Dissertationen: „Particle formation and transformation“

1

Kalokhtina, Olena. „Etude par Sonde Atomique Tomographique de la formation de nano-particules dans les aciers ODS et NDS“. Phd thesis, Université de Rouen, 2012. http://tel.archives-ouvertes.fr/tel-00751814.

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Les aciers ferritiques-martensitiques (FeCr) renforcés par une dispersion fine et dense d'oxydes (acier ODS - Oxide Dispersion Strengthened) possèdent une bonne résistance à l'irradiation et des propriétés mécaniques élevées à haute température. Les aciers ODS sont ainsi de bons candidats comme matériaux des structures de cœur des réacteurs de Génération IV. Il est envisageable de renforcer ces aciers par des nitrures nanométriques plutôt que par des oxydes (aciers NDS - Nitride Dispersion Strengthened). Dans cette thèse, des aciers ODS et NDS élaborés au CEA Saclay par 2 procédés distincts (mécanosynthèse et nitruration) sont étudiés par sonde atomique tomographique et d'autres techniques complémentaires, à différentes étapes du procédé d'élaboration (brut de broyage/nitruration, après recuit, après consolidation). Dans les aciers ODS, il apparait que deux mécanismes se produisent pendant la mécanosynthèse : la dissolution de la poudre d'oxyde d'yttrium initiale et la formation d'amas riches en Y et O. Il n'a pas été possible de déterminer si ces amas résultent d'un phénomène de précipitation ou d'une dissolution incomplète de l'oxyde initial. Pendant les recuits et la consolidation, ces amas servent de germes à la formation de particules riches en Y, Ti et O. En ce qui concerne les aciers NDS, que la mécanosynthèse est un procédé efficace pour obtenir une fine et dense dispersion de nitrures. Ces nitrures germent pendant l'étape de broyage mécanique. La taille et la densité numérique de ces nano-renforts dans le matériau consolidé sont similaires à ce qui est généralement observé dans les aciers ODS. Concernant le procédé de nitruration, différents nitrures sont observés (CrN, TiN). Il apparait que la microstructure obtenue est très hétérogène et que le procédé doit être optimisé.

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2

Sathyamoorthy, Sekhar. „Particle formation during anatase precipitation“. Thesis, University of Cambridge, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.621988.

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3

Hirasawa, Tetsu. „Organizational identity formation and transformation“. Thesis, University of Cambridge, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.607893.

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4

Ensign, Laura Marie. „Protein particle formation for pulmonary delivery“. Connect to resource, 2007. http://hdl.handle.net/1811/28925.

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Thesis (Honors)--Ohio State University, 2007.
Title from first page of PDF file. Document formatted into pages: contains 34 p.; also includes graphics. Includes bibliographical references (p. 32-34). Available online via Ohio State University's Knowledge Bank.

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5

Iglesias, Victor Alejandro. „Genetic transformation studies in wheat using particle bombardment /“. [S.l.] : [s.n.], 1994. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=10628.

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6

Leswin, Joost Sieger Kaspar. „Particle Formation in RAFT-mediated Emulsion Polymerization“. University of Sydney, 2007. http://hdl.handle.net/2123/2176.

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Doctor of Philosophy(PhD)
Particle formation in RAFT-mediated emulsion polymerization has been studied using reaction calorimetry. By measuring the heat flow during controlled feed ab-initio emulsion polymerization in the presence of amphipathic RAFT agents, particle formation by self-assembly of these species could be observed. Two different monomer systems, i.e. styrene and n-butyl acrylate, and various degrees of hydrophobicity of the initial macro-RAFT agents have been studied and compared. The different macro-RAFT agents were synthesized by first forming a hydrophilic block of poly(acrylic acid) that would later on act as the electrosteric stabilizing group for the particles. Subsequently, different lengths of hydrophobic blocks were grown at the reactive end of the poly(acrylic acid) hydrophilic block via the RAFT-mediated controlled radical polymerization, either comprised of n-butyl acrylate or styrene. Two processes govern particle formation: adsorption of macro-RAFT agents onto growing particles and formation of new particles by initiation of micellar aggregates or by homogeneous nucleation. Competition between these processes could be observed when monomers with a relatively high (n-butyl acrylate) or low (styrene) propagation rate coefficient were used. A model describing particle formation has been developed and the results of model calculations are compared with experimental observations. Preliminary modeling results based on a set of reasonable physico-chemical parameters already showed good agreement with the experimental results. Most parameters used have been verified experimentally. The development of the molecular weight distribution of the macro-RAFT agents has been analyzed by different techniques. Quantification of the particle formation process by analytical techniques was difficult, but qualitative insights into the fundamental steps governing the nucleation process have been obtained. The amount of macro-RAFT agents initially involved in particle formation could be determined from the increase of molecular weight. The particle size distribution has been measured by capillary hydrodynamic fractionation, transmission electron microscopy and dynamic light scattering. From the data obtained from these particle-sizing techniques, the number of particles during the reaction could be monitored, leading to an accurate estimate for the particle formation time. Upon implementation of the experimental data obtained for the surface active macro-RAFT systems, the model demonstrated to be very sensitive towards the “headgroup” area of the macro-RAFT species. Three nucleation cases based on the initial surface activity of the macro-RAFT species in the aqueous phase are proposed to explain the deviations from the assumptions of the nucleation model. Even though the macro-RAFT species have a narrow molecular weight distribution, they are nevertheless made up of a distribution of block lengths of polystyrene upon a distribution of block lengths of poly(acrylic acid). The resulting differences in initial surface activity are the most probable reason for the observed differences between model calculations and experimental results for the nucleation time and particle size distribution of the final latex product. With the procedure described above, latexes have been synthesized without using conventional surfactants and the mechanisms involved in the particle formation for these systems have been elucidated. The results of this work enable production of latex systems with well defined molecular mass distributions and narrow particle size distributions. Furthermore, the technique based on the application of amphipathic RAFT agents is promising for the production of complex polymeric materials in emulsion polymerization on a technical scale.

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7

Watson, Paul David Julian. „Geotextile filter design and particle bridge formation“. Thesis, Queen Mary, University of London, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.307520.

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8

Parsons, Stephen H. „Comparing orchid transformation using agrobacterium tumefaciens and particle bombardment“. Virtual Press, 1995. http://liblink.bsu.edu/uhtbin/catkey/941350.

