/87957.
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Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2014.Cataloged from PDF version of thesis. "February 2014."
Includes bibliographical references (pages 106-110).
Chemical looping combustion (CLC) is one of the most promising technologies to achieve carbon capture in fossil fuel power generation plants. A novel rotary-bed reactor concept was proposed by Zhao et. al. [1] in 2013. It is a compact gas fueled CLC reactor that could achieve high fuel conversion and carbon separation efficiencies. It is different from the widely applied and tested fluidized-bed reactor that employs metal oxides coated on particle shaped support materials as the reaction median. In the new reactor, the active metal oxidizes are coated on the surfaces of channel shaped structural material in the new reactor. Due to the different reaction mechanism, an alternative experimental platform with the capability of performing reaction kinetic analysis for disk or channel shaped samples was required needed. The sample selection, characterization and preparation methods are discussed, followed by the introduction of the experimental system design and initial calibration and tuning results. Preliminary oxidation kinetic studies are carried out using the real-time gas analysis system to obtain the concentration contours of the effluent gas species. Commercial 13 wt% copper(II) oxide particles prepared through impregnation method are used as the reaction median. The reactant gas used in the oxidation cycles is 8%, 13% and 21% oxygen in argon, operated at 700 - 800 *C; and 10% hydrogen in argon is used for the reducing cycles.
by Tianjiao Chen.
S.M.
6
Engblom, Stefan. „Numerical Solution Methods in Stochastic Chemical Kinetics“. Doctoral thesis, Uppsala universitet, Avdelningen för teknisk databehandling, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-9342.
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This study is concerned with the numerical solution of certain stochastic models of chemical reactions. Such descriptions have been shown to be useful tools when studying biochemical processes inside living cells where classical deterministic rate equations fail to reproduce actual behavior. The main contribution of this thesis lies in its theoretical and practical investigation of different methods for obtaining numerical solutions to such descriptions. In a preliminary study, a simple but often quite effective approach to the moment closure problem is examined. A more advanced program is then developed for obtaining a consistent representation of the high dimensional probability density of the solution. The proposed method gains efficiency by utilizing a rapidly converging representation of certain functions defined over the semi-infinite integer lattice. Another contribution of this study, where the focus instead is on the spatially distributed case, is a suggestion for how to obtain a consistent stochastic reaction-diffusion model over an unstructured grid. Here it is also shown how to efficiently collect samples from the resulting model by making use of a hybrid method. In a final study, a time-parallel stochastic simulation algorithm is suggested and analyzed. Efficiency is here achieved by moving parts of the solution phase into the deterministic regime given that a parallel architecture is available. Necessary background material is developed in three chapters in this summary. An introductory chapter on an accessible level motivates the purpose of considering stochastic models in applied physics. In a second chapter the actual stochastic models considered are developed in a multi-faceted way. Finally, the current state-of-the-art in numerical solution methods is summarized and commented upon.
7
PAUL, DEBDAS. „Efficient Parameter Inference for Stochastic Chemical Kinetics“. Thesis, KTH, Beräkningsbiologi, CB, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-146869.
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Parameter inference for stochastic systems is considered as one of the fundamental classical problems in the domain of computational systems biology. The problem becomes challenging and often analytically intractable with the large number of uncertain parameters. In this scenario, Markov Chain Monte Carlo (MCMC) algorithms have been proved to be highly effective. For a stochastic system, the most accurate description of the kinetics is given by the Chemical Master Equation (CME). Unfortunately, analytical solution of CME is often intractable even for considerably small amount of chemically reacting species due to its super exponential state space complexity. As a solution, Stochastic Simulation Algorithm (SSA) using Monte Carlo approach was introduced to simulate the chemical process defined by the CME. SSA is an exact stochastic method to simulate CME but it also suffers from high time complexity due to simulation of every reaction. Therefore computation of likelihood function (based on exact CME) in MCMC becomes expensive which alternately makes the rejection step expensive. In this generic work, we introduce different approximations of CME as a pre-conditioning step to the full MCMC to make rejection cheaper. The goal is to avoid expensive computation of exact CME as far as possible. We show that, with effective pre-conditioning scheme, one can save a considerable amount of exact CME computations maintaining similar convergence characteristics. Additionally, we investigate three different sampling schemes (dense sampling, longer sampling and i.i.d sampling) under which convergence for MCMC using exact CME for parameter estimation can be analyzed. We find that under i.i.d sampling scheme, better convergence can be achieved than that of dense sampling of the same process or sampling the same process for longer time. We verify our theoretical findings for two different processes: linear birth-death and dimerization.Apart from providing a framework for parameter inference using CME, this work also provides us the reasons behind avoiding CME (in general) as a parameter estimation technique for so long years after its formulation
8
Tomlin, Alison Sarah. „Bifurcation analysis for non-linear chemical kinetics“. Thesis, University of Leeds, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.255345.
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9
Shaw, Rebecca Custis Riehl. „Combining combustion simulations with complex chemical kinetics“. Thesis, University of Cambridge, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.648248.
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10
Poole, Anthony John. „Reaction-diffusion structures in nonlinear chemical kinetics“. Thesis, University of Leeds, 1998. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.712528.
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11
Grigsby, Charles Owen 1951. „Kinetics of rock-water reactions“. Thesis, Massachusetts Institute of Technology, 1989. http://hdl.handle.net/1721.1/37986.
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12
Shi, Youchun. „A Kinetic Study of the Recombination Reacton Na + SO₂ + Ar“. Thesis, University of North Texas, 1990. https://digital.library.unt.edu/ark:/67531/metadc504481/.
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The recombination reaction Na + S02 + Ar was investigated at 787 16 K and at pressures from 1.7 to 80 kPa. NaI vapor was photolyzed by an excimer laser at 308 nm to create Na atoms, whose concentration was monitored by time-resolved resonance absorption at 589 nm. The rate constant at the low pressure limit is ko = (2.7 0.2) x 10-21 cm6 molecule-2 s~1. The Na-SO 2 dissociation energy E0 = 170 35 kJ mol1 was calculated with RRKM theory. The equilibrium constant gave a lower limit E0 > 172 kJ mol~ 1. By combination of these two results, E0 = 190 15 kJ mol~ 1 is obtained. The high pressure limit is k, = (1 - 3) x 10-10 cm3 molecule 1 s~1, depending on the extrapolation method used. Two versions of collision theory were employed to estimate k,.. The 'harpoon' model shows the best agreement with experiment.
13
Vaidyaraman, Sundar. „Kinetics of the bosch reaction“. Thesis, Georgia Institute of Technology, 1992. http://hdl.handle.net/1853/10277.
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14
Thornton, Stephen S. „Design, synthesis, and kinetics of novel acetylcholinesterase inhibitors“. Thesis, Georgia Institute of Technology, 1989. http://hdl.handle.net/1853/26964.
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15
Beaulieu-Bergeron, Sebastien. „Intrinsic kinetics of clathrate hydrate formation“. Thesis, McGill University, 2009. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=66683.
