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Levis, Shirley L. "Transitional objects and phenomena existence and uses across the life span." Click here for text online. The Institute of Clinical Social Work Dissertations website, 1994. http://www.icsw.edu/_dissertations/levis_1994.pdf.
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Dissertation (Ph.D.) -- The Institute for Clinical Social Work, 1994.A dissertation submitted to the faculty of the Institute of Clinical Social Work in partial fulfillment for the degree of Doctor of Philosophy.
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Mielke, Eric. "Study on the Transport Phenomena in Complex Micro-Reactors." Thesis, Université d'Ottawa / University of Ottawa, 2017. http://hdl.handle.net/10393/36040.
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Continuous processing in the pharmaceutical and fine chemical industries, particularly in micro/milli-scale reactors, has been a topic of interest in literature in recent years due to the advantages offered over batch reactions. One such advantage is the enhanced transport properties of operating at smaller scales, although the quantification of the transport phenomena is not straightforward when wall and entrance effects cannot be neglected.
In the first study presented, various micro-mixer geometries and scales were considered to increase the mixing efficiency in liquid-liquid systems of diverse interfacial tensions for fast reactions. The conditions were varied over different flow regimes; including slug flow, parallel flow, and drop flow. A mass-transfer-limited test reaction was used to evaluate the overall volumetric mass transfer coefficients (Korga) as a function of the average rate of energy dissipation (ε) for each mixer design. The onset of drop flow occurred at a lower ε for the LL-Triangle mixer when compared with the Sickle or LL-Rhombus mixers for low interfacial-tension systems (i.e., n-butanol-water). In the drop flow regime for energy dissipation rates of around 20 to 500 W/kg, Korga values ranged from approximatively 0.14 to 0.35 s-1 and 0.004 to 0.015 s-1 for the relatively low and high interfacial-tension (i.e., toluene-water) systems, respectively.
The second investigation explored the heat transfer properties of a FlowPlate® system by Ehrfeld Mikrotechnik BTS. First, in a non-reactive system with rectangular serpentine channels (d_h<1mm, 400
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Thorn, Nathaniel C. "Disappearance and Return: Psychoanalytic Perspectives on the Past." Antioch University / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=antioch1333975762.
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Affede, Giulia. "Donald W. Winnicott’s Transitional Phenomena and the Re-Emergence of the Self in David Foster Wallace’s The Broom of the System and Infinite Jest." Doctoral thesis, Urbino, 2020. http://hdl.handle.net/11576/2674932.
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Jahnke, José Ricardo Riambau. "COMO AS MARCAS INFLUENCIAM NA ESTRUTURAÇÃO PSÍQUICA DO SER HUMANO: UMA VISÃO SOBRE A REDE DE FAST FOOD MCDONALD S." Universidade Federal de Santa Maria, 2013. http://repositorio.ufsm.br/handle/1/10335.
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This master s dissertation comes to meet with our concerns about how is the phenomenon of adherence to brands in behalf of other social valuations traditionally accepted and anchored in the personal skills to interact with their peers than by dictates artificially constructed. We un-derstand that to achieve this goal is to start from a historicity of how a brand is does exist for both chose Network Fast Food McDonald's because of it being positioned as a leading pro-vider of the world's food and have about seventy years of existence. To build our theoretical model we rely primarily on the teachings of psychoanalytic Winnicott and Melanie Klein for the initial training of the human psyche. They argue about the importance of relationships and primal as a sufficiently good environment becomes important to healthy human psychic makeup. We spend the following to influences coming from the food traditions and their complementarity to the structure of the sense of belonging in human identity. Then explore how technological changes in food preservation, resulting in the last century, caused profound changes in human commensal references. Finally we enter the magical world of advertising and how these disciplines, over time, became the major guiding environmental changes more profound and fruitful unprecedented in human civilization. These changes were made primari-ly through the deconstruction of the way of realizing the needs to live well. The dictates is given by the imperative of disposal of products now produced on a large scale. Through this consumerist bias noised, we move from a world guided by the principle of reality where the individual is held to be, to another, now headed by the pleasure principle, where one relativiz-es their existence seem like something that has been mediated by the media, this new modus vivendi everything should be easy and pleasurable to have value.Esta dissertação de mestrado vem ao encontro de nossas inquietações sobre como se dá o fe-nômeno da adesão às marcas em detrimento de outras valorações sociais tradicionalmente aceitas e fundeadas nas habilidades pessoais de interação com seus iguais do que por ditames artificialmente construídos. Entendemos que para alcançarmos este objetivo há de se partir de uma historicidade de como uma marca ser faz existir, para tanto escolhemos a Rede de Fast Food McDonald s em virtude da mesma estar posicionada como uma das maiores fornecedo-ras de alimentos do mundo e ter aproximadamente setenta anos de existência. Para construir-mos nosso modelo teórico nos apoiamos principalmente nos ensinamentos psicanalíticos de Melanie Klein e Winnicott para a formação inicial da psique humana. Estes argumentam so-bre a importância dos relacionamentos primais e de como um ambiente suficientemente bom se faz importante à saudável composição psíquica humana. Passamos a seguir às influências oriundas da tradição alimentar e da sua complementaridade à estruturação do sentido de per-tencimento na identidade humana. Em seguida exploramos de que forma as mudanças tecno-lógicas na conservação dos alimentos, advindas no século passado, ocasionaram alterações profundas nos referenciais comensais do ser humano. Por último adentramos no mundo mági-co da publicidade e propaganda e de como estas disciplinas, ao longo do tempo, tornaram-se as grandes norteadoras das mudanças ambientais mais profundas e profícuas jamais vistas na civilização humana. Estas transformações se fizeram principalmente através da desconstrução do modo de se aperceber as necessidades ao bem viver. Os ditames se deram pelo imperativo de escoar produtos, agora, produzidos em larga escala. Através deste viés consumista propa-lado, passamos de um mundo norteado pelo princípio de realidade onde o indivíduo se realiza em ser, a um outro, capitaneado agora pelo princípio do prazer, onde a pessoa relativiza sua existência em parecer algo que lhe foi mediado pela mídia, neste novo modus vivendi tudo deve ser fácil e prazeroso para ter valor.
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Martin, Adrian Peter. "Cosmological phase transition phenomena." Thesis, University of Cambridge, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.389880.
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Perversi, Giuditta. "Ordering phenomena in iron-containing spinels." Thesis, University of Edinburgh, 2018. http://hdl.handle.net/1842/31242.
