Dissertations / Theses on the topic 'Chemical engineering – Mathematical models'
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Fourie, Johan George. "The mathematical modelling of heat transfer and fluid flow in cellular metallic foams." Thesis, Stellenbosch : Stellenbosch University, 2000. http://hdl.handle.net/10019.1/51994.
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Dissertation (PhD)--University of Stellenbosch, 2000.ENGLISH ABSTRACT: A mathematical model is presented which conceptualises fluid flow and heat transfer in cellular metallic foams completely saturated with a fluid in motion. The model consists of a set of elliptic partial differential governing equations describing, firstly, a momentum balance in the fluid by the spatial distribution of its locally mean velocity, and secondly, an energy balance in the fluid and in the solid matrix of the metallic foam, by the spatial and temporal distribution of their locally mean temperatures. The separate energy balance descriptions for the fluid and the solid matrix extend the application of the model to conditions of thermal equilibrium and thermal non-equilibrium between the fluid and the solid matrix. A computational solution algorithm is presented which allows the universal application of the model to porous domains of arbitrary shape, with spatially and temporally variable heat loads in a variety of forms.
AFRIKAANSE OPSOMMING: 'n Wiskundige model word voorgestel wat vloei en warmteoordrag voorspel in sellulêre metaalsponse wat in geheel gevul is deur 'n bewegende vloeier. Die vloeier kan in gasof vloeistoffase verkeer. Die model bestaan uit 'n stel elliptiese parsiële differensiaalvergelykings wat in die eerste plek 'n momentum-ewewig in die vloeier beskryf in terme van 'n ruimtelike, lokaal-gemiddelde snelheidsveld, en wat tweedens 'n energie-ewewig in die vloeier en in die soliede matriks van die metaalspons beskryf in terme van ruimtelike en tydelike lokaal-gemiddelde temperatuur verspreidings. Die aparte energie-ewewig beskrywings vir die vloeier en vir die soliede matriks van die metaalspons brei die aanwending van die model uit na gevalle waar die vloeier en die soliede matriks in termiese ewewig of in termiese onewewig verkeer. 'n Numeriese oplossingsalgoritme word ook voorgestel vir die universele toepassing van die model op ruimtelik-arbitrêre metaalspons geometrië wat onderwerp word aan 'n aantal verskillende ruimtelik-en tydveranderlike termiese laste.
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Marks, Marguerite Colasurdo. "Incorporating Chemical Activity and Relative Humidity Effects in Regional Air Quality Modeling of Organic Aerosol Formation." PDXScholar, 2013. https://pdxscholar.library.pdx.edu/open_access_etds/1511.
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Atmospheric particulate matter is known to have significant effects on human health, visibility, and global climate. The magnitudes of these effects, however, depend in complex ways on chemical composition, relative humidity, temperature, phase state, and other parameters. Current regional air quality models such as CMAQ (Community Multiscale Air Quality model) ignore many of these considerations, and consider that the formation of secondary organic aerosol (SOA) can be calculated by assuming thermodynamic ideality in the organic particulate matter (OPM) phase as well as negligible uptake of water into the OPM phase. Theoretical predictions and model simulations considering non-ideality and water uptake show that the standard model assumptions can lead to large errors in predicted SOA mass, and that the magnitude of these errors is sensitive to the composition of the OPM phase.
The SOA module in CMAQ v4.7.1 has been revised in this work to allow consideration of the effects of both non-ideality and water uptake. First, a reasonable specific surrogate structure was assigned to each of the lumped products assumed to be produced by reaction of the different precursor hydrocarbons considered in CMAQ (e.g., isoprene, benzene, and toluene). Second, the CMAQ code was modified to allow iterative calculation (at each point in space and time) of the gas/particle partitioning coefficient for each of the SOA-forming products and for water. Third, model simulations were performed for the Eastern US at a resolution of 36-km x 36-km for late summer 2006, under a range of relative humidity conditions.
When compared with an appropriate base case, the modified code produced increases in SOA ranging from 0.17 to 0.51 micrograms per cubic meter. The average change was 0.30 micrograms per cubic meter, corresponding to a 37% increase in SOA formation. Incorporation of phase separation effects would likely lead to further increases in predicted SOA levels.
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Mwale, Adolph Ntaja. "A mathematical model for predicting classification performance in wet fine screens." Master's thesis, University of Cape Town, 2015. http://hdl.handle.net/11427/20122.
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Screening is a well-known classification process in the minerals processing industry. The process involves separation of fine particles from coarse particles based on size and is applicable to both dry and fine screening. Fine screening is normally carried out wet. Until recently, fine wet screening had been limited to relatively low throughput applications. Developments in the recent past have seen the evolution of fine screening to high capacity applications. It has found application in operations such as closed circuits with a mill in place of hydrocyclones. However, even though developments are increasing, there has been a process model developmental lag. A fine wet screen model that can be used for unit simulation purposes to predict screen performance outcomes or integration into other models to simulate and predict process performance is necessary. Most existing screen models are for dry and coarse screening applications. This thesis is aimed at developing a fine wet screen process model for predicting wet screening performance in the 45 - 150 μm range. Pilot plant testwork was conducted using a UG2-Chrome ore blend as feed.
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Knobel, Anthony N. "A mathematical model of a high sulphate wastewater, anaerobic treatment system." Master's thesis, University of Cape Town, 1999. http://hdl.handle.net/11427/19419.
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Includes bibliographic references.High sulphate wastewaters, originating from industrial activity or from the biological oxidation of sulphide ores (acid mine drainage), cannot be discharged into the environment untreated. Apart from the high sulphate levels, these waters may be very acidic and have high dissolved heavy metal concentrations. One promising treatment technology is biological sulphate reduction in anaerobic reactors. During anaerobic treatment, sulphate is reduced to sulphide and alkalinity is generated, raising the pH and precipitating many of the heavy metals. The process requires a carbon source as an electron donor. This may be simple organics such as ethanol or volatile fatty acids, which are directly utilized by the sulphate reducing bacteria, or complex organics such as sewage sludge which must first undergo solubilization and fermentation by a different microbial group. As an aid to the design and operation of this treatment process, a mathematical model describing an anaerobic digester treating high sulphate waste waters has been developed. Apart from sulphate reduction, the model includes those reactions which occur either prior to sulphate reduction, or in competition with it. These include hydrolysis of solid substrates, acidogenesis, beta oxidation of long chain fatty acids, acetogenesis and methanogenesis. By incorporating terms for these reactions, the model is able to simulate sulphate reduction using a wide range of carbon sources. A comprehensive literature survey of the kinetic parameters for the above reactions was undertaken. Apart from the Monod equation describing substrate uptake the kinetic expressions used in the model also includes terms for: unionized fatty acid inhibition; unionized or total sulphide inhibition; hydrogen inhibition and hydrogen product regulation where appropriate; pH inhibition; and dual substrate uptake where appropriate. Acid/base equilibrium chemistry has been included in order to predict the pH and unionized component concentrations (needed for calculating inhibition). The weak acids, H₂CO₃, H₂S, a number of SCFAs, NH₃, and their ions, as well as the strongly dissociating sulphates Na₂SO₄ and H₂SO₄ are included. An activity based model was used, with the activity coefficients calculated using Debye-Hilckle theory. The mass transfer rates of hydrogen, methane, carbon dioxide and hydrogen sulphide from the liquid to the vapour phase are also included. A final aspect of the model is the equations describing the reactor geometry. A number of different reactors may be simulated, including a dynamic batch, steady state CSTR and dynamic CSTR. By separating the hydraulic and solids residence times, high rate reactors such as UASB and packed bed reactors may also be simulated. The model has been used to successfully predict the dynamic and steady state behaviour of a number of different reactor types, utilizing both simple and complex carbon sources.
