Dissertations / Theses on the topic 'Physical processes'
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Mitic, Slobodan. "Physical Processes In Complex Plasma." Diss., lmu, 2010. http://nbn-resolving.de/urn:nbn:de:bvb:19-118825.
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Weikel, Ross R. "Physical Transformations for Greener Chemical Processes." Diss., Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/11654.
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Homogenous acid catalysts are prevalent throughout the chemical industry but all have the drawback of requiring post reaction neutralization and subsequent downstream removal of the product salt. The use of a base to neutralize the acid and the processing of the salt are ancillary to the process and the disposal of the salt is an environmental concern. The work presented here shows the use of alkylcarbonic acids, which form in situ with CO₂ pressure and neutralize on loss of CO₂ pressure rather than requiring a base. Thus CO₂ can be used to "switch" the acid on and off.
The properties of alkylcarbonic acids are explored to gain understanding of the mechanisms by which they act. The acids are also used to catalyze the synthesis of α-pinene, methyl yellow, and benzyl iodide. These reactions are examples of common acid catalyzed reactions where this technology could be implemented.
The second half of the work explores two other "switches". The first is using temperature to break an emulsion with a novel thermally cleavable surfactant. This technology has potential applications in a wide range of fields where surfactants are used including polymerization, oil recovery, and biosynthesis. The second is using CO₂ to liquefy a solid ionic compound to allow its use as a solvent. This would greatly increase the number of ionic species available for use in ionic liquid-CO₂ biphasic systems.
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Thompson, William Travis. "Impact of physical processes on maritime frontogenesis." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1994. http://handle.dtic.mil/100.2/ADA283105.
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Crocker, Gregory Bruce. "Physical processes in Antarctic landfast sea ice." Thesis, University of Cambridge, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.278282.
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Han, Hwang-Jin. "Physical processes in hollow cathode discharge sources." Thesis, Monterey, California. Naval Postgraduate School, 1989. http://hdl.handle.net/10945/27208.
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Jones, Bethan. "Effects of physical processes in baroclinic waves." Thesis, University of Reading, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.306365.
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Coutinho, Mariane M. "Optimal midlatitude growth : impact of physical processes." Thesis, University of Reading, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.414569.
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Harris, Daniel. "Physical processes and morphodynamics of coral reefs." Thesis, The University of Sydney, 2013. http://hdl.handle.net/2123/10435.
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Coral reefs are valuable ecosystems due to their ability to support many diverse biological and geological assemblages. They are also of social and economic significance with the Great Barrier Reef (GBR) an important national symbol for Australia and a UNESCO world heritage site. Ecological studies have observed a decline in coral reef health in many parts of the world over the last few decades, due to human pressures (both local and global) in addition to natural variations of the environmental setting. However, the spatial and temporal resolution of most ecological assessments is inevitably limited, particularly on the scales of decadal to millennial coral reef change. Geological studies on the other hand accurately assess coral reef evolution over thousands of years but struggle with small scale changes in geomorphology and biological assemblages. Studies with a geomorphic and morphodynamic focus are required in order to bridge the gap between the ecological and geological understanding of coral reef evolution and provide information regarding the decadal to millennial change in reef geomorphology and carbonate production. In spite of this, physical process studies on coral reefs are few, particularly when compared to siliciclastic settings (such as estuaries and beaches) with a limited understanding of the mechanisms initiating geomorphic change in coral reef systems. The physical processes (waves and currents) acting on a coral reef windward platform and back-reef sand apron were assessed, along with morphological surveys and sedimentologic and chronostratigaphic reconstruction of sand apron evolution. Dating of dead patch-reefs buried by sand apron accretion was conducted in order to examine long-term sand apron evolution. Sampling and dating of fossil micro-atolls was also conducted in order to establish potential sea level history for the southern GBR. The sand apron geomorphology was shown to have channel formations as well as shallower areas which were associated with buried patch reefs. These features affected current flow on the sand apron with channels directing current off the sand apron, mainly during ebb tides (ebb dominated), into the lagoon or towards the reef crest and the shallow areas which were dominated by lagoonward directed flow across the sand apron (flood dominated). This is similar to the processes in siliciclastic environments, such as estuaries, and indicates that morphodynamic relationships between current flow and geomorphology occur in coral reef environments. In spite of this, average current flow did not exceed the required velocity to entrain sediment; sediment entrainment was only caused by short term peaks in current due to waves. These results showed that sediment entrainment under modal low-energy conditions does occur in back-reef environments; albeit on a small scale (only 3.5% of all recorded waves could entrain sediment). Most entrainment occurred at higher tidal stages (when depth over the reef platform (hd > 1 m) when potential mobility PM of sediment could be up to 40%. Spatial variation in PM and significant wave height (Hs) were found to extend beyond cross-reef attenuation of wave height and energy. The attenuation of Hs across the sand apron could be reasonably described based on the changes in offshore wave height, depth over the reef platform, and cross-reef distance from the reef rim (Xd). However, these variables could not explain along-reef trends within the data. To assess the along-reef variation in wave characteristics an additional distance value was introduced (Xpd) which combined the cross-reef distance to the reef rim (Xd) and the along-reef distance from the initial point of wave refraction on the reef rim (Xp). Spatial changes in wave height, PM wave velocity and grain size correlated with changes in Xpd. An empirical model was developed which could calculate wave height based on a few basic inputs of offshore wave weight, offshore wave direction, Xd and Xp. This model can be used in windward reef environments to not only assess the spatial variation in wave characteristics but also potential areas of sediment mobility and trends in sediment grain size. Radiocarbon ages and elevations of the fossil micro-atolls show that relative sea level was between 1-1.3 m higher than present between 3800-2200 cal. yr. BP. This data set is the first direct constraint through fixed biological indicators on sea level during the Holocene highstand in the southern GBR. These dates suggest that the Holocene sea level for the southern GBR follows a similar trend to current sea level curves for the east Australian coastline where the Holocene highstand was between 7000-2000 cal. yr. BP before falling to its present level. Rapid sand apron development occurred between 6000-2000 cal. yr. BP with most of the sand apron established during this period. Little or no sand apron development has occurred in the last 2000 years. This correlates with the micro-atoll data in this thesis and the sea level fall observed in previous studies at approximately 2000 cal. yr. BP. The fall in sea level caused an ecological shift on the reef platforms from live coral to algal dominated turning off the majority of carbonate production. It is likely that this led to a hiatus in sand apron development that has persisted for 2000 years. A conceptual model was developed that describes the non-linear lagoonal infill and sand apron development during the Holocene due to variations in sea level. In this model, rapid development of both reef platforms and back-reef sedimentary formations initially occurred during catch-up reef growth phase or when the windward margins reached sea level. This highly productive state may persist if sea level remains consistent and allows for productive live coral growth on reef platforms. A fall in sea level strands live coral on the reef platforms, leading to a turn-off of carbonate production and sediment input resulting in a reduction in the rate of lagoon infill. This conceptual framework has significant consequences for traditional reef growth models which generally show linear trajectories of reef evolution and also for assessments of coral reef response under future climate change predicted variations in sea level.
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Peters, Kyle C. "Sustainable Materials and Processes for Optoelectronic Applications." Case Western Reserve University School of Graduate Studies / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=case1554397264722736.
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Salter, Victoria Clare. "Anodic processes on aluminium." Thesis, University of Cambridge, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.387987.
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Hensley, Patricia Jane. "Accelerated physical modelling of transport processes in soil." Thesis, University of Cambridge, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.292742.
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Davies, Philip Andrew. "Physical and engineering aspects of protein separation processes." Thesis, University of Oxford, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.253017.