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The spinel structure (general formula AB2O4) is widely occurring in natural and synthetic materials, and has a marked technological and scientific significance due to its magnetic, electric and multiferroic behaviours. The presence of transition metal cations with multiple oxidation state and the resulting charge, orbital and spin degrees of freedom of the partially occupied d-orbitals lead to uniquely ordered ground states. The coupling of all the three degrees of freedom can result in a structurally distorted ground state where the direct metal-metal interaction forms atomic clusters, or 'orbital molecules'. The Verwey phase of magnetite (Fe3O4), occurring below TV ~ 125 K, is driven by a cooperative bond distortion that forms linear Fe3+-Fe2+-Fe3+ arrangement (trimeron). The effect of non-stoichiometry and chemical modification on this complex structure has been investigated with a variety of samples through microcrystal synchrotron XRD. A mineral sample (Al, Si, Mg and Mn impurities, TV = 119 K) confirms the Verwey phase as the most complex long-range electronic order known to occur naturally; its relevance in space sciences is discussed. Moreover, the structural analysis of two synthetic magnetites (Fe3(1-δ)O4 with 3δ = 0.012 and TV = 102 K, Fe3-xZnxO4 with x = 0.03 and TV = 90 K) univocally confirmed the persistence of the transition, and its first order, at doping level > 1 %, contrary to previous reports. Moreover, the temperature evolution of the trimerons and their persistence above TV was probed through X-ray Pair Distribution Function analysis on pure Fe3O4: the data analysis between 90 K < T < 923 K show that the Verwey phase goes from long-range ordered (T < 125 K) to short-range ordered (T > 850 K). Magnetite can thus only be considered to have a regular cubic spinel structure above the Curie temperature (TC = 858 K). The pyrochlore lattice of B cations in a spinel gives the structure the potential for frustration upon antiferromagnetic ordering. Fe2GeO4 and γ-Fe2SiO4 were synthesised through conventional solid state routes, with the use of high-pressure synthesis for the latter. Magnetometry and heat capacity measurements highlighted two transitions (Tm1 = 8.6 K and Tm2 = 7.2 K, and Tm1 = 11.2 K and Tm2 = 7.5 K respectively). Powder neutron diffraction data between 2 K < T < 25 K showed that both materials stay undistorted below TN. Magnetic Rietveld refinement led to two highly unconventional magnetic structures, with incommensurate propagation vectors and modulation of the moment magnitude. γ-Fe2SiO4 also shows a spin-ice order below Tm2. The results are unique and unusual for transition metal oxides; the models are systematised by proposing a 'frustration wave' model, in which the degree of frustration is a spatial quantity that can be distributed through the structure in order to stabilise the ground state.
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Watson, Martin James. "Flow regime transitions and associated phenomena." Thesis, Imperial College London, 1999. http://hdl.handle.net/10044/1/8790.
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Spalek, Leszek Jedrzej. "Emergent phenomena near selected phase transitions." Thesis, University of Cambridge, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.608135.
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Darbellay, Georges Alexis. "Wetting and capillary condensation transitions in novel geometries." Thesis, University of Oxford, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.303592.
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Moon, Chang Man. "Molecular dynamics study of phase transition phenomena." Thesis, University of Edinburgh, 2000. http://hdl.handle.net/1842/12675.
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This computer simulation study carried out by classical the molecular dynamics technique (MD) investigates structural phase transitions of various atomic and molecular condensed matter systems. Particularly, our attention is focused on the signals for their observation. Classical nucleation theory is briefly reviewed in relation to the present study. An overall review is made on the methodology of the MD simulation technique such as the integration of the equations of motion, the rotational motion of molecules which is dealt with the four-component quaternion, and other various techniques involved with the simulation of atomic clusters, the simulation of bulk molecular systems using periodic boundary conditions, and isobaric molecular dynamics. There are also reviews on measurements of thermodynamic quantities which are monitored during the simulation including the pressure, the kinetic energy, and the potential energy as well as their corrections due to the spherical cutoff. In addition, various analysis techniques for the observation of the signals of structural phase transitions are discussed. All the potential functions used in this study are of the pairwise additive atom-atom Lennard-Jones interaction for both the atomic and the molecular systems. A small cluster of a binary mixture of krypton and argon atoms is studied by triggered breathing motions to investigate anharmonic motion which involves the structural phase transitions. A small cluster of krypton atoms is also simulated and discussed in detail concerning the very first moment of nucleation in relation to five-fold symmetric structures. In simulations of sulphurhexafluoride molecule systems, artifacts of finite size and periodic boundary conditions are investigated. Freezing the system by MD is investigated since it is known to supercool in computer simulations. Furthermore, accelerating the nucleation process by various methods such as shear flow, accelerated layer, inclusion of defect molecules, and pressure fluctuations is investigated.
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Marais, Simon. "Phenomena due to strain coupling in phase transitions." Thesis, University of Cambridge, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.239588.
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Arunasalam, Somasuntharam. "Non-perturbative phenomena and the electroweak phase transition." Thesis, The University of Sydney, 2019. http://hdl.handle.net/2123/20768.
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The aim of this thesis is to investigate various non-perturbative phenomena within and beyond the standard model and their implications on the electroweak phase transition. The perturbative spectrum of the standard model is well-known and its properties have been measured to great precision. However, the same cannot be said for the non-perturbative spectrum. We first show the existence of electroweak monopoles with finite energy in a Born-Infeld extension of the standard model. We calculate this mass and discuss experimental constraints from light by light scattering and vector boson scattering processes. We also show that these monopoles are a source of B+L - and CP-violation which could potentially provide a novel method of detecting them. We then propose a new mechanism of baryogenesis through B+L - and CP-violating monopole-antimonopole annihilation processes. The phenomenon of scale invariance is an elegant solution to the hierarchy problem. We consider a model in which the standard model is a low energy effective theory with a UV completion that exhibits scale invariance. We compute the thermal effective potential for this model and show that the electroweak phase transition is dramatically different in this theory, only occurring after the QCD chiral phase transition. We also discuss phenomenological implications of this scenario. Finally, we inspect the role of gravity in quantum electrodynamics. We show that quantum gravity effects driven by electrically charged gravitational instantons give rise to a topologically non-trivial vacuum structure resulting in important phenomenological consequences like the violation of CP and the quantisation of electric charge. These models demonstrate that the detailed study of non-perturbative phenomena can yield interesting and significant results and can be the key to answering the unanswered questions in particle physics and cosmology.
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Lopes, Marinho Antunes. "Phase transitions and nonlinear phenomena in neuronal network models." Doctoral thesis, Universidade de Aveiro, 2014. http://hdl.handle.net/10773/14132.
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Doutoramento em FísicaCommunication and cooperation between billions of neurons underlie the power of the brain. How do complex functions of the brain arise from its cellular constituents? How do groups of neurons self-organize into patterns of activity? These are crucial questions in neuroscience. In order to answer them, it is necessary to have solid theoretical understanding of how single neurons communicate at the microscopic level, and how cooperative activity emerges. In this thesis we aim to understand how complex collective phenomena can arise in a simple model of neuronal networks. We use a model with balanced excitation and inhibition and complex network architecture, and we develop analytical and numerical methods for describing its neuronal dynamics. We study how interaction between neurons generates various collective phenomena, such as spontaneous appearance of network oscillations and seizures, and early warnings of these transitions in neuronal networks. Within our model, we show that phase transitions separate various dynamical regimes, and we investigate the corresponding bifurcations and critical phenomena. It permits us to suggest a qualitative explanation of the Berger effect, and to investigate phenomena such as avalanches, band-pass filter, and stochastic resonance. The role of modular structure in the detection of weak signals is also discussed. Moreover, we find nonlinear excitations that can describe paroxysmal spikes observed in electroencephalograms from epileptic brains. It allows us to propose a method to predict epileptic seizures. Memory and learning are key functions of the brain. There are evidences that these processes result from dynamical changes in the structure of the brain. At the microscopic level, synaptic connections are plastic and are modified according to the dynamics of neurons. Thus, we generalize our cortical model to take into account synaptic plasticity and we show that the repertoire of dynamical regimes becomes richer. In particular, we find mixed-mode oscillations and a chaotic regime in neuronal network dynamics.