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Lo, Yu-Wen. "Mathematical models for the coextrusion and the calendering process in a converging section." Ohio : Ohio University, 1989. http://www.ohiolink.edu/etd/view.cgi?ohiou1182442464.
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Psofogiannakis, George. "A mathematical model for a direct propane phosphoric acid fuel cell." Thesis, University of Ottawa (Canada), 2003. http://hdl.handle.net/10393/26424.
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In direct hydrocarbon fuel cells, a hydrocarbon fuel is oxidised in the anode electrode. This thesis presents a mathematical model to predict the performance of a unit cell that utilises propane as the fuel, oxygen as the oxidant, phosphoric acid as the electrolyte, and platinum as the catalyst, supported on porous carbon electrodes. The phenomena considered include the electrochemical reactions of propane oxidation and oxygen reduction on platinum, the diffusion of the gases in gas-filled electrode pores, the dissolution and diffusion of dissolved gases in liquid-filled electrode pores as well as ionic conduction of protons. The model was based on the multi-layered physical structure of a modern unit fuel cell.
The model was first applied to a phosphoric acid fuel cell cathode electrode.
Subsequently, the model was applied to a direct propane-oxygen cell. (Abstract shortened by UMI.)
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Moles, Joshua Stephen. "Chemical Reaction Network Control Systems for Agent-Based Foraging Tasks." PDXScholar, 2015. https://pdxscholar.library.pdx.edu/open_access_etds/2203.
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Chemical reaction networks are an unconventional computing medium that could benefit from the ability to form basic control systems. In this work, we demonstrate the functionality of a chemical control system by evaluating classic genetic algorithm problems: Koza's Santa Fe trail, Jefferson's John Muir trail, and three Santa Fe trail segments. Both Jefferson and Koza found that memory, such as a recurrent neural network or memories in a genetic program, are required to solve the task. Our approach presents the first instance of a chemical system acting as a control system. We propose a delay line connected with an artificial neural network in a chemical reaction network to determine the artificial ant's moves.
We first search for the minimal required delay line size connected to a feed forward neural network in a chemical system. Our experiments show a delay line of length four is sufficient. Next, we used these findings to implement a chemical reaction network with a length four delay line and an artificial neural network. We use genetic algorithms to find an optimal set of weights for the artificial neural network. This chemical system is capable of consuming 100% of the food on a subset and greater than 44% of the food on Koza's Santa Fe trail.
We also show the first implementation of a simulated chemical memory in two different models that can reliably capture and store information over time. The ability to store data over time gives rise to basic control systems that can perform more complex tasks. The integration of a memory storage unit and a control system in a chemistry has applications in biomedicine, like smart drug delivery. We show that we can successfully store the information over time and use it to act as a memory for a control system navigating an agent through a maze.
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KOPAYGORODSKY, EUGENE M. "MATHEMATICAL MODEL OF ULTRA-RAPID PSA." University of Cincinnati / OhioLINK, 2001. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1002135981.
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Wong, Meng Angela. "Development of a mathematical model for blowdown of vessels containing multi-component hydrocarbon mixtures." Thesis, University College London (University of London), 1998. http://discovery.ucl.ac.uk/1317912/.
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This thesis describes the development of a mathematical model, BLOWSIM, for simulating vapour space blowdown of an isolated vessel containing single (vapour) or two-phase (vapour and liquid) hydrocarbon mixtures based on three Cubic Equations of State (CEOS). These include Soaves Redlich-Kwong (SRK), Peng- Robinson (PR) and the recently developed Twu-Coon-Cunningham (TCC) CEOS. The performances of the above equations are first evaluated by comparing their predictions for a range of important thermophysical properties (including vapour/liquid equilibrium data, speed of sound and fluid densities) with experimental data for single and multi-component hydrocarbon systems. These data are reported as a function of reduced pressures and temperatures in the ranges 0.00053 - 43.41 and 0.33 - 2.09 respectively. Typical systems tested include pure alkanes as well as mixtures containing methane, ethane, propane, H₂S, CO₂, N₂ and trace amounts of heavy hydrocarbons. The above is then followed by applications of all three equations in the blowdown model and comparing the results with those obtained from a number of experiments relating to the blowdown of the various hydrocarbon systems from a maximum pressure of 120 atm and ambient temperature. Typical output include the variations of fluid pressure, temperature (both liquid and vapour), discharge rate as well as the wetted and unwetted wall temperatures with time. Another major part of the study includes investigating the effects of different assumptions relating to the estimation of the liquid/wall heat transfer coefficient, the thermodynamic trajectory of the fluid in the vessel as well as the fluid phase at the orifice on blowdown predictions. We find that in general all three CEOS provide a similar level of accuracy with TCC CEOS providing the best performance in terms of predicting vapour speed of sound at Pr > 3. However, the equation gives rise to relatively large errors in predicting liquid speed of sound at Tr \leq 0.6. Typical accuracy of the blowdown model in terms of predicting fluid and wall temperatures during depressurisation are ±7 and 5K respectively.
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kahwaji, janho michel E. "FORMULATION AND USE OF A PERVAPORATION MATHEMATICAL MODEL." Cleveland State University / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=csu1432111781.
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Deshpande, Rutooj D. "UNDERSTANDING AND IMPROVING LITHIUM ION BATTERIES THROUGH MATHEMATICAL MODELING AND EXPERIMENTS." UKnowledge, 2011. http://uknowledge.uky.edu/cme_etds/4.
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There is an intense, worldwide effort to develop durable lithium ion batteries with high energy and power densities for a wide range of applications, including electric and hybrid electric vehicles. For improvement of battery technology understanding the capacity fading mechanism in batteries is of utmost importance. Novel electrode material and improved electrode designs are needed for high energy- high power batteries with less capacity fading. Furthermore, for applications such as automotive applications, precise cycle-life prediction of batteries is necessary.
One of the critical challenges in advancing lithium ion battery technologies is fracture and decrepitation of the electrodes as a result of lithium diffusion during charging and discharging operations. When lithium is inserted in either the positive or negative electrode, there is a volume change associated with insertion or de-insertion. Diffusion-induced stresses (DISs) can therefore cause the nucleation and growth of cracks, leading to mechanical degradation of the batteries. With different mathematical models we studied the behavior of diffusion induces stresses and effects of electrode shape, size, concentration dependent material properties, pre-existing cracks, phase transformations, operating conditions etc. on the diffusion induced stresses. Thus we develop tools to guide the design of the electrode material with better mechanical stability for durable batteries.
Along with mechanical degradation, chemical degradation of batteries also plays an important role in deciding battery cycle life. The instability of commonly employed electrolytes results in solid electrolyte interphase (SEI) formation. Although SEI formation contributes to irreversible capacity loss, the SEI layer is necessary, as it passivates the electrode-electrolyte interface from further solvent decomposition. SEI layer and diffusion induced stresses are inter-dependent and affect each-other. We study coupled chemical-mechanical degradation of electrode materials to understand the capacity fading of the battery with cycling. With the understanding of chemical and mechanical degradation, we develop a simple phenomenological model to predict battery life.
On the experimental part we come up with a novel concept of using liquid metal alloy as a self-healing battery electrode. We develop a method to prepare thin film liquid gallium electrode on a conductive substrate. This enabled us to perform a series of electrochemical and characterization experiments which certify that liquid electrode undergo liquid-solid-liquid transition and thus self-heals the cracks formed during de-insertion. Thus the mechanical degradation can be avoided. We also perform ab-initio calculations to understand the equilibrium potential of various lithium-gallium phases.
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Raud, Pettersson Laura. "Mathematical Modelling of Reversed Sulfur Reduction in Microaerobic Biofilm." Thesis, KTH, Skolan för kemi, bioteknologi och hälsa (CBH), 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-278841.
