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1
Veluswamy, Ganesh Kumar. "Hydrodynamics of industrial scale FCCU stripper." Thesis, Curtin University, 2010. http://hdl.handle.net/20.500.11937/1965.
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Stripper is an important component of a fluid catalytic cracking (FCCU) unit. It strips and recovers the adsorbed/deposited light hydrocarbons on the catalyst particle surface using steam in a counter current flow process. The common flow problems encountered in an FCC stripper unit include channelling, bridging and maldistribution. In this work the hydrodynamics of industrial scale FCC Strippers was studied and investigated using 3D computational fluid dynamics (CFD) simulations and experiments. The CFD and experimental studies showed that internals and inlet configurations play a vital role in determining the hydrodynamics of the Stripper unit.
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Whitcombe, Joshua Matthew, and n/a. "Study of Catalyst Particle Emissions From a Fluidized Catalytic Cracker Unit." Griffith University. School of Environmental Engineering, 2003. http://www4.gu.edu.au:8080/adt-root/public/adt-QGU20031003.152200.
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The control of particle emissions from an oil refinery is often difficult, due to changing operational conditions and the limited range of available treatment options. Excessive particle emissions have often been attributed start up problems with Fluidized Catalytic Cracker Units (FCCU) and little information is available regarding the exact composition and nature of these excessive emissions. Due to the complex nature of a FCCU, it has in the past been difficult to identify and control emissions, without the use of expensive end of pipe technologies. An Australian Oil Refinery, concerned with their catalyst emissions, sponsored this study of FCCU particle emissions. Due to the industrial nature of the project, a holistic approach to the management of emissions was taken, instead of a detailed investigation of a single issue. By looking at the broader range of issues, practical and useful outcomes can be achieved for the refinery. Initially, detailed emissions samplings were conducted to investigate the degree of particle emissions under start up conditions. Stack emissions were collected during a standard start up, and analysed to determine the particle size distribution and metal concentration of the emitted material. Three distinct stages of emissions were discovered, initially a high concentration of larger particles, followed by a peak in the very fine particles and finally a reduction of particle emissions to a more steady or normal operational state. The variation in particle emissions was caused by operational conditions, hardware design and catalyst characteristics. Fluctuations in the gas velocity through the system altered the ability of the cyclones to collect catalyst material. Also, the low bed level allowed air bypass to occur more readily, contributing to the increased emissions levels seen during the initial stage of the start up. Reduced fluidity characteristics of the circulating catalyst also affected the diplegs operations, altering the collection efficiency of the cyclone. During the loading of catalyst into the system, abraded material was quickly lost due to its particle size, contributing to fine particle emissions levels. More importantly, thermal fracturing of catalyst particles occurred when the cold catalyst was fed into the hot regenerator. Catalyst particles split causing the generation of large amounts of fine particle material, which is easily lost from the system. This loading of catalyst directly linked to the period of high concentration of fine particles in the emissions stream. It was found that metals, and in particular iron, calcium and silicon form a thick layer on the outside of the catalyst, with large irregular shaped metal ridges, forming along the surface of the particle. These ridges reduce the fluidity of the catalyst, leading to potential disruptions in the regenerator. In addition to this, the metal rich ridges are preferentially removed via attrition, causing metal rich material to be emitted into the atmosphere. To overcome these high particle emissions rates from the FCCU the refinery should only use calcinated catalyst to reduce the influence of thermal process and particle fracture and generation. Although the calcinated catalyst can fracture when added to the system, it is far less than that obtained with uncalicinated catalyst. To further reduce the risk of particle fracture due to thermal stresses the refinery should consider reducing the temperature gradients between the hot and cold catalyst. Due to the economics involved with the regenerator, possible pre-warming of catalyst before addition into system is the preferred option. This pre-heating of catalyst should also incorporate a controlled attrition stage to help remove the build up of metals on the surface of the particles whilst allowing this material to be collected before it can be released into the atmosphere. The remove of the metal crust will also improve the fluidity of the system and reduce the chance of catalyst blockages occurring. Finally, modelling of the system has shown that control of key parameters such as particle size and gas velocity are essential to the management of air emissions. The refinery should look at adjusting start up procedures to remove fluctuations in these key parameters. Also the refinery should be careful in using correlation found in the literature to predicted operational conditions in the system as these correlations are misleading when used under industrial situations.
3
Whitcombe, Joshua Matthew. "Study of Catalyst Particle Emissions From a Fluidized Catalytic Cracker Unit." Thesis, Griffith University, 2003. http://hdl.handle.net/10072/367301.
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The control of particle emissions from an oil refinery is often difficult, due to changing operational conditions and the limited range of available treatment options. Excessive particle emissions have often been attributed start up problems with Fluidized Catalytic Cracker Units (FCCU) and little information is available regarding the exact composition and nature of these excessive emissions. Due to the complex nature of a FCCU, it has in the past been difficult to identify and control emissions, without the use of expensive end of pipe technologies. An Australian Oil Refinery, concerned with their catalyst emissions, sponsored this study of FCCU particle emissions. Due to the industrial nature of the project, a holistic approach to the management of emissions was taken, instead of a detailed investigation of a single issue. By looking at the broader range of issues, practical and useful outcomes can be achieved for the refinery. Initially, detailed emissions samplings were conducted to investigate the degree of particle emissions under start up conditions. Stack emissions were collected during a standard start up, and analysed to determine the particle size distribution and metal concentration of the emitted material. Three distinct stages of emissions were discovered, initially a high concentration of larger particles, followed by a peak in the very fine particles and finally a reduction of particle emissions to a more steady or normal operational state. The variation in particle emissions was caused by operational conditions, hardware design and catalyst characteristics. Fluctuations in the gas velocity through the system altered the ability of the cyclones to collect catalyst material. Also, the low bed level allowed air bypass to occur more readily, contributing to the increased emissions levels seen during the initial stage of the start up. Reduced fluidity characteristics of the circulating catalyst also affected the diplegs operations, altering the collection efficiency of the cyclone. During the loading of catalyst into the system, abraded material was quickly lost due to its particle size, contributing to fine particle emissions levels. More importantly, thermal fracturing of catalyst particles occurred when the cold catalyst was fed into the hot regenerator. Catalyst particles split causing the generation of large amounts of fine particle material, which is easily lost from the system. This loading of catalyst directly linked to the period of high concentration of fine particles in the emissions stream. It was found that metals, and in particular iron, calcium and silicon form a thick layer on the outside of the catalyst, with large irregular shaped metal ridges, forming along the surface of the particle. These ridges reduce the fluidity of the catalyst, leading to potential disruptions in the regenerator. In addition to this, the metal rich ridges are preferentially removed via attrition, causing metal rich material to be emitted into the atmosphere. To overcome these high particle emissions rates from the FCCU the refinery should only use calcinated catalyst to reduce the influence of thermal process and particle fracture and generation. Although the calcinated catalyst can fracture when added to the system, it is far less than that obtained with uncalicinated catalyst. To further reduce the risk of particle fracture due to thermal stresses the refinery should consider reducing the temperature gradients between the hot and cold catalyst. Due to the economics involved with the regenerator, possible pre-warming of catalyst before addition into system is the preferred option. This pre-heating of catalyst should also incorporate a controlled attrition stage to help remove the build up of metals on the surface of the particles whilst allowing this material to be collected before it can be released into the atmosphere. The remove of the metal crust will also improve the fluidity of the system and reduce the chance of catalyst blockages occurring. Finally, modelling of the system has shown that control of key parameters such as particle size and gas velocity are essential to the management of air emissions. The refinery should look at adjusting start up procedures to remove fluctuations in these key parameters. Also the refinery should be careful in using correlation found in the literature to predicted operational conditions in the system as these correlations are misleading when used under industrial situations.Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Environmental Engineering
Faculty of Environmental Sciences
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Sarginson, James Stanley. "Vanadium interaction with FCC catalysts." Thesis, Open University, 1997. http://oro.open.ac.uk/57712/.
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Fluidised cracking catalysts, which contain a form of zeolite-Y as the main catalytically active component, are widply used commercially for the conversion of crude oil into more profitable product streams. During the cracking reaction, these catalysts are contaminated with vanadium which has a marked effect on the crystallinity of the zeolite-Y component and, as a consequence, activity and selectivity for hydrocarbon processing is degraded. The purpose of this work has been to carry out a detailed investigation, on the laboratory scale, of the effect of vanadium contaminatioil on both commercial and model rare earth ion-exchanged zeolite-Y catalysts. Vanadium contamination was achieved using a standard (Mitchell) method and catalysts were subject to treatment conditions similar to those found in the regenerator part of a fluidised catalytic cracking unit using a specially constructed furnace. Investigations of the solid state chemical reactions between vanadium and rare earth compounds, both in the presence and absence of silica and alumina support materials typical of those found in commercial catalysts, extend the study. Extensive use is made of magic-angle-spinning nuclear magnetic resonance spectroscopy (5 IV and 27AI), X-ray powder diffraction and surface area measurements for sample characterisation. The apparatus for surface area measurements was constructed during the course of the work. It is suggested that the reduction in crystallinity of rare earth ion-exchanged zeolite-Y in the presence of vanadium is associated with the removal of rare earth ions from the cage structure of the zeolite. The extent of this process depends upon the details of the treatment conditions and important factors are identified. The observation of the formation of LaV04 in a range of hydrothermally treated lanthanum ion-exchanged zeolite-Y samples supports the proposed model.
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Lin, Chuang-Chia 1968. "Cyclic deformation of FCC crystals." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/37757.
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Godard, Desmarest Sophie. "The processing, microstructure and creep properties of Pb-free solders for harsh environments." Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:c9f90f13-fcc3-4bb4-8a2c-b980aacb89c9.