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The present thesis focuses on the intrinsic kinetics of clathrate hydrate formation to provide the fundamental data and modeling needed to predict hydrate growth. A novel hydrate growth model based on particle size distribution measurements and a concentration driving force was proposed. The reaction rate constant of propane hydrate formation was determined using the aforementioned model. The mole fraction of carbon dioxide and methane in the bulk liquid phase was measured at the onset of hydrate growth and thereafter in a semi-batch stirred tank crystallizer. It was found that the guest mole fraction in the bulk liquid phase increases with pressure, decreases with temperature and remains constant during at least the first thirteen minutes of the growth stage. Based on such measurements, an alternate formulation of the hydrate growth model, independent of the dissolution rate at the vapor-liquid water interface, was suggested. As a result, the reaction rate constant of both carbon dioxide and methane clathrate formation was determined and found to follow an Arrhenius-type relationship, increasing with temperature over a four-degree interval, while being insensitive to pressure over the range investigated. The temperature trend of the reaction rate constant of hydrate formation yielded positive activation energies for both carbon dioxide and methane hydrate growth. The carbon dioxide and methane solubility dependency on temperature in water under hydrate-liquid water and vapor-liquid water equilibrium was also demonstrated using fundamental thermodynamics.La présente thèse traite de la cinétique de formation des hydrates de gaz afin d'établir les données et la modélisation nécessaires à l'étude de leur croissance. Un modèle cinétique pour la formation des hydrates de gaz, intégrant des mesures de taille de particules et une force d'entraînement de concentration, a été développé et utilisé pour calculer la constante de vitesse de réaction des hydrates de propane. Des mesures de la fraction molaire du composé gazeux dans la phase liquide, au moment de la formation des hydrates et tout au long de leur croissance, ont été obtenues pour le dioxyde de carbone et le méthane. Les résultats ont démontré que cette fraction molaire augmente avec la pression, diminue avec la température et demeure constante durant au moins les premières treize minutes de la phase de croissance. Ces mesures ont permis de modifier le modèle cinétique pour le rendre indépendant de l'interface vapeur-eau liquide. Également, il a été démontré que la constante de vitesse de réaction des hydrates de dioxyde de carbone et de méthane obéit à la loi d'Arrhénius, augmentant avec la température sur un intervalle de quatre degrés centigrades, en plus d'être constante pour l'écart de pression considéré. L'effet de la température sur la constante de vitesse de réaction a permis de calculer une énergie d'activation positive pour la croissance des hydrates de dioxyde de carbone et de méthane. Enfin, l'effet de la température sur la solubilité du dioxyde de carbone et du méthane dans l'eau, tant pour un équilibre hydrate-eau liquide que vapeur-eau liquide, a été démontré à l'aide de la thermodynamique.
16
Lungu, Cristian 1968. „Crystallization behavior and kinetics of polyolefins“. Thesis, McGill University, 2000. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=31061.
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In order to understand crystallization behavior and to predict polymer resin properties, crystallization kinetics and morphology studies are performed. Thermal analysis of sixteen polyethylene and polypropylene resins was carried out, using Differential Scanning Calorimetry (DSC) to study the crystallization kinetics and mechanism of crystallization. Attention is given to different polyethylene grades, particularly linear low-density polyethylenes (LLDPE) manufactured with Ziegler-Natta and metallocene catalysts. The polymers are obtained with different monomers (1-butene, 1-hexene or 1-octene). Some polymers are based on gas phase polymerization, while others are based on solution polymerization. The isothermal crystallization data were treated to account for transients and to compensate for instrument errors. The data were fitted to the Avrami and Tobin equations, and the corresponding kinetic parameters are reported. The non-isothermal data were fitted to the Ziabicki equation, in order to determine the relevant parameters. Subsequently, the non-isothermal data were compared to the predictions of the Nakamura equation, with good agreement. An effort was made to compare the isothermal and non-isothermal crystallization behavior of the various resins to evaluate the effect of co-monomer and catalyst type. The results indicate significant differences among the resins, and reveal the utility of the DSC as a tool for distinguishing the characteristics of the various resins.
17
Lewis, Randy Stewart. „Nitric oxide kinetics in biological systems“. Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/36947.
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18
Sircar, Sanjoy. „Kinetics of gelation in photoreversible gels“. Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/62737.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, February 2011."September 2010." Cataloged from PDF version of thesis.
Includes bibliographical references.
Smart materials, or materials that respond to some stimulus by changing their properties, make up an active area of research in many fields. Light can be considered an especially attractive choice of stimulus because it can be applied with precise spatial and temporal control, and is non-invasive. This thesis explores light sensitive gels and colloids, which could be used as valves in microfluidics devices, as tunable templates for the production of nanoparticles, or as devices for capturing pollutants or delivering drugs. At the basis of the sensitivity to light is the azobenzene chemical group, which isomerizes from cis to trans under visible light and the reverse under UV light. When this group is embedded in the hydrophobic tail of a surfactant, the aggregation properties of the surfactant become light-sensitive. The trans form of the azobenzene surfactant is more likely to form micelles than the cis. When mixed with a hydrophobically modified polymer, these micelles can act as crosslinking sites for a gel network. Upon UV irradiation, the crosslinking is disrupted and the gel transitions to a solution state. NMR methods were used to characterize the micelles and gels, and to understand the steps that control the kinetics in these photoreversible systems. The gelation process can be considered to consist of photoreaction, micelle formation, and possibly polymer relaxation. It was found that the photon flux through the material limits the rate of reaction, which then controls the remaining processes in the system. The photoreaction was studied under varying conditions, including concentration, light intensity, and wavelength. Due to their optical thickness, these materials are possibly better suited for use as thin films. NMR experiments were also used to probe the interactions between the polymer and surfactant. In contrast to surfactant-only solutions, trans-dominated and cis-dominated micelles appeared equally likely to form aggregates with an appropriate polymer. The cis-rich aggregates failed to effectively crosslink the polymer and form a gel. This was confirmed by using diffusion measurements to monitor the size of crosslinked polymer clusters. This cluster growth correlated well with previous rheology results, but the high tendency of cis samples to form aggregates had not been anticipated. It is hypothesized that cisdominated aggregates are too small and unstable to act as crosslinking sites. In an effort to create a wider array of tunable colloids, the azobenzene surfactant was then mixed with a traditional surfactant of opposite charge. Solutions consisting of oppositely charged surfactants have been known to result in unilamellar vesicles, when prepared at appropriate concentrations and mixing ratios. The size, type and number density of the aggregates in this work were found to be controllable through the use of light. Depending on the light conditions, either nanodiscs or vesicles could be observed.
by Sanjoy Sircar.
Ph.D.
19
Perrman, Delmar. „Nonlinear effects in chemical dynamics and chemical kinetics: Chaos in physical chemistry“. Thesis, University of Ottawa (Canada), 1994. http://hdl.handle.net/10393/9500.
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This work shows that nonlinear dynamic systems are quite different from linear dynamic systems. The usual phase plots of linear and nonlinear dynamical systems are also distinctly different, even before damping or forcing terms are added. It is also shown that the usual phase plot allows for the visualization of unobservable information that is present in the times series. The higher-order phase plots give yet additional information that is not present in the existing methods of plotting the data. Higher-order phase plots were originated and applied for the first time to a dynamical system (Morse oscillator) for the purpose of earlier detection of nonlinear effects. The dynamics of a weakly forced and weakly damped Morse oscillator is examined. The novel tool of higher-order phase plots is used to visualize the importance of the higher harmonics in the phase which are essential for the dynamics to be complicated and dissociative. Expansions of the higher-order phase plots in regions about x$\sp{(n-1)}$ = 0, x$\sp{(n)}$ = 0 are considered and it is shown that there is a topological change that occurs sequentially for each higher-order phase plot. After the topological change, which occurs at a critical value of initial total energy E(0) for a particular value of forcing F, the higher-order phase space structure has a circular loop. As F or E(0) is further increased the phase space trajectory loops an increasing number of times in the higher-order phase plot. It is shown that for F = $1.0\times10\sp{-3}$ the topological change occurs around E(0) = 0.96 for the fifth-order phase plot and around E(0) = 0.94 for the eleventh-order phase plot. This is also illustrated with a series of higher-order phase plots (2$\sp{nd}$-10$\sp{th}$) for F = $1\times10\sp{-3}$ and E(0) = 0.97. These plots indicate that although the 5$\sp{th}$ order phase plot forms loops the 4$\sp{th}$ forms only half-loops. Thus the higher-order phase plots are increasingly sensitive probes of the phase space dynamics as the order increases. Qualitatively this is because, as the order increases, part of each higher-order phase space structure is increasingly close to the point (x$\sp{(n)}$,x$\sp{(n-1)}$) = (0,0). For larger values of F the topological change occurs at a smaller value of E(0) for each higher-order phase plot, as the radius of the loop centered on x$\sp{(n-1)}$ = 0, x$\sp{(n)}$ = 0 is larger. While the phase space trajectory loops the energy is approximately constant with small oscillations. The circular loop in the higher-order phase plot is the higher-order space structure that is expected for the weakly forced and weakly damped free particle. The significance of the circular loop is that the lower the order of the higher-order phase plot in which the phase space trajectory loops, the closer the Morse oscillator is to dissociation. From this viewpoint, the Morse oscillator dissociates when the value of F or E(0) becomes sufficiently large that the topological change occurs in the usual phase plot. That is, the Morse oscillator dissociates when the phase space structure becomes open for the usual phase plot. (Abstract shortened by UMI.)