A comunicação e a cooperação entre milhares de milhões de neurónios está na base do poder do cérebro. Como é que funções cerebrais complexas emergem da dinâmica celular? Como é que grupos de neurónios se auto-organizam em padrões de atividade? Estas são questões cruciais em neurociências. Para as responder é necessário ter um sólido conhecimento teórico sobre como os neurónios comunicam ao nível microscópico, bem como de que forma ocorre atividade coletiva. Nesta tese pretendemos compreender como ´e que fenómenos coletivos complexos podem emergir num modelo simples de redes neuronais. Usando um modelo com excitação e inibição balanceadas e uma arquitectura de rede complexa, desenvolvemos métodos analíticos e numéricos para descrever a sua dinâmica neuronal. Estudamos como é que a interação entre neurónios gera vários fenómenos coletivos, tais como o aparecimento espontâneo de oscilações de rede e convulsões epilépticas, assim como também examinamos a forma de antecipar as transições para esses estados. No nosso modelo mostramos que os vários regimes dinâmicos são separados por transições de fase, e investigamos as correspondentes bifurcações e fenómenos críticos. Isto permite-nos sugerir uma explicação qualitativa do efeito Berger, e investigar fenómenos tais como avalanches, filtro passa-faixa, e ressonância estocástica. O papel da estrutura modular na deteção de sinais fracos é também discutido. Além disso, encontramos excitações não-lineares que podem descrever spikes paroxísticos observados em eletroencefalogramas de cérebros epilépticos. Tal permite-nos propor um método para prever convulsões epilépticas. A memória e a aprendizagem são funções chave no cérebro. Existem evidências de que estes processos resultam de alterações dinâmicas na estrutura cerebral. Ao nível microscópico, as conexões sinápticas são plásticas e são modificadas de acordo com a dinâmica dos neurónios. Por isso, generalizamos o nosso modelo de modo a considerar a plasticidade sináptica e mostramos que o conjunto de regimes dinâmicos se torna mais rico. Em particular, encontramos oscilações de modo misto e um regime de atividade neuronal caótica.
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Ilic, Stefan. "Quantum coherent phenomena in disordered transition metal dichalcogenide monolayers." Thesis, Université Grenoble Alpes (ComUE), 2019. http://www.theses.fr/2019GREAY038.
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Les monocouches de dichalcogénures de métaux de transition (TMDC) sont des matériaux bidimensionnels découverts récemment. Ils possèdent un fort couplage spin-orbite (SOC) intrinsèque qui agit comme un champ Zeeman effectif perpendiculaire, mais avec des orientations opposées dans chaque vallée située autour des points +K et -K de la zone Brillouin. En présence de désordre, ce SOC influence fortement les phénomènes quantiques cohérents dans les TMDC. Dans cette thèse, nous étudions deux de ces phénomènes : la supraconductivité et les corrections à la conductance dues aux interférences quantiques, telles que la localisation ou l’anti-localisation faible, ainsi que les fluctuations universelles de la conductance.Une supraconductivité a été identifiée expérimentalement dans plusieurs TMDC, aussi bien dans les régimes dopés n (MoS2, WS2) que p (NbSe2, TaS2). Dans ces matériaux, le SOC intrinsèque provoque un "appariement d'Ising" inhabituel des paires de Cooper. En effet, celles-ci sont formées avec des électrons provenant de vallées opposées, donc leurs spins sont figés perpendiculairement à la couche. Un champ magnétique appliqué parallèlement à la couche n’est donc pas efficace pour briser les paires de Cooper par l'effet paramagnétique, ce qui entraîne une augmentation considérable du champ critique dans le plan. C’est la signature principale de la supraconductivité d'Ising. Dans la première partie de ce travail, nous calculons le champ critique et la densité des états dans les TMDC supraconducteurs désordonnés. Nous montrons que la diffusion intra-vallée n'affecte pas ces propriétés. En revanche, elles dépendent fortement de la diffusion inter-vallée qui produit un mécanisme de brisure des paires de Cooper. Dans les supraconducteurs Ising dopés p, dans lesquels plusieurs bandes croisent le niveau de Fermi, nous identifions la diffusion inter-bande comme un autre mécanisme important de brisure des paires. Nous montrons qu'une faible diffusion inter-vallée ou inter-bande peut expliquer les observations expérimentales dans les supraconducteurs TMDC dopés n ou p, respectivement.Dans la deuxième partie de ce travail, nous calculons les corrections à la conductance dues aux interférences quantiques dans les TMDC métalliques. Leur mesure peut servir de sonde indépendante pour identifier la nature du SOC et du désordre. En raison de l'interaction entre la structure de la vallée et le SOC, ces matériaux présentent un riche comportement de localisation (ou anti-localisation) faible et des fluctuations universelles de la conductance, qui sont qualitativement différents des autres systèmes bidimensionnels, comme les métaux conventionnels ou le graphène. Nos résultats peuvent également être utilisés pour décrire les hétéro-structures graphène/TMDC, dans lesquelles le SOC est induit dans la couche de graphène. Nous discutons différents régimes de paramètres qui permettent d’interpréter des expériences récentes et d’évaluer l’intensité du SOC et du désordre. En outre, nous montrons qu'un champ Zeeman dans le plan peut être utilisé pour distinguer les contributions de différents types de SOC à la localisation ou l’anti-localisation faibleTransition metal dichalcogenide monolayers (TMDCs) are recently discovered two-dimensional materials. They host a strong intrinsic spin-orbit coupling (SOC), that acts as an effective Zeeman field with opposite, out-of-plane orientations in the +K and –K corners of the Brillouin zone (valleys). This SOC, and its interplay with disorder, strongly influences the behavior of quantum coherent phenomena in TMDCs. In this thesis, we investigate two such phenomena: superconductivity and interference corrections to the conductance, which include weak (anti-) localization and universal conductance fluctuations.Several superconducting TMDCs have been experimentally found in both n-doped (MoS¬2, WS2) and p-doped (NbSe2, TaS2) regimes. Here, the intrinsic SOC causes unusual “Ising pairing” of the Cooper pairs, formed of electrons from opposite valleys with strongly pinned out-of-plane spins. In-plane magnetic fields are thus not efficient in breaking the Cooper pairs by the paramagnetic effect, which results in a large enhancement of the in-plane upper critical field – the main signature of Ising superconductivity. In the first part of this work, we calculate the upper critical field as well as the density of states of disordered superconducting TMDCs. We show that intravalley scattering does not affect these properties, but that they strongly depend on intervalley scattering, which provides a depairing mechanism. In p-doped Ising superconductors, where multiple bands cross the Fermi level, we identify interband scattering as another important mechanism. We show that weak intervalley and interband scattering can explain experimental observations in n- and p-doped TMDC superconductors, respectively.In the second part of this work, we calculate the interference corrections to the conductance in the normal state of TMDCs, which can serve as an independent probe of SOC of disorder. Because of the interplay between valley structure and SOC, these materials exhibit a rich behavior of weak (anti-) localization and universal conductance fluctuations, which is qualitatively different from other two-dimensional systems such as conventional metals or graphene. Our results can also be used to describe graphene/TMDC heterostructures, where SOC is induced in the graphene sheet. We discuss parameter regimes that can be used to interpret recent experiments and assess the strength of SOC and disorder. Furthermore, we show that an in-plane Zeeman field can be used to distinguish contributions of different kinds of SOC to the weak (anti-) localization
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Park, Hyunhang. "Spin Systems far from Equilibrium: Aging and Dynamic Phase Transition." Diss., Virginia Tech, 2013. http://hdl.handle.net/10919/19323.