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The constitutive mechanical behaviour with a focus on creep of Sn-Pb and various Sn-Ag-Cu based Pb-free solders in the 25-150°C temperature range has been studied using nanoindentation and various new meso-scale tests. All alloys have been studied as bulk wave soldering bars, as-received solder balls and solder joints. Ball Grid Array (BGA) solder joints in a typical electronic configuration were manufactured in-house using both Cu and Pd-Ag metallizations. Microstructural characterisation of all configurations used various types of optical and electron microscopy and showed that the solder pad metallization type played a major role in intermetallic compound (IMC) formation. There were comparatively fine and coarse-grained microstructures in both as-received solder balls and BGA solder joints depending on ball diameter. Nanoindentation creep measurements in the stress range 20-500MPa showed that grain boundary sliding occurred together with dislocation glide and dislocation climb in the low temperature (25-50°C) and high temperature (100-150°C) regimes respectively. Smaller grain sizes (<20µm) encouraged grain boundary sliding that enhanced creep. New elevated temperature mechanical tests were developed using the nanoindentation platform to enable testing of entire solder joints in shear and compression, with stresses in the 1E-2 - 3MPa range, more relevant to in-service conditions than those in nanoindentation. Meso-scale spherical indentation creep behaviour in compression on as-reflowed solder balls showed good agreement with that obtained by conventional nanoindentation. However, when BGAs were tested in shear, the solder microstructure had relatively little influence on the creep response, which was significantly less creep resistant than individual phases in the ball obtained by nanoindentation or the ball itself obtained by meso-scale spherical indentation. In shear, the creep conformed to diffusion controlled behaviour and interfacial microstructure was suggested to now control creep response, with the microstructure of the majority of the solder joint playing only a minor role.
7
Chang, Zhongwen. "Modelling of Dislocation Bias in FCC Materials." Licentiate thesis, KTH, Reaktorfysik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-122407.
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Irradiation induced void swelling is problematic for the application of austenitic steels under high dose irradiation. In this thesis, the swelling is characterized by dislocation bias. The dislocation bias is obtained using the finite element method, accounting for fcc copper and nickel under electron irradiation. The methodology is implemented with the interaction energies between an edge dislocation and point defects. Analytically derived interaction energies, which are based on elasticity theory, are compared with interaction energies obtained from atomistic model using semi-empirical atomic potentials as physics basis. The comparison shows that the description of analytical interaction energies is inaccurate in the dislocation core regions. The bias factor dependence on dislocation density and temperature is presented and discussed. At high temperatures or low dislocation densities, the two approaches tend to converge. However, the dislocation bias based on the interaction energies from the two approaches, reveals larger discrepancy for nickel than for copper. The impact on dislocation bias from the different stacking fault energies of copper and nickel is elaborated. Nickel, which has a larger stacking fault energy, is predicted to have larger swelling rate than copper under the same irradiation conditions.QC 20130530
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Kortunov, Pavel, Sergey Vasenkov, Jörg Kärger, Elía M. Fé, M. Perez, Michael Stöcker, George K. Papadopoulos, et al. "Investigations of molecular diffusion in FCC catalysts." Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-196587.
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Kortunov, Pavel, Sergey Vasenkov, Jörg Kärger, Elía M. Fé, M. Perez, Michael Stöcker, George K. Papadopoulos, et al. "Investigations of molecular diffusion in FCC catalysts." Diffusion fundamentals 2 (2005) 97, S. 1-2, 2005. https://ul.qucosa.de/id/qucosa%3A14435.
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Sengupta, Rohini. "Long-Lived Particles at the FCC-ee." Thesis, Uppsala universitet, Tillämpad kärnfysik, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-444329.
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The presented project explores the current theoretical and experimental tools available within the study group for the Future Circular Collider (FCC) with focus on the electron-positron collider. The aim of the study is to evaluate the current frameworks used for simulation, and investigate the possibility of simulating long-lived particles, that could be dark matter candidates, through them. Pythia cards were run through the framework of Delphes and several different software packages were studied on the journey through the work. It was found that the current framework reconstructs the masses of a Z bosons and Higgs bosons accurately from the ZH signal, which is central for the analysis at the FCC-ee. When the same analysis was applied for the new physics case of a dark matter particle included in the new card for study, a ROOT file was produced indicating that the framework was able to handle the new case. When this card was run through the analysis software however, difficulties arose and a final output could not be achieved. Conclusively, it can be said that the current framework has the possibilities of handling new physics cases but further study is required to be able to run certain software packages on these cases.
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Mallory, Donald Paul. "Co-diffusion of particles in biological systems studied using PIE-FCCS." University of Akron / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=akron1627666937482877.
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Lustig, Steven K. "Microstructural analysis of finite deformation in FCC polycrystals." Thesis, Georgia Institute of Technology, 1995. http://hdl.handle.net/1853/15916.
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Rong, Yu. "FCC regeneration process design for co2 emissions reduction." Thesis, University of Manchester, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.505485.
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Chalapati, Sachin. "Toluene Mediated FCC of LDPE Using Ionic liquids." Thesis, Högskolan i Borås, Institutionen Ingenjörshögskolan, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:hb:diva-17973.
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Polyethylene is one of the most widely used synthetic materials produced by mankind and its accumulation in the biosphere is exceeding at an alarming rate. There are several methods to recycle or remediate the waste polyethene apart from land filling and generation of useful products from the waste is on demand for research and development. Ionic liquids are aggressively replacing several organic compounds due to their robust nature and also have novel properties that allow depolymerization of synthetic materials into simpler short chained paraffins. Initial dissolution of polymer using hot toluene followed by agitated depolymerization using EMIM-Cl (AlCl3) ionic liquid for producing fuel grade high calorie organic molecules might be proven successful. This method uses proton sources like sulphuric acid, hydrochloric acid or waters that aid saturation of organic compounds by hydrogen ion exchange. This could be a novel procedure that aims to produce fuel grade products from waste synthetic polymers like polyethene.Program: Master of Science with a Major in Resource recovery – Industrial biotechnology
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Vieira, William Gonçalves. "FCC : controle preditivo e identificação via redes neurais." [s.n.], 2002. http://repositorio.unicamp.br/jspui/handle/REPOSIP/267590.
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Orientadores: Ana Maria Frattini Fileti, Florival Rodrigues de CarvalhoTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Quimica
Made available in DSpace on 2018-08-03T02:39:01Z (GMT). No. of bitstreams: 1 Vieira_WilliamGoncalves_D.pdf: 7050309 bytes, checksum: c1e288d81c3eebed686e86e3bcc5edda (MD5) Previous issue date: 2002
Resumo: A unidade de Craqueamento Catalítico em Leito Fluido - FCC, modelo Kellogg Orthoflow F., representa um processo de refino de petróleo apresentando característica altamente não linear, possuindo fortes interaçães entre as variáveis de produção, e condições de operação extremamente severas. Essas unidades são constituídas basicamente de duas seções: uma de reação catalítica na qual ocorrem as reações de quebra de cadeia hidrocarbônica e também há formação de coque, desativando o catalisador; e outra seção onde ocorre a regeneração do catalisador desativado. O objetivo dessa unidade é transformar produtos de elevado peso molecu1ar, que apresentam baixo valor agregado, em compostos de elevado valor comercial. As unidades FCC, devido às condições severas de operação, necessitam de um controle rigoroso de determinadas variáveis operacionais. Apesar de existirem instalados controladores avançados baseados em modelos de convolução, fteqüentemente essas unidades são reguladas por meio de controladores PID padrões e também através de controle manual baseado no conhecimento de operadores das refinarias. O presente estudo tem como objetivo desenvolver um controlador preditivo multivariável (Multivariable Predictive Control - MPC) para ser implementado na unidade FCC, utilizando Redes Neurais Artificiais (RNA) como modelo interno do controlador. Inicialmente é previsto realizar a identificação do processo da FCC em RNA, obedecendo a seguinte estratégia: usando um modelo fenomenológico que representa a unidade industrial, e partindo de um estado inicial são aplicados diversos degraus nas variáveis manipuladas analisando as respostas nas variáveis controladas do processo. A partir destas simulações são gerados diversos conjuntos de dados divididos em grupos de treinamento, validação e teste. Diversas redes neurais do tipo multicamada feedforward são então criadas para representar o modelo fenomenológico, sendo selecionada aquela que apresenta melhor desempenho, quando comparada com o modelo. A configuração da RNA escolhida como modelo interno foi 8x15x4 (camadas de entrada, escondida e de saída, respectivamente) apresentando um erro relativo máximo de 1% quando comparado com os resultados do modelo rigoroso. Posteriormente, foi previsto desenvolver um controlador preditivo multivariável usando como modelo interno esta rede selecionada. Este controlador foi implementado dentro da rotina do modelo fenomenológico, sendo então realizados testes para verificar seu desempenho, comparando o resultado com o sistema aberto e também com o controlador DMC (Dynamic Matrix Contro!) existente. Diversos horizontes de predição e controle foram analisados, sendo selecionados aqueles que apresentaram melhor desempenho. Foi introduzido um ruído nos sinais do modelo fenomenológico para testar a robustez do controlador proposto. O controlador apresentou bom desempenho mesmo na presença de ruídos de 1,5%, levando sempre as variáveis controladas para seus valores de referência, o que comprova sua robustez. Baseados nestes resultados, conclui-se que um controlador preditivo multivariável baseado em RNA é perfeitamente capaz de controlar um sistema não linear de porte do FCC, onde elevada interação entre suas variáveis operacionais e fortes restrições estão presentes. Isto nos permite extrapolar que são boas as expectativas para uma futura utilização na unidade industrial, principalmente devido à sua simplicidade, robustez e facilidade de implementação, a despeito da dificuldade de sintonia do controlador
Abstract: The Fluid Cracking Catalytic unit - FCC, Kellogg Orthotlow F. model, represents a very strong nonlinear process, with severe interactions among the process variables, and extremely severe operation conditions. The unit is composed of two sections: one is the catalytic reaction, where the hydrocarbon breaks chain reactions and coke deposition take place becoming the catalyst inactive, and the other where the catalyst regeneration happens. The objective is to transform products derived ITom petroleum, with high molecular weight and low added value, into products with higher profit. Due to the severe operation conditions, rigorous control of some variable is needed. In spite of the existence of advanced control based on a convolution model, in practice, FCC units are ftequently regulated by standard PID controllers, and also through manual control actions based on the knowledge of the refinery operators. The objective of this study is to develop a Multivariable Predictive Control (MPC) to be implemented in the FCC unit, using the Artificial Neural Networks (ANN) as internal model. Initially, the process identification in ANN of the FCC was done by the following strategy: an initial state was fust achieved using numerical simulations based on the phenomenological mo deI. Then, several steps changes were applied to the manipulated variables and the response in the controlled variables were monitored and recorded. From these simulations, several groups of data were generated for training, validation and testing. The Neural Network of multilayer feedforward type were created to represent the phenomenological model, being selected the one that better represents the phenomenological model. The ANN configuration chosen to be the internal model was 8x15x4 (Input x Hidden x Output) architecture, with a maximum relative error below 1 % when comparing the results with the phenomenological model results. Later on, it was developed a multivariable predictive control based on this internal model. This control was implemented inside the routine of the phenomenological model. The performance tests were evaluated comparing the results with the open system and with the Dynamics Matrix Control (DMC). Several prediction and control horizons were analyzed. The ANN control presented good performance even in the presence of noise of 1,5% of intensity, taking back the controlled variables to its setpoints, proving its robustness. Based on these results, a multivariable predictive control based on ANN showed be perfectly able to control a nonlinear system like a FCC unit, where high interactions among process variables, and strong restriction conditions exists. This allows us to have good expectations for a future use in the industrial unit, mainly due to its simplicity, robustness and facility ofuse, in spite ofthe difliculty oftune control
Doutorado
Sistemas de Processos Quimicos e Informatica
Doutor em Engenharia Química
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Swisher, Douglas Lee. "Deformation banding and grain refinement in FCC materials." Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2003. http://library.nps.navy.mil/uhtbin/hyperion-image/03Mar%5FSwisher.pdf.