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chalhoub, Elie R. "An In silico Liver: Model of gluconeogenesis." Cleveland State University / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=csu1363603404.
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O'Brien, Colleen S. "A Mathematical Model for Colloidal Aggregation." [Tampa, Fla.] : University of South Florida, 2003. http://purl.fcla.edu/fcla/etd/SFE0000161.
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Adotey, Bless. "MATHEMATICAL MODELING OF CLOSTRIDIUM THERMOCELLUM’S METABOLIC RESPONSES TO ENVIRONMENTAL PERTURBATION." UKnowledge, 2011. http://uknowledge.uky.edu/bae_etds/1.
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Clostridium thermocellum is a thermophilic anaerobe that is capable of producing ethanol directly from lignocellulosic compounds, however this organism suffers from low ethanol tolerance and low ethanol yields. In vivo mathematical modeling studies based on steady state traditional metabolic flux analysis, metabolic control analysis, transient and steady states’ flux spectrum analysis (FSA) were conducted on C. thermocellum’s central metabolism. The models were developed in Matrix Laboratory software ( MATLAB® (The Language of Technical Computing), R2008b, Version 7.7.0.471)) based on known stoichiometry from C. thermocellum pathway and known physical constraints. Growth on cellobiose from Metabolic flux analysis (MFA) and Metabolic control analysis (MCA) of wild type (WT) and ethanol adapted (EA) cells showed that, at lower than optimum exogenous ethanol levels, ethanol to acetate (E/A) ratios increased by approximately 29% in WT cells and 7% in EA cells. Sensitivity analyses of the MFA and MCA models indicated that the effects of variability in experimental data on model predictions were minimal (within ±5% differences in predictions if the experimental data varied up to ±20%). Steady state FSA model predictions showed that, an optimum hydrogen flux of ~5mM/hr in the presence of pressure equal to or above 7MPa inhibits ferrodoxin hydrogenase which causes NAD re-oxidation in the system to increase ethanol yields to about 3.5 mol ethanol/mol cellobiose.
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Kaul, Himanshu. "A multi-paradigm modelling framework for simulating biocomplexity." Thesis, University of Oxford, 2013. https://ora.ox.ac.uk/objects/uuid:a3e6913d-b4c1-49fd-88fb-7e7155de2e2f.
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The following thesis presents a computational framework that can capture inherently non-linear and emergent biocomplex phenomena. The main motivation behind the investigations undertaken was the absence of a suitable platform that can simulate, both the continuous features as well as the discrete, interaction-based dynamics of a given biological system, or in short, dynamic reciprocity. In order to determine the most powerful approach to achieve this, the efficacy of two modelling paradigms, transport phenomena as well as agent-based, was evaluated and eventually combined. Computational Fluid Dynamics (CFD) was utilised to investigate optimal boundary conditions, in terms of meeting cellular glucose consumption requirements and exposure to physiologically relevant shear fields, that would support mesenchymal stem cell growth in a 3-dimensional culture maintained in a commercially available bioreactor. In addition to validating the default bioreactor configuration and operational parameter ranges as suitable towards sustaining stem cell growth, the investigation underscored the effectiveness of CFD as a design tool. However, due to the homogeneity assumption, an untenable assumption for most biological systems, CFD often encounters difficulties in simulating the interaction-reliant evolution of cellular systems. Therefore, the efficacy of the agent-based approach was evaluated by simulating a morphogenetic event: development of in vitro osteogenic nodule. The novel model replicated most aspects observed in vitro, which included: spatial arrangement of relevant players inside the nodule, interaction-based development of the osteogenic nodules, and the dependence of nodule growth on its size. The model was subsequently applied to interrogate the various competing hypotheses on this process and identify the one that best captures transformation of osteoblasts into osteocytes, a subject of great conjecture. The results from this investigation annulled one of the competing hypotheses, which purported the slow-down in the rate of matrix deposition by certain osteoblasts, and also suggested the acquisition of polarity to be a non-random event. The agent-based model, however, due to being inherently computationally expensive, cannot be recommended to model bulk phenomena. Therefore, the two approaches were integrated to create a modelling platform that was utilised to capture dynamic reciprocity in a bioreactor. As a part of this investigation, an amended definition of dynamic reciprocity and its computational analogue, dynamic assimilation, were proposed. The multi-paradigm platform was validated by conducting melanoma chemotaxis under foetal bovine serum gradient. Due to its CFD and agent-based modalities, the platform can be employed as both a design optimisation as well as hypothesis testing tool.
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Shallman, Julie M. "Galvanic and Pitting Corrosion of a Fastener Assembly." University of Akron / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=akron1525950441877742.
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Stachiw, Rosalvo. "Modelagem e simulação do processo de adsorção de compostos orgânicos em xisto, catalisador exaurido de FCC e carvão ativado em pó." Universidade Tecnológica Federal do Paraná, 2008. http://repositorio.utfpr.edu.br/jspui/handle/1/135.
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O alto custo do carvão ativado tem motivado a busca por materiais adsorvedores de baixo custo, como os subprodutos industriais. Neste sentido, o uso dos subprodutos industriais de xisto: finos de xisto (XC), xisto retortado (XR) e xisto retortado com pneus (XRP), proveniente do processo PETROSIX/PETROBRAS, e o catalisador exaurido (CAT), da unidade de FCC (Craqueamento Catalítico em Leito Fluidizado), foram caracterizados e utilizados neste trabalho na adsorção de compostos orgânicos de efluente líquido industrial. O objetivo geral deste estudo é modelar matematicamente o processo de adsorção de compostos orgânicos em xisto, catalisador exaurido de FCC e carvão ativado em pó, utilizando o modelo HSDM (Modelo de Difusão por Superfície Homogênea), e o comportamento hidráulico do sistema adsorvedor. A caracterização estrutural e química de várias amostras de xisto (finos de xisto, xisto retortado e xisto retortado com pneus) e do catalisador exaurido de FCC, além do desenvolvimento de um modelo computacional para a simulação do processo de adsorção são contribuições adicionais ao trabalho. Os resultados de caracterização dos adsorventes de xisto mostram que estes materiais são basicamente macroporosos e com área superficial em torno de 0,51 a 3,36 2 . 1 m g , além de apresentarem as mesmas estruturas cristalinas, e micrografias características dos argilominerais. Já o adsorvente CAT mostrou-se formado basicamente por faujasita, sílica e alumina, apresentando-se na forma de grânulos esféricos, irregulares e microporosos, com área superficial característica de materiais zeolíticos (148 e 155 2 . 1 m g ). Os ensaios de adsorção realizados nos efluentes sintéticos e industriais (Fenólico e Petroquímico) mostraram que existe potencial de aplicação dos subprodutos industriais de xisto e CAT na remoção de compostos orgânicos (corantes, fenóis e COT) destes efluentes. Os resultados das simulações obtidos do modelo proposto mostraram que o tratamento unicamente por adsorção em xisto ou CAT, tendo em vista os padrões ambientais de descarte de efluente (resolução CONAMA 357), é inviável. Isto por que a quantidade de adsorvente requerida é muito elevada. Entretanto, tais adsorventes podem ser utilizados na redução da carga orgânica de ambos os efluentes. Por questões de transporte, é indicado que cada subproduto industrial seja utilizado na própria indústria que lhe deu origem. Ou seja, o CAT é indicado para o tratamento do efluente Petroquímico e os adsorventes de xisto para o Fenólico.The high cost of the activated carbon has motivated the search of low cost adsorbents such as industrial by-products. In this sense, the use of industrial by-products of oil shale: Oil Shale (XC), Pirolized Oil Shale (XR) and Pirolized Oil Shale with Tires (XRP), from PETROSIX/PETROBRAS, and the spent catalyst (CAT), from FCC (Fluid Catalytic Cracking) unit were characterized and used in this work in the adsorption of organics compounds of industrial liquid effluent. The main contribution of this thesis is to propose a mathematical model to the adsorption process of organic compounds in oil shale, spent catalyst of FCC and powdered activated carbon. This model is based on HSDM (Homogeneous Surface Diffusion Model) model and on the hydraulic behavior of the adsorbent system. Other contribution is the structural and chemical characterization of several samples of oil shale (oil shale, Pirolized oil shale and Pirolized oil shale with Tires) and of the spent catalyst of FCC. A computational model to simulate the adsorption process of these materials is also developed and can be considered an additional contribution of this work. Experimental and simulated results allow characterization of the oil shale adsorbent as basically macroporous and with superficial area about 0.51 to 3.36 m2.g-1. In addition, they present the same crystal structures and clay micrografies characteristics. The adsorbent CAT is composed basically by Faujasite, silica and alumina. They present spherical beads, irregular forms and micropores, with superficial area characteristics of zeolitic materials (148 and 155 m2.g-1). The adsorption tests realized in the synthetic and industrial effluents (Phenolic and Petrochemical) showed the potential of application of the industrial by-products of oil shale and CAT in the removal of organics compounds (dyes, Phenol and COT) of these effluents. In respect of environmental standards to effluents disposal (CONAMA resolution 357), simulations results, obtained with the proposed model, has demonstrated that the use of only oil shale or CAT is not viable, because the high quantity of adsorbents required. However, such adsorbents can be used in the reduction of organic loads in both effluents, when combined with other processes. Each adsorbent showed be used where it is produced because of transportation cost. The CAT is indicated for the treatment of Petrochemical effluent while the others adsorbents may be applied in the phenolic effluent treatment.