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Lau, Sze Chun Gary. "Physical characteristics of flocs in water treatment processes." Thesis, University College London (University of London), 2005. http://discovery.ucl.ac.uk/1444945/.
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Aluminium sulphate, calcium nitrate, and two cationic polymers have been used to coagulate and flocculate dilute kaolin and latex suspensions (< 100 mg/1) in a stirred vessel. The effects of the different destabilising agents on the resulting floes have been monitored using a simple continuous optical technique based on turbidity fluctuations and the behaviour of these floes under shear conditions and the possibility of subsequent floe re-formation have been investigated. The results showed vast differences in behaviour regarding to floe breakage and re formation between the systems. For a low molecular weight, high charge polymer (A) and calcium nitrate, floe breakage was almost completely reversible. However, for aluminium sulphate, limited floe re-formation was observed on restoring previous shear conditions after breakage. For a high molecular weight polymer (B), limited floe breakage was observed. Moreover, a new automated monitoring technique based on cake and vacuum filtration has been developed to assess the filterability of floes. The technique is reliable and provides reproducible results. The results showed that polymer A was more effective in enhancing filterability than polymer B for both kaolin and latex suspensions. However, polymers do not have a significant influence on the filterability of floes if the primary particles involved have high sphericity.
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Wheeler, J. "Physical and chemical processes in ductile shear zones." Thesis, University of Leeds, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.375358.
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Spray, Christopher Mark. "Goal orientation and motivational processes in physical education." Thesis, University of Exeter, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.337753.
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Fernandes, Roberto Cid. "Physical processes in active galactic nuclei and starbursts." Thesis, University of Cambridge, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.363192.
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Burroughes, Jeremy Henley. "The physical processes in organic semiconducting polymer devices." Thesis, University of Cambridge, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.306360.
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Dyer, Amy Nicole. "Family structure, couple processes and child physical abuse." Pullman, Wash. : Washington State University, 2009. http://www.dissertations.wsu.edu/Thesis/Spring2009/A_Dyer_042709.pdf.
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Thesis (M.A. in human development)--Washington State University, May 2009.Title from PDF title page (viewed on June 9, 2009). "Department of Human Development." Includes bibliographical references (p. 57-63).
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Harding, Mark S. "The kinetics of interfacial processes." Thesis, University of Oxford, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.336113.
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Zauner, Rudolf. "Scale-up of precipitation processes." Thesis, University College London (University of London), 1999. http://discovery.ucl.ac.uk/1317927/.
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This thesis concerns the scale-up of precipitation processes aimed at predicting product particle characteristics. Although precipitation is widely used in the chemical and pharmaceutical industry, successful scale-up is difficult due to the absence of a validated methodology. It is found that none of the conventional scale-up criteria reported in the literature (equal power input per unit mass, equal tip speed, equal stirring rate) is capable of predicting the experimentally observed effects of the mixing conditions on kinetic rates and particle characteristics. As a result of high gradients in the supersaturation field during precipitation, particularly in the feed zone, high local gradients in the nucleation rate are to be expected. In this thesis, a compartmental mixing model (Segregated Feed Model SFM) linked to the population balance is proposed for scaling up both continuous and semibatch precipitation processes, and is validated with experiments on different scales. Experiments were carried out using two chemical systems (calcium oxalate CaC₂O₄ and calcium carbonate CaCO₃), varying the residence time/feed time, feed concentration, feed point position, impeller type, feed tube diameter and stirring rate in geometrically similar reactors ranging from 0.3 to 301. A new procedure is introduced in order to solve the inverse problem for determination of the kinetic parameters for nucleation, growth, disruption and agglomeration from the particle size distributions obtained in the continuous laboratory-scale experiments. This method, where the kinetic rates were extracted separately and sequentially from the particle size distribution, was found to be a reliable alternative to the conventional simultaneous estimation of all kinetic parameters from the distribution. Using the kinetic parameters extracted from the laboratory-scale experiments, the population balance is solved within the Segregated Feed Model. The local mixing parameters also required for solving the SFM are obtained from a sliding mesh Computational Fluid Dynamics (CFD) model. These are used to specify the different micromixing and mesomixing conditions in the feed and bulk zones of the reactor. The model accurately predicts the mean size, coefficient of variation and nucleation rate on different scales for different process and mixing conditions in both continuous and semibatch mode of operation. Furthermore, the model confirms the observed greater effect of mixing on product particle characteristics in semibatch than in continuous operation. This is thought to be due to direct mixing of the feed solution in semibatch operation with the other component already present in the reactor. The methodology proposed here for the scale-up of precipitation processes is very versatile and computationally efficient. It combines the advantages of both a CFD and a population balance approach without having to solve the equations together, which is currently still impracticable due to the excessive computational demand and simulation time required.
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Heal, Mathew R. "Laser studies of gas phase processes." Thesis, University of Oxford, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.303577.
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Schwede, Dirk Alexander. "Towards a Universal and Integrated Digital Representation of Physical Processes." Thesis, The University of Sydney, 2006. http://hdl.handle.net/2123/1433.
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This thesis describes the exploration and the development of computational means to investigate the behaviour of design objects before they are available for investigation in the physical world. The motivation is to inform the design process about the design object’s performance in order to achieve better – more performance-oriented – design outcomes in the sense of energy efficiency and comfort performance than can be achieved by conventional design techniques. The research is structured into five successive parts. - Concept Development – A review of the objective domains comfort assessment and energy efficiency assessment is conducted and the design process, human design activity and the application of simulation in the architectural domain is discussed in order to identify requirements for the development of computational means for design analysis. Requirements regarding model content, model features and model integration are developed. The main requirements are that a highly integrated, three-dimensional and dynamic representation of physical processes is needed and that a universal and integrated representation is required. - Concept Formulation – Based on the identified requirements, the concept for a model is formulated. In order to achieve a universal and integrated representation of physical processes the concept uses the approach of a constructive language. Space is represented with autonomous spatial elements, called congeneric cells. Interaction between the cells is represented by near- and remote-conjunctions. Physical and geometric self-contained formulations of the model reduce the model input requirements, so that geometric information and simple property specification (material, activity) is sufficient to describe the design object in the model. - Model Development – The concept is formulated in mathematical physical terms based on well known physical laws and building physical models (first-principle approach). Heat and moisture conduction, diffusion of various components and a flow model is formulated as near-conjunction processes. Heat radiation, light and sound are modelled with a radiosity approach as remote-conjunctions. The simulation algorithm, which governs the interaction between the cells in order to represent the behaviour of space, is explained. - Computational Implementation – The concept and the model is tested by implementation of a prototype using C++ and OpenGL on a conventional Pentium 4 notebook. The prototype consists of three parts: user-interface, model translator and simulation engine. The user interface functions as model-input and result-output device. The implementation of the concept and of further model parts is described in detail. - Assessment and Testing – The developed concept and the model, as implemented in the prototype, are tested and assessed against the initially developed requirements. The physical model is assessed in regard to plausibility and accuracy of the representation of the physical phenomena. At the end of the thesis the project is summarized, the achievements of the project’s objectives are discussed critically and issues for future research are suggested. Possible applications of the developed model are listed, and the contributions to the application of computational simulation in the architectural domain, developed in this research, are named. At the current stage the required processing time and high memory requirements prevent implementation of a design assessment system, following the suggested concept, at a useful scale. Also the developed physical models require further refinement and testing. Although the general feasibility of the concept and the model was successfully demonstrated, its implementation in a fully applicable design assessment system based on the universal and integrated representation of physical processes was not achieved at this stage. While detailed description and analysis is given in the body of the thesis, detailed formulations of the work and the developed model are given in the appendix. The body and the appendix together provide a complete picture of the research presented.