20
Bakhtina, Marina M. „Application of chemical probes to study the kinetic mechanism of DNA polymerases“. Columbus, Ohio : Ohio State University, 2006. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1148915981.
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21
Monks, Paul S. „Kinetics of radical reactions of tropospheric importance“. Thesis, University of Oxford, 1991. http://ora.ox.ac.uk/objects/uuid:57362031-6d04-481e-8b23-cc2cefa1cc5c.
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The object of the research described in this thesis is to provide, by means of laboratory experiments, data required to understand the atmospheric chemistry of the nitrate radical, from both a mechanistic and kinetic point of view. The low pressure discharge-flow kinetic technique coupled detection of the NO3 radical by optical absorption was used to measure the temperature-dependent rate coefficients for the reaction of NO3 with 1-butene, 1-chloro-l-butene, 2-chloro-2-butene, 3-chloro-l-butene, 1-chloro-2-butene, 2-chloro-2-butene, 1-chloromethylpropene, 3-chloromethylpropene, 3-bromo-1-butene, 4-bromo-l-butene and 2-bromo-2-butene. The atmospheric implications for the reaction of NO3 with these compounds are discussed. In order to understand the patterns of reactivity towards NO3 exhibited by these compounds, a number of approaches were adopted. First, a non-quantitative approach employing the simple ideas of inductive and mesomeric effects. Secondly the observed reactivity of NO3 towards these compounds was discussed, quantitatively, in terms of the relative energies of the interacting orbitals. This quantitative analysis required an extensive set of molecular orbital calculations were undertaken at various levels of sophistication. A good correlation was found, for compounds not containing vinylic halogen atoms, between -E(HOMO) and the measured rate constant; the data were used also to calculate "group-reactivity factors". In an extension to this work a new empirical correlation is presented that takes account of the contribution, in terms of the atomic orbital coefficients, of vinylic halogen atoms to the observed rate constant. To provide support for these calculations, work was undertaken using photoelectron spectroscopy to characterise experimentally the individual molecular orbitals. A correlation between the inverse of the molecular polarisability and the activation energy of the reaction is also described. Complementary work was undertaken in a unconventional flash-photolysis system to look at the kinetics of the reaction NO3 + NO3 andlongrightarrow; 2 NO2 + O2 over a pressure range of 2 to 100 Torr in helium. The measured rate coefficient was found to be pressure independent and to have a value of (2.2±1.0) x 10-16 cm3 molecule-1 s-1. The experimental work on the nitrate radical was extended to look at the laser-induced fluorescence (LIF) spectrum and at the quenching of the excited state of the nitrate radical.
22
Goto, Masashi. „Kinetics of atmospheric chemical reactions of fluorinated hydrocarbons“. 京都大学 (Kyoto University), 2005. http://hdl.handle.net/2433/145179.
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Kyoto University (京都大学)0048
新制・課程博士
博士(地球環境学)
甲第11759号
地環博第1号
新制||地環||1(附属図書館)
23402
UT51-2005-D508
京都大学大学院地球環境学舎地球環境学専攻
(主査)教授 川崎 昌博, 教授 田村 類, 助教授 川崎 三津夫
学位規則第4条第1項該当
23
Sayin, Hasan McKee Michael L. „Quantum chemical studies and kinetics of gas reactions“. Auburn, Ala, 2006. http://repo.lib.auburn.edu/2006%20Fall/Dissertations/SAYIN_HASAN_39.pdf.
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24
Wilson, Claire Louise. „Applications of pulsed CO₂ lasers in chemical kinetics“. Thesis, Heriot-Watt University, 1986. http://hdl.handle.net/10399/1070.
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25
Reutershan, Trevor. „Chemical Kinetics and Adsorption in Wastewater Treatment Systems“. Thesis, California State University, Long Beach, 2018. http://pqdtopen.proquest.com/#viewpdf?dispub=10752236.
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The purpose of this thesis is to provide a combined theoretical and experimental approach to solve several enduring questions in wastewater chemistry. Firstly, the sulfate radical has been proposed as an alternative oxidant in advanced oxidation processes (AOPs). Its reactivity with dissolved organic matter (DOM) has not yet been studied and will be quantied in this work using electron pulse radiolysis. Next, it has been shown that DOM present in wastewater can act to impede the remediation of harmful pharmaceutical contaminants in the AOP. Using a new binding model presented here, this association was quantied in terms of equilibrium constants. Lastly, due to the use of bleach to prevent biofouling of the membrane bioreactor in wastewater treatment facilities, chlorine atom chemistry is becoming increasingly important to study regarding AOPs. A numerical system is provided in this thesis to understand the reactivity of chlorine atoms in the presence of wastewater constituents.
26
Rickards, Andrew M. J. „Hygroscopic organic aerosol : thermodynamics, kinetics, and chemical synthesis“. Thesis, University of Bristol, 2015. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.686238.
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Aerosols play a crucial role in many areas of scientific relevance including in new technologies to deliver medicine to the lungs, and in fuel injection and spray drying. Aerosols have a profound impact on the atmosphere, influencing radiative forcing both by scattering solar radiation and by influencing cloud properties. Organic aerosols are a major component, making up 20 - 90 % of the submicron mass by region, and are emitted from many natural and anthropogenic sources. This thesis presents new measurements of the hygroscopic behaviour of single organic droplets confined using two techniques: aerosol optical tweezers (AOT) and an electrodynamic balance (EDB). Values of the hygroscopicity parameter (K) are derived and added to a comprehensive literature survey to elucidate a relationship with droplet composition, in terms of the molecular ratio of oxygen to carbon atoms (OIC). These data are shown to be in broad qualitative agreement. However, variation in K for droplets of the same OIC is found to be significant, and discrepancies between subsaturated and supersaturated data are evident. The variabilities and uncertainties associated with characterising the kinetics of water transport in ultraviscous sucrose droplets are also presented. Droplets are exposed to a perturbation in relative humidity, and the resultant characteristic relaxation timescale (r) is determined from stimulated Raman spectra. Comparison of the experimental· evaporation data with simulated timescales shows excellent agreement, and r is shown to increase strongly with droplet radius. Qualitative agreement between experimental condensation data and simulated timescales is presented, and r is shown to increase with wait time (the time the perturbation is applied for). Finally, factors influencing the ability to perform controlled chemical synthesis in single droplets are investigated. The formation of Nylon-6,1 0 at the droplet-gas phase interface is used as a test case of the system, and the interplay between droplet volatility and reactivity is shown to be crucial for controlling the reaction. Further investigations demonstrate synthesis of picomolar concentrations (equivalent to a single dose) of a functionalised caprolactam anti-cancer drug. The challenges in reliably validating drug formation in aerosol are presented.
27
Bandstra, Joel Zachary. „Kinetic modeling of heterogeneous chemical reactions with applications to the reduction of environmental contaminants on iron metal“. Full text open access at:, 2005. http://content.ohsu.edu/u?/etd,280.
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28
Alecu, Ionut M. „Kinetic studies and computational modeling of atomic chlorine reactions in the gas phase“. Thesis, University of North Texas, 2009. https://digital.library.unt.edu/ark:/67531/metadc12071/.
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The gas phase reactions of atomic chlorine with hydrogen sulfide, ammonia, benzene, and ethylene are investigated using the laser flash photolysis / resonance fluorescence experimental technique. In addition, the kinetics of the reverse processes for the latter two elementary reactions are also studied experimentally. The absolute rate constants for these processes are measured over a wide range of conditions, and the results offer new accurate information about the reactivity and thermochemistry of these systems. The temperature dependences of these reactions are interpreted via the Arrhenius equation, which yields significantly negative activation energies for the reaction of the chlorine atom and hydrogen sulfide as well as for that between the phenyl radical and hydrogen chloride. Positive activation energies which are smaller than the overall endothermicity are measured for the reactions between atomic chlorine with ammonia and ethylene, which suggests that the reverse processes for these reactions also possess negative activation energies. The enthalpies of formation of the phenyl and β-chlorovinyl are assessed via the third-law method. The stability and reactivity of each reaction system is further rationalized based on potential energy surfaces, computed with high-level ab initio quantum mechanical methods and refined through the inclusion of effects which arise from the special theory of relativity. Large amounts of spin-contamination are found to result in inaccurate computed thermochemistry for the phenyl and ethyl radicals. A reformulation of the computational approach to incorporate spin-restricted reference wavefunctions yields computed thermochemistry in good accord with experiment. The computed potential energy surfaces rationalize the observed negative temperature dependences in terms of a chemical activation mechanism, and the possibility that an energized adduct may contribute to product formation is investigated via RRKM theory.