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Jin, Xin. "Coal Electrolysis to Produce Hydrogen at Intermediate Temperatures." Ohio University / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1250785769.
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LEE, HANYONG. "A MODEL FOR DRY- AND WET-CASTING OF POLYMERIC MEMBRANES INCORPORATING CONVECTION DUE TO DENSIFICATION - APPLICATION TO MACROVOID FORMATION." University of Cincinnati / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1131561287.
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Santos, Vinícius Nobre dos. "Estudo cinético da copolimerização estireno-divinilbenzeno." Universidade de São Paulo, 2015. http://www.teses.usp.br/teses/disponiveis/3/3137/tde-22072016-162616/.
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As redes poliméricas são materiais amplamente estudados, pois suas propriedades especiais permitem que sejam aplicadas em áreas como indústria de fertilizantes, medicina, bioquímica, análises químicas dentre outras. A microestrutura de uma rede polimérica, em geral, exerce grande influência sobre as propriedades macroscópicas desses materiais e o interesse da influência dessa microestrutura nas propriedades finais são de interesse estratégico. As reações de ciclização influenciam no controle da microestrutura das redes poliméricas, é sabido que um aumento na diluição do sistema aumenta a incidência deste tipo de reações. A modelagem matemática da copolimerização do estireno-divinilbenzeno é um assunto amplamente estudado, porém poucos estudos foram realizados considerando as reações de ciclização com uma cinética definida e não um problema tipo caixa-preta. Este trabalho teve como principal objetivo o estudo da copolimerização de estireno-divinilbenzeno em solução e sua modelagem matemática com a inclusão das reações de ciclização intramoleculares. Sendo assim, reações de copolimerização de estireno-divinilbenzeno em soluções com baixas concentrações de monômeros foram realizadas em batelada em um reator de vidro, inicialmente foram utilizados dois modelos matemáticos para estudar o comportamento do sistema nestas condições, denominados: Modelo A e Modelo B. O Modelo A foi desenvolvido através do balanço de massa de todas as espécies no meio reacional e inclusão das reações de ciclização. O tamanho máximo dos polímeros mortos considerados neste modelo foi de 300 unidades monoméricas, pois devido à diluição acreditava-se que este tamanho máximo abrangesse todos os tamanhos de polímeros mortos, porém sua comparação com dados experimentais mostrou o contrário. O Modelo B foi baseado no modelo desenvolvido por Aguiar (2013) e utiliza o balanço de massa para as espécies não poliméricas e método dos momentos para as espécies poliméricas (radicais poliméricos e polímeros mortos). Este modelo utiliza também o Fracionamento Numérico para determinação das massas moleculares e ponto de gel, as reações de ciclização foram incluídas através do Método dos Caminhos. Quando comparados aos dados experimentais, o Modelo B mostrou-se mais realista com menores tempos de simulação e com menores problemas numéricos que o Modelo A, portanto este foi utilizado para o estudo do sistema em questão. Os resultados apresentados através do Modelo B indicam que o parâmetro atribuído à cinética das ligações cruzadas (Cp) foi de 0,05 e o valor do parâmetro de ciclização do menor segmento ciclizável (3 unidades monoméricas) foi de 130 s-1 para a temperatura de 90ºC, os valores para os demais tamanhos foram calculados através da equação de Rolfes e Stepto. Este trabalho é uma continuação ao trabalho de Aguiar (2013) e seus resultados mostraram que as simulações das variáveis: concentração de duplas ligações pendentes, Massa Molecular Mássica Média (Mw) e polidispersidade aproximaram-se mais dos dados experimentais quando as ciclizações são incluídas no modelo quando comparadas à abordagem sem a inclusão das reações de ciclização.Polymer networks are widely studied materials; their especial properties allow them to be applied in areas such as the fertilizer industry, medicine, biochemistry, chemical analysis among others. In general, the polymer network microstructure has influence in macroscopic properties of materials, hence the interest of such microstructure in final properties are of strategic interest. The cyclization reactions influence in the microstructure control of polymer networks. It is known that an increase in systems dilution can increase the cyclization reactions incidence. Mathematical modeling of copolymerization of styrene-divinylbenzene is a widely studied subject, but few studies have been conducted considering the cyclization reactions with a defined kinetic and not a problem black-box type. This work aimed to study the styrene-divinylbenzene copolymerization solutions and their mathematical modeling with the inclusion of intramolecular cyclization reactions. Thus, solution copolymerization of styrene and divinylbenzene was carried out at low concentration of monomers in batch reactor. Two mathematical models were initially used to analize the behavior of the system, which were called: Model A and Model B. The Model A was developed by molar balance of species in the reaction medium and includes cyclization reactions, which were considered to happen in polymer chains with 300 or less monomer units. Due the dilution was believed that this number of units covering all sizes of dead polymers, but comparison between Model A an experimental data proved otherwise. The Model B was based in model of Aguiar (2013), and uses the mass balance for non-polimerics species and moments methods for polimerics species. Model B also uses numerical fractionation for average molecular weight and gel point determination, and the method of paths to approach cyclization reactions. When compared to experimental data, Model B proved more realistic, presenting shorter simulation times and less numerical problems than Model A. Therefore Model B was chosen to represent the system. The results presented by Model B indicate that the parameter assigned to the kinetics os crosslink (Cp) was fitted at 0,05 and cyclization rate constant for paths with 3 monomer units was fitted 130 s-1 at temperature of 90°C. The cyclization rate constants for longer paths were calculated trough Rolfes and Steptos equation. This work is a follow up to Aguiars work (2013) and the results showed that the simulation of variables: concentration of pendant double bonds, average molecular weight and polidispersity better predicted when the cyclization rate constants are greater than zero.
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DeGagne, Julia Lynn. "Acid-Base Equilibria in Organic-Solvent/Water Mixtures and Their Relevance to Gas/Particle Partitioning in the Atmosphere and in Tobacco Smoke." PDXScholar, 2016. http://pdxscholar.library.pdx.edu/open_access_etds/2733.