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Momot, Konstantin Igorevitch 1970. "Studies of nuclear magnetic relaxation processes in paramagnetic metalloporphyrin complexes." Diss., The University of Arizona, 1998. http://hdl.handle.net/10150/282591.
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Temperature dependence of Nuclear Magnetic Resonance (NMR) chemical shifts and longitudinal and transverse relaxation times (T₁ and T₂) was studied for the pyrrole protons in a number of six-coordinate S = 1/2 iron(III) tetraphenylporphyrin (TPP) and tetramesitylporphyrin (TMP) complexes in the temperature range 190--310 K. In all complexes, temperature behavior of the chemical shifts and relaxation times is consistent with the presence of a low spin - high spin exchange caused by the dissociation of one axial ligand. In symmetric sterically hindered complexes, cyclic exchange induced by the synchronous rotation of axial ligands is also present. In all complexes, T₂s are considerably shorter than T₁s. Relaxation times in the TMP complexes are generally longer than corresponding values for the TPP complexes. Estimate of the electronic T₁ is given and mechanisms of nuclear relaxation are discussed. The rate of NOE buildup for a pair of pyrrole protons in [TMPFe(2-MeImH)₂]⁺ was measured; it is consistent with the Stokes rotational correlation time. A method is proposed to predict the detectability and optimum detection conditions of NOE between a pair of structurally rigid protons in similar complexes. Contrary to previous studies, no NOE is detected between pyrrole protons of two unsymmetrically substituted bis-N-methylimidazole Fe(III) TPP complexes. Two NMR approaches were utilized to measure the rate constant of axial ligand rotation in the TMP complex. Saturation transfer measurements yield overestimated rate constant. The measurement based on the temperature dependence of the T₂s(ΔH‡ = 48 ± 1 kJ/mol, ΔS‡ = -10 ± 6 J/K · mol) is consistent with previous studies. Modified MM2 potentials were also used to study the rotation of axial ligands in [TMPFe(1,2-Me₂Im)₂]⁺ and [TPPFe(1-MeIm)₂]⁺. Adiabatic potential energy surfaces (PES) for rotation of axial ligands were constructed for both complexes. Synchronous rotation of the axial ligands (ΔH‡ = 48 kJ/mol) is highly preferable in the TMP complex. For the TPP complex, the enthalpy barriers to synchronous and asynchronous rotation are 3.3 and 5.4 kJ/mol, respectively. The relationship between the orientation of axial ligands, distortion of metalloporphyrin core from planarity, and the bulkiness of axial ligands and porphyrin substituents is discussed.
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Kraljic, Katarina. "Links between galaxy evolution, morphology and internal physical processes." Thesis, Paris 11, 2014. http://www.theses.fr/2014PA112286/document.
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Cette thèse a pour but de faire le lien entre l’évolution des galaxies, leur morphologie et les processus physiques internes, notamment la formation stellaire comme le résultat du milieu interstellaire turbulent et multiphase, en utilisant les simulations cosmologiques zoom-in, les simulations des galaxies isolées et en interaction, et le modèle analytique de la formation stellaire. Dans le chapitre 1, j’explique la motivation pour cette thèse et je passe brièvement en revue le contexte nécessaire lié à la formation des galaxies et la modélisation en utilisant les simulations numériques. Tout d’abord, j’explore l’évolution de la morphologie des galaxies du type de la Voie Lactée dans la série des simulations cosmologiques zoom-in à travers l’analyse des barres. J’analyse l’évolution de la fraction des barres avec le redshift, sa dépendance en fonction de la masse stellaire et l’histoire d’accrétion de galaxies individuelles. Je montre en particulier, que la fraction de barres décroit avec le redshift croissant, en accord avec les observations. Ce travail montre également que les résultats obtenus suggèrent que l’époque de la formation des barres correspond à la transition entre une phase précoce “violente” de la formation de galaxies spirales à z > 1, pendant laquelle elles sont souvent perturbées par les fusions avec les galaxies de masse comparable ou par multiple fusions avec les galaxies de petite masse, mais aussi les instabilités violentes de disque, et une phase "séculaire" tardive à z < 1, quand la morphologie finale est généralement stabilisée vers une structure dominée par le disque. Cette analyse est présentée dans le chapitre 2. Étant donné que ces simulations cosmologiques forment trop d'étoiles trop tôt par rapport aux populations de galaxies observées, je me concentre dans le chapitre 3 sur la formation stellaire dans un échantillon de simulation de galaxies en isolation, à bas redshift, et à résolution du parsec et sous-parsec. J'étudie l'origine physique de leurs relations de formation stellaire avec les cassures, et montre que le seuil de densité surfacique pour une formation stellaire efficace peut être lié à la densité caractéristique d'apparition de turbulence supersonique. Ce résultat s'applique aussi bien aux galaxies qui fusionnent, dans lesquelles l'augmentation de la turbulence compressive déclenchée par les marées compressives les conduit au régime de sursaut de formation d'étoiles. Un modèle analytique idéalisé de formation stellaire liant la densité surfacique de gaz au taux de formation stellaire comme une fonction de la présence de turbulence supersonique et la structure associée du milieu interstellaire est ensuite présenté dans le chapitre 4. Ce modèle prédit une cassure à basse densité de surface qui est suivie par un régime de loi de puissance à haute densité dans différents systèmes en accord avec les relations de formation stellaire des galaxies observées et simulées. La dernière partie de cette thèse est dédiée à la technique alternative de zoom-in cosmologique (Martig et al. 2009) et son implémentation dans le code à raffinement de maillage adaptatif RAMSES. Dans le chapitre 5, je présente les caractéristiques de base de cette technique aussi bien que certains de nos tout premiers résultats dans le contexte de l'accrétion cosmologique diffuseThis thesis aims at making the link between galaxy evolution, morphology and internal physical processes, namely star formation as the outcome of the turbulent multiphase interstellar medium, using the cosmological zoom-in simulations, simulations of isolated and merging galaxies, and the analytic model of star formation. In Chapter 1, I explain the motivation for this thesis and briefly review the necessary background related to galaxy formation and modeling with the use of numerical simulations. I first explore the evolution of the morphology of Milky-Way-mass galaxies in a suite of zoom-in cosmological simulations through the analysis of bars. I analyze the evolution of the fraction of bars with redshift, its dependence on the stellar mass and accretion history of individual galaxies. I show in particular, that the fraction of bars declines with increasing redshift, in agreement with the observations. This work also shows that the obtained results suggest that the bar formation epoch corresponds to the transition between an early "violent" phase of spiral galaxies formation at z > 1, during which they are often disturbed by major mergers or multiple minor mergers as well as violent disk instabilities, and a late "secular" phase at z < 1, when the final morphology is generally stabilized to a disk-dominated structure. This analysis is presented in Chapter 2. Because such cosmological simulations form too many stars too early compared to observed galaxy populations, I shift the focus in Chapter 3 to star formation in a sample of low-redshift galaxy simulations in isolation at parsec and sub-parsec resolution. I study the physical origin of their star formation relations and breaks and show that the surface density threshold for efficient star formation can be related to the typical density for the onset of supersonic turbulence. This result holds in merging galaxies as well, where increased compressive turbulence triggered by compressive tides during the interaction drives the merger to the regime of starbursts. An idealized analytic model for star formation relating the surface density of gas and star formation rate as a function of the presence of supersonic turbulence and the associated structure of the ISM is then presented in Chapter 4. This model predicts a break at low surface densities that is followed by a power-law regime at high densities in different systems in agreement with star formation relations of observed and simulated galaxies. The last part of this thesis is dedicated to the alternative cosmological zoom-in technique Martig et al. 2009 and its implementation in the Adaptive Mesh Refinement code RAMSES. In Chapter 5, I will present the basic features of this technique as well as some of our very first results in the context of smooth cosmological accretion
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Waring, Michael J. "Gatekeeping processes : grounded theory, young people and physical activity." Thesis, Loughborough University, 1995. https://dspace.lboro.ac.uk/2134/7158.