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The Wheeler Orchid Collection is home to some of the most endangered species of orchids in the world. This fantastic reservoir of endangered species has been enhanced and broadened by its function as a plant rescue station for the U.S. customs service. Unfortunately, this responsibility increases the risk of bringing orchids, which harbor contageous diseases, into the greenhouse where sap transmitted diseases such as the Tobacco Mosaic Virus (TMV), can run rampant. Although manipulation of orchid characteristics is typically done by classical plant breeding techniques, genetic engineering is emerging as a useful technique for the introduction of desirable traits into the orchid genome. Through the use of genetic engineering techniques it may be possible to mitigate the symptoms associated with this destructive virus. Virus resistance may be achieved through the expression of either the sense or antisense viral coat protein gene in orchid tissues if an efficient means of orchid transformation is developed. In this research two transformation protocols were examined for their ability to efficiently transform orchid tissue. The first transformation protocol explored utilized the native ability of Aq bacterium tumefaciens to incorporate DNA into host plants to achieve transformation. The second mechanism explored was particle bombardment transformation.Many strains of A. tumefaciens were employed using direct exposure of Cattleya_ orchid protocorm and callus tissue. Particle bombardment using DNA coated 0.5 um diameter tungsten particles and high pressure helium tank acceleration was employed. The particle bombardment procedure employed the pG35barB plasmid which confers herbicide resistance to the herbicide basta when integrated and expressed in plant tissues.GUS fluorescence assays and PCR analysis indicate that T-DNA is present in orchid tissues, while Southern blot analysis was unable to display that integration had occurred. Particle bombardment yielded herbicide resistant orchid tissues which have yet to be analyzed by Southern blot analysis to confirm integration due to limited tissue quantities.
Department of Biology

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9

Huff, Jason. „Particle formation of smelt in a fluidized bed“. Diss., Georgia Institute of Technology, 2001. http://hdl.handle.net/1853/7037.

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10

Pettibone, Alicia Stanier Charles O. „Toward a better understanding of new particle formation“. [Iowa City, Iowa] : University of Iowa, 2009. http://ir.uiowa.edu/etd/420.

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11

Lian, Zhuoyang. „Biodegradable polymer particle formation using supercritical carbon dioxide“. Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file 2.84 Mb., 293 p, 2006. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:1435248.

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12

Rödner, Sandra. „Interfacial colloidal particle films and their structure formation“. Licentiate thesis, KTH, Chemistry, 2002. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-1505.

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Abstract toInterfacial colloidal particle films andtheir structure formation; a licentiate thesis, whichwill be presented by Sandra Rödner in Q2, 29 November 2002at 13.00.

Colloidal particles can be made to organise themselves intoordered arrays. These colloidal structures acquire interestingand useful properties, not only from their constituentmaterials but also from the spontaneous emergence of mesoscopicorder that characterises their internal structure. Orderedarrays of colloidal particles, with lattice constants rangingfrom a few nanometers to a few microns, have potentialapplications as optical computing elements and chemicalsensors, and also has an important influence on the mechanicalproperties and optical appearance of paint films and papercoatings.

The control of colloidal structure formation starts with theparticle interactions (attractive or repulsive) and colloidaldynamics, which is the topic of this thesis. To enable adetailed understanding of the different factors that controlthe formation of dense 2D colloidal films, a method forstructural characterisation was developed. The degree of orderin the hexagonal close-packed structure, displayed by thecolloidal films, was characterised by the size of ordereddomains and by the distribution of pore sizes. The size ofordered domains was obtained from the pair distributionfunction, and the distribution of pores from a Delaunaytriangulation procedure. These methods are based on theparticle positions in the film, which were determined by lightmicroscopy and processed digital images.

The two methods were used to study the effect of particleinteractions on the structure of colloidal monoparticulatefilms, formed at the air-liquid interface. The size of theordered domains decreased exponentially with increasing bondstrength, while the pore density increased. The transfer andsubsequent drying of the formed film on a solid substrateinduced structural changes; the capillary forces transformedsmall pores into triangular order while some of the largervoids and cracks increased in size.

The structural features of colloidal monolayers, formed bydrying a dilute silica suspension on a substrate, wereinvestigated. Addition of small amounts of salt resulted indrastic changes of the particle film structure. The size of theordered domains decreased exponentially with increasing amountsof added salt (0-2.9% NaCl/Silica ratio), with a simultaneousincrease of the concentration of large defects. This suggeststhat loss of colloidal stability and onset of particle adhesionto the substrate inhibit rearrangement and ordering. Theevaporation rate was controlled by varying the relativehumidity during drying. Colloidal monolayers with the largestordered domains and the lowest concentration of stacking faultswere formed at an intermediate humidity (55% RH).

The rearrangement process during drying of dilute silicasuspensions was followed in detail by studying the changes inthe structural features during growth of colloidal monolayers.Low crystal growth rate promoted the transition of squarelattice domains to a hexagonal close-packed structure. Additionof salt to the electrostatically stabilised dispersionincreased the formation of square structured regions at thecrystal-suspension interface, due to increasing adhesion to thesubstrate. The loss of colloidal stability inhibited therearrangement process, resulting in higher concentrations ofsquare lattice domains at large distances from the crystal edgecompared to systems without added salt.

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13

Gjervan, Torbjørn. „Studies of bimetallic particle formation in reforming catalysts“. Doctoral thesis, Norwegian University of Science and Technology, Department of Chemical Engineering, 2000. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-1482.

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14

Mikkanen, Pirita. „Fly ash particle formation in kraft recovery boilers /“. Espoo [Finland] : Technical Research Centre of Finland, 2000. http://www.vtt.fi/inf/pdf/publications/2000/P421.pdf.

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15

Moghadasi, Jamshid. „Particle movement and scale formation in porous media“. Thesis, University of Surrey, 2002. http://epubs.surrey.ac.uk/844246/.

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The flow of particulate suspensions and brines in porous media is encountered in a wide range of industrial situations such as oil production, soil erosion, and ground water pollution and in the operation of filter beds. Three major classes of such problems are addressed in this thesis, namely particle movement, scale formation and filtration. Particle movement and scale formation are known to be serious problems in oil reservoirs where incompatible brine is brought into contact with the formation. Dramatic reductions in permeability are observed in such cases due to the release of fine particles that subsequently plug flow channels downstream. This study deals with an experimental and theoretical study of formation damage resulting from particle movement and scale formation in porous media. An experimental investigation was undertaken to look into the possible causes of the injectivity loss in a typical Iranian oilfield. Sets of experimental investigations were undertaken with different objectives in mind. Glass and sand bead packs were used to test the experimental set up and to observe the general behavior of fine particle movement and scale formation in porous media. The experiments were conducted with injection rates from 25 cm3/min to 100 cm3/min. Particles of alumina oxide were suspended in the injected water to simulate fine particle migration in porous media. The particles were injected at concentrations ranging from 500 ppm to 2000 ppm. It was observed that the build-up of flow resistance was mostly due to frontal face plugging. Alumina particles were added to the glass beads to study the effect of particles initially present in the glass bead pack. A mathematical model is presented that simulates the porosity impairment by particle movement. This model, which is based on the mass balance of particles flowing through the porous media, at first, proposes an overall equation to determine the porosity and by a special mechanism it can predict the overall change in porosity. The equations are quite general and can be used to model the permeability reduction for any given pore or particle size distribution. Also this study aims to investigate the calcium sulphate and calcium carbonate scaling in a porous medium to discover its possible effect upon the permeability of the porous medium. The information on the effect of scale deposition is obtained experimentally by flooding porous medium with incompatible brines. The experimental data are used to develop and validate models for predicting the permeability decline caused by scale. The model is intended to provide a link between what is known or can be assumed about brines in an oil reservoir. A computer program was developed which can predict the scaling tendency of the sulphate minerals and calcium carbonate, in water disposal wells, water injection systems, surface equipments and facilities that commonly form scale. This program is based on the latest correlations of experimental data relating to North Sea and Iranian oilfields. It is used to determine the degree to which brine becomes supersaturated with a scale forming mineral under specified conditions. Processes capable of creating supersatuartion in oilfields are described and it is shown that the distribution of scale depends on the process involved.