Full textAbstract:
Acid-base equilibria in organic particulate matter (PM) are poorly understood, but have important implications for air quality and public health. First, acid-base reactions in organic particulate matter affect the gas/particle partitioning of organic compounds in the atmosphere, and these processes are not currently represented in atmospheric and climate change models. Second, the acid-base balance of tobacco smoke affects the amount of nicotine absorbed by the smoker, and a greater understanding of this balance would help to relate cigarette smoke composition to the addictive properties of cigarettes. This work presents data related to both air quality and tobacco smoke modeling.
The gas/particle partitioning behavior of organic acids and bases is highly dependent on acid-base equilibria and speciation between neutral and ionic forms, because ionic compounds do not volatilize. Descriptions of acid dissociation behavior in atmospheric PM have, to date, focused primarily on phases in which the solvent is water; however, atmospheric PM may include up to 90% organic matter. Data is presented here describing the acid dissociation behavior of organic acids and protonated amines in organic/aqueous mixtures (chosen to approximate the characteristics of organic PM) with varying levels of water content. In such mixtures, the preferential solvation of ions and neutral molecules (by the aqueous portion or the organic portion, respectively) affects the acid-base equilibria of the solutes. It is demonstrated that neutralization reactions between acids and bases that create ions are likely to have non-negligible effects on gas/particle partitioning under certain atmospheric conditions. Thus, including acid-base reactions in organic gas/particle partitioning models could result in a greater proportion of acidic and basic compounds partitioning to the particulate phase. In addition, the acid dissociation constants (pKa values) of atmospherically-relevant acids and bases vary with water content. Specifically, as water content increases, the pKa values of organic acids decrease dramatically, while the pKa values of protonated amines changes only slightly. This situation can result in drastically different speciations and partitioning behavior depending on water content.
This second part of this work reports some of the data needed to develop an acid-base balance for tobacco smoke PM using electroneutrality as a governing principle. Five brands of cigarettes were sampled and the smoke PM extracted. Cations (sodium, potassium, and ammonia) and anions (organic acids, nitrate, nitrite, and chloride) were measured using ion chromatography. Ammonia and organic acids were also re-measured after the acidification of the sample in order to determine whether "bound" forms of these compounds exist in cigarette PM. Weak acids were determined by acid-base titration to determine whether or not all of the weak acids (including organic acids) had been accounted for by the ion chromatography. Weak bases were also determined by acid-base titration, and the majority of weak base is expected to be accounted for by total nicotine (to be measured in a separate analysis). In terms of total acidic species and total basic species, two of the five cigarette brands measured were relatively basic, and three were relatively acidic. Between 50% and 89% of the titrated acids were accounted for by the anionic species measured in ion chromatography. Based on samples tested after sample acidification, about half of the potential ammonia in tobacco smoke PM exists in "bound" form. The speciation of weak acids and bases in tobacco smoke PM cannot be determined from this data alone, because the equilibrium constants of acid-base reactions are not understood in complex organic media. The data presented here, when combined with data from free-base and total nicotine analyses, represent a first step toward a predictive model of acid-base behavior in tobacco smoke PM.
23
Parsons, R. W. "Mathematical models of chemical reactions." Thesis, Bucks New University, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.371228.
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Elele, Nwabuisi N. O. "Mathematical modeling of multistep chemical combustion: The hydrogen-oxygen system." Diss., The University of Arizona, 1988. http://hdl.handle.net/10150/184573.
Full textAbstract:
A model of premixed lean Hydrogen-Oxygen flame is studied by singular perturbation techniques based on high activation energy. The model is built from four reaction steps consisting of two chain branching steps, a chain propagating step, and a recombination step. The analysis, in this case, gives rise to a layer phenomenon different from what is currently seen in combustion literature. First, there is a basic layer similar to those obtained for the one step reaction model. Then embedded in the first layer is a thinner layer giving rise to an interesting system of nonlinear boundary value problems. This system of nonlinear problems does not meet standard existence criterium and also involves an unknown parameter. Hence existence results are called for. Existence is proved for both the boundary value problem and the unknown parameter, and numerical solutions are obtained in support of the existence results. A numerical estimate of the unknown parameter is obtained. A generalization of the model for different reaction parameter ranges is made. Two new thin layers emerge. The structure of one of the new thin layers turns out to be exactly the same as that just described, hence the existence results do carry over. The boundary value problem resulting from the second of the new thin layers turned out to be quite simple and a solution could be written down explicitly.
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Thornton, Paul D. "A chemical casualty model." Thesis, Monterey, California : Naval Postgraduate School, 1990. http://handle.dtic.mil/100.2/ADA239450.
Full textAbstract:
Thesis (M.S. in Operations Research)--Naval Postgraduate School, September 1990.Thesis Advisor(s): Johnson, Laura. Second Reader: Parry, Sam H. "September 1990." Description based on title screen as viewed on December 21, 2009. DTIC Identifier(s): Chemical Warfare Casualties, Chemical Warfare Agents, Mathematical Models. Author(s) subject terms: Chemical Casualties, Chemical Warfare, Regression, CHEMCAS. Includes bibliographical references (p. 36-37). Also available in print.
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Shepherd, Tricia D. "Models for chemical processes : activated dynamics across stochastic potentials." Diss., Georgia Institute of Technology, 2002. http://hdl.handle.net/1853/27062.
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Xu, Jin, and 徐进. "A study of chemical reaction optimization." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2012. http://hub.hku.hk/bib/B48199242.
Full textAbstract:
Complex optimization problems are prevalent in various fields of science and
engineering. However, many of them belong to a category of problems called NP-
hard (nondeterministic polynomial-time hard). On the other hand, due to the
powerful capability in solving a myriad of complex optimization problems, metaheuristic
approaches have attracted great attention in recent decades. Chemical
Reaction Optimization (CRO) is a recently developed metaheuristic mimicking
the interactions of molecules in a chemical reaction. With the flexible structure
and excellent characteristics, CRO can explore the solution space efficiently to
identify the optimal or near optimal solution(s) within an acceptable time. Our
research not only designs different versions of CRO and applies them to tackle
various NP-hard optimization problems, but also investigates theoretical aspects
of CRO in terms of convergence and finite time behavior.
We first focus on the problem of task scheduling in grid computing, which
involves seeking the most efficient strategy for allocating tasks to resources. In
addition to Makespan and Flowtime, we also take reliability of resource into
account, and task scheduling is formulated as an optimization problem with three
objective functions. Then, four different kinds of CRO are designed to solve this
problem. Simulation results show that the CRO methods generally perform better
than existing methods and performance improvement is especially significant in
large-scale applications.
Secondly, we study stock portfolio selection, which pertains to deciding how to
allocate investments to a number of stocks. Here we adopt the classical Markowitz
mean-variance model and consider an additional cardinality constraint. Thus,
the stock portfolio optimization becomes a mixed-integer quadratic programming
problem. To solve it, we propose a new version of CRO named Super Molecule-based
CRO (S-CRO). Computational experiments suggest that S-CRO is superior
to canonical CRO in solving this problem.
Thirdly, we apply CRO to the short adjacent repeats identification problem
(SARIP), which involves detecting the short adjacent repeats shared by multiple
DNA sequences. After proving that SARIP is NP-hard, we test CRO with both
synthetic and real data, and compare its performance with BASARD, which is
the previous best algorithm for this problem. Simulation results show that CRO
performs much better than BASARD in terms of computational time and finding
the optimal solution.