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Ross, Seamus. "Dress pins from Anglo-Saxon England : their production and typo-chronological development." Thesis, University of Oxford, 1992. http://ora.ox.ac.uk/objects/uuid:3976b772-fccd-41fe-b8c7-f4ae08ac0295.
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This thesis examines the development, production and function of dress pins in Anglo- Saxon England. It proposes a dated typology for the mid-5th to the mid-llth century and notes the implications of this for discussions of contact and cultural interaction between England and other parts of Europe. Chapter 1 defines the parameters of the study, and describes the data that was assembled on Anglo-Saxon pins. An evaluation of the previous work on pins from Northern Europe (Chapter 2) is followed by an investigation in Chapter 3 of the methods and process of typological analysis. After arguing that one of the most important (and neglected) aspects of typological research is 'the process of study1 the chapter provides terminological definitions for the components of pins. Chapter 4 examines the problems, principal methods and developments in pin production and discusses how changes in method reflected changes both in fashion and metalworking techniques. Building on this, Chapter 5 defines the groups of pins that have been found on sites of the Anglo-Saxon period, including: (1) definition of the types and sub-types; (2) determination of their date ranges; (3) description of their distribution; and (4) suggestions about the origin of each type. In Chapter 6 the types are put into chronological order, to demonstrate which types existed simultaneously and how pins developed over time. The function of pins is considered in Chapter 7 and several tentative hypotheses are put forward. The final chapter draws a number of conclusions from the study including: (1) Anglo-Saxon pins display a great deal of insularity during all periods, but particularly in the 8th and 9th centuries; (2) while regionalism may have been a feature of 6th century pins, it ceases to be important by the 8th century when many finds from middle Saxon trading sites seem consistently to be the same types, suggesting that in addition to trade between England and the Continent and Scandinavia it is time to evaluate the micro-economic and information exchange networks in Anglo- Saxon England; (3) lastly it notes the problem of dissemination of artefactual analyses and the difficulties to be encountered in using typologies and it puts forward a preliminary proposal for the use of expert systems (computer programs that simulate human performance in specialist task areas) as a tool to distribute this information. An example of a knowledge base that might be used to disseminate the typology presented here, The Anglo-Saxon Pin Identification Assistant, is to be found in Appendix 2, as are several sample identification sessions.
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Kelly, Luke. "A stochastic Dollo model for lateral transfer." Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:6884785c-fccc-4044-b5b2-7a8b7015b2a5.
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Lateral transfer, a process whereby species exchange evolutionary traits through non-ancestral relationships, is a frequent source of model misspecification in phylogenetic inference. Lateral transfer obscures the phylogenetic signal in the data - the signal of the taxa ancestry - as the histories of affected traits are mosaics of the species phylogeny and may conflict with the underlying phylogeny. We control for the effect of lateral transfer in a Stochastic Dollo model and a Bayesian setting. We infer rooted phylogenetic trees. Our likelihood is highly intractable as its parameters are given by the solution of a sequence of systems of differential equations which represent the expected evolution of traits along a tree and grow exponentially in dimension with the number of taxa under consideration. We construct an accurate parameter approximation framework, and from this we derive an efficient exact-approximate inference scheme. We illustrate our method on data sets of lexical traits in Eastern Polynesian and Indo-European languages and obtain improved fits over the corresponding model without lateral transfer.
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Raeside, Alexander. "The effect of low temperature on alternative splicing in barley." Thesis, University of Dundee, 2016. https://discovery.dundee.ac.uk/en/studentTheses/f29963da-fcc3-4b73-82aa-d882b8382923.
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Major changes in expression occur in Arabidopsis in response to cold. It is now clear that genome-wide changes in alternative splicing (AS) also occur in Arabidopsis during the cold-response and many of the genes which undergo cold-induced AS have been linked to roles in either the regulation of the cold-response or regulation of AS. Mutations in splicing factors in Arabidopsis, such as STA1 and SRL1 have been shown to lead to both changes in AS and changes in cold-sensitivity/tolerance, suggesting an important the role for AS in regulating the cold-response. Less is known about the effect of cold on AS in barley or how AS impacts the barley cold-response. There are only a few studied examples of cold-induced AS changes in barley genes, although this is rapidly changing due to both the publication of the barley genome and next generation sequencing of the transcriptome. To investigate AS in the barley cold response, 11 barley genes with cold-induced AS changes were identified and the AS change was analyzed in detail. The barley genes FRY2 and SUA change AS after 30 minutes exposure to cold and are both genes have been linked to roles in regulating AS, indicating a complex role for AS in the earliest stages in the cold-response. The Serine Arginine (SR)-Rich protein genes have been shown to change AS and affect AS under stress conditions in Arabidopsis, rice and other plant species but little is known about the SR protein genes in barley or how the genes change splicing/expression in response to cold. The 16 members of the barley SR protein gene family were identified and analyzed for cold-induced expression changes using available microarray and RNA-Seq data. The HvRS41 gene showed a >2 fold increase in expression after 3h exposure to 6°C in a cold-based microarray experiment. A cold-based microarray experiment in Arabidopsis showed a similar cold-induced expression of the AtRS40 gene, a RS-type SR protein gene with high homology to HvRS41. The cold-induced expression of HvRS41 and AtRS40 indicate a role for the RS-type SR protein genes in the cold response. The RS-type SR proteins form a splicing complex with FRY2 which could potentially be regulated through both AS and expression change during the cold-response. The Barley SR Proteins were dived into six sub-groups previously established for plant SR protein genes. Five out of the six sub-groups of the barley SR protein genes contained AS which could be validated through RT-PCR based methods. The SR-type SR protein genes contained was shown to contain three genes (HvSR34, HvSR30a and HvSR34) within barley. All 3 barley SR-type protein genes showed AS change in response to low temperatures, indicating a role for the barley SR-type SR protein genes in regulating AS during the cold-response. The role for SR-type SR protein genes in regulating AS was tested through a creation of a barley transgenic line over-expressing gene the HvSR34. The HvSR34 overexpression lines are in the process of being tested for changes in AS and cold tolerance.
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Huang, Leilei. "Fabrication and characterisation of ultrafast direct laser written waveguides." Thesis, University of Oxford, 2015. https://ora.ox.ac.uk/objects/uuid:7e40e1ee-fcc3-4797-953d-8be5c7af1334.
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A novel ultrafast direct laser writing (DLW) system using adaptive optics is proposed and demonstrated. This system has the potential to generate high-quality three-dimensional (3D) optical waveguides and components. The experimental setup and procedures for the DLW process are studied, after which various optical waveguides are fabricated in different transparent materials. The resulting waveguides are characterised by the measurement of the near-field laser coupling profiles in combination with optical microscopy techniques. Quantum random number generation (QRNG) and the potential application of the DLW technique in quantum information is also discussed. To completely understand the fabrication procedures for the DLW system, the experimental equipment and effects of different fabrication parameters are studied and analysed. With the use of a liquid-crystal spatial light modulator (SLM) in the DLW system, dynamic control of phase modulation can be provided to correct aberrations adaptively. An SLM can also make the cross-sectional profile of the written waveguides more circular and facilitate the fabrication of more complex 3D structures. Experiments reveal that the shape of the focal spot can be improved dramatically with adaptive optics, resulting in higher-quality optical waveguides. The refractive-index information of the written waveguides and their optical properties are measured using the propagation-mode near-field method (PMNFM). Simulation results and experimental measurements of a commercial single-mode fiber and a waveguide sample are demonstrated and compared. Quantitative phase measurement is also applied via the transport of intensity equation (TIE) to monitor the refractive-index change during fabrication. The propagation losses of the waveguides are measured and discussed. Different optical waveguides are fabricated using DLW in fused silica, potassium dihydrogen phosphate (KDP), and lithium niobate (LiNbO3) crystals. Different materials have different characteristics and properties, requiring different fabrication parameters and resulting in waveguides exhibiting different properties. Waveguides at various depths are demonstrated both with and without effects of adaptive optics. Experimental results indicate great improvements in the quality of the written waveguides after aberration correction. With an understanding of the optical properties of the straight waveguides using the characterisation methods, modelling and fabrication of bend waveguides and y-splitters are presented and studied. A high-speed QRNG system is also demonstrated in this thesis, with potential implementation using the DLW technique for a more compact and stable system. Finally, the possibility of the DLW fabrication of complex 3D optical components and their applications are discussed for future work.
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Jones, Christina Jane. "The utility of social cognition models in explaining adherence to self-care behaviours amongst adolescents and young adults with food allergy." Thesis, University of Brighton, 2012. https://research.brighton.ac.uk/en/studentTheses/970af16a-fcc4-4175-8827-e00a24e4bfb9.