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16

Pettibone, Alicia J. „Toward a better understanding of new particle formation“. Diss., University of Iowa, 2009. https://ir.uiowa.edu/etd/420.

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The creation of new atmospheric particles via nucleation is an important source of particles, and may influence climate by altering the aerosol size distribution. The objectives of my dissertation research were to better understand the process by which new particles are created (homogeneous nucleation), and how these particles are modified throughout their lifetime in the atmosphere. The approach combined field-measurements and observations with advanced instrumentation development and extensive data analysis. In the laboratory, a Dry-Ambient Aerosol Size Spectrometer (DAASS) was constructed. The DAASS is an automated combination of aerosol sizing instruments and supporting equipment that measures aerosol size distributions from 10.9 nm to 10 µm at both ambient and dry relative humidities and was deployed during the MILAGRO field campaign. The design and construction of a Differential Mobility Analyzer from parts was also completed in order to provide the capability to perform Tandem DMA (or TDMA) measurements. New particle formation events, occurring in both rural (Midwest United States) and urban (Mexico City) locations were analyzed. In the Midwest, the temporal pattern, frequency, associated meteorology and contributing factors were quantified for the first time in this location. The urban observations were conducted in Mexico City, Mexico, as part of an international field campaign known as MILAGRO (Megacity Initiative: Local and Global Research Observations 2006). It was determined that new particle formation in Mexico City occurs following periods of decreased pre-existing aerosol surface area. These sharp decreases in pre-existing aerosol surface area are tied to the rapid ventilation of the Mexico City basin that occurs in the early afternoon as a result of its unique geographical setting in a mountain basin. Number-based emission factors representative of Mexico City were determined using a method of signal peak identification in collocated SMPS and CO2 measurements. The emission factor as a function of time of day, day of week, and wind direction were examined. The overall emission factor is size resolved, and comparisons to other size resolved emission factors determined in other locations (such as Los Angeles) were performed.

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17

Canals, Valérie. „Formation-insertion et transformation du rapport salarial“. Montpellier 1, 2000. http://www.theses.fr/2000MON10054.

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Liee a l'ampleur et a la duree du chomage, l'insertion correspond a un processus en voie de structuration entre l'ecole et l'emploi. Cette periode de transition s'allonge et se complexifie, en particulier sous l'influence de la politique publique de l'emploi. Dans ce domaine, l'importance prise par la formation favorise l'eloignement du referencement par rapport a l'emploi. Les trajectoires d'insertion tendent a montrer que ce processus a une coherence. Aucun corpus theorique ne traite l'insertion de maniere specifique. Cela temoigne sans doute d'un objet en voie de constitution, encore fortement tributaire des remontees empiriques. Aujourd'hui, leur diversite engage a avancer dans la voie de la restitution theorique a partir d'hypotheses concernant la periode elle-meme. Dans cette optique, nous considererons que la formation insertion peut etre assimilee a une activite correspondant a des transformations en cours dans le systeme de l'emploi.

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18

Lyyränen, Jussi. „Particle formation, deposition, and particle induced corrosion in large-scale medium-speed diesel engines /“. Espoo VTT, 2006. http://www.vtt.fi/inf/pdf/publications/2006/P598.pdf.

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19

Thoms, S. „Studies in mixed species charged particle beam dynamics“. Thesis, University of Oxford, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.380004.

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20

Suzuki, Kiyoshi. „Control of Particle Size through Understanding of Mechanism of Particle Formation and Growth in Microemulsions“. Kyoto University, 1999. http://hdl.handle.net/2433/181684.

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21

Tai, Xiuyu. „Experimental studies of sulfuric acid particle formation and growth“. Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq22931.pdf.

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22

Chong, Kin Hung. „Modelling and simulation of particle formation in laminar flames“. Thesis, University of Cambridge, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.336552.

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23

Sajjadi, Emami Shahriar. „Particle formation and growth in semibatch emulsion polymerisation reactors“. Thesis, Loughborough University, 1998. https://dspace.lboro.ac.uk/2134/12373.

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An investigation of emulsion polymerisation of butyl acrylate in batch and semibatch reactors has been carried out. The important phenomena of particle formation and kinetics in semibatch emulsion reactors with neat monomer feed and monomer emulsion feed have been studied. An investigation of batch emulsion polymerisation of butyl acrylate was also undertaken in order to provide the supporting evidence to elucidate particle formation in the semibatch emulsion process. Different start-up procedures were studied to determine their effect on the particle formation and kinetics of the polymerisation reaction. The effects of monomer distribution, emulsifier distribution, initiator distribution, feed rate, temperature and pre-period time on the particle formation and steady-state rate of polymerisation were investigated. Experimental studies reveal that particle formation in semibatch emulsion polymerisation is influenced by partitioning of ingredients, such as emulsifier and monomer, between the charge and the feed rate and controlling the growth rate of particles at monomer-starved conditions. The latter is applied by adjusting the monomer or monomer emulsion feed rate at a desired level. Changes in start-up procedure were found to have a significant effect not only on the transients before a steady-state, but also on the ultimate steady-state rate of polymerisation reaction achieved and final number of particles obtained. All variables affecting primary and secondary particle formation, and especially emulsifier concentration, could equally influence the steady-state rate of polymerisation reaction. Evidence was obtained indicating that secondary nucleation can occur through homogenous nucleation. The particle size distribution (PSD) development in the course of reaction for the semibatch emulsion process was investigated. Partitioning of ingredients between the charge and the feed and monomer starved nucleation were founa to be the main two factors that control the PSD and number of particles formed.

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24

Handscomb, Christopher Samuel. „Simulating droplet drying and particle formation in spray towers“. Thesis, University of Cambridge, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.611175.

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25

Wood, Paul D. „Elements of solar activity : particle acceleration and filament formation“. Thesis, University of St Andrews, 2005. http://hdl.handle.net/10023/11309.