29
Tenney, Joel David. „The kinetics of the chlorine dioxide generation reaction“. Thesis, Georgia Institute of Technology, 1988. http://hdl.handle.net/1853/10020.
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30
Wallin, Peter John. „The mathematical modelling of flotation kinetics“. Thesis, University of Manchester, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.314632.
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31
Holmes, R. „Reaction kinetics of oil coke particles“. Thesis, University of Portsmouth, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.376048.
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32
Cho, Yong Kweon. „Kinetic and Chemical Mechanism of Pyrophosphate-Dependent Phosphofructokinase“. Thesis, University of North Texas, 1988. https://digital.library.unt.edu/ark:/67531/metadc332128/.
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Data obtained from isotope exchange at equilibrium, exchange of inorganic phosphate against forward reaction flux, and positional isotope exchange of 18O from the (βγ-bridge position of pyrophosphate to a (β-nonbridge position all indicate that the pyrophosphate-dependent phosphofructokinase from Propionibacterium freudenreichii has a rapid equilibrium random kinetic mechanism. All exchange reactions are strongly inhibited at high concentrations of the fructose 6-phosphate/Pi and MgPPi/Pi substrate-product pairs and weakly inhibited at high concentrations of the MgPPi/fructose 1,6-bisphosphate pair suggesting three dead-end complexes, E:F6P:Pi, E:MgPPi:Pi, and E:FBP:MgPPi. Neither back-exchange by [32p] nor positional isotope exchange of 18O-bridge-labeled pyrophosphate was observed under any conditions, suggesting that either the chemical interconversion step or a step prior to it limits the overall rate of the reaction. Reduction of the pyridoxal 5'-phosphate-inactivated enzyme with NaB[3H]4 indicates that about 7 lysines are modified in free enzyme and fructose 1,6-bisphosphate protects 2 of these from modification. The pH dependence of the enzyme-reactant dissociation constants suggests that the phosphates of fructose 6-phosphate, fructose 1,6-bisphosphate, inorganic phosphate, and Mg-pyrophosphate must be completely ionized and that lysines are present in the vicinity of the 1- and 6-phosphates of the sugar phosphate and bisphosphates probably directly coordinated to these phosphates. The pH dependence of kinetic parameters suggests that the enzyme catalyzes its reaction via general acid-base catalysis with the use of a proton shuttle. The base is required unprotonated in both reaction directions. In the direction of fructose 6-phosphate phosphorylation the base accepts a proton from the hydroxyl at C-l of F6P and then donates it to protonate the leaving phosphate. The maximum velocity of the reaction is pH independent in both reaction directions while V/K profiles exhibit pKs for binding groups (including enzyme and reactant functional groups) as well as pKs for enzyme catalytic groups. These data suggest that reactants bind only when correctly protonated and only to the correctly protonated form of the enzyme.
33
Wilkinson, Sam K. „Reaction kinetics in formulated industrial catalysts“. Thesis, University of Birmingham, 2014. http://etheses.bham.ac.uk//id/eprint/5113/.
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In heterogeneous catalysis, a fundamental understanding of the necessary physico-chemical requirements for a catalyst formulation is essential to its success. Understanding of reaction kinetics via modelling can demonstrate how catalysts work, providing functional information around surface active sites and reaction mechanism. This tool, combined with well-designed laboratory experiments to test a catalyst under steady and/or non-steady state conditions, can provide insight into the links between catalyst formulation and reaction performance. The aim of this project is to develop novel strategies and methods in these areas utilising a range of Johnson Matthey catalysts and reaction systems. This thesis places significant focus on obtaining mechanistically and statistically sound kinetic models with reliable model parameter estimates. Methods for this are developed using a batch liquid phase hydrogenation system using a Pt/TiO2 catalyst. Subsequently, non-steady state analysis of catalyst formulations has been explored. This includes the initial transient behaviour of a fresh vanadium phosphorus oxide selective oxidation catalyst under reaction conditions which allowed understanding of the evolution of distinct active site populations on the catalyst surface. A subsequent study of copper-based methanol synthesis catalysts explored the impact of gas phase conditions on the catalyst state. A mixture of steady-state testing and transient response experiments (i.e. via an imposed change in gas phase conditions over the catalyst) provided new insights into the evolution of active site populations and populations of surface species on the catalyst surface. Overall, the reaction kinetics studies demonstrated across this thesis demonstrate not only a series of methods to understand catalyst behaviour in depth but also to understand the key functional requirements for an effective industrial catalyst.
34
Zhang, Ziji. „Theoretical and computational study of coupling of soot, gas kinetics and radiation in diffusion flames using reduced mechanisms /“. Digital version accessible at:, 1998. http://wwwlib.umi.com/cr/utexas/main.
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35
Hersey, Michelle. „Oxidation of Arsenite Via Chelator-mediated Fenton Systems“. Fogler Library, University of Maine, 2006. http://www.library.umaine.edu/theses/pdf/HerseyMX2006.pdf.
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36
Davies, Matthew Lloyd. „Exploiting nonlinear kinetics to enhance process operability“. Thesis, University of Leeds, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.270897.
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37
Kang, Myungsun(Myungsun Sunny). „Optimizing vaccine dosing kinetics for stronger antibody response“. Thesis, Massachusetts Institute of Technology, 2018. https://hdl.handle.net/1721.1/124586.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemical Engineering, 2019Cataloged from PDF version of thesis. "The pagination in this thesis reflects how it was delivered to the Institute Archives and Special Collections. The Table of Contents does not accurately represent the page numbering"--Disclaimer Notice page.
Includes bibliographical references (pages 95-102).
One of the barriers to rational vaccine design against evolving pathogens is our lack of mechanistic understanding of how innate and adaptive immune response systematically emerge and evolve. Immune response is comprised of dynamic events that require many components to cooperate collectively in a manner that spans a range of scales. These characteristics make it hard to predict mechanisms for immune response based solely on experimental observations. This thesis investigates various aspects of affinity maturation that are relevant to vaccination and therapeutic strategies but are not yet fully understood mechanistically, ranging from the evolution of the heterogeneity of the antibody population with respect to affinity to optimal design parameters for temporal dosing of vaccines. Our approach is to apply computational techniques to mathematically model the immune system, and being synergistic with complementary experiments. 1.
As affinity maturation ensues, average affinity of antibodies increase with time while resulting affinity distribution becomes increasingly heterogeneous. To shed light on how the extent of this heterogeneity evolves with time during affinity maturation, we have taken advantage of previously published data of antibodies isolated from individual serum samples. Using the ratio of the strongest to the weakest binding subsets as a metric of heterogeneity (or affinity inequality), we find that after a single injection of small antigen doses, the ratio decreases progressively over time. This is consistent with Darwinian evolution in the strong selection limit. By contrast, neither the average affinity nor the heterogeneity evolves much with time for high doses of antigen, as competition between clones of the same affinity is minimal. 2.
What are the aspects of affinity maturation being altered by various temporal patterns of antigen dosing? Certain extended-duration dosing profiles increase the strength of the humoral response, with exponentially-increasing(EI) dosage providing the greatest enhancement. While this is an exciting result, it is necessary to establish a mechanistic understanding of how immune response be enhanced to further engineer and optimize the temporal patterns. From our computational model, the effect is driven by enhanced capture of antigen in lymph nodes by evolving higher-affinity antibodies early in the GC response. We validate the prediction from independent experimental data, where EI dosage result in promoted capture and retention of the antigen in lymph nodes. To our knowledge, this work is the first to demonstrate a key mechanism for vaccine kinetics in the response of B cells to immunization, and may prove to be an effective method for increasing the efficacy of subunit vaccines. 3.