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Anaphylaxis can be triggered by a number of allergens the most common being food, medications, insect venom and latex. Due to the sudden onset and potentially fatal nature of anaphylaxis, successful management requires prompt and appropriate use of emergency medication. A failure to follow recommended medical advice remains a barrier to the control of many medical conditions, and food allergy and anaphylaxis are no exception. Studies have shown that use of emergency medication for anaphylaxis, by both health professionals and patients, is suboptimal. Identification of the nature and extent of health professionals' and patients' poor management of anaphylaxis enabled better understanding of the factors influential in the successful management of anaphylaxis, and guided the application of two Social Cognition Models in this area. This thesis explores the Health Belief Model (HBM) and the Common Sense Model (CSM) to determine if either can explain adherence to self-care behaviours (SCBs) amongst adolescents and young adults with food allergy. A systematic review was conducted of peer reviewed articles to identify health professionals' and patients' poor management of anaphylaxis. Based on these findings, two further systematic reviews were undertaken investigating the effectiveness of HBM and CS M-interventions in improving adherence. Original data was collected in a cross-sectional study of food allergic participants aged 13- 19 years with a prescription of auto-injectable epinephrine recruited from hospital allergy clinics. A postal self-completion questionnaire explored their health beliefs and illness perceptions derived from the models. Clinical and demographic information was collected based on findings from the first systematic review. The systematic review of anaphylaxis management found that poor management was frequently attributed to lack of knowledge and practical ability. However, adherence to preventive SCBs such as allergen avoidance and carrying emergency medication were rarely measured. The HBM and the CSM were found to have been successfully applied to eight and two adherence-related interventions respectively. In the population of 188 allergic adolescents investigated in this study, the HBM, specifically the constructs perceived severity, benefits and barriers, explained the greatest proportion of variance in adherence to SCBs. Gender and having an anaphylaxis management plan were also found to explain variance in adherence behaviours (all ps<.OS). The application and investigation of psychological model constructs proved useful in this population of food allergic individuals and identified targets for future interventions. The results show a strong beneficial link between adherence and possessing a management plan and provide evidence for promoting their use in food allergic individuals. Interventions designed to elicit personal barriers to adherence and address perceptions of severity surrounding food allergy may be more effective than a focus on knowledge and practical ability in improving adherence to SCBs.
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Schreiner, Jennifer Ann. "Women working for their freedom : FCWU and AFCWU and the women question." Master's thesis, University of Cape Town, 1987. http://hdl.handle.net/11427/15841.
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Bibliography: leaves 192-203.This thesis has two parallel processes of investigation. Firstly, it is an investigation of the extent to which a trade union can successfully participate in the struggle for working women's rights at work and concerning motherhood and childcare, and in the struggle for the realisation of the political aspirations of women workers within a capitalist society. Secondly, the thesis examines the ideological position of the Food and Canning Workers Union in order to refine the theoretical understanding of the woman question in South Africa. Research methods have relied on use of archival documents, both published and unpublished; oral history; secondary sources on the union being studied and on South African society; as well as classical and contemporary texts on the theory of women's oppression and its interconnection with exploitation. The research has been hindered by the historical repression meted out by the South African state, which has forced people into exile, banned written sources, and removed archival material from South Africa. The recent repression has severely hampered the extent of interviewing and discussion, as well as made the process of research and writing of the thesis a difficult undertaking. The union's organising strategy is examined in terms of the following three issues: 1. Because of their dual responsibilities as worker and mother, and because of their relatively unorganised position, women workers are ultra-exploited. What role can a union play in fighting against the various aspects of this? The specific aspects of ultra-exploitation found in the food and canning industry are temporary employment and periodic unemployment; child labour; piece-work; excessive overtime. 2. The inclusion of women into wage labour faces them with a task of combining motherhood and wage labour. How can a union win demands to assist these women workers with this task? The two ways in which the union confronted this question were maternity rights and childcare facilities. 3. The assault on working class in terms of the right to work, the right to live where one chooses, the right to family life, and the right to a decent standard of living was a burden to working class women in particular.
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Sinclair, Chad. "Co-deformation of a two-phase FCC/BCC material /." *McMaster only, 2001.
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Spearot, Douglas Edward. "Atomistic Calculations of Nanoscale Interface Behavior in FCC Metals." Diss., Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/7230.
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This dissertation focuses on the behavior of homogeneous FCC metallic interfaces on the nanoscale. Specifically, atomistic calculations (molecular statics and molecular dynamics) with embedded-atom method potentials are used to study the fundamental failure processes that occur at a bicrystal interface in Cu and Al as a result of a mechanical deformation. There are four primary objectives to this dissertation. First, molecular statics calculations are used to determine the most appropriate (minimum energy) structure of homogeneous bicrystal interfaces in Cu and Al. Interface structures and energies are reported in this work, with comparison to both theoretical and experimental characterizations of interface configuration. Second, molecular dynamics simulations are performed to provide a characterization of atomic scale inelastic behavior, including both dislocation and void nucleation activities which lead to interfacial failure. Specifically, two types of interfaces are highlighted in this work: a mirror symmetric interface in aluminum and an asymmetrically dissociated interface in copper. Distorted interface structures (after the dislocation nucleation event) are discussed in terms of partial dislocations or disclinations. Third, molecular dynamics simulations are used to investigate potential relationships between interface structure and interface properties or morphology. The orientation of the primary slip planes with respect to the loading direction and the porosity within the interface region are found to be critical factors in defining the strength of the bicrystal interface, for example. Finally, results of the atomistic calculations are utilized to motivate improved forms for continuum interface separation potentials, ultimately increasing the applicability of these relationships to include cohesive failure in ductile crystalline materials.
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Leonel, Raquel Folmann. "Estudo dos mecanismos de reativação de catalisadores FCC eletrorremediados." reponame:Repositório Institucional da UFPR, 2016. http://hdl.handle.net/1884/45441.
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Orientador: Prof. Dr. Haroldo de Araújo PonteCoorientador: Profª. Drª. Maria José J. de Santana Ponte
Tese (doutorado) - Universidade Federal do Paraná, Setor de Tecnologia, Programa de Pós-Graduação em Engenharia e Ciência dos Materiais - PIPE. Defesa: Curitiba, 26/07/2016
Inclui referências : f. 87-93
Área de concentração: Engenharia e ciência de materiais
Resumo: A crescente geração de catalisador desativado nas unidades de Craqueamento Catalitico Fluidizado e sua elevada importância como insumo nas refinarias brasileiras motiva estudos para seu reaproveitamento. Apos o uso e desativação dos catalisadores, estes sao destinados a aterros Classe I, devido a sua periculosidade, por conterem metais tóxicos e acidez elevada, ou ao coprocessamento em cimenteiras. A eletrorremediação de catalisadores, em desenvolvimento nos laboratorios do GEA na UFPR, tem apresentado melhorias na área superficial e na remoção de contaminantes metálicos dos catalisadores desativados. Assim o objetivo desse trabalho e estudar os mecanismos que recuperam a capacidade catalitica do catalisador apos o processo de eletrorremediacao. Através da eletrorremediacao o catalisador tratado poderia retornar para a refinaria de origem ou para uma refinaria com um corte diferente de petróleo; também os elementos metálicos removidos do catalisador poderiam ser reaproveitados trazendo ganhos econômicos. O tratamento eletroquímico pode diminuir a periculosidade do resíduo e/ou aumentar o ciclo de vida do catalisador; diminuindo o impacto ambiental do setor. Os resultados indicam que a remedição eletrocinetica promoveu uma reorganização nos componentes do catalisador, melhorando sua cristalinidade e diminuindo os contaminantes presentes, especialmente nas remediações acidas. Os espectros de RMN 27Al mostraram que as remediações acidas (com acido sulfúrico ou acido cítrico) lixiviaram seletivamente espécies de alumínio tetraédricos e penta-coordenados. A remediacao com citrato de sódio manteve a proporção entre o alumínio nas posições tetraedrais/octaedrais, removendo apenas espécies de alumínio penta-coordenadas (típicas de um ambiente químico altamente distorcido). A avaliação da acidez através do Infravermelho com piridina adsorvida mostrou a geração de sítios ácidos de Bronsted (especialmente nas remediacoes acidas) e a variação na forca dos sítios de Bronsted e Lewis, que foi inversamente proporcional a temperatura de dessorcao. A remoção de metais (vanádio e lantânio) dos catalisadores foi estimada por FRX e EDS e foi proporcional ao potencial utilizado e a concentração e forca do eletrólito empregado. As analises por EPR indicaram que o vanádio encontra-se em estado de oxidação +4 e simetria C4v, possivelmente em coordenação octaédrica com oxigênios da matriz ou da zeolita, ocupando posições na estrutura do catalisador. Os testes de conversão mostraram elevada atividade e baixa seletividade para o catalisador remediado com acido sulfúrico, enquanto o remediado com citrato de sódio gerou mais gasolina e menos coque em relação ao desativado de partida. A recuperação parcial da atividade catalítica dos catalisadores apos a eletrorremediação foi devido ao aumento da área superficial e remoção de contaminantes, que permitiram uma melhor acessibilidade aos sítios ácidos disponíveis para catalise. Palavras-chave: Remediacao eletrocinetica. Catalisador desativado de FCC. Ácidos de Bronsted. Ácidos de Lewis.
Abstract: The rising generation of deactivated catalyst in Fluidized Catalytic Cracking units and its high importance in Brazilian refineries motivates studies for its reuse. After use and deactivation of the catalysts, these are intended to Class I landfills due to its dangerousness, their toxic metals and high acidity, or yet coprocessing in cement factories with some restrictions. The electroremediation technique in development at the GEA laboratories at UFPR, has shown improvements in surface area and in the removal of metallic contaminants from spent catalysts. So the aim of this work is to study the mechanisms that recover the catalytic ability of the catalyst after electroremediation process. Through electroremediation the treated catalyst might return to the original refinery or to a refinery with a different oil cut; the metallic elements removed from the catalyst could also be reused bringing economic gains. The electrochemical treatment can reduce the hazard of the waste and / or increase the life cycle of the catalyst; reducing the environmental impact of the sector. The results indicated that the electrokinetic remediation promoted a reorganization of the catalyst components, improving crystallinity and reducing contaminants, especially in acidic solutions. The 27Al NMR spectra showed that the acid remediation (sulfuric acid or citric acid) selectively leached tetrahedral and penta-coordinated aluminum species. The remediation with sodium citrate kept the ratio of aluminum in tetrahedral / octahedral positions, removing only penta-coordinated aluminum species (typical of a highly distorted chemical environment). The evaluation of acidity by pyridine adsorbed Infrared showed the generation of Bronsted acid sites (especially in the acid remediation), and the variation in the strength of Bronsted and Lewis sites, which was inversely proportional to the desorption temperature. The removal of metals (vanadium and lanthanum) of the catalyst was estimated by XRF and EDS and was proportional to the electric potential and the concentration and the strength of the electrolyte used. The EPR analyzes indicated that the vanadium is in oxidation state +4 and C4V symmetry, possibly in octahedral coordination with oxygen atoms of the matrix or zeolite, occupying positions in the catalyst structure. Conversion tests showed high activity and low selectivity for the catalyst remedied with sulfuric acid, while the remedied with sodium citrate produced more gasoline and less coke in relation to the starting deactivated. The partial recovery of the catalytic activity of the catalysts after electrorremediation was due to increased surface area and removal of contaminants, which allowed easier access to the acid sites available for catalysis. Keywords: Electrokinetic remediation. FCC deactivated catalyst. Bronsted and Lewis acids.