We also propose a parallel version of CRO (named PCRO) with a synchronous
communication scheme. To test its efficiency, we employ PCRO to solve the
Quadratic Assignment Problem (QAP), which is a classical combinatorial optimization
problem. Simulation results show that compared with canonical sequential
CRO, PCRO can reduce the computational time as well as improve the
quality of the solution for instances of QAP with large sizes.
Finally, we perform theoretical analysis on the convergence and finite time
behavior of CRO for combinatorial optimization problems. We explore CRO
convergence from two aspects, namely, the elementary reactions and the total
system energy. Furthermore, we also investigate the finite time behavior of CRO
in respect of convergence rate and first hitting time.published_or_final_version
Electrical and Electronic Engineering
Doctoral
Doctor of Philosophy
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TONELLATO, PETER JOHN. "CRITICAL BEHAVIOR OF AN IGNITION MODEL IN CHEMICAL COMBUSTION." Diss., The University of Arizona, 1985. http://hdl.handle.net/10150/188056.
Full textAbstract:
A model for the hot slab ignition problem is analyzed to determine critical conditions based on the parameters of the system. Activation energy asymptotics, a singular perturbation approach, is applied to the governing equation resulting in a Volterra integral equation of the second kind whose solution represents the temperature perturbation at the surface of the hot slab. The system is said to be supercritical for given parameter values when the temperature perturbation blows up in small finite time, an indication of ignition, or subcritical when the blow up time is large, indicating that heat loss effects overcome the hot slab ignition mechanisms. Comparison principles for integral equations are used to construct upper and lower solutions of the equation. The exact solution as well as the upper and lower solutions depend on two parameters ε, the Zeldovich number a measure of the heat release and λ, the scaled hot slab size. Upper and lower bounds on the transition region, delineating the super-critical from the sub-critical region, are derived based upon the lower and upper solution behavior. The product integration method is used to compute solutions of the Volterra equation for values of ε and λ in the transition region. The computations indicate that a critical curve, λ(c) lying between the analytic bounds, exists.
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Zhu, Dewei. "Development and validation of mathematical models for chemical vapor deposition processes /." The Ohio State University, 1991. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487686243822723.
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Duursma, Gail Rene. "Mathematical modelling of fluidization phenomena." Thesis, University of Oxford, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.305995.
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Mjalli, Farouq S. "Mathematical modelling and control of agitated extraction columns." Thesis, Aston University, 2003. http://publications.aston.ac.uk/9652/.
Full textAbstract:
Liquid-liquid extraction has long been known as a unit operation that plays an important role in industry. This process is well known for its complexity and sensitivity to operation conditions. This thesis presents an attempt to explore the dynamics and control of this process using a systematic approach and state of the art control system design techniques. The process was studied first experimentally under carefully selected. operation conditions, which resembles the ranges employed practically under stable and efficient conditions. Data were collected at steady state conditions using adequate sampling techniques' for the dispersed and continuous phases as well as during the transients of the column with the aid of a computer-based online data logging system and online concentration analysis. A stagewise single stage backflow model was improved to mimic the dynamic op.eration of the column. The developed model accounts for the variation in hydrodynamics, mass transfer, and physical properties throughout the length of the column. End effects were treated by addition of stages at the column entrances. Two parameters were incorporated in the model namely; mass transfer weight factor to correct for the assumption of no mass transfer in the. settling zones at each stage and the backmixing coefficients to handle the axial dispersion phenomena encountered in the course of column operation. The parameters were estimate.d by .. minimizing the differences between the experimental and the model predicted concentration profiles at steady state conditions using non-linear optimisation technique. The estimated values were then correlated as functions of operating parameters and were incorporated in·the .. model equations. The model equations comprise a stiff differential~algebraic system. This system was solved using the GEAR ODE solver. The calculated concentration profiles were compared to those experimentally measured. A very good agreement of the two profi1es was' achieved within a percent relative error of ±2.S%.The developed rigorous dynamic model of the extraction column was. \ls~d to derive linear time-invariant reduced-order models that relate the input variables (agitatorsjJeed, . solvent feed flowrate and concentration, feed concentration andflowrate) to the output variables (raffinate concentration and extract concentration) using the asymptotic method of system identification. The reduced-order models were shown to be accurate in capturing the dynamic behaviour of the process with a maximum modelling prediction error of I %. The simplicity and accuracy of the derived reduced-order models allow for control system design and analysis of such complicated processes. The extraction column is a typical multi variable process with agitator speed and solvent feed flowrate considered as manipulative variables; raffinate concentration and extract concentration as controlled variables and the feeds concentration and feed flowrate as disturbance variables. The control system design of the extraction process was tackled as multi-loop decentralised S1S0 (Single Input Single Output) as well as centralised MIMO (Multi-Input Multi-Output) system using both conventional and model-based control techniques such as IMC (Internal Model Control) and MPC (Model Predictive Control). Control performance of each control scheme was. studied in terms oJ stahilit~, speed of response, sensitivity to modelling errors (robustness), setpoint tracking capabilities ahd load rejection. For decentralised control, multiple loops were assigned to pair .each manipulated variable with each controlled variable according to the interaction analysis and other pairing criteria such as relative gain array (RGA), singular value analysis (SVD) and Jacobi eigenvalue criterion. Loops namely Rotor speed-Raffinate concentration and Solvent flowrateExtract concentration showed weak interaction. Multivariable MPC has shown more effective performance compared to other conventional techniques since it accounts for loops interaction, time delays, and input-output variables constraints
32
Harris, David Wayne. "A degradation analysis methodology for maintenance tasks." Thesis, Georgia Institute of Technology, 1985. http://hdl.handle.net/1853/24867.
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Wincure, Benjamin 1966. "Mathematical modelling of self-cycling fermentation (SCF)." Thesis, McGill University, 1994. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=68058.
Full textAbstract:
A mathematical model that predicts the biomass, limiting substrate, and dissolved oxygen concentrations during the periodic steady state operation of Self-Cycling Fermentation (SCF) was created. The model was used to develop a computer simulation for SCF. To validate the model, predictions from the computer simulation were compared to experimental SCF laboratory data using the bacteria A. calcoaceticus with ethanol as the limiting substrate. The successful fit of the model to the laboratory data supports the hypotheses that, at periodic steady state, cells in the SCF are always growing exponentially, biomass growth is proportional to both the limiting substrate depletion and to oxygen consumption by the organism, and k$ sb{ rm L}$a and the dissolved oxygen level at 100% saturation are constant. The SCF model predicts that SCF will stabilize into a periodic steady state for all emptying/refilling fractions greater than 0 but less than 1.
34
Thornham, S. A. "The mathematical modelling of two problems in chemical engineering." Thesis, University of Manchester, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.382778.
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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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Wade, Adrian Paul. "Modern mathematical methods in analytical chemistry." Thesis, Swansea University, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.329720.
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Manning, Charles Roger 1956. "Infiltration parameters for mathematical models of furrow irrigation." Thesis, The University of Arizona, 1993. http://hdl.handle.net/10150/278286.
Full textAbstract:
The effort to improve furrow irrigation design and management by use of mathematical models is hampered by the difficulty of obtaining infiltration parameters that adequately describe the infiltration process in furrows. This difficulty is related to the effect on infiltration of the variability of wetted width of a furrow with depth. Detailed field measurements of twelve furrow irrigations were used to develop infiltration parameters based on three different assumptions regarding the variation of wetted width with depth. These infiltration parameters were used as input into a mathematical model of furrow irrigation, SRFR. Comparison of measured advance times, water surface elevations and volume of water infiltrated with these values computed by SRFR indicates that SRFR gives consistent results based on the input parameters.
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Terciyanli, Erman. "Alternative Mathematical Models For Revenue Management Problems." Master's thesis, METU, 2009. http://etd.lib.metu.edu.tr/upload/12610711/index.pdf.