Are there optimal dosing profiles that maximize total protection? That is, lead to the evolution of the most antibodies of high affinity? In extension of mechanistic studies in 2, we propose a stochastic simulation method that can be used as a tool for optimizing dosage protocols for vaccine delivery. Using this tool, we analyze experimental conditions for EI dosage induce suboptimal immune response and investigate two approaches for the optimization. Specifically, reducing the total dosage optimizes affinity of resulting antibodies, while total protection is optimal neither at constant or EI dosage but that corresponding to a "linear-like" dosing profile. Our approach can be extended to broader applications in vaccine design.
by Myungsun (Sunny) Kang.
Ph. D.
Ph.D. Massachusetts Institute of Technology, Department of Chemical Engineering
38
Yee, Nathan W. (Nathan Wa-Wai). „Predictive chemical kinetics for auto ignition of fuel blends“. Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/115698.
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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemical Engineering, 2018.Cataloged from PDF version of thesis.
Includes bibliographical references.
Predictive chemical kinetics plays an important part in the study of chemical systems by reducing the need for expensive experiments. The size and complexity of modem chemical mechanisms increasingly require the use of automated mechanism generators, such as the Reaction Mechanism Generator (RMG). Use of these automated generators for creating quality chemical mechanisms necessitates accurate reaction rates. Unfortunately, the vast majority of kinetic parameters governing rate constants are not known. The goals of this thesis are the accurate estimation of kinetic parameters and its application to the prediction of auto ignition in fuel blends. At the molecular scale, quantum chemical methods can give kinetic coefficients with accuracy nearing those of experiments. Even when specific kinetic parameters are unavailable, rates can be evaluated by analogy to similar molecules. RMG uses an averaging scheme based on arranging functional groups in a hierarchical tree structure. We have been able to continue expansion of the database to species with nitrogen and sulfur, improve methods for structural representation, and showcase validation for thermochemistry and kinetic parameter estimates. Studying kinetics at the mechanistic level allows insight into the interaction between chemical reactions. Specifically, we have been interested in finding and analyzing the reaction pathways relevant to auto ignition, simplifying well-studied fuel mechanisms for propane and methanol. We were able to define clear stages of ignition and report the controlling chemistry during each stage. Understanding of these base fuels provides the basis to analyzing ignition for larger and more novel fuels. Finally, from a macroscopic perspective we studied ignition for blends of phenolic additives in gasoline. Chemical mechanisms generated by RMG were modeled in a variable volume reactor that emulate end gas conditions of the CRF engine used to evaluate Research Octane Number (RON). We predicted the effect each additive has on the timing of ignition, which were later proven to be reasonably accurate by experimental validation. The chemical pathways that affect the ignition were analyzed and discussed. Finally, we developed a framework for predicting several different aspects of potential fuel additives, which could help eliminate costly experiments by identifying unsuitable candidates before they are even synthesized.
by Nathan W. Yee.
Ph. D.
39
Van, Orman James Ashton 1969. „Kinetics of chemical exchange during melting of planetary interiors“. Thesis, Massachusetts Institute of Technology, 2000. http://hdl.handle.net/1721.1/57964.
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Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, September 2000.Includes bibliographical references.
Experimental and numerical modeling studies are used to place constraints on the kinetics of chemical exchange during partial melting within the mantles of the terrestrial planets. Chapter 1 presents experiments on the diffusion rates of La, Ce, Nd, Dy and Yb in diopside at pressures of 0 to 2.5 GPa and temperatures of 1050 to 1450 'C. The results demonstrate a large variation in diffusivity among the rare earth elements, with the diffusion coefficient for La a factor of -35 smaller than for Yb at a given temperature and pressure. Chapter 2 presents experiments on the diffusion of Sm, Dy and Yb in pyrope at 2.8 GPa and 1200-1450 "C. No significant difference in diffusivity is found among these elements, and their absolute diffusion rates are similar to those of the heavy rare earth elements in diopside at the same pressure and temperature. Chapter 3 presents a numerical model for diffusion-controlled fractionation of trace elements during adiabatic decompression melting of a polyphase solid. The model is used to simulate the fractionation of rare earth elements between solid and melt during partial melting of Earth's upper mantle. Diffusion is found to exert a strong control on the evolution of the system at conditions typical of melting beneath ocean spreading centers, leading to less efficient fractionation of the rare earth elements than under conditions of local chemical equilibrium. Chapter 4 presents experiments on the diffusion of U and Th in diopside at I atm pressure. Uranium and thorium are found to diffuse at similar rates, and diffusive fractionation between these elements is therefore unlikely to be significant during partial melting in Earth's upper mantle. Thorium and radium may be diffusively fractionated, however, enhancing the production of 22 Ra/230Th radioactive disequilibrium during partial melting while inhibiting chromatographic fractionation during melt transport. Chapter 5 presents phase equilibrium and dissolution kinetics experiments that constrain hypotheses for the origin of lunar high-Ti ultramafic glasses. The experimental results demonstrate that assimilation of ilmenite-bearing cumulates is not a viable mechanism for production of the high-Ti glasses. It is proposed that the source of the high-Ti ultramafic glasses formed by shallow level mixing and reaction of late-stage magma ocean liquids with underlying olivine-orthopyroxene cumulates, followed by sinking of these dense hybrid materials into the lunar mantle.
by James Ashton Van Orman.
Ph.D.
40
Allen, Joshua W. (Joshua William). „Predictive chemical kinetics : enabling automatic mechanism generation and evaluation“. Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/81677.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2013.Cataloged from PDF version of thesis.
Includes bibliographical references.
The use of petroleum-based fuels for transportation accounted for more than 25% of the total energy consumed in 2012, both in the United States and throughout the world. The finite nature of world oil reserves and the effects of burning petroleum-based fuels on the world's climate have motivated efforts to develop alternative, renewable fuels. A major category of alternative fuels is biofuels, which potentially include a wide variety of hydrocarbons, alcohols, aldehydes, ketones, ethers, esters, etc. To select the best species for use as fuel, we need to know if it burns cleanly, controllably, and efficiently. This is especially important when considering novel engine technologies, which are often very sensitive to fuel chemistry. The large number of candidate fuels and the high expense of experimental engine tests motivates the use of predictive theoretical methods to help quickly identify the most promising candidates. This thesis presents several contributions in the areas of predictive chemical kinetics and automatic mechanism generation, particularly in the area of reaction kinetics. First, the accuracy of several methods of automatic, high-throughput estimation of reaction rates are evaluated by comparison to a test set obtained from the NIST Chemical Kinetics Database. The methods considered, including the classic Evans-Polanyi correlation, the "rate rules" method currently used in the RMG software, and a new method based on group contribution theory, are shown to not yet obtain the order-of-magnitude accuracy desired for automatic mechanism generation. Second, a method of very accurate computation of bimolecular reaction rates using ring polymer molecular dynamics (RPMD) is presented. RPMD rate theory enables the incorporation of quantum effects (zero-point energy and tunneling) in reaction kinetics using classical molecular dynamics trajectories in an extended phase space. A general-purpose software package named RPMD-rate was developed for conducting such calculations, and the accuracy of this method was demonstrated by investigating the kinetics and kinetic isotope effect of the reaction OH + CH4 --> CH3 + H2O. Third, a general framework for incorporating pressure dependence in thermal unimolecular reactions, which require an inert third body to provide or remove the energy needed for reaction via bimolecular collisions, was developed. Within this framework, several methods of reducing the full, master equation-based model to a set of phenomenological rate coefficients k(T, P) are compared using the chemically-activated reaction of acetyl radical with oxygen as a case study, and recommendations are made as to when each method should be used. This also resulted in a general-purpose code for calculating pressure-dependent kinetics, which was applied to developing an ab initio model of the reaction of the Criegee biradical CH 200 with small carbonyls that reproduces recent experimental results. Finally, the ideas and techniques of estimating reaction kinetics are brought together for the development of a detailed kinetics model of the oxidation of diisopropyl ketone (DIPK), a candidate biofuel representative of species produced from cellulosic biomass conversion using endophytic fungi. The model is evaluated against three experiments covering a range of temperatures, pressures, and oxygen concentrations to show its strengths and weaknesses. Our ability to automatically generate this model and systematically improve its parameters without fitting to the experimental results demonstrates the validity and usefulness of the predictive chemical kinetics paradigm. These contributions are available as part of the Reaction Mechanism Generator (RMG) software package.
by Joshua W. Allen.