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This thesis studies the acceleration of particles to super-thermal energies in explosive solar events as well as the magnetic changes in connectivity that may be responsible for changes in the morphology of quiescent filaments. Firstly a review of some of the observations of solar flare dynamics is given, as well as an introduction to the competing theories attempting to explain both particle acceleration and filament formation. An explanation of the numerical FORTRAN code that is used to calculate the trajectories of particle distribution functions in prescribed electromagnetic fields is given. Examples of known fields are used to test the accuracy of the code and the simple example of the well-known Litvinenko current sheet field is investigated. The results of charged particle orbit calculations in prescribed electric and magnetic fields motivated by magnetic reconnection models are then presented. The electromagnetic fields are chosen to resemble a current sheet with a localised reconnection region. The dependence of the model on the important physical parameters is considered. An introduction to the mathematical formulation of a collapsing magnetic trap is given. The same numerical code is used to calculate single electron orbits in this more complicated time dependent electromagnetic field. Consideration of important previous work is given before describing the best attempts to model the movement of flare loops in a realistic fashion. Finally the process of flux cancellation and filament formation is studied using a range of data including ground-based Hα and SoHO MDI magnetograms. It is found that the cancellation occurs at the ends of Hα sections of the filament and is accompanied by a noticeable increase in the Hα intensity and linkage of the sections. Measurements of the amount of flux cancelled at each site show it is in agreement with an estimate of the axial flux contained in the filament.

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26

Jewett, Steven P. „Five dimensions for spiritual transformation“. Theological Research Exchange Network (TREN), 1995. http://www.tren.com.

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27

Schmid, Jean. „Transformation through Asian religions“. Theological Research Exchange Network (TREN), 1992. http://www.tren.com.

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28

Elversson, Jessica. „Spray-Dried Powders for Inhalation : Particle Formation and Formulation Concepts“. Doctoral thesis, Uppsala University, Department of Pharmaceutical Chemistry, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-5904.

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Spray drying is a method with a high potential in the preparation of protein particles suitable for pulmonary delivery. However, surface induced denaturation of bio-molecules during atomization and subsequent drying can be substantial and it is therefore important to develop new formulation concept for concurrent encapsulation and stabilization of proteins during spray drying. Hence, with an overall objective to increase the knowledge of the formation of particulate systems for systemic administration of proteins by spray drying, the first part of this thesis, systematically investigated the particle formation by droplet size and particle size measurements. It was described how specific properties, such as the solubility and the crystallization propensity of the solute, can affect the product, e.g. the particle size, internal structures, and possibly particle density. A new method using atomic force microscopy (AFM) for the assessment of the effective particle density of individual spray-dried particles was demonstrated. In the second part, two different formulation concepts for encapsulation of protein during spray drying were developed. Both systems used non-ionic polymers for competitive adsorption and displacement of protein from the air/water interface during spray drying. The aqueous two-phase system (ATPS) of polyvinyl alcohol (PVA) and dextran, and the surface-active polymers, hydroxypropyl methylcellulose (HPMC) and triblock co-polymer (poloxamer 188) used for in situ coating, proved efficient in encapsulation of a model protein, bovine serum albumin (BSA). Inclusion of polymeric materials in a carbohydrate matrix also influenced several particle properties, such as the particle shape and the surface morphology, and was caused by changes in the chemical composition of the particle surface and possibly the surface rheology. In addition, powder performance of pharmaceutical relevance, such as dissolution and flowability, were affected.

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29

Griscik, Gregory J. „Wax particle formation from the rapid expansion of supercritical solutions“. Diss., Georgia Institute of Technology, 1996. http://hdl.handle.net/1853/11110.

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30

Stinson, Gregory. „Supernova feedback in smoothed particle hydrodynamics simulations of galaxy formation /“. Thesis, Connect to this title online; UW restricted, 2007. http://hdl.handle.net/1773/5428.

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31

Liebhart, Ewlad. „Particle deposition and cake formation in filters with shearing flows“. Thesis, Kingston University, 2000. http://eprints.kingston.ac.uk/20654/.