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Among the many non-equilibrium processes encountered in nature we deal with two different but related aspects. One is the non-equilibrium relaxation process that is at the origin of \'aging phenomena••, and the other one is a non-equilibrium phase transition, called ••dynamic phase transition••. One of the main purposes of our research is to explore more realistic situations than studied previously. Indeed, in the study of aging phenomena certain kinds of disorder effects are considered, and we introduce the ••surface•• as a spatial boundary to the system undergoing the dynamic phase transition. In order to observe these processes as clearly as possible, we study in both cases simple spin systems.
Using Monte Carlo simulations we first investigate aging in three-dimensional Ising spin glasses as well as in two-dimensional Ising models with disorder quenched to low temperatures. The time-dependent dynamical correlation length L(t) is determined numerically and the scaling behavior of various two-time quantities as a function of L(t)/L(s) is discussed where t and s are two different times. For disordered Ising models deviations of L(t) from algebraic growth law show up. The generalized scaling forms as a function of L(t)/L(s) reveal a generic simple aging scenario for Ising spin glasses as well as for disordered Ising ferromagnets.
We also study the local critical phenomena at a dynamic phase transition by means of numerical simulations of kinetic Ising models with surfaces subjected to a periodic oscillating field. We examine layer-dependent quantities, such as the period-averaged magnetization per layer Q(z) and the layer susceptibility ¥ö(z), and determine local critical exponents through finite size scaling. Both for two and three dimensions, we find that the values of the surface exponents differ from those of the equilibrium critical surface. It is revealed that the surface phase diagram of the non-equilibrium system is not identical to that of the equilibrium system in three dimensions.Ph. D.
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Smug, D. "Critical Transitions in financial models : bifurcation- and noise-induced phenomena." Thesis, University of Exeter, 2019. http://hdl.handle.net/10871/36063.
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A so-called Critical Transition occurs when a small change in the input of a system leads to a large and rapid response. One class of Critical Transitions can be related to the phenomenon known in the theory of dynamical systems as a bifurcation, where a small parameter perturbation leads to a change in the set of attractors of the system. Another class of Critical Transitions are those induced by noisy increments, where the system switches randomly between coexisting attractors. In this thesis we study bifurcation- and noise-induced Critical Transitions applied to a variety of models in finance and economy. Firstly, we focus on a simple model for the bubbles and crashes observed in stock prices. The bubbles appear for certain values of the sensitivity of the price based on past prices, however, not always as a Critical Transition. Incorporating noise to the system gives rise to additional log-periodic structures which precede a crash. Based on the centre manifold theory we introduce a method for predicting when a bubble in this system can collapse. The second part of this thesis discusses traders' opinion dynamics captured by a recent model which is designed as an extension of a mean-field Ising model. It turns out that for a particular strength of contrarian attitudes, the traders behave chaotically. We present several scenarios of transitions through bifurcation curves giving the scenarios a market interpretation. Lastly, we propose a dynamical model where noise-induced transitions in a double-well potential stand for a company shifting from a healthy state to a defaulted state. The model aims to simulate a simple economy with multiple interconnected companies. We introduce several ways to model the coupling between agents and compare one of the introduced models with an already existing doubly-stochastic model. The main objective is to capture joint defaults of companies in a continuous-time dynamical system and to build a framework for further studies on systemic and individual risk.
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Murray, Christopher A. "Dispersion phenomena and the glass transition in thin polymer films." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/MQ61934.pdf.
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Harding, Nathan. "Critical phenomena in spatial epidemic models with heterogeneous social dynamics." Thesis, University of Sydney, 2020. https://hdl.handle.net/2123/23410.
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Epidemics are a constant threat, able to bring the entire world to a halt in the case of extreme outbreaks. Computational epidemiology seeks to understand the spread of disease at a population rather than individual level. In this understanding, the field hopes to predict the spread of disease by either simulating microscopic interactions giving rise to infection, or by using mean-field models to emulate the average resultant epidemic spread. This knowledge can be used to predict the future spread of disease and create specific intervention strategies which exploit our understanding of disease spread. The epidemic threshold, the level of infectiousness below which epidemics will not persist, but above which, large levels of infections are maintained, is key to this epidemic analysis. In this pursuit, understanding criticality in the form of the epidemic threshold is frequently studied, however many questions remain unanswered. Another significant challenge to epidemic modeling is the accurate representation of population mobility, as it forms the basis of long range transmission events, and its accuracy directly impacts the relevance of a model to real scenarios. In particular, moving beyond a static treatment of mobility factors into dynamic treatments presents a significant additional step in both modeling and criticality analysis. Specifically, some open challenges addressed in this thesis are: i) Understanding critical thresholds of epidemics in the language of statistical mechanics where phase transitions are rigorously defined. ii) Improving frameworks for the treatment of mobility in epidemic models and criticality analysis of models with dynamic mobility. iii) Extending analysis of critical phenomena for epidemic models with dynamic mobility . iv) Understanding the specific implications of Australian demographics, mobility and geography on the critical dynamics of epidemic spread.
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Wilkinson, Aidan. "Transport phenomena in two-phase systems." Thesis, Loughborough University, 2017. https://dspace.lboro.ac.uk/2134/25574.
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The physics of two-phase systems is explored here, particularly magneto-transport and low temperature d.c. conductivity in thin films. The extraordinary magnetoresistance (EMR) effect was analysed in the context of previous experimental and theoretical considerations. The magnetoresistance (MR) may be enhanced by up to two orders of magnitude by changing the geometry. This was investigated using finite element analysis. Thin film samples consisting of a layered structure of Germanium-Tin-Germanium (Ge-Sn-Ge) were created in collaboration with Shandong University in China. Ge layers were kept at a constant thickness across all samples, with variable Sn thickness. Regions of Sn form island-like shapes ten times larger than the average film thickness, as is seen in scanning electron microscope (SEM) images. Raman spectroscopy was conducted on these samples, from which it is concluded that the Ge layers are amorphous in nature. It was seen that there is a relationship between the electrical resistance and the film thickness which is indicative of a metal-insulator transition (MIT). The temperature dependence of resistivity was subsequently investigated. The temperature coefficient of resistivity (TCR) of the samples is seen to become negative as the thickness of the Sn layer is reduced below a certain critical thickness. Depending on their thickness, samples were designated as metallic or insulator, and various models associated with metals and insulators fitted to the data. While it is impossible to be absolutely certain of the validity of each of the models, some are a better fit than others. The same temperature dependence of resistivity was measured with an applied magnetic field. This is compared with the previous EMR investigation, however the MR of the samples is only of the order of a few percent which corresponds to ordinary MR, seen in most metals. The magnetic field measurements suppress a resistivity down-turn at very low temperatures (T < 10K) which suggests the presence of superconductivity. Analysis of dr=dT shows that the onset of superconductivity is lower for samples with a lower Sn thickness. Additionally, the deposition rate of the Sn layer affects the resistivity significantly; a higher deposition rate causes a decrease in resistivity. It is supposed that this is due to a change in the microstructure of the film. Finally, piezo-resistivity was considered by applying mechanical compression to the samples. The added pressure causes a drop in resistivity.
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Aalberts, Daniel Paul 1966. "Phase transition phenomena in quantum spin systems and in polyampholyte gels." Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/36495.
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Chirazi, Ali. "Multi-scale numerical modelling of phase transition phenomena in metallic alloys." Thesis, University of Greenwich, 2000. http://gala.gre.ac.uk/10686/.