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Jennings, G. "Ultra-violet photoelectron spectroscopy of BCC- and FCC- iron." Thesis, University of Cambridge, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.306636.
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Bacroix, Brigitte. "Prediction of high temperature deformation textures in FCC metals." Thesis, McGill University, 1986. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=74036.
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Nazarov, Andrei V., Alexander A. Mikheev, Irina V. Valikova, Aung Moe, and Alexander G. Zaluzhnyi. "Kinetic of void growth in fcc and bcc metals." Universitätsbibliothek Leipzig, 2016. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-193483.
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Qiu, Yishan. "Finite element simulation of plastic deformation of FCC polycrystals." Thèse, Université de Sherbrooke, 1995. http://savoirs.usherbrooke.ca/handle/11143/1648.
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A finite element formulation based on crystal plasticity constitutive models has been developed for metal forming modelling. This formulation can be applied to nonhomogeneous boundary-value problems of polycrystal metals under large deformation which are characterized by deformation-induced anisotropy. An important feature of this model is its capability simulate the evolution of crystallographic texture and estimate its influences on the material behaviour during the deformation processes of FCC metals deforming by crystallographic slip. Using the developed finite element code, uniaxial behaviours of aluminum polycrystals under uniform deformation have been studied. The influence of the slip-rate sensitivity, latent hardening and the imposed strain rate on the constitutive responses have been investigated. The results have revealed that microstructure and microscopic properties play important roles on the stress-strain responses, as well as on texture evolution. Tensile instability in a round bar, as a typical strain localization mode, has been analysed with the concern on the influences of various microscopic and macroscopic parameters on development of instability. The main features of the overall responses and the texture evolution have been nicely captured by our analyses. The formability of FCC polycrystalline metals has been simulated numerically by the finite element analysis. In particular, the influences of microstructure and texture on the forming limit diagram are assessed. Critical strains for localized necking failures in thin sheets are determined for a variety of deformation paths. Various microstructural effects considered, which include slip-system hardening, material strain-rate sensitivity, initial texture, as well as the evolution of texture and microstructural hardening. Finally, the macro and microscopic aspects of large strain torsion of both fixed-end and free-end solid bars have been analysed using the polycrystal deformation model and a specific finite element mesh. Again, the effects of microscopic parameters are assessed. The predicted overall responses and textures are in reasonably qualitative agreement with experiments. Overall, the good predictive capabilities of the developed finite element formulation for simulating the stress-strain responses and the evolution of texture under both homogeneous and nonhomogeneous deformation conditions are demonstrated by comparing numerical simulations against experimental measurements and the predictions using other models in various deformation modes. The crystal constitutive model has been implemented as a user subroutine in the commerical finite element code ABAQUS (1995). A description of the implementation is given in this thesis.
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Ribeiro, Pleycienne Trajano. "Modelagem e controle de unidades de craqueamento catalitico - FCC." [s.n.], 2007. http://repositorio.unicamp.br/jspui/handle/REPOSIP/266266.
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Orientador: Rubens Maciel FilhoDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Quimica
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Resumo: Por representar um importante processo de conversão da indústria petroquímica, o craqueamento catalítico é um dos processos de conversão mais estudados. Nele, moléculas de alto peso molecular são quebradas em moléculas com menor peso molecular, obtendo-se assim produtos economicamente mais desejáveis. Os estudos do processo, de sua modelagem matemática e dos seus sistemas de controle, podem garantir o conhecimento necessário para alcançar condições operacionais ótimas que levem à máxima conversão da carga. Neste contexto, este trabalho teve como objetivos: a pesquisa e utilização de uma modelagem matemática para o conversor FCC (Fluid Catalytic Cracking); o estudo do processo sob influência de um controlador PID clássico, muito utilizado em refinarias; a estruturação de uma rede neural artificial (RNA) e o seu posterior uso como modelo interno de um controlador avançado tipo preditivo desenvolvido a partir dos estudos feitos no processo de craqueamento catalítico. Em paralelo, foi cirada uma ferramenta de simulação que possibilitou o meio mais amigável e prático para realização de todas as simulações necessárias para o desenvolvimento do presente trabalho. O FCCGUI (Fluid Catalytic Cracking Graphical User Interface), nome dado ao simulador, proporciona a escolha de parâmetros de simulação, diferentes estruturas de controle (PID, DMC e MPC - baseado em redes neurais), a visualização de diferentes variáveis manipuladas, controladas e sinais de válvulas e facilidades para perturbar o sistema. Através das simulações foi possível acompanhar o comportamento das variáveis de processo em diferentes condições testadas, realizar a estruturação da rede neural e obter as respostas das variáveis controladas para os dois tipos de controladores estudados. Os resultados obtidos foram bastante satisfatórios, visto que a modelagem matemática escolhida representa bem o sistema e o controlador MPC-Neural desenvolvido se mostrou eficiente, por conseguir manter o processo estável e próximo ao set point, mesmo após a aplicação de perturbações no processo
Abstract: Catalytic cracking is one of the most studied conversion processes due its importance in the petrochemical industry. In this process high weight molecules are broken into lighter ones, yielding more economically valuable products. The study about the process, its mathematical modeling, and its control systems may guarantee the necessary knowledge needed to reach optimal operational conditions which lead to maximum load conversion. In this context, the present work thesis has as main objectives the research and use of a mathematical modeling for a FCC (Fluid Catalytic Cracking) conversion unit, the study of the system under PID control loop widely used in refineries, structuring of an artificial neural network (ANN) with its use as an internal model of a predictive control system developed for catalytic cracking. Parallel to this, it was developed a computational tool which in a friendly and practical way made possible to carry out simulations needed to accomplish this work. FCCGUI (Fluid Catalytic Cracking Graphical User Interface), name given to this simulator, allows to choose simulation parameters, different control systems (PID, DMC, and MPC-ANN Based), graphical visualization of many different variables, such as manipulated and controlled variables plus valve signals, also it allows for and easy means for disturbing the system while the simulation continues. Through the simulations it was possible to follow the behavior of many process variables under different tested operational conditions, to structure the neural network, and to obtain controlled variables responses for both types of control systems studied. The obtained results were quite satisfactory since the chosen mathematical modeling represents well the system and the developed MPC-ANN controller showed to be efficient to maintain the process stable and close to the set points even after the introduction of disturbances in the process. Taking all these into account, compared to PID controller, MPC-ANN showed to be less oscillatory and to be more effective
Mestrado
Desenvolvimento de Processos Químicos
Mestre em Engenharia Química
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Nazarov, Andrei V., Alexander A. Mikheev, Irina V. Valikova, Aung Moe, and Alexander G. Zaluzhnyi. "Kinetic of void growth in fcc and bcc metals." Diffusion fundamentals 6 (2007) 28, S. 1-2, 2007. https://ul.qucosa.de/id/qucosa%3A14203.
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Yellakara, Ranga Nikhil. "Computational Study of Dislocation Based Mechanisms in FCC Materials." Thesis, University of North Texas, 2014. https://digital.library.unt.edu/ark:/67531/metadc699921/.
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Understanding the relationships between microstructures and properties of materials is a key to developing new materials with more suitable qualities or employing the appropriate materials in special uses. In the present world of material research, the main focus is on microstructural control to cost-effectively enhance properties and meet performance specifications. This present work is directed towards improving the fundamental understanding of the microscale deformation mechanisms and mechanical behavior of metallic alloys, particularly focusing on face centered cubic (FCC) structured metals through a unique computational methodology called three-dimensional dislocation dynamics (3D-DD). In these simulations, the equations of motion for dislocations are mathematically solved to determine the evolution and interaction of dislocations. Microstructure details and stress-strain curves are a direct observation in the simulation and can be used to validate experimental results. The effect of initial dislocation microstructure on the yield strength has been studied. It has been shown that dislocation density based crystal plasticity formulations only work when dislocation densities/numbers are sufficiently large so that a statistically accurate description of the microstructure can be obtainable. The evolution of the flow stress for grain sizes ranging from 0.5 to 10 µm under uniaxial tension was simulated using an improvised model by integrating dislocation pile-up mechanism at grain boundaries has been performed. This study showed that for a same initial dislocation density, the Hall–Petch relationship holds well at small grain sizes (0.5–2 µm), beyond which the yield strength remains constant as the grain size increases.
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Lea, Lewis John. "Structural evolution in the dynamic plasticity of FCC metals." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/273897.
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Above true strain rates of $10^4$ s$^{-1}$ FCC metals exhibit a rapid increase in strength. Understanding of the physical mechanisms behind this strength transition is hindered by the number and interdependence of candidate mechanisms. Broadly, contributions to strength can be split into `instantaneous' effects and the more permanent `structural' ones. In this thesis a series of experiments are presented which are designed to separate the two types of contribution. Chapter 2 outlines the basics of dislocation plasticity, based on the seminal works of Taylor and Orowan. It then progresses on to discuss recent experimental and theoretical work on the understanding of slip as avalanche behaviour. Chapter 3 summarises traditional modelling approaches for instantaneous strength contributions which are routinely applied below $10^4$ s$^{-1}$. It then continues on to outline a number of different approaches which have been adopted to attempt to explain and model the strength transition. Chapter 4 outlines the methods used in the earliest stages of the study: Instron and split Hopkinson pressure bar methods. Both methods are well established, and cover the majority of the range of rates under study. Emphasis is made on minimising experimental sources of error, and subsequently accounting for those which are unavoidable. Finally, the specimen material is introduced and is shown to be fit for purpose. Chapter 5 presents a set of mechanical tests of specimens at strain rates between $10^4-10^5$~s$^{-1}$. The softening of the specimens with increased temperature is observed to increase with strain rate, both in absolute terms and when normalised to the 300 K measurement for each strain rate. The observations are most easily explained if the strength transition is due to an increase in early stage work hardening, however, some anomalous behaviours remain. Chapter 6 introduces a new experimental technique; direct impact Hopkinson pressure bars, required to perform experiments shown to be necessary by the results of Chapter 5. Photon Doppler velocimetry is applied to the projectiles used in experiments, removing one of the most significant flaws of the technique, and creating a more confident basis with which to perform further experimental work. Chapter 7 presents a series of `jump tests' at ambient temperatures. Specimens are deformed at strain rates ranging from $10^{-2}$ to $10^5$~s$^{-1}$ to a fixed strain of 0.1, then reloaded to yield at a strain rate of $10^{-1}$. The yield point at reload is shown to have the same rapid upturn as seen when the specimens were deforming at high rates, providing strong evidence that the increase in strength is due to changes in the underlying dislocation structure, rather than a dynamic effect, as it remains even when the high strain rate is removed. Chapter 8 continues on from the conclusions of Chapter 7. Jump tests are expanded to a variety of temperatures and strains, to provide a more complete characterisation of metal behaviour. No dramatic change in the saturation of work hardening is observed to coincide with the increase in early stage work hardening. Chapter 9 discusses discrepancies between contemporary high rate models and recent developments in the understanding of plasticity being an avalanche process. Potential consequences of incorporating avalanche plasticity into high rate models are explored. Particular attention is paid to Brown's observation that based on quasi static observations of avalanche behaviour, the formation of dislocation avalanches will begin to fail at strain rates of approximately $10^4$ s$^{-1}$. Consequences of the progressive breakdown of avalanche behaviour are discussed with respect to the experimental observations presented in earlier chapters. In Chapter 10, we will discuss the key conclusions of the work. Finally, a number of avenues are proposed for building upon the current work both theoretically and experimentally.