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Existing theories for the mechanical response of particle fluid mixtures have been reviewed and extended. They are made appropriate to geometries in which the dominant loading is a shearing one. The theories are then applied to the description of filtration experiments (these were performed by researchers dn a parallel research programme at Loughborough University). Two limits are distinguished: one in which particles experience a strong double layer interaction and one in which the particles are neutral and the fluid is the only significant force-mediating medium. The existing theories that have been reviewed and used are the quasi-static two-phase continuum mechanics framework (including seepage effects), the granular temperature theory for neutral particles and the common consolidation theory for strongly interacting particles. To extend these general theories - and especially to enter reliable constitutive relations - a micromechanical analysis is carried out and methods are developed to arrive at expressions for bulk properties. An analysis is performed of the response to a small localised fluctuation in either stress or solidosity of a particle-fluid mixture under arbitrary mean loading conditions. This analysis leads to a condition for stability of a mixture in terms of the solidosity sensitivity of the particle pressure and the solidosity sensitivity of the viscous constitutive parameters of the mixture given a mean loading regime. In the analysis it is recognised that a slurry in motion (especially shear) will always experience fluctuations. Two applications of the stability analysis are then presented. First it is recognised that homogenisation is impossible when the system is unstable. Second the border between a stable (packed) region and a free flowing region is defined by the edge of the stability condition, as made appropriate to the prevailing loading conditions. This piece of fundamental analysis is then used to describe filtration experiments, notably ones in which shear plays a distinctive role - these are torsion shear filtration and crossflow filtration. In order to analyse torsion shear filtration a calculation is carried out of a Newtonian fluid in a cylindrical vessel, loaded at the top by a rotating piston. A range of result is obtained: flow in an infinite cylinder, flow in a cylinder of finite length and flow in a finite cylinder with two immiscible fluids, occupying various sections of the cylindrical domain. The latter problem is particularly relevant to the torsion shear filtration problem as it shows that no significant shearing stress reaches, the cake until the fluid region near the piston is of the order of magnitude of the particle size of the mixture. Once shear can penetrate the cake the effects of it are noticed in that in a stable heterogeneous medium structures formation takes place in the direction of the major principal stress, implying that the greater the shear that is applied the greater the angle at which structures form. Then a calculation is presented to demonstrate the reduction in uniaxial stiffnes due to structures formation and the experimental result is recovered that for neutral particles cakes becoine denser when the shear is increased. This result is qualitative, though quantitative formulas are presented. The latter require parameters such as an estimate of the magnitude of the stiffness fluctuations that are hard to determine from current experiments. For double layer interacting particles the effects of shear are noticed at an earlier stage in the filtration process as particle interactions transmit the forces exerted externally on the mixture. The overall stiffness due to shearing is then estimated (stability is here required) and it is shown that the normal stress on the medium is reduced due to the fluctuations induced by the shearing. A lattice-Boltzmann, simulation of the same configuration confirms this interesting result. A crossflow setup has been analysed. A somewhat simplified one dimensional investigation is presented. The key point is that the edge of the cake near the septum is defined by the edge of stability analysis and this piece of information enables' a full survey of experimental results with a wide range of process paraméters (feed solidosity, crossflow velocity, crossflow pressure, particle type, pH). Two key experimental parameters are predicted: the end of filtration filtrate flow and time constant with which this end stage is reached. Double layer interacting particles and neutral particles have been explored. Some key findings pertaining especially to cases of thisn cakes are as follows. Double layer interacting particles: the end of filtration filtrate flux depends on the ratio of the crossflow velocity and feed solidosity only. The time constant depends Existing theories for the mechanical response of particle fluid mixtures have been reviewed and extended. They are made appropriate to geometries in which the dominant loading is a shearing one. The theories are then applied to the description of filtration experiments (these were performed by researchers dn a parallel research programme at Loughborough University). Two limits are distinguished: one in which particles experience a strong double layer interaction and one in which the particles are neutral and the fluid is the only significant force-mediating medium. The existing theories that have been reviewed and used are the quasi-static two-phase continuum mechanics framework (including seepage effects), the granular temperature theory for neutral particles and the common consolidation theory for strongly interacting particles. To extend these general theories - and especially to enter reliable constitutive relations - a micromechanical analysis is carried out and methods are developed to arrive at expressions for bulk properties. An analysis is performed of the response to a small localised fluctuation in either stress or solidosity of a particle-fluid mixture under arbitrary mean loading conditions. This analysis leads to a condition for stability of a mixture in terms of the solidosity sensitivity of the particle pressure and the solidosity sensitivity of the viscous constitutive parameters of the mixture given a mean loading regime. In the analysis it is recognised that a slurry in motion (especially shear) will always experience fluctuations. Two applications of the stability analysis are then presented. First it is recognised that homogenisation is impossible when the system is unstable. Second the border between a stable (packed) region and a free flowing region is defined by the edge of the stability condition, as made appropriate to the prevailing loading conditions. This piece of fundamental analysis is then used to describe filtration experiments, notably ones in which shear plays a distinctive role - these are torsion shear filtration and crossflow filtration. In order to analyse torsion shear filtration a calculation is carried out of a Newtonian fluid in a cylindrical vessel, loaded at the top by a rotating piston. A range of result is obtained: flow in an infinite cylinder, flow in a cylinder of finite length and flow in a finite cylinder with two immiscible fluids, occupying various sections of the cylindrical domain. The latter problem is particularly relevant to the torsion shear filtration problem as it shows that no significant shearing stress reaches, the cake until the fluid region near the piston is of the order of magnitude of the particle size of the mixture. Once shear can penetrate the cake the effects of it are noticed in that in a stable heterogeneous medium structures formation takes place in the direction of the major principal stress, implying that the greater the shear that is applied the greater the angle at which structures form. Then a calculation is presented to demonstrate the reduction in uniaxial stiffnes due to structures formation and the experimental result is recovered that for neutral particles cakes becoine denser when the shear is increased. This result is qualitative, though quantitative formulas are presented. The latter require parameters such as an estimate of the magnitude of the stiffness fluctuations that are hard to determine from current experiments.
For double layer interacting particles the effects of shear are noticed at an earlier stage in the filtration process as particle interactions transmit the forces exerted externally on the mixture. The overall stiffness due to shearing is then estimated (stability is here required) and it is shown that the normal stress on the medium is reduced due to the fluctuations induced by the shearing. A lattice-Boltzmann simulation of the same configuration confirms this interesting result. A crossflow setup has been analysed. A somewhat simplified one dimensional investigation is presented. The key point is that the edge of the cake near the septum is defined by the edge of stability analysis and this piece of information enables a full survey of experimental results with a wide range of process parameters (feed solidosity, crossflow velocity, crossflow pressure, particle type, pH).

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Lys, Thomas. „Mechasnisms of particle formation and growth in bimodal PVC latexes“. Lyon 1, 2004. http://www.theses.fr/2004LYO10018.

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Parmi les nombreuses applications utilisant le PVC (Poly(chlorure de vinyle), un des secteurs les plus concurrentiels est celui des plastisols, application pour les sols (surface) et pour les murs (papiers peints). Le plastisol est une dispersion de et de latex de PVC préalablement atomisés, obtenu par polymérisation en émulsion du Chlorure de Vinyle Monomère. Ces produits dans leur mise en forme nécessite un contrôle précis de leur viscosité. Celle-ci est directement lié à la taille des particules constituant la dispersion. Ce sujet de thèse traite donc de l'étude des paramètres intervenant dans le procédé industriel d'obtention de latex PVC sur la distribution de tailles de particules des latex finaux. Le résultat majeur de cette thèse est la mise en évidence de l'effet du tensio-actif de couverture sur la granulométrie finale des latex, en particulier si la distribution est bimodale. En modifiant les conditions d'ajout de ce tensio-actif, le diamètre des particules ainsi que la fraction volumique de petites particules par rapport aux grosses particules en est modifiée. Un contrôle précis de ce paramètre est à prévoir en milieu industriel pour assurer la reproductibilité du procédé
The main objective of the research reported here was to understand the mechanism of formation and growth of particles in the production of bimodal PVC latexes via a seeded polymerization process. A number of parameters were investigated such as the flow rate of initiator, the flow rate of coverage surfactant, the conversion at which the coverage surfactant had to be injected. The coverage surfactant was found to be the parameter principally affecting the final PSD of bimodal latexes. Depending on the feed rate of the surfactant or the time of injection of the surfactant, the volume fraction of small particles could be strongly modified. On a mechanism point of view, we demonstrated that homogenous nucleation occurred from the beginning to the end of the polymerization and was the major factor of particles growth The small particles were found to be detected once the surface of the seed particles was enough saturated with surfactant and showed a good stability. Then the added surfactant covers the unstable particles generated in the aqueous phase, preventing them from coagulating and allowing them to grow independently of the large particles

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33

Takahashi, Kazuo. „Solid Particle Formation and Strongly Coupled Phenomena in Nonequilibrium Plasmas“. Kyoto University, 2001. http://hdl.handle.net/2433/151558.

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34

Schmidt, Marek Wojciech, und Marek Schmidt@rl ac uk. „Phase formation and structural transformation of strontium ferrite SrFeOx“. The Australian National University. Research School of Physical Sciences and Engineering, 2001. http://thesis.anu.edu.au./public/adt-ANU20020708.190055.