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A multiscale numerical model of the solidification process involving the metallic alloys is proposed. The purpose of this model is to increase our basic knowledge of the physics of the solidification by incorporating atomic aspects of the phase change and, therefore, to predict the rnicrostructural features of the phase transformation based on the alloy parameters, such as the solute concentration and the process parameters, such as the cooling rate and surface roughness. The proposed multiscale strategy, is based on the parametric study of the solidification process at atomistic (nano), microscopic (rneso) and macroscopic levels. Once the major parameters, influencing the process at each scale, are identified, the three different levels are linked via the creation of relevant databases and the passage of information from one scale to another is implemented by using these databases. The multiscale model utilises the Molecular Dynamics (MD) methods at the atomic level, the Cellular Automaton (CA) method at the microscale and the Finite Volume (FV) models at the macroscale. The combination of these methods allowed us to study the phase transition beginning from the atomic clusterisation, progressing to the microstructure formation and culminating in the bulk formation at the macro level.
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Li, Yichen. "Phase-field Modeling of Phase Change Phenomena." Thesis, Virginia Tech, 2020. http://hdl.handle.net/10919/99148.
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The phase-field method has become a popular numerical tool for moving boundary problems in recent years. In this method, the interface is intrinsically diffuse and stores a mixing energy that is equivalent to surface tension. The major advantage of this method is its energy formulation which makes it easy to incorporate different physics. Meanwhile, the energy decay property can be used to guide the design of energy stable numerical schemes.
In this dissertation, we investigate the application of the Allen-Cahn model, a member of the phase-field family, in the simulation of phase change problems. Because phase change is usually accompanied with latent heat, heat transfer also needs to be considered. Firstly, we go through different theoretical aspects of the Allen-Cahn model for nonconserved interfacial dynamics. We derive the equilibrium interface profile and the connection between surface tension and mixing energy. We also discuss the well-known convex splitting algorithm, which is linear and unconditionally energy stable. Secondly, by modifying the free energy functional, we give the Allen-Cahn model for isothermal phase transformation. In particular, we explain how the Gibbs-Thomson effect and the kinetic effect are recovered. Thirdly, we couple the Allen-Chan and heat transfer equations in a way that the whole system has the energy decay property. We also propose a convex-splitting-based numerical scheme that satisfies a similar discrete energy law. The equations are solved by a finite-element method using the deal.ii library. Finally, we present numerical results on the evolution of a liquid drop in isothermal and non-isothermal settings. The numerical results agree well with theoretical analysis.Master of Science
Phase change phenomena, such as freezing and melting, are ubiquitous in our everyday life. Mathematically, this is a moving boundary problem where the phase front evolves based on the local temperature. The phase change is usually accompanied with the release or absorption of latent heat, which in turn affects the temperature. In this work, we develop a phase-field model, where the phase front is treated as a diffuse interface, to simulate the liquid-solid transition. This model is consistent with the second law of thermodynamics. Our finite-element simulations successfully capture the solidification and melting processes including the interesting phenomenon of recalescence.
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Russi, Luigi. "Socio-materiality as phenomenon : growing Transition culture." Thesis, University of Exeter, 2015. http://hdl.handle.net/10871/18003.
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This thesis innovates on existing literature on the Transition movement by relinquishing stock academic definitions of its ends and means, which purportedly spell out what Transition 'is'. In its stead, it approaches Transition as phenomenon, namely as an evolving socio-material formation that proliferates a cultural repertoire to sustain a growing range of concerted everyday activities. This is the difference between an instrumental focus, whereby Transition is reduced to a strategy which is oriented towards an unchanging programmatic definition, and an orientational one; the latter attuned to the contingent process by which a movement expresses form and orientation in emergent fashion. The monograph and the introductory chapter contribute to this task in different ways. Everything Gardens and Other Stories undertakes a rich description of various practical realms of Transition and, to capture the coming into being of a phenomenon, it pays particular attention to its developmental trajectory. This entails focusing on the generative movement of the culture of Transition, as it emerges from the attempt to address embodied disquiets originally elicited by information about peak oil and climate change. That initial focus, however, forms merely a station along a path in which new sources of anxiety find validation and prompt further cultural production. The monograph also describes the tensions arising in the process, as a growing body of discursive and material resources have to negotiate an accommodation, in order to become reciprocally recognisable as participant parts enfolded in a common cultural milieu. The introductory chapter supports this account by fleshing out a methodological paradigm that helps direct attention to the unfolding of a socio-material phenomenon in its dilemmatic moments and continual negotiations. For this purpose, starting from canonical sources in phenomenology, it goes on to situate the 'unfolding' of a phenomenon in the proliferation of entanglements between actors, human and nonhuman. In the 'mattering' of a phenomenon so understood, dilemmatic moments call forth an ethical questioning and an ontological politics immanent to the very process of cultural production. This, it is submitted, is precisely how an orientational focus allows to access Transition as phenomenon, beyond the bounds of academic definitions.
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Al, Mamun Md Abdullah. "Nuclei, Nucleons and Quarks in Astrophysical Phenomena." Ohio University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1563991151449461.
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Ruhunusiri, Wellalage Don Suranga. "Investigation of collective phenomena in dusty plasmas." Diss., University of Iowa, 2014. https://ir.uiowa.edu/etd/1391.
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I study dusty plasma produced by electrostatically confining melamine formaldehyde microparticles in a radio-frequency glow discharge plasma. Dusty plasma is a mixture of particles of solid matter (dust), electrons, ions, and neutral gas atoms. The dust particles have a very high charge and a mass compared to the electrons and ions in the ambient plasma. As a consequence, a dusty plasma exhibits collective phenomena such as dust acoustic waves, crystallization, and melting. The discrete nature of dust particles gives rise to compressibility.
In this thesis I report findings of four tasks that were performed to investigate dust acoustic waves, compressibility, and melting. First, the nonlinear phenomenon of synchronization was characterized experimentally for the dust acoustic wave propagating in a dust cloud with many layers. I find four synchronized states, with frequencies that are multiples of 1, 2, 3, and 1/2 of the driving frequency. Comparing to phenomena that are typical of the van der Pol paradigm, I find that synchronization of the dust acoustic wave exhibits the signature of the suppression mechanism but not that of the phaselocking mechanism. Additionally, I find that the synchronization of the dust acoustic wave exhibits three characteristics that differ from the van der Pol paradigm: a threshold amplitude that can be seen in the Arnold tongue diagram, a branching of the 1:1 harmonic tongue at its lower extremity, and a nonharmonic state.
Second, to assess which physical processes are important for a dust acoustic instability, I derived dispersion relations that encompass more physical processes than commonly done. I investigated how various physical processes affect a dust acoustic wave by solving these dispersion relations using parameters from a typical dust acoustic wave experiment. I find that the growth rate diminishes for large ion currents. I also find that the compressibility, a measure of the coupling between the dust particles, have a strong effect on the wave propagation. Comparing the kinetic vs. hydrodynamic descriptions for ions, I find that under typical laboratory conditions the inverse Landau damping and the ion-neutral collisions contribute about equally to the dust acoustic instability.
Third, I performed dust acoustic wave experiments to resolve a previously unremarked discrepancy in the literature regarding the sign of the compressibility of a strongly-coupled dust component in a dusty plasma. According to theories compressibility is negative, whereas experiments suggest that it is positive. I find that the compressibility is positive. This conclusion was reached after allowing for a wide range of experimental uncertainties and model dependent systematic errors.
Finally, the polygon construction method of Glaser and Clark was used to characterize crystallization and melting in a single-layer dusty plasma. Using particle positions measured in a previous dusty plasma experiment, I identified geometrical defects, which are polygons with four or more sides. These geometrical defects are found to proliferate during melting. I also identify a possibility of latent heat involvement in melting and crystallization processes of a dusty plasma.