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Morales, Soler Mauricio Enrique. "Atomic scale study of mechanical spectroscopy in FCC metals." Tesis, Universidad de Chile, 2016. http://repositorio.uchile.cl/handle/2250/143495.
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Magíster en Ciencias, Mención FísicaLa fricción interna corresponde a la capacidad de los materiales de disipar la energía de ondas de sonido. Esta capacidad depende del tipo de material así como del tipo y cantidad de defectos que contenga. Durante muchos años se ha utilizado la espectroscopía mecánica para obtener información del material a través de distintos experimentos, midiendo por ejemplo la fricción interna de un material específico. A pesar de la capacidad para medir fricción interna, hasta ahora es difícil conocer con precisión cuales son los mecanismos microscópicos que dan origen a la disipación de energía al interior del material. De particular interés es un pico en la curva de disipación interna versus temperatura llamado pico de Bordoni. La evidencia sugiere que la generación de este pico se debe a propiedades de las dislocaciones. Modelos teóricos que usan mecánica del continuo permiten una descripción cualitativa, pero no cuantitativa, del efecto. Hasta ahora se ha estudiado el pico de Bordoni desde el punto de vista experimental y desde la mecánica del contínuo. En este trabajo se propone estudiar este efecto desde las simulaciones atomísticas a través de dinámica molecular. Para ello se generó una muestra de cobre de 892800 átomos con dos dislocaciones ancladas y se generaron ondas de corte en el material. Se midió la tensión generada en la muestra y se encontraron las curvas de tensión-deformación. Luego se estudió la disipación de energía generada por la interacción de las ondas con las dislocaciones a través de una posible histéresis en las curvas de tensión-deformación. Estas simulaciones se realizaron a las temperaturas de 0, 50, 100, 150, 200 y 250 K, con períodos de 125 ps y 38 ps y un máximo de deformación de 0.0008 y 0.008. Para estimar el orden de magnitud esperado para la respuesta del sistema se usó un modelo de cuerda sobreamortiguada, lo que también permitió estimar el período de forzamiento para el cual las pérdidas deberían ser máximas. Todo esto llevó a una estimación del cuociente entre energía disipada por ciclo y energía acumulada máxima del orden de 10^{-4} lo cual se ajusta a los resultados experimentales. Para estimar el valor de los parámetros que aparecen en el modelo analítico se realizaron simulaciones con las dislocaciones desancladas. Dentro de la precisión numérica utilizada, no se encontró histéresis. Se deduce que la barrera de Peierls es muy pequeña para permitir detección de la histéresis. Se establece una cota para la precisión en las mediciones para cuantificar la fricción interna en el futuro. Posibles direcciones de trabajo futuro incluyen la disminución de las fluctuaciones en las mediciones de la tensión, lo que se podría lograr con un mayor número de ciclos generados en las ondas de corte y promediando sobre muchas realizaciones. Otra opción es realizar las simulaciones en otros materiales, con mayores coeficientes de fricción, para aumentar la energía disipada.
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Aleknevičius, Marius. "The influence of oil cracking catalyst waste on the properties of refractory castables." Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2011. http://vddb.laba.lt/obj/LT-eLABa-0001:E.02~2010~D_20110120_134405-85598.
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Fluidized bed catalytic cracking catalyst waste is a zeolite material. Its unique properties are underused in cementitious materials production technology. Various additives, modifiers used in refractory castables are very expensive, so the use of catalyst waste as a modifying additive of castable properties has not only an ecological (waste recycling) but also an economical basis. Medium cement refractory castable was developed using 70 % and 40 % of aluminium oxide containing aluminate cement and catalyst waste additive, respectively 2,5 % and 5,0 %. The work also reveals an efficient effect of catalyst waste on alumina cement hydration, structure formation during cement solidification and after treatment at high temperature.Naftos krekinge naudotas katalizatorius yra ceolitinė medžiaga, kurios unikalios savybės mažai išnaudojamos cementinių medžiagų gamybos technologijoje. Ugniai atspariuose betonuose naudojami įvairūs priedai-modifikatoriai yra labai brangūs, todėl naudoto katalizatoriaus panaudojimas, kaip modifikuojančio betono savybes priedo, turi ne tik ekologinį (atliekų utilizavimas) bet ir ekonominį pagrindą. Vykdant šį darbą sukurti vidutinio cemento kiekio ugniai atsparūs šamotbetoniai su 70 % ir 40 % aliuminio oksido turinčiais aliuminatiniais cementais ir naudoto katalizatoriaus priedu atitinkamai 2,5 % ir 5,0 %. Darbe taip pat atskleistas efektyvus katalizatoriaus poveikis aliuminatinio cemento hidratacijai, cemento akmens struktūros susidarymui kietėjimo metu ir jos pokyčiams veikiant aukštoms temperatūroms.
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Aleknevičius, Marius. "Naftos krekinge naudoto katalizatoriaus poveikis ugniai atsparių betonų savybėms." Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2011. http://vddb.laba.lt/obj/LT-eLABa-0001:E.02~2010~D_20110120_134413-03760.
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Naftos krekinge naudotas katalizatorius yra ceolitinė medžiaga, kurios unikalios savybės mažai išnaudojamos cementinių medžiagų gamybos technologijoje. Ugniai atspariuose betonuose naudojami įvairūs priedai-modifikatoriai yra labai brangūs, todėl naudoto katalizatoriaus panaudojimas, kaip modifikuojančio betono savybes priedo, turi ne tik ekologinį (atliekų utilizavimas) bet ir ekonominį pagrindą. Vykdant šį darbą sukurti vidutinio cemento kiekio ugniai atsparūs šamotbetoniai su 70 % ir 40 % aliuminio oksido turinčiais aliuminatiniais cementais ir naudoto katalizatoriaus priedu atitinkamai 2,5 % ir 5,0 %. Darbe taip pat atskleistas efektyvus katalizatoriaus poveikis aliuminatinio cemento hidratacijai, cemento akmens struktūros susidarymui kietėjimo metu ir jos pokyčiams veikiant aukštoms temperatūroms.Fluidized bed catalytic cracking catalyst waste is a zeolite material. Its unique properties are underused in cementitious materials production technology. Various additives, modifiers used in refractory castables are very expensive, so the use of catalyst waste as a modifying additive of castable properties has not only an ecological (waste recycling) but also an economical basis. Medium cement refractory castable was developed using 70 % and 40 % of aluminium oxide containing aluminate cement and catalyst waste additive, respectively 2,5 % and 5,0 %. The work also reveals an efficient effect of catalyst waste on alumina cement hydration, structure formation during cement solidification and after treatment at high temperature.
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Martignoni, Waldir Pedro. "Modelling and simulation of FCC riser reactors, an heterogeneous approach." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq31116.pdf.
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Komarasamy, Mageshwari. "Deformation Micro-mechanisms of Simple and Complex Concentrated FCC Alloys." Thesis, University of North Texas, 2015. https://digital.library.unt.edu/ark:/67531/metadc822829/.
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The principal objective of this work was to elucidate the effect of microstructural features on the intrinsic dislocation mechanisms in two FCC alloys. First alloy Al0.1CoCrFeNi was from a new class of material known as complex concentrated alloys, particularly high entropy alloys (HEA). The second was a conventional Al-Mg-Sc alloy in ultrafine-grained (UFG) condition. In the case of HEA, the lattice possess significant lattice strain due to the atomic size variation and cohesive energy differences. Moreover, both the lattice friction stress and the Peierls barrier height are significantly larger than the conventional FCC metals and alloys. The experimental evidences, so far, provide a distinctive identity to the nature and motion of dislocations in FCC HEA as compared to the conventional FCC metals and alloys. Hence, the thermally activated dislocation mechanisms and kinetics in HEA has been studied in detail. To achieve the aim of examining the dislocation kinetics, transient tests, both strain rate jump tests and stress relaxation tests, were conducted. Anomalous behavior in dislocation kinetics was observed. Surprisingly, a large rate sensitivity of the flow stress and low activation volume of dislocations were observed, which are unparalleled as compared to conventional CG FCC metals and alloys. The observed trend has been explained in terms of the lattice distortion and dislocation energy framework. As opposed to the constant dislocation line energy and Peierls potential energy (amplitude, ΔE) in conventional metals and alloys, both line energy and Peierls potential undergo continuous variation in the case of HEA. These energy fluctuations have greatly affected the dislocation mobility and can be distinctly noted from the activation volume of dislocations. The proposed hypothesis was tested by varying the grain size and also the test temperature. Activation volume of dislocations was a strong function of temperature and increased with temperature. And the reduction in grain size did not affect the dislocation mechanisms and kinetics. This further bolstered the hypothesis. The second part deals with deformation characteristics of Al-Mg-Sc alloy. The microstructure obtained from the severe plastic deformation (SPD) techniques differ in dislocation density, grain/cell size, and in the grain boundary character distribution. Therefore, it is vital to understand the deformation behavior of the UFG materials produced by various SPD techniques, as the microstructural features basically control the deformation mechanisms. In this study, a detailed analysis was made to understand the deformation mechanisms operative in various regimes of a stress-strain in UFG Al-Mg-Sc alloy produced via friction stir processing. The stress-strain curves exhibited serrations from the onset of yielding to the point of sample failure. The serration amplitude and frequency was higher in UFG material as compared to CG material. Furthermore, the microstructural features that result in the serrated flow were investigated along with the avalanche characteristics. The presence of both ultrafine grains and Al3Sc precipitates were the necessary conditions to reach the critical stress required to push the grain boundary into a critical state to set off an avalanche. The microstructural conditions that did not satisfy both the requirements did not exhibit deep serrations.