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Non-stoichiometric strontium iron oxide is described by an abbreviated formula SrFeOx (2.5 ≤ x ≤ 3.0) exhibits a variety of interesting physical and chemical properties over a broad range of temperatures and in different gaseous environments. The oxide contains a mixture of iron in the trivalent and the rare tetravalent state. The material at elevated temperature is a mixed oxygen conductor and it, or its derivatives,can have practical applications in oxygen conducting devices such as pressure driven oxygen generators, partial oxidation reactors in electrodes for solid oxide fuel cells (SOFC). ¶ This thesis examines the behaviour of the material at ambient and elevated temperatures using a broad spectrum of solid state experimental techniques such as: x-ray and neutron powder diffraction,thermogravimetric and calorimetric methods,scanning electron microscopy and Mossbauer spectroscopy. Changes in the oxide were induced using conventional thermal treatment in various atmospheres as well as mechanical energy (ball milling). The first experimental chapter examines the formation of the ferrite from a mixture of reactants.It describes the chemical reactions and phase transitions that lead to the formation of the oxide. Ball milling of the reactants prior to annealing was found to eliminate transient phases from the reaction route and to increase the kinetics of the reaction at lower temperatures. Examination of the thermodynamics of iron oxide (hematite) used for the reactions led to a new route of synthesis of the ferrite frommagnetite and strontium carbonate.This chapter also explores the possibility of synthesis of the material at room temperature using ball milling. ¶ The ferrite strongly interacts with the gas phase so its behaviour was studied under different pressures of oxygen and in carbon dioxide.The changes in ferrite composition have an equilibrium character and depend on temperature and oxygen concentration in the atmosphere. Variations of the oxygen content x were described as a function of temperature and oxygen partial pressure, the results were used to plot an equilibrium composition diagram. The heat of oxidation was also measured as a function of temperature and oxygen partial pressure. ¶ Interaction of the ferrite with carbon dioxide below a critical temperature causes decomposition of the material to strontium carbonate and SrFe12O19 . The critical temperature depends on the partial pressure of CO2 and above the critical temperature the carbonate and SrFe12O19 are converted back into the ferrite.The resulting SrFe12O19 is very resistant towards carbonation and the thermal carbonation reaction does not lead to a complete decomposition of SrFeOx to hematite and strontium carbonate. ¶ The thermally induced oxidation and carbonation reactions cease at room temperature due to sluggish kinetics however,they can be carried out at ambient temperature using ball milling.The reaction routes for these processes are different from the thermal routes.The mechanical oxidation induces two or more concurrent reactions which lead to samples containing two or more phases. The mechanical carbonation on the other hand produces an unknown metastable iron carbonate and leads a complete decomposition of the ferrite to strontiumcarbonate and hematite. ¶ Thermally and mechanically oxidized samples were studied using Mossbauer spectroscopy. The author proposes a new interpretation of the Sr4Fe4O11 (x=2.75) and Sr8Fe8O23 (x=2.875)spectra.The interpretation is based on the chemistry of the compounds and provides a simpler explanation of the observed absorption lines.The Mossbauer results froma range of compositions revealed the roomtemperature phase behaviour of the ferrite also examined using x-ray diffraction. ¶ The high-temperature crystal structure of the ferrite was examined using neutron powder diffraction.The measurements were done at temperatures up to 1273K in argon and air atmospheres.The former atmosphere protects Sr2Fe2O5 (x=2.5) against oxidation and the measurements in air allowed variation of the composition of the oxide in the range 2.56 ≤ x ≤ 2.81. Sr2Fe2O5 is an antiferromagnet and undergoes phase transitions to the paramagnetic state at 692K and from the orthorhombic to the cubic structure around 1140K.The oxidized formof the ferrite also undergoes a transition to the high-temperature cubic form.The author proposes a new structural model for the cubic phase based on a unit cell with the Fm3c symmetry. The new model allows a description of the high-temperature cubic form of the ferrite as a solid solution of the composition end members.The results were used to draw a phase diagramfor the SrFeOx system. ¶ The last chapter summarizes the findings and suggests directions for further research.

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Beck, Markus. „Boron in Palladium: interaction, phase formation and phase transformation“. [S.l. : s.n.], 2001. http://www.bsz-bw.de/cgi-bin/xvms.cgi?SWB9556602.

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36

Bate, Matthew Russell. „The role of accretion in binary star formation“. Thesis, University of Cambridge, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.388852.

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37

Valdés, Julio R. „Fines migration and formation damage - microscale studies“. Diss., Georgia Institute of Technology, 2002. http://hdl.handle.net/1853/19303.

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38

Aboofazeli, Reza. „The formation and characterization of phospholipid microemulsions“. Thesis, King's College London (University of London), 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.307045.

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39

Bürzle, Florian [Verfasser]. „Numerical Studies in Star Formation using Smoothed Particle Magnetohydrodynamics / Florian Bürzle“. München : Verlag Dr. Hut, 2012. http://d-nb.info/1021719439/34.

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40

Garrity, Mary Patricia 1961. „Particle formation during reactive ion etching of silicon with SF(6)“. Diss., The University of Arizona, 1997. http://hdl.handle.net/10150/282512.

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Particle formation during low pressure SF6/argon etching of silicon in a single wafer parallel plate reactor is studied. Particles are extracted from the exhaust and collected on the wafer. Particle composition and morphology depend on plasma power, etch time, gas composition, and pressure. Primary particles are tens of nanometers in diameter and spherical and chain aggregates as large as 5 mum are observed. Critical powers and etch times are required for the formation of these aggregates. The presence of major gas phase species is determined using mass spectroscopy and optical emission spectroscopy. A three stage mechanism for describing the particle formation (nucleation, heterogeneous growth, and coagulation) is presented. Particle precursor and heterogeneous sources are determined from plasma-dependent, homogeneous, gas-phase reactions and etch product distributions predicted from electrical and etch rate measurements. Dissociation of SF6 into lower molecular weight SFx species and unsaturated SiFx species are primarily responsible for nuclei formation and subsequent, rapid heterogeneous growth by attachment of positive ions.

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41

Helble, Joseph John. „Mechanisms of ash particle formation and growth during pulverized coal combustion“. Thesis, Massachusetts Institute of Technology, 1987. http://hdl.handle.net/1721.1/14860.

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42

Forgan, Duncan Hugh. „Probing self-gravitating protostellar discs using smoothed particle hydrodynamics and radiative transfer“. Thesis, University of Edinburgh, 2011. http://hdl.handle.net/1842/4883.