Ph.D.
41
Cowles, Heather Jane. „Kinetics and thermodynamics of chemical reactions in aqueous solutions“. Thesis, University of Leicester, 1990. http://hdl.handle.net/2381/34067.
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The kinetics of reaction and solvation properties of binary aqueous mixtures are discussed from different theoretical standpoints. Kinetic data are reported for reactions involving several Iron (II) complex cations in binary aqueous mixtures. The Savage-Wood Additivity Group Scheme (SWAG) is applied to kinetic data for the aquation of [Fe (5-nitro-1, 10-phenanthroline) 3]2+ in binary aqueous mixtures. Limitations of the theory are examined. The theory works well for reactions in alcohol-water and some carboxylic acid-water mixtures but not for reactions in urea-water and cyclic ether-water mixtures. The conclusion is reached that this theory can only be applied to relatively simple solutions. Otherwise, the assumptions made in the theory are not valid. Attention is then turned to the Kirkwood-Buff theory which can be applied to reactions in mixtures containing significant amounts of the cosolvent. Few assumptions are made in its derivation. This theory is used to probe the properties of a wide range of binary aqueous mixtures. Kinetic data describing reactions in these binary mixtures are then examined, leading to a consideration of preferential solvation. Finally, the possibility of monitoring chemical reactions under isochoric conditions is considered. A meaningful isochoric volume is defined. Kinetic and equilibrium reaction data are then analysed under these isochoric conditions.
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Nengovhela, Nkhangweleni Ryneth. „Kinetics of the chemical and biological iron (II) oxydation“. Diss., University of Pretoria, 2003. http://hdl.handle.net/2263/30337.
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Amikiya, Emmanuel Adoliwine. „Numerical simulation of chemical kinetics transport and flow processes“. Thesis, University of Pretoria, 2020. http://hdl.handle.net/2263/77830.
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In this thesis, numerical solution procedures are developed for simulating chemical
phenomena. Mathematical models for phenomena involving flow, transport and reaction
of chemical species are computationally challenging to simulate due to stiffness, high degrees
of freedom and spatial dependence. Such challenges are resolved (in this thesis)
by combining model decoupling techniques with compatible efficient numerical schemes.
Chemical phenomena is decomposed into well-mixed chemical systems, poorly-mixed systems
(or spatial dependent kinetics) and flow with reactive transport systems. Mathematical
models for the systems are Ordinary Differential Equations (ODEs), parabolic
Partial Differential Equations (PDEs) and hyperbolic PDEs, respectively. In the ODE
model, stiffness is resolved by positivity-preserving implicit schemes while the large degrees
of freedom is reduced by stoichiometric and continuous-time iteration methods. In
the parabolic model, model decoupling techniques are employed to reduce the degrees of
freedom while Implicit-Explicit numerical schemes are presented for resolving stiffness.
Further, numerical schemes that have dispersion-dissipation-preserving properties have
also been discussed. In the hyperbolic model, model decoupling techniques have been presented
for reducing the degrees of freedom while shock-capturing, well-balanced numerical
schemes have been presented for resolving nonlinear hyperbolic effects. The results from
experiments show that the proposed numerical solution procedures can efficiently resolve
the challenges in simulating chemical phenomena.Thesis (PhD)--University of Pretoria, 2020.
Mathematics and Applied Mathematics
PhD
Unrestricted
44
Olsen, Amanda Albright. „Forsterite Dissolution Kinetics: Applications and Implications for Chemical Weathering“. Diss., Virginia Tech, 2007. http://hdl.handle.net/10919/28213.
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Silicate minerals are the most common mineral group in the earth's crust so it is not surprising that their weathering reactions dominate the chemistry of many earth surface processes. This project used forsterite as a model system to identify the important factors that affect silicate mineral dissolution rates and grain lifetimes in the weathering environment.
I determined an empirical rate law for forsterite dissolution of forsterite in oxalic acid solutions: based on a series of 124 semi-batch reactor experiments over a pH range of 0 to 7 and total oxalate concentrations between 0 and 0.35 m at 25°C. These experiments show that oxalate-promoted dissolution rates depend upon both oxalate concentration and pH. I propose a reaction mechanism in which a hydrogen ion and an oxalate ion are simultaneously present in the activated complex for the reaction that releases H4SiO4 into solution. By analogy, I propose that water acts as a ligand in the absence of oxalate.
I also ran 82 batch reactor experiments in magnesium and sodium sulfate and magnesium and potassium nitrate solutions. These experiments show that ionic strength up to 12 m, log mMg up to 4 m, and log mSO4 up to 3 m have no effect on forsterite dissolution rates. However, decreasing aH2O slows forsterite dissolution rates. The effect of decreasing dissolution rates with decreasing aH2O is consistent with the idea that water acts as a ligand that participates in the dissolution process.Forsterite dissolution rate data from previously published studies were combined with results from my experiments and regressed to produce rate laws at low and high pH. For pH < 5.05 or and for pH > 5.05 or I then developed a diagram that shows the effect rate-determining variables on the lifetime of olivine grains in weathering environments using these rate laws.Ph. D.
45
Haworth, Naomi Louise. „Quantum Chemical Studies of Thermochemistry, Kinetics and Molecular Structure“. Thesis, The University of Sydney, 2003. http://hdl.handle.net/2123/509.
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This thesis is concerned with a range of chemical problems which are amenable to theoretical investigation via the application of current methods of computational quantum chemistry. These problems include the calculation of accurate thermochemical data, the prediction of reaction kinetics, the study of molecular potential energy surfaces, and the investigation of molecular structures and binding. The heats of formation (from both atomisation energies and isodesmic schemes) of a set of approximately 120 C1 and C2 fluorocarbons and oxidised fluorocarbons (along with C3F6 and CF3CHFCF2) were calculated with the Gaussian-3 (G3) method (along with several approximations thereto). These molecules are of importance in the flame chemistry of 2-H-heptafluoropropane, which has been proposed as a potential fire retardant with which to replace chloro- and bromofluorocarbons (CFC�s and BFC�s). The calculation of the data reported here was carried out in parallel with the modelling studies of Hynes et al.1-3 of shock tube experiments on CF3CHFCF3 and on C3F6 with either hydrogen or oxygen atoms. G3 calculations were also employed in conjunction with the experimental work of Owens et al.4 to describe the pyrolysis of CFClBr2 (giving CFCl) at a radiation wavelength of 265 nm. The theoretical prediction of the dissociation energy of the two C-Br bonds was found to be consistent with the energy at which carbene production was first observed, thus supporting the hypothesis that the pyrolysis releases two bromine radicals (rather than a Br2 molecule). On the basis of this interpretation of the experiments, the heat of formation of CFClBr2 is predicted to be 184 � 5 kJ mol-1, in good agreement with the G3 value of 188 � 5 kJ mol-1. Accurate thermochemical data was computed for 18 small phosphorus containing molecules (P2, P4, PH, PH2, PH3, P2H2, P2H4, PO, PO2, PO3, P2O, P2O2, HPO, HPOH, H2POH, H3PO, HOPO and HOPO2), most of which are important in the reaction model introduced by Twarowski5 for the combustion of H2 and O2 in the presence of phosphine. Twarowski reported that the H + OH recombination reaction is catalysed by the combustion products of PH3 and proposed two catalytic cycles, involving PO2, HOPO and HOPO2, to explain this observation. Using our thermochemical data we computed the rate coefficients of the most important reactions in these cycles (using transition state and RRKM theories) and confirmed that at 2000K both cycles have comparable rates and are significantly faster than the uncatalysed H + OH recombination. The heats of formation used in this work on phosphorus compounds were calculated using the G2, G3, G3X and G3X2 methods along with the far more extensive CCSD(T)/CBS type scheme. The latter is based on the evaluation of coupled cluster energies using the correlation consistent triple-, quadruple- and pentuple-zeta basis sets and extrapolation to the complete basis set (CBS) limit along with core-valence correlation corrections (with counterpoise corrections for phosphorus atoms), scalar relativistic corrections and spin-orbit coupling effects. The CCSD(T)/CBS results are consistent with the available experimental data and therefore constitute a convenient set of benchmark values with which to compare the more approximate Gaussian-n results. The G2 and G3 methods were found to be of comparable