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This thesis has two purposes: firstly, to develop grounded theory methodology and secondly, to apply it in order to establish and further investigate those processes which structure young peoples' participation in physical activity. To satisfy the first of these aims, the Helix Model was created to provide a systematic framework to the grounded theory analysis. This Model was then employed to address the second aim, as it was used to analyse interviews conducted with a mixed sex sample of twenty nine very active and very inactive children and their parents. These young people were selected as a result of completing, on four occasions, a 24 hour self-report questionnaire specifically designed for them. The grounded theory analysis identified a series of interrelated 'gatekeeping processes' which construct those opportunities for young people to participate in physical activity. Several evolving processes, varying according to the context and nature of the physical activity, interrelate with one another to create a complex causal web. The gatekeeping processes are consciously, as well as unconsciously, manipulated relative to the social and physical context in which the young person and the other gatekeeping agents (parents, school, peers) exist and find themselves. The interrelationships between these agents, especially the young person and their parents, work through compromise and coercion to satisfy each of their personal agendas. The nature of each agenda is based on the definition associated with the three roles which gatekeepers adopt (guardian, facilitator, enforcer). The definition of each role affects the manner in which young people individually, as well as collectively with the gatekeepers, construct networks to accomplish an evolving combination of: independence, maximisation of the available resources, rewards, and care and control. The interrelationship between these factors and the extent to which participation in physical activity can achieve them, is what determines the likelihood of the young person's participation in that activity. However, physical activity has to compete with a myriad of the other activities the young person is involved in. These are activities, which for the more sedentary young person, are perceived to be more successful at providing the desired rewards.
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Greenhough, John. "Signatures of highly-correlated processes in complex physical systems." Thesis, University of Warwick, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.397525.
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Saffin, Leo John. "Linking weather forecast errors with the physical processes responsible." Thesis, University of Reading, 2017. http://centaur.reading.ac.uk/74257/.
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Progress in numerical weather prediction (NWP) is made through better understand¬ing of the physical processes represented in numerical models and their impacts on the dynamics of large-scal~ weather systems. Here, potential vorticity (PV) tracer diagnostics are used to investigate the representation of processes in the Met Office Unified Model (MetG:l1). An exact budget of the PV tracers is derived and a "dynamics-tracer inconsistency" diagnostic implemented to quantify non-conservation of PV by the dynamical core which was not previously accounted for. It is shown that non-conservation of PV by the dy¬namical core can have comparable tendencies to the dominant physical processes implying that non-conservation of PV by a dynamical core can, and should, be quantified alongside PV modification by physical processes. Recent work has shown that the sharpness of the extratropical tropopause declines with lead time in KWP models. In the MetUM, the advection scheme is shown to result in an exponential decay of tropopause sharpness and non-conservative processes are shown to sharpen the tropopause. The systematic errors in tropopause-level PV are comparable to the tendencies associated with physical processes, suggesting that the systematic error in tropopause sharpness could be significantly rednced through realistic adjustments to the model physics. I' Turbulent mixing within the boundary layer has been previously shown to produce positive PV anomalies that can be advected into cyclones and reduce growth rates through an increase in static stability; however, it is unclear whether N\VP models correctly represent this mechanism. In the MetUM, the generation of these positive PV anomalies is found to be less clear due to large cancellations with other physical processes in the cold sector. Front-relative compositing .is used to separate the cold and warm sectors, providing the basis for investigating PV generation in the boundary layer systematically by compositing over many fronts.
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Deering, Scott E. (Scott Earl) 1967. "Mathematical and physical modeling of flip-chip soldering processes." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/11115.
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El, Aouni Anass. "Lagrangian coherent structures and physical processes of coastal upwelling." Thesis, Bordeaux, 2019. http://www.theses.fr/2019BORD0146.
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L’étude des processus physiques d’un système d’upwelling est essentielle pour comprendre sa variabilité actuelle et ses changements passés et futurs. Cette thèse présente une étude interdisciplinaire du système d’upwelling côtier à partir de différentes données acquises par satellite, l’accent étant mis principalement sur le système d’upwelling d’Afrique du Nord-Ouest (NWA). Cette étude interdisciplinaire aborde (1) le problème de l’identification et de l’extraction automatiques du phénomène d’upwelling à partir d’observations satellitaires biologiques et physiques. (2) Une étude statistique de la variation spatio-temporelle de l’upwelling de la NWA tout au long de son extension et de ses différents indices d’upwelling. (3) Une étude des relations non linéaires entre le mélange de surface et l’activité biologique dans les régions d’upwelling. (4) études lagrangiennes de tourbillons cohérents; leurs propriétés physiques et identification automatique. (5) L’étude des transports effectués par les tourbillons lagrangiens de la NWA Upwelling et leur impact sur l’océanStudying physical processes of an upwelling system is essential to understand its present variability and its past and future changes. This thesis presents an interdisciplinary study of the coastal upwelling system from different satellite acquired data, with the main focus placed on the North West African (NWA) upwelling system. This interdisciplinary study covers (1) the problem of the automatic identification and extraction of the upwelling phenomenon from biological and physical satellite observations. (2) A statistical study of the spatio-temporal variation of the NWA upwelling throughout its extension and different upwelling indices. (3) A Study of the nonlinear relationships between the surface mixing and biological activity in the upwelling regions. (4) Lagrangian studies of coherent eddies; their physical properties and automatic identification. (5) The study of transport made by Lagrangian eddies off the NWA Upwelling and their impact on the open ocean. [...]
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Collins, Charine. "The dynamics and physical processes of the Comoros Basin." Doctoral thesis, University of Cape Town, 2013. http://hdl.handle.net/11427/6467.
Full textAbstract:
Includes abstract.Includes bibliographical references.
The main objective of this thesis was to investigate the circulation in the ComorosBasin using observed and model datasets. These data were used to establish whether or not a Comoros Gyre exists and to investigate the nature of the eddy variability in the basin.The water masses in the Comoros Basin emulate those found further south in the Mozambique Channel. The presence of AAIW north of Madagascar confirmed that this water mass enters the Comoros Basin from the east while the presence of North Atlantic Deep Water showed that this water mass is capable of spreading northward over the Davie Ridge. The main currents in the Comoros Basin, the westward flowing NEMC and a poleward current along the western boundary, are under the influence of the monsoon winds. The NEMC intensifies during the Southwest monsoon in response to a strong wind jet which develops off the northern tip of Madagascar, whereas the poleward current weakens due to the opposing force imposed by the southwesterlies. Additionally, the circulation in the basin consist of meso-scale eddies of both polarities. Anti-cyclonic eddies, with lifespans of
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Tedesco, Letizia <1978>. "Modelling coupled physical-biogeochemical processes in ice-covered oceans." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2009. http://amsdottorato.unibo.it/1996/1/letizia_tedesco_phd_thesis.pdf.