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Khan, Hasan. "Quantum Fluctuations Across the Superconductor-Insulator Transition." The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1553188107263297.
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Clarke, Warrick Robin Physics Faculty of Science UNSW. "Quantum interaction phenomena in p-GaAs microelectronic devices." Awarded by:University of New South Wales. School of Physics, 2006. http://handle.unsw.edu.au/1959.4/32259.
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In this dissertation, we study properties of quantum interaction phenomena in two-dimensional (2D) and one-dimensional (1D) electronic systems in p-GaAs micro- and nano-scale devices. We present low-temperature magneto-transport data from three forms of low-dimensional systems 1) 2D hole systems: in order to study interaction contributions to the metallic behavior of 2D systems 2) Bilayer hole systems: in order to study the many body, bilayer quantum Hall state at nu = 1 3) 1D hole systems: for the study of the anomalous conductance plateau G = 0.7 ???? 2e2/h The work is divided into five experimental studies aimed at either directly exploring the properties of the above three interaction phenomena or the development of novel device structures that exploit the strong particle-particle interactions found in p-GaAs for the study of many body phenomena. Firstly, we demonstrate a novel semiconductor-insulator-semiconductor field effect transistor (SISFET), designed specifically to induced 2D hole systems at a ????normal???? AlGaAs-on-GaAs heterojunction. The novel SISFETs feature in our studies of the metallic behavior in 2D systems in which we examine temperature corrections to ????xx(T) and ????xy(T) in short- and long-range disorder potentials. Next, we shift focus to bilayer hole systems and the many body quantum Hall states that form a nu = 1 in the presence of strong interlayer interactions. We explore the evolution of this quantum Hall state as the relative densities in the layers is imbalanced while the total density is kept constant. Finally, we demonstrate a novel p-type quantum point contact device that produce the most stable and robust current quantization in a p-type 1D systems to date, allowing us to observed for the first time the 0.7 structure in a p-type device.
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Kunz, Rainer. "Conventional and new growth phenomena during metal deposition on transition metal dichalcogenides." [S.l.] : [s.n.], 2006. http://e-diss.uni-kiel.de/diss_1682/d1682.pdf.
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Kugler, Johannes. "Transition phenomena for the maximum of a random walk with small drift." Diss., Ludwig-Maximilians-Universität München, 2014. http://nbn-resolving.de/urn:nbn:de:bvb:19-181574.
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Atkinson, I. "Acoustic relaxation phenomena in crystalline gallium arsenide doped with transition metal ions." Thesis, University of Nottingham, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.372661.
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Ando, Hideo. "Molecular Insights into Spin Crossover Phenomena of 1st-Row Transition Metal Complexes." 京都大学 (Kyoto University), 2013. http://hdl.handle.net/2433/174958.
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著作権表示ページを末尾に追加 (2019.12.11)Kyoto University (京都大学)
0048
新制・課程博士
博士(工学)
甲第17592号
工博第3751号
新制||工||1572(附属図書館)
30358
京都大学大学院工学研究科分子工学専攻
(主査)教授 佐藤 啓文, 教授 田中 一義, 教授 北川 進
学位規則第4条第1項該当
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Sorenson, Peter David, and peter sorenson@rmit edu au. "Signs of mid-life: images from the contemporary Australian mid-life male psyche." RMIT University. Applied Communication, 2005. http://adt.lib.rmit.edu.au/adt/public/adt-VIT20060428.113457.
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This research project investigates images from the contemporary Australian mid-life psyche, exploring the contribution to individual transformation made through the creation of, and reflective engagement with, personal imagery. Asking the question: 'What do contemporary Australian mid-life males consider to be a rich and sustaining inner life?' This project documents the visual images, descriptions, and reflections of a group of five participants, discussing the individuals' experiences of aesthetic self-inquiry with reference to divergent theories of psychology, art therapy and philosophy of aesthetics.
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Dounia, Omar. "Numerical investigation of gas explosion phenomena in confined and obstructed channels." Phd thesis, Toulouse, INPT, 2018. http://oatao.univ-toulouse.fr/20584/1/DOUNIA_Omar.pdf.
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Mining, process and energy industries suffer from billions of dollars of worldwide losses every year due to Vapour Cloud Explosions (VCE). Moreover, explosion accidents are often tragic and lead to a high number of severe injuries and fatalities. The VCE scenario is complex and controlled by various mechanisms. The interplay among them is still not entirely understood. Understanding all these intricate processes is of vital importance and requires detailed experimental diagnostics. Coupling accurate numerical simulations to well documented experiments can allow an elaborate description of these phenomena. This thesis focuses on explosions occurring on configurations that are either semi-confined or confined. In such configurations, the explosion is generally initiated by a mild ignition and a subsonic flame front emerges from the ignition source. An important feature of self-propagating flames lies in their intrinsically unstable nature. When they propagate in an environment with high levels of confinement and congestion, which is the case in most industrial sites, a Flame Acceleration (FA) process is often observed that can give rise to very fast flames, known for their destructive potential. In some cases, the FA process can create the appropriate conditions for the initiation of detonations, which corresponds to a rapid escalation of the explosion hazard. To reproduce the confinement and congestion conditions that one can find in industrial sites, the university of Munich TUM equipped a confined chamber with a series of obstacles and analysed the influence of repeated obstructions on the propagation of hydrogen/air deflagrations. This experimental study showed a strong influence of the mixture composition on the acceleration process. A Deflagration to Detonation Transition (DDT) has also been observed for a certain range of equivalence ratio. This configuration is therefore ideal to study the mechanisms of flame acceleration as well as the intricate DDT process. A numerical study of both scenarios is performed in this thesis: -First for a lean premixed hydrogen/air mixture, a strong flame acceleration is observed experimentally without DDT. The characteristic features of the explosion are well reproduced numerically using a Large Eddy Simulation (LES) approach. The crucial importance of confinement and repeated flame-obstacle interactions in producing very fast deflagrations is highlighted. -DDT is observed experimentally for a stoichiometric hydrogen/air mixture. This thesis focuses on the instants surrounding the DDT event, using Direct Numerical Simulations (DNS). Particular attention is drawn to the impact of the chemistry modelling on the detonation scenario. The failure of preventive measures is often observed in many explosion accidents. To avoid a rapid escalation of the explosion scenario, mitigative procedures must be triggered when a gas leak or an ignition is detected. Metal salts (like potassium bicarbonate and sodium bicarbonate) have received considerable attention recently because well-controlled experiments showed their high efficiency in inhibiting fires. The last part of the thesis focused on the mechanism of flame inhibition by sodium bicarbonate particles. First, criteria based on the particle sizes are established to characterize the inhibition efficiency of the particles. Second, two dimensional numerical simulations of a planar flame propagating in a stratified layer of very fine sodium bicarbonate particles showed that under certain conditions these powders can act as combustion enhancers. These results echo a number of experimental observations on the possible counter-effects of the inhibitors.
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Mboukam, Jean Jules. "Magnetocaloric effect and critical behaviour near the magnetic phase transition temperature in rare-earth compounds." University of the Western Cape, 2018. http://hdl.handle.net/11394/6218.
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Magister Scientiae - MSc (Physics)Rare-earth intermetallic compounds continue to draw considerable attention, due to their fundamental importance in understanding physical properties and potential applications based on a variety of phenomena. The focus of this project is to employ two family of rare-earth intermetallic compounds: RE2Pt2In (RE = Pr, Nd) and RE8Pd24Ga (RE = Gd, Tb, Dy) ternary intermetallic systems as a model candidate to uncover the underlying ground state properties that result in a strong coupling between the conduction electron and the 4f-electron of the rare-earth ions.