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Souza, Thiago Xavier Rocha de. "Propriedades magnéticas do modelo de Hubbard em estruturas tipo FCC." Universidade Federal de Sergipe, 2012. https://ri.ufs.br/handle/riufs/5345.
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Coordenação de Aperfeiçoamento de Pessoal de Nível SuperiorThe study about magnetic properties of strongly correlated electrons has been an problem of interest in physics by the great technological importance of various materials with this characteristic. A well-known theoretical approach, known as the Hubbard model, has been used in an attempt to describe such phenomena. This model considers the interactions and electron mobility in a simplified way for describing phenomena like itinerant magnetism and the metal-insulator transition. In this study were analyzed the thermodynamic clusters properties of structures with fcc lattice symmetry containing 4, 5, 6, 7 and 8 sites. An exact numerical diagonalization method was used, where the subspaces of the problem were separatly analyzed and put together on, which is a procedure that reduces the processing data time. In order to improve the diagram of quantum states also carried out a ground state analysis of the clusters, known in the literature and obtained from systems with 4, 5 and 6 sites. On this subject a new diagram was developed showing the quantum states transition using the Lanczos method, applied to clusters with 4 to 8 sites in this case. Finally, a comparison was made between the thermodynamic properties and the results found in the new quantum state diagram. The agreement between them is good.
O estudo de propriedades magnéticas de elétrons fortemente correlacionados tem sido um problema de interesse da física pela grande importância tecnológica de vários materiais com essa característica. Uma famosa abordagem teórica, conhecida como modelo de Hubbard, vem sendo utilizada na tentativa de descrever esse tipo fenômeno. Esse modelo considera interações e a mobilidade eletrônica descrevendo de forma simplificada fenômenos como magnetismo itinerante e transição metal-isolante. Neste trabalho foram analisadas propriedades termodinâmicas de clusters de estruturas com simetria da rede fcc contendo 4, 5, 6, 7 e 8 sítios. Foi utilizado um método de diagonalização numérica exata, onde os subespaços do problema foram analisados separadamente e reunidos posteriormente, procedimento que reduz o tempo de processamento dos dados. Foi também realizada uma análise do estado fundamental dos clusters com o intuito de aprimorar o diagrama de estados quânticos, conhecido na literatura, obtido a partir de sistemas com 4, 5 e 6 sítios. Sobre esse assunto, foi desenvolvido um novo diagrama que indica a transição de estados quânticos a partir da utilização do método de Lanczos, neste caso, aplicado a clusters de 4 a 8 sítios. Por fim, foi feita uma análise comparativa entre as propriedades termodinâmicas e os resultados encontrados no novo diagrama de estados quânticos que mostraram boa coerência entre si.
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Rohatgi, Aashish. "A microstructural investigation of shock-loading effects in FCC materials /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 1999. http://wwwlib.umi.com/cr/ucsd/fullcit?p9944211.
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Liu, Gang. "Nucleation and cross-slip of partial dislocations in FCC metals." Diss., [Riverside, Calif.] : University of California, Riverside, 2009. http://proquest.umi.com/pqdweb?index=0&did=1957327601&SrchMode=2&sid=4&Fmt=2&VInst=PROD&VType=PQD&RQT=309&VName=PQD&TS=1269015486&clientId=48051.
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Thesis (Ph. D.)--University of California, Riverside, 2009.Includes abstract. Available via ProQuest Digital Dissertations. Title from first page of PDF file (viewed March 20, 2010). Includes bibliographical references. Also issued in print.
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Kempton, James Russell. "Sites and diffusion of muons in FCC metal hydride systems." W&M ScholarWorks, 1987. https://scholarworks.wm.edu/etd/1539623772.
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A positive muon can be considered an isotope of hydrogen due to similarities in spin and charge. For metal hydride systems, the muon enters the sample "as the last hydrogen added," and competes for the same sites as the hydrogen atoms. to observe the site competition and diffusion of both particles (muon and proton), several FCC metal hydrides, TiH{dollar}\sb{lcub}1.83{rcub}{dollar}, TiH{dollar}\sb{lcub}1.97{rcub}{dollar}, TiH{dollar}\sb{lcub}1.99{rcub}{dollar}, YH{dollar}\sb{lcub}1.77{rcub}{dollar}, YH{dollar}\sb2{dollar}, ZrH{dollar}\sb{lcub}1.94{rcub}{dollar}, and LaH{dollar}\sb{lcub}2.06{rcub}{dollar}, were studied using transverse-, zero-, and low longitudinal-field {dollar}\mu{dollar}SR. The low temperature region results indicate that the muon predominately occupies octahedral sites for the FCC metal hydrides in this study. The probability for a muon to occupy a tetrahedral site in titanium and zirconium hydrides at these temperatures is proportional to the vacancy concentration. Whereas the probability for T site occupation in yttrium hydride is proportional to the number of protons not occupying these sites which increases with hydrogen concentration. Muon T site occupancy below room temperature for LaH{dollar}\sb{lcub}2.06{rcub}{dollar} was not observed and was not expected since these sites are occupied by protons. Around 300 K, the muon diffuses over interstitial O sites to vacancies in the H sublattice of TiH{dollar}\sb{lcub}1.99{rcub}.{dollar} The vibration of the hydrogen lattice is found to be the mechanism responsible for the activation of the muon out of the O site. Above room temperature, the muon occupies tetrahedral sites in yttrium and titanium hydrides. at high temperatures, the field-correlation time for a muon in titanium and yttrium hydrides is approximately one to two orders of magnitude greater than for a proton as measured by NMR. The results of a Monte Carlo simulation indicate that the presence of the muon inhibits the motion of the nearest-neighbor protons at high temperatures. The dynamics of the proton spins are observed by zero- and low longitudinal-field {dollar}\mu{dollar}SR through the oscillation of the muon polarization at long times for a static muon in a T or O site. This observation is not predicted by the Kubo-Toyabe treatment for a stationary muon.
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Svenningsson, Leo. "Fourier transform of BCC andFCC lattices for MRI applications." Thesis, Uppsala universitet, Institutionen för informationsteknologi, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-257148.
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The Cartesian Cubic lattice is known to be sub optimal when consideringband-limited signals but is still used as standard in three-dimensional medical magneticresonance imaging. The optimal sampling lattices are the body-centered cubic latticeand the face-centered cubic lattice. This report discusses the possible use of thesesampling lattices in MRI and presents verification of the non standard Fouriertransform method that is required for MR image creation for these sampling lattices.The results show that the Fourier transform is consistent with analytical models.
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Cristina, Bezerra Azedo de Melo Ana. "Validação de modelos matemáticos para descrever a fluidodinâmica de um riser a frio utilizando atenuação Gama." Universidade Federal de Pernambuco, 2004. https://repositorio.ufpe.br/handle/123456789/9568.
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Previous issue date: 2004O comportamento fluidodinâmico do riser de um modelo a frio tipo FCC foi investigado por meio das medidas da distribuição da concentração do catalisador com atenuação gama e simulação com modelo matemático. No riser do modelo a frio, MEF, com 0,032 m de diâmetro 2,3 m de comprimento circula o leito fluidizado cujos componentes são ar e catalisador de FCC. A unidade MEF opera com controle automático e instrumentos de medidas das variáveis fluidodinâmicas. A distribuição axial da concentração do catalisador foi medida utilizando-se uma fonte de Am-241 e detector de NaI(Tl) associado a multicanal com software de aquisição e avaliação de dados. O MEF foi adaptado para a validação de modelo fluidodinâmico que descreve o escoamento no riser, como por exemplo, a introdução de injetor para controle do fluxo de sólidos em circulação. Modelos matemáticos foram selecionados na literatura, analisados e testados para simular a fluidodinâmica do riser. Foi estudada e implementada uma metodologia para validar modelos fluidodinâmicos. As etapas do trabalhos foram desenvolvidas de acordo com a metodologia de validação, como planejamento de dados experimentais, estudo das equações que descrevem a fluidodinâmica, aplicação de solvers computacionais e avaliação da simulação em comparação com os dados experimentais. Corridas foram realizadas com as condições do MEF definidas para medir a concentração do catalisador e sendo medidas simultaneamente as variáveis fluidodinâmicas, velocidade dos componentes e variação da pressão no riser. Em seguida foram comparados valores simulados e valores experimentais, com o tratamento estatístico dos dados, visando a precisão requerida para validar o modelo fluidodinâmico. Os testes de comparação entre dados experimentais e simulados foram realizados sob os critérios de validação. O comportamento fluidodinâmico do riser foi analisado, os resultados e a concordância com a literatura foram discutidos. O modelo adotado foi validado nas condições de operação do riser do MEF, para uma faixa de vazão do gás de 3 a 6 m/s e o valor da razão de escorregamento entre 1 e 2
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Chmyrov, Volodymyr. "Fluorescence fluctuation studies of biomolecular interactions in solutions, biomembranes and live cells." Doctoral thesis, KTH, Experimentell biomolekylär fysik, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-187708.
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Fluorescence spectroscopy and imaging have a very broad spectrum of applicationswithin the life sciences, in particular for detection and characterization ofbiomolecular dynamics and interactions in different environments. This thesis comprisesprojects that strive to further expand the information content extracted fromthe detected fluorescence, leading to sensitive readout parameters for studies ofbiomolecular dynamics and interactions. Two major strategies are presented toachieve this aim. The first strategy is based on the expansion of the availablereadout parameters beyond the "traditional" fluorescence parameters: intensity,wavelength, polarization and fluorescence lifetime. The additional parameters arebased on blinking properties of fluorescent labels. In particular on transitions betweensinglet and triplet states, and transitions between the trans- and cis-isomersof fluorophores. Two publications in the thesis are based on this strategy (paperI and IV). The second strategy is based on the utilization of fluorescence intensityfluctuations in order to detect the oligomerization mechanisms of fluorescentlylabeled peptides and proteins. This strategy combines the intensity fluctuationanalysis and the readout of distance dependent energy transfer between fluorescentmolecules together with the correlation analysis of fluorescence from two labeledproteins emitting at different wavelengths. Another two publications presented inthe thesis are based on the second comprehensive strategy (papers II and III).The work presented in this thesis shows that the blinking kinetics of fluorescentlabels contain significant information that can be exploited by a combination of fluctuationsanalysis with distance dependent excitation energy transfer between thefluorescent molecules, or by analysis of fluorescence covariance between moleculesthat emit at different wavelengths. These fluorescence-based methods have a significantpotential for molecular interaction studies in the biomedical field.QC 20160527
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Isler, Jeremy Payton. "Interactions of Lanthanides and Liquid Alkali Metals for "Liquid-Like" Lanthanide Transport in U-Zr Fuel." The Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1492607350430645.