Full textAbstract:
The last decades have seen a large effort of the scientific community to study and understand the physics of sea ice. We currently have a wide - even though still not exhaustive - knowledge of the sea ice dynamics and thermodynamics and of their temporal and spatial variability. Sea ice biogeochemistry is instead largely unknown. Sea ice algae production may account for up to 25% of overall primary production in ice-covered waters of the Southern Ocean. However, the influence of physical factors, such as the location of ice formation, the role of snow cover and light
availability on sea ice primary production is poorly understood. There are only sparse localized observations and little knowledge of the functioning of sea ice biogeochemistry at larger scales.
Modelling becomes then an auxiliary tool to help qualifying and quantifying the role of sea ice biogeochemistry in the ocean dynamics. In this thesis, a novel approach is used for the modelling and coupling of sea ice biogeochemistry - and in particular its primary production - to sea ice physics. Previous attempts were based on the coupling of rather complex sea ice physical models to empirical or relatively simple biological or biogeochemical models. The focus is moved here to a more biologically-oriented point of view. A simple, however comprehensive, physical model of the sea ice thermodynamics (ESIM) was developed and coupled to a novel sea ice implementation (BFM-SI) of the Biogeochemical Flux Model (BFM). The BFM is a comprehensive model, largely used and validated in the open ocean environment and in regional seas. The physical model has been developed having in mind the biogeochemical properties of sea ice and the physical inputs required to model sea ice biogeochemistry. The central concept of the coupling is the modelling of the Biologically-Active-Layer (BAL), which is the time-varying fraction of sea ice that is continuously connected to the ocean via brines pockets and channels and it acts as rich habitat for many microorganisms. The physical model provides the key physical properties of the BAL (e.g., brines volume, temperature and salinity), and the BFM-SI simulates the physiological and ecological response of the biological community to the physical enviroment. The new biogeochemical model is also coupled to the pelagic BFM through the exchange of organic and inorganic matter at the boundaries between the two systems . This is done by computing the entrapment of matter and gases when sea ice grows and release to the ocean when sea ice melts to ensure mass conservation. The model was tested in different ice-covered regions of the world ocean to test the generality of the parameterizations. The focus was particularly on the regions of landfast ice, where primary production is generally large. The implementation of the BFM in sea ice and the coupling structure in General Circulation Models will add a new component to the latters (and in general to Earth System Models), which will be able to provide adequate estimate of the role and importance of sea ice biogeochemistry in the global carbon cycle.
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Tedesco, Letizia <1978>. "Modelling coupled physical-biogeochemical processes in ice-covered oceans." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2009. http://amsdottorato.unibo.it/1996/.
Full textAbstract:
The last decades have seen a large effort of the scientific community to study and understand the physics of sea ice. We currently have a wide - even though still not exhaustive - knowledge of the sea ice dynamics and thermodynamics and of their temporal and spatial variability. Sea ice biogeochemistry is instead largely unknown. Sea ice algae production may account for up to 25% of overall primary production in ice-covered waters of the Southern Ocean. However, the influence of physical factors, such as the location of ice formation, the role of snow cover and light
availability on sea ice primary production is poorly understood. There are only sparse localized observations and little knowledge of the functioning of sea ice biogeochemistry at larger scales.
Modelling becomes then an auxiliary tool to help qualifying and quantifying the role of sea ice biogeochemistry in the ocean dynamics. In this thesis, a novel approach is used for the modelling and coupling of sea ice biogeochemistry - and in particular its primary production - to sea ice physics. Previous attempts were based on the coupling of rather complex sea ice physical models to empirical or relatively simple biological or biogeochemical models. The focus is moved here to a more biologically-oriented point of view. A simple, however comprehensive, physical model of the sea ice thermodynamics (ESIM) was developed and coupled to a novel sea ice implementation (BFM-SI) of the Biogeochemical Flux Model (BFM). The BFM is a comprehensive model, largely used and validated in the open ocean environment and in regional seas. The physical model has been developed having in mind the biogeochemical properties of sea ice and the physical inputs required to model sea ice biogeochemistry. The central concept of the coupling is the modelling of the Biologically-Active-Layer (BAL), which is the time-varying fraction of sea ice that is continuously connected to the ocean via brines pockets and channels and it acts as rich habitat for many microorganisms. The physical model provides the key physical properties of the BAL (e.g., brines volume, temperature and salinity), and the BFM-SI simulates the physiological and ecological response of the biological community to the physical enviroment. The new biogeochemical model is also coupled to the pelagic BFM through the exchange of organic and inorganic matter at the boundaries between the two systems . This is done by computing the entrapment of matter and gases when sea ice grows and release to the ocean when sea ice melts to ensure mass conservation. The model was tested in different ice-covered regions of the world ocean to test the generality of the parameterizations. The focus was particularly on the regions of landfast ice, where primary production is generally large. The implementation of the BFM in sea ice and the coupling structure in General Circulation Models will add a new component to the latters (and in general to Earth System Models), which will be able to provide adequate estimate of the role and importance of sea ice biogeochemistry in the global carbon cycle.
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Casadei, Roberto <1990>. "Engineering Self-Adaptive Collective Processes for Cyber-Physical Ecosystems." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2020. http://amsdottorato.unibo.it/9380/3/casadei_roberto_tesi.pdf.
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The pervasiveness of computing and networking is creating significant opportunities for building valuable socio-technical systems. However, the scale, density, heterogeneity, interdependence, and QoS constraints of many target systems pose severe operational and engineering challenges. Beyond individual smart devices, cyber-physical collectives can provide services or solve complex problems by leveraging a “system effect” while coordinating and adapting to context or environment change. Understanding and building systems exhibiting collective intelligence and autonomic capabilities represent a prominent research goal, partly covered, e.g., by the field of collective adaptive systems. Therefore, drawing inspiration from and building on the long-time research activity on coordination, multi-agent systems, autonomic/self-* systems, spatial computing, and especially on the recent aggregate computing paradigm, this thesis investigates concepts, methods, and tools for the engineering of possibly large-scale, heterogeneous ensembles of situated components that should be able to operate, adapt and self-organise in a decentralised fashion. The primary contribution of this thesis consists of four main parts. First, we define and implement an aggregate programming language (ScaFi), internal to the mainstream Scala programming language, for describing collective adaptive behaviour, based on field calculi. Second, we conceive of a “dynamic collective computation” abstraction, also called aggregate process, formalised by an extension to the field calculus, and implemented in ScaFi. Third, we characterise and provide a proof-of-concept implementation of a middleware for aggregate computing that enables the development of aggregate systems according to multiple architectural styles. Fourth, we apply and evaluate aggregate computing techniques to edge computing scenarios, and characterise a design pattern, called Self-organising Coordination Regions (SCR), that supports adjustable, decentralised decision-making and activity in dynamic environments.Con lo sviluppo di informatica e intelligenza artificiale, la diffusione pervasiva di device computazionali e la crescente interconnessione tra elementi fisici e digitali, emergono innumerevoli opportunità per la costruzione di sistemi socio-tecnici di nuova generazione. Tuttavia, l'ingegneria di tali sistemi presenta notevoli sfide, data la loro complessità—si pensi ai livelli, scale, eterogeneità, e interdipendenze coinvolti. Oltre a dispositivi smart individuali, collettivi cyber-fisici possono fornire servizi o risolvere problemi complessi con un “effetto sistema” che emerge dalla coordinazione e l'adattamento di componenti fra loro, l'ambiente e il contesto. Comprendere e costruire sistemi in grado di esibire intelligenza collettiva e capacità autonomiche è un importante problema di ricerca studiato, ad esempio, nel campo dei sistemi collettivi adattativi. Perciò, traendo ispirazione e partendo dall'attività di ricerca su coordinazione, sistemi multiagente e self-*, modelli di computazione spazio-temporali e, specialmente, sul recente paradigma di programmazione aggregata, questa tesi tratta concetti, metodi, e strumenti per l'ingegneria di ensemble di elementi situati eterogenei che devono essere in grado di lavorare, adattarsi, e auto-organizzarsi in modo decentralizzato. Il contributo di questa tesi consiste in quattro parti principali. In primo luogo, viene definito e implementato un linguaggio di programmazione aggregata (ScaFi), interno al linguaggio Scala, per descrivere comportamenti collettivi e adattativi secondo l'approccio dei campi computazionali. In secondo luogo, si propone e caratterizza l'astrazione di processo aggregato per rappresentare computazioni collettive dinamiche concorrenti, formalizzata come estensione al field calculus e implementata in ScaFi. Inoltre, si analizza e implementa un prototipo di middleware per sistemi aggregati, in grado di supportare più stili architetturali. Infine, si applicano e valutano tecniche di programmazione aggregata in scenari di edge computing, e si propone un pattern, Self-Organising Coordination Regions, per supportare, in modo decentralizzato, attività decisionali e di regolazione in ambienti dinamici.