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Stars are likely to form with non-zero initial angular momentum, and will consequently possess a substantial gaseous protostellar disc in the early phases of their evolution. At this early stage, the disc mass is expected to be comparable to the mass of the protostar. The disc’s self-gravity therefore plays an important role in the subsequent evolution of the system, regulating the accretion of matter onto the protostar, as well as being potentially capable of forming low mass stars and massive planets by disc fragmentation. The protostellar disc may later evolve into a protoplanetary disc, providing the feedstock for planet formation. Therefore, if the current stellar populations and exoplanetary systems are to be understood, an understanding of the evolution of protostellar discs is crucial, especially their earliest self-gravitating phases. I have used various methods of numerical simulation to probe the physics of self-gravitating protostellar discs and their constituents. When constructing a model for self-gravitating protostellar discs, including detailed thermodynamics and radiative transfer is essential. I have developed two distinct numerical techniques for incorporating radiative transfer into Smoothed Particle Hydrodynamics (SPH) simulations. The first allows the modelling of frequency-averaged radiative transfer during the SPH simulation, in effect approximating radiative SPH (RSPH) with only a marginal increase in runtime (around 6%). The second takes the output from SPH simulations, and creates synthetic, wavelength-dependent telescope images and spectra of SPH systems. This allows the direct construction of observables from SPH simulations, providing, for the first time, a direct connection between the output of SPH simulations and observations. I have used these numerical methods to analyse, in detail, the local angular momentum transport induced by self-gravity in protostellar discs, testing the robustness of the “pseudo-viscous” analytical approximation for local disc stresses. I confirm that semi-analytical disc modellers are justified in using the pseudo-viscous approximation in some cases, but I also outline the limits in which non-local transport effects causes the approximation to fail. Also, I have investigated the evolution of protostellar discs when perturbed by a secondary companion, in particular identifying whether such events will in general trigger a) a disc fragmentation event, or b) a stellar outburst event. For case a), I found no significant evidence that perturbation by a companion improves the possibility of disc fragmentation in compact discs - in case b), I found that stellar outburst events do indeed occur, but they are unlikely to be seen by observers due to their rare occurrence, as well as due to self-obscuration effects.

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Guidi, Lionel. „Particle flux transformation in the mesopelagic water column: process analysis and global balance“. Diss., Texas A&M University, 2008. http://hdl.handle.net/1969.1/85946.

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Marine aggregates are an important means of carbon transfers downwards to the deep ocean as well as an important nutritional source for benthic organism communities that are the ultimate recipients of the flux. During these last 10 years, data on size distribution of particulate matter have been collected in different oceanic provinces using an Underwater Video Profiler. The cruise data include simultaneous analyses of particle size distributions as well as additional physical and biological measurements of water properties through the water column. First, size distributions of large aggregates have been compared to simultaneous measurements of particle flux observed in sediment traps. We related sediment trap compositional data to particle size (d) distributions to estimate their vertical fluxes (F) using simple power relationships (F=Ad^b). The spatial resolution of sedimentation processes allowed by the use of in situ particle sizing instruments lead to a more detailed study of the role of physical processes in vertical flux. Second, evolution of the aggregate size distributions with depth was related to overlying primary production and phytoplankton size-distributions on a global scale. A new clustering technique was developed to partition the profiles of aggregate size distributions. Six clusters were isolated. Profiles with a high proportion of large aggregates were found in high-productivity waters while profiles with a high proportion of small aggregates were located in low-productivity waters. The aggregate size and mass flux in the mesopelagic layer were correlated to the nature of primary producers (micro-, nano-, picophytoplankton fractions) and to the amount of integrated chlorophyll a in the euphotic layer using a multiple regression technique on principal components. Finally, a mesoscale area in the North Atlantic Ocean was studied to emphasize the importance of the physical structure of the water column on the horizontal and vertical distribution of particulate matter. The seasonal change in the abundance of aggregates in the upper 1000 m was consistent with changes in the composition and intensity of the particulate flux recorded in sediment traps. In an area dominated by eddies, surface accumulation of aggregates and export down to 1000 m occured at mesoscale distances (<100 km).

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Da, Silva Marcio Faria. „Understanding Kafrin microparticle formation and morphology“. Diss., University of Pretoria, 2016. http://hdl.handle.net/2263/66261.

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A laboratory process exists for the extraction of kafirin protein from sorghum grain in order to form kafirin encapsulating microparticles. This laboratory process extracts approximately 2 g of protein and takes in excess of 60 hours from start to finish. A scaled-up extraction process based on the current laboratory process, consisting of a 100 L extraction vessel, was established in order to extract large volumes of kafirin protein from sorghum grain. Approximately 2.5 kg of kafirin protein, which contained approximately 80 % protein after defatting, was extracted from red sorghum grain. This blended kafirin protein, which was the product of combining 9 batches done on the up-scaled process, was needed in order to obtain a consistent base raw material for further experimentation. The blended kafirin was used to investigate the formation of kafirin encapsulating microparticles. This was achieved by means of the solvent phase separation technique with acetic acid as the solvent phase. A series of experiments, selected from a partial factorial design, were used to screen how the formation of microparticles was affected by various parameters. The parameters investigated were solvent to protein ratio, stirring speed, water addition rate and number of water droplets. The morphology of the various microparticles produced was analysed by means of light microscopy, FTIR and particle size analysis, and the different formed microparticles characterised. From the screening partial factorial experimental design, it was determined that the acetic acid concentration was crucial for the formation of microparticles. Microparticles did not form at a low mass ratio (2.3) of glacial acetic acid solvent to protein. Water addition rate and stirring rate also affected microparticle formation while the number of water droplets was insignificant. Therefore, using a high solvent to protein mass ratio (6.8), additional refined partial factorial experiments were conducted. These experiments focused on the effect of water addition rate and stirring speed on the final kafirin microparticle size. Ultimately, a polynomial model was developed to predict the final kafirin microparticle size using only the water addition rate and stirring speed as inputs. The model had an R2 value of 0.986 and was found to relatively accurate during validation. The model also identified that three distinct regions existed within the workspace: _ A region containing large particles due to protein mass agglomeration and crosslinking, which occurs at low stirring speeds (< 400 rpm) and high water addition rates (> 5 mL/min) _ A region where only small individual microparticles exist, which occurs at high stirring speeds (< 800 rpm) and low water addition rates (> 2 mL/min) _ A region where moderate particles existed as uniform agglomerates of the microparticles, which occurs at moderate stirring speeds (+- 600 rpm) and moderate water addition rates (+- 3.5 mL/min) Ultimately these kafirin microparticles, prepared from protein extracted in an up scaled process, were used to form qualitative microparticle films. The microparticle films were made without plasticiser and without dewatering the microparticles. Furthermore these films were made from microparticles in the regions identified in the model. This qualitative film formation showed that agglomerated microparticles can form films. This could be beneficial for the feasibility of a commercialised process for kafirin microparticle films since the production time would be shorter and less energy intensive.
Dissertation (MEng)--University of Pretoria, 2016.
Chemical Engineering
MEng
Unrestricted

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BOURGEOIS, JEAN PIERRE. „Les cheminements de formation en institut universitaire de formation des maitres. Processus de transformation des personnes“. Nantes, 2000. http://www.theses.fr/2000NANT3027.