accuracy, however both schemes consistently underestimated the benchmark atomisation energies. The performance of G3X is significantly better, having a mean absolute deviation (MAD) from the CBS results of 1.8 kcal mol-1, although the predicted atomisation energies are still consistently too low. G3X2 (including counterpoise corrections to the core-valence correlation energy for phosphorus) was found to give a slight improvement over G3X, resulting in a MAD of 1.5 kcal mol-1. Several molecules were also identified for which the approximations underlying the Gaussian-n methodologies appear to be unreliable; these include molecules with multiple or strained P-P bonds. The potential energy surface of the NNH + O system was investigated using density functional theory (B3LYP/6-31G(2df,p)) with the aim of determining the importance of this route in the production of NO in combustion reactions. In addition to the standard reaction channels, namely decomposition into NO + NH, N2 + OH and H + N2O via the ONNH intermediate, several new reaction pathways were also investigated. These include the direct abstraction of H by O and three product channels via the intermediate ONHN, giving N2 + OH, H + N2O and HNO + N. For each of the species corresponding to stationary points on the B3LYP surface, valence correlated CCSD(T) calculations were performed with the aug-cc-pVxZ (x = Q, 5) basis sets and the results extrapolated to the complete basis set limit. Core-valence correlation corrections, scalar relativistic corrections and spin orbit effects were also included in the resulting energetics and the subsequent calculation of thermochemical data. Heats of formation were also calculated using the G3X method. Variational transition state theory was used to determine the critical points for the barrierless reactions and the resulting B3LYP energetics were scaled to be compatible with the G3X and CCSD(T)/CBS values. As the results of modelling studies are critically dependent on the heat of formation of NNH, more extensive CCSD(T)/CBS calculations were performed for this molecule, predicting the heat of formation to be 60.6 � 0.5 kcal mol-1. Rate coefficients for the overall reaction processes were obtained by the application of multi-well RRKM theory. The thermochemical and kinetic results thus obtained were subsequently used in conjunction with the GRIMech 3.0 reaction data set in modelling studies of combustion systems, including methane / air and CO / H2 / air mixtures in completely stirred reactors. This study revealed that, contrary to common belief, the NNH + O channel is a relatively minor route for the production of NO. The structure of the inhibitor Nd-(N'-Sulfodiaminophosphinyl)-L-ornithine, PSOrn, and the nature of its binding to the OTCase enzyme was investigated using density functional (B3LYP) theory. The B3LYP/6-31G(d) calculations on the model compound, PSO, revealed that, while this molecule could be expected to exist in an amino form in the gas phase, on complexation in the active site of the enzyme it would be expected to lose two protons to form a dinegative imino tautomer. This species is shown to bind strongly to two H3CNHC(NH2)2+ moieties (model compounds for arginine residues), indicating that the strong binding observed between inhibitor and enzyme is partially due to electrostatic interactions as well as extensive hydrogen bonding (both model Arg+ residues form hydrogen bonds to two different sites on PSO). Population analysis and hydrogen bonding studies have revealed that the intramolecular bonding in this species consists of either single or semipolar bonds (that is, S and P are not hypervalent) and that terminal oxygens (which, being involved in semipolar bonds, carry negative charges) can be expected to form up to 4 hydrogen bonds with residues in the active site. In the course of this work several new G3 type methods were proposed, including G3MP4(SDQ) and G3[MP2(Full)], which are less expensive approximations to G3, and G3X2, which is an extension of G3X designed to incorporate additional electron correlation. As noted earlier, G3X2 shows a small improvement on G3X; G3MP4(SDQ) and G3[MP2(Full)], in turn, show good agreement with G3 results, with MAD�s of ~ 0.4 and ~ 0.5 kcal mol-1 respectively. 1. R. G. Hynes, J. C. Mackie and A. R. Masri, J. Phys. Chem. A, 1999, 103, 5967. 2. R. G. Hynes, J. C. Mackie and A. R. Masri, J. Phys. Chem. A, 1999, 103, 54. 3. R. G. Hynes, J. C. Mackie and A. R. Masri, Proc. Combust. Inst., 2000, 28, 1557. 4. N. L. Owens, Honours Thesis, School of Chemistry, University of Sydney, 2001. 5. A. Twarowski, Combustion and Flame, 1995, 102, 41.
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Haworth, Naomi Louise. „Quantum Chemical Studies of Thermochemistry, Kinetics and Molecular Structure“. University of Sydney. Chemistry, 2003. http://hdl.handle.net/2123/509.
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This thesis is concerned with a range of chemical problems which are amenable to theoretical investigation via the application of current methods of computational quantum chemistry. These problems include the calculation of accurate thermochemical data, the prediction of reaction kinetics, the study of molecular potential energy surfaces, and the investigation of molecular structures and binding. The heats of formation (from both atomisation energies and isodesmic schemes) of a set of approximately 120 C1 and C2 fluorocarbons and oxidised fluorocarbons (along with C3F6 and CF3CHFCF2) were calculated with the Gaussian-3 (G3) method (along with several approximations thereto). These molecules are of importance in the flame chemistry of 2-H-heptafluoropropane, which has been proposed as a potential fire retardant with which to replace chloro- and bromofluorocarbons (CFC�s and BFC�s). The calculation of the data reported here was carried out in parallel with the modelling studies of Hynes et al.1-3 of shock tube experiments on CF3CHFCF3 and on C3F6 with either hydrogen or oxygen atoms. G3 calculations were also employed in conjunction with the experimental work of Owens et al.4 to describe the pyrolysis of CFClBr2 (giving CFCl) at a radiation wavelength of 265 nm. The theoretical prediction of the dissociation energy of the two C-Br bonds was found to be consistent with the energy at which carbene production was first observed, thus supporting the hypothesis that the pyrolysis releases two bromine radicals (rather than a Br2 molecule). On the basis of this interpretation of the experiments, the heat of formation of CFClBr2 is predicted to be 184 � 5 kJ mol-1, in good agreement with the G3 value of 188 � 5 kJ mol-1. Accurate thermochemical data was computed for 18 small phosphorus containing molecules (P2, P4, PH, PH2, PH3, P2H2, P2H4, PO, PO2, PO3, P2O, P2O2, HPO, HPOH, H2POH, H3PO, HOPO and HOPO2), most of which are important in the reaction model introduced by Twarowski5 for the combustion of H2 and O2 in the presence of phosphine. Twarowski reported that the H + OH recombination reaction is catalysed by the combustion products of PH3 and proposed two catalytic cycles, involving PO2, HOPO and HOPO2, to explain this observation. Using our thermochemical data we computed the rate coefficients of the most important reactions in these cycles (using transition state and RRKM theories) and confirmed that at 2000K both cycles have comparable rates and are significantly faster than the uncatalysed H + OH recombination. The heats of formation used in this work on phosphorus compounds were calculated using the G2, G3, G3X and G3X2 methods along with the far more extensive CCSD(T)/CBS type scheme. The latter is based on the evaluation of coupled cluster energies using the correlation consistent triple-, quadruple- and pentuple-zeta basis sets and extrapolation to the complete basis set (CBS) limit along with core-valence correlation corrections (with counterpoise corrections for phosphorus atoms), scalar relativistic corrections and spin-orbit coupling effects. The CCSD(T)/CBS results are consistent with the available experimental data and therefore constitute a convenient set of benchmark values with which to compare the more approximate Gaussian-n results. The G2 and G3 methods were found to be of comparable accuracy, however both schemes consistently underestimated the benchmark atomisation energies. The performance of G3X is significantly better, having a mean absolute deviation (MAD) from the CBS results of 1.8 kcal mol-1, although the predicted atomisation energies are still consistently too low. G3X2 (including counterpoise corrections to the core-valence correlation energy for phosphorus) was found to give a slight improvement over G3X, resulting in a MAD of 1.5 kcal mol-1. Several molecules were also identified for which the approximations underlying the Gaussian-n methodologies appear to be unreliable; these include molecules with multiple or strained P-P bonds. The potential energy surface of the NNH + O system was investigated using density functional theory (B3LYP/6-31G(2df,p)) with the aim of determining the importance of this route in the production of NO in combustion reactions. In addition to the standard reaction channels, namely decomposition into NO + NH, N2 + OH and H + N2O via the ONNH intermediate, several new reaction pathways were also investigated. These include the direct abstraction of H by O and three product channels via the intermediate ONHN, giving