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Coleby, Susan Elizabeth. "Reactions and rate processes in supercritical fluids." Thesis, University of Leeds, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.305609.
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Lo, Dixon. "Experiential Augmentation: Representing Invisible Digital Processes with Intuitive Physical Properties." Research Showcase @ CMU, 2017. http://repository.cmu.edu/theses/117.
Full textAbstract:
As we move toward a world of ubiquitous computing, it is important to think about how computing should communicate with us when it is distributed in our environment. Designers of ubiquitous computing will meet two challenges. The first is the challenge of invisibility, technology will have to find new ways to communicate with us without the advantage of smartphone or desktop screens. The second challenge is that of calmness, ubiquitous technology must communicate in a way that doesn’t overwhelm the user. This thesis shows that one possible way to meet the two challenges is for computing to communicate in a way similar to the language of objects in our environment. Our environment communicates with a qualitative and experiential language. Thus, this thesis studies the simulation of experiential physical phenomena in augmented reality, to give representation to invisible processes in objects. To explore this direction of augmented reality, a body of twenty one experiments were created and tested with participants. Participant interpretations of experiential augmentations were then gathered and distilled into a three-pointed model for categorization. The study ends with a series of recommendations for designers interested in pursuing similar types of object augmentation.
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Grue, Nathalie. "Illustration, explanation and navigation of physical devices and design processes." Thesis, Georgia Institute of Technology, 1994. http://hdl.handle.net/1853/9228.
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Barker, Hugh Richard. "Physical modelling of construction processes in the mini-drum centrifuge." Thesis, University of Cambridge, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.445548.
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Dixon, Christopher Mark. "Modelling and simulation of physical processes occuring in circuit breakers." Thesis, University of Liverpool, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.544370.
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Tharakan, Ajay. "Modelling of physical and chemical processes in the small intestine." Thesis, University of Birmingham, 2009. http://etheses.bham.ac.uk//id/eprint/330/.
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Chemical and physical processing in the small intestine is an important step for food digestion and absorption. Having reviewed the literature, a relevant model has been developed which enabled investigation into the fluid flow, mixing mechanisms and delivery of nutrients to the wall of the model small intestine. Designing, developing and using the Small Intestinal Model (SIM), a physical model of a section of the small intestine, mimicking the physiological contractions, allowed mass transfer to be measured using different process conditions and ingredients. Experiments were carried out using the SIM to study mass transfer, starch digestion and flow visualisation. While simulating the small intestinal flow profile, experiments have shown that the functional ingredient guar gum reduces the mass transfer coefficient of the model nutrient riboflavin. This together with computational modelling suggests an explanation for the observed functionality of guar gum to reduce the peak increase in blood glucose levels after ingestion of test meals. Industrial implications are to give a scientific and engineered design methodology for novel food formulations by understanding the food product behaviour in the SIM. Optimisation of formulation candidates going to the human trial stage and improvement of speed to market of new product introductions is intended.
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Moore, Christopher Mark. "Small scale physical processes and phytoplankton growth in shelf seas." Thesis, University of Southampton, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.394103.
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Raman, Dhruva Venkita. "On the identifiability of highly parameterised models of physical processes." Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:f58aa335-db0a-495b-8eef-1ddb363cbd19.
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This thesis is concerned with drawing out high-level insight from otherwise complex mathematical models of physical processes. This is achieved through detailed analysis of model behaviour as constituent parameters are varied. A particular focus is the well-posedness of parameter estimation from noisy data, and its relationship to the parametric sensitivity properties of the model. Other topics investigated include the verification of model performance properties over large ranges of parameters, and the simplification of models based upon their response to parameter perturbation. Several methodologies are proposed, which account for various model classes. However, shared features of the models considered include nonlinearity, parameters with considerable scope for variability, and experimental data corrupted by significant measurement uncertainty. We begin by considering models described by systems of nonlinear ordinary differen- tial equations with parameter dependence. Model output, in this case, can only be obtained by numerical integration of the relevant equations. Therefore, assessment of model behaviour over tracts of parameter space is usually carried out by repeated model simulation over a grid of parameter values. We instead reformulate this as- sessment as an algebraic problem, using polynomial programming techniques. The result is an algorithm that produces parameter-dependent algebraic functions that are guaranteed to bound user-defined aspects of model behaviour over parameter space. We then consider more general classes of parameter-dependent model. A theoretical framework is constructed through which we can explore the duality between model sensitivity to non-local parameter perturbations, and the well-posedness of parameter estimation from significantly noisy data. This results in an algorithm that can uncover functional relations on parameter space over which model output is insensitive and parameters cannot be estimated. The methodology used derives from techniques of nonlinear optimal control. We use this algorithm to simplify benchmark models from the systems biology literature. Specifically, we uncover features such as fast-timescale subsystems and redundant model interactions, together with the sets of parameter values over which the features are valid. We finally consider parameter estimation in models that are acknowledged to im- perfectly describe the modelled process. We show that this invalidates standard statistical theory associated with uncertainty quantification of parameter estimates. Alternative theory that accounts for this situation is then developed, resulting in a computationally tractable approximation of the covariance of a parameter estimate with respect to noise-induced fluctuation of experimental data.
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McKinley, Stephen Peter. "Physical chemical processes and environmental impacts associated with home composting." Thesis, University of Southampton, 2008. https://eprints.soton.ac.uk/73701/.
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This thesis reports on experimental and modelling work carried out in order to make quantitative estimates on the environmental impacts of home composting. The focus of the work was climate relevant gaseous emissions, and developing and utilising a methodology for quantifying them. Experiments using 220L open bottomed home compost bins, alongside purpose built 200L composting reactors with airflow control were performed. A variety of composting conditions were tested, using different compositions of garden and kitchen wastes. The experiments were monitored for headspace gas composition, including CO2, O2, NH3, N2O, CH4 and volatile organic compounds, as well as temperature, humidity, moisture and solids losses and pH. From the CO2 emission rates calculated from the reactor experiments, theoretical analysis and modelling and airflow pathway tests on home compost bins, it was concluded that molecular diffusion, rather than bulk convective flow, is the dominant gas transfer mechanism from home compost bins. There were no detected emissions of N2O but emissions of NH3 up to 16 g/T feed. Only a few cases of CH4 emission were detected, typically in the first 2-3 days following a feed addition, with the highest single concentration measured at 86 ppm within the headspace. The total anthropogenic greenhouse gas emissions from home composting were estimated as between 3 and 12 Kg CO2E/Tw with almost 90% coming from the lifecycle of the compost bin. This compares with between 20 and 56 Kg CO2E/Tw from centralised facilities, at least more than double that for home composting. Total anthropogenic CO2-equivalent emissions from home composting in the UK in 2008 were estimated to be in the region of 7 thousand tonnes CO2E.