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Nous etudions les effets internes de formation, les transformations de conceptions et de valeurs des personnes en formation, leurs modalites de relation aux dispositifs objectifs de formation. Certaines modalites relevent de conduites d'evitement de l'objet << formation >> dans ce qu'il peut avoir de destabilisant. D'autres sont au contraire des modalites de relation d'apprentissage, impliquant un veritable rapport a l'objet << formation >>. Considerees globalement, ces modalites peuvent etre eclairees par les theories du rapport au savoir chariot, bautier, rochex). Dans le detail, les modalites d'evitement de la relation a la formation objective relevent des theories de l'affectivite (psychanalyse), et les modalites du rapport direct a la formation objective, de la theorie piagetienne de l'apprentissage comme dialectique << assimilationaccommodation >>. Dans ce dernier cas, soit la formation est vecue comme devant repondre aux exigences des structures mentales prealables du sujet, l'apprentissage consistant a prelever ce qu'il y a de plus efficace dans le service << formation >> : c'est le paradigme technologique. Soit la formation est vecue comme processus de destabilisation et de transformation au contact de l'objet, la personne evoluant dans ses conceptions, son rapport au savoir : c'est le paradigme biologique, proche de la conception piagetienne de l'apprentissage comme reequilibration majorante du rapport << assimilationaccommodation >>. Nous nous demandons enfin ce qui, dans les dispositifs de formation, peut entraver ou faciliter l'apprentissage de la formation.

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Kamilli, Katharina A. [Verfasser], und Andreas [Akademischer Betreuer] Held. „Organic particle formation in halogen-influenced environments / Katharina Kamilli. Betreuer: Andreas Held“. Bayreuth : Universität Bayreuth, 2015. http://d-nb.info/1082289159/34.

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47

Whitehouse, Stuart Charles. „Radiative transfer using smoothed particle hydrodynamics and its application to star formation“. Thesis, University of Exeter, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.421588.

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48

Üçer, Defne. „Nonlinear waves, structure formation and particle acceleration by waves in space physics /“. Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2004. http://wwwlib.umi.com/cr/ucsd/fullcit?p3138833.

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49

Singer, Jared Wesley. „Formation and Transformation of Amorphous Calcium-Magnesium Carbonates in Synthetic Seawater“. Thesis, Alfred University, 2018. http://pqdtopen.proquest.com/#viewpdf?dispub=10184519.

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The aqueous chemistry, precipitation, and crystallization of metal-carbonates comprises a vast field of research that underlies the urgency of CO₂ sequestration, ocean-acidification, and biomineralization. The results of recent experimental and computational studies suggest that amorphous calcium and magnesium carbonates are precipitated from supersaturated aqueous conditions by non-classical aggregation of ion pairs, dimers, dynamically-ordered-liquid-likeoxypolymers (DOLLOPS), and prenucleation clusters (PNCs). We present the first high field (20 T) ⁴³Ca and ²⁵Mg NMR studies of amorphous calcium-magnesium carbonates (ACC, ACMC, AMC) materials. Direct integration of computational techniques with experimental NMR provides a novel step forward toward multi-scale integration of computational and experimental techniques. Supporting information is derived from X-ray diffraction (XRD), thermogravimetric/differential thermal analysis (TGA-DTA), and scanning electron microscopy—energy dispersive spectroscopy (SEM-EDS) and provides important comparison to the bulk structures and composition.

High field NMR of amorphous carbonates demonstrates that amorphous carbonates contain various types of local disorder, but does not corroborate the theory of polyamorphism nor nano scale phase separations postulated by other workers. Carbon (¹³C) NMR of ¹³Cenriched materials indicates a degree of Ca-Mg solid solution in ACMCs, as ACMC ¹³C resonances cannot be adequately reconstructed from the pure ACC and AMC ¹³C resonances. However, with increasing Mg-content (and therefore H₂O content) ¹³C NMR resonances are strongly influenced by water-carbonate hydrogen bonding, shifting to lower resonance frequency and broadening. The ¹³C-NMR are well-fit with single Gaussian distributions, suggesting that two-phase models of ACMCs are not required to explain our ¹³C NMR observations. Protoncarbon cross polarization indicates that there is a H population proximal to carbonate groups for all amorphous phases. ⁴³Ca NMR yields line shapes that span the resonance frequency range of all known crystalline calcium carbonate polymorphs and is well fit with a single Gaussian distributions. ⁴³Ca NMR does not support a theory of polyamorphisms, but rather suggests an unstructured, continuous distribution of local environments that is unlike any specific crystalline phase. The mean ⁴³Ca chemical shifts vary 0.77 ppm from compositions x = 0 to 0.5 [x = Mg/(Mg + Ca)], demonstrating that Mg²⁺ has very little influence on the molecular-scale ⁴³Ca environment in ACMCs. Through integration of quantum mechanical calculations, classical MD, and NMR we ascertain a maximum mean Ca-O bond distance in our ACCs/ACMCs of 2.45 ± 1 Å that is independent of composition. Unlike the indistinguishable local calcium environments, ²⁵Mg NMR of amorphous material gives evidence for several distinct overlapping quadrupolar line shapes. These sites do not generate NMR resonances that are perfect matches for known crystalline polymorphs of magnesian carbonates and extend toward lower resonance frequencies far beyond the range of known equilibrium analogs. By comparison to the range of reference phases, the low frequency singularities of ACMC-AMC resonances are consistent with some population of Mg-O bond distances greater than 2.10 Å and/or some fraction of sites with high coordination numbers (up to 8). The local Mg environment of a protodolomite crystallization [x = Mg/(Mg + Ca) = 0.6] exhibits ²⁵Mg NMR parameters most similar to the asymmetric Mg²⁺ coordination environment of lansfordite [Mg(CO₃)2(H₂O)₄]^2– or huntite. Although H-C cross polarization indicates no H-bonding with carbonate the XRD gives not longrange indications of huntite. The large effective radius of strongly hydrated Mg in the protodolomite likely provides a driving force for cation ordering in dolomite.

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Papaloï, Evangelia. „La transformation de l'implication et des representations professionnelles des employes apres un stage de formation“. Toulouse 2, 2001. http://www.theses.fr/2001TOU20005.

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Les mutations et les crises socio-economiques qui secouent le monde du travail, imposent des changements a la structure et au fonctionnement des services publics : la complexite croissante des systemes de production, la perte du monopole et la necessite d'organiser leurs departements d'apres les regles du marche libre, obligent les organisations a caractere public, a modifier leurs structures pour mieux s'adapter a un contexte concurrentiel et exigeant international. La gestion des ressources humaines et la formation, determinees par des instances administratives, deviennent les strategies mobilisees pour faciliter l'adoption de nouvelles activites et qualites au travail dites << innovantes >>. Les contextes de travail et ceux de formation apparaissent particulierement pertinents pour observer et s'interroger sur les pratiques, les representations sociales et professionnelles des employes ainsi que sur le role de la formation a la preparation au changement. Afin de devoiler ce qui se passe dans l'organisation, quels sont les facteurs qui determinent le niveau de l'implication professionnelle des employes, nous avancons l'hypothese qu'il y a une relation dialectique entre l'organisation, l'employe et la formation et que la formation a une placr preponderante parmi les facteurs susceptibles de transformer les representations des employes. La formation, en mettant au centre de son interet l'homme, peut aider au renforcement de l'implication professionnelle, au developpement personnel des employes et, par consequent, peut conduire le systeme organisationnel a l'evolution et au progres.

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Dissertationen zum Thema „Particle formation and transformation“

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