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Kuznetsova, Yelena Anatolyevna. "Atomic and nuclear interference phenomena and their applications." Texas A&M University, 2005. http://hdl.handle.net/1969.1/2428.
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In this work, interference and coherence phenomena, appearing in atomic and
molecular ensembles interacting with coherent light sources, as electromagnetically
induced transparency (EIT), coherent population trapping (CPT), and slow group
velocity of light are investigated. The goal of the project is to make the steps towards
various applications of these phenomena, first, by studying them in solid media (which
are the most advantageous for applications), second, by suggesting some novel applications
such as CPT-based plasma diagnostics, and realization of new types of
solid-state lasers (based on suppression of excited-state absorption via EIT). The
third goal of the project is extension of coherence and interference effects well-known
in optics to the gamma-ray range of frequencies and, correspondingly, from atomic to
nuclear transitions. A particular technique of chirped pulse compression applied to
M??ossbauer transitions is considered and the possibility of compression of M??ossbauer
radiation into ultrashort gamma-ray pulses is analyzed.
The theoretical treatment of the interference and coherence effects is based on
the semiclassical description of atom-light interaction, which is sufficient for correct
analysis of the phenomena considered here. Coherent media are considered in two-,
three-, and four-level approximations while their interaction with light is studied both
analytically and numerically using the Maxwell-Bloch set of equations.
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Teixeira, Paulo Ivo Cortez. "Statistical mechanical theories of the anchoring transition and related phenomena in liquid crystals." Thesis, University of Southampton, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.239535.
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Ahlberg, Martina. "Critical Phenomena and Exchange Coupling in Magnetic Heterostructures." Doctoral thesis, Uppsala universitet, Materialfysik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-168310.
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The continuous phase transition in thin magnetic films and superlattices has been studied using the magneto-optical Kerr effect (MOKE) and polarized neutron scattering (PNR). It has been shown that the critical behavior of amorphous thin films belonging to the 2D XY universality class can be described within the same theory as crystalline sample. This means that quenched disorder only serves as a marginal perturbation in systems with this symmetry. The connection between interlayer exchange coupling and the observed critical behavior in Fe/V superlattices was explored. The results prove that the origin of unusually high values of the exponent β can be traced to a position dependence of the magnetization at elevated temperatures. The magnetization of the outermost layers within the superlattice shows a more pronounced decrease at lower temperatures, compared to the inner layers, which in turn have a more abrupt decrease in the vicinity of the critical temperature. This translates to a high exponent, especially when the layers are probed by a technique where more weight is given to the layers close to the surface, e.g.MOKE. The interlayer exchange coupling as a function of spacer thickness and temperature was also studied in its own right. The data was compared to the literature, and a dependence on the thickness of the magnetic layers was concluded. The phase transition in amorphous FeZr/CoZr multilayers, where the magnetization emanates from ferromagnetic proximity effects, was investigated. Even though the determined exponents of the zero-field magnetization, the susceptibility and the critical isotherm did not correspond to any universality class, scaling plots displayed an excellent data collapse. Samples consisting of Fe δ-layers (0.3-1.4 monolayers) embedded in Pd were studied using element-specific resonant x-ray magnetic scattering. The magnetization of the two constituents showed distinctly different temperature dependences.
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Chono, Hiroomi. "Nonequilibrium quantum phenomena and topological superconductivity in atomic layer materials." Doctoral thesis, Kyoto University, 2021. http://hdl.handle.net/2433/263449.
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Cheung, Sai-Kit. "The study of weak localization effects on wave dynamics in mesoscopic media in the diffusive regime and at the localization transition /." View abstract or full-text, 2006. http://library.ust.hk/cgi/db/thesis.pl?PHYS%202006%20CHEUNG.
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Burkhardt, Simon [Verfasser]. "Exploration of Charge Transport Phenomena in Transition Metal Oxides for Energy Technologies / Simon Burkhardt." Gießen : Universitätsbibliothek, 2020. http://d-nb.info/1209135485/34.
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Bonhomme, Didier. "Phenomenes critiques dans les transitions structurales de rb#2zncl#4." Le Mans, 1993. http://www.theses.fr/1993LEMA1004.
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Le spectre de resonance paramagnetique electronique du compose modele rb#2zncl#4 dope mn#2#+ est utilise pour etudier le comportement critique des deux transitions structurales exemplaires qui limitent la phase incommensurable. L'une est de second ordre et appartient a la classe (d=3, n=2). L'autre est une transition d'ancrage du premier ordre. Une procedure de traitement fin du spectre de traceur rpe de l'ion mn#2#+ en toute circonstance est prealablement mis au point. Pour la premiere transition le comportement asymptotique du parametre d'ordre et de la singularite de la chaleur specifique, approchee d'une facon originale, apparait etre de type universel xy. Nous situons nos resultats dans un ensemble de resultats recents relatifs a la classe (d=3, n=2). Le regime de solitons etroits, a l'approche de la transition d'ancrage, est clairement observe. Des etudes complementaires par diffraction de bragg et par mesures de pertes dielectriques a 10 ghz montrent que ce regime est pilote par les defauts. Les mesures de pertes dielectriques sont obtenues en modifiant le spectrometre rpe. Dans les cristaux de haute qualite, nous pensons observer la condensation de la partie de la branche de phason qui conduit a la polarisation statique du cristal
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Pépin, Catherine. "Phenomenes critiques autour de la transition magnetique dans les fermions lourds." Université Joseph Fourier (Grenoble), 1996. http://www.theses.fr/1996GRE10135.
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Nous etudions differents aspects de la competition entre magnetisme localise et effet kondo dans les fermions lourds. Dans le cadre du modele du reseau kondo, nous sommes parvenus a traiter les fluctuations de spin sur le meme plan que les effets d'ecrantage kondo, grace a une approche alternative au developpement en 1/n qui met en uvre une transformation de hubbard-stratonovich generalisee. Nous retrouvons, a partir d'un modele microscopique, la nature duale des excitations magnetiques observees par diffusion inelastique de neutrons: la susceptibilite magnetique est la somme d'une contribution quasielastique typique du liquide de fermi et d'une composante inelastique caracteristique des interactions rkky. Poussant le developpement perturbatif a un niveau self-consistent dans les champs de soin et de charge, nous donnons ensuite une description des phenomenes critiques autour du point de transition vers l'etat ordonne. Ce point critique decrit qualitativement le passage d'un liquide de fermi a un regime de magnetisme localise. Deux lignes de cross-over sont determinees, qui distinguent les variations avec la temperature de la susceptibilite statique, de la chaleur specifique et de la longueur de correlation. L'exposant dynamique depend de la constante de couplage j entre impuretes magnetiques et electrons de conduction. Afin de prendre en compte profondement les effets du magnetisme localise, nous introduisons dans la deuxieme partie une nouvelle representation du spin de l'impurete localisee, dans laquelle une fraction du spin est representee par des fermions appropries a la descrption de l'effet kondo, la fraction restante est representee par des bosons adaptes a la description du magnetisme localise. La thermodynamique s'ecrit alors dans une formulation supersymetrique de l'integrale fonctionnelle. Directement appliquee au modele du reseau kondo, cette representation donne de facon asymptotique les proprietes de magnetisme localise. Enfin, nous proposons dans la troisieme partie un calcul numerique de la susceptibilite magnetique sur des structures de bande realistes, qui nous permet de discuter les effets de nesting dans les fermions lourds
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Pickles, Thomas Stanley. "Ordering transitions and localisation properties of frustrated systems." Thesis, University of Oxford, 2009. http://ora.ox.ac.uk/objects/uuid:2cc83b99-3733-4900-9ba5-d7b8476b62b2.