N2 + OH, H + N2O and HNO + N. For each of the species corresponding to stationary points on the B3LYP surface, valence correlated CCSD(T) calculations were performed with the aug-cc-pVxZ (x = Q, 5) basis sets and the results extrapolated to the complete basis set limit. Core-valence correlation corrections, scalar relativistic corrections and spin orbit effects were also included in the resulting energetics and the subsequent calculation of thermochemical data. Heats of formation were also calculated using the G3X method. Variational transition state theory was used to determine the critical points for the barrierless reactions and the resulting B3LYP energetics were scaled to be compatible with the G3X and CCSD(T)/CBS values. As the results of modelling studies are critically dependent on the heat of formation of NNH, more extensive CCSD(T)/CBS calculations were performed for this molecule, predicting the heat of formation to be 60.6 � 0.5 kcal mol-1. Rate coefficients for the overall reaction processes were obtained by the application of multi-well RRKM theory. The thermochemical and kinetic results thus obtained were subsequently used in conjunction with the GRIMech 3.0 reaction data set in modelling studies of combustion systems, including methane / air and CO / H2 / air mixtures in completely stirred reactors. This study revealed that, contrary to common belief, the NNH + O channel is a relatively minor route for the production of NO. The structure of the inhibitor Nd-(N'-Sulfodiaminophosphinyl)-L-ornithine, PSOrn, and the nature of its binding to the OTCase enzyme was investigated using density functional (B3LYP) theory. The B3LYP/6-31G(d) calculations on the model compound, PSO, revealed that, while this molecule could be expected to exist in an amino form in the gas phase, on complexation in the active site of the enzyme it would be expected to lose two protons to form a dinegative imino tautomer. This species is shown to bind strongly to two H3CNHC(NH2)2+ moieties (model compounds for arginine residues), indicating that the strong binding observed between inhibitor and enzyme is partially due to electrostatic interactions as well as extensive hydrogen bonding (both model Arg+ residues form hydrogen bonds to two different sites on PSO). Population analysis and hydrogen bonding studies have revealed that the intramolecular bonding in this species consists of either single or semipolar bonds (that is, S and P are not hypervalent) and that terminal oxygens (which, being involved in semipolar bonds, carry negative charges) can be expected to form up to 4 hydrogen bonds with residues in the active site. In the course of this work several new G3 type methods were proposed, including G3MP4(SDQ) and G3[MP2(Full)], which are less expensive approximations to G3, and G3X2, which is an extension of G3X designed to incorporate additional electron correlation. As noted earlier, G3X2 shows a small improvement on G3X; G3MP4(SDQ) and G3[MP2(Full)], in turn, show good agreement with G3 results, with MAD�s of ~ 0.4 and ~ 0.5 kcal mol-1 respectively. 1. R. G. Hynes, J. C. Mackie and A. R. Masri, J. Phys. Chem. A, 1999, 103, 5967. 2. R. G. Hynes, J. C. Mackie and A. R. Masri, J. Phys. Chem. A, 1999, 103, 54. 3. R. G. Hynes, J. C. Mackie and A. R. Masri, Proc. Combust. Inst., 2000, 28, 1557. 4. N. L. Owens, Honours Thesis, School of Chemistry, University of Sydney, 2001. 5. A. Twarowski, Combustion and Flame, 1995, 102, 41.
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Khan, Ahmed Faraz. „Chemical kinetics modelling of combustion processes in SI engines“. Thesis, University of Leeds, 2014. http://etheses.whiterose.ac.uk/7554/.
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The need for improving the efficiency and reducing emissions is a constant challenge in combustion engine design. For spark ignition engines, these challenges have been targeted in the past decade or so, through ‘engine downsizing’ which refers to a reduction in engine displacement accompanied by turbocharging. Besides the benefits of this, it is expected to aggravate the already serious issue of engine knock owing to increased cylinder pressure. Engine knock which is a consequence of an abnormal mode of combustion in SI engines, is a performance limiting phenomenon and potentially damaging to the engine parts. It is therefore of great interest to develop capability to predict autoignition which leads to engine knock. Traditionally, rather rudimentary skeletal chemical kinetics models have been used for autoignition modelling, however, they either produce incorrect predictions or are only limited to certain fuels. In this work, realistic chemical kinetics of gasoline surrogate oxidation has been employed to address these issues. A holistic modelling approach has been employed to predict combustion, cyclic variability, end gas autoignition and knock propensity of a turbocharged SI engine. This was achieved by first developing a Fortran code for chemical kinetics calculations which was then coupled with a quasi-dimensional thermodynamic combustion modelling code called LUSIE and the commercial package, GT-Power. The resulting code allowed fast and appreciably accurate predictions of the effects of operating condition on autoignition. Modelling was validated through comparisons with engine experimental data at all stages. Constant volume chemical kinetics modelling of the autoignition of various gasoline surrogate components, i.e. iso-octane, n-heptane, toluene and ethanol, by using three reduced mechanisms revealed how the conversion rate of relatively less reactive blend components, toluene and ethanol, is accelerated as they scavenge active radical formed during the oxidation of n-heptane and iso-octane. Autoignition modelling in engines offered an insight into the fuel-engine interactions and that how the composition of a gasoline surrogate should be selected. The simulations also demonstrated the reduced relevance of research and motor octane numbers to the determination of gasoline surrogates and that it is crucial for a gasoline surrogate to reflect the composition of the target gasoline and that optimising its physicochemical properties and octane numbers to match those of the gasoline does not guarantee that the surrogate will mimic the autoignition behaviour of gasoline. During combustion modelling, possible deficiencies in in-cylinder turbulence predictions and possible inaccuracies in turbulent entrainment velocity model required an optimisation of the turbulent length scale in the eddy burn-up model to achieve the correct combustion rate. After the prediction of a correct mean cycle at a certain engine speed, effects of variation in intake air temperature and spark timing were studied without the need for any model adjustment. Autoignition predictions at various conditions of a downsized, turbocharged engine agreed remarkably well with experimental values. When coupled with a simple cyclic variability model, the autoignition predictions for the full spectrum of cylinder pressures allowed determination of a percentage of the severely autoigniting cycles at any given spark timing or intake temperature. Based on that, a knock-limited spark advance was predicted within an accuracy of 2° of crank angle.
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Calderini, Danilo. „Kinetics and dynamics for chemical reactions in gas phase“. Doctoral thesis, Scuola Normale Superiore, 2016. http://hdl.handle.net/11384/85818.
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A deep understanding of molecular reactions is a challenging task since the range of time and energy covered implies a wide and dense grid for the numerical representation of the reactive Hamiltonian.
For a computational chemist, the accurate prediction of its value starting from the definition of reactants and products is fascinating and demanding, but can be extremely useful for further investigation and optimization problems.
Several methods, all derived by the Transition State Theory, have been developed to avoid the computational cost of the Hamiltonian representation on a large, multidimensional grid; we investigate these strategies both in the time and energy domain to explore the advan- tages and drawbacks of these reciprocal spaces.
Since we want to increase the range of applicability of the calcula- tion of thermal rate constants to medium size molecules, which can have floppy geometries with low frequency modes, we introduce a dedicated treatment of such modes based on the Intrinsic Reaction Path of Fukui.
In Part i, we introduce the theoretical instrument used to perform our calculation, both in energy and time domain; Part ii is devoted to the presentation of the applications, mainly focused on current issues in astrochemical studies. Appendices treat specific topics, like Möller operators, essential for the comprehension of the theory but too long to be inserted in Part i.
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Rufeger, Waltraud. „An analysis of the oregonator“. Diss., Georgia Institute of Technology, 1996. http://hdl.handle.net/1853/29853.
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Mangan, Lee S. „Equilibrium and disequilibrium aspects of contact metamorphism : the Ross of Mull granite aureole, Scotland“. Thesis, University of Liverpool, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.295820.
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