Full textAbstract:
In this study, the seat inventory control problem is considered for airline networks from the
perspective of a risk-averse decision maker. In the revenue management literature, it is generally
assumed that the decision makers are risk-neutral. Therefore, the expected revenue is
maximized without taking the variability or any other risk factor into account. On the other
hand, risk-sensitive approach provides us with more information about the behavior of the
revenue. The risk measure we consider in this study is the probability that revenue is less
than a predetermined threshold level. In the risk-neutral cases, while the expected revenue
is maximized, the probability of revenue being less than such a predetermined level might
be high. We propose three mathematical models to incorporate the risk measure under consideration.
The optimal allocations obtained by these models are numerically evaluated in
simulation studies for example problems. Expected revenue, coefficient of variation, load factor
and probability of the poor performance are the performance measures in the simulation
studies. According to the results of these simulations, it shown that the proposed models can
decrease the variability of the revenue considerably. In other words, the probability of revenue
being less than the threshold level is decreased. Moreover, expected revenue can be increased
in some scenarios by using the proposed models. The approach considered in this thesis is especially proposed for small scale airlines because risk of obtaining revenue less than the
threshold level is more for this type of airlines as compared to large scale airlines.
39
Tabb, Jeremiah R. "Using wavelets and principle components analysis to model data from simulated sheet forming processes." Thesis, Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/10146.
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Haines, Alastair Neil. "The mathematical modelling of industrial electrolytic reactions." Thesis, Teesside University, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.235728.
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King, Brian J. "Object-oriented product models in process engineering." Thesis, University of Newcastle Upon Tyne, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.294495.
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Wijaya, Catherina D. (Catherina Dewi). "Developing fundamentally based models for autoignition." Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/32326.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2005.Includes bibliographical references (p. 166-173).
There is renewed interest in autoignition, especially due to the recent development of the homogenous charge compression ignition (HCCI) engine, highly promising with its low Nox and particulate emissions and high efficiency. However it is difficult to control HCCI autoignition. In general accurate prediction of the autoignition behavior of fuel/air mixtures has been difficult, due to inadequate knowledge of low temperature (< 1000K) oxidation. The reactions of peroxy radical RO₂ are hydroperoxyalkyl radical .QOOH are especially problematic. In the first part of this thesis we compute rate parameters for three important reaction pathways from the .QOOH: .QOOH cyclization to form cyclic ether and .OH, .OH migration in .QOOH, and [beta]-scission of [gamma].QOOH. These reactions are competitive with the main chain branching pathway, so their rate constants affect the ignition timing of the system. There are no direct measurement experimental results available for these reactions. We used quantum chemistry, mainly the complete-basis-set extrapolation (CBS-QB3), and calculated the rate constants using the well-known transition state theory (TST). The effects of substituent, nature of radical center, and ring size were also studied. Generalized rate estimation rules for these reactions were derived for later use in automated generation of oxidation mechanisms. The second part of this thesis reports the construction of a rate rules library and rate rules trees for the major reaction families in combustion, useful for automated generation of reaction mechanisms. A detailed oxidation mechanism consists of thousands of reactions, and building such a large mechanism is a laborious task if done manually by hand.
(cont.) Using a hierarchical library of rate estimation rules allows fast on-line estimation of the rate constant of each reaction generated. We derived > 800 rate rules for 14 major reaction families, with emphasis on reaction families important in oxidation. Most of the rate rules were derived from literature kinetic data. These rate rules are stored in a library, based on the reactant classifications in rate rules trees.
by Catherina D. Wijaya.
Ph.D.
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Collins, David Michael 1975. "Tools to analyse cell signaling models." Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/36322.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2004.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Includes bibliographical references (v. 2, leaves 345-369).
Diseases such as diabetes, some forms of cancer, hyper-tension, auto-immune diseases, and some viral diseases are characterized by complex interactions within the human body. Efforts to understand and treat these diseases have only been partially successful. There is currently a huge commercial and academic effort devoted to computational biology to address the shortfalls of qualitative biology. This research has become relevant due to the vast amounts of data now available from high-throughput techniques such as gene-chips, combinatorial chemistry, and fast gene sequencing. The goal of computational biology is to use quantitative models to test complex scientific hypotheses or predict desirable interventions. Consequently, it is important that the model is built to the minimum fidelity required to meet a specific goal, otherwise valuable effort is wasted. Unlike traditional chemical engineering, computational biology does not solely depend on deterministic models of chemical behavior. There is also widespread use of many types of statistical models, stochastic models, electro-static models, and mechanical models. All of these models are inferred from noisy data. It is therefore important to develop techniques to aide the model builder in their task of verifying and using these models to make quantitative predictions. The goal of this thesis is to develop tools for analysing the qualitative and quantitative characteristics of cell-signaling models. The qualitative behavior of deterministic models is studied in the first part of this thesis and the quantitative behavior of stochastic models is studied in the second part. A kinetic model of cell signaling is a common example of a deterministic model used in computational biology.
(cont.) Usually such a model is derived from first-principles. The differential equations represent species conservation and the algebraic equations represent rate equations and equations to estimate rate constants. The researcher faces two key challenges once the model has been formulated: it is desirable to summarize a complex model by the phenomena it exhibits, and it is necessary to check whether the qualitative behavior of the model is verified by experimental observation. The key result of this research is a method to rearrange an implicit index one DAE into state-space form efficiently, amenable to standard control engineering analysis. Control engineering techniques can then be used to determine the time constants, poles, and zeros of the system, thus summarizing all the qualitative behavior of the system. The second part of the thesis focuses on the quantitative analysis of cell migration. It is hypothesized that mammalian cell migration is driven by responses to external chemical, electrical and mechanical stimulus. It is desirable to be able to quantify cell migration (speed, frequency of turning) to correlate output to experimental conditions (ligand concentration, cell type, cell medium, etc). However, the local concentration of signaling molecules and receptors is sufficiently low that a continuum model of cell migration is inadequate, i.e., it is only possible to describe cell motion in a probabilistic fashion ...
by David Michael Collins.
Ph.D.
44
Palmer, Kurt D. "Data collection plans and meta models for chemical process flowsheet simulators." Diss., Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/24511.
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Worth, David J. "Mathematical modelling of a multichannel catalytic monolith combustor." Thesis, University of Bath, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.239944.
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Sinangil, Mehmet Selcuk. "Modeling and control on an industrial polymerization process." Thesis, Georgia Institute of Technology, 1995. http://hdl.handle.net/1853/10150.
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Pikunic, Jorge. "Realistic Molecular Models for Disordered Porous Carbons." NCSU, 2003. http://www.lib.ncsu.edu/theses/available/etd-08172003-203233/.
Full textAbstract:
The complex pore morphology and topology of many non-graphitizable porous carbons is not captured by the current molecular models that are used in analysis of adsorption isotherms. We present a novel constrained reverse Monte Carlo method to build models that quantitatively match carbon-carbon pair correlation functions obtained from experimental diffraction data of real nanoporous carbons. Our approach is based on reverse Monte Carlo with carefully selected constraints on the bond angles and carbon coordination numbers to describe the three-body correlations. Through successive Monte Carlo moves, using a simulated annealing scheme, the model structure is matched to the experimental diffraction data, subject to the imposed three-body constraints. We modeled a series of saccharose-based carbons and tested the resulting models against high resolution transmission electron microscopy (TEM) data. Simulated TEM images of the resulting structural models are in very good agreement with experimental ones. For the carbons studied, the pore structure is highly convoluted, and the commonly used slit pore model is not appropriate. We simulated adsorption of nitrogen and argon at 77 K using grand canonical Monte Carlo, and diffusion of argon at 300 K using canonical molecular dynamics simulations. The isosteric heats of adsorption at 77 K are in excellent agreement with experimental results. The adsorption isotherms and heats of adsorption in these models do not resemble those for fluids in slit pores having the same pore size distribution. We found that diffusion in the structural models is non-Fickian. Instead, a strong single-file character is observed, revealed by the proportionality of the mean square displacement to the square root of time at relatively long times. The single-file mode is a consequence of the small sizes of the quasi one-dimensional pores in the adsorbent models.