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Morgan, Kevin. "Effects of teaching behaviours on motivational processes in physical education." Thesis, Cardiff Metropolitan University, 2005. http://hdl.handle.net/10369/7578.
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This thesis comprises of a collection of four research studies in the area of motivational climate in physical education (PE). In the first study, a computer based observational measure of the teaching behaviours that influence motivational climate (TARGET) was developed and the degree of congruence between the observational measure and pupils' and teachers' subjective perceptions of the motivational climate was evaluated. Results revealed mastery and performance involving teaching behaviours, congruency between teaching behaviours and subjective perceptions of the climate, and significant differences between teachers' and pupils' perceptions of the motivational climate. The second study further validated the measure of teaching behaviours by comparing teacher behaviours and pupils' perceptions of the motivational climate in a cross-cultural study. Results indicated significantly higher levels of performance involving teaching behaviours and higher levels of a perceived performance climate in Singapore compared to the UK. Based on findings related to the authority structure in the cross-cultural study, the third study examined the effects of different teaching styles on the TARGET behaviours and pupils' focus group responses in PE lessons in the UK. Results revealed that pupil-centred teaching styles resulted in more mastery involving teaching behaviours and more adaptive motivational responses than the more teacher-centred style. Based on these findings, the final study instigated a mastery intervention programme for teacher education based on self-observation of filmed PE lessons and evaluated its effect on the TARGET behaviours, pupils' perceptions of the motivational climate and cognitive and affective responses. The mastery intervention programme was successful in fostering more mastery involving teaching behaviours. Contrary to the hypothesis, pupils' perceptions of the motivational climate were more performance involved post-intervention, which may have been due to the public nature of the recognition and evaluation of effort and improvement (mastery coded). Further, results revealed that low affect pupils significantly increased their cognitive and affective responses from pre- to post-intervention.
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Chevance, Mélanie. "Physical processes in the interstellar medium of the Magellanic Clouds." Thesis, Sorbonne Paris Cité, 2016. http://www.theses.fr/2016USPCC242/document.
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Le milieu interstellaire (MIS) joue un rôle important dans l'évolution des galaxies. Les radiations et vents stellaires, ainsi que les supernovae par exemple, sont à l'origine de nombreux processus ayant un impact sur les propriétés globales des galaxies. Cependant, l'efficacité des ces processus est liée aux propriétés et à la structure des différentes phases du MIS, et est souvent incertaine. Grace à la sensibilité et résolution accrues des nouveaux télescopes observant dans l'infrarouge lointain (FIR) et le submillimetrique (comme par exemple le Herschel Space Observatory, SOFIA et ALMA), il est désormais possible d'étudier en détail les interactions réciproques entre la formation stellaire et les différentes phases du MIS environnant. Ce travail est axé sur les propriétés physiques du gaz dans les Nuages de Magellan. Le Grand Nuage de Magellan et le Petit Nuage de Magellan, nos plus proches voisins, tout deux à métallicité sub-solaire, sont de bons laboratoires pour étudier les interactions entre la formation stellaire et l'environnement. La région 30 Doradus, dans le Grand Nuage de Magellan, l'une des plus massives et des plus actives régions de formation stellaire connues dans notre voisinage, est étudiée en détail. Les observations des télescopes spatiaux Herschel et Spitzer sont utilisées pour contraindre la pression, le champ de radiation ainsi que la structure tri-dimensionnelle des régions de photo-dissociation (PDR), en combinaison avec le code PDR de Meudon. Cette modélisation permet également d'estimer la fraction de gaz moléculaire qui n'est pas détectée par le traceur généralement utilisé CO. Cette méthode est ensuite appliquée à d'autres régions de formation stellaire dans les Nuages de Magellan, présentant différents environnements. Cette étude permet d'évaluer les diagnostiques clés du chauffage et du refroidissement du gaz à faible métallicité dans des régions actives de formation stellaire, avec une bonne résolution spatiale. Ceci constitue une première étape pour mieux comprendre les observations non résolues de telles régions dans des galaxies lointainesThe interstellar medium (ISM) plays a major role in galaxy evolution. Feedback from stars, in particular, drives several processes responsible for the global properties of a galaxy. However, the efficiency of these processes is related to the properties and structure of the different gas and dust ISM phases and remains uncertain. Due to the increased sensitivity and resolution of the new far-infrared (FIR) and submillimeter facilities (such as the Herschel Space Observatory, SOFIA and ALMA, in particular), it now becomes possible to study in detail the interplay between star formation and the surrounding ISM phases. This work focuses on the physical properties of the gas in the Magellanic Clouds. The Large Magellanic Cloud and the Small Magellanic Cloud, our closest neighbors, both at subsolar metallicity, are good laboratories to study the interaction between star formation and environment.The 30 Doradus region, in the Large Magellanic Cloud, one of the most massive and active star forming region known in our neighborhood, is first studied in detail. We use the FIR and mid-infrared tracers, provided by the space telescopes Herschel and Spitzer, to bring constrains on the pressure, radiation field and 3D structure of the photo-dissociation regions (PDR) in this extreme region, using the Meudon PDR code. This modeling allows us to estimate the fraction of molecular gas not traced by CO, also known as the "CO-dark" molecular gas.We apply this method to other star forming regions of the Magellanic Clouds, which are characterized by different environmental conditions. This study allows us to evaluate key diagnostics of the gas heating and cooling of low metallicity resolved starburst regions. This is a first step toward understanding similar but unresolved regions, in high-redshift galaxies
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RAFFONE, FEDERICO. "Physical processes and materials in memristive devices: a theoretical study." Doctoral thesis, Politecnico di Torino, 2017. http://hdl.handle.net/11583/2667596.
Full textAbstract:
Memristors are ideal devices able to switch among different resistive states and to retain the most recent one even if the input voltage is removed. With such a characteristic memristors would be able to mimic the brain functions or to behave as universal memory device. The existence of the memristor was theorized by Leon Chua in 1971 but only in 2008 a first prototype device based on the use of an oxide layer was realized, later addressed as a redox-based resistance (switching) random access memory (RRAM). Since its discovery, scientists have been working to understand the mechanism behind the device switching and to eliminate the intrinsic device failures and poor reproducibility, that differentiate the real RRAM from the ideal memristor and that prevent its application in circuitry.
There exist two main memristor designs, the valence change memory cell (VCM) and the electrochemical metallization memory cell (ECM). These devices rely both on the switching between a high resistance state (HRS) and a low resistance state (LRS) through the application of a high voltage. Along the same two electric terminals that led to the switching, the resistance state is measured by means of a low voltage.
Aim of thesis is to study the yet unclear RRAM physical processes and switching mechanisms in order to pave the way for overcoming existing device weak points. In particular, in the first part we focused on understanding the mechanism of the most basic realization of a VCM memristor, i.e. the thin-film based one. Afterwards, we explained some controversial experimental results on more advanced ECM memristors, namely nanowire-based devices, revising the applicability of currently established conventional theories and proposing an alternative operational mechanism. Finally, we presented the stability and the electrical properties of a new two-dimensional material, i.e. MoS2, which could be applied in the memristive field.