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In this work we investigate themes related to many-body systems in which multiple ground states are accessible, a condition known as frustration. Frustration can arise in a number of contexts, and we consider the consequences of this situation with some examples from condensed-matter physics. In some magnetic materials interactions between spins are such that no single spin configuration provides a unique ground state. In the class of frustrated magnets where the number of ground states is extensive, thermal fluctuations are strong even at temperatures significantly below the interaction strength. At such temperatures spins are highly correlated, and small perturbations may have profound consequences. In this thesis we provide an example of this. By considering classical n-component spins with nearest-neigbour exchange on a frustrated octahedral lattice we show that – in the limit where exchange interactions are large – the system is in a disordered, correlated phase where correlations have the form of a dipole field. This is termed a Coulomb phase. From this phase we induce an ordering transition, lifting the degeneracy with weak, additional short-range interactions. By studying the transition in the solvable limit of n → ∞, we discover that the transition has identical thermodynamics to that of a magnetic system interacting through long-range, dipolar forces. Finally, we provide a more apposite characterisation of the transition, where the high-temperature side of the transition is described through the fluctuations of solenoidal fields, and the ordering corresponds to a condensation of these fields. In a separate part of the thesis, we investigate the influence of disorder on frustrated lattices. We study a two-dimensional tight-binding model with nearest-neighbour hopping and on-site disorder. Restricting the allowed states to being those from the low-lying manifold of ground states, the disorder feeds through to act as effective disorder in the hopping terms, which decay algebraically with distance. The quasi-long range nature of this effective hopping leads to a situation in which the resultant single-particle eigenstates are critical, and we probe their behaviour numerically with a transfer matrix calculation.
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Poehler, Scott A. "Transport Phenomena of CVD Few-Layer MoS2 As-grown on an Al2O3 Substrate." The Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1440181154.
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Falicov, Alexis 1968. "Phase transition phenomena in electronic systems and in systems with quenched field and bond randomness." Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/28118.
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Brock, Jeffrey Adams. "AN EXPERIMENTAL STUDY OF MAGNETIC AND STRUCTURAL PHASE TRANSITIONS AND ASSOCIATED PHENOMENA IN SELECTED NI-MN-DERIVATIVE HEUSLER ALLOYS." Miami University / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=miami1500906786979139.
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Li, Qi 1976. "Competing orders in s-wave and p-wave superconductors." Thesis, University of Oregon, 2008. http://hdl.handle.net/1794/8285.
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xiii, 110 p. A print copy of this thesis is available through the UO Libraries. Search the library catalog for the location and call number.This dissertation investigates the interplay between, and the possible coexistence of, magnetic and superconducting order in metals. We start with studying the electromagnetic properties of s-wave superconductors near a ferromagnetic instability. By using a generalized Ginzburg-Landau theory and scaling arguments, we show that competition between magnetic order and superconducting order can change the scaling of observables. For instance, the exponent for the temperature dependence of the critical current can deviate from the Ginzburg-Landau value of 3/2. These results may be relevant to understanding the observed behavior of MgCNi 3 . We then study the nature of the superconductor-to-normal-metal transition in p-wave superconductors. Although the phase transition is continuous at a mean- field level, a more careful renormalization-group analysis in conjunction with large-n expansion techniques strongly suggest that the transition is first order. This conclusion is the same as for s-wave superconductors, where these techniques also predict a first-order transition. In p-wave superconductors, topological excitations known as skyrmions are known to exist in addition to the more common vortices. In the third part of this dissertation, we study the properties of skyrmion lattices in an external magnetic field. We propose iv experiments to distinguish vortex lattices from skyrmion lattices by means of their melting curves and their μSR signatures.
Adviser: Dietrich Belitz
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Liu, Yuzhi. "Renormalization group and phase transitions in spin, gauge, and QCD like theories." Diss., University of Iowa, 2013. https://ir.uiowa.edu/etd/4872.
Full textAbstract:
In this thesis, we study several different renormalization group (RG) methods, including the conventional Wilson renormalization group, Monte Carlo renormalization group (MCRG), exact renormalization group (ERG, or sometimes called functional RG), and tensor renormalization group (TRG).
We use the two dimensional nearest neighbor Ising model to introduce many conventional yet important concepts. We then generalize the model to Dyson's hierarchical model (HM), which has rich phase properties depending on the strength of the interaction. The partition function zeros (Fisher zeros) of the HM model in the complex temperature plane is calculated and their connection with the complex RG flows is discussed. The two lattice matching method is used to construct both the complex RG flows and calculate the discrete β functions. The motivation of calculating the discrete β functions for various HM models is to test the matching method and to show how physically relevant fixed points emerge from the complex domain.
We notice that the critical exponents calculated from the HM depend on the blocking parameter b. This motivated us to analyze the connection between the discrete and continuous RG transformation. We demonstrate numerical calculations of the ERG equations. We discuss the relation between Litim and Wilson-Polchinski equation and the effect of the cut-off functions in the ERG calculation.
We then apply methods developed in the spin models to more complicated and more physically relevant lattice gauge theories and lattice quantum chromodynamics (QCD) like theories. Finite size scaling (FSS) technique is used to analyze the Binder cumulant of the SU(2) lattice gauge model. We calculate the critical exponent nu and omega of the model and show that it is in the same universality class as the three dimensional Ising model. Motivated by the walking technicolor theory, we study the strongly coupled gauge theories with conformal or near conformal properties. We compare the distribution of Fisher zeros for lattice gauge models with four and twelve light fermion flavors. We also briefly discuss the scaling of the zeros and its connection with the infrared fixed point (IRFP) and the mass anomalous dimension.
Conventional numerical simulations suffer from the critical slowing down at the critical region, which prevents one from simulating large system. In order to reach the continuum limit in the lattice gauge theories, one needs either large volume or clever extrapolations. TRG is a new computational method that may calculate exponentially large system and works well even at the critical region. We formulate the TRG blocking procedure for the two dimensional O(2) (or XY ) and O(3) spin models and discuss possible applications and generalizations of the method to other spin and lattice gauge models.
We start the thesis with the introduction and historical background of the RG in general.
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Liu, Dazhi Ph D. Massachusetts Institute of Technology. "Studies of liquid-liquid phase transition and critical phenomena in supercooled confined water by neutron scattering." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/53260.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2008.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 69-72).
Small angle neutron scattering (SANS) is used to measure the density of water contained in 1-D cylindrical pores of a mesoporous silica material MCM-41-S. By being able to suppress the homogenous nucleation process inside the narrow pore, one can keep water in the liquid state down to at least 160 K. We observe a density minimum at 210±5 K. This is the first experimental evidence of the existence of the density minimum in supercooled water. We show that the results are consistent with the predictions of molecular dynamics simulations of supercooled bulk water. From a combined analysis of SANS data from both H20 and D20 hydrated samples, we determined the absolute value of the density of water in the 1-D confined geometry. We found that the average density of water inside the fully hydrated MCM-41-S is higher than that of the bulk water. Pore size and hydration level dependences of the density are also studied. The temperature derivative of the density shows a pronounced peak signaling the crossing of the Widom line and confirming the existence of a liquid-liquid critical point at an elevated pressure.
by Dazhi Liu.
Ph.D.