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Zheng, Huan Ph D. Massachusetts Institute of Technology. "Multi-scale models of T cell activation." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/62065.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2010.Cataloged from PDF version of thesis.
Includes bibliographical references.
The overarching theme of this thesis is to develop and apply multi-scale computational techniques adopted from physical sciences to study a key phenomenon underlying the adaptive immune response: the activation of T cells. The specific objectives are: 1) develop efficient and versatile computational frameworks to study multi-scale biological systems in silico; 2) obtain mechanistic insights into how T cells are triggered in vivo. The first problem investigated in this thesis addressed a controversy regarding when and how T cells alter migratory patterns in lymphoid tissues, as observed in intravital microscopy experiments. By developing a lattice-based model for T cell migration coupled with a mechanistically motivated simple scheme for T cell activation, I showed that the quantity and quality of cognate antigen (Ag) presented by dendritic cells (DC) dictate such changes. The results from theoretical and computational analyses were not only in agreement with synergistic experiments, but also made predictions that have been tested positively. Furthermore, I identified a consolidated measure of Ag quantity and quality, which provides a unifying conceptual framework for considering diverse future experimental results. The results from this study also suggested that T cells may integrate sub-optimal signals derived from successive encounters with DCs to achieve full activation. However, an underlying molecular mechanism that may confer such "short term memory" of exposure to Ag is not known. I explored the possibility that the hysteresis resulting from positive feedback regulation of the catalytic conversion of a G-protein RasGDP to RasGTP in the T cell receptor (TCR) membrane-proximal signaling network may enable such "short term memory". I developed a multiscale computational model that combines stochastic simulations of the TCR membrane-proximal signaling network with T cell migration. The results showed that this hysteresis can enable T cells to integrate signals derived from weakly stimulatory DCs and may greatly enhance the detection sensitivity during disease onset when Ag presentation is low. The computational framework developed in this study can be readily adapted to examine diverse biological systems where signaling and cell motion need to be studied simultaneously. For example, the model was modified to investigate a DC-mediated mechanism for signal integration, and our results suggest that this mechanism is less likely. Initial steps were also taken to construct a macroscopic model that aims to study how T cell activation impacts observations at the organismic level. Preliminary results for how microscopic receptor-ligand interactions affect the proliferation of different T cell types are presented. Directions for future research are suggested based on these findings.
by Huan Zheng.
Ph.D.
49
Underhill, Patrick Theodore. "Systematic development of coarse-grained polymer models." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/37274.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2006.Includes bibliographical references (p. [159]-163).
The coupling between polymer models and experiments has improved our understanding of polymer behavior both in terms of rheology and dynamics of single molecules. Developing these polymer models is challenging because of the wide range of time and length scales. Mechanical models of polymers have been used to understand average heological properties as well as the deviation a single polymer molecule has from the average response. This leads to more physically significant constitutive relations, which can be coupled with fluid mechanic simulations to predict and understand the theological response of polymer solutions and melts. These models have also been used in conjunction with single molecule polymer experiments. While these have provided insight into the dynamics of polymers in rheological flows, they have also helped to design single molecule manipulation experiments. Promising research in this area includes DNA separation and stretching devices. A typical atomic bond has a length of 10-10m and vibration time scale of 10-14s. A typical experiment in a microfluidic device has lengths of order 10-5m and times of order 102s. It is not possible to capture these larger length and time scales of interest while capturing exactly the behavior at the smaller length and time scales.
(cont.) This necessitates a process of coarse-graining which sacrifices the details at the small scale which are not necessary while retaining the important features that do affect the response at the larger scales. This thesis focuses on the coarse-graining of polymers into a series of beads connected by springs. The function which gives the retractive force in the spring as a function of the extension is called the spring force law. In many new microfluidic applications the previously used spring force laws produce significant errors in the model. We have systematically analyzed the coarse-graining and development of the spring force law to understand why these force laws fail. In particular, we analyzed the force-extension behavior which quantifies how much the polymer extends under application of an external force. We identified the key dimensionless group that governs the response and found that it is important to understand the different constraints under which the polymer is placed. This understanding led to the development of new spring force laws which are accurate coarse-grained models by construction. We also examined the response in other situations such as weak and strong flows.
(cont.) This further illustrated the disadvantages of the previous force laws which were eliminated by using the new force laws. This thesis will have practical impact because the new spring force laws can easily be implemented in current polymer models. This will improve the accuracy of the models and place the models on firmer theoretical footing. Because the spring force law has been developed independently of other coarse-grained interactions, this thesis will also help in determining the best parameters for other interactions because they will not need to compensate for an error in the spring force law. These new spring force laws will help form the framework of coarse-grained models which can help understand a wide range of situations in which the behavior at a small scale affects the large time and length scale behavior.
by Patrick Theodore Underhill.
Ph.D.
50
Zhou, Lifang Ph D. Massachusetts Institute of Technology. "Mathematical modeling and design of novel semi-continuous and continuous crystallizations." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/101476.
Full textAbstract:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemical Engineering, 2014.Cataloged from PDF version of thesis.
Includes bibliographical references.
Crystallization is an important separation technology used for the purification of products during their final stages of manufacturing. Novel semi-continuous and continuous crystallization process designs are receiving increasing attention in pharmaceutical industry due to significant advantages in terms of process, operation and costs. This dissertation aims to develop mathematical models for describing three newly designed crystallization processes (semi-continuous crystallization, layer crystallization, and falling film crystallization) and examining mass and heat transport, crystal growth, and impurity migration. The first study investigates a new process for crystal size distribution (CSD) control that combines antisolvent crystallization in a dual impinging jet crystallizer with cooling crystallization in a mixing tank. This proposed semi-continuous process provides higher degrees of control of the CSD than those obtainable with past crystallizer designs. The proposed approach extends that the supersaturation is time-varying instead of specified at a constant controlled value. This study also examines the potential benefits of additional practical degrees of freedom: control of volume of the mixers, jet flow rates, jet mixing temperatures, antisolvent-solvent flow rate ratios, and supersaturation in the stirred tank. The results support the process design and motivate future experimental implementations. For the second design, a solution layer crystallization process in a concentric annulus is presented that removes the need for filtration. A dynamic model for layer crystallization with and without a recirculation loop is developed in the form of coupled partial differential equations describing the effects of mass transfer, heat transfer, and crystallization kinetics. The model predicts the variation of the temperature, concentration, and dynamic crystal thickness along the pipe length, and the concentration and temperature along the pipe radius. The model predictions are shown to closely track experimental data that were not used in the model's construction, and also compared to an analytical solution that can be used for quickly obtaining rough estimates when there is no recirculation loop. The model can be used to optimize product yield and crystal layer thickness uniformity, with constraints on the supersaturation to avoid bulk nucleation by adjusting cooling temperatures in the core and jacket. The third design is a cyclic process of falling film crystallization that combines cooling and evaporation to improve the yield and purity of host molecules in a solution. A mathematical model is developed to predict the parameters of this process at various operational conditions for separating ibuprofen from an ethanol-water mixture in the presence of impurity, ketoprofen. The distribution coefficients of ibuprofen between crystal phase and solution phase is determined. The numerical results are compared to experimental values to validate the model and the model predicts concentration and crystal layer thickness from different conditions.
by Lifang Zhou.
Ph. D.