In thin-film based VCM devices, it is argued that the resistance switching occurs due to the motion of crystallographic defects under the effect of an electric field. These defects locally dope the insulating oxide increasing its conductivity. Once a filament of stacked defects connects the two electrodes an abrupt change in current is measured externally. Nevertheless, not much it is known about the atomistic nature of the switching, even less about its link with measurable external quantities such as total current. In this thesis work, we proposed a mixed continuum and Kinetic Monte Carlo (KMC) simulation to take into account both atomic-level properties, like defect diffusivity, and macroscopic quantities like internal temperature and overall device current. Thanks to this combination of computational methods, temperature can dynamically change during the course of the simulation. Results show how the height of defect diffusion barrier influences the switching mechanism. When the barriers are low (≈0.4 eV) the defects move as soon as the voltage is applied and correspondingly the device switching is fast, however at room temperature the resistance state is volatile. By contrast, if the barriers are relatively high (≈1.1 eV) the oxide has first to heat up in order for the defects to have enough energy to overcome the barriers. Therefore the temperature, although not generally controlled or explicitly considered in the experiments, plays a fundamental role in the switching. Such a heating stage provides the required state retention for practical applications.
ECM devices are asymmetric structures composed by an electrochemically active electrode like Cu, a thin film that functions as an electrolyte, either a transition metal oxide or a germanium chalcogenide, and an inactive electrode, such as Pt. The switching from HRS to LRS is thought to take place when, due to the high electric field established by the external bias, atoms of the electrochemically active contact dissolve into the insulating oxide or chalcogenide thin film to form a conductive filament with the opposite contact. Recently, nanomaterials, particularly micrometer-long nanowires, have been applied as an insulating layer between the metallic electrodes thanks to the improved endurance and LRS/HRS ratio that they ensure. Surprisingly, in these devices the LRS is achieved even if no continuous filament was detected. By means of Density Functional Theory simulations, we proposed a mechanism valid for Cu/ZnO-NW/Pt devices in which atoms belonging to the electrochemically active electrode (Cu), rather than aggregating into a filament, spread on the surface. Particularly when in form of adatom, the adsorbed Cu dope the NW surface creating a conductive channel. Copper adatoms are easily dragged by electric field once the diffusion barrier is overcome thanks to the polarizing effect of the surface. In absence of an external voltage clustering is hindered by the same barrier. As opposed to this, the atoms from the inactive electrode (Pt), although they are as mobile as the Cu atoms on the NW surface, are extremely hard to extract from the contact therefore they do not participate in the switching process.
Finally, in collaboration with Prof. Jeffrey Grossman at Massachusetts Institute of Technology, we focused our attention on one of the materials that lately has been applied in numerous fields including resistive switching memories: MoS2. Due to its phase-dependent conductivity MoS2 could be applied to RRAM once the control on its phases is achieved. To this aim we proposed a new technique for the stabilization of the metastable metallic MoS2 T-phase over the stable semiconducting MoS2 H-phase by alloying with another metal dichalcogenide, SnS2, existing in the T-phase only. A combined Cluster Expansion and DFT approach was exploited to theoretically predict the phase diagram of MoxSn1-xS2 compounds. Our results show that the addition of impurities efficiently lowers the energetic cost of the MoS2 T-phase, and that alloying is an effective way to tune the TMD electronic properties. In a RRAM made with a MoxSn1-xS2 sheet the electric field may alter the local distribution of substitutional atoms so to induce a phase change only in a small portion of the material and alter the overall resistance state. Additionally, the reported intra-phase metal-semiconductor transition occurring for a slightly doped material could be useful for memristive applications.
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Bézenac, Emmanuel de. "Modeling physical processes with deep learning : a dynamical systems approach." Electronic Thesis or Diss., Sorbonne université, 2021. http://www.theses.fr/2021SORUS203.
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L'apprentissage profond s'impose comme un outil prédominant pour l'IA, avec de nombreuses applications fructueuses pour des taches où les données sont abondantes et l'accès aux connaissances préalables est difficile. Cependant ce n'est pas encore le cas dans le domaine des sciences naturelles, et encore moins pour l'étude des systèmes dynamiques. En effet, ceux-ci font l'objet d'études depuis des siècles, une quantité considérable de connaissances a ainsi été acquise, et des algorithmes et des méthodes ingénieux ont été développés. Cette thèse a donc deux objectifs principaux. Le premier concerne l'étude du rôle que l'apprentissage profond doit jouer dans ce vaste écosystème de connaissances, de théories et d'outils. Nous tenterons de répondre à cette question générale à travers un problème concret: la modélisation de processus physiques complexes à l'aide de l'apprentissage profond. Le deuxième objectif est en quelque sorte son contraire; il concerne l'analyse les algorithmes d'apprentissage profond à travers le prisme des systèmes dynamiques et des processus physiques, dans le but d'acquérir une meilleure compréhension et de développer de nouveaux algorithmes pour ce domaineDeep Learning has emerged as a predominant tool for AI, and has already abundant applications in fields where data is abundant and access to prior knowledge is difficult. This is not necessarily the case for natural sciences, and in particular, for physical processes. Indeed, these have been the object of study since centuries, a vast amount of knowledge has been acquired, and elaborate algorithms and methods have been developped. Thus, this thesis has two main objectives. The first considers the study of the role that deep learning has to play in this vast ecosystem of knowledge, theory and tools. We will attempt to answer this general question through a concrete problem: the one of modelling complex physical processes, leveraging deep learning methods in order to make up for lacking prior knowledge. The second objective is somewhat its converse: it focuses on how perspectives, insights and tools from the field of study of physical processes and dynamical systems can be applied in the context of deep learning, in order to gain a better understanding and develop novel algorithms
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Pritchard, Keith L. "Fundamental processes governing calcite dissolution at high pH." Thesis, University of Oxford, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.238178.
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Shaw, Jonathan. "NMR studies of adsorption processes upon activated carbon." Thesis, Durham University, 1998. http://etheses.dur.ac.uk/4827/.
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This thesis is concerned with the adsorption behaviour of adsorbate molecules upon activated carbon. Limitations in bulk gravimetric measurements mean that the mechanism of adsorption for adsorbates upon carbonaceous materials is poorly characterised. The information obtained from NMR experiments performed upon the adsorbate molecules is applied to provide additional understanding of the adsorption process. A systematic study of a phosphate/phosphonate - adsorbent system is performed, and a theoretical basis for the results observed is discussed in terms of molecular mobility and the penetration of molecules into pores of differing sizes. Calculated pore volumes obtained from NMR data are discussed. It is demonstrated that phosphate and phosphonate molecules adsorb initially within larger pores at the surface of the adsorbent and subsequently progress deeper within the porous volume. The effects of magic-angle spinning and proton decoupling upon the adsorbate spectra obtained are also addressed. Relaxation measurements are used to study the motional freedom of adsorbed molecules and the measurements provide further corroboration to the interpretation of spectra expounded. The study is then extended to analyse the adsorption of adsorbate molecules upon carbon adsorbents with other adsorbate molecules pre-adsorbed. Analysis of spectra provides information upon the movement of both the primarily adsorbed material and secondary adsorbate within the pore volume. Preferential adsorption of phosphate molecules over water molecules is demonstrated. Finally, dynamic NMR techniques are used to characterise the exchange of adsorbate within the porous volume with excess adsorbate upon the exterior of the carbon adsorbent.
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Evans, Nicholas John. "Development of electrochemical techniques for investigating interfacial processes." Thesis, University of Warwick, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.340484.
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Gooding, J. Justin. "The study of interfacial processes using channel electrode systems." Thesis, University of Oxford, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.359440.
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