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Boum, Alexandre Teplaira. "Commande prédictive d'un craqueur catalytique à lit fluidisé avec estimation des paramètres clés." Thesis, Université de Lorraine, 2014. http://www.theses.fr/2014LORR0033/document.
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Le craquage catalytique à lit fluidisé (FCC) est l'un des procédés les plus importants au sein d'une raffinerie moderne et joue un rôle économique primordial. Le fonctionnement du FCC pose des problèmes d'opération liés à sa complexité. L'étude a porté sur la simulation du FCC, sa commande prédictive multivariable et l'estimation de paramètres-clés. Après une revue de la littérature sur les FCC et les différentes approches de modélisation ainsi que des cinétiques de craquage, un modèle du FCC qui intègre les dynamiques importantes a été choisi pour les besoins de la commande prédictive. La simulation du riser a été effectuée pour différents modèles de craquage et a montré de grandes disparités entre modèles, créant une difficulté à définir un modèle général de riser pour les FCC. Outre le nombre de groupes considérés, les différences concernent la chaleur de réaction globale, les lois de formation de coke sur le catalyseur et la désactivation de ce dernier. Des algorithmes de commande prédictive linéaire et non linéaire basée sur le modèle ont été utilisés pour commander le FCC en tenant compte de sa nature multivariable et des contraintes imposées aux variables manipulées. Les sorties commandées, température en haut du riser et température du régénérateur ont été maintenues proches des consignes, tant en régulation qu'en poursuite, tout en respectant les contraintes portant sur les deux variables manipulées, le débit de catalyseur régénéré et le débit d'air entrant dans le régénérateur. Une commande à trois entrées manipulées, incluant le débit d'alimentation, a également été testée avec succès. La commande prédictive linéaire avec observateur a fourni des résultats encore meilleurs que la commande linéaire quadratique. La commande prédictive non linéaire a été testée mais présente des problèmes pour une implantation en temps réel. L'estimation du coke sur le catalyseur a été réalisée par le filtre de Kalman étendu, mais les erreurs d'estimation sont importantes, probablement à cause du choix insuffisant des mesures effectuées. L'ensemble de l'étude a montré que la commande avancée prédictive du FCC est performante et doit être recommandée, mais peut encore être améliorée en particulier par son réglage et l'estimation des étatsFluid catalytic cracking (FCC) is one of the most important processes in a modern refinery and is of essential economic importance. The FCC operation presents difficulties related to its complexity. The study was related to its simulation, multivariable control and estimation of key parameters. After a litterature review of the FCC, the different approaches of modelling and cracking kinetics, a FCC model that takes into account the important dynamics was chosen for model predictive control purposes. The riser simulation was carried out for different cracking models and shows great differences between these models, which makes it difficult to define a general riser model for the FCC. Besides the number of lumps, differences deal with the global heat of reaction, the coke formation laws and its deactivation functions. Linear and nonlinear model predictive algorithms were used for FCC control taking into account its multivariable nature and the constraints imposed on the manipulated variables. The controlled outputs, temperature at the riser top and temperature in the regenerator were maintained close to their respective set points in regulation and tracking modes while respecting the constraints on the two manipulated variable, the flow rate of regenerated catalyst and the flow rate of air entering the regenerator. A control with three manipulated variables including the feed flow rate was also successfully tested. Linear predictive control with an observer gave better results than linear quadratic control. Nonlinear predictive control was tested but presents problems for real time implementation. The estimation of coke on the catalyst was carried out using extended Kalman filter, but the estimation errors are important, probably due to an insufficient choice of measurements. The overall study showed that advanced predictive control of the FCC is efficient and must be recommended, but it can still be improved upon particularly by its tuning and state estimation
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Silva, Douglas Luís da. "Recuperação de terras raras contidas em catalisadores exauridos utilizados no craqueamento do petróleo (FCC), e em pós-fosfóricos de lâmpadas fluorescentes descartadas." Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/59/59138/tde-21062017-112107/.
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As zeólitas sintéticas contendo terras raras (TR) são os componentes principais de catalisadores FCC (Fluid Catalytic Cracking) empregados no craqueamento do petróleo e a porcentagem de TR nestes catalisadores pode chegar a 5%. As TR são adicionadas às zeólitas tipo Y para melhorar sua estabilidade térmica e hidrotérmica durante o processo de refino do petróleo. A produção brasileira destes catalisadores está em torno de 25 mil toneladas por ano, necessitando, para tanto, de 900 toneladas de óxido de lantânio no mesmo período. Atualmente, a China é responsável por 90% da produção e comercialização mundial das TR. Desde 2010, a China controla os preços das mesmas (ao final de 2011 chegou a elevar o preço do lantânio em mais de 20 vezes), bem como reduziu substancialmente sua cota de exportação. É nesse contexto que surge a necessidade da reciclagem de materiais que possuem TR em sua constituição, como é o caso dos catalisadores FCC provenientes do craqueamento do petróleo. Outra fonte que merece destaque, tendo sido igualmente explorada neste trabalho, é os pós-fosfóricos responsáveis por gerar a luz branca em lâmpadas fluorescentes. Atualmente a Rhodia, do grupo Solvay, já iniciou a recuperação das TR em pós-fosfóricos. As principais TR utilizadas em lâmpadas fluorescentes são La, Ce, Eu, Tb e Y, encontrados nos compostos Y2O3:Eu3+, BaMgAl10O17:Eu2+ e LaPO4:Ce3+,Tb3+. Os elementos Eu, Tb e Y têm alto valor agregado, representando de 5 a 20% em massa dos pós-fosfóricos. Sendo assim, o objetivo deste trabalho foi desenvolver uma metodologia economicamente viável e, sobretudo, com baixa utilização e produção de substâncias perigosas para a separação e recuperação de íons de TR contidos na zeólita tipo Y, componente dos catalisadores FCC desativados, previamente empregados no craqueamento de petróleo, bem como em lâmpadas fluorescentes. Inicialmente, realizou-se a caracterização preliminar dos componentes dos catalisadores FCC desativados. Posteriormente, buscou-se o desenvolvimento de metodologias de separação química para obtenção dos elementos de TR e caracterização dos mesmos por diversas técnicas, tais como espectroscopia de fotoluminescência, fluorescência de Raios-X, titulometria de complexação, microscopia eletrônica de varredura e espectroscopia de infravermelhoSynthetic zeolites containing rare earths (RE) are the major components of FCC (Fluid Catalytic Cracking) catalysts used in petroleum cracking, where the percentage of such elements is about 5%. RE ions improve the thermal and hydrothermal stability of zeolites-Y during the petroleum refining process. The Brazilian production of these catalysts is around 25 thousand tons per year, requiring 900 tons of lanthanum oxide in the same period. Currently, China is responsible for 90% of the world production and market of RE. Since 2010, China controls the prices of RE elements and substantially reduced the exportation quota. For instance, by the end of 2011 the price of lanthanum was risen by more than 20 times. In this context, the search for recycling materials that have rare earths in their constitution becomes crucial, as is the case of the FCC catalysts from the cracking of petroleum. Another source that deserves significant attention is the phosphoric powders that generate white light in fluorescent lamps, which were also investigated in this work. Rhodia from the Solvay group has already begun the recovery of rare earths in phosphoric powders. The main RE used in fluorescent lamps are La, Ce, Eu, Tb and Y, which occur as Y2O3: Eu3+, BaMgAl10O17:Eu2+ and LaPO4:Ce3+, Tb3+. Eu, Tb and Y are high-value elements, representing by 5 20% of the total mass of phosphoric powders. Therefore, the aim of this work was to develop economically feasible and environmental friendly methodologies for the separation and recovery of RE ions from zeolite-Yin deactivated FCC catalysts and from fluorescent lamp phosphors. To this end, we firstly performed a preliminary characterization of the components of deactivated FCC catalysts. The following steps comprised the development of chemical separation methodologies to obtain rare earth elements and their characterization by several techniques such as photoluminescence spectroscopy, X-ray fluorescence, complexation titration, scanning electron microscopy and infrared spectroscopy
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Ahmadi, Motlagh Amir Hossein. "CFD simulation of two- and three-phase flow in FCC reactors." Thesis, University of British Columbia, 2015. http://hdl.handle.net/2429/52621.
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Liquid distribution and evaporation in Fluid Catalytic Cracking (FCC) reactors are investigated
numerically. The well-documented inaccuracy of conventional two-fluid modeling of hydrodynamics in fluidized beds of Geldart Group A particles is revisited. A new force-balance (FB) sub-grid-scale model, introduced and applied to the conventional Wen-Yu drag correlation, analyzes the balance of van der Waals, drag, gravity and buoyancy forces. It predicts formation of agglomerates inside the bed, updating the drag calculations by applying a correction factor to the conventional drag models. Good predictions are obtained of fluidization regimes and bed
expansion, and there is promising agreement with experimental time-average radial voidage
profiles reported by Dubrawski et al. (2013). Good quantitative agreement between discrete
element models (DEM) and two-fluid predictions of minimum bubbling velocity is also observed
when the model is used to predict minimum bubbling velocity, in contrast to the predictions from
a non-cohesive, Wen-Yu model.
Liquid injection experiments on a lab-scale fluidized bed were conducted, at the Institute of
Chemical and Fuels from Alternative Sources (ICFAR) in London, Ontario to study the
distribution, as well as the penetration, of liquid into catalyst pores. The results shed light on complexities involved in the injection zone to understand the effect of superficial gas velocity on evaporation and imbibition of liquid into particle pores. A methodology is developed to couple and incorporate existing liquid imbibition (into particle pores) models with evaporation models in the CFD code. The results are compared to another set of lab-scale experiments conducted at the British Columbia Research Institute (BCRI) facilities in Burnaby, BC. Simulation results demonstrate that CFD models can capture correct qualitative behavior of liquid injection and evaporation inside the bed. However, quantitative deviations revealed the likely effect of hydrodynamic properties on drying from both the liquid film around the particles and inside the pores. The deviations also imply that the assumption of convection- or diffusion-dominant drying might be unsuitable, and the two should be combined. Based on experimental results, a methodology is proposed to include the effect of hydrodynamic properties such as superficial gas velocity and particle impact velocity on drying.Applied Science, Faculty of
Chemical and Biological Engineering, Department of
Graduate
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Lin, Peter Keng-Yu. "Evolution of grain boundary character distributions in FCC and BCC materials." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp02/NQ27994.pdf.
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